| Foreword | 4 |
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| Preface | 6 |
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| Contents | 8 |
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| Contributors | 9 |
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| The University of California-Davis Methodology for Deriving Aquatic Life Pesticide Water Quality Criteria | 10 |
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| 1 Introduction | 11 |
| 1.1 Definition of Numeric Criteria | 12 |
| 1.2 Goal and Level of Organization to Protect | 14 |
| 2 Data for Criteria Generation | 15 |
| 2.1 Kinds of Data | 15 |
| 2.1.1 Acute vs. Chronic Toxicity Data | 16 |
| 2.1.2 Hypothesis Tests vs. Regression Analysis | 18 |
| 2.1.3 Endpoints | 20 |
| 2.1.4 Multispecies (Field/Semi-field, Laboratory) Data | 22 |
| 2.1.5 Data from Multi-pathway Exposures | 23 |
| 2.1.6 Toxicity Data that Incorporate Time | 23 |
| 2.2 Filling Data Gaps with Estimation Techniques | 24 |
| 2.2.1 Quantitative Structure Activity Relationships (QSARs) | 24 |
| 2.2.2 Interspecies Correlations for Estimation of Toxicity | 25 |
| 2.2.3 Estimating Chronic Toxicity from Acute Data | 25 |
| 2.3 Data Sources and Literature Searches | 26 |
| 2.4 Data Summaries of Ecotoxicity Data | 29 |
| 2.5 Data Evaluation | 29 |
| 2.5.1 Physical--Chemical Data | 31 |
| 2.5.2 Ecotoxicity Data Evaluation | 34 |
| 2.6 Data Quantity -- Ecotoxicity | 41 |
| 2.7 Data Reduction | 44 |
| 3 Criteria Calculation | 46 |
| 3.1 SSD Procedure | 47 |
| 3.1.1 Distribution Shape and Fit | 47 |
| 3.1.2 Percentile Cutoff | 61 |
| 3.1.3 Level of Confidence | 62 |
| 3.1.4 Aggregation of Taxa and Outliers | 63 |
| 3.1.5 Comparison of Methods | 64 |
| 3.1.6 SSDs in the UCDM | 68 |
| 3.2 AF Procedure | 69 |
| 3.2.1 Appropriate Use of AFs | 71 |
| 3.2.2 Toxicity Values | 72 |
| 3.2.3 Magnitude Factors | 73 |
| 3.2.4 Acute Factors | 73 |
| 3.2.5 Acute-to-Chronic Ratios (ACRs) | 75 |
| 3.3 Averaging Periods | 78 |
| 3.4 Allowable Frequency of Exceedance | 80 |
| 3.4.1 Review of the Literature | 80 |
| 3.4.2 Allowable Frequency of Exceedance -- Conclusion | 84 |
| 4 Water Quality Effects | 85 |
| 4.1 Bioavailability | 85 |
| 4.2 Mixtures | 89 |
| 4.2.1 Additivity | 90 |
| 4.2.2 Non-additivity: Synergism and Antagonism | 93 |
| 4.2.3 Combined Models | 94 |
| 4.2.4 Conclusions on Mixtures | 96 |
| 4.3 Other Water Quality Effects | 96 |
| 5 Check Criteria Against Ecotoxicity Data | 96 |
| 5.1 Sensitive Species | 97 |
| 5.2 Ecosystem and Other Studies | 97 |
| 5.3 Threatened and Endangered Species | 97 |
| 6 Partitioning to Other Environmental Compartments | 98 |
| 6.1 Bioaccumulation/Secondary Poisoning | 98 |
| 6.2 Harmonization with Sediment and Air Criteria | 101 |
| 7 Assumptions and Limitations | 102 |
| 7.1 Assumptions, Limitations, and Uncertainties of the UCDM | 102 |
| 7.2 Data Generation to Improve Criteria Derivation | 103 |
| 8 Guideline Format | 104 |
| 9 The UCD Methodology | 104 |
| 9.1 Goals and Definitions | 104 |
| 9.1.1 Relevant Compounds | 105 |
| 9.1.2 Definition of Numeric Criteria | 105 |
| 9.1.3 Overview | 105 |
| 9.2 Data | 105 |
| 9.2.1 Data Collection | 107 |
| 9.2.2 Data Evaluation | 110 |
| 9.2.3 Filling Chronic Toxicity Data Gaps with Estimation Techniques | 112 |
| 9.2.4 Data Reduction | 112 |
| 9.2.5 Data Graphing | 114 |
| 9.3 Acute Criterion Derivation | 114 |
| 9.3.1 Data Requirements Applicable to Use of the SSD | 114 |
| 9.3.2 Derivation of a Criterion Using an SSD | 115 |
| 9.3.3 Derivation of an Acute Criterion Using an AF | 122 |
| 9.4 Chronic Criterion Derivation | 123 |
| 9.4.1 Derivation of a Chronic Criterion Using an SSD | 123 |
| 9.4.2 Derivation of a Chronic Criterion Using an ACR | 123 |
| 9.4.3 Derivation of a Chronic Criterion for a Herbicide | 126 |
| 9.5 Incorporation of Water Quality Effects into Criteria Compliance | 126 |
| 9.5.1 Bioavailability | 127 |
| 9.5.2 Mixtures | 128 |
| 9.5.3 Temperature, pH, and Other Effects | 130 |
| 9.6 Checking Criteria Against Ecotoxicity Data | 133 |
| 9.6.1 Sensitive Species | 133 |
| 9.6.2 Ecosystem and Other Studies | 134 |
| 9.6.3 Threatened and Endangered Species | 134 |
| 9.7 Partitioning to Other Environmental Compartments | 136 |
| 9.7.1 Bioaccumulation/Secondary Poisoning | 136 |
| 9.7.2 Harmonization with Air or Sediment Criteria | 141 |
| 9.8 Reviewing Assumptions and Limitations to Derived Criteria | 142 |
| 9.9 Final Criteria Statement | 143 |
| 10 Summary | 143 |
| Acknowledgments | 145 |
| Appendix: Acute Chlorpyrifos Data Collected for Criteria Derivation Using the UCDM Derivation | 146 |
| References | 151 |
| Index | 165 |