Environmental Fate and Ecological Risk Assessment 

for the Proposed Registration of 

Dimethyl Disulfide (DMDS) for use on Tomatoes, 

Peppers, Eggplant, Cucumbers, Squash, Melons, 

Strawberries, Onions, Field Grown Ornamentals, and 

Forest Nursery Crops 

Prepared by:

Gabe Rothman, Environmental Scientist 

Valerie Woodard, Biologist

Reviewed by: 

Mah Shamim, Branch Chief 

Keith Sappington, Senior Biologist 

Michael Barrett, Senior Chemist 

U. S. Environmental Protection Agency

Office of Pesticide Programs 

Environmental Fate and Effects Division 

Environmental Risk Branch IV 

Ariel Rios Building (Mail Code 7507C) 

1200 Pennsylvania Ave., NW

Washington, DC 20460
2 

4

4

4

7

8

9

9

11

12

16

16

16

16

18

19

19

21

21

21

22

22

25

25

25

25

26

33

33

36

36

39

45

45

54

54

58

61

63

63

63

68

69

71

TABLE OF CONTENTS 

I. EXECUTIVE SUMMARY ..................................................................................................

I.A NATURE OF CHEMICAL STRESSOR ................................................................................

I.B. POTENTIAL RISKS TO NON-TARGET ORGANISMS .........................................................

I.C. CONCLUSIONS - EXPOSURE CHARACTERIZATION ........................................................

I.D. CONCLUSIONS - EFFECTS CHARACTERIZATION ...........................................................

I.E. DATA GAPS AND UNCERTAINTIES.................................................................................. I.E.1. Environmental Fate and Exposure .........................................................................................

I.E.2. Ecological Effects.................................................................................................................

I.F. ENDANGERED SPECIES SUMMARY MATRIX ................................................................

II. PROBLEM FORMULATION ......................................................................................

II.A NATURE OF REGULATORY ACTION .............................................................................

II.B. STRESSOR SOURCE AND DISTRIBUTION....................................................................... II.B.1. Nature of the Chemical Stressor......................................................................................

II.B.2. Overview of Pesticide Usage ...........................................................................................

II.C. RECEPTORS............................................................................................................... II.C.1. Aquatic and Terrestrial Effects........................................................................................

II.C.2. Ecosystems Potentially at Risk.........................................................................................

II.D. ASSESSMENT ENDPOINTS .........................................................................................

II.E. CONCEPTUAL MODEL .................................................................................................. II.E.1. Risk Hypothesis................................................................................................................

II.E.2. Conceptual Diagram........................................................................................................

II.F. ANALYSIS PLAN ............................................................................................................ II.F.1. Preliminary Identification of Data Gaps and Analysis Plan ...........................................

II.F.1.a Environmental Fate .........................................................................................................

II.F.1.b Ecological Effects............................................................................................................

II.F.2. Measures of Effect and Exposure.....................................................................................

III. ANALYSIS ......................................................................................................................

III.A. USE CHARACTERIZATION ........................................................................................

III.B. EXPOSURE CHARACTERIZATION ............................................................................. DMDS is a reduced organosulfur compound. Its physical chemical properties and environmental 

fate are summarized below in Tables III-2 and III-3. A description of detailed environmental fate and 

transport characteristics of DMDS can be found in Section III.B.1 below and in Appendix A. .........

III.B.1. Environmental Fate and Transport Characterization .....................................................

III.B.2 Measures of Aquatic Exposure .......................................................................................

III.B.2.a. Aquatic Exposure Modeling........................................................................................

III.B.2.c. Aquatic Exposure Monitoring (Field Data).....................................................................

III.B.3 Measures of Terrestrial Exposure....................................................................................

III.C.1. Aquatic Effects Characterization.....................................................................................

III.C.2. Terrestrial Effects Characterization ................................................................................

IV. RISK CHARACTERIZATION.....................................................................................

IV.A. RISK ESTIMATION - INTEGRATION OF EXPOSURE AND EFFECTS DATA................. IV.A.1. Non-target Aquatic Animals and Plants ..........................................................................

IV.A.2 Non-Target Terrestrial Species.......................................................................................

IV.B. RISK DESCRIPTION................................................................................................... IV.B.2 Risk to Terrestrial Organisms.........................................................................................
3 

72

73

73

74

74

75

75

76

78

78

78

79

80

Terrestrial Risk Conclusions...............................................................................................................

IV.B.3. Review of Incident Data...................................................................................................

IV.B.4 Endocrine Disruption......................................................................................................

IV.B.5. Federally Threatened and Endangered (Listed) Species Concerns.................................

IV.B.5.a. Action Area ..........................................................................................................................

IV.B.5.b Taxonomic Groups Potentially at Risk .................................................................................

IV.B.5.b.1. Discussion of Risk Quotients ............................................................................................

IV.B.5.b.2. Probit Dose Response Relationship..................................................................................

IV.B.5.c. Data Related to Under-represented Taxa........................................................................

IV.B.5.d. Implications of Sublethal Effects......................................................................................

IV.B.5.e. Indirect Effects Analysis ..................................................................................................

IV.B.5.f. Critical Habitat................................................................................................................

IV.B.5.g. Co-occurrence Analysis...................................................................................................
4 

I. Executive Summary 

I.A Nature of Chemical Stressor 

Dimethyl disulfide (DMDS) is a new active ingredient proposed for use on 

fruiting vegetables (restricted to tomatoes, peppers, and eggplant), curcurbit crops 

(restricted to cucumbers, squash, and melons), small fruit crops (restricted to 

strawberries, and blueberries), field-grown ornamentals, and forestry nursery crops. 

DMDS is used to control nematodes in the soil. For nematodes, DMDS acts by blocking 

the cytochrome oxydase mechanism necessary for mitochondrial respiration (Charles, 

2003). DMDS can also be used control weeds, as well as soil-bourne fungus, and 

bacteria. The exact mechanism of action for these target pests are unknown. DMDS is a 

transparent light yellow liquid with a strong garlic-like odor. The intended use of DMDS 

is for pre-plant soil fumigation, implying that dimethyl disulfide converts to and acts as a 

stressor within the gas phase. Given its high vapor pressure and solubility, physical 

chemical properties, volatilization followed by leaching are expected to be the main 

dissipation pathways for DMDS. Dimethyl disulfide gradually degrades to major 

degradates methanesulfonic acid and carbon dioxide in soil as well as major degradates 

methanesulfonic acid, methanesulfinic acid, and sulfuric acid in water through 

photodegradation in water. There is limited information regarding the environmental fate 

and ecological toxicity of methanesulfonic acid and methanesulfinic in the open literature 

and the ECOTOX database. However, structural activity relationship models such as 

ECOSAR indicate that Methanesulfonic acid may not be as toxic as parent dimethyl 

disulfide. In addition, it is not anticipated that dimethyl disulfide residues will be subject 

to photodegradation in nearby water bodies adjacent to fumigated fields by in large. 

Therefore, it is not expected that large quantities of methanesulfinic acid or sulfuric acid, 

will form in significant quantities in water. Therefore, dimethyl disulfide appears to be 

the main stressor for aquatic and terrestrial organisms associated with soil fumigation. 

 The maximum proposed individual dimethyl disulfide application rate for all 

crops is 455 lb a.i./A with one application allowed per season. The PaladinTM label 

contains 98.8 percent a.i. at 8.85 lbs. of a.i. per gallon of solution and PaladinTM EC label 

contains 93.8 percent a.i. at 8.83 lbs. of a.i. per gallon of solution. PaladinTM can only be 

applied through broadcast or bedded shank injection into the soil. The PaladinTM EC 

formulation can only be applied via chemigation through surface or buried drip tape 

under the soil. The drip tape must be buried under the tarp. Immediately following the 

application, covering using a virtually impermeable film (VIF) or high barrier tarp is 

required and remain on the field undisturbed for a minimum of 12 days for both 

formulations. 

I.B. Potential Risks to Non-target Organisms 

DMDS is applied using drip irrigation and shank injection and covered with a 

tarp. The tarp is removed after a minimum 12 days. No spray drift or runoff is expected 

for the first 12 days. Runoff is possible after 12 days when the tarp is cut. However, no 
5 

spray drift is expected because DMDS is applied through drip irrigation systems or shank 

injected into the soil.. An effect to both aquatic and terrestrial species is expected from 

the use of DMDS. Both drip irrigation and shank injection are evaluated for risk to 

aquatic species. Risk to terrestrial animal species via exposure in air is evaluated only for 

shank injection to raised beds and does account for the tarping practice. PRZM/EXAMS 

modeling will be used to estimate the effects to aquatic species. The PERFUM model 

will be used to estimate the effects to terrestrial species. 

Conclusions for the effect of DMDS on aquatic species and aquatic plants were 

based on lines of evidence including fate and transport characteristics, toxicity endpoints, 

results from conventional and refined models for aquatic exposure, as well as reviewing 

incidents reported to the EIIS database. RQS are estimated from the PRZM/EXAMS 

model which accounted for volatility and off-site movement to water bodies following 

the removal of the tarp 12 days after the application. The resulting RQs are compared to 

a Level of Concern (LOC) for the species and exposure route, and were used to develop 

the overall conclusions. No aquatic animal or plant incidents have been reported in the 

EIIS database. 

RQs were estimated for both drip irrigation and shank injection for each use. 

There is potential acute risk to freshwater fish and freshwater invertebrates based on RQ 

exccedence. Drip irrigation RQs exceed the endangered species LOC for freshwater fish 

(RQs=0.003-0.212) and freshwater invertebrates (RQs=0.001-0.125) for FL cucumber, 

FL strawberry and GA onion uses. 

There is no potential for acute risk for any surrogate species using the shank 

injection method. No modeled uses resulted in LOC exceedences. 

There is potential acute risk for chronic effects to freshwater and estuarine/marine 

fish based on the uncertainty due to the persistence of DMDS in water and absence of 

chronic toxicity data. 

RQs for non-listed species are estimated for vascular plants (Lemna) and 

nonvascular plants (Anabaena) using the EC50. There was no RQ exceedence for vascular 

using Lemna as a surrogate or for non-vscaular using Anabaena as a surrogate for either 

drip irrigation or shank injection for any uses. 

Risk is presumed for chronic effects to freshwater and estuarine/marine fish and 

invertebrates based on the uncertainty due to the persistence of DMDS in water and 

absence of chronic toxicity data. 
6 

Conclusions for the effect of DMDS on terrestrial species including birds, 

mammals and terrestrial invertebrates were based on lines of evidence including fate and 

transport characteristics, toxicity endpoints, results from screening level and refined 

models for terrestrial exposure, as well as reviewing incidents reported to the EIIS 

database. Risks to reptiles and terrestrial-phase amphibians are represented using the bird 

as a surrogate. No dietary exposure to birds is expected since residues are not expected to 

be taken up by terrestrial plants, or residues resulting from gas phase deposition are not 

expected to be retained by plants given its high diffusivity. DMDS is hypothesized to 

expose terrestrial wildlife via inhalation. 

The proposed label for DMDS includes instructions to cover the field with a tarp 

for the first 12 days. Specifically, high barrier tarps such as VIF (Virtually Impermable 

Films) tarps are required to be used on the proposed label; therefore the conclusions are 

based on the effect the VIF tarp use pattern. In addition, an analysis using low barrier 

tarps using a screening method with the SCREEN3 model is presented Appendix G. The 

PERFUM model describes the effect from the use of VIF tarps such as proposed on the 

label. Although there is no inhalation LOC available to compare with the RQ, this 

analysis uses the current bird endangered species LOC=0.1 used to evaluate dietary 

effect, to determine the effect of DMDS use. RQs for chronic effects were not modeled 

due to the absence of chronic toxicity data. No terrestrial animal incidents have been 

reported in the EIIS database. 

Risk conclusions for avian and mammal species were developed based on EECs 

from an analysis using high barrier tarps and endpoints from a non-guideline bird 

inhalation study. In addition, due to the volatility of DMDS, it is expected to expose 

terrestrial wildlife via air residues. There is no potential risk for birds based air 

concentrations estimated from PERFUM modeling based on the Tifton field scenarios 

which used covering of VIF tarps to a field treated with dimethyl disulfide indicated no 

risk to birds. 

Although there is no model available to estimate the effects on the honeybee, the 

results for the toxicity test are classified as to the impact. There is no risk for non-listed 

insects based on the honeybee toxicity test, which resulted in a classification of 

practically non-toxic. The risk to other terrestrial invertebrates that are not soil dwelling 

would be represented by the honeybee estimate. 

There is no risk to other off-site terrestrial invertebrates that burrow in the soil 

since the dominant routes of dissipation for DMDS is expected to be leaching into ground 

water or volatilization into the air.. 
7 

DMDS is used to kill weeds as a target, therefore it is expected to kill plants on 

the field. There is no current toxicity test compatible with the existing modeling methods 

available to estimate the effect of DMDS total residues to terrestrial plants through air 

exposure. Therefore, risk is presumed to non-target terrestrial plants off the treated field 

due to its herbicidal properties. Runoff is not expected to be the primary exposure route 

associated with DMDS fumigations. Therefore, TerrPlant was not used to estimate this 

exposure pathway from DMDS.

I.C. Conclusions - Exposure Characterization 

Dimethyl disulfide’s vapor pressure of 22.55 torr at 20oC, high solubility of 2,702 

mg/l, and low soil-water partition coefficient (Kd = 0.641 ml/g) suggest that the major 

routes of dissipation of dimethyl disulfide are volatilization and to a lesser extent, 

leaching. Given its high mobility indicated by its low Kd value, dissolved DMDS 

residues may also be transported to water bodies nearby application sites via runoff. As 

such, recommended label language mitigating the risk of exposure to DMDS runoff in the 

environment is provided in the transmittal memo. In addition, since DMDS in the soil 

are highly soluble, soil bound DMDS residues may leach to ground water upon removal 

of the tarp or in areas where the water table is shallow and recharging occurs. Therefore, 

a prospective ground water monitoring study for DMDS may be requested in the future to 

address any compliance issues with mitigation language placed on the label as needed. 

DMDS residues appear to biodegrade in soil substantially and rapidly over time. 

The aerobic soil metabolism study results suggest that DMDS rapidly diffuses to air 

space (within 5 minutes after the application) and then is redeposited to soil as major 

degradates methanesulfonic acid and carbon dioxide are subsequently formed in soil and 

gradually build to significant quantities over time. This scenario is very possible in the 

field as tarps can trap DMDS gas from escaping to the atmosphere, especially 

considering that DMDS was applied in a closed system in the aerobic soil metabolism 

study. Considering the diffusion-deposition behavior of the chemical and the tarping 

required on the label, the half life of DMDS in the soil is calculated between 2.86 days 

and 3.74 days assuming that the formation of methanesulfonic acid is completely due to 

DMDS degradation in the soil. 

There is limited information about the degradation of DMDS in water. DMDS 

has an aqueous photolyis half-life of 1.17 days corrected for degradation in the dark and 

exposure to natural light intensity was determined for DMDS. Two out of three of the 

degradates, Methanesulfonic acid, methanesulfinic acid, and sulfuric acid were detected 

in major quantities. The nature of biodegradation of DMDS in aquatic water bodies is 

unknown. No aerobic or anaerobic aquatic metabolism studies (OPPTS Guideline Nos. 

835.4300) were submitted to the Agency and remains an outstanding data gap in this risk 

assessment. 
8 

 An upper-bound estimate of 16.89 percent of applied DMDS was determined to 

be available for off-site movement when the tarp covering is removed after the minimum 

period of 12 days as required on the label. The PRZM/EXAMS modeling used to 

estimate water column concentrations assumed this small initial loading. Therefore, 

EECs in surface water are reflective of small loading available to runoff after the required 

12 day tarp covering as well as the continuation of rapid biodegradation as well as 

volatilization as simulated in PRZM/EXAMS. 

The product labels for DMDS require that virtually impermeable film (VIF) tarps 

be used on the field consistent with agricultural practices associated with controlling 

volatile emissions from fumigated fields. One field volatility study was conducted using 

VIF tarps in Tifton, GA in February , and DMDS flux only accounted for 35 percent loss 

of the applied amount from the soil. Upper-bound EECs in air predicted by the PERFUM 

model were not of concern based on this field volatility study. However, this is a sparse 

dataset. Therefore, there may be differing flux profiles at different times of the year for 

differing locations. A screening analysis using the SCREEN3 model indicates that there 

may be a concern for mammals and birds associated with DMDS application in other 

areas during other times of the year. However, this analysis was based on field volatility 

studies that were not conducted with VIF tarps, rather with low density polyethylene and 

metallized tarps. Dimethyl disulfide flux that was measured from the soil with these 

tarps were higher than observed in the VIF study in five out of seven studies accounting 

for approximately 38 – 81 percent of the applied amount for studies conducted in Georgia 

(2 studies), Florida (1 study), California (1 study), and Arizona (1 study) during the 

winter, spring, summer, and fall months, respectively. Two other field voaltililty studies 

contained total measured DMDS flux below the VIF study. DMDS flux accounted for 27 

percent of the applied in Nipomo, California during June using a low density 

polyethylene tarp. In addition, DMDS only accounted for approximately 8.1 percent 

based on field flux measured at Dover, FL using a less permeable metalized film tarp 

during April. Although the VIF tarp shows a lower flux from the soil than five out of 

seven field volatility studies using less permeable tarp material, the flux from soil 

covered with a VIF tarp may vary from factors such as the time of year as well as the 

location of the field. Hence, a robust dataset of field volatility studies which are 

conducted during typical fumigation seasons over multiple regions of the country using 

VIF tarps is an outstanding data gap in this risk assessment. 

I.D. Conclusions - Effects Characterization 

 DMDS is considered moderately toxic to freshwater fish (lowest LC50 = 960 

ppb) and to marine fish (LC50=5600 ppb), It is considered moderately toxic to freshwater 

invertebrates (LC/EC50 = 1610 ppb) and to marine invertebrates (LC50=4900ppb). It is 

practically non-toxic to honeybees (LD50 > 100 ug/bee). No chronic fish or aquatic 

invertebrate data is available. For terrestrial animals, inhalation exposure will be the 

primary exposure. The acute bird inhalation LC50= 17 mg/L and the acute mammal 

inhalation LC50 in rats is 17 mg/L. 
9 

The most sensitive aquatic plant based on EC50 is the non-vascular plant 

Anabaena flos-aquae (0.32 mg/L) while the most sensitive vascular plant was Lemna, 

with an EC50 = 28 mg/L. A terrestrial plant vegetative vigor study shows the most 

sensitive monocot NOAEC = 55 lb ai/A and most sensitive dicot NOAEC = 100 lb ai/A. 

Ecological risks to terrestrial organisms via the dietary and uptake routes are not 

expected to be at risk considering pre-plant soil incorporated uses of DMDS. DMDS 

application modeling using PRZM indicated that there are no residues that are taken up 

by any of the labeled crops. 

I.E. Data Gaps and Uncertainties 

 I.E.1. Environmental Fate and Exposure 

 The following studies are being requested by EFED at this time: 

• Environmental Chemistry Methods (ECMs) and Independent 

Laboratory Validations 

• Aerobic and Anaerobic Aquatic Metabolism (OPPTS Gudeline Nos. 

835.4300) 

• Field Volatility Studies (OPPTS Guideline No. 835.8100) 

• Ambient Air Quality Monitoring Data (Special Study – On Reserve) 

Environmental Chemistry Methods (ECMs) and Independent Laboratory Validations 

(ILVs) for Soil, Water, and Air 

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

and air. ECMs establishes transparency and demonstrates that analytical methods are 

repeatable for all field and laboratory studies. ECMs are required for DMDS; further, 

multi-residue methods (MRMs) for soil and water are preferred. The following are major 

degradates for each media: 

Soil – parent DMDS and methanesulfonic acid 

Water – parent DMDS, methanesulfonic acid, methanesulfinic acid, sulfuric acid, 

any additional degradates identified from aerobic and anaerobic aquatic metabolism 

studies. 

Air – parent DMDS 

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

an independent laboratory should be submitted. These reports will be evaluated by 

EFED. According to NAFTA Guidance, they should include the following information: 

(a) Recovery level(s) of the test compound(s) from the soil and water (substrates) at 

various relevant fortification level(s) using the residue analytical methodology; (b) a 

validated method sensitivity level; (c) results of the study and statistical test applied, 

including a stepwise presentation of the procedure for calculating percent recovery from 

the raw data; (d) all the data/ information necessary to independently verify the results; 
10 

(e) summary of the results; and, (f) discussion and conclusions of the results. 

Aerobic and Anaerobic Aquatic Metabolism

 Submission of the aerobic and anaerobic aquatic metabolism study on the DMDS 

technical product will enable the reviewer to calculate half-lives of DMDS in water. 

These results will result in more refined EECs in surface water and benthic water pores. 

Retrievals of all degradates identified in the proposed degradation pathway (to be 

submitted with the study) should be attempted to account for the full material balance 

over time. 

Field Volatility Studies

Additional field volatility studies using PaladinTM and PaladinTM EC with VIF 

tarp coverings are required for drip irrigation and broadcast applications at this time. The 

studies should be located in anticipated use regions other than the Southeastern United 

States such as California and be conducted at times of the year when typical fumigation 

occurs in those regions. These studies should be conducted using the generic OPPTS 

guidelines. In addition, Johnson et al., 1999, Majewski et al., 1990, or Wilson and Shum, 

1992 should be referenced for additional guidance regarding study designs, development 

of flux profiles, and land surface/flux footprint considerations (e.g., fetch distances along 

the treated field to the instrumentation towers). All studies should include collection of 

on-site meteorological data. If on-field towered sampling is conducted, all measurements 

of wind speed and temperature should be rapidly sampled on the order of every 1 minute. 

Furthermore, retrievals of all degradates identified in the degradation pathway shown in 

Figure III-1 of this document should be attempted. 

Ambient Air Quality Monitoring Data (On reserve)

 

 Ambient air quality monitoring studies may be requested in any high DMDS use 

areas in the future. The data will be used in registration review or with any proposed new 

uses to consider the potential for acute and chronic effects of DMDS, sulfuric acid, and 

ozone associated with a high volume of DMDS use occurring within an airshed. Air 

quality related values of concern will include concentrations of DMDS and ozone in the 

air close to ground level and sulfuric acid in rain water. To address DMDS’s contribution 

to ozone and sulfuric acid, the measured ambient levels of DMDS in air and sulfuric acid 

in water to historical background levels in the same sampling regions before the inception 

of large scale DMDS fumigation should be compared. 

Uncertainties 

There are uncertainties in estimating DMDS exposure in surface water. First, the 

biodegradation and dissipation of DMDS in water is unknown. Second, the impact of 

tarping cannot be explicitely modeled in the PRZM model. Therefore, aquatic exposure 

estimated concentrations in the water column were solely based on the tarp removed with 

an adjusted loading of DMDS which accounts for biodegration of residues under the tarp 
11 

after the required 12 days which the tarp covering is required. However, it is possible 

that there can be seepage under the tarps, but this is not anticipated to contribute in a 

large enough manner to effect aquatic exposure estimates. Third, there is uncertainty 

related to the environmental fate and ecological toxicity of the major degradate 

methanesulfonic acid which forms in aerobic soil where the bulk of DMDS residues are 

expected to reside after fumigation. However, structural activity relationship models 

indicate that methanesulfonic acid is less toxic to all taxa represented in this risk 

assessment than parent DMDS. 

 There are uncertainties with modeling of air residues for the purpose of estimating 

DMDS exposure in air to terrestrial wildlife. There is a limited dataset of field volatility 

studies for high barrier films used with Virtually Impermeable Films (VIF). A screening 

analysis using the SCREEN3 dispersion model with measured flux from field volatility 

studies using less permeable tarps than virtually impermeable filems, indicates EECs of 

concern for mammals and birds. This screening analysis supports the need for more field 

volatility studies in other regions of the U.S. besides the Southeast where fumigants are 

typically used such as the Southwest should be conducted. Therefore, additional field 

volatility studies with drip irrigation and broadcast shank injection should be conducted 

in conjunction with VIF tarping. In addition, upper-bound DMDS EECs in air may not 

account for temperature inversions which are associated with stagnant air and may 

consequently result in high air pollutant concentrations. Therefore, the reviewer has 

provided recommended mitigation language regarding these meteorological regimes. 

Furthermore, DMDS EECs using the PERFUM modeling for high barrier films are based 

on receptor heights 1.5 meters above ground level, which may be slightly different than 

ground level. Furthermore, to address the risk for possible acute and chronic exposure to 

DMDS and degradates ozone and sulfuric acid, the reviewer may request ambient air 

quality monitoring data in the future. 

I.E.2. Ecological Effects 

 Appendix F lists the status of the ecological effects data requirements for DMDS. 

The following effects data are needed for ecological risk assessment for DMDS: 

 

850.1300 Aquatic Invertebrate Life Cycle (Freshwater). This study is required 

based on the outdoor use and uncertainty concerning aquatic exposure and persistence. ). 

850.1350 Aquatic Invertebrate Life Cycle (saltwater). This study is required 

based on outdoor use and current aquatic modeling indicating the potential for chronic 

aquatic exposure to DMDS. There is also uncertainty concerning the persistence of the 

pesticide in water(40CFR Part 158). 

850.1400 Early Life-stage Fish (freshwater). This study is required based on the 

outdoor use and uncertainty concerning aquatic persistence. Current aquatic modeling 

indicates the potential for chronic aquatic exposure to DMDS. Also, the acute aquatic 

EEC is > 0.01 of the acute LC50 for freshwater fish (40CFR Part 158). 

Comment [mts1]: Please state if this 

study is required or not required 

Comment [mts2]: This is conflicting 

statement. Please clarify. Also, state if the 

study is required or not 

Comment [mts3]: Please state if this 

study is required or not required
12 

850.1400 Early Life-stage Fish (saltwater). This study is required based on 

outdoor use and current aquatic modeling indicating the potential for chronic aquatic 

exposure to DMDS. There is also uncertainty concerning persistence in the aquatic 

environment(40CFR Part 158). 

Terrestrial Plant (special study for gases) – MRID 47471202 has been submitted 

and reviewed by EFED. However, the toxicity metric provided is not compatible with 

the existing modeling methods available to estimate the effect of DMDS total residues to 

terrestrial plants through air exposure. This study can become upgradable if data 

regarding the headspace volume is provided. If this is not possible, a new study is 

requested and EFED recommends that the registrant submits a protocol for the Agency to 

review. 

 

 Uncertainties

Chronic aquatic exposures are possible, in part due to repeat or continuous input 

to the aquatic environment. There is uncertainty about the persistence of DMDS in the 

aquatic environment, which would impact chronic endpoints. As noted above, aquatic 

invertebrate life-cycle and fish early life-stage studies (with freshwater and 

marine/estuarine organisms) are needed for risk assessment. These will help the Agency 

determine whether there is further chronic aquatic risk beyond that already identified and 

enable further analysis of the chronic aquatic risk. 

The toxicity test to evaluate the effect of air concentration exposure to birds is 

based on a non-guideline study. In addition there is no threshold LOC to evaluate the 

effects of inhalation for birds. The toxicity test to evaluate the effects of air 

concentrations on terrestrial plants is based on a non-guideline study. Also there is no 

LOC to represent the threshold for exposure to air concentrations. 

I.F. Endangered Species Summary Matrix 

Listed species risks are associated with direct or indirect effects due to 

applications of DMDS to tomatoes, peppers, cucumbers, strawberries, onions, nursery 

and Christmas trees if organisms in listed taxa are exposed (direct effects) or are 

dependent on other organisms that are exposed (indirect effects). Risks are based on 

available reviewed data. Submission and review of the data requested in this review (see 

above) may result in identification of additional potential effects. A summary of listed 

species by taxa is presented in Appendix F. 

There is the potential for direct effects for listed freshwater fish and aquatic 

invertebrates from the use of DMDS based on RQs exceeding the LOC. Drip irrigation 

RQs exceed the endangered species LOC for FL cucumber, FL strawberry and GA onion. 

Drip irrigation RQs range from 0.01 to 0.21 and shank injection RQs from 0 to 0.01 for 
13 

fish. Drip irrigation RQs range from 0.001 to 0.125 and shank injection RQs from 0 to 

0.006 for invertebrates. Based on the direct effect RQs, any freshwater fish species or 

aquatic invertebrates consuming those taxa will be adversely impacted for indirect 

effects. 

There is the potential for chronic risks to freshwater and estuarine/marine fish and 

invertebrates due to the uncertainty concerning persistence in aquatic environments. 

There is no potential direct or indirect effect on listed estuarine/marine fish or 

invertebrates from drip irrigation or shank injection for any use. Drip irrigation RQs 

range from 0 to 0.036 and shank injection RQs from 0 to 0.002 for fish. Drip irrigation 

RQs range from 0 to 0.041 and shank injection RQs from 0 to 0.001 for invertebrates. 

There is no potential risk for direct or indirect effects to listed aquatic vascular 

plants represented by Lemna based on no RQ exceedence using the EC05. No RQs for 

either drip irrigation or shank injection exceeded the LOC. 

Although there are no aquatic non-vascular plants included in Federal listings of 

threatened and endangered species at the present time, an assessment of the effect of 

DMDS on those plants is provided to evaluate potential contributions to indirect effects 

to other taxa and as a record of exceedances should future listings of non-vascular aquatic 

plants warrant additional evaluation of Federal actions. 

There is potential risk for direct or indirect effects to listed aquatic non-vascular 

plants represented by Anabaena based on RQ exceedence using the EC05. There was no 

RQ exceedence for vascular using using Anabaena as a surrogate for shank injection for 

any uses. 

There is potential risk based on the uncertainty from the absence of data to 

estimate the effect of the gas to terrestrial plants. 

Habitat Modification

Habitat modification includes effects from reduction in prey as well as effects on 

plants. There is the potential for indirect effects for listed freshwater fish and aquatic 

invertebrates from the use of DMDS based on RQs exceeding the LOC. Drip irrigation 

RQs exceed the endangered species LOC for FL cucumber, FL strawberry and GA onion. 

There is the potential for chronic risks to freshwater and estuarine/marine fish and 

invertebrates due to the uncertainty concerning persistence in aquatic environments. 

The effect of plants is also used to assess the effect of DMDS on habitat 

modification. There is potential risk to listed aquatic non-vascular plants represented by 

Anabaena based on RQ exceedence using the EC05. RQs are estimated for listed species 
14 

using the EC05 toxicity value. RQs exceeded the LOC for drip irrigation for listed 

nonvascular plants for CA tomato, FL tomato, FL pepper, FL cucumber, FL strawberry, 

GA onion, MI nursery, NJ nursery and OR Christmas tree uses. No RQs for shank 

injection for nonvascular plants exceeded the LOC for any uses. 

There is potential risk based on the uncertainty from the absence of data to 

estimate the effect of the gas to terrestrial plants. 

Listed Taxon Direct Effects Indirect Effects3 

Terrestrial and semiaquatic plants – 

monocots 

Yes(Additional data required4

) Yes(Additional data required4

) 

Terrestrial and semiaquatic plants – dicots No (semi-aquatic plants) No 

Terrestrial 

Invertebrates No No 

Birds No No 

Terrestrial phase 

amphibians1 No No 

Reptiles1 No No 

Mammals No No 

Aquatic non-vascular 

plants* Yes Yes 

Aquatic vascular 

plants No No 

Freshwater fish Yes – (Additional chronic data 

needed) 4 Yes 

Aquatic phase 

amphibians2 

Yes – (Additional chronic data 

needed) 4 Yes 

Freshwater 

crustaceans Yes Yes 

Mollusks NA NA 

Marine/estuarine fish No –(Additional chronic data 

needed) 4 No 

Marine/estuarine 

crustaceans 

No (Additional chronic data 

needed) 4 No 
15 

* At the present time no aquatic non-vascular plants are included in Federal listings of threatened and 

endangered species. The taxonomic group is included here for the purposes of evaluating potential 

contributions to indirect effects to other taxa and as a record of exceedances should future listings of 

non-vascular aquatic plants warrant additional evaluation of Federal actions.

1

Risk assessment is based on avian assessment. 

2

Risk assessment is based on freshwater fish assessment. 

3

Indirect effects are considered possible for every taxonomic group when one or more direct effect 

LOCs are met/exceeded. Listed species could be affected by the loss of other species that they depend 

on for food, cover, and/or reproduction (e.g., pollination, seed dispersal). This is only a screening 

assessment. A refined assessment will consider the specifics of the food, cover, and reproduction needs 

of each listed species. 

4 Requested data may result in additional potential direct effects. 
II. Problem Formulation 

The purpose of this problem formulation is to provide the foundation for the 

ecological risk assessment being conducted for DMDS. As such, it articulates the 

purpose and objectives of the risk assessment, evaluates the nature of the problem, and 

provides a plan for analyzing the data and characterizing the risk (US Environmental 

Protection Agency, 1998) and is consistent with procedures and methodology outlined in 

the Overview Document (US Environmental Protection Agency 2004). 

. 

II.A Nature of Regulatory Action 

 Under the authority of the Federal Insecticide, Fungicide and Rodenticide Act 

(FIFRA), the registrant UPI/Arkema is seeking the Section 3 registration for the new 

active ingredient, DMDS, for use as a pre-plant fumigant. 

II.B. Stressor Source and Distribution 

II.B.1. Nature of the Chemical Stressor 

DMDS is a new fumigant proposed for use to control (or suppression) of weeds, 

soil-borne plant pathogens and nematodes. For nematodes, DMDS acts by blocking the 

cytochrome oxydase mechanism necessary for mitochondrial respiration (Charles, 2003). 

This process has shown been shown to decrease intracellular ATP production and reduce 

the neuronal activity in insects (Dugravot et al., 2003). The mechanism of action is 

unknown for the other target pests. DMDS is formed as part of the global tropospheric 

sulfur cycle. DMDS is emitted into the atmosphere as a result of decay of organic 

material, biological waste products, and as a by-product of several plant and 

phytoplankton biological functions (Graedel, 1986). A brief summary of the product 

chemistry data on DMDS is provided in Table II-1.

Table II-1. Nature of the Chemical Stressor.

Common name dimethyl disulfide 

Chemical name disulfide, dimethyl 

Structure 

Pesticide type Soil Fumigant 

Chemical class Reduced Organosulfur Compound 

CAS number 000624-92-0 

Empirical formula C2H6S2

Molecular mass (g/mol) 94.2 

Vapor pressure at 20oC 22.5 torr 

16 
17 

Table II-1. Nature of the Chemical Stressor.

Common name dimethyl disulfide 

Henry’s Law Constant at 20oC 0.001 atm·m3

/mol 

Solubility in water (mg/L)at 200C 2,702 (pH 6) 

Log Kow 1.77 

DMDS biodegrades to methanesulfonic acid in significant quantities in soil and 

may be available to runoff. In water, DMDS can degrade to methanesulfonic acid, 

methanesulfinic acid, and sulfuric acid via photolysis in significant levels as well. 

Structural activity relationship models such as ECOSAR indicate that 

methanesulfonic acid may not be as toxic as parent DMDS. ECOSAR, a utility under 

EPISuite 4, estimates the toxicity of chemicals discharged to water. ECOSAR predicts 

toxicity to fish, aquatic invertebrates and algae using an extensive set of structure-activity 

relationships (SARs). The program estimates a chemical's acute (short-term) toxicity 

and, when available, and chronic (long-term or delayed) toxicity (USEPA, 2010[5]). 

Table II-2b shows that ECOSAR indicates that DMDS has a lower toxicity and 

methanesulfonic acid for all aquatic taxa by a factor of at least 4,758 and as much as 

1,181,295. Table II-2a does indicate that DMDS’s toxicity is underpredicted by the 

model for all taxa. However, the margin of the underprediction is far surpassed by the 

margin that ECOSAR predicts higher toxicity for parent DMDS as compared to 

methanesulfonic acid. In fact, all predictions of ECOSAR toxicity for methanesulfonic 

acid are beyond the solubility limit of methanesulfonic acid (methanesulfonic solubility = 

29,180 mg/l at 25oC, EPISuite 4). DMDS acute lethality toxicity thresholds for all taxa 

occur at concentrations much lower than this level. 

Table II-2a. DMDS Measured Versus ECOSAR Predicted Toxicity. 

Taxa Endpoint 

Dimethyl 

Disulfide 

Measured 

Toxicity 

(ppm) 

Dimethyl 

Disulfide 

ECOSAR 

Toxicity 

(ppm) 

ECOSAR 

Departure 

Factor 

Freshwater Fish 96-hr LC50

(Acute) 

0.96 93.84 97.75

Daphnid 48-hr LC50

(Acute) 

1.61 51.93 32.25

Marine Fish 96-hr LC50

(Acute) 

5.60 131.73 23.52 

Mysid 96-hr LC50

(Acute) 

4.90 102.43 20.90 

Green Algae 96-hr EC50

(Acute) 

5.73 23.33 4.07 

1. ECOSAR Departure Factor = DMDS ECOSAR Toxicity/DMDS Measured Toxicity. 
18 

Table II-2b. DMDS Versus Methanesulfonic Acid ECOSAR Predicted Toxicity. 

Taxa Endpoint 

DMDS 

ECOSAR 

Toxicity 

(ppm) 

Methanesulfonic 

Acid ECOSAR 

Toxicity 

(ppm) 

Methanesulfonic 

Acid 

Departure 

Factor 

Freshwater 

Fish 

96-hr LC50

(Acute) 

93.84 5.31 x 106 56,586

Daphnid 48-hr LC50

(Acute) 

51.93 1.57 x 106 30,233

Marine Fish 96-hr LC50

(Acute) 

131.73 1.03 x 107 78,190 

Mysid 96-hr LC50

(Acute) 

102.43 1.21 x 108 1,181,295 

Green Algae 96-hr EC50

(Acute) 

23.33 1.11 x 105 4,758 

1. Methanesulfonic Departure Factor = Methanesulfonic Acid ECOSAR Toxicity/DMDS 

ECOSAR Toxicity. 

In addition, it is not anticipated that DMDS residues will be subject to 

photodegradation in nearby water bodies adjacent to fumigated fields by in large. 

Therefore, it is not expected that large quantities of methanesulfinic acid or sulfuric acid, 

will form in significant quantities in water. Therefore, DMDS appears to be the main 

stressor for aquatic and terrestrial organisms associated with soil fumigation. 

II.B.2. Overview of Pesticide Usage 

 DMDS is proposed as a new soil fumigant. Like other soil fumigants, DMDS will 

be used to fumigant the upper 6 to 12 inches of the soil to control soil borne pests such as 

nematodes, soil pathogens, and fungi. DMDS can also be used to control weeds. DMDS 

is currently used as an agent for petrochemical and pharmaceutical products, a gas 

odorant, and as an agent to control hydrogen sulfide gas emissions from oil refineries 

There are two formulations of DMDS condidered for registration. Paladin TM is a 

liquid concentrate to be used in shank injection applications only. Paladin TM EC is 

proposed for use for chemigation through drip irrigation systems only. Paladin TM is 

proposed for use before planting of fruiting vegetables (specifically, tomatoes, peppers, 

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

onions, field grown ornamentals, and forest nursery crops. Paladin TM EC is proposed for 

use on all of these except onions. Immediately after fumigation, virtually impermeable 

films are required to cover the field with broadcast fumigation or rows for raised bedded 

fumigation. 
19 

II.C. Receptors 

II.C.1. Aquatic and Terrestrial Effects 

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

Environmental Protection Agency, 1998). The receptor is the biological entity that is 

exposed to the stressor (EPA, 1998.) 

Consistent with the process described in the Overview Document (US 

Environmental Protection Agency, 2004), this risk assessment uses a surrogate species 

approach in its evaluation of DMDS. Toxicological data generated from surrogate test 

species, which are intended to be representative of broad taxonomic groups, are used to 

extrapolate to potential effects on a variety of species (receptors) included under these 

taxonomic groupings. 

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

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

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

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

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

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

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

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

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

affected communities. 

Table II-3 provides examples of taxonomic groups and the surrogate species tested to 

help understand potential ecological effects of pesticides to these non-target taxonomic 

groups. Based on a preliminary review of the ecological effects data, DMDS is highly 

toxic to cold-water fish, represented by the rainbow trout and moderately toxic to warm 

water fish, represented by the zebrafish. It is also moderately toxic to freshwater 

invertebrates. Ecological toxicity studies for terrestrial species include effects to birds, 

mammals and terrestrial invertebrates. Although there is an acceptable acute oral toxicity 

study for birds (MRID 470528-13) and rats (MRID 451179-02 ), dietary effects are not 

expected from exposure to DMDS. 

Table II-3. Test Species Evaluated for Assessing Potential Ecological Effects of DMDS 

and the Associated Acute Toxicity Classification 

Taxonomic Group Example(s) of Surrogate Species Acute Toxicity Classification 

Highly 

Toxic for acute oral 

Not Exposure Route Birds1 Bobwhite (Colinus virginians) 

No Classification for Inhalation 

Slightly Toxic Mammals Laboratory rat (Rattus norvegicus) No Classification for Inhalation 

Insects Honey bee 

(Apis mellifera L.) MRID 474712-03 Practically non-toxic 
20 

Table II-3. Test Species Evaluated for Assessing Potential Ecological Effects of DMDS 

and the Associated Acute Toxicity Classification 

Taxonomic Group Example(s) of Surrogate Species Acute Toxicity Classification 

Zebrafish (Danio rerio) Moderately toxic 

Freshwater fish2 

Rainbow trout (Oncorhynchus mykiss) Highly toxic 

Freshwater invertebrates Water flea (Daphnia magna) Moderately toxic 

Estuarine/marine fish Sheepshead minnow (Cyprinodon 

variegates) Moderately Toxic 

Estuarine/marine 

invertebrates Mysid (Americamysis bahia) Moderately Toxic 

Terrestrial plants3

Monocots – oat (Avena sativa) 

MRID 474712-02 

Dicots – tomato (Lycopersicon 

esculentum) 

MRID 474712-02 

Not classified 

Duckweed (Lemna gibba) 

MRID474712-04 Not Classified 

FW: Green algae (Pseudokirchneriella 

subcapitat) Aquatic plants and algae Not Classified 

FW: (Anabaena flos-aquae) 

MRID 474712-05 Not Classified 

1

 Birds represent surrogates for terrestrial-phase amphibians and reptiles. 2

 Freshwater fish may be surrogates for aquatic-phase amphibians. 

3

 Four species of two families of monocots, of which one is corn; six species of at least four dicot families, of which 

one is soybeans. 
21 

II.C.2. Ecosystems Potentially at Risk 

The ecosystems potentially at risk are often extensive in scope; therefore, it may 

not be possible to identify specific ecosystems during the development of a nation-wide 

ecological risk assessment. However, in general terms, terrestrial ecosystems potentially 

at risk could include the treated field and immediately adjacent areas that may receive 

drift or runoff. Areas adjacent to the treated field could include cultivated fields, 

fencerows and hedgerows, meadows, fallow fields or grasslands, woodlands, riparian 

habitats, and other uncultivated areas. 

Aquatic ecosystems potentially at risk include water bodies adjacent to, or down 

stream from, the treated site and might include impounded bodies such as ponds, lakes 

and reservoirs, or flowing waterways such as streams or rivers including all adjacent offchannel habitats that are permanently or intermittently connected to flowing waters. For 

uses in coastal areas, aquatic habitat also includes marine ecosystems, including estuaries, 

embayments, and near shore environments. 

II.D. Assessment Endpoints 

Assessment endpoints represent the actual environmental value that is to be 

protected, defined by an ecological entity (species, community, or other entity) and its 

attribute or characteristics (US Environmental Protection Agency, 1998). For DMDS, the 

ecological entities include the following: birds, mammals, freshwater fish and 

invertebrates, estuarine/marine fish and invertebrates, terrestrial plants, insects, and 

aquatic plants and algae. The attributes for each of these entities may include survival, 

growth, and reproduction. (See Table II.3 in Section II.F.2, the Analysis Plan, for further 

discussion.) 

II.E. Conceptual Model 

For a pesticide to pose an ecological risk, it must reach ecological receptors in 

biologically significant concentrations. An exposure pathway is the means by which a 

pesticide moves in the environment from a source to an ecological receptor. For an 

ecological pathway to be complete, it must have a source, a release mechanism, an 

environmental transport medium, a point of exposure for ecological receptors, and a 

feasible route of exposure. 

A conceptual model is intended to provide a written description and visual 

representation of the predicted relationships between DMDS, potential routes of 

exposure, and the predicted effects for the assessment endpoint. A conceptual model 

consists of two major components: the risk hypothesis and the conceptual diagram (US 

Environmental Protection Agency, 1998). 
22 

II.E.1. Risk Hypothesis 

 For Dimethyl Disulfide (DMDS), the following ecological risk hypothesis is 

being employed for this baseline risk assessment: 

DMDS, when used in accordance with the label, results in potential adverse 

effects upon the survival, growth, and reproduction of non-target terrestrial and 

aquatic organisms. Given the high application rate and potential for of DMDS 

residues to dissolve in water, there is a likelihood of exposure to terrestrial and/or 

aquatic organisms.

II.E.2. Conceptual Diagram 

The potential exposure pathways and effects of DMDS in terrestrial and aquatic 

environments are depicted in Figure II-1 and Figure II-2, respectively. Solid arrows 

represent the most likely routes of exposure and effects; dashed lines represent potential 

routes of exposure that are not considered likely for DMDS. If direct effects to nontarget terrestrial and/or aquatic organisms occur, terrestrial and/or aquatic animals may in 

turn be affected through the reductions in primary productivity and habitat and/or loss of 

prey items, for example. No dietary exposure is expected due to DMDS remaining in a 

gas phase. It is thus expected to expose terrestrial wildlife via inhalation. In addition, due 

to the volatility of DMDS, it is expected to expose terrestrial wildlife via air residues. 

Terrestrial plants may be exposed to DMDS residues via runoff and air exposure. 
Figure II-1. Conceptual model depicting potential risks to terrestrial animals and 

plants from the use of DMDS as a fumigant to control root-infesting nematodes, 

fungal plant diseases, weeds, and soil borne pathogens1

23 

 

Pre-plant soil incorporation via broadcast drip 

irrigation, drip irrigation to raised beds, or shank 

injection to raised beds and broadcast shank 

injection with VIF Tarp Covering

Leaching and Runoff 

of Water 

Plant Matter Volatilization 

Ingestion Direct Contact/Root 

Uptake 

Direct Contact/Root 

Uptake 

Direct Contact 

Integument/Inhalation 

Uptake 

Terrestrial plants Terrestrial Plants Terrestrial Vertebrates

Terrestrial Plants 

Source/Transport

Pathways

Source/Exposure

Media

Reduced Survival and

Growth 

Reduced Survival,Growth, 

and Reproduction

 Reduced Survival,

Growth and Reproduction

Receptors 

Exposure

Dimethyl Disulfide ground application for Tomatoes,

Peppers, Eggplant, Cucumbers, Squash, Melons, 

Strawberries, Blueberries, Onions, Ornamentals, and

Terrestrial Animal/Plant Risk 

Stressor 

Attribute

1

 Solid lines represent major and dashed lines represent minor routes of exposure. 
Figure II-2. Conceptual model depicting potential risks to aquatic animals and 

plants from the use of DMDS as a fumigant to control root-infesting nematodes, 

fungal plant diseases, weeds, and soil borne pathogens2

24 

 

Runoff of Water & 

Sediment/Suspended 

Solids 

Volatilization 

Ingestion Direct Contact 

Integument Uptake 

Aquatic Plants 

Aquatic Vertebrates 

and Invertebrates 

Vascular and 

Nonvascular 

Aquatic Plants 

Aquatic Vertebrates 

and 

Invertebrates 

Source/Transport

Pathways

Source/Exposure

Media

Reduced Survival and 

Growth 

Aquatic Animal/Plant Risk 

Pre-plant soil incorporation via 

drip irrigation or shank 

injection with VIF Tarp 

Covering

Dimethyl Disulfide ground application for Tomatoes, 

Peppers, Eggplant, Cucumbers, Squash, Melons, 

Strawvberries, Blueberries, Onions, Ornamentals, and 

Reduced Survival, 

Growth and Reproduction

Reduced Survival, 

Growth and Reproduction

Receptors 

Exposure 

Stressor 

Attribute 

2

 Solid lines represent major and dashed lines represent minor routes of exposure. 
25 

II.F. Analysis Plan 

II.F.1. Preliminary Identification of Data Gaps and Analysis Plan 

II.F.1.a Environmental Fate 

 The following are outstanding data environmental fate study requirements that 

EFED is requesting at this time or may request in the future: 

• Environmental Chemistry Methods (ECMs) and Independent 

Laboratory Validations 

• Aerobic and Anaerobic Aquatic Metabolism (OPPTS Guideline Nos. 

835.4300) 

• Field Volatility Studies (OPPTS Guideline No. 835.8100) 

• Ambient Air Quality Monitoring Data (Special Study – On Reserve) 

Details of the justifications for this data as well as the test substances of concern are 

presented in Section I.E.1. 

II.F.1.b Ecological Effects 

A total of 17 registrant-submitted studies are available for assessing the potential 

effects of DMDS on non-target organisms. The results (and adequacy) of these will be 

presented in the risk assessment. These include avian acute oral and acute inhalation; 

freshwater fish and aquatic invertebrate toxicity; estuarine/marine fish, mollusk and 

shrimp toxicity; terrestrial and aquatic plant toxicity; and bee toxicity. The principal data 

gaps at this point appear to be for fish early life-stage and aquatic invertebrate life-cycle 

studies due to the uncertainty about DMDS persistence in the water column. 

Appendix F lists the status of the ecological effects data requirements for DMDS. The 

following effects data are needed for ecological risk assessment for DMDS: 

850.1300 Aquatic Invertebrate Life Cycle (Freshwater). This study is required 

based on the outdoor use and uncertainty concerning aquatic exposure and persistence. 

850.1350 Aquatic Invertebrate Life Cycle (saltwater). This study is required 

based on outdoor use and current aquatic modeling indicating the potential for chronic 

aquatic exposure to DMDS. In addition, there is uncertainty about the persistence of 

DMDS in the aquatic environment (40CFR Part 158). 

850.1400 Early Life-stage Fish (freshwater). This study is required based on the 

outdoor use and uncertainty concerning aquatic persistence. Current aquatic modeling 

indicates the potential for chronic aquatic exposure to DMDS. 
26 

850.1400 Early Life-stage Fish (saltwater). This study is required based on 

outdoor use and current aquatic modeling indicating the potential for chronic aquatic 

exposure to DMDS. In addition, there is uncertainty concerning the persistence of 

DMDS in water. 

850.1350 Aquatic Invertebrate life cycle (estuarine/marine). Current aquatic modeling 

indicates the potential for chronic aquatic exposure to DMDS. Also, the acute aquatic 

EEC for ornamentals is > 0.01 of the acute LC50 for marine/estuarine invertebrates 

(40CFR Part 158). 

850.1400 Early Life-stage Fish (saltwater). Current aquatic modeling indicates the 

potential for chronic aquatic exposure to DMDS. Also, the acute aquatic EEC for 

ornamentals is > 0.01 of the acute LC50 for marine/estuarine fish (40CFR Part 158). 

850.1400 Early Life-Stage Fish (freshwater). Current aquatic modeling indicates the 

potential for chronic aquatic exposure to DMDS. Also, the chronic 60-day aquatic EECs 

for both turf and ornamentals are > 0.1 of the NOAEL in the early life-stage study with 

freshwater fish (40CFR Part 158). 

850.1350 Aquatic Invertebrate life cycle (freshwater). Current aquatic modeling 

indicates the potential for chronic aquatic exposure to DMDS. Also, the acute aquatic 

EEC for ornamentals is > 0.01 of the acute LC50 for marine/estuarine invertebrates 

(40CFR Part 158). 

Terrestrial Plant (special study for gases) – MRID 47471202 has been submitted and 

reviewed by EFED. However, the toxicity metric provided is not compatible with the 

existing modeling methods available to estimate the effect of DMDS total residues to 

terrestrial plants through air exposure. This study can become upgradable if data 

regarding the headspace volume is provided. If this is not possible, a new study is 

requested and EFED recommends that the registrant submits a protocol for the Agency to 

review. 

II.F.2. Measures of Effect and Exposure 

II.F.2.a Exposure

To address the potential for aquatic exposure to DMDS and major degradates, 

PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) will be used to estimate 

one-in-ten year surface water acute and chronic estimated exposure concentrations 

(EECs). Since major degradates such as methanesulfonic acid, methanesulfinic acid, and 

sulfuric acid are not expected to be of toxicological concern (as discussed in Section 

II.B.1), EECs are based on parent DMDS alone. 

Since DMDS has a high vapor pressure and is used as a soil fumigant, volatility 

and diffusion is an important dissipation process from the soil. The volatility algorithm 

in PRZM has not been fully validated in EFED as of this time. However, considering the 
volatile nature of this fumigant, EECs will be calculated using the consideration to 

volatility or tarps in risk estimates for aquatic plants and animals presented in Section 

IV.A. The volatility routine used in PRZM for this risk assessment assumed a static 

temperature in the soil over time. Therefore, the modeling assumes that otherwise 

temperature dependent variables such as soil degradation rates and Henry’s Law Constant 

remain constant over time. 

One other important consideration in the exposure estimation for DMDS for 

aquatic animals and plants includes the determination of DMDS loadings in the field after 

tarp removal 12 days after the application, as required by the proposed label It is possible 

to adjust the application rate to account for thie loss in loading in the soil due to 

biodegration under the tarp to determine EECs effectively modeling the fate and transport 

of DMDS after the tarp is removed. Given the limited field volatility dataset for DMDS 

applications accompanied with VIF tarp covering, it is assumed that there is no loss of 

DMDS due to volatile residues diffusing through the soil and tarp throughout the twelve 

day period following the application. For aerobic soil metabolism, the following reaction 

rate equation for first-order degradation can be used to estimate the percent of DMDS 

loadings after 12 days: 

[ ]

[ ]

27 

t kt e

DMDS

DMDS − =

0

where [DMDS]t represents the concentration or loading of DMDS after 12 days, 

[DMDS]0 represents the initial concentration or loading of DMDS, t is the time period of 

interest (12 days), and k is the rate constant which is equal to the following equation for 

first-order degradation: 

lifehalf

k − = 2ln

 Since DMDS is highly soluble in water, ground water contamination of DMDS 

either under the tarp in areas with shallow ground water or due to leaching associated 

with rain events after the tarp is removed is possible. The Tier I model Screening 

Concentration in Ground Water (SCI-GROW v2.3, Jul. 29, 2003; USEPA, 2002b) is used 

to calculate acute and chronic EECs of DMDS in water associated with fumigations. 

Volatilization is not taken into account in this model. Furthermore, since DMDS ground 

water contamination is possible under the tarp, the full loading of applied DMDS is 

considered for EECs. Since major degradates were not found to be of toxicological 

conern, only DMDS EECs are evaluated. 

To address the potential of terrestrial exposure to DMDS residues in the air, the 

Probablistic Exposure and Risk Model for Fumigants (PERFUM) (v. 2.5.1, 7/2/2008) 

will be used estimate the concentration of DMDS residues in the air. Field volatilization 

flux rates are entered into PERFUM consistent with meteorological data in terms of the 

time of day that the flux was measured. The upper-bound air EEC is the 90th percentile 

predicted concentration corresponding to the time period which results in the highest 

concentrations close to the edge of the field. Since PERFUM is not an EFED model, risk 

determinations are presented in the Risk Description Section in Section IV.B.2. The risk 
28 

will only be described with the EECs estimated from field flux in field volatility studies 

where high barrier tarps were used, which are most representative to the label 

requirements of the application of a VIF tarp. However, additional characterization will 

be provided using the remaining field volatility studies which measured flux from low 

barrier tarps. Screening tools which are currently being validated be EFED, such as the 

Screening Tool for Inhalation Risk (STIR) are not appropriate for a fumigant risk 

assessment since the risk hypothesis already assumes that ecological risk exists due to 

exposure to air residues of DMDS given its exceptionally high vapor pressure. 

 II.F.2.b Effects 

Table II-4 lists the measures of environmental exposure and ecological effects 

used to assess the potential risks of DMDS to non-target organisms. The methods used to 

assess the risk are generally consistent with those outlined in the document “Overview of 

the Ecological Risk Assessment Process in the Office of Pesticide Programs (2004)” 
29 

Table II.4. Measures of Ecological Effects and Exposure for DMDS 

Assessment Endpoint Surrogate Species and 

Measures of Ecological Effect1 

Measures of Exposure 

Survival 

Bobwhite acute inhalation LC50

Bobwhite 

Birds2 

Reproduction and 

growth 

Bobwhite and mallard chronic 

reproduction NOAEC and 

LOAEC (no studies 

available) 

Survival Laboratory rat acute inhalation 

LC50

Mammals 

Reproduction and 

growth 

Laboratory rat oral reproduction 

chronic NOAEC and 

LOAEC 

Air Concentration 

Survival 

Rainbow trout and bluegill 

sunfish acute LC50

(Zebrafish study available) 

Peak EEC4 

Freshwater 

fish3

Reproduction and 

growth 

Fathead minnow 

chronic (early life-stage) 

NOAEC and LOAEC 

(No study available) 

60-day average EEC4 

Survival Water flea (and other freshwater 

invertebrates) acute EC50 

Peak EEC4 

Freshwater 

inverte 

-brates 

Reproduction and 

growth 

Water flea chronic (life cycle) 

LOAEC 

(No study available) 

21-day average EEC4 

Survival Sheepshead minnow acute LC50 Peak EEC4 

Estuarine/

marine fish 

Reproduction and 

growth 

Sheepshead minnow chronic 

(early life-stage) NOAEC 

and LOAEC 

(No study available) 

60-day average EEC4 
30 

Table II.4. Measures of Ecological Effects and Exposure for DMDS 

Assessment Endpoint Surrogate Species and 

Measures of Ecological Effect1 

Measures of Exposure 

Survival Eastern oyster acute EC50 and 

mysid acute LC50 

(No study available) 

Peak EEC4 

Estuarine/

marine 

inverte 

-brates 

Reproduction and 

growth 

Mysid chronic NOAEC and 

LOAEC (No study 

avalable) 

21-day average EEC4 

Terrestrial 

plants5

Survival and growth Monocot and dicot seedling 

emergence and vegetative 

vigor EC25, EC05, and 

NOAEC values

Air cocentrations to non-target 

areas 

Insects 

Survival (not 

quantitatively assessed) 

Honeybee acute contact (MRID) Maximum application rate 

Aquatic 

plants and 

algae Survival and growth 

Algal and vascular plant (i.e., 

duckweed) EC50 and 

NOAEC values for growth 

rate and biomass 

measurements

Peak EEC 

1 If species listed in this table represent most commonly encountered species from registrant-submitted studies, 

 risk assessment guidance indicates most sensitive species tested within taxonomic group are to be used for 

baseline risk assessments. 

2 Birds represent surrogates for amphibians (terrestrial phase) and reptiles. 

3 Freshwater fish may be surrogates for amphibians (aquatic phase). 

4 One in 10-year return frequency. 

5 Four species of two families of monocots - one is corn, six species of at least four dicot families, of which one 

is soybeans. LD50 = Lethal dose to 50% of the test population; NOAEC = No observed adverse effect 

concentration; LOAEC = Lowest observed adverse effect concentration; LC50 = Lethal concentration to 50% of 

the test population; EC50/EC25 = Effect concentration to 50%/25% of the test population. 
31 

Birds

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

the effect for all birds, as well as reptiles and terrestrial-phase amphibians. In an acute 

inhalation toxicity study, 16- to 17-week old northern bobwhite quail were exposed by 

whole-body inhalation to DMDS (purity ≥98.53%) for 4 hours. The LC50= 1.7mg/L will 

be used in this assessment. 

No avian reproductive study is available or requested based on persistence data in 

the terrestrial environment (in air) and because residues are not expected to be uptake by 

crops due to pre-plant soil incorporation applications for this fumigant. 

Fish

 Fish are represented by a warm-water species and a cold-water species. An 

acceptable acute Zebra fish (Danio rerio) study resulted in a 96 hour LC50=7.50mg/L 

(MRID 470528-15). Based on the results of this study, DMDS would be classified as 

moderately toxic to Zebrafish (Danio rerio) in accordance with the classification system 

of the U.S. EPA. 

 An acceptable acute Rainbow trout (Oncorhynchus mykiss) study (MRID 470528-

14) resulted in an LC50=0.96 mg/L that will be used in this assessment. Based on the 

results of this study, DMDS would be classified as highly toxic to Rainbow Trout in 

accordance with the classification system of the U.S. EPA. 

No chronic fish studies are available. Due to the acute risks identified for fish and 

the uncertainty from the absence of data for persistence in the aquatic environment, a 

chronic fish study will be requested. 

Aquatic Invertebrates

 The effect of DMDS to aquatic invertebrates is represented by Daphnia magna. An 

acceptable 48 hour acute toxicity test (MRID 470528-16) for DMDS was received. The 

48-hour LC50/EC50 was 1.61 mg ai/L. Based on the results of this study, DMDS would be 

classified as moderately toxic to Daphnia magna in accordance with the classification 

system of the U.S. EPA. 

 

Estuarine/marine fish

 In an acceptable 96-h acute toxicity study (MRID 473075-04), Sheepshead 

Minnow (Cyprinodon variegates) were exposed to DMDS under static renewal 

conditions. Based on the results of this study, DMDS would be classified as moderately 

toxic to Sheepshead Minnow (Cyprinodon variegatus) on an acute toxicity basis in 

accordance with the classification system of the U.S. EPA. 

 
32 

Estuarine/marine invertebrates

 The effect of DMDS on marine invertebrates is represented by the mysid. An 

acceptable acute mysid toxicity test resulted in an LC50=4.9mg/L (3.9-6.1) (MRID 

473075-05). Based on the LC50 in this study (4.9 mg ai/L), DMDS would be categorized 

as moderately toxic to mysid shrimp on an acute toxicity basis. This value will be used in 

the assessment. 

Terrestrial Plants

 A supplemental vegetative vigor study was received to demonstrate the effect of 

DMDS on plants. The effect on DMDS on the vegetative vigor of monocot (corn, Zea 

mays; onion, Allium cepa; oat, Avena sativa; and ryegrass, Lolium perenne) and dicot 

(cabbage, Brassica oleracea; soybean, Glycine max; sugarbeet, Beta vulgaris; lettuce, 

Lactuca sativa; tomato, Lycopersicon esculentum; and radish, Rapahnus sativus) crops 

was studied at nominal concentrations of 18.8, 37.5, 75, 150, and 300 lbs a.i./A. 

The highest application rate used in the study was 300lb/A. This is below the 

proposed application rate of 455lb/A. The most sensitive dicot for both height and weight 

was tomato. An acceptable study resulted in an EC25=82 lbs/A for dry weight and an 

EC25=55 lbs/A for height. The NOAEC=37.5lb/A for tomato. 

Terrestrial Invertebrates

 The effect of DMDS on terrestrial invertebrates is represented by the Honey bee 

(Apis mellifera). This acceptable study resulted in a 48 hour LD50>100μg/bee (MRID 

474712-03). This classifies DMDS as practically nontoxic to bees. This value will be 

used in the assessment. 

Aquatic Plants 

 The effect of DMDS on vascular plants is represented by toxicity results for 

Lemna. An acceptable study resulted in a Frond EC50 =28mg/L. This value will be used 

in this assessment. 

 

 The most sensitive nonvascular plant species was Anabaena flos-aquae. An 

acceptable study (MRID 474712-05) resulted in a NOAEC <0.17mg/L, an EC05= 0.011 

mg/L to be used to assess listed species, and a 96h EC50=0.32mg/L (0.11-0.90 mg/L) for 

cell density. 

 

 
33 

III. Analysis 

III.A. Use Characterization 

Table III-1 is a summary of the new use patterns for DMDS. Two formulations 

of DMDS are proposed for registration: PaladinTM (98.8% a.i.) and Paladin TM EC 

(93.8% ai). Paladin TM is a liquid applied to the soil by shank injection. An illustration 

of broadcast shank injection shown in Figure III-1, and raised bed shank injection is 

shown in Figure III-2. Paladin EC TM is an emulsifiable liquid concentrate applied to the 

soil by chemigation through drip tapes. Both formulations are applied in the solution 

phase and then are expected to volatilize in the soil given the high vapor pressure and 

mechanism of action as a fumigant. Both formulations are also applied to the soil before 

plating then covered with a virtually impermeable film. For all crops and formulations, 

the maximum application rate is 455 lbs. a.i./A to be applied once per season. Both 

formulations may be used for all crops except for onions where only the PaladinTM 

formulation is applied. 

Table III-1. Summary of labeled uses and application methods for Paladin TM and 

Paladin EC TM DMDS formulations. 

Table III-1. Summary of labeled uses and application methods for Paladin TM and 

Paladin EC TM DMDS formulations. 

USE Formulation 

SINGLE 

APP. RATE 

(lbs. a.i./A) 

NUMBER 

OF APPS.

SEASONAL 

APP. RATE 

(lbs. a.i./A) 

INTERVAL 

BETWEEN 

APPS. (days) 

APPLICATION 

METHOD 

Fruiting 

Vegetables

• Tomatoes 

• Peppers 

• Eggplant 

Paladin TM 

and 

Paladin TM 

EC 

455 1 455 N/A • Drip 

Irrigation 

• Shank 

Injection to 

Raised Beds 

• Broadcast 

Shank 

Injection 

Curcurbit Crops

• Cucumbers 

• Squash 

• Melons 

Paladin TM 

and 

Paladin TM 

EC 

355 - 455 1 355 - 455 N/A • Drip 

Irrigation 

• Shank 

Injection to 

Raised Beds 

• Broadcast 

Shank 

Injection 
Table III-1. Summary of labeled uses and application methods for Paladin TM and 

Paladin EC TM DMDS formulations. 

SINGLE SEASONAL INTERVAL 

34 

USE Formulation 

APP. RATE NUMBER 

(lbs. a.i./A) OF APPS.

APP. RATE 

(lbs. a.i./A) 

BETWEEN APPLICATION 

APPS. (days) METHOD 

Small Fruit 

Crops

• Strawberries 

• Blueberries 

Field Grown 

Ornamentals

Forest Nursery 

Crops

Paladin TM 

and 

Paladin TM 

EC 

310 - 455 1 310 - 455 N/A • Drip 

Irrigation 

• Shank 

Injection to 

Raised Beds 

• Broadcast 

Shank 

Injection 

Onions Paladin TM 310 - 455 1 310 - 455 N/A • Drip 

Irrigation 

• Shank 

Injection to 

Raised Beds 

• Broadcast 

Shank 

Injection 

The label requires the fields or beds remained covered with the tarp, which is to 

remain undisturbed for a minimum of 12 days. For chemigation, all drip tapes must be 

buried under the tarp as well. An illustration of flat-fume or broadcast fumigation, which 

is most commonly carried out with shank injection, is shown in Figure III-1. An 

illustration of fumigation with raised beds which is shown for shank injection but is often 

also employed with drip irrigation is shown in Figure III-2. 

Figure III-1. Photograph of flat fume or broadcast fumigation. 
Figure III-2. Photograph of raised bed fumigation. 

.Many of the management practices that are typically required for other fumigants 

are required on the label. Soil temperatures of 55oF to 90 oF are required on the label. At 

the lower end of this temperature range, volatilization of DMDS will be limited, with 

increased volatilization rates at the upper end of the temperature range. Given that the 

vapor pressure is directly related to temperature, higher temperatures would imply that 

evaporation rates would increase. In addition, the label requires that soil moisture be 

maintained by at least 75 percent of field capacity from two inches below the soil surface 

to the depth of injection for shank applications, or at or near field capacity for drip 

irrigation. Such conditions help seal the fumigant under the ground as DMDS is very 

soluble (University of Wisconsin, 2010). 

Fumigants are typically used to treat the upper 6 -12 inches of the soil. As such, 

fumigants are typically shank injected to depths of approximately 25 cm. (Gilreath and 

Santos, 2004). Fumigation occurs as volatilized residues move upwards and horizontally 

in the soil column. Fumigants are also applied via drip irrigation chemigation at the 

surface or buried under the ground. However, water sealing methods such as required for 

DMDS on the label enable the chemical to be distributed to approximately a depth of 5 

inches below the ground (Overman, et al., 1987). 

 VIF tarps are required on the label to cover a treated field with DMDS for at least 

12 days after the application. A range of tarps including low density polyethylene 

(LDPE), metalized tarps, and VIF tarps were tested under field conditions with diemthyl 

disulfide. This is further discussed in Section III.B.1.b and Appendix G. LDPE is 

composed of single layers of material. However, VIF tarps are composed of multiple 

layers of material consisting of a dense material such as ethylene vinyl alcohol or nylon 

between two layers of polyethylene (Papiernik and Yates, 2001). Metalized films are 

often composed of multiple layers of material, including one layer of plastic material with 

a metal layer interwoven. It is thought that metal provides an added level of 

35 
impermeability due to its rigid properties (Mapleston, 1992). Since VIF tarps are 

required on the label, the one submitted study conducted with the VIF tarp is only 

considered for the inhalation assessment for mammals and birds. However, other field 

volatility studies with higher permeable tarp material conducted during warmer times of 

the year, at other multiple locatoions, and with different application methods than shank 

injection to raided beds justify the need for additional field volatility studies to be 

conducted with VIF tarps (see Appendix G). The loss due to volatilization through the 

tarp is not considered in the reduction of loadings for the aquatic exposure assessment. 

III.B. Exposure Characterization 

DMDS is a reduced organosulfur compound. Its physical chemical properties and 

environmental fate are summarized below in Tables III-2 and III-3. A description of 

detailed environmental fate and transport characteristics of DMDS can be found in 

Section III.B.1 below and in Appendix A. 

Table III-2: Selected physical and chemical properties of DMDS.

Parameter Value Reference

Chemical Structure 

PC Code 029088 

CAS number 624-92-0 

Common name Dimethyl Disulfide 

SMILES Notation S(SC)C 

Molecular formula C2H6S2

Molecular weight 94.2 g/mol MRID# 46903506 

IUPAC name methyldisulfanylmethane Chemindustry.com 

CAS name Dimethyl Disulfide Epi Suite 

Physical State Clear Liquid MRID#s 46903505 and 46903511 

Melting point/range -84.7oC MRID # 46903506 

Boiling point/range 109 - 110 oC MRID # 46903509 

Density 1.062 g/ml at at 20oC MRID #s 46903509 and 46903511 

Water solubility 2,702 mg/L at 20oC MRID# 46903510 

Vapor pressure 22.55 torr at 20oC MRID# 46903506 

Henry’s Law Constant 0.001 atm·m3

/mol MRID # 46903510 

Octanol/water partition 

coefficient (Log KOW) 

1.77 MRID # 46903509 

36 
37 

Table III-2: Selected physical and chemical properties of DMDS.

Parameter Value Reference

Octanol/air partition coefficient 

(Log KOA) 

3.076 EPI Suite 

Table III-3. Environmental Fate Properties of DMDS.

Parameter Value Reference/Comments

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

Photolysis t1/2 in 

water 

1.3 days, 

possible degradates: methanesulfonic acid (CH4S), 

methanesufinic acid (CH4O2S), or sulfuric acid (H2SO4) 

(total 54.2 percent) 

MRID# 42900201 

Supplemental 

Photolysis t1/2 on 

soil 

N/A Waived 

Degradation t1/2 in 

air 

34 minutes (atmospheric half life, reaction with OH 

radicals) 

42 minutes (atmospheric lifetime, reaction with OH 

radicals) 

EPI Suite 

Wine et al., 1981 

Soil metabolism, 

Aerobic t1/2

Total System France Clay Loam –3.74 days 

Total System Switzerland Clay – 2.86 days 

Florida Sand – No major transformation through 120 

 days 

California Sandy Loam – No major transformation 

 through 120 days 

Major degradates: 

Methanesulfonic acid – soil (<33.17 percent) 

Cabron dioxide (CO2) – air (<30.81 percent) 

MRID 47052819 

Half-lives back calculated 

assuming DMDS residues 

degrade contribute to the 

total formation of 

methanesulfonic acid 

residues 

Foreign soils taxonomically 

representative of US soils 

Aquatic metabolism 

Anaerobic t1/2

Unknown Outstanding Data Gap 

Aquatic metabolism 

Aerobic t1/2

Unknown Outstanding Data Gap 

Soil-Water Partition 

Coefficient (Kd) 

California, USA Sandy Loam – 0.54 mL/g (0.6 % OC) 

Speyer, Germany Sandy Loam – 0.68 mL/g (2.3 % 

 OC) 

Mechtildshausen, Germany 

Loam – 0.60 mL/g (1.28 % 

 OC) 

Mussig, France Clay Loam – 0.55 mL/g (2.98 % OC) 

Bretagne, France Silt Loan -0.86 mL/g (2.0 % OC) 

MRID 46917014 

MRID 46917015 

Foreign soils taxonomically 

representative of US soils 
38 

Table III-3. Environmental Fate Properties of DMDS.

Parameter Value Reference/Comments

Field Volatility Yuma, AZ Loamy Sand - 

Shank Injection to Raised Beds (LDPE Tarp) 

3,797 μg/m2

s cumulative flux; 81.43 percent mass loss 

at 780 lbs. a.i./A through 65 hours postapplication 

Nipomo, CA Sandy Loam - 

Drip Irrigation to Raised Beds (LDPE Tarp) 

1,295 μg/m2

s cumulative flux; 27.64 percent mass loss 

at 602 lbs. a.i./A through 72 hours postapplication 

Cantua Creek, CA Clay Loam

Broadcast Shank Injection (LDPE Tarp) 

2,451 μg/m2

s cumulative flux; 54.29 percent mass loss 

at 580 lbs. a.i./A through 72 hours postapplication 

Dover, FLLoamy Sand

Shank Injection to Raised Beds (Metalized Tarp) 

383.53 μg/m2

s cumulative flux; 8.1 percent mass loss at 

608 lbs. a.i./A through 48 hours postapplication 

Bradenton, FL Sand

Shank Injection to Raised Beds (LDPE Tarp) 

2,848 μg/m2

s cumulative flux; 57.82 percent mass loss 

at 633 lbs. a.i./A through 48 hours postapplication 

Tifton, GA (Field 1) Loamy Sand (VIF Tarp)

Pre Bedded Shank Injection 

613.69 μg/m2

s cumulative flux; 35.20 percent mass loss 

at 546.7 lbs. DMDS/A through 320 hours postapplication 

Tifton, GA (Field 2) Loamy Sand (LDPE Tarp)

Pre Bedded Shank Injection 

1,589 μg/m2

s cumulative flux; 69.74 percent mass loss 

at 538.8 lbs. DMDS/A through 320 hours postapplication 

Tifton, GA (Field 3) Sand (LDPE Tarp)

Pre Bedded Shank Injection 

842.97 μg/m2

s cumulative flux; 38.33 percent mass loss 

at 568.9 lbs. DMDS/A through 320 hours postapplication 

MRID 47052821 

MRID 47052822 

MRID 47052823 

MRID 47052824 

MRID 47820001 

Terrestrial Field 

Dissipation 

N/A Waived 

Aquatic Field 

Dissipation 

N/A Waived 
39 

Table III-3. Environmental Fate Properties of DMDS.

Parameter Value Reference/Comments

Accumulation in 

Fish, max. BCF 

N/A Waived 

III.B.1. Environmental Fate and Transport Characterization 

The loss of DMDS in terrestrial environments appears to be predominantly 

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

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

atm•m3

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

(MRID No. 46903510). The importance of other competing processes such as leaching, 

biodegradation, and adsorption to the soil particles will certainly depend on DMDS 

emission rate from the fumigated fields, which may be mitigated by a substantial amount 

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

proposed label requirements of VIF tarp covering. 

III.B.1.a Fate and Transport in Soil and Water

In soil, the aerobic metabolism of DMDS (MRID No. 4705282) in a closed system 

laboratory study suggests that biodegradation occurred via a diffusion – deposition 

equilibrium process as evidenced by the observation that the vast majority of DMDS was 

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

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

metabolite detected from the soil was methanesulfonic acid which accounted for a 

maximum of 33.17 percent of the material balance 14 days after application in France 

clay loam soil, and 32.86 percent of the material balance 21 days after application in 

Switzerland clay soil. Methanesulfonic acid forms through the breaking of the disulfide 

bond in DMDS. Only trace amounts of DMDS were extracted throughout each study. In 

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

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

percent of the material balance at 120 days after application in Switzerland clay soil (both 

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

was observed as most DMDS residues remained in the headspace over time. The 

diffusion-deposition process apparent from the France clay loam soil and Switzerland 

clay soil is possible in the environment under field conditions given the vapor pressure of 

22.55 torr and temperature of 20o

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

addition, this process has been documented with numerous reduced sulfur compounds, 

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

observation and the observation that trace amounts of DMDS were 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 III-4 for France clay loam and Switzerland clay soil. The half lives of DMDS in 
40 

soil ranged from between 2.86 days in France clay loam to 3.74 days in Switzerland clay 

soil. 

Table III-4. Formation of methanesulfonic acid and decline of DMDS in France clay 

loam aerobic soil metabolism laboratory study. 

Time Switzerland clay France clay loam 

(Days) Methanesulfonic 

acid 

Estimate 

DMDS 

Methanesulfonic 

acid 

Estimate 

DMDS 

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 

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

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

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

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

volatilization and photolysis are the primary environmental routes of dissipation from 

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

biodegradation of DMDS in the aquatic environment is unknown. The calculated halflife of 1.17 days in 0.01 M phosphate (pH 7) when irradiated with a xenon light source 

for a period of 24 hours. Two major degradates were detected and may have included 

either methanesulfonic acid, methanesulfinic acid, or sulfuric acid (MRID 47052818) 

were detected at a maximum total of 54.2 percent of the material balance, although a test 

to definitively identify the degradates was not performed. The registrant proposed that 

formaldehyde may form intermediate to the degradates identified. However, 

formaldehyde was not detected with the limited sampling that was conducted during the 

aquatic photolysis experiment. 

III.B.1.a.1 Potential Impacts of Soil 

Acidification from DMDS 

Soil acidification from methanesulfonic acid is especially possible on soils with 

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

acid is a major degradation product of DMDS degradation in soil, one mole of DMDS 

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

) from dissociation of 

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

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

an application of 455 lbs of DMDS would require a lime application rate of 968 lbs 

CaCO3/A for complete neutralization. 
41 

 III.B.1.b Fate and Transport in Atmosphere 

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

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

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

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

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

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

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

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

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

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

occurred during the afternoon hours. The flux temporal profiles for the lower barrier 

films are shown in Appendix G since these are not the basis of the risk assessment given 

the label restriction to VIF tarps. 

In addition, there were two studies that were conducted with higher barrier films. 

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

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

applied to via a pre-bedded shank application in one field of Tifton, GA with a VIF tarp. 

Here, DMDS residues in air accounted for 35.20 percent of the amount applied over a 

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

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

remained in the soil in response to the high performance of the VIF tarp. Generally 

speaking, absolute peaks in flux also occurred in the afternoon hours after the application 

with flux gradually decreasing afterwards. However, the amplitude of absolute peaks in 

the field volatility were generally were not as large as the studies conducted with the low 

density polyethylene tarps. Table III-5 shows the flux profiles and percent of applied 

diffused from the soil in the Tifton field volatility site with VIF tarps. The flux profiles 

for 7 other studies where LDPE and metalized films are used are shown in Appendix G. 

Table III-5. Field flux from Tifton, GA Field 1 DMDS Shank Injection to Raised 

Beds with High Density Polyethene Tarp Study (application rate = 546.7 lbs. a.i./A). 

Sample Time 

DMDS Volatile 

Flux during 

Period 

(μg/m2s) 

DMDS Percent of 

Applied during 

Period 

(%) 

Time Duration 

(hours) 

Day 0, Hours 0 – 5 3.35 0.10 5

Day 0, Hours 5 – 11 3.16 0.11 6

Day 0, Hours 11 – 17 16.21 0.57 6

Day 0, Hours 17 – 23 21.47 0.76 6

Day 0, Hour 23 – 

Day 1, Hour 5 14.33 0.51 6

Day 1, Hours 5 – 11 22.06 0.78 6

Day 1, Hours 11 – 17 42.84 1.51 6
42 

Table III-5. Field flux from Tifton, GA Field 1 DMDS Shank Injection to Raised 

Beds with High Density Polyethene Tarp Study (application rate = 546.7 lbs. a.i./A). 

Sample Time 

DMDS Volatile 

Flux during 

Period 

(μg/m2s) 

DMDS Percent of 

Applied during 

Period 

(%) 

Time Duration 

(hours) 

Day 1, Hours 17 – 23 53.37 1.88 6

Day 1, Hour 23 – 

Day 2, Hour8 8.93 0.47 9

Day 2, Hours 8 – 20 54.37 3.83 12

Day 2, Hour 20 – 

Day 3, Hour 8 19.24 1.36 12

Day 3, Hours 8 – 20 38.66 2.73 12

Day 3, Hour 20 – 

Day 4, Hour 8 29.13 2.05 12

Day 4, Hours 8 – 20 21.73 1.53 12

Day 4, Hour 20 – 

Day 5, Hour 8 19.84 1.40 12

Day 5, Hours 8 – 20 13.79 0.97 12

Day 5, Hour 20 – 

Day 6, Hour 8 8.01 0.56 12

Day 6, Hours 8 – 20 12.85 0.91 12

Day 6, Hour 20 – 

Day 7, Hour 8 10.20 0.72 12

Day 7, Hours 8 – 20 9.52 0.67 12

Day 7, Hour 20 – 

Day 8, Hour 8 5.32 0.37 12

Day 8, Hours 8 – 20 18.54 1.31 12

Day 8, Hour 20 – 

Day 9, Hour 8 9.17 0.65 12

Day 9, Hours 8 – 20 7.30 0.51 12

Day 9, Hour 20 – 

Day 10, Hour 8 4.49 0.32 12

Day 10, Hours 8 - 20 

Day 10, Hour 20 – 

Day 11, Hour 8 

16.47 1.16 12

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 
Table III-5. Field flux from Tifton, GA Field 1 DMDS Shank Injection to Raised 

Beds with High Density Polyethene Tarp Study (application rate = 546.7 lbs. a.i./A). 

43 

Sample Time 

DMDS Volatile 

Flux during 

Period 

(μg/m2s) 

DMDS Percent of 

Applied during 

Period Time Duration 

(%) (hours) 

Application Start Time Afternoon of February 7 

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

 % DMDS Mass Loss = ∑ (DMDS Flux 

=

n

i 1

i x Sample Period i)

 DMDS Field Study Application Rate. 

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

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

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

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

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

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

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

19 cm2

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

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

An atmospheric degradation mechanism including the interaction between 

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

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

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

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

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

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

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

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

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

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

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

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

1990[2]). 
Figure III-1. The atmospheric degradation pathways of DMDS. 

 

III.B.1.b.1 Ozone Depletion Potential 

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

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

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

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

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

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

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

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

components within DMDS which would contribute to the destruction of stratospheric 

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

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

stratospheric ozone depletion. 

 III.B.1.b.2 Global Warming Potential

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

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

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

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

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

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

personal communication, 2009). 

44 
III.B.1.b.3 Acid Rain

 Sulfates in the atmosphere, forming from anthroprogenically emitted sulfur 

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

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

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

sulfuric acid is: 

 SO3 + H2O H2SO4

 

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

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

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

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

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

IV of the Clean Air Act. 

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

concern given low emissions from high barrier tarps as specified on the label. However, 

aggregate emissions of DMDS throughout an area with high use may contribute to acid 

rain events. To address the potential for acid rain, the monitoring data of rainfall which 

occurs over high use areas of DMDS may be requested in the future (see Section I.E.1). 

III.B.1.b.4 Photochemical Ozone Creation 

Potential 

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

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

nitrogen oxides to produce ground-level ozone. Ground-level ozone is recognized by the 

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

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

III-1 shows that although ozone is not a direct product through any step of its 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. 

III.B.2 Measures of Aquatic Exposure 

III.B.2.a. Aquatic Exposure Modeling 

PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are fate and 

tranpsport simulation models coupled together with the input shell pe5.pl (Aug 2007) to 

generate daily exposures and 1-in-10 year EECs of DMDS that may occur in surface 

water and benthic water pore concentrations in water bodies adjacent to application sites 

receiving DMDS through runoff . PRZM simulates pesticide application, movement and 

45 
46 

transformation on an agricultural field and the resultant pesticide loadings to a receiving 

water body (e.g., the Georgia farm pond scenario) via runoff and erosion. In the case of a 

volatile pesticide, its vapor pressure and enthalpy of vaporization determines the phase of 

the chemical (e.g., solution versus vapor phase). If the chemical is in the gas phase, 

runoff flux is determined from the chemical’s Henry’s Law Constant for partitioning of 

the gas to the water. EXAMS simulates the fate of the pesticide and resulting 

concentrations in surface water and benthic pore water concentrations considering the 

mass transfer between the sediment and water compartments. The standard scenario used 

for ecological pesticide assessments assumes application to a 10-hectare agricultural field 

that drains into an adjacent 1-hectare water body that is 2 meters deep (20,000 m3

volume) with no outlet. The measure of exposure for aquatic species is the 1-in-10 year 

return peak or rolling mean concentration. The 1-in-10 year peak is used for estimating 

acute exposures of direct effects to aquatic organisms. The 1-in-10-year 21-day mean is 

used for assessing aquatic invertebrate chronic exposure. The 1-in-10-year 60-day mean 

is used for assessing chronic exposure to fish and aquatic-phase amphibians. 

Since the PaladinTM and Paladin ECTM product labels require VIF tarps, it is not 

expected that DMDS residues will be available to runoff during the 12 day period which 

is required for the tarp to cover the field. Therefore, aquatic exposure modeling using 

PRZM/EXAMS only addresses the scenario after the tarp is removed. Degradation of 

DMDS residues can occur under the tarp during the 12 day period. Therefore, the 

maximum application rate of 455 lbs. a.i./A is adjusted for biodegradation which may 

occur under the tarp for the 12 day period. This adjustment is made due to the reduction 

of loading as determined assuming a first-order decay of DMDS as determined from the 

first-order rate reaction equation shown in Section II.F.2.a. This equation indicates that 

16.88 percent of DMDS residues remain in the soil after 12 days according to the rate 

constant based on the 90th percentile aerobic soil metabolism half life as shown in Table 

III-5 below. 

Also, since DMDS is a fumigant, an additional refinement accounting for 

volatilization was considered. However, the validation of this component of the PRZM 

model has not been completed. Despite this, given the volatile nature and use of DMDS 

as a soil fumigant, the volatility algorithm was used to determine EECs in the water 

column. Additional chemical specific physical parameters such as vapor phase diffusion 

coefficient (DAIR) and enthalpy of vaporization (ENPY) were activated during the 

PRZM/EXAMS simulation accounting for volatilization. The volatilization routine used 

assumes that temperature in the soil does not change over time. Therefore, temperaturedependent variables such as Henry’s Law Constant and soil degradation rates remain 

constant. However, risk quotients for aquatic organisms will be based on EECs predicted 

using the volatility algorithm. This is consistent with historical risk assessments with 

other fumigants. 

For shank injection, chemical application method (CAM) of 8 was used in 

mimicking application of DMDS to simulate injection at a 25 cm through vapor 

diffusion, reflecting typical agricultural practices for fumigants (Gilreath and Santos, 

2004). For chemigation, a CAM of 4 and an injection depth of 5 inches (12.7 cm) was 
47 

selected reflecting the intention of maintaining a uniform distribution of the fumigant 

under the tarp in this layer (Overman, et al., 1987). Although drip tapes can be placed at 

the surface, water sealing methods, required tarping, and diffusion under the tarp 

contribute towards this regime in the transport of the chemical under the soil in this 

manner. 

Six field scenarios - were used in estimating EECs using highest application rate 

of 455 lbs. a.i./Acre. All crops on the label were represented and included regions where 

fumigation typically occurs frequently. The scenarios included Florida tomato, Florida 

pepper, Florida cucumber, Florida Strawberry, California Onion, Georgia Onion, 

Califonia nursery, New Jersey nursery, and Oregon Christmas tree. 

Table III-6 summarizes the environmental fate related input parameters for into 

PRZM-EXAMS. It is important to note that the risk determination will be based on the 

parent DMDS only and that major degradates (including methanesulfonic acid, 

methanesulfinic acid, and sulfuric acid) are neglected since these constituents are not of 

toxicological conern as discussed in Section II.B.1. Table III-7 summarizes the crop 

management input into PRZM-EXAMS. 

Table III-6. PRZM/EXAMS DMDS Environmental Fate Input Parameter Values in All 

Scenarios.

PRZM/EXAMS Input 

Parameter 

Input Value 

and Unit 

Comment Source 

Molecular Weight 94.2 g/mol Product 

Chemistry - 

MRID 46903506 

Hydrolysis (t1/2) 0 Stable MRID 46903532 

Aerobic soil metabolism 

(t1/2) 

4.66 days 90th percentile value 

between the French 

clay loam and 

Switzerland clay soil 

studies (2.86 and 

3.74 days 

respectively) based 

on total DMDS 

degradation in the 

system 

EFED Input 

Parameter 

Guidance 

MRID 47052819 

Aerobic aquatic metabolism 

(t1/2) 

9.32 days No data available 

and stable to 

hydrolysis. 

Computed from 

EFED Input 

Parameter 

Guidance 

MRID 47052819 
48 

Table III-6. PRZM/EXAMS DMDS Environmental Fate Input Parameter Values in All 

Scenarios.

PRZM/EXAMS Input 

Parameter 

Input Value 

and Unit 

Comment Source 

twice the parent 

aerobic soil 

metabolism half-life 

of 4.66 days. 

Anaerobic aquatic 

metabolism (t1/2) 

0 Stable. Conservative 

assumption 

considering the 

anaerobic soil 

metabolism study. 

EFED Input 

Parameter 

Guidance 

MRID 47052820 

Vapor Pressure at 20 oC 22.55 torr Product 

Chemistry - 

MRID 46903506 

Solubility in Water at 20oC 27,020 mg/L Product Chemistry x 

10 

EFED Input 

Parameter 

Guidance 

MRID 46903510 

Soil-Water Partition 

Coefficient (Kd) 

0.641 ml/g Mean of Kd in 5 

batch equilibrium 

studies 4 

Soil-water partition 

coefficient not found 

to correlate well with 

organic carbon 

content in batch 

equilibrium studies 

MRID 46917014 

MRID 46917015 

Henry’s Law Constant 0.001 

atm·m3

/mol 

Product Chemistry Product 

Chemistry - 

MRID 46903510 

Aqueous Photolysis (t1/2) 1.17 days 

(parent) 

Dark controlled 

aqueous photolysis 

half-life for parent. 

EFED Input 

Parameter 

Guidance 

MRID 47052818 

Diffusion in Air (cm2/day)1 8,006.83 Extrapolated from 

Graham’s Law based 

on methanol 

diffusion in air value 

EPA On-line 

Tools for Site 

Assessment 

Calculation 3
49 

Table III-6. PRZM/EXAMS DMDS Environmental Fate Input Parameter Values in All 

Scenarios.

PRZM/EXAMS Input 

Parameter 

Input Value 

and Unit 

Comment Source 

of 0.159 cm2/sec 

(13,737.6 cm2

/day)2 

Enthalpy (kcal/mol)1 9.19 “DMDS 

Chemical and 

Physical 

Properties”4

1 PRZM-EXAMS ran with and without volatilization for characterization purposes. 

2 Diffusion in air coefficient for DMDS is calculated using Graham’s Law extrapolation 

and methanol diffusion properties [DMDS Dair = 0.159 cm2

/sec x (32 g/mol ÷ 94.20 

g/mol)1/2]. 

3 Available on-line: < http://www.epa.gov/athens/learn2model/part-two/onsite/ 

estdiffusion.htm>. 

4 Available on-line: <http://www.arkema-inc.com/literature/pdf/791.pdf>.

Table III-7. PRZM/EXAMS Crop Management Input Parameters

PRZM/EXAMS Input 

Parameter 

Input Value and Unit Comment 

Application Rate and Interval 76.82 lb a.i./A (86.11 kg 

a.i./ha) at one application 

per season 

PaladinTM and 

PaladinTM EC label 

Crop Scenarios and 

(Application Date) 

Fruiting Vegetables 

(Tomotoes, Peppers, and 

Eggplant)

CA Tomato (Feb. 15) 

FL Tomato (Jan. 1) 

FL Peppers (Aug 1) 

Curcurbit Crops 

(Cucumbers, Squash, and 

Melons)

FL Cucumber (Sept. 15) 

Small Fruit Crops

(Strawberries and 

Blueberries)

FL Strawberries (Sept. 1) 

Onions

CA Onion (Nov. 15) 

GA Onion (Aug. 15) 

Field Grown 

Ornamentals

CA Nursery (Feb. 1) 

Assumed 25 days 

prior to crop 

emergence as 

specified in PRZM 

crop scenarios 
50 

Table III-7. PRZM/EXAMS Crop Management Input Parameters

PRZM/EXAMS Input 

Parameter 

Input Value and Unit Comment 

MI Nursery (Dec 1) 

Forest Nursery Crops

OR Xmas Tree (Dec. 1) 

Chemical Application Method and 

(Incorporation Depth) 

CAM = 4 soil applied, 

uniform over incorporation 

depth (12.7cm) 

CAM = 8 soil applied, 

entirely at incorporation 

depth (25.0 cm) 

Drip Irrigation 

Shank Injection 

Application Efficiency 1.0 

1.0 

Drip Irrigation 

Shank Injection 

Spray Drift Fraction 0 

0 

Drip Irrigation 

Shank Injection 

Several labeled uses are grouped together to estimate the effects from the use of 

DMDS. Eggplant is modeled using the tomato scenario. Squash and melons are modeled 

with the cucumber scenario. The labeled uses for blueberries are modeled using the 

strawberry scenario. In addition, application dates were selected based in part by the 

minimum plantback interval on the label of 35 days. Therefore, the application dates 

were determined to be approximately 25 days prior the crop emergence date as specified 

in the PRZM/EXAMS crop scenarios since fumigation occurs 35 days before planting, 

the modeled application with the tarp removed will not address the12 days after the 

application which elapses while the tarp is on the field , and the accounting of a 3 day 

time allowance for seed germination. 

Table III-8 presents the PRZM-EXAMS estimated concentrations in surface 

water. This modeling addresses fate and transport modeling of available DMDS residues 

after the tarp is removed. The DMDS available for transport after the tarp is removed are 

subject to biotic and abiotic degradation from the soil and water as well as dissipation 

processes such as runoff and volatilization from the soil. Sample output files are 

provided in the Appendix C. 
51 

Table III-8. Estimated 1-in-10 yr. exposure concentration in surface water for DMDS. 

Peak Conc. 21-day Conc. 60-day Conc. 

Crop Scenarios and Management (μg/L) (μg/L) (μg/L) 

Tomatoes and Eggplant

California Tomato Drip Irrigation 30.293 7.473 2.680 

California Tomato Shank Injection 4.77x 10-8 1.26 x 10-8 5.20 x 10-9

Florida Tomato Drip Irrigation 18.301 3.386 1.189 

Florida Tomato Shank Injection 5.572 1.121 0.401

Peppers

Florida Peppers Drip Irrigation 46.887 7.860 2.761 

Florida Peppers Shank Injection 4.434 0.878 0.315

Cucumbers, Melons, and Squash

Florida Cucumber Drip Irrigation 150.899 24.900 8.742 

Florida Cucumber Shank Injection 9.984 1.810 0.637

Strawberries and Blueberries

Florida Strawberry Drip Irrigation 203.228 45.948 16.151 

Florida Strawberry Shank Injection 3.559 0.762 0.274

Onions

California Onion Drip Irrigation 2.550 0.850 0.318 

California Onion Shank Injection 0.239 0.074 0.027

Georgia Onion Drip Irrigation 129.477 24.390 8.594 

Georgia Onion Shank Injection 3.248 0.674 0.252

Ornamentals

California Nursery Drip Irrigation 7.074 2.213 0.796 

California Nursery Shank Injection 0.375 0.133 0.048

Michigan Nursery Drip Irrigation 32.240 28.065 15.092

Michigan Nursery Shank Injection 0.227 0.192 0.101

Forestry Nursery Crops

Oregon Xmas Tree Drip Irrigation 19.674 6.733 2.455 

Oregon Xmas Tree Shank Injection 0.206 0.075 0.027

1 Maximum values shown in bold. 

III.B.2.b. Ground Water Exposure 

 Since DMDS is highly soluble and mobile, leaching and potential ground water 

contamination is possible. Cases of ground water contamination may especially occur in 

areas over and around aquifers where water tables may be shallow and recharging of 

ground water may occur. Therefore, DMDS may reach ground water irregardless of tarps 

cover. 

The Tier I model Screening Concentration in Ground Water (SCI-GROW v2.3, 

Jul. 29, 2003; USEPA, 2002b) is used to calculate acute and chronic DMDS EECs in 

ground water. Ground water concentrations generated by SCI-GROW are based on the 

largest 90-day average estimated during the sampling period. Since there is relatively 
52 

little temporal variation in ground water concentrations compared to surface water, the 

model predicted value can be considered to represent both the acute and chronic values. 

Since major degradates were not found to be of toxicological conern as discussed in 

Section II.B.1, only DMDS EECs are evaluated. 

 Input parameters for the SCI-GROW model appear in Table III-9. These inputs 

were determined in accordance with current divisional guidance (USEPA, 2002b). The 

mean of two half-lives (based on France clay loam soil and Switzerland clay soil) was 

used as input. In addition, the median of five reported soil –water partition coefficients 

were selected. This was used in lieu of the organic carbon soil-water partition coefficient 

since individual soil-water partition coefficients were not found to be well correlated with 

the organic carbon content of the particular soils tested. All inputs in the model were 

determined from individual samples of physical chemical and environmental fate 

parameter values shown in Tables III-2 and III-3. 

Table III-9. SCI-GROW Input Parameters for DMDS (Source data are in Tables III-2 

and III-3)

Input Parameter Value Comments Source

Application Rate 

(lbs a.i./A) 455 lbs a.i./A Maximum proposed single application 

rate for all uses. 

Proposed 

PaladinTM and 

PaladinTM EC 

labels 

Applications per Year 1 

Maximum proposed number of 

applications per year at the maximum 

proposed single application rate. 

Proposed 

PaladinTM and 

PaladinTM EC 

labels 

Soil-Water Partition 

Coefficient (Kd) (L/kg) 0.60 

Represents the median of five reported 

Kd values 

Soil-water partition coefficient not 

found to correlate well with organic 

carbon content in batch equilibrium 

studies 

MRID 46917014 

MRID 46917015

Aerobic Soil Metabolism 

Half-life (days) 3.3 Represents the mean half life of France 

clay loam and Switzerland clay soils 

MRID 47052819 

 This model simulation represents impacts to ground water from a single 

application at the maximum application rate of 455 lbs. DMDS/A as specified on the 

PaladinTM and PaladinTM EC labels. However, despite this, Table III-10 shows that 

DMDS predicted ground water EECs are very low. This is likely due to the rapid 

biodegradation of DMDS residues in the soil. Volatilization is not accounted for in this 

model. However, loss due to volatilization is expected to be minimized in the presence 

of tarps. 
53 

Table III-10. Estimated Environmental Concentrations of DMDS in Ground Water

Use 

(modeled annual rate) 

Acute (ppb) Chronic (ppb)

All uses shown in Table III-1 

(455 lbs. a.i./A, single application) 1.99 1.99 
 

54 

III.B.2.c. Aquatic Exposure Monitoring (Field 

Data) 

No products containing DMDS, for use outdoors, are available in the market at 

this time; accordingly, no monitoring studies are publicly available concerning aquatic 

exposure (both surface and ground waters). However, environmental concentrations have 

been qualitatively detected in ground water and drinking water sources at various 

locations across the country (Fresenius, 1994; USEPA, 1975; Bertsch, et al., 1975; 

Wakeham, 1983). In general, the study sites were nearby discharge sources and estuaries 

where decaying biomass may result in the formation of DMDS. Furthermore, DMDS 

was detected at levels of 30 - 900 ng/kg in Vineyard Sound, MA between December 1978 

and March 1979 (Mantoura et al., 1982), and detected at levels at concentrations < 0.1 

ppm in the River Lee in England (Waggot, 1981). Although detected concentrations are 

low, these detections suggest that DMDS can exist in surface and ground water for some 

period of time. 

III.B.3 Measures of Terrestrial Exposure 

Exposure of terrestrial organisms to DMDS air residues is estimated using the 

Probablistic Exposure Model for Fumigants (PERFUM - v. 2.5.1, 7/2/2008) and 

TerrPlant (v. 1.2.2; 12/26/06). The PERFUM model will be used to assess inhalation 

exposure to terrestrial animals. This model is used because of the volatility of DMDS, 

which is higher than most foliar-applied pesticides. The PERFUM model was initially 

developed to address the issue of worker and bystander exposures to fumigants following 

applications to bare fields, and was evaluated during the FIFRA Science Advisory Panel 

in August 2004. However, EFED has used PERFUM model historically in refined air 

quality risk assessments for the fumigants Chloropicrin and Metam Sodium including for 

the California Red Legged Frog Endangered Species Assessment3

. 

The typical terrestrial exposure assessment model (TREX) for dietary exposure 

was not used because DMDS is applied during pre-planting, is highly soluble and mobile, 

and is not expected to result in systematic accumulation in plants and insects given its 

high solubility and low octanol-water partition coefficient. Therefore, subsequent dietary 

exposure to terrestrial vertebrates is considered negligible. In addition, the typical 

terrestrial exposure model (TERRPLANT) was not used since the dominant route of 

exposure to plants is expected to be via air exposure to DMDS residues. 

Risk to plants, mammals, and birds are based on exposure to the volatile flux of 

DMDS from the field. There is no plant model available to evaluate the effect of 

exposure to air for terrestrial plants. However, a dispersion model such as PERFUM can 

be used assuming the appropriate toxicological endpoint is given in a unit mass per 

3

 EPA OPP California Red Legged Frog website is accessed on-line at 

http://www.epa.gov/espp/litstatus/effects/redleggedfrog/. 
volume. In this case, the endpoint is given in terms of an application rate (see Table III12). 

 The PERFUM model is a processor of the ISCST3 model (Reiss, 2008), which 

has been developed from EPA’s Office of Air Quality Planning and Standards4

. 

PERFUM can calculate upper-bound gaseous residue EECs in air at the edge or at a 

downwind distance of a treated field. The ISCST3 model which PERFUM is based on 

uses a Gaussian plume model that incorporates source related flux and 5 years of 

meteorological data such as wind speed, wind direction, and insolation. Figure III-1

illustrates the plume structure along with the Gaussian nature of the contaminant 

concentrations which is determined by mixing within the plume. It is assumed that the 

pollutant does not undergo any chemical reactions, and that no other removal processes, 

such as wet or dry deposition, act on the plume during its transport from the source. The 

Gaussian model equations and the interactions of the source-related and meteorological 

factors are described in Volume II of the ISC User's Guide (USEPA, 1995), and in the 

Workbook of Atmospheric Dispersion Estimates (Turner, 1970). PERFUM estimates a 

concentration about either side of the plume centerline directly downwind from the 

source. The size of the plume and plume rise is determined by the degree of turbulence 

in the atmosphere, which is parameterized according to stability class (A = unstable; B= 

unstable; C= unstable; D= neutral; E= stable; F = stable) where the unstable regime refers 

to turbulent conditions and the stable regime refers to stagnate conditions. The stability 

classes are determined by incorporating wind speed and insolation (e.g., cloud cover) 

data using empirical methods (Turner, 1970). The 10-meter wind speed governing the 

transport of the plume is adjusted to the ground release height according to the Log Law 

(USEPA, 1995). 

Figure III-11. Plume structure in the PERFUM model. 

A, range of area source sizes may be specified in PERFUM. In this case, a 

variety of area source sizes from 1 acre to 80 acres were modeled considering the 

possibilities that can exist with fumigant use. The flux profile, or DMDS emissions per 

unit area, from the field volatility studies are input into PERFUM and matched with the 

meteorological data consistent with the time of day the flux data were measured. This is 

done since flux can also be dependent on the time of day as well. EEC distributions are 

55 

 

4

 The ISCST3 model documentation can be accessed on-line at: http://www.epa.gov/scram001/

dispersion_alt.htm 
calculated at an array of points (at 1.5 meters above ground level) originating from 

around the edge of the field to a downwind distance 1,440 meters from the edge of the 

field. An illustration of the spatial nature of the model output is shown in Figure III-2. 

The EEC distributions are divided by each ring of points, known as receptors shown in 

Figure III-2 for each time of day (based on the averaging period) about the treated field. 

Figure III-2. Receptors (dotted points) where PERFUM air concentrations are 

predicted around a treated field (area shaded in black and green). 

As stated above, PERFUM requires parameters for the treated field such as the 

pesticide flux rate, the dimensions of the area source, and the height of the release 

specified. However, PERFUM has the added ability to consider averaging periods. To 

account for the acute time period of concern for mammals and birds and in consideration 

to the highly amplified spikes in DMDS volatile flux possible from the soil after 

application, a one-hour averaging period for exposure is selected for this modeling. In 

addition, DMDS flux profiles from the Tifton, GA field volatility study, the only study 

where a VIF tarp was used, was modeled in PERFUM. This flux profiles from this study 

was selected since it best represents the management practices prescribed on the label 

which requires a Virtually Impermeable (VIF) tarp. This daily flux profile is ran 

repeatedly through 5 years of meteorological data, which in this assessment, consisted of 

Yakima (WA), Bakersfield (CA), Bradenton (FL), Ventura (CA), Flint (MI), and 

Tallahassee (FL) locations. The start time of the daily flux profile is consistent with the 

start time of the application for each field volatility study. The input parameters for the 

PERFUM model is shown in Table III-12 and the flux profile values and times specified 

in the model are shown in Table III-13 for the Tifton, GA study. This flux profile is 

repeated continuously through the 5 year series of meteorological data. 

Table III-12. Input Parameters Utilized in PERFUM.

Input Parameter Tifton, GA Study Basis 

Source Type Area 

Averaging Period 1-hour 

Application Start Time 5 pm 

Emission Rate (μg/m2s) See Table III-13 

Source Height (m) 0 

Length of Large Sides of 

Source (m) 

63.6, 142.2, 201.2, 284.5, 

402.3, 492.8, and 569 

56 
57 

Table III-12. Input Parameters Utilized in PERFUM.

Input Parameter Tifton, GA Study Basis 

Length of Smaller Sides of 

Source (m) 

63.6, 142.2, 201.2, 284.5, 

402.3, 492.8, and 569 

Downwind Distance of 

EEC Receptors Around 

Field (m) 

5, 7, 10, 15, 20, 30, 50, 70, 

80, 90, 100, 120, 150, 180, 

210, 240, 270, 300, 360, 

420, 480, 540, 600, 720, 

840, 960, 1080, 1200, 1320, 

1400 1

Receptor Height (m) 1.5 1

Meteorological Data 

Locations 

Yakima (WA), Bakersfield 

(CA), Bradenton (FL), 

Ventura (CA), Flint (MI), 

and Tallahassee (FL) 

1. Values cannot be controlled in present version of PERFUM.

Table III-13. Temporal flux profiles 

input in PERFUM. 

Tifton, GA Study Basis1

Time Ranges 

Flux Each Hour In 

Time Range 

(μg/m2s) 

Day 0 5 pm – 8 pm 2.7

Day 0 8 pm – 2 am 13.5

Day 0 2 am – 8 am 17.9

Day 0 8 am – 9 am 11.9 

Day 0 9 am – 5 pm 2.7

Day 1 5 pm – 8 pm 18.4

Day 1 8 pm – 2 am 35.6

Day 1 2 am – 8 am 44.4 

Day 1 8 am – 9 am 7.4

Day 1 9 am – 2 pm 11.9

Day 1 2 pm – 5 pm 18.4

Day 2 5 pm – 5 am 45.3

Day 2 5 am – 9 am 16

Day 2 9 am – 5 pm 7.4

1. Flux profile extracted based on the third treatment to Field 1. 

2. Flux values scaled from values shown in Table III-4 to 455 lbs. a.i./acre. 

Consistent with EFED risk assessments conducted for fumigants, risk quotients 

were developed based on the 90th percentile EECs based on the ring closest to the edge of 

the field at the time of day with the highest predicted EECs. This ring most likely 

represents the maximum concentration that is possible anywhere in the field since air 

residue mass accumulates at this point from many plume elements which are emitted on 
58 

the treated field. 

The upper-bound PERFUM EECs is 720 μg/m3

. This modeling addresses the 

flux measured from the field at Tifton, GA while the VIF tarp was in place. The upperbound EEC was identified at a distance of 5 meters from the edge of an 80-acre field and 

occurred between 5 am – 6 am consistent with the Bradenton, FL meteorological data. 

Sample model outputs are shown in Appendix D.

III.C. Ecological Effects Characterization 

 Effects characterization describes the potential effects a pesticide can produce in 

an aquatic or terrestrial organism. This characterization is typically based on studies that 

describe acute and chronic effects toxicity information for various aquatic and terrestrial 

animals and plants. Appendix H summarizes the results of the toxicity studies used to 

characterize effects for this risk assessment. Toxicity testing reported in this section does 

not represent all species of birds, mammals, or aquatic organisms. Only a few surrogate 

species for both freshwater fish and birds are used to represent all freshwater fish (2000+) 

and bird (680+) species in the United States. For mammals, acute studies are usually 

limited to Norway rat or the house mouse. Estuarine/marine testing is usually limited to a 

crustacean, a mollusk, and a fish. Also, neither reptiles nor amphibians are tested. The 

risk assessment assumes that avian and reptilian and terrestrial-phase amphibian toxicities 

are similar. The same assumption is used for fish and aquatic-phase amphibians. 

 In general, categories of acute toxicity ranging from “practically nontoxic” to 

“very highly toxic” have been established for aquatic organisms (based on LC50 values), 

mammals (based on LD50 values), avian species (based on LD50 and LC50 values), and 

non-target insects (based on LD50 values for honey bees) (EPA, 2001). These categories 

are presented in Appendix F. 

III.C.1. Aquatic Effects Characterization 

The most sensitive acute toxicity reference values associated with DMDS 

exposure to aquatic organisms are summarized in Table III-14. Summaries of other 

submitted studies are presented in Appendix H.

Table III-14. DMDS Toxicity Reference Values (TRVs) (ppb of Active Ingredient) for 

Aquatic Organisms

Exposure 

Scenario Species 

Exposure 

Duration

Toxicity Reference Value 

(μg/L a.i.) Reference

Freshwater Fish

Acute Rainbow trout 96 hours LC50 = 960 MRID 470528-14 

Acceptable 
59 

Table III-14. DMDS Toxicity Reference Values (TRVs) (ppb of Active Ingredient) for 

Aquatic Organisms

Exposure 

Scenario Species 

Exposure 

Duration

Toxicity Reference Value 

(μg/L a.i.) Reference

Acute Zebrafish 96 hours LC50=7500 Acceptable 

Chronic NA NA NA NA 

Freshwater Invertebrates

Acute Daphnia magna 48 hours EC50 =1610 μg/L (1310-1990 

μg/L) 

MRID 470528-16 

Acceptable 

Chronic NA NA NA NA 

Estuarine/Marine Fish

Acute Sheepshead 96 h LC50=5600μg/L (4000-6900 

μg/L 

MRID473075-04 

Chronic NA NA NA NA 

Estuarine/Marine Invertebrates

 Acute Mysid NA LC50=4900 μg/l (3900-

96100μg/L) 

MRID473075-05 

Chronic NA NA NA NA 

Aquatic Plants

Vascular Lemna gibba NA EC50=28000 (22000-

36000μg/L) 

MRID 474712-04 

Acceptable

Nonvascular Anabaena flosaquae 

Cell Density EC50=320 μg/L 

(110-900 μg/L) 

MRID 474712-05 

Acceptable 

NA = Data appropriate for quantitative use are not available.

 Acute Toxicity to Freshwater Fish 
60 

Fish are represented by a warm-water species and a cold-water species with the 

most sensitive endpoint utilized in the assessment. The acute toxicity of DMDS to 

freshwater fish was evaluated in a cold-water species, rainbow trout (Oncorhynchus 

mykiss) and a warm-water species, zebra fish (Danio rerio), with the lowest LC50s of 0.96 

mg/L and 7.5 mg/L, respectively. Therefore, the rainbow trout value is used as the 

toxicity value for assessing acute risks to fish from exposure to DMS. 

In addition to the acute fish studies, chronic toxicity studies are evaluated to 

determine the effect of DMDS on fish. However, no chronic fish studies are available. 

 

 Acute Toxicity to Freshwater Invertebrates

 

The acute effect of DMDS to aquatic invertebrates is represented by Daphnia 

magna. An acceptable acute study (MRID 470528-16) resulted in an acute 

EC50=1.61mg/L that will be used in this assessment. This value will also be used to 

estimate the effect of DMDS to benthic organisms. 

Acute Toxicity to Estuarine/Marine organisms 

Estuarine/Marine Fish 

The sheepshead minnow is used as a surrogate for estuarine/marine fish to 

estimate the acute effect from the use of DMDS. An acceptable study (MRID 473075-

04) resulted in an acute LC50=5.6 mg a.i./L (4.0-6.9mg/L) that will be used in this 

assessment. 

Estuarine/Marine Invertebrates 

 The acute effect of DMDS to estuarine/marine invertebrates is represented by the 

mysid. An acceptable study (MRID 473075-05) resulted in an acute LC50=4.9 mg a.i./L 

(3.9-6.1 mg/L) that will be used in this assessment. 

Acute Toxicity to Aquatic Plants 

 The acute toxicity of DMDS to aquatic plants has been assessed in vascular 

aquatic plants (duckweed, Lemna gibba) and non-vascular plants represented by 

Anabaena flos-aquae. The EC50 is used to estimate the effect of DMDS to non-listed 

species and the EC05 is used to estimate the effect on listed species. There was an 

EC50=28mg/L and an EC05=6.0 mg/L for Lemna. The most sensitive endpoint is for cell 

density for Anabaena flos-aquae, with an EC50=0.320mg/L and an EC05=0.011, which 

will be used in this assessment. 
61 

 III.C.2. Terrestrial Effects Characterization 

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

mammals are summarized in Table III-15. A more detailed summary of the available 

terrestrial toxicity data is given in Appendix F. 

Table 1II-15. Toxicity Reference Values (TRVs) for Terrestrial Species for DMDS 

Exposure 

Scenario

Species Exposure 

Duration

Toxicity 

Reference Value1

Reference

Mammals

Acute 

inhalation 

Rat 4-hour inhalation LC50 = 17 ppm (M) and 19 

ppm (F) 

[conv. to mg/L: Section 

IV.B.2] 

MRID 45117902 

Acceptable/Nonguideline 

Birds

Quail 4-hour Inhalation Male LC50=1.97 mg/L 

(1.62-2.41 mg/L) 

Female LC50=1.73 mg/L 

(1.55-1.93 mg/L) 

Combined LC50=1.84 

(1.64-2.06 mg/L) 

MRID 469170-13 

Acceptable 

Acute 

Inhalation 

1

Data from HED DMDS Risk Assessment. 

Mammalian Species

 

An acceptable rat inhalation study (MRID 45117902) was submitted for DMDS. 

Because inhalation is the expected exposure route, the rat inhalation toxicity value will be 

used in this assessment. 

Avian Species 

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

the effect for all birds. Although an acute oral toxicity study (MRID470528-13) was 

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

expected from the use of DMDS. An inhalation study was classified as supplemental 

(MRID 469170-13) because it is a non-guideline study. The female Bobwhite (Colinus 

virginianus) acute inhalation LC50=1.73 mg/L (1.55-1.93 mg/L) 
62 

Plant Species 

Toxicity values for plant species are summarized in Table III-16. A 

supplemental nonguideline study was submitted to illustrate the effect of DMDS as a gas 

on plants. The most sensitive vegetative vigor monocot (EC25 for oat=100 lb/A) and 

dicot toxicity values (EC25 for tomato=55 lb/A) were reported in the study. However, 

there is insufficient data to estimate the effect on plants. This study maybe upgraded if 

acceptable information on the size of the plastic bag used to contain the gas is submitted. 

Table III-16. Toxicity Reference Values (TRVs) for Terrestrial Plants for DMDS 

Exposure 

Scenario

Species Endpoint Toxicity 

Reference Value

Reference

Vegetative Vigor 

Monocot Oat Dry weight EC25 = 100 lb/A 

EC05=37.5 lb/A 

Dicot Height EC25 = 55 lb/A 

 

Tomato 

EC05 =37.5 lb/A 

MRID 474712-02 

Acceptable/Guideline 
63 

IV. Risk Characterization 

IV.A. Risk Estimation - Integration of Exposure and Effects Data 

IV.A.1. Non-target Aquatic Animals and Plants 

Risk quotients for aquatic animals are presented in Table IV-1 for aquatic 

animals based on surface water EECs, and Table IV-2 for plants based on surface water 

EECs. The risk quotients are calculated using the toxicity values summarized in Table 

III-14 and EECs from PRZM/EXAMS summarized in Table III-8. For assessing acute 

risks, the 24-hour (daily average) peak concentration is used with the lowest (most 

sensitive) fish LC50, aquatic invertebrate EC/LC50, and aquatic plant LC50. For assessing 

risk to endangered/ threatened plant species, the EC05 is used. For assessing chronic 

risks, the 21-day concentration is used with the invertebrate life-cycle NOAEC and the 

60-day concentration is used with the fish early life-stage NOAEC. 

Table IV-1. Surface Water Risk Quotients (RQs) for Aquatic Species. 

Exposure 

Scenario

Drip 

Irrigation 

Peak 

Exposure 

(μg/L)

Drip 

Irrigation 

Risk 

Quotient**

Shank 

Injection 

Peak 

Exposure 

(μg/L)

Shank 

Injection 

Risk 

Quotient**

Freshwater Fish (LC50=960 μg/L)

California tomato 30.29 0.031 4.77E-08 4.97 x 10-11

Florida tomato 18.3 0.019 5.57 0.006

Florida peppers 46.89 0.049 4.43 0.005

Florida cucumber 150.9 0.157* 9.98 0.010

Florida strawberry 203.23 0.212* 3.56 0.004

California onion 2.55 0.003 0.24 2.50 x 10-4

Georgia onion 129.48 0.135* 3.25 0.003

California nursery 7.07 0.007 0.37 3.85 x 10-4

Michigan nursery 32.24 0.033 0.23 2.40 x 10-4

New Jersey nursery 21.83 0.023 0.16 1.67 x 10-4
64 

Table IV-1. Surface Water Risk Quotients (RQs) for Aquatic Species. 

Exposure 

Scenario

Drip 

Irrigation 

Peak 

Exposure 

(μg/L)

Drip 

Irrigation 

Risk 

Quotient**

Shank 

Injection 

Peak 

Exposure 

(μg/L)

Shank 

Injection 

Risk 

Quotient**

Oregon Christmas tree 19.67 0.020 0.21 2.19 x 10-4

Marine Fish LC50=5600 μg/L 

California tomato 30.29 0.005 4.77E-08 8.52 x10-12

Florida tomato 18.3 0.003 5.57 9.95 x 10-4

Florida pepper 46.89 0.008 4.43 7.91 x 10-4

Florida cucumber 150.9 0.027 9.98 0.002 

Florida strawberry 203.23 0.036 3.56 0.001 

California onion 2.55 0.000 0.24 4.29 x 10-5

Georgia onion 129.48 0.023 3.25 5.8 x 10-4

California nursery 7.07 0.001 0.37 6.61 x 10 -5

Michigan nursery 32.24 0.006 0.23 4.11 x 10-5

New Jersey nursery 21.83 0.004 0.16 2.86 x 10-5

Oregon Christmas tree 19.67 0.003 0.21 3.75 x 10-5

Freshwater Aquatic Invertebrates EC50=1610 μg/L

California tomato 30.29 0.019 4.77E-08 2.94 x 10-11

Florida tomato 18.3 0.011 5.57 0.003

Florida peppers 46.89 0.029 4.43 0.003

Florida cucumber 150.9 0.093 9.98 0.006

Florida strawberry 203.23 0.125 3.56 0.002

California onion 2.55 0.001 0.24 1.48 x 10-4

Georgia onion 129.48 0.080* 3.25 0.002

California nursery 7.07 0.004 0.37 2.28 x 10-4

Michigan nursery 32.24 0.020 0.23 1.42 x 10-4
65 

Table IV-1. Surface Water Risk Quotients (RQs) for Aquatic Species. 

Exposure 

Scenario

Drip 

Irrigation 

Peak 

Exposure 

(μg/L)

Drip 

Irrigation 

Risk 

Quotient**

Shank 

Injection 

Peak 

Exposure 

(μg/L)

Shank 

Injection 

Risk 

Quotient**

New Jersey nursery 21.83 0.013 0.16 9.88 x 10-5

Oregon Christmas tree 19.67 0.012 0.21 1.3 x 10-4

Marine Invertebrates EC50=4900 μg/L 

California tomato 30.29 0.006 4.77E-08 9.73 x10-12

Florida tomato 18.3 0.004 5.57 0.001

Florida peppers 46.89 0.009 4.43 0.001

Florida cucumber 150.9 0.031 9.98 0.002

Florida strawberry 203.23 0.041 3.56 0.001

California onion 2.55 0.000 0.24 4.9E-05

Georgia onion 129.48 0.026 3.25 0.001

California nursery 7.07 0.001 0.37 7.55 x 10-5

Michigan nursery 32.24 0.006 0.23 4.69 x 10-5

New Jersey nursery 21.83 0.004 0.16 3.27 x 10-5

Oregon Christmas tree 19.67 0.004 0.21 4.29 10-5

*Exceeds acute endangered species LOC (> 0.05) 

Bold: Exceeds acute endangered species LOC, acute restricted use LOC, and acute risk LOC (> 0.5) 

Acute RQ values are derived from peak EECs and toxicity values for each 

surrogate species. RQs are presented for both drip irrigation and shank injection for each 

use. Drip irrigation RQs exceed the endangered species LOC for freshwater fish and 

freshwater invertebrates for FL cucumber, FL strawberry and GA onion uses. 

Drip irrigation RQs do not exceed the endangered species LOC for freshwater fish 

and freshwater invertebrates for CA tomato, FL tomato, FL pepper, CA onion, CA 

nursery, MI nursery NJ nursery and OR Christmas tree uses. Drip irrigation RQs do not 

exceed the acute risk LOC for any uses for any surrogate aquatic species. Drip irrigation 

RQs do not exceed the endangered species LOC for estuarine/marine fish and 

estuarine/marine invertebrates. Shank injection RQs do not exceed either the acute or 
66 

endangered species LOC for any use for any surrogate aquatic species. 

Table IV-2. Surface Water Risk Quotients (RQs) for Aquatic Plant Species.

Exposure 

Scenario

Drip 

Irrigation 

Peak 

Exposure 

(μg/L)

Drip Irrigation 

Risk 

Quotient**

Shank 

Injection 

Peak 

Exposure 

(μg/L)

Shank 

Injection 

Risk 

Quotient**

Freshwater Vascular Plants: (Lemna EC50=28000 μg/L)

California tomato 30.29 0.001 4.77E-08 1.70 x 10-12

Florida tomato 18.3 0.001 5.57 1.99 x 10-4

Florida peppers 46.89 0.002 4.43 1.58 x 10-4

Florida cucumber 150.9 0.005 9.98 3.56 x 10-4

Florida strawberry 203.23 0.007 3.56 1.27 x 10-4

California onion 2.55 9.11E-05 0.24 8.57 x 10-6

Georgia onion 129.48 0.005 3.25 1.16 x 10-4

California nursery 7.07 0.000 0.37 1.32 x 10-5

Michigan nursery 32.24 0.001 0.23 8.21 x 10-6

New Jersey nursery 21.83 0.001 0.16 5.71 x 10-6

Oregon Christmas tree 19.67 0.001 0.21 7.50 x 10-6

Freshwater Aquatic Nonvascular Plants EC50=320 μg/L 

California tomato 30.29 0.095 4.77E-08 1.49 x 10-10

Florida tomato 18.3 0.057 5.57 0.017

Florida peppers 46.89 0.146 4.43 0.014

Florida cucumber 150.9 0.471 9.98 0.031

Florida strawberry 203.23 0.635 3.56 0.011

California onion 2.55 0.008 0.24 0.001

Georgia onion 129.48 0.405 3.25 0.010

California nursery 7.07 0.022 0.37 0.001
67 

Table IV-2. Surface Water Risk Quotients (RQs) for Aquatic Plant Species.

Exposure 

Scenario

Drip 

Irrigation 

Peak 

Exposure 

(μg/L)

Drip Irrigation 

Risk 

Quotient**

Shank 

Injection 

Peak 

Exposure 

(μg/L)

Shank 

Injection 

Risk 

Quotient**

Michigan nursery 32.24 0.101 0.23 0.001

New Jersey nursery 21.83 0.068 0.16 0.007 

Oregon Christmas tree 19.67 0.061 0.21 0.001

Freshwater Aquatic Nonvascular Plants EC05=11 μg/L

California tomato 30.29 2.754 4.77E-08 4.34 x 10-9

Florida tomato 18.3 1.664 5.57 0.506

Florida peppers 46.89 4.263 4.43 0.403

Florida cucumber 150.9 13.718 9.98 0.907

Florida strawberry 203.23 18.475 3.56 0.324

California onion 2.55 0.232 0.24 0.022

Georgia onion 129.48 11.771 3.25 0.295

California nursery 7.07 0.643 0.37 0.034

Michigan nursery 32.24 2.931 0.23 0.020

New Jersey nursery 21.83 1.985 0.16 0.015

Oregon Christmas tree 19.67 1.788 0.21 0.019

Bold: Exceeds plant LOC (>1) 

RQs for non-listed species are estimated for vascular plants (Lemna) and 

nonvascular plants (Anabaena) using the EC50. There was no RQ exceedence for vascular 

using Lemna as a surrogate or for non-vscaular using Anabaena as a surrogate for either 

drip irrigation or shank injection for any uses. 

RQs are estimated for listed species using the EC05 toxicity value. 
68 

RQs exceeded the LOC for drip irrigation for listed nonvascular plants for CA 

tomato, FL tomato, FL pepper, FL cucumber, FL strawberry, GA onion, MI nursery, NJ 

nursery or OR Christmas tree uses. No RQs exceeded the plant LOC for non-vascular 

plants for CA onion and CA nursery uses. No RQs for shank injection for nonvascular 

plants exceeded the LOC for any uses. 

IV.A.2 Non-Target Terrestrial Species 

Risk quotients for air exposure to mammal and avian species are calculated based 

on the upper-bound PERFUM EEC in air determined at 720 μg/m3

 for an 80 acre field 

using based on the combination of field flux data measured at Tifton, GA and Bradenton, 

FL meteorological data. Along with the EEC in air, the risk quotients are calculated 

using the toxicity values summarized in Table III-15. The risk quotients for mammals 

and birds are shown in Table IV-3. Risk quotients are not exceeded for any entity of 

mammals or birds. 

Table IV-3. Inhalation risk quotients for mammal species (LD50 = 17 ppm or 65,496 

μg/m3

) and avian species (LD50 = 1.73 mg/l or 1.73 x 106 μg/m3).

Table IV-3. Risk Quotients in air based on PERFUM upper-bound EECs based on 

Tifton, GA Shank Injection to Raised Beds with VIF Tarp

Species Toxicity Endpoint (μg/m3

) EEC (μg/m3) RQ 

Mammals LD50 = 65,496 720 0.011 

Birds LD50 = 1.73 x 106 720 0.0004 1

 Toxicity endpoint for birds is 1.73 mg/L or 1.73 x 106 μg/m3 2

 Toxicity endpoint for mammals is 17 ppm or 6,549.6 μg/m3for mammals (6,549.6 μg/m3 = 0.1 x (17 ppm x 94.2 

g/mol)/(24.45 mol/L).
69 

IV.A.3. Non-target Terrestrial and Semi-aquatic 

Plants 

Risk to terrestrial plants is expected from exposure to air concentrations. There is 

no model currently available to estimate those effects for plants. Risk may be estimated 

from toxicity values from EECs calculated from the PERFUM model along with 

submitted toxicity endpoints reflecting exposure from air concentrations if available. 

However, additional data from the toxicity study is needed to complete the assessment. 

IV.B. Risk Description 

IV.B.1 Risk to Aquatic Organisms 

 Consistent with the risk hypothesis stated in Section II.E.1, dimethyl 

disulfide residues may adversely affect aquatic aquatic species via runoff of dissolved 

residues of dimethyl disulfide remaining on treated fields when tarps are removed after 

12 days. Therefore, the risk estimation for aquatic exposure accounts for the impact of 

aerobic soil degradation to residue loadings available to runoff prior to the removal of the 

tarp 12 days after the application. In addition, since dimethyl disulfide is a volatile 

chemical, considerations of risk estimates must also take into account dissipation of 

dimethyl disulfide from the soil due to off-gassing in estimating concentrations for water 

after the tarp is removed. Risk quotients are calculated from dimethyl disulfide EECs in 

surface water from PRZM-EXAMS with the volatility algorithm representative of 

processes and dimethyl disulfide loadings available after tarp removal 12 days after the 

dimethyl disulfide application. 

In addition, DMDS is sufficiently volatile that there may also be inhalation 

exposure and potential risk to birds and mammals as well as air exposure to plants. The 

risk estimation for air exposure to terrestrial plants, birds, and mammals accounts for the 

possible scenario for terrestrial organisms to be impacted on and off of a single treated 

field from dimethyl disulfide. The risk estimation accounts for the requirement of VIF 

tarps that are required to be applied immediately after application and remain undisturbed 

for 12 days according to the product labels. Risk quotients are calculated from dimethyl 

disulfide EECs in air from PERFUM based on flux measured at a Tifton, GA fallow field 

which was covered with a tarp immediately after applications for approximately 12 days 

after the application. According to the risk quotients for terrestrial exposure, the risk 

hypothesis was not verified. 

 Toxicity studies were reviewed to provide endpoints to estimate RQs. Mortality 

and sub-lethal effects were noted in the assessment. Not all sub-lethal effects could be 

statistically analyzed due to the subjective nature of the observation. 

 
70 

A refinement to the model allowed EECs to be estimated using the volatility 

paradigm to describe the effect with the tarp removed. EECs for both drip irrigation and 

shank injection were reported, and were based on a load adjusted for biodegradation 

which occurs under the tarp for the required 12 days which is specified on the label. 

Sublethal effects were noted in the acute marine fish study (MRID 473075-04). 

There were no sub-lethal effects observed in the control treatment group. Sub-lethal 

effects were noted in all subsequent treatment levels. Loss of equilibrium was observed in 

the 2.3 mg a.i./L treatment group at 72 hours. Loss of equilibrium was observed in the 4.0 

mg a.i./L treatment group at 1.5, 24, 48, 72 and 96 hours. Surfacing and lying on the 

bottom was also observed in the 4.0 mg a.i./L treatment group at 72 hours. Surfacing and 

lethargy was additionally noted in the 4.0 mg a.i./L treatment group at 96 hours. Loss of 

equilibrium was observed in the 6.9 mg a.i./L treatment group at 48 and 72 hours. Lying 

on the bottom was also observed in the 6.9 mg a.i./L treatment group at 72 hours. 

Lethargy was additionally observed in the 6.9 mg a.i./L treatment group at 96 hours. 

Surfacing was observed in the 10 mg a.i./L treatment group at 24 hours. Lying on the 

bottom was noted in the 10 mg a.i./L treatment group at 48 hours. 

Risk Conclusions for Aquatic Organisms

Conclusions for the effect of DMDS on aquatic species and aquatic plants were 

based on lines of evidence including fate and transport characteristics, toxicity endpoints, 

results from conventional and refined models for aquatic exposure, as well as reviewing 

incidents reported to the EIIS database. Water column estimated exposure concentrations 

(EECs) were estimated from PRZM/EXAMS modeling simulating dimethyl disulfide fate 

and transport, including volatilization, after the tarp is removed to calculate an RQ. The 

resulting RQs are compared to a Level of Concern (LOC) for the species and exposure 

route. No aquatic animal or plant incidents have been reported in the EIIS database. 

RQs were estimated for both drip irrigation and shank injection for each use. 

There is potential acute risk to freshwater fish and freshwater invertebrates based on RQ 

exccedence. Drip irrigation RQs exceed the endangered species LOC for freshwater fish 

(RQs=0.003-0.212) and freshwater invertebrates (RQs=0.001-0.125) for FL cucumber, 

FL strawberry and GA onion uses. These RQs could be further refined by addressing the 

uncertainties in the persistence of DMDS residues in water if additional data is provided. 

DMDS was modeled as moderately persistent with a half life of 9.32 days in aerobic 

water metabolism following EFED input parameter guidance assuming a doubling of the 

soil half-life due to lack of an aerobic aquatic metabolism study. 

There is no potential for acute risk for any surrogate species using the shank 

injection method. No modeled uses resulted in LOC exceedences. 

There is potential chronic risk to freshwater and estuarine/marine fish based on 

the uncertainty due to the persistence of DMDS in water and absence of chronic toxicity 

data. 
71 

RQs for non-listed species are estimated for vascular plants (Lemna) and 

nonvascular plants (Anabaena) using the EC50. There was no RQ exceedence for vascular 

using Lemna as a surrogate or for non-vscaular using Anabaena as a surrogate for either 

drip irrigation or shank injection for any uses. 

 

Proposed Risk Mitigation

In Section III.A.1, it was determined that loadings in the soil may degradate by 

approximately 83.12 percent (16.22 percent of DMDS residues remain based rate 

constant detetermined from the 90th percentile half life in two aerobic soil metabolism 

studies) over 12 days residues under the Virtually Impermeable Film (VIF) tarp. 

However, considering there are small risks to various aquatic organisms of concern, and 

that there is a benefit of the tarp for preventing risks to both aquatic organisms via runoff 

suppression and terrestrial organisms via suppression to volatilization and off-gassing, 

EFED will recommend label language to mitigate the risk of runoff by restricting tarp 

cutting activities from occurring when rainfall is forecasted within 48 hours. 

 In addition, since degradates were not found to be of toxicological concern based 

on structural activity relationships shown in Tables II.2a and II.2b and discussion in 

Section II.B.1, additional data on the environmental fate and ecological toxicity of these 

degradates will not be requested at this time.

IV.B.2 Risk to Terrestrial Organisms

 Terrestrial animals and plants on or near treated fields could be susceptible to 

acute exposure to DMDS from residues in the air (due to the volatility of DMDS). 

Chronic exposure from a single treated field is not likely to occur due to the short halflife of DMDS. However, chronic exposure may be possible due to repeat exposures from 

multiple fields. To address this possibility, ambient air quality monitoring data will be 

requested as needed in any area where the DMDS use volume is high. 

 Dimethyl disulfide pre-plant soil fumigation is not expected to be of concern via 

the dietary exposure route for birds and mammals as crops are not expected to uptake any 

residues. In addition, dimethyl disulfide low persistence in soils and high mobility and 

diffusivity in the soil are all factors which suggest that there is not a high probability of 

DMDS residues to be ingested. 

Risk from Inhalation

DMDS is applied as a fumigant using drip irrigation and shank injection and 

covered with a tarp. The tarp is removed after 12 days. No spray drift or runoff is 

expected for the first 12 days. Therefore, an effect to avian and mammal species via the 

inhalation route is expected from the use of DMDS, consistent with the risk hypothesis. 
72 

The PERFUM model with field flux measured at Tifton, GA field treated with a raised 

bedded application to DMDS with immediate covering by a VIF tarp is used to estimate 

the exposure to terrestrial species. There was no inhalation risk found to mammals or 

birds associated with this use pattern. 

 Limitations of the air modeling include the uncertainty in air concentration 

at ground-level at any given point in time. Difference in air concentrations between these 

two levels are determined based on the rise and reflection of the plume to the surface. 

However, since EECs are reported at only 1.5 meters above ground level, it is not 

expected that the 90th percentile concentration around the edge at a certain time of day 

would not vary tremendously from one level to the other. One other limitation is the 

inability for PERFUM to account for plume meandering during inversion conditions, 

when a highly concentrated plume can impact a large perimeter within a short time period 

(USEPA, 2009[4]). To protect against this uncertainty, inversion mitigation language 

restricting DMDS applications during large-scale extended inversion events is proposed. 

Furthermore, EECs are ultimately based on the performance of the VIF tarp at one site. 

However, screening-level EECs using the SCREEN3 dispersion model indicate that 

EECs in air may be of concern to mammals and birds at other locations, times, and 

methods in which DMDS applications occur. This analysis is presented in Appendix G. 

However, these EECs are based on low density polythelene tarps and metalized tarps 

which may be less permeable to DMDS volatile residues. Therefore, more field volatility 

studies conducted with VIF tarps are being requested at this time to address these 

uncertainties. 

Terrestrial Risk Conclusions 

The proposed label for DMDS includes instructions to cover the field with a tarp 

for the first 12 days. Specifically, high barrier tarps such as VIF (Virtually Impermable 

Films) tarps are required to be used on the proposed label; therefore the conclusions are 

based on the effect using those tarps. The PERFUM model describes the effect from the 

use of high barrier tarps such as proposed on the label. Although there is no inhalation 

LOC available to compare with the RQ, this analysis uses the current bird endangered 

species LOC=0.1 used to evaluate dietary effect, to determine the effect of DMDS use. 

Although there is no risk anticipated based on the single field volatility study that used a 

VIF tarp in Tifton, Georgia, an analysis using low barrier tarps using a screening method 

with the SCREEN3 model, presented Appendix G., justifies the need for more field 

volatility studies as there are risks to birds and mammals based on other field volatility 

studies conducted with other tarps showed RQs of concern at other locations, times of 

year, and application methods other than shank injection to raised beds. RQs for chronic 

effects were not modeled due to the absence of chronic toxicity data. However, this is 

not expected to be be of concern due to DMDS’s low persistence in air. However, repeat 

exposures may occur in high use areas. No terrestrial animal incidents have been 

reported in the EIIS database. 
73 

Although there is no model available to estimate the effects on the honeybee, the 

results for the toxicity test are classified as to the impact. There is no risk for non-listed 

insects based on the honeybee toxicity test, which resulted in a classification of 

practically non-toxic. The risk to other terrestrial invertebrates that are not soil dwelling 

would be represented by the honeybee estimate. 

There is no risk to other off-site terrestrial invertebrates that burrow in the soil 

since the dominate routes of dissipation for DMDS is expected to be leaching into ground 

water or volatilization into the air.. 

Terrestrial Plants 

DMDS is used to kill weeds as a target, therefore it is expected to kill plants on 

the field. There is potential risk based on the absence of acceptable data to estimate the 

effect of DMDS as a gas to terrestrial plants. The dominant route of exposure is thought 

to be inhalation rather than runoff. 

Proposed Risk Mitigation

Since field volatility studies suggest there is no risk to birds and mammals from 

air residues of DMDS which are emitted from fields covered with a VIF tarp and there 

are no risk from DMDS residues in runoff from treated fields, there is no mitigation 

proposed besides the label maintaing the label requirement that fields be covered with a 

VIF tarp for 12 days after the application. However, to address the uncertainty related to 

air residues which may potentially exist during inversion conditions, it is recommended 

that DMDS applications be restricted from occurring under such conditions. Growers 

and applicators are required to use advisory products from the National Weather Service 

and identify indicators of inversion conditions such as light wind speeds to identify 

present or future stagnate air conditions. 

 IV.B.3. Review of Incident Data 

 

 DMDS has no registered outdoor pesticide uses and has no incidents in EFED’s 

Ecological Incident Information System (EIIS) (data base checked 02/22/10). 

 

 Given the risk quotients discussed above, there is a potential for fish and aquatic 

plant incidents under the proposed use. 

IV.B.4 Endocrine Disruption 

As required under FFDCA section 408(p), EPA has developed the Endocrine 

Disruptor Screening Program (EDSP) to determine whether certain substances (including 

pesticide active and other ingredients) may have an effect in humans or wildlife similar to 

an effect produced by a “naturally occurring estrogen, or other such endocrine effects as 
74 

the Administrator may designate.” The EDSP employs a two-tiered approach to making 

the statutorily required determinations. Tier 1 consists of a battery of 11 screening assays 

to identify the potential of a chemical substance to interact with the estrogen, androgen, 

or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening 

and are found to have the potential to interact with E, A, or T hormonal systems will 

proceed to the next stage of the EDSP where EPA will determine which, if any, of the 

Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to 

identify any adverse endocrine related effects caused by the substance, and establish a 

dose-response relationship between the dose and the E, A, or T effect. 

Between October 2009 and February 2010, EPA is issuing test orders/data call-ins 

for the first group of 67 chemicals, which contains 58 pesticide active ingredients and 9 

inert ingredients. This list of chemicals was selected based on the potential for human 

exposure through pathways such as food and water, residential activity, and certain postapplication agricultural scenarios. This list should not be construed as a list of known or 

likely endocrine disruptors. 

DMDS is not among the group of 58 pesticide active ingredients on the initial list 

to be screened under the EDSP. Under FFDCA sec. 408(p) the Agency must screen all 

pesticide chemicals. Accordingly, EPA anticipates issuing future EDSP test orders/data 

call-ins for all pesticide active ingredients. 

For further information on the status of the EDSP, the policies and procedures, the 

list of 67 chemicals, the test guidelines and the Tier 1 screening battery, please visit our 

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

IV.B.5. Federally Threatened and Endangered (Listed) Species 

Concerns 

 IV.B.5.a. Action Area 

 For listed species assessment purposes, the action area is considered to be the area 

affected directly or indirectly by the Federal action and not merely the immediate area 

involved in the action. At the initial Level I screening assessment, broadly described 

taxonomic groups are considered and thus conservatively assumes that listed species 

within those broad groups are co-located with the pesticide treatment area. This means 

that terrestrial plants and wildlife are assumed to be located on or adjacent to the treated 

site, and aquatic organisms are assumed to be located in a surface water body adjacent to 

the treated site. The assessment also assumes that the listed species are located within an 

assumed area with the relatively highest potential exposure to the pesticide, and that 

exposures are likely to decrease with distance from the treatment area. Section II. B of 

this risk assessment presents the pesticide use sites that are used to establish initial 

collocation of species with treatment areas. 
75 

 If the assumptions associated with the screening-level action area result in RQs 

that are below the listed species LOCs, a "no effect" determination conclusion may be 

made with respect to listed species in that taxa, and no further description of an action 

area is necessary. Furthermore, RQs below the listed species LOCs for a given 

taxonomic group indicate indirect effects upon listed species that depend upon the 

taxonomic group covered by the RQ as a resource. 

 However, in situations where the screening assumptions lead to RQs in excess of 

the listed species LOCs for a given taxonomic group, a potential for a "may affect" 

conclusion exists and may be associated with direct effects on listed species belonging to 

that taxonomic group or may extend to indirect effects upon listed species that depend 

upon that taxonomic group as a resource. In such cases, additional information on the 

biology of listed species, the locations of these species, fate and transport properties of 

the chemical, and the locations of use sites could be considered to determine the extent to 

which screening assumptions regarding an action area apply to a particular listed 

organism. These subsequent refinement steps could consider how this information would 

impact the action area for a particular listed organism and may potentially include areas 

of exposure that are downwind and downstream of the pesticide use site. 

IV.B.5.b Taxonomic Groups Potentially at Risk 

 The Level I screening assessment process for listed species uses the generic 

taxonomic group-based process to make inferences on direct effects for listed species. 

The first iteration of reporting the results of the Level I screen is a listing of pesticide use 

sites and taxonomic groups for which RQ calculations reveal values that meet or exceed 

the listed species LOCs. In the majority of cases, the screening-level risk assessment 

process reports RQ calculations for the following broad taxonomic groupings: 

 

 Freshwater fish (also used as a surrogate for aquatic phase amphibians) 

 Freshwater invertebrates 

 Estuarine/marine fish 

 Estuarine/marine invertebrates 

 Non-vascular Plants 

 There may also be taxonomic groups of listed species for which screening tools 

are not fully developed nor represented through surrogacy with existing tools. For 

example, there is no RQ calculation process for either fungi or terrestrial invertebrates. 

IV.B.5.b.1. Discussion of Risk Quotients 
76 

Endangered Species LOCs are exceeded for freshwater fish, freshwater 

invertebrates and for plant LOCs for nonvascular aquatic plants. All terrestrial impacts 

are based on inhalation exposure. Based on inhalation exposure, no LOCs are exceeded 

for birds and mammals. 

 

Terrestrial invertebrates and fungi are target species and thus non-target terrestrial 

invertebrates and fungi may also be at risk. Should estimated exposure levels resulting in 

RQs at or above the endangered species LOC occur in proximity to listed resources, the 

available screening level information suggests a potential risk for direct acute effects on 

listed freshwater fish, marine fish, freshwater invertebrates, marine invertebrates and 

aquatic plants, associated with use of DMDS. 

IV.B.5.b.2. Probit Dose Response Relationship 

An analysis has been conducted of the probability of individual mortality at an 

LOC of 0.1, the acute endangered species LOC for terrestrial wildlife. It is recognized 

that extrapolation of very low probability events is associated with considerable 

uncertainty in the resulting estimates. The analysis uses the EFED spreadsheet 

IECv1.1.xls, developed by EFED (USEPA, 2004). 

For birds, a bobwhite quail LC50 of 1.73 mg/kg (MRID 47035302) is used for the 

assessment of inhalation risk from exposure to DMDS. A probit slope (10.1) and 95% 

confidence interval (1.76 – 18.44) are provided in the data review. Based on these inputs 

and an assumption of a probit dose response relationship, the IEC spreadsheet indicates 

an estimated chance of individual mortality associated with the listed species LOC of 0.1, 

the acute toxic endpoint for birds, of approximately one in 3.62E+23. To explore 

possible bounds to this estimate, the upper and lower values for the mean slope estimate 

were used to calculate upper and lower estimates of the effects probability associated 

with the listed species LOC. These values are approximately one in 2.55E+01 and one in 

3.19E+75. 

For the rat as a surrogate for mammals, an LC50 of 17 ppm (MRID 4470528-14) is 

used for the assessment of inhalation risk from exposure to DMDS. There was not a 

good fit for the probit analysis. No slope was reported, therefore the default probit slope 

(4.5) and 95% confidence interval (2 – 9) are provided in the data review. Based on these 

inputs and an assumption of a probit dose response relationship, the IEC spreadsheet 

indicates an estimated chance of individual mortality associated with the listed species 

LOC of 0.1, the acute toxic endpoint for mammals, of approximately one in 2.94E+05. 

To explore possible bounds to this estimate, the upper and lower values for the mean 

slope estimate were used to calculate upper and lower estimates of the effects probability 

associated with the listed species LOC. These values are approximately one in 4.40E+01 

and one in 8.86E+18. 

An analysis has been conducted of the probability of individual mortality at an LOC of 

0.05, the acute endangered species LOC for aquatic animals. It is recognized that 
77 

extrapolation of very low probability events is associated with considerable uncertainty in 

the resulting estimates. The analysis uses the EFED spreadsheet IECv1.1.xls, developed 

by EFED (USEPA, 2004). 

For freshwater fish, a rainbow trout LC50 of 0.96 ppm (MRID 4470528-14) is 

used for the assessment of acute risk from exposure to DMDS. There was not a good fit 

for the probit analysis. No slope was reported, therefore the default probit slope (4.5) and 

95% confidence interval (2 – 9) are provided in the data review. Based on these inputs 

and an assumption of a probit dose response relationship, the IEC spreadsheet indicates 

an estimated chance of individual mortality associated with the listed species LOC of 

0.05, the acute toxic endpoint for fish, of approximately one in 4.18E+08. To explore 

possible bounds to this estimate, the upper and lower values for the mean slope estimate 

were used to calculate upper and lower estimates of the effects probability associated 

with the listed species LOC. These values are approximately one in 2.16E+02 and one in 

1.75E+31. 

For estuarine/marine fish, a sheepshead minnow LC50 of 5.6 ppm (MRID 473075-

04) is used for the assessment of acute risk from exposure to DMDS. There was not a 

good fit for the probit analysis. No slope was reported, therefore the default probit slope 

(4.5) and 95% confidence interval (2 – 9) are provided in the data review. Based on these 

inputs and an assumption of a probit dose response relationship, the IEC spreadsheet 

indicates an estimated chance of individual mortality associated with the listed species 

LOC of 0.05, the acute toxic endpoint for fish, of approximately one in 4.18E+08. To 

explore possible bounds to this estimate, the upper and lower values for the mean slope 

estimate were used to calculate upper and lower estimates of the effects probability 

associated with the listed species LOC. These values are approximately one in 2.16E+02 

and one in 1.75E+31. 

For freshwater invertebrates, a daphnid LC50 of 1.6 ppm (MRID 470528-16) is 

used for the assessment of acute risk from exposure to DMDS. There was not a good fit 

for the probit analysis. No slope was reported, therefore the default probit slope (4.5) and 

95% confidence interval (2 – 9) are provided in the data review. Based on these inputs 

and an assumption of a probit dose response relationship, the IEC spreadsheet indicates 

an estimated chance of individual mortality associated with the listed species LOC of 

0.05, the acute toxic endpoint for fish, of approximately one in 4.18E+08. To explore 

possible bounds to this estimate, the upper and lower values for the mean slope estimate 

were used to calculate upper and lower estimates of the effects probability associated 

with the listed species LOC. These values are approximately one in 2.16E+02 and one in 

1.75E+31. 

 

For estuarine/marine invertebrates, a mysid LC50 of 4.9 ppm (MRID 473075-05) 

is used for the assessment of acute risk from exposure to DMDS. There was not a good 

fit for the probit analysis. No slope was reported, therefore the default probit slope (4.5) 

and 95% confidence interval (2 – 9) are provided in the data review. Based on these 

inputs and an assumption of a probit dose response relationship, the IEC spreadsheet 
78 

indicates an estimated chance of individual mortality associated with the listed species 

LOC of 0.05, the acute toxic endpoint for fish, of approximately one in 4.18E+08. To 

explore possible bounds to this estimate, the upper and lower values for the mean slope 

estimate were used to calculate upper and lower estimates of the effects probability 

associated with the listed species LOC. These values are approximately one in 2.16E+02 

and one in 1.75E+31. 

Although the Agency has assumed a probit dose response relationship in 

establishing the listed species LOCs, the available data for the toxicity study generating 

RQs for this taxonomic group do not support a probit dose response relationship, and so 

the confidence in estimated event probabilities based on this dose response relationship 

and the listed species LOC is low. 

IV.B.5.c. Data Related to Under-represented Taxa 

 Although the Level I screening assessment process relies on RQ calculations that 

use toxicity endpoints selected from the most sensitive species tested within broad 

taxonomic groups, there may be situations in which additional effects data from one or 

more sources may suggest that a given suite of listed taxa may be more or less sensitive 

than suggested by the effects data used for RQ calculations. In these circumstances, the 

screening level RQs are not changed, but effects data more specific to listed species may 

be used to evaluate the extent to which screening-level RQs adequately represent 

conclusions regarding effects on specific listed taxa. However, this does not appear to 

apply to DMDS. 

IV.B.5.d. Implications of Sublethal Effects 

 Sub-lethal adverse effects were seen in a variety of acute studies. For example, 

nasal effects were seen in mammal inhalation studies. Thus, it is expected that sub-lethal 

effects could be seen in listed species, if exposed at levels comparable to those producing 

effects in the lab. This potentially could cause adverse effects upon listed species. For 

example, if DMDS caused effects to the sense of smell, it could impact foraging or 

predator avoidance. 

IV.B.5.e. Indirect Effects Analysis 

 The Agency acknowledges that pesticides have the potential to exert indirect 

effects upon the listed organisms by perturbing forage or prey availability or altering the 

extent and nature of nesting habitat, for example. In conducting a screen for indirect 

effects, the Agency uses the direct effects LOCs for each taxonomic group to make 

inferences concerning the potential for indirect effects upon listed species that rely upon 

non-endangered organisms in these taxonomic groups as resources critical to their life 

cycle. 
79 

 For DMDS, direct effect LOCs are exceeded for fish, aquatic invertebrates, and 

plants, as indicated above. In addition to these potential direct effects, there may thus be 

a potential for indirect effects to those listed species that are dependent upon fish, aquatic 

invertebrates, and/or aquatic plants. 

IV.B.5.f. Critical Habitat 

 In the evaluation of pesticide effects on designated critical habitat, consideration 

is given to the physical and biological features (constituent elements) of a critical habitat 

identified by the U.S Fish and Wildlife and National Marine Fisheries Services as 

essential to the conservation of a listed species and which may require special 

management considerations or protection. The evaluation of impacts for a screening 

level pesticide risk assessment focuses on the biological features that are constituent 

elements and is accomplished using the screening-level taxonomic analysis (risk 

quotients, RQs) and listed species levels of concern (LOCs) that are used to evaluate 

direct and indirect effects to listed organisms. 

 The screening-level risk assessment has identified potential risks for indirect 

effects on listed species for those organisms dependant upon mammals, birds, fish, 

aquatic invertebrates, and/or plants. In light of the potential for indirect effects, the next 

step for EPA and the Service(s) is to identify which listed species and critical habitat are 

potentially implicated. Analytically, the identification of such species and critical habitat 

can occur in either of two ways. First, the agencies could determine whether the action 

area overlaps critical habitat or the occupied range of any listed species. If so, EPA 

would examine whether the pesticide's potential impacts on non-endangered species 

would affect the listed species indirectly or directly affect a constituent element of the 

critical habitat. Alternatively, the agencies could determine which listed species depend 

on biological resources, or have constituent elements that fall into, the taxa that may be 

directly or indirectly impacted by the pesticide. Then EPA would determine whether use 

of the pesticide overlaps the critical habitat or the occupied range of those listed species. 

At present, the information reviewed by EPA does not permit use of either analytical 

approach to make a definitive identification of species that are potentially impacted 

indirectly or critical habitats that is potentially impacted directly by the use of the 

pesticide. EPA and the Service(s) are working together to conduct the necessary 

analysis. 

 This screening-level risk assessment for critical habitat provides a listing of 

potential biological features that, if they are constituent elements of one or more critical 

habitats, would be of potential concern. These correspond to the taxa identified above as 

being of potential concern for indirect effects and include mammals, birds, fish, terrestrial 

invertebrates, and/or plants. This list should serve as an initial step in problem 

formulation for further assessment of critical habitat impacts outlined above, should 

additional work be necessary. 
80 

IV.B.5.g. Co-occurrence Analysis 

 The goal of the analysis for co-location is to determine whether sites of pesticide 

use are geographically associated with known locations of listed species. At the 

screening level, this analysis is accomplished using the LOCATES database. The 

database uses location information for listed species at the county level and compares it 

to agricultural census data for crop production at the same county level of resolution. 

The product is a listing of federally listed species that are located within counties known 

to produce the crop upon which the pesticide will be used. Because the Level I screening 

assessment considers both direct and indirect effects across generic taxonomic 

groupings, it is not possible to exclude any taxonomic group from a LOCATES database 

run for a screening risk assessment. 

DMDS is proposed for pre-plant soil incorporated uses. These uses could 

potentially occur in any county in the United States. Thus a screen for both direct and 

indirect effects in all counties would essentially include all known federally-listed species 

for all taxonomic groups in all counties. A list of these (organized by taxon), as compiled 

by EFED in 2009, is provided in Appendix H. 

The registrant must provide information on the proximity of all federally-listed 

species to the proposed use sites. This requirement may be satisfied in one of three ways: 

1) having membership in the FIFRA Endangered Species Task Force (Pesticide 

Registration [PR] Notice 2000-2); 2) citing FIFRA Endangered Species Task Force data; 

or 3) independently producing these data, provided the information is of sufficient quality 

to meet FIFRA requirements. The information will be used by the OPP Endangered 

Species Protection Program to develop recommendations to avoid adverse effects to 

listed species. 

Listed species risks are associated with direct or indirect effects due to 

applications of DMDS to tomatoes, peppers, cucumbers, strawberries, onions, nursery 

and Christmas trees if organisms in listed taxa are exposed (direct effects) or are 

dependent on other organisms that are exposed (indirect effects). Risks are based on 

available reviewed data. Submission and review of the data requested in this review (see 

above) may result in identification of additional potential effects. A summary of listed 

species by taxa is presented in Appendix F. 

There is the potential for direct effects for listed freshwater fish and aquatic 

invertebrates from the use of DMDS based on RQs exceeding the LOC. Drip irrigation 

RQs exceed the endangered species LOC for FL cucumber, FL strawberry and GA onion. 

Drip irrigation RQs range from 0.01 to 0.21 and shank injection RQs from 0 to 0.01 for 

fish. Drip irrigation RQs range from 0.001 to 0.125 and shank injection RQs from 0 to 

0.006 for invertebrates. Based on the direct effect RQs, any freshwater fish species or 

aquatic invertebrates consuming those taxa will be adversely impacted for indirect 
81 

effects. 

There is no potential direct or indirect effect on listed estuarine/marine fish or 

invertebrates from drip irrigation or shank injection for any use. Drip irrigation RQs 

range from 0 to 0.036 and shank injection RQs from 0 to 0.002 for fish. Drip irrigation 

RQs range from 0 to 0.041 and shank injection RQs from 0 to 0.001 for invertebrates. 

There is no potential risk for direct or indirect effects to listed aquatic vascular 

plants represented by Lemna based on no RQ exceedence using the EC05. No RQs for 

either drip irrigation or shank injection exceeded the LOC. 

Although there are no aquatic non-vascular plants included in Federal listings of 

threatened and endangered species at the present time, an assessment of the effect of 

DMDS on those plants is provided to evaluate potential contributions to indirect effects 

to other taxa and as a record of exceedances should future listings of non-vascular aquatic 

plants warrant additional evaluation of Federal actions. 

There is potential risk for direct or indirect effects to listed aquatic non-vascular 

plants represented by Anabaena based on RQ exceedence using the EC05. There was no 

RQ exceedence for vascular using using Anabaena as a surrogate for shank injection for 

any uses. 

There is potential for direct or indirect chronic effects for freshwater fish and 

aquatic invertebrates based on the uncertainty for persistence in aquatic environments. 

There is no potential direct or indirect acute effects on listed estuarine/marine fish 

or invertebrates from drip irrigation or shank injection for any use. Drip irrigation RQs 

range from 0 to 0.036 and shank injection RQs from 0 to 0.002 for fish. Drip irrigation 

RQs range from 0 to 0.041 and shank injection RQs from 0 to 0.001 for invertebrates. 

There is potential for direct or indirect chronic effects for estuarine/marine fish 

and aquatic invertebrates based on the uncertainty for persistence in aquatic 

environments. 

Habitat Modification

Habitat modification includes effects from reduction in prey as well as effects on 

plants. There is the potential for indirect effects for listed freshwater fish and aquatic 

invertebrates from the use of DMDS based on RQs exceeding the LOC. Drip irrigation 

RQs exceed the endangered species LOC for FL cucumber, FL strawberry and GA onion. 

The effect of plants is also used to assess the effect of DMDS on habitat 

modification. There is potential risk to listed aquatic non-vascular plants represented by 

Anabaena based on RQ exceedence using the EC05. RQs are estimated for listed species 

using the EC05 toxicity value. RQs exceeded the LOC for drip irrigation for listed 
82 

nonvascular plants for CA tomato, FL tomato, FL pepper, FL cucumber, FL strawberry, 

GA onion, MI nursery, NJ nursery and OR Christmas tree uses. No RQs for shank 

injection for nonvascular plants exceeded the LOC for any uses. 

Listed Taxon Direct Effects Indirect Effects3 

Terrestrial and semiaquatic plants – 

monocots 

Yes (Additional data required) Yes (Additional data required) 

Terrestrial and semiaquatic plants – dicots No (semi-aquatic plants) No 

Terrestrial 

Invertebrates No No 

Birds No No 

Terrestrial phase 

amphibians1 No No 

Reptiles1 No No 

Mammals No No 

Aquatic non-vascular 

plants* Yes Yes 

Aquatic vascular 

plants No No 

Freshwater fish Yes – (Additional chronic data 

needed) 4 Yes 

Aquatic phase 

amphibians2 

Yes – (Additional chronic data 

needed) 4 Yes 

Freshwater 

crustaceans Yes Yes 

Mollusks NA NA 

Marine/estuarine fish No –(Additional chronic data 

needed) 4 No 

Marine/estuarine 

crustaceans 

No (Additional chronic data 

needed) 4 No 
83 

* At the present time no aquatic non-vascular plants are included in Federal listings of threatened and 

endangered species. The taxonomic group is included here for the purposes of evaluating potential 

contributions to indirect effects to other taxa and as a record of exceedances should future listings of 

non-vascular aquatic plants warrant additional evaluation of Federal actions.

1

Risk assessment is based on avian assessment. 

2

Risk assessment is based on freshwater fish assessment. 

3

Indirect effects are considered possible for every taxonomic group when one or more direct effect 

LOCs are met/exceeded. Listed species could be affected by the loss of other species that they depend 

on for food, cover, and/or reproduction (e.g., pollination, seed dispersal). This is only a screening 

assessment. A refined assessment will consider the specifics of the food, cover, and reproduction needs 

of each listed species. 

4 Requested data may result in additional potential direct effects. 
84 

V. Literature Cited

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

calculation of photochemical ozone creation potentials (POCP) under European 

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

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

Box 470 86, 402 58 Göteborg, Sweden. 

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

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

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

Soils Treated with Sulfur –Containing Organic Materials. Soil Biology and 

Biochemistry, Vol. 8, pp. 439 - 443. 

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

Water by Gas Chromatography – Mass Spectrometry with Glass Capillary Columns; 

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

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

Elsevier Science B.V., Amesterdam, The Netherlands. 

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

system documentation. National Exposure Research Laboratory. U.S. Environmental 

Protection Agency, Research Triangle Park, NC 27711. 

http://www.epa.gov/ceampubl/swater/exams/index.htm

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

Algorithms, and Other Components of the Models-3 Community Multiscale Air Quality 

(CMAQ) Modeling System. U.S. Environmental Protection Agency, Office of Research 

and Development, Atmospheric Sciences Modeling Division, Research Triangle Park, 

NC. 

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

PRZM-3, A Model for Predicting Pesticide and Nitrogen Fate in the Crop Root and 

Unsaturated Soil Zones: Users Manual for Release 3.0. National Exposure Research 

Laboratory, Office of Research and Development, U.S. Environmental Protection 

Agency, Athens, GA. http://www.epa.gov/ceampubl/gwater/przm3/index.htm

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

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

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

Castro, M.S. and Galloway, J.N., 1991. A Comparison of Sulfur-Free and Ambient Air 
85 

Enclosure Techniques for Measuring the Exchange of Reduced Sulfur Gases Between 

Soils and the Atmosphere. Journal of Geophysical Research, Vol. 96 No. D8, pp. 15427-

15437. 

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

Research Conference on Methyl Bromide Alternatives and Emissions Reductions, 

MBAO, pp. 23-1-23-4. 

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

March 2010. 

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

Huignard, J., Lapied, B., 2002. Dimethyl disulfide exerts insecticidal neurotoxicity 

through miochodrial dysfunction and activation of Insect KATP Channels. J. 

Neurophysiolol. 90: 259 – 270. doi:10.1152/jn.01096.20020022-3077/03. 

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

and dimethyl disulfide. I: Mechanism Development. Journal of Atmospheric 

Chemistry. 11: 309 – 364. 

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

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

Atmospheric Chemistry. 11: 365 - 399. 

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

Chemical Society, Division of Environmental Chemistry. Preprint Extended Abstract, 

208th ACS National Meeting. Vol. 34, pp. 596 – 599. 

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

Evaluations for Soilborne Pest and Cyperus rotundus Control in Fresh Market Tomato. 

Crop Prot. 23: 889-893. 

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

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

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

modeling analysis of air concentration measurements. EH99-03. California 

Environmental Protection Agency, Department of Pesticide Regulation, Environmental 

Monitoring and Pest Management Branch, Environmental Hazards Assessment Program. 

Sacramento, California 95814-3510 <http://www.cdpr.ca.gov/docs/dprdocs 

/methbrom/comp_modeling.htm>.

Mapleston, P. 1992 , Barrier film coatings add performance options. Modern Plastics,

pp.48-50 
86 

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. 

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

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

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

Sci.Soc.Fla.Proc. 4-7. 

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

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

Alternatives and Emissions Reductions 10:16 (Abstr.). 

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

Model for FUMigants (PERFUM), Version 2. Arysta LifeScience North America 

Corporation. Cary, North Carolina. 

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

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

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

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

Accessed March 2010. 

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

An Interim Report to Congress. June 1975. 

USEPA. 1995. Industrial Source Complex (ISC3) Dispersion Model User's Guide. EPA454/B-95-003b. U.S. Environmental Protection Agency, Research Triangle Park, NC. 

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

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

USEPA 2009 [2]. Ozone Layer Depletion. Office of Atmopsheric Programs. 

Washington, D.C. Available on-line: <http://www.epa.gov/ozone/strathome.html>. 

Accessed February 2009. 

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

for Greenhouse Gases Under Section 202(a) of the Clean Air Act”, in Federal Register, 

Vol. 74, No. 78, 2009, pp. 18886 - 18910. US EPA, Office of Air and Radiation. 

Washington, DC. 

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

Available on-line: <http://www.epa.gov/acidrain/>. Accessed March 2010. 
87 

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

D.C.. Available on-line: < http://www.epa.gov/air/ozonepollution/>. Accessed March 

2010. 

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

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

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

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

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

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

19March2009.pdf >. Accessed March 2010. 

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

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

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

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

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

nsDATGuidance.pdf>. Accessed March 2010. 

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

pp. 55 – 59. 

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

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

and Aquatic Science, Vol. 40, pp. 304 – 331. 

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

flux method for estimating volatilisation from circular plots. Agriculture Forest Meteor. 

Vol 57:281-295. 

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

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

CH3SSCH3. Journal of Physical Chemistry, 85: 2660 - 2665. 

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

Terrestrial Ecosystem. Symposia Papers Presented Before the Division of Environmental 

Chemistry, American Chemical Society, Preprints of Extented Abstracts, 39(1): pp. 16 – 

18.