UNITED STATES ENVIRONMENTAL 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: Environmental Fate and Ecological Risk Assessment 

for use on Tomatoes, Peppers, Eggplant, Cucumbers, Squash, Melons, 

Strawberries, Blueberries, Onions, Field 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 and Effects Division (7507P) 

APPROVED BY: Mah Shamim, Branch Chief 

 Environmental Risk Branch V 

 Environmental Fate and Effects Division (7507P) 

 

The attached document contains the Environmental Fate and Effects Division’s (EFED) 

screening-level environmental fate and ecological risk assessment of dimiethyl disulfide 

(DMDS) for the proposed uses on tomatoes, Peppers, Eggplant, Cucumbers, Squash, Melons, 

Strawberries, Blueberries, Onions, Field Grown Ornamentals, and Forest Nursery crops as a preplant soil fumigant to control nematodes, weeds, and soil-borne pathogens. An evaluation of 

environmental risk to aquatic and terrestrial organisms as a result of the use of DMDS is 

summarized in the Executive Summary and the Risk Characterization sections of the attached 

document. This memorandum also provides the outstanding data gaps and the label 

recommendations for dimethyl disulfide use. 

1 
Outstanding Data Gaps

Environmental Fate: 

835.4400 Aerobic and 835.4500 Anaerobic 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 identified 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 irrigation and broadcast applications at this time. The studies 

should be located in anticipated use regions other than the Southeastern United States such as 

California and be conducted at times of the year when typical fumigation occurs in those regions. 

These studies should be conducted using the generic OPPTS guidelines. In addition, Johnson et 

al., 1999, Majewski et al., 1990, or Wilson and Shum, 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) and Independent Laboratory Validations (ILVs) 

for Soil, Water, and Air 

This information is required for all laboratory and field studies for the soil, water, and air. 

ECMs establish transparency and demonstrate 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 following 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 aerobic and anaerobic aquatic metabolism studies. 

Air – parent DMDS 

In addition, a full description of the method validation procedures performed by an 

independent laboratory is required 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 (substrates) at various relevant fortification 

2 
level(s) using the residue analytical methodology; (b) a validated method sensitivity level; (c) 

results of the study and statistical test applied, including a stepwise presentation of the procedure 

for calculating percent recovery from the raw data; (d) all the data/ information necessary to 

independently verify the results; (e) summary of the results; and, (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 chronic effects of dimethyl disulfide, sulfuric acid, 

and ozone associated with a high volume of dimethyl 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 and 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 background levels in the same sampling regions before the 

inception of large scale dimethyl disulfide fumigation should be compared. 

Ecological Effects:

850.1300 Aquatic Invertebrate Life Cycle (Freshwater). There is uncertainty concerning 

the aquatic exposure and persistence for aquatic invertebrates (40CFR Part 158). 

850.1350 Aquatic Invertebrate Life Cycle (saltwater). Current aquatic modeling 

indicates the potential for chronic 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 exposure 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 exposure to DMDS. There is uncertainty in the persistence for 

estuarine/marine fish (40CFR Part 158). 

 850.5400 Vegetative Vigor. A supplemental non-guideline toxicity study (MRID 

474712-02) was received for DMDS. Additional information to calculate the headspace volume 

is necessary to estimate the effect of DMDS on vegetative vigor exposed through air 

concentrations. 

3 
EFED Label Recommendations 

The following label statements are recommended, based in part on the OPP Label Review 

Manual (3rd edition, 8/2003). 

 i.. Surface and Ground Water Advisory for Tarped Scenario 

 

Dimethyl disulfide has certain properties and characteristics associated with 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 especially 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 several 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 under 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 those 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 Unfavorable 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 wind 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 persist for more than 18 

consecutive hours after the start of the application. 

Detailed local forecasts for weather conditions, wind speed, and air stagnation 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

4 
Unfavorable weather conditions block upward movement of air, which results in trapping 

fumigant vapors near the ground. The resulting air mass can move off-site in unpredictable 

directions. These conditions typically exist prior to sunset and continue 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 indicated 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. Measurement of wind speed can be determined by taking 

measurements every minute for a ten-minute period. The wind speed is the average of the oneminute measurements over this ten-minute period. 

5 
EFED 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 Inhalation 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–rainbow 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 

6 
7 

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 Volatility1 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 Quality Data On Reserve ----- NA 

NA means not applicable. 

1

 Despite acceptable study classifications of submitted studies, more studies are needed with 

VIF tarps to account for soil and weather conditions over different geographic regions and pest 

management practices (e.g. broadcast shank injection, drip irrigation applications).