UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

OFFICE OF PREVENTION, PESTICIDES, AND

TOXIC SUBSTANCES PC Code: 005209 DP BARCODE: D361926 MEMORANDUM July 24 , 2009 SUBJECT: Tier I Drinking Water Exposu re Assessment for the Section 3 New Use of

Triisopropanolamine Salt of Aminopyralid on Field Corn and Field Corn Grown for Ensilage. TO: Douglas Dotson , Chemist

Health Effects Division (7509P) Kathry n Montague, Product Manager Registration Division (75 05P) FROM: Reuben Baris, Environmental Scientist

Environmental Fate and Effects Division (7507P) Office of Pesticide Programs REVI EWED BY: Marietta Echeverria, Senior Environmental Scientist

Environmental Fate and Effects Division (7507P) Office of Pest icide Programs
THRU: Elizabeth Behl, Branch Chief

Environmental Fate and Effects Division (7507P) Office of Pesticide Programs This memo summarizes the Tier I estimated drinking water concentrations (EDWC) for Triisopropanolamine Salt of Aminopy ralid (TIPA Salt) in surface water and in ground water in support of the Section 3 New Use on field corn and field corn grown for ensilage . Aminopy ralid is a py ridine carbox yl ic acid herbicide to be used for annual and per ennial broadleaf weed control for field corn and field corn grown for ensilage . Based on available data, aminopy ralid is moderatel y persistent to persistent and highl y mobile. The EDWCs for both surface and ground water recommended for use in HED’s huma n health risk assessment are summarized in Table 1 and are based on the registered use on rangel an d grasses and wheat
. The E DW Cs resulting from the proposed application rate are lower than the E DW Cs for surface and ground water in the previous drinking water assessment for aminop yr alid (D301682 )
. Since t he proposed applicationrates for field corn and field corn grown for ensilage are lower than other registered uses, it is

expected that the EDWCs resulting from the proposed application rates for field corn and field corn grown for ensilage wil l be lower, all other variables being equal. EFED used the screening model FIRST (FQPA In dex Reservoir Screening Tool, version 1. 1 , 0 1 /01/0 7 ) to calculate the surface water EDWCs. The FIRST
- calcul ated acute value represents a 1
- in
- 10 y ear peak value an d the chronic value represents the 1
- in
- 10 y ear annual mean. Estimated ground water EDWCs were calculated using the screening model SCI
- GROW (Screening Concentrations in Ground Water, version 2.3, 07/29/ 03). The SCI
- GROW
- calculated value should be used t o represent both acute and chronic exposure. Table 1. Tier I EDWCs for drinking water risk assessment based on aminopyralid use on rangeland grasses (application rate of 0.11 lbs a.e./A/yr) (D301682)

Surface water drinking water sources acute: 10.024 ppb chronic: 1.937 ppb Groundwater drinking water sources 0.630 ppb

The concentrations presented in Table s 2 and 3 are the result of an implied maximum application rate (0.57 fluid oz/acre) on the proposed supplemental label for use on field corn and field corn grown for ensilage
. The l abel indicates, in the section titled “ Maximum Application Rate ” , “ Use Precautions and Restrictions ” section :

“An application rate of Milestone in excess of 0.57 fluid oz per acre can [cause

] [ injur y ] to corn and redu ce yield.” While our assessment, EFED assumes this represents the maximum application rate, in fact there is no maximum rate on the label. Revising th e label to stipulate a maximum rate would eliminate this uncertainty (e.g. “do not exceed 0.57 fluid oz per acre for a single application.” ). Although t here is little difference in the peak and chronic E DW Cs resulting from 3 applications at the lower rate vs. a single application at the maximum annual rate, the revised language will avoid mis interpretation and p otential injury to the crop. This assessment uses data from registrant
- submitted fate studies for aminopy ralid
. Both the aminopy

ralid TI PA salt and aminopy ralid acid will dissociate in the environment to y ield the free anion (PC code: 005100) . T he dissociation process is governed by an equilibrium constant which is so low (pKa of 2.56) that greater than 99.9% of the compound will be in the anion form at environmental pH ranges, regardless of the original molecular species (US EPA, 2005)
. A minopy ra lid is expected to be moderatel y persistent to persistent and highly mobile in the environment. Since it is stable to hy drol ys is and aerobic and anaerobic aquatic metabolism, and moderatel y degraded b y aerobic metabolism in some soils, transport of aminop yr alid to surface water and ground water is likely
.T he 2005 Aminopy ralid: Tier I Estimated Drinking Water Concentrations (EDWC) for Use in the Human Health Risk Assessment was conducted for the parent compound. The only degradates of aminop yr alid were observed in the a queous photoly sis study (MRI D 46235727) , identified as oxamic acid (CAS#471
- 47
- 6) and malonamic acid (CAS# 2345
- 56
- 4), plus unidentified degradates 2
- 3
- carbons long, with O, N, and other substituents. No environmental degradates other than CO 2 and bound residues were observed in the remaining fate studies (D301682)
. Based on the available information, HED does not believe that it is appropriate to include residues of either oxamic acid or malonamic acid in dietary risk assessments; theref

ore, these compounds should not be included in estimates of residues of concern in drinking water (D301689)
. Both chemicals are small amino acid analogs. Following uptake, HED indicated they are expected to be readily metabolized and/or rapidl y excreted w ithout any significant biological effects. A summary

of the model input parameter values used in FIRST is presented in Table 2
. A summary

of the model input parameter values used in SCI
- GROW is presented in Table 3
. Input parameters were selected in a ccordance with EFED’s “Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides,” Version II ( February 28 , 20 02). For FIRST surface water modeling, the soil sorption coefficient (K d ) was used instead of the organic carbon partition coefficient (K OC ) because correlation of K d with organic carbon was low (R 2 = 0.3656) for the eight soils tested, suggesting that the adsorption of aminopy ralid is not closely related to organic carbon content (MRID 46235732 )
. Therefore, K d , the sorption coefficient uncorrected for organic carbon, was assumed to better represent sorption in soil. The aerobic soil metabolism half
- life was calculated by

nonlinear two
- parameter exponential decay anal ys is, and then that value was multiplied by 3 to account for the uncertainty associated with using a single value. The proposed label allows for ground spray applications and tank mixes ; a broadcast ground spray

was modeled as the method of application in order to be protective of all application scenarios. The aerobic aquatic metabolism half
- lives were calculated using first
order linear regression on log
- transformed data, then the 90 th percentile of the upper confidence bound on the mean of the three half
- lives was calculated. The aqueous photoly sis study was continuously

illuminated and the aqueous photol ys is half
- life input value was adjusted to reflect photoly sis in summer sunlight at 40 o N latitude . There was no degradation observed in the dark controls and no dark
- control corr ection necessary
. The FIRST output file is located in A ppendix 1 . The SCI
- GROW output file is located in Appendix 2
.Ta ble 2 . FIRST ( v1.1.0 ) input parameter values and results for TIPA Salt of aminopyralid

applied to field corn and field corn grown for ensilage .

Param eter Value Source Application Rate (lb a. e ./A) 1 0.57 fl oz/A ( 0.0089 lbs a . e . /A ) Annual maximum: 1.7 fl oz/A/yr ( 0.0266 lbs a
. e . /A/y

r) Proposed label. Number of Applications 3 Proposed label. Interval between Applications (days) 5 Assumed. Not specified on proposed label. Soil Sorption Coefficient (K d ; mL/g) 0.03 Represents the lowest non
- sand value am ong eight values ranging from 0.03 to

0.72 mL/g; MRID: 46235732. Aerobic Soil Metabolism Half
- life (days) 116.1 Determined by m ultiplying the calculated half

- life (38.7) by 3 to account for the uncertainty associated with using a single value; MRID:

46235729. Wetted in? No Proposed label. Depth of Incorporation (inches) 0 Proposed label. Method of Application ground spray Propo sed label. Percent Cropped Area 0.46 PRZM input guidance (US EPA, 2002) Solubility in Water @ 20 O C, unbuffered (mg/L or ppm) 2480 MRID: 46235701. Aerobic Aquatic Metabolism Half
life (days) 107 4 Represents the 90 th percentile of the upper confidence b ound on the mean of three half
- life values (772.9). MRID: 46235731. Hy droly sis Half

- life @ pH 7 (days) stable MRID: 46235726. Aq uatic Photolysis Half

- life @ pH 5 (days) 0.6 MRID: 46235727.

FIRST Results (EDWCs for surface water drinking water sources) 3 applications per year at 0.57 fl oz/A ( 0.0089 lbs a.e./A ) Acute Concentration: 1.25 μg/L Chronic Concentration: 0.24 μg/L Maximum annual application rate 1.7 fl oz/A/yr ( 0.0266 lbs a.e./A/yr ) Acute Concentration: 1.28 μg/L Chronic Concentration: 0.2 5 μg/L 1 Application rates are given in lbs acid equivalents (a.e.)/A. The acid equivalen t for aminopyralid is 21.1%
- 2lb/gal. Therefore the conversion from fl oz/A to lbs a.e./A is completed using the following formula: X fl oz/A * 1 gal/128 fl oz * 2 lb a.i/gal = X lbs a.e./ATable 3 . SCI - GROW (v2.3) input parameter values and results for aminopyralid applied

to field corn and field corn grown for ensilage . Param eter Value Source and/or Comments Maximum Application Rate (lb a.e./A) 1 1.7 fl oz/A/y r ( 0.0266 lb a.e./A ) Proposed label. Number of Applications per Year 1 Represents the most conservative label
allow ed scenario in which the total maximum rate per year is applied in one

application. Aerobic Soil Metabolism Half
- life (days) 38.7 R epres ents one value for the aerobic soil metabolism of the parent compound; MRID: 46235729. Organic Carbon Partition Coefficient (K oc ; mL/g) 2 1.05 Represents the lowest value of eight values ranging from 1.05 to 24.30 mL/g for the parent compound; MRID:

462357 32. Results (EDWC for groundwater drinking water sources) Concentration: 0.15 μg/L
1 See footnote 1 in Table 2. 2 K oc was used for ground water modeling as per US EPA, 2002 Guidance for Selecting I nput Parameters in Modeling the Environmental Fate and T ransport of Pesticides
.References:

DP 301682. US EPA. 2005. Aminopy ralid: Tier I Estimated Drinking Water Concentrations (EDWC) for Use in the Human Health Risk Assessment. US EPA, Office of Pesticide Programs, Environmental fate and Effects Division, 1200 Pennsy lvania Ave., NW Washington, DC. DP 301689. US EPA. 2005. Aminopy ralid: Aggregate Human Health Risk Assessment for the Proposed Uses on Wheat, Grasses, Non
- cropland Areas, and Natural Areas. US EPA, Office of Pesticide Programs, Environmental fate and Effects Division, 1200 Pennsy lvania Ave., NW Washington, DC. US EPA. 2005. Environmental Fate and Ecological Risk Assessment for the Registration of Aminopy ralid (PC Codes: 005100, 005209). US EPA, Office of Pesticide Programs, Environmental fate and Effects Division, 1200 Pennsy lvania Ave., NW Washington, DC.Appendix 1. FIRST Modeling Output file

Recommended Application Rate RUN No. 1 FOR aminopyralid ON fieldcorn * INPUT VALUES *

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

-------------------------------------------------------------------- .009( .026) 3 5 .0 2480.0 GROUND( 6.4) 46.0 .0 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIE LD) RAIN/RUNOFF (RESERVOIR) (RES.

- EFF) (RESER.) (RESER.)

-------------------------------------------------------------------- 116.10 2 N/A .60

- 74.40 ****** 69.58 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB )) Ver 1.1.0 JAN 1, 2007

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

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

1.246 .241 Annual Maximum Application Rate RUN No. 2 FOR aminopyralid ON fieldcorn_ * INPUT VALUES *

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

-------------------------------------------------------------------- .027( .027) 1 1 . 0 2480.0 GROUND( 6.4) 46.0 .0 FIELD AND RESERVOIR HALFLIFE VALUES (DAYS)

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

-------------------------------------------------------------------- 116.10 2 N/A .60

- 74.40 ****** 69.58 UNTREATED WATER CONC (MICROGRAMS/LITER (PPB)) Ver 1.1.0 JAN 1, 2007

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

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

1.279 .247Appendix 2. SCIGROW Modeling Output File 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:aminopyralid time is 6/10/2009 15:10:45

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

------------------------------------------------------------------------ 0.027 1.0 0.027 1.05E+00 38.7

------------------------------------------------------------------------ groundwater screening cond (ppb) = 1.55E
- 01 ************************************************************************