# Proposed Registration of the New Active Ingredient Dimethyl Disulfide (DMDS) for Pre-Plant Use to Fumigate Fields used to Grow Blueberries, Cucurb it Vegetables, Fruiting Vegetables, Strawberries, Field-Grown Ornamentals, and Forest Nursery Crops

May 24, 2010

U.S. Environmental Protection Agency Office of Pesticide Programs Registration DivisionProposed Registration of th e New Active Ingredient, Dime thyl Disulfide for Use on Blueberries, Cucurbit Vegetables, Fr uiting Vegetables, Strawberries, Field-Grown Ornamentals, and Forest Nursery Crops

I. REGULATORY PROPOSAL SUMMARY

The U.S. Environmental Protection Agency (E PA or the Agency) is proposing to register the new soil fumigation active ingredient, dimethyl disulf ide (DMDS), under the Federal Insecticide, Fungicide and Rode nticide 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 c overed with a tarp to prevent volatilization. The pr oposed uses are for tomatoes, peppers, eggplant, cucumbers, squash (all), melons (all), st rawberries, onions, field grown or namentals, and forest nursery crops. DMDS end-use products are packaged as Paladin (98.8% active in gredient) and Paladin EC (93.8% active ingredient). DMDS may be combined with chlo ropicrin and is expected to serve as one of the methyl bromide replacement fumigants.

Although DMDS will be used as an agricultura l 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 resi dues must dissipate in th e soil prior to planting so as not to be phytotoxic to the crop. Therefore, this fumi gant does not requi re establishing food tolerances and is not subject to the amendments of the Federal Food, Drug, and Cosmetic Act (FFDCA) and the Federal Insecticide, Fung icide and Rodenticide Ac t (FIFRA) promulgated under the Food Quality Protection Act (FQPA) of 1996.

II. STRUCTURE and NOMENCLATURE

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

Table 1: Structure and Nomenclature of Dimethyl Disulfide

Chemical structure

Common name Dimethyl Disulfide, DMDS

Molecular formula C 2 H 6 S 2 Molecular weight 94.2 g/mol

IUPAC name (methyldisulfanyl)methane

CAS name Dimethyl Disulfide

CAS number 624-92-0

PC Code 029088

3III. PHYSICAL and CHEMICAL PROPERTIES

A listing of the physical and ch emical 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 (pK

a ) This substance does not dissociate.

IV. HUMAN HEALTH RISK ASSESSMENT

A summary of the human health risk, as it wa s assessed in the Agency document entitled “Human-Health Risk Assessment, Dimethyl Disu lfide, March 10, 2010,” is provided below. The following summary information identifies th e 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 i nhalation exposure to the genera l 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 anal ysis of residential bystander inhalation exposure has been performed as part of the DMDS risk assessment. This analysis takes into account individuals who may live dir ectly next to a field treated with DMDS. Inputs used in the

assessment were chosen to assure that the i nhalation component of the aggregate exposure assessment will be protective of all potent ial exposed populations, including populations specifically targeted for possible environmental ju stice concerns such as low income residents and minorities. Risk assessment endpoints were se lected considering the potential susceptibility of infants, children, and pregnant women to a ssure protection of these populations. Since (a)

inhalation risks will drive this assessment and wi ll 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 assessme nt 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 bys tanders who could be exposed when performing crop-production tasks (but not inside) DMDS treated areas were assessed. Based on the volatility of DMDS,

4dermal 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 un likely and quantifying any potential low level exposures very difficult. Ther efore, a quantitative dermal e xposure assessment has not been conducted. However, the Agency is requiring th at handlers who may come in contact with DMDS liquid must wear personal protective equi pment (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 Rf C 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 strawb erry, tomato, carrot and radish conducted in CA, FL and WI were submitted to the Agency. Soil was trea ted at 790 lb DMDS per acre (almost 2x the currently proposed maximum label application ra te of 455 lbs DMDS per acre) by raised bed shank injection at a 6-inch depth and the soil wa s 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 stra wberries, tomatoes and carrots. Residues were found in both the treated (0.11-0.24 ppm) and untreat ed (0.09-0.24 ppm) radish plot s. 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 volat ile 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 (str awberries, blueberries, fruiting vegetables, cucurbits, and ornamentals) are considered nonf ood uses. Therefore, acute and chronic dietary risk assessments are not necessary. A qua litative DMDS drinking water assessment was performed for this risk assessment. DMDS ma y transport to nearby surface water through runoff and erosion, especially if an application of DMDS coincides w ith, or is closely followed by a rain event after tarp removal. However, rapi d volatilization of DMDS from surface water is expected to be an important route of dissipati on. Based on environmental fate data and modeling estimates the Agency does not expect the pestic idal uses of DMDS to adversely impact ground

water or surface water.

5B. Occupational and Non-Occupational Risk

Fields treated areas of DMDS are cove red with a tarp for 12 days to prevent volatilization; however, DM DS, 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 handli ng 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, nasa l irritation, is the most sensitive endpoint for DMDS. Systemic toxicity was only observed at hi gher concentrations in the form of decreased food consumption and body weights. Irritation typically increased in severity and progressed deeper in the nose with increas ing concentrations. Repeat inhalation studies suggest nasal irritation is driven by concentr ation since lower LOAELs were not observed in repeat exposure

studies. The concentration at whic h nasal irritation occurs is sim ilar 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 identifie d. 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 magnit ude below the level that nasal ir ritation is identified. The strong odor of DMDS may therefore “war n” individuals of the presence of the compound in the area.

DMDS did not produce developmental or repr oductive toxicity via the inhalation route below maternally toxic concentrations in the rat or rabbit studies.

Although DMDS is highly volatile, a speci ally designed 28-day repeat dermal rabbit study is available that in dicates repeat dermal exposure to DM DS is severely irritating and may cause severe systemic toxicity including death (secondary to dermal irri tation). It is noted, however, that this study was desi gned to keep DMDS on the skin instead of volatizing as would typically occur. Severe irrita tion 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, seve re irritation was also observed in the acute dermal rabbit study (crackin g/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 seve re irritation and toxicity. The Agency is requiring that handlers who may come in contact with DMDS liquid mu st 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

6been 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 li terature review conducted by the registrant suggests that the mean odor threshold for DM DS 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 inhala tion studies. This suggests that in dividuals near a treated field are likely to detect the odor of DMDS before it reaches a concentrati on at which it would begin to produce nasal irritation. However, the time requi red 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 wo rkers appear to presen t the greatest risk

concern. This is due to the concentration of the chem ical as it moves off or drifts from the field. Public health data for other fumigant chemical s 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, th is 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 be lieves exposures can be acute (less than 24 hours), short-term (1-30 days), and/or intermed iate-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 exposur e. The port-of-entry NOAEL (No observable adverse eff ect level) is 9 ppm. The port-of-entry LOAEL (lowest observable adverse effect level) of 12.5 ppm wa s based on the incidence of microscopic lesions of the nasal tissues, the incidence of degeneratio n in multiple nasal levels and inflammation of the olfactory and respiratory epit helia. Since nasal irritation is dependent upon concentration and not duration of exposure, a single HEC is appropr iate for all durations and both occupational and non-occupational scenarios.

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

short- and intermediate-term non- occupational and occupational human equivalent concentration (HEC) is 1.65 ppm. EPA’s Rf C methodology incorporat es some pharmacokinetic differences between rats and humans; therefore the interspecies extrapolation fa ctor 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).

7Dermal irritation was observed in rat and rabbit irritation studie s 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 Ag ency did not conduct a quantitative dermal risk assessment at the present time. It should be not ed, however, that there is potential for severe

irritation if DMDS does come into contact with th e 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 seve re irritation of DMDS to skin.

The methods and dosimetry equations describe d 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 addr esses 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 por t-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 concentr ation to cause nasal irritation and longer exposures do not increase the severity of the irrita tion. 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/m 3 ).

A summary of the endpoints used to estimate risk from inha lation 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.

83. Occupational Risk

Occupational handler and post-application e xposure is expected via the inhalation route of exposure. Potential inhalation exposure and risk to occupational ha ndlers, to occupational reentry workers who could be exposed when entering DMDS treated areas to perform cropproduction tasks, and to occupa tional bystanders who could be exposed when performing cropproduction tasks (but not inside) DMDS treated areas were assesse d. 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 emi ssion 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 re movers, involved in preplant field fumigation were evaluated using DMDS-specific handler monitoring data. Acut e inhalation risks to handlers exceed the Agency’s level of concern (M OE < 30) for many of the sample points at the baseline level (no respirator). However, with the addition of an or ganic 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 in termediate-term risks to handlers also exceed the Agency’s level of concern (MOE < 30) for many occupational activiti es at the baseline le vel (no respirator). However, with the addition of a PF 10 respirator, all of the short- and in termediate 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 sour ces) 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 eval uated using surrogate methyl bromide monitoring

data from California.

Eight field volatility studies that quantifie d DMDS emissions from treated fields were used to assess bystander exposure to DMDS resu lting from single application sites (e.g., area sources such as farm fields). These data indica te the potential for risks of concern associated

with DMDS use. These data are limited in their utility because they prov ide 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 understa nding 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 es timates for bystanders associated with DMDS

9uses ( http://www.epa.gov/scram001/dispersion_alt.htm ). DMDS PERFUM analyses were performed for 1, 5, 10, 20, and 40 acre fields (propos ed DMDS labels restri ct 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) ta rps are required on the label (only two of the eight vola tility studies used high barrier ta rps). No emissions data are

available to reflect the use of high barrier tarps for the broadcas t shank injection and raised bed drip irrigation application scenarios. The rais ed bed shank injection hi gh barrier studies were used as surrogates where the Agency deemed it appropriate and applicab le (e.g., the raised bed drip irrigation application scenario). The Ag ency does not recommend use of the raised bed shank injection high barrier studies as surrogate s for the broadcast shank injection application

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

to estimate buffer distances until a broadcast sh ank injection emissions study using high barrier tarps is performed.

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

With regard to potential multiple sources of e xposure 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 th e potential for exposure to DMDS in ambient air, the DMDS inhalation to xicity endpoints were co mpared to the ambient air levels that were quantified for methyl br omide which is a highly used and highly volatile fumigant. In all cases, this comparison resulted in risks that do not excee d 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 rela tive 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-occupationa l (bystander) exposure/risk

assessment.

10V. ENVIRONMENTA L RISK ASSESSMENT

A summary of the environmental risk assessment titled “Environmental Fate and Ecological Risk Assessment for the Proposed Re gistration 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 usi ng drip irrigation and shank inje ction and covered with a tarp. Given its high vapor pressure and solubilit y, physical chemical pr operties, volatilization followed by leaching are expected to be the ma in 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 da ys, as the field is covered with a tarp; however, runoff is possible after 12 days when the tarp is cut. Although there is po tential for runoff, it is not anticipated to be of significant concern.

A. Environmental Fate

DMDS is a soil fumigant that is applied using drip irrigati on and shank injection and covered with a tarp. The major route of envi ronmental exposure is expected to occur through volatilization. However, runoff into surface wa ter, and leaching into groundwater may be possible after the tarp is removed, given the hi gh 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 s ubstantially 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 subse quently formed in soil and gradually build to significant quantities over time. An aerobic soil metabolism study i ndicated that th e 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, especi ally on soils with low bufferi ng capacities and low free carbonate

content.

2. Water

The high solubility of DMDS in water (2,702 mg/l), and low average K d 0.641 mL/g suggest that residues are readil y 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 rout es of dissipation from surface

water.

11There are uncertainties in estimating DMDS exposure in surface water. First, the biodegradation and dissipation of DMDS in wate r 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 biodegrada tion of residues under the tarp after the required 12 days. However, it is possible that there can be seep age 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 environm ental 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 mob ile, leaching and potential groundwater contamination is possible. Cases of groundwater contamination may occur in areas over and around aquifers where water tables may be shallo w and recharging of gro undwater 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 concentr ations of DMDS in the air from field applications. A field volatility st udy conducted in Tifton, GA s uggests that DMDS air concentrations can be attenuated by the applicati on 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 sha nk injection, including vari ations in application timing and geographic location. However, strato spheric ozone depletion and climate change impacts are not expected based on the low persiste nce 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 Com pound (VOC), DMDS ma y contribute to groundlevel ozone production and acid rain wher e 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 e ffects. The means of in tegrating the results of exposure and ecotoxicity data is called the quo tient method. For this method, risk quotients (RQs) are calculated by dividing exposure es timates 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 indicat e potential risk to nont arget organisms. The criteria indicate that a pesticide, when used as directed, has the potential to cause adverse effects to nontarget organisms.

12The ecotoxicity endpoints derived from the resu lts of short-term laboratory studies that assess acute effects are: (1) LC 50 (fish and birds); (2) LD 50 (birds and mammals); (3)EC 50 (aquatic plants and aquatic invertebrates); (4) EC 25 (terrestrial plants). Typically, the endpoints

derived from the results of l ong-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 DM DS, no chronic modeling was performed because of

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

LOCs are shown in Table 4 below.



### Table 4. Risk Presumption s 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 scr eening level assessment. Screening level assessments are based on conservative assumptions. For example, screening level assessments assume maximum labeled application rate, th e maximum number of applications, and the shortest treatment interval between applications.

13Aquatic 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 irrigati on applications do not exceed the Agency’s level of concern. For th e 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 we re not estimated because no chronic toxicity

studies are available.

2. Aquatic Vascular and Non-Vascular Plants

For aquatic vascular and non-va scular plants, the acute RQs for non-listed species are <1 for the drip irrigation method and shank inje ction application methods. RQs for non-listed species are estimated for vascular plants ( Lemna) and nonvascular plants ( Anabaena) using the

EC 50

.

RQs are estimated for listed species using the EC 05 toxicity value. RQs ranged from 0 to 18 and exceeded the LOC for drip irrigation appl ication method for listed nonvascular plants for CA tomato, FL tomato, FL pepper, FL cucu mber, 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 app lication 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 μ g/m 3

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 inje ction application method with VIF tarps. Along with the EEC in air, the ri sk quotients were calcu lated 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 therefor e, are not of concern.

2. Terrestrial Invertebrates

Although there is no model available to estima te the effects on the honeybee, the results for the toxicity test are classified as to the imp act. There is no risk fo r non-listed insects based on the honeybee toxicity test, which resulted in a cl assification of practically non-toxic. The risk

to other terrestrial i nvertebrates that are not soil dwe lling are represented by the honeybee

estimate.

143. Terrestrial Plants

Risk to terrestrial plants is expected from exposure to air concentrations. The Agency was unable to estimate air exposure to plants gi ven 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 concentr ations 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.

15VI. PROPOSED REGULATORY DECISION

During February 2007 the Agency received fr om 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 vegeta ble crops, fruit crops, floral crops, nursery crops, and forest nursery crops were to be grown. Th e post-application sites were later specified as fruiting vegetable (tomato, pepper, and eggplant) crops, cucurbit vegetable (cucumber, squash, and melon) crops, berry (strawbe rry and blueberry) crops, orname ntal (field grown) crops, and forest nursery crops. Pests controlled are weeds such as nutsedge (purple and yellow), chickweed, lambsquarters, purslane, and gra sses; soil-borne plant pathogens such as Verticillium

spp., Fusarium spp., Pythium spp., Sclerotinia spp., and Rhizoctonia spp.; and nematodes such as Root Knot (Southern, Norther n, and Colombian), Stubby Root, Lesion, Stunt, and Sting. The application techniques specified on the Paladi n 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 phas e-out effort that is administered by a United Nations committee, pursuant to the “Montreal Pr otocol on Substances th at Deplete the Ozone Layer.” It would therefore be likely that registration of DMDS as another soil fumigation alternative to methyl bromide w ould be in the public interest.

The Agency is proposing to conditionally register the Pala din 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, a nd eggplant), cucurbit vegetable (cucumber, squash, and melon), berry (strawberry and bluebe rry), ornamental (field grown), and forest nursery crops will be grown. Given the availabl e 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 ac tive ingredient, DMDS. It was published in the Federal Register on May 1, 2009. No comments we re 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.

16Human Health Assessment

The human health risk assessment concluded that the databases are adequate for dietary, non-occupational (bystander), and occupational e xposures to support a conditional registration for the proposed uses and app lication 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 mutageni city study (initial study was judged to be unacceptable) to satisfy Part 158 Guidelines. Ho wever, 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 sy stemic 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 nasa l irritation. Therefore, the Agency is waiving these two study requirements for DMDS.

Occupational and Residential Exposure

The studies listed below ar e 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 hi gh-barrier tarps for the broadcast shank injection and raised bed drip irrigation appli cation scenarios. The current risk

assessment is considered conservative and EPA belie ves that use of polyet hylene tarps represents a worst-case scenario. However, the proposed labe ls require use the of hi gh-barrier tarps. When these studies are submitted, these data will a llow the Agency to better refine the exposure potential of DMDS under the condi tions required on the label.

• Field Volatility from Soil (Guideline Nu mber (GLN) 835.8100) (for broadcast shank, raised-bed shank, and raised-bed drip irri gation applications; to determine flux from treated fields when high barrier tarp is used).

• Estimation of Inhalation Exposure, Out door 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 appl ied by a certified applicator. If a fumigant is not applied correctly, bystanders may be exposed to concentr ations 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 at mosphere. Specialized eq uipment is also often

17needed to apply soil fumigant safely and accurately (e.g., tarp e quipment; self-contained breathing apparatus). Therefore, the Agency feel s that DMDS meets the standard for restricted use designation because:

• The application of this fumigant invol ves complex operations requiring specialized training and/or experience; • Fumigant label directions cal l for specialized apparatus and protective equipment that is

not available to the general public; and

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

Labeling Requirements

Buffer Zones

The human health risk assessm ent 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 bys tanders 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 va rious application methods. For all application methods on the proposed DMDS product labels, buffer zones are based on the 75 th 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 whic h is detectable at co ncentrations that are orders of magnitude below the toxi cological point of departure. They are also health protective because the buffer zones are based on a toxicologi cal endpoint effect of nasal irritation and not more severe systemic effects.

18Table 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

19Table 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 fu ll 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 hour ly intervals thereafter, handlers can remove their air-purifying respirators moment arily to determine if the garlic-like odor is still detectable. If detectable, the respirat or must be put back on.

In addition, tractor drivers and tr actor co-pilots in enclosed cabs can use a tractor equipped with a working-area air-fan dilution sy stem consisting of a ducted fan/blower which provides air flow to the breathing zone of the tr actor 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 mu st be capable of operating at a minimum of 1,600 revolutions per minute and producing a minimu m flow rate of 3,000 cubic feet of air per

minute.

Incident Data

Experimental Use Perm it (EUP) Applications

An incident occurreed in Tifton, GA afte r an application of DMDS to a field approximately 1 acre in size. The field was treate d with DMDS at an application rate of 600 lbs ai/treated acre and a standard polyethylene tarp wa s 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 7 th and two days later on February 9 th , several residents of a local community notified the local police and fire depart ment of an odor in their community. Several

20residents also complained of headaches. The lo cal police and fire department did not detect an odor in the community but did det ect an odor at the treated field. No residents were treated for any symptoms but several residents were temporar ily relocated. It was noted that a low level atmospheric inversion occurred on February 8 th and persisted for two days. This likely prevented typical dispersion of DMDS vapors.

An incident occurred in Flor al City, FL after two applic ations of DMDS to fields approximately 7.5 and 2.5 acres in size. Both fiel ds were treated with DMDS at an application rate in accordance with the EUP label using shan k injection equipment and polyethylene tarps. The applications occurred on September 8 th and 9 th . On September 9 th the farm manager was contacted by the local police department rega rding a potential propane leak (DMDS has a propane/garlic like odor). A drip applica tion field trial of 0.25 acres using DMDS was performed on September 13 th on the same farm. On September 17 th the farm manager was contacted via email by a local resident regardi ng an “awful odor” that occurred in the mornings and evenings over the previous week or two. Th e email mentioned that several local residents had become ill during the time that the odor existe d. The farm manager visited the resident who emailed him on September 17 th to provide details of the EUP a nd 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 pot ential exposure to DMDS. The fa rm 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 conditi onal 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 Inde pendent Laboratory Validations for Soil, Water and Air;

• Field Volatility Studies (GLN 835.8100); and

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

21Ecological Effects

There are four ecological e ffects studies that are requi red to support the DMDS use patterns proposed for registration. These stud ies are required for the registration of DMDS.

• Aquatic Invertebrate Life-Cycle Toxicity (Freshwater (850.1300) and Saltwater(850.1350);

• Vegetative Vigor (upgrade to a prev iously 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 solubil ity of 2,702 mg/l, and low soil-water partition coefficient (K d = 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 K d value, dissolved DMDS residues may also be transported to water bodies nearby application sites via runoff. To minimize the potential for runo ff, the Agency is requiring the label language below to mitigate th e risk of exposure due to DMDS runoff in the environment.

In addition, upper-bound DMDS EECs in air ma y 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 PE RFUM to account for plume meandering during inversion conditions, when a highl y concentrated plume can impact a large perimeter within a short time period. To protect against this uncer tainty, 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 wa shwater or rinsate.

Dimethyl disulfide has certain properties and char acteristics 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 unde r 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 thos e fumigations lasting for more than 24 hours, the National Weather Service weather forecast for the day of the application and the 48-hour

22period following the fumigation must be checked to determine if unfavorable weather conditions exist or are predicted (see Identifying Unfavo rable 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 wi nd 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 pe rsist for more than 18 consecutive hours after the start of the application.

Detailed local forecasts for weather conditions , wind speed, and air stag nation 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 mo vement of air, which results in trapping fumigant vapors near the ground. The resulting air mass can move off-site in unpredictable directions. These conditions typica lly exist prior to sunset and c ontinue 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 indi cated 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. Measuremen t of wind speed can be determined by taking measurements every minute for a ten-minute peri od. The wind speed is the average of the oneminute measurements over this ten-minute period.

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

Section 3(c)(7)(C) of FIFRA authorizes the Ag ency to issue a conditi onal registration for a pesticide product containing a new active ingredient , in the absence of cert ain required data, if the Agency determines that one or more of the fo llowing considerations is true: 1) since the data requirement was imposed, there has been insufficien t time for the data to have been generated, 2) during the period of the conditiona l registration, use of the pestic ide will not cause unreasonable adverse effect on the environment, and 3) use of the pesticide is in the public interest.

Two human health-related studi es are required as a conditi on of registration: Field Volatility from Soil (GLN 835.8100) and Estimati on of Inhalation Exposure, Outdoor Sites (GLN 835.1300). Both (a single well-designed st udy could fulfill both of these requirements) must be run using high barrier ta rp for all application methods. These studies are intended to confirm the assumptions made about DMDS emi ssions 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 Aqua tic Metabolism; 4) Vegetative Vigor (upgrade to a previously submitted study); 5) Field Volatility Studies; 6) a nd 7) Aquatic Invertebrate LifeCycle Toxicity (Freshwater and Sa ltwater); and 8) Fish Early Li fe-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 expe cted 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 Mont real Protocol Treaty, to which the U.S. is a party, has called for the phase out of ozone depleting substances such as methyl brom ide. 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 ha s been shown to be as effective as methyl bromide in the wide variety of climate/geophysic al/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 de scribed in the Federal Regi ster (Vol. 51, No. 43, pp. 7632-7633, March 5, 1986), as a “replacement for another pest icide that is of continuing concern to the Agency.” For additional information on the pub lic interest finding, plea se see the document titled “Evaluation of a Request fo r a Public Interest Finding fo r the Conditional Registration of DMDS (dimethyl disulfide) DP#367368,” dated December 2, 2009.

Agency’s Proposed Decision

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

disulfide will cause no unreasonable adverse envi ronmental effects during the time required to develop those data, and 2) regist ration of DMDS for use in pr e-plant fumigation treatment of fields in which fruiting vegeta ble (tomato, pepper, and eggplan t) crops, cucurbit vegetable (cucumber, squash, and melon) cr ops, berry (strawberry and bluebe rry) crops, ornamental (field grown) crops, and forest nursery crops will be grown while awaiting the required data is in the

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

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

• Field Volatility from Soil (Guideline Nu mber (GLN) 835.8100) (for broadcast shank, raised-bed shank, and raised-bed drip irri gation applications; to determine flux from treated fields when high barrier tarp is used) 1 ;

• Estimation of Inhalation Exposure, Out door Sites (GLN 835.1300) (occupational inhalation exposure for all three types of applications when high barrier tarp is used);

• Environmental Chemistry Methods and Inde pendent 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 de nied in 2009, this study is now required.

25