UNITED STA TES ENVIRONMENTA L PROTECTION AGENCY WA SHINGTON D.C., 20460

OFFICE OF PREVENTION, PESTICIDES AND TOXIC SUBSTANCES MEMORANDUM DATE: 9 September 2009 DP Barcode: 361314 PC Code: 117403
SUBJECT: Tier I Dri nking Water Assessment for Proposed New Use of Clopyralid on

Swiss Chard, Bushberry Subgroup 13 - 07B and Annual Strawberry FROM: Andrew Shelby

Physical Scientist, Environmental Risk Branch II Environmental Fate and Effects Division (7507P) William P. Eckel, Ph.D. Senior Scientist, Environmental Risk Branch II Environmental Fate and Effects Division (7507P) THRU: Tom Bailey, Branch Chief

Environmental Risk Branch II Environmental Fate and Effects Division (7507P) TO: Laura Nollen

Registrat ion Division (7505C) This assessment contains estimated drinking water concentrations (EDWCs) for both surface and ground water for clopy

ralid (3,6

- dichloro

- 2
- py

ridinecarboxylic acid; CAS Reg. No. 1702

- 17
- 6) on Swiss chard, Bushberry subgroup 13

- 07B and annual strawberry . Because of the chemical’s persistence, only

the parent compound is assessed. Contact Andrew Shelby at 703
- 347
- 0119 if there are any

questions. EXECUTIVE SUMMARY Clopy ralid is an herbicide within the pry ridinecarboxylic acid family th at mimics the plant growth hormone auxin. This sy stemic hormone mimic causes uncontrolled and disorganized plant growth that leads to plant death. Current agricultural uses include asparagus, barley , canola, corn, crambe, cranberry , fallow land, flax see d, garden beet, grasses, head and stem Brassica , hops, mustard greens, oats, pasture, rangeland, rapeseed, sod farms, spinach, stone fruits, sugar beets, tree plantations, turnip, and wheat. Non

- agricultural uses include non

residential turfgrass and non

- residential lawn. The proposed uses assessed here are Swiss chard, strawberry

and Bushberry

subgroup 13

- 07B. Bushberry subgroup 13

- 07B includes aronia berry , highbush blueberry , lowbush blueberry , buffalo currant, Chilean guava, highbush cranberry , black currant, red currant, European barberry , gooseberry , edible honey suckle, huckleberry , jostaberry , Juneberry , lingonberry , native currant, salal and sea buckthorn.Screening Concentration in Ground Water (SCI GROW) and FQPA Index Reservoir

Screening Tool (FIRST) models were parameterized for maximum application rates and used to determine Estimated Drinking Water Concentrations (EDWCs). The following table summarizes results for hazard maximizing modeling scenarios. Table 1. Maximum Tier I Estimated D rinking Water Concentrations (EDWCs) for drinking water assessment based on ground application of Stinger Herbicide DRINKING WATER SOURCE (MODEL USED) USE (rate modeled) MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION (EDWC) (ppb) Groundwater (SCIGROW) Bu shberry (0.25 lbs a.i./A) Acute and Chronic 0.39 Groundwater (monitoring) NAWQA, Alabama Acute 13 Surface water (FIRST) Bushberry (0.25 lbs a.i./A) Acute 41.1 Bushberry

(0.25 lbs a.i./A) Chronic 10.8 Non
- crop (0.5 lbs a.i./ A) Acute 45.0 Non
- crop (0.5 lbs a.i./ A) Chronic 11.9 PROBLEM FORMULATION This is a Tier I

drinking water assessment that uses modeling and available monitoring data to estimate the ground water and surface water concentrations of pesticides in drinking water source water (p re - treatment) resulting from pesticide use on sites that are highly vulnerable. This initial tier screens out chemicals with low potential risk and provides estimated exposure concentrations for the human health dietary risk assessment. Background The p roposed new use of clopy ralid on Swiss chard, Bushberry subgroup 13

- 07B and annual strawberry

is the first assessment on clopy ralid since multiple new uses and special local needs were assessed from 1999 to 2002, the last of which was dated June 26, 2002 f or canola in Colorado. This assessment determined estimated environmental concentrations (EECs) based on a maximum application rate of 0.1875 lbs a.i./A. Previous assessments found clopy ralid is miscible in water (1 x 10 4 ppm), does not hydroly ze in wate r, is stable to photoly sis, is persistent under laboratory conditions in aerobic soil (DT90 greater than 78 day s) and is very mobile in soil (K OC = 0.4 mL/g o.c.). Based on these characteristics, previous assessments recommended a groundwater advisory on the label: This chemical demonstrates the properties and characteristics associated with chemicals detected in ground water. The use of this chemical in areas where soils are permeable, particularly where the water table is shallow, may result in groun d water contamination Use Characterization The new use assessed here calls for a maximum application rate of 0.25 lbs a.i./A for Bushberry subgroup 13

- 07B and annual strawberry and maximum application rate of 0.188 lbs a.i./A for Swiss chard. Each new proposed use would be applied via ground spray . Bushberry subgroup 13
- 07B is the only

use modeled in this assessment because it has the highest single applicationrate and highest potential number of applications. These maximum single application rates a re less than the label maximum application rate of 0.5 lbs a.i./A for non

- crop land. This maximum application rate is also modeled in this assessment and resultant EDWCs should be used for assessing risk. The proposed new uses for Swiss chard and strawbe rry call for foliar, broadcast applications at 30 day s and 7 day s prior to harvest respectively with one application per year. The proposed new use for Bushberry subgroup 13

- 07B calls for application to the soil from the plants to the row middle without c ontacting the foliage or woody portions. The label also allows for one additional application with minimum interval of 14 day s between applications. All above use information is summarized in the following table: Table 2: Summary of maximum use informat ion for clopyralid, based on Stinger Herbicide labels USE SINGLE

APP. RATE (lbs a.i./A) NUMBER

OF APPS. SEASONAL

APP. RATE (lbs a.i./A) INTERVAL

BETWEEN APPS. (days) APP.

METHOD INCORPORATION

DEPTH (inches)
Bushberry Subgroup 0.25 2 0.5 14 Ground Spray 0 Swiss Chard 0.25 1 0.25 N/A Ground Spray 0 Annual Strawberry 0.188 1 0.188 N/A Ground Spray 0
Fate and Transport Characterization Clopy ralid is non

- volatile thereby limiting transport in air. The chemical also has a low rate of soil sorption (K OC = 0.4 mL/g o.c.) restricting storage within soil. The dominating environmental compartment is water due to these characteristics and the chemical’s miscibility
. Clopy ralid is stable to photoly sis and anaerobic metabolism and moderately stable to aerobic me tabolism. Due to anaerobic metabolism stability and high mobility , the chemical is likely to persist in groundwater. Aerobic metabolism is expected to be the primary pathway of degradation for clopy

ralid in the environment. Though aerobic aquatic meta bolism is the anticipated primary route of degradation, it is currently a data gap for this chemical. Modeling guidance assumes aerobic aquatic metabolism half

- life to be double that of aerobic soil metabolism in the absence of data. Although this is a c onservative assumption, it should be well noted that the primary route of degradation for this chemical is not well

- characterized. Clopy ralid has been found to survive the composting process when yard clippings are collected and composted ( Washington St ate University ). The chemical becomes concentrated in the final compost, which then may be toxic to plants to which it is applied. Plant material from treated areas should therefore not be used as compost feedstocks. Clopy ralid degradates are not modele d in this assessment because the aerobic soil metabolism study

did not produce metabolites representing at least 10% of the applied dose.However, these degradates were not identified and whether they are of toxicological concern is a source of uncertainty. Additionally , a different suite of metabolites potentially present in larger concentrations could be produced from aerobic aquatic metabolism relative to aerobic soil metabolism. However, due to the small size of the molecule, large variations in degr adates is not expected. Though new studies are not available for this assessment, a more accurate determination of aerobic soil metabolism half

- life has been made using second

- order degradation kinetics. Degradation, especially

through metabolism, often do es not follow strict first order kinetics which is only

dependent on the concentration of the parent compound. More nuanced models such as first

- order multi

- compartment (FOMC), intermediate order rate equation (I ORE) and second

- order rate equation take into account heterogeneous media and/or interactions from degradates. Data from a clopy ralid aerobic soil metabolism study (MRI D 43891403 ) was found to match most closely

to a second

- order rate equation. Though second

- order degradation most accurately

refl ects the data, FIRST and SCI GROW are based on first

- order kinetics. This distinction requires that first

- order degradation be used to derive modeling parameters and second

- order degradation only be used to better characterize the chemical. The following table outlines clopy

ralid chemical characteristics. Table 3: Summary of physical/chemical and environmental fate and transport properties of clopyralid. PARAMETER VALUE(S) (units) SOURCE COMMENT Chemical Name 3,6
- dichloro

- 2
-

py ridinecarboxylic acid Mol ecular Weight 192 Solubility Miscible Vapor Pressure (25 0 C) 1.26 x 10 - 6 mm Hg pKa 2.30 Senseman 2007 Octanol

- Water Partition Coefficient (K OW ) 21.81 Senseman 2007 Hydroly sis Half

life Stable MRI D 42805701 Soil Photoly sis Half

- life Stable M RID 43891402 Aerobic Soil Metabolism Half

life 16.8 day s x 3 = 50.4

day s DT50: 7 to 14 day s DT90 > 78 day s MRI D 43891403 Three times first

- order half

- life used as per 2002 Input Parameter Guidance 2 nd Order Degradation; DT90/3.32 = 34.6 day s Anaerobic Aquatic Metabolism Half

life Stable MRI D 43891405 Aerobic Aquatic Metabolism Half

life Data gap; used 100

day s (2X aerobic soil metabolism half

- life)Organic Carbon

Partition Coefficient (K OC ) 0.4 ml/g o.c. MRI D 40095701
Terrestrial Field Dissipati on Half

life 10.7 day s
– 25.2

day s MRI D 43891406
Drinking Water Exposure Modeling SCI GROW (Screening Concentration in Ground Water) is a regression model used as a screening tool to estimate pesticide concentrations found in ground water used as drinki ng water. SCI GROW was developed by fitting a linear model to groundwater concentrations with the Relative Index of L eaching Potential (RI LP ) as the independent variable. Groundwater concentrations were taken from 90

- day average high concentrations from Pr ospective Ground Water studies; the RI LP is a function of aerobic soil metabolism and the soil

- water partition coefficient. The output of SCI GROW represents the concentrations that might be expected in shallow unconfined aquifers under sandy soils, which is representative of the ground water most vulnerable to pesticide contamination likely to serve as a drinking water source. FIRST (FQPA Index Reservoir Screening Tool) is a metamodel of PRZM and EXAMS used as a screening tool to estimate pesticide concentrations found in surface water used as drinking water. FIRST was developed by making multiple runs of PRZM using varying sorption coefficients and determining the concentration in the EXAMS index reservoir scenario after a two

- inch single storm event. ( The Index Reservoir is a standard water body used by the Office of Pesticide Programs to assess drinking water exposure (Office of Pesticide Programs, 2002). It is based on a real reservoir (albeit not currently in active use as a drinking water supply ), Shipman City

L ake in I llinois, that is known to be vulnerable to pesticide contamination.) The single runoff event moves a maximum of 8% of the applied pesticide into the reservoir. This amount can be reduced by degradation or effects of binding to soil in the field. Additionally , FIRST can account for spray drift and adjusts for the area within a watershed that is planted with the modeled crop (Percent Crop Area). Spray drift (modeled as direct deposition of the pesticide into the reservoir) is assumed to be 16% of the applied active ingredient for aerial application, 6.3% for orchard air blast application, and 6.4% for other group spray application. Despite being a single event model, FIRST can account for spray drift from multiple applications. The default agricultural Percent Cropped Area (PCA) is 87%. The PRZM scenario used for FIRST development was among the most vulnerable, and thus resulting surface water concentrations represent the upper bound values on the concentrations that might be found in drinking water from the use of a pesticide. Modeling Approach and Input Parameters Input parameters were determined based on “Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides” (Version I I, February 28, 2002). The following tables display input parameters for SCI GROW and FIRST models respectively and provide explanation for the determination of the parameter. The same modeling inputs were used for determining non

- crop EDWCs with exceptions for “Max imum Application Rate” (0.5) and “Number of Applications per Year” (1).Table 4: SCIGROW (v2.3) input parameters for Clopyralid u se on Berry s ubgroup 13 - 07B,

Annual Strawberry and Swiss c hard. PARAMETER (units) VALUE(s) SOURCE/RATIONALE Maximum Applic ation Rate (lbs a.i./A) 0.25 Attached IR
- 4 documents; Petition: 8E7481 Number of Applications per Year 2 Attached IR
- 4 documents; Range including maximum possible applications in season Organic Carbon Partition Coefficient (K OC ;mL/g o.c.) 0.4 Minimum no n - sand value; MRID 40095701 Aerobic Soil Metabolism Half

life (day s) 16.8 1 st Order Degradation; MRID 43891403, Acc. Nos. 099727 and 099728. .
Table 5 : FIRST (v1.1.0) input parameters for Clopyralid u se on Berry s ubgroup 13 - 07B , Annual Strawberry and Swiss c hard. PARAMETER (units) VALUE(s) SOURCE/RATIONALE Application rate (pounds a.i. acre - 1 ) 0.25 Attached IR
- 4 documents; Petition: 8E7481 Number of applications (per year) 2 Attached IR
- 4 documents; Maximum possible applications in season Applicati on interval (day s) 14 Attached IR
- 4 documents Percent Crop Area 0.87 Since no PCA has been determined, 0.87 is the recommended value from Guidance K OC 0.4 Minimum non

- sand value; MRID 40095701 Aerobic soil t 1/2 (day s) 50.4 1 st Order Degradation; MRID 43 891403, Acc. Nos. 099727 and 099728. Half

- life value (16.8 day s) multiplied by

three. Is the pesticide wetted

in? No Section 3 label Method of application B Ground (all uses), 6.4% drift Depth of incorporation (inches) 0 Section 3 label Solubility (mg/L ) 10,000 Miscible Aerobic aquatic t 1/2 (day s) 100.8 2 x (aerobic soil metabolism parameter) Photoly sis Half

- life (day s) 0 Stable. Acc. Nos. 099727 and 099728Modeling Results

SCI GROW concentration (ppb) represents the groundwater concentration that might be expected in shallow unconfined aquifers under sandy soils. Output is used for both acute and chronic endpoints. FIRST concentrations (ppb) represent untreated surface water concentrations. The one

- in

- 10
- ye ar peak day

concentration is used for acute endpoints and the one

- in

- 10
- ye ar average concentration is used for chronic endpoints. The estimated concentrations provided in this assessment are conservative estimates of concentrations in drinking water. I f dietary risks require refinement, higher tiered crop

- specific models and modeling scenarios can be used. Table 6: Maximum Tier I Estimated Drinking Water Concentrations (EDWCs) for drinking water risk assessment based on ground application of Clopyralid. DRINKING WATER SOURCE (MODEL US ED) USE (rate modeled) MAXIMUM ESTIMATED DRINKING WATER CONCENTRATION (EDWC) (ppb) Groundwater (SCIGROW) Bushberry (0.25 lbs a.i./A) Acute and Chronic 0.39 Groundwater (monitoring) NAWQA, Alabama Acute 13 Surface water (FIRST) Bushberry (0.25 lbs a.i./A ) Acute 41.1 Bushberry

(0.25 lbs a.i./A) Chronic 10.8 Surface water (FIRST Non
- crop (0.5 lbs a.i./ A) Acute 45.0 Non
- crop (0.5 lbs a.i./ A) Chronic 11.9 Monitoring Data Monitoring data provide different kinds of information than modeling estimates . For example, monitoring data consist of actual information from the field, reflecting current use pattern and usually underestimating frequency of occurrence. Monitoring data does not alway s include peak values, and inputs for monitoring cannot be adju sted as modeled ones can. In addition, monitoring is often conducted for purposes other than characterizing exposure from a particular pesticide, and as a consequence is used to complement modeling rather than to refine it. In general, a useful interpret ation of monitoring values requires in

- depth assessment of the data, which is beyond the scope of a Tier I assessment. Several incidences of monitoring concentrations exceeding EDWCs have occurred. Groundwater concentrations as high as 13 ppb have been detected in Alabama and surface water concentrations of 41 and 42 ppb have been detected in North Carolina, I llinois and Ohio (NAWQA). Peak groundwater concentrations greatly exceed the groundwater EDWC and peak surface water concentrations slightly excee d the associated EDWC. It cannot be assumed that these monitoring data represent peak clopy ralid concentrations. Considering this, use of EDWCs in any assessment should be qualified with these monitoring data to indicate uncertainty
. Drinking Water Trea tmentNo data are available to indicate the effectiveness of drinking water treatment on the degradation

of clopy ralid. CONCLUSIONS Clopy ralid is a persistent chemical that partitions to water. Degradation is driven by aerobic aquatic metabolism thou gh this pathway is not directly

characterized through a guideline study
. Further, degradation behavior best fits second

- order kinetics though first

- order kinetics are used to derive and parameterize FIRST and SCI GROW. Second

- order kinetics, in this case, provides a substantially

larger half

- life estimate than first

- order kinetics. Finally , monitoring data indicate concentrations exceeding EDWCs and it can be assumed that this is an underestimate of peak concentrations in the environment. Though FIRST and SCI GROW, by definition, provide conservative estimates of surface water and groundwater concentrations, the preceding qualifiers should be considered when using these EDWCs in any

assessment. REFERENCES Senseman, S. S., ed. 2007. Herbicide Handbook. 9th ed. L awrence, KS: Weed Science Society

of America USGS National Water Quality Assessment Data Warehouse http://water.usgs.gov/nawqa/ Washington State University , Clopy ralid Contaminated Compost FACT SH EET December 27, 2001, http://cahenews.wsu.edu/clopy ralid.htm