UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

PC Code: 118602

DP Barcode: 402305

Date: August 16, 2012

MEMORANDUM

SUBJECT: Tier I Drinking Water Assessment for the Section 3 Proposed Registration of 

Imazosulfuron on Melon Subgroup 9A and Tuberous and Corm Subgroup 1C

TO: Andrew Ertman, Risk Manager Reviewer

Barbara Madden, Risk Manager 

Herbicide Branch

Registration Division

FROM: Faruque Khan, Ph.D., Senior Scientist

Environmental Risk Branch I

Environmental Fate and Effects Division

APPROVED

BY: Nancy Andrews, Ph.D., Branch Chief

Sujatha Sankula, Ph.D., Lead Biologist

Environmental Risk Branch I

Environmental Fate and Effects Division

A Tier I screening-level drinking water assessment was conducted to support the human health 

risk assessment for the Section 3 proposed new use registration of imazosulfuron. Modeled 

application rates represent the maximum application rates on the proposed label for use on the 

melon subgroup 9A and the tuberous subgroup IC (EPA Reg. No. pending). Foliar ground spray 

application (ground spray) is proposed for new uses. Tier 1 surface water and groundwater 

modeling was conducted for two ground spray applications with 45 days interval for the tuberous 

and corm subgroup 1C at a rate of 0.15 lb a.i./A. In addition, Tier 1 surface water modeling was 

also conducted for one ground spray application for melon subgroup 9A use at a rate of 0.3 lb

a.i./A per year.

The estimated drinking water concentrations (EDWCs) for tier 1 models are listed in Table 1. 

These values are lower than the previously reported EDWC of 278.9 μg/L for acute and chronic 

exposures for surface water based on rice scenario and 4.8 μg/L for acute and chronic exposures

for ground water based on turf scenario (USEPA 2010a, DP 362654). Therefore, the previously 
recommended EDWCs should be retained for drinking water exposure assessment for human 

health risk assessment purposes.

Table 1. Tier I EDWCs for Imazosulfuron for Melon Crop Subgroup 9A and Tuberous and Corm

Subgroup 1C uses

Drinking 

Water Source 

Models Application 

rate (lbs 

a.i./A/year)

Application 

Frequency

Acute (μg/L) Chronic (μg/L)

Surface water FIRST 0.15 2 27.0 8.9

0.30 1 25.1 8.2

Groundwater SCI-GROW 0.15

0.30

2

1

0.4

0.4

0.4

0.4

1.1 Drinking Water Exposure Modeling

The EDWCs were generated using EFED’s standard suite of models. Since there is no 

modification of input parameters for FIRST and SCIGROW models, detailed description of 

models and inputs parameters can be obtained from the previous assessment (USEPA, 2010a,. 

However, inputs for FIRST in Table A-1 and for SCIGROW in Table A-2 as well as outputs of 

FIRST and SCIGROW models for proposed uses were provided in the Appendix A.

Descriptions of all executable versions of current models used in drinking water exposure can be 

obtained from URL link (http://www.epa.gov/oppefed1/models/water/).

Standard percent cropped areas (PCA) were used for proposed uses as estimates of the extent of 

watershed on which crops is grown. The default agricultural PCA of 1.0 was used for the 

proposed uses because imazosulfuron can be used for agricultural and non-agricultural settings 

(USEPA 2010b). 

1.2 Monitoring Data

There were no national-scale monitoring data available for this new chemical assessment. 

1.3 Drinking Water Treatment

There is no available information on the drinking water treatment effects on imazosulfuron.

2 Conclusions

The estimated drinking water concentrations (EDWCs) for surface water and groundwater are 

lower than the previously reported EDWC of 278.9 μg/L for acute and chronic exposures for 

surface water based on rice scenario and 4.8 μg/L for acute and chronic exposures for ground 

water based on turf scenario (USEPA 2010a, DP 362654). Therefore, the previously

recommended EDWCs should be retained for drinking water exposure assessment for human 

health risk assessment purposes.
The estimated concentrations provided in this assessment are conservative estimates of 

imzosulfuron concentrations in untreated drinking water. A major source of uncertainty is the 

nature of the non-extractable residues formed during degradation in soils. Non-extractable 

residues were identified at maximums of 33-88% of applied radioactivity in aerobic soil, aerobic 

and ananerobic aquatic metabolism studies. The non-extractable residues are uncharacterized and 

it is uncertain whether they consist of degradates of risk concern. Under sterile conditions these 

non-extractables were not formed suggesting that the formation of them is microbially mediated. 

If dietary risks require refinement, higher tiered models and modeling scenarios can be utilized

to characterize EDWCs upon request.

Appendix A

Table 3. FIRST (v 1.1) input parameter values for total residuea of imazosulfuron applied by ground spray

Parameter Value Source Comments

Application Rate (lb a.i./A) 0.3 As per V-10142 label 

Direction ---

Number of Applications

2 (Crop subgroup 

1C))

1 (Crop subgroup 

9A)

As per V-10142 label 

Direction ---

Minimum Application 

Intervals (days)

45 (Crop subgroup 

1C))

As per V-10142 label 

Direction For Ground Application 

Soil Partitioning Coefficient 

(Kfoc; ml/goc) 98 MRID 47305122 lowest non-sand valueb

Aerobic Soil Metabolism t1/2

(d) 207.15

MRID 473051-17 

MRID 477668-01

90th percentile upper confidence 

bound on the mean half-life of 

total toxic residue of 

imazosulfuron

Wetted in? No foliar applied As per V-10142 label Direction

Depth of Incorporation 

(inches) 0 foliar applied As per V-10142 label Direction

Methods of Application Ground spray As per V-10142 label 

Direction As per V-10142 label Direction

Percent Cropped Area 0.87 National default

Input parameter guidance

(USEPA, 2002)

Solubility in Water (mg/L) 419 Product chemistry data

Input parameter guidance

(USEPA, 2009)

Aerobic Aquatic Metabolism 

t1/2 (d) 192.03

MRID 476397-02

MRID 476791-05

90th percentile upper confidence 

bound on the mean half-life of 

total toxic residue of 

imazosulfuron
Table 3. FIRST (v 1.1) input parameter values for total residuea of imazosulfuron applied by ground spray

Parameter Value Source Comments

Hydrolysis t1/2 at pH 7.0

(days)

0 MRID 473051-19 Stable to hydrolysis @ pH 7.0

Aquatic Photolysis t1/2 (d) 61.69 MRID 473051-20

90th percentile upper confidence 

bound on the mean of IM and 

PM rings of imazosulfuron

a = Residues of concern (Parent plus degradates, i.e., HMS, IPSN, UDPM, ADPM and SDPM) recommended by 

Residues of Concern Knowledgebase Subcommittee (ROCKS) 

b = According to Guidance for selecting input parameters in modeling for environmental fate and transport of 

pesticides. Version II. October, 2009.

Table 4. SCIGROW 2.3 input parameter values for total residue of Imazosulfuron applied by ground spray.

Parameter Value Source Comments

Maximum Application 

Rate (lb a.i./A/application)

0.67 Ground Application As per V-10142 label Direction

Maximum Number of 

Applications per Year

2 Ground Application As per V-10142 label Direction

Aerobic Soil Metabolism 

Half-life (d)

94.3 MRID 473051-22 Mean Value a

Organic Carbon Partition 

Coefficient (Kfoc, ml/goc)

98 MRID 473051-17 Lowest non-sand value a

a = According to Guidance for selecting input parameters in modeling for environmental fate and transport of 

pesticides. Version II. October, 2009.
References

Environmental Fate and Effects Division. 2009. Guidance for Selecting Input Parameters in 

Modeling the Environmental Fate and Transport of Pesticides, Version II. U. S. Environmental 

Protection Agency. Washington, D.C. http://www.epa.gov/oppefed1/models/water/

US EPA. 2010a. 2010. Tier I Drinking Water Assessment for the Section 3 Proposed

Registration of Imazosulfuron on Turf, Tomato, Peppers (Bell and Non-bell) and Rice (DP 

362654)

US EPA. 2010b. Guidance on development and use of the index reservoir in drinking water 

exposure assessment. http://www.epa.gov/oppefed1/models/water/index_reservoir_dwa.html 
Appendix A

Surface water (FRIST)

Ground Application

RUN No. 1 FOR Imazosulfuron ON Melon * INPUT VALUES * 

 --------------------------------------------------------------------

 RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

 ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

 --------------------------------------------------------------------

 .300( .300) 1 1 98.0 419.0 GROUND( 6.4) 100.0 .0

 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

 --------------------------------------------------------------------

 METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

 (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.-EFF) (RESER.) (RESER.) 

 --------------------------------------------------------------------

 207.20 2 N/A 61.69- 7649.56 192.03 187.33

 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 JAN 1, 2007

 --------------------------------------------------------------------

 PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

 CONCENTRATION CONCENTRATION 

 --------------------------------------------------------------------

 26.972 8.863

 RUN No. 2 FOR Imazosulfuron ON Tuberous * INPUT VALUES * 

 --------------------------------------------------------------------

 RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP

 ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

 --------------------------------------------------------------------

 .150( .279) 2 45 98.0 419.0 GROUND( 6.4) 100.0 .0

 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

 --------------------------------------------------------------------

 METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

 (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.-EFF) (RESER.) (RESER.) 

 --------------------------------------------------------------------

 207.20 2 N/A 61.69- 7649.56 192.03 187.33

 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 JAN 1, 2007

 --------------------------------------------------------------------

 PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

 CONCENTRATION CONCENTRATION 

 --------------------------------------------------------------------

 25.082 8.241
 

 

Ground water

 SCIGROW

 VERSION 2.3

 ENVIRONMENTAL FATE AND EFFECTS DIVISION

 OFFICE OF PESTICIDE PROGRAMS

 U.S. ENVIRONMENTAL PROTECTION AGENCY

 SCREENING MODEL

 FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3

chemical:Imazosulfuron

time is 8/15/2012 10:57:46

------------------------------------------------------------------------

 Application Number of Total Use Koc Soil Aerobic

 rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------

 0.150 2.0 0.300 9.80E+01 94.3

------------------------------------------------------------------------

groundwater screening cond (ppb) = 3.99E-01 

************************************************************************

SciGrow version 2.3

chemical:Imazosulfuron

time is 8/15/2012 10:58: 0

------------------------------------------------------------------------

 Application Number of Total Use Koc Soil Aerobic

 rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------

 0.300 1.0 0.300 9.80E+01 94.3

------------------------------------------------------------------------

groundwater screening cond (ppb) = 3.99E-01 

************************************************************************