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 of53Page 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

P

repared by: Joe Decant, Ecologist Gabe Rothman, M.S., Environmental Scientist U.S. Environmental Protection Agency Office of Pesticide Programs

E nvironmental Fate and Effects Division
E nvironmental Risk Branch I V 1200 Pennsylvania Ave., NW
M

ail Code 7507P Washington, DC 20460 R eviewed by: Mah Shamim, Ph.D., Chief ERB5

December 3, 2013Page 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 ......................................... 50Page 4 of 53 

## 1. Executive summary

The Environmental Fate and Effects Division (E FED) has completed the preliminary problem formulation for the ecological risk, environmenta l fate, endangered species, and drinking water assessments to be conducted as part of the regi stration review of dimet hyl 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 eff ects, 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 produc ts. PaladinTM is a nearly pure DMDS (98.8% active ingredient) formulation intended for use in bedded a nd broadcast sh ank injection applications. Paladin ECTM is an emulsifiable concentrate (93.8% active ingredient) formulation intended for drip chemigation applications to rais ed beds. The labels require immediate covering of the beds or entire field with virtually imperm eable film (VIF) tarp ma terial immediately after application. DMDS will be consid ered the primary stressor in this risk assessment since DMDS is more toxic than its main degradate methanesul fonic acid (MSA) in soil, where its formation is minimized by the limited residence time of DMDS in soil due to volatil ization. In addition, degradation of DMDS in water is not anticipated to be a signi ficant process since evaporation from water is the main loss process, occurring very rapidly on the order of several hours. Transformation processes in the atmosphere pot entially contributing to the formation of groundlevel ozone and acid rain are expected to be mi nimal 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 degr adates 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 toxi cological endpoint values for its main degradate MSA in soil using ECOSAR 1 is shown in Appendix 1

.

The collection of field volatility st udies indicate that off-site tr ansport of DMDS mainly occurs through volatilization and resul ting escape into the atmosphere . Factors such as weather conditions ( e.g. , air temperature), an d 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 abi lity to be transfered through the tarp. It may also be possible that DMDS could diffuse late rally 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 tim es in water. Therefor e, 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.htmPage 5 of 53 is expected to reduce exposure poten tial 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 ph ase DMDS is expected. To estimate exposures to DMDS, a tiered approach will be used. Both the American Meteorological Society/Environmental Protection Agency Re gulatory Screening M odel (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 down wind from the application site. In addition, PERFUM will be used to predict fu migant air concentratio ns at specified points
downwind from the treated field if there are exceed ances with levels of concern. Terrplant (v. 1.2.2) will be used to capture the upper-bound e xposure 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 emi ssions from broadcast applications with VIF tarps. There is currently only one field volatility study available and it was conducted for bedded applications. To addr ess this uncertainty, a field volatility study encompassing broadcast applications is being re quested. A major uncertainty for terrestrial exposure is that EECs are based on the conservati ve assumption that birds and mammals are not
transient and are therefore c ontinuously 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 poten tially large exposures occurring at durations of less than one hour would not be captured . Such exposure may occur with temperature inve rsions when light and variable wind speeds and highly stagnant air with limited mixing can occur. However, , current labels contain specific language re stricting applications during temperature inversions citing a number of criteria indicating the presence of a forecasted temperat ure inversion. Therefore, it is not expected that this limitation in the model w ould be relevant for the risk assessment.

The data needs for environm ental fate are listed below:

 835.8100 Field Volatility Study. Virtually impe rmeable film (VIF) tarps are required on the label. One field volatility study is av ailable only for drip chemigation bedded applications with VIF tarps. However, other field volatility studies re quested at this time for for broadcast shank injection applicati ons 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 ecologica l effects are listed below:

 850.4150 Vegetative Vigor Tier II. A supplem ental non-guideline toxicity study (MRID 47471202) was received for DMDS. Additional in formation related to the temperatures during the existing study as well as the temperature dependence for DMDS vapor pressure are necessary for the interpretati on on the measured effect of DMDS on the vegetative vigor of plants exposed to DMDS va pors in the air (pleas e refer to DP Barcode 405334, dated 4/30/13, for further information).

 Non-Guideline Acute Honey Bee Vapor Exposur e 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 gi ven 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 evaluate d the most recent ecol ogical risk assessments for dimethyl disulfide (h ereafter referred to as DMDS) in as sociation 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, eggplan t, cucumbers, squash, melons, strawberries, blueberries, field grown ornament als, and forest nursery crops. The structure of DMDS as well
as the chemical names and othe r identifiers can be found in Table 2 of this document.

DMDS is a transparent light yell ow liquid with a str ong garlic-like odor. DM DS is used for preplant soil fumigation, acting as a stressor w ithin 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 lim ited 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 mitig ated by virtually imperm eable 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 ac id and carbon dioxide in soil. DMDS also degrades to major degradates methanesulfonic ac id, 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 emulsifi able concentrate (93.8% active ingredient) formulation intended for drip chem igation applications. DMDS target pests includeweeds, soil-bourne bacteria, plant pa thogens, 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 fruiti ng vegetables (specifically tomatoes, peppers, and eggplant), cucurbit crops (specifically cucumbers, squash, and melons), stra wberries, blueberries, field grown ornamentals, and fo rest 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 disu lfide 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 be ds. Furthermore, all applicati ons require immediate covering ofPage 8 of 53 the treated field or bed by tarps composed of vi rtually 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 inj ection depths, minimum tarp re moval 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 in ches 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 br oadcast shank injection application followed by tarp covering.Page 9 of 53 Credit: USEPA, 2005 Figure 2. Photograph showing shank injection a pplication 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. Therefor e, current DMDS usage is anticipated to expand in the future. DMDS applications are not approve d 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 presente d in the assessment are described below.



### 4.1 Ecological Risk Assessments

Inhalation of DMDS vapor following soil fumigati on is considered to be the major route of exposure for terrestrial organisms. The analys is in Section 3 of the New Chemical Risk Assessment, which used honey bee contact toxi city 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 Expos ure and Risk Model for Fumigants (PERFUM), showed that DMDS applications di d not appear to indicate a potenti al for acute concern to birds, mammals, terrestrial phase amphibians, rept iles 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 assess ment for broadcast applications could not be completed due to the absence of a field volatil ity study with a broadcast DMDS application.

For aquatic organisms, acute risks of concern were identified for endangered freshwater fish species, aquatic-phase amphibian endangered sp ecies, freshwater invertebrate endangered species, and non-vascular aquatic endangered plants. EECs for aquatic animals and plants were based on upper-bound Pesticide Root Zone Mode l/Exposure Analysis Modeling System (PRZM v. 3.12.3/EXAMS v. 2.98.04.06) surface water concentratio ns 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 plan t study. However, labels indicate terrestrial plants as a target species and exposure is predicted. *A qualitative assessment was performed for terrestrial invert ebrates 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 considere d. An aerobic aquatic laboratory metabolism study(MRID No. 48662502) recently submitted to the Agency indicated that DMDS possessed a
DT 90 of around 2.5 – 3 hours from water to volatile tr aps in the headspace in two water/sedimentPage 11 of 53 systems; therefore, DMDS’s residence time in wa ter 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 assessmen t was not conducted for DMDS, in agreement
with the Health Effects Divisi on (HED), due low exposure potent ial. Information regarding DMDS’s residence time in water supports this finding. An aerobic aquatic laboratory study (MRID No. 48662502) shows that the DT 90 of DMDS due to volatili zation is between 2.5 – 3
hours. Please refer to Section 7 for further details behind the determination of the DT 90 . 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, gr ound 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 impairme nt for any water bodies listed as impaired under section 303(d) of the Clean Water Ac t, 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) crit eria have been developed for DMDS, based on information provided at http://iaspub.epa.gov/tmdl_waters10/attains_ nation.tmdl_pollutant_de tail?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 exte nt possible, data should conform to the quality standards in Appendix A of the OPP Standard Operating Procedur e: Inclusion of Impaired Water Body and Other Water Quality Data in OPP’s Regist ration Review Risk Assessment and Management Process (see: http://www.epa.gov/oppsrrd1/regist ration_review/water_quality_sop.htm ), in order to ensure they can be used quantitatively or qual itatively in pesticide risk assessments.



## 5. Environmental Fate and Transport

DMDS is a transparent light yellow liquid with a strong ga rlic-like odor. It is highly soluble and has high vapor pressure. Based on Henr y’s Law Constant value of 0.001 atm-m 3 /mol and DT 90 in water of between 2.5 – 3 hours, volatilization of DMDS from soil and water surfaces is expected to be the most significant transport a nd 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 ch emical properties of DMDS

. Property Value and units MRID or Source

Structure EPISUITE ver 4.1

Chemical Formula C 2 H 6 S 2 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·m 3 /mol MRID 46903510

Water Solubility (20°C) 2,702 mg/L MRID 46903510

Octanol – water partition

coefficient (log K O W ) 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 appear s 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 conducte d with bedded tarped applications and VIF tarp cove ring accounted for 35.20% of DMDS lost from soil, which is on the low end of the range. This suggests that so il emissions will be minimized in labeled DMDS applications since the label requires the use of VI F tarps. However, additional studies with other application methods, such as broadcast tarped applications, are n eeded to confirm the effectiveness of VIF tarps to minimize DMDS emi ssions. It should also be noted that residual DMDS also biodegrades to methanesulfonic aci d (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 hyd roxyl 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 vol atility 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 t 1/2 Stable at pH 5, 7, and 9
- MRID 46903532 Acceptable

Photolysis t 1/2 in

water 1.3 days Methanesulfonic acid
Methanesulfinic acid
Sulfuric acid MRID 42900201 Supplemental

Photolysis t 1/2 on soil N/A - N/A Waived

Degradation t 1/2 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 t 1/2 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 t 1/2 California WaterSandy Loam Soil 78.9 days Methanesulfonic Acid
Methane thiol MRID 47052820 SupplementalPage 14 of 53 Parameter Value Major Degradates Reference Study
Classification/

Comments

Aerobic Aquatic
metabolism t 1/2 Missouri Water-Silt
Loam Sediment

DT 50 = 1.21 hours
DT 90 = ~ 3 hours

Georgia Water-Sand
Sediment

DT 50 = 0.77 hours
DT 90 = ~2.5 hours - MRID 48662502 Supplemental

Main loss in
water due to
volatilization and escape to headspace vapor trap

Anaerobic Aquatic
metabolism t 1/2 Missouri Water-Silt
Loam Sediment

DT 50 = 1.27 days
DT 90 = ~ 8 days

Georgia Water-Sand
Sediment

DT 50 = 1.55 days
DT 90 = ~ 10 days - MRID 48662501 Supplemental

Main loss in
water due to
volatilization and escape to headspace vapor trap

Soil-Water
Partition Coefficient (K d ) 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 WaivedPage 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 Study 1

(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-applicationPage 16 of 53 Field Volatility Study 1

(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 through320 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 Acceptabl e 10.67 69.74 percent through320 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 lossthrough 320 hours postapplication

1 Tarp Materials: LDPE = Low density polye thylene; VIF = Virtually Impermeable Film

2 Peak flux rate refers to the average over ~ 4 hour s as per the sampling periods in the field volatility studies.Page 17 of 53Table 5. Environmental degradates of DMDS.Code Name/ SynonymChemical NameChemical StructureStudy TypeRef.(MRID)Maximum%AR (day)Final %AR(study length)Parent CompoundDMDSDimethyl disulfideCAS No.:624-92-0Formula:C2H6S2MW:94.19 g/molMAJOR TRANSFORMATION PRODUCTSMSAMethanesulfonic AcidCAS No.75-75-2Formula:CH4SO3MW:96.1g/molAqueous Photolysis 47052818< 54.2(24 hours)< 54.2(24 hours)Aerobic Soil Metabolism(France Clay Loam Soil)47052819 33.17(14 days)2.02(59 days)Aerobic Soil Metabolism(Switzerland Clay Soil)47052819 32.86(21 days)5.76(120 days)Anaerobic Soil Metabolism(California Water – SandyLoam Soil System)47052820< 38.5(21 days, total)< 11.9(71 days, water)< 27.5(21days, air)< 29.9(71 days, total)< 11.9(71 days, water)< 18.0(71 days, air)Degradation in AirFangdongetal., 1990NA NAMethanesulfinic AcidMethanesulfinic AcidCAS No.17696-73-0Formula:CH4SO2MW:80.1g/molAqueous Photolysis 47052818< 54.2(24 hours)< 54.2(24 hours)CH3SSCH3S CH3OOHOPage 18 of 53Code Name/ SynonymChemical NameChemical StructureStudy TypeRef.(MRID)Maximum%AR (day)Final %AR(study length)Sulfuric AcidSulfuric AcidCAS No.7664-93-9Formula:H2SO4MW:98.07 g/molAqueous Photolysis 47052818< 54.2(24 hours)< 54.2(24 hours)Degradation in AirFangdongetal., 1990NA NACarbon DioxideCarbon DioxideCAS No.124-38-9Formula:CO2MW:44.01 g/molAerobic Soil Metabolism(France Clay Loam Soil)4705281930.81(59 days)30.81(59 days)Aerobic Soil Metabolism(Switzerland Clay Soil)4705281927.24(120 days)27.24(120 days)MTMethane thiolMethyl mercaptanCAS No.74-93-1Formula:CH4SMW:48.1 g/molAnaerobic Soil Metabolism(California Water-Sandy LoamSoil)4705282016.0(14 days, air)Not Detected(71 days)Degradation in AirFangdongetal., 1990NA NA*%AR means percent ofapplied radioactivity.**NA means that material balance is not available from study.C OOPage 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 Agen cy, 2004), this risk assessment uses a surrogate species approach in its evaluation of DMDS. Toxicological data generated from surrogate test species, which are intend ed to be representative of broad taxonomic groups, are used to extrapolat e to potential effects on a vari ety of species (receptors)
included under these ta xonomic groupings.

Acute and chronic toxicity data from studies submitted by the pesticide registrant along with the available open literatu re 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 ope n 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 evaluati on 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 st ructure 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 LC 50 = 960 MRID 47052814 Acceptable

Chronic NA NA NA NA

Freshwater Invertebrates

Acute Daphnia magna 48 hours EC 50 =1610 MRID 47052816 Acceptable

Chronic NA NA NA NAPage 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 LC 50 =5600 MRID 47307504 Acceptable

Chronic NA NA NA NA

Estuarine/Marine Invertebrates

Acute Mysidopsis
bahia 96 hours LC 50 =4900 MRID 47307505 Acceptable

Chronic NA NA NA NA

Aquatic Plants

Vascular Lemna gibba 7 days EC 50 =28000
EC 05 = 6000 MRID 47471204 Acceptable

Nonvascular Anabaena flosaquae 96 hours Cell Density EC 50 =320
EC 05 = 110 MRID 47471205 Acceptable

NA = Data appropriate for quantitative use are not available.



### 6.2 Effects to Terrestrial Organisms

The toxicity endpoints used to characteri ze 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
Inhalation 1 Rattus norvegicus 4-hour inhalation LC 50 males > 3.18 mg/L (3.18 – 6.19 mg/L)

LC 50 females = 5.22 mg/L (4.56 – 5.97 mg/L)

LC 50 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 LC 50 =1.97 mg/L (1.62-2.41 mg/L)

Female LC 50 =1.73 mg/L (1.55-1.93 mg/L)

Combined LC 50 =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 combin ed value represents a reasonable combination of the definitive with the non-definitive endpoint.

A 90 day repeated-dose inhalation study for th e rat was reported under OECD guidelines (ELF ATOCHEM, January 1992). This st udy resulted in no adverse effects. A developmental toxicity study through i nhalation (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 acu te oral toxicity study (MRID47052813) was submitted, the LD 50 will not be used in this assess ment 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 de termined that the female quail (acute
inhalation LC 50 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 illustra te the effect of gaseous DMDS on plants.
There is insufficient data to estimate the e ffect 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 EC 25 = 290 MRID
47381001 Supplemental NOAEC = 75

Dicot Sugarbeet Beta vulgaris Dry weight EC 25 = 91

NOAEC = 75

Vegetative Vigor

Monocot Oat
Avena sativa Dry weight EC 25 = 100 MRID
47471202 Supplemental EC 05 =37.5

Dicot Tomato Lycopersicon esculentum Height EC 25 = 55

EC 05 =37.5Page 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 obs erved 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 incide nt resulted from pesticide exposu re. The Avian Monitoring System (AIMS) is a database administered by the Amer ican Bird Conservancy th at contains publicly available data on reported avian in cidents involving pest icides. Many of the incidents listed in
this database are also in the EIIS. The followi ng 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 id entified no ecological in cidents involving DMDS.



### 7. Exposure Pathways of Concern

Given DMDS’s volatile characteri stics, its broad spectrum mode of action as a fumigant, and application methods in soil, th e following lists the major expect ed 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 qua ntities 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 be dded tarped application methods. Therefore, the air exposure pathway will be addressed. The labeled application rates and methods along with newly submitted field vola tility studies will be considered. Since all DMDS soil uses are incorporated un der 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 expe cted from applications on and possibly adjacent
to the treated field. DMDS’s br oad spectrum mode of action as a fumigant, large application rates to soil, and the mobile and diffuse nature of DM DS as a vapor in soil all justify th is exposure pathway.Page 24 of 53  Aquatic exposure for freshwater and estuarin e/marine animals, and aquatic plants

The previous Section 3 New Chemical Assessmen t 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 lim ited. 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 experime ntal systems in the aerobic aquatic study within an 8 hour period after ap plication can be attributed to lo ss due to volatiliz ation (MRID No. 48662502). Therefore, acute and chronic aquatic expos ure 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 th e sediment/water system due to volatilization over time (blue line), to the headspace (red lin e) in the Georgia water-sand sediment system (left) and Missouri water-silt l oam sediment system (right).

 Drinking water exposure for mammals and birds

While dietary and drinking water exposures are po ssible for mammals and birds, acute risk from inhalation is determined to be the primary route of exposure for several re asons. 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 ca lculations 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 m odel, the upper bound daily drinking water intake dose for a bird is 2,189 mg/kg bw. Multiplying th e 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 i nhalation exposure of a bird to DMDS is 0 10 20 30 40 50 60 70 80 90 100

02468PercentofAppliedDMDS(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

02468PercentofAppliedDMDS(percent)

Time After Application (hours) Aerobic Water

‐ Silt Loam Sediment System

DMDS in Water

DMDS in Headspace

DT 90 = 2.5 hours DT 90 = 3.0 hoursPage 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 exposur e 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 i nvertebrate 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 e xposures 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 determina tion is discussed further in Section 8.1 below. EECs will be calculated for air and soil using various environm ental 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 co mpute 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 va rious 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 EC OSAR 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 be ing potentially of toxicologica l 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 wa ter is expected to be mediated mainly by volatilization resulting in escape or applied residues to the atmosphe re. Some residual DMDS in soil may biodegrade to MSA and ma y potentially be available to runoff from the treated field. MSA was observed to form to levels up to 33.1 7 percent in the aerobic soil metabolism study. However, considering this moderate level of fo rmation, MSA will be excluded from a residue of concern also considering its lower toxicity co mpared to DMDS as estimated by ECOSAR shown
in Appendix 3 . In addition, the degradates MSA and su lfuric acid which were observed to formPage 26 of 53 in a controlled aquatic photodegr adation study (MRID No. 42900201) ar e not expected to form to any great extent in the environment as suggest ed 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 th ese degradates are expected to be of equal or lesser toxi city than DMDS. Therefore, any acute risk to eco logical species resulting from e xposure to these degradates will adequately be captured considering untransf ormed DMDS emissions to the atmosphere.

Since DMDS is a reactive volatile organic compound, it also has the potentia l to contribute to the formation of ground-level ozone. In addition, re-deposition of su lfates and sulfuric acid, which form from DMDS emissions, to te rrestrial and aquatic e nvironments may result in added risks to ecologically relevant species within areas close to or within a region wh ere DMDS is intensely used. However, given the limited scope of its usag e at the present time, significant generation of ozone or acidic sulfur deposition resulting from DM DS fumigant applications is not expected at this time. However, DMDS usage may increase ove r time since it is considered to be a methyl bromide replacement. Therefore, DMDS’s cont ribution 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 a nd terrestrial organisms are derived from the utilization of environmental fate and transpor t 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 ga s-phase exposure are determined using the EECs from atmospheric dispersion models relying on th e input of DMDS atmospheric flux measurements from the collection of volatility (flux) studies conducted for DMDS app lications in the field. The Agency’s recommended screening near-field dispersion model the American Meteorological Society/EPA Regulatory Screening Model (AER SCREEN v. 11060), will be used to generate Tier I EECs. The Tier I analysis will consider the maximum flux rate fo r each application method
from the collection of DMDS flux studies and wo rst-case meteorological c onditions (light winds and stagnant conditions) to calculate peak air EECs, represen ting one-hour average
concentrations. Documentation on th e AERSCREEN model is available at http://www.epa.gov/scram 001/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 e valuated in Tier 1 analysis.

If the Tier 1 EECs for either surface or incorporat ed applications result in an exceedance of the LOC, EECs will be further examined using the Ti er 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. PERF UM considers these flux values with a robust statistical sampling of meteorol ogical 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 prev iously recommended atmospheric dispersion model in the near field, the Industri al 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 disper sion 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 ne cessary, a higher averaging period equivalent to the exposure durati on in toxicity studies will be used to characterize the RQs resulting from utilizing the one-hour peak EECs. The highest 90 th percentile estimated air concentration from all averaging periods from the r eceptor 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 accumula te to maximum levels along the fetch of wind blowing over the treated field. Wind, Dispersion,
and
Accumulation
of Va p ors or Gas

Volatilization of
residues in soil Soil incorporated and chemigation fumigant applicationPage 28 of 53 Figure 6. Illustration of the spatial and te mporal aspects of the source to receptor configuration in PERFUM. The wind rose (lef t) 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 base d on field volatility flux data normalized to the maximum field sizes specified by application met hod on the labels. Therefore, the modeling will
be based on a maximum field size of 40 acres fo r 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 overal l 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 th e replacement has been approved prior to the initiation of the risk assessment, th is 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 identif ied using EPA’s ECOTOXicology database (ECOTOX) (USEPA, 2007b), which employs a literature search engine fo r locating chemical toxicity data for aquatic life, terrestrial plants, and wild life. The evaluation of both sour ces of data can also provide insight into the direct and indirect effects of pe sticides 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 threat ened and/or endangered (listed) species from Treated
Field Receptor RingsPage 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 testi ng. 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 ar e two scenarios where DM DS under tarps may move to ground water which should be mentioned and in clude the following: 1.) DMDS under tarps may become entrained into ground water via rechar ge 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 leac h 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 trans ported to well intakes as well depths are often 15 – 30 feet below the surface. Addressing scen ario 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 wate r and ground water exposure potential presented above, a drinking water assessment will not be c onducted 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) afte r three-way application of DMDS, me tam sodium, and chloropicrin. VIF tarps were used in Site 1, and low density polyet hylene (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 classifi cations and whether or not furthe r 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 NoPage 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 4 7052821 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) NoPage 32 of 53 

### 9.2 Ecological Toxicity

Table 10 identifies ecological effects studies by MR ID that offer data for each guideline requirement, as well as study classifi cations and whether or not furthe r data are needed in order to support risk assessment. Rationale for the ad ditional data requested is presented below.

Table 10. Submitted aquatic and terrestri al 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–
b luegill
Zebrafish 47052815 Acceptable N

850.1075 Fish Acute Toxicity–
rainbow trou t 47052814 Acceptable N

850.1010 Aquatic
Invertebrate Acute Toxicity–
freshwate r 47052816 Acceptable N

850.1075 Marine/
Estuarine Acute Toxicity–Fish 47307504 Acceptable N

850.1025 Marine/
Estuarine Acute Toxicity– Mollusk (shell deposition) 47307503 Invalid NPage 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–
freshwate r ------------- ------------- 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 Vigo r –Tier I Vegetative Vigo r –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 du ring 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 NPage 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 St udy – 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 othe r non-target plants downwind from release points of DMDS. If the terrestrial plant sp ecial 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 Ag ency’s future decision-making? If future endangered species risk assessments are perfor med without these data, the Agency would assume that DMDS may affect endangered terrestria l plant species directly and subsequently endangered species may depend on these plants. Use of DMDS may need to be restricted in areas where enda ngered 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 restrictio ns 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 thei r 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 thatthe 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 environm ent. Of particular interest is quantification of a toxicity endpoint, i.e., a 4-hour LC 50 , that can be used to derive risk quotients. In the absence of vapor exposure data specific for honey bees, risk to terrestrial invert ebrates, including listed species, will be assumed.

How could the data impact the Ag ency’s future decision-making? If future ecological risk assessments ar e performed without these data, the Agen cy 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 re stricted in areas where honey bees, othe r 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

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Arkema, 2010. Dimethyl disulfide chemical a nd 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. Evol ution of Volatile Sulfur Compounds From Soils Treated with Sulfur –Containing Organic Materials. Soil Biol ogy and Biochemistry, Vol. 8, pp.
439 - 443.

Bertsch W., Anderson, E. and Holzer, G, 1975. Tr ace 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 Laborato ry. 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 G overning Equations, Com putational Algorithms, and Other Components of the Models-3 Commun ity Multiscale Air Qu ality (CMAQ) Modeling System. U.S. Environmental Protection Agen cy, Office of Research and Development, Atmospheric Sciences Modeling Divi sion, Research Triangle Park, NC.

Carsel, R.F.; Imhoff, J.C.; Hu mmel, PR; Cheplick, JM; and Donigian, AS Jr., 1998. PRZM-3, A Model for Predicting Pesticide a nd Nitrogen Fate in the Crop R oot and Unsaturated Soil Zones: Users Manual for Release 3.0. National Exposure Research Laboratory, Of fice 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 Ma lkina I.L. (1995) Environmental chamber study of maximum incremental reactivitie s of volatile organic compounds, Atmos. Environ., 29, No. 18, pp 2499-2511.

Castro, M.S. and Galloway, J.N., 1991. A Comparis on of Sulfur-Free and Ambient Air Enclosure Techniques for Measuring the Exchange of Re duced 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. A nnual International Research Conference on Methyl Bromide Alte rnatives and Emissions Reductions, MBAO, pp.
23-1-23-4.

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Dugravot, S., Grolleau, F., Macherel, D., Rochetai ng, A., Hue, B., Stankiewicz, M., Huignard, J., Lapied, B., 2002. Dimethyl disulfide exerts in secticidal neurotoxic ity through miochodrial dysfunction and activation of Insect K ATP 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 Developmen t. Journal of Atmospheric Chemistry. 11: 309 –
364.

Fangdong, Y., Grosjean, D., Flagan, R.C., and Sein feld, J.H., 1990. Photooxidation of dimethyl sulfide and dimethyl disulfide. II: Mechanism Evaluation. J ournal of Atmospheric Chemistry.
11: 365 - 399.

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Gilreath, J. P., Jones, J. P., Santos, B. M., a nd Overman, A. J. (2004). Soil Fumigant Evaluations for Soilborne Pest and Cyperus rotundus Control in Fresh Market Tomato. Crop Prot. 23: 889-
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Johnson, Bruce, Terrell Barry, and Pamela Wofford. 1999. Workbook for gaussian modeling analysis of air concentrati on measurements. EH99-03. California Environmental Protection Agency, Department of Pesticide Regulation, E nvironmental Monitoring and Pest Management Branch, Environmental Hazards Assessmen t 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 K ey, FL, Soil Crop Sci.Soc.Fla.Proc. 4-7.

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2010.

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U.S. EPA, 2005. Overview of the use and usage of soil fumigants. Bi ological and Economic Analysis Division. Office of Pes ticide 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 De pletion. Office of Atmopsheric Programs. Washington, D.C. Available on-line: <http://www.epa.gov/ozone/s trathome.html>. Accessed February 2009.

USEPA 2009 [3]. “Adoption Proposed Endangerm ent 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 Ai r and Radiation. Washington, DC.

USEPA 2010 [1]. “Acid Rain”, Office of Atmo spheric Programs. Washington, D.C.. Available on-line: <http://www.epa.gov/acid rain/>. Accessed March 2010.

USEPA 2010 [2]. “Ground-level Ozone”, Office of Air and Radiation. Washington, D.C.. Available on-line: < http://www.epa.gov/ai r/ozonepollution/>. Accessed March 2010.Page 39 of 53 USEPA 2010 [3]. “On-line Tools for Site Assess ment 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/e pisuite.htm>. Accessed March 2010.

U.S. National Park Service, 2010. “Guidance on Sulfur and Nitrogen Deposition Analysis
Thresholds”. Available on-line: <h ttp://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. Ca nadian Journal of Fisheries and Aquatic Science, Vol. 40, pp. 304 – 331.

Wilson, J.D., and W.K.N. Shum. 1992. A re-exa mination 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., Gu mp, C.A., Ravishankara, and A.R. 1981. Kinetics of OH Reactions with the Atmospheirc Suflur Compounds H 2 S, CH 3 SH, CH3SCH3, and CH 3 SSCH 3

. 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 Befo re 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 ex tent 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•m 3 /mol suggest that high vola tilization 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 cove ring. Other fate and transport processes such as leaching, biodegradation, and adsorpti on 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 applicati on, and subsequent buildup of degradates in the soil in France clay loam soil and Sw itzerland 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 af ter application in France clay loam soil, and 32.86 percent of the material balance 21 da ys after application in Switzerland clay soil. Methanesulfonic acid forms through th e breaking of the disu lfide bond in DMDS. Only trace amounts of DMDS were extr acted 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, a nd 27.24 percent of the material balance at 120 days after applica tion 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 condi tions given the vapor pressure of 22.55 torr and temperature of 20 o C with soil and airspace under a high barrier tarp. In addition, this process has been documented with numer ous 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. Th e 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 K d of 0.641 mL/g (range 0.54 mL/g – 0.86 mL/g for five soil s) suggest that resi dues can readily be transported via water and are weakly retain ed by soil. The high Henry’s Law Constant

of 0.001 atm•m 3 /mol and rapid photodegr adation of DMDS from water suggest that volatilization and photolysis are the primary environmental r outes 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 peri od of 24 hours. Two major degradates were detected, and may have included either meth anesulfonic acid, meth anesulfinic 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 perf ormed. The registrant proposed that formaldehyde may form interm ediate to the degradates identified. However, formaldehyde was not detected w ith the limited sampling that was conducted during the aquatic photo lysis 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 fr ee carbonates. Since methanesulfonic acid is a major degradation product of DMDS degr adation in soil, one mole of DMDS (CH 3 - S-S-CH 3 ) can theoretically form 4 moles of hydrogen (H + ) from dissociation of
CH 3 SO 3 H and oxidation of sulfuric acid. Th e acid equivalence ratio of calcium
carbonate or CaCO 3 (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 CaCO 3 /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 st udy sites in Florida, California, Georgia, and Arizona using a variety of applicati on 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 a tmosphere 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-applicati on. In addition, abso lute peaks of flux occurred during the afternoon hours. In addition, there are two studies conducte d 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 Dove r, 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 applicati on 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 s ite 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/m 2 s) 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 12Page 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/m 2 s) 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 applica tion 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 degrad ation 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 flus hed 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 mechanis m including the interaction between hydroxyl radicals and photodissociation has be en developed and evaluated for DMDS. The DMDS hydroxyl adduct is ini tially formed. Subsequent ab straction in parallel with the photodissociation of DM DS forms the methyl thio l radical. With further photoionization and addition of atmospheric ni trogen oxides to methyl thiol, methyl thionitrite is expected to form. Methyl th iol 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 st eps 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 precipita tion. 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-pl ant 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 th erefore possesses the largest concern for the destruction of stratospheric ozone. All Class I Ozone De pleting 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 contribu te to the destruction of stratospheric ozone. Furthermore, DMDS is expected to degrade quickly in the troposphere. Therefore, emissions of DMDS are not expect ed to contribute to any process related to stratospheric ozone depletion.

Global Warming Potential

DMDS’s methyl components may have th e potential to cont ribute to climate change. Methylated compounds can be pot ent greenhouse gases, and thus have the potential to absorb outgoing long-wave in frared radiation eff ectively (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 we t deposition of sulfuric acid. Wet deposition of sulfuric acid is commonly known as acid rain. The reaction show ing the formation of
sulfuric acid is:

SO 3 + H 2 O H 2 SO 4

Acid rain is recognized by the Agency as having adverse impacts to plants and aquatic habitats (USEPA[1], 2010). Federa l Land Managers are obligated towards the protection of air quality part icularly in National Park Areas under the Clean Air Act amendments of 1977. Consequently, sulfur de position 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 fr om a single DMDS applicati on would not likely be of concern given low emissions from the use of hi gh barrier tarps as spec ified on the label. However, aggregate emissions of DMDS throughout an area with high use may
contribute to acid rain events. To address th e 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 orga nic compound (VOC) in the atmosphere, there is a potential for it to interact w ith atmospheric hydroxyl radicals, oxygen, and nitrogen oxides to produce ground-level ozone. Ground-level ozone is recognized by thePage 47 of 53 Agency as having adverse impacts to plants and terrestrial anim als (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 st ep 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 exposu re 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 Chem ical 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 Molecu lar 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/m 3 ) 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 25 o C; 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) 2188.6200Page 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 assump tion 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

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-------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 waterPage 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

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