Potential Risks of Atrazine Use to Federally Threatened California Red-legged Frog (Rana aurora draytonii) and Delta Smelt (Hypomesus transpacificus) Pesticide Effects Determinations Environmental Fate and Effects Division Office of Pesticide Programs Washington, D.C. 20460 February 19, 2009 Primary Authors: Mark Corbin, Senior Scientist Brian Anderson, Biologist Secondary Review: Paige Doelling, Ph.D., Acting Risk Assessment Process Leader James Hetrick, Ph.D., Senior Environmental Scientist Branch Chief, Environmental Risk Branch 3: Dana Spatz 2 Table of Contents 1. Executive Summary..............................................................................................................7 1.1. Purpose of Assessment ..................................................................................................7 1.2. Assessed Chemicals.......................................................................................................7 1.3. Assessment Procedures..................................................................................................7 1.4. Atrazine Uses Assessed .................................................................................................9 1.5. Summary of Conclusions.............................................................................................10 2. Problem Formulation .........................................................................................................13 2.1 Purpose...........................................................................................................................13 2.2 Scope..............................................................................................................................15 2.3 Previous Assessments ....................................................................................................18 2.4 Stressor Source and Distribution ...................................................................................20 2.5 Assessed Species............................................................................................................26 2.6. Designated Critical Habitat............................................................................................31 2.7 Action Area....................................................................................................................33 2.8 Assessment Endpoints and Measures of Ecological Effect ...........................................35 2.9 Conceptual Model..........................................................................................................38 2.10 Analysis Plan ...............................................................................................................40 3. Exposure Assessment..........................................................................................................44 3.1 Label Application Rates and Intervals...........................................................................44 3.2 Aquatic Exposure Assessment.......................................................................................46 3.3. Terrestrial Animal Exposure Assessment......................................................................57 4. Effects Assessment ..............................................................................................................61 4.1. Ecotoxicity Study Data Sources.....................................................................................61 4.2. Toxicity Categories........................................................................................................62 4.3. Toxicity of Chemical Mixtures......................................................................................62 4.4 Toxicity of Atrazine to Aquatic Organisms...................................................................63 4.5 Toxicity of Atrazine to Terrestrial Organisms...............................................................74 4.6 Use of Probit Slope Response Relationship to Provide Information on the Endangered Species Levels of Concern....................................................................................................84 4.7 Incident Database Review..............................................................................................85 5. Risk Characterization.........................................................................................................86 5.1 Risk Estimation..............................................................................................................86 5.2 Risk Description...........................................................................................................101 5.3. Modification of Designated Critical Habitat................................................................115 6. Uncertainties......................................................................................................................118 6.1 Exposure Assessment Uncertainties ............................................................................118 6.2 Effects Assessment Uncertainties................................................................................122 7. Risk Conclusions ...............................................................................................................125 8. References..........................................................................................................................129 3 Appendices Appendix A Ecological Effects Data Appendix B Terrestrial RQs for degradates Appendix C Multi-ai Product Analysis Appendix D RQ Method and LOC Definitions Appendix E Accepted ECOTOX Data Table (sorted by effect) Appendix F ECOTOX Bibliography of accepted and rejected papers Appendix G Bibliography of Registrant-Submitted Studies Sorted by Guideline Appendix H Discussion of Atrazine Incidents Appendix I Riparian Habitat Discussion Attachment 1 Life History Information for the CRLF Attachment 2 Baseline Status and Cumulative Effects for the CRLF Attachment 3 Life History Information for the DS Attachment 4 Baseline Status and Cumulative Effects for the DS List of Tables Table 1.1 Effects Determination Summary for Effects of Atrazine on the CRLF and the DS ................................................................................................................................11 Table 1.2 Effects Determination Summary for Atrazine Use and CRLF and DS Critical Habitat Impact Analysis...............................................................................................11 Table 2.1 Summary of Formation Pathway of Atrazine Degradates............................................16 Table 2.2 Comparison of Acute Freshwater Toxicity Values for Atrazine and Degradates ........17 Table 2.3 Summary of Available Degradate Toxicity Data in Birds and Mammals....................17 Table 2.4 Summary of California Department of Pesticide Registration (CDPR) Pesticide Use Reporting (PUR) Data from 1999 to 2006 for Currently Registered Atrazine Uses...............................................................................................................24 Table 2.5 Summary of Current Distribution, Habitat Requirements, and Life History Information for the Assessed Listed Species1..............................................................27 Table 2.6 Designated Critical Habitat PCEs for the CRLF and Delta Smelt1,2. .........................32 Table 2.7 Taxa Used in the Analyses of Direct and Indirect Effects for the Assessed Listed Species. .............................................................................................................36 Table 2.8 Assessment Endpoints Used to Evaluate the Potential for the Use of Atrazine to Result in Direct and Indirect Effects to the CRLF and the DS................................36 Table 3.1 Atrazine Label Application Information for the CRLF & Delta Smelt Assessmenta .................................................................................................................46 Table 3.2 Summary of PRZM Scenarios .......................................................................................49 Table 3.3 Summary of PRZM/EZAMS Environmental Fate Data Used for Aquatic Exposure Inputs for Atrazine.......................................................................................52 Table 3.4 Aquatic EECs (μg/L) for Atrazine Uses in California...................................................53 Table 3.5 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based Exposures of the CRLF and its Prey to Atrazine.........................................................58 4 Table 3.6 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via Effects to Terrestrial Invertebrate Prey Items ..............................................................................59 Table 3.7 Screening-Level Exposure Estimates for Terrestrial Plants to Atrazine ......................60 Table 4.1 Categories of Acute Toxicity for Aquatic Organisms ..................................................62 Table 4.2 Aquatic Toxicity Profile for Atrazine...........................................................................64 Table 4.3 Data on the toxicity of atrazine to Eurytemora affinis..................................................70 Table 4.4 Acute and Chronic Aquatic Invertebrate Toxicity Values Used in Risk Estimation of Atrazine .................................................................................................72 Table 4.5 Summary of available acute and reproduction