Proposed Registration of the New Active 

 Ingredient Dimethyl Disulfide (DMDS) for 

Pre-Plant Use to Fumigate Fields used to Grow 

 Blueberries, Cucurbit Vegetables, Fruiting 

 Vegetables, Strawberries, Field-Grown 

 Ornamentals, and Forest Nursery Crops

 May 24, 2010 

 

 

 U.S. Environmental Protection Agency 

 Office of Pesticide Programs 

 Registration Division 

Proposed Registration of the New Active Ingredient, Dimethyl Disulfide for Use on 

Blueberries, Cucurbit Vegetables, Fruiting Vegetables, Strawberries, 

Field-Grown Ornamentals, and Forest Nursery Crops 

I. REGULATORY PROPOSAL SUMMARY 

 The U.S. Environmental Protection Agency (EPA or the Agency) is proposing to register 

the new soil fumigation active ingredient, dimethyl disulfide (DMDS), under the Federal 

Insecticide, Fungicide and Rodenticide Act (FIFRA), as amended. DMDS is a broad-spectrum 

fumigant used for the control or suppression of nematodes, various soil borne pathogens, and 

weeds. DMDS is applied using drip irrigation or shank injection and covered with a tarp to 

prevent volatilization. The proposed uses are for tomatoes, peppers, eggplant, cucumbers, 

squash (all), melons (all), strawberries, onions, field grown ornamentals, and forest nursery 

crops. DMDS end-use products are packaged as Paladin (98.8% active ingredient) and Paladin 

EC (93.8% active ingredient). DMDS may be combined with chloropicrin and is expected to 

serve as one of the methyl bromide replacement fumigants. 

 

Although DMDS will be used as an agricultural pesticide, it is considered a non-food use 

chemical since it is applied pre-plant and is quickly degraded or metabolized into non-toxic 

degradates in the soil. Furthermore, DMDS residues must dissipate in the soil prior to planting 

so as not to be phytotoxic to the crop. Therefore, this fumigant does not require establishing 

food tolerances and is not subject to the amendments of the Federal Food, Drug, and Cosmetic 

Act (FFDCA) and the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) promulgated 

under the Food Quality Protection Act (FQPA) of 1996. 

II. STRUCTURE and NOMENCLATURE 

The structure and relevant nomenclature for DMDS are presented below in Table 1. 

Table 1: Structure and Nomenclature of Dimethyl Disulfide

Chemical structure 

Common name Dimethyl Disulfide, DMDS 

Molecular formula C2H6S2

Molecular weight 94.2 g/mol 

IUPAC name (methyldisulfanyl)methane 

CAS name Dimethyl Disulfide 

CAS number 624-92-0 

PC Code 029088 

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III. PHYSICAL and CHEMICAL PROPERTIES 

A listing of the physical and chemical properties of DMDS is presented below in Table 2. 

Table 2: Physicochemical Properties of the Technical Grade Test Compound

Parameter Value/Description 

Physical State Pale yellow liquid 

Melting point/range -84.7 °C 

Boiling point/range 109-110 °C 

Density 1.062 g/mol @ 20 °C 

Water Solubility 1-10 g/L @ 20 °C 

Solvent Solubility Completely miscible with n-hexane at all temperatures. 

Vapor Pressure 29.0 mmHg @ 25 °C 

22.5 mmHg @ 20 °C 

Dissociation constant (pKa) This substance does not dissociate. 

IV. HUMAN HEALTH RISK ASSESSMENT 

A summary of the human health risk, as it was assessed in the Agency document entitled 

“Human-Health Risk Assessment, Dimethyl Disulfide, March 10, 2010,” is provided below. The 

following summary information identifies the risk resulting from exposure to DMDS. 

 Based on the proposed use pattern, exposure to DMDS by the general public is not 

expected to occur via dietary exposure since the proposed uses of DMDS are classified as nonfood uses and DMDS is unlikely to contaminate drinking water. However, DMDS is a soil 

fumigant and post-application inhalation exposure to the general population can occur as a result 

of the proposed uses. This inhalation exposure may not be limited to occupational workers, but 

may occur for bystanders located in proximity to treated fields. 

 Based on the exposure pattern, an extensive analysis of residential bystander inhalation 

exposure has been performed as part of the DMDS risk assessment. This analysis takes into 

account individuals who may live directly next to a field treated with DMDS. Inputs used in the 

assessment were chosen to assure that the inhalation component of the aggregate exposure 

assessment will be protective of all potential exposed populations, including populations 

specifically targeted for possible environmental justice concerns such as low income residents 

and minorities. Risk assessment endpoints were selected considering the potential susceptibility 

of infants, children, and pregnant women to assure protection of these populations. Since (a) 

inhalation risks will drive this assessment and will be protective of all populations, (b) food and 

drinking water exposure will not occur, and (c) no additional unique exposures are anticipated 

for this chemical, the aggregate DMDS assessment will be protective of potential exposures and 

risks to all populations. 

 Potential inhalation exposures and risk to occupational handlers, to occupational reentry 

workers who could be exposed when entering DMDS treated areas to perform crop-production 

tasks, and to occupational bystanders who could be exposed when performing crop-production 

tasks (but not inside) DMDS treated areas were assessed. Based on the volatility of DMDS, 

4
dermal exposure is not expected due to the delivery systems used (e.g., soil injection or drip 

irrigation) and emission reduction technologies (e.g., tarping). The physiochemical properties of 

DMDS also make significant dermal exposure unlikely and quantifying any potential low level 

exposures very difficult. Therefore, a quantitative dermal exposure assessment has not been 

conducted. However, the Agency is requiring that handlers who may come in contact with 

DMDS liquid must wear personal protective equipment (PPE) due to the potential for severe 

irritation of DMDS to skin. Risks from acute inhalation occupational exposures to DMDS were 

estimated. 

 When conducting inhalation risk assessments, the magnitude of the uncertainty factor 

(UF) applied is dependent on the methodology used to calculate risk. For studies in the DMDS 

risk assessment with inhalation animal data, UFs are based on the reference concentration (RfC) 

methodology developed by the EPA’s Office of Research and Development (ORD) for the 

derivation of inhalation RfCs and human equivalent concentrations (HECs) for use in margin of 

exposure (MOE) calculations. Since the RfC methodology takes into consideration the 

pharmacokinetic (PK) differences but not the pharmacodynamic (PD) differences, the UF for 

interspecies extrapolation may be reduced to 3X (to account for the PD differences) while the UF 

for intraspecies variation is retained at 10X. Thus, the UF when using the RfC methodology is 

customarily 30X. 

A. Acute and Chronic Dietary Exposure and Risk 

 DMDS field trials on strawberry, tomato, carrot and radish conducted in CA, FL and WI 

were submitted to the Agency. Soil was treated at 790 lb DMDS per acre (almost 2x the 

currently proposed maximum label application rate of 455 lbs DMDS per acre) by raised bed 

shank injection at a 6-inch depth and the soil was immediately covered with a polyethylene tarp. 

Strawberry and tomato transplants were planted through the barrier and seed of carrot and radish 

were planted after removing the barrier. The strawberry, tomato and carrot data are supported by 

adequate concurrent recovery data at 0.01 ppm. Residues of DMDS were less than 0.01 ppm 

(the limit of detection) in strawberries, tomatoes and carrots. Residues were found in both the 

treated (0.11-0.24 ppm) and untreated (0.09-0.24 ppm) radish plots. The DMDS residues found 

in radishes are supported by studies in the scientific literature that show that many Raphanus and 

Brassica species are known to naturally produce volatile sulfur compounds, including DMDS. It 

should be noted that Raphanus and Brassica are not in the proposed use pattern. 

 Given the available crop field trial data and the results of the aerobic soil metabolism 

study; the uses on the proposed DMDS labels (strawberries, blueberries, fruiting vegetables, 

cucurbits, and ornamentals) are considered nonfood uses. Therefore, acute and chronic dietary 

risk assessments are not necessary. A qualitative DMDS drinking water assessment was 

performed for this risk assessment. DMDS may transport to nearby surface water through runoff 

and erosion, especially if an application of DMDS coincides with, or is closely followed by a 

rain event after tarp removal. However, rapid volatilization of DMDS from surface water is 

expected to be an important route of dissipation. Based on environmental fate data and modeling 

estimates the Agency does not expect the pesticidal uses of DMDS to adversely impact ground 

water or surface water. 

5
B. Occupational and Non-Occupational Risk 

 Fields treated areas of DMDS are covered with a tarp for 12 days to prevent 

volatilization; however, DMDS, like the other soil fumigants, has the potential to move off-site 

through ambient air following field applications. Off-site movement of DMDS could result in 

exposure to bystanders near treated areas and to people far away from treated areas through 

ambient air. Exposure to DMDS may also occur to those handling the pesticide or working in 

treated fields. Acute inhalation exposures to bystanders and workers appear to present the 

greatest risk concern. 

1. Toxicity Profile 

 DMDS has a robust inhalation toxicity database with studies varying from acute to repeat 

exposure studies. Port-of-entry irritation, nasal irritation, is the most sensitive endpoint for 

DMDS. Systemic toxicity was only observed at higher concentrations in the form of decreased 

food consumption and body weights. Irritation typically increased in severity and progressed 

deeper in the nose with increasing concentrations. Repeat inhalation studies suggest nasal 

irritation is driven by concentration since lower LOAELs were not observed in repeat exposure 

studies. The concentration at which nasal irritation occurs is similar for a single exposure as for 

longer-term exposures. The acute inhalation port-of-entry NOAEL is therefore appropriate for 

longer-term scenarios. 

 Individuals may smell DMDS before nasal irritation is identified. The pungent odor of 

DMDS is described as rotting or decaying matter or as garlic. The odor threshold of DMDS is 

reported to be orders of magnitude below the level that nasal irritation is identified. The strong 

odor of DMDS may therefore “warn” individuals of the presence of the compound in the area. 

 DMDS did not produce developmental or reproductive toxicity via the inhalation route 

below maternally toxic concentrations in the rat or rabbit studies. 

 Although DMDS is highly volatile, a specially designed 28-day repeat dermal rabbit 

study is available that indicates repeat dermal exposure to DMDS is severely irritating and may 

cause severe systemic toxicity including death (secondary to dermal irritation). It is noted, 

however, that this study was designed to keep DMDS on the skin instead of volatizing as would 

typically occur. Severe irritation in the form of erythema, edema, and ischemic necrosis was 

observed at the lowest concentration tested beginning on the second day of application. 

Although studies indicate that DMDS is a toxicity category III for skin, severe irritation was also 

observed in the acute dermal rabbit study (cracking/thickening/sloughing of the skin on Day 7 

until Day 14). Therefore, DMDS should be handled with extreme care since any dermal 

exposure will likely lead to severe irritation and toxicity. The Agency is requiring that handlers 

who may come in contact with DMDS liquid must wear personal protective equipment (PPE) 

due to the potential for severe irritation of DMDS to skin. 

 There is neither a pharmacokinetic nor a metabolism study available for DMDS and the 

metabolic pathway has not been determined. The insecticidal mode of action acts through the 

dysfunction of mitochondria. The mammalian mode of action or metabolic pathway has not 

6
been determined. Based on the lack of systemic toxicity in any of the DMDS toxicity studies, a 

rat metabolism study would not provide significant information for risk assessment. 

 The odor of DMDS has been described in the literature as pungent garlic, propane, 

decaying fish, or decomposing materials. A literature review conducted by the registrant 

suggests that the mean odor threshold for DMDS is 7 to 12 ppb (0.007 – 0.012 ppm), which is 

approximately three orders of magnitude below the concentration at which nasal irritation is 

observed in rodent inhalation studies. This suggests that individuals near a treated field are 

likely to detect the odor of DMDS before it reaches a concentration at which it would begin to 

produce nasal irritation. However, the time required for a person to detect the odor and the 

variability and aversion to the odor among various individuals is not currently known for DMDS. 

2. Inhalation Endpoints 

 

 Acute inhalation exposures to bystanders and workers appear to present the greatest risk 

concern. This is due to the concentration of the chemical as it moves off or drifts from the field. 

Public health data for other fumigant chemicals suggest that bystander exposure results mainly 

from this drift. Port-of-entry irritation in the form of nasal degeneration is the most sensitive 

effect and therefore is appropriate for use in the DMDS risk assessment. As with the other 

hazard assessments for fumigant chemicals, this hazard assessment applied the Reference 

Concentration (RfC) methodology to the DMDS hazard assessment. The endpoints for the 

inhalation scenarios used in the risk assessment and the relevant calculations using EPA’s RfC 

methodology for the acute, short-, and intermediate-term scenarios are discussed below. 

 Based on current DMDS labels, the Agency believes exposures can be acute (less than 24 

hours), short-term (1-30 days), and/or intermediate-term (1 month-6 months) in duration. Longterm exposure is not anticipated for DMDS based on proposed labeled uses. 

 Based on the specific toxicity profile of DMDS, the 24-hour acute inhalation rat study 

was selected for estimating inhalation risk for all durations of exposure. The port-of-entry 

NOAEL (No observable adverse effect level) is 9 ppm. The port-of-entry LOAEL (lowest 

observable adverse effect level) of 12.5 ppm was based on the incidence of microscopic lesions 

of the nasal tissues, the incidence of degeneration in multiple nasal levels and inflammation of 

the olfactory and respiratory epithelia. Since nasal irritation is dependent upon concentration and 

not duration of exposure, a single HEC is appropriate for all durations and both occupational and 

non-occupational scenarios. 

 Based on the use of the inhalation reference concentration (RfC) methodology, the acute, 

short- and intermediate-term non-occupational and occupational human equivalent concentration 

(HEC) is 1.65 ppm. EPA’s RfC methodology incorporates some pharmacokinetic differences 

between rats and humans; therefore the interspecies extrapolation factor is reduced to 3x. The 

EPA uses a 10x factor to account for intraspecies variability. Therefore, a margin of exposure 

(MOE) of 30 defines the Agency’s level of concern (LOC). 

7
 Dermal irritation was observed in rat and rabbit irritation studies with severity of 

irritation varying based on length of exposure. However, the Agency does not anticipate dermal 

exposure resulting from typical use of DMDS. This is due the enclosed systems that are required 

to keep DMDS as a liquid. As a result, the Agency did not conduct a quantitative dermal risk 

assessment at the present time. It should be noted, however, that there is potential for severe 

irritation if DMDS does come into contact with the skin. Therefore, the Agency is requiring that 

handlers who may come in contact with DMDS liquid must wear personal protective equipment 

(PPE) due to the potential for severe irritation of DMDS to skin. 

 The methods and dosimetry equations described in the Agency’s reference concentration 

(RfC) guidance were used to convert the inhalation NOAEL and LOAEL (endpoint values 

determined via tests on rats) to human equivalent concentrations (HECs) for use in margin of 

exposure (MOE) analyses. The RfC guidance addresses properties of gases and particles, 

properties of reactive and non-reactive compounds, and differences in the structure of the 

respiratory tract between laboratory animals and humans, as well as using dosimetry equations, 

to calculate the HECs. It was only necessary to calculate the HEC for port-of-entry effects; a 

second HEC is not needed for systemic effects. The HEC also did not require time adjustments 

because it takes only a brief threshold concentration to cause nasal irritation and longer 

exposures do not increase the severity of the irritation. The only type of port-of-entry effect for 

which it was necessary to calculate a HEC was an extrathoracic one. The value calculated was 

1.65 ppm (6.36.mg/m3

). 

A summary of the endpoints used to estimate risk from inhalation exposure to DMDS is 

presented in Table 3 below. 

 

Table 3. Summary of Toxicological Dose and Endpoints for Use in DMDS Human Health 

Inhalation Risk Assessment

Risk Assessment Study NOAEL/LOAEL Endpoint 

Human 

Equivalent 

Concentrations 

(HEC) 

Nonoccupational 24 hr Inhalation NOAEL= 9 ppm 

LOAEL = 12.5 ppm 

Inflammation & Nasal 

irritation in all 6 levels in 

male rats 

HEC = 1.65 ppm 

UF = 30 

Acute 

Inhalation 

Occupational 24 hr Inhalation NOAEL= 9 ppm 

LOAEL = 12.5 ppm 

Inflammation & Nasal 

irritation in all 6 levels in 

male rats 

HEC = 1.65 ppm 

UF = 30 

Nonoccupational 24 hr Inhalation NOAEL= 9 ppm 

LOAEL = 12.5 ppm 

Inflammation & Nasal 

irritation in all 6 levels in 

male rats 

HEC = 1.65 ppm 

UF = 30 

Short- and 

IntermediateTerm 

Inhalation 

(1-6 months) Occupational 24 hr Inhalation NOAEL= 9 ppm 

LOAEL = 12.5 ppm 

Inflammation & Nasal 

irritation in all 6 levels in 

male rats 

HEC = 1.65 ppm 

UF = 30 

Long-term 

Inhalation 

(> 6 months) 

Use pattern does not apply to long-term exposure 

Cancer Not required. 

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3. Occupational Risk 

 Occupational handler and post-application exposure is expected via the inhalation route 

of exposure. Potential inhalation exposure and risk to occupational handlers, to occupational 

reentry workers who could be exposed when entering DMDS treated areas to perform cropproduction tasks, and to occupational bystanders who could be exposed when performing cropproduction tasks (but not inside) DMDS treated areas were assessed. Based on the volatility of 

DMDS, dermal exposure is not expected due to the delivery systems used (e.g., soil injection or 

drip irrigation) and emission reduction technologies (e.g., tarping). The physiochemical 

properties of DMDS also make significant dermal exposure unlikely and quantifying any 

potential low level exposures very difficult. Therefore, a quantitative dermal exposure 

assessment has not been completed. 

 Risks to occupational handlers (for soil fumigations), including tractor drivers, co-pilots, 

shovelers, soil sealers, tarp punchers and tarp removers, involved in preplant field fumigation 

were evaluated using DMDS-specific handler monitoring data. Acute inhalation risks to 

handlers exceed the Agency’s level of concern (MOE < 30) for many of the sample points at the 

baseline level (no respirator). However, with the addition of an organic vapor respirator 

(assumed to have a protection factor of 10), most of the handler risks do not exceed the Agency’s 

level of concern. Short- and intermediate-term risks to handlers also exceed the Agency’s level 

of concern (MOE < 30) for many occupational activities at the baseline level (no respirator). 

However, with the addition of a PF 10 respirator, all of the short- and intermediate handler risks 

do not exceed the Agency’s level of concern. 

4. Non-occupational Exposure Assessment 

 Releases of fumigants, such as DMDS, can be categorized in two distinct manners 

including bystander exposures from single application sites (i.e., treated farm fields) such as area 

sources (hereon discussed as near field sources) and by ambient air monitoring data where 

residues could result from many applications within a region (hereon discussed as ambient 

sources). Risks from near field sources were evaluated using monitoring data and modeling 

techniques. Risks from ambient air were evaluated using surrogate methyl bromide monitoring 

data from California. 

 Eight field volatility studies that quantified DMDS emissions from treated fields were 

used to assess bystander exposure to DMDS resulting from single application sites (e.g., area 

sources such as farm fields). These data indicate the potential for risks of concern associated 

with DMDS use. These data are limited in their utility because they provide results only for the 

specific conditions under which the experiment was conducted. Therefore, an air modeling 

system was used for risk assessment purposes to develop a better understanding of the potential 

for risks associated with DMDS use under varied meteorological conditions. 

 The Agency utilized the Probabilistic Exposure and Risk Model for FUMigants 

(PERFUM) to assess DMDS bystander exposures and risks. PERFUM was developed in 

response to the Agency’s use of the EPA's Industrial Source Complex: Short-Term Model 

(ISCST3) which was first used to develop risk estimates for bystanders associated with DMDS 

9
uses (http://www.epa.gov/scram001/dispersion_alt.htm). DMDS PERFUM analyses were 

performed for 1, 5, 10, 20, and 40 acre fields (proposed DMDS labels restrict application to 40 

acres per day) using 100%, 90%, 80%, 70%, 60%, and 50% of the maximum proposed label 

application rate. 

 The Agency utilized all eight available field volatility studies in the PERFUM analyses 

even though use of Virtually Impermeable Film (VIF or high barrier) tarps are required on the 

label (only two of the eight volatility studies used high barrier tarps). No emissions data are 

available to reflect the use of high barrier tarps for the broadcast shank injection and raised bed 

drip irrigation application scenarios. The raised bed shank injection high barrier studies were 

used as surrogates where the Agency deemed it appropriate and applicable (e.g., the raised bed 

drip irrigation application scenario). The Agency does not recommend use of the raised bed 

shank injection high barrier studies as surrogates for the broadcast shank injection application 

scenario. In that case the broadcast shank injection emission study using LDPE should be used 

to estimate buffer distances until a broadcast shank injection emissions study using high barrier 

tarps is performed. 

 PERFUM results are presented in the appendices to the document entitled “HumanHealth Risk Assessment, Dimethyl Disulfide, March 10, 2010.” 

 With regard to potential multiple sources of exposure from ambient air, no direct ambient 

air monitoring data are available for DMDS. Although there are industrial and commercial uses 

of DMDS, it is not routinely screened for in ambient air by CARB (California Air Resources 

Board) or similar organizations. In order to qualitatively characterize the potential for exposure 

to DMDS in ambient air, the DMDS inhalation toxicity endpoints were compared to the ambient 

air levels that were quantified for methyl bromide which is a highly used and highly volatile 

fumigant. In all cases, this comparison resulted in risks that do not exceed the Agency’s level of 

concern for DMDS (MOEs > 30). This comparison should be considered conservative in nature 

because there is less potential for exposure with DMDS than with methyl bromide because of the 

environmental fate characteristics of DMDS relative to methyl bromide (i.e., DMDS is not as 

volatile as methyl bromide, DMDS dissipates/degrades faster in the environment than methyl 

bromide). 

C. Residential Risk 

 There are no proposed residential uses for DMDS so a residential exposure/risk 

assessment was not needed. Residential exposures resulting from off-site movement of DMDS 

after field applications are covered by the non-occupational (bystander) exposure/risk 

assessment. 

 

 

10
V. ENVIRONMENTAL RISK ASSESSMENT 

 A summary of the environmental risk assessment titled “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,” dated April 20, 2010, is provided below. 

DMDS is a reduced organosulfur compound that is applied as a pre-plant soil fumigant to 

various field and nursery crops using drip irrigation and shank injection and covered with a tarp. 

Given its high vapor pressure and solubility, physical chemical properties, volatilization 

followed by leaching are expected to be the main dissipation pathways for DMDS. No spray 

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

the soil. No runoff is expected for the first 12 days, as the field is covered with a tarp; however, 

runoff is possible after 12 days when the tarp is cut. Although there is potential for runoff, it is 

not anticipated to be of significant concern. 

A. Environmental Fate 

DMDS is a soil fumigant that is applied using drip irrigation and shank injection and 

covered with a tarp. The major route of environmental exposure is expected to occur through 

volatilization. However, runoff into surface water, and leaching into groundwater may be 

possible after the tarp is removed, given the high mobility of DMDS. DMDS gradually degrades 

to methanesulfonic acid and carbon dioxide in soil as well as methanesulfonic acid, 

methanesulfinic acid, and sulfuric acid in water through photodegradation. DMDS is not 

anticipated to bioaccumulate in fish due to the low potential for significant runoff. 

1. Soil 

Studies suggest that DMDS residues 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. An aerobic soil metabolism study indicated that the half life of 

DMDS in the soil is 2.86 to 3.74 days. The acid breakdown products of DMDS give it the 

potential to acidify soil, especially on soils with low buffering capacities and low free carbonate 

content. 

2. Water 

The high solubility of DMDS in water (2,702 mg/l), and low average Kd 0.641 mL/g 

suggest that residues are readily transported by water and weakly retained by soil. DMDS is 

moderately persistent with a half life of 9.32 days and is stable to hydrolysis at pHs of 4, 7, and 9 

at 50°C. The high Henry’s Law Constant and rapid photodegradation in water suggest that 

volatilization and photolysis are the primary environmental routes of dissipation from surface 

water. 

11
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 explicitly modeled in the PRZM model. Therefore, aquatic exposure estimated 

concentrations in the water column are solely based on the tarp removed with an adjusted 

loading of DMDS, which accounts for biodegradation of residues under the tarp after the 

required 12 days. However, it is possible that there can be seepage under the tarps, but this is 

not anticipated to contribute in large enough quantities to affect 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. 

Since DMDS is highly soluble and mobile, leaching and potential groundwater 

contamination is possible. Cases of groundwater contamination may occur in areas over and 

around aquifers where water tables may be shallow and recharging of groundwater is possible. 

However, based on environmental fate data and modeling estimates the Agency does not expect 

the pesticidal uses of DMDS to adversely impact groundwater. 

3. Air 

Given its high volatility, there is the potential for high concentrations of DMDS in the air 

from field applications. A field volatility study conducted in Tifton, GA suggests that DMDS air 

concentrations can be attenuated by the application of VIF tarps as some fields used standard 

polyethylene tarps and others used VIF tarps. However, there is uncertainty associated with 

application methods other than raised bed shank injection, including variations in application 

timing and geographic location. However, stratospheric ozone depletion and climate change 

impacts are not expected based on the low persistence of DMDS in the atmosphere and the fact 

that DMDS does not contain halogenated molecular components. Given that DMDS is a highly 

reactive organosulfur Volatile Organic Compound (VOC), DMDS may contribute to groundlevel ozone production and acid rain where it is used in a high volume. 

B. Ecological Risk 

Ecological risk characterization integrates the results of the exposure and ecotoxicity data 

to evaluate the likelihood of adverse ecological effects. The means of integrating the results of 

exposure and ecotoxicity data is called the quotient method. For this method, risk quotients 

(RQs) are calculated by dividing exposure estimates by ecotoxicity values, both acute and 

chronic (RQ = Exposure/Toxicity). RQs are then compared to EPA’s levels of concern (LOCs). 

The LOCs are criteria used by the Agency to indicate potential risk to nontarget organisms. The 

criteria indicate that a pesticide, when used as directed, has the potential to cause adverse effects 

to nontarget organisms. 

12
The ecotoxicity endpoints derived from the results of short-term laboratory studies that 

assess acute effects are: (1) LC50 (fish and birds); (2) LD50 (birds and mammals); (3)EC50 

(aquatic plants and aquatic invertebrates); (4) EC25 (terrestrial plants). Typically, the endpoints 

derived from the results of long-term laboratory studies that assess chronic effects are the 

NOAEL and LOAEL for birds and mammals and no observed adverse effect concentration 

(NOAEC) and the lowest observed adverse effect concentration (LOAEC) for fish and aquatic 

invertebrates. However, in the case of DMDS, no chronic modeling was performed because of 

the absence of chronic toxicity data. Risk presumptions along with corresponding RQs and 

LOCs are shown in Table 4 below. 

Table 4. Risk Presumptions for Non-target Organisms 

Risk Presumption RQ LOC 

Terrestrial Animals

 Acute High Risk EEC*/LC50 or LD50/sqft2 or LD50/day ≥0.5 

 Acute Restricted Use EEC/LC50 or LD50/sqft2 or LD50/day (or LD50 < 50 mg/kg) ≥0.2 

 Acute Endangered Species EEC/LC50 or LD50/sqft2 or LD50/day ≥0.1 

 Chronic Risk EEC/NOAEL ≥1 

Aquatic Animals 

 Acute High Risk EEC/LC50 or EC50 ≥0.5 

 Acute Restricted Use EEC/LC50 or EC50 ≥0.1 

 Acute Endangered Species EEC/LC50 or EC50 ≥0.05 

 Chronic Risk EEC/NOAEC ≥1 

Terrestrial and Semi-Aquatic Plants 

 Acute High Risk EEC/EC25 ≥1 

 Acute Endangered Species EEC/EC50 or NOAEC ≥1 

Aquatic Plants 

 Acute High Risk EEC/EC50 ≥1 

 Acute Endangered Species EEC/EC50 or NOAEC ≥1 

*Estimated Exposure Concentration (EEC) 

 Calculated risk quotients represent a screening level assessment. Screening level 

assessments are based on conservative assumptions. For example, screening level assessments 

assume maximum labeled application rate, the maximum number of applications, and the 

shortest treatment interval between applications. 

13
Aquatic Animals and Plants

 

1. Fish and Aquatic Invertebrates

The acute RQs for the active ingredient DMDS range from 0.0 to 0.21 for drip irrigation 

application method, and LOCs for endangered species are slightly exceeded for applications to 

FL cucumber, FL strawberry and GA onion uses. All other drip irrigation applications do not 

exceed the Agency’s level of concern. For the shank injection application method, the acute 

RQs are less than 0.01 for the shank injection application method, and therefore do not exceed 

the Agency’s level of concern. Chronic RQs were not estimated because no chronic toxicity 

studies are available. 

2. Aquatic Vascular and Non-Vascular Plants

For aquatic vascular and non-vascular plants, the acute RQs for non-listed species are <1 

for the drip irrigation method and shank injection application methods. RQs for non-listed 

species are estimated for vascular plants (Lemna) and nonvascular plants (Anabaena) using the 

EC50. 

RQs are estimated for listed species using the EC05 toxicity value. RQs ranged from 0 to 

18 and exceeded the LOC for drip irrigation application method 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. For nonvascular plants, no RQs exceeded the LOC for any 

uses when shank injection application method was modeled. 

Terrestrial Animals and Plants

1. Mammals and Birds 

Risk quotients for air exposure to mammal and avian species are calculated based on the 

upper-bound PERFUM estimated exposure concentration (EEC) in air determined at 720 μg/m3

for an 80 acre field, based on the combination of field flux data and meteorological data. The 

field volatility study was conducted using the raised bed shank injection application method with 

VIF tarps. Along with the EEC in air, the risk quotients were calculated using the toxicity. The 

RQ for mammals is 0.01 and the RQ for birds is <0.01. Acute risks are not exceeded for either 

mammals or birds and therefore, are not of concern. 

 

2. Terrestrial Invertebrates 

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 are represented by the honeybee 

estimate. 

14
3. Terrestrial Plants 

Risk to terrestrial plants is expected from exposure to air concentrations. The Agency 

was unable to estimate air exposure to plants given information gaps in the submitted vegetative 

vigor study. Risk quotients to plant species off of the treated field 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. Since DMDS has the 

potential for phytotoxicity to plants, the Agency is presuming risk until further information 

regarding the vegetative vigor study is submitted and the assessment is completed. 

 

15
VI. PROPOSED REGULATORY DECISION 

 During February 2007 the Agency received from Arkema, Inc., applications for the 

registration of three products--Paladin Technical, Paladin, and Paladin EC--containing the new 

active ingredient DMDS. The end-use products Paladin and Paladin EC had proposed labeling 

for pre-plant treatment of fields in which vegetable crops, fruit crops, floral crops, nursery crops, 

and forest nursery crops were to be grown. The post-application sites were later specified as 

fruiting vegetable (tomato, pepper, and eggplant) crops, cucurbit vegetable (cucumber, squash, 

and melon) crops, berry (strawberry and blueberry) crops, ornamental (field grown) crops, and 

forest nursery crops. Pests controlled are weeds such as nutsedge (purple and yellow), 

chickweed, lambsquarters, purslane, and grasses; soil-borne plant pathogens such as Verticillium

spp., Fusarium spp., Pythium spp., Sclerotinia spp., and Rhizoctonia spp.; and nematodes such as 

Root Knot (Southern, Northern, and Colombian), Stubby Root, Lesion, Stunt, and Sting. The 

application techniques specified on the Paladin label are raised-bed and broadcast shank 

injection. The application technique specified by the Paladin EC label is raised-bed drip 

irrigation. 

 The registrant has claimed that DMDS is a replacement for methyl bromide, a fumigant 

with numerous registered uses. Because of its negative impact on atmospheric ozone, methyl 

bromide has been the subject of a worldwide phase-out effort that is administered by a United 

Nations committee, pursuant to the “Montreal Protocol on Substances that Deplete the Ozone 

Layer.” It would therefore be likely that registration of DMDS as another soil fumigation 

alternative to methyl bromide would be in the public interest. 

 

 The Agency is proposing to conditionally register the Paladin Technical product for use 

in formulating the two end-use DMDS products. Also, the Agency is proposing to conditionally 

register the Paladin and Paladin EC end-use products for pre-plant treatment of the soil in fields 

in which fruiting vegetable (tomato, pepper, and eggplant), cucurbit vegetable (cucumber, 

squash, and melon), berry (strawberry and blueberry), ornamental (field grown), and forest 

nursery crops will be grown. Given the available crop field trial data and the results of the 

aerobic soil metabolism study, the Agency agrees that the uses on the proposed DMDS labels 

should be considered nonfood uses and tolerances are not required. However, additional field 

trial data may be required in the future if DMDS registrations for uses on other crops are 

requested. 

 As required by FIFRA, the Agency published a Notice of Receipt of applications to 

register pesticide products containing the new active ingredient, DMDS. It was published in the 

Federal Register on May 1, 2009. No comments were received in response to this Federal 

Register Notice. Because the applications did not require the establishment of a tolerance(s) no 

notice of filing was published. 

16
Human Health Assessment 

The human health risk assessment concluded that the databases are adequate for dietary, 

non-occupational (bystander), and occupational exposures to support a conditional registration 

for the proposed uses and application rates for the DMDS end-use products Paladin and Paladin 

EC. 

Data Needs 

Toxicology

For the proposed use patterns, the Agency would typically require an immunotoxicity 

study - rat (new requirement) and a mutagenicity study (initial study was judged to be 

unacceptable) to satisfy Part 158 Guidelines. However, the Agency has determined that these 

two studies would not contribute quantitatively to the DMDS hazard database or risk assessment 

based on: 1) the lack of target organ and any systemic toxicity observed in the rodent inhalation 

database; 2) the negative mutagenicity studies currently available; and 3) the most sensitive 

endpoint in the inhalation risk assessment is nasal irritation. Therefore, the Agency is waiving 

these two study requirements for DMDS. 

 

Occupational and Residential Exposure

The studies listed below are required for the registration of DMDS. The Agency 

conducted the risk assessment assuming that polyethylene tarps would be used during 

application, as no emissions data are available to reflect the use of high-barrier tarps for the 

broadcast shank injection and raised bed drip irrigation application scenarios. The current risk 

assessment is considered conservative and EPA believes that use of polyethylene tarps represents 

a worst-case scenario. However, the proposed labels require use the of high-barrier tarps. When 

these studies are submitted, these data will allow the Agency to better refine the exposure 

potential of DMDS under the conditions required on the label. 

• Field Volatility from Soil (Guideline Number (GLN) 835.8100) (for broadcast shank, 

raised-bed shank, and raised-bed drip irrigation applications; to determine flux from 

treated fields when high barrier tarp is used). 

• Estimation of Inhalation Exposure, Outdoor Sites (GLN 835.1300) (occupational 

inhalation exposure for all three types of applications when high barrier tarp is used). 

Restricted Use Product Status 

 The Agency is designating products that contain DMDS as Restricted Use Products 

(RUPs)—products that must be applied by a certified applicator. If a fumigant is not applied 

correctly, bystanders may be exposed to concentrations that exceed levels of concern and which 

could result in adverse effects. The application of DMDS, like most other fumigants, requires 

specialized training or experience to perform properly, both in its application to the treated areas 

and in the subsequent covering of the treated areas with plastic tarp for 12 days, so as to 

minimize the release of this fumigant into the atmosphere. Specialized equipment is also often 

17
needed to apply soil fumigant safely and accurately (e.g., tarp equipment; self-contained 

breathing apparatus). Therefore, the Agency feels that DMDS meets the standard for restricted 

use designation because: 

 • The application of this fumigant involves complex operations requiring specialized 

 training and/or experience; 

 • Fumigant label directions call for specialized apparatus and protective equipment that is 

 not available to the general public; and 

 • A minor failure to follow label directions may result in adverse effects. 

Labeling Requirements 

Buffer Zones

The human health risk assessment indicates that bystanders may be exposed to DMDS air 

concentrations following application to fields. In general, the risk from inhalation exposures 

decreases as the distance from the field where bystanders are located increases. Because of this 

relationship, the Agency has determined that a buffer zone must be established around the 

perimeter of each application block where DMDS is applied. The Agency acknowledges that 

buffer zones alone will not mitigate all risks or eliminate incidents caused by equipment failure, 

human error, adverse weather (e.g., temperature inversions), or other events. The Agency 

however does believe that buffer zones along with other mitigation measures required by this 

decision described below will mitigate risks so that bystanders will not experience unreasonable 

adverse effects. 

For DMDS, the Agency determined the percentiles and MOEs that were used for 

selecting buffer zones for the various application methods. For all application methods on the 

proposed DMDS product labels, buffer zones are based on the 75th percentile and an MOE of 20. 

The resulting buffer zones can be viewed in Table 5, and 6, below. The Agency believes that the 

resulting buffer zones are protective of human health based on the warning properties provided 

to exposed people by the pungent odor of DMDS which is detectable at concentrations that are 

orders of magnitude below the toxicological point of departure. They are also health protective 

because the buffer zones are based on a toxicological endpoint effect of nasal irritation and not 

more severe systemic effects. 

18
Table 5. Buffer Zone Distance Table for Raised Bed, Chemigation Applications 

(buffers in feet) 

Application Block Size (acres) 

Broadcast equivalent 

Application Rate lbs/A 

(gal/A) 

1 5 10 15 20 25 30 35 40 

112 (12.6) 25 25 25 25 25 25 25 25 30 

118 (13.3) 25 25 25 25 25 25 25 35 45 

121 (13.6) 25 25 25 25 25 25 25 35 50 

130 (14.7) 25 25 25 25 25 30 35 55 70 

133 (15.0) 25 25 25 25 25 35 45 60 75 

136 (15.3) 25 25 25 25 25 35 45 65 80 

140 (15.8) 25 25 25 25 25 40 55 70 85 

143 (16.2) 25 25 25 25 25 45 60 75 90 

146 (16.5) 25 25 25 25 30 50 65 80 95 

152 (17.2) 25 25 25 25 40 60 75 90 105 

155 (17.5) 25 25 25 25 45 70 80 95 110 

162 (18.3) 25 25 25 30 55 75 90 105 120 

170 (19.2) 25 25 25 35 60 80 95 115 130 

180 (20.3) 25 25 25 40 70 90 105 125 140 

186 (21.0) 25 25 25 50 75 95 115 135 150 

190 (21.4) 25 25 30 55 80 100 120 140 155 

200 (22.5) 25 25 35 60 90 110 130 150 170 

205 (23.1) 25 25 35 65 95 115 135 155 175 

209 (23.6) 25 25 40 65 95 115 135 155 175 

212 (23.9) 25 25 40 70 100 120 140 160 180 

219 (24.7) 25 25 45 75 105 125 145 165 185 

228 (25.7) 25 25 50 80 110 135 155 175 195 

238 (26.8) 25 25 60 90 115 140 160 185 205 

249 (28.1) 25 25 65 95 120 145 165 190 210 

251 (28.3) 25 25 65 95 125 150 170 195 215 

260 (29.3) 25 25 70 100 130 155 180 200 220 

273 (30.8) 25 25 75 105 135 160 185 210 230 

282 (31.8) 25 25 75 110 140 165 190 215 240 

285 (32.2) 25 25 80 110 140 165 190 215 240 

288 (32.5) 25 25 75 105 135 160 185 210 230 

297 (33.6) 25 25 75 110 140 165 190 215 240 

300 (34.0) 25 25 80 110 140 165 190 215 240 

 Note: Minimum allowable buffer zone is 25 feet 

19
Table 6. Buffer Zone Distance For Broadcast/Flat Fume Shank Injected Applications 

(buffers in feet) 

Application Block Size (acres) 

Broadcast Application 

Rate lbs/A (gal/A) 1 5 10 15 20 25 30 35 40 

199 (22.4) 25 95 170 225 275 315 355 395 430 

230 (25.9) 25 110 175 240 300 345 390 435 475 

240 (27.1) 25 115 195 255 315 360 405 450 490 

266 (30.1) 25 125 215 280 340 385 430 475 520 

290 (32.7) 25 140 230 295 360 410 455 505 550 

304 (34.3) 25 145 240 305 370 420 470 520 565 

342 (38.6) 30 160 260 330 400 455 505 555 605 

380 (42.9) 40 170 275 345 415 470 525 580 635 

418 (47.2) 50 180 290 365 435 495 550 610 665 

455 (51.3) 55 190 305 380 455 515 575 635 690 

 Note: Minimum allowable buffer zone is 25 feet 

Respirators

All handlers are required to wear a half face or full face air-purifying respirator with a 

pesticide-approved organic vapor cartridge filter or equivalent (NIOSH approved number prefix 

TC-23C). These respirators must be worn if the garlic-like odor of this product can be detected. 

Any handlers not wearing respirators must cease operations and leave the application block and 

surrounding buffer zone. After one hour and at hourly intervals thereafter, handlers can remove 

their air-purifying respirators momentarily to determine if the garlic-like odor is still detectable. 

If detectable, the respirator must be put back on. 

In addition, tractor drivers and tractor co-pilots in enclosed cabs can use a tractor 

equipped with a working-area air-fan dilution system consisting of a ducted fan/blower which 

provides air flow to the breathing zone of the tractor driver and co-pilot in lieu of an airpurifying respirator. The fan/blower must be mounted so that the fan/blower intake is at least 

126 inches from the ground, and the fan/blower must be capable of operating at a minimum of 

1,600 revolutions per minute and producing a minimum flow rate of 3,000 cubic feet of air per 

minute. 

Incident Data 

Experimental Use Permit (EUP) Applications

An incident occurreed in Tifton, GA after an application of DMDS to a field 

approximately 1 acre in size. The field was treated with DMDS at an application rate of 600 lbs 

ai/treated acre and a standard polyethylene tarp was used to cover the raised beds. This is in 

accordance with the EUP label directions for using shank injection equipment. The application 

occurred on February 7th and two days later on February 9th, several residents of a local 

community notified the local police and fire department of an odor in their community. Several 

20
residents also complained of headaches. The local police and fire department did not detect an 

odor in the community but did detect an odor at the treated field. No residents were treated for 

any symptoms but several residents were temporarily relocated. It was noted that a low level 

atmospheric inversion occurred on February 8th and persisted for two days. This likely prevented 

typical dispersion of DMDS vapors. 

An incident occurred in Floral City, FL after two applications of DMDS to fields 

approximately 7.5 and 2.5 acres in size. Both fields were treated with DMDS at an application 

rate in accordance with the EUP label using shank injection equipment and polyethylene tarps. 

The applications occurred on September 8th and 9th. On September 9th the farm manager was 

contacted by the local police department regarding a potential propane leak (DMDS has a 

propane/garlic like odor). A drip application field trial of 0.25 acres using DMDS was 

performed on September 13th on the same farm. On September 17th the farm manager was 

contacted via email by a local resident regarding an “awful odor” that occurred in the mornings 

and evenings over the previous week or two. The email mentioned that several local residents 

had become ill during the time that the odor existed. The farm manager visited the resident who 

emailed him on September 17th to provide details of the EUP and the application of DMDS. At 

this time, the farm manager was not made aware of any medical issues that the resident was 

experiencing as a result of potential exposure to DMDS. The farm manager also talked to 

several neighbors living in the vicinity of the emailing resident, none of whom noticed the odor 

referenced in the email. It appears that no residents were treated for any symptoms resulting 

from the three applications of DMDS at Floral City, FL in September 2009. 

Ecological Fate and Effects Assessment 

The ecological fate and effects database is adequate to support the screening level 

assessment that was conducted for the conditional registration of the proposed uses and 

application rates of DMDS. 

Data Needs 

Environmental Fate

There are four environmental fate studies that are required to support the DMDS use patterns 

proposed for registration. These studies are required for the registration of DMDS. 

• Environmental Chemistry Methods and Independent Laboratory Validations for Soil, 

Water and Air; 

• Field Volatility Studies (GLN 835.8100); and 

• Aerobic and Anaerobic Aquatic Metabolism (835.4400, and 835.4500). 

21
Ecological Effects

 There are four ecological effects studies that are required to support the DMDS use 

patterns proposed for registration. These studies are required for the registration of DMDS. 

• Aquatic Invertebrate Life-Cycle Toxicity (Freshwater (850.1300) and 

Saltwater(850.1350); 

• Vegetative Vigor (upgrade to a previously submitted study) (850.5400); and 

• Fish Early Life-Stage Toxicity, Freshwater and Saltwater (850.1400). 

Labeling Requirements 

The high vapor pressure of DMDS (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 DMDS 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. To minimize the potential for runoff, the Agency is requiring the 

label language below to mitigate the risk of exposure due to DMDS runoff in the environment. 

In addition, upper-bound DMDS EECs in air may not account for temperature inversions 

associated with stagnant air and may consequently result in high air pollutant concentrations. 

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. To protect against this uncertainty, inversion mitigation language restricting 

DMDS applications during large-scale extended inversion events is specified below. 

 Surface and Ground Water Advisory for Tarped Scenario

Do not apply directly to water or to areas where surface water is present or to intertidal areas 

below the mean high water mark. Do not contaminate water when cleaning equipment or 

disposing of equipment washwater or rinsate. 

Dimethyl disulfide has certain properties and characteristics in common with chemicals that 

have been detected in groundwater (dimethyl disulfide is highly soluable in water and has low 

adsorption to soil. 

To address this concern for ground water quality and surface runoff, for broadcast applications, 

tarps must be sliced or removed before noon and only when rainfall is not expected within 12 

hours. (Falling temperatures typically found in the late afternoon and evening will not promote 

dissipation of remaining DMDS under the sliced tarp and rainfall may cause remaining dimethyl 

disulfide under the sliced tarp to leach into ground water.) 

Air Stagnation and Temperature Inversions

Prior to fumigation, and on a daily basis for those fumigations lasting for more than 24 hours, 

the National Weather Service weather forecast for the day of the application and the 48-hour 

22
period following the fumigation must be checked to determine if unfavorable weather conditions 

exist or are predicted (see Identifying Unfavorable Weather Conditions section) and whether 

fumigation should proceed. 

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

Do not apply if there are light wind conditions observed (under 2 mph) or if the wind speed is 

forecast to remain below 5 mph during the application. 

Do not apply if still or stagnant wind conditions are forecast to persist for more than 18 

consecutive hours after the start of the application. 

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

be obtained on-line at: http://www.nws.noaa.gov, on weather radio, or by contacting your local 

National Weather Service Forecasting Office. 

Identifying Unfavorable Weather Conditions

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

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

directions. These conditions typically exist prior to sunset and continue past sunrise and persist 

as late as noontime. Unfavorable conditions are common on nights with limited cloud cover and 

light to no wind and their presence can be indicated by ground fog or smog and can also be 

identified by smoke from a ground source that flattens out below a ceiling layer and moves 

laterally in a concentrated cloud. Measurement of wind speed can be determined by taking 

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

23
Section 3(c)(7)(C) Finding 

 Section 3(c)(7)(C) of FIFRA authorizes the Agency to issue a conditional registration for 

a pesticide product containing a new active ingredient, in the absence of certain required data, if 

the Agency determines that one or more of the following considerations is true: 1) since the data 

requirement was imposed, there has been insufficient time for the data to have been generated, 2) 

during the period of the conditional registration, use of the pesticide will not cause unreasonable 

adverse effect on the environment, and 3) use of the pesticide is in the public interest. 

 Two human health-related studies are required as a condition of registration: Field 

Volatility from Soil (GLN 835.8100) and Estimation of Inhalation Exposure, Outdoor Sites 

(GLN 835.1300). Both (a single well-designed study could fulfill both of these requirements) 

must be run using high barrier tarp for all application methods. These studies are intended to 

confirm the assumptions made about DMDS emissions resulting from the use of high barrier 

tarps and the occupational exposure that results from these emissions. Eight environmental fate 

and ecological effects studies still must be submitted to complete the database for DMDS: 1) 

environmental chemistry methods and independent laboratory validations of them must be 

completed; 2) and 3) Aerobic and Anaerobic Aquatic Metabolism; 4) Vegetative Vigor (upgrade 

to a previously submitted study); 5) Field Volatility Studies; 6) and 7) Aquatic Invertebrate LifeCycle Toxicity (Freshwater and Saltwater); and 8) Fish Early Life-Stage Toxicity (Freshwater 

and Saltwater). The Agency will require all of the above studies as conditions of the registration 

of the DMDS products. They are generally expected to provide data confirmatory of the 

assumptions and conclusions made during the Agency review of DMDS. 

As discussed previously, DMDS is potentially a replacement for the soil fumigant methyl 

bromide. The broad applicability and effectiveness of methyl bromide made it the gold standard 

of fumigants. However, the Montreal Protocol Treaty, to which the U.S. is a party, has called for 

the phase out of ozone depleting substances such as methyl bromide. Each fumigant that has 

been considered a potential alternative to methyl bromide has attributes and efficacy that may be 

specific for some use sites, but generally, none has been shown to be as effective as methyl 

bromide in the wide variety of climate/geophysical/pest situations where methyl bromide has 

been used historically. DMDS could provide an important alternative to methyl bromide for 

situations where other treatments may not be feasible. Therefore, DMDS fulfills the criteria for a 

public interest finding as described in the Federal Register (Vol. 51, No. 43, pp. 7632-7633, 

March 5, 1986), as a “replacement for another pesticide that is of continuing concern to the 

Agency.” For additional information on the public interest finding, please see the document 

titled “Evaluation of a Request for a Public Interest Finding for the Conditional Registration of 

DMDS (dimethyl disulfide) DP#367368,” dated December 2, 2009. 

 

Agency’s Proposed Decision 

 The Agency therefore believes, in accordance with FIFRA 3(c)(7)(C), that 1) dimethyl 

disulfide will cause no unreasonable adverse environmental effects during the time required to 

develop those data, and 2) registration of DMDS for use in pre-plant fumigation treatment of 

fields in which fruiting vegetable (tomato, pepper, and eggplant) crops, cucurbit vegetable 

(cucumber, squash, and melon) crops, berry (strawberry and blueberry) crops, ornamental (field 

grown) crops, and forest nursery crops will be grown while awaiting the required data is in the 

24
public interest. Therefore, the Agency proposes to register dimethyl disulfide with the 

conditions that the data listed below be submitted within 2 years of the date of registration. 

• Field Volatility from Soil (Guideline Number (GLN) 835.8100) (for broadcast shank, 

raised-bed shank, and raised-bed drip irrigation applications; to determine flux from 

treated fields when high barrier tarp is used)1; 

• Estimation of Inhalation Exposure, Outdoor Sites (GLN 835.1300) (occupational 

inhalation exposure for all three types of applications when high barrier tarp is used); 

• Environmental Chemistry Methods and Independent Laboratory Validations for Soil, 

Water and Air; 

• Aerobic and Anaerobic Aquatic Metabolism (835.4400, and 835.4500) 2; 

• Vegetative Vigor (upgrade to a previously submitted study) (850.5400); 

• Aquatic Invertebrate Life-Cycle Toxicity (Freshwater (850.1300) and 

Saltwater(850.1350) 3; and 

• Fish Early Life-Stage Toxicity (Freshwater and Saltwater (850.1400) 3. 

1 This guideline is now required for this use pattern. 

2 This guideline was originally reserved; however, the Agency recently determined that it is 

required. 

3 The company’s waiver request in was denied in 2009, this study is now required. 

25