# EFED's Reregistration Eligibility Decision

Chapter for Sethoxy dim

Michael Davy , Agronomist William Eckel, Ph.D., Agronomist Shannon Borges, Biologist
Environmental Fate and Ecological Effects Division (7507C)

Office of Pesticide Programs Environmental Protection Agency

June 22, 2005

Secondary Review: Dana Spatz, Risk Assessment Process L eader Donna Randall, Senior Scientist Environmental Risk Branch I I Environmental Fate and Effects Division (7507C)

Branch Chief Approval: Tom Bailey , Ph.D., Chief Environmental Risk Branch I I Environmental Fate and Effects Division (7507C)-2-

I. Executive Summary

.................................................... -6- A. Nature of Chemical Stressor

....................................... -6- B. Potential Risks to Non-target Organisms

.............................. -7- C. Conclusions - Exposure Characterization

............................. -7- D. Conclusions - Effects Characterization

............................... -8- E. Uncertainties and Data Gaps

....................................... -9-
II. Problem Formulation

................................................ -10- A. Stressor Source and Distribution

................................... -10- 1. Phy sical/Chemical/Fate and Transport Properties

.................... -10- 2. Pesticide Ty

pe, Class, and Mode of Action

........................ -14- 3. Overview of Pesticide Formulation and Usage

...................... -14- B. Receptors and Assessment Endpoints

............................... -14- 1. Measures of Ecological Effect

.................................. -14- a. Terrestrial Organisms

................................... -15- Acute Toxicity to Birds

.............................. -15- Chronic Toxicity to Birds

............................ -16- Acute Toxicity to Mammals

.......................... -16- Chronic Toxicity to Mammals

......................... -16- Toxicity to Plants

................................... -16- b. Aquatic Organisms

..................................... -17- Acute Toxicity to Aquatic Organisms

................... -17- Chronic Toxicity to Aquatic Organisms

................. -17- c. Discussion

............................................ -17- 2. Measures of Exposure

........................................ -19- Aquatic Sy stems

.......................................... -20- Terrestrial Sy stems

........................................ -21- C. Conceptual Model

.............................................. -21- 1. Risk Hy

potheses

.......................................... -21- 2. Diagram

................................................ -22- a. Aquatic Exposure

...................................... -23- b. Terrestrial Exposure

.................................... -23- D. Key Uncertainties and Information Gaps

............................. -25- E. Analy sis Plan

.................................................. -26- 1. Assessment

.............................................. -26- (a) Fate and Exposure

..................................... -26- (b) Toxicity

............................................. -26- (c) Risk Quotient and L evels of Concern

...................... -27-
III. Analy sis

............................................................ -29- A. Use Characterization

............................................ -29--3- Characterization of Production Areas and Soils

....................... -31- Soy beans

..................................................... -31- Cotton and Peanuts

............................................. -31- Other Cotton Areas

............................................. -31- Other Crops

................................................... -32- B. Exposure Characterization

........................................ -32- 1. Environmental Fate and Transport Characterization

.............. -32- Degradation Scheme for Sethoxydim

......................... -35- 2. Measures of Aquatic Exposure

.................................. -37- a. Aquatic Exposure Modeling

.......................... -37- Spray Drift Exposure from Formulated Sethoxydim

........ -39- b. Aquatic Exposure Monitoring and Field Data

............... -40- 3. Measures of Terrestrial Exposure

............................... -42- a. Terrestrial Exposure Modeling

............................ -42- Residues on Avian Food I tems

........................ -43- Residues on Mammalian Food I tems

................... -44- Terrestrial Plant EEC

................................ -44- C. Measures of Ecological Effects

.................................... -46- 1. Aquatic Effects

........................................... -46- a. Aquatic Animals

................................... -46-

Acute Effects

.................................... -46- Chronic Effects

.................................. -47- Field Studies

.................................... -47- b. Aquatic Plants

..................................... -47- 2. Terrestrial Effects

............................................ -48- a. Terrestrial Animals

................................. -48- Acute Effects

.................................... -48- Chronic Effects

.................................. -48- Field Studies

..................................... -48- b. Terrestrial Plants

................................... -49- 3. ECOTOX Database

........................................... -49-
IV

. Risk Characterization

................................................ -50- A. Risk Estimation - Integration of Exposure and Effects Data

.............. -50- 1. Non-target Aquatic Animals

................................ -50- Runoff

................................................. -50- 2. Non-target Terrestrial Animal

............................... -51- 3. Non-target Plants

......................................... -53- Terrestrial

............................................... -53- Aquatic Plants

........................................... -54- B. Risk Description

................................................ -54- 1. Risks to Aquatic Animals and Plants

.......................... -54- Summary of Major Conclusions

............................. -54--4- Discussion

.............................................. -55- Aquatic animals

.......................................... -55- Aquatic Plants

........................................... -57- 2. Risks to Terrestrial Organisms

.................................. -57- Summary of Major Conclusions

............................. -57- Discussion

.............................................. -58- Terrestrial animals

........................................ -58- 3. Review of Incident Data

...................................... -61- 4. Endocrine Disrupter

.......................................... -61- C. Threatened and Endangered Species Concerns

........................... -62- 1. Taxonomic Groups Potentially at Risk

........................ -62- 2. Probit Slope Analy sis

...................................... -65- 3. Indirect Effect Analy ses .................................... -67- 4. Critical Habitats

.......................................... -68- D. Description of Assumptions, Uncertainties, Strengths, and L imitations

..... -69- 1. Assumptions and L imitations Related to Exposure for all Taxa

..... -69- 2. Assumptions and L imitations Related to Exposure for Terrestrial Species

....................................................... -70- a. Location of Wildlife Species

........................... -70- b. Routes of Exposure

.................................. -70- c. Residue L evels Selection

............................. -71- d. Dietary Intake - Differences Between Laboratory and Field Conditions

........................................ -71- e. Estimated Environmental Concentrations to Non-Target Plants

................................................. -72- f. Data gaps

.......................................... -72- 3. Assumptions and L imitations Related to Aquatic Effects Assessment -72- a. Age Class and Sensitivity of Effects Thresholds

............ -72- b. Use of the Most Sensitive Species Tested

................ -73- c. Data Gaps

......................................... -73- d. Aquatic Environment Effects

.......................... -73- e. Aquatic Environment Exposure

........................ -74- Appendix A. Environmental Fate Studies

................................. -75- Appendix B Summary of Public L iterature from ECOTOX database

........... -83- Appendix C Summary of Public L iterature that were excluded from ECOTOX database

....................................................... -90- Appendix D Li st of Exclusion Terms Utilized under the ECOTOX Database

...................................................... -128- Appendix E Ecological Effects Data

................................... -130- Appendix F. Input Parameters For GENEEC2 Runs for Sethoxydim Total Toxic

Residues

............................................... -140- Appendix G Environmental Fate Data Requirements

...................... -142- Appendix H Use Closure Memorandum

................................. -144--5-

Appendix I Ecological Data Requirements

.............................. -146- Appendix J Structures of Degradates

.................................. -148- Appendix K Sethoxy dim MRI D Bibliography

............................ -156- Appendix L Li sted Species by State and Crops

........................... -166- Appendix M Full list of listed species in states in which sethoxy dim is applied.

. . -187- Appendix N AgDrift Aquatic Model Runs

............................... -205- Appendix O AgDrift Model Runs for Plants

............................. -211- Appendix P TerrPlant Model Results

.................................. -219--6-

I. Executive Summary A. Nature of Chemical Stressor There are two chemical stressors in this risk assessment. The first is the active ingredient, sethoxy dim (PC code 121001) and its degradates, and the second is the petroleum solvent (CAS Registry Number 64742-94-5) that is used in the end-use formulations POAST® and POAST® Plus. The solvent is known to contain several percent by weight of Naphthalene, which is also a registered active ingredient (PC code 055801). Sethoxydim is responsible for all presumed risks to plants and birds, and the petroleum solvent is responsible for presumed risks to fish and aquatic invertebrates (fresh- and salt-water). Sethoxydim . The first chemical stressor in this assessment is the cyclohexenone-class herbicide sethoxy dim and its eight degradates. The eight degradates are grouped into three sets. These are (1) the sulfoxide (M-SO) and sulfone (M-SO2) of the parent chemical, (2) the hydroly sis product M1-S, its sulfoxide (M1-SO), and sulfone (M1-SO2), and (3) the hydroly sis/ring closure product (M2-S), and its sulfoxide (M2-SO) and sulfone (M2-SO2). Structures of all the degradates are given in Appendix J, and the degradation scheme showing the relationship of the parent to the degradates is given in section B.1. The major degradates present in soil are the parent sulfoxide and sulfone (M-SO and M-SO2). These compounds may revert to parent sethoxydim by chemical reduction (loss of the added oxygen atoms) under anaerobic conditions. Each of these compounds is mobile in soil-water sy stems. The major degradates formed in water are the hydroly sis product (M1-S) and the resulting ringclosure product M2-S. As noted, each of these has a sulfoxide and a sulfone. The M1 series of degradates are mobile in soil-water sy stems, as is parent sethoxy dim and its sulfoxide and sulfone. The M2 series, being a fused two-ring sy stem (tetrahydrobenzoxazole) is less mobile. For this assessment, all of the degradates are assumed to be equally as toxic as parent sethoxy dim. Therefore, a Total Toxic Residue approach is used for the assessment of risks to aquatic organisms and plants from sethoxydim per se. Petroleum Solvent . This solvent (CAS Registry Number 64742-94-5) is used to stabilize the manufacturing use product (MUP) and is present in the end-use products POAST® and POAST® Plus. I t contains Naphthalene, a polycy clic aromatic hydrocarbon, which is known to be toxic to fish and invertebrates. The toxicity of POAST® (18% active ingredient by weight) is similar to the toxicity of Naphthalene, rather than that of pure sethoxydim. For this reason, the presumed risks to aquatic animals in this assessment are attributable to the petroleum solvent, rather than sethoxydim itself.-7-

B. Potential Risks to Non-target Organisms Risk from sethoxy dim:

• Chronic risk to birds from sethoxy dim is expected.

• It is expected that risk to non-target aquatic plants is limited to aquatic grasses, due to the mode of action of sethoxydim and terrestrial plant data. The risk cannot be quantified, because there are no toxicity testing data for aquatic grasses (family Poaceae).

• The terrestrial listed plant L OC (family Poaceae) is exceeded from spray drift from ground and aerial application and from runoff to low semi-aquatic areas. No LOC Exceeded

• LOC for acute risk for fish and aquatic invertebrates from run-off or spray drift to the pond is not exceeded.

• There are no LOC exceedances to algae or diatoms.

• LOC for chronic risk for aquatic estuarine animals from runoff to the standard farm pond is not exceeded.

• Avian or mammalian acute L OC is not exceeded.

• The chronic LOC is not exceeded for mammals.

• LOC for non-grass plant species are not exceeded.

C. Conclusions - Exposure Characterization Terrestrial . The exposure of terrestrial animals and plants was assessed by standard methods (Hoerger-Kenaga nomogram for dietary exposure to animals, 1% or 5% spray drift for plants in adjacent fields and wetlands, and AgDrift for spray drift exposure of plants). For animals, exposure on food items at maximum labeled rates, with minimum application intervals, triggered only chronic (reproductive) risk to birds via dietary intake. This was true with the assumption of either the 35-day default foliar dissipation half-life on food items, or a refined assumption of a one-day foliar dissipation half-life for the Hoerger-Kenaga analy sis (T--8-

REX model). The exposure that would not trigger this risk is not known, since a no-effect concentration was not established. For plants, the runoff exposure from spray drift was estimated as 1% or 5% of the application rate for ground and aerial applications, respectively . Exposure to non-target plants from runoff was estimated with 5% runoff factor that took into consideration the solubility of sethoxy dim. Spray drift exposure of 1-5% and runoff exposure was sufficient to trigger risk concern for terrestrial grasses. Aquatic . The exposure of aquatic animals and plants was estimated by standard Tier 1 methods (GENEEC model, version 2.0). Screening-level (Tier 1) exposure analy sis was done because it was not anticipated that sethoxydim would reach concentrations sufficient to trigger either acute or chronic risk in animals. The Tier 1 EECs were below 100 ppb, which was indeed insufficient to trigger acute or chronic risk to animals from sethoxydim alone. Screening-level estimates of exposure to the petroleum solvent from aerial spray drift to a 6-inch wetland were up to 350 ppb. This was sufficient to trigger acute risk concerns in fish and invertebrates. The exposure analy sis was done with non-guideline fate data, however, and so is more uncertain than a standard Tier 1 assessment.
It is not known whether the estimated exposure in the standard 6-foot deep farm pond (about 100 ppb) is sufficient to affect sensitive aquatic plants, since there are no toxicity data for aquatic grasses.

D. Conclusions - Effects Characterization

• Sethoxy dim technical is practically non-toxic to aquatic and terrestrial animals on an acute basis.

• The petroleum solvent that contains Naphthalene is moderately toxic to aquatic animals on an acute basis. The toxicity of POAST® is slightly less toxic than that of Naphthalene to aquatic animals.

• The sheepshead minnow early life stage study found no chronic effects (NOAEC > 98 ppm ai) and the my sid shrimp life cy cle study found reproductive effects at 13 ppm ai (NOAEC = 6.5 ppm a.i.).

• Sethoxy dim technical and TEP appear to be phy totoxic to grass species only

.

• Birds may experience a decrease in normal hatchlings when dietary exposure is as low as 100 ppm ai. Mammals may show tail abnormalcies at dietary concentrations as low as 3000 ppm (NOAEL = 600 ppm).-9-

E. Uncertainties and Data Gaps

• Risk to non-target terrestrial plants from spray drift is underestimated because the vegetative vigor study was conducted on the technical sethoxydim and not on the TEP (POAST®).

• Risk to non-target aquatic grass species can not be certain or quantified due to lack of data.

• The avian chronic reproduction study in the mallard duck did not achieve a NOAEL

. Chronic avian toxicity is underestimated.

• The estuarine Fish Early Li fe Stage and Estuarine Invertebrate Life Cycle tests were conducted with 40 and 43% active ingredient formulations respectively , and it is unclear whether the petroleum solvent was present in these test substances. It is uncertain as to what the results of the studies represent.

• The submitted Terrestrial Field Dissipation studies (164-1) were judged to be unacceptable because total sethoxydim residues were analy zed, rather than the parent compound and its eight degradates. However, due to the large uncertainty that exists for the degradates of sethoxydim, additional data need to be generated to lower the level of uncertainty on the fate of sethoxydim. I f the assumption that the degradates are equally as toxic as the parent is adequate for risk assessment, then the studies do not need to be repeated.

• Additional information is needed to determine if the submitted Aerobic Aquatic Metabolism study (162-3) is acceptable. There is uncertainty in this study that needs to be clarified.

• EEC for 6-inch shallow pond scenario was not attempted. Many species of fish and invertebrates breed in shallow waters. There is uncertainty as to whether there may be risk to aquatic animals that spend part of life cycle in these shallow water bodies.-10-

II. Problem Formulation A. Stressor Source and Distribution
1. Phy sical/Chemical/Fate and Transport Properties Sethoxy dim is a highly soluble compound (4700 mg/L in pH 7 water) with a low octanol/water partition coefficient (K ow for Sethoxy dim is 45.1). Sethoxy dim is labile and mobile in the environment. The transformation of parent Sethoxydim, primarily by photodegradation, aerobic metabolism in water and soil, and acid-cataly zed hy droly sis, is rapid (half-lives on the order of hours to day s). Sethoxy dim total residues (Sethoxy dim plus Sethoxy dim transformation products) are determined using a common moiety method that cannot distinguish parent Sethoxy dim from its transformation products. These rearrangement products are more persistent in the environment than Sethoxydim (half-lives on the order of weeks to months) and potentially mobile. Because of its low vapor pressure (1.6x10 -7 mm Hg) and Henry 's Law Constant (1.47x10 -11 atm-m3/mol), Sethoxydim is not expected to be highly volatile. For the aquatic (but not terrestrial) ecological assessment of sethoxydim, we have assumed that the stressor is sethoxy dim Total Toxic Residues, that is, the sum of the parent and its eight degradates. This assumption is justifiable on several bases. First, in aerobic soil metabolism studies, the degradation half-life of parent sethoxydim is less than one day . The resulting metabolites are the sulfoxide (M-SO) and the sulfone (M-SO2). Because the re-application interval is 14 day s, and the degradates are more persistent, it is reasonable to conclude that M-SO and M-SO2 are the forms that have biological activity

. Second, the oxidation process that forms M-SO and M-SO2 is in principle reversible, that is, under chemically reducing (anaerobic) conditions, the degradates could be re-oxidized to the parent compound. This behavior was observed in the unacceptable Anaerobic Aquatic Metabolism study (MRI D 42165603), in which the concentration of parent sethoxydim declined to 16.5% at 0.5 months, and then rose again to 34.3% at 1 month. So, in a sense, parent sethoxy dim is not irreversibly lost by aerobic soil metabolism. Third, the water exposure models that EFED uses do not account for reversible (or equilibrium)processes such as reversible sulfoxidation. To avoid underestimation of exposure, M-SO and MSO2 were considered to be the same chemical entity , since their reversion to parent could not be modeled with the computer. Fourth, the submitted Terrestrial Field Dissipation studies (MRI D 41510608, 41510609, and 41510610) used a common moiety analy tical method that reported total residues, rather than the parent and degradates individually ( the studies were judged to be unacceptable for this reason). This is an indication that the registrant considers soil degradates to be as important as the parent. For the aquatic assessment, the decision to use parent-only or total toxic residues (TTR) does not-11-

affect the outcome of the assessment, since the TTR exposure estimates were well below toxicity endpoints (L C50s) for the technical compound. However, it does result in a more conservative assessment. For the terrestrial assessment, the standard assumption of a 35-day half-life on food items was used, as well as the refined assumption of a one-day half-life. Under either assumption, chronic risk concerns in birds were triggered. Neither of these assumptions has any relationship to the formation of the eight degradates of sethoxydim, since the half-lives only refer to the rate of disappearance of the parent. However, the 35-day half-life is not unreasonable given that sethoxy dim TTR has a half-life of about one month in aerobic soil.-12- 

### C H 3



### N O C H 3 

### O H C H 3 

### S H 3 

### C O Below is the chemical structure of Sethoxydim (Figure 1) and Table 1 showing the Phy sicalChemical Properties of Sethoxy dim Figure 1: Structure of Sethoxydim. CAS Reg. No. 74051-80-2, Formula C 17 H 29 NO 3 S-13-

Table 1: Physical-Chemical Properties of Sethoxydim Property Value Reference Solubility in Water 257 mg/L at pH 5 and 25°C 4700 mg/L at pH 7 and 25°C 16,200 mg/L at pH 9 and 25°C

25 mg/L at pH 4 and 20°C EFED one-liner database 9/14/1993 EFGWB update memo on Reregistration package 12/26/1990 Tomlin, C (1997) cited in EPI -Suite v3.12

Lo g K ow 3.51 at pH 5 1.65 at pH 7 -0.032 at pH 9 EFED one-liner database 9/14/1993 EFGWB update memo on Reregistration package 12/26/1990 Vapor Pressure 1.6x10 -7 mm Hg EFED one-liner database 9/14/1993 Henry ’s Law Constant 1.47x10 -11 atm-m3/mol Molecular Weight Molecular Formula 327.48 g/mol C 17 H 29 NO 3 S pKa (acid dissociation constant) 4.62

SMI LES code CCCC(=NOCC)C1=C(O)CC (CC(C)SCC)CC1=O EPI -Suite v3.12
Phy sical State amber oily liquid EFED one-liner database 9/14/1993 CAS Registry number 71441-80-0 74051-80-2 EPI -Suite v3.12 EFED one-liner database 9/14/1993; Merck Index 10 th Ed.-14- 2. Pesticide Ty

pe, Class, and Mode of Action Sethoxy dim is a member of the Cyclohexanedione class of chemicals. The mode of action for this herbicide is L ipid Biosy nthesis Inhibition. Selectivity is shown to be due to the greater susceptibility at acetyl-coenzy me A carboxylase (ACCase) of grassy species. Susceptible grassy species are killed by inhibition of the ACCase which is a key enzy me in the lipid biosy

nthetic pathway

. 3. Overview of Pesticide Formulation and Usage Sethoxy dim is a sy stemic herbicide which is registered for selective postemergence control of a wide spectrum of annual and perennial grasses. I t is applied either by aerial or ground methods and is registered for many different agricultural and residential uses throughout the United States.
Sethoxy dim is formulated with Naphthalene-containing solvents. Material Safety Data Sheets for POAST® (Reg. No. 7969-58-51036) http://www.cdms.net/ldat/mp5KM007.pdf and POAST® Plus (Reg. No. 7969-88-51036) http://www.cdms.net/ldat/mp5KN001.pdf indicate that POAST® contains 74% petroleum solvent including 7% Naphthalene, and that POAST® Plus contains 87% inerts including 1.3% Naphthalene. Due to its high content of Naphthalene, toxicity data for Naphthalene will be used as surrogate toxicity data for the solvent. I t is likely that the other constituents of Naphthalene-containing solvents (petroleum distillates) have toxicity similar to that of Naphthalene, especially if the toxic effect is simple narcosis.
B. Receptors and Assessment Endpoints Assessment endpoints are defined as “explicit expressions of the actual environmental value that is to be protected.” Two criteria are used to select the appropriate ecological assessment endpoints: 1) identification of the valued attributes of the environment that are considered to be at risk, and 2) the operational definition of assessment endpoints in terms of an ecological entity (i.e., a community of fish and aquatic invertebrates) and its attributes (i.e., survival and reproduction). Therefore, the selection of assessment endpoints is based on valued entities (i.e., ecological receptors), the ecosy stems potentially at risk, the migration pathway s of pesticides, and the routes by which ecological receptors are exposed to pesticide-related contamination. The selection of clearly defined assessment endpoints is important because they provide direction and boundaries in the risk assessment for addressing risk management issues of concern.

1. Measures of Ecological Effect Ecosy stems potentially at risk are expressed in terms of the selected assessment endpoints. The ty pical assessment endpoints for screening-level pesticide ecological risks are reduced survival and reproductive and growth impairment for both aquatic and terrestrial receptors. A set of-15-

surrogate species is used to provide an estimation of ecological risk. Ecological relevance and sensitivity are essential for selecting receptors and assessment endpoints that are scientifically defensible. Surrogate species include freshwater fish and invertebrates, estuarine/marine fish and invertebrates, and amphibians. In the absence of toxicity data on amphibians, it is assumed that aquatic-phase amphibians are approximately as sensitive as fish to the potential effects of a pesticide. Terrestrial animals used as test species include birds and small mammals. The risk assessment assumes that reptiles and terrestrial-phase amphibians are approximately as sensitive to pesticide-induced effects as are birds in the absence of toxicity data. Potential effects to benthic organisms may also be evaluated if environmental fate data indicate that the assessed chemical may partition to the sediment or if sediment organisms are particularly sensitive species. For both aquatic and terrestrial receptors, direct acute and direct chronic effects are considered. Although these endpoints are measured at the individual level, they provide insight about risks at higher levels of biological organization (i.e., populations and communities). For example, pesticide effects on individual survivorship have important implications for both population-level effects as well as habitat carry ing capacity . Indirect effects on critical habitat are only considered in the risk characterization for the potential effects on endangered species, provided that the risk quotient demonstrates probable risk. For plants in terrestrial and semi-aquatic environments, the screening assessment endpoint is the perpetuation of populations of non-target species (both crop and non-crop species). Endpoints assessed include height measurement and plant weight from seedling emergence and vegetative vigor studies. Although it is recognized that the seedling emergence and vegetative vigor endpoints may not address all plant life cycle components, it is assumed that impacts at emergence and during active growth may impact individual competitive ability and reproductive success. Data on the formulated product (as opposed to the active ingredient) are used to characterize plant exposure effects. I f the maximum exposure rate results in an effect level that is less than 25% in a Tier I study , low risk is presumed and a Tier I I s tudy is not required. However, if the effect level is less than 25% but greater than 5% in a Tier I study , potential risk may still occur to listed species that cannot be quantified.

a. Terrestrial Organisms Acute Toxicity to Birds Technical Sethoxydim is practically non-toxic to the mallard duck on an acute oral basis, and practically non-toxic to the mallard duck and the bobwhite quail on a subacute dietary basis. The surrogate chemical (Naphthalene) for the Petroleum solvent is also non-toxic to the bobwhite quail on an acute oral basis (L D50 is 2690 mg/kg) and subacute dietary basis (L C50 is > 5620 ppm). Therefore, no adverse effects to birds are expected from acute exposure to either Sethoxydim or Petroleum solvent, and no acute risk assessment for birds will be done.-16- Chronic Toxicity to Birds A reproduction study in bobwhite quail resulted in no treatment-related effects, with a NOAEC of >1000 ppm. However, the number of normal hatchlings was affected in the mallard duck, with a L OAEC of 100 ppm, and no NOAEC established. Both tests were performed using the technical active ingredient (96.8%). Therefore, a chronic risk assessment based on the reproductive risk to birds, as represented by the mallard duck, will be performed. A single application of 0.47 lb/A assuming a foliar dissipation half-life of 1 day gives chronic RQ of >1.13 for birds consuming short grass food items. EFED will conclude that there is a presumption of chronic (reproductive) risk to birds.

Acute Toxicity to Mammals The acute toxicity of technical (94-99%) Sethoxydim, and of the 18.0% formulated product (POAST®) was tested on laboratory rats. The LD50 of the technical ingredient was 3125 mg/kg in male rats, and 2676 mg/kg in females. The LD50 of the 18% formulation was 5000 mg/kg in male rats, and 4385 mg/kg in female rats. These results indicate that Sethoxydim and its 18% formulation are practically non-toxic to rats. Therefore, an acute risk assessment for mammals will not be done.

Chronic Toxicity to Mammals A two-generation reproduction study in rats was performed with technical (94-99%) Sethoxydim. The reproductive toxicity NOAEC value (3000 ppm) indicates that Sethoxydim does not cause reproductive effects at expected exposure levels in rats (as a surrogate for all mammals); however, developmental effects were observed in offspring and the developmental toxicity NOAEC was 600 ppm.

Toxicity to Plants Phy totoxicity data indicate that Sethoxy dim is practically nontoxic to dicots and a non-grass monocot (onion). I t is, however, toxic to grasses. The phy totoxicity data that can be used isfrom vegetative vigor and seedling emergence studies which is used to determine risk to nontarget plants from spray drift and runoff, respectively . However, vegetative vigor study was done with the technical grade Sethoxydim. The Agency ’s guidelines call for the vegetative vigor study to be conducted with the TEP because of enhanced penetration of the herbicide with adjuvants to penetrate the plant epidermis. The plant risk assessment will focus on risks to non-target grassy plants (including listed grass species) from spray drift and runoff, and possibly indirect risks to listed animal and non-grass species that may depend on them. There is added uncertainty in the assessment of risk to non-target terrestrial plants from spray drift (due to no phy totoxic data using the TEP). Risk to non-target terrestrial plants from spray drift may be underestimated from lack of TEP phy

totoxic data.-17- b. Aquatic Organisms Acute Toxicity to Aquatic Organisms The acute toxicity data for technical Sethoxydim show that it is practically non-toxic to the rainbow trout, bluegill sunfish, sheepshead minnow, eastern oy ster, and my sid shrimp, and only slightly toxic to the waterflea ( Daphnia magna ).
In contrast, acute toxicity data for 18.0, 19.3 and 20.4% formulated products indicate moderate toxicity to the rainbow trout, bluegill sunfish, waterflea, and sheepshead minnow, and high toxicity to the eastern oy ster and my sid shrimp. EFED concludes that the observed acute toxicity of formulated Sethoxydim is due to the action of the petroleum solvent. The acute hazard to aquatic and estuarine organisms is therefore due to the solvent, and not the active ingredient, Sethoxydim.

Chronic Toxicity to Aquatic Organisms No chronic studies were submitted for freshwater invertebrates or fish. The only available chronic toxicity data for aquatic organisms are for an estuarine fish (sheepshead minnows) and an estuarine invertebrate (my sid shrimp). Both studies were rated as “supplemental” because they were conducted using 40 and 43% sethoxydim formulations respectively

. No adverse effects were observed in the sheepshead minnow at the highest tested concentration of 98 ppm (the solubility of Sethoxy dim is 4700 ppm). For the my sid shrimp, both survival and length were affected. The NOAEC (no observed effect concentration) was 6.5 ppm ai, and the LOAEC (lowest observed effect concentration) was 13 ppm ai.

c. Discussion For aquatic plants, the assessment endpoint is the maintenance and growth of standing crop or biomass. Measures of effect focus on algal and vascular plant (i.e., duckweed) growth rates and biomass measurements. The ecological relevance of selecting the above-mentioned assessment endpoints is three-fold: 1) complete exposure pathway s exist for the receptors; 2) the receptors are potentially sensitive to pesticides in the affected media and from residues on plants, seeds, insects, and other food sources; and 3) the receptors could inhabit areas where pesticides are applied or where runoff and/or spray drift could impact sites containing available suitable habitat.-18-

Each assessment endpoint requires one or more “measures of ecological effect,” which are defined as changes in the attributes of an assessment endpoint itself or changes in a surrogate entity or attribute in response to pesticide exposure. Ecological measures of effectfor the screening level risk assessment are based on a suite of registrant-submitted toxicity studies performed on a limited number of organisms in the following broad groupings:

• Birds (mallard duck and bobwhite quail) used as surrogate species for terrestrialphase amphibians and reptiles

• Mammals (laboratory rat)

• Freshwater fish (bluegill sunfish and rainbow trout) used as a surrogate for aquatic phase amphibians

• Freshwater invertebrates (water flea - Daphnia magna)

• Estuarine/marine fish (sheepshead minnow)

• Estuarine/marine invertebrates (Eastern oy ster and my sid shrimp)

• Terrestrial plants (various crop species)

• Algae and aquatic plants (algae, diatoms, and duckweed) A discussion of toxicity data available for this risk assessment and the resulting measures of effect selected for each taxonomic group are included in Section I II C of this document. A summary of the assessment and measures of effect selected to characterize potential ecological risk associated with Sethoxy dim exposure is provided in Table 2. Table 2. Summary of Assessment and Measurement Endpoints Assessment Endpoint Measurement Endpoint

1. Abundance (i.e., survival, reproduction, and growth) of individuals and populations of birds 1a. Mallard duck oral LD50 1b. 1b. Bobwhite quail and mallard duck subacute dietary LC50 1c. Bobwhite quail and mallard duck chronic reproduction NOAEC and LOAEC (one acceptable study and one supplemental study)
2. Abundance (i.e., survival, reproduction, and growth) of individuals and populations of mammals 2a. Laboratory rat acute oral LD50 2b. Laboratory rat chronic NOAEC (2-generation rat reproductive study)

3. Survival and reproduction of individuals and communities of freshwater fish and invertebrates 3a. Rainbow trout acute LC50 3b. Fathead minnow or rainbow trout chronic early life stage NOAEC (weight & length) NO STUDY SUBMITTED 3c. Water flea acute LC50 3d. Water flea life cycle chronic NOAEC (offspring) - NO STUDY SUBMITTED-19-

4. Survival and reproduction of individuals and communities of estuarine/marine fish and invertebrates 4a. Sheepshead minnow acute LC50 4b. Estuarine/marine fish chronic NOAEC & LOAEC 4c. Eastern oyster and mysid shrimp acute LC50 4d. Estuarine/marine invertebrate (mysid shrimp) chronic NOAEC & LOAEC 5. Perpetuation of individuals and populations of non-target terrestrial plants (crops and non-crop plant species) 5a. Monocot and dicot seedling emergence EC25 5b. Monocot and dicot vegetative vigor EC25 -STUDY NEEDED WITH TEP

6. Survival of beneficial insect populations 6a. Honeybee acute contact LD50
7. Maintenance and growth of individuals and populations of aquatic plants from standing crop or biomass 7a. Algae and duckweed acute EC50

LD50 = Lethal dose to 50% of the test population NOAEC = No observed adverse effect concentration LOAEC - Lowest observed adverse effect concentration LC50 = Lethal concentration to 50% of the test population EC50/EC25 = Effect concentration to 50%/25% of the test population

2. Measures of Exposure Methods used to determine exposure concentrations of a pesticide are dependent on its environmental fate and phy sicochemical properties, the application method, and the presence of reliable monitoring data that are considered representative of the proposed use sites. Initial factors considered for the exposure assessment are provided in Table 3 below. Table 3. Factors that may affect the exposure to Sethoxydim Consideration Sethoxydim -specific data Conclusion Monitoring data No appropriate or targeted mo nitoring data are currently available to EFED EECs will be determined using EFED’s exposure models
Degradation degradation: Sethoxydim is very rapidly metabolized in soil to sulfoxide and sulfone degradates as we ll as hydrolysis products (M1 and M2 series) EECs will be calculated for Total Residues including M-SO, M-SO2, M1-S, M1-SO, M1-SO2, M2-S, M2-SO, and M2-SO2
Mobility Sethoxydim and its degradates are highly mobile in soil-water systems Runoff will need to be considered

Bioconcentration BCF values for Sethoxydim are low : 21x in whole fish Bioconcentration w ill not be mo deled Application method Ground or air spray Spray drift and runoff need to be considered in this assessment-20-

Formulation Naphthalene-containing solvent is demonstrably more toxic to aquatic organisms than Sethoxydim Toxicity of solvent will be considered w

hen exposure to active ingredient and solvent is simultaneous (spray drift)
Aquatic Sy stems For aquatic organisms, such as plants, fish, aquatic-phase amphibians, and invertebrates, OPP generally uses computer simulation models to estimate exposure to a pesticide active ingredient. These models calculate estimated environmental concentrations (EECs)in surface water using laboratory data that describe the rate at which the pesticide breaks down and how it moves into the environment. Monitoring data, if available, may also be used to determine EECs or to support the model’s calculations. EECs for aquatic organisms were generated with the Tier 1 model GENEEC2.0 for this assessment. No EECs are generated in instances where no toxicity was observed at concentrations above the active ingredient’s water solubility or at or above the recommended limit concentration for a particular ty

pe of study . Due to the presence of multiple Sethoxydim transformation products, it is necessary to examine exposure to both the parent and the products. Although fate data indicate that parent Sethoxy dim degrades rapidly in soil (< 1 day ) the application intervals (14 day s) indicate that herbicidal activity lasts longer than one day . Thus, some of the degradates seen in soil metabolism studies (especially M-SO and M-SO2) must retain some herbicidal activity . In addition, the sulfoxidation process is in principle reversible, so the parent could be regenerated from the M-SO degradate under reducing conditions. Because we have no separate data on the activity of the degradates, we will assume that the activity of the degradates is equal to that of the parent.
It is assumed that the active ingredient and the Naphthalene-containing solvent will become separated by fate processes before run-off into the pond. Therefore, run-off exposure to aquatic organisms will consider only the active ingredient, and toxicity data on the technical-grade active ingredient will be used to calculate RQs. A separate screening-level assessment of possible exposure to the Naphthalene-containing solvent will also be conducted, to indicate if further study is warranted.
In the case of spray drift, parent Sethoxydim and its Naphthalene-containing solvent should reach water bodies before any degradation occurs. Thus, exposure will be to the Ty pical End Use Product (TEP). Therefore, toxicity data on the TEP will be used.-21- Terrestrial Sy stems Terrestrial wildlife exposure estimates are ty pically calculated for birds and mammals, emphasizing a dietary exposure route for uptake of pesticide active ingredients. These exposures are considered as surrogates for terrestrial-phase amphibians and reptiles. For terrestrial organism exposure, OPP primarily looks at the residues of pesticides on food items and assumes that organisms are exposed to a single pesticide residue in a given exposure scenario. For spray applications, estimation of pesticide concentrations in wildlife food items focuses on quantify ing possible dietary ingestion of residues on vegetative matter and insects. The residue estimates are based on a nomogram that relates food item residues to pesticide application rates (Fletcher et al., 1994). The first tier of the nomogram uses the maximum predicted residues. Subsequent refinements may consider mean residues. However, maximum residue concentration is converted to daily oral doses based on fractions of body weight consumed daily as estimated from mammalian allometric relationships in EPA’s Wildlife Exposure Factors Handbook. I n all screening-level assessments, the organisms are assumed to consume 100% of their diet as one food ty pe. C. Conceptual Model
1. Risk Hypotheses Ecological receptors that may potentially be exposed to sethoxy dim, its degradates, and the various products that make up the Ty pical End Use product (TEP) include terrestrial and semi-aquatic wildlife (i.e., mammals, birds, and reptiles), plants, and soil invertebrates. In addition to terrestrial ecological receptors, aquatic receptors (e.g., freshwater and estuarine/marine fish and invertebrates, amphibians, and obligate aquatic plants) may also be exposed to potential migration of pesticides from the site of application to various watersheds and other aquatic environments via runoff and spray drift.-22-



### Stre ssor Set hoxydi m To ta l T oxi c R esi dues AN

D/ OR Pe tr ol eum So lv ent



### Sour ce/ Tr anspor t Pa th wa ys Di re ct De posi tio n Ru nof f/ Er osi on Leac

hi ng (In filtr at io n/ Per col at io n


### Sour ce/ Ex posur e Me di a Food I te ms Up

la nd So il Ri par

ia n/ We tla nd S oi l Re cei vi ng Wa te r B ody/ Se di me nt Gr

oundw at er



### Ex posur e Ro ut e In ges tio n Di re

ct cont act / Ro ot Up ta ke Di re ct cont ac t/ Ro ot Up ta ke Gi ll/

In te gum ent Up ta ke



### Re cept or s

At tri but e Ch anges Ter

re st ria l V er te br at es Bi rd s, Ma mma ls , Re pt ile s, Ter re st ri al Ph ase A mp hi bi ans Ter

re st ri al Up la nd Pl ant s

Re duced sur vi val Re duced gr ow th Re duced re pr oduc tio n Aquat ic In ver te br at es Aquat ic Ver te br at es We tla nd/ Ri par ia n Pl ant s

Se edl in g em er genc e Ve get at iv e vi gor Re duced su rv iv al Re duced gr ow th Re duced re pr oduct io n Pl ant popul at io n Re duced popul at io n gr ow th Aq uat ic Pl ant s Up ta ke/ Adsor pt io n



### Fi gur e 2: Co nceptual Mo

del fo r Se th ox ydi m An d Petro le um Sol vent Stre ssor Set hoxydi m To ta l T oxi c R esi dues AN

D/ OR Pe tr ol eum So lv ent



### Sour ce/ Tr anspor t Pa th wa ys Di re ct De posi tio n Ru nof f/ Er osi on Leac

hi ng (In filtr at io n/ Per col at io n


### Sour ce/ Ex posur e Me di a Food I te ms Up

la nd So il Ri par

ia n/ We tla nd S oi l Re cei vi ng Wa te r B ody/ Se di me nt Gr

oundw at er



### Ex posur e Ro ut e In ges tio n Di re

ct cont act / Ro ot Up ta ke Di re ct cont ac t/ Ro ot Up ta ke Gi ll/

In te gum ent Up ta ke



### Re cept or s

At tri but e Ch anges Ter

re st ria l V er te br at es Bi rd s, Ma mma ls , Re pt ile s, Ter re st ri al Ph ase A mp hi bi ans Ter

re st ri al Up la nd Pl ant s

Re duced sur vi val Re duced gr ow th Re duced re pr oduc tio n Aquat ic In ver te br at es Aquat ic Ver te br at es We tla nd/ Ri par ia n Pl ant s

Se edl in g em er genc e Ve get at iv e vi gor Re duced su rv iv al Re duced gr ow th Re duced re pr oduct io n Pl ant popul at io n Re duced popul at io n gr ow th Aq uat ic Pl ant s Up ta ke/ Adsor pt io n



### Fi gur e 2: Co nceptual Mo

del fo r Se th ox ydi m An d Petro le um Sol vent Sp ra y D rift 2. Diagram-23- a. Aquatic Exposure For aquatic exposure, ecological receptors that may potentially be exposed to Sethoxy diminclude wildlife living in semiaquatic areas (mammals, birds, and reptiles), plants in semiaquatic and aquatic areas, and other aquatic receptors (freshwater and estuarine/marine fish and invertebrates, amphibians). Aquatic receptors (e.g., freshwater and estuarine/marine fish and invertebrates, amphibians) may also be exposed to potential migration of pesticides from the site of application to various watersheds and other aquatic environments via runoff and spray drift. (a) Potentially Complete and Quantitatively Evaluated Pathway s As shown in Figure 2, quantifiable Sethoxydim or petroleum solvent exposure pathway s and risks to aquatic ecological receptors include:

• Aquatic life (fish, invertebrates, amphibians) exposed through contact and uptake of Naphthalene-containing solvent in surface water from spray drift or runoff.

(b) Potentially Complete But Not Quantitatively Evaluated Pathway s The following pathway s were not quantitatively evaluated in the screening level risk assessment because exposure was identified as negligible and would not contribute measurably to risk or exposure estimates:

• Aquatic life exposed through contact and uptake of Sethoxydim in groundwater

• Aquatic life exposed through contact, uptake, and ingestion of Sethoxydim due to sediment partitioning, as well as through off-target surface water and sediment

• Terrestrial animals (birds, mammals, reptiles) that live in aquatic environments exposed through contact, uptake, and ingestion of Sethoxydim from target surface water, sediment, and off-target water and sediment b. Terrestrial Exposure Pesticides simultaneously reach several environmental compartments when applied. Sethoxydim is applied to terrestrial fields as an herbicide. As a result, much of the applied compound may be intercepted by foliage instead of reaching soil directly . For terrestrial exposure, ecological receptors that may potentially be exposed to Sethoxy dim include wildlife living in terrestrial and semiaquatic areas (i.e., mammals, birds, land-phase amphibians and reptiles), plants in terrestrial and semi-aquatic areas, and soil invertebrates. The source and mechanism of release of Sethoxy dim are ground or aerial application to agricultural crops (alfalfa, cotton, soy beans, dry beans, corn, potato, peanut, sunflower ) and ground only for turf, trees, fruits (including citrus), vegetables, berries, grapes, nuts and other registered uses. Surface water runoff from the areas of application is assumed to follow topography . Additional release mechanisms include spray drift, and wind erosion, which may potentially transport site-related contaminants to the surrounding air and later to off-site terrestrial or aquatic sites. Potential emission of volatile compounds is not considered as a viable release mechanism for Sethoxydim, since volatilization is not expected to-24-

be a significant route of dissipation for this chemical.

(a) Potentially Complete and Quantitatively Evaluated Pathway s As shown in Figure 2, quantifiable Sethoxydim exposure pathway s and risks to ecological receptors from terrestrial application include: 1. On-site exposure of animals (mammals, birds, reptiles) exposed by contact with or ingestion of vegetation or insects contaminated by direct spraying. 2. On-site exposure of beneficial insects exposed by contact with residues on plants contaminated by direct spraying. 3. Off-site exposure of non-target terrestrial plants (wetland or upland grasses only ) by spray drift or runoff.
(b) Potentially Complete But Not Quantitatively Evaluated Pathway s The following pathway s were not quantitatively evaluated in the screening level risk assessment because exposure was identified as negligible and would not contribute measurably to risk or exposure estimates:

• All off-site exposure of terrestrial animals, since on-site exposure is greater, and screening level analy sis indicates only chronic risk to birds and reptiles. The chronic risk cannot be quantitatively evaluated because a NOAEC was not found for the mallard duck.

• On-site exposure of plants, since on-site grasses are target organisms.

• On-site exposure of animals, including insects, directly to residues in the soil, or in rainwater puddles, or to residues taken up from the soil by plants, since direct spraying exposures are expected to be greater.

• On-site exposure of terrestrial invertebrates, since we have no toxicity data for such organisms-25-

D

. Key Uncertainties and Information Gaps The following uncertainties and information gaps were identified as part of the problem formulation:

• The avian chronic (reproductive) toxicity study used in this assessment did not find a noobserved-adverse-effect-concentration (NOAEC). Adverse effects on the number of normal mallard duck hatchlings were found the lowest dietary level tested (100 ppm in feed). Thus the risk quotients for chronic risks to birds (and as a surrogate, to reptiles) are minimums (“greater than” values). The chronic level of concern (RQ = 1) was exceeded even if a foliar dissipation half-life of one day , rather than the default of 35 day s, was used in the T-REX model. In order to come to a firm conclusion on the possible chronic risk to birds and reptiles, a NOAEC in the mallard duck needs to be established.

• It is uncertain what the foliar dissipation half-lives are on terrestrial food items. Magnitude-of-the-residue studies (guideline 171-4C) need to be examined to establish Sethoxy dim-specific foliar dissipation half-lives. Due to time constraints, and the fact that a refined assumption of a one-day foliar dissipation half-life results in chronic risk to birds above the L OC, this has not been done.

• The eight degradates of Sethoxydim are assumed to be as toxic as the parent in the assessment of risk to aquatic freshwater and estuarine organisms. Thus, a total toxic residue approach is used in the water exposure modeling. Data on the acute and chronic toxicity of the degradates would help to refine this assessment.

• Submitted aquatic vascular plant phy totoxicity data were on a dicot, Lemna gibba. There are no current guidelines for the testing of aquatic grasses. Sethoxydim only adversely affects grasses. There is much uncertainty of the effects of POAST® to non-target aquatic grasses.

• The mode of herbicidal action to plants indicates adverse effects to grasses. Vegetative vigor studies (Tier I I) and seedling emergence (Tier I) also confirms this. Available vegetative vigor phy

totoxicity data were only done for Sethoxy dim technical grade and not POAST®. Therefore, toxicity to grasses from spray drift may be underestimated.-26-

E. Analysis Plan Ecological risk assessment is a process that evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors (US EPA, 1998). This risk assessment examines the ecological risk of Sethoxydim herbicide use, and attempts to determine at what level Sethoxydim herbicides can be used to minimize deleterious effects on the environment. These negative effects on include structural and/or functional characteristics or components of ecosy stems. In order to estimate the ecological risk associated with Sethoxy dim use, use information, chemical and phy sical properties, fate/transport data, and toxicity data were examined for Sethoxydim, application methods, and chemical formulations.

1. Assessment (a) Fate and Exposure Parent Sethoxy dim degrades rapidly (< 1 day ) in soil to produce its sulfoxide (M-SO) and sulfone (M-SO2). I t is possible, under reducing conditions, that these could revert to the parent compound. The hydroly sis products M1-S and M2-S are also formed in major amounts. Because these degradates are believed to retain their toxicity , a Total Toxic Residue approach will be used for the assessment of risks to aquatic freshwater and estuarine organisms. Sethoxy dim and its degradates have very low Kd values, and will therefore be mobile in soilwater sy stems. Transport to surface water bodies is expected to be in the dissolved phase, rather than by sorption onto soil particles. The sulfoxide (M-SO) and sulfone (M-SO2) may pose a ground water contamination problem, given their high mobility and longer persistence than the parent. Because of the low vapor pressure and high solubility of Sethoxy dim, it is not expected to partition from water bodies to the atmosphere. Off-site transport via air will be due to spray drift only

. Photoly sis data indicate that Sethoxy dim total residues decline with half-lives of 20 hours on soil and 19.8 day s in water. Sethoxy dim’s high solubility (4700 ppm) and low Kd values indicate high mobility , and also suggest that it may be removed easily from plant surfaces by rainfall. Thus, an assumption of a quicker dissipation from leaf surfaces than the default value (35-day half-life) is justified. Sethoxy dim’s low Kd values indicate little tendency to partition to bottom sediments in water bodies. Thus, exposure of bottom-dwelling organisms is expected to be via degradates dissolved in the water column. This exposure is adequately described by GENEEC2 modeling of total toxic residues. (b) Toxicity-27-

Aquatic and terrestrial non-target toxicity endpoints (animals and plants) are provided by the acute and chronic toxicity data. These toxicity endpoints are compared with the estimated environmental concentrations of Sethoxydim, which are based on fate properties, chemical ty pe, exposure method, etc. For this assessment, the most sensitive toxicity endpoints for each surrogate taxa (ie. freshwater fish and invertebrates, estuarine/marine fish and invertebrates, aquatic plants, terrestrial plants, birds, and mammals) will be used in Risk Quotient (RQ) calculation with various exposure values (see above).
Li sted species analy sis will be performed using the EFED LOCATES Listed Species Database to determine presence of listed or threatened species in counties where specific crops are grown. A species profile analy sis will be performed to determine whether there are any potential risk scenarios to listed species in those identified areas.
In addition to the data submitted in support of registration and the information compiled through the Agency pesticide review process the ECOTOX database was used to identify additional toxicity data from the open literature. The ECOTOX database is a user-friendly , publicly

available, quality -assured, comprehensive tool for locating toxicity data from the open literature and is maintained by EPA Mid-Atlantic Ecology Division. More information on ECOTOX can be found at: http://www.epa.gov/ecotox. Research papers are thoroughly screened using standard procedures before being accepted into ECOTOX thereby ensuring consistent, high quality information. Appendices B lists references related to Sethoxydim toxicity that were accepted by ECOTOX. Appendix C lists Sethoxy dim references that were not accepted by ECOTOX lists the criteria for rejection; the criteria codes are also defined in Appendix D.
In some cases, a risk assessment may benefit from information in a reference that was rejected by ECOTOX. Rejection by ECOTOX does not necessarily infer a lack of study quality but can be due to a number of reasons including the lack of toxicity data or the lack of a sensitive endpoint.

(c) Risk Quotient and L evels of Concern Risk characterization integrates exposure and ecotoxicity data to evaluate the likelihood of adverse effects. For ecological effects, the Agency accomplishes this integration using the risk quotient method. Risk quotients (RQs) are calculated by dividing exposure estimates by acute and chronic ecotoxicity values.

RQ = EXPOSURE / TOXI CI TY RQs are then compared to the Office of Pesticide Program’s levels of concern (LOCs) to assess potential risk to non-target organisms and the need to consider regulatory action. Calculation of an RQ that exceeds the L OC indicates that a particular pesticide use poses a presumed risk to non-target organisms. LOCs currently address the following categories of presumed risk:

• acute - potential for acute risk is high and regulatory action bey ond restricted use classification may be warranted

• acute restricted - the potential for acute risk is high, but may be mitigated-28- through restricted use classification

• acute listed species - threatened and listed species may be adversely affected

• chronic risk - the potential for chronic risk is high and regulatory action may be warranted. The ecotoxicity values used in the acute and chronic risk quotients are endpoints derived from required laboratory toxicity studies. Ecotoxicity endpoints derived from short-term laboratory studies that assess acute effects are:

• LC 50 - fish and birds

• LD50 - birds and mammals

• EC50 - aquatic plants and aquatic invertebrates

• EC25 - terrestrial plants The NOAEC (No Observable Adverse Effect Concentration) is the endpoint used to assess chronic effects. Table 5 gives formulas for calculating RQs and LOCs for various risk presumptions.

Table 5. Formulas for RQ calculations and L OC used for risk assessment of Sethoxy dim Risk Presumption RQ LOC Terrestrial Anim als Acute Risk EEC 1 /LC 50 0.5 Acute Restricted Use EEC/LC 50 0.2 Acute Listed Species EEC/LC 50 0.1 Chronic Risk EEC/NOAEC 1.0 Aquatic Anim als Acute Risk EEC/LC 50 or EEC/EC 50 0.5 Acute Restricted Use EEC/LC 50 0.1 Acute Listed Species EEC/LC 50 0.05 Chronic Risk EEC/NOAEC 1.0

Terrestrial plants and plants inhabiting sem i-aquatic habitats Acute Risk EEC/EC 25 1.0 Acute Listed Species EEC/NOAEC or EC 05 1.0 Aquatic Plants Acute Risk EEC/EC 50 1.0 Acute Listed Species EEC/NOAEC or EC 05 1.0 1 abbreviation for estimated environmental concentration-29-

III. Analysis There are two chemical stressors in this risk assessment. The first is the active ingredient, sethoxy dim (PC code 121001) and its degradates, and the second is the petroleum solvent (CAS Registry Number 64742-94-5) that is used in the end-use formulations POAST® and POAST® Plus. The solvent is known to contain several percent by weight of Naphthalene, which is also a registered active ingredient (PC code 055801). Sethoxydim is responsible for all presumed risks to plants and birds, and the petroleum solvent is responsible for presumed risks to fish and aquatic invertebrates (fresh- and salt-water).
A. Use Characterization Sethoxy dim is a sy stemic herbicide which is registered for selective postemergence control of a wide spectrum of annual and perennial grasses. I t is formulated with a naphthalene-containing petroleum solvent. Single active ingredient formulations include emulsifiable concentrates (13- 43.3% ai) which are applied by aerial or ground (banding, broadcast, spot) methods at an application rate of 0.28 - 0.47 lbs. ai/acre/application up to four times per season. According to the BEAD usage report (Halvorson 2004), Sethoxydim is used on at least 86 different crops. The principal uses are on Soy beans (400,000 lb annually ), Sunflowers (80,000 lb), Alfalfa (60,000 lb), Dry Peas/Beans (40,000 lb), Sugar beets (30,000 lb), Peanuts (20,000 lb), Corn (20,000 lb), Oranges (10,000 lb), Potatoes (10,000 lb), and Cotton (10,000 lb). All other uses were estimated as 7,000 lb per y ear or less. The crops with the highest estimated percent crop treated are Sunflowers and Dry Peas/Beans (15-20%), Watermelons (10-15%), Sugar Beets (10%), Cantaloupes and Celery (5-15%), Green Beans, Onions, Cucumbers, Cabbage, Peppers, Pumpkins, Squash, Strawberries (5-10%). According to USEPA (1996a), approximately 960,000 lbs of Sethoxy dim a.i. are applied each ye ar in the U.S., with about 97% of this applied to agricultural sites. The largest agricultural use of Sethoxy dim (45-60%) is on soy beans. Approximately 3.1 million acres are treated annually , representing about 5% of the soy beans acreage in the U.S. Cotton, sugar beets, peanuts and alfalfa each account for 4-8% of total Sethoxydim use. Approximately 2% of the total Sethoxy dim use is used on turf, which accounts for 13-22% of the annual turf crop. Nurseries, lawn care and cemetery use account for the remaining non-agricultural uses.-30--31- Characterization of Production Areas and Soils Soy beans The largest agricultural use of Sethoxydim (45-60%) is on soy beans. Soy

bean production is widespread in the U.S., ranging from the western Plains States through the eastern and southern U.S. (Kellogg, et al., 1992, USDA, 1997, USGS, ND).

Cotton and Peanuts Cotton production occurs principally in the southeastern U.S., along the Mississippi River in eastern Arkansas, western Tennessee, and Mississippi, Texas, southern Arizona, southern California and in the Central Valley of California. (Kellogg, et al., 1992, USDA, 1997, USGS, ND). Peanut production occurs in the southeastern U.S. from northern Florida to Virginia and west to northern Texas and southern Oklahoma. (Kellogg, et al., 1992, USDA, 1997, USGS, ND). Sethoxy dim is used on cotton and peanuts in the southeastern U.S. The southeastern U.S. is characterized by two major land resource areas: 1) Atlantic and Gulf Coast Lowland Forest and Truck Crop Region and 2) South Atlantic and Gulf Slope Cash Crop, Forest and L ivestock Region (Austin, 1972). The Atlantic and Gulf Coast L owland area consists of nearly level areas of the Atlantic and Gulf Coastal Plains crossed by many broad valley s. Precipitation ranges from 40-50 inches annually and is highest in the summer. Most of the soils are too wet to be used for crops without drainage; however, peanuts are grown on the better drained soils. The predominant soils are Aquults (Austin, 1972 and 1981). The South Atlantic and Gulf Slope region consists of gently sloping to rolling Piedmont and upper Coastal Plain. Average annual precipitation ranges from 40-60 inches. Cotton is the main crop in this area with some peanuts. (Austin, 1972 and 1981).

Other Cotton Areas The Mississippi Delta region also has significant cotton production. This area is principally flood plain and terraces of the Mississippi River with annual precipitation ranging from 45-65 inches. The soils are poorly drained but can be highly productive if drained. (Austin, 1972 and 1981, USGS, ND). Cotton production in Texas is focused in the north central and "Panhandle" areas. The area is characterized by smooth high plains with gentle slopes, ranging in elevation from 1,500-5,000 feet. Precipitation fluctuates widely from y ear to y ear with an annual average rainfall ranges from 15-30 inches. The highest precipitation occurs in the late spring through autumn. There are-32-

few perennial streams in these areas, and cotton is extensively grown under irrigation from wells. Water tables are declining in these areas from withdrawals for irrigation. (Austin, 1972 and 1981, USGS, ND). Irrigated cotton is grown in southern Arizona and southeastern California. This area consists of broad basins, valley s and old lake beds, ranging in elevation from -280 to 4,000 feet. This area is semi-desert to desert with 2-20 inches of precipitation annually , which is evenly distributed throughout the y ear. Water is scarce and irrigation comes principally from the major rivers, such as the Colorado, Gila and Salt Rivers. Deep irrigation wells are also used in south-central and southeast Arizona. (Austin, 1972 and 1981, USGS, ND). The southern part of the Central Valley of California also produces cotton. The southern Central Valley is broad, smooth and nearly level. I t ranges in elevation from sea level to 500 feet. Precipitation ranges from 5-25 inches annually . The region has a long growing season with a long dry period in the summer. L ow rainfall and small streams result in a shortage of water. Irrigation is from the mountains and from wells. There is a diminishing supply of well water due to dropping water tables. (Austin, 1972 and 1981, USGS, ND).

Other Crops Sugar beet production is focused in southern I daho, the Red River Valley (MN-ND), and along the Wy oming-Nebraska-Kansas-Colorado borders. Lesser production occurs along the MontanaWy oming borders, in southern Michigan, northern Texas, southeast Oregon, eastern Washington, and the Yuma and Imperial Valley s of Arizona and California. Alfalfa production is widespread in the U.S. Areas of high production include southern California, eastern Texas and Oklahoma, southern I llinois, central Wisconsin, western Dakota, western Nebraska, and numerous individual counties scattered throughout the U.S. Alfalfa production in the western U.S. is often irrigated. (Kellogg, et al., 1992, USGS, ND). The use of Sethoxy dim on citrus is very limited in the U.S. Significant citrus production occurs on the vulnerable, sandy soils of central Florida where Sethoxydim could be used. Rainfall and ground water are abundant in this area and annual precipitation ranges from 50-57 inches. Precipitation is highest in the summer and early autumn. The elevation of the region ranges from 50-150 feet. (Austin, 1972 and 1981, Kellogg, et al., 1992, USGS, ND).

B. Exposure Characterization
1. Environmental Fate and Transport Characterization
In terrestrial environments, photodegradation, aerobic metabolism, and acid-cataly zed hy droly sis appear to be the primary routes of dissipation for Sethoxy dim and for Sethoxy dim total residues. The calculated soil photoly tic half-lifes are 1 hour for Sethoxydim and 20 hours for Sethoxy dim-33-

residues (parent + transformation products), indicating rapid transformation of Sethoxydim and its residues after application. Other potential routes of dissipation are microbial-mediated degradation and surface water runoff. Under aerobic conditions, Sethoxydim degrades in less than 1 day , while Sethoxy dim residues have half-lives which range from 7 to 30 day s. Under anaerobic conditions, Sethoxydim and its residues are more persistent with half-lives greater than 60 day s. Unacceptable field dissipation studies (two locations in California, one cotton and one forage), indicated a moderately rapid rate of dissipation of Sethoxydim residues with half-lives measuring 32 day s in the 0- to 6-inch soil layer.
In aquatic environments, the major route of dissipation for total Sethoxydim residues is aqueous photoly sis (t1/2=19.8 day s), followed by microbial-mediated degradation. In aerobic aqueous studies, half-lives are on the order of about one month (32.9-38.1 day s), while under anaerobic aqueous conditions, Sethoxy dim and its residues are more persistent (half-lives range from 132- 187 day s). Aquatic field dissipation studies (four rice paddies in different states) showed that Sethoxy dim residues degraded faster in the field than in the laboratory with half-lives on the order of 1-9 day s. In the field, many processes may occur simultaneously and many variables may effect these processes. For example, the presence of significant microbial populations in the floodwater, the presence of natural photosensitizers that may accelerate photoly sis, intensity of sunlight, cloud cover, and temperature can affect the dissipation rate in the field. Sethoxy dim is a highly soluble compound (4700 mg/L in pH 7 water) with a low octanol/water partition coefficient (K ow for Sethoxy dim is 45.1). Despite its high solubility and mobility , parent Sethoxy dim is unlikely to pose a threat to surface and ground waters because it does not persist under most conditions. Sethoxy dim transformation products, however, may be persistent and mobile enough to pose a potential threat to water resources. The extent of this impact on water resources, though, cannot be determined until EFED receives additional data on the fate of these transformation products. Acceptable and supplemental environmental fate data indicate that Sethoxydim is labile and mobile in the environment. The transformation of parent Sethoxydim, primarily by photodegradation, aerobic metabolism in water and soil, and acid-cataly zed hy droly sis, is rapid (half-lives on the order of hours to day s). Sethoxy dim transformation products, though, result from modifications to functional groups rather than the main structure and are of potential biological concern. Sethoxydim total residues (Sethoxy dim plus Sethoxy dim transformation products) are determined using a common moiety method that cannot distinguish parent Sethoxy dim from its transformation products. These rearrangement products are more persistent in the environment than Sethoxydim (half-lives on the order of weeks to months) and potentially mobile. Laboratory studies show that Sethoxy dim is a highly soluble compound (4700 mg/L in water) and that it hydroly

zes at moderately rapid rates at low pH's, but is more stable at high pH's. The calculated half-lives are 8.7, 155, and 284 day s in pH 5, 7, and 9 solutions, respectively . The major observed hydroly sis transformation product is M2-S or 6-(2-(ethylthio)propyl)-4-oxo-2- propyl-4,5,6,7-tetrahydrobenzoxazole. In contrast, evaluation of the data of Sethoxydim total-34-

residues shows that they remain stable at all three pHs tested. Sethoxy dim and Sethoxy dim total residues degrade photoly tically in both water and soil. In pH buffered water, the calculated half-life of Sethoxydim is 5.23 day s, and the major transformation product is M1-S or 2-(1-aminobutylidene)-5-(2-(ethylthio)-propyl)-cy clohex-1,3-dione. In sandy loam soil irradiated with a xenon light source, the half-life of Sethoxydim is approximately 1 hour, and the major transformation product is M-SO or 2-(1-ethoxyiminobutyl)-5-(2- (ethylsulfinyl)propyl)-3-hydroxy cy clohex-2-enone. Sethoxy dim total residues photodegrade slower than parent Sethoxydim in soil and water. Using a linear regression analy sis, EFED calculated a half-life of 19.8 day s for the photoly sis in water of Sethoxy dim total residues and a half-life of 20 hours in soil. Under aerobic conditions, parent Sethoxydim transformed with short half-lives (<1 day ) both in soil and aquatic environments. I t degraded with a half life of less than one day in sandy loam and sandy clay loam soils. The major transformation product at 2 months was M-SO, and after 12 months the major product was CO2. Using aerobic clay loam soil:water and aerobic clay soil:water sy stems, it was determined that, under aerobic aquatic conditions, Sethoxydim transformed with a half-life of <1 day . After 28 day s, the major transformation products were CO2, M-SO, M2-S, and M-SO2 or 2-(1-ethoxyiminobutyl)-5(2-(ethylsulfonyl)propyl)-3- hy droxy cy clohex-2-enone. In contrast to parent Sethoxydim, Sethoxy dim total residues were more persistent. The observed half-life was 1 month for Sethoxydim total residues in the aerobic sandy loam study , and 7 day s in the aerobic sandy clay loam study . In an aerobic clay loam soil:water sy stem, the calculated half-life for Sethoxydim total residues was 38.1 day s, while in an aerobic clay soil:water sy stem the half-life was 32.9 day s. Under anaerobic conditions, parent Sethoxydim is even more persistent than under aerobic conditions. I t transformed with half-lives of 11 to >60 day s under anaerobic soil conditions and 25-39 day s in anaerobic aquatic metabolism studies. M-SO was the major transformation product in both studies. I t was observed that M2-S, which was a major transformation product in the hy droly sis study , was only a minor transformation product in the anaerobic aquatic metabolism study . Anaerobic studies with Sethoxy dim total residues showed that they were more persistent than parent Sethoxydim. A half-life of 91.6 day s was observed in the anaerobic soil metabolism study , while half-lives of 132-187 day s were observed in the anaerobic aquatic metabolism study

. Based on batch equilibrium experiments, Sethoxydim and its transformation products, M2-SO2, M-SO, M-SO2, and M2-SO, were determined to be mobile to very mobile in sterile (autoclaved) sand, sandy loam, sandy clay loam, silt loam, and clay loam soils. Freundlich Kads values were <1.00 for Sethoxy dim and its transformation products M-SO and M-SO2. The Freundlich Kads values for M2-SO and M2-SO2 ranged from 0.06 to 9.12.
In formation from two unacceptable terrestrial field dissipation studies indicated that total (uncharacterized) Sethoxydim residues dissipated with half-lives of about 32 day s in two California soils with cotton and forage crops. This study showed two detections of Sethoxydim-35-

near the quantitation level below the 0- to 6-inch depth.
In aquatic field studies, total (uncharacterized) Sethoxydim residues dissipated fairly rapidly , with half-lives of 1-9 day s in the floodwater of rice paddies in California, Mississippi, and Lo uisiana, and 10-13 day s in the soils of nonflooded rice paddies in Mississippi and Louisiana that were subsequently flooded 4-5 day s after application. Residues were detected in the 0- to 6- inch soil lay er in both paddies. When Sethoxydim was applied to flooded paddies, most of the residues remained in the floodwater. When applied to the soil prior to flooding, there were no detectable residues in the water samples. The low octanol/water partition coefficient (Kow = 45.1) for Sethoxydim suggests that Sethoxy dim has a low tendency to bioaccumulate or bioconcentrate. The calculated BCF's for Sethoxy dim and total residues were 7X, 25X, and 21X for edible, nonedible, and whole fish, respectively . Depuration was fast, with a half-life of 3.6 day s. Based on the information provided, bioaccumulation is not likely to occur. Because of its low vapor pressure (1.6x10-7 mm Hg) and Henry 's Law Constant (1.47x1011 atmm3/mol), Sethoxydim is not expected to be highly and the Agency is waiving the volatility studies. Degradation Scheme for Sethoxydim Scheme I represents the relationship between parent Sethoxydim (M) and its eight identified degradates. There are three groups of degradates: a group formed from the parent by oxidation of the sulfur atom (M group), the “amines” or M1 group, and the tetrahydrobenzoxazoles, or M2 group. The first M1 group daughter (M1-S) is formed by cleavage of the ethoxyimino group to an amino group, either by hy droly sis or aqueous photoly sis. The first member of the M2 group (M2-S) is then formed from M1-S by ring closure to produce a tetrahydrobenzoxazole ring. Each of the three groups of degradates also has a sulfoxide (-SO) and a sulfone (-SO2), to round out the total of eight degradates. This reaction dominates in aerobic soil metabolism and soil photoly sis experiments, especially to form the M-SO and M-SO2 degradates. Scheme I
M 

### 6 M1-S 

### 6 M2-S 

### 9 9 9 M-SO 

### 6 M1-SO 

### 6 M2-SO 

### 9 9 9 M-SO2 

### 6 M1-SO2 

### 6 M2-SO2 The eight degradates include 2 daughter products, which are formed from the parent by a single reaction ( M1-S and M-SO ), 3 granddaughter products that are two reactions removed from the parent ( M-SO2, M2-S, and M1-SO ), 2 great-granddaughters that are three reactions removed-36-

( M1-SO2 and M2-SO ), and one great-great-granddaughter that is four reactions removed (M2- SO2).
It is important to note that M1-SO, M2-SO, M1-SO2, and M2-SO2 may be formed by more than one pathway , and that the sulfur oxidation may be reversible under reducing conditions, so that the kinetics of the formation is very complicated, and probably cannot be elucidated with any confidence from the current fate data. Because parent Sethoxydim is very rapidly (half-life < 1 day ) degraded to its sulfoxide (M-SO) in soil, it is reasonable to conclude that some of the degradates retain some herbicidal activity

. There are no data on the toxicity of the separate degradates. However, the Sethoxydim used in the toxicity tests was subject to the same degradation mechanisms, so the actual exposure was to a mixture of Sethoxydim and its degradation products. For this reason, we decided to use a “total toxic residues” approach to modeling the decay . In other words, the calculated half-lives will include the concentrations of the parent plus the major degradates. For purposes of modeling the decay of total Sethoxy dim residues, it is therefore most important to include the two daughter products, M-SO and M1-S. The next group to be included in the total residues would be the 3 granddaughters (M2-S, M1-SO, and M-SO2). We will neglect degradates that are present in only minor amounts (generally < 10% of the applied radiation of the parent), or that are kinetically far-removed from the parent, as long as the calculated half-life is not greatly changed. Table 6 and 7 below describes the environmental fate properties of Sethoxydim and it’s residues and the mobility of Sethoxy dim and transformation products. Table 6: Environmental Fate Properties of Sethoxydim and its Residues Sethoxydim Residues Hydrolysis pH 5.0 t1/2=8.7 days pH 7.0 t1/2=155 days pH 8.6 t1/2=284 days stable at all pH's

Photodegradation in w ater t1/2=5.23 days t1/2=19.8 days Photodegradation on soil t1/2=1 hour t1/2=20 hours Aerobic soil metabolism t1/2<1 day t1/2=7-30 days

Anaerobic soil metabolism t1/2>60 days t1/2=78-91.6 days Aerobic aquatic metabolism t1/2=0.7-1.0 days t1/2=32.9-38.1 days Anaerobic aquatic metabolism t1/2=39.9 days t1/2=132-187 days Terrestrial Field Dissipation N/A 32 days in two locations in CA (cotton and forage)-37-

Aquatic Field Dissipation N/A 1-9 days in four rice paddies in various states. Terrestrial Field Dissipation: detection limit 0.01 ppm application rate 0.5 lb ai/A x 3, during a 3 w eek period two detections near the quantification level were found below the 0-6 inch soil level during the study Table 7: Mobility of Sethoxy dim and transformation products: Kads ml/g Parent Sethoxydim 0.03-0.94 M-SO 0.02-0.17 M-SO2 0.02-0.13 M2-SO 0.06-9.12 M2-SO2 sterile 0.12-8.43 nonsterile 0.14-9.03
2. Measures of Aquatic Exposure

a. Aquatic Exposure Modeling
EFED uses GEN eric E xpected E nvironmental C oncentration Program (GENEEC) as described in the surface water section on page 21 to calculate EECs that are used for assessing acute and chronic risks to aquatic organisms. Acute risk quotients are calculated using peak EEC values for single and multiple applications, while chronic risk quotients are calculated using the 21-day EECs for invertebrates and 56-day EECs for fish. The GENEEC program uses basic environmental fate data and pesticide label application information to estimate EECs following treatment of a 10-hectare field. The model calculates the concentration (i.e., EEC) of a pesticide in a 1-hectare, 2-meter deep pond, taking into account the following factors: (1) adsorption to soil or sediment (2) soil incorporation (3) degradation in soil before washoff to a water body and (4) degradation within the water body . The model also accounts for direct deposition of spray drift into the water body (the GENEEC v. 2.0 model determines spray drift percentage based on the other model inputs). GENEEC v. 2.0 was used to estimate sethoxy dim total residues concentrations in the standard pond. The environmental fate parameters used in the model for this pesticide are: soil Kd = 0.03 ml/g (MRI D 41475212), solubility = 4700 ppm, aerobic soil metabolism half-life = 30 day s (MRI D 41475210), water photoly sis half-life = 19.8 day s (MRI D 41475208), aquatic metabolism half-life = 38.1 day s (MRI D 42165604). The calculated peak GENEEC EECs for Sethoxydim total residues were 87 and 110 ug/l. The maximum “peak” occurred when the modeling was based on a total of four applications per season at 0.47 lb ai/A.-38--39-

Table 8 Input Parameters For GENEEC2 Runs for Sethoxydim Total Toxic Residues Parameter Value Source Maximum Application Rate 0.47 lb a.i./acre at 4x @ 14 days) Use Closure Memorandum

Aerobic Soil Half-life 54 days (90 th upper % ile of 2 values) EFGWB Environmental Fate Chapter, March 1997 MRID 41475210 Aerobic Aquatic Half-life 44 days (90 th upper % ile of 2 values) EFGWB Environmental Fate Chapter, March 1997 MRID 42165604 Distribution Coefficient, Kd 0.03 (minimum value for parent) EFGWB Environmental Fate Chapter, March 1997 MRID 41475212 Solubility 4700 ppm (parent at pH7) EFGWB Environmental Fate Chapter, March 1997 Aqueous Photolysis Half-life 19.8 days EFGWB Environmental Fate Chapter, March 1997 MRID 41475208 Application type Aerial, no incorporation label Droplet Size (Spray Drift) Fine to Medium (13%) GENEEC default Wet-in? No label Distance to Pond Zero feet Default assumption
Table 9 RUN No. 1 FOR Sethoxydim ON four apps * INPUT VALUES *

-------------------------------------------------------------------- RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) ZONE(FT) (IN)

-------------------------------------------------------------------- .470( 1.465) 4 14 .0 4700.0 AERL_B( 13.0) .0 .0

FIELD AND STANDARD POND HALF-LIFE VALUES (DAYS)

-------------------------------------------------------------------- METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND)

-------------------------------------------------------------------- 54.00 2 N/A 19.80- 2455.20 44.00 43.23
GENERIC EECs (IN MICROGRAMS/LITER (PPB)) Version 2.0 Aug 1, 2001

-------------------------------------------------------------------- PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

---------------------------------------------------------------------40- 87.07 86.00 79.90 67.94 60.37 Spray Drift Exposure from Formulated Sethoxydim and Sethoxydim. Formulated Sethoxy dim may reach water bodies directly as a result of spray drift from aerial or ground applications. Ecotoxicity studies done with the TEP were provided to the Agency

. Therefore, a spray drift EEC needs to take into account the TEP concentrations. Ecotoxicity studies done with TEP usually are measuring the active ingredient (ai) concentration. That measured active ingredient concentration is back-calculated to the toxicity measured effect in terms of ppm product using the percentage active ingredient in the TEP. There are three different percentages of the active ingredient sethoxydim in the ecotoxicity studies. There are 19.3% ai (trout and Daphnia ), 18.0% ai (sheepshead minnow and my sid shrimp), and 20.4% ai (oy ster). A single application of POAST® was modeled using 0.47 lb ai/A of sethoxydim. For the input of application rate into the model, the 0.47 lb ai/A was divided by each of the different sethoxy dim ai percentage used in the studies to produce the amount of POAST® in the spray drift that would go into the 6 foot farm pond. The AgDrift model was used to estimate concentrations of sethoxydim (a.i.) and POAST®in the standard 6-foot deep farm pond. Tier 1 aquatic assessments were performed, assuming either aerial or ground application. The ground spray assessment assumed a high boom applicator, ASAE very fine to fine spray droplet size, and 90 th percentile exposure. The aerial spray assessment assumed ASAE very fine to fine spray droplet size. Tables 10A and 10B give the EECs in the pond for aerial and ground spraying of sethoxydim a.i. and the TEP, respectively

. Table 10A. Aerial and Ground Spray Drift EEC of Sethoxy dim a.i. Applied at 0.47 lb/acre Application Method EEC in Standard Pond (ppb) ground 1.6 aerial 6.4-41-

Table 10B. Aerial and Ground Spray Drift EEC of TEP Applied at 0.47 lb ai/acre rate. Application Method Percentage of active

ingredient in POAST Input of Application Rate

(0.47 lb ai / % ai in POAST) EEC of TEP in Standard Pond (ppb)
ground 19.3 2.4 8.3 aerial 19.3 2.4 32.6 ground 18.0 2.6 9.0 aerial 18.0 2.6 35.3 ground 20.4 2.3 7.9 aerial 20.4 2.3 31.3

b. Aquatic Exposure Monitoring and Field Data Ground and Surface W

ater Monitoring Data The Pesticides in Ground Water Database report (EPA 734-12-92-001, Sept. 1992) states that Sethoxy dim was analy

zed in 65 Missouri wells in 1986, and was not detected. Sethoxy dim was not detected (LOD of <0.2 ug/L) in 40 domestic wells in agricultural areas of SE Missouri. The agency has high confidence in the sampling of the 40 domestic wells, which appear to be representative of rural drinking water wells in the agricultural areas of SE Missouri. However, EFED has low confidence in the samples from the public water supply wells and the five surface water samples because of the high limits of detection (L OD’s of 2 and 5 ug/L, respectively ). Since Sethoxy dim appears to degrade rapidly in the environment and since the public drinking water supply wells are significantly deeper than the domestic wells, the Agency would not expect to find parent Sethoxydim residues in the public drinking water wells in this area. The lack of detections supports the environmental fate laboratory studies which indicate that Sethoxydim degrades rapidly in the terrestrial environment. Sethoxy dim was detected in both surface and ground water in the Nomini Creek Watershed in Westmoreland County , Virginia from 1986-1990 to assess the effectiveness of Best Management Practices (BMP’s). Three detections of 2.1, 4.07, and 41.89 ug/L were reported in monitoring wells. However, it is not known if the monitoring wells were representative of drinking water sources in this area. There was also one detection of 0.87 ug/L in surface water. There were no monitoring data in STORET for Sethoxydim. The USGS Pesticide National Synthesis Project (http://ca.water.usgs.gov/pnsp/ ) did not include-42-

Sethoxy dim (nor any of its degradates) in its list of pesticides for laboratory analy sis of ground water and surface water samples.-43- 3. Measures of Terrestrial Exposure a. Terrestrial Exposure Modeling Hoerger and Kenaga (1973), as modified by Fletcher et al. (1994), empirically derived residue concentrations on avian and mammalian dietary food items immediately following application of any pesticide at 1 pound of active ingredient per acre (lb ai/A). Due to the lack of a measured foliage residue half-life, EFED assumes 35-day half life for the residues on the food items. These EECs are given in Table 11. Table 11. Estimated Environmental Concentrations (EECs) on Avian and Mammalian Food Items for a 1 lb ai/A Application

. Food Item EEC (ppm) Predicted Maximum Residue EEC (ppm) Predicted Mean Residue
Short grass 240 85 Tall grass 110 36 Broad-leaved/forage plants, and small insects 135 45 Fruits, pods, seeds, and large insects 15 7Terrestrial exposure was modeled with the T-REX v.1.1 model, which automates HoergerKenaga nomogram exposure and RQ calculations. One, 2, 3, or 4 applications at 14-day intervals were modeled at the maximum application rate of 0.47 lb ai/A, and 3 applications were modeled at an application rate of 0.28 lb ai/A. The default assumption for the decay rate on foliage (35-day half-life) was used. Tables 12, 13, and 14 give the predicted maximum residues of Sethoxy dim that are expected to occur on selected avian or mammalian dietary food items. For chronic risk, Sethoxydim transformation products are assumed to be as toxic as the parent. The environmental fate data indicates that the transformation products are more persistent; how persistent is not known, therefore predicted maximum residues will be used in the chronic risk assessment for birds and mammals.-44-

Residues on Avian Food I tems

Table 12 Maximum Residues on terrestrial food items for wildlife Body Weight and Size 1 (EEC in mg/kg-bw) Site (not inclusive) No. of Apps. App.Rate (lbs ai/A) Food Items Maximum EEC (ppm) Mean

EEC (ppm) Small 20 g Medium

100 g Large

1000 g Citrus, tree nuts
4 0.47 Short grass 312 111 356 203 91 Tall grass 143 47 163 93 41 Broadleaf plants/Insects 176 59 200 114 51
Seeds 20 9 22 13 6 Alfalfa, birdfoot trefoil, sainfoin, clover, cotton,

3 0.47 Short grass 263 93 300 171 76 Tall grass 121 40 137 78 35 Broadleaf plants/Insects 148 49 169 96 43
Seeds 16 8 19 11 5 Soybeans, grape, berries, peanut,

Head & petiole vegetable crop subgroup, mint, pea, potato, safflower, sugar beets, Christmas tree farms, ornamentals, rights of

way, roadsides, turf
2 0.47 Short grass 198 70 80 46 20

Tall grass 91 30 34 19 9

Broadleaf plants/Insects 112 37 42 24 11

Seeds 12 6 7 4 2 Fruiting and leafy vegetable crop

group

3 0.28 Short grass 156 56 Tall grass 72 24 Broadleaf plants/Insects 88 30
Seeds 10 5 Orchard floor middles, strawberry, sunflower

1 0.47 Short grass 113 40 46 26 12 Tall grass 52 17 19 11 5
Broadleaf plants/Insects 63 21 24 14 6
Seeds 7 3 4 2 1 1 20-gram body weight = 114% of body weight consumed; 100-gram body weight = 65% of body weight consumed; 1000-gram body weight = 29% of body weight consumed.-45-

Residues on Mammalian Food I tems Environmental Concentrations (EECs) on Mammalian Food Items for Sethoxy dim Application at the Maximum Use Rate and Frequency (T-REX v.1.1 ) using Kenaga maximum residues (EEC equivalent dose (mg/kg-bw)). Table 13 EEC equivalent dose (mg/kg-bw) 4X @ 0.47 lb ai/A; 14 day interval Mammalian Classes and Body weight Herbivores/ insectivores 15 g 35 1000 g Short Grass 297 206 47 Tall Grass 136 94 21 Broadleaf plants/sm Insects 167 116 26 Fruits/pods/seeds/lg insects 19 13 3 Granivores Fruits/pods/seeds/lg insects 4 3 1
Table 14 EEC equivalent dose (mg/kg-bw) 3X @ 0.47 lb ai/A; 14 day interval Mammalian Classes and Body weight Herbivores/ insectivores 15 g 35 1000 g Short Grass 250 174 39 Tall Grass 115 80 18 Broadleaf plants/sm Insects 141 98 22 Fruits/pods/seeds/lg insects 16 11 2 Granivores Fruits/pods/seeds/lg insects 3 2 0
Terrestrial Plant EEC

Spray Drift EFED estimates risk quotients to non-target plants from runoff with seedling emergence (Tier I I) data. The TerrPlant model is used for runoff. The AgDrift model will be used to determine the terrestrial non-target plant EEC from spray drift. A single application of Sethoxydim was modeled using 0.47 lb ai/A of sethoxydim since there are no phy

totoxicity data using TEP. The AgDrift model was used to estimate concentrations of sethoxy dim (a.i.) residues on non-target plants over an area of one acre. Tier 1 terrestrial assessments were performed, assuming either aerial or ground application. The ground spray assessment assumed a low boom applicator, ASAE medium to coarse droplet size, and 90 th-46-

percentile exposure. The aerial spray assessment assumed ASAE medium to coarse droplet size. The model runs are located in Appendix O. The summary of EEC results from the AgDrift model are below: Table 15a No. of application (0.47 lb ai/A) distance from edge

of field % of application rate EEC (lb ai/A) method
1 0 feet 50 0.235 Aerial 1 50 feet 11.1 0.052 Aerial 1 100 feet 5.6 0.026 Aerial 1 200 feet 2.5 0.012 Aerial 1 300 feet 1.5 0.007 Aerial 1 10 feet 2.8 0.013 Ground 1 50 feet 0.7 0.004 Ground Runoff The standard runoff assumption in the EEC are 5% since solubility is greater than 100 ppm (Appendix P). The LOC for non-target plants is 1. Below is Table 15b which shows the EEC for runoff to non-targeted plants as per the TerrPlant model. Details for the TerrPlant model run (see Appendix P) are as follows: - Application rate are 0.47 and 0.28 lb ai/A - Runoff factor from solubility is 5% - Toxicity endpoints used are mentioned above. - The aerial spray drift uses an assumption of 1% for ground spray and 5% for aerial spray .-47-

Table 15b Non-listed Species Method Application Rate Total Loading to Adjacent Areas Total Loading to Semi-Aquatic Areas ground 0.47 lb ai/A 0.0282 0.2397 aerial 0.47 lb ai/A 0.0376 0.1645 ground 0.28 lb ai/A 0.0282 0.2397 aerial 0.28 lb ai/A 0.0376 0.1645 Listed Species ground 0.47 lb ai/A 0.0282 0.2397 aerial 0.47 lb ai/A 0.0376 0.1645 ground 0.28 lb ai/A 0.0282 0.2397 aerial 0.28 lb ai/A 0.0376 0.1645

C. Measures of Ecological Effects
In screening-level ecological risk assessments, the Measures of Ecological Effects Section describes the ty

pes of effects a pesticide can produce in an organism or plant. This characterization is based on registrant-submitted studies that describe acute and chronic toxicity information for various aquatic and terrestrial animals and plants. In addition, other sources of information, including reviews of the open literature and the Ecological Incident Information Sy stem (EI IS ), are conducted to further refine the characterization of potential ecological effects. Appendix E summarizes the results of the registrant-submitted 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. Mammalian acute studies are usually limited to Norway Rat or the house mouse. Estuarine/marine testing is usually limited to a crustacean, a mollusk, and a fish. Also, neither reptiles nor amphibians are tested. The risk assessment assumes that avian and reptilian toxicities are similar. The same assumption is used for fish and amphibians.

1. Aquatic Effects

a. Aquatic Animals (1). Acute Effects-48- Freshwater Sethoxy dim technical is practically non-toxic to freshwater fish (L C 50 = 170 ppm ai for rainbow trout) on an acute basis. Sethoxydim technical is slightly toxic to freshwater invertebrate (L C 50 = 78.1 ppm ai for Daphnia magna ) on an acute basis. The formulated product is moderately toxic to freshwater fish (L C 50 = 6.2 ppm product for rainbow trout) and to freshwater invertebrates (LC 50 = 13.5 ppm product for Daphnia magna ) on an acute basis. The dose response slope for the formulated product of Sethoxydim tested on Daphnia magna is 4.73723. Naphthalene as part of the formulation of the TEP for Sethoxydim (POAST®) will be considered in this risk assessment as a surrogate for solvent containing Naphthalene. Naphthalene is moderately toxic to freshwater fish (rainbow trout L C 50 = 2.0 ppm) and freshwater invertebrates (LC 50 = 1.6 ppm for Daphnia magna ) on an acute basis.
Estuarine Sethoxy dim technical is practically non-toxic to estuarine fish (L C 50 > 145.8 ppm a.i. for sheepshead minnow) and estuarine invertebrate (LC 50 > 141.8 ppm a.i. for eastern oy ster and 141,8 ppm for my sid shrimp) on an acute basis. The formulated product is moderately toxic to estuarine fish (L C 50 = 19.4 ppm product for sheepshead minnow) and estuarine invertebrates (LC 50 = 4.4 ppm product for my sid shrimp and 4.4 ppm product for eastern oy ster (embry o-larvae)) on an acute basis. The dose response slope for the formulated product of Sethoxydim tested on eastern oy ster is 4.83123.

(2). Chronic Effects Currently there are no chronic toxicity data available to evaluate the chronic toxic effects of Sethoxy dim technical on freshwater fish or invertebrates. There is a high value in submitting the data in order to determine chronic toxicity to freshwater organisms. The supplemental chronic toxicity study on the formulated product indicated that no significant effect on marine/estuarine fish occurred in the study (NOAEC = 98 ppm). The formulated product chronic toxicity study on a marine/estuarine invertebrate (my sid shrimp) indicated NOAEC of 6.5 ppm a.i. and a L OAEC = 13 ppm a.i. for effects on length and survival. (3). Field Studies Currently , there are no field studies available for Sethoxydim.

b. Aquatic Plants Sethoxy dim technical is of low toxicity to a vascular dicot, duckweed ( Lemna gibba ), with an EC 50 > 0.281 ppm ai. However, this herbicide is considered to be toxic to grass species, which-49-

are monocots. There are no available phy totoxicity data on aquatic grasses. I t is very uncertain what the toxicity of Sethoxy dim is to aquatic grasses without data.

2. Terrestrial Effects

a. Terrestrial Animals (1). Acute Effects Sethoxy dim technical is practically non-toxic to birds on a subacute dietary basis (L C50 >5620 ppm a.i.) and practically nontoxic on an acute oral basis (L D 50 > 2510 mg ai/kg-bw in mallard duck). No mortalities were observed at the highest dose. Currently , there are no avian acute toxicity data on the formulated product of Sethoxydim. Sethoxy dim technical is practically nontoxic to rats on an acute oral basis (L D 50 = 2676 mg/kgbw for females, 3125 mg/kg-bw for males). The available mammalian acute toxicity data on the formulated product indicate that formulated Sethoxydim is practically non-toxic to mammals on an acute basis (LD 50 = 4385 mg/kg-bw for females, 5000 mg/kg-bw for males).

(2). Chronic Effects Avian reproductive studies on bobwhite quail showed no effects at concentrations up to 1000 ppm a.i. from Sethoxydim technical, but significant effects were noted to the mallard duck for the number of normal hatchlings at the 100 and 500 ppm levels. The NOAEC was not determined in this study . The LOAEC is 100 ppm a.i.. No avian reproductive study was done with the formulated product of Sethoxydim. There is an uncertainty in the mallard duck study since the NOAEC was not determined. Data from another mallard reproductive study using the technical Sethoxydim would be very useful in lowering the uncertainties that exist for chronic risk to birds. Mammalian reproductive study (2-generation rat reproduction) showed a reproductive NOAEC of 3000 ppm (150 mg/kg-bw/day ) and a developmental NOAEC of 600 ppm (30 mg/kg-bw/day ). The rat 2-generation reproduction study (1983, MRI D 41510606, 43366401) demonstrated both a sy stemic NOAEC and L OAEC of 

### $ 150 mg/kg/day . There were no adverse effects on the reproductive performance in either sex. In addition, the study demonstrated a developmental toxicity NOAEC and LOAEC of 30 and 150 mg/kg/day , respectively , for the offspring based on tail abnormalities seen in F 1a and F 1b offspring. Malformations were only observed in one F 1b and two F 2b pups. The malformations were described as thread-like tail, no anal opening, malformed hindlimb, malpositioned kidney s, cleft lip, cleft palate and microphthalmia. There were no dose-related gross or microscopic lesions, or developmental variations (cannibalism complicated the evaluation).

(3). Field Studies-50-

No terrestrial field studies were found using Sethoxydim.

b. Terrestrial Plants Sethoxy dim is a herbicide that is part of the Cyclohexanediones class of chemicals. The mode of action for this herbicide is L ipid Biosy nthesis Inhibition. Selectivity is shown to be due to susceptibility at acetyl-coenzy me A carboxylase (ACCase). Susceptible grass species are killed by inhibiting the ACCase which is a key enzy me in the lipid biosy

nthetic pathway . This herbicide is not expected to adversely affect dicot plant families or monocot non-grass families of plants. A submitted vegetative vigor toxicity study confirms this expectation. None of the dicots showed any significant adverse effects from Sethoxydim up to 0.5 lb ai/a. Also, the onion (a non- grass monocot) did not show any adverse effects from Sethoxydim exposure. The most sensitive grass in the vegetative vigor study was the ry egrass with an EC 25 of 0.029 lb ai/A (C.I . = 0.023 - 0.037), EC 50 = 0.038 lb ai/A (C.I . =0.033-0.044) and a NOAEC of 0.025 lb ai/A. The slope of the dose response curve is 5.75. This study is classified as supplemental since it was tested with the technical grade Sethoxydim and not the ty pical end product (TEP). I t is important that terrestrial plants be tested with the TEP which also contains adjuvants that help the active ingredient to penetrate the leaf surface. A seedling emergence study was submitted. The seedling emergence study on three grass species (ry egrass, corn and oat) using the TEP found that the most sensitive seedling emergence EC 25 = 0.078 lb ai/A and the NOAEC = 0.0587 lb ai/A for ry egrass. The slope is 2.21. The study also reveals that the percentage of emergence was significantly reduced at 0.1175 lb. The EC 25 value is used to assess risk to non-target non-listed plant species. The NOAEC value will be the toxicity endpoint used to assess risk to listed species.

3. ECOTOX Database No toxicity endpoints or literature sources were used from the ECOTOX database. The reasons for not using the endpoints or the literatures are found in Appendix B and Appendix C. Of the excluded data from the ECOTOX database, non were found to be pertinent to the risk assessment.-51-

IV

. Risk Characterization
A. Risk Estimation - Integration of Exposure and Effects Data Results of the exposure and toxicity effects data are used to evaluate the likelihood of adverse ecological effects on non-target species. For the assessment of Sethoxydim risks, the risk quotient (RQ) method is used to compare exposure and measured toxicity values. Estimated environmental concentrations (EECs) are divided by acute and chronic toxicity values. The resulting RQs are compared to the Agency ’s levels of concern (LOCs). These LOCs are the Agency ’s interpretive policy and are used to analy ze potential risk to non-target organisms and assess the need to consider regulatory action. These criteria are used to indicate when a pesticide’s directed label use has the potential to cause adverse effects on non-target organisms. In section 2.E.1.c. of this document, the L evels of Concern are described and presented in tabular form.
1. Non-target Aquatic Animals

Runoff The most sensitive aquatic fish species (freshwater and estuarine) for acute toxicity is rainbow trout with an LC 50 = 170 ppm ai for the technical grade Sethoxydim. The maximum EEC (0.47 lb ai/A applied 4X) generated by the GENEEC aquatic exposure model is 87 ppb for technical sethoxy dim. The RQ = 0.0005 for the technical Sethoxydim (87/170,000). The technical Sethoxy dim RQ are below all L OCs including listed species from runoff exposure. The most sensitive aquatic invertebrates species (freshwater and estuarine) for acute toxicity is the daphnid (EC 50 = 78.1 ppm ai) for the technical Sethoxydim. The maximum EEC (0.47 lb ai/A applied 4X) generated by the GENEEC aquatic exposure model is 87 ppb for Sethoxydim technical. The RQ = 0.001 for the technical Sethoxydim (87/78,100). The technical Sethoxydim RQ is below all L OCs including listed species. The Sethoxy dim chronic LOC for estuarine fish and invertebrates has not been exceeded for listed species (NOAEC = 6.5 ppm a.i. for my sid shrimp and 98 ppm a.i. for sheepshead minnow) since the EEC (0.087 ppm) is less than the toxicity value.

Spray Drift The maximum Sethoxy dim TEP EEC modeled from AgDrift is 35.3 ppb of TEP in 6 feet farm pond model. The TEP L C 50 for freshwater fish is 6.2 ppm product and the EC 50 for freshwater invertebrates (

Daphnia magna ) is 13.5 ppm product. The RQs are 0.006 for freshwater fish and 0.003 for freshwater invertebrates, respectively . These are below all LOCs. The estuarine fish LC 50 is 19.4 ppm product and the estuarine invertebrate EC 50 is 4.4 ppm product. The RQs are 0.002 for the estuarine fish and 0.008 for the estuarine invertebrates,-52-

respectively . These are below all LOCs. The most sensitive aquatic plant’s EC 50 is 250 ppb ai which is well below all L OCs.

2. Non-target Terrestrial Animal There are no avian acute levels of concern since the data provided indicate that sethoxydim is practically non-toxic to birds and no mortalities were observed at the highest dose tested. All of the uses of Sethoxy dim potentially exceeds the chronic level of concern since the avian chronic NOAEL was not determined. The lowest dose tested was used as the toxic measure of effect until additional avian reproduction studies provide additional data. Below are the Chronic RQ tables for birds exposed to Sethoxydim at different applications.
Table 16 Avian Organism Chronic Risk Quotient (Chronic Level of Concern = 1) with NOAEC <100ppm

Site (not inclusive) No. of Apps. App.Rate (lbs ai/A) Food Items Avian Chronic Risk Quotient based on Max. EEC and NOAEC < 100 ppm Avian Chronic Risk Quotient based on Mean EEC and NOAEC < 100 ppm Citrus, tree nuts
4 0.47 Short grass >3.12 >1.11 Tall grass >1.43 >0.47 Broadleaf plants/I nsect >1.76 >0.59

Seeds >0.20 >0.09 Alfalfa, birdfoot trefoil, sainfoin, clover,

cotton, 3 0.47 Short grass >2.63 >0.93 Tall grass >1.21 >0.39 Broadleaf plants/I nsect >1.48 >0.49

Seeds >0.16 >0.08 Fruiting and leafy vegetable crop group

3 0.28 Short grass >1.57 >0.56 Tall grass >0.72 >0.24 Broadleaf plants/I nsect >0.88 >0.29

Seeds >0.10 >0.05 Soybeans, grape, berries, peanut, Head & petiole vegetable crop subgroup, mint, pea, potato, safflower, sugar beets, Christmas tree farms, ornamentals, rights of way, roadsides, turf

2 0.47 Short grass >1.98 >0.70

Tall grass >0.91 >0.30
Broadleaf plants/I nsect >1.12 >0.37

Seeds >0.12 >0.06Table 16 Avian Organism Chronic Risk Quotient (Chronic Level of Concern = 1) with NOAEC <100ppm Site (not inclusive) No. of Apps. App.Rate (lbs ai/A) Food Items Avian Chronic Risk Quotient based on Max. EEC and NOAEC < 100 ppm Avian Chronic Risk Quotient based on Mean EEC and NOAEC < 100 ppm

-53- Orchard floor middles, strawberry, sunflower

1 0.47 Short grass >1.13 >0.40 Tall grass >0.52 >0.17 Broadleaf plants/I nsect >0.63 >0.21

Seeds >0.07 >0.03 There are no avian or mammalian acute LOC exceedances from the use of Sethoxydim. Avian and acute toxicity studies show Sethoxy dim to be practically non-toxic with no mortalities observed at the highest dose concentrations. The mammalian RQ < 0.1 (L OC for listed species) at the highest potential labeled exposure. Since no definitive chronic avian NOAEC value was established in the available chronic avian toxicity studies, all chronic avian RQ values are “greater than” values and therefore all potentially exceed the chronic LOC of 1.0. The chronic avian RQ values are described below. When Sethoxy dim is applied 4 or 3 times a season at the maximum application rate of 0.47 lb ai/A with 14-day intervals, the chronic L OC is exceeded for all birds feeding on short grass, tall grass, and broadleaf plants/insects, and the chronic LOC is potentially exceeded (RQ>0.2 based on maximum EEC) for birds feeding only on seeds. When Sethoxy dim is applied 3 times a season at a maximum application rate of 0.28 lb ai/A with 14-day intervals, the chronic L OC is exceeded for birds that feed exclusively on short grass, and is potentially exceeded for birds feeding on tall grass, broadleaf plants/insects, and seeds. When sethoxy dim is applied 2 times a season at the maximum application rate of 0.47 lbs a.i./A with 14-day intervals, the chronic L OC is exceeded for birds feeding on short grass and broadleaf plants/insects, and the chronic L OC is potentially exceeded for birds feeding on tall grass and seeds. When sethoxy dim is applied once at the maximum application rate of 0.47 lbs a.i./A, the chronic LOC is exceeded for birds feeding on short grass, and potentially exceeded for birds feeding on tall grass, broadleaf plants/insects, and seeds. There are no chronic LOC exceedances for mammals because the chronic RQ is <1 for mammals at the highest exposure (297 ppm/600 ppm = 0.5 RQ).-54- 3. Non-target Plants Terrestrial The vegetative vigor (Tier I I) EC 25 = 0.029 lb ai/A. The NOAEC value will be the toxicity endpoint used to assess risk to listed species and it is 0.025 lb ai/A for ry egrass. The RQs may be underestimated because the phy totoxicity endpoint was determined using the technical grade Sethoxy dim instead of the TEP. A seedling emergence study was submitted. The seedling emergence study on three grass species (ry egrass, corn and oat) using the TEP found that the most sensitive seedling emergence EC 25 = 0.078 lb ai/A and the NOAEC = 0.0587 lb ai/A for ry egrass. The slope is 2.21. The study also reveals that the percentage of emergence was significantly reduced at 0.1175 lb ai/A. The seedling emergence EC 25 is available to use in this risk assessment for non-target plants exposed to sethoxy dim from runoff. The EC 25 value is used to assess risk to non-target nonlisted plant species. The NOAEC value will be the toxicity endpoint used to assess risk to listed species. Spray Drift A single application of Sethoxydim was modeled using 0.47 lb ai/A of sethoxydim since there are no phy

totoxicity data using TEP. The AgDrift model was used to estimate concentrations of sethoxy dim (a.i.) residues on non-target plants over an area of one acre. AgDrift Tier 1 terrestrial assessments were performed, assuming either aerial or ground application. The ground spray assessment assumed a high boom applicator, ASAE medium to coarse spray droplet size, and 90 th percentile exposure. The aerial spray assessment assumed ASAE medium to coarse spray droplet size. The toxicity measurement of effect (EC 25 ) is 0.029 lb ai/A for non-listed species and 0.025 lb ai/A (NOAEC) for listed species. The model runs are located in Appendix O. The RQ results based on the AgDrift model are below: Table 17a Li sted and Non-listed Plant Species No. of application (0.47 lb ai/A) distance from edge

of field % of application rate EEC (lb ai/A) Non-listed RQ Listed

RQ method
1 0 feet 50 0.235 8.1 9.4 Aerial 1 50 feet 11.1 0.052 1.8 2.1 Aerial 1 100 feet 5.6 0.026 0.9 1.0 Aerial 1 200 feet 2.5 0.012 0.4 0.5 Aerial 1 300 feet 1.5 0.007 0.2 0.3 Aerial 1 10 feet 2.8 0.013 0.4 0.5 Ground 1 50 feet 0.7 0.004 0.1 0.2 Ground Non-listed and listed plant species L OCs (RQ = 1) are exceeded from edge of field up to 50 feet for nonlisted species and up to 100 feet for listed species with aerial application. There are no-55-

LOC exceedances from ground applied spray drift.

Runoff Below is Table 17b which shows the EEC and Risk Quotients for runoff to non-targeted plants. The inputs for the TerrPlant model (Appendix P). The model uses spray drift assumption of 1% for ground spray and 5% for aerial spray

. Table 17b Non-listed Species Method Application

Rate Total Loading to

Adjacent Areas Total Loading to

Semi-Aquatic Areas RQ for

Adjacent Areas RQ for Semiaquatic Areas Spray

Drift RQ 1 ground 0.47 lb ai/A 0.0282 0.2397 <1 3.1 <1 aerial 0.47 lb ai/A 0.0376 0.1645 <1 2.1 <1 ground 0.28 lb ai/A 0.0282 0.2397 <1 1.8 <1 aerial 0.28 lb ai/A 0.0376 0.1645 <1 1.3 <1 Listed Species ground 0.47 lb ai/A 0.0282 0.2397 <1 4.1 <1 aerial 0.47 lb ai/A 0.0376 0.1645 <1 2.8 <1 ground 0.28 lb ai/A 0.0282 0.2397 <1 2.4 <1 aerial 0.28 lb ai/A 0.0376 0.1645 <1 1.7 <1 1 Spray drift assumptions of 1% for ground application and 5% for aerial application were used. Non-listed and listed plant species L OCs (RQ = 1) are exceeded for runoff to low semi-aquatic areas only with RQs ranging from 1.3 to 4.1. Aquatic Plants Sethoxy dim technical is of low toxicity to a vascular dicot, duckweed ( Lemna gibba ) where EC 50 > 0.281 ppm ai (highest dose tested). The maximum EEC (based on 4 applications of 0.47 lb ai/A) generated from the GENEEC model is 111 ppb. The aquatic plant LOC (including listed species) is not exceeded. However, this herbicide is considered to be toxic to grass species, a monocot. There are no available phy totoxic data on aquatic grasses (obligate aquatic Poaceae family ). I t is very uncertain what the toxicity of Sethoxydim is to aquatic grasses without data.

B. Risk Description
1. Risks to Aquatic Animals and Plants Summary of Major Conclusions-56-

• There is no exceeded acute risk LOC for aquatic animals from the Sethoxydim per se. Sethoxy dim itself (the technical grade active ingredient) is not acutely toxic to aquatic animals at the expected exposures. There is a possibility of acute risk to aquatic animals from exposure to the petroleum solvent (CAS Reg. No. 64742-94-5) used in POAST®, which contains Naphthalene.

• No chronic risk is expected for aquatic estuarine animals from runoff to the standard farm pond.

• The risk to aquatic plants is limited to aquatic grasses, due to the mode of action of Sethoxy dim. The risk cannot be quantified, because there are no toxicity testing data for aquatic grasses. These data are being requested.

• The LOC is not exceeded for algae or diatoms.

Discussion Aquatic animals. Toxicity. Technical sethoxydim is not toxic to aquatic animals at estimated concentrations. However, the TEP is more toxic than the technical at two orders of magnitude. The greater toxicity of the formulated product to aquatic organisms may be attributed to the petroleum solvent (CAS Registry No. 64742-94-5). This solvent is known to contain seven percent of Naphthalene by weight. I t is likely that the other constituents of the petroleum solvent have toxicity similar to that of Naphthalene, especially if the toxic effect is simple narcosis. A comparison of Subdivision N Guideline acute toxicity data for Naphthalene (PC code 055801) to the data for formulated (18.0 - 20.4%) and technical Sethoxydim shows that the median lethal concentrations for Naphthalene and formulated sethoxydim are similar for the trout, bluegill, and waterflea (see table 4). Also, the toxicity of formulated Sethoxydim to estuarine organisms is in the same low ppm range as the toxicity of Naphthalene to coho salmon. Formulated product (POAST®) was tested on aquatic freshwater animals (see Appendix E). See below showing the LC 50 /EC 50 (in ppb) comparison among the Sethoxydim, POAST®, and Naphthalene (MRI D 45030801, 44302702, 44302701, ACC249909):-57-

Table 18 organism Sethoxydim POAST® 1 Naphthalene Rainbow trout 170,000 6,200 2,000 bluegill 265,000 8,300 3,200 Daphnia magna 78,100 13,500 1,600 Coho salmon na na 2,100 Sheepshead minnow 145,800 19,400 na Eastern oyster >109,000 4,400 na Mysid shrimp 141,800 4,400 na 1) POAST® values are in ppb product. na = not available Toxicity of Sethoxy dim is under estimated and thereby the risk is also underestimated if the petroleum solvents that also contain Naphthalene are not taken into consideration. Runoff Uncertainty for Petroleum Solvent . There is much uncertainty as to the amounts of the petroleum solvent to which aquatic organisms are exposed, since the exposure modeling was done only on the Sethoxy dim technical and not on the Naphthalene component nor on POAST®. It is difficult to model POAST® without chemical, phy sical and fate data on POAST® as a whole. The fate properties of Naphthalene are very different from the properties of Sethoxydim. These differences in properties will cause the two chemicals to separate from each other during a runoff scenario, thereby creating different load or exposure time lines to aquatic organisms. Below is a table of some of the Fate properties of Naphthalene: Table 19: Fate Data on Naphthalene organic carbon partitioning coefficient (Koc) 1837 mL/g EPI Suite estimate

Soil metabolism half-life 48 day s Howard et al., 1991 Water metabolism Half-life 20 day s Howard et al., 1991 Aqueous Photoly sis half-life 71 day s Howard et al., 1991 Volatility of Petroleum Solvent . According to Merck Index (tenth edition, paragraph 6220), Naphthalene has moderate volatility which may cause it to evaporate from where it is spray ed, and be transported in the atmosphere. Spray drift exposure could be augmented by later volatilization and transport of petroleum solvent vapors to ponds or wetlands. The exposure of the TEP to non-target plants and water bodies could be underestimated. Potential for Risk from Spray Drift of TEP to W etlands. Aerial spraying of the TEP in a 6-inch deep wetland scenario may pose a potential risk to aquatic animal species including listed-58-

species. Chemical concentrations in a 6-inch scenario are usually about 13X higher than in a 6 foot farm pond scenario. Aerial spray drift can transport the TEP to nearby wetlands that contain 6 inch deep shallow pools. Many aquatic fish and invertebrate species spend part of their reproductive life cycle in these shallow water bodies. The timing of application of POAST® may intersect with the time period that the aquatic species inhabit these water bodies. Since the TEP is much more toxic than the technical sethoxy dim, potential risk cannot be discounted from these species. Chronic Risk. Estuarine chronic risk quotients were calculated for the estuarine fish and invertebrates since chronic toxicity data are available. There are no freshwater fish or invertebrate chronic toxicity data available. The chronic toxicity endpoint (NOAEC) that was used to calculate RQ’s was derived from testing of a formulation containing 40% Sethoxydim. Because of the lack of acute toxicity of Sethoxy dim to aquatic organisms, we are presuming that the chronic toxicity of technical Sethoxy dim would be less sensitive than that of a TEP containing petroleum solvent. Chronic toxicity data are still needed to assess chronic risk to freshwater fish and invertebrates using technical Sethoxydim and the TEP.

Aquatic Plants Sethoxy dim technical is of low toxicity to a vascular aquatic dicot, duckweed ( Lemna gibba ) where EC 50 > 281 ppb ai. An assumption is made that only aquatic grasses (obligate aquatic Poaceae family

) are potentially at risk, since available data indicate that Sethoxydim is only toxic to terrestrial grass species. In addition, the herbicidal mode of action of sethoxydim is L ipid Biosy nthesis Inhibition. Selectivity is shown to be due to the greater susceptibility at acetylcoenzy me A carboxylase (ACCase) of grassy species. Susceptible grassy species are killed by inhibition of the ACCase which is a key enzy me in the lipid biosy

nthetic pathway . The risk cannot be quantified because we do not have toxicity data for aquatic grass. However, there is some uncertainty in this assumption. The exposure route for an aquatic grass would likely be different that for a terrestrial grass (foliar rather than by foliar and root uptake). Another uncertainty is the differences in aquatic plant phy siology as compared to terrestrial plants such as many terrestrial plants tend to need oxygen for their root zones whereas the obligate aquatic plant does not have much oxygen in their root zones thereby rely on other means to get the oxygen down to the roots. Unicellular aquatic plants (algae) appear to have no adverse effect from the exposure of Sethoxy dim.
2. Risks to Terrestrial Organisms-59- Summary of Major Conclusions



### ! Chronic L OCs are exceeded for birds.



### ! LOCs are exceeded for listed and non-listed grass species (Poaceae family ) from spray drift from aerial and spray -drift from irrigated applications. There are no LOC exceedances for non-target listed grass species from ground applied spray drift.



### ! No avian or mammalian acute LOC are exceeded.



### ! No chronic LOCs are exceeded for mammals.



### ! There appear to be no LOC exceedances for non-target plants that are not members of the Poaceae family

.


### ! LOCs are exceeded for terrestrial non-target grasses from runoff to low semi-aquatic areas.

Discussion

Terrestrial animals Acute risk to birds and mammals. No acute RQ calculations were made for birds because avian acute and subacute dietary studies suggest that Sethoxydim technical is practically non-toxic to birds. At the highest dose, no mortalities were observed. Thus, no listed species concern was triggered. Rat acute oral toxicity studies suggest that Sethoxydim technical and POAST® are practically non-toxic to mammals. Since there were some mortalities observed in the studies, RQ calculations were done at the maximum exposure to mammals and no L OC was exceeded. No listed species L OC was triggered. Chronic risk to birds and mammals. Avian reproduction studies were conducted with the technical active ingredient of Sethoxydim. In these studies, the bobwhite quail showed no treatment related effects up to 1000 ppm of Sethoxydim exposure. The mallard duck showed the number of normal hatchlings was significantly less than the control at the lowest dose tested, which was 100 ppm. Thereby , the NOAEC was not determined. There is uncertainty in this study as to what the no adverse observed concentration thresholds really are. Another mallard reproduction study is needed to lower the amount of uncertainty for chronic reproductive risk to avian populations. All of the chronic avian RQs are “greater than” values because the NOAEC used to calculate the RQs was a “less than” value. Therefore, all chronic avian RQ values potentially exceed the-60-

chronic LOC. The rat 2-generation reproduction study indicates no adverse effects in the study at 3000 ppm (150 mg/kg/day

). However, the offspring/developmental toxicity NOAEC was 600 ppm (30 mg/kg/day

) and the LOAEC was 150 mg/kg/day for the offspring based on tail abnormalities seen in F1a and F1b offspring. The 600 ppm NOAEC measure of effect is determined on standard FDA lab rat conversion of 20 X 30 mg/kg-diet = ppm-diet. Malformations were only observed in one F 1b and two F 2b pups. The malformations were described as thread-like tail, no anal opening, malformed hindlimb, malpositioned kidney s, cleft lip, cleft palate and microphthalmia. There were no dose-related gross or microscopic lesions, or developmental variations (cannibalism complicated the evaluation). There are no chronic LOC exceedances for mammals because the most sensitive chronic endpoint (600 ppm) is much greater than the highest exposure concentration (297 ppm).

Terrestrial Plants Risk to Non-Target Grass. Phy totoxicity data were submitted for vegetative vigor study on 10 species of crops. All of the dicot species showed no effects at the highest concentration. Onion, a monocot, also showed no effects at the highest rate tested. Onion is a monocot specie that is not a member of the grass family . The herbicidal mode of action for Sethoxydim is lipid biosy nthesis inhibition. Selectivity is shown to be due to susceptibility at acetyl-coenzy me A carboxylase (ACCase). Susceptible grass species are killed by inhibiting the ACCase which is a key enzy me in the lipid biosy

nthetic pathway . This herbicide is not expected to adversely affect dicot plant families or monocot non-grass families of plants. A submitted vegetative vigor toxicity study confirms this expectation. Therefore, it appears that only non-target grass species are expected to be adversely impacted from off-site movement of Sethoxydim. Vegetative vigor tests. Results from vegetative vigor studies are used to assess risk to non-target plants from spray drift. A vegetative vigor study (MRI D 41885906) with EC 25 = 0.029 lb ai/A and NOAEC = 0.038 lb ai/A showed the ry egrass to be the most sensitive species tested (four monocots of which three are grasses and six dicots). This study was conducted with Sethoxydim technical instead of the required POAST®. This creates uncertainty in the estimates of risk since it is generally recognized that formulated herbicides are more potent toward susceptible plant species than the technical active ingredients. Therefore, the risk to non-target plants is underestimated. Non-listed and listed plant species L OCs (RQ = 1) are exceeded from edge of field up to 50 feet for nonlisted species and up to100 feet for listed species with aerial application. There are no non-target plant LOC exceedances from ground applied spray drift. The estimated risk to non-target plants is underestimated due to lack of valid vegetative vigor studies conducted with the TEP. Using the TEP in terrestrial plant studies is important because most herbicides use adjuvants to penetrate the plant cuticle and other plant defenses in order to get the active ingredient into the plant to adversely affect the plant. Another tier I I v egetative vigor study conducted with POAST® on at least three grass species including corn should be conducted to assess risk to non-target grass species. There are currently no information on-61-

estimating definitely how much more toxic the TEP is as compared to the technical sethoxydim. Seedling Emergence tests. Seedling emergence studies are used to assess risk to non-target plant species from the exposure to runoff. One seedling emergence study on three grass species (ry egrass, corn and oat) using the TEP found that the most sensitive plant EC 25 = 0.078 lb ai/A and the NOAEC = 0.0587 lb ai/A for ry egrass. The slope is 2.21. The study also reveals that the percentage of emergence was significantly reduced at 0.1175 lb ai/A. Using TerrPlant model the L OC is exceeded for non-target grass species (including listed species) only to low semi-aquatic areas from runoff. The range of RQ is 1.3 to 3.1 for non-listed grasses and 1.7 to 4.1 for listed species. Since an assumption of 1% and 5% for spray drift was built into the TerrPlant model and the AgDrift model has much higher percentage of spray drift (50% at edge of field to 10 % at 300 feet from edge of field) movement off-site than TerrPlant, EFED can assume that the risk may be underestimated.

3. Uncertainty in Fate Data Terrestrial Field Dissipation . The submitted Terrestrial Field Dissipation studies (164-1) were judged to be unacceptable because total Sethoxydim residues, rather than the parent compound and its eight degradates were analy zed. However, due to the large uncertainty that exists for the degradates of Sethoxydim, additional data need to be generated to lower the amount of uncertainties on the fate of Sethoxydim. I f the assumption that the degradates are equally as toxic as the parent is adequate for risk assessment, then the studies do not need to be repeated. Aerobic Aquatic Metabolism . Additional information is needed to determine if the submitted Aerobic Aquatic Metabolism study (162-3) is acceptable. There is uncertainty in this study that needs to be clarified.

4. Review of Incident Data There have been two incidents related to Sethoxydim reported to the Environmental Incident In formation Sy stem (EI IS ) database. One incident occurred in 1992 at an unrecorded location. POAST-Plus Herbicide ® (Sethoxy dim) and L orsban 15G ® Granular Insecticide (chlorpy rifos) were applied to peanuts that were approximately 60 y ards away from a farm pond. Pix ® (mepiquat chloride) was also applied to cotton, which was about 40 yards away from the pond. Two inches of rain fell after the application, and about 300 fish ( Lepomis and Centrarchidae spp.) were observed dead in the pond 8 - 10 day s later. The EI IS report states that chlorpy rifos is believed to be the primary cause of this kill, but that sethoxy dim and mepiquat chloride could have also contributed to the toxicity observed in this incident. Chlorpyrifos is very highly toxic to several freshwater fish species on an acute basis, and all LOCs are exceeded for freshwater fish for all uses of chlorpy rifos. Mepiquat chloride is practically non-toxic to freshwater fish species on an acute basis, and the analy sis for this chemical indicated that no acute L OC are exceeded for freshwater fish (see links to chlorpy rifos I RED and mepiquat chloride RED at URL : http://cfpub.epa.gov/oppref/rereg/status.cfm?show=rereg Analy sis also concludes that, despite-62-

moderate acute toxicity of sethoxy dim formulated product, no L OCs are exceeded for non-listed freshwater fish in a standard pond. Therefore, it appears unlikely that sethoxy dim contributed to the toxicity leading to this fish kill. A second incident occurred in 2001, in which Checkmate ® (Sethoxy dim) and endosulfan were misdirected during accidental misuse. Dozens of white Amur grass carp ( Ctenopharyngondon idella ) were killed. The EI IS report states that endosulfan was likely the primary cause of mortality , but that Sethoxy dim was believed to contribute to the mortality of the fish. Given that endosulfan is very highly toxic to freshwater fish on an acute basis and all acute aquatic L OCs are exceeded for endosulfan (see endosulfan RED at URL: http://www.epa.gov/oppsrrd1/REDs/endosulfan_red.pdf ), it appears unlikely that sethoxy dim contributed to the toxicity leading to this incident.

5. Endocrine Disrupter EPA is required under the FFDCA, as amended by FQPA, to develop a screening program to determine whether certain substances (including all pesticide active and other ingredients) "may have an effect in humans that is similar to an effect produced by a naturally occurring estrogen, or other such endocrine effects as the Administrator may designate." Following the recommendations of its Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC), EPA determined that there was scientific bases for including, as part of the program, the androgen and thy

roid hormone sy stems, in addition to the estrogen hormone sy stem. EPA also adopted EDSTAC’s recommendation that the Program include evaluations of potential effects in wildlife. For pesticide chemicals, EPA will use FI FRA and, to the extent that effects in wildlife may help determine whether a substance may have an effect in humans, FFDCA authority to require the wildlife evaluations. As the science develops and resources allow, screening of additional hormone sy stems may be added to the Endocrine Disruptor Screening Program (EDSP). When the appropriate screening and/or testing protocols being considered under the Agency ’s EDSP have been developed, Sethoxydim may be subjected to additional screening and/or testing to better characterize effects related to endocrine disruption.
C. Threatened and Endangered Species Concerns
1. Taxonomic Groups Potentially at Risk The Agency ’s levels of concern for listed birds, terrestrial plants, and possibly aquatic grasses are exceeded for uses of Sethoxydim. By extension, endangered and threatened amphibians and reptiles may also be affected. Appendix L provides a list of listed species for each crop in which Sethoxy dim is used terrestrially in each state. A full list of listed species and the crops with which they are associated is in Appendix M

. The registrant must provide information on the proximity of Federally listed endangered species to the Sethoxy dim usage sites. This requirement may be satisfied in one of three way s: 1) having-63-

membership in the FI FRA Endangered Species Task Force (Pesticide Registration Notice 2000- 2); 2) citing FI FRA Endangered Species Task Force data; or 3) independently producing these data, provided the information is of sufficient quality to meet FI FRA requirements. The information will be used by the OPP Endangered Species Protection Program to develop recommendations to avoid adverse effects to listed species. The preliminary risk assessment for endangered species indicates that Sethoxydim exceeds the listed species L OCs for the following combinations of analy zed uses and species groups:

• Birds (chronic):

• Chronic RQs indicate that the following groups of listed birds are at risk under the uses and application scenarios indicated:



### N Birds consuming short grass, tall grass, broadleaf plants, small insects: Citrus, tree nuts (4 applications at maximum rate of 0.47 lbs ai/A); alfalfa, legume seeds, cotton (3 applications at maximum rate).


### N Birds consuming short grass: fruiting and leafy vegetable crops (3 applications at maximum rate); soy

beans, grapes, caneberries, peanuts, potatoes (excluding sweet potatoes), mint, turf, nursery crops, sugar beets, vegetable and flower seed (2 applications at maximum rate); orchards, strawberries, sunflower (1 application at maximum rate).

• All other listed birds are possibly at risk on a chronic basis. RQs cannot be estimated for birds associated with other crops and/or food ty pes, so the assumption of risk must be extended to all birds until sufficient data are provided.

• Plants: Alfalfa, berries, citrus, cotton, nursery crops, grapes, melons, orchards, tree nuts, turf, strawberries, sugar beets, vegetable and flower seeds, fruiting and leafy vegetables, potatoes (excluding sweet potatoes), peanuts, soy beans, legume seeds, sunflower seed, mint, vegetable and flower seed (2 to 4 aerial applications at maximum rate). Applications of Sethoxy dim pose risk to aquatic and terrestrial listed species : Amphibians Nineteen listed species inhabit 12 states in which Sethoxydim is used. Of the major crops on which Sethoxy dim is used, 15 species are associated with uses on alfalfa, 13 species are associated with uses in cotton, 6 with uses on soy beans, and 12 are associated with uses on vegetable crops. In addition, 10 species are associated with nursery crops, 17 species are associated with uses on orchard crops. Many of these species occur in only one state. Birds Fifty -seven listed species of birds live in 48 states in which Sethoxydim is used. Of the major-64-

crops on which Sethoxy dim is used, 19 species are associated with uses on soy beans, 14 species are associated with uses in peanuts, 25 species are associated with cotton, 14 species are associated with uses on sugar beets, and 36 species are associated with alfalfa crops. In other crops, 39 are associated with uses in citrus, 54 with nursery crops, 28 with turf (harvested sod), and 55 are associated with vegetable crops. Reptiles Twenty -eight listed species of reptiles live in 19 states in which Sethoxydim is used. Of the major crops on which Sethoxydim is used, 21 species are associated with uses in alfalfa, 14 with uses in cotton, 13 with uses in soy beans, 6 with uses in peanuts. In addition, 16 species are associated with uses in citrus, 23 with nursery crops, 26 with orchard crops, 17 with turf, 5 with sugar beets, and 25 are associated with uses in vegetable crops. Plants The LOCATES database does not delineate between terrestrial and aquatic plants or between grasses and other non-grass plants, so none are listed here. However, over 500 listed species of plants are associated with crops on which Sethoxydim is used.

• Direct Effects Guideline studies used in this ecological risk assessment indicate the possible effects that may occur to listed taxa if directly exposed to Sethoxy dim. Acute effects to birds are not expected; however, reproductive effects were observed in the avian chronic test with the mallard and bobwhite. A reduction in the number of eggs laid was observed in quail at the 500 ppm level; however, this effect was not considered to be treatment related. I n tests with the mallard, reduced number of normal hatchlings was observed in all concentrations (100, 500, and 1000 ppm). Other effects that were observed were a reduction in the number of eggs set the number of live embryos (observed at the 500 ppm concentration). Acute effects to fish from exposure to sethoxydim technical grade active ingredient (TGAI ) is not expected. Acute tests with TGAI in rainbow trout showed mortality (60%) occurring at only the highest concentration tested (180 mg/l). Effects were not observed at the other four concentrations ranging from 18 - 100 mg/l. However, higher mortality was observed when sethoxy dim TEP was tested in the same species, (100% at the two highest concentrations of 2.7 and 1.7 mg/l, 10% at the mid-range concentration of 1.0 mg/l). Mortality was not observed at the three lower concentrations of 0.21, 0.37, and 0.59 mg/l. No other effects (e.g., behavioral changes) were noted in these studies. Acute effects to aquatic invertebrates from exposure to sethoxydim technical grade active ingredient (TGAI ) is not expected. Immobility was observed in Daphnia when tested with both sethoxy dim TGAI and TEP. The acute test with TGAI describes cumulative effects with TGAI-65-

of 0%, 15%, 85%, 95%, and 100% at concentrations of 32, 51, 100, 180, and 320 mg/l, respectively . With TEP, 100% effects were observed in the two highest concentrations of 4.6 and 8.9 mg/l, 5% and 20% were observed at 0.57 and 2.4 mg/l respectively , and no effects were observed at the second highest concentration (1.1 mg/l). Other direct effects among the test organisms were not noted. Acute effects to marine/estuarine fish from exposure to sethoxydim technical grade active ingredient (TGAI ) is not expected. Mortality was not observed in the sheepshead minnow in acute tests with TGAI , but was observed when tested with the TEP (100% mortality at the four highest concentrations of 4.5, 7.2, 10.8, and 18 mg/l. Behavioral effects of loss of equilibrium and surfacing and gasping were observed at all but the 4.5 mg/l concentration, even the lowest (2.7 mg/l). These sublethal effects could have indirect consequences leading to mortality ; for example, they may lead to increased vulnerability to predators. The sheepshead minnow early life stage test did not result in any apparent direct effects. For this test, it is unclear whether TGAI or TEP was used, but percentage of active ingredient was 40.7%. Concentrations tested ranged from 6.6 to 98 mg/l. Acute effects to marine/estuarine invertebrates from exposure to sethoxydim technical grade active ingredient (TGAI ) is not expected. Mortality and other effects were observed in acute toxicity tests with marine/estuarine invertebrates. Mortality was observed in an acute test with the my sid using Sethoxy dim TGAI (30% at 141.8 mg/l). With the TEP, 100% mortality was observed at the three highest concentrations tested (1.1, 1.8, and 3.0 mg/l), 10% was observed at the second highest concentration (0.7 mg/l), and no mortality was observed at the lowest concentration of 0.5 mg/l. Effects were observed in the my sid life cy cle test. I t is unclear whether the test was performed with TGAI or TEP (43.1% a.i. is noted for the test material), but the magnitude of effects with this test are more consistent with acute tests using TEP. At the two highest concentrations of 59 and 120 mg/l, 100% effects were observed. At the other concentrations of 7.6, 14, and 29 mg/l, effects were observed at 17%, 26% and 70%. Mortality and the presence of abnormal individuals are potential direct effects in marine/estuarine invertebrates. Tests with the Eastern oy ster demonstrated direct effects. For acute tests with TGAI on oy ster larvae, mortality was not observed. However, abnormal individuals were observed in the control (7%) and at the concentration tested (109 mg/l). Sethoxydim was measured in the control, but this did not affect the classification of the study . Mortality was observed in all concentrations tested on Eastern oy ster using the TEP in acute tests. Concentrations were 0.4, 0.6, 1.0, 1.5, and 2.5 mg/l, and effects were observed at 2%, 12%, 62%, 95% and 89%, respectively . No other direct effects were reported, but the number of abnormal individuals was measured during the test. Direct effects are expected for plants exposed to sethoxydim, and especially for grasses. Among the species tested, ry egrass was the most sensitive species based on EC values for percent change in weight compared to controls. The rates tested ranged from 0.0031 - 0.05 lb a.i./A, and percent changes in weight ranged from 1.97 x 10 -8 to 75.5. As a result, we expect that listed species of grasses might be directly affected by exposure to sethoxy dim.-66- 2. Probit Slope Analy sis The probit slope response relationship is evaluated to calculate the chance of an individual event corresponding to the listed species acute LOCs. I f information is unavailable to estimate a slope for a particular study , a default slope assumption of 4.5 is used as per original Agency assumptions of ty

pical slope cited in Urban and Cook (1986).
It is recognized that extrapolation of very low probability events is associated with considerable uncertainty in the resulting estimates. To explore possible bounds to such estimates, the upper and lower values for the mean slope estimate can be used to calculate upper and lower estimates of the effects probability associated with the listed species L OC. However, the 95% confidence intervals for the slopes are unavailable in cases where slope is based on a default assumption of 4.5. Our analy sis using the exposure scenario of a 6-foot pond indicates that listed freshwater invertebrate species LOCs are exceeded when EECs are calculated for formulated petroleum solvents. RQs calculated using EECs for formulated petroleum solvents in a 6-inch wetland exceeded listed and non-listed species L OCs for freshwater fish and invertebrates. Therefore, mortality and other direct effects may be observed in freshwater animals inhabiting ponds orflowing waters, as well as those inhabiting wetland environments. Since both listed and nonlisted L OCs are exceeded for the wetland scenario, and more taxa are at risk, it is possible that effects are more likely to occur in those environments compared to pond and other non-wetland habitats. For this reason, the 6-inch wetland scenario is included in the discussion of the probability of individual direct effects, as well as the discussion of indirect effects below. Freshwater Fish Raw data are not available from the two rainbow trout studies with technical Sethoxydim (MRI D 42815) and the formulated product (MRI D 41885902) to calculate a slope. Therefore, the default slope of 4.5 was used to calculate the event probability for freshwater fish LOC. Based on an assumption of a probit dose response relationship with a mean estimated slope of 4.5, the corresponding estimated chance of individual mortality associated with the listed species L OC of 0.05 is 1 in 417,000,000 for technical. Freshwater Invertebrates A slope of 5.84 (95% CI : 3.84 - 7.86) was estimated using data from the study with technical Sethoxy dim in Daphnia magna (MRI D 42816). Based on an assumption of a probit dose response relationship using this slope, the corresponding estimated chance of individual mortality associated with the listed species L OC of 0.05 is 1 in 6.57 x 10 13 . The upper and lower estimates of the effects probability associated with the listed species L OC are, respectively , 1 in 3,410,000 and 

### # 1 in 1 x 10 16 (this value is the limit of probability for the program used to estimate the probability of mortality

). Individual mortality associated with the calculated RQ value for Daphnia magna exposed to technical Sethoxydim (0.001) is estimated to be 

### # 1 in 1 x 10 16 . The-67-

RQs calculated for freshwater invertebrates exposed to technical Sethoxydim fell below the L OC of 0.05, resulting in estimated probability of individual mortality of 

### # 1 in 2.8 x 10 9

. Marine/Estuarine Fish Raw data are not available from the sheepshead minnow studies with Sethoxydim technical to calculate a slope. Therefore, the default slope of 4.5 was used to calculate the event probability for marine/estuarine fish LOC. Based on an assumption of a probit dose response relationship with a mean estimated slope of 4.5, the corresponding estimated chance of individual mortality associated with the listed species L OC of 0.05 is 1 in 417,000,000 for technical Sethoxydim. The RQs calculated using EECs from the GENEEC model for marine/estuarine fish exposed to technical Sethoxydim fell below the L OC of 0.05, resulting in estimated probability of individual mortality of 

### # 1 in 2.8 x 10 9

. Marine/Estuarine Invertebrates Raw data are not provided in the Eastern oy ster study (MRI D 42537401) using technical Sethoxy dim to calculate a slope, or in the study with my sid shrimp. Therefore, the default slope of 4.5 was used to calculate the event probability for marine/estuarine invertebrate LOC. Based on an assumption of a probit dose response relationship with a mean estimated slope of 4.5, the corresponding estimated chance of individual mortality associated with the listed species L OC of 0.05 is 1 in 417,000,000 for technical Sethoxy dim in these species. With EECs calculated using the GENEEC model, the RQs for marine/estuarine fish exposed to technical Sethoxydim fell below the L OC of 0.05, resulting in estimated probability of individual mortality of 

### # 1 in 2.8 x 10 9

. Birds Because there were no demonstrable effects in acute toxicity tests with birds, a slope cannot be calculated to use in estimating the probability of individual effects on birds. Mammals Because mortality occurred at higher doses in the toxicity test with mammals, a probit-slope analy sis must be performed for this taxon. Raw data are not provided in toxicity studies involving laboratory rats and technical Sethoxydim (MRI D 00045847) or its formulated product (MRI D 00046326) in order to calculate a slope. Therefore, the default slope of 4.5 was used to calculate the event probability for mammal L OC. Based on an assumption of a probit dose response relationship with a mean estimated slope of 4.5, the corresponding estimated probability of mortality associated with the listed species L OC of 0.1 is 1 in 294,038.

3. In direct Effect Analy ses-68-

The Agency acknowledges that pesticides have the potential to exert indirect effects upon the listed organisms by , for example, perturbing forage or prey availability , altering the extent of nesting habitat, creating gaps in the food chain, etc.
In conducting a screen for indirect effects, direct effect LOCs for each taxonomic group are used to make inferences concerning the potential for indirect effects upon listed species that rely upon non-listed organisms in these taxonomic groups as resources critical to their life cycle. Because screening-level acute RQs have been exceeded for certain taxa, the Agency uses the dose response relationship from the toxicity study used for calculating the RQ to estimate the probability of acute effects on these taxa associated with an exposure equivalent to the EEC. This information serves as a guide to establish the need for and extent of additional analy sis that may be performed using Services-provided “species profiles” as well as evaluations of the geographical and temporal nature of the exposure to ascertain if a “not likely to adversely affect” determination can be made. The degree to which additional analy ses are performed is commensurate with the predicted probability of adverse effects from the comparison of the dose response information with the EECs. The greater the probability that exposure will produce effects on a taxon, the greater the concern for potential indirect effects for listed species dependent on that taxon, and therefore, the more intensive the analy sis on the potential listed species of concern, their locations relative to the use site, and information regarding the use scenario (e.g., timing, frequency , and geographical extent of pesticide application). RQs calculated from GENEEC-generated EECs in a standard pond did not exceed listed L OC for freshwater fish or invertebrates, so indirect effects resulting from losses of fish in these environments are not expected. Chronic L OCs are potentially exceeded for all birds on all food items at all use sites until additional avian chronic data is made available. At present, we have insufficient data to determine whether chronic LOCs are exceeded with use of sethoxydim on other crops and/or in other avian groups. Therefore, we must assume a direct chronic risk to all listed and non-listed avian species where sethoxydim is used. As a consequence, there is concern for indirect effects to generalist and obligate listed species dependent on birds, including mammals and other birds. LOCs are exceeded for listed and non-listed terrestrial grass species (family Poaceae) from Sethoxy dim applied by aerial or irrigated sy stems and from runoff to low semi-aquatic areas. Therefore, listed species in all taxa depending on plants that are exposed in these scenarios may be indirectly affected. Because sethoxydim is considered to be toxic to grasses, listed species obligate on grasses may have a higher likelihood of being indirectly affected than listed species that do not consume grass or are plant generalists. Information is lacking about effects to aquatic grasses, but additional data may indicate effects to aquatic grasses, which will also have indirect effects on listed species depending on these plants. Further analy sis will be necessary to confirm this possibility once these data are obtained, and will need to be conducted for all listed taxa, since loss of plants could result in loss of food resources or other important habitat elements or functions (e.g., cover from predators, loss of breeding and/or nesting sites, provision of shade to-69-

water bodies, etc.). Because LOCs are exceeded for birds, amphibians and reptiles may also be affected by exposure to Sethoxy dim. Therefore, listed species that are dependent on these taxa may be indirectly affected by their loss. The above are only general descriptions of the listed species that may be indirectly affected by applications of Sethoxydim. Further analy sis using geographic information of use sites and species occurrence (available in the LOCATES database), “species profiles” provided by the Services and other sources, and information regarding the temporal nature of Sethoxydim applications is necessary to determine the true indirect effects to listed species.

4. Critical Habitats
In the evaluation of pesticide effects on designated critical habitat, consideration is given to the phy sical 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 analy sis (risk quotients, RQs) and listed species levels of concern (L OCs) that are used to evaluate direct and indirect effects to listed organisms. The screening-level risk assessment has identified potential concerns for indirect effects on listed species for those organisms dependant upon birds and terrestrial plants. In light of the potential for indirect effects, the next step for EPA and the Service(s) is to identify which listed species and critical habitat are potentially implicated. Analy tically , the identification of such species and critical habitat can occur in either of two way s. First, the agencies could determine whether the action area overlaps critical habitat or the occupied range of any listed species. I f so, EPA would examine whether the pesticide's potential impacts on non-endangered species would affect the listed species indirectly or directly affect a constituent element of the critical habitat. Alternatively , the agencies could determine which listed species depend on biological resources, or have constituent elements that falls into, the taxa that may be directly or indirectly impacted by the pesticide. Then EPA would determine whether use of the pesticide overlaps the critical habitat or the occupied range of those listed species. At present, the information reviewed by EPA does not permit use of either analy tical 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 analy sis. This screening-level risk assessment for critical habitat provides a listing of potential biological features that, if they are constituent elements of one or more critical habitats, would be of potential concern. These correspond to the taxa identified above as being of potential concern for indirect effects and include the following: birds and terrestrial plants. This list should serve-70-

as an initial step in problem formulation for further assessment of critical habitat impacts outlined above, should additional work be necessary

.

D. Description of Assumptions, Uncertainties, Strengths, and L imitations
1. Assumptions and L imitations Related to Exposure for all Taxa Sethoxy dim Total Toxic Residues are expected to persist in treated terrestrial and aquatic areas with half-lives of about 30 day s, based on laboratory studies. There were eight degradates observed in the laboratory studies. Two of these (the sulfoxide and sulfone of the parent) were observed in soil. At environmentally relevant pH values, the Sethoxydim and degradates will all be present to some degree. 2. Assumptions and L imitations Related to Exposure for Terrestrial Species a. Location of W

ildlife Species For screening terrestrial risk assessments for listed species, a generic bird or mammal is assumed to occupy either the treated field or adjacent areas receiving pesticide at a rate commensurate with the treatment rate on the field. Spray drift model predictions suggest that this assumption leads to an overestimation of exposure to species that do not occupy the treated filed. For screening risk assessment purposes, the actual habitat requirements of any particular terrestrial species are not considered, and it assumed that species occupy , exclusively and permanently , the treated area being modeled. This assumption leads to a maximum level of exposure in the risk characterization. Terrestrial EEC are based on peak value of the Kenaga nomogram as modified by Fletcher. The residues from the Kenaga nomogram are measured immediately after application. The peak maximum value is the upper limit value and may be conservative. Sethoxydim is applied to plants after crops are up and the grasses appear up to about 30 day s or more prior to harvest. A variety of avian populations are nested in cotton, potato, alfalfa, orchards, and clover fields. The LOC for avian reproductive impairment is exceeded for Sethoxydim application, and based on this timing information, it is apparent that wildlife will be present in the fields during the period of application. b. Routes of Exposure Screening-level risk assessments for spray applications of pesticides consider dietary exposure alone. Other routes of exposure, not considered in this assessment, are discussed below:

• In cidental soil ingestion exposure - This risk assessment does not consider incidental soil ingestion. Available data suggests that up to 15% of the diet can consist of incidentally ingested soil depending on the species and feeding strategy-71- (Bey er et al., 1994).

• In halation exposure - The screening risk assessment does not consider inhalation exposure. Such exposure may occur through three potential sources: (1) spray material in droplet form at the time of application (2) vapor phase pesticide volatilizing from treated surfaces, and (3) airborne particulate (soil, vegetative material, and pesticide dusts).

• Dermal Exposure - The screening assessment does not consider dermal exposure, except as it is indirectly included in calculations of RQs based on lethal doses per unit of pesticide treated area. Dermal exposure may occur through three potential sources: (1) direct application of spray to terrestrial wildlife in the treated area or within the drift footprint, (2) incidental contact with contaminated vegetation, or (3) contact with contaminated water or soil.

• Drinking Water Exposure - Drinking water exposure to a pesticide active ingredient may be the result of consumption of surface water or consumption of the pesticide in dew or other water on the surfaces of treated vegetation. For pesticide active ingredients with a potential to dissolve in runoff, puddles on the treated field may contain the chemical. c. Residue Levels Selection As discussed earlier in the exposure section of this document, the Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide residues in wildlife dietary items. The Agency believes that these residue assumptions reflect a realistic upper-bound residue estimate, although the degree to which this assumption reflects a specific percentile estimate is difficult to quantify . I t is important to note that the field measurement efforts used to develop the Fletcher estimates of exposure involve highly varied sampling techniques. I t is entirely possible that much of these data reflect residues averaged over entire above ground plants in the case of grass and forage sampling. Depending upon a specific wildlife species’ foraging habits, whole aboveground plant samples may either underestimate or overestimate actual exposure.

d. Dietary Intake - Differences Between Laboratory and Field Conditions The acute and chronic characterization of risk rely on comparisons of wildlife dietary residues with L C 50 or NOAEC values expressed in concentrations of pesticides in laboratory feed. These comparisons assume that ingestion of food items in the field occurs at rates commensurate with those in the laboratory . Although the screening assessment process adjusts dry -weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food intake estimates, it does not allow for gross energy and assimilative efficiency differences between wildlife food items and laboratory feed. On gross energy content alone, direct comparison of a laboratory dietary concentration- based-72-

effects threshold to a fresh-weight pesticide residue estimate would result in an underestimation of field exposure by food consumption by a factor of 1.25 - 2.5 for most food items. Only for seeds would the direct comparison of dietary threshold to residue estimate lead to an overestimate of exposure. Differences in assimilative efficiency between laboratory and wild diets suggest that current screening assessment methods do not account for a potentially important aspect of food requirements. Depending upon species and dietary matrix, bird assimilation of wild diet energy ranges from 23 - 80%, and mammal’s assimilation ranges from 41 - 85% (U.S. Environmental Protection Agency , 1993). I f it is assumed that laboratory chow is formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for underestimation of exposure may exist by assuming that consumption of food in the wild is comparable with consumption during laboratory testing. In the screening process, exposure may be underestimated because metabolic rates are not related to food consumption. Finally , the screening procedure does not account for situations where the feeding rate may be above or below requirements to meet free living metabolic requirements. Gorging behavior is a possibility under some specific wildlife scenarios (e.g., bird migration) where the food intake rate may be greatly increased. Kirkwood (1983) has suggested that an upper-bound limit to this behavior might be the ty

pical intake rate multiplied by a factor of 5. e. Estimated Environmental Concentrations to Non-Target Plants Currently the model (TerrPlant) for predicting the exposure to non-target plants adjacent to application sites and also to low-lying wetlands are based on the application rate, method of application (aerial or ground), and the solubility of the pesticide. Several transport factors are not incorporated into the model. The exposure prediction may be underestimated or overestimated. The model also assumes 5% aerial spray drift when aerially applied. AgDrift usually predicts about 10% and up to 15% spray drift at the edge of the field. The aerial application EEC in this risk assessment may be underestimated if use based on 5%.

f. Data gaps

• The submitted Terrestrial Field Dissipation studies (164-1) were judged to be unacceptable because total Sethoxydim residues, rather than the parent compound and its eight degradates were analy zed. However, due to the large uncertainty that exists for the degradates of Sethoxydim, additional data needs to be generated to lower the amount of uncertainties on the fate of Sethoxydim. I f the assumption that the degradates are equally as toxic as the parent is adequate for risk assessment, then the studies do not need to be repeated.

• Additional information is needed to determine if the submitted Aerobic Aquatic Metabolism study (162-3) is acceptable. There is uncertainty in this study that needs to be clarified.-73-

3. Assumptions and L imitations Related to Aquatic Effects Assessment

a. Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the observed sensitivity to a toxicant. The screening risk assessment acute toxicity data for fish are collected on juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on recommended immature age classes (e.g., first instar for daphnids, second instar for amphipods, stoneflies and may flies, and third instar for midges). Similarly , acute dietary testing with birds is also performed on juveniles, with mallard being 5-10 day s old and quail 10-14 day s old. Testing of juveniles may overestimate toxicity at older age classes for pesticidal active ingredients, such as Sethoxydim, that act directly because y ounger age classes may not have the enzy matic sy stems associated with detoxifying xenobiotics. The screening risk assessment has no current provisions for a generally applied method that accounts for this uncertainty . In so far as the available toxicity data may provide ranges of sensitivity information with respect to age class, the risk assessment uses the most sensitive life-stage information as the conservative screening endpoint.

b. Use of the Most Sensitive Species Tested Although the screening risk assessment relies on a selected toxicity endpoint from the most sensitive species tested, it does not necessarily mean that the selected toxicity endpoints reflect sensitivity of the most sensitive species existing in a given environment. The relative position of the most sensitive species tested in the distribution of all possible species is a function of the overall variability among species to a particular chemical. In the case of listed species, there is uncertainty regarding the relationship of the listed species’ sensitivity and the most sensitive species tested. The Agency is not limited to a base set of surrogate toxicity information in establishing risk assessment conclusions. The Agency also considers toxicity data on non-standard test species when available.

c. Data Gaps The following data gaps were identified with respect to the submitted ecotoxicity effects data:

• Risk to non-target terrestrial plants from spray drift is underestimated because the vegetative vigor study was conducted on the technical Sethoxydim and not on the TEP (POAST®).

• Risk to non-target aquatic grass species can not be certain or quantified due to lack of-74-

data.

• Avian chronic reproduction study did not achieve a NOAEC. Chronic avian toxicity is underestimated. d. Aquatic Environment Effects Aquatic toxicity data demonstrate that the Sethoxydim technical is less toxic than the TEP

. Comparison of the TEP toxicity data to Naphthalene toxicity data strongly suggest that the observed toxicity of the TEP is due to the petroleum solvent alone. The petroleum solvent (Naphthalene log K ow = 3.3) is more likely to bioaccumulate than Sethoxy dim (logK ow = 1.38). This property is likely to increase the petroleum solvent’s potential adverse effects.

e. Aquatic Environment Exposure Exposure to Sethoxy dim from terrestrial use can occur from both spray drift and runoff. Detailed modeling to determine which of these two routes is predominant has not been done; however Sethoxy dim is prone to runoff due to its high solubility (4700 ppm), low Kd values, and low Henry ’s Law constant (i.e., it tends to remain in water rather than sorb to soil or evapoarate). The petroleum solvent’s fate properties (as exemplified by Naphthalene) differ from Sethoxydim enough that they are expected to separate after application to a field. Naphthalene’s lower solubility (31 ppm) and higher vapor pressure (0.085 mmHg) promote evaporation, while its octanol-water partition coefficient (log K ow = 3.3) indicates a greater tendency to sorb to soil. The higher logK ow also indicates a greater tendency to bioaccumulate. Thus, we expect that runoff will carry Sethoxy dim to a greater extent than it will carry the petroleum solvent (i.e., the mixture in the runoff will contain proportionately less solvent than the spray mixture).