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

OFFICE OF PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES

DP Barcode: 362366/362365

PC Code: 121011 October 1, 2009

MEMORANDUM

SUBJECT: Drinking water assessment for Clethodim on Caneberry, Bushberry, Peach,

and Artichoke.

TO: Paula Deschamp Registration Action Branch 3

Health and Effects Division

and

Jim Stone

Herbicide Branch Registration Division

FROM: Tiffany Mason, Environmental Engineer

Environmental Risk Branch II

Environmental Fate and Effects Division

THRU: William P. Eckel, PhD, Senior Scientist

Environmental Risk Branch II

Environmental Fate and Effects Division

Jean Holmes, PhD, RAPL

Environmental Risk Branch II

Environmental Fate and Effects Division

Tom Bailey, PhD, Branch Chief

Environmental Risk Branch II

Environmental Fate and Effects Division

CONCLUSIONS

This drinking water assessment is for Clethodim and its sulfoxide and sulfone degradates. Clethodim is used as a post-emergence herbicide against a wide range of annual and perennial grasses (monocotyledon plant species) in a wide va riety of broad leaf crops including soybeans,2 cotton, flax, peanuts, sunflowers, sugar beets, potatoes, alfalfa and vegetables. The proposed new uses of caneberry, bushberry, peach and artichoke, have a maximum use rate per season, as specified on the label to be four applications, fourt een days apart, at the rate of 0.12 lb. a.i./acre. Based on the proposed application rates and the environmental fate properties of clethodim, surface and ground water contamination may occur from clethodim as well as its sulfoxide and sulfone degradates. The risk of water contamination is primarily associated with clethodim sulfone and clethodim sulfoxide rather than pa rent clethodim based on greater persistence and mobility for the degradates. Thus, this assessment is based on total toxic residues rather than parent only.

EFED recommends that total toxic residues estimated environmental concentrations (EEC’s) generated by the FIRST model and listed above be used instead of EEC’s for parent clethodim. For drinking water derived from surface water, the acute concentrations to be used for drinking water are 38.9 μg/l for the use on flax, leafy greens, sesame, safflower, herbs, hops, asparagus, legumes (DW assessment November 30, 2006). However, the chronic (annual mean) values for clethodim in surface water used as drinking water is 13.0 μg/l (Table 1) for the use on caneberry, bushberry, peach, and artichoke.

For drinking water derived from ground water, the SCI-GROW model estimates total toxic clethodim concentrations of 9.8 μg/l for the use on caneberry, bushberry, peach, and artichoke (Table 1). These SCI-GROW values should be used for acute, chronic, and cancer risk assessment on each of their respective crops.

Based on FIRST and SCI-GROW modeling, the dr inking surface and groundwater Expected Environmental Concentrations (EEC) of Clethodi m and its sulfoxide and sulfone degradates for the use on caneberry, bushberry, peach, and artichoke are shown in Table 1.

Table 1. Tier I EEC's for Clethodim and its sulfoxide and sulfone degradates for the use on caneberry, bushberry, peach, and artichoke using FIRST and SCI-GROW models.

Compound Peak EEC (ug/L) Annual Mean EEC (ug/L)

Total Toxic Clethodim (parent + sulfoxide + sulfone); (four apps of 0.12 lbs. ai/A at 14-day interval) 37.3 13.0

SCI-GROW EEC (ug/L) 9.8

Environmental Fate Summary3 Surface and ground water contamination may occur from the sulfoxide and sulfone degradates of clethodim, as well as from parent clethodim. However, the risk of water contamination is primarily associated with clethodim sulfone and clethodim sulfoxide rather than parent clethodim based on greater persistence and mobility for the degradates.

The only significant routes of dissipation of cl ethodim are microbial degradation in soil and movement by leaching or runoff. Parent clethodim is moderately persistent to hydrolysis at pH 5 with half-lives of 26-42 days and stable at pH 7 and 9 with half-lives of greater than 300 days. Even though the acceptable aqueous photolysis study shows half-lives of 2.2 days at pH 5, 7.1 days at pH 7, and 11.8 days at pH 9, this may not be an important route of dissipation because of suspended sediment and shading. Photolysis is onl y an important route of dissipation in shallow, well-mixed surface water with no shading. The half-lives in aerobic soil are 86.4 to 97.6 days for total toxic residues (parent + sulfoxide + sulfone). The sulfoxide and sulfone metabolites are more persistent than parent clethodim and are formed in significant quantities in soil. All residues of clethodim (parent and metabolites) are very mobile in soil with five out of six soil desorption coefficients (K d ) less than one. The field dissipation studies show that parent clethodim was only found at levels at or near the quantitation limit of 0.02 ppm, which is consistent with the rapid degradation in soil. Clethodim sulfoxide had an apparent half-life of 2.5 to 3.7 days, indicating that movement from th e treated field may have been an important route of dissipation.

Water Resources Summary

A. Monitoring

The EFED currently has no monitoring data on the concentrations of clethodim or its major degradates in surface or groundwater.

B. Surface Water

The Tier I screening models FIRST Version 1.1.1 (FQPA I ndex R eservoir S creening T ool) with Percent Crop Area adjustment factor was used to determine drinking water concentrations of Clethodim and its sulfoxide and sulfone degradates derived from surface water sources.

Parent clethodim may move from the treated fi eld to surface water or ground water through runoff or leaching which occurs shortly after application (e.g. rainfall). Also, the sulfoxide and sulfone degradates may migrate by runoff or leach ing for longer periods of time because they are more persistent. All residues of clethodim (parent and degradates) are very mobile in soil. Tier 1 drinking water concentrations derived from surface water for total toxic residues (parent + sulfoxide + sulfone) were estimated using Version 1.1.1 of FIRST model. Input values for the FIRST model are reported in Table 2.

Table 2. FIRST Input Parameters for Clethodim a nd its sulfoxide and sulfone degradates use on4 caneberry, bushberry, peach, and artichoke.

Parameter Input value Data Source/Rationale*

Application Rate (lbs ai/A) 0.12 IR-4 labels

Maximum No. of Applications/season 4 IR-4 labels

Application Interval (days) 14 IR-4 labels

Percent Cropped Area (as decimal) 0.87 Default

Incorporation depth (inch) 0 Broadcast application

K

oc 5 Lowest Koc from 5 soils (MRID 40974523), range of 5-271 for parent.

Aerobic Soil Metabolic Halflife (days)

Total Toxic residue 92 Average half-lives for total toxic residue. Half-lives 86.4 and 97.6. (MRID’s 40974521 and 41376801).

Is the pesticide wetted-in? No

Method of application B Ground

Solubility (ppm) 5400 Joint meeting of the FAO panel of experts on pesticide residues in food and the environment and the WHO expert group on pesticide residues (Italy, 1994).

Aerobic aquatic t 1/2 (days) 184 2 x (aerobic soil value)

Photolysis Half-life (days) 7.1 MRID 41030134 * Parameters were selected in accordance with the Proposed Interim Guidance for Input Values document, dated September 22, 2009.5 C. Ground Water

SCI-GROW model (Screening Concentrati on in Ground Water Program (SCI-GROW) VERSION 2.3.0 was used to predict the maximum chronic and acute concentration of parent Clethodim and its sulfoxide and sulfone degr adates derived from shallow ground water.

Parent clethodim is mobile, but has a short metabolic half-life in soil under aerobic conditions. Therefore, parent compound should not be a ground water concern in most environments. While EFED expects the parent to be transformed to sulfoxide or sulfoxone products fairly quickly by soil metabolism (t 1⁄2 = 1 - 3 days), it may be more persistent since it is leached below the more biologically active topsoil. In such instances (i.e., leaching rainfall shortly after application) parent clethodim concentrations may be higher than estimated. In the event that parent clethodim did reach ground water, the available r outes of disappearance would be dilution, some metabolism to persistent degradates, and slows hydrolysis with the rate depending on the pH of the ground water. Table 3 below summarizes the results of the screening level groundwater model, SCIGROW 2.3.0, for the total toxic clethodim (parent + sulfoxide+sulfone).

Table 3. SCIGROW input parameters used to estimate total toxic clethodim concentrations for the use on caneberry, bushberry, peach, artichoke.

Parameter Input value Data Source/Rationale*

K

oc (l/kg)

5 Lowest Koc from 5 soils (MRID 40974523), range of 5-271 for

parent.

Application Rate (lbs ai/A) 0.12 IR-4 Labels

Maximum No. of Applications 4 IR-4 Labels

Aerobic soil metabolism half-life (days

total toxic residue.

92 Average half-lives for total toxic

residue. Half-lives 86.4 and 97.6. (MRID’s 40974521 and 41376801).



# APPENDIX I6 

### FIRST modeling input and output for the use of clethodim on caneberry, bushberry, peach, and artichoke

SCIGROW

VERSION 2.37 

### ENVIRONMENTAL FATE AND EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL FOR AQUATIC PESTICIDE EXPOSURE