Risks of Chlorpyrifos Use to Federally Threatened & Endangered California red-legged frog (Rana aurora draytonii), California tiger salamander (Ambystoma californiense), San Francisco garter snake (Thamnophis sirtalis tetrataenia), California clapper rail, (Rallus longirostris obsoletus), Salt marsh harvest mouse (Reithrodontomys raviventris), Bay checkerspot butterfly (Euphydryas editha bayensis), Valley elderberry longhorn beetle (Desmocerus californicus dimorphus), San Joaquin kit fox (Vulpes macrotis mutica), California freshwater shrimp (Syncaris pacifica), and Delta smelt (Hypomesus transpacificus) Pesticide Effects Determinations Environmental Fate and Effects Division Office of Pesticide Programs Washington, D.C. 20460 October 16, 2009 Primary Authors: Mark Corbin, Senior Environmental Scientist Rebecca Daiss, Senior Biologist Donna R. Judkins, Ph.D., Biologist Secondary Review: James K. Wolf, Ph.D., Soil Physicist Pamela Hurley, Senior Toxicologist Dana Spatz, Branch Chief Environmental Risk Assessment Branch 3 2 Table of Contents 1 Executive Summary...............................................................................................8 2 Problem Formulation ..........................................................................................16 2.1 Purpose..........................................................................................................................16 2.2 Scope..............................................................................................................................18 2.3 Previous Assessments...................................................................................................19 2.4 Stressor Source and Distribution ...............................................................................22 2.4.1 Environmental Fate Properties ..........................................................................22 2.4.2 Environmental Transport Mechanisms.............................................................26 2.4.3 Mechanism of Action ...........................................................................................27 2.4.4 Use Characterization ...........................................................................................27 2.5 Assessed Species ...........................................................................................................44 2.6 Designated Critical Habitat ........................................................................................50 2.7 Action Area...................................................................................................................53 2.8 Assessment Endpoints and Measures of Ecological Effect ......................................54 2.8.1 Assessment Endpoints .........................................................................................55 2.8.2 Assessment Endpoints for Designated Critical Habitat ...................................59 2.9 Conceptual Model ........................................................................................................61 2.9.1 Risk Hypotheses ...................................................................................................61 2.9.2 Diagram ................................................................................................................61 2.10 Analysis Plan ................................................................................................................63 2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model................64 2.10.2 Data Gaps .............................................................................................................68 3 Exposure Assessment...........................................................................................68 3.1 Label Application Rates and Intervals ......................................................................69 3.2 Aquatic Exposure Assessment ....................................................................................74 3.2.1 Modeling Approach .............................................................................................74 3.2.2 Model Inputs.........................................................................................................75 3.2.3 Results ...................................................................................................................77 3.2.4 Existing Monitoring Data....................................................................................83 3.3 Terrestrial Animal Exposure Assessment .................................................................87 3.4 Terrestrial Plant Exposure Assessment.....................................................................93 4 Effects Assessment ...............................................................................................93 4.1 Toxicity of Chlorpyrifos to Aquatic Organisms........................................................96 4.1.1 Toxicity to Freshwater Fish and Aquatic-Phase Amphibians .........................98 4.1.2 Toxicity to Freshwater Invertebrates...............................................................102 4.1.3 Toxicity to Estuarine/Marine Fish ...................................................................103 4.1.4 Toxicity to Estuarine/Marine Invertebrates....................................................103 4.1.5 Toxicity to Aquatic Plants.................................................................................103 4.1.6 Freshwater Field/Mesocosm Studies................................................................104 4.2 Toxicity of Chlorpyrifos to Terrestrial Organisms.................................................105 4.2.1 Toxicity to Birds, Reptiles, and Terrestrial-Phase Amphibians....................107 4.2.2 Toxicity to Mammals .........................................................................................112 4.2.3 Toxicity to Terrestrial Invertebrates ...............................................................116 4.2.4 Toxicity to Terrestrial Plants............................................................................117 3 4.3 Use of Probit Slope Response Relationship to Provide Information on the Endangered Species Levels of Concern .....................................................................................................117 4.4 Incident Database Review .........................................................................................118 4.5 Toxicity of Chlorpyrifos Oxon..................................................................................118 5 Risk Characterization........................................................................................120 5.1 Exposures in the Aquatic Habitat ............................................................................120 5.1.1 Freshwater Fish and Aquatic-phase Amphibians...........................................121 5.1.2 Freshwater Invertebrates..................................................................................124 5.1.3 Estuarine/Marine Fish.......................................................................................126 5.1.4 Estuarine/Marine Invertebrates.......................................................................127 5.1.5 Non-vascular Aquatic Plants ............................................................................127 5.2 Exposures in the Terrestrial Habitat .......................................................................128 5.2.1 Birds (surrogate for Reptiles and Terrestrial-phase amphibians)................128 5.2.2 Mammals ............................................................................................................131 5.2.3 Terrestrial Invertebrates...................................................................................134 5.2.4 Terrestrial Plants ...............................................................................................135 5.3 Primary Constituent Elements of Designated Critical Habitat.............................137 5.4 Spatial Extent of Potential Effects............................................................................137 5.4.1 Spray Drift..........................................................................................................138 5.4.2 Downstream Dilution Analysis .........................................................................138 5.4.3 Overlap between CRLF and SFB Species habitat and Spatial Extent of Potential Effects ..............................................................................................138 5.5 Risk Description.........................................................................................................139 5.5.1 Direct Effects ......................................................................................................144 5.5.2 Indirect Effects...................................................................................................156 5.5.3 Potential Modification of Habitat.....................................................................160 5.5.4 Modification of Designated Critical Habitat ...................................................161 6 Uncertainties.......................................................................................................162 6.1 Exposure Assessment Uncertainties.........................................................................162 6.1.1 Oxon Exposure and Risk...................................................................................162 6.1.2 Maximum