Dimethoate Human Health Risk Assessment DP No. 0 4 16010 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

DA TE: 15-SEP-2015 

SUBJECT: Dimethoate: Human Health Risk Assessment for Registration Review 

PC Code: 03500 l 

Decision No.: 484715 

Petition No.: NA 

DP Barcode: D41 6010 

Registration No.: NA 

Regulatory Action: Registration Review 

Risk Assessment Type: Single ChemicaVAggregate Case No.: 0088 

TXR No.: NA CAS No.: 60-51 -5 

MRID No.: NA 40 CFR: § l 80.204 

FROM: ill/ ¥Y1; LIU -/ ..f!Ar- Monique M. Perron, Sc.D., Toxicologist / ""' · 

George F. Kramer. Ph.D., Senior Chemist 

Jennifer 

Kelly M. 

R. 

Lowe

Tyler

, SeniorEnvfs·r 

, Chemist 

nmen!aj~~nti~ ~~ ~~~ - Risk Assessment Branch 1 · B 1 f . Julie L. Van Alstine, MPH, Environmental Health Scientist 

Risk Assessment Branch I (RA86) 

Health Effects Division (HED; 7509P) 

THROUGH: Thurston Morton, Acting Branch Chief I; 

TO: 

RABl /HED (7509P) / '-' 

And 

Sheila Piper, Risk Assessment Review Committee (RARC) Reviewer ~JL_ QP"J 

J

K

eff 

elly 

Dawson

Ballard 

, RARC Reviewer ~ 

Neil Anderson 

Risk Management and Implementation Branch I 

Pesticide Re-Evaluation Division (PRD) (7508P) 

This document provides the HED's hwnan health risk assessment for the Registration Review of 

dimethoate ( 0 , 0 -dimethyl S-[2-(methylamino )-2-oxoethyl] phosphorodithioate). The hazard 

characterization, endpoint selection, and risk assessment were provided by Monique Perron 

(RAB l ); the residue chemistry assessment was provided by George Kramer (RAB 1 ), dietary 

exposure assessments were provided by Julie Van Alstine (RAB6); the occupational and 

residential exposure assessment was provided by Kelly Lowe and Jennifer Tyler (RABI); and 

the drinking water assessment was provided by Jose Melendez of the Environmental Fate and 

Effects Division (EFED). 

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Dimethoate Hwnan Health Risk Assessment DP No. 0416010 

Table of Contents 

1.0 Executive Summary ............................................................................................................. 4 

2.0 HED Recommendations ....................................................................................................... 8 

2.1 Data Deficienci es ............................................................................................................. 8 

2.2 Tolerance Considerations ................................................................................................. 8 

2.2.1 Enforcement Analytical Method ............................................................................... 8 

2.2.2 International Harmonization .......................................................................... ........... 9 

2.2.3 Recommended Tolerances .................................................. ........... ................... ........ 9 

2.2.4 Revisions to Established Tolerances ......................................................................... 9 

2.3 Label Recornmendations ................................................................................................ l 0 

2.3. l Recommendations from Residential Assessment .......... ............... .......................... 10 

3.0 Introduction ........................................................................................................................ 10 

3.1 Chemical Identity .... ....................................................................................................... 10 

3.2 Physical/Chemical Characteristics ................................................................................. 11 

3.3 Pesticide Use Pattern ...................................................................................................... 1 I 

3.4 Anticipated Exposure Pathways ..................................................................................... 11 

3.5 Consideration of Environmental Justice ........................................................................ 11 

4.0 Hazard Characterization and Dose-Response Assessment.. ...... .... ........... ......................... 12 

4.1 Toxicology Studies Available for Analysis ................................................................... 12 

4.2 Absorption, Distribution, Metabolism, & Excretion (ADME) ...................................... 13 

4.2.1 Dimethoate ........................................... ..... .............................................................. 13 

4.2.2 Omethoate .......... ......... ............................................................................................ 14 

4.2.3 Dermal Absorption .................................................................................................. 14 

4.3 Toxicological Effects ..................................................................................................... 15 

4.3. l Critical Durations of Exposure ............................................................................... 16 

4.4 Literature Review on Neurodevelopment Effects .......................................................... 17 

4.5 Safety Factor for lnfants and Children (FQPA SF) .................................................... .... 22 

4.5. l Completeness of the Toxicology Database ................................................... ...... .... 22 

4.5.2 Evidence of Neurotoxicity ............................................ .......................................... 23 

4.5.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal ......... 23 

4.5.4 Residual Uncertainty in the Exposure Database ..................................................... 23 

4.5 Toxicity Endpoint and Point of Departure Selections .................................................... 23 

4.5.1 Dose-Response Assessment.. .................................................................................. 23 

4.5.2 Toxicity Adjustment Factors for Omethoate .......................................................... 27 

4.5.3 Recommendation for Combining Routes of Exposures for Risk Assessment.. ...... 28 

4.5.4 Cancer Classification and Risk Assessment Recommendation .............................. 28 

4.5.5 Summary of Points of Departure and Toxicity Endpoints Used in Human Risk 

Assess1nent ............................................................................ ................................................ 28 

4.6 Endocrine Disruption ......................... ..................................... ....................................... 30 

5.0 Dietary Exposure and Risk Assessment .............................. ............... ............................... 31 

5.1 Metabolite/Oegradate Residue Profile ............................. .............................................. 31 

5.1. l Summary of Plant and Animal Metabolism Studies ............................................... 31 

5.1.2 Summary of Environmental Degradation ............................................................... 31 

5.1 .3 Comparison of Metabolic Pathways ....................................................................... 32 

5.1.4 Residues of Concern Summary and Rationale ........................................................ 32 

5.2 Food Residue Profile ................................................................................. ..................... 32 

5.3 Water Residue Profile ................................................................. ................................... 33 

5.4 Dietary Risk Assessment. .................................. ..... ........................................................ 34 

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5.4.1 Overview of Residue Data Used............................................................................. 34

5.4.2 Percent Crop Treated Used in Dietary Assessment ................................................ 35

5.4.3 Acute Dietary Risk Assessment.............................................................................. 35

5.4.4 Steady-State Dietary Risk Assessment ................................................................... 36

5.4.5 Cancer Dietary Risk Assessment............................................................................ 36

5.4.6. Dietary Assessment Summary Tables ........................................................................ 37

6.0 Residential (Non-Occupational) Exposure/Risk Characterization .................................... 47

6.1 Residential Handler Exposure........................................................................................ 47

6.2 Post-Application Exposure............................................................................................. 47

7.0 Non-Occupational Bystander Post-Application Inhalation Exposure and Risk Estimates 47

8.0 Non-Occupational Spray Drift Exposure and Risk Estimates........................................... 47

8.1 Combined Risk Estimates from Lawn Deposition Adjacent to Applications................ 49

9.0 Aggregate Exposure/Risk Characterization....................................................................... 50

10.0 Cumulative Exposure/Risk Characterization..................................................................... 51

11.0 Occupational Exposure/Risk Characterization .................................................................. 51

11.1 Short- and Intermediate-Term Handler Risk.............................................................. 51

11.2 Short-/Intermediate-Term Post-Application Risk ...................................................... 58

11.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates...................... 58

11.2.2 Occupational Post-application Dermal Exposure/Risk Estimates.......................... 58

12.0 References.......................................................................................................................... 71

Appendix A. Toxicology Profile.................................................................................................. 74

A.1 Toxicology Data Requirements...................................................................................... 74

Appendix B. Summary of OPP’s Cholinesterase Policy & Use of BMD Modeling................... 85

Appendix C. Summary Tables of Benchmark Dose (BMD) Analyses in Rat Toxicity Studies . 87

Appendix D. Tolerance Summary for Dimethoate ...................................................................... 89

Appendix E. Physical/Chemical Properties................................................................................. 91

Appendix F. Use Summary for Dimethoate ................................................................................ 92

Appendix G. International Residue Limits.................................................................................. 99

Appendix H – Summary of Surface Water EDWCs using Maximum and Typical Application 

Rates............................................................................................................................................ 102
Dimethoate Human Health Risk Assessment DP No. D416010

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1.0 Executive Summary

Background

Dimethoate is a general use systemic, organophosphate (OP) insecticide/acaricide that is used to 

control a wide variety of insect pests. There are numerous end-use product labels registered with 

dimethoate as the active ingredient. These include liquid and water-soluble packets (WSP)

formulations. The labeled use sites include various agricultural crops, Christmas tree farms,

trees grown for pulp, and ornamentals in outdoor nurseries. Most of the registered products are 

applied via aerial, chemigation, airblast, groundboom, or with handheld equipment. For most 

use sites/crops, the maximum application rate is 2 lb ai/A, but for ornamentals in outdoor 

nurseries, the maximum application rate is 4.15 lb ai/A for airblast applications specifically. 

There are currently no registered or proposed residential uses of dimethoate.

Hazard Assessment

Dimethoate is a member of the OP class of pesticides. Like other OPs, the initiating event in the

adverse-outcome pathway (AOP)/mode of action (MOA) for dimethoate involves inhibition of 

the enzyme acetylcholinesterase (AChE) via phosphorylation of the serine residue at the active 

site of the enzyme. This inhibition leads to accumulation of acetylcholine and ultimately to 

neurotoxicity in the central and/or peripheral nervous system. For dimethoate, AChE inhibition 

is the most sensitive endpoint in the toxicology database in multiple species, durations, 

lifestages, and routes. Dimethoate, like some other OPs, requires metabolic activation to its oxon 

metabolite (omethoate) to inhibit AChE, with subsequent metabolism that leads to detoxification. 

OPs also exhibit a phenomenon known as steady-state AChE inhibition. After repeated dosing at 

the same dose level, the degree of inhibition comes into equilibrium with the production of new, 

uninhibited enzyme. Therefore, a steady-state exposure assessments of 21 days and longer were

conducted instead of the traditional chronic or long-term assessments. 

The toxicology databases for dimethoate and omethoate are complete for risk assessment. There 

are acceptable studies available for toxicity endpoint selection. Dimethoate and omethoate have

high-quality dose-response data across multiple lifestages, durations, and routes for both red 

blood cell (RBC) and brain AChE inhibition. High-quality dermal and inhalation studies allow 

for route-specific evaluation. Clinical signs of neurotoxicity can be found throughout the 

databases at doses much higher than those causing inhibition of AChE. No studies in the 

toxicology databases suggest quantitative sensitivity to dimethoate/omethoate based on AChE 

inhibition. Increased pup mortality was observed in several studies, but regulation of exposure to 

dimethoate and its oxon omethoate using brain AChE inhibition is protective of the observed pup 

mortality. For all exposure scenarios, interspecies (10X) and intraspecies (10X) uncertainty 

factors were applied. The Food Quality Protection Act (FQPA) Safety Factor (SF) has been 

retained for infants, children, youths, and women of childbearing age for all exposure scenarios 

due to uncertainty in the human dose-response relationship for neurodevelopmental effects (see 

Section 4.4). As a result, the FQPA SF was applied to all exposure scenarios except for dietary 

exposures for the adult population subgroup 50-99 years old, where the FQPA SF did not apply 

(total uncertainty factor = 100X).
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Dimethoate is classified as a Group C carcinogen (possible human carcinogen). The Agency 

determined that quantification of risk using a non-linear approach would adequately account for 

all chronic toxicity, including carcinogenicity that could result from exposure to dimethoate.

Toxicity Adjustment Factors

As the oxon metabolite of dimethoate, omethoate has been found to be a more potent AChE 

inhibitor. To account for the increased potency of omethoate in risk estimates, benchmark dose 

(BMD) modeling was used to evaluate relative potency for dimethoate and omethoate and to 

estimate the toxicity adjustment factors (TAFs) for acute and steady-state exposure durations. 

The acute TAF from the Reregistration Eligibility Document (RED) for omethoate has been 

updated to 8X. The steady-state TAF of 3X for omethoate used in the RED was verified with 

additional data; therefore, no changes were made to the steady-state TAF.

Dietary (Food and Water) Exposure and Risk

Highly refined acute and steady-state dietary exposure and risk assessments for dimethoate and 

its metabolite omethoate were conducted using the Dietary Exposure Evaluation Model software 

with the Food Commodity Intake Database (DEEM-FCID) Version 3.18. This model uses 2003-

2008 food consumption data from the U.S. Department of Agriculture’s (USDA’s) National 

Health and Nutrition Examination Survey, What We Eat in America, (NHANES/WWEIA). The 

steady-state dietary assessments provide a conservative estimate of 21-day average daily 

exposures using two-day average dietary exposure and 21-day rolling water averages. Acute and 

steady-state assessments were conducted for food only, drinking water only, and for food and 

drinking water. 

The acute and steady-state dietary exposure assessments incorporated USDA Pesticide Data 

Program (PDP) data for dimethoate and omethoate, percent crop treated (PCT) data from the 

Biological and Economic Analysis Division (BEAD), empirical and default processing factors, 

and cooking factors derived from literature studies. Additionally, acute and steady-state TAFs of 

3X and 8X, respectively, were applied for omethoate residues. EFED provided daily time-series 

outputs that simulate 29 years of residues in drinking water for 44 different application scenarios. 

These scenarios encompass both maximum (24 scenarios) and typical (20 scenarios) application 

rates for agricultural and non-agricultural uses of dimethoate. The drinking water distributions 

assume 100% conversion of dimethoate to omethoate1and incorporate the acute and steady-state

TAF values. For steady-state assessments, 21-day rolling water averages were used to estimate 

21-day average daily food and drinking water exposures. 

The acute dietary (food only) exposure estimates exceed HED’s level of concern (LOC; >100%

of the acute population adjusted dose (aPAD)) for the U.S. population and all population 

subgroups at the 99.9th percentile. The U.S. population was 270% of the aPAD and children 1-2 

years old, the most highly exposed population subgroup, was 640% of the aPAD. For the acute 

drinking water only runs, all (24) of the maximum application rate and 19 of the typical 

application rate drinking water scenarios resulted in risks of concern at the 99.9th percentile. 

Since the food alone and drinking water alone assessments result in risks of concern, acute food 

and drinking water analyses were not completed for all of the scenarios since they would also 

 

1 MRID 48041103 - Marin, J.E. 2010. Determination of the effect of chlorination on the degradation of dimethoate 

in water. 
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result in risks of concern at the 99.9th percentile. Overall, acute food and drinking water analyses 

were conducted for 27 (7 maximum application rate and 20 typical application rate) drinking 

water scenarios. All infants (<1 year old) was the most highly exposed population subgroup for 

11 of the scenarios, with food and drinking water risk estimates that ranged from 710-1100% of 

the aPAD at the 99.9th percentile. Children 1-2 years old was the most highly exposed 

population subgroup for 16 of the scenarios, with food and drinking water risk estimates that 

ranged from 640-680% of the aPAD at the 99.9th percentile. 

The food only steady-state results exceed HED’s LOC (>100% of the steady-state populationadjusted dose (ssPAD)) for the U.S. population and all population subgroups at the 99.9th

percentile. The U.S. population was 410% of the ssPAD and children 1-2 years old, the most 

highly exposed population subgroup, was 810% of the ssPAD. For the steady-state drinking 

water only analyses, all (24) of the maximum application rate and 19 of the typical application 

rate drinking water scenarios resulted in risks of concern at the 99.9th percentile. Since the food 

alone and drinking water alone assessments result in risks of concern, steady-state food and 

drinking water analyses were not completed for all of the scenarios since they would also result 

in risks of concern at the 99.9th percentile. Overall, food and drinking water steady-state 

analyses were conducted for 23 drinking water scenarios (3 maximum application rate and 20 

typical application rate). All infants (<1 year old) was the most highly exposed population 

subgroup for six of the scenarios, with food and drinking water risk estimates that ranged from 

970-1200% of the ssPAD at the 99.9th percentile. Children 1-2 years old was the most highly 

exposed population subgroups for 17 of the scenarios, with food and drinking water risk

estimates that ranged from 810-880% of the ssPAD at the 99.9th percentile. 

 

Residential (Non-Occupational) Exposure and Risk

All residential and other non-occupational uses of dimethoate were voluntarily cancelled, 

effective March 13, 2002 (Federal Register Notice/Vol. 67, No. 84/Wednesday, May 01, 

2002/Notices/21669). 

Non-Occupational Spray Drift Exposure and Risk 

A quantitative non-occupational spray drift assessment was conducted for the registered uses of 

dimethoate. The assessment takes into consideration both dimethoate residues and residues of 

the major metabolite, omethoate. Adult dermal and children’s (1 to < 2 year old) dermal and 

incidental oral risk estimates from indirect exposure related to spray drift exceed HED’s level of 

concern (MOEs < 1000) at a range of distances from the edge of the field depending on the 

spray-drift scenario (e.g., 0 to >300 feet). Results indicate that the major spray-drift risk 

concerns are from aerial applications. 

Volatilization/Residential Bystander

Volatilization of pesticides may be a source of post-application inhalation exposure to 

individuals nearby pesticide applications. The agency has developed a Volatilization Screening 

Tool and a subsequent Volatilization Screening Analysis, and during Registration Review, the 

Agency will utilize this analysis to determine if data (i.e., flux studies) or further analyses are 

required for dimethoate.
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Aggregate

The registered dimethoate uses are not anticipated to result in residential exposure and thus the 

acute and steady-state dietary exposure estimates represent the acute and steady-state aggregate 

exposure. Dimethoate is classified as a Group C carcinogen (possible human carcinogen). 

Quantification of risk using a non-linear approach will adequately account for all chronic 

toxicity, including carcinogenicity that could result from exposure to dimethoate.

Occupational Exposure and Risk

Occupational handler dermal and inhalation exposure and risk estimates were calculated for the 

registered uses of dimethoate. The occupational handler exposure and risk estimates indicate 

that the dermal and inhalation combined MOEs are of concern to HED (i.e., MOEs < 1000) for 

most scenarios assuming the use of label-required PPE. As was noted above, the inhalation risk 

estimates are considered to be a conservative estimate of exposure to dimethoate residues 

considering the inhalation POD was selected from an omethoate toxicity study. Only five 

scenarios (out of 40) reach an MOE above the LOC of 1000 at some level of PPE (above what is 

currently required on the labels) or with engineering controls.

Occupational post-application dermal exposure and risk estimates were assessed for all

registered uses of dimethoate using submitted chemical-specific dislodgeable foliar residue 

(DFR) data. The post-application assessment takes into consideration both dimethoate residues 

and residues of the major metabolite, omethoate; both of which were measured in the available 

DFR studies. Based on the current exposure assessment, post-application risk estimates remain a 

concern in some situations for more than 30 days after application (i.e., MOEs < 1000). Current 

product-label REIs range from 48 hours to 24 days depending on the crop and geographic 

location (i.e., arid versus non-arid). Even though REIs of 12 and 24 hours may be long enough 

for MOEs to reach the LOC of 1000 for some crops/activities, HED recommends a minimum 

REI of 48 hours (72 hours in arid regions) to be protective of potential for exposure to omethoate 

which is known to form after application. These REIs are in line with the 40 CFR 156.208 (c) 

(2) assignments for active ingredients that are classified as Toxicity Category I for acute dermal, 

eye irritation, and primary skin irritation.

Based on the Agency's current practices, a quantitative non-cancer occupational post-application 

inhalation exposure assessment was not performed for dimethoate at this time. If new policies or 

procedures are put into place, the Agency may revisit the need for a quantitative occupational 

post-application inhalation exposure assessment for dimethoate.

Human Studies Review:

This risk assessment relies in part on data from studies in which adult human subjects were 

intentionally exposed to a pesticide or other chemical. These data, which include studies from 

Pesticide Handler Exposure Database (PHED) 1.1, Outdoor Residential Exposure Task Force 

(ORETF), the Agricultural Handlers Exposure Task Force (AHETF) database, and the 

Agricultural Reentry Task Force (ARTF) database are (1) subject to ethics review pursuant to 40 

CFR 26, (2) have received that review, and (3) are compliant with applicable ethics 

requirements. For certain studies, the ethics review may have included review by the Human 
Dimethoate Human Health Risk Assessment DP No. D416010

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Studies Review Board. Descriptions of data sources, as well as guidance on their use, can be 

found at the Agency website2. 

2.0 HED Recommendations

2.1 Data Deficiencies

There are no data deficiencies for the Registration Review eligibility of dimethoate.

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

Plants: For the purpose of Registration Review, adequate methods are available for the 

enforcement of plant commodity tolerances. The Pesticide Analytical Manual (PAM) Vol. II 

lists three gas-liquid chromatography (GLC) methods (Methods A, B, and C) using flame 

photometric detection, and a colorimetric procedure (Method D) for analysis of residues of 

dimethoate and its oxygen analog in/on plant commodities. A second colorimetric procedure 

(Method E) is listed for the determination of residues of dimethoate per se. The limit of 

quantitation (LOQ) for the GLC methods is 0.05 ppm. A thin-layer chromatography (TLC)

method is also listed (Method I) for determination of residues of dimethoate and its oxygen 

analog in/on plant commodities. The QuEChERS multiresidue method has also been validated 

for determination of dimethoate and omethoate (https://www.chromspec.com/pdf/e/uct19.pdf).

Livestock: For the purpose of Registration Review, an adequate method is available for the 

enforcement of livestock commodity tolerances. The method was modified from the

QuEChERS multiresidue method. Briefly, samples are extracted with acetonitrile (ACN) or 

ACN/water (fat), shaken, and sonicated. The extract is partitioned with magnesium sulfate, 

sodium chloride, and a citrate buffer (sodium citrate dibasic sesquihydrate and sodium citrate 

tribasic dehydrate). The citrate buffer is not added for eggs. An aliquot of the organic layer 

extract is cleaned-up using dispersive solid-phase extraction (dSPE) PSA/ENVI-Carb SPE 

Clean-Up Tubes, filtered, diluted with ACN, and analyzed by liquid chromatography-mass 

spectroscopy/mass spectroscopy (LC-MS/MS) using electrospray ionization (ESI) in the 

positive-ion mode. The method monitors three ion transitions for determination of dimethoate 

and omethoate. The validated LOQ (determined as the lowest level of method validation, 

LLMV) is 0.001 ppm for each analyte in all livestock matrices. The reported limit of detection 

(LOD) is 0.0005 ppm for each analyte in egg, muscle, liver, kidney, and fat and 0.00025 ppm in 

milk.

Multiresidue Methods: The data requirements for multiresidue methods (MRMs) are fulfilled. 

The 1/94 Food and Drug Administration (FDA) PESTDATA database (PAM Volume I, 

Appendix I) indicates that residues of dimethoate and omethoate are completely recovered 

(>80%) by MRM Section 302 (Luke Method; Protocol D) but are not recovered by MRM 

Sections 303 (Mills, Onley, Gaither Method; Protocol E, nonfatty) and 304 (Mills fatty food 

method; Protocol E, fatty).

 

2 http://www.epa.gov/pesticides/science/handler-exposure-data.html and 

http://www.epa.gov/pesticides/science/post-app-exposure-data.html
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2.2.2 International Harmonization

U.S. permanent tolerances (listed in 40 CFR §180.204) plus Mexican, Canadian, and Codex 

maximum residue levels (MRLs) are summarized in Appendix G. The U.S. and Canadian 

residue definitions are harmonized (parent plus omethoate); however, the Codex residue 

definition is parent only. For some raw agricultural commodities, the levels of the 

tolerances/MRLs for the U.S., Canada, Mexico, and Codex are harmonized; however, there are 

many commodities for which the levels are not harmonized. Harmonization of the 

tolerance/MRL levels for beans, cauliflower, celery, pea, pepper, potato, tomato, turnip tops, and 

wheat, straw is not possible, as the U.S. use patterns require a higher tolerance. Harmonization 

of the tolerance/MRL levels for livestock meat byproducts, milk, egg, and citrus is not possible 

as the U.S. tolerances are significantly lower. Harmonization of the tolerance/MRL level for 

wheat, grain is possible as the U.S. tolerance level (0.04 ppm) is only slightly lower that the 

Codex MRL level (0.05 ppm).

2.2.3 Recommended Tolerances

Permanent tolerances have been established in 40 CFR §180.204 for the total residues of the 

insecticide dimethoate (O,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorodithioate) 

including its oxygen analog in/on various raw agricultural commodities ranging from 0.002 ppm 

to 5.0 ppm.

The tolerance expression for dimethoate [40 CFR §180.204(a)(1) and 40 CFR §180.204(c)] has 

been reviewed and should be updated as follows based on HED’s Interim Guidance on Tolerance 

Expressions (S. Knizner, 27-MAY-2009).

Tolerances are established for residues of the insecticide dimethoate, including its 

metabolites and degradates, in or on the commodities in the table below. Compliance 

with the tolerance levels specified below is to be determined by measuring only the sum 

of dimethoate (O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] phosphorodithioate) and 

its oxygen analog (O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] phosphorothioate), 

calculated as the stoichiometric equivalent of dimethoate, in or on the commodity.

A summary of the established and HED-recommended tolerances for residues of dimethoate can be 

found in Appendix D. 

2.2.4 Revisions to Established Tolerances

HED is recommending for revisions to the tolerance expression in order to conform to current 

Agency policy. In addition, HED is recommending for the establishment of a tolerance for residues 

in/on fruit, citrus, group 10-10 concomitant with the deletion of the tolerances for residues in/on the 

individual members of the crop group; revocation of the tolerance for residues in/on sweet corn 

forage as there is no registered use on sweet corn; correction of the commodity definition for lima 

bean; increasing the tolerance for residues in/on ruminant meat byproducts and revocation of the 

tolerance for residues in/on poultry meat byproducts and eggs based on the results of new livestock 

feeding studies, and increasing the tolerance for residues in/on wheat grain in order to harmonize 

with the Codex MRL. HED previously recommended for establishment of tolerances for residues 
Dimethoate Human Health Risk Assessment DP No. D416010

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in/on alfalfa seed and cotton gin byproducts and revisions to the tolerances for residues in/on 

livestock commodities (M. Sahafeyan; 24-MAY-2011; D232849) and for establishment of 

tolerances for residues in/on grass forage and hay (M. Sahafeyan; 12-NOV-2013; D239886). 

Additionally, the notation for blueberries in the e-40 CFR should be corrected to indicate that there 

are no U.S. registrations for blueberries as of August 16, 1996. Currently the e-CFR omits the word 

“no.”

2.3 Label Recommendations

No label recommendations have been identified. A summary of the risk estimates has been 

provided, and shows that there are risk estimates of concern for registered uses of dimethoate

based on the use information, label-required personal protective equipment (PPE; i.e., 

engineering controls), and REIs.

2.3.1 Recommendations from Residential Assessment

Adult dermal and children’s (1 to < 2 year old) dermal and incidental oral risk estimates from 

indirect exposure related to spray drift exceed HED’s LOC (MOEs < 1000) at a range of 

distances from the field depending on the spray-drift scenario (e.g., 0 to >300 feet) (see Section 

6.4.1). Appropriate drift reduction technologies such as changing the spray type/nozzle 

configuration to coarser spray applications may result in less drift and reduced risk concerns (i.e., 

higher MOEs) from aerial applications. Similarly, using coarser sprays and lowering boom 

height for groundboom sprayers reduces risk concerns.

3.0 Introduction

3.1 Chemical Identity

Table 3.1. Test Compound Nomenclature.

Chemical Structure

Empirical Formula C5H12NO3PS2

Common Name Dimethoate

IUPAC name O,O-dimethyl S-methylcarbamoylmethyl phosphorodithioate or 

2-dimethoxyphosphinothioylthio-N-methylacetamide

CAS Name O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] phosphorodithioate

CAS Registry Number 60-51-5

End-use products Dimate 4E, Dimethoate 4E, Cymate 267, Dimethoate 2.67 EC, etc.

Chemical Class OP
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Table 3.1. Test Compound Nomenclature.

Chemical Structure

Empirical Formula C5H12NO4PS

Common Name Omethoate

IUPAC name O,O-dimethyl S-methylcarbamoylmethyl phosphorothioate

CAS Name O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] phosphorothioate

CAS Registry Number 1113-02-6

3.2 Physical/Chemical Characteristics

Pure dimethoate is a colorless crystalline solid with an odor of mercaptan. Technical dimethoate 

(about 93% pure) varies from off-white crystals to a grey semi-crystalline material. Dimethoate 

is highly soluble in chloroform, methylene chloride, benzene, toluene, alcohols, esters, and 

ketones, slightly soluble in xylene, carbon tetrachloride, and aliphatic hydrocarbons, and partly 

soluble in water (log KOW = 0.70) with a vapor pressure of 1.85 x 10-6 mm Hg at 20°C. A table 

of physical/chemical properties for dimethoate can be found in Appendix E.

3.3 Pesticide Use Pattern

There are numerous end-use product labels registered with dimethoate as the active ingredient

including liquid and WSP formulations. The labeled use sites include various agricultural crops, 

Christmas tree farms, trees grown for pulp, and ornamentals in outdoor nurseries. Most of the 

registered products are applied via aerial, chemigation, airblast, groundboom, or with handheld 

equipment. For most use sites/crops, the maximum application rate is 2 lb ai/A, but for 

ornamentals in outdoor nurseries, the maximum application rate is 4.15 lb ai/A for airblast 

applications specifically. A summary of registered labels and dimethoate use directions are 

included in Appendix F. 

3.4 Anticipated Exposure Pathways

Humans may be exposed to dimethoate, and its metabolite omethoate, in food and drinking 

water, since dimethoate may be applied directly to growing crops and application may result in 

dimethoate reaching sources of drinking water. There are no residential uses of dimethoate; 

however, there is the potential for short-term non-occupational exposure (dermal and incidental 

oral) to dimethoate and omethoate as a result of spray drift. 

Based on the registered use pattern for dimethoate, short- and intermediate-term dermal and 

inhalation exposures are anticipated for occupational handlers and post-application workers. 

Occupational handlers are anticipated to be exposed to the parent, dimethoate, only. 

Occupational post-application workers may be exposed to residues of both dimethoate and 

omethoate 

3.5 Consideration of Environmental Justice
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Potential areas of environmental justice concerns, to the extent possible, were considered in this 

human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal Actions 

to Address Environmental Justice in Minority Populations and Low-Income Populations," 

(http://epa.gov/compliance/ej/resources/policy/exec_order_12898.pdf). As a part of every 

pesticide risk assessment, OPP considers a large variety of consumer subgroups according to 

well-established procedures. In line with OPP policy, HED estimates risks to population 

subgroups from pesticide exposures that are based on patterns of that subgroup’s food and water 

consumption, and activities in and around the home that involve pesticide use in a residential 

setting. Extensive data on food consumption patterns are compiled by the USDA under the 

NHANES/WWEIA and are used in pesticide risk assessments for all registered food uses of a 

pesticide. These data are analyzed and categorized by subgroups based on age and ethnic group. 

Additionally, OPP is able to assess dietary exposure to smaller, specialized subgroups and 

exposure assessments are performed when conditions or circumstances warrant. Whenever 

appropriate, non-dietary exposures based on home use of pesticide products and associated risks 

for adult applicators and for toddlers, youths, and adults entering or playing on treated areas 

post-application are evaluated. Further considerations are currently in development as OPP has 

committed resources and expertise to the development of specialized software and models that 

consider exposure to bystanders and farm workers as well as lifestyle and traditional dietary 

patterns among specific subgroups.

4.0 Hazard Characterization and Dose-Response Assessment

Dimethoate is a member of the OP class of pesticides. Like other OPs, the initiating event in the

AOP/MOA, for dimethoate involves inhibition of the enzyme AChE via phosphorylation of the 

serine residue at the active site of the enzyme. Dimethoate must be metabolized (activated) to 

the oxon metabolite (omethoate), which is the active AChE inhibiting moiety. This inhibition 

leads to accumulation of acetylcholine and ultimately to neurotoxicity in the central and/or 

peripheral nervous system (see Figure 1). For dimethoate and omethoate, AChE inhibition is the 

most sensitive endpoint in the toxicology database in multiple species, durations, lifestages, and 

routes. AChE inhibition is the focus of this hazard characterization; the availability of reliable 

AChE inhibition dose response data is one of the key determinants in evaluating the toxicology 

database. 

Figure 1. AOP for OPs.

4.1 Toxicology Studies Available for Analysis

The toxicology database for dimethoate is complete for risk assessment. The acceptable 

dimethoate studies available for risk assessment include: 

 subchronic oral toxicity studies in rats and dogs 

Target 

Tissue 

Dose

Phosphorylation 

of the active site 

of AChE

Neurotoxicity

Accumulation 

of 

acetylcholine
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 chronic oral toxicity studies in rats and dogs 

 carcinogenicity studies in rats and mice 

 developmental studies in rats and rabbits 

 reproduction toxicity study in rats 

 acute and subchronic neurotoxicity studies in rats

 developmental neurotoxicity (DNT) study in rats 

 acute and repeated comparative cholinesterase assays (CCA) in juvenile and adult 

rats

 special cross-fostering study in rats

 delayed neurotoxicity study in hens 

 subchronic dermal toxicity study in rats 

 in vivo dermal penetration studies in rats 

 immunotoxicity study in mice 

 mutagenicity studies

 metabolism studies in rats 

Although never registered as an active ingredient in the U.S., omethoate has in the past been 

registered in other countries and, as a result, there is an extensive toxicity database for 

omethoate. The acceptable omethoate studies available for risk assessment include: 

 chronic oral toxicity studies in rats and dogs

 carcinogenicity studies in rats and mice 

 developmental studies in rats and rabbits

 reproduction toxicity studies in rats

 acute neurotoxicity study in rats

 acute and repeated CCA studies in rats 

 special studies investigating AChE inhibition in rats and dogs

 delayed neurotoxicity study in hens 

 repeated dosing inhalation study in rats 

 mutagenicity studies

 metabolism studies in rats

Additionally studies have also been submitted demonstrating no significant AChE inhibition

from multiple degradates of dimethoate, including hydroxy dimethoate, O-desmethyl omethoate 

carboxylic acid, des-o-methyl isodimethoate, O-desmethyl omethoate, and dimethoate carboxylic 

acid.

4.2 Absorption, Distribution, Metabolism, & Excretion (ADME)

4.2.1 Dimethoate

Dimethoate, like some other OPs, requires metabolic activation to its oxon metabolite 

(omethoate) to inhibit AChE, with subsequent metabolism that leads to detoxification. 

Generally, absorption and distribution are rapid with extensive metabolism and no accumulation 

in the tissues. 
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In a rat metabolism study, rats were administered [14C]-dimethoate as a single oral dose (10 or 

100 mg/kg), an intravenous dose (10 mg/kg), or 14-day repeated oral doses of dimethoate at 10 

mg/kg followed by a single oral dose of [14C]-dimethoate at 10 mg/kg. Dimethoate was rapidly 

absorbed, metabolized, and eliminated in rats for all dosing regimens. Consistent with the results 

of the AChE studies, there were no remarkable sex-, dose-, or treatment-related differences in the 

absorption, distribution, and elimination of dimethoate in rats. Dimethoate was absorbed and 

distributed quickly with time to peak plasma concentrations (Tmax) reached less than 1 hour postdosing. Total recovery of radioactivity ranged between 91% and 97% of the administered dose. 

Most of the radioactivity was excreted via the urine (85-91% of the dose). A small amount of 

radioactivity was found in feces (1-2% of the dose), in the tissues and remaining carcass (1-2% 

of the dose), and in the expired air as carbon dioxide (2-3% of the dose). 

In the rat, dimethoate is metabolized via hydrolytic and oxidative pathways (based on urine 

analyses). The hydrolytic pathway (major) involves cleavage of the C-N bond to yield 

dimethoate carboxylic acid that was subsequently metabolized to dimethyldithiophosphate, 

dimethylthiophosphoric acid, and dimethylphosphoric acid. A minor metabolic pathway 

involves oxidation of dimethoate to its oxon analogue, omethoate, which was subsequently 

metabolized to dimethylthiophosphoric acid and dimethylphosphoric acid. Loss of the methoxy 

groups of the parent to yield carbon dioxide is a minor metabolic pathway.

4.2.2 Omethoate

In a rat metabolism study with omethoate, male and female rats exhibited signs of toxicity, 

including trembling, salivation, high breathing rate, and congestion of the eyes, at 0.5-4 hours

post-dosing. Overall recovery of administered radioactivity was 88-98%. There were no 

remarkable sex-, dose-, or treatment-related differences in the absorption, distribution, and 

elimination of omethoate in rats. Absorption rates were rapid and Tmax was reached within 1 

hour post-dosing. Omethoate was excreted within 48 hours with the majority excreted via the 

urine (85-97% of the administered dose). The remainder of the administered radioactivity was 

excreted via the feces (2-4% of the administered dose). Biliary excretion was found to account 

for the majority of the fecal metabolite content. Based upon tissue burden data, omethoate 

and/or its metabolites do not appear to undergo any significant sequestration.

Omethoate appeared to be metabolized to a greater extent in males than in females as evidenced 

by higher percentages of parent compound remaining in urine from females and a higher 

percentage of omethoate metabolites in urine of males. The metabolite profile for urine included 

the parent compound (26-62% of the administered dose), N-methyl-2-(methylsulfinyl)-acetamide 

(16-35% of the administered dose), and O-desmethylated omethoate (4-9% of the administered 

dose). The same metabolites were also identified in the feces.

4.2.3 Dermal Absorption

There are two acceptable in vivo dermal penetration rat studies in the database for dimethoate. In 

the first study (MRID 43964001), dermal absorption (based on total amount of radioactivity 

recovered from urine, tissues, and feces after 6 hours of dermal exposure) was estimated to be 8-

11% and 1-2% of the administered dose from rats treated at 10 and 100 mg/kg, respectively. 

There were no sex-related differences observed in absorption patterns. In the second study 

(MRID 45530501), dermal absorption (based on excreta, cage wash, and carcass) was estimated 
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at doses of 0.67 and 13.3 mg/kg to be approximately 6% after 1 hour of exposure and 25-38% 

after 10-24 hours of exposure. Since a route-specific dermal toxicity study was selected as the 

endpoint for dermal exposure assessments (see Section 4.5.1), a dermal absorption factor is not 

needed for this risk assessment.

4.3 Toxicological Effects

Dimethoate and omethoate have high-quality dose-response data across multiple lifestages, 

durations, and routes for both RBC and brain AChE inhibition. Many of these studies have been

evaluated using BMD modeling techniques. BMD estimates are similar across age, sex, and 

method of administration (gavage, feeding, drinking water) for dimethoate and omethoate 

(Appendix 9 of USEPA 2004). High-quality studies in the dermal and inhalation routes with 

dimethoate and omethoate, respectively, allow for route-specific evaluation. 

Using AChE inhibition as the critical endpoint for risk assessment purposes protects for other 

cholinergic effects, such as clinical signs, which are seen at doses much higher than those 

causing inhibition of AChE. In the case of dimethoate and omethoate, brain AChE inhibition 

provides the basis for human health risk extrapolations with the rat being the most sensitive 

species for dimethoate and omethoate exposures. Details of numerous dimethoate studies can be 

found in the toxicology disciplinary chapter for the Reregistration Eligibility Document (RED; P. 

Chin, 04-MAR-1997; D229308). Relevant omethoate studies are summarized in a 2005 review 

(P. Chin; 31-MAY-2005; TXR# 0051425). 

In the acute and repeated CCA studies, juvenile rats, pregnant dams, fetuses and non-pregnant 

adults displayed similar results in both blood and brain measurements. In developmental and

reproduction toxicity studies, AChE inhibition in fetuses/offspring was seen at or above dose 

levels eliciting inhibition in parental animals.

Increased qualitative susceptibility to offspring was observed in the toxicological databases. 

Several studies (i.e., range-finding and main DNT, cross-fostering, and one-generation 

reproductive toxicity studies with dimethoate, as well as the omethoate reproductive toxicity 

studies) demonstrate increased pup mortality following maternal exposure; however, the 

increased pup mortality occurred at doses at or above those causing decreased brain AChE 

activity in parental animals. The underlying basis of pup mortality is not fully understood 

though and the available data do not support maternal toxicity as being the only determinant of 

pup mortality. The pup mortality has been extensively reviewed by OPP and the Office of 

Research and Development (ORD) along with the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP). A more detailed discussion of the 

pup mortality observations can be found in the revised post-SAP HED Chapter of the RED

(D325201; 31-JAN-2006).

It has been concluded that regulation of dimethoate exposure at levels below those causing brain 

AChE inhibition will protect against brain AChE inhibition, as well as increased pup mortality, 

based on the following:

1) Comparison of benchmark dose levels for brain AChE inhibition and pup mortality 

following repeated dosing indicates that AChE inhibition occurs at doses similar to 

those associated with increases in pup mortality. 
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2) The evaluation of pup mortality data from the cross-fostering study reveals that 

increases in mortality from short-term exposures (10-15 doses) only occurred at the 

highest dose tested, indicating that increased mortality at lower doses requires longer 

durations of repeated dosing. 

3) Comparison of the no-observed adverse-effect level (NOAEL) for increased pup 

mortality to the BMD10 for brain AChE inhibition following a single dose indicates 

that brain AChE inhibition occurs at doses below those causing a clear increase in 

pup mortality. 

These conclusions regarding the interpretation of pup mortality seen in the dimethoate and 

omethoate database were supported by the 2005 FIFRA SAP. The SAP further supported the use 

of brain AChE inhibition for deriving PODs as protective of the pup mortality.

Dimethoate is classified as having low acute toxicity via the oral, dermal, and inhalation routes 

(Toxicity Category III or IV). It was found to be a moderate eye irritant, but not a dermal irritant 

or dermal sensitizer. Omethoate is classified as acutely toxic via the oral, dermal, and inhalation 

routes (Toxicity Category I or II).

There was no evidence of immunotoxicity up to 36 mg/kg/day in a recently submitted 

immunotoxicity study with dimethoate (MRID 48572807 and 48997901).

Dimethoate is classified as a Group C carcinogen - possible human carcinogen (Memo; K. 

Dearfield; 29-AUG-1991). The classification is based upon equivocal hemolymphoreticular 

tumors in male B6C3F1 mice, the compound-related (no dose response) weak effect of combined 

spleen (hemangioma and hemangiosarcoma), skin (hemangiosarcoma), and lymph (angioma and 

angiosarcoma) tumors in male Wistar rats, and positive mutagenic activity associated with 

dimethoate. On June 25, 1992, the FIFRA SAP concurred with the Agency's classification of 

dimethoate as a Group C carcinogen. The Agency determined that quantification of risk using a 

non-linear approach would adequately account for all chronic toxicity, including carcinogenicity 

that could result from exposure to dimethoate.

4.3.1 Critical Durations of Exposure

One of the key elements in risk assessment is the appropriate integration of temporality between 

the exposure and hazard assessments. One advantage of an AOP understanding is that human 

health risk assessments can be refined, focused on the most relevant durations of exposure. The 

following text provides an analysis of the temporal pattern of AChE inhibition from acute 

(single) and repeated-dosing studies in laboratory animals for dimethoate. This analysis provides 

the basis for determining which exposure durations are appropriate for assessing human health 

risk. Table 4.3.1.1 provides a summary of the selected results from experimental toxicology 

studies with dimethoate. 

Table 4.3.1.1. Dimethoate BMD10 and BMDL10 Results (mg/kg/day) for Brain AChE Inhibition Over Time 

in Adult Rats.

Days of Dosing

Males Females

BMD10 BMDL10 BMD10 BMDL10

1

a 2.5 1.7 2.2 1.3

11a 0.49 0.37 0.37 0.27
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14a NA NA 0.34 0.28

91b 0.40 0.29 0.48 0.40

205c 0.34 0.19 0.45 0.25

BMD10 = estimated dose where AChE is inhibited by 10% compared to background.

BMDL10 = lower confidence bound on the BMD10. 

NA = not applicable; measurements at this time point were for pregnant females on gestational day 20.

a MRID 45529702 - CCA study.

b MRID 46348201 - One-generation range finding study.

c MRID 46181001 - Two-generation reproduction toxicity study.

As shown in Table 4.3.1.1, the acute (single-day) BMD values are the largest in the table, 

whereas BMD values from repeated exposures are remarkably similar. Although studies with 

AChE measurements were more limited with omethoate, a similar pattern was observed. OPs 

exhibit a phenomenon known as steady-state AChE inhibition. After repeated dosing at the same 

dose level, the degree of inhibition comes into equilibrium with the production of new, 

uninhibited enzyme. At this point, the amount of AChE inhibition at a given dose remains 

consistent across duration. In general, OPs reach steady-state within 2-3 weeks, but this can vary 

among OPs. In the case of dimethoate, the results in Table 4.3.1.1 show a clear pattern of 

steady-state reached by 11 days of exposure. Given the results in Table 4.3.1.1 for dimethoate, 

acute (single-day) and steady-state durations are appropriate for human health risk assessment. 

As such, the endpoint selection discussed below focuses on acute (single-day) effects and steadystate effects. 

Although there are data at a shorter time period than 21 days (i.e., 11 days), exposure 

assessments of 21 days and longer will be conducted for all routes of exposure (i.e., oral, dermal 

and inhalation) for all single chemical OP assessments. Although the durations of the toxicity 

and exposure assessments may differ, an exact match is not necessary and would suggest a level 

of precision that the toxicity data do not support. Given this, the 21-day and longer exposure 

assessment is scientifically supportable and also provides consistency with the OP cumulative 

risk assessment (OP CRA; 2002, 2006) and across the single chemical risk assessment for the 

OPs. 

4.4 Literature Review on Neurodevelopment Effects

For the OPs, historically the Agency has used inhibition of AChE as the POD for human health 

risk assessment; at present time, this policy continues. This science policy is based on decades 

of work which shows that AChE inhibition is the initial event in the pathway to acute cholinergic 

neurotoxicity. The use of AChE inhibition data for deriving PODs was supported by the FIFRA 

SAP (2008, 2012) for chlorpyrifos as the most robust source of dose-response data for 

extrapolating risk and is the source of data for PODs for dimethoate/omethoate. A detailed 

review of the epidemiological studies used in this review can be found either in the 2014 

chlorpyrifos revised draft human health risk assessment (D. Drew; 29-DEC-2014; D424485) or 

in the 2015 literature review for other organophosphates (OPP/USEPA; 15-SEP-2015; 

D331251). 

Newer lines of research on OPs in the areas of potential AOPs, in vivo animal studies, and 

notably epidemiological studies in mothers and children, have raised some uncertainty about the 

agency’s risk assessment approach with regard to the potential for neurodevelopmental effects in 

fetuses and children. Many of these studies have been the subject of review by the agency over 

the last several years as part of efforts to develop a risk assessment for chlorpyrifos (D. Drew; 
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29-DEC-2014; D424485). Initially, the agency focused on studies from three US cohorts: 1) 

The Mothers and Newborn Study of North Manhattan and South Bronx performed by the 

Columbia Children’s Center for Environmental Health (CCCEH) at Columbia University; 2) the 

Mt. Sinai Inner-City Toxicants, Child Growth and Development Study or the “Mt. Sinai Child 

Growth and Development Study;” and 3) the Center for Health Assessment of Mothers and 

Children of Salinas Valley (CHAMACOS) conducted by researchers at University of California 

Berkeley. The agency has evaluated these studies and sought external peer review (FIFRA SAP 

reviews in 2008 and 2012; federal panel, 20133) and concludes they are of high quality. In the 

three US epidemiology cohort studies, mother-infant pairs were recruited for the purpose of 

studying the potential health effects of environmental exposures during pregnancy on subsequent 

child development. Each of these cohorts evaluated the association between prenatal chlorpyrifos 

and/or OP exposure (with adverse neurodevelopmental outcomes in children through age 7 

years). For the 2014 chlorpyrifos revised human health risk assessment (D. Drew; 29-DEC2014; D424485), EPA included epidemiologic research results from these three US prospective 

birth cohort studies but primarily focused on the results of CCCEH since this cohort has 

published studies on the association between cord blood levels of chlorpyrifos and 

neurodevelopmental outcomes. The agency retained the FQPA 10X Safety Factor (SF) in the 

2014 chlorpyrifos revised risk assessment, in large part, based on the findings of these studies.

In the 2015 updated literature review (OPP/USEPA; 15-SEP-2015; D331251), the agency 

conducted a systematic review expanding the scope of the 2012/2014 review focused on US 

cohort studies with particular emphasis on chlorpyrifos. The expanded 2015 review includes 

consideration of the epidemiological data on any OP pesticide, study designs beyond prospective 

cohort studies, and non-U.S. based studies. The updated literature review identified seven studies 

which were relevant (Bouchard et al., 2010; Fortenberry et al., 2014; Furlong et al., 2014; 

Guodong et al., 2012; Oulhote and Bouchard, 2013; Zhang et al., 2014; Shelton et al., 2014). 

These seven studies have been evaluated in context with studies from the 2012/2014 review (D. 

Drew; 29-DEC-2014; D424485). Only a brief summary is provided below.

The OP exposure being assessed in many of these studies used concentrations of urinary dialkyl 

phosphate metabolites (DAPs) as the urinary biomarker. Total DAPs is a non-specific measure 

of OP exposure and is the sum of six separate molecules - three dimethyl alkylphosphate 

(DMAP) molecules of DMP, DMTP, DMDTP, and three diethyl alkylphosphate (DEAP) 

molecules of DEP, DETP, and DEDTP. Each metabolite is a breakdown product from multiple 

OPs (Table 4.4.1; CDC, 2008)4. Specifically, DMP, DMTP, and DMDTP are associated with 

18, 13, and 5 OPs, whereas DEP, DETP, and DEDTP are associated with 10, 10, and 4 OPs, 

respectively. Thus, using urinary DAPs alone as an exposure measure, it is not possible to 

separate the exposure and associated effects for single, specific OPs. 

Table 4.4.1.CDC Table of organophosphate pesticides and their dialkyl phosphate metabolites (2008). 

Pesticide DMP DMTP DMDTP DEP DETP DEDTP

Azinphos methyl X X X

Chlorethoxyphos X X

Chlorpyrifos X X

Chlorpyrifos methyl X X

 

3 http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2008-0850-0170

4 http://www.cdc.gov/nchs/data/nhanes/nhanes_03_04/l26opd_c_met_organophosphorus_pesticides.pdf
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Coumaphos X X

Dichlorvos (DDVP) X

Diazinon X X

Dicrotophos X

Dimethoate X X X

Disulfoton X X X

Ethion X X X

Fenitrothion X X

Fenthion X X

Isazaphos-methyl X X

Malathion X X X

Methidathion X X X

Methyl parathion X X

Naled X

Oxydemeton-methyl X X

Parathion X X

Phorate X X X

Phosmet X X X

Pirimiphos-methyl X X

Sulfotepp X X

Temephos X X

Terbufos X X X

Tetrachlorviphos X

Trichlorfon X

DMP = dimethylphosphate; DEP = diethylphosphate; DMTP = dimethylthiophosphate; DMDTP = dimethyldithiophosphate; DETP = 

diethylthiophosphate; DEDTP = diethyldithiophosphate.

For studies which measured urinary 3,5,6-trichloro-2-pyridinol (TCPy) (e.g., Fortenberry et al., 

2014; Eskenazi et al., 2007; Whyatt et al., 2009), this metabolite can be derived from 

chlorpyrifos, chlorpyrifos-methyl, and the herbicide triclopyr. TCPy is also the primary 

environmental degradate of chlorpyrifos, chlorpyrifos-methyl, and triclopyr; thus exposure can 

be found directly on food treated with these pesticides. CCCEH studies have largely used 

chlorpyrifos measured in cord blood as the specific biomarker (e.g., Lovasi et al., 2010; Whyatt 

et al., 2004; Rauh et al., 2011). The CHARGE study (Shelton et al., 2015) did not measure 

biomarkers but instead used geospatial analysis to focus on the residential proximity to OP 

exposure using data from the California Department of Pesticide Regulation, with five OPs 

accounting for a total of 73% of the pesticide applied near residential settings (chlorpyrifos, 

acephate, diazinon, bensulide, and dimethoate). 

Similarly, DAPs can be found directly on food following OP applications (Zhang et al, 2008; 

Chen et al, 2012). Specifically, studies have shown that DAPs may form as environmental 

degradates from abiotic hydrolysis, photolysis, and plant metabolism (Zhang et al, 2008; Chen et 

al, 2012; Racke et al, 1994). Furthermore, since these DAPs are excreted more rapidly and 

extensively than the parent OPs (Zhang et al, 2008; Forsberg et al, 2008), direct exposure to 

DAPs may lead to an overestimate of OP exposure when using urinary DAPs as a biomarker of 

OP exposure. The agency recognizes that this is a source of uncertainty when using DAPs for 

assessing OP exposure and will continue to monitor this issue in future assessments. 

With respect to neurological effects near birth, the CHAMACOS and Mt. Sinai cohorts measured 

neurological effects at birth, and observed a putative association with total DEAP, total DMAP, 

and total DAP exposure (Engel et al., 2007; Young et al., 2005). Similarly, a Chinese study 

(Zhang et al., 2014) reported statistically significant associations between total DEAPs, total 

DMAPs, and total DAPs from prenatal OP pesticide exposure and neonatal neurodevelopment 
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assessed 3 days after birth. However, another cross-sectional Chinese study, Guodong et al 

(2012), observed no association with urinary DAPs and a developmental quotient score for 23-25 

month old children.

The 3 US cohorts (CCCEH, Mt. Sinai, CHAMACOS) each reported evidence of impaired mental 

and psychomotor development, albeit not consistent by age at time of testing (ranging from 6 

month to 36 months across the three cohorts). Attentional problems and ADHD were reported 

by three prospective cohorts [Rauh et al, 2006; Eskenazi et al., 2007; Marks et al, 2010; and 

Fortenberry et al (2014)] investigators with additional support from a case control study, 

Bouchard et al. (2010). The exposure metric varied among these studies. Specifically, 

Fortenberry et al (2014) found suggestive evidence of an association with TCPy and ADHD in 

boys whereas statistically significant associations were observed by Rauh et al (2006) with 

chlorpyrifos exposure and ADHD. Eskenazi et al (2007) reported associations with total 

DMAPs and total DAPs and ADHD; Marks et al (2010) reported associations with total DEAP, 

DMAP, and total DAP exposure and ADHD. In a national cross-sectional study of Canadian 

children, using 2007-2009 data for children age 6-11 years (Oulhote and Bouchard, 2013), there 

were no overall statistically significant associations observed between child urinary DEAP, 

DMAP, or total DAP metabolite levels and parentally reported behavioral problems. In contrast, 

Bouchard et al. (2010), looking at U.S. children age 8-15 years in the 2000-2004 National Health 

and Nutrition Examination Survey (NHANES), observed a positive association between 

attention and behavior problems and total DAPs and DMAPs, but not DEAPs. As part of their 

analysis, Oulhote and Bouchard (2013) noted that their outcome assessment for behavioral 

problems may not have been as sensitive as Bouchard et al (2010), which may in part account for 

the difference in the observed results from these studies. 

In addition, the three US cohorts and the CHARGE study have reported suggestive or positive 

associations between OP exposure and autism spectrum disorders (Rauh et al., 2006; Shelton et 

al., 2014; Eskenazi et al, 2007; Furlong et al., 2014). Specifically, Furlong et al (2014) 

documented suggestive evidence of an association between total DEAP exposure and reciprocal 

social responsiveness among blacks and boys. Eskenazi et al (2007) reported a statistically 

significant association between pervasive developmental disorder (PDD) and total DAP 

exposure, whereas Eskenazi et al (2010) reported non-significant, but suggestive, increased odds 

of PDD of 2.0 (0.8 to 5.1; p=0.14). Rauh et al (2006) documented a significant association 

between PDD and specifically chlorpyrifos exposure. Both PDD and reciprocal social 

responsiveness are related to the autism spectrum disorder. Using a different exposure 

assessment method (geospatial analysis and residential proximity to total OP exposure), Shelton 

et al (2014) also showed statistically significant associations between total OP exposure and 

ASD. While these studies vary in the magnitude of the overall strength of association, they have 

consistently observed a positive association between OP exposure and ASD. Finally, CCCEH, 

Mt. Sinai, CHAMACOS have reported an inverse relation between the respective prenatal 

measures of chlorpyrifos and intelligence measures at age 7 years (Rauh et al. ,2011; Engel et al., 

2011; Bouchard et al., 2011). 

Across the epidemiology database of studies, the maternal urine, cord blood, and other 

(meconium) measures provide evidence that exposure did occur to the fetus during gestation but 

the actual level of such exposure during the critical window(s) of susceptibility is not known. 

While significant uncertainties remain about the actual exposure levels experienced by mothers 

and infant participants in the children’s health cohorts, it is unlikely that these exposures resulted 
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in AChE inhibition. As part of the CHAMACOS study, Eskenazi et al. (2004) measured AChE 

activity and showed that no differences in AChE activity were observed. The biomarker data 

(chlorpyrifos) from the Columbia University studies are supported by the agency’s dose 

reconstruction analysis using the PBPK-PD model (D424485, D. Drew et al, 12/29/2014). 

Following the recommendation of the FIFRA SAP (2012), the agency conducted a dose 

reconstruction analysis of residential uses available prior to 2000 for pregnant women and young 

children inside the home. The PBPK-PD model results indicate for the highest exposure 

considered (i.e., indoor broadcast use of a 1% chlorpyrifos formulation) <1% RBC AChE 

inhibition was produced in pregnant women. While uncertainty exists as to actual OP exposure 

at (unknown) critical windows of exposure, EPA believes it is unlikely individuals in the 

epidemiology studies experienced RBC AChE inhibition.

A review of the scientific literature on potential modes of action/adverse outcome pathways 

(MOA/AOP)5leading to effects on the developing brain was conducted for the 2012 FIFRA SAP 

meeting (USEPA, 2012) and updated for the December 2014 chlorpyrifos revised risk 

assessment (D. Drew; 29-DEC-2014; D424485). In short, multiple biologically plausible 

hypotheses and pathways are being pursued by researchers that include targets other than AChE 

inhibition, including cholinergic and non-cholinergic systems, signaling pathways, proteins, and 

others. However, no one pathway has sufficient data to be considered more credible than the 

others. The fact that there are, however, sparse AOP data to support the in vitro to in vivo

extrapolation, or the extrapolation from biological perturbation to adverse consequence 

significantly limits their quantitative use in risk assessment. The SAP concurred with the agency 

in 2008 and 2012 about the lack of definable key events in a MOA/AOP leading to 

developmental neurobehavioral effects. However, since the 2014 literature review, there are no 

substantive changes in the ability to define and quantitate steps in an MOA/AOP leading from 

exposure to effects on the developing brain. Published and submitted guideline DNT laboratory 

animal studies have been reviewed for OPs as part of the 2012/2014 review (D424485, D. Drew 

et al, 12/29/2014) and the updated 2015 review (OPP/USEPA; 15-SEP-2015; D331251). 

Neurobehavioral alterations in laboratory animals were often reported, albeit at AChE inhibiting 

doses, but there was generally a lack of consistency in terms of pattern, timing, or dose-response 

for these effects, and a number of studies were of lower quality. However, this information does 

provide evidence of long-lasting neurodevelopmental disorders in rats and mice following 

gestational exposure.

At this time, a MOA(s)/AOP(s) has/have not been established for neurodevelopmental outcomes. 

This growing body of literature does demonstrate, however, that OPs are biologically active on a 

number of processes that affect the developing brain. Moreover, there is a large body of in vivo

laboratory studies which show long-term behavioral effects from early life exposure, albeit at 

doses which cause AChE inhibition. EPA considers the results of the toxicological studies 

relevant to the human population, as qualitatively supported by the results of epidemiology 

studies. The agency acknowledges the lack of established MOA/AOP pathway and uncertainties 

associated lack of ability to make strong causal linkages and unknown window(s) of 

susceptibility. These uncertainties do not undermine or reduce the confidence in the findings of 

the epidemiology studies. The epidemiology studies reviewed in the 2012/2014 and 2015 

literature reviews represent different investigators, locations, points in time, exposure assessment 

procedures, and outcome measurements. Despite all these differences in study design, with the 

 

5 Mode of action (MOA) and adverse outcome pathways (AOPs) describe a set of measureable key events that make 

up the biological processes leading to an adverse outcome and the causal linkages between such events. 
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exception of two negative studies in the 2015 literature review (Guodong et al, 2012; Oulhote 

and Bouchard, 2013), authors have identified associations with neurodevelopmental outcomes 

associated with OP exposure across four cohorts and twelve study citations. Specifically, there is 

evidence of delays in mental development in infants (24-36 months), attention problems and 

autism spectrum disorder in early childhood, and intelligence decrements in school age children 

who were exposed to OPs during gestation. Investigators reported strong measures of statistical 

association across several of these evaluations (odds ratios 2-4 fold increased in some instances), 

and observed evidence of exposures-response trends in some instances, e.g., intelligence 

measures.

As section 408(b)(2)(C) of the FFDCA instructs EPA, in making its “reasonable certainty of no 

harm” finding, that in “the case of threshold effects, an additional tenfold margin of safety for the 

pesticide chemical residue and other sources of exposure shall be applied for infants and children 

to take into account potential pre- and postnatal toxicity and completeness of data with respect to 

exposure and toxicity to infants and children.” Section 408 (b)(2)(C) further states that “the 

Administrator may use a different margin of safety for the pesticide chemical residue only if, on 

the basis of reliable data, such margin will be safe for infants and children.” Given the totality of 

the evidence, there is sufficient uncertainty in the human dose-response relationship for 

neurodevelopmental effects which prevents the agency from reducing or removing the statutory 

10X FQPA Safety Factor. For the dimethoate DRA, a value of 10X has been applied. Similarly, 

a database uncertainty factor of 10X will be retained for occupational risk assessments. The 

agency will continue to evaluate the epidemiology studies and pursue approaches for quantitative 

or semi-quantitative comparisons between doses which elicit AChE inhibition and those which 

are associated with neurodevelopmental outcomes prior to a revised human health risk 

assessment. 

4.5 Safety Factor for Infants and Children (FQPA SF)

As noted above, the lack of an established MOA/AOP makes quantitative use of the 

epidemiology studies in risk assessment challenging, particularly with respect to determining 

dose-response, critical duration of exposure, and window(s) of susceptibility. However, 

exposure levels in the range measured in the epidemiology studies are likely low enough that 

they are unlikely to result in AChE inhibition. Epidemiology studies consistently identified 

associations with neurodevelopmental outcomes associated with OP exposure such as delays in 

mental development in infants (24-36 months), attention problems and autism spectrum disorder 

in early childhood, and intelligence decrements in school age children. Therefore, there is a need 

to protect children from exposures that may cause these effects; this need prevents the agency 

from reducing or removing the statutory FQPA Safety Factor. Thus, the FQPA 10X Safety 

Factor will be retained for dimethoate/omethoate for the population subgroups that include 

infants, children, youths, and women of childbearing age for all exposure scenarios. 

4.5.1 Completeness of the Toxicology Database

The existing toxicological databases are complete and adequate for characterizing dimethoate 

and omethoate toxicity. Available dimethoate studies for FQPA evaluation include 

developmental studies in the rat and rabbit, reproductive toxicity studies, CCA studies, 

neurotoxicity studies (acute, subchronic, and developmental), and a special cross-fostering study. 
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Available omethoate studies for FQPA evaluation include CCA studies, developmental studies in 

the rat and rabbit, reproductive toxicity studies, and an acute delayed hen neurotoxicity study.

As discussed in Section 4.4, there is uncertainty in the human dose-response relationship for 

neurodevelopmental effects and this warrants retention of the FQPA Safety Factor for the 

population subgroups that include infants, children, youths, and women of childbearing age for 

all exposure scenarios.

4.5.2 Evidence of Neurotoxicity

Dimethoate and omethoate are OPs with an established neurotoxic AOP. AChE inhibition is the 

most sensitive effect in all species, routes, and lifestages and is being used in deriving the PODs. 

4.5.3 Evidence of Sensitivity/Susceptibility in the Developing or Young Animal

There is no evidence of increased quantitatively sensitivity/susceptibility to offspring following 

exposure to dimethoate/omethoate based on AChE inhibition. In some studies, increased pup 

mortality was observed at doses causing decreased brain AChE activity in parental animals 

indicating increased qualitative susceptibility. Regulation of dimethoate exposure at levels 

below those causing brain AChE inhibition will protect against brain AChE inhibition in adults 

and offspring, as well as the observed increase in pup mortality (see Section 4.3).

As discussed in Section 4.4, there is uncertainty in the human dose-response relationship for 

neurodevelopmental effects and this warrants retention of the FQPA Safety Factor for the 

population subgroups that include infants, children, youths, and women of childbearing age for 

all exposure scenarios.

4.5.4 Residual Uncertainty in the Exposure Database

There are no residual uncertainties with regard to dietary and occupational exposure assessments. 

The dietary exposure assessments use PDP data, PCT estimates, empirical and default processing 

factors, cooking factors derived from literature studies, and the acute and steady-state TAFs 

which account for the greater toxicity of the omethoate metabolite. The food and water dietary 

assessments incorporate 29 years of modeled water residues which assume 100% conversion of 

dimethoate to omethoate and were adjusted using the acute and steady-state TAFs. Although 

data were used to refine the dietary exposure assessments, the assessments are not expected to 

underestimate dietary (food and water) exposures. 

4.5 Toxicity Endpoint and Point of Departure Selections

4.5.1 Dose-Response Assessment

Table 4.5.4.1 summarizes the dimethoate toxicity endpoints and PODs selected from an 

evaluation of the database. This endpoint selection was based on a weight of the evidence 

evaluation using the following considerations:

 Relative sensitivity of the brain and RBC compartments: For dimethoate and omethoate, 

across most studies, durations, lifestages, and routes, the brain is similarly or more 
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sensitive than RBCs. As such, OPP has emphasized the brain data in POD derivation as

these data represent the target tissue and brain data tend to be less variable than RBC 

data.

 Potentially susceptible populations (fetuses, juveniles, pregnancy): The available AChE 

data across multiple lifestages (adults, pregnant adults, fetuses, juveniles) show no 

quantitative lifestage sensitivity for dimethoate and omethoate. In several studies, 

increased pup mortality was observed at doses at or above those causing decreased brain 

AChE activity in parental animals. 

 Route of exposure: It is preferred to match, to the degree possible, the route of exposure 

in the toxicity study with that of the exposure scenario(s) of interest. There are oral and 

dermal studies with dimethoate, as well as an inhalation study with omethoate, which 

contain high-quality dose-response AChE data.

 Duration of exposure: It is preferred to match, to the degree possible, the duration of 

toxicity study with that of the exposure duration of interest. There are single-day and 

steady-state oral studies, but only steady-state dermal and inhalation studies are available. 

 Consistency across studies: In cases where multiple datasets are available for a single 

duration, it is important to evaluate the extent to which data are consistent (or not) across 

studies. The dimethoate and omethoate databases have striking consistency across 

studies, which allows the PODs to be derived from multiple critical studies, thereby 

increasing the confidence in such values. 

Consistent with risk assessments for other AChE-inhibiting compounds, OPP has used a 

benchmark response (BMR) level of 10% and has thus calculated BMD10 and BMDL10 values 

(See Appendix B for summary of OPP’s ChE policy). The BMD10 is the estimated dose where 

AChE is inhibited by 10% compared to background. The BMDL10 is the lower confidence 

bound on the BMD10. As a matter of science policy, the Agency uses the BMDL, not the BMD, 

for use as the POD (USEPA, 2012). All BMD/BMDL modeling for all individual datasets was 

completed using USEPA BMD Software to fit an exponential model to the data. BMD results 

from the OP CRA (2002, 2006) were included in the endpoint selection weight-of-evidence 

evaluation. 

Studies used for endpoint selection are supported by the 2005 FIFRA SAP. BMD values for 

studies applicable to endpoints selection (dimethoate CCA, dimethoate dermal, and omethoate 

inhalation studies) were recalculated using up-to-date BMD software, which resulted in slight 

adjustments in the POD values derived from the acute dimethoate CCA study (MRID 45529702) 

and the dimethoate dermal toxicity study (MRID 44999101). The TAFs for omethoate were 

derived using BMD10 values (see Section 4.5.2). All remaining POD values did not change from 

the RED. This approach is consistent with the OP CRA and the previous dimethoate RED 

document (C. Jarvis; 31-JAN-2006; D325201). 

Summary tables of BMD analyses can be found in Appendix C and the technical details of the 

analysis can be found in the BMD analysis memo (M. Perron; 15-SEP-2015; TXR# 0057249). 

Acute Dietary (all populations) 

A POD for the acute dietary (all populations) exposure scenario was derived from the results of a 

high-quality, well-conducted dimethoate CCA rat study (MRID 45529702). A BMDL10 of 0.91 

mg/kg/day associated with brain AChE inhibition in PND11 female pups was selected as a 
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suitable POD for the acute dietary (all populations) exposure scenario. The corresponding 

BMD10 was 1.55 mg/kg/day. 

Brain AChE inhibition was selected for the POD since the brain is a principal target organ for 

OP pesticides and the brain AChE data was more robust than RBC AChE data. Data from the 

PND11 pups represent highly exposed sub-populations (infants and young children) and thus are 

appropriate for POD derivation. 

An uncertainty factor of 1000X (10X to account for interspecies extrapolation, 10X for 

intraspecies variation, and 10X FQPA SF due to uncertainty in the human dose-response 

relationship for neurodevelopmental effects (see Section 4.4)) is applied to the BMDL10 to obtain 

an aPAD of 0.00091 mg/kg/day for exposure scenarios with infants, children, youths, and 

women of childbearing age. The only population subgroup that the FQPA SF is not retained for 

is adults 50-99; therefore, the aPAD for this population subgroup is 0.0091 mg/kg/day.

Steady-State Dietary (all populations)

There is remarkable similarity in BMD estimates across multiple dimethoate studies, durations, 

lifestages, and compartments in studies 11 days and longer (Table 4.3.1.1; Appendix 9 of 

USEPA 2004). Because of this consistency, OPP has elected to use BMD/BMDL estimates 

reported in the OP CRA (2002, 2006) for deriving the steady-state oral POD. Results of the OP 

CRA incorporate multiple time points together in a single BMD/BMDL analysis and are thus 

highly robust. Specifically, in the OP CRA, EPA performed a sophisticated statistical analysis 

using nonlinear mixed effects models that allow for combining the results of multiple studies and 

multiple time points into a single BMD estimate. These procedures were reviewed favorably by 

the FIFRA SAP in February 2002. 

For the OP CRA, the available AChE data for dimethoate at durations of 21 days and longer in 

adult rats were extracted from the combined chronic oral toxicity/carcinogenicity study in rats 

(MRID 00164177). The plot of the brain AChE data from this study can be found in Figure 

4.5.1.1. A BMDL10 of 0.22 mg/kg/day associated with brain AChE inhibition in male and 

female adult rats was selected as a suitable POD for the steady-state dietary (all populations) 

exposure scenario. The corresponding BMD10 was 0.25 mg/kg/day. 

An uncertainty factor of 1000X (10X to account for interspecies extrapolation, 10X for 

intraspecies variation, and 10X FQPA SF due to uncertainty in the human dose-response 

relationship for neurodevelopmental effects (see Section 4.4)) is applied to the BMDL10 to obtain 

a ssPAD of 0.00022 mg/kg/day for exposure scenarios with infants, children, youths, and women 

of childbearing age. The only population subgroup that the FQPA SF is not retained for is adults 

50-99; therefore, the ssPAD for this population subgroup is 0.0022 mg/kg/day.

Figure 4.5.1.1. BMD Results(Red = males; Blue = females) from the OP CRA (2002, 2006) 

for Dimethoate (extracted from USEPA, 2002, Appendix III.B).
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Incidental Oral, Steady-State

For the purpose of assessing potential risk associated with incidental oral exposure from steadystate durations, OPP selected the dose and endpoint from the OP CRA, which is based on

available AChE data for dimethoate at durations of 21 days and longer in adult rats from the 

combined chronic oral toxicity/carcinogenicity study in rats (USEPA, 2002 and 2006). 

Quantitation of incidental oral risks was performed using the BMDL10 value of 0.22 mg/kg and 

the BMD10 of 0.25 mg/kg based on brain AChE inhibition. These values do not specifically 

represent the subpopulations of interest (infants, toddlers, young children) for incidental oral 

exposure; however, there was no evidence of quantitative susceptibility in repeated dosing 

studies. A total uncertainty factor of 1000X is appropriate for incidental oral exposures (10X for 

interspecies extrapolation, 10X for intraspecies variation, and 10X FQPA SF due to uncertainty 

in the human dose-response relationship for neurodevelopmental effects (see Section 4.4). 

Dermal, Steady-State

A dermal POD was selected from a 28-day dermal dimethoate toxicity study (MRID 44999101) 

in rats based on brain AChE inhibition in female rats (BMDL10 = 20.2 mg/kg/day; BMD10 = 28.5 

mg/kg/day). A total uncertainty factor of 1000X is appropriate for dermal exposures (10X for 

interspecies extrapolation, 10X for intraspecies variation, and a 10X FQPA SF for residential 

assessments or as a database uncertainty factor in occupational assessments due to uncertainty in 

the human dose-response relationship for neurodevelopmental effects (see Section 4.4). 

Inhalation Steady-State

A route-specific inhalation toxicity study with dimethoate is not available to assess AChE 

inhibition due to repeated exposure. An inhalation POD was selected from a 28-day inhalation 

toxicity study with omethoate (MRID 46358601) based on brain AChE inhibition in male rats 

(BMDL10 = 0.38 mg/m3/day or 0.00038 mg/L/day; BMD10 = 0.51 mg/m3/day or 0.00051 
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mg/L/day). Due to the lack of characterization of particle sizes in the study, the mass median 

aerodynamic diameter (MMAD) and geometric standard deviation (GSD) could not be 

determined. As a result, human-equivalent concentrations could not be estimated for the 

systemic effects (AChE inhibition) from inhalation exposure. For occupational scenarios, 

duration adjustments were made to extrapolate exposure in the animal study (6 hours/day; 5 

days/week) to a typical occupational exposure (8 hours/day; 5 days/week). The resulting 

duration adjusted value for occupational exposures is 0.285 mg/m3. For estimating occupational 

inhalation risks from different occupational activities, inhalation doses of 0.016, 0.033, and 0.057 

mg/kg/day corresponding to the breathing rates of 8.3, 16.7, or 29 L/min were calculated using 

this duration adjusted value. For inhalation exposures, a total uncertainty factor of 1000X was 

applied (10X for interspecies extrapolation, 10X for intraspecies variation, and a 10X database 

uncertainty factor in occupational assessments due to uncertainty in the human dose-response 

relationship for neurodevelopmental effects (see Section 4.4)).

4.5.2 Toxicity Adjustment Factors for Omethoate

As the oxon metabolite of dimethoate, omethoate has been found to be a more potent AChE 

inhibitor. To account for the increased potency of omethoate in risk estimates, BMD modeling 

was used to evaluate relative potency for dimethoate and omethoate and to estimate the TAFs for 

acute and steady-state exposure durations. As described in the guidance document for CRA

(USEPA, 2002), comparisons of toxic potency should be made using a uniform basis of 

comparison, by using to the extent possible a common response derived from a comparable 

measurement methodology, species, and sex for all the exposure routes of interest. Doseresponse modeling is preferred over the use of no- or lowest-observed adverse-effect levels 

(NOAELs/LOAELs) for determining relative toxic potency. NOAELs and LOAELs do not 

necessarily reflect the relationship between dose and response for a given chemical, nor do they 

reflect a uniform response across different chemicals. 

TAFs have been estimated previously for dimethoate and omethoate (A. Lowit; 11-APR-2005; 

TXR# 0052940). Updated acute TAFs were calculated since previous values were based only on 

the limited data available at that time. Recently received omethoate CCA data can be 

incorporated into the acute analysis to derive sex- and age-specific values. To calculate acute 

TAFs, BMD10 values obtained from the acute CCAs in adult and juvenile rats were utilized. The 

sex- and age-specific acute TAF applied to residues of omethoate corresponds to the age and sex 

of the animal used for endpoint selection (i.e., the acute TAF of 8 will be used to assess acute 

dietary exposures because the POD value is based on brain AChE inhibition in female PND11 

pups).

The originally calculated steady-state TAF of 3 was derived using the BMD10 values from the 

combined chronic oral toxicity/carcinogenicity study for dimethoate and a 28-day subchronic 

oral toxicity study for omethoate (A. Lowit; 24-APR-2002; TXR# 0050651). This value has 

since been verified using data from a two-year feeding study with omethoate; therefore, no 

changes were made to the steady-state TAF (A. Lowit; 10-JUL-2002; TXR# 0050901). 

Table 4.5.2.1. Acute TAFsa Calculated for Adult and Juvenile Rats Using BMD of Brain AChE Inhibition 

After a Single Dose.

Male Female
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Adults

Dimethoate BMD10 (mg/kg/day) 2.5 2.2

Omethoate BMD10 (mg/kg/day) 0.2 0.3

Acute TAF 13 7

Pups (PND11)

Dimethoate BMD10 (mg/kg/day) 1.8 1.6

Omethoate BMD10 (mg/kg/day) 0.2 0.2

Acute TAF 9 8

a TAF = dimethoate BMD10 ÷ omethoate BMD10.

4.5.3 Recommendation for Combining Routes of Exposures for Risk Assessment

When there are potential occupational and residential exposures to a pesticide, the risk 

assessment must address exposures from three major sources (oral, dermal, and inhalation) and 

determine whether the individual exposures can be combined if they have the same toxicological 

effects. PODs for the incidental oral, dermal, and inhalation routes are all derived from brain 

AChE inhibition. As a result, exposure from all routes can be combined. 

4.5.4 Cancer Classification and Risk Assessment Recommendation

Dimethoate is classified as a Group C carcinogen - possible human carcinogen (Memo; K. 

Dearfield; 29-AUG-1991). On June 25, 1992, the FIFRA SAP concurred with the Agency's 

classification of dimethoate as a Group C carcinogen. Quantification of risk using a non-linear 

approach will adequately account for all chronic toxicity, including carcinogenicity that could 

result from exposure to dimethoate.

4.5.5 Summary of Points of Departure and Toxicity Endpoints Used in Human Risk 

Assessment

Table 4.5.5.1. Summary of Toxicological Doses and Endpoints for Dimethoate for Use in Dietary and Non-Occupational Human 

Health Risk Assessments.

Exposure/

Scenario POD UFsa LOC Study and Toxicological Effects

Acute Dietary 

(all populations

except adults 50-

99 years old)

BMDL10 = 

0.91 mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 10X

aRfD = 0.00091

aPAD = 0.00091

CCA study in rats 

(MRID 45529702)

BMD10 = 1.55 mg/kg/day

Inhibition of brain AChE in female rat pups.

Acute Dietary 

(adults 50-99 

years old)

BMDL10 = 

0.91 mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 1X

aRfD = 0.0091

aPAD = 0.0091

CCA study in rats 

(MRID 45529702)

BMD10 = 1.55 mg/kg/day

Inhibition of brain AChE in female rat pups.

Steady-State

Dietary

(all populations

except adults 50-

99 years old)

BMDL10 = 

0.22 mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 10X

ssRfD = 0.00022

ssPAD = 0.00022

Combined chronic oral toxicity/carcinogenicity 

study 

(OP CRA 2002, 2006; MRID 00164177)

BMD10 = 0.25 mg/kg/day

Inhibition of brain AChE in adult rats.
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Table 4.5.5.1. Summary of Toxicological Doses and Endpoints for Dimethoate for Use in Dietary and Non-Occupational Human 

Health Risk Assessments.

Exposure/

Scenario POD UFsa LOC Study and Toxicological Effects

Steady-State 

Dietary

(adults 50-99 

years old)

BMDL10 = 

0.22 mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 1X

ssRfD = 0.0022

ssPAD = 0.0022

Combined chronic oral toxicity/carcinogenicity 

study 

(OP CRA 2002, 2006; MRID 00164177)

BMD10 = 0.25 mg/kg/day

Inhibition of brain AChE in adult rats.

Incidental Oral

Steady-State

BMDL10 = 

0.22 mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 10X

Residential LOC 

for MOE < 1000

Combined chronic oral toxicity/carcinogenicity 

study (OP CRA 2002, 2006; MRID 00164177)

BMD10 = 0.25 mg/kg/day

Inhibition of brain AChE in adult rats.

Dermal SteadyStateBMDL10 = 

20.2 mg/kg/day

UFA = 10X

UFH = 10X

FQPA SF = 10X

Residential LOC 

for MOE < 1000

28-day rat dermal toxicity 

(MRID 44999101)

BMD10 = 28.5 mg/kg/day

Inhibition of brain AChE in adult rats.

Cancer (oral, 

dermal, 

inhalation)

Classification: Group C carcinogen (possible human carcinogen).

Point of departure (POD) = A data point or an estimated point that is derived from observed dose-response data and 

used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human 

exposures. UF = uncertainty factor. UFA = extrapolation from animal to human (interspecies). UFH = potential 

variation in sensitivity among members of the human population (intraspecies). FQPA SF = FQPA Safety Factor. 

PAD = population adjusted dose (a = acute, ss = steady-state). RfD = reference dose (a = acute, ss = steady-state). 

MOE = margin of exposure. LOC = level of concern. BMD10 = estimated dose where AChE is inhibited by 10% 

compared to background. BMDL10 = lower confidence bound on the BMD10.

a FQPA SF retained for infants, children, youths, and women of childbearing age for all exposure scenarios due to 

uncertainty in the human dose-response relationship for neurodevelopmental effects (see Section 4.4). This includes 

all exposure scenarios, except the dietary exposure scenarios for the population subgroup adults 50-99 for which the 

FQPA SF has been reduced to 1X. 

 

Table 4.5.5.2. Summary of Toxicological Doses and Endpoints for Dimethoate for Use in Occupational Human Health 

Risk Assessments.

Exposure/

Scenario POD UFs LOC Study and Toxicological Effects

Dermal SteadyStateBMDL10 = 

20.2 mg/kg/day

UFA = 10X

UFH = 10X

UFDB = 10Xb

Occupational 

LOC for MOE <

1000

28-day rat dermal toxicity 

(MRID 44999101)

BMD10 = 28.5 mg/kg/day

Inhibition of brain AChE in adult rats.

Inhalation SteadyStateBMDL10 =

0.38 mg/m3/daya

UFA = 10X

UFH = 10X

UFDB = 10Xb

Occupational 

LOC for MOE <

1000

Omethoate 21-day inhalation rat study

(MRID 46358601)

BMD10 = 0.51 mg/m3/day

Inhibition of brain AChE in adult rats.

Cancer (oral, 

dermal, inhalation) Classification: Group C carcinogen (possible human carcinogen).

Point of departure (POD) = A data point or an estimated point that is derived from observed dose-response data and 

used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human 

exposures. UF = uncertainty factor. UFA = extrapolation from animal to human (interspecies). UFH = potential 

variation in sensitivity among members of the human population (intraspecies). MOE = margin of exposure. LOC 
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= level of concern. BMD10 = estimated dose where AChE is inhibited by 10% compared to background. BMDL10 = 

lower confidence bound on the BMD10. 

a

Inhalation doses corresponding to the breathing rates of 8.3, 16.7, and 29 L/min were calculated as 0.016, 0.033, 

and 0.057 mg/kg/day, respectively, for occupational activities using a duration adjusted value of 0.285 mg/m3.

b UFDB for occupational dermal and inhalation exposures = database uncertainty factor due to uncertainty in the 

human dose-response relationship for neurodevelopmental effects (see Section 4.4)

4.6 Endocrine Disruption

As required by FIFRA and the Federal Food, Drug, and Cosmetic Act (FFDCA), EPA reviews 

numerous studies to assess potential adverse outcomes from exposure to chemicals. 

Collectively, these studies include acute, subchronic, and chronic toxicity, including assessments

of carcinogenicity, neurotoxicity, developmental, reproductive, and general or systemic toxicity. 

These studies include endpoints that may be susceptible to endocrine influence, including effects

on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual maturation, 

fertility, pregnancy rates, reproductive loss, and sex ratios in offspring. For ecological hazard 

assessments, EPA evaluates acute tests and chronic studies that assess growth, developmental 

and reproductive effects in different taxonomic groups. As part of its reregistration decision for 

dimethoate, EPA reviewed these data and selected the most sensitive endpoints for relevant risk 

assessment scenarios from the existing hazard database. However, as required by FFDCA 

section 408(p), dimethoate is subject to the endocrine screening part of the Endocrine Disruptor 

Screening Program (EDSP). 

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

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

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

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

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

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

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

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

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

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

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

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

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

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list 

of chemicals identified for EDSP screening was published on June 14, 20136and includes some 

pesticides scheduled for Registration Review and chemicals found in water. Neither of these 

lists should be construed as a list of known or likely endocrine disruptors.

Dimethoate is on List 1 for which EPA has received all the required Tier 1 assay data. The 

Agency has reviewed all of the assay data received for the appropriate List 1 chemicals and the 

conclusions of those reviews are available in the chemical-specific public dockets (see EPA-HQOPP-2009-0059). For further information on the status of the EDSP, the policies and 

 

6 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals.
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procedures, the lists of chemicals, future lists, the test guidelines and the Tier 1 screening battery, 

please visit our website.

7

5.0 Dietary Exposure and Risk Assessment 

5.1 Metabolite/Degradate Residue Profile

5.1.1 Summary of Plant and Animal Metabolism Studies

The qualitative nature of the residue in plants is adequately understood. Dimethoate is readily 

taken up and translocated by plants, and is metabolized hydrolytic and oxidative processes to 

omethoate, dimethoate carboxylic acid, dimethyl hydrogen phosphate and O,O-dimethyl 

hydrogen phosphorodithioate, indicating oxidation to omethoate, omethoate carboxylic acid, and 

dimethoate carboxylic acid, and cleavage of the P-S linkage either before or after oxidation. The 

residues to be regulated in plants are dimethoate and its oxygen analog, omethoate. The current 

tolerance expression for plant commodities is adequate. 

In the confined rotational crop study, a substantial proportion of the residue was characterized as 

polar compounds or polar hydroxy compounds. Based on the current studies and registered 

rates, inadvertent residues dimethoate and omethoate in rotational crops are expected to be

insignificant; the low residue levels consisted mainly of polar metabolites. 

The qualitative nature of the residue in eggs, poultry tissues, and ruminant tissue is adequately 

understood. The available livestock metabolism data indicate that metabolism occurs via 

conversion of dimethoate to omethoate, followed by cleavage of the P-S bond resulting in 

phosphorylation of natural products. The established tolerances for dimethoate residues in 

livestock commodities are currently expressed in terms of the total residues of dimethoate and its 

oxygen analog, omethoate. 

5.1.2 Summary of Environmental Degradation

Dimethoate is highly mobile and relatively non-persistent. The primary route of dissipation is 

microbially mediated hydrolytic and oxidative degradation in aerobic soil, particularly under 

moist conditions, with a half-life of 2.2 days. Dimethoate does not photodegrade. Volatilization 

of dimethoate from the soil surface appears to be moderate and it is not expected to be a 

significant route of dissipation compared to other routes of dissipation. It hydrolyzes very 

slowly in sterile buffered solutions at pHs 5 and 7 (156 and 68 days, respectively), but 

hydrolyzes rapidly to desmethyl dimethoate and dimethyl thiophosphoric acid with a half-life of 

4.4 days at pH 9. The anaerobic half-life was found to be approximately 22 days, with the major 

non-volatile degradate being desmethyl dimethoate. Once dimethoate is applied by foliar 

application, it is expected to reach the crop, but it can also be transported offsite by spray drift 

and/or surface (dissolved) runoff occurring within days to weeks after applications. The 

chemical is not expected to leach substantially due to its relatively low persistence in soil. 

Dimethoate is systemic (although it also has contact activity), so it is also expected to move 

through vegetation and/or root systems. The primary toxic degradate, omethoate, was found 

under field conditions in the top layer (0-6”) of soil in all five field studies, though it was not 

 

7 http://www.epa.gov/endo/
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detected in the laboratory degradation and/or soil and sediment metabolism studies. The 

presence of omethoate has been established through field studies in insects, plants, and 

mammals. It is also formed during drinking water treatment. Omethoate was the only degradate 

analyzed in the dimethoate field-dissipation study. The other degradates identified in the 

laboratory studies were not included in the analysis because it is believed that: 1) based on the 

aerobic soil metabolism study, they would not persist in the field; and, 2) they are not 

toxicologically significant.

5.1.3 Comparison of Metabolic Pathways

Extensive studies have been conducted on the metabolism of dimethoate in both plants and 

mammals. The major route of metabolism in mammals appears to be through the thiocarboxy 

derivative to the corresponding dimethyl esters of phosphoric, thiophosphoric, or 

dithiophosphoric acids. The oxygen analog of dimethoate forms in animals, although this route 

is minor with respect to the principle route. In plants, the formation of the oxygen analog is a 

major route of metabolism. However, various investigators are not in agreement regarding the 

quantitative nature of this oxidation route, nor are they in agreement on quantitative nature of the 

other pathways of metabolism, which involve hydrolysis and demethylation. 

5.1.4 Residues of Concern Summary and Rationale

The residue of concern in crops and livestock, for purposes of tolerance enforcement and risk 

assessment are dimethoate (dimethoate (O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] 

phosphorodithioate) and omethoate, its oxygen analog, (O,O-dimethyl S-[2-(methylamino)-2-

oxoethyl] phosphorothioate. The residues of concern in drinking water are dimethoate and 

omethoate. 

Table 5.1.4. Summary of Metabolites and Degradates to be included in the Risk Assessment and Tolerance 

Expression.

Matrix Residues included in Risk 

Assessment

Residues included in 

Tolerance Expression

Plants Primary Crop Dimethoate and omethoate Dimethoate and omethoate

Rotational Crop Dimethoate and omethoate Not Applicable

Livestock Ruminant Dimethoate and omethoate Dimethoate and omethoate

Poultry Dimethoate and omethoate Dimethoate and omethoate

Drinking Water Dimethoate and omethoate Not Applicable

Toxicological studies have been submitted for several dimethoate metabolites, including 

omethoate, hydroxy dimethoate, O-desmethyl omethoate carboxylic acid, des-o-methyl 

isodimethoate, O-desmethyl omethoate, and dimethoate carboxylic acid. Omethoate was the 

only metabolite that demonstrated significant inhibition of AChE and is thus the only metabolite 

of concern. 

5.2 Food Residue Profile

HED has previously evaluated residue data depicting the magnitude of dimethoate residues of 

concern in/on all registered crops. Quantifiable residues were found in crops with short preharvest intervals (PHIs; e.g., celery, beans, citrus), resulting in tolerance levels of up to 5.0 ppm 

in food commodities. Dimethoate was generally the major component of the total residue. 
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Extensive USDA PDP monitoring data for residues of dimethoate and omethoate in numerous 

commodities are available. The PDP was specifically designed for risk assessment; analysts 

prepare samples in a manner similar to typical consumer practices, such as washing, 

coring/pitting, and/or peeling. The PDP samples are collected at large-scale distribution centers, 

just prior to sale in grocery stores, and are more likely to reflect “dinner plate” residues. 

Previous dietary assessments for dimethoate have used FDA surveillance data; however, these 

data are considerably older than the available PDP data, and were not used in this assessment. 

Dimethoate and/or omethoate residues were detected by PDP in the following 

commodities/processed foods with registered tolerances: potatoes without peel (2 detects/1544 

samples); leaf lettuce (7 detects/782 samples); celery (253 detects/1480 samples); broccoli (40 

detects/1400 samples); cauliflower (9 detects/923 samples); kale (13 detects/802 samples); fresh 

green beans (84 detects/1480 samples); canned green beans (1 detect/928 samples); frozen green 

beans (8 detects/555 samples); fresh snap peas (420 detects/1487 samples); frozen sweet peas 

(90 detects/744 samples); fresh tomatoes (6 detects/1481 samples); canned tomatoes (1 

detect/737 samples); bell peppers (80 detects/1671 samples); non-bell peppers (90 detects/739 

samples); cantaloupes (19 detects/1482 samples); watermelons (15 detects/371 samples); 

tangerines (2 detects/1426 samples); pears (3 detects/1485 samples); cherries (1 detect/419 

samples); blueberries (10 detects/1477 samples); and fresh asparagus (2 detects/1488 samples). 

HED has evaluated residue data pertaining to the potential for concentration of dimethoate 

residues of concern in processed commodities. Significant concentration of residues was seen 

only in dried citrus pulp. PDP data are available for the following processed foods: tomato 

paste, canned tomatoes, orange juice, canned black, kidney, pinto, and garbanzo beans, canned 

peas, canned pears, and green bean, pea, and pear baby food. Residues of dimethoate and/or 

omethoate were not detected in any sample, except as outlined above.

5.3 Water Residue Profile

The residues of concern in drinking water for purposes of risk assessment are dimethoate and 

omethoate. EFED provided estimated drinking water concentrations (EDWCs) in the following 

drinking water assessment: “Tier II Drinking Water Assessment for Dimethoate for the Use in 

Human Health Risk Assessment in the Registration Review Risk Assessment (J. Meléndez, 28-

JUL-2014; D415002). The EDWCs were calculated using the Tier II Surface Water 

Concentration Calculator (SWCC), the Tier II Pesticide Root Zone Model-Groundwater (PRZMGW), and the Tier I Screening Concentration in Ground Water (SCI-GROW) models; however, 

dietary assessments were not completed using groundwater values since the peak EDWCs for 

groundwater were substantially lower than those for surface waters. Groundwater values and 

characterization are summarized in the most recent dietary memo (J. Van Alstine; 15-SEP-2015; 

D418590).

Surface water runs were initially performed at the maximum application rate and number of 

applications, minimum reapplication interval, and default national percent cropped area (PCA; 

equal to 0.91 or 91% for agricultural crops and 1.0 or 100% for non-agricultural uses) using the 

Tier II SWCC model. Preliminary dietary exposure assessments indicated that the maximum 

application rate EDWCs resulted in dietary exposure estimates that were above the LOC for 

many scenarios. Therefore, modeling with typical application rates and regional PCA for 

agricultural uses was conducted to provide typical rate EDWCs for dietary assessments. No 
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typical usage data were available for the non-agricultural uses; therefore, typical non-agricultural 

scenarios were modeled with lower rates using a set of assumptions that are discussed in the 

most recent drinking water memo (J. Meléndez, 28-JUL-2014; D415002).

Daily time-series outputs that simulate 29 years (1962-1990) of residues of dimethoate in surface 

drinking water for the 44 different scenarios were modeled using the Tier II SWCC. These 

scenarios were selected based on the use rates and encompass both maximum (24 scenarios) and 

typical (20 scenarios) application rates for agricultural and non-agricultural uses of dimethoate. 

Additional details regarding the selection of the scenarios can be found in the most recent 

drinking water memo (J. Meléndez, 28-JUL-2014; D415002). Since omethoate was not 

observed in the environmental fate studies in significant amounts, the omethoate equivalent 

values were expressed based on its toxicity relative to dimethoate. All of the time-series data 

were adjusted to reflect 100% conversion of dimethoate to omethoate8by multiplying the 

residues by the acute (8X) and steady-state (3X) TAFs. Therefore, EFED provided a total of 88 

distributions: 44 distributions that were adjusted using the acute TAF (“acute distributions”) and 

44 distributions that were adjusted using the steady-state TAF (“steady-state distributions”). No 

further adjustments were made to the acute distribution files. Since the steady-state average 

dietary assessments used 21-day rolling averages for drinking water, the steady-state

distributions were further adjusted to be 21-day rolling averages. In the 21-day rolling average 

distributions, the first data point is the average of days 1-21, the second data point is the average 

of days 2-22, the third data point is the average of days 3-23, etc. The 21-day rolling average 

continues until the last 20 days of residues of the final distribution year (1990). For these 

residues, the average was taken only of the remaining days, resulting in residue values that are 

not 21-day averages. 

Summary tables for EDWCs using maximum and typical application rates can be found in 

Appendix H.

5.4 Dietary Risk Assessment

Highly refined acute and steady-state (two-day average) dietary exposure and risk assessments 

for dimethoate and its metabolite omethoate were conducted using DEEM-FCID Version 3.18. 

This model uses 2003-2008 food consumption data from USDA’s NHANES/WWEIA. Acute 

and steady-state assessments were conducted for food only, drinking water only, and for food 

and drinking water. When a drinking water only assessment resulted in a risk of concern at the 

99.9th percentile, a food and drinking water assessment was not conducted for that drinking water 

scenario since the combined assessment would also result in risks of concern at the 99.9th

percentile. 

5.4.1 Overview of Residue Data Used

The residue chemistry database is adequate to support current Registration Review requirements. 

Both the acute and steady-state assessments were refined using distributions and point estimates 

derived from PDP monitoring data, PCT data, empirical and default processing factors, and 

cooking factors derived from literature studies. If monitoring data were not available for a 

particular commodity (i.e., mung beans), but were available for a similar commodity (i.e., black 

 

8 MRID 48041103 - Marin, J.E. 2010. Determination of the effect of chlorination on the degradation of dimethoate 

in water.
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beans), the available data were translated to the similar crop. HED SOP 99.3, HED SOP 2000.1, 

and use pattern information were used as guidance for translations. When data were translated, 

the residue distribution file (RDF) was adjusted to account for differences in PCT. All RDFs 

were adjusted to account for the acute (8X) and steady-state (3X) omethoate TAFs. Tolerancelevel values were used for pecan, sorghum, safflower, and cottonseed since monitoring data were 

not available for these commodities. HED previously recommended that tolerances for residues 

of dimethoate and omethoate in/on egg and poultry meat byproducts should be revoked (M. 

Sahafeyan D232849; 24-MAY-2011); however, the 40 CFR still includes tolerances for these 

commodities. Egg and poultry meat byproduct PDP data were included in the assessments as a 

conservative assumption.

The most recent dietary memo (J. Van Alstine; 15-SEP-2015; D418590) summarizes the residue 

inputs (RDFs used, point estimates, processing and cooking factors, PCT, etc.), empirical 

processing factor calculations, residue data used for each commodity, procedures for combining 

residues of dimethoate and omethoate, and all of the RDF files used for the acute and steadystate assessments. 

5.4.2 Percent Crop Treated Used in Dietary Assessment

The acute and steady-state analyses incorporated maximum PCT data provided by BEAD for the 

following commodities: alfalfa (<2.5%); asparagus (5%); beans, green (20%); broccoli (55%);

cantaloupes (10%); cauliflower (45%); celery (35%); cherry (15%); corn (<2.5%); cotton

(<2.5%); dry beans/peas (10%); grapefruit (15%); lemons (20%); lettuce (35%); oranges (25%);

pears (<2.5%); peas, green (25%); pecan (5%); peppers (25%); potatoes (15%); sorghum 

(<2.5%); soybeans (<2.5%); tangerines (5%); tomatoes (40%); watermelons (10%); and wheat 

(<2.5%).

5.4.3 Acute Dietary Risk Assessment

The food only acute dietary risk estimates are summarized in Table 5.4.6.1 and are above HED’s 

LOC (>100% of the aPAD) for the U.S. population and all population subgroups at the 99.9th

percentile. The U.S. population was 270% of the aPAD and children 1-2 years old, the most 

highly exposed population subgroup, was 640% of the aPAD. For the acute drinking water only 

runs, all (24) of the maximum application rate and 19 of the typical application rate drinking 

water scenarios resulted in risks of concern at the 99.9th percentile. 

Since the food alone and drinking water alone assessments result in risks of concern, acute food 

and drinking water analyses were not completed for all of the scenarios since they would also 

result in risks of concern at the 99.9th percentile. Overall, acute food and drinking water analyses 

were conducted for the 27 (7 maximum application rate and 20 typical application rate) drinking 

water scenarios and are summarized in Tables 5.4.6.3 and 5.4.6.4 for the most highly exposed 

population subgroups. Infants and children 1-2 years old were the most highly exposed 

population subgroups for these scenarios, with risk estimates that ranged from 710-1100% of the 

aPAD and 640-680% of the aPAD at the 99.9th percentile, respectively. The results for all 

population subgroups (general U.S. population, all infants (<1 year old), children 1-2, children 3-

5, children 6-12, youth 13-19, females 13-49, adults 20-49, and adults 50-99 years) for all runs 

are summarized in the most recent dietary memo (J. Van Alstine; 15-SEP-2015; D418590).
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5.4.4 Steady-State Dietary Risk Assessment

The food only steady-state results are summarized in Table 5.4.6.2 and are above HED’s LOC 

(>100% of the ssPAD) for the U.S. population and all population subgroups at the 99.9th

percentile. The U.S. population was 410% of the ssPAD and children 1-2 years old, the most 

highly exposed population subgroup, was 810% of the ssPAD. For the steady-state drinking 

water only analyses, all (24) of the maximum application rate and 19 of the typical application 

rate drinking water scenarios resulted in risks of concern at the 99.9th percentile. 

Since the food alone and drinking water alone assessments result in risks of concern, steady-state 

food and drinking water analyses were not completed for all of the scenarios since they would 

also result in risks of concern at the 99.9th percentile. Overall, food and drinking water steadystate analyses were conducted for 23 drinking water scenarios (3 maximum application rate and 

20 typical application rate) and are summarized in Tables 5.4.6.5 and 5.4.6.6 for the most highly 

exposed population subgroups. Infants and children 1-2 years old were the most highly exposed 

population subgroups for these scenarios, with risk estimates that ranged from 970-1200% of the 

ssPAD and 810-880% of the ssPAD at the 99.9th percentile, respectively. The results for all 

population subgroups (general U.S. population, all infants (<1 year old), children 1-2, children 3-

5, children 6-12, youth 13-19, females 13-49, adults 20-49, and adults 50-99 years) for all runs 

are summarized in the most recent dietary memo (J. Van Alstine; 15-SEP-2015; D418590)

5.4.5 Cancer Dietary Risk Assessment

Dimethoate is classified as a Group C carcinogen (possible human carcinogen). Quantification 

of risk using a non-linear approach will adequately account for all chronic toxicity, including 

carcinogenicity that could result from exposure to dimethoate.
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5.4.6. Dietary Assessment Summary Tables

Table 5.4.6.1. Summary of Acute Dietary (Food Only) Exposure and Risk for Dimethoate and 

Omethoate1.

Population Subgroup aPAD 

(mkd)2

95th Percentile 99th Percentile 99.9th Percentile

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

General U.S. Population

0.00091

0.000630 69 0.001192 130 0.002501 270

All Infants (<1 year old) 0.000933 100 0.001668 180 0.002506 280

Children 1-2 years old 0.001691 190 0.002912 320 0.005779 640

Children 3-5 years old 0.001267 140 0.002226 240 0.005053 560

Children 6-12 years old 0.000762 84 0.001394 150 0.002811 310

Youth 13-19 years old 0.000452 50 0.000929 100 0.001683 180

Adults 20-49 years old 0.000391 43 0.000735 81 0.001447 160

Adults 50-99 years old 0.000370 4.1 0.000652 7.2 0.001346 15

Females 13-49 years old 0.000380 42 0.000758 83 0.001399 150

Residue file: Dimethoate Acute File December 19 2014__FOOD ONLY.R08; Residue file dated: 12-19-2014/16:47:51

1 Population with the greatest exposure is in bold. The exposure assessment was run using a rounded aPAD value of 0.009 mkd. 

The %aPAD values have been updated to reflect the unrounded aPAD value and have been rounded to two significant figures.

2 mkd = mg/kg/day. Includes 10x FQPA SF for all population subgroups except adults 50-99 years old. The aPAD 

for adults 50-99 years old is 0.0091 mkd.

Table 5.4.6.2. Summary of Steady-State (Two-Day Average) Dietary (Food Only) Exposure and Risk for 

Dimethoate and Omethoate1.

Population Subgroup ssPAD 

(mkd)2

95th Percentile 99th Percentile 99.9th Percentile

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

General U.S. Population

0.00022

0.000276 130 0.000493 220 0.000909 410

All Infants (<1 year old) 0.000410 190 0.000670 300 0.000974 440

Children 1-2 years old 0.000706 320 0.001022 460 0.001775 810

Children 3-5 years old 0.000516 230 0.000772 350 0.001465 670

Children 6-12 years old 0.000331 150 0.000496 230 0.000964 440

Youth 13-19 years old 0.000196 89 0.000302 140 0.000508 230

Adults 20-49 years old 0.000159 72 0.000255 120 0.000475 220

Adults 50-99 years old 0.000145 6.6 0.000231 11 0.000435 20

Females 13-49 years old 0.000158 72 0.000259 120 0.000458 210

Residue file: Dimethoate Steady-state File December 30 2014__FOOD ONLY_ssRfD.R08; Residue file dated: 12-30-2014/10:45:39

1 Population with the greatest exposure is in bold. The exposure assessment was run using the rounded ssPAD value of 0.002 

mkd. The %ssPAD values have been updated to reflect the unrounded ssPAD value and have been rounded to two significant 

figures.

2 mkd = mg/kg/day. Includes 10x FQPA SF for all population subgroups except adults 50-99 years old. The ssPAD 

for adults 50-99 years old is 0.0022 mkd. 
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Table 5.4.6.3. Summary of Acute Assessment Results for Maximum Application Rate Drinking Water Scenarios (Water Only: 95th and 99.9th Percentiles; 

Food+Water: 99.9th Percentile). (Values <100% aPAD are Shaded and in Bold.)

Drinking Water 

Scenario (bold font)/ 

Crops/Uses 

Represented

Acute WATER ONLY (All Infants <1 year 

old) Acute WATER ONLY (Children 1-2 years old) Acute FOOD and WATER Highest Exposure Estimate

95th 99.9th 95th 99.9th

Population Subgroup

99.9th

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

01_CA wine grapes/

Agricultural 

uncultivated areas (CA 

only) (Noncropland 

adjacent to vineyards)

0.003130 340 0.047486 5200 0.001596 180 0.023139 2500 N/C N/C N/C

03_MN alfalfa/

Alfalfa, Sainfoin 0.002260 250 0.012488 1400 0.001083 120 0.006579 720 N/C N/C N/C

04_CA cole crops/

Broccoli, Cauliflower; 

Additionally, Brussels 

sprouts (aerial, some 

labels allow use only 

in CA)

0.004635 510 0.028422 3100 0.002352 260 0.015074 1700 N/C N/C N/C

06_CA row crops/

Celery 0.001555 170 0.008732 960 0.000760 84 0.004674 510 All Infants (<1 year old) 0.008981 990

07_FL cabbage/

Turnip (greens) 0.002608 290 0.016004 1800 0.001328 150 0.008751 960 N/C N/C N/C

08_CA potato/ Turnip 

(roots) 0.002330 260 0.012046 1300 0.001178 130 0.006658 730 N/C N/C N/C

09_WA orchards/

Cherry (only in ID, 

MT, OR, UT and WA)

0.002461 270 0.009575 1100 0.001173 130 0.005499 600 All Infants (<1 year 

old) 0.009749 1100

10_WA orchards/

Cherry (only in ID, 

MT, OR, UT and WA)

0.002797 310 0.009974 1100 0.001303 140 0.005854 640 All Infants (<1 year 

old) 0.010227 1100

12_OR Xmas trees/

Douglas fir (seed 

orchards) (only in OR 

and WA)

0.002453 270 0.013023 1400 0.001266 140 0.007147 790 N/C N/C N/C

13_CA forestry/

Cottonwood (forest/ 

shelterbelt)

0.009973 1100 0.036147 4000 0.004655 510 0.021136 2300 N/C N/C N/C
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Table 5.4.6.3. Summary of Acute Assessment Results for Maximum Application Rate Drinking Water Scenarios (Water Only: 95th and 99.9th Percentiles; 

Food+Water: 99.9th Percentile). (Values <100% aPAD are Shaded and in Bold.)

Drinking Water 

Scenario (bold font)/ 

Crops/Uses 

Represented

Acute WATER ONLY (All Infants <1 year 

old) Acute WATER ONLY (Children 1-2 years old) Acute FOOD and WATER Highest Exposure Estimate

95th 99.9th 95th 99.9th

Population Subgroup

99.9th

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

18_NJ nursery/

Ornamental 

herbaceous plants1

0.007523 830 0.096285 11000 0.004324 480 0.048787 5400 N/C N/C N/C

20_FL peppers/

Peppers 0.002748 300 0.034351 3800 0.001500 160 0.017000 1900 N/C N/C N/C

21_FL peppers/

Peppers 0.002044 220 0.033765 3700 0.001176 130 0.016433 1800 N/C N/C N/C

22_MI beans/ Beans 

(includes dry beans, 

excludes cowpeas), 

Garbanzos (includes 

chick peas), Lupine

0.001478 160 0.009937 1100 0.000744 82 0.005244 580 All Infants (<1 year 

old) 0.010354 1100

24_PA Tomato/ 

Tomato 0.001825 200 0.032938 3600 0.000936 100 0.015693 1700 N/C N/C N/C

25_CA citrus/ 

Grapefruit, Kumquat, 

Lemon, Lime, Orange, 

Pummelo (shaddock), 

Tangelo, Tangerine

0.000889 98 0.006597 720 0.000513 56 0.003575 390 All Infants (<1 year 

old) 0.006881 760

26_FL citrus/ Same 

crops as above 0.001208 130 0.025690 2800 0.000759 83 0.012608 1400 N/C N/C N/C

27_ID potatoes/ 

Potatoes 0.003140 350 0.015391 1700 0.001564 170 0.008542 940 N/C N/C N/C

05_CA cole crops/

Brussels sprouts 

(ground)

0.003661 400 0.044642 4900 0.002022 220 0.022424 2500 N/C N/C N/C

14_OR Xmas trees/

Hybrid 

cottonwood/poplar 

plantations (some 

labels allow use in ID, 

OR and WA)

0.009177 1000 0.037244 4100 0.004391 480 0.021056 2300 N/C N/C N/C
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Table 5.4.6.3. Summary of Acute Assessment Results for Maximum Application Rate Drinking Water Scenarios (Water Only: 95th and 99.9th Percentiles; 

Food+Water: 99.9th Percentile). (Values <100% aPAD are Shaded and in Bold.)

Drinking Water 

Scenario (bold font)/ 

Crops/Uses 

Represented

Acute WATER ONLY (All Infants <1 year 

old) Acute WATER ONLY (Children 1-2 years old) Acute FOOD and WATER Highest Exposure Estimate

95th 99.9th 95th 99.9th

Population Subgroup

99.9th

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

Exposure 

(mkd)

%

aPAD

10b_WA orchards/

Cherry (only in ID, 

MT, OR, UT and WA)

0.001378 150 0.004921 540 0.000642 71 0.002894 320 Children 1-2 years old 0.006152 680

15_CA nursery/

Citrus, non-bearing 

and nursery stock 

(only in CA and AZ)

0.001228 130 0.006874 760 0.000645 71 0.00378 420 All Infants (<1 year 

old) 0.007164 790

23_MS Cotton/ 

Cotton 0.001079 120 0.012753 1400 0.000601 66 0.006364 700 N/C N/C N/C

17_OR nursery/ 

Ornamental woody 

shrubs and vines; 

Ornamental and/or 

shade trees

0.005901 650 0.023714 2600 0.002798 310 0.013584 1500 N/C N/C N/C

Bold and shaded values are <100% of the aPAD. N/C = not calculated. Since the food alone and drinking water alone assessments result in risks of concern, acute food and drinking water analyses 

were not completed for the majority of the scenarios since they would also result in risks of concern at the 99.9th percentile. Food and drinking water exposure assessments were conducted for a 

subset of drinking water scenarios as an example of the combined dietary exposures and risks even though food alone and water alone resulted in risks of concern. The exposure assessments were run 

using a rounded aPAD value of 0.009 mkd. The %aPAD values have been updated to reflect the unrounded aPAD value of 0.00091 mkd and were adjusted to two significant figures. The results for 

all population subgroups (general U.S. population, all infants (<1 year old), children 1-2, children 3-5, children 6-12, youth 13-19, females 13-49, adults 20-49, and adults 50-99 years) for all runs are 

summarized in the most recent dietary memo (J. Van Alstine; 15-SEP-2015; D418590). 

1 A maximum rate of 6.5 lb ai/A for this use appears to be a label error; therefore, these results are not considered representative. A drinking water only assessment was completed using this 

distributions since the label has not yet been modified. 

Table 5.4.6.4. Summary of Acute Assessment Results for Typical Application Rate Drinking Water Scenarios (Water Only: 95th and 99.9th Percentiles; 

Food+Water: 99.9th Percentile). (Values <100% aPAD are Shaded and in Bold.)

Drinking Water Scenario 

(bold font)/ Crops/Uses 

Represented

Acute WATER ONLY (All Infants <1 year 

old)

Acute WATER ONLY (Children 1-2 years 

old)

Acute FOOD and WATER Highest Exposure 

Estimate

95th 99.9th 95th 99.9th

Population Subgroup

99.9th

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

03c_MN alfalfa/ Alfalfa 0.000444 49 0.003749 410 0.000231 25 0.001913 210 Children 1-2 years old 0.005846 640

04b_CA cole crops/

Broccoli 0.000773 85 0.007920 870 0.000409 45 0.004006 440 All Infants (<1 year old) 0.008169 900
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 5.4.6.4. Summary of Acute Assessment Results for Typical Application Rate Drinking Water Scenarios (Water Only: 95th and 99.9th Percentiles; 

Food+Water: 99.9th Percentile). (Values <100% aPAD are Shaded and in Bold.)

Drinking Water Scenario 

(bold font)/ Crops/Uses 

Represented

Acute WATER ONLY (All Infants <1 year 

old)

Acute WATER ONLY (Children 1-2 years 

old)

Acute FOOD and WATER Highest Exposure 

Estimate

95th 99.9th 95th 99.9th

Population Subgroup

99.9th

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

17b_OR nursery/ 

Ornamental woody shrubs 

and vines; Ornamental 

and/or shade trees

0.000368 40 0.002475 270 0.000194 21 0.001305 140 Children 1-2 years old 0.005798 640

18b_NJ nursery/

Ornamental herbaceous 

plants

0.000281 31 0.003593 390 0.000161 18 0.001820 200 Children 1-2 years old 0.005836 640

22c_MI beans/ Dry beans, 

peas

0.000350 38 0.004195 460 0.000194 21 0.002109 230 Children 1-2 years old 0.005875 650

23c_MS Cotton/ Cotton 0.000171 19 0.003917 430 0.000109 12 0.001907 210 Children 1-2 years old 0.005835 640

24b_PA Tomato/ Tomato 0.000187 21 0.002325 260 0.000098 11 0.001128 120 Children 1-2 years old 0.005831 640

26b_FL citrus/ Oranges 0.000226 25 0.005462 600 0.000141 15 0.002659 290 Children 1-2 years old 0.005987 660

27c_ID potatoes/ Potatoes 0.001333 150 0.006605 730 0.000665 73 0.003655 400 All Infants (<1 year 

old) 0.006905 760

27d_ID potatoes/ Potatoes 0.000629 69 0.003762 410 0.000328 36 0.002042 220 Children 1-2 years old 0.005869 640

28_IL corn/ Corn 0.000451 50 0.007578 830 0.000243 27 0.003537 390 All Infants (<1 year 

old) 0.007916 870

29_KS sorghum/ Sorghum 0.000267 29 0.006286 690 0.000151 17 0.003154 350 All Infants (<1 year 

old) 0.006488 710

30_MS soybeans/ 

Soybeans 0.000282 31 0.003531 390 0.000167 18 0.001744 190 Children 1-2 years old 0.00584 640

31_OR snap beans/ Lima 

beans 0.000547 60 0.002682 290 0.000272 30 0.001503 170 Children 1-2 years old 0.005807 640

32_ND wheat/ Spring 

wheat 0.000205 23 0.001274 140 0.000112 12 0.000700 77 Children 1-2 years old 0.005815 640

33_ND wheat/ Winter 

wheat 0.000255 28 0.001587 170 0.000139 15 0.000872 96 Children 1-2 years old 0.005788 640

13b_CA forestry/

Cottonwood (forest/ 

shelterbelt)

0.001209 130 0.006982 770 0.000610 67 0.003794 420 All Infants (<1 year 

old) 0.007370 810

14b_OR Xmas trees/

Hybrid cottonwood/poplar 0.001083 120 0.005602 620 0.000558 61 0.003099 340 Children 1-2 years old 0.006109 670
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 5.4.6.4. Summary of Acute Assessment Results for Typical Application Rate Drinking Water Scenarios (Water Only: 95th and 99.9th Percentiles; 

Food+Water: 99.9th Percentile). (Values <100% aPAD are Shaded and in Bold.)

Drinking Water Scenario 

(bold font)/ Crops/Uses 

Represented

Acute WATER ONLY (All Infants <1 year 

old)

Acute WATER ONLY (Children 1-2 years 

old)

Acute FOOD and WATER Highest Exposure 

Estimate

95th 99.9th 95th 99.9th

Population Subgroup

99.9th

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

Exposure 

(mkd)

% 

aPAD

plantations (some labels 

allow use in ID, OR and 

WA)

15b_CA nursery/ Citrus, 

non-bearing and nursery 

stock (only in CA and AZ)

0.000108 12 0.000604 66 0.000057 6.3 0.000332 36 Children 1-2 years old 0.00578 640

12b_OR Xmas trees/

Douglas fir (seed orchards) 

(only in OR and WA)

0.000546 60 0.002896 320 0.000282 31 0.00159 170 Children 1-2 years old 0.005807 640

Bold and shaded values are <100% of the aPAD. N/C = not calculated. The exposure assessments were run using a rounded aPAD value of 0.009 mkd. The %aPAD values have 

been updated to reflect the unrounded aPAD value of 0.00091 mkd and were adjusted to two significant figures. The results for all population subgroups (general U.S. population, 

all infants (<1 year old), children 1-2, children 3-5, children 6-12, youth 13-19, females 13-49, adults 20-49, and adults 50-99 years) for all runs are summarized in the most recent 

dietary memo (J. Van Alstine; 15-SEP-2015; D418590).

Table 5.4.6.5. Summary of Steady-State (Two-Day Average) Assessment Results for Maximum Application Rate Drinking Water Scenarios (Water Only: 95th and 

99.9th Percentiles; Food+Water: 99.9th Percentile). (Values <100% ssPAD are Shaded and in Bold.)

Drinking Water Scenario 

(bold font)/ Crops/Uses 

Represented

Two-Day Average WATER ONLY 

(All Infants <1 year old)

Two-Day Average WATER ONLY 

(Children 1-2 years old)

Two-Day Average FOOD and WATER 

Highest Exposure Estimate

95th 99.9th 95th 99.9th

Population 

Subgroup

99.9th

Exposure (mkd) % 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

01_CA wine grapes/

Agricultural uncultivated 

areas (CA only) 

(Noncropland adjacent to 

vineyards)

0.001087 490 0.016100 7300 0.000562 260 0.007729 3500 N/C N/C N/C

03_MN alfalfa/ Alfalfa, 

Sainfoin 0.000818 370 0.004016 1800 0.000392 180 0.002055 930 N/C N/C N/C

04_CA cole crops/

Broccoli, Cauliflower; 

Additionally, Brussels 

sprouts (aerial, some 

0.001730 790 0.009069 4100 0.000872 400 0.004692 2100 N/C N/C N/C
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Table 5.4.6.5. Summary of Steady-State (Two-Day Average) Assessment Results for Maximum Application Rate Drinking Water Scenarios (Water Only: 95th and 

99.9th Percentiles; Food+Water: 99.9th Percentile). (Values <100% ssPAD are Shaded and in Bold.)

Drinking Water Scenario 

(bold font)/ Crops/Uses 

Represented

Two-Day Average WATER ONLY 

(All Infants <1 year old)

Two-Day Average WATER ONLY 

(Children 1-2 years old)

Two-Day Average FOOD and WATER 

Highest Exposure Estimate

95th 99.9th 95th 99.9th

Population 

Subgroup

99.9th

Exposure (mkd) % 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

labels allow use only in 

CA)

06_CA row crops/

Celery 0.000570 260 0.002854 1300 0.000279 130 0.001469 670 N/C N/C N/C

07_FL cabbage/ Turnip 

(greens) 0.000976 440 0.005096 2300 0.000501 230 0.002641 1200 N/C N/C N/C

08_CA potato/ Turnip 

(roots) 0.000871 400 0.003973 1800 0.000432 200 0.002099 950 N/C N/C N/C

09_WA orchards/

Cherry (only in ID, MT, 

OR, UT and WA)

0.000888 400 0.002903 1300 0.000415 190 0.001652 750 N/C N/C N/C

10_WA orchards/

Cherry (only in ID, MT, 

OR, UT and WA)

0.000993 450 0.003111 1400 0.000465 210 0.001773 810 N/C N/C N/C

12_OR Xmas trees/

Douglas fir (seed 

orchards) (only in OR 

and WA)

0.000940 430 0.003944 1800 0.000456 210 0.002166 980 N/C N/C N/C

13_CA forestry/

Cottonwood (forest/ 

shelterbelt)

0.003578 1600 0.011923 5400 0.001671 760 0.006713 3100 N/C N/C N/C

18_NJ nursery/

Ornamental herbaceous 

plants1

0.003069 1400 0.029122 13000 0.001702 770 0.014279 6500 N/C N/C N/C

20_FL peppers/ Peppers 0.001110 500 0.010331 4700 0.000591 270 0.005063 2300 N/C N/C N/C

21_FL peppers/ Peppers 0.000859 390 0.010034 4600 0.000478 220 0.004894 2200 N/C N/C N/C

22_MI beans/ Beans 

(includes dry beans, 

excludes cowpeas), 

Garbanzos (includes 

chick peas), Lupine

0.000545 250 0.003227 1500 0.000276 130 0.001625 740 N/C N/C N/C
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Table 5.4.6.5. Summary of Steady-State (Two-Day Average) Assessment Results for Maximum Application Rate Drinking Water Scenarios (Water Only: 95th and 

99.9th Percentiles; Food+Water: 99.9th Percentile). (Values <100% ssPAD are Shaded and in Bold.)

Drinking Water Scenario 

(bold font)/ Crops/Uses 

Represented

Two-Day Average WATER ONLY 

(All Infants <1 year old)

Two-Day Average WATER ONLY 

(Children 1-2 years old)

Two-Day Average FOOD and WATER 

Highest Exposure Estimate

95th 99.9th 95th 99.9th

Population 

Subgroup

99.9th

Exposure (mkd) % 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

24_PA Tomato/ Tomato 0.000675 310 0.011389 5200 0.000348 160 0.005484 2500 N/C N/C N/C

25_CA citrus/ 

Grapefruit, Kumquat, 

Lemon, Lime, Orange, 

Pummelo (shaddock), 

Tangelo, Tangerine

0.000381 170 0.001826 830 0.000194 88 0.000975 440 Children 1-2 

years old 0.001929 880

26_FL citrus/ Same 

crops as above 0.000551 250 0.007940 3600 0.000307 140 0.003761 1700 N/C N/C N/C

27_ID potatoes/ 

Potatoes 0.001161 530 0.004764 2200 0.000568 260 0.002548 1200 N/C N/C N/C

05_CA cole crops/

Brussels sprouts 

(ground)

0.001412 640 0.014579 6600 0.000776 350 0.007200 3300 N/C N/C N/C

14_OR Xmas trees/

Hybrid 

cottonwood/poplar 

plantations (some labels 

allow use in ID, OR and 

WA)

0.003320 1500 0.011918 5400 0.001574 720 0.006844 3100 N/C N/C N/C

10b_WA orchards/

Cherry (only in ID, MT, 

OR, UT and WA)

0.000489 220 0.001542 700 0.000229 100 0.000877 400 Children 1-2 

years old 0.001913 870

15_CA nursery/ Citrus, 

non-bearing and nursery 

stock (only in CA and 

AZ)

0.000481 220 0.001987 900 0.000235 110 0.001081 490 All Infants (<1 

year old) 0.002124 970

23_MS Cotton/ Cotton 0.000433 200 0.004079 1900 0.000234 110 0.002005 910 N/C N/C N/C

17_OR nursery/ 

Ornamental woody 

shrubs and vines; 

Ornamental and/or shade 

trees

0.002123 970 0.007785 3500 0.001009 460 0.004241 1900 N/C N/C N/C
Dimethoate Human Health Risk Assessment DP No. D416010

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Bold and shaded values are <100% of the ssPAD. N/C = not calculated. Since the food alone and drinking water alone assessments result in risks of concern, steady-state (twoday average) food and drinking water analyses were not completed for the majority of the scenarios since they would also result in risks of concern at the 99.9th percentile. Food 

and drinking water exposure assessments were conducted for a subset of drinking water scenarios as an example of the combined dietary exposures and risks even though food 

alone and water alone resulted in risks of concern. The exposure assessments were run using a rounded ssPAD value of 0.002 mkd. The %ssPAD values have been updated to 

reflect the unrounded ssPAD value of 0.00022 mkd and were adjusted to two significant figures. The results for all population subgroups (general U.S. population, all infants (<1 

year old), children 1-2, children 3-5, children 6-12, youth 13-19, females 13-49, adults 20-49, and adults 50-99 years) for all runs are summarized in the most recent dietary memo 

(J. Van Alstine; 15-SEP-2015; D418590).

Table 5.4.6.6. Summary of Steady-State (Two-Day Average) Assessment Results for Typical Application Rate Drinking Water Scenarios (Water Only: 95th and 

99.9th Percentiles; Food+Water: 99.9th Percentile). (Values <100% ssPAD are Shaded and in Bold.)

Drinking Water 

Scenario (bold font)/ 

Crops/Uses 

Represented

Two-Day Average WATER ONLY 

(All Infants <1 year old)

Two-Day Average WATER ONLY 

(Children 1-2 years old)

Two-Day Average FOOD and WATER 

Highest Exposure Estimate

95th 99.9th 95th 99.9th

Population Subgroup

99.9th

Exposure (mkd) % 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

03c_MN alfalfa/

Alfalfa 0.000170 77 0.001220 550 0.000085 39 0.000591 270 Children 1-2 years old 0.001802 820

04b_CA cole crops/

Broccoli 0.000291 130 0.002549 1200 0.000153 70 0.001241 560 All Infants (<1 year old) 0.002687 1200

17b_OR nursery/ 

Ornamental woody 

shrubs and vines; 

Ornamental and/or 

shade trees

0.000142 65 0.000761 350 0.000071 32 0.000396 180 Children 1-2 years 

old 0.001792 810

18b_NJ nursery/

Ornamental 

herbaceous plants

0.000114 52 0.001087 490 0.000064 29 0.000533 240 Children 1-2 years 

old 0.001792 810

22c_MI beans/ Dry 

beans, peas 0.000141 64 0.001328 600 0.000074 34 0.00064 290 Children 1-2 years old 0.001805 820

23c_MS Cotton/ 

Cotton 0.000081 37 0.00117 530 0.000046 21 0.000566 260 Children 1-2 years old 0.001790 810

24b_PA Tomato/ 

Tomato 0.000071 32 0.000787 360 0.000036 16 0.000385 180 Children 1-2 years old 0.001789 810

26b_FL citrus/ 

Oranges 0.000101 46 0.001687 770 0.000057 26 0.000797 360 Children 1-2 years old 0.001821 830

27c_ID potatoes/ 

Potatoes 0.000494 220 0.002050 930 0.000242 110 0.001092 500 All Infants (<1 year old) 0.002183 990

27d_ID potatoes/ 

Potatoes 0.000244 110 0.001088 490 0.000121 55 0.000571 260 Children 1-2 years old 0.001810 820
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Table 5.4.6.6. Summary of Steady-State (Two-Day Average) Assessment Results for Typical Application Rate Drinking Water Scenarios (Water Only: 95th and 

99.9th Percentiles; Food+Water: 99.9th Percentile). (Values <100% ssPAD are Shaded and in Bold.)

Drinking Water 

Scenario (bold font)/ 

Crops/Uses 

Represented

Two-Day Average WATER ONLY 

(All Infants <1 year old)

Two-Day Average WATER ONLY 

(Children 1-2 years old)

Two-Day Average FOOD and WATER 

Highest Exposure Estimate

95th 99.9th 95th 99.9th

Population Subgroup

99.9th

Exposure (mkd) % 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

Exposure 

(mkd)

% 

ssPAD

28_IL corn/ Corn 0.000169 77 0.002382 1100 0.000092 42 0.001147 520 All Infants (<1 year 

old) 0.002480 1100

29_KS sorghum/ 

Sorghum 0.000108 49 0.002212 1000 0.000058 26 0.001033 470 All Infants (<1 year old) 0.002362 1100

30_MS soybeans/ 

Soybeans 0.000122 55 0.00103 470 0.000066 30 0.000517 240 Children 1-2 years old 0.001793 820

31_OR snap beans/ 

Lima beans 0.000202 92 0.000825 380 0.000099 45 0.000458 210 Children 1-2 years old 0.001794 820

32_ND wheat/ Spring 

wheat 0.000082 37 0.000381 170 0.000041 19 0.000202 92 Children 1-2 years old 0.001786 810

33_ND wheat/ 

Winter wheat 0.000102 46 0.000474 220 0.000051 23 0.000252 110 Children 1-2 years old 0.001787 810

13b_CA forestry/

Cottonwood (forest/ 

shelterbelt)

0.000455 210 0.002198 1000 0.000219 100 0.001155 530 All Infants (<1 year 

old) 0.002338 1100

14b_OR Xmas trees/

Hybrid 

cottonwood/poplar 

plantations (some 

labels allow use in ID, 

OR and WA)

0.000415 190 0.001671 760 0.000201 91 0.000912 410 Children 1-2 years 

old 0.001909 870

15b_CA nursery/

Citrus, non-bearing 

and nursery stock 

(only in CA and AZ)

0.000042 19 0.000175 80 0.000021 10 0.000095 43 Children 1-2 years 

old 0.001777 810

12b_OR Xmas trees/

Douglas fir (seed 

orchards) (only in OR 

and WA)

0.000209 95 0.000877 400 0.000101 46 0.000482 220 Children 1-2 years 

old 0.001796 820

Bold and shaded values are ≤100% of the ssPAD. The exposure assessments were run using a rounded ssPAD value of 0.002 mkd. The %ssPAD values have been updated to reflect the unrounded 

ssPAD value of 0.00022 mkd and were adjusted to two significant figures. The results for all population subgroups (general U.S. population, all infants (<1 year old), children 1-2, children 3-5, 

children 6-12, youth 13-19, females 13-49, adults 20-49, and adults 50-99 years) for all runs are summarized in the most recent dietary memo (J. Van Alstine; 15-SEP-2015; D418590).
Dimethoate Human Health Risk Assessment DP No. D416010

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6.0 Residential (Non-Occupational) Exposure/Risk Characterization

All residential and other non-occupational uses of dimethoate were voluntarily cancelled, 

effective March 13, 2002.

9

 Currently, dimethoate is registered solely for use on occupational 

sites. 

6.1 Residential Handler Exposure

HED uses the term “handlers” to describe those individuals who are involved in the pesticide 

application process. There are currently no registered or proposed residential uses for 

dimethoate; therefore, a residential handler assessment was not performed. 

6.2 Post-Application Exposure

There are currently no registered or proposed residential uses for dimethoate. The potential for 

non-occupational post-application exposure from agricultural applications of dimethoate has 

been assessed below in Section 8.0. 

7.0 Non-Occupational Bystander Post-Application Inhalation Exposure and Risk 

Estimates

Volatilization of pesticides may be a source of post-application inhalation exposure to 

individuals nearby pesticide applications. The Agency sought expert advice and input on issues 

related to volatilization of pesticides from its FIFRA SAP in December 2009, and received the 

SAP’s final report on March 2, 2010.

10

 The Agency has evaluated the SAP report and has 

developed a Volatilization Screening Tool and a subsequent Volatilization Screening Analysis.

11

 

During Registration Review, the Agency will utilize this analysis to determine if data (i.e., flux 

studies) or further analyses are required for dimethoate.

8.0 Non-Occupational Spray Drift Exposure and Risk Estimates

Off-target movement of pesticides can occur via many types of pathways and it is governed by a 

variety of factors. Sprays that are released and do not deposit in the application area end up offtarget and can lead to exposures to those it may directly contact. They can also deposit on 

surfaces where contact with residues can eventually lead to indirect exposures (e.g., children 

playing on lawns where residues have deposited next to treated fields). The potential risk 

estimates from these residues can be calculated using drift modeling onto 50-feet-wide lawns 

coupled with methods employed for residential risk assessments for turf products.

The approach to be used for quantitatively incorporating spray drift into risk assessment is based 

on a premise of compliant applications that, by definition, should not result in direct exposures to 

individuals because of existing label language and other regulatory requirements intended to 

prevent them.12 Direct exposures would include inhalation of the spray plume or being sprayed 

directly. Rather, the exposures addressed here are thought to occur indirectly through contact 

 

9 Federal Register Notice/Vol. 67, No. 84/Wednesday, May 01, 2002/Notices/21669

10 http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html

11 http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219

12 This approach is consistent with the requirements of the EPA’s Worker Protection Standard.
Dimethoate Human Health Risk Assessment DP No. D416010

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with impacted areas, such as residential lawns, when compliant applications are conducted. 

Given this premise, exposures for children (1 to 2 years old) and adults who have contact with 

turf where residues are assumed to have deposited via spray drift thus resulting in an indirect 

exposure are the focus of this analysis analogous to how exposures to turf products are 

considered in risk assessment. 

In order to evaluate the drift potential and associated risks, an approach based on drift modeling 

coupled with techniques used to evaluate residential uses of pesticides was utilized. Essentially, 

a residential turf assessment based on exposure to deposited residues has been completed to 

address drift from the agricultural applications of dimethoate. In the spray drift scenario, the 

deposited residue value was determined based on the amount of spray drift that may occur at 

varying distances from the edge of the treated field using the AgDrift® (v2.1.1) model and the 

Residential Exposure Assessment Standard Operating Procedures Addenda 1: Consideration of 

Spray Drift Policy. Once the deposited residue values were determined, the remainder of the 

spray drift assessment was based on the algorithms and input values specified in the recently 

revised (2012) Standard Operating Procedures For Residential Risk Assessment (SOPs). 

For dimethoate, chemical-specific turf transferrable residue (TTR) data are not available, 

therefore, the estimated TTR are based on a default assumption from the 2012 Residential SOPs 

that the transferable residue available for exposure is 1% of the total deposited residue, which is 

assumed to be equivalent to the maximum application rate. In order to account for the formation 

of the metabolite, omethoate, an assumption was made that 5% of the dimethoate residues would 

metabolize to omethoate. This assumption is based on a review of available TTR and DFR data 

for other OPs where both the parent and metabolite were measured in residue samples. Five 

percent was found to be the high-end value for the percent of parent that metabolized during the 

course of the residue studies. Once the estimated omethoate residues were calculated 

(dimethoate residues x 5%), the resulting values were adjusted further by the steady-state TAF 

value of 3 to account for the increased potency of omethoate since a dimethoate-specific dermal 

toxicity study was used for calculation of the risk estimates. 

A screening approach was developed based on the use of the AgDrift® model in situations where 

specific label guidance that defines application parameters is not available.13 AgDrift® is 

appropriate for use only when applications are made by aircraft, airblast orchard sprayers, and 

groundboom sprayers. When AgDrift® was developed, a series of screening values (i.e., the Tier 

1 option) were incorporated into the model and represent each equipment type and use under 

varied conditions. The screening options specifically recommended in this methodology were 

selected because they are plausible and represent a reasonable upper bound level of drift for 

common application methods in agriculture. These screening options are consistent with how 

spray drift is considered in a number of ecological risk assessments and in the process used to 

develop drinking water concentrations used for risk assessment. In all cases, each scenario is to 

be evaluated unless it is not plausible based on the anticipated use pattern (e.g., herbicides are 

not typically applied to tree canopies) or specific label prohibitions (e.g., aerial applications are 

not allowed). Section 8.1 provides the screening-level drift-related risk estimates. In many 

cases, risks are of concern when the screening-level estimates for spray drift are used as the basis 

for the analysis. In order to account for this issue and to provide additional risk management 

 

13http://www.agdrift.com/ 
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options, additional spray drift deposition fractions were also considered. These drift estimates 

represent plausible options for pesticide labels.

8.1 Combined Risk Estimates from Lawn Deposition Adjacent to Applications

The spray drift risk estimates are based on an estimated deposited residue concentration as a 

result of the screening level agricultural application scenarios. Dimethoate is registered on 

various agricultural crops, Christmas tree farms, trees grown for pulp, and ornamentals in 

outdoor nurseries. Most of the registered products are applied either via aerial, chemigation, 

groundboom, airblast or with handheld equipment. For most use sites, the maximum application 

rate is 2 lb ai/A, but for ornamentals in outdoor nurseries, the maximum application rate is 4.15 

lb ai/A for airblast applications specifically. The recommended drift scenario screening level 

options are listed below: 

 Groundboom applications are based on the AgDrift® option for high boom height and 

using very fine to fine spray type using the 90th percentile results. 

 Orchard airblast applications are based on the AgDrift® option for sparse 

(young/dormant) tree canopies.

 Aerial applications are based on the use of AgDrift® Tier 1 aerial option for a fine to 

medium spray type and a series of other parameters that will be described in more detail 

below (e.g., wind vector assumed to be 10 mph in a downwind direction for entire 

application/drift event).14

In addition to the screening-level spray-drift scenarios described above, additional results are 

provided which represent viable drift-reduction options that represent potential risk-management 

options. In particular, different spray qualities have been considered as well as the impact of 

other application conditions (e.g., boom height, use of a helicopter instead of fixed-wing aircraft, 

crop canopy conditions).

Dermal risk estimates were calculated for adults. For adults, when an endpoint is not sexspecific (i.e., the endpoints are based on developmental or fetal effects) a body weight of 80 kg is 

typically used in risk assessment; however, in this case, a female-specific body weight of 69 kg 

was used. While the endpoint of concern, brain AChE inhibition, is not sex-specific, the femalespecific body weight was used to protect for pregnant women due to uncertainty in the human 

dose-response relationship for neurodevelopmental effects (see Section 4.4). Dermal and 

incidental oral risk estimates for children (1 to <2 years old) were combined because the toxicity 

endpoint for each route of exposure is same (i.e., inhibition of brain AChE). The total applicable 

LOC is 1000, therefore MOEs < 1000 represent risk estimates of concern. 

Adult dermal and children’s (1 to < 2 year old) dermal and incidental oral risk estimates related 

to spray drift exceed HED’s LOC (MOEs < 1000) at a range of distances from the edge of the

field depending on the spray drift scenario. These are summarized in Table 8.1.1. All drift 

calculations are provided in the most recent ORE memo (K. Lowe; 15-SEP-2015; D418589). 

 

14 AgDrift® allows for consideration of even finer spray patterns characterized as very fine to fine. However, this 

spray pattern was not selected as the common screening basis since it is used less commonly for most agriculture. If 

assessors identify this use pattern it should be used as the screening criteria and deposition values associated with it 

are provided in Table 1 below. Justification for including this spray quality should be included in any assessment 

based on specific label directions for its use.
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Results indicate that the major risk concern is from aerial applications. Appropriate drift 

reduction technologies such as changing the spray type/nozzle configuration to coarser spray 

applications may result in less drift and reduced risk concerns (i.e., higher MOEs) from aerial 

applications. Similarly, using coarser sprays and lowering boom height for groundboom 

sprayers reduces risk concerns.

Table 8.1.1. Summary of Spray Drift Buffers for Dimethoate.

Crop 

Category Crops

Application 

rate (lb 

ai/A)

Adult Buffer Summary Children 1 < 2 years Buffer Summary 

(Dermal + Incidental Oral)

Buffers Necessary to reach MOE of 

1000

Buffers Necessary to reach MOE of 

1000

Aerial Groundboom Airblast Aerial Groundboom Airblast

Forestry Cottonwoods grown 

for pulp 2

100 -

>300 NA

NA

>300 NA

NA

High 

Acreage 

Crops

Alfalfa (field and 

seed crop), Beans 

(fresh, snap, lima, 

dry, not cowpeas), 

Corn (field and 

popcorn), Cotton, 

Grass grown for seed, 

Potatoes, Safflower, 

Sorghum, Soybeans, 

Wheat

0.5 25 -

>300 0 - 25 125 ->300 10 -150

Typical 

Acreage 

Crops

Brussels sprouts 1

50 -

>300 0 - 50 200 ->300 25 - 250

Asparagus, Broccoli, 

Cauliflower, Celery, 

Garbanzo beans, 

Lentils, Melons, Peas, 

Tomatoes, 

Watermelon

0.5 10 -

>300 0 - 10 125 ->300 10 - 125

Peas, dry; Peas, 

succulent; Peppers 0.33 0 - 200 0 - 10 75 - >300 10 - 75

Kale, Mustard greens, 

Turnip 0.25 0 - 150 0 - 10 75 - >300 10 - 75

Peas 0.16 0 - 75 0 50 - >300 0 - 50

Nurseries / 

Orchard

Ornamentals in 

outdoor nurseries 4.15

NA

0 - 100

NA

25 -

250

Citrus - non-bearing 

and nursery stock, 

Cherries (preharvest 

and postharvest), 

Christmas tree 

nurseries, Citrus, 

Pears (including nonbearing and nursery 

stock)

1 0 - 25 0 - 100

Lupine 0.5 0 - 10 0 - 75

Orchard Pecans 0.33 0 - 10 0 - 50

9.0 Aggregate Exposure/Risk Characterization

In accordance with the FQPA, HED must consider and aggregate (add) pesticide exposures and 

risks from three major sources: food, drinking water, and residential exposures. In an aggregate 

assessment, exposures from relevant sources are added together and compared to quantitative 

estimates of hazard (e.g., a NOAEL or PAD), or the risks themselves can be aggregated. When 
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aggregating exposures and risks from various sources, HED considers both the route and 

duration of exposure. The registered dimethoate uses are not anticipated to result in residential 

exposure and thus the acute and steady-state dietary exposure estimates provided in Section 5.4.3 

and 5.4.4 represent the acute and steady-state aggregate exposure.

Dimethoate is classified as a Group C carcinogen (possible human carcinogen). Quantification 

of risk using a non-linear approach will adequately account for all chronic toxicity, including 

carcinogenicity that could result from exposure to dimethoate.

10.0 Cumulative Exposure/Risk Characterization

OPs, like dimethoate/omethoate, share the ability to inhibit AChE through phosphorylation of the 

serine residue on the enzyme leading to accumulation of acetylcholine and ultimately cholinergic 

neurotoxicity. This shared MOA/AOP is the basis for the OP common mechanism grouping per 

OPP’s Guidance For Identifying Pesticide Chemicals and Other Substances that have a Common 

Mechanism of Toxicity (USEPA, 1999). The 2002 and 2006 CRAs used brain AChE inhibition 

in female rats as the source of dose response data for the relative potency factors and PODs for 

each OP, including dimethoate/omethoate. Prior to the completion of Registration Review, OPP 

will update the OP CRA on AChE inhibition to incorporate new toxicity and exposure 

information available since 2006. 

As described in Section 4.4, OPP has retained the FQPA Safety Factor for OPs, including 

dimethoate/omethoate, due to uncertainties associated with neurodevelopmental effects in 

children and exposure to OPs. There is a lack of an established MOA/AOP for the 

neurodevelopment outcomes which precludes the agency from formally establishing a common 

mechanism group per the Guidance For Identifying Pesticide Chemicals and Other Substances 

that have a Common Mechanism of Toxicity (USEPA, 1999) based on that outcome. Moreover, 

the lack of a recognized MOA/AOP and other uncertainties with exposure assessment in the 

epidemiology studies prevent the agency from establishing a causal relationship between OP 

exposure and neurodevelopmental outcomes. The agency will continue to evaluate the 

epidemiology studies associated with neurodevelopmental outcomes and OP exposure prior to 

the release of the revised DRA. During this period, the agency will determine whether or not it 

is appropriate to apply the draft guidance document entitled, Pesticide Cumulative Risk 

Assessment: Framework for Screening Analysis for the neurodevelopment outcomes. 

11.0 Occupational Exposure/Risk Characterization

11.1 Short- and Intermediate-Term Handler Risk

HED uses the term handlers to describe those individuals who are involved in the pesticide 

application process. HED believes that there are distinct job functions or tasks related to 

applications and exposures can vary depending on the specifics of each task. Job requirements 

(amount of chemical used in each application), the kinds of equipment used, the target being 

treated, and the level of protection used by a handler can cause exposure levels to differ in a 

manner specific to each application event. 

For occupational handlers, exposure is anticipated to be to the parent, dimethoate, only. The 

dermal route of exposure is assessed using a dimethoate-specific toxicity study; therefore, no 

TAFs were used in the dose calculations. The inhalation route of exposure is assessed using an 
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omethoate-specific toxicity study since a dimethoate-specific inhalation toxicity study is not 

available. No TAFs were used in the inhalation dose calculations, but it should be noted that the 

risk estimates presented are representative of exposure to the more toxic metabolite, omethoate, 

and, therefore, are conservative risk estimates of potential exposure to dimethoate. 

The quantitative exposure/risk assessment developed for occupational handlers is based on the 

following scenarios, which cover all the registered uses of dimethoate: 

 Mixing/loading liquids and WSPs to support aerial applications,

 Mixing/loading liquids and WSPs to support airblast applications,

 Mixing/loading liquids to support chemigation applications,

 Mixing/loading liquids and WSPs to support groundboom applications, 

 Applying sprays with aircraft,

 Applying sprays with groundboom equipment,

 Applying sprays with airblast equipment,

 Flagging to support aerial spray applications, 

 Mixing/loading/applying liquids via backpack,

 Mixing/loading/applying liquids via mechanically-pressurized handgun, and

 Mixing/loading/applying liquids via manually-pressurized handwand.

Occupational Handler Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational 

handler risk assessments. Assumptions and factors, as well as algorithms used to estimate noncancer exposure and dose for occupational handlers are detailed in the most recent ORE memo 

(K. Lowe; 15-SEP-2015; D418589). 

The steady-state approach is appropriate for dimethoate given the toxicological and exposure 

profile. The steady-state endpoint selection for dimethoate overlaps with HED’s traditional 

short-term exposure duration endpoint selection and is considered health protective for 

occupational handlers that apply commercially over longer periods of time (i.e., intermediateterm exposures).

Most of the dimethoate registered labels require handlers to wear a single layer of clothing (longsleeved shirt and long pants), shoes plus socks, protective eyewear (either goggles or face 

shield), chemical-resistant gloves, a National Institute for Occupational Safety and Health 

(NIOSH)-approved dust/mist filtering respirator with Mine Safety and Health Administration 

(MSHA)/NIOSH approval number prefix TC-21C or a NIOSH-approved respirator with any N, 

R, P, or HE filter, and a chemical-resistant apron when mixing, loading, cleaning up spills, or 

equipment. 

For adults, when an endpoint is not sex-specific (i.e., the endpoints are based on developmental 

or fetal effects) a body weight of 80 kg is typically used in risk assessment; however, in this case, 

a female-specific body weight of 69 kg was used. While the endpoint of concern, brain AChE 

inhibition, is not sex-specific, the female-specific body weight was used to protect for pregnant 

women due to uncertainty in the human dose-response relationship for neurodevelopmental 

effects (see Section 4.4). 
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Dermal and inhalation risk estimates were combined in this assessment, since the toxicological 

effects for these exposure routes were similar. The occupational handler exposure and risk 

estimates indicate that the dermal and inhalation combined MOEs are of concern to HED (i.e., 

MOEs ≤ 1000) for most scenarios assuming the use of label-required PPE (noted by the 

highlighted column in Table 11.1.1 – single layer of clothing, gloves and a PF5 respirator). As 

was noted above, the inhalation risk estimates are considered to be a conservative estimate of 

exposure to dimethoate residues considering the inhalation POD was selected from an omethoate 

toxicity study. Only five scenarios (out of 40) reach an MOE above the LOC of 1000 at some 

level of PPE (above what is currently required on the labels) or with engineering controls.

HED has no data to assess exposures to pilots using open cockpits. The only data available is for 

exposure to pilots in enclosed cockpits. Therefore, risks to pilots are assessed using the 

engineering control (enclosed cockpits) and baseline attire (long-sleeve shirt, long pants, shoes, 

and socks); per the Agency’s Worker Protection Standard stipulations for engineering controls, 

pilots are not required to wear protective gloves for the duration of the application. With this 

level of protection, there are no risk estimates of concern for applicators.

The Agency matches quantitative occupational exposure assessment with appropriate 

characterization of exposure potential. While HED presents quantitative risk estimates for 

human flaggers where appropriate, agricultural aviation has changed dramatically over the past 

two decades. According the 2012 National Agricultural Aviation Association (NAAA) survey of 

their membership, the use of Global Positioning System (GPS) for swath guidance in agricultural 

aviation has grown steadily from the mid-1990s. Over the same time period, the use of human 

flaggers for aerial pesticide applications has decreased steadily from ~15% in the late 1990s to 

only 1% in the most recent (2012) NAAA survey. The Agency will continue to monitor all 

available information sources to best assess and characterize the exposure potential for human 

flaggers in agricultural aerial applications. HED recommends that the PPE on the registered 

dimethoate labels for flaggers be revised to reflect the requirements identified above (and 

in Table 9.1.1) to reach acceptable MOEs, or that flaggers be prohibited on the label. 
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Table 11.1.1. Occupational Handler Non-Cancer Exposure and Risk Estimates for Dimethoate.

Exposure 

Scenario Crop or Target1

Dermal Unit 

Exposure

(μg/lb ai)2

Inhalation 

Unit Exposure

(μg/lb ai)2

Maximum 

Application 

Rate3

Area 

Treated4

Total MOE5(LOC = 1000)

SL/No G

No-R

SL/G

No-R

DL/G

No-R

SL/No G

PF5 R

SL/G

PF5-R

DL/G

PF5-R

SL/No G

PF10 R

SL/G

PF10-R

DL/G

PF10-R

EC

Mixer/Loader

M/L liquids for 

aerial applications

and chemigation8

Nursery

SL/No G 220

SL/G 37.6

DL/G 29.1

EC 8.6

No-R 0.219

PF5 R 0.0438

PF10 R 0.0219

EC 0.083

1 lb ai/A 60 A 67 130 140 98 360 420 100 450 540 610

Orchard6

0.33 lb ai/A

350 A

34 70 74 49 190 210 52 240 280 320

1.0 lb ai/A 11 24 25 16 63 72 17 80 95 110

1.33 lb ai/A 8.6 17 18 12 46 52 13 59 69 78

Typical field crops7

0.5 lb ai/A 22 46 48 32 120 140 34 150 190 210

1 lb ai/A 11 24 25 16 63 72 17 80 95 110

High-acreage field 

crops

0.5 lb ai/A 1200 A 6.7 13 14 9.8 36 42 10 45 54 61

Forestry (aerial only) 2 lb ai/A 7500 A 0.26 0.54 0.57 0.38 1.5 1.7 0.4 1.8 2.2 2.4

M/L liquids for 

airblast 

applications

Nursery 4.15 lb ai/A 20 A 48 100 110 68 260 300 72 330 440 440

Orchard 1.33 lb ai/A 40 A 74 150 160 110 410 470 110 510 610 690

M/L liquids for 

groundboom 

applications

Nursery 0.5 lb ai/A 60 A 130 270 290 190 700 820 200 890 1,100 1,200

Typical field crops 2 lb ai/A 80 A 25 51 53 36 130 150 38 170 210 230

High-acreage field 

crops

0.5 lb ai/A 200 A 39 79 83 56 220 250 59 270 320 370

M/L WSP for 

aerial applications

Orchard

EC 9.8 EC 0.24

1 lb ai/A 350 A ND ND ND ND ND ND ND ND ND 42

High-acreage field 

crops

0.5 lb ai/A 1,200 ND ND ND ND ND ND ND ND ND 24

M/L WSP for 

airblast 

applications

Orchard 1 lb ai/A 40 A ND ND ND ND ND ND ND ND ND 370

M/L WSP for 

groundboom 

applications

High-acreage field 

crops

0.5 lb ai/A 200 A ND ND ND ND ND ND ND ND ND 140
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Table 11.1.1. Occupational Handler Non-Cancer Exposure and Risk Estimates for Dimethoate.

Exposure 

Scenario Crop or Target1

Dermal Unit 

Exposure

(μg/lb ai)2

Inhalation 

Unit Exposure

(μg/lb ai)2

Maximum 

Application 

Rate3

Area 

Treated4

Total MOE5(LOC = 1000)

SL/No G

No-R

SL/G

No-R

DL/G

No-R

SL/No G

PF5 R

SL/G

PF5-R

DL/G

PF5-R

SL/No G

PF10 R

SL/G

PF10-R

DL/G

PF10-R

EC

Applicator

Applying sprays 

via aerial 

equipment

Nursery

EC 2.08 EC 0.0049

1 lb ai/A 60 A ND ND ND ND ND ND ND ND ND 2,800

Orchard 1.33 lb ai/A

350 A

ND ND ND ND ND ND ND ND ND 360

Typical field crops 1 lb ai/A ND ND ND ND ND ND ND ND ND 480

High-acreage field 

crops

0.5 lb ai/A 1,200 A ND ND ND ND ND ND ND ND ND 280

Forestry 2 lb ai/A 7,500 A ND ND ND ND ND ND ND ND ND 11

Applying sprays 

via airblast 

equipment9

Nursery SL/No G 1,770

SL/G 1,590

DL/G 1,480

EC 14.6

No-R 4.71

PF5 R 0.942

PF10 R 0.471

EC 0.068

4.15 lb ai/A 20 A 2.2 2.2 2.2 5.7 6.2 6.2 7.1 7.9 7.9 170

Orchard 1.33 lb ai/A 40 A 3.4 3.5 3.5 8.9 9.3 9.9 11 12 13 260

Applying sprays 

via groundboom 

equipment

Nursery SL/No G 78.6

SL/G 16.1

DL/G 12.6

EC 5.1

No-R 0.34

PF5 R 0.068

PF10 R 0.034

EC 0.043

0.5 lb ai/A 60 A 93 110 110 280 460 470 380 800 850 2,300

Typical field crops 2 lb ai/A 80 A 17 19 19 52 84 87 71 150 160 430

High-acreage field 

crops

0.5 lb ai/A 200 A 27 31 31 85 140 140 120 230 250 680

Flagger

Flagger

Nursery

SL/No G 11

SL/G 12

DL/G 10.6

No-R 0.35

PF5 R 0.07

PF10 R 0.035

1 lb ai/A 60 A 170 170 170 650 630 660 1,000 950 1,000 ND

Orchard 1.33 lb ai/A

350 A

22 22 22 83 81 84 130 120 130 ND

Typical field crop 1 lb ai/A 29 29 30 110 110 110 170 160 170 ND

High-acreage field 

crop

0.5 lb ai/A 59 58 59 220 220 220 340 320 350 ND

Mixer/Loader/Applicator

M/L/A liquids 

ground 

applications (soil 

directed) with 

backpack

Orchard

SL/No G 8,260

SL/G 8,260

DL/G 4,120

No-R 2.58

PF5 R 0.516

PF10 R 0.258

0.005 lb ai/gal

40 gal

710 710 1,200 820 820 1,600 830 830 1,600 ND

Christmas tree farm 0.025 lb ai/gal 140 140 250 160 160 320 170 170 330 ND

Forestry 0.04 lb ai/gal 92 92 150 110 110 200 110 110 200 ND

Nursery 0.08 lb ai/gal 45 45 79 51 510 100 52 52 110 ND
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Table 11.1.1. Occupational Handler Non-Cancer Exposure and Risk Estimates for Dimethoate.

Exposure 

Scenario Crop or Target1

Dermal Unit 

Exposure

(μg/lb ai)2

Inhalation 

Unit Exposure

(μg/lb ai)2

Maximum 

Application 

Rate3

Area 

Treated4

Total MOE5(LOC = 1000)

SL/No G

No-R

SL/G

No-R

DL/G

No-R

SL/No G

PF5 R

SL/G

PF5-R

DL/G

PF5-R

SL/No G

PF10 R

SL/G

PF10-R

DL/G

PF10-R

EC

M/L/A liquids 

broadcast 

applications with 

backpack

Christmas tree farm

SL/No G 

58400

SL/G 30500

DL/G 16900

No-R 69.1

PF5 R 13.8

PF10 R 6.9

0.025 lb ai/gal 17 25 34 22 40 64 23 43 72 ND

Nursery 0.08 lb ai/gal 5 8 11 7 12 20 7 13 23 ND

Forestry

SL/No G 8,260

SL/G 8,260

DL/G 4,120

No-R 2.58

PF5 R 0.516

PF10 R 0.258

0.04 lb ai/gal 11 16 21 14 25 40 14 27 45 ND

M/L/A liquids 

foliar applications 

with manuallypressurized 

handgun

Christmas tree farm SL/No G 

100,000

SL/G 430

DL/G 365

No-R 30

PF5 R 6

PF10 R 3

0.025 lb ai/gal

40 gal

13 120 130 14 550 560 14 920 970 ND

Nursery 0.08 lb ai/gal 4 39 40 4.3 170 180 4.4 290 310 ND

M/L/A liquids 

foliar applications 

with mechanicallypressurized 

handgun

Orchard

SL/No G 6050

SL/G 2050

DL/G 1360

No-R 8.68

PF5 R 1.74

PF10 R 0.87

0.0025 lb ai/gal 1,000 gal 61 110 130 83 210 280 88 230 330 ND

Christmas tree farm

Nursery

Typical field crop

M/L/A liquids 

drench/soil/ground 

directed 

applications with 

mechanicallypressurized 

handgun

Orchard

Nursery

Typical field crop

Shaded column = current PPE required on labels. Bold MOE values indicate the LOC has been exceeded with label-recommended and/or additional PPE.

1. Typical field crops include asparagus, broccoli, cauliflower, Brussels sprouts, celery, endive, leaf lettuce, Swiss chard, garbanzo beans, kale, lentils, melons, mustard greens, peas, peppers, 

tomatoes, turnips, and watermelon. High-acreage field crops included alfalfa, beans, corn, cotton, grass grown for seed, potatoes, safflower, sorghum, soybeans, and wheat. Orchard crops include 

cherries, citrus, pears, and pecans. Nurseries include citrus, lupine, ornamentals in outdoor nurseries. Forestry includes trees grown for pulp.

2. Based on the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (August 2015); Level of mitigation: SL/No G No-R = Single layer clothing, no gloves, no respirator; 

SL/G No-R = Single layer clothing, gloves, no respirator; DL/G No-R = Double layer clothing, gloves, no respirator; SL/No G PF5 R = Single layer clothing, no gloves, PF5 respirator; SL/G PF5 R 

= Single layer clothing, gloves, PF5 respirator; DL/G PF5 R = Double layer clothing, gloves, PF5 respirator; SL/No G PF10 R = Single layer clothing, no gloves, PF10 respirator; SL/G PF10 R = 

Single layer clothing, gloves, PF10 respirator; DL/G PF10 R = Double layer clothing, gloves, PF10 respirator; EC = Engineering Controls. ND = no data.

3. Based on registered labels.

4. Exposure Science Advisory Council Policy #9.1.

5. Total MOE = 1 ÷ (1/Dermal MOE) + (1/Inhalation MOE).

6. Application rates for orchard crops: Pecans (0.33 lb ai/A); Pears and Citrus (1 lb ai/A); Cherries (1.33 lb ai/A).

7. Dimethoate 400 label (67760-118); Label lists maximum application rate for Brussels Sprout as 0.5 lb ai/A, but also indicates 38.2 fl oz. product/A, which is 1 lb ai/A.
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8. Only the scenarios assessed at 350 A are applicable for chemigation applications. 

9. For airblast applications to nurseries and orchards, additional PPE could include chemical-resistant headgear (CRH). The addition of CRH resulted in MOEs that exceed HED’s LOC: Nursery -

SL/G/CRH = 24, DL/G/CRH - 27; Orchard SL/G/CRH = 37, DL/G/CRH - 41.
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11.2 Short-/Intermediate-Term Post-Application Risk

HED uses the term post-application to describe exposures that occur when individuals are 

present in an environment that has been previously treated with a pesticide (also referred to as reentry exposure). Such exposures may occur when workers enter previously treated areas to 

perform job functions, including activities related to crop production, such as scouting for pests 

or harvesting. Post-application exposure levels vary over time and depend on such things as the 

type of activity, the nature of the crop or target that was treated, the type of pesticide application, 

and the chemical’s degradation properties. In addition, the timing of pesticide applications, 

relative to harvest activities, can greatly reduce the potential for post-application exposure.

For occupational post-application workers, exposure is anticipated to be to both dimethoate and 

omethoate. Since the dermal route of exposure is assessed using a dimethoate-specific toxicity 

study, the omethoate residues have been adjusted by a TAF to account for the increased potency 

of omethoate. 

11.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates

There are multiple potential sources of post-application inhalation exposure to individuals 

performing post-application activities in previously treated fields. These potential sources 

include volatilization of pesticides and resuspension of dusts and/or particulates that contain 

pesticides. The Agency sought expert advice and input on issues related to volatilization of 

pesticides from its FIFRA SAP in December 2009, and received the SAP’s final report on March 

2, 201015. The Agency has evaluated the SAP report and has developed a Volatilization 

Screening Tool and a subsequent Volatilization Screening Analysis16. During Registration 

Review, the Agency will utilize this analysis to determine if data (i.e., flux studies) or further 

analysis is required for dimethoate.

In addition, the Agency is continuing to evaluate the available post-application inhalation 

exposure data generated by the ARTF. Given these two efforts, the Agency will continue to 

identify the need for and, subsequently, the way to incorporate occupational post-application 

inhalation exposure into the Agency's risk assessments.

11.2.2 Occupational Post-application Dermal Exposure/Risk Estimates

Occupational Post-application Dermal Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational 

post-application risk assessments. Assumptions and factors, as well as the algorithms used to 

estimate non-cancer exposure and dose for occupational post-application workers are detailed in 

the most recent ORE memo (K. Lowe; 15-SEP-2015; D418589). 

 

15 http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html

16 http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219. 
Dimethoate Human Health Risk Assessment DP No. D416010

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The steady-state approach is appropriate for dimethoate given the toxicological and exposure 

profile. The “steady-state” endpoint selection for dimethoate overlaps with HED’s traditional 

short-term exposure duration endpoint selection as well as being appropriately health protective 

for workers that are exposed over longer periods of time (i.e., intermediate-term exposures).

For adults, when an endpoint is not sex-specific (i.e., the endpoints are based on developmental 

or fetal effects) a body weight of 80 kg is typically used in risk assessment; however, in this case, 

a female-specific body weight of 69 kg was used. While the endpoint of concern, brain AChE 

inhibition, is not sex-specific, the female-specific body weight was used to protect for pregnant 

women due to uncertainty in the human dose-response relationship for neurodevelopmental 

effects (see Section 4.4). 

Chemical-specific DFR data have been submitted for dimethoate. Four studies were submitted 

that examined residues of dimethoate and its metabolite, omethoate, on the following crops: 

grapes (MRID 44788201), tomato (MRID 44690302), lettuce (MRID 44690301), and apple 

(MRID 44827601). All four studies have been reviewed by HED and found to be acceptable for 

risk assessment. The grape DFR data were not used in this risk assessment since dimethoate is 

no longer registered for use on grapes. 

A summary of how the DFR data were used is summarized in Table 11.2.2.1 and discussed in the 

most recent ORE memo (K. Lowe; 15-SEP-2015; D418589).

Table 11.2.2.1. Summary of DFR Data Use in Occupational Post-application Assessment for Dimethoate

Crop for which DFR 

data available Locations included in study Crops for which DFR data used as surrogate

Apple

Michigan (MI) - non-arid

New York (NY) - non-arid

Washington (WA) - arid 

Cherries, Christmas trees, Forestry, Grapefruit, Lemons, 

Ornamentals (nursery crop), Orange, Pear, Pecan

Lettuce

Pennsylvania (PA) - non-arid

Florida (FL) - non-arid

California (CA) -- arid

Kale, Leaf lettuce, Mustard greens, Green pea, Swiss 

chard, Turnip

Tomato

Pennsylvania (PA) - non-arid

Florida (FL) - non-arid

California (CA) -- arid

Alfalfa, Asparagus, Dry beans and peas, Broccoli, 

Brussels sprouts, Cauliflower, Celery, Field Corn, Pop 

corn, Cotton, Forage crop, Bell Pepper, Potato, 

Safflower, Grain sorghum, Soybean, Tomato, 

Watermelon, Spring wheat, Winter wheat

Each of the studies measured the amount of dimethoate residues remaining on treated leaves 

following applications, and also measured, when present, omethoate residues. Typically, when 

omethoate was present in the studies, it peaked in quantity a few days after the application, and 

then gradually dissipated over time. Dimethoate residues peaked immediately after application 

and dissipated over time thereafter. In general, omethoate was a significant factor in arid areas 

(i.e., areas where the average annual rainfall is less than 25 inches per year). Since dissipation 

rates at the arid sites were significantly different from those at the non-arid sites, the results are 

reported separately for all study sites.
Dimethoate Human Health Risk Assessment DP No. D416010

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As mentioned earlier, omethoate is a metabolite of dimethoate and is 3 times more 

toxicologically potent than dimethoate. Since the POD for the dermal route of exposure was 

chosen from a dimethoate toxicity study, a TAF of 3 was chosen to account for the increased 

potency of omethoate in exposure calculations. A total toxic residue approach was used whereby 

residues of omethoate were adjusted by the TAF and total residues (dimethoate + adjusted 

omethoate) were included in exposure calculations17. In those studies where omethoate was not 

found, the post-application risks were assessed using only the dimethoate residues.

Occupational Post-application Non-Cancer Dermal Risk Estimates

The post-application exposure scenarios associated with the registered uses of dimethoate are 

summarized in Tables 11.2.2.2 through 11.2.2.4. The results of the risk assessment for postapplication exposures indicate that the location and/or the environmental conditions (i.e., arid 

versus non-arid) near the time of application influence the length of time following application 

until risks are below HED’s LOC (i.e., MOEs are greater than or equal to 1000) as does the type 

of plant to which the application is directed. For most crops, the post-application assessment 

indicates that following applications in arid areas (i.e., outdoor areas where average annual 

rainfall is less than 25 inches), residues persist longer than in non-arid areas. 

For the orchard crops, using the apple DFR data, there are risks of concern for most of the high 

contact post-application activities associated with each crop (e.g., hand harvesting, handset 

irrigation, etc). Some crop/activity combinations do not reach an acceptable MOE (LOC = 1000) 

even up to 30 days after application. 

For the field crops using the lettuce DFR data, there are risks of concern for certain high contact 

activities (e.g., hand harvesting, hand weeding, etc). Some crop/activity combinations do not 

reach an acceptable MOE (LOC = 1000) until 7 days after application. 

For the field crops using the tomato DFR data, there are risks of concern for certain high contact 

activities (e.g., hand harvesting, hand weeding, etc). Some crop/activity combinations do not 

reach an acceptable MOE (LOC = 1000) until 14 days after application. 

 

17 Total DFR, ug/cm2 = [ (Omethoate residue, ug/cm2

) * TAF] + [Dimethoate residue, ug/cm2) 
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 11.2.2.2. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Apples/MRID 44827601)

Crop

Policy 

Crop 

Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

APPLE STUDY DATA

MI NY WA MI NY WA MI NY WA MI NY WA

Cherry

Tree, 

"fruit", 

deciduous

1.33

Orchard maintenance; 

Weeding, Hand; Bird 

Control; Propping

100

12 hr 1.89 2.35 2.70 0.022 0.027 0.031 920 740 640

1 3 6 1.64 1.72 1.63 0.019 0.020 0.019 1,100 1,000 1,100

Transplanting 230

12 hr 1.89 2.35 2.70 0.050 0.063 0.072 400 320 280

7 11 15 0.72 0.74 0.76 0.019 0.020 0.020 1,000 1,000 1,000

Scouting; Pruning, 

Hand; Training 580

12 hr 1.89 2.35 2.70 0.127 0.158 0.182 160 130 110

14 20 26 0.28 0.29 0.30 0.019 0.019 0.022 1,100 1,000 1,000

Harvesting, Hand 1400

12 hr 1.89 2.35 2.70 0.306 0.382 0.439 66 53 46

20 29 30 0.12 0.11 0.21 0.020 0.018 0.035 1000 1,100 580

Thinning Fruit 3600

12 hr 1.89 2.35 2.70 0.787 0.982 1.128 26 21 18

27 30 30 0.05 0.10 0.21 0.019 0.042 0.089 1,000 480 230

Christmas 

tree

Tree, 

"fruit", 

evergreen

1

Weeding, Hand;

Grading/Tagging 100

12 hr 1.42 1.77 2.03 0.016 0.021 0.024 1,200 980 860

N/A 1 2 N/A 1.59 1.71 N/A 0.018 0.020 N/A 1,100 1,000

Transplanting 230

12 hr 1.42 1.77 2.03 0.038 0.047 0.054 530 430 370

5 9 12 0.71 0.69 0.74 0.019 0.018 0.020 1,100 1,100 1,000

Scouting; Shaping 580

12 hr 1.42 1.77 2.03 0.095 0.119 0.137 210 170 150

12 17 23 0.27 0.30 0.29 0.018 0.020 0.019 1,100 1,000 1,000

Harvesting, Hand 1400

12 hr 1.42 1.77 2.03 0.230 0.287 0.330 88 70 61

18 26 30 0.12 0.12 0.16 0.020 0.019 0.026 1,000 1,100 780

Irrigation (hand set) 1900

12 hr 1.42 1.77 2.03 0.312 0.390 0.447 65 52 45

20 29 30 0.09 0.08 0.16 0.020 0.019 0.035 1,000 1,100 570

Forestry Unassigned 2 Weeding, Hand 100

12 hr 2.84 3.54 4.06 0.033 0.041 0.047 610 490 430

4 7 10 1.64 1.70 1.74 0.019 0.020 0.020 1,100 1,000 1,000
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Table 11.2.2.2. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Apples/MRID 44827601)

Crop

Policy 

Crop 

Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

APPLE STUDY DATA

MI NY WA MI NY WA MI NY WA MI NY WA

Transplanting 230

12 hr 2.84 3.54 4.06 0.076 0.094 0.108 270 210 190

10 15 20 0.72 0.74 0.75 0.019 0.020 0.020 1,100 1,000 1,000

Pruning, Hand 580

12 hr 2.84 3.54 4.06 0.191 0.238 0.273 110 85 74

17 24 30 0.28 0.29 0.32 0.019 0.019 0.018 1,100 1,000 940

Harvesting, Seed Cone 

(Conifers) 1400

12 hr 2.84 3.54 4.06 0.460 0.574 0.659 44 35 31

23 30 30 0.12 0.15 0.32 0.020 0.025 0.044 1,000 810 390

Irrigation (hand set) 1900

12 hr 2.84 3.54 4.06 0.625 0.779 0.895 32 26 23

25 30 30 0.09 0.15 0.32 0.020 0.034 0.060 1,000 600 290

Harvesting, Seedling 

Production 6700

12 hr 2.84 3.54 4.06 2.203 2.749 3.156 9.2 7.3 6.4

30 30 30 0.05 0.15 0.32 0.036 0.119 0.210 560 170 81

Grapefruit, 

Lemon, 

Orange

Tree, 

"fruit", 

evergreen

1

Orchard maintenance; 

Weeding, Hand; 

Baiting/Trapping; 

Weeding, Hand

100

12 hr 1.42 1.77 2.03 0.016 0.08 0.024 1,200 980 860

N/A 1 2 N/A 1.59 1.71 N/A 0.018 0.020 N/A 1,100 1,000

Transplanting 230

12 hr 1.42 1.77 2.03 0.038 0.047 0.054 530 430 370

5 9 12 0.71 0.69 0.74 0.019 0.018 0.020 1,100 1,100 1,000

Scouting; Pruning, 

Hand 580

12 hr 1.42 1.77 2.03 0.095 0.119 0.137 210 170 150

12 17 23 0.27 0.30 0.29 0.018 0.020 0.019 1,100 1,000 1,000

Harvesting, Hand 1400

12 hr 1.42 1.77 2.03 0.230 0.287 0.330 88 70 61

18 26 30 0.12 0.12 0.16 0.020 0.019 0.26 1,000 1,100 780

Nursery Crop 

(Ornamentals, 

Non-bearing 

Plants)

Unassigned 4.15

Harvesting, Hand; 

Pruning, Hand; 

Scouting; Container 

Moving; Weeding, 

Hand; Transplanting; 

Grafting; Propagating; 

230

12 hr 5.89 7.34 8.43 0.157 0.196 0.225 130 100 90

15 22 29 0.75 0.73 0.72 0.020 0.020 0.019 1,000 1,000 1,000
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 11.2.2.2. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Apples/MRID 44827601)

Crop

Policy 

Crop 

Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

APPLE STUDY DATA

MI NY WA MI NY WA MI NY WA MI NY WA

Pinching; 

Tying/Training

Irrigation (hand set) 1900

12 hr 5.89 7.34 8.43 1.296 1.617 1.857 16 12 11

30 30 30 0.10 0.32 0.67 0.021 0.070 0.147 950 290 140

1

Harvesting, Hand; 

Pruning, Hand; 

Scouting; Container 

Moving; Weeding, 

Hand; Transplanting; 

Grafting; Propagating; 

Pinching; 

Tying/Training

230

12 hr 1.42 1.77 2.03 0.038 0.047 0.054 530 430 370

5 9 12 0.71 0.69 0.74 0.019 0.018 0.020 1,100 1,100 1,000

Irrigation (hand set) 1900

12 hr 1.42 1.77 2.03 0.312 0.316 0.447 65 52 45

20 29 30 0.03 0.08 0.14 0.020 0.019 0.035 1,000 1,100 570

Pear

Tree, 

"fruit", 

deciduous

1

Orchard maintenance; 

Weeding, Hand; 

Propping

100

12 hr 1.42 1.77 2.03 0.016 0.021 0.024 1,200 980 860

N/A 1 2 N/A 1.59 1.71 N/A 0.018 0.020 N/A 1,100 1,000

Transplanting 230

12 hr 1.42 1.77 2.03 0.038 0.042 0.054 530 430 370

5 9 12 0.71 0.69 0.74 0.019 0.018 0.020 1,100 1,100 1,000

Scouting; Pruning, 

Hand; Training 580

12 hr 1.42 1.77 2.03 0.095 0.107 0.137 210 170 150

12 17 23 0.27 0.30 0.29 0.018 0.020 0.019 1,100 1,000 1,000

Harvesting, Hand 1400

12 hr 1.42 1.77 2.03 0.230 0.287 0.330 88 70 61

18 26 30 0.12 0.12 0.16 0.020 0.019 0.026 1,000 1,100 780

Thinning Fruit 3600

12 hr 1.42 1.77 2.03 0.592 0.738 0.848 34 27 24

25 30 30 0.05 0.08 0.16 0.019 0.032 0.067 1,100 630 300

Pecan Tree, "nut" 0.33

Poling; Orchard 

maintenance; Weeding, 

Hand

100 12 hr 0.47 0.58 0.67 0.005 0.007 0.008 3,700 3,000 2,600
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 11.2.2.2. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Apples/MRID 44827601)

Crop

Policy 

Crop 

Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

APPLE STUDY DATA

MI NY WA MI NY WA MI NY WA MI NY WA

Harvesting, Mechanical 

(shaking) 190 0.010 0.013 0.015 2,000 1,600 1,400

Transplanting 230 0.012 0.016 0.018 1,600 1,300 1,100

Pruning, Hand; 

Scouting 580

0.031 0.039 0.045 640 510 450

4 7 10 0.27 0.28 0.29 0.018 0.019 0.019 1,100 1,100 1,000

Bold MOE values are below the LOC of 1000. Shaded cells indicate the MOE is still below the LOC 30 days after application (i.e., an REI of >30 days would be necessary to achieve a MOE greater than the LOC).

1. DFR = Combined residues of dimethoate and omethoate from an apple study, adjusted to account for application rate differences and for differences in toxicity of omethoate. 

2. Daily Dermal Dose = [DFR (μg/cm2) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day]  BW (69 kg).

3. MOE = POD (20.2 mg/kg/day) / Daily Dermal Dose. 

Table 11.2.2.3. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Lettuce/MRID 44690301)

Crop Policy Crop 

Group Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

LETTUCE STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Kale, Leaf 

Lettuce, 

Mustard 

Green, 

Swiss 

Chard

Vegetable, leafy 0.25

Weeding, Hand; Thinning Plants 70

12 hr 0.27 0.11 0.52

0.002 0.001 0.004 9,100 24,000 4,800

Scouting 210 0.007 0.003 0.013 3,000 7,800 1,600

Transplanting 230 0.007 0.003 0.014 2,800 7,200 1,500

Harvesting, Hand 1100

0.035 0.014 0.066 580 1,500 310

1 N/A 5 0.10 N/A 0.15 0.012 N/A 0.019 1,700 N/A 1,100

Irrigation (hand set) 1900

12 hr 0.27 0.11 0.52 0.060 0.023 0.114 340 870 180

2 1 7 0.03 0.04 0.09 0.007 0.009 0.020 2,800 2,300 1,000

0.16 Weeding, Hand 70 12 hr 0.17 0.07 0.33 0.001 0.001 0.003 14,000 37,000 7,500
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 11.2.2.3. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Lettuce/MRID 44690301)

Crop Policy Crop 

Group Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

LETTUCE STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Pea, 

Green

Field / row crop, 

low / medium

Scouting 210 0.004 0.002 0.008 4,700 12,000 2,500

Harvesting, Hand 1100

0.022 0.009 0.042 910 2,300 480

1 N/A 3 0.06 N/A 0.16 0.008 N/A 0.020 2,600 N/A 1,000

Irrigation (hand set) 1900

12 hr 0.17 0.07 0.33 0.039 0.015 0.073 520 1,400 280

1 N/A 6 0.06 N/A 0.08 0.013 N/A 0.017 1,500 N/A 1,200

Turnip Vegetable, "root" 0.25

Weeding, Hand; Thinning Plants 70

12 hr 0.27 0.11 0.52

0.002 0.001 0.004 9,100 24,000 4,800

Scouting 210 0.007 0.003 0.013 3,000 7,800 1,600

Harvesting, Hand 1100

0.035 0.014 0.066 580 1,500 310

1 N/A 5 0.10 N/A 0.15 0.012 N/A 0.019 1,700 N/A 1,100

Irrigation (hand set) 1900

12 hr 0.27 0.11 0.52 0.060 0.023 0.114 340 870 180

2 1 7 0.03 0.04 0.09 0.007 0.009 0.020 2,800 2,300 1,000

Bold MOE values are below the LOC of 1000. 

1. DFR = Combined residues of dimethoate and omethoate from a lettuce study, adjusted to account for application rate differences and for differences in toxicity of omethoate. 

2. Daily Dermal Dose = [DFR (μg/cm2) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day]  BW (69 kg).

3. MOE = POD (20.2 mg/kg/day) / Daily Dermal Dose. 

Table 11.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302)

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

0.5 Scouting 1100 12 hr 0.48 0.66 0.36 0.061 0.084 0.046 330 240 440
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 11.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302)

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Alfalfa, Dry 

Beans, Dry 

Peas, Forage 

Crop

Field / row crop, low / 

medium

2 2 4 0.06 0.11 0.16 0.008 0.006 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Asparagus Vegetable, stem / stalk 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Transplanting 230 0.013 0.018 0.010 1,600 1,100 2,100

Harvesting, Hand 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Broccoli, 

Cauliflower

Vegetable, head and stem 

Brassica 0.5

Transplanting 230

12 hr 0.48 0.66 0.36

0.013 0.018 0.010 1,600 1,100 2,100

Scouting

Thinning Plants 330

0.018 0.025 0.014 1,100 800 1,500

N/A 1 N/A N/A 0.27 N/A N/A 0.010 N/A N/A 2,000 N/A

Weeding, Hand 1400

12 hr 0.48 0.66 0.36 0.077 0.107 0.058 260 190 350

2 2 6 0.06 0.11 0.10 0.010 0.017 0.017 2,000 1,200 1,200

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Scouting

Harvesting, Hand

Weeding, Hand

4200

12 hr 0.48 0.66 0.36 0.232 0.322 0.174 87 63 120

3 4 11 0.02 0.02 0.04 0.011 0.009 0.018 1,800 2,400 1,100

Brussels 

Sprouts

Vegetable, head and stem 

Brassica 1

Transplanting 230

12 hr 0.95 1.32 0.71 0.025 0.035 0.019 800 570 1,100

1 1 N/A 0.35 0.53 N/A 0.009 0.014 N/A 2,200 1,400 N/A

Scouting 330 12 hr 0.95 1.32 0.71 0.036 0.051 0.027 560 400 740
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 11.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302)

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

1 2 2 0.35 0.21 0.58 0.013 0.008 0.018 1,500 2,500 1,100

Irrigation (hand set) 1900

12 hr 0.95 1.32 0.71 0.210 0.291 0.157 96 69 130

3 3 10 0.05 0.09 0.09 0.010 0.019 0.020 2,000 1,100 1,000

Scouting

Harvesting, Hand

Topping

Weeding, Hand

4200

12 hr 0.95 1.32 0.71 0.463 0.644 0.348 44 31 58

4 4 14 0.02 0.03 0.04 0.008 0.017 0.020 2,500 1,200 1,000

Celery Vegetable, leafy 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Transplanting 230 0.013 0.018 0.010 1,600 1,100 2,100

Harvesting, Hand 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Field Corn

and Popcorn Field / row crop, tall 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting

210 0.012 0.016 0.009 1,700 1,300 2,300

1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.016 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Cotton Field / row crop, low / 

medium 0.5

Weeding, Hand 70

12 hr

0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Pepper, bell Vegetable, fruiting 0.33 Weeding, Hand 70 0.31 0.44 0.24 0.003 0.004 0.002 7,900 5,700 11,000
Dimethoate Human Health Risk Assessment DP No. D416010

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Table 11.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302)

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Scouting 210 0.008 0.011 0.006 2,600 1,900 3,500

Transplanting 230 0.008 0.012 0.006 2,400 1,700 3,200

Harvesting, Hand

Tying/Training 1100

0.040 0.056 0.030 500 360 670

1 2 2 0.17 0.07 0.16 0.015 0.009 0.020 1,400 2,200 1,000

Irrigation (hand set)

1900 12 hr 0.31 0.44 0.24 0.069 0.096 0.052 290 210 390

2 2 5 0.06 0.07 0.08 0.009 0.016 0.019 2,200 1,300 1,100

Potato Vegetable, "root" 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Irrigation (hand set) 1900

0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Safflower Field / row crop, low / 

medium 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,000

Sorghum, 

grain Field / row crop, tall 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Soybean Field / row crop, low / 

medium 0.5

Weeding, Hand 70 0.004 0.005 0.003 5,200 3,800 7,000

Scouting 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Tomato Vegetable, fruiting 0.5

Pruning, Hand

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300
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Table 11.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302)

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Transplanting 230 0.013 0.018 0.010 1,600 1,100 2,100

Harvesting, Hand

Tying/Training 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Watermelon Vegetable, cucurbit 0.5

Scouting

Weeding, Hand

Pruning, Hand

Thinning Fruit

90

12 hr 0.48 0.66 0.36

0.005 0.007 0.004 4,100 2,900 5,400

Transplanting 230 0.013 0.018 0.010 1,600 1,100 2,100

Harvesting, Hand

Turning

Harvesting, 

Mechanicallyassisted

Training

550

0.030 0.042 0.023 670 480 890

2 1 1 0.06 0.27 0.29 0.011 0.017 0.019 1,800 1,200 1,100

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Wheat (spring

and winter)

Field / row crop, low / 

medium 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,100

Bold MOE values are below the LOC of 1000.

1. DFR = Combined residues of dimethoate and omethoate from a tomato study, adjusted to account for application rate differences and for differences in toxicity of omethoate. 

2. Daily Dermal Dose = [DFR (μg/cm2) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day]  BW (69 kg).

3. MOE = POD (20.2 mg/kg/day) / Daily Dermal Dose. 
Dimethoate Human Health Risk Assessment DP No. D416010

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Restricted-Entry Interval (REI)

Current product-label REIs range from 48 hours to 24 days depending on the crop and location 

(i.e., arid versus non-arid areas). Based on the current post-application dermal exposure 

assessment (Tables 11.2.2.2 - 11.2.2.4), REIs of 12 hours to more than 30 days would be 

necessary to reach acceptable MOEs (i.e., MOEs ≥ 1000) from exposure to the combined 

residues of dimethoate and omethoate. Table 11.2.2.5 provides a summary of the current REIs 

on product labels and the REIs based on the quantitative post-application exposure assessment 

for dimethoate that would be needed to achieve risks that were not of concern. 

Even though REIs of 12 and 24 hours are long enough for MOEs to reach the LOC of 1000 for 

some crops/activities, HED recommends a minimum REI of 48 hours (72 hours in arid regions) 

to be protective of potential for exposure to omethoate, which is known to form after application. 

These REIs are in line with the 40 CFR 156.208 (c) (2) assignments for active ingredients that 

are classified as Toxicity Category I for acute dermal, eye irritation, and primary skin irritation.

Table 11.2.2.5. Summary of Restricted Entry Intervals

Crop Current REI on product labels HED recommended REI

Non-Arid Arid Non-Arid Arid

Cherry 10 days 14 days >30 days >30 days

Christmas tree 10 days 14 days 29 days >30 days

Forestry 14 days 24 days >30 days >30 days

Grapefruit 10 days 14 days 26 days >30 days

Lemon 10 days 14 days 26 days >30 days

Orange 10 days 14 days 26 days >30 days

Nursery Crop 

(Ornamentals, 

Non-bearing 

Plants)

Woody ornamentals 10 days 14 days

29 days

(>30 days if 

airblast >1 

lb ai/A)

>30 days

(>30 days

if airblast 

>1 lb 

ai/A)

Herbaceous 

ornamentals 48 hours

Conifer seed orchards

48 hours 

(16 days if airblast 

>1 lb ai/A)

4 days

(25 days if 

airblast >1 lb 

ai/A)

Pear 10 days 14 days >30 days >30 days

Pecan

48 hours

7 days 10 days

Kale

48 hours1 7 days Lettuce, leaf

Mustard Green

Swiss Chard 

Pea, Green 48 hours1 6 days

Turnip 48 hours1 7 days

Alfalfa

Asparagus 3 days 7 days

Bean, dry, and Pea, dry

Broccoli 48 hours 72 hours 4 days 11 days

Brussels Sprouts 48 hours 72 hours 4 days 14 days

Cauliflower 48 hours 72 hours 4 days 11 days

Celery 48 hours 3 days 7 days

Field Corn and Popcorn 48 hours (4 days 

for detasseling)

48 hours (15 days 

for detasseling) 3 days 7 days

Cotton 48 hours 48 hours1 72 hours1
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Table 11.2.2.5. Summary of Restricted Entry Intervals

Crop Current REI on product labels HED recommended REI

Non-Arid Arid Non-Arid Arid

Forage Crop 48 hours 3 days 7 days

Pepper, bell 48 hours 2 days 5 days

Potato 48 hours 3 days 7 days

Safflower 48 hours 3 days 7 days

Sorghum, grain 48 hours 48 hours1 72 hours1

Soybean 48 hours 48 hours 4 days

Tomato 48 hours 3 days 7 days

Watermelon 48 hours 3 days 7 days

Wheat (spring and winter) 48 hours 48 hours 4 days

1. Even though REIs of 12 and 24 hours are long enough for MOEs to reach the LOC of 100 for some crops/activities, HED recommends a 

minimum REI of 48 hours (72 hours in arid regions) for the product labels to be protective of the acute toxicity of omethoate.

12.0 References

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Dimethoate. Response to Reregistration Requirements: Supplemental Data Pertaining to Characterization of 

Radioactive Residues in Milk, Radiovalidation of the Livestock Analytical Method, Storage Stability Intervals, 

Magnitude of Residues for Cotton Gin By-Product and Alfalfa Grown for Seed, Safflower Processing and an 

(Unsolicited) Olive Metabolism Study. D232849, 24-MAY-2011, M. Sahafeyan.

Dimethoate. Response to Deficiency: New Ruminant and Poultry Livestock Feeding Studies; A New Enforcement 

Method for Livestock Commodities Including a Final Method Validation; Storage Stability of Livestock Tissues; 

Magnitude of Residues on Grass Grown for Seed. D239886, 12-NOV-2013, M. Sahafeyan.

Tier II Drinking Water Assessment for Dimethoate for the Use in Human Health Risk Assessment in the 

Registration Review Risk Assessment. D415002, 28-JUL-2014, J. Meléndez.

Bouchard MF, Chevrier J, Harley KG, Kogut K, Vedar M, Calderon N, et al. Prenatal Exposure to

Organophosphate Pesticides and IQ in 7-Year-Old Children. Environ Health Perspectives. 2011;119:1189-

1195.

Bouchard M.F., Bellinger D.C., Wright R.O., Weisskopf M.G., (2010). Attention-Deficit/Hyperactivity

Disorder and Urinary Metabolites of Organophosphate Pesticides. PEDIATRICS

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Chen L, Zhao T, Pan C, Ross JH, Krieger RI. (2012) Preformed biomarkers including dialkylphosphates (DAPs) in 

produce may confound biomonitoring in pesticide exposure and risk assessment. J Agric Food Chem. 2012 

Sep 12;60(36):9342-51. doi: 10.1021/jf303116p. Epub 2012 Sep 4.

Engel SM, Berkowitz GS, Barr DB, Teitelbaum SL, Siskind J, Meisel SJ, Wetmur JG, Wolff MS. Prenatal 

Organophosphate Metabolite and Organochlorine Levels and Performance on the Brazelton Neonatal 

Behavioral Assessment Scale in a Multiethnic Pregnancy Cohort. American Journal of Epidemiology. 

2007;165:1397-1404.

Engel SM, Wetmur J, Chen J, Zhu C, Barr DB, Canfield RL, Wolff MS. Prenatal Exposure to Organophosphates, 

Paraoxonase 1, and Cognitive Development in Childhood. Environmental Health Perspectives. 

2011;119:1182-1188. 
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Utero Organophosphate Pesticide Exposure and Fetal Growth and Length of Gestation in an Agricultural 

Population. Environmental Health Perspectives. 2004;115:792–798.

Eskenazi B, Marks AR, Bradman A, Harley K, Barr DB, Johnson C, Morga N, Jewell NP. Organophosphate 

Pesticide Exposure and Neurodevelopment in Young Mexican-American Children. Environmental Health 

Perspectives. 2007;115:792–798.

FIFRA Scientific Advisory Panel. (2012). Transmittal of the Meeting Minutes from the FIFRA Scientific Advisory 

Panel Meeting of April 10-12, 2012. FIFRA Scientific Advisory Panel, Office of Science Coordination and 

Policy, Office of Prevention, Pesticides and Toxic Substances, U.S. Environmental Protection Agency. 

Washington, DC. Available: http://www.epa.gov/scipoly/sap/meetings/2012/041012meeting.html

Fortenberry, GZ, Meeker, JD, Sánchez, BN, Barr, DB, Panuwet, P, Bellinger, D, Schnaas, L, Solano-González, M, 

Ettingera, AS, Hernandez-Avila, M, Hu, H, Tellez-Rojoj, MM. Urinary 3,5,6-trichloro-2-pyridinol (TCPY) 

in pregnant women from Mexico City: Distribution, temporal variability, and relationship with child 

attention and hyperactivity. International Journal of Hygiene and Environmental Health 217 (2014): 405–

412.

Forsberg ND, Rodriguez-Proteau R, Mab L, Morréc J, Christensen JM, Maierc CS, Jenkins JJ, Anderson

KA. Organophosphorus pesticide degradation product in vitro metabolic stability and timecourse uptake and elimination in rats following oral and intravenous dosing. Xenobiotica, 2011;

41(5): 422–429. 

Furlong, Melissa A., Engel, Stephanie M., Boyd Barr, Dana, Wolff, Mary S. Prenatal exposure to organophosphate 

pesticides and reciprocal social behavior in childhood. 2014. Environment International 70:125-131.

Guodong, Ding, Pei, Wang, Ying, Tian, Jun, Zhang, Yu, Gao, Xiaojin, Wang, Rong, Shi, Guoquan, Wang, and 

Xiaoming, Shen. Organophosphate Pesticide Exposure and Neurodevelopment in Young Shanghai 

Children. Environmental Science and Technology 46:2911-2917, 2012.

Marks AR, Harley K, Bradman A, Kogut K, Barr DB, Johnson C, et al. Organophosphate Pesticide Exposure and 

Attention in Young Mexican-American Children: The CHAMACOS Study. Environmental Health 

Perspectives. 2010;118:1768-1774.

Oulhote, Youssef and Bouchard, Maryse F. Urinary Metabolites of Organophosphate and Pyrethroid Pesticides and 

Behavioral Problems in Canadian Children. Environmental Health Perspectives. 121:1378-1384 (2013) 

Racke J.D. Degradation of organophosphorous insecticidesin environmental matrices. In: Organophosphates 

Chemistry, Fate and Effects. Academic Press, Inc., San Diego, CA, 1992, pp 47–72.

Rauh VA, Garfinkel R, Perera FP, Andrews HF, Hoepner L, Barr DB, Whitehead R, Tang D, Whyatt RW. Impact of 

Prenatal Chlorpyrifos Exposure on Neurodevelopment in the First 3 Years of Life Among Inner-City 

Children. Pediatrics. 2006;18(6): 1835-1859.

Rauh V, Arunajadai S, Horton M, Perera F, Hoepner L, Barr DB, et al. 2011. Seven-Year Neurodevelopmental 

Scores and Prenatal Exposure to Chlorpyrifos, a Common Agricultural Pesticide. Environmental Health 

Perspectives. 2011;119:1196-1201.

Shelton, Janie F., Geraghty, Estella M., Tancredi, Daniel J., Delwiche, Lora D., Schmidt, Rebecca J., Ritz, Beate, 

Hansen, Robin L., and Hertz-Picciotto, Irva. Neurodevelopmental disorders and prenatal residential 

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Characterization. http://www.epa.gov/scipoly/sap/meetings/2008/091608_mtg.htm

U.S. Environmental Protection Agency. (2012). Draft Issue Paper: Scientific Issues Concerning Health Effects of 

Chlorpyrifos. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0040-0002

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Association Between In Utero Organophosphate Pesticide Exposure and Abnormal Reflexes in Neonates. 

NeuroToxicology. 2005;26:199–209.

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Yingzi, Tian, Ying. Prenatal exposure to organophosphate pesticides and neurobehavioral development of 

neonates: A birth cohort study in Shenyang, China. PlosOne 47:80–85, 2014.

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RDI: RAB1 (9/15/2015)

cc: M.M. Perron

M.M. Perron: S10955:PY-S:(703)347-0395:7509P:RAB1
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Appendix A. Toxicology Profile 

A.1 Toxicology Data Requirements

Study requirements (40 CFR 158.340) for dimethoate are presented below. Use of the new 

guideline numbers does not imply that the new (1998) guideline protocols were used.

Study

Technical

Required Satisfied

870.1100 Acute Oral Toxicity.......................................................

870.1200 Acute Dermal Toxicity..................................................

870.1300 Acute Inhalation Toxicity..............................................

870.2400 Acute Eye Irritation.......................................................

870.2500 Acute Dermal Irritation .................................................

870.2600 Skin Sensitization..........................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

yes

870.3100 90-Day Oral Toxicity in Rodents..................................

870.3150 90-Day Oral Toxicity in Nonrodents.............................

870.3200 21/28-Day Dermal Toxicity ..........................................

870.3250 90-Day Dermal Toxicity ...............................................

870.3465 90-Day Inhalation Toxicity ...........................................

yes

yes

yes

no

yes

yes

yes

yes

--

yes1

870.3700a Prenatal Developmental Toxicity (rodent) ....................

870.3700b Prenatal Developmental Toxicity (nonrodent) ..............

870.3800 Reproduction and Fertility Effects ................................

yes

yes

yes

yes

yes

yes

870.4100a Chronic Toxicity (rodent)..............................................

870.4100b Chronic Toxicity (nonrodent)........................................

870.4200a Carcinogenicity (rat)......................................................

870.4200b Carcinogenicity (mouse) ...............................................

870.4300 Combined Chronic Toxicity/Carcinogenicity ...............

yes

yes

yes

yes

yes

yes2

yes

yes2

yes

yes

870.5100 Mutagenicity—Bacterial Reverse Mutation Test..........

870.5300 Mutagenicity—Mammalian Cell Gene Mutation Test..

870.5xxx Mutagenicity— Structural Chromosomal Aberrations..

870.5xxx Mutagenicity—Other Genotoxic Effects.......................

yes

yes

yes

yes

yes

yes

yes

yes

870.6100 Acute Delayed Neurotoxicity (hen)

870.6200a Acute Neurotoxicity Screening Battery (rat).................

870.6200b 90-Day Neurotoxicity Screening Battery (rat) ..............

870.6300 Developmental Neurotoxicity .......................................

no

yes

yes

yes

--

yes

yes

yes

870.7485 Metabolism and Pharmacokinetics................................

870.7600 Dermal Penetration........................................................

870.7800 Immunotoxicity .............................................................

yes

no

yes

yes

--

yes

1 An inhalation study with omethoate, which is more potent than dimethoate, is available.

2 The combined chronic toxicity/carcinogenicity study satisfies the requirement of the study.
Dimethoate Human Health Risk Assessment DP No. D416010

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A.2. Toxicity Profiles

Table A.2.1. Acute Toxicity Profile - Dimethoate 

Guideline No. Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral (rat) 48890603 LD50 = 550 mg/kg (F) III

870.1200 Acute dermal (rabbit) 48890604 LD50 > 5000 mg/kg IV

870.1300 Acute inhalation (rat) 48890605 LC50 > 2.1 mg/L IV

870.2400 Acute eye irritation (rabbit) 48890606 Moderate irritant II

870.2500 Acute dermal irritation (rabbit) 48890607 Not a dermal irritant IV

870.2600 Skin sensitization (guinea pig) 48890608 Not a sensitizer N/A

Table A.2.2. Acute Toxicity Profile - Omethoate 

Guideline No. Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral (rat) 46099809 LD50= 22/28 mg/kg (M/F) I

870.1200 Acute dermal (rat) 46099810 LD50= 215 mg/kg I

870.1300 Acute inhalation (rat) 46099813 LC50= 0.28 mg/kg II

Note: Studies have not been updated to reflect current HED policy. Endpoint selection was 

driven by BMD modeling of the AChE activity to obtain BMD10 and BMDL10 values. As a 

result, updates to NOAEL/LOAEL values (or NOEL/LOEL values) in these studies would not 

ultimately impact current PODs or risk estimates. Consequently, the Agency did not find it 

necessary to update these studies at this time.

Table A.2.3. Subchronic, Chronic, and Other Toxicity Profile - Dimethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.3100 90-Day Oral 

Toxicity in Rodents 

(rat)

00051675, 0077532

0,2,8,32,50, or 400 ppm 

(0, 0.1, 0.4, 1.6, 2.5, or 20 

mg/kg/d)

Acceptable/guideline

Cholinesterase NOEL = 32 ppm (1.6 mg/kg/d)

Cholinesterase LOEL = 50 ppm (2.5 mg/kg/d) 

based on the depression of plasma, RBC, and brain 

cholinesterase

Systemic NOEL = 50 ppm (2.5 mg/kg/d)

Systemic LOEL = 400 ppm (20 mg/kg/d) based on 

decreased growth and food consumption and 

increased kidney and liver weight ratios

870.3150 90-Day Oral 

Toxicity in NonRodent (dog)

00051676

0, 2, 10, 50, or 1500-3000 

ppm

(0, 0.05, 0.25, 1.25, or 

37.5-75 mg/kg/d)

Acceptable/Non-guideline 

(with chronic dog)

Cholinesterase NOEL = 2 ppm (0.05 mg/kg/d)

Cholinesterase LOEL = 10 ppm (0.25 mg/kg/d) 

based on depression of RBC cholinesterase

Systemic NOEL = 50 ppm (1.25 mg/kg/d)

Systemic LOEL = 1500 ppm (37.5 mg/kg/d) based 

on tremors and decreased food consumption in 

females

Only 1-2 dogs treated per group
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Table A.2.3. Subchronic, Chronic, and Other Toxicity Profile - Dimethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.3200 Dermal Toxicity 

(rat)

5-day exposure

(using 43.5% a.i. 

formulation)

44818902 (1999)

0, 5, 10, 20, 40, or 100 

mg/kg/d

Acceptable/non-guideline

Males:

NOAEL = 40 mg/kg/d

LOAEL = 100 mg/kg/d based on statistically 

significant inhibition of RBC and brain 

cholinesterase activity

Females:

NOAEL = 10 mg/kg/d

LOAEL = 20 mg/kg/d based on statistically 

significant inhibition of RBC and brain 

cholinesterase activity

870.3200 28-Day Dermal 

Toxicity (rat)

44999101 (1999)

0, 10.5, 21, 31.5, or 63 

mg/kg/d

Acceptable/guideline

NOAEL = 10.5 mg/kg/d

LOAEL = 21 mg/kg/d based on reduced brain 

cholinesterase activity (both sexes)

No systemic or dermal toxicity

870.3700a Prenatal 

Developmental in 

Rodent (rat)

00150130 (1984)

0, 3, 6, or 18 mg/kg/d

Acceptable/guideline

Maternal NOEL = 3 mg/kg/d 

Maternal LEL = 6 mg/kg/d based on increased 

reaction to sounds and touch stimuli, body tremors, 

and unsteady gate

Developmental NOEL = 18 mg/kg/d

Developmental LEL not established

870.3700b Prenatal 

Developmental in 

Non-Rodent (rabbit)

00149126, 00159760 

(1984)

0, 10, 20 or 40 mg/kg/d

Acceptable/guideline

Maternal NOEL = 10 mg/kg/d

Maternal LEL = 20 mg/kg/d based on decreased 

food consumption and clinical signs

Developmental NOEL = 20 mg/kg/d

Developmental LEL = 40 mg/kg/d based on 

decreased fetal body weight

870.3800 Reproduction and 

Fertility Effects (rat)

42251501 (1992)

0, 1, 15, or 65 ppm

(0, 0.08, 1.2, or 5.46 

mg/kg/d)

Acceptable/guideline

Cholinesterase NOEL = 0.08 mg/kg/d

Cholinesterase LEL = 1.2 mg/kg/d based on 

decreased plasma, erythrocyte and brain 

cholinesterase activity 

Parental NOEL = 0.08 mg/kg/d 

Parental LEL = 1.2 mg/kg/d based on decreased 

cholinesterase activity in both sexes and generations

Reproductive NOEL = 1.2 mg/kg/d

Reproductive LEL= 5.46 mg/kg/d based on 

decreased fertility index, pup survival and body 

weights
Dimethoate Human Health Risk Assessment DP No. D416010

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Table A.2.3. Subchronic, Chronic, and Other Toxicity Profile - Dimethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.3800 Reproduction and 

Fertility Effects (rat)

46181001 (2003)

0, 0.2, 1, or 6.5 mg/kg/d

Acceptable/guideline

Parental NOAEL = 0.2 mg/kg/d

Parental LOAEL = 1 mg/kg/d based on decreased 

erythrocyte and brain cholinesterase activity

Offspring NOAEL = 1 mg/kg/d

Offspring LOAEL = 6.5 mg/kg/d based on 

decreased brain cholinesterase activity in females

Developmental NOAEL = 6.5 mg/kg/d

Developmental LOAEL = not established

870.3800 Reproduction and 

Fertility Effects (rat)

One-generation 

range finding

46348201 (1990)

0, 50, 75, or 100 ppm

(0, 2.9, 4.4, or 6.1 

mg/kg/d in males and 0, 

3.9, 5.8, or 7.5 mg/kg/d in 

females)

Parental NOAEL = not established

Parental LOAEL = 2.9/3.9 mg/kg/d (M/F) based on 

decreased plasma, erythrocyte and brain 

cholinesterase activity

Offspring NOAEL = not established

Offspring LOAEL = 2.9/3.9 mg/kg/d based on 

decreased plasma, erythrocyte and brain 

cholinesterase activity and decreased body weight

870.4100a Chronic Toxicity

(rat)

See 870.4300 See 870.4300

870.4100b Chronic Toxicity

(dog)

41939801, 42192301 

(1990)

0, 5, 20, or 125 ppm

(0, 0.18, 0.70, or 4.18 

mg/kg/d in males and 0, 

0.19, 0.76, or 4.31 

mg/kg/d in females)

Acceptable/guideline

Cholinesterase NOEL = not established

Cholinesterase LEL = 0.18 mg/kg/d based on 

decreased brain cholinesterase. Additionally, RBC

cholinesterase decreased in the mid- and high-dose 

groups and plasma cholinesterase decreased in the 

high-dose group.

Systemic NOEL = not established

Systemic LEL = 0.18 mg/kg/d based on decreased 

liver weights in females and presence of a brown, 

granular pigment in the liver of both sexes. 

Decreased heart weights in the high-dose group.

870.4200a Carcinogenicity (rat) See 870.4300 See 870.4300

870.4200b Carcinogenicity 

(mouse)

00163800 (1986)

0, 25, 100 or 200 ppm

(0, 3.75, 15 or 30 

mg/kg/d)

Acceptable/guideline

Cholinesterase NOEL= not established

Cholinesterase LEL = 3.75 mg/kg/d based on 

decreased plasma and erythrocyte cholinesterase. 

No brain cholinesterase measurements taken.

Systemic NOEL = not established

Systemic LEL = 3.75 mg/kg/d based on 

cholinesterase depression in both sexes and 

hepatocytic vacuolization in female mice

Liver tumors in female mice and lung and 

hemolymphoreticular system tumors in male mice 

observed at 30 mg/kg/d
Dimethoate Human Health Risk Assessment DP No. D416010

Page 78 of 104

Table A.2.3. Subchronic, Chronic, and Other Toxicity Profile - Dimethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.4300 Combined Chronic 

Toxicity/

Carcinogenicity (rat)

00164177 (1986)

0, 1, 5, 25 or 100 ppm

(0, 0.05, 0.25, 1.25, or 5 

mg/kg/d)

Acceptable/guideline

Cholinesterase NOEL = 0.05 mg/kg/d

Cholinesterase LEL = 0.25 mg/kg/d based on 

decreased brain and RBC holinesterase activity

Systemic NOEL = 1.25 mg/kg/d 

Systemic LEL = 5 mg/kg/d based on increased 

mortality (females), anemia (males) and increased 

leukocytes (both sexes)

In males only, dose-related trends for spleen 

hemangiosarcomas, spleen 

hamangiomas/hemangiosarcomas combined, and 

combined spleen hemagniomas/hemangiosarcomas 

and skin hemangiosarcomas. Additionally, there 

were increases in the incidences of spleen 

hemangioma/hemangiosarcomas combined and of 

angiogenic tumors at all sites in high dose males. 

870.5100 Bacterial reverse 

mutation

00063996 (1977)

Acceptable

Dimethoate and isodimethoate classified as nonmutagenic

870.5300 In vitro mammalian 

cell gene mutation

00151223(1985)

Acceptable

Compound-related increases in mutant frequency 

(MF) were considered equivocal (technical 

problems with assay and increased MFs did not 

exceed normal background rates of mutation)

870.5385 In vivo bone marrow 

cytogenetics (rat)

00150579 (1985)

Acceptable

No clastogenic response up to 150 mg/kg 

870.5395 Mammalian 

micronucleus 

(mouse)

00146521 (1985)

Acceptable

Did not induce any significant increase in the 

number of polychromatic erythrocytes (PCE)

containing micronuclei with single or multiple 

doses of 55 mg/kg

870.5450 Dominant Lethal 

Assay (mouse)

00150578 (1985)

Acceptable

No clastogenic response up to 20 mg/kg/d

870.5500 Unscheduled DNA 

synthesis (UDS) in 

mammalian cells

43151801 (1990)

Acceptable

Positive for inducing UDS in rat hepatocytes 

exposed to 763.33 ug/ml and above

Positive for inducing UDS in rat hepatocytes 

exposed to doses up to the highest dose tested of 

2290 ug/ml 

870.6100 Acute Delayed 

Neurotoxicity (hen)

42884401 (1991)

Acceptable/guideline

No clinical signs of acute delayed neurotoxicity and 

no compound-related histological changes in nerve 

tissue
Dimethoate Human Health Risk Assessment DP No. D416010

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Table A.2.3. Subchronic, Chronic, and Other Toxicity Profile - Dimethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.6200a Acute Neurotoxicity 

Screening Battery 

(rat)

42865102 (1993)

0, 2, 20, or 200 mg/kg

Acceptable/guideline

Systemic NOEL = 20 mg/kg 

Systemic LEL = 200 mg/kg based on decreased 

body weight

Neurotoxicity NOEL = 2 mg/kg

Neurotoxicity LEL = 20 mg/kg based on pupil 

response. 

At highest dose tested, additional effects were 

observed including tremors, decreased motor 

activity, decreased body temperature, increased 

catalepsy time and eleven other parameters which 

indicated coordination, sensory and motor systems 

were affected

870.6200b Subchronic 

Neurotoxicity 

Screening Battery 

(rat)

43128201 (1994)

0, 1, 50 or 125 ppm

(0, 0.06, 3.22, or 8.13 

mg/kg/d for males and 0, 

0.08, 3.78 or 9.88 mg/kg/d 

for females)

Acceptable/guideline

Cholinesterase NOEL = 0.06/0.08 mg/kg/d (M/F)

Cholinesterase LOEL = 3.22/3.78 mg/kg/d (M/F) 

based on decreased cholinesterase activity in the 

plasma and RBCs. Brain cholinesterase activity 

reduced at the highest dose tested.

870.6300 Developmental 

Neurotoxicity (rat)

45529703 (2001)

0, 0.1, 0.5, or 3 mg/kg/d

Acceptable/guideline

Maternal NOAEL = 3 mg/kg/d

Maternal LOAEL = not established

Offspring NOAEL = 0.1 mg/kg/d

Offspring LOAEL = 0.5 mg/kg/d based on 

increased pup death and increased motor activity 

(horizontal activity)

870.7485 Metabolism and 

Pharmacokinetics

43964001 (1995)

Acceptable

- Single oral dose (10 or 

100 mg/kg) of 14Cdimethoate

- Intravenous dose (10 

mg/kg) of 14C-dimethoate

- 14 day repeated oral 

dose of dimethoate 

followed by single oral 

dose of 14C-dimethoate

No sex-, dose- or treatment-related differences in 

the absorption, distribution, and elimination of 

dimethoate. Tmax reached less than 1 hour postdosing. Total recovery of radioactivity ranged 91-

97% of the administered dose. Most of the 

radioactivity was excreted via the urine (85-91% of 

the dose). A small amount of radioactivity was 

found in feces (1-2% of the dose), in the tissues and 

remaining carcass (1-2% of the dose), and in the 

expired air as carbon dioxide (2-3% of the dose). 

Dimethoate is metabolized via hydrolytic and 

oxidative pathways (based on urine analyses). 

Metabolites include dimethoate carboxylic acid, 

dimethyldithiophosphate, dimethylthiophosphoric 

acid, dimethylphosphoric acid, and the oxon 

analogue, omethoate.

870.7485 Metabolism and 

Pharmacokinetics

46497601(2004) A metabolism study with human volunteers was 

evaluated; however, due to the limitations of the 

study, including a limited number of subjects and 

only one dose, it was not useful for dose-response 

evaluation and not reliable for risk assessment.
Dimethoate Human Health Risk Assessment DP No. D416010

Page 80 of 104

Table A.2.3. Subchronic, Chronic, and Other Toxicity Profile - Dimethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.7600 Dermal Absorption 43964001

Acceptable

10 or 100 mg/kg

Dermal absorption (based on a total amount of 

radioactivity recovered from urine, tissues, and 

feces) was 8-11% and 1-2% of the administered 

dose from rats treated at 10 and 100 mg/kg, 

respectively. No marked sex-related difference was 

observed in the absorption patterns. The amount of 

radioactivity recovered from skin wash, extracts 

from dressing, and treated skin was 62-84%, 1.4-

3.6%, and 2-17% of the administered dose, 

respectively. Total recovery of radioactivity ranged 

between 89-93% of the administered dose for all 

tested groups within 5 days after dosing.

870.7600 Dermal Absorption 45530501

Acceptable/guideline

0.02, 0.4 and 4.0 mg/cm2

Results from the high dose not included because 

excessive amount of applied material found on the 

application site cover and surrounding skin.

At low- (0.67 mg/kg) and mid-dose (13.3 mg/kg)

levels, dermal absorption (based on excreta, cage 

wash, and carcass) was 6% after 1 hr and ranged 

from 25-38% at 10 and 24 hours.

870.7800 Immunotoxicity 48572807, 48997901 

(2011)

Acceptable/guideline

0, 5, 25, 75, or 200 ppm 

(0, 1, 5, 14.2, or 36.4 

mg/kg/d)

Systemic NOAEL = not established

Systemic LOAEL = 1 mg/kg/d based on decreased 

brain cholinesterase levels

Immunotoxicity NOAEL = 36.4 mg/kg/d 

Immunotoxicity LOAEL = not established

Special Studies

Cross-fostering 

Study

46214501 (2004)

Acceptable/non-guideline

0, 3, or 6 mg/kg/day

Maternal NOAEL = not established

Maternal LOAEL = 3 mg/kg/day based on clinical 

observations of forelimb hair loss and increased 

incidences of restlessness and scattering of pups

Offspring NOAEL = not established

Offspring LOAEL = 3 mg/kg/day based on reduced 

milk consumption, increased levels of urea in the 

blood, and increased mortality

Direct pre- and post-natal toxicity of the offspring 

to dimethoate could not be disregarded as 

significant contributing factors to overall mortality

Comparative 

Cholinesterase 

Study

45529702 (2001)

Acceptable/non-guideline

0, 0.1, 0.5, or 3.0 mg/kg/d

Acute NOAEL = 0.5 mg/kg/day

Acute LOAEL = 3.0 mg/kg/day based on decreased 

blood, RBC and plasma cholinesterase

Repeated NOAEL = 0.1 mg/kg/day

Repeated LOAEL = 0.5 mg/kg/day based on 

decreased brain cholinesterase
Dimethoate Human Health Risk Assessment DP No. D416010

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Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile - Omethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.3200 21-Day Dermal 

Toxicity (rat)

46099804 (1979)

Unacceptable

0, 2.5, or 20 mg/kg/day

Systemic and dermal NOAEL = 20 mg/kg/day

Systemic and dermal LOAEL = not established

Cholinesterase NOAEL = not established 

Cholinesterase LOAEL = 2.5 mg/kg/day based on 

inhibition of brain cholinesterase activity in females

Deficiencies: only 2 dose groups, no dose selection 

rationale, lack of details regarding substance 

preparation, age of rabbits and acclimation period 

not provided, analyses for homogeneity, stability 

and concentration were not performed, food 

consumption was not measured, neurological testing 

and opthalmological exams were not performed, 

and lack of measurements for recommended 

hematology and clinical chemistry parameters

870.3465 Subchronic 

Inhalation Study 

(rat)

46358601 (1979)

Acceptable/non-guideline

0, 0.96, 2.3 or 7.5 mg/m3

NOAEL = not established

LOAEL = 0.96 mg/m3 based on depressed 

cholinesterase activity in brain (males) and RBCs

(both sexes)

870.3700a Prenatal 

Developmental in 

Rodent (rat)

46099806 (1990)

Acceptable/guideline

0, 0.3, 1.0 or 3.0 

mg/kg/day

Maternal NOAEL = 0.3 mg/kg/day

Maternal LOAEL = 1.0 mg/kg/day based on body 

weight decrements

Developmental NOAEL = 1.0 mg/kg/d

Developmental LOAEL = 3.0 mg/kg/d based on

decreased placental weights

870.3700b Prenatal 

Developmental in 

Non-Rodent (rabbit)

46099807 (1990)

Acceptable/guideline

0, 0.2, 1.0, or 5.0 

mg/kg/day

Cholinesterase NOAEL = 0.2 mg/kg/d

Cholinesterase LOAEL = 1 mg/kg/d based on 

inhibition of RBC and brain cholinesterase activity

Maternal NOAEL = 0.2 mg/kg/d

Maternal LOAEL = 1 mg/kg/d based on body 

weight decrements

Developmental NOAEL = 0.2 mg/kg/d

Developmental LOAEL = 1 mg/kg/d based on 

increased number of resorptions, increased postimplantation loss and increased incidence of 

arthrogryposis and epignathus
Dimethoate Human Health Risk Assessment DP No. D416010

Page 82 of 104

Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile - Omethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.3800 Reproduction and 

Fertility Effects (rat)

46195301 (1981)

Unacceptable

0, 0.05, 0.15, or 0.5 

mg/kg/day

Parental NOAEL = 0.5 mg/kg/d 

Parental LOAEL = not established

Reproductive NOAEL = 0.15 mg/kg/day

Reproductive LOAEL= 0.5 mg/kg/day based on 

slight reductions in the gestation indices during the 

second mating of F0 and F1 females

Offspring NOAEL = 0.05 mg/kg/day

Offspring LOAEL = 0.15 mg/kg/day based on 

decreased in body weight and survival indices

870.3800 Reproduction and 

Fertility Effects (rat)

Exposure through 

drinking water

45806201 (1992), 

46099802 (1994)

Acceptable/guideline

0, 0.5, 3.0, or 18 ppm

Parental NOAEL = not established

Parental LOAEL = 0.5 ppm based on decreased 

brain cholinesterase activity

Reproductive NOAEL = 3 ppm

Reproductive LOAEL = 18 ppm based on decreased 

fertility and conception rates, increased precoital 

interval, decrease in the number of pups/litter and 

lesions of the epidydymal epithelium (P and F1

males)

Offspring NOAEL = 3 ppm

Offspring LOAEL = 18 ppm based on decreased 

body weight and reduced survival 

870.4100b Chronic Toxicity

(dog)

46099805 (1984)

Supplemental/guideline

0, 0.025, 0.125, or 0.625 

mg/kg/day

Systemic NOAEL = 0.625 mg/kg/day

Systemic LOAEL = not established

Cholinesterase NOAEL = 0.025/0.125 mg/kg/day 

(M/F)

Cholinesterase LOAEL = 0.125/0.625 mg/kg/day 

(M/F) based on inhibition of brain and erythrocyte 

cholinesterase activity

870.4200a Carcinogenicity (rat)

Feeding study

46119402 (1979)

Unacceptable

0, 0.015, 0.05, 0.15, or 0.5 

mg/kg/day

Cholinesterase NOAEL = 0.05 mg/kg/day

Cholinesterase LOAEL = 0.15 mg/kg/day based on 

inhibition of cholinesterase activity in the brain, 

erythrocytes and plasma

Systemic NOAEL = 0.5 mg/kg/day

Systemic LOAEL = not established

Deficiencies: lack of homogeneity and stability 

data, weekly clinical examination, eye 

examinations, serum electrolyte measurements, and 

tabulation of microscopic lesions; animals could 

have tolerated a higher dose
Dimethoate Human Health Risk Assessment DP No. D416010

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Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile - Omethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.4200b Carcinogenicity 

(mouse)

Exposure through 

drinking water

46126002 (2001)

Acceptable/guideline

0, 0.5, 4 or 32 ppm

(0, 0.10, 0.82, or 6.48 

mg/kg/day in males and 0, 

0.11, 0.80, 6.61 

mg/kg/day in females) 

Cholinesterase NOAEL = 0.5 ppm 

Cholinesterase LOAEL = 4 ppm based on decreased 

cholinesterase activity in plasma, erythrocytes, and 

brain

Systemic NOAEL = 4 ppm

Systemic LOAEL = 32 ppm based on tremors in 

both sexes

No significant increase in neoplasms

870.4300 Combined Chronic 

Toxicity/

Carcinogenicity (rat)

Exposure through 

drinking water

46126001 (1995)

Acceptable/guideline

0, 0.5, 4 or 32 ppm

(0, 0.04, 0.30, or 2.92 

mg/kg/day in males and 0, 

0.05, 0.44, or 3.93 

mg/kg/day in females)

Cholinesterase NOAEL = not established

Cholinesterase LOAEL = 0.5 ppm based on 

inhibition of erythrocyte cholinesterase activity in 

males. At 4 ppm, brain and erythrocyte activity 

decreased in both sexes. Plasma activity decreased 

at the highest dose tested.

Systemic NOAEL = 4 ppm

Systemic LOAEL = 32 ppm based on transient 

decreases in body weight, clinical signs indicative 

of neurotoxicity, and lesions in the eyes and 

forestomach in both sexes; vacuolation of the 

epididymal epithelium in males; mammary gland 

hyperplasia in females

870.5100 Mammalian 

Activation Gene 

Mutation Assay

46098604 (1988)

Acceptable/guideline

No evidence of induced mutant colonies 

870.5300 In vitro mammalian 

cell gene mutation

46098612 (1988)

Acceptable/guideline

Strong evidence of a concentration related positive 

response of sister chromatid exchange induced over 

background; statistically and biologically significant 

≥1700 μg/ml

870.5385 In vivo bone marrow 

cytogenetics (mice)

46098608 (1988)

Acceptable/guideline

No statistically significant increase in frequency of 

micronucleated PCE

870.5450 Dominant Lethal 

Assay (mouse)

46098605 (1991)

Unacceptable

No response up to 20 mg/kg/d

Deficiency: no concurrent positive control data

870.5500 Unscheduled DNA 

synthesis in 

mammalian cells

46098613 (1989)

Acceptable/guideline

No evidence of unscheduled DNA synthesis up to 

30 mg/kg

870.5550 Unscheduled DNA 

synthesis in rat 

hepatocytes

46098603 (1989)

Acceptable/guideline

Evidence of dose related positive response; 

unscheduled DNA synthesis induced at dose levels 

≥256 μg/ml

870.5915 In vivo cytogenetic 

mutagenicity

46098607 (1990)

Acceptable/guideline

No evidence of sister chromatid exchange (SCE) 

induction up to 20 mg/kg/day

870.6100 Acute Delayed 

Neurotoxicity (hen)

46099801(1993)

Acceptable/non-guideline

140 mg/kg

No treatment-related pathological changes in nerve 

tissues
Dimethoate Human Health Risk Assessment DP No. D416010

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Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile - Omethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

870.6200a Acute Neurotoxicity 

Screening Battery 

(rat)

46167701 (2003)

Acceptable/guideline

0, 0.2, 0.25, 0.35, or 5 

mg/kg

ChE NOAEL = 0.25 mg/kg

ChE LOAEL = 0.35 mg/kg

Systemic NOAEL = 0.2 mg/kg 

Systemic LOAEL = 0.25 mg/kg based on FOB 

effects

870.7485 Metabolism and 

Pharmacokinetics

46099808

Male and female rats exhibited signs of toxicity at 

0.5-4 hrs post-dosing including trembling, 

salivation, high breathing rate, and congestion of the 

eyes. Overall recovery of administered radioactivity 

was 88-98%. There were no remarkable sex-, doseor treatment-related differences in the absorption, 

distribution, and elimination of omethoate. 

Absorption rates were rapid and Tmax was reached 

within 1 hour post-dosing. Omethoate was rapidly 

excreted within 48 hours with the majority excreted 

via the urine (85-97% of the administered dose). 

The remainder of the administered radioactivity was 

excreted via the feces (2-4% of the administered 

dose). Biliary excretion was found to account for 

the majority of the fecal metabolite content. Based 

upon tissue burden data, omethoate and/or its 

metabolites do not appear to undergo any significant 

sequestration. Omethoate appeared to be 

metabolized to a greater extent in males than in 

females.

Special Studies

Investigation of 

Effects on LongTerm Cholinesterase 

Activity

Exposure through 

drinking water for 

32 weeks

46099816 (1994)

Acceptable/non-guideline

0, 100 or 300 ppb

Designed to determine a drinking water dose that 

would result in no inhibition of RBC, plasma or 

brain cholinesterase activity in young adult rats. No 

cholinesterase inhibition was observed in any 

examined compartment for all doses.

Cholinesterase 

Activity (dog)

Gavage for 13 

weeks

46099814 (1991)

Acceptable/non-guideline

0 or 0.0125 mg/kg/day No inhibition of cholinesterase activity 

In vivo mammalian 

gene mutation – spot 

test in mice

46098606 (1990)

Acceptable/non-guideline

0, 4, 8, or 16 mg/kg/day

Statistically significant, dose-dependent increase in 

number of relevant F1 coat spots in dose groups
Dimethoate Human Health Risk Assessment DP No. D416010

Page 85 of 104

Table A.2.4. Subchronic, Chronic, and Other Toxicity Profile - Omethoate

Guideline No. Study Type

MRID No. (year)/ 

Classification /Doses Results

Acute Comparative 

Cholinesterase 

Assay

48779401 (2012)

0, 0.1, 0.3, 0.6, or 0.9 

mg/kg

NOAEL for RBC cholinesterase inhibition=0.1 

mg/kg

LOAEL for RBC cholinesterase inhibition=0.3 

mg/kg

NOAEL for brain cholinesterase inhibition = 0.1 

mg/kg

LOAEL for brain cholinesterase inhibition = 0.3 

mg/kg

Appendix B. Summary of OPP’s Cholinesterase Policy & Use of BMD Modeling

OPP’s cholinesterase (ChE) policy (USEPA, 200018) describes the manner in which ChE data are 

used in human health risk assessment. The following text provides a brief summary of that 

document to provide context to points of departure selected. 

AChE inhibition can be inhibited in the central or peripheral nervous tissue. Measurements of 

AChE or ChE inhibition in peripheral tissues (e.g., liver, diaphragm, heart, lung, etc.) are rare. 

As such, experimental laboratory studies generally measure brain (central) and blood (plasma 

and RBC) ChE. Blood measures do not represent the target tissue, per se, but are instead used as 

surrogate measures for peripheral toxicity in studies with laboratory animals or for peripheral 

and/or central toxicity in humans. In addition, RBC measures represent AChE, whereas plasma 

measures are predominately butyryl-ChE (BuChE). Thus, RBC AChE data may provide a better 

representation of the inhibition in target tissues. As part of the dose response assessment, 

evaluations of neurobehavior and clinical signs are performed to consider the dose response 

linkage between AChE inhibition and apical outcomes.

Refinements to OPP’s use of ChE data have come in the implementation of BMD approaches in 

dose response assessment. Beginning with the OP CRA, OPP has increased its use of BMD 

modeling to derive PODs for AChE inhibiting compounds. Most often the decreasing 

exponential empirical model has been used. 

OPP does have not a defined BMR for OPs. However, the 10% level has been used in the 

majority of dose response analyses conducted to date. This 10% level represents a 10% 

reduction in AChE activity (i.e., inhibition) compared to background (i.e., controls). 

Specifically, the BMD10 is the estimated dose where ChE is inhibited by 10% compared to 

background. The BMDL10 is the lower confidence bound on the BMD10. 

 

18 USEPA (2000) Office of Pesticide Programs, US Environmental Protection Agency, Washington DC 20460. 

August 18, 2000 Office of Pesticide Programs Science Policy of The Use of Data on Cholinesterase Inhibition

for Risk Assessments of Organophosphorous and Carbamate Pesticides.
Dimethoate Human Health Risk Assessment DP No. D416010

Page 86 of 104

The use of the 10% BMR is derived from a combination of statistical and biological 

considerations. A power analysis was conducted by ORD on over 100 brain AChE datasets 

across more than 25 OPs as part of the OP CRA (USEPA, 2002). This analysis demonstrated 

that 10% is a level that can be reliably measured in the majority of rat toxicity studies. In 

addition, the 10% level is generally at or near the limit of sensitivity for discerning a statistically 

significant decrease in ChE activity in the brain compartment and is a response level close to the 

background brain ChE level. With respect to biological considerations, a change in 10% brain 

AChE inhibition is protective for downstream clinical signs and apical neurotoxic outcomes. 

With respect to RBC AChE inhibition, these data tend to be more variable than brain AChE data. 

OPP begins its BMD analyses using the 10% BMR for RBC AChE inhibition but BMRs up to 

20% could be considered on a case-by-case basis as long as such PODs are protective for brain 

AChE inhibition, potential peripheral inhibition, and clinical signs of neurotoxicity.
Dimethoate Human Health Risk Assessment DP No. D416010

Page 87 of 104

Appendix C. Summary Tables of Benchmark Dose (BMD) Analyses in Rat Toxicity 

Studies

New studies or studies used as points of departure were analyzed using the most recent version 

of EPA’s Benchmark Dose Software (Version 2.4). Results and technical details for these 

analyses can be found in the latest BMD analysis memo (M. Perron; 15-SEP-2015; TXR# 

0057249). All other results were obtained using previous versions of the modeling software and 

reported in previous risk assessments.

Table C.1. Summary of BMD Results Following Acute Exposures to Dimethoate.

Study Age Compartment

Males Females

BMD10

(mg/kg/day)

BMDL10

(mg/kg/day)

BMD10

(mg/kg/day)

BMDL10

(mg/kg/day)

Comparative 

Cholinesterase 

Assay

(MRID 48779401)

Adult Brain 2.52 1.74 2.2 1.3

Offspring (PND11) Brain 1.77 1.47 1.55 0.91

Table C.2. Summary of BMD Results Following Acute Exposures to Omethoate.

Study Age Compartment

Males Females

BMD10

(mg/kg/day)

BMDL10

(mg/kg/day)

BMD10

(mg/kg/day)

BMDL10

(mg/kg/day)

Comparative 

Cholinesterase 

Assay

(MRID 45529702)

Adult Brain 0.15 0.12 0.25 0.20

Offspring (PND11) Brain 0.16 0.14 0.16 0.15

Adult RBC 0.19 0.16 0.22 0.14

Offspring (PND11) RBC 0.13 0.11 0.14 0.13

Acute 

Neurotoxicity 

Study

(MRID 46167701)

Adult Brain 0.26 0.17 0.18 0.11

Table C.3. Summary of BMD Results Following Repeated Exposures to Dimethoate.

Study Age Compartment

Males Females

BMD10

(mg/kg/day)

BMDL10

(mg/kg/day)

BMD10

(mg/kg/day)

BMDL10

(mg/kg/day)

Comparative 

Cholinesterase 

Assay

(MRID 48779401)

Fetal (GD20) Brain N/A N/A 0.89 0.70

Dams (GD20) Brain N/A N/A 0.34 0.28

Offspring (PND4) Brain NF NF NF NF

Offspring (D21) Brain 0.39 0.32 0.54 0.44

Adult (D11) Brain 0.49 0.37 0.37 0.27

28-day Rat Oral 

Toxicity Study 

(MRID 46288001)

Adult Brain 1.0 0.8 0.8a 0.7a

DNT RangeFinding

(MRID 45529701)

Dams (GD20) Brain N/A N/A 0.2 0.2

Fetus (GD20) Brain 1.0 0.3 1.0 0.4

Offspring (PND21) Brain 0.4 0.3 0.5 0.4

Two-generation 

Reproduction 

Toxicity Study 

(MRID 42251501)

Adult

(P generation; day 224) Brain 0.7 0.7 0.3 0.3

Adult

(F1 generation; day 308) Brain 0.4 0.3 0.4 0.3

Two-generation 

Reproduction 

Adult

(P generation; day 205) Brain 0.3 0.2 0.5 0.3
Dimethoate Human Health Risk Assessment DP No. D416010

Page 88 of 104

Table C.3. Summary of BMD Results Following Repeated Exposures to Dimethoate.

Study Age Compartment

Males Females

BMD10

(mg/kg/day)

BMDL10

(mg/kg/day)

BMD10

(mg/kg/day)

BMDL10

(mg/kg/day)

Toxicity Study 

(MRID 46181001)

Adult

(F1 generation; day 218) Brain 0.8 0.4 0.6a 0.5a

One-generation 

Reproduction 

Toxicity Study 

(MRID 46348201)

Adult

(P generation; day 91) Brain 0.4 0.3 0.5 0.4

Adult

(F1 generation; day 42) Brain 0.3a 0.2a 0.4 0.3

Chronic Oral 

Toxicity Study 

(MRID 00164177)

Adult Brain 0.25b 0.22b- -

Dermal Toxicity 

Study (MRID 

44999101)

Adult Brain 31.3 24.8 28.5 20.2

N/A = not applicable; NF = no reliable fit.

a Noted as having a poor model fit.

b Value calculated using both sexes and all time points from the chronic oral toxicity study for the OP CRA (2002, 2006).

Table C.4. Summary of BMD Results Following Repeated Exposures to Omethoate.

Study Age Compartment

Males Females

BMD10

(mg/m3/day)

BMDL10

(mg/m3/day)

BMD10

(mg/m3/day)

BMDL10

(mg/m3/day)

Omethoate 

Inhalation Toxicity 

Study (MRID 

46358601)

Adult Brain 0.51 0.38 1.24 1.05
Dimethoate Human Health Risk Assessment DP No. D416010

Page 89 of 104

Appendix D. Tolerance Summary for Dimethoate

Table D.1. Tolerance Summary for Dimethoate (40 CFR §180.204).

Commodity

Established 

Tolerance 

(ppm)

HEDRecommended 

Tolerance (ppm)

Comments

(a) General.

Alfalfa, forage 2.0 2.0

Alfalfa, hay 2.0 2.0

Alfalfa, seed - 4.0 Recommended in Memo M. Sahafeyan D232849; 

24-MAY-2011

Bean, dry, seed 2.0 2.0

Bean, lima 2.0 2.0 Bean, lima, succulent

Bean, snap, succulent 2.0 2.0

Blueberry1 1.0 1.0

Broccoli 2.0 2.0

Cattle, meat byproducts 0.02 0.10

Recommended in Memo M. Sahafeyan D232849; 

24-MAY-2011

Cauliflower 2.0 2.0

Celery 2.0 2.0

Citrus, dried pulp 5.0 5.0

Corn, field, forage 1.0 1.0

Corn, field, grain 0.1 0.10

Corn, field, stover 1.0 1.0

Corn, pop, grain 0.1 0.10

Corn, pop, stover 1.0 1.0

Corn, sweet, forage 1.0 - Revoke- no registered use on sweet corn

Cotton, undelinted seed 0.1 0.10

Cotton, gin byproducts - 4.0 Recommended in Memo M. Sahafeyan D232849; 

24-MAY-2011

Egg 0.02 -

Revocation recommended in Memo M. Sahafeyan 

D232849; 24-MAY-2011

Endive 2.0 2.0

Fruit, citrus, group 10-10 - 2.0 Crop group tolerance is being established rather 

than individual tolerances

Goat, meat byproducts 0.02 0.10

Recommended in Memo M. Sahafeyan D232849; 

24-MAY-2011

Grapefruit 2.0 -

Delete individual commodities and establish group 

10-10 tolerance

Hog, meat byproducts 0.02 0.10 Recommended in Memo M. Sahafeyan D232849; 

Horse, meat byproducts 0.02 0.10 24-MAY-2011

Kale 2.0 2.0

Lemon 2.0 -

Delete individual commodities and establish group 

10-10 tolerance

Lettuce, leaf 2.0 2.0

Melon 1.0 1.0

Milk 0.002 0.002
Dimethoate Human Health Risk Assessment DP No. D416010

Page 90 of 104

Table D.1. Tolerance Summary for Dimethoate (40 CFR §180.204).

Commodity

Established 

Tolerance 

(ppm)

HEDRecommended 

Tolerance (ppm)

Comments

Mustard greens 2.0 2.0

Orange 2.0 -

Delete individual commodities and establish group 

10-10 tolerance

Pea 2.0 2.0

Pear 2.0 2.0

Pecan 0.1 0.10

Pepper 2.0 2.0

Potato 0.2 0.20

Poultry, meat byproducts 0.02 -

Revocation recommended in Memo M. Sahafeyan 

D232849; 24-MAY-2011

Safflower, seed 0.1 0.10

Sheep, meat byproducts 0.02 0.10

Recommended in Memo M. Sahafeyan D232849; 

24-MAY-2011

Sorghum, grain, forage 0.1 0.10

Sorghum, grain, grain 0.1 0.10

Sorghum, grain, stover 0.1 0.10

Soybean, forage 2.0 2.0

Soybean, hay 2.0 2.0

Soybean, seed 0.05 0.05

Swiss chard 2.0 2.0

Tangerine 2.0 -

Delete individual commodities and establish group 

10-10 tolerance

Tomato 2.0 2.0

Turnip, roots 0.2 0.20

Turnip, tops 2.0 2.0

Wheat, grain 0.04 0.05 Harmonize with Codex MRL

Wheat, hay 2.0 2.0

Wheat, straw 2.0 2.0

Wheat, forage 2.0 2.0

(c) Tolerances with regional registrations.

Asparagus 0.15 0.15

Brussels sprouts 5.0 5.0

Cherry, sweet 2.0 2.0

Cherry, tart 2.0 2.0

Grass, forage - 0.05 Recommended in Memo M. Sahafeyan D239886; 

Grass, hay - 0.05 12-NOV-2013

1 There are no U.S. registrations as of August 16, 1996.
Dimethoate Human Health Risk Assessment DP No. D416010

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Appendix E. Physical/Chemical Properties

Table E.1. Physical/Chemical Properties of Dimethoate.

Parameter Value Reference

Molecular Weight 229.25 g mol

pH 3.39 MRID# 48696601

Water solubility (25°C) 39.8 g/L MRID# 48696601

Solvent solubility (25°C)

140 g/100 mL acetone

140 g/100 mL acetonitrile

120 g/100 mL cyclohexanone

0.043 g/100 mL dodecane

150 g/100 mL ethanol

120 g/100 mL ethyl acetate

0.030 g/100 mL hexane

120 g/100 mL 2-propanol

160 g/100 mL methanol

150 g/100 mL dichloromethane

52 g/100 mL 1-octanol

100 g/100 mL toluene

31 g/100 mL xylenes

120 g/100 mL 1,2-dichloroethane

0.024 g/100 mL n-heptane

http://www.fao.org/fileadmin/templ

ates/agphome/documents/Pests_Pest

icides/JMPR/Evaluation98/dimetho.

PDF

Vapor pressure (25°C) 1.85 x 10-6 mPa MRID# 48696601

Octanol/water partition coefficient, 

log KOW

0.70 MRID# 48696601

UV/Vis absorption

The mean molar absorption coefficient 

and mean bandwidth for pH 7.10 (at 

203.0 ± 0.0 nm) were determined to 

be 7661 L/mol-cm and 16.5 nm.

MRID# 47622901
Dimethoate Human Health Risk Assessment DP No. D416010

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Appendix F. Use Summary for Dimethoate

Table F.1. Summary of Registered Labels for Dimethoate.

Product Name/Formulation Registration No

Gowan Dimethoate E267 10163-56

Drexel Dimethoate 4EC 19713-231

Drexel Dimethoate 2.67 19713-232

Dimethoate 400 34704-207

Dimethoate 2.67 EC 34704-489

Dimethoate 4E 66330-223

Dimethoate 25 WP 66330-237

Dimethoate 2.67 EC 66330-244

Cymate 267 66330-245

Dimethoate 400 67760-118

Dimethoate 4E 67760-44

Agrisolutions Dimate 4E 9779-273

Clean Crop Dimethoate 400 CA970003

Dimethoate 4E ID110008

Dimethoate 400 ID120004

Clean Crop Dimethoate 400 ID980006

Dimethoate 400 OR050019
Dimethoate Human Health Risk Assessment DP No. D416010

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Table F.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Applic.Rate

Max 

Seasonal 

Applic. Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Agricultural 

uncultivated areas 

(Noncropland 

adjacent to 

vineyards)

Groundboom/

Handgun 

application

Liquid

2 lb ai/A

0.0025 lb ai/gal 

(Mech HG)

NS NS 2 per year NS NS

Alfalfa (field and 

seed crop)

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 0.5 lb ai/A NS

30

1 per crop 

cycle or 

cutting; 3 

per year

48 hours 10

Asparagus

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 1 lb ai/A NS

14 2 48 hours 180

Beans (fresh, snap, 

lima, dry, not 

cowpeas)

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A NS

14 2 48 hours

NS

0

2

Broccoli, 

Cauliflower

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1.5 lb ai/A 7 3

48 hours; increased to 72 hours 

in outdoor areas where the 

average annual rainfall is less 

than 25 inches per year.

7

Brussel sprouts

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/Aa 1.5 lb ai/A 7 3

48 hours; increased to 72 hours 

in outdoor areas where the 

average annual rainfall is less 

than 25 inches per year.

10

Celery

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 1.5 lb ai/A 7 3 48 hours 7

Cherries (preharvest 

and postharvest)

Aerial, Airblast, 

Chemigation Liquid 1.33 lb ai/A 1.33 lb ai/A NS NS

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per year.

21b

Christmas tree 

nurseries

Aerial, Airblast, 

Chemigation, 

Handheld; Soil 

injectors (some 

labels restrict aerial 

and chemigation)

Liquid

1 lb ai/A

0.025 lb ai/gal

0.0025 lb ai/gal 

(Mech HG)

3 lb ai/A 14 3

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per year

NA
Dimethoate Human Health Risk Assessment DP No. D416010

Page 94 of 104

Table F.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Applic.Rate

Max 

Seasonal 

Applic. Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Citrus - non-bearing 

and nursery stock

Aerial, Airblast, 

Chemigation, 

Handheld (some 

labels restrict aerial 

and chemigation)

Liquid

1 lb ai/A

foliar spray: 0.005 

lb ai/gal

0.0025 lb ai/gal 

(Mech.HG)

soil drench: 2 lb 

ai/A

1 lb ai/A NS NS

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per year

NA

Citrus (grapefruit, 

kumquat, lemons, 

limes, oranges 

pummelo, tangelo, 

and tangerines)

Aerial, Airblast, 

Chemigation, 

Handheld (some 

labels restrict aerial 

and chemigation)

Liquid 1 lb ai/A 1 lb ai/A NS

NS

no more than 

2 apps to 

mature fruit

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per year

15-45 

(depending 

on pest)

Corn (field and 

popcorn)

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 0.5 lb ai/A NS NS

3

48 hours; 4 days for detasseling 

tasks in non-arid areas and 15 

days in outdoor areas where the 

average annual rainfall is less 

than 25 inches per year.

14c

14 (forage)

14 (grain)

28 (grain)

28 (forage)

42 (grain)

Cotton

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A

14

14 when 

water is 

used for 

dilution; 

40 when 

once 

refined 

vegetable 

oil is used 

for 

dilution.

2 48 hours 14
Dimethoate Human Health Risk Assessment DP No. D416010

Page 95 of 104

Table F.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Applic.Rate

Max 

Seasonal 

Applic. Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Endive, Leaf 

lettuce, Swiss chard

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.25 lb ai/A 0.75 lb ai/A 7 3 48 hours 14

Garbanzo beans

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 1 lb ai/A 14 2 48 hours 0

2

Grass grown for 

seed

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 1 lb ai/A 90 NS 48 hours NS

14

Kale

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid

0.25 lb ai/A

(Label 66330-

244: indicates 1.5 

pt/A = 0.5 lb ai/A)

0.5 lb ai/A 15 2 48 hours 14

Lentils

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A NS

7

2 48 hours

0

2

14

Lupine

Aerial, 

Groundboom, 

Chemigation, 

Handheld 

Liquid

0.5 lb ai/A

0.0025 lb ai/gal 

(Mech HG)

1 lb ai/A 14 2 48 hours 0

Melons

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A NS

7

NS

2

48 hours 3

Mustard greens

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.25 lb ai/A 0.5 lb ai/A 9 2 48 hours 14
Dimethoate Human Health Risk Assessment DP No. D416010

Page 96 of 104

Table F.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Applic.Rate

Max 

Seasonal 

Applic. Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Ornamentals in 

outdoor nurseries 

Aerial, Airblast, 

Chemigation, 

Handheld; Soil 

injectors (some 

labels restrict aerial 

and chemigation)

Liquid

4.15 lb ai/A 

(airblast)

1 lb ai/A

0.08 lb ai/gal

0.0025 lb ai/gal 

(Mech.HG)

soil drench: 0.06 

lb ai/gal and 5.5 

lb ai/A

soil injection: 

0.004 lb ai/inch of 

tree 

circumference

4.15 lb ai/A 

(airblast 

only)

3 lb ai/A

14 3

woody ornamentals: 10 days; 

increased to 14 days in outdoor 

areas where the average annual 

rainfall is less than 25 inches per 

year

herbaceous ornamentals: 48 

hours

conifer seed orchards: 48 hours 

(16 days if airblast >1 lb ai/A); 

increased to 4 days (25 days if 

airblast >1 lb ai/A) in outdoor 

areas where the average annual 

rainfall is less than 25 inches per 

year 

NA

Ornamentals in 

outdoor nurseries 

(trees grown for 

pulp -- forestry)

Aerial, Airblast, 

Chemigation, 

Handheld; Soil 

injectors 

Liquid

2 lb ai/A

0.04 lb ai/gal

0.0025 lb ai/gal 

(Mech HG)

soil injection: 

0.0025 lb ai/inch 

tree 

circumference

6 lb ai/A NS 3

14 days; increased to 24 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per year.

NA

Pears (including 

non-bearing and 

nursery stock)

Aerial, Airblast, 

Chemigation, 

Handheld (some 

labels restrict 

chemigation)

Liquid

1 lb ai/A

0.005 lb ai/gal; 

0.0025 lb ai/gal 

(Mech HG)

1 lb ai/A NS NS

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per year

28

Aerial, Airblast WSB 1 lb ai/A 1 lb ai/A
Dimethoate Human Health Risk Assessment DP No. D416010

Page 97 of 104

Table F.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Applic.Rate

Max 

Seasonal 

Applic. Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Peas

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.16 lb ai/A 0.16 lb ai/A NS

7

NS 48 hours 0

2

Peas (dry; some 

labels limit to those 

in ID, OR and WA 

only)

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid

0.33 lb ai/A

0.5 lb ai/A 

(allowed on SLN)

0.5 lb ai/A NS

7

NS

3

d 48 hours 0

5-14d

Peas (succulent; 

some labels limit to 

those in ID, OR and 

WA only)

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid

0.33 lb ai/A

0.5 lb ai/A 

(allowed on SLN)

0.5 lb ai/A

NS

7

14

NS

3

e 48 hours NS

5-14e

Pecans

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.33 lb ai/A 0.33 lb ai/A NS NS 48 hours 21

Peppers

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.33 lb ai/A 1.65 lb ai/A 7 5 48 hours

NS

0

2

f

Potatoes

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid

0.5 lb ai/A 1 lb ai/A 7 2 48 hours

NS

0

2

g

Aerial, 

Groundboom WSB

Safflower

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 0.5 lb ai/A NS

14

NS

1

2 at lower 

rateh

48 hours 14h

Sorghum

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial

and chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A 7 2 48 hours 28
Dimethoate Human Health Risk Assessment DP No. D416010

Page 98 of 104

Table F.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Applic.Rate

Max 

Seasonal 

Applic. Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Soybeans

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A 7 2 48 hours 21

28i

Tomatoes

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A 6 2 48 hours 7

Turnip

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.25 lb ai/A 1.75 lb ai/A 3 7 48 hours 14

Watermelon

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A 7 2 48 hours 3

Wheat

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 0.5 lb ai/A NS 2 (at lower 

rates) 48 hours

35

45

60

a. Label 67760-118: directions state max of 0.5 lb ai/A, but also indicate 38.2 fl oz/A = 1 lb ai/A.

b. Label 66330-223 lists the PHI as 21 days; but then also says interval b/t last app and harvest is 28 days.

c. Labels listed various PHIs; not clear if which are correct.

d. Max # apps and PHI listed on SLN.

e. Max of 3 apps listed on label 67760-118; PHI listed on SLNs.

f. Labels 66330-244 and 66330-245 list PHI of 2 days.

g. Labels 66330-244 and 66330-245 list PHI of 2 days.

h. A couple of labels (e.g., 34704-489) list RTI of 14 days and no more than two apps.

i. One label (67760-118) listed a longer PHI.
Dimethoate Human Health Risk Assessment DP No. D416010

Page 99 of 104

Appendix G. International Residue Limits

(035001; 09/29/14)

Table G.1. Summary of U.S. Tolerances and International MRLs. 

U.S. Canada Mexico1 Codex2

Residue Definition:

40CFR180.204

(a) General. Tolerances are established for 

total residues of the insecticide dimethoate 

(O,O-dimethyl S-(Nmethylcarbamoylmethyl) 

phosphorodithioate) including its oxygen 

analog (O,O-dimethyl S-(Nmethylcarbamoylmethyl) phosphorothioate) 

O,O-dimethyl S-(Nmethylcarbamoylmethyl)

phosphorodithioate, including 

the metabolite

omethoate

Dimethoate

Commodity Tolerance (ppm)/Maximum Residue Limit (mg/kg)

Commodity U.S. Canada Mexico1 Codex2

Alfalfa, forage 2.0

Alfalfa, hay 2.0

Bean, dry, seed 2.0

Bean, lima 2.0 1 beans

Bean, snap, succulent 2.0

Blueberry3 1.0 1

Broccoli 2.0 2

Cattle, meat byproducts 0.02 0.05 (*)

Cauliflower 2.0 2 0.2

Celery 2.0 1 0.5

Citrus, dried pulp 5.0

Corn, field, forage 1.0

Corn, field, grain 0.1

Corn, field, stover 1.0

Corn, pop, grain 0.1

Corn, pop, stover 1.0

Corn, sweet, forage 1.0

Cotton, undelinted seed 0.1

Egg 0.02 0.05 (*)

Endive 2.0

Goat, meat byproducts 0.02

Grapefruit 2.0 1.5 citrus fruits 5 citrus fruits (excluding 

kumquats)

Hog, meat byproducts 0.02

Horse, meat byproducts 0.02

Kale 2.0 2

Lemon 2.0 1.5 citrus fruits 5 citrus fruits (excluding 

kumquats)

Lettuce, leaf 2.0 2 lettuce

Melon 1.0

Milk 0.002 0.05 (*) milk of cattle, 

goats and sheep

Mustard greens 2.0

Orange 2.0 1.5 citrus fruits 5 citrus fruits

Pea 2.0 0.5

1 peas (pods and 

succulent=immature 

seeds)
Dimethoate Human Health Risk Assessment DP No. D416010

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Table G.1. Summary of U.S. Tolerances and International MRLs. 

U.S. Canada Mexico1 Codex2

Pear 2.0 2 1

Pecan 0.1

Pepper 2.0 0.5

3 peppers Chili, dried

0.5 peppers, sweet 

(including pimento or 

pimiento)

Potato 0.2 0.05

Poultry, meat byproducts 0.02 0.05 (*)

Safflower, seed 0.1

Sheep, meat byproducts 0.02 0.05 (*)

Sorghum, grain, forage 0.1

Sorghum, grain, grain 0.1

Sorghum, grain, stover 0.1

Soybean, forage 2.0

Soybean, hay 2.0

Soybean, seed 0.05

Swiss chard 2.0 2

Tangerine 2.0 1.5 citrus fruits 5 citrus fruits (excluding 

kumquats)

Tomato 2.0 0.5

Turnip, roots 0.2

Turnip, tops 2.0 2 1 turnip greens

Wheat, forage 2.0

Wheat, grain 0.04 0.05

Wheat, hay 2.0

Wheat, forage 2.0

Wheat, straw 2.0 1 wheat straw and fodder, 

dry

MRLs with NO US Equivalent

Artichoke, globe 0.05

Barley 2

Cabbage, savoy 2 cabbages 0.05 (*)

Lettuce, head 0.3

Mammalian fats (except milk 

fats) 0.05 (*)

Mango 1 Po

Meat of cattle, goats, horses, 

pigs and sheep 0.05 (*)

Olives 0.5

Poultry, fats 0.05 (*)

Poultry, meat 0.05 (*)

Spices, fruits and berries 0.5

Spices, roots and rhizomes 0.1 (*)

Spices, seeds 5

Sugar beet 0.05

Turnip, garden

Apples 2

Garden beet tops 2

Spinach 2

Strawberries 1

Sunflower seeds 0.1

Completed by: M. Negussie; 10/06/14

1 Mexico defers to US tolerances and/or Codex MRLs for its export purposes. 
Dimethoate Human Health Risk Assessment DP No. D416010

Page 101 of 104

2

(*) = absent at the limit of quantitation. Po = postharvest treatment, such as treatment of stored grains.

3 There are no U.S. registrations as of August 16, 1996.

(c) Tolerances with regional registrations. Tolerances with regional registration, as defined in §180.1(l), are 

established for total residues of dimethoate including its oxygen analog in or on the following food commodities:

Commodity US Canada Mexico1 Codex2

Asparagus 0.15 0.05 (*)

Brussels sprouts 5.0 0.2

Cherry, sweet 2.0 2 cherries 2 cherries Cherry, tart 2.0
Dimethoate Human Health Risk Assessment DP No. D416010

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Appendix H – Summary of Surface Water EDWCs using Maximum and Typical 

Application Rates

Table H.1. Dimethoate EDWCs (μg/L) for Dimethoate Uses in the U.S. Corrected for National PCA, Using Maximum 

Application Rates.

PRZM Scenario 

(bold font)/ Uses 

Represented

App 

Method

Date of 

First 

Application

(DD-MM)

App Rate

kg ai/A 

(lb ai/A)

No. of 

Apps.

App. 

Interval 

(days)

Natl. 

PCA

EDWCs (μg/L)1

Acute Chronic Cancer/ 

Chronic

01_CA wine 

grapes/

Agricultural 

uncultivated areas 

(CA only)

(Noncropland 

adjacent to 

vineyards)

Groundboom, 

handgun 

app.

15-02 2.13 (1.9) 2 180 0.91 24.7 3.26 1.74

03_MN alfalfa/

Alfalfa, Sainfoin Aerial 20-05 0.560 (0.5)

1/CC

3/year 30 0.91 11.0 1.32 0.928

04_CA cole crops/

Broccoli, 

Cauliflower; 

Additionally, 

Brussels sprouts 

(aerial, some labels 

allow use only in 

CA)

Aerial 25-01 0.560 

(0.5) 3 7 0.91 27.3 3.49 1.90

05_CA cole crops/

Brussels sprouts 

(ground)

Ground 18-01 0.841 

(0.75) 2 7 0.91 43.9 5.66 1.88

06_CA row crops/

Celery Aerial 05-03 0.560 (0.5) 3 7 0.91 7.37 1.00 0.606

07_FL cabbage/

Turnip (greens) Aerial 15-01 0.281 (0.251) 7 3 0.91 17.5 1.52 0.983

08_CA potato/

Turnip (roots) Aerial 01-05 0.281 (0.251) 7 3 0.91 9.19 0.974 0.814

09_WA orchards/

Cherry (only in ID, 

MT, OR, UT and 

WA)

Aerial 15-10 (preharvest)

1.51 

(1.35) 1 N/A 0.91 6.77 1.06 1.00

10_WA orchards/

Cherry (only in ID, 

MT, OR, UT and 

WA)

Aerial 15-11 (postharvest)

1.51 

(1.35) 1 N/A 0.91 6.77 1.16 1.09

10b_WA 

orchards/ Cherry 

(only in ID, MT, 

OR, UT and WA)

Ground 15-11 (postharvest)

1.51 

(1.35) 1 N/A 0.91 3.31 0.586 0.539

20_FL peppers/

Peppers Aerial 20-10 0.377 (0.336) 5 7 0.91 40.0 2.52 1.21

21_FL peppers/

Peppers Ground 20-10 0.377 (0.336) 5 7 0.91 39.8 2.39 1.03

22_MI beans/ 

Beans (includes dry 

beans, excludes 

cowpeas), 

Garbanzos 

(includes chick 

peas), Lupine

Aerial 20-07 0.560 

(0.5) 2 14 0.91 8.90 0.847 0.578

23_MS Cotton/ 

Cotton Aerial 20-07 0.560 (0.5) 2 14 0.91 13.8 0.865 0.480

24_PA Tomato/ 

Tomato Aerial 20-09 0.560 (0.5) 2 6 0.91 18.1 1.77 0.919
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Table H.1. Dimethoate EDWCs (μg/L) for Dimethoate Uses in the U.S. Corrected for National PCA, Using Maximum 

Application Rates.

PRZM Scenario 

(bold font)/ Uses 

Represented

App 

Method

Date of 

First 

Application

(DD-MM)

App Rate

kg ai/A 

(lb ai/A)

No. of 

Apps.

App. 

Interval 

(days)

Natl. 

PCA

EDWCs (μg/L)1

Acute Chronic Cancer/ 

Chronic

25_CA citrus/ 

Grapefruit, 

Kumquat, Lemon, 

Lime, Orange, 

Pummelo 

(shaddock), 

Tangelo, Tangerine

Aerial 01-06 1.121 (1) 1 N/A 0.91 5.40 0.389 0.355

26_FL citrus/ 

Same crops as 

above

Aerial 01-06 1.121 (1) 1 N/A 0.91 38.9 1.95 0.659

27_ID potatoes/ 

Potatoes Aerial 20-08 0.560 (0.5) 2 7 0.91 13.7 1.55 1.26

12_OR Xmas 

trees/ Douglas fir 

(seed orchards) 

(only in OR and 

WA)

Airblast 01-06 5.04 (4.5) 1 N/A 1.0 9.46 0.990 0.927

13_CA forestry/

Cottonwood (forest/ 

shelterbelt)

Aerial 01-06 2.24 (2) 3 14 1.0 24.8 3.73 3.68

14_OR Xmas 

trees/ Hybrid 

cottonwood/poplar 

plantations (some 

labels allow use in 

ID, OR and WA)

Aerial 01-06 2.24 (2) 3 10 1.0 26.7 3.40 3.27

15_CA nursery/

Citrus, non-bearing 

and nursery stock 

(only in CA and 

AZ)

Soil 

drench 01-06 2.13 (1.9) 1 N/A 1.0 5.13 0.489 0.462

17_OR nursery/ 

Ornamental woody 

shrubs and vines; 

Ornamental and/or 

shade trees

Aerial 01-06 1.12 (1) 3 14 1.0 20.8 2.44 2.10

18_NJ nursery/

Ornamental 

herbaceous plants2

Soil 

drench 01-06 7.29 (6.5) 1 N/A 1.0 1052

7.662 3.53

Bolded and shaded values are the highest EDWCs.

1 Concentrations are modified using a national PCA, but not using a TAF. Application rates in kg ai/ha (lb ai/A). EDWCs were 

rounded to three significant figures.

2 A maximum rate of 6.5 lb ai/A for this use appears to be a label error; therefore, these results are not considered representative.

Table H.2. Dimethoate EDWCs (μg/L) for Dimethoate Uses in the U.S. Corrected for Regional PCA, Using Typical 

Application Rates and Numbers of Applications1

Scenario (bold 

font)/ Crops/Uses 

Represented

App 

Method

Date of 

First 

Application

(DD-MM)

Aver. 

App Rate

kg ai/A 

(lb ai/A)

Aver. 

Number 

of Apps

App 

Interval 

(days)

Reg. 

PCA

EDWCs (μg/L)1

Acute Chronic Cancer/ 

Chronic

03c_MN alfalfa/

Alfalfa Aerial 20-05 0.409 (0.365) 1 (1.1) N/A 0.91 3.39 0.345 0.178

04b_CA cole 

crops/ Broccoli Aerial 25-01 0.535 (0.477) 1 (1.3) N/A 0.61 8.97 0.988 0.381

22c_MI beans/ 

Dry beans, peas Aerial 20-07 0.405 (0.361) 1 (1.1) N/A 0.81 4.38 0.352 0.162

23c_MS Cotton/ 

Cotton Aerial 20-07 0.307 (0.274) 1 (1.2) N/A 0.86 5.76 0.305 0.107

24b_PA Tomato/ 

Tomato Aerial 20-09 0.498 (0.444) 1 (1.3) N/A 0.34 1.38 0.132 0.0850

26b_FL citrus/ 

Oranges Aerial 01-06 0.546 (0.487) 1 (1.1) N/A 0.41 8.28 0.410 0.129
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Table H.2. Dimethoate EDWCs (μg/L) for Dimethoate Uses in the U.S. Corrected for Regional PCA, Using Typical 

Application Rates and Numbers of Applications1

Scenario (bold 

font)/ Crops/Uses 

Represented

App 

Method

Date of 

First 

Application

(DD-MM)

Aver. 

App Rate

kg ai/A 

(lb ai/A)

Aver. 

Number 

of Apps

App 

Interval 

(days)

Reg. 

PCA

EDWCs (μg/L)1

Acute Chronic Cancer/ 

Chronic

27c_ID potatoes/ 

Potatoes Aerial 20-08 0.369 (0.329) 2 (1.6) 7 0.66 5.99 0.673 0.541

27d_ID potatoes/ 

Potatoes2 Aerial 20-08 0.369 (0.329) 1 (1.6)2 N/A 0.66 3.41 0.345 0.269

28_IL corn/ Corn Aerial 10-09 0.338 

(0.302) 1 (1.1) N/A 0.88 10.1 0.878 0.261

29_KS sorghum/ 

Sorghum Aerial 20-08 0.298 (0.266) 1 (1.0) N/A 0.87 4.23 0.340 0.152

30_MS soybeans/ 

Soybeans Aerial 01-09 0.484 (0.432) 1 (1.0) N/A 0.86 4.37 0.282 0.132

31_OR snap 

beans/ Lima 

beans

Aerial 01-08 0.546 

(0.487) 2 (1.6) 14 0.66 2.26 0.235 0.197

32_ND wheat/ 

Spring wheat Aerial 20-06 0.273 (0.244) 1 (1.0) N/A 0.91 0.956 0.103 0.0811

33_ND wheat/ 

Winter wheat3 Aerial 20-063 0.340 (0.303) 1 (1.0) N/A 0.91 1.18 0.128 0.101

12b_OR Xmas 

trees/ Douglas fir 

(seed orchards) 

(only in OR and 

WA)

Airblast 01-06 1.121 (1) 1 N/A 1.0 2.10 0.220 0.206

13b_CA forestry/

Cottonwood 

(forest/ 

shelterbelt)

Aerial 01-06 1.121 (1) 1 N/A 1.0 3.97 0.452 0.470

14b_OR Xmas 

trees/ Hybrid 

cottonwood/poplar 

plantations (some 

labels allow use in 

ID, OR and WA)

Aerial 01-06 1.121 (1) 1 N/A 1.0 3.97 0.425 0.407

15b_CA nursery/

Citrus, nonbearing and 

nursery stock 

(only in CA and 

AZ)

Soil 

drench 01-06 1.121 (1) 1 N/A 1.0 0.450 0.0429 0.0406

17b_OR nursery/ 

Ornamental 

woody shrubs and 

vines; Ornamental 

and/or shade trees

Aerial 01-06 0.280 

(0.25) 1 N/A 1.0 2.06 0.199 0.147

18b_NJ nursery/

Ornamental 

herbaceous plants

Soil 

drench 01-06 0.272 (0.243) 1 N/A 1.0 3.93 0.286 0.132

Bolded and shaded values are the highest EDWCs.

1 Concentrations are modified using a PCA, but not using a TAF. Application rates in kg ai/ha (lb ai/A). EDWCs were rounded to three 

significant figures.

2 For the ID potato scenario, one and two applications were modeled.

3 The ND wheat scenario is set so that crop occurs in the spring; therefore, the application rate for winter spring was used, but the chemical was 

set to be applied during the spring instead of the winter.

4 For the non-agricultural crops, no typical/average use information was available. EFED made certain assumptions which are described in 

Memo, J. Meléndez, 28-JUL-2014; D415002.