UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM September 17, 2015 

Subject: 

To: 

From: 

Through: 

Registration Review - Preliminary Ecological Risk Assessment for Dimethoate 

(PC Code 035001 ; DP Barcode D421ll7) 

Kelly Ballard, Risk Manager Reviewer 

Neil Anderson, Branch Chief 

Risk Management and Implementation Branch I 

Pesticide Re-evaluation Division (7508P) 

Mah Shamim, Ph.D., Branch Chief 

Environmental Risk Branch 5 ~ 

' qi 18/lb 

Environmental Fate and Effects Division (7507P) 

The Environmental Fate and Effects Division (EFED) has completed the preliminary ecological 

risk assessment of the organophosphate insecticide/acaricide, dimethoate (PC Code 035001). This 

assessment, conducted as prut of the Registration Review, builds on the preliminary problem 

formulation for dimethoate that was completed in 2008 (D355609) and available in the docket 

(EPA-HQ-OPP-2009-0059 in http://www.regulations.gov/#!home). In addition, both open 

literature and studies submitted by the technical registrants in response to data requirements further 

inform this risk assessment. This document therefore provides a synthesis of the environmental 

fate and ecotoxicity information to evaluate potential risk to non-target terrestrial and aquatic 

plants and animals. 

Page 1 of 144 
Page 2 of 144

Preliminary Ecological Risk Assessment in

Support of the Registration Review of Dimethoate

Dimethoate (CAS 60-51-5)

Prepared by:

Hannah Yingling, Biologist

José Meléndez, Chemist

U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch V

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Keith Sappington, Senior Science Advisor

Mah Shamim, Ph.D., Branch Chief

Office of Chemical Safety

and Pollution Prevention
Page 3 of 144

Table of Contents

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

1.0 Problem Formulation ................................................................................................ 6

1.1 Nature of Regulatory Action........................................................................................ 6

1.2 Stressor Source and Distribution ................................................................................. 6

1.3 Stressors of Concern .................................................................................................... 8

1.4 Risk Hypothesis........................................................................................................... 9

2.0 Exposure Characterization ..................................................................................... 10

2.1 Use and Usage Information ....................................................................................... 10

2.2 Environmental Fate and Transport............................................................................. 16

2.3 Aquatic Exposure Modeling Approach ..................................................................... 23

2.4 Monitoring ................................................................................................................. 31

2.5 Terrestrial Exposure Modeling .................................................................................. 33

3.0 Ecological Toxicity................................................................................................... 41

3.1 Aquatic Organisms..................................................................................................... 41

3.2 Terrestrial Organisms................................................................................................. 43

3.3 Degradate toxicity...................................................................................................... 46

3.4 Incident data............................................................................................................... 50

4.0 Risk Characterization.............................................................................................. 52

4.1 Risk Estimation for Aquatic Organisms.................................................................... 54

4.2 Terrestrial Organisms................................................................................................. 60

4.3 Risk Description......................................................................................................... 75

4.4 Characterization of Omethoate .................................................................................. 84

4.5 Endangered species.................................................................................................... 85

4.6 Uncertainties, Limitations, and Identification of Data Gaps ..................................... 86

5.0 References................................................................................................................. 93

Appendix A. Fate Bibliography. .......................................................................................... 96

Appendix B. Eco Bibliography .......................................................................................... 101

Appendix C. Dimethoate and its transformation products................................................. 118

Appendix D. Sample SWCC Output File........................................................................... 120

Appendix E. T-REX example output ................................................................................. 123

Appendix F. Example STIR Output................................................................................. 126

Appendix G. Example SIP Output ..................................................................................... 127

Appendix H. Terrplant example output.............................................................................. 128

Appendix I. Classifications of Environmental Fate Studies............................................... 129

Appendix J. Reviewed studies submitted in support of PRA............................................. 131

Appendix K. Incident Summaries...................................................................................... 133

Appendix L. ECOTOX Selected Articles of Interest......................................................... 143
Page 4 of 144

Executive Summary

Dimethoate is an insecticide/acaricide belonging to the organophosphate (OP) class of pesticides 

which act through inhibition of acetylcholinesterase leading to neurological effects in sensitive 

taxa. The compound is used on a variety of agricultural crops including alfalfa, broccoli, corn, 

cotton, dry beans/peas, oranges, potatoes, soybeans, tomatoes, and wheat. While primarily 

applied as a foliar spray, soil and bark drenches are registered as well. Dimethoate is 

characterized as a highly mobile, generally non-persistent organophosphate insecticide. The 

primary route of dissipation is microbially-mediated degradation in aerobic soil. Consistent with 

laboratory-based degradation studies, terrestrial dissipation studies indicate that dimethoate 

rapidly dissipates from soil and foliar surfaces. Although not observed in environmental fate 

laboratory studies, the degradate omethoate was detected in soils of terrestrial field dissipation 

studies as well as monitoring studies in multiple environmental compartments. Given that 

omethoate acts through the same mode of action as the parent compound and depending on the 

species tested, can be as toxic if not more toxic than the parent compound, it is considered a 

residue of concern. Neither the parent nor its omethoate transformation product are expected to 

bioaccumulate.

Dimethoate is moderately toxic to fish (and to aquatic-phase amphibians for which fish serve as 

surrogates) and is highly toxic to aquatic invertebrates on an acute exposure basis. The 

compound is moderately to very highly toxic to birds (and to terrestrial-phase amphibians and 

reptiles for which birds serve as surrogates) and moderately toxic to mammals on an acute 

exposure basis. The compound is highly toxic to beneficial insects such as bees on an acute oral 

and contact exposure basis.

Table 1 provides a summary of the environmental risk conclusions for aquatic and terrestrial 

organisms based on risk quotient (RQ) values and whether they exceed levels of concern (LOCs) 

for Federally-listed threatened and endangered species (hereafter refers to as listed species) and 

non-listed species.

Table 1. Summary of Ecological Risk Conclusions for the Proposed Dimethoate Uses

Taxonomic Group Summarized Risk Characterization and Major Uncertainties

Fish and Aquatic 

Invertebrates (freshwater 

and estuarine/marine)

(plus aquatic-phase 

amphibians for which fish 

serve as surrogates)

The potential for acute or chronic risk to freshwater and 

estuarine/marine fish is considered low, as acute or chronic RQ 

values do no exceed the risk to listed species LOC of 0.05.

A potential for acute and chronic risk to freshwater and 

estuarine/marine invertebrates is identified. Specifically, there are 

LOC exceedances across all dimethoate application scenarios for the 

listed species LOC of 0.05 for acute risk and 1.0 for chronic risk. 

The chronic risk findings are uncertain because they are based on 

chronic values derived using acute-to-chronic ratios in the absence of

dimethoate-specific chronic toxicity data for invertebrates.

Aquatic and Terrestrial 

Plants

The potential for risk to aquatic and terrestrial plants is considered 

low, as RQ values do not exceed the LOC values for risk to listed 

and non-listed aquatic or terrestrial plants.
Page 5 of 144

Table 1. Summary of Ecological Risk Conclusions for the Proposed Dimethoate Uses

Taxonomic Group Summarized Risk Characterization and Major Uncertainties

Birds (plus terrestrial-phase 

amphibians and reptiles for 

which birds serve as 

surrogates) 

There is a potential for acute and chronic risk to birds, reptiles and 

terrestrial-phase amphibians. Specifically, acute dose-based RQ 

values exceed the risk to listed species LOC of 0.1 for at least one 

avian dietary forage category and size class across all uses. Acute 

and chronic diet-based RQs also exceed the risk to listed species 

LOC of 0.1 for at least one avian dietary class across all uses.

Mammals There is a potential for acute and chronic risk to mammals. RQ 

values exceed the chronic risk LOC by several orders of magnitude. 

Bees Tier 1 Risk Assessment. Based on Tier 1 acute contact and acute 

oral risk assessment of adult honey bees, RQ values exceed the acute 

risk LOC. Based on information on dimethoate toxicity to individual 

bee larvae, Tier 1 risks to larval bees are also indicated, primarily for 

the non-food uses. It is noted, however, that label requirements 

preclude application of dimethoate when bees are actively foraging

(an assumption of Tier 1 risk assessment), thus mitigating acute 

contact risks for bees foraging in the treated site. Because dimethoate 

undergoes systemic transport in plants, applications prior to bloom 

could result in exposure of bees via oral routes. 

Tier 2 Risk Assessment. No tier 2 (semi-field) studies were 

submitted for dimethoate. However, its use as a reference toxicant at 

0.53 lb a.i./A suggest that at least short term risks to bees are 

possible as a result of foliar spray applications (even residues are 

allowed to dry prior to bees foraging). Information reviewed on the 

potential for long-term effects of dimethoate on brood development 

was considered inconclusive.

Tier 3 Risk Assessment. A tier 3 full-field study with free foraging 

bees indicates high mortality and reduced foraging of adult bees 

shortly after exposure to dried residues on blooming foliage. 

Mortality rates and foraging activity appeared to recover to levels 

similar to controls within 3 to 4 days. However, effects on 

developing brood were only qualitatively assessed in this study. 

Therefore, the potential for long-term exposure and effects could not 

be assessed due to limitations in available data. 
Page 6 of 144

1.0 Problem Formulation

As part of the Registration Review process, a detailed Problem Formulation (DP Barcode 

D355609) for this risk assessment was published to the docket [Docket ID: EPA-HQ-OPP-2009-

0059] in December 3, 2008. The following section summarizes some of the key points of that 

document and discusses any differences between the analysis outlined previously and the 

analysis conducted in this risk assessment.

1.1 Nature of Regulatory Action

This risk assessment is conducted as part of the Agency’s Registration Review process for 

pesticide active ingredients. The Registration Review process was established under the Food 

Quality Protection Act (FQPA 1996).

1.2 Stressor Source and Distribution

1.2.1 Mechanism of Action

Dimethoate [O,O-dimethyl S-(N-methylcarbamoyl methyl)phosphorodithioate; CAS No. 60-51-

5; PC Code 035001], is an insecticide/acaricide belonging to the organophosphate (OP) class of 

pesticides. The pesticide acts through inhibition of acetylcholinesterase (AChE) a choline 

hydrolase. According to Fukuto 1990 AChE is responsible for the rapid hydrolytic degradation 

of the neurotransmitter acetylcholine into the inactive products choline and acetic acid. 

Acetylcholine is one of a number of physiologically important neurotransmiters and is involved 

in the transmission of nerve impulses to effector cells at cholinergic, synaptic, and 

neuromuscular junctions. When AChE is inactivated, the enzyme is no longer able to hydrolyze 

acetylcholine and concentrations of neurotransmitter in the junction remains high resulting in 

continuous stimulation of the muscle or nerve fiber, resulting eventually in exhaustion and 

tetany.

As indicated in the Problem Formulation document, as a phosphorodithioate organophosphate, 

the chemical is subject to bioactivation into its oxon form (omethoate) similar to other members 

of this class. Omethoate was not observed in any of the environmental fate laboratory studies, 

with the exception of a special study to evaluate the effects of chlorination treatment of water; 

however, omethoate was observed in the soils of the terrestrial field dissipation studies. 

Omethoate has the same mode of action as the parent compound. The rate at which a 

phosphorodithioate pesticide is transformed to its oxon and the rate at which the oxon is 

subsequently detoxified can influence toxicity. According to labels for dimethoate, the 

compound “has systemic and contact activity against a broad spectrum of piercing, sucking and 

chewing insects.”

1.2.2 Use Characterization

Currently, dimethoate is used for control of a variety of insect pests on a number of fruit, 

vegetable, grain, and field crops, as well as ornamentals and non-cropland adjacent to 
Page 7 of 144

agricultural fields.

The pesticide is primarily applied as a foliar spray (using aerial or ground application methods); 

however, soil and bark drench uses are registered. Dimethoate is applied in liquid formulations 

(emulsifiable concentrate, wettable powder or soluble concentrate (liquid)) aerially or by ground 

methods of applications. Dimethoate also has uses on certain trees (e.g., Douglas fir, 

cottonwood, etc.). Methods of application include ground, aerial and chemigation. Air blast

applications are allowed on Douglas fir (seed orchard).

According to the labels, dimethoate is a IRAC1 Mode of Action Classification Group 1 (AChE 

inhibitors, subgroup B (organophosphates) of the insecticide/miticide, to which target pests can 

develop cross-resistance when applied with other chemicals within the subgroup consecutively 

or repeatedly in the same field and/or in consecutive years. For that reason, it is recommended to 

avoid its consecutive use and/or the consecutive use of other group 1B insecticides and to base 

its use on a comprehensive Integrated Pest Management (IPM) program (for example, refer to 

the label for Dimethoate 4EC).

1.2.3 Exposure

Terrestrial wildlife exposure estimates are typically calculated for birds and mammals by 

emphasizing the dietary exposure route of uptake of pesticide active ingredients. These 

exposures are considered to be surrogates for exposures to terrestrial-phase amphibians and 

reptiles. For exposures to terrestrial organisms, such as birds and mammals, pesticide residues on 

food items are estimated based on the assumption that organisms are exposed to pesticide 

residues as a function of the pesticide use pattern. However, other pathways of exposure may 

also be important to consider, including the inhalation and drinking water pathways. 

Subsequent to the publication of the dimethoate preliminary Problem Formulation and issuance 

of generic data call-in (DCI2

), EFED developed exposure pathway screening models for 

inhalation and drinking water which address the potential relevance of these exposure pathways 

to birds. The Screening Tool for Inhalation Risk (STIR; version 1.0) and Screening Imbibition 

Program (SIP3; version 1.0) evaluate these two pathways of exposure4.

The STIR model was used to calculate an upper-bound estimate of exposure using dimethoate’s 

vapor pressure and molecular weight for vapor phase exposure as well as the maximum 

application rate and method of application for spray drift. STIR incorporates results from several 

 1 IRAC. 2014. Insect Resistance Action Committee (IRAC) MoA Classification Scheme. Prepared by IRAC 

International MoA Working Group. Version 7.3. Issued February 2103. Available on line at: http://www.iraconline.org/documents/moa-classification/?ext=pdf 2 USEPA. 2010. Dimethoate Generic Data Call In (GDCI-035001-874). 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2009-0059-0022 3 USEPA. 2014. Pesticides: Science and Policy. Terrestrial Models. STIR Version 1.0 (Screening Tool for 

Inhalation Risk). http://www.epa.gov/oppefed1/models/terrestrial/#stir 4 USEPA. 2014. Pesticides: Science and Policy. Terrestrial Models. SIP Version 1.0 (Screening Imbibition 

Program). http://www.epa.gov/oppefed1/models/terrestrial/#sip
Page 8 of 144

toxicity studies including acute oral and inhalation rat toxicity endpoints obtained from the “sixpack” of core studies, which are a series of six guideline studies of mammals (including acute 

oral, acute inhalation, acute dermal contact, and others) that are submitted to the Registration 

Division of the Office of Pesticide Programs for technical and formulated products of a pesticide 

(rat oral LD50 = 358 mg/kg bw, MRID 00164219; and rat inhalation LC50 > 2 mg/L, MRID 

00060719, respectively) as well as the most sensitive acute oral avian toxicity endpoint, i.e., red 

wing blackbird (Agelaius phoeniceus) 5 with a median lethal dose for 50% of the birds tested 

(LD50)of 5.4 mg/kg bw (MRID 00020560). Based on the results of the STIR model (Appendix 

4), exposure through inhalation of spray drift of the vapor phase of dimethoate was determined to 

be a potential pathway of concern for all application rates above 0.19 lb a.i./A for avian species 

on an acute exposure basis for ground sprays. 

Another run of STIR was used to evaluate the potential exposure via volatilization of the 

transformation product omethoate, which is also considered by EFED to be of toxicological 

relevance to birds and mammals. Toxicity for omethoate to mammals are available (rat oral 

LD50 = 22 mg/kg bw, MRID 46099809; and rat inhalation LC50 = 0.267 mg/L, MRID 46099813, 

respectively) as well as the most sensitive acute oral avian toxicity endpoint, i.e., bobwhite quail, 

(Colinus virginianus of LD50 = 9.6 mg/kg bw (MRID 47769703). Based on the results from the 

STIR model for vapor-phase exposure (Appendix 4), inhalation of the vapor phase of omethoate 

is not a potential pathway of concern for avian species on an acute exposure basis. 

The inhalation pathway via spray drift of the pesticide is of potential significance to avian taxa 

for parent dimethoate alone. It is noted however, that this result was indicated for all uses except 

for succulent peas and other unspecified peas.

Drinking water was also screened as an exposure route using SIP; the screening toolwas used to 

calculate an upper-bound estimate of exposure based on dimethoate’s solubility (39,800 mg/L), 

the most sensitive acute and chronic avian toxicity endpoints, i.e., blackbirds acute oral LD50 of 

5.4 mg/kg bw and a bobwhite quail chronic no observed effect concentration (NOAEC) of 4.0 

mg/kg diet, respectively, and the most sensitive acute oral (LD50=358 mg/kg bw) and chronic

oral equivalent mammalian no observed adverse effect level (NOAEL=0.1 mg/kg diet. 

Drinking water alone was determined to be a potential pathway of concern for both avian and 

mammalian species on an acute and chronic exposure basis.

1.3 Stressors of Concern

In addition to parent dimethoate, the primary toxic degradate of concern for dimethoate is 

omethoate. Available data indicate that omethoate is as toxic to amphibians as the parent 

compound (Sparling and Fellars 2007) while data on aquatic invertebrates indicate that they can 

be considerably more sensitive to omethoate compared to the parent compound on an acute 

exposure basis (Song et al. 1997). Also, omethoate as a major degradate is at least as toxic as the 

parent to birds. Submitted environmental fate studies for dimethoate do not identify omethoate, 

as it does not form >10% of residues, indicating that it is not expected to be a major degradate of 

dimethoate in aquatic and terrestrial environments. However, omethoate has been detected in 

 5 Body weight of the red wing blackbird obtained from: http://birds.audubon.org/species/redbla3
Page 9 of 144

air, precipitation and surface water samples, demonstrating that it is present in the environment. 

Furthermore, it has been detected in terrestrial field dissipation studies, as described later in this 

assessment. Since laboratory data are not available to estimate the formation and decline of 

omethoate from dimethoate, and omethoate was not detected in any of the laboratory based 

environmental fate studies, results from the terrestrial field dissipation studies were used to make 

rough estimates of aquatic exposures using the Surface Water Concentration Calculator (SWCC)

(for additional details, refer to section on Aquatic Modeling Approach below; see also the 

Uncertainties section).

The stressors of concern for this assessment include dimethoate and omethoate. Another major 

degradate observed in some of the fate studies, desmethyldimethoate was found to be much less 

toxic than the parent compound. Exposures in aquatic habitats will be quantified considering 

dimethoate first (since omethoate was not formed in any of the laboratory degradation studies); 

however additionally, available data on the formation of omethoate (from terrestrial field 

dissipation studies) is used to bracket potential exposure of aquatic organisms to the oxon 

degradate. Exposures in terrestrial habitats will consider dimethoate only, since available data 

indicate similar acute toxicity of omethoate and dimethoate to birds and mammals. 

Although previous analyses have indicated that formulated products of dimethoate are less toxic 

than the technical grade active ingredient (TGAI), the assessment will continue to analyze the 

toxicity of formulated products (including formulations involving more than one active 

ingredient) and will determine whether any additional formulated products are more toxic than 

the TGAI data used for assessing both direct and indirect risks. 

1.4 Risk Hypothesis

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

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

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

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

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

The risk hypothesis for dimethoate provides a written description of the predicted relationships 

between dimethoate, potential routes of exposure, and the predicted effects for the assessment 

endpoint. These previous assessments highlighted in the preliminary problem formulation and 

more recent data serve as a basis for the risk hypothesis and conceptual model developed for 

current registered uses of dimethoate. 

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

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

following ecological risk hypothesis is being employed for this national-level ecological risk 

assessment:

Dimethoate, when used in accordance with current labels, can result in offsite movement of the compound and its oxon transformation product
Page 10 of 144

(omethoate) via runoff, spray-drift, and atmospheric transport leading to 

exposure of non-target plants and animals. Monitoring data indicate frequent 

detections of dimethoate and its degradate omethoate in surface waters and 

at sites distant from use areas. Applications to foliar surfaces may serve as 

a major source of dimethoate exposure to terrestrial and aquatic organisms. 

This potential exposure pathway may result in adverse effects upon the 

survival, growth, and reproduction of non-target organisms. These nontarget organisms may include Federally-listed threatened and endangered 

species.

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

to identify specific ecosystems during the development of a nationwide ecological risk 

assessment. However, in general terms, terrestrial ecosystems potentially at risk could include 

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

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

fields or grasslands, woodlands, riparian habitats, and other uncultivated areas. 

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

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

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

marine ecosystems, including estuaries. 

2.0 Exposure Characterization

2.1 Use and Usage Information

Currently, dimethoate is used for control of a variety of insect pests on a number of fruit, 

vegetable, grain, and field crops, as well as ornamentals and non-cropland adjacent to 

agricultural fields. The pesticide is primarily applied as a foliar spray (using aerial or ground 

application methods); however, soil and bark drench uses are registered. Dimethoate is applied 

in liquid formulations (emulsifiable concentrate, wettable powder or soluble concentrate (liquid)) 

aerially or by ground methods of applications. Table 2 shows the maximum application rates 

and maximum number of applications for the different crops for dimethoate. It also shows the 

application methods, pre-harvest intervals, and for certain crops, the timing of application. As 

indicated earlier, dimethoate is used on several food crops and ornamentals; however, it also has 

uses on certain trees (e.g., Douglas fir, cottonwood, etc.). Methods of application include 

ground, aerial and chemigation. Airblast applications are allowed on Douglas fir (seed orchard)..
Page 11 of 144

Table 2. Summary of use information for dimethoate, formulated as emulsifiable concentrate

(EC), wettable powder (WP) or soluble concentrate (SC), i.e., liquid formulations. Assumptions 

made regarding the use pattern are shaded

Use

Maximum 

Single App. 

Rate

(lb. a.i./A)

Number of 

Apps. at 

Max Rate

Maximum 

Seasonal 

App. Rate

(lb. a.i./A)

Minimum 

Interval 

Between Apps.

(days)1

Application Method

/ Timing of 

Application

Pre 

Harvest 

Interval

(days)

Agricultural uncultivated 

areas (CA) (Noncropland 

adjacent to vineyards)

1.9 2 3.8* 180 Groundboom/

Handgun app N/A

Alfalfa, Sainfoin 0.5 1/CC

3/year 1.5* 30 A or G: B, C, S 10

Asparagus (not allowed in 

CA and AZ) 0.5 2* 1 14 A or G: B, C, S/ Postharvest 180

Beans (includes dry beans, 

excludes cowpeas), 

Garbanzos (includes chick 

peas), Lupine

0.5 2* 1 14 A or G: B, C, S 0

Lentils (some labels allow 

use in WA) 0.5 2 1 7 A or G: B, C, S 14

Dried peas (ID, OR, WA) 0.5 1* 0.5 N/A A or G: B, S 0

Succulent peas 0.156 1* 0.156 N/A A or G: B, C, S 0

Succulent peas (CA only) 0.16 3* 0.5 14 A or G: B, C, S 0

Succulent peas (ID, OR, 

WA) 0.5 1* 0.5 N/A A or G: B, C, S 0

Unspecified peas 0.167 1 0.167 N/A A or G: B, C, S 0

Unspecified peas (ID) 0.321;

0.25x2 2 0.5 (ID) 14 A or G: B, S 0

Unspecified peas (WA) 0.323 2 0.67 (WA) 14 A or G: B, S 0

Broccoli, Cauliflower 0.5 3 1.5 7 A or G: B, C, S 7

Brussels sprouts (some 

labels allow use only in 

CA)

0.5 3* 1.5 7 A or G: B, C, S 10

Brussels sprouts (some 

labels allow use only in 

CA)

1;

0.75x2 2* 1.5 7 G: B, C, S 10

Celery (some labels allow 

use in FL) 0.5 3 1.5 7 A or G: B, C, S 7

Lettuce (leaf), Endive, 

Swiss chard 0.255 3 0.752 7 A or G: B, C, S 14

Kale 0.5 1* 0.5 N/A A or G: B, C, S 14

Turnip (greens) 0.255;

0.251x7 7* 1.755 3 A or G: B, C, S 14

Turnip (roots) 0.255;

0.251x7 7* 1.755 3 A or G: B, C, S 14

Mustard greens 0.25 2* 0.5 9 A or G: B, C, S 14

Cherry (only in ID, MT, 

OR, UT and WA) 1.35 1 1.35 N/A

A or G: B, C, S/ 

Preharvest and 

Postharvest

21

Christmas tree plantation 1 3* 3 14 A or G: B, C, S N/A

Seed orchard trees 1 1* 1 N/A A or G: B, C, S, FT N/A

Conifers (seed orchard) 1 1* 1 N/A A or G: B, C, S N/A

Douglas fir (seed orchard) 1 1* 1 (A) N/A A or G: B, C, S N/A

Douglas fir (seed orchards) 

(only in OR and WA) 4.5 (AB) 1* 4.5 (AB) N/A G (AB) N/A

Cottonwood (forest/ 

shelterbelt) 2 3 6 14 A or G: B, C, S N/A

Hybrid cottonwood/poplar 

plantations (some labels 

allow use in ID, OR and 

WA)

2 3 6 10 A or G: B, C, S, SI N/A
Page 12 of 144

Table 2. Summary of use information for dimethoate, formulated as emulsifiable concentrate

(EC), wettable powder (WP) or soluble concentrate (SC), i.e., liquid formulations. Assumptions 

made regarding the use pattern are shaded

Use

Maximum 

Single App. 

Rate

(lb. a.i./A)

Number of 

Apps. at 

Max Rate

Maximum 

Seasonal 

App. Rate

(lb. a.i./A)

Minimum 

Interval 

Between Apps.

(days)1

Application Method

/ Timing of 

Application

Pre 

Harvest 

Interval

(days)

Grapefruit, Kumquat, 

Lemon, Lime, Orange, 

Pummelo (shaddock), 

Tangelo, Tangerine (some 

labels allow uses in AZ 

and CA, some disallow 

some uses in FL, some 

have no restrictions)

1 1* 1 N/A A or G: B, C, S, SD, 

FT 10-15

Citrus, non-bearing and 

nursery stock (only in CA 

and AZ)

0.5 (A)

1 (G)

1 & 1.9+ SD

2 (A)

1* (G)

1* (SD)

1

10*

N/A

N/A

A or G: B, C, S, SD N/A

Grass grown for seed 0.33 3* 1 90 A or G: B, C, S N/A

Grass grown for seed 

(allow use in WA, OR and 

ID)

0.5 2* 1 90 A or G: B, C, S N/A

Melon, Watermelon 0.5 2 1 7 A or G: B, C, S 3

Ornamental woody shrubs 

and vines 1 3* 3 14 A or G: B, C, S, SD, drench, soil injection N/A

Ornamental and/or shade 

trees (some labels disallow 

uses in CA)

1 3* 3 14

A or G: B, C, S, 

drench, drip line app, 

bark treatment, soil 

injection

N/A

Ornamental herbaceous 

plants

0.25

6.5+ (SD) 1 0.25 N/A A or G: B, C, S, SD, 

drench N/A

Pear (some labels disallow 

use in CA) 1 1* 1 N/A A or G: B, C, S 28

Pecans 0.336 1 0.336 N/A A or G: B, C, S 21

Peppers 0.336 5* 1.67 7 A or G: B, C, S 0

Tomatoes 0.5 2* 1 6 A or G: B, C, S 7

Potatoes 0.5 2 1 7 A or G: B, C, S 0

Field corn or pop corn 0.5 1* 0.5 NS A or G: B, C, S 28 (grain)

14 (forage)

Cotton 0.5 2 1 14* A or G: B, C, S 14

Safflower 0.5 1 CC 0.5/cutting 14 A or G: B, C, S 14

Safflower (CA and AZ 

only) 0.5 1 CC 0.5/cutting 14 A or G: B, C, S 14

Sorghum 0.5 2 1 7 A or G: B, C, S 28

Soybeans 0.5 2 1 7 A or G: B, C, S 21

Wheat, Triticale 0.5 1 0.5 N/A A or G: B, C, S 35

Metfile=meteorological file; NS=Not specified; N/A=does not apply; G=ground; A=aerial, B=broadcast, C=chemigation, 

S=spray (low or high volume), AB=airblast; SD=soil drench; FT=foliar treatment; SI=soil injection treatment; CC=crop cycle.

Assumptions in the table are bolded

*Calculated value, based on the number of applications, or the seasonal application rate.

+For citrus, the label indicated 1.9 lb a.i./A and for ornamental herbaceous plant (soil drench applications) it said 6.5 lb a.i./A, 

both appear to be label errors.

Additionally, data about typical (or average) application rates and average number of 

applications were provided by BEAD for a number of crops. Table 3 summarizes the average 

number of applications and application rates for several of the dimethoate agricultural uses. The 

data is proprietary and it is averaged over the five year period of 2008-2012. Average number of 

applications and application rates are not available for the non-agricultural uses of dimethoate.
Page 13 of 144

Table 3. Average number of applications and 

application rates for several dimethoate agricultural 

crops1

Agricultural Crop Average 

AI rate2

Average 

# apps

Alfalfa 0.365 1.1

Almonds 0.625 2.0

Asparagus 0.500 1.5

Beans (Snap, Bush, Pole, String) 0.422 2.2

Broccoli 0.477 1.3

Cabbage 0.412 1.5

Cantaloupes 0.414 1.0

Carrots 0.502 1.0

Cauliflower 0.470 1.7

Celery 0.457 2.2

Cherries 1.202 1.0

Corn 0.302 1.1

Cotton 0.274 1.2

Cucumbers 0.470 1.0

Dry Beans/Peas 0.361 1.1

Garlic 0.500 1.3

Grapefruit 0.499 1.0

Grapes, Raisin 2.001 1.0

Grapes, Table 0.579 1.2

Lemons 1.749 1.1

Lettuce 0.250 1.2

Lima Beans 0.487 1.6

Onions 0.464 1.5

Oranges 0.680 1.1

Peanuts 0.301 1.3

Peas (Fresh/Green/Sweet) 0.293 1.2

Pecans 0.306 1.5

Peppers 0.267 2.6

Potatoes 0.329 1.6

Pumpkins 0.455 1.0

Sorghum (Milo) 0.266 1.0

Soybeans 0.432 1.0

Squash 0.499 4.0

Strawberries 0.408 3.7

Sugar Beets 0.250 2.0

Sunflowers 0.326 1.7

Sweet Corn 0.234 4.0

Tomatoes 0.444 1.3

Watermelons 0.469 2.7

Wheat, Spring 0.244 1.0

Wheat, Winter 0.303 1.0

1 Proprietary data averaged 2008-2012, provided by BEAD.

2 Application rate in units of lb a.i./A.
Page 14 of 144

For dimethoate, there are no spray buffer zone restrictions. One of the label restrictions for 

dimethoate products is the wind speed limitation. Applications must be done when the wind 

speed is less than or equal to 10 mph. Additionally, for groundboom or aerial applications, the 

droplet must be medium or coarser according to ASABE6 572 definition for standard nozzles, or 

droplet size with volume median diameter (VMD) of 300 μm or greater for spinning atomizer

nozzles. The maximum recommended release height is 4 ft above ground or crop canopy for 

groundboom applications and 10 ft for aerial applications.

According to the labels, dimethoate is a IRAC7 Mode of Action Classification Group 1 (AChE 

inhibitors, subgroup B (organophosphates) of the insecticides/miticides, to which target pests can 

develop cross-resistance when applied with other chemicals within the subgroup consecutively 

or repeatedly in the same field and/or in consecutive years. For that reason, it is recommended to 

avoid its consecutive use and/or the consecutive use of other group 1B insecticides and to base 

its use on a comprehensive Integrated Pest Management (IPM) program.

The following environmental hazard statements appear in dimethoate products:

“ENVIRONMENTAL HAZARDS

Do not apply directly to water, or to areas where surface water is present or to 

intertidal areas below the mean high water mark. Do not contaminate water when 

disposing of equipment washwater or rinsate.

Dimethoate is known to leach through soil into ground water under certain conditions 

as a result of label use.

Use of this chemical in areas where soils are permeable, particularly where the water 

table is shallow, may result in groundwater contamination.

This product may contaminate water through drift of spray in wind.

This product has a high potential for runoff for several days after application.

Poorly draining soils and soils with shallow water tables are more prone to produce 

runoff that contains this product. A level well-maintained vegetative buffer strip 

between areas to which this product is applied and surface water features such as 

ponds, streams, and springs will reduce the potential for contamination of water from 

rainfall-runoff.

Runoff of this product will be reduced by avoiding applications when rainfall is 

forecasted to occur within 48 hours.

 6 ASABE stands for American Society of Agricultural and Biological Engineers. 7 IRAC. 2014. Insect Resistance Action Committee (IRAC) MoA Classification Scheme. Prepared by IRAC 

International MoA Working Group. Version 7.3. Issued February 2103. Available on line at: http://www.iraconline.org/documents/moa-classification/?ext=pdf
Page 15 of 144

A vegetative filter strip constructed and maintained in accordance with the 2000 

Natural Resources Conservation Service publication "Conservation Buffers to Reduce 

Pesticide Losses" (http://www.nrcs.usda.gov/feature/buffers/) will significantly 

reduce the potential for contamination of water from rainfall-runoff.

This pesticide is highly toxic to bees exposed to direct treatment or residues on 

blooming crops or weeds. Do not apply this product or allow it to drift to blooming 

crops or weeds if bees are visiting the treatment area.”

According to the Screening-Level Usage Analysis (SLUA), dated September 27, 2013

(Reporting Timeframe: 2004-2011), major agricultural uses for dimethoate (at or above an 

average of 30,000 lb a.i./year), were: alfalfa, broccoli, corn, cotton, dry beans/peas, oranges, 

potatoes, soybeans, tomatoes, and wheat. Sources of the SLUA included the following:

• USDA-NASS (United States Department of Agriculture’s National Agricultural 

Statistics Service) – pesticide usage data from 2004 to 2011.

• Private pesticide market research – pesticide usage data from 2004 to 2011.

• California Department of Pesticide Regulation (DPR) Pesticide Use Reporting 

(PUR) data for 2004 to 2010.

For most of the crops, the maximum percent crop treated (PCT) is relatively low. From the 

crops listed above, exceptions include: broccoli (maximum PCT = 55%), oranges (25%), and 

tomatoes (40%). For the other crops listed above (with high usage), the maximum PCT is 15%.
Page 16 of 144

Figure 1. Dimethoate Use Intensity by Crop Reporting District (2007-2011)

BEAD provided a use intensity map (USEPA 2013b), covering the years 2007-2011 (Figure 1). 

Based on the map in Figure 1 dimethoate has been used all across the continental U.S. 

2.2 Environmental Fate and Transport

Registrant-submitted data defining the physical, chemical, fate and transport characteristics 

associated with dimethoate are summarized in Table 4. Dimethoate is a highly mobile to mobile 

(FAO 2000), generally non-persistent organophosphate insecticide. Microbially-mediated 

degradation in aerobic soils appears to be one of the important fate processes for the dissipation 

of dimethoate. Consistent with laboratory-based degradation studies, terrestrial dissipation 

studies indicate that dimethoate rapidly dissipates from soil and foliar surfaces. It should be 

stressed that in the field, processes other than degradation may also occur (e.g., leaching and 

runoff). Results of fate and transport studies associated with dimethoate are also briefly 

described below.
Page 17 of 144

Table 4. Summary of physicochemical and environmental fate and transport properties for 

parent Dimethoate**

Parameter Value (s) (units) Source Comments

Selected Chemical/Physical Parameters

CAS Chemical Name O,O-dimethyl S-[2-(methylamino)-2-

oxoethyl] phosphorodithioate -- --

Molecular Weight 229.25 g mol -- --

Solubility (25°C) 39800 mg/L 43461402, 

48696601 Soluble

Vapor Pressure (25°C)

8.5 x 10-6 torr;

1.85 x 10-6 torr

Dimethoate lies between ‘non-volatile’ 

and ‘intermediate to high volatility’ under 

field conditions.

00245601/ 

00245604;

48696601

Volatility classified 

per USEPA 2010

Henry’s Law constant (25°C) 1.40 x 10-11 atm-m3/mol Calculated2

Estimated from 

vapor pressure and 

water solubility.

Octanol-Water Partition 

Coefficient (KOW) KOW = 5.06 (Log KOW = 0.704) 43274001 Hydrophilic

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.

47622901 --

No significant absorption was observed 

above 260 nm, in the UV/Vis spectrum 

provided in the study.

43276401 --

pH 3.39 in 1% freshly boiled & cooled water 48696601 --

Persistence

Hydrolysis Half-life 

[pH 5, 7, 9; (23-25°C)]

pH 5: 156 days

pH 7: 68 days

pH 9: 4.4 days

00159761 Moderately low 

route of degradation.

Aqueous Photolysis Half-life 

(pH 7) 353 days 00159762

Not an important 

degradation 

pathway.

Soil Photolysis Half-life No significant degradation 43276401 Considered 

relatively stable

Aerobic Soil Metabolism 

Half-life (250C)

Somersham sandy loam 1: 2.4 days

Riverside clay loam: 1.68 days3

Middelfield silty clay loam: 1.65 days3

Somersham sandy loam 2: 3.01 days3

42843201, 

46719202

Significant 

degradation 

pathway.

Anaerobic Soil Metabolism

Half-life Somersham sandy loam: 22 days 42884402

Moderate 

degradation 

pathway.

Aerobic Aquatic Metabolism 

Half-life (250C)2

North Carolina clay loam: 20.2 days3

Maryland loamy sand: 16.5 days3 48945601

Moderate 

degradation 

pathway.

Anaerobic Aquatic 

Metabolism Half-life (250C)2

North Carolina clay loam: 17.1 days3

North Dakota loamy sand: 6.78 days3 48945501

Moderately rapid

degradation 

pathway.

Mobility

Soil Partition Coefficient Sand 0.06 mL/g-soil 00164959 Based on a column 
Page 18 of 144

Table 4. Summary of physicochemical and environmental fate and transport properties for 

parent Dimethoate**

Parameter Value (s) (units) Source Comments

(Kd) Sandy loam: 0.30 mL/g-soil

Silt loam: 0.57 mL/g-soil

Clay loam: 0.66 mL/g-soil

leaching study.

Mean Kd = 0.398 

mL/g-soil

RSD = 68%

Organic Carbon Partition

Coefficient (KOC)

Sand 6.7 mL/gOC

Sandy loam: 20 mL/gOC

Silt loam: 16 mL/gOC

Clay loam: 16 mL/gOC

00164959

Based on a column 

leaching study.

Mean Koc = 14.7 

mL/gOC

RSD = 38%

Laboratory Volatility

Volatile organics: 2% AR. Mean. daily air

concentration:. 1.29 μg/m3. 

Volatilization rate of organic volatiles: 

1.08x10-4 μg/cm2/hour (expressed as

dimethoate equivalents).

43276402 Slightly volatile

Field Dissipation

Terrestrial Field Dissipation 

Half-life

CA loamy sand: 11 days

CA sandy loam ~ 9 days

CA sandy loam: ~16 days

TX silt loam: ~ 9 days

NY sandy loam: ~5 days

42884403,

43388001, 

43388002

--

Fish Bioconcentration

Bioconcentration in Fish

(Maximum BCF)

Data requirement was waived based on 

its low KOW.

-- Not expected to 

bioaccumulate

Other Studies

Effects of chlorination on the 

degradation of dimethoate

Maximum level of omethoate was 23% of 

the applied at 24 and 48 hours posttreatment.

48041103 Based on the results, 

EFED assumes

100% conversion.

Foliar Dissipation Half-life 2.82 days (from 24 values) D291565 Refer to Table 4

RSD=relative standard deviation (coefficient of variation) **This table includes half-lives for the parent compound only (i.e., it does not 

include the parent plus unextracted residues nor omethoate). 1 Note that all chemicals may volatilize to some extent; this classification simply indicates that the volatility potential is intermediate. For 

classification scheme, see the “Guidance for Reporting on the Environmental Fate and Transport of the Stressors of Concern in Problem 

Formulations,” available at:

http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/endangered_species_reregistration_workgroup/esa_reporting_fate.

htm#I (USEPA 2010a), accessed July 18, 2014. 2 Calculated using the equation Henry’s Law Constant = (Vapor Pressure x Molecular Weight) / (760 x solubility). 3 Half-lives were adjusted to a standard temperature of 25°C from an experimental temperature of 20°C using a Q10 of 2 (USEPA 2010b).

Omethoate was not reported in laboratory fate studies involving degradation of dimethoate. It 

was, however, observed in terrestrial field dissipation and foliar dissipation studies. Additionally, 

it was observed in a chlorination treatment study. Table 5 provides available physicochemical 

and environmental fate properties available for omethoate.
Page 19 of 144

Table 5. Summary of physicochemical and environmental fate and transport properties of 

Dimethoate’s ecologically significant transformation product, Omethoate

Parameter Value (s) (units) Source Comments

Selected Chemical/Physical Parameters

CAS Chemical Name O,O-dimethyl S-[2-(methylamino)-2-

oxoethyl] phosphorothioate -- --

Molecular Weight 213.19 g mol EPISUITE v.4.1 --

Solubility 1 x 106 mg/L EPISUITE v.4.1 Unspecified temp.

Vapor Pressure (20°C)

2.48 x 10-5 torr

Omethoate lies between ‘non-volatile’ to 

‘intermediate to high volatility’ under 

field conditions.

EPISUITE v.4.1 Volatility classified 

per USEPA 2010

Henry’s Law constant 4.56 x 10 -14 atm-m3/mol EPISUITE v.4.1 --

Octanol-Water Partition 

Coefficient (KOW)

KOW = 0.18

(Log KOW = -0.74 at 20oC) EPISUITE v.4.1 Hydrophilic

Persistence

Aerobic Aquatic Metabolism 

Half-life (250C)1

Netherlands sandy clay loam: 2.7 days1

Netherlands sand: 1.69 days1

(Water pH 8.1-8.5 could have promoted 

hydrolysis of omethoate.)

47477303

Significant 

degradation 

pathway.

Mobility

Organic Carbon Partition

Coefficient (KOC)

Standard Soil 2.1 low humus sand:

110 mL/goc

Standard Soil 2.2 high humus loamy 

sand: 52.1mL/goc

Standard Soil 2.3 high humus sandy clay: 

174 mL/goc

47477304

Testing was 

conducted at a single 

concentration.

Soil Partition Coefficient 

(Kd)

Standard Soil 2.1 low humus sand:

1.05 mL/g-soil

Standard Soil 2.2 high humus loamy 

sand: 1.26 mL/g-soil

Standard Soil 2.3 high humus sandy clay: 

1.98 mL/g-soil

47477304

Testing was 

conducted at a single 

concentration.

1 Half-lives were adjusted to a standard temperature of 25°C from an experimental temperature of 22°C using a Q10 of 2 (USEPA 2010).

Dimethoate underwent biotic degradation relatively rapidly under aerobic conditions, and at 

moderate rates in an anaerobic soil, and under aerobic and anaerobic aquatic conditions. 

Laboratory studies of abiotic degradations indicate that dimethoate hydrolyses slower at pH 7

than pH 9, and it photolyzes slowly in water and on soils. Dimethoate residues on foliage 

showed half-lives of a few days (for further details, see below). Upon chemical application, it 

can be transported offsite by spray drift and/or surface (dissolved) runoff occurring within a few 

days to weeks after applications. The chemical is considered highly mobile. Dimethoate shows

relatively low persistence in soil. According to the labels, dimethoate is systemic (it also has 

contact activity), so in this assessment it is assumed to be taken up by plants and distributed

through vegetation and/or root systems. Even though omethoate was not observed in the 

laboratory soil and sediment metabolism studies, the transformation product was observed in 

terrestrial field dissipation studies and also formed upon chlorination during water treatment. 

Note that water chlorination is a pathway that is only relevant to human health risk, for 

additional details about the chlorination study, see below.
Page 20 of 144

2.2.1 Degradation and Metabolism

The primary route of dissipation for dimethoate is degradation in aerobic soil, particularly under 

moist conditions. In one aerobic soil metabolism study, dimethoate degraded rapidly, with a 

half-life of 2.4 days. The majority of dimethoate residues in this study were composed of carbon 

dioxide, accounting for >50% of total residues by Day 7 of the test and approximately 75% by 

Day 181. Two non-volatile degradates, O-desmethyldimethoate and dimethylthiophosphoric 

acid (these two degradates are not oxons), were identified, but were present at less than 2% of 

the applied radioactivity during the aerobic soil metabolism study. In three additional aerobic 

soils conducted at 20°C in which degradates were not looked for (since the study used cold 

material), dimethoate degraded with temperature-adjusted (25°C, using a Q10 of 2) half-lives of 

1.65-3.01 days. Although not as rapidly as under aerobic conditions, dimethoate degrades under 

anaerobic soil conditions (half-life of ca. 22 days), generating the major non-volatile degradate, 

O-desmethyldimethoate. 

Dimethoate hydrolyzes very slowly at pH’s 5 and 7 (half-lives of 156 and 68 days, respectively), 

but degrades rapidly under alkaline conditions to O-desmethyldimethoate and dimethylthiophosphoric acid (half-life of 4.4 days at pH 9). O-desmethyldimethoate was detected at all pH 

levels (maxima 12%, 22% and 62% of the applied, respectively), while dimethylthiophosphoric 

acid was a major degradate only at pH 9, with a maximum of 36%.

Under aerobic aquatic conditions, dimethoate degraded in two sediment systems with 

temperature-corrected (from 20 to 25oC, using a Q10 of 2) half-lives of 16.5-20.2 days. The 

major degradate was O-desmethyldimethoate. Under anaerobic aquatic metabolism conditions, 

it degraded with slightly lower temperature-corrected (from 20 to 25oC, using a Q10 of 2) halflives of 6.78-17.1 days. The major degradate was also O-desmethyldimethoate.

Data available about the aerobic aquatic metabolism of omethoate indicate that it degraded with 

temperature-adjusted (from 22 to 25oC, using a Q10 of 2) half-lives of 1.69-2.7 days. The major 

degradate observed was O-methyl-S-(2-methylamino-2-oxoethyl) thiophosphate.

Dimethoate photodegrades slowly in water (half-life of 353 days), and is relatively stable to 

photodegradation on the soil surface. 

2.2.2 Transport

Dimethoate is mobile to highly mobile in soils (FAO 2000). For this chemical, sorption 

appeared to be correlated with organic carbon, making KOC is a better model of sorption than Kd

(the coefficient of variation for KOC was smaller than for Kd). In a soil column leaching study, 

72-100% of applied radioactivity was eluted from the columns (loam, silt loam, sandy loam, and 

sand). Calculated soil dissociation constant (Kd) values based on these column studies ranged 

from 0.06 L/kg for sand to 0.66 L/kg for clay loam. Organic carbon partition coefficients (Koc) 

values were in the range of 6.7 mL/goc for a sand to 20 mL/goc for a sandy loam. Degradate 

mobility has not been well defined, except for omethoate, for which analysis was performed at a 

single concentration. In three soils, the Kd values were 1.05-1.98 L/kg and Koc’s were 52.1-174 
Page 21 of 144

L/kgoc. 

Volatilization of dimethoate from the soil surface is not expected to be a significant route of 

dissipation, compared to metabolism. In a study measuring the volatility of dimethoate from the 

soil surface, 2.7% of the applied radioactivity had volatilized by 30 days, 0.7% of which was 

CO2. The majority of the radioactivity (83%) was extracted from the soil and most of this 

(93.2%) was dimethoate. Based on the Henry’s Law Constant (1.40 x 10-11 atm-m3/mol), 

volatilization from moist soil or water will not be a significant route of dissipation for the parent 

compound. However, the degradate omethoate has been detected in both air and precipitation in 

California (refer to section on monitoring, reference: Majewski et al. 2006), indicating that 

omethoate may be transported in the atmosphere. Based on a vapor pressure of 2.48 x 10-5 torr, 

it is not expected to volatilize from dry soil, but omethoate should exist in both the vapor and 

particulate phases in the atmosphere.

2.2.3 Terrestrial Field Dissipation

The results of five terrestrial field studies indicate that dimethoate dissipates with half-lives 

ranging from <5 to 16 days when applied post-emergence to green beans, grapes, and bare 

ground in California, grain sorghum in Texas, and bare ground in New York. These results are 

reasonably consistent with those that might be expected from the laboratory studies, although the 

persistence is somewhat longer in the field studies. Generally, factors that could influence the 

half-lives in the field could include the temperature, rainfall, viability of the soils, sunlight 

intensity, soil moisture, pH, and others. When detected, dimethoate was mostly in the top layer 

of soil (0-6”), with some detections below 6”. Omethoate was found under field conditions, 

although it was not detected in the laboratory studies. 

Omethoate was detected in the top layer (0-6”) of soil in all five field dissipation studies, at 

amounts ranging from <1 to 24% of the total residues detected in that layer (note: the 24% level 

was observed only in one replicate of only one of the field studies). In the California bare 

ground study, omethoate was found through Day 159 of the study. Omethoate is also formed 

during drinking water treatment using oxidizing agents such as chlorine, although this formation 

pathway is only important for human health exposure.

2.2.4 Bioaccumulation

The data requirement for a bioaccumulation in fish study was waived because dimethoate has a 

octanol/water partition coefficient (Kow) lower than 1000. Therefore, bioaccumulation of 

dimethoate by aquatic organisms is not considered an exposure pathway of concern. 

2.2.5 Drinking Water Treatment Study

To determine the extent to which the parent and its omethoate transformation product may be 

present in treated drinking water, chlorinated deionized laboratory water (free chlorine [Cl2] 

concentration 1.0 ± 0.4 mg/L), at a pH of 6.7, was treated with dimethoate at a nominal 

concentration of 30.0 μg/L and the solution was maintained at 200C for up to 72 hours (3 days). 

The pH of the solutions ranged from 6.36 to 6.75. Samples were routinely taken in duplicates 
Page 22 of 144

quenched with sodium thiosulfate to prevent further residue degradation, and monitored for 

contents of dimethoate and omethoate. Immediately after treatment, dimethoate concentrations

ranged from 6.58 to 10.6 μg/L (22-34% of the applied); afterwards,. dimethoate was not detected 

throughout the remainder of the sampling period. Omethoate however, was detected in all the 

samples at concentrations ranging from 11-12% of the applied immediately after treatment, to 

13-23% of the applied in all subsequent intervals. Concentration appeared to be maintained at 

close to 20% of the applied at and after 2 hours post-treatment. Formation of omethoate upon 

chlorination is not considered a relevant exposure pathway for ecological risk assessments; 

however, it is important for human health exposure and risk assessment.

2.2.6 Foliar Dissipation

Multiple foliar dissipation studies are available for dimethoate and were evaluated previously 

(DP Barcode D291607; note that these are not dislodgeable foliar residue studies). A summary 

of results is provided in Table 6. The upper 90 percent confidence bound on the mean foliar 

dissipation half-life value (over the 29 values available) is 2.82 days. This value was used in

models to estimate terrestrial (i.e., T-REX) and aquatic exposure (i.e., SWCC).

A study (MRID 46486401) provided information on the degradation of dimethoate, and the 

formation and decline of omethoate on ground-level vegetation and canopy arthropods in a 

mandarin orchard in Spain. The half-life of dimethoate was found to be 1.7 days on the 

vegetation and 0.86 days on the canopy arthropods. Using a kinetics model that assumed that 

100% of the dimethoate formed omethoate, the degradation half-life of omethoate was 

determined to be 0.33 days on the foliage and 0.30 days on the arthropods. For plant materials, 

these data are within the range of half-lives seen below for the parent. No other measurements 

exist for omethoate on plant material or either omethoate or dimethoate in arthropods (source: 

DP Barcode D323951+).

Table 6. Foliar dissipation data for dimethoate (Source of table: DP Barcode D323951+)

Crop Reference Comment T1⁄2 (days)

Apple Pree et al. 1976 5.4

Alfalfa Shaw and Ziener, 1964 1.4

Apple Pree et al., 1976 7.2

Apple Pree et al., 1976 80 mm rain 2.6

Apple Pree et al., 1976 11 mm rain 4.1

Birdsfoot trefoil Shaw and Ziener, 1966 2.1

Sorghum Dorough et al. 1966 4

Ladino clover Shaw and Ziener, 1966 1.8

Lemon Bellows et al., 1985 2.2

Coastal bermuda 

Grass

Beck et al., 1966 22.6 mm rain 3.1

Corn Beck et al., 1966 90.2 mm rain 2.7

Soybeans Beck et al., 1966 0 mm rain 0.9

Beet Vail et al., 1967 0 mm rain 2.5

Broccoli Nelson et al., 1966 3

Cabbage Nelson et al., 1966 1.7

Chard Vail et al., 1967 5.1 mm rain 2.6
Page 23 of 144

Collards Nelson et al., 1966 2.5

Leaf lettuce Vail et al., 1967 5.1 mm rain 2.8

Lima beans Nelson et al., 1966 2.2

Snap beans Nelson et al., 1966 2.6

Soybeans Nelson et al., 1966 1.2

Turnip Vail et al., 1967 83.8 mm rain 3.1

Turnip Nelson et al., 1966 3.2

Wheat Lee and Westcott, 1981 2.5

Wheat MRID 466780-01 8.0

Wheat MRID 466780-01 16.3

Wheat MRID 466780-05 3.6

Wheat MRID 466780-05 6.6

Wheat MRID 466780-10 15.6

2.3 Aquatic Exposure Modeling Approach

A brief description of the aquatic models used in this risk assessment follows. Additional 

information about these models is provided in the Agency’s website at 

http://www.epa.gov/pesticides/science/models_pg.htm#aquatic. For agricultural and certain nonagricultural uses, exposure concentrations for surface drinking waters assessments are estimated 

based on EFED’s Tier II aquatic model Pesticide Root Zone Model coupled with the Variable 

Volume Water body Model (PRZM/VVWM). A graphical user interface Surface Water 

Concentration Calculator (SWCC v.1.106; May 6, 2014), developed by the EPA, was used to 

facilitate inputting chemical and use specific parameters into the appropriate input files and 

chemical files, which used PRZM3 and the Exposure Analysis Model System (EXAMS); the 

SWCC replaced the older PRZM/EXAM (PE5) shell (November 2006),. The SWCC estimates 

pesticide concentrations in water bodies that result from pesticide applications to land. The 

calculator was designed for regulatory applications as applied in the Office of Pesticide 

Programs, USEPA, as well as Health Canada’ Pest Management Regulatory Agency (PMRA). 

The calculator uses the PRZM (v5.0+, May 6, 2014) and the VVWM (May 6, 2014; a 

replacement for the older EXAMS model). The PRZM field or orchard crop scenario is the basic 

file which describes the local or regional climatological information, soil hydrology, soil 

characteristics, crop characteristics, and the pesticide properties necessary to determine pesticide 

loadings to surface water. This basic file constitutes the first part of the “exposure scenario.” It 

simulates the processes in the agricultural field, such as runoff and erosion, on a daily time step. 

The runoff and erosion flux output data from PRZM are used as chemical loadings to the 

VVWM, which simulates surface water, in order to generate estimated environmental 

concentrations (EECs). 

The VVWM is conceptually similar to the current EXAMS-based model in that both are 2-

compartment models driven by first-order processes. It simulates theEPA standard water bodies 

(i.e., farm pond and/or index reservoir) but with greater efficiency and flexibility for 

incorporation into a user interface. The VVWM can also allow for variations in water body 

volume on a daily basis due to runoff, precipitation, and evaporation (note that for the standard 

pond, this feature is not used and the volume is held constant). Temperature, wind speeds, and

pesticide degradatio, sediment sorption and mass trasnsfer between water column and benthic 
Page 24 of 144

compartments are also simulated on a daily basis . EECs were determined using the standard 

pond which is expected to represent vulnerable surface water scenario for the VVWM 

component of the modeling exercise.

Table 7 provides a summary of chemical input parameters for dimethoate in the SWCC, to 

estimate surface waters EECs. Input values were based on the EFED Guidance on Input 

Parameters v.2.1, dated October 22, 2009 and approved November 10, 2009 (USEPA 20098)

Application information is summarized in Tables 2 and 3 while the dates of first application are 

given in Tables 9 and 10. For each crop, the meteorological file used is the standard one 

suggested for the modeled scenario. Even though dimethoate shows high mobility, it was found 

that there was better correlation of binding with organic carbon (OC); thus, the average KOC was 

employed in the model (i.e., the coefficient of variation was higher for the Kd’s than for the 

KOC’s). For the aerobic soil metabolism, there were four available half-lives from two studies. 

The model input value was the 90 percent upper confidence limit on the mean half-life. 

Similarly, for aerobic and anaerobic aquatic metabolism, two values were available (for each of 

these parameter), and the 90 percent upper confidence limit on the mean half-life served as input. 

The hydrolysis half-life for the parent at pH 7 was entered (68 days). Finally, a foliar dissipation 

half-life (2.82 days) was derived in a previous review and used in the model (see Table 6).

Table 7. Input parameters utilized in the surface water concentration calculator (SWCC) for 

dimethoate

Parameter (units) Value(s)1 Sources Comments

Output File Name Dimethoate --- ---

Chemical Name Dimethoate Label ---

Application Rate Kg a.i./ha

Refer to Table 9

(lb a.i./A)

(Refer to Table 9)

Maximum allowed by the 

label and/or supplemental 

labels; focus was placed on 

crops with the highest 

seasonal rates.

Number of Applications 

Allowed Refer to Table 9 Maximum allowed by the labels. ---

Interval between 

Applications (days) Refer to Table 9 Minimum allowed by the labels. ---

Crop Names and Days of 

Application (day-month) Refer to Table 9 Labels ---

PRZM Scenario and 

Metfile

As suggested by the shell for 

the SWCC. SWCC ---

KOC (ml/goc) 14.7 00164959

Represents the mean KOC

value among four values 

ranging from 6.7 to 20 ml/goc; 

the KOC model was utilized 

because it represents the 

mobility of dimethoate better 

than Kd. Binding appears to 

be correlated with OC.

 8 USEPA. 2009. Revision on Input Parameter Guidance. Memorandum from Donald Brady, Division Director. 

Dated November 10, 2009. Available on line at: 

http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.pdf
Page 25 of 144

Table 7. Input parameters utilized in the surface water concentration calculator (SWCC) for 

dimethoate

Parameter (units) Value(s)1 Sources Comments

Aerobic Soil Metabolism 

(days)

= 2.71

42843201, 46719202

90 percent upper confidence 

limit on the mean half-life 

value: four values are 

available: 2.4, 1.68, 1.65, 3.01 

days at 25°C; mean = 2.185 

days, std. dev. = 0.6501 days, 

n = 4, t90,n-1 = 1.638.

Method of Application Ground, aerial or airblast 

(Refer to Table 9) Labels ---

Buffer Zone (ft.) 0 Labels ---

Application Efficiency 

(fraction)

0.99 ground,

0.95 aerial --- ---

Spray Drift (fraction)

0.062 ground apps;

0.125 for aerial apps;

0.042 for airblast apps.

AgDRIFT v. 2.1.1; 

USEPA 2013 ---

Solubility in Water (ppm) 39,800 mg/L 43461402 Solubility at 25oC.

Aerobic Aquatic 

Metabolism (days)

= 24.0

48945601

90 percent upper confidence

limit on the mean half-life 

value: two values are 

available: 20.2, 16.5 days at 

25°C; mean = 18.35 days, std. 

dev. = 2.616 days, n = 2, t90,n-1

= 3.078.

Anaerobic Aquatic 

Metabolism (days)

= 27.8

48945501

90 percent upper confidence 

limit on the mean half-life 

value: two values are 

available: 17.1, 6.78 days at 

25°C; mean = 11.94 days, std. 

dev. = 7.297 days, n = 2, t90,n-1

= 3.078.

Hydrolysis (days) 0 00159761 At pH 7.

Aqueous Photolysis (days) 353 00159762 ---

Aqueous Photolysis 

Reference Latitude (o) 34 00159762 Envelope reference latitudes include 34o for Arizona

Molecular Weight (g/mole) 229.25 EPISUITE v.4.12 ---

Vapor Pressure (torr) 1.85 x 10-6 48696601 VP at 25oC

Field Size EPA pond (eco. effects) --- --

Incorporation Depth (cm) 0.0 Labels ---

CAM (Chemical 

Application Method)

Foliar, except for soil drench 

applications, which are 

ground.

Labels ---

IPSCND (Condition for 

disposition of pesticide 

remaining on foliage after 

harvest)

1 (default value) Labels

1 = pesticide remaining on 

foliage is converted to surface 

application to the top soil 

layer

PLDKRT, Foliar half-life 

(days) 2.82 Refer to Table 6

90 percent upper confidence 

limit on the mean half-life 

value out of 29 values 1 Data were selected according to EFED Guidance on Input Parameters v.2.1, dated October 22, 2009 and approved November 10, 2009 

(USEPA 2009).

2 USEPA. 2014. Estimation Program Interface (EPI) Suite. http://www.epa.gov/opptintr/exposure/pubs/episuite.htm

After further consideration, additional refinements were included and are summarized in Table 

8. For the refinements, typical (average) application information was utilized, and a refined 

value for spray drift was used, based on the droplet size stated in the labels (medium or coarse). 

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )
Page 26 of 144

Typical (average) use information is provided in Table 3. No typical rate information was 

available for the non-agricultural uses of dimethoate.

Table 8. Additional refinements to the input parameters utilized in the the surface water 

concentration calculator (SWCC) for dimethoate, for use with typical application rates and 

numbers of application

Parameter (units) Value(s)1 Sources Comments

Application Rate Kg a.i./ha

Refer to Table 16

(lb a.i./A)

Refer to Table 16 ---

Number of Applications 

Allowed Refer to Table 16 Average number of apps. ---

Interval between 

Applications (days) Refer to Table 16 Minimum allowed by the labels. ---

Crop Names and Days of 

Application (day-month) Refer to Table 16 Labels

Whenever possible, the same 

date of application used from 

Table 15 was used with the 

typical rate (see Table 16).

Spray Drift (fraction) 0.089 for aerial apps AgDRIFT v. 2.1.1; 

USEPA 2013

Value for medium/coarse 

droplets1

1 Guidance on Modeling Offsite Deposition of Pesticides via Spray Drift for Ecological and Drinking Water Assessments, 

dated December 19, 2013 and approved December 20, 2013 (USEPA 2013a)

A set of runs was performed for a subgroup of scenarios, using the half-lives that included the 

unextracted residues (UERs). These runs would provide upper-bound estimates of the EECs, 

assuming that all the UERs are potentially residues of toxicological concern. Table 9 shows the 

input parameters for such runs.

Table 9. Input parameters utilized in the surface water concentration calculator (SWCC) for 

dimethoate plus the unextracted residues

Parameter (units) Value(s)1 Sources Comments

Aerobic Soil Metabolism 

(days)

= 147

42843201, 46719202

Only a single study tracked 

the radioactivity associated 

with dimethoate and residues. 

For the study, the half-life 

associated to dimethoate plus 

UERs was 49 days at 25°C. 

The input value is three times 

as much to account for 

variability associated to lack 

of additional studies.

Aerobic Aquatic 

Metabolism (days)

= 47.6

48945601

90 percent upper confidence 

limit on the mean half-life 

value: two values are 

available: 39.3 days (SFO), 

53.1 days (IORE) at 20°C; 

temperature corrected halflives are 27.8 and 37.5 days at 

25°C, respectively; mean = 

32.65 days, std. dev. = 6.86

days, n = 2, t90,n-1 = 3.078.

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )
Page 27 of 144

Table 9. Input parameters utilized in the surface water concentration calculator (SWCC) for 

dimethoate plus the unextracted residues

Parameter (units) Value(s)1 Sources Comments

Anaerobic Aquatic 

Metabolism (days)

= 37.8

48945501

90 percent upper confidence 

limit on the mean half-life 

value: two values are 

available: 29.5 days (SFO), 

21.5 days (IORE) at 20°C; 

temperature corrected halflives are 20.9 and 15.2 days at 

25°C, respectively; mean = 

25.50 days, std. dev. = 5.66

days, n = 2, t90,n-1 = 3.078. 1 Data were selected according to EFED Guidance on Input Parameters v.2.1, dated October 22, 2009 and approved November 10, 2009 

(USEPA 2009).

None of the environmental fate laboratory studies shows omethoate in significant amounts 

(≥10% AR); however, it was previously estimated that a maximum of 24% of the total residues in 

replicate 2 of the terrestrial field dissipation study conducted in California bareground was 

omethoate. In order to obtain a rough estimate of the likely residues of omethoate, this 

percentage was used to calculate the application rate. The crops that yielded the highest EECs 

(i.e., FL citrus and CA cole crops) were modeled under the assumptions for omethoate presented 

in Table 10. Since omethoate was not observed in the aquatic metabolism studies in significant 

amounts, omethoate drift was assumed to be negligible and the chemical was assumed to be soil 

applied.

Table 10. Input parameters utilized in the surface water concentration calculator (SWCC) 

for omethoate

Parameter (units) Value(s)1 Sources Comments

Output File Name Omethoate --- ---

Chemical Name Omethoate Label ---

Application Rate

Kg a.i./ha

CA cole crops 0.202

FL citrus 0.269

(lb a.i./A)

0.75 x 24/100 = 0.18

1.0 x 24/100 = 0.24

Maximum allowed by the 

label. Residues of omethoate 

were a rough estimate from 

the maximum observed in the 

terrestrial field dissipation 

study.

Number of Applications 

Allowed

CA cole crops 2

FL citrus 1

Maximum allowed by 

the labels. ---

Interval between 

Applications (days)

CA cole crops 7

FL citrus N/A

Minimum allowed by 

the labels. ---

Crop Names and Days of 

Application (day-month)

CA cole crops 18-01

FL citrus 01-06 Labels Crops that yielded the highest EECs for dimethoate

PRZM Scenario and 

Metfile

As suggested by the shell for 

the SWCC. SWCC ---

Kd (ml/g) 1.43 47477304

Represents the mean Kd value 

among three values ranging 

from 1.05 to 1.98 ml/g; the Kd

model was utilized because it 

represents the mobility of 

omethoate better than KOC. 

Binding does not appear to be 

correlated with OC.

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )
Page 28 of 144

Table 10. Input parameters utilized in the surface water concentration calculator (SWCC) 

for omethoate

Parameter (units) Value(s)1 Sources Comments

Aerobic Soil Metabolism 

(days) 3.75 No data available, use 47477303

In the absence of data, 

assumed to be similar to the 

aerobic aquatic metabolism 

input value (see below).

Method of Application Aerial (but soil applied) Labels

Omethoate was observed only 

in the terrestrial field 

dissipation.

Buffer Zone (ft.) 0 Labels ---

Application Efficiency 

(fraction) 1.00 soil applied --- ---

Spray Drift (fraction) 0.00 (no drift) --- It is assumed to be formed in 

soils, not in water.

Solubility in Water (ppm) 1 x 106 EPISUITE v.4.1 ---

Aerobic Aquatic 

Metabolism (days)

= 3.75

47477303

90 percent upper confidence 

limit on the mean half-life 

value: two values are 

available: 1.69, 2.7 days at 

25°C; mean = 2.195 days, std. 

dev. = 0.714 days, n = 2, t90,n-1

= 3.078.

Anaerobic Aquatic 

Metabolism (days) 0 No data available Assume stable.

Hydrolysis (days) 0 No data available Assume stable.

Aqueous Photolysis (days) 0 No data available Assume stable.

Aqueous Photolysis 

Reference Latitude (o) 40 No data available Assumed reference latitude.

Molecular Weight (g/mole) 213.19 EPISUITE v.4.1 ---

Vapor Pressure (torr) 2.48 x 10-5 EPISUITE v.4.1 ---

Field Size EPA pond (eco. effects) ---

Incorporation Depth (cm) 0.0 Labels ---

CAM (Chemical 

Application Method) Ground Labels ---

IPSCND (Condition for 

disposition of pesticide 

remaining on foliage after 

harvest)

Surface applied Labels ---

PLDKRT, Foliar half-life 

(days) 2.82 Refer to Table 4

90 percent upper confidence

limit on the mean of the 29 

available half-life values. 

Assumed to be similar to 

dimethoate. 1 Data were selected according to EFED Guidance on Input Parameters v.2.1, dated October 22, 2009 and approved November 10, 2009 

(USEPA 2009).

A summary of dimethoate modeled results related to the maximum application rate is presented 

in Table 11. Table 12 shows a summary of modeled dimethoate EECs for the typical (average) 

application rates provided by BEAD. Table 13 summarizes EECs based on the maximum 

application rate and those crops that yielded the highest EECs among the agricultural and nonagricultural crops using half-lives that included dimethoate plus the unextracted residues (UERs). 

Using the typical application rate, the crop that yielded the highest EECs was run using the halflives for the total toxic residues, dimethoate plus the UERs (Table 14).

t t

t s

n input

n

= + −

1 2

90 1

/

, ( )
Page 29 of 144

Table 11. Water column estimated environmental concentrations (EECs) in μg/L for dimethoate uses in the US, using the 

maximum application rate1

Scenario (bold font)/ 

Crops/Uses Represented

App

Method

Date of 

First 

Application

(dd-mm)

App 

Rate

kg a.i./A

(lb a.i./A)

Number 

of Apps

App

Interval 

(days)

Water Column

Peak 

EEC

(μg/L)

21-day 

average

EEC

(μg/L)

60-day 

average

EEC

(μg/L)

03_MN alfalfa/ Alfalfa, Sainfoin Aerial 20-05 0.560 (0.5) 1/CC

3/year 30 8.57 6.41 4.99

05_CA cole crops/ Brussels 

sprouts (ground) Ground 18-01 0.841 (0.75) 2 7 23.2 20.9 15.4

10_WA orchards/ Cherry (only 

in ID, MT, OR, UT and WA) Aerial 15-11 (postharvest) 1.51 (1.35) 1 N/A 9.44 7.97 6.08

12_OR Xmas trees/ Douglas fir 

(seed orchards) (only in OR and 

WA)

Airblast 01-06 5.04 (4.5) 1 N/A 10.6 8.65 5.74

14_OR Xmas trees/ Hybrid 

cottonwood/poplar plantations 

(some labels allow certain uses in 

ID, OR and WA)

Aerial 01-06 2.24 (2) 3 10 34.1 26.7 20.2

15_CA nursery/ Citrus, nonbearing and nursery stock (only in 

CA and AZ)

Soil drench 01-06 2.13 (1.9) 1 N/A 6.60 5.07 3.28

17_OR nursery/ Ornamental 

woody shrubs and vines; 

Ornamental and/or shade trees

Aerial 01-06 1.12 (1) 3 14 21.2 17.6 14.1

20_FL peppers/ Peppers Aerial 20-10 0.377 

(0.336) 5 7 22.2 17.6 13.1

23_MS Cotton/ Cotton Aerial 20-07 0.560 (0.5) 2 14 9.71 6.74 4.48

26_FL citrus/ Grapefruit, 

Kumquat, Lemon, Lime, Orange, 

Pummelo (shaddock), Tangelo, 

Tangerine

Aerial 01-06 1.121 (1) 1 N/A 22.1 14.7 8.21

`1 All EECs were rounded to three significant figures.

Table 12. Water column estimated environmental concentrations (EECs) in μg/L for dimethoate uses in the U.S. 

using typical application rates1

Scenario (bold font)/ 

Crops/Uses Represented

App

Method

Date of 

First 

Application

(dd-mm)

Aver. 

App Rate

kg a.i./A

(lb a.i./A)1

No. of 

Apps 

(aver. no. 

of apps)1

App 

Interval 

(days)

Water Column

Peak 

EEC

(μg/L)

21-day 

average

EEC

(μg/L)

60-day 

average

EEC

(μg/L)

03c_MN alfalfa/ Alfalfa Aerial 20-05 0.409 

(0.365) 1 (1.1) N/A 2.76 2.23 1.49

04b_CA cole crops/ Broccoli Aerial 25-01 0.535 

(0.477) 1 (1.3) N/A 7.69 6.33 4.45

10c_WA orchards/ Cherry (only 

in ID, MT, OR, UT and WA) Aerial 15-11 (postharvest) 1.35 (1.202) 1 (1.0) N/A 6.01 5.08 3.88

20b_FL peppers/ Peppers Aerial 20-10 0.299 

(0.267) 3 (2.6) 7 16.4 11.5 8.46

23c_MS Cotton/ Cotton Aerial 20-07 0.307 

(0.274) 1 (1.2) N/A 3.69 2.58 1.44

26b_FL citrus/ Grapefruit, 

Kumquat, Lemon, Lime, Orange, 

Pummelo (shaddock), Tangelo, 

Tangerine

Aerial 01-06 0.546 

(0.487) 1 (1.1) N/A 9.89 6.59 3.64

1 All EECs were rounded to three significant figures. Average numbers of applications & application rates for the agricultural crops were provided by BEAD and 

represent data from 2008-2012.
Page 30 of 144

Table 13. Water column estimated environmental concentrations (EECs) in μg/L for dimethoate uses in the U.S. 

Special runs including dimethoate and the unextracted residues.1

Scenario (bold font)/ 

Crops/Uses Represented

App

Method

Date of 

First 

Application

(dd-mm)

App 

Rate

kg a.i./A

(lb a.i./A)

Number 

of Apps

App

Interval 

(days)

Water Column

Peak 

EEC

(μg/L)

21-day 

average

EEC

(μg/L)

60-day 

average

EEC

(μg/L)

05b_CA cole crops/ Brussels 

sprouts (ground) Ground 18-01 0.841 (0.75) 2 7 31.7 27.2 20.7

14b_OR Xmas trees/ Hybrid 

cottonwood/poplar plantations 

(some labels allow certain uses in 

ID, OR and WA)

Aerial 01-06 2.24 (2) 3 10 36.0 30.2 23.8

1 All EECs were rounded to three significant figures. These runs represent the crops with the highest EECs among the agricultural and non-agricultural crops.

Table 14. Water column estimated environmental concentrations (EECs) in μg/L for dimethoate uses in the U.S. 

using typical application rates. Special run including dimethoate and the unextracted residues.

1

Scenario (bold font)/ 

Crops/Uses Represented

App

Method

Date of 

First 

Application

(dd-mm)

Aver. 

App Rate

kg a.i./A

(lb a.i./A)1

No. of 

Apps

Modeled

(aver. no. 

of apps)1

App 

Interval 

(days)

Water Column

Peak 

EEC

(μg/L)

21-day 

average

EEC

(μg/L)

60-day 

average

EEC

(μg/L)

26c_FL citrus/ Grapefruit, 

Kumquat, Lemon, Lime, Orange, 

Pummelo (shaddock), Tangelo, 

Tangerine

Aerial 01-06 0.546 

(0.487) 1 (1.1) N/A 12.1 9.47 6.15

1 All EECs were rounded to three significant figures. Average numbers of applications & application rates for the agricultural crop were provided by BEAD and 

represent data from 2008-2012.

Special runs were performed for omethoate, using the assumptions outlined in Table 10 (the 

most critical assumption is the 24% formation of omethoate, based on one terrestrial field 

dissipation study). EECs are provided in Table 15.

Table 15. Water column estimated environmental concentrations (EECs) in μg/L for omethoate due to 

dimethoate uses in the U.S.1

Scenario (bold font)/ 

Crops/Uses Represented

App

Method

Date of 

First 

Application

(dd-mm)

App 

Rate

kg a.i./A

(lb a.i./A)

Number 

of Apps

App

Interval 

(days)

Water Column

Peak 

EEC

(μg/L)

21-day 

average

EEC

(μg/L)

60-day 

average

EEC

(μg/L)

05_CA cole crops/ Brussels 

sprouts (ground) Ground 18-01 0.202 (0.18) 2 7 3.70 2.33 1.19

26_FL citrus/ Grapefruit, 

Kumquat, Lemon, Lime, Orange, 

Pummelo (shaddock), Tangelo, 

Tangerine

Aerial 01-06 0.269 (0.24) 1 N/A 3.40 0.856 0.305

1 All EECs were rounded to three significant figures.
Page 31 of 144

2.4 Monitoring

The technical registrant (Cheminova, Inc.) submitted a summary of available monitoring data 

(MRID 49178403). It provides data from 2001 from two sources: the USDA's Agricultural 

Marketing Service (AMS) Pesticide Data Program (PDP) (note that this monitoring pertains only 

to drinking water sources), and U.S. Geological Survey’s (USGS) National Water-Quality 

Assessment Program (NAWQA) (see additional details below). A previous review provides a 

summary of monitoring data from early years (Jones 2005, DP Barcode D291603).

2.4.1 Agricultural Marketing Service (AMS) Pesticide Data Program 

(PDP) Monitoring (2001-2011)

The U.S. Department of Agriculture’s (USDA) Agricultural Marketing Service (AMS) Pesticide 

Data Program (PDP) has conducted monitoring of a total of 9209 samples tested for dimethoate 

since 2001 to 2011 (surface, ground and bottled water). EFED added to the summary 253 

samples taken in 2012 (the last year available online) (USDA, 2014). Except for the 

groundwater samples, sites selected must be in community water systems where surface water is 

the primary source of drinking water, and located in heavy agriculture sites (not further 

characterized), where the target pesticides have been applied (USDA, 2014, p. 13). The 2012 

PDP results (USDA, 2014) indicated that EFED had recommended to focus monitoring on sites 

where carbamates and organophosphate pesticides have been applied. It should be noted that the 

focus of the PDP monitoring is on human drinking water sources; whereas, this risk assessment

focuses on surface water which serves as habitat for non-target aquatic organisms.

During the years 2001 to 2012, analysis for dimethoate was conducted in 4,066 finished and 

2,351 untreated drinking water samples. Dimethoate was detected in three of these 6,417 

drinking water samples. Additionally, analysis for omethoate has been incorporated more 

recently. Out of 2,076 samples tested (1,029 finished and 1,047 untreated drinking water 

samples), omethoate was detected in one sample in 2008, and three samples in 2009 (all four 

samples were of finished water). It should also be noted that while for omethoate the limit of 

detection (LOD) ranged between 0.3-7.5 ng/L (parts per trillion or ppt) (0.3 ppt for all years, 

except 2012), for dimethoate it has varied over time, and has been as high as 63 ppt. Dimethoate 

may have been present and reported as undetected in certain samples with concentrations below 

60 ppt.

It is important to realize that the above mentioned monitoring is related to drinking waters and is 

less relevant to ecological exposure.

2.4.2 National Water-Quality Assessment (NAWQA) Groundwater 

Monitoring (2001-2012)

The U.S. Geological Survey’s National Water-Quality Assessment Program (NAWQA) 

groundwater monitoring was summarized per year and by type of land use (agricultural, urban, 
Page 32 of 144

mixed or other; MRID 49178403). Out of 5,236 samples tested for dimethoate throughout the 

period (2001-2012), there were no detects reported (0%). The LODs were reported to be 

between 0.0021 and 0.06 μg/L (parts per billion or ppb). According to the submission, NAWQA 

does not analyze for omethoate.

2.4.3 National Water-Quality Assessment Program (NAWQA) 

Surface Water Monitoring (2001-2012)

The NAWQA surface water monitoring data were summarized per year and by type of land use 

(i.e., agricultural, urban, mixed, or other; MRID 49178403). Out of 8,726 samples tested 

throughout the period (2001-2012), there were 138 detects reported for dimethoate (1.6%), 

ranging from 0.0036-0.494 ppb. The LODs were reported to be between 0.0021 and 0.10 ppb.

When ‘agricultural’ or ‘mixed land’ categories were taken individually, the percent of 

dimethoate detects was higher (2.8% for ‘agricultural land’, and 2.8% for ‘mixed land’). 

Meanwhile, for ‘urban’ and ‘other’ categories, the percent of dimethoate detects was smaller 

(0.3% and 0.2%, respectively). The highest concentration detected, i.e., 0.494 ppb (or 494 ppt), 

was reported for a sample from agricultural land in 2010. Even though there were detections at 

up this level in surface waters in 2010, it appears that this value does not necessarily reflect the 

peak concentration in the field. Although monitoring showed a maximum concentration of 0.494 

ppb, modeling yielded peak EECs ranging from 5.07 ppb to 44.3 ppb; therefore, the monitoring 

was around one order of magnitude lower than the modeling. New restrictions were imposed in 

the dimethoate labels as per the Revised Interim Reregistration Eligibility Decision (RED) 

document issued in 2008 (USEPA 2008). It was noted that the highest detected dimethoate 

concentration was reported in 2010; however, a specific trend (increasing or decreasing 

concentrations) was not observed in the NAWQA monitoring results. In general, the NAWQA 

results appear to support a low frequency of detections. Despite what appears to be a low level 

of detections, EFED believes that modeling reflects concentrations in surface waters which are 

realistically conservative for each site represented.

The monitoring programs analyzed for this risk assessment do not specifically target dimethoate. 

Consequently, detections cannot be directly associated with a particular use pattern or site, nor 

are the detections expected to represent the potential peak dimethoate or omethoate exposures.

The reported concentrations from monitoring data are lower than estimated concentrations 

derived from modeling. This result may be attributed to the fact that water monitoring sampling 

programs do not specifically target dimethoate use areas, may not represent high dimethoate use 

areas, and may not correspond with applications of dimethoate; therefore, peak concentrations of 

dimethoate and omethoate may not be detected. For most monitoring locations, sampling 

frequencies are not designed to capture peak concentrations, and are unlikely to do so by chance. 

Because currently available monitoring data likely underestimate maximum dimethoate and 

omethoate concentrations, monitoring results are not an appropriate predictor of the potential 

peak exposure resulting from dimethoate use. For these reasons, EFED does not recommend that 

dimethoate and omethoate water monitoring data be used to generate risk quotient values.
Page 33 of 144

2.4.4 Precipitation Samples (Majewski et al. 2006)

Dimethoate has been detected in precipitation samples in California. According to Majewski et 

al. 2006, dimethoate was detected in 5% of rainfall samples (n=136) at a maximum 

concentration of 0.102 μg/L. Based on these data, it is possible that dimethoate can be deposited 

on land in precipitation. At this time, the Agency does not have an approved model for 

estimating atmospheric transport of pesticides and resulting exposure to organisms in areas 

receiving pesticide deposition from the atmosphere.

2.5 Terrestrial Exposure Modeling

2.5.1 Exposure to Birds and Mammals

Terrestrial wildlife are exposed to dimethoate via consumption of residues on food items 

generated by spray applications. For spray applications, the T-REX model (Terrestrial Residue 

EXposure model; v. 1.5.2; June 6, 20132) is used to predict dietary exposure to dimethoate

residues on foliar surfaces and insects using the Kenaga nomogram as modified by Fletcher 

(Hoerger and Kenaga 1972, Fletcher et al. 1994). A default 35-day foliar dissipation half-life is

typically used for terrestrial exposure modeling in this assessment; however, suitable foliar 

dissipation data specific to dimethoate are available (Willis and McDowell 1987; MRID 

46486401) and a mean value of 2.82 days was used in T-REX. Estimated exposures of terrestrial 

insects to dimethoate are evaluated in terms of the insects’ potential relevance as dietary items 

for terrestrial vertebrates and for use in risk characterization for listed terrestrial invertebrates. TREX is unable to simulate label specifications for certain uses of dimethoate such as soil drench

and soil injection uses.. 

T-REX is used to calculate dietary and dose-based EECs of dimethoate residues on food items 

for mammals and birds as a result of spray applications at the labeled maximum use rates. Input 

values for the use scenarios used to derive EECs using T-REX and terrestrial plant (TerrPlant) 

tool are located in Table 16 for foliar spray uses that represent a range of single as well as 

seasonal application rates. Upper-bound Kenaga nomogram values are used to derive EECs for 

dimethoate exposures to terrestrial mammals and birds based on a 1-year time period. 

Consideration is given to different types of feeding strategies for mammals, including herbivores, 

insectivores and granivores. Dose-based exposures are estimated for three weight classes of birds 

(20 g, 100 g, and 1000 g) and three weight classes of mammals (15 g, 35 g, and 1000 g). 

Table 16. Input parameters for deriving screening-level terrestrial estimated environmental 

concentrations (EECs) for labeled spray uses of dimethoate related to terrestrial plants and 

animals. A foliar dissipation half-life of 2.82 days was used

Use

Maximum 

Single App. 

Rate (lb. 

a.i./A)

Number of Apps. 

a Max Rate

Maximum 

Seasonal App. Rate

(lb. a.i./A)

Minimum 

Interval 

Between 

Apps. (days)1

Application 

Method Used 

in Modeling

PreHarvest 

Interval 

(days)

Non-Food Uses

Douglas fir (seed 

orchards) (only in OR 

and WA)

4.5 (AB) 1* 4.5 (AB) N/A G (AB) N/A

Hybrid 

cottonwood/poplar 

plantations (some labels 

2 3 6 10 A or G: spray N/A
Page 34 of 144

Table 16. Input parameters for deriving screening-level terrestrial estimated environmental 

concentrations (EECs) for labeled spray uses of dimethoate related to terrestrial plants and 

animals. A foliar dissipation half-life of 2.82 days was used

Use

Maximum 

Single App. 

Rate (lb. 

a.i./A)

Number of Apps. 

a Max Rate

Maximum 

Seasonal App. Rate

(lb. a.i./A)

Minimum 

Interval 

Between 

Apps. (days)1

Application 

Method Used 

in Modeling

PreHarvest 

Interval 

(days)

allow use in ID, OR and 

WA)

Ornamental woody 

shrubs and vines 1 3* 3 14 A or G: spray N/A

Ornamental Herbaceous 

plants 0.25 1 0.25 N/A A or G: spray N/A

Food Uses

Cherry 1.35 1 1.35 N/A A or G: spray 21

Soybeans 0.5 2 1 7 A or G: spray 21

Peppers 0.336 5* 1.67 7 A or G: spray 0

Succulent peas 0.156 1* 0.156 N/A A or G: spray 0

N/A=does not apply; G=ground; A=aerial, S=spray (low or high volume), AB=airblast

*Calculated value, based on the number of applications, or the seasonal application rate.

Differences in exposures between ground and aerial applications cannot be assessed with the 

current T-REX model; exposure and risk estimates from the T-REX model are considered 

relevant to both application scenarios. A further uncertainty with the model is the inability to 

model systemic chemicals like dimethoate as T-REX only simulates residues directly on food 

items.

Some use patterns of dimethoate employ a soil drench method. T-REX is not able to simulate a 

soil drench scenario as the resultant EECs and RQs would assume that the entire application rate 

would be sprayed on terrestrial food items as they are for conventional aerial and ground 

applications. For soil drench, even though the label does not specifically preclude application on 

foliage, it is expected to take place on the root ball of the crop. Since dimethoate is systemic

chemical in plants, food items are likely to contain dimethoate residues even if it is not directly 

applied, when it is translocated across plant tissue. However, the levels or concentrations of 

dimethoate in food items are uncertain for the soil drench applications.
Page 35 of 144

Table 17. Screening-level dose-based estimated environmental concentrations (EECs) in mg/kg bw as food residues for birds from 

labeled uses of dimethoate (T-Rex v. 1.5.2). toxicity to birds is based on acute oral toxicity data for dimethoate

Primary Feeding Strategy 

 Herbivores and Omnivores Insectivores Granivores

Animal Size*  Small Med Large Small Med Large Small Med Large

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s)1 

Non-Food Uses

Douglas fir (seed orchards) 

(only in OR and WA) 1230 563 691 76.8 701 321 394 43.8 314 143 176 19.6 481 274 123 17.0 9.74 4.36

Hybrid cottonwood/poplar 

plantations (some labels allow 

use in ID, OR and WA)

600 275 337 37.5 342 156 192 21.4 153 70.2 86.2 9.58 235 134.1 60.03 8.34 4.75 2.13

Ornamental woody shrubs and 

vines 283 129 159 17.6 161 73.9 90.8 10.0 72.2 33.1 40.6 4.52 110 63.2 28.3 3.93 2.24 1.00

Ornamental Herbaceous plants 68.3 31.3 38.4 4.27 38.9 17.8 21.9 2.44 17.4 8.00 9.81 1.09 26.7 15.2 6.83 0.95 0.54 0.24

Food Uses

Cherry 369 169 207 23.1 210 96.4 118 13.1 94.2 43.1 52.9 5.89 144 82.4 36.9 5.13 2.92 1.31

Soybeans 162 74.2 91.1 10.1 92.3 42.3 51.9 5.77 41.3 18.9 23.2 2.59 63.4 36.1 16.2 2.25 1.28 0.57

Peppers 112 51.6 63.4 7.05 64.2 29.4 36.1 4.02 28.7 13.1 16.1 1.80 44.1 25.1 11.2 1.57 0.89 0.40

Succulent peas 42.6 19.5 23.9 2.67 24.3 11.1 13.6 1.52 10.8 4.99 6.12 0.68 16.7 9.52 4.26 0.59 0.34 0.15
Page 36 of 144

Table 18. Screening-level dose-based estimated environmental concentrations (EECs) in mg/kg bw as food residues for mammals from 

labeled uses of dimethoate (T-Rex v. 1.5.2) 

Primary Feeding Strategy  Herbivores and Omnivores Insectivores Granivores

Animal Size*  Small Med Large Small Med Large Small Med Large

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s)1 

Non-Food Uses

Douglas fir (seed orchards) (only in 

OR and WA) 1030 471 579 64.3 711 326 400 44.4 165 75.6 92.8 10.3 403 278 64.6 14.3 9.88 2.29

Hybrid cottonwood/poplar plantations 

(some labels allow use in ID, OR and 

WA)

502 230 282 31.4 347 159 195 21.7 80.5 36.9 45.3 5.03 196 136 31.5 6.98 4.32 1.12

Ornamental woody shrubs and vines 237 108 133 14.8 163 75.0 92.1 10.2 37.9 17.4 21.3 2.37 92.8 64.1 14.8 3.29 2.27 0.53

Ornamental Herbaceous plants 57.2 26.2 32.1 3.58 39.5 18.1 22.2 2.47 9.17 4.20 5.16 0.57 22.4 15.4 3.59 0.79 0.55 0.13

Food Uses

Cherry 308 141 173 19.3 213 97.8 120 13.3 49.5 22.6 27.8 3.09 121 83.6 19.3 4.29 2.97 0.69

Soybeans 135 62.1 76.2 8.48 93.7 42.9 52.7 5.86 21.7 9.96 12.2 1.36 53.1 36.7 8.51 1.88 1.30 0.30

Peppers 94.3 43.2 53.0 5.90 65.2 29.8 36.6 4.08 15.1 6.93 8.51 0.95 36.9 25.5 5.92 1.31 0.91 0.21

Succulent peas 35.7 16.3 20.0 2.23 24.6 11.3 13.8 1.54 5.72 2.62 3.22 0.36 13.9 9.66 2.24 0.50 0.34 0.08
Page 37 of 144

Table 19. Screening-level dietary-based estimated environmental concentrations (EECs) in mg/kg 

bw as food residues for mammals, and birds from labeled uses of dimethoate (T-Rex v. 1.5.2)

Primary Feeding Strategy  Herbivores, Omnivores, and Granivores Insectivores

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Use(s) 

Arthropods

Non-Food Uses

Douglas fir (seed orchards) (only in OR and WA) 1080 495 607 67.5 423

Hybrid cottonwood/poplar plantations (some labels 

allow use in ID, OR and WA) 527 241 296 32.9 206

Ornamental woody shrubs and vines 248 113 139 15.5 97.3

Ornamental Herbaceous plants 60.0 27.5 33.7 3.75 23.5

Food Uses

Cherry 324 148 182 20.2 126

Soybeans 142 65.2 80.0 8.89 55.7

Peppers 98.9 45.3 55.6 6.19 38.7

Succulent peas 37.4 17.1 21.0 2.34 14.6
Page 38 of 144

2.5.2 Bees

In addition to the terrestrial exposure modeling for birds and mammals, Tier 1 (screening level) 

exposure estimates were also derived for pollinating bees, using the honey bee as a surrogate. 

These exposure estimates include contact and dietary exposure pathways for both foliar and soil 

applications based on the EFED guidance document for assessing pesticide risk to bees (USEPA 

20149). Tier 1 estimates of daily exposure values in μg a.i./bee were derived for adult as well as 

for larval life stages of honey bees for both non-food and food uses that represent a range in 

dimethoate application rates. For contact exposure of adult foragers to foliar sprays, EECs were 

based on the application rate (lb a.i./A) and the unit dose estimate of 2.7 ug ai/bee per lb a.i./A as 

described in USEPA (201310; 2014). For oral (dietary) exposure via pollen and nectar with foliar 

sprays, EECs were based on the application rate, T-REX estimated unit residue (110 ug ai/g per 

lb ai/A), and the caste-specific consumption rate of nectar and pollen (292 mg/d for adult 

foragers, 124 mg/d for larvae). These honey bee castes represent those with the highest expected 

exposures via oral ingestion (e.g., adult foragers, 5-d old larvae). Table 24 lists input 

parameters used for deriving exposure values for bees; Table 25 presents the Tier 1 EECs for 

foliar spray applications, with additional details provided in Appendix 11.

 9

http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/terrestrial_biology_tech_team/GuidanceAssessingPesticideRisk2Bees.

pdf

10 http://www.cdpr.ca.gov/docs/emon/surfwtr/presentations/epa_whitepaper.pdf

Table 20. Input parameters for deriving screening-level terrestrial estimated environmental 

concentrations (EECs) in pollen and nectar from systemic residues for soil drench uses of 

dimethoate

Use

Maximum 

Single App. 

Rate (lb. 

a.i./A)

Number of 

Apps. a 

Max Rate

Maximum 

Seasonal 

App. Rate

(lb. a.i./A)

Minimum 

Interval 

Between Apps.

(days)1

Application Method 

Used in Modeling

PreHarvest 

Interval 

(days)

Hybrid cottonwood/poplar 

plantations 2 3 6 10 SI N/A

Ornamental woody shrubs 

and vines 1 3* 3 14 SI N/A

Melon, Watermelon 0.5 2 1 7 C 3

Succulent peas 0.156 1* 0.156 N/A C 0

N/A=does not apply; C=chemigation, SD=soil drench; SI=soil injection treatment

Assumptions in the table are shaded grey.

*Calculated value, based on the number of applications, or the seasonal application rate.
39

Table 21. Tier I Screening-level estimated environmental concentrations (EECs) for honey 

bees based on foliar applications of dimethoate.

Use Pattern

Assessed 

Application 

Rate

(lb ai/A)

Adult Larvae

Acute 

Contact

(μg a.i./bee/

day)

Acute 

Oral

(μg a.i./bee/

day)

Chronic

(μg a.i./bee/

day)

Non-Food Uses

Douglas fir (seed orchards) (only in OR 

and WA) 4.5 12.2 144.5 61.4

Hybrid cottonwood/poplar plantations 

(some labels allow use in ID, OR and 

WA)

2 5.4 64.2 27.3

Ornamental woody shrubs and vines 1 2.7 32.1 13.6

Ornamental Herbaceous plants 0.25 0.68 8.0 3.4

Food Uses

Cherry 1.35 3.65 43.4 18.4

Soybeans 0.5 1.35 16.1 6.8

Peppers 0.336 0.91 10.8 4.6

Succulent peas 0.156 0.42 5.0 2.1

For applications of dimethoate to soil, bees are expected to be exposed primarily through the oral 

(ingestion) route due to systemic uptake of dimethoate by plants. As described in USEPA 

(2014), Tier 1 estimates of pesticide residues in pollen and nectar are derived using the Briggs 

model (a component of PRZM) and the pesticide application rate. The oral EECs are then 

determined using the same pollen and nectar consumption rates described previously for foliar 

applications. Table 22 presents the exposure values for soil applications with additional details 

provided in Appendix 11.

Table 22. Tier I Screening-level estimated environmental concentrations (EECs) for honey bees 

based on soil drench applications of dimethoate

Use Pattern

Assessed 

Application Rate

(lb ai/A)

Adult Larvae

Oral 

(μg a.i./bee/day)

Hybrid cottonwood/poplar plantations 6 1.897 0.806

Ornamental woody shrubs and vines 3 0.949 0.403

Melon, Watermelon 1 0.316 0.134

Succulent peas 0.156 0.049 0.021

2.5.3 Runoff and Spray Drift to Terrestrial and Semi-Aquatic Plants 

The TerrPlant (v. 1.2.2; December 26, 2006) model is used to derive EECs relevant to terrestrial 

and wetland plants for dimethoate. The model employs the assumption that default fractions of 

the intended application are transported to an adjacent field through runoff and spray drift. 
40

Measures of exposure to terrestrial plants are expressed as a fraction of the mass of the 

dimethoate applied to the treated field. 

Loading via spray drift to dry, non-target, adjacent areas is assumed to occur from one acre of treated 

land to one acre of an adjacent non-target area. Runoff is also expected to be a source of pesticide 

loading to non-target areas. TerrPlant calculates EECs as a function of application rate, solubility, 

and default assumptions regarding spray drift. The default spray drift assumptions are 1% of the 

application rate for ground spray applications and 5% for aerial spray applications (USEPA 2006b). 

The EECs for terrestrial and semi-aquatic plants for a single application of dimethoate at the 

maximum labeled rates for representative uses are presented in Table 23 (see example output in 

Appendix 6).

Table 23. Estimated environmental concentrations (EECs) for terrestrial plants based on 

various application rates and either ground or aerial spray application methods (TerrPlant 

v.1.2.2)

Crop

Single 

Max. 

Application 

Rate (lbs 

a.i./A)

EECs (lbs a.i./A)

Runoff to 

dry areas

Runoff to 

semiaquatic 

areas

Spray drift Total for 

dry areas

Total for 

semi-aquatic 

areas

Non-food uses

Douglas Fir Aerial: 4.5 0.225 2.25 0.225 0.45 2.47

Ground: 4.5 0.225 2.25 0.045 0.27 2.29

Hybrid 

cottonwood

Aerial: 2 0.1 1 0.1 0.2 1.1

Ground: 2 0.1 1 0.02 0.12 1.02

Ornamental 

woody shrubs 

and vines

Aerial: 1 0.05 0.5 0.05 0.1 0.55

Ground: 1 0.05 0.5 0.01 0.06 0.51

Ornamental 

Herbaceous 

plants

Aerial: 0.25 0.0125 0.125 0.0125 0.025 0.137

Ground: 

0.25 0.0125 0.125 0.0025 0.015 0.127

Food Uses

Cherry

Aerial: 1.35 0.0675 0.675 0.0675 0.135 0.742

Ground: 

1.35 0.0675 0.675 0.0135 0.081 0.688

Soybeans Aerial: 0.5 0.025 0.25 0.025 0.05 0.275

Ground: 0.5 0.025 0.25 0.005 0.03 0.255

Peppers

Aerial: 

0.336 0.0168 0.168 0.0168 0.0336 0.184

Ground: 

0.336 0.0168 0.168 0.00336 0.0201 0.171

Succulent peas

Aerial: 

0.156 0.0078 0.078 0.0078 0.0156 0.0858

Ground: 

0.156 0.0078 0.078 0.00156 0.00936 0.0795
41

2.5.4 Bioaccumulation

Bioaccumulation will not be assessed in this PRA because both dimethoate and its 

transformation product omethoate have very low KOW values (i.e., dimethoate KOW = 5.06; 

omethoate estimated KOW = 0.18) and neither compound is expected to bioaccumulate 

extensively in aquatic organisms. As a result, the BCF study was previously waived for 

dimethoate, and EFED does not anticipate these two compounds bioaccumulating in the food 

chain sufficiently to lead to exposure of concern in birds, reptiles, terrestrial-phase amphibians, 

or mammals that feed on aquatic food items.

3.0 Ecological Toxicity

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

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

1998). For dimethoate, the ecological entities include the following: birds, reptiles, terrestrialphase amphibians, mammals, freshwater fish, freshwater aquatic-phase amphibians and 

invertebrates, estuarine/marine fish and invertebrates, terrestrial plants, insects, aquatic plants, 

and algae. The attributes for each of these entities include growth, reproduction, and survival. 

The ecological effects characterization for dimethoate is based upon registrant-submitted toxicity 

data for the TGAI (parent compound) and for specified formulations. The ecotoxicity data for

dimethoate and its associated products have been reviewed previously in the Problem 

Formulation for Registration Review assessment (USEPA 2008). Various studies with terrestrial 

and aquatic plants, birds, and aquatic animals exposed to either the TGAI, formulated 

dimethoate, omethoate and other degradates have been received since the preliminary Problem 

Formulation was issued. Those data that were reviewed and provided a more sensitive endpoint 

than those in the Problem Formulation have been included in Tables 7 and 8 along with those 

data identified previously where more sensitive data have not been identified . A comprehensive 

list of data submitted since the preliminary Problem Formulation can be found in Appendix 8

with their classification and a brief summary; some data are still in review.

A search of the ECOTOXicology database in 2013, yielded additional data to complement those 

data submitted by the registrant. The database was reviewed for studies, which meet data quality 

standards, with relevant endpoints considered to be more sensitive than those considered in the 

assessment. A cursory review of these studies was conducted to evaluate their potential utility 

in characterizing the potential risk associated with the use of dimethoate. Additionally, the 

bibliography of acceptable studies considered in this assessment can be found in Appendix 10.

3.1 Aquatic Organisms

Technical grade dimethoate is classified as moderately toxic to freshwater fish and aquatic-phase 

amphibians and very highly toxic to freshwater and estuarine/marine aquatic invertebrates on an 

acute exposure basis. The 2008 Problem Formulation provides a summary of the methods used 

in estimating the acute-to-chronic ratio (ACR) for extrapolating the value used for chronic 
42

freshwater invertebrates in Table 24 below for which dimethoate-specific empirical data were 

not available. Additionally, the salt water mosquito (Aedes taeniorhynchus) and the freshwater 

stonefly (Pteronarcys californica) were found to be more acutely sensitive to dimethoate than the 

freshwater daphnid (Daphnia magna) and estuarine/marine mysid shrimp (Americamysis bahia). 

Dimethoate is practically nontoxic to estuarine/marine fish on an acute exposure basis. Chronic 

exposure to dimethoate resulted in decreased growth in freshwater fish. 

Aquatic vascular aquatic plants (Table 24) were relatively insensitive to dimethoate (Lemna 

gibba EC50 >92.6 mg/L) compared to nonvascular aquatic plants (Anabaena flos-aquae IC50=20 

mg/L).

The available information reported in the Interim Reregistration Eligibility Decision (IRED) 

document (USEPA 2000) indicates that aquatic organisms are more sensitive to the TGAI than to

the formulated products of dimethoate; therefore, the focus of this assessment is on the TGAI of 

dimethoate and its transformation product omethoate. Toxicity data for omethoate are discussed 

later in the document.

An acute non-guideline toxicity study of dimethoate conducted using tadpoles of the African 

Clawed Frog (Xenopus laevis)was submitted in support of this assessment (MRID 48634201). A 

review of the study shows the endpoint to be greater than that of the LC50 of 6.2 mg/L for 

rainbow trout (Oncorhynchus mykiss), thus freshwater fish will be continue to be used a 

surrogate for aquatic-phase amphibians.

Table 24. Most sensitive aquatic species evaluated for assessing potential ecological effects of 

dimethoate

Study Type Tested Species Toxicity Endpoint

Study MRID and 

Toxicity 

Classification

850.1075 Acute Freshwater Fish Rainbow trout 

(Oncorhynchus mykiss) LC501 = 6.2 mg/L 40094602Moderately toxic

850.1400 Chronic Freshwater 

Fish

Rainbow Trout

(Oncorrhynchus mykiss) NOAEC = 0.43 mg/L 43106303

850.1010 Acute Freshwater 

Invertebrate

Stonefly

(Pteronarcys californica) EC50 = 0.043 mg/L 00003503Very highly toxic

850.1300 Chronic Freshwater 

Invertebrate

Stonefly

(Pteronarcys californica

NOAEC2= 0.0005 

mg/L Estimated using ACR

850.1075 Acute Estuarine/marine 

Fish

Sheepshead Minnow

(Cyprinodon variegatus) LC50 >111 mg/L 42760001Practically non-toxic

850.1400 Chronic 

Estuarine/marine fish

Sheepshead Minnow

(Cyprinodon variegatus) NOAEC3

=1.2 mg/L 48772901

48-hour Acute 

Estuarine/marine 

Invertebrate

Salt Marsh Mosquito

(aedes taeniorhynchus) LC50 = 0.031 mg/L Song et al. 1997

Very highly toxic

850.1350

Chronic 

Estuarine/marine 

Invertebrate

Salt Marsh Mosquito

(Aedes taeniorhynchus)

NOAEC4 = 0.0002

mg/L

NA

850.4400 Vascular Plant Duckweed

(Lemna gibba)

EC50 >92.6 mg/L

NOAEC = 92.6 mg/L 47709703

850.4550 Nonvascular Plant Cyanobacteria

Anabaena flos-aquae

EC50 = 20.0 mg/L

NOAEC = 9.0 mg/L 48572804

1 Freshwater fish are considered surrogates for aquatic-phase amphibians.
43

There are two studies available on the toxicity of the dimethoate formulation. Available data on 

the 4.0 emulsifiable (EC) dimethoate formulation indicate the formulation is less acutely toxic to 

rainbow trout when compared to the TGAI by about an order of magnitude; the acute LC50 for 

rainbow trout was found to 59.8 mg/L (48298302) as compared to the parent toxicity of 6.2 mg/L 

(40094602). Another study conducted using the bluegill found an LC50 of 44.5 mg/L 

(48298303) as compared to the parental toxicity of 31.5 mg/L (48821401). 

3.2 Terrestrial Organisms

The most sensitive toxicity endpoints for dimethoate with terrestrial organisms are shown in 

Table 25. Dimethoate is moderately to very highly toxic to birds (and to terrestrial-phase 

amphibians and reptiles for which birds serve as surrogates) and is moderately toxic to mammals 

on an acute oral exposure basis, and ranges from slightly to highly toxic to birds on a subacute 

dietary exposure basis. Chronic exposure to dimethoate resulted in decreased reproduction and 

survival in birds and decreased survival in mammals. 

Terrestrial plant toxicity studies (seedling emergence and vegetative vigor) resulted in nondefinitive endpoint for the monocotyledenous (monocot) onion (Allium cepa). For 

dicotyledenous (dicot) plants, the seedling emergence study yielded a definitive EC25 of 0.84 lbs 

ai/A for sugar beets (Beta vulgaris) while the vegetative vigor study yielded a non-definitive 

EC25 of greater than 1.51 lbs ai/A. 

2 Estimated using acute-to-chronic ratio (ACR) with Daphnia magna data (ACR=EC50/NOAEC = 83); acute daphnid effects based on 

immobility while chronic effects included impaired reproduction, growth, and survival. 3 NOAEC based on growth; study classified as supplemental because time to hatch was not assessed

4

Estimated using ACR with Americamysis bahia data (ACR=EC50/NOAEC = 107); acute mysid effects based on immobility while chronic 

effects included impaired reproduction, growth and survival.

Table 25. Most sensitive terrestrial species evaluated for assessing potential ecological effects of 

dimethoate.

Study Type Tested Species Toxicity Endpoint

Study MRID 

and Toxicity 

Classification

850.2100 Avian Acute Oral Red-winged Blackbird

(Agelaius phoneniceus) LD50= 5.4 mg/kg bw

00020560

Very highly 

toxic

850.2200 Avian Dietary Northern Bobwhite Quail

(Colinus virginianus) LC50= 150 mg/kg diet 47769705Highly toxic

850.2300 Avian Reproduction Northern Bobwhite Quail

(Colinus virginianus) NOAEC = 4.0 mg/kg diet 44049001

- Mammalian Acute 

Oral

Norway Rat

(Rattus novegicus) LD50 = 358 mg/kg bw 00164200Moderately toxic

- Mammalian 

Reproduction

Norway Rat

(Rattus novegicus) NOAEL = 0.1 mg/kg bw 45529703

Non-Gdln Honeybee Acute Oral 

Adult Toxicity

Honeybee

(Apis mellifera) Oral LD50= 0.056 μg/bee 00026489Highly toxic

850.3020

Honeybee Acute 

Contact Adult 

Toxicity

Honeybee

(Apis mellifera)

Contact LD50 = 0.16 

μg/bee

00026489

Highly toxic
44

3.2.1 Terrestrial Invertebrates

Bees (Tier 1 Individual Organism Effects):

Dimethoate is classified as highly toxic to adult honeybees (Apis mellifera) on both an acute oral 

and contact exposure basis (Table 24).No data are available for determining acute or chronic 

LD50 values for larval honey bees. However, in a recent chronic toxicity test of sulfoxaflor 

submitted to the Agency, a daily dose of 1 μg dimethoate/bee/d for 5 days resulted in 98% 

mortality of larval honey bees by day 7 (MRID 48755603). 

Bees (Tiers 2 Colony Level Effects):

Similarly, no Tier 2 (semi-field, tunnel) studies have been submitted to the Agency for 

dimethoate. However, dimethoate is commonly used as a reference toxicity in Tier 2 tunnel 

studies. In a recent pesticide ecological risk assessment with sulfoxaflor11, EPA summarized 

results from several Tier 2 tunnel studies in which dimethoate was used as the reference toxicant. 

Generally, foliar spray application of dimethoate at 600 g a.i./ha (0.53 lb a.i./A) to bees foraging 

on Phacelia during bloom resulted in sustained increases in worker bee mortality, reduced flight 

activity and behavioral abnormalities (MRID 48445807). Impacts on brood development were 

not clear due to limitations in the submitted Tier 2 studies. It is noted that this application rate 

(0.53 lb a.i./A) is well within the range of registered application rates of dimethoate (see Table 

2).

Bees (Tiers 3 Colony Level Effects):

Study Design/Methods: A Tier 3 (full field) study was conducted in July-August 2004 to 

investigate the effects of dimethoate EC formulation 400 g/L on honey bee colony health (MRID 

481013-02). Dimethoate was applied to flowering Phacelia tanacetifolia which were sown at a 

seeding rate of 11 kg/ha ca. 10 weeks before the start of the experiment. The study evaluated the 

impact of a single application of dimethoate (0.67 lb ai/A) in the evening after bee flight, and 

thus was designed to estimate the effects from presumably dried residues on foliage. Control and 

dimethoate-treated plots (~2,500 m2) were separated by 2 km and applications were made during 

full bloom although the percent bloom was not quantified. A total of 4 colonies each containing 

9 and 11 frames in the lower and upper boxes (including 5 brood frames with brood in all stages) 

were distributed in each plot 4 days prior to pesticide application. The Phacelia bloomed for 17 

days post application, after which colonies were moved to an untreated meadow approximately 

10 km away for continued monitoring. Colonies were queen right and reportedly had a low 

incidence of mite (Varroa destructor) infestation (< 1 mite/colony/day), although the method of 

 11 http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2010-0889-0022

850. 4100 Seedling Emergence

Monocot: Onion

(Allium cepa)

EC25 >1.48 lb a.i./A

NOAEC = 0.745 lb a.i./A 48628101 Dicot: Sugar beet

(Beta vulgaris)

EC25 = 0.84 lb a.i./A

NOAEC <0.23 lb a.i./A

850.4150 Vegetative Vigor

Monocot: Onion

(Allium cepa)

EC25 > 1.46 lb a.i./A

NOAEC = 0.48 lb a.i./A 48572802 Dicot: Sugar beet

(Beta vulgaris)

EC25 >1.51 lb a.i./A

NOAEC = 0.5 lb a.i./A
45

Varroa monitoring may have underestimated actual mite loads. No evaluation of pathogen load 

(e.g., fungal Nosema ceranae; N. apis) was indicated. Mortality, foraging activity, hive weight, 

brood development, food stores, and behavioral abnormalities of the bees were assessed 

periodically before and after application. Samples of flowers, pollen, and nectar were not 

collected for analysis of residues nor were samples from inside the hives collected for the 

determination of residues and confirmation of exposure. However, the presence of Phacelia

pollen relative to other pollen sources was estimated visually by color through Day 7 following

application. 

Mortality, Flight Activity, Behavior: Mean daily bee mortality in hives at the control plot 

ranged from 1 to 70 dead bees/day from Days 1 through 7 after application. Following 

application of dimethoate, statistically significant (p<0.05) increases in mean daily mortality of 

bees occurred from hives at the treated site relative to controls (1,100 vs 41 dead bees, 

respectively). Daily bee mortality decreased to 212 and 116 bees on Days 2 and 3 post 

application, but these were not statistically significant from controls. From Day 4 through Day 7 

post application, bee mortality rates from dimethoate-treated site were comparable to controls. 

Similar to the pattern observed for mortality, the incidence of abnormal behavior (uncoordinated 

movement, lethargy, aggressiveness) increased on Days 1 and 2 relative to controls. From Days 

3-7, no further behavioral impairments, aside from aggressiveness, were observed through the 

duration of the study. Flight activity of bees was comparable among the control and treated 

hives prior to pesticide application, but was consistently reduced to approximately 1⁄3 of controls 

through post application Day 7. 

Hive Weight, Pollen Collection): All colonies lost weight over the 29 day course of the 

experiment, with treated colonies losing 3.5 kg on average compared to 3.0 kg for controls. 

From Days 0 - 7, hives at the treated site lost more weight than controls (-2.4 kg vs -0.1 in 

controls). By Day 14 through Day 29, changes in hive weights were comparable among control 

and treated hives. The greatest period of weight loss corresponded to reductions in foraging 

activity and high bee mortality in the dimethoate-treated colonies. Observation of pollen from 

bees returning to the hives indicated that bees from the treated site did not return with Phacelia

pollen (purple in color) from 1-3 Days after application, unlike controls in which 50% of bees 

were observed with Phacelia pollen. After 3 days, bees from the treated site intermittently 

returned with Phacelia pollen. After colonies were moved from the sites to the meadow on Day 

17, pollen from multiple sources (colors) was observed from both controls and treated hives. 

Overall, the pollen observations suggest that bees foraged on Phacelia pollen during the 

exposure period, although it is possible that bees foraging on treated plants died soon after 

application and did not return to the hive. 

Brood and Colony Condition. At the beginning of the study, colonies in the two treatment 

groups showed all brood (i.e., egg, larvae, and pupae) stages, and sufficient amounts of nectar 

and pollen storage. Eight days following the application, all brood stages were still seen in 

colonies from controls and treated plots. The study authors report a decrease in the number of 

brood rearing areas of colony frames (not quantified) in the colonies of the dimethoate-treated 

plot relative to controls. At 29 days following the application, the study deemed a “sufficient” 

amount of nectar was found in all treatment groups and the amount of brood were comparable in 

both treatment groups with to indication of test-related effect in the dimethoate-treated colonies. 
46

Either the queens or her eggs were found in all eight colonies during the brood checks indicating 

the queens were alive and reproducing. The study authors report that less detailed observations 

were made on Day 14 and Day 21. However, they noted that all brood stages were present on 

combs and that different sources of pollen were also present based on differences in pollen color. 

Conclusions/Interpretation. It can be concluded from this study that exposure to dried 

dimethoate residues on Phacelia foliage resulting from a single 0.67 lb ai/A spray application at 

full bloom leads to elevated forage bee mortality, reduced foraging activity, increased behavioral 

abnormalities and reduced pollen collection from 3 to 7 days after application. The study authors 

reported a temporary reduction in brood area in hives from the treated site, but did not conduct a 

quantitative analysis of the comb to support this conclusion. No colonies were lost 29 days after 

application and colonies appeared healthy according to the study authors. In this specific study, 

the treated colonies were able to recover 29 days after application. However, the study contains 

a number of limitations for risk assessment, including:

• Use of an application rate (0.67 lb ai/A) well below the maximum application rate for 

some uses (e.g., 4.5 lbs ai/A for forestry uses). 

• The test plots were small (50m x 50m) compared to typical agricultural fields.

• Use of 4 colonies at a single site represents pseudo replication since the treatment unit is 

the field and not the colony, which brings the statistical comparisons into question 

(multiple sites/treatment should have been used for true replication). 

• Conclusions regarding brood development were not supported by a quantitative analysis 

of comb area measurements; no estimates of numbers of bees was made.

3.3 Degradate toxicity

3.3.1 Aquatic Organisms

There were a number of toxicity studies conducted using dimethoate degradates in support of this

PRA. Comparison of acute toxicity studies conducted using the rainbow trout, bluegill sunfish 

(Lepomis macrochirus) and, D. magna have been tabulated in Table 26. The available acute 

toxicity data for rainbow trout indicate that dimethoate and omethoate are of similar toxicity with 

LC50 values of 6.2 mg/L and 5.0 mg/L, respectively. The other degradates, i.e.,

dimethylthiophosphoric acid (sodium [Na]-salt), O-desmethyl dimethoate (Na-salt), and 

dimethylphosphoric acid, (Na-salt) are less toxic to rainbow trout than the parent dimethoate, 

with non-definitive LC50 values (ranging from >80.8 mg/L to >1000 mg/L). Examination of 

the acute toxicity data for the bluegill indicate that omethoate is more toxic by about a factor of 

four when compared to dimethoate TGAI. There are no chronic toxicity data available with 

which to compare dimethoate to omethoate for freshwater fish. With D. magna, available data 

indicate that omethoate is more toxic than dimethoate by a factor of four; whereas omethoate is 

less toxic by about a factor of three on a chronic exposure basis.
47

Table 26. Comparison of Acute toxicities (96-hr LC50) of dimethoate and degradates to freshwater fish and 

invertebrates

Species Endpoint Dimethoate Omethoate

Dimethylthiophosphoric 

acid, Na-salt

O-Desmethyl 

Dimethoate, 

Na-salt

Dimethyl 

phosphoric 

Acid, Na-salt

Dimethoate 

Formulation

Rainbow 

Trout 

LC50

(95% CI)

6.2 mg/L

(40094602)

5.0 mg/L

(4.4 – 5.8)

(48821404)

>961 mg/L

(48298308)

>80.8 mg/L

(48298305)

>1000 mg/L

(48298311)

59.8 mg/L

(48298302)

NOAEC 1.5 mg/L

(49083401) -- -- -- -- --

Bluegill LC50

(95% CI)

31.5 mg/L

(19.0 – 60.3)

(48821401)

7.7 mg/L

(5.7 – 9.5)

(48821402)

-- -- -- 44.5 mg/L

(48298303)

Daphnid

EC50

1.6 mg/L

(48298306

0.0325 mg/L

(48821405)

66.7 mg/L

(48298307)

>82.9 mg/L

(48298304) -- --

NOAEC 0.04 mg/L

(42864701)

0.119 μg/L

(48821413) -- -- -- --
48

3.3.2Terrestrial organisms

Acute and chronic toxicity data are available to compare the toxicities of dimethoate to 

omethoate to birds (Table 27). Omethoate appears to be of similar acute oral toxicity to the 

red-neck pheasant (Phasianus colchicus) when compared to dimethoate (i.e., LC50 values are 

within a factor of 2X and confidence intervals overlap). The acute oral toxicity of dimethoate 

and omethoate are virtually identical with bobwhite quail as well. The subacute dietary LC50 

values of dimethoate and omethoate for bobwhite quail are also within a factor of two with 

overlapping 95% confidence intervals. 

Regarding chronic dietary toxicity to birds, an avian reproduction study (MRID 4816201) was 

conducted to compare the effects of dietary exposure of omethoate and dimethoate in separate 

groups of 27-week old bobwhite quail. The study evaluated effects on adult health, body 

weight, and food consumption as well as the number of eggs laid, normal development of 

eggs, embryo viability, hatchability, number of offspring and egg shell thickness. A number 

of sublethal effects were reported in both the omethoate and dimethoate treatment groups

including reduced reaction to external stimuli, lethargy, loss of coordination, wing droop, and 

lower limb weakness. The most sensitive endpoints evaluated for dimethoate were number of 

eggs laid per pen, mean food consumption and adult female body weight gain; these resulted 

in a NOAEC of 10.7 mg ai/kg diet. The most sensitive endpoint evaluated for omethoate was 

female adult body weight gain resulting in a NOAEC of 4.44 mg ai/kg diet. Omethoate

appears to be of similar toxicity as dimethoate when considering normal variability in toxicity 

test data.

Table 27. Comparison of toxicity of technical grade dimethoate to omethoate for 

birds

Species Dimethoate

(MRID)

Omethoate

(MRID)

Acute Oral LD50

Red-winged Blackbird

(Agelaius phoeniceus)

5.4 mg/kg-bw

(00020560) --

Canary

(Serinus canaria)

145 mg/kg-bw

(49096101) --

Ring-necked pheasant

(Phasianus colchicus)

14.1 mg/kg-bw

95% CI = 10-20 mg/kg-bw

(47769702)

28 mg/kg-bw

95% CI = 15-NC mg/kg-bw

(47769704)

Starling

(Sturnus vulgaris)

32 mg/kg-bw

(00020560) --

Mallard

(Anas platyrhynchos)

41.6 mg/kg-bw

(115198) --

Northern Bobwhite

(Colinus virginianus)

10.9 mg/kg-bw

95% CI = 5-20 mg/kg-bw

(47769701)

9.6 mg/kg-bw

95% CI = 6.1-15 mg/kg-bw

(47769703)

Japanese Quail

(Coturnix japonica) -- --
49

Table 27. Comparison of toxicity of technical grade dimethoate to omethoate for 

birds

Species Dimethoate

(MRID)

Omethoate

(MRID)

Dietary LC50

Ring- necked pheasant

(Phasianus colchicus)

353 mg/kg-diet

(47769706)

Northern Bobwhite

(Colinus virginianus)

150 mg/kg-diet

95% CI = 68.7-210 mg/kg bw

(47769705)

81.7 mg/kg-diet

(47709501)

Mallard

(Anas platyrhynchos)

1077 mg/kg-diet

(47744401) --

Chronic NOAEC

Northern Bobwhite

(Colinus virginianus)

10.7 mg/kg-diet

(4816201)

4.44 mg/kg-diet

(4816201)

*These studies were mentioned in the Evaluation of Fully Approved or Provisionally Approved Products, Evaluation 

on Omethoate, 1994. The specific studies from which these endpoints were derived were not cited within the 

document.

In addition, mammalian data on omethoate and dimethoate are available for comparison as 

well. Omethoate is a more potent AChE inhibitor. To account for the increased potency of 

omethoate in risk estimates, benchmark dose 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. As described in the Office of Pesticide Programs’ Health 

Effects Division guidance document for cumulative risk assessment (USEPA, 2002), to the 

extent possible comparisons of toxic potency should be made using a uniform basis of 

comparison, by deriving a common response from a comparable measurement methodology, 

species, and sex for all the exposure routes of interest. TAFs have been estimated previously 

for dimethoate and omethoate by the Human Effect Division within the EPA (A. Lowit; 11-

APR-2005; TXR# 0052940). The originally calculated steady-state TAF of 3 (A. Lowit; 24-

APR-2002) was verified by HED with additional subchronic and chronic studies; therefore no 

changes were made to the steady state TAF.

It is noted here that the TAF of 3 used by the Health Effects Division to assess potential risks 

to human health is based on AChE inhibition. For ecological risk assessment, the relationship 

between AChE inhibition and apical endpoints of interest (i.e., impaired growth, survival, 

reproduction) has not been quantitatively established. However, for the purposes of this 

assessment, omethoate will be assumed to have toxicity 3X greater than that of dimethoate; 

comparable acute mammalian data for omethoate is not available at this time.

Acute toxicity data for honeybees indicates a similar toxicity for the parent dimethoate and its 

omethoate degradate. In an acute contact study, the reported LD50 was 0.048 μg/bee for 

honeybees exposed to technical omethoate (DEFRA 1993). As discussed above, the most 

conservative acute contact honey bee LD50 for dimethoate is 0.05 μg/bee.
50

3.4 Incident data

3.4.1 EIIS

A review of the Ecological Incident Information System (EIIS) database for ecological 

incidents involving dimethoate was completed on November 2014. This database consists of 

incident reports submitted to the EPA from 1972 to present. A summary of these incidents can 

be found in Appendix K; this table is divided into incidents involving aquatic organisms 

only, terrestrial organisms only, and both aquatic and terrestrial organisms. Within each of 

these sections of the table, incidents are ordered by date beginning with the earliest incident. 

Incidents listed in EIIS are categorized by certainty index, i.e., the likelihood that a particular 

pesticide is associated with that particular incident. These classifications include highly 

probable, probable, possible, unlikely or unrelated. “Highly probable” incidents usually 

require measured residues of the suspected compound in the affected organism or clear 

circumstances regarding the exposure. “Probable” incidents include those where residue 

information was not available or circumstances were less clear than those for “highly 

probable.” Incidents categorized as “possible” occur when multiple chemicals may have been 

involved and the contribution of an individual chemical is not obvious. An incident 

categorized as “unlikely” when a given chemical is considered nontoxic to the type of 

organism involved or the chemical analysis indicated no residues in the samples. Incidents 

categorized as “unrelated” are those where an investigation demonstrated that the loss did not 

involve pesticides. No incidents categorized as “unrelated” were listed for dimethoate. 

The number of incidents listed in the EIIS database is believed to be only a small fraction of 

the total incidents involving organismal mortality and damage caused by pesticides. 

Therefore, the absence of incident reports or a limited number of incident reports cannot be 

construed as the absence of incidents or that there were in fact a limited number of incidents.

The EIIS database contained 27 incident reports associated with dimethoate. The majority of 

the incident reports involved terrestrial ecosystems (23 or 85% of the total incidents) while 4

(15%) of incident reports involve aquatic ecosystems. Washington state with 10 reports was 

the most represented among the 50 states followed by California (6), Idaho (3), North 

Carolina (2) and Illinois, South Dakota, New York, Colorado and Minnesota with 1 each. 

There was an additional report from China. Additional characterization of these incidents is 

provided below. 

Of the 27 incidents, 5 (19%) are categorized as ‘highly probable’ and 10 (27%) have been 

classified as ‘probable’. Collectively, the ‘highly probable’ and ‘probable’ categories 

represent 56% of the reported incidents. Regarding the legal status (i.e., whether the incident 

resulted from a misuse/label violation), the ‘unknown’ and ‘misuse’ represent the largest 

legality categories with 41% and 26% of the incident reports, respectively. Approximately 

33% of the reports were the result of registered uses. 

Of the incident reports categorized as ‘highly probable’ and ‘probable’ and that involved 
51

registered uses, most described runoff to an aquatic habitat following periods of rainfall or 

drift to an off-site field where bees were actively foraging. Of the 27 incidents, 21 of them 

involved application of other chemicals as well, where dimethoate was classified as ‘possible’ 

for 10, ‘probable’ for 8, and ‘highly probable for 3 of the incidents. 

Aquatic Incidents:

All four aquatic incident reports involved mortality to fish. None of the aquatic incidents 

involved aquatic invertebrates, but the likelihood of observing impacts to aquatic 

invertebrates is likely low compared to fish. Of the 4 aquatic incidents, 3 (75%) are classified 

as ‘probable’ and one is classified as ‘possible’ in the context of dimethoate use. 

Terrestrial Incidents:

Of the 21 terrestrial incident reports, 7 of them involved avian species and 14 of them 

involved pollinators. Of the 7 incidents involving avian species, 4 were classified as ‘highly 

probable; and 2 were classified as ‘probable.’ Within the seven, two of these incidents were 

classified as an ‘accidental misuse’ and one was an ‘intentional misuse.’ Affected avian 

species included cedar waxwing (Bombycilla cedrorum), Canadian geese (Branta canadensis) 

and rock dove (Columba livia). 

Fourteen of the 21 terrestrial incident reports involved bees. Ten of the incidents were 

classified as ‘possible’ and 4 were classified as ‘probable.’ A majority of these incidents 

indicate that bees were exposed to the chemical because the bees were actively foraging on 

the use site during application, or were actively foraging on an adjacent site and came into 

contact via spray drift.

Plant Incidents:

There were 2 incidents reported involving plants; one was classified as ‘highly probable’ and 

one was classified as ‘probable’. Both incidents were due to equipment malfunction and were 

classified as an ‘accidental misuse.’ 
Page 52 of 144

3.4.2 Other Incident Databases

The American Bird Conservancy (ABC) Avian Incident Monitoring System (AIMS12) was 

searched in May 2014 and returned nine records of incidents associated with dimethoate (ABC, 

2007). All of these incidents are recorded in the EIIS and discussed in the preceding section .

A search in May 2014 of the Incident Database System (IDS) maintained by OPP’s Information 

Technology and Resource Management Division (ITRMD) yielded no incidents for dimethoate

in the main database nor in the aggregate incident module. Measures of Exposure

4.0 Risk Characterization

As discussed in the problem formulation, risk characterization integrates EECs and toxicity 

estimates and evaluates the likelihood of adverse ecological effects to non-target species. For 

dimethoate, a deterministic approach is used to evaluate the likelihood of adverse ecological 

effects to non-target species. In this approach, RQs are calculated by dividing EECs by acute 

and chronic ecotoxicity values for non-target species. 

Risk Quotient (RQ) = Exposure Estimate/Toxicity Estimate

The RQ value is a unitless number and for this reason, the magnitude of the RQ value cannot be 

used to quantitatively gauge the likelihood or magnitude of an adverse effect resulting from 

exposure to dimethoate. Rather, the resulting RQ values are compared to LOCs (Table 28) 

which serve as thresholds above which exposure from the labeled use (or proposed use) of the 

pesticide is considered to have the potential to cause adverse effects for the non-target 

organisms/taxa for which the value is intended to represent. The LOCs currently address the 

following risk presumption categories:

Animals:

• Acute risk—potential for acute risk to non-target organisms which may warrant regulatory 

action in addition to restricted classification

• Acute risk, restricted use—potential for acute risk to non-target organisms, but may be 

mitigated through restricted use classification

• Acute risk, listed species—listed species may be potentially affected by use

• Chronic risk—potential for chronic risk may warrant regulatory action, listed species may 

potentially be affected through chronic exposure

Plants:

• Non-listed plant risk—potential for effects in non-target (non-endangered) plants

• Listed plant risk—potential for effects in endangered plants

 12 American Bird Conservancy. 2014. Avian Incident Monitoring System. 

http://www.abcbirds.org/abcprograms/policy/toxins/aims/aims/login.cfm
Page 53 of 144

In the following sections, RQ values are calculated for aquatic and terrestrial organisms (Table 

29 – 41). In this assessment, RQs that exceed the risk to non-listed species LOC also exceed the 

risk to listed species LOC. Note that with plants, unlike with animals, RQ values are not 

presented for acute risk separately from chronic risk; instead, RQ values are presented for risk to 

listed and non-listed species based on a comparison of a given EEC to NOAEL and EC25/EC50

values, respectively. A discussion of the RQ values for dimethoate and of other information that 

provides context for the interpretation of potential risk to various taxa is presented in the Risk 

Description.

Table 28. Agency Risk Quotient (RQ) Metrics and Levels of Concern (LOC) Per Risk Class.

Risk Class Risk Description RQ LOC

Aquatic Animals (fish and invertebrates)

Acute Risk to 

non-listed 

Species

Potential for effects to non-listed animals from acute 

exposures

Peak EEC/LC501 0.5

Acute 

Restricted Use

Potential for effects to animals from acute exposures

Risks may be mitigated through restricted use classification Peak EEC/LC501 0.1

Acute Risk to 

Listed Species

Listed species may be potentially affected by acute 

exposures

Peak EEC/LC501 0.05

Chronic Potential for effects to non-listed and listed animals from 

chronic exposures

60-day EEC/NOAEC 

(fish) 1

21-day EEC/NOAEC 

(invertebrates)

Aquatic Plants

Non-Listed Potential for effects to non-listed plants from exposures Peak EEC/LC501 1

Listed Potential for effects to listed plants from exposures Peak EEC/NOAEC 1

Terrestrial Animals (mammals and birds)2

Acute Risk to 

non-listed 

Species

Potential for effects to non-listed animals from acute 

exposures

EEC/LC50 (Dietary)

0.5

EEC/LD50 (Dose)

Acute 

Restricted Use

Potential for effects to animals from acute exposures

Risks may be mitigated through restricted use classification

EEC/LC50 (Dietary) 0.2

EEC/LD50 (Dose)

Acute Risk to 

Listed Species

Listed species may be potentially affected by acute 

exposures

EEC/LC50 (Dietary) 0.1

EEC/LD50 (Dose)

Chronic Risk Potential for effects to non-listed and listed animals from 

chronic exposures EEC/NOAEC 1

Terrestrial and Semi-Aquatic Plants

Non-Listed Potential for effects to non-target, non-listed plants from 

exposures

EEC/ EC25 1

Listed Plant Potential for effects to non-target, listed plants from 

exposures

EEC/ NOAEC

1

EEC/ EC05
Page 54 of 144

4.1 Risk Estimation for Aquatic Organisms

4.1.1 Freshwater and Estuarine/Marine fish

Maximum acute RQ values from freshwater and estuarine/marine fish are one to two orders of 

magnitude below the acute risk to listed species LOC (Table 29). The RQs for freshwater fish 

ranged from 0.001 to 0.006 while the RQs for estuarine marine fish were all <0.001. None of the 

RQ values exceed the chronic risk LOC for freshwater and estuarine/marine fish with RQ values 

ranging from 0.009 to 0.047 and 0.005 and 0.017, respectively. 
Page 55 of 144

Table 29. Acute and chronic risk quotients (RQs) for direct effects to freshwater and estuarine/marine fish from dimethoate technical 

grade active ingredient (TGAI)

1

Use(s) Scenario App. 

Method

Peak 

EECs

(μg 

ai/L)

Freshwater

EC50 = 6,200

μg/L

Estuarine/

Marine

EC50 = >111,000

μg/L

60-day 

EECs

(μg 

ai/L)

Freshwater

NOAEC =430

μg/L

Estuarine/

marine 

NOAEC =

1,200 μg/L

Acute RQ Chronic RQ

03_MN_alfalfa Alfalfa, sainfoin Aerial 8.5 0.001 <0.001 4.9 0.012 0.004

05_CA_Cole crops Brussels Sprouts (ground) Ground 23 0.004 <0.001 15 0.036 0.013

10_WA_Orchards Cherry (only in ID, MT, 

OR, UT or WA) Aerial 9.4 0.002 <0.001 6.0 0.014 0.005

12_OR_Xmas trees

Douglas fir (seed 

orchards) (only in OR and 

WA)

Airblast 10 0.002 <0.001 5.7 0.013 0.005

14_OR_Xmas trees

Hybrid 

cottonwood/poplar 

plantations (some labels 

allow certain uses in ID, 

OR and WA)

Aerial 34 0.006 <0.001 20 0.047 0.017

15_CA_Nursery

Citrus, non-bearing and 

nursery stock (only in CA 

and AZ)

Soil 

drench 6.6 0.001 <0.001 3.2 0.009 0.003

17_OR_Nursery

Ornamental woody 

shrubs and vines; 

Ornamental and/or shade 

trees

Aerial 21 0.003 <0.001 14 0.033 0.012

20_FL_Peppers Peppers Aerial 22 0.004 <0.001 13 0.030 0.011

23_MS_Cotton Cotton Aerial 9.7 0.002 <0.001 4.4 0.010 0.004

26_FL_Citrus

Grapefruit, kumquat, 

lemon, lime, orange, 

pumello (shaddock), 

tangelo, tangerine

Aerial 22 0.004 <0.001 8.2 0.019 0.007

App. = Application 1

Acute risk listed species LOC = 0.05; acute restricted use LOC = 0.1, acute risk to non-listed species LOC = 0.5; chronic risk to listed and non-listed species LOC = 1
Page 56 of 144

4.1.2 Freshwater and Estuarine/Marine Invertebrates

There are a number of acute and chronic risk LOC exceedances for invertebrates (Table 30). 

For freshwater and estuarine/marine invertebrates, acute RQ values exceed the acute risk to listed 

species LOC of 0.05 for all uses assessed; whereas, the risk to non-listed species LOC of 0.5 was 

exceeded in four of the 10 crop scenarios assessed. Chronic RQs for freshwater invertebrates 

exceed the LOC for all uses and ranged from roughly 10 to 53. The RQs for estuarine/marine 

invertebrates also exceed the chronic risk LOC across all uses and ranged from roughly 25 to 

133. 
Page 57 of 144

Table 30. Acute and chronic risk quotients (RQs) for direct effects to freshwater and estuarine/marine invertebrates from 

dimethoate technical grade active ingredient (TGAI)

1

Use(s) Scenario App. 

Method

Peak 

EECs

(μg 

ai/L)

Freshwater

EC50 = 4.3 x 

10-5 μg/L

Estuarine/

Marine

EC50 = 3.1 x 10-5

μg/L

21-day 

EECs

(μg 

ai/L)

Freshwater

NOAEC =5 

x 10-7 μg/L

Estuarine/

marine 

NOAEC = 2 

x 10-7 μg/L

Acute RQ Chronic RQ

03_MN_alfalfa Alfalfa, sainfoin Aerial 8.5 0.199* 0.276* 6.4 12 32

05_CA_Cole 

crops Brussels Sprouts (ground) Ground 23 0.54 0.74 20 40 100

10_WA_Orchards Cherry (only in ID, MT, OR, 

UT or WA) Aerial 9.4 0.22* 0.30* 7.9 15 39

12_OR_Xmas 

trees

Douglas fir (seed orchards) 

(only in OR and WA) Airblast 10 0.24* 0.34* 8.6 17 42

14_OR_Xmas 

trees

Hybrid cottonwood/poplar 

plantations (some labels 

allow certain uses in ID, OR 

and WA)

Aerial 34 0.79 1.1 26 53 133

15_CA_Nursery

Citrus, non-bearing and 

nursery stock (only in CA 

and AZ)

Soil drench 6.6 0.15* 0.23* 5.0 10 25

17_OR_Nursery

Ornamental woody shrubs 

and vines; Ornamental 

and/or shade trees

Aerial 21 0.44* 0.68 17 35 88

20_FL_Peppers Peppers Aerial 22 0.51 0.71 17 35 88

23_MS_Cotton Cotton Aerial 9.7 0.22* 0.31* 6.7 13 33

26_FL_Citrus

Grapefruit, kumquat, lemon, 

lime, orange, pumello 

(shaddock), tangelo, 

tangerine

Aerial 22 0.51 0.71 14 29 73

App. = Application 1

Acute risk to listed species LOC = 0.05; acute restricted use LOC = 0.1, acute risk to non-listed species LOC = 0.5; chronic risk to listed and non-listed species LOC = 1

Bolded values indicate exceedance of LOC for risk to non-listed species.

* indicates LOC exceedance for risk to listed species.
Page 58 of 144

4.1.3 Aquatic Plants

The RQ values for aquatic nonvascular plants and aquatic vascular plants do not exceed the LOC 

for risk to listed or non-listed species (Table 31). The RQs for listed aquatic nonvascular plants 

range from 0.001 to 0.004; the RQs for non-listed aquatic nonvascular plants range from <0.001 

to 0.002. The RQs for listed and non-listed vascular plants are <0.001 across all scenarios.
Page 59 of 144

Table 31. Risk quotient (RQ) values for direct effects to aquatic nonvascular and vascular plants from dimethoate technical 

grade active ingredient (TGAI)

1

Use(s) Scenario

Applica

tion 

Method

Peak 

EECs 

(μg ai/L)

Aquatic Nonvascular Plants

EC50 = 20,000 μg/L

NOAEL = 9,000 μg/L

Aquatic Vascular Plants

EC50 >92,600 μg/L

NOAEL = 92,600 μg/L

Listed RQs2 Non-listed

RQs3 Listed RQs2 Non-listedRQs3

03_MN_alfalfa Alfalfa, sainfoin Aerial 8.5 0.001 <0.001 <0.001 <0.001

05_CA_Cole crops Brussels Sprouts (ground) Ground 23 0.003 0.001 <0.001 <0.001

10_WA_Orchards Cherry (only in ID, MT, 

OR, UT or WA) Aerial 9.4 0.001 <0.001 <0.001 <0.001

12_OR_Xmas trees Douglas fir (seed orchards) 

(only in OR and WA) Airblast 10 0.001 0.001 <0.001 <0.001

14_OR_Xmas trees

Hybrid cottonwood/poplar 

plantations (some labels 

allow certain uses in ID, 

OR and WA)

Aerial 34 0.004 0.002 <0.001 <0.001

15_CA_Nursery

Citrus, non-bearing and 

nursery stock (only in CA 

and AZ)

Soil 

drench 6.6 0.001 <0.001 <0.001 <0.001

17_OR_Nursery

Ornamental woody shrubs 

and vines; Ornamental 

and/or shade trees

Aerial 21 0.002 0.001 <0.001 <0.001

20_FL_Peppers Peppers Aerial 22 0.002 0.001 <0.001 <0.001

23_MS_Cotton Cotton Aerial 9.7 0.001 <0.001 <0.001 <0.001

26_FL_Citrus

Grapefruit, kumquat, 

lemon, lime, orange, 

pumello (shaddock), 

tangelo, tangerine

Aerial 2 0.002 0.001 <0.001 <0.001

1Risk to listed aquatic plant LOC = 1; Risk to non-listed aquatic plant LOC = 1 2

Estimated by dividing the peak EEC by the most sensitive NOAEC

3

Estimated by dividing the peak EEC by the most sensitive EC50
Page 60 of 144

4.2 Terrestrial Organisms 

4.2.1 Acute Dose- Based Risk to Birds

Acute dose-based RQs for birds exceed the acute risk to listed and non-listed LOCs for nearly all 

scenarios and all bird sizes (Table 32). RQs exceed the LOC for risk to listed and non-listed 

species for all uses for a small bird consuming short grass, tall grass, broadleaf plants, fruits and 

arthropods. Acute RQ values that exceed the LOCs for acute risk to non-listed and listed species 

ranged from roughly 9 to 262 for short grass, 4 to 120 for tall grass, 5 to 147 for broadleaf plants, 

0.57 to 16 for fruits and 3.5 to 103 for arthropods. For a small bird consuming grains, RQs 

exceeding the LOC for listed species ranged from 0.13 to 0.48 and RQs exceeding the LOC for 

risk to non-listed species range from roughly 1.1 to 3.6.

For medium-sized birds, acute, dose-based RQ values exceed the LOC for risk to listed and nonlisted species for all uses with short grass, tall grass, broadleaf plants and arthropods. For a 

medium-sized birds consuming fruits, the dose-based RQ values exceed the acute risk LOC for 

non-listed species for all but two scenarios. The dose-based RQ values that exceed the acute risk

LOC for non-listed species range from roughly 4 to 117 for short grass, 1.9 to 54 for tall grass, 

2.3 to 66 for broadleaf plants, 1.6 to 46 for arthropods and 0.67 to 7.3 for fruits; RQ values that 

only exceed the LOC for acute risk to listed species range from 0.25 to 0.41 for medium-sized

birds consuming fruit. For a medium-sized bird consuming grains, RQ values range from 

roughly 0.06 to 1.6; RQs that exceed the LOC for risk to listed species range from 0.15 to 0.49 

and RQ values that exceed the LOC for acute risk to non-listed species ranged from roughly 0.80

to 1.63.

For large-sized birds, dose-based RQ values exceed the acute risk LOC for listed and non-listed 

species for all scenarios with short grass, tall grass, broadleaf plants and arthropods. Dose-based 

RQ values that exceed the acute risk LOC for non-listed species range from roughly 1.3 to 37 for 

short grass, 0.59 to 17 for tall grass, 0.7 to 21 for broadleaf plants and 0.5 to 15 for arthropods. 

The dose-based RQ values for large-sized birds consuming fruits exceed the acute risk LOC for 

listed species and range from 0.13 to 0.21; RQ values that exceed the acute risk LOC for nonlisted species range from roughly 0.5 to 2.3. For a large-sized birds consuming grains, dosebased RQ values range from 0.02 to 0.52 and for those that exceed the acute risk LOC for listed 

species ranged from 0.12 to 0.25; only one RQ value exceeds the acute risk LOC for non-listed 

large birds consuming grains at 0.52.
Page 61 of 144

Table 32. Acute dose-based risk quotient (RQ) values for birds exposed to technical grade dimethoate (T-REX v. 1.5.2)1,2

Primary 

Feeding 

Strategy 

Herbivores and Omnivores Insectivores Granivores

Animal Size 

 Sm Med Lg Sm Med Lg Sm Med Lg

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s) 

Non-Food Uses

Douglas fir (seed 

orchards) (only in 

OR and WA)

262 120 147 16 117 53 66 7.3 37 17 20 2.3 102 45 14 3.6 1.63 0.52

Hybrid 

cottonwood/poplar 

plantations (some 

labels allow use in 

ID, OR and WA)

127 58 71 8.0 57 26 32 3.5 18 8.3 10 1.1 50 22 7 1.7 0.80 0.25*

Ornamental 

woody shrubs and 

vines

60 27 33 3.7 27 12 15 1.6 8.5 3.9 4.8 0.54 23 10 3.3 0.84 0.38* 0.12*

Ornamental 

Herbaceous plants 14 6 8 0.91 6.5 2.9 3.6 0.41* 2.0 0.95 1.1 0.13* 5.7 2.5 0.81 0.20* 0.09 0.03

Food Uses

Cherry 78 36 44 4.9 35 16 19 2.2 11 5 6 0.70 30 13 4.3 1.1 0.49* 0.16*

Soybeans 34 15 19 2.2 15 7.1 8.7 0.97 4.9 2.3 2.7 0.31* 13 6.1 1.9 0.48* 0.21* 0.07

Peppers 24 11 13.5 1.50 10 4.9 6.0 0.67 3.4 1.5 1.9 0.21* 9.4 4.2 1.3 0.33* 0.15* 0.05

Succulent peas 9.1 4.1 5.1 0.57 4.1 1.8 2.2 0.25* 1.2 0.59 0.73 0.08 3.5 1.5 0.51 0.13* 0.06 0.02

1 RQ values in bold exceed the acute risk to non-listed species LOC of 0.5. Values with an asterisk indicate that the RQ exceeds the LOC for acute risk to listed birds. 2

Acute risk to listed species LOC = 0.1; acute restricted use LOC = 0.2; acute risk to non-listed species LOC = 0.5
Page 62 of 144

4.2.2 Acute Dietary Risk to Birds

Dietary-based RQ values can be found in Table 33. RQ values exceed the acute risk LOC for all

but two uses for those birds which consume short grass, tall grass, broad leaf plants and 

arthropods. The uses of dimethoate on ornamental herbaceous plants and succulent peas are the 

only uses that do not result in exceedance of the acute risk to non-listed species LOC of 0.5.
Page 63 of 144

Table 33. Acute dietary-based risk quotients (RQs) for birds of Different Feeding Classes (T-REX v. 1.5.2)1,2

Primary Feeding Strategy  Herbivores, Omnivores, and Granivores Insectivores

Dietary Items 

Short Grass Tall Grass Broad-leaf Plants Fruits, pods, 

seeds, etc. Arthropods

Use(s) 

Non-Food Uses

Douglas fir (seed orchards) (only in OR and WA) 7.2 3.3 4.0 0.45* 2.8

Hybrid cottonwood/poplar plantations (some labels allow use in ID, OR 

and WA) 3.5 1.6 1.9 0.22* 1.3

Ornamental woody shrubs and vines 1.6 0.7 0.93 0.10* 0.65

Ornamental Herbaceous plants 0.40* 0.18* 0.23* 0.03 0.16*

Food Uses

Cherry 2.1 0.90 1.2 0.14* 0.85

Soybeans 0.95 0.43* 0.53 0.06 0.37*

Peppers 0.66 0.30* 0.37* 0.04 0.26*

Succulent peas 0.25* 0.11* 0.14* 0.02 0.10*

1RQ values in bold exceed the non-listed species LOC of 0.5. 

*Indicate RQ value exceeding the listed species LOC of 0.05

2

Acute risk to listed species LOC = 0.1; acute restricted use LOC = 0.2; acute risk to non-listed species LOC = 0.5
Page 64 of 144

4.2.3 Chronic Risk to Birds

Dietary based RQ values for birds exceed the chronic risk LOC for birds foraging on short grass, 

tall grass, broad-leaf plants and arthropods (Table 34). For birds consuming short grass, RQ

values exceed the chronic risk LOC across all uses and ranged from roughly 9.3 to 270. For 

birds consuming tall grass, RQs exceed the chronic risk LOC across all uses and ranged from

roughly 4.3 to 123. For birds consuming broad-leaf plants, RQs exceed the chronic risk LOC 

across all uses and ranged from roughly 5.2 to 151. For birds consuming fruits, pods, seeds etc., 

RQs ranged from 0.59 to roughly 16. For birds consuming arthropods, RQs exceed the chronic 

risk LOC across all uses and ranged from 3.6 to 105.
Page 65 of 144

Table 34. Chronic dietary-based risk quotients (RQs) for Birds of different feeding classes (T-REX v. 1.5.2)

Primary Feeding Strategy  Herbivores, Omnivores, and Granivores Insectivores

Dietary Items 

Short Grass Tall Grass Broad-leaf 

Plants

Fruits, pods, 

seeds, etc. Arthropods

Use(s) 

Non-Food Uses

Douglas fir (seed orchards) (only in OR and WA) 270 123 151 16 105

Hybrid cottonwood/poplar plantations (some labels allow use in ID, OR 

and WA) 131 60 74 8.2 51

Ornamental woody shrubs and vines 62 28 34 3.8 24

Ornamental Herbaceous plants 15 6.8 8.4 0.94 5.8

Food Uses

Cherry 81 37 45 5.0 31

Soybeans 35 16 20 2.2 13

Peppers 24 11 13 1.5 9.6

Succulent peas 9.3 4.3 5.2 0.59 3.6

RQ values in bold exceed the LOC of 1 for chronic risk to both listed and non-listed species.
Page 66 of 144

4.2.4 Acute Risk to Mammals

Dose-based RQs for mammals exposed to dimethoate exceed LOCs for acute risk to listed and 

non-listed species for multiple uses; the majority of the exceedances are for small-sized

herbivorous and omnivorous mammals. These results are tabulated in Table 35.

For small-sized mammals consuming short grass, RQs range from 0.05 to 1.3; four of the 

scenarios result in RQs that exceed the LOC for acute risk to listed species and range from 0.12 

to 0.39; two scenarios resulted in RQs that exceed the LOC for acute risk non-listed species at 

0.64 and 1.3. For small mammals consuming tall grass, RQs ranged from 0.02 to 0.60; three of 

the scenarios resulted in RQs that exceed the LOC for acute risk to listed species and range from 

0.14 to 0.29; one RQ exceeds the LOC for acute risk to non-listed species at 0.60. For small 

mammals consuming broad-leaf plants, RQs range from 0.03 to 0.74; four of the scenarios result 

in RQs that exceed the LOC for acute risk to listed species and range from 0.1 to 0.36; only one 

scenario has an RQ that exceeds the LOC for acute non-listed species at 0.74. For small 

mammals consuming arthropods, RQs ranged from 0.02 to 0.51; three of the scenarios have RQs 

that exceed the LOC for acute risk to listed species and range from 0.12 to 0.25; one scenario has 

an RQ that exceeds the LOC for acute risk to non-listed species at 0.51. For small mammals 

consuming fruits, the RQs range from <0.01 to 0.08; within this foraging category there is only 

one RQ that exceeds the LOC for acute risk to listed species. None of the RQ values for 

medium-sized mammals consuming grains exceed the acute risk LOCs as RQs range from <0.01 

to 0.02.

For medium-sized mammals consuming short grass, RQs range from 0.04 to 1.1; four of the 

scenarios result in RQs that exceed the LOC for acute risk to listed species and range from 0.10 

to 0.34; two of the scenarios result in RQs that exceed the LOC for acute risk to non-listed 

species at 0.55 and 1.1. For medium-sized mammals consuming tall grass, the RQs range from 

0.02 to 0.51; four of the scenarios result in RQs that exceed the LOC for risk to listed species and 

range from 0.12 to 0.25; one of the scenarios exceeds the LOC for risk to non-listed species at 

0.51. For medium-sized mammals consuming broadleaf plants, RQs range from 0.02 to 0.63; 

three of the scenarios result in RQs that exceed the LOC for risk to listed species and range from 

0.14 to 0.31; only one scenario with an RQ of 0.63 exceeds the LOC for risk to non-listed 

species. For medium-sized mammals consuming arthropods, overall RQs range from 0.02 to 

0.44 with four scenarios that exceed the LOC for risk to listed species and ranged from 0.10 to 

0.44; there were no RQs that exceed the LOC for risk to non-listed species. For medium-sized

mammals consuming fruits, RQs range from 0.00 to 0.07 with only one RQ of 0.07 that exceeds

the LOC for risk to listed species. There are no RQ exceedances for medium-sized mammals 

consuming grains. 

For large-sized mammals consuming short grass, overall the RQs range from 0.02 to 0.06; three 

of the scenarios result in RQs that exceed the LOC for acute risk to listed species and range from 

0.14 to 0.29; there is one RQ that exceeds the LOC for acute risk to non-listed species at 0.60. 

For large-sized mammals consuming tall grass, overall RQs range from 0.01 to 0.27; there are 

two scenarios where the RQs exceed the LOC for acute risk to listed species at 0.13 and 0.27; 

there are no LOC exceedances for acute risk to non-listed species. For large-sized mammals 

consuming broadleaf plants, overall RQs range from 0.01 to 0.34; there are three scenarios that 
Page 67 of 144

exceed the LOC for acute risk to listed species and range from 0.10 to 0.34; none of the RQs for 

large mammals foraging on broadleaf plants exceed the LOC for risk to non-listed species. For 

large mammals consuming fruits, overall RQs range from 0.01 to 0.23; there are two scenarios 

where RQs exceed the LOC for risk to listed species at 0.11 and 0.23; there are no exceedances 

for acute risk to non-listed species. There are no RQs that exceed the LOC for risk to listed or 

non-listed species for large mammals consuming fruits or grains as RQ values range from 0.0 to 

0.04 and <0.01 to 0.01, respectively.
Page 68 of 144

Table 35. Acute dose-based risk quotient (RQ) values for mammals exposed to dimethoate (T-REX v. 1.5.2)1

Primary Feeding 

Strategy  Herbivores and Omnivores Insectivores Granivores

Animal Size  Sm Med Lg Sm Med Lg Sm Med Lg

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, etc.

Use(s) 

Non-Food Uses

Douglas fir (seed orchards) 

(only in OR and WA) 1.3 0.60 0.74 0.08* 1.1 0.51 0.63 0.07* 0.60 0.27* 0.34* 0.04 0.51 0.44* 0.23* 0.02 0.02 0.01

Hybrid cottonwood/poplar 

plantations (some labels allow 

use in ID, OR and WA)

0.64 0.29* 0.36* 0.04 0.55 0.25* 0.31* 0.03 0.29* 0.13* 0.16* 0.02 0.25* 0.21* 0.11* 0.01 0.01 <0.01

Ornamental woody shrubs and 

vines 0.30* 0.14* 0.17* 0.02 0.26* 0.12* 0.14* 0.02 0.14* 0.06 0.08 0.01 0.12* 0.10* 0.05 <0.01 <0.01 <0.01

Ornamental Herbaceous plants 0.07 0.03 0.04 0.00 0.06 0.03 0.03 0.00 0.03 0.02 0.02 0.00 0.03 0.02 0.01 <0.01 <0.01 <0.01

Food Uses

Cherry 0.39* 0.18* 0.22* 0.02 0.34* 0.15* 0.19* 0.02 0.18* 0.08 0.10* 0.01 0.15* 0.13* 0.07 0.01 <0.01 <0.01

Soybeans 0.17* 0.08 0.10* 0.01 0.15* 0.07 0.08 0.01 0.08 0.04 0.04 0.00 0.07 0.06 0.03 <0.01 <0.01 <0.01

Peppers 0.12* 0.05 0.07 0.01 0.10* 0.05 0.06 0.01 0.05 0.03 0.03 0.00 0.05 0.04 0.02 <0.01 <0.01 <0.01

Succulent peas 0.05 0.02 0.03 0.00 0.04 0.02 0.02 0.00 0.02 0.01 0.01 0.00 0.02 0.02 0.01 <0.01 <0.01 <0.01

1 RQ values in bold exceed the acute risk to non-listed species LOC of 0.5. Values with an asterisk indicate that the RQ exceeds the LOC for acute risk to listed species. 
Page 69 of 144

4.2.5 Chronic Dose- Based Risk to Mammals

Dose-based RQ values for mammals result in LOC exceedances for chronic risk to listed and 

non-listed species across all scenarios (Table 36). 

For small-sized mammals chronic RQs exceed the chronic risk LOC by up to three orders of 

magnitude; the ranges of the RQs across scenarios for small mammals consuming the following 

food items are: 162 to 4685 for short grass, 74 to 2147 for tall grass, 91 to 2635 for broadleaf

plants, 10 to 292 for fruits, 63 to 1834 for arthropods and 1.9 to 55 for grain. For medium-sized

mammals RQs also exceed the chronic risk LOC by up to three orders of magnitude; ranges RQs 

across scenarios and food items are: 138 to 4001 for short grass, 63to 1834 for tall grass, 78 to 

2251 for broadleaf plants, 8.6 to 250 for fruits, 54 to 1567 for arthropods, and 1.9 to 55 for 

grains. For large-sized mammals, chronic RQs ranges across all scenarios and forage categories 

are: 74 to 2145 for short grass, 34 to 983 for tall grass, 41to 1206 for broadleaf plants, 4.6 to 134 

for fruits, 29 to 840 for arthropods, and 1.0 to 29 for grains.
Page 70 of 144

Table 36. Chronic dose-based risk quotient (RQ) values for mammals exposed to dimethoate (T-REX v.1.5.2).1,2

Primary Feeding Strategy  Herbivores and Omnivores Insectivores Granivores

Animal Size  Sm Med Lg Sm Med Lg Sm Med Lg

Dietary Items 

Short Grass

Tall Grass

Broad-leaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Short Grass

Tall Grass

Broadleaf 

Plants

Fruits, pods, 

seeds, etc.

Arthropods Seeds, grains, 

etc.

Use(s) 

Non-Food Uses

Douglas fir (seed orchards) (only in OR 

and WA) 4685 2147 2635 292 4001 1834 2251 250 2145 983 1206 134 1835 1567 840 65 55 29

Hybrid cottonwood/poplar plantations 

(some labels allow use in ID, OR and 

WA)

2286 1048 1286 142 1953 895 1098 122 1047 479 588 65 895 765 410 31 27 14

Ornamental woody shrubs and vines 1078 494 606 67 920 422 518 57 493 226 277 30 422 360 193 15 12 6

Ornamental Herbaceous plants 260 119 146 16 222 101 125 13 119 54 67 7.4 101 87 46 3.6 3.0 1.7

Food Uses

Cherry 1405 644 790 87 1200 550 675 75 643 295 362 40 550 470 252 19 16 8.9

Soybeans 617 282 347 38 527 241 296 32 282 129 158 17 241 206 110 8.5 7.3 3.9

Peppers 429 196 241 26 366 168 206 22 196 90 110 12 168 143 77 5.9 5.0 2.7

Succulent peas 162 74 91 10 138 63 78 8.6 74 34 41 4.6 63 54 29 2.2 1.9 1.0 1

RQ values in bold exceed the chronic risk LOC of 1 for both listed and non-listed species.2Using adjusted NOAEL values of 23.30, 18.85, and 8.15 for small, medium, and large mammals, 

respectively.

2

Chronic risk to listed and non-listed species LOC = 1.
Page 71 of 144

4.2.6 Chronic Dietary-Based Risk to Mammals

Dietary-based RQs for mammals exceed the chronic risk LOC across all forage items and for all 

scenarios (Table 37). The range of RQs across forage items is 18 to 540 for mammals

consuming short grass, 8.5 to 247 for mammals consuming tall grass, 10 to 303 for mammals 

consuming broadleaf plants, 1.1 to 33 for mammals consuming fruits and 7.3 to 211 for 

mammals consuming arthropods.

Table 37. Chronic dietary-based risk quotient (RQ) values for mammals exposed to dimethoate 

(T-REX v.1.5.2)1,2

Primary Feeding Strategy  Herbivores, Omnivores, and Granivores Insectivores

Dietary Items 

Short Grass Tall Grass Broad-leaf 

Plants

Fruits, 

pods, 

seeds, 

etc.

Arthropods

Use(s) 

Non-Food Uses

Douglas fir (seed orchards) (only in OR and 

WA) 540 247 303 33 211

Hybrid cottonwood/poplar plantations (some 

labels allow use in ID, OR and WA) 263 120 148 16 103

Ornamental woody shrubs and vines 124 56 69 7.7 48

Ornamental Herbaceous plants 30 13 16 1.8 11

Food Uses

Cherry 162 74. 91 10 63

Soybeans 73 32 40 4.4 27

Peppers 49 22 27 3.0 19

Succulent peas 18 8.5 10 1.1 7.3

1Bolded cells indicate that the dietary-based RQ exceeds the LOC for chronic risk to listed and non-listed mammals. 2Chronic risk LOC = 1, NOAEL used for RQ estimation is 0.1 mg/kg bw.

4.2.7 Risk to Honey Bees

Tier 1 Risk Assessment

Tier 1 (screening-level) RQ values for bees are derived below by dividing the contact or oral 

EEC by the acute contact or oral LD50 values (Table 25), respectively. These Tier 1 RQ values 

are then compared to the acute risk LOC of 0.4, which corresponds to a 10% probability of 

mortality based on the median probit mortality slope across multiple pesticides. Tier 1 RQ 

values for selected foliar and soil applications of dimethoate are provided in Table 38 and Table 

39, respectively. Since data on the acute toxicity of dimethoate to honey bee larvae were not 

available, RQ values could not be determined for larval bees. Although dimethoate is commonly 

used as a reference toxic
Page 72 of 144

As indicated in Tables 38 and 39, the Tier 1 acute RQ values for adult honey bees exceed the 

acute risk LOC of 0.4 for all use categories and exposure routes assessed. Specifically, acute 

contact RQ values derived for foliar applications range from 4.2 to 76 while acute oral RQ 

values range from 89 to 2580. For soil applications, Tier 1 acute RQ values for adult honey bees 

range from 0.88 to 34. These findings of potential risk of dimethoate to honey bees are not 

unexpected given its high acute toxicity to honey bees and also because it is commonly used as a 

reference toxicant in laboratory-based studies as well as in semi-field (tunnel) studies conducted 

at similar application rates (e.g., 600 g a.i./ha or 0.54 lb a.i./A).

Table 38. Tier I risk quotient (RQ) values for honey bees exposed to dimethoate through foliar 

spray applications

Use Pattern

Adult Larvae

Contact* Dietary* Dietary*

Non-Food Uses

Douglas fir (seed orchards) (only in OR and WA) 76 2580 N/A

Hybrid cottonwood/poplar plantations (some labels allow use in ID, 

OR and WA) 34 1150 N/A

Ornamental woody shrubs and vines 17 574 N/A

Ornamental Herbaceous plants 4.2 143 N/A

Food Uses

Cherry 23 774 N/A

Soybeans 8.4 287 N/A

Peppers 5.7 193 N/A

Succulent peas 2.6 89 N/A

* Adult contact LD50 = 0.16 μg a.i./bee; adult oral LD50 = 0.056 μg a.i./bee. Data on the toxicity of dimethoate to honey bee larvae are not 

available. EECs for foliar applications are provided in Table 14.

**Values in bold exceed the acute risk LOC of 0.4.

Table 39. Tier I risk quotient (RQ) values for honey bees exposed to dimethoate through soil 

applications

Use Pattern

Adult* Larvae*

Dietary

Hybrid cottonwood/poplar plantations 34 N/A

Ornamental woody shrubs and vines 17 N/A

Melon, Watermelon 5.6 N/A

Succulent peas 0.88 N/A

* Adult contact LD50 = 0.16 μg a.i./bee; adult oral LD50 = 0.056 μg a.i./bee. Data on the acute toxicity of dimethoate to honey bee larvae are 

not available. EECs for soil applications are provided in Table 15. 

**Values in bold exceed the acute risk LOC of 0.4.

Although RQ values could not be calculated for larval bees due to the lack of a larval LD50 value 

with dimethoate, dimethoate is routinely used as a reference toxicity in larval bee toxicity 

studies. In these tests, a single dose of dimethoate is used to demonstrate exposure and toxicity 

to bees. Although an LD50 for dimethoate cannot be calculated from these studies, the toxicity 
Page 73 of 144

associated with the administered dose to larval bees can be used to provide context to the 

calculated Tier 1 EECs for honeybee larvae. For example, in a recent study with sulfoxaflor and 

honeybee larvae (MRID 48755603), dimethoate was administered at 1 ug a.i./larval bee/day for 5 

days. By day 7, 98% mortality was observed with larval honeybees. Data from later portions of 

this study could not be used due to high mortality of control bees during pupation. Nonetheless, 

it is evident that Tier 1 screening EECs honeybee larvae determined with foliar applications of 

dimethoate (2.1 – 61 ug a.i./bee/d; Table 21) are 2X to 60X greater than the dose causing near 

complete mortality in larval bees (1 ug a.i./bee/d). This suggests risk to larval bees based on Tier 

1 exposure modeling. The Tier 1 EECs determined for soil drench applications (0.021 – 0.81 ug 

a.i./bee/d; Table 22) are lower than dose associated with 98% mortality of larval bees (1 ug 

a.i./bee/d). Since a dose-response relationship is not available for dimethoate and larval 

honeybees, it cannot be determined to what extent soil drench applications may result in risk to 

larval bees.

Higher Tier Risk Assessment:

Although risks to adult honey bees are indicated based on Tier 1 risk assessment, it is desirable to 

evaluate risks at higher tiers of refinement, particularly since higher tier studies evaluate the 

effects on whole colonies whereas Tier 1 studies evaluate effects on individual bees. As noted 

previously in the characterization of effects of dimethoate on bees, no Tier 2 (semi-field) studies 

were submitted to the Agency in order to evaluate the potential for colony-level effects under 

semi-controlled conditions. However, relevant information can be gleaned from the use of 

dimethoate as a reference toxicant in semi-field (tunnel) studies13. Available data indicate that a 

foliar application of 0.53 lb a.i./A to blooming Phacelia with bees actively foraging in tunnels, 

sustained increases in worker bee mortality, decreases in flight activity and behavioral 

abnormalities occurred (MRID 48755603). Effects on brood development was inconclusive due 

to limitations in the design and execution of the tunnel studies considered in that assessment. 

The results from the Tier 3 full field study with dimethoate indicates that acute mortality was 

observed, which is consistent with what dose- and dietary-based RQs would suggest. However, at 

the whole colony level, the bees appeared to recover. Although the Tier 1 and Tier 2 risk 

assessment identifies the uncertainty related to risk to larvae, the Tier 3 field study suggests that 

under the conditions tested, larvae appeared to be less sensitive than adults; however, the extent of 

exposure experienced by bees in the Tier 3 field study is uncertain. There is also uncertainty given 

that the application rate in the study is lower than the maximum allowed and it is unclear as to the 

extent to which bees foraged on the treated site.

4.2.8 Risk to Terrestrial Plants

None of th RQs exceed the LOC for risk to non-target monocots adjacent to dimethoate use 

areas for spray drift only as a route of exposure, and runoff and spray drift in dry areas as a route 

of exposure. For runoff and spray drift in semi-aquatic areas, there are RQs that exceed the LOC 

for risk to both listed and non-listed terrestrial plant species. For non-listed species in a semi-

 13 http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2010-0889-0022
Page 74 of 144

aquatic area exposed via runoff and spray drift, overall RQs range from <0.1 to 1.67, with two 

RQ scenarios exceeding the LOC at 1.55 and 1.67; for listed species, RQs range from 0.17 to 

3.32 with five scenarios exceeding the LOC with values ranging from 1.00 to 3.32. Results have 

been tabulated in Table 40.

Table 40. Risk quotient (RQ) values for non-target monocots plants adjacent to dimethoate Use 

Areas1

Crop

Single Max. 

Application 

Rate

(lbs ai/A)

Monocot RQ Values

Spray Drift Only

Runoff and 

Spray Drift 

(Dry Areas)

Runoff and 

Spray Drift

(Semi-Aquatic 

Areas)

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Non-listed 

Species

Listed 

Species

Douglas Fir Aerial: 4.5 0.15 0.47 0.30 0.60 1.67 3.32

Ground: 4.5 <0.1 <0.1 0.18 0.36 1.55 3.08

Hybrid cottonwood Aerial: 2 <0.1 0.21 0.14 0.27 0.74 1.48

Ground: 2 <0.1 <0.1 <0.1 0.16 0.69 1.37

Ornamental woody 

shrubs and vines

Aerial: 1 <0.1 0.10 <0.1 0.13 0.37 0.74

Ground: 1 <0.1 <0.1 <0.1 <0.1 0.34 0.68

Ornamental Herbaceous Aerial: 0.25 <0.1 <0.1 <0.1 <0.1 <0.1 0.18

Ground: 0.25 <0.1 <0.1 <0.1 <0.1 <0.1 0.17

Cherry Aerial: 1.35 <0.1 0.14 <0.1 0.18 0.50 1.00

Ground: 1.35 <0.1 <0.1 <0.1 0.11 0.47 0.92

Soybeans Aerial: 0.5 <0.1 <0.1 <0.1 <0.1 0.19 0.37

Ground: 0.5 <0.1 <0.1 <0.1 <0.1 0.17 0.34

Peppers Aerial: 0.336 <0.1 <0.1 <0.1 <0.1 0.12 0.25

Ground: 0.336 <0.1 <0.1 <0.1 <0.1 0.12 0.23

Succulent peas Aerial: 0.156 <0.1 <0.1 <0.1 <0.1 <0.1 0.12

Ground: 0.156 <0.1 <0.1 <0.1 <0.1 <0.1 0.11

1

LOCfor listed and non-listed species = 1; values in bold exceed the LOC

None of the RQs exceed the LOC for risk to non-listed dicots adjacent to dimethoate use area

for crops exposed via spray drift only. For listed non-target dicots, RQs range from <0.1 to 1.96 

with two scenarios resulting in RQ values with LOC exceedances at 1.17 and 1.96. There are

LOC exceedances for risks to both non-listed and listed dicot species exposed via runoff and 

spray drift in a semi aquatic area; overall, RQs range from <0.1 to 2.95 for non-listed species and 

0.35 to 10.76 for listed species. There were four scenarios that result in LOC exceedances for 

risk to non-listed species with RQs ranging from 1.21 to 2.95; there are 10 scenarios that result in 

LOC exceedances for risk to listed species with RQ values ranging from 1.11 to 10.76. Results 

have been tabulated in Table 41.
Page 75 of 144

Table 41. Risk quotient (RQ) values for non-target dicot plants adjacent to dimethoate use areas1

Crop

Single Max. 

Application 

Rate

(lbs ai/A)

Dicot RQ Values

Spray Drift Only

Runoff and 

Spray Drift 

(Dry Areas)

Runoff and 

Spray Drift

(Semi-Aquatic Areas)

Nonlisted 

Species

Listed 

Species

Nonlisted 

Species

Listed 

Species

Non-listed 

Species

Listed 

Species

Food crops

Douglas Fir Aerial: 4.5 0.27 0.98 0.54 1.96 2.95 10.76

Ground: 4.5 <0.1 0.20 0.32 1.17 2.73 9.98

Hybrid cottonwood Aerial: 2 0.12 0.43 0.24 0.87 1.31 4.78

Ground: 2 <0.1 <0.1 0.14 0.52 1.21 4.43

Ornamental woody 

shrubs and vines

Aerial: 1 <0.1 0.22 0.12 0.43 0.65 2.39

Ground: 1 <0.1 <0.1 <0.1 0.26 0.61 2.22

Ornamental Herbaceous Aerial: 0.25 <0.1 <0.1 <0.1 0.11 0.16 0.60

Ground: 0.25 <0.1 <0.1 <0.1 <0.1 0.15 0.55

Cherry Aerial: 1.35 <0.1 0.29 0.16 0.59 0.88 3.23

Ground: 1.35 <0.1 <0.1 <0.1 0.35 0.82 2.99

Soybeans Aerial: 0.5 <0.1 0.11 <0.1 0.22 0.33 1.20

Ground: 0.5 <0.1 <0.1 <0.1 0.13 0.30 1.11

Peppers Aerial: 0.336 <0.1 <0.1 <0.1 0.15 0.22 0.80

Ground: 0.336 <0.1 <0.1 <0.1 <0.1 0.20 0.75

Succulent peas Aerial: 0.156 <0.1 <0.1 <0.1 <0.1 0.10 0.37

Ground: 0.156 <0.1 <0.1 <0.1 <0.1 <0.1 0.35

1

LOC for listed and non-listed species = 1; values in bold exceed the LOC

4.3 Risk Description

In risk description, the results from the risk estimation are interpreted and synthesized into 

overall risk conclusions. This description considers other lines of evidence (e.g., monitoring data, 

field data, refined exposure and effects modeling) for characterizing ecological risk. In addition, 

the risk description also contains a discussion of relevant sources of uncertainty in the risk 

assessment and sensitivity of the risk assessment findings to important methodological 

assumptions. The risk description also addresses other concerns including risks to threatened 

and endangered species, a discussion of uncertainty, and the sensitivity of risk conclusions to 

assumptions made in the assessment. 

Based on the preliminary problem formulation written in support of the Registration Review of 

dimethoate, the risk hypothesis indicated that when used in accordance with current labels, offsite movement of dimethoate and its omethoate transformation product can occur via runoff, 

spray-drift, and atmospheric transport leading to exposure of non-target plants and animals. 

Monitoring data indicate detections of dimethoate and omethoate in surface waters and at sites 

distant from use areas. Therefore, applications to foliar surfaces may serve as a major source of 

dimethoate exposure to terrestrial and aquatic organisms. These potential exposure pathways

may result in adverse effects upon the survival, growth, and reproduction of non-target 

organisms. Based on exposure and effects data presented in the preceding section, potential risks 

to multiple taxa are identified. Other lines of evidence are considered in this section in order to 

put risk estimates into context and to highlight uncertainties and underlying assumptions that can 
Page 76 of 144

affect the assessment.

4.3.1Risk to Aquatic Organisms

A summary of the maximum dimethoate acute and chronic RQ values derived for aquatic 

animals is shown in Table 42. None of the RQ values for freshwater fish and estuarine/marine 

fish exceed the applicable acute or chronic risk LOCs; specifically, the acute RQ values are two 

orders of magnitude below the acute risk to non-listed species LOC of 0.5. The RQ values are 

also two orders of magnitude below the chronic risk LOC of 1.0. Both acute and chronic 

freshwater and estuarine/marine invertebrate RQs exceed the respective LOCs of 0.5 and 1.0. 

For estuarine/marine invertebrates, the RQs exceed the chronic risk LOC of 1.0 by 2 orders of 

magnitude. 

Table 42. Summary of aquatic animal risk profile for Dimethoate

Exposure FW Fish RQ SW Fish RQ FW Invert. RQ SW Invert. RQ

Acute 0.006 <0.001 0.793 1.110

Chronic 0.047 0.013 53.40 133.5

RQ values based on the maximum aquatic EECs derived from the 14 OR Christmas trees exposure scenario; see Risk Estimation Section 5.1

for derivation of these RQ values 

Monitoring data found dimethoate to be present in surface water. Based on NAWQA data, there 

were 8,726 samples taken from 2001 to 2012; dimethoate was detected in 128 of the samples and 

ranged from 0.0036 to 0.494 ppb while the LODs were reported to be between 0.0021 and 0.10 

ppb. The highest concentration of 0.494 ppb was taken in 2010, modeling yielded peak EECs 

ranging from 5.07 ppb to 44.3 ppb; therefore, the monitoring was around one order of magnitude 

lower than the modeling, which is expected for non-targeted monitoring; however, the 

monitoring results appear to support a low frequency of detection. Despite the low level of 

detection seen in the monitoring data, EFED believes the concentrations used for modeling 

surface waters are realistically conservative such that the low risk to fish and potential risk to 

aquatic invertebrates are considered reasonable. 

4.3.2 Risk to Freshwater and Estuarine/Marine Fish

None of the RQ values for freshwater fish and estuarine/marine fish exceed the applicable acute 

or chronic risk LOC.

There were four incidents reported in EIIS involving fish kills from 1972 to 1995. Two of the 

incidents were considered to be the result of misuse of the registered products and outside of the 

registered used of dimethoate and thus will not be considered here. Two of the incidents were a 

result of a ‘registered use’ of dimethoate; one was classified as ‘probable’ and the other 

classified as ‘possible.’ There were few details provided in the incidents regarding application 

scenarios or events leading up to the fish kill; additionally in both incidents, dimethoate was 

found in addition to other chemicals. While the incidents demonstrate the potential for a 
Page 77 of 144

complete exposure pathway for dimethoate to harm aquatic organisms, there is uncertainty 

regarding the role of other chemicals; furthermore, RQ values for are well below the acute risk 

LOCs (maximum RQ=0.006) and chronic risk LOC (maximum RQ=0.036).

4.3.3 Risk to Aquatic Invertebrates

Based on the results of risk estimation, there is potential risk to both freshwater and 

estuarine/marine invertebrates on an acute and chronic exposure basis using maximum labeled 

use rates.

To evaluate potential risks, EECs were also calculated using typical use rates found in Table 12. 

The RQs calculated using the typical use rates can be found in Table 43. Typical use rates were 

only available for certain agricultural crops; however, 14_OR_Xmas trees (a non-agricultural 

crop) which had the maximum EEC and use rate was not included in this analysis since there is 

no average application rate for this crop. Uses that were modeled using both labeled rates and 

typical rates will be compared here. 

On an acute exposure basis, the RQs for freshwater invertebrates when modeled using maximum 

labeled rates range from 0.199 to 0.540 and exceed LOCs for acute risk to listed and non-listed 

species, with 3 of the scenarios exceeding the listed species LOC and 3 exceeding the non-listed 

species LOC. When freshwater invertebrates are modeled using typical rates, the RQs range 

from 0.089 to 0.381 and exceed the LOC for acute risk to listed species across all scenarios 

while none of the RQ values exceed the LOC for acute risk to non-listed species. 

For estuarine/marine invertebrates, the RQs based on maximum rates range from 0.276 to 0.748 

and with 3 of the scenarios exceeding the acute risk to listed species LOC and 3 exceeding the

acute risk to non-listed species LOC. When estuarine/marine invertebrates are modeled using 

typical use rates, the RQs range from 0.119 to 0.529 and exceed the LOC for acute risk to listed 

species in 5 of the scenarios and one scenario exceeding the LOC for acute risk to non-listed 

species at 0.529.

On a chronic exposure basis, the RQs for freshwater invertebrates and estuarine/marine 

invertebrates exceed the chronic risk LOC across all scenarios when modeled using the 

maximum labeled rates as well as the typical use rates.

There is some uncertainty surrounding the chronic value for freshwater invertebrates as it was 

calculated through the use of an acute-to-chronic ratio. The most sensitive value for acute 

freshwater invertebrates was 0.043 mg/L for the stone fly (MRID 00003503). An ACR was 

calculated using D. magna data (ACR=83); the acute daphnid effects were based on immobility 

while the chronic effects included impaired reproduction, growth and survival. However, an RQ 

based on the empirical daphnid NOAEC of 0.041 mg/L and 21-d EECs did not exceed the LOC 

for chronic risk.
Page 78 of 144

There is additional uncertainty surrounding the chronic toxicity value for estuarine/marine 

invertebrates as it too was calculated using an ACR. The most sensitive value for acute 

estuarine/marine invertebrates was 0.031 mg/L for the salt marsh mosquito. An ACR was 

calculated using data from mysids (ACR=107); the acute mysid effects were based on 

immobility while the chronic effects included impaired reduction, growth and survival. 
Page 79 of 144

Table 43. Risk quotient (RQ) values for invertebrates using estimated environmental concentrations (EECs) calculated 

using typical use rates

Use (s) Scenarios App. 

Method

Peak 

EECs

Acute RQ s 21-d 

EECs

Chronic RQs

Freshwater Estuarine/

Marine Freshwater Estuarine/Marine

03_MN_alfalfa Alfalfa Aerial 2.76 0.064* 0.089* 2.23 4.4 11

05_CA_Cole 

crops

Broccoli Ground 7.69 0.17* 0.24* 6.33 12 31

10_WA_Orchards

Cherry (only in 

ID, MT, OR, UT 

and WA)

Aerial 6.01 0.14* 0.19* 5.08 10 25

20_FL_Peppers Peppers Aerial 16.4 0.38* 0.52 11.5 23 57

23_MS_Cotton Cotton Aerial 3.69 0.086* 0.11* 2.58 5.1 12

26_FL_Citrus

Grapefruit, 

Kumquat, Lemon, 

Lime, Orange, 

Pummelo 

(shaddock), 

Tangelo, 

Tangerine

Aerial 9.89 0.23* 0.31* 6.59 13 32

*Indicates the RQ exceeds the listed species LOC of 0.05

Bolded text indicated the RQ exceeds the risk to non-listed species LOC of 0.5

Shaded cell indicates RQ exceeded risk to non-listed species LOC with labeled use rates, but only exceeds risk to listed species LOC when modeled with typical use rates
Page 80 of 144

Invertebrate RQs were also calculated for dimethoate including unextracted residues. The EEC 

values for unextracted residues can be found in Table 13. The resulting RQ values exceed LOCs 

for acute and chronic risk to listed and non-listed species.

Table 44. Risk quotient (RQ) values using estimated environmental concentrations (EECs) for 

dimethoate plus unextracted residues

Use Peak 

EEC

Acute RQs 21-day 

EEC

Chronic RQs

Freshwater Estuarine/Marine Freshwater Estuarine/Marine

CA_cole 31.7 0.76 1.02 27.2 54 136

FL_Citrus 36 0.83 1.16 30.2 60 151

Bolded values exceed LOC for risk

4.3.4 Risk to Aquatic Plants

RQ values calculated using the maximum peak aquatic EEC and the lowest toxicity endpoint for 

aquatic vascular and non-vascular plats are two to three orders of magnitude below the LOC. 

This finding, combined with the knowledge of the mode of action of dimethoate as an AChE 

agonist supports a conclusion of low potential risk to aquatic plants.

4.3.5Risk to Terrestrial Organisms

A summary of the overall acute and chronic risk profile for dimethoate based on the exposure 

scenario producing the highest terrestrial EECs and the most sensitive species within each 

taxonomic group is shown in Table 44. Results indicate a potential for acute and chronic risk to 

birds, reptiles and terrestrial-phase amphibians (using birds as a surrogate), and mammals. In 

addition to LOC exceedances, there were incidents that involved avian species and pollinators.

Table 44. Summary of the avian and mammalian risk profile for dimethoate with 

uses that produced the greatest terrestrial estimated environmental concentrations 

(EECs)

Exposure Avian Dose 

RQ

Avian Dietary 

RQ

Mammalian 

Dose RQ

Mammalian 

Dietary RQ

Acute 262 7.2 1.3 n/a

Chronic n/a 270 4685 540

RQ values based on the terrestrial EECs derived from Douglas Fir 1 x 4.5 lb ai/A; see Risk Estimation for derivation of 

these RQ values

* Refined RQ estimate using a foliar dissipation half-life of 2.82 days

Bolded values exceed LOC for risk

4.3.6 Risk Characterization Birds

For birds (also used as a surrogate for terrestrial-phase amphibians and reptiles), a potential for 

acute and chronic risks was identified using the dose-based and dietary-based RQ values. For 

acute dose-based and acute dietary-based risk estimates, there was a general trend of 

exceedances for herbivorous and insectivorous birds as well as birds consuming fruits, pods and 
Page 81 of 144

seeds, with fewer exceedances as the body size increased. Comparatively, there were fewer 

scenarios which resulted in LOC exceedances for birds consuming seeds and grains. Dietary 

acute-based risk exhibited a similar trend.

For chronic dietary-based risk estimates, the LOC was exceeded for all scenarios for birds 

consuming short grass, tall grass, broadleaf plants, and arthropods. For birds consuming fruits, 

pods and seeds, a majority of the scenarios exceeded the chronic risk RQ.

For further examination the Upper Bound Kenaga values, as part of the T-REX output, for the 

maximum food use and non-food use were analyzed. For the Douglas Fir scenario, the avian 

chronic LOC is exceeded for 24 days. For the cherry scenario, the maximum rate for food uses,

the avian chronic LOC is exceeded for 19 days.

There are seven incidents involving birds that were reported in EIIS. The incidents occurred 

from 1972 to 2000. Three of the incidents are classified as a misuse of the product and thus will 

not be considered here. Of the remaining four incidents, three of them are classified as ‘highly 

probable.’ Two of them involved the Cedar Waxwing species and two involved Canadian Geese. 

Significant mortality of 60-80 Cedar Waxwing birds were found in one incident, with 40 and 25 

Canadian Geese mortality in the other two incidents. The findings reported in EIIS demonstrate 

that there is a complete exposure pathway for avian species. 

The SIP and STIR tools flagged contaminated water and inhalation of spray drift as a potential 

routes of exposure for avian species. These pathways are of concern but are currently 

unaccounted for as EFED does not currently have standard models for addressing these specific 

routes of exposure

4.3.7 Risk Characterization Mammals

For mammals, the acute dose base risk estimates varied with concentrated LOC exceedances 

with smaller mammals and highest application rates. For mammals consuming fruits, seeds and 

pods, or arthropods or seeds and grains there were significantly fewer scenarios that exceeded 

the LOC.

Chronic risk concerns are identified for mammals across all feed items and scenarios. For 

chronic-dose based risk to mammals. The RQ values calculated across all mammal sizes, 

foraging categories and scenarios exceed the chronic risk LOC for listed and non-listed 

mammals. For chronic-dietary based risk to mammals, the maximum RQ is 540 for small 

mammals consuming short grass. There is significant uncertainty associated with chronic-dose 

based RQ values pertaining to the duration over which chronic effects to mammals are likely to 

manifest. These RQ values are derived using the maximum peak concentration of dimethoate 

that is predicted to occur on the dietary forage items. 

For further examination the Upper Bound Kenaga values, as part of the T-REX output, for the 

maximum food use and non-food use were analyzed. For the Douglas Fir scenario, the 

mammalian chronic LOC is exceeded for 36 days. For the cherry scenario, the maximum rate 

for food uses, the mammalian chronic LOC is exceeded for 31 days.
Page 82 of 144

There were no incidents reported in EIIS related to mammals.

SIP (Screening Imbibition Tool) was used to evaluate an upper-bound estimate of exposure to 

ingestion of contaminated water using dimethoate’s solubility and a suite of toxicity studies. 

Drinking water alone is identified as potential pathway of concern for mammalian species on an 

acute and chronic exposure basis. Although this exposure pathway is of concern, it is currently 

unaccounted for as EFED does not currently have a standard model for addressing this specific 

route of exposure.

4.3.8 Risk Characterization for Bees

There are multiple lines of evidence to suggest risk to bees from registered uses of dimethoate

for foliar and soil applications. First, screening-level (Tier 1) analysis suggests potential risk of 

acute lethality to adult bees resulting from acute oral and contact exposure routes (Tables 38 and 

39). Although the Tier 1 exposure estimates represent “high end” exposure values for screening 

purposes, the acute risk LOC of 0.4 is exceeded by up to four orders of magnitude. This

suggests that the risk estimates are not likely to be sensitive to the conservatism of the Tier 1 

exposure estimates. Second, available data from ecological incident reports is suggestive, 

though not conclusive, that dimethoate use may be associated with a number of bee kill incidents 

in the U.S. For two reported incidents (I024335-001 and I013884-033), dimethoate was the 

only pesticide reportedly applied at the time of the incident with “probable” and “possible” 

certainty designations assigned, respectively. However, the legality of these dimethoate 

applications is undetermined. Two other bee kill incidents indicate dimethoate applications with

“probable” certainty, although other pesticides were also applied near the vicinity and time of 

these incidents. Third, available information from a full field study indicates increased bee 

mortality, reduced foraging activity, and increased behavior abnormalities is associated soon 

after foliar applications of 0.67 lb ai/A dimethoate to Phacelia at bloom just prior to bees

foraging. Long-term effects on brood development and overall colony performance were not 

indicated and may suggest possible recovery; however, there are substantial limitations with the 

field study. Lastly, the mode of action and use of dimethoate as a reference toxicant in semifield (tunnel) studies at application rates comparable to those registered in the U.S. also supports 

at least short-term risk to bees from applications near or during foraging. 

At the time of this assessment, available data were inadequate to address a number of 

uncertainties, including lack of chronic toxicity data to larvae and adult bees, lack of exposure 

data on dimethoate residues in pollen and nectar, and lack of robust, higher-tier studies to 

quantify long-term impacts of dimethoate to developing brood and colony survival. Since most 

of these studies have only recently been required by EPA for pesticide registration decisions, 

these data gaps will be addressed in the future with a DCI once they are identified as critical data 

gaps.

4.3.9 Risk Characterization Terrestrial Plants
Page 83 of 144

Risks to terrestrial plants from the currently labeled uses of dimethoate are not expected based on 

the available toxicity data and model-generated exposure estimates. This risk conclusion is 

supported by the mode of action of dimethoate, which would not be expected to affect plants at 

the levels applied to address target insects. Despite the lack of predicted risk to plants, there 

were two incidents reported in the EIIS database. Both incidents were due to a malfunction of 

machinery and were classified as a misuse.
Page 84 of 144

4.4 Characterization of Omethoate

4.4.1 Aquatic Species

A comparison of aquatic toxicity data of dimethoate and omethoate can be found in Table 26. 

Omethoate data are only available for freshwater fish and freshwater invertebrates; there are no 

estuarine/marine data available for omethoate. Comparison of available data indicate that the 

sensitivity to each chemical is species and taxa specific. 

For the rainbow trout, dimethoate has an LC50 of 6.2 mg/L (MRID 40094602) and omethoate has 

a roughly equivalent LC50 of 5.0 mg/L (MRID 48821404). However, for the bluegill sunfish, 

dimethoate has an LC50 of 31.5 mg/L (MRID 48821401) while omethoate exhibited increased 

toxicity with an LC50 of 7.7 mg/L. For dimethoate, acute RQs are below the risk to listed species 

LOC of 0.05 by a factor of 10 or greater for both rainbow trout and bluegill. Given that the LC50

values of both parent and omethoate are roughly equivalent for rainbow trout and the LC50 of 

omethoate is about 1⁄4 that of the parent for bluegill, consideration of omethoate in the EEC 

would not affect the final risk conclusion for this taxa.

For aquatic invertebrates, dimethoate has an EC50 of 1.6 mg/L while omethoate has increased 

toxicity to daphnids at an EC50 of 0.0325 mg/L. The inclusion of omethoate in the EEC 

calculation will alter the risk conclusions based on just the parent alone. EECs for omethoate 

were calculated in (Aquatic Modeling Approach) Table 15. Using the peak EEC for omethoate 

and the invertebrate EC50 values for dimethoate and omethoate, a dimethoate Toxic Equivalent 

EEC was calculated14; this value was then added to the dimethoate EEC to get a total EEC 

reflecting toxic equivalency of dimethoate. This Total EEC was then used to calculate an RQ 

that would incorporate both dimethoate and omethoate exposure and toxicity. The calculation 

has been summarized below in Table 45. According to this calculation, inclusion of omethoate 

increased the RQ by greater than 8 fold, and indicates the potential for acute risk to listed aquatic 

invertebrate species.

Table 45. Acute risk Quotient (RQ) values based on omethoate for freshwater aquatic 

invertebrates

Omethoate 

EEC

(peak)

μg/L

Dimethoate 

Toxic 

Equivalent 

EEC

Dimethoate 

EEC

(peak)

μg/L

Total 

EEC

Total RQ

(Dimethoate 

LC50 = 1600 

μg/L)

Dimethoate 

RQ

05_CA_Cole_Crops 3.70 182 23.2 205 0.128 0.0145

26_FL_CITRUS 3.40 167 22.1 189 0.118 0.013

 14 Dimethoate toxic equivalent EEC = (Dimethoate LC50 / Omethate LC50) * Dimethoate EEC
Page 85 of 144

Omethoate also displayed increased toxicity to freshwater invertebrates on a chronic exposure

basis with a daphnid NOAEC of 0.119 μg/L as compared to the dimethoate NOAEC of 41 μg/L. 

According to the calculation of a combined dimethoate and omethoate outlined in Table 46,

where RQ estimations previously did not exceed the chronic risk LOC, the inclusion of 

omethoate results in an exceedance for the chronic LOC by a factor of 20. However, there is a 

degree of uncertainty associated with these equations because they assumed that acute and 

chronic exposure are occurring at the same time; since omethoate was not observed in the 

aquatic metabolism studies, here it was assumed to be applied via the soil instead of via foliar 

application with drift. The acute and chronic exposure may not occur simultaneously. Therefore 

there is uncertainty concerning the toxic equivalent conversion concurrent to the acute and 

chronic exposure uncertainty. 

Table 46. Estimation of chronic risk quotient (RQ) values based on omethoate for

freshwater invertebrates

Omethoate 

EEC

(21-day)

μg/L

Dimethoate 

Toxic 

Equivalent 

EEC

Dimethoate 

EEC

(21-day)

μg/L

Total 

EEC

Total RQ

(Dimethoate 

LC50 = 1600 

μg/L)

Dimethoate 

RQ

05_CA_Cole_Crops 2.33 783 20 803 20 0.5

26_FL_CITRUS 0.856 287 14.7 301 7.5 0.36

Risk conclusions from Tables 29 and 30 have been made using risk quotients calculated using 

toxicity values for the Stonefly because it presents a more sensitive species than the daphnid; 

however, omethoate toxicity estimation in this section has used data available for daphnid. 

There is some uncertainty assuming that the differential acute toxicity observed with the daphnid 

applies to the stonefly as well. 

4.4.2Terrestrial Species

A comparison of avian toxicity data for dimethoate and omethoate can be found in Table 27. 

Omethoate data are available for acute oral toxicity, sub-acute dietary toxicity and chronic

toxicity. The comparison shows the sensitivity to each chemical is species specific. Based on 

these data, omethoate and dimethoate exhibit similarly toxic for birds on an acute, sub-acute and 

chronic exposure basis. With available data, we are uncertain as to whether or not inclusion of 

omethoate would substantially increase the risk estimates for terrestrial animals. 

There is some uncertainty concerning the toxicity of omethoate to mammals. HED had 

previously concluded a 3-fold increase in the toxicity of omethoate in terms of AChE inhibition

in mammals; however, there is uncertainty in applying this factor to the apical endpoints of 

survival, growth and reproduction. 

4.5 Endangered species

In November 2013, the EPA, along with the U.S. Fish & Wildlife Service (USFWS), the 
Page 86 of 144

National Marine Fisheries Service (NMFS) (collectively, the Services), and the U.S. Department 

of Agriculture (USDA) released a summary of their joint Interim Approaches for assessing risks 

to listed species from pesticides. The Interim Approaches were developed jointly by the 

agencies in response to the National Academy of Sciences’ (NAS) recommendations and reflect 

a common approach to risk assessment shared by the agencies as a way of addressing scientific 

differences between the EPA and the Services. The NAS report outlines recommendations on 

specific scientific and technical issues related to the development of pesticide risk assessments 

that EPA and the Services must conduct in connection with their obligations under the

Endangered Species Act (ESA) and FIFRA. 

The joint Interim Approaches were released prior to a stakeholder workshop held on November 

15, 2013. In addition, the EPA presented the joint Interim Approaches at the December 2013 

Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues Research and 

Evaluation Group (SFIREG) meetings, and held a stakeholder workshop in April 2014, allowing 

additional opportunities for stakeholders to comment on the Interim Approaches. As part of a 

phased, iterative process for developing the Interim Approaches, the agencies will also consider 

public comments on the Interim Approaches in connection with the development of upcoming 

Registration Review decisions. The details of the joint Interim Approaches are contained in the 

white paper “Interim Approaches for National-Level Pesticide Endangered Species Act 

Assessments Based on the Recommendations of the National Academy of Sciences April 2013 

Report,” dated November 1, 2013. 

Given that the agencies are continuing to develop and work toward implementation of the 

Interim Approaches to assess the potential risks of pesticides to listed species and their 

designated critical habitat, this preliminary risk assessment for dimethoate does not contain a 

complete ESA analysis that includes effects determinations for specific listed species or 

designated critical habitat. Although EPA has not yet completed effects determinations for 

specific species or habitats, for this preliminary assessment EPA conducted a screening-level 

assessment for all taxa of non-target wildlife and plants that assumes for the sake of the

assessment that listed species and designated critical habitats may be present in the vicinity of 

the application of dimethoate. This screening level assessment will allow EPA to focus its 

future evaluations on the types of species where the potential for effects exists once the scientific 

methods being developed by the agencies have been fully vetted. This screening-level risk 

assessment for dimethoate indicates potential risks of direct effects to listed freshwater and 

estuarine/marine invertebrates, avian species and mammals on some of its registered use sites. 

Once the agencies have fully developed and implemented the scientific methods necessary to 

complete risk assessments for endangered and threatened (listed) species and their designated 

critical habitats, these methods will be applied to subsequent analyses for dimethoate as part of 

completing this registration review. 

4.6 Uncertainties, Limitations, and Identification of Data Gaps

4.6.1 Environmental Fate Database

Regarding the input values used in this risk assessment, the environmental fate database for 
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dimethoate was considered to be complete and no estimated values, or uncertainty factors were 

used. Three of the aerobic soil metabolism values were derived from non-labeled studies. 

Usually, studies conducted with non-labeled compounds show recoveries within a range of 70-

120% of the applied, while the ones conducted with labeled compounds range from 90-110% of 

the applied radioactivity. The one study conducted with radiolabeled compound had a half-life 

which was very similar than the studies conducted with non-radiolabeled compounds (2.4 days 

for the labeled compound compared to 1.65-3.01 days for the non-radiolabeled compounds).

4.6.2 Modeling Omethoate in the SWCC

Although omethoate was not observed in any of the laboratory environmental fate studies, some 

fate data was available for the chemical (e.g., mobility and aerobic aquatic metabolism). In this 

assessment, the rate of formation of omethoate was based on the maximum observed in 

terrestrial field dissipation studies. This brings uncertainty to the analysis since in field 

dissipation studies several processes may be occurring simultaneously, like for example leaching 

and runoff, besides degradation. The exposure may have been underestimated. With respect to 

the aquatic modeling, since there was no aerobic soil metabolism half-life, it was assumed to be 

similar to the aerobic aquatic metabolism half-life.

Omethoate was modeled separately from dimethoate (i.e., an approach similar to the residue 

summation was used). The EECs for omethoate are rough estimates which, as indicated above, 

are based on the maximum amount observed in the terrestrial field dissipation studies. However, 

there is a degree of uncertainty associated with these equations because they assumed that acute 

and chronic exposure are occurring at the same time; since omethoate was not observed in the 

aquatic metabolism studies, here it was assumed to be applied via the soil instead of via foliar

application with drift. The acute and chronic exposure may not occur simultaneously. Therefore 

there is uncertainty concerning the toxic equivalent conversion concurrent to the acute and 

chronic exposure uncertainty.

4.6.3 Application Information

Meteorological data and crop profiles, as well as best professional judgment, were used to 

establish an application date for modeling; however, the selected date may not represent the 

intended or actual application dates. The application date used for model runs can significantly 

alter the EECs; thus, EECs reported could over or under predict actual exposure. The dates of 

application used in this risk assessment were generally selected based on the crop cycle to make 

sure that the applications were to foliage (unless otherwise specified on the label). It is unclear 

how much the application dates differ from the typical timing of application, which is based on 

pest pressure.

4.6.4 Number of Seasons per Year

Many dimethoate labels include application restrictions on a per season basis; however, for some 

crops there can be multiple growing seasons per year. For modeling purposes one season was 

considered to be equal to one year. If multiple crop seasons are possible per year it is 

conceivable then EECs reported in this document are more likely to underestimate actual 
Page 88 of 144

exposure. In general, this assessment makes conservative assumptions regarding re-cropping 

and rotations (i.e., applications on the same crop every year for a period of 30 consecutive years). 

EFED evaluated a number of labels for specific information regarding application methods and 

timing, and noted some application rates provided on the label are on a per season basis. The 

yearly/seasonal application rates used in this assessment are primarily based on data from 

BEAD’s label data report and supplemented by the review of a number of labels.

Some of the labels do not provide maximum single or annual application rates for dimethoate or 

number of applications or application retreatment intervals. When this information is not 

specified on the label, a conservative application scenario was modeled, based on assumptions. 

These assumptions are shaded grey in Table 2.

4.6.5 Use of Maximum Labeled Rates

According to the labels, dimethoate is a IRAC MoA subgroup 1B insecticide/miticide, to which 

target pests can develop resistance if the chemical is applied consecutively or repeatedly in the 

same field and/or in consecutive years with other chemicals belong to subgroup 1B. For that 

reason, it is recommended to avoid its consecutive use of the compound, as well as the 

consecutive use of other group 1B insecticides and to base dimethoate’s use on a comprehensive 

Integrated Pest Management program. Thus, even though the initial EECs were based on 

maximum application rates and minimum intervals between applications, it appears unlikely that 

users will apply this chemical under these circumstances, and on a yearly basis for 30 

consecutive years, as assumed in the modeling performed in this ecological risk assessment. In 

this risk assessment, results from typical (or average) application rates and number of 

applications were presented in addition to the maximum application rates, although applications 

during 30 consecutive years were also assumed. The frequency at which actual uses approach 

this maximum use scenario may be dependent on pest resistance, timing of applications, cultural 

practices, and market forces.

4.6.6 Volatility of Dimethoate

In a laboratory volatility study, dimethoate showed some potential for volatilization. At the end 

of the study 2% of AR was volatile organics. The SWCC accounts for this route of dissipation 

partially when the solubility and vapor pressure are entered; however, it is uncertain as to what 

degree the chemical would be lost in the environment to volatilization under field conditions. 

Compared to other routes of dissipation for dimethoate, it appears that volatilization is not a 

significant dissipation pathway for the chemical. At the present time, the volatility routine of 

PRZM has not been incorporated in the SWCC.

4.6.7 Unextracted Residues

Issues with un-extracted radioactivity were identified in the laboratory-based aquatic metabolism 

studies. Regarding the aerobic and anaerobic aquatic metabolism studies, there were observed 

levels of unextracted radioactive residues. Nonetheless, these levels only reached up to 12.9% 

AR (with the exception of the last test interval) under aerobic aquatic condition, and 13.3% AR 

under anaerobic aquatic conditions. Although these levels were considered only marginally 
Page 89 of 144

high, and, to help clear this uncertainty, modeling of total toxic residues comprising parent plus 

unextracted radioactivity was performed.

4.6.8 Aquatic Modeling with the SWCC

The standard ecological water body scenario (VVWM standard pond) used to calculate potential 

aquatic exposure to pesticides such as dimethoate is intended to represent conservative water 

concentration estimates, and to avoid underestimating most actual exposures. The standard 

scenario assumes pesticide application to a 10-hectare field bordering a 1-hectare, 2-meter deep 

(20,000 m3) pond with no outlet. Exposure estimates generated using the VVWM pond are

intended to represent a wide variety of vulnerable water bodies that occur at the top of 

watersheds including prairie pot holes, playa lakes, wetlands, vernal pools, man-made and 

natural ponds, and intermittent and lower order streams. As a group, there are factors that may 

make such water bodies either more or less vulnerable than the VVWM pond. Static water 

bodies that have larger ratios of pesticide-treated drainage area to water body volume would be 

expected to have higher potential peak EECs than the VVWM pond. These water bodies may be 

either smaller in size or have larger drainage areas. Smaller water bodies have less dilution 

volume, may have less ability to store excess inflow, and thus may periodically overflow and 

export pesticide in the discharge; whereas, the VVWM pond has no discharge. As watershed 

size increases beyond 10-hectares, it presumably becomes increasingly less likely that the entire 

watershed is planted with a single crop that is all treated simultaneously with the pesticide. 

Headwater streams can also exhibit peak concentrations higher than those in the VVWM pond, 

but that persist for shorter periods of time as they are then carried and dissipated (advected)

downstream.

In general, the linked PRZM/VVWM model (through the SWCC GUI) produces EECs that are 

expected to be exceeded once within a ten-year period. PRZM is a process or “simulation” 

model that calculates runoff of a pesticide from an agricultural field on a daily temporal 

resolution, over a period of decades. It considers factors such as rainfall and plant transpiration 

of water, as well as how and when the pesticide is applied. It has two major components: 

hydrology and chemical transport. Water movement is simulated by the use of generalized soil 

parameters, including field capacity, wilting point, and saturation water content. The chemical 

transport component can simulate pesticide application on the soil or on the plant foliage. 

Dissolved, adsorbed, and vapor-phase concentrations in the soil are estimated by simultaneously 

considering the processes of pesticide uptake by plants, surface runoff, erosion, decay, 

volatilization, foliar wash-off, sorption and leaching.

Uncertainties associated with each of these individual components add to the overall uncertainty 

of the modeled concentrations. Additionally, model inputs from the environmental fate 

degradation studies are chosen to reflect the upper 90 percent upper confidence limits on mean 

half-lives. Mobility input values (soil sorption coefficients) are chosen to represent average 

sorption in the environment. The natural variation in soils adds to the uncertainty of modeled 

values. Factors such as application date, crop emergence date, and canopy cover can also affect 

estimated concentrations, adding to the uncertainty of modeled values. Factors within the 

ambient environment such as soil temperatures, sunlight intensity, antecedent soil moisture, and 

surface water temperatures can cause actual aquatic concentrations to differ for the modeled 
Page 90 of 144

values.

4.6.9 Uncertainties Regarding Dilution and Chemical 

Transformations in Estuaries

The SWCC-modeled EECs are intended to represent exposure of aquatic organisms in relatively 

small ponds, low-order streams, and other vulnerable water bodies. It is likely that EECs 

generated from the SWCC model over-estimate (especially on an acute basis) potential 

concentrations in larger receiving water bodies including estuaries, embayments, and coastal 

marine areas because chemicals in runoff water (or spray drift, etc.) is diluted by larger volumes

of water. In addition, as chemical constituents in water draining from freshwater streams 

encounter brackish or other near-marine-associated conditions, there is potential for new

chemical transformations to occur. Many chemical compounds can undergo changes in mobility, 

toxicity, or persistence when changes in pH, Eh (redox potential), salinity, dissolved oxygen 

(DO) content, or temperature are encountered. For example, desorption and re-mobilization of 

some chemicals from sediments can occur with changes in salinity (Jordan et al., 2008; Means, 

1995; Swarzenski et al., 2003), changes in pH (e.g., Wood and Baptista 1993), Eh changes 

(Velde and Church, 1999; Wood and Baptista, 1993), and other factors. Thus, although 

chemicals in discharging rivers may be diluted by large volumes of water within receiving 

estuaries and embayments, the hydrochemistry of the marine-influenced water may negate some 

of the attenuating impact of the greater water volume; for example, the effect of dilution may be 

confounded by changes in chemical mobility (and/or bioavailability) in brackish water. In 

addition, freshwater contributions from discharging streams and rivers do not instantaneously 

mix with more saline water bodies. In estuarine settings, water is often vertically stratified, with 

fresh water lying atop denser, higher salinity water – meaning that exposure to concentrations 

found all in discharging stream water may propagate some distance beyond the point of the

confluence with higher salinity water (especially near the water surface) without substantial 

dilution occurring. Therefore, it is not assumed that discharging water will be rapidly diluted by 

the entire water volume within an estuary, embayment, or other coastal aquatic environment. 

SWCC model results should be considered consistent with concentrations that might be found 

near the head of an estuary unless there is specific information – such as monitoring data – to 

indicate otherwise. Conditions nearer to the mouth of a bay or estuary, however, may be closer 

to a marine-type system, and thus more subject to the notable buffering, mixing, and diluting 

capacities of an open marine environment. Conversely, tidal effects (pressure waves) can 

propagate much further upstream than the actual estuarine water, so discharging river water may 

become temporarily partially impounded near the mouth (discharge point) of a channel, and 

resistant to mixing until tidal forces are reversed.

The Agency does not currently have sufficient information regarding the hydrology and 

hydrochemistry of estuarine aquatic habitats to develop alternate scenarios for assessed species 

that inhabit these types of ecosystems. The Agency acknowledges that there are unique brackish 

and estuarine habitats that may not be accurately captured by SWCC modeling results, and may, 

therefore, under- or over-estimate exposure, depending on the aforementioned variables.
Page 91 of 144

4.6.10Uncertainties regarding Acute to Chronic Ratio

The chronic values for estuarine/marine invertebrates and freshwater invertebrates were 

estimated using an acute to chronic ratio (See Table 24). For freshwater invertebrates, a study 

conducted using the stonefly (Pteronarcys californica) was found to have a more sensitive EC50

than Daphnia magna; thus this endpoint was used as the regulatory endpoint in risk estimation. 

In using an Acute to Chronic Ratio, it is assumed that the increased sensitivity the stonefly 

exhibited on an acute basis, will be exhibited on a chronic basis and may result in an 

overestimation of toxicity to the organism, thus there is some uncertainty surrounding the use of 

ACR risk estimation of the stonefly and Salt Marsh Water Mosquito.

4.7Endocrine Disruption Screening Program

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 which may be susceptible to endocrine influence, including effects 

on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual maturation, 

fertility, pregnancy rates, reproductive loss, and sex ratios in offspring. For ecological hazard 

assessments, EPA evaluates acute tests and chronic studies that assess growth, developmental and 

reproductive effects in different taxonomic groups. As part of the Preliminary Problem 

Formulation for Registration Review D355609, 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, 2013[1] and includes some pesticides 

 [1] See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals.
Page 92 of 144

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 of 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. For further information on the status of the 

EDSP, the policies and procedures, the lists of chemicals, future lists, the test guidelines and Tier 

1 screening battery, please visit our website[2].

 [2] Available: http://www.epa.gov/endo/
Page 93 of 144

5.0 References

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http://www.epa.gov/oppfead1/endanger/consultation/ecorisk-overview.pdf (accessed July 

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http://www.epa.gov/pesticides/reregistration/REDs/dimethoate_ired_revised.pdf

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of Concern in Problem Formulations for Registration Review, Registration Review Risk 

Assessments, Listed Species Litigation Assessments, New Chemical Risk Assessments, 

and Other Relevant Risk Assessments. Memorandum from Donald Brady dated January 

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and PE5 and WQTT Advisory Note Number 9: Temperature Adjustments for Aquatic 

Metabolism Inputs to EXAMS and PE5. OCSPP/OPP/Environmental Fate and Effects 

Division. Dated 09/21/2010 and approved 10/18/2010.

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Ecological and Drinking Water Assessments, dated December 19, 2013. Memorandum 

from Donald Brady dated and approved December 20, 2013. Office of Pesticide Programs. 

Environmental Fate and Effects Division.

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H. and L. L. McDowell. 1987.

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Appendix A.

035001 Dimethoate Fate Chemistry Bibliography 

161-1 Hydrolysis

MRID Citation Reference

159761 Hawkins, D.; Kirkpatrick, D.; Till, C.; et al. (1986) The Hydrolysis of [Carbon-14]-

Dimethoate: Report No. HRC/DTF 6A/86268. Un- published study prepared by 

Huntingdon Research Centre, Ltd. 40 p. 

161-2 Photodegradation-water

MRID Citation Reference

159762 Hawkins, D.; Kirkpatrick, D.; Till, C. et al. (1986) The Photodegradation of [Carbon14]-Dimethoate in Water. Report No. HRC/ DTF 6b/86231. Unpublished study 

prepared by Huntingdon Research Centre Ltd. 29 p. 

161-3 Photodegradation-soil

MRID Citation Reference

77535 Dauterman, W.C.; Viado, G.B.; Casida, J.E. et al. (1959) Persistence of Dimethoate 

and Metabolites following Foliar Application to Plants: Contract No. AT(11-1); Project 

No. 14. (Univ. of Wisconsin, Dept. of Entomology for U.S. Atomic Energy 

Commission; unpublished study; CDL:109340-AG) 

135671 Melnikoff, N. (1974) Pesticides and the environment: Decomposition of 

organophosphorus pesticides. Khimiia Sel'skom Khoziaistve 12(4):289-297. (Also In 

unpublished submission received Dec 4, 1974 under 5F1531; submitted by 

American Cyanamid Co., Princeton, NJ; CDL:094151-U) 

159763 Hawkins, D.; Kirkpatrick, D.; Till, C. et al. (1986) The Photolysis of Dimethoate on 

Soil: Report No. HRC/DTF 6C/86318. Unpublished study prepared by Huntingdon 

Research Centre Ltd. 35 p. 

159791 Duff, W.; Menzer, R. (1973) Persistence, mobility, and degradation of [carbon-14]-

dimethoate in soils. Environmental Entomology 2(3):309-318. Includes 9 pages of 

unpublished test data. 

164958 Hawkins, D.; Kirkpatrick, D.; Till, C. et al. (1986) The Photo- lysis of [Carbon 14]-

dimethoate on Soil: HRC Rept. No. DTF 6C/ 86318. Unpublished study prepared by 

Huntingdon Research Centre Ltd. 49 p. 

43276401 Skinner, W.; Shepler, K. (1994) Photodegradation of (carbon 14)Dimethoate in/on 

Soil by Natural Sunlight: Lab Project Number: 414W. Unpublished study prepared by 
Page 97 of 144

PTRL West, Inc. 101 p. 

162-1 Aerobic soil metabolism

MRID Citation Reference

52091 Getzin, L.W.; Rosefield, I. (1968) Organophosphorus insecticide deradation by heatlabile substances in soil. Journal of Agricultural and Food Chemistry 16(4):598-601. 

(Also In unpublished submission received Dec 4, 1974 under 5F1531; submitted by 

American Cyanamid Co., Princeton, N.J.; CDL:094151-M) 

52099 Montedison, S.p.A. (1972) Laboratory Tests on the Degradation of Dimethoate 

(Rogor) in Soil as a Function of the Pollution Hazards Possibly Deriving from This 

Active Substance: Report No. 88/1972. (Unpublished study received Dec 4, 1974 

under 5F1531; submitted by American Cyanamid Co., Princeton, N.J.; CDL:094151-

W) 

42843201 Hawkins, D.; Kirkpatrick, D.; Shaw, D.; et al. (1988) The Metabolism of (carbon 14)-

Dimethoate in Soil Under Aerobic Conditions: Lab Project Number: 

HRC/DTF/7/881515. Unpublished study prepared by Huntingdon Research Centre 

Ltd. 60 p. 

52086 Bro-Rasmussen, F.; Noddegaard, E.; Voldum-Clausen, K. (1970) Comparison of the 

disappearance of eight organophosphorus insecticides from soil in laboratory and in 

outdoor experiments. Pes- ticide Science 1(?/Sep-Oct):179-182. (Also In

unpublished submission received Dec 4, 1974 under 5F1531; submitted by 

American Cyanamid Co., Princeton, N.J.; CDL:094151-H) 

162-2 Anaerobic soil metabolism

MRID Citation Reference

159764 Hawkins, D.; Kirkpatrick, D.; Till, C. et al. (1986) The Metabolism of [Carbon-14]-

Dimethoate in Soil under Anaerobic Conditions: Report No. HRC/DTF 6d/86368. 

Unpublished study prepared by Huntingdon Research Centre Ltd. 31 p. 

160148 Hawkins, D.; Kirkpatrick, D.; Till, C. et al. (1986) The Metab lism of [Carbon 14]-

dimethoate in Soil under Anaerobic Conditions: HRC/DTF 6d/86368. Unpublished 

study prepared by Hunting- don Research Centre Ltd. 35 p. 

42884402 Hawkins, D.; Kirkpatrick, D.; Shaw, D. et al. (1990) The Metabolism of (Carbon 14)-

Dimethoate in Sandy Loam Soil Under Anaerobic Conditions: Final Report: Lab 

Project Number: HRC/DTF/ 13/901535. Unpublished study prepared by Huntingdon 

Research Centre Ltd. 86 p. 

163-1 Leach/adsorption/desorption

MRID Citation Reference
Page 98 of 144

52092 Graham-Bryce, L.J. (1969) Diffusion of organophosphorus insecticides in soils. 

Journal of Science and Food Agriculture 20 (?/Aug):489-494. (Also In unpublished 

submission received Dec 4, 1974 under 5F1531; submitted by American Cyanamid 

Co., Princeton, N.J.; CDL:094151-N) 

52094 Kawamori, I.; Saito, T.; Iyatomi, K. (1971) Fate of organophosphorus insecticides in 

soils. Part I. Botyu-Kagaku 36(? ):7-12. (Also In unpublished submission received 

Dec 4, 1974 under 5F1531; submitted by American Cyanamid Co., Princeton, N.J.; 

CDL:094151-Q) 

52095 Kawamori, I.; Saito, T.; Iyatomi, K. (1971) Fate of organophosphorus insecticides in 

soils. Part II. Botyu-Kagaku 36:12-17. (Also In unpublished submission received Dec 

4, 1974 under 5F1531; submitted by American Cyanamid Co., Princeton, N.J.; 

CDL:094151-R) 

52098 Mishra, R.C.; Gupta, D.S. (1972) Persistence of Dimethoate in soils. Pesticides 

(Nov):28-30. (Also In unpublished study received Dec 4, 1974 under 5F1531; 

submitted by American Cyanam- id Co., Princeton, N.J.; CDL:094151-V) 

52099 Montedison, S.p.A. (1972) Laboratory Tests on the Degradation of Dimethoate 

(Rogor) in Soil as a Function of the Pollution Hazards Possibly Deriving from This 

Active Substance: Report No. 88/1972. (Unpublished study received Dec 4, 1974 

under 5F1531; submitted by American Cyanamid Co., Princeton, N.J.; CDL:094151-

W) 

52100 Parker, B.L.; Dewey, J.E. (1965) Decline of Phorate and Dimethoate residues in 

treated soils based on toxicity to Drosophila melanogaster. Journal of Economic 

Entomology 58(1):106-111. (Also iniunpublished submission received Dec 4, 1974 

under 5F1531; submitted by American Cyanamid Co., Princeton, N.J.; CDL:094151-

X) 

157237 Sato, Y.; Miyamoto, J. (1967) [An aspect concerning the movement of dimethoate 

from its granular formulation in soil]. Unknown Japanese source 16:23-28. 

164959 Hawkins, D.; Kirkpatrick, D.; Till, C.; et al. (1986) The Mobility of [Carbon 14]-

dimethoate in Soil: HRC Rept. No. HRC/DTF/6e/ 86806. Unpublished study 

prepared by Huntingdon Research Centre Ltd. 66 p. 

163-2 Volatility - lab

MRID Citation Reference

159765 Huntingdon Research Centre Ltd. (1986) [The Mobility of Dimethoate on Soil]: 

Summary: DTF6e. Unpublished study. 10 p. 

162776 Sanders, P. (1986) Cygon Systemic Insecticide-miticide, Dimethoate (AC 12,880): 

Volatilization from Soil: Report No. PD-M Volume 23-24: Project No. 0423. 

Unpublished study prepared by American Cyanamid Co. 35 p. 

43276402 Skinner, W. (1994) Laboratory Volatility of (carbon 14)Dimethoate: Lab Project 

Number: 415W. Unpublished study prepared by PTRL West, Inc. 76 p. 

164-1 Terrestrial field dissipation
Page 99 of 144

MRID Citation Reference

33896 Bohn, W.R. (1962?) The Disappearance of Dimethoate from Soil. (Unpublished 

study received May 6, 1965 under 241-94; submitted by American Cyanamid Co., 

Princeton, N.J.; CDL:001779-C) 

52085 Bohn, W.R. (1964) The disappearance of Dimethoate from soil. Journal of Economic 

Entomology 57(6):798-799. (Also In unpublished submission received Dec 4, 1974 

under 5F1531; submitted by American Cyanamid Co., Princeton, N.J.; CDL:094151-

G) 

52086 Bro-Rasmussen, F.; Noddegaard, E.; Voldum-Clausen, K. (1970) Comparison of the 

disappearance of eight organophosphorus insecticides from soil in laboratory and in 

outdoor experiments. Pes- ticide Science 1(Sep-Oct):179-182. (Also In unpublished 

sub- mission received Dec 4, 1974 under 5F1531; submitted by American Cyanamid 

Co., Princeton, N.J.; CDL:094151-H) 

52089 Duff, W.G.; Menzer, R.E. (1973) Persistence, mobility, and degradation of ^14ICDimethoate in soils. Environmental Entomology 2 (3):309-318. (Also In unpublished 

submission received Dec 4, 1974 under 5F1531; submitted by American Cyanamid 

Co., Princeton, N.J.; CDL:094151-K) 

52097 Manuel, A.J. (1972) Cygon(R) 267 and 25 WP: Dimethoate and Dimethoxon 

Residues in Soil: Report No. C-334. Includes method M- 220 dated Aug 3, 1971. 

(Unpublished study received Dec 4, 1974 under 5F1531; submitted by American 

Cyanamid Co., Princeton, N.J.; CDL:094151-T) 

52100 Parker, B.L.; Dewey, J.E. (1965) Decline of Phorate and Dimethoate residues in 

treated soils based on toxicity to Drosophila melanogaster. Journal of Economic 

Entomology 58(1):106-111. (Also~In~unpublished submission received Dec 4, 1974 

under 5F1531; submitted by American Cyanamid Co., Princeton, N.J.; CDL:094151-

X) 

52103 American Cyanamid Company (1964) Dimethoate--Soils--Gainesville (Nov. 1964). 

(Unpublished study received Dec 4, 1974 under 5F1531; CDL:094151-AC) 

75600 Bohn, W.R. (1962?) The Disappearance of Dimethoate from Soil. (Unpublished 

study, including letter dated Apr 6, 1964 from F.R. Barron, Jr. to J.A. Shaughnessy, 

received Apr 28, 1964 under 241-78; submitted by American Cyanamid Co., 

Princeton, N.J.; CDL:120250-A) 

75602 Orloski, E.J. (1964) Letter sent to F. Ray Barron, Jr. dated Feb 20, 1964: Cygon soil 

residue study. (Unpublished study received Feb 25, 1964 under 241-78; submitted 

by American Cyanamid Co., Princeton, N.J.; CDL:120258-A) 

75663 Duff, W.G. (1972) Persistence, Mobility, and Degradation of Dimethoate in Soils. 

Master's thesis, Univ. of Maryland. (Unpublished study received Mar 4, 1975 under 

5F1531; submitted by American Cyanamid Co., Princeton, N.J.; CDL:094152-A) 

42884403 Becker, S. (1991) Dissipation of Dimethoate from Soil following Application to Bean, 

Grape, and Bareground Plots Located in Fresno County, CA, USA: Amended Final 

Report: Lab Project Number: 135-005. Unpublished study prepared by EPL BioAnalytical Services, Inc. 633 p. 

43388001 Jacobson, B.; Williams, B. (1994) Dissipation of Dimethoate in Soil Under Field 

Conditions with Grain Sorghum in Texas: Lab Project Number: 40972. Unpublished 

study prepared by ABC Labs, Inc. 160 p. 
Page 100 of 144

43388002 Jacobson, B.; Williams, B. (1994) Dissipation of Dimethoate in Soil Under Field 

Conditions when Applied to Bare Ground in New York: Lab Project Number: 40971. 

Unpublished study prepared by ABC Labs, Inc. 152 p. 

Non Guideline Selections

85344 Mendoza, C.E.; Wales, P.J.; Grant, D.L.; et al. (1969) Effect of bromine and 

ultraviolet light on eight pesticides detected with liver esterases of five species. 

Journal of Agricultural and Food Chemistry 17(6):1196-1198. (Also In unpublished 

submission received Aug 28, 1972 under 279-2280; submitted by FMC Corp., 

Philadelphia, Pa.; CDL:120619-G) 
Page 101 of 144

Appendix B

035001 Dimethoate Eco Effects Bibliography Revised 18 July 2014

71-1 Avian Single Dose Oral Toxicity

MRID Citation Reference

95520 Bunyan, P.J.; Jennings, D.M.; Taylor, A. (1968) Diagnosis of poisoning in 

pheasants owing to a number of common pesticides. Journal of 

Agricultural and Food Chemistry 16(2):332-229. (Sub- mitter 22721; 

also~In~unpublished submission received Aug 10, 1970 under 3125-111; 

submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:006922-L) 

116057 Bunyun, P.; Jennings, D.; Taylor, A. (1968) Organophosphorus poisoning: 

Diagnosis of poisoning in pheasants owing to a num- ber of common 

pesticides. J. Agr. Food Chem. 16(2):332-339. (Also In unpublished 

submission received 1970 under 1E1082; submitted by Shell International

Chemical Co., Ltd., London, Eng.; CDL:090840-AI) 

47769701 Zok, S. (3001) Dimethoate - Acute Toxicity in the Northern Bobwhite 

Quail (Colinus virginianus) after Single Oral Administration (LD50). 

Project Number: 11W0466/99128, 441/008, 470/DMT. Unpublished study 

prepared by BASF Aktiengesellschaft, Labor fuer Oekotoxicologie. 71 p.

47769702 Zok, S. (2001) Dimethoate - Acute Toxicity in the Ring-Necked Pheasant 

(Phasianus colchicus) after Single Oral Administration (LD50). Project 

Number: 12W0466/99126, 441/007, 471/DMT. Unpublished study 

prepared by BASF Aktiengesellschaft, Labor fuer Oekotoxicologie. 67 p.

47769703 Gallagher, S.; Grimes, J.; Beavers, J. (2003) Omethoate: An Acute Oral 

Toxicity Study with the Northern Bobwhite. Project Number: 542/101, 

0/811/002, 581/DMT. Unpublished study prepared by Wildlife 

International, Ltd. 67 p. Omethoate degradate

47769704 Gallagher, S.; Grimes, J.; Beavers, J. (2003) Omethoate: An Acute Oral 

Toxicity Study with the Ring-Necked Pheasant. Project Number: 542/102, 

0/811/001. Unpublished study prepared by Wildlife International, Ltd. 69 

p. Omethoate degradate

850.2100 Avian acute oral toxicity test

MRID Citation Reference

48964901 Hubbard, P.; Beavers, J. (2012) Dimethoate Technical: An Acute Oral 

Toxicity Study with the Mallard. Project Number: 232/159. Unpublished 

study prepared by Wildlife International, Ltd. 68p.

49096101 Hubbard, P.; Martin, K.; Beavers, J. (2013) Dimethoate: An Acute Oral 

Toxicity Study with the Canary. Project Number: 232/165. Unpublished 

study prepared by Wildlife International, Ltd. 95p.
Page 102 of 144

71-2 Avian Dietary Toxicity

MRID DOC NUM Citation Reference

51679 Edson, E.F.; Lade, B.I.; Barron, J.R. (1958) The Toxicology of N.C.262 

(Rogor): Recovery from Acute Poisoning in the Rat and Hen: Report No. 

22. (Unpublished study received Jul 18, 1963 under PP0385; prepared by 

Fisons Pest Control, Ltd., submitted by American Cyanamid Co., 

Princeton, N.J.; CDL:090415-T) 

159767 Munk, R. (1984) Preliminary Study with Dimethoate on the Bobwhite 

Quail (Colinus virginianus) by Administration in the Diet for a Period of 4 

Weeks: Test Report: Project No. 71W326/82. Unpub- lished study 

prepared by BASF Toxikologie. 52 p. 

47744401 Hubbard, P.; Martin, K.; Beavers, J. (2009) Dimethoate: A Dietary LC50 

Study with the Mallard. Project Number: 232/148, 

232/021809/MLCB/100P. Unpublished study prepared by Wildlife 

International Ltd. 113 p.

47769705 Zok, S. (2001) Dimethoate - Avian Dietary LC50 Test in Chicks of the 

Bobwhite Quail (Colinus virginianus). Project Number: 31W0466/99127, 

445/010, 469/DMT. Unpublished study prepared by BASF 

Aktiengesellschaft, Labor fuer Oekotoxicologie. 59 p.

47769706 Zok, S. (2001) Dimethoate - Avian Dietary LC50 Test in Chicks of the 

Ring-Necked Pheasant (Phasianus colchicus). Project Number: 

36W0466/99130, 445/009. Unpublished study prepared by BASF 

Aktiengesellschaft. 57 p.

48680201 Hubbard, P.M., J.B. Beavers, and K.H. Martin. 2010. Dimethoate 

Technical: A One-Day Acute Dietary Exposure Study With The Northern 

Bobwhite Including An Assessment Of Avoidance Behavior. Unpublished 

study performed by Wildlife International, Ltd., Easton, Maryland. Project 

No. 542-107. Study sponsored and submitted by Cheminova A/S, EU 

Regulatory Office, Harrogate, HG3 1RY, United Kingdom. Study initiated 

July 9, 2010 and completed December 16, 2010.

71-4 Avian Reproduction

MRID Citation Reference

159768 Munk, R. (1986) 1-Generation Reproduction Study with Dimethoate on 

the Mallard Duck (Anas platyrhynchos L.) by Administration in the Diet: 

Test Report: Project No. 72W326/82. Unpublished study prepared by 

BASF Toxikologie. 190 p. 

162777 Munk, R. (1986) 1-Generation Reproduction Study with Dimethoate... on 

the Bobwhite Quail (Colinus virginianus) after Administration in the Diet: 

Project No. 71W326/8256. Unpublished study pre- pared by BASF AG. 

314 p. 
Page 103 of 144

43661501 Cheminova Agro A/S. (1995) Six-Week Dimethoate Avian Pilot 

Reproduction Study With Mallard Ducks: Preliminary Data. Unpublished 

study prepared by Wildlife Int'l. 4 p. 

43967101 Gallagher, S.; Foster, J.; Beavers, J. et al. (1996) Dimethoate: A 

Reproduction Study with the Mallard (Anas platyrhynchos): (Final Report): 

Lab Project Number: 232-116: 232/050995/MR.WC/CHP82. Unpublished 

study prepared by Wildlife International Ltd. 205 p. 

44049001 Gallagher, S.; Foster, J.; Beavers, J.; et al. (1996) Dimethoate: A 

Reproduction Study with the Northern Bobwhite (Colinus virginianus): 

Amended Report: Lab Project Number: 232-115: 

232/050995/QR.WC/CHP: 2/050995/QR.WC/CHP82. Unpublished study 

prepared by Wildlife International Ltd. 208 p. 

48033005 Albers, P.; Hoffman, D. (1984) Evaluation of Potential Embryotoxicity and 

Teratogenicity of 42 Herbicides, Insecticides, and Petroleum 

Contaminants to Mallard Eggs. Archives of Environmental Contamination 

and Toxicology 13: 15-27.

850.2300 Avian reproduction test

MRID Citation Reference

48216201 Temple, D.; Martin, K.; Beavers, J.; et al. (2010) Omethoate and 

Dimethoate: A Comparative Reproduction Study with the Northern 

Bobwhite: Final Report. Project Number: 232/149. Unpublished study 

prepared by Wildlife International, Ltd. 300 p.

48216202 Allemang, D. (2010) Second Waiver Request: Omethoate OneGeneration Avian Reproduction Studies. Unpublished study prepared 

by Cheminova, Inc. 13 p.

71-5 Simulated or Actual Field Testing

MRID Citation Reference

75575 Wang, G.T. (1971) Letter sent to R.J. Little dated Dec 21, 1971: 

Necropsy of linnets and starlings. (Unpublished study received Jun 11, 

1973 under 3F1301; submitted by American Cyanamid Co., Princeton, 

N.J.; CDL:092203-F) 

75585 Boudreau, G.W. (1971) Report of Cygon Systemic 25W Test in Grapes. 

(Unpublished study received Oct 29, 1971 under 0F0928; prepared by 

Almaden Vineyards, submitted by American Cyanamid Co., Princeton, 

N.J.; CDL:093234-B) 

77485 Boudreau, G.W. (1972) Effects on Birds of Cygon 2E Applied in Feedlots To Control Houseflies. (Unpublished study, including let- ter dated 

May 11, 1972 from G.T. Wang to R.J. Little and Jul 18, 1972 from F.R. 

Barron, Jr. to Pat C. Williams, received Jul 27, 1972 under 241-82; 

submitted by American Cyanamid Co., Prince- ton, N.J.; CDL:100007-
Page 104 of 144

A) 

97399 Barron, F.R., Jr. (1971) Letter sent to Pat C. Williams dated Oct 27, 

1971: Cygon 267 systemic insecticide. (Unpublished study received Oct 

29, 1971 under 241-94; submitted by American Cyanamid Co., 

Princeton, N.J.; CDL:001977-A) 

107310 American Cyanamid Co. (1973) Summary of Report Submitted to EPA 

on May 3, 1973, in Connection with PP No. 3F1301. (Unpublished 

study received Apr 21, 1976 under 241-233; CDL:224122-C) 

139969 American Cyanamid Company (1973) Summary of Report Submitted to 

EPA on May 3, 1973, in Connection with PP No. 3F1301. (Unpublished study received May 14, 1976 under 241-175; CDL:224705-B) 

40919001 Barrett, G.; Darnell, R. (1967) Effects of dimethoate on small mammal 

populations. American Midland Naturalist 77(1):164-175. 

93912 Westlake, G.E.; Bunyan, P.J.; Martin, A.D.; et al. (1981) Organophosphate poisoning. Effects of selected organophosphate pesti- cides 

on plasma enzymes and brain esterases of Japanese quail (?~Coturnix 

coturnix japonica~?). Journal of Agricultural and Food Chemistry 

29(4):772-778. (Also~In~unpublished submission received Jan 26, 

1982 under 239-2471; submitted by Chevron Chem- ical Co., 

Richmond, Calif.; CDL:246657-I) 

46486401 Knabe, S. (2004) Residues of Dimethoate and Omethoate in Different 

Feed Sources for Wild Birds After Application of an EC Formulation 

Containing 400 g/L Dimethoate, (Spain 2003): (Final Report). Project 

Number: 20031130/S1/FNTO, SCI/100/033067, 030317SB. 

Unpublished study prepared by GAB Biotechnologie Gmbh, Dr. U. 

Noack-Laboratorium fuer and Huntingdon Life Sciences, Ltd. 238 p.

46486403 Rodgers, M. (2004) EC Formulation of Dimethaote Containing 400 G/L. 

Assessment to Determine the Effect on Palatability via Drinking Water 

in the Bobwhite Quail. Project Number: SCI/085/030117, SCI/085. 

Unpublished study prepared by Huntingdon Life Sciences, Ltd. 42 p.

35180 Fowle, C.D. (1966) Effects of Forest-Spray Pesticides on New 

Brunswick Birds: Effects of Phosphamidon and Experimental 

Insecticides on Birds. (Unpublished study received Jan 28, 1970 under 

241-216; prepared by York Univ., Dept. of Biology, submitted by 

American Cyanamid Co., Princeton, N.J.; CDL:002057-Z)

72-1 Acute Toxicity to Freshwater Fish

MRID Citation Reference

6043 Walker, C.P. (1963) Results of Preliminary Screening of Compounds 

Submitted by American Cyanamid Co. in a 24 Hour Bioassay Conduc-
Page 105 of 144

ted at Selected Concentrations of Commodity under Standard Conditions at 12^oIC. in Reconstituted Water. (Unpublished study received 

Dec 2, 1965 under 595-265; prepared by U.S. Fish and Wildlife 

Service, Fish Control Laboratory, submitted by Haviland Agricultural 

Chemical Co., Grand Rapids, Mich.; CDL:128248-A) 

70341 Walker, C.R. (1963) Letter sent to Elton L. Clark dated Oct 22, 1963: 

Fish toxicity test with~n~-dodecylguanidine acetate (Cy- prex 5,223 

tech.). (U.S. Fish and Wildlife Service, Fish Con- trol Laboratory; 

CDL:109804-F) 

75541 Chambers, H.; Fabacher, D.L. (1974) Acute toxicity of pesticides to 

channel catfish fingerlings. MAFES Research Highlights 37(2):1. 

(Also~In~unpublished submission received on unknown date under 

538-135; submitted by O.M. Scott & Sons Co., Marysville, Ohio; 

CDL:221963-A) 

77504 McCann, J. (1970) ?Cygon 267: Goldfish (~Carassius auratus~)|: Test 

No. 292. (U.S. Agricultural Research Service, Pesticides Regulation 

Div.; unpublished study; CDL:129659-A) 

102572 Cope, O. (19??) Sport fishery investigations. Pages 29-30,38, In Fish 

and Wildlife Service Circular 199. By U.S. Fish and Wild- life Service, 

Div. of Fishery Research. ?S.l.|: USFWS. (In- complete; published 

study; CDL:003596-D) 

115880 Baywood Chemicals, Ltd. (1965) Placement of Disyston for Carrot Fly 

Control; Fish Toxicity Tests--5006. London, Eng.: BCL. (Sub- mitter 

16569; technical bulletin 21/65; also In unpublished sub- mission 

received Sep 23, 1968 under 3125-73; submitted by Mobay Chemical 

Corp., Kansas City, MO; CDL:007009-Q) 

119954 Watkins, J. (1966) Letter sent to K. Jackson dated Oct 26, 1966: Bioassays: ?Methyl-trithion 4E and other pesticides' toxicity to coho fry|: 

File No. 34-5-2-4. (Unpublished study received Dec 1, 1970 under 

1F1129; prepared by Government of Canada, sub- mitted by Stauffer 

Chemical Co., Richmond, CA; CDL:090905-J) 

45202909 Grande, M.; Andersen, S.; Berge, D. (1994) Effects of pesticides on 

fish: experimental and field studies. Norwegian Journal of Agricultural 

Sciences Suppl. 13: 195-209. 

850.1075 Fish acute toxicity test, freshwater and marine

MRID Citation Reference

48821401 Brougher, D.; Kendall, T.; Gallagher, S.; et al. (2012) Dimethoate: A 96-

Hour Static-Renewal Acute Toxicity Test with Bluegill (Lepomis 

macrochirus): Final Report. Project Number: 232A/135. Unpublished study 

prepared by Wildlife International, Ltd. 61p.

48821402 Brougher, D.S., Kendall, T.Z., Gallagher, S.P., Krueger, H.O. 2012. Omethoate: A 

96-Hour Static-Renewal Acute Toxicity Test with the Bluegill (Lepomis 

macrochirus). Study performed by Wildlife International, Ltd., Easton, 

Maryland. Study number 232A-137A. Study sponsored by Cheminova A/S/ 
Page 106 of 144

and submitted to Cheminova, Inc. Study initiated 02 January 2012 and 

completed 18 April 2012.

48821403 Brougher, D.; Kendall, T.; Gallagher, S.; et al. (2012) Dimethoate: A 96-

Hour Static-Renewal Acute Toxicity Test with the Rainbow Trout 

(Oncorhynchus mykiss): Final Report. Project Number: 232A/136A. 

Unpublished study prepared by Wildlife International, Ltd. 61p.

48821404 Brougher, D.S., Kendall, T.Z., Gallagher, S.P., Krueger, H.O. 2012. 

Omethoate: A 96-Hour Static-Renewal Acute Toxicity Test with the 

Rainbow Trout (Oncorhynchus mykiss). Study performed by Wildlife 

International, Ltd., Easton, Maryland. Study number 232A-138. Study 

sponsored by Cheminova A/S and submitted to Cheminova, Inc. Study 

initiated 16 December 2011 and completed 28 February 2012. 

48298301 Armstrong, K.; Caley, C.; Cameron, B.; et al. (1984) Prolonged Toxicity 

Test (LC50) of EC Formulation of Dimethoate Containing 400 g.1^-1 to 

Rainbow Trout (21 Day, Semi-Static). Project Number: 380500, 6914, 

119/DMT. Unpublished study prepared by Inveresk Research International. 

92 p.

48298302 Caley, C.; Cameron, B.; Knight, B.; et al. (1984) EC Formulation of 

Dimethoate Containing 400 g.1^-1: Determination of Acute Toxicity (LC50) 

to Rainbow Trout (96 h, Semi-Static). Project Number: 380474, 6912, 

120/DMT. Unpublished study prepared by Inveresk Research International. 

91 p.

48298303 Caley, C.; Cameron, B.; Knight, B.; et al. (1984) Determination of Acute 

Toxicity (LC50) of EC Formulation of Dimethoate Containing 400 g.1^-1 to 

Bluegill Sunfish (96 h, Semi-Static). Project Number: 380495, 6944, 

121/DMT. Unpublished study prepared by Inveresk Research International. 

92 p.

850. Amphibian acute toxicity test, freshwater 

MRID Citation Reference

48634201 Schneider, S.; Kendall, T.; Gallagher, S.; et al. (2011) Dimethoate 

Technical: A 96-Hour Flow-Through Acute Toxicity Test with Tadpoles of 

the African Clawed Frog (Xenopus laevis): Final Report. Project Number: 

232A/133. Unpublished study prepared by Wildlife International, Ltd. 66p.

72-2 Toxicity To Freshwater Invertebrates

37343 Muncy, R.J.; Oliver, A.D., Jr. (19??) Toxicity of ten insecticides to the red 

crawfish,~Procambarus clarki~(Girard). Pages 428- 431,~In~?Without 

Title|. N.P. (Published study; CDL:091902-C) 

57053 Sanders, H.O. (1969) Toxicity of Pesticides to the Crustacean 

?~Gammarus lacustris~. By U.S. Fish and Wildlife Service, Fish-Pesticide 
Page 107 of 144

Research Laboratory. Washington, D.C.: USFWS. (Incomplete; technical 

paper # 25, published study; CDL: 228727-AG) 

850.1010 Aquatic invertebrate acute toxicity, test, freshwater 

daphnids

MRID Citation Reference

48298306 Hertl, J. (2002) Acute Toxicity of Dimethoate to Daphnia magna in a 48-

Hour Immobilization Test. Project Number: 10591220, 482/DMT. 

Unpublished study prepared by Institut fuer Biologische Analytik und 

Consulting IBACON. 68 p.

48298309 Heintze, A. (2002) Assessment of Side Effects of Dimethoate on Larvae of 

the Midge, Chironomus riparius with the Laboratory Test Method: Final 

Report. Project Number: 20011123/01/ASCR, 446/003, 521/DMT. 

Unpublished study prepared by GAB Biotechnologie Gmbh. 131 p.

48821405 Simon, M. 2012. Daphnia magna, Acute Immobilization Test (OECD 202) 

Static Exposure. Unpublished study performed by Fraunhofer-Institute for 

Molecular Biology and Applied Ecology (IME), 57377 Schmallenberg, 

Germany. CHA Doc. No. 1364 DMT. Study sponsored by the Dimethoate 

Task Force and submitted by Cheminova A/S, Lemvig, Denmark. Study

initiated July 27, 2010 and (amended final report) submitted April 26, 2012. 

72-3 Acute Toxicity to Estuarine/Marine Organisms

MRID Citation Reference

42760001 Graves, W.; Swigert, J. (1993) Dimethoate: A 96-Hour Static Acute Toxicity 

Test with the Sheepshead Minnow (Cyprinodon variegatus): Final Report: 

Lab Project Number: 242A-101. Unpublished study prepared by Wildlife 

International Ltd. 79 p. 

42760002 Graves, W.; Swigert, J. (1993) Dimethoate: A 96-Hour Shell Deposition 

Test with the Eastern Oyster (Crassostrea virginica): Final Report: Lab 

Project Number: 242A-104. Unpublished study prepared by Wildlife 

International Ltd. 70 p. 

42760003 Graves, W.; Swigert, J. (1993) Dimethoate: A 96-Hour Static Acute Toxicity 

Test with the Saltwater Mysid (Mysidopsis bahia): Final Report: Lab 

Project Number: 242A-102. Unpublished study prepared by Wildlife 

International Ltd. 81 p. 
Page 108 of 144

850.1350 Mysid chronic toxicity test

MRID Citation Reference

48804201 Claude, M.; Kendall, T.; Gallagher, S.; et al. (2012) Dimethoate Technical: 

A Flow-Through Life-Cycle Toxicity Test with the Saltwater Myseid 

(Americamysis bahia): Final Report. Project Number: 232A/139, 

232/101311/MYS/LC/SUB232. Unpublished study prepared by Wildlife 

International, Ltd. 121p.

72-4 Fish Early Life Stage/Aquatic Invertebrate Life Cycle Study

MRID Citation Reference

45273 Fabacher, D.L.; Chambers, H. (1973) Acute Toxicity of Three Pes- ticides 

to Channel Catfish Fingerlings: Report No. 40426. (Un- published study 

received Mar 7, 1975 under 5F1559; prepared by Mississippi State Univ., 

Agricultural and Forestry Experiment Station, Dept. of Entomology, 

submitted by Mobay Chemical Corp., Kansas City, Mo.; CDL:094870-A) 

55391 Alabaster, J.S.; Edson, E.F. (1959) The Toxicology of Rogor (N.C.262): 

Toxicity to Rainbow Trout: Report No. 28. (Unpub- lished study received 

Mar 1, 1960 under PP0255; prepared by Fi- sons Pest Control, Ltd., 

England, submitted by Fisons (Canada), Ltd., Agricultural Chemicals Div., 

Toronto, Ontario; CDL: 090281-Y) 

42864701 Wuthrich, V. (1990) Influence of Dimethoate on the Reproduction of 

Daphnia Magna: Final Report: Lab Project Number: 264464. Unpublished 

study prepared by RCC Umweltchemie AG 462 p. 

43106301 Strawn, T.; Muckerman, M. (1994) Early Life-stage Toxicity of Dimethoate 

to the Rainbow Trout (Oncorhynchus mykiss) Under Flow-through 

Conditions: Final Report: Lab Project Number: 40864. Unpublished study 

prepared by ABC Labs, Inc. 436 p. 

43106302 Strawn, T.; Muckerman, M. (1994) Raw Data Report for: Early Life-stage 

Toxicity of Dimethoate to the Rainbow Trout (Oncorhynchus mykiss) Under 

Flow-Through Conditions: Final Report: Lab Project Number: 40864R. 

Unpublished study prepared by ABC Labs, Inc. 1359 p. 

850.1400 Fish early-life stage toxicity test

MRID Citation Reference

48772901 Hurd, K.; Sharpe, A. (2011) Dimethoate Technical: Determination of the 

Effects on the Early-life Stage of the Sheepshead minnow (Cyprinodon 

variegatus). Project Number: BR0555/B. Unpublished study prepared by 

AstraZeneca UK, Ltd. 53p.
Page 109 of 144

49083401 Hicks, S. (2013) Dimethoate: Early Life-Stage Toxicity Test with the 

Rainbow Trout, Oncorhychus mykiss, Under Flow Through Conditions. 

Project Number: 68796. Unpublished study prepared by ABC Laboratories, 

Inc. 175p.

123-1 ( 850.4100 or 850.4150)Terrestrial Plant Toxicity 

47709701 Porch, J.; Krueger, H.; kendall, T. (2009) Dimethoate: A Toxicity Test to 

Determine the Effects of the Test Substance on Vegetative Vigor of Ten 

Species of Plants: Final Report. Project Number: 232/140, 

232/110408/VEGVIG10/SUB232. Unpublished study prepared by Wildlife 

International, Ltd. 295 p.

47709702 Porch, J.; Kendall, T.; Krueger,H. (2009) Dimethoate: A Toxicity Test to 

Determine the Effects of the Test Substance on Seedling Emergence of 

Ten Species of Plants: Final Report . Project Number: 232/139, 

232/100708/SEEDEM/10/SUB232. Unpublished study prepared by Wildlife 

Internationa,l Ltd. 283 p.

850.4225 Seedling emergence, Tier II

MRID Citation Reference

48572801 Porch, J.; Krueger, H.; Martin, K. (2011) Dimethoate TEP and TGAI: A Tier 

II Toxicity Test to Determine the Effects of the Test Substances on 

Seedling Emergence of Ten Species of Plants: Final Report. Project 

Number: 232/151. Unpublished study prepared by Wildlife International, 

Ltd. 246p.

48628101 Porch, J.; Krueger, H.; Martin, K. (2011) Dimethoate TEP and TGAI: A Tier 

II Toxicity Teest to Determine the Effects of the Test Substances on 

Seedling Emergence of Ten Species of Plants: Final Report. Project 

Number: 232/151. Unpublished study prepared by Wildlife International, 

Ltd. 248p.

850.4250 Vegetative vigor, Tier II

MRID Citation Reference

48572802 Porch, J.; Krueger, H.; Martin, K. (2011) Dimethoate TEP and TGAI: A Tier 

II Toxicity Test to Determine the Effects of the Test Substances on 

Vegetative Vigor of Ten Species of Plants: Final Report. Project Number: 

232/152. Unpublished study prepared by Wildlife International, Ltd. 290p.

123-2 Aquatic plant growth
Page 110 of 144

MRID Citation Reference

43679309 Ibrahim, E. (1983) Effects of some common pesticides on growth and 

metabolism of the unicellular algae Skeletonema costatum, Amphiprora 

paludosa, and Phaeodactylum tricornutum. Aquatic Toxicology (3):1-14. 

43679310 Ibrahim, A. (1984) Effect of growth rate of the microscopic algae 

Ankistrodesmus falcatus (Corda) ralfs, Scenedesmus quadricauda (Turp.) 

breb. and Phaeodactylum tricornutum (bohlin). Aqua 5:303-306. 

47784001 Cally, C.; Cameron, B.; Knight, B.; et al. (1992) Alga, Growth Inhibition 

(72h, EC 50) with Technical Dimethoate: IRI Project No. 381038. Project 

Number: 381038, 8077, 123/DMT. Unpublished study prepared by 

Inveresk Research International. 85 p.

850.4400 Aquatic plant toxicity test using Lemna spp. Tiers I and II

MRID Citation Reference

47709703 Porch, J.; Kendall, T.; Krueger, H. (2009) Dimethoate: A 7-Day StaticRenewal Toxicity Test with Duckweed (Lemna gibba G3): Final Report. 

Project Number: 232A/118, 

232/120508/LEM7D/SR/OECD/OPPTS/SUB232. Unpublished study 

prepared by Wildlife International, Ltd. 157 p.

850.5400 Algal toxicity, Tiers 1 and II

MRID Citation Reference

48572803 Porch, J.; Kendall, T.; Krueger, H. (2011) Dimethoate TGAI: A 96-Hour 

Toxicity Test with the Marine Diatom (Skeletonema costatum): Final Report. 

Project Number: 232A/130. Unpublished study prepared by Wildlife 

International, Ltd. 68p.

48572804 Porch, J.; Kendall, T.; Krueger, H. (2011) Dimethoate TGAI: A 96-Hour 

Toxicity Test with the Freshwater Alga (Anabaena flos-aquae): Final Report. 

Project Number: 232A/125B. Unpublished study prepared by Wildlife 

International, Ltd. 67p.

48572805 Porch, J.; Kendall, T.; Krueger, H. (2011) Dimethoate TGAI: A 96-Hour 

Toxicity Test with the Freshwater Alga (Pseudokirchneriella subcapitata): 

Final Report. Project Number: 232A/129. Unpublished study prepared by 

Wildlife International, Ltd. 68p.

48572806 Porch, J.; Kendall, T.; Krueger, H. (2011) Dimethoate TGAI: A 96-Hour 

Toxicity Test with the Freshwater Diatom (Navicula pelliculosa): Final Report. 

Project Number: 232A/128. Unpublished study prepared by Wildlife 

International, Ltd. 68p.
Page 111 of 144

141-1 Honey bee acute contact

MRID Citation Reference

45024201 Thompson, H. (1999) Flusilazole 40EC (400 G/L): Acute Oral and 

Contact Toxicity to the Honey Bee, Apis mellifera L: Final Report: Lab 

Project Number: GQ8400: DUPONT-3296: 3296. Unpublished study 

prepared by Central Science Lab. 46 p. {OPPTS 850.320} 

45024202 Thompson, H. (2000) Flusilazole 40EC (400 G/L): Acute Oral and 

Contact Toxicity to the Honey Bee, Apis mellifera L: Report Amendment 

No. 1: Lab Project Number: DUPONT-3296: GQ8400: 3296. 

Unpublished study prepared by Central Science Lab. 5 p. {OPPTS 

850.3020} 

30454 Kerry, J.C.; Weighton, D.M. (1977) ?Toxicity Studies on Bees|. 

(Unpublished study including French text, received Apr 9, 1980 under 

43142-EX-1; prepared in cooperation with France, Ministry of 

Agriculture, Dept. of Zoology, Research Station for Bees and Social 

Insects, submitted by Boots Hercules Agrochemicals Co., Wilmington, 

Del.; CDL:099369-M) 

45044 Clark, A.M. (1976) Permethrin: Oral and Contact Toxicity to Honeybees of Technical Material and an Encapsulated Emulsion: TMJ 1273 A. 

(Unpublished study received Dec 20, 1976 under 100- EX-53; prepared 

by Plant Protection, Ltd., submitted by Ciba- Geigy Corp., Greensboro, 

N.C.; CDL:095990-B) 

45046 Johansen, C.; Mayer, D.; Madsen, R.; et al. (1975) Bee Research 

Investigations, 1975. (Unpublished study received Dec 20, 1976 under 

100-EX-53; prepared by Washington State Univ., submitted by CibaGeigy Corp., Greensboro, N.C.; CDL:095990-E) 

59971 Cole, J.H. (1974) The Acute Contact and Oral Toxicity to Worker Honey 

Bees of Technical Dowco 290: DWC246/74726. (Unpublished study 

received Nov 12, 1980 under 464-563; prepared by Hunting- don 

Research Centre, England, submitted by Dow Chemical U.S.A., 

Midland, Mich.; CDL:099724-F) 

108108 Fraser, W.; Jenkins, G. (1971) The Acute Contact and Oral Tox- icities of 

CP67573 and MON2139 to Worker Honey Bees: 5369/72/ 765. 

(Unpublished study received Jul 12, 1974 under 5F1536; prepared by 

Huntingdon Research Centre, Eng., submitted by Monsanto Co., 

Washington, DC; CDL:094171-J) 

81595 Cole, J.H. (1974) The Acute Contact and Oral Toxicity to Worker Honey 

Bees of Technical Dowco 290: DWC246/74726. (Unpublished study 

received Jul 30, 1979 under 464-EX-55; prepared by Hunt- ingdon 

Research Centre, England, submitted by Dow Chemical U.S.A., 

Midland, Mich.; CDL:098875-I) 

49178402 Zenker, K. (2011) Acute Toxicity of Dimethoate 400 g/L EC to the 

Honeybee Apis mellifera L. Under Laboratory Conditions: Final Report. 

Project Number: DE/81265162, 1171/DMT, 11/10/48/003/D. 

Unpublished study prepared by Biochem Agrar, Labor fuer Biologische 

und Chemische. 49p.
Page 112 of 144

49178404 Gough, H.; Mcindoe, E.; Lewis, G. (1994) The Use of Dimethoate as a 

Reference Compound in Laboratory Acute Toxicity Tests on Honey 

Bees (Apis mellifera L.) 1981-1992. Journal of Apicultural Research 

33(2): 119-125.

26489 or 

67044

Fraser, W.D.; Jenkins, G. (1972) The Acute Contact and Oral Toxicities 

of CP67573 and Mon2139 to Worker Honey Bees. (Unpublished study 

received on unknown date under 4G1444; prepared by Huntingdon 

Research Centre, submitted by Monsanto Co., Washington, D.C.; 

CDL:093848-R)

42805203 Pietrzik, J. (1991) Assessment of Side Effects of Dimethoate EC 400 g/l 

(SAG 103 20) on the Ground Beetle, Poecilus cupreus L. in the 

Laboratory: Translation of Final Report to Study 120/01-Pc: Lab Project 

Number: 120/01-PC: 946-005: Dimethoate EC 400 G/L (SAG 103 20). 

Unpublished study prepared by GAB Biotechnologie GmbH. 17 p. 

42805204 Petto, R. (1993) Effects of an EC Formulation of Dimethoate Containing 

400 g/l on Aphidius matricariae HAL (Hymenoptera, Aphidiidae) in the 

Laboratory: Lab Project Number: 946-007: 322806. Unpublished study 

prepared by RCC Umweltchemie GmbH & Co. KG. 28 p. 

42805205 Decker, U. (1993) The Effects of Larval and Pupal Exposure to the EC 

Formulation of Dimethoate Containing 400 g/l on the Hover-Fly, Syrphus 

corollae Fabr. (syn.: Eupeodes Corollae) (Diptera: Syrphidae) in the 

Laboratory: Lab Project Number: 325078: 946-008. Unpublished study 

prepared by RCC, Research & Consulting Co., Ltd. and BRL, Biological 

Research Labs, Ltd. 59 p. 

42805206 Pietrzik, J. (1992) Assessment of Side Effects of Dimethoate EC 400 g/l 

(SAG 103 20) on the Predatory Mite, Typhlodromus pyri Scheuten in the 

Laboratory: Translation of Final Report to Study 120/01-Tp: Lab Project 

Number: 120/01-TP: 946-006: Dimethoate EC 400 G/L (SAG 103 20). 

Unpublished study prepared by GAB Biotechnologie GmbH. 23 p. 

42805207 Kuhner, C. (1993) Assessment of Side-Effects of SAG 10320 on the 

Lady-Bird Beetle, Coccinella septempunctata L. in the Laboratory: 

Translation of Final Report to the Study: Lab Project Number: 120/02-

CS: 946-001: SAG 10320. Unpublished study prepared by Institut fur 

Umweltanalytik und Biotechnologie GmbH. 26 p. 

42805208 Kuhner, C. (1993) Assessment of Side-Effects of an EC-Formulation 

Containing 400 g/l of Dimethoate (SAG 10320) on the Green Lacewing, 

Chrysoperla carnea Steph. in the Laboratory: Translation of Final Report 

to the Study: Lab Project Number: 120/01-CC: 946-002: SAG 10320. 

Unpublished study prepared by GAB Biotechnologie GmbH. 22 p. 

47841001 Barber, I.; Ebeling, M.; Edwards, P.; et al. (2005) Review on Initial 

Residue Levels of Pesticides in Arthropods Samples in Field Studies. 

Project Number: RC05/029, 3151957. Unpublished study prepared by 

RIFCon GmbH. 59 p.

142-3 Simulated or Actual Field Testing Pollinators

MRID Citation Reference
Page 113 of 144

82973 Duval, C.T. (1969) Pesticides and the honey bee. Pest Articles and 

News Summaries 15(3):321-324. (Also~In~unpublished sub- mission 

received Apr 26, 1977 under 464-402; submitted by Dow Chemical 

U.S.A., Midland, Mich.; CDL:230691-N) 

88398 Johansen, C.; Eves, J. (1970) Bee Research Investigations, 1970. 

(Unpublished study received Feb 1, 1973 under unknown admin. no.; 

prepared by Washington State Univ., submitted by Shell Chemical Co., 

Washington, D.C.; CDL:222266-D) 

105372 Alexandrescu, S.; Serban, M. (1966) Toxicitatea unor insecticide fata de 

albine, determinata in laborator si camp. ?Toxicity to bees of some 

insecticides, as determined by laboratory and field tests|. An. Inst. 

Cercet. Prol. Plant, Inst. Cent. Cercet. Agr. IV:411-417. (Rumanian text; 

also In unpublished submission received Nov 1, 1970 under unknown 

admin. no.; submitted by Hercules, Inc., Agricultural Chemicals, 

Wilmington, DE; CDL: 005103-AN) 

5000837 Johansen, C.A. (1972) Toxicity of field-weathered insecticide residues to 

four kinds of bees. Environmental Entomology 1(3):393-394. 

5008360 Hoy, M.A.; Flaherty, D.; Peacock, W.; Culver, D. (1979) Vineyard and 

laboratory evaluations of methomyl, dimethoate, and permethrin for a 

grape pest management program in the San Joaquin Valley of 

California. Journal of Economic Entomology 72(2):250-255. 

115038 Lemon, R. (1973) Bee Toxicity Tests--NC 8458: Biosc/73/1/35. (Unpublished study received Apr 12, 1974 under 10065-EX-4; prepared by 

Fisons Ltd., Eng., submitted by Fisons Corp., Agricultural Chemicals 

Div., Bedford, MA; CDL:127694-D) 

125900 Sarrazin, R., ed. (1976) The Ecological Impact of Forest Insect Control 

Operations in Quebec during 1976: ?Submitter| 50217. (Unpublished 

study received Jun 26, 1978 under 3125-EX-150; prepared by Canada, 

Dept. of Tourism, Fish and Game, submitted by Mobay Chemical Corp., 

Kansas City, MO; CDL:234509-K) 

138669 Waller, G.; Barker, R. (1979) Effects of dimethoate on honey bee 

colonies. Journal of Economic Entomology 72(4): 549-551. (Also In 

unpublished submission received Jan 11, 1984 under 4581-292; 

submitted by Agchem Div., Pennwalt Corp., Philadelphia, PA; 

CDL:252448-I) 

47800504 Decourtye, A.; Devillers, J.; Genecque, E.; et al. (2005) Comparative 

Sublethal Toxicity of Nine Pesticides on Olfactory Learning 

Performances of the Honeybee Apis mellifera. Archives of 

Environmental Contamination and Toxicology 48:242-250. 

47800506 Porrini, C.; Sabatini, A.; Girotti, S.; et al. (2003) The Death of Honey 

Bees and Environmental Pollution by Pesticides: The Honey Bees as 

Biological Indicators. Bulletin of Insectology 56(1):147-152. 

47800519 Incerti, F.; Bortolotti, L.; Porrini, C.; et al. (2003) An Extended Laboratory 

Test to Evaluate the Effects of Pesticides on Bumblebees: Preliminary 

Results. Bulletin of Insectology 56(1):159-164. 

48101301 Habig, C. (2010) Summary of a Dimethoate Field Pollinator Study 

Entitled: Toxicity Testing of an EC Formulation Containing 400g/L 

Dimethoate (BAS 152 11 I) on Honeybees (Apis mellifera L.) in the Field. 
Page 114 of 144

Unpublished study prepared by Exponent, Inc., and Institut fuer 

Biologische Analytik und Consulting IBACON GmbH. 21 p.

48101302 Schmitzer, S. (2005) Toxicity Testing of an EC Formulation Containing 

400 g/L Dimethoate (BAS 152 11 I) on Honey Bees (Apis mellifera L.) in 

the Field. Project Number: 21551039, 448/014, 695/DMT. Unpublished 

study prepared by Institut fuer Biologische Analytik und Consulting 

IBACON GmbH. 76 p.

Non Target Beneficial Insect Studies

42805201 Pietrzik, J. (1991) Assessment of Side Effects of Dimethoate EC 400 g/l 

(SAG 103 20) on the Rove Beetle, Aleochara bilineata Gyll, In the 

Laboratory: Translation of Final Report to Study 120/01-Ab: Lab Project 

Number: 120/01-AB: 946-003: Dimethoate EC 400 G/L (SAG 103 20). 

Unpublished study prepared by GAB Biotechnologie GmbH. 19 p. 

42805202 Kuhner, C. (1991) Effect of Dimethoate EC 400 g/l (SAG 103 20) on 

Trichogramma cacoeciae Marchal (Hym., Trichogrammatidae) as a 

Representative of Microhymenoptera in the Laboratory: Translation of 

Final Report to the Study: Lab Project Number: 120/01-TC: Dimethoate 

EC 400 G/L (SAG 10320): 946-004. Unpublished study prepared by 

GAB Biotechnologie GmbH. 24 p. 

49187601 Halsall, N. (2001) A Field Study to Evaluate the Effects of Drift Rates of 

the Insecticide Dimethoate on Parasitic Wasps. Project Number: 

BASF/00/8, 532/DMT, 449/012. Unpublished study prepared by MamboTox, Ltd. 53p.

49187602 Muther, J. (2001) A Field Study to Evaluate the Effects of BAS 152 11 I 

on Predatory Mites and Other Beneficial Arthropods in an Apple Orchard 

in Germany: Final Report. Project Number: 99023/G3/NFTP, 

G00N046E, 535/DMT. Unpublished study prepared by 

Arbeitsgemeinschaft GAB Biotechnologie. 81p.

49187603 Muther, J. (2001) A Field Study to Evaluate the Effects of BAS 152 11 I 

on Predatory Mites and Other Beneficial Arthropods in an Apple Orchard 

in Germany: Final Report. Project Number: 99023/G1/NFTP, 

G00N037E, 536/DMT. Unpublished study prepared by 

Arbeitsgemeinschaft GAB Biotechnologie. 81p.

49187604 Muther, J. (2001) A Field Study to Evaluate the Effects of BAS 152 11 I 

on Predatory Mites and Other Beneficial Arthropods in an Apple Orchard 

in Germany: Final Report. Project Number: 99023/G2/NFTP, 449/015, 

537/DMT. Unpublished study prepared by Arbeitsgemeinschaft GAB 

Biotechnologie. 82p.

49187605 Knabe, S. (2009) A Field Trial Assessing the Impact of Two Applications 

of Dimethoate 400 g/L EC on the Non-Target Arthropod Fauna of Alfalfa 

(Medicago sativa) Crop (Germany). Project Number: S08/01268, 

816/DMT. Unpublished study prepared by Eurofins - GAB GmbH. 460p.

890.1100 Amphibian Metamorphosis (Frog)
Page 115 of 144

MRID Citation Reference

48670601 Schneider, S.; Kendall, T.; Krueger, H. (2012) Dimethoate: Amphibian 

Metamorphosis Assay: Final Report. Project Number: 232A/132A. 

Unpublished study prepared by Wildlife International, Ltd. 139p.

48670602 Schneider, S.; Kendall, T.; Krueger, H. (2012) Dimethoate Technical: 

Amphibian Metamorphosis Range Finding Assay: Final Report. Project 

Number: 232A/134. Unpublished study prepared by Wildlife International, 

Ltd. 76p.

890.1350 Fish Short-Term Reproduction

MRID Citation Reference

48670603 Schneider, S.; Martin, K.; Kendall, T.; et al. (2012) Dimethoate: Fish 

Short-Term Reproduction Assay with the Fathead Minnow (Pimephales 

promelas): Final Report. Project Number: 232A/131. Unpublished study 

prepared by Wildlife International, Ltd. 163p.

Non-Guideline Study

MRID Citation Reference

51681 Sutherland, G.L. (1960?) Cholinesterase Inhibitory Activity of Dimethoate 

and Its Metabolites. (Unpublished study received Jul 18, 1963 under 

PP0385; submitted by American Cyanamid Co., Princeton, N.J.; 

CDL:090415-V) 

52093 Graham-Bryce, I.J.; Etheridge, P. (1967) Effect of soil moisture conditions 

on uptake of systemic insecticides from soil by plants. Proceedings, 4th 

British Insecticide Fungicide Confer- ence 1:336-343. 

(Also~In~unpublished submission received Dec 4, 1974 under 5F1531; 

submitted by American Cyanamid Co., Princeton, N.J.; CDL:094151-O)

52104 Zaki, M.; Reynolds, H.T. (1961) Effects of various soil types and methods 

upon uptake of three systemic insecticides by cotton plants in the 

greenhouse. Journal of Economic Entomology 54(3): 568-572. 

(Also~In~unpublished submission received Dec 4, 1974 under 5F1531; 

submitted by American Cyanamid Co., Princeton, N.J.; CDL:094151-AD)

56466 Kenaga, E.E. (1973) Factors to be considered in the evaluation of the 

toxicity of pesticides to birds in their environment. Pages 166-

181,~In~Environmental Quality and Safety: Global Aspects of Chemistry, 

Toxicology and Technology As Applied to the Environ- ment: Vol. II. Edited 

by F. Coulston and F. Korte. Stuttgart, W. Germany: Georg Thieme 
Page 116 of 144

Publishers; New York, N.Y.: Academic Press, Inc. (Also~In~unpublished 

submission received Jun 21, 1976 under 464-512; submitted by Dow 

Chemical U.S.A., Midland, Mich.; CDL:224700-G) 

57054 Coppage, D.L. (1972) Organophosphate pesticides: Specific level of brain 

ACHE inhibition related to death in sheepshead minnows. Transactions of 

the American Fisheries Society 101(3):534-536. (Also In unpublished 

submission received Mar 21, 1977 under 352- 338; submitted by E.I. du 

Pont de Nemours & Co., Wilmington, Del.; CDL:228727-AJ) 

126904 Menzie, C. (19??) Acute Toxicity of Some Organophosphorus Pesti- cides 

against Fish & Aquatics: ?Sumithion|. (Unpublished study received Mar 15, 

1973 under 10308-2; prepared by U.S. Dept. of Interior, submitted by 

Sumitomo Chemical Co., Ltd., Baltimore, MD; CDL:004892-F) 

47164602 Holmes, C.; Vamshi, R. (2007) Data and Methodology Used for Spatial 

Analysis of California Red Legged Frog Observations and Proximate Land 

Cover Characteristics. Project Number: 3152007, WEI/252/03. 

Unpublished study prepared by Waterborne Environmental, Inc. (WEI). 19 

p.

48033001 Andersen, H.; Vinggaard, A.; Rasmussen, T.; et al. (2002) Effects of 

Currently Used Pesticides in Assays for Estrogenicity, Androgenicity, and 

Aromatase Activity in vitro. Toxicology and Applied Pharmacology 179: 1-

12.

77534 Sutherland, G.L. (1959) Mammalian Toxicity of the Oxy-carboxy Metabolite 

of Dimethoate. (Unpublished study received Mar 21, 1960 under unknown 

admin. no.; submitted by American Cyanamid Co., Princeton, N.J.; 

CDL:109340-AF)

48065601 Allemang, D. (2010) Evaluation of the Cholinesterase Inhibiting Potential of 

the Plant Metabolites of Dimethoate, O-Desmethyl Omethoate Carboxylic 

Acid (Metabolite XX) and Des-O-Methyl Isodimethoate (Metabolite XII) in 

Comparison with the Parent Compound. Unpublished study prepared by 

Cheminova A/S. 32 p.

48065602 Barnett, J. (2009) Oral (Gavage) Acute Dose Range-Finding 

Cholinesterase Depression Study of Dimethoate, O-DesmethylOmethoate-Carboxylic Acid, di-Na-Salt and Des-O-Methyl Isodimethoate, 

Na-Salt in Rats: Final Report. Project Number: TQC00034. Unpublished 

study prepared by Charles River Laboratories. 183 p.

48065603 Barnett, J. (2009) Oral (Gavage) Acute Dose Range-Finding Study of ODesmethyl-Omethoate-Carboxylic Acid, di-Na-Salt and Des-O-Methyl 

Isodimethoate, Na-Salt in Rats: Final Report. Project Number: TQC00047. 

Unpublished study prepared by Charles River Laboratories. 183 p.

48160705 Chen, H.; Xiao, J.; Hu, G.; et al. (2002) Estrogenicity of Organophosphorus 

and Pyrethroid Pesticides. Journal of Toxicology and Environmental Health 

65:1419-1435.

48298310 Stabler, D. (2002) Dimethoate: Assessment of Effects on Reproduction 

and Growth on Eisenia foetida in Artificial Soil: Final Report. Project 

Number: 20011123/01/NREF, 449/018, 522/DMT. Unpublished study 

prepared by GAB Biotechnologie Gmbh. 53 p.

48298314 Stabler, D. (2001) Acute Toxicity of Dimethoate on Earthworms, Eisenia 

foetida Using an Artificial Soil Test. Project Number: 20011123/01/NLEF, 
Page 117 of 144

721/DMT. Unpublished study prepared by GAB Biotechnologie Gmbh. 61 

p.
Page 118 of 144

Appendix C. Dimethoate and its transformation products

Code Name/ 

Synonym

Nomenclature, formula, molecular 

weight, SMILES Code Structure

Dimethoate IUPAC: O,O-dimethyl S-methylcarbamoylmethyl 

phosphorodithioate

CAS: O,O-dimethyl S-[2-(methylamino)-2-

oxoethyl] phosphorodithioate

CAS No.: 60-51-5

Formula: C5H12NO3PS2

MW: 229.3 g/mol

SMILES: O=C(NC)CSP(OC)(OC)=S

O

H C N 3

H

O C H 3

P

O C H 3 S

C S

H 2

Omethoate CAS: O,O-Dimethyl S-[2-(methylamino)-2-

oxoethyl] phosphorothioate

CAS No.: 1113-02-6

Formula: C5H12NO4PS2

MW: 213.2 g/mol

SMILES: CNC(=O)CSP(=O)(OC)OC

N

H

H C3

O

C

H 2

S

P

O O C H 3

O C H 3

Desmethyl 

dimethoate

CAS: Phosphorodithioc acid, O-methyl S-[2-

(methylamino)-2-oxoethyl ester

Formula: C4H10NO3PS2

MW: 215.2 g/mol

SMILES: CNC(=O)CSP(=S)(O)OC

N

H

H C3

O

C

H 2

S

P

S O C H 3

O H

Des-O-methyl 

isodimethoate

CAS: S-(methyl)-S-[(N-carbamoyt)methyl]-

phosphorodithioic acid

Formula: C4H10NO3PS2

MW: 215.2 g/mol

SMILES: CNC(=O)CSP(=O)(O)SC

N

H

H C3

O

C

H 2

S

P

O S C H 3

O

O-desmethyl 

dimethoate 

carboxylic acid

IUPAC: 2-

[Hydroxy(methoxy)phosphinothioyl]sulfanylacetic 

acid

Formula: C3H7O4PS2

MW: 202.2 g/mol

SMILES: COP(=S)(O)SCC(=O)O

H O

O

C

H 2

S

P

S O C H 3

O H

O-desmethyl 

omethoate 

carboxylic acid

IUPAC: 2-

[hydroxy(methoxy)phosphoryl]sulfanylacetic acid

Formula: C3H7O5PS

MW: 186.12 g/mol

SMILES: COP(=O)(O)SCC(=O)O H O

O

C

H 2

S

P

O O C H 3

O H
Page 119 of 144

Methyl phosphate IUPAC: Methyl dihydrogen phosphate

Formula: CH5O4P

MW: 112.0 g/mol

SMILES: COP(=O)(O)O H O

P

O O C H 3

O H

O-desmethyl 

omethoate

CAS: Phosphoric acid, O-methyl S-[2-

(methylamino)-2-oxoethyl] ester

Formula: C4H10NO4PS

MW: 199.16 g/mol

SMILES: CNC(=O)CSP(=O)(O)OC

P

O H

O C H 3 O

C S

H 2

O

H C N 3

H

S-methyl 

phosphorothioate

IUPAC: Methoxy(methylsulfanyl)phosphinic acid

Formula: C2H7O3PS

MW: 142.1 g/mol

SMILES: COP(=O)(O)SC

P

O H

S C H 3 O

H C O 3

Oxithiaphosphiran Formula: C4H12NO3PS2

MW: 217.25 g/mol

SMILES: CNC(=O)CSP(O)(OC)S P

S O

O C H 3 C S

H 2

N

H

H C3

O
Page 120 of 144

Appendix D. Sample SWCC Output File

Example for the MN alfalfa modeling scenario

Summary of Water Modeling of Dimethoate and the USEPA Standard 

Pond

Estimated Environmental Concentrations for Dimethoate are presented in Table 1 for the 

USEPA standard pond with the MNalfalfaOP field scenario. A graphical presentation of the yearto-year peaks is presented in Figure 1. These values were generated with the Surface Water 

Concentration Calculator (SWCC Version 1.106). Critical input values for the model are 

summarized in Tables 2 and 3.

This model estimates that about 1.4% of Dimethoate applied to the field eventually reaches the 

water body. The main mechanism of transport from the field to the water body is by spray drift 

(89.1% of the total transport) followed by runoff (10.9%).

In the water body, pesticide dissipates with an effective water column half-life of 33.7 days. 

(This value does not include dissipation by transport to the benthic region; it includes only 

processes that result in removal of pesticide from the complete system.) The main source of 

dissipation in the water column is metabolism (effective average half-life = 66.9 days) followed 

by hydrolysis (68 days), photolysis (67604 days), and volatilization (1.76249E+07 days).

In the benthic region, pesticide dissipates (53.8 days). The main source of dissipation in the 

benthic region is metabolism (effective average half-life = 77.5 days) followed by hydrolysis 

(176 days). Most of the pesticide in the benthic region (61%) is sorbed to sediment rather than 

in the pore water.

Table 1. Estimated Environmental Concentrations (ppb) for Dimethoate.

Peak (1-in-10 yr) 8.57

4-day Avg (1-in-10 yr) 8.10

21-day Avg (1-in-10 yr) 6.41

60-day Avg (1-in-10 yr) 4.99

365-day Avg (1-in-10 yr) 1.32

Entire Simulation Mean 1.12

Table 2. Summary of Model Inputs for Dimethoate.

Scenario MNalfalfaOP

Cropped Area Fraction 1

Koc (ml/g) 14.7

Water Half-Life (days) @ 25 °C 24.0

Benthic Half-Life (days) @ 25 °C 27.8
Page 121 of 144

Photolysis Half-Life (days) @ 34 

°Lat

353

Hydrolysis Half-Life (days) 68

Soil Half-Life (days) @ 25 °C 2.71

Foliar Half-Life (days) 2.82

Molecular Wt 229.25

Vapor Pressure (torr) 1.85e-6

Solubility (mg/l) 39800

Table 3. Application Schedule for Dimethoate.

Date (Mon/Day) Type Amount (kg/ha) Eff. Drift

05/20 Foliar 0.560 0.95 0.125

06/19 Foliar 0.560 0.95 0.125

07/19 Foliar 0.560 0.95 0.125

Figure 1. Yearly Peak Concentrations
Page 122 of 144

Sample output screenshot from SWCC Pond

5.1
Page 123 of 144

Appendix E. T-REX example output

Summary of Risk Quotient Calculations Based on Upper-Bound Kenaga Estimated 

Environmental Concentrations (EECs) for Applications of Dimethoate to Douglas fir 

(seed orchards) (only in OR and WA).

Table 1.1. Upper Bound Kenaga, Acute Avian Dose-Based Risk Quotients

Size 

Class

(grams

)

Adjuste

d

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ

EE

C RQ EEC RQ

EE

C RQ

20 4.69

1230.0

1

262.1

2

563.7

6

120.1

4

691.8

8 147.44

76.8

8 16.38

481.7

5

102.6

6

17.0

8

3.6

4

100 5.97 701.40

117.4

1

321.4

8 53.81

394.5

4 66.04

43.8

4 7.34

274.7

2 45.99 9.74

1.6

3

1000 8.44 314.03 37.21

143.9

3 17.06

176.6

4 20.93

19.6

3 2.33

122.9

9 14.58 4.36

0.5

2

Table 1.2. Upper Bound Kenaga, Subacute Avian Dietary Based Risk Quotients

LC50

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

150 1080.00 7.20

495.0

0 3.30

607.5

0 4.05 67.50 0.45 423.00 2.82

Size class not used for dietary risk quotients 

Table 1.3. Upper Bound Kenaga, Chronic Avian Dietary Based Risk Quotients

NOA

EC 

(ppm

)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/S

eeds Arthropods

EEC RQ

EE

C RQ

EE

C RQ EEC RQ EEC RQ

4

1080.0

0

270.0

0

495.

00

123.

75

607.

50

151.

88 67.50 16.88

423.

00

105.7

5

Size class not used for dietary risk quotients
Page 124 of 144

Table 1.4. Upper Bound Kenaga, Acute Mammalian Dose-Based Risk Quotients 

Size 

Class

(gra

ms)

Adjus

ted

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/

Seeds Arthropods Granivore

EEC RQ

EE

C RQ

EE

C RQ EEC RQ EEC RQ

EE

C RQ

15 786.82

1029.

70 1.31

471.

94 0.60

579.

20 0.74 64.36 0.08

403.2

981

0.512

565

14.3

01

0.01

82

35 636.62

711.6

6 1.12

326.

18 0.51

400.

31 0.63 44.48 0.07

278.7

329

0.437

83

9.88

41

0.01

55

1000 275.36

165.0

0 0.60

75.6

3 0.27

92.8

1 0.34 10.31 0.04

64.62

521

0.234

694

2.29

17

0.00

83
Page 125 of 144

Table 1.5. Upper Bound Kenaga, Acute Mammalian Dietary Based Risk Quotients

LC50 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

N/A

1080.0

0 N/A

495.0

0 N/A

607.5

0 N/A 67.50 N/A 423.0 N/A

Size class not used for dietary risk quotients

N/A = Not available

Table 1.6. Upper Bound Kenaga, Chronic Mammalian Dietary Based Risk Quotients

NOAE

C 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/Seeds/Larg

e Insects Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

2

1080.0

0

540.0

0

495.0

0

247.5

0

607.5

0

303.7

5 67.50 33.75

423.0

0

211.5

0

Size class not used for dietary risk quotients 

Table 1.7. Upper Bound Kenaga, Chronic Mammalian Dose-Based Risk Quotients

Size Class

(grams)

Adjusted 

NOAEL

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 0.22 1029.70 4685.06 471.94 2147.32 579.20 2635.35 64.36 292.82 403.30 1834.98

35 0.18 711.66 4001.95 326.18 1834.23 400.31 2251.10 44.48 250.12 278.73 1567.43

1000 0.08 165.00 2145.20 75.63 983.22 92.81 1206.68 10.31 134.08 64.63 840.20
Page 126 of 144

Appendix F. Example STIR Output

Input

Application and Chemical Information

Enter Chemical Name Dimethoate

Enter Chemical Use AirBlast - Doug Fir

Is the Application a Spray? (enter y or n) y

If Spray What Type (enter ground or air) ground

Enter Chemical Molecular Weight (g/mole) 229.25

Enter Chemical Vapor Pressure (mmHg) 1.85E-06

Enter Application Rate (lb a.i./acre) 4.5

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 5.4

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.051

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 358

Enter Lowest Rat Inhalation LC50 (mg/L) 2

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m3) 2.28E-02

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.87E-03

Adjusted Inhalation LD50 2.03E-01

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.41E-02 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 4.76E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 2.34E+00 Proceed to Refinements

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m3) 2.28E-02

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 3.61E-03

Adjusted Inhalation LD50 1.19E+02

Ratio of Vapor Dose to Adjusted Inhalation LD50 3.03E-05 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 5.98E-01

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 5.02E-03 Exposure not Likely Significant

**NOTE**: When entering values, pres 

in order to update linked cells.
Page 127 of 144

Appendix G. Example SIP Output

Table 1. Inputs

Parameter Value

Chemical name Dimethoate

Solubility (in water at 25oC; mg/L) 39800

Mammalian LD50 (mg/kg-bw) 358

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg-bw) 0.005

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Avian LD50 (mg/kg-bw) 5.4

Avian test species other

Body weight (g) of "other" avian species 51

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet)

Bobwhite quail NOAEC (mg/kg-diet) 4

NOAEC (mg/kg-diet) for other bird species

Body weight (g) of other avian species

NOAEC (mg/kg-diet) for 2nd other bird species

Body weight (g) of 2nd other avian species

Enter body weight of 'other' avian species for LD50.

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 6845.6000 6845.6000

Adjusted toxicity value (mg/kg-bw) 275.3595 0.0038

Ratio of exposure to toxicity 24.8606 1780018.4489

Conclusion*

Exposure through drinking 

water alone is a potential 

concern for mammals

Exposure through drinking 

water alone is a potential 

concern for mammals

Table 3. Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 32238.0000 32238.0000

Adjusted toxicity value (mg/kg-bw) 4.6926 0.4252

Ratio of exposure to acute toxicity 6869.9782 75819.6361

Conclusion*

Exposure through drinking 

water alone is a potential 

concern for birds

Exposure through drinking 

water alone is a potential 

concern for birds

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, 

when aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through drinking water 

may contribute to a total exposure that has potential for effects to non-target animals.
Page 128 of 144

Appendix H. Terrplant example output

TerrPlant v. 1.2.2

Green values signify user inputs (Tables 1, 2 and 4). 

Input and output guidance is in popups indicated by red arrows.

Chemical Name

PC code

Use

Application Method

Application Form 

Solubility in Water (ppm)

Input Parameter Symbol Value Units

Application Rate A 4.5 lb. a.i/A

Incorporation I 1 none

Runoff Fraction R 0.05 none

Drift Fraction D 0.05 none

Equation EEC

(A/I)*R 0.225

(A/I)*R*10 2.25

A*D 0.225

((A/I)*R)+(A*D) 0.45

((A/I)*R*10)+(A*D) 2.475

Plant type EC25 NOAEC EC25 NOAEC 

Monocot 1.48 0.745 1.46 0.48

Dicot 0.84 0.23 1.51 0.5

Plant Type Listed Status Dry Semi-Aquatic Spray Drift

Monocot non-listed 0.30 1.67 0.15

Monocot listed 0.60 3.32 0.47

Dicot non-listed 0.54 2.95 0.27

Dicot listed 1.96 10.76 0.98

Total for semi-aquatic areas

Table 1. Chemical Identity.

Dimethoate 

Douglas fir (seed orchards) (only in OR and WA)

Table 2. Input parameters used to derive EECs.

Aerial

Airblast

39800

128975

Table 3. EECs for Dimethoate . Units in lb. a.i/A.

Runoff to dry areas

Runoff to semi-aquatic areas

Spray drift

Total for dry areas

Description

*If RQ > 1.0, the LOC is exceeded, resulting in potential for risk to that plant group.

Seedling Emergence Vegetative Vigor

Table 5. RQ values for plants in dry and semi-aquatic areas exposed to Dimethoate through runoff 

and/or spray drift.*

Table 4. Plant survival and growth data used for RQ derivation. Units are in lb. a.i/A.
Page 129 of 144

Appendix I. Classifications of Environmental Fate Studies

Table A7.1. Classification of Environmental Fate Studies Conducted on Dimethoate

Guideline 

No.

Data 

Requirement Study ID Study Classification

Classification Justifications or Comments (for Supplemental 

and Unacceptable Studies)

835.2120 Hydrolysis 00159761 Acceptable ---

835.2240 Photolysis in 

Water 

00159762 Acceptable ---

835.2410 Photodegradation 

on Soil

43276401 Acceptable ---

835.2370 Photodegradation 

in Air

No data 

submitted

N/A N/A

835.4100 Aerobic Soil 

Metabolism

42843201;

46719202

Acceptable;

Supplemental

---

Concurrent recoveries were outside the recommended ranges of 70-120% 

of the applied for the Riverside and Middlefield soils in some instances. 

The soils used in this study were of foreign origin and comparison with 

domestic soils should be provided (i.e., USDA soil orders and WRB 

classifications are needed). The soil textures according to USDA 

classification could not be confirmed. The soils were maintained at 40% 

of MWHC, but the moisture content could not be related in pF units.

835.4200 Anaerobic Soil 

Metabolism

42884402 Acceptable ---

835.4300 Aerobic Aquatic 

Metabolism

48945601 Supplemental Material balances were incomplete in the latter test intervals (starting from 

day 14 for the Calwich, U.K. test system). Levels of unextracted residues 

were very high in the latter test intervals (starting from day 14 for the 

Calwich test system). Given the high level of uncertainty related to the 

unextracted residues and recoveries of the Calwich system, its results were

not used quantitatively in risk assessment until these and other 

deficiencies are explained.

835.4400 Anaerobic 

Aquatic 

Metabolism

48945501 Supplemental The material balances were incomplete in the latter test intervals, 

particularly in the pond water:clay loam sediment system. The water and 

sediment pH increased throughout the study duration, which may have 

promoted hydrolysis. A polar product detected at ≥10% of the applied 

was not adequately identified. The position of the radiolabel may have 

limited potential for identification of products of dimethoate.

835.1230 LeachingAdsorption/ 

Desorption

00164959; 

47477301, 

49300701

Acceptable; 

Supplemental

---

Material balances were incomplete.

835.1410 Laboratory 

Volatility

43276402 Acceptable ---

835.6100 Terrestrial Field 

Dissipation

42884403;

43388001;

43388002

Acceptable;

Acceptable;

Acceptable

---

835.6100 Long-term Soil 

Dissipation

No data 

submitted

N/A N/A

835.6200 Aquatic 

Dissipation

No data 

submitted

N/A N/A

835.6300 Forestry No data 

submitted

N/A N/A

835.6400 Combination and 

Tank Mixes

No data 

submitted

N/A N/A

860.1400 Accumulation in 

Irrigated Crops

No data 

submitted

N/A N/A

850.1730 Accumulation in 

Fish

No data 

submitted

Waived Waived on 3/1/93 (DP Barcode D176363).
Page 130 of 144

Guideline 

No.

Data 

Requirement Study ID Study Classification

Classification Justifications or Comments (for Supplemental 

and Unacceptable Studies)

850.1950 Aquatic Nontarget OrganismNo data 

submitted

N/A N/A

835.7100 Ground Water 

Monitoring

No data 

submitted

N/A N/A

835.8100 Field Volatility No data 

submitted

N/A N/A

NonguidelinePercolation 

Behavior of 

dimethoate in

lysimeter trial

48298315 Supplemental It could not be determined if the test substance was applied to the soil at 

the highest recommended label rate. Data supporting the stability of 

dimethoate in soil and water was not reported. The material balance and 

the amounts of [

14C]-C02 and of volatile compounds emitted to the 

atmosphere from the soil were not measured directly; they were estimated 

by subtracting the radioactivity found from that which was applied to the 

lysimeters and therefore could not be verified. The unextracted residues 

were unacceptably high and there were no attempts to further extract the 

additional radioactivity.

NonguidelineEffects of 

chlorination on 

the degradation of 

dimethoate

48041103 Supplemental Control samples, containing no chlorine were not tested at the same time 

than the treated samples. These samples would have allowed confirming 

the presence of undegraded dimethoate in treated samples with no 

chlorination, or the possible hydrolysis of the chemical under the testing 

conditions. No mass balance could be established.

850.6100 ECM/ILV in Soil 42884403 Acceptable ILV report was generated by BEAD’s contractor.

ECM/ILV in 

Water

46276301 Unacceptable Portions of this study submission may be used in the future to support a 

complete submission to satisfy the ECM/ILV data requirement for 

dimethoate.

N/A = Not applicable; ECM=Environmental Chemistry Method; ILV=Independent Laboratory Validation

Table A7.2. Classification of Environmental Fate Studies Conducted on Omethoate

Guideline 

No.

Data 

Requirement Study ID Study Classification

Classification Justifications or Comments (for Supplemental 

and Unacceptable Studies)

835.4300 Aerobic Aquatic 

Metabolism

47477303, 

49300701

Supplemental No GLP standards were cited and/or Quality Assurance statements were 

provided. The first sampling interval occurred too late to confirm the 

application rate. The water:sediment ratio was atypical of aerobic aquatic 

studies. All transformation products detected at ≥10% of the applied may 

not have been identified. No attempt was made to characterize the 

significant levels (>50%) of unextracted sediment residues.

835.1230 LeachingAdsorption/ 

Desorption

47477304,

49300701

Supplemental The study was conducted using a single test concentration. Material 

balances were not reported. It was not reported whether the study was 

conducted in the dark. A total of three test soils were used. A desorption 

phase was not conducted.
Page 131 of 144

Appendix J. Reviewed studies submitted in support of PRA

Table 6.1. Species evaluated for assessing potential ecological effects of Dimethoate.

Guideline Test Substance Tested Species Toxicity Endpoint

Study MRID 

and 

Acceptability

850.1010 Dimethoate Daphnid 

(Daphnia Magna) EC50 = 1.6 mg/L 48298306Acceptable

850.1010 Dimethylthiophosphoric 

acid, Na-salt

Daphnid 

(Daphnia Magna) EC50 = 66.7 mg/L 48298307Acceptable

850.1010 O-desmethyl Dimethoate, 

Na-salt

Daphnid 

(Daphnia Magna) EC50 >82.9.7 mg/L 48298304Acceptable

850.1010 Omethoate Daphnid

(Daphnia Magna) EC50 = 32.5 ug/L 48821405Acceptable

850.1075 Omethoate Bluegill 

(Lepomis macrochirus) LC50 = 7.7 mg/L 48821402Acceptable

850.1075 Dimethoate Bluegill 

(Lepomis macrochirus) LC50 = 31.5 mg/L 48821401Acceptable

850.1075 Dimethoate Formulation Bluegill 

(Lepomis macrochirus) LC50 = 44.5 mg/L 48298303Acceptable

850.1075 Omethoate Rainbow Trout

(Oncorhynchus mykiss) LC50 = 5 mg/L 48821404Acceptable

850.1075 Dimethoate Rainbow Trout

(Oncorhynchus mykiss) LC50 = 23 mg/L 48821403Acceptable

850.1075 Dimethoate Formulation Rainbow Trout

(Oncorhynchus mykiss) LC50 =59.8 mg/L 48298302Acceptable

850.1075 O Desmethyl Dimethoate 

Potassium Salt

Rainbow Trout

(Oncorhynchus mykiss) LC50 >80.8 mg/L 48298305Acceptable

850.1075 Dimethylthiophosphoric 

acid, Na-salt

Rainbow Trout

(Oncorhynchus mykiss) LC50 >961 mg/L 48298308Supplemental

850.1075 Dimethyl phosphoric acid, 

Na-salt

Rainbow Trout

(Oncorhynchus mykiss) LC50 >1000 mg/L 48298311Acceptable

850.1400 Dimethoate Rainbow Trout

(Oncorhynchus mykiss)

NOAEC = 1.25 

mg/L

49083401

Acceptable

850.1400 Dimethoate Sheepshead minnow

(Cyprinodon variegatus) NOAEC = 1.2 mg/L 48772901Supplemental

850.4550 Dimethoate Cyanobacteria

(Anabaena flos-aquae) EC50 = 20 mg/L 48572804Acceptable

850.4550 Dimethoate Marine Diatom

(Navicula pelliculosa) EC50 >98 mg/L 48572806Acceptable

850.4550 Dimethoate

Green Algae

(Pseudokirchneriella 

subcapitata)

EC50 = 23 mg/L 48572803

Acceptable

850.4550 Dimethoate Marine Diatom

(Skeletonema costatum) EC50 >96 mg/L 48572803Acceptable

850.2100 Dimethoate Mallard

(Anas platyrhynchos)

LD50 = 44.1 mg/kg 

bw

48964901

Invalid

850.2200 Omethoate Northern Bobwhite

(Colinus Virginianus)

LC50 = 81.7 mg/kg 

bw

47709501

Acceptable

850.2200 Omethoate Mallard

(Anas platyrhynchos)

LC50 >1500 mg/kg 

bw

47709502

Supplemental

850.2300 Dimethoate Northern Bobwhite

(Colinus Virginianus) -- 48216201Supplemental
Page 132 of 144

850.2300 Omethoate Northern Bobwhite

(Colinus Virginianus) -- 48216201Supplemental

850.4400 Dimethoate Duckweed

Lemna gibba EC50 >92.6 mg/L 47709703Supplemental

850.4225 Dimethoate Most sensitive species NA -- 48572801

Supplemental

850.4225 Dimethoate 400 Sugar beet EC25 = 0.84 la / A 48572802

Supplemental

850.4150 Dimethoate Most sensitive species NA -- 4857802

Acceptable

850.4150 Dimethoate 400 Most sensitive species NA -- 4857802

Acceptable

NG 

850.2200 Dimethoate Bobwhite(Colinus Virginianus) 36-week bobwhite 48680201Supplemental

NG 

850.1075 Dimethoate Rainbow Trout(Oncorhynchus mykiss) 21-day exposure 48153501Supplemental
Page 133 of 144

Appendix K. Incident Summaries

Incident ID Use Site Date State County Certainty Legal Code Species Magnitude Effect Summary Description

TERRESTRIAL AVIAN INCIDENTS

B0000-219-

02 I005754-

003

Ornamental

/woody

3/22/1972 CA Tulare Highly 

probable

Registered 

Use

Cedar waxing 60-80 MOR 60 dead and 20 sick cedar waxing birds 

were found in a residential area within the 

vicinity of a treated area. Birds in the area 

were observed to be feeding on pyracantha 

berries. 

Gizzard contents were found to contain 1.1 

ppm dimethoate. 

10 days later additional birds were found 

outside the areas spray but contained over 

ripe pyrancantha berries. Investigators 

were unable to determine whether these 

birds died from the ingestion of treated 

berries or intoxication resulting from the 

ingestion of fermented berries.

B0000-219-

03

Garden 5/1/1971 CA Contra 

Contra

Highly 

probable

Registered 

Use

Cedar Waxing N/R MOR Other chemicals involved:

Dieldrin: Unlikely (0.15 ppm)

Diazinon Possible (0.75 ppm)

Number of Cedar Waxing birds found 

dead in residential yard which contained 

over-ripe pyracantha berries. Garden had 

been treated with dieldrin and diazinon on 

April 10 and dimethoate on April 18. 

Sample of gizzard contents and berries 

were analyzed and found to have 5.1 ppm 

dimethoate. 
Page 134 of 144

I000920-001 Seed alfalfa 6/10/1993 ID Canyon Highly 

probable

Registered 

Use

Canadian 

Geese

40 MOR Other chemicals involved:

Carbofuran: (0.52-2.9 ppm)

Bird kill occurred after the application of 

dimethoate and carbofuran to seed alfalfa. 

Tissue from the craw stomach and liver 

contained 2.4-4.0 ppm dimethoate and 

foliage samples contained 0.45-0.076 ppm 

dimethoate.

I005524-004 Alfalfa 2/10/1986 CA Imperial Possible Registered 

Use

Canadian 

Geese

25 MOR Other chemicals involved:

Carbofuran: highly probable (2-9.9 ppm)

No other details were provided.

I005572-003 Seed alfalfa 5/22/1988 ID N/R Probable Accidental 

Misuse

Canadian 

Geese

150 MOR Other chemicals involved:

Disulfuton: Probable

Carbofuran: Probable

Bird kill was found the day after the 

application of disulfuton, dimethoate and 

carbofuran to seed alfalfa.

I005751-001 Alfalfa 5/1/1988 ID N/R Probable Accidental 

Misuse

Canadian 

Geese

Hundreds MOR Other chemicals involved:

Dilsulfoton: Probable

Carbofuuran: Highly probable

Farmer applied a mixture of disulfoton, 

dimethoate and carbofuran to a 50 acre 

field of alfalfa. The use was a violation of 

a Migratory Bird Act.

I010916-001 Bait 8/9/2000 NY Onondag

a

Highly 

probable

Intentional 

Misuse

Rock Dove 1 MOR Dead rock dove was found and sent in for 

study; it was found to have consumed bird 

seed and corn at the time of death. 

Pesticide screen revealed a concentration 

of 5.31 ppm dimethoate.

It is suspected that dimethoate was 

purposefully used as bait to purposefully 

poison the bird.
Page 135 of 144

TERRESTRIAL HONEYBEE INCIDENTS

I003826-

009

Orchard 4/28/1995 NC Henderson

ville

Probable Undetermined Honeybee N/R MOR Other chemicals involved:

Methyl parathion: highly probable 

(3.1 ppm)

Carbaryl: Unlikely

Endosulfan: Possible (0.20 ppm)

Chlorpyrifos (0.10 ppm)

Combination of dimethoate, methy 

parathion, carbaryl, endosulfan and 

captan. Dead bee tissue contained 

concentrations of a number of 

different chemicals. 

I013587-

012

Alfalfa 7/14/1999 WA Grant Possible Undetermined Honeybee 150 Hives MOR Other chemicals involved:

Carbaryl: Possible

Chlorothalonil: possible

Methamidophos: Possible

Be kill reported following the 

aerial application of dimethoate, 

carbaryl, chlorthalonil and 

methamisophos on alfalfa. The 

incident indicated that the carbaryl 

applications began after sunrise 

when the bees were atticely 

foraging; this is a violation of the 

labeling instructions. 

Tissue samples found dimethoate 

concentrations ranging from 

0.0222 to 0.041 ppm.
Page 136 of 144

I013883-

018

Potato 7/15/1997 WA Grant Possible Registered Use Leafcutter 

Bee

N/R MOR Other chemicals involved;

Carbofuran: Possible

Methamidophos: Possible

Bee kill reported following the 

application of dimethoate, 

methamidphose and carofuran onto 

a potato field. The materials 

drifted to a nearby field of alfalfa 

where the cutter bees had been 

actively foraging. 

Tissue samples showed dimethoate 

at a concentration of 0.087 to 0.12

I013884-

020

Bean 8/12/1998 WA Adams Possible Registered Use Honeybee 20 colonies MOR Bee kill was reported after a bean 

field with blooming weeds was 

sprayed with dimethoate. Bees had 

been observed foraging on the 

beans but laboratory analysis did 

not detect the presence of the 

pesticide. The incident did state 

that there was an off site detection 

of dimethoate but no other details 

were included. 

I013884-

024

Bean 8/21/1998 WA Adams Possible Undetermined Honeybee 20 colonies MOR Other chemicals involved:

Naled: Possible

Bee kill occurred after aerial 

application of dimethoate and 

naled. 

Incident was reported as part of a 

spreadsheet form the Washington 

State Dept. of Agriculture and 

included minimal detail.
Page 137 of 144

I013884-

028

Orchard 4/15/1998 WA Yakima Possible Registered Use Honeybee N/R MOR Other chemicals involved:

Chlorpyrifos: possible

Bee kill was reported 4 to 8 days 

following the application of 

dimethoate and chlorpyrifos.

Dimethoate was found in tissue 

samples at a concentration of 0.26 

ppm.

Incident was reported as part of a 

spreadsheet form the Washington 

State Dept. of Agriculture and 

included minimal detail.

I013884-

033

I014341-

026

Bean 7/8/1998 WA Yakima Possible Registered Use Leafcutter 

bee

N/R MOR Bee kill was reported after aerial 

application of dimethoate to a field 

of beans. Material drifted to a 

nearby blooming field of alfalfa 

where the bees has been actively 

foraging.

Tissue samples found dimethoate 

at a concentration of 0.5 ppm.

Incident was reported as part of a 

spreadsheet form the Washington 

State Dept. of Agriculture and 

included minimal detail.

I014341-

006

Orchard 1/1/1996 WA Benton Possible Undetermined Honeybee 1,256 bees MOR Other chemicals involved:

Chlorpyrifos: possible

Bee kill was reported after aerial 

application of dimethoate and 

chlorpyrifos to an orchard.

Incident was reported as part of a 

spreadsheet form the Washington 

State Dept. of Agriculture and 

included minimal detail.
Page 138 of 144

I014341-

015

Bean 1/1/1998 WA Grant Possible Undetermined Honeybee 20 hives MOR Other chemicals involved:

Naled: Possible

Bee kill was reported after aerial 

application of dimethoate and 

naled to a field of beans. 

Incident was reported as part of a 

spreadsheet form the Washington 

State Dept. of Agriculture and 

included minimal detail.

I014341-

016

N/R 1/1/1998 WA Grant Possible Undetermined Honeybee 20 hives MOR Other chemicals involved:

Bentazon: possible

Tissue samples of bees found 0.55 

ppm concentration of dimethoate.

Incident was reported as part of a 

spreadsheet form the Washington 

State Dept. of Agriculture and 

included minimal detail.

I020741-

001

Corn 7/19/2006 CO Larimer Probable Undetermined Honeybee Half worker 

bees in 22 

hives

MOR Other chemicals involved:

Spiromesifen: unlikely

Dimethoate and spromesifen were 

sprayed aerially on a cornfield. 

Bee hives that were the most 

damaged were within 200 yards of 

the treatment site. Corn field had 

blooming weed within the field an 

it is believes that bees made direct 

contact with the pesticide in their 

active foraging or their hives were 

exposed through spray drift of the 

pesticide off site.
Page 139 of 144

I023107-

019

Cotton 7/26/2011 CA Kings Probable Undetermined Honeybee Effects in 92 

hives

Complete 

loss 12 hives

MOR Other chemicals involved:

Lambda-cyhalothrin: possible

Methoxyfenozide: unlikely

Dimethoate and lambda 

cyhalothrin were applied aerially to 

a field of cotton. There was an 

additional ground application of 

lambda cyhalothrin and 

methoxyfenozide to a pistachio 

orchard. 

Bee swabs and samples show 

dimethoate present at 0.007 and 

0.0024 ppm. 

I024335-

001

Soybean 7/31/2012 MI St. Clair Probable Undetermined Honeybee 60% foraging 

bees

7-9 Hives

MOR Bees had been actively foraging at 

the time of the application of 

dimethoate in the vicinity of a 

soybean field. It was stated that 

the grower was unware the bees 

were actively foraging when the 

dimethoate was applied. 

I026191-

001

Onion August 2013 China Shijzhuang Possible Undetermined Honeybee 106 boxes MOR Other chemicals involved:

Dichlorvos: possible

No other details on the incident 

were provided.
Page 140 of 144

TERRESTRIAL PLANTS

I013587-

025

Lentils 7/17/1999 WA Spoanoke Probable Misuse Grass N/R/ Plant 

Damag

e

Plant damage was reported due to 

spray drift of dimethaote following 

an aerial application in unfavorabl 

conditions. Three foliage samples 

tested positive for dimethoate. 

I016940-

010

Corn 3/3/2005 Imperial CA Highly 

probable

Misuse Corn 30 acres Plant 

Damag

e

Other chemicals involved:

Cyfluthrin: highly probable

Cornfields showed symptoms after 

a crop duster experienced 

mechanical problems and 

discharged dimethoate and 

cyfluthrin onto the field. Grower 

disposed of 2,500 pounds of corn 

which had been shown to have 

199.2 ppm of dimethoate.
Page 141 of 144

AQUATIC FISH INCIDENTS

B0000-

219-12

I005754-

017

Loading 

Area

1972-1973 CA Riverside Probable Misue-Accident Fish—

unknown 

species

13,000 MOR Other chemicals involved:

Methyl parathion: possible (2.96 

ppm)

Parathion: possible (1.04 ppm)

Diazinon: (0.27 ppm)

Malathion: (1.46 ppm)

Thiodan: (0.17 ppm)

Fish kill reported after heavy rain 

resulted in substantial runoff of 

pesticides from a crop dusting 

loading area. 

Water analysis showed presence o 

dimethoate, diazinon, methyl 

parathion, parathion, malathion, 

and thiodan. Dimethoate was 

found at a concentration of 5.7 

ppm.

I000403-

001

Soybeans 8/13/1988 IL Tazewell Probable Registered Use Bass

Bullhead

Carp

Channel 

catfish

Drum

Minnow

Shad

Sucker

Sunfish

White 

bass

9,242 MOR Other chemicals involved:

Chlorpyrifos: probable

No residue analysis was conducted 

on the water, soil, sediment or 

individual fish.
Page 142 of 144

I000804-

014

Lake 6/24/1991 SD Haakon Probable Intentional 

Misuse

Fish—

unknown 

species

N/R MOR Other chemicals involved:

2,4-D: possible

Unknown number of fish found 

dead after the operator of a 

spraying service used a barrel 

containing dimethoate and a barrel 

containing 2,4-D. The sprayer 

admitted that disposal of the 

pesticide containers was not in 

accordance with regulations. 

I003826-

002

N/R 6/12/1995 NC Johnston Possible Undetermined Fish—

unknown 

species

N/R MOR Other chemicals involved:

Dissulfton:Possible

2,4-D: Unlikely

Aldicarb: Possible

Dead fish noticed in a pond and 

reported 4 days later.

Samples of water, soil, sediment 

and vegetation showed the 

presence of disulfoton, 2,4-D, 

aldicarb and dimethoate. 

Dimethoate was found at a 

concentration of 0.2 ppm.
Page 143 of 144

Appendix L. ECOTOX Selected Articles of Interest

Species Effect Endpoint Duration Concentration Unit

Measured or 

Unmeasured 

concentrations

Test ID Reference

Midge MOR LC50 96 h 1.29 ug/L M 2053647

Single Versus Combined Lethal Effects of 

Three Agricultural Insecticides on Larvae of 

the Freshwater Insect Chironomus dilutus

Mosquito MOR LC50 48 h 31 ug/L U 1203438

Comparative Toxicity of Four Insecticides, 

Including Imidacloprid and Tebufenozide, 

to Four Aquatic Arthropods

Common Carp MOR LC50 96 h 1.61 mg/L U 2084953

Acute Toxicity and Behavioral Responses of 

Common Carp Cyprinus carpio (Linn.) to an 

Organophosphate (Dimethoate)

Zebra Danio MOR LC50 96 h 21.64 ug/L U 2084967

Embryo and Fingerling Toxicity of 

Dimethoate and Effect on Fecundity, 

Viability, Hatchability and Survival of 

Zebrafish, Danio rerio (Cyprinidae)

Rainbow Trout MPH NOAEL 5 d 0.735 mg/L U 2084764

Endocrine Disruption and Altered 

Biochemical Indices in Male Oncorhynchus 

mykiss in Response to Dimethoate

Indian Catfish MOR LC50 96 h 2.98 mg/L U 2084734

Acute Toxicity Bioassay of Dimethoate on 

Freshwater Airbreathing Catfish, 

Heteropneustes fossilis (Bloch)

Skipping Frog MOR LC50 96 h 36 mg/L U 1226902

Toxic Effects of Dimethoate and Methyl 

Parathion on Glycogen Reserves of Male 

and Female Rana cyanophlyctis

Common 

Hourglass Tree 

Frog

MOR LC50 48 h 8.4 ppm U 2049627

Toxicity of Agrochemicals to Common 

Hourglass Tree Frog (Polypedates cruciger) 

in Acute and Chronic Exposure

Common Bay 

Mussel,Blue 

Mussel

ENZ NOAEL 14 d 15.75 ug/L U 2084926

The Use of Selected Biomarkers, 

Phagocytic and Cholinesterase Activity to 

Detect the Effects of Dimethoate on Marine 

Mussel (Mytilus edulis)

Mussel MOR LC50 96 h 36.34 mg/L U 2084829

Acute Toxicity and Behavioural Responses 

of a Freshwater Mussel Lamellidens 

marginalis (Lamarck) to Dimethoate 

Exposure
Page 144 of 144

Blue-Green 

Algae POP EC50 15 d 0.2 ppm U 2084808

Differential Response of Cyanobacteria to 

an Organo-Phosphate Pesticide, Rogor 

(Dimethoate 30 EC)

Green Algae BCM NOAEL 2 h 1 uM/L U 1264603

Comparative Toxicity of Two 

Organophosphorus Insecticides on 

Membrane Integrity of Chlorella vulgaris. I. 

Effect on Membrane Permeability

Honey Bee DVP NOAEL ma 0.156 ug/g U 451681

Laboratory Studies of Honeybee Larval 

Growth and Development as Affected by 

Systemic Insecticides at Adult-Sublethal 

Levels

Honey Bee MOR NOAEL 6 d 0.8 ug/org U 2084991

Honey Bee Risk Assessment: New 

Approaches for In Vitro Larvae Rearing and 

Data Analyses

Honey Bee MOR NOEC 7 d 2.5 mg/kg U 468461

Toxicity of Dimethoate and Fenoxycarb to 

Honey Bee Brood (Apis Mellifera), Using a 

new In Vitro Standardized Feeding Method

Norway Rat MOR LD50 72 h 152 mg/kg U 2084565 Acute Oral Toxicity of Dimethoate in 

Albino Rats Fed a Protein-Deficient Diet

Grass Family POP NOAEL 2 yr 0.336 AI kg/ha U 569739 Effects of Insecticide Application on Weed 

and Pasture Plant Communities

Alfalfa POP NOAEL 1 gs 0.21 AI kg/ha U 447455

Field Evaluation of Insecticides for Control 

of the Alfalfa Blotch Leafminer and Its 

Effect on Alfalfa Yield in Prince Edward 

Island

Pea POP NOAEL hv 0.167 AI lb/acre U 2080801 Control of Insects in Spring Peas, 1996

Shepherd's 

Purse REP NOAEL 21 d 400 ai g/L U 413393 Insecticides and Arable Weeds: Effects on Germination and Seedling Growth