# Environmental Fate and Ecological Risk Assessment for the Proposed Registration of Dimethyl Disulfide (DMDS) for use on Tomatoes, Peppers, Eggplant, Cucumbers, Squash, Melons, Strawberries, Onions, Field Grown Ornamentals, and Forest Nursery Crops

Prepared by:

Gabe Rothman, Environmental Scientist Valerie Woodard, Biologist

Reviewed by:

Mah Shamim, Branch Chief Keith Sappington, Senior Biologist Michael Barrett, Senior Chemist U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch IV

Ariel Rios Buildin g (Mail Code 7507C) 1200 Pennsylvania Ave., NW Washington, DC 204602 4

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### TABLE OF CONTENTS

I. EXECUTIVE SUMMARY

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I.A N ATURE OF C HEMICAL S TRESSOR

................................................................................ I.B. P OTENTIAL R ISKS TO N ON

- TARGET O RGANISMS

......................................................... I.C. C ONCLUSIONS

- E XPOSURE C HARACTERIZATION

........................................................ I.D. C ONCLUSIONS

- E FFECTS C HARACTERIZATION

........................................................... I.E. D ATA G APS AND U NCERTAINTIES

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I.E.1. Environmental Fate and Exposure

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

................................................................................................................. I.F. E NDANGERED S PECIES S UMMARY M ATRIX

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II. PROBLEM FORMULATION

......................................................................................

II.A N ATURE OF R EGULATORY A CTION

............................................................................. II.B. S TRESSOR S OURCE AND D ISTRIBUTION

.......................................................................

II.B.1. Nature of the Chemical Stressor

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

........................................................................................... II.C. R ECEPTORS

...............................................................................................................

II.C.1. Aquatic and Terrestrial Effects

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

......................................................................................... II.D. A SSESSMENT E NDPOINTS

......................................................................................... II.E. C ONCEPTUAL M ODEL

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II.E.1. Risk Hypothesis

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

........................................................................................................ II.F. A NALYSIS P LAN

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

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

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

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

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III. ANALYSIS

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III.A. U SE C HARACTERIZATION

........................................................................................ III.B. E XPOSURE C HARACTERIZATION

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DMDS is a reduced organosulfur compound. Its physical chemical properties and environmental fate are summarized below in Tables III-2 and III-3. A description of detailed environmental fate and transport characteristics of DMDS can be found in Section III.B.1 below and in Appendix A.

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

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

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

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

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

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

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

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

IV.A. R ISK E STIMATION

- I NTEGRATION OF E XPOSURE AND E FFECTS D ATA

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IV.A.1. Non-target Aquatic Animals and Plants

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

....................................................................................... IV.B. R ISK D ESCRIPTION

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IV.B.2 Risk to Terrestrial Organisms

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80 Terrestrial Risk Conclusions

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

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

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

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

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

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

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

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

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

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

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

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

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### I. Executive Summary

I.A Nature of Chemical Stressor

Dimethyl disulfide (DMDS) is a new active ingredient proposed for use on fruiting vegetables (restricted to tomatoes, peppers, and eggplant), curcurbit crops (restricted to cucumbers, squash, and melons), small fruit crops (restricted to strawberries, and blueberries), field-grown ornamentals, and forestry nursery crops. DMDS is used to control nematodes in the soil. For nematodes, DMDS acts by blocking the cytochrome oxydase mechanism necessary for mitochondrial respiration (Charles, 2003). DMDS can also be used control weeds, as well as soil-bourne fungus, and bacteria. The exact mechanism of action for these target pests are unknown. DMDS is a transparent light yellow liquid with a strong garlic-like odor. The intended use of DMDS is for pre-plant soil fumigation, implying that dimethyl disulfide converts to and acts as a stressor within the gas phase. Given its high vapor pressure and solubility, physical chemical properties, volatilization followed by leaching are expected to be the main dissipation pathways for DMDS. Dimethyl disulfide gradually degrades to major degradates methanesulfonic acid and carbon dioxide in soil as well as major degradates methanesulfonic acid, methanesulfinic acid, and sulfuric acid in water through photodegradation in water. There is limited information regarding the environmental fate and ecological toxicity of methanesulfonic acid and methanesulfinic in the open literature and the ECOTOX database. However, structural activity relationship models such as

ECOSAR indicate that Methanesulfonic acid may not be as toxic as parent dimethyl disulfide. In addition, it is not anticipated that dimethyl disulfide residues will be subject to photodegradation in nearby water bodies adjacent to fumigated fields by in large. Therefore, it is not expected that large quantities of methanesulfinic acid or sulfuric acid, will form in significant quantities in water. Therefore, dimethyl disulfide appears to be the main stressor for aquatic and terrestrial organisms associated with soil fumigation.

The maximum proposed individual dimethyl disulfide application rate for all crops is 455 lb a.i./A with one application allowed per season. The PaladinTM label contains 98.8 percent a.i. at 8.85 lbs. of a.i. per gallon of solution and PaladinTM EC label contains 93.8 percent a.i. at 8.83 lbs. of a.i. per gallon of solution. PaladinTM can only be applied through broadcast or bedded shank injection into the soil. The PaladinTM EC formulation can only be applied via chemiga tion through surface or buried drip tape under the soil. The drip tape must be buri ed under the tarp. Immediately following the application, covering using a virtually impermeable film (VIF) or high barrier tarp is required and remain on the field undisturbed for a minimum of 12 days for both

formulations.



### I.B. Potential Risks to Non-target Organisms

DMDS is applied using drip irrigation and shank injection and covered with a tarp. The tarp is removed after a minimum 12 days. No spray drift or runoff is expected for the first 12 days. Runoff is possible after 12 days when the tarp is cut. However, no5 spray drift is expected because DMDS is applied through drip irrigation systems or shank injected into the soil.. An effect to both aquatic and terrestrial species is expected from the use of DMDS. Both drip irrigation and shank injection are evaluated for risk to aquatic species. Risk to terrestrial animal species via exposure in air is evaluated only for shank injection to raised beds and does account for the tarping practice. PRZM/EXAMS modeling will be used to estimate the effects to aquatic species. The PERFUM model will be used to estimate the effects to terrestrial species.

Conclusions for the effect of DMDS on aquatic species and aquatic plants were based on lines of evidence including fate and transport characteristics, toxicity endpoints, results from conventional and refined models for aquatic exposure, as well as reviewing incidents reported to the EIIS database. RQS are estimated from the PRZM/EXAMS model which accounted for volatility and off-site movement to water bodies following the removal of the tarp 12 days after the application. The resulting RQs are compared to a Level of Concern (LOC) for the species and exposure route, and were used to develop the overall conclusions. No aquatic animal or plant incidents have been reported in the

EIIS database.

RQs were estimated for both drip irrigation and shank injection for each use. There is potential acute risk to freshwater fish and freshwater invertebrates based on RQ exccedence. Drip irrigation RQs exceed the endangered species LOC for freshwater fish (RQs=0.003-0.212) and freshwater invertebrates (RQs=0.001-0.125) for FL cucumber, FL strawberry and GA onion uses.

There is no potential for acute risk for any surrogate species using the shank injection method. No modeled uses resulted in LOC exceedences.

There is potential acute risk for chronic effects to freshwater and estuarine/marine fish based on the uncertainty due to the persistence of DMDS in water and absence of chronic toxicity data.

RQs for non-listed species are estimated for vascular plants ( Lemna) and nonvascular plants ( Anabaena) using the EC 50

. There was no RQ exceedence for vascular using Lemna as a surrogate or for non-vscaular using Anabaena as a surrogate for either drip irrigation or shank injection for any uses.

Risk is presumed for chronic effects to freshwater and estuarine/marine fish and invertebrates based on the uncertainty due to the persistence of DMDS in water and absence of chronic toxicity data.6 Conclusions for the effect of DMDS on terrestrial species including birds, mammals and terrestrial invertebrates were based on lines of evidence including fate and transport characteristics, toxicity endpoints, results from screening level and refined models for terrestrial exposure, as well as reviewing incidents reported to the EIIS

database. Risks to reptiles and terrestrial-phase amphibians are represented using the bird as a surrogate. No dietary exposure to birds is expected since residues are not expected to be taken up by terrestrial plants, or residues resulting from gas phase deposition are not expected to be retained by plants given its high diffusivity. DMDS is hypothesized to expose terrestrial wildlife via inhalation.

The proposed label for DMDS includes instructions to cover the field with a tarp for the first 12 days. Specifically, high barri er tarps such as VIF (Virtually Impermable Films) tarps are required to be used on the proposed label; therefore the conclusions are based on the effect the VIF tarp use pattern. In addition, an analysis using low barrier tarps using a screening method with the SCREEN3 model is presented Appendix G. The PERFUM model describes the effect from the use of VIF tarps such as proposed on the label. Although there is no inhalation LOC available to compare with the RQ, this analysis uses the current bird endangered species LOC=0.1 used to evaluate dietary effect, to determine the effect of DMDS use. RQs for chronic effects were not modeled due to the absence of chronic toxicity data. No terrestrial animal incidents have been reported in the EIIS database.

Risk conclusions for avian and mammal species were developed based on EECs from an analysis using high barrier tarps and endpoints from a non-guideline bird inhalation study. In addition, due to the volatility of DMDS, it is expected to expose terrestrial wildlife via air residues. There is no potential risk for birds based air concentrations estimated from PERFUM modeling based on the Tifton field scenarios which used covering of VIF tarps to a field treated with dimethyl disulfide indicated no

risk to birds.

Although there is no model available to estimate the effects on the honeybee, the results for the toxicity test are classified as to the impact. There is no risk for non-listed insects based on the honeybee toxicity test, which resulted in a classification of practically non-toxic. The risk to other terr estrial invertebrates that are not soil dwelling would be represented by the honeybee estimate.

There is no risk to other off-site terrestrial invertebrates that burrow in the soil since the dominant routes of dissipation for DM DS is expected to be leaching into ground

water or volatilization into the air..7 DMDS is used to kill weeds as a target, th erefore it is expected to kill plants on the field. There is no current toxicity test compatible with the existing modeling methods available to estimate the effect of DMDS total residues to terrestrial plants through air exposure. Therefore, risk is presumed to non-target terrestrial plants off the treated field due to its herbicidal properties. Runoff is not expected to be the primary exposure route associated with DMDS fumigations. Therefore, TerrPlant was not used to estimate this exposure pathway from DMDS.



### I.C. Conclusions - Expo sure Characterization

Dimethyl disulfide’s vapor pressure of 22.55 torr at 20oC, high solubility of 2,702 mg/l, and low soil-water partition coefficient (K d = 0.641 ml/g) suggest that the major routes of dissipation of dimethyl disulfide are volatilization and to a lesser extent, leaching. Given its high mobility indicated by its low K d value, dissolved DMDS residues may also be transported to water bodies nearby application sites via runoff. As such, recommended label language mitigating the risk of exposure to DMDS runoff in the environment is provided in the transmittal memo. In addition, since DMDS in the soil are highly soluble, soil bound DMDS residues may leach to ground water upon removal of the tarp or in areas where the water table is shallow and recharging occurs. Therefore, a prospective ground water monitoring study for DMDS may be requested in the future to address any compliance issues with mitigation language placed on the label as needed.

DMDS residues appear to biodegrade in soil substantially and rapidly over time. The aerobic soil metabolism study results suggest that DMDS rapidly diffuses to air space (within 5 minutes after the application) and then is redeposited to soil as major degradates methanesulfonic acid and carbon dioxide are subsequently formed in soil and gradually build to significant quantities over time. This scenario is very possible in the field as tarps can trap DMDS gas from escaping to the atmosphere, especially considering that DMDS was applied in a closed system in the aerobic soil metabolism study. Considering the diffusion-deposition behavior of the chemical and the tarping required on the label, the half life of DMDS in the soil is calculated between 2.86 days and 3.74 days assuming that the formation of methanesulfonic acid is completely due to DMDS degradation in the soil.

There is limited information about the degradation of DMDS in water. DMDS has an aqueous photolyis half-life of 1.17 days corrected for degradation in the dark and exposure to natural light intensity was determined for DMDS. Two out of three of the degradates, Methanesulfonic acid, methanesulfinic acid, and sulfuric acid were detected in major quantities. The nature of biodegradation of DMDS in aquatic water bodies is unknown. No aerobic or anaerobic aquatic metabolism studies (OPPTS Guideline Nos. 835.4300) were submitted to the Agency and remains an outstanding data gap in this risk

assessment.8 An upper-bound estimate of 16.89 percent of applied DMDS was determined to be available for off-site movement when the tarp covering is removed after the minimum period of 12 days as required on the label. The PRZM/EXAMS modeling used to estimate water column concentrations assumed this small initial loading. Therefore, EECs in surface water are reflective of small loading available to runoff after the required 12 day tarp covering as well as the continuation of rapid biodegradation as well as

volatilization as simulated in PRZM/EXAMS.

The product labels for DMDS require that virtually impermeable film (VIF) tarps be used on the field consistent with agricultural practices associated with controlling volatile emissions from fumigated fields. One field volatility study was conducted using VIF tarps in Tifton, GA in February , and DMDS flux only accounted for 35 percent loss of the applied amount from the soil. Upper-bound EECs in air predicted by the PERFUM model were not of concern based on this field volatility study. However, this is a sparse dataset. Therefore, there may be differing flux profiles at different times of the year for differing locations. A screening analysis using the SCREEN3 model indicates that there may be a concern for mammals and birds associated with DMDS application in other areas during other times of the year. However, this analysis was based on field volatility studies that were not conducted with VIF tarps, rather with low density polyethylene and metallized tarps. Dimethyl disulfide flux that was measured from the soil with these tarps were higher than observed in the VIF study in five out of seven studies accounting for approximately 38 – 81 percent of the applied amount for studies conducted in Georgia (2 studies), Florida (1 study), California (1 study), and Arizona (1 study) during the winter, spring, summer, and fall months, respectively. Two other field voaltililty studies contained total measured DMDS flux below the VIF study. DMDS flux accounted for 27 percent of the applied in Nipomo, California during June using a low density polyethylene tarp. In addition, DMDS only accounted for approximately 8.1 percent based on field flux measured at Dover, FL using a less permeable metalized film tarp during April. Although the VIF tarp shows a lower flux from the soil than five out of seven field volatility studies using less permeable tarp material, the flux from soil covered with a VIF tarp may vary from factors such as the time of year as well as the location of the field. Hence, a robust dataset of field volatility studies which are conducted during typical fumigation seasons over multiple regions of the country using VIF tarps is an outstanding data gap in this risk assessment.



### I.D. Conclusions - Effe cts Characterization

DMDS is considered moderately toxic to freshwater fish (lowest LC50 = 960 ppb) and to marine fish (LC50=5600 ppb), It is co nsidered moderately toxic to freshwater invertebrates (LC/EC50 = 1610 ppb) and to marine invertebrates (LC50=4900ppb). It is practically non-toxic to honeybees (LD50 > 100 ug/bee). No chronic fish or aquatic invertebrate data is available. For terrestrial animals, inhalation exposure will be the primary exposure. The acute bird inhalation LC50= 17 mg/L and the acute mammal inhalation LC50 in rats is 17 mg/L.9 The most sensitive aquatic plant based on EC50 is the non-vascular plant Anabaena flos-aquae (0.32 mg/L) while the most sensitive vascular plant was Lemna

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

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

Ecological risks to terrestrial organisms via the dietary and uptake routes are not expected to be at risk considering pre-plant soil incorporated uses of DMDS. DMDS application modeling using PRZM indicated that there are no residues that are taken up by any of the labeled crops.



### I.E. Data Gaps and Uncertainties

I.E.1. Environmental Fate and Exposure

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

• Environmental Chemistry Methods (ECMs) and Independent Laboratory Validations

• Aerobic and Anaerobic Aquatic Metabolism (OPPTS Gudeline Nos. 835.4300)

• Field Volatility Studies (OPPTS Guideline No. 835.8100)

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

Environmental Chemistry Methods (ECMs) and Independent Laboratory Validations (ILVs) for Soil, Water, and Air

This information is required for all laboratory and field studies for the soil, water, and air. ECMs establishes transparency and demonstrates that analytical methods are repeatable for all field and laboratory studi es. ECMs are required for DMDS; further, multi-residue methods (MRMs) for soil and wate r are preferred. The following are major degradates for each media:

Soil – parent DMDS and methanesulfonic acid

Water – parent DMDS, methanesulfonic acid, methanesulfinic acid, sulfuric acid, any additional degradates identified from aerobic and anaerobic aquatic metabolism

studies.

Air – parent DMDS

In addition, a full description of the method validation procedures performed by an independent laboratory should be submitted. These reports will be evaluated by EFED. According to NAFTA Guidance, they should include the following information: (a) Recovery level(s) of the test compound(s) from the soil and water (substrates) at various relevant fortification level(s) using the residue analytical methodology; (b) a validated method sensitivity level; (c) results of the study and statistical test applied, including a stepwise presentation of the procedure for calculating percent recovery from the raw data; (d) all the data/ information necessary to independently verify the results;10 (e) summary of the results; and, (f) discussion and conclusions of the results.

Aerobic and Anaerobic Aquatic Metabolism

Submission of the aerobic and anaerobic aquatic metabolism study on the DMDS technical product will enable the reviewer to calculate half-lives of DMDS in water. These results will result in more refined EECs in surface water and benthic water pores. Retrievals of all degradates identified in the proposed degradation pathway (to be submitted with the study) should be attempted to account for the full material balance

over time.

Field Volatility Studies

Additional field volatility studies using PaladinTM and PaladinTM EC with VIF tarp coverings are required for drip irrigation and broadcast applications at this time. The studies should be located in anticipated use regions other than the Southeastern United States such as California and be conducted at times of the year when typical fumigation occurs in those regions. These studies should be conducted using the generic OPPTS guidelines. In addition, Johnson et al., 1999, Majewski et al., 1990, or Wilson and Shum, 1992 should be referenced for additional guidance regarding study designs, development of flux profiles, and land surface/flux footprint considerations (e.g., fetch distances along the treated field to the instrumentation towers). All studies should include collection of on-site meteorological data. If on-field towered sampling is conducted, all measurements of wind speed and temperature should be rapidly sampled on the order of every 1 minute. Furthermore, retrievals of all degradates identified in the degradation pathway shown in Figure III-1 of this document should be attempted.

Ambient Air Quality Monitoring Data (On reserve)

Ambient air quality monitoring studies may be requested in any high DMDS use areas in the future. The data will be used in registration review or with any proposed new uses to consider the potential for acute and chronic effects of DMDS, sulfuric acid, and ozone associated with a high volume of DMDS use occurring within an airshed. Air quality related values of concern will include concentrations of DMDS and ozone in the air close to ground level and sulfuric acid in rain water. To address DMDS’s contribution to ozone and sulfuric acid, the measured ambien t levels of DMDS in air and sulfuric acid in water to historical background levels in the same sampling regions before the inception of large scale DMDS fumigation should be compared.

Uncertainties

There are uncertainties in estimating DMDS exposure in surface water. First, the biodegradation and dissipation of DMDS in water is unknown. Second, the impact of tarping cannot be explicitely modeled in the PRZM model. Therefore, aquatic exposure

estimated concentrations in the water column were solely based on the tarp removed with an adjusted loading of DMDS which accounts for biodegration of residues under the tarp11 after the required 12 days which the tarp covering is required. However, it is possible that there can be seepage under the tarps, but this is not anticipated to contribute in a large enough manner to effect aquatic exposure estimates. Third, there is uncertainty related to the environmental fate and ecological toxicity of the major degradate

methanesulfonic acid which forms in aerobic soil where the bulk of DMDS residues are expected to reside after fumigation. However, structural activity relationship models indicate that methanesulfonic acid is less toxic to all taxa represented in this risk assessment than parent DMDS.

There are uncertainties with modeling of air residues for the purpose of estimating DMDS exposure in air to terrestrial wildlife. There is a limited dataset of field volatility studies for high barrier films used with Virtually Impermeable Films (VIF). A screening analysis using the SCREEN3 dispersion model with measured flux from field volatility studies using less permeable tarps than virt ually impermeable filems, indicates EECs of concern for mammals and birds. This screening analysis supports the need for more field volatility studies in other regions of the U.S. besides the Southeast where fumigants are typically used such as the Southwest should be conducted. Therefore, additional field volatility studies with drip irrigation and broadcast shank injection should be conducted in conjunction with VIF tarping. In addition, upper-bound DMDS EECs in air may not account for temperature inversions which are associated with stagnant air and may consequently result in high air pollutant concentrations. Therefore, the reviewer has provided recommended mitigation language regarding these meteorological regimes. Furthermore, DMDS EECs using the PERFUM modeling for high barrier films are based on receptor heights 1.5 meters above ground level, which may be slightly different than ground level. Furthermore, to address the risk for possible acute and chronic exposure to DMDS and degradates ozone and sulfuric acid, the reviewer may request ambient air quality monitoring data in the future.

I.E.2. Ecological Effects

Appendix F lists the status of the ecolo gical effects data requirements for DMDS. The following effects data are needed for ecological risk assessment for DMDS:

850.1300 Aquatic Invertebrate Life Cycle (Freshwater). This study is required based on the outdoor use and uncertainty concerning aquatic exposure and persistence. ).

850.1350 Aquatic Invertebrate Life Cycle (saltwater). This study is required based on outdoor use and current aquatic modeling indicating the potential for chronic aquatic exposure to DMDS. There is also uncertainty concerning the persistence of the pesticide in water(40CFR Part 158).

850.1400 Early Life-stage Fish (freshwater)

. This study is required based on the outdoor use and uncertainty concerning aquatic persistence. Current aquatic modeling indicates the potential for chronic aquatic exposure to DMDS. Also, the acute aquatic

EEC is > 0.01 of the acute LC 50 for freshwater fish (40CFR Part 158). Comment [mts1]: Please state if this study is required or not required

Comment [mts2]: This is conflicting statement. Please clarify. Also, state if the study is required or not

Comment [mts3]: Please state if this study is required or not require d12 850.1400 Early Life-stage Fish (saltwater) . This study is required based on outdoor use and current aquatic modeling indicating the potential for chronic aquatic exposure to DMDS. There is also uncertainty concerning persistence in the aquatic environment(40CFR Part 158).

Terrestrial Plant (special study for gases) – MRID 47471202 has been submitted and reviewed by EFED. However, the toxicity metric provided is not compatible with the existing modeling methods available to estimate the effect of DMDS total residues to terrestrial plants through air exposure. This study can become upgradable if data regarding the headspace volume is provided. If this is not possible, a new study is requested and EFED recommends that the registrant submits a protocol for the Agency to

review.

Uncertainties

Chronic aquatic exposures are possible, in part due to repeat or continuous input to the aquatic environment. There is uncertainty about the persistence of DMDS in the aquatic environment, which would impact ch ronic endpoints. As noted above, aquatic invertebrate life-cycle and fish early life-stage studies (with freshwater and marine/estuarine organisms) are needed for ri sk assessment. These will help the Agency determine whether there is further chronic aqua tic risk beyond that already identified and enable further analysis of the chronic aquatic risk.

The toxicity test to evaluate the effect of air concentration exposure to birds is based on a non-guideline study. In addition there is no threshold LOC to evaluate the effects of inhalation for birds. The toxicity test to evaluate the effects of air concentrations on terrestrial plants is based on a non-guideline study. Also there is no LOC to represent the threshold for exposure to air concentrations.



### I.F. Endangered Species Summary Matrix

Listed species risks are associated with direct or indirect effects due to applications of DMDS to tomatoes, peppers, cucumbers, strawberries, onions, nursery and Christmas trees if organisms in listed taxa are exposed (direct effects) or are dependent on other organisms that are expos ed (indirect effects). Risks are based on available reviewed data. Submission and review of the data requested in this review (see above) may result in identification of additional potential effects. A summary of listed species by taxa is presented in Appendix F.

There is the potential for direct effects for listed freshwater fish and aquatic invertebrates from the use of DMDS based on RQs exceeding the LOC. Drip irrigation RQs exceed the endangered species LOC for FL cucumber, FL strawberry and GA onion. Drip irrigation RQs range from 0.01 to 0.21 and shank injection RQs from 0 to 0.01 for13 fish. Drip irrigation RQs range from 0.001 to 0.125 and shank injection RQs from 0 to 0.006 for invertebrates. Based on the direct effect RQs, any freshwater fish species or aquatic invertebrates consuming those taxa will be adversely impacted for indirect

effects.

There is the potential for chronic risks to freshwater and estuarine/marine fish and invertebrates due to the uncertainty concer ning persistence in aquatic environments.

There is no potential direct or indirect effect on listed estuarine/marine fish or invertebrates from drip irrigation or shank injection for any use. Drip irrigation RQs range from 0 to 0.036 and shank injection RQs from 0 to 0.002 for fish. Drip irrigation RQs range from 0 to 0.041 and shank injection RQs from 0 to 0.001 for invertebrates.

There is no potential risk for direct or indirect effects to listed aquatic vascular plants represented by Lemna based on no RQ exceedence using the EC 05

. No RQs for either drip irrigation or shank injection exceeded the LOC.

Although there are no aquatic non-vascular plants included in Federal listings of threatened and endangered species at the present time, an assessment of the effect of DMDS on those plants is provided to evaluate potential contributions to indirect effects to other taxa and as a record of exceedances should future listings of non-vascular aquatic plants warrant additional evaluation of Federal actions.

There is potential risk for direct or indirect effects to listed aquatic non-vascular plants represented by Anabaena based on RQ exceedence using the EC 05

. There was no RQ exceedence for vascular using using Anabaena as a surrogate for shank injection for

any uses.

There is potential risk based on the uncertainty from the absence of data to estimate the effect of the gas to terrestrial plants.

Habitat Modification

Habitat modification includes effects from reduction in prey as well as effects on plants. There is the potential for indirect effects for listed freshwater fish and aquatic invertebrates from the use of DMDS based on RQs exceeding the LOC. Drip irrigation RQs exceed the endangered species LOC for FL cucumber, FL strawberry and GA onion.

There is the potential for chronic risks to freshwater and estuarine/marine fish and invertebrates due to the uncertainty concer ning persistence in aquatic environments.

The effect of plants is also used to assess the effect of DMDS on habitat modification. There is potential risk to listed aquatic non-vascular plants represented by

Anabaena based on RQ exceedence using the EC 05

. RQs are estimated for listed species14 using the EC 05 toxicity value. RQs exceeded the LOC for drip irrigation for listed nonvascular plants for CA tomato, FL tomato, FL pepper, FL cucumber, FL strawberry, GA onion, MI nursery, NJ nursery and OR Christmas tree uses. No RQs for shank injection for nonvascular plants exceeded the LOC for any uses.

There is potential risk based on the uncertainty from the absence of data to estimate the effect of the gas to terrestrial plants.

Listed Taxon Direct Effects Indirect Effects 3

Terrestrial and semiaquatic plants –

monocots Yes(Additional data required 4 ) Yes(Additional data required 4 )

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

Terrestrial

Invertebrates No No

Birds No No

Terrestrial phase amphibians 1 No No

Reptiles 1 No No

Mammals No No

Aquatic non-vascular plants* Yes Yes

Aquatic vascular plants No No

Freshwater fish Yes – (Additional chronic data needed) 4 Yes

Aquatic phase amphibians 2 Yes – (Additional chronic data needed) 4 Yes

Freshwater

crustaceans Yes Yes

Mollusks NA NA

Marine/estuarine fish No –(Additional chronic data needed) 4 No

Marine/estuarine

crustaceans No (Additional chronic data needed) 4 No15 * At the present time no aquatic non-vascular plants are included in Federal listings of threatened and endangered species. The taxonomic group is included here for the purposes of evaluating potential

contributions to indirect effects to other taxa and as a record of exceed ances should future listings of non-vascular aquatic plants warrant additional evaluation of Federal actions.

1 Risk assessment is based on avian assessment.

2 Risk assessment is based on freshwater fish assessment.

3 Indirect effects are considered possible for every taxonomic group when one or more direct effect LOCs are met/exceeded. Listed species could be affected by the loss of other species that they depend on for food, cover, and/or reproduction (e.g., pollination, seed dispersal). This is only a screening assessment. A refined assessment will consider the specifics of the food, cover, and reproduction needs of each listed species.

4 Requested data may result in additional potential direct effects.

### II. Problem Formulation

The purpose of this problem formulation is to provide the foundation for the ecological risk assessment being conducted for DMDS. As such, it articulates the purpose and objectives of the risk assessment, evaluates the nature of the problem, and provides a plan for analyzing the data and characterizing the risk (US Environmental Protection Agency, 1998) and is consistent wi th procedures and methodology outlined in the Overview Document (US Environmental Protection Agency 2004).

.

II.A Nature of Regulatory Action

Under the authority of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the registrant UPI/Arkema is seeking the Section 3 registration for the new active ingredient, DMDS, for use as a pre-plant fumigant.

II.B. Stressor Source and Distribution

II.B.1. Nature of the Chemical Stressor

DMDS is a new fumigant proposed for use to control (or suppression) of weeds, soil-borne plant pathogens and nematodes. For nematodes, DMDS acts by blocking the cytochrome oxydase mechanism necessary for mitochondrial respiration (Charles, 2003). This process has shown been shown to decrease intracellular ATP production and reduce the neuronal activity in insects (Dugravot et al., 2003). The mechanism of action is unknown for the other target pests. DMDS is formed as part of the global tropospheric sulfur cycle. DMDS is emitted into the atmosphere as a result of decay of organic material, biological waste products, and as a by-product of several plant and phytoplankton biological functions (Graedel, 1986). A brief summary of the product chemistry data on DMDS is provided in Table II-1.

Table II-1. Nature of the Chemical Stressor.

Common name dimethyl disulfide

Chemical name disulfide, dimethyl

Structure

Pesticide type Soil Fumigant

Chemical class Reduced Organosulfur Compound

CAS number 000624-92-0 Empirical formula C 2 H 6 S 2 Molecular mass (g/mol) 94.2 Vapor pressure at 20 o C 22.5 torr

1617 Table II-1. Nature of the Chemical Stressor.

Common name dimethyl disulfide Henry’s Law Constant at 20 o C 0.001 atm·m 3 /mol Solubility in water (mg/L)at 20 0 C 2,702 (pH 6) Log K
ow 1.77

DMDS biodegrades to methanesulfonic acid in significant quantities in soil and may be available to runoff. In water, DMDS can degrade to methanesulfonic acid, methanesulfinic acid, and sulfuric acid via photolysis in significant levels as well.

Structural activity relationship models such as ECOSAR indicate that methanesulfonic acid may not be as toxic as parent DMDS. ECOSAR, a utility under EPISuite 4, estimates the toxicity of chemi cals discharged to water. ECOSAR predicts toxicity to fish, aquatic invertebrates and alga e using an extensive set of structure-activity relationships (SARs). The program estimate s a chemical's acute (short-term) toxicity and, when available, and chronic (long-term or delayed) toxicity (USEPA, 2010[5]).

Table II-2b shows that ECOSAR indicates that DMDS has a lower toxicity and methanesulfonic acid for all aquatic taxa by a factor of at least 4,758 and as much as 1,181,295. Table II-2a does indicate that DMDS’s toxicity is underpredicted by the model for all taxa. However, the margin of the underprediction is far surpassed by the margin that ECOSAR predicts higher toxi city for parent DMDS as compared to methanesulfonic acid. In fact, all predicti ons of ECOSAR toxicity for methanesulfonic acid are beyond the solubility limit of methan esulfonic acid (methanesulfonic solubility = 29,180 mg/l at 25oC, EPISuite 4). DMDS acut e lethality toxicity thresholds for all taxa

occur at concentrations much lower than this level.

Table II-2a. DMDS Measured Vers us ECOSAR Predicted Toxicity.

Taxa Endpoint Dimethyl

Disulfide

Measured

Toxicity

(ppm) Dimethyl

Disulfide

ECOSAR Toxicity

(ppm) ECOSAR Departure

Factor

Freshwater Fish 96-hr LC 50 (Acute) 0.96 93.84 97.75

Daphnid 48-hr LC 50 (Acute) 1.61 51.93 32.25

Marine Fish 96-hr LC 50 (Acute) 5.60 131.73 23.52

Mysid 96-hr LC 50 (Acute) 4.90 102.43 20.90

Green Algae 96-hr EC 50 (Acute) 5.73 23.33 4.07

1. ECOSAR Departure Factor = DMDS ECOSAR Toxicity/DMDS Measured Toxicity.18 Table II-2b. DMDS Versus Methanesulfonic Acid ECOSAR Predicted Toxicity.

Taxa Endpoint DMDS

ECOSAR Toxicity

(ppm) Methanesulfonic

Acid ECOSAR Toxicity

(ppm) Methanesulfonic

Acid Departure

Factor

Freshwater

Fish 96-hr LC 50 (Acute) 93.84 5.31 x 10 6 56,586

Daphnid 48-hr LC 50 (Acute) 51.93 1.57 x 10 6 30,233

Marine Fish 96-hr LC 50 (Acute) 131.73 1.03 x 10 7 78,190

Mysid 96-hr LC 50 (Acute) 102.43 1.21 x 10 8 1,181,295

Green Algae 96-hr EC 50 (Acute) 23.33 1.11 x 10 5 4,758

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

In addition, it is not anticipated that DMDS residues will be subject to photodegradation in nearby water bodies adjacent to fumigated fields by in large. Therefore, it is not expected that large quantities of methanesulfinic acid or sulfuric acid, will form in significant quantities in water. Therefore, DMDS app ears to be the main stressor for aquatic and terrestrial organisms associated with soil fumigation.

II.B.2. Overview of Pesticide Usage

DMDS is proposed as a new soil fumigant. Like other soil fumigants, DMDS will be used to fumigant the upper 6 to 12 inches of the soil to control soil borne pests such as nematodes, soil pathogens, and fungi. DMDS can also be used to control weeds. DMDS is currently used as an agent for petrochemical and pharmaceutical products, a gas odorant, and as an agent to control hydrogen sulfide gas emissions from oil refineries

There are two formulations of DMDS condidered for registration. Paladin TM is a liquid concentrate to be used in shank injection applications only. Paladin TM EC is proposed for use for chemigation through drip irrigation systems only. Paladin TM is proposed for use before planting of fruiting vegetables (specifically, tomatoes, peppers, and eggplant), cucurbit crops (specifically, cucumbers, squash, and melons), strawberries, onions, field grown ornamentals, and forest nursery crops. Paladin TM EC is proposed for use on all of these except onions. Immediately after fumigation, virtually impermeable films are required to cover the field with broadcast fumigation or rows for raised bedded fumigation.19 II.C. Receptors

II.C.1. Aquatic and Terrestrial Effects

The receptor is the biological entity that is exposed to the stressor (US Environmental Protection Agency, 1998). The receptor is the biological entity that is exposed to the stressor (EPA, 1998 .)

Consistent with the process described in the Overview Document (US Environmental Protection Agency, 2004), this risk assessment uses a surrogate species approach in its evaluation of DMDS. Toxicological data generated from surrogate test species, which are intended to be representative of broad taxonomic groups, are used to extrapolate to potential effects on a variety of species (receptors) included under these taxonomic groupings.

Acute and chronic toxicity data from studies submitted by the pesticide registrant along with the available open literature may be used to evaluate potential direct effects of DMDS to the aquatic and terrestrial receptors. These data include toxicity studies on the technical grade active ingredient. The open literature studies are identified through EPA’s ECOTOX database ( http://cfpub.epa.gov/ecotox/ ), which employs a literature search engine for locating chemical toxicity data for aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of data may also provide insight into the direct and indirect effects of DMDS on biotic communities from loss of species that are sensitive to the chemical and changes in structure and functional characteristics of the

affected communities.

Table II-3 provides examples of taxonomic groups and the surrogate species tested to help understand potential ecological effects of pesticides to these non-target taxonomic groups. Based on a preliminary review of the ecological effects data, DMDS is highly toxic to cold-water fish, represented by the rainbow trout and moderately toxic to warm water fish, represented by the zebrafish. It is also moderately toxic to freshwater invertebrates. Ecological toxicity studies for terrestrial species include effects to birds, mammals and terrestrial invertebrates. Although th ere is an acceptable acute oral toxicity study for birds (MRID 470528-13) and rats (MRID 451179-02 ), dietary effects are not expected from exposure to DMDS.

Table II-3. Test Species Evaluated for Assessing Potential Ecological Effects of DMDS and the Associated Acute Toxicity Classification

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

Toxic for acute oral Not Exposure Route Birds 1 Bobwhite ( Colinus virginians )

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

Insects Honey bee ( Apis mellifera L. ) MRID 474712-03 Practically non-toxic20 Table II-3. Test Species Evaluated for Assessing Potential Ecological Effects of DMDS and the Associated Acute Toxicity Classification
Taxonomic Group Example(s) of Surrogate Species Acute Toxicity Classification Zebrafish ( Danio rerio ) Moderately toxic

Freshwater fish 2
Rainbow trout ( Oncorhynchus mykiss ) Highly toxic

Freshwater invertebrates Water flea ( Daphnia magna ) Moderately toxic

Estuarine/marine fish Sheepshead minnow ( Cyprinodon variegates ) Moderately Toxic

Estuarine/marine

invertebrates Mysid ( Americamysis bahia ) Moderately Toxic

Terrestrial plants 3 Monocots – oat ( Avena sativa )

MRID 474712-02 Dicots – tomato ( Lycopersicon

esculentum )

MRID 474712-02 Not classified

Duckweed ( Lemna gibba )

MRID474712-04 Not Classified

FW: Green algae ( Pseudokirchneriella subcapitat ) Not Classified Aquatic plants and algae

FW: ( Anabaena flos-aquae )

MRID 474712-05 Not Classified

1 Birds represent surrogates for terres trial-phase amphibians and reptiles.

2 Freshwater fish may be surrogates for aquatic-phase amphibians.

3 Four species of two families of monocots, of which one is corn; six species of at least four dicot families, of which one is soybeans.21 II.C.2. Ecosystems Potentially at Risk

The ecosystems potentially at risk are often extensive in scope; therefore, it may not be possible to identify specific ecosystems during the development of a nation-wide ecological risk assessment. However, in general terms, terrestrial ecosystems potentially

at risk could include the treated field and immediately adjacent areas that may receive drift or runoff. Areas adjacent to the treated field could include cultivated fields, fencerows and hedgerows, meadows, fallow fields or grasslands, woodlands, riparian habitats, and other uncultivated areas.

Aquatic ecosystems potentially at risk include water bodies adjacent to, or down stream from, the treated site and might include impounded bodies such as ponds, lakesand reservoirs, or flowing waterways such as streams or rivers including all adjacent offchannel habitats that are permanently or intermittently connected to flowing waters. For uses in coastal areas, aquatic habitat also includes marine ecosystems, including estuaries, embayments, and near shore environments.

II.D. Assessment Endpoints

Assessment endpoints represent the actual environmental value that is to be protected, defined by an ecological entity (species, community, or other entity) and its attribute or characteristics (US Environmental Protection Agency, 1998). For DMDS, the ecological entities include the following: birds, mammals, freshwater fish and invertebrates, estuarine/marine fish and inve rtebrates, terrestrial plants, insects, and aquatic plants and algae. The attributes for each of these entities may include survival, growth, and reproduction. (See Table II.3 in Section II.F.2, the Analysis Plan, for further discussion.)

II.E. Conceptual Model

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically significant concentrations. An exposure pathway is the means by which a pesticide moves in the environment from a source to an ecological receptor. For an ecological pathway to be complete, it must have a source, a release mechanism, an environmental transport medium, a point of exposure for ecological receptors, and a feasible route of exposure.

A conceptual model is intended to provide a written description and visual representation of the predicted relationships between DMDS, potential routes of exposure, and the predicted effects for the assessment endpoint. A conceptual model consists of two major components: the risk hypothesis and the conceptual diagram (US Environmental Protection Agency, 1998).22 II.E.1. Risk Hypothesis

For Dimethyl Disulfide (DMDS), the following ecological risk hypothesis is being employed for this baseline risk assessment:

DMDS, when used in accordance with the label, results in potential adverse effects upon the survival, growth, and reproduction of non-target terrestrial and aquatic organisms. Given the high application rate and potential for of DMDS residues to dissolve in water, there is a likelihood of exposure to terrestrial and/or aquatic organisms.

II.E.2. Conceptual Diagram

The potential exposure pathways and effects of DMDS in terrestrial and aquatic environments are depicted in Figure II-1 and Figure II-2 , respectively. Solid arrows represent the most likely routes of exposure and effects; dashed lines represent potentialroutes of exposure that are not considered likely for DMDS. If direct effects to nontarget terrestrial and/or aquatic organisms occu r, terrestrial and/or aquatic animals may in turn be affected through the reductions in primary productivity and habitat and/or loss of prey items, for example. No dietary exposure is expected due to DMDS remaining in a gas phase. It is thus expected to expose terrestrial wildlife via inhalation. In addition, due to the volatility of DMDS, it is expected to expose terrestrial wildlife via air residues. Terrestrial plants may be exposed to DMDS residues via runoff and air exposure.Figure II-1. Conceptual model depicting potential risks to terrestrial animals and plants from the use of DMDS as a fumigant to control root-infesting nematodes, fungal plant diseases, weeds, and soil borne pathogens 1

23 Pre-plant soil incorporation via broadcast drip irrigation, drip irrigation to raised beds, or shank

injection to raised beds and broadcast shank

in j ection with VIF Tar p Coverin g

Leaching and Runoff
of Water Plant Matter Volatilization

In g estion Direct Contact/Root Uptake Direct Contact/Root Uptake Direct Contact Integument/Inhalation Uptake

Terrestrial plants Te r r es t r i a l Pl ant s T e rre s tria l V e rt ebr ate s Terre str i a l P l an ts Source/Tra n s port
Path w a y s

Source /Expo s ure Me dia

Red u c ed Sur v i v al a n d
Gro w th Redu ce d Sur v i v al ,Gro w t h,

a n d Re prod u c t i on Redu ce d S u r v iva l

, Gr o w th an d R epro duc tio n Rece p tors Ex p os u r e Dim e thy l Dis u lf ide gro und app lic at ion fo r T o mat oes, Pepper s, E g g p la nt, C u c u mb er s

, Sq uas h, M e lon s

, S t r a w b e r r i e s , Bl ue be r r i e s

, On io ns

, Or na m e n t al s

, a n d



### Terrestri a l An imal /Plant Risk

Stress or

A ttr i b u t e

1 So lid l i ne s r e pr e s e n t m a jo r a n d da she d line s re pre s e n t m i nor r oute s o f e x p o s u re

.Figure II-2. Conceptual model depictin g potential risks to aquatic animals and plants from the use of DMDS as a fumigan t to control root-infesting nematodes, fungal plant diseases, weeds, and soil borne pathogens 2

24 Runoff of Water & Sediment/Suspended
Solids Volatilization

In g estion Direct Contact Integument Uptake

Aquatic Plants Aquatic Vertebrates

and Invertebrates Vascular and

Nonvascular Aquatic Plants Aquatic Vertebrates

and
Invertebrates Source/Transport

Path w a y s

Source/Exposure

Me dia

Reduced Survival and
Growth 

### Aquatic Animal/Plant Risk

Pre-plant soil incorporation via drip irrigation or shank injection with VIF Tarp
Coverin g Dimethyl Disulfide ground application for Tomatoes, Peppers, Eggplant, Cucumbers, Squash, Melons, Strawvberries, Blueberries, Onions, Ornamentals, and

Reduced Survival,
Gro w th an d R e p r odu cti o n Reduced Survival,
Gro w th and Re produ c t i o n Rece p tors Ex p osure

Stressor

Attribute

2 Solid lines represent major and dashed lines represent minor routes of exposure.25 II.F. Analysis Plan

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

II.F.1.a Environmental Fate
The following are outstanding data environmental fate study requirements that EFED is requesting at this time or may request in the future:

• Environmental Chemistry Methods (ECMs) and Independent Laboratory Validations

• Aerobic and Anaerobic Aquatic Metabolism (OPPTS Guideline Nos. 835.4300)

• Field Volatility Studies (OPPTS Guideline No. 835.8100)

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

Details of the justifications for this data as well as the test substances of concern are presented in Section I.E.1.

II.F.1.b Ecological Effects

A total of 17 registrant-submitted studies are available for assessing the potential effects of DMDS on non-target organisms. The results (and adequacy) of these will be presented in the risk assessment. These include avian acute oral and acute inhalation; freshwater fish and aquatic invertebrate toxicity; estuarine/marine fish, mollusk and shrimp toxicity; terrestrial and aquatic plant toxicity; and bee toxicity. The principal data gaps at this point appear to be for fish early life-stage and aquatic invertebrate life-cycle studies due to the uncertainty about DMDS persistence in the water column.

Appendix F lists the status of the ecological effects data requirements for DMDS. The following effects data are needed for ecological risk assessment for DMDS:

850.1300 Aquatic Invertebrate Life Cycle (Freshwater). This study is required based on the outdoor use and uncertainty concerning aquatic exposure and persistence.

850.1350 Aquatic Invertebrate Life Cycle (saltwater). This study is required based on outdoor use and current aquatic modeling indicating the potential for chronic aquatic exposure to DMDS. In addition, there is uncertainty about the persistence of DMDS in the aquatic environment (40CFR Part 158).

850.1400 Early Life-stage Fish (freshwater)

. This study is required based on the outdoor use and uncertainty concerning aquatic persistence. Current aquatic modeling indicates the potential for chronic aquatic exposure to DMDS.26 850.1400 Early Life-stage Fish (saltwater) . This study is required based on outdoor use and current aquatic modeling indicating the potential for chronic aquatic exposure to DMDS. In addition, there is uncertainty concerning the persistence of

DMDS in water.

850.1350 Aquatic Invertebrate life cycle (estuarine/marine). Current aquatic modeling indicates the potential for chronic aquatic exposure to DMDS. Also, the acute aquatic

EEC for ornamentals is > 0.01 of the acute LC 50 for marine/estuarine invertebrates (40CFR Part 158).

850.1400 Early Life-stage Fish (saltwater) . Current aquatic modeling indicates the potential for chronic aquatic exposure to DMDS. Also, the acute aquatic EEC for

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

850.1400 Early Life-Stage Fish (freshwater). Current aquatic modeling indicates the potential for chronic aquatic exposure to DMDS. Also, the chronic 60-day aquatic EECs

for both turf and ornamentals are > 0.1 of the NOAEL in the early life-stage study with freshwater fish (40CFR Part 158).

850.1350 Aquatic Invertebrate life cycle (freshwater). Current aquatic modeling indicates the potential for chronic aquatic exposure to DMDS. Also, the acute aquatic

EEC for ornamentals is > 0.01 of the acute LC 50 for marine/estuarine invertebrates (40CFR Part 158). Terrestrial Plant (special study for gases) – MRID 47471202 has been submitted and reviewed by EFED. However, the toxicity metric provided is not compatible with the existing modeling methods available to estimate the effect of DMDS total residues to terrestrial plants through air exposure. This study can become upgradable if data regarding the headspace volume is provided. If this is not possible, a new study is requested and EFED recommends that the regist rant submits a protocol for the Agency to

review.

II.F.2. Measures of Effect and Exposure

II.F.2.a Exposure

To address the potential for aquatic exposure to DMDS and major degradates, PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) will be used to estimate one-in-ten year surface water acute and chronic estimated exposure concentrations (EECs). Since major degradates such as methanesulfonic acid, methanesulfinic acid, and sulfuric acid are not expected to be of toxicological concern (as discussed in Section II.B.1), EECs are based on parent DMDS alone.

Since DMDS has a high vapor pressure and is used as a soil fumigant, volatility and diffusion is an important dissipation process from the soil. The volatility algorithm in PRZM has not been fully validated in EFED as of this time. However, considering thevolatile nature of this fumigant, EECs will be calculated using the consideration to volatility or tarps in risk estimates for aquatic plants and animals presented in Section IV.A. The volatility routine used in PRZM for this risk assessment assumed a static temperature in the soil over time. Therefore, the modeling assumes that otherwise temperature dependent variables such as soil degradation rates and Henry’s Law Constant

remain constant over time.

One other important consideration in the exposure estimation for DMDS for aquatic animals and plants includes the determination of DMDS loadings in the field after tarp removal 12 days after the application, as required by the proposed label It is possible to adjust the application rate to account for thie loss in loading in the soil due to biodegration under the tarp to determine EECs effectively modeling the fate and transport of DMDS after the tarp is removed. Give n the limited field volatility dataset for DMDS applications accompanied with VIF tarp covering, it is assumed that there is no loss of DMDS due to volatile residues diffusing through the soil and tarp throughout the twelve day period following the application. For aerobic soil metabolism, the following reaction rate equation for first-order degradation can be used to estimate the percent of DMDS loadings after 12 days: 

## [ ] [ ]

27 kt t e DMDS DMDS

− =

0 where [DMDS] t represents the concentration or loading of DMDS after 12 days, [DMDS] 0 represents the initial concentration or loading of DMDS, t is the time period of interest (12 days), and k is the rate constant which is equal to the following equation for first-order degradation:

lifehalf k

−

= 2ln

Since DMDS is highly soluble in water, ground water contamination of DMDS either under the tarp in areas with shallow ground water or due to leaching associated with rain events after the tarp is removed is possible. The Tier I model Screening Concentration in Ground Water (SCI-GROW v2.3, Jul. 29, 2003; USEPA, 2002b) is used to calculate acute and chronic EECs of DMDS in water associated with fumigations. Volatilization is not taken into account in this model. Furthermore, since DMDS ground water contamination is possible under the tarp, the full loading of applied DMDS is considered for EECs. Since major degradates were not found to be of toxicological conern, only DMDS EECs are evaluated.

To address the potential of terrestrial exposure to DMDS residues in the air, the Probablistic Exposure and Risk Model for Fumigants (PERFUM) (v. 2.5.1, 7/2/2008)

will be used estimate the concentration of DMDS residues in the air. Field volatilization flux rates are entered into PERFUM consistent with meteorological data in terms of the time of day that the flux was measured. The upper-bound air EEC is the 90 th percentile predicted concentration corresponding to the time period which results in the highest concentrations close to the edge of the field. Since PERFUM is not an EFED model, risk determinations are presented in the Risk Description Section in Section IV.B.2. The risk28 will only be described with the EECs estimated from field flux in field volatility studies where high barrier tarps were used, which are most representative to the label requirements of the application of a VIF tarp. However, additional characterization will be provided using the remaining field volatility studies which measured flux from low barrier tarps. Screening tools which are currently being validated be EFED, such as the Screening Tool for Inhalation Risk (STIR) are not appropriate for a fumigant risk assessment since the risk hypothesis already assumes that ecological risk exists due to exposure to air residues of DMDS given its exceptionally high vapor pressure.

II.F.2.b Effects

Table II-4 lists the measures of environmental exposure and ecological effects used to assess the potential risks of DMDS to non-target organisms. The methods used to assess the risk are generally consistent with those outlined in the document “Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs (2004)”29 Table II.4. Measures of Ecological Effects and Exposure for DMDS

Assessment Endpoint Surrogate Species and Measures of Ecological Effect 1 Measures of Exposure

Survival Bobwhite acute inhalation LC 50 Bobwhite Birds 2

Reproduction and growth Bobwhite and mallard chronic reproduction NOAEC and LOAEC (no studies available)

Survival Laboratory rat acute inhalation

LC 50 Mammals

Reproduction and growth Laboratory rat oral reproduction

chronic NOAEC and

LOAEC Air Concentration

Survival Rainbow trout and bluegill

sunfish acute LC 50 (Zebrafish study available) Peak EEC 4 Freshwater

fish 3

Reproduction and growth Fathead minnow chronic (early life-stage)

NOAEC and LOAEC (No study available) 60-day average EEC 4

Survival Water flea (and other freshwater invertebrates) acute EC 50 Peak EEC 4 Freshwater

inverte

-brates

Reproduction and growth Water flea chronic (life cycle)

LOAEC (No study available) 21-day average EEC 4

Survival Sheepshead minnow acute LC 50 Peak EEC 4 Estuarine/
marine fish

Reproduction and growth Sheepshead minnow chronic (early life-stage) NOAEC

and LOAEC (No study available) 60-day average EEC 430 Table II.4. Measures of Ecological Effects and Exposure for DMDS

Assessment Endpoint Surrogate Species and Measures of Ecological Effect 1 Measures of Exposure

Survival Eastern oyster acute EC 50 and mysid acute LC 50 (No study available) Peak EEC 4 Estuarine/
marine
inverte
-brates

Reproduction and growth Mysid chronic NOAEC and LOAEC (No study avalable) 21-day average EEC 4

Terrestrial plants 5

Survival and growth Monocot and dicot seedling emergence and vegetative vigor EC 25, EC 05 , and

NOAEC values Air cocentrations to non-target

areas

Insects
Survival (not quantitatively assessed) Honeybee acute contact (MRID) Maximum application rate

Aquatic plants and algae Survival and growth Algal and vascular plant (i.e., duckweed) EC 50 and NOAEC values for growth

rate and biomass

measurements Peak EEC

1 If species listed in this table represent most commonly encountered species from registrant-submitted studies, risk assessment guidance indicates most sensitive species tested within taxonomic group are to be used for

baseline risk assessments.

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

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

4 One in 10-year return frequency.

5 Four species of two families of monocots - one is corn, six species of at least four dicot families, of which one is soybeans. LD 50 = Lethal dose to 50% of the test population; NOAEC = No observed adverse effect concentration; LOAEC = Lowest observed adverse effect concentration; LC 50 = Lethal concentration to 50% of the test population; EC 50 /EC 25 = Effect concentration to 50%/25% of the test population.31 Birds

The effect of DMDS on the Bobwhite quail ( Colinus virginianus ) is used to represent the effect for all birds, as well as reptiles and terrestrial-phase amphibians. In an acute inhalation toxicity study, 16- to 17-week old northern bobwhite quail were exposed by whole-body inhalation to DMDS (purity ≥ 98.53%) for 4 hours. The LC50= 1.7mg/L will

be used in this assessment.

No avian reproductive study is available or requested based on persistence data in the terrestrial environment (in air) and because residues are not expected to be uptake by crops due to pre-plant soil incorporation applications for this fumigant.

Fish

Fish are represented by a warm-water species and a cold-water species. An acceptable acute Zebra fish ( Danio rerio ) study resulted in a 96 hour LC 50 =7.50mg/L (MRID 470528-15). Based on the results of this study, DMDS would be classified as moderately toxic to Zebrafish ( Danio rerio ) in accordance with the classification system

of the U.S. EPA.

An acceptable acute Rainbow trout ( Oncorhynchus mykiss ) study (MRID 470528- 14) resulted in an LC 50 =0.96 mg/L that will be used in this assessment. Based on the results of this study, DMDS would be classified as highly toxic to Rainbow Trout in accordance with the classification system of the U.S. EPA.

No chronic fish studies are available. Due to the acute risks identified for fish and the uncertainty from the absence of data for persistence in the aquatic environment, a chronic fish study will be requested.

Aquatic Invertebrates

The effect of DMDS to aquatic invertebrates is represented by Daphnia magna. An acceptable 48 hour acute toxicity test (MRID 470528-16) for DMDS was received. The

48-hour LC 50 /EC 50 was 1.61 mg ai/L. Based on the results of this study, DMDS would be classified as moderately toxic to Daphnia magna in accordance with the classification system of the U.S. EPA.

Estuarine/marine fish

In an acceptable 96-h acute toxicity study (MRID 473075-04), Sheepshead Minnow ( Cyprinodon variegates ) were exposed to DMDS under static renewal conditions. Based on the results of this study, DMDS would be classified as moderately toxic to Sheepshead Minnow ( Cyprinodon variegatus ) on an acute toxicity basis in accordance with the classification system of the U.S. EPA.32 Estuarine/marine invertebrates

The effect of DMDS on marine invertebrates is represented by the mysid. An acceptable acute mysid toxicity test resulted in an LC50=4.9mg/L (3.9-6.1) (MRID 473075-05). Based on the LC 50 in this study (4.9 mg ai/L), DMDS would be categorized as moderately toxic to mysid shrimp on an acute toxicity basis. This value will be used in

the assessment.

Terrestrial Plants

A supplemental vegetative vigor study was received to demonstrate the effect of DMDS on plants. The effect on DMDS on the vegetative vigor of monocot (corn, Zea

mays ; onion, Allium cepa ; oat, A vena sativa; and ryegrass, Lolium perenne ) and dicot (cabbage, Brassica oleracea ; soybean, Glycine max ; sugarbeet, Beta vulgaris ; lettuce,

Lactuca sativa ; tomato, Lycopersicon esculentum ; and radish, Rapahnus sativus ) crops was studied at nominal concentrations of 18.8, 37.5, 75, 150, and 300 lbs a.i./A.

The highest application rate used in the study was 300lb/A. This is below the proposed application rate of 455lb/A. The most sensitive dicot for both height and weight was tomato. An acceptable study resulted in an EC 25 =82 lbs/A for dry weight and an

EC 25 =55 lbs/A for height. The NOAEC=37.5lb/A for tomato.

Terrestrial Invertebrates

The effect of DMDS on terrestrial invertebrates is represented by the Honey bee ( Apis mellifera ). This acceptable study resulted in a 48 hour LD 50 >100μg/bee (MRID 474712-03). This classifies DMDS as practically nontoxic to bees. This value will be

used in the assessment.

Aquatic Plants

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

Lemna . An acceptable study resulted in a Frond EC 50 =28mg/L. This value will be used

in this assessment.

The most sensitive nonvascular plant species was Anabaena flos-aquae . An acceptable study (MRID 474712-05) resulted in a NOAEC <0.17mg/L, an EC 05 = 0.011 mg/L to be used to assess listed species, and a 96h EC50=0.32mg/L (0.11-0.90 mg/L) for cell density.33 

### III. Analysis

III.A. Use Characterization

Table III-1 is a summary of the new use patterns for DMDS. Two formulations of DMDS are proposed for registration: PaladinTM (98.8% a.i.) and Paladin TM EC (93.8% ai). Paladin TM is a liquid applied to the soil by shank injection. An illustration of broadcast shank injection shown in Figure III-1, and raised bed shank injection is

shown in Figure III-2 . Paladin EC TM is an emulsifiable liquid concentrate applied to the soil by chemigation through drip tapes. Both formulations are applied in the solution phase and then are expected to volatilize in the soil given the high vapor pressure and mechanism of action as a fumigant. Both formulations are also applied to the soil before plating then covered with a virtually impermeable film. For all crops and formulations, the maximum application rate is 455 lbs. a.i./A to be applied once per season. Both formulations may be used for all crops except for onions where only the PaladinTM formulation is applied.

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

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

Paladin EC TM DMDS formulations.

USE Formulation SINGLE

APP. RATE (lbs. a.i./A) NUMBER

OF APPS. SEASONAL

APP. RATE (lbs. a.i./A) INTERVAL

BETWEEN APPS. (days) APPLICATION

METHOD
Fruiting Vegetables

• Tomatoes

• Peppers

• Eggplant Paladin TM

and

Paladin TM

EC 455 1 455 N/A • Drip Irrigation

• Shank

Injection to

Raised Beds

• Broadcast

Shank Injection

Curcurbit Crops

• Cucumbers

• Squash

• Melons Paladin TM

and

Paladin TM

EC 355 - 455 1 355 - 455 N/A • Drip Irrigation

• Shank

Injection to

Raised Beds

• Broadcast

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

Paladin EC TM DMDS formulations.

SINGLE SEASONAL INTERVAL

34 USE Formulation APP. RATE NUMBER (lbs. a.i./A) OF APPS. APP. RATE (lbs. a.i./A) BETWEEN APPLICATION APPS. (days) METHOD

Small Fruit Crops

• Strawberries

• Blueberries

Field Grown

Ornamentals

Forest Nursery Crops Paladin TM

and

Paladin TM

EC 310 - 455 1 310 - 455 N/A • Drip Irrigation

• Shank

Injection to

Raised Beds

• Broadcast

Shank Injection

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

• Shank

Injection to

Raised Beds

• Broadcast

Shank Injection

The label requires the fields or beds remained covered with the tarp, which is to remain undisturbed for a minimum of 12 days. For chemigation, all drip tapes must be buried under the tarp as well. An illustration of flat-fume or broadcast fumigation, which is most commonly carried out with shank injection, is shown in Figure III-1. An illustration of fumigation with raised beds which is shown for shank injection but is often also employed with drip irrigation is shown in Figure III-2.

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

.Many of the management practices that are typically required for other fumigants are required on the label. Soil temperatures of 55oF to 90 oF are required on the label. At the lower end of this temperature range, volatilization of DMDS will be limited, with increased volatilization rates at the upper end of the temperature range. Given that the vapor pressure is directly related to temperature, higher temperatures would imply that evaporation rates would increase. In addition, the label requires that soil moisture be maintained by at least 75 percent of field capacity from two inches below the soil surface to the depth of injection for shank applications, or at or near field capacity for drip irrigation. Such conditions help seal the fumigant under the ground as DMDS is very soluble (University of Wisconsin, 2010).

Fumigants are typically used to treat the upper 6 -12 inches of the soil. As such, fumigants are typically shank injected to depths of approximately 25 cm. (Gilreath and Santos, 2004). Fumigation occurs as volatilized residues move upwards and horizontally in the soil column. Fumigants are also applied via drip irrigation chemigation at the surface or buried under the ground. However, water sealing methods such as required for DMDS on the label enable the chemical to be distributed to approximately a depth of 5 inches below the ground (Overman, et al., 1987).

VIF tarps are required on the label to cover a treated field with DMDS for at least 12 days after the application. A range of tarps including low density polyethylene (LDPE), metalized tarps, and VIF tarps were tested under field conditions with diemthyl disulfide. This is further discussed in Section III.B.1.b and Appendix G. LDPE is composed of single layers of material. However, VIF tarps are composed of multiple layers of material consisting of a dense material such as ethylene vinyl alcohol or nylon between two layers of polyethylene (Papiernik and Yates, 2001). Metalized films are often composed of multiple layers of material, including one layer of plastic material with a metal layer interwoven. It is thought that metal provides an added level of

35impermeability due to its rigid properties (Mapleston, 1992). Since VIF tarps are required on the label, the one submitted study conducted with the VIF tarp is only considered for the inhalation assessment for mammals and birds. However, other field volatility studies with higher permeable tarp material conducted during warmer times of the year, at other multiple locatoions, and with different application methods than shank injection to raided beds justify the need for additional field volatility studies to be conducted with VIF tarps (see Appendix G). The loss due to volatilization through the tarp is not considered in the reduction of loadings for the aquatic exposure assessment.

III.B. Exposure Characterization

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

environmental fate are summarized below in Tables III-2 and III-3 . A description of detailed environmental fate and transport characteristics of DMDS can be found in Section III.B.1 below and in Appendix A.

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

Parameter Value Reference

Chemical Structure

PC Code 029088

CAS number 624-92-0

Common name Dimethyl Disulfide

SMILES Notation S(SC)C

Molecular formula C 2 H 6 S 2
Molecular weight 94.2 g/mol MRID# 46903506

IUPAC name methyldisulfanylmethane Chemindustry.com

CAS name Dimethyl Disulfide Epi Suite

Physical State Clear Liquid MRID#s 46903505 and 46903511

Melting point/range -84.7oC MRID # 46903506

Boiling point/range 109 - 110 oC MRID # 46903509

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

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

Vapor pressure 22.55 torr at 20oC MRID# 46903506

Henry’s Law Constant 0.001 atm

· m 3 /mol MRID # 46903510

Octanol/water partition coefficient (Log K OW ) 1.77 MRID # 46903509

3637 Table III-2: Selected physical and chemical properties of DMDS.

Parameter Value Reference

Octanol/air partition coefficient (Log K OA ) 3.076 EPI Suite

Table III-3. Environmental Fate Properties of DMDS.

Parameter Value Reference/Comments

Hydrolysis t 1/2 Stable at pH 5, 7, and 9 MRID# 46903532

Photolysis t 1/2 in

water 1.3 days,

possible degradates: methanesulfonic acid (CH 4 S), methanesufinic acid (CH 4 O 2 S), or sulfuric acid (H 2 SO 4 ) (total 54.2 percent) MRID# 42900201 Supplemental

Photolysis t 1/2 on soil N/A Waived

Degradation t 1/2 in

air 34 minutes (atmospheric half life, reaction with OH radicals)

42 minutes (atmospheric lifetime, reaction with OH radicals) EPI Suite

Wine et al., 1981

Soil metabolism,

Aerobic t 1/2 Total System France Clay Loam –3.74 days Total System Switzerland Clay – 2.86 days Florida Sand – No major transformation through 120 days California Sandy Loam – No major transformation through 120 days

Major degradates: Methanesulfonic acid – soil (<33.17 percent) Cabron dioxide (CO2) – air (<30.81 percent) MRID 47052819

Half-lives back calculated assuming DMDS residues degrade contribute to the

total formation of

methanesulfonic acid

residues Foreign soils taxonomically representative of US soils

Aquatic metabolism

Anaerobic t 1/2 Unknown Outstanding Data Gap

Aquatic metabolism

Aerobic t 1/2 Unknown Outstanding Data Gap

Soil-Water Partition Coefficient (K d ) California, USA Sandy Loam – 0.54 mL/g (0.6 % OC) Speyer, Germany Sandy Loam – 0.68 mL/g (2.3 % OC) Mechtildshausen, Germany Loam – 0.60 mL/g (1.28 % OC) Mussig, France Clay Loam – 0.55 mL/g (2.98 % OC) Bretagne, France Silt Loan -0.86 mL/g (2.0 % OC) MRID 46917014

MRID 46917015 Foreign soils taxonomically representative of US soils38 Table III-3. Environmental Fate Properties of DMDS.

Parameter Value Reference/Comments

Field Volatility Yuma, AZ Loamy Sand

- Shank Injection to Raised Beds (LDPE Tarp)
3,797 μ g/m 2 s cumulative flux; 81.43 percent mass loss at 780 lbs. a.i./A through 65 hours postapplication

Nipomo, CA Sandy Loam

- Drip Irrigation to Raised Beds (LDPE Tarp)
1,295 μ g/m 2 s cumulative flux; 27.64 percent mass loss at 602 lbs. a.i./A through 72 hours postapplication

Cantua Creek, CA Clay Loam Broadcast Shank Injection (LDPE Tarp)
2,451 μ g/m 2 s cumulative flux; 54.29 percent mass loss at 580 lbs. a.i./A through 72 hours postapplication

Dover, FLLoamy Sand Shank Injection to Raised Beds (Metalized Tarp)

383.53 μ g/m 2 s cumulative flux; 8.1 percent mass loss at 608 lbs. a.i./A through 48 hours postapplication

Bradenton, FL Sand Shank Injection to Raised Beds (LDPE Tarp)
2,848 μ g/m 2 s cumulative flux; 57.82 percent mass loss at 633 lbs. a.i./A through 48 hours postapplication

Tifton, GA (Field 1) Loamy Sand (VIF Tarp) Pre Bedded Shank Injection

613.69 μ g/m 2 s cumulative flux; 35.20 percent mass loss at 546.7 lbs. DMDS/A through 320 hours postapplication

Tifton, GA (Field 2) Loamy Sand (LDPE Tarp) Pre Bedded Shank Injection
1,589 μ g/m 2 s cumulative flux; 69.74 percent mass loss at 538.8 lbs. DMDS/A through 320 hours postapplication

Tifton, GA (Field 3) Sand (LDPE Tarp) Pre Bedded Shank Injection

842.97 μ g/m 2 s cumulative flux; 38.33 percent mass loss at 568.9 lbs. DMDS/A through 320 hours postapplication MRID 47052821

MRID 47052822

MRID 47052823

MRID 47052824

MRID 47820001

Terrestrial Field Dissipation N/A Waived

Aquatic Field Dissipation N/A Waived39 Table III-3. Environmental Fate Properties of DMDS.

Parameter Value Reference/Comments

Accumulation in Fish, max. BCF N/A Waived

III.B.1. Environmental Fate and Transport Characterization

The loss of DMDS in terrestrial environments appears to be predominantly dependent on volatilization and to a lesser extent on leaching and soil biodegradation. DMDS’s vapor pressure of 22.55 torr at 20°C and Henry’s Law Constant of 0.001

atm•m 3 /mol suggest that high volatilization rates can occur in soil and water respectively (MRID No. 46903510). The importance of other competing processes such as leaching, biodegradation, and adsorption to the soil particles will certainly depend on DMDS emission rate from the fumigated fields, whic h may be mitigated by a substantial amount using high barrier tarps with material of low permeability which is representative proposed label requirements of VIF tarp covering.

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

In soil, the aerobic metabolism of DMDS (MRID No. 4705282 ) in a closed system laboratory study suggests that biodegradation occurred via a diffusion – deposition equilibrium process as evidenced by the observation that the vast majority of DMDS was detected in the headspace within 5 minutes of the application, and subsequent buildup of degradates in the soil in France clay loam soil and Switzerland clay soil. The major

metabolite detected from the soil was methanesulfonic acid which accounted for a maximum of 33.17 percent of the material ba lance 14 days after application in France clay loam soil, and 32.86 percent of the material balance 21 days after application in Switzerland clay soil. Methanesulfonic acid forms through the breaking of the disulfide bond in DMDS. Only trace amounts of DMDS were extracted throughout each study. In addition, carbon dioxide was detected in the headspace, accounting for 30.81 percent of the material balance in France clay loam soil and at 59 days after application, and 27.24 percent of the material balance at 120 days after application in Switzerland clay soil (both at study termination). In California loamy sand soil and Florida sand soil, no degradation was observed as most DMDS residues remained in the headspace over time. The diffusion-deposition process apparent from the France clay loam soil and Switzerland clay soil is possible in the environment under field conditions given the vapor pressure of 22.55 torr and temperature of 20 o C with soil and airspace under a high barrier tarp. In addition, this process has been documented with numerous reduced sulfur compounds, including DMDS (Castro, 1991; Banwart and Bremner 1976). Considering this

observation and the observation that trace amounts of DMDS were retrieved from the soil, a half life for DMDS in the soil was back-calculated attributing the formation of methanesulfonic acid to the decline of DMDS in the total system. This is demonstrated

Table III-4 for France clay loam and Switzerland clay soil. The half lives of DMDS in40 soil ranged from between 2.86 days in France clay loam to 3.74 days in Switzerland clay

soil.

Table III-4. Formation of methanesulfonic acid and decline of DMDS in France clay loam aerobic soil metabolism laboratory study.

Switzerland clay France clay loam Time (Days) Methanesulfonic

acid Estimate

DMDS Methanesulfonic

acid Estimate

DMDS

0 1.42 98.58 1.45 98.55

1 8.09 91.91 6.17 93.83

4 17.47 82.53 21.68 78.32

7 25.67 74.33 29.1 70.9

11 30.34 69.66 32.5 67.5

14 32.16 67.84 33.17 66.83

21 32.86 67.14 32.97 67.03

59 26.8 73.2 35.3 64.7

120 5.76 94.24

In water, DMDS’s high solubility in water of 2,702 mg/l and low average K d of 0.641 mL/g (range 0.54 mL/g – 0.86 mL/g for five soils) suggest that residues can readily be transported via water and is weakly retained by soil. The high Henry’s Law Constant

of 0.001 atm•m 3 /mol and rapid photodegradation of DMDS from water suggest that volatilization and photolysis are the primary environmental routes of dissipation from surface water. DMDS was stable to hydrolysis at pHs 4, 7, and 9 at 50oC. The extent ofbiodegradation of DMDS in the aquatic environment is unknown. The calculated halflife of 1.17 days in 0.01 M phosphate (pH 7) when irradiated with a xenon light source for a period of 24 hours. Two major degradates were detected and may have included either methanesulfonic acid, methanesulfinic acid, or sulfuric acid (MRID 47052818) were detected at a maximum total of 54.2 percent of the material balance, although a test to definitively identify the degradates was not performed. The registrant proposed that formaldehyde may form intermediate to the degradates identified. However, formaldehyde was not detected with the limited sampling that was conducted during the aquatic photolysis experiment.

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

Acidification from DMDS

Soil acidification from methanesulfonic acid is especially possible on soils with low buffering capacities (sands) and absence of free carbonates. Since methanesulfonic acid is a major degradation product of DMDS degradation in soil, one mole of DMDS (CH 3 -S-S-CH 3 ) can theoretically form 4 moles of hydrogen (H + ) from dissociation of

CH 3 SO 3 H and oxidation of sulfonic acid. The acid equivalence ratio of calcium

carbonate or CaCO 3 (100 grams/mole/ 2) /DMDS (94 grams mole/4) is 2.127. Therefore, an application of 455 lbs of DMDS would require a lime application rate of 968 lbs

CaCO 3 /A for complete neutralization.41 III.B.1.b Fate and Tran sport in Atmosphere

A series of field volatility studies were conducted using both low barrier and high barrier tarps for DMDS Field volatility studies were conducted. Low density polyethylene (LDPE) low barrier tarps were applied in several study sites in Florida, California, Georgia, and Arizona using a variety of application methods on the label such as broadcast shank injection, shank injection to raised beds, and drip irrigation to raised beds. In general, diffusion into the atmosphere was large and accounted for 38.33 – 81.43 percent of the amount applied, with the exception of Nipomo, CA where DMDS volatile flux only accounted for approximately 27.64 percent of the amount applied. In general, low air concentrations and therefore fl ux in the vicinity of application sites were observed after 48 – 72 hours post-application. In addition, absolute peaks of flux occurred during the afternoon hours. The flux temporal profiles for the lower barrier films are shown in Appendix G since these are not the basis of the risk assessment given the label restriction to VIF tarps.

In addition, there were two studies that were conducted with higher barrier films. DMDS volatile flux accounted for 8.1 percent of the amount applied for metalized film applied after shank injection to raised beds in Dover, FL. Furthermore, DMDS was applied to via a pre-bedded shank application in one field of Tifton, GA with a VIF tarp. Here, DMDS residues in air accounted for 35.20 percent of the amount applied over a 320 hour period post-application. It is likely that DMDS flux was observed over a much larger period in Georgia than with the LDPE tarps since much of the DMDS material that remained in the soil in response to the high performance of the VIF tarp. Generally speaking, absolute peaks in flux also occurred in the afternoon hours after the application with flux gradually decreasing afterwards. Ho wever, the amplitude of absolute peaks in the field volatility were generally were not as large as the studies conducted with the low density polyethylene tarps. Table III-5 shows the flux profiles and percent of applied diffused from the soil in the Tifton field volatility site with VIF tarps. The flux profiles for 7 other studies where LDPE and metalized films are used are shown in Appendix G.

Table III-5. Field flux from Tifton, GA Field 1 DMDS Shank Injection to Raised Beds with High Density Polyethene Tarp Study (application rate = 546.7 lbs. a.i./A).

Sample Time DMDS Volatile Flux during

Period ( μ g/m 2 s) DMDS Percent of Applied during

Period

(%) Time Duration (hours) Day 0, Hours 0 – 5 3.35 0.10 5 Day 0, Hours 5 – 11 3.16 0.11 6 Day 0, Hours 11 – 17 16.21 0.57 6 Day 0, Hours 17 – 23 21.47 0.76 6 Day 0, Hour 23 – Day 1, Hour 5 14.33 0.51 6

Day 1, Hours 5 – 11 22.06 0.78 6 Day 1, Hours 11 – 17 42.84 1.51 642 Table III-5. Field flux from Tifton, GA Field 1 DMDS Shank Injection to Raised Beds with High Density Polyethene Tarp Study (application rate = 546.7 lbs. a.i./A).

Sample Time DMDS Volatile Flux during

Period ( μ g/m 2 s) DMDS Percent of Applied during

Period

(%) Time Duration (hours) Day 1, Hours 17 – 23 53.37 1.88 6 Day 1, Hour 23 – Day 2, Hour8 8.93 0.47 9

Day 2, Hours 8 – 20 54.37 3.83 12 Day 2, Hour 20 – Day 3, Hour 8 19.24 1.36 12

Day 3, Hours 8 – 20 38.66 2.73 12 Day 3, Hour 20 – Day 4, Hour 8 29.13 2.05 12

Day 4, Hours 8 – 20 21.73 1.53 12 Day 4, Hour 20 – Day 5, Hour 8 19.84 1.40 12

Day 5, Hours 8 – 20 13.79 0.97 12 Day 5, Hour 20 – Day 6, Hour 8 8.01 0.56 12

Day 6, Hours 8 – 20 12.85 0.91 12 Day 6, Hour 20 – Day 7, Hour 8 10.20 0.72 12

Day 7, Hours 8 – 20 9.52 0.67 12 Day 7, Hour 20 – Day 8, Hour 8 5.32 0.37 12

Day 8, Hours 8 – 20 18.54 1.31 12 Day 8, Hour 20 – Day 9, Hour 8 9.17 0.65 12

Day 9, Hours 8 – 20 7.30 0.51 12 Day 9, Hour 20 – Day 10, Hour 8 4.49 0.32 12

Day 10, Hours 8 - 20 Day 10, Hour 20 – Day 11, Hour 8 16.47 1.16 12

Day 11, Hours 8 – 20 27.60 1.95 12 Day 11, Hour 20 – Day 12, Hour 0 16.93 0.60 6

Day 12, Hours 0 – 6 30.06 1.06 6 Day 12, Hours 6 – 18 32.43 2.29 12 Day 12 Hour 18 – Day 13 Hour 6 15.91 1.12 12

Day 13 Hours 6 – 18 6.41 0.45 12

Total Volatile Flux 613.69 35.20 320Table III-5. Field flux from Tifton, GA Field 1 DMDS Shank Injection to Raised Beds with High Density Polyethene Tarp Study (application rate = 546.7 lbs. a.i./A).

43 Sample Time DMDS Volatile Flux during

Period ( μ g/m 2 s) DMDS Percent of Applied during

Period Time Duration

(%) (hours) Application Start Time Afternoon of February 7

1. Exact start time of application in study unspecified.

2 Percent of DMDS flux from soil to air calculated using the formula,

% DMDS Mass Loss = 

# ∑ (DMDS Flux

= n

i 1 i x Sample Period i )

DMDS Field Study Application Rate.

Several studies and calculations indicate that the primary sink of DMDS in the atmosphere is reactivity with hydroxyl radicals and photodissociation. AOP v1.92 in EPISuite estimates DMDS’s atmospheric half life at 34 minutes due to hydroxyl radical reactivity. A laboratory degradation in air study in the open literature utilized a flash photolysis-resonance fluorescence technique to measure DMDS’s atmospheric lifetime at 42 minutes. In this experiment, DMDS was exposed to a mercury lamp at a monitoring wavelength of 185 nm (ultraviolet radiation) with an absorption cross section of 159 x 10 -

19 cm 2 in a jacketed Pyrex reaction cell flushed with water which was converted to hydroxyl radicals when exposed to the artificial light (Wine et al., 1981).

An atmospheric degradation mechanism including the interaction between hydroxyl radicals and photodissociation has been developed and evaluated for DMDS. The DMDS hydroxyl adduct is initially formed . Subsequent abstraction in parallel with the photodissociation of DMDS forms the methyl thiol radical. With further photoionization and addition of atmospheric nitrogen oxides to methyl thiol, methyl thionitrite is expected to form. Methyl thio l may also oxidize into a methylated sulfur dioxide and then be reduced to methylated sulfur monoxide. This atmospheric oxidation and reduction cycle repeats in two additional steps until methane sulfonic acid forms. In addition, the three atmospheric oxidation and reduction steps can also result in individual sulfur oxides to dissociate from the methylated sulfur oxides, which eventually lead to the formation of sulfuric acid from sulfates combining with water from phenomena such as water vapor, cloud droplets, or precipitation. The entire atmospheric chemistry mechanism of DMDS is shown in Figure II-1 (Fangdong et al., 1990[1], Fangdong et al., 1990[2]).Figure III-1. The atmospheric degradation pathways of DMDS.

III.B.1.b.1 Ozone Depletion Potential

DMDS is being marketed as a methyl bromide alternative. Methyl bromide has been a widely used fumigant for pre-plant soil incorporated and food commodity applications. However, methyl bromide is designated as a Class I Ozone Depleting Substance by the EPA Office of Air, and therefore possesses the largest concern for the destruction of stratospheric ozone. All Class I Ozone Depleting substances are being phased out as per the Montreal Protocol (US EPA, 2009[2]). DMDS registered uses are similar to some past and current critical exemption uses of methyl bromide.

DMDS is a reduced organosulfur compound. As such, there are no halogenated components within DMDS which would contribute to the destruction of stratospheric ozone. Furthermore, DMDS is expected to degrade quickly in the troposphere. Therefore, emissions of DMDS are not expected to contribute to any process related to stratospheric ozone depletion.

III.B.1.b.2 Global Warming Potential

DMDS’s methyl components may have the potential to contribute to climate change. Methylated compounds can be a potent greenhouse gas, and thus have the potential to absorb outgoing long-wave infrared radiation effectively (USEPA, 2002; USEPA, 2009[3]). However, given DMDS’s short residence time in the atmosphere, global warming potential is likely to be small. Constituents with residence times less than one year are not anticipated to have large global warming potentials (Don Wuebbles, personal communication, 2009).

44III.B.1.b.3 Acid Rain

Sulfates in the atmosphere, forming from anthroprogenically emitted sulfur dioxide as well as from atmospheric DMDS, as demonstrated in Figure III-1, are known to mix with precipitation and can result in wet deposition of sulfuric acid. Wet deposition of sulfuric acid is commonly known as acid rain. The reaction showing the formation of

sulfuric acid is:

SO 3 + H 2 O H 2 SO 4

Acid rain is recognized by the Agency as having adverse impacts to plants and aquatic habitats (USEPA[1], 2010). Federal Land Managers are obligated towards the protection of air quality particularly in National Park Areas under the Clean Air Act amendments of 1977. Consequently, sulfur deposition thresholds of concern have been established (U.S. National Park Service, 2010). Acid deposition is regulated under Title

IV of the Clean Air Act.

Acid rain contribution from a single DMDS application would not likely be of concern given low emissions from high barrier tarps as specified on the label. However, aggregate emissions of DMDS throughout an area with high use may contribute to acid rain events. To address the potential for acid rain, the monitoring data of rainfall which occurs over high use areas of DMDS may be requested in the future (see Section I.E.1).

III.B.1.b.4 Photochemical Ozone Creation

Potential

As DMDS is a reactive volatile organic compound (VOC) in the atmosphere, there is a potential for it to interact with atmospheric hydroxyl radicals, oxygen, and nitrogen oxides to produce ground-level ozone. Ground-level ozone is recognized by the Agency as having adverse impacts to plants and terrestrial animals (USEPA, 2010[2]), and is regulated under Title I of the The Clean Air Act as a criteria air pollutant. Figure III-1 shows that although ozone is not a direct product through any step of its degradation pathway, its chemical reaction with various trace atmospheric gases may facilitate the formation of ozone near ground-level. To address the potential risk of ozone formation from an airshed with significant DMDS use, ozone air quality air concentration monitoring data may be requested in the future.

III.B.2 Measures of Aquatic Exposure

III.B.2.a. Aquatic Exposure Modeling

PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are fate and tranpsport simulation models coupled together with the input shell pe5.pl (Aug 2007) to generate daily exposures and 1-in-10 year EECs of DMDS that may occur in surface water and benthic water pore concentrations in water bodies adjacent to application sites receiving DMDS through runoff . PRZM simulates pesticide application, movement and

4546 transformation on an agricultural field and the resultant pesticide loadings to a receiving water body (e.g., the Georgia farm pond scenario) via runoff and erosion. In the case of a volatile pesticide, its vapor pressure and enth alpy of vaporization determines the phase of the chemical (e.g., solution versus vapor phase). If the chemical is in the gas phase, runoff flux is determined from the chemical’s Henry’s Law Constant for partitioning of the gas to the water. EXAMS simulates the fate of the pesticide and resulting concentrations in surface water and benthic pore water concentrations considering the mass transfer between the sediment and water compartments. The standard scenario used for ecological pesticide assessments assumes application to a 10-hectare agricultural field that drains into an adjacent 1-hectare water body that is 2 meters deep (20,000 m 3
volume) with no outlet. The measure of exposure for aquatic species is the 1-in-10 year return peak or rolling mean concentration. The 1-in-10 year peak is used for estimating acute exposures of direct effects to aquatic organisms. The 1-in-10-year 21-day mean is used for assessing aquatic invertebrate chronic exposure. The 1-in-10-year 60-day mean is used for assessing chronic exposure to fish and aquatic-phase amphibians.

Since the PaladinTM and Paladin ECTM produc t labels require VIF tarps, it is not expected that DMDS residues will be available to runoff during the 12 day period which is required for the tarp to cover the field. Therefore, aquatic exposure modeling using PRZM/EXAMS only addresses the scenario after the tarp is removed. Degradation of DMDS residues can occur under the tarp during the 12 day period. Therefore, the maximum application rate of 455 lbs. a.i./A is adjusted for biodegradation which may occur under the tarp for the 12 day period. This adjustment is made due to the reduction of loading as determined assuming a first-order decay of DMDS as determined from the first-order rate reaction equation shown in Section II.F.2.a. This equation indicates that 16.88 percent of DMDS residues remain in the soil after 12 days according to the rate

constant based on the 90 th percentile aerobic soil metabolism half life as shown in Table

III-5 below.

Also, since DMDS is a fumigant, an additional refinement accounting for volatilization was considered. However, the validation of this component of the PRZM model has not been completed. Despite this, given the volatile nature and use of DMDS as a soil fumigant, the volatility algorithm was used to determine EECs in the water column. Additional chemical specific physical parameters such as vapor phase diffusion coefficient (DAIR) and enthalpy of vaporization (ENPY) were activated during the PRZM/EXAMS simulation accounting for volatilization. The volatilization routine usedassumes that temperature in the soil does not change over time. Therefore, temperaturedependent variables such as Henry’s Law Constant and soil degradation rates remain constant. However, risk quotients for aquatic organisms will be based on EECs predicted using the volatility algorithm. This is consistent with historical risk assessments with other fumigants.

For shank injection, chemical application method (CAM) of 8 was used in mimicking application of DMDS to simulate injection at a 25 cm through vapor diffusion, reflecting typical agricultural practices for fumigants (Gilreath and Santos, 2004). For chemigation, a CAM of 4 and an injection depth of 5 inches (12.7 cm) was47 selected reflecting the intention of maintaining a uniform distribution of the fumigant under the tarp in this layer (Overman, et al., 1987). Although drip tapes can be placed at the surface, water sealing methods, require d tarping, and diffusion under the tarp contribute towards this regime in the transport of the chemical under the soil in this

manner.

Six field scenarios - were used in estimating EECs using highest application rate of 455 lbs. a.i./Acre. All crops on the label were represented and included regions where fumigation typically occurs frequently. The scenarios included Florida tomato, Florida pepper, Florida cucumber, Florida Strawberry, California Onion, Georgia Onion, Califonia nursery, New Jersey nursery, and Oregon Christmas tree.

Table III-6 summarizes the environmental fate related input parameters for into PRZM-EXAMS. It is important to note that the risk determination will be based on the parent DMDS only and that major degradates (including methanesulfonic acid, methanesulfinic acid, and sulfuric acid) are ne glected since these constituents are not of toxicological conern as discussed in Section II.B.1. Table III-7 summarizes the crop management input into PRZM-EXAMS.

Table III-6. PRZM/EXAMS DMDS Environmental Fate Input Parameter Values in All

Scenarios. PRZM/EXAMS Input

Parameter Input Value

and Unit Comment Source

Molecular Weight 94.2 g/mol Product Chemistry -

MRID 46903506 Hydrolysis (t 1/2 ) 0 Stable MRID 46903532

Aerobic soil metabolism (t 1/2 ) 4.66 days 90 th percentile value

between the French clay loam and Switzerland clay soil studies (2.86 and 3.74 days respectively) based

on total DMDS degradation in the
system EFED Input

Parameter

Guidance

MRID 47052819

Aerobic aquatic metabolism (t 1/2 ) 9.32 days No data available

and stable to hydrolysis. Computed from EFED Input

Parameter

Guidance

MRID 4705281948 Table III-6. PRZM/EXAMS DMDS Environmental Fate Input Parameter Values in All

Scenarios. PRZM/EXAMS Input

Parameter Input Value

and Unit Comment Source

twice the parent

aerobic soil

metabolism half-life of 4.66 days. Anaerobic aquatic metabolism (t 1/2 ) 0 Stable. Conservative assumption considering the

anaerobic soil metabolism study. EFED Input

Parameter

Guidance

MRID 47052820

Vapor Pressure at 20 oC 22.55 torr Product Chemistry -

MRID 46903506 Solubility in Water at 20oC 27,020 mg/L Product Chemistry x

10 EFED Input

Parameter
Guidance

MRID 46903510

Soil-Water Partition Coefficient (K d ) 0.641 ml/g Mean of K d in 5 batch equilibrium

studies 4

Soil-water partition

coefficient not found

to correlate well with organic carbon

content in batch equilibrium studies MRID 46917014

MRID 46917015

Henry’s Law Constant 0.001

atm·m 3 /mol Product Chemistry Product Chemistry -

MRID 46903510 Aqueous Photolysis (t 1/2 ) 1.17 days (parent) Dark controlled aqueous photolysis half-life for parent. EFED Input

Parameter

Guidance

MRID 47052818

Diffusion in Air (cm 2 /day) 1 8,006.83 Extrapolated from

Graham’s Law based

on methanol

diffusion in air value EPA On-line

Tools for Site

Assessment

Calculation 349 Table III-6. PRZM/EXAMS DMDS Environmental Fate Input Parameter Values in All

Scenarios. PRZM/EXAMS Input

Parameter Input Value

and Unit Comment Source

of 0.159 cm 2 /sec (13,737.6 cm 2 /day) 2

Enthalpy (kcal/mol) 1 9.19 “DMDS

Chemical and Physical Properties” 4

1 PRZM-EXAMS ran with and without volatilization for characterization purposes.

2 Diffusion in air coefficient for DMDS is ca lculated using Graham’s Law extrapolation and methanol diffusion properties [DMDS Dair = 0.159 cm 2 /sec x (32 g/mol ÷ 94.20 g/mol) 1/2 ].

3 Available on-line: < http://www.epa.gov/athens/learn2model/part-two/onsite/

estdiffusion.htm>.

4 Available on-line: <http://www.arkema-inc.com/literature/pdf/791.pdf>.

Table III-7. PRZM/EXAMS Crop Management Input Parameters

PRZM/EXAMS Input

Parameter Input Value and Unit Comment

Application Rate and Interval 76.82 lb a.i./A (86.11 kg a.i./ha) at one application

per season PaladinTM and

PaladinTM EC label

Crop Scenarios and (Application Date) Fruiting Vegetables (Tomotoes, Peppers, and Eggplant) CA Tomato (Feb. 15) FL Tomato (Jan. 1) FL Peppers (Aug 1) Curcurbit Crops (Cucumbers, Squash, and Melons) FL Cucumber (Sept. 15) Small Fruit Crops (Strawberries and Blueberries) FL Strawberries (Sept. 1)

Onions CA Onion (Nov. 15) GA Onion (Aug. 15)

Field Grown

Ornamentals CA Nursery (Feb. 1) Assumed 25 days prior to crop

emergence as specified in PRZM crop scenarios50 Table III-7. PRZM/EXAMS Crop Management Input Parameters

PRZM/EXAMS Input

Parameter Input Value and Unit Comment

MI Nursery (Dec 1) Forest Nursery Crops OR Xmas Tree (Dec. 1) Chemical Application Method and (Incorporation Depth) CAM = 4 soil applied, uniform over incorporation depth (12.7cm)

CAM = 8 soil applied, entirely at incorporation depth (25.0 cm) Drip Irrigation

Shank Injection

Application Efficiency 1.0

1.0 Drip Irrigation

Shank Injection Spray Drift Fraction 0

0 Drip Irrigation

Shank Injection

Several labeled uses are grouped together to estimate the effects from the use of DMDS. Eggplant is modeled using the tomato scenario. Squash and melons are modeled with the cucumber scenario. The labeled uses for blueberries are modeled using the strawberry scenario. In addition, application dates were selected based in part by the minimum plantback interval on the label of 35 days. Therefore, the application dates were determined to be approximately 25 days prior the crop emergence date as specified in the PRZM/EXAMS crop scenarios since fumigation occurs 35 days before planting, the modeled application with the tarp removed will not address the12 days after the application which elapses while the tarp is on the field , and the accounting of a 3 day time allowance for seed germination.

Table III-8 presents the PRZM-EXAMS estimated concentrations in surface water. This modeling addresses fate and transport modeling of available DMDS residues after the tarp is removed. The DMDS availabl e for transport after the tarp is removed are subject to biotic and abiotic degradation from the soil and water as well as dissipation processes such as runoff and volatilization from the soil. Sample output files are provided in the Appendix C.51 Table III-8. Estimated 1-in-10 yr. exposure concentration in surface water for DMDS.

Peak Conc. 21-day Conc. 60-day Conc. Crop Scenarios and Management ( μ g/L) ( μ g/L) ( μ g/L) Tomatoes and Eggplant California Tomato Drip Irrigation 30.293 7.473 2.680 California Tomato Shank Injection 4.77x 10 -8 1.26 x 10 -8 5.20 x 10 -9 Florida Tomato Drip Irrigation 18.301 3.386 1.189 Florida Tomato Shank Injection 5.572 1.121 0.401 Peppers Florida Peppers Drip Irrigation 46.887 7.860 2.761 Florida Peppers Shank Injection 4.434 0.878 0.315 Cucumbers, Melons, and Squash Florida Cucumber Drip Irrigation 150.899 24.900 8.742 Florida Cucumber Shank Injection 9.984 1.810 0.637
Strawberries and Blueberries Florida Strawberry Drip Irrigation 203.228 45.948 16.151 Florida Strawberry Shank Injection 3.559 0.762 0.274
Onions California Onion Drip Irrigation 2.550 0.850 0.318 California Onion Shank Injection 0.239 0.074 0.027 Georgia Onion Drip Irrigation 129.477 24.390 8.594 Georgia Onion Shank Injection 3.248 0.674 0.252
Ornamentals California Nursery Drip Irrigation 7.074 2.213 0.796 California Nursery Shank Injection 0.375 0.133 0.048 Michigan Nursery Drip Irrigation 32.240 28.065 15.092 Michigan Nursery Shank Injection 0.227 0.192 0.101 Forestry Nursery Crops Oregon Xmas Tree Drip Irrigation 19.674 6.733 2.455 Oregon Xmas Tree Shank Injection 0.206 0.075 0.027

1 Maximum values shown in bold.

III.B.2.b. Ground Water Exposure

Since DMDS is highly soluble and mobile, leaching and potential ground water contamination is possible. Cases of ground water contamination may especially occur in areas over and around aquifers where water tables may be shallow and recharging of ground water may occur. Therefore, DMDS may reach ground water irregardless of tarps

cover.

The Tier I model Screening Concentration in Ground Water (SCI-GROW v2.3, Jul. 29, 2003; USEPA, 2002b) is used to calculate acute and chronic DMDS EECs in ground water. Ground water concentrations generated by SCI-GROW are based on the largest 90-day average estimated during the sampling period. Since there is relatively52 little temporal variation in ground water concen trations compared to surface water, the model predicted value can be considered to represent both the acute and chronic values. Since major degradates were not found to be of toxicological conern as discussed in Section II.B.1, only DMDS EECs are evaluated.

Input parameters for the SCI-GROW model appear in Table III-9 . These inputs were determined in accordance with current divisional guidance (USEPA, 2002b). The mean of two half-lives (based on France clay loam soil and Switzerland clay soil) was used as input. In addition, the median of five reported soil –water partition coefficients were selected. This was used in lieu of the organic carbon soil-water partition coefficient since individual soil-water partition coefficients were not found to be well correlated with the organic carbon content of the particular soils tested. All inputs in the model were determined from individual samples of physical chemical and environmental fate parameter values shown in Tables III-2 and III-3.

Table III-9. SCI-GROW Input Parameters for DMDS (Source data are in Tables III-2 and III-3)

Input Parameter Value Comments Source

Application Rate (lbs a.i./A) 455 lbs a.i./A Maximum proposed single application

rate for all uses. Proposed

PaladinTM and

PaladinTM EC

labels

Applications per Year 1 Maximum proposed number of applications per year at the maximum proposed single application rate. Proposed

PaladinTM and

PaladinTM EC

labels

Soil-Water Partition Coefficient (K d ) (L/kg) 0.60 Represents the median of five reported

K d values

Soil-water partition coefficient not found to correlate well with organic carbon content in batch equilibrium

studies MRID 46917014

MRID 46917015

Aerobic Soil Metabolism Half-life (days) 3.3 Represents the mean half life of France clay loam and Switzerland clay soils MRID 47052819

This model simulation represents impacts to ground water from a single application at the maximum application rate of 455 lbs. DMDS/A as specified on the PaladinTM and PaladinTM EC labels. However, despite this, Table III-10 shows that DMDS predicted ground water EECs are very low. This is likely due to the rapid biodegradation of DMDS residues in the soil. Volatilization is not accounted for in this model. However, loss due to volatilization is expected to be minimized in the presence of tarps.53 Table III-10. Estimated Environmental Concentrations of DMDS in Ground Water

Use (modeled annual rate) Acute (ppb) Chronic (ppb)

All uses shown in Table III-1 (455 lbs. a.i./A, single application) 1.99 1.9954 III.B.2.c. Aquatic Exposure Monitoring (Field Data)

No products containing DMDS, for use outdoors, are available in the market at this time; accordingly, no monitoring studies are publicly available concerning aquatic exposure (both surface and ground waters). However, environmental concentrations have been qualitatively detected in ground water and drinking water sources at various locations across the country (Fresenius, 1994; USEPA, 1975; Bertsch, et al., 1975; Wakeham, 1983). In general, the study sites were nearby discharge sources and estuaries where decaying biomass may result in the formation of DMDS. Furthermore, DMDS was detected at levels of 30 - 900 ng/kg in Vineyard Sound, MA between December 1978 and March 1979 (Mantoura et al., 1982), and detected at levels at concentrations < 0.1 ppm in the River Lee in England (Waggot, 1981). Although detected concentrations are low, these detections suggest that DMDS can exist in surface and ground water for some period of time.

III.B.3 Measures of Terrestrial Exposure

Exposure of terrestrial organisms to DMDS air residues is estimated using the Probablistic Exposure Model for Fumigants (PERFUM - v. 2.5.1, 7/2/2008) and TerrPlant (v. 1.2.2; 12/26/06). The PERFUM model will be used to assess inhalation exposure to terrestrial animals. This model is used because of the volatility of DMDS, which is higher than most foliar-applied pesticides. The PERFUM model was initially developed to address the issue of worker and bystander exposures to fumigants following applications to bare fields, and was evaluated during the FIFRA Science Advisory Panel in August 2004. However, EFED has used PERFUM model historically in refined air quality risk assessments for the fumigants Chloropicrin and Metam Sodium including for the California Red Legged Frog Endangered Species Assessment 3

.

The typical terrestrial exposure assessment model (TREX) for dietary exposure was not used because DMDS is applied during pre-planting, is highly soluble and mobile, and is not expected to result in systematic accumulation in plants and insects given its high solubility and low octanol-water partition coefficient. Therefore, subsequent dietary exposure to terrestrial vertebrates is considered negligible. In addition, the typical terrestrial exposure model (TERRPLANT) was not used since the dominant route of exposure to plants is expected to be via air exposure to DMDS residues.

Risk to plants, mammals, and birds are based on exposure to the volatile flux of DMDS from the field. There is no plant model available to evaluate the effect of exposure to air for terrestrial plants. However, a dispersion model such as PERFUM can be used assuming the appropriate toxicological endpoint is given in a unit mass per

3 EPA OPP California Red Legged Frog website is accessed on-line at http://www.epa.gov/e spp/litstatus/effect s/redleggedfrog/.volume. In this case, the endpoint is given in terms of an application rate (see Table III12).

The PERFUM model is a processor of the ISCST3 model (Reiss, 2008), which has been developed from EPA’s Office of Air Quality Planning and Standards 4

. PERFUM can calculate upper-bound gaseous residue EECs in air at the edge or at a

downwind distance of a treated field. The ISCST3 model which PERFUM is based on uses a Gaussian plume model that incorporates source related flux and 5 years of meteorological data such as wind speed, wind direction, and insolation. Figure III-1 illustrates the plume structure along with the Gaussian nature of the contaminant concentrations which is determined by mixing within the plume. It is assumed that the pollutant does not undergo any chemical reacti ons, and that no other removal processes, such as wet or dry deposition, act on the plume during its transport from the source. The Gaussian model equations and the interacti ons of the source-related and meteorological factors are described in Volume II of the ISC User's Guide (USEPA, 1995), and in the Workbook of Atmospheric Dispersion Estimates (Turner, 1970). PERFUM estimates a concentration about either side of the plume centerline directly downwind from the source. The size of the plume and plume rise is determined by the degree of turbulence in the atmosphere, which is parameterized according to stability class (A = unstable; B= unstable; C= unstable; D= neutral; E= stable; F = stable) where the unstable regime refers to turbulent conditions and the stable regime refers to stagnate conditions. The stability classes are determined by incorporating wind speed and insolation (e.g., cloud cover) data using empirical methods (Turner, 1970). The 10-meter wind speed governing the transport of the plume is adjusted to the ground release height according to the Log Law (USEPA, 1995).

Figure III-11. Plume structure in the PERFUM model.

A, range of area source sizes may be specified in PERFUM. In this case, a variety of area source sizes from 1 acre to 80 acres were modeled considering the possibilities that can exist with fumigant use. The flux profile, or DMDS emissions per unit area, from the field volatility studies are input into PERFUM and matched with the meteorological data consistent with the time of day the flux data were measured. This is done since flux can also be dependent on the time of day as well. EEC distributions are

55 4 The ISCST3 model documentation can be accessed on-line at: http://www.epa.gov/scram001/ dispersion_alt.htmcalculated at an array of points (at 1.5 meters above ground level) originating from around the edge of the field to a downwind distance 1,440 meters from the edge of the field. An illustration of the spatial nature of the model output is shown in Figure III-2

. The EEC distributions are divided by each ring of points, known as receptors shown in Figure III-2 for each time of day (based on the averaging period) about the treated field.

Figure III-2. Receptors (dotted points ) where PERFUM air concentrations are predicted around a treated field (area shaded in black and green).

As stated above, PERFUM requires parameters for the treated field such as the pesticide flux rate, the dimensions of the area source, and the height of the release specified. However, PERFUM has the added ability to consider averaging periods. To account for the acute time period of concern for mammals and birds and in consideration to the highly amplified spikes in DMDS volatile flux possible from the soil after application, a one-hour averaging period for exposure is selected for this modeling. In addition, DMDS flux profiles from the Tifton, GA field volatility study, the only study where a VIF tarp was used, was modeled in PERFUM. This flux profiles from this study was selected since it best represents the management practices prescribed on the label which requires a Virtually Impermeable (VIF) tarp. This daily flux profile is ran repeatedly through 5 years of meteorological data, which in this assessment, consisted of Yakima (WA), Bakersfield (CA), Bradenton (FL), Ventura (CA), Flint (MI), and Tallahassee (FL) locations. The start time of th e daily flux profile is consistent with the start time of the application for each field volatility study. The input parameters for the

PERFUM model is shown in Table III-12 and the flux profile values and times specified

in the model are shown in Table III-13 for the Tifton, GA study. This flux profile is repeated continuously through the 5 year series of meteorological data.

Table III-12. Input Parame ters Utilized in PERFUM.

Input Parameter Tifton, GA Study Basis Source Type Area Averaging Period 1-hour Application Start Time 5 pm Emission Rate ( μ g/m 2 s) See Table III-13 Source Height (m) 0 Length of Large Sides of Source (m) 63.6, 142.2, 201.2, 284.5, 402.3, 492.8, and 569

5657 Table III-12. Input Parame ters Utilized in PERFUM.

Input Parameter Tifton, GA Study Basis Length of Smaller Sides of Source (m) 63.6, 142.2, 201.2, 284.5, 402.3, 492.8, and 569

Downwind Distance of EEC Receptors Around Field (m) 5, 7, 10, 15, 20, 30, 50, 70, 80, 90, 100, 120, 150, 180,

210, 240, 270, 300, 360, 420, 480, 540, 600, 720, 840, 960, 1080, 1200, 1320,

1400 1
Receptor Height (m) 1.5 1

Meteorological Data

Locations Yakima (WA), Bakersfield (CA), Bradenton (FL), Ventura (CA), Flint (MI),

and Tallahassee (FL)

1. Values cannot be controlled in present version of PERFUM.

Table III-13. Temporal flux profiles input in PERFUM. Tifton, GA Study Basis 1

Time Ranges Flux Each Hour In Time Range

( μ g/m 2 s) Day 0 5 pm – 8 pm 2.7 Day 0 8 pm – 2 am 13.5 Day 0 2 am – 8 am 17.9 Day 0 8 am – 9 am 11.9 Day 0 9 am – 5 pm 2.7 Day 1 5 pm – 8 pm 18.4 Day 1 8 pm – 2 am 35.6 Day 1 2 am – 8 am 44.4 Day 1 8 am – 9 am 7.4 Day 1 9 am – 2 pm 11.9 Day 1 2 pm – 5 pm 18.4 Day 2 5 pm – 5 am 45.3 Day 2 5 am – 9 am 16 Day 2 9 am – 5 pm 7.4

1. Flux profile extracted based on the third treatment to Field 1.

2. Flux values scaled from values shown in Table III-4 to 455 lbs. a.i./acre.

Consistent with EFED risk assessments conducted for fumigants, risk quotients were developed based on the 90 th percentile EECs based on the ring closest to the edge of the field at the time of day with the highest predicted EECs. This ring most likely represents the maximum concentration that is possible anywhere in the field since air residue mass accumulates at this point from many plume elements which are emitted on58 the treated field.

The upper-bound PERFUM EECs is 720 μ g/m 3 . This modeling addresses theflux measured from the field at Tifton, GA while the VIF tarp was in place. The upperbound EEC was identified at a distance of 5 meters from the edge of an 80-acre field and occurred between 5 am – 6 am consistent with the Bradenton, FL meteorological data. Sample model outputs are shown in Appendix D.

III.C. Ecological Effects Characterization

Effects characterization describes the potential effects a pesticide can produce in an aquatic or terrestrial organism. This char acterization is typically based on studies that describe acute and chronic effects toxicity information for various aquatic and terrestrial animals and plants. Appendix H summarizes the results of the toxicity studies used to characterize effects for this risk assessment. Toxicity testing reported in this section does not represent all species of birds, mammals, or aquatic organisms. Only a few surrogate species for both freshwater fish and birds are used to represent all freshwater fish (2000+) and bird (680+) species in the United States. For mammals, acute studies are usually limited to Norway rat or the house mouse. Estuarine/marine testing is usually limited to a crustacean, a mollusk, and a fish. Also, neither reptiles nor amphibians are tested. The risk assessment assumes that avian and repti lian and terrestrial-phase amphibian toxicities are similar. The same assumption is used for fish and aquatic-phase amphibians.

In general, categories of acute toxicity ranging from “practically nontoxic” to “very highly toxic” have been established for aquatic organisms (based on LC 50 values), mammals (based on LD 50 values), avian species (based on LD 50 and LC 50 values), and non-target insects (based on LD 50 values for honey bees) (EPA, 2001). These categories are presented in Appendix F.

III.C.1. Aquatic Effects Characterization

The most sensitive acute toxicity refe rence values associated with DMDS exposure to aquatic organisms are summarized in Table III-14. Summaries of other submitted studies are presented in Appendix H.

Table III-14. DMDS Toxicity Reference Values (TRVs) (ppb of Active Ingredient) for Aquatic Organisms

Exposure

Scenario Species Exposure

Duration Toxicity Reference Value ( μ g/L a.i.) Reference

Freshwater Fish

Acute Rainbow trout 96 hours LC 50 = 960 MRID 470528-14 Acceptable59 Table III-14. DMDS Toxicity Reference Values (TRVs) (ppb of Active Ingredient) for Aquatic Organisms

Exposure

Scenario Species Exposure

Duration Toxicity Reference Value ( μ g/L a.i.) Reference

Acute Zebrafish 96 hours LC50=7500 Acceptable

Chronic NA NA NA NA

Freshwater Invertebrates

Acute Daphnia magna 48 hours EC 50 =1610 μ g/L (1310-1990

μ g/L) MRID 470528-16 Acceptable

Chronic NA NA NA NA

Estuarine/Marine Fish

Acute Sheepshead 96 h LC50=5600 μ g/L (4000-6900

μ g/L MRID473075-04

Chronic NA NA NA NA

Estuarine/Marine Invertebrates

Acute Mysid NA LC50=4900 μ g/l (3900-

96100 μ g/L) MRID473075-05

Chronic NA NA NA NA

Aquatic Plants

Vascular Lemna gibba NA EC 50 =28000 (22000-

36000 μ g/L) MRID 474712-04 Acceptable

Nonvascular Anabaena flosaquae Cell Density EC50=320 μ g/L (110-900 μ g/L) MRID 474712-05 Acceptable

NA = Data appropriate for quantitative use are not available.

Acute Toxicity to Freshwater Fish60 Fish are represented by a warm-water species and a cold-water species with the most sensitive endpoint utilized in the assessment. The acute toxicity of DMDS to freshwater fish was evaluated in a cold-water species, rainbow trout ( Oncorhynchus mykiss ) and a warm-water species, zebra fish ( Danio rerio ), with the lowest LC 50 s of 0.96 mg/L and 7.5 mg/L, respectively. Therefore, the rainbow trout value is used as the toxicity value for assessing acute risks to fish from exposure to DMS.

In addition to the acute fish studies, chronic toxicity studies are evaluated to determine the effect of DMDS on fish. However, no chronic fish studies are available.

Acute Toxicity to Freshwater Invertebrates

The acute effect of DMDS to aquatic invertebrates is represented by Daphnia

magna. An acceptable acute study (MRID 470528-16) resulted in an acute

EC 50 = 1.61mg/L that will be used in this assessment. This value will also be used to estimate the effect of DMDS to benthic organisms.

Acute Toxicity to Estuarine/Marine organisms

Estuarine/Marine Fish

The sheepshead minnow is used as a surrogate for estuarine/marine fish to estimate the acute effect from the use of DMDS. An acceptable study (MRID 473075- 04) resulted in an acute LC 50 =5.6 mg a.i./L (4.0-6.9mg/L) that will be used in this

assessment.

Estuarine/Marine Invertebrates

The acute effect of DMDS to estuarine/marine invertebrates is represented by the mysid. An acceptable study (MRID 473075-05) resulted in an acute LC 50 =4.9 mg a.i./L (3.9-6.1 mg/L) that will be used in this assessment.

Acute Toxicity to Aquatic Plants

The acute toxicity of DMDS to aquatic plants has been assessed in vascular aquatic plants (duckweed, Lemna gibba ) and non-vascular plants represented by Anabaena flos-aquae . The EC 50 is used to estimate the effect of DMDS to non-listed species and the EC05 is used to estimate the effect on listed species. There was an

EC 50 =28mg/L and an EC 05 =6.0 mg/L for Lemna . The most sensitive endpoint is for cell density for Anabaena flos-aquae, with an EC 50 =0.320mg/L and an EC05=0.011, which

will be used in this assessment.61 III.C.2. Terrestrial Effects Characterization

The toxicity endpoints used to character ize risks of DMDS exposure to birds and

mammals are summarized in Table III-15. A more detailed summary of the available terrestrial toxicity data is given in Appendix F.

Table 1II-15. Toxicity Reference Values (TRVs) for Terrestrial Species for DMDS

Exposure

Scenario Species Exposure

Duration Toxicity

Reference Value 1 Reference

Mammals

Acute

inhalation Rat 4-hour inhalation LC 50 = 17 ppm (M) and 19 ppm (F) [conv. to mg/L: Section IV.B.2] MRID 45117902Acceptable/Nonguideline

Birds

Quail 4-hour Inhalation Male LC 50 =1.97 mg/L (1.62-2.41 mg/L)

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

Combined LC 50 =1.84 (1.64-2.06 mg/L) MRID 469170-13 Acceptable

Acute

Inhalation

1 Data from HED DMDS Risk Assessment.

Mammalian Species

An acceptable rat inhalation study (MRID 45117902) was submitted for DMDS. Because inhalation is the expected exposure route, the rat inhalation toxicity value will be

used in this assessment.

Avian Species

The effect of DMDS on the Bobwhite quail ( Colinus virginianus ) is used to estimate the effect for all birds. Although an acute oral toxicity study (MRID470528-13) was submitted, the LD 50 will not be used in this assessment because no dietary exposure is expected from the use of DMDS. An inhalati on study was classified as supplemental (MRID 469170-13) because it is a non-guideline study. The female Bobwhite ( Colinus virginianus ) acute inhalation LC 50 =1.73 mg/L (1.55-1.93 mg/L)62 Plant Species

Toxicity values for plant species are summarized in Table III-16. A supplemental nonguideline study was submitted to illustrate the effect of DMDS as a gas on plants. The most sensitive vegetative vigor monocot (EC25 for oat=100 lb/A) and dicot toxicity values (EC25 for tomato=55 lb/A) were reported in the study. However, there is insufficient data to estimate the effect on plants. This study maybe upgraded if acceptable information on the size of the plastic bag used to contain the gas is submitted.

Table III-16. Toxicity Reference Values (TRVs) for Terrestrial Plants for DMDS

Exposure

Scenario Species Endpoint Toxicity

Reference Value Reference

Vegetative Vigor

Dry weight EC25 = 100 lb/A Monocot Oat

EC05=37.5 lb/A

Height EC25 = 55 lb/A Dicot Tomato

EC05 =37.5 lb/A MRID 474712-02Acceptable/Guideline63 

### IV. Risk Characterization

IV.A. Risk Estimation - Integration of Exposure and Effects Data

IV.A.1. Non-target Aquatic Animals and Plants

Risk quotients for aquatic animals are presented in Table IV-1 for aquatic animals based on surface water EECs, and Table IV-2 for plants based on surface water EECs. The risk quotients are calculated using the toxicity values summarized in Table

III-14 and EECs from PRZM/EXAMS summarized in Table III-8 . For assessing acute risks, the 24-hour (daily average) peak concentration is used with the lowest (most sensitive) fish LC 50 , aquatic invertebrate EC/LC 50 , and aquatic plant LC 50 . For assessing risk to endangered/ threatened plant species, the EC 05 is used. For assessing chronic risks, the 21-day concentration is used with the invertebrate life-cycle NOAEC and the 60-day concentration is used with the fish early life-stage NOAEC.

Table IV-1. Surface Water Risk Quotients (RQs) for Aquatic Species.

Exposure

Scenario Drip Irrigation

Peak Exposure

( μ g/L ) Drip Irrigation

Risk Quotient** Shank Injection

Peak Exposure

( μ g/L ) Shank Injection

Risk Quotient **

Freshwater Fish (LC 50 =960 μ g/L)

California tomato 30.29 0.031 4.77E-08 4.97 x 10 -11

Florida tomato 18.3 0.019 5.57 0.006

Florida peppers 46.89 0.049 4.43 0.005

Florida cucumber 150.9 0.157* 9.98 0.010

Florida strawberry 203.23 0.212* 3.56 0.004

California onion 2.55 0.003 0.24 2.50 x 10 -4

Georgia onion 129.48 0.135* 3.25 0.003

California nursery 7.07 0.007 0.37 3.85 x 10 -4

Michigan nursery 32.24 0.033 0.23 2.40 x 10 -4

New Jersey nursery 21.83 0.023 0.16 1.67 x 10 -464 Table IV-1. Surface Water Risk Quotients (RQs) for Aquatic Species.

Exposure

Scenario Drip Irrigation

Peak Exposure

( μ g/L ) Drip Irrigation

Risk Quotient** Shank Injection

Peak Exposure

( μ g/L ) Shank Injection

Risk Quotient **

Oregon Christmas tree 19.67 0.020 0.21 2.19 x 10 -4

Marine Fish LC50=5600 μ g/L

California tomato 30.29 0.005 4.77E-08 8.52 x10 -12

Florida tomato 18.3 0.003 5.57 9.95 x 10 -4

Florida pepper 46.89 0.008 4.43 7.91 x 10 -4

Florida cucumber 150.9 0.027 9.98 0.002

Florida strawberry 203.23 0.036 3.56 0.001

California onion 2.55 0.000 0.24 4.29 x 10 -5

Georgia onion 129.48 0.023 3.25 5.8 x 10 -4

California nursery 7.07 0.001 0.37 6.61 x 10 -5

Michigan nursery 32.24 0.006 0.23 4.11 x 10 -5

New Jersey nursery 21.83 0.004 0.16 2.86 x 10 -5

Oregon Christmas tree 19.67 0.003 0.21 3.75 x 10 -5

Freshwater Aquatic Invertebrates EC50=1610 μ g/L

California tomato 30.29 0.019 4.77E-08 2.94 x 10 -11

Florida tomato 18.3 0.011 5.57 0.003

Florida peppers 46.89 0.029 4.43 0.003

Florida cucumber 150.9 0.093 9.98 0.006

Florida strawberry 203.23 0.125 3.56 0.002

California onion 2.55 0.001 0.24 1.48 x 10 -4

Georgia onion 129.48 0.080* 3.25 0.002

California nursery 7.07 0.004 0.37 2.28 x 10 -4

Michigan nursery 32.24 0.020 0.23 1.42 x 10 -465 Table IV-1. Surface Water Risk Quotients (RQs) for Aquatic Species.

Exposure

Scenario Drip Irrigation

Peak Exposure

( μ g/L ) Drip Irrigation

Risk Quotient** Shank Injection

Peak Exposure

( μ g/L ) Shank Injection

Risk Quotient **

New Jersey nursery 21.83 0.013 0.16 9.88 x 10 -5

Oregon Christmas tree 19.67 0.012 0.21 1.3 x 10 -4

Marine Invertebrates EC50=4900 μ g/L

California tomato 30.29 0.006 4.77E-08 9.73 x10 -12

Florida tomato 18.3 0.004 5.57 0.001

Florida peppers 46.89 0.009 4.43 0.001

Florida cucumber 150.9 0.031 9.98 0.002

Florida strawberry 203.23 0.041 3.56 0.001

California onion 2.55 0.000 0.24 4.9E-05

Georgia onion 129.48 0.026 3.25 0.001

California nursery 7.07 0.001 0.37 7.55 x 10 -5

Michigan nursery 32.24 0.006 0.23 4.69 x 10 -5

New Jersey nursery 21.83 0.004 0.16 3.27 x 10 -5

Oregon Christmas tree 19.67 0.004 0.21 4.29 10 -5

*Exceeds acute endangered species LOC (> 0.05) Bold: Exceeds acute endangered species LOC, acute restricted use LOC, and acute risk LOC (> 0.5)

Acute RQ values are derived from peak EECs and toxicity values for each surrogate species. RQs are presented for both drip irrigation and shank injection for each use. Drip irrigation RQs exceed the endangered species LOC for freshwater fish and freshwater invertebrates for FL cucumber, FL strawberry and GA onion uses.

Drip irrigation RQs do not exceed the endangered species LOC for freshwater fish and freshwater invertebrates for CA tomato, FL tomato, FL pepper, CA onion, CA nursery, MI nursery NJ nursery and OR Christmas tree uses. Drip irrigation RQs do not exceed the acute risk LOC for any uses for an y surrogate aquatic species. Drip irrigation RQs do not exceed the endangered species LOC for estuarine/marine fish and estuarine/marine invertebrates. Shank injection RQs do not exceed either the acute or66 endangered species LOC for any use for any surrogate aquatic species.

Table IV-2. Surface Water Risk Quotients (RQs) for Aquatic Plant Species.

Exposure

Scenario Drip Irrigation

Peak Exposure

( μ g/L ) Drip Irrigation

Risk Quotient** Shank Injection

Peak Exposure

( μ g/L ) Shank Injection

Risk Quotient **

Freshwater Vascular Plants: ( Lemna EC50=28000 μ g/L)

California tomato 30.29 0.001 4.77E-08 1.70 x 10 -12

Florida tomato 18.3 0.001 5.57 1.99 x 10 -4

Florida peppers 46.89 0.002 4.43 1.58 x 10 -4

Florida cucumber 150.9 0.005 9.98 3.56 x 10 -4

Florida strawberry 203.23 0.007 3.56 1.27 x 10 -4

California onion 2.55 9.11E-05 0.24 8.57 x 10 -6

Georgia onion 129.48 0.005 3.25 1.16 x 10 -4

California nursery 7.07 0.000 0.37 1.32 x 10 -5

Michigan nursery 32.24 0.001 0.23 8.21 x 10 -6

New Jersey nursery 21.83 0.001 0.16 5.71 x 10 -6

Oregon Christmas tree 19.67 0.001 0.21 7.50 x 10 -6

Freshwater Aquatic Nonvascular Plants EC50=320 μ g/L

California tomato 30.29 0.095 4.77E-08 1.49 x 10 -10

Florida tomato 18.3 0.057 5.57 0.017

Florida peppers 46.89 0.146 4.43 0.014

Florida cucumber 150.9 0.471 9.98 0.031

Florida strawberry 203.23 0.635 3.56 0.011

California onion 2.55 0.008 0.24 0.001

Georgia onion 129.48 0.405 3.25 0.010

California nursery 7.07 0.022 0.37 0.00167 Table IV-2. Surface Water Risk Quotients (RQs) for Aquatic Plant Species.

Exposure

Scenario Drip Irrigation

Peak Exposure

( μ g/L ) Drip Irrigation

Risk Quotient** Shank Injection

Peak Exposure

( μ g/L ) Shank Injection

Risk Quotient **

Michigan nursery 32.24 0.101 0.23 0.001

New Jersey nursery 21.83 0.068 0.16 0.007

Oregon Christmas tree 19.67 0.061 0.21 0.001

Freshwater Aquatic Nonvascular Plants EC 05 =11 μ g/L

California tomato 30.29 2.754 4.77E-08 4.34 x 10 -9

Florida tomato 18.3 1.664 5.57 0.506

Florida peppers 46.89 4.263 4.43 0.403

Florida cucumber 150.9 13.718 9.98 0.907

Florida strawberry 203.23 18.475 3.56 0.324

California onion 2.55 0.232 0.24 0.022

Georgia onion 129.48 11.771 3.25 0.295

California nursery 7.07 0.643 0.37 0.034

Michigan nursery 32.24 2.931 0.23 0.020

New Jersey nursery 21.83 1.985 0.16 0.015

Oregon Christmas tree 19.67 1.788 0.21 0.019

Bold: Exceeds plant LOC (>1 )

RQs for non-listed species are estimated for vascular plants ( Lemna) and nonvascular plants ( Anabaena) using the EC 50

. There was no RQ exceedence for vascular using Lemna as a surrogate or for non-vscaular using Anabaena as a surrogate for either drip irrigation or shank injection for any uses.

RQs are estimated for listed species using the EC 05 toxicity value.68 RQs exceeded the LOC for drip irrigation for listed nonvascular plants for CA tomato, FL tomato, FL pepper, FL cucumber, FL strawberry, GA onion, MI nursery, NJ nursery or OR Christmas tree uses. No RQs exceeded the plant LOC for non-vascular plants for CA onion and CA nursery uses. No RQs for shank injection for nonvascular plants exceeded the LOC for any uses.

IV.A.2 Non-Target Terrestrial Species

Risk quotients for air exposure to mammal and avian species are calculated based on the upper-bound PERFUM EEC in air determined at 720 μ g/m 3 for an 80 acre field using based on the combination of field flux data measured at Tifton, GA and Bradenton, FL meteorological data. Along with the EEC in air, the risk quotients are calculated using the toxicity values summarized in Table III-15. The risk quotients for mammals

and birds are shown in Table IV-3. Risk quotients are not exceeded for any entity of

mammals or birds.

Table IV-3 . Inhalation risk quotients for mammal species (LD50 = 17 ppm or 65,496

μ g/m 3 ) and avian species (LD50 = 1.73 mg/l or 1.73 x 10 6 μ g/m 3 ).

Table IV-3. Risk Quotients in air based on PERFUM upper-bound EECs based on Tifton, GA Shank Injection to Raised Beds with VIF Tarp Species Toxicity Endpoint ( μ g/m 3 ) EEC ( μ g/m 3 ) RQ

Mammals LD50 = 65,496 720 0.011

Birds LD50 = 1.73 x 10 6 720 0.0004

1 Toxicity endpoint for birds is 1.73 mg/L or 1.73 x 10 6 μ g/m 3

2 Toxicity endpoint for mammals is 17 ppm or 6,549.6 μ g/m 3 for mammals (6,549.6 μ g/m 3 = 0.1 x (17 ppm x 94.2 g/mol)/(24.45 mol/L).69 IV.A.3. Non-target Terrestrial and Semi-aquatic

Plants

Risk to terrestrial plants is expected from exposure to air concentrations. There is no model currently available to estimate those effects for plants. Risk may be estimated from toxicity values from EECs calculated from the PERFUM model along with submitted toxicity endpoints reflecting exposure from air concentrations if available. However, additional data from the toxicity study is needed to complete the assessment.

IV.B. Risk Description

IV.B.1 Risk to Aquatic Organisms

Consistent with the risk hypothesis stated in Section II.E.1, dimethyl disulfide residues may adversely affect aquatic aquatic species via runoff of dissolved residues of dimethyl disulfide remaining on treated fields when tarps are removed after 12 days. Therefore, the risk estimation for aquatic exposure accounts for the impact of aerobic soil degradation to residue loadings avai lable to runoff prior to the removal of the tarp 12 days after the application. In addition, since dimethyl disulfide is a volatile chemical, considerations of risk estimates must also take into account dissipation of dimethyl disulfide from the soil due to off-gassing in estimating concentrations for water after the tarp is removed. Risk quotients are calculated from dimethyl disulfide EECs in surface water from PRZM-EXAMS with the volatility algorithm representative of processes and dimethyl disulfide loadings available after tarp removal 12 days after the dimethyl disulfide application.

In addition, DMDS is sufficiently volatile that there may also be inhalation exposure and potential risk to birds and mammals as well as air exposure to plants. The risk estimation for air exposure to terrestrial plants, birds, and mammals accounts for the possible scenario for terrestrial organisms to be impacted on and off of a single treated field from dimethyl disulfide. The risk estimation accounts for the requirement of VIF tarps that are required to be applied immedi ately after application and remain undisturbed for 12 days according to the product labels. Risk quotients are calculated from dimethyl disulfide EECs in air from PERFUM based on flux measured at a Tifton, GA fallow field which was covered with a tarp immediately after applications for approximately 12 days after the application. According to the risk quotients for terrestrial exposure, the risk hypothesis was not verified.

Toxicity studies were reviewed to provide endpoints to estimate RQs. Mortality

and sub-lethal effects were noted in the assessment. Not all sub-lethal effects could be statistically analyzed due to the subj ective nature of the observation.70 A refinement to the model allowed EECs to be estimated using the volatility paradigm to describe the effect with the tarp removed. EECs for both drip irrigation and shank injection were reported, and were based on a load adjusted for biodegradation which occurs under the tarp for the required 12 days which is specified on the label.

Sublethal effects were noted in the acute marine fish study (MRID 473075-04). There were no sub-lethal effects observed in the control treatment group. Sub-lethal effects were noted in all subsequent treatment levels. Loss of equilibrium was observed in the 2.3 mg a.i./L treatment group at 72 hours. Loss of equilibrium was observed in the 4.0 mg a.i./L treatment group at 1.5, 24, 48, 72 and 96 hours. Surfacing and lying on the bottom was also observed in the 4.0 mg a.i./L treatment group at 72 hours. Surfacing and lethargy was additionally noted in the 4.0 mg a.i./L treatment group at 96 hours. Loss of equilibrium was observed in the 6.9 mg a.i./L treatment group at 48 and 72 hours. Lying on the bottom was also observed in the 6.9 mg a.i./L treatment group at 72 hours. Lethargy was additionally observed in the 6.9 mg a.i./L treatment group at 96 hours. Surfacing was observed in the 10 mg a.i./L treatment group at 24 hours. Lying on the bottom was noted in the 10 mg a.i./L treatment group at 48 hours.

Risk Conclusions for Aquatic Organisms

Conclusions for the effect of DMDS on aquatic species and aquatic plants were based on lines of evidence including fate and transport characteristics, toxicity endpoints, results from conventional and refined models for aquatic exposure, as well as reviewing incidents reported to the EIIS database. Water column estimated exposure concentrations (EECs) were estimated from PRZM/EXAMS modeling simulating dimethyl disulfide fate and transport, including volatilization, after the tarp is removed to calculate an RQ. The resulting RQs are compared to a Level of Concern (LOC) for the species and exposure route. No aquatic animal or plant incidents have been reported in the EIIS database.

RQs were estimated for both drip irrigation and shank injection for each use. There is potential acute risk to freshwater fish and freshwater invertebrates based on RQ exccedence. Drip irrigation RQs exceed the endangered species LOC for freshwater fish (RQs=0.003-0.212) and freshwater invertebrates (RQs=0.001-0.125) for FL cucumber, FL strawberry and GA onion uses. These RQs could be further refined by addressing the uncertainties in the persistence of DMDS residues in water if additional data is provided. DMDS was modeled as moderately persistent with a half life of 9.32 days in aerobic water metabolism following EFED input parameter guidance assuming a doubling of the soil half-life due to lack of an aerobic aquatic metabolism study.

There is no potential for acute risk for any surrogate species using the shank injection method. No modeled uses resulted in LOC exceedences.

There is potential chronic risk to freshwater and estuarine/marine fish based on the uncertainty due to the persistence of DMDS in water and absence of chronic toxicity

data.71 RQs for non-listed species are estimated for vascular plants ( Lemna) and nonvascular plants ( Anabaena) using the EC 50

. There was no RQ exceedence for vascular using Lemna as a surrogate or for non-vscaular using Anabaena as a surrogate for either drip irrigation or shank injection for any uses.

Proposed Risk Mitigation

In Section III.A.1, it was determined that loadings in the soil may degradate by approximately 83.12 percent (16.22 percen t of DMDS residues remain based rate

constant detetermined from the 90 th percentile half life in two aerobic soil metabolism studies) over 12 days residues under the Virtually Impermeable Film (VIF) tarp. However, considering there are small risks to various aquatic organisms of concern, and that there is a benefit of the tarp for preventing risks to both aquatic organisms via runoff suppression and terrestrial organisms via suppression to volatilization and off-gassing, EFED will recommend label language to mitigate the risk of runoff by restricting tarp cutting activities from occurring when rainfall is forecasted within 48 hours.

In addition, since degradates were not found to be of toxicological concern based on structural activity relationships shown in Tables II.2a and II.2b and discussion in Section II.B.1, additional data on the environmental fate and ecological toxicity of these degradates will not be requested at this time.

IV.B.2 Risk to Terrestrial Organisms

Terrestrial animals and plants on or near treated fields could be susceptible to acute exposure to DMDS from residues in the air (due to the volatility of DMDS).Chronic exposure from a single treated field is not likely to occur due to the short halflife of DMDS. However, chronic exposure may be possible due to repeat exposures from multiple fields. To address this possibility, ambient air quality monitoring data will be requested as needed in any area where the DMDS use volume is high.

Dimethyl disulfide pre-plant soil fumigation is not expected to be of concern via the dietary exposure route for birds and mamm als as crops are not expected to uptake any residues. In addition, dimethyl disulfide low persistence in soils and high mobility and diffusivity in the soil are all factors which suggest that there is not a high probability of DMDS residues to be ingested.

Risk from Inhalation

DMDS is applied as a fumigant using drip irrigation and shank injection and covered with a tarp. The tarp is removed after 12 days. No spray drift or runoff is expected for the first 12 days. Therefore, an effect to avian and mammal species via the inhalation route is expected from the use of DMDS, consistent with the risk hypothesis.72 The PERFUM model with field flux measured at Tifton, GA field treated with a raised bedded application to DMDS with immediate covering by a VIF tarp is used to estimate the exposure to terrestrial species. There was no inhalation risk found to mammals or birds associated with this use pattern.

Limitations of the air modeling include the uncertainty in air concentration at ground-level at any given point in time. Difference in air concentrations between these two levels are determined based on the rise and reflection of the plume to the surface. However, since EECs are reported at only 1.5 meters above ground level, it is not expected that the 90 th percentile concentration around th e edge at a certain time of day would not vary tremendously from one level to the other. One other limitation is the inability for PERFUM to account for plume meandering during inversion conditions, when a highly concentrated plume can impact a large perimeter within a short time period (USEPA, 2009[4]). To protect against this uncertainty, inversion mitigation language restricting DMDS applications during large-scale extended inversion events is proposed. Furthermore, EECs are ultimately based on the performance of the VIF tarp at one site. However, screening-level EECs using the SCREEN3 dispersion model indicate that EECs in air may be of concern to mammals and birds at other locations, times, and methods in which DMDS applications occur. This analysis is presented in Appendix G. However, these EECs are based on low density polythelene tarps and metalized tarps which may be less permeable to DMDS volatile residues. Therefore, more field volatility studies conducted with VIF tarps are being requested at this time to address these

uncertainties.

Terrestrial Risk Conclusions

The proposed label for DMDS includes instructions to cover the field with a tarp for the first 12 days. Specifically, high barri er tarps such as VIF (Virtually Impermable Films) tarps are required to be used on the proposed label; therefore the conclusions are based on the effect using those tarps. The PERFUM model describes the effect from the use of high barrier tarps such as proposed on the label. Although there is no inhalation LOC available to compare with the RQ, this analysis uses the current bird endangered species LOC=0.1 used to evaluate dietary effect, to determine the effect of DMDS use. Although there is no risk anticipated based on the single field volatility study that used a VIF tarp in Tifton, Georgia, an analysis using low barrier tarps using a screening method with the SCREEN3 model, presented Appendix G., justifies the need for more field volatility studies as there are risks to birds and mammals based on other field volatility studies conducted with other tarps showed RQs of concern at other locations, times of year, and application methods other than shank injection to raised beds. RQs for chronic effects were not modeled due to the absence of chronic toxicity data. However, this is not expected to be be of concern due to DMDS’s low persistence in air. However, repeat exposures may occur in high use areas. No terrestrial animal incidents have been reported in the EIIS database.73 Although there is no model available to estimate the effects on the honeybee, the results for the toxicity test are classified as to the impact. There is no risk for non-listed insects based on the honeybee toxicity test, which resulted in a classification of practically non-toxic. The risk to other terr estrial invertebrates that are not soil dwelling would be represented by the honeybee estimate.

There is no risk to other off-site terrestrial invertebrates that burrow in the soil since the dominate routes of dissipation for DMDS is expected to be leaching into ground

water or volatilization into the air..

Terrestrial Plants

DMDS is used to kill weeds as a target, th erefore it is expected to kill plants on the field. There is potential risk based on the absence of acceptable data to estimate the effect of DMDS as a gas to terrestrial plants. The dominant route of exposure is thought

to be inhalation rather than runoff.

Proposed Risk Mitigation

Since field volatility studies suggest there is no risk to birds and mammals from air residues of DMDS which are emitted from fields covered with a VIF tarp and there are no risk from DMDS residues in runoff from treated fields, there is no mitigation proposed besides the label maintaing the label requirement that fields be covered with a VIF tarp for 12 days after the application. However, to address the uncertainty related to air residues which may potentially exist duri ng inversion conditions, it is recommended that DMDS applications be restricted from occurring under such conditions. Growers and applicators are required to use advisory products from the National Weather Service and identify indicators of inversion conditions such as light wind speeds to identify present or future stagnate air conditions.

IV.B.3. Review of Incident Data

DMDS has no registered outdoor pesticide uses and has no incidents in EFED’s Ecological Incident Information System (EIIS) (data base checked 02/22/10).

Given the risk quotients discussed above, there is a potential for fish and aquatic plant incidents under the proposed use.

IV.B.4 Endocrine Disruption

As required under FFDCA section 408(p), EPA has developed the Endocrine Disruptor Screening Program (EDSP) to determine whether certain substances (including pesticide active and other ingredients) may have an effect in humans or wildlife similar to an effect produced by a “naturally occurring estrogen, or other such endocrine effects as74 the Administrator may designate.” The EDSP employs a two-tiered approach to making the statutorily required determinations. Tier 1 co nsists of a battery of 11 screening assays to identify the potential of a chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to identify any adverse endocrine related effects caused by the substance, and establish a dose-response relationship between the dose and the E, A, or T effect.

Between October 2009 and February 2010, EPA is issuing test orders/data call-ins for the first group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. This list of chemicals was selected based on the potential for human exposure through pathways such as food and wa ter, residential activity, and certain postapplication agricultural scenarios. This list should not be construed as a list of known or likely endocrine disruptors.

DMDS is not among the group of 58 pesticide active ingredients on the initial list to be screened under the EDSP. Under FFDCA sec. 408(p) the Agency must screen all pesticide chemicals. Accordingly, EPA anticipates issuing future EDSP test orders/data call-ins for all pesticide active ingredients.

For further information on the status of the EDSP, the policies and procedures, the list of 67 chemicals, the test guidelines and the Tier 1 screening battery, please visit our

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

.

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

Concerns

IV.B.5.a. Action Area

For listed species assessment purposes, the action area is considered to be the area affected directly or indirectly by the Federal action and not merely the immediate area involved in the action. At the initial Level I screening assessment, broadly described taxonomic groups are considered and thus conservatively assumes that listed species within those broad groups are co-located with the pesticide treatment area. This means that terrestrial plants and wildlife are assumed to be located on or adjacent to the treated site, and aquatic organisms are assumed to be located in a surface water body adjacent to the treated site. The assessment also assumes that the listed species are located within an assumed area with the relatively highest potential exposure to the pesticide, and that exposures are likely to decrease with distance from the treatment area. Section II. B of this risk assessment presents the pesticide use sites that are used to establish initial collocation of species with treatment areas.75 If the assumptions associated with the sc reening-level action area result in RQs that are below the listed species LOCs, a "no effect" determination conclusion may be made with respect to listed species in that taxa, and no further description of an action area is necessary. Furthermore, RQs below the listed species LOCs for a given taxonomic group indicate indirect effects upon listed species that depend upon the taxonomic group covered by the RQ as a resource.

However, in situations where the screening assumptions lead to RQs in excess of the listed species LOCs for a given taxonomic group, a potential for a "may affect" conclusion exists and may be associated with direct effects on listed species belonging to that taxonomic group or may extend to indirect effects upon listed species that depend upon that taxonomic group as a resource. In such cases, additional information on the biology of listed species, the locations of these species, fate and transport properties of the chemical, and the locations of use sites could be considered to determine the extent to which screening assumptions regarding an action area apply to a particular listed organism. These subsequent refinement steps could consider how this information would impact the action area for a particular listed organism and may potentially include areas of exposure that are downwind and downstream of the pesticide use site.

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

The Level I screening assessment process for listed species uses the generic taxonomic group-based process to make inferences on direct effects for listed species. The first iteration of reporting the results of the Level I screen is a listing of pesticide use sites and taxonomic groups for which RQ calculations reveal values that meet or exceed the listed species LOCs. In the majority of cases, the screening-level risk assessment process reports RQ calculations for the following broad taxonomic groupings:

 Freshwater fish (also used as a surrogate for aquatic phase amphibians)

 Freshwater invertebrates

 Estuarine/marine fish

 Estuarine/marine invertebrates

 Non-vascular Plants

There may also be taxonomic groups of listed species for which screening tools are not fully developed nor represented through surrogacy with existing tools. For example, there is no RQ calculation process for either fungi or terrestrial invertebrates.

IV.B.5.b.1. Discussion of Risk Quotients76 Endangered Species LOCs are exceeded for freshwater fish, freshwater invertebrates and for plant LOCs for nonvascul ar aquatic plants. All terrestrial impacts are based on inhalation exposure. Based on inhalation exposure, no LOCs are exceeded

for birds and mammals.

Terrestrial invertebrates and fungi are targ et species and thus non-target terrestrial invertebrates and fungi may also be at risk. Should estimated exposure levels resulting in RQs at or above the endangered species LOC occur in proximity to listed resources, the available screening level information suggests a potential risk for direct acute effects on listed freshwater fish, marine fish, freshwater invertebrates, marine invertebrates and aquatic plants, associated with use of DMDS.

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

An analysis has been conducted of the pr obability of individual mortality at an LOC of 0.1, the acute endangered species LOC for terrestrial wildlife. It is recognized that extrapolation of very low probability events is associated with considerable uncertainty in the resulting estimates. The analysis uses the EFED spreadsheet IECv1.1.xls, developed by EFED (USEPA, 2004).

For birds, a bobwhite quail LC 50 of 1.73 mg/kg (MRID 47035302) is used for the assessment of inhalation risk from exposure to DMDS. A probit slope (10.1) and 95% confidence interval (1.76 – 18.44) are provided in the data review. Based on these inputs and an assumption of a probit dose response relationship, the IEC spreadsheet indicates an estimated chance of individual mortality associated with the listed species LOC of 0.1, the acute toxic endpoint for birds, of approximately one in 3.62E+23. To explore possible bounds to this estimate, the upper and lower values for the mean slope estimate were used to calculate upper and lower estimates of the effects probability associated with the listed species LOC. These values are approximately one in 2.55E+01 and one in

3.19E+75.

For the rat as a surrogate for mammals, an LC 50 of 17 ppm (MRID 4470528-14) is used for the assessment of inhalation risk from exposure to DMDS. There was not a good fit for the probit analysis. No slope was reported, therefore the default probit slope (4.5) and 95% confidence interval (2 – 9) are provided in the data review. Based on these inputs and an assumption of a probit dose response relationship, the IEC spreadsheet indicates an estimated chance of individual mortality associated with the listed species LOC of 0.1, the acute toxic endpoint for mammals, of approximately one in 2.94E+05. To explore possible bounds to this estimate, the upper and lower values for the mean slope estimate were used to calculate upper a nd lower estimates of the effects probability associated with the listed species LOC. These values are approximately one in 4.40E+01

and one in 8.86E+18.

An analysis has been conducted of the probability of individual mortality at an LOC of 0.05, the acute endangered species LOC for aquatic animals. It is recognized that77 extrapolation of very low probability events is associated with considerable uncertainty in the resulting estimates. The analysis uses the EFED spreadsheet IECv1.1.xls, developed by EFED (USEPA, 2004).

For freshwater fish, a rainbow trout LC 50 of 0.96 ppm (MRID 4470528-14) is used for the assessment of acute risk from exposure to DMDS. There was not a good fit for the probit analysis. No slope was reported, therefore the default probit slope (4.5) and 95% confidence interval (2 – 9) are provided in the data review. Based on these inputs and an assumption of a probit dose response relationship, the IEC spreadsheet indicates an estimated chance of individual mortality associated with the listed species LOC of 0.05, the acute toxic endpoint for fish, of approximately one in 4.18E+08. To explore possible bounds to this estimate, the upper and lower values for the mean slope estimate were used to calculate upper and lower estimates of the effects probability associated with the listed species LOC. These values are approximately one in 2.16E+02 and one in

1.75E+31.

For estuarine/marine fish, a sheepshead minnow LC 50 of 5.6 ppm (MRID 473075- 04) is used for the assessment of acute risk from exposure to DMDS. There was not a good fit for the probit analysis. No slope was reported, therefore the default probit slope (4.5) and 95% confidence interval (2 – 9) are provided in the data review. Based on these inputs and an assumption of a probit dose response relationship, the IEC spreadsheet indicates an estimated chance of individual mortality associated with the listed species LOC of 0.05, the acute toxic endpoint for fish, of approximately one in 4.18E+08. To explore possible bounds to this estimate, the upper and lower values for the mean slope estimate were used to calculate upper and lower estimates of the effects probability associated with the listed species LOC. These values are approximately one in 2.16E+02

and one in 1.75E+31.

For freshwater invertebrates, a daphnid LC 50 of 1.6 ppm (MRID 470528-16) is used for the assessment of acute risk from exposure to DMDS. There was not a good fit for the probit analysis. No slope was reported, therefore the default probit slope (4.5) and 95% confidence interval (2 – 9) are provided in the data review. Based on these inputs and an assumption of a probit dose response relationship, the IEC spreadsheet indicates an estimated chance of individual mortality associated with the listed species LOC of 0.05, the acute toxic endpoint for fish, of approximately one in 4.18E+08. To explore possible bounds to this estimate, the upper and lower values for the mean slope estimate were used to calculate upper and lower estimates of the effects probability associated with the listed species LOC. These values are approximately one in 2.16E+02 and one in

1.75E+31.

For estuarine/marine invertebrates, a mysid LC 50 of 4.9 ppm (MRID 473075-05) is used for the assessment of acute risk from exposure to DMDS. There was not a good fit for the probit analysis. No slope was reported, therefore the default probit slope (4.5) and 95% confidence interval (2 – 9) are provided in the data review. Based on these inputs and an assumption of a probit dose response relationship, the IEC spreadsheet78 indicates an estimated chance of individual mortality associated with the listed species LOC of 0.05, the acute toxic endpoint for fish, of approximately one in 4.18E+08. To explore possible bounds to this estimate, the upper and lower values for the mean slope estimate were used to calculate upper and lower estimates of the effects probability associated with the listed species LOC. These values are approximately one in 2.16E+02

and one in 1.75E+31.

Although the Agency has assumed a probit dose response relationship in establishing the listed species LOCs, the available data for the toxicity study generating RQs for this taxonomic group do not support a probit dose response relationship, and so the confidence in estimated event probabilities based on this dose response relationship and the listed species LOC is low.

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

Although the Level I screening assessment process relies on RQ calculations that use toxicity endpoints selected from the most sensitive species tested within broad taxonomic groups, there may be situations in which additional effects data from one or more sources may suggest that a given suite of listed taxa may be more or less sensitive than suggested by the effects data used for RQ calculations. In these circumstances, the screening level RQs are not changed, but effect s data more specific to listed species may

be used to evaluate the extent to whic h screening-level RQs adequately represent conclusions regarding effects on specific listed taxa. However, this does not appear to apply to DMDS.

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

Sub-lethal adverse effects were seen in a variety of acute studies. For example, nasal effects were seen in mammal inhalation studies. Thus, it is expected that sub-lethal effects could be seen in listed species, if exposed at levels comparable to those producing effects in the lab. This potentially could cause adverse effects upon listed species. For example, if DMDS caused effects to the sense of smell, it could impact foraging or predator avoidance.

IV.B.5.e. Indirect Effects Analysis

The Agency acknowledges that pesticides have the potential to exert indirect effects upon the listed organisms by perturbing forage or prey availability or altering the extent and nature of nesting habitat, for example. In conducting a screen for indirect effects, the Agency uses the direct effects LOCs for each taxonomic group to make inferences concerning the potential for indirect effects upon listed species that rely upon non-endangered organisms in these taxonomic groups as resources critical to their life cycle.79 For DMDS, direct effect LOCs are exceeded for fish, aquatic invertebrates, and plants, as indicated above. In addition to these potential direct effects, there may thus be a potential for indirect effects to those listed species that are dependent upon fish, aquatic invertebrates, and/or aquatic plants.

IV.B.5.f. Critical Habitat

In the evaluation of pesticide effects on designated critical habitat, consideration is given to the physical and biological features (constituent elements) of a critical habitat identified by the U.S Fish and Wildlife and National Marine Fisheries Services as essential to the conservation of a listed species and which may require special management considerations or protection. The evaluation of impacts for a screening level pesticide risk assessment focuses on the biological features that are constituent elements and is accomplished using the screening-level taxonomic analysis (risk quotients, RQs) and listed species levels of concern (LOCs) that are used to evaluate direct and indirect effects to listed organisms.

The screening-level risk assessment has identified potential risks for indirect effects on listed species for those organisms dependant upon mammals, birds, fish, aquatic invertebrates, and/or plants. In light of the potential for indirect effects, the next step for EPA and the Service(s) is to identif y which listed species and critical habitat are potentially implicated. Analytically, the identification of such species and critical habitat can occur in either of two ways. First, the agencies could determine whether the action area overlaps critical habitat or the occupied range of any listed species. If so, EPA would examine whether the pesticide's potential impacts on non-endangered species would affect the listed species indirectly or directly affect a constituent element of the critical habitat. Alternatively, the agenci es could determine which listed species depend on biological resources, or have constituent elements that fall into, the taxa that may be directly or indirectly impacted by the pes ticide. Then EPA would determine whether use of the pesticide overlaps the critical habitat or the occupied range of those listed species. At present, the information reviewed by EPA does not permit use of either analytical approach to make a definitive identification of species that are potentially impacted indirectly or critical habitats that is potentially impacted directly by the use of the pesticide. EPA and the Service(s) are working together to conduct the necessary analysis.

This screening-level risk assessment for critical habitat provides a listing of potential biological features that, if they are constituent elements of one or more critical habitats, would be of potential concern. These correspond to the taxa identified above as being of potential concern for indirect effect s and include mammals, birds, fish, terrestrial invertebrates, and/or plants. This list should serve as an initial step in problem formulation for further assessment of critical habitat impacts outlined above, should additional work be necessary.80 IV.B.5.g. Co-occurrence Analysis

The goal of the analysis for co-location is to determine whether sites of pesticide use are geographically associated with known locations of listed species. At the screening level, this analysis is accom plished using the LOCATES database. The database uses location information for listed species at the county level and compares it to agricultural census data for crop production at the same county level of resolution. The product is a listing of federally listed species that are located within counties known to produce the crop upon which the pesticide will be used. Because the Level I screening

assessment considers both direct and indirect effects across generic taxonomic groupings, it is not possible to exclude any taxonomic group from a LOCATES database run for a screening risk assessment.

DMDS is proposed for pre-plant soil incorporated uses. These uses could potentially occur in any county in the United States. Thus a screen for both direct and

indirect effects in all counties would essen tially include all known federally-listed species for all taxonomic groups in all counties. A list of these (organized by taxon), as compiled by EFED in 2009, is provided in Appendix H.

The registrant must provide information on the proximity of all federally-listed species to the proposed use sites. This requirement may be satisfied in one of three ways: 1) having membership in the FIFRA Endangered Species Task Force (Pesticide Registration [PR] Notice 2000-2); 2) citing FIFRA Endangered Species Task Force data; or 3) independently producing these data, provided the information is of sufficient quality to meet FIFRA requirements. The informa tion will be used by the OPP Endangered Species Protection Program to develop recommendations to avoid adverse effects to listed species.

Listed species risks are associated with direct or indirect effects due to applications of DMDS to tomatoes, peppers, cucumbers, strawberries, onions, nursery and Christmas trees if organisms in listed taxa are exposed (direct effects) or are dependent on other organisms that are expos ed (indirect effects). Risks are based on available reviewed data. Submission and review of the data requested in this review (see above) may result in identification of additional potential effects. A summary of listed species by taxa is presented in Appendix F.

There is the potential for direct effects for listed freshwater fish and aquatic invertebrates from the use of DMDS based on RQs exceeding the LOC. Drip irrigation RQs exceed the endangered species LOC for FL cucumber, FL strawberry and GA onion. Drip irrigation RQs range from 0.01 to 0.21 and shank injection RQs from 0 to 0.01 for fish. Drip irrigation RQs range from 0.001 to 0.125 and shank injection RQs from 0 to 0.006 for invertebrates. Based on the direct effect RQs, any freshwater fish species or aquatic invertebrates consuming those taxa will be adversely impacted for indirect81 effects.

There is no potential direct or indirect effect on listed estuarine/marine fish or invertebrates from drip irrigation or shank injection for any use. Drip irrigation RQs range from 0 to 0.036 and shank injection RQs from 0 to 0.002 for fish. Drip irrigation RQs range from 0 to 0.041 and shank injection RQs from 0 to 0.001 for invertebrates.

There is no potential risk for direct or indirect effects to listed aquatic vascular plants represented by Lemna based on no RQ exceedence using the EC 05

. No RQs for either drip irrigation or shank injection exceeded the LOC.

Although there are no aquatic non-vascular plants included in Federal listings of threatened and endangered species at the present time, an assessment of the effect of DMDS on those plants is provided to evaluate potential contributions to indirect effects to other taxa and as a record of exceedances should future listings of non-vascular aquatic plants warrant additional evaluation of Federal actions.

There is potential risk for direct or indirect effects to listed aquatic non-vascular plants represented by Anabaena based on RQ exceedence using the EC 05

. There was no RQ exceedence for vascular using using Anabaena as a surrogate for shank injection for

any uses.

There is potential for direct or indirect chronic effects for freshwater fish and aquatic invertebrates based on the uncertainty for persistence in aquatic environments.

There is no potential direct or indirect acute effects on listed estuarine/marine fish or invertebrates from drip irrigation or shank injection for any use. Drip irrigation RQs range from 0 to 0.036 and shank injection RQs from 0 to 0.002 for fish. Drip irrigation RQs range from 0 to 0.041 and shank injection RQs from 0 to 0.001 for invertebrates.

There is potential for direct or indirect chronic effects for estuarine/marine fish and aquatic invertebrates based on the uncertainty for persistence in aquatic

environments.

Habitat Modification

Habitat modification includes effects from reduction in prey as well as effects on plants. There is the potential for indirect effects for listed freshwater fish and aquatic invertebrates from the use of DMDS based on RQs exceeding the LOC. Drip irrigation RQs exceed the endangered species LOC for FL cucumber, FL strawberry and GA onion.

The effect of plants is also used to assess the effect of DMDS on habitat modification. There is potential risk to listed aquatic non-vascular plants represented by

Anabaena based on RQ exceedence using the EC 05

. RQs are estimated for listed species using the EC 05 toxicity value. RQs exceeded the LOC for drip irrigation for listed82 nonvascular plants for CA tomato, FL tomato, FL pepper, FL cucumber, FL strawberry, GA onion, MI nursery, NJ nursery and OR Christmas tree uses. No RQs for shank injection for nonvascular plants exceeded the LOC for any uses.

Listed Taxon Direct Effects Indirect Effects 3

Terrestrial and semiaquatic plants –

monocots Yes (Additional data required) Yes (Additional data required)

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

Terrestrial

Invertebrates No No

Birds No No

Terrestrial phase amphibians 1 No No

Reptiles 1 No No

Mammals No No

Aquatic non-vascular plants* Yes Yes

Aquatic vascular plants No No

Freshwater fish Yes – (Additional chronic data needed) 4 Yes

Aquatic phase amphibians 2 Yes – (Additional chronic data needed) 4 Yes

Freshwater

crustaceans Yes Yes

Mollusks NA NA

Marine/estuarine fish No –(Additional chronic data needed) 4 No

Marine/estuarine

crustaceans No (Additional chronic data needed) 4 No83 * At the present time no aquatic non-vascular plants are included in Federal listings of threatened and endangered species. The taxonomic group is included here for the purposes of evaluating potential

contributions to indirect effects to other taxa and as a record of exceedances should future listings of non-vascular aquatic plants warrant additional evaluation of Federal actions.

1 Risk assessment is based on avian assessment.

2 Risk assessment is based on freshwater fish assessment.

3 Indirect effects are considered possible for every taxonomic group when one or more direct effect LOCs are met/exceeded. Listed species could be affected by the loss of other species that they depend on for food, cover, and/or reproduction (e.g., pollination, seed dispersal). This is only a screening assessment. A refined assessment will consider the specifics of the food, cover, and reproduction needs of each listed species.

4 Requested data may result in additional potential direct effects.84 

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