1

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

 OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

MEMORANDUM Date: April 3, 2012

DP Barcode: D393777 and 397770

PC Code 129081

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

of Sulfentrazone on Rhubarb, Turnip roots and tops, Sunflower Subgroup 

20B, Succulent Cowpea, Succulent Lima Bean, Wheat (Spring), Citrus Fruit 

Crop Group 10-10, Low Growing Berry Crop Group 13-07, Tree Nut Crop 

Group 14 and Pistachios, and Crop Group 18: Nongrass Animal Feeds

TO: Barbara Madden, Risk Manager

Laura Nollen, Risk Manager Reviewer

Registration Division (7504P)

Julie Langsdale Van Alstine, Chemist

Dana Vogel, Chief

Risk Assessment Branch 1

Health Effects Division (7509P)

FROM: Michael R. Barrett, Senior 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)

EFED has evaluated the proposed new uses on several crops (listed in Table 1 and determined 

that no changes are needed in the sulfentrazone drinking water exposure estimates from the 

previous assessment (see DP Barcode D349322; dated 8/28/2008; updated modeling showing no 

change in the estimated drinking water concentrations is located in the Appendix to this review). 
2

Application rates for the new uses (up to 0.375 lbs ai/A per season) are the same as for 

previously assessed uses and the addition of these uses does not change exposure estimates from 

the previous assessment (see Table 2 for a summary of these estimates). In general, sulfentrazone 

is persistent and mobile (for example, a 545-day aerobic soil half-life1 and an average Koc 

coefficient of 45 ml/g), and has a strong potential to leach into groundwater (this conclusion is 

reinforced by the four completed small-scale prospective ground-water monitoring studies for 

sulfentrazone) and move offsite to surface water, discussed below).

Table 1. New use information for sulfentrazone (based on proposed labels).

PROPOSED USE

EPA 

Reg NO.

SINGLE 

APP. 

RATE 

(lb. 

a.i./A)

NUMBER 

OF APPS.

SEASONAL 

APP. RATE 

(lb. a.i./A)

INTERVAL 

BETWEEN 

APPS. (days)

APP.

METHOD

PHI

(days)

Rhubarb

279-

3149

279-

3189

0.07-

0.375 1-2 or Not 

Specified 0.375 Not specified

Preplant, Preemergent

Ground

(Broadcast 

soil, banded, 

chemigation )

3-120

Turnip roots and tops

Sunflower Crop Subgroup 

20B

Spring wheat

Succulent cowpea

Succulent lima beans

Tree nut Crop Group 14 

including pistachios

Citrus Crop Group 10

Small berry and fruit Crop 

Group 13-07 

Non-grass animal feed 

Crop Group 18

Table 2. Estimated Tier 1 Concentrations of sulfentrazone and 3-carboxylic acid sulfentrazone in 

drinking water due to the use of sulfentrazone on crop sites such as sugarcane, cabbage, potatoes, 

mint, or horseradish.

Chemical Surface Water (ug/L) Groundwater (ug/L)

Acute Chronic Acute and Chronic

Sulfentrazone 32.1 5.1 15.7

3-Carboxylic Acid Sulfentrazone 3.7 2.7 10.3

Total 35.8 7.8 26.0

 1 90th percentile upper confidence interval of the mean half-life for all soils tested.
3

Prospective groundwater monitoring data have been submitted to the Agency for four sites 

tracking the movement of sulfentrazone and its degradate through the soil profile into 

groundwater after application. Maximum groundwater concentrations observed in each of these 

four studies are summarized in Table 3. The four sites were selected by the registrant to be 

representative of >99th (NC1 site), 95th (IN1 site), 85th (IN2 site), and 75th (IN3 site) percentile 

groundwater vulnerability in likely sulfentrazone use areas at the time of the studies. Although 

the maximum concentration observed at the NC1 site was higher than the estimated exposure 

from all sources for the combined residues, we continue to recommend use of the modeled 

values for Tier 1 drinking water estimation. This is because the conditions at this study site (by 

far the most vulnerable conditions of the test sites, but all four sites had high groundwater 

vulnerability) are unlikely to be reproduced at a drinking water well site. 

Table 3. Maximum observed concentrations of sulfentrazone and its acid degradate in shallow 

groundwater below or immediately downgradient of treated fields at four sites compared to Tier 

1 estimated concentrations using the SCI-GROW model.

Chemical NC1 

Site

IN1 

Site

IN2

Site

IN3 

Site

SCIGROW

Concentration in ppb (days after initial applic. of obs.)

Sulfentrazone 37.4

(160d)

0.86 

(577d)

0.11

(153d)

0.26

(634d)

15.7

3-Carboxylic Acid Sulfentrazone 11.4

(160d)

2.50 

(455d)

<5

(variable)

1.61

(1499d)

10.3

SITE DESCRIPTIONS:

NC1 = The test site was located near the town of near Tarboro in Edgecombe County, North Carolina, and was 

located in a setting classified as vey high vulnerability to groundwater contamination. Soil series = Tarboro sand to 

loamy sand. Sulfentrazone application rate = 0.50 lb ai/acre. (MRID 43345434 and 43926814). Average depth to 

groundwater = 9.2 feet. 

IN1 = The test site was located near the town of Leesburg in Kosciusko County, Indiana, and was located in a 

setting classified as 85th percentile in terms of vulnerability to groundwater contamination. Soil series = Tyner 

loamy sand to sandy loam. Sulfentrazone application rate = 0.17 lb ai/acre. Average depth to groundwater = 18.9 

feet. (MRID 46816001). 

IN2 = The test site was located near the town of Hanna in LaPorte County, Indiana, and was located in a setting 

classified as 95th percentile in terms of vulnerability to groundwater contamination. Soil series = Shipshe loamy sand 

to sandy loam. Sulfentrazone application rate = 0.22 to 0.44 lb ai/acre. Average depth to groundwater = 30 feet. 

(MRID 47453601).

IN3 = The test site was located near the town of La Porte in LaPorte County, Indiana, and was located in a setting 

classified as 75th percentile in terms of vulnerability to groundwater contamination. Soil series = Coupee silt loam. 

Sulfentrazone application rate = 0.22 lb ai/acre. Average depth to groundwater = 21 feet. (MRID 47453602).
4

The following conclusions from previous drinking water assessments are still appropriate with 

the addition of the newly requested uses on rhubarb, turnip roots and tops, and the sunflower 

group 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 3.82 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

 2 Current model runs estimate a peak of 3.735 ppb which is not significantly different.
5

APPENDIX

Updated FIRST Modeling Inputs and Results (for additional details see DP Barcode: D28497; 

review dated 4/17/2003):

FIRST Output File

 RUN No. 1 FOR Sulfentrazone ON Citrus etc * 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 ****** 58.66

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

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

 PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

 CONCENTRATION CONCENTRATION 

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

 32.102 5.047

 RUN No. 3 FOR Sulfentraz. acid ON Citrus Etc * INPUT VALUES * 

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

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

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

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

 .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 1.1.0 JAN 1, 2007

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

 PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) 

 CONCENTRATION CONCENTRATION 

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

 3.735 2.678
6

 

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

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

Results of Vadose Zone Monitoring at Four Prospective Groundwater 

Monitoring Sites

Table 4. Maximum observed concentrations of sulfentrazone and its acid degradate in soil-pore 

water 7- to 9-feet below the surface of treated fields at four sites compared to Tier 1 estimated 

concentrations using the SCI-GROW model.

Chemical NC1 

Site

IN1 

Site

IN2

Site

IN3 

Site

SCIGROW

Sulfentrazone 22.5

(186d)

0.28

(911d)

0.35* 

(1229d)

0.09

(1149d)

15.7

3-Carboxylic Acid Sulfentrazone 38.1

(186d)

4.28 

(577d)

3.36

(363d)

0.07

(753d)

10.3

* Also at 0.44 ppb 2135 days after the original application after an additional application 1961 days after the initial 

application. The degradate was detected at a maximum concentration of 0.33 ppb at 2226 days after this last 

application.