UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

December 3, 2013 

MEMORANDUM 

TO: Garland Waleko, Chemical Review Manager 

Cathryn Britton, Team Leader 

Kevin Costello, Chief, RMIB 2 

Pesticide Re-evaluation Division (7508P) 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

PC Code: 029008

DP Barcode: 412524 

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation (attached) for the ecological risk, environmental fate, endangered species, and 

drinking water assessments to be conducted as part of the registration review for dimethyl 

disulfide. The problem formulation draws on information from both open literature and studies 

submitted by the technical registrants in response to data requirements. This document is 

intended to provide an overview of what is currently known and the uncertainties regarding the 

environmental fate and ecological effects associated with dimethyl disulfide. It describes the 

conceptual model and the processes that will be used during the completion of drinking water 

exposure and ecological risk assessments in support of registration review. This document also 

recommends studies that may be included in a data call-in (DCI) to address uncertainties 

surrounding the environmental fate and potential ecological effects of dimethyl disulfide. 

Page I of53 
Page 2 of 53 

 

Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review for Dimethyl Disulfide 

 

 Dimethyl Disulfide

CAS No. 624-92-0 

PC Code 029088 

Prepared by:

Joe Decant, Ecologist 

Gabe Rothman, M.S., Environmental Scientist 

U.S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division 

Environmental Risk Branch IV

1200 Pennsylvania Ave., NW 

Mail Code 7507P 

Washington, DC 20460

Reviewed by: 

Mah Shamim, Ph.D., Chief ERB5

December 3, 2013 

 
Page 3 of 53 

Table of Contents

1. Executive summary .................................................................................................. 4

2. Introduction .............................................................................................................. 7

3. Use Characterization ................................................................................................ 7

4. Conclusions from Previous Risk Assessments ....................................................... 10

4.1 Ecological Risk Assessments ................................................................................. 10

4.2 Drinking Water Assessments ................................................................................. 11

4.3 Clean Water Act Programs ..................................................................................... 11

5. Environmental Fate and Transport ......................................................................... 11

6. Receptors ................................................................................................................ 19

6.1 Effects to Aquatic Organisms ................................................................................. 19

6.2 Effects to Terrestrial Organisms ............................................................................. 20

6.3 Ecological Incidents ............................................................................................... 23

8. Analysis Plan .......................................................................................................... 25

8.1 Stressors of Concern ............................................................................................... 25

8.2 Measures of Exposure ............................................................................................ 26

8.3 Measures of Effect .................................................................................................. 28

8.4 Endangered Species Assessments .......................................................................... 28

8.5 Endocrine Disruptor Screening Program ............................................................... 29

8.6 Drinking Water Assessment ................................................................................... 29

9. Preliminary Identification of Data Gaps ................................................................ 30

9.1 Environmental Fate ................................................................................................ 30

9.2 Ecological Toxicity ................................................................................................ 32

10. References .............................................................................................................. 36

Appendix 1 – Detailed Environmental Fate Summary for DMDS ............................................... 40

Appendix 2 – Establishment of Inhalation as Dominant Exposure Pathway for Birds and 

Mammals ................................................................................................................ 48

Appendix 3 – ECOSAR Runs for DMDS and Methanesulfonic Acid ......................................... 50
Page 4 of 53 

1. Executive summary 

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation for the ecological risk, environmental fate, endangered species, and drinking water 

assessments to be conducted as part of the registration review of dimethyl disulfide (DMDS). 

The problem formulation describes the methods that will be used during the completion of 

drinking water and ecological risk assessments in support of registration review. It provides an 

overview of the environmental fate, ecological effects, and potential risks associated with the 

uses of DMDS and related uncertainties unique to the risk assessment. This document also 

identifies additional studies that may be required to complete an ecological risk assessment. 

There are currently two registered DMDS products. PaladinTM is a nearly pure DMDS (98.8% 

active ingredient) formulation intended for use in bedded and broadcast shank injection 

applications. Paladin ECTM is an emulsifiable concentrate (93.8% active ingredient) formulation 

intended for drip chemigation applications to raised beds. The labels require immediate covering 

of the beds or entire field with virtually impermeable film (VIF) tarp material immediately after 

application. DMDS will be considered the primary stressor in this risk assessment since DMDS 

is more toxic than its main degradate methanesulfonic acid (MSA) in soil, where its formation is 

minimized by the limited residence time of DMDS in soil due to volatilization. In addition, 

degradation of DMDS in water is not anticipated to be a significant process since evaporation 

from water is the main loss process, occurring very rapidly on the order of several hours. 

Transformation processes in the atmosphere potentially contributing to the formation of groundlevel ozone and acid rain are expected to be minimal considering the current limited scope of 

DMDS usage. Please refer to Section 8.1 for the detailed discussion on the exposure and relative 

toxicity for DMDS as compared to the degradates as well as a detailed discussion on its 

contribution to ground-level ozone and acid rain formation. In addition, the comparison of 

ecotoxicological endpoints between DMDS and the estimated toxicological endpoint values for 

its main degradate MSA in soil using ECOSAR1

 is shown in Appendix 1. 

The collection of field volatility studies indicate that off-site transport of DMDS mainly occurs 

through volatilization and resulting escape into the atmosphere. Factors such as weather 

conditions (e.g., air temperature), and soil conditions (e.g., soil temperature and soil moisture), 

appear to mediate flux rates to the atmosphere. Field volatility studies conducted with a variety 

of tarp materials indicate that DMDS has the ability to be transfered through the tarp. It may 

also be possible that DMDS could diffuse laterally and upward in the soil space between bedded 

tarps. The field volatility studies also indicate that VIF tarps may potentially reduce emissions of 

DMDS from the soil, as only 35.2 percent of applied DMDS is lost, compared to some 

applications with lower density tarp material where up to 81.43 percent has been observed to be 

lost. 

DMDS is not expected to have large residence times in water. Therefore, aquatic exposure and 

surface drinking water exposure are not expected to be significant. Refer to Section 7 for a full 

justification for this determination. In addition, the VIF tarp requirement for DMDS applications 

 

1

 EPISuite, v 4.1: http://www.epa.gov/opptintr/exposure/pubs/episuite.htm 
Page 5 of 53 

is expected to reduce exposure potential via ground water. Refer to Section 8.6 for a full 

discussion. . 

For DMDS and terrestrial animals, the main route of exposure is expected to be via inhalation. 

For terrestrial plants, some exposure to vapor phase DMDS is expected. To estimate exposures 

to DMDS, a tiered approach will be used. Both the American Meteorological 

Society/Environmental Protection Agency Regulatory Screening Model (AERSCREEN v. 

11060 - tier 1) and the Probabilistic Exposure and Risk Model for Fumigants (PERFUM v. 2.5.1 

- tier 2), if necessary, will be used to predict upper bound air estimated exposure concentrations 

(EECs) at a point near the edge of the treated field directly downwind from the application site. 

In addition, PERFUM will be used to predict fumigant air concentrations at specified points 

downwind from the treated field if there are exceedances with levels of concern. Terrplant (v. 

1.2.2) will be used to capture the upper-bound exposure scenario which may occur from the 

transport of DMDS to the edge of the treated field where seeds may reside. 

The largest uncertainty for DMDS exposure is related to its emissions from broadcast 

applications with VIF tarps. There is currently only one field volatility study available and it 

was conducted for bedded applications. To address this uncertainty, a field volatility study 

encompassing broadcast applications is being requested. A major uncertainty for terrestrial 

exposure is that EECs are based on the conservative assumption that birds and mammals are not 

transient and are therefore continuously exposed to emissions of DMDS downwind from the 

treated field. Such an assumption is perhaps more representative for plants since they are 

stationary. In addtion, peak hourly air concentrations during temperature inversions may be 

underestimated since potentially large exposures occurring at durations of less than one hour 

would not be captured . Such exposure may occur with temperature inversions when light and 

variable wind speeds and highly stagnant air with limited mixing can occur. However, , current 

labels contain specific language restricting applications during temperature inversions citing a 

number of criteria indicating the presence of a forecasted temperature inversion. Therefore, it is 

not expected that this limitation in the model would be relevant for the risk assessment. 

The data needs for environmental fate are listed below:

 835.8100 Field Volatility Study. Virtually impermeable film (VIF) tarps are required on 

the label. One field volatility study is available only for drip chemigation bedded 

applications with VIF tarps. However, other field volatility studies requested at this time 

for for broadcast shank injection applications and bedded shank injection applications 

with VIF tarps are required at this time. Flux values from the study will be used to 

determine air exposure resulting from DMDS broadcast field applications. 
Page 6 of 53 

The data needs for ecological effects are listed below:

 850.4150 Vegetative Vigor Tier II. A supplemental non-guideline toxicity study (MRID 

47471202) was received for DMDS. Additional information related to the temperatures 

during the existing study as well as the temperature dependence for DMDS vapor 

pressure are necessary for the interpretation on the measured effect of DMDS on the 

vegetative vigor of plants exposed to DMDS vapors in the air (please refer to DP Barcode 

405334, dated 4/30/13, for further information). 

 Non-Guideline Acute Honey Bee Vapor Exposure Study. As discussed further in this 

problem formulation, respiration exposure is determined to be the primary route of 

exposure for the terrestrial risk assessment. Inhalation studies are available for mammals 

(MRID 41277004) and birds (MRID 48788401) and given the volatile nature of DMDS, 

vapor exposure risk would also be applicable to terrestrial invertebrates using the honey 

bee as a surrogate. See the justification table below for more information. 

 
Page 7 of 53 

2. Introduction 

For this Problem Formulation (PF), EFED evaluated the most recent ecological risk assessments 

for dimethyl disulfide (hereafter referred to as DMDS) in association with any updated toxicity, 

exposure, and usage information to determine if sufficient data are available and if further 

updates are needed to support registration review. The most recent risk assessment for DMDS 

was the Section 3 New Chemical Risk Assessment completed in 2010 (DP Barcodes 339685 and 

363748, dated April 20, 2010). This risk assessment addressed pre-plant bare soil uses for 

various crops including tomatoes, peppers, eggplant, cucumbers, squash, melons, strawberries, 

blueberries, field grown ornamentals, and forest nursery crops. The structure of DMDS as well 

as the chemical names and other identifiers can be found in Table 2 of this document. 

DMDS is a transparent light yellow liquid with a strong garlic-like odor. DMDS is used for preplant soil fumigation, acting as a stressor within the gas phase. Given its high vapor, 

volatilization is expected to be the main dissipation pathway for DMDS. The impacts of any 

DMDS which may runoff is expected to be limited by its tendency to rapidly evaporate from 

surface water. Please refer to Section 7 for a complete discussion. DMDS is also very soluble, 

but its potential to leach to ground water is mitigated by virtually impermeable film (VIF) tarps 

that are required on the label. Please refer to Section 8.6 for further details. DMDS gradually 

degrades to major degradates methanesulfonic acid and carbon dioxide in soil. DMDS also 

degrades to major degradates methanesulfonic acid, methanesulfinic acid, and sulfuric acid in 

water via photodegradation. However, formation of these degradates will be limited due to the 

tendency of DMDS to evaporate rapidly from water. 

DMDS acts by blocking the cytochrome oxydase mechanism necessary for mitochondrial 

respiration in order to control nematodes (Charles, 2003). DMDS is also used to control weeds, 

as well as soil-bourne fungi and bacteria. However, the exact mechanism of action for these 

target pests is unknown. 

3. Use Characterization 

DMDS is used as a soil fumigant in fields. It is formulated in two active end-use products. 

PaladinTM is a nearly pure DMDS (98.8% active ingredient) liquid formulation intended for use 

in shank injection applications. Paladin ECTM is an emulsifiable concentrate (93.8% active 

ingredient) formulation intended for drip chemigation applications. DMDS target pests 

includeweeds, soil-bourne bacteria, plant pathogens, and nematodes. . The maximum 

application rate for dimethyl disulfide is 455 lbs. a.i./A for all uses. Both PaladinTM and 

PaladinTM EC are used before planting of fruiting vegetables (specifically tomatoes, peppers, and 

eggplant), cucurbit crops (specifically cucumbers, squash, and melons), strawberries, blueberries, 

field grown ornamentals, and forest nursery crops. The plant-back interval for DMDS 

applications is at least 21 days. DMDS is applied once per year before planting. 

Labels restrict dimethyl disulfide soil application methods to shank injection and drip 

chemigation applications. DMDS can be applied to the whole field via broadcast applications or 

applied exclusively to raised beds. Furthermore, all applications require immediate covering of 
Page 8 of 53 

the treated field or bed by tarps composed of virtually impermeable film (VIF) material. Two of 

the application methods for DMDS are illustrated in Figure 1, Figure 2, and Figure 3. Labels 

also have several other mandatory requirements for each application method, such as the 

consideration of minimum injection depths, minimum tarp removal times, and maximum field 

sizes. These requirements are listed below: 

Drip Chemigation VIF Tarped Application:

 Minimum days to remove tarp from the field = 12 days after application 

 Maximum field size = 40 acres 

Shank Injection VIF Tarped Application: 

 Minimum shank injection depth = 8 inches below the ground (broadcast)

= Depth not exceeding below bed furrow (bedded)

 Minimum days to remove tarp from field = 12 days after application

 Maximum field size = 40 acres

Credit: http://www.goodfruit.com

Figure 1. Photograph showing flat fume or broadcast shank injection application followed 

by tarp covering. 
Page 9 of 53 

Credit: USEPA, 2005 

Figure 2. Photograph showing shank injection application to raised beds followed by tarp 

covering. 

Credit: USEPA, 2005 

Figure 3. Photograph showing tarped drip chemigation application to raised beds. 

Since DMDS was registered in 2010, there has not been any definitive usage information 

compiled. DMDS is an alternative to methyl bromide which is currently being phased out under 

the Montreal Protocol. Therefore, current DMDS usage is anticipated to expand in the future. 

DMDS applications are not approved in California at this time. However, future approval of 

DMDS use in California is also expected to contribute to the expansion of the overall usage 

volume of DMDS (USEPA Analysis, 2012). 
Page 10 of 53 

4. Conclusions from Previous Risk Assessments 

The Section 3 New Chemical Risk Assessment (DP Barcodes 339685 and 363748, dated April 

20, 2010) for DMDS discussed in Section 2 serves as the basis of this scoping document. The 

major ecological risk conclusions presented in the assessment are described below. 

4.1 Ecological Risk Assessments 

Inhalation of DMDS vapor following soil fumigation is considered to be the major route of 

exposure for terrestrial organisms. The analysis in Section 3 of the New Chemical Risk 

Assessment, which used honey bee contact toxicity data, mammal and avian inhalation data, 

monitoring data from a field volatility study, and the estimated upper-bound edge-of-field air 

concentrations from the Probabilistic Exposure and Risk Model for Fumigants (PERFUM), 

showed that DMDS applications did not appear to indicate a potential for acute concern to birds, 

mammals, terrestrial phase amphibians, reptiles and terrestrial invertebrates (RQ < 0.011). 

However, this was based on field volatility emission data only for DMDS bedded drig 

chemigation VIF tarped applications. An assessment for broadcast applications could not be 

completed due to the absence of a field volatility study with a broadcast DMDS application. 

For aquatic organisms, acute risks of concern were identified for endangered freshwater fish 

species, aquatic-phase amphibian endangered species, freshwater invertebrate endangered 

species, and non-vascular aquatic endangered plants. EECs for aquatic animals and plants were 

based on upper-bound Pesticide Root Zone Model/Exposure Analysis Modeling System (PRZM 

v. 3.12.3/EXAMS v. 2.98.04.06) surface water concentrations for DMDS, with the volatilization 

algorithm activated. The summary of the previous conclusions for ecological risk based on the 

data for DMDS is shown in Table 1.

Table 1. Summary of risk concerns identified for DMDS in previous assessments.

Birds Mammals Terr. 

Plants 

Terr. 

Inverts* Fish BCF Aquatic Inverts 

Aquatic 

Plants 

Ground 

Water 

Contami 

-nation 

Persistence Degradates 

of Concern 

Bedded Apps. – 

No 

Broadcast Apps. 

Uncertain 

Possible No Yes No Yes Yes Possible No None 

Yes = at least one LOC has been exceeded in previous assessments. 

No = LOCs have not been exceeded in previous assessments. 

Uncertain = RQs for mammals and birds have not been calculated previously as there is no field volatility study for 

broadcast applications. Furthermore, RQs for terrestrial plants were not calculated due to limitations in the terrestrial plant 

study. However, labels indicate terrestrial plants as a target species and exposure is predicted. 

*A qualitative assessment was performed for terrestrial invertebrates based on the lack of a quantitative risk assessment 

framework at the time. 

Since the Section 3 New Chemical Risk Assessment, additional information about DMDS 

residence time in water has been considered. An aerobic aquatic laboratory metabolism 

study(MRID No. 48662502) recently submitted to the Agency indicated that DMDS possessed a 

DT90 of around 2.5 – 3 hours from water to volatile traps in the headspace in two water/sediment 
Page 11 of 53 

systems; therefore, DMDS’s residence time in water is diminished to the point where aquatic 

exposure is not expected to be significant. The analysis showing these results for DMDS’s 

volatilization from water is shown in Section 7. 

4.2 Drinking Water Assessments 

A quantitative drinking water exposure assessment was not conducted for DMDS, in agreement 

with the Health Effects Division (HED), due low exposure potential. Information regarding 

DMDS’s residence time in water supports this finding. An aerobic aquatic laboratory study 

(MRID No. 48662502) shows that the DT90 of DMDS due to volatilization is between 2.5 – 3 

hours. Please refer to Section 7 for further details behind the determination of the DT90. Given 

the rapid volatilization of DMDS in the water column, significant exposure in surface water is 

not expected. Therefore, on this basis, there is a low potential for acute, chronic, and cancer 

exposure occurring from DMDS being transported to surface water off of treated fields. 

DMDS’s possesses high solubility, however, ground water contamination will be mitigated by 

the use of VIF tarps required on the label. Please refer to Section 8.6 for further details. 

4.3 Clean Water Act Programs 

DMDS is not identified as a cause of impairment for any water bodies listed as impaired under 

section 303(d) of the Clean Water Act, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=88

5. No Total Maximum Daily Load (TMDL) criteria have been developed for DMDS, based on 

information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id

=885&p_pollutant_group_name=PESTICIDES. More information on impaired water bodies and 

TMDLs can be found at http://www.epa.gov/owow/tmdl/. The Agency invites submission of 

water quality data for this pesticide. To the extent possible, data should conform to the quality 

standards in Appendix A of the OPP Standard Operating Procedure: Inclusion of Impaired 

Water Body and Other Water Quality Data in OPP’s Registration Review Risk Assessment and 

Management Process (see: 

http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm), in order to ensure 

they can be used quantitatively or qualitatively in pesticide risk assessments. 

5. Environmental Fate and Transport 

DMDS is a transparent light yellow liquid with a strong garlic-like odor. It is highly soluble and 

has high vapor pressure. Based on Henry’s Law Constant value of 0.001 atm-m3

/mol and DT90

in water of between 2.5 – 3 hours, volatilization of DMDS from soil and water surfaces is 

expected to be the most significant transport and loss process from the terrestrial and aquatic 

environments. The pertinent physical, chemical, and environmental fate properties relating to 

DMDS are illustrated Table 2. 
Page 12 of 53 

Table 2. Physical and chemical properties of DMDS. 

Property Value and units MRID or Source 

Structure EPISUITE ver 4.1

Chemical Formula C2H6S2 MRID 46903506 

Molecular Weight 94.2 g/mol MRID 46903506 

Vapor pressure 

(20°C) 22.5 torr MRID 46903506 

Henry’s Law Constant 

(20°C) 1.04 x 10-3 atm·m3

/mol MRID 46903510 

Water Solubility 

(20°C) 2,702 mg/L MRID 46903510 

Octanol – water partition 

coefficient (log KOW) 1.77 MRID 46903509 

An average of 46.6 percent of applied DMDS is lost from soil due to volatilization (range 8.01 – 

81.43 percent of applied material, n= 8 field volatility studies) over time periods ranging from 48 

to 320 hours after application. The variation appears to be mediated by a combination of factors 

including tarp material, weather conditions (e.g., air temperature) and soil conditions (e.g., soil 

temperature and soil moisture). One field volatility study conducted with bedded tarped 

applications and VIF tarp covering accounted for 35.20% of DMDS lost from soil, which is on 

the low end of the range. This suggests that soil emissions will be minimized in labeled DMDS 

applications since the label requires the use of VIF tarps. However, additional studies with other 

application methods, such as broadcast tarped applications, are needed to confirm the 

effectiveness of VIF tarps to minimize DMDS emissions. It should also be noted that residual 

DMDS also biodegrades to methanesulfonic acid (MSA) and carbon dioxide in the brief time it 

resides in soil. Once DMDS is volatilized, it degrades rapidly to methanesulfonic acid, sulfuric 

acid, and other sulfates in the atmosphere via hydroxyl radical reactions. DMDS’s half-life in 

the atmosphere is short at 34 minutes. 

Table 3 lists the environmental fate properties of DMDS. Table 4 provides detailed information 

on DMDS lost from soil in the various field volatility studies conducted across the country, in 

sites where soil fumigants are typically used. Detailed information on DMDS degradates is 

presented in Table 5. A detailed description of the fate and transport of DMDS in the 

environment is presented in Appendix 1. 

Table 3. Summary of DMDS environmental fate properties. 
Page 13 of 53 

Parameter Value

Major 

Degradates Reference 

Study 

Classification/ 

Comments

Hydrolysis t1/2 Stable at pH 5, 7, and 9 - MRID 46903532 Acceptable 

Photolysis t1/2 in 

water 

1.3 days Methanesulfonic acid 

Methanesulfinic acid 

Sulfuric acid 

MRID 42900201 Supplemental 

Photolysis t1/2 on 

soil N/A - N/A Waived 

Degradation t1/2 in 

air 

34 minutes (atmospheric 

half life, reaction with 

OH radicals) 

42 minutes (atmospheric 

lifetime, reaction with 

OH radicals) 

Methansulfonic acid 

Methane thiol 

Sulfuric acid 

Sulfates 

EPI Suite 

Wine et al., 1981 

Fangdong et al., 

1990 

The EPI Suite 

estimate of OH 

radical reaction 

compares 

favorably with the 

open literature 

result, with a 

value of 34 

minutes. 

Aerobic Soil 

metabolism t1/2

France Clay Loam 2.86 

days 

Switzerland Clay 3.74 

days 

Florida Sand

No major transformation 

through 120 days 

California Sandy 

Loam

No major transformation 

through 120 days 

Methanesulfonic Acid 

Carbon dioxide 

MRID 47052819 Supplemental 

Half-lives back 

calculated 

assuming that the 

total formation of 

methanesulfonic 

acid residues are 

attributed 

completely to the 

presence of 

DMDS. 

Foreign soils 

taxonomically 

representative of 

US soils 

Anaerobic Soil 

metabolism t1/2

California WaterSandy Loam Soil

78.9 days 

Methanesulfonic Acid 

Methane thiol 

MRID 47052820 Supplemental 
Page 14 of 53 

Parameter Value

Major 

Degradates Reference 

Study 

Classification/ 

Comments

Aerobic Aquatic 

metabolism t1/2

Missouri Water-Silt 

Loam Sediment

DT50 = 1.21 hours 

DT90 = ~ 3 hours 

Georgia Water-Sand 

Sediment

DT50 = 0.77 hours 

DT90 = ~2.5 hours 

- MRID 48662502 Supplemental 

Main loss in 

water due to 

volatilization and 

escape to 

headspace vapor 

trap 

Anaerobic Aquatic 

metabolism t1/2

Missouri Water-Silt 

Loam Sediment

DT50 = 1.27 days 

DT90 = ~ 8 days 

Georgia Water-Sand 

Sediment

DT50 = 1.55 days 

DT90 = ~ 10 days 

- MRID 48662501 Supplemental 

Main loss in 

water due to 

volatilization and 

escape to 

headspace vapor 

trap 

Soil-Water 

Partition 

Coefficient (Kd) 

California, USA Sandy 

Loam 

0.54 mL/g (0.6 % OC) 

Speyer, Germany 

Sandy Loam

0.68 mL/g (2.3 % OC) 

Mechtildshausen, 

Germany Loam 

0.60 mL/g (1.28 % OC) 

Mussig, France Clay 

Loam 

0.55 mL/g (2.98 % OC) 

Bretagne, France Silt 

Loam

0.86 mL/g (2.0 % OC) 

- MRID 46917014 

MRID 46917015 

Supplemental 

Foreign soils 

taxonomically 

representative of 

US soils 

Terrestrial Field 

Dissipation 

N/A - N/A Waived 

Aquatic Field 

Dissipation 

N/A - N/A Waived 
Page 15 of 53 

Parameter Value

Major 

Degradates Reference 

Study 

Classification/ 

Comments

Field Volatility See Table 4 below - MRIDs: 

47052821 

47052822 

47052823 

47052824 

47820001 

Acceptable 

Acceptable 

Acceptable 

Acceptable 

Acceptable 

Accumulation in 

Fish, max. BCF 

N/A - N/A Waived 

1 All studies used DMDS as the test substance. 

2

 Dashes mean no constituents found or measured. 

3

 N/A means not applicable.

Table 4. Description of DMDS field volatility studies and volatile flux measurements.

Field Volatility Study1

(Application Rate) 

Time 

Applied MRID Study Classification 

Peak 

Flux 

Rate 2

() 

Cumulative 

Mass Loss 

(%) 

Yuma, AZ Loamy Sand

Shank Injection to Raised 

Beds, 8 inch depth with LDPE 

Tarp Covering 

(780 lbs. a.i./A) 

August 17 

7:00 am – 

2:17 pm 

47052821 Acceptable 27.34 81.43 percent through 65 

hours post-application 

Nipomo, CA Sandy Loam

Drip Irrigation to Raised Beds 

with LDPE Tarp Covering 

(602 lbs. a.i./A) 

June 21 

9:01 am – 

2:33 pm 

47052822 Acceptable 10.99 27.64 percent through 72 

hours post-application 

Cantua Creek, CA Sandy 

Loam

Broadcast Shank Injection, 12 

inch depth with LDPE Tarp 

Covering 

(580 lbs. a.i./A) 

Nov. 14 

7:08 am – 

4:37 pm 

47052823 Acceptable 6.91 54.29 percent through 72 

hours post-application 

Dover, FL Loamy Sand

Shank Injection to Raised 

Beds, shallow depth with 

Metalized Tarp Covering 

(608 lbs. a.i./A) 

April 29 

9:57 am – 

4:58 pm 

47052824 Acceptable 2.72 8.1 percent through 48 

hours post-application 

Bradenton, FL Sand

Shank Injection to Raised 

Beds, shallow depth with 

LDPE Tarp Covering 

(633 lbs. a.i./A) 

April 29 

9:57 am – 

4:58 pm 

47052824 Acceptable 24.13 57.82 percent through 48 

hours post-application 
Page 16 of 53 

Field Volatility Study1

(Application Rate) 

Time 

Applied MRID Study Classification 

Peak 

Flux 

Rate 2

() 

Cumulative 

Mass Loss 

(%) 

Tifton, GA Loamy Sand

(Field 1)

Pre Bedded Shank Injection, 8 

inch depth with VIF Tarp 

Covering 

(546.7 lbs. a.i./A) 

February 7 

12:47 pm – 

2:20 pm 

47820001 Acceptable 3.83 35.20 percent through 

320 hours postapplication 

Tifton, GA Loamy Sand 

(Field 2)

Pre Bedded Shank Injection, 8 

inch depth with LDPE Tarp 

Covering 

(538.8 lbs. a.i./A) 

February 7 

3:19 pm – 

4:44 pm 

47820001 Acceptable 10.67 69.74 percent through 

320 hours postapplication 

Tifton, GA Sand (Field 3)

Pre Bedded Shank Injection, 8 

inch depth with LDPE Tarp 

Covering 

(568.9 lbs. a.i./A) 

February 7 

5:40 pm – 

7:57 pm 

47820001 Acceptable 6.02 38.33 percent mass loss 

through 320 hours postapplication 

1

 Tarp Materials: LDPE = Low density polyethylene; VIF = Virtually Impermeable Film 2

 Peak flux rate refers to the average over ~ 4 hours as per the sampling periods in the field volatility studies. 
Page 17 of 53 

Table 5. Environmental degradates of DMDS. 

Code Name/ Synonym Chemical Name Chemical Structure Study Type Ref. (MRID) Maxi

%AR 

Parent Compound

DMDS Dimethyl disulfide 

CAS No.: 624-92-0

Formula: C2H6S2

MW: 94.19 g/mol 

MAJOR TRANSFORMATION PRODUCTS 

MSA Methanesulfonic Acid 

CAS No. 75-75-2Formula: CH4SO3MW: 96.1 g/mol

Aqueous Photolysis 47052818 < 5

(24 h

Aerobic Soil Metabolism 

(France Clay Loam Soil) 

47052819 33

(14 d

Aerobic Soil Metabolism 

(Switzerland Clay Soil) 

47052819 32

(21 d

Anaerobic Soil Metabolism 

(California Water – Sandy 

Loam Soil System) 

47052820 

< 3

(21 day

< 1

(71 days

< 2

(21day

Degradation in Air Fangdong et al. , 1990 N

Methanesulfinic Acid Methanesulfinic Acid 

CAS No. 17696-73-0Formula: CH4SO2

MW: 80.1 g/mol Aqueous Photolysis 47052818 

< 5

(24 h

CH3

S

S

CH3

S CH3

OOH

O
Page 18 of 53 

Code Name/ Synonym Chemical Name Chemical Structure Study Type Ref. (MRID) Maxi

%AR 

Sulfuric Acid Sulfuric Acid 

CAS No. 7664-93-9 Formula: H2SO4

MW: 98.07 g/mol 

Aqueous Photolysis 47052818 < 5

(24 h

Degradation in Air Fangdong et al., 1990 N

Carbon Dioxide Carbon Dioxide 

CAS No. 124-38-9 Formula: CO2MW: 44.01 g/mol 

Aerobic Soil Metabolism 

(France Clay Loam Soil) 47052819 30

(59 d

Aerobic Soil Metabolism 

(Switzerland Clay Soil) 47052819 27

(120 

MT Methane thiol 

Methyl mercaptan CAS No. 74-93-1 Formula: CH4S

MW: 48.1 g/mol 

Anaerobic Soil Metabolism 

(California Water-Sandy Loam 

Soil) 

47052820

16

(14 day

Degradation in Air Fangdong et al. , 1990 N

*%AR means percent of applied radioactivity. **NA means that material balance is not available from study. 

O C O
Page 19 of 53 

6. Receptors 

The receptor is the biological entity that is exposed to the stressor (US Environmental 

Protection Agency, 1998). Consistent with the process described in the Overview 

Document (US Environmental Protection Agency, 2004), this risk assessment uses a 

surrogate species approach in its evaluation of DMDS. Toxicological data generated 

from surrogate test species, which are intended to be representative of broad taxonomic 

groups, are used to extrapolate to potential effects on a variety of species (receptors) 

included under these taxonomic groupings. 

Acute and chronic toxicity data from studies submitted by the pesticide registrant along 

with the available open literature may be used to evaluate potential direct effects of 

DMDS to the aquatic and terrestrial receptors. These data include toxicity studies on the 

technical grade active ingredient. The open literature studies are identified through 

EPA’s ECOTOX database (http://cfpub.epa.gov/ecotox/), which employs a literature 

search engine for locating chemical toxicity data for aquatic life, terrestrial plants, and 

wildlife. The evaluation of both sources of data may also provide insight into the direct 

and indirect effects of DMDS on biotic communities from loss of species that are 

sensitive to the chemical and changes in structure and functional characteristics of the 

affected communities. 

6.1 Effects to Aquatic Organisms 

The most sensitive acute toxicity reference values associated with DMDS exposure to 

aquatic organisms are summarized in Table 6. 

Table 6. DMDS Toxicity Reference Values (TRVs) (ppb of Active Ingredient) for 

Aquatic Organisms

Exposure 

Scenario Species 

Exposure 

Duration

Toxicity Reference Value 

(g a.i./L) Reference

Freshwater Fish 

Acute Oncorhynchus 

mykiss

96 hours LC50 = 960 MRID 47052814 

Acceptable 

Chronic NA NA NA NA 

Freshwater Invertebrates

Acute Daphnia magna 48 hours EC50 =1610 MRID 47052816 

Acceptable 

Chronic NA NA NA NA 
Page 20 of 53 

Table 6. DMDS Toxicity Reference Values (TRVs) (ppb of Active Ingredient) for 

Aquatic Organisms

Exposure 

Scenario Species 

Exposure 

Duration

Toxicity Reference Value 

(g a.i./L) Reference

Estuarine/Marine Fish

Acute Cyprinodon 

variegatus) 

minnow 

 96 h LC50=5600 MRID 47307504 

Acceptable 

Chronic NA NA NA NA 

Estuarine/Marine Invertebrates

 Acute Mysidopsis 

bahia 

 96 hours LC50=4900 MRID 47307505 

Acceptable 

Chronic NA NA NA NA 

Aquatic Plants

Vascular Lemna gibba 7 days EC50=28000 

EC05 = 6000 

MRID 47471204 

Acceptable

Nonvascular Anabaena flosaquae 96 hours Cell Density EC50=320 

EC05 = 110 

MRID 47471205 

Acceptable 

NA = Data appropriate for quantitative use are not available.

6.2 Effects to Terrestrial Organisms 

The toxicity endpoints used to characterize risks of DMDS exposure to birds and 

mammals are summarized in Table 7. 
Page 21 of 53 

Table 7. Toxicity Reference Values (TRVs) for Terrestrial Species for DMDS 

Exposure 

Scenario

Species Exposure 

Duration

Toxicity 

Reference Value

Reference

Mammals

870.1300 

Acute 

Inhalation1

Rattus 

norvegicus 4-hour inhalation 

LC50 males > 3.18 mg/L 

(3.18 – 6.19 mg/L) 

LC50 females = 5.22 

mg/L 

(4.56 – 5.97 mg/L) 

LC50 combined = 4.91 

mg/L 

(4.38 – 5.52 mg/L) 

MRID 46903516 

Acceptable 

Birds

Non-Guideline 

Acute 

Inhalation 

Colinus 

virginianus 4-hour Inhalation 

Male LC50=1.97 mg/L 

(1.62-2.41 mg/L) 

Female LC50=1.73 mg/L 

(1.55-1.93 mg/L) 

Combined LC50=1.84 

mg/L (1.64-2.06 mg/L) 

MRID 46917013 

Supplemental 

 

1

Data from HED DMDS Risk Assessment (D339675). 

Mammalian Species

 

An acceptable rat inhalation study (MRID 46903516) was submitted for DMDS. Because 

inhalation is the expected exposure route, the rat inhalation toxicity value of 4.91 mg/L is 

used in this assessment based on the combined endpoint for male and female rats. The 

combined endpoint will be used because of the uncertainty in the non-definitive endpoint 

for male rats, and the combined value represents a reasonable combination of the 

definitive with the non-definitive endpoint. 

A 90 day repeated-dose inhalation study for the rat was reported under OECD guidelines 

(ELF ATOCHEM, January 1992). This study resulted in no adverse effects. A 

developmental toxicity study through inhalation (ATOCHEM, December 1991) also 

resulted in no effects. 
Page 22 of 53 

Avian Species 

The effect of DMDS on the Bobwhite quail (Colinus virginianus) is used to estimate the 

effect for all birds. Although an acute oral toxicity study (MRID47052813) was 

submitted, the LD50 will not be used in this assessment because no dietary exposure is 

expected from the use of DMDS. An acute avian inhalation study conducted with the 

bobwhite quail (Colinus virginianus) (MRID 46917013) is classified as supplemental 

because it is a non-guideline study. This study determined that the female quail (acute 

inhalation LC50 is =1.73 mg/L (1.55-1.93 mg/L). 

Plant Species 

Toxicity values for plant species are summarized in Table 8. Two supplemental nonguideline studies were submitted to illustrate the effect of gaseous DMDS on plants. 

There is insufficient data to estimate the effect on plants. These studies maybe upgraded 

if acceptable information on the headspace for the plastic bag used to contain the gas is 

submitted. 

Table 8. Toxicity Reference Values (TRVs) for Terrestrial Plants for DMDS 

Exposure 

Scenario

Species Endpoint Toxicity 

Reference Value 

(lbs a.i./A)

Reference

Seedling Emergence 

Monocot Ryegrass 

Lolium perenne 

Dry weight EC25 = 290 MRID 

47381001 

NOAEC = 75 Supplemental

Dicot Sugarbeet 

Beta vulgaris 

Dry weight EC25 = 91 

NOAEC = 75 

Vegetative Vigor 

Monocot Oat 

Avena sativa Dry weight 

EC25 = 100 MRID 

47471202 

Supplemental 

EC05=37.5 

Dicot Tomato 

Lycopersicon esculentum Height 

EC25 = 55 

EC05 =37.5 
Page 23 of 53 

6.3 Ecological Incidents 

The ecological incident information system (EIIS) is an OPP database that houses ecological 

incidents that have been reported to the Agency. When available, EIIS includes date and location 

of an incident, type and magnitude of effects observed in various species, use(s) of pesticides 

known or suspected of contributing to the incident, and results of any chemical residue analysis or 

other analyses conducted during incident investigation. EIIS incidents are categorized according 

to the certainty that the incident resulted from pesticide exposure. The Avian Monitoring System 

(AIMS) is a database administered by the American Bird Conservancy that contains publicly 

available data on reported avian incidents involving pesticides. Many of the incidents listed in 

this database are also in the EIIS. The following are results of the queries conducted for DMDS 

as of April 2013: 

EIIS returned no incident reports for DMDS. In addition, registrants have not reported any minor 

plant or animal incidents. Finally, AIMS identified no ecological incidents involving DMDS. 

7. Exposure Pathways of Concern 

Given DMDS’s volatile characteristics, its broad spectrum mode of action as a fumigant, and 

application methods in soil, the following lists the major expected pathways of exposure: 

 Inhalation exposure for mammals, birds

 Vapor-phase exposure to terrestrial invertebrates 

 Vapor-phase exposure for plants 

DMDS has been shown to escape to the atmosphere from soil in large quantities over short time 

frames close to the time of application, from the collection of field volatility studies submitted to 

the Agency. This is the case even with the use of VIF tarps, which are required on the label, as 

DMDS may be transferred upward through tarps or in the soil space in between beds. Although 

previous risk assessments have not quantitatively identified risks to mammals and birds due to 

DMDS air exposure based on available data, this risk assessment will address present 

uncertainties and consider additional data for scenarios other than bedded tarped application 

methods. Therefore, the air exposure pathway will be addressed. The labeled application rates 

and methods along with newly submitted field volatility studies will be considered. Since all 

DMDS soil uses are incorporated under the surface, spray drift is not expected to be of concern 

for terrestrial organisms. 

 Soil exposure for plant seeds 

DMDS exposure to plant seedlings in soil is expected from applications on and possibly adjacent 

to the treated field. DMDS’s broad spectrum mode of action as a fumigant, large application rates 

to soil, and the mobile and diffuse nature of DMDS as a vapor in soil all justify this exposure 

pathway. 
Page 24 of 53 

 Aquatic exposure for freshwater and estuarine/marine animals, and aquatic plants 

The previous Section 3 New Chemical Assessment identified risks to aquatic invertebrates, 

freshwater fish, and non-vascular aquatic plants. However, a recent aerobic aquatic metabolism 

study (MRID No. 48662502) indicates that the retention time of DMDS in water is short enough 

that exposure and related toxicity would be limited. Therefore, aquatic exposure of DMDS is not 

expected to be significant with its current uses. Figure 4 below shows that the majority of 

DMDS declines in water from two water experimental systems in the aerobic aquatic study within 

an 8 hour period after application can be attributed to loss due to volatilization (MRID No. 

48662502). Therefore, acute and chronic aquatic exposure is not expected to be of concern since 

the exposure duration of DMDS in water is expected to be much less than one day. 

*Data from MRID No. 48662502 

Figure 4. Plots showing DMDS decline in the sediment/water system due to volatilization 

over time (blue line), to the headspace (red line) in the Georgia water-sand sediment system 

(left) and Missouri water-silt loam sediment system (right). 

 Drinking water exposure for mammals and birds

While dietary and drinking water exposures are possible for mammals and birds, acute risk from 

inhalation is determined to be the primary route of exposure for several reasons. First, as DMDS 

is highly volatile, concentrations on food items or water puddles on the field are expected to be 

short lived due to volatilization. 

For birds, based on DMDS vapor pressure and calculations using the STIR model, the maximum 

1-hour vapor inhalation dose for birds is 14,300 mg/kg bw. By contrast, based on DMDS’s 

solubility limit and calculations using the SIP model, the upper bound daily drinking water intake 

dose for a bird is 2,189 mg/kg bw. Multiplying the STIR estimate of one hour by 12 (to match 

the daily exposure duration of the SIP estimate) gives a result 100X higher than the SIP drinking 

water dose. This suggests that the potential daily inhalation exposure of a bird to DMDS is 

0

10

20

30

40

50

60

70

80

90

100

02468

Percent of Applied DMDS (percent)

Time After Application (hours)

Aerobic Water‐Sand Sediment

System

DMDS in Water

DMDS in Headspace

0

10

20

30

40

50

60

70

80

90

100

02468

Percent of Applied DMDS (percent)

Time After Application (hours)

Aerobic Water‐Silt Loam Sediment

System

DMDS in Water

DMDS in Headspace

DT90 = 2.5 hours DT90 = 3.0 hours 
Page 25 of 53 

substantially greater than the potential daily drinking water exposure of a bird for the same period 

of time, thus indicating that inhalation exposure will be of more concern. Please refer to 

Appendix 2 for the modeling analysis comparison. 

 Dietary exposure of birds or mammals from exposed food items in the soil

Exposure to residues from soil invertebrate food items for birds and mammals is not expected 

given that DMDS residues are not expected to build up to any significant quantity in the soil 

based on a comparison of upper-bound estimated exposures in soil biota using the Earthworm 

fugacity model, versus in air at the breathing zone (STIR). Please refer to Appendix 2 for the 

modeling analysis comparison. 

8. Analysis Plan 

The ecological risk assessment will focus on DMDS as the main stressor of concern for air and 

soil exposure. This determination is discussed further in Section 8.1 below. EECs will be 

calculated for air and soil using various environmental fate and transport models discussed in 

Section 8.2 below. The EECs will be compared with toxicological endpoints from various 

aquatic and terrestrial taxa to quantitatively compute a risk quotient (RQ). The RQ will be 

compared to the Agency’s levels of concern (LOC) to determine the risk to organisms resulting 

from DMDS applications. 

8.1 Stressors of Concern 

Table 3 and Table 5 show degradates which form in soil, water, and air resulting from the 

application of DMDS in soil. Structural activity relationships (SARs) of the degradates and the 

resulting estimated toxicity endpoint values for various aquatic and terrestrial taxa were compared 

to DMDS’s measured toxicity values to the same organisms to identify the toxic residues of 

concern. This analysis was conducted using ECOSAR version 1 (February 2, 2009). The results 

are shown in Appendix 3. Among the major degradates found in environmental fate studies, 

none have been identified as being potentially of toxicological concern compared to DMDS. 

Furthermore, DMDS exposure is expected to surpass degradate exposure for reasons described 

below. 

Degradates in Soil and Water 

The major loss process of DMDS in soil and water is expected to be mediated mainly by 

volatilization resulting in escape or applied residues to the atmosphere. Some residual DMDS in 

soil may biodegrade to MSA and may potentially be available to runoff from the treated field. 

MSA was observed to form to levels up to 33.17 percent in the aerobic soil metabolism study. 

However, considering this moderate level of formation, MSA will be excluded from a residue of 

concern also considering its lower toxicity compared to DMDS as estimated by ECOSAR shown 

in Appendix 3. In addition, the degradates MSA and sulfuric acid which were observed to form 
Page 26 of 53 

in a controlled aquatic photodegradation study (MRID No. 42900201) are not expected to form to 

any great extent in the environment as suggested by the aerobic aquatic laboratory study (MRID 

48662502) in which volatilization was the main loss pathway for DMDS from water . Therefore, 

this observed behavior of the fate of DMDS provides additional justification for considering 

DMDS as the primary stressor of concern in the environment. 

Degradates in Air, Ground-Level Ozone Formation, and Acid Deposition/Rain 

There are several known degradates resulting from natural DMDS emissions to the atmosphere as 

part of the atmospheric sulfur cycle. Among them include MSA, MT, sulfuric acid, and sulfates. 

The toxicity of all of these degradates are expected to be of equal or lesser toxicity than DMDS. 

Therefore, any acute risk to ecological species resulting from exposure to these degradates will 

adequately be captured considering untransformed DMDS emissions to the atmosphere. 

Since DMDS is a reactive volatile organic compound, it also has the potential to contribute to the 

formation of ground-level ozone. In addition, re-deposition of sulfates and sulfuric acid, which 

form from DMDS emissions, to terrestrial and aquatic environments may result in added risks to 

ecologically relevant species within areas close to or within a region where DMDS is intensely 

used. However, given the limited scope of its usage at the present time, significant generation of 

ozone or acidic sulfur deposition resulting from DMDS fumigant applications is not expected at 

this time. However, DMDS usage may increase over time since it is considered to be a methyl 

bromide replacement. Therefore, DMDS’s contribution to acid rain and ground-level ozone 

generation will be re-examined at the time of the registration review risk assessment. 

8.2 Measures of Exposure 

Measures of exposure of DMDS to aquatic and terrestrial organisms are derived from the 

utilization of environmental fate and transport models. Exposures resulting from DMDS soil 

fumigant applications will be estimated based on maximum application rates and all application 

methods cited in Section 3. 

DMDS acute exposures of birds and mammals through inhalation as well as terrestrial 

invertebrates and plants via gas-phase exposure are determined using the EECs from atmospheric 

dispersion models relying on the input of DMDS atmospheric flux measurements from the 

collection of volatility (flux) studies conducted for DMDS applications in the field. The 

Agency’s recommended screening near-field dispersion model the American Meteorological 

Society/EPA Regulatory Screening Model (AERSCREEN v. 11060), will be used to generate 

Tier I EECs. The Tier I analysis will consider the maximum flux rate for each application method 

from the collection of DMDS flux studies and worst-case meteorological conditions (light winds 

and stagnant conditions) to calculate peak air EECs, representing one-hour average 

concentrations. Documentation on the AERSCREEN model is available at 

http://www.epa.gov/scram001/dispersion_screening.htm. The exposure scenario evaluated in the 

Tier 1 analysis will assume that the terrestrial receptors are directly downwind from the emissions 

source. This is illustrated in Figure 5 below. 
Page 27 of 53 

Figure 5. Schematic showing soil fumigant air exposure scenario due to volatilization and 

subsequent release from soil evaluated in Tier 1 analysis. 

If the Tier 1 EECs for either surface or incorporated applications result in an exceedance of the 

LOC, EECs will be further examined using the Tier 2 model, the Probabilistic Exposure and Risk 

Model for Fumigants (PERFUM v. 2.5.1). PERFUM is parameterized by time series of flux data 

obtained from field volatility studies. PERFUM considers these flux values with a robust 

statistical sampling of meteorological data from points within rings surrounding a treated field 

(usually 5 years of hourly meteorological data). The current version of PERFUM processes 

estimated air concentrations from EPA’s previously recommended atmospheric dispersion model 

in the near field, the Industrial Source Complex Short-Range Model, Version 3 (ISCST3). 

ISCST3 has since been replaced by the refined mode of AERSCREEN, the AERMOD model, as 

the recommended refined dispersion model in the near field. However, both ISCST3 and 

AERMOD are similar in that they both use Gaussian plume dispersion principles. The framework 

for PERFUM is illustrated in Figure 6 below. Estimated air concentrations are calculated and 

binned by percentile distributions within each ring and averaging time period. First, a peak onehour averaging period will be used to calculate air EECs. If necessary, a higher averaging period 

equivalent to the exposure duration in toxicity studies will be used to characterize the RQs 

resulting from utilizing the one-hour peak EECs. The highest 90th percentile estimated air 

concentration from all averaging periods from the receptor ring closest to the edge of the field will 

be considered as the upper-bound EEC to determine the RQ. The PERFUM model is publically 

available on the web from the following link: 

http://www.exponent.com/projectdetail.aspx?project=450. For this soil fumigant assessment, 

maximum air exposure will occur at the edge of the field corresponding to where DMDS mass 

emissions from the treated field will accumulate to maximum levels along the fetch of wind 

blowing over the treated field. 

Wind, Dispersion, 

and 

Accumulation 

of Vapors or Gas

Volatilization of 

residues in soil

Soil incorporated and 

chemigation fumigant 

application 
Page 28 of 53 

Figure 6. Illustration of the spatial and temporal aspects of the source to receptor 

configuration in PERFUM. The wind rose (left) illustrates the frequency distribution of 

variations in wind speed and wind direction that PERFUM accounts for in the transport of 

the vapor plume from the treated source to receptors (right).

All modeling scenarios will be parameterized based on field volatility flux data normalized to the 

maximum field sizes specified by application method on the labels. Therefore, the modeling will 

be based on a maximum field size of 40 acres for all applications as specified on the label. 

For exposure to plant seedlings, TerrPlant (ver 1.2.2) will be used. Although TerrPlant EECs are 

based on runoff, TerrPlant will capture the overall exposure of plant seedlings whether it occurs 

from diffusion in the gas phase or runoff of dissolved DMDS. The Agency is currently 

developing a replacement model for TerrPlant. If the replacement has been approved prior to the 

initiation of the risk assessment, this new model will be used instead. 

8.3 Measures of Effect 

Toxicity data presented in Sections 6.1 and 6.2 of this problem formulation will be used with 

EECs to calculate risk quotients. Any additional information submitted by the registrant or found 

in the open literature prior to conduct of the risk assessment will also be considered. The open 

literature studies are identified using EPA’s ECOTOXicology database (ECOTOX) (USEPA, 

2007b), which employs a literature search engine for locating chemical toxicity data for aquatic 

life, terrestrial plants, and wildlife. The evaluation of both sources of data can also provide 

insight into the direct and indirect effects of pesticides on biotic communities from loss of species 

that are sensitive to the chemicals and from changes in structure and functional characteristics of 

the affected communities. 

8.4 Endangered Species Assessments 

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to federally threatened and/or endangered (listed) species from 

Treated 

Field 

Receptor 

Rings 
Page 29 of 53 

registered uses of pesticides in registration review. These assessments will be conducted in 

accordance with standard EPA procedures and good scientific judgment. 

8.5 Endocrine Disruptor Screening Program

DMDS was not included in the first group of 67 chemicals or second group of 109 chemicals 

issued an order to conduct Tier 1 EDSP testing. For additional information the EDSP program, 

visit http://www.epa.gov/endo/. 

8.6 Drinking Water Assessment

DMDS surface water exposure within reservoirs is not expected given the DT90 values ranging 

between 2.5 – 3.0 hours in water (MRID No. 48662502). Please refer to Section 7 for further 

details regarding the dissipation of DMDS from surface water. 

Despite the high solubility of DMDS, reduced exposure in ground water is expected due to the 

required use of VIF tarps. However, there are two scenarios where DMDS under tarps may move 

to ground water which should be mentioned and include the following: 1.) DMDS under tarps 

may become entrained into ground water via recharge processes especially for deeply applied 

DMDS in locations over shallow water tables, and 2.) DMDS applied under bedded tarps may 

leak laterally into a furrow between the beds beneath the ground uncovered by a tarp. DMDS in 

the unsealed furrow may then be available to leach to ground water given that a rain event occurs 

coincidentally. 

While DMDS may be entrained in ground water as described in scenario 1, it is unlikely that 

DMDS under this dissipation pathway will be transported to well intakes as well depths are often 

15 – 30 feet below the surface. Addressing scenario 2, there is a study which suggests that 

DMDS lateral leakage is minimal in comparison to the amount that remains under the bed 

(Chellemi et al., 2011). Figure 7 shows that a shank injected mixture of DMDS, metam sodium, 

and chloropicrin leaked at a very small amount compared to the amount which remained under 

the tarp. This was especially the case where a VIF tarp was used, such as shown at site 1 in 

Figure 7. 

Considering all lines of evidence for surface water and ground water exposure potential presented 

above, a drinking water assessment will not be conducted for DMDS. DMDS’s rapid evaporation 

from surface water and reduced exposure in ground water under broadcast and bedded tarped 

conditions both justify this de minimis determination for the drinking water assessment. 
Page 30 of 53 

Figure 7. In-bed and between-bed concentrations of VOCs two days (black box plot) and five 

days (gray box plot) after three-way application of DMDS, metam sodium, and chloropicrin. VIF 

tarps were used in Site 1, and low density polyethylene (LDPE) tarps were used at Sites 2 and 3. 

Figure courtesy of Chellemi et al., 2011. 

9. Preliminary Identification of Data Gaps 

9.1 Environmental Fate

Table 9 identifies environmental fate studies by MRID that offer data for each guideline 

requirement, as well as study classifications and whether or not further data are needed in order to 

support the risk assessment. 

Table 9. Submitted environmental fate data for DMDS. 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Justification and assumptions EPA 

will make in the absence of data 

835.2120 Hydrolysis 46903532 Acceptable No 

835.2240 Aqueous 

photolysis 

42900201 Supplemental No

835.2410 Soil photolysis (None) (Not 

Applicable) 

No

835.4100 Aerobic soil 

metabolism 

47052819 Supplemental No

835.4200 Anaerobic soil 

metabolism 

47052820 Supplemental No

835.4300 Aerobic aquatic 

metabolism 

48662502 Supplemental No
Page 31 of 53 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Justification and assumptions EPA 

will make in the absence of data 

835.4400 Anaerobic 

aquatic 

metabolism 

48662501 Supplemental No

835.1230 

835.1240 

Adsorption/ 

desorption and 

leaching 

46917014 Supplemental No

46917015 Supplemental 

835.1410 Volatility – 

laboratory 

(None) (Not 

Applicable) 

No

835.8100 

850.6100 

Volatility - field 47052821 Acceptable Yes Virtually impermeable film (VIF) tarps 

required on the label. Only one field 

volatility study is available for drip 

chemigation bedded applications using 

VIF tarps. However, another field 

volatility study is requested at this time 

for broadcast shank injection and 

bedded drip chemigation applications. 

Flux values from the study will be used 

to determine air exposure resulting from 

DMDS broadcast field applications. 

Without the data, EFED will assume 

risk to all terrestrial species that reside 

nearby fields fumigated with broadcast 

applications of DMDS. 

47052822 Acceptable

47052823 Acceptable

47052824 Acceptable

47820001 Acceptable

Analytical 

method in air 

48535303 Acceptable No 

835.6100 

850.6100 

Terrestrial field 

dissipation 

(None) (Not 

Applicable) 

No

Analytical 

method in soil 

49173201 In Review No

835.6200 

850.6100 

Aquatic field 

dissipation 

(None) (Not 

Applicable) 

No

Analytical 

method in water 

48575201 Supplemental No 

165-4 

(850.1730) 

Fish 

bioconcentration 

(None) (Not 

Applicable) 

No
Page 32 of 53 

9.2 Ecological Toxicity 

Table 10 identifies ecological effects studies by MRID that offer data for each guideline 

requirement, as well as study classifications and whether or not further data are needed in order to 

support risk assessment. Rationale for the additional data requested is presented below. 

Table 10. Submitted aquatic and terrestrial ecological effects data for DMDS.

Guideline Data 

Requirement 

Submitted 

Studies 

Study 

Classification

Are data 

needed to 

conduct 

risk 

assessment?

Justification 

850.2100 Avian Acute 

Oral 

47052813 Acceptable N 

Nonguideline Avian Acute 

Inhalation 

46917013 Acceptable N 

850.2200 Avian Dietary–

quail 

------------ ------------ N The primary route of exposure is expected 

to be through inhalation. 

850.2200 Avian Dietary–

mallard 

------------ ------------- N The primary route of exposure is expected 

to be through inhalation. 

Nonguideline Avian 

Subchronic/ 

Chronic 

Inhalation 

------------- ------------- N The primary route of exposure is expected 

to be through inhalation. This inhalation 

exposure is also expected to be acute and 

not chronic. 

850.1075 Fish Acute 

Toxicity–

bluegill 

Zebrafish 

47052815 Acceptable N 

850.1075 Fish Acute 

Toxicity–

rainbow trout

47052814 Acceptable N 

850.1010 Aquatic 

Invertebrate 

Acute Toxicity–

freshwater

47052816 Acceptable N 

850.1075 Marine/ 

Estuarine Acute 

Toxicity–Fish 

47307504 Acceptable N 

850.1025 Marine/ 

Estuarine Acute 

Toxicity–

Mollusk (shell 

deposition) 

47307503 Invalid N 
Page 33 of 53 

Guideline Data 

Requirement 

Submitted 

Studies 

Study 

Classification

Are data 

needed to 

conduct 

risk 

assessment?

Justification 

850.1035 Marine/ 

Estuarine Acute 

Toxicity–

Shrimp 

47307505 Acceptable N 

850.1350 Aquatic 

Invertebrate 

Life Cycle – 

marine/estuarine 

----------- ------------ N Current data indicate that chronic exposure 

to aquatic organisms is unlikely given the 

volatility of DMDS. 

850.1400 Fish Early Life 

Stage–

freshwater

------------- ------------- N Current data indicate that chronic exposure 

to aquatic organisms is unlikely given the 

volatility of DMDS. 

850.1400 Fish Early Life 

Stage– 

marine/estuarine 

------------ ------------- N Current data indicate that chronic exposure 

to aquatic organisms is unlikely given the 

volatility of DMDS. 

850.1300 Aquatic 

Invertebrate 

Life Cycle –

freshwater 

----------- ------------ N Current data indicate that chronic exposure 

to aquatic organisms is unlikely given the 

volatility of DMDS. 

 

Nonguideline Vegetative 

Vigor–Tier I 

Vegetative 

Vigor–Tier II 

47381002 

47471202 

Supplemental 

Supplemental 

Y A supplemental non-guideline tier II 

toxicity study (MRID 47471202) was 

received for DMDS. Additional 

information to calculate the headspace 

volume was submitted to estimate the 

effect of DMDS on vegetative vigor 

exposed through air concentrations. 

However, information on the temperature 

dependence of the saturated vapor pressure 

as well as information on the temperatures 

in the environment during the study are 

needed. Please see D405534 for more 

information. 

850.4500 

850.4550 

Aquatic Plant 

Growth – Tier II 

47471204 

47471205 

47471206 

47471207 

47052817 

Acceptable N 

850.3020 Honeybee Acute 

Contact 

47471203 Acceptable N 
Page 34 of 53 

Guideline Data 

Requirement 

Submitted 

Studies 

Study 

Classification

Are data 

needed to 

conduct 

risk 

assessment?

Justification 

Nonguideline Acute Honey 

Bee Vapor 

Exposure Study 

------------- ------------ Y As discussed further in this problem 

formulation, respiration exposure is 

determined to be the primary route of 

exposure for the terrestrial risk assessment. 

Inhalation studies are available for 

mammals (MRID 41277004) and birds 

(MRID 48788401) and given the volatile 

nature of DMDS, vapor exposure risk 

would also be applicable to terrestrial 

invertebrates using the honey bee as a 

surrogate. See the justification table below 

for more information. 

 
Page 35 of 53 

Guideline Number: N/A (Non-guideline study) 

Study Title: Terrestrial Plant Vapor Phase Study – Seedling Emergence and Vegetative Vigor 

Rationale for Requiring the Data 

Practical Utility of the Data 

How will the data be used? 

With these studies, the Agency will be able to assess risks to endangered and other non-target plants downwind 

from release points of DMDS. If the terrestrial plant special studies shows that DMDS exceeds the Agency’s level 

of concern for federally-listed or other terrestrial plant species, the Agency may be able to use this data to mitigate 

risks. 

How could the data impact the Agency’s future decision-making? 

If future endangered species risk assessments are performed without these data, the Agency would assume that 

DMDS may affect endangered terrestrial plant species directly and subsequently endangered species may depend 

on these plants. Use of DMDS may need to be restricted in areas where endangered species could be exposed. The 

lack of these data will limit the flexibility the Agency and registrants have in complying with the Endangered 

Species Act and could result in use restrictions for DMDS that are unnecessarily severe. 

Guideline Number: N/A (Non-Guideline Study) 

Study Title: Acute Honey Bee Vapor Exposure Study 

Rationale for Requiring the Data 

Due to the fate properties of fumigants, in particular their high volatility, it is expected that honey bees and other 

insect pollinators will be exposed to fumigants in the vapor phase. Neither of the standard Tier I toxicity studies 

with honey bees (i.e., acute contact or acute oral toxicity studies for honey bees) account for exposure to vapor 

phase pesticides. Therefore, to assess risks of DMDS to bees, EFED recommends that the Agency require a nonguideline acute honey bee vapor exposure study for DMDS, to be conducted. 

Practical Utility of the Data 

How will the data be used? 

Data from an acute honey bee vapor exposure study will be used to determine the potential for DMDS to affect 

non-target terrestrial invertebrates in the terrestrial environment. Of particular interest is quantification of a toxicity 

endpoint, i.e., a 4-hour LC50, that can be used to derive risk quotients. In the absence of vapor exposure data 

specific for honey bees, risk to terrestrial invertebrates, including listed species, will be assumed. 

How could the data impact the Agency’s future decision-making? 

If future ecological risk assessments are performed without these data, the Agency would have to presume risk to 

non-target terrestrial invertebrates, including honey bees, from use of DMDS. Therefore, use of DMDS and its 

formulated products may need to be restricted in areas where honey bees, other pollinator insects, or listed insects 

could be exposed. The lack of these data will limit the flexibility the Agency and registrants have in mitigating 

potential risks and could result in use restrictions for DMDS that are unnecessarily severe. 

 
Page 36 of 53 

10. References 

Altenstedt J. and Pleijel K. (1998) Sensitivity testing of the model set-up used for 

calculation of photochemical ozone creation potentials (POCP) under European 

conditions, Status report for the IVL jointly funded research program 9.1.1. 

’Photochemical oxidant potentials for organic species’, IVL-report L 98/32, IVL, 

Box 470 86, 402 58 Göteborg, Sweden. 

Arkema, 2010. Dimethyl disulfide chemical and physical properties. Available on-line: < 

http://www.arkema-inc.com/literature/pdf/791.pdf>. Accessed March 2010. 

Banwart, W.L. and Bremner, J.M., 1976. Evolution of Volatile Sulfur Compounds From Soils 

Treated with Sulfur –Containing Organic Materials. Soil Biology and Biochemistry, Vol. 8, pp. 

439 - 443. 

Bertsch W., Anderson, E. and Holzer, G, 1975. Trace Analysis of Organic Volatiles in Water by 

Gas Chromatography – Mass Spectrometry with Glass Capillary Columns; Journal of 

Chromatogrpaphy, Vol. 112, pp. 701- 718. 

Bouwman, A.F, 1998. Approaches to Scaling of Trace Gas Fluxes in Ecosystems. Elsevier 

Science B.V., Amesterdam, The Netherlands. 

Burns, L.A., 2002. Exposure Analysis Modeling System (EXAMS): User Manual and system 

documentation. National Exposure Research Laboratory. U.S. Environmental Protection Agency, 

Research Triangle Park, NC 27711. http://www.epa.gov/ceampubl/swater/exams/index.htm

Byun, D., Schere, K.L., 2004. Review of the Governing Equations, Computational Algorithms, 

and Other Components of the Models-3 Community Multiscale Air Quality (CMAQ) Modeling 

System. U.S. Environmental Protection Agency, Office of Research and Development, 

Atmospheric Sciences Modeling Division, Research Triangle Park, NC. 

Carsel, R.F.; Imhoff, J.C.; Hummel, PR; Cheplick, JM; and Donigian, AS Jr., 1998. PRZM-3, A 

Model for Predicting Pesticide and Nitrogen Fate in the Crop Root and Unsaturated Soil Zones: 

Users Manual for Release 3.0. National Exposure Research Laboratory, Office of Research and 

Development, U.S. Environmental Protection Agency, Athens, GA. 

http://www.epa.gov/ceampubl/gwater/przm3/index.htm

Carter W.P.L., Pierce J.A., Luo D. and Malkina I.L. (1995) Environmental chamber 

study of maximum incremental reactivities of volatile organic compounds, Atmos. 

Environ., 29, No. 18, pp 2499-2511. 

Castro, M.S. and Galloway, J.N., 1991. A Comparison of Sulfur-Free and Ambient Air Enclosure 

Techniques for Measuring the Exchange of Reduced Sulfur Gases Between Soils and the 

Atmosphere. Journal of Geophysical Research, Vol. 96 No. D8, pp. 15427-15437. 
Page 37 of 53 

Charles, P., 2003. DMDS: A new alternative for soil disinfestations. Annual International 

Research Conference on Methyl Bromide Alternatives and Emissions Reductions, MBAO, pp. 

23-1-23-4. 

Chemindusry.com. Available on-line < http://www.chemindustry.com/>. Accessed March 2010. 

Chellemi, D. O., H. A. Ajwa, D. A. Sullivan, R. Alessandro, J. P. Gilreath, and S. R. Yates. 2011. 

Soil fate of agricultural fumigants in raised-bed, plasticulture systems in the Southeastern United 

States. J. Environ. Qual. 40:1204–1214. CrossRef, PubMed. 

Dugravot, S., Grolleau, F., Macherel, D., Rochetaing, A., Hue, B., Stankiewicz, M., Huignard, J., 

Lapied, B., 2002. Dimethyl disulfide exerts insecticidal neurotoxicity through miochodrial 

dysfunction and activation of Insect KATP Channels. J. Neurophysiolol. 90: 259 – 270. 

doi:10.1152/jn.01096.20020022-3077/03. 

Fangdong, Y., Grosjean, D., and Seinfeld, J.H., 1990. Photooxidation of dimethyl sulfide and 

dimethyl disulfide. I: Mechanism Development. Journal of Atmospheric Chemistry. 11: 309 – 

364. 

Fangdong, Y., Grosjean, D., Flagan, R.C., and Seinfeld, J.H., 1990. Photooxidation of dimethyl 

sulfide and dimethyl disulfide. II: Mechanism Evaluation. Journal of Atmospheric Chemistry. 

11: 365 - 399. 

Fresenius W., 1994. Contaminants from Solid Wastes in Groundwater. American Chemical 

Society, Division of Environmental Chemistry. Preprint Extended Abstract, 208th ACS National 

Meeting. Vol. 34, pp. 596 – 599. 

Gilreath, J. P., Jones, J. P., Santos, B. M., and Overman, A. J. (2004). Soil Fumigant Evaluations 

for Soilborne Pest and Cyperus rotundus Control in Fresh Market Tomato. Crop Prot. 23: 889-

893. 

Graedel T.E., Hawkins, D.T., Claxton, L.D., 1986. Atmospheric Chemical Compounds. Sources, 

Occurrence, and Bioassay. Orlando,FL: Academic Press Inc, p. 444 

Johnson, Bruce, Terrell Barry, and Pamela Wofford. 1999. Workbook for gaussian modeling 

analysis of air concentration measurements. EH99-03. California Environmental Protection 

Agency, Department of Pesticide Regulation, Environmental Monitoring and Pest Management 

Branch, Environmental Hazards Assessment Program. Sacramento, California 95814-3510 

<http://www.cdpr.ca.gov/docs/dprdocs 

/methbrom/comp_modeling.htm>.

Mapleston, P. 1992 , Barrier film coatings add performance options. Modern Plastics, pp.48-50 

Mantoura R.F., Geschwend P.M., Zafiriou, O.C., and Clarke, K.R., 1982. Volatile Organic 

Compounds at a Coastal Site. 2. Short-Term Variations. Environmental Science and 

Technology, Vol. 16, pp. 38-45. 
Page 38 of 53 

Overman, A. J., Csizinszky, A. A., Jones, J. P., and Stanley, C. D. (1987). Efficacy of Metam 

Sodium Applied via Drip Irrigation on Tomato. In: 46th Annu.Meet.of the Soil and Crop 

Sci.Soc.of Fla., Oct.14-16, 1986, Longboat Key, FL, Soil Crop Sci.Soc.Fla.Proc. 4-7. 

Papiernik, S.K. and Yates, S.R. 2001. Transport of fumigant compounds through HDPE and 

virtually impermeable films. Proc. Annu. Intl. Res. Conf. Methyl Bromide Alternatives and 

Emissions Reductions 10:16 (Abstr.). 

Reiss, R. and Griffin, J. 2006. User’s Guide for the Probablistic Exposure and Risk Model for 

FUMigants (PERFUM), Version 2. Arysta LifeScience North America Corporation. Cary, North 

Carolina. 

Turner, D.B. 1970. Workbook of Atmospheric Dispersion Estimates. Revised, Sixth printing, 

Jan. 1973. Office of Air Programs Publication No. AP-26. 

University of Wisconin Agirultural Extension Service, 2010. Lawn and Garden Pesticides. 

Available on-line: http://clean-water.uwex.edu/pubs/pdf/home.lgpesti.pdf. Accessed March 

2010. 

USEPA, 1975. Preliminary Assessment of Suspected Carcinogens in Drinking Water. An 

Interim Report to Congress. June 1975. 

USEPA. 1995. Industrial Source Complex (ISC3) Dispersion Model User's Guide. EPA-454/B95-003b. U.S. Environmental Protection Agency, Research Triangle Park, NC. 

U.S. EPA, 2005. Overview of the use and usage of soil fumigants. Biological and Economic 

Analysis Division. Office of Pesticide Programs. Washington, D.C. 

USEPA, 2009 [1]. What is Acid Rain? Available on-line: <http://www.epa.gov/ 

acidrain/what/index.html>. Accessed August 2009. 

USEPA 2009 [2]. Ozone Layer Depletion. Office of Atmopsheric Programs. Washington, D.C. 

Available on-line: <http://www.epa.gov/ozone/strathome.html>. Accessed February 2009. 

USEPA 2009 [3]. “Adoption Proposed Endangerment and Cause or Contribute Findings for 

Greenhouse Gases Under Section 202(a) of the Clean Air Act”, in Federal Register, Vol. 74, No. 

78, 2009, pp. 18886 - 18910. US EPA, Office of Air and Radiation. Washington, DC. 

USEPA 2010 [1]. “Acid Rain”, Office of Atmospheric Programs. Washington, D.C.. Available 

on-line: <http://www.epa.gov/acidrain/>. Accessed March 2010. 

USEPA 2010 [2]. “Ground-level Ozone”, Office of Air and Radiation. Washington, D.C.. 

Available on-line: < http://www.epa.gov/air/ozonepollution/>. Accessed March 2010. 
Page 39 of 53 

USEPA 2010 [3]. “On-line Tools for Site Assessment Calculation”. National Exposure Research 

Laboratory. Athens, GA. <Avaialable on-line: http://www.epa.gov/athens/

learn2model/part-two/onsite/estdiffusion.html>. Accessed March 2010. 

USEPA 2010 [4]. “AERMOD Implementation Guide”. Office of Air Quality Planning and 

Standards. Research Triangle Park, NC/ Available on-line: 

<http://www.epa.gov/scram001/7thconf/aermod/aermod_implmtn_guide_

19March2009.pdf >. Accessed March 2010. 

USEPA 2010 [5]. “Estimation Tool Interface (EPI) Suite. Office of Pollution Prevention and 

Toxic Substances. Washington, DC. <Avaialable on-line: 

http://www.epa.gov/oppt/exposure/pubs/episuite.htm>. Accessed March 2010. 

U.S. National Park Service, 2010. “Guidance on Sulfur and Nitrogen Deposition Analysis 

Thresholds”. Available on-line: <http://www.nature.nps.gov/air/Pubs/pdf/flag/ 

nsDATGuidance.pdf>. Accessed March 2010. 

Waggot A, 1981 Trace Organic Substances in the River Lee. Chemical Water Reuse, pp. 55 – 

59. 

Wakeham S.G., Goodwin, J.T., and Davis A.C., 1983. Distributions and Fate of Volatile Organic 

Compounds in Narragansett Bay, Rhode Island. Canadian Journal of Fisheries and Aquatic 

Science, Vol. 40, pp. 304 – 331. 

Wilson, J.D., and W.K.N. Shum. 1992. A re-examination of the integrated horizontal flux 

method for estimating volatilisation from circular plots. Agriculture Forest Meteor. Vol 57:281-

295. 

Wine, P.H., Kreutter, N.M., Gump, C.A., Ravishankara, and A.R. 1981. Kinetics of OH 

Reactions with the Atmospheirc Suflur Compounds H2S, CH3SH, CH3SCH3, and CH3SSCH3. 

Journal of Physical Chemistry, 85: 2660 - 2665. 

Yang, Z., Zhang, J., and Wang, S., 1999. Emission of Reduced Sulfur Gases from Terrestrial 

Ecosystem. Symposia Papers Presented Before the Division of Environmental Chemistry, 

American Chemical Society, Preprints of Extented Abstracts, 39(1): pp. 16 – 18. 
Page 40 of 53

Appendix 1 – Detailed Environmental Fate Summary for DMDS

The loss of DMDS in terrestrial environments appears to be predominantly 

dependent on volatilization and to a lesser extent on leaching and soil biodegradation. 

DMDS’s vapor pressure of 22.55 torr at 20°C and Henry’s Law Constant of 0.001 

atm•m3/mol suggest that high volatilization rates can occur in soil and water respectively 

(MRID No. 46903510). DMDS emission rates may be mitigated by a substantial amount 

using high barrier tarps with material of low permeability which is representative of 

proposed label requirements of VIF tarp covering. Other fate and transport processes 

such as leaching, biodegradation, and adsorption are also possible to a lesser extent. 

Fate and Transport in Soil and Water

In soil, the aerobic metabolism of DMDS (MRID No. 4705282) laboratory study 

suggests that biodegradation occurred via a diffusion – deposition equilibrium process as 

evidenced by the observation that the vast majority of DMDS was detected in the 

headspace within 5 minutes of the application, and subsequent buildup of degradates in 

the soil in France clay loam soil and Switzerland clay soil. The major metabolite 

detected from the soil was methanesulfonic acid which accounted for a maximum of 

33.17 percent of the material balance 14 days after application in France clay loam soil, 

and 32.86 percent of the material balance 21 days after application in Switzerland clay 

soil. Methanesulfonic acid forms through the breaking of the disulfide bond in DMDS. 

Only trace amounts of DMDS were extracted throughout each study. In addition, carbon 

dioxide was detected in the headspace, accounting for 30.81 percent of the material 

balance in France clay loam soil at 59 days after application, and 27.24 percent of the 

material balance at 120 days after application in Switzerland clay soil (both at study 

termination). In California loamy sand soil and Florida sand soil, no degradation was 

observed as most DMDS residues remained in the headspace over time. The diffusiondeposition process apparent from the France clay loam soil and Switzerland clay soil is 

possible in the environment under field conditions given the vapor pressure of 22.55 torr 

and temperature of 20o

C with soil and airspace under a high barrier tarp. In addition, this 

process has been documented with numerous reduced sulfur compounds, including 

DMDS (Castro, 1991; Banwart and Bremner 1976). Considering this observation and the 

observation that trace amounts of DMDS are retrieved from the soil, a half-life for 

DMDS in the soil was back-calculated, attributing the formation of methanesulfonic acid 

to the decline of DMDS in the total system. This is demonstrated Table 1-1 for France 

clay loam and Switzerland clay soil. The half lives of DMDS in soil ranged from 

between 2.86 days in France clay loam to 3.74 days in Switzerland clay soil. 

Table 1-1. Formation of Methanesulfonic Acid and Decline of DMDS in France 

Clay Loam Aerobic Soil Metabolism Laboratory Study. 
Page 41 of 53

Time 

(Days) 

Switzerland clay France clay loam 

Methanesulfonic 

acid 

(%AR) 

Estimate 

DMDS 

(%AR) 

Methanesulfonic 

acid 

(%AR) 

Estimate 

DMDS 

(%AR) 

0 1.42 98.58 1.45 98.55 

1 8.09 91.91 6.17 93.83 

4 17.47 82.53 21.68 78.32 

7 25.67 74.33 29.1 70.9 

11 30.34 69.66 32.5 67.5 

14 32.16 67.84 33.17 66.83 

21 32.86 67.14 32.97 67.03 

59 26.8 73.2 35.3 64.7 

120 5.76 94.24 

%AR means percent of applied radioactivity. 

In water, DMDS’s high solubility of 2,702 mg/l and low average Kd of 0.641 

mL/g (range 0.54 mL/g – 0.86 mL/g for five soils) suggest that residues can readily be 

transported via water and are weakly retained by soil. The high Henry’s Law Constant 

of 0.001 atm•m3/mol and rapid photodegradation of DMDS from water suggest that 

volatilization and photolysis are the primary environmental routes of dissipation from 

surface water. DMDS was stable to hydrolysis at pHs 4, 7, and 9 at 50oC. The extent of 

biodegradation of DMDS in the aquatic environment is unknown. The environmental 

phototransformation half-life of DMDS is 1.17 days in 0.01 M phosphate (pH 7) when 

irradiated with a xenon light source for a period of 24 hours. Two major degradates were 

detected, and may have included either methanesulfonic acid, methanesulfinic acid, or 

sulfuric acid (MRID 47052818), at a maximum total of 54.2 percent of the material 

balance. A test to definitively identify the degradates was not performed. The registrant 

proposed that formaldehyde may form intermediate to the degradates identified. 

However, formaldehyde was not detected with the limited sampling that was conducted 

during the aquatic photolysis experiment. 

Potential Impacts of Soil Acidification from DMDS 

Soil acidification from methanesulfonic acid is especially possible on soils with low 

buffering capacities (sands) and absence of free carbonates. Since methanesulfonic acid 

is a major degradation product of DMDS degradation in soil, one mole of DMDS (CH3-

S-S-CH3) can theoretically form 4 moles of hydrogen (H+) from dissociation of 

CH3SO3H and oxidation of sulfuric acid. The acid equivalence ratio of calcium 

carbonate or CaCO3 (100 grams/mole/ 2) to DMDS (94 grams mole/4) is 2.127. 

Therefore, an application of 455 lbs of DMDS would require a lime application rate of 

968 lbs CaCO3/A for complete neutralization. 
Page 42 of 53

Fate and Transport in Atmosphere

 A series of field volatility studies conducted using both low barrier and high 

barrier tarps for DMDS Field volatility studies were submitted. Low density 

polyethylene (LDPE) low barrier tarps were applied in several study sites in Florida, 

California, Georgia, and Arizona using a variety of application methods on the label, such 

as broadcast shank injection, shank injection to raised beds, and drip irrigation to raised 

beds. In general, diffusion into the atmosphere was large and accounted for 38.33 – 

81.43 percent of the amount applied, with the exception of Nipomo, CA where DMDS 

volatile flux only accounted for approximately 27.64 percent of the amount applied. In 

general, low air concentrations and therefore flux in the vicinity of application sites are 

observed after 48 – 72 hours post-application. In addition, absolute peaks of flux 

occurred during the afternoon hours. 

In addition, there are two studies conducted with higher barrier films. DMDS 

volatile flux accounted for 8.1 percent of the amount applied for metalized film applied 

after shank injection to raised beds in Dover, FL. Furthermore, DMDS was applied via a 

pre-bedded shank application in one field of Tifton, GA with a VIF tarp. Here, DMDS 

residues in air accounted for 35.20 percent of the amount applied over a 320-hour period 

post-application. It is likely that DMDS flux was observed over a much larger period in 

Georgia than with the LDPE tarps since much of the DMDS material that remained in the 

soil in response to the high performance of the VIF tarp. Generally speaking, absolute 

peaks in flux also occurred in the afternoon hours after the application with flux gradually 

decreasing afterwards. However, the amplitude of absolute peaks in the field volatility 

are generally not as large as the studies conducted with the low density polyethylene 

tarps. Table 1-2 shows the flux profiles and percent of applied diffused from the soil in 

the Tifton field volatility site with VIF tarps. 

 
Page 43 of 53

Table 1-2. Field flux from Tifton, GA Field 1 DMDS Shank Injection to Raised 

Beds with High Density Polyethelene Tarp Study (application rate = 546.7 lbs. 

a.i./A) 

Sample Time 

DMDS Volatile 

Flux during 

Period 

(g/m2s) 

DMDS Percent of 

Applied during 

Period 

(%) 

Time Duration 

(hours) 

Day 0, Hours 0 – 5 3.35 0.10 5

Day 0, Hours 5 – 11 3.16 0.11 6

Day 0, Hours 11 – 17 16.21 0.57 6

Day 0, Hours 17 – 23 21.47 0.76 6

Day 0, Hour 23 – 

Day 1, Hour 5 14.33 0.51 6

Day 1, Hours 5 – 11 22.06 0.78 6

Day 1, Hours 11 – 17 42.84 1.51 6

Day 1, Hours 17 – 23 53.37 1.88 6

Day 1, Hour 23 – 

Day 2, Hour8 8.93 0.47 9

Day 2, Hours 8 – 20 54.37 3.83 12

Day 2, Hour 20 – 

Day 3, Hour 8 19.24 1.36 12

Day 3, Hours 8 – 20 38.66 2.73 12

Day 3, Hour 20 – 

Day 4, Hour 8 29.13 2.05 12

Day 4, Hours 8 – 20 21.73 1.53 12

Day 4, Hour 20 – 

Day 5, Hour 8 19.84 1.40 12

Day 5, Hours 8 – 20 13.79 0.97 12

Day 5, Hour 20 – 

Day 6, Hour 8 8.01 0.56 12

Day 6, Hours 8 – 20 12.85 0.91 12

Day 6, Hour 20 – 

Day 7, Hour 8 10.20 0.72 12

Day 7, Hours 8 – 20 9.52 0.67 12

Day 7, Hour 20 – 

Day 8, Hour 8 5.32 0.37 12

Day 8, Hours 8 – 20 18.54 1.31 12

Day 8, Hour 20 – 

Day 9, Hour 8 9.17 0.65 12

Day 9, Hours 8 – 20 7.30 0.51 12

Day 9, Hour 20 – 

Day 10, Hour 8 4.49 0.32 12

Day 10, Hours 8 - 20 

Day 10, Hour 20 – 

Day 11, Hour 8 

16.47 1.16 12
Page 44 of 53

Table 1-2. Field flux from Tifton, GA Field 1 DMDS Shank Injection to Raised 

Beds with High Density Polyethelene Tarp Study (application rate = 546.7 lbs. 

a.i./A) 

Sample Time 

DMDS Volatile 

Flux during 

Period 

(g/m2s) 

DMDS Percent of 

Applied during 

Period 

(%) 

Time Duration 

(hours) 

Day 11, Hours 8 – 20 27.60 1.95 12

Day 11, Hour 20 – 

Day 12, Hour 0 16.93 0.60 6

Day 12, Hours 0 – 6 30.06 1.06 6

Day 12, Hours 6 – 18 32.43 2.29 12

Day 12 Hour 18 – 

Day 13 Hour 6 15.91 1.12 12

Day 13 Hours 6 – 18 6.41 0.45 12

Total Volatile Flux 613.69 35.20 320 

Application Start Time Afternoon of February 7 

1. Exact start time of application in study unspecified. 2 Percent of DMDS flux from soil to air calculated using the formula, 

 % DMDS Mass Loss = 

n

i 1

(DMDS Flux i x Sample Period i)

 DMDS Field Study Application Rate. 

Several studies and calculations indicate that the primary sink of DMDS in the 

atmosphere is reactivity with hydroxyl radicals and photodissociation. AOP v1.92 in 

EPISuite estimates DMDS’s atmospheric half-life at 34 minutes due to hydroxyl radical 

reactivity. A laboratory degradation in air study in the open literature utilized a flash 

photolysis-resonance fluorescence technique to measure DMDS’s atmospheric lifetime at 

42 minutes. In this experiment, DMDS was exposed to a mercury lamp at a monitoring 

wavelength of 185 nm (ultraviolet radiation) with an absorption cross section of 159 x 10-

19 cm

2

 in a jacketed Pyrex reaction cell flushed with water which was converted to 

hydroxyl radicals when exposed to the artificial light (Wine et al., 1981). 
Page 45 of 53

An atmospheric degradation mechanism including the interaction between 

hydroxyl radicals and photodissociation has been developed and evaluated for DMDS. 

The DMDS hydroxyl adduct is initially formed. Subsequent abstraction in parallel with 

the photodissociation of DMDS forms the methyl thiol radical. With further 

photoionization and addition of atmospheric nitrogen oxides to methyl thiol, methyl 

thionitrite is expected to form. Methyl thiol may also oxidize into a methylated sulfur 

dioxide and then be reduced to methylated sulfur monoxide. This atmospheric oxidation 

and reduction cycle repeats in two additional steps until methane sulfonic acid forms. In 

addition, the three atmospheric oxidation and reduction steps can also result in individual 

sulfur oxides to dissociate from the methylated sulfur oxides, which eventually lead to the 

formation of sulfuric acid from sulfates combining with water from phenomena such as 

water vapor, cloud droplets, or precipitation. The entire atmospheric chemistry 

mechanism of DMDS is shown in Figure 1-1 (Fangdong et al., 1990[1], Fangdong et al., 

1990[2]). 

Figure 1-1. The atmospheric degradation pathways of DMDS. 

 

Ozone Depletion Potential 

 DMDS is being marketed as a methyl bromide alternative. Methyl bromide has 

been a widely used fumigant for pre-plant soil incorporated and food commodity 

applications. However, methyl bromide is designated as a Class I Ozone Depleting 

Substance by the EPA Office of Air, and therefore possesses the largest concern for the 

destruction of stratospheric ozone. All Class I Ozone Depleting substances are being 

phased out as per the Montreal Protocol (US EPA, 2009[2]). DMDS registered uses are 

similar to some past and current critical exemption uses of methyl bromide. 
Page 46 of 53

DMDS is a reduced organosulfur compound. As such, there are no halogenated 

components within DMDS which would contribute to the destruction of stratospheric 

ozone. Furthermore, DMDS is expected to degrade quickly in the troposphere. 

Therefore, emissions of DMDS are not expected to contribute to any process related to 

stratospheric ozone depletion. 

Global Warming Potential

DMDS’s methyl components may have the potential to contribute to climate 

change. Methylated compounds can be potent greenhouse gases, and thus have the 

potential to absorb outgoing long-wave infrared radiation effectively (USEPA, 2002; 

USEPA, 2009[3]). However, given DMDS’s short residence time in the atmosphere, 

global warming potential is likely to be small. Constituents with residence times less 

than one year are not anticipated to have large global warming potentials (Don Wuebbles, 

personal communication, 2009). 

Acid Rain

 Sulfates in the atmosphere, forming from anthroprogenically emitted sulfur 

dioxide as well as from atmospheric DMDS, as demonstrated in Figure III-1, are known 

to mix with precipitation and can result in wet deposition of sulfuric acid. Wet deposition 

of sulfuric acid is commonly known as acid rain. The reaction showing the formation of 

sulfuric acid is: 

 SO3 + H2O H2SO4

 

 Acid rain is recognized by the Agency as having adverse impacts to plants and 

aquatic habitats (USEPA[1], 2010). Federal Land Managers are obligated towards the 

protection of air quality particularly in National Park Areas under the Clean Air Act 

amendments of 1977. Consequently, sulfur deposition thresholds of concern have been 

established (U.S. National Park Service, 2010). Acid deposition is regulated under Title 

IV of the Clean Air Act. 

 Acid rain contribution from a single DMDS application would not likely be of 

concern given low emissions from the use of high barrier tarps as specified on the label. 

However, aggregate emissions of DMDS throughout an area with high use may 

contribute to acid rain events. To address the potential for acid rain, monitoring data of 

rainfall which occurs over high use areas of DMDS may be requested in the future (see 

Section I.E.1). 

Photochemical Ground-Level Ozone Creation Potential 

 As DMDS is a reactive volatile organic compound (VOC) in the atmosphere, 

there is a potential for it to interact with atmospheric hydroxyl radicals, oxygen, and 

nitrogen oxides to produce ground-level ozone. Ground-level ozone is recognized by the 
Page 47 of 53

Agency as having adverse impacts to plants and terrestrial animals (USEPA, 2010[2]), 

and is regulated under Title I of the the Clean Air Act as a criteria air pollutant. Figure 1-

1 shows that although ozone is not a direct product through any step of the DMDS 

degradation pathway, its chemical reaction with various trace atmospheric gases may 

facilitate the formation of ozone near ground-level. To address the potential risk of 

ozone formation from an airshed with significant DMDS use, ozone air quality air 

concentration monitoring data may be requested in the future. 

 
Page 48 of 53

Appendix 2 – Establishment of Inhalation as Dominant 

Exposure Pathway for Birds and Mammals 

STIR versus SIP result below show that inhalation exposure dose is much more 

significant than drinking water exposure dose for both mammals and birds. 

STIR Model INPUT/OUTPUT Results 

Welcome to the EFED 

Screening Tool for Inhalation Risk 

This tool is designed to provide the risk assessor with a rapid method for 

determining the potential 

significance of the inhalation exposure route to birds and mammals in a risk 

assessment. 

 

Input 

Application and Chemical Information 

Enter Chemical Name DMDS

Enter Chemical Use soil fumigant

Is the Application a Spray? (enter y or n) n

If Spray What Type (enter ground or air) ground

Enter Chemical Molecular Weight (g/mole) 94.2

Enter Chemical Vapor Pressure (mmHg) 2.25E+01

Enter Application Rate (lb a.i./acre) 449.5

 

 

Output 

Results Avian (0.020 kg ) 

Maximum Vapor Concentration in Air at Saturation (mg/m3) 1.14E+05

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 1.43E+04

SIP MODEL Input/Output 

Table 1. Inputs 

Parameter Value 

Chemical name DMDS 

Solubility (in water at 25oC; mg/L) 2702 

 

Table 2. Mammalian Results 

Parameter Acute 

Upper bound exposure (mg/kg-bw) 464.7440 

 

Table 3. Avian Results 

Parameter Acute 

Upper bound exposure (mg/kg-bw) 2188.6200 
Page 49 of 53

STIR versus Earthworm Fugacity models results below show that inhalation 

exposure dose is much more significant than dietary exposure dose for both 

mammals and birds. 

Parameter DMDS 

Application Rate 

(lbs. a.i./A) 

455 

Molecular Weight 

(g/mol) 

94.2 

Vapor Pressure 

(torr) 

22.5 

Kd (L/kg) 0.641 

Log Kow 1.77 

Earthworn Conc 

g/kg 

0.00284 

Mammal Diet Dose 

mg/kg 

0.34 

Avian Diet Dose 

mg/kg 

0.40 

Air conc. 1.14EE5 

Mammal Inhaled 

Dose mg/kg 

1.80EE4 

Avian Inhaled 

Dose mg/kg 

1.43EE4 

______________________________________________________________________ 

15 g mammal, 20g bird STIR model and Earthworm Fugacity Model. 

Depth 10 cm for earthworm exposure zone 

1

 Based on average of measured KOC values and assumption of 1 percent soil organic carbon content. 

2

Shaded rows depict highest exposure dose.

 
Page 50 of 53

Appendix 3 – ECOSAR Runs for DMDS and 

Methanesulfonic Acid 

Figure 3-1. Dimethyl disulfide ECOSAR Run. 

SMILES : S(SC)C 

CHEM : Disulfide, dimethyl 

CAS Num: 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C2 H6 S2 

MOL WT : 94.19 

Log Kow: 1.87 (KowWin estimate) 

Melt Pt: 

Wat Sol: 3000 mg/L (experimental database) 

ECOSAR v1.00 Class(es) Found 

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

Neutral Organics 

 

Predicted 

ECOSAR Class Organism Duration End Pt 

mg/L (ppm) 

=========================== ================== ======== ====== 

========== 

Neutral Organics : Fish 96-hr LC50 

93.840 

Neutral Organics : Fish 14-day LC50 

94.690 

Neutral Organics : Daphnid 48-hr LC50 

51.934 

Neutral Organics : Green Algae 96-hr EC50 

23.332 

Neutral Organics : Fish 30-day ChV 

9.694 

Neutral Organics : Daphnid ChV 

5.901 

Neutral Organics : Green Algae ChV 

8.729 

Neutral Organics : Fish (SW) 96-hr LC50 

131.726 

Neutral Organics : Mysid Shrimp 96-hr LC50 

102.433 

Neutral Organics : Fish (SW) ChV 

12.708 

Neutral Organics : Mysid Shrimp (SW) ChV 

9.193 

Neutral Organics : Earthworm 14-day LC50 

168.789 

 Note: * = asterisk designates: Chemical may not be soluble 

 enough to measure this predicted effect. 

 

Neutral Organics: 
Page 51 of 53

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

 For Fish LC50 (96-h), Daphnid LC50, Mysid: If the log Kow is greater 

than 5.0, or if the compound is solid and the LC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted. 

 

 For Fish LC50 (14-day) and Earthworm LC50: If the log Kow is greater 

than 6.0, or if the compound is solid and the LC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted. 

 

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical 

is 

greater than 6.4, or if the compound is solid and the EC50 exceeds the 

water 

solubility by 10X, no effects at saturation are predicted for these 

endpoints. 

 

 For All Chronic Toxicity Values: If the log Kow of the chemical is 

greater 

than 8.0, or if the compound is solid and the ChV exceeds the water 

solubility 

by 10X, no effects at saturation are predicted for these endpoints. 

 

ECOSAR v1.00 SAR Limitations: 

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50, Mysid LC50) 

Maximum LogKow: 6.0 (Fish 14-day LC50; Earthworm LC50) 

Maximum LogKow: 6.4 (Green Algae EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 

 

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

------- 
Page 52 of 53

Figure 3-2. Methanesulfonic Acid ECOSAR Run. 

SMILES : O=S(=O)(O)C 

CHEM : Methanesulfonic acid 

CAS Num: 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C1 H4 O3 S1 

MOL WT : 96.10 

Log Kow: -2.38 (KowWin estimate) 

Melt Pt: 

Wat Sol: 1E+006 mg/L (experimental database) 

ECOSAR v1.00 Class(es) Found 

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

Neutral Organics-acid 

 

Predicted 

ECOSAR Class Organism Duration End Pt 

mg/L (ppm) 

=========================== ================== ======== ====== 

========== 

--> Acid moeity found: Predicted values multiplied by 10 

Neutral Organics-acid : Fish 96-hr LC50 

5.31e+006 * 

Neutral Organics-acid : Fish 14-day LC50 

5e+006 * 

Neutral Organics-acid : Daphnid 48-hr LC50 

1.57e+006 * 

Neutral Organics-acid : Green Algae 96-hr EC50 

1.11e+005 

Neutral Organics-acid : Fish 30-day ChV 

4.12e+005 

Neutral Organics-acid : Daphnid ChV 

90723.766 

Neutral Organics-acid : Green Algae ChV 

20415.420 

Neutral Organics-acid : Fish (SW) 96-hr LC50 

1.03e+007 * 

Neutral Organics-acid : Mysid Shrimp 96-hr LC50 

1.21e+008 * 

Neutral Organics-acid : Fish (SW) ChV 

62332.531 

Neutral Organics-acid : Mysid Shrimp (SW) ChV 

3.82e+007 * 

Neutral Organics-acid : Earthworm 14-day LC50 

4756.764 

 Note: * = asterisk designates: Chemical may not be soluble 

 enough to measure this predicted effect. 

 

Neutral Organics: 

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

 For Fish LC50 (96-h), Daphnid LC50, Mysid: If the log Kow is greater 

than 5.0, or if the compound is solid and the LC50 exceeds the water 
Page 53 of 53

solubility by 10X, no effects at saturation are predicted. 

 

 For Fish LC50 (14-day) and Earthworm LC50: If the log Kow is greater 

than 6.0, or if the compound is solid and the LC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted. 

 

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical 

is 

greater than 6.4, or if the compound is solid and the EC50 exceeds the 

water 

solubility by 10X, no effects at saturation are predicted for these 

endpoints. 

 

 For All Chronic Toxicity Values: If the log Kow of the chemical is 

greater 

than 8.0, or if the compound is solid and the ChV exceeds the water 

solubility 

by 10X, no effects at saturation are predicted for these endpoints. 

 

ECOSAR v1.00 SAR Limitations: 

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50, Mysid LC50) 

Maximum LogKow: 6.0 (Fish 14-day LC50; Earthworm LC50) 

Maximum LogKow: 6.4 (Green Algae EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 

 

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

-------