United States Prevention, Pesticides EPA 738 R 04 003 Environmental Protection and Toxic Substances September 2003 Agency ( 7508C)

Reregistration Eligibility Decision for Oxadiazon ii CERTIFIED MAIL Dear Registrant:

This is to inform you that the Environmental Protection Agency ( hereafter referred to as EPA or the Agency) has completed its review of the available data and public comments received related to the risk assessment for the oxadiazole pesticide, oxadiazon ( Ronstar ® ) . Based on its review, EPA has identified risk mitigation measures that the Agency believes are necessary to address the human health and environmental risks associated with the current use of oxadiazon. The EPA is now publishing its reregistration eligibility and risk management decisions for the current uses of oxadiazon, and its associated human health and environmental risks. The enclosed " Reregistration Eligibility Decision for Oxadiazon," which was approved on September 15, 2003, contains the Agency's decision on the individual chemical oxadiazon.

A Notice of Availability for this Reregistration Eligibility Decision ( RED) for oxadiazon is published in the Federal Register. To obtain a copy of the RED document, please contact the OPP Public Regulatory Docket ( 7502C), US EPA, Ariel Rios Building, 1200 Pennsylvania Avenue NW, Washington, DC 20460, telephone ( 703) 305 5805. Electronic copies of the RED and all supporting documents are available on the Internet. See http:// www. epa. gov/ pesticides.

This document and the process used to develop it are the result of a pilot process to facilitate greater public involvement and participation in the reregistration and/ or tolerance reassessment decisions for pesticides. As part of the Agency's effort to involve the public in the implementation of the Food Quality Protection Act of 1996 ( FQPA), the Agency is undertaking a special effort to maintain open public dockets and to engage the public in the reregistration and tolerance reassessment processes for these chemicals. The human health and environmental risk assessments were placed in the public docket and an invitation for public comment was announced in the Federal Register on February 19, 2003.

Please note that the oxadiazon risk assessments and the attached RED concern only this particular chemical. Oxadiazon is a member of the oxadiazole class of herbicides. While current data are limited, EPA has evidence that compounds within a class may share a common mechanism of toxicity. At this time, the Agency does not have sufficient data concerning common mechanism issues to determine whether or not oxadiazon shares a common mechanism of toxicity with other substances, including other oxadiazoles or iii other probable human carcinogens. Therefore, for the purposes of this risk assessment, the Agency has assumed that oxadiazon does not share a common mechanism of toxicity with any other chemicals.

End use product labels should be revised by the manufacturer to adopt the changes set forth in Section V of this document. Instructions for registrants on submitting revised labeling and the time frame established to do so can be found in Section V of this document.

If you have questions on this document or the proposed label changes, please contact the Special Review and Reregistration Division representative, Mark Seaton, at ( 703) 306 0469. For questions about product reregistration and/ or the Product DCI that accompanies this document, please contact Bentley Gregg at ( 703) 308 8178.

Betty Shackleford, Acting Director Special Review and Reregistration Division Attachment iv Reregistration Eligibility Decision for Oxadiazon List B Case 2485 v Table of Contents Glossary of Terms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Oxadiazon Reregistration Eligibility Decision Team . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 II. Chemical Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 A. Chemical Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 B. Use Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 C. Estimated Usage of Pesticide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 D. Regulatory History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 III. Summary of Oxadiazon Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 A. Human Health Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Toxicity of Oxadiazon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2. Dose Response Assessment and Toxicity Endpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. FQPA Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4. Dietary Risk from Drinking Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Residential and Other Non occupational Post application Risks . . . . . . . . . . . . . . . . . . . . 16 6. Occupational Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7. Incident Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 B. Environmental Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 vi 1. Environmental Fate and Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2. Water Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3. Ecological Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 4. Endangered Species Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 IV. Risk Management, Reregistration and Tolerance Reassessment Decision . . . . . . . . . . . . . . . . . . . . . 36 A. Determination of Reregistration Eligibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 B. Tolerance Reassessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 C. Regulatory Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 1. FQPA and Aggregate Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2. Endocrine Disruptor Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3. Cumulative Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4. Benefits Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 D. Tolerance Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 E. Human Health Risk Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1. Dietary ( Drinking Water) Risk Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2. Non occupational Post application Risk Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3. Occupational Risk Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 4. Inhalation Toxicity and Exposure Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 F. Environmental Risk Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 1. Terrestrial Organism Risk Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2. Aquatic Organism Risk Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 G. Other Labeling Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 1. Endangered Species Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2. Spray Drift Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 V. Actions Required of Registrants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 A. Manufacturing Use Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 1. Additional Generic Data Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 vii 2. Labeling for Manufacturing Use Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 B. End Use Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 1. Additional Product Specific Data Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2. Labeling for End Use Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 C. Labeling Requirements Summary Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 D. Existing Stocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 viii Glossary of Terms and Abbreviations AGDCI Agricultural Data Call In ai Active Ingredient aPAD Acute Population Adjusted Dose AR Anticipated Residue BCF Bioconcentration Factor CFR Code of Federal Regulations cPAD Chronic Population Adjusted Dose CSF Confidential Statement of Formula CSFII USDA Continuing Surveys for Food Intake by Individuals DCI Data Call In DEEM Dietary Exposure Evaluation Model DFR Dislodgeable Foliar Residue DWLOC Drinking Water Level of Comparison.

EC Emulsifiable Concentrate Formulation EEC Estimated Environmental Concentration.

EP End Use Product EPA Environmental Protection Agency FDA Food and Drug Administration FIFRA Federal Insecticide, Fungicide, and Rodenticide Act FFDCA Federal Food, Drug, and Cosmetic Act FQPA Food Quality Protection Act FOB Functional Observation Battery G Granular Formulation GENEEC Tier I Surface Water Computer Model GLN Guideline Number HAFT Highest Average Field Trial IR Index Reservoir LC50 Median Lethal Concentration. A statistically derived concentration of a substance that can be expected to cause death in 50% of test animals. It is usually expressed as the weight of substance per weight or volume of water, air or feed, e. g., mg/ l, mg/ kg or ppm. ix LD50 Median Lethal Dose. A statistically derived single dose that can be expected to cause death in 50% of the test animals when administered by the route indicated ( oral, dermal, inhalation). It is expressed as a weight of substance per unit weight of animal, e. g., mg/ kg.

LOC Level of Concern LOD Limit of Detection LOAEL Lowest Observed Adverse Effect Level MATC Maximum Acceptable Toxicant Concentration

g/ g Micrograms Per Gram

g/ L Micrograms Per Liter mg/ kg/ day Milligram Per Kilogram Per Day mg/ L Milligrams Per Liter MOE Margin of Exposure MUP Manufacturing Use Product MRID Master Record Identification ( number). EPA's system of recording and tracking studies submitted.

NA Not Applicable NAWQA USGS National Water Quality Assessment NPDES National Pollutant Discharge Elimination System NR Not Required NOAEL No Observed Adverse Effect Level OP Organophosphate OPP EPA Office of Pesticide Programs OPPTS EPA Office of Prevention, Pesticides and Toxic Substances PCA Percent Crop Area PAD Population Adjusted Dose PDP USDA Pesticide Data Program PHED Pesticide Handler's Exposure Data PHI Preharvest Interval ppb Parts Per Billion PPE Personal Protective Equipment ppm Parts Per Million PRZM/

EXAMS Tier II Surface Water Computer Model Q1* The Carcinogenic Potential of a Compound, Quantified by the EPA's Cancer Risk Model RAC Raw Agriculture Commodity RED Reregistration Eligibility Decision x REI Restricted Entry Interval RfD Reference Dose RQ Risk Quotient SCI GROW Tier I Ground Water Computer Model SAP Science Advisory Panel SF Safety Factor SLC Single Layer Clothing SLN Special Local Need ( Registrations Under Section 24( c) of FIFRA)

TGAI Technical Grade Active Ingredient TRR Total Radioactive Residue USDA United States Department of Agriculture USGS United States Geological Survey UF Uncertainty Factor UV Ultraviolet WPS Worker Protection Standard xi Oxadiazon Reregistration Eligibility Decision Team Office of Pesticide Programs:

Biological and Economic Analysis Division Stephen Smearman Economic Analysis Branch William Chism Herbicide and Insecticide Branch Environmental Fate and Effects Division Mike Rexrode Environmental Risk Branch 5 Jose Melendez Environmental Risk Branch 4 Faraque Khan Environmental Risk Branch 4 Health Effects Division Nancy McCarroll Toxicology Branch 1 Sheila Piper Chemistry and Exposure Branch 1 Seyed ( Nader) Tadayon Chemistry and Exposure Branch 1 Ken Dockter Reregistration Branch 2 Registration Division Joanne Miller Herbicide Branch Gene Wilson Herbicide Branch Special Review and Reregistration Division Mark Seaton Reregistration Branch 2 Tom Myers Reregistration Branch 2 1 Executive Summary This document presents the Environmental Protection Agency's ( the Agency) decision regarding the reregistration eligibility of the registered uses of oxadiazon. The Agency made its reregistration eligibility determination based on the data required for reregistration, the current guidelines for conducting acceptable studies to generate such data, and published scientific literature. The Agency has found that currently registered uses of oxadiazon are eligible for reregistration, provided specified changes are made to the label.

Oxadiazon is a herbicide registered for use on golf course and commercial turf, and on ornamental plants and shrubs by horticultural nurseries. There are no registered homeowner uses. EPA estimates that approximately 250,000 pounds of active ingredient are used annually, about 80% of which is applied to golf course turf.

Overall Risk Summary EPA's human health risk assessment for oxadiazon suggests dietary ( drinking water) and occupational risks of concern. Risk estimates based on refined ( Tier II) models indicate a chronic cancer risk of concern from exposure to drinking water from surface water sources. To further assess the risk from drinking water exposure, the Agency is requiring the registrant to submit three years of drinking water monitoring data collected from sites determined by the Agency to be likely to result in upper bound exposures.

In addition, there is a cancer risk of concern for handlers who mix/ load/ apply wettable powder formulations. To mitigate the cancer risk to handlers, the Agency is requiring changes to packaging, as well as changes to the required personal protective equipment for handlers who mix/ load/ apply wettable powder formulations.

The ecological risk assessment suggests potential chronic risks of concern to aquatic organisms from application of oxadiazon at the maximum application rate of 8 lbs ai/ A/ year to golf courses. In order to further assess the risk to fish and invertebrates from oxadiazon exposure, the Agency is requiring that the registrant submit additional early stage fish toxicity data and invertebrate life cycle toxicity data.

Dietary Risk Acute, chronic and cancer dietary risk from food are not of concern since there are no food tolerances and no registered food uses. Acute and chronic ( non cancer) risks from oxadiazon in groundwater and surface water are also not of concern. Cancer risks from surface water are potentially of concern for the general population based on modeled estimates of environmental concentrations of oxadiazon in surface water from use on golf courses. To address potential drinking water risks associated with estimated surface water concentrations resulting from the use of oxadiazon on golf course turf, the registrant has agreed to reduce the maximum annual application rate at 6 lbs ai/ A, with the exception that areas heavily infested with weeds may be treated with up to 8 lbs ai/ A. The registrant has agreed to provide additional water monitoring data to refine exposure estimates. 2 Occupational Risks Risks for occupational handlers of oxadiazon are of concern. Exposures of concern include mixing/ loading/ applying wettable powder formulations. To mitigate the cancer risk to handlers, the registrant has agreed that wettable powder formulations of oxadiazon be packaged in water soluble packaging. In addition, wettable powder product labels will require that handlers wear chemical resistant gloves in addition to long pants and a long sleeved shirt during mixing/ loading/ applying activities.

Occupational post application scenarios assessed for oxadiazon include golf course and sod farm workers engaged in turf maintenance. There are no risks of concern from occupational post application exposure scenarios.

Residential Risk There were no exposure scenarios of concern for residential risk.

Ecological Risks Oxidiazon use on golf course turf is of concern given the maximum application rates for turf and the likelihood of golf course runoff to move toward surface water. Acute risks for birds, mammals, fish, aquatic invertebrates and aquatic plants at the typical application rates for golf course turf are not of concern. Chronic risks are not a concern for birds or mammals, but are potentially of concern for aquatic organisms at the maximum application rate of 6 lbs ai/ A/ year for turf. In order to further assess the risk to fish and invertebrates from oxadiazon exposure, the Agency is requiring that the registrant submit additional toxicity data including early stage estuarine fish studies and life cycle estuarine/ marine invertebrate studies. Also, enhanced toxicity through exposure to high levels of solar radiation may increase risk to aquatic organisms that inhabit small, shallow water bodies. Therefore, EPA is requiring a study on the phototoxicity of oxadiazon in fathead minnows.

Reregistration Eligibility Decision As required under Section 4( g)( 2)( A) of FIFRA, the Agency has completed its review of oxadiazonspecific data, and has determined that the data are sufficient to support reregistration of all products containing oxadiazon provided that certain data gaps are addressed, the risk reduction measures outlined in this document are adopted and labels are amended to implement these measures. The reviewed data were sufficient to allow the Agency to determine that oxadiazon can be used without resulting in unreasonable adverse effects to humans and the environment. The Agency, therefore, finds that all products containing oxadiazon as the active ingredient are eligible for reregistration, provided specified changes are made to the label. Actions needed to reregister particular products are addressed in Section V of this document The Agency concludes that these label changes address the current risk estimates and reflect the use of all acceptable data available at this time together with uncertainty factors where data gaps exist. 3 4 I. Introduction The Federal Insecticide, Fungicide, and Rodenticide Act ( FIFRA) was amended in 1988 to accelerate the reregistration of products with active ingredients registered prior to November 1, 1984. The amended Act calls for the development and submission of data to support the reregistration of an active ingredient, as well as a review of all submitted data by the U. S. Environmental Protection Agency ( referred to as EPA or " the Agency"). Reregistration involves a thorough review of the scientific database underlying a pesticide's registration. The purpose of the Agency's review is to reassess the potential hazards arising from the currently registered uses of the pesticide; to determine the need for additional data on health and environmental effects; and to determine whether or not the pesticide meets the " no unreasonable adverse effects" criteria of FIFRA.

On August 3, 1996, the Food Quality Protection Act ( FQPA) was signed into law. This Act amends FIFRA to require tolerance reassessment during reregistration. It also requires that by 2006, EPA must review all tolerances in effect on the day before the date of the enactment. FQPA also amends the Federal Food, Drug, and Cosmetic Act ( FFDCA) to require a safety finding in tolerance reassessment based on factors including an assessment of cumulative effects of chemicals with a common mechanism of toxicity.

With respect to tolerances for oxadiazon, there have been no active food use registrations since 1991. The tolerance for rice straw was revoked as of the July 1, 2001 revision to 40 CFR 180.346. In a confirmatory letter to EPA, dated January 24, 2001, the registrant maintained its previous position that it would not support the sixteen remaining oxadiazon tolerances. Therefore, effective April 24, 2003, EPA revoked all the tolerances in 40 CFR 180.346 for the combined residues of the herbicide oxadiazon and its metabolites in the following commodities: in or on milk; cattle, fat; cattle, meat; cattle, meat byproducts; goats, fat; goats, meat; goats, meat byproducts; hogs, fat; hogs, meat; hogs, meat byproducts; horses, fat; horses, meat; horses, meat byproducts; sheep, fat; sheep, meat; and sheep, meat byproducts. In addition, because EPA determined on April 21, 2002 that there is no reasonable expectation of finite residues of oxadiazon and its metabolites in or on meat, milk, poultry, and egg commodities, the sixteen associated tolerances for livestock commodities were considered by the Agency to no longer be needed under 40 CFR 180.6( a)( 3). Therefore, on June 3, 2002, the Agency considered the FQPA safety finding to be met and counted the sixteen oxadiazon livestock tolerances as reassessed.

Given that all tolerances for oxadiazon have been revoked, this pesticide no longer falls under the scope of FQPA. As such, no quantitative aggregate assessment of risk from dietary and residential exposures was completed as part of the reregistration process. EPA has evaluated the likelihood of concurrent exposures to oxadiazon for the general population, including children. Because of the relatively low volume of use of oxadiazon on sites other than golf courses, its specialized use pattern, and its relatively high cost, concurrent exposures are not likely.

At this time, the Agency has not made a decision as to whether oxadiazon shares a common mechanism of toxicity with other oxadiazoles, or any other pesticide. A careful evaluation of all the available data is still needed, as well as peer review by the FIFRA Scientific Advisory Panel, before a formal decision is made. Therefore, for the purposes of this risk assessment, the Agency has assumed that oxadiazon does not share a 5 common mechanism of toxicity with other pesticides. After a decision is made regarding common mechanism of toxicity, and if the Agency has determined that a cumulative assessment is necessary, the Agency will address any outstanding risk concerns at that time.

This document presents the Agency's decision regarding the reregistration eligibility of the registered uses of oxadiazon, including the consideration of risk to infants, children and adults for any potential food, drinking water, dermal, inhalation or oral exposures. In an effort to simplify the RED, the information presented herein is summarized. More detailed information can be found in the technical supporting documents for oxadiazon referenced in this RED. The revised risk assessments and related addenda are not included in this document, but are available on the Agency's web page at www. epa. gov/ pesticides, and in the Public Docket.

This document consists of six sections. Section I is the introduction. Section II provides a profile of the use and usage of oxadiazon, and its regulatory history. Section III gives an overview of the human health and environmental assessments, based on the data available to the Agency. Section IV presents the reregistration eligibility and risk management decisions. Section V summarizes the necessary label changes based on the risk mitigation measures outlined in Section IV. Finally, the Appendices list all related documents and how to access them, and Data Call In ( DCI) information. 6 II. Chemical Overview A. Chemical Identification ° Common name: Oxadiazon ° Chemical name: [ 2 tert butyl 4( 2,4 dichloro 5 isopropoxyphenyl)  2 1,3,4 oxadiazoline 5 one]

° Empirical formula: C 15 H 18 Cl 2 N 2 O 3 ° CAS Registry No.: 19666 30 9 ° Case number: 2485 ° OPP Chemical Code: 109001 ° Molecular weight: 345.2 ° Trade name: Ronstar ° Basic manufacturer: Bayer Environmental Science Technical oxadiazon is a white, crystalline powder with a melting point of 90

C. Oxadiazon is stable for 30 days at 55

C, and is stable in the presence of aluminum, iron and tin powders ( but not ferric chloride). The water solubility of oxadiazon is 0.7 mg/ L at 20

C. Oxadiazon has a vapor pressure of 7.76 x 10 7 mm Hg.

B. Use Profile Oxadiazon is labeled for professional use only. The label indicates that the purchase, storage and application of this pesticide are limited to commercial nursery, turf and landscape personnel. The product is 7 not available to homeowners. The following is information on the currently registered uses of oxadiazon. A detailed table of the uses of oxadiazon eligible for reregistration is contained in Appendix A.

° Type of Pesticide and Target Pests: Oxadiazon is a pre emergent or early post emergent oxadiazole herbicide used to control grassy weeds ( e. g., goosegrass and crabgrass) and broadleaf weeds in turf and ornamentals. Oxadiazon works by interfering with the pathway for chlorophyll production, and results in a breakdown of plant tissue on exposure to light.

° Use Sites: Oxadiazon is registered for commercial use on residential turf ( i. e., apartment/ condominium complexes, parks, athletic fields, playgrounds, and cemeteries) and on golf courses ( predominant use). In addition, oxadiazon is used on sod farms and on conifer nurseries and landscapes ( i. e., industrial sites, ornamental, roadside plantings, woody, ornamental shrubs, vines and trees, and herbaceous ornamentals). Oxadiazon use sites are classified as nonfood sites ( i. e., primarily golf course fairways), residential outdoor use, roadsides and nurseries.

° Formulation Types Registered: Oxadiazon is formulated as a granular ( predominant formulation, ~ 90% of total use) and wettable powder.

° Method and Rates of Application Equipment: Granular formulas are applied using mechanical spreaders, manual spreaders ( i. e., belly grinder, push type spreader) or tractor drawn spreaders. Methods of application associated with the other formulation and use patterns of oxadiazon include: groundboom, rights of way sprayer, handgun sprayer, backpack sprayer, low pressure handwand, high pressure handwand, and lawn handgun.

Rates: The frequency of application ranges from 1 to 3 applications per season. Oxadiazon can be applied at a minimum single application rate of 2.0 pounds active ingredient per acre ( ai/ A) up to a maximum single application rate of 4.0 pounds ai/ A to turf and ornamentals. The annual maximum application rate is 8 lbs ai/ A/ year.

Use Classification: Not classified.

C. Estimated Usage of Pesticide Approximately 250,000 pounds of oxadiazon are applied to approximately 50,000 acres annually. Oxadiazon is used primarily in southern states and predominantly on golf courses. Table 1 summarizes the EPA's best available estimates for the pesticide uses of oxadiazon. These estimates are derived from a variety of published and proprietary sources available to the Agency.

Table 1. Oxadiazon Usage Summary 8 Crop Lbs. Active Ingredient Applied ( Wtd. Avg.) 1 Percent Crop Treated ( Likely Maximum) Percent Crop Treated ( Wtd. Avg.) 1 Turf:

Golf Courses 160,000 6% 3%

Landscape, Rights of way, Parks 28,000

Horticultural Nurseries 56,000

1Wtd Avg ( weighted average): the most recent years and more reliable data are weighted more heavily.

: missing information or lack of confidence in the data.

D. Regulatory History Oxadiazon was registered in 1978. A Phase Four generic data call in ( DCI) was issued in May of 1991. Due to additional data required under FIFRA as amended in 1988, the oxadiazon registrant decided to no longer support food uses of oxadiazon. With respect to tolerances for oxadiazon, there have been no active food use registrations since 1991. The tolerance for rice straw was revoked as of the July 1, 2001 revision to 40 CFR 180.346. In a confirmatory letter to EPA, dated January 24, 2001, the registrant maintained its previous position that it would not support the sixteen remaining oxadiazon tolerances. Therefore, effective April 24, 2003, EPA revoked all the tolerances in 40 CFR 180.346 for the combined residues of the herbicide oxadiazon and its metabolites in the following commodities: in or on milk; cattle, fat; cattle, meat; cattle, meat byproducts; goats, fat; goats, meat; goats, meat byproducts; hogs, fat; hogs, meat; hogs, meat byproducts; horses, fat; horses, meat; horses, meat byproducts; sheep, fat; sheep, meat; and sheep, meat byproducts. In addition, because EPA determined on April 21, 2002 that there is no reasonable expectation of finite residues of oxadiazon and its metabolites in or on meat, milk, poultry, and egg commodities, the sixteen associated tolerances for livestock commodities were considered by the Agency to no longer be needed under 40 CFR 180.6( a)( 3). Therefore, on June 3, 2002, the Agency considered the FQPA safety finding to be met and counted the sixteen oxadiazon livestock tolerances as reassessed. There are no CODEX, Canadian, or Mexican tolerances for oxadiazon residues. 9 III. Summary of Oxadiazon Risk Assessments A. Human Health Risk Assessment 1. Toxicity of Oxadiazon Details of the hazard assessment of oxadiazon can be found in the revised Human Health Risk Assessment for Oxadiazon, dated June 6, 2003 ( McCarroll, 2003). Major features of the toxicology profile are presented below. In acute studies, oxadiazon was only slightly toxic to rats and rabbits. In rabbits, oxadiazon was mildly irritating to ocular tissue and negligibly irritating to the skin, and in guinea pig studies, oxadiazon was not a dermal sensitizer ( Table 2).

Table 2. Acute Toxicity Data on Oxadiazon Guideline No./ Study Type MRID No. Results Toxicity Category 870.1100 Acute oral toxicity ( rat) 41866501 ( 97.5% a. i.) LD50 > 5000 mg/ kg

,  combined IV 870.1200 Acute dermal toxicity ( rabbit) 41866502 ( 97.5% a. i.) LD50 > 2000 mg/ kg,

,  combined III 870.1300 Acute inhalation toxicity ( rat) 41866503 ( 93.7% a. i.) LC50 > 1.94 mg/ L

,  combined III 870.2400 Acute eye irritation ( rabbit) 41866504 ( 97.5% a. i.) Mild irritant to ocular tissues III 870.2500 Acute dermal irritation ( rabbit) 41866505 ( 97.5% a. i.) Negligibly irritating to skin III 870.2600 Skin sensitization ( guinea pig) 41230401 ( 93.7% a. i.) Not a dermal sensitizer ( Buehler test)

In both subchronic and chronic studies, the major target organ of oxadiazon toxicity was the liver. Effects were consistent among the species tested ( rat, dog, mouse) and typically included enlarged livers along with increases in serum clinical chemistry parameters associated with hepatotoxicity such as alkaline phosphatase and serum aspartate or alanine aminotransferase.

Following long term dietary administration, oxadiazon caused an increased incidence of hepatocellular adenoma and carcinoma in rats and mice. Consistent findings were reported in a total of four acceptable 10 studies in two species ( two mouse and two rat studies). A third mouse study was unacceptable, although increased hepatocellular tumors were also observed in mice of both sexes. A classification of " likely to be carcinogenic to humans" was assigned by the Cancer Assessment Review Committee ( CARC). A quantitative risk ( Q 1*) of 7.11 x 10 2 ( mg/ kg/ day) 1 was calculated as the most potent unit risk, based on the incidence of male mouse liver adenoma and/ or carcinoma combined tumor rates in the ICR JCL mouse.

In a special submitted mechanistic study in rats and a published study in rats, mice and dogs, oxadiazon induced peroxisomal proliferation ( based on liver enlargement, peroxisomal enzyme induction and electron microscopy) after a 14 day dietary administration. Some peroxisomal proliferator compounds are known to be liver carcinogens, but the Health Effects Division Mechanism of Toxicity Assessment Review Committee ( MTARC) concluded that there is insufficient evidence to support peroxisome proliferation as a mechanism of carcinogenicity for oxadiazon due to insufficient data showing hepatocellular proliferation, lack of concordance between the enzyme induction dose response and tumor formation, and an unexplained decrease in catalase, which is normally significantly increased by peroxisomal proliferator compounds.

Oxadiazon did not show mutagenic potential in any in vitro assays with bacteria ( S. typhimurium and E. coli) or mammalian cells ( TK +/ mouse lymphoma cells), did not show clastogenic potential in the in vitro Chinese hamster ovary cell chromosomal aberration assays and did not induce unscheduled DNA synthesis in cultured primary rat hepatocytes. However, a dose related increase in transformation frequencies was observed in an in vitro Syrian hamster kidney BHK21 C13/ HRC1 cell transformation assay.

Significant fetal toxicity ( fetal loss due to resorptions and post implantation loss, decreased fetal weight, skeletal variations) was observed in developmental toxicity studies in both rats and rabbits. These fetal effects occurred at the same dose levels at which slight maternal toxicity ( decreased weight gain/ weight loss) were observed. Offspring survival effects were also observed in the rat two generation reproduction study. No toxicity was reported at the lowest dose tested; however, in the range finding phase of the reproduction study at higher dose levels, fetal and neonatal survival were also sharply reduced. The decreased neonatal survival was due at least in part to effects on lactation, based on findings of inactive mammary glands in the dams at necropsy. Neonatal loss may have resulted from starvation and would, therefore, be an effect of direct maternal toxicity. Inactivity of the mammary tissue as a possible effect of endocrine disruption was considered by the Hazard Identification Assessment Review Committee ( HIARC) but was not found to be likely since there was no evidence from any other study in the database suggesting endocrine disruption. No fetal malformations were observed in the rat or rabbit developmental toxicity studies; however, some skeletal variations ( delayed ossification, asymmetric pelvis) were reported. The above findings indicate that there is no quantitative evidence of increased susceptibility of rats or rabbits following in utero or postnatal exposure to oxadiazon.

Neurotoxicity studies are not required for oxadiazon because no clinical signs of toxicity suggestive of neurobehavioral alterations nor evidence of neuropathological effects were observed in any of the available toxicity studies. There was no evidence of neurotoxicity of oxadiazon in the rat and rabbit developmental toxicity studies, nor in the rat two generation reproduction toxicity study.

Based on the available data, the Metabolism Assessment Review Committee ( MARC) concluded that the only residue of concern is the parent compound, oxadiazon, because major degradation products would only be minor components in the environment and are not likely to be significantly more toxic than the parent. 11 The only toxicity data gap that has been identified at this time is a 28 day inhalation study ( OPPTS No. 870.3465). This study is being required by the Agency because some currently registered products of oxadiazon include spray formulations which could result in exposure via the inhalation route.

2. Dose Response Assessment and Toxicity Endpoints The HIARC concluded that neither an acute nor a chronic reference dose ( RfD) was required for oxadiazon because there are no food or feed uses. A short term oral endpoint was selected for incidental oral exposure in children, using a No Observed Adverse Effect Level ( NOAEL) of 12 mg/ kg/ day based on a statistically significant decrease in maternal body weight gains at 40 mg/ kg/ day ( LOAEL) in a developmental study in rats ( Table 3). The same endpoint was selected for short term and intermediate dermal exposure.

In the absence of food or feed uses, HIARC did not select an acute RfD for oxadiazon. In order to estimate acute drinking water risk, EPA has used the same study and endpoint described above for short term incidental exposure. For the acute drinking water assessment an uncertainty factor of 100 was applied, based on a 10X for intraspecies variation and a 10X for interspecies extrapolation. Therefore, the " theoretical acute RfD" would be 0.12 mg/ kg/ day. When maternal toxicity can be attributed to a single dose ( e. g, body weight loss in the early dosing period), the developmental studies can be selected for the acute RfD, the short term ( 1 7 days) incidental oral exposure and/ or the intermediate ( 7 days to several months) because the critical effect ( in the case of oxadiazon, body weight loss at days 16 20 which was possibly due to resorption of fetuses) occurred during the treatment period which encompasses both exposure periods of concern. It is reasonable to assume that effects were possibly manifested by exposure to a single dose and the resulting body weight loss did not become apparent until after 7 days.

A chronic RfD was not selected by HIARC because the lack of food or feed uses. However, for the purpose of assessing potential risks from drinking water, EPA has used the chronic/ oncogenicity feeding study. For the chronic drinking water assessment, an uncertainty factor of 100 was applied based on a 10x factor for intraspecies variation and a 10x factor for interspecies extrapolation. This chronic oral endpoint was based on increased incidence of swollen cells in the central lobe of the livers of male rats observed at the LOAEL of 3.5 mg/ kg/ day. The NOAEL in this study was 0.36 mg/ kg/ day. Therefore, the " theoretical chronic RfD" would be 0.0036 mg/ kg/ day. For long term dermal exposure, this same endpoint was selected. The HIARC recommended that a dermal absorption factor of 9% be used in the calculations, based on a dermal penetration study.

Due to a lack of inhalation studies, the HIARC selected an endpoint from oral studies for inhalation risk assessments. For short and intermediate term inhalation exposure, the same oral study was chosen as for dermal exposure of these durations, with a NOAEL of 12 mg/ kg/ day. The same chronic/ oncogenicity feeding study in rats chosen for dermal exposure of this duration was selected for the long term inhalation exposure, with a NOAEL of 0.36 mg/ kg/ day. An absorption factor of 100% was applied for inhalation exposures.

A level of concern, referred to as a Margin Of Exposure or MOE, of 100 for occupational and residential exposure scenarios was calculated using a 10x factor for intraspecies variation and a 10x factor for interspecies extrapolation. Because the effects from dermal and inhalation exposure are the same, the doses for these routes and duration were combined. Dermal and incidental oral exposures for toddlers were also combined to reflect a total exposure burden. 12 Table 3: Endpoints for Oxadiazon Risk Assessment EXPOSURE SCENARIO DOSE ( mg/ kg/ day) ENDPOINT STUDY Incidental Oral, Short Term and Intermediate Term NOAEL= 12 Maternal effects Reduced body weight/ body weight gain at 40 mg/ kg/ day ( LOAEL). Developmental Toxicity  Rat MRID No. 40470202 Dermal, Short Term and Intermediate Term NOAEL= 12 Maternal effects/ Developmental effects Reduced body weight/ body weight gain at 40 mg/ kg/ day ( LOAEL) / Increased fetal resorptions/ postimplantation loss, increased incidence of incomplete ossification at 40 mg/ kg/ day ( LOAEL). For this risk assessment, the dermal absorption rate of 9% is applied. Developmental Toxicity  Rat MRID No. 40470202 Dermal, Long Term NOAEL= 0.36 Increased centrilobular swelling in male livers at 3.5 mg/ kg/ day ( LOAEL). For this risk assessment, the dermal absorption rate of 9% is applied. Combined Chronic Feeding/

Oncogenicity  Rat MRID Nos. 40993401, 00149003/ 00157780 Inhalation, Short Term and Intermediate Term NOAEL= 12 Maternal effects/ Developmental effects Reduced body weight/ body weight gain at 40 mg/ kg/ day ( LOAEL) / Increased fetal resorptions/ postimplantation loss, increased incidence of incomplete ossification at 40 mg/ kg/ day ( LOAEL). For this risk assessment, a 100% absorption rate is applied Developmental Toxicity  Rat MRID No. 40470202 Dietary, Long term NOAEL= 0.36 Increased centrilobular swelling in male livers at 3.5 mg/ kg/ day ( LOAEL). Combined Chronic Feeding/

Oncogenicity  Rat MRID Nos. 40993401, 00149003/ 00157780 Inhalation, Long Term NOAEL= 0.36 Increased centrilobular swelling in male livers at 3.5 mg/ kg/ day ( LOAEL). A 100% absorption rate applied. Combined Chronic Feeding/

Oncogenicity  Rat MRID Nos. 40993401, 00149003/ 00157780 Cancer Q 1* of 7.11 x 10 2 ( mg/ kg/ day) 1 Significant increase ( pair wise and trend, p< 0.01) in liver adenomas and/ or carcinomas combined in males at

9.3 mg/ kg/ day). Combined Chronic Feeding/

Carcinogenicity  Mouse MRID Nos. 40993301 3. FQPA Considerations On August 3, 1996, the Food Quality Protection Act of 1996 ( FQPA) was signed into law. This Act amends FIFRA to require tolerance reassessment during reregistration. With respect to tolerances for oxadiazon, there have been no active food use registrations since 1991. Effective April 24, 2003, EPA revoked all the tolerances in 40 CFR 180.346 for the combined residues of the herbicide oxadiazon and its metabolites. In addition, the Agency considered the FQPA safety finding to be met and counted the sixteen oxadiazon livestock tolerances as reassessed.

Given that there are no remaining food/ feed uses for oxadiazon, and given that all food tolerances have been revoked, this pesticide no longer falls under the scope of FQPA. As such, no quantitative aggregate 13 assessment of risk from dietary and residential was conducted. EPA has qualitatively evaluated the likelihood of concurrent exposures from different sources of oxadiazon for the general population, including children. Because of the relatively low volume of oxadiazon use on sites other than golf courses, its specialized use pattern, and its relatively high cost, concurrent exposures are not expected.

Only 15% ( or about 28,000 pounds) of the oxadiazon that is applied each year is used on parks, landscapes, rights of way, etc., and this use is distributed across five or more states. An even smaller portion of the 28,000 pounds is used on sites where people, including children could be exposed, such as parks. Because of its comparatively high cost, oxadiazon is not routinely used in residential lawn care. Furthermore, the exposure assumption in both the residential and drinking water assessments are sufficiently protective to account for the unlikely event of exposure from more than one source.

With respect to sensitivity in children, there is no evidence of either a qualitative or quantitative increase in susceptibility of rats or rabbits to in utero and/ or postnatal oxadiazon exposure. Although significant fetal toxicity was observed in developmental toxicity studies in both rats and rabbits ( i. e., fetal loss due to resorptions and post implantation loss) and in a two generation reproduction study ( i. e., reduced neonatal survival), these fetal/ neonatal effects occurred at the same doses that caused maternal toxicity. It is also likely that neonatal losses resulted from starvation and could, thus, be a possible direct maternal toxic effect. Inactivity of the mammary tissue as a possible endocrine disruption effect was considered but was found to be unlikely since there was no evidence from any other study in the database suggesting endocrine disruption.

4. Dietary Risk from Drinking Water Since there are no food/ feed uses of oxadiazon and no tolerances exist, dietary risk from oxadiazon can only result through exposure in drinking water. Drinking water exposure to pesticides can occur through ground and surface water contamination. EPA considers acute, chronic non cancer, and chronic cancer drinking water risks and uses modeling and monitoring data, if available, to estimate those risks. To determine the maximum contribution from water allowed in the diet, EPA first looks at how much of the overall allowable risk is contributed by food and then determines a " drinking water level of comparison" ( DWLOC) to ascertain whether or not modeled or monitored concentrations exceed this level. In the case of oxadiazon, there is no contribution from food. Estimated environmental concentrations ( EECs) that are above the corresponding DWLOC exceed the Agency's level of concern.

Based on its review of submitted studies, the EPA has concluded that oxadiazon would be stable and persistent under typical terrestrial environmental conditions. In the absence of measured environmental concentrations of oxadiazon from monitoring studies, and based on environmental fate characteristics, potential oxadiazon concentrations in unfinished drinking water were estimated using Tier 2 PRZM/ EXAMS ( surface water) and Tier 1 SCIGROW ( ground water) models. The PRZM/ EXAMS model as used here is a standard turf scenario that includes a two centimeter layer of thatch, and is referred to as the Florida Turf Scenario.

The combined (" linked") PRZM/ EXAMS model is typically used by EPA in estimating pesticide concentrations in surface waters. The PRZM model estimates the amount of pesticide that reaches a body of surface water as a result of runoff. The EXAMS model estimates pesticide concentrations by taking into account different mechanisms for dissipation, weather patterns, and periodic application of pesticide, for 14 several years. The PRZM/ EXAMS model generates concentration estimates of acute ( one in ten year peak concentration), non cancer chronic ( one in ten year mean concentration) and chronic cancer ( 36 year mean concentration).

As used here, the PRZM/ EXAMS estimates of pesticide concentrations in surface water generated by this linked model can be considered to be upper bound estimates. Several conservative parameter values have been incorporated into the mathematical formulas, including a calculated factor for the half life of oxadiazon in water. The Florida Turf Scenario introduces a two inch thatch layer as an intercept to incorporation of oxadiazon with soil particles. As typically applied, oxadiazon granules are watered into the soil surface, thereby mediating the potential effects of the thatch layer. Also, an assumption in the current model is that oxadiazon is applied as a wettable powder formulation ( i. e., applied as a spray), and therefore the model includes a value for spray drift into water bodies.

An additional conservative parameter incorporated into the model is the value for percent crop area ( PCA). The term PCA refers to the area of land around a watershed that is planted with crops to which a specific pesticide will be applied. In the example of oxadiazon, the primary application site is golf course turf. In the present model, a PCA value of 94% was used to account for the land area of a typical golf course that is greens, tees, fairway ( 27%) and rough ( 67%). The EPA makes the protective assumption that 94% of land area around a particular watershed might possibly be made up of golf course, and that 100% of the golf courses in the watershed apply oxadiazon at the maximum application rate and frequency. Registrants have submitted a GIS analysis suggesting that the upper bound limit of PCA for turf ( including golf courses and other recreational turf) in south Florida is substantially less than 94%. Model derived surface water EECs and DWLOCs are summarized in Table 4.

The SCIGROW model is typically used for Tier 1 screening purposes for pesticides applied to soils. The SCIGROW model is based on leaching studies conducted in sandy soils above shallow aquifers, and estimates likely groundwater concentration. In areas with those characteristics, groundwater is particularly vulnerable to contamination. The SCIGROW model estimated environmental concentration for oxadiazon in groundwater is 0.59 ppb.

Table 4. Surface Water DWLOC and EEC Comparisons Acute DWLOC ( ppb) Acute EEC ( ppb) Chronic ( noncancer

DWLOC ( ppb) Chronic ( noncancer

EEC ( ppb) Chronic ( cancer)

DWLOC ( ppb) Chronic ( cancer)

EEC ( ppb)

Infants (< 1 year) 1200 181 36 65 0.49 56 Children ( 1 6 years) 1200 36 Females ( 13 50 years) 3600 108 U. S. population 4200 126 Ground Water DWLOC and EEC Comparisons Table 4. Surface Water DWLOC and EEC Comparisons 15 Infants (< 1 year) 1200 0.59 36 0.59 0.49 0.59 Children ( 1 6 years) 1200 36 Females ( 13 50 years) 3600 108 U. S. population 4200 126 a. Acute Drinking Water Risk Acute DWLOCs were calculated for oxadiazon based on results of a developmental toxicity study. The No Observable Adverse Effect Level ( NOAEL) was 12 mg/ kg/ day, with the toxicity endpoint being a reduction in maternal body weight gain at the Lowest Observable Adverse Effect Level ( LOAEL) of 40 mg/ kg/ day. The rationale for selection of this endpoint is provided in the " Dose Response and Toxicity Endpoint" section of this document. Based on a comparison of DWLOCs to the corresponding PRZM/ EXAMS ( surface water) and SCIGROW ( groundwater) estimates ( EECs), the EECs for surface water ( 181 ppb) and groundwater ( 0.59 ppb) were less than the DWLOCs calculated for all populations ( 1200  4200 ppb) and, thus, the Agency concludes that acute exposure to residues of oxadiazon in surface and groundwater sourced drinking water is not of concern.

b. Chronic Drinking Water Risk Chronic DWLOCs were calculated based on a chronic toxicity/ carcinogenicity study. The NOAEL was 0.36 mg/ kg/ day, based on the endpoint of centrilobular swelling in male rats, observed at the LOAEL of 3.5 mg/ kg/ day. The rationale for selection of this endpoint is provided in the " Dose Response and Toxicity Endpoint" section of this document. Using the PRZM/ EXAMS model estimates, the EECs for surface water ( 65 ppb) were higher than the DWLOCs calculated for infants and children ( 36 ppb) ( Table 4) and thus, potentially of concern. The chronic ground water EEC of 0.59 ppb was less than the chronic ( noncancer) DWLOC of 36 for the most sensitive subpopulations ( children less than 1, and children 1 6 years) and is not a concern.

c. Cancer Drinking Water Risk For the cancer exposure calculations, the Agency used multi year mean water concentration values. The DWLOC cancer is the concentration in drinking water that results in a negligible cancer risk of one in a milion ( 1.0 x 10 6). The cancer ground water EEC of 0.59 ppb slightly exceeds the DWLOC of 0.49. However, given the protective exposure assumptions, this slight exceedence is not of concern. The cancer EEC for surface water ( 56 ppb) exceeds the cancer DWLOC ( 0.49 ppb) ( Table 4) and thus, is potentially of concern.

5. Residential and Other Non occupational Post application Risks Since oxadiazon is only available to professional turf, landscape, and nursery personnel, there are no residential handler scenarios. Although oxadiazon is not available for homeowner use, the Agency has determined that there are potential postapplication exposures to residents entering oxadiazon treated turf and 16 lawns. A complete discussion of potential residential exposures, including the sources of exposure data and toxicity information is found in the document " Revised Occupational and Residential Exposure Assessment and Recommendations for the Reregistration Eligibility Decision Document for Oxadiazon" dated June 7, 2003 ( Tadayon, 2003) on the Agency's web page at www. epa. gov/ pesticides, and in the Public Docket.

The scenarios likely to result in postapplication exposures in non occupational situations are presented below. The duration of postapplication dermal exposure is expected to be either short term or intermediateterm based on oxadiazon turf residue dissipation data. Oxadiazon has a half life on turf of up to 1.4 days ( irrigated) and 1.7 days ( non irrigated) after spraying, requiring several days to dissipate to non detectable levels of transferable residues ( MRID # 435178 01). Because the label prohibits application more than 3 times per year, and even with the slow dissipation rates, it is not expected that individual residential exposure duration would exceed 30 days in duration. Exposure on a residential lawn would diminish continuously with time, while exposure through recreation turf contact would more likely be random intermittent events of varying doses, all less than the dose predicted in this assessment. Residential postapplication exposure assessments assume that residents wear the following attire: short sleeved shirt, short pants, shoes and socks, and no gloves or respirator. The scenarios likely to result in postapplication exposures are as follows:

° dermal postapplication risks to adults and toddlers when entering oxadiazon treated turf and lawns;

° oral postapplication risks to toddlers from " hand to mouth" ( i. e., ingestion of grass, soil, granular pellets, or hand to mouth contact) exposure when reentering lawns treated with granular and wettable powder formulations.

Representative turf reentry activities include, but are not limited to:

° Adults involved in a low exposure activity, such as golfing or walking on treated turf.

° Toddlers involved in a low exposure activity, such as walking on treated turf.

° Adults mowing or other moderate contact activity, for 1 2 hours.

° Adults involved in a high exposure activity, such as heavy yard work ( doses similar to occupational scenarios for cutting and harvesting sod).

° Toddlers involved in high exposure activities on turf.

For risk assessment purposes, Margins of Exposure ( MOEs) compare the estimated exposure concentration to a No Observed Adverse Effect Level ( NOAEL) from an animal study. In the case of oxadiazon, the Agency's level of concern for residential post application risk is exceeded if MOEs fall below 100. The target MOE of 100 for non occupational exposure scenarios was selected based on the uncertainty factors of 10x for intraspecies variation and 10x for interspecies extrapolation.

The registrant submitted a study on turf transferable residues ( TTR) in response to an occupational/ residential exposure Data Call In, and in support of oxadiazon re registration requirements. Ronstar ® 50 WP a wettable powder product containing ~ 50 % oxadiazon, was applied to turf in North Carolina. The study was conducted in order to quantify the dermal exposure associated with re entry onto oxadiazon treated turf. Ronstar ® 50 WP which is labeled for use on dormant, Bermuda grass, St. Augustine grass and Zoisia turf in areas such as fairways, parks, and lawns was used at a maximum label rate of 3 .0 lb ai/ A. Two different exposure scenarios were monitored: 17  Application at the maximum label rate followed by re entry as soon as the turf was dry.

 Application followed within 30 minutes by sprinkler irrigation of 1/ 10 inch of water with re entry occurring as soon as the turf is dry.

Utilizing the transferable residue data and revised residential SOPs, all of the non cancer risk scenarios developed for adults and children had short term and intermediate term dermal MOEs greater than 100. The cancer risks for all adult, non occupational, dermal, post application exposures ranged from 6 x 10 6 to 8 x 10 7 . Although the estimated cancer risk slightly exceeds the Agency's level of concern ( 1.0 x 10 6), that estimate is conservative given that the risk assessment was performed with a spray application, whereas approximately 90% of oxadiazon is applied as a granular formulation. The granule size for a typical end use product, Ronstar G, is 20/ 50 Mesh, or 300 850 microns. In all instances, the granules are designed to fall below the grass canopy and into the thatch layer. If used according to label directions, it is unlikely that oxadiazon granules would be accessible to a child or adult. According to the registrant, for best results oxadiazon granules should be watered in as soon as is practical following application. Watering in the granules will carry them further into the thatch layer, and will further decrease the likelihood of dermal exposure.

Estimated incidental oral short term exposures (" hand to mouth") for children had an MOE of 100 using the TTR default values from the residential SOP; when the TTR data from a submitted oxadiazon study were used, the MOEs were 240 and 90 for irrigated and non irrigated turf, respectively.

MOEs were not calculated for the incidental ingestion of oxadiazon granules because, as discussed above, the very small granules would not be available on the lawn surface and thus not accessible to children. It is thought, therefore, that the incidental ingestion of granules is not likely to be a cause for concern.

6. Occupational Risk a. Occupational Toxicity For risk assessment purposes, Margins of Exposure ( MOEs) compare the estimated exposure concentration to a No Observed Adverse Effect Level ( NOAEL) from an animal study. In the case of oxadiazon, the Agency's level of concern for occupational risk is exceeded if MOEs fall below 100. The target MOE of 100 for occupational exposure scenarios was selected based on the uncertainty factors of 10x for intraspecies variation and 10x for interspecies extrapolation. The short term and intermediate term MOEs for occupational risk were calculated based on a NOAEL of 12 mg/ kg/ day from a rat developmental toxicity study. The LOAEL in this study was 40 mg/ kg/ day; the endpoint is reduced bodyweight gain.

The short term and intermediate term MOEs for dermal and inhalation exposures were calculated using an oral NOAEL of 12 mg/ kg/ day for both exposure durations ( see Human Health Risk Assessment Section 3.3 Dose Response Assessment). The Agency also used route to route extrapolations to convert this oral dose to dermal and inhalation doses. A dermal absorption rate of 9% was applied to the dermal exposure assessments and an inhalation absorption rate of 100% was applied to the inhalation exposure assessments. 18 Since the effects from dermal and inhalation exposure are based on the same oral study ( i. e. rat developmental toxicity study), the exposures for these routes and durations were combined.

b. Occupational Handler Exposure Occupational exposure to oxadiazon via the dermal and inhalation routes may occur during mixing, loading and applying through the use of ground spray, granular and other turf application methods. Based on the use patterns, 14 major occupational exposure scenarios were identified for oxadiazon:

( 1a) mixing/ loading wettable powders for chemigation application;

( 1b) mixing/ loading wettable powders for groundboom application;

( 1c) mixing/ loading wettable powders for rights of way sprayer;

( 2) loading granular formulations;

( 3) applying sprays with a groundboom;

( 4) applying sprays with a rights of way sprayer;

( 5) applying wettable powder sprays with handgun sprayer;

( 6) applying granules with a tractor drawn spreader;

( 7) mixing/ loading/ applying sprays with a backpack sprayer;

( 8) mixing/ loading/ applying sprays with a low pressure handwand ( wettable powder formulations);

( 9) mixing/ loading/ applying sprays with a high pressure handwand ( wettable powder formulations);

( 10) mixing/ loading/ applying sprays with a lawn handgun ( wettable powder formulations);

( 11) mixing/ loading/ applying granules with a push type spreader; and,

( 12) mixing/ loading/ applying granules with a bellygrinder.

Maximum single application rates for oxadiazon range from 3 to 4 lb. ai/ acre, with the higher rate being applied to golf courses, roadside turf, lawns, parks, recreational areas and woody ornamentals.

The exposure scenarios are of short term ( 1 30 days) and intermediate term ( 30 days to several months). Since the use patterns for oxadiazon do not suggest any long term use, exposure scenarios of a longer duration were not considered. The estimated exposures considered:

 baseline protection ( long pants, long shirts and no gloves  dermal; no respirator  inhalation),

 additional PPE ( long pants, long shirts and chemical resistant gloves and/ or double layer of clothing  dermal; plus 80% protection from dust/ mist respirator  inhalation), and  engineering controls ( use of water soluble packages for wettable powder formulations).

EPA completed handler exposure assessments first assuming the baseline level of protection and, if required, increasing levels of risk mitigation ( PPE and engineering controls) to achieve an MOE of 100 or 19 more for non cancer risks. The Agency's assumptions for specific categories of handlers and equipment are as follows:

$ all occupational handlers are wearing footwear ( socks plus shoes or boots)

$ occupational mixers and loaders using open mixing techniques are wearing long sleeved shirts and long pants and gloves; this represents minimum PPE $ occupational mixers and loaders using open mixing techniques are wearing long sleeved shirts and long pants, coveralls and gloves; this represents maximum PPE $ occupational applicators who use open cab tractor driven application equipment are wearing longsleeved shirts and long pants and gloves; this represents minimum PPE.

$ Also, if necessary, dust/ mist respirator represented by 5 fold protection factor or an organic vapor respirator represented by a 10 fold protection factor are added to mitigate the risks.

Engineering control assumptions are as follows:

$ engineering controls are not available for occupational handlers ( mixers, loaders, and applicators) who use hand held application equipment.

$ occupational mixers and loaders handling liquid formulations using a closed system are wearing chemical resistant gloves plus long sleeved shirts and long pants.

$ occupational mixers and loaders handling wettable powders using a closed system ( water soluble packages) are wearing long sleeved shirts and long pants, and chemical resistant gloves.

$ occupational applicators who use tractor driven application equipment are located in enclosed cabs are wearing long sleeved shirts and long pants, and no gloves.

Chemical specific data for assessing human exposures during pesticide handling activities were not submitted to the Agency in support of the reregistration of oxadiazon. In such instances, it is the policy of the EPA to use data from the Pesticide Handlers Exposure Database ( PHED) Version 1.1 to assess handler exposures for regulatory actions when chemical specific monitoring data are not available. EPA's level of confidence in these data are explained in detail in the " Revised Occupational and Residential Exposure Assessment and Recommendations for the Reregistration Eligibility Decision Document for Oxadiazon" dated June 7, 2003 ( Tadayon, 2003).

c. Occupational Risk ( noncancer)

The results of the short and intermediate term handler assessments are presented in Table 5 and indicate that potential non cancer exposure scenarios have MOE( s) greater than or equal to 100 at either the baseline ( i. e., long pants, long sleeved shirts, no gloves), PPE ( i. e., long pants, long sleeved shirts, and chemical resistant gloves while using open systems) or using engineering controls ( i. e., water soluble packages). The only exception, for which engineering controls are not feasible, is scenario 8 ( low pressure handwand wettable powder formulations), with a total MOE of 46 with maximum PPE. The low pressure hand wand applicator is likely to be used in non turf areas of golf courses, such as landscaping. 20 Table 5: Exposure Variables ( Noncancer) and MOEs for Uses of Oxadiazon Exposure Scenario ( Scenario #) Crop Type App Rates ( lb ai/ acre) Daily Acres Treated Total MOEs Base line PPE Eng. Control Mixer/ Loader Mixing/ Loading Wettable Powders for Chemigation Application ( 1a) sod farms 3 350 2 35 610 Mixing/ Loading Wettable Powders for Groundboom Application ( 1b) conifer nurseries, woody ornamentals 4 40 12 220 NA herbaceous ornamentals 3 40 16 300 NA sod farms 3 80 8 150 NA golf courses 4 40 12 220 NA Mixing/ Loading Wettable Powders for Rights of Way Sprayer ( 1c) roadside turf, ornamentals 4 40 12 220 NA Loading Granular formulations ( 2) sod farms, conifers forest 4 80 920 NA NA golf course turf, parks, recreational areas 4 40 1800 NA NA woody ornamentals 4 40 1800 NA NA Applicator Applying with a Groundboom ( 3) sod farms 3 80 1500 NA NA herbaceous ornamentals 3 40 3000 NA NA golf courses 4 40 2300 NA NA conifer nurseries, woody ornamentals 4 40 2300 NA NA Applying with a Rights of Way Sprayer ( 4) roadsides 4 40 37 120 NA Applying Wettable Powders for Handgun Applicators ( ORETF) ( 5) lawns, parks, recreational areas 4 5 See PPE 540 NA Applying Granular with a Tractor Drawn Spreader ( 6) sod farms 4 80 1100 NA NA golf courses 4 40 2200 NA NA Mixer/ Loader/ Applicator Backpack Sprayer ( LCO) ( 7) l awn s , g o l f c ou r se s , ornamentals nurseries 4 5 See PPE 140 NA Low Pressure Handwand  Wettable Powder Formulations ( LCO) ( 8) lawns, golf courses, nursery stock 4 5 10 46 NF High Pressure Handwand  ( Wettable Powder Formulations) ( 9) woody ornamentals, conifer nurseries. 4 5 See PPE 100 NA Table 5: Exposure Variables ( Noncancer) and MOEs for Uses of Oxadiazon Exposure Scenario ( Scenario #) Crop Type App Rates ( lb ai/ acre) Daily Acres Treated Total MOEs Base line PPE Eng. Control 21 Lawn Handgun ( Wettable Powder Formulations) ( ORETF) ( 10) ornamentals, lawns, parks rec areas 4 5 280 NA NA Granulars with a Push Type Spreader ( ORETF) ( 11) lawns, golf courses, parks, r ecreat iona l ar ea s , ornamentals 4 5 1100 NA NA Granulars with a Bellygrinder ( LCO) ( 12) golf courses, parks, rec areas. 4 1 190 NA NA Baseline dermal unit exposure scenarios includes long pants, long shirts and no gloves.

Baseline inhalation unit exposure represents no respirator PPE dermal unit exposure includes long pants, long shirts and gloves for scenarios 5, 7, and 9.

PPE dermal unit exposure includes long pants, long shirts gloves and double layer ( 50% protection) for scenarios 1a, 1b, 1c, and 8.

PPE inhalation unit exposure represents dust/ mist respirator ( 80 % protection) for scenarios 1a, 1b, 1c, and 8.

Engineering Control dermal unit exposure scenarios includes long pants, long shirts, gloves and water soluble packages for scenario 1a.

Engineering inhalation unit exposure represents no respirator.

NA = Not applicable.

NF = Not Feasible. No engineering controls are available to mitigate risk. 22 d. Occupational Handler Risk ( cancer)

The cancer risk assessments for handlers used baseline PPE and, as needed, increasing levels of risk mitigation ( PPE and engineering controls) to achieve cancer risks below EPA's level of concern. As noted previously, the Agency's level of concern for cancer risks for occupational exposure to pesticides ranges from 1.0 x 10 4 to 1.0 x 10 6, depending on the feasibility, availability, and cost of various mitigation options.

Potential cancer risks to handlers were assessed using the following assumptions:

$ an average typical adult body weight of 70kg;

$ typical working lifetime of 35 years;

$ 70 year lifetime;

$ dermal absorption of 9% and inhalation absorption of 100% of the oral dose.

Based on the scenarios identified above, the Agency estimates that cancer risks from occupational dermal and inhalation exposures to oxadiazon range from 1.7 x 10 2 to 4.7 x 10 7 during " baseline" conditions ( i. e. long pants, long sleeves, no gloves). Cancer risk ranges from 1.0 x 10 3 to 1.4 x 10 7 when PPE was used. The Agency estimates that cancer risk decreases to a range of 5 x 10 5 to 1 x 10 8 with engineering controls. Engineering controls included the use of chemical resistant gloves along with water soluble packaging for wettable powder formulations. Overall these estimates suggest that when PPE and/ or engineering controls are used, none of the evaluated scenarios have cancer risks that exceed 1.0 x10 4 , but most are in the range where further consideration is warranted.

e. Occupational Exposure and Risk, Post application ( non cancer)

EPA uses the term " post application" to describe those individuals who can be exposed to pesticides after entering areas previously treated with pesticides and performing certain tasks or activities ( also often referred to as reentry exposure). Most of the oxadiazon used is applied either pre plant or when the crops are quite small ( early post emergence). This fact, and the degree of mechanization, minimizes the postapplication contact of workers with oxadiazon. However, the Agency has determined that there are potential post application exposures to individuals re entering oxadiazon treated areas for the purpose of:

° Roadsides: mowing ° Bermuda grass rights of way: mowing ° Sod farms: mowing and harvesting ° Golf course turf: mowing Based on usage information provided by the registrants for reregistration, the most common postapplication exposures for oxadiazon will occur for workers on turf. Based on label restrictions and pattern of use, oxadiazon is applied early in the season, either pre plant or before weeds emerge ( pre emergence). Mowing would be a common post application activity after either spraying method. Treated turf or grasses 23 will routinely require reentry activities, such as mowing and watering, and eventually harvesting in the case of sod farms.

Because oxadiazon has a low vapor pressure ( 1.0 x 10 6mm Hg) and is only used outdoors, the inhalation component of post application exposure is anticipated to be negligible. Therefore, all calculations of post application risk estimates have been done for dermal exposure only.

For short and intermediate term non cancer risks, mowing ( e. g., golf courses, roadsides, and sod farms) and harvesting ( e. g., sod farms) scenarios were considered. Transfer coefficients of 500 and 16,500 cm2/ hr were used, based on the Agricultural Re entry Task Force data ( refer to EPA Exposure SAC Policy guidance 3.1, 8/ 00). Occupational post application activities had MOEs of 30 1000 at day 0. This information is summarized below in Table 6.

f. Occupational Risk, Post application ( cancer)

Cancer risks for occupational post application scenarios were estimated not to exceed EPA's level of concern ( i. e.  1.0 x 10 4; Table 6).

Table 6: Occupational Short and Intermediate Term Postapplication Risks for Oxadiazon at Day 0 Crop/ Use Pattern Application Rate ( lb ai/ acre) Postapplication Activity Transfer Coefficienta Cancer Risk MOEb LADDc mg/ kg/ day Riskd Golf Course Turf 4 Mow, seed, scout, mechanical weed, aerate, fertilize, prune 500 1000 4.23e 5 3.01e 6 Transplant, hand weed 16,500 30 1.39e 3 9.92e 5 Sod Farms 4 Mow, scout, mechanical weed, irrigate 500 1000 4.23e 5 3.01e 6 Transplant, hand weed, harvest ( hand or mechanical) 16,500 30 1.39e 3 9.92e 5 Bermuda Grass Rights of Way 4 Mow, seed, scout, mechanical weed, aerate, fertilize 500 1000 4.23e 5 3.01e 6 aTransfer coefficient from Science Advisory Council for Exposure: Policy Memo # 003 .1 " Agricultural Transfer Coefficients," Revised  August 7, 2000.

bMOE = Short term NOAEL ( 12 mg/ kg/ day; based on a dermal study) / dermal dose where absorbed dose = TTR (

g/ cm2) x TC ( cm2/ hr) x conversion factor ( 1 mg/ 1,000

g) x exposure time( 8hrs/ day) x dermal absorption ( 9 %) / body weight ( 60 kg; adult).

CAbsorbed dermal dose where absorbed dose = TTR (

g/ cm2) x TC ( cm2/ hr) x conversion factor ( 1 mg/ 1,000

g) x exposure time ( 8 hrs/ day) x dermal absorption ( 9 %) / body weight ( 70 kg) x ( Number of days ( 3) exposure per year applicator) / 365 days per year) x 35 years worked/ 70 year lifetime dCancer Risk = LADD ( mg/ kg/ day) x ( Q1*), where Q1* = 7.11e 2 ( mg/ kg/ day) 1.

7. Incident Data 24 Oxadiazon has not been reported to cause life threatening illness or death in humans. On the list of the top 200 chemicals for which National Pesticide Information Center ( NPIC, formerly National Pesticide Telecommunications Network) received calls from 1984 1991 inclusively, oxadiazon was ranked 192nd with 12 incidents in humans reported and five incidents in animals ( mostly pets). Most of the cases appear to be related to irritation to the skin, eyes and mucous membranes.

B. Environmental Risk Assessment A summary of the Agency's environmental fate and effects risk assessment is presented below. More detailed information on the environmental and ecological risks associated with the use of oxadiazon may be found in the " EFED Revised Risk Assessment for the Reregistration Eligibility Decision of Oxadiazon," dated June 11, 2003. Since that document was completed, the Agency made changes to refine its assessment of the chronic surface water concentrations of oxadiazon associated with the use on turf. Specifically, the Tier 1 model simulations were refined using the Tier 2 PRZM/ EXAMS model simulation with a turf scenario. The linked PRZM/ EXAMS models are typically used by EPA in estimating pesticide concentrations in surface waters. The PRZM model estimates the amount of pesticide that reaches a body of surface water as a result of runoff. The EXAMS model estimates pesticide concentrations by taking into account different mechanisms for dissipation, weather patterns, and periodic application of pesticide, for several years. The complete environmental fate and effects risk assessment and related addenda are not included in this document, but are available on the Agency's web page at www. epa. gov/ pesticides, and in the Public Docket.

1. Environmental Fate and Transport Based on the fate studies reviewed, oxadiazon would be stable and persistent under typical terrestrial environment conditions. Soil photolysis and hydrolysis under acidic and basic conditions do not appear to be an important dissipation mechanism. However, direct aqueous photolysis halflife of about three days ( summer sunlight conditions in Florida) suggests that in clear and shallow surface water bodies where sunlight penetration can be significant, photolytic degradation of oxadiazon is possible. The photolytic effect may substantially diminish in turbid and deeper water bodies.

Microbial metabolism in soil and aquatic environments under either aerobic and anaerobic conditions is not expected to cause any significant transformation of oxadiazon, although a number of degradates have been reported from the different chemical and biological fate studies.

Studies on equilibrium sorption and aged/ unaged oxadiazon indicate that the pesticide has low environmental mobility ( K d's ranged from 8.17 to 22.83; K oc's ranged from 1409 to 3268). Thus, oxadiazon is likely to be transported, via surface runoff, bound to erodible soil particles, to nearby surface water bodies. Leaching from surficial soils to groundwater is expected to be low or 25 negligible, unless the soil is very porous or has some cracks that favor preferential flow. Oxadiazon exhibited slow dissipation in two terrestrial field studies conducted in California and North Carolina.

2. Water Resources The potential impact to water quality from the use of oxadiazon on turf is essentially due to the parent ( as opposed to possible degradates). Oxadiazon appears to be persistent under most environmental conditions making the chemical available for surface runoff. The remaining factor which affects the impact of oxadiazon on water quality is mobility in soils. A soil column leaching study, and supplemental batch equilibrium studies, indicate that oxadiazon has low mobility in the various soils tested. Ordinarily this would mean that the chemical would remain soil bound and would be transported to a water body on eroded soil. Turf scenarios, however, offer different challenges than typical agricultural crops. The turf itself offers a vegetative interception layer ( including thatch) that prevents rapid deposition of the oxadiazon on the surface of the soil. Both liquid and granular formulation labels of oxadiazon recommend mowing the grass prior to application. Also, both liquid and granular formulation labels of oxadiazon specify that the chemical's effectiveness is improved if it is wetted in after application. Oxadiazon is more likely to bind to soil particles if the turf is watered after application of the pesticide.

The models used for the Tier 1 determination of the water exposures were FIRST, GENEEC 2.0 for surface waters, and SCIGROW for ground waters. The models are screening tools designed to provide upper bound estimates of the concentrations that might be found due to the use of oxadiazon. For drinking water, a Tier II refinement was performed, using PRZM/ EXAMS. In the Tier II refinement, a scenario that incorporates three applications ( 1 @ 4 lb a. i./ A and 2 @ 2 lb ai/ A) was used. Surface water monitoring data for oxadiazon is limited and has not been used to represent possible concentrations of oxadiazon in surface waters. The chemical is not included in the NAWQA monitoring studies. The STORET database contained only two samples taken from the same location within an interval of only four days. The estimated recommended acute and long term drinking water concentrations are detailed in Chapter 6 of the document " EFED Revised Risk Assessment for the Reregistration Eligibility Decision of Oxadiazon," dated June 11, 2003.

3. Ecological Risk Risk characterization integrates the results of the exposure and ecotoxicity data to evaluate the likelihood of adverse ecological effects. The Agency calculates risk quotients ( RQs) by dividing exposure estimates by acute and chronic ecotoxicity values:

RQ = EXPOSURE/ TOXICITY RQs are then compared to OPP's levels of concern ( LOCs). These LOCs are criteria used by EPA to indicate potential risk to nontarget organisms. The criteria indicate that a pesticide used as directed has the potential to cause adverse effects on nontarget organisms. The exposure and effects inputs to a screening level assessment are by design assumed to overestimate likely exposures and 26 effects of pesticides. Exceedence of an LOC indicates that risks of concern are possible, but the likelihood, magnitude, and/ or severity of the risk cannot be quantified. Risk presumptions, along with the corresponding LOCs, are given in Table 7 below.

Table 7. Risk Presumptions for Terrestrial and Aquatic Animals Risk Presumption LOC terrestrial animals LOC aquatic animals Acute Risk there is potential for acute risk; mitigation may be warranted in addition to restricted use classification, 0.5 0.5 Acute Restricted Use  there is potential for acute risk, but may be mitigated through restricted use classification, 0.2 0.1 Acute Endangered Species  endangered species may be adversely affected, 0.1 0.05 Chronic Risk  there is potential for chronic risk; regulatory action may be warranted. 1 1 Aquatic and terrestrial risk assessments were conducted by using standard ecotoxicity endpoints ( i. e., LD 50 and LC 50 values, and NOAEC values). The toxicity endpoints chosen for use in the ecological risk assessment are summarized below in Table 8.

Table 8. Toxicological Endpoints Used to Determine Risk Quotients ( RQs)

Type Of Toxicity Organism Species Toxicological Endpoint Oral Acute Bird Mallard 1040 mg/ kg Dietary Bobwhite/ Mallard > 5000 ppm Chronic Bobwhite 500 ppm 1 Oral Acute Mammal Rat > 5000 mg/ kg Chronic Rat 200 ppm 2 Acute Freshwater Fish Rainbow trout/ Bluegill 0.88 ppm Chronic Rainbow trout 0.88 ppb 3 Acute Freshwater Invertebrates Daphnid 2.18 ppm Chronic Daphnid 0.03 ppm Acute Estuarine Fish Sheepshead Minnow 1.5 ppm Chronic Sheepshead Minnow 0.0015 ppm 4 Table 8. Toxicological Endpoints Used to Determine Risk Quotients ( RQs)

Type Of Toxicity Organism Species Toxicological Endpoint 27 Acute Estuarine Invertebrates Mysid 0.27 ppm Chronic Mysid 0.0037ppm4 Acute Aquatic Plants ( vascular) duckweed EC50 = 41 ppb NOAEC = < 8 ppb ( Nonvascular) marine diatom EC50 = 5.2 ppb 1 No effects on any reproductive parameter or viability of F1 offspring at the highest dose tested, 1000 ppm; however due to excessive mortality ( 33%) of adult female birds in that dose level, a NOAEC for chronic effects was set at 500 ppm.

2 LOAEL of > 38 mg/ kg/ day for inactive mammary tissue and fetal/ pup death observed in the one year range finding test of a rat reproduction study. NOAEC > 200 ppm.

3 Rainbow trout was more sensitive than the fathead minnow ( fathead minnow NOAEC= 33 ppb).

4 Extrapolation from acute/ chronic ratio.

j. Risks to Birds Table 9 provides avian acute and chronic RQs from exposure to multiple applications of oxadiazon EC to turf for the maximum three application rates ( 4.0, 3.0 and 2.0 lbs ai/ A) and two split applications ( 1.0 lb ai/ A, 4 times/ 6 months; 1.3 lbs ai/ A, 3 times/ 6 months). The maximum three applications have the potential for chronic exposure to birds that feed on plants and grass ( e. g., ducks, geese) and may result in risk to these birds ( RQ = 1.0  2.0). The split application appears to lower this chronic exposure and risk ( RQ = < 1). The EC formulation was evaluated because it presents an upper bound estimate of risk. The majority of oxadiazon is applied as a granular formulation. Exposure from the granular formulation was evaluated because birds may be exposed to granular pesticides through ingestion when foraging for food or grit. RQ values were calculated for three weight classes of birds ( 1000g waterfowl, 180g upland game bird, and 20g songbird). All scenarios for the granular resulted in no acute risk to birds ( RQ < 0.5). However, the potential chronic concern noted for non endangered birds suggest that oxadiazon may present a risk to endangered species ( RQ > 0.1).

Pesticide dissipation from foliar surfaces is primarily due to degradation or dissipation by one or more processes including photolysis, hydrolysis, microbial degradation and volatilization. Since adequate foliar dissipation data are not available for oxadiazon, a default half life of 35 days was used in the EEC calculations. 28 Table 9. Avian Acute and Chronic Risk Quotients a Site Application Rate lbs ai/ A (# appl) Food Item Maximum EECs ( ppm) Acute RQ ( EEC/ LC50) Chronic RQ ( Max.

EEC/ NOAEC)

Turf ( EC)

4.0 ( 2) Short grass Tall grass Broadleaf plants/ insects Seeds 984.1 451.1 553.6 61.5 < 0.2 < 0.1 < 0.1 < 0.0 2.0 1.0 0.1 0.1 Turf ( EC)

3.0 ( 2) Short grass Tall grass Broadleaf plants/ insects Seeds 739.6 339.0 416.0 46.2 < 0.1 0.0 < 0.1 0.0 1.5 1.0 1.0 0.1 Turf ( EC)

2.0 ( 2) Short grass Tall grass Broadleaf plants/ insects Seeds 493.1 226.0 277.3 30.8 < 0.1 0.0 0.0 0.0 1.0 0.4 0.5 0.1 Turf ( EC)

1.0 ( split 4 applications/ 6 months) Short grass Tall grass Broadleaf plants/ insects Seeds 424.4 194.5 238.7 26.5 < 0.1 0.0 0.0 0.0 1.0 0.4 0.5 0.1 Turf ( EC)

1.3 ( split 3 applications/ 6 months) Short grass Tall grass Broadleaf plants/ insects Seeds 257.0 117.8 144.6 16.1 < 0.1 0.0 0.0 0.0 1.0 0.4 0.5 0.1 aAvian acute and chronic risk quotients ( RQ's) as generated through ELL FATE for broadcast ground spray applications for oxadiazon. RQ's are based on mallard duck LC50 > 5,000 ppm and NOAEC = 500 ppm. The EEC reflects the turf use with the three highest use rate ( 4.0, 3.0 and 2.0 lbs ai/ A, 2 applications) and two split applications ( 1.0 lb ai/ A, 4 times/ 6 months; 1.3 lbs ai/ A, 3 times/ 6 months). 29 b. Risks to Mammals The Agency has concluded that for the EC formulation of oxadiazon the assessed single applicaton rates ( 4.0, 3.0 and 2.0 lbs ai/ A), as well as the split use rates ( 1.0 and 1.3 lbs ai/ A) should not result in acute risk to mammals ( RQ < 0.2). However, these application scenarios can result in chronic exposure and risk to mammalian herbivores and insectivores ( 15g, 35g, and 1000g) with RQ values ranging from 0.1 to 4.9 ( Table 10). This chronic risk to non endangered mammalian species also suggests the potential for impact to endangered species.

Table 10. Mammalian Chronic Risk Quotientsa Crop Application Rate lbs ai/ A ( # of applications) Food Items Max.

EEC ( ppm) Chronic RQ ( Max. EEC/ NOAEC) b Turf ( EC)

4.0 ( 2) Short Grass Tall Grass Broadleaf plant/ Insects Seeds 986.1 452.0 554.7 61.6 4.9 2.3 2.8 0.3 Turf ( EC)

3.0 ( 2) Short Grass Tall Grass Broadleaf plant/ Insects Seeds 739.6 339.0 416.0 46.2 3.7 1.7 2.1 0.2 Turf ( EC)

2.0 ( 2) Short Grass Tall Grass Broadleaf plant/ Insects Seeds 493.1 226.0 227.3 30.8 2.4 1.1 1.4 0.1 Turf ( EC)

1.0 ( split 4 applications/

6 months) Short Grass Tall Grass Broadleaf plant/ Insects Seeds 424.4 194.5 238.7 26.5 2.4 1.1 1.3 0.1 Turf ( EC)

1.3 ( split 3 applications/

6 months) Short Grass Tall Grass Broadleaf plant/ Insects Seeds 257.0 117.8 144.6 16.1 1.6 1.0 1.0 0.1 aMammalian chronic risk quotients as generated through ELL FATE for ground application of an emulsifiable concentrate of oxadiazon are based on rat ( Rattus norvegicus) NOAEC = 200 ppm. The EEC reflects the three highest assessed application rates ( 4.0, 3.0 and 2.0 lbs ai/ A, 2 applications) and two split applications ( 1.0 lb ai/ A, 4 times/ 6 months; 1.3 lbs ai/ A, 3 times/ 6 months).

b Chronic risk ( LOC > 1) 30 c. Risks to Fish and Aquatic Invertebrates Tables 11 and 12 provide acute and chronic RQ values for oxadiazon exposure to freshwater and estuarine/ marine species for turf use patterns ( application rates for EC at 2.0  4.0 lbs ai/ A and 4.0 lbs ai/ A for granular). Although our assessment suggests that oxadiazon acute exposure may result in low acute risk to fish ( RQ = 0.1  0.2) and invertebrates ( RQ = 0.3  0.5), there is uncertainty regarding the potential for enhanced risk that may occur through phototoxicity. Since oxadiazon is a light dependent peroxidizing herbicide ( LDPH), enhanced toxicity through exposure to high levels of solar radiation is a possible concern regarding aquatic organisms that inhabit small, shallow water bodies.

EPA's Tier I ( GENEEC) risk assessment suggests that chronic exposure to this compound can result in risk to freshwater and estuarine/ marine fish ( RQ = 39.3  131.8) and aquatic invertebrates ( RQ = 3.9  36.7). Endangered species concerns are also suggested, as acute RQs exceeded the level of concern ( 0.1). Also, enhanced toxicity through exposure to high levels of solar radiation may increase toxic risk to aquatic organisms that inhabit small, shallow water bodies. Therefore, EPA is requiring a study on the phototoxicity of oxadiazon in fathead minnows.

The Tier I GENEEC model 60 day EEC for oxadiazon in surface water following 2 4 lb applications of granular oxadiazon was 142 ppb. However, the conservative Tier I model does not account for the effect of established golf course turf on reducing sediment run off. Tier II PRZM/ EXAMS estimates of EECs for drinking water, although not directly applicable to the risk assessment for aquatic organisms, suggest that the golf course scenario greatly reduces run off. Tier II estimates of oxadiazon concentrations in surface sourced drinking water were approximately sixfold lower than the Tier I GENEEC estimate described above. It is reasonable to assume that Tier II EECs for a pond scenario would likewise be reduced.

Table 11. Acute and Chronic RQ's for Oxadiazon Exposure to Fish a Crop App. Rate ( lbs ai/ A; # App.) Organism Acute ( LC50, ppm) Chronic ( NOAEC, ppm) EEC Peak ( ppm) EEC 60 Day Avg.

( ppm) Acute RQ ( EEC/ LC50) Chronic RQ d ( EEC/ NOAEC)

Turf ( EC)

4.0 ( 2) Freshwater 0.88 0.00088 0.143 0.116 0.2 c 131.8 Estuarine/

Marine 1.5 0.0015 b 0.143 0.116 0.1 c 77.3 Turf ( EC)

3 ( 2) Freshwater 0.88 0.00088 0.130 0.122 0.1 c 139.0 Estuarine/

Marine 1.5 0.0015 b 0.130 0.122 0.1 c 81.3 Turf ( EC)

2 ( 2) Freshwater 0.88 0.00088 0.088 0.083 0.1 c 94.3 Table 11. Acute and Chronic RQ's for Oxadiazon Exposure to Fish a 31 Estuarine/

Marine 1.5 0.0015 b 0.088 0.083 0.0 55.3 Turf ( Granular)

4.0 ( 2) Freshwater 0.88 0.00088 0.122 0.099 0.1 c 112.5 Estuarine/

Marine 1.5 0.0015 b 0.122 0.099 0.1 c 66.0 aAcute and chronic RQ's for evaluating toxic risk of oxadiazon exposure to fish ( freshwater and estuarine/ marine). RQ's are based on the bluegill ( Lepomis macrochirus) LC50 = 0.88 ppm, rainbow trout ( Oncorhynchus mykiss) NOAEC = 0.00088 ppm and sheepshead minnow ( Cyprinodon variegatus) LC50 = 1.5 ppm., NOAEC = 0.0015 ppm1. EEC values are generated from GENEEC and reflect three of the highest assessed EC application rates, and the maximum assessed granular use rate ( 4.0, 3.0, and 2.0 lbs ai/ A, 2 applications each; 4.0 lbs ai/ A, 2 applications, respectively) for turf use.

b Extrapolated chronic value using acute/ chronic freshwater toxicity ratio c Acute restricted use (> 0.1), acute species d Chronic concern (> 1.0) 32 Table 12. Acute and Chronic Risk Quotients for Aquatic Invertebratesa Crop App. Rate ( lbs ai/ A) # App. ( days) Organism Acute ( EC50, ppm) Chronic ( NOAEC, ppm) EEC Peak ( ppm) EEC 21 Day Ave.

( ppm) Acute RQ ( EEC/

LC50) Chronic RQ ( EEC/ NOAEC)

Turf ( EC)

4.0 ( 2) Freshwater 2.18 0.03 0.143 0.136 0.12 4.51 Estuarine/

Marine 0.27 0.0037 0.143 0.136 0.52 36.71 Turf ( EC)

3.0 ( 2) Freshwater 2.18 0.03 0.130 0.127 0.52 4.21 Estuarine/

Marine 0.27 0.0037 0.130 0.127 0.52 34.33 Turf ( EC)

2.0 ( 2) Freshwater 2.18 0.03 0.088 0.086 0.0 2.93 Estuarine/

Marine 0.27 0.0037 0.088 0.086 0.32 23.23 Turf ( Granular)

4.0 ( 2) Freshwater 2.18 0.03 0.122 0.116 0.0 3.91 Estuarine/

Marine 0.27 0.0037 0.122 0.116 0.42 31.31 aAcute and chronic risk RQ's for evaluating toxic risk of oxadiazon exposure to aquatic invertebrates ( freshwater and estuarine / marine). RQ's are based on Daphnia ( Daphnia magna) EC50 = 2.18 ppm, NOAEC = 0.03 ppm and the Mysid shrimp ( Americamysis bahia) EC50 = 0.27 ppm, NOAEC = 0.0037 ppm1. EEC values are generated from GENEEC and reflect three of the highest proposed EC application rates, and the maximum granular use rate ( 4.0, 3.0, and 2.0 lbs ai/ A, 2 applications each; 4.0 lbs ai/ A, 2 applications, respectively) for turf use.

1 Extrapolated chronic value using acute/ chronic freshwater toxicity ratio 2 Acute restricted use (> 0.1)

3 Chronic concern (> 1.0) 33 d. Risk to Benthic Organisms Oxadiazon residues can accumulate in sediments and may increase the risk from chronic exposure of benthic and epibenthic organisms aquatic organisms that live in or on the sediment. In order to better understand this potential risk, EPA is requiring appropriate acute and chronic sediment toxicity testing on this compound.

e. Risks to Aquatic Plants Exposure to non target aquatic plants may occur through runoff or spray drift from adjacent treated sites. An aquatic plant acute risk assessment is usually made for aquatic vascular plants from the surrogate duckweed Lemna gibba. Non vascular acute aquatic plant risk assessments are performed using either algae or a diatom, whichever is the most sensitive species. Runoff and drift exposure are computed from GENEEC2 and the risk quotient is determined by dividing the pesticide's initial or peak concentration in water by the plant EC 50 value. Acute risk quotients for vascular and non vascular plants are tabulated in Table 13.

Aquatic plant acute risk levels of concern are exceeded ( Table 13) for both vascular and nonvascular plants. The RQs range from 1.1 to 4.2 for vascular plants and from 8.5  33 for nonvascular plants. The acute plant risk level of concern is exceeded for vascular plants with RQs ranging of 5.5  22. Currently, EPA does not perform assessments for chronic risk to aquatic plants.

The Tier I GENEEC model 60 day EEC of oxadiazon in surface water following 2 4 lb applications of granular oxadiazon was 142 ppb. However, the conservative Tier I model does not account for the effect of established golf course turf on reducing sediment run off. Tier II PRZM/ EXAMS estimates of EECs for drinking water, although not directly applicable to the risk assessment for aquatic organisms, suggest that the golf course scenario greatly reduces run off. Tier II estimates of oxadiazon concentrations in surface sourced drinking water were approximately sixfold lower than the Tier I GENEEC estimate described above. It is reasonable to believe that Tier II EECs for a pond scenario would likewise be reduced. 34 Table 13. Acute Risk Quotients for Aquatic Plants a Turf/ Rate of Application in lbs ai/ A ( Number of Applications). Species EC50 ( ppm) EEC ( ppm) Non target plant RQ ( EEC/ EC50)

4 ( 2) duckweed 0.041 0.173 4.2 4 ( 1) " 0.041 0.089 2.2 3 ( 1) " 0.041 0.067 1.6 2 ( 1) " 0.041 0.044 1.1 4 ( 2) diatom 0.0052 0.173 33.3 4 ( 1) " 0.0052 0.089 17.1 3 ( 1) " 0.0052 0.067 12.9 2 ( 1) " 0.0052 0.044 8.5 aAcute risk quotients for aquatic plants are based upon a duckweed ( Lemna gibba) EC50 of 41 ppb and a nonvascular plant ( marine diatom) EC50 of 5.2 ppb.

4. Endangered Species Risk Assessment Endangered species LOCs for liquid and granular formulations of oxadiazon are exceeded for acute risks to birds, mammals, freshwater and estuarine fish and invertebrates and aquatic vascular plants. Although the terrestrial plant data are outstanding, it is assumed that endangered terrestrial plants are at risk since oxadiazon is an herbicide. Although the endangered species LOC for estuarine invertebrates has been exceeded, there are no listed species in this group.

The Agency is currently engaged in a Proactive Conservation Review with the Fish and Wildlife Service ( FWS) and the National Marine Fisheries Service under section 7( a)( 1) of the Endangered Species Act. The objective of this review is to clarify and develop consistent processes for endangered species risk assessments and consultations. Subsequent to the completion of this process, the Agency will reassess the potential effects of oxadiazon use to federally listed threatened and endangered species. At that time the Agency will also consider any regulatory changes recommended in the RED that are being implemented. Until such time as this analysis is completed, the overall environmental effects mitigation strategy articulated in this document and any County Specific Pamphlets described in section IV of the RED which address oxadiazon, will serve as interim protection measures to reduce the likelihood that endangered and threatened species may be exposed to oxadiazon at levels of concern. 35 IV. Risk Management, Reregistration and Tolerance Reassessment Decision A. Determination of Reregistration Eligibility Section 4( g)( 2)( A) of FIFRA calls for the Agency to determine, after submission of relevant data concerning an active ingredient, whether or not products containing the active ingredient are eligible for reregistration. The Agency has previously identified and required the submission of the generic ( i. e., active ingredient specific) data required to support reregistration of products containing oxadiazon as an active ingredient. The Agency has completed its review of these generic data, and has determined that the data are sufficient to support reregistration of all products containing oxadiazon provided that certain data gaps are addressed, the risk reduction measures outlined in this document are adopted and labels are amended to implement these measures. Appendix B identifies the generic data requirements that the Agency reviewed as part of its determination of reregistration eligibility of oxadiazon.

These data were sufficient to allow the Agency to determine that oxadiazon can be used without resulting in unreasonable adverse effects to humans and the environment. The Agency, therefore, finds that all products containing oxadiazon as the active ingredient are eligible for reregistration, provided specified changes are made to the label. Actions needed to reregister particular products are addressed in Section V of this document. Those actions are the result of risk management steps summarized in Chapter 4. The Agency concludes that these label changes address the current risk estimates and reflect the use of all acceptable data available at this time together with uncertainty factors where data gaps exist.

The Agency may take appropriate regulatory action if new information comes to the Agency's attention regarding the reregistration of oxadiazon. The Agency may also require the submission of additional data ( 1) to support the registration of products containing oxadiazon, ( 2) if the data requirements for registration change, or ( 3) if the guidelines for generating such data change.

B. Tolerance Reassessment With respect to tolerances for oxadiazon, there have been no active food use registrations since 1991. The tolerance for rice straw was revoked as of the July 1, 2001 revision to 40 CFR 180.346. In a confirmatory letter to EPA, dated January 24, 2001, the registrant maintained its previous position that it would not support the sixteen remaining oxadiazon tolerances. Therefore, effective April 24, 2003, EPA revoked all the tolerances in 40 CFR 180.346 for the combined residues of the herbicide oxadiazon and its metabolites in the following commodities: in or on milk; cattle, fat; cattle, meat; cattle, meat byproducts; goats, fat; goats, meat; goats, meat byproducts; hogs, fat; hogs, meat; hogs, meat byproducts; horses, fat; horses, meat; horses, meat byproducts; sheep, fat; sheep, meat; and sheep, meat byproducts. In addition, because EPA determined on April 21, 2002 that there is no reasonable expectation of finite residues of oxadiazon and its metabolites in or on meat, milk, poultry, and egg commodities, the sixteen associated tolerances for livestock commodities were considered by the Agency to no longer be needed under 40 CFR 180.6( a)( 3). Therefore, on June 3, 2002, the Agency considered the FQPA safety finding to be met and counted the sixteen oxadiazon livestock tolerances as reassessed. There are no CODEX, Canadian, or Mexican tolerances for oxadiazon residues. 36 C. Regulatory Position 1. FQPA and Aggregate Risk Given that all tolerances for oxadiazon have been revoked, this pesticide no longer falls under the scope of FQPA. As such, no quantitative aggregate assessment of risk from dietary and residential exposures was completed as part of the reregistration process. EPA has qualitatively evaluated the likelihood of combined exposures for the general population, including children. Because of the relatively low volume of use of oxadiazon on sites other than golf courses, its specialized use pattern, and its relatively high cost, neither concurrent nor aggregate exposures from different sources of oxadiazon are likely. If EPA receives a petition for food/ feed uses and/ or tolerances, EPA will perform an FQPA evaluation at that time.

2. Endocrine Disruptor Effects 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 recommendations of its Endocrine Disruptor Screening and Testing Advisory Committee ( EDSTAC), EPA determined that there was scientific basis for including, as part of the program, the androgen and thyroid hormone systems, in addition to the estrogen hormone system. EPA also adopted EDSTAC's recommendation that EPA include evaluations of potential effects in wildlife. For pesticides, EPA will use FIFRA 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 systems may be added to the Endocrine Disruptor Screening Program ( EDSP).

When the appropriate screening and/ or testing protocols being considered under the EDSP have been developed, oxadiazon may be subject to additional screening and/ or testing to better characterize effects related to endocrine disruption.

3. Cumulative Risks For the purposes of this risk assessment, the Agency has assumed that oxadiazon does not share a common mechanism of toxicity with other oxadiazoles or carcinogenic chemicals.

4. Benefits Assessment The EPA has concluded that there are no suitable selective pre emergence alternatives to oxadiazon currently available. Oxadiazon is expensive in comparison to other goosegrass controls, but those controls are not as selective, as they kill non target plants as well. Because oxadiazon is 37 expensive ( estimated $ 100  $ 200 per acre in 2003), it is expected that mainly high end golf courses are going to use the herbicide.

D. Tolerance Summary All tolerances for oxadiazon have been revoked. No maximum residue limits for oxadiazon have been established by Codex for any agricultural commodities. Therefore, there are no issues regarding compatibility with respect to U. S. tolerances.

E. Human Health Risk Mitigation 1. Dietary ( Drinking Water) Risk Mitigation Screening level estimates ( EECs) of potential drinking water exposure from ground water sources do not exceed the acute or chronic ( non cancer and cancer) DWLOC values, and therefore, are not of concern. However, exposure from surface water sources after application to golf courses is potentially of concern for chronic non cancer and chronic cancer dietary risk.

The Tier II modeled estimate of average concentrations in surface water associated with the use of oxadiazon on golf courses is 56 ppb. That value exceeds the Agency's level of concern by 100 fold. However, it should be noted that this estimate was derived using an assumption that oxadiazon is applied as a wettable powder formulation ( i. e., applied as a spray), and therefore includes a value for spray drift into water bodies. However, the predominant formulation for oxadiazon applied to golf course turf is granular, and typically the herbicide is encapsulated in a granular fertilizer.

Additionally, the Tier II assessment of EECs used an annual application rate of 8 lbs ai/ A. Discussions with the oxadiazon registrant and golf course personnel indicate that the cost of oxadiazon limits the frequency of use of the 8 lbs ai/ A annual rate to areas with heavy weed infestation, as might be encountered during the first year during which golf course turf is being established. Following the first year at the 8 lbs ai/ A rate, more typical rates of 2 6 lbs ai/ A/ yr are used on established turf. The registrant has agreed to set the maximum application rate at 6 lbs a. i./ A/ yr ( typically applied in multiple applications) except in areas of heavy weed infestation. In areas with heavy weed infestation, the maximum application rate will be 8 lbs a. i./ A/ yr. The maximum single application rate is 4 lbs ai/ A.

When the typical annual maximum application rate ( 6 lbs ai/ A) and the impact of a granular formulation versus a wettable powder formulation are considered, the surface water EEC decreases to approximately 25 ppb. This value is below the level of concern for chronic non cancer risk, but is still 50 fold greater than the chronic cancer DWLOC.

Limited water monitoring data from three states indicate that oxadiazon, though detected in surface water bodies, is present at concentrations below the Agency's level of concern. Additionally, preliminary data from a study designed to measure pesticide concentrations in golf course runoff, and performed under an EPA grant, suggest that oxadiazon concentrations in surfacesourced drinking water will not exceed the Agency's level of concern ( DWLOC = 0.49 ppb). 38 One factor that may be contributing to the apparent discrepancy between model estimates and measured concentrations is the percent crop area ( PCA) value. This value is used in the PRZM/ EXAMS models as the percentage of land area, within a specific watershed, that is made up of the crop of interest, in this case golf course turf. In characterizing oxadiazon, the Agency has used a PCA value of 94% to account for the land area of a typical golf course that is tees and greens ( 4%), fairway ( 23%) and rough ( 67%). Using the 94% PCA value results in an upper bound estimate of the potential environmental concentrations of oxadiazon if 94% of a watershed was golf course turf, and on each golf course 100% of available turf was treated with oxadiazon at the maximum application rate.

The registrant has submitted Geographic Information System ( GIS) data that localizes golf courses in Florida, along with watershed boundary information. That data suggests that the upper bound PCA for golf course turf in Florida is substantially less than 94%. The Agency took that information into account when it concluded that although oxadiazon is eligible for reregistration, water monitoring studies are required.

As noted above, the currently supported maximum rate of 8 lbs ai/ A/ year might be applied to turf with heavy weed infestation during the first year in which a golf course is being established. Thereafter, because of the expense of treating with oxadiazon, typical application rates of 2 6 lbs ai/ A would be used, depending on location. For most locations, a single 2 4 lb ai application per year is sufficient to control goosegrass. However, in the extreme southern locations ( e. g., south Florida) where the growing season is continuous, two applications of 3 lbs ai/ A are typical. Similarly, economic factors limit the use of oxadiazon on golf course roughs. Since roughs make up approximately 67% of golf course turf area, the limited use on roughs can have a great impact on the total pounds applied.

The estimated EECs in surface water were derived using the high end values discussed above, in addition to others that, when combined, lead to an upper bound estimate of risk. For example, when estimating the chronic cancer risk, the assumption is made that an individual drinks from the same water source every day for a 70 year lifetime. After characterizing the assumptions used to derive the estimates of oxadiazon concentrations in drinking water, the Agency has concluded that the actual concentrations of oxadiazon in drinking water are likely to be below the Agency's level of concern. To confirm the absence of chronic exposure to oxadiazon in drinking water at concentrations that exceed the Agency's cancer level of concern, the Agency is requiring the registrant to submit three years of drinking water monitoring data collected from sites determined by the Agency to be likely to result in upper bound exposures, with interim reporting after the first season. In addition to providing real world measures of oxadiazon concentrations in drinking water, the monitoring data may prove to be useful in on going efforts to validate a refined PCA value for turf. In the event that interim data indicate concentrations of oxadiazon in drinking water do exceed the Agency's level of concern, registrants have agreed to consider further mitigation measures, such as, further rate reductions and limitations on the areas of golf courses that can be treated. Regardless of the outcome of the water monitoring study, the registrant has agreed to establish a 15 foot " no apply" zone around bodies of water that may serve as sources of drinking water. 39 2. Non occupational Post application Risk Mitigation a. Non cancer risk mitigation Because oxadiazon is not available for sale to homeowners, residential handler scenarios do not exist. All of the non cancer post application risk scenarios for adults and toddlers had short term and intermediate term dermal MOEs greater than 100. Therefore, no mitigation measures are needed.

Estimated incidental, oral short term exposures (" hand to mouth") for children had an MOE of 100 using the TTR default values from the residential SOP. When the TTR data from the submitted oxadiazon study were used, the MOEs were 90 and 240 for non irrigated and irrigated dormant grass, respectively. The MOE of 90 for non irrigated grass does not meet or exceed the target value of 100, and is therefore potentially of concern. However, the risk estimate can be considered to be an upper bound for several reasons: 1) the submitted TTR study data were obtained using the wettable powder formulation, whereas the formulation more likely to be used on residential turf is granular oxadiazon. The granule size for a typical end use product, Ronstar G, is 20/ 50 Mesh, or 300 850 microns. In all products, the formulated granules are designed to fall below the grass canopy into the thatch layer. If used according to label directions, it is unlikely that oxadiazon granules would be accessible to a child. According to the registrant, for best results oxadiazon granules should be watered in as soon as is practical following application. Watering in the granules will carry them further into the thatch layer, and will further decrease the likelihood for exposure. When compared to values for granular formulations, TTR values are generally 10 100 fold greater for liquid formulations; 2) the highest mean residues from the Jazzercize study described above were used to estimate exposures between zero and one days after treatment, and the hand to mouth risk estimates were generated at those high end exposure levels; and 3) the risk estimates were generated assuming 20 hand to mouth events per hour for a two hour duration. That value was taken from observations of children in an indoors setting, and is likely an overestimate when considering an outdoor scenario.

Given that the estimate of risk from incidental, oral short term exposures (" hand to mouth") for children resulted from the combined use of these high end exposure assumptions, the EPA concludes that the risk estimate that results in an MOE of 90 for non irrigated dormant grass is likely to be an overestimate and not a cause for concern. No mitigation measures are required to address the non cancer chronic risk from non occupational post application exposure.

MOEs were not calculated for the incidental ingestion of oxadiazon granules because, as discussed above, the very small granules would not be available on the lawn surface and thus not accessible to children. It is thought, therefore, that the incidental ingestion of granules is not likely to be a cause for concern.

b. Cancer risk mitigation The cancer risks for all adult post application exposures were between 6.22 x 10 6 and 7.51 x 10 7. Exposure scenarios ranged from adults involved in low exposure activities on turf such as mowing with a push mower ( Transfer Coefficient = 500 cm2/ hour; cancer risk = 7.51 x 10 7) and golfing ( Transfer Coefficient = 500 cm2/ hour; cancer risk = 1.50 x 10 6) to adults involved in high 40 exposure activities on turf such as heavy yard work ( Transfer Coefficient = 14,500 cm2/ hr; cancer risk = 6.22 x 10 6 on non irrigated turf). The cancer risk estimates were based on several upperbound assumptions, including: 1) the maximum application rate of 4 lbs ai/ A; 2) an exposure concentration based on the residue concentration at day 0 1 after treatment with a wettable powder formulation; and 3) three exposures to oxadiazon treated turf per year for 35 years.

Those assumptions are thought to be upper bound, since: 1) although the maximum single application rate is 4 lbs ai/ A, the typical application rate for residential and golf course turf is 2 3 lbs ai/ A; 2) based on residue data, the dissipation half life for oxadiazon on turf is approximately 1.5 days. As such, it is unlikely that an individual would golf or perform heavy yard work, and thereby be exposed to the maximum residue concentration, each time oxadiazon is applied over a 35 year period; and 3) typically oxadiazon is applied once per year to residential turf, and twice per year to golf course turf in areas with extended growing seasons ( e. g. south Florida).

Given the combination of upper bound assumptions, as described above, the Agency concludes that the cancer risk equation, as used in the assessment of cancer risk from postapplication non occupational exposure to oxadiazon, is likely to result in an overestimate of risk. No mitigation measures are required to address the risk of cancer from post application, nonoccupational exposure to oxadiazon.

3. Occupational Risk Mitigation a. Handlers ( 1.) Non cancer risk mitigation The results of the short and intermediate term handler assessments are presented in Table 5 and indicate that all, but one, potential non cancer exposure scenarios provide at least one application rate with a total MOE( s) greater than or equal to 100 at either the baseline ( i. e., long pants, long sleeved shirts, no gloves) using open systems, PPE ( i. e., long pants, long sleeved shirts, and chemical resistant gloves while using open systems), or using engineering controls ( i. e., closed systems). The only exception, with the feasible level of mitigation, is application of wettable powder formulations with a low pressure handwand, with an MOE of 46.

This scenario assumes that a worker would treat five acres per day using a low pressure hand wand. The highest volume use of a low pressure hand wand applicator is likely to be on nonturf areas of golf courses ( e. g., in areas under and around trees, shrubs, and ornamentals). According to golf course personnel, a typical worker would likely cover a maximum of one acre a day when applying oxadiazon with a low pressure hand wand. The total area on a golf course likely to be treated with a low pressure handwand is approximately two acres. Using a conservative assumption that in a worst case scenario a worker might treat three acres in a day, and considering PPE, the MOE for this scenario would increase to the target MOE of 100. The Agency concludes that the non cancer risk does not exceed the Agency's level of concern, therefore, no mitigation is required to address the non cancer risks from occupational handler exposures to oxadiazon. 41 ( 2.) Cancer risk mitigation The cancer risk assessments for handlers used baseline exposure scenarios and, as needed, increasing levels of risk mitigation ( PPE and engineering controls) to achieve cancer risks that would be considered of no concern. According to Agency policy, the level of concern for cancer risks from occupational exposure to pesticides ranges from 1.0 x 10 4 to 1.0 x 10 6, depending on the feasibility, availability, and cost of various mitigation options.

Based on the scenarios identified previously, the Agency estimates that the risk of developing cancer from occupational dermal and inhalation exposures to oxadiazon ranges from 1.7 x 10 2 to 4.7 x 10 7 during " baseline" conditions ( i. e., long pants, long sleeves, no gloves). Cancer risk ranges from 1 x 10 3 to 1 x 10 7 when personal protective equipment ( PPE) ( i. e., long pants, long sleeved shirt, and chemical resistant gloves) was used. The Agency estimates that cancer risk decreases to a range of 5 x 10 5 to 1 x 10 8 with engineering controls. Engineering controls included the use of chemical resistant gloves along with water soluble packaging for wettable powder formulations. Overall these data suggest that when PPE and engineering controls are used, none of the evaluated scenarios have cancer risks that exceed 1.0 x 10 4 . Therefore, the Agency is requiring that wettable powder formulations of oxadiazon be packaged in water soluble packaging. In addition, wettable powder product labels will require that handlers wear chemical resistant gloves in addition to long pants and a long sleeved shirt during mixing/ loading/ applying scenarios.

b. Post application The Agency uses the term " post application" to describe those individuals who can be exposed to pesticides when entering areas previously treated with pesticides and performing certain jobs, tasks or activities. This is also often referred to as reentry exposure. The Agency has determined that there are potential post application exposures to individuals re entering oxadiazon treated areas for the purpose of:

Roadsides: mowing Bermuda grass rights of way: mowing Sod farms: mowing, hand weeding, and harvesting Golf course turfgrass: mowing and hand weeding For short and intermediate term non cancer risks, mowing ( e. g., golf courses, roadsides, and sod farms) and harvesting ( e. g., sod farms) scenarios were considered for post application occupational exposure. Calculations for mowing activities resulted in MOEs of 1000.

Calculations for hand weeding and harvesting activities on golf courses and sod farms resulted in MOEs of 30, less than the target MOE of 100 for post application occupational exposures. However, the values used to calculate the hand weeding and harvesting MOEs likely result in an over estimate of risk. For example, the calculation for hand weeding on golf courses assumes that a worker would perform that activity for 8 hours/ day on the day following application of oxadiazon at the maximum application rate. Based on the quality of turf present on high end golf courses most likely to apply oxadiazon, it is unlikely that golf course personnel would spend more than one or two hours per day performing hand weeding activities. The Agency concludes that the risk from post application hand weeding of golf courses does not exceed the level of concern. No mitigation measures will be required. 42 With respect to risk concerns from post application activities on sod farms, while the oxadiazon label does not prohibit its use, the cost of treating with oxadiazon is prohibitive. Due to its cost, less than 20% of sod farmers are using oxadiazon. Those sod farmers that are using oxadiazon apply it as a wettable powder formulation at 2 3 lbs ai/ A immediately after planting ( aka sprigging) to control weeds during sod establishment. Harvesting activities occur six to nine months following application, depending on the variety of grass being grown. As noted above, the scenario with respect to hand weeding assumes an 8 hour workday, which is unlikely. The foliar dissipation half life for oxadiazon ( approximately 1.5 days) is such that after three days post application, the MOE would rise above 100. Therefore, the Agency concludes that the risk from post application harvesting on sod farms does not exceed the level of concern. No mitigation measures will be required.

Cancer risks for occupational postapplication scenarios were estimated not to exceed EPA's level of concern.

4. Inhalation Toxicity and Exposure Uncertainties The Agency is concerned about potential inhalation risk to applicators using wettable powder formulations.

The following confirmatory data are required:

° 870.3465 28 day inhalation toxicity study F. Environmental Risk Mitigation 1. Terrestrial Organism Risk Mitigation Using the EC formulation, at application rates of 2.0  4.0 lbs ai/ A ( 2 applications/ 6 months) and two split applications ( 1.0 lbs ai/ A applied 4 times/ 6 months and 1.3 lbs ai/ A applied 3 times/ 6 months), model estimates indicate that oxadiazon may pose a chronic risk to mammals that eat plants and insects. RQs range from 1 to 5.

The Agency does not currently perform screening level assessments of chronic risk to birds and mammals from granular formulations. Here, the emulsifiable concentrate ( EC) formulation was used to estimate chronic risk to birds and mammals. The emulsifiable concentrate formulation likely represents an upper bound scenario in terms of oxadiazon exposure to birds and mammals that might feed on grasses and insects on golf course turf. Approximately 90% of oxadiazon is applied as a granular formula. Unlike the residue that would remain on grass and foliage following a spray application, granules of oxadiazon would settle to the thatch or soil layer. This is especially true when the turf is watered following application, as many end product labels currently recommend. The granule size for a typical end use product, Ronstar G, is 20/ 50 Mesh, or 300 850 microns. In all products, the formulated granules are designed to fall below the grass canopy. If used according to label directions, it is unlikely that oxadiazon granules would be accessible to birds and mammals that feed on grasses. According to the registrant, for best results oxadiazon granules should be wateredin as soon as is practical following application. Watering in the granules will carry them further into 43 the thatch layer, and will further decrease the likelihood for exposure. As such, the amount of oxadiazon available for ingestion by birds and mammals is likely to be less than was used in calculating the RQ values, and it is likely that the actual exposures would result in RQ values significantly less than the range of 1 to 5 obtained by assessing the emulsifiable concentrate formulation. The Agency concludes that the chronic risk to terrestrial organisms from exposure to oxadiazon does not exceed the level of concern. No mitigation measures will be required.

2. Aquatic Organism Risk Mitigation a. Fish and Invertebrates Tier 1 model estimates of oxadiazon concentrations in water suggest that acute exposures pose low risk to fish ( RQ = 0.1 0.2) and invertebrates ( RQ= 0.3  0.5); however, there is some uncertainty about the role of sunlight on oxadiazon toxicity in clear, shallow bodies of water. GENEEC model outputs suggest that chronic exposure to oxadiazon may result in risk to freshwater and estuarine/ marine fish. RQs range from 94 to 139 ( freshwater) and 55 to 81 ( estuarine/ marine), depending on application rate and formulation. Likewise, model estimates indicate that chronic exposure to oxadiazon may result in chronic risk to freshwater and estuarine/ marine invertebrates. RQs range from 2.9 to 4.5 ( freshwater) and 23 to 37 ( estuarine/ marine), depending on application rate and formulation.

The Tier I GENEEC model 60 day EEC of oxadiazon in surface water following two fourpound applications of granular oxadiazon was 142 ppb. However, the conservative Tier I model does not account for the effect of established golf course turf on reducing run off. Tier II PRZM/ EXAMS estimates of EECs for drinking water, although not directly applicable to the risk assessment for aquatic organisms, suggest that the golf course scenario greatly reduces run off. Tier II estimates of oxadiazon concentrations in surface sourced drinking water were approximately sixfold lower than the Tier I GENEEC estimate described above. It is reasonable to believe that Tier II EECs for a pond scenario would likewise be reduced.

In order to further assess the risk to fish and invertebrates from oxadiazon exposure, the Agency is requiring that the registrant submit toxicity data from early stage estuarine fish studies and life cycle estuarine/ marine invertebrate studies. Also, enhanced toxicity through exposure to high levels of solar radiation may increase toxic risk to aquatic organisms that inhabit small, shallow water bodies. Therefore, EPA is requiring a study on the phototoxicity of oxadiazon in fathead minnows.

b. Benthic Organisms Oxadiazon residues can accumulate in sediments and may increase the risk from chronic exposure of benthic and epibenthic organisms ( aquatic organisms that live in or on the sediment) to the pesticide. In order to better understand this potential risk, EPA is requiring appropriate sediment toxicity testing, both acute and chronic, on this compound. 44 c. Aquatic Plants For aquatic plants, RQs for acute exposure are relatively high, ranging from 1.1 to 4.2 for duckweed, and 8.5 to 33 for diatoms, depending on application rates and formulation.

The Tier I GENEEC model 60 day EEC of oxadiazon in surface water following two fourpound applications of granular oxadiazon was 142 ppb. However, the conservative Tier I model does not account for the effect of established golf course turf on reducing sediment run off. Tier II PRZM/ EXAMS estimates of EECs for drinking water, although not directly applicable to the risk assessment for aquatic organisms, suggest that the golf course scenario greatly reduces run off. Tier II estimates of oxadiazon concentrations in surface sourced drinking water were approximately sixfold lower than the Tier I GENEEC estimate described above. It is reasonable to assume that Tier II EECs for a pond scenario would likewise be reduced.

Currently, the Agency does not have sufficient data with respect to the toxic effects of oxadiazon on aquatic organisms on which to base an effective risk management strategy. To help clarify the risks to aquatic plant species, the Agency is requiring that the registrant submit the following studies: aerobic aquatic metabolism, seedling germination/ emergence, vegetative vigor, and aquatic phototoxicity.