Risks of Linuron Use to Federally Threatened California Red-legged Frog (Rana aurora draytonii) Pesticide Effects Determination Environmental Fate and Effects Division Office of Pesticide Programs Washington, D.C. 20460 June 19, 2008 Primary Authors: Michael Davy, Agronomist Wm. J. Shaughnessy, Ph.D, Environmental Scientist Environmental Risk Branch II Environmental Fate and Effects Division (7507C) Secondary Review: Donna Randall, Senior Effects Scientist Nelson Thurman, Senior Fate Scientist Environmental Risk Branch II Environmental Fate and Effects Division (7507P) Branch Chief, Environmental Risk Assessment Branch #: Arthur-Jean B. Williams, Acting Branch Chief Environmental Risk Branch II Environmental Fate and Effects Division (7507P) 2 Table of Contents 1. Executive Summary.................................................................................................8 2. Problem Formulation .............................................................................................14 2.1 Purpose...........................................................................................................................14 2.2 Scope..............................................................................................................................16 2.3 Previous Assessments ....................................................................................................18 2.4 Stressor Source and Distribution ...................................................................................19 2.4.1 Environmental Fate Properties...............................................................................19 2.4.2 Environmental Transport Mechanisms..................................................................21 2.4.3 Mechanism of Action.............................................................................................21 2.4.4 Use Characterization..............................................................................................22 2.5 Assessed Species............................................................................................................27 2.5.1 Distribution ............................................................................................................27 2.5.2 Reproduction..........................................................................................................32 2.5.3 Diet.........................................................................................................................32 2.5.4 Habitat....................................................................................................................33 2.6 Designated Critical Habitat............................................................................................34 2.7 Action Area....................................................................................................................36 2.8 Assessment Endpoints and Measures of Ecological Effect ...........................................40 2.8.1. Assessment Endpoints for the CRLF.....................................................................40 2.8.2 Assessment Endpoints for Designated Critical Habitat.........................................42 2.9 Conceptual Model..........................................................................................................44 2.9.1 Risk Hypotheses.....................................................................................................44 2.9.2 Diagram..................................................................................................................44 2.10 Analysis Plan .................................................................................................................48 2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model ......................48 2.10.1.1 Measures of Exposure............................................................................ 48 2.10.1.2 Measures of Effect ................................................................................. 50 2.10.1.3 Integration of Exposure and Effects ...................................................... 51 2.10.2 Data Gaps...............................................................................................................52 3. Exposure Assessment.............................................................................................52 3.1 Label Application Rates and Intervals...........................................................................52 3.2 Aquatic Exposure Assessment.......................................................................................53 3.2.1 Modeling Approach ...............................................................................................53 3.2.2 Model Inputs ..........................................................................................................53 3.2.3 Results....................................................................................................................54 3.2.4 Existing Monitoring Data ......................................................................................55 3.2.5 Spray Drift Buffer Analysis...................................................................................56 3.2.6 Downstream Dilution Analysis..............................................................................58 3.3 Terrestrial Animal Exposure Assessment......................................................................58 3.4 Terrestrial Plant Exposure Assessment..........................................................................60 4. Effects Assessment ................................................................................................60 4.1 Toxicity of Linuron to Aquatic Organisms....................................................................63 4.1.1 Toxicity to Freshwater Fish ...................................................................................64 4.1.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies......................................... 64 3 4.1.1.2 Freshwater Fish: Chronic Exposure (Growth/Reproduction) Studies ................. 64 4.1.1.3 Freshwater Fish: Sublethal Effects and Additional Open Literature Information ........................................................................................................... 66 4.1.2 Toxicity to Freshwater Invertebrates .....................................................................66 4.1.2.1 Freshwater Invertebrates: Acute Exposure Studies ............................................. 66 4.1.2.2 Freshwater Invertebrates: Chronic Exposure Studies.......................................... 67 4.1.2.3 Freshwater Invertebrates: Open Literature Data.................................................. 69 4.1.3 Toxicity to Aquatic Plants .....................................................................................69 4.1.3.1 Aquatic Plants: Laboratory Data........................................................................... 69 4.1.3.1 Aquatic Plants: Open Literature Data................................................................... 69 4.2 Toxicity of Linuron to Terrestrial Organisms................................................................70 4.2.1 Toxicity to Birds ....................................................................................................71 4.2.1.1 Birds: Acute Exposure (Mortality) Studies........................................................... 71 4.2.1.2 Birds: Chronic Exposure (Growth, Reproduction) Studies ................................. 71 4.2.2 Toxicity to Mammals.............................................................................................72 4.2.2.1 Mammals: Acute Exposure (Mortality) Studies ................................................... 72 4.2.2.2 Mammals: Chronic Exposure (Growth, Reproduction) Studies........................... 72 4.2.3 Toxicity to Terrestrial Invertebrates ......................................................................72 4.2.4 Toxicity to Terrestrial Plants .................................................................................72 4.3 Use of Probit Slope Response Relationship to Provide Information on the Endangered Species Levels of Concern.........................................................................................................74 4.4 Incident Database Review..............................................................................................74 4.4.1 Terrestrial Incidents ...............................................................................................75 4.4.2 Plant Incidents........................................................................................................75 5.1 Risk Estimation..............................................................................................................77 5.1.1 Exposures in the Aquatic Habitat ..........................................................................77 5.1.1.1 Direct Effects to Aquatic-Phase CRLF................................................................. 77 5.1.1.2 Indirect Effects to Aquatic-Phase CRLF via Reduction in Prey (non-vascular aquatic plants, aquatic invertebrates, fish, and frogs)........................................... 79 5.1.1.3 Indirect Effects to CRLF via Reduction in Habitat and/or Primary Productivity (Freshwater Aquatic Plants).................................................................................. 80 5.1.2 Exposures in the Terrestrial Habitat ......................................................................81