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Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review of Methomyl 

N

O

O

N

S

H

CAS Registry Number: 16752-77-5 

PC Code: 090301 

Prepared by:

Melissa Panger, Ph.D., Biologist 

Greg Orrick, Environmental Scientist 

Reviewed by: 

R. David Jones, Ph.D., Senior Agronomist 

Thomas Steeger, Ph.D., Senior Biologist 

Mark Corbin, Acting Branch Chief

U.S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division 

Environmental Risk Branch IV 

1200 Pennsylvania Ave., NW 

Mail Code 7507P 

Washington, DC 20460

July 16, 2010 
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Table of Contents 

1. Purpose....................................................................................................................................... 4 

2. Problem Formulation ................................................................................................................. 4 

2.1. Nature of Regulatory Action............................................................................................... 4 

2.2. Previous Assessments ......................................................................................................... 4 

2.2.1. Ecological Risk Assessments....................................................................................... 4 

2.2.2. Drinking Water Exposure Assessments....................................................................... 6 

3. Stressor Source and Distribution ............................................................................................... 7 

3.1. Mechanism of Action.......................................................................................................... 7 

3.2. Overview of Pesticide Use and Usage................................................................................ 7 

3.3. Environmental Fate and Transport.................................................................................... 13 

3.4. Water Quality.................................................................................................................... 17 

4. Receptors.................................................................................................................................. 17 

4.1. Effects to Aquatic Organisms ........................................................................................... 18 

4.2. Effects to Terrestrial Organisms ....................................................................................... 20 

4.3. Incident Databases Review............................................................................................... 23 

4.4. Ecosystems Potentially at Risk ......................................................................................... 24 

5. Assessment Endpoints ............................................................................................................. 25 

6. Conceptual Model.................................................................................................................... 25 

6.1. Risk Hypothesis ................................................................................................................ 26 

6.2. Conceptual Diagram ......................................................................................................... 26 

7. Analysis Plan ........................................................................................................................... 28 

7.1. Stressors of Concern ......................................................................................................... 29 

7.2. Measures of Exposure....................................................................................................... 29 

7.3. Measures of Effect ............................................................................................................ 30 

7.4. Integration of Exposure and Effects ................................................................................. 31 

7.5. Deterministic and Probabilistic Assessment Methods...................................................... 32 

7.6. Endangered Species Assessments..................................................................................... 32 

7.7. Drinking Water Assessment ............................................................................................. 32 

7.8. Preliminary Identification of Data Gaps........................................................................... 33 

7.8.1. Fate............................................................................................................................. 33 

7.8.2. Effects Data................................................................................................................ 35 

8. References................................................................................................................................ 39 

APPENDIX A: Registered Uses and Application Rates for Methomyl...................................... 47 

APPENDIX B. Toxicity Data for Methomyl:.............................................................................. 57 

APPENDIX C. Schematic for Assessing Exposure from Methomyl Scatter Bait Uses.............. 67 

APPENDIX D. Major Environmental Degradates of Methomyl. ............................................... 68 

APPENDIX E: Data Call-In Tables............................................................................................. 70 
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1. Purpose 

The purpose of this problem formulation is to provide an understanding of what is known about 

the environmental fate and ecological effects of methomyl, considering its currently registered 

uses. Methomyl is an N-methylcarbamate insecticide currently registered for use 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 no residential uses for 

methomyl. Some formulations of methomyl are classified as “restricted use” pesticides and can 

only be applied by certified applicators. This document will provide a plan for analyzing data 

relevant to methomyl and for conducting environmental fate, ecological risk, endangered species, 

and drinking water exposure assessments for its registered uses. Additionally, this problem 

formulation is intended to identify data gaps, uncertainties, and potential assumptions used to 

address those uncertainties relative to characterizing the ecological risk associated with the 

registered uses of methomyl. 

2. Problem Formulation 

2.1. Nature of Regulatory Action 

Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), all pesticides distributed 

or sold in the United States generally must be registered by the Environmental Protection 

Agency (EPA). In determining whether a pesticide can be registered in the U.S., the Agency 

evaluates its safety to non-target species based on a wide range of environmental and health 

effects studies. In 1996, FIFRA was amended by the Food Quality Protection Act, and the 

Agency was mandated to implement a new program for the periodic review of pesticides, i.e., 

registration review (http://www.epa.gov/oppsrrd1/registration_review/). The Registration 

Review program is intended to ensure that, as the ability to assess risk evolves and as policies 

and practices change, all registered pesticides continue to meet the statutory standard of no 

unreasonable adverse effects to human health and the environment. Changes in science, public 

policy, and pesticide use practices will occur over time. Through the new Registration Review 

program, the Agency periodically reevaluates pesticides to make sure that as change occurs, 

products in the marketplace can be used safely. 

As part of the implementation of the new Registration Review program pursuant to Section 3(g) 

of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the Agency is beginning its 

evaluation of methomyl to determine whether it continues to meet the FIFRA standard for 

registration. This problem formulation for the environmental fate, ecological risk, endangered 

species, and drinking water assessment chapter in support of the registration review will be 

posted in the initial docket which will open the public phase of the review process. 

2.2. Previous Assessments 

2.2.1. Ecological Risk Assessments 

Several ecological risk assessments for methomyl have been completed since it was first 

registered in 1968. The most encompassing assessment was for the Reregistration Eligibility 
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Decision (RED) process and was completed in 1998 (USEPA 1998b). The current risk 

assessment builds upon the 1998 risk assessment, which determined that acute and chronic risk 

quotients (RQ) exceeded risk levels of concern (LOC) for endangered/threatened birds (and, 

thus, reptiles and terrestrial-phase amphibians), mammals, and aquatic vertebrates (and, thus, 

aquatic-phase amphibians) and invertebrates. 

The Agency consulted with the U.S. Fish and Wildlife Service in 1989 regarding methomyl 

impacts on some endangered species (USFWS 1989). As a result, the U.S. Fish and Wildlife 

Service issued a formal Biological Opinion that identified reasonable and prudent measures and 

alternatives to mitigate effects of methomyl use on endangered species. 

Subsequent to the RED, the registrant submitted several studies including, but not limited to, two 

predatory mite studies (MRID 451255-01, 451255-02); two aphid studies (MRID 451333-01, 

451333-02); two earthworm studies (MRID 454592-01, 449693-01); and an acute oral and 

contact honey bee study (MRID 450930-01). These studies have been reviewed and will be 

incorporated into the risk assessment. The assessment will also build on the previous RED by 

incorporating open literature (from the ECOTOX search engine) and assessing indirect effects, 

including those effects caused by the potential loss of food items (e.g., terrestrial and aquatic 

invertebrates). 

On April 1, 2003, the Agency initiated formal consultation with the National Marine Fisheries 

Service relative to an effects determination regarding methomyl’s potential effects to 26 

Environmentally Significant Units (ESUs) of Pacific salmon and steelhead. That assessment 

determined that use of methomyl would have no effect (NE) on two ESU’s based on lack of use 

in proximity to waters supporting these two ESUs and that methomyl was Likely to Adversely 

Affect (LAA) 24 ESUs both directly and indirectly based on effects to the aquatic invertebrate 

prey base. In response to the Agency's effects determination and consultation, NMFS issued a 

Biological Opinion (BO) in 2009 (NMFS, 2009). In the BO NMFS concluded that the use of 

methomyl is likely to jeopardize the continued existence of 18 salmonid ESUs and destroy or 

adversely modify designated critical habitat for 16 species. To achieve the protections sought 

under the reasonable and prudent alternatives proposed by NMFS, the agency plans to implement 

several measures that would be accomplished by changes to pesticide labeling. These include 

buffers (that will vary depending on application rate, spray droplet size, and water body size), 

wind speed restrictions (applications will not be permitted when winds are >10 mph immediately 

prior to application); and soil moisture restrictions (the pesticide may not be applied when soil 

moisture is at field capacity or when a storm event that could cause runoff is forecast to occur 

within 48 hours following application). Additionally, the Agency will require that incidents of 

fish mortality which occur within four days of application and in the vicinity of a methomyl 

application in the Pacific Northwest be reported to the pesticide registrant who is then required to 

submit the information to the Agency [under 6(a)(2)] (USEPA, 2010). 

On July 20, 2007, the Agency submitted a risk assessment and effects determination to the 

United States Fish and Wildlife Service for the California red-legged frog (Rana aurora 

draytonii) (CRLF) (and its designated critical habitat) relative to the use of methomyl in 

California. A LAA effects determination was made based on the potential for direct effects to 

both aquatic- and terrestrial-phase CRLF and the potential for indirect effects to prey taxa (for 
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both aquatic- and terrestrial-phase CRLF). Additionally, a ‘habitat modification’ effects 

determination was made for CRLF designated critical habitat based on the potential for effects to 

prey items for both aquatic- and terrestrial-phase CRLF. 

2.2.2. Drinking Water Exposure Assessments 

Drinking water exposure assessments conducted for methomyl and thiodicarb (which degrades 

into two methomyl molecules; USEPA 1997a and 1997b; DP barcodes not reported) were 

conducted in May, 1997 in support of the 1998 RED. The respective 1-in-10-year peak 

estimated drinking water concentrations (EDWC) of methomyl in surface water for the 

maximum use patterns of methomyl or thiodicarb were 99 μg/L or 151 μg/L. Non-targeted 

monitoring data indicated that methomyl was detected in ground water at concentrations up to 20 

μg/L (the highest value was detected in drinking water in Suffolk County, New York) and in 

surface water at concentrations up to 1.9 μg/L (the highest value was detected in South Florida). 

In 2007, the Agency conducted a surface water drinking water exposure assessment for 

thiodicarb and methomyl in which thiodicarb was assumed to rapidly degrade to methomyl. 

While exposure was estimated for applications of thiodicarb and/or methomyl, estimated 

concentrations represented methomyl only (USEPA 2007a; DP 339492). Monitoring data were 

not assessed. Resulting 1-in-10-year peak EDWCs for the maximum use patterns were 99 μg/L 

from use of methomyl, 86 μg/L from use of thiodicarb, and 69 μg/L from separate applications 

of both compounds on the same crop. 

Most recently, a surface water drinking water exposure assessment for use on lettuce alone was 

conducted in 2009 (USEPA 2009; DP 365917). The resulting 1-in-10-year peak EDWC for the 

maximum use pattern was 220 μg/L. Assessment of the remaining labeled uses of methomyl is 

expected to be completed in 2010. 

A cumulative human health risk assessment (CRA) for the N-methylcarbamate (NMC) class of 

pesticides was completed in 2007 (USEPA 2007b). The NMC CRA concluded that there is a 

reasonable certainty that no harm to human health will result from cumulative exposure to the 

NMC pesticides, including methomyl and thiodicarb, presuming the risk mitigations proposed in 

the individual chemical REDs are implemented. 
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3. Stressor Source and Distribution

Methomyl is registered for use on a wide variety of sites including field, vegetable, and orchard 

crops; turf (sod farms only); livestock quarters; commercial premises; and refuse containers. As 

in previous ecological assessments conducted by the Agency for methomyl, methomyl resulting 

from the degradation of thiodicarb will not be considered in the ecological risk assessment 

conducted as part of the Registration Review process. However, the potential simultaneous use 

of methomyl within the same areas as thiodicarb will be considered. Modeled exposure 

estimates resulting from methomyl use (and potentially any thiodicarb use in the vicinity) will 

reflect the predicted environmental fate of the parent alone since there are no degradates of 

toxicological concern for methomyl. 

3.1. Mechanism of Action 

Methomyl is an N-methylcarbamate insecticide. Carbamate insecticides act by inhibiting 

acetylcholinesterase, thereby reducing the degradation of the cholinergic neurotransmitter 

acetylcholine. As a result, intersynaptic concentrations of acetylcholine increase as the 

neurotransmitter accumulates leading to increased firing of the postsynaptic neurons. This may 

ultimately lead to convulsions, paralysis, and death of an organism exposed to the chemical. 

3.2. Overview of Pesticide Use and Usage 

Methomyl was first registered in the United States in 1968. Methomyl is currently registered for 

use on a wide variety of sites including field, vegetable, and orchard crops; turf (sod farms only); 

livestock quarters; commercial premises; and refuse containers (see Table 3.1). Seven end-use 

products containing methomyl are currently registered for use in the United States (see Table 

3.2). Three of the end-use products are for agricultural use and are labelled ‘restricted use’ 

(Methomyl 5G Granules, Lannate® LV and Lannate® SP), indicating that only certified pesticide 

applicators are legally allowed to apply the product. The other four end-use products are for 

scatter bait/bait station uses and are not labelled ‘restricted use’. Low volume aerial applications 

(a minimum of 1 gallon of tank mixture/acre) are allowed for a variety of non-orchard 

agricultural uses (see APPENDIX A). For the purposes of this assessment ‘agricultural uses’ 

refer to all field and vegetable crops and sod farms. Orchard uses are analyzed separately from 

other agricultural uses because of their different use patterns. 
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TABLE 3.1. Summary of the Methomyl Uses Considered in Registration Review. 

USE 

CATEGORY

USES

Agricultural Alfalfa, anise, asparagus, barley, beans (succulent and dry), beets, Bermuda grass 

(pasture), blueberries, broccoli, broccoli raab, Brussels sprouts, cabbage, carrot, 

cauliflower, celery, chicory, Chinese broccoli, Chinese cabbage, collards (fresh 

market), corn, corn (sweet), corn (field and popcorn), corn (seed), cotton, cucumber, 

eggplant, endive, garlic, horseradish, leafy green vegetables, lentils, lettuce (head and 

leaf), lupine, melons, mint, nonbearing nursery stock (field grown), oats, onions (dry 

and green), peanuts, peas, peppers, potato, pumpkin, radishes, rye, sorghum, 

soybeans, spinach, sugar beet, summer squash, sweet potato, tobacco, tomatillo, 

tomato, turf (sod farms only), wheat 

Orchard Apple, avocado, grapefruit, lemon, nectarines, oranges, peaches, pears (northeastern 

U.S. only), pecans (southeastern U.S. only), pomegranates, tangelo, tangerine 

Non-Agricultural Bakeries, beverage plants, broiler houses, canneries, commercial dumpsters which are 

enclosed, commercial use sites (unspecified), commissaries, dairies, dumpsters, fast 

food establishments, feedlots, food processing establishments, hog houses, kennel, 

livestock barns, meat processing establishments, poultry houses, poultry processing 

establishments, restaurants, supermarkets, stables, warehouses 
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Table 3.2. Currently Registered Methomyl End-Use Products. 

FORMULATION EPA REG. 

NO. 

% ACTIVE METHODS OF 

APPLICATION 

USE RESTRICTIONS 

LANNATE® SP 

(There are 15 

SLNs) 

352-342 90% by 

weight 

Ground 

Aerial 

- Do not apply through any type of irrigation 

system 

- Do not apply by ground equipment within 25 ft, 

or by air within 100 feet of lakes, reservoirs, 

rivers, estuaries, commercial fish ponds, and 

natural, permanent streams, marshes, or ponds 

(increase buffer to 450 ft with ultra low volume 

application). 

- Use only in commercial and farm plantings (not 

for home plantings or for U-Pick operations). 

- Use of hand held application equipment is 

prohibited. 

LANNATE® LV 

(There are 3 SLNs) 

352-384 29% by 

weight (2.4 

lbs a.i./gallon)

Ground 

Aerial 

Chemigation 

- Overhead sprinkler chemigation is allowed for 

alfalfa, barley, succulent and dried beans, oats, 

onion, succulent peas, potatoes, rye, sweet corn 

(not in CA), sugar beets, and wheat. Drip 

chemigation is allowed for onions. Refer to 

supplemental label, Special Local Need (SLN) 

label, or crop specific sections of this label for 

direction for chemigation. Do not apply this 

product through any other type of irrigation 

systems, except those allowed by instructions 

provided in supplemental, SLN or this product 

label. 

- Do not apply by ground equipment within 25 ft, 

or by air within 100 feet of lakes, reservoirs, 

rivers, estuaries, commercial fish ponds, and 

natural, permanent streams, marshes, or ponds 

(increase buffer to 450 ft with ultra low volume 

application). 

- Use only in commercial and farm plantings (not 

for home plantings or for U-Pick operations). 

- Use of hand held application equipment is 

prohibited. 

FARNAM DIE 

FLYTM

270-255 1% Scatter bait 

Bait station 

STIMUKIL® FLY 

BAIT 

53871-3 1% Scatter bait 

Bait station 

Brush on paste 

LURECTRON®

SCATTERBAIT 

7319-6 1% Scatter bait 

Bait station 

Paste 

GOLDEN 

MALRIN® RF-128 

FLY KILLER 

2724-274 1.1% Scatter bait 

Bait station 

- Not to be used inside or around homes, or any 

other place where children or pets are likely to be 

present. 

- Place scatterbait in areas inaccessible to 

livestock. Keep children and pets out of treated 

areas. Do not place scatterbait around commercial 

dumpsters that are not enclosed. 

- Bait stations should be at least 4’ above ground 

and in areas not accessible to children, pets, and 

livestock. 

- Brush paste on outside of structures so that it is 

inaccessible to children, pets, and livestock. 

METHOMYL 5G 

GRANULES 

(granular) 

57242-2 5% Ground, banded 

application 

- Do not apply within 25 ft of lakes, reservoirs, 

rivers, estuaries, commercial fishponds, and 

natural, permanent streams, marshes or natural, 

permanent ponds. 

- Not for use in home plantings or U-Pick 

operations. 
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For agricultural and orchard uses, the maximum single application rate allowed on the labels is 

0.9 pounds of active ingredient per acre (lbs a.i./A), which is the most common single maximum 

application rate for all agricultural uses (see Table 3.3 for a summary and APPENDIX A for a 

complete list of registered uses and application rates). 

Table 3.3. Application Rates and Intervals for Methomyl Uses. 

USES MAXIMUM 

SINGLE 

APPLICATION 

RATE (lbs ai/A) 

# 

APPLICATIONS/ 

CROP 

MINIMUM 

APPLICATION 

INTERVAL 

Alfalfa, lupine 0.9 5 5 

Avocado 0.9 1 5 

Grapefruit, lemon, oranges, tangerines, tangelo 0.9 3 5 

Broccoli, Chinese broccoli, broccoli raab, cabbage, Chinese 

cabbage, cauliflower, horseradish, leafy green vegetables 

0.9 8 2 

Corn (field and popcorn), corn (seed), corn (sweet), corn 0.45 14 1 

Cotton 0.675 2 3 

Apples, nectarines, peaches, pomegranates 0.9 6 5 

Garlic 0.45 6 5 

Brussels sprouts, chicory, endive, escarole, lettuce (head), 

lettuce (leaf), spinach 

0.9 8 2 

Cucumber, eggplant, melons, pumpkin, summer squash 0.9 6 5 

Nonbearing fruit, grape, and nut nursery stock 0.9 5 5 

Onions (green), onions (bulb), radishes 0.9 6 5 

Potato, sweet potato 0.9 5 5 

Bermuda grass (pasture) 0.9 1 5 

Anise, asparagus, beans (succulent), beans (interplanted with 

nonbearing almonds, plums, prunes, peaches and walnuts), 

beets (table), carrots, celery, lentils, peas (succulent), peppers, 

soybeans, soybeans (interplanted with nonbearing almonds, 

plums, prunes, peaches and walnuts) 

0.9 8 5 

Sugar beet 0.9 5 5 

Tomato, tomatillo 0.9 7 5 

Sod farms 0.9 4 5 

Barley, oats, rye, sorghum, wheat 0.45 4 5 

Blueberries 0.9 4 5 

Mint 0.9 2 5 

Scatter bait 0.22 263 5 
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Maximum seasonal labeled application rates (indicated on the label as maximum application 

rates per crop) for agricultural uses range from 0.9 lbs a.i./A/crop [i.e., Bermuda grass (pasture), 

avocado, lentils, beans (interplanted with trees), sorghum, and soybeans (interplanted with trees)] 

to 7.2 lbs a.i./acre/crop [i.e., cabbage, lettuce (head), cauliflower, broccoli raab, celery, and 

Chinese cabbage]. 

Several methomyl crops can be grown more than one time per year in the United States (i.e., they 

have multiple crop cycles). Therefore, for those methomyl uses that have more than one crop 

cycle per year, the maximum allowable yearly application rate will be higher than the maximum 

seasonal application rate. For perennial crops (e.g., alfalfa), the number of cuttings per year may 

be considered the number of crop cycles per year. The maximum number of times a crop can be 

grown in California will be used to represent other areas of the United States where multiple 

croppings can occur (e.g., Texas and Florida). Considering the labeled application rates and 

information from the Agency’s Office of Pesticide Programs’ Biological and Economic Analysis 

Division (BEAD) on the number of times each crop for which methomyl is registered for use can 

be grown in California (USEPA, 2007), the maximum annual application rates for methomyl are 

32.4 lbs a.i./acre/year (alfalfa) and 21.6 lbs a.i./acre/year (broccoli raab, cabbage, and Chinese 

cabbage) for agricultural crops; 5.4 lbs a.i./acre/year (peaches) for orchards; and 0.22 lbs 

a.i./acre/application for non-agricultural uses (no maximum application/acre/year is provided on 

the non-agricultural use labels). Maximum annual application rates for other areas of the United 

States will differ to the degree that the number of crops per year in these areas differs from that 

in California. Additional information that identifies the number of crops (for which methomyl is 

registered) per year that can be grown in areas outside of California would help reduce the 

uncertainty associated with estimating maximum yearly application rates at a national-level in 

the risk assessment conducted for Registration Review. 

All orchard and most agricultural uses involve foliar application. The only granular 

agricultural/orchard use is for corn (which also has a foliar use). Since the maximum seasonal 

application rate for methomyl use on corn is the same for the foliar and granular formulations 

and no spray drift is expected for granular use, the granular use is expected to yield equal or 

lower EECs when compared to the foliar use. Therefore, we will only evaluate foliar 

applications for corn in this assessment. 

All non-agricultural and non-orchard outdoor uses for methomyl are limited to scatter baits and 

bait stations around agricultural (e.g., animal premises) and commercial structures and 

commercial dumpsters, where children or animals are not likely to contact the pesticide. The 

scatter bait can also be mixed with water to form a paste which can be brushed onto walls, 

window sills, and support beams. Since the bait station use involves placing the pesticide within 

the bait station and hanging the bait station at least four feet off the ground (as stipulated on the 

labels), no spray drift or runoff is expected from this use. 

For scatter bait uses that do not involve bait stations, no off-site exposure via spray drift is 

expected from the scatter bait uses since they are granular (or a paste). However, there is 

potential for off-site exposure via runoff from scatter bait uses. The maximum application rate 

for the scatter bait use is 0.22 lbs a.i./A (0.0025 lbs a.i./500 ft2

). It is unlikely that applications 

would involve a full acre, however, since the outside use of the scatter bait is limited to areas 
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around structures and dumpsters. No minimum application interval or maximum application rate 

per year is provided on the scatter bait labels. Because there is potential exposure to the 

environment, the scatter bait uses that do not involve bait stations will be assessed in the risk 

assessment conducted for Registration Review. 

According to the United States Geological Survey’s national pesticide usage data (based on 

information from 1999 to 2004), an average of 576,926 lbs of methomyl per year are applied 

nationally to agriculture in the United States (see Figure 3.1). Based on these data, 

approximately 21% of the average pounds of methomyl used per year is applied to sweet corn, 

approximately 13% is applied to lettuce, and from 3% to 6% is applied to dry onions, peanuts, 

alfalfa hay, tomatoes, green beans, cucumbers and pickles, strawberries, and cotton. Based on a 

Screening Level Usage Analysis conducted by the Agency (USEPA 2009a), using data from 

2001 to 2007, there is an estimated 800,000 pounds of methomyl used per year [most of which is 

used on sweet corn (200,000 lbs), lettuce (100,000 lbs), onions (70,000 lbs) and tomatoes 

(50,000 lbs)]. 

FIGURE 3.1. Estimated, Annual, National, Agricultural Methomyl Usage (USGS 2010).

[The pesticide use maps available from this site show the average annual pesticide use intensity expressed as 

average weight (in pounds) of a pesticide applied to each square mile of agricultural land in a county. The area of 

each map is based on state-level estimates of pesticide use rates for individual crops that were compiled by the 

CropLife Foundation, Crop Protection Research Institute based on information collected during 1999 through 2004 
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and on 2002 Census of Agriculture county crop acreage. The maps do not represent a specific year, but rather show 

typical use patterns over the five year period 1999 through 2004.].

3.3. Environmental Fate and Transport 

Methomyl (S-methyl-N-(methylcarbamoyl)oxy)thioacetimadate; CAS No. 16752-77-5; PC code 

090301) is a registered pesticide as well as the primary degradate of another registered pesticide, 

thiodicarb. The dominant routes of dissipation of methomyl are metabolism, leaching, and 

runoff. Environmental fate and transport properties of methomyl are summarized in Table 3.4. 

Because of its low affinity for adsorption (KOC of 46 L/kgOC), methomyl is likely to dissipate 

rapidly through washoff from plant surfaces and through leaching and runoff from soil surfaces. 

Methomyl has fate characteristics, which are moderate persistence, high water solubility, and 

low sorption coefficient, that suggest transport to waters resources is likely. Methomyl’s 

persistence in water bodies is uncertain; however, the compound undergoes substantial 

hydrolysis only in alkaline water approximately pH 9 or above. 

TABLE 3.4. Summary of Environmental Fate and Transport Properties of Methomyl. 

Parameter Value Source 

Physical/Chemical Parameters

Molecular weight 162.2 g/mol (calculated) 

Solubility in water (25°C) 5.5 x 104 mg/L MRID 41402101 

Vapor pressure (25°C) 5.4 x 10-6 torr MRID 41209701 

Henry’s law constant 2.1 x 10-11 atm-m3/mol (calculated) 

KOW 1.31 MRID 00157991 

Persistence in Water

pH 2.09-7.11: >413 d pH 8.88: 14.6 d 

pH 7.40: 337 d pH 8.89: 16.1 d 

pH 7.67: 206 d pH 9.45: 4.77 d 

pH 7.92: 123 d pH 9.92: 1.66 d 

pH 8.42: 40.8 d 

Strathmann and Stone, 

2002 (values calculated 

from rate constants) 

Hydrolysis half-life (25°C) 

pH 5: no evidence of degradation 

pH 7: no evidence of degradation 

pH 9: 36 d 

MRID 00131249 

Aqueous photolysis half-life 50 d (natural water) 

4.9 d – stable (pH 7 buffer w/ 0-1000 M 

excess nitrate) 

MRID 43823305 B

Persistence in Soil

Aerobic soil metabolism half-life Flanagan silt loam: 44 d (109 d) MRID 00008568 

of parent (of total residues A) Madera, CA loam: 12 d (25 d) MRID 43217901 

Anaerobic soil metabolism halflife (of total residues A) 

Madera, CA loam: 14 d (47 d) MRID 43217902 

Soil photolysis half-life 33 d MRID 00163745 

Mobility 

Organic carbon-normalized 

adsorption coefficient (KOC) 

46 ± 13 L/kgOC (n=4) MRID 00161884 
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Parameter Value Source 

Field Dissipation 

Terrestrial field dissipation halflife (from surface) 54 d (CA sandy loam cropped to cabbage); 

leached to deepest sample depth (60-90 cm) 

4-6 d (MS loam cropped to cabbage); leached 

to 15-30 cm sample depth 

MRID 41623901/ 

41623902 

MRID 42288001/ 

43217903 

0.5 d (mint) Kiigemagi and Deinzer, 

1979 

Foliar degradation half-life 

2.5 d (Bermuda grass) Sheets et al., 1982 A Total residues include the parent compound and unextracted residues. 

B

 These data are provisional, as the study is under review. 

Laboratory studies indicate that methomyl is moderately persistent and mobile. There is no 

significant degradation by hydrolysis at lower pHs (neutral to acidic), and methomyl degrades at 

a moderate rate (with a half-life of 16 or 36 d) at pH 9 based on two studies. Methomyl degrades 

in clear water by indirect photolysis (i.e., oxidation from exposure to photoproducts of dissolved 

nutrients) that is moderate to rapid (half-life range of 5-50 d), depending on the nature of the 

dissolved oxidants. Biodegradation is moderate in soil and uncertain in water. In the presence of 

ferrous iron, methomyl is unstable. Field studies show varying dissipation rates of the chemical 

in soils. Dissipation rates were related primarily to differences in soil moisture content, which 

may have affected the microbial activity, and water inputs (i.e., rainfall and irrigation), which 

could have influenced leaching. 

Chemical and Metabolic Degradation. A guideline hydrolysis study (MRID 00131249) 

conducted for 30 days did not show evidence of degradation by hydrolysis at pH 5 and 7 and 

only slow degradation in pH 9 buffered solutions with a half-life of 36 days. Open literature data 

(Strathmann and Stone, 2002) confirm that methomyl does not substantially degrade by 

hydrolysis at pH 5 and 7. However, hydrolysis was observed at pH 8.9 with a half-life of 16 

days. The major hydrolysis degradate in the guideline study was methomyl oxime with up to 

44% of the applied after 30 days (degradate names, structures, and reported amounts are in 

Table D.1 of Appendix D). 

Methomyl degrades by indirect photolysis in water (i.e., oxidation from exposure to oxidant 

photoproducts of dissolved nutrients) at a variable rate depending on the nature of the dissolved 

oxidants, according to a study in review (half-lives of 4.9 to 50 d; degradates weren’t identified; 

MRID 43823305). There was no measureable degradation in the dark controls or in an irradiated 

system buffered at pH 7. In separate studies with poor material balances, the major degradates 

were acetonitrile, found at 55-68% of the applied radioactivity 2-15 days after treatment (MRID 

6161885), or methomyl oxime, found at up to 32% of the applied 14 days after treatment, and 

carbon dioxide, found at 56% of the applied at study termination, 56 days after treatment (MRID 

22439). Methomyl degraded moderately by photolysis on soil (half-life of 33 d; MRID 163745). 

Acetonitrile was the major photolysis degradate on soil, with a peak concentration of 40% of the 

applied at study termination, 30 days after treatment. 

In two aerobic soil metabolism studies, methomyl degraded with half-lives of 44 days in a 

Flanagan silt loam and 12 days in a loam soil from Madera, California (MRID 8568, 43217901). 

The major degradate was 14CO2 (23% of the applied after 45 days in the silt loam soil, and 75% 
-15 of 75-

of the applied at 3 months in the loam soil). Unextractable residues peaked at 26% of the applied 

after 45 days in the silt loam soil and 25% of the applied in the loam soil. Half-lives for soil 

metabolism that treat the unextracted, unidentified material as if it were parent (total residues 

method) are 109 and 25 days for the Flanagan and Madera soils, respectively. Methomyl oxime 

was a minor degradate accounting for 3% of the applied. 

Under anaerobic conditions, methomyl degraded in loam soil with a half-life of 14 days in static 

conditions (nitrogen atmosphere) and 13 days in dynamic conditions (flowing nitrogen 

atmosphere) following 14 days of aerobic incubation (MRID 43217902). In the dynamic system, 

the major degradate was 14CO2, which comprised 30% of the applied during the 14 days of 

aerobic incubation, and an additional 23% after 60 days of anaerobic incubation. Unextracted 

residues peaked at 36% of the applied after 7 days of anaerobic incubation. More rapid 

degradation under anaerobic conditions may be catalyzed by the presence of dissolved (ferrous) 

iron (MRID 43708806; Smelt et al., 1983; Bromilow et al., 1986). The proposed chemical 

reaction is: 

 Fe2+

CH3-C=N-O-C=O ------------> CH3CN 

 | | 

 S-CH3 NH-CH3

In a supplemental aerobic aquatic metabolism study (MRID 43325401) with two water-sediment 

systems from Great Britain, methomyl degraded with half-lives of 4.0 and 4.6 days in an 

Auchingilsie clay loam and Hinchingbrooke silty clay loam, respectively. However, results from 

these systems were uncertain due to low material balances from 14 to 102 days after treatment. 

Initial pH was 6.8 for the Auchingilsie system and 7.6 for Hinchingbrooke. As is typical for 

these experiments with water-sediment systems, they had mixed redox potentials and were 

neither completely aerobic nor anaerobic. Unextracted and unidentified residues in the sediment 

were a significant component of the radioactive residues in these experiments with up 16% in the 

Auchingilsie system and 20% in the Hinchingbrooke system. The unextracted residues were 

decreasing with time at the end of the experiment in both systems indicating that these residues 

were still available. Half-lives estimated by combining the methomyl parent with the 

unextracted residues (total toxic residues method) were 6.3 days for Auchingilsie and 7.4 days 

for Hinchingbrooke. Methomyl oxime was a maximum of 13% of the applied at 2 days and did 

not persist. Acetonitrile was a maximum of 21% of the applied at 7 days in solution, and a 

maximum of 27% of the applied at 60-102 days in the volatile traps. Acetamide and carbonate 

accounted for up to 14% of the applied (at day 7) and 15% of the applied (at day 14), 

respectively. 14CO2 comprised 46% of the applied by study termination (day 102). 

The only non-volatile degradate found in the laboratory studies was methomyl oxime. It was 

present at high concentrations in the alkaline hydrolysis study, one photolysis study, and the 

aerobic aquatic metabolism study, but was only a minor degradate in the soil metabolism studies 

(3% of the applied at all test intervals). 

Several studies showed that dissipation of methomyl is rapid on foliage (Willis and McDowell, 

1987). Of the ten studies for methomyl identified in this review of foliar dissipation, three 
-16 of 75-

measured total residues on the leaves rather than dislodgeable residues. One of these three 

studies had significant rainfall during the study. The remaining two remaining studies, one on 

mint and the other on Bermuda grass, had half-lives of 0.5 and 2.5 days, respectively. Because 

these studies only had rainfall after the pesticide is mostly dissipated and volatilization is likely 

to be very small for methomyl (see next section), the dominant route of foliar dissipation is likely 

aerobic metabolism on the leaf surface. 

Mobility. Methomyl is mobile in soils as demonstrated by soil thin-layer chromatography (TLC; 

Rf values 0.64-0.79; MRID 44306). A batch equilibrium study shows that methomyl has a low 

affinity to bind to soil (see Table 3.5), further indicating that the chemical will be mobile (MRID 

161884). Methomyl binding (which is low) is significantly correlated with soil organic carbon 

content, with a mean KOC of 46 ± 13 L/kgOC. 

TABLE 3.5. Summary of Soil Batch Equilibrium Parameters for Methomyl. A

Soil Fraction of 

Organic Carbon Mean Kd KOC KF 1/n KFOC

Cecil sandy loam 0.012 0.79 65 0.73 0.85 61 

Flanagan silt Loam 0.025 1.1 45 1.0 0.87 41 

Keyport silt loam 0.043 1.6 36 1.4 0.86 32 

Woodstown sandy loam 0.006 0.24 39 0.23 0.88 37 

A Kd is the soil-water partition coefficient. KOC is the organic carbon-normalized partition coefficient based on 

mean Kd’s. KF is the Freundlich coefficient. 1/n is the Freundlich exponent. KFOC is similar to KOC except based on 

Freundlich coefficients 

Methomyl is a highly soluble chemical in water (5.5 x 104 mg/L; MRID 41402101). Its vapor 

pressure (5.4 x 10-6 torr) and Henry’s Law Constant (2.1 x 10-11 atm-m3/mol) indicate that it has 

a low potential to volatilize (MRID 41209701). 

Bioaccumulation. The low octanol/water partition coefficient of 1.31 ± 0.02 (mean ± std. error; 

MRID 157991) suggests that the chemical will have a low tendency to accumulate in aquatic 

biota. 

Field Dissipation. Two guideline terrestrial field dissipation studies are available for methomyl 

(MRID 41623901/41623902, 42288001/43217903). Dissipation half-lives from the surface soil 

of cropped cabbage fields ranged from 4-6 days in Mississippi to 54 days in California. Two 

factors may explain the differences in dissipation between the two sites. Soil moisture content, 

which may affect the level of biological activity, varied between the two sites (moisture contents 

ranged from 2.5% to 17% in the California soils and averaged 16% over the first 15 days in the 

Mississippi soils). The Mississippi site received more rainfall, which may have led to more 

leaching out of the surface. In both studies most of the methomyl residues were found in the 

upper 30 cm of soil. 

Prospective Ground Water Study. A small-scale prospective ground-water monitoring study was 

conducted for methomyl (MRID 43568301). Lannate L, a formulated product of methomyl, was 

applied in August 1992 to a site cropped in sweet corn in Cook County, Georgia. Monitoring 

continued until October 1994 when the study was terminated. The study was conducted by DuPont 

in a highly vulnerable, high use area of Georgia. Methomyl was applied to the crop at 0.45 lbs 
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a.i./A 25 times over 63 days for a total of 11.25 lbs a.i./A. Although this rate represents 1.5x the 

maximum label rate per crop of sweet corn, the study was conducted to support a potential increase 

in the maximum label rate. Ground water was monitored monthly for a period of 27 months. 

Methomyl was not detected in ground water when detections occurred in 12-foot depth suction 

lysimeters at concentrations up to 0.943 μg/L. Out of the 156 samples taken from six downgradient wells in this study, only six samples from five wells contained methomyl residues. 

Concentrations ranged from 0.110 to 0.428 μg/L, using a detection limit of 0.1 μg/L, at 62 and 117 

days after the initial treatment (DAIT). Sampling continued for 789 (DAIT), but no detections were 

seen after 117 DAIT. 

3.4. Water Quality 

Thiodicarb and methomyl are not identified as causes for any water bodies listed as impaired 

under section 303(d) of the Clean Water Act (based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=88

5, accessed April 22, 2010). In addition, no Total Maximum Daily Loads (TMDL) have been 

developed for thiodicarb or methomyl (based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id

=885&p_pollutant_group_name=PESTICIDES, accessed April 22, 2010). More information on 

impaired water bodies and TMDLs can be found at http://www.epa.gov/owow/tmdl/. The 

Agency invites submission of water quality data for these pesticides. To the extent possible, data 

should conform to the quality standards in Appendix A of the OPP Standard Operating 

Procedure: Inclusion of Impaired Water Body and Other Water Quality Data in OPP’s 

Registration Review Risk Assessment and Management Process (see: 

http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf), in order to ensure 

they can be used quantitatively or qualitatively in pesticide risk assessments. 

4. Receptors 

Consistent with the process described in the Overview Document (USEPA 2004), the risk 

assessment for methomyl relies on a surrogate species approach. Toxicological data generated 

from surrogate test species, which are intended to be representative of broad taxonomic groups, 

are used to extrapolate the potential effects on a variety of species (receptors) included under 

these taxonomic groupings. 

Acute and chronic toxicity data from studies submitted by pesticide registrants along with the 

available open literature are used to evaluate the potential direct and indirect effects of methomyl 

to aquatic and terrestrial receptors. This includes toxicity on the technical grade active 

ingredient, degradates, and when available, formulated products (e.g., “Six-Pack” studies). The 

open literature studies are identified through EPA’s ECOTOXicology (ECOTOX) database, 

which employs a literature search engine for locating chemical toxicity data for aquatic life, 

terrestrial plants, and wildlife. The evaluation of both sources of data may also provide insight 

into the direct and indirect effects of methomyl on biotic communities from loss of species that 

are sensitive to the chemical and from changes in structure and functional characteristics of the 

affected communities. Open literature data from an ECOTOX run conducted on 3/17/07 for 

methomyl have been fully reviewed as part of this Problem Formulation. Information from an 
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up-dated ECOTOX run for methomyl will be evaluated for possible quantitative and/or 

qualitative inclusion in the risk assessment in support of Registration Review. 

A summary of the most sensitive data representing non-target organisms exposed to methomyl in 

aquatic and terrestrial habitats is provided in Section 4.1. A summary of ecological incidents 

associated with methomyl and a description of ecosystems potentially at risk are provided in 

Section 4.2. 

4.1. Effects to Aquatic Organisms 

Based on the available data, methomyl is characterized as very highly toxic to freshwater fish 

and invertebrates (freshwater and estuarine/marine) and moderately toxic to estuarine/marine fish 

on an acute exposure basis (see Table 4.1). A summary of all available ecotoxicity data for 

methomyl is provided in Appendix B. No aquatic plant data are currently available for 

methomyl.

Regarding chronic exposure, toxicity data for methomyl are available for freshwater fish, 

estuarine/marine fish, freshwater invertebrates, and estuarine/marine invertebrates. No toxicity 

data from chronic exposure to methomyl are available for the most acutely sensitive freshwater 

fish species, the channel catfish (Ictalurus punctatus) (LC50 = 0.320 mg a.i./L). Therefore, an 

acute-to-chronic ratio (ACR) is used to calculate a chronic freshwater fish endpoint using acute 

and chronic data from the fathead minnow (for which both acute and chronic toxicity data are 

available). The most sensitive no observed adverse effect concentration (NOAEC) and lowest 

observed adverse effect concentration (LOAEC) for freshwater fish [fathead minnows 

(Pimephales promelas)] are 0.057 and 0.117 mg a.i./L, respectively, based on reduced survival 

(MRID 131255). The ACR for fathead minnow, i.e. ACR = 26.3, results in a NOAEC of 0.012 

mg a.i./L for the channel catfish [(1.5 mg/L)/(0.057 mg/L) = (0.320 mg/L)/(x mg/L)]. 

For estuarine/marine fish, an early life-stage toxicity study (MRID: 450132-02) with sheepshead 

minnows resulted in a NOAEC of 0.26 mg a.i./L, and a LOAEC of 0.49 mg a.i./L, based on both 

reduction in total length and wet weight. Fish with deformed bodies and lethargy/erratic 

swimming were noted at 1.0 mg a.i./L. No other sub-lethal effects (other than length and weight 

reductions) were noted at any other time or concentration. 

A 21-day life-cycle toxicity study of Daphnia magna resulted in a NOAEC of 0.0007 mg. a.i./L 

and a LOAEC of 0.001 mg a.i./L based on delayed reproduction (MRID 131254). The NOAEC 

and LOAEC are 0.0016 and 0.0035 mg a.i./L, respectively, based on the number of young 

produced. No other sub-lethal effects were noted at any other concentration. 

For estuarine/marine invertebrates, the most acutely sensitive species tested is the northern pink 

shrimp (Penaeus duorarum) (LC50 = 0.019 mg a.i./L). Since no toxicity data from chronic 

exposure to methomyl are available for the northern pink shrimp, an ACR is used to calculate a 

chronic estuarine/marine endpoint using acute and chronic data from mysid shrimp 

(Americamysis bahia) (for which both acute and chronic data are available). The most sensitive 

no observed adverse effect concentration (NOAEC) and lowest observed adverse effect 

concentration (LOAEC) for mysid shrimp are 0.0291 and 0.0591 mg a.i./L, respectively, based 
-19 of 75-

on reduced number of young per surviving female (MRID 450132-03). The ACR for mysid 

shrimp, i.e. ACR = 8.07, results in a NOAEC of 0.0024 mg a.i./L for the northern pink shrimp 

[(0.234 mg/L)/(0.029 mg/L) = (0.019 mg/L)/(x μg/L)]. 

TABLE 4.1. Summary of the Most Sensitive Endpoints from Submitted Aquatic Toxicity 

Studies for Methomyl. 

Species Taxa Represented Toxicity Value MRID # Classification Comment 

Channel catfish 

(Ictalurus 

punctatus) 

96-hr LC50 = 

0.320 mg a.i./L 

40098001 Supplemental Slope = 4.2 (2.3 – 

6.2) 

Channel catfish 

(Ictalurus 

punctatus) 

Freshwater fish and 

aquatic-phase 

amphibians NOAEC = 0.012 

mg a.i./L N/A N/A 

Based an acute to 

chronic ratio (ACR)1

using acute and 

chronic data from the 

fathead minnow and 

acute data from the 

channel catfish. 

48-hr EC50 = 

0.005 mg a.i./L 

40098001 Supplemental A slope could not be 

Daphnid determined 

(Daphnia 

magna) 

Freshwater 

invertebrates NOAEC = 0.0007 

mg a.i./L 

1312541 Acceptable 

The LOAEC is 0.001 

mg a.i./L based on 

delayed reproduction. 

96-hr LC50 = 1.16 

mg a.i./L Sheepshead 41441202 Acceptable Slope = 8.0 

minnow 

(Cyprinodon 

variegatus) 

Estuarine/marine 

fish NOAEC = 0.260 

mg a.i./L 45013202 Acceptable 

The LOAEC is 0.490 

mg a.i./L based on 

reduced growth 

Eastern oyster 

(Crassostrea 

virginica) 

EC50 >140 mg 

a.i./L 42074601 Acceptable 

Shell deposition 

study; NOAEC = 

0.12 mg a.i./L 

96-hr LC50 = 

0.019 mg a.i./L 00009134 Acceptable A slope could not be determined 

Northern pink 

shrimp 

(Penaeus 

duorarum) 

Estuarine/marine 

invertebrates 

NOAEC = 0.0024 

mg a.i./L N/A N/A 

Based an acute to 

chronic ratio (ACR)2

using acute and 

chronic data from 

mysid and acute data 

from the Northern 

pink shrimp 

Non-vascular aquatic plants No data available N/A N/A N/A 

Vascular aquatic plants No data available N/A N/A N/A 1

 Fathead minnow LC50 (1.5 mg/L) divided by the NOAEC (0.057 mg/L) yields an ACR of 26.3; ACR of 26.3 in 

turn divided into the channel catfish LC50 (0.320 mg/L) yields an estimated chronic NOAEC (0.102 mg/L) for 

channel catfish. 

1

 Mysid shrimp LC50 (0.234 mg/L) divided by the NOAEC (0.029 mg/L) yields an ACR of 8.07; ACR of 8.07 in 

turn divided into the northern pink shrimp LC50 (0.019 mg/L) yields an estimated chronic NOAEC (0.0024 mg/L) 

for northern pink shrimp. 

An outdoor microcosm study (MRID 437444-02) was conducted with the formulated methomyl 

product Lannate L [24% a.i. (methomyl)] to evaluate the fate in tank water and hydrosoil and 

assess the effects on populations of phytoplankton, zooplankton, macroinvertebrates, and bluegill 

sunfish (Lepomis macrochirus). Applications were performed over a period of 22 days (22 daily 
-20 of 75-

applications) to 28 days (4 applications with a 7-day reapplication interval); the total length of 

the study was 35 days. Treatment groups were defined by the amount of test substance added at 

each application (0.48 or 0.048 g a.i.; test vessel volume = 5,900 L; nominal treatment 

concentrations were not provided) and by the interval between test substance applications [1 day 

(total of 22 applications), 3 days (total of 8 applications), or 7 days (total of 4 applications)]. 

Before the start of the study, each of the 56 tanks used in the study was stocked with bluegill 

sunfish and inoculated with aquatic plants and animals (invertebrates) from an untreated, preexisting pond on site, colonized by native invertebrates. 

At the end of the study, phytoplankton showed no apparent methomyl-related effects. 

Zooplankton showed mixed results; the abundance of adult copepods and rotifers generally 

increased following methomyl applications, however, cladoceran abundance was reduced (to less 

than 1% of the abundance of the control group) in the methomyl-treated groups and their 

numbers did not recover during the study period. Bluegill survival was not affected in any of the 

microcosm treatment levels. Body length and body weight at harvest, however, were 

significantly reduced (up to 18.5%) at all methomyl treatment levels when compared with 

controls. The size reductions were attributed to a decrease in food resources, particularly 

cladocerans. 

4.2. Effects to Terrestrial Organisms 

Table 4.2 summarizes the most sensitive terrestrial toxicity endpoints for methomyl based on an 

evaluation of submitted studies. Methomyl is classified as highly toxic to birds, mammals, and 

honey bees on an acute exposure basis. There are currently no methomyl vegetative vigor or 

seedling emergence toxicity data available for terrestrial plants. 

An avian reproduction study was performed on methomyl with the northern bobwhite quail 

(Colinus virginianus). In this study, the LOAEC is 500 mg/kg-diet based on fewer eggs laid and 

eggs set and the NOAEC is 150 mg a.i./kg-diet (MRID: 41898602). In a 2-generation 

reproduction study with rats (Rattus norvegicus), the NOAEL for parental systemic toxicity is 

3.75 mg/kg-bw and the LOAEL is 30 mg/kg-bw based on decreased growth (body weight) and 

food consumption and altered hematology parameters. The NOAEL for offspring toxicity is also 

3.75 mg/kg-bw and the LOAEL is 30 mg/kg-bw based on decreases in both survival (the mean 

number of live pups) and growth (mean body weights of offspring) (MRIDs: 43250701, 

43769401). 
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TABLE 4.2. Summary of the Most Sensitive Endpoints from Submitted Terrestrial 

Toxicity Studies for Methomyl. 

Species Taxa 

Represented 

Toxicity Value MRID # Classification Comment 

LD50 = 24.2 mg/kg-bw 00161886 Acceptable None 

LC50 = 1,100 mg/kgdiet 22923 Acceptable None 

Bobwhite quail 

(Colinus 

virginianus)

Birds, reptiles, 

and terrestrialphase 

amphibians 

NOAEC = 150 mg/kgdiet 41898602 Acceptable LOAEC = 500 mg 

a.i./kg-diet, based 

on reduction in 

number of eggs 

laid/hen

Laboratory rat 

(Rattus norvegicus) 

LD50 = 30 mg a.i./kgbw 

42140101 Acceptable None 

Laboratory rat 

Mammals NOAEL = 75 mg 

a.i./kg-diet (3.75 mg 

a.i./kg/day) 

LOAEL = 600 mg 

a.i./kg-diet (30 mg 

a.i./kg/day) 

43250701, 

43769401 

Acceptable NOAEL based on 

decreases in both 

the mean number 

of live pups and 

mean body weights 

of offspring 

LD50 = 0.28 μg a.i./bee Acute oral; 

NOAEL = 0.09 μg 

a.i./bee Honey bee 

(Apis mellifera) LD50 = 0.16 μg a.i./bee 

45093001 Acceptable 

Acute contact; 

NOAEL = 0.08 μg 

a.i./bee 

Wasp (Aphidius 

rhopalosiphi) 

Terrestrial 

invertebrates 

48-hr LC50 = 0.00022 

lbs a.i./acre 

45133301 Supplemental 

(not adequate 

for RQ 

calculation) 

Scientifically 

sound, but a nonguideline study and 

not adequate for 

RQ calculation (it 

involves a product 

not currently 

registered in the 

U.S.) 

Terrestrial Plants No data available N/A N/A N/A 

There are no acceptable terrestrial plant guideline toxicity studies available for methomyl, 

several efficacy studies that were conducted to test the effects of methomyl on a variety of target 

and non-target invertebrate pests also supplied information on effects to plants after methomyl 

applications. Due to a lack of information on study design and data analyses, these efficacy 

studies are classified as ‘supplemental’ and are not adequate for plant (or terrestrial invertebrate) 

RQ calculation. None of the studies showed any adverse effects to plants at the highest 

treatment levels tested (most of which were at or above the maximum allowable single 

application rate for methomyl of 0.9 lbs a.i./acre) and the NOAEC from the studies represented 
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the highest treatment rates examined (see Table 4.3). However, because none of the studies 

addressed potential risks to monocots, or effects on seedling emergence and some N-methyl 

carbamates are plant auxins and are used to thin fruit (e.g., carbaryl), risks to plants from the use 

of methomyl cannot be precluded using the available data. 

TABLE 4.3. Measures of Effects to Plants from Methomyl Efficacy Studies that Included 

Information on Effects to Plants. 

PLANT SPECIES NOAEL HIGHEST 

LEVEL 

TESTED?1

EFFECT 

MEASURED2

ECOTOX NO./REFERENCE 

Alfalfa 

(Medicago sativa) 

≥0.9 lbs a.i./acre Yes Growth 88088/Laub et al. (1999) 

≥3.6 lbs a.i./acre Yes Growth 

Injury 

Eggplant 74745/Morale and Kurundkar (1989) 

(Solanum melongena) 

≥1,000 ppm Yes Growth 89394/Sharma et al. (1997)

Common Bean 

(Phaseolus vulgaris) 

≥0.9 lbs a.i./acre Yes Injury 88838/Ghidiu (1988) 

≥946 ml/acre Yes Growth 82231/Stansly and Cawley (1993) 

≥0.9 lbs a.i./acre Yes Growth 82730/Schuster (1994) 

Bell pepper 

(Capsicum annuum) 

≥0.9 lbs a.i./acre Yes Biomass 82246/Zehnder and Speese (1992) 

Cabbage 

(Brassica oleracea) 

≥0.9 lbs a.i./acre Yes Injury 88084/Edelson et al. (1999) 

Hybrid strawberry 

(Fragaria x ananassa) 

≥0.9 lbs a.i./acre Yes Photosynthesis 88792/Carson et al. (1986) 

Lettuce 

(Lactuca sativa) 

≥1 lbs a.i./acre Yes Abundance 82237/Palumbo et al. (1991) 

Peony 

(Paeonia lactiflora) 

≥20.0 lbs 

a.i./acre 

Yes Abundance 89251/Schmitt et al. (1974) 

Peach 

(Prunus persica) 

≥0.23 lbs a.i./100 

gallon 

Yes Injury 88091/Hull (1999) 

Pigeonpea 

(Cajanus cajan) 

≥0.53 lbs 

a.i./acre 

Yes Abundance 82560/Giraddi et al. (2002) 

Potato 

(Solanum tuberosum) 

≥1.0 lbs a.i./acre Yes Injury 77263/Raman and Palacios (1986) 

≥0.45 lbs 

a.i./acre 

Yes Injury 74169/Walgenbach et al. (1991) 

≥0.9 lbs a.i./acre Yes Injury 88062/Carson et al. (1999) 

≥0.9 lbs a.i./acre Yes Injury 88089/Kund et al. (1999) 

≥0.9 lbs a.i./acre Yes Injury 88089/Kund et al. (1999) 

≥0.45 lbs 

a.i./acre 

Yes Injury 88269/Stansly et al. (1999) 

Tomato 

(Solanum 

lycopersicum) 

≥4.0 lbs a.i./acre Yes Biomass 89472/McLeod (1972) 

Wild celery 

(Apium graveolens) 

≥0.9 lbs a.i./acre Yes Injury 82728/Carson et al. (1994) 

1 ‘Highest Level Tested’ refers to whether the NOAEL represents the highest level tested. 2 ‘Effect Measured’ refers to the effect that was measured in the study. Because the NOAELs represent the highest 

level tested in each study, no adverse effects to plants were observed in any of the studies. 
-23 of 75-

4.3. Incident Databases Review 

Preliminary reviews of the Ecological Incident Information System (EIIS, version 2.1) and the 

Avian Incident Monitoring System (AIMS)1

 were conducted on February 17, 2010. A total of 

10 incidents associated with methomyl use (not including those classified as ‘unlikely’ due to 

methomyl use) have been reported (8 involving terrestrial organisms – all birds -and 2 involving 

aquatic organisms – all fish). The reported incidents occurred between 1976 and 2006. The 

certainty in which these incidents were a result of methomyl use was described as highly 

probable in two incidents, highly likely in two incidents, probable in four incidents, and possible 

in two incidents. Two of the incidents were the result of registered use, five were the result of 

misuse (intentional baiting); however, it is unknown if the other three incidents resulted from 

misuse or registered uses. Specific details of the incidents are described below. 

In addition to the incidents recorded in EIIS and AIMS, additional incidents have been reported 

to the Agency in aggregated incident reports. Pesticide registrants report certain types of 

incidents to the Agency as aggregate counts of incidents occurring per product per quarter. 

Ecological incidents reported in aggregate reports include those categorized as ‘minor fish and 

wildlife’ (W-B), ‘minor plant’ (P-B), and ‘other non-target’ (ONT) incidents. ‘Other non-target’ 

incidents include reports of adverse effects to insects and other terrestrial invertebrates. For 

methomyl, as of February 17, 2010, registrants have reported 7 minor fish and wildlife incidents, 

all of which occurred between 2000 and 2007. The number of individual organisms affected in 

these incidents was not specified. Unless additional information on these aggregated incidents 

become available, they will be assumed to be representative of registered uses of methomyl in 

the risk assessment. 

Terrestrial Incidents 

Five of the terrestrial incidents (one from New York, one from Maine, two from Florida, and one 

from Greece) were the result of intentional baiting and involved mortality in the following birds: 

rock dove (Columba livia), egret (species not provided), crow (Corvis sp.), red-tailed hawk 

(Buteo jamaicensis), American kestrel (Falco sparverius), Eleanora’s falcon (Falco eleonorae), 

and grackle (Quiscalus spp.) [Incident #/Event ID: (EIIS) I009064-001, I011181-001, and 

I017139-001; (AIMS) 1841 and 1953]. The legality of use for another of the incidents, which 

occurred in the British Virgin Islands and involved the death of 13 gulls and one cattle egret 

(Bubulcus ibis), was undetermined (Incident #: I1018980-10). Oxamyl, which is classified as 

very highly toxic to birds on an acute exposure basis, was also suspected in this incident. Two of 

the incidents occurred in France and involved the registered use (in France) of methomyl on 

cabbage (methomyl is also registered for use on cabbage in the United States). Incident # 

I006382-001 occurred in 1989 from a foliar spray of methomyl at a rate of 0.225 lbs a.i./acre. 

This incident, which was classified as ‘probable’, resulted in the mortality of at least 52 finches. 

The other French incident (I006382-002; 1992) was also classified as ‘probable’ and involved 

the registered use of methomyl (foliar spray) on cabbage. This incident involved the 

incapacitation of 31 birds and mortality in 35 birds (finches and linnets) after the birds were 

observed drinking dew from the cabbage field the day after methomyl application. 

 

1

 http://www.abcbirds.org/abcprograms/policy/pesticides/aims/aims/index.cfm 
-24 of 75-

Aquatic Incidents 

In a report from the California Fish and Game Department (Incident # I000108-001), there was a 

large fish kill, i.e., several thousand threadfin shad (Dorosoma petenense) and catfish (Ictalurus 

spp.), in the San Joaquin River near the town of Lathrop, California on October 16, 2001. The 

treatment site is unknown, and it is unknown if the kill was the result of misuse or registered use. 

The certainty that the kill resulted from methomyl was listed as ‘possible’. However, upon 

further review of the incident, it was acknowledged by California Fish and Game that un-ionized 

ammonia was the cause of the fish kill. Analyses of composited gill samples found the presence 

of several pesticides (i.e., dioxathion = 121.1 ppm; carbaryl = 1.75 ppm; carbofuran = 4.51 ppm; 

fenuron = 0.78 ppm; methomyl = 5.08 ppm; monuron = 5.83 ppm). However, these pesticides 

were not detected in the water samples and no mention was made in the California Fish and 

Game report that these pesticides may have been important factors in the fish kill. 

 

A fish kill incident occurred in Seminole County, Georgia, on June 16, 1992 (Incident # I00108-

001). The treatment site was corn, and it is unknown if the kill was the result of misuse or 

registered use. Also, the certainty that the kill resulted from methomyl was listed as ‘probable’. 

Upon further review of the incident report, it was assumed that runoff from a 200-acre plot of 

sweet corn treated with fertilizer and insecticides killed 125 bluegill, bowfin (Amia calva), and 

carp (Cyprinus spp). During a rainy two week period prior to the fish kill, the corn plot had been 

treated with 5 applications of methomyl (aerial, 1.5 pints/acre), 4 applications of chlorpyrifos, 4 

applications of fertilizer, and 2 applications of borax. The suspected cause of the fish kill was 

methomyl, as Lannate LV, toxicosis. Measured concentrations of methomyl were found in water 

samples taken from the pond and pond-overflow area. 

Due to limitations with data in the EIIS, a low number or lack of reported incidents in the 

database cannot be construed as evidence that additional incidents have not occurred. Incident 

reports for non-target plants and animals typically provide information on mortality events only. 

Reports for other adverse effects, such as reduced growth or impaired reproduction, are rarely 

received. EPA’s changes in the registrant reporting requirements of incidents may also account 

for the reduced number of reported incidents. Registrants are now only required to submit 

detailed information on ‘major’ incidents. Minor incidents are generally reported aggregately 

and are not included in EIIS. In addition, there have been reductions in state monitoring efforts 

due to lack of resources. 

4.4. Ecosystems Potentially at Risk 

The ecosystems at risk are often extensive in scope; therefore, it may not be possible to identify 

specific ecosystems during the development of a nation-wide ecological risk assessment. 

However, in general terms, terrestrial ecosystems potentially at risk could include the treated 

field and immediately adjacent areas that may receive drift or runoff. Areas adjacent to the 

treated field could include cultivated fields, fencerows and hedgerows, meadows, fallow fields or 

grasslands, woodlands, riparian habitats and other uncultivated areas. 
-25 of 75-

Aquatic ecosystems potentially at risk include water bodies adjacent to, or down stream from, the 

treated field and could include impounded bodies such as ponds, lakes and reservoirs, or flowing 

waterways such as streams or rivers. For uses in coastal areas, aquatic habitat also includes 

marine ecosystems, including estuaries. 

5. Assessment Endpoints 

Assessment endpoints represent the actual environmental value that is to be protected, defined by 

an ecological entity (species, community, or other entity) and its attribute or characteristics 

(USEPA 1998a). For methomyl, the ecological entities may include the following: birds, 

mammals, terrestrial-phase amphibians, reptiles, freshwater fish and invertebrates, aquatic-phase 

amphibians, estuarine/marine fish and invertebrates, terrestrial plants, terrestrial invertebrates, 

and aquatic plants. The attributes for each of these entities include growth, reproduction, and 

survival. 

6. Conceptual Model 

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must have a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors, and a feasible route of exposure. 

The conceptual model for methomyl provides a written description and visual representation of 

the predicted relationships between methomyl, potential routes of exposure, and the predicted 

effects for the assessment endpoint. A conceptual model consists of two major components: risk 

hypothesis and a conceptual diagram (USEPA 1998a). 

Based on the submitted environmental fate data, methomyl is not expected to volatilize or persist 

in soil or water; however, its persistence in acidic to pH neutral water is uncertain. The 

compound may potentially leach to ground water and move to surface water through runoff and 

spray drift. Methomyl is degraded mainly by metabolism and also slowly by photolysis in clear 

water and hydrolysis in alkaline water approximately pH 9 or above. Due to its low KOW value, 

methomyl is not expected to bioaccumulate in aquatic or terrestrial food chains. 

Based on previous ecological risk assessments for methomyl, there is the potential for risk for 

Federally listed threatened/endangered (hereafter referred to as “listed”) birds (and, thus, reptiles 

and terrestrial-phase amphibians), listed and non-listed mammals, and aquatic vertebrates 

(freshwater and estuarine/marine) (and, thus, aquatic-phase amphibians) and invertebrates. 

Because of the potential risk for direct effects to taxa (both listed and non-listed) described 

above, listed species in all taxa may potentially be affected indirectly due to alterations in their 

habitat and prey items (e.g., food sources, shelter, and areas to reproduce). These preliminary 

conclusions are used to derive the risk hypothesis and conceptual diagram discussed below. 
-26 of 75-

6.1. Risk Hypothesis 

A risk hypothesis describes the predicted relationship among the stressor, exposure, and 

assessment endpoint response along with the rationale for their selection. For methomyl, the 

following ecological risk hypothesis is being employed for this ecological risk assessment: 

Based on the application methods, mode of action, fate and transport, and the sensitivity 

of non-target aquatic and terrestrial species, methomyl has the potential to reduce 

survival, reproduction, and/or growth in non-target terrestrial and aquatic organisms 

when used in accordance with the current labels. These non-target organisms include 

listed and non-listed species. 

6.2. Conceptual Diagram 

The environmental fate properties of methomyl indicate that runoff, spray drift and direct spray 

represent potential transport mechanisms to aquatic and terrestrial habitats where non-target 

organisms may be exposed. These transport mechanisms (i.e., sources) are depicted in the 

conceptual diagrams below (Figures 6.1 and 6.2) along with the receptors of concern and the 

potential attribute changes in the receptors due to exposures of methomyl. Although methomyl 

may leach to ground water, it is not expected to persist long enough to contaminate the base flow 

of surface water bodies. 
-27 of 75-

FIGURE 6.1. Conceptual Model for Methomyl Effects on Aquatic Organisms. Dotted 

Lines Indicate Exposure Pathways that Have a Low Likelihood of Contributing to Ecological 

Risk. 

Stressor 

Source

Receptors 

Attribute 

Change 

Methomyl applied to use site 

Spray drift 

Fish/aquatic-phase 

amphibians 

Eggs 

Larvae 

Juveniles / Adults 

Individual organisms 

Reduced survival 

Reduced growth 

Reduced reproduction 

Food chain 

Reduction in algae 

Reduction in prey 

Habitat integrity 

Reduction in primary productivity

Reduced cover 

Community change 

Surface water/ 

Sediment 

Runoff 

Aquatic Animals 

Invertebrates 

Vertebrates 

Exposure 

Media 

Uptake/gills 

or integument 

Ingestion Ingestion

Long-range 

atmospheric 

transport 

Wet/dry deposition 

Soil Ground water 

Uptake/gills 

or integument 

Aquatic Plants 

Non-vascular 

Vascular 

Uptake/cell, 

roots, leaves Riparian plant

terrestrial 

exposure 

pathways see 

Figure 6.2 
-28 of 75-

FIGURE 6.2. Conceptual Model for Methomyl Effects on Terrestrial Organisms. Dotted 

Lines Indicate Exposure Pathways that Have a Low Likelihood of Contributing to Ecological 

Risk. 

7. Analysis Plan 

In order to address the risk hypothesis, the potential for adverse effects on the environment will 

be estimated. The use, environmental fate, and ecological effects of methomyl will be 

characterized and integrated to assess the risks. Risk quotients (RQ) will be derived for 

methomyl by dividing estimated environmental concentrations (EEC) by the most sensitive 

endpoint from the relevant, available toxicity data for methomyl. 

This analysis plan will be revisited and may be revised depending upon a full review of the data 

available in the open literature and the information submitted by the public in response to the 

opening of the Registration Review docket. 

Stressor 

Source

Receptors 

Attribute 

Change 

Methomyl applied to use site 

Direct 

application Spray drift 

Birds / 

Terrestrial-phase 

amphibians / 

reptiles /

Terrestrial 

invertebrat

Individual organisms 

Reduced survival 

Reduced growth 

Reduced reproduction 

Food chain 

Reduction in prey

Habitat integrity 

Reduction in primary productivity

Reduced cover 

Community change 

Terrestrial/riparian plants 

grasses/forbs, fruit, seeds 

(trees, shrubs) 

Runoff 

Mammals

Exposure 

Media 

Soil 

Ingestion 

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion 

Long-range 

atmospheric 

transport 

Root uptake 

Wet/dry deposition 

Birds / 

Amphibians

Ingestion 
-29 of 75-

7.1. Stressors of Concern 

The residues of concern in this assessment will include methomyl and any degradates determined 

to be of toxicological concern. At this time, however, none of the degradates of methomyl are of 

toxicological concern. Modeled exposure estimates resulting from methomyl use (and 

potentially any local thiodicarb use) will reflect the predicted environmental fate of methomyl 

(and any residues of concern). 

In its ecological risk assessments, the Agency does not routinely include an evaluation of 

mixtures of active ingredients, either those mixtures of multiple active ingredients in product 

formulations or those in the applicator’s tank. In the case of the product formulations of active 

ingredients (that is, a registered product containing more than one active ingredient), each active 

ingredient is subject to an individual risk assessment for regulatory decision regarding the active 

ingredient on a particular use site. If effects data are available for a formulated product 

containing more than one active ingredient, the data may be used qualitatively or quantitatively 

in accordance with the Agency’s Overview Document and the Services’ Evaluation 

Memorandum (USEPA 2004; USFWS/NMFS 2004). 

Available toxicity data for environmental mixtures of methomyl with other pesticides will be 

presented as part of the ecological risk assessment. It is expected that the toxic effect of 

methomyl, in combination with other pesticides used in the environment, is likely to be a 

function of many factors including but not necessarily limited to: (1) the exposed species, (2) the 

co-contaminants in the mixture, (3) the ratio of methomyl and co-contaminant concentrations, (4) 

differences in the pattern and duration of exposure among contaminants, and (5) the differential 

effects of other physical/chemical characteristics of the receiving waters (e.g. organic matter 

present in sediment and suspended water). Quantitatively predicting the combined effects of all 

these variables on mixture toxicity to any given taxa with confidence is beyond the capabilities 

of the available data and methodologies. However, a qualitative discussion of implications of the 

available pesticide mixture effects data on the confidence of risk assessment conclusions will be 

addressed as part of the uncertainty analysis. 

7.2. Measures of Exposure 

In order to estimate risks of methomyl exposures in aquatic and terrestrial environments, all 

exposure modeling and resulting risk conclusions will be made based on maximum application 

rates for the currently registered uses [i.e., field, vegetable, and orchard crops; turf (sod farms 

only); livestock quarters; commercial premises; and refuse containers] as discussed in Section 

3.2. Measures of exposure are based on aquatic and terrestrial models that estimate 

environmental concentrations of methomyl using maximum labeled application rates and 

application methods that have the greatest potential for off-site transport of the chemical. The 

models used to generate aquatic estimated environmental concentrations (EEC) are the Pesticide 

Root Zone Model (PRZM) coupled with the EXposure Analysis Model System (EXAMS). The 

model used to produce terrestrial EECs on food items is T-REX. The model used to derive EECs 

relevant to terrestrial and wetland plants is TerrPlant. These models are parameterized using 

relevant reviewed registrant-submitted environmental fate data. 
-30 of 75-

PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are screening simulation 

models coupled with the graphical user interface, PE (v5.0, November 2006) to generate daily 

exposures and 1-in-10-year EECs of methomyl that may occur in surface water bodies adjacent 

to application sites receiving methomyl through runoff and spray drift. PRZM simulates 

pesticide application, movement and transformation on an agricultural field and the resultant 

pesticide loadings to a receiving water body via runoff, erosion, and spray drift. EXAMS 

simulates the fate of the pesticide and resulting concentrations in the water body. The standard 

watershed geometry used for ecological pesticide assessments assumes application to a 10-

hectare agricultural field that drains into an adjacent 1-hectare water body that is 2 meters deep 

(20,000 m3

 volume) with no outlet. The composite model PRZM/EXAMS is used to estimate 

screening-level exposure of aquatic organisms to methomyl. The measure of exposure for 

aquatic species is the 1-in-10-year peak or rolling mean concentration. The 1-in-10-year peak is 

used for estimating acute exposures of direct effects to aquatic organisms. The 1-in-10-year 60-

day mean is used for assessing the effects to fish and aquatic-phase amphibians from chronic 

exposure. The 1-in-10-year 21-day mean is used for assessing the effects on aquatic 

invertebrates from chronic exposure. 

For the scatter bait use pattern, the impervious and residential PRZM/EXAMS scenarios will 

post-processed to obtain EECs in accordance with the conceptual model described in 

APPENDIX C. The conceptual model includes the assumption that 50% of the modeled area is 

impervious, and that 3% of the impervious area is treated. 

Exposure estimates for terrestrial animals assumed to be in the target area or in an area exposed 

to spray drift are derived using the T-REX model (version 1.4.1, 10/08/2008). This model 

incorporates the Kenaga nomograph, as modified by Fletcher et al. (1994), which is based on a 

large set of actual field residue data. The upper limit values from the nomograph represent the 

95th percentile of residue values from actual field measurements (Hoerger and Kenaga 1972). 

The Fletcher et al. (1994) modifications to the Kenaga nomograph are based on measured field 

residues from 249 published research papers, including information on 118 species of plants, 121 

pesticides, and 17 chemical classes. If terrestrial plant toxicity data are available, EECs for 

terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant (version 1.2.2, 

12/26/2006). This model uses estimates of pesticides in runoff and in spray drift to calculate 

EECs. EECs are based upon solubility, application rate and minimum incorporation depth. 

The AgDRIFT spray drift model (v2.01; May 2001) is used to assess exposures of organisms to 

methomyl deposited on terrestrial habitats by spray drift. 

7.3. Measures of Effect 

 

Ecological effects data are used as measures of direct and indirect effects to biological receptors. 

Data are obtained from registrant-submitted studies or from literature studies identified by 

ECOTOX. The ECOTOX database provides more ecological effects data in an attempt to bridge 

existing data gaps. ECOTOX is a source for locating single chemical toxicity data and potential 

chemical mixture toxicity data for aquatic life, terrestrial plants, and wildlife. ECOTOX was 

created and is maintained by the USEPA, Office of Research and Development, and the National 

Health and Environmental Effects Research Laboratory's Mid-Continent Ecology Division. 
-31 of 75-

Information on the potential effects of methomyl on non-target animals is also collected from the 

Ecological Incident Information System (EIIS; USEPA 2007c). The EIIS is a database 

containing adverse effect (typically mortality) reports on non-target organisms where such 

effects have been associated with the use of pesticides. 

Incidents reported in the aggregate incident reports and the Avian Incident Monitoring System 

(AIMS) will also be searched. AIMS is a database administered by the American Bird 

Conservancy (it was partially funded by the EPA). It contains publicly available data on 

reported avian incidents involving pesticides 

(http://www.abcbirds.org/abcprograms/policy/pesticides/aims/aims/index.cfm). 

Where available, sub-lethal effects observed in both registrant-submitted and open literature 

studies will be evaluated qualitatively. Such effects may include behavioral changes (e.g., 

lethargy and changes in coloration). Quantitative assessments of risks, though, are limited to 

those endpoints that can be directly linked to the Agency’s assessment endpoints of impaired 

survival, growth and reproduction. 

The assessment of risk for direct effects to non-target organisms makes the assumption that 

toxicity of methomyl to birds is similar to terrestrial-phase amphibians and reptiles. The same 

assumption is made for fish and aquatic-phase amphibians. 

The acute measures of effect used for animals in this assessment are the LD50, LC50 and EC50. 

LD stands for "Lethal Dose", and LD50 is the amount of a material, given all at once, that is 

estimated to cause the death of 50% of the test organisms. LC stands for “Lethal Concentration” 

and LC50 is the concentration of a chemical that is estimated to kill 50% of the test organisms. 

EC stands for “Effective Concentration” and the EC50 is the concentration of a chemical that is 

estimated to produce a specific effect in 50% of the test organisms. Endpoints for chronic 

measures of exposure for listed and non-listed animals are the NOAEL/NOAEC and NOEC. 

NOAEL stands for “No Observed-Adverse-Effect-Level” and refers to the highest tested dose of 

a substance that has been reported to have no harmful (adverse) effects on test organisms. The 

NOAEC (i.e., “No-Observed-Adverse-Effect-Concentration”) is the highest test concentration at 

which none of the observed effects were statistically different from the control. The NOEC is 

the No-Observed-Effects-Concentration. For non-listed plants, only acute exposures are 

assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants); for listed plants either the 

NOAEC or EC05 is used. 

7.4. Integration of Exposure and Effects 

Risk characterization is the integration of exposure and ecological effect characterizations to 

determine the potential ecological risk from the use of methomyl and the likelihood of direct and 

indirect effects to non-target organisms in aquatic and terrestrial habitats. The exposure and 

effects data are integrated in order to evaluate potential adverse ecological effects on non-target 

species. For the assessment of methomyl risks, the risk quotient (RQ) method is used to compare 

estimated exposure and measured toxicity values. Acute and chronic EECs are divided by acute 

and chronic toxicity values. The resulting RQs are then compared to the Agency’s Levels of 
-32 of 75-

Concern (LOC) (USEPA 2004). These criteria are used to indicate when methomyl’s use, as 

directed on the labels, has the potential to cause adverse direct or indirect effects to non-target 

organisms. In addition, incident data from EIIS, aggregate incident reports, and AIMS will be 

considered as part of the risk characterization. 

7.5. Deterministic and Probabilistic Assessment Methods 

The quantitative assessment of risk will primarily depend on the deterministic point estimatebased approach described in the risk assessment. Depending on the risk manager’s need for 

additional information regarding risk, an effort will be made to further qualitatively describe risk 

using probabilistic tools that the Agency has developed. These tools have been reviewed by 

FIFRA Scientific Advisory Panels (http://www.epa.gov/scipoly/sap/index.htm) and have been 

deemed as appropriate means of refining assessments where deterministic approaches have 

identified risks. 

7.6. Endangered Species Assessments 

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to Federally-listed threatened and/or endangered (listed) species from 

registered uses of methomyl. This assessment will be conducted in accordance with the 

Overview Document (USEPA 2004), provisions of the ESA, and the Services’ Endangered 

Species Consultation Handbook (USFWS/NMFS 1998). 

The assessment of effects associated with the registration of methomyl is based on an action 

area. The action area is considered to be the area directly or indirectly affected by the federal 

action, as indicated by the exceedance of Agency Levels of Concern (LOCs) used to evaluate 

direct or indirect effects. The Agency’s approach to defining the action area under the provisions 

of the Overview Document (USEPA 2004) considers the results of the risk assessment process to 

establish boundaries for that action area with the understanding that exposures below the 

Agency’s defined LOCs constitute a no-effect threshold. For the purposes of this assessment, 

attention will be focused on the footprint of the action (i.e., the area where methomyl application 

occurs), plus all areas where offsite transport (i.e., spray drift, runoff, etc.) may result in potential 

exposure that exceeds the Agency’s LOCs. Specific measures of ecological effect that define the 

action area for listed species include any direct and indirect effects and/or potential modification 

of its critical habitat, including reduction in survival, growth, and reproduction as well as the full 

suite of sub-lethal effects available in the effects literature. Therefore, the action area extends to 

a point where environmental exposures are below any measured lethal or sub-lethal effect 

threshold for any biological entity at the whole organism, organ, tissue, and cellular level of 

organization. In situations where it is not possible to determine the threshold for an observed 

effect, the action area will be assumed to encompass the entire United States. 

7.7. Drinking Water Assessment 

A drinking water assessment will be conducted to support future human health risk assessments 

of methomyl. The drinking water assessment will incorporate model estimates of methomyl 

residues of concern, including methomyl and any degradates or predecessors determined of 
-33 of 75-

toxicological concern, in surface and ground waters. In contrast to the approach for ecological 

assessment, all sources of methomyl and thiodicarb, which degrades to methomyl, will be 

considered. Whether exposure estimates will reflect methomyl separately from thiodicarb or 

assess thiodicarb in methomyl equivalents will depend on the toxicity differential of the 

compounds. Concentrations of methomyl residues of concern in surface water will be estimated 

using PRZM/EXAMS (see description in Section 7.2). Ground water exposure estimates for 

methomyl residues of concern will be estimated using the Screening Concentration in Ground 

Water (SCI-GROW) model (v.2.3, July 2003) followed by a higher tier model if necessary. The 

drinking water assessment will also include a summary of available surface and ground water 

monitoring data. 

7.8. Preliminary Identification of Data Gaps 

 7.8.1. Fate 

The studies submitted to fulfill environmental fate data requirements for methomyl are not 

sufficient for exposure assessment. The submitted aqueous photolysis studies either have poor 

material balances or did not analyze for transformation products of methomyl. Therefore, a 

guideline-compliant study is requested (similar to MRID 43823305 but that adequately 

characterizes the transformation products of methomyl). 

The submitted aerobic aquatic metabolism (MRID 43325401) and anaerobic aquatic metabolism 

(MRID 73214) studies have poor material balances. Therefore, new studies are requested in 

order to describe the fate of methomyl in surface water bodies down gradient from terrestrial use 

sites. Two of the anaerobic systems are requested to be iron-poor, while a third anaerobic system 

is requested to be iron-rich. Methomyl is expected to be unstable in the presence of ferrous iron. 

Study of anaerobic systems with different concentrations of iron may result in additional 

information on the degradation kinetics of methomyl in these systems. Care should be taken to 

confirm the radioactivity in the dosing solution and in day 0 systems as soon after dosing as 

possible. If these studies are to be useful in exposure assessment, they must be able to quantify 

the degradation rate of methomyl in the presence of ferrous iron. All aerobic and anaerobic 

systems should be maintained at pH values below seven. 

Table 7.1 identifies studies by MRID that offer data for each guideline requirement, as well as 

study classifications and whether or not further data are needed in order to support risk 

assessment (i.e., whether there is a data gap). Draft Data Call-In (DCI) tables for requested data 

are provided in APPENDIX E. 
-34 of 75-

TABLE 7.1. Environmental Fate Data Requirement Table for Methomyl.

OCSPP 

Guideline 

Data 

Requirement 

Submitted Studies 

(MRID) 

Classification Data 

Gap? 

Comments 

835.2120 Hydrolysis 8844 Unacceptable 

131249 Acceptable 

No. -- 

8844 Unacceptable 

22439 (In review) A

161885 Unacceptable 

835.2240 Aqueous 

photolysis 

43823305 (In review) A

Yes. A guideline-compliant study with a 

reasonable mass balance and 

characterization of photoproducts is 

requested. 

835.2410 Soil photolysis 163745 Acceptable No. -- 

Fung and Uren, 1977 Unacceptable 

8567 Supplemental 

8568 Acceptable 

8844 Unacceptable 

9325 Unacceptable 

133187/155756 Unacceptable 

43217901 Acceptable 

835.4100 Aerobic soil 

metabolism 

45473401 (In review) A

No. -- 

835.4200 Anaerobic soil 

metabolism 

43217902 Acceptable No. -- 

835.4300 Aerobic aquatic 

metabolism 

43325401 Supplemental Yes. A guideline-compliant study with a 

reasonable mass balance is requested. 

835.4400 Anaerobic 

aquatic 

metabolism 

73214 Unacceptable Yes. A guideline-compliant study of three 

acidic systems (two ferrous iron-poor, 

one ferrous iron-rich) with a reasonable 

mass balance is requested. 

44306 Acceptable 

161884 Acceptable 

Fung and Uren, 1977 Unacceptable 

835.1230 

835.1240 

Adsorption/ 

desorption and 

leaching 

Fung and Briner, 1977 Unacceptable 

No. -- 

8260 Unacceptable 

9324 Unacceptable 

9326 Unacceptable 

133188 (8844) Unacceptable 

41623901/41623902 Acceptable 

Terrestrial field 

dissipation 

42288001/43217903 Supplemental 

Storage stability 43708807 (In review) A

Reeves and Woodham, 

1974 

Upgradeable 

Fung, 1976 Upgradeable 

41623901/42288001 Upgradeable 

43117401 Acceptable 

835.6100 

Analytical 

method in soil, 

sediment, and/or 

water 

43117402 (p. 78-95) Upgradeable 

Currently, 

no. 

MRID 43117401 describes acceptable 

ELISA methods in soil, sediment, and 

water that have a range up to 5.0 ppb. 

The following submitted analytical 

methods are not acceptable (i.e., are 

upgradeable) without independent 

validation. Reeves and Woodham 

(1974) describe a method in soil, 

sediment, and water. Fung (1976) 

describes a method in soil and water. 

MRIDs 41623901 and 42288001 

describe a similar method in soil. 

MRID 43117402 describes methods in 

water (p. 78-95) and in soil (p. 116-

119). Independent validation of 
-35 of 75-

OCSPP 

Guideline 

Data 

Requirement 

Submitted Studies 

(MRID) 

Classification Data 

Gap? 

Comments 

43117402 (p. 116-119) Upgradeable methods in soil that support field 

studies is necessary for study 

evaluation. However, due to the 

availability of alternative acceptable 

methods, additional data are not 

requested at this time. 

835.7100 Ground water 40643001/40532201 Unacceptable 

monitoring 43568301 Acceptable 

No. -- 

850.1730 Fish 

bioconcentration 

131251 Unacceptable No. Fish bioconcentration data are not 

needed for compounds with low KOW. 

43708801 Supplemental 

43708802 Supplemental 

43708803 Supplemental 

43708804 Supplemental 

Aquatic reservoir 

monitoring 

(Non-guideline) 

43744401 Supplemental 

Foliar dissipation 158689 Acceptable 

(Non-guideline) 42271701 Acceptable 

(None) 

Chlorination 

(Non-guideline) 

46210701 Acceptable 

No. -- 

A The four studies currently in review are not expected to alter the identified data gaps. The aqueous photolysis 

studies in review (MRID 22439 and 43823305) preliminarily appear unacceptable. The storage stability (MRID 

43708807) and aerobic soil metabolism (MRID 45473401) studies in review have not been preliminarily classified. 

If MRID 45473401 is classified acceptable, it could reduce exposure estimates in the assessments.

7.8.2. Effects Data 

Although many submissions have been made to provide data on the effects of methomyl to 

aquatic and terrestrial organisms, data gaps still exist (Tables 7.2-7.4). Data gaps include the 

following: avian acute oral toxicity, avian reproduction, terrestrial plant, and aquatic plant 

toxicity studies. These data gaps are discussed below. 
-36 of 75-

TABLE 7.2. Available Ecological Effects Data for Terrestrial Animals Exposed to 

Methomyl and Remaining Data Gaps.

Guideline Description MRID/ 

Accession 

Classification Data 

Gap? 

Comments 

850.2100 Avian acute oral 

toxicity 

00161886 Acceptable Yes* 

45299802 Acceptable 

45299801 Acceptable 

850.2200 Avian sub-acute 

dietary toxicity 

00022923 Acceptable 

No 

850.2300 Avian reproduction 41898602 Acceptable Yes** 

850.3020 Honeybee acute 

contact toxicity 

45093001 Acceptable No 

*Avian acute oral toxicity data 

are not available for 

passerines, which are required 

under the new 40 CFR Part 

158. Therefore, this is 

identified as a data gap. 

** Data are required on 

waterfowl and upland game 

species. Currently acceptable 

data are only available for 

upland game species. Based 

on available data for another 

N-methyl carbamate (i.e., 

thiodicarb), mallard ducks 

appear more sensitive than 

bobwhite quail on a chronic 

exposure basis. Therefore, 

chronic toxicity data for 

mallard ducks exposed to 

methomyl could result in a 

more sensitive avian chronic 

toxicity endpoint and this is, 

thus, identified as a data gap. 
-37 of 75-

TABLE 7.3. Available Ecological Effects Data for Aquatic Animals Exposed to Methomyl 

and Remaining Data Gaps.

Guideline Description MRID/ 

Accession Classification Data Gap? comments 

850.1075 Freshwater fish – 

Acute toxicity 40098001 Supplemental No 

850.1075 Saltwater fish – 

Acute toxicity 41441202 Acceptable No 

40098001 Supplemental 

850.1010 00019977 Acceptable 

Freshwater 

invertebrates – 

Acute toxicity 40094602 Acceptable 

No 

00009134 Acceptable 

41441201 Acceptable 850.1025 

850.1035 

Saltwater invertebrates 

– 

Acute toxicity 42074601 Acceptable 

No 

850.1300 

Freshwater 

invertebrate – 

 life cycle test 

00131254 Acceptable No 

850.1350 

Saltwater invertebrates 

– 

life cycle test 

45013203 Supplemental No 

850.1400 Freshwater fish – 

early life stage test 00131255 Acceptable No 

850.1500 Fish life cycle test 43072101 Acceptable No 

850.1400 Saltwater fish – 

early life stage test 45013202 Acceptable No 

None 
-38 of 75-

TABLE 7.4. Available Ecological Effects Data for Plants Exposed to Methomyl and 

Remaining Data Gaps.

Guideline Description MRID Classification Data 

Gap? comments 

850.4100 

Terrestrial Plant 

toxicity: Tier I seedling 

emergence 

None Not applicable Yes* 

850.4100 

Terrestrial Plant 

toxicity: Tier 2 seedling 

emergence 

None Not applicable No 

850.4150 

Terrestrial Plant 

toxicity: Tier I 

vegetative vigor 

None Not applicable Yes* 

850.4150 

Terrestrial Plant 

toxicity: Tier 2 

vegetative vigor 

None Not applicable No 

850.5400 Aquatic Plant Growth: 

algae None Not applicable Yes* 

850.4400 Aquatic Plant Growth: 

vascular plants None Not applicable Yes* 

* Toxicity data for terrestrial 

plants and vascular and nonvascular aquatic plants, which 

are required, are not currently 

available. Therefore, these are 

identified as data gaps. 

Avian Acute Oral and Reproduction Toxicity 

Acceptable acute avian oral toxicity data were submitted for exposures of bobwhite quail and 

mallard duck to methomyl; however, data are not available for passerines, which are required 

under the new 40 CFR Part 158 (Oct. 26, 2007) data requirements for conventional pesticides 

(72 FR 60934; USEPA 2007d). The new Part 158 data requirements specify that acute avian 

oral toxicity data be submitted for either a mallard duck or bobwhite quail and a passerine 

species. Therefore, an avian oral toxicity test (OCSPP Guideline 850.2100) is required for 

passerine birds, as specified in 40 CFR Part 158 (Oct. 26, 2007). EFED recommends that the 

Pesticide Re-evaluation Division (PRD) request submission of a passerine study protocol for 

review by the Agency prior to initiation of this study. If oral acute toxicity data are not 

submitted for passerines, EFED will assume acute risk for passerine species. 

Under the 40 CFR Part 158 (Oct. 26, 2007) data requirements for conventional pesticides avian 

reproduction data are required on waterfowl and upland game species (OCSPP 850.2300). 

Currently acceptable data for methomyl are only available for an upland game species (Bobwhite 

quail). Data from another N-methylcarbamate (i.e., thiodicarb) suggest that mallard ducks may 

be more sensitive than Bobwhite quail on a chronic-exposure basis. The chronic toxicity data 

available for birds indicate that mallard ducks (NOAEC = 500 mg a.i./kg-diet; LOAEC = 1,000 

mg a.i./kg-diet, based on a reduction in number of eggs laid) (MRID 43313004) are more 

sensitive to thiodicarb than bobwhite quail (no reproductive effects seen at any concentration 

tested; highest concentration tested = 1,000 mg a.i./kg-diet) (MRID 43313003). Additionally, 

bobwhite quail appear more sensitive to methomyl than to thiodicarb based on chronic exposure 

(for methomyl, NOAEC = 150 mg a.i./kg-diet; LOAEC = 500 mg a.i./kg-diet, based on fewer 

eggs laid and eggs set) (MRID 41898602). Therefore, based on available data, it is reasonable to 
-39 of 75-

assume that mallard ducks may be more sensitive to methomyl than bobwhite quail on a chronic 

exposure basis. Therefore, since additional avian reproduction data for methomyl could result in 

a more sensitive avian reproductive endpoint, and, thus, could alter the estimated level of risk for 

birds (and by extension to terrestrial-phase amphibians and reptiles) from the use of methomyl, 

we recommend requesting these data for methomyl at this time. 

Terrestrial Plant Studies 

Terrestrial plant toxicity studies and associated risk analysis of plants are required for 

registration of pesticides with outdoor uses (CFR Part 158). For terrestrial plants, Tier II studies 

are required when potential concerns are triggered (i.e., when there is some indication that there 

may be significant toxicity to plants). These indicators may be an herbicidal mode of action or 

statements on the label indicating toxicity to plants. None of these indicators are present for 

methomyl. 

Several efficacy studies that were conducted to test the effects of methomyl on a variety of target 

and non-target invertebrate pests also supplied information on effects to plants after methomyl 

applications. Due to a lack of information on study design and data analyses, these efficacy 

studies are classified as ‘supplemental’ and are not adequate for plant (or terrestrial invertebrate) 

RQ calculation. None of the studies showed any adverse effects to plants at the highest 

treatment levels tested (most of which were at or above the maximum allowable single 

application rate for methomyl of 0.9 lbs a.i./acre) and the NOAEC from the studies represented 

the highest treatment rates examined (see Table 4.3). However, because none of the studies 

addressed potential risks to monocots or effects on seedling emergence and some N-methyl 

carbamates are plant auxins that are used to thin fruit (e.g., carbaryl), risks to plants from the use 

of methomyl cannot be precluded using the available data. Tier I seedling emergence and 

vegetative vigor studies (OCSPP Guidelines 850.4100 and 850.4150) are, therefore, required. If 

toxicity data for terrestrial plants are not submitted for methomyl, EFED will assume risk for 

terrestrial plants. 

Vascular and Non-vascular Aquatic Plant Studies

Aquatic plant toxicity studies and associated risk analysis of plants are required for registration 

of pesticides with outdoor uses (40 CFR Part 158). Toxicity data for both vascular and nonvascular aquatic plants (Tier I, OCSPP Guidelines 850.4400 and 850.5400) are required but are 

not available for methomyl. Although, there is evidence to suggest that methomyl is not toxic to 

terrestrial plants (see above), such data are not available for aquatic plants. Therefore, we 

recommend requesting toxicity data on vascular and non-vascular aquatic plants for methomyl. 

If toxicity data for aquatic plants are not submitted for methomyl, EFED will assume risk for 

aquatic plants. 

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Contamination and Toxicology, 100:21-73. 

SUBMITTED ENVIRONMENTAL FATE STUDIES:

MRID:

8568 Harvey, J., Jr. 1977. Degradation of 14C-Methomyl in Flanagan Silt Loam in Biometer Flasks.

Unpublished study received Feb 28, 1977 under 352-342; prepared in cooperation with Univ. of 

Delaware, Soil Testing Laboratory, submitted by E.I. du Pont de Nemours & Co., Wilmington, Del.; 

CDL:096026-B. 
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8844 Harvey, J. 1964? Exposure of S-Methyl N-(methylcarbamoyl)oxy|-thioacetimidate in Sunlight, Water, 

and Soil. Unpublished study received Dec 28, 1968 under 8F0671; submitted by E.I. du Pont de 

Nemours & Co., Inc., Wilmington, Del.; CDL:091179-V. 

9324 Harvey, J., Jr. and H. L. Pease. 1971? Decomposition of Methomyl in Soil. Unpublished study received 

May 5, 1977 under 352-342; submitted by E.I. du Pont de Nemours & Co., Wilmington, Del.; 

CDL:229711-D. 

9326 E.I. du Pont de Nemours & Company. 1971. Methomyl Decomposition in Muck Soil--A Field Study.

Unpublished study received May 5, 1977 under 352-342; CDL:229711-F. 

44306 Khasawinah, A.M. and G. C. Holsing. 1976. UC 51762 Pesticide: Mobility on Soil Thin-Layer 

Chromatograms: File No. 22754. Unpublished study received Sep 10, 1980 under 264-341; submitted 

by Union Carbide Agricultural Products Co., Ambler, Pa.; CDL: 099602-J. 

131249 Friedman, P. 19?? Hydrolysis of 1-14C-methomyl: Document No. AMR- 109-83. Unpublished study 

received Oct 3, 1983 under 352-366; submitted by E.I. du Pont de Nemours & Co., Inc., Wilmington, 

DE; CDL:251424-B. 

157991 Collins, R., and F. Kenny. 1986. Octanol-Water Partition Coefficient of Nudrin Insecticide. Code 5-8-

0-0. RIR-25-009-86. Unpublished study prepared by Shell Development Co. 

161884 Priester, T. 19?? Batch Equilibrium (Adsorption/desorption) and Soil Thin-layer Chromatography 

Studies with Methomyl: Document No. AMR-174-84. Unpublished. 

161885 Harvey, J. 19?? Photolysis of [1-Carbon 14] Methomyl: Document No. AMR-121-83. Unpublished 

study prepared by E. I. du Pont de Nemours and Co., Inc. 14 p. 

163745 Swanson, M. 1986. Photodegradation of [1-Carbon 14]Methomyl on Soil: Document No. AMR-611-

86. Unpublished study prepared by E.I. du Pont de Nemours and Co., Inc. 25 p. 

41209701 Barefoot, A. C. and L. A. Cooke. 1989. Vapor Pressure of Methomyl. Laboratory Project ID AMR1268-88. Submitted by E. I. Du Pont de Nemours & Company. Wilmington, DE. 

41402101 Hoffman, R. 1988. Determination of the Water Solubility of Methomyl, X1179: Lab Project Number: 

X1179.B. Unpublished study prepared by E. I. du Pont de Nemours and Co. 12 p. 

41623901 Kennedy, S. 1989. Field Soil Dissipation of Lannate L Insecticide: Lab Project Number: 

ML88/0078/DUP. Unpublished study prepared by Morse laboratories, Inc. 84 p. 

41623902 Kennedy, S. 1989. Field Soil Dissipation of Lannate L insecticide: Lab Project Number: 

ML88/0078/DUP. Unpublished study prepared by Morse Laboratories, Inc. 41 p. 

42288001 Kennedy, C. 1991. Field Soil Dissipation of Lannate L Insecticide--a 1991 Study. Lab Project 

Number: AMR-1921-91: ML91-0242-DUP: 9100135. Unpublished study prepared by Morse Labs 

and Harris Environmental Technologies, Inc. 64 p. 

43217901 Malik, N. and T. Zwick. 1990. Aerobic Metabolism of (1-carbon 14) Methomyl in Madera, California 

Soil: Final Report: Lab Project Number: SC890027: AMR/1543/89. Unpublished study prepared by 

Battelle Memorial Institute. 40 p. 

43217902 Malik, N., and T. Zwick, 1990. Anaerobic Metabolism of (1-carbon 14) Methomyl in Madera, 

California Soil: Final Report: Lab Project Number: SC890028: AMR/1544/89. Unpublished study 

prepared by Battelle Memorial Institute. 45 p. 
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43217903 Kennedy, C. 1992. Field Soil Dissipation of Lannate L Insecticide: A 1991 Study: Supplement. Lab 

Project Number: AMR/1921/91: ML91/02420DUP: 9100135. Unpublished study prepared by Morse 

Lab., Inc.; Harris Environmental Technologies, Inc. 34 p. 

43325401 Mayo, B. 1994. Degradability and Fate of (1-(carbon 14))Methomyl in Water/Sediment Systems: Lab 

Project Number: DPT/295/932544: AMR/2590/92. Unpublished study prepared by Huntingdon 

Research Centre, Ltd. 112 p. 

43568301 Russell, Mark., Andrew M. Hiscock, and James M. DeMartinis and Janet C. Ruhl. 1995. A SmallScale Prospective Groundwater Monitoring Study for Methomyl: Final Report: Lab Project Number: 

AMR/2311/92: ML92/0335/DUP: 423/04. Unpublished study prepared by Blasland, Bouck & Lee, 

Inc. and other facilities. Submitted by E. I. du Pont de Nemours and Company. 619 p. 

43599801 Russell, M. and L. Bergstrom. 1995. Modeling of the Results from a Small-Scale Prospective 

Groundwater Study for Methomyl: Lab Project Number: 423.13: AMR 3405-95. Unpublished study 

prepared by Blasland, Bouck & Lee, Inc. and DuPont Agricultural Products. 136 p. 

43708801 Naylor, M., D. Palmer, and H. Krueger. 1994. An Aquatic Residue Monitoring Study of Methomyl in 

and Around Apple Orchards in Michigan: Lab Project Numbers: 112-292: AMR 2278-92: 91-4-3722. 

Unpublished study prepared by DuPont Agricultural Products; Morse Labs.; and Wildlife Int'l. Ltd. 

555 p. 

43708802 Leva, S. 1995. An Aquatic Residue Monitoring Study of Lannate L Insecticide in and Around Sweet 

Corn Fields in Illinois. Unpublished study prepared by DuPont Agricultural Products; Morse Labs.; 

and Wildlife Int'l. Ltd. 584 p. 

43708803 Armbrust, K. 1995. An Aquatic Residue Monitoring Study of Methomyl in and Around Cucurbit 

Fields in California: Lab Project Numbers: AMR 2469-92: 92195: ML93-0445-DUP. Unpublished 

study prepared by DuPont Agricultural Products; Morse Labs.; and ABC Labs., Inc. 432 p. 

43708804 Leva, S. and S. McKelvey. 1995. An Aquatic Residue Monitoring Study of Methomyl in and Around 

Lettuce Fields in Florida: Lab Project Numbers: AMR 2512-92: ML93-0423-DUP: 112-333. 

Unpublished study prepared by DuPont Agricultural Products; Morse Labs.; and Wildlife Int'l, Inc. 475 

p. 

43744402 Samel, A. 1995. An Evaluation of the Effects and Fate of Methomyl Insecticide Exposure in Outdoor 

Microcosms: Lab Project Number: AMR 2389-92: ML93-0445-DUP: 112-299. Unpublished study 

prepared by Morse Labs and Wildlife International, Ltd. 877 p. 

43823305 Armbrust, K. and D. Reilly. 1995. Indirect Photodegredation of Methomyl in Aqueous Solutions. 

Lab Project Number: AMR 2975-94. Unpublished study prepared by DuPont Agricultural Products. 

103 p. 

SUBMITTED EFFECTS STUDIES:

MRID:

9061 Schneider, P.W., Jr. (1976) 96-Hour LCI50^ to Bluegill Sunfish: Haskell Laboratory Report No. 710-

76. (Unpublished study received Jun 21, 1979 under 352-342; submitted by E.I. du Pont de Nemours & 

Co., Wilmington, Del.; CDL:238781-A) 

9134 Sleight, B.H., III (1973) Bioassay Report Submitted to E.I. DuPont de Nemours & Company, Newark, 

Delaware: Acute Toxicity of H- 7946, MR-581 to Grass Shrimp (Palaemenetes vulgaris), Pink Shrimp 

(Penaeus duorarum) and Mud Crab (Neopanope texana). (Unpublished study received May 6, 1976 

under 352- 342; prepared by Bionomics, Inc., submitted by E.I. du Pont de Nemours & Co., 

Wilmington, Del.; CDL:224073-AI). 
-44 of 75-

9230 Bentley, R. (1973) Acute Toxicity of H-8385 to Grass Shrimp (Palaemonetes vulgaris) and Fiddler 

Crab (Uca pugilator). (Unpublished study received May 5, 1977 under 352-342; prepared by 

Bionomics, Inc., submitted by E.I. du Pont de Nemours & Co., Wilmington, Del.; CDL:229718-A) 

19977 Goodman, N.C. (1978) 48-Hour LC50^2I to~Daphnia magna~: Haskell Laboratory Report No. 165-

78. (Unpublished study received May 22, 1978 under 352-342; submitted by E.I. du Pont de Nemours 

& Co., Wilmington, Del.; CDL:233993-B) 

22923 Hill, E.F.; Heath, R.G.; Spann, J.W.; et al. (1975) Lethal Dietary Toxicities of Environmental 

Pollutants to Birds: Special Scientific Report--Wildlife No. 191. (U.S. Dept. of the Interior, Fish and 

Wildlife Service, Patuxent Wildlife Research Center; unpublished report) 

115198 Tucker, R.; Crabtree, D. (1970) Handbook of Toxicity of Pesticides to Wildlife. By U.S. Fish and 

Wildlife Service, Denver Wildlife Research Center. Washington, DC: USFWS. (Resource publication 

no. 84; available from: Superintendent of Documents, U.S. Government Printing Office, Washington, 

DC 20402; published study; CDL:228345-M) 

131254 Britelli, M.; Muska, C. (1982) Chronic Toxicity of Methomyl to Daphnia magna: Haskell Laboratory 

Report No. 46-82; MR No. 0581- 930. (Unpublished study received Oct 3, 1983 under 352-366; 

submitted by E.I. du Pont de Nemours & Co., Inc., Wilmington, DE; CDL:251426-B) 

131255 Driscoll, R.; Muska, C. (1982) Early Life Stage Toxicity of Metho- myl to Fathead Minnow: Haskell 

Laboratory Report No. 528-82; MR No. 0581-930. (Unpublished study received Oct 3, 1983 under 

352-366; submitted by E.I. du Pont de Nemours & Co., Inc., Wil- mington, DE; CDL:251426-C) 

161886 Beavers, J. (1983) An Acute Oral Toxicity Study in the Bobwhite with H-15,000: Final Report: Project 

No.: 112-142. Unpublished study prepared by WIldlife International Ltd. 15 p. 

40098001 Mayer, F.; Ellersieck, M. (1986) Manual of Acute Toxicity: Interpretation and Data Base 410 

Chemicals and 66 Species of Fresh-Water Animals. US Fish & Wildlife Service; Resource Publica tion 

(160): 579 p. 

40094602 Johnson, W.; Finley, M. (1980) Handbook of Acute Toxicity of Chemicals to Fish and Aquatic 

Invertebrates: Resource Publication 137. US Fish and Wildlife Service, Washington, D.C. 106 p. 

41441201 Ward, T.; Boeri, R. (1989) Static Acute Toxicity of Methomyl to the Mysid, Mysidopsis bahia: Lab 

Project Number: 8963-DU. Unpublished study prepared by EnviroSystems Div., Resource Analysts, 

Inc. 32 p. 

41441202 Boeri, R.; Ward, T. (1989) Static Acute Toxicity of Methomyl to the Sheepshead Minnow, Cyprinodon 

variegatus: Lab Project Number: 8964-DU. Unpublished study prepared by EnviroSystems Div., 

Resource Analysts, Inc. 32 p. 

41898602 Beavers, J.; Hawrot, R.; Lynn, S.; et al. (1991) H-17940: A One- Generation Reproduction Study with 

the Northern Bobwhite (Coli- nus virginianus): Lab Project No: 112/227. Unpublished study prepared 

by Wildlife International Ltd. 168 p. 

42140101 Sarver, J. (1991) Acute Oral Toxicity Study with DPX-X1179-394 in Male and Female Rats: Lab 

Project Number: 9182-001. Unpub- lished study prepared by E. I. du Pont de Nemours and Co., Inc. 33 

p. 

43250701 Lu, C. (1983) Nudrin Two-Generation Reproduction Study in Rats: Lab Project Number: WRC RIR275. Unpublished study prepared by WIL Research Lab., Inc. 1144 p. 
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45125502 Adelberger, I. (2000) Methomyl 25 WP: A Dose/Response Test to Evaluate the Effects on the 

Predatory Mite, Typhlodromus pyri Scheuten (Acri, Phytoseiidae) in the Laboratory: Lab Project 

Number: 2914: 99342/01-NLTP. Unpublished study prepared by IFU Umweltanalytik GmbH. 33 p. 

45133301 Schuld, M. (2000) Methomyl 20L: A Dose/Response Test to Evaluate the Effects on the Aphid 

Parasitoid Aphidius rhopalosiphi (Hymenoptera, Braconidae) in the Laboratory: Lab Project Number: 

99205/01-NLAP: 2669. Unpublished study prepared by IFU Umweltanalytik GmbH. 39 p. 

42074601 Ward, T. (1991) Acute Flow-through Mollusc Shell Deposition with DPX-X1179-394 (Methomyl): 

Lab Project Number: MR-8808-001. Unpublished study prepared by EnviroSystems, Inc. incoop. with 

Dupont Haskell Labs. 31 p. 

45299801 Medlicott, B.; Harris, T. (2000) Methomyl (DPX-X1179) Technical: Avian Acute Dietary Toxicity 

Test with Northern Bobwhite (Colinus virginianus): Lab Project Number: DUPONT-4378: 00022. 

Unpublished study prepared by Genesis Laboratories, Inc. 51 p. 

45299802 Medlicott, B.; Harris, T. (2000) Methomyl (DPX-X1179) Technical: Avian Acute Dietary Toxicity 

Test with the Mallard Duck (Anas platyrhynchos): Lab Project Number: DUPONT-4379: 00023. 

Unpublished study prepared by Genesis Laboratories, Inc. 51 p. 

43072101 Strawn, T.; Rhodes, J.; Leak, T. (1993) Full Life-Cycle Toxicity of DPX-X1179-394 (Methomyl) to 

the Fathead Minnow (Pimephales promelas) Under Flow-Through Conditions: Final Report: Lab 

Project Number: 39293: HLO 47-93. Unpublished study prepared by ABC Laboratories, Inc. 3582 p. 

43744402 Samel, A. (1995) An Evaluation of the Effects and Fate of Methomyl Insecticide Exposure in Outdoor 

Microcosms: Lab Project Number: AMR 2389-92: ML93-0445-DUP: 112-299. Unpublished study 

prepared by Morse Labs and Wildlife International, Ltd. 877 p. 

43769401 Hurtt, M. (1995) Nudrin--Two Generation Reproduction Study in the Rat: Supplement No.1: Lab 

Project Number: RA274: WRC RIR-275: HLO 519-95. Unpublished study prepared by WIL Research 

Labs, Inc. 149 p. 

44969301 Wachter, S. (1999) Methomyl Technical: Acute Toxicity to the Earthworm, Eisenia foetida

Michaelsen. Unpublished study performed by Arbeitsgemeinschaft, GAB Biotechnologie GmbH & 

IFU Umweltanalytik GmbH Eutinger Straβe 24, D-75223 Niefern-Öschelbronn, Germany. Sponsor: E. 

I. Du Pont de Nemours and Company, Wilmington, DE 19898. 

45013202 Boeri, R.; Magazu, J.; Ward, T. (1998) Methomyl Technical: Flow-Through Early Life Stage Toxicity 

to the Sheepshead Minnow, Cyprinodon variegatus. Unpublished study performed by T.R. Wilbury 

Laboratories, Inc. Marblehead, MA. 

45013203 Ward, T.; Magazu, J.; Boeri, R. (1999) Methomyl Technical: Flow-Through Chronic Toxicity to the 

Mysid, Americamysis bahia (Formerly Known as Mysidopsis bahia). Unpublished study performed by 

T.R. Wilbury Laboratories, Inc. Marblehead, MA. 

45093001 Schur, A. (2000) Methomyl Technical: Acute Oral and Contact Toxicity to the Honeybee, Apis 

mellifera L. Unpublished study performed by Arbeitsgemeinschaft, GAB Biotechnologie GmbH & 

IFU Umweltanalytik GmbH Eutinger Straβe 24, Niefern-Öschelbronn, Germany. 

45125501 Aldelberger, I. (2000) Methomyl 20L: A Dose/Response Test to Evaluate the Effects on the Predatory 

Mite, Typhlodromus pyri Scheuten (Acari, Phytoseiidae) in the Laboratory. Unpublished study 

performed by Arbeitsgemeinschaft, GAB Biotechnologie GmbH & IFU Umweltanalytik GmbH 

Eutinger Straβe 24, D-75223 Niefern-Öschelbronn, Germany. Sponsor: E. I. Du Pont de Nemours and 

Company, Wilmington, DE 19898. 
-46 of 75-

45133302 Schuld, M. (2000) Methomyl 25 WP: A Dose/Response Test to Evaluate the Effects on the Aphid 

Parasitoid Aphidius rhopalosiphi (Hymenoptera, Braconidae) in the Laboratory: Lab Project Number: 

2915: 99342/01-NLAP. Unpublished study prepared by IFU Umweltanalytik GmbH. 38 p. 

45459201 Ulf Luhrs (2001) Methomyl 20L: Effects on Reproduction and Growth of the Earthworm, Eisenia 

fetida (Savigny 1826), in Artificial Soil: Lab Project Number: 6216022: 5503. Unpublished study 

prepared by Institut fur Biologische Analytik. 43 p. 
-47 of 75-

APPENDIX A: Registered Uses and Application Rates for Methomyl. 

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Alfalfa Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 3.6 lbs a.i./A 10 9** 32.4 lbs a.i./A

Anise (Fennel) Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 4.5 lb a/A 10 2 9 lbs a.i./A 

Apple Lannate LV 

(ground only) Lannate SP 

0.9 lbs a.i./A 7 4.5 lbs a.i./A 5 1 4.5 lbs a.i./A 

Asparagus Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 8 1 4.5 lbs a.i./A 

Avocado Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 0.9 lbs a.i./A 2 1 0.9 lbs a.i./A 

Barley Lannate LV LV

Lannate SP 

0.45 lbs a.i./A 5 1.8 lbs a.i./A 4 1 1.8 lb a.i/.A 

Beans, Succulent Lannate LV LV

(kidney, lima, 

mung, Navy, 

pinto, snap, wax, 

broad, fava, 

asparagus beans, 

blackeyed peas, 

cowpeas) 

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 10 1 4.5 lb a.i/.A 

Sweet Lupine, 

White Sweet 

Lupine, White 

Lupine, Grain 

Lupine 

Lannate SP 0.9 lbs a.i./A 5 4.5 lbs a.i./A 10 1 4.5 lbs a.i./A 

Beans, Dry Lannate LV LV

(same as succulent 

beans) 

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 10 1 4.5 lb a.i/.A 

BeansSLN

(interplanted with 

nonbearing 

almonds, plums, 

prunes, peaches, 

and walnuts) (CA770431) 

Lannate SP 0.45 lbs a.i./A 5 0.9 lbs a.i./A 2 1 0.9 lb a.i/.A 

Beets (table) Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 3.6 lbs a.i./A 8 2 7.2 lb a.i/.A 

Bermudagrass Lannate LV 

(pasture) Lannate SP 

0.9 lbs a.i./A 5 0.9 lbs a.i./A 4 1 0.9 lb a.i/.A 

Blueberries Lannate LV 

(ground only) Lannate SP 

0.9 lbs a.i./A 5 3.6 lbs a.i./A 4 1 3.6 lbs a.i./A 

Broccoli Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 2 6.3 lbs a.i./A 10 Imperial 

Valley: 1 

Coastal 

Valleys: 3 

San Joaquin 

Valley: 2 

6.3 lbs a.i./A 

18.9 lbs a.i./A

12.6 lbs a.i./A
-48 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Broccoli, 

ChineseSLN

(CA-860059) 

Lannate SP 0.9 lbs a.i./A 5 4.5 lbs a.i./A 5 2 9 lbs a.i./A 

Broccoli RaabSLN

(CA-900034) 

Lannate SP 0.9 lbs a.i./A 5 7.2 lbs a.i./A 10 Imperial 

Valley: 1 

Coastal 

Valleys: 3 

San Joaquin 

Valley: 2 

7.2 lbs a.i./A 

21.6 lbs a.i./A

14.4 lbs a.i./A

Brussels Sprouts Lannate LV LV Lannate SP 

0.9 lbs a.i./A 2 5.4 lbs a.i./A 10 1 5.4 lbs a.i./A 

Cabbage Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 2 7.2 lbs a.i./A 15 3 21.6 lbs a.i./A

Carrot Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 6.3 lbs a.i./A 10 1 6.3 lbs a.i./A 

Cauliflower Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 2 7.2 lbs a.i./A 10 Coastal 

Region: 2 

San Joaquin 

Valley: 1 

14.4 lbs a.i./A

7.2 lbs a.i./A 

Celery Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 7.2 lbs a.i./A 10 2.5 18 lbs a.i./A 

Chicory Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 1.8 lbs a.i./A 2 San Joaquin 

Valley: 2 

Desert: 1 

3.6 lbs a.i./A 

1.8 lbs a.i./A 

Chinese Cabbage Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 7.2 lbs a.i./A 10 3 21.6 lbs a.i./A

Collards Lannate LV LV (fresh 

market only) Lannate SP 

0.9 lbs a.i./A 5 5.4 lbs a.i./A 8 3 16.2 lbs a.i./A

Corn (field and Lannate LV 

popcorn) Lannate SP 

0.45 lbs a.i./A 5 2.25 lbs a.i./A 10 1 2.25 lbs a.i./A

Corn (seed) LV Lannate SP 0.45 lbs a.i./A 5 2.25 lbs a.i./A 10 1 2.25 lbs a.i./A

Corn (sweet) Lannate LV LV

Lannate SP 

0.45 lbs a.i./A 1 6.3 lbs a.i./A 28 3 18.9 lbs a.i./A

Corn LV Methomyl 5G 

Granules 

0.15 lbs a.i./A NR 6.3 lbs a.i./A 10 3 18.9 lbs a.i./A

Cotton Lannate LV 2, LV

Lannate SP 

0.675 lbs 

a.i./A 

3 1.8 lbs a.i./A 8 1 1.8 lbs a.i./A 

Cucumber Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 5.4 lbs a.i./A 12 1 5.4 lbs a.i./A 

Eggplant Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 10 1 4.5 lbs a.i./A 

Endive, Escarole Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 8 2 

(less in 

desert) 

9 lbs a.i./A 

Garlic Lannate LV 

Lannate SP 

0.45 lbs a.i./A 5 2.7 lbs a.i./A 6 1 2.7 lbs a.i./A 

Grapefruit Lannate LV 3

Lannate SP 

0.9 lbs a.i./A 5 2.7 lbs a.i./A 4 1 2.7 lbs a.i./A 

Horseradish Lannate LV 

(ground Only) Lannate SP 

0.45 lbs a.i./A 5 1.8 lbs a.i./A 4 1 1.8 lbs a.i./A 
-49 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Leafy Green Lannate LV 

Vegetables 

(beet tops, 

dandelions, kale, 

mustard greens, 

parsley, Swiss 

chard, turnip 

greens) 

Lannate SP 

0.9 lbs a.i./A 5 3.6 lbs a.i./A 8 4 14.4 lbs a.i./A

Lemon Lannate LV 3

Lannate SP 

0.9 lbs a.i./A 5 2.7 lbs a.i./A 4 1 2.7 lbs a.i./A 

Lentils Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 0.9 lbs a.i./A 2 1 

 

0.9 lbs a.i./A 

Lettuce Lannate LV LV (head 

varieties) Lannate SP 

0.9 lbs a.i./A 2 7.2 lbs a.i./A 15 Central 

Coast: 2 

Central 

Valley: 2 

Other 

Regions: 1 

14.4 lbs a.i./A

14.4 lbs a.i./A

7.2 lbs a.i./A 

Lettuce Lannate LV LV (leaf 

varieties) Lannate SP 

0.9 lbs a.i./A 2 3.6 lbs a.i./A 8 Desert: 1 

Other 

Regions: 2 

3.6 lbs a.i./A 

7.2 lbs a.i./A 

Melons Lannate LV LV

(cantaloupe, 

casaba, Santa 

Claus, Crenshaw, 

honeydew, honey 

balls, Persian, 

golden pershaw, 

mango melon, 

pinapple melon, 

snake, 

watermelon) 

Lannate SP 

0.9 lbs a.i./A 5 5.4 lbs a.i./A 12 1 5.4 lbs a.i./A 

Mint Lannate LV LV

(peppermint, 

spearmint) 

Lannate SP 

0.9 lbs a.i./A 5 1.8 lbs a.i./A 4 Peppermint: 

1** 

Spearmint: 

2** 

1.8 lbs a.i./A 

3.6 lbs a.i./A 

Nectarine3 Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 2.7 lbs a.i./A 3 1 2.7 lbs a.i./A 

Nonbearing Fruit, 

Grape, and Nut 

Nursery Stock 

(field grown)SLN

(CA-770308) 

Lannate SP 0.9 lbs a.i./A 5 4.5 lbs a.i./A 5 1 4.5 lbs a.i./A 

Oats Lannate LV LV

Lannate SP 

0.45 lbs a.i./A 5 1.8 lbs a.i./A 4 1 1.8 lbs a.i./A 

Onions (green) Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 5.4 lbs a.i./A 8 3 16.2 lbs a.i./A

Onions (dry bulb) Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 3.6 lbs a.i./A 8 1 3.6 lbs a.i./A 

Oranges Lannate LV 3

Lannate SP 

0.9 lbs a.i./A 5 2.7 lbs a.i./A 4 1 2.7 lbs a.i./A 
-50 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Peaches Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 5.4 lbs a.i./A 6 1 5.4 lbs a.i./A 

Peanuts Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 3.6 lbs a.i./A 8 N/A N/A 

Pears (Northeast Lannate LV 

only) Lannate SP 

0.9 lbs a.i./A 5 1.8 lbs a.i./A 2 1 1.8 lbs a.i./A 

Peas, succulent Lannate LV LV

(pigeon peas, 

chick, garbanzo, 

dwarf peas, garden 

peas, green peas, 

English peas, Field 

peas, edible pod 

peas) 

Lannate SP 

0.9 lbs a.i./A 3 2.7 lbs a.i./A 6 1 2.7 lbs a.i./A 

Pecans (Southeast Lannate LV 

only) Lannate SP 

0.9 lbs a.i./A 5 6.3 lbs a.i./A 7 1 6.3 lbs a.i./A 

Peppers Lannate LV LV (bell, 

hot, pimentos, 

sweet) 

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 10 1 4.5 lbs a.i./A 

Pomegranates Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 1.8 lbs a.i./A 2 1 1.8 lbs a.i./A 

Potato Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 10 1 4.5 lbs a.i./A 

PumpkinsSLN (CA910011) (San 

Joaquin, 

Stanislaus, 

Merced, 

Sacramento, and 

Riverside 

Counties) 

Lannate SP 0.9 lbs a.i./A 5 2.7 lbs a.i./A 3 1 2.7 lbs a.i./A 

RadishesSLN (CA770495) Lannate SP 0.9 lbs a.i./A 5 1.8 lbs a.i./A 2 5 9 lbs a.i./A 

Rye Lannate LV LV

Lannate SP 

0.45 lbs a.i./A 5 1.8 lbs a.i./A 4 1 1.8 lbs a.i./A 

Sorghum (except Lannate LV 

sweet sorghum) Lannate SP 

0.45 lbs a.i./A 5 0.9 lbs a.i./A 2 1 0.9 lbs a.i./A 

Soybeans Lannate LV LV

Lannate SP 

0.45 lbs a.i./A 5 1.35 lbs a.i./A 3 1 1.35 lbs a.i./A

Soybeans SLN 

(interplanted with 

nonbearing 

almonds, plums, 

prunes, peaches, 

and walnuts) (CA770431) 

Lannate SP 0.45 lbs a.i./A 5 0.9 lbs a.i./A 2 1 0.9 lbs a.i./A 

Spinach Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 3.6 lbs a.i./A 8 3 10.8 lbs a.i./A

Sugar Beet Lannate LV LV

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 10 1 4.5 lbs a.i./A 

Summer Squash LV Lannate LV 0.9 lbs a.i./A 5 5.4 lbs a.i./A 12 1 5.4 lbs a.i./A 
-51 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

(crookneck, 

straightneck, 

scallop, vegetable 

marrow, spaghetti, 

hyotan, cucuzza, 

hechima, Chinese 

okra, bitter melon, 

balsam pear, 

balsam apple, 

Chinese 

cucumber) 

Lannate SP 

Sweet PotatoesSNL

(Aerial only) (CA780136) 

Lannate SP 0.9 lbs a.i./A 5 2.7 lbs a.i./A 3 1 2.7 lbs a.i./A 

Tangelo, Lannate LV 

Tangerine3 Lannate SP 

0.9 lbs a.i./A 5 2.7 lbs a.i./A 4 1 2.7 lbs a.i./A 

Tobacco (except Lannate LV 

shade) Lannate SP 

0.45 lbs a.i./A 5 2.25 lbs a.i./A 5 1 2.25 lbs a.i./A

Tomato Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 6.3 lbs a.i./A 16 1 6.3 lbs a.i./A 

Tomatillo Lannate LV 

Lannate SP 

0.9 lbs a.i./A 5 4.5 lbs a.i./A 5 1 4.5 lbs a.i./A 

Turf (sod farms Lannate LV 

only) Lannate SP 

0.9 lbs a.i./A 5 3.6 lbs a.i./A 4 2 7.2 lbs a.i./A 

Wheat Lannate LV LV

Lannate SP 

0.45 lbs a.i./A 5 1.8 lbs a.i./A 4 1 1.8 lbs a.i./A 

Farnam Die 

Fly (scatter 

bait) 

1 

Stimukil Fly 

Bait (scatter 

bait) 

NR 

Lurectron 

Scatterbait 

(scatter bait; 

bait stations) 

3 

Feedlots (outside) 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2

1 

NR NR N/A 

Dairies (outside) Farnam Die 

Fly (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) 

1 

Stables (outside) Farnam Die 

Fly (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) 

1 NR NR N/A 
-52 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Farnam Die 

Fly (scatter 

bait) 

1 

Stimukil Fly 

Bait (bait 

station) 

NR 

Broiler Houses 

(outside) 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2 1 

NR NR N/A 

Hog Houses 

(outside) 

Farnam Die 

Fly (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) 

1 NR NR N/A 

Farnam Die 

Fly (scatter 

bait) 

1 

Stimukil Fly 

Bait (scatter 

bait) 

NR 

Lurectron 

Scatterbait 

(scatter bait; 

bait stations; 

paste) 

3 

Livestock Barns 

(outside) 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2

1 

NR NR N/A 

Farnam Die 

Fly (scatter 

bait) 

1 

Stimukil Fly 

Bait (bait 

station; scatter 

bait) 

NR 

Lurectron 

Scatterbait 

(scatter bait; 

bait stations) 

3 

Meat Processing 

Establishments 

(outside) 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2

1 

NR NR N/A 
-53 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Farnam Die 

Fly (scatter 

bait) 

1 

Stimukil Fly 

Bait (bait 

station; scatter 

bait) 

NR 

Lurectron 

Scatterbait 

(scatter bait; 

bait stations) 

3 

Poultry Processing 

Establishments 

(outside) 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2

1 

NR NR N/A 

Farnam Die 

Fly (scatter 

bait) 

1 

Stimukil Fly 

Bait (bait 

station; scatter 

bait) 

NR 

Lurectron 

Scatterbait 

(scatter bait; 

bait stations) 

3 

Beverage Plants 

(outside) 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2

1 

NR NR N/A 

Farnam Die 

Fly (scatter 

bait) 

Canneries 1 

(outside) 

Stimukil Fly 

Bait (scatter 

bait; bait 

station) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2

NR 

NR NR N/A 
-54 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Lurectron 

Scatterbait 

(scatter bait; 

bait stations) 

3 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

1 

Farnam Die 

Fly (scatter 

bait) 

1 

Stimukil Fly 

Bait (bait 

station) 

NR 

Lurectron 

Scatterbait 

(scatter bait; 

bait stations) 

3 

Food Processing 

Establishments 

(outside) 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2

1 

NR NR N/A 

Farnam Die 

Fly (bait 

station) 

0.22 lbs 

a.i./acre 

(2 bait 

stations/500 

ft2

) 

Stimukil Fly 

Bait (bait 

station) 

2 bait 

stations/500 

ft2

Stimukil Fly 

Bait (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) 

Stimukil Fly 

Bait (brush 

on) 

NR 

Commercial use NR 

Sites (unspecified) 

Lurectron 

Scatterbait 

(scatter bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) 

3 

NR NR N/A 

Stimukil Fly 

Bait (bait 

station) 

Kennels (outside) NR 

Lurectron 

Scatterbait 

(bait station) 

2 bait 

stations/500 

ft2

3 

NR NR N/A 
-55 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 

Stimukil Fly 

Bait (bait 

station) 

NR 

Lurectron 

Scatterbait 

(bait station) 

2 bait 

stations/500 

ft2

3 

Dumpsters 

(associated with 

above uses) 

Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 

NR NR N/A 

Stimukil Fly 

Bait (bait 

station) 

NR 

Lurectron 

Scatterbait 

(bait station) 

2 bait 

stations/500 

ft2

3 

Restaurants 

(outside) 

Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 

NR NR N/A 

Stimukil Fly 

Bait (bait 

station) 

NR 

Lurectron 

Scatterbait 

(bait station) 

2 bait 

stations/500 

ft2

3 

Supermarkets 

(outside) 

Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 

NR NR N/A 

Stimukil Fly 

Bait (bait 

station) 

2 bait 

stations/500 

ft2

Commissaries NR 

(outside) 

Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 

NR NR N/A 

Stimukil Fly 

Bait (bait 

station) 

NR 

Lurectron 

Scatterbait 

(bait station) 

2 bait 

stations/500 

ft2

3 

Bakeries (outside) 

Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 

NR NR N/A 
-56 of 75-

USE PRODUCT MAX APPL. 

RATE 

MIN 

APP. 

INTERVAL1

MAX APPL. 

RATE/ 

CROP 

MAX 

NO. OF 

APPL./ 

CROP 

MAX NO. 

OF 

CROPS/ 

YEAR* 

MAX APPL. 

RATE/ 

YEAR 

Stimukil Fly 

Bait (scatter 

bait) 

Poultry houses NR 

Lurectron 

Scatterbait 

(scatter bait; 

bait stations; 

paste) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) or 2 bait 

stations/500 

ft2

3 

NR NR N/A 

Stimukil Fly 

Bait (scatter 

bait) 

NR 

Lurectron 

Scatterbait 

(scatter bait) 

3 

Commercial 

Dumpsters which 

are enclosed 

Golden 

Malrin Fly 

Killer (scatter 

bait) 

0.22 lbs 

a.i./acre 

(4 ounces of 

product/500 

ft2

) 

1 

NR NR N/A 

Stables Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 NR NR N/A 

Fast Food 

Establishments 

Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 NR NR N/A 

Warehouses Golden 

Malrin Fly 

Killer (bait 

station) 

4 bait 

stations/500 

ft2

1 NR NR N/A 

LV Low volume aerial applications (a minimum of 1 gallon of tank mixture/acre) is allowed 1

 5 days was used unless otherwise stated on the label. 

2

 Different rates depending on geographic region; the listed rates are for California. 

3

 Limited to use in CA, AZ, and HI 

SLN = California Special Local Needs (FIFRA §24(c)) 

* Based on data regarding California agriculture provided in a memo from BEAD. 

** For perennial crops, the number of cuttings per year was used. 
-57 of 75-

APPENDIX B. Toxicity Data for Methomyl: 

TABLE 1. Available Toxicity Data for Methomyl (Excluding Invalid Studies): 

TAXON ENDPOINT FORMULATION MRID 

STUDY 

CLASSIFICATION 

COMMENTS 

BIRDS 

Birds (Acute) 

Bobwhite quail 

(Colinus 

virginianus) 

LD50 = 24.2 mg 

a.i./kg-bw TGAI 00161886 Acceptable None 

Birds (Acute/Sub-Acute)

Mallard duck 

(Anas 

platyrhynchos) 

96-hr LC50 = 

3,602 mg 

a.i./kg=diet 

TGAI 45299802 Acceptable None 

Mallard duck 

(Anas 

platyrhynchos) 

96-hr LC50 = 

2,883 mg 

a.i./kg=diet 

TGAI 22923 Acceptable None 

Bobwhite quail 

(Colinus 

virginianus) 

96-hr LC50 = 

5,080 mg 

a.i./kg=diet 

TGAI 45299801 Acceptable None 

Bobwhite quail 

(Colinus 

virginianus) 

96-hr LC50 = 

1,100 mg 

a.i./kg=diet 

TGAI 22923 Acceptable None 

Ring-necked 

Pheasant 

(Phasianus 

colchicus)

96-hr LC50 = 

1,975 mg 

a.i./kg=diet 

TGAI 22923 Acceptable None 

Birds (Chronic) 

Bobwhite quail 

(Colinus 

virginianus) 

NOAEC = 150 

mg a.i./kg-diet 

LOAEC = 500 

mg a.i./kg-diet 

TGAI 41898602 Acceptable LOAEC based on fewer eggs 

laid and fewer eggs set 

MAMMALS 

Mammals (Acute) 

Rat (Rattus 

rattus) 

LD50 = 30 

mg/kg-bw TGAI 42140101 Acceptable None 

Mammals (Chronic) 

Rat (Rattus 

rattus) 

NOAEL = 3.75 

mg/kg-bw 

LOAEL = 30 

mg/kg-bw 

TGAI 43250701, 

43769401 Acceptable 

LOAEL is based on decreased 

body weight and food 

consumption and altered 

hematology parameters 

TERRESTRIAL INVERTEBRATES 

Honey bee 

(Apis mellifera) 

48-hr LD50 = 

0.28 μg a.i./bee TGAI 45093001 Acceptable Acute oral study 

Honey bee 

(Apis mellifera) 

48-hr LD50 = 

0.16 μg a.i./bee TGAI 45093001 Acceptable Acute contact study 

Wasp (Aphidius 

rhopalosiphi) 

48-hr LC50 = 

0.00027 lbs 

a.i./acre 

Formulation 

(Methomyl®

25WP) 

45133302 Supplemental 

Supplemental 

(non-guideline, but 

scientifically sound) 

Wasp (Aphidius 48-hr LC50 = Formulation 45133301 Supplemental Supplemental 
-58 of 75-

TAXON ENDPOINT FORMULATION MRID 

STUDY 

CLASSIFICATION 

COMMENTS 

rhopalosiphi) 0.00022 lbs 

a.i./acre 

(Methomyl® 20L) (non-guideline, but 

scientifically sound) 

Mite 

(Typhlodromus 

pyri)

7-day LC50 = 

0.0114 lbs 

a.i./acre 

Formulation 

(Methomyl® 20L) 45125501 Supplemental 

Supplemental 

(non-guideline, but 

scientifically sound) 

Mite 

(Typhlodromus 

pyri)

7-day LC50 = 

0.01115 lbs 

a.i./acre 

Formulation 

(Methomyl®

25WP) 

45125502 Supplemental 

Supplemental 

(non-guideline, but 

scientifically sound) 

Earthworms 

(Eisenia fetida) 

28-day LC50 = > 

12 mg a.i./kg 

dry soil (no 

mortalities at 

hoighest 

treatment 

concentration) 

Formulation 

(Methomyl® 20L) 45459201 Supplemental Supplemental 

(non-guideline, but 

scientifically sound) 

Earthworms 

(Eisenia fetida) 

14-day LC50 = 

23 mg a.i./kg 

dry soil 

TGAI 44969301 Supplemental 

Supplemental 

(non-guideline, but 

scientifically sound) 

FRESHWATER FISH 

Freshwater Fish (Acute) 

See Table 3

Freshwater Fish (Chronic) 

Fathead 

minnow 

(Pimephales 

promelas) 

NOAEC = 

0.057 mg a.i./L 

LOAEC = 

0.117 mg a.i./L 

TGAI (>99%) 131255 Acceptable Early life-stage; LOAEC 

based on reduced survival. 

Fathead 

minnow 

(Pimephales 

promelas) 

NOAEC = 

0.076 mg a.i./L 

LOAEC = 

0.142 mg a.i./L 

TGAI (>99%) 43072101 Acceptable 

Full life-cycle; LOAEC based 

on reduced growth of the 

parental and F1 generation fish 

ESTUARINE/MARINE FISH 

Estuarine/Marine Fish (Acute) 

Sheepshead 

minnow 

(Cyprinodon 

variegates) 

LC50 = 1.16 mg 

a.i./L TGAI (98.4%) 45013202 Acceptable None 

Estuarine/Marine Fish (Chronic)

Sheepshead 

minnow 

(Cyprinodon 

variegates) 

NOAEC = 

0.260 mg a.i./L 

LOAEC = 

0.490 mg a.i./L 

TGAI (98.6%) 45013202 Acceptable LOAEC based on reduction in 

total length and wet weight. 

FRESHWATER INVERTEBRATES 

Freshwater Invertebrates (Acute) 

See Table 4

Freshwater Invertebrates (Chronic) 

Daphnid 

(Daphnia 

magna) 

NOAEC = 

0.0007 mg 

a.i./L TGAI (>99%) 131254 Acceptable LOAEC based on delayed 

reproduction 
-59 of 75-

TAXON ENDPOINT FORMULATION MRID 

STUDY 

CLASSIFICATION 

COMMENTS 

LOAEC = 

0.001 mg a.i./L 

ESTUARINE/MARINE INVERTEBRATES 

Estuarine/Marine Invertebrate (Acute) 

Northern pink 

shrimp 

(Penaeus 

duorarum) 

LC50 = 0.019 

mg a.i./L TGAI (90%) 00009134 Acceptable None 

Mysid 

(Americamysis 

bahia ) 

LC50 = 0.234 

mg a.i./L TGAI (98.4%) 41441201 Acceptable None 

Grass shrimp 

(Palaemonetes 

vulgaris) 

LC50 = 0.049 

mg a.i./L TGAI (90%) 00009134 Acceptable None 

Eastern oyster 

(Crassostrea 

virginica) 

LC50 = >140 mg 

a.i./L TGAI (98.4%) 42074601 Acceptable Shell deposition study 

Mud crab 

(Neopanope 

texana) 

EC50 = 0.41 mg 

a.i./L TGAI (90%) 00009134 Acceptable None 

Estuarine/Marine Invertebrate (Chronic)

Mysid 

(Americamysis 

bahia ) 

NOAEC = 

0.029 mg a.i./L 

LOAEC = 0.59 

mg a.i./L 

TGAI (98.6%) 45013203 Supplemental 

LOAEC based on reduced 

number of young per 

surviving female 
-60 of 75-

Table 2. Summary of Acute Toxicity Values for Methomyl and Freshwater Fish. 

Species Compound 

(% a.i.)

LC50 

(96-h, μg 

a.i./L)

MRID Classification Notes:

560 400980-01 Supplemental Temp = 17̊C 

pH = 7.5 

Hardness = 40 mg/L 

640 400980-01 Supplemental Temp = 12̊C 

pH = 6.0 

Hardness = 40 mg/L 

700 400980-01 Supplemental Temp = 12̊C 

pH = 6.5 

Hardness = 40 mg/L 

1000 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 12 mg/L 

1050 400980-01 Supplemental Temp = 12̊C 

pH = 8.5 

Hardness = 40 mg/L 

1120 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

1150 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

99 

1220 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

29 1200 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

Salmo salar

Atlantic salmon 

24 1400 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

480 400980-01 Supplemental Temp = 17̊C 

pH = 6.5 

Hardness = 40 mg/L 

600 400980-01 Supplemental Temp = 17̊C 

pH = 7.5 

Hardness = 40 mg/L 

620 400980-01 Supplemental Temp = 17̊C 

pH = 8.5 

Hardness = 40 mg/L 

840 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 320 mg/L 

860 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

Lepomis 

macrochirus

Bluegill sunfish 

95 

940 400980-01 Supplemental Temp = 17̊C 

pH = 6.0 

Hardness = 40 mg/L 
-61 of 75-

Species Compound 

(% a.i.)

LC50 

(96-h, μg 

a.i./L)

MRID Classification Notes:

1050 400980-01 Supplemental Temp = 20̊C 

pH = 7.2 

Hardness = 40 mg/L 

1150 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 40 mg/L 

1200 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 40 mg/L 

2000 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 40 mg/L 

670 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 44mg/L 

29 

670 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

370 400980-01 Supplemental Temp = 20̊C 

pH = 7.4 

Hardness = 40 mg/L 

430 400980-01 Supplemental Temp = 27̊C 

pH = 7.4 

Hardness = 40 mg/L 

560 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 40 mg/L 

560 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

600 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

710 400980-01 Supplemental Temp = 20̊C 

pH = 7.2 

Hardness = 40 mg/L 

1200 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 40 mg/L 

1800 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 40 mg/L 

24 

2800 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 272 mg/L 

degradate 462,000 00009061 Supplemental Test compound is a 

degradate of 

methomyl 
-62 of 75-

Species Compound 

(% a.i.)

LC50 

(96-h, μg 

a.i./L)

MRID Classification Notes:

1500 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

99 

2200 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

Salvelinus 

fontinalis

Brook trout 

24 1220 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

95 530 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

320 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

<560 400980-01 Supplemental Temp = 25̊C 

pH = 7.4 

Hardness = 40 mg/L 

swim-up fry tested 

760 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

fingerlings tested 

Ictalurus 

punctatus

Channel catfish 

24 

1800 400980-01 Supplemental Temp = 25̊C 

pH = 7.4 

Hardness = 40 mg/L 

yolk-sac fry tested 

99 2800 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 45 mg/L 

29 1500 400980-01 Supplemental Temp = 17̊C 

pH = 7.2 

Hardness = 46 mg/L 

Pimephales 

promelas

Fathead minnow 

24 1800 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

95 1250 400980-01 Supplemental Temp = 22̊C 

pH = 7.2 

Hardness = 40 mg/L 

Micropterus 

salmoides

Largemouth bass 

24 760 400980-01 Supplemental Temp = 22̊C 

pH = 7.2 

Hardness = 40 mg/L 

860 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 40 mg/L 

1050 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 40 mg/L 

Oncorhyncus 

mykiss

Rainbow trout 

95 

1100 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 
-63 of 75-

Species Compound 

(% a.i.)

LC50 

(96-h, μg 

a.i./L)

MRID Classification Notes:

1200 400980-01 Supplemental Temp = 12̊C 

pH = 8.5 

Hardness = 40 mg/L 

1400 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 320 mg/L 

1500 400980-01 Supplemental Temp = 12̊C 

pH = 6.5 

Hardness = 40 mg/L 

1600 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

1700 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 40 mg/L 

2000 400980-01 Supplemental Temp = 7̊C 

pH = 7.4 

Hardness = 40 mg/L 

29 1200 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 40 mg/L 

1200 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

1300 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 40 mg/L 

Swim-up fry tested 

1400 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

1400 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

1-day degradation 

1400 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

3-day degradation 

1400 400980-01 Supplemental Temp = 17̊C 

pH = 7.2 

Hardness = 40mg/L 

1500 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

7-day degradation 

24 

2000 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 
-64 of 75-

Species Compound 

(% a.i.)

LC50 

(96-h, μg 

a.i./L)

MRID Classification Notes:

2100 400980-01 Supplemental Temp = 10̊C 

pH = 7.2 

Hardness = 40 mg/L 

2300 400980-01 Supplemental Temp = 10̊C 

pH = 7.2 

Hardness = 40 mg/L 

>2500 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 272 mg/L 

Flow-through test 

3200 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

Yolk-sac fry 

32,000 400980-01 Supplemental Temp = 10̊C 

pH = 7.2 

Hardness = 40 mg/L 

Eyed egg tested 
-65 of 75-

Table 3. Summary of Acute Toxicity Values for Methomyl and Freshwater Invertebrates. 

LC50 (μg 

Species a.i./L) Compound 

(% a.i.) 48-h 96-h

MRID Classification Notes:

95 88 -- 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

Chironomus 

plumosus

Midge 

24 32 -- 400980-01 Supplemental Temp = 20̊C 

pH = 7.4 

Hardness = 272 mg/L 

95 8.8 – 400980-01 Supplemental Temp = 21̊C 

pH = 7.4 

Hardness = 272 mg/L 

>99 31.7 – 19977 Acceptable Temp = 20̊C 

pH = 6.8-8.6 

Hardness = 92.8 mg/L 

Daphnia magna

Water flea 

24 5.0 – 400980-01 Supplemental Temp = 20̊C 

pH = 7.2 

Hardness = 40 mg/L 

99 -- 920 400980-01 Supplemental Temp = 17̊C 

pH = 7.1 

Hardness = 40 mg/L 

-- 720 400980-01 Supplemental Temp = 17̊C 

pH = 7.4 

Hardness = 40 mg/L 

-- 1050 400980-01 Supplemental Temp = 12̊C 

pH = 7.4 

Hardness = 274 mg/L 

Flow-through test 

1050 -- 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

1050 -- 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 1-

day degradation 

750 -- 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 3-

day degradation 

Gammarus 

pseudolimnaeus

scud 

24 

340 -- 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 7-

day degradation 

95 – 343 400980-01 Supplemental Temp = 7.0̊C 

pH = 7.5 

Hardness = 42 mg/L 

Isogenus sp. 

Stonefly 

24 – 29 400980-01 Supplemental Temp = 7.0̊C 

pH = 7.5 

Hardness = 42 mg/L 
-66 of 75-

LC50 (μg 

Species a.i./L) Compound 

(% a.i.) 48-h 96-h

MRID Classification Notes:

95 -- 69 400980-01 Supplemental Temp = 7.0̊C 

pH = 7.5 

Hardness = 40 mg/L 

Pteronarcella 

badia

Stonefly 

24 -- 60 400980-01 Supplemental Temp = 7.0̊C 

pH = 7.5 

Hardness = 40 mg/L 

95-98 – 34 400946-02 Acceptable Temp = 7.0̊C 

pH = N/A 

Hardness = N/A 

Skwala sp. 

Stonefly 

24 – 29 400946-02 Acceptable Temp = 7.0̊C 

pH = N/A 

Hardness = N/A 
-67 of 75-

APPENDIX C. Schematic for Assessing Exposure from Methomyl Scatter Bait Uses. 

For scatter bait uses, this assessment considers a 10-hectare plot that has 50% impervious and 

50% pervious land cover and a 160,000 ft2

 commercial structure. If a 10-foot wide area around 

the structure is treated with scatter bait, this results in 16,400 ft2

 being treated, which is 1.5% of 

the entire 10-hectare plot and 3% of the 5-hectare impervious area (including the commercial 

structure). If the scatter bait is applied at the maximum single application rate of 0.25 lbs 

a.i./500 ft2, then a total of 8.2 lbs a.i. will be applied to the plot. This assessment approach is 

likely conservative for a typical scatter bait application because of the following assumptions: 1) 

the structure involved in the treatment is a large, warehouse-type retailer; 2) the treatment area 

includes an area surrounding the entire structure; 3) and the treatment area is 10 feet wide. 

~1,038 ft 

~1,038 ft

~734 ft

~734 ft

~400 ft

Pervious Land Cover

Commercial Structure

Scatter Bait Application Area (10 ft wide)

Impervious Land Cover

~400 ft
-68 of 75-

APPENDIX D. Major Environmental Degradates of Methomyl. Table D.1. Chemical Names, Structures, and Maximum Reported Amounts of Methomyl’s Major Degrad

Code Name/ 

Synonym Chemical NameA Chemical Structure Study Type MRID Ma

%A

PARENT

Methomyl 

IUPAC: S-methyl (EZ)-N-(methylcarbamoyloxy)thioacetimidate CAS: Methyl N-[[(methylamino)carbonyl]oxy]ethanimidothioate CAS-no: 16752-77-5 

Formula: C5H10N2O2S 

MW: 162.21 g/mol 

N

O

O

N

S

H

(syn-methomyl displayed) 

MAJOR (>10%) DEGRADATES

Hydrolysis -pH 9 131249 

22439 

Aqueous photolysis 161885 

8568 

Aerobic soil 43217901 

45473401 

Anaerobic soil 43217902 

Methomyl oxime 

S-methyl-N-hydroxythioacetimidate Formula: C3H7NOS 

MW: 105.16 g/mol 

O

N

S

H

(syn-methomyl oxime displayed) 

Aerobic aquatic 43325401 

Aqueous photolysis 161885 Soil photolysis 163745 

Acetonitrile 

Methyl cyanide; cyanomethane Formula: C2H3N 

MW: 41.05 g/mol 

N

Aerobic aquatic 43325401 21 

27 (

Acetamide 

Ethanamide; acetic acid amide Formula: C2H5NO 

MW: 59.07 g/mol NH2

O

Aerobic aquatic 43325401 

Carbonate 

Carbonate Formula: CO32-MW: 60.01 g/mol 

O

-O O

Aerobic aquatic 43325401 
-69 of 75-

Code Name/ 

Synonym Chemical NameA Chemical Structure Study Type MRID Ma

%A

Aqueous photolysis 22439 

8568 

Aerobic soil 43217901 

45473401 

Anaerobic soil 43217902 

Carbon dioxide 

Carbon dioxideFormula: CO2

MW: 44.01 g/mol O O

Aerobic aquatic 43325401 4

A. IUPAC and CAS chemical names were sourced from the Compendium of Pesticide Common Names (Copyright © 1995–2009 Alan Wood). Online 

http://www.alanwood.net/pesticides/ 
-70 of 75-

APPENDIX E: Data Call-In Tables. 

The Environmental Fate and Effects Division (EFED) has completed a Data Call-In (DCI) table 

for the methomyl environmental fate and effects data gaps identified in Registration Review. 

The attached DCI table, which includes the guideline number and study title for required data, 

also provides a rationale for requiring the data, an explanation of how the data will be used, and a 

brief description of how the data could impact the Agency’s future decision-making. 

Guideline Number: 835.2240 

Study Title: Photodegradation in Water 

Rationale for Requiring the Data 

The Agency has a limited understanding of how methomyl behaves in clear, aquatic environments under 

irradiation. Depending on how quickly, to what extent, and to which transformation products the 

compound degrades, methomyl may or may not pose potential exposure concern in water. Submitted 

aqueous photolysis studies of methomyl were invalid (MRID 8844), had poor material balances (MRID 

22439, 161885) or did not analyze for transformation products (MRID 43823305). Because methomyl 

photodegradation in water is not well understood, the Agency is requiring an OCSPP guideline-compliant 

aqueous photolysis study conducted similarly to MRID 43823305 with quantification and identification 

of the transformation products as well as analysis of indirect photolysis resulting from the presence of 

dissolved oxidants. 

Practical Utility of the Data 

How will the data be used? 

Aqueous photolysis data will facilitate a better understanding of the fate of methomyl residues in water. 

If data indicate that photodegradation occurs rapidly in shallow, clear, well-lit water and produces 

nontoxic transformation products, then the Agency could potentially determine that methomyl residues of 

concern do not persist in water under these conditions. If data indicate that photodegradation is not 

appreciable in shallow, clear, well-lit water or that the transformation products are of similar or higher 

toxicity than the parent compound, then the Agency could conclude that methomyl residues of concern 

persist in water. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the requested data, methomyl will be conservatively assumed stable to photolysis in 

water bodies. Risk assessment conclusions and associated labeled use precautions and/or restrictions 

could be made less restrictive if the required data indicate that methomyl is rapidly photodegraded to 

nontoxic transformation products or could be made more restrictive if the required data indicate that 

methomyl is photodegraded to transformation products more toxic than the parent compound. 

Guideline Number: 835.4300 

Study Title: Aerobic Aquatic Metabolism 

Rationale for Requiring the Data 

The Agency has a limited understanding of how methomyl behaves in aerobic aquatic environments once 

applied. Depending on how quickly, to what extent, and to which transformation products the compound 

degrades, methomyl may or may not pose potential exposure concern in water. An aerobic aquatic 

metabolism study of methomyl (MRID 43325401) was submitted to the Agency. However, the results of 

the study are uncertain due to poor material balances. Because methomyl degradation in water is not well 

understood, the Agency is requiring an OCSPP guideline-compliant aerobic aquatic metabolism study 

with systems maintained at pH values below seven. 
-71 of 75-

Practical Utility of the Data 

How will the data be used? 

Aerobic aquatic metabolism data will facilitate a better understanding of the fate of methomyl residues in 

water. If data indicate that degradation in aerobic conditions occurs rapidly in water and produces 

nontoxic transformation products, then the Agency could potentially determine that methomyl residues of 

concern do not persist in water under aerobic conditions. If data indicate that degradation is not 

appreciable in water or that the transformation products are of similar or higher toxicity than the parent 

compound, then the Agency could conclude that methomyl residues of concern persist in water under 

aerobic conditions. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the requested data, methomyl aerobic aquatic metabolism half-lives will be 

conservatively assumed two-fold greater than aerobic soil metabolism half-lives. If the required data 

indicate that methomyl in aerobic aqueous environments is rapidly biodegraded, then risk assessment 

conclusions and associated labeled use precautions and/or restrictions could be made less restrictive. 

Guideline Number: 835.4400 

Study Title: Anaerobic Aquatic Metabolism 

Rationale for Requiring the Data 

The Agency has a limited understanding of how methomyl behaves in anaerobic aquatic environments 

once applied. Depending on how quickly, to what extent, and to which transformation products the 

compound degrades, methomyl may or may not pose potential exposure concern in water. An anaerobic 

aquatic metabolism study of methomyl (MRID 00073214) was submitted to the Agency. However, the 

results of the study are uncertain due to poor material balances and the inability to detect methomyl in 

any sample including those collected on the day of treatment (likely due to rapid degradation in the 

presence of ferrous iron). Because methomyl degradation in anaerobic surface water systems is not well 

understood, the Agency is requiring an OCSPP guideline-compliant anaerobic aquatic metabolism study 

with three systems maintained at pH values below seven, two of which that are iron-poor and one of 

which that is iron-rich. The radioactivity in the dosing solution should be confirmed as well as in the day 

0 systems as soon after dosing as possible. 

Practical Utility of the Data 

How will the data be used? 

Anaerobic aquatic metabolism data will facilitate a better understanding of the fate of methomyl residues 

in water. If data indicate that degradation in anaerobic conditions occurs rapidly in acidic aquatic 

systems and produces nontoxic transformation products, then the Agency could potentially determine that 

methomyl residues of concern do not persist in these systems. If data indicate that degradation is not 

appreciable in acidic aquatic systems or that the transformation products are of similar or higher toxicity 

than the parent compound, then the Agency could conclude that methomyl residues of concern persist in 

acidic aquatic systems under anaerobic conditions. If data indicate that degradation rates in acidic, 

anaerobic aquatic systems are largely determined by the availability of ferrous iron, then the Agency 

could potentially refine its conclusions to consider additional environmental conditions. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the requested data, methomyl anaerobic aquatic metabolism half-lives will be 

conservatively assumed two-fold greater than anaerobic soil metabolism half-lives. If the required data 

indicate that methomyl in anaerobic aquatic environments is rapidly biodegraded to nontoxic degradation 

products, including in acidic, ferrous iron-poor conditions, then risk assessment conclusions and 

associated labeled use precautions and/or restrictions could be made less restrictive. 
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Guideline Number: 850.2100 

Study Title: Avian Acute Oral Toxicity Test 

Rationale for Requiring the Data 

Acceptable acute avian oral toxicity data were submitted for exposures of bobwhite quail and mallard 

ducks to methomyl; however, data are not available for a passerine species, which is now required under 

the 40 CFR Part 158 (Oct. 26, 2007) data requirements for conventional pesticides. The new Part 158 

data requirements specify that acute avian oral toxicity data be submitted for either mallard duck or 

bobwhite quail and a passerine species. Therefore, an avian oral toxicity test is required for passerine 

birds, as specified in 40 CFR Part 158. A passerine study protocol must be submitted for review by the 

Agency prior to initiation of this study. 

Practical Utility of the Data 

How will the data be used? 

Acute avian oral toxicity data for passerine species will be used to refine the screening-level assessment 

by determining whether there are differences in avian species sensitivity to methomyl between passerines 

and upland game and waterfowl species. If oral acute toxicity data are not submitted for passerines, risk 

will be assumed for all passerine species. 

How could the data impact the Agency’s future decision-making? 

If future endangered species risk assessments are performed without these data, the Agency would have 

to assume that methomyl “may affect” listed passerine birds directly (and listed species from other taxa 

indirectly), and use of methomyl and its formulated products may need to be restricted in areas where 

listed species could be exposed. The lack of these data will limit the flexibility the Agency and registrants 

have in coming into compliance with the Endangered Species Act and could result in use restrictions for 

methomyl use that are unnecessarily severe. 

Guideline Number: 850.2300 

Study Title: Avian Reproduction Test (Mallard duck) 

Rationale for Requiring the Data 

Under the 40 CFR Part 158 (Oct. 26, 2007) data requirements for conventional pesticides avian 

reproduction data are required on waterfowl and upland game species (OCSPP 850.2300). Currently 

acceptable data for methomyl are only available for an upland game species (Bobwhite quail). Data from 

another N-methyl carbamate (i.e., thiodicarb) suggest that mallard ducks may be more sensitive than 

bobwhite quail on a chronic-exposure basis. The chronic toxicity data available for birds indicate that 

mallard ducks (NOAEC = 500 mg a.i./kg-diet; LOAEC = 1,000 mg a.i./kg-diet, based on a reduction in 

number of eggs laid) (MRID 43313004) are more sensitive to thiodicarb than bobwhite quail (no 

reproductive effects seen at any concentration tested; highest concentration tested = 1,000 mg a.i./kgdiet) (MRID 43313003). Additionally, Bobwhite quail appear more sensitive to methomyl than to 

thiodicarb based on chronic exposure (for methomyl, NOAEC = 150 mg a.i./kg-diet; LOAEC = 500 mg 

a.i./kg-diet, based on fewer eggs laid and eggs set) (MRID 41898602). Therefore, based on available 

data, it is reasonable to assume that mallard ducks may be more sensitive to methomyl than Bobwhite 

quail on a chronic exposure basis. Since additional avian reproduction data for methomyl could result in 

a lower avian reproductive endpoint, and, thus, could alter risk conclusions for birds from the use of 

methomyl, EFED recommends requesting these data for methomyl at this time. 

Practical Utility of the Data 

How will the data be used? 

Reproduction data for mallard ducks will be used to reduce uncertainties associated with using data from 

a potentially-less sensitive species (Bobwhite quail) to assess chronic risks to birds and by extension to 

terrestrial-phase amphibians and reptiles from methomyl exposure. If reproduction data are not 

submitted for mallard ducks, the risks to birds from chronic exposure will be assumed to be higher than 
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predicted when using the chronic toxicity endpoint from Bobwhite quail. 

How could the data impact the Agency’s future decision-making? 

If future endangered species risk assessments are performed without these data, the Agency would have 

to assume that methomyl “may affect” listed birds, reptiles, and terrestrial-phase amphibians directly (and 

listed species from other taxa indirectly), and use of methomyl and its formulated products may need to 

be restricted in areas where listed species could be exposed. The lack of these data will limit the 

flexibility the Agency and registrants have in coming into compliance with the Endangered Species Act 

and could result in use restrictions for methomyl use that are unnecessarily severe. 

Guideline Numbers: 850.4100 and 850.4150 

Study Title: Terrestrial Plant Toxicity Tests (Tier I) 

Rationale for Requiring the Data 

Terrestrial plant toxicity studies and associated risk analysis of plants are required for registration of 

pesticides with outdoor uses (CFR Part 158). For terrestrial plants, Tier II studies are required when 

potential concerns are triggered (i.e., when there is some indication that there may be significant toxicity 

to plants). These indicators may be an herbicidal mode of action or statements on the label indicating 

toxicity to plants. None of these indicators are present for methomyl. 

Several efficacy studies available for methomyl supply information on effects to plants after methomyl 

applications. None of the studies showed any adverse effects to plants at the highest treatment levels 

tested. However, because none of the studies addressed potential risks to monocots or effects on seedling 

emergence and some N-methyl carbamates are plant auxins that are used to thin fruit (e.g., carbaryl), 

risks to plants from the use of methomyl cannot be precluded using the available data. Tier I seedling 

emergence and vegetative vigor studies (OCSPP Guidelines 850.4100 and 850.4150) are, therefore, 

required. 

Practical Utility of the Data 

How will the data be used? 

Tier I vegetative vigor and seedling emergence data for terrestrial plants will be used to determine the 

potential for methomyl to affect non-target plant species in the terrestrial environment. In the absence of 

data specific for these plants, risk to terrestrial plants will be assumed. 

How could the data impact the Agency’s future decision-making? 

If future endangered species risk assessments are performed without these data, the Agency would have 

to presume risk to non-target terrestrial plants from use of methomyl. Therefore, use of methomyl and its 

formulated products may need to be restricted in areas where listed species could be exposed. The lack of 

these data will limit the flexibility the Agency and registrants have in coming into compliance with the 

Endangered Species Act and could result in use restrictions for methomyl that are unnecessarily severe. 

Guideline Number: 850.4400 

Aquatic Plant Growth Tier I Study (Vascular Aquatic Plant) 

Rationale for Requiring the Data 

Aquatic (both vascular and non-vascular species) toxicity studies and associated risk analysis of plants 

are required for registration of pesticides with outdoor uses (CFR Part 158). There are currently no data 

available to determine the levels of methomyl that could result in effects to aquatic vascular plants. 

Therefore, effects on non-target aquatic plants cannot be discounted, and the level of risk is unknown. 

Therefore, an aquatic vascular plant study is required as specified in 40 CFR Part 158 (OCSPP Guideline 

850.4400). 
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Practical Utility of the Data 

How will the data be used? 

Data from Tier I aquatic plant toxicity studies will be used to estimate potential risks to aquatic plants 

from methomyl exposure. The data will reduce uncertainties associated with the current risk assessment 

for plants and will improve our understanding of the potential effects of methomyl use on aquatic plants. 

Because plants form the basis of most habitats and significantly contribute to overall environmental 

quality, a solid understanding of the potential risks to aquatic plants is essential for sound environmental 

management. The data will also be used in determining whether a “may affect” to Federally-listed 

threatened and endangered species is likely under the Endangered Species Act. 

Additionally, the need for labeling language to mitigate effects on non-target aquatic plant species is 

unknown. Results of this study would be used to determine if surface water exposure concentrations, due 

to run-off, are below levels of concern at the current label rates and to identify what, if any, label 

language is needed to mitigate identified risks. 

How could the data impact the Agency’s future decision-making? 

Without aquatic plant growth data for methomyl, the Agency cannot determine the levels of methomyl 

that result in effects to vascular aquatic plants. Until these data are available, the registration decision 

will be based on the information listed on the label. The lack of these data will limit the flexibility the 

Agency and registrants have in coming into compliance with the Endangered Species Act, and could 

result in use restrictions for methomyl which may otherwise be avoided, or which are unnecessarily 

severe.

Guideline Number: 850.5400 

Aquatic Plant Growth Tier I Study (Non-vascular Aquatic Plant) 

Rationale for Requiring the Data 

Aquatic (both vascular and non-vascular species) toxicity studies and associated risk analysis of plants 

are required for registration of pesticides with outdoor uses (CFR Part 158). There are currently no data 

available to determine the levels of methomyl that could result in effects to aquatic non-vascular plants. 

Therefore, effects on non-target aquatic plants cannot be discounted, and the level of risk is unknown. 

Therefore, an aquatic non-vascular plant study is required as specified in 40 CFR Part 158 (OCSPP 

Guideline 850.5400). 

Practical Utility of the Data 

How will the data be used? 

Data from Tier I aquatic plant toxicity studies will be used to estimate potential risks to aquatic plants 

from methomyl exposure. The data will reduce uncertainties associated with the current risk assessment 

for plants and will improve our understanding of the potential effects of methomyl use on aquatic plants. 

Because plants form the basis of most habitats and significantly contribute to overall environmental 

quality, a solid understanding of the potential risks to aquatic plants is essential for sound environmental 

management. The data will also be used in determining whether a “may affect” to Federally-listed 

threatened and endangered species is likely under the Endangered Species Act. 

Additionally, the need for labeling language to mitigate effects on non-target aquatic plant species is 

unknown. Results of this study would be used to determine if surface water exposure concentrations, due 

to run-off, are below levels of concern at the current label rates and to identify what, if any, label 

language is needed to mitigate identified risks. 

How could the data impact the Agency’s future decision-making? 

Without aquatic plant growth data for methomyl, the Agency cannot determine the levels of methomyl 
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that result in effects to non-vascular aquatic plants. Until these data are available, the registration 

decision will be based on the information listed on the label. The lack of these data will limit the 

flexibility the Agency and registrants have in coming into compliance with the Endangered Species Act, 

and could result in use restrictions for methomyl which may otherwise be avoided, or which are 

unnecessarily severe.