[Federal Register Volume 60, Number 188 (Thursday, September 28, 1995)]
[Notices]
[Pages 50338-50377]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-24112]
[[Page 50337]]
_______________________________________________________________________
Part IV
Environmental Protection Agency
_______________________________________________________________________
Dichlorvos; Notice of Preliminary Determination to Cancel Certain
Registrations and Draft Notice of Intent to Cancel; Notice
Federal Register / Vol. 60, No. 188 / Thursday, September 28, 1995 /
Notices
[[Page 50338]]
ENVIRONMENTAL PROTECTION AGENCY
[OPP-30000/56; FRL-4954-7]
Dichlorvos; Notice of Preliminary Determination to Cancel Certain
Registrations and Draft Notice of Intent to Cancel
AGENCY: Environmental Protection Agency (EPA).
ACTION: Notice of preliminary determination.
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SUMMARY: This Notice sets forth EPA's preliminary determination
regarding the continued registration of pesticide products containing
dichlorvos and sets forth the Agency's assessment of the risks and
benefits associated with dichlorvos products. This Notice announces the
Agency's preliminary determination to propose cancellation of certain
registrations of dichlorvos products and to propose modification to
other registrations which would not be canceled. In addition, this
Notice serves as a Draft Notice of Intent to Cancel.
DATES: Written comments must be received on or before December 27,
1995.
ADDRESSES: Submit three copies of written comments bearing the docket
control number ``OPP-30000-56'' by mail to: Public Response and Program
Resources Branch, Field Operations Division (7506C), Office of
Pesticide Programs, Environmental Protection Agency, 401 M St., SW.,
Washington, DC 20460. In person, deliver comments to: Rm. 1128, Crystal
Mall #2, 1921 Jefferson Davis Highway, Arlington, VA 22202.
Comments and data may also be submitted electronically by sending
electronic mail (e-mail) to: [email protected]. Electronic
comments must be submitted as an ASCII file avoiding the use of special
characters and any form of encryption. Comments and data will also be
accepted on disks in WordPerfect in 5.1 file format or ASCII file
format. All comments and data in electronic form must be identified by
the docket number ``OPP-30000/56.'' No Confidential Business
Information (CBI) should be submitted through e-mail. Electronic
comments on this document may be filed online at many Federal
Depository Libraries. Additional information on electronic submissions
can be found in Unit VII. of this document.
Information submitted as a comment concerning this document may be
claimed confidential by marking any part or all of that information as
confidential business information (CBI). Information so marked will not
be disclosed except in accordance with procedures set forth in 40 CFR
part 2. A copy of the comment that does not contain CBI must be
submitted for inclusion in the public record. Information not marked
confidential may be disclosed publicly by EPA without prior notice. All
written comments will be available for public inspection in Rm. 1132 at
the address given above, from 8 a.m. to 4:30 p.m., Monday through
Friday, except legal holidays.
FOR FURTHER INFORMATION CONTACT: By mail: Dennis Utterback, Special
Review and Reregistration Division (7508W), Office of Pesticide
Programs, Environmental Protection Agency, 401 M St., SW., Washington,
DC 20460. Office location and telephone number: Special Review Branch,
3rd floor, Crystal Station #1, 2800 Crystal Drive, Arlington, VA,
Telephone: 703-308-8026: e-mail: [email protected].
SUPPLEMENTARY INFORMATION: This Notice is organized into the following
units: Unit I. is the introduction which includes background
information related to dichlorvos, a description of the Agency's
Special Review process, and the regulatory history of dichlorvos (2,2-
dichlorovinyl dimethyl phosphate), also known as DDVP, including the
initiation of Special Review. Unit II. summarizes the risk assessment.
Unit III. summarizes the benefits of dichlorvos uses. Unit IV. explains
the Agency's risk/benefit analysis and proposed regulatory decisions.
Unit V. describes the Agency's existing stocks policy. Unit VI.
describes the procedures related to the referral of this document to
the U.S. Department of Agriculture and FIFRA Scientific Advisory Panel.
Unit VII. describes the opportunity for public comment, and Unit VIII.
describes the availability of information in the Public Docket.
Finally, Unit IX. lists references to this document.
I. Introduction
A. Summary
EPA has concluded that the risks outweigh the benefits for most
uses of dichlorvos, and therefore, recommends a variety of measures to
reduce those risks. Dichlorvos poses carcinogenic risks of concern to
the general population from dietary exposure and risks of
cholinesterase inhibition (including cholinergic signs) to individuals
mixing, loading, and applying this pesticide, as well as to those
reentering treated areas. The Agency believes that the economic
benefits associated with the continued use of dichlorvos are not
significant for most uses. After careful consideration of the risks and
benefits, EPA is proposing the following actions: Cancellation of all
uses in or on residences, tobacco warehouses, ornamental lawns, turf
and plants, commercial, institutional and industrial areas, airplanes,
trucks, shipholds, and rail cars, warehouses, and use on bulk, packaged
or bagged nonperishable processed and raw food (except for impregnated
resin strips in silos). In addition, EPA is proposing to cancel other
registrations unless certain modifications are made to the label,
including: prohibit hand-held application in mushroom houses,
greenhouses, on food and nonfood animals (other than poultry), and in
passenger buses; allow other application methods in mushroom houses,
greenhouses or passenger buses, as long as the applicator and others
are prohibited from remaining in these facilties during treatment;
restrict all remaining registered products to use by certified
applicators only, except for impregnated resin strips used in museums
(closed spaces) and in insect traps, and require personal protective
equipment (PPE) during handling; and require reentry intervals for
mushroom houses, greenhouses and passenger buses. EPA is proposing to
retain the following uses: mushroom houses and greenhouses (only
automatic foggers or fogging through a port, and restricted reentry),
kennels, feedlots, insect traps, garbage dumps, direct application to
poultry, automated application to livestock, animal premises, manure,
and buses (fogger use).
In addition to the Special Review, there are three activities which
may affect dichlorvos registrations. First, EPA published the Final
Revocation Notice for the food additive regulation (FAR) of dichlorvos
residues on packaged or bagged nonperishable processed food in the
Federal Register of November 10, 1993 (58 FR 59667). The effective date
of this Notice was stayed indefinitely. Second, if that revocation
becomes effective, under current policy, EPA would issue a notice of
its intent to cancel the related uses under the Federal Insecticide,
Fungicide, and Rodenticide Act (FIFRA). Third, EPA received a request
from Amvac Chemical Corporation, the sole technical registrant of
dichlorvos, to voluntarily delete several uses from its technical
label. EPA intends to accept Amvac's request unless the Company
withdraws or modifies its request.
[[Page 50339]]
B. The Statute
A pesticide may be sold or distributed in the United States only if
it is registered or exempt from registration under FIFRA as amended (7
U.S.C. 136 et. seq.). Before a product can be registered
unconditionally, it must be shown that it can be used without
``unreasonable adverse effects on the environment'' (FIFRA section
3(c)(5)), that is, without causing ``any unreasonable risk to man or
the environment, taking into account the economic, social, and
environmental costs and benefits of the use of the pesticide'' (FIFRA
section 2(bb)). The burden of proving that a pesticide meets this
standard for registration is, at all times, on the proponent of initial
or continued registration. If, at any time, the Agency determines that
a pesticide no longer meets this standard for registration, then the
Administrator may cancel the registration under section 6 of FIFRA.
C. Regulatory Background
Dichlorvos is an organophosphate insecticide registered for use in
controlling flies, mosquitos, gnats, cockroaches, fleas, and other
insect pests. Amvac Chemical Corporation is the sole producer of
technical grade dichlorvos in the U.S. There are currently 182 product
registrations for formulations containing dichlorvos. In addition,
there are three section 24(c) Special Local Need Registrations.
Formulations include: Pressurized liquids, granulars, dusts, wettable
powders, emulsifiable concentrates, total release aerosols, and
impregnated materials. Applications are made with aerosols and fogging
equipment, with ground spray equipment, and through slow release from
impregnated materials, such as resin strips and pet collars.
Dichlorvos has been registered in the U.S. since 1948. The Shell
Chemical Company marketed the product under the trademark Vapona, and,
in 1963, Shell began marketing the No-Pest Strip. In 1985,
approximately 2 million pounds of dichlorvos active ingredient were
used annually in the U.S. on a variety of sites. At that time,
agricultural applications constituted 60 percent of the total
dichlorvos usage, including use on beef and dairy cattle, poultry,
sheep, livestock living quarters and other farm buildings, greenhouses,
mushroom houses, stored agricultural products, stored food facilities,
and tobacco warehouses. In addition, approximately 25 percent was used
on commercial, institutional, and industrial sites, including food
processing areas, food handling establishments, sewage and dump sites,
lawns, and turf. The remaining 15 percent was applied in and around
homes and on pets. These estimates are based on 1985 data and it is
believed that dichlorvos usage has declined significantly in recent
years (currently 250,000 to 500,000), but not necessarily
proportionally across all sites.
Amvac has also notified EPA that it is not supporting uses on the
following sites and requests their voluntary cancellation: Rangeland
grasses, greenhouse food crops (cucumber, tomato, lettuce, radish),
greenhouse non-food crops, tobacco, tobacco warehouses, tomato (post
harvest), domestic dwellings (except for impregnated resin strips,
total release foggers, and crack and crevice treatment; impregnated
resin strips will not be permitted in kitchens); aircraft and buses;
food service establishments, including eating establishments (except
for non-food service areas); food manufacturing establishments,
including bottling plants and frozen food plants (except for non-food
manufacturing areas); food processing establishments, including meat,
poultry and seafood slaughtering and/or packing plants, and dairy
product plants (except for non-food processing areas); and all aerial
applications. EPA has published a notice of receipt of voluntary
cancellation request for these uses in the Federal Register pursuant to
section 6(f) of FIFRA on April 19, 1995 (60 FR 19580).
In 1980, the Agency referred dichlorvos to the Rebuttable
Presumption Against Registration or RPAR process under FIFRA, now
called the Special Review process. The RPAR referral was based on
scientific studies which indicated that dichlorvos was mutagenic and
might cause cancer, nerve damage, and birth defects in laboratory
animals.
In 1982, the Agency issued a document reporting the results of its
evaluation of dichlorvos (47 FR 45075). Initial concern had been based
on the results of animal studies that were later found to be equivocal
or to show no positive evidence of the suspected effects of exposure to
dichlorvos. The Agency concluded that the existing information did not
support the initiation of the RPAR process at that time. However, a
determination was made to review results of carcinogenicity studies
being conducted for the National Cancer Institute/National Toxicology
Program when completed, and to issue a Data Call-In (DCI) for four
mutagenicity studies in March 1983.
The Natural Resources Defense Council (NRDC), et al., brought suit
against the Agency in 1983, in part, to require a reassessment of
several RPAR decisions. A settlement agreement was reached in September
1984, in which the Agency agreed to reassess the pre-RPAR decision on
dichlorvos. The parties also agreed that reassessment of dichlorvos
would begin once the mutagenicity and carcinogenicity studies were
received and evaluated.
The dichlorvos Registration Standard, issued in September 1987,
stated that the Agency was considering further regulatory action for
all registered uses of dichlorvos. The Registration Standard classified
all dichlorvos products as restricted use, except for resin pest
strips, pet uses, and all remaining products allowing household use
only. The Agency also determined that all products must contain a
hazard warning for cancer, liver effects, and cholinesterase
inhibition. An interim 48-hour reentry interval was imposed for the
agricultural and commercial uses of dichlorvos. The Registration
Standard also identified and required additional data necessary to
evaluate fully the human and environmental risks associated with the
use of dichlorvos as an insecticide.
Amvac Chemical Corporation formally requested that EPA reconsider
the requirements for a cancer warning statement and 48-hour reentry
interval in February 1988. In September 1988, EPA formally deferred
imposition of all Registration Standard label modifications and data
requirements pending evaluation of comments and additional data
regarding the label requirements, due to uncertainty concerning the
cancer classification of dichlorvos. (These data requirements were
later reinstated in August 1991 and January 1994.) Registrants were
also informed that the Agency would amend the dichlorvos Registration
Standard after completion of the reassessment.
On February 24, 1988, EPA initiated a Special Review for pesticide
products containing dichlorvos. EPA determined that exposure to
dichlorvos from the registered uses may pose an unreasonable
carcinogenic risk and inadequate margins of exposure for cholinesterase
inhibition and liver effects to exposed individuals. The risks of
concern detailed in the Notice were for the general population from
consumption of foods containing residues of dichlorvos, for those
involved in the application of dichlorvos, for workers reentering
treated areas, for residents/occupants of treated areas, for people
exposed to pets
[[Page 50340]]
treated with dichlorvos, and for pets treated with dichlorvos.
On May 25, 1989, the State of California, NRDC, Public Citizen, the
AFL-CIO, and several individuals filed a petition which asked the
Agency to revoke FARs for seven potentially carcinogenic substances,
including FARs for residues of dichlorvos in or on dried figs, and on
packaged or bagged nonperishable processed food. The petitioners argued
that these FARs should be revoked because the seven pesticides to which
the regulations applied were animal carcinogens and thus the
regulations violated the Delaney clause of section 409 of the Federal
Food, Drug and Cosmetic Act (FFDCA). The Delaney clause provides that a
FAR may not be approved for a food additive if it ``is found to induce
cancer when ingested by man or animal. . . .'' 21 U.S.C. 348(c). In
responding to the petition, EPA reiterated its 1988 interpretation that
the Delaney clause is subject to an exception for pesticide uses which
posed no greater than a de minimis cancer risk (56 FR 7750, February
25, 1991). Although EPA concluded that several of the challenged
regulations met this de minimis standard, EPA found that the dichlorvos
FAR for packaged or bagged nonperishable processed food did not meet
this standard.
Therefore, in the Federal Register of October 3, 1991 (56 FR
50190), EPA proposed to revoke the FAR for residues of the pesticide
dichlorvos on packaged or bagged nonperishable processed food, under
section 409 of the FFDCA. Subsequent to that Notice, on July 8, 1992,
in, Les v. Reilly, 968 F.2d 985 (9th Cir.), the Ninth Circuit Court
ruled that the Delaney clause was not subject to an exception rule for
those pesticides that pose a de minimis cancer risk. Following the
Ninth Circuit Court decision, EPA revoked the section 409 FAR of
dichlorvos on packaged or bagged nonperishable processed food (58 FR
59663, November 10, 1993) on the basis that it was in violation of the
Delaney clause. EPA later stayed the 120-day effective date
indefinitely, pending Agency consideration of a request for a hearing
from Amvac. Legal pesticide residues on food are permitted by FFDCA;
however, the use of a pesticide is permitted separately under FIFRA.
Because the revocation was stayed, residues in food are currently
allowed. When the stay is lifted, pesticide residues will be illegal;
however, the use of dichlorvos will still be permitted under FIFRA.
Therefore, under current policy, EPA intends to cancel the related uses
as soon as possible after the FAR revocation becomes final. That
cancellation will prevent the potential situation in which foods
legally treated with dichlorvos under FIFRA would be considered
adulterated and subject to seizure under FFDCA.
In August 1991, EPA reimposed indoor use data requirements that
were required in the 1987 Registration Standard, and were deferred in
1988. These data have since been submitted by Amvac and reviewed by the
Agency, and are used in the risk assessment presented here. In
addition, the 1987 residential outdoor and terrestrial non-food use
data requirements were reimposed on January 3, 1994. Another DCI was
issued on February 22, 1994, for additional studies to support
terrestrial non-food and residential outdoor uses. EPA has received
some studies as a result of this DCI and the last study is due in March
1996. A further DCI was issued on November 10, 1994, for residue data
relating to crack and crevice treatment around packaged and bagged
food.
Based on information received in public comments and on additional
analyses performed since the Special Review process began, EPA is now
issuing this Notice of Preliminary Determination. Issuance of this
Notice means that the Agency has assessed the potential adverse effects
and the benefits associated with the use of pesticide products
containing dichlorvos and that the Agency has preliminarily determined
that, unless the terms and conditions of registration are modified as
proposed in this Notice, the risks from the use of dichlorvos outweigh
the benefits of their continued use.
EPA's position and a summary of the rationale underlying that
position are set forth in this Notice. The basis for EPA's action is
explained more fully in documents contained in the dichlorvos docket.
The docket also contains references and background information
pertinent to the registration of pesticide products containing
dichlorvos.
This Notice serves both as a preliminary determination of the
Special Review process and as a draft Notice of Intent to Cancel
dichlorvos registrations. FIFRA requires that a draft Notice of Intent
to Cancel be prepared and forwarded to the Scientific Advisory Panel
(SAP) and the Secretary of the United States Department of Agriculture
(USDA) to permit their review of the Agency's proposed action. The
draft Notice of Intent to Cancel is not now legally effective but is
intended only to provide a basis for comment by the SAP, USDA,
registrants, and the public. EPA's compliance with this review
requirement is discussed in Unit VII. of this Notice. Comments on this
preliminary determination and Draft Notice of Intent to Cancel must be
filed within 90 days of the issuance of this Notice.
II. Risk Assessment
A. Summary of Risk Assessment
Risk assessment is the process used to estimate the likelihood and
magnitude of health effects that result from environmental exposures.
This process consists of the following four components: Hazard
identification, dose-response assessment, exposure assessment, and risk
characterization. The first component, hazard identification, is a
determination whether a particular chemical is or is not causally
linked to particular adverse health effects. Dose-response assessment
estimates the amount of a chemical that could potentially cause an
adverse health effect. The amount of a chemical that did not result in
an observable or measurable effect in an animal study is the no-
observed-effect level (NOEL). All substances can cause a toxic effect
at some level. The extent to which a chemical is toxic depends on the
amount of the chemical needed to produce the adverse effect. Low
toxicity chemicals require a large amount of the chemical to produce
the adverse health effect, while highly toxic chemicals require only a
small dose to produce the toxic effect. Exposure assessment describes
the level or magnitude of exposure to the chemical, the route of
exposure (inhalation, dermal, or oral), and the frequency of the
exposure. Finally, risk characterization involves describing the nature
and magnitude of human risk. The dose-response and exposure assessments
are combined to estimate some measure of human risk. The potential for
possible non-cancer health effects in humans is generally expressed as
the margin of exposure (MOE) which is the ratio of the NOEL (dosage
producing no effects) to the estimated exposure. For cancer, the risk
is expressed as a probability of developing cancer over a lifetime,
which is based on exposure and the chemical's cancer potency. The risk
characterization component also summarizes the major strengths and
weaknesses of the risk assessment.
In the case of dichlorvos, the Agency has determined that the
adverse effects of primary concern for dichlorvos are those related to
cancer and inhibition of cholinesterase activity including cholinergic
signs (clinical signs indicative of cholinesterase inhibition in test
animals). Based on data from
[[Page 50341]]
several carcinogenicity studies, the Agency has concluded that
dichlorvos meets the criteria for a Group C (possible human)
carcinogen. Dichlorvos has been shown to induce forestomach tumors in
mice and leukemia in rats. Results from acute/short-term, subchronic
and chronic toxicity studies have shown dichlorvos to be a potent
inhibitor of plasma, red blood cell and brain cholinesterase in several
mammalian species, and to produce cholinergic signs.
In the Notice initiating the Special Review, EPA estimated cancer
risks for those individuals potentially exposed to dichlorvos through
dietary and non-dietary (i.e. inhalation and dermal contact) routes.
Since that time, EPA has determined that it is not appropriate to
extrapolate from oral carcinogenicity data for estimation of excess
individual cancer risks for exposure by the dermal and inhalation
routes. Therefore, cancer risk estimates for workers and residents
exposed to dichlorvos by the dermal and inhalation routes are not
included in this revised risk assessment. EPA only estimated excess
individual lifetime cancer risks for dietary exposure to the general
population.
Dietary exposure to dichlorvos residues may occur as a result of
use on a variety of sites, including greenhouse food crops, mushroom
houses, bulk-stored and packaged or bagged nonperishable processed and
raw food, commercial food processing plants, groceries, eating
establishments, and direct animal treatment. Some of these exposures
and resulting risks may be eliminated due to voluntary cancellations or
cancellation of uses related to the revocation of the FAR for packaged
or bagged nonperishable processed food; however, since these actions
are not final yet, for purposes of this document, EPA will assume that
these uses will continue. EPA estimates dietary cancer risks from
registered uses of dichlorvos to be 4.4 x 10-6. The major source
of this estimated risk is from consumption of bulk, packaged or bagged
nonperishable raw and processed food treated with dichlorvos (3.4 x
10-6).
In addition to registered uses of dichlorvos, naled provides an
additional source of dietary risk from dichlorvos. Naled, an
insecticide, is metabolized to dichlorvos by plants. As a result, the
Agency felt it appropriate to characterize the total risk from
dichlorvos even though naled itself is not under Special Review. The
combined dietary cancer risk from dichlorvos is 5.1 x 10-6 which
includes risk directly from dichlorvos (4.4 x 10-6) and from
naled-derived dichlorvos (7.2 x 10-7).
EPA completed a series of exposure assessments in 1987 for the
Registration Standard and PD 1 that estimated the exposure to
individuals mixing, loading and applying dichlorvos, as well as to
those reentering areas treated with dichlorvos. These estimates were
based on the best available data, which in most cases were exposure
data derived from other pesticides applied in a similar manner as
dichlorvos. Additional exposure data have been submitted since that
time and the Agency has determined that revisions to the original
assessments are appropriate based on these new data. EPA has revised
its original exposure estimates for several uses of dichlorvos,
including: Crack and crevice application, greenhouses, mushroom houses,
dairy barns and milk rooms, household aerosol and total release fogger
products.
Red blood cell, plasma and brain cholinesterase inhibition and/or
cholinergic signs are the basis for the short-term, intermediate, and
long-term MOE estimates. For pesticides, EPA classifies occupational/
residential exposure patterns as short-term (1 to 7 days), intermediate
(1 week to several months per year), or long-term (a substantial
portion of the lifetime). These scenarios could vary by region or from
year-to-year depending on the severity of the pest problem. Separate
NOELs were selected from acute (0.5 mg/kg/day), subchronic (0.1 mg/kg/
day), and chronic (0.05 mg/kg/day) toxicity studies to estimate MOEs
for varying durations of exposure. Margins of exposure are outlined in
Table 1 in Unit II. of this document for individuals reentering treated
facilities and for individuals exposed during the application of
dichlorvos. Most of the MOEs are below the level which the Agency
believes is protective of public health (100).
B. Effects of Concern
1. Carcinogenicity. EPA has determined that the risk criteria for
carcinogenicity as set forth in 40 CFR 154.7 (a)(2) has been exceeded
for dietary exposure. Based on the studies described below, EPA has
classified dichlorvos as a Group C (possible human) carcinogen (Ref. 1)
.
i. Hazard identification. In July 1987, the Office of Pesticide
Program's Carcinogenicity Peer Review Committee (CPRC) classified
dichlorvos as a Group B2 (probable human) carcinogen, based primarily
on the results of National Toxicology Program (NTP) studies in mice and
rats. Since that time, EPA has reevaluated the carcinogenic potential
of dichlorvos and concluded that dichlorvos is a Group C (possible
human) carcinogen. The basis for that determination is summarized
below.
(a) Mouse study. Dichlorvos was administered by gavage to B6C3F1
mice (60/sex/group) for 103 weeks (5 days/week) using corn oil as the
vehicle (Ref. 2). Doses were 0, 10, or 20 mg/kg/day for male mice and
0, 20, or 40 mg/kg/day for females. Administration of dichlorvos to
female mice was associated with a statistically significant dose-
related trend and statistically significant increase in squamous cell
forestomach papillomas and combined squamous cell forestomach
papillomas and carcinomas at the high-dose. The forestomach tumors were
outside the historical control range. In male mice, an increase in
squamous cell forestomach papillomas was associated with a significant
dose-related trend, but was not statistically significant by pairwise
comparison at either dose level. No other tumor types were identified
in this study. No malignant squamous cell tumors were found in the
historical controls.
(b) Rat study. Dichlorvos was administered, with corn oil as the
vehicle, by gavage to F344 rats (60/sex/group) for 103 weeks (five
days/week) (Ref. 3). The dosages were 0, 4, or 8 mg/kg/day. The study
resulted in a statistically-significant increase in mononuclear cell
leukemia in males by pairwise comparison at both dosage levels. The
increase in leukemia also exhibited a statistically significant
positive dose-related trend. There was an increased incidence of lung
adenomas in high-dose male rats which was significant only for a dose-
related trend. In addition, dichlorvos administration was associated
with a statistically significant increased incidence of mammary gland
adenomas and all mammary gland tumors at the low-dose only (by pairwise
comparison) in rats. However, the incidence of lung adenomas and
mammary gland tumors were within the historical control range.
(c) Reexamination of cancer classification. The FIFRA Scientific
Advisory Panel (SAP) reviewed the CPRC's Group B2 cancer classification
and concluded that dichlorvos should be classified as a Group C
(possible human) carcinogen since: (1) only benign tumors were induced
by dichlorvos; (2) they were not dose-related; and (3) dichlorvos was
not mutagenic in in vivo assays (although it was mutagenic in several
in vitro test systems with and without metabolic activation) (Ref. 4).
[[Page 50342]]
The CPRC met for a second time on September 29, 1987, to examine
the issues raised by the SAP with respect to the classification of the
carcinogenicity of dichlorvos (Ref. 5). Upon reconsideration, the
Committee concluded that the results of the NTP studies indicate that
dichlorvos demonstrates sufficient evidence of carcinogenicity in the
male rat and female mouse to confirm the initial classification of
dichlorvos as a Group B2 carcinogen.
The committee concluded that ``the results of the NTP bioassays
indicate that DDVP demonstrates sufficient evidence of carcinogenicity
in the male rat and in the female mouse since: (1) A dose-response
relationship of statistical significance was seen for pancreatic
adenomas (which have the potential to progress towards malignancy) and
mononuclear cell leukemia in male rats, (2) a dose-response
relationship of statistical significance was seen in the female mouse
for forestomach squamous cell papillomas which have the potential to
progress to carcinomas, (3) the presence of some forestomach carcinomas
(which are rare) was seen in the female mouse, (4) a significant
positive trend was seen for forestomach papillomas in male mice at a
dose that did not achieve an MTD, (5) supporting evidence provided by a
statistically significant increase in mammary tumors at the low dose in
the female rat which was associated with a significant trend, and (6)
mutagenicity data was available indicating that DDVP is positive for
mutagenicity in vitro in bacterial and mammalian cells both with and
without metabolic activation. The Committee, thereby, confirmed their
initial classification of DDVP as a B2 oncogen.''
The CPRC had a third meeting on June 2, 1988, to review the
conclusions of an April 1988 meeting of NTP Panel of Experts on the
carcinogenic classification of dichlorvos (Ref. 6). Scientists at NTP
had resectioned the pancreas of all test groups in the rat bioassay.
The additional sectioning of pancreata resulted in an increased number
of tumors in the control animals, thus diminishing the statistical
significance of this lesion. Based on this finding, the NTP scientists
concluded that the evidence for carcinogenicity in male rats should be
downgraded from clear evidence to some evidence. The CPRC considered
the NTP's information and concluded that dichlorvos should remain
classified as a Group B2 carcinogen, because: (1) The incidence of
mononuclear cell leukemia in dichlorvos treated F344 rats was
treatment-related; (2) although the results of longitudinal sectioning
of the pancreas diminished the significance of the pancreatic acinar
adenomas in male rats, the incidence of animals with multiple adenomas
was still increased with dichlorvos treatment; and (3) dichlorvos is a
direct acting mutagen. The Committee considered this as an interim
classification until the following additional data had been reviewed:
(1) the results of a Japanese study in which dichlorvos was
administered in drinking water to Fischer 344 rats and B6C3F1 mice; (2)
additional data on a chronic rat inhalation study; (3) additional in
vivo mutagenicity data, and (4) additional historical control
information on pancreatic acinar adenomas.
The CPRC met for a fourth time on July 19, 1989, the conclusions of
which serve as the basis for the cancer hazard assessment in this
proposed determination (Ref. 7). The purpose of this meeting was to
reconsider the NTP rat study in light of the recent NTP Panel of
Experts report, evaluate new oncogenicity studies with DDVP
administered by inhalation or in drinking water and consider other
ancillary information.
As mentioned earlier, the NTP reexamined the pancreata of male and
female rats using longitudinal sections which diminished the
statistical significance of this lesion. The NTP analysis of the
combined data indicated a statistically significant difference between
the treated and control groups with a positive dose-related trend using
the logistic regression analysis. However, EPA scientists concluded
that the increase in pancreatic acinar tumors was neither significant
in the Fischer Exact test for pairwise comparison, nor positive in the
Cochran-Armitage test for dose-related trend, which are typically used
for testing dose groups having no survival disparities. The incidence
of animals with multiple pancreatic adenomas was still increased with
dichlorvos treatment and outside of the historical control range.
The Committee also reevaluated an inhalation oncogenicity study in
which 50 CFE rats/sex/dose were exposed to concentrations of 0.05, 0.5
or 5.0 mg/m3 of technical dichlorvos 23 hours per day for 2 years.
This study was reviewed for the dichlorvos Registration Standard and
the Agency considered the study inadequate for evaluating the
carcinogenicity of the chemical. The study was upgraded after the
individual animal data were submitted to the Agency. Agency scientists
have concluded that administration of dichlorvos did not alter the
tumor incidence in this study.
In addition to the Japanese drinking water study in Fischer 344
rats, Amvac Chemical Corporation submitted a study to the Agency in
March 1989, using B6C3F1 mice which was also conducted in Japan. In
both studies, dichlorvos was administered in drinking water for 2
years. The CPRC considered both studies to be deficient in conduct and
reporting, including incomplete histopathologic evaluation, absence of
water consumption data, and failure to include individual animal data
in the final report. As a result of these deficiencies, the studies are
not amenable to statistical analyses. However, the studies are useful
in identifying a qualitative trend in that dichlorvos treatment induced
some tumors similar to those induced in the oral gavage studies. In the
rat study, there appeared to be an increased incidence of mononuclear
cell and lymphocytic leukemia in treated males, as well as mammary
gland fibroadenomas in females. In the mouse study, there appeared to
be an increased incidence of fibrous histiocytomas and thymomas in
males.
The Committee agreed, based upon the available information to
reclassify dichlorvos as a Group C carcinogen, in accordance with the
Agency's Guidelines for Carcinogenic Risk Assessment. This downgrading
from the previous classification as Group B2 was due to: (1) Erosion of
the evidence on the pancreatic acinar adenomas in male rats; (2)
upgrading and consideration of the negative inhalation study in CFE
rats; and (3) questions regarding the biological significance of the
primary tumors in the NTP studies, i.e., leukemia in rats (variable
tumors in historical controls) and forestomach tumors in mice and its
relevance to man.
ii. Weight-of-the-evidence for carcinogenicity. In its most recent
evaluation, the fourth cancer peer review, the CPRC considered the
weight-of-the-evidence and concluded that dichlorvos should be
classified as a Group C (possible human) carcinogen based on inadequate
human data and limited data from animal bioassays. The Group C
classification is supported by the following points:
(a) In B6C3F1 mice, dichlorvos induced a statistically significant
increase in forestomach squamous cell papillomas and combined
forestomach squamous cell carcinomas and papillomas in high-dose
females. This tumor-type (squamous cell papillomas) was also increased
in high-dose males but was significant only for a positive dose-related
trend.
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(b) In Fischer 344 rats, dichlorvos was associated with a
statistically significant increase, with a positive dose-related trend,
in leukemia (of all sites and types) in males at both dosage levels.
This evidence is supported by the results of the transplantable rat
mononuclear cell leukemia model. The treatment was also associated with
a numerical (not statistically significant) increase in pancreatic
acinar adenomas in males. The incidence of animals with multiple
pancreatic acinar adenomas was also increased.
(c) The Group C classification is further supported by studies
indicating that dichlorvos is a direct acting gene mutagen in bacteria,
fungi and mammalian cells in vitro, and suggesting in vivo mutagenic
activity. (Refs. 8-17). Dichloroacetaldehye, a product of hydrolytic or
oxidative cleavage of dichlorvos, has also been reported to be
mutagenic in the scientific literature (Ref. 18). Additionally,
dichlorvos is structurally similar to known chemical mutagens/
carcinogens (i.e., tetrachlorvinphos and phosphamidon).
iii. Dose-response assessment. The CPRC concluded that a
quantitative estimate of the carcinogenic potency should be performed
for dichlorvos. Cancer potency (or Q1*) is a quantitative estimate
of the relationship between exposure to increasing doses of a chemical
and the chemical's ability to induce tumors (i.e., increased number of
tumors per unit dose). Because most animal studies do not include a
sample size large enough to detect carcinogenic responses at low doses
comparable to environmental exposures, the Agency normally estimates
the cancer potency of a chemical by extrapolating from responses in
high-dose animal experiments.
Several mathematical models have been developed to estimate the
cancer potency. In the absence of information demonstrating a more
appropriate model, the Agency generally uses the linearized multi-stage
model to extrapolate from effects seen at high-doses in laboratory
studies to predict tumor response at low-doses. This model is based on
the biological theory that a single exposure to a carcinogen can
initiate an irreversible series of transformations in a single cell
that will eventually lead to a tumor. In addition, the linearized
multi-stage model assumes that the probability of each transformation
is linearly related to the degree of exposure (i.e., a threshold does
not exist for carcinogenicity).
Using this model, the Agency estimated the cancer potency
(Q1*) for dichlorvos based on the tumor incidence data in female
mice and male rats in the NTP studies. The cancer potency in human
equivalents is 1.22 x 10-1 (mg/kg/day)-1, which is the
geometric mean of the Q1* for female mouse forestomach tumors and
the Q1* for leukemia in male rats (Ref. 19). The Q1*
represents the 95 percent upper confidence limit of tumor induction
likely to occur from a unit-dose.
The CPRC (fourth cancer peer review) also recommended not to
quantify the cancer risk by a low-dose extrapolation model for the
inhalation route of exposure. The primary basis for this recommendation
was the upgrading of a 2-year inhalation study in rats which did not
result in an increased tumor incidence. The recommendation was based on
the following considerations: The quality of the oral cancer data, the
route specificity of the target organs, the reliability and accuracy in
estimating the target-dose and the unlikelihood that exposure via the
inhalation route would lead to the formation of a reactive metabolite.
In addition, the OPP Reference Dose Committee concluded that
extrapolating the results from the oral gavage studies to the dermal
route of exposure is not appropriate for dichlorvos (Ref. 20). This
decision was based on the following considerations: (1) There was no
dose-response relationship in the leukemia observed in male Fisher 344
rats; (2) the tumors observed in female B6C3F1 mice were contact site
tumors, the relevance of which to humans is unknown, and the incidence
of which, at all dose levels, including the concurrent controls, was
outside the National Toxicology Program's control range; (3) the
dynamics of absorption, distribution, metabolism and excretion do not
favor retention of the chemical in animal tissues and makes it
difficult to determine accurately the concentration at the target site;
and (4) it is not expected that topically applied doses would reach the
target organ(s) in sufficient quantity to produce a carcinogenic
response or would be sufficient to alkylate macromolecules in the
target tissues to produce contact site tumors. Therefore, extrapolation
from oral data to dermal or inhalation routes is not appropriate, for
estimation of excess individual cancer risk, for exposure to
dichlorvos.
2. Cholinesterase inhibition. Cholinesterase (ChE) refers to a
family of enzymes that are essential to the normal functioning of the
nervous system. These enzymes are necessary for the transmission of
nerve impulses. Inhibition of ChE activity can result in a number of
cholinergic signs and symptoms in humans, depending on the rate and
magnitude of exposure, including: Headaches, dizziness, nausea,
vomiting, diarrhea and increased urination, blurred vision, pinpoint
pupils, increased salivation, labored breathing, muscle paralysis, slow
heart rate, respiratory depression, convulsions, coma and even death.
These enzymes have been identified in nearly every tissue of the body;
however, ChE activity is usually measured in blood plasma and red blood
cells in humans, while ChE levels in laboratory animals are measured in
plasma, red blood cells as well as brain tissue.
Organophosphate pesticides, such as dichlorvos, are known to
inhibit ChE activity and some cause delayed neurotoxic effects. EPA has
evaluated the available information and concluded that dichlorvos is a
potent ChE inhibitor. This determination is based on toxicological data
using laboratory animals, human poisoning incidents, and limited human
toxicity information, which are discussed below.
i. Laboratory data. Acute, subchronic and chronic laboratory
studies using experimental animals have shown dichlorvos to be a potent
ChE inhibitor, significantly reducing blood plasma, red blood cell and
brain ChE. ChE inhibition has been demonstrated in several mammalian
species following oral, inhalation, and dermal administration of
dichlorvos. Only the primary studies selected for use in assessing risk
from short-term, intermediate, and long-term exposures are discussed
below.
(a) Acute toxicity data. Acute neurotoxicity data are limited in
comparison to available subchronic and chronic data, but are more
relevant for assessing risk from single and short-term repeated
exposure scenarios. Acute neurotoxicity studies have been conducted in
both hens and rats. An acute neurotoxicity study in rats evaluated the
neurobehavioral signs and the neuropathological effects following
single exposures, but did not measure ChE inhibition (Ref. 21). Groups
of 12 male and female Sprague-Dawley rats were administered single oral
doses of 0, 0.5, 35 or 70 mg/kg/day by gavage. At the mid- and high-
doses, administration of dichlorvos resulted in a variety of
neurological and physiological changes (e.g., alterations in posture,
mobility and gait, reduced or absent forelimb/hindlimb grasp, tremors).
Most of these changes were observed about 15 minutes after compound
administration, while no toxicity was apparent for the survivors (there
were several deaths at the high-dose) 7 days following administration
of dichlorvos at all dose
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levels. Based on the study results, the NOEL for signs associated with
ChE inhibition was established at 0.5 mg/kg/day.
An acute delayed neurotoxicity study in hens resulted in
cholinergic signs of ChE inhibition and neuropathic effects (Ref. 22).
Ten birds were administered a single dose of 16.5 mg/kg/day by oral
intubation. The test birds were given another oral dose at 21 days and
observed for an additional 21 days. Dichlorvos-treated birds
demonstrated signs of ChE inhibition shortly after dosing, including:
lethargy and depression, incoordination, limb weakness, wing drop, and
reduced reaction to external stimulation. The birds were asymptomatic
by day 3 after dosing. Administration of dichlorvos did not produce
overt signs of acute delayed neurotoxicity, but neuropathic effects
(peripheral nerve lesions which are associated with paralysis) did
occur in one hen. A NOEL was not shown for this effect in this one dose
study.
Additional information about short-term exposure is provided by a
range-finding study in which dogs (one male and one female for each
dose) were administered dichlorvos by capsule for 2 weeks at the
following doses: 0, 0.1, 1.0, 5.0, 10, 15, 30, or 60 mg/kg/day (Ref.
23). Plasma and red blood cell ChE levels were decreased in the 1.0 mg/
kg/day group and above as early as 6 days after dosing. The degree of
ChE inhibition increased with dose. During the first week following
dosing, severe cholinergic signs were observed in animals at 30 and 60
mg/kg/day and death occurred at these doses during the second week of
dosing. However, this study is not appropriate for short-term risk
assessment because only a limited number of animals were treated at
each dose and dichlorvos was administered repeatedly. This study
indicates that short-term exposure to dichlorvos at low levels produces
ChE inhibition in plasma, red blood cells and brain tissue, and
contributes to the overall weight-of-the-evidence.
(b) Subchronic toxicity data. A study was performed in rats
providing ChE inhibition data following subchronic exposure to
dichlorvos (Ref. 24). Groups of 10 male and 10 female rats were
administered doses of 0, 0.1, 1.5 or 15 mg/kg/day by oral gavage for 13
weeks (5 days/week). Observations recorded approximately 30 to 60
minutes post-dose included salivation in 7 males and 4 females treated
with 15 mg/kg/day. Urine stains were also seen in 7 males and 5 females
at this dose. These observations were seen on certain days during weeks
6 through 12 for males and 8 through 12 for females. At week 7, plasma
ChE activity was significantly reduced in mid- and high-dose male and
high-dose female rats when compared to the controls. Mid- and high-dose
male and female rats also demonstrated significantly reduced red blood
cell (RBC) ChE activity when compared to the controls at 7 weeks. At
the 14-week interval, plasma ChE activity was significantly reduced in
high-dose males and females, while RBC activity was significantly lower
than controls in mid- and high-dose animals. Red blood cell ChE
activity was also reduced in low-dose (0.1 mg/kg/day) females at 14
weeks; however, the RBC ChE inhibition was not considered biologically
significant since it was less than 10 percent below ChE activity in
control animals. Brain ChE activity in high-dose female rats was 49
percent lower than in control females and was statistically
significant, while brain ChE activity in high-dose males was reduced 28
percent below control males but inhibition was not statistically
significant. The data presented support a NOEL of 0.1 mg/kg/day based
on plasma and red blood cell ChE inhibition at doses of 1.5 mg/kg/day
and above.
An additional subchronic study in rats evaluated neurobehavioral
signs, neuropathological effects, and also measured ChE activity (Ref.
25). Dichlorvos was administered by oral gavage to male and female rats
at doses of 0, 0.1, 7.5, or 15 mg/kg/day (15 animals/sex/dose) for 90
days. There were no significant differences between the control and
treated animals with respect to the functional observational battery or
locomotor activity evaluations, nor were any neuropathological lesions
attributable to dichlorvos. However, administration of dichlorvos was
accompanied by cholinergic signs (tremors, salivation, exophthalmos,
lacrimation) approximately 15 minutes after dosing in the high-dose
animals and, to a lesser extent, in the mid-dose animals. In general,
cholinergic signs occurred during the first dosing week in high-dose
animals and during the third dosing week in mid-dose animals and
persisted to study termination in both groups. Plasma ChE inhibition
was statistically significant at all time periods measured; however,
RBC ChE inhibition was only statistically significant for high-dose
males at week 3. ChE levels in RBC were reduced 23, 12, and 18 percent
in the mid-dose males and 35, 8, and 11 percent in the high-dose males
compared to controls during weeks 3, 7, and 13, respectively. In
females, RBC ChE inhibition of 13, 38, and 33 percent at the mid-dose,
and of 4, 42, and 35 percent at the high-dose were noted during weeks
3, 7, and 13, respectively. Brain stem and brain cortex ChE activity
were also reduced from 11 to 12 percent in low-dose animals and from 10
to 16 percent in high-dose rats as compared to controls. Inhibition of
brain stem ChE activity was statistically significant in high-dose
males only, while in the cerebral cortex ChE was significantly reduced
for animals in the mid- and high-dose groups. The NOEL from this study
was 0.1 mg/kg/day based on ChE inhibition (plasma, RBC, brain) and
cholinergic signs occurring at 7.5 mg/kg/day.
A developmental toxicity study in New Zealand white rabbits
produced signs of ChE inhibition at similar dose levels as the
subchronic rat studies (Ref. 26). Groups of 16 pregnant females were
administered doses of 0, 0.1, 2.5, or 7.0 mg/kg/day by oral gavage on
gestation days 7 through 19, inclusive. The doses were selected based
on the results of a range-finding study conducted in the same strain of
pregnant rabbits at dose levels of 0, 0.1, 1.0, 2.5, 5.0 or 10 mg/kg/
day (8 per group, except for 7 in the 2.5 mg/kg/day group) in which
there were statistically significant reductions in maternal plasma and
RBC ChE activity in a dose-related manner at all doses except 0.1 mg/
kg/day. Profound treatment-related maternal mortality (5/8 died) and
cholinergic signs occurred at 10 mg/kg/day. In the definitive
developmental toxicity study, mortality was observed at 2.5 mg/kg/day
(13 percent) and 7.0 mg/kg/day (25 percent). ChE inhibition was not
measured; however, apparent anticholinesterase-related signs and
symptoms were observed at the high-dose, including ataxia, prone
positioning, tremors, excitation, salivation, diarrhea and difficulty
in breathing. Based on the range-finding and definitive study results,
the maternal toxicity NOEL and Lowest Effect Level (LEL) were
demonstrated at 0.1 and 2.5 mg/kg/day, respectively.
An inhalation developmental toxicity study in rabbits produced
findings similar to those of the oral developmental toxicity study
(Ref. 27). Groups of 20 female Dutch rabbits were exposed to 0, 0.25,
1.25, or 6.25 g/L of dichlorvos for 23 hours per day, from day
1 of mating to gestation day 28. No cholinergic signs were noted at 0,
0.25, or 1.25 g/L, but severe toxicity and mortality occurred
after the 6th day of exposure to 6.25 g/L. Cholinergic signs
observed included anorexia, lethargy, muscular tremors, mucous nasal
discharge and diarrhea. Sixteen of the 20 does at the high-dose died or
were killed because of intoxication. There
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were statistically significant reductions in plasma, RBC and brain ChE
activity at 1.25 and 6.25 g/L, while at 0.25 g/L ChE
activity was depressed less than 15 percent. The NOEL for this study is
0.25 g/L based on ChE inhibition in plasma, RBC and brain
tissue. The NOEL of 0.25 g/L corresponds to approximately 0.14
mg/kg/day. In converting from g/L to mg/kg/day, EPA assumed
that 100 percent of the dichlorvos vapor is absorbed by inhalation and
also that the rabbit breathing rate is constant over time.
Additional information on neuropathological effects can be drawn
from a 28-day delayed neurotoxicity study in hens, from which
preliminary results were submitted to the Agency (Ref. 28). This study
was required based on the results of the acute study in hens discussed
above. Groups of 21 hens were administered dichlorvos orally at doses
of 0, 0.3, 1.0, or 3.0 mg/kg/day for 28 days. These data suggest that
significant axonal degeneration in the spinal cord occurred following
oral administration of 1 and 3 mg/kg/day, while at 0.3 mg/kg/day only
minor effects were noted. While such findings must be regarded as
preliminary, they should be regarded as potentially serious, since such
lesions represent an irreversible and relatively serious effect. In
addition, this report notes that significant (34 to 63 percent) brain
ChE inhibition was seen at 1 and 3 mg/kg/day. The final report was
submitted to the Agency and is currently under review.
(c) Chronic toxicity data. Both oral and inhalation toxicity data
demonstrate that long-term exposure to dichlorvos results in plasma,
RBC, and brain ChE inhibition. In a chronic rat inhalation study,
groups of 50 male and 50 female CFE rats per dose level were exposed to
0, 0.05, 0.48, or 4.7 mg/m3 of dichlorvos for 2 years (Ref. 29).
There was a statistically significant decrease in ChE activity in
plasma, red blood cells, and brain in the mid- and high-dose groups
(76, 72, 90 percent and 83, 68, 90 percent of control activity in mid-
dose males and females; and 38, 4, 21 and 22, 5, 16 percent of control
activity in high-dose males and females, respectively). Red blood cell
ChE was reduced to 88 percent of control activity in females dosed at
0.05 mg/m3, but this decrease was not statistically significant.
The NOEL was established at 0.05 mg/m3 based on ChE inhibition in
plasma, red blood cells and brain tissue. The concentration of 0.05 mg/
m3 corresponds to approximately 0.055 mg/kg/day, assuming a
constant breathing rate in rats and 100 percent absorption of
dichlorvos vapor.
Groups of 4 male and 4 female dogs were administered dichlorvos by
capsule 7 days per week at doses of 0, 0.05 (0.1 for the first 3 weeks
of study), 1.0 or 3.0 mg/kg/day for 1 year (Ref. 30). Plasma ChE was
inhibited (21.1 to 66.6 percent) in males and females in the 0.1, 1.0,
and 3.0 mg/kg/day groups during week 2. The low-dose was consequently
reduced to 0.05 mg/kg/day on day 22 due to the plasma ChE inhibition
(26 percent in females) noted after 12 days of dichlorvos
administration. Red blood cell ChE was only slightly decreased (less
than 2 percent) in the 0.1 mg/kg/day group at week 2, while animals in
the 1.0 and 3.0 mg/kg/day groups exhibited RBC ChE inhibition of 33 to
75 percent. Statistical analyses were not conducted prior to week 13.
Statistically significant depression in plasma and RBC ChE occurred at
week 13 in males and females in the 1.0 and 3.0 mg/kg/day groups. In
addition, brain ChE was significantly reduced in males and females in
the high-dose group and in the males of the mid-dose group at
termination. Brain ChE activity was inhibited approximately 22 percent
in males in the 1.0 mg/kg/day group and 47 percent and 29 percent,
respectively, in males and females in the 3.0 mg/kg/day group compared
to controls. Study results correspond to a NOEL of 0.05 mg/kg/day,
based on plasma, RBC, and brain ChE inhibition.
A two-generation reproductive study was conducted in which Sprague-
Dawley rats were exposed via the drinking water to dichlorvos at
concentrations of 0, 5, 20, or 80 ppm (males - 0.5, 1.9 or 7.2 mg/kg/
day; females - 0.6, 2.3, or 8.3 mg/kg/day) (Ref. 31). ChE assays
(plasma, RBC and brain) were performed on males and females of both the
F0 and F1 generations at terminal sacrifice. The data
indicate that RBC ChE was inhibited in both males and females at all
doses and in a dose-related manner. At the low-dose, RBC ChE activity
was decreased 7 to 14 percent in males and 17 to 23 percent in females.
RBC ChE inhibition was statistically significant for both males and
females at all dose levels, except for the F0 males at 0.5 mg/kg/
day (7 percent inhibition). Plasma ChE inhibition was statistically
significant for both males and females at the mid- and high-dose
levels. The plasma ChE inhibition for F1 males at the low-dose
(0.5 mg/kg/day) was also statistically significant (15 percent). In
addition, brain ChE activity was inhibited in males and females of both
generations at all dose levels. Statistically significant reductions
occurred only at the mid- and high-doses. The study results establish a
NOEL of less than 5 ppm for RBC and plasma ChE inhibition (males - 0.5
mg/kg/day; females - 0.6 mg/kg/day).
ii. Human data--(a) Toxicity data. EPA reviewed several studies in
the scientific literature that measured ChE inhibition in humans
following exposure to dichlorvos (Ref. 32). The studies only covered a
few exposure scenarios, including occupant exposure to resin pest
strips and workers reentering treated warehouses. There were few, if
any, adverse effects following most resin pest strip exposures. Only
one headache was reported which may have been associated with
dichlorvos exposure. Usually only plasma ChE inhibition was
statistically significant with statistically significant RBC ChE
inhibition occurring only rarely. However, interpretation of the study
results is difficult because of methodological problems and utilization
of outdated methods for measuring ChE activity. In addition, the
studies only examined small numbers (less than 20) in any one test
group.
(b) Poisoning incidents. Exposure to dichlorvos has resulted in
poisoning incidents. Although the number of incidents is not large, it
is sufficient to be of concern and can be viewed as confirmatory of the
inadequate MOEs. Several sources are available indicating that exposure
to dichlorvos has resulted in poisoning incidents. As part of the
assessment for the dichlorvos Registration Standard, the Agency
reviewed the Pesticide Incident Monitoring System (PIMS) data base
covering a period from 1964 to 1980 (Ref. 33). Only 182 of the 598
dichlorvos incidents could be identified as involving products that
contained dichlorvos as the sole active ingredient. A majority (147) of
these 182 reports involve humans and domestic animals in the home
environment, with 114 incidents resulting from ingestion and
application of dichlorvos. One death was reported. Ingestion incidents
usually involved children chewing flea collars and resin pest strips.
Most of the application incidents involved situations where the
existing label precautions were not followed. Of the remaining 416
incidents in which dichlorvos was cited in combination with other
chemicals, there were 9 human fatalities reported. EPA's Incident Data
System, in operation since June 1992, does not contain any human
poisoning incidents attributed to dichlorvos exposure.
Case reports from the California Pesticide Illness Surveillance
Program are available for dichlorvos from 1982 to
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1990 (Ref. 34). A total of 78 poisoning incidents were attributed to
dichlorvos exposure. Sixty were classified as systemic poisonings, 12
caused eye problems and the remaining 6 resulted in skin irritation.
The majority of these incidents involved active ingredients in addition
to dichlorvos. In addition, poisonings were attributed to both
occupational and residential exposures.
Finally, the American Association of Poison Control Centers (AAPCC)
reported that for the years 1985 - 1992 there were 21,006 exposures of
all kinds for dichlorvos alone and 21,844 exposures for dichlorvos
alone and in combination with other active ingredients (Refs. 35 and
36). Of the 21,006 exposures, 2,671 individuals were treated and
released and 350 were hospitalized. There were 259 occupational cases
involving dichlorvos alone and an additional 57 occupational cases
involving dichlorvos in a mixture with another pesticide. Of the 259
cases, 99 workers were treated and released and 13 were hospitalized.
Only one of the occupational cases was considered life-threatening,
while 10 of the non-occupational cases were so categorized.
iii. Animal health and safety data. EPA reviewed 3 animal heath and
safety data studies which examined the effect on dogs and cats of
wearing registered cat and dog flea collar products. These studies
provide strong evidence that dichlorvos, used in combination with other
active ingredients, has a significant effect on reducing ChE activity
in dogs. Although the ChE inhibition could result in part from another
pesticide active ingredient, the Agency has no data to disprove that
ChE depression is a result of dichlorvos exposure (Refs. 37-39).
In the first study, groups of 3 male and 3 female dogs per group
served either as controls, or wore 1, 3, or 5 collars containing 9.3
percent dichlorvos and 4.2 percent chlorpyrifos. In the 1-collar group,
5 out of 6 dogs averaged RBC ChE inhibition (statistically significant)
of 20 to 30 percent during the period day 3 through week 2. Plasma ChE
inhibition was even greater, averaging 65.6 percent as compared to pre-
test values during the perod day 3 through week 4 in 5 animals.
Another study was conducted in which 3 male and 3 female dogs were
each assigned to a control group, a group wearing a collar containing
7.8 percent dichlorvos and 4.34 percent chlorpyrifos, a group wearing a
collar containing 8.87 percent dichlorvos and 4.44 percent
chlorpyrifos, and a group wearing an 8 percent chlorpyrifos collar. The
mean percentage plasma ChE activity was significantly different from
that of the control group among dogs wearing collars containing
dichlorvos from day 7 through week 6. Differences in RBC ChE activity
were not statistically significant. More specifically, in animals
wearing the product containing 7.8 percent dichlorvos, plasma and RBC
ChE activity were inhibited 49 percent and 19 percent as compared to
pre-test values. This study demonstrates that plasma and RBC ChE
inhibition also can occur from use of these products.
In the last study, ChE activity was measured in dogs over a 98-day
period, during which time the dogs wore a placebo collar or 1, 3, or 5
collars containing a mixture of 7 percent dichlorvos and 9 percent
propoxur. There was a considerable drop in plasma ChE activity in the
first 7 days of exposure (in 1-collar dogs by 30 percent, in 3-collar
dogs by 57 percent, and in 5-collar dogs by about 63 percent). In the
1-collar exposure group there was essentially complete plasma ChE
recovery by day 56; however, in the 3 and 5-collar females there was
still significant plasma ChE inhibition (35 and 43 percent,
respectively) on day 98. There was no evidence of any RBC ChE
inhibition in any group at any time during this study.
iv. Dose-response assessment. Results from acute, subchronic, and
chronic toxicity studies have shown dichlorvos to be a potent inhibitor
of plasma, RBC, and brain ChE. In most instances, inhibition of brain
ChE occurred at similar doses as plasma and RBC ChE inhibition.
Moreover, cholinergic signs were usually associated with actual
measurements of ChE inhibition. Neurotoxicity data indicate a
correlation between ChE inhibition and neuropathological effects.
Overall, the various indicators of ChE inhibition (i.e., altered ChE
activity in plasma, RBC, brain, neuropathological effects or
cholinergic signs) are observed within a relatively narrow dose range.
In addition, the effects indicative of ChE inhibition observed in
laboratory studies are further validated by actual human poisonings
accompanied by cholinergic signs.
Dose-response data for ChE inhibition and/or cholinergic signs are
available for acute, subchronic, and chronic toxicity studies using
rats, rabbits, dogs and hens as the test species. EPA selected the
lowest NOELs from acute, subchronic, and chronic toxicity studies to
calculate MOEs of exposure for individuals exposed to dichlorvos for
varying durations of time. The NOELs are based on either brain ChE
inhibition and/or cholinergic signs following administration of
dichlorvos by the oral and inhalation routes of exposure. Neurotoxicity
data following dermal administration of dichlorvos are not available.
(a) Acute/short-term exposure. EPA scientists believe that a NOEL
of 0.5 mg/kg/day is most suitable for calculating MOEs of exposure for
acute dietary and short-term occupational or residential (1 to 7 days)
exposure scenarios. This NOEL is based on the acute neurotoxicity study
in rats resulting in neurological and physiological changes observed
shortly after dosing, including alterations in posture, mobility, and
gait, reduced or absent forelimb/hindlimb grasp, increased time to
first step, pupillary constriction, tremors, clonic convulsions,
increased response time, catalepsy, and reduction in body temperature
at 35 mg/kg/day. ChE activity was not measured in this study. There is
some uncertainty with this acute NOEL because of the wide gap between
dose levels (0, 0.5, 35, or 70 mg/kg/day). Since there are no
intermediate doses between the no effect level of 0.5 mg/kg/day and the
next level, 35 mg/kg/day, at which a variety of behavior changes were
seen, it is possible that additional data might result in a slightly
higher NOEL. However, Agency scientists do not believe that such a new
acute NOEL would differ greatly from 0.5 mg/kg/day because short-term
exposure data from other studies yielded similar results.
(b) Intermediate exposure. EPA selected a NOEL of 0.1 mg/kg/day for
assessing intermediate occupational and residential exposure (1 week to
several months) to dichlorvos. This NOEL was derived from examining
several oral and inhalation toxicity studies. In the subchronic rat
neurotoxicity study, administration of dichlorvos at 7.5 mg/kg/day
inhibited plasma, RBC, and brain ChE activity, as well as producing
cholinergic signs during the third week of dosing. Based on these
findings, a NOEL was established at 0.1 mg/kg/day. The inhalation
developmental toxicity study in rabbits demonstrated a NOEL of 0.14 mg/
kg/day (converted from 0.25 g/L) based on statistically
significant plasma, RBC and brain ChE inhibition occurring at 0.71 mg/
kg/day. A maternal toxicity NOEL of 0.1 mg/kg/day was demonstrated in
the oral developmental toxicity study in rabbits, based on the results
of the range-finding and definitive studies. In the range-finding
study, statistically significant plasma and RBC ChE inhibition occurred
at all doses except 0.1 mg/kg/day, while cholinergic signs occurred at
2.5 mg/kg/day and above. ChE inhibition was not measured in the
definitive study, but 2
[[Page 50347]]
deaths (13 percent) occurred at 2.5 mg/kg/day. The developmental
toxicity study results are supported by the 1 year dog study in which
significant plasma and RBC ChE inhibition occurred as early as 2 weeks
following administration of 1.0 and 3.0 mg/kg/day. In addition, plasma
ChE inhibition ranged from 21 to 26 percent in the 0.1 mg/kg/day group
at 2 weeks. These studies indicate that effects associated with ChE
inhibition occur at levels slightly higher than 0.1 mg/kg/day.
Therefore, EPA has determined that the study results support a NOEL of
0.1 mg/kg/day for calculating margins of exposure for intermediate
exposure.
(c) Chronic/long-term exposure. The oral and inhalation toxicity
studies that EPA has evaluated resulted in comparable NOELs for
assessing chronic dietary and long-term occupational and/or residential
exposure (substantial portion of a lifetime). The inhalation study in
rats demonstrated a NOEL of 0.055 mg/kg/day (converted from 0.05 mg/
m3) based on statistically significant ChE inhibition in plasma,
RBC, and brain at 0.48 mg/m3. The oral study in dogs resulted in a
NOEL of 0.05 mg/kg/day, based on statistically significant plasma, RBC,
and brain ChE inhibition at 1.0 mg/kg/day. EPA rounded the inhalation
NOEL to 0.05 mg/kg/day for ease in calculating MOEs. In addition, there
is uncertainty associated with converting from mg/m3 to mg/kg/day
in the chronic inhalation study.
3. Adverse liver effects. The PD 1 also cited a concern for adverse
liver effects resulting from exposure to dichlorvos. A 2-year dog
feeding study indicated increased liver weight and enlargement of liver
cells with a NOEL of 0.08 mg/kg/day. EPA recently reevaluated this
study and downgraded its acceptability from minimum to invalid. The
study was reclassified because the actual dose ingested by the animals
cannot be confirmed, due to impurities and decomposition products in
the test material.
In addition, the 1 year oral dog study cited above was reviewed for
the purpose of evaluating the validity of the liver effect concern. No
liver effects were reported after 1 year of treatment at higher doses
than the doses in the invalidated 2-year study. Therefore, this
endpoint is no longer of regulatory concern.
C. Exposure Analysis
1. Dietary exposure--i. Background. Dietary exposure to a pesticide
depends on two components: the amount of pesticide residue on a
commodity and how much of that commodity is consumed. In estimating
dichlorvos residues on food, EPA relied on a variety of data for
dichlorvos, including tolerance levels (the legal maximum residue) and
field trial data (measured residues resulting from actual application
of dichlorvos). In addition, these estimated residues can be further
refined by taking into account the effects of processing and cooking on
treated foods, and by estimating the percent of the crop that is
treated.
The Agency currently uses food consumption values derived from a
USDA survey to estimate dietary exposure to pesticides. The USDA
conducted a nationwide survey (1977-1978) of the food consumption
patterns of 30,770 individuals for 3 days. Based on this survey, EPA
can estimate the dietary exposure and risk for the U.S. population and
22 subgroups of the total population using a computer-based tool called
the Dietary Risk Evaluation System (DRES). DRES multiplies the average
daily consumption values by residue information for each commodity to
obtain the total dietary exposure. In the absence of data for residues
of dichlorvos on crops and an estimate of the percent of the crop
treated with a pesticide, EPA estimates exposure based on the
Theoretical Maximum Residue Contribution (TMRC). The TMRC assumes
residues on crops are present at tolerance levels (the maximum residue
limit allowed by law) and 100 percent of the crop is treated. When EPA
has additional data to refine the TMRC, based on residue data and
estimates of percent of crop treated, the Agency uses this new
information to calculate the Anticipated Residue Contribution (ARC).
When available, the ARC is used instead of the TMRC in estimating
residues.
Dietary exposure to dichlorvos residues may occur as a result of
use on a variety of sites. These sites include greenhouse food crops,
food or feed containers, bulk-stored, bagged or packaged nonperishable
raw agricultural commodities (RACs) food, and bulk stored, bagged or
packaged nonperishable processed commodities, commercial food
processing plants, groceries, eating establishments, livestock (direct
animal treatment), swine feed (as a dewormer), and food in homes where
resin pest strips are located.
Tolerances and FARs exist for residues of dichlorvos in or on raw
agricultural and processed products and on meat, milk, poultry and
eggs. As noted in the Registration Standard, even though dichlorvos is
registered for use in food handling establishments (including food
processing, food manufacturing and eating establishments), there are no
FARs for the related uses.
In estimating dietary exposure for the initiation of Special Review
in 1988, the Agency did not have sufficient data on actual residue
levels. Therefore, EPA's dietary exposure estimate at that time was
based on the assumption that residues were present at tolerance levels
(40 CFR 180.235). Residues were adjusted based on cooking data on small
grains and on an estimate of percent of crop treated. At the time of
the initiation of Special Review, EPA estimated that the average
consumer in the U.S. population was exposed to 4.2 x 10-2 mg/kg/
day of dichlorvos. This may have been an overestimate of chronic
exposure because tolerance level residues were assumed. However,
limited data available at that time suggested that some residues were
at or above tolerance levels (nonperishable stored foods). In addition,
exposure could have been underestimated because, in the absence of a
FAR for food handling uses, the exposure estimate did not consider
residues from food handling uses, or any degradation resulting from two
related pesticides, naled and trichlorfon.
Amvac recently notified the Agency (Ref. 40) that it is not
supporting the reregistration of greenhouse food and nonfood uses and
that it requests voluntary deletion of those uses. Therefore, some
exposure may be eliminated as a result of these voluntary deletions, or
due to cancellation of uses related to the revocation of the FAR for
packaged or bagged nonperishable processed food. However, since these
actions have not occurred, EPA will continue to consider these residues
for this proposed determination.
ii. Naled and trichlorfon. Naled and trichlorfon degrade to
dichlorvos through plant metabolism. Three factors will significantly
affect dietary exposure to dichlorvos from registered uses of naled and
trichlorfon; these include, the preharvest interval (PHI), the
condition and length of storage, and cooking and processing. Naled is
metabolized to dichlorvos by plants. Plant metabolism studies show that
dichlorvos residues are formed 1 to 3 days after treatment with naled
and trichlorfon; however, dichlorvos residues are less than the limit
of detection (0.01 to 0.05 ppm) 7 days after treatment. In general,
registered uses of naled have PHIs of less than 7 days, while
trichlorfon registrations have PHIs greater than 7 days. Because of the
short PHIs for naled products, measurable residues of dichlorvos may be
present in the U.S. diet from naled treated food. EPA does not expect
measurable residues from
[[Page 50348]]
trichlorfon because of the longer PHIs. As a result, the dietary
exposure assessment for dichlorvos includes residues of dichlorvos
resulting from the application of naled but not from trichlorfon.
Neither naled or trichlorfon, themselves, have carcinogenic potential
in humans as concluded by EPA (Refs. 41 and 42)
iii. Data available for determining the ARC. Possible sources of
data to estimate the levels of residues to which the public is exposed,
when consuming treated commodities include: Tolerance levels,
controlled field trials, Food and Drug Administration (FDA)
surveillance and compliance monitoring data, FDA Total Diet Study data
(market basket survey based on a random sampling of residues on food in
grocery stores), USDA pesticide data program, and USDA/FSIS (Food
Safety Inspection Service) livestock monitoring data. The estimated
levels of residues can then be adjusted for the effects of processing
using processing studies, including commercial processing studies,
washing studies, cooking studies, and residue degradation studies. Of
these sources, the Agency relied on tolerance levels and field trial
data (adjusted for the effects of processing and cooking) to estimate
dietary exposure to dichlorvos. For a variety of reasons, the other
sources did not provide useful data (Ref. 43).
(a) Tolerance levels. Tolerance levels are used for an initial
dietary exposure analysis. Use of tolerance levels typically
overestimate chronic exposure because tolerance levels are set at a
level that is not likely to be exceeded when the pesticide is used
according to the label. Tolerance levels are also used in dietary
exposure assessments when no other appropriate data are available. In
the case of dichlorvos, no other data are available which reflect
currently registered uses on cucumber, lettuce, tomato, and radish,
and, therefore, tolerance levels are used here to estimate residues on
these crops.
(b) Field trials. Data from controlled field trials which reflect
currently registered uses are not available for most agricultural uses
of dichlorvos, since these uses are not being supported for
reregistration. Field trial data are available for mushrooms and figs,
and data from direct dermal treatments to cattle and poultry are
discussed in the dichlorvos Registration Standard. Field trial data are
also available for use on packaged or bagged food, use in food
manufacturing and processing facilities, and for secondary residues in
livestock commodities. EPA is including residue estimates for figs (raw
and dried), even though these tolerances were revoked, because figs may
be located in warehouses or areas where similar packaged, bagged, or
bulk commodities are treated.
(c) Processing and cooking studies. Residues for raw commodities
can be modified by processing factors to account for changes during
commercial or other processing and cooking. Processing, cooking and
decline (half-life) studies were available for cocoa beans, dry pinto
beans, tomato juice, ground roasted coffee beans, raw hamburger meat,
raw eggs, and raw whole milk. The resulting cooking factors were used
to reduce the Agency's estimate of residues for these commodities and
were translated to other commodities based on similarity of cooking
time and temperature. Additional cooking studies were available and
discussed in the Residue Chemistry Chapter of the Registration
Standard. Half-lives of dichlorvos in various commodities ranged from 0
to over 1,000 hours. The reduction of dichlorvos in cooking appeared to
be related to the length of time and temperature used in cooking.
Residues were adjusted based on these cooking factors to obtain the
ARC.
(d) Anticipated residues for dichlorvos--(1) Raw commodities. The
following registered uses are not being supported for reregistration
and the Agency does not have residue data reflecting current uses:
tomatoes, cucumbers, lettuce, and radishes. Therefore, current
tolerance levels are assumed in the exposure assessment. Amvac has
requested voluntary deletion of these uses from their labels; however,
because the deletion of these uses is not final, EPA is including these
commodities in the exposure assessment. Anticipated residues for raw
commodities as bulk, packaged, or bagged food are discussed below.
(2) Meat, milk, poultry and eggs. Residues in livestock tissues,
including milk and eggs, may result from consumption of dichlorvos
treated livestock feeds, direct dermal treatments, or from use as a
drug in swine. Livestock metabolism studies done at exaggerated rates
in ruminants and poultry have demonstrated that oral ingestion of
dichlorvos by cattle and poultry will not result in detectable
residues. This conclusion can be extended to the drug use of dichlorvos
in swine. Secondary residues in livestock from consumption of treated
feed are expected to be so low that EPA is estimating these residues as
zero. Data reflecting direct livestock treatments are discussed in the
Residue Chemistry Chapter of the Dichlorvos Registration Standard. Data
from direct dermal studies indicate that detectable residues are not
expected, except in skin. Residues are non-detectable (<0.01 ppm) in
cattle tissue and milk, and non-detectable (<0.05 ppm) in poultry
tissues and eggs. The exposure assessment uses one-half the limit of
detection in both cases. In the absence of direct dermal studies for
swine, the Agency estimated the residue on swine to be 0.08 ppm. This
estimate was based on a study in poultry that approximated the rate for
direct dermal swine treatment.
(3) Bulk stored, packaged or bagged commodities, food and feed
handling uses. The ARCs used in the exposure assessment for packaged,
bagged or bulk stored food are based on studies submitted by Amvac
(Ref. 44). Residue data were submitted for many commodities. For those
commodities where data were not submitted, EPA translated residue data
from similar commodities. For example, data on dry beans are translated
to other legumes; data on wheat flour are translated to all flours and
meals, etc. In addition, residue data were provided for corn and oats
at various points during processing, and for flour, sugar, dried milk,
dried eggs, shortening, and baking mix from a treated manufacturing
facility. Bulk stored commodities are assumed to be uncovered when
treated. Although pesticide labels state that bulk or unpackaged foods
should be covered or removed before spraying, it is not possible to
assess the effect of covering food since the type of material used in
the cover is not specified and the manner in which food is covered
would vary considerable. Therefore, food is assumed to be uncovered.
Since the proportion of commodities stored in bulk vs. packaged/bagged
is unknown, the ARCs are based on an average of the residues found in
bulk and packaged/bagged food for any particular commodity.
The FAR in 40 CFR 185.1900 for packaged or bagged nonperishable
processed foods and the tolerance in 40 CFR 180.235 for nonperishable
packaged, bagged or bulk raw food do not refer to specific commodities.
Therefore, EPA has developed a list of commodities likely to be treated
with dichlorvos that are covered by tolerances and/or FARs. Because
these tolerances and FARs were established to cover residues resulting
from use at different sites (for example, wheat could be treated in its
raw form in a silo, later as flour, during processing into cake mixes,
and finally as a stored packaged commodity), cancellation of any one of
the site-specific uses does not necessarily eliminate the risk of a
[[Page 50349]]
commodity from dichlorvos treatment. EPA did not combine the residues
from different sites in creating the ARCs, although the cumulative
residues from treating a commodity at different sites are considered in
the estimation of percent of crop treated (see paragraph (e) below).
Dichlorvos is registered for use in a variety of food handling
establishments, including: food service establishments (such as
restaurants and other locations where food is served and grocery
stores); manufacturing establishments (such as candy plants, spaghetti
and macaroni plants, bottling plants, and pizza plants); and processing
establishments (such as meat, poultry and seafood packing plants,
dairies and dairy product plants, frozen fresh food plants and grain
mills). EPA has data for estimating residues in manufacturing
establishments and processing establishments; however, there are no
data for estimating residues in eating and serving areas of food
service establishments. EPA did not include residues from this use in
its exposure assessment. Therefore, to the extent that dichlorvos is
used in food service establishments, the Agency's exposure assessment
is an underestimate of potential dichlorvos dietary exposure.
(4) Use of naled. All naled tolerances in 40 CFR 180.215 were
evaluated as a potential source of dichlorvos residues. Anticipated
residues are based on either tolerance levels or field trials. Naled
and dichlorvos residue estimates were reduced when data were available
for the effects of washing, cooking, and processing. In addition, wide
area application of naled in mosquito and fly control use could result
in residues potentially on all crops in the Agency's Dietary Risk
Evaluation System. Therefore, EPA included all these crops in its
estimate of anticipated dichlorvos residues. Although it is possible
that dichlorvos residues could occur on any raw agricultural commodity
from this use of naled, it is unlikely that residues would be found on
all commodities. As a result, this inclusion of residues from all raw
crops presents a possible source of overestimation of dietary exposure.
As discussed earlier, EPA does not expect measurable residues from the
use of trichlorfon because of the longer PHI for trichlorfon than for
naled.
(5). Percent of crop treated information. In conducting a chronic
risk assessment, EPA refines its estimate of dietary exposure based on
percent of crop treated when such information is available. In the
absence of this information, EPA assumes that 100 percent of the crop
is treated. Where a range of percent crop treated values are supplied
for this analysis, the upper end of that range is assumed (Refs. 45-
47).
(i) Dichlorvos. Although no quantitative estimates of percent of
crop treated were given for the agricultural sites of dichlorvos
(radishes, mushrooms, cucumbers, lettuce, and tomatoes), the Agency
assumed that less than one percent of these crops has dichlorvos
residues, because EPA's proprietary data indicates little or no use.
EPA earlier assumed, in the proposed revocation of the FAR for residues
of dichlorvos on packaged or bagged nonperishable processed food, that
the percent of crop treated estimate of 7.5 percent for food processing
plants should be applied to all sites, and therefore, to all raw and
processed non-perishable packaged or packaged food. The present
analysis assumes that the percent of sites treated at various points in
the processing and distribution channels should be added rather than
averaged, because, as discussed earlier, cancellation of any one of the
site-specific uses does not necessarily eliminate the risk of a
commodity from dichlorvos treatment. EPA now estimates that 20 percent
of the crop is treated based on the sum of percent of crop treated
estimates for bulk storage, processing plants, and warehouses.
(ii) Naled. Naled is used for mosquito and fly abatement in
municipalities, residential areas, swamps, tidal marshes, and
woodlands. Naled is also registered for controlling pests on several
specific agricultural sites. Application of wide area mosquito control
by air can result in drift or direct treatment to small crop areas or
margins of large fields. Because the mosquito and fly abatement use is
applied in agricultural settings without regard to a specific crop, EPA
has no way of eliminating any crops from its anticipated residue
estimate. Therefore, EPA is assuming that one percent of all
agricultural crops may potentially have dichlorvos residues resulting
from mosquito and fly abatement use. For certain crops which are grown
in water-filled areas (such as sugarcane) this may be an underestimate.
However, this one percent is considered an overestimate of percent of
crop treated across all commodities. For registered uses of naled on
specific crops, EPA used that specific percent of crop treated data
instead.
2. Occupational and residential exposure. Dichlorvos is used in a
wide variety of situations, involving different application methods and
equipment; at home, at work and in public areas. Individuals are
exposed to dichlorvos as professional applicators, and as reentry
workers. Residents are exposed from applying dichlorvos themselves at
home and from post application exposure. Individuals can also receive
post-application exposure at work or in public places. Pet flea collars
may pose a risk for both the pet and people who come in contact with
the dog or cat. Depending on the method of application or use, exposure
to dichlorvos can occur by either the dermal or inhalation route or
both. Because of the wide variety of uses for dichlorvos it is
difficult to estimate exposure for every possible situation. Therefore,
the purpose of this assessment is to estimate exposure in those
situations thought to have the greatest exposure and potential for the
greatest risks. The Agency would particularly like comments regarding
any uses with a significant exposure scenario not described in this
Notice.
EPA completed a series of exposure assessments in August 1987 for
the Registration Standard and PD 1. Many of the exposure assessments
were based on limited data. Since that time, additional exposure data
have been submitted to the Agency. These data have been evaluated and
EPA has determined that revisions to the original assessments are
appropriate. Based on this analysis, the Agency has revised exposure
estimates for the following uses: Crack and crevice application;
application to greenhouses, mushroom houses, dairy barns and milk
rooms. In addition, new data are available which allow the Agency to
estimate exposure from use of household aerosol and total release
fogger products. New exposure estimates have been developed for
warehouse treatment, and use on dairy cattle, buses, and commercial
vehicles. EPA used a variety of data for estimating occupational and
residential exposures. These data included studies which measured
dichlorvos following the use of a registered pesticide, surrogate
studies involving other chemicals which used the same or similar
application methods that would be used for dichlorvos uses, and in the
absence of these two data sources, the Agency used its best
professional judgment in estimating exposure. EPA's exposure estimates,
including assumptions, are presented in Table 1 in Unit II.C.2. of this
document (Refs. 48- 51).
The revised exposure estimate for crack and crevice treatment by
pest control operators (PCOs) considered data that were not available
at the time of the original assessment. Under most conditions, the
Agency assumed that professional applicators would wear a long sleeve
shirt, long pants, and gloves.
Data are also available to revise exposure estimates for
application to greenhouses, mushroom houses, and
[[Page 50350]]
dairy barns (milk rooms). Because a variety of application equipment
could be used to treat these sites, depending on product formulation,
the specific pest problem and personal preference of the applicator,
EPA evaluated several studies, each using a variety of application
equipment. Since these studies varied in design, it was not possible to
pool the data into one large data set. Therefore, EPA calculated
exposures separately for each study design, using correction factors
for protective clothing where necessary. Normal work clothing (i.e.,
long sleeve shirt and long pants) was assumed to offer 50 percent
protection, while gloves, coveralls and shoes were assumed to decrease
exposure 90 percent. This approach resulted in a range of estimated
exposures for each of the three sites. Table 1 in Unit II.C.2. of this
document summarizes these data.
The potential exposure of applicators using household aerosol
products was not directly addressed in earlier Agency assessments.
Since that time, EPA has received a study monitoring the exposure of
individuals during application of a one percent propoxur aerosol
product. This study can be used as a surrogate study for aerosol
products containing dichlorvos. EPA believes that application of one
entire can of pressurized aerosol represents a reasonable exposure
estimate for acute exposure scenarios. This may be a conservative
estimate in that not every resident will use an entire can at one time;
however, it is reasonable to assume that some individuals may choose to
apply an entire can. Exposure estimates were calculated for four
different clothing scenarios: (1) Long sleeve shirt, long pants, and
shoes; (2) short sleeve shirt, long pants, and shoes; (3) short sleeve
shirt, shorts, and shoes; and (4) and minimal clothing consisting of
shorts and shoes only. EPA is using a conservative clothing assumption
of only shorts and shoes because insects may present the greatest
nuisance in the summer when residents are likely to wear the least
amount of clothing.
EPA has also estimated exposures for individuals occupying or
reentering residences following treatment of rooms with a total release
fogger. These exposure estimates are also applicable to individuals
reentering homes following crack and crevice treatment and aerosol
spray application. The exposure estimates are based on a study that
measured potential exposure by monitoring urinary amounts of dimethyl
phosphate (DMP), a metabolite of dichlorvos, and by using whole body
dosimeters consisting of cotton shirts, tights, gloves, socks and
underpants. Because it appears that dichlorvos passed through the
dosimeters, use of the dosimeter data alone would underestimate
exposure. Therefore, EPA calculated total exposure by adding the
biomonitoring component and the amount trapped by the whole body
dosimeters. This is a conservative approach because it assumes that the
entire amount of dichlorvos trapped in the clothing could serve as a
pool for subsequent absorption. It is likely that some loss of
dichlorvos from the clothing would occur and, therefore, would not be
available for absorption. When biological monitoring alone is
performed, it is not possible to separate the dermal and respiratory
components of exposure. For this reason and because the study addresses
a homeowner/resident scenario where protective clothing and respiratory
protection do not apply, EPA has not separated these components but
rather addressed the total exposure of the volunteers without regard to
route. In addition, EPA is unable to estimate daily exposure values
because biomonitoring data were collected over a 2-day period in this
study. Rather, EPA estimated total exposure to individuals performing
activities at various intervals following treatment on 2 consecutive
days.
Table 1.--Summary of Dichlorvos Non-Dietary Risks
----------------------------------------------------------------------------------------------------------------
Exposure (mg/kg/day) Margin of
-------------------------------------- Exposure
Uses Notes Exposure Pattern1 (Cholinesterase
Dermal Inhalation Inhibition)
----------------------------------------------------------------------------------------------------------------
Domestic 2
Dwellings
(application)
Pressurized 3 0.097 3.3 x 10-7 Short-term 47
aerosol
----------------------------------------------------------------------------------------------------------------
Crack and 4 0.018 2.3 x 10-4 Long-term 23
crevice
treatment
----------------------------------------------------------------------------------------------------------------
Domestic No data
Dwellings (post-
application)
Total release 5 0.03 Short-term 17
fogger
Pressurized 6 0.03 Short-term 17
aerosol
Crack and 7 0.03 Long-term 2
crevice
treatment
Resin pest 8 2.5 x 10-3 Long-term 20
strips
Pet flea 9 2.1 x 10-4 Long-term 240
collars
----------------------------------------------------------------------------------------------------------------
Occupational 10
Exposure
----------------------------------------------------------------------------------------------------------------
Crack & crevice 11 0.078 negligible Long-term 6
treatment in
homes
----------------------------------------------------------------------------------------------------------------
Mushroom House 12
[[Page 50351]]
Applicator 4.0 x 10-5 to 1.8 x 10-5 to 6.7 Intermediate Majority of
0.74 x 10-4 scenarios have
MOEs less than
50, and some are
less than 10
Reentry ND 1.5 x 10-2 Short-term 21
----------------------------------------------------------------------------------------------------------------
Greenhouse 13
Applicator 2.6 x 10-5 to 4.4 x 10-4 to ND Short-term Majority of
0.48 scenarios have
MOEs less than
100, and 30% of
scenarios have
MOEs less than
50
Reentry 2.7 x 10-4 0.18 Short-term 2.8
----------------------------------------------------------------------------------------------------------------
Domestic food/ 14 0.15 No data Intermediate 6.1
nonfood animals
(non-poultry)
----------------------------------------------------------------------------------------------------------------
Domestic food/ 15 < non-poultry No data Intermediate > 100
nonfood animals
(poultry)
----------------------------------------------------------------------------------------------------------------
Domestic animal 16
premises (food
and non-food)
(Dairy barns)
Applicator 1.2 x 10-5 to ND - 2.0 x 10-4 Short-term > 100
0.03
Reentry No data No data Short-term > 100
----------------------------------------------------------------------------------------------------------------
Feedlots 17 < greenhouse < greenhouse Short-term > 100
----------------------------------------------------------------------------------------------------------------
Manure 18 < greenhouse < greenhouse Short-term > 100
----------------------------------------------------------------------------------------------------------------
Tobacco warehouse 19
Applicator - 0.2 ND Long-term 2
sprinkling
with water can
Mixer-loader 1.4 x 10-5 ND Long-term 32,500
Warehouse No data 0.20 Long-term 0.3
worker
(reentry)
----------------------------------------------------------------------------------------------------------------
Ornamental lawns, 20
turf and plants
Applicator 2.6 x 10-5 to 4.4 x 10-4 -- ND Short-term 32
0.48
Similar to power
sprayer in green
house
----------------------------------------------------------------------------------------------------------------
Warehouse 21
treatment
(affects
nonperishable
bulk, packaged
and bagged raw
and processed
commodities)
Application 0.1 0.002 Short-term 38
[[Page 50352]]
Reentry 2.7 x 10-4 0.18 Short-term 2.8
----------------------------------------------------------------------------------------------------------------
Kennels 22
Applicator similar to dairy similar to dairy Short-term > 100
barn barn
----------------------------------------------------------------------------------------------------------------
Insect traps 23 negligible negligible Short-term negligible risk
----------------------------------------------------------------------------------------------------------------
Garbage dumps 24 < greenhouse < greenhouse Short-term > 81
----------------------------------------------------------------------------------------------------------------
Commercial, 25
institutional
and industrial
areas
Application 0.1 0.002 Short-term 38
Reentry 2.7 x 10-4 0.18 Short-term 2.8
----------------------------------------------------------------------------------------------------------------
Commercial
transportation
vehicles
Airplanes 26
(disinsection of
aircraft)
Passenger - No data 3.7 x 10-3 Short-term 135
post-
application
Applicator No data 3.7 x 10-3 Long-term 14
----------------------------------------------------------------------------------------------------------------
Buses - passenger 27 9.2 x 10-3 Short-term 55
Truck, shipholds, 28
rail cars
Applicator < warehouse < warehouse Short-term > warehouse
Reentry negligible 2.45 x 10-2 Short-term 20
----------------------------------------------------------------------------------------------------------------
ND--Not Detectable
Notes: The following notes define the assumptions used in
calculating the margins of exposure.
1. Short-term MOEs based on NOEL of 0.5 mg/kg/day; Intermediate
MOEs based on NOEL of 0.1 mg/kg/day; Long-term MOEs based on NOEL of
0.05 mg/kg/day.
2. An average resident weighs 70 kg and has a respiratory volume
of 1.7 m3 per hour. No protective clothing is assumed.
3. Resident use of pressurized aerosol product is based on
application of an entire one percent 16 ounce can of pressurized
aerosol. EPA estimated the risk to residents for different clothing
scenarios. The MOE of 47 assumes the resident is wearing only shorts
and shoes. Pressurized aerosol products containing dichlorvos do not
have any clothing requirements, therefore EPA is assuming that
dichlorvos is applied during hot weather when an individual will be
wearing the least amount of clothing.
4. Dichlorvos is applied once per week for 44 weeks while
wearing no protective clothing.
5. Assumes less than 24 days of exposure per year and less than
2 days/month. The value 0.03 reported in the table includes both
dermal and inhalation, since it is based on biomonitoring data
(blood samples) and represents the dose to the individual rather
than exposure. All other dermal exposure values in the table must be
adjusted by the dermal absorption factor of 0.11 to arive at the
dose.
6. Same as for fogger.
7. Same as for fogger.
8. Assumes 365 days of exposure per year, 24 hours per day.
9. Assumes 365 days of exposure per year, 24 hours per day.
10. An average worker weighs 70 kg and has a respiratory volume
of 1.7 m3 per hour. For mushroom houses, dairy barns, and
greenhouses it is difficult to provide a single exposure estimate
because of the variety of possible application equipment and
differences in how studies were conducted. Therefore, a variety of
scenarios are presented for these three uses. At a minimum, the
following protective clothing was used in the exposure scenarios:
gloves, long-sleeve shirt, long pants.
11. A 0.5% solution of dichlorvos is applied using a hand held
low pressure sprayer. It is assumed that dichlorvos is applied by
PCO 10 times per day 1 day a week for 44 weeks. An average
commercial applicator wears coveralls, chemical resistant gloves,
and shoes. A respirator is not worn.
12. An average mushroom house has a volume of 30,000 ft3.
Dichlorvos is applied at a rate of 3.0 grams of active ingredient
per 1000 ft3 or 30 grams per treatment; 16 days per year, 10
houses per day; 4 minutes per house or 40 minutes per day.
Protective clothing was slightly different for each application
method. For reentry exposure, EPA assumed that a worker reenters a
ventilated mushroom house 24 hours after treatment and is exposed
for 8 hours. Dermal exposure is assumed to be negligible compared to
respiratory exposure.
13. A typical greenhouse operation consists of seven
greenhouses, each with a volume of 85,000 ft3. All seven
greenhouses are treated in one day. There are a maximum of three
applications per crop and three crops are produced per year.
Dichlorvos is applied at the rate of 1.4 grams of active ingredient
per 1000 ft3. The total time spent applying the insecticide is
26.25 minutes per day or 3.94 hours per year. The exposure value
assumes that, at a minimum, a worker wears a long sleeve shirt,
impervious gloves. In the absence of reentry data for a greenhouse,
EPA is assuming that reentry exposure is similar to that of a
warehouse.
14. Worker exposure from direct application to animals is based
on dairy cattle treatment. EPA does not believe that direct
application with a handheld sprayer is used primary method of
application. However, since several registered products provide
guidance on use with a handheld sprayer, the exposure and risk are
estimated here for that application method. A one percent solution
of dichlorvos is applied with a handheld sprayer. An average herd of
dairy cattle consists of 65 head, each requiring 24 seconds to
spray, two times per day during treatment. Fly control is required
from May to October with application
[[Page 50353]]
occurring weekly during this time (26 times per year). Personal
protective equipment consisting of impervious gloves (90 percent
protection), long sleeve shirt and long pants (50 percent)
protection are worn.
15. Data for cattle cannot be extrapolated to poultry, because
of the different application method and less frequent applications
for poultry. As a result, exposure from applying dichlorvos to
poultry is expected to be much lower than for cattle.
16. An average dairy barn has the dimensions 30 ft x 100 ft x 9
ft (total area covered is 4340 ft2 ). Dichlorvos is applied at
two week intervals for 22 weeks, one barn per day. A 1.0 percent
solution of dichlorvos is applied using a low pressure hand sprayer
at a rate of 3.4 gallons per hour. Daily exposure time is 0.20
hours. A worker wears a long sleeve shirt, long trousers, shoes and
impervious gloves at a minimum. Gloves offer 90 percent protection
to the hands and the other garments 50 percent protection. Coveralls
are assumed to offer 90 percent protection.
17. Feedlots include stockyards, corrals, holding pens and other
areas where groups of animals are contained. This application method
would probably be used for controlling insects on cattle. EPA
assumes that some type of power sprayer capable of treating a large
number of animals in a short time is probably used. A short
application time period in an outdoor or partially enclosed area
would minimize exposure to less than that of a greenhouse.
18. MOE is expected to be greater than 100 for manure use.
Application equipment may be similar to those used in a greenhouse;
however, the application time would probably be less and the treated
area would be well ventilated - either outdoors or in a partially
enclosed area.
19. Tobacco warehouse mixer/loader/applicator exposure is
expected occur twice a week for 27 weeks, totaling 54 days of
exposure. Warehouse reentry workers are expected to be exposed six
days a week for 27 weeks per year.
20. Use on ornamental lawns, turf and plants are expected to
have an exposure pattern similar to a greenhouse sprayer.
21. Dichlorvos can be applied to warehouses manually using
foggers or with wall-mounted automatic foggers. Exposure to mixer/
loaders through automatic application is expected to be negligible;
however, there would still be reentry exposure. In estimating
reentry exposure, EPA assumed six hours elapsed before reentry is
allowed, as required on labels; and that workers spend eight hours
per day in the treated area for the next three days. In estimating
exposure from manual application, EPA assumed that an average
warehouse has a volume of two million ft3; dichlorvos is
applied at the rate of 2.0 grams active ingredient per 1000 ft3
over a period of 125 minutes per application. On average, dichlorvos
is applied 12 times per year. Protective clothing consisted of
impervious gloves, an apron, coveralls, boots, hood, goggles and a
respirator during application.
22. Exposure in a kennel is believed to be similar to a dairy
barn.
23. Exposure is believed to be negligible since the pesticide is
in the form of an impregnated strip and the traps are placed in
outdoor areas (such as forests) where there is no human exposure.
24. Exposure at a garbage dump is believed to be less than
greenhouse exposure.
25. Exposure is believed to be similar to warehouse exposure.
26. Aircraft personnel are exposed to dichlorvos 30 minutes once
per week, 52 times per year. No protective clothing is worn,
representing a chronic exposure scenario. Passenger exposure is an
acute scenario.
27. Passengers are exposed to airborne dichlorvos for four hours
in buses following two hours aeration. Passenger respiratory volume
is assumed to be 0.44 m3/hour which is less than for workers
because passengers are at rest.
28. EPA is assuming that exposure from application should be
less than that for warehouses because of the smaller area to treat -
therefore less exposure time. However, because a short term exposure
scenario is involved, EPA is concerned about the potential risks
from any type of hand application, assuming no respiratory
protection. For reentry, the MOE of 20 is based on 8 hours of
exposure after a 12-hour reentry period. Even a 24 hour reentry
peroiod results in an MOE of 60.
D. Risk Characterization
1. Chronic dietary. This section summarizes chronic risk estimates
from dietary exposure to dichlorvos, including risks due to direct
application of dichlorvos and dichlorvos which occurs as a metabolite
from the use of naled. In initiating the Special Review in 1988, EPA
estimated the upper bound dietary cancer risk from dichlorvos
application alone to be 8.4 x 10-5 or in the range of 10-4,
for the general U.S. population. EPA believed this to be an
overestimate because it was based on a number of conservative
assumptions. The Agency is now able to provide a more realistic dietary
risk estimate based on field trial data, processing and cooking data,
and refinements in percent of crop treated data (Refs. 52 and 53).
i. Noncancer. The Agency estimates chronic dietary risks for
noncancer endpoints by comparing dietary exposure to the Reference Dose
(RfD). The RfD is an estimate of the daily oral exposure to humans over
a lifetime that is not expected to result in adverse health effects.
The RfD is based on the determination of a critical effect from a
review of all toxicity data and a judgment of uncertainty. In the case
of dichlorvos, the RfD is 0.0005 mg/kg body weight/day, based on a NOEL
of 0.05 mg/kg body weight/day and an uncertainty factor of 100 to
account for extrapolation from animal data to humans and variability in
the human population. The NOEL, was taken from a 1 year feeding study
in dogs in which plasma and red blood cell ChE inhibition (ChE) were
the effects observed in males and females; in addition, brain ChE
inhibition was observed in males (Ref. 54).
Using anticipated residues and percent of crop treated data, EPA
estimated the exposure from registered uses of dichlorvos to be
0.000054 mg/kg body weight/day, which represents 11 percent of the RfD
for the general U.S. population. EPA estimates that the ARC to the most
highly exposed population subgroup, non-nursing infants under 1 year,
is 0.000143 mg/kg body weight/day, or 29 percent of the RfD. The ARC
for the U.S. population from dichlorvos derived from registered uses of
naled is 0.000016 mg/kg body weight/day or 3 percent of the RfD. EPA
estimates that the ARC to the most highly exposed population subgroup,
``non-nursing infants under 1 year,'' is 0.000057 mg/kg body weight/
day, or 11 percent of the RfD. EPA concludes that the risk from ChE
inhibition due to chronic dietary exposure is minimal and not of
concern.
The Agency does not have a concern for cholinesterase inhibition
from DDVP use on foods at this time. This conclusion is based on the
dietary risk assessment for DDVP alone. If exposure from other
cholinesterase inhibitors, either on the same or different foods in
addition to DDVP were considered, a cumulative exposure may trigger a
risk concern. The Agency currently has no methodology for assessing
cumulative exposure from cholinesterase inhibitors via ingestion of
treated foods. However, the Agency plans to pursue options towards this
end in the coming years and at that time will solicit public input on
possible methodologies.
ii. Cancer. In estimating the upper bound cancer risk, chronic
dietary exposure is multiplied by the cancer potency of the chemical.
This analysis uses the upper bound cancer potency factor (or Q1*)
for dichlorvos of 1.22 x 10-1 (mg/kg/day)-1 and assumes that
an individual is exposed over a 70-year lifetime. Based on these
assumptions, the estimated upper-bound excess individual lifetime
cancer risk from direct application of dichlorvos is 4.4 x 10-6
and from naled-derived dichlorvos it is 7.2 x 10-7 for a total of
5.1 x 10-6 (see Table 2 of this paragraph). At a future date, EPA
will issue a Reregistration Eligibility Document for naled which
provides further analysis of naled-derived dichlorvos. The major source
of estimated risk is dichlorvos residues from use on packaged, bagged
or bulk nonperishable processed or raw food (3.4 x 10-6). The
estimated risk from the three individual tolerances and FAR (bulk raw,
packaged or bagged raw,
[[Page 50354]]
and packaged or bagged processed) cannot be separated because, as
discussed earlier, a single commodity may be treated more than once at
different stages of production. EPA has published a final revocation
notice for the FAR for residues of dichlorvos on packaged or bagged
nonperishable processed food. If this revocation becomes effective and
the related uses are canceled under FIFRA, this source of dietary risk
will be eliminated.
Table 2.--Upper Bound Cancer Risk Estimates from use of Dichlorvos
------------------------------------------------------------------------
Tolerance Expression Upper Bound Cancer Risk
------------------------------------------------------------------------
Use of Dichlorvos
------------------------------------------------------------------------
Packaged or bagged, non-perishable 3.4 x 10-6
processed food and RACs (including
bulk stored, regardless of fat
content)
------------------------------------------------------------------------
Milk 6.2 x 10-7
------------------------------------------------------------------------
Eggs 7.1 x 10-8
------------------------------------------------------------------------
Red Meat 1.1 x 10-7
------------------------------------------------------------------------
Poultry 3.7 x 10-8
------------------------------------------------------------------------
Agricultural uses 2.1 x 10-7
Lettuce 1.6 x 10-7
Cucumbers 2.6 x 10-8
Tomatoes 1.4 x 10-8
Mushrooms 2.6 x 10-9
Radishes 9.8 x 10-10
------------------------------------------------------------------------
Naled derived dichlorvos 7.2 x 10-7
------------------------------------------------------------------------
Total 5.1 x 10-6
------------------------------------------------------------------------
2. Occupational and residential risks--i. Carcinogenicity. The PD 1
in 1988 estimated risks from cancer to pesticide workers and residents
based on dermal and inhalation exposure. Since that time, as discussed
earlier in this unit, EPA has decided that it is no longer appropriate
to quantify cancer risk for the inhalation and dermal routes, as
discussed above in Unit II. Therefore, cancer risks for workers and
residents by the inhalation and dermal routes are no longer a concern
for this preliminary determination.
ii. ChE inhibition. The duration and frequency of exposure vary
considerably for the numerous uses of dichlorvos. MOEs are based upon
comparison of exposure estimates against NOELs of 0.5 mg/kg/day for
short-term, 0.1 mg/kg/day for intermediate, and 0.05 mg/kg/day for
long-term exposure scenarios. The NOELs are based on brain ChE and/or
cholinergic signs, and were derived from toxicological studies by the
oral route; however, dermal exposure is an important route of
occupational/residential exposure. Therefore, the Agency's oral
exposure estimates are adjusted for the dermal absorption of dichlorvos
(factor of 0.11), to account for the route-to-route extrapolation.
For most uses in Table 1 of Unit II.C.2. of this document, a single
exposure estimate and corresponding MOE are given. However, this was
not possible for mushroom houses, greenhouses, and dairy barns because
of the number of potential application methods and the inability to
combine the various studies into one data set. The Agency does not
believe there are any naled-derived dichlorvos risks resulting from
occupational/residential exposure because a tank mix study showed that
naled did not readily degrade to dichlorvos under actual use
conditions. This is consistent with the finding that dichlorvos results
from plants metabolizing naled, as discussed above.
MOEs are used by EPA as an indication of the level of risk from ChE
inhibition. EPA is generally concerned about exposures to humans where
the MOEs are less than 100, since they may not provide an adequate MOE
after accounting for uncertainty (i.e, extrapolation from animals to
humans and variability in the human population). MOEs are less than the
uncertainty factor of 100 for the majority of sites examined in this
assessment, and some are less than 10. MOEs fall below 100 for both the
applicator of dichlorvos and for individuals living or working in
treated areas (Ref. 55).
The occupational and residential risk assessment contains the
following uncertainties that could result in an underestimate or
overestimate of the true risk: (1) In the absence of actual dermal
toxicity studies, toxicity by the dermal and oral routes were assumed
to be comparable after adjusting for differences in absorption, (2)
subchronic and chronic inhalation data are available, and EPA assumed
that toxicity by the oral and inhalation routes are comparable, (3) the
NOEL used to calculate short-term MOEs is based on cholinergic signs,
(4) the exposure parameters are dated and may have changed for some
scenarios, (5) in many cases surrogate exposure data were used for
estimating occupational and residential exposure, and in the absence of
such data, the Agency made assumptions that a particular exposure
should not exceed that of a scenario where surrogate or actual data
existed, and (6) MOE estimates may vary significantly depending on the
method of application and protective clothing assumptions.
There are additional uncertainties regarding potential risks to
children exposed to dichlorvos from residential uses, including
variability in activity patterns, the extent of non-dietary oral
ingestion, due to hand object-to-mouth activity, respiratory rate and
tidal volume, surface area to volume ratio, dermal absorption, and
toxicological susceptibility. Consideration of children's risk could
possibly have resulted in lower MOEs. However, the Agency believes that
the proposed actions will nonetheless serve to adequately protect
children from residential exposure. The Agency is currently conducting
research to provide refinements to assess children's exposure, and is
working to update our guidelines for household and work related
exposures.
3. Analysis of comments on the PD 1. The Agency received comments
relating to risks discussed in the PD 1. Rebuttal comments and complete
Agency responses are on file in the dichlorvos Public Docket. The
following is a summary of the major comments, and the Agency's
responses.
Comment. Amvac Chemical Corporation argued that the ``weight-of-the
evidence'' from animal studies is limited or inadequate to assess human
cancer risk, and that the Group B2 classification is not appropriate.
Agency Response. This comment is moot since dichlorvos was
reclassified from a B2 to a C carcinogen, as explained above.
Comment. With regard to the pancreatic tumors seen in F344 rats,
``Since there are no pharmacokinetic or physiological reasons to expect
females to be unique in their responsiveness to dichlorvos, the absence
of an effect in females weakens the significance of the effect increase
in males.''
Agency Response. The pancreatic acinar adenomas were eliminated
from consideration in the fourth cancer peer review.
Comment. With regard to the dichlorvos swine feeding study, the
registrant states that the ``histopathological results are of value for
the assessment of the carcinogenicity of dichlorvos in a third
species.''
Agency Response. The Agency does not believe that this study would
be
[[Page 50355]]
adequate as an oncogenicity study in a third species because of the
limited duration of the study and the limited histopathology apparently
conducted.
Comment. With regard to the dichlorvos dog feeding study (2-year),
the registrant stated that ``[t]he study showed no suggestion of
carcinogenic effects of DDVP in dogs.''
Agency Response. The Agency does not believe that a 2-year feeding
study in the dog is of long enough duration to conclude that there are
no carcinogenic effects of dichlorvos.
Comment. With regard to the mutagenicity of dichlorvos, the
registrant states that ``dichlorvos has not been shown to present a
significant risk of mutagenic effects to animals or humans.''
Agency Response. The comment did not include a discussion of
results of mutagenicity studies conducted by the NTP in conjunction
with conducting the bioassays on dichlorvos. Dichlorvos was found to be
positive in two mammalian systems, for point mutations in the mouse
L5178 lymphoma cell assay without metabolic activation (assay with
activation was not done) and for sister chromatid exchanges in Chinese
hamster ovary cells both with and without metabolic activation.
Comment. Amvac has supplied the Agency with additional information
on the chronic rat inhalation study indicating that the test animals
may have been exposed to substantially more dichlorvos than was
measured in the inhalation chambers. The registrant estimated that the
high-dose animals may have been exposed to 10 mg/rat/day, equivalent to
25 mg/kg/day in males and 34 mg/kg/day in females.
Agency Response. The Agency believes that the additional
information provided by Amvac does not provide sufficient evidence to
support adjusting the doses administered to the test animals.
Comment. Amvac stated that the dog study, which formed EPA's
initial concern about liver toxicity, did not satisfy Subdivision F
guidelines.
Agency Response. EPA has invalidated this study and liver effects
are no longer of concern.
Comment. Pest Control Services, Inc. commented that the Agency
overestimated the exposure for the No-Pest strip for use in museums.
Agency Response. First, EPA's exposure estimate was based on
residential use where individuals are constantly exposed to dichlorvos.
Because there are so many uses of dichlorvos, it is difficult to
anticipate every possible exposure scenario. To protect the public
health, the Agency focused on the high exposure scenario in the home.
Use in museums (i.e., enclosed spaces such as display cabinets, display
drawers, etc.) would be similar to that of grain silos, in that
individuals would not be constantly exposed to the No-Pest Strip.
Therefore, this preliminary determination does not propose any risk
mitigation for use of No-Pest Strips in enclosed spaces in museums. In
addition, an error in the Agency's 1987 exposure estimate has been
corrected, reducing the residential exposure estimate from 9.6 mg/kg/yr
to 0.93 mg/kg/yr. Even with this reduction in estimated exposure, the
short-term and long-term MOEs for residential use are still far below
100.
III. Benefits Assessment
A. Summary of Benefits Assessment
EPA conducted a benefits assessment which concludes that the
overall annual economic impact of a dichlorvos cancellation to users
and consumers is not expected to be significant for most sites (Ref.
56). EPA knows of no major benefits from retaining most uses of
dichlorvos with the probable exception of packaged or bagged
nonperishable raw and processed food; poultry and livestock premises;
feedlots; and possibly mushroom houses. Furthermore, for most of the
individual dichlorvos use sites, a number of alternatives are
registered and available. Any economic impacts are expected to diminish
over time as users adjust to the alternative control measures. The
major benefits of dichlorvos relate to its chemical properties:
knockdown action and vapor activity. Its quick knockdown ability makes
dichlorvos desirable for fly control, although it has little residual
activity. In addition, dichlorvos is said to have vapor action which
gives it penetration characteristics similar to a fumigant. Because of
this characteristic, some users claim that there are no equivalent
alternatives for certain uses.
B. Background
Dichlorvos, an organophosphate insecticide, kills insects on
contact. Products containing dichlorvos are registered for use in
controlling various invertebrate pests (insects, mites, spiders,
scorpions, and sowbugs) in diverse situations. Dichlorvos is formulated
alone and in combination with other active ingredients as emulsifiable
concentrates, soluble concentrate liquids, granulars, pressurized
liquids and dusts, smoke generators, impregnated materials, pellets/
tablets, liquids (ready to use), total release aerosols, and wettable
powders. Although dichlorvos has little residual activity, the
knockdown action and vapor activity of the chemical are said to make it
a versatile and effective chemical for pest control. Applications are
made with aerosol and fogging equipment, smoke generators, hand-held
sprayers, other ground spray equipment, and through slow release from
impregnated materials, such as resin strips and pet collars. Amvac
Chemical Corporation is the sole producer of technical grade dichlorvos
in the United States. Dichlorvos is registered for use on a number of
diverse indoor and outdoor sites.
C. Usage Information
Total annual usage of dichlorvos is estimated to range from about
250,000 to 500,000 pounds of active ingredient. The Agency believes
that most of the dichlorvos is used for animal, livestock and premise
treatments, and on bulk, packaged or bagged raw or processed food. EPA
estimates that these sites account for between 45 and 83 percent of the
dichlorvos used in the United States annually. Most of the remaining
dichlorvos is used in greenhouses, homes, and mushroom houses.
D. Method
The approach of the benefits analysis was to evaluate, on the basis
of available information, the potential economic impacts associated
with the switch to alternative pest control technologies caused by the
possible cancellation of certain dichlorvos uses. Future Agency action
could change the availability and use of the alternatives. However,
this analysis does not anticipate or speculate on the possible effects
due to specific regulatory actions on the other chemical alternatives
identified.
The following analysis is qualitative in scope. The information
presented in the specific site assessments identifies the major pests
controlled by dichlorvos for these sites, identifies the major
registered alternatives and their availability, estimates the change in
pest control costs associated with the use of the alternatives, and,
where possible, evaluates impacts to users.
Usage estimates for the major dichlorvos use sites were based on
various proprietary and non-proprietary usage data. Prices for
dichlorvos and alternative products were based on pesticide product
catalogues, quotes from pesticide distributors, and market surveys of
consumer products. Determination of primary pests and major
alternatives was based upon previous site-specific assessments prepared
by a USDA/National Agricultural Pesticide Impact Assessment Program
(NAPIAP)
[[Page 50356]]
Assessment Team, a DPRA Inc. Benefits Assessment (a private source of
benefits information), and Preliminary Benefits Assessments (PBAs) by
EPA. If specific site assessments were not available, then state
recommendations, specimen label guides, the 1992 Insect Control Guide,
and the EPA Index to Pesticide Chemicals provided information about the
primary pests and alternative chemical controls for each site.
USDA completed a benefits assessment for dichlorvos in early 1990,
based on survey data and expert opinion, that estimates the average
annual benefit to be at least $120 million. This estimate was based on
data from the mid-80's when usage was much higher than it is now. EPA
estimates that dichlorvos usage has declined from approximately 2
million pounds annually at the time of the PD 1 (1985 data) to about
250,000 to 500,000 pounds per year at present. In addition, Amvac has
requested voluntary deletion of several uses, which account for some of
the current usage. Therefore, the use deletions will reduce usage even
further.
In conducting the benefits assessment, each site was analyzed to
determine the impacts that would result if dichlorvos were canceled for
that site, (See Table 3 in this Unit). Comparative performance data
were not available; therefore, the analyses were based on comparative
cost assessments under the assumption that sufficient products were
available which would provide adequate control of the pests.
The alternatives to dichlorvos include carbamates,
organophosphates, natural pyrethrins and synthetic pyrethroid
compounds. EPA has identified the following insecticides as likely
alternatives to dichlorvos: bendiocarb, carbaryl, chlorpyrifos,
diazinon, malathion, naled, phosmet, propoxur, permethrin, pyrethrins,
resmethrin, and tetrachlorvinphos. In addition, non-chemical
alternatives were also identified where information was available. In
most cases these non-chemical alternatives help control insect
populations which may result in a decrease in the frequency of chemical
treatments. It is unlikely that these non-chemical alternatives would
replace dichlorvos to the extent that a chemical alternative would.
E. Individual Sites
Table 3 in Unit III.F. of this document lists detailed information
on the benefits for each site.
1. In and around domestic buildings. Dichlorvos is used in and
around domestic buildings primarily as an aerosol treatment to control
a variety of insects. It is also used in foggers and impregnated resin
pest strips. A variety of chemical alternatives are available. In the
absence of efficacy data, EPA is assuming that the alternatives would
provide similar levels of control. Non-chemical alternatives are also
available. EPA estimates that less than 1 percent of total dichlorvos
is used in the home; however, it is unknown how much of this is applied
by commercial applicators.
2. Pets. Dichlorvos is used to control fleas and ticks on dogs and
cats through the use of impregnated plastic flea and tick pet collars.
There are a variety of alternative chemicals available to dichlorvos,
some of which have had reports of tick and flea resistance. Due to the
lack of comparative efficacy and resistance data, EPA assumes that
collars with and without dichlorvos have equal efficacy. There are also
non-chemical alternatives available which can reduce the frequency of
pesticide treatment, including: sanitation, vacuuming pet living and
sleeping quarters, and washing or replacing bedding. EPA estimates that
pet collars represent 3 percent of total dichlorvos usage. EPA does not
expect the economic impact from cancellation of dichlorvos to be
significant, because dichlorvos is not one of the major insecticides
used in cat and dog collars.
3. Mushroom houses. Dichlorvos is used only as a space spray to
control the adult mushroom fly complex after surface sprays and
larvacides no longer provide adequate control; therefore, only
permethrin is considered an actual alternative (Ref. 57). Non-chemical
controls include black light traps to monitor fly emergence and
quantify fly influx. There may be some pest resistance to both
dichlorvos and permethrin; however, due to the lack of comparative
efficacy or resistance data, EPA assumes that acceptable levels of
control would be provided by both chemicals. EPA estimates that 2
percent of total dichlorvos is used on mushrooms. The Agency has
information that suggests dichlorvos is primarily used as an emergency
treatment if larval treatments fail. Economic impacts to the mushroom
industry cannot be accurately assessed due to the limited usage data
available regarding the use of the alternative chemicals. Based on
limited information, some impacts are possible; however, economic
impacts are not expected to be significant if dichlorvos is not
available.
4. Greenhouses. Dichlorvos is used primarily as a space spray for
control of a variety of insects on both food and nonfood greenhouse
plants. The major direct alternatives, used as space sprays, aerosols,
bombs, or pressure fumigators (smoke generators) include nicotine,
pyrethrins, and resmethrin. There are also a variety of other
alternatives used as greenhouse surface treatments and direct
application to plants. There are reports that some whitefly species may
be resistant to resmethrin; however, in the absence of comparative
efficacy or resistance data EPA assumes that similar levels of control
would be provided by the alternatives. Non-chemical mitigation measures
to reduce pesticide applications include: sticky board traps, good
sanitation practices and the use of insect free transplants. Total
usage in greenhouses is less than 2 percent of total dichlorvos usage;
however, available usage data do not separate food and non-food use of
dichlorvos in greenhouses. If the number of applications is assumed to
be equal for dichlorvos and the alternatives, then economic impacts
resulting from the loss of dichlorvos are not expected to be
significant.
5. Direct application to animals and animal premises. Dichlorvos is
applied directly to domestic food and non-food animals primarily to
control flies. Other insects are also controlled with dichlorvos (See
Table 3 in Unit III.F. of this document). There are various
alternatives available, which vary somewhat for each type of livestock
and poultry. There are reports that flies are resistant to permethrin;
however, in the absence of comparative efficacy or resistance data, EPA
assumes that all products would perform similarly. Non-chemical control
measures include the use of parasitic and predatory wasps that have not
gained much commercial acceptance; upgraded/improved sanitary
conditions involving manure management, trapping insects, and the
introduction of bacteria and viruses that are pathogenic to the pests.
Most uses on animals make use of some type of automatic method rather
than hand-held application, therefore the loss of hand-held application
should not result in a significant impact on users.
Dichlorvos is used as a space spray, animal spray, residual
treatment, or bait in controlling flies in animal premises. There are a
variety of chemical alternatives available. There are reports that
flies are resistant to permethrin; however, in the absence of
comparative efficacy or resistance data, EPA assumes that all products
would perform similarly. Non-chemical controls include improved manure
management, use of parasites, traps, sanitation, and electrocutors. EPA
estimates the total usage for direct animal treatment and premise
treatment for all domestic
[[Page 50357]]
animals is 100,000 to 200,000 pounds of active ingredient or between 27
percent and 54 percent of all dichlorvos usage. The actual cost of
alternatives depends on the number of treatments needed to replace
dichlorvos. Based on limited information, it is probable that some
localized impacts would occur if dichlorvos were not available;
however, EPA does not expect economic impacts to be significant overall
(Refs. 58 and 59).
6. Feedlots. Dichlorvos is used in feedlots (including areas around
feedlots, stockyards, corrals, holding pens, fences etc.) primarily as
a space spray (fog) and as an indoor residual premise treatment to
control flies. There are chemcial alternatives for space sprays and
indoor residual premise sprays. Non-chemical alternatives include
parasites, predators, and sanitation practices (removal of manure and
organic matter). Based on information from USDA NAPIAP (Ref. 60) there
are probable benefits from use of dichlorvos in feedlots. Depending on
the alternative, loss of dichlorvos could result in cost increases or
decreases. Overall, the economic impact due to loss of dichlorvos is
not expected to be significant.
7. Manure. Dichlorvos is applied directly to manure (including
dairy and beef cattle, and poultry) on farms to control flies. There
are chemical alternatives for use as a direct manure treatment and as
bait treatments. Non-chemical alternatives include the use of
predators, parasites, insect traps, electrocutors, repellors, and
removal of manure and organic matter. The cost per application is
expected to be less for the alternatives. Therefore, the economic
impact due to loss of dichlorvos is not expected to be significant.
8. Garbage dumps. Dichlorvos is used as a surface spray or bait
treatment in garbage dumps to control flies. Chemical alternatives
exist for each application method, all of which are believed to provide
similar levels of fly control. The nonchemical alternative is
sanitation - i.e. frequent removal or burial of garbage. Use of
alternatives is expected to result in cost increases; however, actual
costs would vary according to application rate and frequency. Because
of the existance of chemical and non-chemical control measures, the
economic impact due to loss of dichlorvos is not expected to be
significant for this site.
9. Ornamental lawns and turf. Dichlorvos is used to control a
variety of insects and related pests on these sites through the use of
multi-active ingredient products. The major alternatives are considered
to be equal to or superior to the efficacy of dichlorvos. Depending on
the turf site and pest species, a wide variety of non-chemical control
measures are available, including nematodes, flushing with water,
improved management of turf, and use of resistant varieties of grass.
EPA has no information suggesting that there is any significant usage
of products containing dichlorvos on turf. The Agency believes that any
such usage is likely to be by commercial applicators with multi-active
ingredients containing both dichlorvos and chlorpyrifos. Because usage
of products containing dichlorvos on turf appears to be negligible and
the cost and efficacy of many of the alternatives are comparable to
dichlorvos products, the impact of canceling dichlorvos on turf is
expected to be negligible.
10. Ornamental plants. Dichlorvos is used on a variety of
ornamental plants, including shade trees, hardwoods, flowering trees,
conifers, evergreens, woody shrubs, vines, flowering plants and grasses
(excluding turf). A variety of alternatives are used which depend on
the pest and host plant. No comparative efficacy data are available;
therefore, the Agency assumes that similar levels of control would be
provided by all the chemicals listed in Table 3 in Unit III.F. of this
document. Depending on the host plant and pest species, a wide variety
of non-chemical control measures are available, including hand picking,
sanitation, mulching, and improved cultural management. Dichlorvos
usage information is not available. However, economic impacts are not
expected to be significant due to the availability of several
alternatives.
11. Bulk, packaged or bagged nonperishable processed and raw food.
Dichlorvos is registered for use on bulk, packaged or bagged
nonperishable processed and raw food to control a number of stored
product insect pests. EPA believes that dichlorvos is used primarily as
a space treatment with aerosols, foggers or as a fine stream applied to
the cracks, crevices, and general storage areas of warehouses and
similar facilities.
EPA believes that the major alternative to dichlorvos when used as
a space treatment would be the pyrethrins. No comparative efficacy data
for dichlorvos and pyrethrins are available to EPA at this time;
therefore, EPA assumes that all the registered pesticides would provide
adequate control of the pests. However, dichlorvos, unlike pyrethrins,
is said to possess fumigant-like properties (high vapor pressure) and
to rapidly penetrate throughout areas containing stacked commodities.
Due to the different properties of dichlorvos and pyrethrins, EPA
believes dichlorvos has the potential to be a more effective
insecticide than pyrethrins by requiring fewer treatments to provide
the same level of control in these situations. The Agency does not have
data available to be able to estimate the number of applications needed
for dichlorvos compared to pyrethrins. Without these data, the Agency
can only estimate the cost difference on a per application basis.
The cost of treating 1,000 cubic feet would be $0.18 for pyrethrins
and $0.04 for dichlorvos. Thus pyrethrins would cost $0.14 more than
dichlorvos. EPA estimated that 50,000 to 75,000 lbs of the active
ingredient of dichlorvos are applied to approximately 2 to 3 billion
cubic feet of warehouse space for packaged or bagged nonperishable
processed and raw food.
The characteristics of pyrethrins suggest that fumigations with
methyl bromide or aluminum phosphide may be needed to supplement
pyrethrins. Without the use of additional fumigants to supplement the
pyrethrins, there could be some loss in overall control; however, EPA
has no basis to confirm or estimate the resulting loss. EPA estimates
the additional cost of using pyrethrins instead of dichlorvos to be $12
million per year. The additional cost of supplemental fumigations would
be about $33 million with methyl bromide and $44 million per year with
aluminum phosphide.
12. Kennels. Dichlorvos is used primarily as a residual surface
spray for treating outside runways, window sills and ledges in kennels,
to control fleas, ticks, flies, and mosquitoes. There are a variety of
chemical alternatives available. There are reports of flea resistance
to chlorpyrifos, propoxur, and carbaryl; however, due to the lack of
comparative efficacy or resistance data, the Agency assumes similar
levels of control would be provided by the various alternatives. Non-
chemical alternatives include sanitation practices such as cleaning of
kennels, laundering of bedding, and frequent changing of litter when
used in combination with chemical treatment. There are no data on usage
in kennels. No adverse economic impacts are expected to result from the
cancellation of dichlorvos, since several alternatives are available
and may cost less than dichlorvos per application.
13. Insect traps. Dichlorvos is used in pheromone traps to monitor
heavy populations of gypsy moths and other insects in remote forested
areas. In other situations adhesive coatings are used. Non-chemical
adhesive coatings can be
[[Page 50358]]
as effective or more effective except when large numbers of insects
entirely coat the strips. Economic impacts from cancellation would be
negligible, since monitoring would only be less effective for heavy
populations of insects.
14. Commercial, institutional, and industrial areas. Dichlorvos is
used primarily as a residual surface spray or space treatment in
restaurants, food processing and storage areas, transportation
facilities, lodging, schools, and hospitals, to control a variety of
insects. There are a variety of alternative chemicals; however, due to
the lack of comparative efficacy data or resistance data, EPA assumes
these alternatives will provide equal efficacy. Economic impacts are
not expected to be significant if dichlorvos is canceled, although
there could be a slight increase in costs from use of alternatives.
15. Commercial transportation vehicles--i. Airplanes and buses.
Dichlorvos is used primarily as a space treatment in airplanes and
buses for the control of a variety of pests including ants,
cockroaches, fleas, flies, and quarantine pests. The major alternatives
are phenothrin, pyrethrins, and resmethrin all of which are assumed to
offer comparable efficacy to dichlorvos. No economic impacts are
expected since current dichlorvos use is believed to be minimal.
ii. Trucks, shipholds, and railroad cars. Dichlorvos is used
primarily as a space treatment in these vehicles primarily to control a
variety of stored product pests. Major alternatives are pyrethrins and
resmethrin, and equal efficacy to dichlorvos is assumed. A variety of
non-chemical alternatives are available, including sanitation, modified
atmospheres, irradiation, and controlled temperatures (hot and cold).
Economic impacts are not expected to be significant, based on the
availability of alternatives and the similarity in costs.
F. Strengths and Uncertainties of Benefits Assessment
The strengths of the benefits assessment include the identification
of pests on which dichlorvos is used, alternative pesticides, methods
of application, and application rates. There are also weaknesses in
this benefits assessment: specific use and usage information is dated;
many dichlorvos labels include a wide range of generalized use sites,
making it difficult to describe specific uses (e.g. warehouses);
comparative efficacy and product performance data do not exist for
dichlorvos and its alternatives; there are no data regarding the number
of treatments needed with an alternative to replace dichlorvos
treatments; and there are no data regarding pest resistance to
alternatives. Because of limited use and usage information, the
benefits may be understated for fly control in feedlots, on livestock
and livestock premises, and pest control in storage areas.
Little usage information for dichlorvos is available. Products
containing dichlorvos come in several formulations, may be applied by
several different methods, and can be used in many situations (for
example, different types of warehouses); therefore, determining the
usage for a particular site is difficult. The lack of comparative
efficacy and product performance data also presented problems when
trying to compare dichlorvos to the alternatives. This lack of data led
the Agency to assume that all products listed would provide adequate
control of the pests identified for each site unless otherwise noted.
EPA is aware that some of the pests may be resistant to some of the
chemicals listed; however, without supporting data the Agency cannot be
more specific or come to a more definitive conclusion regarding the
effectiveness of the chemicals. Other areas of difficulty involved
determining the amount of product applied per application, the number
of treatments needed, and the effect these factors had on the cost per
application. For example, dichlorvos products are applied on the basis
of cubic feet of space (as a space treatment), per square feet (as a
surface treatment), some for a certain length of time, others as crack
and crevice or spot treatments, some as baits, and still others
directly to animals. This diversity of area treated and the number of
applications needed or recommended (for example, based on the season,
geographical area, and pests) created difficulties for making
comparisons between products. Until more information is made available,
the Agency assumes, for most sites, that single treatments are
equivalent.
The Agency has no information regarding the use of dichlorvos on
the following outdoor sites: Outdoor areas under the general category
of farm buildings, outside surfaces of buildings, enclosed outdoor
utility equipment, or urban and rural outdoor areas. Due to the
complete lack of information, these sites have not been addressed in
this assessment document. Table 3 below summarizes the benefits
assessment for dichlorvos uses. In aggregate, the overall annual
economic impact of a dichlorvos cancellation to users and consumers is
expected to be negligible. Furthermore, for most of the individual
dichlorvos use sites a number of alternatives are registered and
available. Any economic impacts would be expected to diminish over time
as uses adjusted to the use of these alternative control materials.
EPA's benefits assessment is based on information currently available
to the Agency. EPA would consider new information from interested
parties that might modify this benefits assessment.
[[Page 50359]]
Table 3.--Summary of Dichlorvos Benefits by Site
----------------------------------------------------------------------------------------------------------------
Extent of Usage
--------------------------------------
Lbs Active Major Economic Impact
Site Ingredient/Year Percent of Site Pests Alternatives Extent and
(Percent of Total Treated Significance
Dichlorvos Use)**
----------------------------------------------------------------------------------------------------------------
In and around 3,000-4,000 (1%) unknown ants Aerosols (for Not expected to
domestic bees homeowner use): be significant
dwellings bedbugs bendiocarb
cockroaches chlorpyrifos
firebrats diazinon
flies malathion
hornets permethrin
mosquitoes propoxur
silverfish pyrethrins
spiders resmethrin
wasps
yellow jackets
----------------------------------------------------------------------------------------------------------------
Domestic animals 9,000-10,000 (3%) unknown American dog tick Impregnated Not expected to
(cats and dogs) brown dog tick collars: be significant
cat flea carbaryl
chlorpyrifos
naled
phosmet
propoxur
pyrethrins
tetrachlorvinphos
----------------------------------------------------------------------------------------------------------------
Mushroom House 6,000 - 7,000 12.5% of site phorid flies Space spray: Possible impacts
(2%) treated scairid files Permethrin
----------------------------------------------------------------------------------------------------------------
Greenhouse uses: Total Greenhouse unknown aphids malathion Not expected to
Ornamentals and usage for both leafminers nicotine be significant
Food crops ornamentals and leafrollers pyrethrins
(primarily food crops: mealybugs resmethrin
cucumbers, 6,000-6,500 (2%) mites
lettuce, thrips
tomatoes) whiteflies
scale insects
spider mites
----------------------------------------------------------------------------------------------------------------
Direct Total animal
application to usage for direct
domestic food/ application and
non-food their premises:
animals: 100,000-200,000
(27-54%)
------------------ ---------------------------------------------------------------------------
Livestock (beef unknown face fly coumaphos Probable regional
and dairy stable fly fenvalerate impacts
cattle) house fly lindane
horn fly malathion
methoxychlor
permethrin
phosmet
pyrethrins
tetrachlorvinphos
------------------ ---------------------------------------------------------------------------
Poultry unknown northern fowl carbaryl Possible regional
mite permethrin impacts
------------------ ---------------------------------------------------------------------------
[[Page 50360]]
Horses (including unknown house fly permethrin Possible regional
ponies) stable fly pyrethrins impacts
face fly tetrachlorvinphos
horn fly
mosquitoes
------------------ ---------------------------------------------------------------------------
Swine/hogs unknown house fly malathion Possible regional
stable fly permethrin impacts
horse fly tetrachlorvinphos
little house fly
dump flies
mosquitoes
biting gnats
psychodid flies
screwworms
------------------ ---------------------------------------------------------------------------
Sheep/goats unknown horn fly coumaphos Possible regional
house fly diazinon impacts
stable fly fenvalerate
lice lindane
ticks malathion
sheep ked methoxychlor
wool maggots permethrin
----------------------------------------------------------------------------------------------------------------
In and around Total animal
premises housing usage for direct
food and non- application and
food animals: their premises:
100,000-200,000
(27-54%)
------------------ ---------------------------------------------------------------------------
Dairy rooms and unknown house fly Space sprays:
milk houses permethrin
Possible regional
------------------ ---------------------------------------------------------------------------
Furbearing animal unknown flies methomyl (bait) Possible regional
units permethrin impacts
pyrethrins
tetrachlorvinphos
Such as mink
farms
------------------ ---------------------------------------------------------------------------
[[Page 50361]]
Poultry houses unknown house fly (adult)
Space sprays:
Possible regional
----------------------------------------------------------------------------------------------------------------
Feedlots, unknown unknown house fly Outdoor Space
including around stable fly Sprays/Fog:
feedlots, horn fly malathion
stockyards, face fly naled
corrals, holding
pens, fences,
etc.
Probable regional
----------------------------------------------------------------------------------------------------------------
Manure (poultry unknown unknown house fly dimethoate Negligible
and livestock horn fly malathion
manure) face fly tetrachlorvinphos
treatments on
farm premises
----------------------------------------------------------------------------------------------------------------
Ornamental lawns Little or no use Little or no use ants For commercial Negligible
and turf expected expected armyworm complex applicator use
billbugs only:
chiggers acephate
chinch bugs bendiocarb
clover mite carbaryl
crickets chlorpyrifos
cutworms diazinon
earwigs isofenphos
fleas isazofos
grasshoppers malathion
hyperodes weevils
sod webworms
ticks
white grubs
----------------------------------------------------------------------------------------------------------------
Ornamental plants unknown unknown aphids acephate Not expected to
(excluding lawns bagworms carbaryl be significant
and turf) borers chlorpyrifos
cutworms diazinon
eastern tent malathion
caterpillar
gypsy moth
leafhoppers
mealybugs
webworms
mites
spittlebugs
whiteflies
----------------------------------------------------------------------------------------------------------------
[[Page 50362]]
Nonperishable 20,000-35,000 (5- 5% almond Space sprays: Not expected to
bulk-stored 9%) moth pyrethrins be significant
agricultural angoumois grain
commodities (raw moth
and processed) cigarette beetle
confused flour
beetle
flat grain beetle
granary weevil
Indianmeal moth
lesser grain
borer
red flour beetle
rice weevil
sawtoothed grain
beetle
----------------------------------------------------------------------------------------------------------------
Packaged or 50,000-75,000 (13- 5-10% for both almond moth Space sprays: $12 million for
bagged non- 20%) for both raw and angoumois grain pyrethrins both raw and
perishable raw and processed non- moth processed non-
processed and processed non- perishable cadelle perishable
raw food perishable packaged or cigarette beetle packaged or
packaged or bagged cockroaches bagged
bagged agricultural confused flour agricultural
agricultural commodities beetle commodities plus
commodities dermestid beetles the cost of
drugstore beetle additional
flat grain weevil fumigations if
granary weevil needed.
Indianmeal moth
lesser grain
borer
Mediterranean
flour moth
merchant grain
beetle
red flour weevil
rice weevil
sawtoothed grain
beetle
tobacco moth
----------------------------------------------------------------------------------------------------------------
Kennels unknown unknown fleas carbaryl Not expected to
ticks chlorpyrifos be significant
house fly diazinon
mosquitoes
----------------------------------------------------------------------------------------------------------------
Insect traps 50-100 (0.01- unknown Adults of: None Not expected to
(Monitoring 0.03%) gypsy moth be significant
purposes only) spruce budworm
forest tent
caterpillar
fruit flies
codling moth
corn borers
weevils
----------------------------------------------------------------------------------------------------------------
[[Page 50363]]
Garbage dumps unknown unknown Flies (adults and Surface sprays:
maggots) chlorpyrifos
diazinon
propoxur
Not expected to
----------------------------------------------------------------------------------------------------------------
Commercial, unknown unknown ants Surface sprays:
Institutional, cockroaches chlorpyrifos
and Industrial fleas cypermethrin
areas flies diazinon
moths propetamphos
silverfish propoxur
sowbugs
spiders
stored product
pests
wasps
Not expected to
----------------------------------------------------------------------------------------------------------------
Commercial unknown unknown
transportation
vehicles:
Airplanes, ants phenothrin Not expected to
buses cockroaches pyrethrins be significant
fleas resmethrin
flies
moths
scorpions
silverfish
spiders
ticks
wasps
quarantine pests
------------------ --------------------------------------------------------
[[Page 50364]]
Other angoumois grain pyrethrins Not expected to
transportation moth be significant
vehicles ants
including cadelle
trucks, cheese mite
shipholds, and cigarette beetle
railroad cars confused flour
beetle
dermestids
drugstore beetle
flat grain beetle
granary weevil
Indian meal moth
lesser grain
borer
mealworms
Mediterranean
flour moth
red flour beetle
rice weevil
sawtoothed grain
beetle
----------------------------------------------------------------------------------------------------------------
Total usage 250,000-500,000
accounted for (52-90%)
above
----------------------------------------------------------------------------------------------------------------
**Note: The total used in calculating percentage of dichlorvos
use for a given site is based on the mid point (375,000) of the
total range 250,000 - 500,000.
G. Analysis of Comments
Comment. The Southeastern Peanut Association (SPA) commented that
the substitutes to dichlorvos are substantially less effective on
peanuts and not fully available for commercial use.
Agency response. The Agency cannot fully respond to this comment as
the substitutes for dichlorvos were not identified in the letter from
the SPA. The Agency has identified the pyrethrins as a possible
alternative to dichlorvos. Because the pyrethrins are registered for
use in much the same way as dichlorvos and due to the lack of
comparative efficacy or resistance data, EPA assumes that they would
provide acceptable levels of insect control. Regarding the availability
of the pyrethrins, because the growing conditions that affect
chrysanthemums (the source from which pyrethrins are derived) can vary
from year-to-year, the Agency recognizes that the availability and
price of pyrethrins will fluctuate as well.
Comment. The California Department of Food and Agriculture (CDFA)
commented that dried fruit and tree nuts can be kept insect free if
fumigated before entering storage and once in storage, receive regular
treatments of dichlorvos. CDFA states that alternate methods of insect
control, irradiation and controlled atmospheres are not feasible.
Agency response. The Agency believes that the pyrethrins would
serve to control insects in the above situation if used in the same
manner as dichlorvos. EPA does not have data that indicate the number
of treatments needed for the pyrethrins to replace dichlorvos and still
provide the same level of control. The Agency also believes that as the
fumigant methyl bromide is phased out under the Clean Air Act,
alternative measures such as irradiation, heat, cold, and controlled
atmospheres will become more important.
Comment. The American Corn Millers Federation (ACMF) commented that
the use of pyrethrins or resmethrin as alternatives to dichlorvos are
not as efficacious in storage areas, warehouses, or processing areas of
plants.
Agency response. The Agency has identified the pyrethrins and
resmethrin (aerosol treatments) as potential alternatives to fogging
with dichlorvos in commercial, industrial, and institutional areas. The
ACMF did not submit data to support their contentions of inadequate
efficacy of the alternatives. In the absence of comparative efficacy
and/or resistance data, EPA assumes that these registered alternatives
would provide adequate levels of insect control.
Comment. Two representatives from the popcorn industry commented
that there are no replacements for the use of dichlorvos pest strips in
popcorn storage facilities.
Agency response. The Agency has no specific information regarding
insect control in stored popcorn; however, EPA does have information
regarding
[[Page 50365]]
the treatment of other stored grain products. EPA believes the
pyrethrins could be used as a head space treatment; however, EPA does
not know how many treatments of pyrethrins it would take to provide the
same level of control as obtained with the dichlorvos pest strips,
which can last for several months.
Comment. The Department of Defense (DOD), Armed Forces Pest
Management Board, commented on the use of dichlorvos as a fogging
material in warehouses containing food products and textiles. The DOD
lists pyrethroids, pyrethrins, aluminum phosphide, and the use of
residual sprays as either not as effective or not as available as
dichlorvos.
Agency response. In the most current benefits assessment, the
Agency identified the pyrethrins and resmethrin as the most likely
substitutes for dichlorvos when used as an aerosol or fog application.
The Agency also listed products containing chlorpyrifos, cypermethrin,
diazinon, propetamphos, or propoxur as surface residual treatments that
could replace dichlorvos. In the absence of comparative efficacy or
resistance data (DOD included no data with their comments), EPA has
assumed that all registered alternative active ingredients would
provide adequate control of the insect pests involved with these sites.
Comment. The Grocery Manufacturers of America (GMA) commented that
the alternatives to dichlorvos were unsuitable because they are more
expensive, less effective, require more frequent applications, and some
may result in off-flavors to the stored foods.
Agency response. The GMA did not identify the alternatives and did
not include any data to substantiate the contentions made. The Agency
believes that dichlorvos is used primarily as an aerosol in commercial,
industrial, and institutional areas. In the current benefits
assessment, the Agency has identified resmethrin and pyrethrins as
possible aerosol alternatives for dichlorvos and chlorpyrifos,
cypermethrin, diazinon, propetamphos, or propoxur as residual surface
treatments that could replace the use of dichlorvos. In the absence of
comparative efficacy or resistance data, EPA assumes that all
registered active ingredients listed would provide adequate pest
control. EPA has no data regarding the off-flavoring of stored foods
for any of the alternative products.
Comment. The National Food Processors Association (NFPA) commented
that many of its members depend on dichlorvos for insect control in
food processing plants, warehouses, and mushroom houses. NFPA stated
that smaller amounts of dichlorvos are needed than the alternatives to
control the pests, and that some pests have become resistant to the
alternatives.
Agency response. NFPA did not include comparative efficacy and/or
resistance data to support their contentions. In the current EPA
benefits assessment of dichlorvos, EPA concludes that the use of
surface sprays (diazinon, propoxur, or pyrethrins) and larvicides
(diflubenzuron or methoprene) are the primary methods of insect control
currently used in mushroom houses. In the absence of comparative
efficacy or resistance data, EPA assumes that the alternative methods
would provide adequate levels of control.
The Agency believes that dichlorvos is used primarily as an aerosol
treatment in commercial, industrial, and institutional areas (including
food processing plants and warehouses). In the current benefits
assessment, the Agency identifies resmethrin and pyrethrins as possible
alternatives for aerosol dichlorvos and chlorpyrifos, cypermethrin,
diazinon, propetamphos, or propoxur as residual surface treatments that
could replace the use of dichlorvos. In the absence of comparative
efficacy and/or resistance data, EPA assumes that all registered active
ingredients listed would provide adequate pest control.
Comment. A representative from the fumigation industry commented
that the grain, seed, popcorn, and food processing industries do not
need dichlorvos. Alternatives to dichlorvos were listed as pyrethrins,
resmethrin, sanitation, monitoring with pheromone traps, and the use of
grain protectants.
Agency response. In the current benefits assessment, EPA has
identified several alternative active ingredients that could replace
the use of dichlorvos in the above-mentioned areas. EPA also listed
several non-chemical methods of insect control including sanitation,
use of pheromone traps, predators, parasites, the use of heat or cold,
exclusion, and irradiation. The Agency realizes that some of these
methods may require more research before acceptance by industry and
that many facilities would require additional construction before
implementation could occur. In the absence of comparative efficacy or
resistance data (none were included with the above comments), EPA
assumes that the chemical alternatives to dichlorvos would provide
adequate control of the insect pests. The Agency believes that the non-
chemical methods cited could aid in insect control when used alone, in
combination with each other, or in combination with insecticides.
Comments. Comments from the Pesticide Impact Assessment Program at
the University of Idaho presented dichlorvos application and usage
information for 1988 in the state of Idaho.
Agency response. While EPA appreciates and needs this type of
information in order to conduct a benefits assessment, EPA believes the
data gathered in 1988 may not be accurate at this time. The Agency
believes that the volume of dichlorvos produced and sold in the United
States has decreased over the last 5 to 6 years and assumes that this
trend has occurred in Idaho as well.
Comment. Reliable Services commented that the loss of dichlorvos
would be detrimental to the food related industries and that no
effective alternatives exist for the use of dichlorvos strips in sewer
catch basins for mosquito control. The alternatives identified for use
in warehouses and food processing areas were identified as pyrethrins
and resmethrin. Reliable Services estimates that for the alternatives,
the number of applications are greater and the cost of materials are
significantly higher than dichlorvos.
Agency response. Several pest strips containing dichlorvos are
registered for use in catch basins to control adult mosquitoes.
Although there are no direct alternatives for these pest strips,
different formulations of other active ingredients are available that
provide control of the larval and pupal stages of mosquitoes occurring
in catch basins. EPA could find no state pest control guides
recommending the use of pest strips for mosquito control at this
particular site. EPA lacks sufficient use, usage, and efficacy data on
dichlorvos to conduct a benefits assessment for this site/pest
combination.
In the absence of comparative efficacy or resistance data, EPA
assumes that all active ingredients listed would provide adequate pest
control. The Agency also recognizes the importance of sanitation,
exclusion, and trapping (pheromone traps) to control insect populations
in storage facilities; however, EPA has no data indicating what
percentage of insect control is accomplished by these methods.
Comment. The National Pest Control Association (NPCA) commented
that dichlorvos is important to the structural pest control and food
industries (transportation, storage, and processing facilities).
Agency response. EPA recognizes the important role dichlorvos has
played in keeping insect populations under
[[Page 50366]]
control in the above areas. In the current benefits assessment, the
Agency has identified alternative active ingredients (pyrethrins or
resmethrin as aerosol sprays; chlorpyrifos, cypermethrin, diazinon,
propetamphos, or propoxur as residual surface sprays) as well as non-
chemical practices (sanitation, exclusion, heat, cold, modified
atmospheres, pheromones, parasites, etc,) that, alone or in
combination, may replace the use of dichlorvos. In the absence of
comparative efficacy or resistance data, EPA assumes that the
registered alternative active ingredients identified would provide
adequate levels of insect control. EPA is not certain what percentage
of insect control can be attributed to the non-chemical control methods
discussed.
Comment. WHB Specialty Products Co. (WHB) commented that because of
declining usage after 1983, any regulatory action taken by the U.S. EPA
would have no economic impact on sales of their end-use products, which
are used for control of insects on beef and dairy cattle and in
livestock buildings.
Agency response. This comment is consistent with the Agency's
information that usage is declining.
Comment. Consumers Union commented that the benefits of dichlorvos
use in ``bug sprays,'' flea collars, and resin strips are negligible.
Agency response. EPA's current benefits assessment for dichlorvos
has identified from one to several alternatives for the use of
dichlorvos in ``bug sprays'' (In and Around Domestic Dwellings), resin
strips (numerous sites), and pet flea collars (Domestic Animals). Based
on the information available at this time, it is the Agency's opinion
that the benefits for dichlorvos use in the areas mentioned above are
negligible. In the absence of comparative efficacy or resistance data,
EPA assumes that available registered alternatives would provide
adequate control of the insect pests.
Comment. Amvac Chemical Corporation commented on the use of
dichlorvos in warehouses and food processing areas. Amvac states that
the alternatives are not as effective and are more expensive than
dichlorvos.
Agency response. The current EPA benefits assessment (commercial,
industrial, and institutional areas) and the comments from Amvac are in
agreement as to pests controlled, primary methods in which dichlorvos
is applied, and the potential alternatives to dichlorvos. Amvac states
that the alternatives are not as effective as dichlorvos and refers to
a survey and personal communications as the source for their
conclusions. In the absence of comparative efficacy or resistance data,
the Agency assumes that the registered alternatives would provide
adequate control of the insect pests in warehouses and food processing
plants. In addition, the Agency identified several non-chemical methods
of insect control in warehouses and food processing facilities that
Amvac did not include in their comments. EPA believes that in recent
years alternative methods such as sanitation, exclusion, heat, cold,
modified atmospheres, parasites, and the use of pheromone traps have
become more common but the Agency has no data that identifies the
percentage of insect control that can be attributed to these methods.
Comment. Amvac Chemical Corporation commented on the benefits and
use of dichlorvos to control insects on dairy and beef cattle and in
the premises housing these animals. Amvac states that resistance to
some of the alternatives is a problem.
Agency response. The current EPA benefits assessment for dichlorvos
includes the following sites that relate to food or nonfood animals and
their premises: direct application to food and nonfood animals, in and
around premises housing food and nonfood animals, manure treatments,
and feedlots. The pests and their potential damage to animals, the
primary methods of using dichlorvos, and the potential alternatives
identified are similar in both the EPA assessment and Amvac's comments.
EPA is aware that resistance to some of the alternatives may have
occurred; however, EPA does not have any data identifying specific
compounds, insect species, or the extent of any resistance problem.
Amvac relied on personal communications and surveys to support their
statements but did not submit data to substantiate their claims
regarding efficacy or resistance. In the absence of comparative
efficacy or resistance data, EPA assumes that all registered products
would provide adequate insect control.
Comment. Amvac Chemical Corporation commented on the benefits and
use of dichlorvos in domestic dwellings and in pet flea collars. Amvac
states that the alternatives are not as efficacious as dichlorvos
(based on personal communications) but includes no comparative efficacy
and/or resistance data with their comments.
Agency response. In the current benefits assessment, EPA addressed
these sites under the headings in and around domestic dwellings and
domestic animals (Cats and Dogs). The EPA list of pests, primary
methods of dichlorvos applications, and potential alternatives for
these two sites was similar to the information provided by Amvac. In
the absence of efficacy and/or resistance data, the Agency assumes that
the identified registered alternatives would provide adequate control
of the pests.
Comment. Amvac Chemical Corporation commented on the benefits and
use of dichlorvos in food markets and eating establishments. Amvac
stated that the alternatives are less effective and more costly.
Agency response. The section titled ``Commercial, Industrial, and
Institutional Areas'' in the current EPA benefits assessment for
dichlorvos includes information on eating establishments. Because of
the lack of information, EPA did not include food markets in the
benefits assessment. The EPA assessment for eating establishments
included many of the same pests, the same primary methods of dichlorvos
application, and the same potential alternatives as identified in the
Amvac comments. Although Amvac states that the alternatives are less
effective and more costly, they did not include supporting data with
the comments. In the absence of data, the Agency assumes that the
identified alternatives would provide adequate control of the pests.
Comment. Amvac Chemical Corporation commented on the benefits and
use of dichlorvos resin strips in popcorn storage bins. Amvac
identified the pyrethrins as a fogging treatment in bin head spaces or
actellic (pirimiphos-methyl) as a protectant applied to the popcorn.
Amvac states that neither the pyrethrins nor pirimiphos-methyl is as
cost effective or efficacious as dichlorvos.
Agency response. The Agency has no specific information regarding
insect control in stored popcorn and did not include this specific site
in the current assessment; however, EPA does have information for the
treatment of other stored grain products. The Agency believes that the
pyrethrins can be used as a head space treatment; however, EPA has no
information concerning the number of treatments of pyrethrins it would
take to provide the same level of control as obtained with the
dichlorvos pest strips. The dichlorvos impregnated resin pest strips
can provide insect control for several months.
IV. Risk/Benefit Analysis and Proposed Regulatory Decisions
A. Summary of Risk/Benefit Analysis
EPA has concluded that the risks outweigh the benefits for most
uses of dichlorvos, and therefore, proposes a
[[Page 50367]]
variety of measures to reduce risks to the acceptable level, including:
Cancellation of some uses, requiring protective clothing, specifying
reentry intervals, and restricting use to certified applicators. Tables
4 and 5, in this unit, summarize EPA's risk/benefit analyses and
proposals for risk mitigation. The benefits are not expected to be
significant for most sites, with the possible exceptions of packaged or
bagged nonperishable raw and processed food, livestock, poultry, and
mushroom houses. The lack of known significant benefits for most sites
is outweighed by the potential total dietary cancer risk of 4.4 x
10-6 from use of dichlorvos and 5.1 x 10-6 from dichlorvos
residues due to dichlorvos plus naled, and the occupational and
residential risks involving several MOEs less than 100 (some less than
10) for ChE inhibition.
EPA considered measures short of cancellation to reduce
occupational and residential risks, such as restricted reentry
intervals, personal protective equipment, and restricting use to
certified applicators. Where appropriate, these measures are proposed;
however, cancellation is proposed for several uses because risk
mitigation measures are not expected to reduce risk sufficiently.
There are a variety of alternatives available for dichlorvos,
varying from use to use. EPA compared the toxicity of several
alternatives for some major sites to understand the effect of canceling
dichlorvos. This discussion of alternatives relates to the hazards
posed by each pesticide in its technical form and does not take into
account differing exposures resulting from application equipment used,
or frequency or rate of application. The risk from a pesticide is a
function of both the hazard or toxicity of the pesticide and the extent
to which an individual is exposed. Alternatives fall into three
chemical types, organophosphates, carbamates, and others.
Organophosphates and carbamates inhibit ChE activity and result in
neurotoxic effects. Several of the other alternatives are pyrethroids,
including cypermethrin, permethrin, d-phenothrin and resmethrin. The
pyrethrins and pyrethroid compounds present less of an acute hazard
than the ChE-inhibiting alternatives. Exposure to the pyrethroids and
pyrethrins can result in neurotoxicity, but the effects are rapidly
reversible and only occur at much higher doses than for
organophosphates. Pesticide poisoning incidents involving workers have
been reported for several registered alternatives including,
chlorpyrifos, diazinon, and malathion. Dichlorvos is a Group C
(possible human) carcinogen, while for some alternatives there is no
evidence of carcinogenicity or there are data gaps. Propoxur is a Group
B2 (probable human) carcinogen and permethrin is a Group C. Dichlorvos
has a higher cancer potency than either of these two chemicals. Also,
the pyrethroids and pyrethrins are less toxic than dichlorvos following
chronic exposure. Of all registered alternatives, only diazinon had an
RfD lower than dichlorvos. Finally, no significant developmental or
reproductive effects were reported for dichlorvos or any of the
alternatives.
B. Proposed Regulatory Actions
1. Dietary risk. EPA is proposing cancellation of dichlorvos for
use on bulk, packaged, and bagged nonperishable raw and processed food,
because of the unacceptable risk posed by this use. Table 4, in this
unit, compares the dietary cancer risk before and after the actions
proposed in this notice. The estimated upperbound excess individual
lifetime dietary cancer risk (before EPA's proposed action) from
application of dichlorvos is 4.4 x 10-6 and from naled-derived
dichlorvos is 7.2 x 10-7, for a total of 5.1 x 10-6. The
major source of estimated dietary risk is packaged, bagged or bulk
nonperishable processed or raw food (3.4 x 10-6). The estimated
risk from the three individual tolerances and FAR (bulk raw, packaged
or bagged raw, and packaged or bagged processed) cannot be separated
because, as discussed earlier, a single commodity may be treated more
than once at different stages of production. Following EPA's proposed
actions, discussed below, the remaining total dietary risk would be 1.7
x 10-6, including dichlorvos derived from naled. This estimated
dietary risk is believed to overestimate the actual risk because: (1)
The estimated risk from naled residues is probably high because EPA
assumed that the mosquito/fly control use (without regard to specific
crops) would result in one percent of all commodities having residues;
(2) EPA is assuming that 100 percent of the naled residues will
metabolize into dichlorvos, which is probably not the case; and (3) the
risk from milk (6.2 x 10-7 or about one-third of the risk after
the proposed action) is believed to be an overestimate because the
anticipated residues used in the risk assessment are based on one-half
the limit of detection, which was used because no residues were found
in milk following exaggerated application of dichlorvos. This dietary
risk assessment could underestimate dietary risks from treated food in
food handling establishments, since this risk in not included in the
risk assessment; however, if the proposal to cancel use in commercial
establishments, due to applicator and reentry risks, is finalized, this
potential dietary risk will no longer exist.
2. Use on bulk, packaged or bagged nonperishable raw and processed
food. EPA is proposing cancellation of these uses because of
unacceptable dietary risks, and because of the unacceptable risk to
workers from applying dichlorvos to stored food and reentering treated
areas. (See paragraph 3--Warehouses in this unit.)
i. The estimated dietary risk from dichlorvos, 3.4 x 10-6, is
of concern because it exceeds the Agency's 10-6 negligible risk
level. This group of uses is treated as one use here for purposes of
risk estimation because consumption data do not permit a more detailed
breakdown. This is an unusual site in that it is not specific to a
location such as greenhouses or tobacco warehouses. Bulk, packaged, or
bagged food can be found in a variety of locations including food
handling establishments (food service, food manufacturing, and food
processing establishments), in warehouses, shipholds, trucks and any
other location where food is stored. Since the proportion of
commodities stored in bulk compared to packaged/bagged food is unknown,
it is not possible to clearly separate these risks or limit the scope
of this proposal. Also, EPA does not believe that it is possible to
reduce the frequency or amount of dichlorvos applications to decrease
dietary risk to an acceptable level.
ii. There are potentially significant benefits for this use. The
major alternatives are pyrethrins, and the absence of dichlorvos may
require fumigant treatments. Cancellation of this use would result in
increased costs estimated to be $12 million to replace dichlorvos with
pyrethrins, plus, if needed, the additional cost of supplemental
fumigations would be about $33 million with methyl bromide or $44
million per year with aluminum phosphide. Without the use of fumigants
in supplementing pyrethrins there could be some loss in efficacy;
however, EPA has no basis to confirm or estimate this loss. Although
there are potential significant economic impacts, EPA believes that the
dietary cancer risks to the general public outweigh the benefits.
Therefore, EPA is proposing cancellation of use on bulk, packaged or
bagged nonperishable raw and processed food. EPA is interested in
comments on the effect of this proposal. The dietary risk discussed may
also be affected by the pending revocation of the section 409 FAR for
residues of dichlorvos on packaged or bagged
[[Page 50368]]
nonperishable processed food and the possible cancellation of the
related uses. However, because those actions have not occurred, the
Agency is proposing action at this time based on unacceptable dietary
and worker risks (see warehouse discussion below).
3. Warehouses. MOEs from applying dichlorvos in warehouses and
reentering treated areas are unacceptable, with the exception of
impregnated resin pest strips in closed areas such as silos. EPA is,
therefore, proposing cancellation of this use. Even if applicator
exposure were minimized through the use of automatic application
equipment, the MOEs from reentry would still be unacceptable. EPA
assumes that a variety of tasks are performed in a warehouse including
inventory, stocking and retrieving stored commodities, all of which
would require entry into the warehouse soon after application to
perform these tasks, and would result in prolonged exposure to a
worker. Therefore, EPA does not believe it is feasible to mitigate the
risk to workers reentering treated areas.
If dichlorvos can no longer be used in warehouses, areas where food
is stored, due to worker risk, then the dietary risk from bulk stored,
packaged or bagged raw and processed food would be eliminated.
Therefore, the benefits for warehouses and for bulk stored, packaged or
bagged food would be similar. As discussed in paragraph 2 above, there
are potentially significant benefits for the use on bulk stored
packaged and bagged food in warehouses. There are alternatives to
dichlorvos for this use; however, cancellation of this use would result
in increased costs as described in paragraph 2 above. These benefits do
not justify MOEs of 38 for applicators and 2.8 for reentry workers.
Based on unacceptable MOEs for applicators and reentry workers, EPA
believes the risks outweigh the benefits, and therefore, products
registered for the warehouse use should be canceled.
4. Commercial, institutional, and industrial areas. The risks posed
by these uses, which include food handling establishments, are
estimated to be similar to risks from warehouse uses, involving MOEs of
38 for applicators and 2.8 for persons reentering treated areas. There
are a variety of registered alternatives in the absence of dichlorvos,
and the benefits are not expected to be significant. EPA is, therefore,
proposing to cancel these uses because the risks outweigh the benefits.
Any dietary risk resulting from food handling use, although not
estimated here, would be eliminated.
5. Greenhouses. The estimated dietary risk from dichlorvos use in
greenhouses is 2.0 x 10-7, which is negligible. However, the MOEs
for workers performing most methods of application in greenhouses are
less than 100, and about one-third are less than 50, since they involve
the applicator remaining in the greenhouse during application. In
addition, the MOE for reentry workers 24 hours after application is 21.
There are a variety of registered alternatives available as a space
treatment, surface treatment or direct treatment to plants. Assuming an
equal number of applications to replace dichlorvos, the cancellation of
dichlorvos should not result in significant economic impacts. These
applicator and reentry risks are unacceptable, and thus, EPA is
proposing to cancel registrations of products labeled for use in
greenhouses unless the following changes are made to the label which
will reduce risks to an acceptable level: Eliminate hand-held
application methods and require use of automatic foggers inside the
greenhouse or fogging through a port on the side of a greenhouse. In
either case, no one (including the applicator) would be allowed in the
greenhouse during the application. In addition, because of low MOEs for
workers reentering greenhouses, the Agency is proposing to limit
exposure by prohibiting entry by anyone, including handlers (except in
an emergency) within the first 4 hours following application. For the
remainder of the first 48 hours following application, the Agency is
proposing to allow one hour per day entry into dichlorvos-treated
greenhouses by trained pesticide handlers who are equipped with handler
personal protective equipment (including an organic-vapor-cartridge
respirator) and who are performing a handling task. Handling tasks are
defined by the Worker Protection Standard (40 CFR part 170) and include
operating ventilation equipment and checking air concentration levels.
Entry by workers to perform non-handler tasks, such as harvesting,
cultivation, and irrigation-related tasks would be prohibited for the
entire 48-hour period. It is unclear what effect, if any, the reentry
restrictions proposed in this action will have on the greenhouse
industry, since the Agency has no information regarding the need for
reentry tasks during the first 48 hours following application of
dichlorvos.
If the application and reentry restrictions proposed here are not
feasible to implement, EPA does not believe that the loss of dichlorvos
in greenhouses would have a significant impact on the greenhouse
industry; benefits from the use of dichlorvos in greenhouses are
expected to be minimal due to the availability of alternatives.
Therefore, EPA is proposing these restrictions because, without them,
the applicator and reentry risks outweigh the benefits. Note that the
entry restrictions being proposed by the Agency are based on the
assumption that the treated area would not be ventilated for the entire
48-hour period following application. The Agency would consider data,
if submitted, that indicate that a specified number of air exchanges or
a specified number of hours of mechanical ventilation would reduce the
dichlorvos air concentration level to an acceptable level for safe
entry for workers (without respirators) in less than the proposed 48-
hour entry-restricted period. This 48-hour reentry period exceeds the
24-hour period required in the Worker Protection Standard; however,
based on the exposure data for dichlorvos, EPA believes that this
longer reentry period is necessary to reduce worker risk to an
acceptable level.
6. Mushroom houses. The estimated dietary risk from use of
dichlorvos in mushroom houses is 2.6 x 10-9, which is negligible.
However, the MOEs for most methods of applying dichlorvos in mushroom
houses are less than 100, and some are less than 10, since they involve
the applicator remaining in the house during application. In addition,
the MOE for reentry workers following 24 hours after application is 21.
These applicator and reentry risks are unacceptable, and thus, EPA is
proposing to cancel registrations of products labeled for use in
mushroom houses unless the following changes are made to the label
which will reduce risks to an acceptable level: Eliminate hand-held
application methods, and require use of automatic foggers inside the
mushroom house or fogging through a port on the side of a mushroom
house. In either case, no one (including the applicator) would be
allowed in the mushroom house during the application. In addition,
because of low MOEs from reentering mushroom houses, the Agency is
proposing to limit exposure by prohibiting entry by anyone, including
handlers (except in an emergency) within the first 4 hours following
application. For the remainder of the first 48 hours following
application, the Agency is proposing to allow one hour per day entry
into dichlorvos-treated mushroom houses by trained pesticide handlers
who are equipped with handler personal protective equipment (including
an
[[Page 50369]]
organic-vapor-cartridge respirator) and who are performing a handling
task. Handling tasks are defined by the Worker Protection Standard (40
CFR part 170) and include operating ventilation equipment and checking
air concentration levels. Entry by workers to perform non-handler
tasks, such as harvesting, cultivation, and irrigation-related tasks
would be prohibited for the entire 48-hour period. The economic impact
resulting from these restrictions is not expected to be significant
since dichlorvos is only used for insect control after surface sprays
and larvacides have been used, and permethrin is available as a direct
alternative to dichlorvos. It is unclear what effect, if any, the
reentry restrictions proposed in this action will have on the mushroom
industry, since the Agency has no information showing whether reentry
to perform crop cultivation tasks is necessary during the first 48
hours following application. EPA acknowledges that there may be impacts
due to these restrictions; however in the absence of data, EPA is
assuming no impact. Therefore, EPA is proposing these restrictions
because, without them, the applicator and reentry risks outweigh the
benefits. Note that the entry restrictions being proposed by the Agency
are based on the assumption that the treated area would not be
ventilated at all during the entire 48-hour period following
application. The Agency would consider data, if submitted, that
indicate that a specified number of air exchanges or a specified number
of hours of mechanical ventilation would reduce the dichlorvos air
concentration level to an acceptable level for safe entry for workers
(without respirators) in less than the proposed 48-hour entry-
restricted period. This 48-hour reentry period exceeds the 24-hour
period required in the Worker Protection Standard; however, based on
exposure data for dichlorvos, EPA believes that this longer reentry
period is necessary to reduce worker risk to an acceptable level.
7. Direct treatment to domestic food and non-food animals (non-
poultry). EPA is proposing cancellation of all products registered for
hand-held application methods to domestic animals. The MOE for hand
application is approximately 6. Other direct application methods that
do not involve hand-held application are not expected to exceed the
Agency's level of concern and would still be allowed. These include:
face and back rubbers, and devices which automatically apply dichlorvos
to the animals. The loss of dichlorvos for hand-held treatment of
animals should not have a major economic impact since there are easily
available alternatives similar in cost to dichlorvos, and dichlorvos
can still be used by other methods. Therefore, EPA believes that the
risks outweigh the benefits for hand-held methods of application to
food and non-food animals, excluding poultry.
8. Direct treatment to domestic food and non-food animals
(poultry). EPA is proposing to retain the use of dichlorvos on poultry
because the risks from application are not unreasonable. Dichlorvos is
mainly used as a space spray to treat poultry premises, but it is also
used for direct animal treatment. EPA does not have data to estimate
risk from treating poultry; however, the Agency believes that both the
application method and fewer number of applications will result in much
lower exposure and risk than for cattle treatment. The benefits for
poultry treatment cannot be separated out from the use on domestic
animals and their premises. However, EPA believes there is a benefit
for controlling mites on laying hens. As a result EPA is believes the
benefits of dichlorvos use exceeds the risks and is proposing retention
of this use.
9. Treatment of domestic animal (food and non-food) premises. EPA
is proposing to retain the use of dichlorvos for treatment of domestic
animal premises. The Agency estimates that MOEs for applying dichlorvos
are greater than 100. Because there may be some benefits for the
combined direct animal and premise treatment, and the estimated risk is
very low, EPA believes that the benefits of this use outweigh the
risks. Therefore, EPA is proposing retention of this use.
10. Feedlots (including around feedlots, stockyards, corrals, and
holding pens). EPA proposes to retain the use of dichlorvos in
feedlots. The Agency estimates that the MOEs for applying dichlorvos
are greater than 100. Also application of dichlorvos in feedlots
generally involves application over a short period of time in a well
ventilated area, which together, further reduces the risk of exposure.
There are various alternatives to dichlorvos for controlling flies in
feedlots. Because there are probable regional impacts resulting from
cancellation of this use, and the MOEs are greater than 100, EPA is
proposing to retain this use. Therefore, the benefits outweigh the
risks in this case.
11. Manure. EPA proposes retaining the use of dichlorvos on manure.
The Agency estimates that the MOEs for applying dichlorvos on manure
are greater than 100. In addition, manure is generally located outdoors
or in well-ventilated areas, thereby reducing exposure to dichlorvos.
There are various alternatives to dichlorvos for controlling flies on
manure. There may be some benefits from the use of dichlorvos on
manure, although not significant, and because this use is not a risk of
concern, EPA is proposing to retain the use on manure.
12. Tobacco warehouse. EPA is proposing cancellation of products
registered for this use because both applicator and reentry MOEs are
low: 2 for application and 0.3 for reentry. Although EPA did not
conduct a benefits analysis for this use site, EPA believes that little
or no dichlorvos is used for tobacco warehouses, and Amvac has
requested voluntary cancellation for this use site. The Agency does not
anticipate a significant economic impact from cancellation; therefore,
the risks of this use outweigh its benefits.
13. Residential uses. The Agency is proposing cancellation of all
products registered for residential uses, including use by residents
and by professional applicators, and for use on pets. EPA has
determined that the MOEs are significantly less than 100 for all
methods of application in the home and for post-application exposure to
residents. The animal health and safety data discussed earlier also
indicate an unacceptable risk for pets. Overall, the effect of
cancellation of all residential uses is not expected to be significant,
since there are several alternatives available. Therefore, EPA believes
that the risks to residents and pets outweigh the benefits of this use.
14. Ornamental lawns, turf and plants. EPA is proposing to cancel
dichlorvos products registered for these uses. The estimated risks from
application of dichlorvos to ornamental lawns, turf, and plants are low
(32 - similar to a greenhouse power sprayer). The economic impact
resulting from the cancellation of this use is not expected to be
significant since there are alternatives available which, in some
cases, cost less than dichlorvos. Therefore, the risks outweigh the
benefits.
15. Kennels. EPA is proposing to retain use in kennels. The Agency
estimates that the MOE for applying dichlorvos in kennels is similar to
that of a dairy barn or at least 225. There may be some benefits from
the use of dichlorvos in kennels, although not significant, and because
this use is not a risk of concern, EPA is proposing to retain this use.
[[Page 50370]]
16. Insect traps. EPA is proposing to retain the use of dichlorvos
in insect traps. The risk to applicators is expected to be negligible
because of the short amount of time that the applicator is in contact
with the trap, and because the traps are located outside away from
people. The only alternative, adhesive strips, may not be as effective
as dichlorvos in cases where there are heavy insect populations.
Although the overall benefits are not expected to be significant, the
benefits for heavy insect problems outweigh the negligible risks.
17. Garbage dumps. EPA proposes retaining the use of dichlorvos on
garbage dumps. The Agency estimates that the MOE for applying
dichlorvos on a garbage dump are greater than 100. In addition, garbage
is generally located outdoors or in a separate room, thereby reducing
exposure. There are various alternatives to dichlorvos for controlling
flies on garbage. There may be some benefits from the use of dichlorvos
on garbage dumps, although not significant, and because this use is not
a risk of concern, EPA is proposing to retain the use on garbage dumps.
18. Commercial transportation vehicles. There are unacceptable
applicator and reentry risks for all commercial transportation uses.
Due to a very low MOE of 14 for applicators on airplanes, EPA is
proposing to cancel dichlorvos products registered for this use. EPA
does not believe it is possible to reduce this risk. The benefits are
not expected to be significant, since EPA estimates the use to be
minimal and Amvac has requested voluntary cancellation of this use.
Therefore, EPA believes the risks outweigh the benefits of continued
use in airplanes.
The Agency believes that risk mitigation measures are possible for
use of dichlorvos in buses. For passenger buses, EPA is proposing to
eliminate applicator exposure by limiting application to only foggers,
and requiring a 6-hour ventilation period following treatment. With
these measures required, the benefits of use of dichlorvos in buses
would outweigh its risk.
EPA is proposing to cancel products registered for use in other
vehicles (trucks/shipholds/railroad cars). EPA does not believe it is
feasible to mitigate the risk from reentry. A 36-hour reentry period
would be required to achieve an MOE above 100, which is not practical
for commercial vehicles. The economic impact resulting from the
cancellation of this use is not expected to be significant since there
are alternatives available which would result in similar treatment
costs. Therefore, the risks outweigh the benefits.
19. Restricted use. With the exception of certain uses listed
below, EPA is proposing that all registered products be restricted to
use by certified applicators only. This proposal is based on the acute
toxicity of dichlorvos (Toxicity Category I, the most toxic
classification) and the existence of poisoning incidents. This is not
expected to be a major burden since most commercial use products
already have a label statement limiting sale and use to pest control
operators. In addition, the Registration Standard recommended
classification of all products, except those labeled for household use
only, as restricted use. EPA is therefore proposing to restrict the use
of all products except those registered for only the following uses:
impregnated strips in enclosed spaces within a museum and insect traps.
20. PPE requirements. EPA proposes to cancel the registration of
all remaining dichlorvos products unless the labels are amended to
require users to wear: a long sleeved shirt, long pants, gloves, socks
and shoes. EPA estimates of acceptable MOEs for some uses are based on
wearing these protective clothing. The PPE proposed in this Notice are
the minimum needed to eliminate unreasonable risks from use of
dichlorvos. If the presence of additional active ingredients in
specific end-use products result in more restrictive PPE requirements
then the more restrictive requirements must be placed on the end-use
label.
If the acute inhalation toxicity of the end-use product is in
category I or II, and therefore, a respirator is required for pesticide
handlers, the following type of respirator is appropriate to mitigate
dichlorvos inhalation concerns: a respirator with either an organic-
vapor-removing cartridge with a prefilter approved for pesticides
(MSHA/NIOSH approval number prefix TC-23C), or a canister approved for
pesticides (MSHA/NIOSH approval number prefix TC-14G).
21. Retained uses. EPA is proposing to retain the following uses;
however, the related registrations will be canceled unless the labels
conform to the above cancellations, restricted use, reentry and
protective clothing requirements: mushroom houses and greenhouses (only
automatic foggers or fogging through a port), kennels, feedlots, insect
traps, garbage dumps, direct application to poultry, automated
application to livestock, animal premises, manure, and buses.
Table 4.--Upper Bound Cancer Risk Estimates from use of Dichlorvos and
Naled
------------------------------------------------------------------------
Risk Before Agency Risk After Agency
Use Proposed Action Proposed Action
------------------------------------------------------------------------
Packaged or bagged, non- 3.4 x 10-6 0
perishable processed food and
RACs (including bulk stored,
regardless of fat content)
------------------------------------------------------------------------
Milk 6.2 x 10-7 6.2 x 10-7
------------------------------------------------------------------------
Eggs 7.1 x 10-8 7.1 x 10-8
------------------------------------------------------------------------
Red Meat 1.1 x 10-7 1.1 x 10-7
------------------------------------------------------------------------
Poultry 3.7 x 10-8 3.7 x 10-8
------------------------------------------------------------------------
Agricultural uses 2.1 x 10-7 2.1 x 10-7
Lettuce 1.6 x 10-7 1.6 x 10-7
Cucumbers 2.6 x 10-8 2.6 x 10-8
Tomatoes 1.4 x 10-8 1.4 x 10-8
[[Page 50371]]
Mushrooms 2.6 x 10-9 2.6 x 10-9
Radishes 9.8 x 10-10 9.8 x 10-10
------------------------------------------------------------------------
Dichlorvos from application of:
Dichlorvos 4.4 x 10-6 1 x 10-6
Naled 7.2 x 10-7 7.2 x 10-7
Total 5.1 x 10-6 1.7 x 10-6
------------------------------------------------------------------------
Table 5.--Summary of Dichlorvos Risks and Benefits
----------------------------------------------------------------------------------------------------------------
Non-Dietary Margin of
Exposure: Dietary Upper Bound
Uses Cholinesterase Cancer Risk Benefits Proposed Action
Inhibition
----------------------------------------------------------------------------------------------------------------
Domestic Dwellings
(Application)
Pressurized Aerosol 47 N/A Benefits in and Cancel
around domestic
dwellings are not
expected to be
significant
Crack and crevice 23 N/A Cancel
treatment
----------------------------------------------------------------------------------------------------------------
Domestic Dwellings
(Post-Application)
Total release 17 N/A Benefits in and Cancel
fogger around domestic
dwellings are not
expected to be
significant
Pressurized Aerosol 17 N/A Cancel
Crack and crevice 2 N/A Cancel
treatment
Resin Pest strips 20 N/A Cancel
Pet Flea collars 240 N/A Cancel
----------------------------------------------------------------------------------------------------------------
Occupational Exposure
----------------------------------------------------------------------------------------------------------------
Mushroom House
Applicator Majority of MOEs less 2.6 x 10-9 Benefits are not Allowable
than 50 and some expected to be Application Methods
less than 10 significant -Automatic foggers
-Thermal foggers
through a port
[[Page 50372]]
Reentry
After 24 hours 21 (no respirator) Reentry Restrictions
After 48 hours 289 (no respirator) Limited reentry
during first 48
hours following
treatment. No entry
within first 4
hours; limited
reentry (one hour
per 24 hours) for
handling activities
only.
----------------------------------------------------------------------------------------------------------------
Greenhouse
Applicator Majority of MOEs less 1.6 x 10-7 (lettuce) Not expected to be Allowable
than 100 and 30% 2.6 x 10-8 significant Application Methods
less than 50 (cucumbers) -Automatic foggers
1.4 x 10-8 (tomatoes) -Thermal foggers
8.8 x 10-10 through a port
(radishes)
Reentry
After 24 hours 21 (no respirator) Reentry Restrictions
After 48 hours 289 (no respirator) Limited reentry
during first 48
hours following
treatment. No entry
within first 4
hours; limited
reentry (one hour
per 24 hours) for
handling activities
only.
----------------------------------------------------------------------------------------------------------------
Domestic food/nonfood
animals (non-
poultry)
Applicator 6.1 6.2 x 10-7 (milk) Probable regional Cancel all hand
impacts application methods
to both food and
nonfood animals
[[Page 50373]]
1.1 x 10-7 (red meat) Other uses are
permitted such as
back and face
rubbers, and
automatic
application
systems.
----------------------------------------------------------------------------------------------------------------
Domestic food/nonfood > 100 7.1 x 10-8 (eggs) Possible regional Retain Use
animals (poultry) impacts
3.7 x 10-8 (poultry)
----------------------------------------------------------------------------------------------------------------
Domestic animal
premises (food and
non-food) (includes
dairy barns, mink
farms, barns,
stables, poultry
houses)
Applicator > 100 N/A Probable regional Retain uses
impacts
Reentry > 100 N/A
----------------------------------------------------------------------------------------------------------------
Feedlots >100 N/A Probable regional Retain use
impacts
----------------------------------------------------------------------------------------------------------------
Manure >100 N/A Benefits not expected Retain use
to be significant
----------------------------------------------------------------------------------------------------------------
Tobacco warehouse N/A Benefits not expected Cancel
to be significant
Applicator- 2
sprinkling
Mixer-loader 32,500
Warehouse worker 0.3
(reentry)
----------------------------------------------------------------------------------------------------------------
Ornamental lawns, 32 (similar to N/A Not expected to be Cancel
turf and plants greenhouse power significant
sprayer)
----------------------------------------------------------------------------------------------------------------
Warehouse treatment
(affects
nonperishable bulk,
packaged and bagged
raw and processed
commodities)
Application 38 3.4 x 10-6 $12 million for both Cancel all
raw and processed application methods
nonperishable bulk, except for
packaged, or bagged impregnated resin
agricultural strips which are
commodities plus the limited to closed
cost of additional areas such as
fumigations if silos.
needed.
Reentry 2.8
----------------------------------------------------------------------------------------------------------------
Kennels > 100 (similar to N/A Not expected to be Retain use
dairy barn) significant
[[Page 50374]]
----------------------------------------------------------------------------------------------------------------
Insect traps negligible risk N/A Not expected to be Retain use
significant
Applicator
----------------------------------------------------------------------------------------------------------------
Garbage dumps > 81 (less than N/A Not expected to be Retain use
greenhouse risk) significant
----------------------------------------------------------------------------------------------------------------
Commercial,
institutional and
industrial areas
(includes food
service, food
processing, end food
manufacturing
possibilities)
Applicator 38 Potential dietary Not expected to be Cancel all uses
risks significant
Reentry 2.8
----------------------------------------------------------------------------------------------------------------
Commercial
transportation
vehicles
----------------------------------------------------------------------------------------------------------------
Airplanes N/A Not expected to be Cancel use on
(disinsection of significant airplanes
aircraft)
Passenger - post- 135
application
Applicator 14
----------------------------------------------------------------------------------------------------------------
Buses-passenger 55 N/A Not expected to be Retain only fogger
significant use on buses and
require a 6-hour
ventilation period
before reentry.
----------------------------------------------------------------------------------------------------------------
Truck, shipholds,
rail cars
Application > warehouse Potential dietary Not expected to be Cancel use
risk significant
Reentry 20
----------------------------------------------------------------------------------------------------------------
Note: Amvac has requested voluntary deletion of the following
uses from their technical and end-use labels. In response to the
Federal Register Notice announcing Amvac's request, no one expressed
interest in retaining these uses, with the exception of greenhouses
and outdoor household use. Therefore, the Agency intends to follow
through with Amvac's request to delete these uses, excluding the two
exceptions. Any risks associated with these uses will be eliminated.
- Domestic dwellings (except for impregnated resin pest strips,
total release foggers, and crack and crevice treatment). There is
interest in supporting outdoor household use and this use will not
be immediately deleted. However, based on risk/benefit
considerations, the Agency is proposing to cancel this use.
- Greenhouses. Because there is interest in supporting use in
greenhouses, this use will not be immediately deleted. However,
based on risk/benefit considerations, the Agency is proposing to
cancel this use, unless certain use restrictions are put into place.
- Tobacco and tobacco warehouses
- Food service establishments, food manufacturing establishments
and food processing establishments, with the exception of nonfood-
processing areas. - Aircraft and buses
The following uses which Amvac is requesting to delete are not
included in the above risk/benefit table: tomatoes, rangeland
grasses, and aerial application.
V. Existing Stocks
Under the authority of FIFRA section 6(a)(1), EPA will establish
certain limitations on the distribution and use of existing stocks of
dichlorvos products subject to any final cancellation notice. EPA
defines the term ``existing stock'' to mean any quantity of dichlorvos
products in the United States on the effective date of the Final Notice
of Intent To Cancel certain registrations, or on the effective date an
application for amendment of registration is granted by the Agency.
Such existing stocks include dichlorvos products that have been
formulated, packaged, and labeled and are being held for shipment or
release or have been shipped or released into commerce.
EPA is proposing not to permit the continued sale, distribution, or
use of dichlorvos products affected by this Notice after the effective
date of the Final Cancellation Notice. EPA reserves the right to amend
this existing stocks provision, should conditions warrant
[[Page 50375]]
such amendment. The final cancellation notice may amend the existing
stocks provisions in the Use Deletion Notice published on April 19,
1995 (60 FR 19580).
VI. Procedural Matters
As required by FIFRA sections 6(b) and 25(d), and 40 CFR 154.31(b),
EPA has transmitted copies of a draft Notice of Intent to Cancel based
on this Notice, together with the support documents, to the Secretary
of Agriculture and the Scientific Advisory Panel for comment. EPA will
publish any comments received from the Secretary or the Panel, and
EPA's responses, in the Notice of Final Determination.
VII. Public Record and Opportunity for Comment
The Agency is providing a 90-day period for the public to comment
on this Notice and on the dichlorvos Special Review Docket. Comments
must be submitted by December 27, 1995. All comments and information
should be submitted in triplicate to the address given in the Notice
under ``ADDRESSES.'' All comments should be identified with the public
docket number (OPP-30000/56). All comments, information, and analyses
which come to the attention of EPA may serve as a basis for final
determination of regulatory action during the Special Review.
A public version of this record, including printed, paper versions
of electronic comments, which does not include any information claimed
as CBI, is available for inspection from 8 a.m. to 4:30 p.m., Monday
through Friday, excluding legal holidays. The public record is located
in Rm. 1132 of the Public Response and Program Resources Branch, Field
Operations Division (7506C), Office of Pesticide Programs,
Environmental Protection Agency, Crystal Mall #2, 1921 Jefferson Davis
Highway, Arlington, VA.
Electronic comments can be sent directly to EPA at:
[email protected]
Electronic comments must be submitted as an ASCII file avoiding the
use of special characters and any form of encryption.
The official record for this Notice, as well as the public version,
as described above will be kept in paper form. Accordingly, EPA will
transfer all comments received electronically into printed, paper form
as they are received and will place the paper copies in the official
record which will also include all comments submitted directly in
writing. The official record is the paper record maintained at the
address in ``ADDRESSES'' at the beginning of this document.
VIII. Public Docket
Pursuant to 40 CFR 154.15, the Agency has established a public
docket [OPP-30000/56] for the dichlorvos Special Review. This public
docket will include: (1) This Notice; (2) any other notices pertinent
to the dichlorvos Special Review; (3) non-CBI documents and copies of
written comments submitted to the Agency in response to the pre-Special
Review registrant notification, the Federal Register Notice initiating
Special Review, this Notice, any other Notice regarding dichlorvos
submitted at any time during the Pre-Special Review process by persons
outside government; (4) a transcript of any public meetings held by EPA
for the purpose of gathering information on dichlorvos; (5) memoranda
describing each meeting held during the Special Review process between
Agency personnel and persons outside government pertaining to
dichlorvos; and (6) a current index of materials in the public docket.
IX. References
1. U.S. EPA, George Z. Ghali, Fourth Peer Review of Dichlorvos
(DDVP), memorandum to George LaRocca (September 18, 1989).
2. National Toxicology Program (NTP), Pathology Working Group
Report (1986), Dichlorvos Two Year B6C3f1 Mouse Corn Oil Gavage Study
(Southern Research Institute, No. 5049, Test 2, NTP C#00113b). MRID
006019.
3. NTP (National Toxicology Program), Pathology Working Group
Report (1986), Two Year Gavage Study of Dichlorvos in F344 Rats,
(Southern Research Institute, Number 504).
4. U.S. EPA., FIFRA Scientific Advisory Panel, Transmittal of FIFRA
Scientific Advisory Panel Reports on the September 23, 1987 Meeting
Regarding the Peer Review Classification of Dichlorvos as a B2 Oncogen,
to Douglas D. Campt, October 1, 1987.
5. U.S. EPA, Judith W. Hauswirth, Second Peer Review of Dichlorvos
Reevaluation Following the September 23, 1987 Science Advisory Panel
Review, Memorandum to George LaRocca, March 16, 1988.
6. U.S. EPA, Memorandum, Judith W. Hauswirth, Third Peer Review of
Dichlorvos - Reevaluation Following the April 18, 1988 Meeting of the
NTP Panel of Experts, to George LaRocca, August 17, 1988.
7. U.S. EPA, Memorandum, George Z. Ghali, Fourth Peer Review of
Dichlorvos (DDVP), to George LaRocca, September 18, 1989.
8. Shirasu, U. et. al. (1976) Mutagenicity Screening of Pesticides
in the Microbial System. Mutation Research 40: 19-30; also in
submission to EPA received May 28, 1980, submitted by Upjohn Co.
9. Bridges, B. (1978) On the detection of volatile liquid mutagens
with bacteria; experiments with dichlorvos and epichlorhydrin, Mutation
Research 54:367-371. MRID 40303301.
10. Rosenkranz, H. (1973) Preferential effect of dichlorvos
(Vapona) on bacteria deficient in DNA polymerase, Cancer Research
33:458-459, MRID 40304402.
11. Sobels, F., et al. (1979) Absence of a mutagenic effect of
dichlorvos in Drosophilla melanogaster, Mutation Research 67:89-92,
MRID 40304403.
12. Moriya, M., et al. (1978) Effects of cysteine and a liver
metabolic activation system on the activities of mutagenic pesticides,
Mutation Research 57:259-263.
13. Wile, D. (1973) Chemical induction of Streptomycin-resistant
mutation in Escherichia coli; Dose and mutagenic effects of dichlorvos
and methyl methanesulfonate, Mutation Research 19:33-41, MRID 40303306.
14. Hanna, P., et al., (1975) Mutagenicity of organophosphorus
compounds in bacteria and Drosophila, Mutation Research, 28:405-420,
MRID # 00142663.
15. Mohn, G. (1973) 5-Methyltryptophan resistance mutations in
Escherichia coli K-12: Mutagenic activity of monofunctional alkylating
agents including organophosphorus insecticides, Mutation Research.
20:7-15, MRID # 001146101.
16. SDS Biotech Corporation, D-5455c, Report undated. L5178YTK+/-
Mouse Lymphoma Forward Mutation Assay with T=169-1.
17. SDS Biotech Corporation, D-5456C, Report undated. A dominant
lethal assay in Mice with T-169-1.
18. Lofroth, A. Naturforsch, C:biosci.:33c:783-5, 1978; and
Fischer, et al. Chem.-Biol. Interact. 19:205214, 1977.
19. U.S. EPA, Stephen A. Schaible , Addendum to DDVP Chronic
Exposure Analyses and Cancer Risk Assessments Evaluating Dietary Risk
for the DDVP PD 2/3, memorandum to Dennis Utterback, March 6, 1995.
20. U.S. EPA, George Ghali, Dichlorvos (DDVP): Reconsideration of
Quantification of Human Risk, Memorandum to George LaRocca and Dennis
Utterback (July 7, 1993).
21. I.C. Lamb, An Acute Neurotoxicity Study of Dichlorvos in Rats,
Unpublished report submitted by
[[Page 50376]]
Amvac Chemical Corp. and conducted at Wil Research Labs., Inc.,
Ashland, Oh, Study No. Wil 188003, Study date January 1, 1993, MRID #
426553-01.
22. J. Beavers, C.P. Driscoll, V. Dukes and M. Jaber. DDVP: An
Acute Delayed Neurotoxicity Study in Laying Hens, Unpublished report
submitted by Amvac Chemical Corp. and conducted at Wildlife
International Ltd., Easton, Md, Study No. 246-103. Study date -
December 29, 1988, MRID # 410047-02.
23. A 2-week Range-Finding Study on DDVP in Dogs, Unpublished
report submitted by Amvac Chemical Corp. and conducted at Hazleton
Laboratories America, Inc., Vienna, VA. HLA Study No. 2534-101, Study
date - August 6, 1990, MRID # 415931-01.
24. J.M. Kleeman, Thirteen Week Gavage Toxicity Study with DDVP in
Rats, Unpublished study submitted by Amvac Chemical Corp. and conducted
at Hazleton Laboratories America, Madison, WI, Study No. HLA 6274-102,
Study date - December 28, 1988, Mrid #410047-01.
25. I.C. Lamb, Subchronic Neurotoxicity Study (13 Week) of
Dichlorvos in Rats, Unpublished report submitted by Amvac Chemical
Corp. and conducted at Wil Research Labs, Inc., Ashland, Oh, Study No.
WIL 188003, Study date September 30, 1993. MRID # 429581-01.
26. Tyl, R.W., M.C. Marr and C.B. Myers, Developmental Toxicity
Evaluation of DDVP Administered by Gavage to New Zealand White Rabbits,
Unpublished report submitted by Amvac Chemical Corp. and conducted at
Research Triangle Institute, Research Triangle Park, NC, Study No. 60C-
4629-30/40, Study date - February 22, 1991, MRID # 418024-01.
27. E. Thorpe, A.b. Wilson, K.M. Dix and D. Blair, Teratological
Studies with Dichlorvos Vapour and in Rabbits and Rats, Archives of
Toxicology 30:29-38 (1972).
28. Dichlorvos (DDVP) 28-Day Neurotoxicity Study in Hens (6(a)(2)
Notification), Unpublished report submitted by Amvac Chemical Corp. and
conducted at Huntingdon Research Centre, Cambridgeshire, England, MRID
# 42586200-01.
29. Blair, D., K.M. Dix and P.F. Hunt, Two Year Inhalation Exposure
of Rats to Dichlorvos Vapor, Unpublished report submitted by Fermenta
Animal Health Company and conducted at Tunstall Laboratory,
Sittingbourne Research Center, Study No. TLGR. 0026. 74, Study date -
June 1974, MRID # 00057695 00632569.
30. V.R. Markiewicz, A 52-Week Chronic Toxicity Study on DDVP in
Dogs, Unpublished report submitted by Amvac Chemical Corp. and
conducted at Hazleton Laboratories America, Inc., Vienna, VA, HLA Study
No. 2534-102, Study date - August 6, 1990, MRID #415931-01.
31. R.W. Tyl, C.B. Myers, and M.C. Marr, Two-Generation
Reproductive Toxicity Study of DDVP Administered in the Drinking Water
to CD (Sprague-Dawley Rats), Unpublished report submitted by Amvac
Chemical Corp. and conducted at Reproductive and Developmental
Toxicology Laboratory, Research Triangle Park, NC, Report No. 60C-4629-
170, Study date - August 31, 1992, MRID # 424839-01.
32. U.S. EPA. J.E. Stewart, Review of Human Toxicology Data on
Dichlorvos (DDVP), Memorandum to the Toxicology Branch Files (April 8,
1993).
33. U.S. EPA, Guidance for the Reregistration of Pesticide Products
Containing DDVP as the Active Ingredient, September 1987: p. 35.
34. Mehler, L. Case Reports Received by the California Surveillance
Program in which Health Effects were Attributed to DDVP, April 1993.
35. American Association of Poison Control Centers. 1993-1994. DDVP
Exposure Experience Data 1985 through 1992. American Association of
Poison Control Centers, Washington, DC.
36. U.S. EPA. Jerome Blondell, Review of Poison Control Center Data
Call-In, December 5, 1994.
37. U.S. EPA, B.T. Backus, EPA File Symbol: 778-IG Seargant's Fast-
Acting Flea Tick Collar for Dogs, Memorandum to George LaRocca,
September 21, 1983.
38. U.S. EPA, Byron T. Backus, A.H. Robins DDVP Dog Collar,
Memorandum to George LaRocca, September 18, 1984.
39. U.S. EPA, Byron T. Backus, Data Evaluation Report VII:
Cholinesterase (98 day collar exposure) - dog, May 27, 1986.
40. Letter from Amvac Chemical Corporation to George Larocca,
November 2, 1994.
41. U.S. EPA. Report of EPA Cancer Peer Review Committee on
Trichlorfon, February 28, 1995.
42. U.S. EPA. Report of Reference Dose Committee on Naled, August
31, 1994.
43. U.S. EPA, Susan V. Hummel, Dichlorvos (DDVP; 084001):
Registration Case No. 0310 Anticipated Residues Resulting From Use of
Dichlorvos and Naled for Carcinogenic Dietary Exposure Assessment,
memorandum to Dennis Utterback, September 12, 1994.
44. U.S. EPA, Susan V. Hummel, Dichlorvos (084001) Reregistration
Case No. 0310, Processing studies on field corn, wheat, rice,
cottonseed and soybeans, memorandum to Brigid Lowery, July 18, 1994.
45. U.S. EPA, John Faulkner and Douglas Sutherland. DDVP and Naled
Usage and Use Patterns, memorandum to Debra Edwards, October 26, 1994.
46. U.S. EPA, Note from Doug Sutherland and John Faulkner to Dennis
Utterback, January 27, 1995.
47. U.S. EPA, Doug Sutherland and John Faulkner, Usage of DDVP
applied to dairy cattle and their premises in California, Note to
Dennis Utterback, February 1, 1995.
48. U.S. EPA, David Jacquith, Revisions to Exposure Assessment for
DDVP, memorandum to Dennis Utterback, April 15, 1993.
49. U.S. EPA, David Jaquith, Amendments/Clarifications of Exposure
Assessments for DDVP, Memorandum to Mike Beringer, September 2, 1993.
50. EPA, David Jaquith, Documentation of Reentry Intervals for Use
of DDVP in Mushroom Houses, for Use in Buses, and in Trucks/Shipholds/
Railroad Cars, Memorandum to Dennis Utterback, August 25, 1994.
51. U.S. EPA, Michael J. Beringer, Updated DDVP Occupational/
residential Risk Assessment, Memorandum to Dennis Utterback, February
23, 1994.
52. U.S. EPA, Stephen A. Schaible, Acute and Chronic Dietary
Exposure Analyses for DDVP, Memorandum to Dennis Utterback and Michael
Beringer, December 2, 1994.
53. U.S. EPA, Stephen A. Schaible, Addendum to DDVP Chronic
Exposure Analyses and Cancer Risk Assessments Evaluating Dietary Risk
for the DDVP PD 2/3, Memorandum to Dennis Utterback, March 6, 1995.
54. U.S. EPA, G. Ghali memorandum to G. LaRocca and L. Rossi, June
10, 1992.
55. U.S. EPA, Mike Beringer, Occupational and Residential Risk
Assessment for DDVP, memorandum to Dennis Utterback, September 8, 1993.
56. U.S. EPA, Allen Jennings, Transmittal of Dichlorvos PD2/3 and
Supporting Benefits Assessments, memorandum to Daniel Barolo, November
16, 1993.
57. U.S. EPA, Douglas W. S. Sutherland, DDVP Use in Mushroom
Houses, Note to Michael Beringer, February 23, 1994.
58. Mary S. Partridge, William G. Smith and Donald A. Rutz, Pest
and Pesticide Use Assessment for Poultry Production Systems in New York
State and the Commonwealth of Pennsylvania for 1992, Pesticide
Management Program, Cornell University, Ithaca, NY.
59. Mary S. Partridge, William G. Smith and Donald A. Rutz, Pest
and Pesticide Use Assessment for Dairy Cattle and Cabbage Production
Systems
[[Page 50377]]
in New York State for 1991, Pesticide Management Education Program,
Cornell University, Ithaca, NY.
60. U.S. EPA, Douglas Sutherland, Note regarding a Variety of
Sites, to Mike Beringer, March 29, 1994.
List of Subjects
Environmental protection.
Dated: September 22, 1995.
Lynn R. Goldman,
Assistant Administrator for Prevention, Pesticides and Toxic
Substances.
[FR Doc. 95-24112 Filed 9-27-95; 8:45 am]
BILLING CODE 6560-50-F