Date: 

Subject: 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

15-SEP-2015 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

Dimethoate. Occupational and Residential Exposure and Risk Assessment for 

Registration Review 

PC Code: 03500 I DP Barcode: 0418589 

Decision Nos.: 484715 Registration Nos.: NIA 

Petition No.: NIA Regulatory Action: Registration Review 

Risk Assessment Type: Single Chemical Case No.: 0088 

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

MRJD No.: NA 40 CFR: §180.204 

From: 

Jennifer 

Kelly Lowe, 

Tyler

Environmen~tal , Chemist Scienti~ (/ ~j ~ · 

Risk Assessment Branch (RABI 

/ 

L 

Health Effects Division (HED; 7509P) // ;f L, tr; 

Through: Thurston Morton, Acting Branch Chief ( p~~ HED (7509P) 

To: 

Introduction 

and 

Margarita Collantes, Review r '77J~ r:&..~. ~{11- ({.z.­ Nancy Keller, Reviewer 

Exposure Science Advisory Committee (Expo I HED 

Thomas Moriarty 

Kelly Ballard 

Pesticide Re-evaluation Division (PRD) 

As part of Registration Review, the Pesticide Re-evaluation Division (PRD) of OPP has 

requested that HED evaluate the hazard and exposure data and conduct occupational and 

residential exposure assessments, as needed, to estimate the risk to human health that will result 

from the currently registered uses of pesticides. This memorandum serves as HED's 

Registration Review assessment of the occupational and residential handler and post-application 

exposure and risk from the currently registered uses of dimethoate. 

Pagt: I of 56 
It is HED policy to use the best available data to assess exposure. Several sources of generic 

data were used in this assessment as surrogate data in the absence of chemical-specific data, 

including Pesticide Handlers Exposure Database Version 1.1 (PHED I. I); the Agricultural 

Handler Exposure Task Force (AHETF) database; the Outdoor Residential Exposure Task Force 

(ORETF) database; and the Agricultural Reentry Task Force (ARTF) database. Some of these 

data are proprietary, and subject to the data protection provisions of the Federal Insecticide, 

Fungicide, and Rodenticide Act (FlFRA). 

Note: This memorandum was reviewed by the Exposure Science Advisory Committee 

(ExpoSAC) on 10-09-2014. 

Page 2 of56 
Page 3 of 56

Table of Contents

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

2.0 Risk Assessment Conclusions and Recommendations........................................................ 7

2.1 Summary of Risk Estimates............................................................................................. 7

2.2 Label Recommendations.................................................................................................. 8

2.3 Data Deficiencies and Requirements ............................................................................... 8

3.0 Hazard Characterization....................................................................................................... 8

4.0 Exposure and Use Profile................................................................................................... 11

5.0 Residential Exposure and Risk Estimates.......................................................................... 12

6.0 Non-Occupational Spray Drift Exposure and Risk Estimates........................................... 12

7.0 Non-Occupational Bystander Post-Application Inhalation Exposure and Risk Estimates 15

8.0 Occupational Exposure and Risk Estimates ...................................................................... 16

8.1 Occupational Handler Exposure/Risk Estimates............................................................ 16

8.2 Occupational Post-application Exposure/Risk Estimates .............................................. 24

8.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates...................... 24

8.2.2 Occupational Post-application Dermal Exposure/Risk Estimates.......................... 24

Appendix A. Summary of Occupational and Residential Non-cancer Algorithms..................... 39

Appendix B. Summary of Available DFR Data for Dimethoate ................................................. 42

Appendix C. Use Summary for Dimethoate ................................................................................ 46

Appendix D. Spray Drift Calculations (see excel files)............................................................... 56
Page 4 of 56

1.0 Executive Summary

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

control a wide variety of insect pests. The mode of action for dimethoate toxicity involves 

inhibition of the enzyme acetylcholinesterase (AChE) via phosphorylation of the serine residue 

at the active site of the enzyme. The exposure/risk assessment for dimethoate also takes into 

consideration the toxicity and potential exposure to its major metabolite, omethoate, because 

omethoate plays a role in the toxicity of dimethoate, and is also found in residue studies. 

Dimethoate must be metabolized (activated) to omethoate, which is the active AChE inhibiting 

moiety. Omethoate is registered as an active ingredient (ai) internationally, but not in the United 

States. This document assesses exposures and risk estimates from the registered uses of 

dimethoate (which include agricultural crops, Christmas tree farms, trees grown for pulp, and

ornamentals in outdoor nurseries) required during Registration Review. There are currently no 

registered residential uses; however, there is the potential for non-occupational exposure as a 

result of spray drift.

Use Profile

There are numerous end-use product labels registered with dimethoate as the ai. These include 

liquids and water soluble package (WSP) formulations. Most of the registered products are 

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

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

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

Exposure Profile

Occupational handlers are anticipated to be exposed to dimethoate only (i.e., not its metabolite, 

omethoate). Due to the degradation of dimethoate once applied, post-application workers may 

be exposed to residues of both dimethoate and omethoate. In terms of personal protective 

equipment (PPE), most of the dimethoate registered labels require handlers to wear a single layer 

of clothing (long sleeved shirt and long pants), shoes plus socks, protective eyewear (either 

goggles or face shield), chemical-resistant gloves, a NIOSH-approved dust/mist filtering 

respirator with MSHA/NIOSH approval number prefix TC-21C or a NIOSH-approved respirator 

with any N, R, P, or HE filter, and a chemical-resistant apron when mixing, loading, cleaning up 

spills, or equipment. Depending on the crop and geographical area of application (i.e., arid 

versus non-arid), the registered labels for dimethoate recommend a range of restricted entry 

intervals (REIs) from 48 hours to 24 days. As noted above, there are currently no registered 

residential uses; however, there is the potential for non-occupational exposure (dermal and 

incidental oral) as a result of spray drift. 

Hazard Profile and Dose Response 

Since this assessment considers exposure and risk from both dimethoate and its metabolite, 

omethoate, toxicity and hazard information related to both are included in the hazard 

characterization. All of the toxicity studies currently available for both dimethoate and 

omethoate have been utilized in picking endpoints and points of departure (PODs) for the various 

routes of exposure. 
Page 5 of 56

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

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

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

routes (Category I or II).

Dimethoate is an OP with a neurotoxic adverse outcome pathway (AOP); neurotoxicity is the 

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

Dimethoate must be metabolized (activated) to omethoate, which is the active AChE inhibiting 

moiety. Dimethoate and omethoate have high quality dose response data across multiple 

lifestages, durations, and routes for both red blood cell (RBC) and brain AChE inhibition. Many 

of these studies have been evaluated using benchmark dose (BMD) modeling techniques. BMD 

estimates are similar across age, sex, and method of administration (gavage, feeding, drinking 

water) for dimethoate and omethoate (Appendix 9 of USEPA 20041). High quality studies for

the dermal and inhalation routes with dimethoate and omethoate, respectively, allow for route 

specific evaluation. 

The steady-state incidental oral POD (BMDL10 = 0.22 mg/kg) was selected from the OP 

Cumulative Risk Assessment (CRA) (USEPA, 2002 and 2006), and is based on a dimethoate 

combined chronic oral toxicity/carcinogenicity study. The BMD10 of 0.25 mg/kg was based on 

brain AChE inhibition. The steady-state dermal POD was selected from a dimethoate 28-day 

dermal toxicity study in rats based on brain AChE inhibition in female rats (BMDL10 = 20.2 

mg/kg/day; BMD10 = 28.5 mg/kg/day). The steady-state inhalation POD was selected from an 

omethoate 28-day inhalation toxicity study based on brain AChE inhibition in male rats 

(BMCL10 = 0.38 mg/m3/day or 0.00038 mg/L/day; BMC10 = 0.51 μg/L/day or 0.00051 

mg/L/day). 

Omethoate has been found to be a more potent AChE inhibitor than dimethoate. Because of this, 

and because the PODs for risk assessment are based on both dimethoate and omethoate toxicity 

studies, the potential exposure profiles were examined to determine if adjustment factors were 

necessary to account for the increased potency of omethoate. For occupational handlers,

exposure is anticipated to be to the parent, dimethoate, only. The dermal route of exposure is 

assessed using a dimethoate-specific toxicity study; therefore, no toxicity adjustment factors 

(TAFs) were used in the dose calculations. The inhalation route of exposure is assessed using an 

omethoate-specific toxicity study since a dimethoate-specific inhalation toxicity study is not 

available. No TAFs were used in the dose calculations, but it should be noted that the risk 

estimates presented are representative of exposure to the more toxic metabolite, omethoate, and, 

therefore, are a conservative estimate of potential exposure to dimethoate. For occupational 

post-application workers, exposure is anticipated to be to both dimethoate and omethoate. Since

the dermal route of exposure is assessed using a dimethoate-specific toxicity study, the 

omethoate residues have been adjusted by a TAF to account for the increased potency of 

omethoate. 

Resulting occupational dermal and inhalation risk estimates were combined since the same 

effects were observed for both routes of exposure (brain AChE inhibition). Residential post-

 

1 Appendix 9: BMD Analysis of Brain Cholinesterase Inhibition Data. November 2, 2004. SAP Meeting “Dimethoate: Issues 

Related to the Hazard and Dose Response Assessment.” ttp://www.epa.gov/scipoly/sap/meetings/2004/november/appendix9.pdf
Page 6 of 56

application dermal and incidental oral risk estimates were also combined since the same effects 

were observed for both routes of exposure (brain AChE inhibition). For residential incidental 

oral and dermal scenarios, a total uncertainty factor of 1000X was applied (10X for interspecies 

extrapolation, 10X for intraspecies variation, and a 10X Food Quality Protection Act (FQPA)

safety factor (SF) due to uncertainty in the human dose-response relationship for 

neurodevelopmental effects2). For occupational dermal and inhalation scenarios, a total 

uncertainty factor of 1000X was applied (10X for interspecies extrapolation, 10X for intraspecies 

variation, and a 10X database uncertainty factor due to uncertainty in the human dose-response 

relationship for neurodevelopmental effects).

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

Dearfield; 29-AUG-1991). On June 25, 1992, the FIFRA SAP concurred with the Agency's 

classification of dimethoate as a Group C carcinogen. Quantitative risk assessment for 

dimethoate using the RfD approach will adequately account for all chronic toxic effects, 

including carcinogenicity. 

Residential Exposure and Risk

There are currently no registered residential uses of dimethoate. 

Non-Occupational Spray Drift Exposure and Risk 

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

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

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

incidental oral risk estimates from indirect exposure related to spray drift are of concern (MOEs 

≤ 1000) at a range of distances from the edge of the field depending on the spray-drift scenario 

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

applications. 

 

Occupational Exposure and Risk

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

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

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

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

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

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

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

currently required on the labels) or with engineering controls.

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

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

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

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

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

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

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

 

2 For more details, see Section 4.4 in the human health risk assessment: Memo, M. Perron et al, 15-SEP-2015, D416010.
Page 7 of 56

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

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

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

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

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

eye irritation, and primary skin irritation.

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

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

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

post-application inhalation exposure assessment for dimethoate.

Human Studies Review

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

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

the PHED 1.1, ORETF, the AHETF database, and the ARTF database are (1) subject to ethics 

review pursuant to 40 CFR 26, (2) have received that review, and (3) are compliant with 

applicable ethics requirements. For certain studies, the ethics review may have included review 

by the Human Studies Review Board. Descriptions of data sources, as well as guidance on their 

use, can be found at the Agency website3. 

2.0 Risk Assessment Conclusions and Recommendations

2.1 Summary of Risk Estimates

 The occupational handler exposure and risk estimates indicate that the steady-state

dermal and inhalation combined MOEs are of concern for many scenarios with the use of 

label-recommended PPE, and continue to be a concern even with highest level of PPE

and/or mitigation (i.e., engineering controls) available. 

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

uses and based on the current exposure assessment, REIs of 12 hours to more than 30

days are necessary to reach acceptable MOEs (i.e., MOEs ≥ 1000). Even though REIs of 

12 and 24 hours may be long enough for MOEs to reach the LOC of 1000 for some 

crops/activities, HED recommends a minimum REI of 48 hours (72 hours in arid regions) 

to be protective of potential for exposure to omethoate which is known to form after 

application. Current product label REIs range from 48 hours to 24 days depending on the 

crop and location. 

 The spray drift assessment indicates that risk management options such as buffers may be 

necessary for certain use site/application scenarios, and/or label modifications designed 

to reduce risks may be necessary to reduce drift such as nozzles in the drift reduction 

technology program.

 

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

http://www.epa.gov/pesticides/science/post-app-exposure-data.html
Page 8 of 56

2.2 Label Recommendations 

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

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

based on the label-required personal protective equipment and restricted entry intervals (REIs).

2.3 Data Deficiencies and Requirements

In accordance with 40CFR158, TTR data are required for all occupational (e.g., sod farms, golf 

courses, parks, and recreational areas) or residential turf uses that could result in post-application 

exposure to turf, and DFR data are required for all occupational (e.g., crop, nursery, greenhouse 

use sites) or residential (e.g., ornamental and vegetable gardens, pick your own farms, retail tree 

farms) uses that could result in post-application exposure to foliage. In the absence of chemicalspecific TTR and/or DFR data, EPA uses default values. In the case of dimethoate, there are no 

registered turf uses; therefore, TTR data are not required at this time. Acceptable DFR studies 

have been submitted and incorporated into the current Registration Review assessment. 

3.0 Hazard Characterization

This assessment considers exposure and risk from both dimethoate and its metabolite, 

omethoate; therefore, toxicity and hazard information related to both are included in the hazard 

characterization. The database of toxicology studies for dimethoate is considered complete. 

Although never registered as an ai in the U.S., omethoate has in the past been registered in other 

countries and, as a result, there is an extensive toxicity database for omethoate. All of the 

toxicity studies currently available for both dimethoate and omethoate have been utilized in 

picking endpoints and PODs for the various routes of exposure. 

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

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

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

routes (Category I or II). Tables 3.1 and 3.2 present a summary of the acute toxicity information 

for dimethoate and omethoate, respectively.

Table 3.1. Acute Toxicity Profile – Dimethoate.

Guideline No. Study Type MRID(s) Results Toxicity 

Category

870.1100 Acute oral (rat) 48890603 LD50 = 550 mg/kg (F) III

870.1200 Acute dermal (rabbit) 48890604 LD50 > 5000 mg/kg IV

870.1300 Acute inhalation (rat) 48890605 LC50 > 2.1 mg/L IV

870.2400 Acute eye irritation (rabbit) 48890606 Moderate irritant II

870.2500 Acute dermal irritation (rabbit) 48890607 Not a dermal irritant IV

870.2600 Skin sensitization (guinea pig) 48890608 Not a sensitizer N/A

Table 3.2. Acute Toxicity Profile – Omethoate.

Guideline No. Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral (rat) 46099809 LD50= 22/28 mg/kg (M/F) I

870.1200 Acute dermal (rat) 46099810 LD50= 215 mg/kg I

870.1300 Acute inhalation (rat) 46099813 LC50= 0.28 mg/kg II
Page 9 of 56

Dimethoate is an OP with a neurotoxic AOP; neurotoxicity is the most sensitive effect in all 

species, routes, and lifestages, and is being used in deriving PODs. Dimethoate must be 

metabolized (activated) to omethoate, which is the active AChE inhibiting moiety. Dimethoate

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

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

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

administration (gavage, feeding, drinking water) for dimethoate and omethoate (Appendix 9 of 

USEPA 2004). High quality studies for the dermal and inhalation routes with dimethoate and 

omethoate, respectively, allow for route specific evaluation. 

OPs exhibit a phenomenon known as steady state AChE inhibition. After repeated exposure at 

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

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

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

among OPs. In the case of dimethoate, the pattern of steady state is reached at or near 11 days of 

exposure. In addition to the consistency across durations, the data across multiple repeat dosing 

studies in rats are similar. For the purposes of the occupational and residential risk assessment, 

only the steady-state duration is relevant to the exposure scenarios.

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

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

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

The BMDL10 is the lower confidence bound on the BMD10. As a matter of science policy, the 

agency uses the BMDL, not the BMD, for use as the POD (USEPA, 20124). 

The steady-state incidental oral POD (BMDL10 = 0.22 mg/kg) was selected from the OP CRA

(USEPA, 2002 and 2006), and is based on a dimethoate combined chronic oral 

toxicity/carcinogenicity study. The BMD10 of 0.25 mg/kg was based on brain AChE inhibition.

The steady-state dermal POD was selected from a dimethoate 28-day dermal toxicity study in 

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

mg/kg/day). 

The steady-state inhalation POD was selected from an omethoate 28-day inhalation toxicity 

study based on brain AChE inhibition in male rats (BMCL10 = 0.38 mg/m3/day or 0.00038 

mg/L/day; BMC10 = 0.51 μg/L/day or 0.00051 mg/L/day). Due to the lack of characterization of 

particle sizes in the study, the mass median aerodynamic diameter (MMAD) and geometric 

standard deviation could not be determined. As a result, human equivalent concentrations could 

not be estimated for the systemic effects (AChE inhibition) from inhalation exposure. For 

occupational scenarios, duration adjustments were made to extrapolate exposure in the animal 

study (6 hours/day; 5 days/week) to a typical occupational exposure (8 hours/day; 5 days/week). 

The resulting duration adjusted value for occupational exposures is 0.285 mg/m3. For the 

purpose of estimating occupational inhalation risks from different occupational activities, 

 

4 USEPA (U.S. Environmental Protection Agency). 2012. Benchmark Dose Technical 

Guidance. http://www.epa.gov/raf/publications/pdfs/benchmark_dose_guidance.pdf
Page 10 of 56

inhalation doses corresponding to the breathing rates for each activity (8.3, 16.7, or 29 L/min) 

were calculated using this duration adjusted value. 

For residential incidental oral and dermal scenarios, a total uncertainty factor of 1000X was 

applied (10X for interspecies extrapolation, 10X for intraspecies variation, and a 10X FQPA 

safety factor due to uncertainty in the human dose-response relationship for neurodevelopmental 

effects5). For occupational dermal and inhalation scenarios, a total uncertainty factor of 1000X 

was applied (10X for interspecies extrapolation, 10X for intraspecies variation, and a 10X 

database uncertainty factor due to uncertainty in the human dose-response relationship for 

neurodevelopmental effects).

Omethoate has been found to be a more potent AChE inhibitor than dimethoate. Because of this, 

and because the PODs for risk assessment are based on both dimethoate and omethoate toxicity 

studies, the potential exposure profiles were examined to determine if TAFs were necessary to 

account for the increased potency of omethoate. For occupational handlers, exposure is 

anticipated to be to the parent, dimethoate, only. The dermal route of exposure is assessed using 

a dimethoate-specific toxicity study, therefore, no adjustments were made to the doses 

calculated. The inhalation route of exposure is assessed using an omethoate-specific toxicity 

study since a dimethoate-specific inhalation toxicity study is not available. No adjustments to 

the doses were made, but it should be noted that the risk estimates presented are representative of 

exposure to the more toxic metabolite, omethoate, and, therefore, are a conservative estimate of 

potential exposure to dimethoate. For occupational post-application workers, exposure is 

anticipated to be to both dimethoate and omethoate. Residues of both have been measured in 

submitted DFR studies. Since the dermal route of exposure is assessed using a dimethoatespecific toxicity study, the omethoate residues have been adjusted by a TAF to account for the 

increased potency of omethoate. TAFs were estimated previously using BMD modeling to 

evaluate relative potency for dimethoate and omethoate (A. Lowit; 11-APR-2005; TXR# 

0052940). The originally calculated steady-state TAF of 3 for omethoate (A. Lowit; 24-APR2002) was verified with additional subchronic and chronic studies. For this risk assessment, no 

changes were made, and this value has been used in the post-application exposure calculations 

for Registration Review.

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

Dearfield; 29-AUG-1991). On June 25, 1992, the FIFRA SAP concurred with the Agency's 

classification of dimethoate as a Group C carcinogen. Quantification of risk using a non-linear 

approach will adequately account for all chronic toxicity, including carcinogenicity that could 

result from exposure to dimethoate.

Table 3.3. Summary of Toxicological Doses and Endpoints for Dimethoate for Use in Non-Occupational and 

Occupational Human Health Risk Assessments

Exposure/

Scenario

Point of Departure 

(POD)

Uncertainty 

Factorsa

Level of Concern

(LOC)

Study and Toxicological

Effects

Incidental Oral

Steady State

(21 days and 

longer)

BMDL10 =

0.22 mg/kg/day

UFA = 10x

UFH = 10x

FQPA SF = 10x

Residential LOC 

for MOE = 1000

Dimethoate Combined chronic oral 

toxicity/carcinogenicity study (OP CRA 

2002, 2006; MRID 00164177)

BMD10 = 0.25 mg/kg/day

 

5 For more details, see Section 4.4 in the human health risk assessment: Memo, M. Perron et al, 15-SEP-2015, D416010.
Page 11 of 56

Table 3.3. Summary of Toxicological Doses and Endpoints for Dimethoate for Use in Non-Occupational and 

Occupational Human Health Risk Assessments

Exposure/

Scenario

Point of Departure 

(POD)

Uncertainty 

Factorsa

Level of Concern

(LOC)

Study and Toxicological

Effects

Inhibition of brain AChE in adult rats

Dermal Steady 

State

(21 days and 

longer)

BMDL10 =

20.2 mg/kg/day

UFA = 10x

UFH = 10x

FQPA SF / 

UFDB = 10x

Occupational / 

Residential LOC 

for MOE = 1000

Dimethoate 28-day rat dermal toxicity

(MRID 44999101)

BMD10 = 28.5 mg/kg/day

Inhibition of brain AChE in adult rats

Inhalation 

Steady State

(21 days and 

longer)

BMCL10 =

0.38 mg/m3/dayb

UFA = 10x

UFH = 10x

UFDB = 10x

Occupational 

LOC for MOE = 

1000

Omethoate 21-day inhalation rat study

(MRID 46358601)

BMC10 = 0.51 mg/m3/day

Inhibition of brain AChE in adult rats

Cancer (oral, 

dermal, 

inhalation)

Classification: Group C carcinogen (possible human carcinogen)

a. For residential incidental oral and dermal scenarios, FQPA SF retained for infants, children, youths, and women of 

childbearing age for all exposure scenarios due to uncertainty in the human dose-response relationship for 

neurodevelopmental effects (see Section 4.4 of the human health risk assessment, D416010). For occupational dermal 

and inhalation scenarios, UFDB = database uncertainty factor for uncertainty in the human dose-response relationship 

for neurodevelopmental effects (see Section 4.4 of the human health risk assessment, D416010).

b. Occupational inhalation PODs = 0.016, 0.033, and 0.057 mg/kg/day for the breathing rates of 8.3, 16.7, and 29 L/min, 

respectively.

Point of departure (POD) = A data point or an estimated point that is derived from observed dose-response data and used to mark 

the beginning of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL = 

no-observed adverse-effect level. LOAEL = lowest-observed adverse-effect level. UF = uncertainty factor. UFA = extrapolation 

from animal to human (interspecies). UFH = potential variation in sensitivity among members of the human population 

(intraspecies). MOE = margin of exposure. LOC = level of concern. BMD = benchmark dose. BMDL = lower 95% confidence 

interval for benchmark dose. 

Absorption: Since the dermal and inhalation PODs were based on route-specific toxicity studies, 

absorption factors were not necessary to estimate exposure. 

Body Weight: For adults, when an endpoint is not sex-specific (i.e., the endpoints are not based 

on developmental or fetal effects) a body weight of 80 kg is typically used in risk assessment; 

however, in this case, a female-specific body weight of 69 kg was used. While the endpoint of 

concern, brain AChE inhibition, is not sex-specific, the female-specific body weight was used to 

protect for pregnant women due to uncertainty in the human dose-response relationship for 

neurodevelopmental effects6. A body weight of 11 kg was used to assess exposure to children 

(1 to <2 years old) from spray drift.

4.0 Exposure and Use Profile 

There are numerous end-use product labels registered with dimethoate as the ai. These include 

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

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

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

 

6 For more details, see Section 4.4 in the human health risk assessment: Memo, M. Perron et al, 15-SEP-2015, D416010.
Page 12 of 56

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

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

applications specifically. 

Based on the registered use pattern for dimethoate, dermal and inhalation exposures are 

anticipated for occupational handlers and post-application workers. Occupational handlers are 

anticipated to be exposed to the parent, dimethoate, only. Occupational post-application workers 

may be exposed to residues of both dimethoate, and its metabolite, omethoate. In terms of 

personal protective equipment (PPE), most of the dimethoate registered labels require handlers to 

wear a single layer of clothing (long sleeved shirt and long pants), shoes plus socks, protective 

eyewear (either goggles or face shield), chemical-resistant gloves, a NIOSH-approved dust/mist 

filtering respirator with MSHA/NIOSH approval number prefix TC-21C or a NIOSH-approved 

respirator with any N, R, P, or HE filter, and a chemical-resistant apron when mixing, loading, 

cleaning up spills, or equipment. Depending on the crop and geographical area of application

(i.e., arid versus non-arid), the registered labels for dimethoate recommend a range of restricted 

entry intervals (REIs) from 48 hours to 24 days. As noted above, there are currently no 

registered residential uses; however, there is the potential for non-occupational exposure (dermal 

and incidental oral) as a result of spray drift. A summary of registered labels and dimethoate use 

directions are included in Appendix C. 

5.0 Residential Exposure and Risk Estimates

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

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

2002/Notices/21669). Currently, dimethoate is registered solely for use on occupational sites. 

6.0 Non-Occupational Spray Drift Exposure and Risk Estimates

Off-target movement of pesticides can occur via many types of pathways and it is governed by a 

variety of factors. Sprays that are released and do not deposit in the application area end up offtarget and can lead to exposures to those it may directly contact. They can also deposit on 

surfaces where contact with residues can eventually lead to indirect exposures (e.g., children 

playing on lawns where residues have deposited next to treated fields). The potential risk 

estimates from these residues can be calculated using drift modeling onto 50 feet wide lawns 

coupled with methods employed for residential risk assessments for turf products.

The approach to be used for quantitatively incorporating spray drift into risk assessment is based 

on a premise of compliant applications which, by definition, should not result in direct exposures 

to individuals because of existing label language and other regulatory requirements intended to 

prevent them.7 Direct exposures would include inhalation of the spray plume or being sprayed 

directly. Rather, the exposures addressed here are thought to occur indirectly through contact 

with impacted areas, such as residential lawns, when compliant applications are conducted. 

Given this premise, exposures for children (1 to 2 years old) and adults who have contact with 

turf where residues are assumed to have deposited via spray drift thus resulting in an indirect 

 

7 This approach is consistent with the requirements of the EPA’s Worker Protection Standard.
Page 13 of 56

exposure are the focus of this analysis analogous to how exposures to turf products are 

considered in risk assessment. 

In order to evaluate the drift potential and associated risks, an approach based on drift modeling 

coupled with techniques used to evaluate residential uses of pesticides was utilized. Essentially, a 

residential turf assessment based on exposure to deposited residues has been completed to 

address drift from the agricultural applications of dimethoate. In the spray drift scenario, the 

deposited residue value was determined based on the amount of spray drift that may occur at 

varying distances from the edge of the treated field using the AgDrift (v2.1.1) model and the 

Residential Exposure Assessment Standard Operating Procedures Addenda 1: Consideration of 

Spray Drift Policy. Once the deposited residue values were determined, the remainder of the 

spray drift assessment was based on the algorithms and input values specified in the recently 

revised (2012) Standard Operating Procedures For Residential Risk Assessment (SOPs). 

For dimethoate, chemical-specific TTR data are not available, therefore, the estimated TTR are 

based on a default assumption from the 2012 Residential SOPs that the transferable residue 

available for exposure is 1% of the total deposited residue, which is assumed to be equivalent to 

the maximum application rate. In order to account for the formation the metabolite, omethoate, 

an assumption was made that 5% of the dimethoate residues would metabolize to omethoate. 

This assumption is based on a review of available TTR and DFR data for other OPs where both 

the parent and metabolite were measured in residue samples. Five percent was found to be the 

high-end value for the percent of parent that metabolized during the course of the residue studies. 

Once the estimated omethoate residues were calculated (dimethoate residues * 5%), the resulting 

values were adjusted further by the TAF value of 3 to account for the increased potency of 

omethoate since a dimethoate-specific dermal toxicity study was used for calculation of the risk 

estimates. 

A screening approach was developed based on the use of the AgDrift model in situations where 

specific label guidance that defines application parameters is not available.8 AgDrift is 

appropriate for use only when applications are made by aircraft, airblast orchard sprayers, and 

groundboom sprayers. When AgDrift was developed, a series of screening values (i.e., the Tier 

1 option) were incorporated into the model and represent each equipment type and use under 

varied conditions. The screening options specifically recommended in this methodology were 

selected because they are plausible and represent a reasonable upper bound level of drift for 

common application methods in agriculture. These screening options are consistent with how 

spray drift is considered in a number of ecological risk assessments and in the process used to 

develop drinking water concentrations used for risk assessment. In all cases, each scenario is to 

be evaluated unless it is not plausible based on the anticipated use pattern (e.g., herbicides are 

not typically applied to tree canopies) or specific label prohibitions (e.g., aerial applications are 

not allowed). In many cases, risks are of concern when the screening level estimates for spray 

drift are used as the basis for the analysis. In order to account for this issue and to provide 

additional risk management options additional spray drift deposition fractions were also 

considered. These drift estimates represent plausible options for pesticide labels.

Combined Risk Estimates from Lawn Deposition Adjacent to Applications

 

8 http://www.agdrift.com/ 
Page 14 of 56

The spray drift risk estimates are based on an estimated deposited residue concentration as a 

result of the screening level agricultural application scenarios. Dimethoate is registered on 

various agricultural crops, Christmas tree farms and trees grown for pulp, and ornamentals in 

outdoor nurseries. Most of the registered products are applied either via aerial, chemigation, 

groundboom, airblast or with handheld equipment. For most use sites, the maximum application 

rate is 2 lb ai/A; but for ornamentals in outdoor nurseries, the maximum application rate is 4.15 

lb ai/A for airblast applications specifically. The recommended drift scenario screening level 

options are listed below: 

 Groundboom applications are based on the AgDrift option for high boom height and 

using very fine to fine spray type using the 90th percentile results. 

 Orchard airblast applications are based on the AgDrift option for Sparse 

(Young/Dormant) tree canopies.

 Aerial applications are based on the use of AgDrift Tier 1 aerial option for a fine to 

medium spray type and a series of other parameters which will be described in more 

detail below (e.g., wind vector assumed to be 10 mph in a downwind direction for entire 

application/drift event).

In addition to the screening level spray drift scenarios described above, additional results are 

provided which represent viable drift reduction technologies (DRTs) that represent potential risk 

management options. In particular, different spray qualities have been considered as well as the 

impact of other application conditions (e.g., boom height, use of a helicopter instead of fixed 

wing aircraft, crop canopy conditions).

Dermal risk estimates were calculated for adults. Dermal and incidental oral risk estimates for 

children (1 to <2 years old) were combined because the toxicity endpoint for each route of 

exposure is the inhibition of brain cholinesterase (ChE). The total applicable LOC is 1000, so 

MOEs < 1000 represent risk estimates of concern. 

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

to spray drift result in a range of buffers depending on the spray drift scenario. These are 

summarized in Table 6.0.1 (all drift calculations are provided in Appendix D as excel files). 

Results indicate that the major risk concern is from aerial applications. Appropriate drift 

reduction technologies such as changing the spray type/nozzle configuration to coarser spray 

applications may result in less drift and reduced risk concerns (i.e., higher MOEs) from aerial 

applications. Similarly, using coarser sprays and lowering boom height for groundboom 

sprayers reduces risk concerns.

Table 6.0.1. Summary of Spray Drift Buffers for Dimethoate.

Crop 

Category Crops

Application 

rate (lb 

ai/A)

Adult Buffer Summary Children 1 < 2 years Buffer Summary 

(Dermal + Incidental Oral)

Buffers Necessary to reach MOE of 

1000

Buffers Necessary to reach MOE of 

1000

Aerial Groundboom Airblast Aerial Groundboom Airblast

Forestry Cottonwoods grown 

for pulp 2

100 -

>300 NA NA >300 NA NA
Page 15 of 56

Table 6.0.1. Summary of Spray Drift Buffers for Dimethoate.

Crop 

Category Crops

Application 

rate (lb 

ai/A)

Adult Buffer Summary Children 1 < 2 years Buffer Summary 

(Dermal + Incidental Oral)

Buffers Necessary to reach MOE of 

1000

Buffers Necessary to reach MOE of 

1000

Aerial Groundboom Airblast Aerial Groundboom Airblast

High 

Acreage 

Crops

Alfalfa (field and 

seed crop), Beans 

(fresh, snap, lima, 

dry, not cowpeas), 

Corn (field and 

popcorn), Cotton, 

Grass grown for seed, 

Potatoes, Safflower, 

Sorghum, Soybeans, 

Wheat

0.5 25 -

>300 0 - 25 125 ->300 10 -150

Typical 

Acreage 

Crops

Brussels sprouts 1

50 -

>300 0 - 50 200 ->300 25 - 250

Asparagus, Broccoli, 

Cauliflower, Celery, 

Garbanzo beans, 

Lentils, Melons, Peas, 

Tomatoes, 

Watermelon

0.5 10 -

>300 0 - 10 125 ->300 10 - 125

Peas, dry; Peas, 

succulent; Peppers 0.33 0 - 200 0 - 10 75 - >300 10 - 75

Kale, Mustard greens, 

Turnip 0.25 0 - 150 0 - 10 75 - >300 10 - 75

Peas 0.16 0 - 75 0 50 - >300 0 - 50

Nurseries / 

Orchard

Ornamentals in 

outdoor nurseries 4.15

NA

0 - 100

NA

25 -

250

Citrus - non-bearing 

and nursery stock, 

Cherries (preharvest 

and postharvest), 

Christmas tree 

nurseries, Citrus, 

Pears (including nonbearing and nursery 

stock)

1 0 - 25 0 - 100

Lupine 0.5 0 - 10 0 - 75

Orchard Pecans 0.33 0 - 10 0 - 50

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

Estimates

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

individuals nearby pesticide applications. The agency sought expert advice and input on issues 

related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act 

Scientific Advisory Panel (SAP) in December 2009, and received the SAP’s final report on

March 2, 2010 (http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The 

agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a 

subsequent Volatilization Screening Analysis 

(http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219). During Registration 
Page 16 of 56

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

analysis are required for dimethoate.

8.0 Occupational Exposure and Risk Estimates

8.1 Occupational Handler Exposure/Risk Estimates

HED uses the term handlers to describe those individuals who are involved in the pesticide 

application process. HED believes that there are distinct job functions or tasks related to 

applications and exposures can vary depending on the specifics of each task. Job requirements 

(amount of chemical used in each application), the kinds of equipment used, the target being 

treated, and the level of protection used by a handler can cause exposure levels to differ in a 

manner specific to each application event. 

The quantitative exposure/risk assessment developed for occupational handlers is based on the 

following scenarios which cover all the registered uses of dimethoate: 

 Mixing/loading liquids and water soluble packets to support aerial applications,

 Mixing/loading liquids and water soluble packets to support airblast applications,

 Mixing/loading liquids to support chemigation applications,

 Mixing/loading liquids and water soluble packets to support groundboom applications,

 Applying sprays with aircraft,

 Applying sprays with groundboom equipment,

 Applying sprays with airblast equipment,

 Flagging to support aerial spray applications, 

 Mixing/loading/applying liquids via backpack,

 Mixing/loading/applying liquids via mechanically-pressurized handgun, and

 Mixing/loading/applying liquids via manually-pressurized handwand.

Occupational Handler Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational 

handler risk assessments. Each assumption and factor is detailed below on an individual basis.

Application Rate: The application rates used in this assessment are provided in Appendix C. For 

similar crop/application method scenarios, the highest application rate was assessed assuming 

this would be protective of lower application rates. 

Unit Exposures: It is the policy of HED to use the best available data to assess handler exposure. 

Sources of generic handler data, used as surrogate data in the absence of chemical-specific data, 

include PHED 1.1, the AHETF database, the Outdoor Residential Exposure Task Force 

(ORETF) database, or other registrant-submitted occupational exposure studies. Some of these 

data are proprietary (e.g., AHETF data), and subject to the data protection provisions of FIFRA. 

The standard values recommended for use in predicting handler exposure that are used in this 

assessment, known as “unit exposures”, are outlined in the “Occupational Pesticide Handler Unit 
Page 17 of 56

Exposure Surrogate Reference Table9”, which, along with additional information on HED policy 

on use of surrogate data, including descriptions of the various sources, can be found at the 

Agency website10. 

Area Treated or Amount Handled: The inputs for area treated were based on information in 

ExpoSAC Policy 9.1. The following summarizes the inputs used for estimating handler 

exposures: 

 7500 acres for aerial application to forestry crops,

 1200 acres for aerial application to high acreage crops,

 350 acres for aerial application to typical acreage crops and orchards,

 350 acres for chemigation applications,

 350 acres for flaggers,

 200 acres for ground application to high acreage crops,

 80 acres for ground application to typical acreage crops,

 60 acres for aerial, chemigation, and groundboom applications to nurseries,

 40 acres for airblast applications to orchards,

 20 acres for airblast applications to nurseries,

 40 gallons for backpack and manually-pressurized handwand applications, and

 1000 gallons for mechanically-pressurized handgun.

 

Exposure Duration: HED typically classifies exposures from 1 to 30 days as short-term and 

exposures 30 days to six months as intermediate-term. Exposure duration is determined by many 

things, including the exposed population, the use site, the pest pressure triggering the use of the 

pesticide, and the cultural practices surrounding that use site. For the organophosphate 

pesticides, the match between the toxicological endpoint selection and the exposure duration is 

different than HED’s approach for conventional chemicals. The endpoint selection for 

organophosphate pesticides involves a “single day” and “steady state” approach based on an 

individual chemical’s cholinesterase inhibition. The steady state approach is appropriate for 

dimethoate given the toxicological and exposure profile. The “steady state” endpoint selection 

for dimethoate overlaps HED’s traditional short-term exposure duration endpoint selection and is 

considered health protective for occupational handlers that apply commercially over longer 

periods of time (i.e., intermediate-term exposures).

For most agricultural uses, it is reasonable to believe that occupational handlers will not apply 

the same chemical every day for more than a one-month time frame; however, there may be a 

large agribusiness and/or commercial applicators who may apply a product over a period of 

weeks (e.g., completing multiple applications for multiple clients within a region). The available 

product labels for dimethoate indicate that the products can be applied anywhere from once per 

season up to three times per season.

Mitigation/Personal Protective Equipment: Estimates of dermal and inhalation exposure were 

calculated for various levels of personal protective equipment (PPE). Results are presented for 

“baseline,” defined as a single layer of clothing consisting of a long sleeved shirt, long pants, 

 

9 Available: http://www.epa.gov/opp00001/science/handler-exposure-table.pdf

10 Available: http://www.epa.gov/pesticides/science/handler-exposure-data.html
Page 18 of 56

shoes plus socks, no protective gloves, and no respirator, as well as baseline with various levels 

of PPE as necessary (e.g., gloves, respirator, etc). Most of the dimethoate registered labels 

require handlers to wear a single layer of clothing (long sleeved shirt and long pants), shoes plus 

socks, protective eyewear (either goggles or face shield), chemical-resistant gloves, a NIOSHapproved dust/mist filtering respirator with MSHA/NIOSH approval number prefix TC-21C or a 

NIOSH-approved respirator with any N, R, P, or HE filter, and a chemical-resistant apron when 

mixing, loading, cleaning up spills, or equipment.

Occupational Handler Non-Cancer Exposure and Risk Estimate Equations

The algorithms used to estimate non-cancer exposure and dose for occupational handlers can be 

found in Appendix A.

Combining Exposures/Risk Estimates

Dermal and inhalation risk estimates were combined in this assessment, since the toxicological 

effects for these exposure routes were similar. It should be noted, however, that a dimethoate 

dermal toxicity study was used to estimate dermal risks and an omethoate inhalation toxicity 

study was used to estimate inhalation risks. The inhalation risk estimates are considered to be a 

conservative estimate of exposure to dimethoate for handlers. Dermal and inhalation risk 

estimates were combined using the following formula:

Total MOE = 1 ÷ (1/Dermal MOE) + (1/Inhalation MOE)

Summary of Occupational Handler Non-Cancer Exposure and Risk Estimates

The occupational handler exposure and risk estimates indicate that the dermal and inhalation 

combined MOEs are of concern to HED (i.e., MOEs ≤ 1000) for most scenarios assuming the 

use of label-required PPE (noted by the highlighted column in Table 8.1.1 – single layer of 

clothing, gloves and a PF5 respirator). As was noted above, the inhalation risk estimates are 

considered to be a conservative estimate of exposure to dimethoate residues considering the 

inhalation POD was selected from an omethoate toxicity study. Only five scenarios (out of 40) 

reach an MOE above the LOC of 1000 at some level of PPE (above what is currently required on 

the labels) or with engineering controls.

HED has no data to assess exposures to pilots using open cockpits. The only data available is for 

exposure to pilots in enclosed cockpits. Therefore, risks to pilots are assessed using the 

engineering control (enclosed cockpits) and baseline attire (long-sleeve shirt, long pants, shoes, 

and socks); per the Agency’s Worker Protection Standard stipulations for engineering controls, 

pilots are not required to wear protective gloves for the duration of the application. With this 

level of protection, there are no risk estimates of concern for applicators.

The Agency matches quantitative occupational exposure assessment with appropriate 

characterization of exposure potential. While HED presents quantitative risk estimates for human 

flaggers where appropriate, agricultural aviation has changed dramatically over the past two 

decades. According the 2012 National Agricultural Aviation Association (NAAA) survey of 

their membership, the use of GPS for swath guidance in agricultural aviation has grown steadily 

from the mid 1990’s. Over the same time period, the use of human flaggers for aerial pesticide 

applications has decreased steadily from ~15% in the late 1990’s to only 1% in the most recent 

(2012) NAAA survey. The Agency will continue to monitor all available information sources to 
Page 19 of 56

best assess and characterize the exposure potential for human flaggers in agricultural aerial 

applications. HED recommends that the PPE on the registered dimethoate labels for 

flaggers be revised to reflect the requirements identified above (and in Table 8.1.1) to reach 

acceptable MOEs, or that flaggers be prohibited on the label. 
Page 20 of 56

Table 8.1.1. Occupational Handler Non-Cancer Exposure and Risk Estimates for Dimethoate.

Exposure 

Scenario Crop or Target1

Dermal Unit 

Exposure

(μg/lb ai)2

Inhalation 

Unit Exposure

(μg/lb ai)2

Maximum 

Application 

Rate3

Area 

Treated4

Total MOE5(LOC = 1000)

SL/No G

No-R

SL/G

No-R

DL/G

No-R

SL/No G

PF5 R

SL/G

PF5-R

DL/G

PF5-R

SL/No G

PF10 R

SL/G

PF10-R

DL/G

PF10-R

EC

Mixer/Loader

M/L liquids for 

aerial applications

and chemigation8

Nursery

SL/No G 220

SL/G 37.6

DL/G 29.1

EC 8.6

No-R 0.219

PF5 R 0.0438

PF10 R 0.0219

EC 0.083

1 lb ai/A 60 A 67 130 140 98 360 420 100 450 540 610

Orchard6

0.33 lb ai/A

350 A

34 70 74 49 190 210 52 240 280 320

1.0 lb ai/A 11 24 25 16 63 72 17 80 95 110

1.33 lb ai/A 8.6 17 18 12 46 52 13 59 69 78

Typical field crops7

0.5 lb ai/A 22 46 48 32 120 140 34 150 190 210

1 lb ai/A 11 24 25 16 63 72 17 80 95 110

High-acreage field 

crops

0.5 lb ai/A 1200 A 6.7 13 14 9.8 36 42 10 45 54 61

Forestry (aerial only) 2 lb ai/A 7500 A 0.26 0.54 0.57 0.38 1.5 1.7 0.4 1.8 2.2 2.4

M/L liquids for 

airblast 

applications

Nursery 4.15 lb ai/A 20 A 48 100 110 68 260 300 72 330 440 440

Orchard 1.33 lb ai/A 40 A 74 150 160 110 410 470 110 510 610 690

M/L liquids for 

groundboom 

applications

Nursery 0.5 lb ai/A 60 A 130 270 290 190 700 820 200 890 1,100 1,200

Typical field crops 2 lb ai/A 80 A 25 51 53 36 130 150 38 170 210 230

High-acreage field 

crops

0.5 lb ai/A 200 A 39 79 83 56 220 250 59 270 320 370

M/L WSP for 

aerial applications

Orchard

EC 9.8 EC 0.24

1 lb ai/A 350 A ND ND ND ND ND ND ND ND ND 42

High-acreage field 

crops

0.5 lb ai/A 1,200 ND ND ND ND ND ND ND ND ND 24

M/L WSP for 

airblast 

applications

Orchard 1 lb ai/A 40 A ND ND ND ND ND ND ND ND ND 370

M/L WSP for 

groundboom 

applications

High-acreage field 

crops

0.5 lb ai/A 200 A ND ND ND ND ND ND ND ND ND 140
Page 21 of 56

Table 8.1.1. Occupational Handler Non-Cancer Exposure and Risk Estimates for Dimethoate.

Exposure 

Scenario Crop or Target1

Dermal Unit 

Exposure

(μg/lb ai)2

Inhalation 

Unit Exposure

(μg/lb ai)2

Maximum 

Application 

Rate3

Area 

Treated4

Total MOE5(LOC = 1000)

SL/No G

No-R

SL/G

No-R

DL/G

No-R

SL/No G

PF5 R

SL/G

PF5-R

DL/G

PF5-R

SL/No G

PF10 R

SL/G

PF10-R

DL/G

PF10-R

EC

Applicator

Applying sprays 

via aerial 

equipment

Nursery

EC 2.08 EC 0.0049

1 lb ai/A 60 A ND ND ND ND ND ND ND ND ND 2,800

Orchard 1.33 lb ai/A

350 A

ND ND ND ND ND ND ND ND ND 360

Typical field crops 1 lb ai/A ND ND ND ND ND ND ND ND ND 480

High-acreage field 

crops

0.5 lb ai/A 1,200 A ND ND ND ND ND ND ND ND ND 280

Forestry 2 lb ai/A 7,500 A ND ND ND ND ND ND ND ND ND 11

Applying sprays 

via airblast 

equipment9

Nursery SL/No G 1,770

SL/G 1,590

DL/G 1,480

EC 14.6

No-R 4.71

PF5 R 0.942

PF10 R 0.471

EC 0.068

4.15 lb ai/A 20 A 2.2 2.2 2.2 5.7 6.2 6.2 7.1 7.9 7.9 170

Orchard 1.33 lb ai/A 40 A 3.4 3.5 3.5 8.9 9.3 9.9 11 12 13 260

Applying sprays 

via groundboom 

equipment

Nursery SL/No G 78.6

SL/G 16.1

DL/G 12.6

EC 5.1

No-R 0.34

PF5 R 0.068

PF10 R 0.034

EC 0.043

0.5 lb ai/A 60 A 93 110 110 280 460 470 380 800 850 2,300

Typical field crops 2 lb ai/A 80 A 17 19 19 52 84 87 71 150 160 430

High-acreage field 

crops

0.5 lb ai/A 200 A 27 31 31 85 140 140 120 230 250 680

Flagger

Flagger

Nursery

SL/No G 11

SL/G 12

DL/G 10.6

No-R 0.35

PF5 R 0.07

PF10 R 0.035

1 lb ai/A 60 A 170 170 170 650 630 660 1,000 950 1,000 ND

Orchard 1.33 lb ai/A

350 A

22 22 22 83 81 84 130 120 130 ND

Typical field crop 1 lb ai/A 29 29 30 110 110 110 170 160 170 ND

High-acreage field 

crop

0.5 lb ai/A 59 58 59 220 220 220 340 320 350 ND

Mixer/Loader/Applicator

M/L/A liquids 

ground 

applications (soil 

directed) with 

backpack

Orchard

SL/No G 8,260

SL/G 8,260

DL/G 4,120

No-R 2.58

PF5 R 0.516

PF10 R 0.258

0.005 lb ai/gal

40 gal

710 710 1,200 820 820 1,600 830 830 1,600 ND

Christmas tree farm 0.025 lb ai/gal 140 140 250 160 160 320 170 170 330 ND

Forestry 0.04 lb ai/gal 92 92 150 110 110 200 110 110 200 ND

Nursery 0.08 lb ai/gal 45 45 79 51 510 100 52 52 110 ND
Page 22 of 56

Table 8.1.1. Occupational Handler Non-Cancer Exposure and Risk Estimates for Dimethoate.

Exposure 

Scenario Crop or Target1

Dermal Unit 

Exposure

(μg/lb ai)2

Inhalation 

Unit Exposure

(μg/lb ai)2

Maximum 

Application 

Rate3

Area 

Treated4

Total MOE5(LOC = 1000)

SL/No G

No-R

SL/G

No-R

DL/G

No-R

SL/No G

PF5 R

SL/G

PF5-R

DL/G

PF5-R

SL/No G

PF10 R

SL/G

PF10-R

DL/G

PF10-R

EC

M/L/A liquids 

broadcast 

applications with 

backpack

Christmas tree farm

SL/No G 

58400

SL/G 30500

DL/G 16900

No-R 69.1

PF5 R 13.8

PF10 R 6.9

0.025 lb ai/gal 17 25 34 22 40 64 23 43 72 ND

Nursery 0.08 lb ai/gal 5 8 11 7 12 20 7 13 23 ND

Forestry

SL/No G 8,260

SL/G 8,260

DL/G 4,120

No-R 2.58

PF5 R 0.516

PF10 R 0.258

0.04 lb ai/gal 11 16 21 14 25 40 14 27 45 ND

M/L/A liquids 

foliar applications 

with manuallypressurized 

handgun

Christmas tree farm SL/No G 

100,000

SL/G 430

DL/G 365

No-R 30

PF5 R 6

PF10 R 3

0.025 lb ai/gal

40 gal

13 120 130 14 550 560 14 920 970 ND

Nursery 0.08 lb ai/gal 4 39 40 4.3 170 180 4.4 290 310 ND

M/L/A liquids 

foliar applications 

with mechanicallypressurized 

handgun

Orchard

SL/No G 6050

SL/G 2050

DL/G 1360

No-R 8.68

PF5 R 1.74

PF10 R 0.87

0.0025 lb ai/gal 1,000 gal 61 110 130 83 210 280 88 230 330 ND

Christmas tree farm

Nursery

Typical field crop

M/L/A liquids 

drench/soil/ground 

directed 

applications with 

mechanicallypressurized 

handgun

Orchard

Nursery

Typical field crop

Shaded column = current PPE required on labels. Bold MOE values indicate the LOC has been exceeded with label-recommended and/or additional PPE.

1 Typical field crops include asparagus, broccoli, cauliflower, Brussel sprouts, celery, endive, leaf lettuce, Swiss chard, garbanzo beans, kale, lentils, melons, mustard greens, 

peas, peppers, tomatoes, turnips, and watermelon. High acreage field crops included alfalfa, beans, corn, cotton, grass grown for seed, potatoes, safflower, sorghum, soybeans 

and wheat. Orchard crops include cherries, citrus, pears and pecans. Nurseries include citrus, lupine, ornamentals in outdoor nurseries. Forestry includes trees grown for pulp.

2 Based on the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table” (September 2015); Level of mitigation: SL/No G No-R = Single layer clothing, no 

gloves, no respirator; SL/G No-R = Single layer clothing, gloves, no respirator; DL/G No-R = Double layer clothing, gloves, no respirator; SL/No G PF5 R = Single layer 

clothing, no gloves, PF5 respirator; SL/G PF5 R = Single layer clothing, gloves, PF5 respirator; DL/G PF5 R = Double layer clothing, gloves, PF5 respirator; SL/No G PF10 R = 

Single layer clothing, no gloves, PF10 respirator; SL/G PF10 R = Single layer clothing, gloves, PF10 respirator; DL/G PF10 R = Double layer clothing, gloves, PF10 respirator; 

EC = Engineering Controls. ND = no data.

3 Based on registered labels.

4 Exposure Science Advisory Council Policy #9.1.

5 Total MOE = 1 ÷ (1/Dermal MOE) + (1/Inhalation MOE).

6 Application rates for orchard crops: Pecans (0.33 lb ai/A); Pears and Citrus (1 lb ai/A) Cherries (1.33 lb ai/A).
Page 23 of 56

7 Dimethoate 400 label (67760-118); Label lists maximum application rate for Brussels Sprout as 0.5 lb ai/A, but also indicates 38.2 fl oz. product/A, which is 1 lb ai/A.

8 Only the scenarios assessed at 350 A are applicable for Chemigation applications. 

9 For airblast applications to nurseries and orchards, additional PPE could include chemical-resistant headgear (CRH). The addition of CRH resulted in MOEs that exceed HED’s 

LOC: Nursery – SL/G/CRH = 24, DL/G/CRH – 27; Orchard SL/G/CRH = 37, DL/G/CRH – 41.
Page 24 of 56

8.2 Occupational Post-application Exposure/Risk Estimates

HED uses the term post-application to describe exposures that occur when individuals are 

present in an environment that has been previously treated with a pesticide (also referred to as reentry exposure). Such exposures may occur when workers enter previously treated areas to 

perform job functions, including activities related to crop production, such as scouting for pests 

or harvesting. Post-application exposure levels vary over time and depend on such things as the 

type of activity, the nature of the crop or target that was treated, the type of pesticide application, 

and the chemical’s degradation properties. In addition, the timing of pesticide applications, 

relative to harvest activities, can greatly reduce the potential for post-application exposure.

8.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates

There are multiple potential sources of post-application inhalation exposure to individuals 

performing post-application activities in previously treated fields. These potential sources 

include volatilization of pesticides and resuspension of dusts and/or particulates that contain 

pesticides. The agency sought expert advice and input on issues related to volatilization of 

pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel 

(SAP) in December 2009, and received the SAP’s final report on March 2, 2010 

(http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The agency has 

evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent 

Volatilization Screening Analysis (http://www.regulations.gov/#!docketDetail;D=EPA-HQOPP-2014-0219). During Registration Review, the agency will utilize this analysis to determine 

if data (i.e., flux studies) or further analysis is required for dimethoate.

In addition, the Agency is continuing to evaluate the available post-application inhalation 

exposure data generated by the Agricultural Reentry Task Force. Given these two efforts, the 

Agency will continue to identify the need for and, subsequently, the way to incorporate 

occupational post-application inhalation exposure into the agency's risk assessments.

8.2.2 Occupational Post-application Dermal Exposure/Risk Estimates

Occupational Post-application Dermal Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational 

post-application risk assessments. Each assumption and factor is detailed below on an individual 

basis. 

Exposure Duration: The endpoint selection for organophosphate pesticides involves a “single 

day” and “steady state” approach based on an individual chemical’s cholinesterase inhibition. 

The steady state approach is appropriate for dimethoate given the toxicological and exposure 

profile. The “steady state” endpoint selection for dimethoate overlaps HED’s traditional shortterm exposure duration endpoint selection as well as being appropriately health protective for 

workers that are exposed over longer periods of time (i.e., intermediate-term exposures).
Page 25 of 56

Transfer Coefficients: It is the policy of HED to use the best available data to assess postapplication exposure. Sources of generic post-application data, used as surrogate data in the 

absence of chemical-specific data, are derived from ARTF exposure monitoring studies, and, as 

proprietary data, are subject to the data protection provisions of FIFRA. The standard values 

recommended for use in predicting post-application exposure that are used in this assessment, 

known as “transfer coefficients”, are presented in the ExpoSAC Policy 311” which, along with 

additional information about the ARTF data, can be found at the Agency website12. 

Application Rate: The application rates used in this assessment are provided in Appendix C. 

Exposure Time: The average occupational workday is assumed to be 8 hours. 

DFR Data: Chemical-specific DFR data have been submitted for dimethoate. Four studies were 

submitted that examined residues of dimethoate and its metabolite, omethoate, on the following 

crops: grapes (MRID 44788201), tomato (MRID 44690302), lettuce (MRID 44690301), and 

apple (MRID 44827601). All four studies have been reviewed by HED (see Appendix B) and 

found to be acceptable for risk assessment. The grape DFR data were not used in this risk 

assessment since dimethoate is no longer registered for use on grapes. 

A summary of how the DFR data were used is summarized in Table 8.2.2.1.

Table 8.2.2.1. Summary of DFR Data Use in Occupational Post-application Assessment for Dimethoate.

Crop for which DFR 

data available Locations included in study Crops for which DFR data used as surrogate

Apple

Michigan (MI) – non-arid

New York (NY) – non-arid

Washington (WA) – arid 

Cherries, Christmas trees, Forestry, Grapefruit, Lemons, 

Ornamentals (nursery crop), Orange, Pear, Pecan

Lettuce

Pennsylvania (PA) – non-arid

Florida (FL) – non-arid

California (CA) -- arid

Kale, Leaf lettuce, Mustard greens, Green pea, Swiss chard, 

Turnip

Tomato

Pennsylvania (PA) – non-arid

Florida (FL) – non-arid

California (CA) -- arid

Alfalfa, Asparagus, Dry beans and peas, Broccoli, Brussels 

sprouts, Cauliflower, Celery, Field Corn, Pop corn, Cotton, 

Forage crop, Bell Pepper, Potato, Safflower, Grain sorghum, 

Soybean, Tomato, Watermelon, Spring wheat, Winter wheat

Data from the apple study were used in the post-application assessment for all tree fruit and nut 

crops, Christmas trees, forestry, and ornamentals/nursery crops. The apple data (MRID# 

44827601) represent DFR levels obtained at an application rate of 1.0 lb ai/acre. The DFR 

residues (μg/cm2) were adjusted to account for any differences in application rates for the 

registered crops.

Data from the tomato study (MRID# 44690302) were used for crops with an application rate 

ranging from 0.33 lb ai/acre and higher (except tree and woody crops), since the data represent 

non-woody plants and DFR levels were obtained at an application rate of 0.5 lb ai/acre. For 

application rates other than 0.5 lb ai/acre, the DFR levels (μg/cm2) were adjusted to account for 

any differences in application rates. 

 

11 Available: http://www.epa.gov/pesticides/science/exposac_policy3.pdf

12 Available: http://www.epa.gov/pesticides/science/post-app-exposure-data.html
Page 26 of 56

Data from the lettuce study (MRID# 44690301) were used for crops with an application rate of 

0.25 lb ai/acre and less, since the data represent DFR levels obtained at an application rate of 

0.25 lb ai/acre. For application rates other than 0.25 lb ai/acre, the DFR levels (μg/cm2) were 

adjusted to account for any differences in application rates. 

Summaries of the data are provided in Appendix B. 

Each of the studies measured the amount of dimethoate residues remaining on treated leaves 

following applications, and also measured, when present, omethoate residues. Typically, when 

omethoate was present in the studies, it peaked in quantity a few days after the application, and 

then gradually dissipated over time. Dimethoate residues peaked immediately after application 

and dissipated over time thereafter. In general, omethoate was a significant factor in arid areas 

(i.e., areas where the average annual rainfall is less than 25 inches per year). Since dissipation 

rates at the arid sites were significantly different from those at the non-arid sites, the results are 

reported separately for all study sites.

As mentioned earlier, omethoate is a metabolite of dimethoate and is three times more 

toxicologically potent than dimethoate. Since the POD for the dermal route of exposure was 

chosen from a dimethoate toxicity study, a TAF of three was chosen to account for the increased 

potency of omethoate in exposure calculations. A total toxic residue approach was used whereby 

residues of omethoate were adjusted by the TAF, and total residues (dimethoate + adjusted 

omethoate) were include in exposure calculations13. In those studies where omethoate was not 

found, the post-application risks were assessed using just the dimethoate residues.

Occupational Post-application Non-Cancer Dermal Exposure and Risk Estimate Equations

The algorithms used to estimate non-cancer exposure and dose for occupational post-application 

workers can be found in Appendix A.

Occupational Post-application Non-Cancer Dermal Risk Estimates

The post-application exposure scenarios associated with the registered uses of dimethoate are 

summarized in Tables 8.2.2.2 through 8.2.2.4. The results of the risk assessment for postapplication exposures indicate that the location and/or the environmental conditions (i.e., arid 

versus non-arid) near the time of application influence the length of time following application 

until risks are below HED’s level of concern (i.e., MOEs are greater than or equal to 1000) as 

does the type of plant to which the application is directed. For most crops, the post-application

assessment indicates that following applications in arid areas (i.e., outdoor areas where average 

annual rainfall is less than 25 inches), residues persist longer than in non-arid areas. 

For the orchard crops, using the apple DFR data, there are risks of concern for most of the high 

contact post-application activities associated with each crop (e.g., hand harvesting, handset 

irrigation, etc). Some crop/activity combinations do not reach an acceptable MOE (LOC = 1000) 

even up to 30 days after application. 

 

13 Total DFR, ug/cm2 = [ (Omethoate residue, ug/cm2

) * TAF] + [Dimethoate residue, ug/cm2) 
Page 27 of 56

For the field crops using the lettuce DFR data, there are risks of concern for certain high contact 

activities (e.g., hand harvesting, hand weeding, etc). Some crop/activity combinations do not 

reach an acceptable MOE (LOC = 1000) until 7 days after application. 

For the field crops using the tomato DFR data, there are risks of concern for certain high contact 

activities (e.g., hand harvesting, hand weeding, etc). Some crop/activity combinations do not 

reach an acceptable MOE (LOC = 1000) until 14 days after application. 
Page 28 of 56

Table 8.2.2.2. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Apples/MRID 44827601).

Crop

Policy 

Crop 

Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless specified)

DFR1 Dermal Dose (mg/kg/day)2 MOE3 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

APPLE STUDY DATA

MI NY WA MI NY WA MI NY WA MI NY WA

Cherry

Tree, 

"fruit", 

deciduous

1.33

Orchard maintenance; 

Weeding, Hand; Bird 

Control; Propping

100

12 hr 1.89 2.35 2.70 0.022 0.027 0.031 920 740 640

1 3 6 1.64 1.72 1.63 0.019 0.020 0.019 1,100 1,000 1,100

Transplanting 230

12 hr 1.89 2.35 2.70 0.050 0.063 0.072 400 320 280

7 11 15 0.72 0.74 0.76 0.019 0.020 0.020 1,000 1,000 1,000

Scouting; Pruning, 

Hand; Training 580

12 hr 1.89 2.35 2.70 0.127 0.158 0.182 160 130 110

14 20 26 0.28 0.29 0.30 0.019 0.019 0.022 1,100 1,000 1,000

Harvesting, Hand 1400

12 hr 1.89 2.35 2.70 0.306 0.382 0.439 66 53 46

20 29 30 0.12 0.11 0.21 0.020 0.018 0.035 1000 1,100 580

Thinning Fruit 3600

12 hr 1.89 2.35 2.70 0.787 0.982 1.128 26 21 18

27 30 30 0.05 0.10 0.21 0.019 0.042 0.089 1,000 480 230

Christmas 

tree

Tree, 

"fruit", 

evergreen

1

Weeding, Hand;

Grading/Tagging 100

12 hr 1.42 1.77 2.03 0.016 0.021 0.024 1,200 980 860

N/A 1 2 N/A 1.59 1.71 N/A 0.018 0.020 N/A 1,100 1,000

Transplanting 230

12 hr 1.42 1.77 2.03 0.038 0.047 0.054 530 430 370

5 9 12 0.71 0.69 0.74 0.019 0.018 0.020 1,100 1,100 1,000

Scouting; Shaping 580

12 hr 1.42 1.77 2.03 0.095 0.119 0.137 210 170 150

12 17 23 0.27 0.30 0.29 0.018 0.020 0.019 1,100 1,000 1,000

Harvesting, Hand 1400

12 hr 1.42 1.77 2.03 0.230 0.287 0.330 88 70 61

18 26 30 0.12 0.12 0.16 0.020 0.019 0.026 1,000 1,100 780

Irrigation (hand set) 1900

12 hr 1.42 1.77 2.03 0.312 0.390 0.447 65 52 45

20 29 30 0.09 0.08 0.16 0.020 0.019 0.035 1,000 1,100 570

Forestry Unassigned 2

Weeding, Hand 100

12 hr 2.84 3.54 4.06 0.033 0.041 0.047 610 490 430

4 7 10 1.64 1.70 1.74 0.019 0.020 0.020 1,100 1,000 1,000

Transplanting 230

12 hr 2.84 3.54 4.06 0.076 0.094 0.108 270 210 190

10 15 20 0.72 0.74 0.75 0.019 0.020 0.020 1,100 1,000 1,000
Page 29 of 56

Table 8.2.2.2. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Apples/MRID 44827601).

Crop

Policy 

Crop 

Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless specified)

DFR1 Dermal Dose (mg/kg/day)2 MOE3 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

APPLE STUDY DATA

MI NY WA MI NY WA MI NY WA MI NY WA

Pruning, Hand 580

12 hr 2.84 3.54 4.06 0.191 0.238 0.273 110 85 74

17 24 30 0.28 0.29 0.32 0.019 0.019 0.018 1,100 1,000 940

Harvesting, Seed Cone 

(Conifers) 1400

12 hr 2.84 3.54 4.06 0.460 0.574 0.659 44 35 31

23 30 30 0.12 0.15 0.32 0.020 0.025 0.044 1,000 810 390

Irrigation (hand set) 1900

12 hr 2.84 3.54 4.06 0.625 0.779 0.895 32 26 23

25 30 30 0.09 0.15 0.32 0.020 0.034 0.060 1,000 600 290

Harvesting, Seedling 

Production 6700

12 hr 2.84 3.54 4.06 2.203 2.749 3.156 9.2 7.3 6.4

30 30 30 0.05 0.15 0.32 0.036 0.119 0.210 560 170 81

Grapefruit, 

Lemon, 

Orange

Tree, 

"fruit", 

evergreen

1

Orchard maintenance; 

Weeding, Hand; 

Baiting/Trapping; 

Weeding, Hand

100

12 hr 1.42 1.77 2.03 0.016 0.08 0.024 1,200 980 860

N/A 1 2 N/A 1.59 1.71 N/A 0.018 0.020 N/A 1,100 1,000

Transplanting 230

12 hr 1.42 1.77 2.03 0.038 0.047 0.054 530 430 370

5 9 12 0.71 0.69 0.74 0.019 0.018 0.020 1,100 1,100 1,000

Scouting; Pruning, 

Hand 580

12 hr 1.42 1.77 2.03 0.095 0.119 0.137 210 170 150

12 17 23 0.27 0.30 0.29 0.018 0.020 0.019 1,100 1,000 1,000

Harvesting, Hand 1400

12 hr 1.42 1.77 2.03 0.230 0.287 0.330 88 70 61

18 26 30 0.12 0.12 0.16 0.020 0.019 0.26 1,000 1,100 780

Nursery Crop 

(Ornamentals, 

Non-bearing 

Plants)

Unassigned 4.15

Harvesting, Hand; 

Pruning, Hand; 

Scouting; Container 

Moving; Weeding, 

Hand; Transplanting; 

Grafting; Propagating; 

Pinching; 

Tying/Training

230

12 hr 5.89 7.34 8.43 0.157 0.196 0.225 130 100 90

15 22 29 0.75 0.73 0.72 0.020 0.020 0.019 1,000 1,000 1,000

Irrigation (hand set) 1900 12 hr 5.89 7.34 8.43 1.296 1.617 1.857 16 12 11
Page 30 of 56

Table 8.2.2.2. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Apples/MRID 44827601).

Crop

Policy 

Crop 

Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless specified)

DFR1 Dermal Dose (mg/kg/day)2 MOE3 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

APPLE STUDY DATA

MI NY WA MI NY WA MI NY WA MI NY WA

30 30 30 0.10 0.32 0.67 0.021 0.070 0.147 950 290 140

1

Harvesting, Hand; 

Pruning, Hand; 

Scouting; Container 

Moving; Weeding, 

Hand; Transplanting; 

Grafting; Propagating; 

Pinching; 

Tying/Training

230

12 hr 1.42 1.77 2.03 0.038 0.047 0.054 530 430 370

5 9 12 0.71 0.69 0.74 0.019 0.018 0.020 1,100 1,100 1,000

Irrigation (hand set) 1900

12 hr 1.42 1.77 2.03 0.312 0.316 0.447 65 52 45

20 29 30 0.03 0.08 0.14 0.020 0.019 0.035 1,000 1,100 570

Pear

Tree, 

"fruit", 

deciduous

1

Orchard maintenance; 

Weeding, Hand; 

Propping

100

12 hr 1.42 1.77 2.03 0.016 0.021 0.024 1,200 980 860

N/A 1 2 N/A 1.59 1.71 N/A 0.018 0.020 N/A 1,100 1,000

Transplanting 230

12 hr 1.42 1.77 2.03 0.038 0.042 0.054 530 430 370

5 9 12 0.71 0.69 0.74 0.019 0.018 0.020 1,100 1,100 1,000

Scouting; Pruning, 

Hand; Training 580

12 hr 1.42 1.77 2.03 0.095 0.107 0.137 210 170 150

12 17 23 0.27 0.30 0.29 0.018 0.020 0.019 1,100 1,000 1,000

Harvesting, Hand 1400

12 hr 1.42 1.77 2.03 0.230 0.287 0.330 88 70 61

18 26 30 0.12 0.12 0.16 0.020 0.019 0.026 1,000 1,100 780

Thinning Fruit 3600

12 hr 1.42 1.77 2.03 0.592 0.738 0.848 34 27 24

25 30 30 0.05 0.08 0.16 0.019 0.032 0.067 1,100 630 300

Pecan Tree, "nut" 0.33

Poling; Orchard 

maintenance; Weeding, 

Hand

100

12 hr 0.47 0.58 0.67

0.005 0.007 0.008 3,700 3,000 2,600

Harvesting, Mechanical 

(shaking) 190 0.010 0.013 0.015 2,000 1,600 1,400

Transplanting 230 0.012 0.016 0.018 1,600 1,300 1,100
Page 31 of 56

Table 8.2.2.2. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Apples/MRID 44827601).

Crop

Policy 

Crop 

Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless specified)

DFR1 Dermal Dose (mg/kg/day)2 MOE3 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

APPLE STUDY DATA

MI NY WA MI NY WA MI NY WA MI NY WA

Pruning, Hand; 

Scouting 580

0.031 0.039 0.045 640 510 450

4 7 10 0.27 0.28 0.29 0.018 0.019 0.019 1,100 1,100 1,000

Bold MOE values are below the LOC of 1000. Shaded cells indicate the MOE is still below the LOC 30 days after application (i.e., an REI of >30 days would be necessary to achieve a MOE greater 

than the LOC).

1 DFR = Combined residues of dimethoate and omethoate from an apple study, adjusted to account for application rate differences and for differences in toxicity of omethoate. 

2 Daily Dermal Dose = [DFR (μg/cm2) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day]  BW (69 kg).

3 MOE = POD (20.2 mg/kg/day) / Daily Dermal Dose. 

Table 6.2.2.3. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Lettuce/MRID 44690301

Crop Policy Crop 

Group Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

LETTUCE STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Kale, Leaf 

Lettuce, 

Mustard 

Green, 

Swiss 

Chard

Vegetable, leafy 0.25

Weeding, Hand; Thinning Plants 70

12 hr 0.27 0.11 0.52

0.002 0.001 0.004 9,100 24,000 4,800

Scouting 210 0.007 0.003 0.013 3,000 7,800 1,600

Transplanting 230 0.007 0.003 0.014 2,800 7,200 1,500

Harvesting, Hand 1100

0.035 0.014 0.066 580 1,500 310

1 N/A 5 0.10 N/A 0.15 0.012 N/A 0.019 1,700 N/A 1,100

Irrigation (hand set) 1900

12 hr 0.27 0.11 0.52 0.060 0.023 0.114 340 870 180

2 1 7 0.03 0.04 0.09 0.007 0.009 0.020 2,800 2,300 1,000

Pea, 

Green

Field / row crop, 

low / medium 0.16

Weeding, Hand 70

12 hr 0.17 0.07 0.33

0.001 0.001 0.003 14,000 37,000 7,500

Scouting 210 0.004 0.002 0.008 4,700 12,000 2,500

Harvesting, Hand 1100

0.022 0.009 0.042 910 2,300 480

1 N/A 3 0.06 N/A 0.16 0.008 N/A 0.020 2,600 N/A 1,000
Page 32 of 56

Table 6.2.2.3. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Lettuce/MRID 44690301

Crop Policy Crop 

Group Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

LETTUCE STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Irrigation (hand set) 1900

12 hr 0.17 0.07 0.33 0.039 0.015 0.073 520 1,400 280

1 N/A 6 0.06 N/A 0.08 0.013 N/A 0.017 1,500 N/A 1,200

Turnip Vegetable, "root" 0.25

Weeding, Hand; Thinning Plants 70

12 hr 0.27 0.11 0.52

0.002 0.001 0.004 9,100 24,000 4,800

Scouting 210 0.007 0.003 0.013 3,000 7,800 1,600

Harvesting, Hand 1100

0.035 0.014 0.066 580 1,500 310

1 N/A 5 0.10 N/A 0.15 0.012 N/A 0.019 1,700 N/A 1,100

Irrigation (hand set) 1900

12 hr 0.27 0.11 0.52 0.060 0.023 0.114 340 870 180

2 1 7 0.03 0.04 0.09 0.007 0.009 0.020 2,800 2,300 1,000

Bold MOE values are below the LOC of 1000. 

1 DFR = Combined residues of dimethoate and omethoate from a lettuce study, adjusted to account for application rate differences and for differences in toxicity of omethoate. 

2 Daily Dermal Dose = [DFR (μg/cm2) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day]  BW (69 kg).

3 MOE = POD (20.2 mg/kg/day) / Daily Dermal Dose. 

Table 6.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Alfalfa, Dry 

Beans, Dry 

Peas, Forage 

Crop

Field / row crop, low / 

medium 0.5

Scouting 1100

12 hr 0.48 0.66 0.36 0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.006 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Asparagus Vegetable, stem / stalk 0.5 Weeding, Hand 70 12 hr 0.48 0.66 0.36 0.004 0.005 0.003 5,200 3,800 7,000
Page 33 of 56

Table 6.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Transplanting 230 0.013 0.018 0.010 1,600 1,100 2,100

Harvesting, Hand 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Broccoli, 

Cauliflower

Vegetable, head and stem 

Brassica 0.5

Transplanting 230

12 hr 0.48 0.66 0.36

0.013 0.018 0.010 1,600 1,100 2,100

Scouting

Thinning Plants 330

0.018 0.025 0.014 1,100 800 1,500

N/A 1 N/A N/A 0.27 N/A N/A 0.010 N/A N/A 2,000 N/A

Weeding, Hand 1400

12 hr 0.48 0.66 0.36 0.077 0.107 0.058 260 190 350

2 2 6 0.06 0.11 0.10 0.010 0.017 0.017 2,000 1,200 1,200

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Scouting

Harvesting, Hand

Weeding, Hand

4200

12 hr 0.48 0.66 0.36 0.232 0.322 0.174 87 63 120

3 4 11 0.02 0.02 0.04 0.011 0.009 0.018 1,800 2,400 1,100

Brussels 

Sprouts

Vegetable, head and stem 

Brassica 1

Transplanting 230

12 hr 0.95 1.32 0.71 0.025 0.035 0.019 800 570 1,100

1 1 N/A 0.35 0.53 N/A 0.009 0.014 N/A 2,200 1,400 N/A

Scouting 330

12 hr 0.95 1.32 0.71 0.036 0.051 0.027 560 400 740

1 2 2 0.35 0.21 0.58 0.013 0.008 0.018 1,500 2,500 1,100

Irrigation (hand set) 1900

12 hr 0.95 1.32 0.71 0.210 0.291 0.157 96 69 130

3 3 10 0.05 0.09 0.09 0.010 0.019 0.020 2,000 1,100 1,000

Scouting

Harvesting, Hand

Topping

4200

12 hr 0.95 1.32 0.71 0.463 0.644 0.348 44 31 58

4 4 14 0.02 0.03 0.04 0.008 0.017 0.020 2,500 1,200 1,000
Page 34 of 56

Table 6.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Weeding, Hand

Celery Vegetable, leafy 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Transplanting 230 0.013 0.018 0.010 1,600 1,100 2,100

Harvesting, Hand 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Field Corn 

and Popcorn Field / row crop, tall 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting

210 0.012 0.016 0.009 1,700 1,300 2,300

1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.016 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Cotton Field / row crop, low / 

medium 0.5

Weeding, Hand 70

12 hr

0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Pepper, bell Vegetable, fruiting 0.33

Weeding, Hand 70

0.31 0.44 0.24

0.003 0.004 0.002 7,900 5,700 11,000

Scouting 210 0.008 0.011 0.006 2,600 1,900 3,500

Transplanting 230 0.008 0.012 0.006 2,400 1,700 3,200

Harvesting, Hand

Tying/Training 1100

0.040 0.056 0.030 500 360 670

1 2 2 0.17 0.07 0.16 0.015 0.009 0.020 1,400 2,200 1,000

Irrigation (hand set)

1900 12 hr 0.31 0.44 0.24 0.069 0.096 0.052 290 210 390

2 2 5 0.06 0.07 0.08 0.009 0.016 0.019 2,200 1,300 1,100
Page 35 of 56

Table 6.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Potato Vegetable, "root" 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Irrigation (hand set) 1900

0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Safflower Field / row crop, low / 

medium 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,000

Sorghum, 

grain Field / row crop, tall 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Soybean Field / row crop, low / 

medium 0.5

Weeding, Hand 70 0.004 0.005 0.003 5,200 3,800 7,000

Scouting 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Tomato Vegetable, fruiting 0.5

Pruning, Hand

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 210 0.012 0.016 0.009 1,700 1,300 2,300

Transplanting 230 0.013 0.018 0.010 1,600 1,100 2,100

Harvesting, Hand

Tying/Training 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,000

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Watermelon Vegetable, cucurbit 0.5 Scouting

Weeding, Hand 90 12 hr 0.48 0.66 0.36 0.005 0.007 0.004 4,100 2,900 5,400
Page 36 of 56

Table 6.2.2.4. Dimethoate Occupational Post-application Risk Estimates Using Chemical-specific Data (Tomato/MRID 44690302

Crop Policy Crop Group 

Category

Application 

Rate (lb 

ai/A)

Activities

Transfer 

Coefficients 

(cm2/hr)

Time Following 

Application 

(days, unless 

specified)

DFR1 Dermal Dose 

(mg/kg/day)2 MOE3

 (LOC = 1000)

Non-Arid Arid Non-Arid Arid Non-Arid Arid Non-Arid Arid

TOMATO STUDY DATA

PA FL CA PA FL CA PA FL CA PA FL CA

Pruning, Hand

Thinning Fruit

Transplanting 230 0.013 0.018 0.010 1,600 1,100 2,100

Harvesting, Hand

Turning

Harvesting, 

Mechanicallyassisted

Training

550

0.030 0.042 0.023 670 480 890

2 1 1 0.06 0.27 0.29 0.011 0.017 0.019 1,800 1,200 1,100

Irrigation (hand set) 1900

12 hr 0.48 0.66 0.36 0.105 0.146 0.079 190 140 260

2 3 7 0.06 0.04 0.09 0.014 0.010 0.019 1,400 2,100 1,100

Wheat (spring 

and winter)

Field / row crop, low / 

medium 0.5

Weeding, Hand 70

12 hr 0.48 0.66 0.36

0.004 0.005 0.003 5,200 3,800 7,000

Scouting 1100

0.061 0.084 0.046 330 240 440

2 2 4 0.06 0.11 0.16 0.008 0.014 0.020 2,500 1,500 1,100

Bold MOE values are below the LOC of 1000. 

1 DFR = Combined residues of dimethoate and omethoate from a tomato study, adjusted to account for application rate differences and for differences in toxicity of omethoate. 

2 Daily Dermal Dose = [DFR (μg/cm2) × Transfer Coefficient × 0.001 mg/μg × 8 hrs/day]  BW (69 kg).

3 MOE = POD (20.2 mg/kg/day) / Daily Dermal Dose. 
Page 37 of 56

Restricted Entry Interval (REI)

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

(i.e., arid versus non-arid areas). Based on the current post-application dermal exposure 

assessment (Tables 8.2.2.2 – 8.2.2.4), REIs of 12 hours to more than 30 days would be necessary 

to reach acceptable MOEs (i.e., MOEs ≥ 1000) from exposure to the combined residues of 

dimethoate and omethoate. Table 8.2.2.5 provides a summary of the current REIs on product 

labels and the REIs based on the quantitative post-application exposure assessment for 

dimethoate which would be needed to achieve risks which were not of concern. 

Even though REIs of 12 and 24 hours are long enough for MOEs to reach the LOC of 1000 for 

some crops/activities, HED recommends a minimum REI of 48 hours (72 hours in arid regions) 

to be protective of potential for exposure to omethoate which is known to form after application. 

These REIs are in line with the 40 CFR 156.208 (c) (2) assignments for active ingredients that 

are classified as Toxicity Category I for acute dermal, eye irritation, and primary skin irritation.

Table 8.2.2.5. Summary of Restricted Entry Intervals

Crop

Current REI on product labels HED recommended REI

Non-Arid Arid Non-Arid Arid

Cherry 10 days 14 days >30 days >30 days

Christmas tree 10 days 14 days 29 days >30 days

Forestry 14 days 24 days >30 days >30 days

Grapefruit 10 days 14 days 26 days >30 days

Lemon 10 days 14 days 26 days >30 days

Orange 10 days 14 days 26 days >30 days

Nursery Crop 

(Ornamentals, 

Non-bearing 

Plants)

Woody ornamentals 10 days 14 days

29 days

(>30 days if 

airblast >1 

lb ai/A)

>30 days

(>30 days

if airblast 

>1 lb 

ai/A)

Herbaceous 

ornamentals 48 hours

Conifer seed orchards

48 hours 

(16 days if airblast 

>1 lb ai/A)

4 days

(25 days if 

airblast >1 lb 

ai/A)

Pear 10 days 14 days >30 days >30 days

Pecan

48 hours

7 days 10 days

Kale

48 hours1 7 days

Lettuce, leaf

Mustard Green

Swiss Chard 

Pea, Green 48 hours1 6 days

Turnip 48 hours1 7 days

Alfalfa

Asparagus 3 days 7 days

Bean, dry, and Pea, dry

Broccoli 48 hours 72 hours 4 days 11 days

Brussels Sprouts 48 hours 72 hours 4 days 14 days
Page 38 of 56

Table 8.2.2.5. Summary of Restricted Entry Intervals

Crop

Current REI on product labels HED recommended REI

Non-Arid Arid Non-Arid Arid

Cauliflower 48 hours 72 hours 4 days 11 days

Celery 48 hours 3 days 7 days

Field Corn and Popcorn 48 hours (4 days 

for detasseling)

48 hours (15 days 

for detasseling) 3 days 7 days

Cotton 48 hours 48 hours1 72 hours1

Forage Crop 48 hours 3 days 7 days

Pepper, bell 48 hours 2 days 5 days

Potato 48 hours 3 days 7 days

Safflower 48 hours 3 days 7 days

Sorghum, grain 48 hours 48 hours1 72 hours1

Soybean 48 hours 48 hours 4 days

Tomato 48 hours 3 days 7 days

Watermelon 48 hours 3 days 7 days

Wheat (spring and winter) 48 hours 48 hours 4 days

1. Even though REIs of 12 and 24 hours are long enough for MOEs to reach the LOC of 100 for some crops/activities, HED recommends a 

minimum REI of 48 hours (72 hours in arid regions) for the product labels to be protective of the acute toxicity of omethoate.
Page 39 of 56

Appendix A. Summary of Occupational and Residential Non-cancer Algorithms

OCCUPATIONAL NON-CANCER HANDLER ALGORITHMS

Potential daily exposures for occupational handlers are calculated using the following formulas:

E=UE * AR * A * 0.001 mg/ug

where:

E = exposure (mg ai/day),

UE = unit exposure (μg ai/lb ai),

AR = maximum application rate according to proposed label (lb ai A or lb ai/gal), and

A = area treated or amount handled (e.g., A/day, gal/day).

The daily doses are calculated using the following formula:

ADD= 

E * AF

BW

where:

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),

AF = absorption factor (dermal and/or inhalation), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each application handler scenario are 

calculated using a Margin of Exposure (MOE), which is a ratio of the toxicological endpoint to 

the daily dose of concern. The daily dermal and inhalation dose received by occupational 

handlers are compared to the appropriate POD to assess the risk to occupational handlers for 

each exposure route. All MOE values are calculated using the following formula:

MOE= 

POD

ADD

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).
Page 40 of 56

OCCUPATIONAL NON-CANCER POST-APPLICATION ALGORITHMS

Potential daily exposures for occupational post-application workers are calculated using the 

following formulas:

DFRt=AR * F* (1-D)t* (4.54E8

ug

lb) * (2.47E-8

A

cm2

)

where:

DFRt = dislodgeable foliage residue on day "t" (μg/cm2),

AR = application rate (lb ai/acre),

F = fraction of ai retained on foliage or 25% (unitless),

D = fraction of residue that dissipates daily or 10% (unitless), and

t = number of days after application day (days).

DFR from chemical-specific studies were used in the post-application calculations. The DFR 

data represented both dimethoate and omethoate residues, if both were measured in the studies. 

Omethoate residues, when measured, were adjusted for differences in toxicity (TAF value of 3) 

and then combined with dimethoate residues to obtain a total combined residue value for use in 

post-application calculations. If omethoate was not found in the studies, only dimethoate 

residues were used in calculations. DFR data were also adjusted for any differences in 

application rates between study rates and registered label rates. 

Total DFR,

ug

cm2

= [(Omethoate residue, 

ug

cm2

) *TAF]+ [Dimethoate residue, 

ug

cm2

]

Once the DFR was calculated, post-application exposure was calculated using the following 

formula:

E=TC * DFR t * ET * 0.001

mg

ug

where:

E = exposure (mg ai/day),

TC = transfer coefficient (cm2/hr),

DFRt = dislodgeable foliar residue on day “t” (μg/cm2), and

ET = exposure time (hours/day).

The daily doses are calculated using the following formula:

ADD= 

E * AF

BW
Page 41 of 56

where:

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),

AF = absorption factor (dermal and/or inhalation), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each scenario are calculated using a Margin 

of Exposure (MOE), which is a ratio of the toxicological endpoint to the daily dose of concern. 

The daily dermal dose received by occupational post-application workers is compared to the 

appropriate POD to assess the risk to occupational post-application workers. All MOE values 

are calculated using the following formula:

MOE= 

POD

ADD

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).
Page 42 of 56

Appendix B. Summary of Available DFR Data for Dimethoate

MRID # 447882-01. Prochaska, Lee M. Dissipation of Dimethoate and its Metabolite 

Omethoate Dislodgeable Foliar Residues on Grapes Treated with Clean Crop® Dimethoate 400, 

Phase I Field Investigation & Phase II Analytical, March, 1999.

Reviewed by HED: D254794

This study met most of the OPPTS Series 875 Group B Occupational and Residential Exposure 

Test Guidelines. The most important deviation was that the study was not conducted at the 

maximum application rate.

The study was conducted in three geographical locations: in the California Central Valley, near 

Porterville, in Tulare County; in upstate New York, near Dundee, in Yates County; and in the 

Washington State central valley, 8 miles south of Quincy, in Grant County. At each of the test 

sites, two plots were established. One plot was left untreated and served as a control. The other 

plot was divided into 3 subplots for leaf disc collection. Sampling rows were selected to 

minimize edge effects and spray overlap. Clean Crop® Dimethoate 400 was applied to the 

vineyards twice during the growing season from a few days to a month after “veraison,” which is 

the point at which the grape enters the ripening period (i.e., “green” to mature fruit). Both 

applications were applied at 1 lb ai/A, not the label permitted maximum rate of 2 lbs ai/A. 

Airblast sprayers were used at all test sites. No rain events are noted in California; irrigation 

occurred three times (4 inches each time); these did not coincide with pesticide applications. In 

New York, there were 16 rain events; these did not coincide with pesticide applications. In 

Washington, there were 10 rain events and two irrigation events; these did not coincide with 

pesticide applications. Foliage samples were collected as soon as sprays had dried (e.g., no later 

than 4 hours postapplication), 12 hours, 1, 2, 3, 5, 7, 10, 14, 21, 28, and 35 days after the last 

application. 

MRID# 446903-02. Bookbinder, M.G. Dissipation of Dislodgeable Foliar Residues of

Dimethoate (O,O-dimethyl S-[N-[methylcarbamoyl]methyl] phosphorodithioate) and its 

Metabolite Omethoate (O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] phorphorothioate) after 

Application of CLEAN CROP® DIMETHOATE 400 Insecticide to Tomato Plants. October, 

1998. 

Reviewed by HED: D251129

This study met most of the requirements of the Environmental Protection Agency’s (US-EPA) 

OPPTS Series 875, Occupational and Residential Exposure Test Guidelines, Group B: 

Postapplication Exposure Monitoring Test Guidelines. The following major issue was noted: 

residue values were calculated even for samples with concentrations below the LOQ, which may 

have affected the half life calculations.

The study was conducted in three geographical locations: near Porterville in Tulare County, 

California; near Hobe Sound, Martin County, Florida; and near Germansville in Lehigh County, 

Pennsylvania. According to the 1998 Agricultural Statistics Handbook (NASS, USDA), as cited 

in the study report, the test states and adjacent states produced 78 percent of the 1997 U.S. 
Page 43 of 56

tomato acreage. At each of the test sites, two plots were established. One plot, located upwind 

from the other, was left untreated and served as a control. The other plot was divided into 3 

subplots. Sampling rows were selected to minimize edge effects and spray overlap. During the 

field trial, test plots were maintained according to normal regional practice for tomato culture. 

The test plots received 2 applications, 7 or 8 days apart, of CLEAN CROP® DIMETHOATE 

400 insecticide. As prescribed on the label, the dimethoate was formulated as a 42.9 percent EC 

containing 4 lbs active ingredient (ai) per gallon. The dimethoate was applied at the maximum 

registered application rate for tomatoes of 0.5 lb ai/acre, using CO2 powered backpack boom 

equipment at the Florida site, and tractor-mounted PTO-powered groundboom equipment at the 

California and Pennsylvania sites. The California test plots received furrow irrigation totaling 22 

inches during the trial period, but no rainfall. The Florida sites received drip irrigation totaling 

2.16 inches and rain on days 4, 11, 12, and 13 after the second application. No irrigation was 

applied to the Pennsylvania site, but rain was recorded on days 3, 4, 5, 6, 10, 11, 12, and 14 after 

the second application -- with a one-day high rainfall event of 2.2 inches on day 6 after the 

second application. Tomato DFR leaf-punch samples of approximately 400 cm2of surface (twosided) were collected using a 1-inch diameter Birkestrand leaf punch sampler plots prior to each 

application, as soon as the spray had dried (Day 0), and on days 1, 2, 3, 5, 7, 10, 14, 21, 28, and 

35 after the second application. Samples collected after 14 days after the second application 

were not analyzed, because residues had dropped to below the limit of quantification (LOQ) by 

that time. 

Summary of DFR Values and EPA Regression Analysis Results for Treated Tomato with Dimethoate 

(MRID# 446903-02).

Site CA PA FL

Study Target Rate (lb ai/A) 0.5 0.5 0.5

Measured Average Day 0 Residue 

(μg/cm2)

0.572 0.6983 1.2107

Linear Regression Predicted Day 0 

Residue (μg/cm2) 0.357 0.476 0.661

Slope -0.205 -1.008 -0.909

Half-life (days) 3.4 0.7 0.8

R

2 0.8441 0.9117 0.7719

MRID# 446903-01. Bookbinder, M. G. Dissipation of Dislodgeable Foliar Residues of 

Dimethoate (O,O-dimethyl S-[N-[methylcarbamoyl]methyl] phosphorodithioate) and its 

Metabolite Omethoate (O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] phorphorothioate) after 

Application of CLEAN CROP® DIMETHOATE 400 Insecticide to Leaf Lettuce. October, 1998.

Reviewed by HED: D251129

This DFR study met most of the requirements of the Environmental Protection Agency’s (USEPA) OPPTS Series 875, Occupational and Residential Exposure Test Guidelines, Group B: 

Postapplication Exposure Monitoring Test Guidelines. In addition, some discrepancy and minor 

issues were noted in this review.
Page 44 of 56

The study was conducted in three geographical locations: near Porterville in Tulare County, 

California; near Hobe Sound in Martin County, Florida; and near Germansville in Lehigh 

County, Pennsylvania. According to the 1998 Agricultural Statistics Handbook (NASS, USDA), 

as cited in the study report, the test states and adjacent states produced 100 percent of the 1997 

U.S. leaf lettuce crop. At each of the test sites, two plots were established. One plot was left 

untreated and served as a control. The other plot was divided into 3 subplots for leaf disc 

collection. Sampling rows were selected to minimize edge effects and spray overlap. The test 

plots received 2 applications, 7 or 8 days apart, of CLEAN CROP® DIMETHOATE 400 

insecticide. The dimethoate was formulated as a 42.9 percent EC containing 4 lbs active 

ingredient (ai) per gallon. The dimethoate was applied at the maximum registered application 

rate of 0.25 lb ai/acre, using CO2 powered backpack boom equipment at the Florida site, and 

tractor-mounted PTO-powered groundboom equipment at the California and Pennsylvania sites. 

Application equipment was calibrated prior to application. Leaf disk samples of approximately 

400 cm2of surface (two-sided) were collected from both the control and test plots prior to each 

application, as soon as the spray had dried (Day 0), and on 1, 2, 3, 5, 7, 10, 14, 21, 28, and 35 

days after the second application. Samples collected subsequent to 14 days after the second 

application were not analyzed, because residues had dropped to below the limit of quantification 

(LOQ) by that time. Daily rainfall data were obtained onsite. Rainfall at the Florida and 

Pennsylvania sites during the sampling period totaled approximately 160 and 130% respectively 

of the 10 year regional precipitation avenge for the trial period. The California site received no 

rainfall during the study period. 

Summary of DFR Values and EPA Regression Analysis Results for Treated Lettuce with Dimethoate 

(MRID# 446903-01).

Site CA PA FL

Study Target Rate (lb ai/A) 0.25 0.25 0.25

Measured Average Day 0 Residue 

(μg/cm2)

0.64 0.348 0.1293

Linear Regression Predicted Day 0 

Residue (μg/cm2) 0.519 0.273 0.106

Slope -0.247 -1.053 -0.995

Half-life (days) 2.8 0.7 0.7

R

2 0.9575 0.97 0.9532

MRID# 448276-01. Prochaska, Lee M. Dissipation of Dimethoate and its Metabolite 

Omethoate Dislodgeable Foliar Residues on Apples Treated with CLEAN CROP® 

DIMETHOATE 400 - Phase I: Field Investigation and Phase 2: Analytical. May 4, 1999. 

Reviewed by HED: D256309

This study met most of the requirements of the Environmental Protection Agency’s (US-EPA) 

OPPTS Series 875, Occupational and Residential Exposure Test Guidelines, Group B: 

Postapplication Exposure Monitoring Test Guidelines. The major deviation was that the study 

was conducted using an application rate of 1.0 lb ai/acre as opposed to the label specified 

maximum application rate of 0.5 lb ai/acre. 
Page 45 of 56

Clean Crop® Dimethoate 400 was applied using airblast sprayers twice during the growing

season in August to apple trees in three locations. An application rate of 1.0 lb. active 

ingredient/ Acre (a.i./A) was employed. Application equipment was calibrated prior to 

application. Foliage samples were collected as soon as sprays had dried (e.g., no later than 4 

hours postapplication), 12 hours, 1, 2, 3, 5, 7, 10, 14, 21, 28, and 35 days after the last 

application. The first study site was in Ottawa County, near Marne, Michigan; the second was in 

upstate New York, in Wayne County near Alton, NY; and the third site was in the Washington 

State central valley, in Grant County, near Ephrata, WA. In 1997, the top three U.S. appleproducing states were Washington, Michigan, and New York; these states together produced 69 

percent of the total U.S. crop (USDA, Agricultural Statistics, 1997). Historical meteorological 

conditions at the three sites seem to indicate nearly normal conditions in these areas at the time 

of the study. There was no rainfall within 24 hours before or after application. Irrigation was 

applied to the plots in Washington State on the fifth day after application. Cheminova analyzed 

the dissipation data using a nonlinear regression fit to a first order decay equation. Residues 

were still detectable 35 days after the application at all locations. 

Summary of DFR Values and EPA Regression Analysis Results for Treated Apples with Dimethoate 

(MRID# 448276-01).

Site MI NY WA

Study Target Rate (lb ai/A) 1 1 1

Measured Average Day 0 Residue 

(μg/cm2)

2.0062 2.1775 2.4612

Linear Regression Predicted Day 0 

Residue (μg/cm2) 1.418 1.769 2.031

Slope -0.137 -0.105 -0.085

Half-life (days) 5.1 6.6 8.2

R

2 0.9748 0.9456 0.9195
Page 46 of 56

Appendix C. Use Summary for Dimethoate

Table C.1. Summary of Registered Labels for Dimethoate

Product Name/Formulation Registration No

Gowan Dimethoate E267 10163-56

Drexel Dimethoate 4EC 19713-231

Drexel Dimethoate 2.67 19713-232

Dimethoate 400 34704-207

Dimethoate 2.67 EC 34704-489

Dimethoate 4E 66330-223

Dimethoate 25 WP 66330-237

Dimethoate 2.67 EC 66330-244

Cymate 267 66330-245

Dimethoate 400 67760-118

Dimethoate 4E 67760-44

Agrisolutions Dimate 4E 9779-273

Clean Crop Dimethoate 400 CA970003

Dimethoate 4E ID110008

Dimethoate 400 ID120004

Clean Crop Dimethoate 400 ID980006

Dimethoate 400 OR050019
Page 47 of 56

Table C.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Application Rate

Max 

Seasonal 

Applicatio

n Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Agricultural 

uncultivated areas 

(Noncropland 

adjacent to 

vineyards)

Groundboom/

Handgun 

application

Liquid

2 lb ai/A

0.0025 lb ai/gal 

(Mech HG)

NS NS 2 per year NS NS

Alfalfa (field and 

seed crop)

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 0.5 lb ai/A NS

30

1 per crop 

cycle or 

cutting; 3 per 

year

48 hours 10

Asparagus

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 1 lb ai/A NS

14 2 48 hours 180

Beans (fresh, snap, 

lima, dry, not 

cowpeas)

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A NS

14 2 48 hours

NS

0

2

Broccoli, 

Cauliflower

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1.5 lb ai/A 7 3

48 hours; increased to 72 hours 

in outdoor areas where the 

average annual rainfall is less 

than 25 inches per year.

7

Brussel sprouts

Aerial, 

Groundboom,

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/Aa 1.5 lb ai/A 7 3

48 hours; increased to 72 hours 

in outdoor areas where the 

avenige annual rainfall is less 

than 25 inches per year.

10
Page 48 of 56

Table C.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Application Rate

Max 

Seasonal 

Applicatio

n Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Celery

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 1.5 lb ai/A 7 3 48 hours 7

Cherries (preharvest 

and postharvest)

Aerial, Airblast, 

Chemigation Liquid 1.33 lb ai/A 1.33 lb ai/A NS NS

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per year.

21b

Christmas tree 

nurseries

Aerial, Airblast, 

Chemigation, 

Handheld; Soil 

injectors (some 

labels restrict aerial 

and chemigation)

Liquid

1 lb ai/A

0.025 lb ai/gal

0.0025 lb ai/gal 

(Mech HG)

3 lb ai/A 14 3

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per vear

NA

Citrus - non-bearing 

and nursery stock

Aerial, Airblast, 

Chemigation, 

Handheld (some 

labels restrict aerial 

and chemigation)

Liquid

1 lb ai/A

foliar spray: 0.005 

lb ai/gal

0.0025 lb ai/gal 

(Mech.HG)

soil drench: 2 lb 

ai/A

1 lb ai/A NS NS

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per vear

NA
Page 49 of 56

Table C.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Application Rate

Max 

Seasonal 

Applicatio

n Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Citrus (grapefruit, 

kumquat, lemons, 

limes, oranges 

pummelo, tangelo, 

and tangerines)

Aerial, Airblast, 

Chemigation, 

Handheld (some 

labels restrict aerial 

and chemigation)

Liquid 1 lb ai/A 1 lb ai/A NS

NS

no more than 

2 apps to 

mature fruit

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per vear

15-45 

(depending 

on pest)

Corn (field and 

popcorn)

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 0.5 lb ai/A NS NS

3

48 hours; 4 days for detasseling 

tasks in nonarid areas and 15 

days in outdoor areas where the 

average annual rainfall is less 

than 25 inches per year.

14c

14 (forage)

14 (grain)

28 (grain)

28 (forage)

42 (grain)

Cotton

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A

14

14 when 

water is 

used for 

dilution; 

40 when 

once 

refined 

vegetable 

oil is used 

for 

dilution.

2 48 hours 14
Page 50 of 56

Table C.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Application Rate

Max 

Seasonal 

Applicatio

n Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Endive, Leaf 

lettuce, Swiss chard

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.25 lb ai/A 0.75 lb ai/A 7 3 48 hours 14

Garbanzo beans

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 1 lb ai/A 14 2 48 hours 0

2

Grass grown for 

seed

Aerial, 

Groundboom, 

Chemigation

Liquid 0.5 lb ai/A 1 lb ai/A 90 NS 48 hours NS

14

Kale

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid

0.25 lb ai/A

(Label 66330-

244: indicates 1.5 

pt/A = 0.5 lb ai/A)

0.5 lb ai/A 15 2 48 hours 14

Lentils

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A NS

7

2 48 hours

0

2

14

Lupine

Aerial, 

Groundboom, 

Chemigation, 

Handheld 

Liquid

0.5 lb ai/A

0.0025 lb ai/gal 

(Mech HG)

1 lb ai/A 14 2 48 hours 0

Melons

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A NS

7

NS

2

48 hours 3
Page 51 of 56

Table C.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Application Rate

Max 

Seasonal 

Applicatio

n Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Mustard greens

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.25 lb ai/A 0.5 lb ai/A 9 2 48 hours 14

Ornamentals in 

outdoor nurseries 

Aerial, Airblast, 

Chemigation, 

Handheld; Soil 

injectors (some 

labels restrict aerial 

and chemigation)

Liquid

4.15 lb ai/A 

(airblast)

1 lb ai/A

0.08 lb ai/gal

0.0025 lb ai/gal 

(Mech.HG)

soil drench: 0.06 

lb ai/gal and 5.5 

lb ai/A

soil injection: 

0.004 lb ai/inch of 

tree 

circumference

4.15 lb ai/A 

(airblast 

only)

3 lb ai/A

14 3

woody ornamentals: 10 days; 

increased to 14 days in outdoor 

areas where the average annual 

rainfall is less than 25 inches per 

year

herbaceous ornamentals: 48 

hours

conifer seed orchards: 48 hours 

(16 days if airblast >1 lb ai/A); 

increased to 4 days (25 days if 

airblast >1 lb ai/A) in outdoor 

areas where the average annual 

rainfall is less than 25 inches per 

year 

NA
Page 52 of 56

Table C.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Application Rate

Max 

Seasonal 

Applicatio

n Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Ornamentals in 

outdoor nurseries 

(trees grown for 

pulp -- forestry)

Aerial, Airblast, 

Chemigation, 

Handheld; Soil 

injectors 

Liquid

2 lb ai/A

0.04 lb ai/gal

0.0025 lb ai/gal 

(Mech HG)

soil injection: 

0.0025 lb ai/inch 

tree 

circumference

6 lb ai/A NS 3

14 days; increased to 24 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per year.

NA

Pears (including 

non-bearing and 

nursery stock)

Aerial, Airblast, 

Chemigation, 

Handheld (some 

labels restrict 

chemigation)

Liquid

1 lb ai/A

0.005 lb ai/gal; 

0.0025 lb ai/gal 

(Mech HG)

1 lb ai/A

NS NS

10 days; increased to 14 days in 

outdoor areas where the average 

annual rainfall is less than 25 

inches per vear

28

Aerial, Airblast WSB 1 lb ai/A 1 lb ai/A

Peas

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid 0.16 lb ai/A 0.16 lb ai/A NS

7

NS 48 hours 0

2

Peas (dry; some 

labels limit to those 

in ID, OR and WA 

only)

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid

0.33 lb ai/A

0.5 lb ai/A 

(allowed on SLN)

0.5 lb ai/A NS

7

NS

3

d 48 hours 0

5-14d
Page 53 of 56

Table C.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Application Rate

Max 

Seasonal 

Applicatio

n Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Peas (succulent; 

some labels limit to 

those in ID, OR and 

WA only)

Aerial, 

Groundboom, 

Chemigation (some 

labels restrict 

chemigation)

Liquid

0.33 lb ai/A

0.5 lb ai/A 

(allowed on SLN)

0.5 lb ai/A

NS

7

14

NS

3

e 48 hours NS

5-14e

Pecans

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.33 lb ai/A 0.33 lb ai/A NS NS 48 hours 21

Peppers

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.33 lb ai/A 1.65 lb ai/A 7 5 48 hours

NS

0

2

f

Potatoes

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid

0.5 lb ai/A 1 lb ai/A 7 2 48 hours

NS

0

2

g

Aerial, 

Groundboom WSB

Safflower

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 0.5 lb ai/A NS

14

NS

1

2 at lower 

rateh

48 hours 14h
Page 54 of 56

Table C.2. Summary of Use Directions for Dimethoate.

Crop Applic. Timing, 

Type, and Equip. Formulation Maximum Application Rate

Max 

Seasonal 

Applicatio

n Rate

RTI 

(days)

Max No. 

Apps per 

Season

REI PHI (days)

Sorghum

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A 7 2 48 hours 28

Soybeans

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A 7 2 48 hours 21

28i

Tomatoes

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A 6 2 48 hours 7

Turnip

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.25 lb ai/A 1.75 lb ai/A 3 7 48 hours 14

Watermelon

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 1 lb ai/A 7 2 48 hours 3

Wheat

Aerial, Airblast, 

Chemigation (some 

labels restrict aerial 

and chemigation)

Liquid 0.5 lb ai/A 0.5 lb ai/A NS 2 (at lower 

rates) 48 hours

35

45

60

a. Label 67760-118:directions state max of 0.5 lb ai/A, but also indicate 38.2 fl oz/A = 1 lb ai/A

b. Label 66330-223 lists the PHI as 21 days; but then also says interval b/t last app and harvest is 28 days

c. Labels listed various PHI's; not clear if which are correct.

d. Max # apps and PHI listed on SLN
Page 55 of 56

e. Max of 3 apps listed on label 67760-118; PHI listed on SLNs

f. Labels 66330-244 and 66330-245 list PHI of 2 days

g. Labels 66330-244 and 66330-245 list PHI of 2 days

h. A couple of labels (e.g., 34704-489) list RTI of 14 days and no more than 2 apps

i. One label (67760-118) listed a longer PHI
Page 56 of 56

Appendix D. Spray Drift Calculations (see excel files)