United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508C)
EPA-738-F-98-019
December 1998
•&ERA R.E.D. FACTS
Pesticide
Reregistration
Use Profile
Regulatory
History
METHOMYL
All pesticides sold or distributed in the United States must be registered
by EPA, based on scientific studies showing that they can be used without
posing unreasonable risks to people or the environment. Because of advances
in scientific knowledge, the law requires that pesticides which were first
registered before November 1, 1984, be reregistered to ensure that they meet
today's more stringent standards.
In evaluating pesticides for reregistration, EPA obtains and reviews a
complete set of studies from pesticide producers, describing the human health
and environmental effects of each pesticide. The Agency develops any mitiga-
tion measures or regulatory controls needed to effectively reduce each pesti-
cide's risks. EPA then reregisters pesticides that can be used without posing
unreasonable risks to human health or the environment.
When a pesticide is eligible for reregistration, EPA explains the basis for
its decision in a Reregistration Eligibility Decision (RED) document. This fact
sheet summarizes the information in the RED document for reregistration case
0028, methomyl, S-methyl N-((methylcarbamoyl)oxy) thioacetimidate.
Methomyl acts as an insecticide against Lepidopterous, suppresses
Coleopterous and some Hemipterous insect pests. Methomyl acts as an
ovicide against cotton bollworms and budworms. Methomyl is registered on a
wide variety of sites including field, vegetable, and orchard crops; turf (sod
farms only); livestock quarters; commercial premises; and refuse containers.
There are currently 85 tolerances for methomyl. Application types for
methomyl include aircraft (fixed-wing and helicopter), high and low volume
ground sprayer, ultra low volume sprayer, granule applicator, bait box, brush
duster, glove, and shaker can. Methomyl is formulated as a wettable powder,
soluble concentrate/liquid, bait/solid, dust, granular, and solid. There are no
homeowner uses of methomyl.
Methomyl was first registered in the United States in October, 1968 for use as
an insecticide. E.I. du Pont de Nemours and Company Inc., is the current
manufacturer of methomyl. A Registration Standard was issued in April, 1989.
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There are 15 methomyl products registered, along with 23 Special Local
Needs registrations (SLNs). All methomyl products, except the 1% bait
formulations, are classified as restricted use pesticides.
Human Health
Assessment
Toxicity
In acute toxicity testing, methomyl places in Toxicity Category I (the highest
toxicity category out of four) via the oral route and in eye irritation studies.
Methomyl places in Toxicity Category II via the inhalation route. For acute
dermal effects methomyl is in Toxicity Category III. For acute skin irritation,
methomyl produced no irritation (Category IV).
The Agency has classified methomyl as a Group E, not likely to be carcino-
genic to humans via relevant routes of exposure based on the results of the
chronic toxicity and carcinogen!city studies conducted with methomyl which
showed no evidence of carcinogen!city.
In determining whether to retain, reduce, or remove the lOx FQPA safety
factor for infants and children, EPA uses a weight of evidence approach taking
into account the completeness and adequacy of the toxicity data base, the
nature and severity of the effects observed in pre- and post-natal studies, and
exposure. Although the available data provided no indication of increased
sensitivity of rats or rabbits to in utero and/or postnatal exposure to methomyl,
data gaps exist for the acute and subchronic neurotoxicity studies. These
studies would have yielded cholinesterase inhibition and field observation
behavior data, as well as histopathology of the central and peripheral nervous
system which are not presently available for evaluation. The Agency deter-
mined that the lOx safety factor to account for increased sensitivity of infants
and children should be reduced from lOx to 3x.
The Agency has determined that methomyl is a degradate of thiodicarb, which
is a registered pesticide. Therefore, methomyl residues resulting from applica-
tions of both thiodicarb and methomyl have been considered in an aggregate
risk assessment and compared to appropriate toxicological endpoints for
methomyl.
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Dietary Exposure and Risk
The RfD for methomyl was calculated to be 0.008 mg/kg/day from a two-year
feeding study in dogs with a NOEL of 2.5 mg/kg/day for males and females.
The LOEL was 10 mg/kg/day based on histopathological effects in the kidney.
An uncertainty factor (UF) of 100 was applied to account for intraspecies
variability and interspecies extrapolation together with a safety factor of 3x for
FQPA, based on the lack of acute and subchronic neurotoxicity studies (data
gaps).
Acute dietary exposure estimates for methomyl alone were compared to the
methomyl maternal NOEL of 6 mg/kg/day from a rabbit developmental study
based on deaths in dams on days 1-3 after dosing at 16 mg/kg/day. An uncer-
tainty factor (UF) of 100 was applied to account for intraspecies variability and
interspecies extrapolation. For calculating the Margin of Exposure (MOE) for
methomyl, the FQPA safety factor to account for any special sensitivity to
infants and children has been reduced from lOx to 3x to account for the lack of
acute and subchronic neurotoxicity studies. Therefore, a MOE of at least 300
is considered acceptable. The acute Monte Carlo dietary analysis for methomyl
alone indicates that there are adequate margins of exposure for the U.S.
population, children 1 to 6 years old and infants.
For the acute aggregate dietary risk assessment for food, for thiodicarb and
methomyl combined, the acute methomyl (6 mg/kg/day) endpoint was used in
the risk assessment and compared to residues of methomyl from thiodicarb
application plus residues of methomyl from methomyl application. The results
of the acute aggregate exposure analyses for food, for thiodicarb and methomyl
show that there are adequate margins of exposure for the general U.S. popula-
tion, children 1 to 6 years of age, and infants.
For the chronic dietary risk assessment for food, for methomyl alone, the RfD
for methomyl was used in the risk assessment The DRES chronic analysis for
methomyl alone indicates that chronic risk from exposure to methomyl from
food sources is not of concern for the same population groups.
For the chronic aggregate dietary risk assessment for food, for thiodicarb and
methomyl combined, the RfD for methomyl was used in the risk assessment
and compared to residues of methomyl from thiodicarb application plus
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residues of methomyl from methomyl application. The results of the chronic
aggregate exposure analysis indicate that there are no chronic concerns associ-
ated with potential residues of methomyl on foods as the result of application
of thiodicarb and methomyl.
The Agency has calculated drinking water levels of concern (DWLOCs) for
methomyl. The maximum estimated concentrations of methomyl in surface and
ground water are less than the Agency's levels of concern for methomyl in
drinking water as a contribution to acute aggregate exposure. The estimated
average concentrations of methomyl in surface and ground water are less than
OPP's levels of concern for methomyl in drinking water as a contribution to
chronic aggregate exposure.
Occupational Exposure and Risk
Handlers (mixers, loaders, and applicators) of methomyl may be exposed to
methomyl during and after normal use of liquid, wettable powder, pastes, baits,
and dusts formulations. For combined dermal and inhalation exposure, the
Agency is requiring the use of additional personal protective equipment and/or
the use of engineering controls (water soluble bags). The handler information
for methomyl has been integrated with other considerations, including
epidemiologic information and handler incident data in determining the re-
quired PPE.
The calculations of postapplication exposure and risk indicate that for certain
crops, restricted-entry intervals (REIs) based on the short and intermediate
term dermal toxicological endpoint should be considered. This information has
been integrated with other considerations based on epidemiological information
and incident data to determine the required REIs. The required REIs for apple,
cotton, grapefruit, lemon, nectarine, oranges, tangelo, and tangerine is 3 days,
for peaches 4 days, and for grapes 7 days. For other crops and sites, no
additional postapplication mitigation is indicated based on the short and
intermediate term dermal endpoint. For these other crops and sites the REI
should be based on the acute toxicity of methomyl. Since methomyl is in acute
toxicity category 1 for primary eye irritation, a 48 hour REI is indicated.
No data are available for estimating worker's dermal exposures to methomyl
following applications of baits. However, EPA recognizes that dermal expo-
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sures to methomyl following application of baits are likely to be significantly
lower than would result from workers' contact with treated foliage. Therefore,
EPA believes that dermal risk from bait applications would not exceed the risks
estimated above for foliar contact in "low exposure" crops.
Postapplication risk assessments were not completed for dusts, pastes, and
paintbrush applications of methomyl. Dust use scenarios were not assessed,
but are believed to be similar to other postapplication agricultural scenarios
(i.e., postapplication exposure assessments for sprays on various crops were
used to assess risks from dusts). Pastes and paintbrush postapplication expo-
sures are believed to have a low risk due to low potential for exposure (i.e.,
dermal contact with treated surfaces is likely minimal or nonexistent given the
use pattern).
Environmental
Assessment
Environmental Fate
Laboratory studies indicate that methomyl is moderately persistent and highly
mobile. It is stable to hydrolysis at lower pH's (neutral to acidic) and degrades
slowly in alkaline conditions. Methomyl photolyzes quickly in water but more
slowly in soils. It is moderately stable to aerobic soil metabolism but degrades
more rapidly under anaerobic conditions. In laboratory studies, methomyl does
not readily adsorb to soil and has the potential to be very mobile. Field studies
show varying dissipation rates of the chemical in soils. Dissipation rates were
related primarily to differences in soil moisture content, which may affect the
microbial activity, and rainfall/irrigation, which could influence leaching.
Methomyl has been detected in ground water in a prospective ground water
monitoring study and in other reported incidences. While it may reach ground
water under certain conditions, methomyl will not likely persist under many
conditions. Methomyl can contaminate surface water as a result of spray drift
during application or by runoff from treated sites. Methomyl would not be
expected to persist in clear, shallow waters because of its susceptibility to
photolysis. However, methomyl may persist in waters where sunlight penetra-
tion is limited (such as in deeper waters or waters with a significant sediment
load or populations of organisms such as algae).
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Ecological Effects
Laboratory studies show that methomyl is highly toxic to birds and mammals
on an acute oral basis but only slightly toxic to birds on a subacute dietary
basis. Methomyl poses acute risks to birds and mammals that feed on short
and tall grasses, broadleaf plants, and small insects. Methomyl is moderately to
highly toxic to freshwater fish and moderately toxic to estuarine fish. In a
chronic early life-stage study, methomyl significantly reduced fish larvae
survival under flow through conditions.
The major concerns for non-target organisms are chronic risks to non-target
mammalian and freshwater invertebrate organisms. Risks to aquatic inverte-
brates from exposure to methomyl are likely to occur wherever methomyl is
used. Toxicity data suggest that aquatic invertebrates are much more sensitive
to methomyl contamination than either fresh or salt water fish species. Accu-
mulation of methomyl from repeated applications contributes to the chronic
risks.
Ecological Effects Risk Assessment
EPA is generally concerned about the ecological effects to terrestrial wildlife
and aquatic organisms posed by exposure to methomyl. The risk assessment
for methomyl shows various levels of concern regarding avian risk and mam-
malian risk from multiple applications of methomyl at short intervals. In
addition, most agricultural uses present acute and chronic risks of varying
levels to endangered and nonendangered aquatic organisms. The major
concerns for non-target organisms are the chronic risks posed by the use of
methomyl to non-target mammalian and freshwater invertebrate organisms.
With risk mitigation measures in place, the Agency considers these risks
acceptable.
Risk Mitigation To lessen ecological and potential water risks posed by methomyl, the Agency
is requiring the following mitigation for methomyl containing products.
• Based on the environmental risk assessment for methomyl, the following
advisories are required for methomyl: a labeling statement for potential
ground water contamination, a labeling statement to minimize the poten-
tial for surface water contamination and labeling statements on manufac-
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turing use products and end use products based on the toxicity to
nontarget organisms. A bee hazard statement is also required.
• The registrant will reduce the highest seasonal use rates between 11 to
20 percent on eight crops. These crops are generally the crops for which
most methomyl is sold.
The registrant will reduce the single maximum per acre application rate
of methomyl by 50% from 1.8 pounds to 0.9 pounds on peaches and
commercial sod farms. No methomyl crop use will exceed a single
application rate of 0.9 pounds of methomyl per acre.
A statement supporting the use of an Integrated Pest Management (IPM)
plan must be added to the labels.
• Buffer zones have been imposed that will reduce the potential risk to
non-target aquatic organisms from spray drift during aerial or ground
applications.
Additionally, there are risk mitigation measures required in the RED to protect
mixers, loaders, applicators and workers, including water soluble bags, addi-
tional PPE and appropriate REIs. For a detailed list, refer to Chapter V. of the
methomyl RED document.
Additional Data The generic data base supporting the reregi strati on of methomyl for the above
Required eligible uses has been reviewed and determined to be substantially complete.
For methomyl, the following information is being required:
81-8 Acute neurotoxicity study - rat
82-7 Subchronic neurotoxicity study - rat
72-4(a) Estuarine/marine fish early life stage test
72-4(b) Estuarine/marine invertebrate life-cycle tests
860.1380 Storage Stability Data (formerly 171-4e)
860.1500 Magnitude of the Residue in Crop Plants (formerly 171-4k)
860.1850 Confined Accumulation in Rotational Crops (formerly 165-1)
830.7050 UV/Visible Absorption spectrum
Product Labeling
Required
All methomyl end-use products must comply with EPA's current pesti-
Pr°duct labeling requirements and with those labeling requirements
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imposed in the Methomyl RED. For a comprehensive list of labeling require-
ments, please see Section V. of the Methomyl RED document.
Regulatory
Conclusion
Based on the reviews of the generic data for the active ingredient
methomyl, the Agency has sufficient information on the health effects of
methomyl and on its potential for causing adverse effects in fish and wildlife
and the environment. The Agency has determined that methomyl products,
labeled and used as specified in the Reregi strati on Eligibility Decision, will not
pose unreasonable risks to humans or the environment.
For More
Information
EPA is requesting public comments on the Reregi strati on Eligibility
Decision (RED) document for methomyl during a 60-day time period, as
announced in a Notice of Availability published in the Federal Register. To
obtain a copy of the RED document or to submit written comments, please
contact the Pesticide Docket, Public Response and Program Resources
Branch, Field Operations Division (7506C), Office of Pesticide Programs
(OPP), US EPA, Washington, DC 20460, telephone 703-305-5805.
Electronic copies of the RED and this fact sheet are available on the
Internet. See http://www.epa.gov/REDs.
Printed copies of the RED and fact sheet can be obtained from EPA's
National Center for Environmental Publications and Information
(EPA/NCEPI), PO Box 42419, Cincinnati, OH 45242-0419, telephone 513-
489-8190, fax 513-489-8695.
Following the comment period, the Methomyl RED document also will
be available from the National Technical Information Service (NTIS), 5285
Port Royal Road, Springfield, VA 22161, telephone 703-605-6000.
For more information about EPA's pesticide reregi strati on program, the
Methomyl RED, or reregi strati on of individual products containing methomyl,
please contact the Special Review and Reregi strati on Division (7508C), OPP,
US EPA, Washington, DC 20460, telephone 703-308-8000. For information
about the health effects of pesticides, or for assistance in recognizing and
managing pesticide poisoning symptoms, please contact the National Pesticide
Telecommunications Network (NPTN). Call toll-free 1-800-858-7378,
between 6:30 am and 4:30 pm Pacific Time, Monday through Sunday. The
NPTN website is: ace.orst.edu/info/nptn/.
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