### UNITED STATES ENVIRONMEN TAL PROTECTION AGENCY WASHINGTON, D.C. 20460 OFFICE OF PREVENTION, PESTICIDES AND TOXIC SUBSTANCES

PC Code: 029088 DP Barcodes: D339685, 363748

DATE: April 20, 2010

MEMORANDUM

SUBJECT : Dimethyl Disulfide: Environmenta l Fate and Ecological Risk Assessment for use on Tomatoes, Peppers, Eggplant, Cucumbers, Squash, Melons, Strawberries, Blueberries, Onions, Fi eld Grown Ornamentals, and Forest Nursery Crops

TO: Cynthia Giles-Parker, Branch Chief Tony Kish, Review Manager John Bazuin, Risk Manager Reviewer Fungicide Branch Registration Division (7505P)

FROM: Gabe Rothman, Environmental Scientist Valerie Woodard, Biologist Environmental Risk Branch V Environmental Fate a nd Effects Division (7507P)

APPROVED BY: Mah Shamim, Branch Chief Environmental Risk Branch V Environmental Fate and Effects Division (7507P)

The attached document contains the Environm ental Fate and Effects Division’s (EFED) screening-level environmental fate and ecologi cal risk assessment of dimiethyl disulfide (DMDS) for the proposed uses on tomatoes, Pe ppers, Eggplant, Cucumbers, Squash, Melons, Strawberries, Blueberries, Onions , Field Grown Ornamentals, and Forest Nursery crops as a preplant soil fumigant to control ne matodes, weeds, and soil-borne pathogens. An evaluation of environmental risk to aquatic and terrestrial or ganisms as a result of the use of DMDS is summarized in the Executive Summary and the Risk Characterization secti ons of the attached document. This memorandum also provides the outstanding data gaps and the label recommendations for dimethyl disulfide use.

1Outstanding Data Gaps

Environmental Fate:

835.4400 Aerobic and 835.4500 Anaer obic Aquatic Metabolism

Submission of the aerobic and anaerobic aquatic metabolism study on the dimethyl disulfide technical product will enable the reviewer to calculate half-lives of dimethyl disulfide in water. These results will result in more refined EECs in surface water and benthic water pores. Retrievals of all degradates identifie d in the proposed degradation pathway (to be submitted with the study) should be attempted to account for the full material balance over time.

835.8100 Field Volatility Studies

Additional field volatility studies using PaladinTM and PaladinTM EC with VIF tarp coverings are required for drip ir rigation and broadcast applications at this time. The studies should be located in anticipated use regions othe r than the Southeastern United States such as California and be conducted at times of the year wh en typical fumigation occu rs in those regions. These studies should be conducted using the generic OPPTS guideli nes. In addition, Johnson et al., 1999, Majewski et al., 1990, or Wilson and Sh um, 1992 should be referenced for additional guidance regarding study designs, development of flux profiles, and land surface/flux footprint considerations (e.g., fetch distances along the treated field to the instrumentation towers). All studies should include collection of on-site meteorological data. If on-field towered sampling is conducted, all measurements of wind speed and temperature should be rapidly sampled on the order of every 1 minute. Furthermore, retrievals of all degradates identified in the degradation pathway shown in Figure III-1 of this document should be attempted.

----- Environmental Chemistry Methods (ECMs) a nd Independent Laborator y Validations (ILVs) for Soil, Water, and Air

This information is required for all laboratory an d field studies for the so il, water, and air. ECMs establish transparency and de monstrate that analytical methods are repeatable for all field and laboratory studies. ECMs are required for DMDS; further, multi-residue methods (MRMs) for soil and water are preferred. The follo wing are major degradates for each media: Soil – parent DMDS and methanesulfonic acid Water – parent DMDS, methanesulfonic acid , methanesulfinic acid, sulfuric acid, any additional degradates identified from aerobi c and anaerobic aquatic metabolism studies. Air – parent DMDS

In addition, a full description of the method validation procedures performed by an independent laboratory is requir ed to be submitted. These reports are evaluated by EFED according to NAFTA Guidance, which includes the following information: (a) Recovery level(s) of the test compound(s) from the soil and water (s ubstrates) at various relevant fortification

2level(s) using the residue anal ytical methodology; (b) a validate d method sensitivity level; (c) results of the study and statistica l test applied, including a stepwi se presentation of the procedure for calculating percent recovery from the raw da ta; (d) all the data/ information necessary to independently verify the results; (e) summary of the results; a nd, (f) discussion and conclusions of the results.

----- Ambient Air Quality Monitoring Data (On Reserve)

Ambient air quality monitoring studies may be requested in any high dimethyl disulfide use areas in the future. The data will be used in registration review or with any proposed new uses to consider the potential for acute and chroni c effects of dimethyl disulfide, sulfuric acid, and ozone associated with a high volume of dime thyl disulfide use occurring within an airshed. Air quality related values of concern will include concentrations of dimethyl disulfide and ozone in the air close to ground level a nd sulfuric acid in rain water. To address dimethyl disulfide’s contribution to ozone and sulfuric acid, the measured ambient levels of dimethyl disulfide in air and sulfuric acid in water to historical backgroun d levels in the same sampling regions before the inception of large scale dimethyl disu lfide fumigation should be compared.

Ecological Effects:

850.1300 Aquatic Invertebrate Life Cycle (Fresh water). There is uncertainty concerning the aquatic exposure and persiste nce for aquatic invertebrates (40CFR Part 158).

850.1350 Aquatic Invertebrate Life Cycle (saltwater). Current aquatic modeling indicates the potential for chr onic aquatic exposure to DMDS. There is uncertainty in the persistence for estuarine/marine invertebrates (40CFR Part 158).

850.1400 Early Life-stage Fish (freshwater) . Current aquatic modeling indicates the potential for chronic aquatic e xposure to DMDS. There is uncertainty in the persistence for freshwater fish (40CFR Part 158).

850.1400 Early Life-stage Fish (saltwater) . Current aquatic modeling indicates the potential for chronic aquatic e xposure to DMDS. There is uncertainty in the persistence for estuarine/marine fish (40CFR Part 158).

850.5400 Vegetative Vigor. A supplementa l non-guideline toxicity study (MRID 474712-02) was received for DMDS. Additional in formation to calculate the headspace volume is necessary to estimate the effect of DMDS on vegetative vigor exposed through air concentrations.

3EFED Label Recommendations

The following label statements are recommended, based in part on the OPP Label Review Manual (3 rd edition, 8/2003).

i.. Surface and Ground Wat er Advisory for Tarped Scenario

Dimethyl disulfide has certain properties and charac teristics associated w ith chemicals detected in groundwater. DMDS may leach into ground water if used in areas where soils are permeable, particularly where the water table is shallow. Dimethyl disulfide may also impact surface water quality due to runoff of rain water. This is es pecially true for poorly draining soils and soils with shallow ground water. This chemical is classified as having high potential for reaching surface water via runoff sever al days after application.

To address this concern for ground water quality and surface runoff, for broadcast applications, tarps must be sliced or removed before noon and only when rainfall is not expected within 12 hours. (Falling temperatures typically found in the late afternoon and evening will not promote dissipation of remaining MITC unde r the sliced tarp and rainfall may cause remaining dimethyl disulfide under the sliced tarp to leach into ground water.)

ii . Air Stagnation and Temperature Inversions

Prior to fumigation, and on a daily basis for thos e fumigations lasting for more than 24 hours, the National Weather Service weather forecast for the day of the application and the 48-hour period following the fumigation must be checked to determine if unfavorable weather conditions exist or are predicted (see Identifying Unfavo rable Weather Conditions section) and whether fumigation should proceed.

Do not apply if an air stagnation advisory is in effect.

Do not apply if there are light wi nd conditions observed (under 2 mph) or if the wind speed is forecast to remain below 5 mph during the application.

Do not apply if still or stagnant wind conditions are forecast to pe rsist for more than 18 consecutive hours after the start of the application.

Detailed local forecasts for weather conditions , wind speed, and air stag nation advisories may be obtained on-line at: http://www.nws.noaa.gov , on weather radio, or by contacting your local National Weather Service Forecasting Office.

Identifying Unfavorable Weather Conditions

4Unfavorable weather conditions block upward mo vement of air, which results in trapping fumigant vapors near the ground. The resulting air mass can move off-site in unpredictable directions. These conditions typica lly exist prior to sunset and c ontinue past sunrise and persist as late as noontime. Unfavorable conditions are common on nights with limited cloud cover and light to no wind and their presence can be indi cated by ground fog or smog and can also be identified by smoke from a ground source that flattens out below a ceiling layer and moves laterally in a concentrated cloud. Measuremen t of wind speed can be determined by taking measurements every minute for a ten-minute peri od. The wind speed is the average of the oneminute measurements over this ten-minute period.

5EFED Data Requirements

Table 1. Ecological Effects Data Requirements for DMDS

Guideline # Data Requirement Are Additional Data Needed for Risk Assessment? MRID #’s Study Classification

71-1(a) Avian Acute Oral N 470528-13 Acceptable

------ Avian Acute Inhala tion N 469170-13 Acceptable

71-2(a) Avian Dietary–quail N ------------ ------------

71-2(b) Avian Dietary–mallard N ------------ -------------

--------- Avian Subchronic/Chronic Inhalation N ------------- -------------

72-1(a) Fish Acute Toxicity–bluegill Zebrafish N 470528-15 Acceptable

72-1(b) Fish Acute Toxicity–r ainbow trout N 470528-14 Acceptable

72-2(a) Aquatic Invertebrate Acute Toxicity– freshwater N 470528-16 Acceptable

72-3(a) Marine/Estuarine Acute Toxicity–Fish N 473075-04 Acceptable

72-3(b) Marine/Estuarine Acute Toxicity– Mollusk (shell deposition) N ------------ -------------

72-3(c) Marine/Estuarine Acute Toxicity– Shrimp N 473075-05 Acceptable

72-4(a) Fish Early Life Stage–freshwater Y ------------- -------------

72-4(a) Fish Early Life Stage– marine/estuarine Y ------------ -------------

72-4(b) Aquatic Invertebrate Life Cycle– freshwater Y ----------- ------------

123-1(a) Seedling Germination/Seedling Emergence–Tier II N ------------- ------------

123-1(b) Vegetative Vigor–Tier II Y 474712-02 Supplemental

123-2 Aquatic Plant Growth – Tier II N 474712-04, 474712-05, 474712-06 474712-07 470528-17 Acceptable

141-1 Honeybee Acute Contact N 474712-03 Acceptable

67 Table 2. Environmental Fate Data Requirements for: DMDS

Guideline # Data Requirement Are Additional Data Needed

for Risk Assessment? MRID #’s Study Classification

835.2120 Hydrolysis No 46903532 S

835.2240 Photodegradation in water No 42900201 S

835.2410 Photodegradation in soil No ----- W

835.4100 Aerobic soil metabolism No 47052819 S

835.4200 Anaerobic soil metabolism No 47052820 S

835.4300 Aerobic Aquatic Metabolism Yes

----- NA

835.4400 Anaerobic Aquatic Metabolism Yes

----- NA

835.1230 835.1240 Leaching and adsorption/ desorption No 46917014 46917015 S

835.8100 Field Volatility 1 Yes 47052821 47052822 47052823 47052824 47820001 47377801 A A A A A S

835.6100 Terrestrial Field Dissipation No ----- W

850.1710 850.1730 850.1850 Aquatic organisms – bioavailability, biomagnification, toxicity No

----- W

Special Environmental Chemistry Methods and Independent

Laboratory Validation Yes

---- NA

Special Ambient Air Qualit y Data On Reserve ----- NA NA means not applicable.

1 Despite acceptable study classifications of su bmitted studies, more studies are needed with VIF tarps to account for soil and weather conditi ons over different geographic regions and pest management practices (e.g. broadcast shank injection, drip irrigation applications).