UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

 OFFICE OF PREVENTION, PESTICIDES 

 AND TOXIC SUBSTANCES 

 

MEMORANDUM

Date: 17 February 2009

SUBJECT: Imazosulfuron; Occupational and Residential Risk Assessment for Proposed Use 

of Imazosulfuron on Residential Turf, Ornamentals and Bare Ground Non-Crop Areas. 

 

PC Code: 118602 DP Barcode: D349707 

Decision No.: 387737 Registration No.: 59639-RLL 

Petition No.: NA Regulatory Action: Section 3 

Assessment Type: Single Chemical/No Aggregate Case No.: NA 

TXR No.: NA CAS No.: 122548-33-8 

MRID No.: 47305124, 47305125 40 CFR: 

 

FROM: Kelly O’Rourke, Biologist 

Risk Assessment Branch 4 

Health Effects Division (7509P) 

 

THROUGH: Barry O’Keefe, ORE Assessment Team Leader 

Risk Assessment Branch 3 

Health Effects Division (7509P) 

TO: Sheila Healy, Risk Assessor and Toxicologist 

Risk Assessment Branch 3 

Health Effects Division (7509P) 

 

I. CONCLUSIONS 

The V-10142 Herbicide label, EPA Reg. No. 59639-RLL, is not acceptable as written. In 

addition to agricultural sites such as sod farms, imazosulfuron is intended for non-agricultural 

use sites, to which the Worker Protection Standard Restricted Entry Interval does not apply. 

Therefore, the label should be amended to contain language cautioning unprotected persons to 

keep out of treated areas until sprays have dried. The occupational and residential margins of 

exposure (MOEs) for all scenarios reach/surpass the level of concern (LOC) of 100 and 

therefore, are not of concern. 

Page 1 of 12 
II. ACTION REQUESTED 

Provide an occupational and residential exposure and risk assessment for the proposed uses on 

residential turf, ornamentals and bare ground non-crop areas. 

III. BACKGROUND/ EXECUTIVE SUMMARY 

The registrant, Valent U.S.A. Corporation, requests the registration of the product V-10142 

Herbicide (EPA Reg. No. 59639-RLL), containing 75% imazosulfuron, for the control of 

nutsedge and other weeds in turfgrass, ornamentals and bare ground non-crop areas. This 

memorandum assesses the occupational and residential exposure risks from imazosulfuron for 

these proposed uses. An aggregate human health risk assessment is presented in a separate 

Health Effects Division (HED) memorandum. In this memorandum, the ANSI name 

imazosulfuron will be used for the active ingredient (ai) evaluated in this product. 

 Use Profile 

Imazosulfuron is a new active ingredient (ai); there are currently no registered uses in the U.S. It 

is proposed, in the herbicidal product V-10142 (EPA Reg. No. 59639-RLL, formulated as a 

water dispersible granule containing 75% ai), to control nutsedge and other weeds for the 

following use sites: 

• Established turf (residential, commercial, golf course, and sod farms) - proposed 

application rates range from 0.50 to 0.75 lb ai/A, with a second application 21 days later 

using ground broadcast-spraying equipment (not to be applied by air or through irrigation 

systems); 

• Around outdoor ornamentals (field grown conifers, deciduous trees, non-bearing fruit and 

nut trees, and landscape plants) - proposed rates range from 0.50 to 1.0 lb ai/A for preemergence, and 0.50 to 0.75 lb ai/A for post-emergence, to be applied as a directed spray 

(away from plant material) - the number of applications and retreatment intervals are not 

specified; and 

• Maintenance of bare ground non-crop areas - proposed applications rates range from 0.50 

to 1.0 lb ai/A for pre-emergence, and 0.50 to 0.75 lb ai/A for post-emergence, using 

handgun sprayers or aerial application - the number of applications and retreatment 

intervals are not specified. 

Hazard Profile 

Short-term handler exposure is possible via the dermal and inhalation routes, and short-term 

postapplication exposure may occur via the dermal and oral (incidental ingestion for children in 

residential settings) routes based on the proposed use pattern. Intermediate-term and chronic 

exposures are not expected for the proposed use patterns because the application interval is 21 

days and turf transferable residue/terrestrial field dissipation data submitted by the registrant 

indicate that the longest estimated half-life is 6 days. 

Dermal endpoints were not selected for imazosulfuron because no systemic toxicity was 

observed at the limit dose in the dermal study; there was no significant evidence of increased 

Page 2 of 12 
sensitivity or susceptibility; and dermal absorption is expected to be minimal. The short-term 

inhalation and incidental oral endpoints were selected from a two-generation reproduction study 

and a co-critical 90-day oral toxicity study in rats. Toxicity by the inhalation route is assumed to 

be equivalent to oral toxicity, and exposures compared to the parental NOAEL of 235 

mg/kg/day. The endpoint includes mortality, clinical signs, and decreased body weights, body 

weight gain, and food consumption at the LOAEL of 892 mg/kg/day. The level of concern 

(LOC) is a margin of exposure (MOE) less than 100 [10X for interspecies extrapolation and 10X 

for intraspecies variation]. Imazosulfuron is classified as “Not likely to be Carcinogenic to 

Humans” based on the absence of significant tumor increases in two adequate rodent 

carcinogenicity studies. 

Occupational Exposure/Risk

No chemical-specific handler exposure data were submitted in support of this registration. It is 

the policy of the HED to use data from the Pesticide Handlers Exposure Database (PHED) 

Version 1.1 as presented in PHED Surrogate Exposure Guide (8/98) to assess handler exposures 

for regulatory actions when chemical-specific monitoring data are not available (HED Science 

Advisory Council for Exposure Standard Operating Procedure (SOP) #7, dated 1/28/99). The 

handgun sprayer exposure data used in this assessment are from proprietary data (MRID # 

44972201) submitted by the Outdoor Residential Exposure Task Force (ORETF). 

The results of the handler occupational exposure and risk assessment indicate that risks are not 

of concern with baseline clothing. The inhalation MOEs range from 61,000 to 2,300,000; and 

therefore, are not of concern. 

Per the Worker Protection Standard (WPS), the minimum level of PPE for handlers is based on 

the acute toxicity of the end-use product. The Registration Division is responsible for ensuring 

that PPE listed on the product label is in compliance with WPS. 

Occupational postapplication dermal exposure is possible following treatment of turf and 

ornamentals with imazosulfuron. The registrant submitted chemical-specific turf transferrable 

residue (TTR) studies (MRIDs: 47305124 and 47305125) for use in assessing postapplication 

exposure. However, because a dermal endpoint was not identified for this exposure potential, 

and inhalation exposure is expected to be negligible for reentry activities, a postapplication risk 

assessment was not conducted. The imazosulfuron technical material has been classified in 

Toxicity Category III for acute dermal and Toxicity Category IV for primary eye irritation and 

primary skin irritation. Per the Worker Protection Standard (WPS), a 12-hr restricted entry 

interval (REI) is required for chemicals classified under Toxicity Category III or IV. The 

proposed label indicates a 12-hour REI, which complies with the WPS. This product is intended 

for use on sod farms, which are within the scope of the WPS. In addition, imazosulfuron is 

intended for non-agricultural use sites to which the WPS does not apply. The label should be 

amended to contain language cautioning unprotected persons to keep out of treated areas 

until sprays have dried. 

Page 3 of 12 
Residential Exposure/Risk

Imazosulfuron is proposed for use on residential turf and recreational sites such as golf courses. 

The proposed label (V-10142) does not prohibit application by home-owners; therefore, shortterm non-occupational handler exposure was evaluated. HED’s Draft Standard Operating 

Procedures (SOPs) for Residential Exposure Assessments, and Recommended Revisions (HED 

Policy Number 11, revised 22 Feb 2001), were used as the basis for all residential handler 

exposure calculations. Data from the Outdoor Residential Exposure Task Force (ORETF) 

(MRID # 44972201) were used in this assessment in place of PHED data for the garden hose-end 

sprayer scenario, which provided more confidence in the exposure estimate. The MOEs for 

residential handlers are well above the LOC of 100, and are not of concern. 

Residential postapplication exposure via the inhalation route is expected to be negligible, and 

while dermal exposure is likely for adults and children entering treated lawns, there is a lack of 

observable dermal toxicity, as discussed previously. Toddlers may experience exposure via 

incidental non-dietary ingestion (i.e., hand-to-mouth, object-to-mouth (turfgrass), and soil 

ingestion) during postapplication activities on treated turf. The postapplication risk assessment 

is based on generic assumptions as specified by the Recommended Revisions to the Residential 

SOPs and recommended approaches by HED’s Science Advisory Council for Exposure 

(ExpoSAC). 

Residential short-term postapplication MOEs were estimated for “Day 0” exposure (i.e., the 

day of application). The combined short-term MOE for children is 17,000. This MOE is 

greater than the LOC of 100 on the day of application, and therefore, is not of concern. 

Note: 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 studies (listed below) have 

been determined to require a review of their ethical conduct, and have received that review. 

• The PHED Task Force, 1995. The Pesticide Handlers Exposure Database, Version 1.1. 

Task Force members Health Canada, U.S. Environmental Protection Agency, and the 

National Agricultural Chemicals Association, released February, 1995. 

• Klonne, D. (1999) Integrated Report for Evaluation of Potential Exposures to 

Homeowners and Professional Lawn Care Operators Mixing, Loading, and Applying 

Granular and Liquid Pesticides to Residential Lawns: Lab Project Number: OMA005: 

OMA001: OMA002. Unpublished study prepared by Riceerca, Inc., and Morse 

Laboratories. 2213 p. (MRID 44972201).

Page 4 of 12 
IV. RESULTS/DISCUSSION 

1.0 Hazard Profile 

Table 1 presents a summary of the applicable endpoints selected for imazosulfuron by the RAB3 

risk assessment team and confirmed by HED’s Science Advisory Council for Toxicity. A 

summary of the acute toxicity categories for the technical material are included in Table 2. 

Table 1. Summary of Toxicological Dose and Endpoints for Imazosulfuron 

Exposure/ 

Scenario 

Point of 

Departure 

Uncertainty/FQPA 

Safety Factors 

RfD, PAD, 

LOC for Risk 

Assessment 

Study and Toxicological Effects 

Incidental Oral 

Short-

/IntermediateTerm (1-30 days) 

NOAEL= 235 

mg/kg/day 

(MRID 

47305232) 

UFA= 10x 

UFH= 10x 

Residential 

LOC for MOE 

= 100 

Reproduction, 2 generation (rat; MRID 

47305304) and 90-day oral toxicity (rat; 

47305232). 

LOAEL = 892 mg/kg/day based on 

mortality, clinical signs, decreased body 

weights, body weight gains and food 

consumption in parents (MRID 

47305304). LOAEL = 956 mg/kg/day 

based on decreased body weight gains and 

food efficiency (MRID 47305232). 

Dermal Short-/ 

Intermediate-Term 

(1-30 days) 

No systemic toxicity occurred at the limit dose and the primary toxic effects of concern (liver, eye) 

were adequately assessed in a 21-day dermal toxicity study (MRID 47305236). It is concluded that 

this compound is not absorbed or is poorly absorbed through the skin and, therefore, a quantitative 

risk assessment for this route and duration is not necessary. 

Inhalation Short-

/IntermediateTerm (1-30 days) 

NOAEL= 235 

mg/kg/day 

(MRID 

47305232) 

(100% 

absorption) 

UFA= 10x 

UFH= 10x 

Residential 

LOC for MOE 

= 100 

Reproduction, 2 generation (rat; MRID 

47305304) and 90-day oral toxicity (rat; 

47305232). 

LOAEL = 892 mg/kg/day based on 

mortality, clinical signs, decreased body 

weights, body weight gains and food 

consumption in parents (MRID 

47305304). LOAEL = 956 mg/kg/day 

based on decreased body weight gains and 

food efficiency (MRID 47305232). 

Cancer (oral, 

dermal, inhalation) 

Classification: “Not likely to be Carcinogenic to Humans” based on the absence of significant tumor 

increases in two adequate rodent carcinogenicity studies (MRID 47305307, mouse; 47305306, rat). 

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). FQPA SF = FQPA Safety Factor. LOC = level 

of concern. MOE = margin of exposure. 

Page 5 of 12 
Table 2. Acute Toxicity of Imazosulfuron Technical

Guideline 

No. Study Type MRID# Results 

Toxicity 

Category

870.1100 Acute Oral- Rats 47305221 LD50 >5000 mg/kg IV 

870.1200 Acute Dermal- Rat 47305227 LD50 >2000 mg/kg III 

870.1300 Acute Inhalation- Rat 47305228 LC50 >2.12 mg/L IV 

870.2400 Acute Eye Irritation- Rabbit 47305229 Non-irritating IV 

870.2500 Primary Dermal Irritation- Rabbit 47305230 Non-irritating IV 

870.2600 Dermal Sensitization- Guinea pig 47305231 Negative N/A 

2.0 Use Profile

Imazosulfuron is a new active ingredient; there are currently no registered uses in the U.S. It is 

proposed, in the herbicidal product V-10142 (EPA Reg. No. 59639-RLL) for the control of 

nutsedge and other weeds in turfgrass, ornamentals and bare ground non-crop areas. The use 

profile proposed for this Section 3 registration request is summarized in Table 3. 

Table 3. Summary of Use Pattern/Formulation Information

Formulation 

Type

Application 

Method Use Site

Application 

Rate 

(lb ai/A) 

Application 

Interval

Preharvest 

Interval

Groundboom, 

Low-pressure 

Handheld 

Equipment 1

Established 

Turf 

(residential, commercial, golf 

course, and sod farms) 

0.50 – 0.75 21 days 2

Groundboom, 

Low-pressure 

Handheld 

Equipment 

Around Outdoor Ornamentals 

(field grown conifers, 

deciduous trees , non-bearing 

fruit and nut trees, and 

landscape plants) 

V-10142 

Herbicide 

(water 

dispersible 

granule) 

75% ai 

Aerial or 

Handheld 

Equipment 

Bare Ground Non-Crop 

0.50 – 1.0 

(preemergence) 

0.50 – 0.75 

(postemergence) 

Not 

Specified 2

N/A 

1

 For turf, aerial applications are prohibited, and product is not to be applied through any type of irrigation system. 2

 A second application is permitted for turf, however, the number of applications and retreatment intervals are not 

specified for the ornamental and bare ground non-crop use sites. 

Page 6 of 12 
3.0 Occupational Exposure

3.1 Handler Exposure and Risk

There is a potential for exposure to imazosulfuron during mixing, loading, and application 

activities. No chemical-specific handler exposure data were submitted in support of this 

registration. It is the policy of the HED to use data from the Pesticide Handlers Exposure 

Database (PHED) Version 1.1 as presented in PHED Surrogate Exposure Guide (8/98) to assess 

handler exposures for regulatory actions when chemical-specific monitoring data are not 

available (HED Science Advisory Council for Exposure Standard Operating Procedure #7, dated 

1/28/99). There are no PHED unit exposure data for mixing/loading/applying water dispersible 

granules [also called dry flowable] with a low pressure handwand. The scenario evaluated for 

this equipment type using the liquid formulation is considered to be an adequate surrogate for 

estimating exposure from the water dispersible granule formulation. The handler exposure data 

for the turf handgun sprayer scenario are from the Outdoor Residential Exposure Task Force 

(ORETF) (MRID # 44972201), rather than from PHED. The ORETF data were designed to 

replace the present PHED data with higher-confidence, higher quality data that contain more 

replicates than the PHED data for those scenarios. 

Short-term occupational handler exposure is possible via the dermal and inhalation routes based 

on the proposed use pattern. Dermal endpoints were not selected for imazosulfuron because no 

systemic toxicity was observed at the limit dose in the dermal study; there was no significant 

evidence of increased sensitivity or susceptibility; and dermal absorption is expected to be 

minimal. A short-term inhalation endpoint was selected from a two-generation reproduction 

study and a co-critical 90-day oral toxicity study in rats. Toxicity by the inhalation route is 

assumed to be equivalent to oral toxicity, and inhalation exposures compared to the NOAEL of 

235 mg/kg/day. The endpoint includes mortality, clinical signs, and decreased body weights, 

body weight gain, and food consumption at the LOAEL of 892 mg/kg/day. The LOC is an 

MOE less than 100. Imazosulfuron is classified as “Not likely to be Carcinogenic to Humans” 

based on the absence of significant tumor increases in two adequate rodent carcinogenicity 

studies. 

The results of the handler occupational exposure and risk assessment indicate that risks are not of 

concern with baseline clothing (i.e., no respirator). Occupational handlers’ inhalation MOEs 

range from 61,000 to 2,300,000, and are not of concern. Exposure assumptions and MOEs for 

occupational handlers are summarized in Table 4. 

HED recognizes that it is feasible for the same individual to mix/load and apply formulations 

with the groundboom sprayer; however, appropriate data are not available in PHED for which 

unit exposure values for these combined activities can be derived. HED does not recommend 

simply adding the unit exposure values for each job function because any extrapolation error 

(i.e., exposure from the amount of ai handled in the study to that of a real-life application) would 

be magnified, leading to greater uncertainty. For information and characterization purposes, 

even with the over-estimation uncertainty, the MOEs for these combined activities would be 

above the LOC of 100 (i.e., 180,000 and 270,000 for turf and ornamentals, respectively). The 

minimum level of PPE for handlers is based on acute toxicity for the end-use products. The 

Registration Division (RD) is responsible for ensuring that PPE listed on the label is in 

compliance with the Worker Protection Standard (WPS).

Page 7 of 12 
Table 4. Summary of MOEs for Occupational Handlers of Imazosulfuron

Exposure Scenario (Scenario #)

Inhalation 

Unit 

Exposure 

(mg/lb ai)1

Use Site 

Application 

Rate 

(lb ai/A)2

Area 

Treated 

(A/day) 3

Inhalation 

Dose 

(mg/kg/day) 4

ShortTerm 

MOE 5

Mixer/Loader 

(1) Mixing/Loading Dry Flowables for 

Aerial application 

Bare ground 

Non-Crop 1.0 350 0.0039 61,000 

(2) Mixing/Loading Dry Flowables for Turf 0.75 80 0.00066 360,000 

Groundboom application 

0.00077 

Ornamentals 1.0 40 0.00044 530,000 

Applicator 

(3) Applying Sprays with Sprays with 

Fixed-wing Aircraft 0.000068 Bare ground 

Non-Crop 1.0 350 0.00034 690,000 

(4) Applying Sprays with Open Cab Turf 0.75 80 0.00063 370,000 

Groundboom 0.00074 

Ornamentals 1.0 40 0.00042 560,000 

Mixer/Loader/Applicator 

(5) Mixing/Loading Dry Flowables and Turf 0.75 5 0.00010 2,300,000 

Applying with Handgun Sprayer 0.0019 

Ornamentals 

& Non-Crop 1.0 5 0.00014 1,700,000 

(6) Mixing/Loading Liquid and Applying 

with Low-Pressure Handwand 0.03 Turf 0.025 

 (lb ai/gal) 

40 

(gal/day) 0.00043 550,000 

Flagger 

(7) Flagging to Support Aerial 

Applications 0.00035 Bare ground Non-Crop 1.0 350 0.0018 130,000 

1 Inhalation unit exposure values represent no respirator. Values are reported in the PHED Surrogate Exposure Guide dated August 1998, except 

for the handgun value which was obtained from ORETF. 

2 Application rates are based on maximum values presented in proposed label: V-10142 (EPA Reg. No. 59639-RLL). 3 Daily area treated is based on the area or gallons that can be reasonably applied in a single day for each exposure scenario based on the 

application method and formulation/packaging type. (standard EPA/OPP/HED values). 4 Daily Dose (mg/kg/day) = (Inhalation unit exposure * Application rate * Area treated) / 70 kg 5 MOE = NOAEL / Daily Dose; where the short-term NOAEL is 235 mg/kg/day. The LOC is 100. 

 3.2 Occupational Postapplication Exposure and Risk

This registration action for imazosulfuron involves applications to residential and commercial 

turfgrass, golf courses, sod farms, and ornamentals. Therefore, there is a potential for 

postapplication exposure to maintenance workers and sod harvesters. However, because no 

appropriate dermal endpoints were identified for this exposure potential, and postapplication 

inhalation exposure is expected to be negligible, an occupational postapplication risk assessment 

was not conducted. Non-occupational postapplication risk in residential settings is covered in 

Section 4.2 

Page 8 of 12 
4.0 Non-Occupational/Residential Exposure

V-10142 herbicide is proposed for application to residential turfgrass and recreational sites. It 

may be applied to turf at rates ranging from 0.50 to 0.75 lb ai/A, for two applications at an 

interval of 21 days. The labels do not prohibit homeowners from using these products; therefore, 

residential handlers may receive short-term dermal and inhalation exposure to imazosulfuron 

when mixing, loading and applying the formulation. Residential postapplication exposure via 

the inhalation route is expected to be negligible; however, dermal exposure is likely for adults 

and children entering treated lawns. Toddlers may also experience exposure via incidental nondietary ingestion (i.e., hand-to-mouth, object-to-mouth (turfgrass), and soil ingestion) during 

postapplication activities on treated turf. 

As discussed previously, dermal endpoints were not selected for imazosulfuron because no 

systemic toxicity was observed at the limit dose in the dermal study. Short-term inhalation and 

incidental oral exposure was assessed using the same NOAEL (235 mg/kg/day) that was selected 

for occupational inhalation exposure. Toxicity by the inhalation route is assumed to be 

equivalent to oral toxicity. The LOC is an MOE less than 100. 

 4.1 Residential Handler Exposure and Risk 

HED’s Draft Standard Operating Procedures (SOPs) for Residential Exposure Assessments, and 

Recommended Revisions (HED Policy Number 11, revised 22 Feb 2001), were used as the basis 

for the residential handler exposure calculations. Data from the Outdoor Residential Exposure 

Task Force (ORETF) (MRID # 44972201) were used in this assessment in place of PHED data 

for the garden hose-end sprayer scenario, which provided more confidence in the exposure 

estimate. As shown in Table 5, the inhalation MOEs for residential handlers are well above the 

LOC of 100, and are not of concern. 

Table 5. Handler Exposure and Risk Estimates for Residential Lawn Applicators

Handler Scenario

Application 

Rate 1

 (lb ai/A)

Area 

Treated 2

(acres/day)

Inhalation 

Unit 

Exposure 3

(mg/lb ai)

Daily Dose 4

(mg/kg/day) 

Short-Term 

MOE 5

(1) Mix/load and spot application of liquid 

formulation (low-pressure hand sprayer) 0.75 0.023 (1,000 ft2

) 0.030 0.0000074 32,000,000 

(2) Mix/load and broadcast application of liquid 

formulation (garden hose-end sprayer) 0.75 0.50 0.017 0.000091 2,600,000 

1 Application rate is based on maximum values found in proposed label: V-10142 (EPA Reg. No. 59639-RLL). 2 Area treated is based on the area that can be reasonably treated in a single day based on the application method (standard 

EPA/OPP/HED values). 

3 Inhalation unit exposure values represent no respirator. Value for low-pressure handwand is reported in the PHED Surrogate 

Exposure Guide dated August 1998, and that for hose-end sprayer was obtained from the ORETF data. 4 Daily Dose (mg/kg/day) = (Unit Exposure * Application rate * Area treated) / 70 kg. 5 Short-Term MOE = NOAEL (235 mg/kg/day) / Daily Dose. The LOC is 100. 

Page 9 of 12 
Page 10 of 12 

 4.2 Residential Postapplication Exposure and Risk

Turf transferrable residue (TTR) studies were submitted by the registrant (MRIDs: 47305124 and 

47305125) for use in assessing postapplication activities. The data from these studies were not 

used because TTR studies are only relevant for dermal exposure. The incidental ingestion 

assessment was conducted with standard assumptions for the initial fraction of residue available 

as well as other factors as specified by the Recommended Revisions to the Residential SOPs and 

recommended approaches by HED’s Science Advisory Council for Exposure (ExpoSAC). 

The exposure and risk estimates for the residential exposure scenarios are assessed for the day of 

application (day “0") because it is assumed that toddlers could contact the lawn immediately 

after application. The equations used for the exposure calculations and the results are presented 

in Tables 6 through 8. 

The exposure estimates are based on some upper-percentile (i.e., maximum application rate, 

initial amount of transferrable residue and duration of exposure) and some central tendency (i.e., 

surface area and body weight) assumptions and are considered to be representative of high-end 

exposures. The uncertainties associated with this assessment stem from the use of an assumed 

amount of pesticide available from turf, and assumptions regarding transfer of chemical residues 

and hand-to mouth activity. The estimated exposures are believed to be reasonable high-end 

estimates based on observations from chemical-specific field studies and professional judgment. 

The short-term MOEs for each scenario are greater than the LOC of 100, and are not of concern. 

The total short-term MOE resulting from conservatively combining MOEs for children (shown 

in Table 9) is 17,000, which is also above the LOC of 100, and not of concern. 

 4.3 Off Target Non-Occupational Exposure

Spray drift is always a potential source of exposure to residents nearby to spraying operations. 

This is particularly the case with aerial application, but, to a lesser extent, could also be a 

potential source of exposure from the ground application method employed for imazosulfuron. 

The Agency has been working with the Spray Drift Task Force, EPA Regional Offices and State 

Lead Agencies for pesticide regulation and other parties to develop the best spray drift 

management practices. The Agency is now requiring interim mitigation measures for aerial 

applications that must be placed on product labels/labeling. The Agency has completed its 

evaluation of the new data base submitted by the Spray Drift Task Force, a membership of U.S. 

pesticide registrants, and is developing a policy on how to appropriately apply the data and the 

AgDRIFT computer model to its risk assessments for pesticides applied by air, orchard airblast 

and ground hydraulic methods. After the policy is in place, the Agency may impose further 

refinements in spray drift management practices to reduce off-target drift and risks associated 

with aerial as well as other application types where appropriate. Note that imazosulfuron is 

directly applied to residential turf and does not result in exposures of concern. It is unlikely that 

spray drift would result in a higher potential for risk of exposure than the scenarios already 

assessed. 
Page 11 of 12 

Table 6. Postapplication Oral Hand-to-Mouth Exposure and Risk for Children from Treated Law

Application 

Rate 

 (lb ai/A) 

Postapplication 

day (t) 

Fraction of ai 

Transferrable 

from the 

Foliage 

Turf 

Transferrable 

Residue 1

(μg/cm2) 

Hand 

Surface 

Area 

(cm2/event) 

Saliva 

Extraction 

Factor 

 Frequency 

(events/ hr) 

Body 

Weight 

(kg) 

 Daily Dos(mg/kg/da

0.75 0 0.05 0.42 20 50% 20 15 0.011 

1 Turf Transferrable Residue Postapplication day (μg/cm2)= Application rate (lb ai/A) x Fraction of ai Transferrable from the Foliage x (1- Fraction of R

Dissipates Daily, 0.1) Postapplication day x 4.54E+8 μg/lb x 2.47E-8 A/cm2

2 Daily Dose = (Turf Transferrable Residue (μg/cm2) x Hand Surface Area (cm2/event) x Saliva Extraction factor x Frequency (events/hr) x 0.001 Exposure time (2 hrs/day)] / [Body Weight (kg)] 3 Oral MOE = Oral NOAEL/Daily Dose; where Short-term NOAEL = 235 mg/kg/day. 

Table 7. Postapplication Oral Object-to-Mouth (Turfgrass) Exposure and Risk for Children from Treat

Application Rate 

 (lb ai/A) 

Postapplication day 

(t) 

Fraction of ai 

Transferrable 

from the Foliage 

Grass/Object 

Residue 1

(μg/cm2) 

Ingestion Rate 

(cm2/day) 

Body 

Weight 

(kg) 

 Daily Dos(mg/kg/da

0.75 0 0.2 1.7 25 15 0.0028 

1Grass/Object residue Postapplication day (μg/cm2) = Application rate (lb ai/A) x Fraction of ai Transferrable from the Foliage x (1- Fraction of Residue 

Daily) Postapplication day x 4.54E+8 μg/lb x 2.47E-8 A/cm2

2 Daily Dose = [Grass reside (μg/cm2) x Ingestion rate (cm2/day) x 0.001 mg/μg] / [Body Weight (kg)]] 3Oral MOE = Oral NOAEL / Daily Dose; where Short-term NOAEL = 235 mg/kg/day. 

Table 8. Postapplication Incidental Soil Ingestion Exposure and Risk for Children from Treated Lawns

Application Rate 

 (lb ai/A) 

Fraction of ai 

Retained in the 

Soil 

Soil 

Residue 1

(μg/g) 

Ingestion Rate 

(mg/day) 

Body 

Weight 

(kg) 

 Daily Dose2(mg/kg/day) 

Short-term 

Oral 

MOE3

0.75 1 5.6 100 15 0.000038 6,300,000 

1 Soil residue Postapplication day zero (μg/cm2) = Application rate (lb ai/A) x Fraction of ai Retained on the Soil x (4.54E+8 μg/lb x 2.47E-8 A/cm2 x 0.62 Daily Dose = [Soil reside (μg/g) x Ingestion rate (mg/day) x 0.000001 g/μg] / [Body Weight (kg)]] 3 Oral MOE = Oral NOAEL/Daily Dose; where Short-term NOAEL = 235 mg/kg/day.
Table 9. Children’s Aggregate Exposure and Risk Estimates from Residential Lawns 

Children’s Scenarios 

TTR/GR/SR0

(ug/cm2 or g) 1

PDR0-norm

(mg/kg/day) 2

Short-Term 

MOE 3

Total 

Short-Term 

MOE 4

(1) Hand-to-Mouth 0.42 0.011 21,000 

(2) Mouthing Grass 1.7 0.0028 84,000 

(3) Soil Ingestion 5.6 0.000038 6,300,000 

17,000 

1

 TTR=turf transferable residue on day “0"; GR=grass residue on day “0"; SR0=soil residue on day “0". 2

 PDR0norm=potential dose rate on day “0”. 3 MOE = NOAEL/PDR; where Short-term NOAEL = 235 mg/kg/day.

4

 Total MOE = 1/ [(1/MOEHand-to-Mouth) + (1/MOEGrass) + (1/MOESoil)] 

Page 12 of 12