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Docket Number EPA-HQ-OPP-2010-0751

www.regulations.gov

Methomyl Final Work Plan

Registration Review

March 2011

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METHOMYL FINAL WORK PLAN

Introduction

This is the Environmental Protection Agency’s (EPA’s) Final Work Plan for the 

registration review of methomyl. This work plan includes the expected registration review 

timeline. The work plan also addresses public comments received concerning the Preliminary 

Work Plan in the Summary Document, which was posted in the methomyl registration review 

docket (EPA-HQ-OPP-2010-0751), and any other comments concerning the initial docket 

postings. The Summary Document provided information on what EPA knows about the 

pesticide and what additional risk analyses and data or information the Agency believes are 

needed to make a registration review decision.

The Agency is implementing the registration review program pursuant to Section 3(g) of 

the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and will review each 

registered pesticide every 15 years to determine whether it continues to meet the FIFRA standard 

for registration. Changes in science, public policy, and pesticide use practices will occur over 

time. The registration review program is intended to make sure that, as the ability to assess risk 

evolves and as policies and practices change, all registered pesticides continue to meet the 

statutory standard. The public phase of registration review begins when the initial docket is 

opened for each case. Information on this program is provided at: 

http://www.epa.gov/oppsrrd1/registration_review/.

Methomyl is an N-methyl carbamate insecticide currently registered for use on a wide 

variety of sites including field, vegetable, and orchard crops, and on turf (sod farms only). 

Methomyl is generally a restricted use pesticide [based on percent active ingredient (a.i.)] and 

there are currently no homeowner uses. However, certain low percentage a.i. formulations are

not designated as restricted use and can be used around livestock quarters, commercial premises

and refuse containers. Methomyl was first registered in the United States in 1968. A

Reregistration Eligibility Decision (RED) was completed in 1998. Methomyl is the primary 

metabolite of thiodicarb, which is also an insecticide. The thiodicarb registration review docket 

(EPA-HQ-OPP-2009-0432) opened on December 16, 2009.

Methomyl and thiodicarb are members of the N-methyl carbamate (NMC) class of 

chemicals that share a common mechanism of toxicity and inhibit acetylcholinesterase (AChE) 

by carbamylation of the serine hydroxyl group located in the active site of the enzyme. The 

“Revised N-Methyl Carbamate Cumulative Risk Assessment” was completed in September 2007 

and is available in the docket at EPA-HQ-OPP-2007-0935.
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Comments Received on Preliminary Work Plan:

Multiple comments were received during the 60-day public comment period on the planned 

ecological assessment and human health scoping document discussed in the Preliminary Work 

Plan. However, these comments do not alter the Agency’s work plan outlined in the

Preliminary Work Plan. The representative comments and Agency’s responses are summarized 

in this document. In the Preliminary Work Plan, EPA also solicited comments on three specific 

topics: environmental justice, water body impairment, and trade irritants. No comments or 

information were received during the comment period. For further discussion on these 

comments please see the Summary of Comments and Agency Response Section.

Anticipated Risk Assessment and Data Needs

The Agency intends to require data needed to conduct a comprehensive ecological risk 

assessment, including an endangered species risk assessment, and a revised human health risk 

assessment for all uses of methomyl. Below is a summary of the issues relevant to the 

registration review of methomyl and the data the Agency anticipates requiring. 

Ecological Risk:

• The most recent comprehensive risk assessment for methomyl was conducted in 1998 in 

support of the Reregistration Eligibility Decision (RED) document.

• The Agency has conducted several assessments on some endangered species, but has not 

conducted an ecological risk assessment that supports a complete endangered species 

determination for methomyl. The ecological risk assessment planned during registration 

review will allow the Agency to determine whether methomyl’s use has “no effect” or 

“may affect” federally listed threatened or endangered species (listed species) or their 

designated critical habitats. When an assessment concludes that a pesticide’s use “may 

affect” a listed species or its designated critical habitat, the Agency will consult with the

U.S. Fish and Wildlife Service (FWS) and/or National Marine Fisheries Service (NMFS)

(the Services), as appropriate.

• On January 19, 2011, the Center for Biological Diversity and the Pesticide Action 

Network North America filed a lawsuit in the United States District Court for the 

Northern District of California, against the Environmental Protection Agency (EPA) for 

allegedly failing to undergo consultation with the United States Fish and Wildlife Service 

and the National Marine Fisheries Service regarding the effects of over 350 pesticides, 

including methomyl, on over 200 endangered and threatened species throughout the 

United States (Center for Biological Diversity, et al. v. EPA, et al., No. C 11-00293 

(N.D.Cal.).
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• The Agency anticipates needing the following data in order to conduct a complete 

ecological risk assessment, including a complete endangered species assessment, for 

methomyl: 

• GDLN 835.2240 – Aqueous photolysis

• GDLN 835.4100 – Aerobic soil metabolism

• GDLN 835.4300 – Aerobic aquatic metabolism

• GDLN 835.4400 – Anaerobic aquatic metabolism

• GDLN 850.2100 – Avian oral toxicity (passerine species)

• GDLN 850.2300 – Avian reproduction study (mallard duck)

• GDLN 850.4100 – Terrestrial plant toxicity: Tier II Seedling Emergence

• GDLN 850.4150 – Terrestrial plant toxicity: Tier II Vegetative Vigor

• GDLN 850.4400 – Aquatic plant growth: vascular plants 

• GDLN 850.5400 – Aquatic plant growth: nonvascular plants

Please refer to the “Registration Review: Preliminary Problem Formulation for Environmental 

Fate, Ecological Risk, Endangered Species, and Drinking Water Exposure Assessments for 

Methomyl,” dated July16, 2010, for a more detailed discussion of the anticipated ecological risk 

assessment and data needs.

Human Health Risk:

• The most recent comprehensive human health risk assessment for methomyl was 

completed in support of the 1998 RED. A dietary assessment was completed for 

methomyl as part of the NMC Cumulative Risk Assessment. 

• Since the last human health exposure and risk assessment in support of the 1998 RED the 

crop use sites and application scenarios have remained the same with the exception of the 

cancellation of methomyl use on strawberries and grapes, and the restriction on handheld 

devices.

• A revised dietary risk assessment, may be needed to include updated percent crop treated 

estimates, updated monitoring data, changes in toxicological endpoints, and revised 

estimated drinking water concentrations.

• The methomyl tolerance expression in 40 CFR 180.253 will be reviewed during 

registration review to ensure that it appropriately covers the metabolites and degradates 

of methomyl and that it specifies the residues to be measured for each commodity. Any 

proposed revisions would be to the chemical description rather than the individual 

tolerance levels.
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• A residential handler exposure assessment may be needed during registration review. 

Even though there are currently no homeowner uses for methomyl, there is a potential for 

exposure to baits in public areas. In addition, a residential post-application assessment 

may be needed to support the use of methomyl on sod farms. 

• Revised occupational handler and postapplication assessment may be needed based on 

the most current toxicity profile and Agency policies.

• Due to the rapid onset and recovery of AChE effects from methomyl, an acute aggregate 

risk assessment is the only appropriate aggregate assessment that may be needed to 

support registration review. This acute assessment would incorporate any new point of 

departures or uncertainty factors identified for methomyl.

• The Agency anticipates requiring the following data in order to conduct a complete 

human health risk assessment for methomyl:

o GDLN 870.7800 – Immunotoxicity Study

o Non-guideline – Acute Inhalation Study This acute inhalation study would 

provide AChE data showing the time to peak AChE inhibition as well as the doseresponse of AChE inhibition at the peak inhibition. A study protocol should be 

provided to the Agency for review before the onset of such study.

• Prior to a final registration review decision for methomyl, the Agency will determine if 

there is any new information, such as new hazard or exposure data or information on 

changes to the use pattern, that would affect the cumulative risk assessment. Should the 

Agency determine that new information on methomyl is available that could potentially 

impact the cumulative risk assessment and result in a risk of concern, the Agency will 

revisit the cumulative risk assessment.

• Please refer to the “Methomyl: Registration Review Scoping Document for Human Health 

Assessments,” dated July 13, 2010, available in the docket, for a detailed discussion of the 

anticipated human health risk assessment and data needs for methomyl.
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Endocrine Disruptor Screening Program 

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse 

outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and 

chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, 

and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and 

chronic studies that assess growth, developmental and reproductive effects in different 

taxonomic groups. As part of its reregistration decision, EPA reviewed these data and selected 

the most sensitive endpoints for relevant risk assessment scenarios from the existing hazard 

database. However, as required by FFDCA section 408(p), methomyl is subject to the endocrine 

screening part of the Endocrine Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the Administrator 

may designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between October 

2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 chemicals, 

which contains 58 pesticide active ingredients and 9 inert ingredients. Methomyl was included 

on that list and has been issued an order to conduct the Tier 1 testing. Once all required Tier 1 

and Tier 2 data have been received and reviewed, the endpoints and safety factors used for risk 

assessment purposes will be examined and a new risk assessment performed if necessary. For 

further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our 

website: http://www.epa.gov/endo/. 
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Timeline

The Agency has created the following estimated timeline for the completion of the methomyl

registration review.

Registration Review for Methomyl – Projected Registration Review Timeline

Activities Estimated Date

Opening the Docket

Open Docket and Public Comment Period 2010 – September

Close Public Comment 2010 – November

Case Development

Final Work Plan 2011 – March

Issue DCI 2011 – Oct – Dec

Data Submission 2013 – Oct –Dec

Open Public Comment Period for Draft Risk Assessments 2015 – April – June

Close Public Comment Period 2015 – July – Sept

Registration Review Decision

Open Public Comment Period for Proposed Registration Review 

Decision 2015 – Oct – Dec

Close Public Comment Period 2016 – Jan - March

Registration Review Decision and Begin Post-Decision Follow-up 2016

Total (years)

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1. An assessment of the potential cumulative risk from the NMC class of insecticides may impact this time estimate.
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Summary of Comments and Agency Responses:

The methomyl registration review docket was open for a 60-day comment period beginning on 

September 22, 2010. Multiple comments were received from the public and the registrants, 

however, these comments do not alter the Agency’s work plan outlined in the Preliminary Work 

Plan. Below are the Agency’s responses to representative comments concerning data 

requirement. For more detailed/complete responses, please see Agency memos “Methomyl: 

Response to Public Comments on Registration Review Preliminary Work Plan,” dated 

01/25/2011, Agency memo “Response to Public Comments on the Registration Review Problem 

Formulation for Ecological Risk, Environmental Fate, Endangered Species, and Drinking Water 

Assessments for Methomyl,” dated 12/17/2010, and Agency memo “BEAD Response to the 

California Grape and Tree Fruit League (CGTFL) Regarding the Agency’s Action to 

Discontinue Methomyl Use on Table Grapes”, all are available in the docket.

Comments from the Physicians Committee for Responsible Medicine (PCRM)

PCRM Comment 1:

“The Summary Document indicates that the Agency may request testing for avian acute oral 

toxicity. We strongly support the use of the newly revised OECD Test Guideline 223 for the 

acute avian oral toxicity test...”

EPA Response: 

To date the OECD has adopted the TG 223 guideline and has issued a validation report. At this 

time EPA is actively evaluating the results of the OECD validation report to determine if the TG 

223 effects endpoints and dose/response information adequately address the purposes of the 

avian acute oral data requirement as described in 40 CFR Part 158. Until the Agency’s 

evaluation of that validation report is completed, EPA will not classify avian toxicity studies 

performed using the TG 223 protocol and the studies cannot be used to fulfill current data 

requirements. 

PCRM Comment 2:

“In response to past comments on the avian acute oral toxicity test... ‘EPA is not likely to accept 

studies conducted under the OECD guideline unless additional study validation is conducted for 

passerine species (from EFED Response to Comments on Preliminary Work Plan for Sodium 

Acifluorfen)’... If the Agency is interested in collecting all data in consideration of the use of the 

223 then it should not state that it will not accept information gathered according to this 

protocol.”

EPA Response: 

EPA will consider all data submitted regarding the potential toxicity of pesticides. In reading 

through the previous Agency response, we understand how the sentence ‘EPA is not likely to 

accept studies conducted under the OECD guideline...” could be misunderstood. To clarify 
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what was meant, the Agency will not be able to classify studies conducted using TG223 and 

passerines as ‘acceptable’ (and, thus, fulfilling guideline requirements) until it is verified that the 

OECD TG 223 using passerines adequately addresses the purposes of the passerine acute oral 

data requirement as described in 40 CFR Part 158.

Comments from the American Bird Conservancy (ABC)

ABC Comment 1: 

ABC requests that EPA require an avian oral toxicity test using a passerine species and an avian 

reproduction study with the mallard duck.

EPA Response:

EPA will be requiring both of these studies as noted in the methomyl Summary Document and 

the Problem Formulation.

ABC Comment 2:

ABC requests an avian reproductive and developmental study using a passerine species. ABC 

recognizes that EPA does not have an official Standard Operation Procedure (SOP) to 

recommend to registrants for passerine reproductive studies, however, we urge EPA to look 

beyond the lack of SOP and investigate the potential toxicity of this compound.

EPA Response:

No data are available to EPA that show methomyl is more toxic to passerine species than it is to 

bobwhite quail (Colinus virginianus) or mallard ducks (Anas platyrhynchos) on a chronic 

exposure basis as it relates to reproductive endpoints. Therefore, at this time, it is believed that 

the data from the reproductive studies in the bobwhite quail and mallard duck studies will be 

adequate for assessing potential risks of methomyl to birds from chronic exposure. 

ABC Comment 3:

EPA should evaluate the risk from puddles of standing water within 24 hours of irrigation. If the 

puddle model indicates a risk to birds, this method of application should be withdrawn, or 

specific monitoring requirements should be implemented.

EPA Response:

EPA is actively working on tools that will address assessing risks to non-target animals 

(including birds) from exposure through drinking water, including puddles. If these tools are 

available, this potential exposure pathway will be considered quantitatively in the methomyl 

ecological risk assessment conducted for Registration Review. 

ABC Comment 4:

Methomyl is known to be toxic to birds and in one incident was used to deliberately poison 18 

pigeons. ABC request EPA to consider requiring all methomyl end-use products to be labeled as 

restricted use, to prevent further abuse. Because the registration review process is so prolonged, 
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ABC requests that the EPA consider interim label changes such as, lower application rates, 

application right before dark, and requiring the plowing in (incorporation) of the methomyl 5G 

Granule formulation immediately after application.

EPA Response: 

Once the required ecological data are generated and new ecological risk assessments have been 

completed, EPA will recommend that appropriate mitigation be added to labels if the risk 

assessments indicate risks of concern.

Comments from the California Grape and Tree Fruit League (CGTFL) 

CGTFL Comment 1:

2006 Alternatives Assessment did not adequately identify appropriate pests and control for CA 

table grapes. 2006 AA references had very little input from the California table grape industry. 

EPA Response:

The May 17, 2006 Alternatives Assessment for Methomyl on Grapes was for all grapes (raisin, 

table, and wine) nationwide, and therefore, did not focus on any one type of grape or state. 

Information was obtained from the publicly available crop profiles and pest management 

strategic plans available on the Integrated Pest Management Centers website 

(http://www.ipmcenters.org). The Crop Profile for Grapes (Table) in California was produced 

by University researchers, IPM advisors, growers, and a member of the California Table Grape 

Commission under the name "California Grape Advisory Team." 

A subsequent analysis was conducted in 2008 that focused on California table grapes which did 

include industry input. In the 2008 EPA review, the additional pests of concern and their control 

practices specific to California table grapes were considered. In addition, pest information 

specific to California table grapes was submitted in support of an emergency exemption request 

in 2008.

 

Comments from DuPont Crop Protection (DCP)

DCP Comment 1:

For the following studies DuPont believes existing data meets these data needs. 

GDLN 835.2240 – Aqueous Photolysis

GDLN 835.4100 – Aerobic Soil Metabolism

GDLN 835.4300 – Aerobic Aquatic Metabolism

GDLN 835.4400 – Anaerobic Aquatic Metabolism

EPA Response:

The problem formulation for methomyl, which may be found in the docket at 

www.regulations.gov (EPA-HQ-OPP-2010-0751), provides details on the environmental fate 
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data deficiencies and information needed to conduct an exposure assessment for Registration 

Review. We look forward to receiving data that address these needs.

DCP Comment 2:

GDLN 850.2300 – Avian reproduction study (mallard duck). DuPont has conducted an avian 

reproduction study with the mallard (MRID 41898601) that satisfies this data requirement. This 

study was categorized as core and determined to fulfill the guideline requirement in the 

methomyl RED document.

EPA Response:

"The study cited (MRID 41898601) cannot be used to fulfill guideline requirements because 

there were effects noted at all treatment concentrations, a NOAEC was not determined. In 

addition, the NOAEC from the mallard reproduction study is <50 mg a.i./kg-diet based on 

decreases in adult male body weight, which indicates that the mallard duck may be more 

sensitive to methomyl than the bobwhite quail on a chronic exposure basis. Therefore, the 

Agency recommends a reproduction study (GDLN 850.2300) with the mallard duck is needed to 

fulfill this data gap."

DCP Comment 3:

On July 15, 2010, DuPont submitted comments on the NMFS Biological Opinion and EPA’s 

proposed measures. A response from the Agency is pending.

EPA Response:

The Agency has reviewed the comments DuPont submitted relative to the Endangered Species 

Protection Bulletins resulting from ESA consultation with the National Marine Fisheries Service. 

A letter is currently being prepared to explain how the Agency handled all of the comments it 

received on those bulletins.

DCP Comment 4:

Regarding Table 3.2 in the Problem Formulation, “(t)he Lannate® SP formulation should have 

Chemigation listed under Methods of Application.”

EPA Response:

EPA appreciates the information provided by DuPont. EPA will review the Lannate® LV label 

and will make changes to the method of application as appropriate when conducting the 

ecological risk assessment for methomyl during the Registration Review process.

Next Steps:

The Agency plans to issue a DCI for methomyl in 2011 for the data gaps listed under Summary 

of Data Gaps below. The information received in response to this DCI will be used to conduct 

the planned human health, ecological risk, and endangered species assessment for methomyl.
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Summary of Data Gaps – Methomyl

The table below summarizes all outstanding data needs for methomyl

Guideline 

Number Data Requirement

Test 

Material

Estimated 

Timeframe

(Months)

835.2240 Aqueous photolysis TGAI 24

835.4100 Aerobic Soil Metabolism* TGAI 24

835.4300 Aerobic Aquatic Metabolism TGAI 24

835.4400 Anaerobic Aquatic Metabolism TGAI 24

850.2100 Avian Oral Toxicity (passerine species) TGAI 12

850.2300 Avian Reproduction Study (Mallard duck) TGAI 12

850.4100 Terrestrial Plant toxicity: Tier I Seedling Emergence** TGAI 12

850.4150 Terrestrial Plant toxicity: Tier I Vegetative Vigor** TGAI 12

850.4400 Aquatic Plant Growth: Tier II Vascular Plants** TGAI 12

850.5400 Aquatic Plant Growth: Tier II Algae** TGAI 12

Non-GDLN Acute Inhalation Study TGAI 12

870.7800 Immunotoxicity Study TGAI 12

* Foreign Soil Taxonomic Classification. Soil taxonomic classifications for foreign soils studied 

in MRID 45473401 are necessary in order to compare the studied soils to domestic soils 

representative of methomyl use sites.

**Registrants may opt to conduct a Tier I study, with the understanding that any adverse effects 

(even if <25%) will necessitate a Tier II study. A Tier II study will enable the Agency to 

conduct an endangered species assessment for nontarget plants.