### UNITED STATES ENVIRONMEN TAL PROTECTION AGENCY WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION



### PC Code: 129009 DP Barcode: 391086 Date: 3/15/12

MEMORANDUM

SUBJECT: Tier I Estimated Drinking Water C oncentrations of Rimsulfuron, for the Use in the Human Health Risk Assessment: New Use Request for the Use of Rimsulfuron on “Chryosolite” Va riety of Sulfonylurea Tolerant Chicory.

TO: Andrew Ertman, Risk Manager Reviewer Barbara Madden, Risk Manager Herbicide Branch Registration Division (7505P)

AND: Cassi Walls, Lead Assessor Paula Deschamp, Chief Registration Action Branch III Health Effects Division (7509P)

FROM: Michael Barrett, Senior Chemist Environmental Risk Branch 5 Environmental Fate a nd Effects Division (7507P)

THROUGH: Mah Shamim, Ph.D., Branch Chief Environmental Risk Branch 5 Environmental Fate a nd Effects Division (7507P)

This memorandum updates the Tier 1 Estim ated Drinking Waters Concentrations (EDWCs) for surface and ground waters for rimsulfuron, a pyrimidinyl sulfonylurea herbicide (CAS name: N -[[(4,6-dimethoxy-2-pyri midinyl)amino]carbonyl]-3- (ethylsulfonyl)-2-pyridinesul fonamide; CAS No. 122931-48-0), ca lculated using the Tier 1 aquatic models FIRST and SCI-GROW, for us e in the human health risk assessment. This update is based upon a Section 3 New Use request for the use of Rimsulfuron [BASIS® Herbicide (Reg. No. 352-571)]. The a pplication is for the use of this product only on the “Chrysolite” variety of sulf onylurea tolerant chic ory. The proposed

### 2 application rate is 0.3 ounces per acre, which is equivale nt to 0.00938 lb ai/acre. The product, BASIS®, contains two active ingredie nts that include thifensulfuron methyl at 25% and rimsulfuron at 50% by weight; only expos ure to rimsulfuron is addressed in this review.

Drinking water exposure to rimsulfuron has previously been estimated (DP Barcode D384624; 10/27/11) for other uses which dr ive exposure according to the Tier 1 modeling; the new use at a much lower rate (i.e., maximum annual application of 0.00938 lb ai/acre versus 0.06250 lb ai /acre). We have updated, howev er, the previous estimates based upon a revision of the aerobic soil degr adation rate for rimsulfuron using data submitted under MRID 48332003; please see the Appendix for a summary of the model input. We additionally note that there is no difference in the use pattern for the new use on chicory that would modify the inputs for the Tier 1 modeling to the extent that the highest previously calculated estimated dr inking water concentrations would change. Should there be the need; additional levels of refinements are possible with a higher tier
assessment.

For rimsulfuron, the surface water acute dri nking water exposure value has been revised slightly downward to be 5.396 ppb or ug/L (previously 5.596 ppb), and the cancer/ chronic value is now 0.116 ppb (previously it was 0.120 ppb). The groundwater screening concentration from the highest exposure uses of rimsulfuron associated with drinking well water is now 0.029 ppb (previously it was 0.016 ppb of rimsulfuron). The groundwater screening concentration is suitab le for acute and chronic exposure (see the Appendix for further details on the updated modeling).

### 3 

## APPENDIX: Exposure Modeling Input and Output

Below is a revised input parameter model

Table A1. FIRST input parameters for modeling drinki ng water EDWCs

Input Parameter Value* Reference

Application Rate (lb a.i./Acre) 0.0625 (One Application) Maximum label rate/Minimum application intervals (Product Label) Application Intervals (days) Does not apply, 1 applic.
Percent Crop Area 0.83 Corn and soybeans

Partition Coefficient “K OC ” (L/Kg) 19 Lowest non-sand value (MRID 413563-36)

Aerobic Soil Metabolism Half-life (days) 44.8 Determined by calculating 90th percentile confidence bound on the mean half-life value (MRID 413563-34 and 483320-03); the half-lives from th e 3 available studies were 21.3, 21.5, and 48.1 days.

Wetted In? No
Product Label Depth of Incorporation (inches) 0 Method of Application Aerial
Solubility in Water (ppm) 7.3 MRIDs: 419316-02 and 413563-01.
Aerobic Aquatic Metabolism Half-life (days) The experiment was exposed to artificial light source thus the value was not used and hydrolysis half-live was entered.
Hydrolysis Half-life @ pH 7 (days) 7.2 Average value at pH 7 (MRID 413563-33)
Direct Aqueous Photolysis Halflife(days) Stable Half-lives in dark<irradiated samples (MRID 419316-08)
* Fate data values are as per Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides; Version II, February 28, 2002.



### Table 7 . SCI-GROW input parameters for mode ling drinking water from ground water (EDWCs).

Input Parameter Value Reference

Application Rate (lb a.i./Acre) 0.0625 Maximum Yearly Application rate (Product Label) Maximum Number of Applications/Year 1

Partition Coefficient “K oc ” (L Kg -1 ) 55 Median of 4 values (<3 fold variations in K oc s (MRID 413563-36)

Aerobic Soil Metabolism Half-life (days) 30.3 Average of half-lives measured in 3 soils (MRID 413563-34 and 483320-03)

### 4 

## FIRST Model Output files

RUN No. 2 FOR Rimsulfuron ON Fruit Tree * INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- .063( .063) 1 1 19.0 7.3 GROUND( 6.4) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.-EFF) (RESER.) (RESER.)

-------------------------------------------------------------------- 64.00 2 7.20 .00- .00 .00 7.20

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

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

-------------------------------------------------------------------- 5.445 .117

RUN No. 4 FOR Rimsulfuron ON Fruit Tree * INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE %CROPPED INCORP ONE(MULT) INTERVAL Koc (PPM ) (%DRIFT) AREA (IN)

-------------------------------------------------------------------- .063( .063) 1 1 19.0 7.3 GROUND( 6.4) 87.0 .0

FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (RESERVOIR) (RES.-EFF) (RESER.) (RESER.)

-------------------------------------------------------------------- 44.80 2 7.20 .00- .00 .00 7.20

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

-------------------------------------------------------------------- PEAK DAY (ACUTE) ANNUAL AVERAGE (CHRONIC) CONCENTRATION CONCENTRATION

-------------------------------------------------------------------- 5.396 .116

### 5 

## SCI-GROW Model Output files

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:Rimsulfuron time is 3/15/2012 12:50:11

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-- Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

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

-- 30.300 1.0 30.300 5.50E+01 30.3

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

-- groundwater screening cond (ppb) = 1.39E+01

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

SciGrow version 2.3 chemical:Rimsulfuron time is 3/15/2012 12:51:55

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

-- Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

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

-- 0.063 1.0 0.063 5.50E+01 30.3

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

-- groundwater screening cond (ppb) = 2.86E-02

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