Document ID: EPA-HQ-OPP-2008-0125-0006
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-02-02T05:00Z

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 prospective ground-water
monitoring studies) 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



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 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. 

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 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.

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)

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

   .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

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

 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
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