Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review of Thiodicarb 

(3EZ,12EZ)-3,7,9,13-tetramethyl-5,11-dioxa-2,8,14-trithia-4,7,9,12-

tetraazapentadeca-3,12-diene-6,10-dione 

CAS Registry Number: 59669-26-0 

PC Code: 114501 

Prepared by:

Melissa Panger, Ph.D., Biologist 

Greg Orrick, Environmental Scientist 

Reviewed by: 

Anita Pease, Senior Biologist 

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

Elizabeth Behl, 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

August 31, 2009 

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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.................................................................................... 11 

3.3.1. Mobility...................................................................................................................... 12 

3.3.2. Degradation................................................................................................................ 13 

3.3.3. Field Dissipation ........................................................................................................ 14 

3.3.4. Bioaccumulation ........................................................................................................ 14 

3.3.5. Environmental Fate and Transport of Methomyl....................................................... 15 

3.4. Water Quality.................................................................................................................... 19 

4. Receptors.................................................................................................................................. 19 

4.1. Effects to Aquatic Organisms ........................................................................................... 20

4.2. Effects to Terrestrial Organisms ....................................................................................... 24

4.3. Incident Databases Review............................................................................................... 28 

4.4. Ecosystems Potentially at Risk ......................................................................................... 31

5. Assessment Endpoints ............................................................................................................. 31 

6. Conceptual Model.................................................................................................................... 31 

6.1. Risk Hypothesis ................................................................................................................ 32 

6.2. Conceptual Diagram ......................................................................................................... 32 

7. Analysis Plan ........................................................................................................................... 34 

7.1. Stressors of Concern ......................................................................................................... 35 

7.2. Measures of Exposure....................................................................................................... 35 

7.3. Measures of Effect ............................................................................................................ 36 

7.4. Integration of Exposure and Effects ................................................................................. 37 

7.5. Deterministic and Probabilistic Assessment Methods...................................................... 38 

7.6. Endangered Species Assessments..................................................................................... 38 

7.7. Drinking Water Assessment ............................................................................................. 38 

7.8. Preliminary Identification of Data Gaps........................................................................... 39 

7.8.1. Fate............................................................................................................................. 39 

7.8.2. Effects Data for Thiodicarb ....................................................................................... 41 

7.8.3. Effects Data for Methomyl ........................................................................................ 44 

8. References................................................................................................................................ 48 

APPENDIX A. Toxicity Data for Thiodicarb and Methomyl:.................................................... 58 

APPENDIX B. Major Organic Environmental Degradates of Thiodicarb.................................. 73 

APPENDIX C: Data Call-In Tables. ........................................................................................... 75 

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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 thiodicarb, considering its currently registered 

uses. Thiodicarb is a restricted use carbamate insecticide registered for use on cole crops, cotton, 

a variety of leafy vegetables, soybeans, sweet corn, ornamentals (including trees), and non-crop 

areas (which include wastelands, roadsides, rights-of-way, grassways, shelter belts, and 

fencerows). This document will provide a plan for analyzing data relevant to thiodicarb 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 thiodicarb. 

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 thiodicarb 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 

Thiodicarb was first registered in the United States in 1984 for use as an insecticide. Dozens of 

hazard and exposure assessments were conducted in the 1970s and 1980s in support of 

experimental use permits and proposed new uses; however, risk was not quantified in these 

assessments. FIFRA Section 3 new use assessments were conducted in 1990 (record no. 

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2588559) and 1994 (DP barcode 206596) for a proposed use on apples, the former of which was 

not completed due to lack of data at the time of the assessment. The latter assessment identified 

acute risk to mammals, aquatic invertebrates, and federally listed birds and estuarine/marine fish, 

as well as chronic risk to freshwater invertebrates. Data were insufficient to assess chronic risk 

to birds and fish and to assess risk to terrestrial and vascular aquatic plants. No risk was 

identified for non-vascular aquatic plants. Chronic risk to mammals and risk to terrestrial 

invertebrates were not quantified. 

A national-level ecological risk assessment was completed to support the reregistration eligibility 

decision (RED) for thiodicarb in 1998 (USEPA 1998). Risk was evaluated using exposure 

estimates and ecological toxicity endpoints for thiodicarb as well as for the active ingredient 

degradate methomyl (PC code 090301). The RED indicated that the major concerns posed by 

the use of thiodicarb are chronic risk to non-target avian, mammalian, and freshwater 

invertebrate organisms. More specifically, following the use of thiodicarb, the RED identified 

chronic risk to terrestrial animals and aquatic invertebrates from exposure to thiodicarb or to 

methomyl, chronic risk to fish from exposure to methomyl, acute risk to aquatic invertebrates 

from exposure to thiodicarb or to methomyl, and acute risk to terrestrial animals and fish from 

exposure to methomyl. Hazard rather than risk to terrestrial invertebrates was evaluated. 

Ecological risk mitigations identified in the thiodicarb RED included: 

• Limiting the number of 1.0 lb a.i./A single applications per season to four for cole crops 

and to six for cotton; 

• Establishing buffer zones for aerial, ground, and ultra low volume applications; and 

• Adding label advisories promoting: 

o Integrated Pest Management, 

o Addressing the hazards to bees and other nontarget organisms, 

o Addressing the potential for ground water contamination, and 

o Requiring that the potential for surface water contamination via spray drift be 

minimized. 

More recently, FIFRA Section 3 new use assessments were conducted in 2006 and 2007 for 

proposed cotton seed treatments (DP barcode 325684) and soybean seed treatments (DP barcode 

342879), respectively. 

• The assessment of the proposed cotton seed treatment identified acute and chronic risk to 

aquatic invertebrates from exposure to methomyl and to birds and mammals from 

exposure to thiodicarb and/or methomyl. 

• The assessment of the proposed soybean seed treatment identified acute and chronic risk 

to birds from methomyl, acute and chronic risk to mammals from thiodicarb and/or 

methomyl, acute risk to freshwater fish from methomyl, acute risk to aquatic 

invertebrates from thiodicarb and/or methomyl, and chronic risk to freshwater 

invertebrates from methomyl. No acute risk was identified to estuarine/marine fish; no 

chronic risk was identified to freshwater or estuarine/marine fish; and no risk was 

identified for non-vascular aquatic plants. Chronic risk to estuarine/marine invertebrates 

and risk to vascular aquatic plants and terrestrial plants was not quantified due to lack of 

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data. Combined foliar and seed treatments to soybeans resulted in additional risk to all 

assessed taxa than for seed treatment alone. 

2.2.2. Drinking Water Exposure Assessments 

The most recent drinking water exposure assessments conducted specifically for thiodicarb were 

Tier I and Tier II assessments conducted in May, 1997 in support of the 1998 RED (USEPA 

1997a and 1997b; DP barcodes not reported). The Tier II assessment reported the estimated 

drinking water concentrations (EDWC) of thiodicarb and methomyl in surface water listed in 

Table 2.1 for the maximum use pattern of thiodicarb. No monitoring data were available for 

thiodicarb in ground or surface water; however, 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). 

Table 2.1. Tier II EDWCs of thiodicarb and methomyl in surface water from maximum 

use patterns of thiodicarb in 1997 (USEPA 1997b).

Use (modeled rate) Active Ingredient Maximum (μg/L) 90-day mean 

(μg/L)

1-in-10-year annual 

mean (μg/L) 

Cotton (6 applications @ Thiodicarb 21 9 2.3 

0.9 lbs a.i./A) Methomyl 151 120 26 

A drinking water assessment was recently conducted 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 EDWCs for the 

maximum use pattern are listed in Table 2.2. 

Table 2.2. Tier II EDWCs of methomyl in surface water from maximum use patterns of 

thiodicarb in 2007 (USEPA 2007a).

Use (modeled rate) Active Ingredient(s) 

Applied 

1-in-10-year peak

(μg/L)

1-in-10-year annual 

mean (μg/L)

30-year mean 

(μg/L) 

Corn (10 applications @ Thiodicarb 86 2.0 1.4 

0.75 lbs a.i./A) Thiodicarb & methomylA 69 2.1 1.5 

A These EDWCs represent exposure to methomyl following separate applications of thiodicarb and methomyl on 

the same crop. 

A cumulative human health risk assessment (CRA) for the N-methyl carbamate (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 thiodicarb and methomyl, presuming the risk mitigations proposed in 

the individual chemical REDs are implemented. 

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3. Stressor Source and Distribution

Thiodicarb is registered for use on a variety of agricultural, ornamental, and non-agricultural 

areas. The parent compound degrades mainly to methomyl, which is also a pesticide active 

ingredient (PC Code 090301). 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 thiodicarb, methomyl will be considered in the ecological risk assessment 

conducted as part of the Registration Review process only as the main degradate of thiodicarb 

rather than as a primary active ingredient or as a degradate of other pesticide products. Modeled 

exposure estimates resulting from thiodicarb usage will reflect the predicted environmental fate 

of either thiodicarb and methomyl separately or together as methomyl equivalents, depending on 

the toxicity differential of the compounds for assessed organisms. Potential simultaneous use of 

methomyl within the same areas as thiodicarb will be addressed in the ecological and endangered 

species risk assessments for the methomyl registration review rather than in the assessments for 

the thiodicarb registration review. 

The residues of concern for exposure and risk assessment will be reconsidered prior to analysis. 

In the absence of data or structural activity relationships indicating low toxicity concerns for the 

major degradates of thiodicarb and methomyl, they will be assumed of equal toxicity as the 

parent. 

3.1. Mechanism of Action 

Both thiodicarb and its degradate methomyl are N-methyl carbamate insecticides. Carbamate 

insecticides act by inhibiting acetylcholinesterase and reducing the degradation of the 

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 

Thiodicarb was first registered in the U.S. in 1984. Thiodicarb is currently registered for use on 

broccoli, cabbage, cauliflower, cotton, a variety of leafy vegetables, soybeans, sweet corn, 

ornamentals and trees (except forest), and non-crop areas (i.e., wastelands, roadsides, rights-ofway, grassways, shelter belts, and fencerows). There are currently six thiodicarb products 

registered in the U.S.; one product is a technical grade for use in the manufacture of end-use 

products and five are end-use products (see Table 3.1). One of the products [AerisTM SeedApplied Insecticide/ Nematicide (264-1057)] contains two active ingredients (thiodicarb and 

imidacloprid). All of the remaining thiodicarb products contain only one active ingredient 

(thiodicarb). All of the products are Restricted Use Pesticides (RUP). 

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TABLE 3.1. Summary of Thiodicarb Products Registered in the U.S. 

Product Name (EPA Reg. No.) Registrant Percent Active 

Ingredient Use 

Larvin® Technical 

(264-343) Bayer CropScience Thiodicarb: 95% Formulation of insecticides

AerisTM Seed-Applied 

Insecticide/Nematicide 

(264-1057) 

Bayer CropScience Thiodicarb: 24% 

Imidacloprid: 24% 

EXP3 Seed Applied 

Nematicide/Insecticide 

(264-1048) 

Bayer CropScience Thiodicarb: 34% 

Cotton 

Soybean 

Larvin® 3.2 Thiodicarb 

Insecticide/Ovicide 

(264-379) 

Bayer CropScience Thiodicarb: 34% 

Larvin® DF Thiodicarb 

Insecticide/Ovicide 

(264-378) 

Bayer CropScience Thiodicarb: 80% 

Larvin® DF WSP Thiodicarb 

Insecticide/Ovicide 

(264-530) 

Bayer CropScience Thiodicarb: 80% 

Broccoli 

Cabbage 

Cauliflower 

Cotton 

Leafy Vegetables 

Soybeans 

Sweet Corn 

Ornamentals 

Trees 

Non-crop Areas 

Thiodicarb products include aqueous flowable, dry flowable concentrate (water dispersible 

granules), and flowable formulations. According to the labels, thiodicarb can be applied via 

ground [including irrigation systems (center pivot and solid set only)] and aerial equipment and 

as a seed treatment (cotton and soybean only). Thiodicarb can be used nationally (i.e., there are 

no geographic restrictions on where it can be used). The maximum single application rate 

allowed per use ranges from 0.09 lb a.i./acre (cotton seed treatment) to 1 lb a.i./acre (broccoli, 

cabbage, and cauliflower, foliar use) (see Table 3.2). The maximum application rate allowed per 

season ranges from 1.5 lb a.i./acre/season (leafy vegetables, foliar use) to 7.5 lb a.i./acre/season 

(sweet corn, foliar use). The maximum number of applications allowed per season, depending 

on the use, ranges from four (broccoli, cabbage, and cauliflower) to six (cotton, ornamentals and 

trees, and non-crop areas). The maximum number of applications allowed for leafy vegetables, 

sweet corn, and soybeans is not specified on the labels. The minimum application interval 

ranges from 1-day (sweet corn) to 14-day (non-crop areas) depending on the use. The minimum 

application interval is not specified on the labels for broccoli, cabbage, cauliflower, leafy 

vegetables, or ornamentals and trees. Conservative assumptions will be made in the absence of 

labeled directions. 

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TABLE 3.2. Summary of Thiodicarb Application Methods and Rates. 

PRODUCT FORMULATION APPLICATION 

METHOD USE 

MAX 

SINGLE 

APPL RATE 

(lb a.i./acre)

MAX 

NUMBER 

OF APPL/ 

SEASON 

MAX APPL 

RATE/ 

SEASON 

(lb a.i./acre)1

MIN APPL 

INTERVAL

Foliar Applications 

Broccoli 

Cabbage 

Cauliflower

1.0 4 4.0 Not stated 

Cotton 0.90 6 

5.4 (except in 

CA and AZ = 

1.8) 

7-day (at 0.9 

lb a.i./A rate) 

Leafy 

Vegetables2 0.75 NS 1.5 Not stated 

Soybeans 0.75 NS 3.0 7-day (at 0.75 

lb a.i./A rate) 

Sweet Corn 0.75 NS 7.5 1-day 

Ornamentals 

and Trees3 0.75 6 4.5 Not stated 

Larvin® 3.2 Aqueous flowable 

- Ground 

- Aerial 

- Sprinkler irrigation 

system (center pivot 

and solid set only) 

Non-crop 

Areas4 0.75 6 4.5 14-day 

Larvin® DF 

Dry flowable 

concentrate (water 

dispersible granule) 

- Ground 

- Aerial 

- No irrigation 

systems 

Larvin® DF 

WSP 

Dry flowable 

concentrate (water 

dispersible granule) 

- Ground 

- Aerial 

- No irrigation 

systems 

Same as above 

Seed Treatments 

Cotton 

(delinted 

seed only) 

0.095 1 (as a seed 

treatment) 

5.4 (except in 

CA and AZ = 

1.8) 

Not 

applicable AerisTM Flowable Soil incorporated 

(>1 inch) 

Soybeans 0.1256 1 (as a seed 

treatment) 3.0 Not applicable 

Cotton 

(delinted 

seed only) 

0.1357 1 (as a seed 

treatment) 

5.4 (except in 

CA and AZ = 

1.8) 

Not 

applicable EXP3 Flowable Soil incorporated 

(>1 inch) 

Soybeans 0.1258 1 (as a seed 

treatment) 3.0 Not applicable 1

 Maximum application rates are for seed treatments and foliar application combined. 

2

 Leafy vegetables include: Amaranth (Chinese spinach), arugula, cardoon, celery, Chinese celery, celtuce, chervil, 

chrysanthemum, corn salad, cress, dandelion, dock (sorrel), endive (escarole), Florence fennel, lettuce (head, leaf), 

orach, parsley, purslane, radicchio, rhubarb, spinach, and Swiss chard. 

3

 Includes trees (except forest), shrubs, herbaceous bedding plants, and non-bearing fruit trees in commercial 

greenhouses, nurseries, and landscapes. Non-bearing fruit trees include citrus, nut crops, pome fruits, and stone 

fruits. 

4

 Includes wastelands, roadsides, rights-of-way, grassways, shelter belts, and fencerows. 5 1 gallon of product = 2.5 lbs a.i.; the maximum application rate on the proposed label = 25.6 fl oz of 

product/hundredweight of seed; 18 lb seed/acre (from USEPA, 2006); 25.6 fl oz = 0.20 gallon; 0.20 x 2.5 lb = 0.50 

lb a.i./hundredweight of seed; 

 (18 lbs seed/acre)(0.50 lbs a.i./100 lbs seed) = 0.09 lbs a.i./acre. 

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6

 1 gallon of product = 2.5 lb a.i.; the maximum application rate on the proposed label = 6.4 fl oz of 

product/hundredweight of seed; 100 lb seed/acre (from http://www.nsrl.uiuc.edu/aboutsoy/production02.html); 6.4 fl 

oz = 0.05 gallon; 0.05 x 2.5 lb = 0.125 lb a.i./acre. 

7

 1 gallon of product = 3.2 lbs a.i.; the maximum application rate on the proposed label = 30 fl oz of 

product/hundredweight of seed; 18 lb seed/acre (from USEPA, 2006); 30 fl oz = 0.234 gallon; 0.235 x 3.2 lb = 0.75 

lb a.i./hundredweight of seed; 

 (18 lbs seed/acre)(0.75 lbs a.i./100 lbs seed) = 0.135 lbs a.i./acre. 8

 1 gallon of product = 3.2 lb a.i.; the maximum application rate on the proposed label = 5 fl oz of 

product/hundredweight of seed; 100 lb seed/acre (from http://www.nsrl.uiuc.edu/aboutsoy/production02.html); 5 fl 

oz = 0.039 gallon; 0.039 x 3.2 lb = 0.125 lb a.i./acre 

The three foliar-applied thiodicarb products (i.e., Larvin® 3.2 Thiodicarb Insecticide/Ovicide, 

Larvin® DF Thiodicarb Insecticide/Ovicide, and Larvin® DF WSP Thiodicarb 

Insecticide/Ovicide) contain the following label restrictions and recommendations: 

- Do not apply by ground within 25 ft or by air within 100 ft of lakes, reservoirs, rivers, 

estuaries, commercial fish ponds, natural-permanent streams, marshes and naturalpermanent ponds 

- Increase buffer zone to 450 ft with ultra low volume applications (low spray volumes 

only allowed on soybeans and only in MD, VA, NC, DE, SC, GA, AL, MS, LA, AR, 

and MO 

- Spray Drift Restrictions: ≤10 ft application height 

The two seed-treatment products (i.e., AerisTM Seed-Applied Insecticide/Nematicide and EXP3 

Seed Applied Nematicide/Insecticide) contain the following label restrictions: 

- For use only in commercial seed treatment equipment 

 - Treated seed must be planted into the soil at a depth >1 inch 

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

on information from 1999 to 2004), an average of 211,945 lbs of thiodicarb per year are applied 

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

of thiodicarb used in agriculture is applied to soybeans (41%), sweet corn (35%) and cotton 

(19%). The remaining thiodicarb uses combined represent <5% of the average total pounds 

applied per year. Based on a Screening Level Usage Analysis conducted by the Agency, using 

data from 2000 to 2007, there is an estimated ~113,000 lb of thiodicarb used per year [most of 

which is used on sweet corn (60,000 lb), soybeans (30,000 lb), and cotton (10,000 lb)]. 

Estimates of non-agricultural usage of thiodicarb are not available. 

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FIGURE 3.1. Estimated, Annual, National, Agricultural Thiodicarb Usage. (from 

http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=02&map=m8009) [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 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 

Registrant-submitted data defining the physical-chemical and environmental fate characteristics 

of thiodicarb [(3EZ,12EZ)-3,7,9,13-tetramethyl-5,11-dioxa-2,8,14-trithia-4,7,9,12-

tetraazapentadeca-3,12-diene-6,10-dione] are summarized in Table 3.3. These data indicate that 

thiodicarb is semi-volatile in soil, readily soluble and, therefore, slightly volatile in water, and 

moderately mobile to mobile in soil. The compound appears to be readily degraded in the 

environment (mostly to methomyl), with the exception that it may persist in acidic water bodies. 

The persistence of thiodicarb in the environment is uncertain because acceptable aerobic soil 

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metabolism data are available for only one soil and the aerobic aquatic metabolism data 

requirement was waived. Thiodicarb, if not already degraded, may leach to ground water or 

move to surface water bodies through spray drift and/or dissolved in runoff. The compound is 

not expected to bioaccumulate in aquatic or terrestrial organisms. 

TABLE 3.3. General Chemical and Environmental Fate Parameters of Thiodicarb. 

Parameter Value Reference

Selected Physical-Chemical Parameters

Molecular mass 354.5 g/mol (calculated) 

Vapor pressure (20°C) 4.3 x 10-5 torr Worthing and 

Hance 1991 

Water solubility (25°C) 23.5 mg/L MRID 41482002 

Henry’s law constant (20°C); KAW 8.53 x 10-7 atm-m3/mol; 3.55 x 10-5 (calculated) 

Octanol-air partition coefficient (KOA) 8.7 x 105 (calculated) 

Octanol-water partition coefficient (KOW) 30 MRID 41250004 

Bioconcentration 

Fish Bioconcentration Factor (35 d) 4.1X (edible) 

7.1X (inedible) 

5.7X (whole fish) 

MRID 42834002 

Mobility

Organic carbon-normalized Freundlich 

adsorption coefficients (KFOC) 

55 L/kg (sand) 

289 L/kg (sandy loam) 

321 L/kg (silt loam) 

1006 L/kg (clay) 

MRID 41998501 

Laboratory volatilization rate range 6.83-156 ppm of the applied / hr MRID 43222901 

Persistence

Hydrolysis half-life (25°C) 78 d (pH 5) 

32 d (pH 7) 

0.48 d (pH 9) 

MRID 42342601 

Aqueous photolysis half-life (25°C) 9.4 d MRID 41250008 

Soil photolysis half-life (25°C) 44 d MRID 43463401 

Aerobic soil metabolism half-life (25°C) 3.6 d (sandy loam; pH 5.4) MRID 42142601 

Anaerobic aquatic metabolism half-life 

(25°C) 

3 hr (sandy loam sediment, pH 5.9; pond 

water, pH 6.5) 

MRID 42142602 

Field Dissipation

Terrestrial field dissipation half-life; 

maximum leaching depth 

18 d (WA sandy loam); detected below 

deepest sampling depth of 75-90 cm 

MRID 42203901 

3.3.1. Mobility 

Thiodicarb is readily soluble in water (up to 23.5 mg/L at 25°C; MRID 41482002, FAO 2000). 

The compound is also moderately mobile to mobile in soil, based on organic carbon-normalized 

Freundlich adsorption coefficients that range from 55 to 1006 L/kg (MRID 41998501; USEPA 

2006a). These values are 13.8% lower than those used in all previous assessments because, in 

previous calculations, 50% rather than the standard 58% of organic matter was assumed organic 

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carbon. Surface water contamination may occur via spray drift and/or from the transport of 

dissolved residues in runoff. Based on the mobility of thiodicarb and the higher mobility of its 

major degradate, methomyl (discussed in Section 3.3.5), ground water contamination may also 

occur as a result of thiodicarb use. Rapid degradation may result in methomyl accounting for the 

majority of any residues of concern. 

Thiodicarb’s vapor pressure (4.3 x 10-5 torr at 20oC; Worthing and Hance 1991) indicates that the 

compound may be semi-volatile from soil. However, volatilization from soil is not expected to 

be a major route of environmental transport due to rapid degradation in soil. Thiodicarb is only 

slightly volatile from water due to its solubility in water and as indicated by its KAW (calculated 

to be 3.6 x 10-5; 40 FR 26889, Jun. 25, 1975). Submitted environmental fate studies support the 

expectation of low volatility, as it was not observed. 

3.3.2. Degradation 

Thiodicarb degrades by both abiotic and biotic processes. The compound is readily hydrolyzed 

in alkaline water (half-life of 12 hours at pH 9), but persists in acidic to neutral water (half-lives 

of 32 days at pH 7 and 78 days at pH 5), with decreasing degradation as pH decreases (MRID 

42342601). Major hydrolytic degradates include methomyl [(S-methyl (EZ)-N-

(methylcarbamoyloxy)thioacetimidate], at up to 66% of the radioactivity applied in the pH 9 

study after one day, and methomyl oxime [S-methyl-N-hydroxythioacetimidate], at up to 77% of 

the applied radioactivity at termination of the pH 9 study (30 days after treatment). 

The compound was moderately photolyzed in water (9.4-day half-life; MRID 41250008) and 

slowly photolyzed in soil (44-day half-life; MRID 43463401). Reported half-lives are 18-19% 

higher than previously reported values because they are adjusted for dark controls. Major 

photolysis degradates included methomyl (up to 47% of the applied in water at study 

termination, 23 days after treatment, and up to 16% of the applied to soil, 7 days after treatment), 

methomyl oxime in the soil study (up to 27% of the applied at study termination, 30 days after 

treatment), and acetonitrile in the aqueous study (up to 15% of the applied at study termination). 

In an aerobic sandy loam soil (pH 5.4), thiodicarb was readily degraded with a half-life of 3.6 

days (MRID 42142601). Because only one soil was tested, there is high uncertainty in this value 

with respect to its representativeness of the diversity of soils in the environment. Major 

degradates included methomyl (up to 80% of the applied, 7 days after treatment) and carbon 

dioxide (52% of the applied at study termination, 60 days after treatment). 

In an anaerobic aquatic system, thiodicarb appeared to rapidly degrade with an estimated halflife of 3.1 hours (MRID 42142602). This value is uncertain because >99% of the compound 

measured at application degraded in the first 4-hour interval. Methomyl and methomyl oxime 

were not major degradates in this study, as thiodicarb appeared to follow an alternative route of 

transformation under anaerobic conditions. Two unidentified degradates were quickly formed, 

Unknown 3 (up to 60% of the applied at 4 hours after treatment) and Unknown 4 (up to 29% of 

the applied at 2 days after treatment). The study author offered that these unidentified degradates 

were likely the monosulfone derivative of thiodicarb and a related compound; however, the 

oxidation of thiodicarb to its monosulfone under anaerobic conditions is not expected and 

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sufficient information were not provided to support this transformation pathway. Studies with 

major unidentified degradates are typically not classified acceptable; however, this study was 

classified acceptable because reasonable attempts were made to identify the degradates. By 

study termination (14 days after treatment), the primary degradates had further degraded, 

yielding substantial amounts of the volatile compounds acetonitrile (at 73% of the applied) and 

carbon dioxide (at 16% of the applied). 

The residues of concern for exposure and risk assessment will be reconsidered. In the absence of 

data or structural activity relationships indicating low toxicity concerns for the major degradates 

of thiodicarb and methomyl, they will be assumed of equal toxicity as the parent. Past 

assessments of thiodicarb have included thiodicarb and methomyl as the only residues of concern 

because the 1998 RED for thiodicarb stated that “residues of acetamide and acetonitrile resulting 

from the application of thiodicarb or methomyl are not [dietary food] residues of concern in 

animals” (USEPA 1998). Also, degradates of other carbamates for which some degradate 

toxicity data are available, such as oxamyl, are considered much less toxic than the parent 

compound and have not been included as residues of concern in relevant exposure and risk 

assessments (USEPA 2009). However, because evaluations of residues of concern for thiodicarb 

and methomyl have not been conducted regarding drinking water or ecological exposure, these 

evaluations will occur as part of registration review. 

3.3.3. Field Dissipation 

In a terrestrial field dissipation study conducted in sandy loam soil in Washington, six weekly 

applications of thiodicarb were made at 1.12 kg a.i./ha/application (total 6.72 kg a.i./ha) in early 

autumn (MRID 42203901). Filter papers confirmed actual application rates of 81-95% of the 

nominal application rate. Recovery efficiencies from fortified samples ranged from 50% to 80% 

of the applied for thiodicarb and 81% to 120% of the applied for methomyl. No other degradates 

were analyzed in the study. Thiodicarb was detected (at 3 ppb) at the lowest sampled soil depth 

(75-90 cm) immediately after the fifth application. Methomyl was detected (at 2 ppb) at the 

lowest soil depth immediately after the fourth application. Following the sixth application, 

thiodicarb dissipated with a half-life of 18 days; methomyl dissipated with a half-life of 43 days. 

The dissipation half-life from this study is longer than would be expected given the short 

biodegradation half-lives in the laboratory studies and underscores the need for additional 

aerobic soil and aerobic aquatic metabolism laboratory studies in order to understand the 

variability in the compound’s environmental fate.

 3.3.4. Bioaccumulation 

Bioaccumulation in bluegill sunfish (Lepomis macrochirus) was studied for thiodicarb (MRID 

42834002). Bluegill sunfish were continuously exposed under flow-through conditions to a 

mean thiodicarb concentration of 0.05 mg/L for 35 days. Consistent with the low octanol-water 

partition coefficient for thiodicarb (30), bioconcentration factors (BCF) were determined to be 

4.1X for edible tissue, 7.1X for inedible tissue, and 5.7X for whole fish tissues, indicating that 

thiodicarb does not have the potential to bioaccumulate in aquatic organisms. Acetic acid was 

identified as a major radiolabeled compound in the fish tissues; it was 35% of the recovered 

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residues in fish tissues at day 21 and 22% at day 35. After 28 days of depuration, 46-74% of the 

accumulated residues were eliminated from the fish tissues. 

An octanol-air partition coefficient (KOA) of 8.7 x 105

 (log KOA of 5.94) was calculated for 

thiodicarb using its solubility in water, vapor pressure, and octanol-water partition coefficient 

(KOW). Kelly and Gobas (2003) and Armitage and Gobas (2007) concluded that chemicals with 

a log KOW >2 and a log KOA >5 have the potential to biomagnify in terrestrial habitats. Because 

the KOW for thiodicarb is <2 and the compound is not expected to be persistent in most 

environmental compartments, thiodicarb is unlikely to biomagnify in terrestrial habitats. 

 3.3.5. Environmental Fate and Transport of Methomyl 

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

registered pesticide that is also the primary degradate of thiodicarb. The compound is persistent 

in low pH environments and mobile (KOC of 31.3 L/kg) in soil-water systems. The dominant 

routes of dissipation of methomyl are metabolism, leaching, and photolysis in clear waters. 

Environmental fate and transport properties of methomyl are summarized in Table 3.4. Sitespecific factors affecting the persistence of methomyl include aerobicity, organic matter, soil 

moisture content, exposure to sunlight, pH, climate (especially rainfall), and crop management 

factors that influence leaching and runoff. Because of its low affinity for adsorption, methomyl 

is likely to dissipate rapidly from plant and soil surfaces. Methomyl has fate characteristics—

moderate persistence, high water solubility, and low sorption coefficient— that suggest transport 

to waters resources is likely. Waters that are neutral to acidic are particularly vulnerable due to 

methomyl’s persistence in these environments. 

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

Parameter Value Source 

Molecular weight 162.2 g/mol (calculated) 

Solubility in water (20°C) 54.7 g/L MRID 41402101 

Vapor pressure 5.6 x 10-6 torr MRID 41209701 

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

KOW 1.31 MRID 00157991 

stable @ pH = 5 

1300 days @ pH = 7 

13 days @ pH = 9 

Strathmann and 

Stone, 2001, 2002 

Hydrolysis half-life 

stable @ pH = 5 

stable @ pH = 7 

30 days @ pH = 9 

MRID 00131249 

Aqueous photolysis half-life 4.0 d MRID 00161885 

Soil photolysis half-life 34 d MRID 00163745 

Aerobic soil metabolism Flanagan silt loam: 43.9 d (109.2 d) MRID 00008568 

half-life of parent (of TTR) Madera, CA silt loam: 11.6 d (25.0 d) MRID 43217901 

Anaerobic soil metabolism 

half-life 

14 d MRID 43217902 

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Parameter Value Source 

Aerobic aquatic metabolism 

half-life of parent (of TTR) 

Auchingilsie clay loam: 4.0 d (6.3 d) 

Hinchingbrooke silty clay loam: 

4.6 d (7.4 d) 

MRID 43325401 

Organic carbon-normalized 

adsorption coefficient (KOC) 

31.3 L/kg MRID 00161884 

DP barcode 339908 

Terrestrial field dissipation 

half-life (from surface) 

4-54 d MRID 00008844 

MRID 00009324 

MRID 00009326 

MRID 41623901 

MRID 41623902 

0.5 d (mint) Kiigemagi and 

Deinzer, 1979 

Foliar degradation half-life 

2.5 d (Bermuda grass) Sheets et al., 1982 

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 around 13 and 30 d) at pH 9 based on two studies. Methomyl 

photolyzes quickly in clear water (t1/2 = 4 d) but more slowly in soils. It is moderately stable to 

aerobic soil metabolism but degrades more rapidly under anaerobic conditions. In laboratory 

studies, methomyl does not readily adsorb to soil and has the potential to be mobile. Field 

studies show varying dissipation rates of the chemical in soils. Dissipation rates were related 

primarily to differences in soil moisture content, which may have affected the microbial activity, 

and rainfall/irrigation, which could have influenced leaching. 

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

conducted for 30 days showed that methomyl is stable to hydrolysis at pH 5 and 7 and slowly 

degrades in pH 9 buffered solutions (t1/2 ≈ 30 d). However, open literature data (Strathmann and 

Stone, 2001, 2002) indicate that the degradation rate at pH 7 is 1300 days and is 13 days at pH 9, 

while no measurable degradation was observed at pH 5. The major hydrolysis degradate in the 

guideline study is methomyl oxime with up to 44% of the applied after 30 days. In two trials, 

one each at 10 and 100 mg/L, methomyl degraded by photolysis in water with a mean half-life of 

4.0 d ±1.2 d at one standard deviation. There was no measureable degradation in the dark 

control. The major degradate was acetonitrile, which was found at 70.1% of the initial measured 

radioactivity at the termination of the experiment at 15 days. Methomyl degraded more slowly 

on soils (t1/2 = 32 d). As in water, acetonitrile was the major photolysis degradate on soil with a 

peak concentration of 40% of the applied after 30 days at the termination of the study. 

In two aerobic soil metabolism studies, methomyl degraded with half-lives of 34.9 days in a 

Flanagan silt loam and 11.6 days in a loam soil from Madera, CA. The major degradate was 

14CO2 (22.5% of the applied after 45 days in the silt loam soil, and 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 toxic residues method) are 

109 and 25 days for the Flanagan and Madera soils, respectively. Methomyl oxime was a minor 

degradate accounting for ≤2% of the applied. 

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

(nitrogen atmosphere) and <7 days in dynamic conditions (flowing nitrogen atmosphere) on a 

loam soil following 14 days of aerobic incubation. 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, 1983; Bromilow, 1986). The proposed chemical reaction is: 

 Fe2+

CH3-C=N-O-C=O ------------> CH3C/N 

 | | 

 S-CH3 NH-CH3

TABLE 3.5. Methomyl degradates identified in laboratory degradation studies with their 

time and maximal fraction of occurrence. 

Degradate Hydrolysis Aqueous 

Photolysis 

Soil 

Photolysis 

Aerobic 

Soil 

Metabolism 

Aerobic 

Aquatic 

Metabolism 

Methomyl oxime 44% @ 30 d; pH 9 1% @ 1 d < 2% 

Acetonitrile 70.1% @ 15 d 40% @ 30 d 27% @ 102 d 

Acetamide 27% @ 7 d 

Carbon dioxide 46% @ 102 d 

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. 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. 

Acetonitrile averaged a maximum of 17% of the applied at 7 days, and acetamide accounted for 

up to 14% of the applied at day 7. After 102 days, volatilized acetonitrile totaled up to 27% of 

the applied and 14CO2 was up to 46% of the applied. 

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

present at high concentrations in the alkaline hydrolysis study but was only a minor degradate in 

the aerobic soil metabolism, anaerobic soil metabolism, and photolysis in water studies (≤3% of 

the applied at all test intervals). 

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

1987). Of the 10 studies for methomyl identified in this review of foliar dissipation, three 

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 TLC (Rf values 0.46-0.82 and 

0.86-0.93, respectively) (MRID 44306). Results of the batch equilibrium studies show 

methomyl has a low affinity to bind to soil (see Table 3.6) further indicating that the chemical 

will be mobile (MRID 161884). Methomyl binding is significantly correlated with soil organic 

carbon content, with a KOC of 31.3 Lkg based on linear regression of Kd with soil organic carbon 

content. Methomyl is a highly soluble chemical in water (54.7 g/L). Its vapor pressure (5.6 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. 

TABLE 3.6. Summary of Isotherm Parameters from Soil Batch Equilibrium Studies for 

Methomyl. 

Soil Fraction of 

organic matter 

Kd Freundlich 

Coefficient 

Freundlich 

Exponent 

Cecil sandy loam 0.021 0.6036 0.7303 0.852 

Flanagan silt Loam 0.043 0.9031 1.006 0.873 

Keyport silt loam 0.075 1.211 1.374 0.856 

Woodstown sandy loam 0.011 0.2039 0.2337 0.880 

Bioaccumulation. The low octanol/water partition coefficient of 1.31 ± .02σ suggests that the 

chemical will have a low tendency to accumulate in fish. 

Field Dissipation. Five terrestrial field dissipation studies are available for methomyl. Although 

the studies were found acceptable, some have deficiencies that increase the level of uncertainty 

in the results. Dissipation half-lives from the surface soil ranged from 4 to 54 days. Such 

variations can be expected in the terrestrial field dissipation studies because of the large number 

of processes that occur simultaneously and the large number of variables present in the field. 

The moderate persistence of methomyl appears to be tied to the soil conditions. In a muck soil 

(52% organic matter content), no methomyl was detected 7 days after treatment. A quick 

dissipation in a soil with such high organic matter content may be related to microbial activity or 

rapid permeability. Two other studies conducted in sand and silt loam soils show extensive 

dissipation (≥82% of the applied) after 1-3 months, with the remaining radioactivity recovered in 

the upper 8-15 inches of soil. No dissipation half-lives could be calculated in these studies 

because only a few sampling intervals are available. 

In two recent studies conducted in cropped cabbage fields, the dissipation half-life from the 

surface ranged from 4-6 days in Mississippi to 54 days in California. Two factors may explain 

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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, MRID 43599801). Lannate L, a pesticide product 

containing 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 the maximum label rate of 0.45 lbs 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 an increase in the maximum label rate, a label change that was not 

subsequently proposed by the registrant. 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 ppb. 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 ppb, using a detection limit of 0.1 ppb, at Days 62 and 

117. Sampling continued for 789 days, but no detections were seen after Day 117. 

3.4. Water Quality 

Thiodicarb and methomyl are not identified as causes of impairment 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 August 26, 2009). 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 August 26, 2009). 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 thiodicarb 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. Because the thiodicarb degradate methomyl is also a registered 

pesticide (PC Code: 090301), data are available to define the toxicity of this degradate of 

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concern to non-target organisms. To adequately capture the risk from thiodicarb use, the toxicity 

and potential exposure to non-target animals to thiodicarb and its degradate methomyl will be 

considered. The most sensitive endpoints from the available toxicity data for thiodicarb and 

methomyl will be used to quantify risk. 

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 thiodicarb 

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 thiodicarb and its degradate 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. A preliminary review of open 

literature data from ECOTOX on thiodicarb was conducted as part of this Problem Formulation 

to help identify data gaps. A more complete review of the data from ECOTOX will be 

conducted for evaluation for possible quantitative and/or qualitative inclusion in this risk 

assessment. Open literature data from an ECOTOX run conducted on 9/30/04 for methomyl 

have been fully reviewed as part of this Problem Formulation. Information from an up-dated 

ECOTOX run for methomyl will be evaluated for possible quantitative and/or qualitative 

inclusion in this risk assessment. 

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

and methomyl in aquatic and terrestrial habitats is provided in Sections 4.1 and 4.2, respectively. 

A summary of ecological incidents associated with thiodicarb and methomyl and a description of 

ecosystems potentially at risk are provided in Sections 4.3 and 4.4, respectively. 

4.1. Effects to Aquatic Organisms 

Methomyl, based on the available toxicity data for thiodicarb and methomyl, is more toxic or 

equitoxic to aquatic animals than thiodicarb on both an acute and chronic exposure basis with the 

exception of some estuarine/marine animals [i.e., eastern oysters (Crassostrea virginica) and 

sheepshead minnows (Cyprinodon variegatus)] (see below). 

Thiodicarb 

A summary of the most sensitive aquatic toxicity data for thiodicarb from registrant-submitted 

studies is provided in Table 4.1. A summary of all submitted ecotoxicity data for thiodicarb is 

provided in Appendix A. Thiodicarb is classified as moderately toxic to freshwater fish, highly 

toxic to estuarine/marine fish, and very highly toxic to aquatic invertebrates (both freshwater and 

estuarine/marine) on an acute exposure basis. The EC50 for non-vascular aquatic plants 

(Selenastrum capricornutum) is >8.3 mg a.i./L, with a NOAEC of 1.6 mg a.i./L based on percent 

inhibition of growth (MRID 42324801). There are currently no thiodicarb toxicity data available 

for vascular aquatic plants. 

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Regarding chronic effects, the only data currently available for thiodicarb and aquatic organisms 

are for freshwater fish and freshwater invertebrates (i.e., there are currently no chronic data 

available for estuarine/marine fish or invertebrates). For freshwater fish, the most sensitive 

NOAEC is 0.025 mg a.i./L for the fathead minnow (Pimephales promelas) based on reduced 

larval growth (a 4% decrease in total length and 14.3% decrease in wet weight at the 0.053 mg 

a.i./L concentration) (MRID 44484101). The only chronic toxicity data available for freshwater 

invertebrates is for daphnids (Daphnia magna) (MRID 00100688). This study resulted in a 

NOAEC of 0.009 mg a.i./L based on reduced survival and a reduction in the number of young 

produced (LOAEC = 0.018 mg a.i./L). 

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

Studies for Thiodicarb. 

Species Taxa Represented Toxicity Value MRID # Classification Comment 

Bluegill sunfish 

(Lepomis 

macrochirus) 

96-hr LC50 = 1.21 

mg a.i./L 

00044273 Acceptable A slope could not be 

determined 

Fathead 

minnow 

(Pimephales 

promelas) 

Freshwater fish and 

aquatic-phase 

amphibians NOAEC = 0.025 

mg a.i./L 44484101 Supplemental 

The NOAEC is based 

on reduced larval 

growth – total length 

(4%) and wet weight 

(14.3%); LOAEC = 

0.053 mg a.i./L; sublethal signs of 

toxicity were not 

noted 

48-hr EC50 = 

0.0053 mg a.i./L 

00044276 Acceptable A slope could not be 

determined 

Daphnid 

(Daphnia 

magna) 

Freshwater 

invertebrates NOAEC = 0.009 

mg a.i./L 00100688 Acceptable 

The NOAEC is based 

on reduced survival 

and total young 

produced; LOAEC = 

0.018 mg a.i./L 

96-hr LC50 = 0.47 

mg a.i./L 42738501 Acceptable Slope = 4.4 (3.1 – 5.8) 

Sheepshead 

minnow 

(Cyprinodon 

variegatus) 

Estuarine/marine 

fish No chronic data 

available N/A N/A N/A 

Eastern oyster 

(Crassostrea 

virginica) 

EC50 = 0.55 mg 

a.i./L 42834001 Acceptable 

Shell deposition 

study; NOAEC = 

0.12 mg a.i./L 

96-hr LC50 = 

0.0285 mg a.i./L 41891007 Acceptable 

Slope = 5.1 (0.62-

9.6); NOAEC = 

0.018 mg a.i./L 

Mysid 

(Americamysis 

bahia) 

Estuarine/marine 

invertebrates 

No chronic data 

available- N/A N/A N/A 

Algae 

(Selenastrum 

capricornutum) 

Non-vascular 

aquatic plants 

NOAEC = 1.6 mg 

a.i./L 

96-hr EC50 = >8.3 

mg a.i./L 

42324801 Acceptable 

LOAEC = 2.4 mg 

a.i./L based on % 

inhibition of growth 

[max inhibition was 

37% at the highest 

concentration tested 

(8.3 mg a.i./L)] 

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

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Methomyl 

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 4.2). A summary of all available ecotoxicity data for 

methomyl is provided in Appendix A. 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. The most 

sensitive NOAEC and LOAEC for freshwater fish [fathead minnows (Pimephales promelas)] are 

0.057 and 0.117 mg a.i./L, based on reduced survival (MRID 131255). Since no toxicity data 

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

species, the channel catfish (Ictalurus punctatus), an acute to chronic ratio (ACR) is used to 

calculate a chronic freshwater fish endpoint using acute and chronic data from the fathead 

minnow. This 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 fish exhibiting lethargy 

and erratic swimming were noted at 1.0 mg a.i./L on days 4 through 16, but were not observed at 

any other time during the study. 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 time or concentration. 

In a 28-day life-cycle toxicity study, mysid (Americamysis bahia) neonates were exposed under 

flow-through conditions to methomyl at mean measured concentrations ranging from 14.5 to 253 

μg/L (MRID: 450132-03). The most sensitive measure of toxicity was the reduced number of 

young per surviving female, which resulted in a NOAEC of 0.0291 mg a.i./L and a LOAEC of 

0.0591 mg a.i./L. Since no toxicity data from chronic exposure to methomyl were available for 

the most acutely sensitive estuarine/marine invertebrate species, the northern pink shrimp 

(Penaeus duorarum), an acute to chronic ratio (ACR) was used to calculate a chronic 

estuarine/marine endpoint using acute and chronic data from mysids. This resulted 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)]. 

-22 of 83-
TABLE 4.2. 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

 (1.5 mg/L)/(0.057 mg/L) = (0.320 mg/L)/(x mg/L) 

2

 (0.234 mg/L)/(0.029 mg/L) = (0.019 mg/L)/(x μg/L) 

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. Applications were performed over a period of 22 days (22 daily 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)]. 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, pre-existing pond on site, colonized by native 

invertebrates. 

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

Zooplankton showed mixed results; the abundance of adult copepodes 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. 

During the microcosm study, temporary declines in abundance were observed in mayflies and 

three genera of chironomids, however, the results are difficult to assess because they are 

confounded by a low number of organisms and high degree of variability within measurement 

endpoints in each treatment group, including the controls. 

Although macroinvertebrate sensitivity in the microcosm study paralleled results from laboratory 

toxicity tests, the sensitivity of fish in the microcosm study was not consistent with what was 

observed in the laboratory acute toxicity tests. Maximum methomyl concentrations at the 

highest treatment levels in the microcosm study (706 μg/L) were almost twice as high as the 

most sensitive bluegill LC50 value from the submitted laboratory studies (370 μg/L); however, 

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 decrease in body length and weight was not 

strongly associated with the methomyl treatment levels, i.e., none of the measurements displayed 

a graded dose-response across the treatment groups. The size reductions were, thus, attributed to 

a decrease in food resources, particularly cladocerans. 

4.2. Effects to Terrestrial Organisms 

Methomyl, based on the available toxicity data for thiodicarb and methomyl, is more toxic or 

equitoxic to terrestrial animals than thiodicarb on both an acute and chronic exposure basis (see 

below). 

Thiodicarb 

Table 4.3 summarizes the most sensitive terrestrial toxicity endpoints for thiodicarb based on an 

evaluation of submitted studies. Thiodicarb is classified as practically nontoxic to birds and 

honey bees and highly toxic to mammals on an acute exposure basis. Although thiodicarb is 

practically nontoxic to honey bees, it is likely that thiodicarb is more toxic to at least some 

terrestrial invertebrate taxa since it is an insecticide. In a submitted study on a parasitic wasp 

(Aphidius rhopalosiphi), the 48-hr LC50 value is 0.001 lb product (Larvin® SC 375, 38% 

a.i.)/acre (which equals 0.0004 lb a.i./acre) (MRID 45565801). This suggests that this species 

may be more sensitive to thiodicarb than honey bees; however, the wasp endpoint will not be 

used to calculate RQs in the assessment since it involves a product not currently registered for 

use in the U.S. There are currently no thiodicarb toxicity data available for terrestrial plants. 

For chronic exposure, the NOAEC for birds is 500 mg/kg-diet based on a reduction in the 

number of eggs laid per hen at the 1,000 mg a.i./kg-diet concentration in mallard ducks (Anas 

platyrhynchos) (MRID 43313004). For mammals, the chronic endpoint is a NOAEL of 100 

-24 of 83-
mg/kg-diet (5 mg/kg/day) based on decreased fetal body weight and viability at the 300 mg 

a.i./kg-diet concentration in laboratory rats (Rattus norvegicus) (MRID 42381301). 

TABLE 4.3. Summary of the Most Sensitive Endpoints from Submitted Terrestrial 

Toxicity Studies for Thiodicarb. 

Species Taxa 

Represented Toxicity Value MRID # Classification Comment 

Bobwhite quail 

(Colinus 

virginianus)

LD50 = 2,023 mg/kg-bw 46478 Acceptable A NOAEL could 

not be determined 

because there was a 

reduction in weight 

gain al all 

treatment levels; 

slope = 4.1 (1.6 – 

6.6) 

Mallard duck 

(Anas 

platyrhynchos) 

LC50 = >5,620 mg/kgdiet 

46479 Acceptable NOAEC = 1,780 

mg a.i./kg-diet 

(LOAEC = 5,620 

mg a.i./kg-diet 

based on reduction 

in food 

consumption and 

body weight gain) 

Mallard duck 

(Anas 

platyrhynchos)

Birds, reptiles, 

and terrestrialphase 

amphibians 

NOAEC = 500 mg/kgdiet 43313004 Acceptable LOAEC = 1,000 

mg a.i./kg-diet, 

based on reduction 

in number of eggs 

laid/hen

Laboratory rat 

(Rattus norvegicus) 

LD50 = 39.1 mg a.i./kgbw 

00025791 Acceptable None 

Laboratory rat 

Mammals NOAEL = 100 mg 

a.i./kg-diet (5 mg 

a.i./kg/day) 

LOAEL = 300 mg 

a.i./kg-diet (15 mg 

a.i./kg/day) 

42381301 Acceptable NOAEL based on 

decreased fetal 

body weight and 

viability 

Honey bee 

(Apis mellifera)

Terrestrial 

invertebrates 

LD50 = >25 μg a.i./bee 42528501 Acceptable Acute contact; 

NOAEL = 3.1 μg 

a.i./bee; highest 

mortality was 37% 

at the highest 

concentration 

tested (i.e., 25 μg 

a.i./bee)

-25 of 83-
Species Taxa 

Represented Toxicity Value Classification MRID # Comment 

Wasp (Aphidius 

rhopalosiphi) 

48-hr LC50 = 0.001 lb 

product (38% a.i.)/acre 

= 0.0004 lb a.i./acre 

45565801 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; slope = 2.21 

(1.59 – 2.83) 

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

Methomyl 

Table 4.4 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. In a submitted study on a parasitic wasp (Aphidius 

rhopalosiphi), the 48-hr LC50 value is 0.00022 lb a.i./acre (which equals 0.0004 lb a.i./acre) 

(MRID 45565801). This suggests that this species, as with thiodicarb, may be more sensitive to 

methomyl than honey bees, however, the wasp endpoint will not be used to calculate RQs in the 

assessment since it involves a product (Methomyl® 25WP) not currently registered for use in the 

U.S. 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. 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, the 

NOAEL for parental systemic toxicity is 3.75 mg/kg-bw and the LOAEL is 30 mg/kg-bw based 

on decreased 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 the mean number of live pups and mean body weights of offspring (MRIDs: 

43250701, 43769401). 

-26 of 83-
TABLE 4.4. 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 

(Rattus norvegicus) 

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 lb 

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 

Although there are no acceptable terrestrial plant guideline studies available for methomyl, 

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

invertebrate target and non-target 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, however, they are considered scientifically valid. None of the 

studies showed any adverse effects to plants at the highest treatment levels tested (most of which 

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were at or above the maximum allowable single application rate for methomyl of 0.9 lb a.i./acre) 

(see Table 4.5). 

TABLE 4.5. Measures of Effects to Plants from Methomyl Efficacy Studies that Included 

Information on Effects to Plants. 

PLANT SPECIES NOAEL HIGHEST 

LEVEL 

TESTED?1

EFFECT2 ECOTOX NO./REFERENCE 

Alfalfa 

(Medicago sativa) 

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

≥3.6 lb a.i./acre Yes Growth 

Injury 

Auberine 74745/Morale and Kurundkar (1989) 

(Solanum melongena) 

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

Bean 

(Phaseolus vulgaris) 

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

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

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

Bell pepper 

(Capsicum annuum) 

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

Cabbage 

(Brassica oleracea) 

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

Hybrid strawberry 

(Fragaria x ananassa) 

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

Lettuce 

(Lactuca sativa) 

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

Peony 

(Paeonia lactiflora) 

≥20.0 lb a.i./acre Yes Abundance 89251/Schmitt et al. (1974) 

Peach 

(Prunus persica) 

≥0.23 lb a.i./100 

gallon 

Yes Injury 88091/Hull (1999) 

Pigeonpea 

(Cajanus cajan) 

≥0.53 lb a.i./acre Yes Abundance 82560/Giraddi et al. (2002) 

Potato 

(Solanum tuberosum) 

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

≥0.45 lb a.i./acre Yes Injury 74169/Walgenbach et al. (1991) 

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

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

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

≥0.45 lb a.i./acre Yes Injury 88269/Stansly et al. (1999) 

Tomato 

(Solanum sp.) 

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

Wild celery 

(Apium graveolens) 

≥0.9 lb 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’ 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. 

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 June 5 and August 13 2009, 

respectively. There are currently no reported wildlife or plant incidents involving thiodicarb 

listed in the EIIS or AIMS databases. A total of 12 incidents associated with methomyl use, 

 

1

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

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however, have been reported (8 involving terrestrial organisms – all birds -and 4 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, possible in 

two incidents, and unlikely in two incidents. Three of the incidents were the result of registered 

use, five were the result of misuse (intentional baiting); however, it is unknown if the other four 

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. No 

aggregate incident reports have been submitted to the Agency for thiodicarb. For methomyl, 

registrants have reported 7 minor fish and wildlife incidents, all of which occurred between 2000 

and 2007. The number of individuals involved 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 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 one of the incidents, which 

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

Aquatic Incidents 

A fish kill occurred in a canal near Blythe, California on January 7, 1978 (Incident # B0000-501-

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

registered use. Approximately 540 catfish (Ictalurus spp.) and largemouth bass (Micropterus 

-29 of 83-
salmoides) were killed in an area of standing water. Lannate® (methomyl), Thiodan® 

(endosulfan), and parathion were suspected as being the cause of the kill, but analyses of water 

and fish showed only endosulfan to be present. Water samples contained between 0.27 and 0.64 

ppb endosulfan. Also, gills and liver contained 2500 and 1100 ppb endosulfan, respectively, and 

gills of largemouth bass contained 930 ppb endosulfan. This report was listed as ‘unlikely’ 

relative to methomyl being the cause of the incident because only endosulfan was detected in 

water and fish residue samples indicate that endosulfan, and not methomyl, was responsible for 

the fish kill. 

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; 

fenurin = 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. 

A fish kill involving an unknown number and species of fish occurred in Riverside County, 

California, on November 18, 1976 (B0000-216-19). The incident occurred after registered uses 

of endosulfan, mevinphos, and methomyl on lettuce; however, the report states it was ‘unlikely’ 

that methomyl caused the fish kill. 

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

database cannot be used 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 changes in state monitoring efforts due 

to lack of resources. 

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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. 

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 1998). For thiodicarb, 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 thiodicarb provides a written description and visual representation of 

the predicted relationships between thiodicarb (and its degradate 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 1998). 

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

in soil or alkaline water bodies, but may potentially leach to ground water and move to surface 

water through runoff and spray drift. Thiodicarb’s main degradate, methomyl, is also not 

expected to volatilize and may leach to ground water and move to surface water through runoff 

and base flow. Methomyl is degraded by metabolism and photolysis in clear water. Due to 

relatively low BCF and KOW values, thiodicarb and methomyl are not expected to bioaccumulate 

in aquatic or terrestrial food chains. 

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Based on previous ecological risk assessments for thiodicarb, there is the potential for acute and 

chronic risk from the exposure of aquatic invertebrates, fish, birds, and mammals to thiodicarb 

and to the subsequently formed active degradate, methomyl. 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. 

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 thiodicarb, 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, thiodicarb (and its degradate 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 nontarget organisms include Federally-listed threatened and endangered species as well as 

non-listed species. 

6.2. Conceptual Diagram 

The environmental fate properties of thiodicarb and its degradate methomyl indicate that runoff, 

spray drift and direct spray represent potential transport mechanisms of thiodicarb and methomyl 

to aquatic and terrestrial habitats where non-target organisms may be exposed. These transport 

mechanisms (i.e., sources) are depicted in the conceptual models 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 thiodicarb and its degradate methomyl. Although thiodicarb and methomyl may 

leach to ground water, neither compound is expected to persist long enough to contaminate the 

base flow of surface water bodies. 

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Stressor 

Source

Receptors 

Attribute 

Change 

Thiodicarb applied to use site 

Thiodicarb degrading to methomyl 

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 

Surface water/ 

Sediment 

Runoff 

Aquatic Animals 

Invertebrates 

Vertebrates 

Exposure 

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 

Media 

Community change 

FIGURE 6.1. Conceptual Model for Thiodicarb and Methomyl Effects on Aquatic 

Organisms. Dotted Lines Indicate Exposure Pathways that Have a Low Likelihood of 

Contributing to Ecological Risk. 

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Stressor 

Source

Receptors 

Attribute 

Change 

Thiodicarb applied to use site 

Thiodicarb degrading to methomyl 

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 

FIGURE 6.2. Conceptual Model for Thiodicarb and Methomyl Effects on Terrestrial 

Organisms. 

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 thiodicarb and methomyl 

will be characterized and integrated to assess the risks. Exposure to thiodicarb and methomyl 

will reflect the predicted environmental fate of either each compound separately or together as 

methomyl equivalents, depending on the toxicity differential for assessed organisms. Risk 

quotients (RQs) will be derived for thiodicarb and/or methomyl by dividing estimated 

environmental concentrations (EEC) by the most sensitive endpoint from the relevant, available 

toxicity data for thiodicarb and/or 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. 

-34 of 83-
7.1. Stressors of Concern 

The primary degradate of concern, methomyl, is considered to have attributes and effects similar 

to parent thiodicarb. Thus, the residues of concern in this assessment include both thiodicarb and 

methomyl. Modeled exposure estimates resulting from thiodicarb usage will reflect the 

predicted environmental fate of either thiodicarb and methomyl separately or together as 

methomyl equivalents, depending on the toxicity differential of the compounds for assessed 

organisms. 

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 thiodicarb with other pesticides will be 

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

thiodicarb, 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 thiodicarb 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 thiodicarb 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., broccoli, cabbage, cauliflower, cotton, a variety of 

leafy vegetables, soybeans, sweet corn, ornamentals and trees (except forest), and non-crop areas 

(i.e., wastelands, roadsides, rights-of-way, grassways, shelter belts, and fencerows)] as discussed 

in Section 5. Measures of exposure are based on aquatic and terrestrial models that predict 

estimated environmental concentrations (EEC) of thiodicarb using maximum labeled application 

rates and application methods that have the greatest potential for off-site transport of the 

chemical. A method for estimating methomyl exposure resulting from thiodicarb applications 

will be selected based on the available data. The models used to predict aquatic EECs are the 

Pesticide Root Zone Model coupled with the EXposure Analysis Model System 

(PRZM/EXAMS). The model used to predict terrestrial EECs on food items is T-REX. The 

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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. 

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 thiodicarb that may occur in surface water bodies adjacent 

to application sites receiving thiodicarb 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 thiodicarb. 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 chronic exposure to fish and aquatic-phase amphibians. The 1-in10-year 21-day mean is used for assessing aquatic invertebrate chronic exposure. 

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 

thiodicarb 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. 

Information on the potential effects of thiodicarb (and its degradate methomyl) on non-target 

animals is also collected from the Ecological Incident Information System (EIIS; USEPA 

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2007c). The EIIS is a database containing adverse effect (typically mortality) reports on nontarget 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 thiodicarb and 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 effects characterization to 

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

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

toxicity effects data are integrated in order to evaluate the risks of adverse ecological effects on 

non-target species. For the assessment of thiodicarb risks, the risk quotient (RQ) method is used 

to compare exposure and measured toxicity values. EECs are divided by acute and chronic 

toxicity values. The resulting RQs are then compared to the Agency’s Levels of Concern (LOC) 

(USEPA 2004). These criteria are used to indicate when thiodicarb’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. 

-37 of 83-
7.5. Deterministic and Probabilistic Assessment Methods 

The quantitative assessment of risk will primarily depend on the deterministic point-estimate 

based 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 thiodicarb. 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 thiodicarb 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 thiodicarb 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 thiodicarb. The drinking water assessment will incorporate model estimates of thiodicarb 

residues of concern, including methomyl and any other degradates to be determined, in surface 

and ground waters. In contrast to the approach for ecological assessment, all sources of 

thiodicarb and methomyl will be considered, including direct applications of methomyl as a 

pesticide active ingredient. Whether exposure estimates will reflect thiodicarb separately from 

methomyl or as methomyl equivalents will depend on the toxicity differential of the compounds. 

Concentrations of thiodicarb residues of concern in surface water will be estimated using 

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-39 of 83-

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

thiodicarb 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 thiodicarb are sufficient 

for exposure assessment, with two exceptions. The aerobic aquatic metabolism data were 

waived in 1993 when aquatic uses were removed from the labels (DP barcode 186638+); 

however, this study is currently requested in order to describe the fate of thiodicarb in surface 

water bodies down gradient from terrestrial use sites. Submission of an independent laboratory 

validation of the environmental chemistry method in soil is also necessary in order to evaluate 

the submitted terrestrial field dissipation studies. Although not necessary for exposure 

assessment, submission of an environmental chemistry method in water and an associated 

independent laboratory validation is also requested in order to support enforcement and 

monitoring purposes at the federal, state, and local levels. Draft Data Call-In (DCI) tables for 

these data are provided in APPENDIX C. 

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). It is notable that many studies were submitted in 

the 1970s, prior to the publication of FIFRA GLP standards. Most of these studies are expected 

to be deficient relative to current standards and to not provide useful information for risk 

assessment. Therefore, reviews of these studies were not finalized where data requirements were 

met by other acceptable data. If a formal review is available for a study conducted prior to GLP 

standards, the study classification is provided. 
TABLE 7.1. Environmental Fate Data Requirement Table for Thiodicarb.

OPPTS 

Guideline 

Data Requirement Submitted 

Studies 

(MRID) 

Classification Data 

Gap? 

Comments 

44300 (pre-GLP)A 835.2120 Hydrolysis 

42342601 

(same as 

42142901) 

Acceptable 

No. -- 

44301 (pre-GLP)A 835.2240 Aqueous photolysis 

41250008 Acceptable 

No. MRID 41250008 is acceptable with 

additional data submitted to the Agency 

in a letter dated Feb. 6, 1992 and 

reviewed under DP barcode 175388. 

44308 (pre-GLP)A 835.2410 Soil photolysis 

43463401 Acceptable 

No. -- 

44307 (pre-GLP)A 835.4100 Aerobic soil 

metabolism 42142601 Acceptable 

No. -- 

835.4200 Anaerobic soil 

metabolism 

44307 (pre-GLP)A No. Additional data are not expected to alter 

risk conclusions. 

835.4300 Aerobic aquatic 

metabolism 

(none) -- Yes. The data requirement was waived in 1993 

because aquatic uses were deleted from 

the labels (DP barcode 186638+). The 

data are currently requested in order to 

support assessment of the terrestrial uses.

835.4400 Anaerobic aquatic 

metabolism 

42142602 Acceptable No. -- 

44302 (pre-GLP)A

44306 (pre-GLP)A

835.1230 

835.1240 

Adsorption/ 

desorption and 

leaching 41998501 Acceptable 

No. -- 

835.1410 Laboratory 

volatility 

43222901 Acceptable No. -- 

44306 (pre-GLP; 

upgradeable)A

44312 (pre-GLP)A

40643001 Supplemental 

Terrestrial field 

dissipation 

42203901 Upgradeable 

835.6100 

Analytical method 

in soil 

44082 Upgradeable 

Yes. The submitted analytical method in soil 

has not been independently validated. 

The submitted terrestrial field dissipation 

studies are not acceptable without 

independent validation of the analytical 

method in soil. 

835.6200 Analytical method 

in water 

(none) -- Yes. An independently validated analytical 

method in water is requested. 

44304 (pre-GLP)A

44309 (pre-GLP; 

upgradeable)A

44310 (pre-GLP)A

139426 (pre-GLP; 

unacceptable)A

850.1730 Fish 

bioconcentration 

42834002 Acceptable 

No. -- 

A. “Pre-GLP” means that the study was conducted prior to FIFRA GLP standards and is not expected to provide 

useful information. If the data have been reviewed, the classification is added. 

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7.8.2. Effects Data for Thiodicarb 

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

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

following: avian acute oral toxicity, early-life stage estuarine/marine fish toxicity, 

estuarine/marine invertebrate life-cycle, terrestrial plant, and vascular aquatic plant toxicity 

studies. These data gaps are discussed below. 

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

Thiodicarb and Remaining Data Gaps.

Guideline Description MRID/ 

Accession 

Classification Data 

Gap? 

Comments 

850.2100 Avian oral toxicity 46478 Acceptable Yes* 

850.2200 Avian dietary toxicity 46479 Acceptable 

46480 Acceptable 

No 

850.2300 Avian reproduction 43313003 Acceptable No 

43313004 Acceptable No 

850.3020 Honeybee acute 

contact toxicity 

42528501 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. 

-41 of 83-
TABLE 7.3. Available Ecological Effects Data for Aquatic Animals Exposed to Thiodicarb 

and Remaining Data Gaps.

Guideline Description MRID/ 

Accession Classification Data Gap? comments 

41605502 Acceptable 

850.1075 00044273 Acceptable 

Freshwater fish – 

Acute toxicity 

41605501 Acceptable 

No 

42738501 Acceptable 850.1075 Saltwater fish – 

Acute toxicity 41891005 Acceptable 

No 

00100688 Supplemental 

00044276 Acceptable 

41605503 Acceptable 

850.1010 

Freshwater 

invertebrates – 

Acute toxicity 

43052801 Acceptable 

No 

42342501 Supplemental 

42917301 Acceptable 

42834001 Supplemental 

41891006 Supplemental 

42738504 Acceptable 

42738503 Acceptable 

41891007 Acceptable 

00044277 Supplemental 

850.1025 

850.1035 

Saltwater invertebrates 

– 

Acute toxicity 

00044278 Supplemental 

No 

850.1300 

Freshwater 

invertebrate – 

 life cycle test 

00100688 Acceptable No 

850.1350 

Saltwater invertebrates 

– 

life cycle test 

None Not applicable Yes* 

850.1400 Freshwater fish – 

early life stage test 44484101 Supplemental No 

850.1400 Saltwater fish – 

early life stage test None Not applicable Yes* 

*Since the LC50 values for the 

most sensitive 

estuarine/marine fish and 

invertebrate species tested are 

< 1 mg/L, an estuarine/marine 

invertebrate life cycle test and 

an estuarine/marine fish early 

life stage test are required 

under the new 40 CFR Part 

158. Therefore, these are 

identified as a data gaps. 

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TABLE 7.4. Available Ecological Effects Data for Plants Exposed to Thiodicarb and 

Remaining Data Gaps.

Guideline Description MRID Classification Data 

Gap? comments 

850.4100 

Terrestrial Plant 

toxicity: Tier I seedling 

emergence 

None Not applicable Yes* 

850.4225 

Terrestrial Plant 

toxicity: Tier II seedling 

emergence 

None Not applicable No** 

850.4150 

Terrestrial Plant 

toxicity: Tier I 

vegetative vigor 

None Not applicable Yes* 

850.4250 

Terrestrial Plant 

toxicity: Tier II 

vegetative vigor 

None Not applicable No** 

850.5400 Aquatic Plant Growth: 

algae 42324801 Acceptable No 

850.4400 Aquatic Plant Growth: 

vascular plants None Not applicable Yes* 

* Terrestrial plant toxicity data 

are required but are not 

available for thiodicarb. Tier I 

vegetative vigor and seedling 

emergence studies are 

required. Additionally, 

toxicity data for vascular 

aquatic plants, which are 

required, are not currently 

available. 

Therefore, these studies are 

identified as a data gaps. 

** Tier II studies may be 

required depending on the 

results of the Tier I terrestrial 

plant studies. 

Avian Acute Oral Toxicity 

Acceptable acute avian oral toxicity data were submitted for exposures of bobwhite quail to 

thiodicarb; 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 (OPPTS Guideline 850.2100) is required for passerine birds, as specified 

in 40 CFR Part 158 (Oct. 26, 2007). EFED recommends that SRRD 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. 

Chronic Toxicity Studies with Estuarine/Marine Fish and Invertebrates 

Chronic toxicity data for thiodicarb are not available for estuarine/marine fish or invertebrates. 

Since the LC50 values for the most sensitive estuarine/marine fish and invertebrate species tested 

are < 1 mg/L, these data are required under the new 40 CFR Part 158 (Oct. 26, 2007). Although 

thiodicarb is expected to rapidly degrade to methomyl in many aquatic environments, it is 

expected to be moderately persistent in low pH waters. Therefore, chronic exposure to 

estuarine/marine animals from registered uses of thiodicarb is possible. Therefore, an 

estuarine/marine invertebrate life cycle toxicity test (OPPTS Guideline 850.1350) and an 

estuarine/marine fish early life stage toxicity test (OPPTS Guideline 850.1400) are required. In 

the absence of chronic thiodicarb toxicity data for estuarine/marine invertebrates and fish, the 

Agency will assume risks to estuarine/marine animals from the use of thiodicarb. 

-43 of 83-
Terrestrial Plant and Vascular Aquatic Plant Studies 

Aquatic (both vascular and non-vascular species) and 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 (OPPTS Guidelines 850.4225 and 

850.4250) 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. Some thiodicarb labels (i.e., EPA 

Registration No. 264-379, 264-378, and 264-530) do contain the following statement: 

“Horticultural varieties of many plants differ significantly in sensitivity to pesticides. 

Before making applications to plants not listed, it is recommended that a small 

portion of the crop be treated to determine its tolerance to this product. Plants 

stressed from heat, moisture or other factors are usually more sensitive to sprays. 

Phytotoxic reactions can be minimized by spraying when stress is minimal such as 

early mornings or late evenings.” 

The Agency confirmed with the registrant that this label statement is included on the label as a 

general precaution and is not the result of known phytotoxic effects. Therefore, the requirement 

for Tier II plant studies for thiodicarb is not triggered by this label statement. Tier I seedling 

emergence and vegetative vigor studies (OPPTS Guidelines 850.4100 and 850.4150) are, 

however, required. If toxicity data for terrestrial plants are not submitted for thiodicarb, EFED 

will assume risk for terrestrial plants. 

 

Additionally, toxicity data for vascular aquatic plants (Tier I, OPPTS Guideline 850.4400) are 

not currently available for thiodicarb. If toxicity data for vascular aquatic plants are not 

submitted for thiodicarb, EFED will assume risk for vascular aquatic plants. 

7.8.3. Effects Data for Methomyl 

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

aquatic and terrestrial organisms, data gaps still exist (Tables 7.5-7.7). Data gaps include the 

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

toxicity studies. These data gaps are discussed below. 

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TABLE 7.5. 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 oral toxicity 00161886 Acceptable Yes* 

45299802 Acceptable 

45299801 Acceptable 

850.2200 Avian 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, mallard 

ducks appear more sensitive to 

methomyl than to thiodicarb 

and more sensitive than 

bobwhite quail to methomyl on 

a chronic exposure basis. 

Therefore, chronic toxicity 

data for mallard ducks and 

methomyl could result in a 

lower avian chronic toxicity 

endpoint and this is, thus, 

identified as a data gap. 

-45 of 83-
TABLE 7.6. 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 

-46 of 83-
TABLE 7.7. 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** 

*Although data from Tier I 

terrestrial plant studies (unless 

there are known phytotoxic 

concerns) are required, 

methomyl is not expected to 

pose a risk to terrestrial plants. 

Therefore, we do not 

recommend requesting these 

data for methomyl at this time. 

** Toxicity data for vascular 

and non-vascular 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 (OPPTS Guideline 850.2100) is required for 

passerine birds, as specified in 40 CFR Part 158 (Oct. 26, 2007). EFED recommends that SRRD 

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 (OPPTS 850.2300). 

Currently acceptable data for methomyl are only available for upland game species. 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 assume that mallard ducks may be more sensitive to methomyl than to thiodicarb 

and that they may be more sensitive than bobwhite quail to methomyl on a chronic exposure 

-47 of 83-
basis. Therefore, 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 

thiodicarb, 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. Furthermore, methomyl is registered for use on a variety of plants, it has been 

registered since 1968, and there are no terrestrial plant incidents reported for methomyl. 

Additionally, several efficacy studies that were conducted to test the effects of methomyl on a 

variety of invertebrate target and non-target pests also supplied information on effects to plants 

after methomyl applications. None of the studies showed any adverse effects to terrestrial plants 

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

application rate for methomyl) (see Section 4.2). Therefore, the available data based on a lack of 

plant incidents and a lack of effects to plants in efficacy studies suggest that methomyl will not 

adversely affect terrestrial plants. We do not recommend requesting these data for methomyl at 

this time. 

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 (CFR Part 158). Toxicity data for both vascular and non-vascular 

aquatic plants (Tier I, OPPTS 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. 

8. References 

Food and Agriculture Organization of the United Nations (FAO). 2000. Appendix 2. Parameters of pesticides that 

influence processes in the soil. In FAO Information Division Editorial Group (Ed.), Pesticide Disposal 

Series 8. Assessing Soil Contamination: A Reference Manual. Rome: Food & Agriculture Organization of 

the United Nations. http://www.fao.org/DOCREP/003/X2570E/X2570E06.htm

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation of the EPA food-chain 

(Kenaga) nomogram, an instrument for estimating pesticide residues on plants. Environ. Tox. Chem. 

13:1383-1391. 

Hoerger, F. and E. E. Kenaga. 1972. Pesticide Residues on Plants: Correlation of Representative Data as a Basis 

for Estimation of their Magnitude in the Environment. In F. Coulston and F. Korte, eds., Environmental 

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Quality and Safety: Chemistry, Toxicology, and Technology, Georg Thieme Publ., Stuttgart, West 

Germany, pp. 9-28. 

U.S.Department of Agriculture (USDA). 2007. National Agricultural Statistics Service. United States Department 

of Agriculture. http://www.nass.usda.gov/

U.S. Environmental Protection Agency (USEPA). 1997a. Jones, R. D. Tier 1 Estimated Environmental 

Concentrations for Thiodicarb. DP barcode not reported. U.S. Environmental Protection Agency, Office 

of Prevention, Pesticides, and Toxic Substances, Special Review Section. Memorandum to Reregistration 

Section. May 7, 1997. 

USEPA. 1997b. Thurman, N. Tier 2 Estimated Environmental Concentrations for Thiodicarb and Methomyl. DP 

barcode not reported. U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic 

Substances, Environmental Fate and Effects Division. Memorandum to Health Effects Division. May 29, 

1997. 

USEPA. 1998. Guidelines for Ecological Risk Assessment. Risk Assessment Forum, Office of Research and 

Development, Washington, D.C. EPA/630/R-95/002F. April 1998. 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=30759 

USEPA. 1998. Registration Eligibility Decision (RED): Thiodicarb. U.S. Environmental Protection Agency, 

Office of Prevention, Pesticides, and Toxic Substances, Washington, DC. EPA 738-R-98-022. December, 

1998. http://www.epa.gov/oppsrrd1/REDs/2675red.pdf 

USEPA. 2002. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of 

Pesticides, Version II. US Environmental Protection Agency, Washington DC. Online at: 

http://www.epa.gov/oppefed1/models water/input_guidance2_28_02.htm. 

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs. U.S. 

Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of 

Pesticide Programs, Washington DC. January 23, 2004. 

USEPA. 2006a. Standardized Soil Mobility Classification Guidance. U.S. Environmental Protection Agency, 

Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Environmental Fate 

and Effects Division, Memorandum. April 21, 2006. 

USEPA. 2007a. Young, D. Refined Methomyl Surface Water Drinking Water Assessment with Time Series and 

Regional PCA. DP barcode 339492. U.S. Environmental Protection Agency, Office of Prevention, 

Pesticides, and Toxic Substances, Environmental Fate and Effects Division. Memorandum to Health 

Effects Division and Special Review and Reregistration Division. May 16, 2007. 

USEPA. 2007b. Revised N-Methyl Carbamate Cumulative Risk Assessment. U.S. Environmental Protection 

Agency, Office of Pesticide Programs. Sep., 24, 2007. 

USEPA. 2007c. Ecological Incident Information System. http://www.epa.gov/espp/consultation/ecoriskoverview.pdf

USEPA. 2007d. 40 CFR Part 158. Pesticides; Data Requirements for Conventional Chemicals: Final Rule. 72 FR 

60934. October 26, 2007. 

USEPA. 2007e. ECOTOXicology Database. Office of Research and Development National Health and 

Environmental Effects Research Laboratory’s (NHEERL’s) Mid-Continent Ecology Division (MED). 

http://cfpub.epa.gov/ecotox/. 

USEPA. 2009. Orrick, G. Refined Tier II Drinking Water Exposure Assessment for the Section 3 New Use 

Registration of Oxamyl on Sugar Beets. DP Barcode 351367. U.S. Environmental Protection Agency, 

-49 of 83-
Office of Prevention, Pesticides and Toxic Substances, Environmental Fate and Effects Division. 

Memorandum to the Registration Division and Health Effects Division. Initial edition: Mar. 4, 2009; 

replaced: Mar. 25, 2009; replaced: May 11, 2009. 

U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS). 1998. Endangered 

Species Consultation Handbook: Procedures for Conducting Consultation and Conference Activities Under 

Section 7 of the Endangered Species Act. Final Draft. March 1998. 

Worthing, C. R and R. J. Hance, editors. 1991. The Pesticide Manual: A World Compendium (9th edition). British 

Crop Protection Council, Surrey, UK. June, 1991. 

SUBMITTED ENVIRONMENTAL FATE STUDIES (Thiodicarb):

MRID:

41250004 Kurtz, A.; Asbury, C. (1976) Fundamental Studies of Structure-activity in Pesticides...: Project No. 

111A28: File No. 22018. Unpublished study prepared by Union Carbide Corp. 72 p. 

41250008 Feung, C.; Blanton, C. (1987) Larvin: Photolysis of Thiodicarb in Aqueous Buffered Solutions: 

Project No. 804R14: File No. 40254. Unpublished study prepared by Rhone-Poulenc Ag Co. 30 p. 

41482002 Seymour, R. (1988) Thiodicarb Solubility in Water: Lab Project No: 804C10: 40357. Unpublished 

study prepared by Rhone-Poulenc Ag Co. 9 p. 

41998501 Cranor, W. (1991) Soil Adsorption/Desorption with 14C-Thiodicarb: Lab Project Number: 37453. 

Unpublished study prepared by ABC Laboratories. 350 p. 

42142601 Feung, C.; Weisbach, P. (1991) Aerobic Soil Metabolism of Thiodicarb: Lab Project Number: EC-91-

142. Unpublished study prepared by Rhone-Poulenc Ag Co. 74 p. 

42142602 Feung, C.; Weisbach, P. (1991) Metabolism of 14C-Thiodicarb Under Anaerobic Aquatic Conditions: 

Lab Project Number: EC-91-155. Unpublished study prepared by Rhone-Poulenc Ag Co. 72 p. 

42203901 Norris, F. (1991) A Terrestrial Field Soil Dissipation Study with Thiodicarb: Lab Project Number: 

41036: EC-89-036. Unpublished study prepared by Rhone-Poulenc Ag Co., Colorado Analytical 

Research and Devel. Corp. and A & L Eastern Agricultural Labs., Inc. 245 p. 

42342601 Feung, C.; Weisbach, P. (1991) Hydrolysis of Thiodicarb in Aqueous Buffer Solutions: Amended 

Report: Lab Project Number: EC-91-143. Unpublished study prepared by Rhone-Poulenc Ag Co. 42 

p. 

42834002 Blasberg, J.; Hicks, S.; Stuerman, L. (1993) Uptake, Depuration, Bioconcentration, and Metabolism 

of (14C)-Thiodicarb by Bluegill Sunfish (Lepomis macrochirus): Final Report: Lab Project Number: 

40046. Unpublished study prepared by ABC Labs., Inc. 164 p. 

43222901 Flynn, J. (1994) Laboratory Volatility of Thiodicarb from Soil: Lab Project Number: 41352: EC-93-

249. Unpublished study prepared by ABC Laboratories, Inc. 75 p. 

43463401 Das, Y. (1989) Photodegradation of (Acetyl-1-(14C)) Thiodicarb on Soil under Artificial Sunlight: 

Lab Project Number: 89120. Unpublished study prepared by Innovative Scientific Services, Inc. 97 p. 

SUBMITTED ENVIRONMENTAL FATE STUDIES (Methomyl):

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. 

-50 of 83-
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. 

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. 

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 

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. 

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. 

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. 

-51 of 83-
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. 

SUBMITTED EFFECTS STUDIES (Thiodicarb):

MRID:

44277 Vilkas, A.G.; Seminara, J. (1980) The Acute Toxicity of Larvin Thiodicarb Insecticide Fiddler 

Crab,~Uca pugilator~?: UCCES Project No. 11504-25-03. (Unpublished study received Sep 10, 1980 

under 264-341; submitted by Union Carbide Agricultural Products Co., Ambler, Pa.; CDL:099603-K) 

44278 Vilkas, A.G.; Seminara, J. (1980) The Acute Toxicity of Larvin Thiodicarb Insecticide to the Grass 

Shrimp,~Palaemonetes~ ?~pugio~?: UCCES Project No. 11504-25-04. (Unpublished study received 

Sep 10, 1980 under 264-341; submitted by Union Carbide Agricultural Products Co., Ambler, Pa.; 

CDL:099603-L) 

46478 Fink, R.; Beavers, J.B.; Brown, R.; et al. (1978) Final Report: Acute Oral LD50--Bobwhite Quail: 

Project No. 142-117. (Unpub- lished study received Sep 9, 1980 under 264-343; prepared by Wildlife 

International, Ltd. and Washington College, submitted by Union Carbide Agricultural Products Co., 

Inc., Ambler, Pa.; CDL:243243-C) 

44270 Fink, R.; Beavers, J.B.; Grimes, J.; et al. (1978) Final Report: Eight-Day Dietary LC50--Mallard 

Duck: Project No. 142-116. (Un- published study received Sep 10, 1980 under 264-341; prepared by 

Wildlife International, Ltd., submitted by Union Carbide Agri- cultural Products Co., Indianapolis, 

Ind.; CDL:099603-C) 

44271 Fink, R.; Beavers, J.B.; Grimes, J.; et al. (1978) Final Report: Eight-Day Dietary LC50--Bobwhite 

Quail: Project No. 142-115. (Unpublished study received Sep 10, 1980 under 264-341; prepared by 

Wildlife International, Ltd., submitted by Union Carbide Agricultural Products Co., Ambler, Pa.; 

-52 of 83-
CDL:099693-D) 

46479 Fink, R.; Beavers, J.B.; Brown, R.; et al. (1978) Final Report: Eight-Day Dietary LC50--Mallard 

Duck: Project No. 142-116. (Unpublished study received Sep 9, 1980 under 264-343; prepared by 

Wildlife International, Ltd. and Washington College, submit- ted by Union Carbide Agricultural 

Products Co., Inc., Ambler, Pa.; CDL:243243-D) 

46480 Fink, R.; Beavers, J.B.; Brown, R.; et al. (1978) Final Report: Eight-Day Dietary LC50--Bobwhite 

Quail: Project No. 142-115. (Unpublished study received Sep 9, 1980 under 264-343; prepared by 

Wildlife International, Ltd. and Washington College, submit- ted by Union Carbide Agricultural 

Products Co., Inc., Ambler, Pa.; CDL:243243-E) 

43313003 Pedersen, C. (1994) Thiodicarb Technical: Toxicity and Reproduction Study in Bobwhite Quail: Lab 

Project Number: 108/021/07: HWI/6375/108B. Unpublished study prepared by Bio- Life Associates, 

Ltd. 421 p. 

43313004 Pedersen, C.; Solatycki, A. (1994) Thiodicarb Technical: Toxicity and Reproduction Study in Mallard 

Ducks: Lab Project Number: 108/022/08: HWI/6375/108B. Unpublished study prepared by Bio-Life 

Associates, Ltd. 590 p. 

41605501 Bowman, J. (1990) Acute Flow-through Toxicity of Thiodicarb to Blue gill (Lepomis macrochirus): 

Final Report: Lab Project Number: 38365. Unpublished study prepared by Analytical Bio-chemistry 

Laboratories, Inc. 213 p. 

41605502 Bowman, J. (1990) Acute Flow-through Toxicity of Thiodicarb to Rain bow Trout (Oncorhynchus 

mykiss): Final Report: Lab Project No: 38366. Unpublished study prepared by Analytical Biochemistry Laboratories, Inc. 207 p. 

41605503 Burgess, D. (1990) Acute Flow-through Toxicity of Thiodicarb to Daphnia magna: Final Report: Lab 

Project Number: 38367. Unpub- lished study prepared by Analytical Bio-chemistry Laboratories, Inc. 

89 p. 

43052801 Blakemore, G.; Stratton, J.; Bussard, J. (1992) Acute Toxicity of LARVIN 3.2 (Thiodicarb) to 

Daphnia magna Under Flow-through Conditions: Lab Project Number: 39111. Unpublished study 

prepared by ABC Labs, Inc. 583 p. 

41891005 Machado, M. (1991) Thiodicarb Technical--Acute Toxicity to Sheeps- head Minnow (Cyprino-don 

variegatus) under Flow-through Condi- tions: Lab Project Number: 91-4-3731: 10566. 1289. 6155. 

505. Unpublished study prepared by Springborn Labs, Inc. 67 p. 

41891006 Dionne, E. (1991) Thiodicarb Technical--Acute Toxicity to Eastern Oyster (Crassostrea virginica) 

under Flow-through Conditions: Final Report: Lab Project Number: 91-4-3738: 10566.1289.6154.504 

Unpublished study prepared by Springborn Labs, Inc. 65 p. 

41891007 Sousa, J. (1991) Thiodicarb Technical--Acute Toxicity to Mysid Shrimp (Mysidopsis bahia) under 

Flow-through Conditions: Final Report: Lab Project Number: 90-5-3342: 10566. 1289. 6153. 515. 

Unpublished study prepared by Springborn Labs, Inc. 53 p. 

42342501 Dionne, E. (1991) Larvin 3.2--Acute Toxicity to Eastern Oyster (Crassostrea virginica) Under Flowthrough Conditions: Final Report: Lab Project Number: 91-3-3711: 10566.1090.6173.504. 

Unpublished study prepared by Springborn Labs, Inc. 65 p. 

42738501 Sousa, J. (1992) Larvin 3.2--Acute Toxicity to Sheepshead Minnow (Cyprinodon variegatus) under 

Flow-Through Conditions: Final Report: Lab Project Number: 91-8-3897: 10566.0190.6174.505. 

Unpublished study prepared by Springborn Labs, Inc. 62 p. 

42738502 Sousa, J. (1992) Larvin 80DF--Acute Toxicity to Sheepshead Minnow (Cyprinodon variegatus) under 

Flow-Through Conditions. Final Report: Lab Project Number: 91-9-3925: 10566.0190.6171.505. 

Unpublished study prepared by Springborn Labs, Inc. 64 p. 

-53 of 83-
42738503 Sousa, J. (1992) Larvin 3.2--Acute Toxicity to Mysid Shrimp (Mysidopsis bahia) under Flow-Through 

Conditions: Final Report: Lab Project Number: 91-1-3634: 10566.1090.6172.515. Unpublished study 

prepared by Springborn Labs, Inc. 62 p. 

42738504 Sousa, J. (1992) Larvin 80DF--Acute Toxicity to Mysid Shrimp (Mysidopsis bahia) under FlowThrough Conditions: Final Report: Lab Project Number: 91-8-3896: 10566.1090.6169.515. 

Unpublished study prepared by Springborn Labs, Inc. 64 p. 

42834001 Dionne, E. (1993) Larvin 80DF--Acute Toxicity to Eastern Oyster (Crassostrea virginica) under FlowThrough Conditions: Final Report: Lab Project Number: 91-9-3920: 10566.1090.6170.504. 

Unpublished study prepared by Springborn Labs., Inc. 64 p. 

42917301 Dionne, E. (1993) Larvin 80DF-Acute Toxicity to Eastern Oyster (Crassostrea virginica) Under FlowThrough Conditions: Amended Final Report: Lab Project Number: 10566.1090.6170.504: 91-9-3920. 

Unpublished study prepared by Springborn Labs, Inc. 65 p. 

44273 Vilkas, A.G.; Seminara, J. (1980) The Acute Toxicity of Larvin Thiodicarb Insecticide to the Bluegill 

Sunfish,~Lepomis macro~?- ?~chirus~Rafinesque: UCCES Project No. 11504-25-07. (Unpub- lished 

study received Sep 10, 1980 under 264-341; submitted by Union Carbide Agricultural Products Co., 

Ambler, Pa.; CDL: 099603-G) 

44484101 Sousa, J. (1997) Thiodicarb Technical--Early Life-Stage Toxicity Test with Fathead Minnow 

(Pimephales promelas): Final Report: Lab Project Number: 97-1-6867: 10566.0796.6404.120. 

Unpublished study prepared by Springborn Laboratories, Inc. 85 p. (Relates to L0000176) 

42324801 Oldersma, H.; Hanstviet, A. (1991) Effect of Thiodicarb on the Growth of the Alga Selenastrum 

Capricornutum: Lab Project Number: R 90/457. Unpublished study prepared by Rhone-Poulenc. 29 p. 

42528501 Petto, R. (1992) Acute Contact LD50 of Thiodicarb to Honey Bees (Apis mellifera L.) (Hymenoptera, 

Apidae): Lab Project Number: 305201. Unpublished study prepared by RCC Umweltchemie GmbH & 

Co. KG. 20 p. 

 44276 Vilkas, A.G.; Browne, A.M. (1980) The Acute Toxicity of Larvin (Thiodicarb, UC51762) to the Water 

Flea~Daphnia magna~Straus: UCCES Project No. 11504-25. (Unpublished study received Sep 10, 

1980 under 264-341; submitted by Union Carbide Agricultural Products Co., Ambler, Pa.; 

CDL:099603-J) 

44309 Kuc, W.J. (1979) 14C-UC 51762, Bluegill Sunfish Lepomis macrochirus Bioconcentration Study: 

UCES Project No. 11504-20. (Unpublished study received Sep 10, 1980 under 264-341; submitted by 

Union Carbide Agricultural Products Co., Ambler, Pa.; CDL:099602-M) 

44310 Kuc, W.J.; Jones, C.N. (1979) 14C-UC 51762, Channel Catfish, Ictalurus punctatus (Rafinesque) 

Bioconcentration Study: UCES Project No. 11504-20. (Unpublished study including published data, 

received Sep 10, 1980 under 264-341; submitted by Union Carbide Agricultural Products Co., Ambler, 

Pa.; CDL:099602-N) 

100688 Booth, G.; Carter, M.; Price, R.; et al. (1982) The Acute and Chronic Toxicities of Larvin to Daphnia 

Magna Using a Static Renewal System. Final rept. (Unpublished study received May 4, 1982 under 

264-341; submitted by Union Carbide Agricultural Products Co., Inc., Ambler, PA; CDL:247397-A) 

45565801 Nienstedt, K. (2001) Larvin SC 375: Dose Response Toxicity Test with the Parasitic Wasp, Aphidius 

Rhopalosiphi (Hymenoptera: Braconidae): Final Report: Lab Project Number: 1067.007.670: 31570. 

Unpublished study prepared by Springborn Laboratories (Europe) AG. 27 p. 

-54 of 83-
SUBMITTED EFFECTS STUDIES (Methomyl):

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). 

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. 

-55 of 83-
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. 

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. 

-56 of 83-
-57 of 83-

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. 

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. 
APPENDIX A. Toxicity Data for Thiodicarb and Methomyl: 

TABLE 1. Submitted Toxicity Data for Thiodicarb (Excluding Invalid Studies): 

TAXON ENDPOINT FORMULATION MRID 

STUDY 

CLASSIFICATION 

COMMENTS 

BIRDS 

Birds (Acute) 

Bobwhite quail 

(Colinus 

virginianus) 

LD50 = 2,023 

mg a.i./kg-bw TGAI (99+%) 46478 (also, 00044269) Acceptable 

NOAEL could not be 

determined because reductions 

in weight gain at all treatment 

levels; slope = 4.1 (1.6 – 6.6) 

Birds (Acute/Sub-Acute)

Mallard duck 

(Anas 

platyrhynchos) 

96-hr LC50 = 

>5,620 mg 

a.i./kg=diet 

TGAI (99+%) 46479 (also, 

00044270) Acceptable 

NOAEC = 1,780 mg a.i./kgdiet (LOAEC = 5,620 mg 

a.i./kg-diet based on reduction 

in food consumption and body 

weight gain) 

Bobwhite quail 

(Colinus 

virginianus) 

96-hr LC50 = 

>5,620 mg 

a.i./kg=diet 

TGAI (99+%) 46480 (also, 

00044271) Acceptable 

No mortalities associated with 

treatment; NOAEC = 3160 mg 

a.i./kg-diet based on reduced 

food consumption at 5620 mg 

a.i./kg-diet 

Birds (Chronic) 

Bobwhite quail 

(Colinus 

virginianus) 

NOAEC = 

1,000 mg 

a.i./kg-diet 

LOAEC = 

>1,000 mg 

a.i./kg-diet 

TGAI (94.6%) 

43313003 

and 

43389201 

Acceptable No reproductive effects seen 

at any concentration tested. 

Mallard duck 

(Anas 

platyrhynchos) 

NOAEC = 500 

mg a.i./kg-diet TGAI (94.6%) 

43313004 

and 

43389202 

Acceptable 

LOAEC = 1,000 mg a.i./kgdiet, based on reduction in 

number of eggs laid/hen 

MAMMALS 

Mammals (acute) 

Laboratory rat 

(Rattus 

norvegicus)

LD50 = 39.1 mg 

a.i./kg-bw TGAI 00025791 Acceptable None 

Mammals (Chronic)

Laboratory rat 

(Rattus 

norvegicus) 

NOAEL = 100 

mg a.i./kg-diet 

(5 mg 

a.i./kg/day) 

LOAEL = 300 

mg a.i./kg-diet 

(15 mg 

a.i./kg/day) 

TGAI 42381301 Acceptable LOAEL based on decreased 

fetal body weight and viability 

-58 of 83-
TAXON ENDPOINT FORMULATION 

STUDY 

MRID CLASS- COMMENTS 

IFICATION 

TERRESTRIAL INVERTEBRATES 

Honey bee 

(Apis mellifera) 

48-hr LD50 = 

>25 μg a.i./bee TGAI (99.95%) 42528501 Acceptable 

Acute contact; NOAEL = 3.1 

μg a.i./bee; highest mortality 

was 37% at the highest 

concentration tested (i.e., 25 

μg a.i./bee) 

Wasp (Aphidius 

rhopalosiphi) 

48-hr LC50 = 

1.2 g product/ha 

Formulation 

(Larvin® SC 375, 

38% a.i.) 

45565801 

Supplemental 

(not adequate 

for RQ 

calculation – 

not a product 

currently 

registered in 

the US) 

Scientifically sound, but a 

non-guideline study (48-hr 

exposure phase followed by 

24-hr fecundity phase 

followed by 9-10 days 

observation); reduced number 

of eggs/female in all treatment 

groups (NOAEC <0.313 g 

product/ha); slope = 2.21 (1.59 

– 2.83) 

FRESHWATER FISH 

Freshwater Fish (Acute) 

Rainbow trout 

(Oncorhynchus 

mykiss) 

LC50 = 3.45 mg 

a.i./L TGAI (94.5%) 41605502 Acceptable A slope could not be determined 

Bluegill sunfish 

(Lepomis 

macrochirus) 

LC50 = 1.21 mg 

a.i./L TGAI (99%) 00044273 Acceptable A slope could not be determined 

Bluegill sunfish 

(Lepomis 

macrochirus) 

LC50 = 1.47 mg 

a.i./L TGAI (99.95%) 41605501 Acceptable Slope = 6.48 (3.8 – 9.2) 

Freshwater Fish (Chronic) 

Fathead 

minnow 

(Pimephales 

promelas) 

NOAEC = 

0.025 mg a.i./L TGAI (98.9%) 44484101 Supplemental 

Early life-stage; only two 

replicates (instead of 4) were 

used; sub-lethal signs of 

toxicity were not reported; 

LOAEC = 0.053 mg a.i./L 

[based on reduced larval 

growth – total length (4%) and 

wet weight (14.3%)] 

ESTUARINE/MARINE FISH 

Estuarine/Marine Fish (Acute) 

Sheepshead 

minnow 

(Cyprinodon 

variegates) 

96-hr LC50 = 

0.49 mg a.i./L 

Formulation 

(Larvin® 80DF, 

81.1% a.i.) 

42738502 Supplemental 

The NOAEC could not be 

determined; slope = 2.9 (1.8 – 

3.9); formulation not currently 

registered in the U.S. 

Sheepshead 

minnow 

(Cyprinodon 

variegates) 

96-hr LC50 = 

0.47 mg a.i./L 

Formulation 

(Larvin® 3.2, 

33.2% a.i.) 

42738501 Acceptable 

NOAEC could not be 

determined; slope = 4.4 (3.1 – 

5.8) 

Sheepshead 

minnow 

(Cyprinodon 

variegates) 

96-hr LC50 = 

0.53 mg a.i./L TGAI (95.8%) 41891005 Acceptable Slope = 7.1 (4.4 – 9.8) 

-59 of 83-
TAXON ENDPOINT FORMULATION 

STUDY 

MRID CLASS- COMMENTS 

IFICATION 

FRESHWATER INVERTEBRATES 

Freshwater Invertebrates (Acute) 

Daphnid 

(Daphnia 

magna) 

48-hr EC50 = 

~0.050 mg 

a.i./L 

TGAI (97.3%) 00100688 Supplemental Raw data lacking 

Daphnid 

(Daphnia 

magna) 

48-hr EC50 = 

0.0053 mg 

a.i./L 

TGAI (99%) 00044276 Acceptable None 

Daphnid 

(Daphnia 

magna) 

48-hr EC50 = 

0.027 mg a.i./L TGAI (99.95%) 41605503 Acceptable A slope could not be determined 

Daphnid 

(Daphnia 

magna) 

48-hr EC50 = 

0.0488 mg 

a.i./L 

Formulation 

(Larvin® 3.2, 33% 

a.i.) 

43052801 Acceptable A slope could not be 

determined 

Freshwater Invertebrates (Chronic) 

Daphnid 

(Daphnia 

magna) 

NOAEC = 

0.009 mg a.i./L TGAI (97.3%) 00100688 Acceptable Based on reduced survival and total young produced. 

ESTUARINE/MARINE INVERTEBRATES 

Estuarine/Marine Invertebrate (Acute) 

Eastern oyster 

(Crassostrea 

virginica) 

96-hr EC50 = 

1.1 mg a.i./L 

(shell 

deposition) 

Formulation 

(Larvin® 3.2, 

33.2% a.i.) 

42342501 

Supplemental 

(not adequate 

for RQ 

calculation) 

The control oysters did not 

meet the minimum new shell 

growth requirement of 2mm 

(reached 1.49 and 1.59 mm); a 

NOAEC could not be 

calculated 

Eastern oyster 

(Crassostrea 

virginica) 

96-hr EC50 = 

0.55 mg a.i./L 

(shell 

deposition) 

Formulation 

(Larvin® 80DF, 

81.1% a.i.) 

42917301 

(amended 

report 

42834001) 

Acceptable NOAEC = 0.12 mg a.i/.L 

Eastern oyster 

(Crassostrea 

virginica) 

96-hr EC50 = 

could not be 

established 

(shell 

deposition) 

TGAI (95.8%) 41891006 Supplemental 

EC50 was not established due 

to high percentage affected at 

each concentration tested 

(43% to 71% for dosage levels 

0.58 to 4.6 mg a.i./L); effects 

were seen at all concentrations 

(no NOAEL); no raw data 

available to verify results 

Mysid 

(Americamysis 

bahia) 

96-hr LC50 = 

0.075 mg a.i./L 

Formulation 

(Larvin® 80DF, 

81.1% a.i.) 

42738504 Acceptable NOAEC could not be 

determined 

Mysid 

(Americamysis 

bahia) 

96-hr LC50 = 

0.10 mg a.i./L 

Formulation 

(Larvin® 3.2, 

33.2% a.i.) 

42738503 Acceptable NOAEC = 0.035 mg a.i./L; 

slope = 7.4 (4.7 – 10.2) 

Mysid 

(Americamysis 

bahia) 

96-hr LC50 = 

0.0285 mg 

a.i./L 

TGAI (94.5%) 41891007 Acceptable NOAEC = 0.018 mg a.i./L; 

slope = 5.1 (0.62 – 9.6) 

Fiddler crab 

(Uca pugilator) 2.5 mg a.i./L Technical (99%) 44277 Supplemental Slope = 8.5 (3.1 – 13.9) 

Grass shrimp 

(Palaemonetes 

pugio) 

0.067 mg a.i./L Technical (99%) 44278 Supplemental Slope = 4.5 (2.1 – 6.8) 

-60 of 83-
TAXON ENDPOINT FORMULATION 

STUDY 

MRID CLASS- COMMENTS 

IFICATION 

AQUATIC PLANTS 

Aquatic Plants (Non-Vascular) 

Algae 

(Selenastrum 

capricornutum) 

96-hr EC50 = 

>8.3 mg a.i./L 

NOAEC = 1.6 

mg a.i./L 

TGAI (94.5%) 42324801 Acceptable 

LOAEC = 2.4 mg a.i./L based 

on % inhibition of growth 

[max inhibition was 37% at 

the highest concentration 

tested (8.3 mg a.i./L)]; ; 

measured concentrations of 

thiodicarb ranged from 74 to 

88% of nominal at test 

initiation to 21 and 24% 

nominal at termination; 

methomyl went from 5.7 – 

6.4% (study initiation) to 56 – 

60% (at termination) of 

nominal 

-61 of 83-
TABLE 2. 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 lb 

a.i./acre 

Formulation 

(Methomyl®

25WP) 

45133302 Supplemental 

Supplemental 

(non-guideline, but 

scientifically sound) 

Wasp (Aphidius 

rhopalosiphi) 

48-hr LC50 = 

0.00022 lb 

a.i./acre 

Formulation 

(Methomyl® 20L) 45133301 Supplemental 

Supplemental 

(non-guideline, but 

scientifically sound) 

-62 of 83-
TAXON ENDPOINT FORMULATION 

STUDY 

MRID CLASS- COMMENTS 

IFICATION 

Mite 

(Typhlodromus 

pyri)

7-day LC50 = 

0.0114 lb 

a.i./acre 

Formulation 

(Methomyl® 20L) 45125501 Supplemental 

Supplemental 

(non-guideline, but 

scientifically sound) 

Mite 

(Typhlodromus 

pyri)

7-day LC50 = 

0.01115 lb 

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 

LOAEC = 

0.001 mg a.i./L 

TGAI (>99%) 131254 Acceptable LOAEC based on delayed 

reproduction 

-63 of 83-
TAXON ENDPOINT FORMULATION 

STUDY 

MRID CLASS- COMMENTS 

IFICATION 

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 

-64 of 83-
Table 3. 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 

Lepomis 

macrochirus

Bluegill sunfish 

95 

620 400980-01 Supplemental Temp = 17̊C 

pH = 8.5 

Hardness = 40 mg/L 

-65 of 83-
Species Compound LC50 MRID Classification Notes:

(% a.i.) (96-h, 

μg 

a.i./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 

940 400980-01 Supplemental Temp = 17̊C 

pH = 6.0 

Hardness = 40 mg/L 

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 

24 

560 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

-66 of 83-
Species Compound LC50 MRID Classification Notes:

(% a.i.) (96-h, 

μg 

a.i./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 

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 

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 

Ictalurus 

punctatus

Channel catfish 

24 

760 400980-01 Supplemental Temp = 22̊C 

pH = 7.4 

Hardness = 40 mg/L 

fingerlings tested 

-67 of 83-
Species Compound LC50 MRID Classification Notes:

(% a.i.) (96-h, 

μg 

a.i./L)

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 

1100 400980-01 Supplemental Temp = 12̊C 

pH = 7.5 

Hardness = 40 mg/L 

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 

Oncorhyncus 

mykiss

Rainbow trout 

95 

1600 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

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Species Compound LC50 MRID Classification Notes:

(% a.i.) (96-h, 

μg 

a.i./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 

2000 400980-01 Supplemental Temp = 12̊C 

pH = 7.2 

Hardness = 40 mg/L 

24 

2100 400980-01 Supplemental Temp = 10̊C 

pH = 7.2 

Hardness = 40 mg/L 

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Species Compound LC50 MRID Classification Notes:

(% a.i.) (96-h, 

μg 

a.i./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 

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Table 4. Summary of Acute Toxicity Values for Methomyl and Freshwater Invertebrates. 

LC50 (μg 

a.i./L) Species 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 

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-72 of 83-

LC50 (μg 

a.i./L) Species Compound 

(% a.i.)

48-h 96-h

MRID Classification Notes:

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 

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 
APPENDIX B. Major Organic Environmental Degradates of Thiodicarb. 

Table B1. Chemical Names, Structures, and Maximum Reported Amounts of Thiodicarb and Its Major D

Code Name/ Synonym Chemical NameA Chemical Structure Study Type Maxim

%AR (

PARENT

Thiodicarb IUPAC: (3EZ,12EZ)-3,7,9,13-tetramethyl5,11-dioxa-2,8,14-trithia-4,7,9,12-

tetraazapentadeca-3,12-diene-6,10-dione CAS: dimethyl N,N′-

[thiobis[(methylimino)carbonyloxy]]bis[ethanimidothioate] 

CAS-no: 59669-26-0 

Formula: C10H18N4O4S3MW: 354.5 g/mol 

S

N

O

O

N

S

N

O

O

N

S

MAJOR (>10%) DEGRADATES

Hydrolysis -pH 5 Hydrolysis -pH 7 Hydrolysis -pH 9 

20 (336 (3

66 (

Aqueous photolysis 47 (2Soil photolysis 16 (7Aerobic soil 80 (7Anaerobic aquatic 7.2 (

Methomyl IUPAC: S-methyl (EZ)-N- (methylcarbamoyloxy)thioacetimidate 

CAS: methyl N-[[(methylamino)carbonyl]oxy]ethanimidothioateCAS-no: 16752-77-5 

Formula: C5H10N2O2S 

MW: 162.21 g/mol 

N

O

O

N

S

H

Field studies 1.68 ppm 

Hydrolysis -pH 5 Hydrolysis -pH 7 Hydrolysis -pH 9 

0.92 (

3.1 (3

77 (3

Aqueous photolysis 1.7 (2Soil photolysis 27 (3Aerobic soil 3.2 (0Anaerobic aquatic 3.5 (0

Methomyl Oxime 

S-methyl-N-hydroxythioacetimidate Formula: C3H7NOS 

MW: 105.16 g/mol O

N

S

H

Field studies 

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-74 of 83-

Code Name/ Synonym Chemical NameA Chemical Structure Study Type Maxim

%AR (

Hydrolysis Aq. photolysis 15 (2Soil photolysis Aerobic soil 1.8 (6Anaerobic aquatic 73 (1

Acetonitrile Methyl cyanide; cyanomethane 

Formula: C2H3N 

MW: 41.05 g/mol N

Field studies 

Acetamide Ethanamide; acetic acid amide 

Formula: C2H5NO 

MW: 59.07 g/mol NH2

O (all studies) not 

Unknown 3 (not identified) (not identified) Anaerobic aquatic 60 (0.Unknown 4 (not identified) (not identified) Anaerobic aquatic 29 (2

Hydrolysis Aq. photolysis 4.8 (2Soil photolysis Aerobic soil 52 (6Anaerobic aquatic 16 (1

Carbon Dioxide 

Carbon dioxideFormula: CO2

MW: 44.01 g/mol O O

Field studies 

A. IUPAC and CAS chemical names were sourced from the Compendium of Pesticide Common Names (Copyright © 1995–2009 Alan Wood). Onli

http://www.alanwood.net/pesticides/

B. Acetamide was identified as a major degradate of methomyl in an aerobic aquatic metabolism study of methomyl (MRID 43325401). 
APPENDIX C: Data Call-In Tables. 

The Environmental Fate and Effects Division (EFED) has completed a Data Call-In (DCI) table 

for the thiodicarb 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. 

Environmental Fate Data:

Guideline Number: 835.4300 

Study Title: Aerobic Aquatic Metabolism 

Rationale for Requiring the Data 

The Agency has a limited understanding of how thiodicarb behaves in the environment once applied. 

Depending on how quickly, to what extent, and to which transformation products the compound 

degrades, thiodicarb may or may not pose potential exposure concern in water. Because thiodicarb 

degradation in water is not well understood, the Agency is requiring data. 

Practical Utility of the Data 

How will the data be used? 

Aerobic aquatic metabolism data will facilitate a better understanding of the fate of thiodicarb 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 thiodicarb 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 thiodicarb 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, thiodicarb aerobic aquatic metabolism half-lives will be 

conservatively assumed two-fold greater than aerobic soil metabolism half-lives. If the required data 

indicate that thiodicarb in aerobic aqueous environments is rapidly biodegraded, then risk assessment 

conclusions and associated labeled use precautions and/or restrictions could be made less restrictive. 

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Guideline Number: 835.6100 

Study Title: Analytical Method (and Associated Independent Laboratory Validation) for Residues 

in Soil 

Rationale for Requiring the Data 

Independently validated analytical methods for residues in soil, water, sediment, and plant material 

(environmental chemistry methods) submitted by the registrant are used to evaluate analyses described in 

submitted environmental fate and ecological effects studies. Submitted analytical methods are also used 

by various Federal, State, Tribal, and local agencies to detect and monitor residues that are or are 

suspected to be in environmental compartments due to outdoor uses and accidental releases. Independent 

laboratory validations for submitted analytical methods are necessary to confirm that the methods are 

functional and to confirm the levels of detection and quantitation reported in registrant-prepared 

validations. 

An analytical method (a.k.a. environmental chemistry method) for thiodicarb residues in soil was 

submitted by the registrant (MRID 44082). However, an independent validation of this method was not 

submitted with the method. Therefore, an independent laboratory validation of the submitted analytical 

method for thiodicarb residues in soil (MRID 44082) is required to support monitoring for thiodicarb 

residues and to evaluate submitted environmental fate and ecological effects data. Alternatively, a stateof-the-art analytical method and independent laboratory validation may be submitted in lieu of validation 

of the previously submitted method. 

Practical Utility of the Data 

How will the data be used? 

In the absence of independently validated environmental chemistry methods, submitted environmental 

fate and ecological effects data may not be reviewable and entities outside the Agency may lack 

chemical-specific methods for analyses in environmental compartments. Independently validated 

environmental chemistry methods will be used to evaluate submitted environmental fate and ecological 

effects data and will be made available for enforcement and monitoring purposes at the federal, state, and 

local levels. 

How could the data change the Agency’s decision, or impact the Agency’s future decision-making? 

Risk assessment conclusions could be altered if they are not supported by either study data or 

environmental monitoring detections that are based on independently validated environmental chemistry 

methods. Furthermore, while not directly related to Agency decision-making, independently validated 

environmental chemistry methods are necessary to ensure the safety of those in proximity to releases of 

thiodicarb residues in the environment. 

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Guideline Number: 835.6200 

Study Title: Analytical Method (and Associated Independent Laboratory Validation) for Residues 

in Water 

Rationale for Requiring the Data 

Independently validated analytical methods for residues in soil, water, sediment, and plant material 

(environmental chemistry methods) submitted by the registrant are used to evaluate analyses described in 

submitted environmental fate and ecological effects studies. Submitted analytical methods are also used 

by various Federal, State, Tribal, and local agencies to detect and monitor residues that are or are 

suspected to be in environmental compartments due to outdoor uses and accidental releases. Independent 

laboratory validations for submitted analytical methods are necessary to confirm that the methods are 

functional and to confirm the levels of detection and quantitation reported in registrant-prepared 

validations. 

Use of thiodicarb may impact surface water quality due to runoff of rain water and drift of residues. This 

is especially true for poorly draining soils, erodible soils, and soils with shallow ground water. Therefore, 

outside agencies may request analytical methods with which to monitor for thiodicarb residues in water 

and in soil. 

An independently validated environmental chemistry method for thiodicarb residues in water has not 

been submitted by the registrant. If aerobic aquatic metabolism data indicate that thiodicarb is not 

transient in aerobic water bodies, a validated analytic method for residues in water should be available. 

Therefore, an environmental chemistry method for thiodicarb residues of concern in water and an 

independent laboratory validation of the method are required to support monitoring for thiodicarb 

residues and to evaluate newly submitted environmental fate and ecological effects data. 

Practical Utility of the Data 

How will the data be used? 

In the absence of independently validated environmental chemistry methods, submitted environmental 

fate and ecological effects data may not be reviewable and entities outside the Agency may lack 

chemical-specific methods for analyses in environmental compartments. Independently validated 

environmental chemistry methods will be used to evaluate newly submitted environmental fate and 

ecological effects data and will be made available for enforcement and monitoring purposes at the 

federal, state, and local levels. 

How could the data change the Agency’s decision, or impact the Agency’s future decision-making? 

Risk assessment conclusions could be altered if they are not supported by either study data or 

environmental monitoring detections that are based on independently validated environmental chemistry 

methods. Furthermore, while not directly related to Agency decision-making, independently validated 

environmental chemistry methods are necessary to ensure the safety of those in proximity to releases of 

thiodicarb residues in the environment. 

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Thiodicarb Effects Data:

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 to thiodicarb; 

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 (OPPTS Guideline 850.2100). 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 thiodicarb between passerines 

and upland game 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 thiodicarb “may affect” listed passerine birds directly (and listed species from other taxa 

indirectly), and use of thiodicarb 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 

thiodicarb use that are unnecessarily severe. 

Guideline Number: 850.1350 

Study Title: Estuarine/Marine Invertebrate Life Cycle Toxicity Test 

Rationale for Requiring the Data 

Chronic toxicity data for thiodicarb are not available for estuarine/marine invertebrates. Since the LC50

value for the most sensitive estuarine/marine invertebrate species tested is < 1 mg/L, these data are 

required under the new 40 CFR Part 158 (Oct. 26, 2007). Although thiodicarb is expected to rapidly 

degrade to methomyl in many aquatic environments, it is expected to be moderately persistent in low pH 

waters. Therefore, chronic exposure to estuarine/marine animals from registered uses of thiodicarb is 

possible. Therefore, an estuarine/marine invertebrate life cycle toxicity test (OPPTS Guideline 850.1350) 

is required. 

Practical Utility of the Data 

How will the data be used? 

Chronic toxicity data for estuarine/marine invertebrate species will be used to refine the screening-level 

assessment by determining whether there are potential risks to invertebrates inhabiting estuarine/marine 

environments from the use of thiodicarb. If chronic toxicity data are not submitted for estuarine/marine 

invertebrates, risk will be assumed for all invertebrates in estuarine/marine environments potentially 

exposed to thiodicarb. 

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 thiodicarb “may affect” listed estuarine/marine invertebrate species directly (and listed 

species from other taxa indirectly), and use of thiodicarb 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 

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the Agency and registrants have in coming into compliance with the Endangered Species Act and could 

result in use restrictions for thiodicarb use that are unnecessarily severe. 

Guideline Number: 850.1400 

Study Title: Estuarine/Marine Fish Early Life Stage Toxicity Test 

Rationale for Requiring the Data 

Chronic toxicity data for thiodicarb are not available for estuarine/marine fish. Since the LC50 value for 

the most sensitive estuarine/marine fish species tested is < 1 mg/L, these data are required under the new 

40 CFR Part 158 (Oct. 26, 2007). Although thiodicarb is expected to rapidly degrade to methomyl in 

many aquatic environments, it is expected to be moderately persistent in low pH waters. Therefore, 

chronic exposure to estuarine/marine animals from registered uses of thiodicarb is possible. Therefore, 

an estuarine/marine fish early life stage toxicity test (OPPTS Guideline 850.1400) is required. 

Practical Utility of the Data 

How will the data be used? 

Chronic toxicity data for estuarine/marine fish species will be used to refine the screening-level 

assessment by determining whether there are potential risks to fish inhabiting estuarine/marine 

environments from the use of thiodicarb. If chronic toxicity data are not submitted for estuarine/marine 

fish, risk will be assumed for all fish potentially exposed to thiodicarb in estuarine/marine environments. 

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 thiodicarb “may affect” listed estuarine/marine fish species directly (and listed species 

from other taxa indirectly), and use of thiodicarb 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 thiodicarb 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. Some thiodicarb labels (i.e., EPA Registration No. 264-379, 264-378, and 264-530) do 

contain the following statement: 

“Horticultural varieties of many plants differ significantly in sensitivity to pesticides. Before 

making applications to plants not listed, it is recommended that a small portion of the crop be 

treated to determine its tolerance to this product. Plants stressed from heat, moisture or other 

factors are usually more sensitive to sprays. Phytotoxic reactions can be minimized by 

spraying when stress is minimal such as early mornings or late evenings.” 

The Agency confirmed with the registrant that this label statement is included on the label as a general 

precaution and is not the result of known phytotoxic effects. Therefore, the requirement for Tier II plant 

studies for thiodicarb is not triggered by this label statement. Tier I seedling emergence and vegetative 

vigor studies (OPPTS Guidelines 850.4100 and 850.4150) are, however, required. In the absence of such 

data, risks to terrestrial plants from the use of thiodicarb will be assumed in the risk assessment. 

-79 of 83-
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 thiodicarb 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 thiodicarb. Therefore, use of thiodicarb 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 thiodicarb 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 thiodicarb 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 (OPPTS Guideline 

850.4400). 

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 

associated with uses of thiodicarb. The data will reduce uncertainties associated with the current risk 

assessment for plants and will improve our understanding of the potential effects of thiodicarb 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 thiodicarb, the Agency cannot determine the levels of thiodicarb 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 thiodicarb which may otherwise be avoided, or which are unnecessarily severe.

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Methomyl Effects Data:

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 (as a degradate of thiodicarb) “may affect” listed passerine birds directly (and 

listed species from other taxa indirectly), and use of thiodicarb 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 thiodicarb 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 (OPPTS 850.2300). Currently 

acceptable data for methomyl are only available for upland game species. The chronic toxicity data 

available for birds indicate that mallard ducks (Anas platyrhynchos) (MRID 43313004) are more 

sensitive to thiodicarb than bobwhite quail (Colinus virginianus) (MRID 43313003). Additionally, 

bobwhite quail appear more sensitive to methomyl than to thiodicarb based on chronic exposure (MRID 

41898602). Therefore, based on available data, it is reasonable to assume that mallard ducks may be 

more sensitive to methomyl than to thiodicarb and that they may be more sensitive than bobwhite quail to 

methomyl on a chronic exposure basis. Therefore, 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 thiodicarb, we recommend 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 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 predicted when using the chronic toxicity endpoint from 

bobwhite quail. 

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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 (as a degradate of thiodicarb) “may affect” listed birds directly (and listed 

species from other taxa indirectly), and use of thiodicarb 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 thiodicarb use 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 (OPPTS Guideline 

850.4400). 

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 (as a degradate of thiodicarb). The data will reduce uncertainties associated with the 

current risk assessment for plants and will improve our understanding of the potential effects of thiodicarb 

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 thiodicarb 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 thiodicarb 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 (OPPTS 

Guideline 850.5400). 

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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 (as a degradate of thiodicarb). The data will reduce uncertainties associated with the 

current risk assessment for plants and will improve our understanding of the potential effects of thiodicarb 

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 thiodicarb 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 thiodicarb which may otherwise be avoided, or which are unnecessarily severe.