Risks of 2,4-D Use to the Federally Threatened California Red-legged Frog (Rana aurora draytonii) and Alameda Whipsnake (Masticophis lateralis euryxanthus) Pesticide Effects Determination Environmental Fate and Effects Division Office of Pesticide Programs Washington, D.C. 20460 February 20, 2009 1 Primary Authors: Christine Hartless, Ph.D., Wildlife Biologist Marie Janson, M.S., Environmental Scientist, Team Lead Fred Jenkins, M.S., Fisheries Biologist James Lin, Ph.D., Environmental Engineer Anita Ullagaddi, M.S., Environmental Protection Specialist Secondary Review: Faruque Khan, Ph.D., Senior Scientist Edward Odenkirchen, Ph.D., Senior Biologist Branch Chief, Environmental Risk Assessment Branch 1 Nancy Andrews, Ph.D. 2 Table of Contents 1. Executive Summary.................................................................................................. 6 2. Problem Formulation ............................................................................................. 27 2.1 Purpose............................................................................................................. 27 2.2 Scope................................................................................................................. 29 2.3 Previous Assessments...................................................................................... 31 2.4 Stressor Source and Distribution .................................................................. 32 2.4.1. Environmental Fate Bridging Strategy................................................. 32 2.4.2 Physical and Chemical Properties of 2,4-D Acid ................................. 35 2.4.3 Environmental Fate Properties of 2,4-D Acid...................................... 37 2.4.4 Terrestrial Field Dissipation Study Summaries for 2,4-D .................. 39 2.4.5 Aquatic Field Dissipation Study Summaries for 2,4-D........................ 40 2.4.6 Forest Field Dissipation Study Summaries for 2,4-D .......................... 42 2.4.7 Environmental Transport Mechanisms................................................ 43 2.4.8 Mechanism of Action .............................................................................. 45 2.4.9 Use Characterization .............................................................................. 45 2.5 Assessed Species .............................................................................................. 54 2.6 Designated Critical Habitat ........................................................................... 58 2.7 Action Area...................................................................................................... 59 2.8 Assessment Endpoints and Measures of Ecological Effect ......................... 61 2.8.1 Bridging Strategy for Toxicological Data............................................. 61 2.8.2 Assessment Endpoints ............................................................................ 62 2.8.3 Assessment Endpoints for Designated Critical Habitat ...................... 65 2.9 Conceptual Model ........................................................................................... 67 2.9.1 Risk Hypotheses ...................................................................................... 67 2.9.2 Diagram ................................................................................................... 68 2.10 Analysis Plan ................................................................................................... 70 2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model... 71 2.10.2 Data Gaps ................................................................................................ 74 3. Exposure Assessment.............................................................................................. 74 3.1 Label Application Rates and Intervals ......................................................... 74 3.2 Aquatic Exposure Assessment ....................................................................... 78 3.2.1 Surface Water Modeling Approach and Inputs for 2,4-D Acid (all scenarios except rice and direct water application)............................................. 78 3.2.2 Surface Water Modeling Approach and Inputs for 2,4-D Ester Drift Only and Drift+Runoff (all scenarios except rice and direct water applications) 79 3.2.3 Surface Water Modeling Approach and Inputs for Rice Scenario .... 81 3.2.4 Surface Water Modeling Approach and Inputs for Direct Application Scenario 82 3.2.5 Surface Water Modeling Results and Estimated Aquatic EECs........ 83 3.2.6 Groundwater Modeling of 2,4-D Acid .................................................. 88 3.2.7 Existing Monitoring Data....................................................................... 88 3.2.8 Downstream Dilution Analysis ............................................................. 90 3.3 Terrestrial Animal Exposure Assessment .................................................... 90 3 3.4 Terrestrial Plant Exposure Assessment........................................................ 96 4. Effects Assessment .................................................................................................. 99 4.1 Dioxin Contaminant Toxicity to Terrestrial Organisms............................. 101 4.2 Toxicity of 2,4-D to Aquatic Organisms ..................................................... 102 4.2.1 Toxicity to Freshwater Fish and Aquatic-phase Amphibians .......... 104 4.2.2 Toxicity to Freshwater Invertebrates.................................................. 106 4.2.3 Toxicity to Aquatic Plants.................................................................... 107 4.3 Toxicity of 2,4-D to Terrestrial Organisms ................................................ 108 4.3.1 Toxicity to Birds.................................................................................... 110 4.3.2 Toxicity to Mammals ............................................................................ 111 4.3.3 Toxicity to Terrestrial Invertebrates .................................................. 112 4.3.4 Toxicity to Terrestrial Plants............................................................... 112 4.4 Incident Database Review ............................................................................ 113 4.4.1 Terrestrial Incidents ............................................................................. 114 4.4.2 Plant Incidents....................................................................................... 115 4.4.3 Aquatic Incidents .................................................................................. 116 5. Risk Characterization........................................................................................... 117 5.1 Risk Estimation ............................................................................................. 117 5.1.1 Exposures in the Aquatic Habitat ....................................................... 117 5.1.2 Exposures in the Terrestrial Habitat ................................................. 126 5.1.3 Primary Constituent Elements of Designated Critical Habitat........ 140 5.2 Risk Description............................................................................................ 140 5.2.1 Direct Effects ......................................................................................... 147 5.2.2 Indirect Effects (via Reductions in Prey Base)................................... 155 5.2.3 Indirect Effects (via Habitat Effects) .................................................. 160 5.2.4 Modification to Designated Critical Habitat ...................................... 164 6. Uncertainties...................................................................................................... 166 6.1 Exposure Assessment Uncertainties............................................................ 166 6.1.1 Maximum Use Scenario........................................................................ 166 6.1.2 Usage Uncertainties .............................................................................. 166 6.1.3 Aquatic Exposure Modeling of 2,4-D.................................................. 167 6.1.4 Potential Groundwater Contributions to Surface Water Chemical Concentrations ...................................................................................................... 169 6.1.5 Terrestrial Exposure Modeling of 2,4-D............................................. 170 6.1.6 Spray Drift Modeling............................................................................ 170 6.2 Effects Assessment Uncertainties ................................................................ 171 6.2.1 Age Class and Sensitivity of Effects Thresholds ................................ 171 6.2.2 Use of Surrogate Species Effects Data ................................................ 172 6.2.3 Sublethal Effects.................................................................................... 172 7. Risk Conclusions ................................................................................................... 173 8. References.............................................................................................................. 181 4 List of Attachments • Attachment 1: Life History of the California Red-legged Frog • Attachment 2: Baseline Status and Cumulative Effects for the California Red- legged Frog • Attachment 3: Life History of the Alameda Whipsnake • Attachment 4: Baseline Status and Cumulative Effects for the Alameda Whipsnake List of Appendices • Appendix A: Multi-ai