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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

OFFICE OF PREVENTION, PESTICIDES AND TOXIC SUBSTANCES

MEMORANDUM Date: 8/28/08

SUBJECT: Drinking Water Exposure Assessment for the Section 3 New Use Registration 

of Sulfentrazone on Head/Stem Brassica Subgroup 5A, Leafy Greens 

Subgroup 5B, Melon Subgroup 9A, Fruiting Vegetable Group 8, Okra, 

Succulent Pea, Strawberry and Tuberous/Corm Vegetable Subgroup 1C. 

PC Code No.129081; DP Barcode: D349322.

TO: Daniel Rosenblatt, Risk Manager

Registration Division (7504P)

George Kramer, Senior Chemist

Dana Vogel, Chief

Registration Action Branch 1

Health Effects Division (7509P)

FROM: Michael R. Barrett, Chemist

Environmental Risk Branch V 

Environmental Fate and Effects Division (7507P)

THROUGH: Mah T. Shamim, Ph.D., Chief

Environmental Risk Branch V

Environmental Fate and Effects Division (7507P)

The previous assessment for the multiple uses of Sulfentrazone (D284975, D274982, D285501, 

D285504, D285739, D256211, D285274, D284711 and D274569; included in this review was a 

drinking water assessment) can be used in place of a new assessment for the currently proposed 

multiple uses of SPARTAN 4F (39.6% AI) and SPARTAN 75DF (75% AI). Application rates 

(0.1875 to 0.375 lbs ai/A per season) are the same as for previously assessed uses and risks 

should be similar. 

Sulfentrazone appears to be persistent and mobile, and has a strong potential to leach into 

groundwater (this conclusion is reinforced by completed or nearly completed small-scale 
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prospective ground-water monitoring studies1) and move offsite to surface water. The following 

conclusions from the above mentioned drinking water assessments are still appropriate with the 

addition of the newly requested uses on various vegetable crops:

Tier I Estimated Drinking Water Concentrations (EDWCs) for sulfentrazone and its 

major degradate (3-carboxylic acid sulfentrazone) were calculated using FIRST (surface 

water) and SCIGROW (ground water) for use in the human health risk assessment. EFED 

believes that the Tier I models used for these crops provide a reasonable worst case 

scenario and provide estimates suitable for screening purposes. For surface water, the 

acute (peak) sulfentrazone value is 32.0 ppb and the annual average value ranges from 

0.5 ppb in alkaline or neutral waters (most common) to 5.1 ppb in acidic waters. The 

groundwater screening sulfentrazone concentration is 15.7 ppb. For 3-carboxylic acid 

sulfentrazone, the acute peak is 3.8 ppb and the annual average is 2.7 ppb. For 3-

carboxylic acid sulfentrazone in groundwater, the concentration is 10.3 ppb. 

- Source: DP Barcode: D284975, “Tier I Estimated Environmental Concentrations of 

Sulfentrazone and Degradate 3-Carboxylic Acid Sulfentrazone for Use in the Human Health Risk 

Assessment”, review document dated 4/17/2003. See also DP Barcode 284975 et al., “EFED 

Section 3 and IR-4 Registration Chapter for Sulfentrazone...”, review document dated 6/16/2003

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Note that even at sites where sulfentrazone / 3-carboxylic acid sulfentrazone did not leach all the way to ground 

water that the limited amount of net recharge of ground water during the course of the studies limited the amount of 

leaching. Further details on these studies and on other monitoring data for sulfentrazone residues are provided in the 

aforementioned risk assessment documents.
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APPENDIX I: Tier I Drinking Water Memorandum (taken from the original 

electronic document)

U. S. ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, DC 20460

OFFICE OF 

PREVENTION, PESTICIDES

AND TOXIC SUBSTANCES 

April 17, 2003

DP Barcode: D284975

PC Code 129081

MEMORANDUM

SUBJECT: Tier I Estimated Environmental Concentrations of Sulfentrazone and 

Degradate 3-Carboxylic Acid Sulfentrazone for Use in the Human Health 

Risk Assessment

FROM: Ronald Parker, Senior Environmental Engineer, Ph.D.

Larry Liu, Environmental Scientist, Ph.D.

Environmental Risk Branch V

Environmental Fate and Effects Division (7507C)

THROUGH: Mah T. Shamim, Ph.D., Chief

Environmental Risk Branch V

Environmental Fate and Effects Division (7507C)

TO: Joanne Miller, Product Manager

Registration Division 

and George Kramer

Health Effects Division

Summary. This memo presents the Tier I Estimated Drinking Water Concentrations (EDWCs) 

for the herbicide Sulfentrazone and degradate 3-carboxylic acid sulfentrazone. These estimates 

are calculated using FIRST (surface water) and SCIGROW (ground water) for use in the human 

health risk assessment. EFED believes that the Tier I models used for these crops provide a 

reasonable worst case scenario and provide estimates suitable for screening purposes.

For surface water, the acute (peak) value is 32.0 ppb and the annual average value ranges 

from 0.5 ppb in alkaline or neutral waters (most common) to 5.1 ppb in acidic waters. The 

groundwater screening concentration is 15.7 ppb. For 3-carboxylic acid sulfentrazone, the 

degradate of concern, the acute peak is 3.8 ppb and the annual average is 2.7 ppb. The 
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groundwater concentration is 10.3 ppb. See results in Tables 2 and 3 below. These values 

generally represent upper-bound conservative estimates of the total residues concentrations that 

might be found in surface water and groundwater due to the use of Sulfentrazone on sugarcane, 

cabbage, potatoes, mint or horseradish. These crops were chosen for this assessment because the 

label permits use of the maximum application rate (0.375 pounds active ingredient per acre) and 

aerial application. Aerial application has the potential for most spray drift and is not compatible 

with incorporation which would reduce surface water concentration values. Additional 

refinements can be developed should they be needed by HED.

Estimation of Drinking Water Concentrations

Tier I Estimated Drinking Water Concentrations (EDWCs) for the herbicide Sulfentrazone and 

degradate 3-carboxylic acid sulfentrazone were calculated using FIRST (surface water) and 

SCIGROW (ground water) for use in the human health risk assessment. Descriptions of the 

FIRST and SCIGROW screening models are included at the end of this document. 

Modeling Approach for Parent Sulfentrazone:

Sulfentrazone labels indicate that the worst case scenarios are for sugarcane, cabbage, potatoes, 

mint or horseradish. These crops were chosen for this assessment because the label permits use 

of the maximum application rate of 0.375 pounds active ingredient per acre and aerial 

application. Aerial application has the potential for most spray drift and also is not compatible 

with incorporation of the pesticide into the soil which would reduce surface water concentration 

values. The assessment uses the default percent cropped area (PCA) of 0.87. Laboratory studies 

indicate that the main mechanism of degradation is photolysis. The FIRST model assumes a 

fairly cloudy reservoir and so photolysis takes place only near the surface where exposure to 

sunlight is greatest. The photolysis half-life is about 12 hours in acidic waters (pH5) and 

approximately one hour in the more common neutral (pH7) and alkaline (pH9) waters. Acidic 

waters where chronic concentrations would potentially be the highest are most commonly found 

in the northeastern part of the US.

Modeling Approach for Degradate 3-Carboxylic Acid Sulfentrazone:

The primary degradate of concern, 3-carboxylic acid sulfentrazone, was also simulated using the 

screening models, FIRST and SCIGROW. Because there is no environmental fate data for this 

degradate, it is assumed to be completely mobile and persistent. This degradate reaches a 

maximum of 11% of the applied parent. It is simulated by multiplying the label application rate 

by 11% and setting the Koc to zero and the half-life to stable. The FIRST results are shown in 

the output file in Table 2 below.

In the SCIGROW modeling, the maximum concentration value exceeds the model limit (which 

is set at the application rate times 250.) The concentration is therefore set to this limit.(In this 

case this is, 0.375 pounds per acre times 11% times 250.) This gives a value of 10.3 ppb. The 

total value of parent plus degradate is 15.7 plus 10.3 for a total of 26 ppb. 
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Groundwater Monitoring for Parent and Degradate

SCIGROW results presented are consistent with the field monitoring study which shows a 

maximum three month average total parent plus degradate value of from13 to 20 ppb.

Table 1. Summary of Input Parameters for Tier I Estimated Drinking Water Concentrations (EDWC’s)

Parameter Sulfentrazone

Model SCIGROW

Label Application

Rate (lb a.i./A) 

0.375

Label Max. Seasonal Number

of Applications

1 (sugarcane, cabbage, potatoes, 

mint or horseradish)

Mean Aerobic Soil 

Metab. Half-life (Days)

545

(MRIDs 41928203, 42932117)

Median KOC 43

(MRID 41911604, 43355903)

Model FIRST

Upper 90th Percentile Aerobic Soil 

Metab.Half-life (Days)

545

(MRID 41928203, 42932117)

Lowest Non-Sand Koc, (L/kg) 43

(MRID 41911604)

Pesticide Wetted In? No

Method of Application Aerial

Solubility (ppm) 400

(Product Chemistry Submissions)

Aerob. Aquatic Metab 

Half-life (Days)

1095

(2x Aerob. Aquatic 

Metab Half-life)

Hydrolysis, 

Half-life: pH 7 (Days)

Stable

(MRID 41928202)

Aqueous Photolysis 

Half-life: pH 5 (Days)

0.5

(MRID 43345424, 43588601)

Aqueous Photolysis 

Half-life: pH 7-9 (Days)

0.042

(MRID 43345424, 43588601)

PCA (Sugarcane) 0.87

Background Information on FIRST Model:

FIRST is a screening model designed to estimate the pesticide concentrations found in water for 

use in drinking water assessments. It provides high-end values on the concentrations that might 

be found in a small drinking water reservoir due to the use of pesticide. Like GENEEC, the 

model previously used for Tier I screening level, FIRST is a single-event model (one run-off 
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event), but can account for spray drift from multiple applications. FIRST takes into consideration 

the so called Index Drinking Water Reservoir by representing a larger field and pond than the 

standard GENEEC scenario. The FIRST scenario includes a 427 acres field immediately adjacent 

to a 13 acres reservoir, 9 feet deep, with continuous flow (two turnovers per year). The pond 

receives a spray drift event from each application plus one runoff event. The runoff event moves 

a maximum of 8% of the applied pesticide into the pond. This amount can be reduced due to 

degradation on field and the effect of binding to soil. Spray drift is equal to 6.4% of the applied 

concentration from the ground spray application and 16% for aerial applications.

FIRST also makes adjustments for the percent crop area. While FIRST assumes that the entire 

watershed would not be treated, the use of a PCA is still a screen because it represents the highest 

percentage of crop cover of any large watershed in the US, and it assumes that the entire crop is 

being treated. Various other conservative assumptions of FIRST include the use of a small 

drinking water reservoir surrounded by a runoff-prone watershed, the use of the maximum use 

rate, no buffer zone, and a single large rainfall.

Background Information on SCIGROW:

SCIGROW provides a groundwater screening exposure value to be used in determining the 

potential risk to human health from drinking water contaminated with the pesticide. Since the 

SCIGROW concentrations are likely to be approached in only a very small percentage of drinking 

water sources, i.e., highly vulnerable aquifers, it is not appropriate to use SCIGROW for national 

or regional exposure estimates.

SCIGROW estimates likely groundwater concentrations if the pesticide is used at the maximum 

allowable rate in areas where groundwater is exceptionally vulnerable to contamination. In most 

cases, a large majority of the use area will have groundwater that is less vulnerable to 

contamination than the areas used to derive the SCIGROW estimate.
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Table 2. FIRST Modeling Inputs and Results:

FIRST Output File

RUN No. 1 FOR SULFENTRAZONE ON SUGARCANE * INPUT VALUES * 

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

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

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

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

.375( .375) 1 1 43.0 400.0 AERIAL(16.0) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

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

METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

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

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

545.00 2 N/A .50- 62.00 1090.00 58.66

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

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

PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

CONCENTRATION CONCENTRATION 

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

32.169 5.058

RUN No. 2 FOR SULFENTRAZONE ON SUGARCANE * INPUT VALUES * 

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

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

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

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

.375( .375) 1 1 43.0 400.0 AERIAL(16.0) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

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

METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

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

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

545.00 2 N/A .04- 5.17 1090.00 5.14

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

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

PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

CONCENTRATION CONCENTRATION 

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

31.548 .494

RUN No. 1 FOR 3-carboxylic acid ON SUGARCANE * INPUT VALUES * 

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

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

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

.041( .041) 1 1 .0 400.0 GRANUL( .0) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS) 

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

METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

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

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

.00 2 N/A .00- .00 .00 .00

UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.0 AUG 1, 2001

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

PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

CONCENTRATION CONCENTRATION 

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

3.765 2.700

Table 3. SCIGROW Modeling Input and Results

SCIGROW 

VERSION 2.2: NOVEMBER 1, 2001 

RUN No. 1 FOR SULFENTRAZONE ** INPUT VALUES ** 

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

APP RATE APPS/ TOTAL/ SOIL AEROBIC SOIL METAB 

(LBS/AC) YEAR SEASON KOC HALFLIFE (DAYS) 

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

.375 1 .375 43.0 545.00

GROUND-WATER SCREENING CONCENTRATION (IN UG/L - PPB) 

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

15.701670

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