Risks of Endosulfan Use to the Federally Threatened 

California Red-legged Frog (Rana aurora draytonii),

Bay Checkerspot Butterfly (Euphydryas editha bayensis),

Valley Elderberry Longhorn Beetle (Desmocerus californicus 

dimorphus), and California Tiger Salamander (Ambystoma 

californiense)

And the Federally Endangered 

San Francisco Garter Snake (Thamnophis sirtalis tetrataenia),

San Joaquin Kit Fox (Vulpes macrotis mutica), and 

Salt Marsh Harvest Mouse (Reithrodontomys raviventris)

Pesticide Effects Determinations 

Environmental Fate and Effects Division 

Office of Pesticide Programs 

Washington, D.C. 20460 

June 18, 2009

Primary Authors: 

Ecological Effects 

 Keith Sappington, M.S., Biologist, OPP/EFED 

 Glen Thursby, Ph.D, Biologist, ORD/NHEERL/AED 

 Sandy Raimondo, Ph.D., Ecologist, ORD/NHEERL/GED 

Environmental Fate 

 Mohammed Ruhman, Ph.D, Agronomist, OPP/EFED 

Secondary Review: 

 Mah Shamim, Ph.D., Branch Chief, OPP/EFED 

 Environmental Risk Assessment Branch 5

1
Table of Contents

1 Executive Summary.............................................................................................11 

2 Problem Formulation ..........................................................................................25 

2.1 Purpose................................................................................................................................ 25 

2.2 Scope................................................................................................................................... 27 

2.3 Previous Assessments......................................................................................................... 29 

2.4 Stressor Source and Distribution ........................................................................................ 30 

2.4.1 Environmental Fate Properties..................................................................................... 32 

2.4.2 Environmental Transport Mechanisms........................................................................ 36 

2.4.3 Mechanism of Action................................................................................................... 36 

2.4.4 Use Characterization.................................................................................................... 37 

2.5 Assessed Species................................................................................................................. 48 

2.6 Designated Critical Habitat................................................................................................. 53 

2.7 Action Area......................................................................................................................... 55 

2.8 Assessment Endpoints and Measures of Ecological Effect ................................................ 58 

2.8.1 Assessment Endpoints ................................................................................................. 58 

2.8.2 Assessment Endpoints for Designated Critical Habitat............................................... 62 

2.9 Conceptual Model............................................................................................................... 64 

2.9.1 Risk Hypotheses........................................................................................................... 64 

2.9.2 Diagram........................................................................................................................ 65 

2.10 Analysis Plan .................................................................................................................... 66 

2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model .......................... 66 

2.10.1.1 Measures of Exposure......................................................................................... 67 

2.10.1.2 Measures of Effect.............................................................................................. 69 

2.10.1.3 Integration of Exposure and Effects ................................................................... 70 

2.10.2 Data Gaps................................................................................................................... 70 

3 Exposure Assessment...........................................................................................71 

3.1 Label Application Rates, Intervals and Buffers.................................................................. 71 

3.2 Aquatic Exposure Assessment............................................................................................ 73 

3.2.1 Modeling Approach ..................................................................................................... 73 

3.2.2 Model Inputs................................................................................................................ 75 

3.2.3 Results.......................................................................................................................... 76 

3.2.4 Existing Monitoring Data ............................................................................................ 81 

3.2.4.1 Surface Water Monitoring Data............................................................................ 81 

3.2.4.2 Groundwater Monitoring Data.............................................................................. 91 

3.2.4.3 Sediment Monitoring Data.................................................................................... 91 

3.2.4.4 Atmospheric Monitoring Data .............................................................................. 92 

3.3 Terrestrial Animal Exposure Assessment........................................................................... 99 

3.4 Terrestrial Plant Exposure Assessment............................................................................. 103 

4 Effects Assessment.............................................................................................104 

4.1 Toxicity of Endosulfan to Aquatic Organisms................................................................. 106 

4.1.1 Toxicity to Freshwater Fish and Aquatic-Phase Amphibians.................................... 108 

4.1.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies – Registrant submitted .. 108 

4.1.1.2 Freshwater Fish: Acute Exposure (Mortality) Studies—Open Literature .......... 108 

4.1.1.3 Freshwater Fish: Chronic Exposure (Growth/Reproduction) Studies ................ 108 

2
4.1.1.4 Freshwater Fish: Sublethal Effects and Additional Open Literature Information

......................................................................................................................................... 109 

4.1.1.5 Aquatic-phase Amphibian: Acute and Chronic Studies ..................................... 110 

4.1.1.6 Freshwater Fish: Endosulfan Sulfate .................................................................. 110 

4.1.2 Toxicity to Freshwater Invertebrates......................................................................... 110 

4.1.2.1 Freshwater Invertebrates: Acute Exposure Studies............................................ 110 

4.1.2.2 Freshwater Invertebrates: Acute Exposure Studies—Open Literature............... 110 

4.1.2.3 Freshwater Invertebrates: Chronic Exposure Studies......................................... 111 

4.1.2.4 Freshwater Invertebrates: Sub-lethal Effects and Additional Open Literature 

Information ..................................................................................................................... 111 

4.1.2.5 Freshwater Invertebrates: Endosulfan Sulfate .................................................... 111 

4.1.2.6 Freshwater Invertebrates: Sediment Toxicity ..................................................... 112 

4.1.3 Toxicity to Estuarine/Marine Fish ............................................................................. 112 

4.1.3.1 Estuarine/Marine Fish: Acute Exposure (Mortality) Studies.............................. 112 

4.1.3.2 Estuarine/Marine Fish: Acute Exposure (Mortality) Studies—Open Literature 112 

4.1.3.3 Estuarine/Marine Fish: Chronic Exposure (Growth/Reproduction) Studies...... 112 

4.1.4 Toxicity to Estuarine/Marine Invertebrates............................................................... 113 

4.1.4.1 Estuarine/Marine Invertebrates: Acute Exposure (Mortality) Studies................ 113 

4.1.4.2 Estuarine/Marine Invertebrates: Acute Exposure (Mortality) Studies—Open 

Literature......................................................................................................................... 114 

4.1.4.3 Estuarine/Marine Invertebrates: Chronic Exposure (Growth/Reproduction) 

Studies............................................................................................................................. 114 

4.1.4.4 Estuarine/Marine Invertebrates: Open Literature Data....................................... 115 

4.1.4.5 Estuarine/Marine Invertebrates: Endosulfan Sulfate .......................................... 115 

4.1.5 Toxicity to Aquatic-phase Amphibians—Open Literature........................................ 115 

4.1.6 Toxicity to Aquatic Plants ......................................................................................... 117 

4.1.7 Freshwater Field/Mesocosm Studies......................................................................... 118 

4.2 Toxicity of Endosulfan to Terrestrial Organisms ............................................................. 119 

4.2.1 Toxicity to Birds, Reptiles, and Terrestrial-Phase Amphibians ................................ 120 

4.2.1.1 Birds: Acute Exposure (Mortality) Studies......................................................... 120 

4.2.1.2 Birds: Chronic Exposure (Growth, Reproduction) Studies................................ 120 

4.2.1.3 Birds: Open literature Studies............................................................................. 121 

4.2.1.4 Birds: Endosulfan Sulfate ................................................................................... 121 

4.2.2 Toxicity to Mammals................................................................................................. 121 

4.2.2.1 Mammals: Acute Exposure (Mortality) Studies................................................. 121 

4.2.2.2 Mammals: Chronic Exposure (Growth, Reproduction) Studies......................... 122 

4.2.2.3 Mammals: Endosulfan Sulfate............................................................................ 122 

4.2.3 Toxicity to Terrestrial Invertebrates.......................................................................... 122 

4.2.3.1 Terrestrial Invertebrates: Acute Exposure (Mortality) Studies........................... 123 

4.2.3.2 Terrestrial Invertebrates: Open Literature Studies.............................................. 123 

4.2.4 Toxicity to Terrestrial Plants ..................................................................................... 124 

4.3 Use of Probit Slope Response Relationship to Provide Information on the Endangered 

Species Levels of Concern...................................................................................................... 124 

4.4 Ecological Incident Summary........................................................................................... 125 

5 Risk Characterization........................................................................................127 

5.1 Risk Estimation................................................................................................................. 127 

3
5.1.1 Exposures in the Aquatic Habitat .............................................................................. 128 

5.1.1.1 Freshwater Fish and Aquatic-phase Amphibians ............................................... 128 

5.1.1.2 Freshwater Invertebrates..................................................................................... 129 

5.1.1.3 Non-vascular Aquatic Plants............................................................................... 131 

5.1.1.4 Aquatic Vascular Plants...................................................................................... 131 

5.1.2 Exposures in the Terrestrial Habitat .......................................................................... 131 

5.1.2.1 Birds (surrogate for Reptiles and Terrestrial-phase amphibians)....................... 131 

5.1.2.2 Mammals............................................................................................................. 135 

5.1.2.3 Terrestrial Invertebrates...................................................................................... 138 

5.1.2.4 Terrestrial Plants................................................................................................. 140 

5.1.3 Primary Constituent Elements of Designated Critical Habitat .................................. 140 

5.1.4 Spatial Extent of Potential Effects ............................................................................. 140 

5.1.4.1 Spray Drift .......................................................................................................... 140 

5.1.4.2 Downstream Dilution Analysis........................................................................... 141 

5.1.4.3 Overlap between CRLF, CTS, SFGS, BCB, VELB, SMHM, and SJKF habitat 

and Spatial Extent of Potential Effects........................................................................... 141 

5.2 Risk Description................................................................................................................ 143 

5.2.1 California Red-Legged Frog...................................................................................... 163 

5.2.1.1 Direct Effects ...................................................................................................... 163 

5.2.1.2 Indirect Effects to CRLF (via Potential Loss of Prey)........................................ 178 

5.2.1.3 Indirect Effects (via Habitat Effects).................................................................. 185 

5.2.1.4 Effects to Designated Critical Habitat ................................................................ 186 

5.2.2 California tiger salamander........................................................................................ 187 

5.2.2.1 Direct Effects .......................................................................................................... 187 

5.2.2.2 Indirect Effects (via Reductions in Prey Base)................................................... 191 

5.2.2.3 Modification to Designated Critical Habitat....................................................... 193 

5.2.3 San Francisco Garter Snake ....................................................................................... 194 

5.2.3.1 Direct Effects ...................................................................................................... 194 

5.2.3.2 Indirect Effects (via Reductions in Prey Base)................................................... 196 

5.2.3.3 Indirect Effects (via Habitat Effects) .................................................................. 198 

5.2.4 Salt Marsh Harvest Mouse......................................................................................... 199 

5.2.4.1 Direct Effects ...................................................................................................... 199 

5.2.4.2 Indirect Effects (via Reductions in Prey Base)................................................... 202 

5.2.4.3 Indirect Effects (via Habitat Effects) .................................................................. 203 

5.2.5 San Joaquin Kit Fox................................................................................................... 204 

5.2.5.1 Direct Effects ...................................................................................................... 204 

5.2.5.2 Indirect Effects (via Reductions in Prey Base)................................................... 206 

5.2.5.3 Indirect Effects (via Habitat Effects) .................................................................. 208 

5.2.6 Bay Checkerspot Butterfly......................................................................................... 208 

5.2.6.1 Direct Effects ...................................................................................................... 208 

5.2.6.2 Indirect Effects (via Reduction in Prey Base & Habitat Effects) ....................... 210 

5.2.6.3 Modification to Designated Critical Habitat....................................................... 210 

5.2.7 Valley Elderberry Longhorn Beetle........................................................................... 211 

5.2.7.1 Direct Effects ...................................................................................................... 211 

5.2.7.2 Indirect Effects (via Reduction in Prey Base & Habitat Effects) ....................... 212 

5.2.7.3 Modification to Designated Critical Habitat....................................................... 213 

4
6 Uncertainties.......................................................................................................214 

6.1 Exposure Assessment Uncertainties................................................................................. 214 

6.1.1 Maximum Use Scenario............................................................................................. 214 

6.1.2 Aquatic Exposure Modeling of Endosulfan............................................................... 214 

6.1.2.1 Potential Groundwater Contributions to Surface Water Chemical Concentrations

......................................................................................................................................... 216 

6.1.3 Multiple Growing Seasons per Year.......................................................................... 217 

6.1.4 Usage Uncertainties................................................................................................... 217 

6.1.5 Terrestrial Exposure Modeling of Endosulfan........................................................... 217 

6.1.6 Spray Drift Modeling................................................................................................. 219 

6.2 Effects Assessment Uncertainties..................................................................................... 220 

6.2.1 Age Class and Sensitivity of Effects Thresholds....................................................... 220 

6.2.2 Use of Surrogate Species Effects Data ...................................................................... 220 

6.2.3 Sublethal Effects........................................................................................................ 221 

6.2.4 Location of Wildlife Species ..................................................................................... 221 

6.2.5 Endocrine Disruption................................................................................................. 221 

7 Summary and Conclusions................................................................................222 

8 References...........................................................................................................232 

5
Appendices

Appendix A Endosulfan Label Analysis and Memorandum 

Appendix B AgDrift Modeling 

Appendix C Aquatic Exposure Modeling Approach for Endosulfan 

Appendix D RQ Method and LOCs 

Appendix E GIS Maps 

Appendix F T-REX Example Output 

Appendix G Bibliography of ECOTOX Open Literature Not Evaluated 

Appendix H Accepted ECOTOX Data Table (sorted by effect) and Bibliography 

Appendix I KABAM Model Description and Output 

Appendix J Aquatic ECOTOX Data 

Appendix K Terrestrial ECOTOX Data 

Appendix L Endosulfan Incidents 

Appendix M HED Effects Table 

Appendix N Earthworm Fugacity Modeling

Attachments

Attachment 1: Status and Life History for the CRLF 

Attachment 2: Baseline Status and Cumulative Effects for the CRLF 

Attachment 3: Status and Life History for the San Francisco Bay Species 

Attachment 4: Baseline Status and Cumulative Effects for the San Francisco Bay Species 

List of Tables

Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, 

SMHM, SJKF, BCB, AND VELB 15 

Table 1.2 Effects Determination Summary for the Critical Habitat Impact Analysis 22 

Table 2.1 Physiochemical properties of the multi-chemical stressor 32 

Table 2.2 Summary of fate and transport properties for endosulfan isomers and sulfate 33 

Table 2.3 Endosulfan labeled uses assessed for California (No single application rate over 1.5 lbs 

except for orchard crops and strawberries) 37 

Table 2.4 California labeled non-crop use for endosulfan 40 

Table 2.5 Top use patterns for endosulfan for selected years from 1990 to 2002 41 

Table 2.6 Historical usage of endosulfan for 1994 (1st period) and 1995-1997 (2nd period) 43 

Table 2.7 Historical usage of endosulfan for 1998-2004 (3rd period) and 2005-2006 (4th period)

44 

Table 2.8 Summary of Current Distribution, Habitat Requirements, and Life History Information 

for the Assessed Listed Species 49 

Table 2.9 Designated Critical Habitat PCEs for the CRLF, CTS, BCB and VELB 53 

Table 2.10 Taxa Used in the Analyses of Direct and Indirect Effects of Endosulfan for the 

Assessed Listed Species. 60 

Table 2.11 Taxa and Assessment Endpoints Used to Evaluate the Potential for the Use of 

Endosulfan to Result in Direct and Indirect Effects to the Assessed Listed Species. 61 

6
Table 2.12 Summary of Assessment Endpoints and Measures of Ecological Effect for Primary 

Constituent Elements of Designated Critical Habitat for CRLF, BCB, VELB, and CTS.

62 

Table 3.1 Summary of labeled endosulfan uses, scenarios, and application information 71 

Table 3.2 Calculation of application rates for α- and β-endosulfan and endosulfan sulfate) for use 

in modeling (rates are for almond) 74 

Table 3.3 Summary of PRZM/EZAMS environmental fate and transport data of α- and βendosulfan and endosulfan sulfate used as aquatic exposure inputs for this endangered 

species assessment 75 

Table 3.4 Aquatic EECs (μg/L) for endosulfan used in California (α- and β-endosulfan)1 76 

Table 3.5 Aquatic EECs (μg/L) for endosulfan used in California (endosulfan sulfate and total 

stressor) 77 

Table 3.6 Sediment pore water EECs (μg/L) for endosulfan used in California (α- and βendosulfan) 78 

Table 3.7 Sediment pore water EECs (μg/L) for endosulfan used in California (endosulfan 

sulfate and total stressor) 78 

Table 3.8 Sediment EECs (μg/L) for endosulfan used in California (α- and β-endosulfan) 79 

Table 3.9 Sediment EECs (μg/L) for endosulfan used in California (endosulfan sulfate and total 

stressor) 79 

Table 3.10 Total soil and pore water concentrations for selected crop scenarios 81 

Table 3.11 Summary of reported detection limits for the CDPR surface water data 83 

Table 3.12 Summary of CPDR surface water monitoring data for California Counties collected 

for the first monitoring period (1991 to 1996) 83 

Table 3.13 Summary of CPDR surface water monitoring data for California (the 2nd monitoring 

period) 85 

Table 3.14 Summary of STORET surface water monitoring data for California 87 

Table 3.15 A summary of NAWQA monitoring data for surface water from California 89 

Table 3.16 Surface water data summary 90 

Table 3.17 A summary of monitoring data for ground water from California 91 

Table 3.18 A summary for NAWQA monitoring data to base sediment in California 91 

Table 3.19 Summary of bottom sediment monitoring data for California 92 

Table 3.20 Frequency and concentrations of endosulfan species in ambient air 94 

Table 3.21 Frequency and concentrations of endosulfan species in ambient air 96 

Table 3.22 Concentration of pesticides (ng/L) in surface water samples collected at the 

Tablelands (Sequoia National Park), and the Sixty Lake Basin (Kings Canyon National 

Park) California, USA (Fellers et al. 2004). 98 

Table 3.23 Summary of Dose and Dietary-based EECs Used for Estimating Dietary Risks to 

Terrestrial Organisms using T-REX ver. 1.4.1. 100 

Table 4.1 Aquatic Toxicity Profile for Endosulfan (TGAI) 107 

Table 4.2 Categories of Acute Toxicity for Fish and Aquatic Invertebrates 108 

Table 4.3 Terrestrial Toxicity Profile for Endosulfan 119 

Table 4.4. Categories of Acute Toxicity for Avian and Mammalian Studies 119 

Table 4.5 Comparison of Acute Toxicity of Endosulfan and Endosulfan Sulfate To Birds. 120 

Table 5.1 Acute and Chronic RQs for freshwater fish based on EECs for use categories used to 

represent all endosulfan uses in CA. 128 

7
Table 5.2 Acute and Chronic RQs for freshwater invertebrates based on EECs for use categories 

used to represent all endosulfan uses in CA. 130 

Table 5.3 Summary of the acute and chronic dose- and dietary-based RQs for birds (20 g) 

estimated based on the maximum endosulfan foliar spray applications using T-REX 

version 1.4.1. 132 

Table 5.4 Summary of the acute and chronic dose- and dietary-based RQs for mammals 

estimated based on the maximum endosulfan foliar spray applications using T-REX 

version 1.4.1. 136 

Table 5.5 Summary of the acute and chronic dose- and dietary-based RQs terrestrial insects 

estimated based on the maximum endosulfan foliar spray applications using T-REX 

version 1.4.1. 139 

Table 5.6 Summary of the highest RQ to LOC ratios for the two GIS use categories for 

endosulfan 141 

Table 5.7 Summary of average endosulfan usage data and occurrence of the CRLF and the San 

Francisco Bay species at the county level 141 

Table 5.8 Extent and location of overlap between areas of species occurrence and areas of 

potential endosulfan usage 142 

Table 5.9 Risk Estimation Summary for endosulfan - Direct and Indirect Effects 144 

Table 5.10 Risk Estimation Summary for Endosulfan – Effects to Designated Critical Habitat 

(PCEs) 145 

Table 5.11 Summary of the chance of individual acute effects to freshwater animals based on 

acute RQs, the acute listed species LOC, acute toxicity data, and probit slope response 

relationships(1,2). 148 

Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on 

acute RQs, the acute listed species LOC, acute toxicity data, and probit slope response 

relationships. 150 

Table 5.13 Summary of the chance of individual acute effects to herpetofauna based on acute 

RQs, the acute listed species LOC, acute toxicity data, and probit slope response 

relationships. 158 

Table 5.14 Comparison of maximum detected concentrations of total endosulfan in surface 

waters of California to Agency LOC for freshwater fish 166 

Table 5.15 Assumed dietary preferences of small (1.4g), medium (37g) and large (238g) CRLF 

feeding on aquatic biota of the model ecosystem. 169 

Table 5.16 Endosulfan chemical characteristics used as input to KABAM 169 

Table 5.17 Estimated concentrations of endosulfan in ecosystem components for two crop 

exposure scenarios 170 

Table 5.18 Calculation of EECs for CRLF consuming aquatic prey contaminated by endosulfan

171 

Table 5.19 Calculation of RQ values for CRLF consuming aquatic prey contaminated by 

endosulfan. 171 

Table 5.20 Summary of the acute and chronic dose- and dietary-based RQs for herpetofauna 

estimated based on the maximum endosulfan foliar spray applications using T-HERPS 

version 1.0. 174 

Table 5.21 Acute and Chronic RQs for freshwater sediment invertebrates based on EECs for use 

categories used to represent all endosulfan uses in CA 182 

8
Table 5.22 Estimated concentrations of total endosulfan in earthworms and avian risk quotients 

for two crop exposure scenarios. 190 

Table 5.23 Estimated concentrations of total endosulfan in earthworms and mammalian risk 

quotients for two crop exposure scenarios 201 

Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, 

SMHM, SJKF, BCB, AND VELB 222 

Table 7.2 Effects Determination Summary for the Critical Habitat Impact Analysis 229 

List of Figures

Figure 2.1 Chemical structures of endosulfan and related compounds........................................ 31 

Figure 2.2 Endosulfan Use in Total Pounds per County (note vlues are different in chosen 

categories) ..................................................................................................................... 42 

Figure 2.3 Historical usage data for endosulfan .......................................................................... 43 

Figure 2.4 Endosulfan usage and acreage for the top five crop use patterns (CA-PUR data; 

Average for 2005-2006)................................................................................................ 47 

Figure 2.5 Distribution of endosulfan usage for the top usage counties of Fresno, Kings, and 

Imperial ......................................................................................................................... 48 

Figure 2.6 Initial area of concern, or “footprint” of potential use, for endosulfan ....................... 57 

Figure 2.7 Conceptual Model for Endosulfan Effects on the Assessed Species and their Critical 

Habitat in the Aquatic Environment.............................................................................. 65 

Figure 2.8. Conceptual Model for Endosulfan Effects on the Assessed Species and their Critical 

Habitat in the Terrestrial Environment.......................................................................... 66 

Figure 3.1 Detected concentrations of alpha and beta-endosulfan and common degradate in 

California surface waters from 1991 to 2006 (No data were collected from 1996 to 

2000).............................................................................................................................. 82 

Figure 3.2 Detected concentrations of the total endosulfan species in California surface waters 

from 1991 to 2006 ......................................................................................................... 82 

Figure 3.3 CPDR Monitoring data for Imperial County (11 sites, varied times of the year) ....... 84 

Figure 3.4 CDPR Monitoring data for Merced County (4 sites), Stanislaus County (6 sites), San 

Joaquin County (2 sites) and Sacramento County (1 site) at varied times of the year.. 85 

Figure 3.5 Detected concentrations of α- and β-endosulfan and endosulfan sulfate common 

degradate in California surface waters from 2001 to 2008 (STORET data)................. 88 

Figure 3.6 Detected concentrations of the total endosulfan species in California surface waters 

from 2001 to 2008 (STORET data)............................................................................... 88 

Figure 3.7 Detected concentrations of α- and β-endosulfan and endosulfan sulfate common 

degradate in surface waters of five California Counties (Counties with detections over 

the LOQ; 2001 to 2008 STORET data) ........................................................................ 89 

Figure 3.8 Concentration profiles for α- and β- endosulfan at the edge and near-field in ambient 

air following application in San Joaquin County, California........................................ 94 

Figure 3.9 Concentration profiles for α- endosulfan in ambient air during a period of five weeks 

at 4 sites in Fresno County, California.......................................................................... 97 

Figure 5.1 Temporal distribution of endosulfan application in California for 2006 (Source: 

CDPR PUR))............................................................................................................... 164 

Figure 5.2 CRLF Reproductive Events by Month; Adults and juveniles can be present all year.

..................................................................................................................................... 164 

9
Figure 5.3 Species sensitivity distribution of the acute toxicity of endosulfan to freshwater fish

..................................................................................................................................... 167 

Figure 5.4 Species sensitivity distribution of the acute toxicity of endosulfan to freshwater 

invertebrates via water column exposure .................................................................... 180 

Figure 5.5 Species sensitivity distribution of the acute contact toxicity of endosulfan TGAI to 

terrestrial invertebrates based on species mean values. .............................................. 183 

Figure 5.6 CTS Reproductive Events by Month; Adults and juveniles can be present all year. 188 

Figure 5.7 Average Endosulfan Use (2005-2006) in Counties with Reported Occurrence of 

Listed Species, Occupied Core Areas and/or Critical Habitat .................................... 189 

Figure 5.8 SFGS Reproductive Events by Month; Adults can be present all year..................... 195 

Figure 5.9 General Annual Life-History Parameters for the BCB ............................................. 209 

10
1 Executive Summary 

The purpose of this assessment is to evaluate potential direct and indirect effects on the 

following species arising from FIFRA regulatory actions regarding use of endosulfan on 

agricultural sites: 

California red-legged frog (CRLF), Rana aurora draytonii

California Tiger Salamander (CTS), Ambystoma californiense, 

San Francisco Garter Snake (SFGS), Thamnophis sirtalis tetrataenia, 

Salt Marsh Harvest Mouse (SMHM), Reithrodontomys raviventris,

San Joaquin Kit Fox (SJKF), Vulpes macrotis mutica, 

Bay Checkerspot Butterfly (BCB), Euphydryas editha bayensis, and

Valley Elderberry Longhorn Beetle (VELB), Desmocerus californicus dimorphus. 

In addition, this assessment evaluates whether these actions can be expected to result in effects to 

designated critical habitat for the CRLF, CTS, BCB, and VELB; noting that critical habitat has 

not been designated for the SFGS, SMHM and SJKF. This assessment was completed in 

accordance with the U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries 

Service (NMFS) Endangered Species Consultation Handbook (USFWS/NMFS, 1998 and 

procedures outlined in the Agency’s Overview Document (U.S. EPA, 2004). 

The listing date and a general description of the range of each assessed species are as follows. 

• The CRLF was listed as a threatened species by USFWS in 1996. The species is endemic 

to California and Baja California (Mexico) and inhabits both coastal and interior 

mountain ranges. A total of 243 streams or drainages are believed to be currently 

occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and 

Santa Barbara counties (USFWS, 1996) in California. 

• The CTS was listed as threatened by the Fish and Wildlife Service on August 4, 2004 and 

designated critical habitat was established on November 24, 2004. The two distinct 

population segments (one in Santa Barbara County and the other in Sonoma County) 

inhabit freshwater pools or ponds, grassland or oak savannah communities in low foothill 

regions and small mammal burrows. 

• The SFGS was listed as an endangered species by the USFWS in 1967 and was 

grandfathered under the Endangered Species Act (ESA) when it was signed into law in 

1973. The SFGS is endemic to the San Francisco Peninsula and San Mateo County and 

historically inhabited densely vegetated ponds or shallow marshlands near open hillsides 

found from San Francisco to Santa Cruz, including the San Francisco Peninsula. The 

current distribution of the SFGS is unknown because most of their historic range is now 

privately owned; however, it appears that the SFGS can still be found in much of its 

historic range. 

• The SMHM was listed as an endangered species by the USFWS in 1970. The SMHM is 

currently found in tidal and non-tidal salt marshes in San Francisco, San Pablo, and 

Suisun bays. 

• The SJKF was listed as endangered by the USFWS on March 11, 1967. Its current range 

includes Alameda, Contra Costa, Fresno, Kern, Kings, Madera, Merced, Monterey, San 

11
Benito, San Joaquin, San Luis Obispo, Santa Barbara, Santa Clara, Stanislaus, Tulare and 

Ventura counties in California. It inhabits a variety of habitats, including grasslands, 

scrublands, vernal pool areas, oak woodland, alkali meadows and playas, and an 

agricultural matrix of row crops, irrigated pastures, orchards, vineyards, and grazed 

annual grasslands. 

• The BCB was listed as a threatened species in 1987 by the USFWS. The species 

primarily inhabits native grasslands on serpentine outcrops around the San Francisco Bay 

Area in California. The distribution of known BCB populations is currently limited to 

Santa Clara and San Mateo Counties. 

• The VELB was listed as threatened on August 8, 1980 by the USFWS. The species 

inhabits the Central Valley of California (from Shasta County to Fresno County in the 

San Joaquin Valley). The VELB is completely dependent on its host plant, elderberry 

(Sambucus species), which is a common component of the remaining riparian forests and 

adjacent upland habitats of California’s Central Valley. 

Endosulfan is a dioxathiepin broad spectrum contact insecticide and acaricide that is broadly 

classified as a chlorinated hydrocarbon. The chemical is used on major agricultural crops to 

control insect pests such as aphids, fruitworms, beetles, leafhoppers, moth larvae, and whiteflies. 

Labeled uses of endosulfan include a wide variety of vegetables, fruits, nuts, outdoor tree 

nurseries, and cotton. The following uses are considered as part of the federal action evaluated 

in this assessment: nut trees, non-bearing citrus trees, cole crops, fresh market sweet corn, cotton, 

pome/stone fruits, leafy vegetables, cucurbits, outdoor nurseries for ornamentals and shade trees, 

potato, sweet potato, dry beans and peas, carrot, and fruiting vegetables. Endosulfan is applied as 

liquid spray prepared from emulsifiable concentrates and wettable powder formulations using 

aircraft or ground equipment. The pesticide is mostly applied as foliar spray with single rates 

ranging from 0.5 to 2.5 lbs a.i/A at minimum intervals ranging from 5 to 10 days and maximum 

total rate from 0.5 to 3.0 lb a.i/season or year. 

Endosulfan is a 70:30 mixture of two biologically-active isomers (α and β). The isomers differ 

in their physiochemical and fate properties. The chemical is relatively persistent and semivolatile. The β -isomer is generally more persistent and the α-isomer is more volatile. Under 

sterlie neutral/basic conditions, hydrolysis is an important degradation route; however, 

endosulfans are persistent under acidic conditions. With the exception of hydrolysis in alkaline 

conditions, microbial degradation in soils is the predominant route of endosulfan degradation. 

The major transformation products found in the fate studies are endosulfan diol (hydrolysis) and 

endosulfan sulfate (soil metabolism). Both the diol and sulfate transformation products have the 

backbone structures of the parent compound. 

Based on a review of the environmental fate data and use characterization for endosulfan, 

endosulfan sulfate is considered the major degradate of concern that is addressed in this risk 

assessment. Based on limited data, endosulfan sulfate appears to have similar acute toxicity to 

aquatic and terrestrial species (i.e., within an order of magnitude) and is assumed to have similar 

chronic toxicity. Endosulfan sulfate is also more persistent than the parent isomers (alpha, beta 

endosulfan) and tends to be a major component of total endosulfan residues found in biologically 

active environmental media (e.g., aerobic soil). Endosulfan diol appears to form in only minor 

12
quantities in the soil system and is reported to be substantially less toxic than either the parent or 

its major degradation product, endosulfan sulfate.

Endosulfans have a high affinity for sorption onto soil and are not expected to be highly mobile. 

Endosulfan can move via spray drift and run-off causing contamination of surface waters where 

it is expected to reside in sediments. As a result of endosulfan volatility, the chemical can move 

to targets beyond its use area through atmospheric transport (volatilization and/or transport on 

dust particles). In this assessment, spray drift and runoff are considered quantitatively while 

atmospheric transport and volatilization are considered qualitatively as the potential transport 

mechanisms for endosulfan. 

Available monitoring data from California suggest that endosulfan is present in important 

environmental compartments, although endosulfan use and concentrations in surface water 

appear to be declining. The chemical isomers and/or their common sulfate degradate have been 

detected in a variety of off-target locations in California, including rain and snow in the 

mountains (McConnell et al, 1998), ground water (Fellers et al., 2004), surface water (STORET 

database, CDPR, 2000), stream sediment (Weston et al., 2004; U.S. EPA, 1997), tadpole and 

adult frog tissues (Sparling et al., 2001), and ambient air (Air Resource Board “ARB” of 

California ( refer to Section 3.2.4.4 Atmospheric Monitoring Data). 

The effects determinations for each listed species assessed is based on a weight-of-evidence 

method that relies heavily on an evaluation of risks to each taxon relevant to assess both direct 

and indirect effects to the listed species and the potential for effects to their designated critical 

habitat (i.e., a taxon-level approach). Since the assessed species exist within aquatic and 

terrestrial habitats, exposure of the listed species, their prey and their habitats to endosulfan are 

assessed separately for the two habitats. Tier-II aquatic exposure models are used to estimate 

high-end exposures of endosulfan in aquatic habitats resulting from runoff and spray drift from 

different uses. Peak model-estimated environmental concentrations, resulting from different 

endosulfan uses, ranged from 0.72 to 5.88 μg/L for the total α- and β- endosulphan and 

endosulfan sulfate. These estimates are supplemented with analysis of available California 

surface water monitoring data from U. S. Geological Survey’s National Water Quality 

Assessment (NAWQA) program and the California Department of Pesticide Regulation. The 

maximum concentration of endosulfan reported by the California Department of Pesticide 

Regulation surface water database (0.95 μg/L from the 1991 to 2006 time period) is roughly 6 

times lower than the highest peak model-estimated environmental concentration. 

The concentrations of endosulfan reported by NAWQA for California surface waters were below 

the limits of analytical detection (ranging from 0.0047 to 0.022 μg/L depending on the 

endosulfan compound measured). 

To estimate endosulfan exposures to terrestrial species resulting from uses involving endosulfan 

foliar applications, the T-REX model is used. This model provides estimates of endosulfan 

residues on forage items (e.g., short grass, tall grass, insects, and seeds) that result from direct 

deposition on the field. A refinement of this model (T-HERPS) is also used to enable further 

characterization of dietary exposures to terrestrial-phase amphibians and reptiles, based on food 

consumption and dietary preferences specific to herptivores. AgDRIFT and AGDISP (Teske and 

Curbishley, 2003) models are also used to estimate deposition of endosulfan on terrestrial and 

13
aquatic habitats from spray drift. For consumption of contaminated terrestrial prey (e.g., soildwelling invertebrates), a fugacity-based earthworm bioaccumulation model is also used to 

characterize direct or indirect effects on listed species. To address consumption of contaminated 

aquatic prey (e.g., fish and aquatic invertebrates), the KABAM model1 is used to estimate 

endosulfan exposures to listed species via the aquatic food web. 

The effects determination assessment endpoints for the listed species include direct toxic effects 

on the survival, reproduction, and growth of the listed species itself, as well as indirect effects, 

such as reduction of the prey base or modification of its habitat. If appropriate data are not 

available, toxicity data for birds are generally used as a surrogate for reptiles and terrestrialphase amphibians and toxicity data from fish are used as a surrogate for aquatic-phase 

amphibians. For endosulfan, equal toxicity was assumed between the alpha, beta and endosulfan 

sulfate compounds, based on similarity in structures, mode of action, and limited data on the 

comparative acute toxicity of these compounds. Therefore, modeled or measured environmental 

exposures of total endosulfan (sum of alpha, beta and endosulfan sulfate) were compared with 

toxicity data for the Technical Grade Active Ingredient (TGAI). For sediment-borne exposures, 

toxicity data were available only for endosulfan sulfate, and thus, comparisons of total 

endosulfan EECs were made to toxicity estimates for endosulfan sulfate. 

Risk quotients (RQs) are derived as quantitative estimates of potential high-end risk. Acute and 

chronic RQs are compared to the Agency’s levels of concern (LOCs) to identify instances where 

endosulfan use within the action area has the potential to adversely affect the assessed species 

and designated critical habitat if applicable, via direct toxicity or indirectly based on direct 

effects to its food supply or habitat. When RQs for each particular type of effect are below 

LOCs, the pesticide is determined to have “no effect” on the listed species being assessed. 

Where RQs exceed LOCs, a potential to cause adverse effects is identified, leading to a 

conclusion of “may affect.” If a determination is made that use of endosulfan “may affect” the 

listed species being assessed and/or its designated critical habitat (if applicable), additional 

information is considered to refine the potential for exposure and effects. Best available 

information is used to distinguish those actions that “may affect, but are not likely to adversely 

affect” (NLAA) from those actions that are “likely to adversely affect” (LAA) for each listed 

species assessed. For designated critical habitat, distinctions are made for actions that are 

expected to have ‘no effect’ on a designated critical habitat from those actions that may have an 

effect on designated critical habitat. 

Based on the best available information, the Agency makes a May Affect and Likely to 

Adversely Affect (LAA) determination for the CRLF, CTS, SFGS, SMHM, SJKF, BCB, and 

VELB from the use of endosulfan. A summary of the risk conclusions and effects 

determinations for each listed species assessed here and their designated critical habitat (if 

applicable) is presented in Table 1.1 and Table 1.2 Further information on the results of the 

effects determination is included as part of the Risk Description in Section 5.2. Additionally, the 

Agency has determined that there is the potential for effects to critical habitat of CRLF and CTS 

from the use of the chemical. This LAA determination is based on the potential for direct effects 

(to both aquatic and terrestrial-phase CRLF, SFGS, CTS, BCB, VELB, SMHM, SJKF), indirect 

effects due to potential decreases in aquatic and terrestrial prey items, and the potential for 

 

1

 http://www.epa.gov/oppefed1/models/water/index.htm#KABAM 

14
effects to designated critical habitat due to the potential loss of aquatic and terrestrial prey items. 

Given the LAA determination for the CRLF, CTS, SFGS, SMHM, SJKF, BCB, and VELB and 

potential modification of designated critical habitat for CRLF and CTS, a description of the 

baseline status and cumulative effects for the CRLF is provided in Attachment 2 and the 

baseline status and cumulative effects for the SFGS, CTS, BCB, VELB, SMHM and SJKF is 

provided in Attachment 4. 

Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects 

Determination 1

Basis for Determination 

POTENTIAL FOR DIRECT EFFECTS

Aquatic-phase CRLF (Eggs, Larvae, and Adults): 

Freshwater Fish RQ

- Acute RQs for freshwater fish (used as a surrogate for aquatic-phase CRLFs) exceed 

the listed species acute risk LOC for all 20 modeled crop scenarios. 

- Chronic RQs for freshwater fish (used as a surrogate for aquatic-phase CRLFs) 

exceed the chronic risk LOC for all 20 modeled crop scenarios. 

Likelihood of Individual Mortality

-The chance of individual effects (i.e., mortality) for freshwater fish (surrogate for 

aquatic-phase CRLFs) is as high as ~1 in 1. 

Ecological Incident Reports 

- 67 of the 83 endosulfan-associated ecological incidents reported to the Agency 

involve fish and 53 of these are classified as ‘probable’ or ‘highly probable;’ 18 of the 

20 incident reports associated with ‘registered uses’ involved mortality to fish. 

Species Sensitivity Differences

- Model-based EECs exceed the LOC for approximately 80 to 97% of the tested 

freshwater fish species 

Surface Water Monitoring Data

- The highest reported values of total endosulfan in California equal or exceed the 

acute LOC for freshwater fish. 

Bioaccumulation in Aquatic Prey

- Based on consumption of aquatic prey that is predicted to bioaccumulate 

endosulfan, acute dose-based RQs exceed the acute listed LOC in all 20 crop 

exposure scenarios modeled for small, medium and large CRLF. 

Temporal and Spatial Overlap

- Based on current endosulfan use data and potential endosulfan use on agricultural 

crops/orchards/vineyard areas, there appears to be a potential for both temporal and 

spatial overlap between aquatic-phase CRLF distribution and endosulfan agricultural 

use (Appendix E). 

California redlegged frog 

(Rana aurora 

draytonii) 

(CRLF) 

LAA1

Terrestrial-phase CRLF (Juveniles and Adults): 

Direct Deposition on Forage Items: Avian RQ

- Acute-dose based RQs for 20g birds (surrogate for terrestrial-phase amphibians) 

consuming large and small insects contaminated with endosulfan from direct 

deposition exceed LOC for all 20 crop scenarios modeled. 

- Chronic RQs for the small and large insect categories exceed the Agency LOC of 1 

for 20 and 3 crop exposure scenarios, respectively. 

15
Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

Direct Deposition on Forage Items: Refined Herpetofauna Modeling

- Using refined modeling, acute listed LOC was exceeded in 39% or more of the 

acute dose-based; and acute dietary-based species/diet combinations modeled. The 

chronic LOC was exceeded in 46% of the chronic dietary-based species/diet 

combinations modeled. 

Likelihood of Individual Mortality

The chance of individual effects (i.e., mortality) for birds (surrogate for terrestrial -

phase CRLFs) and herpetofauna based on direct deposition onto food items is as high 

as ~1 in 1. 

Temporal and Spatial Overlap

- Based on current endosulfan use data and potential endosulfan use on agricultural 

crops/orchards/vineyard areas, there appears to be a potential for both temporal and 

spatial overlap between terrestrial -phase CRLF distribution and endosulfan 

agricultural use (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS

CRLF Aquatic Prey Items, Aquatic Habitat, Cover and/or Primary Productivity 

Freshwater fish and aquatic-phase amphibians: 

- Acute and chronic RQs exceed the listed species acute and chronic LOCs; high 

likelihood of individual mortality, EECs exceed the LOC for 80% or more of the 

tested fish species and a large number of aquatic incidents involving fish, as 

described above for CRLF (see “Potential Direct Effects; Aquatic Phase CRLF 

[eggs, larvae, adults])” 

.Freshwater Invertebrates: 

-Acute and chronic RQs for freshwater invertebrates exceed the listed species acute 

and chronic risk LOC for all 20 crop exposure scenarios modeled. 

-The chance of individual effects (i.e., mortality) for freshwater invertebrates is as 

high as ~1 in 1. 

- Model-based EECs exceed the LOC for approximately 45% to 60% of the tested 

freshwater invertebrate species 

- The highest reported values of total endosulfan in California equal or exceed the 

listed acute LOC and chronic LOC for freshwater invertebrates. 

CRLF Terrestrial Prey Items, Riparian Habitat 

Terrestrial-phase Amphibians: 

- Exceedence of acute and chronic LOCs for terrestrial-phase amphibians as 

described above for CRLF (see “Potential Direct Effects; Terrestrial Phase CRLF 

[juveniles and adults])” 

Terrestrial Invertebrates: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled. 

- EECs exceed for large and small insects exceed the LD50 values for 80% and 99% 

of the tested terrestrial invertebrate species, respectively. 

-The chance of individual effects (i.e., mortality) for terrestrial invertebrates resulting 

from direct deposition in application sites is as high as ~1 in 1. 

- When indirect effects are considered via exposure of terrestrial insects to spray drift, 

spatial overlap between potential endosulfan use on agricultural crops, orchards, and 

vineyard areas can extend up to 2 miles from the source (Appendix E). 

16
Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

Small Mammals: Direct Deposition on Forage Items 

- Acute and chronic dose-based RQs for small mammals foraging on food items 

receiving direct deposition of applied endosulfan exceed the acute listed LOC for 

mammals in all 20 crop scenarios modeled 

- Chronic diet-based RQs for small mammals foraging on food items receiving direct 

deposition of applied endosulfan exceed the chronic LOC for mammals in 13 of the 

20 crop scenarios modeled 

- The chance of individual effects (i.e., mortality) for small mammals is as high as ~1 

in 1. 

Small Mammals: Bioaccumulation in Terrestrial Prey 

 - RQs exceed of acute listed and chronic LOCs in all 20 exposure scenarios modeled 

based on small mammals eating earthworms that are predicted to bioaccumulate 

endosulfan from soil. 

California POTENTIAL FOR DIRECT EFFECTS 

tiger 

salamander 

(Ambystoma 

californiense

LAA1

Direct Deposition on Forage Items: Avian RQ (Terrestrial-Phase CTS)

- Acute-dose based RQs for 20g birds (surrogate for terrestrial-phase amphibians) 

consuming large and small insects contaminated with endosulfan from direct 

deposition exceed LOC for all 20 crop scenarios modeled. 

- Chronic RQs for the small and large insect categories exceed the Agency LOC of 1 

for 20 and 3 crop exposure scenarios, respectively. 

Direct Deposition on Forage Items: Refined Herpetofauna Modeling

- Using refined modeling, acute listed LOC was exceeded in 39% or more of the 

acute dose-based; acute dietary-based species/diet combinations modeled. The 

chronic LOC was exceeded in 46% of the chronic dietary-based species/diet 

combinations modeled. 

Likelihood of Individual Mortality

The chance of individual effects (i.e., mortality) for birds (surrogate for reptiles and 

terrestrial phase amphibians) and herpetofauna based on direct deposition onto food 

items is as high as ~1 in 1. 

Bioaccumulation in Aquatic Prey

- Based on consumption of aquatic prey that is predicted to bioaccumulate 

endosulfan, acute dose-based RQs exceed the acute listed LOC in all 20 crop 

exposure scenarios modeled for small CRLF (used as surrogate for CTS exposure 

potential). 

Bioaccumulation in Terrestrial Prey

- Based on consumption of terrestrial prey (earthworm) that is predicted to 

bioaccumulate endosulfan, acute dose-based RQs and chronic diet-based RQs for 

small birds (surrogate for terrestrial-phase amphibians) exceed the acute listed and 

chronic LOCs in all 20 crop exposure scenarios modeled. 

Freshwater Fish (Aquatic-phase CTS): 

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, EECs exceed the LOC for 80% or more of the 

tested fish species and a large number of aquatic incidents involve fish, as described 

above for CRLF (see “Potential Direct Effects; Aquatic Phase CRLF [eggs, larvae, 

adults])” 

17
Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of CTS was 

identified. 

- A large amount of spatial overlap between CTS occurrence and current (and 

potential future use) of endosulfan was identified (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS 

Freshwater Fish: 

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, EECs exceed the LOC for 80% or more of the 

tested fish species and a large number of aquatic incidents involve fish, as described 

above for CRLF (see “Potential Direct Effects; Aquatic Phase CRLF [eggs, larvae, 

adults])” 

Freshwater Invertebrates:

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, and exceedence of LOCs for 45-60% of 

freshwater invertebrate species tested, as described above for CRLF (see “Potential 

Indirect Effects; CRLF Aquatic Prey Items, Aquatic Habitat, Cover and/or Primary 

Productivity)” 

Terrestrial Invertebrates: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled, there is a high likelihood of individual 

mortality, and EECs exceed LD50 values for vast majority of tested species, as 

described above for CRLF (see “Potential for Indirect Effects: CRLF Terrestrial Prey 

Items, Riparian Habitat)

San Francisco POTENTIAL FOR DIRECT EFFECTS

garter snake 

(Thamnophis 

sirtalis 

tetrataenia) 

LAA1

Direct Deposition on Forage Items: Avian RQ

- Acute-dose based RQs for 20g birds (surrogate for terrestrial-phase amphibians) 

consuming large and small insects contaminated with endosulfan from direct 

deposition exceed LOC for all 20 crop scenarios modeled. 

- Chronic RQs for the small and large insect categories exceed the Agency LOC of 1 

for 20 and 3 crop exposure scenarios, respectively. 

Direct Deposition on Forage Items: Refined Herpetofauna Modeling

- Using refined modeling, acute listed LOC was exceeded in 39% or more of the 

acute dose-based; and acute dietary-based species/diet combinations modeled. The 

chronic LOC was exceeded in 46% of the chronic dietary-based species/diet 

combinations modeled. 

Likelihood of Individual Mortality

The chance of individual effects (i.e., mortality) for birds (surrogate for reptiles and 

terrestrial phase amphibians) and herpetofauna based on direct deposition onto food 

items is as high as ~1 in 1. 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of SFGS was 

identified. 

- No spatial overlap identified at the County level based on current endosulfan use 

reported for California. If cultivated crop/orchard/vineyard uses are considered areas 

18
Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

of potential endosulfan use in the future, then a substantial amount of spatial overlap 

can be observed relative to the total area of SFGS occurrence sections (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS

Prey Items, Habitat, Cover And/Or Primary Productivity 

Freshwater Fish: 

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, EECs exceed the LOC for 80% or more of the 

tested fish species and a large number of aquatic incidents involve fish, as described 

above for CRLF (see “Potential Direct Effects; Aquatic Phase CRLF [eggs, larvae, 

adults])” 

Freshwater Invertebrates:

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, and exceedence of LOCs for 45-60% of 

freshwater invertebrate species tested, as described above for CRLF (see “Potential 

Indirect Effects; CRLF Aquatic Prey Items, Aquatic Habitat, Cover and/or Primary 

Productivity)” 

Terrestrial Invertebrates: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled, there is a high likelihood of individual 

mortality, and EECs exceed LD50 values for vast majority of tested species, as 

described above for CRLF (see “Potential for Indirect Effects: CRLF Terrestrial Prey 

Items, Riparian Habitat)

Small Terrestrial Vertebrates

- Acute and chronic LOC exceedence for birds (surrogate for reptiles and terrestrialphase amphibians) and herpetofauna for direct deposition on food items, a high 

likelihood of individual mortality, and RQ exceedence of acute listed LOC and 

chronic LOC based on consumption of terrestrial and aquatic prey by birds and 

mammals as described above for the CRLF (see “Potential Direct Effects; 

Terrestrial Phase CRLF [juveniles and adults] and “Potential for Indirect Effects: 

CRLF Terrestrial Prey Items, Riparian Habitat)” 

Salt marsh POTENTIAL FOR DIRECT EFFECTS

harvest mouse 

(Reithrodonto

mys 

raviventris) 

(SMHM) 

LAA1

Direct Deposition on Forage Items: Mammalian RQ 

- Acute and chronic dose-based RQs for small mammals foraging on food items 

receiving direct deposition of applied endosulfan exceed the acute listed LOC for 

mammals in all 20 crop scenarios modeled 

- Chronic diet-based RQs for small mammals foraging on food items receiving direct 

deposition of applied endosulfan exceed the chronic LOC for mammals in 13 of the 

20 crop scenarios modeled 

Likelihood of Individual Mortality

- The chance of individual effects (i.e., mortality) for small mammals resulting from 

direct deposition onto forage items is as high as ~1 in 1. 

Bioaccumulation in Terrestrial Prey 

 - RQs exceed of acute listed and chronic LOCs in all 20 exposure scenarios modeled 

based on small mammals eating earthworms that are predicted to bioaccumulate 

endosulfan from soil. 

Temporal and Spatial 

19
Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

- Temporal overlap between endosulfan application and all life stages of the SMHM 

was identified. 

- A small amount of spatial overlap identified at the County level based on current 

endosulfan use reported for California and based on areas of potential endosulfan use 

in the future (i.e., cultivated crop, orchard and vineyard use areas). 

- The potential for endosulfan to be transported long distances in the atmosphere may 

increase SMHM exposure, particularly in areas of potential endosulfan use west of 

SMHM occurrence sections in Solano County (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS

Prey items, habitat, cover and/or primary productivity 

Terrestrial invertebrates: 

-- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled, there is a high likelihood of individual 

mortality, and EECs exceed LD50 values for vast majority of tested species, as 

described above for CRLF (see “Potential for Indirect Effects: CRLF Terrestrial Prey 

Items, Riparian Habitat)

Small Birds and Mammals (rearing sites): 

- Acute and chronic RQ for birds and mammals (whose rearing sites are potentially 

used by SMHM) exceed listed acute and chronic LOCs as a result of direct deposition 

onto forage items and bioaccumulation in terrestrial prey as described above for the 

CRLF (Potential for Direct Effects: Terrestrial-phase CRLF [Juveniles and Adults])

and for the SMHM (see “Potential for Direct Effects”) 

POTENTIAL FOR DIRECT EFFECTS 

Direct Deposition on Forage Items: Mammalian RQ 

- Acute and chronic dose-based RQs exceed the Agency acute listed and chronic LOC 

in all modeled scenarios (N=20) for large mammals. Chronic dietary-based RQs 

exceed the chronic LOC in all 20 modeled scenarios for large mammals that feed on 

short grass, tall grass, and broadleaf plants/small insects (chronic dietary-based RQs 

for 13/20 scenarios exceed the LOC for large mammals consuming 

fruits/pods/seeds/large insects). 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of SJKF was 

identified. 

- A moderate amount of spatial overlap between SJKF occurrence and current (and 

potential future use) of endosulfan was identified (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS 

San Joaquin 

kit fox 

(Vulpes 

macrotis 

mutica) 

LAA1

Terrestrial Invertebrates: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled, there is a high likelihood of individual 

mortality, and EECs exceed LD50 values for vast majority of tested species, as 

described above for CRLF (see “Potential for Indirect Effects: CRLF Terrestrial Prey 

Items, Riparian Habitat)

Small Birds and Mammals: 

- Acute and chronic RQ for birds and mammals serving as prey to the SJKF exceed 

listed acute and chronic LOCs as a result of direct deposition onto forage items and 

bioaccumulation in terrestrial prey as described above for the CRLF (Potential for 

Direct Effects: Terrestrial-phase CRLF [Juveniles and Adults]) and for the SMHM 

(see “Potential for Direct Effects”) 

20
Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

POTENTIAL FOR DIRECT EFFECTS

Terrestrial Invertebrate RQs: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled. 

- EECs exceed for large and small insects exceed the LD50 values for 80% and 99% 

of the tested terrestrial invertebrate species, respectively. 

Likelihood of Individual Mortality

-The chance of individual effects (i.e., mortality) for terrestrial invertebrates resulting 

from direct deposition in application sites is as high as ~1 in 1. 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of BCB was 

identified. 

- No spatial overlap identified at the County level based on current endosulfan use 

reported for California. If cultivated crop/orchard/vineyard uses are considered areas 

of potential endosulfan use in the future, then a substantial amount of spatial overlap 

can be observed relative to the total area of BCB occurrence sections. 

- When exposure of terrestrial insects via spray drift is considered, spatial overlap 

between potential endosulfan use on agricultural crops, orchards, and vineyard areas 

can extend up to 2 miles from the source. 

- The potential for endosulfan to be transported long distances in the atmosphere may 

increase BCB exposure, particularly in areas of potential endosulfan use west of BCB 

occurrence sections in Santa Clara County (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS

Bay 

checkerspot 

butterfly 

(Euphydryas 

editha 

bayensis) 

(BCB) 

LAA1

-Although effects to terrestrial plants cannot be quantified due to the lack of data, 

aquatic non-vascular plants are not particularly sensitive to endosulfan 

- Endosulfan has a neural toxic mode of action. 

- No studies demonstrating significant adverse effects of endosulfan to any vascular 

aquatic or terrestrial plant have been identified in the open literature. The one toxicity 

study found to be acceptable for quantitative use suggests that aquatic nonvascular 

plants are insensitive relative to aquatic animals. 

- No ecological incidents have been reported to the Agency that involve any plants 

and this was classified with a certainty index of “probable” or higher linking 

endosulfan as a cause, despite that it is regularly directly applied on or near a very 

wide variety of agricultural plants.

Valley POTENTIAL FOR DIRECT EFFECTS

elderberry 

longhorn 

beetle 

(Desmocerus 

californicus 

dimorphus) 

LAA1

Terrestrial Invertebrate RQs: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled. 

- EECs exceed for large and small insects exceed the LD50 values for 80% and 99% 

of the tested terrestrial invertebrate species, respectively. 

Likelihood of Individual Mortality

-The chance of individual effects (i.e., mortality) for terrestrial invertebrates resulting 

from direct deposition in application sites is as high as ~1 in 1. 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of VELB was 

identified. 

- A small amount of spatial overlap identified at the County level based on current 

21
Table 1.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

endosulfan use reported for California. If cultivated crop/orchard/vineyard uses are 

considered areas of potential endosulfan use in the future, then a moderate amount of 

spatial overlap can be observed relative to the total area of VELB occurrence sections 

(Appendix E). 

- When exposure of terrestrial insects via spray drift is considered, spatial overlap 

between potential endosulfan use on agricultural crops, orchards, and vineyard areas 

can extend up to 2 miles from the source 

- The potential for endosulfan to be transported long distances in the atmosphere may 

increase VELB exposure, particularly in areas of potential endosulfan use west of 

VELB occurrence sections. 

POTENTIAL FOR INDIRECT EFFECTS

-Although effects to terrestrial plants cannot be quantified due to the lack of data, 

aquatic non-vascular plants are not particularly sensitive to endosulfan 

- Endosulfan has a neural toxic mode of action. 

- No studies demonstrating significant adverse effects of endosulfan to any vascular 

aquatic or terrestrial plant have been identified in the open literature. The one toxicity 

study found to be acceptable for quantitative use suggests that aquatic nonvascular 

plants are insensitive relative to aquatic animals. 

- No ecological incidents have been reported to the Agency that involve any plants 

and this was classified with a certainty index of “probable” or higher linking 

endosulfan as a cause, despite that it is regularly directly applied on or near a very 

wide variety of agricultural plants. 1

 No effect (NE); May affect, but not likely to adversely affect (NLAA); May affect, likely to adversely affect 

(LAA) 

Table 1.2 Effects Determination Summary for the Critical Habitat Impact Analysis 

Designated 

Critical Habitat 

for: 

Effects 

Determination 1

Basis for Determination 

CRLF May Affect 

-There is a potential for direct effects to the aquatic-phase CRLF and 

indirect effects via reduction of aquatic-phase prey items (aquatic 

invertebrates, fish, and aquatic-phase amphibians) as described in Table 1.1 

above. 

- There is a potential for direct effects to the terrestrial-phase CRLF and 

indirect effects via reduction of terrestrial-phase prey items (mammals, 

amphibians, and terrestrial invertebrates) as described in Table 1.1 above. 

CTS May Affect 

There is a potential for direct effects to the CTF and indirect effects via 

reduction of aquatic-phase prey items (aquatic invertebrates and fish) as 

described in Table 1.1 above. 

- There is a potential for direct effects to the CTF and indirect effects via 

reduction of terrestrial-phase prey items (terrestrial invertebrates) as 

described in Table 1.1 above. 

BCB NE1

-Although effects to terrestrial plants cannot be quantified due to the lack of 

data, aquatic non-vascular plants are not particularly sensitive to endosulfan 

- Endosulfan has a neural toxic mode of action. 

-No studies demonstrating significant adverse effects of endosulfan to any 

vascular aquatic or terrestrial plant have been identified in the open 

literature. The one toxicity study found to be acceptable for quantitative use 

22
suggests that aquatic nonvascular plants are insensitive relative to aquatic 

animals. 

- No ecological incidents have been reported to the Agency that involve any 

plants and this was classified with a certainty index of “probable” or higher 

linking endosulfan as a cause, despite that it is regularly directly applied on 

or near a very wide variety of agricultural plants. 

VELB NE1

-Although effects to terrestrial plants cannot be quantified due to the lack of 

data, aquatic non-vascular plants are not particularly sensitive to endosulfan 

- Endosulfan has a neural toxic mode of action. 

-No studies demonstrating significant adverse effects of endosulfan to any 

vascular aquatic or terrestrial plant have been identified in the open 

literature. The one toxicity study found to be acceptable for quantitative use 

suggests that aquatic nonvascular plants are insensitive relative to aquatic 

animals. 

- No ecological incidents have been reported to the Agency that involve any 

plants and this was classified with a certainty index of “probable” or higher 

linking endosulfan as a cause, despite that it is regularly directly applied on 

or near a very wide variety of agricultural plants. 1

 No effect (NE) 

The Agency has determined that there is No Effect to BCB and VELB designated critical habitat 

from the use of endosulfan. Although there were no reliable data to quantitatively evaluate the 

effects and the potential risks of endosulfan to terrestrial plants, aquatic non-vascular plants are 

not particularly sensitive to endosulfan, endosulfan has a neural toxic mode of action, and no 

studies demonstrating significant adverse effects of endosulfan on growth, survival, or 

reproduction of any vascular aquatic or terrestrial plants have been identified in the open 

literature. Furthermore, of the 83 ecological incidents reported to the Agency involving 

endosulfan, only one was associated with plants (unspecified plant damage) and its certainty 

index was only considered “possible.” Lastly, a review of efficacy studies for endosulfan 

indicates that adverse effects on crops at registered application rates is not likely. 

Based on the conclusions of this assessment, a formal consultation with the U. S. Fish and 

Wildlife Service under Section 7 of the Endangered Species Act should be initiated. 

When evaluating the significance of this risk assessment’s direct/indirect and habitat effects 

determinations, it is important to note that pesticide exposures and predicted risks to the species 

and its resources (i.e., food and habitat) are not expected to be uniform across the action area. In 

fact, given the assumptions of drift and downstream transport (i.e., attenuation with distance), 

pesticide exposure and associated risks to the species and its resources are expected to decrease 

with increasing distance away from the treated field or site of application. Evaluation of the 

implication of this non-uniform distribution of risk to the species would require information and 

assessment techniques that are not currently available. Examples of such information and 

methodology required for this type of analysis would include the following: 

• Enhanced information on the density and distribution of CRLF, SFGS, CTS, 

BCB, VELB, SMHM, and SJKF life stages within the action area and/or 

applicable designated critical habitat. This information would allow for 

quantitative extrapolation of the present risk assessment’s predictions of 

individual effects to the proportion of the population extant within geographical 

23
areas where those effects are predicted. Furthermore, such population 

information would allow for a more comprehensive evaluation of the significance 

of potential resource impairment to individuals of the assessed species. 

• Quantitative information on prey base requirements for the assessed species. 

While existing information provides a preliminary picture of the types of food 

sources utilized by the assessed species, it does not establish minimal 

requirements to sustain healthy individuals at varying life stages. Such 

information could be used to establish biologically relevant thresholds of effects 

on the prey base, and ultimately establish geographical limits to those effects. 

This information could be used together with the density data discussed above to 

characterize the likelihood of adverse effects to individuals. 

• Information on population responses of prey base organisms to the pesticide. 

Currently, methodologies are limited to predicting exposures and likely levels of 

direct mortality, growth or reproductive impairment immediately following 

exposure to the pesticide. The degree to which repeated exposure events and the 

inherent demographic characteristics of the prey population play into the extent to 

which prey resources may recover is not predictable. An enhanced understanding 

of long-term prey responses to pesticide exposure would allow for a more refined 

determination of the magnitude and duration of resource impairment, and together 

with the information described above, a more complete prediction of effects to 

individual species and potential modification to critical habitat. 

24
2 Problem Formulation 

Problem formulation provides a strategic framework for the risk assessment. By identifying the 

important components of the problem, it focuses the assessment on the most relevant life history 

stages, habitat components, chemical properties, exposure routes, and endpoints. The structure 

of this risk assessment is based on guidance contained in U.S. EPA’s Guidance for Ecological 

Risk Assessment (U.S. EPA 1998), the Services’ Endangered Species Consultation Handbook

(USFWS/NMFS 1998) and is consistent with procedures and methodology outlined in the 

Overview Document (U.S. EPA 2004) and reviewed by the U.S. Fish and Wildlife Service and 

National Marine Fisheries Service (USFWS/NMFS 2004). 

2.1 Purpose 

The purpose of this endangered species assessment is to evaluate potential direct and indirect 

effects on individuals of the following Federally Threatened species: 

• California Red-legged Frog (CRLF), Rana aurora draytonii, 

• Bay Checkerspot Butterfly (BCB), Euphydryas editha bayensis, 

• Valley Elderberry Longhorn Beetle (VELB), Desmocerus californicus dimorphus, and 

• California Tiger Salamander (CTS), Ambystoma californiense, 

and the following Federally Endangered species: 

• San Francisco Garter Snake (Thamnophis sirtalis tetrataenia), 

• San Joaquin Kit Fox (Vulpes macrotis mutica), and 

• Salt Marsh Harvest Mouse (Reithrodontomys raviventris)

 

These effects arise from FIFRA regulatory actions regarding use of endosulfan on tree crops 

(nuts, citrus, and other fruits), field crops (cotton, potatoes, and row crops), cucurbits, leafy 

vegetables (lettuce), fruiting vegetables (tomato, strawberry and eggplant), and tree outdoor 

nurseries. In addition, this assessment evaluates whether use on these use sites is expected to 

result in effects to designated critical habitat for the CRLF CTS, BCB, and VELB. This 

ecological risk assessment has been prepared consistent with the settlement agreement in Center for 

Biological Diversity (CBD) vs. EPA et al. (Case No. 02-1580-JSW(JL)) which addresses the CRLF 

and was entered in Federal District Court for the Northern District of California on October 20, 2006. 

This assessment also addresses the SFGS, SMHM, BCB, VELB, SJKF, and CTS for which 

endosulfan was alleged to be of concern in a separate suit (Center for Biological Diversity (CBD) vs. 

EPA et al. (Case No. 07-2794-JCS)). 

In this assessment, direct and indirect effects to the CRLF, CTS, SFGS, SMHM, SJKF, BCB, 

and VELB and potential effects to designated critical habitat for the CRLF, CTS, BCB, and 

VELB are evaluated in accordance with the methods described in the Agency’s Overview 

Document (U.S. EPA 2004). The effects determinations for each listed species assessed is based 

on a weight-of-evidence method that relies heavily on an evaluation of risks to each taxon 

relevant to assess both direct and indirect effects to the listed species and the potential for effects 

to their designated critical habitat (i.e., a taxon-level approach). Screening level methods include 

use of standard models such as PRZM-EXAMS, T-REX, TerrPlant, AgDRIFT, and AGDISP, all 

of which are described at length in the Overview Document. Additional refinements include: 

25
1. Use of T-HERPS model for estimating exposure to terrestrial phase amphibians and 

reptiles

2. Use of the KABAM model for estimating endosulfan accumulation in aquatic food webs 

and subsequent risks to terrestrial wildlife consuming aquatic prey 

3. Use of earthworm fugacity modeling to predict concentrations in terrestrial food items for 

the SMHM, SJKF, and CTS.

Use of such information is consistent with the methodology described in the Overview 

Document (U.S. EPA 2004), which specifies that “the assessment process may, on a case-bycase basis, incorporate additional methods, models, and lines of evidence that EPA finds 

technically appropriate for risk management objectives” (Section V, page 31 of U.S. EPA 2004).

In accordance with the Overview Document, provisions of the ESA, and the Services’ 

Endangered Species Consultation Handbook, the assessment of effects associated with 

registrations of endosulfan is based on an action area. The action area is the area directly or 

indirectly affected by the federal action, as indicated by the exceedence of the Agency’s Levels 

of Concern (LOCs). It is acknowledged that the action area for a national-level FIFRA 

regulatory decision associated with a use of endosulfan may potentially involve numerous areas 

throughout the United States and its Territories. However, for the purposes of this assessment, 

attention will be focused on relevant sections of the action area including those geographic areas 

associated with locations of the CRLF, CTS, SFGS, SMHM, SJKF, BCB, and VELB and their 

designated critical habitat within the state of California. As part of the “effects determination,” 

one of the following three conclusions will be reached separately for each of the assessed species 

regarding the potential use of endosulfan in accordance with current labels: 

• “No effect”; 

• “May affect, but not likely to adversely affect”; or 

• “May affect and likely to adversely affect”. 

The CRLF, BCB, CTS, and VELB have designated critical habitat associated with them. 

Designated critical habitat identifies specific areas that have the physical and biological features, 

(known as primary constituent elements or PCEs) essential to the conservation of the listed 

species. A brief summary of PCEs for these species being assessed is as follows. 

CRLF. The PCEs for CRLF are aquatic and upland areas where suitable breeding and 

non-breeding aquatic habitat is located, interspersed with upland foraging and dispersal 

habitat. 

BCB. The PCEs for BCB include the presence of annual or perennial grasslands with 

little to no overstory and N-S or E-W slopes with a tilt of >7 degrees, areas of serpentinite 

ultramafic rock or similar soils that support the primary larval host plant (i.e., dwarf 

plantain) and at least one of the species’ secondary host plants, the presence of adult 

nectar sources, aquatic features that provide moisture during the spring drought, and the 

presence stable holes and cracks in the soil, and surface rock outcrops that provide shelter 

during the summer diapause. 

26
CTS. The PCEs for CTS include standing bodies of fresh water (e.g., ponds, vernal pools 

and dune ponds, and other ephemeral or permanent water bodies), barrier-free uplands 

adjacent to breeding ponds that contain small mammal burrows (used for habitat), and 

upland areas between breeding locations and areas with small mammal burrows that 

allow for dispersal among such sites 

VELB. The PCEs for VELB include areas containing the host plant of this species [i.e., 

elderberry trees (Sambucus sp.)]. 

If the results of initial screening-level assessment methods show no direct or indirect effects (no 

LOC exceedances) upon individuals or upon the PCEs of the species’ designated critical habitat, 

a “no effect” determination is made for use of endosulfan as it relates to each species and its 

designated critical habitat. If, however, potential direct or indirect effects to individuals of the 

species are anticipated or effects may impact the PCEs of the designated critical habitat, a 

preliminary “may affect” determination is made for the FIFRA regulatory action regarding 

endosulfan. 

If a determination is made that use of endosulfan “may affect” a listed species or its designated 

critical habitat, additional information is considered to refine the potential for exposure and for 

effects to each species and other taxonomic groups upon which these species depend (e.g., prey 

items). Additional information, including spatial analysis (to determine the geographical 

proximity of the assessed species’ habitat and endosulfan use sites) and further evaluation of the 

potential impact of endosulfan on the PCEs is also used to determine whether effects to 

designated critical habitat may occur. Based on the refined information, the Agency uses the 

best available information to distinguish those actions that “may affect, but are not likely to 

adversely affect” from those actions that “may affect and are likely to adversely affect” the 

assessed listed species and/or have “no effect” on or “may affect” the PCEs of its designated 

critical habitat. This information is presented as part of the Risk Characterization in Section 5 of 

this document. 

The Agency believes that the analysis of direct and indirect effects to listed species provides the 

basis for an analysis of potential effects on the designated critical habitat. Because endosulfan is 

expected to directly impact living organisms within the action area (defined in Section 2.7), 

critical habitat analysis for endosulfan is limited in a practical sense to those PCEs of critical 

habitat that are biological or that can be reasonably linked to biologically mediated processes 

(i.e., the biological resource requirements for the listed species associated with the critical habitat 

or important physical aspects of the habitat that may be reasonably influenced through biological 

processes). Activities that may affect critical habitat are those that alter the PCEs and 

appreciably diminish the value of the habitat. Evaluation of actions related to use of endosulfan 

that may alter the PCEs of the assessed species’ critical habitat form the basis of the critical 

habitat impact analysis. Designated critical is discussed further in Section 2.6. 

2.2 Scope 

Endosulfan is mainly used as an agricultural insecticide to control insect pests such as aphids, 

fruit worms, beetles, leafhoppers, moth larvae, and whiteflies. Endosulfan is applied as liquid 

27
spray prepared from emulsifiasble concentrate (EC) and wettable powder (WP) formulations 

using aircraft or ground equipment. The pesticide is mostly applied as foliar spray with single 

rates ranging from 0.5 to 2.5 lbs a.i/A at minimum intervals ranging from 5 to 10 days and 

maximum total rate from 0.5 to 3.0 lb a.i/season or year. The following uses are considered as 

part of the federal action evaluated in this assessment: nut trees (almonds, hazelnuts, and 

walnuts), non-bearing citrus trees, cole crops, fresh market sweet corn, cotton, pome fruits 

(apple, and pear), stone fruits (apricot, nectarine, peach, cherry, , plum, and prune), leafy 

vegetables (lettuce, Brussels sprouts, and celery), cucurbits, outdoor nurseries for ornamentals 

and shade trees, potato, sweet potato, dry beans and peas, carrot, and fruiting vegetables (pepper, 

strawberry, eggplant, and tomatoes). Non-agriculture is a minor use as it is used impregnated in 

cattle ear tags. 

The end result of the EPA pesticide registration process (i.e., the FIFRA regulatory action) is an 

approved product label. The label is a legal document that stipulates how and where a given 

pesticide may be used. Product labels (also known as end-use labels) describe the formulation 

type (e.g., liquid or granular), acceptable methods of application, approved use sites, and any 

restrictions on how applications may be conducted. Thus, the use or potential use of endosulfan 

in accordance with the approved product labels for California is “the action” relevant to this 

ecological risk assessment. 

Although current registrations of endosulfan allow for use nationwide, this ecological risk 

assessment and effects determination addresses currently registered uses of endosulfan in 

portions of the action area that are reasonably assumed to be biologically relevant to the CRLF, 

CTS, SFGS, SMHM, SJKF, BCB, and VELB and their designated critical habitat. Further 

discussion of the action area for the CRLF, CTS, SFGS, SMHM, SJKF, BCB, and VELB and 

their critical habitat, if any, is provided in Section 2.7. 

The two isomers of endosulfan, alpha (α) and beta (β), degrade at different rates into a common 

degradate, the endosulfan sulfate. Although other degradates such as endosulfan diol and ether 

form, expected quantities in the environment are low as they may form as a result of hydrolysis 

of spray drift reaching biologically active water bodies where the sulfate is expected to form 

instead. In this assessment, the highly persistent endosulfan sulfate is included with both isomers. 

This is because endosulfan sulfate is the major degradate forming in the soil system to which the 

major amount of the pesticide is applied. Additionally, endosulfan sulfate is highly persistent in 

the major compartments of the environment. Exposure was determined for both parents and the 

common endosulfan sulfate degradate using PRZM/EXAMS modeling. 

The Agency does not routinely include, in its risk assessments, an evaluation of mixtures of 

active ingredients, either those mixtures of multiple active ingredients in product formulations or 

those in the applicator’s tank. In the case of the product formulations of active ingredients (that 

is, a registered product containing more than one active ingredient), each active ingredient is 

subject to an individual risk assessment for regulatory decision regarding the active ingredient on 

a particular use site. If effects data are available for a formulated product containing more than 

one active ingredient, they may be used qualitatively or quantitatively in accordance with the 

Agency’s Overview Document and the Services’ Evaluation Memorandum (U.S., EPA 2004; 

USFWS/NMFS 2004). 

28
Endosulfan does not have any registered products that contain multiple active ingredients. 

2.3 Previous Assessments 

In February, 2002, the USEPA completed an Environmental Fate and Ecological Risk 

Assessment of endosulfan in support of the re-registration eligibility decision for endosulfan use 

on both food and non food crops (USEPA, 2002; DP Barcode D238673). Based on a screening 

level assessment for terrestrial impacts and a refined assessment for aquatic impacts, it was 

concluded that endosulfan (maximum application rate of 3 lb a.i./A) was likely to result in acute 

and chronic risk to both terrestrial and aquatic organisms. Based on the tomato crop scenario that 

yielded the largest EECs, acute and chronic RQ values ranged from about 23 and 44 for 

freshwater fish, respectively, to about 190 and 490 for estuarine/marine fish, respectively. Acute 

and chronic RQ values for invertebrates ranged from approximately3.3 and 93 for freshwater 

and from 42 to 130 for estuarine/marine fish, respectively. Monitoring data reported in the 

assessment demonstrated widespread contamination of surface water and ecological incident data 

indicated that the use pattern of endosulfan represented a substantial risk of mortality for nontarget aquatic species. Based on the 2002 Environmental Fate and Ecological Risk Assessment 

RQs for birds and mammals exceeded the Agency’s acute and chronic risk LOCs and ranged up 

to a maximum of 2.7 for birds and 40 for mammals. 

The refined aquatic risk assessment used probabilistic exposure assessment techniques and was 

based on actual reported application rates in California coupled with a 300-ft spray drift buffer. 

The refined assessment concluded that on sites prone to runoff within the endosulfan use area, 

mortality to non-target fish is probable in any given year. Furthermore, based on “nonconservative” assumptions (i.e., “typical” application rates and a 300-foot spray drift buffer), 

EFED concluded that the modeled endosulfan use rates on 88% of the crops modeled would 

exceed acute high risk LOCs more than 99% of the time. The assessment’s conclusions were 

supported by incident data indicating multiple fish kill incidents attributable to endosulfan use 

are reported each year. While repopulation of aquatic communities was considered likely in the 

assessment (via migration from unaffected areas), the intermediate effect on food chains was 

considered uncertain. 

In 2007, USEPA published an addendum to the 2002 environmental fate and ecological risk 

assessment in order to evaluate the potential impact of new information related to endosulfan 

toxicity, bioaccumulation, monitoring and transport, and ecological incidence (USEPA 2007; 

D346213). A number of aspects of the 2007 addendum differed from the previous assessment in 

2002: 

• Aquatic exposure modeling considered both the parent isomers and the primary degradate 

of concern (endosulfan sulfate)

• A review of new monitoring data including the long-range transport of endosulfan was 

conducted

• Bioaccumulation potential of endosulfan in aquatic organisms was evaluated using 

empirical data and a food web model 

• New data on the toxicity of endosulfan sulfate was included

• Risk quotients were based on combined exposure to parent and degradate compounds.

29
Risk quotient (RQ) predicted for aquatic organisms resulting from water column exposure to 

endosulfan were about 20% to 40% higher in the 2007 addendum compared to the 2002 ERA. 

This increase reflected the addition of endosulfan sulfate to the exposure modeling and data 

indicating it is of similar acute toxicity to the parent isomers (α and β). Based on the tomato crop 

scenario that yielded the largest EECs, acute and chronic RQ values ranged from about 30 to 60 

for freshwater fish, respectively (compared to 23 and 44 from the 2002 ERA) to about 230 and 

680 for estuarine/marine fish, respectively (compared to 190 and 490 from the 2002 ERA). 

Acute and chronic RQ values for invertebrates ranged from approximately 4 to 130 for 

freshwater (compared to 3.3 and 93 from the 2002 ERA) and from 50 to 190 for estuarine/marine 

(compared to 42 to 130 from the 2002 ERA), respectively. Findings from ecological incidents 

generally supported the findings of endosulfan risk to fish and invertebrates.

Risks to freshwater and estuarine/marine invertebrates resulting from sediment exposure to 

endosulfan are evident from the integration of exposure and effect characterization. The RQ 

values for sediment-dwelling invertebrates range form 0.9 to 2.8 depending on species. These 

RQ values are based on predicted total endosulfan residues compared to endosulfan sulfate 

toxicity values, which assumes similar toxicity of endosulfan sulfate and total endosulfan 

residues. 

Based on preliminary results from an aquatic food web bioaccumulation model, risks to 

piscivorous wildlife appeared relatively modest with mean predicted acute RQ values exceeding 

the Agency acute LOC of 0.1 for one of eight species modeled (0.15 for river otter) and 90th

percentile estimates exceeding the LOC for three of eight species modeled (0.18, 0.39, 0.20 for 

mink, river otter and belted kingfisher, respectively). Predicted chronic RQ values did not 

exceed the Agency LOC for any of the eight species modeled. 

Risks to non-target terrestrial wildlife did not change from the 2002 ERA as a result of this 

addendum, because the currently available terrestrial exposure model could not address total 

residue exposure. Based on the 2002 ERA, RQs for birds and mammals exceeded the Agency’s 

acute and chronic risk LOCs and range up to a maximum of 2.7 for birds and 40 for mammals. 

In summary, the 2007 Addendum concluded there is a concordance of evidence that endosulfan 

is undergoing long-range transport and has moved to sites distant from use areas. Furthermore, 

the sulfate degradate was considered persistent and a significant source for endosulfan to enter 

aquatic and terrestrial food chains. Endosulfan was not expected to biomagnify appreciably in 

aquatic food webs (i.e., increasing concentrations with increasing trophic level), although it was 

found that endosulfan can bioaccumulate substantially, with BCFs ranging from approximately 

1,000 to 3,000 L/kg w.w. Risks to both aquatic and terrestrial animals were identified using the 

latest information available. The Agency is currently responding to public comments received on 

the 2007 Addendum. 

2.4 Stressor Source and Distribution 

This assessment considers the stressor to consist of multiple compounds, namely, endosulfan 

alpha, endosulfan beta and their common degradate endosulfan sulfate. The chemical name of 

endosulfan is 6,7,8,10,10-hexachloro-1,5,51,6,9,9a-hexahydro-6,9-methano-2,4,3-

30
benzadioxathiepin 3-oxide. Endosulfan has two stereo-isomers, endosulfan alpha and beta (αand β-endosulfan). According to the agricultural label, the maximum amount of α is 70% and β

is 30%. Figure 2.1 provides the structures of α. and β-endosulfan and major transformation 

products. 

α-endosulfan (959-98-8) β-endosulfan (3213-65-9) Endosulfan Sulfate (1031-07-8) 

The Multi-Chemical Stressor of Endosulfan 

Endosulfan Diol (2157-19-9) Endosulfan Ether (3369-52-6) Endosulfan Lactone (3868-612-9) 

Other Degradates of Endosulfan 

Figure 2.1 Chemical structures of endosulfan and related compounds 

The source of the stressor is foliar application of endosulfan formulated products including 

wettable powders (WP) and emulsifiable concentrates (EC) by air, ground and airblast 

application methods. In an agricultural setting, major quantities of the applied pesticide active 

ingredient reach target foliage and eventually end-up in the soil system. Smaller quantities of the 

applied pesticide reach nearby field or water bodies initially by drift and followed by 

runoff/erosion and by volatilization. Biologically mediated transformation of α and β-endosulfan 

is expected to occur in the soil system producing endosulfan sulfate (maximum levels >52%), a 

common degradate of toxicological concern. Endosulfan sulfate is added to parent(s) as a 

stressor because it is a major toxic and persistent soil transformation product. In contrast, 

endosulfan diol is not included as a component of the stressor because it is less toxic and 

expected to form in biologically inactive neutral and alkaline systems. Endosulfan diol was a 

major transformation product in sterile aqueous media (maximum levels >82%) and was only a 

31
minor transformation product in aerobic soil systems in the laboratory and the field (maximum 

levels <10 %) (USEPA, 2002; DP Barcode D238673). 

For the purpose of this assessment, the term “endosulfan” refers to the technical grade active 

ingredient (TGAI) unless otherwise indicated. The term “total endosulfan” or “endosulfans” 

refers to the combination of α –endosulfan, β-endosulfan and endosulfan sulfate unless 

otherwise noted.

2.4.1 Environmental Fate Properties 

The physiochemical properties of the multi-chemical stressor are summarized in Table 2.1. Fate 

and transport data for endosulfan isomers and common degradate endosulfan sulfate (the multichemical stressor) are summarized in Table 2.2. Major and minor degradates detected in 

submitted environmental fate and transport studies are also included in the same Table 2.2. 

Table 2.1 Physiochemical properties of the multi-chemical stressor

Property α -endosulfan β-endosulfan Endosulfan sulfate 

Formula C9H6Cl6O3S C9H6Cl6O3S C9H6Cl6SO4

Molecular Weight 406.9 g/mole 406.9 g/mole 422.9 g/mole 

CAS Number 959-98-8 33213-65-9 1031-07-8 

Water Solubility 530 μg/L 280 μg/L 330 μg/L 

Vapor Pressure 1

( torr @ 25 oC) 4.6x10-5; 1.5x10-5 & 3.0x10-6 2.4x10-5; 6.9 & 7.2 x 10-7 9.75x10-6

Henry’s Law Constant 2

(atm-m3 mol-1 @ 25 oC) 3.03x10-6 1.38x10-6 1.64x10-5 

Log Kaw (air/water) 3 -3.56 -4.75 -4.78 

Log Kow (octanol/water) 

3 Corresponds to Kow of:

4.93 

95,499 

4.78 

60,256 

3.71 

5,129 

Log Koa

3 6.41 & 8.64 6.41 & 8.64 8.45 & No value 

1 Vapor pressure for α and β-endosulfan (MRIDs 414215-01 and 400606-01) and for endosulfan sulfate from: Hinckley et 

al (1990)2

 2 All three values were calculated from the 1st vapor pressure values above (in Bold) using molecular weight, solubility & 

25o

C temperature

3 Source of data for partitioning coefficients: Log Kaw and Kow as reported (Schenker et al, 2005)3

 while Log Koa is 

estimated by EPI Suite v4.04; 1st value= EPI Suite estimate & 2nd value= from EPI suite database

 

2

 Daniel A. Hinckley, Terry F. Bidleman, William T. Foreman, Jack R. Tuschall. 1990. Determination of vapor 

pressure for non-polar and semi-polar organic compounds from gas chromatography retention data J. Chem. Eng. 

Data, 1990, 35 (3), pp 232–237 3 Schenker, U., MacLeod, M., Scheringer, M., Hungerbuhler K., 2005. Improving data quality for environmental 

fate models: A least-square adjustment procedure for harmonizing physiochemical properties of organic compounds. 

Environmental Science & Technology 39, 8434-8441. 

4

 The Estimation Programs Interface EPI Suite: http://www.epa.gov/oppt/exposure/pubs/episuitedl.htm 

32
Table 2.2 Summary of fate and transport properties for endosulfan isomers and sulfate 

Study Value (units) Major & Minor Degradates 

Reference & 

Study Status * 

Hydrolysis 

t1⁄2 @ pH 5: stable (>200 days) for both α

and β

t1⁄2 @ pH 7: 19 days for α;11 days for β

endosulfan sulfate: 184 days ** Major: Endosulfan diol 

414129-01(A) for 

only pH 5 and 7 

Aqueous Photolysis Stable, based on absorption spectrum None reported Registrant Data 

Soil Photolysis Stable Minor: Endosulfan diol 414307-01 (A) 

Aerobic Soil 

Metabolism 

(Five soils) 

α-endosulfan: t1⁄2 35-67 days; 90th %= 57 

days 

β-endosulfan: 104-265 days,; 90th %=208 

days 

endosulfan sulfate: Shows no clear decline 

pattern 

Major: Endosulfan Sulfate 

Minor: Endosulfan diol & 

lactone 438128-01 (S) 

Anaerobic Soil 

Metabolism 

 (Two soils, Two phase 

study) 

α-endosulfan: 105 & 124 days; 90th %=115 

days 

β-endosulfan: 136 &161 days; 90th %=149 

days 

endosulfan sulfate: 120 & 165 days; 90th 

%=143 days 

All calculated from the anaerobic phase of 

the experiment 

Major: Endosulfan Sulfate 

Formed during the aerobic 

phase 

Minor: Endosulfan diol & 

lactone 414129-04 (A) 

Organic Carbon based 

Adsorption Coefficient 

(Koc) 

α-endosulfan: Koc 10,600 ml/g (Average for 

4 soils) 

β-endosulfan: Koc 13,500 ml/g (Average for 

4 soils) 

endosulfan sulfate & diol: Qualitatively, 

when compared to parents sulfate is similar 

or slightly more mobile while diol is 

substantially more mobile Not Applicable 

414129-06 (S) 

414129-05 (U) 

No aerobic aquatic metabolism study was submitted; Submitted anaerobic aquatic metabolism study was Un-acceptable 

449178-01 (U) 

Terrestrial Field 

Dissipation 

α-endosulfan: t1⁄2 46 days (GA tomato), 70 

days (CA cotton), and 6-11 days (CA 

cotton) 

β-endosulfan: t1⁄2 90 days (GA tomato), 103 

days (CA cotton) and 19-63 days (CA 

cotton) 

Important Note: t1/2 in soil surface layer, 

encompassing movement as well as 

degradation 

Endosulfan-sulfate and 

endosulfan-diol. The sulfate 

was dominant and appeared 

to be more persistent 

413097-02 (A) 

414686-01 (A) 

430697-01 (A) 

Accumulation in Nontarget Aquatic 

Organisms 

600x in mussels with depuration t1⁄2 of 34 hr 

2,429x for edible tissue and 2,755x for 

whole body of mullet with depuration within 

48 hr Not Applicable 

05003053 (A) 

05005824 (A) 

* Reference Numbers indicated are MRID or Access Numbers, Study Status: A= Acceptable; S= Supplemental and 

33
Study Value (units) 

Reference & 

Major & Minor Degradates Study Status * 

U=Unacceptable 

** An Extrapolated Hydrolysis at pH 7 value reported by Becker et al (2008)5 From Guerin & Kennedy 1992 

The physiochemical data for endosulfan isomers and sulfate indicate that the three chemicals are 

practically insoluble in water. Vapor pressure and Henry’s law constant values for the three 

chemicals suggest that volatility is important in the dissipation of the stressor. Endosulfan 

isomers and common degradate can be considered as semi-volatile compounds and can readily 

partition into air in measurable amounts as indicated by their air/water partition coefficients 

(from -4.78 to -3.56). Air/octanol and octanol/water coefficients suggest the three chemicals 

have high potential for bio-accumulation in aquatic and terrestrial organisms, respectively (Table 

2.1). 

Based on laboratory data, the two biologically-active α- and -β stereo isomers of endosulfan 

differ in physiochemical and fate properties (Table 2.2). The -β isomer is generally more 

persistent and the α-isomer is more volatile. In sterile conditions, α- and -β isomers are highly 

persistent in aqueous acid conditions (t1⁄2>200 days) but highly vulnerable to hydrolysis in 

aqueous neutral conditions (t1⁄2= 11 and 19 days for α- and –β-endosulfan, respectivelly) 

producing a major degradate, the endosulfan diol. Abiotic transformation by photolysis in 

aqueous media or on soil is not important. Both α- and -β endosulfan showed no significant 

absorption peaks in the visible light region of the spectra (290-800 nm). Additionally, the 

isomers had a similar degradation profile in soil exposed to light or kept in a dark control. 

In contrast to abiotic transformation, biotic mediated oxidation in the soil system appears to be 

the dominant pathway for degradation of both endosulfan isomers into endosulfan sulfate. In 

several aerobic soil studies, endosulfan isomers degraded into endosulfan sulfate with half-lives 

ranging from one to two months for α -endosulfan and from three to nine months for β -

endosulfan. Persistence of endosulfan appears to increase under anaerobic conditions. In two 

anaerobic soil metabolism studies, α- and β-endosulfan degraded with half-lives ranging from 

105 to 124 days for α-endosulfan and 136 to 161 days for β-endosulfan. Endosulfan sulfate was 

the major degradate formed during the aerobic phase of the study then degraded with a half-life 

of 120 to 165 days. 

In field dissipation studies, endosulfan persisted in the surface soil for weeks to months after 

application. Field dissipation rates capture a combination of degradation, transport, and uptake 

processes whereas laboratory studies capture only degradation processes. Therefore, field 

dissipation rates can only be compared to laboratory rates when these other transport and uptake 

processes are taken into account. 

The major transformation products found in fate studies are endosulfan diol (hydrolysis in sterile 

conditions) and endosulfan sulfate (soil metabolism). Another minor transformation product is 

endosulfan lactone which was detected at 4-6% in the anaerobic soil system. It is noted that all 

 

5

 L. Becker, U. Schenker and M. Scheringer. 2008. Overall persistence and long range transport potential of 

endosulfan and its transformation products. Swiss Institute of Technology, ETH Zurich, Switzerland

34
three degradation products have backbone structure of the parent compounds (Figure 2.1). 

When considering how to account for degradates, the two major degradates were considered; that 

is endosulfan sulfate and endosulfan diol. Endosulfan sulfate was identified for inclusion as a 

component of the stressor for the following reasons: 

(1) Endosulfan sulfate forms by oxidation in the aerobic soil system (maximum levels >52% 

of the applied). Only minor amounts of endosulfan diol and lactone (<10%) are formed 

in the aerobic soil system. Also, the sulfate is expected to be more persistent than its 

parents in the aerobic soil system. In aerobic soil studies, endosulfan sulfate was the 

major persistent degradate forming from α- and β-endosulfan; 

(2) Endosulfan diol was reported to be less toxic than parent or endosulfan sulfate (Verma et 

al 2006, siddique et al 2003, and others6). The persistent organic pollutants review 

committee stated “Endosulfan is a very toxic chemical for nearly all kind of organisms. 

Metabolism occurs rapidly, but the oxidised metabolite endosulfan sulfate shows an acute 

toxicity similar to that of the parent compound. In contrast, endosulfan-diol, which is 

another metabolite of endosulfan, is found substantially less toxic to fish by about three 

orders of magnitude”7

(3) The bulk of applied pesticide reaches the soil system with relatively small amounts 

reaching water bodies by drift (estimated to be 2.4% with a 300 ft. buffer). 

(4) Endosulfan diol is assumed to form from parent isomers reaching water by drift only in 

abiotic conditions. As most environmentally relevant water bodies are biologically active, 

endosulfan diol is not expected to form in substantial amounts in natural aquatic systems. 

However, no acceptable aerobic or anaerobic aquatic water sediment systems are 

available to confirm this assumption. 

Endosulfan isomers can be considered as hardly mobile in the soil system. The two chemical 

species have relatively high affinity to soil particles (Koc ranges from 10,600 to 13,500 ml/g) 

(Table 2.2). This property causes chemicals to partition into the soil and reduces readiness for 

leaching into ground water. Endosulfan sulfate appear to be similar to parent isomers in mobility 

although the endosulfan diol is substantially more mobile (Table 2.2). 

Laboratory measured Kow values (95,499 for α –endosulfan, 60,256 for β-endosulfan, and 5,129 

for endosulfan sulfate) suggest a relatively high potential to bioconcentrate in aquatic organisms 

such as fish. However, supplemental studies suggest that endosulfan isomers did not bioconcentrate at the high levels suggested by Kow (Table 2.1). In one study conducted with α -

 

6 http://umbbd.msi.umn.edu/end/end_map.html

http://www.ces.clemson.edu/ecl/caseStudy/case2.pdf

7 http://www.unon.org/confss/doc/unep/pops/POPRC_04/POPRC_4_14/K0841692%20POPRC-4-14.pdf

Persistent Organic Pollutants Review Committee; Fourth meeting; Geneva, 13–17 October 2008; Item 7 (a) of the 

provisional agenda: Consideration of chemicals newly proposed for inclusion in nnexes A, B or C of the 

Convention: endosulfan 

35
endosulfan on mussels, the bio-concentration factor was approximately 600X, with a depuration 

half-life of 34 hours (Acc. No. 05003053). In another study, conducted on striped mullet, the bioconcentration factor was 2,400X for combined isomers in edible tissues (Acc. No. 05005824). 

In this study, endosulfan depurated after 48 hours (Table 2.2). Tissue analysis in one study 

revealed the presence of endosulfan sulfate rather than α- and β-endosulfan, suggesting the 

potential accumulation of this degradate. 

2.4.2 Environmental Transport Mechanisms 

Potential transport mechanisms or routes of pesticide exposure include surface water 

runoff/erosion, spray drift, and secondary drift of volatilized or soil-bound residues leading to 

deposition onto nearby or more distant ecosystems. In addition, pesticides can reach shallow 

ground water through leaching when the chemical is characterized by relative high mobility and 

moderate persistence. Low mobility pesticides may also leach into ground water if they can 

persist long enough for such movement to occur. For endosulfan, surface water run-off /erosion, 

drift, and atmospheric transport are expected to be the major routes of exposure. 

A number of studies have documented atmospheric transport and re-deposition of pesticides 

from the Central Valley to the Sierra Nevada Mountains (Fellers et al., 2004, Sparling et al., 

2001, LeNoir et al., 1999, and McConnell et al., 1998). Prevailing winds blow across the 

Central Valley eastward to the Sierra Nevada Mountains, transporting airborne industrial and 

agricultural pollutants into the Sierra Nevada ecosystems (Fellers et al., 2004, LeNoir et al.,

1999, and McConnell et al., 1998). Several sections of the range and/or critical habitat for the 

listed species being evaluated in this assessment are located east of areas of potential endosulfan 

use (Appendix E). The magnitude of transport via secondary drift depends on the ability of 

endosulfan to be mobilized into air and its eventual removal through wet and dry deposition of 

gases/particles and photochemical reactions in the atmosphere. Therefore, physicochemical 

properties of endosulfan that describe its potential to enter the air from water or soil (e.g.,

Henry’s Law constant and vapor pressure), pesticide use data, modeled estimated concentrations 

in water and air, and available air monitoring data from the Central Valley and the Sierra Nevada 

are considered in evaluating the potential for atmospheric transport of endosulfan to locations 

where it could impact the listed species included in this assessment. 

 

In general, deposition of drifting or volatilized pesticides is expected to be greatest close to the 

site of application. Computer models of spray drift (AgDRIFT and/or AGDISP) are used to 

determine potential exposures to aquatic and terrestrial organisms via spray drift. 

The distance of potential impact away from the use sites is determined by the distance required 

to fall below the LOC for the taxonomic groups with the highest RQ to LOC ratio (for 

endosulfan, this consists of terrestrial insects for transport via spray drift and freshwater fish for 

transport via downstream flow). 

2.4.3 Mechanism of Action 

Endosulfan is a dioxathiepin (broadly classified as a chlorinated hydrocarbon) insecticide and 

acaricide. Technical endosulfan is made up of a mixture of two molecular forms (stereo isomers) 

of endosulfan – the alpha (α) and beta (β) isomers. This arylheterocycle acts as a poison to a 

36
wide variety of insects and mites on contact through blockage of GABA- (gamma amino butyric 

acid) gated chloride channels, which in turn induces the uptake of chloride ions by neurons. The 

blockage of the GABA neurotransmitter activity by cyclodiene insecticides like endosulfan 

results in only partial repolarization of the neuron and a state of uncontrolled excitation (Klassen 

& Watkins, 1999). Stimulation of the central nervous system is the major characteristic of 

endosulfan poisoning (Ecobichon 1991). 

Dissociation studies (Rauh et al. 1997) showed that dieldrin, ketoendrin, toxaphene, heptachlor 

epoxide and α- and β-endosulfan competitively bind with GABA receptors. Additionally, animal 

data indicate that toxicity may also be influenced by species and by level of protein in the diet; 

rats which have been deprived of protein are nearly twice as susceptible to the toxic effects of 

endosulfan. Solvent and/or emulsifiers used with endosulfan in formulated products may 

influence its absorption into the system via all routes: technical endosulfan is slowly and 

incompletely absorbed into the body whereas absorption is more rapid in the presence of 

alcohols, oils, and emulsifiers (Gupta and Gupta 1979). 

2.4.4 Use Characterization 

Current labeled use 

 

(a) Nationally 

Current registered uses of endosulfan include a wide variety of food crops, non-food crops and 

ornamentals. The list includes nut trees (almonds, hazelnuts, and walnuts), non-bearing citrus 

trees, cole crops (including Kohlrabi) , fresh market sweet corn, cotton, pome fruits (apple, and 

pear), stone fruits (apricot, nectarine, peach, cherry, plum, and prune), leafy vegetables (lettuce, 

Brussels sprouts), celery, cucurbits, outdoor nurseries for ornamentals and shade trees, potato, 

sweet potato, dry beans and peas, carrot, and fruiting vegetables (pepper, strawberry, eggplant, 

and tomatoes), tobacco (field, seed/plant beds), pineapple (fresh market only), and blueberry. No 

residential or public health uses are labeled for endosulfan although impregnated ear-tags are 

labeled for use on cattle. 

(b) California (CA) 

Labeled endosulfan uses that could potentially be used in California were analyzed in detail 

because it is the critical first step in evaluating the federal action. The current label for 

endosulfan represents the FIFRA regulatory action; therefore, labeled use and application rates 

specified on the label form the basis of this assessment. A summary of these labeled uses for 

endosulfan is included in Table 2.3. Application parameters included in Table 2.3 cover the 

most conservative application parameters and method of application for labeled crops. 

Table 2.3 Endosulfan labeled uses assessed for California (No single application rate over 1.5 lbs except for 

orchard crops and strawberries) 

Application: Maximum Rate, Number and Total 2

Use (Application Method) 1** Single Rate (lb 

a.i./A) Number 

Total/Season Or 

Year 

Minimum 

Application Intervals 

(day) 3

Almond, Hazelnut & Walnut 2.00 1 2.00 NA 

37
Table 2.3 Endosulfan labeled uses assessed for California (No single application rate over 1.5 lbs except for 

orchard crops and strawberries) 

Application: Maximum Rate, Number and Total 2 Minimum 

Application Intervals Single Rate (lb Total/Season Or 

Use (Application Method) 1** a.i./A) Number Year (day) 3

2.50 1 2.50 NA 

Citrus, non-bearing trees only 0.50+2.00 2 2.50 10 

Broccoli, Cabbage, Chinese cabbage & 

Cauliflower 1.00 2 2.00 7 

Collards, Kale & Mustard Green 0.75 1 0.75 NA 

Corn, Sweet for fresh market only 1.50 1 1.50 NA 

1.00 2 2.00 7 

Cotton (Ground) 0.50+1.50 2 2.00 7

Cotton (Aerial) 0.75 2 1.50 7

2.50 1 2.50 10 

Apple 0.50+0.75+1.25 3 2.50 10 

2.50 1 2.50 10 

Apricot, Nectarine, Peach, Cherry, Pear, 

Plum & Prune 0.50+2.00 2 2.50 10 

Lettuce (head & Leaf) 4 & Brussels 

Sprouts 1.00 2 2.00 5 

1.00 2 2.00 7 

Cucumber, Melons, Pumpkin & Squash 5 0.50+0.50+1.0 3 2.00 7 

0.50 1 0.50 NA 

Eggplant 0.25 2 0.50 7 

Ornamentals or shade Trees 6 0.50 6 3.00 10 

1.00 2 2.00 5 

Potato 0.50 4 2.00 5 

Sweet Potato 0.50 3 1.50 5 

Dry Beans, Dry Peas & Pepper 1.00 2 2.00 5 

Carrot 1.00 1 1.00 NA 

1.00 1 1.00 NA 

Celery 0.5 2 1.00 5 

38
Table 2.3 Endosulfan labeled uses assessed for California (No single application rate over 1.5 lbs except for 

orchard crops and strawberries) 

Application: Maximum Rate, Number and Total 2 Minimum 

Application Intervals Single Rate (lb Total/Season Or 

Use (Application Method) 1** a.i./A) Number Year (day) 3

2.00 1 2.00 NA 

Strawberry 1.00 2 2.00 15 

1.00 2 2.00 7 

Tomato 0.5 4 2.00 7 

1 Unless specified, the application method can be any of aerial or ground or airblast for tree crops only 2 In some cases, the number of applications was adjusted in order to always include the maximum single rate and at the 

same time abide by the maximum total applied/season or year. An additional application entry was included for specific 

crops to abide by both the maximum number of applications and the maximum total applied/season or year. Total lbs a.i 

applied/Acre was specified to be either per season or per year, therefore, multiple cropping may occur as follows: Two 

crops for Broccoli & Lettuce; Three crops for Cabbage, Chinese cabbage, Cauliflower, Collards, Mustard Green & 

Sweet Corn; and Four crops for Kale. 3 Application Intervals in italic were assumed as it was not specified on the Label. Assignments were based on previous 

assessments (EPA, 2002) or on similarities in crops and target pest(s); NA= Not Applicable 

4 Lettuce including: head, leaf (black seeded Simpson, and salad. Do not exceed 2 applications after thinning) 5 Squash: including summer, winter, and Hubbard 

6 Outdoor Nursery for Shade trees and Shrubs only 

** Although pineapple was one of the crops labeled for CA, the use was not considered as pineapple is not grown in CA.

Data for Table 2.3 were obtained from the newly revised and USEPA approved 2007-2008 

labels which included the following 2002 RED mitigation measures: 

(1) Deletion of use on succulent beans, succulent peas, spinach, grapes, and pecans; 

(2) Reduction of maximum seasonal application rates (lbs./a.i./A ): 

(a) From 3.0 to 2.5 lbs for pome fruit, stone fruit, and citrus; 

(b) From 3.0 to 2.0 lbs for melons, cucurbits, lettuce, tomatoes, sweet potatoes, 

cotton (ground), broccoli, cauliflower, cabbage, kohlrabi, brussels sprouts, 

strawberries, filberts, walnuts, almonds, macadamia nuts, peppers, eggplant, 

potatoes, carrots, dry beans, dry peas, and tobacco; 

(c) From 3.0 to 1.5 lbs for sweet corn, cotton (aerial) and blueberries; 

(d) From 3.0 to 1.0 lb for celery. 

(3) Requirement of 100 ft. spray buffer for ground applications between a treated area and 

water bodies; 

(4) Requirement of 30 ft. maintained vegetative buffer strip between a treated area and water 

bodies; 

(5) Requirement of all products to be Restricted Use; 

(6) Restriction of use on: 

(a) Cotton to AZ, CA, NM, OK and TX only; and 

(b) Tobacco to IN, KY, OH, PA, TN and WV only. 

Similar mitigation measures apply for California with the following exceptions: 

39
(1) Maximum seasonal rates in lbs a.i. /A/season were reduced to 1.5 lbs for sweet corn, 1.0 

lb for carrots and 0.5 lb for eggplant; 

(2) Deletion of use on tobacco, blueberries, and kohlrabi. 

 

These measures were included in Table 2.3 above. The complete analysis of labeled use along 

with registration numbers is included in Appendix A along with use verification memo of SRRD 

and RD. No 24(c) or sections 18s are relevant to California. 

Finally, slightly different application restrictions are included for use in CA to further reduce 

drift and protect surface waters. For example, at the national level buffer distance is 300 ft for 

aerial application and 100 ft for ground application while the distance in CA is 300 ft for both 

aerial and ground application. A 30 ft vegetative buffer is also included in CA. Other 

restrictions also include: nozzle height maximum of 4 ft above ground or crop canopy; a 

maximum wind speed 10 mph; and the use fine-medium or coarse spray ASAE 573. 

Endosulfan is also labeled for use in ear tags for cattle. The ear tag is impregnated with 

endosulfan (30% a.i.) and is to be attached to animal ears (Table 2.4). 

Table 2.4 California labeled non-crop use for endosulfan 

Use Pattern* Application Information 

Beef Range Feeder Cattle (Meat, All or 

unspecified) 

Dairy Cattle (Lactating or Unspecified) Two ear tags per animal (0.198 lb a.i./Animal) for fly control (e.g., horn fly) 

* Avenger insecticide cattle ear tag (CA registration number 61483- 65-AA; November, 05, 2007)8

In this assessment, the potential use of endosulfan in cattle ear tags within California is not 

evaluated. Most of the endosulfan released from cattle ear tags is expected to volatilize, adsorb 

to the cow and/or wash off into the soil. Given that this particular formulation is not expected to 

be subject to extensive transport, exposure is expected to be deminimus and was not 

quantitatively assessed. 

 

8 http://www.cdpr.ca.gov/cgi-bin/label/labrep.pl

40
Historical usage 

(a) Nationally 

National data show a decline in the estimated endosulfan usage. USGS data show a decreased in 

total usage from 1.79 million lbs in 1992 to 1.52 million lbs in 1997 and 0.79 million lbs in 

20029

. Reported average annual endosulfan usage was estimated at approximately 1.38 million 

lbs, based on available pesticide survey data for the years from 1990 to 1999 (EPA, 2002). A 

summary of data, from both sources, is included in Table 2.5 showing the distribution of lbs 

used for various crops and in Figure 2.2 showing the general spatial distribution of usage 

through out the United States. 

Table 2.5 Top use patterns for endosulfan for selected years from 1990 to 2002 

% of Total for the Year(s) Crop 1992 1997 1990-1999* 2002 

Cotton 25% 29% 21% 20% 

Fruits (apples & pears) 17% 12% 8% 14% 

Potatoes 10% 11% 9% 11% 

Tomatoes 8% 3% 4% 11% 

Pecan 7% 3% 4% ** 

Grapes 7%   **  

Cucurbits: cantaloupe, squash, watermelon & cucumber 6% 8% 6% 8% 

Tobacco *** 11% 5% 7% 

Lettuce 5% 3% 4% 4% 

Alfalfa *** 3% *** ** 

Green beans *** *** *** 4% 

Horticulture *** *** 4% *** 

Others** 15% 17% 35% 21% 

Totals in millions of lbs a.i 1.79 1.52 1.38 0.79 

* Average for the years from 1990 to 1999 Others** = sum of all uses donated as “***” 

Usage data indicate that the top three use patterns were for cotton, certain fruits, and potatoes 

during the period from 1992 to 2002. The 4th and 5th use patterns include combinations of 

tomatoes, tobacco, and cucurbits or pecan, grapes, and cucurbits. As suggested by the 2002 

RED, observed changes in the use pattern may be related to shifts in use in response to the 

dynamics of the agricultural system (e.g., changes in crop area), pest populations (e.g., pest 

outbreaks) changes in pesticide availability (e.g., new pesticides registered and restrictions on 

old pesticides), and the variability in using data from various information sources (EPA, 2002). 

 

9

 Sources of Data for 1992, 1997: URLs 

41
Average annual use of active ingredient (pounds per square mile of agricultural land in county 

1992 1997 2002 

No estimate use No estimated use No estimated use 

0.001 to 0.007 0.001 to 0.006 0.001 to 0.005 

0.008 to 0.028 0.007 to 0.027 0.006 to 0.018 

0.029 to 0.108 0.028 to 0.105 0.019 to 0.064 

0.109 to 0.454 0.106 to 0.480 0.065 to 0.259 

≥ 0.455 ≥ 0.455 ≥ 0.260 

2002 

1997 

1992 

Figure 2.2 Endosulfan Use in Total Pounds per County (note vlues are different in chosen categories) 

(a) California 

The Agency’s Biological and Economic Analysis Division (BEAD) provided an analysis of both 

national- and county-level usage information using state-level usage data obtained from USDANASS10, Doane11 and the California’s Department of Pesticide Regulation Pesticide Use 

Reporting (CDPR PUR) database12. CDPR PUR is considered a more comprehensive source of 

 

10 United States Depart of Agriculture (USDA), National Agricultural Statistics Service (NASS) Chemical Use 

Reports provide summary pesticide usage statistics for select agricultural use sites by chemical, crop and state. See 

http://www.usda.gov/nass/pubs/estindx1.htm#agchem. 11 www.doane.com (the full dataset is not provided due to its proprietary nature) 12 The California Department of Pesticide Regulation’s Pesticide Use Reporting database provides a census of 

pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/purmain.htm. 

42
usage data than the USDA-NASS or EPA proprietary databases, and thus the usage data reported 

for endosulfan by county in this California-specific assessment were generated using CDPR PUR 

data. Thirteen years (1994-2006) of usage data were included in this analysis. Data from CDPR 

PUR were obtained for every pesticide application made on every use site at the section level 

(approximately one square mile) of the public land survey system. BEAD summarized these 

data to the county level by site, pesticide, and unit treated. Calculating county-level usage 

involved summarizing across all applications made within a section and then across all sections 

within a county for each use site and for each pesticide. Figure 2.3 summarizes available 

historical usage data for the application years from 1994 to 2006. 

0

100,000

200,000

300,000

400,000

500,000

600,000

Lbs a.i. Or Acres Treated

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Application Year

Total Lbs of Endosulfan a.i Applied

Total Acres Treated

Figure 2.3 Historical usage data for endosulfan 

Data show a gradual decrease in crop acreage treated and lbs of a.i. used for the treatment from 

1995 to 2006. Four distinct periods can be identified, namely, 1994, 1995-1997, 1998-2004, and 

2005-2006. Usage during these periods decreased from nearly 1⁄2 million lbs (1st period), to 1⁄4 

million lbs (2nd period), to 155 thousand lbs (3rd period), to 88 thousand lbs (4th period). BEAD 

usage data included average annual pounds applied; average annual area treated, and average 95th

and 99th percentile and maximum application rates for only two periods from 1994 to 1998 and 

from 1999 to 2006. Therefore, it was necessary to recalculate this data to reflect the previously 

identified four historical usage periods (Figure 2.3). A summary of this recalculated data is 

provided in Table 2.6 for the 1st and 2nd periods and Table 2.7 for the 4th and 5th periods. Details 

are provided only for currently registered endosulfan uses. 

Table 2.6 Historical usage of endosulfan for 1994 (1st period) and 1995-1997 (2nd period) 

1st Period: 1994 2nd Period: 1995-1997 Averages For: 

Total. Rate (lbs a.i./A) Total Rate (lbs a.i./A) Crop Use Pattern1

Lbs a.i. % Average Maximum Lbs a.i. % Average Maximum 

43
Table 2.6 Historical usage of endosulfan for 1994 (1st period) and 1995-1997 (2nd period) 

1st Period: 1994 2nd Period: 1995-1997 Averages For: 

Total. Rate (lbs a.i./A) Total Rate (lbs a.i./A) Crop Use Pattern1

Lbs a.i. % Average Maximum Lbs a.i. % Average Maximum 

Nut trees 1,430 0.35% 0.79 1.72 2,480 1% 1.52 1.99 

Citrus (Oranges 

only) 0 0.00% - - 3 0.00% 0.75 0.75 

Cole crops 1 6,145 1% 0.22 1.01 7,181 4% 0.71 1.7 

Cole crops 2 28 0.01% 0.06 0.50 311 0.16% 0.76 0.94 

Corn 5,528 1% 0.61 1.51 3,199 2% 0.82 1.19 

Cotton 142,259 35% 0.88 1.10 81,639 42% 0.79 0.93 

Apple 656 0.16% 0.54 1.50 1,122 1% 1.13 2.13 

Fruit trees 3,582 1% 0.81 3.0013 2,004 1% 1.27 2.5 

Lettuce & Brussels 

sprouts 37,570 9% 0.81 1.28 31,687 16% 0.9 1 

Cucurbits2 189,485 46% 0.57 2.64 40,125 20% 0.6 2.15 

Eggplant 213 0.05% 0.41 0.54 88 0.04% 0.45 0.72 

Ornamentals or 

shade trees 433 0.11% 0.59 3.00 307 0.16% 0.64 2.82 

Potato (No sweet 

potatoes) 3,697 1% 0.55 0.89 1,808 1% 0.76 0.96 

Dry Beans/Peas & 

Pepper 9,278 2% 0.35 2.00 5,996 3% 0.61 1.32 

Carrot 726 0.18% 0.35 0.75 819 0.42% 0.88 1.04 

Celery 557 0.14% 0.5 0.75 482 0.25% 0.75 1 

Strawberry 540 0.13% 0.59 2.00 283 0.14% 0.86 1.5 

Tomato 10,145 2% 0.67 2.39 16,640 8% 0.64 1.07 

Currently Labeled 

Total 412,289 100% 0.55 2.64 196,190 100% 0.82 2.82 

Not currently labeled 

Total2 64,760 0.29 1.84 38,373 0.32 1.54 

All Crops 477,049 0.52 2.64 234,563 0.76 2.82 

1

 Nut Trees= Almond, Hazelnut & Walnut; Cole Crops 1= Broccoli, Cabbage & Cauliflower; Cole Crops 2= 

Collards, Kale & Mustard Green; Fruit Trees= Apricot, Nectarine, Peach, Cherry, Pear, Plum & Prune; and 

Cucurbits= Cucumber, Melons, Pumpkin & Squash 

2

 Crops not currently labeled were 14% for the 1st period of which 98% Grapes, Alfalfa & Sugar beet; and 16% 

for the 2nd period of which 95% Grapes, Alfalfa & Sugar beet. Other crops include artichoke, spinach, pecan, 

and canola 

Table 2.7 Historical usage of endosulfan for 1998-2004 (3rd period) and 2005-2006 (4th period) 

3rd Period: 1998-2004 4th Period: 2005-2006 Averages For: 

Total. Rate (lbs a.i./A) Total Rate (lbs a.i./A) Crop Use Pattern1

Lbs a.i. % Avg Max Lbs a.i. % Avg Max 95th % 99th % 

Nut trees 530 0.47% 0.96 1.58 41 0.06% 0.42 0.79 0.82 1.5 

Citrus (Oranges 37 0.03% 1.87 3.00 0 0.00% 0 0 0 0 

 

13 This rate of 3.00 lbs a.i/A (reported in Tables 2.5 and 2.6) donates possible misreporting. This value is excluded 

from calculated statistics because it contains one or more possible misreporting. Misreporting is assumed on a case 

by case basis but it is considered when calculated rates are less than 0.1, less than 1 lb is applied, less than 1 acre is 

treated, area units missing or questionable, and number of records for pounds and area do not match. 

44
Table 2.7 Historical usage of endosulfan for 1998-2004 (3rd period) and 2005-2006 (4th period) 

3rd Period: 1998-2004 4th Period: 2005-2006 Averages For: 

Total. Rate (lbs a.i./A) Total Rate (lbs a.i./A) Crop Use Pattern1

Lbs a.i. % Avg Max Lbs a.i. % Avg Max 95th % 99th % 

only) 

Cole crops 1 3,748 3% 0.85 1.48 764 1% 0.69 0.82 0.83 0.98 

Cole crops 2 80 0.07% 0.9 1.19 1 0.00% 0.23 0.79 0.9 0.93 

Corn 1,027 1% 1.07 1.45 1,143 2% 0.93 0.93 0.93 1 

Cotton 40,335 36% 0.89 1.35 17,977 24% 0.83 0.83 0.83 1.01 

Apple 395 0.35% 1.26 1.79 84 0.11% 1.98 1.98 1.98 2 

Fruit trees 2,520 2% 1.33 2.50 281 0.38% 1.54 2.06 2.08 2.5 

Lettuce & 

Brussels sprouts 25,179 22% 0.92 1.25 27,031 37% 0.38 0.72 0.75 0.99 

Cucurbits2 14,332 13% 0.92 3.00 7,787 11% 0.86 0.98 1 1 

Eggplant 44 0.04% 0.73 0.93 41 0.06% 0.5 0.5 0.5 0.55 

Ornamentals or 

shade trees 248 0.22% 1.11 2.94 53 0.07% 0.29 0.55 0.57 1 

Potato (No sweet 

potatoes) 1,158 1% 0.92 1.00 643 1% 0.95 0.95 0.95 0.96 

Dry Beans/Peas & 

Pepper 2,703 2% 0.78 1.00 2,471 3% 0.85 0.89 0.89 0.99 

Carrot 387 0.34% 0.85 0.93 59 0.08% 0.93 0.93 0.93 0.93 

Celery 108 0.10% 0.67 1.17 73 0.10% 0.39 0.74 0.77 0.77 

Strawberry 83 0.07% 1.14 2.00 2,128 3% 1.2 1.2 1.2 1.51 

Tomato 19,842 18% 0.91 1.40 13,343 18% 0.85 0.85 0.85 1.01 

112,755 100% 1.00 2.94 73,920 100% 0.77 2.06 2.00 2.42 

Crops Not 

currently labeled2 41,887 0.75 3.00 13,672 0.93 1.38 1.46 1.48 

All Crops 154,642 0.99 2.94 87,592 0.78 2.06 1.99 2.41 

1

 Nut Trees= Almond, Hazelnut & Walnut; Cole Crops 1= Broccoli, Cabbage & Cauliflower; Cole Crops 2= 

Collards, Kale & Mustard Green; Fruit Trees= Apricot, Nectarine, Peach, Cherry, Pear, Plum & Prune; and 

Cucurbits= Cucumber, Melons, Pumpkin & Squash 

2

 Crops not currently labeled were 27% for the 3rd period of which 97% Alfalfa, Grapes & Sugar beet; and 16% for 

the 4th period of which 98% Alfalfa, Grapes & Pecans. Other crops include artichoke, spinach, safflower, canola, 

Garlic & Oats

Based on currently registered crops, California usage data can be summarized as follows: 

(1) Most recent usage data suggest that the top five use patterns for endosulfan are lettuce, 

cotton, tomatoes, cucurbits, and dry beans (Table 2.7, 2005-2006 data). The same five 

crops are also the dominant usage for earlier years with cotton being on the top for most 

of the times followed by cucurbits, lettuce, tomatoes, and dry beans (Table 2.6 and Table 

2.7, 1994, 1995-1997 and 1998-2004 data). 

(2) The top five crops constitute between 90 to 94% of the current labeled crop usage, 

therefore special distribution of these five crops can be taken to reflect current most 

important use areas of endosulfan. 

(3) Statistical comparison between current maximum rates for currently registered crops and 

the most recent PUR data suggests that reported actual use rates (i.e., typical rates) are 

45
consistently in the low side. Current labeled rates (lbs a.i./A) compared to reported actual 

use rates are as follows: average 1.83 compared to 0.77 lbs a.i./A; maximum 2.50 

compared to 2.06 lbs a.i./A, ; 95th % 2.55 compared to 2.00 lbs a.i./A, and 99th % 

maximum 2.91compared to 2.42 lbs a.i./A. With few exceptions14, current labeled rates 

are generally higher than the most recent typical use rates. 

Figure 2.4 provides a summary of the most recent endosulfan usage along with the general 

habitat areas of the CRLF and the San Francisco Bay species. Figure 2.4 shows clearly that 

the majority (nearly 82%) of the recent endosulfan use was in three counties: Fresno, Kings, 

and Imperial. Top ten use category constitutes nearly 97% of the use which includes the 

three counties just mentioned in addition to Riverside, Kern, Yolo, Siskiyou, Tulare, and 

Solano counties. In an additional 14 counties, (San Benito, Madera, Monterey, Colusa, 

Merced, Santa Clara, San Joaquin, Ventura, Sonoma, Los Angeles, Placer, Napa, Glenn, and 

Santa Barbar).usage is very small ranging from 1 lb a.i to 647 lbs a.. Maps of species 

occurrence and their designated critical habitat (where applicable) in relation to agricultural 

areas in California are provided in Appendix E. 

 

14 Statistics exclude data where reported rates are exceptionally high due to possible misreporting. Any rate reported 

in Tables 2.5 and 2.6 to equal 3 lbs a.i. /A are excluded because it contains one or more possible misreporting. 

Misreporting is assumed on a case by case basis but is considered when calculated rates are less than 0.1, less than 1 

lb is applied, less than 1 acre is treated, area units missing or questionable and number of records for pounds and 

area do not match. 

46
Figure 2.4 Endosulfan usage and acreage for the top five crop use patterns (CA-PUR data; Average for 2005-

2006) 

Finally, the top usage crops in the three top ranked usage counties are lettuce, tomatoes, 

cucurbits, dry beans, and corn for Fresno County, cotton, tomatoes, and cole crops for Kings 

County, and cucurbits, cotton, and lettuce for Imperial County (Figure 2.5). Alfalfa was the major 

crop used in the “not currently registered category”. 

47
Table 2.8 provides a summary of the current distribution, habitat requirements, and life history 

parameters for the listed species being assessed. More detailed life-history and distribution 

information can be found in Attachments 1 and 3. 

48

0

5,000

10,000

15,000

20,000

25,000

Endosulfan Use (lbs. a.i/Crop)

Lettuce

Cotton

Tomatoes

Cucurbits

Corn

Dry beans

A

Crop 

(Notes: Not currently registered crop was

ll others

Apple & Plums

Cole crops

Not Registered

 mainly alfalfa)

Fresno Kings Imperial

Figure 2.5 Distribution of endosulfan usage for the top usage counties of Fresno, Kings, and Imperial 

2.5 Assessed Species 
Table 2.8 Summary of Current Distribution, Habitat Requirements, and Life History Information for the Assessed Listed Spec

 Assessed 

Species1

Size Current Range Habitat Type Designated 

Critical 

Habitat?

Reproductiv

Cycle

California redlegged frog (Rana aurora draytonii) 

Adult (85-138 cm in length), Females – 9-238 g, Males – 13-163 g; Juveniles (40-84 cm in length) 

Northern CA coast, northern Transverse Ranges, foothills of Sierra Nevada, and in southern CA south of Santa Barbara 

Freshwater perennial or near-perennial aquatic habitat with dense vegetation; artificial impoundments; riparian and upland areas 

Yes Breeding: Nov. to A

Tadpoles: Dec. to MYoung juveniles: M

Sept. 

California tiger salamander (Ambystoma californiense) 

50 g There are two distinct population 

segments; one in Santa Barbara County and the other in Sonoma County. 

Freshwater pools or ponds (natural or man-made, vernal pools, ranch stock ponds, other fishless ponds); Grassland or oak savannah communities, in low foothill regions; Small mammal burrows 

Yes Emerge from burro

breed: fall and wint

rains Eggs: laid in pond 

Feb., hatch: after 10 days Larval stage: 3-6 m

until the ponds dry metamorphose late or early summer, mto small mammal b

San Francisco garter snake (Thamnophis sirtalis tetrataenia) 

Adult (46-131 cm in length), Females – 227 g, Males – 113 g; Juveniles (18–20 cm in length) 

San Mateo County Densely vegetated 

freshwater ponds near open grassy hillsides; emergent vegetation; rodent burrows 

No Oviparous Reprodu

Breeding: Spring (M

and Apr.) and Fall to Nov.) Ovulation and Preg

Late spring and earsummer Young: Born 3-4 m

after mating 

Salt marsh harvest mouse 

Adult 8 – 14 g 

Northern subspecies can be found in Marin, Sonoma, Napa, Solano, 

Dense, perennial cover with preference 

No Breeding: March – 

November 

49
Table 2.8 Summary of Current Distribution, Habitat Requirements, and Life History Information for the Assessed Listed Spec

 Assessed 

Species1

Size Current Range Habitat Type Designated 

Critical 

Habitat?

Reproductiv

Cycle

(Reithrodontomys raviventris) 

and northern Contra Costa counties. The southern subspecies occurs in San Mateo, Alameda, and Santa Clara counties with some isolation populations in Marin and Contra Costa counties. 

for habitat in the middle and upper parts of the marsh dominated by pickleweed and peripheral halophytes as well as similar vegetation in diked wetlands adjacent to the Bay 

Gestation period: 2

days 

San Joaquin kit fox (Vulpes macrotis mutica) 

Adult ~2 kg 

Alameda, Contra Costa, Fresno, Kern, Kings, Madera, Merced, Monterey, San Benito, San Joaquin, San Luis Obispo, Santa Barbara, Santa Clara, Stanislaus, Tulare and Ventura counties 

A variety of habitats, including grasslands, scrublands (e.g., 

chenopod scrub and sub-shrub scrub), vernal pool areas, oak woodland, alkali meadows and playas, and an agricultural matrix of row crops, irrigated pastures, orchards, vineyards, and grazed annual grasslands. Kit foxes dig their own dens, modify and use those already constructed by other animals (ground squirrels, badgers, and coyotes), or use human-made structures .(culverts, abandoned pipelines, or banks in sumps or roadbeds). They 

No, but has 

designated 

core areas 

Mating and concep

late December - MGestation period: 4

days. Litters born: Febru

late March Pups emerge from dens at about 1-moage and may begin disperse after 4 – 5 months usually in ASept. 

50
Table 2.8 Summary of Current Distribution, Habitat Requirements, and Life History Information for the Assessed Listed Spec

 Assessed 

Species1

Size Current Range Habitat Type Designated 

Critical 

Habitat?

Reproductiv

Cycle

move to new dens within their home range often (likely to avoid predation by coyotes) 

Bay checkerspot butterfly (BCB) (Euphydryas editha bayensis)

Adult butterfly - 5 cm in length 

Santa Clara and San Mateo Counties [Because the BCB distribution is considered a metapopulation, any site with appropriate habitat in the vicinity of its historic range (Alameda, Contra Costa, San Francisco, San Mateo, and Santa Clara counties) should be considered potentially occupied by the butterfly (USFWS 1998, p. II-177)]. 

1) Primary habitat – native grasslands on large serpentine outcrops; 2) Secondary habitat – ‘islands’ of smaller serpentine outcrops with native grassland; 3) Tertiary habitat – non-serpentine areas where larval food plants occur 

Yes Larvae hatch in Ma

May and grow to th

instar in about two The larvae enter intperiod of dormancy (diapause) that lastthrough the summelarvae resume activwith the start of the season. Larvae puponce they reach a wof 300 - 500 milligAdults emerge withto 30 days dependinthermal conditions, on nectar, mate and eggs during a flight season lasting 4 -6 from late Feb.- earl

Valley elderberry longhorn beetle (Desmocerus californicus dimorphus) 

Males: 1.25–2.5 cm

length Females: 1.9–2.5 cm length 

Central Valley of California (from Shasta County to Fresno County in the San Joaquin Valley) 

Completely dependent on its host plant, elderberry (Sambucus species), 

which is a common component of the remaining riparian forests and adjacent upland habitats of California’s Central Valley 

Yes The larval stage ma

2 years living withistems of an elderbeplant. Then larvae ethe pupal stage and transform into adulAdults emerge and active from March feeding and matingthe elderberry prodflowers. 

51
52

1 For more detailed information on the distribution, habitat requirements, and life history information of the assessed listed species, see 2 For the purposes of this assessment, tadpoles and submerged adult frogs are considered “aquatic” because exposure pathways in the 

different than those that occur on land. 

3 Oviparous = eggs hatch within the female’s body and young are born live. 
2.6 Designated Critical Habitat 

Critical habitat has been designated for the CRLF, BCB, CTS, and VELB. ‘Critical 

habitat’ is defined in the ESA as the geographic area occupied by the species at the time 

of the listing where the physical and biological features necessary for the conservation of 

the species exist, and there is a need for special management to protect the listed species. 

It may also include areas outside the occupied area at the time of listing if such areas are 

‘essential to the conservation of the species.’ Critical habitat receives protection under 

Section 7 of the ESA through prohibition against destruction or adverse modification 

with regard to actions carried out, funded, or authorized by a federal Agency. Section 7 

requires consultation on federal actions that are likely to result in the destruction or 

adverse modification of critical habitat. 

To be included in a critical habitat designation, the habitat must be ‘essential to the 

conservation of the species.’ Critical habitat designations identify, to the extent known 

using the best scientific and commercial data available, habitat areas that provide 

essential life cycle needs of the species or areas that contain certain primary constituent 

elements (PCEs) (as defined in 50 CFR 414.12(b)). PCEs include, but are not limited to, 

space for individual and population growth and for normal behavior; food, water, air, 

light, minerals, or other nutritional or physiological requirements; cover or shelter; sites 

for breeding, reproduction, rearing (or development) of offspring; and habitats that are 

protected from disturbance or are representative of the historic geographical and 

ecological distributions of a species. Table 2.9 describes the PCEs for the critical habitats 

designated for the CRLF, CTS, BCB, and VELB. 

Table 2.9 Designated Critical Habitat PCEs for the CRLF, CTS, BCB and VELB 

Species PCEs Reference 

Alteration of channel/pond morphology or geometry and/or increase 

in sediment deposition within the stream channel or pond. 

Alteration in water chemistry/quality including temperature, 

turbidity, and oxygen content necessary for normal growth and 

viability of juvenile and adult CRLFs and their food source.

Alteration of other chemical characteristics necessary for normal 

growth and viability of CRLFs and their food source. 

Reduction and/or modification of aquatic-based food sources for premetamorphs (e.g., algae) 

Elimination and/or disturbance of upland habitat; ability of habitat to 

support food source of CRLFs: Upland areas within 200 ft of the 

edge of the riparian vegetation or dripline surrounding aquatic and 

riparian habitat that are comprised of grasslands, woodlands, and/or 

wetland/riparian plant species that provides the CRLF shelter, 

forage, and predator avoidance 

Elimination and/or disturbance of dispersal habitat: Upland or 

riparian dispersal habitat within designated units and between 

occupied locations within 0.7 mi of each other that allow for 

movement between sites including both natural and altered sites 

which do not contain barriers to dispersal 

Reduction and/or modification of food sources for terrestrial phase 

juveniles and adults 

CRLF 

Alteration of chemical characteristics necessary for normal growth 

50 CFR 414.12(b), 

2006 

53
Table 2.9 Designated Critical Habitat PCEs for the CRLF, CTS, BCB and VELB 

Species PCEs Reference 

and viability of juvenile and adult CRLFs and their food source. 

 Standing bodies of fresh water, including natural and man-made 

(e.g., stock) ponds, vernal pools, and dune ponds, and other 

ephemeral or permanent water bodies that typically become 

inundated during winter rains and hold water for a sufficient length 

of time (i.e., 12 weeks) necessary for the species to complete the 

aquatic (egg and larval) portion of its life cycle2

Barrier-free uplands adjacent to breeding ponds that contain small 

mammal burrows. Small mammals are essential in creating the 

underground habitat that juvenile and adult California tiger 

salamanders depend upon for food, shelter, and protection from the 

elements and predation 

California tiger 

salamander 

Upland areas between breeding locations (PCE 1) and areas with 

small mammal burrows (PCE 2) that allow for dispersal among such 

sites 

FR Vol. 69 No. 226 

CTS, 68584, 2004 

The presence of annual or perennial grasslands with little to no 

overstory that provide north/south and east/west slopes with a tilt of 

more than 7 degrees for larval host plant survival during periods 

of atypical weather (e.g., drought). 

The presence of the primary larval host plant, dwarf plantain 

(Plantago erecta) (a dicot) and at least one of the secondary host 

plants, purple owl's-clover or exserted paintbrush, are required for 

reproduction, feeding, and larval development. 

The presence of adult nectar sources for feeding. 

Aquatic features such as wetlands, springs, seeps, streams, lakes, and 

ponds and their associated banks, that provide moisture during 

periods of spring drought; these features can be ephemeral, seasonal, 

or permanent. 

Soils derived from serpentinite ultramafic rock (Montara, Climara, 

Henneke, Hentine, and Obispo soil series) or similar soils 

(Inks, Candlestick, Los Gatos, Fagan, and Barnabe soil series) 

that provide areas with fewer aggressive, nonnative plant species for 

larval host plant and adult nectar plant survival and reproduction.2

Bay 

Checkerspot 

Butterfly 

The presence of stable holes and cracks in the soil, and surface rock 

outcrops that provide shelter for the larval stage of the bay 

checkerspot butterfly during summer diapause.2

66 FR 21449 21489, 

2001 

Valley 

Elderberry 

Longhorn 

Beetle 

Areas that contain the host plant of this species [i.e., elderberry trees 

(Sambucus sp.)] (a dicot) 

43 FR 35636 35643, 

1978 

1 These PCEs are in addition to more general requirements for habitat areas that provide essential life cycle 

needs of the species such as, space for individual and population growth and for normal behavior; food, 

water, air, light, minerals, or other nutritional or physiological requirements; cover or shelter; sites for 

breeding, reproduction, rearing (or development) of offspring; and habitats that are protected from 

disturbance or are representative of the historic geographical and ecological distributions of a species. 2 PCEs that are abiotic, including, physico-chemical water quality parameters such as salinity, pH, and 

hardness are not evaluated because these processes are not biologically mediated and, therefore, are not 

relevant to the endpoints included in this assessment. 

More detail on the designated critical habitat applicable to this assessment can be found 

in Attachment 1 (for the CRLF) and Attachment 3 (for CTS, BCB, and VELB). 

Activities that may destroy or adversely modify critical habitat are those that alter the 

54
PCEs and jeopardize the continued existence of the species. Evaluation of actions related 

to use of endosulfan that may alter the PCEs of the designated critical habitat for the 

CRLF, CTS, BCB, and VELB form the basis of the critical habitat impact analysis. 

As previously noted in Section 2.1, the Agency believes that the analysis of direct and 

indirect effects to listed species provides the basis for an analysis of potential effects on 

the designated critical habitat. Because endosulfan is expected to directly impact living 

organisms within the action area, critical habitat analysis for endosulfan is limited in a 

practical sense to those PCEs of critical habitat that are biological or that can be 

reasonably linked to biologically mediated processes. 

2.7 Action Area 

For listed species assessment purposes, the action area is considered to be the area 

affected directly or indirectly by the federal action and not merely the immediate area 

involved in the action (50 CFR 402.02). It is recognized that the overall action area for 

the national registration of endosulfan is likely to encompass considerable portions of the 

United States based on the large array of agricultural uses. However, the scope of this 

assessment limits consideration of the overall action area to those portions that may be 

applicable to the protection of the CRLF, CTS, SFGS, SMHM, SJKF, BCB, and VELB 

and their designated critical habitat within the state of California. Although the 

watershed for the San Francisco Bay extends northward into the very southwestern 

portion of Lake County, Oregon, and westward into the western edge of Washoe County, 

Nevada, the non-California portions of the watershed are small and very rural with little, 

if any, agriculture. Therefore, no use of endosulfan is expected in these areas, and they 

are not considered as part of the action area applicable to this assessment. 

The definition of action area requires a stepwise approach that begins with an 

understanding of the federal action. The federal action is defined by the currently labeled 

uses for endosulfan. An analysis of labeled uses and review of available product labels 

was completed. Several of the currently labeled uses are special local needs (SLN) uses 

or are restricted to specific states and are excluded from this assessment. In addition, a 

distinction has been made between food use crops and those that are non-food/nonagricultural uses. For those uses relevant to the assessed species, the analysis indicates 

that, for endosulfan, the following agricultural uses are considered as part of the federal 

action evaluated in this assessment: 

(1) Terrestrial Food Crops 

Apricot, Cherry, Nectarine, Peach, Pear, Plum & Prune 

Cabbage & Cauliflower 

Carrot & Celery 

Collards& Kale 

Cucurbits (Cucumber, Melons, Pumpkin & Squash) 

Hazelnuts & Walnuts 

Lettuce & Brussels Sprouts 

Pepper 

55
Strawberry 

(2) Terrestrial + Greenhouse Food Crops 

Tomato 

(3) Terrestrial Food + Feed Crops 

Almonds 

Apple 

Beans & Peas (dry) 

Broccoli 

Cotton 

Eggplant 

Mustard Green 

Potato & Sweet Potato 

Sweet corn for fresh market only 

(4) Terrestrial Non-Food Crops 

Citrus 

Ornamentals or Shade Trees 

Following a determination of the assessed uses, an evaluation of the potential “footprint” 

of endosulfan use patterns (i.e., the area where pesticide application occurs) is 

determined. This “footprint” represents the initial area of concern, based on an analysis 

of available land cover data for the state of California. The initial area of concern is 

defined as all land cover types and the stream reaches within the land cover areas that 

represent the labeled uses described above. A map representing all the land cover types 

that make up the initial area of concern for endosulfan is presented in Figure 2.6. 

56
Figure 2.6 Initial area of concern, or “footprint” of potential use, for endosulfan 

Once the initial area of concern is defined, the next step is to define the potential 

boundaries of the action area by determining the extent of offsite transport via spray drift 

and runoff where exposure of one or more taxonomic groups to the pesticide exceeds the 

listed species LOCs. 

The Agency’s approach to defining the action area under the provisions of the Overview 

Document (USEPA 2004) considers the results of the risk assessment process to establish 

57
boundaries for that action area with the understanding that exposures below the Agency’s 

defined Levels of Concern (LOCs) constitute a no-effect threshold. Deriving the 

geographical extent of this portion of the action area is based on consideration of the 

types of effects that endosulfan may be expected to have on the environment, the 

exposure levels to endosulfan that are associated with those effects, and the best available 

information concerning the use of endosulfan and its fate and transport within the state of 

California. Specific measures of ecological effect for the assessed species that define the 

action area include any direct and indirect toxic effect to the assessed species and any 

potential modification of its critical habitat, including reduction in survival, growth, and 

fecundity as well as the full suite of sublethal effects available in the effects literature. 

Therefore, the action area extends to a point where environmental exposures are below 

any measured lethal or sublethal effect threshold for any biological entity at the whole 

organism, organ, tissue, and cellular level of organization. In situations where it is not 

possible to determine the threshold for an observed effect, the action area is not spatially 

limited and is assumed to be the entire state of California. 

Based on a review of the available toxicity data in ECOTOX and toxicity studies 

submitted to the Agency, several studies were identified that lacked a defined NOAEC 

(i.e., a concentration were no observable adverse effects were documented; see Appendix 

J). For example, Hansen and Cripe (1991; ECOTOX # 115297) reported a LOAEC of < 

0.27 ug a.i./L for sheepshead minnow resulting from 28-d, flow through exposures. Due 

to the lack of a defined NOAEC (i.e., no observed adverse effect concentration), the 

spatial extent of the action area (i.e., the boundary where exposures and potential effects 

are less than the Agency’s LOC) cannot be determined for endosulfan. Therefore, it is 

assumed that the action area encompasses the entire state of California, regardless of the 

spatial extent (i.e., initial area of concern or footprint) of the pesticide use(s). 

2.8 Assessment Endpoints and Measures of Ecological Effect 

Assessment endpoints are defined as “explicit expressions of the actual environmental 

value that is to be protected.”15 Selection of the assessment endpoints is based on valued 

entities (e.g., CRLF, CTS, SFGS, SMHM, SJKF, BCB, and VELB), organisms important 

in the life cycle of the assessed species, and the PCEs of its designated critical habitat), 

the ecosystems potentially at risk (e.g., waterbodies, riparian vegetation, and upland and 

dispersal habitats), the migration pathways of endosulfan (e.g., runoff, spray drift, etc.), 

and the routes by which ecological receptors are exposed to endosulfan (e.g., direct 

contact, etc.). 

2.8.1 Assessment Endpoints 

Assessment endpoints for the CRLF, CTS, SFGS, SMHM, SJKF, BCB, and VELB 

include direct toxic effects on the survival, reproduction, and growth of individuals, as 

well as indirect effects, such as reduction of the prey base or modification of its habitat. 

In addition, potential modification of critical habitat is assessed by evaluating potential 

effects to PCEs, which are components of the habitat areas that provide essential life 

 

15 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001. 

58
cycle needs of the assessed species. Each assessment endpoint requires one or more 

“measures of ecological effect,” defined as changes in the attributes of an assessment 

endpoint or changes in a surrogate entity or attribute in response to exposure to a 

pesticide. Specific measures of ecological effect are generally evaluated based on acute 

and chronic toxicity information from registrant-submitted guideline tests that are 

performed on a limited number of organisms. Additional ecological effects data from the 

open literature are also considered. It should be noted that assessment endpoints are 

limited to direct and indirect effects associated with survival, growth, and fecundity, and 

do not include the full suite of sublethal effects used to define the action area. According 

to the Overview Document (USEPA 2004), the Agency relies on acute and chronic 

effects endpoints that are either direct measures of impairment of survival, growth, or 

fecundity or endpoints for which there is a scientifically robust, peer reviewed 

relationship that can quantify the impact of the measured effect endpoint on the 

assessment endpoints of survival, growth, and fecundity. A complete discussion of all 

the toxicity data available for this risk assessment, including resulting measures of 

ecological effect selected for each taxonomic group of concern, is included in Section 4

of this document. 

As described in the Agency’s Overview Document (U.S. EPA, 2004), the most sensitive 

endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa 

include aquatic-phase amphibians, freshwater fish, freshwater invertebrates, aquatic 

plants, birds (surrogate for terrestrial-phase amphibians and reptiles), mammals, 

terrestrial invertebrates, and terrestrial plants. Acute (short-term) and chronic (long-term) 

toxicity information is characterized based on registrant-submitted studies and a 

comprehensive review of the open literature on endosulfan. 

Table 2.10 identifies the taxa used to assess the potential for direct and indirect effects 

from the uses of endosulfan for each listed species assessed here. The specific 

assessment endpoints used to assess the potential for direct and indirect effects to each 

listed species are provided in Table 2.11. 

59
Table 2.10 Taxa Used in the Analyses of Direct and Indirect Effects of Endosulfan for the Assessed Listed Species. 

Listed Species Birds Mammals Terr. 

Plants 

Terr. 

Inverts. 

FW Fish FW 

Inverts. 

Estuarine

/Marine 

Fish 

Estuarine

/Marine 

Inverts. 

Aquatic 

Plants 

California redlegged frog Direct 

Indirect 

(prey) 

Indirect 

(prey) 

Indirect 

(habitat) 

Indirect 

(prey) 

Direct 

Indirect 

(prey) 

Indirect 

(prey) 

N/A N/A Indirect 

(food/ 

habitat) 

California 

tiger 

salamander 

Direct N/A Indirect 

(habitat) 

Indirect 

(prey) 

Direct 

Indirect 

(prey) 

Indirect 

(prey) 

N/A N/A Indirect 

(food/ 

habitat) 

San Francisco 

garter snake 

Direct 

Indirect 

(prey) 

Indirect 

(prey) 

Indirect 

(habitat) 

Indirect 

(prey) 

Indirect 

(prey) 

Indirect 

(prey) 

N/A N/A Indirect 

(habitat) 

Salt marsh 

harvest mouse 

Indirect 

(rearing 

sites) 

Direct 

Indirect 

(rearing 

sites) 

Indirect 

(food, 

habitat) 

Indirect 

(prey) 

N/A N/A N/A N/A Indirect 

(habitat) 

San Joaquin 

kit fox 

Indirect 

(prey) 

Direct 

Indirect 

(prey) 

Indirect 

(food/ 

habitat) 

Indirect 

(prey) 

N/A N/A N/A N/A N/A 

Bay 

checkerspot 

butterfly 

N/A N/A Indirect 

(food/ 

habitat)

* 

Direct N/A N/A N/A N/A N/A 

Valley 

elderberry 

longhorn 

beetle 

N/A N/A Indirect

(food/ 

habitat)

* 

Direct N/A N/A N/A N/A N/A 

N/A = Not applicable 

Terr. = Terrestrial 

Invert. = Invertebrate

FW = Freshwater 

* = obligate relationship 

60
Table 2.11 Taxa and Assessment Endpoints Used to Evaluate the Potential for the Use of Endosulfan to Result in Direct 

and Indirect Effects to the Assessed Listed Species. 

Taxa Used to Assess 

Direct and/or Indirect 

Effects to Assessed 

Species

Assessed Listed 

Species

Assessment Endpoints Measures of Ecological Effects

Direct Effect – 

-Aquatic-phase CRLF 

- Aquatic-phase CTS 

Survival, growth, and 

reproduction of individuals 

via direct effects 

1. Freshwater Fish and 

Aquatic-phase 

Amphibians

Indirect Effect (prey)

-Aquatic-phase and 

Terrestrial-phase CRLF 

- SFGS 

- CTS 

Survival, growth, and 

reproduction of individuals 

via indirect effects on 

aquatic prey food supply 

(i.e., fish and aquatic-phase 

amphibians) 

1a. Common carp acute LC50 

1b. Common carp NOAEC (estimated 

based on acute-chronic ratio) 

2. Freshwater 

Invertebrates

Indirect Effect (prey)

-Aquatic-phase and 

Terrestrial-phase CRLF 

- SFGS 

- CTS 

Survival, growth, and 

reproduction of individuals 

via indirect effects on 

aquatic prey food supply 

(i.e., freshwater 

invertebrates) 

2a. Mayfly LC50

2b. Mayfly NOAEC (estimated based on 

acute-chronic ratio) 

3. Aquatic Plants 

(freshwater/marine)

Indirect Effect 

(food/habitat)

- Aquatic-phase CRLF 

- SFGS 

- SMHM 

- CTS 

Survival, growth, and 

reproduction of individuals 

via indirect effects on 

habitat, cover, food supply, 

and/or primary productivity 

(i.e., aquatic plant 

community) 

5a. No data for Vascular aquatic plants 

5b. Green alga EC50 

Direct Effect

-Terrestrial-phase CRLF 

- SFGS 

- CTS 

Survival, growth, and 

reproduction of individuals 

via direct effects 

6. Birds

Indirect Effect 

(prey/habitat from nests)

-Terrestrial-phase CRLF 

- SFGS 

- SMHM 

- SJKF 

Survival, growth, and 

reproduction of individuals 

via indirect effects on 

terrestrial prey (birds) 

6a. Mallard LD50 

6b. Mallard NOAEC 

Direct Effect

- SMHM 

- SJKF 

Survival, growth, and 

reproduction of individuals 

via direct effects 

7. Mammals

Indirect Effect 

(prey/habitat from 

burrows)

-Terrestrial-phase CRLF 

- SFGS 

- SMHM 

- SJKF 

Survival, growth, and 

reproduction of individuals 

via indirect effects on 

terrestrial prey (mammals) 

7a. Laboratory rat acute LD50 

7b. Laboratory rat chronic NOAEC 

Direct Effect

- BCB 

- VELB 

Survival, growth, and 

reproduction of individuals 

via direct effects 

8. Terrestrial 

Invertebrates

Indirect Effect (prey) Survival, growth, and 

8a. Beet webworm acute contact LD50 

61
Table 2.11 Taxa and Assessment Endpoints Used to Evaluate the Potential for the Use of Endosulfan to Result in Direct 

and Indirect Effects to the Assessed Listed Species. 

-Terrestrial-phase CRLF 

- SFGS 

- SMHM 

- SJKF 

- CTS 

reproduction of individuals 

via indirect effects on 

terrestrial prey (terrestrial 

invertebrates) 

Indirect Effect 

(food/habitat) (nonobligate relationship)

-Terrestrial-phase CRLF 

- SFGS 

- SMHM 

- SJKF 

- CTS 

9. Terrestrial Plants

Indirect Effect 

(food/habitat) (obligate 

relationship)

- BCB 

- VELB 

Survival, growth, and 

reproduction of individuals 

via indirect effects on food 

and habitat (i.e., riparian 

and upland vegetation) 

9a. No toxicity data for terrestrial plants 

2.8.2 Assessment Endpoints for Designated Critical Habitat 

As previously discussed, designated critical habitat is assessed to evaluate actions related 

to the use of endosulfan that may alter the PCEs of the assessed species’ designated 

critical habitat. PCEs for the assessed species were previously described in Section 2.6. 

Actions that may affect critical habitat are those that alter the PCEs and jeopardize the 

continued existence of the assessed species. Therefore, these actions are identified as 

assessment endpoints. It should be noted that evaluation of PCEs as assessment 

endpoints is limited to those of a biological nature (i.e., the biological resource 

requirements for the listed species associated with the critical habitat) and those for 

which endosulfan effects data are available. 

Some components of these PCEs are associated with physical abiotic features (e.g., 

presence and/or depth of a water body, or distance between two sites), which are not 

expected to be measurably altered by use of pesticides. Measures of ecological effect 

used to assess the potential for effects to the critical habitat of the CRLF, BCB, VELB, 

and CTS are described in Table 2.12. 

Table 2.12 Summary of Assessment Endpoints and Measures of Ecological Effect for Primary 

Constituent Elements of Designated Critical Habitat for CRLF, BCB, VELB, and CTS. 

Taxon Used to 

Assess 

Modification of 

PCE

Assessed Listed 

Species Associated 

with the PCE

Assessment 

Endpoints 

Measures of Ecological Effects

1. Freshwater Fish 

and Aquatic-phase 

Amphibians

Direct Effect – 

-Aquatic-phase 

CRLF

Survival, growth, and 

reproduction of 

individuals via direct 

effects 

1a. Common carp acute LC50 

1b. Common carp NOAEC 

(estimated based on acute-chronic 

ratio) 

62
Table 2.12 Summary of Assessment Endpoints and Measures of Ecological Effect for Primary 

Constituent Elements of Designated Critical Habitat for CRLF, BCB, VELB, and CTS. 

Taxon Used to 

Assess 

Modification of 

PCE

Assessed Listed 

Species Associated 

with the PCE

Assessment 

Endpoints 

Measures of Ecological Effects

Indirect Effect 

(prey)

-Aquatic and 

terrestrial-phase 

CRLF

Modification of critical 

habitat via change in 

aquatic prey food 

supply (i.e., fish and 

aquatic-phase 

amphibians) 

2. Freshwater 

Invertebrates

Indirect Effect 

(prey)

-Aquatic-phase and 

- Terrestrial-phase 

CRLF

Survival, growth, and 

reproduction of 

individuals via indirect 

effects on aquatic prey 

food supply (i.e.,

freshwater 

invertebrates) 

2a. Mayfly LC50

2b. Mayfly NOAEC (estimated 

based on acute-chronic ratio) 

5. Aquatic Plants 

(freshwater/marine)

Indirect Effect 

(food/habitat)

-Aquatic-phase 

CRLF 

- CTS 

Modification of critical 

habitat via change in 

habitat, cover, food 

supply, and/or primary 

productivity (i.e.,

aquatic plant 

community) 

5a. No data for Vascular aquatic 

plants 

5b. Green alga EC50 

Direct Effect

-Terrestrial-phase 

CRLF

Survival, growth, and 

reproduction of 

individuals via direct 

effects 

6. Birds

Indirect Effect 

(prey)

- Terrestrial-phase 

CRLF

Modification of critical 

habitat via change in 

terrestrial prey (birds) 

6a. Mallard LD50 

6b. Mallard NOAEC 

7. Mammals Indirect Effect 

(prey/habitat from 

burrows)

-Terrestrial-phase 

CRLF 

-CTS 

Modification of critical 

habitat via change in 

terrestrial prey 

(mammals) 

7a. Laboratory rat acute LD50 

7b. Laboratory rat chronic 

NOAEC 

Direct Effect

-BCB 

-VELB

Survival, growth, and 

reproduction of 

individuals via direct 

effects 

8. Terrestrial 

Invertebrates

Indirect Effect 

(prey)

-Terrestrial-phase --

CRLF 

-CTS

Modification of critical 

habitat via change in 

terrestrial prey 

(terrestrial 

invertebrates) 

8a. Beet webworm acute contact 

LD50 

9. Terrestrial Plants Indirect Effect 

(food/habitat) (nonobligate 

relationship)

Modification of critical 

habitat via change in 

food and habitat (i.e.,

riparian and upland 

9a. No toxicity data for terrestrial 

plants 

63
Table 2.12 Summary of Assessment Endpoints and Measures of Ecological Effect for Primary 

Constituent Elements of Designated Critical Habitat for CRLF, BCB, VELB, and CTS. 

Taxon Used to 

Assess 

Modification of 

PCE

Assessed Listed 

Species Associated 

with the PCE

Assessment 

Endpoints 

Measures of Ecological Effects

-Terrestrial-phase 

CRLF 

- CTS

Indirect Effect 

(food/habitat) 

(obligate 

relationship)

- BCB 

- VELB

vegetation) 

2.9 Conceptual Model 

2.9.1 Risk Hypotheses 

Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in 

assessment endpoints) and may be based on theory and logic, empirical data, 

mathematical models, or probability models (U.S. EPA, 1998). For this assessment, the 

risk is stressor-linked, where the stressor is the release of endosulfan to the environment. 

The following risk hypotheses are presumed in this assessment: 

The labeled use of endosulfan within the action area may: 

• Directly affect the CRLF, SFGS, SMHM, BCB, VELB, SJKF, and CTS by 

causing mortality or by adversely affecting growth or fecundity; 

• Indirectly affect the CRLF, SFGS, SMHM, BCB, VELB, SJKF, and CTS and/or 

modify their designated critical habitat by reducing or changing the composition of food 

supply; 

• Indirectly affect the CRLF, SFGS, SMHM, and CTS and/or modify their 

designated critical habitat by reducing or changing the composition of the aquatic plant 

community in the species’ current range, thus affecting primary productivity and/or 

cover; 

• Indirectly affect the CRLF, SFGS, SMHM, BCB, VELB, SJKF, and CTS and/or 

modify their designated critical habitat by reducing or changing the composition of the 

terrestrial plant community in the species’ current range; 

• Indirectly affect the CRLF SFGS, SMHM, SJKF, and CTS and/or modify their 

designated critical habitat by reducing or changing aquatic habitat in their current range 

(via modification of water quality parameters, habitat morphology, and/or sedimentation). 

64
2.9.2 Diagram 

The conceptual model is a graphic representation of the structure of the risk assessment. 

It specifies the endosulfan release mechanisms, biological receptor types, and effects 

endpoints of potential concern. The conceptual models for aquatic and terrestrial phases 

of the CRLF, SFGS, SMHM, BCB, VELB, SJKF, and CTS and the conceptual models 

for the aquatic and terrestrial PCE components of critical habitat are shown in Figure 2.7

and Figure 2.8. Although the conceptual models for direct/indirect effects and 

modification of designated critical habitat PCEs are shown on the same diagrams, the 

potential for direct/indirect effects and modification of PCEs will be evaluated separately 

in this assessment. Exposure routes shown in dashed lines are considered insignificant 

routes of exposure (e.g., groundwater seepage into surface water). 

Figure 2.7 Conceptual Model for Endosulfan Effects on the Assessed Species and 

their Critical Habitat in the Aquatic Environment 

Stressor

Source 

Receptors 

Attribute 

Change 

Spray drift 

Fish/aquaticphase amphibians 

**Piscivorous 

mammals and 

birds 

Individual 

organisms 

Reduced survival 

Reduced growth 

Food chain

Reduction in algae 

Reduction in prey 

Modification of PCEs 

related to prey 

availability 

Habitat integrity 

Reduction in primary productivity 

Reduced cover 

Community change 

Modification of PCEs related to 

habitat 

Surface water/ 

Sediment 

Runoff

Aquatic Animals

Invertebrates 

Vertebrates 

Uptake/gills 

or integument 

Ingestion Ingestion 

Uptake/gills 

or integument 

Aquatic Plants

Non-vascular 

Vascular

Uptake/cell, 

roots, leaves Riparian plant

terrestrial 

exposure 

pathways (see 

Figure 2.8) 

Long range 

atmospheric 

transport 

Wet/dry deposition 

Soil Groundwater

Exposure 

Media 

α- and β- Endosulfan Applied to Use Sites + Sulfate Formation 

65
Stressor

Source 

Receptors 

Attribute 

Change 

α- and β- Endosulfan Applied to Use Sites + Sulfate Formation 

Direct 

application Spray drift

Birds/terrestrialphase 

amphibians/ 

reptiles/mammals 

Terrestrial 

insects 

Individual 

organisms 

Reduced survival 

Reduced growth 

Food chain

Reduction in prey 

Modification of 

PCEs related to 

prey availability 

Habitat integrity 

Reduction in primary productivity 

Reduced cover 

Community change 

Modification of PCEs related to 

habitat 

Terrestrial/riparian plants

grasses/forbs, fruit, seeds 

(trees, shrubs) 

Runoff 

Mammals

/ Birds 

Exposure 

Media 

Soil

Ingestion 

Ingestion 

Ingestion 

Ingestion 

Dermal uptake/Ingestion 

Long range 

atmospheric 

transport 

Root uptake 

Wet/dry deposition 

Terrestrialphase 

amphibians 

Ingestion 

Figure 2.8. Conceptual Model for Endosulfan Effects on the Assessed Species and 

their Critical Habitat in the Terrestrial Environment 

 

2.10 Analysis Plan 

In order to address the risk hypothesis, the potential for direct and indirect effects to the 

CRLF, SFGS, SMHM, BCB, VELB, SJKF, and CTS, prey items, and habitat is estimated 

based on a taxon-level approach. In the following sections, the use, environmental fate, 

and ecological effects of endosulfan are characterized and integrated to assess the risks. 

This is accomplished using a risk quotient (ratio of exposure concentration to effects 

concentration) approach. Although risk is often defined as the likelihood and magnitude 

of adverse ecological effects, the risk quotient-based approach does not provide a 

quantitative estimate of likelihood and/or magnitude of an adverse effect. However, as 

outlined in the Overview Document (U.S. EPA, 2004), the likelihood of effects to 

individual organisms from particular uses of endosulfan is estimated using the probit 

dose-response slope and either the level of concern (discussed below) or actual calculated 

risk quotient value. 

2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model 

66
2.10.1.1 Measures of Exposure 

The environmental fate properties of endosulfan along with available monitoring data 

indicate that runoff, spray drift, and long-range atmospheric transport are the principle 

potential transport mechanisms of endosulfan to the aquatic and terrestrial habitats of the 

CRLF, SFGS, SMHM, BCB, VELB, SJKF, and CTS. In this assessment, transport of 

endosulfan through runoff and spray drift is considered in deriving quantitative estimates 

of CRLF, SFGS, SMHM, BCB, VELB, SJKF, and CTS exposure to endosulfan , in 

addition to exposure of their prey and habitats. Assessment of long-range atmospheric 

transport is addressed qualitatively through a review of available monitoring data from 

California but not explicitly modeled due to the lack of models that quantitatively predict 

far-field pesticide concentrations resulting from near-field loadings. 

Measures of exposure are based on aquatic and terrestrial models that predict estimated 

environmental concentrations (EECs) of endosulfan using maximum labeled application 

rates and methods of application. The models used to predict aquatic EECs are the 

Pesticide Root Zone Model coupled with the Exposure Analysis Model System 

(PRZM/EXAMS). The model used to predict terrestrial EECs on food items is T-REX. 

These models are parameterized using relevant reviewed registrant-submitted 

environmental fate data. 

PRZM (Carsel et al 1997) v3.12.2, May 2005 and EXAMS (Burns, 1997) v2.98.4.6, 

April 2005 are screening simulation models coupled with the input shell pe5.pl (Aug 

2007) to generate daily exposures and 1-in-10 year EECs of endosulfan that may occur in 

surface water bodies adjacent to application sites receiving endosulfan through runoff and 

spray drift. PRZM simulates pesticide application, movement and transformation on an 

agricultural field and the resultant pesticide loadings to a receiving water body via runoff, 

erosion and spray drift. EXAMS simulates the fate of the pesticide and resulting 

concentrations in the water body. The standard scenario used for ecological pesticide 

assessments assumes application to a 10-hectare agricultural field that drains into an 

adjacent 1-hectare water body, 2-meters deep (20,000 m3

 volume) with no outlet. 

PRZM/EXAMS was used to estimate screening-level exposure of aquatic organisms to 

endosulfan. The measure of exposure for aquatic species is the 1-in-10 year return peak 

or rolling mean concentration. The 1-in-10-year 60-day mean is used for assessing 

chronic exposure to fish; the 1-in-10-year 21-day mean is used for assessing chronic 

exposure for aquatic invertebrates. 

For endosulfan, aquatic exposures were modeled separately for the parent isomers (ά and 

β) and the primary degradate of concern (endosulfan sulfate). The resulting daily 

concentrations were then summed to form a 30-year time series for total endosulfan (sum 

of ά, β and endosulfan sulfate). Due to similar acute toxicity and structure of the TGAI 

and endosulfan sulfate, modeled or measured environmental exposures of total 

endosulfan (sum of ά, β and endosulfan sulfate) were compared with toxicity data for the 

TGAI. For sediment-borne exposures, toxicity data were available only for endosulfan 

sulfate, and thus, comparisons of total endosulfan EECs were made to toxicity estimates 

for endosulfan sulfate. 

67
Exposure estimates for the terrestrial animals assumed to be in the target area or in an 

area exposed to spray drift are derived using the T-REX model (version 1.4.1, Oct. 9, 

2008). This model incorporates the Kenega nomograph, as modified by Fletcher et al.

(1994), which is based on a large set of actual field residue data. The upper limit values 

from the nomograph represented the 95th percentile of residue values from actual field 

measurements (Hoerger and Kenega, 1972). For the purposes of this assessment, upperbound Kenaga nomogram estimates reported by T-REX are used for derivation of the 

EECs for the terrestrial-phase CRLF, SFGS, SMHM, BCB, VELB, SJKF, CTS and their 

potential prey. 

Birds are currently used as surrogates for terrestrial-phase amphibians and reptiles. 

However, amphibians and reptiles are poikilotherms (body temperature varies with 

environmental temperature) while birds are homeotherms (temperature is regulated, 

constant, and largely independent of environmental temperatures). Therefore, 

amphibians and reptiles tend to have much lower metabolic rates and lower caloric intake 

requirements than birds or mammals. As a consequence, birds are likely to consume 

more food than amphibians and reptiles on a daily dietary intake basis, assuming similar 

caloric content of the food items. Therefore, the use of avian food intake allometric 

equation as a surrogate to amphibians and reptiles is likely to result in an over-estimation 

of exposure and risk for reptiles and terrestrial-phase amphibians. Therefore, T-REX 

(version 1.4.1) has been refined to the T-HERPS model (v. 1.0), which allows for an 

estimation of food intake for poikilotherms using the same basic procedure as T-REX to 

estimate avian food intake. 

Because there is some evidence of the potential for bioaccumulation of endosulfan in 

aquatic organisms, an additional exposure pathway that will be considered in this 

assessment is the consumption of contaminated fish or aquatic invertebrates that have 

bioaccumulated endosulfan dissolved in water and their aquatic diet. The potential risk 

from this pathway will be evaluated and discussed further in the “Risk Description” 

section of the document. Multiple lines of evidence will be used to evaluate 

bioaccumulation potential, including measured bioconcentration factors (BCF), 

bioaccumulation factors (BAF) and a food web bioaccumulation model (Kow-Based 

Aquatic Bioaccumulation Model or KABAM). The bioaccumulation assessment relies on 

predicted water and sediment concentrations from PRZM/EXAMS to estimate 

concentrations of endosulfan in aquatic organisms. These estimated tissue concentrations 

will be compared to toxicity values for various taxonomic groups that may eat aquatic 

organisms in order to evaluate potential risk. 

The potential for exposure of listed species through consumption of contaminated 

terrestrial prey will be evaluated by fugacity modeling for the earthworm based on 

predicted concentrations of endosulfan in soil and soil pore water using PRZM. 

68
Spray drift models, AGDISP and/or AgDRIFT are used to assess exposures of terrestrial 

animals to endosulfan deposited on terrestrial habitats by spray drift. AGDISP (version 

8.13; dated 12/14/2004) is used to simulate aerial and ground applications using the 

Gaussian far-field extension. In addition to the buffered area from the spray drift 

analysis, the downstream extent of endosulfan that exceeds the LOC for the effects 

determination is also considered. 

2.10.1.2 Measures of Effect 

Data identified in Section 2.8 are used as measures of effect for direct and indirect effects 

to the CRLF, SFGS, SMHM, BCB, VELB, SJKF, and CTS. Data were obtained from 

registrant submitted studies or from literature studies identified by ECOTOX. The 

ECOTOXicology database (ECOTOX) was searched in order to provide more ecological 

effects data and in an attempt to bridge existing data gaps. ECOTOX is a source for 

locating single chemical toxicity data for aquatic life, terrestrial plants, and wildlife. 

ECOTOX was created and is maintained by the USEPA, Office of Research and 

Development, and the National Health and Environmental Effects Research Laboratory's 

Mid-Continent Ecology Division. 

The assessment of risk for direct effects to the terrestrial-phase CRLF, CTS, and SFGS 

makes the assumption that toxicity of endosulfan to birds is similar to or less than the 

toxicity to terrestrial-phase amphibians and reptiles (this also applies to potential prey 

items). The same assumption is made for fish and aquatic-phase regarding direct effects 

on CRLF and CTS (again, this also applies to potential prey items). 

The acute measures of effect used for animals in this screening level assessment are the 

LD50, LC50 and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a material, 

given all at once, that is estimated to cause the death of 50% of the test organisms. LC 

stands for “Lethal Concentration” and LC50 is the concentration of a chemical that is 

estimated to kill 50% of the test organisms. EC stands for “Effective Concentration” and 

the EC50 is the concentration of a chemical that is estimated to produce a specific effect in 

50% of the test organisms. Endpoints for chronic measures of exposure for listed and 

non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL stands for “No 

Observed-Adverse-Effect-Level” and refers to the highest tested dose of a substance that 

has been reported to have no harmful (adverse) effects on test organisms. The NOAEC 

(i.e., “No-Observed-Adverse-Effect-Concentration”) is the highest test concentration at 

which none of the observed effects were statistically different from the control. The 

NOEC is the No-Observed-Effects-Concentration. For non-listed plants, only acute 

exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants). 

It is important to note that the measures of effect for direct and indirect effects to the 

assessed species and their designated critical habitat are associated with impacts to 

survival, growth, and fecundity, and do not include the full suite of sublethal effects used 

to define the action area. According the Overview Document (USEPA 2004), the 

Agency relies on effects endpoints that are either direct measures of impairment of 

survival, growth, or fecundity or endpoints for which there is a scientifically robust, peer 

69
reviewed relationship that can quantify the impact of the measured effect endpoint on the 

assessment endpoints of survival, growth, and fecundity. 

2.10.1.3 Integration of Exposure and Effects 

Risk characterization is the integration of exposure and ecological effects characterization 

to determine the potential ecological risk from agricultural uses of endosulfan and the 

likelihood of direct and indirect effects to CRLF, SFGS, SMHM, BCB, VELB, SJKF, 

and CTS in aquatic and terrestrial habitats. The exposure and toxicity effects data are 

integrated in order to evaluate the risks of adverse ecological effects on non-target 

species. For the assessment of endosulfan risks, the risk quotient (RQ) method is used to 

compare exposure and measured toxicity values. EECs are divided by acute and chronic 

toxicity values. For calculation of RQs for aquatic organisms, EECs for total endosulfan 

(sum of ά, β, and endosulfan sulfate) were divided by the appropriate toxicity value for 

the TGAI (or in the case of sediment toxicity, endosulfan sulfate since acceptable data 

were only available for this degradate). The resulting RQs are then compared to the 

Agency’s levels of concern (LOCs) (USEPA, 2004) (see Appendix D). 

For this endangered species assessment, listed species LOCs are used for comparing RQ 

values for acute and chronic exposures of endosulfan directly to the CRLF, SFGS, 

SMHM, BCB, VELB, SJKF, and CTS. If estimated exposures directly to the assessed 

species of endosulfan resulting from a particular use are sufficient to exceed the listed 

species LOC, then the effects determination for that use is “may affect”. When 

considering indirect effects to the assessed species due to effects to prey, the listed 

species LOCs are also used. If estimated exposures to the prey of the assessed species of 

endosulfan resulting from a particular use are sufficient to exceed the listed species LOC, 

then the effects determination for that use is a “may affect.” If the RQ being considered 

also exceeds the non-listed species acute risk LOC, then the effects determination is a 

LAA. If the acute RQ is between the listed species LOC and the non-listed acute risk 

species LOC, then further lines of evidence (i.e. probability of individual effects, species 

sensitivity distributions) are considered in distinguishing between a determination of 

NLAA and a LAA. If the RQ being considered for a particular use exceeds the non-listed 

species LOC for plants, the effects determination is “may affect”. Specifically, any 

exceedances of the listed species LOC for dicots would also result in an LAA for the 

BCB and VELB due to their obligate relationship with dicots. Further information on 

LOCs is provided in Appendix D. 

2.10.2 Data Gaps

Data gaps were identified for several taxa for ecological effects. These include aquatic 

vascular plants, terrestrial monicots, and terrestrial dicots. In addition, no data acceptable 

for quantitative use in this risk assessment was identified for amphibians (aquatic or 

terrestrial phases) and reptiles. 

70
3 Exposure Assessment 

Endosulfan is formulated as wettable powder and emulsifiable concentrate and 

applied as liquid spray only. Application equipment includes various types of ground 

sprayers, airblast sprayers, and aerial sprayers. Aerial application is permitted in all 

crops and therefore was chosen to evaluate exposure because aerial application gave 

the highest exposure because of higher spray drift levels Ground application is also 

considered for cotton as it gave higher exposure values because it is applied at a 

higher rate than aerial application. Furthermore, aquatic EECs for a range of ground 

application scenarios were evaluated and found to be within a factor of two of those 

from the corresponding aerial application scenario (most within 20%). Risk quotients 

from the ground application scenario yielding the lowest EEC (Eggplant) did not 

change appreciably compared to the aerial application eggplant scenario and still 

exceeded the acute and chronic LOCs for aquatic organisms. Terrestrial EECs and 

RQs calculated using T-REX and T-HERPS models do not distinguish ground spray 

from aerial application methods. Therefore, the risk profile from aerial application is 

expected to be applicable to that for ground spray applications, except for some 

reduction in the spray drift distance modeled using AgDRIFT. 

3.1 Label Application Rates, Intervals and Buffers 

Endosulfan labels may be categorized into two types: labels for manufacturing uses 

(including technical grade endosulfan and its formulated products) and end-use products. 

While technical products, which contain endosulfan of high purity, are not used directly 

in the environment, they are used to make formulated products, which can be applied in 

specific areas to control insects. The formulated product labels legally limit endosulfan’s 

potential use to only those sites that are specified on the labels. Uses being assessed are 

summarized in Table 3.1.

 

Table 3.1 Summary of labeled endosulfan uses, scenarios, and application information 

Scenario Crop Represented 

Application Rate 

(lbs/A) 

Number of 

Applications 

Application Window (Interval)

(first Application Date”dd-mm”) 

CA almond 

Almonds, Hazelnuts & 

Walnuts 2.00 1 01-02 to31-08 (NA) (07-02) 

2.50 1 

CA citrus Citrus 0.5+2.00 2 01-06 to 31-10 (10 days) (01-06) 

Broccoli, Cabbage & 

Cauliflower 1.00 2 

CA cole 

crops 

Collards, Kale & 

Mustard Green 0.75 1 

30-01 to 31-08 (7 days) 

(13-02 for Broccoli and 27-03 

for Collards) 

CA corn 

Sweet corn for fresh 

market only 1.5 1 01-05 to 01-09 (NA) (15-05) 

CA cotton 1.00 2 

Cotton (ground 

application) 0.50+1.50 2 

01-06 to 01-09 (7 days) 

Mainly in September 

(15-06 same results as 01-09) 

71
Scenario Crop Represented 

Application Rate 

(lbs/A) 

Number of Application Window (Interval)

Applications (first Application Date”dd-mm”) 

Cotton (aerial 

application) 0.75 2 

2.50 1 

Apple 0.5+0.75+1.25 3 15-04 to 30-05 (10 days) (15-04) 

2.50 1 

CA fruits 

Apricot, Cherry, 

Nectarine, Peach, 

Pear, Plum & Prune 0.50+2.00 2 15-02 to 01-07 (10 days) (15-04) 

CA lettuce 

Lettuce & 

Brussels Sprouts 1.00 2 

01-02 to 01-04; and 

15-09to 30-10 (5 days) (14-02) 

Cucurbits (Cucumber, 1.00 2 

Melons, Pumpkin & 

Squash) 0.50+0.50+1.00 3 30-04 to 01-08 (7 days) (14-05) 

0.50 1 

CA melon Eggplant 0.25 2 01-05 to 31-07 (7 days) (15-05) 

CA nursery 

Ornamentals or Shade 

Trees 0.50 6 15-02 to 15-07 (10 days) (21-02) 

1.00 2 

Potato 0.50 4 01-04 to 01-10 (5 days) (14-04) 

CA potato Sweet Potato 0.50 3 01-05 to 07-06 (5 days) (14-05) 

Beans & Peas (dry) & 

Pepper 1.00 2 01/07 to 01-08 (5 days) (15-07) 

Carrot & Celery 1.00 1 

CA row 

crops Celery 0.50 2 01-03 to 01-10 (5 days) (15-03) 

2.00 1 

CA 

strawberry Strawberry 1.00 2 15-02 to 01-09 (15 days) (21-02) 

1.00 2 

CA tomato Tomato 0.50 4 01-04 to 30-07 (7 days) (15-04) 

In ecological exposure modeling the drift component is usually set to a default value 

of 5% (input parameters guidance, 2002). For endosulfan, the principal mitigation 

measure for reduction of drift is a 300 ft. buffer from surface water bodies. This 

buffer distance is the same for all types of applications in California. In order to arrive 

at an estimate for drift, AgDRIFT was used (a computer model of spray drift). For 

aerial application, AgDRIFT estimated drift beyond the 300 ft buffer to be 2.38% for 

aerial and 0.15% for ground application (Appendix B). 

72
3.2 Aquatic Exposure Assessment 

3.2.1 Modeling Approach 

Aquatic exposures are quantitatively estimated for all of assessed uses using scenarios 

that represent high exposure sites for endosulfan use. Each of these sites represents a 10 

hectare field that drains into a 1-hectare pond that is 2 meters deep and has no outlet. 

Exposure estimates generated using the standard pond are intended to represent a wide 

variety of vulnerable water bodies that occur at the top of watersheds including prairie 

pot holes, playa lakes, wetlands, vernal pools, man-made and natural ponds, and 

intermittent and first-order streams. As a group, there are factors that make these water 

bodies more or less vulnerable than the standard surrogate pond. Static water bodies that 

have larger ratios of drainage area to water body volume would be expected to have 

higher peak EECs than the standard pond. These water bodies will be either shallower or 

have large drainage areas (or both). Shallow water bodies tend to have limited additional 

storage capacity, and thus, tend to overflow and carry pesticide in the discharge whereas 

the standard pond has no discharge. As watershed size increases beyond 10 hectares, at 

some point, it becomes unlikely that the entire watershed is planted to a single crop, 

which is all treated with the pesticide. Headwater streams can also have peak 

concentrations higher than the standard pond, but they tend to persist for only short 

periods of time and are then carried downstream. For uncertainties related to modeling 

EECs in estuarine/marine environments, refer the reader to the Section 6. 

Application of endosulfan is expected to result in movement of its isomers and common 

degradate into surface water by spray drift, run-off, and volatilization. For aquatic 

systems, estimated environmental concentrations (exposure EECs) are obtained by 

PRZM and EXAMS modeling which represent EECs resulting from drift and runoff/erosion. Although volatilization is simulated, as a loss, by PRZM, wet and dry redeposition, of this loss, into aquatic systems is not included in the EXAMS simulation 

and resultant EECs. For endosulfan, modeling for EECs should include species that 

constitutes the multi-chemical stressor, α- and β-endosulfan and endosulfan sulfate 

(referred to in modeling as the total toxic residues or TTR). Therefore, a method should 

be used to determine EECs for the TTR. Among the three methods suggested by EFED 

to assess exposure to parent (here two parents) and degradation products, the SAP 

recommended the use of formation and decline kinetics (FD) and in some cases the 

Residue Summation (RS) or Total Residue (TR) methods (SAP, 2009)16. Currently, the 

FD method can not be used as it requires the use of EXPRESS shell which is the only 

shell capable of facilitating the use of parent/daughter PRZM/EXAMS modeling 

feature17. Therefore, the RS method was used to arrive at exposure EECs for α- and βendosulfan and endosulfan sulfate separately and in total. The procedure is explained in 

 

16 SAP (The FIFRA Scientific Advisory Panel). 2009. Minutes for the SAP Meeting on selected issues 

associated with risk assessment process for pesticides with persistent, bio-accumulative and toxic 

characteristics. October 28-31, 2008. Arlington, VA. (Document No. 2009-01 dated Jan 29, 2009). 

17 At the time of executing modeling, the EXPRESS shell was not formally approved and parent to 

daughter modeling feature of PRZM/EXAMS can not be utilized when PE-5 shell is used. 

73
detail in Appendix C. In summary, the method requires assignment of application rates 

for each of the three species of the stressor. These rates are included in Table 3.2. The 

application rates for the individual residues were normalized according to the percentage 

of maximum residue detected in aerobic soil metabolism studies and the molecular 

weight ratio of degradate and parent compounds. 

Table 3.2 Calculation of application rates for α- and β-endosulfan and endosulfan sulfate) for use in 

modeling (rates are for almond) 

% Maximum in Aerobic Soil Study Chemical 

Species Observed Normalized 

Application Rate 

(kg/ha) 

Molecular 

Ratio 

Required Application 

Rate (kg/ha) 

Alpha 70% 45% 1.009 1 1.009 

Beta 30% 19% 0.426 1 0.426 

SO4 57% 36% 0.807 1.039 0.839 

Total 157% 100% 2.242 

Example calculation given in Table 3.2 is for almonds which is applied at a single rate of 

2 lbs a.i./A (2.242 kg a.i/ha). Rates used in the simulations were 1.009 kg a.i/ha of α- and 

0.426 kg a.i/ha for β-endosulfan and 0.839 kg a.i/ha. All of the three chemicals were 

assumed to be applied at time zero. In this case, it is assumed that the maximum 

degradation of the two parents and the maximum formation of the common degradate 

occur at application. Three PRZM/EXAMS modeling runs were executed using PE-5. 

The first modeling run gives 1-in-10 years exposure EECs for α-endosulfan, the second 

for β-endosulfan, and the third for endosulfan sulfate. EECs for the total residue of 

concern, or the stressor, were calculated by combining daily concentrations from the 

three chemicals (refer to Appendix C for a complete example calculation). 

 

Use-specific management practices for all of the assessed uses of endosulfan were used 

for modeling, including application rates, number of applications per year, application 

intervals, and buffer widths and resulting spray drift values (modeled from AgDRIFT) 

and the first application date for each use. Date of first application was developed based 

on several sources of information including data provided by BEAD, a summary of 

individual applications from the CDPR PUR data, pesticide label (crop stage and pest), 

and Crop Profiles maintained by the USDA18. A sample of the distribution of endosulfan 

applications to selected crops in Appendix C based on CDPR PUR data for 2006. 

 

18 URL: http://pestdata.ncsu.edu/cropprofiles/cropprofiles.cfm

74
 

Data from Appendix C was used to pick two application windows for lettuce from early 

February to early April and from mid September to late October. In contrast, data in 

Appendix C for cotton indicates one major application window from late August to mid 

September. 

3.2.2 Model Inputs 

Environmental fate and transport and other data used for generating the parameters for 

the three PRZM/EXAMS runs are listed in Table 3.3. 

Table 3.3 Summary of PRZM/EZAMS environmental fate and transport data of α- and β-endosulfan 

and endosulfan sulfate used as aquatic exposure inputs for this endangered species assessment 

Value* 

Input Parameter 

1

 (Unit) α-endosulfan β-endosulfan Endosulfan Sulfate 

Molecular Weight g/mole 406.9 406.9 422.9 

Henry’s constant (atm-m3 mol-1 @ 25 oC) 3.0E-6 1.4E-6 1.6E-5 

Vapor Pressure ( torr @ 25 oC) 4.6E-5 2.4E-5 9.8E-6 

Solubility in Water(mg/L) 0.53 0.28 0.33 

Photolysis in Water (t1⁄2 in days @ pH 7) Stable Stable Stable 

Aerobic Soil Metabolism (90th % t1⁄2 in 

days) 57 208 Stable 

Hydrolysis (90th % t1⁄2 in days) 11 19 184 

Aerobic Aquatic Metabolism (water column 

t1⁄2 in days) 2 114 416 Stable 

Anaerobic Aquatic Metabolism (benthic t1⁄2 

in days)3 230 298 286 

Koc (Average in ml/g) 10,600 13,500 12,050 4

Application rate and frequency 

Application intervals Depends on the crop (refer to Table 3.2 for an example)

Chemical Application Method (CAM) 2 

Application Efficiency 95% for aerial and 99% for ground 

Spray Drift Fraction1 0.024 for aerial and 0.002 for ground

* Source of data refer to Table 2.1 and Table 2.2 in the environmental fate properties section above 1

 Inputs determined in accordance with EFED “Guidance for Chemistry and Management Practice Input Parameters for 

Use in Modeling the Environmental Fate and Transport of Pesticides” dated February 28, 2002 2 Estimated 2 X aerobic soil metabolism half-life; 

3

 Estimated 2 X anaerobic soil metabolism half-life 

4

 Assumed to be equal to the average for its parents= 10,600 ml/g and 13,500 ml/g= 12,050 ml/g 

75
PRZM/EXAMS simulation involved execution of three runs, the first run for αendosulfan, the second run is for β-endosulfan, and the third run for endosulfan sulfate. 

3.2.3 Results 

Aquatic EECs 

The aquatic EECs for the various scenarios and application practices are listed in 

Table 3.4 and Table 3.5. The first table contains aquatic exposure EECs resulting from 

the first and second run while the second table contains EECs resulting from the third run 

and the post processed EECs for the total stressor from results of the three runs. An 

example of how the combined EECs were estimated is presented in Appendix C. In 

summary, the process includes combining daily EECs (simple addition for daily 

concentrations) followed by calculating the 1-in-10 year averages using the 90th

percentile procedure. Although more than one run was executed for some crops, the 

more conservative results were chosen. For example, citrus was simulated at 2.5 lb a.i/A 

with one application and 0.50+2.00 lbs a.i. /A in two applications. In 

Table 3.4 and Table 3.5, the highest exposure EEC values were chosen.

Table 3.4 Aquatic EECs (μg/L) for endosulfan used in California (α- and β-endosulfan)1

α-endosulfan β-endosulfan

Crop Run No.* Peak 21-day 60-day Peak 21-day 60-day 

Almonds, Hazelnuts & Walnuts 1 1.44 0.402 0.213 0.60 0.143 0.079 

Citrus 1 1.50 0.371 0.181 0.63 0.127 0.062 

Broccoli, Cabbage & Cauliflower 1 1.21 0.553 0.345 0.55 0.231 0.151 

Collards, Kale & Mustard Green 2 0.70 0.247 0.136 0.30 0.101 0.056 

Sweet corn for fresh market only 1 0.92 0.259 0.141 0.41 0.118 0.069 

Cotton (ground) 2 0.39 0.199 0.162 0.22 0.083 0.067 

Cotton (aerial) 3 0.67 0.310 0.206 0.27 0.112 0.079 

All fruit trees 1 1.50 0.413 0.204 0.63 0.142 0.072 

Lettuce & Brussels Sprouts 1 1.40 0.585 0.356 0.76 0.258 0.159 

Cucurbits 1 0.86 0.429 0.249 0.31 0.114 0.064 

Eggplant 3 0.30 0.076 0.037 0.13 0.029 0.016 

Ornamentals or Shade Trees (Southern Coast) 1 2.24 0.704 0.427 1.19 0.294 0.174 

Ornamentals or Shade Trees (Northern Central coast)) Add 1.95 0.682 0.489 1.02 0.321 0.207 

Potato 1 0.87 0.322 0.208 0.34 0.109 0.074 

Potato (Northern Central coast) Add 1.18 0.410 0.208 0.49 0.162 0.102 

Sweet Potato 3 0.55 0.258 0.150 0.21 0.089 0.052 

Beans & Peas (dry) & Pepper 1 0.81 0.292 0.148 0.33 0.110 0.059 

Carrot & Celery 2 0.63 0.186 0.110 0.27 0.072 0.045 

Strawberry 1 1.27 0.520 0.311 0.59 0.209 0.137 

Tomato 1 0.77 0.309 0.165 0.31 0.111 0.060 

1

 aerial application is used in runs for all crops. For cotton, an additional run is shown for ground application because 

ground application to cotton is at a higher rate compared to aerial application. 

* Add= an additional run using weather station to represent crop growing in areas different than the default areas assigned 

76
α-endosulfan β-endosulfan

Crop Run No.* Peak 21-day 60-day Peak 21-day 60-day 

by the scenario. 

Table 3.5 Aquatic EECs (μg/L) for endosulfan used in California (endosulfan sulfate and total 

stressor) 

Endosulfan Sulfate Total (as parent) 

Crop Run No.* Peak 21-day 60 day Peak 21-day 60 day 

Almonds, Hazelnuts & Walnuts 1 1.41 0.483 0.329 3.35 1.026 0.617 

Citrus 1 1.27 0.344 0.186 3.35 0.900 0.444 

Broccoli, Cabbage & Cauliflower 1 3.82 1.742 1.250 4.81 2.603 1.757 

Collards, Kale & Mustard Green 2 1.22 0.515 0.367 1.67 0.775 0.501 

Sweet corn for fresh market only 1 2.60 0.897 0.658 2.88 1.137 0.774 

Cotton (ground) 2 0.73 0.354 0.287 1.24 0.596 0.521 

Cotton (aerial) 3 0.66 0.357 0.284 1.56 0.824 0.593 

All fruit trees 1 1.33 0.434 0.242 3.40 1.013 0.532 

Lettuce & Brussels Sprouts 1 4.86 1.845 1.381 5.88 2.575 1.854 

Cucurbits 1 1.19 0.490 0.370 1.55 0.815 0.613 

Eggplant 3 0.35 0.122 0.092 0.72 0.237 0.131 

Ornamentals or Shade Trees (Southern Coast) 1 2.14 0.744 0.484 3.43 1.357 1.004 

Ornamentals or Shade Trees (Northern Central coast)) Add 1.82 0.645 0.456 4.38 1.728 1.130 

Potato 1 0.74 0.313 0.202 1.89 0.770 0.492 

Potato (Northern Central coast) Add 1.01 0.413 0.270 2.63 1.011 0.561 

Sweet Potato 3 0.49 0.233 0.151 1.18 0.622 0.358 

Beans & Peas (dry) & Pepper 1 1.59 0.561 0.384 2.00 0.851 0.508 

Carrot & Celery 2 1.55 0.499 0.437 1.72 0.735 0.538 

Strawberry 1 2.27 1.054 0.750 3.64 1.714 1.108 

Tomato 1 0.78 0.375 0.227 1.79 0.808 0.450 

* Add= an additional run using weather station to represent crop growing in areas different than the default areas assigned 

by the scenario. 

 

For total stressor, the highest EECs are associated with lettuce for the peak (5.88 ppb), 

non-leafy cole crops for the 21-day average (2.60 ppb) and lettuce for the 60-day average 

(1.85 ppb). In contrast, the lowest EECs for all time averages are for eggplant (peak= 

0.72 ppb, 21-day= 0.24 ppb, and 60-day= 0.13 ppb). Data suggest that exposure is the 

highest for lettuce and non-leafy cole crops (peak range= 3.43-5.88 ppb), followed by 

Strawberry, fruit/nut trees, citrus, and potatoes grown in the northern part of the central 

coast (peak range from 2.0 to 3.43 ppb), and all other crops except eggplant (1.18 to 1.89 

ppb). Eggplant has the lowest exposure EECS (<1 ppb). 

As expected, the major contributor to exposure is endosulfan sulfate (53% on the 

average) followed by α-endosulfan (34% on the average), and β-endosulfan (14% on the 

average). The results reflect the isomer ratio (70 % for α-endosulfan and 30% for by βendosulfan) and persistence of the common degradate endosulfan sulfate. 

77
Exposure to sediment pore water in aquatic systems was also obtained for the same runs, 

this data are listed in Table 3.6 and Table 3.7. 

Table 3.6 Sediment pore water EECs (μg/L) for endosulfan used in California (α- and β-endosulfan) 

α-endosulfan β-endosulfan

Crop Run No.* Peak 21-day 60-day Peak 21-day 60-day 

Almonds, Hazelnuts & Walnuts 1 0.11 0.110 0.108 0.05 0.046 0.045 

Citrus 1 0.09 0.093 0.086 0.03 0.032 0.030 

Broccoli, Cabbage & Cauliflower 1 0.22 0.214 0.203 0.11 0.107 0.102 

Collards, Kale & Mustard Green 2 0.08 0.083 0.079 0.04 0.036 0.034 

Sweet corn for fresh market only 1 0.08 0.082 0.076 0.05 0.051 0.047 

Cotton (ground) 2 0.10 0.097 0.095 0.05 0.046 0.045 

Cotton (aerial) 3 0.10 0.105 0.102 0.04 0.043 0.042 

All fruit trees 1 0.11 0.105 0.098 0.04 0.041 0.038 

Lettuce & Brussels Sprouts 1 0.22 0.219 0.207 0.11 0.104 0.098 

Cucurbits 1 0.14 0.134 0.127 0.04 0.038 0.035 

Eggplant 3 0.02 0.020 0.018 0.01 0.009 0.009 

Ornamentals or Shade Trees (Southern Coast) 1 0.33 0.323 0.302 0.13 0.131 0.122 

Ornamentals or Shade Trees (Northern Central coast)) Add 0.35 0.345 0.328 0.15 0.147 0.139 

Potato 1 0.10 0.100 0.094 0.04 0.036 0.034 

Potato (Northern Central coast) Add 0.11 0.110 0.104 0.07 0.068 0.064 

Sweet Potato 3 0.08 0.075 0.070 0.03 0.027 0.025 

Beans & Peas (dry) & Pepper 1 0.08 0.082 0.077 0.04 0.039 0.038 

Carrot & Celery 2 0.06 0.063 0.060 0.03 0.027 0.026 

Strawberry 1 0.17 0.166 0.158 0.08 0.080 0.076 

Tomato 1 0.08 0.083 0.077 0.03 0.033 0.031 

* Add= an additional run using weather station to represent crop growing in areas different than the default 

areas assigned by the scenario 

Table 3.7 Sediment pore water EECs (μg/L) for endosulfan used in California (endosulfan sulfate 

and total stressor) 

Endosulfan Sulfate Total (as parent)** 

Crop Run No.* Peak 21-day 60 day Peak 21-day 60 day 

Almonds, Hazelnuts & Walnuts 1 0.22 0.215 0.213 0.37 0.363 0.357 

Citrus 1 0.10 0.101 0.095 0.23 0.222 0.207 

Broccoli, Cabbage & Cauliflower 1 0.89 0.881 0.850 1.18 1.168 1.123 

Collards, Kale & Mustard Green 2 0.27 0.265 0.261 0.38 0.375 0.365 

Sweet corn for fresh market only 1 0.39 0.390 0.383 0.51 0.508 0.492 

Cotton (ground) 2 0.21 0.208 0.206 0.35 0.344 0.339 

Cotton (aerial) 3 0.18 0.183 0.181 0.33 0.324 0.319 

All fruit trees 1 0.16 0.158 0.150 0.30 0.298 0.280 

Lettuce & Brussels Sprouts 1 0.90 0.892 0.873 1.19 1.181 1.145 

Cucurbits 1 0.26 0.254 0.242 0.42 0.416 0.394 

Eggplant 3 0.06 0.064 0.060 0.09 0.090 0.085 

Ornamentals or Shade Trees (Southern Coast) 1 0.35 0.352 0.341 0.80 0.793 0.753 

78
Endosulfan Sulfate Total (as parent)** 

Crop Run No.* Peak 21-day 60 day Peak 21-day 60 day 

Ornamentals or Shade Trees (Northern Central coast)) 1 Add 0.35 0.346 0.332 0.84 0.825 0.786 

Potato 1 0.11 0.113 0.110 0.25 0.245 0.234 

Potato (Northern Central coast) 1 Add 0.20 0.198 0.189 0.37 0.369 0.351 

Sweet Potato 3 0.08 0.082 0.078 0.18 0.181 0.170 

Beans & Peas (dry) & Pepper 1 0.28 0.279 0.267 0.39 0.390 0.373 

Carrot & Celery 2 0.31 0.304 0.290 0.39 0.382 0.364 

Strawberry 1 0.49 0.484 0.466 0.72 0.712 0.682 

Tomato 1 0.17 0.163 0.155 0.28 0.274 0.257 

* Add= an additional run using weather station to represent crop growing in areas different than the default areas assigned 

by the scenario 

** Important Note: This total is a product of simple addition of the 1-10 year data and was not calculated from 

combining daily concentrations (currently PE-5 do not produce a file containing daily concentrations for the pore water) 

Exposure to benthic sediment in aquatic systems was also obtained for selected runs, this 

data are listed in Table 3.8 and Table 3.9. 

Table 3.8 Sediment EECs (μg/L) for endosulfan used in California (α- and β-endosulfan) 

α-endosulfan β-endosulfan

Crop Run No. Peak 21-day 60-day Peak 21-day 60-day 

Broccoli, Cabbage & Cauliflower 1 92 91 86 59 58 55 

Cotton (aerial) 3 45 44 43 24 23 23 

All fruit trees 1 45 45 42 22 22 20 

Lettuce & Brussels Sprouts 1 94 93 88 57 56 53 

Eggplant 3 9 8 8 5 5 5 

Ornamentals or Shade Trees (Southern Coast) 1 139 137 129 72 71 66 

Strawberry 1 71 70 67 44 43 41 

Tomato 1 36 35 33 18 18 17 

Table 3.9 Sediment EECs (μg/L) for endosulfan used in California (endosulfan sulfate and total 

stressor) 

Endosulfan Sulfate Total (as parent)* 

Crop Run No. Peak 21-day 60 day Peak 21-day 60 day 

Broccoli, Cabbage & Cauliflower 1 429 424 410 580 573 551 

Cotton (aerial) 3 89 88 88 158 155 154 

All fruit trees 1 77 76 72 144 143 134 

Lettuce & Brussels Sprouts 1 434 430 422 585 579 563 

Eggplant 3 31 31 29 45 44 42 

Ornamentals or Shade Trees (Southern Coast) 1 171 170 165 382 378 360 

Strawberry 1 235 233 225 350 346 333 

Tomato 1 80 79 75 134 132 125 

* Important Note: This total is a product of simple addition of the 1-10 year data and was not calculated from combining 

daily concentrations (currently PE-5 do not produce a file containing daily concentrations for the pore water) 

79
Bioaccumulation Assessment 

Considering that log KOW values for the parent endosulfan isomers and endosulfan sulfate 

either approach or exceed a log Kow of 4, and that endosulfan can persist for relatively 

long periods of time in aquatic ecosystems, the potential for direct effects on aquaticphase CRLF through consumption of contaminated aquatic prey was investigated. The 

KABAM model (KOW (based) Aquatic BioAccumulation Model) version 1.0 was used to 

evaluate the potential exposure and risk of direct effects to aquatic-phase CRLF via 

bioaccumulation and biomagnification in aquatic food webs. KABAM is used to 

estimate potential bioaccumulation of hydrophobic organic pesticides in freshwater 

aquatic ecosystems and risks to mammals and birds consuming aquatic organisms which 

have bioaccumulated these pesticides. The bioaccumulation portion of KABAM is based 

upon work by Arnot and Gobas (2004) who parameterized a bioaccumulation model 

based on PCBs and some pesticides (e.g., lindane, DDT) in freshwater aquatic 

ecosystems. KABAM relies on a chemical's octanol-water partition coefficient (KOW) to 

estimate uptake and elimination constants through respiration and diet of organisms in 

different trophic levels. Pesticide tissue residues are calculated for different levels of an 

aquatic food web. The model then uses pesticide tissue concentrations in aquatic animals 

to estimate dose- and dietary-based exposures and associated risks to mammals and birds 

consuming aquatic organisms. Previous analyses using an earlier version of the KABAM 

model indicate relatively close agreement between its predicted bioconcentration factor 

(BCF) and those reported from experimental studies for endosulfan (USEPA 2007; 

D346213). 

Details of the bioaccumulation assessment for endosulfan in relation to the CRLF are 

provided in Section 5.2.1.1. 

Soil EECs 

Total soil and pore water concentrations were calculated using PRZM simulations for 

selected crop scenarios. Crop scenarios were selected to include a range of 

concentrations based on aquatic exposure EECs obtained for endosulfan use patterns. 

Two PRZM runs were executed for six crop use patterns, one for aerial application and 

the other for ground application. Results are summarized in Table 3.10 which includes 

results for the ground applications only. Concentrations for aerial applications are not 

included because values were either similar or slightly less. It is noted that total soil and 

soil pore water concentrations are represented by either the highest or the steady state 

values. These values are obtained from plots of the total stressor daily concentrations 

similar to those included in Figures C-1 & C-2 (Appendix C) for the total soil 

concentration and Figures C-3 & C-4 (Appendix C) for the soil pore water 

concentration. Figures C-1 to C-4 suggest the following for total stressor concentration 

in the soil system: 

(1) Concentration is determined by endosulfan sulfate because concentrations for the 

other two endosulfan species (alpha & beta) appear to reach steady state (at very 

low concentrations), rather quickly; and 

80
(2) Concentration does reach steady state for only two use patterns: cotton and 

nursery (Figures C-1 & C-3) while steady state is not reached for the others 

(Figures C-2 & C-4). 

 

Table 3.10 Total soil and pore water concentrations for selected crop scenarios 

Total Soil Concentration Soil Pore Water Concentration 

Crop 

Bulk 

Density 

(kg/ m3)* (mg/kg)* (mg/ m3

)** (mole/ m3)** (mg/L)* (mg/ m3)** (mole/ m3)** 

Concentration 

Reached 

Steady State? 

Fruits 1.70 13.20 22,400 0.055 0.182 182 0.000447 No 

Cole crops 1.50 14.00 21,000 0.052 0.067 67 0.000165 No 

Lettuce 1.58 12.00 18,600 0.046 0.140 140 0.000344 No 

Nursery 1.55 9.80 15,190 0.037 0.181 181 0.000445 Yes 

Cotton 1.45 4.61 6,685 0.016 0.130 130 0.000319 Yes 

Eggplant 1.45 3.59 5,206 0.013 0.066 66 0.000161 No 

* Bulk density from scenario for the top horizon (Top 10 cm); concentrations from PEZM simulation. 

** Calculated values based on bulk density and molecular weight of endosulfan= 406.9 g/mole 

3.2.4 Existing Monitoring Data 

A critical step in the process of characterizing EECs is comparing the modeled estimates 

with available monitoring data. Varied types of monitoring data exist for alpha and beta 

endosulfan and the common degradate endosulfan sulfate. Data cover important 

environmental compartments including surface water, ground water, sediment, and air. 

Included in this assessment are endosulfan data from the USGS NAWQA program, the 

EPA STORET, and the California Department of Pesticide Regulation (CDPR). 

3.2.4.1 Surface Water Monitoring Data 

 CDPR Data

Surface water was monitored from 1991 to 2006 for α- and β-endosulfan and/or 

endosulfan sulfate in thirty three counties in California (California Department of 

Pesticide regulations; CDPR)19. Reported data show relatively high frequency and 

concentrations from 1991 to 1996 particularly for Imperial County. In contrast, 

significantly lower frequency and concentrations were observed in data collected from 

2001 to 2006 for the three species (Figure 3.1) and their total (Figure 3.2). 

 

19California Department of Pesticide Regulations (CDPR) data was obtained from 

URL:http://www.cdpr.ca.gov/docs/emon/surfwtr/surfcont.htm 

http://www.cdpr.ca.gov/docs/emon/grndwtr/list_mon.htm (GW no data) 

http://www.cdpr.ca.gov/docs/emon/pubs/tac/endoslfn.htm (Air) 

81
Figure 3.1 Detected concentrations of alpha and beta-endosulfan and common degradate in 

California surface waters from 1991 to 2006 (No data were collected from 1996 to 2000). 

Out of scale values were for SO4 only. These values occurred on 6/21/1993 and were: 0.562, 0.485, and 0.378 ppb 

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

Jan90Jan91Jan92Dec92Dec93Dec94Dec95Dec96Dec97Dec98Dec99Dec00Dec01Dec02Dec03Dec04Dec05

Monitoring Date

Monitred Concentration (ppb)

Alpha-endosulfan Beta-endosulfan endosulfan sulfate

Figure 3.2 Detected concentrations of the total endosulfan species in California surface waters from 

1991 to 2006

Out of scale values occurred on 6/21/1993 and were 0.952, 0.825 & 0.495 ppb 

0.0000

0.0500

0.1000

0.1500

0.2000

0.2500

0.3000

Jan90Jan91Jan92Dec92Dec93Dec94Dec95Dec96Dec97Dec98Dec99Dec00Dec01Dec02Dec03Dec04Dec05

Monitoring Date

Monitred Concentration (ppb)

Endosulfan Species Total

In interpreting the data, the following should be taken in consideration: 

82
(1) Not all endosulfan species were determined for all the samples suggesting that 

observed total residue concentrations could be higher than that displayed in Figure 3.2

above. 

(2) Reported detection limits for α- and β-endosulfan were mostly 0.005 ppb while it 

ranged from 0.01 to 0.005 ppb for the common endosulfan sulfate degradate (Table 

3.11). 

Table 3.11 Summary of reported detection limits for the CDPR surface water data 

Proportion of Samples Analyzed at the Detection limit (in %) 

Samples With Detections Samples Without Detections 

Reported 

Detection Limit 

(ppb) alpha Beta SO4 alpha Beta SO4 

0.0001 2% 0% 1% 1% 6% 6% 

0.002 NA NA 5% NA NA 11% 

0.001 0% NA NA 10% NA NA 

0.005 98% 100% 50% 74% 70% 29% 

0.01 NA NA 44% NA NA 54% 

0.1 0% 0% NA 15% 24% NA 

(NA= Not Applicable) 

(3) During the first monitoring period (1991 to 1996), nearly 2,000 surface water samples 

were collected from 83 sites in nine counties. In contrast, only 500 surface water samples 

were collected from 153 sites in 24 counties during the second monitoring period. 

(4) During the second monitoring period, sampling was repeated for 7 counties, namely, 

Imperial, Merced, Sacramento, San Joaquin, Sonoma, Stanislaus, and Sutter. 

(5) During the second period rates and uses were reduced. 

For the first monitoring period, data are summarized in Table 3.12. In interpreting this 

data, it is important to note the following: 

• Endosulfan sulfate were determined for nearly 93% of the samples; 

• α- and β-endosulfan were determined for only 31% of the samples; and

• All of the three species were determined for only 26% of the samples. 

Table 3.12 Summary of CPDR surface water monitoring data for California Counties collected for 

the first monitoring period (1991 to 1996) 

Total Number of Detection Distribution 

County Monitoring Years Sites Samples Detect No Detect 

Imperial 93- 94 11 195 64% 36% 

Merced 91- 95 10 381 2% 98% 

Monterey 94- 95 6 213 0% 100% 

Sacramento 90- 92 & 94- 96 11 566 <1% >99% 

San Joaquin 91- 93 2 51 4% 96% 

Santa Cruz 94- 95 4 24 0% 100% 

Sonoma 94- 95 2 153 0% 100% 

Stanislaus 91- 93 10 76 8% 92% 

Sutter 93- 94 1 153 0% 100% 

83
Data in Table 3.12 indicate that at least one of the endosulfan species was observed in 

surface waters from five out of the nine counties including Imperial (64%) followed by 

Stanislaus (8%), San Joaquin (4%), Merced (2%), and Sacramento (<1%). A summary of 

all data is included in Figure 3.3 for Imperial County and Figure 3.4 for Stanislaus, San 

Joaquin, Merced, and Sacramento Counties. 

 

Figure 3.3 CPDR Monitoring data for Imperial County (11 sites, varied times of the year) 

0

0.025

0.05

0.075

0.1

0.125

0.15

0.175

0.2

0.225

C oncentration (ppb)

1 2 3 4 5 6 7 8 910 11

Sampling Sites: All in Imperial County

Alpha Endosulfan Beta Endosulfan Sulfate

Out of scale values are: 0.56 ppb for 1; 0.39 ppb for 2 and 0.49 ppb for 3 

84
Figure 3.4 CDPR Monitoring data for Merced County (4 sites), Stanislaus County (6 sites), San 

Joaquin County (2 sites) and Sacramento County (1 site) at varied times of the year 

0

0.025

0.05

0.075

0.1

0.125

0.15

0.175

0.2

C oncentration (ppb)

ME 1 2 3 4 S T 1 2 3 4 5 6 SJ 1 2 SA

Samplind Sites: (Merced=ME 1-4; Stanislaus=ST 1-6; San Joaquin= SJ 1-2; and Sacramento=SA 

Alpha Endosulfan Beta Endosulfan Sulfate

Observed ranges of concentrations were the highest for the common degradate 

endosulfan sulfate (0.02 to 0.56 ppb) followed by α- and β-endosulfan (0.005 to 0.22 and 

0.005 to 0.17 ppb, respectively). Total endosulfan residue ranged from 0.03 to 0.95 ppb. 

For the second monitoring period (2001 to 2006), monitoring data are summarized in 

Table 3.13. 

Table 3.13 Summary of CPDR surface water monitoring data for California (the 2nd monitoring 

period) 

Total Number Of: Detection Distribution (%) Species Analyzed For* County Monitoring 

Years Sites Samples Detect No Detect Beta 

Alameda 01& 02 2 4 0% 100% No 

Del Norte 02& 03 1 4 0% 100% No 

Glenn 06 2 16 0% 100% Yes 

Humboldt 02& 03 6 20 0% 100% No 

Kern 06 2 4 0% 100% Yes 

Imperial *** 02- 04 12 67 9% 91% No 

Lake 06 1 4 0% 100% Yes 

Los Angeles ** 01& 03 30 62 3% 97% No 

Marin 01& 02 2 4 0% 100% No 

Mendocino 02& 03 3 17 0% 100% No 

Napa 02 1 1 0% 100% No 

Orange 02& 03 8 36 0% 100% No 

Merced*** 06 1 1 0% 100% No 

85
Monitoring Total Number Of: Detection Distribution (%) Species Analyzed For* County Years Sites Samples Detect No Detect Beta 

Riverside 02- 04 8 28 0% 100% No 

Sacramento*** 05- 06 1 18 0% 100% No 

San Bernardino 02- 04 3 9 0% 100% No 

San Diego 02- 04 37 111 0% 100% No 

San Joaquin*** 04- 05 2 22 0% 100% No 

San Mateo 02& 03 6 18 0% 100% No 

Santa Clara 02& 03 3 12 0% 100% No 

Shasta 06 1 2 0% 100% Yes 

Siskiyou 02& 03 9 42 0% 100% No 

Solano 05& 04 4 33 0% 100% Yes 

Tehama 06 1 2 0% 100% Yes 

Trinity 02& 03 2 8 0% 100% No 

Tulare 05& 06 12 58 0% 100% Yes 

Sonoma*** 02- 03 5 35 0% 100% No 

Stanislaus*** 04 1 2 0% 100% Yes 

Sutter*** 06 4 22 0% 100% Yes 

Ventura ** 01 4 7 86% 14% No 

Yolo 05& 06 5 78 0% 100% Yes 

Overall Summary 153 580 3% 97% Yes= 30% 

* α- endosulfan was not determined for all samples; β-endosulfan as indicated in the Table by Yes= 

determined or No= not determined, and 100% of the samples were analyzed for endosulfan sulfate 

** These two counties were the location of the only six samples with endosulfan sulfate detections 

(samples were analyzed for endosulfan sulfate only). Concentrations were: 0.003 to 0.005 ppb from 

three locations in Los Angeles County; and 0.002 to 0.005 ppb from two locations in Ventura County 

*** Counties in which sampling is a repeat (i.e., these counties were also sampled during the first 

period)

Data for the second monitoring period indicate two important points: 

(1) For all counties: observed frequency of detection and ranges of concentrations were 

very low compared to earlier years (1991 to 1996). In fact the only five detections 

were reported for samples collected in 2001 with endosulfan sulfate concentrations in 

the range of 0.002 to 0.005 ppb (α- and β-endosulfan were not determined). Again, 

endosulfan sulfate were determined for nearly 100% of the samples, α- and βendosulfan were determined for only 0% and 30% of the samples, respectively; and 

(2) For Imperial, Stanislaus, San Joaquin, and Merced Counties: Second monitoring 

(2002 to 2006) showed a significant decrease from the first monitoring in earlier 

years. During these recent years, detections were recorded in Imperial County only 

(9% of the samples) with no detections in Stanislaus, San Joaquin, and Merced 

Counties. 

EPA STORET Data

In STORET20, data are reported on monitored surface water from 2001 to 2008 (mostly 

from 2001 to 2003), for α- and β-endosulfan and/or endosulfan sulfate in twenty one 

counties in California (Table 3.14). 

 

20 STORET Data base URL: http://www.epa.gov/storet/dw_home.html 

86
Table 3.14 Summary of STORET surface water monitoring data for California 

Total Number Of: Detects Distribution (%)

County Monitoring month- Year Sites Samples >LOQ <LOQ Total 

Alameda Sep-01; Apr-02 2 6 33% 0% 33% 

Contra Costa Sep-01; Apr & Jun-02 2 5 0% 0% 0% 

Del Norte Feb, Mar & Jun-02 3 8 0% 13% 13% 

Humboldt Feb, Mar & Jun-02 3 5 0% 60% 60% 

Imperial May, Sep & Oct-02 20 44 0% 0% 0% 

Los Angeles Oct & Nov-01; Jan- 03 4 10 40% 0% 40% 

Marin Oct-01; Apr-02 3 4 0% 0% 0% 

Mendocino Feb, Mar & Jun-02 3 10 0% 30% 30% 

Napa 39966 1 1 0% 0% 0% 

Orange Oct-02; Jan, Apr & May-03 10 38 0% 18% 18% 

Riverside May, Sep & Oct-02; Apr & May-03 7 13 0% 0% 0% 

San Bernardino May & Oct-02 3 6 0% 0% 0% 

San Diego Mar, Apr, Jun & Sep-02; Jan, Apr & May-03 15 70 9% 7% 16% 

San Luis Obispo Jul-03; Jan & July-04/05/06/07 & Jan-08 1 20 0% 0% 0% 

San Mateo Apr & Jun-02; Jan-03 4 15 0% 0% 0% 

Santa Barbara Jun-06; Jan-08 3 6 0% 0% 0% 

Santa Clara Apr & Jun-02; Jan-03 4 13 0% 0% 0% 

Siskiyou Feb, Mar & Jun-02 2 6 0% 33% 33% 

Solano Oct-01; Apr & Jun-02 2 3 0% 0% 0% 

Sonoma Feb, Mar, Apr & Jun-02 3 15 0% 33% 33% 

Ventura Nov-02 5 6 50% 0% 50% 

Overall Summary 100 304 6% 9% 16% 

Reported data show relatively low frequency and concentrations. At least one of the 

endosulfan chemical species was detected with an overall frequency of 6% for detections 

over the LOQ, and 9% for detections below the LOQ. Observed concentrations are 

shown in Figure 3.5 for all data/individual endosulfan species, Figure 3.6 for all 

data/total endosulfan species, and Figure 3.7 for data from counties with concentrations 

over the limit of quantification.

87
Figure 3.5 Detected concentrations of α- and β-endosulfan and endosulfan sulfate common degradate 

in California surface waters from 2001 to 2008 (STORET data) 

0.000

0.002

0.004

0.006

0.008

0.010

Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08

Monitoring Date

Concentration (ppb)

Alpha Beta SO4

Data points >0 and <0.002 represent samples with detections over the LOD but lower than the LOQ. These were 

assumed to equal 0.001 ppb because LOD and LOQ were not reported. However, data suggest that the LOQ is 

probably equal to 0.002 ppb. 

Figure 3.6 Detected concentrations of the total endosulfan species in California surface waters from 

2001 to 2008 (STORET data)

0.000

0.002

0.004

0.006

0.008

0.010

Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08

Monitoring Date

Concentration (ppb)

Endosulfan Species Total

Data points >0 and <0.002 represent samples with detections over the LOD but lower than the LOQ. These were 

assumed to equal 0.001 ppb because LOD and LOQ were not reported. However, data suggest that the LOQ is probably 

equal to 0.002 ppb.

88
Figure 3.7 Detected concentrations of α- and β-endosulfan and endosulfan sulfate common degradate 

in surface waters of five California Counties (Counties with detections over the LOQ; 2001 to 2008 

STORET data) 

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

Concentration (ppb)

Alameda San Diego San Diego Los Angeles Ventura

Counties with Detections Over LOQ

Alpha

Beta

SO4

(1) Data points >0 and <0.002 represent samples with detections over the LOD but lower than the LOQ. 

These were assumed to equal 0.001 ppb because LOD and LOQ were not reported. However, data suggest 

that the LOQ is probably equal to 0.002 ppb. 

(2) Samples with no detect are not included. The number of samples with no detects is equal to: 4 for 

Alameda Co.; 58 for San Diego CO.; 6 for Los Angeles Co. & 3 for Ventura Co.

STORET data appear to be comparable to date reported by CDPR for the years following 

2001. For these years, STORET data reported maximum concentrations 0.008 ppb for αendosulfan, 0.0064 ppb for β-endosulfan, 0.005 ppb for endosulfan sulfate, and 0.008 ppb 

for the total (Figure 3.5 and Figure 3.6). For the same period, CDPR data reported the 

same maximum concentrations of 0.005 ppb for endosulfan sulfate (α- and β-endosulfan 

were not determined). 

USGS NAQWA Data

California surface water was monitored by the NAWQA program21 during 1995 and 

from 2001 to 2007 for endosulfan residue including α-, β-, ether- endosulfan, and 

endosulfan sulfate in fifteen sites in five counties. A total of nearly 200 samples were 

collected with no detection reported for any of the endosulfan residue including

ether- endosulfan, and endosulfan sulfate. Detection limits varied for the various 

endosulfan residues: 0.0047 to 0.011 ppb for α-endosulfan, 0.0142 for β-, endosulfan

0.0041to 0.0066 ppb for ether- endosulfan, and 0.0058 to 0.022 ppb for endosulfan 

sulfate (

α-, β-, 

, 

Table 3.15). 

Table 3.15 A summary of NAWQA monitoring data for surface water from California 

Sampling Dates Endosulfan Species Detection Limits (ppb) 

County Site Start Finish 

Number 

of 

Samples Alpha Beta Ether SO4 

Merced Site 1 10-Jan-95 10-Jan-95 1 0.0100 ND ND ND 

Site 2 9-Oct-01 27-Apr-05 23 0.0047 0.0142 0.0041 0.0058 

 

21 NAQWA data was obtained on January 17, 2008: URL: 

http://infotrek.er.usgs.gov/traverse/f?p=NAWQA:HOME:3748645897450568

89
Sampling Dates Endosulfan Species Detection Limits (ppb) 

County Site Start 

Number 

of 

Finish Samples Alpha Beta Ether SO4 

22-Jun-05 15-Feb-06 5 0.0047 ND ND 0.0138 

12-Apr-06 9-Aug-06 3 0.0110 ND ND 0.0220 

13-Jun-05 7-Feb-06 5 0.0047 ND ND 0.0138 

21-Jun-06 21-Jun-06 1 0.0110 ND ND 0.0122 

Riverside Site 1 20-Apr-06 6-Sep-07 20 0.0110 ND ND 0.0220 

15-Jun-05 27-Oct-05 7 0.0047 ND ND 0.0138 

22-Nov-05 15-Mar-06 8 0.0047 ND ND 0.0138 

Site 1 25-Apr-06 24-Sep-07 26 0.0110 ND ND 0.0220 

16-Jun-05 28-Sep-05 8 0.0047 ND ND 0.0138 

31-Oct-05 31-Oct-05 1 0.0047 ND ND ND 

31-Oct-05 31-Oct-05 1 ND ND ND 0.0200 

7-Dec-05 23-Feb-06 2 0.0047 ND ND 0.0138 

Sacramento Site 2 27-Apr-06 2-Aug-06 3 0.0110 ND ND 0.0220 

10-Jan-95 10-Jan-95 1 0.0100 ND ND ND 

16-Oct-02 3-Sep-03 18 0.0047 0.0142 0.0041 0.0058 

19-Oct-04 20-Apr-05 4 0.0047 0.0142 0.0066 0.0138 

22-Jun-05 15-Feb-06 5 0.0047 ND ND 0.0138 

San Joaquin Site 1 26-Apr-06 27-Sep-07 25 0.0110 ND ND 0.0220 

Site 1 10-Jan-95 10-Jan-95 1 0.0100 ND ND ND 

Site 2 10-Jan-95 10-Jan-95 1 0.0100 ND ND ND 

Site 3 10-Jan-95 10-Jan-95 1 0.0100 ND ND ND 

Site 4 10-Jan-95 10-Jan-95 1 0.0100 ND ND ND 

Site 5 10-Jan-95 10-Jan-95 1 0.01 ND ND ND 

Site 6 10-Jan-95 10-Jan-95 1 0.01 ND ND ND 

10-Jan-95 10-Jan-95 4 0.01 ND ND ND 

9-Oct-01 20-Apr-05 20 0.0047 0.0142 0.0041 0.0058 

22-Jun-05 15-Feb-06 5 0.0047 ND ND 0.0138 

Site 7 26-Apr-06 9-Aug-06 3 0.0110 ND ND 0.0220 

Site 8 10-Jan-95 10-Jan-95 1 0.0100 ND ND ND 

Stanislaus Site 9 10-Jan-95 10-Jan-95 1 0.0100 ND ND ND 

In conclusion, surface water monitoring data are summarized in the following Table 

3.16. 

Table 3.16 Surface water data summary

Cnty= No of counties; Site= No of Sites; Smpl= No of Samples 

Data Source CDPR1991-1996 CDPR 2001-2006 STORET 2001-2008 NAQWA (1995 & 2001-2007) 

Total Number of: Cnty Site Smpl Cnty Site Smpl Cnty Site Smpl Cnty Site Smpl 

Endosulfan Species 9 83 2,000 24 153 500 21 100 304 5 15 200 

α (Max ppb) 0.22 Not Determined 0.008 <0.011 

β (Max ppb) 0.17 Not Determined 0.0064 <0.0142 

Sulfate (Max ppb) 0.56 0.005 ppb 0.005 <0.022 

90
3.2.4.2 Groundwater Monitoring Data 

No ground water monitoring data were reported for California by the CDPR for 

endosulfan isomers and the common degradate. However, ground water monitoring data 

were reported by NAWQA for 11 California counties from 149 ground water wells. Data 

showed no detections of α- , β- and ether- endosulfan, and/or endosulfan sulfate. 

Detection limits varied for the various endosulfan species: 0.0047 to 0.011 ppb for αendosulfan, 0.0142 ppb for β- endosulfan, 0.0041 ppb for ether- endosulfan and 0.0058 to 

0.022 ppb for endosulfan sulfate (Table 3.17). Both β- endosulfan and ether- endosulfan 

were not determined for nearly 39% of the samples. 

Table 3.17 A summary of monitoring data for ground water from California 

Well Depths (ft) Endosulfan Species Detection Limits (ppb) 

County 

Number 

of 

Wells Min Max Alpha Beta Ether SO4 Sampling Dates 

7 114 300 0.011 ND ND 0.022 Jun-06; Aug-06 

Fresno 26 68 390 0.0047 0.0142 0.0041 0.0058 Jul-01; Aug-01; Sep-01; Jun-02 

Kern 1 300 300 0.011 ND ND 0.022 Aug-06 

Kings 3 55 244 0.0047 0.0142 0.0041 0.0058 Jul-02 

Madera 6 165 265 0.0047 0.0142 0.0041 0.0058 Sep-01; Jul-02 

5 96 230 0.011 ND ND 0.022 Jun-06; Aug-06 

Merced 13 56 265 0.0047 0.0142 0.0041 0.0058 Oct-01; Jul-02; Aug-02 

Orange 2 942 1,020 0.011 ND ND 0.022 Jun-06 

Sacramento 31 37 200 0.0047 ND ND 0.0138 Jul-05; Aug-05; Sep-05; Aug-06 

San Bernardino 5 234 900 0.011 ND ND 0.022 Jun-06; Aug-06 

1 175 175 0.011 ND ND 0.022 Aug-06 

San Joaquin 14 44 250 0.0047 0.0142 0.0041 0.0058 Sep-01; Oct-01; Sep-02 

3 110 195 0.011 ND ND 0.022 Jun-06; Aug-06 

Stanislaus 18 33 195 0.0047 0.0142 0.0041 0.0058 Oct-01; Nov-01; Jun-02; Aug-02 

3 182 310 0.011 ND ND 0.022 Jun-06; Aug-06 

Tulare 10 118 313 0.0047 0.0142 0.0041 0.0058 Sep-01; Jun-02; Aug-02 

* ND= Chemical species was not determined 

In conclusion, ground water monitoring data are summarized as follows: 

• No CDPR data; and 

• NAQWA (2001-2006): 11 counties; 149 wells: Alpha <0.011 ppb; Beta<0.0142 

ppb; and Sulfate <0.022 ppb

3.2.4.3 Sediment Monitoring Data 

Bottom sediment monitoring data were reported by NAWQA for 18 California counties 

from 49 surface water sites. No detections were observed in the 53 samples which were 

analyzed for α-endosulfan only. Reported values were all less than the limit of detection 

of 0.2 to 2 μg/Kg of α-endosulfan (Table 3.18) 

Table 3.18 A summary for NAWQA monitoring data to base sediment in California 

Number of Concentration 

County Sampling Dates Sites Samples Alpha (μg/Kg) 

Stanislaus (Sept, 01) 1 1 0.2 

91
Number of Concentration 

County Sampling Dates Sites Samples Alpha (μg/Kg) 

Alpine (Sept, 92); Colusa (Oct, 95); El Dorado (Sept, 92); Fresno 

(Oct, 92); Kings (Oct, 92) and Orange (Sept, 98) 1 each 1 each 

Nevada (Sept, 92 & Oct, 96) 1 2 

Shasta (Oct, 95) and Yuba (Nov, 95) 2 each 2 each 

San Joaquin (Oct, 92 & Nov, 97) 2 3 

Riverside (Sept, 98); Sacramento (Oct & Nov, 95); Sutter (Nov & 

Oct, 95); Tehama (Oct, 95) and Yolo (Oct, 95) 3 each 3 each 

Merced (Oct, 92); 4 4 

San Bernardino (Sept & Nov, 98) 6 6 

Stanislaus (Oct, 92 & Nov, 97) 8 10 

1 

Riverside (Sept, 98); and San Bernardino Sept, 98 1 each 1 each 2 

In STORET22, data are reported on monitored sediment (2 meter deep) from September, 

2001 to January, 2003 for α- and β-endosulfan and/or endosulfan sulfate in eleven 

counties in California. Reported data show a single detection (one sample out of 84 

samples) with a concentration of 9.01ng/g for α- and β-endosulfan (Table 3.19). 

Examination of the surface water data associated with this sediment sample shows no 

detection of any endosulfan species 

Table 3.19 Summary of bottom sediment monitoring data for California 

County Monitoring Year(s) No of Sites No of Samples* 

Alameda September, 2001 2 4 

Contra Costa September, 2001 & June, 2002 2 3 

Imperial May, September & October, 2002 20 46 

Los Angeles January, 2003 1 1 

Marin October, 2001 & June 2002 3 4 

Riverside May, September & October, 2002 6 13 

San Bernardino May & October, 2002 2 4 

San Mateo June, 2002 2 3 

Santa Clara June, 2002 2 3 

Solano June, 2002 1 1 

Ventura November, 2001 1 2 

Overall September, 2001 to January, 2003 42 84 

* Number of samples may not match the number of sites because of sampling the same site at different dates 

 

In conclusion, sediment data are summarized as follows: 

• No CDPR data; 

• NAQWA (1992-1998): 18 counties, 49 sites, and 58 samples: Alpha <2 ppb; 

Others Not determined; and 

• STORET (2002-2003) 11 Counties; 42 sites, and 84 samples: Only single sample 

with 9.01 ng/g concentration for alpha endosulfan 

3.2.4.4 Atmospheric Monitoring Data 

 

22 STORET Data base URL: http://www.epa.gov/storet/dw_home.html 

92
α-, β-endosulfan and endosulfan sulfate may be considered as semi-volatile chemicals. 

Vapor pressures for the three chemicals are 4.56x10-5 torr for α-endosulfan, 2.40x10-5 torr 

for β-endosulfan, and 9.75x10-6 torr for endosulfan sulfate. Vapor pressure values 

suggest that the three chemicals may volatilize into the air from dry soil/plant surfaces. 

Calculated Henry’s Law constants are 3.03x10-6 atm m3 mol-1for α-endosulfan, 1.38x10-6 

atm m3 mol-1 for β-endosulfan, and 1.64x10-5 atm m3 mol-1for endosulfan sulfate. Values 

indicate that the three chemicals may also volatilize from water or wet soils. The three 

endosulfan chemical species appear to have the ability to partition into air in relatively 

important amounts and persist long enough to be transported by air into distant areas. 

Reported half lives in the air were 2.7 days for α-endosulfan and 15 days for βendosulfan (Schenker et al. 2005), and 2.6 days for endosulfan sulfate as estimated by 

EpiSuit V 4.023 . Chemicals with half-life of ≥2 days in the air can be considered to be 

persistent in this media (SAP, 2009)24. 

Based on physiochemical and fate properties, endosulfan may move from the application 

site to edge and near-field by drift and can be carried away by short and long-range 

transport. Air monitoring and modeling may be used to evaluate the importance of these 

two dissipation routes for exposure to edge/near field and nearby and far away areas. 

Drift Monitoring (Edge & Near-field) 

A 24-hour drift monitoring study (referred to in the study description as application site 

monitoring) was conducted during the month of April in San Joaquin County (CDPR, 

1998)25. The study included four air sampling stations placed on north, south, east, and 

west sides of an 8.5 acre apple orchard field (at 54, 27, 21 and 33 ft from field edge, 

respectively). Endosulfan was applied by ground equipment at a rate of 1.5 lbs a.i. /A to 

represent application to apples and cherries (current rate can be up to 2.5 lbs a.i. /A). At 

each site, samples were collected at seven intervals: 1.00, 1.90, 4.00, 8.10, 9.50, 23.75, 

and 24.00 hours following application. 

A total of 28 sample events were collected within the 24-hour period at the four field 

locations. This study represents a specific pesticide application followed by drift 

monitoring at specific times/locations for endosulfan leaving the application field. Data 

show relatively high detects/concentrations for alpha endosulfan compared to low 

detect/concentrations for beta endosulfan and no detects for endosulfan sulfate (

Table 3.20). 

 

23 The Estimation Programs Interface EPI Suite: http://www.epa.gov/oppt/exposure/pubs/episuitedl.htm 24 SAP (The FIFRA Scientific Advisory Panel). 2009. Minutes for the SAP Meeting on selected issues 

associated with risk assessment process for pesticides with persistent, bio-accumulative and toxic 

characteristics. October 28-31, 2008. Arlington, VA. (Document No. 2009-01 dated Jan 29, 2009). 

25 CDPR, 1998 Report for the Air Monitoring of Endosulfan in Fresno County (Ambient) and in San 

Joaquin County (Application), Air Resources Board, California Environmental Protection Agency, 

Monitoring and Laboratory Division, Engineering and Laboratory Branch, Project No. C96-034 

Dated April 17, 1998 

93
Table 3.20 Frequency and concentrations of endosulfan species in ambient air 

% of Total Samples in various Detection Categories * 

Endosulfan Species “No Detect” 

Low Concentration 

Detects 

High concentration 

Detects Totals 

Alpha 4% 4% 92% 100% 

Beta 36% 14% 50% 100% 

Sulfate 100% 0% 0% 100% 

* Detection Categories (no categories specified for endosulfan sulfate “SO4”): 

“None”: <3.1 ng/m3

 for alpha, and <6.2 ng/m3 for beta 

“Low Detects” : 3.1 to ≤10 ng/m3 for alpha, and 6.2 to ≤20 ng/m3 for beta

“High Detects”: >10 ng/m3 for alpha; > ng/m3 for beta. These detects ranged from 4.1-140 ng/m3 for 

alpha endosulfan and were only three detects at 13, 13 and 26 ng/ m3

 for beta endosulfan

Detection/Quantification limits (LOD= Limit of detection; LOQ= Limit of quantification 

Assuming 0.96 m3

 samples (8 hours sampling period @ 2 Liters/Min): Alpha: LOD=3.1 ng/m3 and LOQ= 

10 ng/ m3

; Beta: LOD= 6.2 and LOQ= 20 ng/ m3, and LOQ= 19.6 ng/ m3 for SO4 (endosulfan sulfate) 

Figure 3.8 summarizes monitoring data reported for α- and β- endosulfan (endosulfan 

sulfate was not detected over the detection limit). 

0

100

200

300

400

500

600

700

Monitered Concentration (ng/m3)

Alpha

(East)

Beta (East) Alpha

(North)

Beta

(North)

Alpha

(South)

Beta

(South)

Alpha

(West)

Beta

(West)

Monitered Endosulfan Species and direction of the station location from field

Note 1: 4 out of scale concentrations are 1,800; 3,800; 1,200 & 1,200 ng/m3 from left to right, respectively 

Figure 3.8 Concentration profiles for α- and β- endosulfan at the edge and near-field in ambient air 

following application in San Joaquin County, California 

Additionally, data suggest that applied 70:30 mixture of α- and β- endosulfan drifted 

from the application site in disproportional quantities in the four main directions. 

Endosulfan sulfate was not found above the LOQ in any of the application samples. On 

the average, the ratio between α- and β- endosulfan in drifted material was in the range of 

7-23:1 compared to nearly 2:1 in the applied formulation. High concentration of αendosulfan (up to 2xβ- endosulfan) may be explained by the disproportional quantities in 

the applied parent. However, observed enrichment of drifted material with α- endosulfan, 

up to 23xβ- endosulfan, could not be fully explained. Higher vapor pressure of αcompared to β- endosulfan may have contributed to observed result. 

94
Results indicate that concentrations of α- and β- endosulfan were highest in drift moving 

through the east edge of the field followed by the north, then the south with lowest 

concentrations moving to the west. Additionally, peak concentrations in the drift were 

generally observed within the first four hours after application. The relative drift 

distribution was partially related to wind speed and direction. Wind rose data throughout 

the first five periods were from the west and north-west and the south west at the end of 

these periods. Wind directions during the last two periods were from the west, north, 

north-west with additional wind from the north-east at the start of the last period. Other 

factors may have also contributed to observed results such as application direction 

(application started at the north-west corner of the plot with the rows oriented east/west), 

average width of area downwind, distance of sampling station from field edge. Other 

factors may have also contributed to observed variations including temperature, relative 

humidity and sun light. Changes in these parameters are expected because the 

experiment started early in the morning of 4/8/97 at 5:30 AM and ended in the morning 

of 4/10/97 at 8.00 AM. 

Short-Range Transport Monitoring 

Levels of twelve pesticides, including total endosulfan26, were determined in ambient air 

collected at three residential locations within the vicinity of Salinas, California (CDPR, 

1985)27. The study coincided with expected time of pesticide applications but was not 

designed to coincide with any specific pesticide application sites or times. At each site, a 

three day sampling period was used with four six hour sampling times starting from mid 

night, early morning (6:00 AM), noon, and night (6:00 PM). Endosulfan was detected in 

two out of the twelve air samples in a site located 1,200 ft from any agricultural field and 

in four out of 12 samples in another site located at only 190 ft from any agricultural field. 

All of the six detections were within a range of 37- 55 ng/m3

 (31- 46 ppt)28. Positive 

detections were in samples collected early in the day, coinciding with the time when 

pesticides were applied to nearby fields, although wind speeds were lowest. 

In another ambient air monitoring study, α- and β- endosulfan and endosulfan sulfate 

were determined in ambient air collected every 24-hours at five sampling sites in 

relatively high-population areas in Fresno County (CDPR, 1998)29. A total of 125 

samples were collected within five weeks at four sites. Sites were in proximity to cotton 

and grape growing areas (two sites were within 50-100 yards and two were within 0.75-2 

miles). Sampling periods were during the months of July and August to coincide with the 

 

26 Note: It was not clear from the study report whether concentrations were for total endosulfan but it 

appears that at least α- and β- endosulfan were monitored. 27 CDPR, 1985 Monterey County Residential Air Monitoring By R.J. Sava, et al, Environmental Hazards 

Assessment Program, Department of Pesticide Regulation, California Environmental Protection Agency, 

Sacramento, CA 95814-5624 dated December 1985, Reprinted December 1995 28 pptt= ng/m3

 multiplied by 0.833 

29 CDPR, 1998 Report for the Air Monitoring of Endosulfan in Fresno County (Ambient) and in San 

Joaquin County (Application), Air Resources Board, California Environmental Protection Agency, 

Monitoring and Laboratory Division, Engineering and Laboratory Branch, Project No. C96-034 

Dated April 17, 1998 

95
application of endosulfan on cotton and grapes. Again, no specific pesticide application 

sites or times were associated with the study. Data show relatively high 

detects/concentrations for alpha endosulfan compared to low detect/concentrations for 

beta endosulfan and no detects for endosulfan sulfate (Table 3.21). 

Table 3.21 Frequency and concentrations of endosulfan species in ambient air 

% of Total Samples in various Detection Categories * 

Endosulfan Species “None” 

Low Concentration 

Detects 

High Concentration 

Detects Totals 

Alpha 18% 9% 73% 100% 

Beta 68% 29% 3% 100% 

Sulfate 100% 0% 0% 100% 

* Detection Categories (no categories specified for endosulfan sulfate “SO4”): 

“None”: <0.58 ng/m3

 for alpha, and <1.91 ng/m3 for beta 

“Low Detects” : 0.58 to ≤2.49 ng/m3 for alpha, and 1.91 to ≤8.16 ng/m3 for beta

“High Detects”: >2.49 ng/m3 for alpha; >8.16 ng/m3 for beta. These detects ranged from 4.1-140 ng/m3

for alpha endosulfan and were only three detects at 13, 13 and 26 ng/ m3

 for beta endosulfan

Detection/Quantification limits (LOD= Limit of detection; LOQ= Limit of quantification 

Assuming 2.88 m3

 samples (24 hours sampling period @ 2 Liters/Min): Alpha: LOD=1.1 ng/m3 and 

LOQ= 3.8 ng/ m3

; Beta: LOD= 3.8 and LOQ= 12 ng/ m3; and LOQ= 12.8 ng/ m3 for SO4 (endosulfan 

sulfate) 

Data suggest that application of endosulfan may have caused partitioning of α- and βendosulfan into ambient air to support maximum concentrations of 140 ng/m3

 for αendosulfan (the 70% isomer in the formulation) and 26 ng/m3

 for β- endosulfan (the 30% 

isomer in the formulation). The same conclusion applies for detection frequencies of 

low/high concentrations. These frequencies were 82% for α- endosulfan and 31% for βendosulfan (refer to Table 3.21: 82%= 9%+73%; and 31%= 29%+3%). Figure 3.9

summarizes data for the main species detected, α- endosulfan. 

96
Figure 3.9 Concentration profiles for α- endosulfan in ambient air during a period of five weeks at 4 

sites in Fresno County, California. 

0

10

20

30

40

50

Monitered Concentration (ng/m3)

Site 1 Site 2 Site 3 Site 4

Time: From zero to 5 weeks for each site

Note 1: Distance from Cotton fields: sites 1&2 = 150-300 ft.; Site 3= 0.75-1.0 mile; Site 4= 1-2 miles. 

Note 2: The 4 out of scale concentrations are 130, 120, 140, and 70 ng/m3 from left to right, respectively

Based on data shown in Figure 3.9, α- endosulfan appears to be present in the ambient 

air of near field areas where its parent is applied to cotton and grapes. Although 

relatively high spikes of concentrations exist, concentration levels of the chemical appear 

to be mainly in the range of 5 to 35 ng/m3 (4- 29 ppt) which is lower than concentrations 

monitored in 1985 (37- 55 ng/m3 = 31- 46 ppt). These near field areas were in the range 

of 50 yards to 2 miles from possible application sites suggesting that endosulfan had 

partitioned into the air and moved within short-range distances. Dissipation of 

endosulfan into and within the air mass is probably related to a combination of drift and 

volatilization. 

Long-Range Transport Monitoring 

Atmospheric transport from CA central valley and re-deposition in the Sierra Nevada 

Mountains were documented for α- and β- endosulfan and endosulfan sulfate. As a result 

of atmospheric transport, the three chemicals have been found in the mountainous regions 

of California in air surface water, sediment, precipitation/snow-pack, and biota. 

Endosulfans were detected in air samples taken from Sequoia and King Canyon National 

Parks (Landers et al. 2008) in average concentrations of approximately 1,250 pg/g dry 

XAD. Levels of endosulfan detected in the California National Parks were greater than 

those measured in any other park in the study (Sequoia/Kings Canyon, Rocky Mountain, 

Mount Rainier, Glacier, Denali, Noatak, and Gates of the Arctic). 

In surface water, residues of α-, β-endosulfan and endosulfan sulfate were present in 

water from both Tablelands and Sixty Lakes in the Sierra Nevada Mountains of 

California (Fellers et al. 2004). Similar concentrations were detected for α- and βendosulfan from the Tablelands and Sixty Lakes sampling areas, however endosulfan 

sulfate concentrations in Tablelands were almost an order of magnitude higher than in 

97
Sixty Lakes and almost four times greater than β- endosulfan concentrations from the 

same locations (Table 3.22). The α-isomer was also detected at two locations and at 

various depths in Lake Tahoe in concentrations ranging from < 0.004 to 0.26 ng/L which 

are similar to that found in snow in the surrounding basin (McConnell et al. 1998). 

Endosulfan was one of the most common current use pesticide detected in sediment 

collected from lakes in Sequoia and Kings Canyon National Parks with an average flux of 

approximately 130 ng/m2

/y 

Table 3.22 Concentration of pesticides (ng/L) in surface water samples collected at the 

Tablelands (Sequoia National Park), and the Sixty Lake Basin (Kings Canyon National 

Park) California, USA (Fellers et al. 2004). 

Tablelands Sixty Lakes Chemical 

Compound 

Detection limit G049 G054 S545 S471 

α-endosulfan 0.03 0.78 1.0 0.30 0.37 

β-endosulfan 0.05 0.40 0.42 1.8 0.17 

Endosulfan sulfate 0.03 2.9 2.2 0.33 0.40 

In precipitation/snow pack, endosulfan and endosulfan sulfate were detected in seasonal 

snow pack samples at seven national parks in the Western United States, including 

mountainous regions in California (Sequoia, Rocky Mountain, Mount Rainier, Glacier, 

Denali, Noatak, and Gates of the Arctic; Hageman et al. 2006). In this study, 

concentrations of total endosulfan measured in seasonal snow pack ranged from < 0.0040 

to 1.5 ng/L and the percent contribution of endosulfan sulfate to the total endosulfan 

concentration averaged 24.0%. McConnell et al. (1998) reported endosulfan was present 

in snow and rain samples from two elevations in Sequoia National Park and the southern 

Sierras, a region adjacent to California’s Central Valley which is among the heaviest 

pesticide use areas in the U.S. Levels of α-endosulfan found in precipitation range from < 

0.035 to 6.5 ng/L while β-endosulfan ranged from < 0.012 to 1.4 ng/L (McConnell et al. 

1998). 

Endosulfan was also found in mountain yellow-legged frogs (Rana muscosa) from two 

areas in the Sierra Nevada Mountains in California (Sixty Lakes Basin, Kings Canyon 

National Park and Tablelands, Sequoia national Park; Fellers et al. 2004). Of the two 

endosulfan isomers and the sulfate degradate, only the α-isomer was observed at levels 

above quantitation. Concentrations of α-endosulfan averaged 0.56 (± 0.36) and 0.45 (± 

0.24) ng/g wet weight at Tablelands and Sixty Lakes Basin, respectively. These 

Concentrations were not significantly different from the two sites (Fellers et al 2004). 

Endosulfan sulfate was measured in fish from Sequoia and Kings Canyon National Parks 

at average concentrations of approximately 30 ng/g lipid, which was one of the highest 

concentrations reported in fish throughout the western parks (Landers et al. 2008). 

Total Endosulfan (sum of α, β, and sulfate) was measured in lichen and conifer samples 

in Sequoia and Kings Canyon National Parks at average concentrations of 488 and 192 

ng/g, respectively (Landers et al. 2008). In this study endosulfans, along with dacthal, 

dominated the total pesticide laoding in vegetation samples from the lower 48 states. 

98
3.3 Terrestrial Animal Exposure Assessment 

A primary concern of endosulfan application is that birds and mammals may be exposed 

through oral or dietary exposure to vegetative plant material or insects when foraging in 

treated fields for nesting material or food. Estimation of endosulfan concentrations in 

wildlife food items focuses on quantifying possible dietary ingestion of residues on 

vegetative matter and insects. The EFED terrestrial exposure model T-REX (T-REX, 

Version 1.4.1, dated October 9, 2008) simulates a one-year time period and is used to 

estimate exposures and risks to avian (surrogate for terrestrial-phase amphibians and 

reptiles) and mammalian species. Avian and mammalian toxicity, chemical application, 

and foliar dissipation half-life data are input for the model, which provides estimates of 

exposure concentrations (EECs) and risk quotients (RQs). Specifically, the model 

provides estimates of concentrations (upper-bound and mean) of chemical residues on the 

surface of different types of foliage and insects that may be dietary sources of exposure to 

avian, mammalian, reptilian, or terrestrial-phase amphibian receptors. The surface residue 

concentration (ppm) is estimated by multiplying the application rate (pounds active 

ingredient per acre) by a value specific to each food item (termed the Hoerger-Kenaga 

estimates). For multiple applications, the EEC is determined by adding the mass on the 

surface immediately following the application to the mass of the chemical still present on 

the surfaces on the day of application (determined based on first order kinetics using the 

foliar half-life as the rate constant). The Hoerger-Kenaga estimates and a more detailed 

discussion of the methodology implemented by T-REX can be found at 

http://www.epa.gov/oppefed1/models/terrestrial/. 

T-REX is also used to calculate EECs for terrestrial insects exposed to endosulfan via 

spray applications. Dietary-based EECs calculated by T-REX for small (broadleaf 

plants/small insects dietary category) and large (fruits/pods/seeds/large insects dietary 

category) invertebrates (units of a.i./g) are used to bound an estimate of exposure to 

terrestrial invertebrates. Available acute contact toxicity data for bees (or other terrestrial 

invertebrates) exposed to endosulfan (in units of μg a.i./organism), are converted to μg 

a.i./g (of organism) by dividing by the body weight of an individual organism used in the 

test. For honey bees, the body weight of a bee is assumed to be 0.128 g. The EECs are 

later compared to the adjusted acute contact toxicity data for terrestrial invertebrates in 

order to derive RQs for terrestrial invertebrates. 

Terrestrial EECs were derived for use categories (apples, cotton, grapes, lettuce, pecans, 

potatoes, tobacco, and tomatoes) using current application rates and intervals between 

applications. Uncertainties in the terrestrial EECs are primarily associated with a lack of 

data on interception and subsequent dissipation from foliar surfaces. Use-specific input 

values, including number of applications, application rate, foliar half-life and application 

interval are provided in Table 3.23. The maximum number of applications per year, the 

minimum application intervals, and the maximum application rates for each crop selected 

as the representative crop for a “Crop Category” were derived from the product labels 

(Table 2.3) and Willis and McDowell (1987) summarized seven studies which evaluated 

the foliar persistence of endosulfan on a variety of crops. Foliar half-lives ranged from 1 

99
to 5 days on a variety of crops (cotton, grapes, pears, tobacco, alfalfa, beets, and leafy 

vegetables) in studies conducted in California, Arizona, Kentucky, Canada, and 

Australia. The mean of the 13 reported half-life values was 3.2 days (standard deviation 

of 1.4 days). The upper 90th percent confidence interval value for the mean (4 days) was 

used as the foliar dissipation rate for modeling purposes. 

The model was run for agricultural uses with the maximum single application rate and 

number of applications as proposed on the labels; however, it should be noted that in 

some instances recommended label use may include either a single application of the 

maximum allowable seasonal rate or multiple applications of lower rates totaling the 

season maximum. The scenario which yielded the highest EEC and RQ values were used 

for each use category where multiple application methods were possible. The upperbound Kenaga nomogram estimates reported by T-REX have been used for derivation of 

the EECs for the terrestrial organisms and their potential prey (Table 3.23). An example 

output from T-REX is available in Appendix F. 

Table 3.23 Summary of Dose and Dietary-based EECs Used for Estimating Dietary Risks to Terrestrial 

Organisms using T-REX ver. 1.4.1. 

Dose-Based EECs 

Avian size class (grams) 

Mammalian size class 

(grams) Use 

Category 

App 

Rate (lb 

a.i./A, # 

Apps, 

Interval 

(da)) 

Dietary Category 

20 100 1000 15 35 1000 

Dietary 

EECs 

 

Short Grass 546.67 311.74 139.57 457.64 316.29 73.33 480.00 

Tall Grass 250.56 142.88 63.97 209.75 144.97 33.61 220.00 

Broadleaf Plants/ Small Insects 307.50 175.35 78.51 257.42 177.91 41.25 270.00 

Fruits/Pods/ Seeds/ Large Insects 34.17 19.48 8.72 28.60 19.77 4.58 30.00 

Almonds, 

hazelnut & 

walnut 

2, 1, 

Granivore 7.59 4.33 1.94 6.36 4.39 1.02 

Short Grass 683.34 389.67 174.46 572.05 395.37 91.67 600.00 

Tall Grass 313.20 178.60 79.96 262.19 181.21 42.01 275.00 

Broadleaf Plants/ Small Insects 384.38 219.19 98.13 321.78 222.39 51.56 337.50 

Fruits/Pods/ Seeds/ Large Insects 42.71 24.35 10.90 35.75 24.71 5.73 37.50 

Citrus 2.5, 1, 

Granivore 9.49 5.41 2.42 7.95 5.49 1.27 

Short Grass 354.60 202.21 90.53 296.85 205.16 47.57 311.35 

Tall Grass 162.52 92.68 41.49 136.06 94.03 21.80 142.70 

Broadleaf Plants/ Small Insects 199.46 113.74 50.92 166.98 115.40 26.76 175.14 

Fruits/Pods/ Seeds/ Large Insects 22.16 12.64 5.66 18.55 12.82 2.97 19.46 

Broccoli, 

cabbage, 

Chinese 

cabbage, 

cauliflower, 

kohlrabi 

1, 2, 7 

Granivore 4.92 2.81 1.26 4.12 2.85 0.66 

Short Grass 205.00 116.90 52.34 171.62 118.61 27.50 180.00 

Tall Grass 93.96 53.58 23.99 78.66 54.36 12.60 82.50 

Broadleaf Plants/ Small Insects 115.31 65.76 29.44 96.53 66.72 15.47 101.25 

Fruits/Pods/ Seeds/ Large Insects 12.81 7.31 3.27 10.73 7.41 1.72 11.25 

Kale, 

Collards & 

Mustard 

Green 

0.75, 1, 

Granivore 2.85 1.62 0.73 2.38 1.65 0.38 

Short Grass 410.00 233.80 104.68 343.23 237.22 55.00 360.00 

Tall Grass 187.92 107.16 47.98 157.31 108.73 25.21 165.00 

Broadleaf Plants/ Small Insects 230.63 131.51 58.88 193.07 133.44 30.94 202.50 

Sweet corn 1.5, 1, 

Fruits/Pods/ Seeds/ Large Insects 25.63 14.61 6.54 21.45 14.83 3.44 22.50 

100
Table 3.23 Summary of Dose and Dietary-based EECs Used for Estimating Dietary Risks to Terrestrial 

Organisms using T-REX ver. 1.4.1. 

Dose-Based EECs 

Avian size class (grams) 

Mammalian size class 

(grams) 

App 

Use 

Category 

Rate (lb 

a.i./A, # 

Apps, 

Interval 

(da)) 

Dietary Category 

20 100 1000 15 35 

Dietary 

EECs 

1000 

 

Granivore 5.69 3.25 1.45 4.77 3.29 0.76 

Short Grass 273.34 155.87 69.78 228.82 158.15 36.67 240.00 

Tall Grass 125.28 71.44 31.98 104.88 72.48 16.81 110.00 

Broadleaf Plants/ Small Insects 153.75 87.68 39.25 128.71 88.96 20.63 135.00 

Fruits/Pods/ Seeds/ Large Insects 17.08 9.74 4.36 14.30 9.88 2.29 15.00 

Cotton 

(ground) 1, 2, 

Granivore 3.80 2.16 0.97 3.18 2.20 0.51 

Short Grass 265.95 151.66 67.90 222.64 153.87 35.68 233.51 

Tall Grass 121.89 69.51 31.12 102.04 70.52 16.35 107.03 

Broadleaf Plants/ Small Insects 149.60 85.31 38.19 125.23 86.55 20.07 131.35 

Fruits/Pods/ Seeds/ Large Insects 16.62 9.48 4.24 13.91 9.62 2.23 14.59 

Cotton 

(Areal) 0.75, 2, 7 

Granivore 3.69 2.11 0.94 3.09 2.14 0.50 

Short Grass 683.34 389.67 174.46 572.05 395.37 91.67 600.00 

Tall Grass 313.20 178.60 79.96 262.19 181.21 42.01 275.00 

Broadleaf Plants/ Small Insects 384.38 219.19 98.13 321.78 222.39 51.56 337.50 

Fruits/Pods/ Seeds/ Large Insects 42.71 24.35 10.90 35.75 24.71 5.73 37.50 

Apples 2.5, 1, 

Granivore 9.49 5.41 2.42 7.95 5.49 1.27 

Short Grass 683.34 389.67 174.46 572.05 395.37 91.67 600.00 

Tall Grass 313.20 178.60 79.96 262.19 181.21 42.01 275.00 

Broadleaf Plants/ Small Insects 384.38 219.19 98.13 321.78 222.39 51.56 337.50 

Fruits/Pods/ Seeds/ Large Insects 42.71 24.35 10.90 35.75 24.71 5.73 37.50 

Apricot, 

nectarine, 

peach, 

cherry, pear, 

plum & 

prune 

2.5, 1, 

Granivore 9.49 5.41 2.42 7.95 5.49 1.27 

Short Grass 388.26 221.40 99.12 325.03 224.64 52.08 340.91 

Tall Grass 177.95 101.48 45.43 148.97 102.96 23.87 156.25 

Broadleaf Plants/ Small Insects 218.40 124.54 55.76 182.83 126.36 29.30 191.76 

Fruits/Pods/ Seeds/ Large Insects 24.27 13.84 6.20 20.31 14.04 3.26 21.31 

Lettuce & 

Brussels 

sprouts 

1, 2, 5 

Granivore 5.39 3.08 1.38 4.51 3.12 0.72 

Short Grass 354.60 202.21 90.53 296.85 205.16 47.57 311.35 

Tall Grass 162.52 92.68 41.49 136.06 94.03 21.80 142.70 

Broadleaf Plants/ Small Insects 199.46 113.74 50.92 166.98 115.40 26.76 175.14 

Fruits/Pods/ Seeds/ Large Insects 22.16 12.64 5.66 18.55 12.82 2.97 19.46 

Cucumber, 

melons, 

pumpkin & 

squash 

1, 2, 7 

Granivore 4.92 2.81 1.26 4.12 2.85 0.66 

Short Grass 136.67 77.93 34.89 114.41 79.07 18.33 120.00 

Tall Grass 62.64 35.72 15.99 52.44 36.24 8.40 55.00 

Broadleaf Plants/ Small Insects 76.88 43.84 19.63 64.36 44.48 10.31 67.50 

Fruits/Pods/ Seeds/ Large Insects 8.54 4.87 2.18 7.15 4.94 1.15 7.50 

Eggplant 0.5, 1, 

Granivore 1.90 1.08 0.48 1.59 1.10 0.25 

Short Grass 166.01 94.67 42.38 138.97 96.05 22.27 145.76 

Tall Grass 76.09 43.39 19.43 63.70 44.02 10.21 66.81 

Broadleaf Plants/ Small Insects 93.38 53.25 23.84 78.17 54.03 12.53 81.99 

Fruits/Pods/ Seeds/ Large Insects 10.38 5.92 2.65 8.69 6.00 1.39 9.11 

Ornamentals 

& shade 

trees 

0.5, 6, 10 

Granivore 2.31 1.31 0.59 1.93 1.33 0.31 

101
Table 3.23 Summary of Dose and Dietary-based EECs Used for Estimating Dietary Risks to Terrestrial 

Organisms using T-REX ver. 1.4.1. 

Dose-Based EECs 

Avian size class (grams) 

Mammalian size class 

(grams) 

App 

Use 

Category 

Rate (lb 

a.i./A, # 

Apps, 

Interval 

(da)) 

Dietary Category 

20 100 1000 15 35 

Dietary 

EECs 

1000 

 

Short Grass 388.26 221.40 99.12 325.03 224.64 52.08 340.91 

Tall Grass 177.95 101.48 45.43 148.97 102.96 23.87 156.25 

Broadleaf Plants/ Small Insects 218.40 124.54 55.76 182.83 126.36 29.30 191.76 

Fruits/Pods/ Seeds/ Large Insects 24.27 13.84 6.20 20.31 14.04 3.26 21.31 

Potato 1, 2, 5 

Granivore 5.39 3.08 1.38 4.51 3.12 0.72 

Short Grass 218.29 124.48 55.73 182.74 126.30 29.28 191.67 

Tall Grass 100.05 57.05 25.54 83.76 57.89 13.42 87.85 

Broadleaf Plants/ Small Insects 122.79 70.02 31.35 102.79 71.04 16.47 107.81 

Fruits/Pods/ Seeds/ Large Insects 13.64 7.78 3.48 11.42 7.89 1.83 11.98 

Sweet 

potato 0.5, 3, 5 

Granivore 3.03 1.73 0.77 2.54 1.75 0.41 

Short Grass 388.26 221.40 99.12 325.03 224.64 52.08 340.91 

Tall Grass 177.95 101.48 45.43 148.97 102.96 23.87 156.25 

Broadleaf Plants/ Small Insects 218.40 124.54 55.76 182.83 126.36 29.30 191.76 

Fruits/Pods/ Seeds/ Large Insects 24.27 13.84 6.20 20.31 14.04 3.26 21.31 

Dry beans 

(except 

Lima), peas 

& pepper 

1, 2, 5 

Granivore 5.39 3.08 1.38 4.51 3.12 0.72 

Short Grass 273.34 155.87 69.78 228.82 158.15 36.67 240.00 

Tall Grass 125.28 71.44 31.98 104.88 72.48 16.81 110.00 

Broadleaf Plants/ Small Insects 153.75 87.68 39.25 128.71 88.96 20.63 135.00 

Fruits/Pods/ Seeds/ Large Insects 17.08 9.74 4.36 14.30 9.88 2.29 15.00 

Carrot 1, 1, 

Granivore 3.80 2.16 0.97 3.18 2.20 0.51 

Short Grass 273.34 155.87 69.78 228.82 158.15 36.67 240.00 

Tall Grass 125.28 71.44 31.98 104.88 72.48 16.81 110.00 

Broadleaf Plants/ Small Insects 153.75 87.68 39.25 128.71 88.96 20.63 135.00 

Fruits/Pods/ Seeds/ Large Insects 17.08 9.74 4.36 14.30 9.88 2.29 15.00 

Celery 1, 1, 

Granivore 3.80 2.16 0.97 3.18 2.20 0.51 

Short Grass 293.65 167.45 74.97 245.83 169.90 39.39 257.84 

Tall Grass 134.59 76.75 34.36 112.67 77.87 18.05 118.18 

Broadleaf Plants/ Small Insects 165.18 94.19 42.17 138.28 95.57 22.16 145.03 

Fruits/Pods/ Seeds/ Large Insects 18.35 10.47 4.69 15.36 10.62 2.46 16.11 

Strawberry 1, 2, 15 

Granivore 4.08 2.33 1.04 3.41 2.36 0.55 

Short Grass 354.60 202.21 90.53 296.85 205.16 47.57 311.35 

Tall Grass 162.52 92.68 41.49 136.06 94.03 21.80 142.70 

Broadleaf Plants/ Small Insects 199.46 113.74 50.92 166.98 115.40 26.76 175.14 

Fruits/Pods/ Seeds/ Large Insects 22.16 12.64 5.66 18.55 12.82 2.97 19.46 

Tomato 1, 2, 7 

Granivore 4.92 2.81 1.26 4.12 2.85 0.66 

N/A = Non-applicable

Upper-bound Kenega nomogram values reported by T-REX are used for derivation of 

dietary EECs for evaluating direct and/or indirect effects to terrestrial phase CRLF, CTS, 

SFGS, SMHM, SJKF, BCB, and VELB. Potential direct acute and chronic effects of 

endosulfan to the terrestrial-phase CRLF, SFGS and CTS are derived by considering 

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dietary-based exposures modeled in T-REX for a small bird (20g) consuming small 

invertebrates. 

Potential direct acute and chronic effects specifically to the SMHM are derived by 

considering dose- and dietary-based EECs modeled in T-REX for a small mammal (15 g) 

consuming a variety of dietary items (Table 3.23). Potential direct acute and chronic 

effects specifically to the SJKF are derived by considering dose- and dietary-based EECs 

modeled in T-REX for a large mammal (1,000 g) consuming a variety of dietary items 

(Table 3.23). 

3.4 Terrestrial Plant Exposure Assessment 

No terrestrial plant toxicity data were available for endosulfan that were considered 

acceptable for quantitative use in risk estimation. Therefore, risks to terrestrial plants 

could not be quantitatively assessed in this risk assessment but instead were qualitatively 

considered. 

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4 Effects Assessment 

This assessment evaluates the potential for endosulfan (and its primary degradate of 

concern, endosulfan sulfate) to directly or indirectly affect the CRLF, CTS, SFGS, 

SMHM, SJKF, BCB, and VELB or modify their designated critical habitat. As 

previously discussed in Section 2.7, assessment endpoints for the effects determination 

for each assessed species include direct toxic effects on the survival, reproduction, and 

growth, as well as indirect effects, such as reduction of the prey base or modification of 

its habitat. In addition, potential modification of critical habitat is assessed by evaluating 

effects to the PCEs, which are components of the critical habitat areas that provide 

essential life cycle needs of each assessed species. Direct effects to the aquatic-phase 

CRLF and CTS are based on toxicity information for freshwater fish, while terrestrialphase CRLF, CTS and SFGS effects are based on avian toxicity data, given that birds are 

generally used as a surrogate for terrestrial-phase amphibians and reptiles when suitable 

data for terrestrial-phase amphibians are not available. 

As described in the Agency’s Overview Document (U.S. EPA, 2004), the most sensitive 

endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa 

include freshwater fish (used as a surrogate for aquatic-phase amphibians), freshwater 

invertebrates, estuarine/marine fish, estuarine/marine invertebrates, aquatic plants (nonvascular only; no data were available for vascular aquatic plants), birds (used as a 

surrogate for terrestrial-phase amphibians and reptiles), mammals, terrestrial 

invertebrates, and terrestrial plants (plants are only qualitatively evaluated due to lack of 

appropriate data). Acute (short-term) and chronic (long-term) toxicity information is 

characterized based on registrant-submitted studies and a comprehensive review of the 

open literature on endosulfan 

Toxicity endpoints are established based on data generated from guideline studies 

submitted by the registrant, and from open literature studies that meet the criteria for 

inclusion into the ECOTOX database maintained by EPA/Office of Research and 

Development (ORD; http://www.epa.gov/med/Prods_Pubs/ecotox.htm). Open literature 

data presented in this assessment were obtained from ECOTOX information obtained on 

November 5, 2008. In order to be included in the ECOTOX database, papers must meet 

the following minimum criteria: 

(1) the toxic effects are related to single chemical exposure; 

(2) the toxic effects are on an aquatic or terrestrial plant or animal species; 

(3) there is a biological effect on live, whole organisms; 

(4) a concurrent environmental chemical concentration/dose or application 

rate is reported; and 

(5) there is an explicit duration of exposure. 

Data that pass the ECOTOX screen are evaluated along with the registrant-submitted 

data, and may be incorporated qualitatively or quantitatively into this endangered species 

assessment. In general, effects data in the open literature that are more conservative (i.e., 

104
show a lower toxicity endpoint) than the registrant-submitted data are evaluated further. 

The degree to which open literature data are quantitatively or qualitatively characterized 

for the effects determination is dependent on whether the information is relevant to the 

assessment endpoints (i.e., survival, reproduction, and growth) identified in Section 2.8. 

For example, endpoints such as biochemical modifications are likely to be qualitatively 

evaluated, because quantitative relationships between biochemical modifications in the 

laboratory and reduction in species survival, reproduction, and/or growth in the field are 

generally not available. Although this effects determination relies on endpoints that are 

relevant to the assessment endpoints of survival, growth, or reproduction, it is important 

to note that the full suite of sublethal endpoints potentially available in the effects 

literature (regardless of their significance to the assessment endpoints) are considered to 

define the action area for endosulfan. 

The sublethal endpoint used to define the Action Area was based on reduction in growth 

for the sheepshead minnow (Hansen and Cripe, 1991; ECOTOX reference # 14143), who 

reported a LOAEC of < 0.27 ug a.i./L resulting from 28-d, flow through exposures.

Citations of all open literature not evaluated as part of this assessment because they were 

either rejected by the ECOTOX screen or accepted by ECOTOX but not used (e.g., the 

endpoint is less sensitive) are included in Appendix G. Appendix G also includes a 

rationale for rejection of those studies that did not pass the ECOTOX screen and those 

that were not evaluated as part of this endangered species risk assessment. 

A detailed spreadsheet of the available ECOTOX open literature data, including the full 

suite of lethal and sublethal endpoints is presented in Appendix H. Appendix J contains 

a review of all the toxicity data considered in this assessment for aquatic species, while 

Appendix K contains the same information for terrestrial species. Appendix M also 

includes a summary of the human health effects data for endosulfan. Because the stability 

of endosulfan TGAI in aquatic tests is a concern due to its volatility, preference was 

given to those studies that quantified endosulfan exposure via analytical measurements 

and where appropriate, used a flow-through exposure regime. In some cases, however, 

these data were lacking (e.g., aquatic nonvascular plants), and toxicity values based on 

nominal concentrations were used to fulfill a data gap. In general, studies from the open 

literature do not provide sufficient documentation for evaluating all or most of the 

OPPTS Guideline evaluation criteria. Consistent with the Overview Document (U.S.EPA 

2004), if sufficient documentation was provided to judge that the open literature studies 

were scientifically valid and acceptable endpoints were determined that were below the 

‘benchmark’ values, they were typically classified as supplemental--but acceptable for 

quantitative use. If sufficient documentation was not provided to comprehensively judge 

the scientific validity of the study but no information existed that suggested the study 

would be invalid, these studies were typically classified as supplemental--but acceptable 

for qualitative use. This classification was often applied to studies with nominal exposure 

concentrations. 

In addition to registrant-submitted and open literature toxicity information, other sources 

of information, including use of the acute probit dose response relationship to establish 

105
the probability of an individual effect and reviews of the Ecological Incident Information 

System (EIIS), are conducted to further refine the characterization of potential ecological 

effects associated with exposure to endosulfan. A summary of the available aquatic and 

terrestrial ecotoxicity information, use of the probit dose response relationship, and the 

incident information for endosulfan are provided in Sections 4.1 through 4.4, 

respectively. 

As discussed in Section 2.4.1, endosulfan sulfate is the primary degradate of 

toxicological concern for endosulfan (α+β). Available data suggest that the acute toxicity 

of endosulfan sulfate can be similar to the parent isomers, or on occasion, somewhat less 

toxic, depending on the species tested. For example, registrant-submitted studies of the 

TGAI and endosulfan sulfate indicate similar acute toxicity to bluegill (1.7 vs. 3.8 ug/L, 

respectively; MRID 38806 and 46382604). Comparison among two decapod crustaceans 

(grass shrimp and mysid shrimp) indicates the acute toxicity of parent isomers and the 

sulfate degrade are within the same order of magnitude (1.3 and 7.9 μg/L, respectively; 

MRID 5005824 and 46406401). For avian species, registrant-submitted data indicate 

similar acute toxicity of endosulfan TGAI and endosulfan sulfate based on the avian 

acute oral study with bobwhite quail and subacute dietary studies with mallard and 

bobwhite quail (MRID 137189; 136998; 160000; 22923; 46382604). Comparative acute 

toxicity data available in the open literature for Daphnia magna, Hyalella azteca and 

Oncorhynchus mykiss also support the finding of similar acute toxicity of the sulfate 

degradate and parent TGAI; however, the exposure regime used in these tests is uncertain 

due to lack of confirmatory analytical measurements (Wan et al., 2005; ECOTOX 

reference # 87973). 

Acceptable studies comparing the chronic toxicity of the TGAI and sulfate degradate 

were not identified in this review. Therefore, consistent with the available data and the 

previous endosulfan risk assessment (U.S. EPA, 2007; D346213), the acute and chronic 

toxicity of endosulfan (TGAI) and endosulfan sulfate will be assumed to be equivalent. A 

detailed summary of the available ecotoxicity information for all endosulfan degradates 

and formulated products can be found in Appendices H, J and K. 

4.1 Toxicity of Endosulfan to Aquatic Organisms 

Table 4.1 summarizes the most sensitive aquatic toxicity endpoints, based on an 

evaluation of both the submitted studies and the open literature, as previously discussed. 

A brief summary of submitted and open literature data considered relevant to this 

ecological risk assessment for the CRLF, CTS. SFGS, SMHM, SJKF, BCB, and VELB is 

presented below. Additional information on species life history is provided in 

Attachments 1 and 3. 

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Table 4.1 Aquatic Toxicity Profile for Endosulfan (TGAI) 

Assessment 

Endpoint 

Purity 

(% a.i.) 

Surrogate 

Species 

Toxicity Value Used 

for Quantitative 

Risk Estimates 

(μg a.i./L) 

Effects Reference/Acceptability 

Freshwater Fish and Aquatic-phase Amphibians (1)

Survival 96.2 Common Carp 

(Cyprinus carpio) LC50 = 0.1 Mortality Sunderam et al. 1992; ( 

ECOTOX 5850)/ Supplemental 

Reproduction and Growth Not 

Available 

Common Carp 

(Cyprinus carpio) NOAEC = 0.023 Not Available Estimated (2)

Freshwater Invertebrates 

Survival 96 Mayfly (Atalophlebia 

australis) LC50 = 0.6 Mortality Leonard, et al. 1999 (ECOTOX 20012)/Supplemental 

Reproduction and Growth Not 

Available 

Mayfly (Atalophlebia 

australis)) NOAEC = 0.01 Not Available Estimated (3)

Sediment Toxicity(6) 99 

Midge, 

Chironomus tentans

20-d NOAEC = 0.35 Mortality and 

Emergence 47318101 /Acceptable 

Estuarine/Marine Fish 

Survival 96 Spot (Leiostomus 

xanthurus) LC50 = 0.09 Mortality MRID 5005824/Acceptable 

Reproduction and Growth Not 

Available 

Spot (Leiostomus 

xanthurus) NOAEC = 0.045 Not Available Estimated (4)

Estuarine/Marine Invertebrates 

Survival 96 Pink shrimp (Penaeus 

dourarum) LC50 = 0.04 Mortality MRID 5005824/Acceptable 

Reproduction and Growth Not 

Available 

Pink shrimp (Penaeus 

dourarum NOAEC = 0.013 Not Available Estimated(5)

Sediment Toxicity(6) Amphipod 

(Leptocheirus 

plumulosus)

28-d NOAEC = 1.58 Growth 

46929001 / Supplemental 

Aquatic Non Vascular Plants 

Survival and Growth non-vascular 

Green alga 

(Pseudokirchneriella 

subcapitatum) 

EC50 = 428 Growth (Based on 

cell counts) 

DeLorenzo et al. 2002 

(ECOTOX 65915)/Supplemental 

Aquatic Vascular Plants 

Survival and Growth No acceptable data indentified 

(1) Freshwater fish are used as a surrogate for aquatic-phase amphibians because no acceptable data for 

quantitative use currently exist for endosulfan to aquatic-phase amphibians. 

(2) The fathead minnow (Pimephales promelas) acute to chronic ratio (ACR = 4.3) was used to estimate a 

common carp chronic toxicity value because it is the most acutely sensitive freshwater fish species and no 

chronic toxicity data are available for it. 

(3) The daphnid (Daphnia magna) acute to chronic ratio (ACR = 61.5) was used to estimate a freshwater 

shrimp chronic toxicity value because it is the most acutely sensitive freshwater invertebrate species and no 

chronic toxicity data are available for it. 

(4) The sheepshead minnow (Cyprinodon variegatus) acute to chronic ratio (ACR = 2.0) was used to 

estimate a spot chronic toxicity value because it is the most acutely sensitive saltwater fish species and no 

chronic toxicity data are available for it. 

(5) The mysid shrimp (Americanmysis bahia) acute to chronic ratio (ACR = 3.1) was used to estimate a spot 

chronic toxicity value because it is the most acutely sensitive saltwater invertebrate species and no chronic 

toxicity data are available for it. 

(6) Sediment toxicity values are for endosulfan sulfate in sediment pore water. 

Toxicity to fish and aquatic invertebrates is categorized using the system shown in Table 

4.2 (U.S. EPA, 2004). Toxicity categories for aquatic plants have not been defined. 

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Table 4.2 Categories of Acute Toxicity for Fish and Aquatic Invertebrates 

LC50 (ppm) Toxicity Category 

< 0.1 Very highly toxic 

> 0.1 - 1 Highly toxic 

> 1 - 10 Moderately toxic 

> 10 - 100 Slightly toxic 

> 100 Practically nontoxic 

4.1.1 Toxicity to Freshwater Fish and Aquatic-Phase Amphibians 

A summary of acute and chronic toxicity of endosulfan to freshwater fish and aquaticphase amphibians, including the toxicity of the primary degradate of concern (endosulfan 

sulfate), is provided below in Sections 4.1.1.1 through 4.1.1.6. 

4.1.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies – Registrant submitted 

The acute toxicity studies available to the Agency demonstrate that endosulfan can be 

classified as very highly toxic to freshwater fish, with LC50 values ranging from 0.37 to 

3.3 μg a.i./L (see Appendix J for details). The studies also demonstrate that the 

formulated end use products with at least 33% a.i. are of similar acute toxicity to 

freshwater fish (LC50 values from 0.47 to 5.6 μg a.i./L) as the TGAI. One formulation 

containing only 4% endosulfan was substantially less acutely toxic to freshwater fish 

(LC50 of 28 μg a.i./L). 

4.1.1.2 Freshwater Fish: Acute Exposure (Mortality) Studies—Open Literature 

In addition to the acute toxicity studies discussed above, several acute toxicity studies 

with freshwater fish were identified from the open literature (see Appendix J) which 

report more sensitive values. The lowest of these more sensitive acute LC50 values is 0.1 

μg a.i./L (Sunderam et al. 1992; ECOTOX reference #5850) for the common carp, 

Cyprinus carpio. This study was evaluated and considered supplemental but appropriate 

for quantitative use in this risk assessment. Therefore, an acute LC50 value of 0.1 μg 

a.i./L will be used to quantitatively estimate acute risk to freshwater fish. Since no acute 

mortality studies with aquatic-phase amphibians in the open literature have been 

identified as acceptable for quantitative use within the context of this risk assessment, the 

most sensitive LC50 value for freshwater fish will also be used to estimate acute risks to 

aquatic-phase amphibians. 

4.1.1.3 Freshwater Fish: Chronic Exposure (Growth/Reproduction) Studies 

Two acceptable life-cycle studies on fathead minnows (Pimephales promelas) were 

available to the Agency to evaluate the effects of chronic exposure to endosulfan (99% 

a.i.) on freshwater fish (MRID 05008271, 45868601). The first study (MRID 05008271) 

demonstrated that chronic exposure to concentration as low as 0.40 μg a.i./L has the 

potential to cause reproductive toxicity. Only 1% of the eggs hatched at this 

concentration (see Appendix J for details). The NOAEC and LOAEC for this study are 

0.20 and 0.40 μg a.i./L. The second study (MRID 45868601) demonstrated a reduction in 

108
the reproduction and growth of fathead minnows at 0.11 μg a.i./L and a NOAEC at 0.056 

μg a.i./L. Although these studies are considered acceptable, a fathead minnow acute to 

chronic ratio (ACR = 4.3) was used to estimate a common carp chronic toxicity value 

because carp is the most acutely sensitive freshwater fish species (i.e., about a factor of 

10 more sensitive than fathead minnow) and no chronic toxicity data for endosulfan are 

available for it. The estimated chronic NOAEC value for the common carp was 

calculated as follows: 

Acute fathead minnow/chronic fathead minnow= acute carp/chronic carp 

Where: 

the acute fathead minnow value is based on the LC50 value 0.86 μg a.i./L (MRID 

05008271), 

the chronic fathead minnow value is based on the NOAEC of 0.20 μg a.i./L from 

the same study and, 

the acute common carp value is based on the LC50 is 0.1 μg a.i./L as described 

previously (Sunderam et al. 1992; ECOTOX reference #5850). 

Therefore, 0.86/0.20 = 0.1/X 

and, 

Estimated common carp NOAEC = (0.20 x 0.1)/0.86 = 0.023 μg a.i./L. 

This estimated NOAEC of 0.023 μg a.i./L for common carp will be used to quantitatively 

estimate chronic risk of endosulfan to freshwater fish. Since no chronic studies with 

aquatic-phase amphibians in the open literature have been identified as acceptable for 

quantitative use within the context of this risk assessment, the estimated NOAEC of 

0.023 μg a.i./L for freshwater fish will also be used to estimate chronic risk to aquaticphase amphibians. 

4.1.1.4 Freshwater Fish: Sublethal Effects and Additional Open Literature 

Information 

No additional acceptable studies from the open literature were identified for freshwater 

fish that: established more sensitive acute or chronic endpoints than the data listed above; 

filled critical data gaps; presented a toxicity profile for under-represented taxa (e.g., 

toxicity data for amphibians); or provided information on sub-lethal effects that could be 

clearly and reasonable linked to relevant assessment endpoints (i.e., survival, 

reproduction, and growth) at concentrations lower than the most sensitive endpoints used 

to quantitatively evaluate risk. 

109
4.1.1.5 Aquatic-phase Amphibian: Acute and Chronic Studies 

No toxicity data for aquatic-phase amphibians were identified among the submitted 

studies or that were considered acceptable for quantitative use in this risk assessment. 

4.1.1.6 Freshwater Fish: Endosulfan Sulfate

Available data indicates that endosulfan sulfate is of similar acute toxicity to freshwater 

fish as the TGAI. Specifically, the 96-hour LC50 of endosulfan sulfate on bluegill was 

3.8 μg/L and is considered very highly toxic (MRID 46382604; Appendix J). Acute 

toxicity testing of endosulfan sulfate (99.9% radiopurity) was also tested with common 

carp (MRID 45421402), which also indicated that the degradate is very highly toxic (96-

hr LC50 = 2.2 μg/L) to freshwater fish. The study was classified as supplemental since it 

failed to comply with EPA’s recommended species and testing conditions. However, 

results from the submitted and open literature studies are consistent with studies of parent 

endosulfan TGAI where 96-hr LC50 values ranged from 0.37 to 3.3 μg/L. 

4.1.2 Toxicity to Freshwater Invertebrates 

A summary of acute and chronic freshwater invertebrate toxicity data, including data 

published in the open literature is provided below in Sections 4.1.2.1 through 4.1.2.6. 

4.1.2.1 Freshwater Invertebrates: Acute Exposure Studies 

The acute toxicity studies available to the Agency demonstrate that endosulfan can be 

classified as very highly toxic or highly toxic to freshwater invertebrates, with EC50 

values ranging from 2.3 to 166 μg a.i./L. (see Appendix J). There were no studies 

submitted to the Agency on the effect of commercial end use products on freshwater 

invertebrates. 

4.1.2.2 Freshwater Invertebrates: Acute Exposure Studies—Open Literature 

In addition to the aforementioned acute mortality studies with freshwater invertebrates, 

several additional studies (see Appendix J) reported more sensitive values. Two species 

of mayfly nymphs and one genus (species not indicated) of caddisfly larvae were tested 

in static tests in which the concentrations of endosulfan were measured at the beginning 

of each test (Leonard, et al. 1999; ECOTOX reference #20012. The EC/LC50s using 

technical grade endosulfan in this study ranged from 0.4 to 1.8 μg/L, varying based on 

the size of the organisms and the duration of the specific test. The lowest value was for 

caddisfly larvae (Cheumatopsyche sp.); however, since this organism was not identified 

to species this datum will not be used. The next lowest value was for the mayfly 

Atalophlebia australis. The 0.6 μg/L value for A. australis is considered the lowest acute 

value for freshwater invertebrates that is acceptable for quantitative use in this risk 

assessment. There was one study from the open literature that indicated for at least two 

species (Daphnia magna and Hyalella azteca) commercial end use products are not more 

110
toxic than endosulfan applied as the TGAI (Wan et al. 2005; ECOTOX reference # 

87973). 

4.1.2.3 Freshwater Invertebrates: Chronic Exposure Studies 

One chronic exposure study with endosulfan TGAI involving the freshwater invertebrate, 

Daphnia magna, was submitted to the Agency (MRID 5008271). The study examined the 

effects of endosulfan on three consecutive generations of daphnids and noted that the 

poor survival of third generation in the control and the lowest treatment group (2.7 μg/L) 

precluded drawing valid conclusions about the cumulative effects of exposure. However, 

the first generation portion of this study is considered acceptable for quantitative use in 

this risk assessment, and generally coincides with the duration and design of the current 

OPPTS Guideline (OPPTS 850.1300). The NOAEC and LOAEC from the first 

generation of this study are 2.7 and 7.0 μg a.i./L based on reduced survival. Although this 

study is considered acceptable, a daphnia acute to chronic ratio (ACR = 61.5) was used to 

estimate a chronic value for the more acutely-sensitive mayfly, Atalophlebia australis.

No chronic toxicity data are available for this species. The estimated chronic NOAEC 

value for the mayfly was calculated similarly to that for the common carp above: 

Estimated freshwater mayfly NOAEC = (0.6 x 2.7)/166 = 0.01 μg a.i./L. 

This estimated NOAEC of 0.01μg a.i./L for mayflies will be used to quantitatively 

estimate chronic risk to freshwater invertebrates. 

4.1.2.4 Freshwater Invertebrates: Sub-lethal Effects and Additional Open 

Literature Information 

No additional acceptable studies from the open literature, beyond the one already 

discussed, were identified for freshwater invertebrates that: established more sensitive 

acute or chronic endpoints than the data listed above; filled critical data gaps; presented a 

toxicity profile for under-represented taxa; or provided information on sub-lethal effects 

that could be clearly and reasonably linked to relevant assessment endpoints (i.e., 

survival, reproduction, and growth) at concentrations lower than the most sensitive 

endpoints used to quantitatively evaluate risk to freshwater invertebrates. 

4.1.2.5 Freshwater Invertebrates: Endosulfan Sulfate

Acute toxicity testing endosulfan sulfate using Daphnia magna (99.4% active ingredient) 

indicated that the degradate is highly toxic (EC50 = 300 ug/L) to water fleas (MRID 

45421403). The study was classified as supplemental since it was conducted using a 

water hardness (160 - 180 mg/L as CaCO3) outside of the recommended range (40 - 49 

mg/L as CaCO3). These results are similar to the acute toxicity of the parent TGAI to D. 

magna (166 ug/L; MRID 5008271; Appendix J). 

No data were identified on the chronic toxicity of endosulfan sulfate to freshwater 

invertebrates that were considered acceptable for quantitative use in this risk assessment. 

111
4.1.2.6 Freshwater Invertebrates: Sediment Toxicity

Endosulfan sulfate sediment toxicity tests were conducted for the midge, Chironomus 

tentans, in two studies. The 20-day NOAEC and LOAEC determined from pore water 

were measured as 0.35 and 1.2 μg/L respectively, based on mortality and percent 

emergence (MRID 47318101). In a second study classified as supplemental, the most 

sensitive NOAEC and LOAEC were determined as 2.7 and 3.8 μg/L, respectively based 

on growth (MRID 46382605). 

4.1.3 Toxicity to Estuarine/Marine Fish 

Although direct and indirect effects to the listed species are not dependent on 

estuarine/marine fish, toxicity data for estuarine/marine were reviewed in order to 

provide a broader characterization of endosulfan risks to fish. A summary of acute and 

chronic estuarine/marine fish data, including data published in the open literature is 

provided below in Sections 4.1.3.1 through 4.1.3.4. 

4.1.3.1 Estuarine/Marine Fish: Acute Exposure (Mortality) Studies 

The acute toxicity studies submitted to the Agency demonstrate that endosulfan can be 

classified as very highly toxic to estuarine/marine fish, with LC50 values ranging from 

0.09 to 0.38 μg a.i./L for four species of fish (striped bass, striped mullet, pinfish and 

spot; see Appendix J). No acceptable acute toxicity studies were available for 

estuarine/marine fish using formulated end-use products. The most sensitive acute LC50 

value of 0.09 μg a.i./L for spot, Leiostomus xanthurus (MRID 5005824) will be used to 

quantitatively estimate acute risk to estuarine/marine fish.. 

4.1.3.2 Estuarine/Marine Fish: Acute Exposure (Mortality) Studies—Open 

Literature 

In addition to the aforementioned acute mortality studies with estuarine/marine fish an 

additional study was identified in the open literature which reported several LC50 values 

for sheepshead minnows (Cyprinodon variegatus), the preferred test species (Schimmel 

1981; ECOTOX reference # 3740). This study was a report listing the results of an 

interlaboratory comparison of acute toxicity tests using estuarine animals—sheepshead 

minnow was one of the species tested. There were six acute LC50 values based on 

measured, flow-through tests ranging from 0.34 to 1.15 μg a.i./L (see Appendix J). 

While none of these values is lower than the LC50 for the spot listed above, their 

geometric mean (0.76 μg a.i./L) will be used to establish the acute to chronic toxicity 

ratio for estuarine/marine fish used in the next section. 

4.1.3.3 Estuarine/Marine Fish: Chronic Exposure (Growth/Reproduction) Studies 

No acceptable chronic toxicity data were available to the Agency for estuarine/marine 

fish; however, there was a study from the open literature (Hansen and Cripe 1991; 

ECOTOX 115297) summarizing an interlaboratory comparison of the early-life stage 

112
toxicity test using the sheepshead minnow Cyprinodon variegatus. Ten tests conducted 

with measured, flow-through exposures were reported with NOAECs ranging from 0.17 

to 1.2 μg a.i./L. The corresponding LOAECs are based on either survival or growth (see 

Appendix J). The geometric mean of these ten values is 0.38 μg a.i./L. This study fulfills 

a data gap for a chronic test with the preferred estuarine/marine fish. Although these tests 

are considered acceptable for quantitative use in this risk assessment, a sheepshead 

minnow acute to chronic ratio (ACR = 2.0) was used to estimate a spot chronic toxicity 

value because it is the most acutely sensitive estuarine/marine fish species by 

approximately a factor of four compared to sheepshead minnow and no chronic toxicity 

data for endosulfan are available for it. The estimated chronic NOAEC value for the spot 

was calculated similarly to that demonstrated above for the common carp (except with 

the ACR from the sheepshead minnow). 

Estimated spot NOAEC = (0.09 x 0.38)/0.76 = 0.045 μg a.i./L. 

This estimated NOAEC of 0.045 μg a.i./L for spot will be used to quantitatively estimate 

chronic risk to estuarine/marine fish. 

4.1.3.4 Estuarine/Marine Fish: Endosulfan Sulfate

One submitted study was available that evaluated the acute toxicity of endosulfan sulfate 

on estuarine/marine fish. This study was conducted with sheepshead minnow and 

resulted in a 96-hr LC50 of 3.1 μg/L for endosulfan sulfate (MRID 46382603). This 

value is comparable to the range of LC50s for the TGAI with sheepshead minnow 

discussed above. 

4.1.4 Toxicity to Estuarine/Marine Invertebrates 

A summary of acute and chronic estuarine/marine invertebrate data, including data 

published in the open literature, is provided below in Sections 4.1.4.1 through 4.1.4.5. 

4.1.4.1 Estuarine/Marine Invertebrates: Acute Exposure (Mortality) Studies 

The acute toxicity studies available to the Agency demonstrate that endosulfan can be 

classified as highly toxic to very highly toxic to estuarine/marine invertebrates, with 

LC50 values ranging from 0.04 to 790 μg a.i./L (see Appendix J). There was one study 

available that used a formulated end-use product and demonstrated that for the brown 

shrimp that formulated endosulfan can be classified as very highly toxic with an LC50 of 

0.24 μg a.i./L (MRID 1328). The most sensitive LC50 value of 0.04 μg a.i./L (MRID 

5005824) for pink shrimp (Penaeus dourarum) is considered acceptable for quantitative 

use to estimate acute risks to estuarine/marine invertebrates. 

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4.1.4.2 Estuarine/Marine Invertebrates: Acute Exposure (Mortality) Studies—Open 

Literature 

In addition to the aforementioned acute mortality studies with estuarine/marine 

invertebrates, an additional study was identified in the open literature which reported 

several LC50 values for mysids (Americamysis bahia; Schimmel 1981; ECOTOX 

reference # 3740). This study reported the results of an interlaboratory comparison of 

acute toxicity tests using estuarine animals. There were five acute LC50 values based on 

measured, flow-through tests ranging from 0.38 to 1.29 μg a.i./L (see Appendix J). 

While none of these values is lower than the LC50 for the pink shrimp listed above, their 

geometric mean (0.83 μg a.i./L) will be used to establish the acute to chronic toxicity 

ratio for estuarine/marine invertebrates used in the next section. 

4.1.4.3 Estuarine/Marine Invertebrates: Chronic Exposure (Growth/Reproduction) 

Studies 

No acceptable chronic toxicity data were available to the Agency for estuarine/marine 

invertebrates with the endosulfan TGAI; however, one study was identified from the 

open literature (McKenney 1982; ECOTOX reference #3736) that summarized an 

interlaboratory comparison of chronic toxicity tests using the mysid Americamysis bahia. 

Five tests were conducted under measured, flow-through conditions with reported 

NOAECs ranging from 0.14 to 0.52 μg a.i./L. The corresponding LOAECs were based 

primarily on survival (see Appendix J). The geometric mean of these five values is 0.27 

μg a.i./L. The study fulfills a data gap for a chronic test with a preferred estuarine/marine 

invertebrate. Although these tests are considered acceptable for quantitative use in this 

risk assessment, a mysid acute to chronic ratio (ACR = 3.1) was used to estimate a pink 

shrimp chronic NOAEC because it is the most acutely sensitive estuarine/marine 

invertebrate species (i.e., by approximately a factor of 10 compared to Americamysis 

bahia) and no chronic toxicity data for endosulfan are available for pink shrimp. The 

estimated chronic NOAEC value for the pink shrimp was calculated similarly to that 

demonstrated above for the common carp (except with the ACR from the mysid). 

Estimated pink shrimp NOAEC = (0.04 x 0.27)/0.83 = 0.013 μg a.i./L. 

This estimated NOAEC of 0.013 μg a.i./L for pink shrimp will be used to quantitatively 

estimate chronic risk to estuarine/marine invertebrates. 

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4.1.4.4 Estuarine/Marine Invertebrates: Open Literature Data 

No additional acceptable studies from the open literature were identified for 

esturarine/marine invertebrates that: establish more sensitive acute or chronic endpoints 

than the data above; filled critical data gaps; presented a toxicity profile for underrepresented taxa; or provided information on sub-lethal effects that could be clearly and 

reasonably linked to relevant assessment endpoints (i.e., survival, reproduction, and 

growth) at concentrations lower than the most sensitive endpoints used to quantitatively 

evaluate risk. 

4.1.4.5 Estuarine/Marine Invertebrates: Endosulfan Sulfate

A 28-d flow-through, measured chronic toxicity study of the effects of endosulfan sulfate 

was conducted with the mysid, Americamysis bahia (MRID 46781601). Endpoints 

measured included survival, growth (length and dry weight), and reproduction 

(offspring/female/day). The most sensitive endpoint from this study was dry weight of 

male mysids, with a NOAEC and LOAEC of 0.38 and 0.73 μg ai/L, respectively. This 

NOAEC is similar to those reported by McKenney et al 1982 (ECOTOX reference # 

3736) described above (0.14 to 0.52 μg a.i./L). This study is considered supplemental 

because raw data were not provided, terminal growth measurements were not conducted 

and a minor discrepancy was identified in the reported survival of control organisms. 

4.1.5 Toxicity to Aquatic-phase Amphibians—Open Literature

A number of studies involving amphibian toxicity testing and endosulfan were identified 

in the open literature and are summarized below. None of these studies provide reliable 

estimates of toxicity that may be used quantitatively in this risk assessment; however, 

they do provide some information regarding the hazard of endosulfan to amphibians. For 

a comprehensive consideration of all potential effects data and additional information for 

amphibians please refer to the detailed spreadsheet of the available ECOTOX open 

literature data that can be found in Appendix H. 

Bernabò, et al. (2008 ; ECOTOX reference # 103223) and Brunelli, et al. (2009) 

evaluated the effect of endosulfan (99% purity) on tadpoles of the common toad Bufo 

bufo. Four-day-old tadpoles were exposed for 96 hr in a static test. The 96 hr LC50 value 

based on nominal concentrations was 430 μg/L (Bernabò, et al. (2008). In a separate test, 

exposure to 200 μg/L endosulfan resulted in an apparent increase in mucus production by 

the gills, as well as inflammation of the gills. These changes occurred after only 24 hr and 

became more pronounced as the exposure continued (Bernabò, et al. 2008). The same 

group continued their work with endosulfan and this toad species looking for behavior 

and morphological differences, after much longer (43-53 days) exposure durations 

(Brunelli, et al. 2009). Three concentrations and a control were used. There were no 

statistically significant differences between the control and 10 μg/L for survival, the rate 

of deformity or the number of toads metamorphosed (into Gosner stage 46—complete tail 

resorption). However, there was 77% and 97% mortality at 50 and 100 μg/L, 

115
respectively. In addition, 100% of the surviving tadpoles exhibited various degrees of 

deformity and none of the survivors reach stage 46. 

Several papers evaluated the effect of endosulfan on tadpoles of Australian frogs, but all 

were unmeasured tests. Broomhall (2002; ECOTOX reference # 65732) exposed 

tadpoles of Litoria citropa to a single 0.8 μg/L nominal concentration of endosulfan 

(Thiodan) under two different temperature regimes, one more variable than the other over 

the 96 hr test. At ambient temperatures (ca. 20 C) the survival was 89% in the endosulfan 

treatment (100% in the control). Under a similar average temperature, but more variable, 

only 58% of the tadpoles survived, compared to 92% in the controls. After termination of 

the above test, all surviving tadpoles were transferred to clean water and held at 19 C for 

24 days. These tadpoles were then evaluated for their ability to avoid predation by 

odonates. The endosulfan treated animals were more vulnerable to predation, measured 

by a significant decrease in the number of minutes elapsed until capture. 

Broomhall and Shine (2003; ECOTOX reference # 71866) exposed tadpoles of the 

Australian treefrog Litoria freycineta to two different concentrations of endosulfan 

(source not given, but assume was same as Broomhall (2002)—Thiodan). There was no 

effect on survival after 96 hr exposure to 0.03 or 1.3 μg/L a.i. relative to the controls. 

However, exposed tadpoles grew more slowly than controls—although not statistically 

significant. And the survivors at the higher concentration were captured and consumed by 

odonate predators (dragon fly larvae) significantly sooner when tested 15 days after 

transfer to clean water. Broomhall (2004; ECOTOX reference #73400) completed 

another series of experiments similar to the above, using the same exposure 

concentrations with a different species, Limnodynastes peronii, with similar results. 

Canadian frogs were evaluated based on unmeasured concentrations. Green frog eggs and 

larvae (Rana clamitans) were exposed to two different scenarios using Thiodan 50WP 

(Harris, et al. 1998; ECOTOX reference #19300). In the first test series, Gosner stage 8 

embryos through to stage 25 tadpoles were continuously exposed to a treatment for 13 

days (two-thirds renewal of treatment solutions every second day). The 96 hr LC50 was 

greater than the highest concentration tested (11,750 μg/L a.i.); however, the 13 day 

LC50 was 15 μg a.i. /L—suggesting that the earlier embryonic stages were not as 

sensitive to endosulfan. Note, hatching occurred around day eight of the test. A second 

set of exposures in this study consisted of the same exposure for the first 4 days, then a 

period of 7.5 days in reference water, followed by a second 4-day exposure to the same 

concentrations. The 96 hr LC50 was again a greater than, and the 16 day LC50 was the 

same as that in the first test. The frequency of deformities at hatch also was calculated in 

the second test, resulting in an EC50 of 2,430 μg a.i./L. 

The toxicity of Thiodan 4EC (40% emulsified concentrate) was evaluated (Berrill et al. 

1998; ECOTOX reference # 19467) with newly hatched and two-week-old tadpoles of 

the wood frog (Rana sylvatica), the American toad (Bufo americanus), and the green frog 

(Rana clamitans). Embryos of the wood frog were also tested, but were not as sensitive 

as tadpoles; therefore embryos of the other two species were not tested. New hatched 

tadpoles of each species were exposed for 96 hr followed by a 10 day 

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recovery/observation period. Two-week of tadpoles were likewise exposed for 96 hr, and 

followed for and additional 7 day recovery period in clean water. Water concentrations of 

endosulfan were measured, but only after the first hour of the exposure period and the 

treatments were apparently not renewed. Exposure concentrations ranged from 32 to 364 

μg a.i. /L , depending on the life stage and species. There was essentially no mortality for 

either life stage for all three species during the first 96 hr; however, there was extensive 

postexposure mortality. Also, two-week old tadpoles were more sensitive than newly 

hatched tadpoles—no LC50s were calculated. 

Early stage tadpoles of Bufo melaanostictus, Limnonectes limnocharis and Microphyla 

ornata were exposed to a commercial end-use product of endosulfan (35EC) in 96-h 

acute toxicity tests (Dey and Gupta 2002) The authors used 10 animals per container and 

three containers per treatment. The animals were collected from the field and acclimated 

for 3 to 4 days. They did not describe the chambers or the volume of water used. The 

source of the water was dechlorinated tapwater. Control mortality also was not described. 

The 96-h LC50s were based on nominal concentrations and are 20, 1.3 and 0.16 μg/L, 

respectively, for the three species listed above. The relative sensitivity of M. ornate is 

likely due to its much smaller size. This was the likely explanation for the sensitivity of 

this species to the pesticide dichlorvos and the herbicide butachlor (Geng et al. 2005). 

Finally, there is a preprint available that evaluates the growth and survival of the northern 

leopard frog Rana pipiens tadpoles (Shenoy et al. inpress). They exposed four-day-old 

tadpoles to Endosulfan 3EC (33% a.i.) for seven weeks. Each individual was placed into 

a separate 1.5 L of exposure medium with the water changed every 3 days. There were 15 

individuals used for each treatment. Besides the controls, treatments were 0.2, 1 and 5 

μg/L of the active ingredient. Concentrations were not measured. Growth rate (length) 

was not affected in surviving tadpoles in any treatment relative to the controls. No LC50 

values were calculated; however, there was 100% mortality by day 12 and day 28 in the 5 

and 1 μg/L treatments, respectively. Based on the authors’ Figure 1 the control survival 

was approximately 80% at the end of the seven weeks and that in the 0.2 μg/L treatment 

approximately 40%. Although no 96 hr data were presented, the figure suggests that there 

was little of no mortality during the first 4 days of the experiment. Although not 

calculated by the authors the above data suggest that the chronic LC50 would be close to 

0.2 μg/L. 

4.1.6 Toxicity to Aquatic Plants 

For the purposes of this assessment, plant acute EC50 values, rather than NOAEC values, 

are to be used to assess the potential for effects to the aquatic-phase CRLF, CTS, SFGS, 

BCB, VELB, SMHM and SJKF via indirect effects on habitat, cover, food supply, and/or 

primary productivity (i.e., aquatic plant community), because there are no obligate 

relationships between the assessed species and any aquatic plant species. There were no 

acceptable or supplemental data on the toxicity of endosulfan to aquatic vascular or nonvascular plants submitted to the Agency. There were several references available from 

117
the open literature: however, only one of these could be considered as following methods 

suitable to be considered acceptable (DeLorenzo et al 2002; ECOTOX reference # 

65915). This study reported the 96 hr EC50 for the green alga Pseudokirchneriella 

subcapitatum (formerly Selenastrum capricoratum) using a standard ASTM protocol. 

This species is one of the OPP preferred species. The EC50 is 428 μg/L based on nominal 

concentrations of technical grade endosulfan (98.6% a.i.). There were no acceptable data 

identified in the open literature for aquatic vascular plants. 

4.1.7 Freshwater Field/Mesocosm Studies 

There were no acceptable data submitted to the Agency on freshwater field or mesocosm 

studies with endosulfan. There were; however, two studies identified from the open 

literature (Hose et al. 2002; ECOTOX 62267; Hose et al. 2003; ECOTOX 72555). Both 

studies used the same artificial stream experimental design using flow-though river water. 

The flow was stopped during the exposure phase of the experiments. In the first study the 

endosulfan (96% purity) was applied as contaminated sediment slurries. The stream flow 

was blocked for 12 h after the initial exposure, then flow was restored and the 

macroinvertebrate community sampled after an additional 96 h. There was no effect on 

the structure of the macroinvertebrate community at the highest concentration measured 

(6.14 μg/L—interstitial waters of the gravel substrate). The authors state that laboratory 

studies have shown that 12-h exposures to this concentration (without sediment) are 

toxic. However, they further conclude that the presence of fine sediment in the interstitial 

water is likely to reduce the toxicity of endosulfan, presumably by binding the pesticide 

and reducing its bioavailability. Although there were no effects on the community 

structure due to endosulfan exposure, there were differences in the number of individuals 

in the downstream drift of the mesocosms for some of the taxa. For example, the mayfly 

Jappa kutera had increased numbers in the high-dose streams relative to the controls, 

possibly as an avoidance mechanism. 

These same authors conducted a similar study, but with aqueous endosulfan (Hose, et al 

2003). Two separate experiments were carried out; a 12-h and a 48-h exposure 

(endosulfan was measured in the streams for each experiment). The first was a 12-h 

exposure, followed by and additional 96-h of observation. During the 12-h exposure the 

stream flow was stopped. Fifty taxa were recorded in the benthic assemblages during this 

first experiment. The data were analyzed using principle response curves. The 

assemblages at 8.69 μg/L and lower were not statistically different from the controls; 

however, the assemblages at the highest concentration tested (48.87 μg/L) were different 

from the controls—largely due to decreases in the abundance of several key taxa. In the 

48-h study endosulfan was added every 6 h for 48 h. During each 6-h exposure the stream 

flow was stopped. The water was renewed at the beginning of each 6-h exposure. The 

assemblages at 1.00 μg/L were not statistically different from the controls; however, the 

assemblages at the higher concentration tested (6.87 and 30.70 μg/L) were different from 

the controls—as above this was largely due to decreases in the abundance of several key 

taxa. In this latter experiment the authors noted the appearance of blooms of the 

filamentous alga Spyrogyra sp. in the 6.87 and 30.70 μg/L treatments after 13 d. No algae 

were noticed prior to the start of the experiment and none were present in the controls or 

118
1.00 μg/L treatments on day 13. The authors suggested that this was likely associated 

with an apparent reduction in the number of tadpoles at these higher endosulfan 

concentrations—however, the numbers of tadpoles were not quantified. 

4.2 Toxicity of Endosulfan to Terrestrial Organisms 

Table 4.3 summarizes the most sensitive terrestrial toxicity endpoints, based on an 

evaluation of both the submitted studies and the open literature. A brief summary of 

submitted and open literature data considered relevant to this ecological risk assessment 

is presented below. 

Table 4.3 Terrestrial Toxicity Profile for Endosulfan 

Assessment 

Endpoint 

Purity 

(% a.i.) 

Surrogate 

Species 

Toxicity Value Used 

for Quantitative 

Risk Estimates 

(a.i.) 

Effects Reference/Acceptability 

Birds, Terrestrial-phase Amphibians and Reptilesa

Survival 97.2 Mallard duck 

(Anas platyrhynchos) LD50 = 28 mg/kg Mortality MRID 136998/Acceptable 

Survival 96 Northern bobwhite 

quail LC50 = 805 ppm Mortality MRID 22923/Acceptable 

Reproduction and Growth 96 Mallard duck 

(Anas platyrhynchos)

NOAEC = 30 mg/kg-diet

LOAEC = 64 mg/kg-diet 

Eggs laid, 

eggs set, embryo 

viability 

MRID 40335001/Acceptable 

Mammals 

Survival Rat (Rattus norvegicus) LD50 = 10 mg/kg (female)

LD50 = 40 mg/kg (male) Mortality MRID 00038307/Acceptable 

Reproduction and Growth Rat (Rattus norvegicus) NOAEC = 15 mg/kg diet 

LOAEC = 75 mg/kg diet 

Decrease body 

weight MRID 00148264/Acceptable 

Terrestrial Invertebrates 

Survival 100 Beet webworm 

(Pyrausta sticticalis) 

1 d 

LD50 = 0.15 ug a.i./g Mortality Leonova and Slunko 2004/ECOTOX 100430

Terrestrial Plants 

Survival and Growth No acceptable data identified 

a

 Birds are used as a surrogate for terrestrial-phase amphibians and reptiles because no acceptable data for 

quantitative use currently exist for endosulfan toxicity to these taxonomic groups. 

Acute toxicity to terrestrial animals is categorized using the classification system shown 

in Table 4.4 (U.S. EPA, 2004). Toxicity categories for terrestrial plants have not been 

defined. 

Table 4.4. Categories of Acute Toxicity for Avian and Mammalian Studies 

Toxicity Category Oral LD50 Dietary LC50

Very highly toxic < 10 mg/kg < 50 ppm 

Highly toxic 10 - 50 mg/kg 50 - 500 ppm 

Moderately toxic 51 - 500 mg/kg 501 - 1000 ppm 

Slightly toxic 501 - 2000 mg/kg 1001 - 5000 ppm 

Practically non-toxic > 2000 mg/kg > 5000 ppm 

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4.2.1 Toxicity to Birds, Reptiles, and Terrestrial-Phase Amphibians 

As specified in the Overview Document, the Agency uses birds as a surrogate for reptiles 

and terrestrial-phase amphibians when toxicity data for each specific taxon are not 

available (U.S. EPA, 2004). A summary of acute and chronic bird data, including data 

published in the open literature is provided below in Sections 4.2.1.1 through 4.2.1.4. 

4.2.1.1 Birds: Acute Exposure (Mortality) Studies 

The results of the acute oral toxicity studies (MRID 137189, 136998, and 160000) 

available for endosulfan (see Table 4.5 and Appendix K) indicate that endosulfan can be 

classified as moderately toxic to highly toxic to avian species on an acute oral basis with 

LD50 values for Northern bobwhite quail (Colinus virginianus), Mallard duck (Anas 

platyrhynchos), and Ring-necked pheasant (Phasianus colchicus) ranging from 28 to > 

320 mg a.i./kg-body weight. Based on all of the acute oral toxicity data, mallard ducks 

were the most acutely sensitive with LD50 values ranging from 28 to 45 mg a.i./kg-body 

weight. The LD50 value of 28 mg a.i./kg-body weight will be used in the quantitative 

estimate of risk. 

The results of the single sub-acute dietary toxicity study (MRID 22923) available for 

endosulfan indicate that it can be classified as slightly toxic to moderately toxic with 

LC50 values for Northern bobwhite quail (Colinus virginianus), Mallard duck (Anas 

platyrhynchos), Ring-necked pheasant (Phasianus colchicus), and Japanese quail 

(Coturnix japonica) ranging from 805 to 1275 mg a.i./kg-diet. Northern bobwhite quail 

was the species tested with the lowest value. The LC50 value of 805 mg a.i./kg-diet will 

be used in the quantitative estimate of risk. 

Table 4.5 Comparison of Acute Toxicity of Endosulfan and Endosulfan Sulfate To Birds. 

Acute Oral Toxicity Acute Dietary Toxicity 

Endosulfan Endosulfan Sulfate Endosulfan Endosulfan Sulfate 

Species 

LD50 

(ppm) 

Toxicity 

Category 

(MRID) 

LD50 

(ppm) 

Toxicity 

Category 

(MRID) 

5-day 

LC50

(ppm) 

Toxicity 

Category 

(MRID) 

5-day 

LC50

(ppm) 

Toxicity 

Category 

(MRID) 

Northern bobwhite 

quail 

Colinus virginianus

-- -- 44 

highly 

toxic 

(464305-

01) 

805 

moderately 

toxic 

(22923) 

>3528 (46430502)

(a)

Mallard duck 

Anas platyrhynchos

28 

highly 

toxic 

(136998) 

--- 

--- 

1053 

slightly toxic 

(22923) 1642 

slightly 

toxic 

(463826-

01) 

(a) Study classified as supplemental. 

4.2.1.2 Birds: Chronic Exposure (Growth, Reproduction) Studies 

Three avian reproduction studies with mallard ducks (Anas platyrhynchos) and Northern 

bobwhite quail (Colinus virginianus) have been submitted to the Agency for endosulfan 

(MRID 146843, 40335001, and 40335002). Only one test established both NOAEC and 

LOAEC values (see Appendix K). This test was a 22 week study with mallard ducks 

120
(Anas platyrhynchos). The NOAEC was 30 ppm and the LOAEC was 64 ppm (using 

measured dietary concentrations), based on number of eggs laid (53% of control) and 

embryo viability (52% of control) (MRID 40335001). The other mallard duck test had an 

NOAEC < 30 ppm (MRID 146843) and was not used because the measured dietary 

concentrations were not presented. The bobwhite quail test showed an NOAEC = 64 ppm 

and an LOAEC = 134 ppm. The results of these studies indicate that endosulfan may 

have adverse effects on avian reproduction at higher levels of exposure, and the most 

sensitive NOAEC of 30 ppm (mg a.i./kg-diet) will be used to quantitatively estimate the 

risks to birds (and thus, terrestrial-phase amphibians and reptiles) resulting from chronic 

exposure to endosulfan.

4.2.1.3 Birds: Open literature Studies 

No additional acceptable studies from the open literature were identified for birds (or 

terrestrial-phase amphibians or reptiles) that: established more sensitive acute or chronic 

endpoints than existing data; filled critical data gaps; presented a toxicity profile for 

under-represented taxa (e.g., toxicity data for amphibians or reptiles); or provided 

information on sub-lethal effects that could be clearly and reasonably linked to relevant 

assessment endpoints (i.e., survival, reproduction, and growth) at concentrations lower 

than the most sensitive endpoints used to quantitatively evaluate risk. 

4.2.1.4 Birds: Endosulfan Sulfate 

Based on the comparison of parent endosulfan TGAI with the endosulfan sulfate 

degradate using acute dietary LC50s for bobwhite quail and mallard duck, endosulfan 

sulfate appears about equal in toxicity to waterfowl (mallard) and at least a factor of 4 

less toxic to game birds (quail; Table 4.5). No chronic avian studies were identified for 

endosulfan sulfate that were considered acceptable for quantitative use in this risk 

assessment. 

4.2.2 Toxicity to Mammals 

Typically, mammalian toxicity data from the Agency’s Health Effects Division (HED) 

are used to approximate toxicity to mammals. However, wild mammals toxicity tests 

may be required on a case-by-case basis, depending on the results of the lower tier studies 

such as acute and sub-acute testing, intended use pattern, and pertinent environmental 

fate characteristics. No studies evaluating toxicity to wild mammal species have been 

submitted by the registrants for endosulfan. A summary of acute and chronic mammalian 

data, including data published in the open literature, is provided below in Sections 4.2.2.1 

through 4.2.1.3. 

4.2.2.1 Mammals: Acute Exposure (Mortality) Studies 

The acute oral LD50 values for the laboratory rat (Rattus norvegicus) were 10 and 40 

mg/kg for females and males, respectively (MRID 38307). Since acute toxicity estimates 

fall in the range of 10 to 50 mg/kg, endosulfan is classified as highly toxic on an acute 

121
exposure basis (see Appendix K for more detail). Additional data from the open 

literature support the conclusion that female rats are more sensitive to endosulfan than 

males (Gupta 1976; ECOTOX 103467). LD50s for males were greater than those for 

females by about a factor of 2. The LD50s from the submitted data are still the lowest 

numbers. Gupta (1976) also presented LC50 data for mice (Mus musculus). Unlike rats, 

there were no differences in LD50s between male and female mice. However, mice were 

more sensitive than rats in there study. Values ranged from 6.5 to 13.5 mg/kg body 

weight for mice (and 22.1 to 89.4 for rats), depending on the vehicle used to administer 

the endosulfan (see Appendix K). The acute oral LD50 value 10 and 40 mg/kg for 

females and male rats, respective will be used to estimate the risk to mammals from acute 

exposure to endosulfan. The lower value for the mouse was not used because the 

exposure was via intraperitoneal injection rather than through diet. 

4.2.2.2 Mammals: Chronic Exposure (Growth, Reproduction) Studies 

A two-generation rate reproduction study measured the NOAEC and LOAEL as 15 and 

75 ppm, respectively (MRID 148264), with decreased body weight as the most sensitive 

endpoint (see Appendix K for more detail). An additional study from the open literature 

supports the conclusion from Gupta (1976; ECOTOX 103467) that mice are more 

sensitive to endosulfan than rats. Hack et al. (1995; ECOTOX 103384) exposed groups of 

rats and mice for 24 months to various concentrations of endosulfan in their diet. These 

authors concluded that the NOAEC and LOAEC for rats are 15 and 75 ppm, 

respectively—based on final body weight for both males and females (there was no effect 

of endosulfan on rat survival). There was no effect of dietary endosulfan on the growth of 

either male or female mice; however the authors’ data would list the NOAEC and 

LOAEL as 6 and 18 ppm, respectively—based on survival of females. 

Two other open literature studies using oral intubation showed that spermatogenesis in 

rats is reduced significantly at endosulfan doses as low as 2.5 mg/kg body weight after 70 

days of exposure (Sinha et al. 1995; ECOTOX 103592), and that fetal survival and 

development can be impaired at concentrations as low as 1.0 mg/kg body weight fed to 

sexually mature female rats on days 6 to 20 of their pregnancies (Singh et al. 2007; 

ECOTOX 103238). 

4.2.2.3 Mammals: Endosulfan Sulfate 

No acute or chronic mammalian studies were identified for endosulfan sulfate that were 

considered acceptable for quantitative use in this risk assessment. 

4.2.3 Toxicity to Terrestrial Invertebrates 

A summary of terrestrial invertebrate data, including data published in the open literature, 

is provided below in Sections 4.2.3.1 and 4.2.3.2. 

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4.2.3.1 Terrestrial Invertebrates: Acute Exposure (Mortality) Studies 

The only Agency guideline acute study for terrestrial invertebrates is for the honey bee 

(Apis mellifera). A total of four honey bee studies (see Appendix K) are available that 

include acute contact, acute oral and acute contact with treated foliage with TGAI and 

formulated end use product (MRIDs 1999, 05004151, 05008936, and 05012881). The 

acute contact LD50 values are 4.5 and 7.1 μg a.i./bee, both with TGAI. The sole acute 

oral LD50 is 6.9 μg a.i./bee, also with TGAI. Two studies reported exposures based on 

foliar residues. Both studies observed little to no mortality at the highest concentrations 

tested, making the LC50s > 7.1 and >1.10 lb/acre. The acute contact LD50 of 4.5 μg 

a.i./bee is multiplied by 1 bee/0.128g, which is based on the weight of an adult honey 

bee, in order to estimate the toxicity in terms of ppm (μg a.i./g of bee). 

No additional data on the effects of endosulfan to non-target terrestrial invertebrates was 

submitted to the Agency. 

4.2.3.2 Terrestrial Invertebrates: Open Literature Studies 

The ECOTOX database was examined for toxicity data using non-target species with 

endpoints expressed in terms similar to those for the standard test with honey bees. The 

stingless bee and the Indian honey bee were both more sensitive than the standard honey 

bee in comparable tests based on per bee exposure (see Appendix K). However, both the 

stingless bee and the Indian honey bee are smaller than the standard honey bee so the 

conversion used for the honey bee in the last section (1/0.128 g/bee) should not be used. 

Data from the test using the stingless bee Trigona spinipes (Macieira and HebllingBeraldo 1989; ECOTOX reference #51755) is the lowest LC50 (0.21 μg a.i/bee). Three 

different foliar residue studies using three different species of parasitic wasps also are 

listed in Appendix K. Significant mortality occurred at the reported application rates 

(0.50 to 1.50 lb/a). 

Several studies listed in the ECOTOX database used earthworms as the test organism. 

Mosleh et al (2003; ECOTOX reference # 86741; note this is the same data that the 

authors also report in Mosleh et al. 2002; ECOTOX reference #87129) report LC50s 

using a commercial end-use product mixed with natural soil for the earthworm Lumbricus 

terrestris. The LC50s declined as the duration of exposure increased, and ranged from 

3.36 to 12.29 mg endosulfan/kg soil. 

There are numerous studies available from the open literature relative to targeted insect 

studies. The data from studies which calculated contact, oral or foliar residue acute 

LD50s are presented in Appendix K. Most of these data are larvae of several moth 

species. Two studies (Leonova and Slynko 1996, 2004; ECOTOX references #103049 

and 100430) showed that at least for the cotton bollworm and the beet webworm adult 

moths more sensitive that the larvae of these species. As expected, overall these studies 

show that applications of formulated endosulfan are likely to reduce the numbers and 

possibly eliminate populations of arthropods. The lowest acute contact LD50 or 0.15 

μg/g (ppm) for the adult moth of the beet webworm (Pyrasta sticticalis) will be used to 

123
estimate the risk to terrestrial invertebrates from acute exposure to endosulfan. 

4.2.4 Toxicity to Terrestrial Plants 

No data have been submitted to the Agency to evaluate the effects of endosulfan on 

terrestrial plants because historically, terrestrial plant toxicity studies and associated risk 

analysis of plants were not required for registration of a pesticide unless it met specific 

use and pesticide classification criteria which would trigger potential concerns. In 

addition to the lack of registrant-submitted data, no studies demonstrating significant 

adverse effects of endosulfan to any terrestrial plant have been identified in the open 

literature. Although a number of studies involving terrestrial plants and endosulfan were 

identified in the open literature, none of these studies provide reliable estimates of 

toxicity that may be used in this risk assessment. Reasons that these studies were deemed 

unacceptable for use were primarily because these studies were associated with efficacy 

determinations in which observations were confounded by the presence of an insect pest 

complex. As such, plants in these tests generally did not demonstrate any adverse effects 

at any test levels, but did not test up to the maximum allowable rate. For a comprehensive 

consideration of all potential effects data and additional information for terrestrial plants 

please refer to the detailed spreadsheet of the available ECOTOX open literature data that 

can be found in Appendix H. 

4.3 Use of Probit Slope Response Relationship to Provide Information on the 

Endangered Species Levels of Concern 

The Agency uses the probit dose response relationship as a tool for providing additional 

information on the potential for acute direct effects to individual listed species and 

aquatic animals that may indirectly affect the listed species of concern (U.S. EPA, 2004). 

As part of the risk characterization, an interpretation of acute RQs for listed species is 

discussed. This interpretation is presented in terms of the chance of an individual event 

(i.e., mortality or immobilization) should exposure at the EEC actually occur for a species 

with sensitivity to endosulfan on par with the acute toxicity endpoint selected for RQ 

calculation. To accomplish this interpretation, the Agency uses the slope of the dose 

response relationship available from the toxicity study used to establish the acute toxicity 

measures of effect for each taxonomic group that is relevant to this assessment. The 

individual effects probability associated with the acute RQ is based on the mean estimate 

of the slope and an assumption of a probit dose response relationship. In addition to a 

single effects probability estimate based on the mean, upper and lower estimates of the 

effects probability are also provided to account for variance in the slope, if available. 

Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1 

(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP, 

Environmental Fate and Effects Division (June 22, 2004). The model allows for such 

calculations by entering the mean slope estimate (and the 95% confidence bounds of that 

124
estimate) as the slope parameter for the spreadsheet. In addition, the acute RQ is entered 

as the desired threshold. 

4.4 Ecological Incident Summary 

A review of the Ecological Incident Information System (EIIS) database for ecological 

incidents involving endosulfan was completed on March 25, 2009. This database consists 

of exposure incident reports submitted to the EPA from 1994 to present. A summary of 

ecological incidents involving endosulfan are listed in Table L.1 in Appendix L. This 

table is divided into incidents involving aquatic organisms only, terrestrial organisms 

only, and both aquatic and terrestrial organisms. Within each of these sections of the 

table, incidents are ordered by date beginning with the earliest incident. 

Incidents listed in EIIS are categorized by the likelihood that a particular pesticide is 

associated with that particular incident. These classifications include highly probable, 

probable, possible, unlikely or unrelated. “Highly probable” incidents usually require 

carcass residues or clear circumstances regarding the exposure. “Probable” incidents 

include those where residue information was not available or circumstances were less 

clear than those for “highly probable.” “Possible” incidents occur when multiple 

chemicals may have been involved and the contribution of an individual chemical is not 

obvious. An “unlikely” incident classification is given when a given chemical is 

considered nontoxic to the type of organism involved or the chemical was analyzed and 

not detected in samples. The “unrelated” category is used for incidents confirmed not to 

involve pesticides. No unrelated incidents were listed for endosulfan. 

The number of reports listed in the EIIS database is believed to be only a fraction of the 

total incidents involving organismal mortality and damage caused by pesticides. Few 

resources are assigned to incident reporting. Reporting by states is only voluntary, and 

individuals discovering incidents may not be informed on the procedure of reporting 

these occurrences. Additionally, much of the database is generated from registrantsubmitted incident reports. Registrants are legally required to provide detailed reports of 

only “major” ecological incidents involving pesticides, while “minor” incidents are 

reported aggregately. Because of these logistical difficulties, EIIS is most likely a 

minimal representation of all pesticide-related ecological incidents. 

The EIIS database contained 83 incident reports involving endosulfan. Most of the 

incidents involve aquatic ecosystems (75 or 90% of the total incidents). Seven incident 

reports involve terrestrial ecosystems and one involves a combined aquatic/terrestrial 

ecosystem. California was most represented among all 50 states (26 reports) followed by 

North Carolina (9), Louisiana and South Carolina (5 each) and Washington State (4). 

Additional characterization of these incidents is provided below. 

Incident Certainty and Legality

Of the 83 incidents reported, 23 (28%) are categorized as ‘highly probable’ and 40 (48%) 

are categorized as ‘probable.’ Collectively the ‘highly probable’ and ‘probable’ 

125
categories represent 76% of the reported incidents. Regarding the legal status, the 

‘unknown’ and ‘misuse accidental’ represent the largest legality categories with 36% and 

35% of the incident reports, respectively. Approximately 25% of the reports consist of 

registered uses. Lastly, only three of the incident reports involved intentional misuse. 

Of the 15 ‘highly probable’ and ‘probable’ incident reports that involved only ‘registered 

uses,’ most described pesticide runoff following periods of heavy rainfall as the likely 

event that led to the reported incident. The majority of the ‘highly probable’ and 

‘probable’ incidents classified as ‘accidental misuse’ involved aerial application too close 

to bodies of water as stipulated by the label, spills and equipment washing. 

Aquatic Incidents

The vast majority of the aquatic incident reports involved mortality to fish (67), a highly 

sensitive taxonomic group. Only three incidents reportedly involved aquatic 

invertebrates, but the likelihood of observing impacts to aquatic invertebrates is low 

compared to fish. Of the 67 aquatic incidents involving fish, 53 (80%) are classified as 

either ‘highly probable’ or ‘probable’ in the context of endosulfan use. A wide variety of 

fresh and estuarine species were reportedly affected (e.g., carp, catfish, largemouth bass, 

shad, menhaden, mullet, spot, bluegill sunfish, gar and trout). 

Terrestrial Incidents

Of the seven terrestrial incidents, none are classified as ‘highly probable’ and two are 

classified as ‘probable.’ The two ‘probable’ incidents involve birds (blue jay, crow, owl), 

mammals (squirrel, opossum, red fox) and an amphibian (unidentified frog). 

Plant Incidents

Only one reported incident involved plants and this was classified as ‘possible,’ but the 

plant species was not identified. 

126
5 Risk Characterization 

Risk characterization is the integration of the exposure and effects characterizations. 

Risk characterization is used to determine the potential for direct and/or indirect effects to 

the CRLF, CTS, SFGS, SMHM, SJKF, BCB, and VELB or for modification to its 

designated critical habitat from the use of endosulfan in CA. The risk characterization 

provides an estimation (Section 5.1) and a description (Section 5.2) of the likelihood of 

adverse effects; articulates risk assessment assumptions, limitations, and uncertainties; 

and synthesizes an overall conclusion regarding the likelihood of adverse effects to the 

CRLF and other SFB species or their designated critical habitat (i.e., “no effect,” “likely 

to adversely affect,” or “may affect, but not likely to adversely affect”). 

5.1 Risk Estimation 

Risk is estimated by calculating the ratio of exposure to toxicity. This ratio is the risk 

quotient (RQ), which is then compared to pre-established acute and chronic levels of 

concern (LOCs) for each category evaluated (Appendix D). For acute exposures to the 

aquatic animals, as well as terrestrial invertebrates, the LOC is 0.05. For acute exposures 

to the birds (and, thus, reptiles and terrestrial-phase amphibians) and mammals, the LOC 

is 0.1. The LOC for chronic exposures to animals, as well as acute exposures to plants is 

1.0. 

Acute and chronic risks to aquatic organisms are estimated by calculating the ratio of 

exposure to toxicity using 1-in-10 year EECs, based on the label-recommended 

endosulfan usage scenarios, summarized in Table 3.5 and the appropriate aquatic toxicity 

endpoint from Table 4.1. As described in Section 2.10.1 (Problem Formulation), aquatic 

exposures were modeled separately for the parent isomers (ά and β) and the primary 

degradate of concern (endosulfan sulfate). The resulting daily concentrations were then 

summed to form a 30-year time series for total endosulfan (sum of ά, β and endosulfan 

sulfate). Due to similar acute toxicity and structure of the TGAI and endosulfan sulfate, 

modeled or measured environmental exposures of total endosulfan (sum of ά, β and 

endosulfan sulfate) were compared with toxicity data for the TGAI. For sediment-borne 

exposures, toxicity data were available only for endosulfan sulfate, and thus, comparisons 

of total endosulfan EECs were made to toxicity estimates for endosulfan sulfate.

Acute and chronic risks to terrestrial animals are estimated based on exposures resulting 

from applications of endosulfan (Table 3.23) and the appropriate toxicity endpoint from 

Table 4.3. Exposures were not derived for terrestrial plants, as described in Section 3.4. 

127
5.1.1 Exposures in the Aquatic Habitat 

5.1.1.1 Freshwater Fish and Aquatic-phase Amphibians 

Acute risk to freshwater fish and aquatic-phase amphibians, and the potential for direct 

effects to CRLF and CTS specifically, is based on peak EECs in the standard 

PRZM/EXAMS pond and the lowest acute toxicity value for freshwater fish. Currently 

registered agricultural uses of endosulfan within California are listed in Table 3.1. Based 

on freshwater fish toxicity data (LC50 value of 0.1 μg a.i./L for common carp) and 

modeled aquatic peak EECs for various use scenarios used to represent all of the 

agricultural uses of endosulfan in CA, all acute RQs for freshwater fish range from 7.2 

(eggplant) to 58.8 (lettuce and brussels sprouts); therefore, the entire set of 20 modeled 

scenarios used to represent all of the agricultural uses of endosulfan in CA, resulted in an 

exceedance of the Agency’s acute listed species LOC (RQ>0.05)(see Table 5.1). 

Chronic risk to freshwater fish and aquatic-phase amphibians, and the potential for direct 

effects to CRLF specifically, is based on 60-day EECs and the lowest chronic toxicity 

value for freshwater fish. However, in the case of endosulfan, the fathead minnow acute 

to chronic ratio (ACR=4.3) was used to estimate a common carp chronic toxicity 

NOAEC value of 0.023 μg a.i./L because it is the most acutely sensitive freshwater fish 

species and no chronic toxicity data are available for it. Based on 60-day EECs for 

various use scenarios used to represent all of the agricultural uses of endosulfan in CA, 

and the estimated NOAEC of 0.023 μg a.i./L, chronic RQs for freshwater fish range from 

5.7 (eggplant) to 80.6 (lettuce and brussels sprouts. All 20 of the modeled scenarios used 

to represent all of the agricultural uses of endosulfan in CA resulted in an exceedance of 

the Agency’s chronic risk LOC (RQ>1) for freshwater fish (see Table 5.1). 

Based on exceedances of the Agency’s acute listed species LOC (RQ>0.05) for the entire 

set of 20 modeled scenarios used to represent all of the agricultural uses of endosulfan in 

CA, and exceedances of the Agency’s chronic risk LOC (RQ>1) for all 20 of the modeled 

scenarios, endosulfan does have the potential to directly affect the CRLF and CTS. 

Additionally, since the acute and chronic RQs are exceeded, there is a potential for 

indirect effects to those listed species that rely on freshwater fish (and/or aquatic-phase 

amphibians) during at least some portion of their life-cycle (i.e., CRLF, SFGS, and CTS). 

Table 5.1 Acute and Chronic RQs for freshwater fish based on EECs for use 

categories used to represent all endosulfan uses in CA. 

Use Category(1) Run 

No. 

Peak 

EEC 

(μg/L) 

60-

day 

EEC 

(μg/L) 

Acute 

RQ (1)

Chronic 

RQ(1)

Almonds, Hazelnuts & Walnuts 1 3.35 0.62 33.50 26.83 

Citrus 1 3.35 0.44 33.50 19.30 

Broccoli, Cabbage & Cauliflower 1 4.81 1.76 48.10 76.39 

Collards, Kale & Mustard Green 2 1.67 0.50 16.70 21.78 

Sweet corn for fresh market only 1 2.88 0.77 28.80 33.65 

128
Table 5.1 Acute and Chronic RQs for freshwater fish based on EECs for use 

categories used to represent all endosulfan uses in CA. 

Use Category(1) Run 

No. 

Peak 

EEC 

(μg/L) 

60-

day 

EEC 

(μg/L) 

Acute 

RQ (1)

Chronic 

RQ(1)

Cotton (ground) 2 1.24 0.52 12.40 22.65 

Cotton (aerial) 3 1.56 0.59 15.60 25.78 

All fruit trees 1 3.40 0.53 34.00 23.13 

Lettuce & Brussels Sprouts 1 5.88 1.85 58.80 80.61 

Cucurbits 1 1.55 0.61 15.50 26.65 

Eggplant 3 0.72 0.13 7.20 5.70 

Ornamentals or Shade Trees (Southern Coast) 1 3.43 1.00 34.30 43.65 

Ornamentals or Shade Trees (Northern Central 

coast) 1 Add 4.38 1.13 43.80 49.13 

Potato 1 1.89 0.49 18.90 21.39 

Potato (Northern Central coast) 1 Add 2.63 0.56 26.30 24.39 

Sweet Potato 3 1.18 0.36 11.80 15.57 

Beans & Peas (dry) & Pepper 1 2.00 0.51 20.00 22.09 

Carrot & Celery 2 1.72 0.54 17.20 23.39 

Strawberry 1 3.64 1.11 36.40 48.17 

Tomato 1 1.79 0.45 17.90 19.57 

 (1) RQ values in bold indicate exceedence of listed species acute LOC (0.05) and chronic LOC (1.0). Acute RQs were 

calculated based on the peak EEC divided by the LC50 value of 0.1 μg/L for the most sensitive freshwater fish (common 

carp, Cyprinus carpio). Chronic RQs were based on the 60 day average EEC divided by the estimated chronic NOAEC for 

common carp of 0.023 μg/L. 

5.1.1.2 Freshwater Invertebrates 

Acute risk to freshwater invertebrates is based on peak EECs in the standard 

PRZM/EXAMS pond and the lowest acute toxicity value for freshwater invertebrates. 

Based on freshwater invertebrate toxicity data (EC50 value of 0.6 μg a.i./L for mayflies) 

and modeled aquatic peak EECs for various use scenarios used to represent all of the 

agricultural uses of endosulfan in CA, all acute RQs for freshwater invertebrates range 

from 1.20 (eggplant) to 8.02 (broccoli, cabbage, and cauliflower). Therefore, the entire 

set of 20 modeled scenarios used to represent all of the agricultural uses of endosulfan in 

CA, resulted in an exceedance of the Agency’s acute listed species LOC (RQ>0.05)(see 

Table 5.2). 

Chronic risk is based on 21-day EECs and the lowest chronic toxicity value for 

freshwater invertebrates. However, in the case of endosulfan, waterflea acute to chronic 

ratio (ACR=61.5) was used to estimate a mayfly chronic toxicity NOAEC value of 0.01 

μg a.i./L because it is the most acutely sensitive freshwater invertebrate species and no 

chronic toxicity data are available for it. Based on 21-day EECs for various use scenarios 

used to represent all of the agricultural uses of endosulfan in CA, and the estimated 

NOAEC of 0.01 μg a.i./L, all chronic RQs for freshwater invertebrates range from 23.7 

(eggplant) to 260.3 (broccoli, cabbage, and cauliflower); therefore, the entire set of 20 

129
modeled scenarios used to represent all of the agricultural uses of endosulfan in CA, 

resulted in an exceedance of the Agency’s chronic risk LOC (RQ>1) for freshwater 

invertebrates (see Table 5.2). 

Based on exceedances of the Agency’s acute listed species LOC (RQ>0.05) and chronic 

risk LOC (RQ>1) for the entire set of 20 modeled scenarios used to represent all of the 

agricultural uses of endosulfan in CA, there is a potential for direct effects on the CRLF 

and indirect effects CRLF, SFGS, and CTS, the listed species that rely on freshwater 

invertebrates during at least some portion of their life-cycle. 

Table 5.2 Acute and Chronic RQs for freshwater invertebrates based on EECs for use categories 

used to represent all endosulfan uses in CA. 

Use Category(1) Run Acu

No. 

Peak 

EEC 

(μg/L) 

21-day 

EEC 

(μg/L) 

te 

RQ (1)

Chronic 

RQ(1)

Almonds, Hazelnuts & Walnuts 1 3.35 1.03 5.58 102.60 

Citrus 1 3.35 0.90 5.58 90.00 

Broccoli, Cabbage & Cauliflower 1 4.81 2.60 8.02 260.30 

Collards, Kale & Mustard Green 2 1.67 0.78 2.78 77.50 

Sweet corn for fresh market only 1 2.88 1.14 4.80 113.70 

Cotton (ground) 2 1.24 0.60 2.07 59.60 

Cotton (aerial) 3 1.56 0.82 2.60 82.40 

All fruit trees 1 3.4 1.01 5.67 101.30 

Lettuce & Brussels Sprouts 1 5.88 2.58 9.80 257.50 

Cucurbits 1 1.55 0.82 2.58 81.50 

Eggplant 3 0.72 0.24 1.20 23.70 

Ornamentals or Shade Trees (Southern Coast) 1 3.43 1.36 5.72 135.70 

Ornamentals or Shade Trees (Northern Central 

coast) 1 Add 4.38 1.73 7.30 172.80 

Potato 1 1.89 0.77 3.15 77.00 

Potato (Northern Central coast) 1 Add 2.63 1.01 4.38 101.10 

Sweet Potato 3 1.18 0.62 1.97 62.20 

Beans & Peas (dry) & Pepper 1 2 0.85 3.33 85.10 

Carrot & Celery 2 1.72 0.74 2.87 73.50 

Strawberry 1 3.64 1.71 6.07 171.40 

Tomato 1 1.79 0.81 2.98 80.80 

 (1) RQ values in bold indicate exceedence of listed species acute LOC (0.05) and chronic LOC (1.0). Acute RQs were 

calculated based on the peak EEC divided by the LC50 value of 0.6 μg/L for the most sensitive freshwater invertebrate 

(mayfly, Atalophlebia australis). Chronic RQs were based on the 21 day average EEC divided by the estimated chronic 

NOAEC for mayfly of 0.01 μg/L. 

130
5.1.1.3 Non-vascular Aquatic Plants 

Acute risk to aquatic non-vascular plants is based on peak EECs in the standard pond and 

the lowest acute toxicity value. Based on the only aquatic non-vascular plant toxicity 

datum (EC50 = 428 μg a.i./L for the freshwater green alga Pseudokirchneriella 

subcapitatum) and the maximum aquatic peak EEC of all use scenarios representing all 

of the agricultural uses of endosulfan in CA (5.88 for lettuce and brussels sprouts) all 

RQs for aquatic non-vascular plants are ≤ 0.014. Since the RQs do not exceed the 

Agency’s LOC (1) for aquatic non-vascular plants, endosulfan is determined to also have 

no indirect effects to those listed species that rely on non-vascular aquatic plants during at 

least some portion of their life-history (i.e., aquatic-phase CRLF, CTS, SFGS, and 

SMHM). 

5.1.1.4 Aquatic Vascular Plants 

Toxicity data have not been identified for quantitatively estimating risk to vascular 

aquatic plants, and therefore, RQs cannot be calculated at this time for this taxonomic 

group. Discussion regarding lines of evidence for the potential for indirect effects to those 

listed species that rely on vascular plants during at least some portion of their life-history 

(i.e., aquatic-phase CRLF, CTS, SFGS, and SMHM) can be found in the “Risk 

Description” portion of the chapter (Section 5.2). 

5.1.2 Exposures in the Terrestrial Habitat 

5.1.2.1 Birds (surrogate for Reptiles and Terrestrial-phase amphibians) 

As previously discussed in Section 3.3, potential direct effects to terrestrial species are 

based on foliar applications of endosulfan. Potential direct acute effects are derived by 

considering dose- and dietary-based EECs modeled in T-REX for a small bird (20 g) 

consuming a variety of dietary items (Table 3.23) and acute oral and subacute dietary 

toxicity endpoints for avian species. Based on the most sensitive bird acute data 

(LD50=28 mg/kg b.w. for the mallard duck) adjusted for differences in body weight by 

T-REX (LD50=14.54 mg/kg b.w.), and the modeled acute dose-based EECs for various 

use scenarios and diet categories, all RQs for small birds ranged from 0.13 (Eggplant, 

Granivores) to 47 (three different use categories for short grass diet). All 100 acute dosebased RQs for uses of endosulfan in CA resulted in an exceedence of the Agency’s acute 

listed species risk LOC (RQ>0.1) for birds (see Table 5.3). Acute dietary-based EECs 

and the most sensitive bird dietary toxicity value (805 mg/kg diet for bobwhite quail) 

resulted in RQs that ranged from 0.01 (4 different use categories for 

fruit/pods/seeds/large insects dietary category) to 0.75 (3 use categories for short grass). 

Only 57 of the 80 acute dietary-based RQs exceeded the Agency’s acute listed species 

risk LOC (>0.1) for birds (Table 5.3). 

Potential direct chronic effects to terrestrial birds (and reptiles and terrestrial-phase 

amphibians) are derived by considering dietary-based EECs modeled in T-REX for a 

small bird (20 g) consuming a variety of dietary items. Chronic effects are estimated 

131
using the lowest available chronic dietary toxicity data for birds (NOEC= 30 mg/kg diet. 

for mallard duck). Chronic dietary-based RQs ranged from 0.25 (eggplant for 

fruit/pods/seeds/large insects) to 20 (3 different use categories for short grass). Sixtythree of the 80 chronic dietary-based RQs exceeded the Agency’s chronic risk LOC (>1) 

for birds (Table 5.3). 

Based on exceedences of the Agency’s acute risk LOC (RQ>0.1) and chronic risk LOC 

(RQ>1) endosulfan does have the potential to directly effect reptiles and terrestrial-phase 

amphibians (i.e., CRLF, CTS and SFGS) during at least some portion of their life-history. 

In addition, endosulfan also has the potential to indirectly affect the CRLF, SFGS, 

SMHM and SJKF since they potentially rely on birds, reptiles or terrestrial-phase 

amphibians during some portion of their life-history. 

Table 5.3 Summary of the acute and chronic dose- and dietary-based RQs for 

birds (20 g) estimated based on the maximum endosulfan foliar spray applications 

using T-REX version 1.4.1. 

Use Category Run 

No. Dietary Category Acute DoseBased(1)

Sub Acute 

DietaryBased(1)

Chronic 

DietaryBased(1)

Short Grass 37.60 0.60 16.00 

Tall Grass 17.23 0.27 7.33 

Broadleaf Plants/ Small 

Insects 21.15 0.34 9.00 

Fruits/Pods/ Seeds/ Large 

Insects 2.35 0.04 1.00 

Almonds, hazelnut & 

walnut 1 

Granivore 0.52 

Short Grass 47.00 0.75 20.00 

Tall Grass 21.54 0.34 9.17 

Broadleaf Plants/ Small 

Insects 26.44 0.42 11.25 

Fruits/Pods/ Seeds/ Large 

Insects 2.94 0.05 1.25 

Citrus 1 

Granivore 0.65 

Short Grass 24.39 0.39 10.38 

Tall Grass 11.18 0.18 4.76 

Broadleaf Plants/ Small 

Insects 13.72 0.22 5.84 

Fruits/Pods/ Seeds/ Large 

Insects 1.52 0.02 0.65 

Broccoli, cabbage, 

Chinese cabbage, 

cauliflower, kohlrabi 

1 

Granivore 0.34 

Short Grass 14.10 0.22 6.00 

Tall Grass 6.46 0.10 2.75 

Broadleaf Plants/ Small 

Insects 7.93 0.13 3.38 

Fruits/Pods/ Seeds/ Large 

Insects 0.88 0.01 0.38 

Kale, Collards & 

Mustard Green 2 

Granivore 0.20 

Short Grass 28.20 0.45 12.00 

Tall Grass 12.93 0.20 5.50 

Sweet corn 1 

Broadleaf Plants/ Small 

Insects 15.86 0.25 6.75 

132
Table 5.3 Summary of the acute and chronic dose- and dietary-based RQs for 

birds (20 g) estimated based on the maximum endosulfan foliar spray applications 

using T-REX version 1.4.1. 

Use Category Run 

No. Dietary Category Acute DoseBased(1)

Sub Acute 

DietaryBased(1)

Chronic 

DietaryBased(1)

Fruits/Pods/ Seeds/ Large 

Insects 1.76 0.03 0.75 

Granivore 0.39 

Short Grass 18.80 0.30 8.00 

Tall Grass 8.62 0.14 3.67 

Broadleaf Plants/ Small 

Insects 10.58 0.17 4.50 

Fruits/Pods/ Seeds/ Large 

Insects 1.18 0.02 0.50 

Cotton (ground) 1 

Granivore 0.26 

Short Grass 18.29 0.29 7.78 

Tall Grass 8.38 0.13 3.57 

Broadleaf Plants/ Small 

Insects 10.29 0.16 4.38 

Fruits/Pods/ Seeds/ Large 

Insects 1.14 0.02 0.49 

Cotton (Areal) 3 

Granivore 0.25 

Short Grass 47.00 0.75 20.00 

Tall Grass 21.54 0.34 9.17 

Broadleaf Plants/ Small 

Insects 26.44 0.42 11.25 

Fruits/Pods/ Seeds/ Large 

Insects 2.94 0.05 1.25 

Apples 1 

Granivore 0.65 

Short Grass 47.00 0.75 20.00 

Tall Grass 21.54 0.34 9.17 

Broadleaf Plants/ Small 

Insects 26.44 0.42 11.25 

Fruits/Pods/ Seeds/ Large 

Insects 2.94 0.05 1.25 

Apricot, nectarine, 

peach, cherry, pear, 

plum & prune 

1 

Granivore 0.65 

Short Grass 26.71 0.42 11.36 

Tall Grass 12.24 0.19 5.21 

Broadleaf Plants/ Small 

Insects 15.02 0.24 6.39 

Fruits/Pods/ Seeds/ Large 

Insects 1.67 0.03 0.71 

Lettuce & Brussels 

sprouts 1 

Granivore 0.37 

Short Grass 24.39 0.39 10.38 

Tall Grass 11.18 0.18 4.76 

Broadleaf Plants/ Small 

Insects 13.72 0.22 5.84 

Fruits/Pods/ Seeds/ Large 

Insects 1.52 0.02 0.65 

Cucumber, melons, 

pumpkin & squash 1 

Granivore 0.34 

Eggplant 3 Short Grass 9.40 0.15 4.00 

Tall Grass 4.31 0.07 1.83 

133
Table 5.3 Summary of the acute and chronic dose- and dietary-based RQs for 

birds (20 g) estimated based on the maximum endosulfan foliar spray applications 

using T-REX version 1.4.1. 

Use Category Run 

No. Dietary Category Acute DoseBased(1)

Sub Acute 

DietaryBased(1)

Chronic 

DietaryBased(1)

Broadleaf Plants/ Small 

Insects 5.29 0.08 2.25 

Fruits/Pods/ Seeds/ Large 

Insects 0.59 0.01 0.25 

Granivore 0.13 

Short Grass 11.42 0.18 4.86 

Tall Grass 5.23 0.08 2.23 

Broadleaf Plants/ Small 

Insects 6.42 0.10 2.73 

Fruits/Pods/ Seeds/ Large 

Insects 0.71 0.01 0.30 

Ornamentals & shade 

trees 1 

Granivore 0.16 

Short Grass 26.71 0.42 11.36 

Tall Grass 12.24 0.19 5.21 

1 Broadleaf Plants/ Small 

Insects 15.02 0.24 6.39 

Fruits/Pods/ Seeds/ Large 

Insects 1.67 0.03 0.71 

Potato 

Granivore 0.37 

Short Grass 15.01 0.24 6.39 

Tall Grass 6.88 0.11 2.93 

3 Broadleaf Plants/ Small 

Insects 8.45 0.13 3.59 

Fruits/Pods/ Seeds/ Large 

Insects 0.94 0.01 0.40 

Sweet potato 

Granivore 0.21 

Short Grass 26.71 0.42 11.36 

Tall Grass 12.24 0.19 5.21 

1 Broadleaf Plants/ Small 

Insects 15.02 0.24 6.39 

Fruits/Pods/ Seeds/ Large 

Insects 1.67 0.03 0.71 

Dry beans (except 

Lima), peas & pepper 

Granivore 0.37 

Short Grass 18.80 0.30 8.00 

Tall Grass 8.62 0.14 3.67 

2 Broadleaf Plants/ Small 

Insects 10.58 0.17 4.50 

Fruits/Pods/ Seeds/ Large 

Insects 1.18 0.02 0.50 

Carrot 

Granivore 0.26 

Short Grass 18.80 0.30 8.00 

Tall Grass 8.62 0.14 3.67 

2 Broadleaf Plants/ Small 

Insects 10.58 0.17 4.50 

Fruits/Pods/ Seeds/ Large 

Insects 1.18 0.02 0.50 

Celery 

Granivore 0.26 

134
Table 5.3 Summary of the acute and chronic dose- and dietary-based RQs for 

birds (20 g) estimated based on the maximum endosulfan foliar spray applications 

using T-REX version 1.4.1. 

Use Category Run 

No. Dietary Category Acute DoseBased(1)

Sub Acute 

DietaryBased(1)

Chronic 

DietaryBased(1)

Short Grass 20.20 0.32 8.59 

Tall Grass 9.26 0.15 3.94 

2 Broadleaf Plants/ Small 

Insects 11.36 0.18 4.83 

Fruits/Pods/ Seeds/ Large 

Insects 1.26 0.02 0.54 

Strawberry 

Granivore 0.28 

Short Grass 24.39 0.39 10.38 

Tall Grass 11.18 0.18 4.76 

1 Broadleaf Plants/ Small 

Insects 13.72 0.22 5.84 

Fruits/Pods/ Seeds/ Large 

Insects 1.52 0.02 0.65 

Tomato 

Granivore 0.34 

(1) RQ values in bold indicate exceedence of acute LOC (0.1) and chronic LOC (1.0). Acute dose-based RQs were 

based on the dose-based EECs divided by the adjusted LD50 for a 20 g bird (14.54 mg/kg b.w.). Acute dietary-based 

RQs were based on the dietary EECs divided by the avian acute dietary LC50 (805 mg/kg diet). Chronic RQs based 

on the dietary EECs divided by the avian NOEC (30 mg/kg diet). 

5.1.2.2 Mammals 

Potential risks to mammals are derived using T-REX, acute and chronic rat toxicity data, 

and a two body-size and dietary categories. Potential direct acute effects specifically to 

the salt marsh harvest mouse (SMHM) are derived by considering dose- and dietarybased EECs modeled in T-REX for a small mammal (15 g) consuming a variety of 

dietary items (Table 5.4) and acute oral and subacute dietary toxicity endpoints for rats. 

Potential direct acute effects specifically to the San Joaquin kit fox (SJKF) are derived by 

considering dose- and dietary-based EECs modeled in T-REX for a large mammal (1,000 

g) consuming a variety of dietary items (Table 5.4) and acute oral and subacute dietary 

toxicity endpoints for rats. Based on the rat acute data (LD50=10 kg/kg b.w.) adjusted for 

differences in body weight for a 15 g small mammal by T-REX (LD50=21.98) and the 

modeled dose-based EECs for various use scenarios and diet categories, all RQs for small 

mammals ranged from 0.07 to 26.03 with 96 of the 100 modeled scenarios exceeding the 

Agency’s acute listed species risk LOC (0.1). Based on the adjusted LD50 for a large 

mammal (LD50=7.69 mg/kg b.w.), and the modeled EECs, the acute dose-based RQs for 

large mammals ranged from 0.03 to 11.92, with 84 of the 100 modeled scenarios 

exceeding the Agency’s LOC (0.1). 

Potential chronic risks to mammals are derived using a calculated NOAEL (0.75 mg/kg 

b.w.) from T-REX which is based on the chronic dietary NOAEC of 15 mg/kg diet for 

rats. This calculated toxicity value was further adjusted in T-REX based on the size class 

of the mammals (1.65 mg/kg b.w for 15 g and 0.58 mg/kg b.w. for 1000 g). These 

135
adjusted values, coupled with the dose-based EECs, resulted in RQs that range from 0.96 

to 347.04 for the small mammal (15 g) and from 0.44 to 158.9 for the large mammal 

(1000 g) (see Table 5.4). Ninety-nine of the 100 RQs for the small mammal, and 91 of 

100 RQs for the large mammal exceeded the Agency’s chronic risk LOC (RQ>1) for 

mammals. Additional chronic risks to mammals are derived using the chronic dietarybased EECs and the dietary chronic value for rats (15 mg/kg diet). These chronic dietarybased RQs ranged from 0.50 to 40, with 72 of the 100 modeled scenarios resulting in 

RQs exceeding the Agency’s chronic risk LOC (RQ>1) 

Based on exceedences of the Agency’s acute risk LOC (RQ>0.1) and chronic risk LOC 

(RQ>1) endosulfan has the potential to directly affect the SMHM and SJKF. 

Additionally, since the acute and chronic RQs are exceeded, there is a potential for 

indirect effects to those listed species that rely on mammals during at least some portion 

of their life-cycle (i.e., CRLF, SFGS, SMHS, and SJKF). 

Table 5.4 Summary of the acute and chronic dose- and dietary-based RQs for 

mammals estimated based on the maximum endosulfan foliar spray applications 

using T-REX version 1.4.1. 

Use Category Run Dietary Category Acute DoseBased(1)

Chronic DoseBased(1)Chronic 

Dietary(1)- 

No. 15 g 1000 g 15 g 1000 g Based 

Short Grass 20.82 9.53 277.63 127.12 32.00 

Tall Grass 9.54 4.37 127.25 58.26 14.67 

Broadleaf Plants/ Small Insects 11.71 5.36 156.17 71.51 18.00 

Fruits/Pods/ Seeds/ Large Insects 1.30 0.60 17.35 7.95 2.00 

Almonds, 

hazelnut & walnut 1 

Granivore 0.29 0.13 3.86 1.77 

Short Grass 26.03 11.92 347.04 158.90 40.00 

Tall Grass 11.93 5.46 159.06 72.83 18.33 

Broadleaf Plants/ Small Insects 14.64 6.70 195.21 89.38 22.50 

Fruits/Pods/ Seeds/ Large Insects 1.63 0.74 21.69 9.93 2.50 

Citrus 1 

Granivore 0.36 0.17 4.82 2.21 

Short Grass 13.51 6.18 180.09 82.46 20.76 

Tall Grass 6.19 2.83 82.54 37.79 9.51 

Broadleaf Plants/ Small Insects 7.60 3.48 101.30 46.38 11.68 

Fruits/Pods/ Seeds/ Large Insects 0.84 0.39 11.26 5.15 1.30 

Broccoli, 

cabbage, Chinese 

cabbage, 

cauliflower, 

kohlrabi 

1 

Granivore 0.19 0.09 2.50 1.15 

Short Grass 7.81 3.58 104.11 47.67 12.00 

Tall Grass 3.58 1.64 47.72 21.85 5.50 

Broadleaf Plants/ Small Insects 4.39 2.01 58.56 26.82 6.75 

Fruits/Pods/ Seeds/ Large Insects 0.49 0.22 6.51 2.98 0.75 

Kale, Collards & 

Mustard Green 2 

Granivore 0.11 0.05 1.45 0.66 

Short Grass 15.62 7.15 208.22 95.34 24.00 

Tall Grass 7.16 3.28 95.44 43.70 11.00 

Broadleaf Plants/ Small Insects 8.78 4.02 117.13 53.63 13.50 

Fruits/Pods/ Seeds/ Large Insects 0.98 0.45 13.01 5.96 1.50 

Sweet corn 1 

Granivore 0.22 0.10 2.89 1.32 

Short Grass 10.41 4.77 138.82 63.56 16.00 

Tall Grass 4.77 2.18 63.62 29.13 7.33 

Broadleaf Plants/ Small Insects 5.86 2.68 78.08 35.75 9.00 

Cotton (ground) 1 

Fruits/Pods/ Seeds/ Large Insects 0.65 0.30 8.68 3.97 1.00 

136
Table 5.4 Summary of the acute and chronic dose- and dietary-based RQs for 

mammals estimated based on the maximum endosulfan foliar spray applications 

using T-REX version 1.4.1. 

Use Category Run Dietary Category Acute DoseBased(1)

Chronic DoseBased(1)Chronic 

Dietary(1)- 

No. 15 g 1000 g 15 g 1000 g Based 

Granivore 0.14 0.07 1.93 0.88 

Short Grass 10.13 4.64 135.07 61.84 15.57 

Tall Grass 4.64 2.13 61.90 28.35 7.14 

Broadleaf Plants/ Small Insects 5.70 2.61 75.97 34.79 8.76 

Fruits/Pods/ Seeds/ Large Insects 0.63 0.29 8.44 3.87 0.97 

Cotton (Areal) 3 

Granivore 0.14 0.06 1.88 0.86 

Short Grass 26.03 11.92 347.04 158.90 40.00 

Tall Grass 11.93 5.46 159.06 72.83 18.33 

Broadleaf Plants/ Small Insects 14.64 6.70 195.21 89.38 22.50 

Fruits/Pods/ Seeds/ Large Insects 1.63 0.74 21.69 9.93 2.50 

Apples 1 

Granivore 0.36 0.17 4.82 2.21 

Short Grass 26.03 11.92 347.04 158.90 40.00 

Tall Grass 11.93 5.46 159.06 72.83 18.33 

Broadleaf Plants/ Small Insects 14.64 6.70 195.21 89.38 22.50 

Fruits/Pods/ Seeds/ Large Insects 1.63 0.74 21.69 9.93 2.50 

Apricot, nectarine, 

peach, cherry, 

pear, plum & 

prune 

1 

Granivore 0.36 0.17 4.82 2.21 

Short Grass 14.79 6.77 197.18 90.29 22.73 

Tall Grass 6.78 3.10 90.38 41.38 10.42 

Broadleaf Plants/ Small Insects 8.32 3.81 110.91 50.79 12.78 

Fruits/Pods/ Seeds/ Large Insects 0.92 0.42 12.32 5.64 1.42 

Lettuce & 

Brussels sprouts 1 

Granivore 0.21 0.09 2.74 1.25 

Short Grass 13.51 6.18 180.09 82.46 20.76 

Tall Grass 6.19 2.83 82.54 37.79 9.51 

Broadleaf Plants/ Small Insects 7.60 3.48 101.30 46.38 11.68 

Fruits/Pods/ Seeds/ Large Insects 0.84 0.39 11.26 5.15 1.30 

Cucumber, 

melons, pumpkin 

& squash 

1 

Granivore 0.19 0.09 2.50 1.15 

Short Grass 5.21 2.38 69.41 31.78 8.00 

Tall Grass 2.39 1.09 31.81 14.57 3.67 

Broadleaf Plants/ Small Insects 2.93 1.34 39.04 17.88 4.50 

Fruits/Pods/ Seeds/ Large Insects 0.33 0.15 4.34 1.99 0.50 

Eggplant 3 

Granivore 0.07 0.03 0.96 0.44 

Short Grass 6.32 2.90 84.31 38.60 9.72 

Tall Grass 2.90 1.33 38.64 17.69 4.45 

Broadleaf Plants/ Small Insects 3.56 1.63 47.42 21.71 5.47 

Fruits/Pods/ Seeds/ Large Insects 0.40 0.18 5.27 2.41 0.61 

Ornamentals & 

shade trees 1 

Granivore 0.09 0.04 1.17 0.54 

Short Grass 14.79 6.77 197.18 90.29 22.73 

Tall Grass 6.78 3.10 90.38 41.38 10.42 

Broadleaf Plants/ Small Insects 8.32 3.81 110.91 50.79 12.78 

Fruits/Pods/ Seeds/ Large Insects 0.92 0.42 12.32 5.64 1.42 

Potato 1 

Granivore 0.21 0.09 2.74 1.25 

Short Grass 8.31 3.81 110.86 50.76 12.78 

Tall Grass 3.81 1.74 50.81 23.27 5.86 

Broadleaf Plants/ Small Insects 4.68 2.14 62.36 28.55 7.19 

Fruits/Pods/ Seeds/ Large Insects 0.52 0.24 6.93 3.17 0.80 

Sweet potato 3 

Granivore 0.12 0.05 1.54 0.71 

137
Table 5.4 Summary of the acute and chronic dose- and dietary-based RQs for 

mammals estimated based on the maximum endosulfan foliar spray applications 

using T-REX version 1.4.1. 

Use Category Run Dietary Category Acute DoseBased(1)

Chronic DoseBased(1)Chronic 

Dietary(1)- 

No. 15 g 1000 g 15 g 1000 g Based 

Short Grass 14.79 6.77 197.18 90.29 22.73 

Tall Grass 6.78 3.10 90.38 41.38 10.42 

Broadleaf Plants/ Small Insects 8.32 3.81 110.91 50.79 12.78 

Fruits/Pods/ Seeds/ Large Insects 0.92 0.42 12.32 5.64 1.42 

Dry beans 

(except Lima), 

peas & pepper 

1 

Granivore 0.21 0.09 2.74 1.25 

Short Grass 10.41 4.77 138.82 63.56 16.00 

Tall Grass 4.77 2.18 63.62 29.13 7.33 

Broadleaf Plants/ Small Insects 5.86 2.68 78.08 35.75 9.00 

Fruits/Pods/ Seeds/ Large Insects 0.65 0.30 8.68 3.97 1.00 

Carrot 2 

Granivore 0.14 0.07 1.93 0.88 

Short Grass 10.41 4.77 138.82 63.56 16.00 

Tall Grass 4.77 2.18 63.62 29.13 7.33 

Broadleaf Plants/ Small Insects 5.86 2.68 78.08 35.75 9.00 

Fruits/Pods/ Seeds/ Large Insects 0.65 0.30 8.68 3.97 1.00 

Celery 2 

Granivore 0.14 0.07 1.93 0.88 

Short Grass 11.19 5.12 149.13 68.29 17.19 

Tall Grass 5.13 2.35 68.35 31.30 7.88 

Broadleaf Plants/ Small Insects 6.29 2.88 83.89 38.41 9.67 

Fruits/Pods/ Seeds/ Large Insects 0.70 0.32 9.32 4.27 1.07 

Strawberry 2 

Granivore 0.16 0.07 2.07 0.95 

Short Grass 13.51 6.18 180.09 82.46 20.76 

Tall Grass 6.19 2.83 82.54 37.79 9.51 

Broadleaf Plants/ Small Insects 7.60 3.48 101.30 46.38 11.68 

Fruits/Pods/ Seeds/ Large Insects 0.84 0.39 11.26 5.15 1.30 

Tomato 1 

Granivore 0.19 0.09 2.50 1.15 

 (1) RQ values in bold indicate exceedence of listed species acute LOC (0.1) and chronic LOC (1.0). Acute dose-based 

RQs were based on dose-based EECs divided by adjusted rat LD50s (21.98 mg/kg b.w for 15 g and 7.69 mg/kg b.w. for 

1000g). Chronic dose-based RQs were based on dose-based EECs divided by adjusted rat NOAECs (1.65 mg/kg b.w. 

for 15 g and 0.58 mg/kg b.w. for 1000g). Chronic dietary-based RQs were based on dietary EECs divided by the chronic 

dietary NOAEC for rats (15 mg/kg diet). 

5.1.2.3 Terrestrial Invertebrates 

Potential risks to terrestrial invertebrates resulting from foliar spray applications of 

endosulfan are derived using T-REX, and the most sensitive toxicity data available for 

terrestrial invertebrates. In the case of endosulfan, the beet web worm was used as a 

surrogate for evaluating risks of endosulfan to terrestrial invertebrates. The toxicity value 

for terrestrial invertebrates is the lowest available acute contact LD50 (0.15 μg a.i./g) 

EECs in ppm calculated by T-REX for small and large insects are divided by the above 

toxicity value for terrestrial invertebrates. Larvae for both the Bay checkerspot butterfly 

and the Valley elderberry longhorn beetle are considered ‘small insects’ in this 

assessment, while the adults of these species are considered ‘large insects’. Based on the 

EECs and the above contact acute value, all 20 use category RQs for small insects ranged 

from 450 to 2250, and those for large insects ranged from 50 to 250 (Table 5.5). All 20 

138
use category RQs for both size classes exceeded the Agency’s interim LOC for listed 

terrestrial invertebrates (RQ>0.05). Based on the exceedences of the Agency’s interim 

LOC for listed terrestrial invertebrates, endosulfan use in CA does have the potential to 

directly adversely affect the BCB and the VELB (Table 5.5). Additionally, since the RQs 

are exceeded, there is a potential for indirect effects to those listed species that rely on 

terrestrial invertebrates during at least some portion of their life-cycle (i.e., CRLF, SFGS, 

CTS, SMHM, and SJKF. 

Table 5.5 Summary of the acute and chronic dose- and dietary-based RQs terrestrial insects estimated based on 

the maximum endosulfan foliar spray applications using T-REX version 1.4.1. 

Use Category Run No. Dietary Category Small insects(1) Large insects(1)

Broadleaf Plants/ Small Insects 1800 Almonds, hazelnut & walnut 1 

Fruits/Pods/ Seeds/ Large Insects 200 

Broadleaf Plants/ Small Insects 2250 Citrus 1 

Fruits/Pods/ Seeds/ Large Insects 250 

Broccoli, cabbage, Chinese Broadleaf Plants/ Small Insects 1168 

cabbage, cauliflower, kohlrabi 1 

Fruits/Pods/ Seeds/ Large Insects 130 

Broadleaf Plants/ Small Insects 675 Kale, Collards & Mustard Green 2 

Fruits/Pods/ Seeds/ Large Insects 75 

Broadleaf Plants/ Small Insects 1350 Sweet corn 1 

Fruits/Pods/ Seeds/ Large Insects 150 

Broadleaf Plants/ Small Insects 900 Cotton (ground) 1 

Fruits/Pods/ Seeds/ Large Insects 100 

Broadleaf Plants/ Small Insects 876 Cotton (Areal) 3 

Fruits/Pods/ Seeds/ Large Insects 97 

Broadleaf Plants/ Small Insects 2250 Apples 1 

Fruits/Pods/ Seeds/ Large Insects 250 

Apricot, nectarine, peach, cherry, Broadleaf Plants/ Small Insects 2250 

pear, plum & prune 1 

Fruits/Pods/ Seeds/ Large Insects 250 

Broadleaf Plants/ Small Insects 1278 Lettuce & Brussels sprouts 1 

Fruits/Pods/ Seeds/ Large Insects 142 

Cucumber, melons, pumpkin & Broadleaf Plants/ Small Insects 1168 

squash 1 

Fruits/Pods/ Seeds/ Large Insects 130 

Broadleaf Plants/ Small Insects 450 Eggplant 3 

Fruits/Pods/ Seeds/ Large Insects 50 

Broadleaf Plants/ Small Insects 547 Ornamentals & shade trees 1 

Fruits/Pods/ Seeds/ Large Insects 61 

Broadleaf Plants/ Small Insects 1278 Potato 1 

Fruits/Pods/ Seeds/ Large Insects 142 

Broadleaf Plants/ Small Insects 719 Sweet potato 3 

Fruits/Pods/ Seeds/ Large Insects 80 

Dry beans (except Lima), peas & Broadleaf Plants/ Small Insects 1278 

pepper 

1 

Fruits/Pods/ Seeds/ Large Insects 142 

Broadleaf Plants/ Small Insects 900 Carrot 2 

Fruits/Pods/ Seeds/ Large Insects 100 

Broadleaf Plants/ Small Insects 900 Celery 2 

Fruits/Pods/ Seeds/ Large Insects 100 

Broadleaf Plants/ Small Insects 967 Strawberry 2 

Fruits/Pods/ Seeds/ Large Insects 107 

Broadleaf Plants/ Small Insects 1168 Tomato 1 

Fruits/Pods/ Seeds/ Large Insects 130 

139
Table 5.5 Summary of the acute and chronic dose- and dietary-based RQs terrestrial insects estimated based on 

the maximum endosulfan foliar spray applications using T-REX version 1.4.1. 

Small insects(1) Large insects(1) Use Category Run No. Dietary Category 

(2) RQ values in bold indicate exceedence of Agency’s interim LOC for listed terrestrial invertebrates (0.05). Terrestrial insect RQs were 

based on diet category EECs for small and large insects divided by the contact acute value for beet webworm, Pyrausta sticticalis

(LD50=0.15 μg/g).

5.1.2.4 Terrestrial Plants 

Generally, for indirect effects, potential effects on terrestrial vegetation are assessed 

using RQs from terrestrial plant seedling emergence and vegetative vigor EC25 data as a 

screen. However, such toxicity data have not been identified for quantitatively estimating 

risk to terrestrial plants (as described in Section 4.2.4) as a result of endosulfan use; 

therefore, RQs cannot be calculated at this time for this taxonomic group. Discussion 

regarding lines of evidence for the potential for indirect effects to those listed species that 

rely on terrestrial plants during at least some portion of their life-history (i.e., terrestrialphase CRLF, SFGS, CTS, BCB, VELB, SMHM and SJKF) can be found in the ”Risk 

Description” portion of the chapter (Section 5.2). 

5.1.3 Primary Constituent Elements of Designated Critical Habitat 

For endosulfan use, the assessment endpoints for designated critical habitat PCEs involve 

the same endpoints as those being assessed relative to the potential for direct and indirect 

effects to the listed species assessed here. Therefore, the effects determinations for direct 

and indirect effects are used as the basis of the effects determination for designated 

critical habitat. 

5.1.4 Spatial Extent of Potential Effects 

In order to determine the spatial extent of effects on terrestrial and aquatic habitats due to 

endosulfan exposures through spray drift, it is necessary to estimate the distance that 

spray applications can drift from the treated area and still be present at concentrations that 

exceed levels of concern. An analysis of spray drift distances was completed using all 

available tools, including AgDrift, AGDISP and the Gaussian extension to AGDISP. 

5.1.4.1 Spray Drift 

Spray drift analysis determines the additional distance from the treated area where listed 

species LOCs are exceeded as a result of spray drift. This distance is based on the 

taxonomic group that yields the largest RQ to LOC ratio. Both terrestrial and aquatic 

taxonomic groups are considered in this analysis. 

For endosulfan, the results of the screening-level assessment indicate that the required 

values are one value for LOC= 0.05 and two values for RQ (2,250 for apples and 1,350 

for sweet corn). Using these values, AgDrift and AGDISP were not able to estimate 

needed buffer distance, therefore the Gaussian extension to AGDISP was used. Buffer 

distances were determined for two crops, an orchard and a field crop with varying 

140
application parameters as described in details in Appendix G. Spray drift results range 

from 12,266 to 12,775 feet for orchards and 3,383 to 11,279 feet for field crops. 

5.1.4.2 Downstream Dilution Analysis 

Down-stream dilution analysis is necessary to define the full extent of the effects area. 

This is because effects area may be larger than the initial area of concern or “footprint” of 

potential uses. This analysis determines downstream extent of exposure in streams and 

rivers where the EEC could potentially be above levels that would exceed the highest RQ 

to LOC ratio. Based on all aquatic RQs, the greatest RQ to LOC ratio for all aquatic 

organisms (plants and animals) are determined for the two major use patterns (Table 

5.6). 

Table 5.6 Summary of the highest RQ to LOC ratios for the two GIS use categories for endosulfan

Category* Use Pattern Species RQ LOC 

Cultivated Crops Lettuce/Brussels Sprouts 58.8 

Orchards/Vineyards Pear Common Carp 33.5 0.05 

* Two GIS mapping categories. 

The ratios in Table 5.6 would be used to determine the downstream extent of the effects 

area. Results of this analysis for endosulfan suggest that the maximum distance 

downstream is 285 km for cultivated crops and 120 km for orchards. Therefore, exposure 

and possible effects on most sensitive aquatic species may extend to 120 to 285 km 

beyond the initial area of concern shown in Figure 2.6. 

5.1.4.3 Overlap between CRLF, CTS, SFGS, BCB, VELB, SMHM, and SJKF 

habitat and Spatial Extent of Potential Effects 

Table 5.7 shows a summary of recent usage data in counties where the CRLF and the 

San Francisco Bay species occur. 

Table 5.7 Summary of average endosulfan usage data and occurrence of the CRLF and the San Francisco Bay 

species at the county level 

Average Usage (2005-2006) CRLF and San Francisco Bay Species1

 

County lbs % Rank 2

CRLF SFGS SMHM BCB VELB SJKF CTS 

Alameda No Use Reported **** 

Colusa 250.96 0.29% 

Contra Costa No Use Reported 

Fresno 44,937.84 51% 1 

Glenn 4.16 0.00% 

Imperial 7,004.91 8% 3 

Kern 2,584.47 3% 5 

Kings 19,648.25 22% 2 

141
Table 5.7 Summary of average endosulfan usage data and occurrence of the CRLF and the San Francisco Bay 

species at the county level 

CRLF and San Francisco Bay Species1

Average Usage (2005-2006) 

County lbs Rank 2

% CRLF SFGS SMHM BCB VELB SJKF CTS 

Los Angeles 40.13 0.05% 

Madera 468.2 0.53% 

Marin No Use Reported 

Merced 230.2 0.26% 

Monterey 396.45 0.45% 

Napa 4.56 0.01% 

Placer 9.09 0.01% 

Riverside 2,926.87 3% 4 

San Benito 646.58 0.74% 11 

San Bernardino No Use Reported 

San Francisco No Use Reported 

San Joaquin 137.55 0.16% 

San Luis Obispo No Use Reported 

San Mateo 0.25 0.00% 

Santa Barbara 1 0.00% 

Santa Clara 173.33 0.20% 

Santa Cruz No Use Reported 

Siskiyou 2,063.91 2% 7 

Solano 885.72 1% 10 

Sonoma 55.75 0.06% 

Stanislaus No Use Reported 

Sutter 1,027.73 1% 9 

Tulare 1,879.55 2% 8 

Ventura 63.38 0.07% 

Yolo 2,151.40 2% 6 

Total 87,592.24 100% 

Species occurrence= Yes

1California red-legged frog (Rana aurora draytonii) (CRLF), San Francisco Garter Snake (Thamnophis sirtalis 

tetrataenia) (SFGS), Salt Marsh Harvest Mouse (Reithrodontomys raviventris)

(SMHM), Bay Checkerspot Butterfly (Euphydryas editha bayensis) (BCB), Valley Elderberry Longhorn Beetle 

(Desmocerus californicus dimorphus) (VELB), San Joaquin Kit Fox (Vulpes macrotis mutica) (SJKF), and California 

Tiger Salamander (Ambystoma californiense) (CTS). 

2 Top 11 counties with usage over 500 lb/county

In contrast, possible overlap of the species occurrence and potential usage are shown in 

maps included in Appendix E. Co-occurrence data are summarized in Table 5.8. 

Table 5.8 Extent and location of overlap between areas of species occurrence and areas 

of potential endosulfan usage 

Species Extent of possible overlap/Counties of Occurrence 

CRLF Low with high acreage of both cultivated crops and orchards in the following Counties: Santa 

142
Clara, Santa Barbara, Alameda, Contra Costa, Ventura, San Benito, Merced, Stanislaus, and San 

Joaquin 

SFGS High with low acreage of cultivated crops only in San Mateo County 

SMHM Very low with low acreage of cultivated crops in only in Sonoma County 

BCB High with low acreage of cultivated crops and orchards only in Santa Clara County 

VELB Medium with cultivated crops and orchards in only Solano County 

SJKF 

Low with high acreage of mainly cultivated crops in the western edge of the central valley 

counties including: Contra Costa, Alameda, San Bento, Monterey, San Joaquin, Stanislaus, 

Merced, Kings, Fresno and Kern. 

CTS 

Low with high acreage of mainly orchards in the eastern edge of the central valley counties 

including: : Sacramento, Santa Clara, Stanislaus, Alameda, Contra Costa, Merced, Madera, and 

Fresno 

Data show the species occurrence may overlap with potential endosulfan usage although 

the extent appears to be generally limited because it is either low or occurs on limited 

acreage. It is important to note however, the following contradicting factors: 

(1) Drift is expected to cause extension of the initial area of concern for most 

sensitive terrestrial species by 2.1 miles for cultivated crops to 2.4 miles for 

orchards. 

(2) Downstream dilution is expected to cause extension of the initial area of concern 

for most sensitive aquatic species by 75 miles (120 km) for cultivated crops to 

177 miles (285 km) for orchards. 

(3) Areas associated with endosulfan usage are expected to be much smaller than 

those mapped because endosulfan is not used on all cultivated crops or on all 

orchards and vines. 

The first two factors would tend to increase the extent of the area affected while the third 

factor would reduce the possibility of the overlap to occur. 

5.2 Risk Description 

The risk description synthesizes overall conclusions regarding the likelihood of adverse 

impacts leading to an effects determination (i.e., “no effect,” “may affect, but not likely 

to adversely affect,” or “likely to adversely affect”) for the assessed species and the 

potential for effects to their designated critical habitat. 

If the RQs presented in the Risk Estimation (Section 5.1) show no direct or indirect 

effects for the assessed species, and no effects to PCEs of the designated critical habitat, 

a “no effect” determination is made, based on the use of endosulfan within the action 

area. However, if LOCs for direct or indirect effect are exceeded or there may be effects 

to the PCEs of the critical habitat, the Agency concludes a preliminary “may affect” 

determination for the FIFRA regulatory action regarding endosulfan 

Based on exceedances of LOCs, a potential to cause adverse effects to CRLF, SFGS, 

SMHM, BCB, VELB, SJKF and CTS and potential to cause effects designated critical 

habitat (CRLF, BCB, VELB and CTS) has been identified. The Agency concludes a 

143
preliminary “may affect” determination for the CRLF, SFGS, SMHM, BCB, VELB, 

SJKF and CTS based on the currently labeled uses of endosulfan. A summary of the risk 

estimation results are provided in Table 5.9 for direct and indirect effects to the listed 

species assessed here and in Table 5.10 for the PCEs of their designated critical habitat. 

Table 5.9 Risk Estimation Summary for endosulfan - Direct and Indirect Effects 

Taxa(1) LOC Exceedances 

(Y/N) Description of Results of Risk Estimation Assessed Species Potentially Affected 

Direct Effects: 

Aquatic-phase 

CRLF,CTS 

Freshwater Fish and 

Aquatic-phase 

Amphibians 

(Y) 

Acute RQs range from 7.2 to 58.8; exceeding the Agency’s 

acute listed species LOC (0.05) in all 20 crop scenarios. 

Chronic RQs range from 5.7 to 80.6; exceeding the Agency’s 

chronic species LOC (1.0) in all 20 crop scenarios. Indirect Effects: 

Aquatic-phase CRLF, 

SFGS, CTS

Freshwater 

Invertebrates (Y) 

Acute RQs range from 1.2 to 9.8 for freshwater invertebrates; 

exceeding the Agency’s acute listed species LOC (0.05) in all 

20 crop scenarios. 

Chronic RQs range from 23.7 to 260; exceeding the Agency’s 

chronic species LOC (1.0) in all 20 crop scenarios. 

Indirect Effects:

 

Aquatic-phase CRLF, 

SFGS, CTS 

Vascular Aquatic 

Plants (N; however 

effects cannot be 

quantified) 

There are no acceptable vascular aquatic plant data available 

Indirect Effects:

Aquatic-phase CRLF, 

SFGS, SMHM, CTS 

Non-Vascular 

Aquatic Plants (N) There are no exceedances of the Agency’s LOC for aquatic plants (1.0) 

Indirect Effects:

Aquatic-phase CRLF, 

SFGS, SMHM, CTS 

Direct Effects:

Terrestrial-phase 

CRLF, SFGS, CTS 

Birds, Reptiles, and 

Terrestrial-Phase 

Amphibians 

(Y) 

Acute dose diet-based RQs range from 0.15 to 47.0 for short 

grass; 0.07 to 21.5 for tall grass; 0.08 to 26.4 for broadleaf 

plants/small insects; 0.01 to 2.9 for fruits/pods/seeds/large 

insect, and 0.03 to 0.65 for the granivore dietary categories. 

For short-grass, RQs exceed the Agency’s acute listed species 

LOC (0.1) in all 20 crop scenarios and at least one RQ in all 

five dietary categories exceeded the acute listed species LOC 

(0.1). 

Chronic RQs for birds range from 4.0 to 20.0 for short grass; 

1.8 to 9.2 for tall grass; 2.3 to 11.3 for broadleaf plants/small 

insects; and 0.25 to 1.3 for fruits/pods/seeds/large insect 

dietary categories. For short-grass, tall grass, and broadleaf 

plants/small insect dietary categories, RQs exceed the 

Agency’s chronic listed species LOC (1.0) in all 20 crop 

scenarios and at least one RQ in all four dietary categories 

exceeded the acute listed species LOC (1.0). 

Indirect Effects: 

Terrestrial-phase 

CRLF, SFGS, SMHM, 

SJKF 

Mammals 

(Y) 

Acute dose-based RQs for mammals range from 2.4 to 26.0 

for short grass; 1.1 to 11.9 for tall grass; 1.3 to 14.6 for 

broadleaf plants/ small insects; 0.15 to 1.6 for fruits/pods/ 

seeds/large insects; and 0.03 to 0.36 for the granivore dietary 

categories. Acute RQs exceed the Agency’s LOC (0.1) for 

one or more crop scenarios for all five dietary categories. 

Direct Effects:

SMHM; SJKF 

144
Table 5.9 Risk Estimation Summary for endosulfan - Direct and Indirect Effects 

LOC Exceedances Assessed Species Taxa(1) Description of Results of Risk Estimation (Y/N) Potentially Affected 

Chronic dose-based RQs for mammals range from 31.8 to 

347 for short grass; 14.6 to 159 for tall grass; 17.9 to 195 

broadleaf plants/small insects; 2.0 to 21.7 for 

fruits/pods/seeds/large insect; and 0.44 to 4.8 for the 

granivore dietary categories. Chronic RQs exceed the 

Agency’s chronic listed species LOC (1.0) in all 20 crop 

scenarios for four of the five dietary categories modeled. 

Indirect Effects:

Terrestrial-phase 

CRLF, SFGS, SMHM, 

SJKF 

Direct Effects: 

Terrestrial BCB, VELB 

Invertebrates 

(Y) RQs based on EECs for small insects and large insects range 

from 450 to 2250 and 50 to 250, respectively 

Indirect Effects: 

Terrestrial phase 

CRLF, SFGS, 

SMHM, SJKF, CTS 

Terrestrial Plants - 

Monocots 

(N; however 

effects cannot be 

quantified) 

There are no acceptable terrestrial plant data available 

Indirect Effects: 

CRLF, SFGS, 

SMHM, BCB, VELB, 

SJKF, CTS 

Terrestrial Plants - 

Dicots 

(N; however 

effects cannot be 

quantified) 

There are no acceptable terrestrial plant data available 

Indirect Effects: 

CRLF, SFGS, 

SMHM, BCB, VELB, 

SJKF, CTS 

(1) Risks to estuarine/marine fish and invertebrates were not assessed because the listed species for 

endosulfan do not comprise this taxonomic group nor does available life history and critical habitat 

information indicate they would be affected indirectly by effects on estuarine/marine species or this 

habitat. 

Table 5.10 Risk Estimation Summary for Endosulfan – Effects to Designated Critical Habitat (PCEs) 

Taxa(1)

May Affect 

Habitat 

(Y/N) 

Description of Results of Risk Estimation 

Species Associated 

with Designated 

Critical Habitat that 

May be Modified 

Freshwater Fish and 

Aquatic-phase 

Amphibians 

(Y) 

Acute RQs range from 7.2 to 58.8; exceeding the Agency’s 

acute listed species LOC (0.05) in all 20 crop scenarios. 

Chronic RQs range from 5.7 to 80.6; exceeding the Agency’s 

chronic species LOC (1.0) in all 20 crop scenarios. 

CRLF,CTS 

Freshwater 

Invertebrates (Y) 

Acute RQs range from 1.2 to 9.8 for freshwater invertebrates; 

exceeding the Agency’s acute listed species LOC (0.05) in all 

20 crop scenarios. 

Chronic RQs range from 23.7 to 260; exceeding the Agency’s 

chronic species LOC (1.0) in all 20 crop scenarios. 

CRLF,CTS 

Vascular Aquatic 

Plants (N; however 

effects cannot 

be quantified) 

There are no acceptable vascular aquatic plant data available 

CRLF,CTS 

Non-Vascular (N) There are no exceedances of the Agency’s LOC for aquatic CRLF,CTS 

145
Table 5.10 Risk Estimation Summary for Endosulfan – Effects to Designated Critical Habitat (PCEs) 

Taxa(1)

May Affect 

Habitat 

(Y/N) 

Species Associated 

with Designated Description of Results of Risk Estimation Critical Habitat that 

May be Modified 

Aquatic Plants plants (1.0) 

CRLF,CTS 

Birds, Reptiles, and 

Terrestrial-Phase 

Amphibians 

(Y) 

Acute dose diet-based RQs range from 0.15 to 47.0 for short 

grass; 0.07 to 21.5 for tall grass; 0.08 to 26.4 for broadleaf 

plants/small insects; 0.01 to 2.9 for fruits/pods/seeds/large 

insect, and 0.03 to 0.65 for the granivore dietary categories. 

For short-grass, RQs exceed the Agency’s acute listed species 

LOC (0.1) in all 20 crop scenarios and at least one RQ in all 

five dietary categories exceeded the acute listed species LOC 

(0.1). 

Chronic RQs for birds range from 4.0 to 20.0 for short grass; 

1.8 to 9.2 for tall grass; 2.3 to 11.3 for broadleaf plants/small 

insects; and 0.25 to 1.3 for fruits/pods/seeds/large insect 

dietary categories. For short-grass, tall grass, and broadleaf 

plants/small insect dietary categories, RQs exceed the 

Agency’s chronic listed species LOC (1.0) in all 20 crop 

scenarios and at least one RQ in all four dietary categories 

exceeded the acute listed species LOC (1.0). 

Acute dose-based RQs for mammals range from 2.4 to 26.0 

for short grass; 1.1 to 11.9 for tall grass; 1.3 to 14.6 for 

broadleaf plants/small insects; 0.15 to 1.6 for 

fruits/pods/seeds/large insects; and 0.03 to 0.36 for the 

granivore dietary categories. Acute RQs exceed the Agency’s 

LOC (0.1) for one or more crop scenarios for all five dietary 

categories. Mammals 

(Y) 

Chronic dose-based RQs for mammals range from 31.8 to 347 

for short grass; 14.6 to 159 for tall grass; 17.9 to 195 

broadleaf plants/small insects; 2.0 to 21.7 for 

fruits/pods/seeds/large insect; and 0.44 to 4.8 for the 

granivore dietary categories. Chronic RQs exceed the 

Agency’s chronic listed species LOC (1.0) in all 20 crop 

scenarios for four of the five dietary categories modeled. 

CRLF 

Terrestrial 

Invertebrates 

(Y) RQs based on EECs for small insects and large insects range 

from 450 to 2250 and 50 to 250, respectively 

CRLF,CTS 

Terrestrial Plants - 

Monocots 

(N; however 

effects cannot 

be quantified) 

There are no acceptable terrestrial plant data available 

CRLF,BCB, VELB, 

CTS 

Terrestrial Plants - 

Dicots 

(N; however 

effects cannot 

be quantified) 

There are no acceptable terrestrial plant data available 

CRLF,BCB, VELB, 

CTS 

Following a “may affect” determination, additional information is considered to refine 

the potential for exposure at the predicted levels based on the life history characteristics 

(i.e., habitat range, feeding preferences, etc.) of the assessed species. Based on the best 

available information, the Agency uses the refined evaluation to distinguish those actions 

146
that “may affect, but are not likely to adversely affect” from those actions that are “likely 

to adversely affect” the assessed species and its designated critical habitat. 

The criteria used to make determinations that the effects of an action are “not likely to 

adversely affect” the assessed species or its designated critical habitat include the 

following: 

• Significance of Effect: Insignificant effects are those that cannot be meaningfully 

measured, detected, or evaluated in the context of a level of effect where “take” 

occurs for even a single individual. “Take” in this context means to harass or 

harm, defined as the following: 

 Harm includes significant habitat modification or degradation that 

results in death or injury to listed species by significantly impairing 

behavioral patterns such as breeding, feeding, or sheltering. 

 Harass is defined as actions that create the likelihood of injury to listed 

species to such an extent as to significantly disrupt normal behavior 

patterns which include, but are not limited to, breeding, feeding, or 

sheltering. 

• Likelihood of the Effect Occurring: Discountable effects are those that are 

extremely unlikely to occur. 

• Adverse Nature of Effect: Effects that are wholly beneficial without any adverse 

effects are not considered adverse. 

 A description of the risk and effects determination for each of the established assessment 

endpoints for the assessed species and their designated critical habitat is provided in 

Sections 5.2.1 through 5.2.7. The effects determination section for each listed species 

assessed will follow a similar pattern. Each will start with a discussion of the potential 

for direct effects, followed by a discussion of the potential for indirect effects. The 

likelihood of effects occurring will be informed by the probit-based chance of individual 

acute effects for freshwater fish and invertebrates (Table 5.11), terrestrial birds, 

mammals and insects (Table 5.12) and herpetofauna based on T-HERPS modeling 

(Table 5.13). For those listed species that have designated critical habitat, the section 

will end with a discussion on the potential for effects to the critical habitat from the use 

of endosulfan. 

147
148

Table 5.11 Summary of the chance of individual acute effects to freshwater animals based on 

acute RQs, the acute listed species LOC, acute toxicity data, and probit slope response 

relationships(1,2). 

Use Category Run 

No. 

Acute FW 

Fish RQ 

Change of Individual 

Effect at RQ or LOC 

Based on Probit Slope & 

Slope's 95% CI 

Acute FW 

Invert. RQ 

Change of Individual 

Effect at RQ or LOC 

Based on Probit Slope 

& Slope's 95% CI 

N/A N/A LOC = 

0.05 

1 in 4.18E+18 

(1 in 216, 1 in 1.75E+31) 

LOC = 0.05 

1 in 4.18E+18 

(1 in 216, 1 in 1.75E+31) 

Almonds, Hazelnuts & 

Walnuts 1 33.50 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

5.58 

1 in 1.00 

 (1 in 1.07, 1 in 1.00) 

Citrus 1 33.50 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

5.58 

1 in 1.00 

 (1 in 1.07, 1 in 1.00) 

Broccoli, Cabbage & 

Cauliflower 1 48.10 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

8.02 

1 in 1.00 

 (1 in 1.04, 1 in 1.00) 

Collards, Kale & 

Mustard Green 2 16.70 

1 in 1.00 

 (1 in 1.01, 1 in 1.00) 

2.78 

1 in 1.02 

 (1 in 1.23, 1 in 1.00) 

Sweet corn for fresh 

market only 1 28.80 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

4.80 

1 in 1.00 

 (1 in 1.09, 1 in 1.00) 

Cotton (ground) 2 12.40 

1 in 1.00 

 (1 in 1.01, 1 in 1.00) 

2.07 

1 in 1.08 

 (1 in 1.36, 1 in 1.00) 

Cotton (aerial) 3 15.60 

1 in 1.00 

 (1 in 1.01, 1 in 1.00) 

2.60 

1 in 1.03 

 (1 in 1.26, 1 in 1.00) 

All fruit trees 1 34.00 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

5.67 

1 in 1.00 

 (1 in 1.07, 1 in 1.00) 

Lettuce & Brussels 

Sprouts 1 58.80 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

9.80 

1 in 1.00 

 (1 in 1.02, 1 in 1.00) 

Cucurbits 1 15.50 

1 in 1.00 

 (1 in 1.01, 1 in 1.00) 

2.58 

1 in 1.03 

 (1 in 1.26, 1 in 1.00) 

Eggplant 3 7.20 

1 in 1.00 

 (1 in 1.05, 1 in 1.00) 

1.20 

1 in 1.56 

 (1 in 1.78, 1 in 1.31) 

Ornamentals or Shade 

Trees (Southern 

Coast) 

1 34.30 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

5.72 

1 in 1.00 

 (1 in 1.07, 1 in 1.00) 

Ornamentals or Shade 

Trees (Northern 

Central coast) 

1 Add 43.80 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

7.30 

1 in 1.00 

 (1 in 1.04, 1 in 1.00) 

Potato 1 18.90 

1 in 1.00 

 (1 in 1.01, 1 in 1.00) 

3.15 

1 in 1.01 

 (1 in 1.19, 1 in 1.00) 

Potato (Northern 

Central coast) 1 Add 26.30 

1 in 1.00 

4.38 

1 in 1.00 
149

Use Category Run 

No. 

Acute FW 

Fish RQ 

Change of Individual 

Effect at RQ or LOC 

Based on Probit Slope & 

Slope's 95% CI 

Acute FW 

Invert. RQ 

Change of Individual 

Effect at RQ or LOC 

Based on Probit Slope 

& Slope's 95% CI 

 (1 in 1.00, 1 in 1.00) (1 in 1.11, 1 in 1.00) 

Sweet Potato 3 11.80 

1 in 1.00 

 (1 in 1.02, 1 in 1.00) 

1.97 

1 in 1.10 

 (1 in 1.39, 1 in 1.00) 

Beans & Peas (dry) & 

Pepper 1 20.00 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

3.33 

1 in 1.01 

 (1 in 1.17, 1 in 1.00) 

Carrot & Celery 2 17.20 

1 in 1.00 

 (1 in 1.01, 1 in 1.00) 

2.87 

1 in 1.02 

 (1 in 1.22, 1 in 1.00) 

Strawberry 1 36.40 

1 in 1.00 

 (1 in 1.00, 1 in 1.00) 

6.07 

1 in 1.00 

 (1 in 1.06, 1 in 1.00) 

Tomato 1 17.90 

1 in 1.00 

 (1 in 1.01, 1 in 1.00) 

2.98 

1 in 1.02 

 (1 in 1.21, 1 in 1.00) 

(1) Bolded RQs exceed the Agency’s acute listed species LOC (0.05 for aquatic animals). When acute RQs exceed the Agency’s listed 

species LOC, the chance of individual effects was calculated at the RQ and the LOC, whereas if there was no exceedance, then the 

chance of individual effects was calculated only at the LOC. 

(2) Although an LC50 or an EC50 has been established for all aquatic taxonomic groups, information is unavailable to estimate probit 

slopes from the studies from which the endpoints were derived. Therefore, a default slope of 4.5 with an assumed 95% confidence 

interval of 2 and 9 has been assumed as per original Agency assumptions of typical slope cited in Urban and Cook (1986). 
Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on acute RQs, the acute 

acute toxicity data, and probit slope response relationships. Use Category Dietary Category 

20 g Bird 

Acute 

RQ 

Chance of Individual 

Effect at RQ or LOC 

Based on Probit 

Slope & Slope's 95% 

CI 

15 g 

Mammal 

Acute RQ 

Chance of 

Individual Effect at 

RQ or LOC Based 

on Probit Slope & 

Slope's 95% CI 

1000 g 

Mammal 

Acute 

RQ 

Chance of Individu

Effect at RQ or LO

Based on Probit 

Slope & Slope's 95

CI 

N/A N/A LOC = 0.1 1 in 1.05E+17 (1 in 6290, 1 in 3.31E+40) LOC = 0.1 1 in 2.94E+05 (1 in 44, 1 in 8.86E+18) LOC = 0.1 1 in 2.94E+05 (1 in 44, 1 in 8.86E+18) 

Short Grass 37.60 1 in 1.00 (1 in 1.00, 1 in 1.00) 20.82 1 in 1.00 (1 in 1.00, 1 in 1.00) 9.53 1 in 1.00 (1 in 1.03, 1 in 1.0Tall Grass 17.23 1 in 1.00 (1 in 1.00, 1 in 1.00) 9.54 1 in 1.00 (1 in 1.03, 1 in 1.00) 4.37 1 in 1.00 (1 in 1.11, 1 in 1.0Broadleaf Plants/ Small Insects 21.15 1 in 1.00 (1 in 1.00, 1 in 1.00) 11.71 1 in 1.00 (1 in 1.02, 1 in 1.00) 5.36 1 in 1.00 (1 in 1.08, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 2.35 1 in 1.00 (1 in 1.10, 1 in 1.00) 1.30 1 in 1.44 (1 in 1.69, 1 in 1.18) 0.60 1 in 6.42 (1 in 3.06, 1 in 46.4

Almonds, hazelnut & walnut 

Granivore 0.52 

1 in 121.33 

 (1 in 6.46, 1 in 

1.28E+04) 

0.29 

1 in 130.50 

 (1 in 7.11, 1 in 

1.61E+06) 

0.13 

1 in 2.57E+04 

 (1 in 25.29, 1 in 

7.31E+14) 

Short Grass 47.00 1 in 1.00 (1 in 1.00, 1 in 1.00) 26.03 1 in 1.00 (1 in 1.00, 1 in 1.00) 11.92 1 in 1.00 (1 in 1.02, 1 in 1.0Tall Grass 21.54 1 in 1.00 (1 in 1.00, 1 in 1.00) 11.93 1 in 1.00 (1 in 1.02, 1 in 1.00) 5.46 1 in 1.00 (1 in 1.08, 1 in 1.0Broadleaf Plants/ Small Insects 26.44 1 in 1.00 (1 in 1.00, 1 in 1.00) 14.64 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.70 1 in 1.00 (1 in 1.05, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 2.94 1 in 1.00 (1 in 1.05, 1 in 1.00) 1.63 1 in 1.21 (1 in 1.51, 1 in 1.03) 0.74 1 in 3.54 (1 in 2.51, 1 in 8.0

Citrus 

Granivore 0.65 

1 in 17.33 

 (1 in 3.96, 1 in 

153.00) 

0.36 

1 in 42.78 

 (1 in 5.31, 1 in 

2.87E+04) 

0.17 

1 in 4.55E+03 

 (1 in 16.92, 1 in 

9.70E+11) 

Short Grass 24.39 1 in 1.00 (1 in 1.00, 1 in 1.00) 13.51 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.18 1 in 1.00 (1 in 1.06, 1 in 1.0

Broccoli, cabbage, Chinese cabbage, Tall Grass 11.18 1 in 1.00 (1 in 1.00, 1 in 1.00) 6.19 1 in 1.00 (1 in 1.06, 1 in 1.00) 2.83 1 in 1.02 (1 in 1.22, 1 in 1.0

150
Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on acute RQs, the acute 

acute toxicity data, and probit slope response relationships. Use Category Dietary Category 

20 g Bird 

Acute 

RQ 

Chance of Individual 

Effect at RQ or LOC 

Based on Probit 

Slope & Slope's 95% 

CI 

15 g 

Mammal 

Acute RQ 

Chance of 

Individual Effect at 

RQ or LOC Based 

on Probit Slope & 

Slope's 95% CI 

1000 g 

Mammal 

Acute 

RQ 

Chance of Individu

Effect at RQ or LO

Based on Probit 

Slope & Slope's 95

CI 

Broadleaf Plants/ Small Insects 13.72 1 in 1.00 (1 in 1.00, 1 in 1.00) 7.60 1 in 1.00 (1 in 1.04, 1 in 1.00) 3.48 1 in 1.01 (1 in 1.16, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.52 1 in 1.06 (1 in 1.34, 1 in 1.01) 0.84 1 in 2.70 (1 in 2.26, 1 in 3.94) 0.39 1 in 31.64 (1 in 4.89, 1 in 9.86E+03) 

cauliflower, kohlrabi 

Granivore 0.34 

1 in 3.10E+04 

 (1 in 22.08, 1 in 

6.70E+09) 

0.19 

1 in 1.86E+03 

 (1 in 13.69, 1 in 

3.27E+10) 

0.09 

Short Grass 14.10 1 in 1.00 (1 in 1.00, 1 in 1.00) 7.81 1 in 1.00 (1 in 1.04, 1 in 1.00) 3.58 1 in 1.01 (1 in 1.16, 1 in 1.0Tall Grass 6.46 1 in 1.00 (1 in 1.00, 1 in 1.00) 3.58 1 in 1.01 (1 in 1.15, 1 in 1.00) 1.64 1 in 1.20 (1 in 1.50, 1 in 1.0Broadleaf Plants/ Small Insects 7.93 1 in 1.00 (1 in 1.00, 1 in 1.00) 4.39 1 in 1.00 (1 in 1.11, 1 in 1.00) 2.01 1 in 1.09 (1 in 1.37, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 0.88 1 in 3.12 (1 in 2.37, 1 in 4.33) 0.49 1 in 12.43 (1 in 3.75, 1 in 396.26) 0.22 1 in 587.41 (1 in 10.36, 1 in 4.25E+08) 

Kale, Collards & Mustard Green 

Granivore 0.20 

1 in 1.14E+09 

 (1 in 185.19, 1 in 

8.52E+20) 

0.11 

1 in 1.41E+05 

 (1 in 37.27, 1 in 

5.18E+17) 

0.05 

Short Grass 28.20 1 in 1.00 (1 in 1.00, 1 in 1.00) 15.62 1 in 1.00 (1 in 1.01, 1 in 1.00) 7.15 1 in 1.00 (1 in 1.05, 1 in 1.0Tall Grass 12.93 1 in 1.00 (1 in 1.00, 1 in 1.00) 7.16 1 in 1.00 (1 in 1.05, 1 in 1.00) 3.28 1 in 1.01 (1 in 1.18, 1 in 1.0Broadleaf Plants/ Small Insects 15.86 1 in 1.00 (1 in 1.00, 1 in 1.00) 8.78 1 in 1.00 (1 in 1.03, 1 in 1.00) 4.02 1 in 1.00 (1 in 1.13, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.76 1 in 1.02 (1 in 1.23, 1 in 1.00) 0.98 1 in 2.08 (1 in 2.03, 1 in 2.16) 0.45 1 in 17.32 (1 in 4.13, 1 in 1.22E+03) 

Sweet corn 

Granivore 0.39 

1 in 3.70E+03 

 (1 in 14.00, 1 in 

4.07E+07) 

0.22 

1 in 709.49 

 (1 in 10.85, 1 in 

8.62E+08) 

0.10 

151
Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on acute RQs, the acute 

acute toxicity data, and probit slope response relationships. Use Category Dietary Category 

20 g Bird 

Acute 

RQ 

Chance of Individual 

Effect at RQ or LOC 

Based on Probit 

Slope & Slope's 95% 

CI 

15 g 

Mammal 

Acute RQ 

Chance of 

Individual Effect at 

RQ or LOC Based 

on Probit Slope & 

Slope's 95% CI 

1000 g 

Mammal 

Acute 

RQ 

Chance of Individu

Effect at RQ or LO

Based on Probit 

Slope & Slope's 95

CI 

Short Grass 18.80 1 in 1.00 (1 in 1.00, 1 in 1.00) 10.41 1 in 1.00 (1 in 1.02, 1 in 1.00) 4.77 1 in 1.00 (1 in 1.10, 1 in 1.0Tall Grass 8.62 1 in 1.00 (1 in 1.00, 1 in 1.00) 4.77 1 in 1.00 (1 in 1.10, 1 in 1.00) 2.18 1 in 1.07 (1 in 1.33, 1 in 1.0Broadleaf Plants/ Small Insects 10.58 1 in 1.00 (1 in 1.00, 1 in 1.00) 5.86 1 in 1.00 (1 in 1.07, 1 in 1.00) 2.68 1 in 1.03 (1 in 1.24, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.18 1 in 1.38 (1 in 1.67, 1 in 1.21) 0.65 1 in 4.99 (1 in 2.82, 1 in 21.50) 0.30 1 in 111.34 (1 in 6.83, 1 in 9.03E+05) 

Cotton (ground) 

Granivore 0.26 

1 in 2.79E+06 

 (1 in 55.89, 1 in 

3.62E+14) 

0.14 

1 in 1.27E+04 

 (1 in 21.50, 1 in 

4.90E+13) 

0.07 

Short Grass 18.29 1 in 1.00 (1 in 1.00, 1 in 1.00) 10.13 1 in 1.00 (1 in 1.02, 1 in 1.00) 4.64 1 in 1.00 (1 in 1.10, 1 in 1.0Tall Grass 8.38 1 in 1.00 (1 in 1.00, 1 in 1.00) 4.64 1 in 1.00 (1 in 1.10, 1 in 1.00) 2.13 1 in 1.08 (1 in 1.34, 1 in 1.0Broadleaf Plants/ Small Insects 10.29 1 in 1.00 (1 in 1.00, 1 in 1.00) 5.70 1 in 1.00 (1 in 1.07, 1 in 1.00) 2.61 1 in 1.03 (1 in 1.25, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.14 1 in 1.45 (1 in 1.72, 1 in 1.28) 0.63 1 in 5.38 (1 in 2.89, 1 in 27.03) 0.29 1 in 128.84 (1 in 7.09, 1 in 1.54E+06) 

Cotton (Areal) 

Granivore 0.25 

1 in 4.72E+06 

 (1 in 62.15, 1 in 

1.30E+15) 

0.14 

1 in 1.58E+04 

 (1 in 22.60, 1 in 

1.12E+14) 

0.06 

Short Grass 47.00 1 in 1.00 (1 in 1.00, 1 in 1.00) 26.03 1 in 1.00 (1 in 1.00, 1 in 1.00) 11.92 1 in 1.00 (1 in 1.02, 1 in 1.0Tall Grass 

21.54 1 in 1.00 (1 in 1.00, 1 in 1.00) 11.93 1 in 1.00 (1 in 1.02, 1 in 1.00) 5.46 1 in 1.00 (1 in 1.08, 1 in 1.0

Apples 

Broadleaf Plants/ Small Insects 

26.44 1 in 1.00 (1 in 1.00, 1 in 1.00) 14.64 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.70 1 in 1.00 (1 in 1.05, 1 in 1.0

152
Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on acute RQs, the acute 

acute toxicity data, and probit slope response relationships. Use Category Dietary Category 

20 g Bird 

Acute 

RQ 

Chance of Individual 

Effect at RQ or LOC 

Based on Probit 

Slope & Slope's 95% 

CI 

15 g 

Mammal 

Acute RQ 

Chance of 

Individual Effect at 

RQ or LOC Based 

on Probit Slope & 

Slope's 95% CI 

1000 g 

Mammal 

Acute 

RQ 

Chance of Individu

Effect at RQ or LO

Based on Probit 

Slope & Slope's 95

CI 

Fruits/Pods/ Seeds/ Large Insects 2.94 1 in 1.00 (1 in 1.05, 1 in 1.00) 1.63 1 in 1.21 (1 in 1.51, 1 in 1.03) 0.74 1 in 3.54 (1 in 2.51, 1 in 8.0Granivore 0.65 

1 in 17.33 

 (1 in 3.96, 1 in 

153.00) 

0.36 

1 in 42.78 

 (1 in 5.31, 1 in 

2.87E+04) 

0.17 

1 in 4.55E+03 

 (1 in 16.92, 1 in 

9.70E+11) 

Short Grass 47.00 1 in 1.00 (1 in 1.00, 1 in 1.00) 26.03 1 in 1.00 (1 in 1.00, 1 in 1.00) 11.92 1 in 1.00 (1 in 1.02, 1 in 1.0Tall Grass 21.54 1 in 1.00 (1 in 1.00, 1 in 1.00) 11.93 1 in 1.00 (1 in 1.02, 1 in 1.00) 5.46 1 in 1.00 (1 in 1.08, 1 in 1.0Broadleaf Plants/ Small Insects 26.44 1 in 1.00 (1 in 1.00, 1 in 1.00) 14.64 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.70 1 in 1.00 (1 in 1.05, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 2.94 1 in 1.00 (1 in 1.05, 1 in 1.00) 1.63 1 in 1.21 (1 in 1.51, 1 in 1.03) 0.74 1 in 3.54 (1 in 2.51, 1 in 8.0

Apricot, nectarine, peach, cherry, pear, plum & prune 

Granivore 0.65 

1 in 17.33 

 (1 in 3.96, 1 in 

153.00) 

0.36 

1 in 42.78 

 (1 in 5.31, 1 in 

2.87E+04) 

0.17 

1 in 4.55E+03 

 (1 in 16.92, 1 in 

9.70E+11) 

Short Grass 26.71 1 in 1.00 (1 in 1.00, 1 in 1.00) 14.79 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.77 1 in 1.00 (1 in 1.05, 1 in 1.0Tall Grass 12.24 1 in 1.00 (1 in 1.00, 1 in 1.00) 6.78 1 in 1.00 (1 in 1.05, 1 in 1.00) 3.10 1 in 1.01 (1 in 1.19, 1 in 1.0Broadleaf Plants/ Small Insects 15.02 1 in 1.00 (1 in 1.00, 1 in 1.00) 8.32 1 in 1.00 (1 in 1.03, 1 in 1.00) 3.81 1 in 1.00 (1 in 1.14, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.67 1 in 1.03 (1 in 1.27, 1 in 1.00) 0.92 1 in 2.28 (1 in 2.12, 1 in 2.64) 0.42 1 in 21.54 (1 in 4.39, 1 in 2.57E+03) 

Lettuce & Brussels sprouts 

Granivore 0.37 

1 in 7.97E+03 

 (1 in 16.53, 1 in 

2.55E+08) 

0.21 

1 in 1.01E+03 

 (1 in 11.82, 1 in 

3.25E+09) 

0.09 

Cucumber, melons, pumpkin & Short Grass 

24.39 1 in 1.00 (1 in 1.00, 1 in 1.00) 13.51 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.18 1 in 1.00 (1 in 1.06, 1 in 1.0

153
Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on acute RQs, the acute 

acute toxicity data, and probit slope response relationships. Use Category Dietary Category 

20 g Bird 

Acute 

RQ 

Chance of Individual 

Effect at RQ or LOC 

Based on Probit 

Slope & Slope's 95% 

CI 

15 g 

Mammal 

Acute RQ 

Chance of 

Individual Effect at 

RQ or LOC Based 

on Probit Slope & 

Slope's 95% CI 

1000 g 

Mammal 

Acute 

RQ 

Chance of Individu

Effect at RQ or LO

Based on Probit 

Slope & Slope's 95

CI 

Tall Grass 11.18 1 in 1.00 (1 in 1.00, 1 in 1.00) 6.19 1 in 1.00 (1 in 1.06, 1 in 1.00) 2.83 1 in 1.02 (1 in 1.22, 1 in 1.0Broadleaf Plants/ Small Insects 13.72 1 in 1.00 (1 in 1.00, 1 in 1.00) 7.60 1 in 1.00 (1 in 1.04, 1 in 1.00) 3.48 1 in 1.01 (1 in 1.16, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.52 1 in 1.06 (1 in 1.34, 1 in 1.01) 0.84 1 in 2.70 (1 in 2.26, 1 in 3.94) 0.39 1 in 31.64 (1 in 4.89, 1 in 9.86E+03) 

squash 

Granivore 0.34 

1 in 3.10E+04 

 (1 in 22.08, 1 in 

6.70E+09) 

0.19 

1 in 1.86E+03 

 (1 in 13.69, 1 in 

3.27E+10) 

0.09 

Short Grass 9.40 1 in 1.00 (1 in 1.00, 1 in 1.00) 5.21 1 in 1.00 (1 in 1.08, 1 in 1.00) 2.38 1 in 1.05 (1 in 1.29, 1 in 1.0Tall Grass 4.31 1 in 1.00 (1 in 1.01, 1 in 1.00) 2.39 1 in 1.05 (1 in 1.29, 1 in 1.00) 1.09 1 in 1.76 (1 in 1.88, 1 in 1.5Broadleaf Plants/ Small Insects 5.29 1 in 1.00 (1 in 1.00, 1 in 1.00) 2.93 1 in 1.02 (1 in 1.21, 1 in 1.00) 1.34 1 in 1.40 (1 in 1.67, 1 in 1.1Fruits/Pods/ Seeds/ Large Insects 0.59 

1 in 40.31 

 (1 in 4.93, 1 in 

1.02E+03) 

0.33 

1 in 70.91 

 (1 in 6.07, 1 in 

1.75E+05) 

0.15 

1 in 1.01E+04 

 (1 in 20.37, 1 in 

2.02E+13) 

Eggplant 

Granivore 0.13 

1 in 3.53E+13 

 (1 in 1.37E+03, 1 in 

9.08E+31) 

0.07 

1 in 7.05E+06 

 (1 in 88.87, 1 in 

2.03E+24) 

0.03 

Short Grass 11.42 1 in 1.00 (1 in 1.00, 1 in 1.00) 6.32 1 in 1.00 (1 in 1.06, 1 in 1.00) 2.90 1 in 1.02 (1 in 1.22, 1 in 1.0Tall Grass 

5.23 1 in 1.00 (1 in 1.00, 1 in 1.00) 2.90 1 in 1.02 (1 in 1.22, 1 in 1.00) 1.33 1 in 1.41 (1 in 1.67, 1 in 1.1

Broadleaf Plants/ Small Insects 6.42 1 in 1.00 (1 in 1.00, 1 in 1.00) 3.56 1 in 1.01 (1 in 1.16, 1 in 1.00) 1.63 1 in 1.21 (1 in 1.51, 1 in 1.0

Ornamentals & shade trees 

Fruits/Pods/ Seeds/ Large Insects 0.71 1 in 9.39 (1 in 3.34, 1 in 40.29) 0.40 1 in 28.72 (1 in 4.76, 1 in 7.02E+03) 0.18 1 in 2.40E+03 (1 in 14.54, 1 in 8.48E+10) 

154
Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on acute RQs, the acute 

acute toxicity data, and probit slope response relationships. Use Category Dietary Category 

20 g Bird 

Acute 

RQ 

Chance of Individual 

Effect at RQ or LOC 

Based on Probit 

Slope & Slope's 95% 

CI 

15 g 

Mammal 

Acute RQ 

Chance of 

Individual Effect at 

RQ or LOC Based 

on Probit Slope & 

Slope's 95% CI 

1000 g 

Mammal 

Acute 

RQ 

Chance of Individu

Effect at RQ or LO

Based on Probit 

Slope & Slope's 95

CI 

Granivore 0.16 

1 in 1.88E+11 

 (1 in 501.26, 1 in 

2.34E+26) 

0.09 

1 in 1.00E+06 

 (1 in 57.77, 1 in 

1.02E+21) 

0.04 

Short Grass 26.71 1 in 1.00 (1 in 1.00, 1 in 1.00) 14.79 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.77 1 in 1.00 (1 in 1.05, 1 in 1.0Tall Grass 12.24 1 in 1.00 (1 in 1.00, 1 in 1.00) 6.78 1 in 1.00 (1 in 1.05, 1 in 1.00) 3.10 1 in 1.01 (1 in 1.19, 1 in 1.0Broadleaf Plants/ Small Insects 15.02 1 in 1.00 (1 in 1.00, 1 in 1.00) 8.32 1 in 1.00 (1 in 1.03, 1 in 1.00) 3.81 1 in 1.00 (1 in 1.14, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.67 1 in 1.03 (1 in 1.27, 1 in 1.00) 0.92 1 in 2.28 (1 in 2.12, 1 in 2.64) 0.42 1 in 21.54 (1 in 4.39, 1 in 2.57E+03) 

Potato 

Granivore 0.37 

1 in 7.97E+03 

 (1 in 16.53, 1 in 

2.55E+08) 

0.21 

1 in 1.01E+03 

 (1 in 11.82, 1 in 

3.25E+09) 

0.09 

Short Grass 15.01 1 in 1.00 (1 in 1.00, 1 in 1.00) 8.31 1 in 1.00 (1 in 1.03, 1 in 1.00) 3.81 1 in 1.00 (1 in 1.14, 1 in 1.0Tall Grass 6.88 1 in 1.00 (1 in 1.00, 1 in 1.00) 3.81 1 in 1.00 (1 in 1.14, 1 in 1.00) 1.74 1 in 1.16 (1 in 1.46, 1 in 1.0Broadleaf Plants/ Small Insects 8.45 1 in 1.00 (1 in 1.00, 1 in 1.00) 4.68 1 in 1.00 (1 in 1.10, 1 in 1.00) 2.14 1 in 1.07 (1 in 1.34, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 0.94 1 in 2.46 (1 in 2.17, 1 in 2.81) 0.52 1 in 9.96 (1 in 3.51, 1 in 190.27) 0.24 1 in 398.57 (1 in 9.42, 1 in 9.99E+07) 

Sweet potato 

Granivore 0.21 

1 in 2.79E+08 

 (1 in 140.36, 1 in 

2.73E+19) 

0.12 

1 in 8.14E+04 

 (1 in 32.90, 1 in 

6.17E+16) 

0.05 

Short Grass 26.71 1 in 1.00 (1 in 1.00, 1 in 1.00) 14.79 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.77 1 in 1.00 (1 in 1.05, 1 in 1.0

Dry beans (except Lima), peas & pepper Tall Grass 12.24 1 in 1.00 (1 in 1.00, 1 in 1.00) 6.78 1 in 1.00 (1 in 1.05, 1 in 1.00) 3.10 1 in 1.01 (1 in 1.19, 1 in 1.0

155
Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on acute RQs, the acute 

acute toxicity data, and probit slope response relationships. Use Category Dietary Category 

20 g Bird 

Acute 

RQ 

Chance of Individual 

Effect at RQ or LOC 

Based on Probit 

Slope & Slope's 95% 

CI 

15 g 

Mammal 

Acute RQ 

Chance of 

Individual Effect at 

RQ or LOC Based 

on Probit Slope & 

Slope's 95% CI 

1000 g 

Mammal 

Acute 

RQ 

Chance of Individu

Effect at RQ or LO

Based on Probit 

Slope & Slope's 95

CI 

Broadleaf Plants/ Small Insects 15.02 1 in 1.00 (1 in 1.00, 1 in 1.00) 8.32 1 in 1.00 (1 in 1.03, 1 in 1.00) 3.81 1 in 1.00 (1 in 1.14, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.67 1 in 1.03 (1 in 1.27, 1 in 1.00) 0.92 1 in 2.28 (1 in 2.12, 1 in 2.64) 0.42 1 in 21.54 (1 in 4.39, 1 in 2.57E+03) Granivore 0.37 

1 in 7.97E+03 

 (1 in 16.53, 1 in 

2.55E+08) 

0.21 

1 in 1.01E+03 

 (1 in 11.82, 1 in 

3.25E+09) 

0.09 

Short Grass 18.80 1 in 1.00 (1 in 1.00, 1 in 1.00) 10.41 1 in 1.00 (1 in 1.02, 1 in 1.00) 4.77 1 in 1.00 (1 in 1.10, 1 in 1.0Tall Grass 8.62 1 in 1.00 (1 in 1.00, 1 in 1.00) 4.77 1 in 1.00 (1 in 1.10, 1 in 1.00) 2.18 1 in 1.07 (1 in 1.33, 1 in 1.0Broadleaf Plants/ Small Insects 10.58 1 in 1.00 (1 in 1.00, 1 in 1.00) 5.86 1 in 1.00 (1 in 1.07, 1 in 1.00) 2.68 1 in 1.03 (1 in 1.24, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.18 1 in 1.38 (1 in 1.67, 1 in 1.21) 0.65 1 in 4.99 (1 in 2.82, 1 in 21.50) 0.30 1 in 111.34 (1 in 6.83, 1 in 9.03E+05) 

Carrot 

Granivore 0.26 

1 in 2.79E+06 

 (1 in 55.89, 1 in 

3.62E+14) 

0.14 

1 in 1.27E+04 

 (1 in 21.50, 1 in 

4.90E+13) 

0.07 

Short Grass 18.80 1 in 1.00 (1 in 1.00, 1 in 1.00) 10.41 1 in 1.00 (1 in 1.02, 1 in 1.00) 4.77 1 in 1.00 (1 in 1.10, 1 in 1.0Tall Grass 8.62 1 in 1.00 (1 in 1.00, 1 in 1.00) 4.77 1 in 1.00 (1 in 1.10, 1 in 1.00) 2.18 1 in 1.07 (1 in 1.33, 1 in 1.0Broadleaf Plants/ Small Insects 10.58 1 in 1.00 (1 in 1.00, 1 in 1.00) 5.86 1 in 1.00 (1 in 1.07, 1 in 1.00) 2.68 1 in 1.03 (1 in 1.24, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 

1.18 1 in 1.38 (1 in 1.67, 1 in 1.21) 0.65 1 in 4.99 (1 in 2.82, 1 in 21.50) 0.30 1 in 111.34 (1 in 6.83, 1 in 9.03E+05) 

Celery 

Granivore 0.26 

1 in 2.79E+06 

 (1 in 55.89, 1 in 

3.62E+14) 

0.14 

1 in 1.27E+04 

 (1 in 21.50, 1 in 

4.90E+13) 

0.07 

156
Table 5.12 Summary of the chance of individual acute effects to terrestrial animals based on acute RQs, the acute 

acute toxicity data, and probit slope response relationships. Use Category Dietary Category 

20 g Bird 

Acute 

RQ 

Chance of Individual 

Effect at RQ or LOC 

Based on Probit 

Slope & Slope's 95% 

CI 

15 g 

Mammal 

Acute RQ 

Chance of 

Individual Effect at 

RQ or LOC Based 

on Probit Slope & 

Slope's 95% CI 

1000 g 

Mammal 

Acute 

RQ 

Chance of Individu

Effect at RQ or LO

Based on Probit 

Slope & Slope's 95

CI 

Short Grass 20.20 1 in 1.00 (1 in 1.00, 1 in 1.00) 11.19 1 in 1.00 (1 in 1.02, 1 in 1.00) 5.12 1 in 1.00 (1 in 1.08, 1 in 1.0Tall Grass 9.26 1 in 1.00 (1 in 1.00, 1 in 1.00) 5.13 1 in 1.00 (1 in 1.08, 1 in 1.00) 2.35 1 in 1.05 (1 in 1.30, 1 in 1.0Broadleaf Plants/ Small Insects 11.36 1 in 1.00 (1 in 1.00, 1 in 1.00) 6.29 1 in 1.00 (1 in 1.06, 1 in 1.00) 2.88 1 in 1.02 (1 in 1.22, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.26 1 in 1.24 (1 in 1.56, 1 in 1.10) 0.70 1 in 4.13 (1 in 2.65, 1 in 12.37) 0.32 1 in 76.94 (1 in 6.20, 1 in 2.36E+05) 

Strawberry 

Granivore 0.28 

1 in 7.40E+05 

 (1 in 42.65, 1 in 

1.44E+13) 

0.16 

1 in 7.31E+03 

 (1 in 18.90, 1 in 

5.91E+12) 

0.07 

Short Grass 24.39 1 in 1.00 (1 in 1.00, 1 in 1.00) 13.51 1 in 1.00 (1 in 1.01, 1 in 1.00) 6.18 1 in 1.00 (1 in 1.06, 1 in 1.0Tall Grass 11.18 1 in 1.00 (1 in 1.00, 1 in 1.00) 6.19 1 in 1.00 (1 in 1.06, 1 in 1.00) 2.83 1 in 1.02 (1 in 1.22, 1 in 1.0Broadleaf Plants/ Small Insects 13.72 1 in 1.00 (1 in 1.00, 1 in 1.00) 7.60 1 in 1.00 (1 in 1.04, 1 in 1.00) 3.48 1 in 1.01 (1 in 1.16, 1 in 1.0Fruits/Pods/ Seeds/ Large Insects 1.52 1 in 1.06 (1 in 1.34, 1 in 1.01) 0.84 1 in 2.70 (1 in 2.26, 1 in 3.94) 0.39 1 in 31.64 (1 in 4.89, 1 in 9.86E+03) 

Tomato 

Granivore 0.34 

1 in 3.10E+04 

 (1 in 22.08, 1 in 

6.70E+09) 

0.19 

1 in 1.86E+03 

 (1 in 13.69, 1 in 

3.27E+10) 

0.09 

(1) Bolded RQs exceed the Agency’s acute listed species LOC (0.1 for terrestrial animals). When acute RQs exceed the Agency’s listed species LOC, the chance of individual effect

whereas if there was no exceedance, then the chance of individual effects was calculated only at the LOC. 

(2) Although an LD50 has been established for all terrestrial taxonomic groups, information is unavailable to estimate probit slopes from the mammal studies from which the endpoi

of 4.5 with an assumed 95% confidence interval of 2 and 9 has been assumed as per original Agency assumptions of typical slope cited in Urban and Cook (1986). The probit slope confidence limits of 3.6 and 13.4. The probit slope for the insect was 1.91 with 95% confidence intervals of 1.40 and 2.42.

157
Table 5.13 Summary of the chance of individual acute effects to herpetofauna based on acute RQs, the acute liste

toxicity data, and probit slope response relationships. Use Category Dietary Category 

1.4 g 

Herp. 

Acute 

RQ 

Chance of Individual Effect at 

RQ or LOC Based on Probit 

Slope & Slope's 95% CI 

35 g 

Herp. 

Acute 

RQ 

Chance of Individual Effect at 

RQ or LOC Based on Probit 

Slope & Slope's 95% CI 

238 g Herp. 

Acute 

RQ 

N/A N/A LOC = 0.1 1 in 1.05E+17 (1 in 6290, 1 in 3.31E+40) LOC = 0.1 1 in 1.05E+17 (1 in 6290, 1 in 3.31E+40) LOC = 0.1 

Broadleaf Plants/Small Insects 1.08 1 in 1.65 (1 in 1.83, 1 in 1.51) 0.65 1 in 18.60 (1 in 4.04, 1 in 179.07) 0.32 Fruits/Pods/Seeds/Large Insects 0.12 1 in 4.56E+14 (1 in 2.24E+03, 1 in 4.94E+34) 0.07 0.04 Small Herbivore Mammals 11.64 1 in 1.00 (1 in 1.00, 1 in 1.00) 1.37 Small Insectivore Mammal 0.73 1 in 8.34 (1 in 3.23, 1 in 31.32) 0.09 

Almonds, hazelnut & walnut 

Small Amphibians 0.02 0.01 

Broadleaf Plants/Small Insects 1.34 1 in 1.16 (1 in 1.47, 1 in 1.04) 0.81 1 in 4.63 (1 in 2.71, 1 in 9.28) 0.40 Fruits/Pods/Seeds/Large Insects 0.15 1 in 8.99E+11 (1 in 678.21, 1 in 1.09E+28) 0.09 0.04 Small Herbivore Mammals 14.55 1 in 1.00 (1 in 1.00, 1 in 1.00) 1.71 Small Insectivore Mammal 0.91 1 in 2.76 (1 in 2.27, 1 in 3.45) 0.11 

Citrus 

Small Amphibians 0.03 0.01 

Broadleaf Plants/Small Insects 0.70 1 in 10.90 (1 in 3.49, 1 in 55.57) 0.42 1 in 1.49E+03 (1 in 11.47, 1 in 4.68E+06) 0.21 Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.02 Small Herbivore Mammals 7.55 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.89 Small Insectivore Mammal 0.47 1 in 360.53 (1 in 8.33, 1 in 1.63E+05) 0.06 

Broccoli, cabbage, Chinese cabbage, cauliflower, kohlrabi 

Small Amphibians 0.01 0.01 

Broadleaf Plants/Small Insects 0.40 1 in 2.50E+03 (1 in 12.86, 1 in 1.60E+07) 0.24 1 in 1.18E+07 (1 in 74.77, 1 in 1.21E+16) 0.12 Fruits/Pods/Seeds/Large Insects 0.04 0.03 0.01 Small Herbivore Mammals 4.36 1 in 1.00 (1 in 1.01, 1 in 1.00) 0.51 

Kale, Collards & Mustard Green 

Small Insectivore Mammal 0.27 1 in 1.24E+06 (1 in 47.37, 1 in 5.00E+13) 0.03 

158
Table 5.13 Summary of the chance of individual acute effects to herpetofauna based on acute RQs, the acute liste

toxicity data, and probit slope response relationships. Use Category Dietary Category 

1.4 g 

Herp. 

Acute 

RQ 

Chance of Individual Effect at 

RQ or LOC Based on Probit 

Slope & Slope's 95% CI 

35 g 

Herp. 

Acute 

RQ 

238 g Chance of Individual Effect at Herp. RQ or LOC Based on Probit 

Acute Slope & Slope's 95% CI 

RQ 

Small Amphibians 0.01 0.004 Broadleaf Plants/Small Insects 0.81 1 in 4.68 (1 in 2.72, 1 in 9.50) 0.48 1 in 264.86 (1 in 7.76, 1 in 7.89E+04) 0.24 Fruits/Pods/Seeds/Large Insects 0.09 0.05 0.03 Small Herbivore Mammals 8.73 1 in 1.00 (1 in 1.00, 1 in 1.00) 1.03 Small Insectivore Mammal 0.55 1 in 79.19 (1 in 5.83, 1 in 4.76E+03) 0.06 

Sweet corn 

Small Amphibians 0.02 0.01 

Broadleaf Plants/Small Insects 0.54 1 in 91.07 (1 in 6.03, 1 in 6.58E+03) 0.32 1 in 6.52E+04 (1 in 25.81, 1 in 4.01E+10) 0.16 Fruits/Pods/Seeds/Large Insects 0.06 0.04 0.02 Small Herbivore Mammals 5.82 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.68 Small Insectivore Mammal 0.36 1 in 1.06E+04 (1 in 17.58, 1 in 5.08E+08) 0.04 

Cotton (ground) 

Small Amphibians 0.01 0.01 

Broadleaf Plants/Small Insects 0.52 1 in 119.41 (1 in 6.43, 1 in 1.23E+04) 0.31 1 in 1.02E+05 (1 in 28.34, 1 in 1.18E+11) 0.16 Fruits/Pods/Seeds/Large Insects 0.06 0.03 0.02 Small Herbivore Mammals 5.66 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.67 Small Insectivore Mammal 0.35 1 in 1.60E+04 (1 in 19.18, 1 in 1.35E+09) 0.04 

Cotton (Areal) 

Small Amphibians 0.01 0.01 

Broadleaf Plants/Small Insects 1.34 1 in 1.16 (1 in 1.47, 1 in 1.04) 0.81 1 in 4.63 (1 in 2.71, 1 in 9.28) 0.40 Fruits/Pods/Seeds/Large Insects 0.15 1 in 8.99E+11 (1 in 678.21, 1 in 1.09E+28) 0.09 0.04 Small Herbivore Mammals 14.55 1 in 1.00 (1 in 1.00, 1 in 1.00) 1.71 Small Insectivore Mammal 0.91 1 in 2.76 (1 in 2.27, 1 in 3.45) 0.11 

Apples 

Small Amphibians 0.03 0.01 

Apricot, nectarine, peach, cherry, pear, Broadleaf Plants/Small Insects 1.34 1 in 1.16 (1 in 1.47, 1 in 1.04) 0.81 1 in 4.63 (1 in 2.71, 1 in 9.28) 0.40 

159
Table 5.13 Summary of the chance of individual acute effects to herpetofauna based on acute RQs, the acute liste

toxicity data, and probit slope response relationships. Use Category Dietary Category 

1.4 g 

Herp. 

Acute 

RQ 

Chance of Individual Effect at 

RQ or LOC Based on Probit 

Slope & Slope's 95% CI 

35 g 

Herp. 

Acute 

RQ 

238 g Chance of Individual Effect at Herp. RQ or LOC Based on Probit 

Acute Slope & Slope's 95% CI 

RQ 

Fruits/Pods/Seeds/Large Insects 0.15 1 in 8.99E+11 (1 in 678.21, 1 in 1.09E+28) 0.09 0.04 Small Herbivore Mammals 14.55 1 in 1.00 (1 in 1.00, 1 in 1.00) 1.71 Small Insectivore Mammal 0.91 1 in 2.76 (1 in 2.27, 1 in 3.45) 0.11 

plum & prune 

Small Amphibians 0.03 0.01 

Broadleaf Plants/Small Insects 0.76 1 in 6.26 (1 in 2.97, 1 in 17.15) 0.46 1 in 491.37 (1 in 8.94, 1 in 3.37E+05) 0.23 Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.03 Small Herbivore Mammals 8.26 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.97 Small Insectivore Mammal 0.52 1 in 135.66 (1 in 6.63, 1 in 1.66E+04) 0.06 

Lettuce & Brussels sprouts 

Small Amphibians 0.02 0.01 

Broadleaf Plants/Small Insects 0.70 1 in 10.90 (1 in 3.49, 1 in 55.57) 0.42 1 in 1.49E+03 (1 in 11.47, 1 in 4.68E+06) 0.21 Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.02 Small Herbivore Mammals 7.55 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.89 Small Insectivore Mammal 0.47 1 in 360.53 (1 in 8.33, 1 in 1.63E+05) 0.06 

Cucumber, melons, pumpkin & squash 

Small Amphibians 0.01 0.01 

Broadleaf Plants/Small Insects 0.27 1 in 1.62E+06 (1 in 50.03, 1 in 9.61E+13) 0.16 1 in 1.16E+11 (1 in 456.17, 1 in 7.08E+25) 0.08 Fruits/Pods/Seeds/Large Insects 0.03 0.02 0.01 Small Herbivore Mammals 2.91 1 in 1.00 (1 in 1.05, 1 in 1.00) 0.34 Small Insectivore Mammal 0.18 1 in 6.42E+09 (1 in 259.99, 1 in 5.91E+22) 0.02 

Eggplant 

Small Amphibians 0.01 0.003 

Broadleaf Plants/Small Insects 0.33 1 in 5.56E+04 (1 in 24.96, 1 in 2.73E+10) 0.20 1 in 1.07E+09 (1 in 183.02, 1 in 7.36E+20) 0.10 Fruits/Pods/Seeds/Large Insects 0.04 0.02 0.01 

Ornamentals & shade trees 

Small Herbivore Mammals 3.53 1 in 1.00 (1 in 1.02, 1 in 1.00) 0.42 

160
Table 5.13 Summary of the chance of individual acute effects to herpetofauna based on acute RQs, the acute liste

toxicity data, and probit slope response relationships. Use Category Dietary Category 

1.4 g 

Herp. 

Acute 

RQ 

Chance of Individual Effect at 

RQ or LOC Based on Probit 

Slope & Slope's 95% CI 

35 g 

Herp. 

Acute 

RQ 

238 g Chance of Individual Effect at Herp. RQ or LOC Based on Probit 

Acute Slope & Slope's 95% CI 

RQ 

Small Insectivore Mammal 0.22 1 in 8.08E+07 (1 in 109.79, 1 in 1.32E+18) 0.03 Small Amphibians 0.01 0.003 Broadleaf Plants/Small Insects 0.76 1 in 6.26 (1 in 2.97, 1 in 17.15) 0.46 1 in 491.37 (1 in 8.94, 1 in 3.37E+05) 0.23 Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.03 Small Herbivore Mammals 8.26 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.97 Small Insectivore Mammal 0.52 1 in 135.66 (1 in 6.63, 1 in 1.66E+04) 0.06 

Potato 

Small Amphibians 0.02 0.01 

Broadleaf Plants/Small Insects 0.43 1 in 1.11E+03 (1 in 10.74, 1 in 2.32E+06) 0.26 1 in 3.46E+06 (1 in 58.37, 1 in 6.10E+14) 0.13 Fruits/Pods/Seeds/Large Insects 0.05 0.03 0.01 Small Herbivore Mammals 4.65 1 in 1.00 (1 in 1.01, 1 in 1.00) 0.55 Small Insectivore Mammal 0.29 1 in 3.99E+05 (1 in 37.58, 1 in 3.22E+12) 0.03 

Sweet potato 

Small Amphibians 0.01 0.004 

Broadleaf Plants/Small Insects 0.76 1 in 6.26 (1 in 2.97, 1 in 17.15) 0.46 1 in 491.37 (1 in 8.94, 1 in 3.37E+05) 0.23 Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.03 Small Herbivore Mammals 8.26 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.97 Small Insectivore Mammal 0.52 1 in 135.66 (1 in 6.63, 1 in 1.66E+04) 0.06 

Dry beans (except Lima), peas & pepper 

Small Amphibians 0.02 0.01 

Broadleaf Plants/Small Insects 0.54 1 in 91.07 (1 in 6.03, 1 in 6.58E+03) 0.32 1 in 6.52E+04 (1 in 25.81, 1 in 4.01E+10) 0.16 Fruits/Pods/Seeds/Large Insects 0.06 0.04 0.02 Small Herbivore Mammals 5.82 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.68 Small Insectivore Mammal 0.36 1 in 1.06E+04 (1 in 17.58, 1 in 5.08E+08) 0.04 

Carrot 

Small Amphibians 0.01 0.01 

161
162

Table 5.13 Summary of the chance of individual acute effects to herpetofauna based on acute RQs, the acute listetoxicity data, and probit slope response relationships. Use Category Dietary Category 

1.4 g 

Herp. 

Acute 

RQ 

Chance of Individual Effect at 

RQ or LOC Based on Probit 

Slope & Slope's 95% CI 

35 g 

Herp. 

Acute 

RQ 

Chance of Individual Effect at 

RQ or LOC Based on Probit 

Slope & Slope's 95% CI 

238 g Herp. 

Acute 

RQ 

Broadleaf Plants/Small Insects 0.54 1 in 91.07 (1 in 6.03, 1 in 6.58E+03) 0.32 1 in 6.52E+04 (1 in 25.81, 1 in 4.01E+10) 0.16 Fruits/Pods/Seeds/Large Insects 0.06 0.04 0.02 Small Herbivore Mammals 5.82 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.68 Small Insectivore Mammal 0.36 1 in 1.06E+04 (1 in 17.58, 1 in 5.08E+08) 0.04 

Celery 

Small Amphibians 0.01 0.01 

Broadleaf Plants/Small Insects 0.58 1 in 46.81 (1 in 5.12, 1 in 1.43E+03) 0.35 1 in 2.11E+04 (1 in 20.35, 1 in 2.65E+09) 0.17 Fruits/Pods/Seeds/Large Insects 0.06 0.04 0.02 Small Herbivore Mammals 6.25 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.74 Small Insectivore Mammal 0.39 1 in 3.84E+03 (1 in 14.11, 1 in 4.44E+07) 0.05 

Strawberry 

Small Amphibians 0.01 0.01 

Broadleaf Plants/Small Insects 0.70 1 in 10.90 (1 in 3.49, 1 in 55.57) 0.42 1 in 1.49E+03 (1 in 11.47, 1 in 4.68E+06) 0.21 Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.02 Small Herbivore Mammals 7.55 1 in 1.00 (1 in 1.00, 1 in 1.00) 0.89 Small Insectivore Mammal 0.47 1 in 360.53 (1 in 8.33, 1 in 1.63E+05) 0.06 

Tomato 

Small Amphibians 0.01 0.01 

(1) Bolded RQs exceed the Agency’s interim herpetofauna acute listed species LOC (0.1 ). When acute RQs exceed the Agency’s listed species LOC, the chance of individual effect

whereas if there was no exceedance, then the chance of individual effects was calculated only at the LOC. 

(2) Because birds are a surrogate for reptiles and terrestrial-phase amphibian, the probit slopes for birds was used. The probit slope for the bird acute LD50 was 8.5 with 95% confid

slope for the insect was 1.91 with 95% confidence intervals of 1.40 and 2.42. (3) The 1.4 g size class wase used to represent small terrestrial phase CRLF; the 37 g size class was used to represent adult CTS and the 238 g size class was use
5.2.1 California Red-Legged Frog 

5.2.1.1 Direct Effects 

The characterization of the likelihood of direct effects on the CRLF from registered uses of 

endosulfan in California considers multiple lines of evidence. These lines of evidence include: 

• The degree of temporal and spatial overlap between known CRLF habitat and 

endosulfan use (Appendix E). 

• Estimated risks from exposure modeling in aquatic and terrestrial ecosystems 

• The likelihood of impacts to individual CRLF using probit dose-response modeling 

• Estimated risks using monitoring data from aquatic and terrestrial ecosystems 

• Use of refined exposure and risk estimation methods (e.g., T-HERPS modeling for 

herpetofauna, earthworm fugacity modeling for contaminated terrestrial invertebrate 

prey, KABAM modeling for contaminated aquatic prey) 

• Information from reported ecological incidents associated with endosulfan use. 

In addition to these lines of evidence, the robustness of the risk estimation described in 

Section 5.1 is also considered by characterizing the major uncertainties and sensitivity of risk 

projections to underlying assumptions specific to the CRLF assessment. A discussion of each 

of these lines of evidence is presented in the following sections. 

Direct Effects: Aquatic-Phase CRLF 

The aquatic-phase considers life stages of the CRLF that are obligatory aquatic organisms, 

including eggs and larvae. It also considers submerged terrestrial-phase juveniles and adults, 

which spend a portion of their time in water bodies that may receive runoff and spray drift 

containing endosulfan. 

Temporal and Spatial Overlap 

Endosulfan is currently registered for a wide variety of agricultural crops (e.g., cotton, lettuce, 

brussels sprouts, cucurbits, dry beans, cole crops), orchards (e.g., citrus, almonds, walnuts), 

nursery (ornamentals and shade trees) and only one non-agricultural use (ear tags for cattle). 

These agriculture uses span a large variety of use sites and geographical regions throughout 

the entire state of California. Historically, however, the use of endosulfan has changed 

substantially over the last decade, with overall use dropping from approximately 500,000 lbs 

a.i. in 1994 to about 90,000 lbs a.i. in 2006 (Figure 2.3). Therefore, data from the most 

recent reporting years is used here for evaluating the degree of temporal and spatial overlap 

between the CRLF and endosulfan application in California. 

Based on data from the most recent reporting year (2006), the registered endosulfan uses 

allow for the potential for nearly year-round use, with the exception of little or no use during 

November, December and a portion of April (see Figure 5.1). Based on the likely occurrence 

of aquatic life stages of the CRLF (eggs, tadpoles and young juveniles during JanuarySeptember; Figure 5.2) in combination with the CDPR PUR data from 2006 (Figure 5.1), it 

163 
is reasonably expected that the registered use of endosulfan could coincide with each of the 

critical life-stages of the aquatic-phase CRLF. 

Time distribution for the total Lbs of endosulfan a.i applied during the year 2006

0

100

200

300

400

500

600

9-Jan 9-Feb 9-Mar 9-Apr 9-May 9-Jun 9-Jul 9-Aug 9-Sep 9-Oct 9-Nov 9-Dec

Date of Application

Total Endosulfan a.i. Applied (lbs)

Figure 5.1 Temporal distribution of endosulfan application in California for 2006 (Source: CDPR PUR))

Young Juveniles

Tadpoles (except those that overwinter)

Breeding/Egg Masses

J F M A M J J A S O N D 

Figure 5.2 CRLF Reproductive Events by Month; Adults and juveniles can be present all year. 

Table 5.7 summarizes information on the extent that endosulfan use and CRLF could 

potentially coincide spatially based on reported use information from 2005-2006 (CDPR 

PUR) and information on the occurrence of the CRLF or its critical habitat (Appendix E). 

Since pesticide use information is only available at the county level, the degree that the CRLF 

or its critical habitat actually coincides in the same or similar locations cannot be precisely 

determined. Nevertheless, there does appear to be a significant potential for overlap between 

the use of endosulfan and the presence of the CRLF or its critical habitat at least at the county 

level of resolution (Appendix E). Specifically, the CRLF is present in counties with the first, 

164 
fourth, fifth, tenth and eleventh highest reported usage from 2005-2006 (Table 5.7). The 

CRLF is also present in most other counties with lower endosulfan reported use. 

 

 Modeling--Based EECs 

Acute RQs based on modeled EECs for freshwater fish (used as a surrogate for the aquatic 

phase CRLF) range from 7.2 to 58.8, thus exceeding the Agency’s LOC (0.05) in all 20 crop 

scenarios modeled (Table 5.1). Similarly, chronic RQs range from 5.7 to 80.6 and exceed 

the Agency’s LOC (1.0) in all 20 crop scenarios modeled. These exceedences of the 

Agency’s acute and chronic LOCs suggest the potential for direct effects on the CRLF. 

As previously mentioned, EFED also estimates the chance of an individual event (i.e., 

mortality or immobilization) corresponding to the listed species acute LOCs and/or RQs 

should exposure at the EEC actually occur for a species with sensitivity to endosulfan on par 

with the acute toxicity endpoint selected for RQ calculation. To do this, the Agency uses the 

EFED spreadsheet IEC (version 1.1.xls) and the slope of the dose response relationship 

available from the toxicity study used to establish the acute toxicity measures of effect for 

each taxonomic group that is relevant to this assessment. The individual effects probability 

associated with the listed species acute LOCs and/or RQs is based on the mean estimate of the 

slope and an assumption of a probit dose response relationship. In addition to a single effects 

probability estimate based on the mean, available information on the 95% confidence interval 

of the slope is also used to estimate upper and lower estimates of the effects probability to 

account for variance in the slope, if available. If an LD50 or LC50 has been established for a 

particular taxonomic group, but information is unavailable to estimate a slope from a study, a 

default slope assumption of 4.5 (with upper and lower bounds of 2 and 9, respectively) is used 

as per original Agency assumptions of typical slope cited in Urban and Cook (1986). 

Based on a default slope of 4.5 (with upper and lower bounds of 2 and 9), the LC50 of the 

most acutely sensitive freshwater fish (common carp; LC50 = 0.1 μg a.i./L; Sunderam et al., 

1992; ECOTOX ref. # 5850) and the acute listed species LOC of 0.05, the chance of an 

individual mortality for aquatic-phase CRLF is ~ 1 in 4.18 x108 (with lower and upper bounds 

of ~ 1 in 2.16 x102 to ~ 1 in 1.75x1031; Table 5.11). Based on an analysis of the likelihood of 

individual mortality using the highest acute RQ value for freshwater fish (RQ=58.8 for 

Lettuce and Brussels Sprouts) and a default slope of 4.5 (with upper and lower bounds of 2 

and 9), the likelihood of individual mortality is ~ 1 in 1 (with lower and upper bounds of ~ 1 

in 1.00 to 1 in 1.00). At the lowest RQ value (i.e., RQ = 7.2 for Eggplant), the likelihood of 

individual mortality is ~ 1 in 1.00(with lower and upper bounds of ~ 1 in 1.00 to ~ 1 in 1.05). 

Based on: (1) the high probability of an individual mortality occurrence using the highest 

acute RQ (~1 in 1), (2) acute RQs that are above the listed species LOC (0.05) for all 20 

modeled scenarios; (3) chronic RQs that exceed the Agency’s LOC for all 20 modeled 

scenarios (1.0). and (4) the potential for spatial and temporal overlap of endosulfan usage with 

each of the critical life-stages of the aquatic-phase CRLF, it appears that endosulfan is likely 

to cause direct adverse effects to aquatic-phase CRLFs should exposure at the predicted EECs 

actually occur for a CRLF and assuming its sensitivity to endosulfan on par with the acute 

freshwater fish LC50 (common carp; LC50 = 0.1 μg a.i./L) selected for RQ calculation. 

165 
 Monitoring-based EECs 

Available data on the occurrence of endosulfan (and its primary degradate, endosulfan sulfate) 

in surface water were evaluated as another line of evidence for potential risks to aquatic-phase 

CRLF. As described in Section 3.2.4.1, surface water data were compiled from three sources: 

CDPR, EPA’s STORET database, and the USGS NAWQA. As an approximate screen of 

these data, maximum detected values for total endosulfan were used to calculate acute and 

chronic RQs for freshwater fish (used as a surrogate for aquatic-phase CRLF; Table 5.14). 

As described in Section 3.2.4.1, available surface water monitoring data indicate a substantial 

reduction in endosulfan concentrations after 2001 as compared to the early to mid 1990’s. 

Based on this comparison, acute and chronic RQs based on maximum reported concentrations 

range from 9.5 to 41.3, respectively, in the 1991-1996 sampling period but drop to 0.05-0.08 

and 0.22-0.35, respectively, during the 2001-2008 sampling period. Acute RQs based on 

maximum detected concentrations during the 2001 time periods still exceed the Agency’s 

LOC of 0.05 for listed species, but are much lower than in the 1990s. Chronic RQs based on 

maximum detected during the 2001-2008 sampling period do not exceed the Agency’s 

chronic listed LOC of 1.0. 

Several caveats should be considered when interpreting the monitoring data summarized in 

Table 5.14 and in Section 3.2.1.4. First, these data do not represent targeted monitoring data 

that are designed to capture peak concentrations of pesticides in surface waters. Therefore, 

these data likely underestimate peak concentrations of endosulfan and are likely not directly 

comparable to modeling-based peak EECs. Second, the NAWQA data included limits of 

detection that exceeded the concentration corresponding to the Agency listed acute LOC of 

0.05 (i.e., 0.005 ug/L) and therefore are of limited value for estimating the potential for direct 

effects to the CRLF. Despite these limitations, the available monitoring data during the most 

recent sampling period for endosulfan in California surface waters (2001-2008) does suggest 

a potential for acute risk to aquatic-phase CRLF assuming their acute sensitivity is 

comparable to the most sensitive freshwater fish tested. 

Table 5.14 Comparison of maximum detected concentrations of total endosulfan in surface waters of California 

to Agency LOC for freshwater fish 

Data Source(1)

Sampling 

Period 

Total 

Number of 

Samples 

Maximum 

Value Detected 

(ug/L) 

FW Fish 

Acute RQ(3)

FW Fish 

Chronic RQ(4)

CDPR 1991-96 ~ 2000 0.95 9.5 41.3 

2001-06 580 0.005 0.05 0.22 

STORET 2001-08 304 0.008 0.08 0.35 

NAQWA 1995; 01-07 204 ND (2) --- --- (1) See Section 3.2.4.1 for a description of data sources.

(2) Limit of detection typically ranged from 0.01 to 0.02 ug/L for α- and β-endosulfan and/or endosulfan sulfate, 

which exceeded concentrations corresponding to the acute LOC (0.005 ug/L).

(3) RQ based on LC50 for freshwater fish (0.1 ug/L; Sunderam et al, 1992; ECOTOX 5850), which are used as a 

surrogate for aquatic-phase amphibians. Bold values indicate equivalence or exceedence of Agency’s acute listed 

LOC of 0.05. 

(4) RQ is based on a NOAEC for freshwater fish of 0.023 ug/L (estimated using an acute-chronic ratio of 4.3 for 

fathead minnow; see Table 4.1). Bold values indicate exceedence of Agency’s chronic listed LOC of 1.0. 

166 
 Species Sensitivity Analysis 

As indicate above, acute toxicity data for the most sensitive species of freshwater fish 

(common carp, LC50 = 0.1 μg a.i./L) is being used to represent the sensitivity of the aquatic 

phase CRLF due to the absence of acceptable toxicity data for amphibians. To evaluate the 

potential uncertainty of the risk estimation with respect to using the most sensitive fish 

species, the sensitivity of the common carp is put into context of available data for all tested 

freshwater fish (Figure 5.3). In this figure, the geometric mean of LC50 values for each 

species of freshwater fish from both studies submitted to the Agency and those available in 

ECOTOX are provided in the form of a species sensitivity distribution. Geometric mean of 

LC50 values for each species are indicated by a solid circle . Notably, the ECOTOX data that 

were greater than the initial acute toxicity benchmark of 0.83 μg/L were not evaluated beyond 

the initial OPP data screen described in Section 4. The thick blue line designates the LC50

value used in the RQ calculation (0.1 μg/L). The vertical blue lines represent the range of 

predicted peak EECs from the 20 crop exposure scenarios modeled (i.e., 0.72 ug/L for 

Eggplant and 5.88 ug/L for Lettuce and Brussels sprouts scenarios). The vertical red lines 

indicate the range of the peak EECs (0.72 and 5.88 μg/L) divided by the acute listed species 

LOC of 0.05. 

Freshwater Fish

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.10 1.00 10.00 100.00 1000.00

LC50 (μg/L)

Fractional Rank

benchmark

lowest EEC/LOC

highest EEC/LOC

lowest EEC

highest EEC

Figure 5.3 Species sensitivity distribution of the acute toxicity of endosulfan to freshwater fish

Based on the range of modeled peak EECs of 0.72 to 5.88 ug/L determined in Section 3 (see 

Table 5.1), the proportion of species affected would range from approximately the 15th to the 

70th percentiles of the observed species sensitivity distribution blue lines on Figure 5.3). 

167 
Taking into account the acute listed LOC of 0.05, the assumed acute sensitivity of freshwater 

fish would have to be near above the least sensitive species tested in order for the modeled 

EECs (0.72 – 5.88 ug/L) to not exceed the agency LOC. Therefore, this analysis indicates 

that within the context of the sensitivity of freshwater fish, RQ exceedences of the LOC of 

0.05 are not sensitive to the selection of the most acutely sensitive fish species tested (i.e., 

LOC exceedences would occur even the more acutely insensitive species was selected for RQ 

calculation). 

While the previous discussion address sensitivity differences within the context of freshwater 

fish, it does not address potential differences in sensitivity between freshwater fish and 

aquatic-phase amphibians. Although no data were found in the open literature that were 

considered acceptable for quantitative use in this risk assessment, data were found that can be 

used qualitatively for describing the general sensitivity of aquatic-phase amphibians. The 

lowest LC50 in the open literature for endosulfan using amphibians was 0.16 μg a.i./L for 

tadpoles of Micorohyla ornate (see Section 4.1.5), based on unmeasured values. This species 

of amphibian is much smaller than CRLF (22-23 mm snout-vent length for adults—Geng et 

al. 2005). Adults of CRLF range from 85-138 mm SVL (see Attachment 3). It is reasonable 

to assume that smaller animals would be more susceptible to the same toxicant exposure than 

larger ones. However, even if the CRLF has the same acute sensitivity as M. orgata, the 

freshwater fish acute benchmark (LC50 = 0.1 μg a.i./L) should still be protective of the 

aquatic-phase of CRLF. The lowest endosulfan effect concentration for longer exposure 

durations (Rana pipiens—for 7 weeks) suggested a 49 da LC50 of 0.2 μg a.i./L (estimated 

from Shenoy et al., in press). Again, if we assume that the CRLF had this same sensitivity, the 

freshwater chronic benchmark (0.023 μg a.i./L) would likely be protective. At an LC50 of 0.2 

μg a.i./L and the default probit slope of 4.5, the expected mortality at 0.023 μg a.i./L would be 

close to 0%. 

Consumption of Contaminated Aquatic Prey 

Freshwater fish and aquatic invertebrates are a documented component of the diet of the 

aquatic-phase CRLF. For persistent organic chemicals with log KOW values that exceed 4, 

evidence from empirical and modeling studies indicates that biomagnification in aquatic food 

webs can significantly increase exposure to organisms feeding on top trophic level aquatic 

prey (USEPA, 2000; 2003; 2008; Fisk et al., 1998). Log KOW values for α-endosulfan have 

been reported from 3.55 to 4.74 (McConnell et al 1998; MRID 414215-01, respectively). Log 

KOW values for β-endosulfan have been reported from 3.62 to 4.79 (McConnell et al 1998; 

MRID 414215-01, respectively). A log KOW value of 3.71 has been reported for endosulfan 

sulfate (Table 2.1). 

Considering that log KOW values for the parent endosulfan isomers and endosulfan sulfate 

either approach or exceed a log Kow of 4, and that endosulfan can persist for relatively long 

periods of time in aquatic ecosystems, the potential for direct effects on aquatic-phase CRLF 

through consumption of contaminated aquatic prey was investigated. The KABAM model 

(KOW (based) Aquatic BioAccumulation Model) version 1.0 was used to evaluate the potential 

exposure and risk of direct effects to aquatic-phase CRLF via bioaccumulation and 

biomagnification in aquatic food webs. KABAM is used to estimate potential 

168 
bioaccumulation of hydrophobic organic pesticides in freshwater aquatic ecosystems and risks 

to mammals and birds consuming aquatic organisms which have bioaccumulated these 

pesticides. The bioaccumulation portion of KABAM is based upon work by Arnot and Gobas 

(2004) who parameterized a bioaccumulation model based on PCBs and some pesticides (e.g., 

lindane, DDT) in freshwater aquatic ecosystems. KABAM relies on a chemical's octanolwater partition coefficient (KOW) to estimate uptake and elimination constants through 

respiration and diet of organisms in different trophic levels. Pesticide tissue residues are 

calculated for different levels of an aquatic food web. The model then uses pesticide tissue 

concentrations in aquatic animals to estimate dose- and dietary-based exposures and 

associated risks to mammals and birds consuming aquatic organisms. Previous analyses using 

an earlier version of the KABAM model indicate relatively close agreement between its 

predicted bioconcentration factor (BCF) and those reported from experimental studies for 

endosulfan (2007; D346213). 

For the aquatic-phase CRLF analysis, the ecosystem components for avian consumers were 

modeled, as birds are considered surrogates for aquatic-phase amphibians. However, the 

default avian species used in KABAM were altered to more accurately represent the size 

range and dietary preferences of the CRLF. Specifically, three size classes were modeled 

(1.4g, 37g, and 238g) each with a different dietary composition that would be representative 

of its body size and likely feeding pattern (Table 5.15). For each of these size classes, two 

different dietary preferences were selected to bound the range of trophic levels at which the 

CRLF could potentially feed. 

Table 5.15 Assumed dietary preferences of small (1.4g), medium (37g) and large (238g) 

CRLF feeding on aquatic biota of the model ecosystem. 

 Diet for: 

Trophic level in 

diet 

small CRLF 

1 

small 

CRLF 2 

Med 

CRLF 1 

med 

CRLF 2 

large 

CRLF 1 

large 

CRLF 2 

phytoplankton 100.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

Zooplankton 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

Benthic 

invertebrates 

0.0% 100.0% 100.0% 0.0% 100.0% 0.0% 

filter feeders 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

small fish 0.0% 0.0% 0.0% 100.0% 0.0% 0.0% 

Medium fish 0.0% 0.0% 0.0% 0.0% 0.0% 100.0% 

large fish 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

Total 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 

Other chemical and ecosystem-specific parameters selected for the KABAM analysis are 

summarized in Table 5.16 and in Appendix I. 

Table 5.16 Endosulfan chemical characteristics used as input to KABAM 

Characteristic Value Source/Comments 

Log KOW 4.76 Weighted mean of Kow for alpha and beta endosulfan based 

on TGAI (70:30 alpha:beta). MRID 414215-01

169 
KOC (L/kg OC) 10,600 Average value for alpha endosulfan used in PRZM/EXAMS 

modeling (Table 3.3) 

Estimated time to 

steady state (TS; 

days) 

18 This value is calculated automatically from the Log KOW value 

and is used to select the appropriate averaging period for the 

surface water and pore water EEC 

Surface water EEC 

(μg/L) 

0.24-2.60 Range of 21-d surface water EECs for total endosulfan 

(alpha, beta, sulfate) predicted using PRZM/EXAM modeling 

(Table 3.5). Results from each of the 20 crop scenarios were 

modeled separately. 

Pore Water EEC 

(μg/L) 

0.09-1.18 Range of 21-d pore water EECs for total endosulfan (alpha, 

beta, sulfate) predicted using PRZM/EXAM modeling (Table 

3.7). Results from each of the 20 crop scenarios were 

modeled separately. 

Concentrations in aquatic prey predicted using KABAM for the two crop scenarios yielding 

the lowest and highest 21-d average surface and pore water EECs (Eggplant and Broccoli, 

Cabbage & Cauliflower, respectively) are summarized in Table 5.17. Calculation of dose and 

dietary-based EECs for these scenarios are provided in Table 5.18 and the resulting RQ 

values are summarized in Table 5.19. For the scenario yielding the largest surface water and 

pore water EECs (Broccoli, Cabbage & Cauliflower), acute, dose-based RQs range from 0.14 

to 4.0, thus exceeding the acute listed LOC of 0.1 for all six CRLF size class/feeding 

preference combinations. Acute and chronic, dietary-based RQs do not exceed the Agency 

LOCs for the Broccoli, Cabbage & Cauliflower exposure scenario. For the scenario yielding 

the smallest surface water and pore water EECs (Eggplant), acute, dose-based RQs range 

from 0.01 to 0.37 and exceed the acute listed LOC of 0.1 for two of the six CRLF size 

class/feeding preference combinations. Results from aquatic bioaccumulation modeling for all 

20 crop exposure scenarios are summarized in Appendix I. 

Based on these results, it appears that there is a potential for direct effects on aquatic-phase 

CRLF due to the consumption of aquatic prey contaminated with endosulfan, assuming 

similar sensitivity to the most sensitive avian species tested and surface water exposure 

profiles predicted by PRZM/EXAMS. 

Table 5.17 Estimated concentrations of endosulfan in ecosystem components for two crop exposure 

scenarios 

Eggplant (1)

Broccoli, Cabbage & 

Cauliflower (1)

Ecosystem Component 

Total 

concentration 

(μg/kg-ww) 

Lipid 

normalized 

concentration 

(μg/kg-lipid) 

Total 

concentration 

(μg/kg-ww) 

Lipid 

normalized 

concentration 

(μg/kg-lipid) 

Water (total)* 0.237 N/A 2.603 N/A

Water (freely dissolved)* 0.237 N/A 2.603 N/A

Sediment (pore water)* 0.090 N/A 1.181 N/A

Sediment (in solid)** 38 N/A 501 N/A

Phytoplankton 622 31,082 6,828 341,376

Zooplankton 468 15,606 5,142 171,405

170 
Benthic Invertebrates 504 16,808 5,560 185,325

Filter Feeders 333 16,633 3,668 183,403

Small Fish 697 17,432 7,686 192,149

Medium Fish 762 19,047 8,400 209,990

Large Fish 916 22,904 10,075 251,880

* Units: μg/L; **Units: μg/kg-dw 

(1) Total concentrations in aquatic organisms calculated using KABAM v.1.0. Lipid normalized 

concentrations based on lipid fractions of 2% for phytoplankton and filter feeders, 3% for 

zooplankton and benthic macroinvertebrates, and 4% for small, medium and large fish. 

Table 5.18 Calculation of EECs for CRLF consuming aquatic prey contaminated by endosulfan 

Biological Parameters EECs (pesticide intake) (1)

Dose Based 

(mg/kg-bw/d) 

Dietary Based (ppm) 

Wildlife 

Species Body 

Weight 

(kg) 

Dry Food 

Ingestion 

Rate 

(kg-dry 

food/kgbw/day) 

Wet Food 

Ingestion 

Rate 

(kg-wet 

food/kgbw/day) 

Drinking 

Water 

Intake 

(L/d) Eggplant Broccoli, 

Cabbage & 

Cauliflower 

Eggplant Broccoli, 

Cabbage & 

Cauliflower

Small 

CRLF 1 0.0014 0.577 5.767 0.001 3.585 39.37 0.62 6.83 

Small 

CRLF 2 0.0014 0.577 2.403 0.001 1.212 13.36 0.50 5.56 

Med 

CRLF 1 0.037 0.184 0.766 0.006 0.386 4.261 0.50 5.56 

Med 

CRLF 2 0.037 0.184 0.681 0.006 0.475 5.236 0.70 7.69 

Large 

CRLF 1 0.238 0.096 0.400 0.023 0.202 2.225 0.50 5.56 

Large 

CRLF 2 0.238 0.096 0.356 0.023 0.271 2.988 0.76 8.40 

(1) EECs calculated using KABAM v. 1.0 using dietary preferences for the small (1.4g), medium (37g) and large 

(238g) CRLF in Table 5.17 and predicted concentrations in aquatic prey from Table 5.19. 

Table 5.19 Calculation of RQ values for CRLF consuming aquatic prey contaminated by endosulfan. 

Wildlife Species Acute Chronic 

Dose Based(1) Dietary Based (2) Dietary Based (3)

Broccoli, Cabbage & Cauliflower 

small CRLF 1 4.036 0.008 0.228 

small CRLF 2 1.369 0.007 0.185 

med CRLF 1 0.267 0.007 0.185 

med CRLF 2 0.328 0.010 0.256 

large CRLF 1 0.106 0.007 0.185 

171 
Table 5.19 Calculation of RQ values for CRLF consuming aquatic prey contaminated by endosulfan. 

Wildlife Species Acute Chronic 

Dose Based(1) Dietary Based (2) Dietary Based (3)

large CRLF 2 0.142 0.010 0.280 

Eggplant 

small CRLF 1 0.367 0.001 0.021 

small CRLF 2 0.124 0.001 0.017 

med CRLF 1 0.024 0.001 0.017 

med CRLF 2 0.030 0.001 0.023 

large CRLF 1 0.010 0.001 0.017 

large CRLF 2 0.013 0.001 0.025 

(1) Acute dose-based RQs calculated using the dose-based EECs from Table 5.20 and adjusted, 

acute dose-based toxicity values of 9.76, 15.94, and 21.08 mg/kg-bw for the 1.4g, 37g, and 238g 

CRLF, respectively. Unadjusted LD50 = 28 mg/kg-bw based on mallard duck (MRID 136998 ).

(2) Acute diet-based RQs calculated using diet-based EECs from Table 5.20 and a diet-based LC50 

of 805 ppm for bobwhite quail (MRID 22923 ) 

(3) Chronic diet-based RQs calculated using the dietary EECs and an avian dietary NOAEC of 30 

ppm for mallard duck (MRID 40335001)

 Ecological Incident Reports

As summarized in Section 4.4 and Appendix L, the vast majority of the 83 aquatic incident 

reports associated with endosulfan involved mortality to fish (67). A wide variety of fresh and 

estuarine species were reportedly affected (e.g., carp, catfish, largemouth bass, shad, 

menhaden, mullet, spot, bluegill sunfish, gar and trout). These incident reports support the 

findings from laboratory toxicity studies that fish are a highly sensitive taxonomic group to 

endosulfan exposure. Of the 67 aquatic incidents involving fish, 53 (80%) are classified as 

either ‘highly probable’ or ‘probable’ in the context of endosulfan use. Of all the incident 

reports classified as highly probable or probable, about 15 (25%) are associated with a 

‘registered use’ (most are accidental misuse or of unknown causes). Of those associated with 

‘registered uses,’ most described pesticide runoff following periods of heavy rainfall as the 

likely event that led to the reported incident. No incidents were reported for aquatic-phase 

amphibians. As noted in Appendix L, there are a number of uncertainties associated with 

incident reports, including a likely underreporting of actual ecological incidents that occur and 

uncertainty associated with attributing causality. Nevertheless, the information available in 

from the incident reports are not inconsistent with the results from the modeling-based RQs 

that suggest risks to freshwater fish (and by extension, the aquatic-phase CRLF) can exceed 

Agency LOC. 

172 
Direct Effects: Terrestrial-Phase CRLF

 T-REX and T-HERPS Modeling

As described in Section 5.1, risks to terrestrial-phase CRLF were estimated using birds as a 

surrogate using the Agency’s T-REX model. (Table 5.3) Risk quotients from the “broadleaf 

plants/small insect” and “fruits/pods/seeds/large insect” categories were chosen for assessing 

risks to terrestrial phase CRLF because it consumes terrestrial invertebrates and other prey 

types were not represented in T-REX. The dose-based acute RQs calculated for 20g birds 

consuming small and large insects exceed the Agency acute listed LOC (0.1) in all 20 crop 

scenarios modeled (range: 5.3 to 26.4 for small insects; 0.6 to 2.9 for large insects, 

respectively). The acute diet-based RQs exceed the Agency’s acute listed LOC in 19 of the 

20 scenarios modeled for small insects but none of the 20 scenarios modeled for large insects 

(range: 0.08 to 0.42 for small insects; 0.01 to 0.05 for large insects). Chronic RQs for the 

small and large insect categories exceed the Agency LOC of 1 for 20 and 3 crop exposure 

scenarios, respectively. Chronic RQs range from 2.3 to 11.3 for the small insect category and 

0.3 to 1.3 for the large insect dietary category. 

Direct effects on listed reptiles and terrestrial-phase amphibians were evaluated in the same 

manner as above for birds except T-HERPS was used instead of T-REX. The model THERPS is a modified form of T-REX, which is designed to be more reflective of the food 

requirements of amphibians (including consumption of small herbivorous and insectivorous 

mammals and small amphibians) and allow for an estimation of food intake for poikilotherms 

using the same basic procedure as T-REX. This involves adjusting daily food intake with an 

allometric model that accounts for the lower food intake of poikilothermic reptiles and 

amphibians. The net effect of this approach is a reduction in pesticide exposure due to 

reduced food consumption. 

The same bird acute datum (LD50=28 mg/kg b.w. for mallard duck) was used; however, the 

adjusted LD50s for the different size classes were different. These were 9.76 mg/kg b.w. for 

small (1.4 g), 15.94 mg/kg b.w. for medium (37 g) and 21.08 for large (238 g) herpetofauna, 

and were calculated by T-HERPS. All three size classes are used to evaluate the potential for 

direct acute effects on CRLF. Based on the modeled acute dose-based EECs for various use 

scenarios and diet categories and the above acute toxicity data, the RQs for small 

herpetofauna ranged from 0.03 to 1.34, with 24 of the 40 modeled scenarios resulting in 

exceedences of the Agency’s acute listed species LOC (>0.1). Based on the modeled acute 

dose-based EECs for various use scenarios and diet categories and the above acute toxicity 

data, the RQs for medium herpetofauna ranged from 0.006 to 14.55 with 60 of the 100 

modeled scenarios resulting in exceedences of the Agency’s acute listed species LOC (>0.1). 

The acute dose-based RQs for large herpetofauna range from 0.003 to 1.71 with 41 of the 100 

modeled scenarios exceeding the Agency’s LOC (>0.1). The acute dietary-based RQs ranged 

from 0.003 to 0.71, and 39 of the 100 scenarios resulted in RQs that exceeded the agency’s 

LOC (>0.1). Finally, the chronic dietary-based RQs for herpetofauna ranged from 0.078 to 

19.07 with 46 of these values exceeding the LOC for listed species (>1) (see Table 5.20). 

Based on exceedences of the Agency’s acute risk LOC (RQ>0.1) and chronic risk LOC 

(RQ>1), it is concluded that endosulfan has the potential to directly affect reptiles and 

173 
terrestrial-phase amphibians (i.e., CRLF, CTS and SFGS) during at least some portion of their 

life-history. 

Table 5.20 Summary of the acute and chronic dose- and dietary-based RQs for herpetofauna estimated 

based on the maximum endosulfan foliar spray applications using T-HERPS version 1.0. 

 Run 

Acute Dose Based 

Sub 

Acute 

DietaryChronic DietaryUse Category No. Dietary Category 1.4 g 37 g 238 g Based Based 

Broadleaf Plants/Small Insects 1.08 0.65 0.32 0.34 9.00 

Fruits/Pods/Seeds/Large Insects 0.12 0.07 0.04 0.04 1.00 

Small Herbivore Mammals 11.64 1.37 0.57 15.25 

Small Insectivore Mammal 0.73 0.09 0.04 0.95 

Almonds, 

hazelnut & walnut 1 

Small Amphibians 0.02 0.01 0.01 0.31 

Broadleaf Plants/Small Insects 1.34 0.81 0.40 0.42 11.25 

Fruits/Pods/Seeds/Large Insects 0.15 0.09 0.04 0.05 1.25 

Small Herbivore Mammals 14.55 1.71 0.71 19.07 

Small Insectivore Mammal 0.91 0.11 0.04 1.19 

Citrus 1 

Small Amphibians 0.03 0.01 0.01 0.39 

Broadleaf Plants/Small Insects 0.70 0.42 0.21 0.22 5.84 

Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.02 0.02 0.65 

Small Herbivore Mammals 7.55 0.89 0.37 9.90 

Small Insectivore Mammal 0.47 0.06 0.02 0.62 

Broccoli, 

cabbage, 

Chinese 

cabbage, 

cauliflower, 

kohlrabi 

1 

Small Amphibians 0.01 0.01 0.01 0.20 

Broadleaf Plants/Small Insects 0.40 0.24 0.12 0.13 3.38 

Fruits/Pods/Seeds/Large Insects 0.04 0.03 0.01 0.01 0.38 

Small Herbivore Mammals 4.36 0.51 0.21 5.72 

Small Insectivore Mammal 0.27 0.03 0.01 0.36 

Kale, Collards & 

Mustard Green 2 

Small Amphibians 0.01 0.004 0.004 0.12 

Broadleaf Plants/Small Insects 0.81 0.48 0.24 0.25 6.75 

Fruits/Pods/Seeds/Large Insects 0.09 0.05 0.03 0.03 0.75 

Small Herbivore Mammals 8.73 1.03 0.43 11.44 

Small Insectivore Mammal 0.55 0.06 0.03 0.72 

Sweet corn 1 

Small Amphibians 0.02 0.01 0.01 0.23 

Broadleaf Plants/Small Insects 0.54 0.32 0.16 0.17 4.50 

Fruits/Pods/Seeds/Large Insects 0.06 0.04 0.02 0.02 0.50 

Small Herbivore Mammals 5.82 0.68 0.28 7.63 

Small Insectivore Mammal 0.36 0.04 0.02 0.48 

Cotton (ground) 1 

Small Amphibians 0.01 0.01 0.01 0.16 

Broadleaf Plants/Small Insects 0.52 0.31 0.16 0.16 4.38 

Fruits/Pods/Seeds/Large Insects 0.06 0.03 0.02 0.02 0.49 

Small Herbivore Mammals 5.66 0.67 0.28 7.42 

Cotton (Areal) 3 

Small Insectivore Mammal 0.35 0.04 0.02 0.46 

174 
Table 5.20 Summary of the acute and chronic dose- and dietary-based RQs for herpetofauna estimated 

based on the maximum endosulfan foliar spray applications using T-HERPS version 1.0. 

 Run 

Sub 

Acute Dose Based 

Acute Chronic 

Dietary- DietaryUse Category No. Dietary Category 1.4 g 37 g 238 g Based Based 

Small Amphibians 0.01 0.01 0.01 0.15 

Broadleaf Plants/Small Insects 1.34 0.81 0.40 0.42 11.25 

Fruits/Pods/Seeds/Large Insects 0.15 0.09 0.04 0.05 1.25 

Small Herbivore Mammals 14.55 1.71 0.71 19.07 

Small Insectivore Mammal 0.91 0.11 0.04 1.19 

Apples 1 

Small Amphibians 0.03 0.01 0.01 0.39 

Broadleaf Plants/Small Insects 1.34 0.81 0.40 0.42 11.25 

Fruits/Pods/Seeds/Large Insects 0.15 0.09 0.04 0.05 1.25 

Small Herbivore Mammals 14.55 1.71 0.71 19.07 

Small Insectivore Mammal 0.91 0.11 0.04 1.19 

Apricot, 

nectarine, peach, 

cherry, pear, 

plum & prune 

1 

Small Amphibians 0.03 0.01 0.01 0.39 

Broadleaf Plants/Small Insects 0.76 0.46 0.23 0.24 6.39 

Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.03 0.03 0.71 

Small Herbivore Mammals 8.26 0.97 0.40 10.83 

Small Insectivore Mammal 0.52 0.06 0.03 0.68 

Lettuce & 

Brussels sprouts 1 

Small Amphibians 0.02 0.01 0.01 0.22 

Broadleaf Plants/Small Insects 0.70 0.42 0.21 0.22 5.84 

Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.02 0.02 0.65 

Small Herbivore Mammals 7.55 0.89 0.37 9.90 

Small Insectivore Mammal 0.47 0.06 0.02 0.62 

Cucumber, 

melons, pumpkin 

& squash 

1 

Small Amphibians 0.01 0.01 0.01 0.20 

Broadleaf Plants/Small Insects 0.27 0.16 0.08 0.08 2.25 

Fruits/Pods/Seeds/Large Insects 0.03 0.02 0.01 0.01 0.25 

Small Herbivore Mammals 2.91 0.34 0.14 3.81 

Small Insectivore Mammal 0.18 0.02 0.01 0.24 

Eggplant 3 

Small Amphibians 0.01 0.003 0.003 0.08 

Broadleaf Plants/Small Insects 0.33 0.20 0.10 0.10 2.73 

Fruits/Pods/Seeds/Large Insects 0.04 0.02 0.01 0.01 0.30 

Small Herbivore Mammals 3.53 0.42 0.17 4.63 

Small Insectivore Mammal 0.22 0.03 0.01 0.29 

Ornamentals & 

shade trees 1 

Small Amphibians 0.01 0.003 0.004 0.09 

Broadleaf Plants/Small Insects 0.76 0.46 0.23 0.24 6.39 

Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.03 0.03 0.71 

Small Herbivore Mammals 8.26 0.97 0.40 10.83 

Small Insectivore Mammal 0.52 0.06 0.03 0.68 

Potato 1 

Small Amphibians 0.02 0.01 0.01 0.22 

175 
Table 5.20 Summary of the acute and chronic dose- and dietary-based RQs for herpetofauna estimated 

based on the maximum endosulfan foliar spray applications using T-HERPS version 1.0. 

 Run 

Sub 

Acute Dose Based 

Acute Chronic 

Dietary- DietaryUse Category No. Dietary Category 1.4 g 37 g 238 g Based Based 

Broadleaf Plants/Small Insects 0.43 0.26 0.13 0.13 3.59 

Fruits/Pods/Seeds/Large Insects 0.05 0.03 0.01 0.01 0.40 

Small Herbivore Mammals 4.65 0.55 0.23 6.09 

Small Insectivore Mammal 0.29 0.03 0.01 0.38 

Sweet potato 3 

Small Amphibians 0.01 0.004 0.005 0.12 

Broadleaf Plants/Small Insects 0.76 0.46 0.23 0.24 6.39 

Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.03 0.03 0.71 

Small Herbivore Mammals 8.26 0.97 0.40 10.83 

Small Insectivore Mammal 0.52 0.06 0.03 0.68 

Dry beans 

(except Lima), 

peas & pepper 

1 

Small Amphibians 0.02 0.01 0.01 0.22 

Broadleaf Plants/Small Insects 0.54 0.32 0.16 0.17 4.50 

Fruits/Pods/Seeds/Large Insects 0.06 0.04 0.02 0.02 0.50 

Small Herbivore Mammals 5.82 0.68 0.28 7.63 

Small Insectivore Mammal 0.36 0.04 0.02 0.48 

Carrot 2 

Small Amphibians 0.01 0.01 0.01 0.16 

Broadleaf Plants/Small Insects 0.54 0.32 0.16 0.17 4.50 

Fruits/Pods/Seeds/Large Insects 0.06 0.04 0.02 0.02 0.50 

Small Herbivore Mammals 5.82 0.68 0.28 7.63 

Small Insectivore Mammal 0.36 0.04 0.02 0.48 

Celery 2 

Small Amphibians 0.01 0.01 0.01 0.16 

Broadleaf Plants/Small Insects 0.58 0.35 0.17 0.18 4.83 

Fruits/Pods/Seeds/Large Insects 0.06 0.04 0.02 0.02 0.54 

Small Herbivore Mammals 6.25 0.74 0.31 8.19 

Small Insectivore Mammal 0.39 0.05 0.02 0.51 

Strawberry 2 

Small Amphibians 0.01 0.01 0.01 0.17 

Broadleaf Plants/Small Insects 0.70 0.42 0.21 0.22 5.84 

Fruits/Pods/Seeds/Large Insects 0.08 0.05 0.02 0.02 0.65 

Small Herbivore Mammals 7.55 0.89 0.37 9.90 

Small Insectivore Mammal 0.47 0.06 0.02 0.62 

Tomato 1 

Small Amphibians 0.01 0.01 0.01 0.20 

 (2) RQ values in bold indicate exceedence of listed species acute LOC (0.1) and chronic LOC (1.0). Acute dose-base RQs were 

based on dose-based EECs divided by adjusted avian acute LC50s (9.76 mg/kg b.w. for small; 15.94 mg/kg b.w. for medium; 

and 21.08 mg/kg b.w. for large). 

 

176 
 Likelihood of Effects 

 

Based on an observed slope of 8.5 (with upper and lower bounds of 3.6 and 13.4, 

respectively), the corresponding LD50 of the most sensitive avian species tested (mallard 

duck; MRID 136998), and the acute listed species LOC of 0.1, the chance of an individual 

mortality for terrestrial-phase CRLF is ~ 1 in 1.05 x1017 (with upper and lower bounds of ~ 1 

in 6.29 x103 to ~ 1 in 3.31 x1040, respectively, Table 5.13). Using T-HERPS which considers 

the feeding preferences and bioenergetics of amphibians and the observed slope described 

previously, the likelihood of individual mortality to small (1.4g) CRLF using the highest 

acute RQ value (RQ=1.34 for Citrus) is ~ 1 in 1.16 (with lower and upper bounds of ~ 1 in 

1.47 to 1 in 1.04, respectively). For medium size CRLF (37g), the likelihood of individual 

mortality for the highest acute RQ (RQ=14.55 for Citrus) is ~ 1 in 1.00 (with lower and upper 

bounds of ~ 1 in 1.00 to ~ 1 in 1.00). Finally, for large size CRLF (238g), the likelihood of 

individual mortality for the highest acute RQ (RQ=1.71 for Citrus) is ~ 1 in 1.02 (with lower 

and upper bounds of ~ 1 in 1.25 to ~ 1 in 1.00, respectively). Based on the crop exposure 

scenario that results in the smallest RQ values (Eggplant), the likelihood of individual 

mortality for the highest acute RQs (0.27 for 1.4g, 2.91 for 37g and 0.34 for 238g CRLF) are: 

1 in 1.62 x106 (bounds = 1 in 1 in 9.61 x1013 to 1 in 50.0) for 1.4g CRLF; 1 in 1.00 (bounds= 

1 in 1.05 to 1 in 1.00) for 37g CRLF; and 1 in 2.67 x104 (bounds=1 in 4.65 x109 to 1 in 21.4) 

for 238g CRLF. 

 Ecological Incident Reports 

Very few ecological incidents involving endosulfan have been reported for terrestrial 

organisms (Section 4.4 and Appendix L). Of the seven terrestrial incidents that have been 

reported for endosulfan, none are classified as ‘highly probable’ and two are classified as 

‘probable.’ The two ‘probable’ incidents involve birds (blue jay, crow, owl), mammals 

(squirrel, opossum, red fox) and an amphibian (unidentified frog). One of the two probable 

incidents (incident ID: I012626-001) involved morality to a blue jay, a crow, a red fox, and 12 

gray squirrels apparently poisoned from an unknown source. A pooled sample of the 

gastrointestinal tract from four of the gray squirrels was found to have 126 ppm endosulfan. 

The other ‘probable’ ecological incident (ID I010533-001) involved apparent human health 

impacts in addition to anecdotal evidence of food chain transfer and secondary poisoning of 

endosulfan (termite to frog to owl). 

Conclusions Regarding Direct Effects on CRLF

Based on multiple lines of evidence, including: 

(1) RQ exceedence of freshwater fish acute and chronic LOCs using model and 

monitoring-based EEC estimates 

(2) RQ exceedence of acute listed LOC for for small, medium and large CRLF 

consuming aquatic prey predicted to bioaccumulate endosulfan 

(3) RQ exceedence of acute and chronic LOCs for small, medium and large CRLF 

modeled using T-HERPS, 

177 
(4) the high probability of an individual mortality occurrence using the highest acute 

RQ from T-HERPS and for freshwater fish (~1 in 1), 

(5) the spatial and temporal overlap among endosulfan use and CRLF occurrence and 

critical habitat described previously, 

the Agency concludes that agricultural uses of endosulfan in California have a reasonable 

likelihood to cause direct adverse effects to aquatic and terrestrial-phase CRLFs should 

exposure at the predicted EECs actually occur for aquatic and terrestrial-phase CRLF and

assuming the sensitivity of CRLF to endosulfan is similar to the most sensitive freshwater fish 

(for its aquatic phase) and avian species (for its terrestrial-phase) selected for RQ calculation. 

5.2.1.2 Indirect Effects to CRLF (via Potential Loss of Prey) 

As discussed previously in Section 2.5, the diet of aquatic-phase CRLF tadpoles is composed 

primarily of unicellular aquatic plants (i.e., algae and diatoms) and detritus, while the diet of 

terrestrial-phase CRLF includes terrestrial and aquatic invertebrates, mammals, frogs, and 

fish. The main food source for juvenile aquatic- and terrestrial-phase CRLFs is thought to be 

aquatic and terrestrial invertebrates. However, life history data for terrestrial-phase CRLFs 

indicate that large adult frogs also consume terrestrial vertebrates, including mice and frogs. 

Algae (non-vascular plants)

Based on the most sensitive surrogate aquatic non-vascular plant toxicity data (EC50 value of 

428 μg a.i./L for the marine alga, Pseudokirchneriella subcapitatum, and the maximum 

aquatic peak EEC of all use scenarios used to represent all of the agricultural uses of 

endosulfan in CA (5.88 ug/L for Lettuce and Brussels Sprouts), all RQs for aquatic nonvascular plants are ≤ 0.014 (see Section 5.1.1.3). Since the RQs do not exceed the Agency’s 

LOC (1) for aquatic non-vascular plants based on the most sensitive data available to the 

Agency, labeled endosulfan use in California appears not likely to indirectly affect the 

aquatic-phase CRLF via effects to aquatic non-vascular plant food sources. Although the lack 

of risk to non-vascular aquatic plants is consistent with the insecticidal mode of action of 

endosulfan, it should be considered that data were available for only one species of aquatic 

non-vascular plant that was considered suitable for quantitative use in this risk assessment. In 

order for potential effects to non-vascular plants to be identified, an untested species must be 

at least 75 times more sensitive than the available data for P. subcapitatum. Therefore, only 

fish, aquatic invertebrates, and frogs will be characterized for potential indirect effects to the 

aquatic-phase CRLF. 

Freshwater Fish and Aquatic-phase Frogs

The potential for direct effects to listed fish and aquatic-phase frogs is discussed above in 

Section 5.2.1.1. Because fish and frogs are also considered potential prey items for the 

aquatic-phase CRLF, indirect effects via potential prey item reduction are also considered 

here. As previously described, acute RQs based on modeled EECs for freshwater fish (used as 

a surrogate for the aquatic phase CRLF) range from 7.2 to 58.8, thus exceeding the Agency’s 

listed LOC (0.05) in all 20 crop scenarios modeled (Table 5.1). Risk quotients based on 

178 
maximum reported concentrations of total endosulfan in California surface waters also exceed 

the Agency’s acute listed LOC. Similarly, chronic RQs range from 5.7 to 80.6 and exceed the 

Agency’s LOC (1.0) in all 20 crop scenarios modeled. Available information indicates that 

the modeled EECs extend well into the cumulative species sensitivity distribution for 

endosulfan (Figure 5.3). Probit analysis using the default slope of 4.5 for freshwater fish also 

indicates a high probability of an individual mortality occurrence (~1 in 1), even with the RQ 

associated with the smallest peek EEC (7.2 for Eggplant). The preponderance of reported 

ecological incidents involves freshwater fish, which further supports findings of risk to this 

taxonomic group. Therefore, considering the aforementioned lines of evidence and the 

potential spatial and temporal overlap of reported endosulfan use with the occurrence of the 

CRLF (Table 5.7 and Appendix E), there appears to be a reasonable potential for indirect 

effects to the aquatic-phase CRLF from loss of fish/aquatic amphibian prey as result of 

labeled endosulfan use in California provided that exposures occur at or near modeled EECs 

and that the sensitivity of tested fish is similar to those found in aquatic ecosystems from 

which the CRLF obtains prey. 

Freshwater Invertebrates (Water Column Exposure)

Based on surrogate freshwater invertebrate toxicity data (LC50 value of 0.6 μg a.i./L for 

mayfly) and modeled aquatic peak EECs for various use scenarios used to represent all of the 

agricultural uses of endosulfan in CA, acute RQs for freshwater invertebrates range from 1.2 

to 9.8 for freshwater invertebrates; exceeding the Agency’s acute listed species LOC (0.05) in 

all 20 crop scenarios modeled (Table 5.2). Because the acute RQs all substantially exceed the 

acute listed LOC of 0.05, the likelihood of mortality to an individual freshwater invertebrate 

is considered high (e.g., from ~1 in 1.56 to ~1 in 1; Table 5.11). 

Based on the distribution of species-mean acute toxicity values for freshwater invertebrates 

available from ECOTOX and submitted studies, these minimum and maximum peak acute 

EECs would exceed the LOC for approximately 45% and 60% of the tested species, 

respectively (vertical red lines in Figure 5.4). As illustrated in Figure 5.4, the LC50 chosen 

for quantitative use in this risk assessment corresponds to approximately the 15th percentile 

when all available data are included in the distribution (i.e., those considered appropriate only 

for qualitative use in addition to those data considered acceptable for quantitative use for RQ 

calculation). Although those data that fall below the LC50 used for RQ calculation (0.6 ug/L) 

are not considered acceptable for quantitative use due to factors such as use of unmeasured 

exposure concentrations, insufficient documentation of test procedures, inconsistency with the 

results of other acceptable studies (see Appendix J), they do suggest that effects of 

endosulfan might occur at concentrations of about 1/6th that selected for RQ calculation. The 

lowest LC50 value in Figure 5.4 is for the 2nd instar larval stage of the southern house 

mosquito. We did not consider this value usable because the authors of the study did not 

provide adequate documentation on how the study was conducted. The exposure 

concentrations were not listed or measured; the number of organisms used for each treatment 

was not given; and the few details that are given are only listed for the 4th instar. One has to 

assume that the procedures were the same for the other life stages. 

179 
Freshwater Invertebrates

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.001 0.01 0.1 1 10 100 1000 10000 100000

LC50 (μg/L)

Fractional Rank

benchmark

lowest EEC/LOC

highest EEC/LOC

lowest EEC

highest EEC

Figure 5.4 Species sensitivity distribution of the acute toxicity of endosulfan to freshwater invertebrates via 

water column exposure 

Similarly, chronic RQs calculated from the 21-d EECs exceed the Agency LOC of 1 for all 20 

scenarios (Table 5.2). The 21-d EECs range from 0.24 to 2.6 ug/L which correspond to 

chronic RQs 23.7 and 260, respectively, based on the estimated NOAEC of 0.01 ug/L for the 

mayfly, Atalophlebia australis. This NOAEC was estimated using an acute-chronic ratio of 

61.5 derived from Daphnia magna because the mayfly was a much more acutely sensitive 

compared to D. magna. However, use of an estimated NOAEC introduces uncertainty into 

the calculation of the chronic RQ values. Since acceptable data on the chronic toxicity of 

endosulfan to freshwater invertebrates are limited to D. magna, chronic toxicity data for 

estuarine and marine invertebrates are considered here in order to evaluate the uncertainty 

associated with the estimated NOAEC of 0.01 ug/L. Specifically, five chronic tests are 

available for the saltwater mysid, Americamysis bahia, that were conducted using flowthrough and measured exposures (McKenney 1982; ECOTOX reference #3736; Appendix J). 

NOAECs from these five tests (0.14 to 0.52 μg a.i./L) are within an order of magnitude of the 

estimated NOAEC of 0.01 ug/L for D. magna, thus suggesting the estimated NOAEC is not 

unreasonable within the limits of this comparison. Furthermore, if these measured NOAECs 

were used directly for chronic RQ calculation, the resulting RQs would still exceed the 

chronic LOC in all 20 exposure scenarios tested. On the other hand, if the measured chronic 

NOAEC of 2.7 ug/L for D. magna was used for RQ calculation, none of the calculated RQs 

would exceed the LOC of 1 (the highest RQ would approach 1). However, use of this 

NOAEC of 2.7 ug/L is not considered reasonable for estimating risks from chronic exposure 

to freshwater invertebrate assemblages because it exceeds the LC50 values for about 30% of 

180 
the tested species (Figure 5.4), likely because D. magna is a relatively insensitive invertebrate 

species. 

With respect to measured concentrations of endosulfan in surface water, maximum 

concentrations of total endosulfan (0.95 ug/L from 1991-1996; 0.05-0.08 from 2001-2008; 

Table 5.14) correspond to chronic RQ values of 95 and 5 to 8 for the 1991-1996 and 2001-

2008 sampling periods, respectively, based on a NOAEC of 0.01 ug/L for the mayfly. Acute 

RQ values based on an LC50 of 0.6 ug/L for mayfly and these maximum reported endosulfan 

concentrations are 1.6 for the 1991-1996 sampling period and 0.08-0.13 from the 2001-2008 

sampling period and exceed the acute listed LOC of 0.05. Due to the declining pattern of 

endosulfan use in California, data from the 2001-2008 time period are considered more 

representative of current and likely future use of endosulfan in California. The acute and 

chronic RQs based on the maximum reported concentrations from the 2001-2008 time period 

suggest a potential risk to freshwater invertebrates from chronic exposure to endosulfan in 

California. 

In conclusion, based on: (1) the exceedances of listed species acute and chronic risk LOCs for 

freshwater invertebrates for all of the modeled scenarios assessed, (2) the high probability of 

an individual mortality occurrence using both the highest and lowest acute RQ for freshwater 

invertebrates, (3) the spatial overlapping of patterns of endosulfan use in California with 

CRLF habitat (Table 5.7), and (4) the reported aquatic monitoring data that exceed acute 

listed and chronic LOCs, it appears that there are adequate lines of evidence to conclude that 

there is a potential for indirect effects to the aquatic-phase CRLF from loss of freshwater 

invertebrate prey as result of labeled endosulfan use in California provided that exposures 

occur at or near modeled EECs and that the sensitivity of tested freshwater invertebrates is 

similar to those found in aquatic ecosystems from which the CRLF obtains prey. 

Freshwater Invertebrates: Sediment Exposure

As summarized in Section 4.1.2.6, toxicity data are available for freshwater invertebrates via 

exposure to contaminated sediments for endosulfan (as endosulfan sulfate). Exposure via 

sediments is of interested because it can involve both uptake through respiration of pore and 

overlying water in addition to ingestion of contaminated sediment. Chronic risk to freshwater 

sediment invertebrates is based on is based on 21-day EECs and the lowest chronic toxicity 

value for freshwater sediment invertebrates. Based on freshwater sediment toxicity data for 

endosulfan sulfate in porewater (NOAEC=0.35 μg a.i./L for midge) and 21-day EECs for 

various use scenarios used to represent all of the agricultural uses of endosulfan in CA, all 

acute RQs for freshwater invertebrates range from 0.26 (eggplant) to 3.37 (lettuce and 

brussels sprouts). Twelve of the set of 20 modeled scenarios used to represent all of the 

agricultural uses of endosulfan in CA resulted in an exceedance of the Agency’s chronic risk 

LOC (RQ>1) for freshwater invertebrates (see Table 5.21). 

Based on exceedances of the Agency’s chronic risk LOC (RQ>1) for 12 of the set of 20 

modeled scenarios used to represent all of the agricultural uses of endosulfan in CA, there is a 

potential for indirect effects to the CRLF via reduction in its freshwater sediment invertebrate 

prey base, provided that exposures occur at or near modeled EECs and that the sensitivity of 

tested invertebrates via sediment exposure is similar to those found in aquatic ecosystems 

upon which the CRLF relies for prey. 

181 
Table 5.21 Acute and Chronic RQs for freshwater sediment invertebrates based on EECs for use 

categories used to represent all endosulfan uses in CA 

Use Category Run No. 

Peak 

EEC 

(μg/L) 

21-day 

EEC 

(μg/L) 

Chronic 

RQ(2)

Almonds, Hazelnuts & Walnuts 1 0.37 0.36 1.04 

Citrus 1 0.23 0.22 0.63 

Broccoli, Cabbage & Cauliflower 1 1.18 1.17 3.34 

Collards, Kale & Mustard Green 2 0.38 0.38 1.07 

Sweet corn for fresh market only 1 0.51 0.51 1.45 

Cotton (ground) 2 0.35 0.34 0.98 

Cotton (aerial) 3 0.33 0.32 0.93 

All fruit trees 1 0.30 0.30 0.85 

Lettuce & Brussels Sprouts 1 1.19 1.18 3.37 

Cucurbits 1 0.42 0.42 1.19 

Eggplant 3 0.09 0.09 0.26 

Ornamentals or Shade Trees (Southern Coast) 1 0.80 0.79 2.27 

Ornamentals or Shade Trees (Northern Central coast) 1 Add 0.84 0.83 2.36 

Potato 1 0.25 0.25 0.70 

Potato (Northern Central coast) 1 Add 0.37 0.37 1.05 

Sweet Potato 3 0.18 0.18 0.52 

Beans & Peas (dry) & Pepper 1 0.39 0.39 1.11 

Carrot & Celery 2 0.39 0.38 1.09 

Strawberry 1 0.72 0.71 2.03 

Tomato 1 0.28 0.27 0.78 

 (2) RQ values in bold indicate exceedence of chronic LOC (1.0). Chronic RQs were based on the 21 day average EEC divided 

by the chronic NOAEC for the midge Chironomus tentans of 0.35 μg/L (MRID 47318101)

Terrestrial Invertebrates 

Terrestrial invertebrates are one of the prey items for terrestrial phase CRLF. As such, 

impacts to the terrestrial invertebrate prey base of the CRLF have the potential to indirectly 

affect the CRLF. As described in Section 5.1.2.3, the potential risks to terrestrial 

invertebrates resulting from foliar spray applications of endosulfan were derived using TREX, and the most sensitive toxicity data available for terrestrial invertebrates (acute contact 

LD50 (0.15 μg a.i./g) for the beet web worm). EECs from the large and small insect 

categories ranged 37.5 to 337 ppm, respectively, for the crop exposure scenarios yielding the 

lowest and highest EECs (eggplant and citrus fruits, respectively; Table 3.23). The resulting 

RQs for the small insect category ranged from 450 to 2250 and RQs calculated for large 

insects ranged from 50 to 250 (Table 5.5). All 20 use category RQs for both size classes 

substantially exceeded the Agency’s interim LOC for listed terrestrial invertebrates 

(RQ>0.05), which is not unexpected given the insecticidal mode of action of this pesticide. 

182 
When compared to the acute contact toxicity of endosulfan of 35 ug/g based on the honey bee 

(calculated from an LD50 of 4.5 ug/bee using a body weight of 0.128g; MRID 000199), the 

adult beet web worm (a target insect) is approximately 230 times more sensitive (LD50 of 

0.15 ug/g). If RQs were calculated based on the standard honey bee acute contact LD50 (35 

ug/g), the smallest RQ (1.1 for eggplant) would still exceed the Agency’s interim acute listed 

LOC for terrestrial invertebrates by nearly 20-fold. When compared to the distribution of 

acute contact toxicity of endosulfan to terrestrial invertebrates (Figure 5.5), the lowest EEC 

for small insects (337 ppm) and large insects (37.5 ppm) approximate the 99th and 80th

percentiles, respectively. 

Terrestrial Insects

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.1 1 10 100 1000

LD50 (μg/g)

Fractional Rank

Honey Bee

beetle larva

beetle adult

moth larva

moth adult

Figure 5.5 Species sensitivity distribution of the acute contact toxicity of endosulfan TGAI to 

terrestrial invertebrates based on species mean values. 

Given the large acute RQs, the probit-based likelihood estimates of individual mortality all 

indicate a high probability for mortality to individual terrestrial insects (~1 in 1; Table 5.12). 

No reported ecological incidents associated with endosulfan involved terrestrial insects; 

however it is likely that impacts to terrestrial insects would be substantially under-reported in 

the EIIS database due to the difficulty in observing and documenting causal linkages between 

endosulfan use and non-target terrestrial insects. 

Based on the exceedences of the Agency’s interim LOC for listed terrestrial invertebrates, 

endosulfan use in CA does have the potential to indirectly affect the CRLF through reduction 

in terrestrial prey base, provided that exposures occur at or near modeled EECs and that the 

sensitivity of tested terrestrial invertebrates via acute contact exposure is similar to those 

found in terrestrial ecosystems upon which the CRLF utilizes as a prey source. 

183 
Small Terrestrial Vertebrates

For endosulfan spray applications, dietary-based and dose-based exposures of terrestrialphase CRLF to potential small terrestrial vertebrate prey (mammals and amphibians) are 

assessed using small mammals (15 g) which consume short grass, and small birds (20g; they 

represent terrestrial-phase amphibians that it may consume) which consume small (broadleaf 

plants/small insects dietary category) and large (fruits/pods/seeds/large insects dietary 

category) invertebrates using the T-REX model described earlier in Section 5.2.1.1.

RQ values representing direct exposures of endosulfan to terrestrial-phase CRLFs are also 

used to represent exposures of endosulfan to amphibians in terrestrial habitats that may serve 

as prey for the CRLF. For terrestrial-phase amphibians, as described in Section 5.2.1.1, the 

Agency concluded that agricultural uses of endosulfan in California have a reasonable 

likelihood to cause direct adverse effects to terrestrial-phase CRLFs should exposure at the 

predicted EECs actually occur for a terrestrial-phase CRLF and assuming its sensitivity to 

endosulfan is similar to the most sensitive avian species selected for RQ calculation. 

Furthermore, dose-based RQs determined from T-HERPS modeling for the 1.4g and 37g 

amphibians are used to bracket the potential risks to a specific prey item (Pacific tree frog, 

2.3g) of the terrestrial-phase CRLF. Please refer to Section 5.2.1.1 for additional discussion 

and characterization of potential risks to terrestrial-phase amphibians that may serve as prey 

for the terrestrial-phase CRLF. Therefore, that Agency concludes that endosulfan use in CA 

does have the potential to indirectly adversely affect the CRLF through reduction in terrestrial 

vertebrate prey base (birds and other amphibians), provided that exposures occur at or near 

modeled EECs and that the sensitivity of tested avian and amphibian prey is similar to those 

found in terrestrial ecosystems upon which the CRLF utilizes as a prey source. 

Regarding the potential effects on the small mammal prey base of the CRLF, the Agency used 

surrogate toxicity data (LD50=10 mg/kg-bw and NOAEL = 15 mg/kg-diet), the maximum 

allowable application rate (1 application, 2.5 lbs a.i./acre/application), the foliar dissipation 

half-life of 4 days for endosulfan from Willis and McDowell (1987), and upper bound Kenaga 

values from T-REX, there is a potential for direct adverse effects on SMHM individuals from 

foliar spray applications of endosulfan in CA (Table 5.4). Although EECs for small 

mammals feeding on short grass yield the highest risk estimates, it appears that the impacts of 

endosulfan use to the SMHM potentially extend beyond those feeding on short grass. 

For spray applications of endosulfan, the dose-based acute RQs range from 5.21 to 26.03, 

from 2.39 to 11.93, from 2.93 to 14.64, and from 0.33 to 1.63 for the short grass, tall grass, 

broadleaf plants/small insects, and fruits/pods/seeds/large insects dietary categories, 

respectively. For acute dose-based RQs, all modeled scenarios (N=20) resulted in an 

exceedance of the Agency’s acute listed species LOC (RQ>0.1) for mammals that feed on 

short grass, tall grass, broadleaf plants/small insects, and fruits/pods/seeds/large insects. 

The dose-based chronic RQs ranged from 69.41 to 347.04, from 31.81 to 159.06, from 39.04 

to 195.21, and from 4.34 to 21.69, for the short grass, tall grass, broadleaf plants/small insects, 

and fruits/pods/seeds/large insect dietary categories, respectively. For chronic dose-based 

RQs, all modeled scenarios (N=20) resulted in an exceedance of the Agency’s acute listed 

species LOC (RQ≥1) for mammals that feed on short grass, tall grass, broadleaf plants/small 

insects, and fruits/pods/seeds/large insects. 

184 
Estimates of the likelihood of mortality to individual 15g mammalian prey resulting from 

predicted endosulfan EECs range from ~1 in 70 for large insects based on the eggplant crop 

exposure scenario to ~1 in 1 for the citrus fruits exposure scenario. 

The dietary-based chronic RQs range from 8 to 40.00, from 3.67 to 18.33, from 4.50 to 22.50, 

and from 0.50 to 2.50, for the short grass, tall grass, broadleaf plants/small insects, and 

fruits/pods/seeds/large insects dietary categories, respectively. For chronic dietary-based RQs, 

all modeled scenarios (N=20) resulted in an exceedance of the Agency’s acute listed species 

LOC (RQ≥1) for mammals that feed on short grass, tall grass, and broadleaf plants/small 

insects. Thirteen out of 20 modeled scenarios resulted in an exceedance of the Agency’s 

chronic risk LOC (RQ≥1) for mammals that feed on fruits/pods/seeds/large insects. Therefore, 

RQs exceed the Agency’s acute listed species LOC (RQ>0.1) and chronic risk LOC (RQ>1) 

for mammals (see Table 5.4) for foliar spray applications of endosulfan. 

Therefore, that Agency concludes that endosulfan use in CA does have the potential to 

indirectly affect the CRLF through reduction in terrestrial vertebrate prey base (small 

mammals), provided that exposures occur at or near modeled EECs and that the sensitivity of 

tested mammalian prey is similar to those found in terrestrial ecosystems upon which the 

CRLF utilizes as a prey source. 

5.2.1.3 Indirect Effects (via Habitat Effects)

Aquatic plants serve several important functions in aquatic ecosystems. Non-vascular aquatic 

plants are primary producers and provide the autochthonous energy base for aquatic 

ecosystems. Vascular plants provide structure, rather than energy, to the system, as 

attachment sites for many aquatic invertebrates, and refugia for juvenile organisms, such as 

fish and frogs. Emergent plants help reduce sediment loading and provide stability to 

nearshore areas and lower streambanks. In addition, vascular aquatic plants are important as 

attachment sites for egg masses of aquatic species. No toxicity data were available for 

vascular aquatic plants that were considered appropriate for quantitative or qualitative use in 

this assessment. For non-vascular aquatic plants, the maximum RQ calculated is s ≤ 0.014 

(see Section 5.1.1.3). Since the RQs do not exceed the Agency’s LOC (1) for aquatic nonvascular plants based on the most sensitive data available to the Agency, labeled endosulfan 

use in California will not indirectly affect the aquatic-phase CRLF via effects to aquatic 

habitat based on non-vascular aquatic plants. 

Terrestrial plants serve several important habitat-related functions for the listed assessed 

species. In addition to providing habitat and cover for invertebrate and vertebrate prey items 

of the listed assessed species, terrestrial vegetation also provides shelter and cover from 

predators while foraging. Upland vegetation including grassland and woodlands provides 

cover during dispersal. Riparian vegetation helps to maintain the integrity of aquatic systems 

by providing bank and thermal stability, serving as a buffer to filter out sediment, nutrients, 

and contaminants before they reach the watershed, and serving as an energy source. No data 

on the effects of endosulfan on terrestrial plants were considered acceptable for quantitative 

use in this risk assessment. Based on efficacy studies, however, available information 

185 
indicates that agricultural crops are not adversely affected by endosulfan use rates that are 

associated with pest control. This, in conjunction with the insecticidal mode of action of 

endosulfan, suggests that terrestrial plants may not be sensitive to endosulfan compared to 

aquatic and terrestrial animals. However, use of efficacy studies can be confounded by lack 

of experimental controls, multiple stressors (pesticide and insect pest), and plant species that 

may not be representative of those upon which the CRLF may depend. 

5.2.1.4 Effects to Designated Critical Habitat 

 Aquatic-Phase PCEs 

Three of the four assessment endpoints for the aquatic-phase primary constituent elements 

(PCEs) of designated critical habitat for the CRLF are related to potential effects to aquatic 

and/or terrestrial plants: 

• Alteration of channel/pond morphology or geometry and/or increase in sediment 

deposition within the stream channel or pond: aquatic habitat (including riparian 

vegetation) provides for shelter, foraging, predator avoidance, and aquatic dispersal 

for juvenile and adult CRLFs. 

• Alteration in water chemistry/quality including temperature, turbidity, and oxygen 

content necessary for normal growth and viability of juvenile and adult CRLFs and 

their food source. 

• Reduction and/or modification of aquatic-based food sources for pre-metamorphs 

(e.g., algae). 

Conclusions for potential indirect effects to the CRLF via direct effects to aquatic and 

terrestrial plants are used to determine whether effects to critical habitat may occur. As 

discussed above for aquatic plants and terrestrial plants (Section 5.2.1.3), labeled endosulfan 

use in California will not indirectly affect the CRLF via impacts to habitat and/or primary 

production. 

The remaining aquatic-phase PCE is “alteration of other chemical characteristics necessary 

for normal growth and viability of CRLFs and their food source.” Other than impacts to algae 

as food items for tadpoles (discussed above), this PCE is assessed by considering direct and 

indirect effects to the aquatic-phase CRLF via acute and chronic freshwater fish and 

invertebrate toxicity endpoints as measures of effects. Based on the analyses discussed above, 

there is a potential for habitat effects via impacts to aquatic-phase CRLFs (Sections 5.2.1.1) 

and effects to freshwater invertebrates and fish as food items (Sections 5.2.1.2) from 

endosulfan use in California. 

 Terrestrial-Phase PCEs 

Two of the four assessment endpoints for the terrestrial-phase PCEs of designated critical 

habitat for the CRLF are related to potential effects to terrestrial plants: 

• Elimination and/or disturbance of upland habitat; ability of habitat to support food 

source of CRLFs: Upland areas within 200 ft of the edge of the riparian vegetation or 

186 
drip line surrounding aquatic and riparian habitat that are comprised of grasslands, 

woodlands, and/or wetland/riparian plant species that provides the CRLF shelter, 

forage, and predator avoidance. 

• Elimination and/or disturbance of dispersal habitat: Upland or riparian dispersal 

habitat within designated units and between occupied locations within 0.7 mi of each 

other that allow for movement between sites including both natural and altered sites 

which do not contain barriers to dispersal. 

As discussed above for terrestrial plants (Section 5.2.1.3), labeled endosulfan use in 

California will not indirectly affect the CRLF via impacts to habitat and/or primary 

production. 

The third terrestrial-phase PCE is “reduction and/or modification of food sources for 

terrestrial phase juveniles and adults.” To assess the impact of endosulfan on this PCE, acute 

and chronic toxicity endpoints for terrestrial invertebrates, mammals, and terrestrial-phase 

frogs are used as measures of effects. Based on the potential for a reduction in mammalian, 

terrestrial invertebrate, and amphibious prey items from registered endosulfan use (Section 

5.2.1.2), the Agency concludes there is a potential for habitat effects via indirect effects to 

terrestrial-phase CRLFs via reduction in prey base. 

The fourth terrestrial-phase PCE is based on alteration of chemical characteristics necessary 

for normal growth and viability of juvenile and adult CRLFs and their food source. Based on 

the preceding discussions, the Agency concludes there is a potential for habitat effects via

direct (Section 5.2.1.1) and indirect effects (Section 5.2.1.2) to terrestrial-phase CRLFs. 

5.2.2 California tiger salamander 

5.2.2.1 Direct Effects 

Endosulfan is currently registered for numerous diverse agricultural uses that span a large 

variety of geographical regions throughout the entire state of California. Therefore, there is 

the potential for endosulfan use across the state to spatially and temporally coincide with the 

CTS breeding season. 

The CTS has aquatic phase eggs and larvae and terrestrial phase juveniles and adults. 

Aquatic-phase CTS inhabits low elevation vernal pools and seasonal ponds while juvenile and 

adults are found in associated grassland, oak savannah, and coastal scrub plant communities. 

Although aquatic phase CTS are adapted to natural vernal pools and ponds, they are 

frequently found in manmade or modified ephemeral and permanent ponds, including stock 

ponds. Terrestrial phase CTS prefer open grassland to areas of continuous woody vegetation 

and may live for up to 10 years, spending the majority of their lives in the upland habitats. 

The upland component typically consists of grassland savannah, but also can consist of 

grasslands with scattered oak trees, and scrub and chaparral habitats. Juvenile and adult CTS 

spend the dry summer and fall months in the burrows of California ground squirrels 

(Spermophilus beecheyi) and Botta’s pocket gopher (Thomomys bottae). California tiger 

187 
salamanders cannot dig their own burrows, and as a result their presence is associated with 

active burrows of small mammals such as ground squirrels and pocket gophers. 

The young aquatic larvae eat small crustaceans, algae, and mosquito larvae. When they are 

large enough, they begin to take advantage of aquatic insects, invertebrates and tadpoles of 

Pacific treefrogs, California red-legged frogs, western toads, and spadefoot toads. Once they 

reach metamorphosis, which is usually by late spring or early summer, juveniles are ready to 

roam to their terrestrial nesting habitat and may disperse up to two miles from their natal 

ponds. As adults, CTS feed on terrestrial invertebrates, insects, frogs, and worms. 

 

From southern Colusa County south to northern Kern County, CTS habitat is disjunct remnant 

vernal pool complexes and isolated ponds scattered mainly along narrow strips of rangeland 

on each side of the Central Valley. From Suisun Bay south to the Temblor Range, CTS are 

found in sag ponds and human-maintained stock ponds in the coastal ranges. Populations of 

CTS are also located in Sonoma and Santa Barbara counties. 

Temporal and Spatial Overlap

A comparison of Figure 5.1 and Figure 5.6 indicates that endosulfan use and CTS sensitive 

life stages (larvae, young juveniles) could potentially overlap in time. A peak in endosulfan 

application in Feb-March coincides with larval development. Application from May - October 

coincides with young juvenile dispersal. 

 Young Juveniles 

Larvae 

Breeding/Egg 

Masses 

 

 

 

J F M A M J J A S O N D 

Figure 5.6 CTS Reproductive Events by Month; Adults and juveniles can be present all year 

Since pesticide use information is only available at the county level, the degree that the CTS 

or its critical habitat actually coincides in the same or similar locations cannot be precisely 

determined. With this limitation in mind, the spatial overlap of average endosulfan use for 

2005-06 reported by CDPR/PUR and CTS distribution (including critical habitat) is 

summarized at the county level in Table 5.7. Figure 5.7 summarizes the overlap in average 

endosulfan use and species/habitat occurrence for all 7 species assessed. For the CTS, 

Approximately 85% of endosulfan use (74,196 lbs) is applied in counties in which the CTS or 

its critical habitat occurs. 

While Figure 5.7 suggests a significant potential overlap in endosulfan use and the 

occurrence of CTS or its critical habitat at the county level, review of the overlap between 

cultivated and orchard crop use and the occurrence of the CTS (or its critical habitat) suggests 

a much smaller amount of spatial overlap currently occurs (Figure E.7 of Appendix E). 

Specifically, most of the CTS habitat is on the fringe of the cultivated crop/orchard land use 

area of the San Joaquin valley. However, due to the documented long-range transport of 

188 
endosulfan to the Sierra Nevada mountains of California (e.g., Fellers et al., 2004), the critical 

habitat east of the cultivated crop/orchard use area may be subject to endosulfan exposure. 

53,053

0.25 1,120 0.00 4.56

71,104 74,196

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

CRLF SFGS SMHM BCB VELB SJKF CTS

Species

Average Use (lbs)

Figure 5.7 Average Endosulfan Use (2005-2006) in Counties with Reported Occurrence of Listed Species, 

Occupied Core Areas and/or Critical Habitat 

Direct Exposure of Aquatic and Terrestrial Phase CTS

The RQ values representing exposures of endosulfan to freshwater fish and aquatic-phase 

amphibians that described the direct effects to aquatic-phase CRLF are also used to represent 

exposures of endosulfan to the aquatic-phase CTS. As described in Section 5.2.1.1, the 

Agency determined a reasonable potential for direct effects on freshwater fish and aquaticphase amphibians based on LOC exceedences from model- and monitoring-based RQs, the 

high probability of individual mortality, and ecological incident reports. Similarly, the 

Agency determined a reasonable potential exists for direct effects on birds (surrogate for 

terrestrial phase amphibians) based on exposure to food items receiving direct deposition 

from endosulfan application (i.e., T-REX, T-HERPS modeling) and consumption of 

contaminated aquatic prey (i.e., KABAM bioaccumulation modeling for small CRLF which 

was used as a surrogate for estimating CTS exposure potential). 

Consumption of Contaminated Terrestrial Prey 

The CTS is also known to consume worms as part of its diet. The T-REX model is useful for 

assessing exposures of terrestrial animals to pesticides through consumption of foliar surfaces 

of crops and insects on the treated site. The model cannot be used to assess pesticide 

exposures to terrestrial animals resulting from consumption of soil dwelling invertebrates 

which have accumulated the pesticide in their tissues. In order to explore the potential 

exposures of terrestrial-phase CTS to total residues of endosulfan that have accumulated in 

earthworms inhabiting endosulfan-treatment sites, a simple fugacity approach was employed 

to estimate endosulfan concentrations in earthworms based on predicted concentrations in 

soil. As with the T-REX modeling, birds were used as a surrogate for terrestrial-phase CTS. 

Therefore, application rates, the foliar dissipation rate, toxicity data, body weights and 

189 
consumption weights were identical to that used for the avian T-REX modeling described in 

Section 5.1. A log Kow for endosulfan of 4.76 was used based on the weighted mean Kow 

for alpha and beta isomers of 70:30, respectively (MRID 414215-01). A soil distribution 

coefficient (Kd) of 69 cm3

/g was used based on the weighted mean Kd for alpha and beta 

isomers of 70:30, respectively (MRID 414129-06). This Kd represents the lower range of 

four Kd values available for different soils in this study, wherein an upper range of Kd were 

320 and 428 cm3

/g for alpha and beta endosulfan was reported. Using the lower value for Kd 

represents a conservative assumption since for a given Kow, concentrations in earthworms 

increase with decreasing Kd. For this analysis, the two crop exposure scenarios that produce 

the highest and lowest dietary EECs (Citrus/Fruits and Eggplant, respectively) resulting from 

soil exposure via fugacity modeling were evaluated in order to provide information on the 

overall range of potential risks to terrestrial-phase CTS consuming contaminated earthworms. 

Risks were evaluated for the 20g and 100g avian size classes, which bracket the estimated 

mass of adult CTS (50g). Details on this approach are provided in Appendix N. 

PRZM estimated endosulfan concentrations in soil and soil pore water of 22.4 and 0.183 g/m3

, 

respectively, for the Citrus and 5.3 and 0.066 g/m3, respectively, for the Eggplant crop 

exposure scenarios. Based on these concentrations, the estimated concentration of endosulfan 

in earthworms is 223 and 64 ppm for Citrus and Eggplant, respectively (Table 5.22). These 

values translate into dose-based EECs that range from 41.7 to 254 mg/kg-bw, depending on 

body weight and the crop exposure scenario. Acute dose-based RQs (2.3-17.5) exceed the 

avian, acute listed species LOC of 0.1 for both crop exposure scenarios, regardless of body 

weight. Acute dietary-based RQs (0.08-0.28) exceed the avian, acute listed LOC for the Citrus 

crop scenario but approach the LOC for the Eggplant scenario. Finally, chronic dietary-based 

RQs (2.1-7.4) exceed the LOC of 1 for both crop scenarios. Sensitivity analysis indicates that 

LOCs would be exceeded even if the higher Kd values were selected. Therefore, based on the 

assumptions that: (1) the sensitivity and exposures to small and medium size birds are 

reasonable surrogates for the CTS and (2) the CTS receives 100% of its diet from 

earthworms, there is a potential for direct effects on terrestrial-phase CTS from the 

consumption of contaminated earthworms from fields treated with endosulfan. It is noted that 

even if the dose of endosulfan to the CTS was reduced to 50% of current estimate, (i.e., 

through lower earthworm consumption rates or lower concentrations), exceedence of acute 

and chronic LOC would still occur. 

Table 5.22 Estimated concentrations of total endosulfan in earthworms and avian risk quotients for two 

crop exposure scenarios. 

Eggplant Citrus 

Results* 20g 100g 20g 100g 

Dose-based EEC (1)

(mg/kg-bw) 73.1 41.7 254 145

Acute Dose-based RQ (2,3) 5.0 2.3 17.5 7.8

Diet-based EEC (1)

(ppm w.w. in earthworm) 64 223 

Acute Dietary-based RQ (2,4) 0.08 0.28 

Chronic Dietary-based RQ (2,5) 2.1 7.4 

190 
* Birds are used as a surrogate for terrestrial-phase amphibians 

 (1) Based on fugacity modeling for earthworm using total endosulfan concentrations in soil and soil 

pore water of 22.4 and 0.183 g/m3, respectively for Citrus and 5.3 and 0.066 g/m3, respectively, for 

Eggplant exposure scenarios; See Appendix N for details. 

(2) RQ values in bold exceed the acute listed species LOC of 0.1 or the chronic LOC of 1.0 

(3) Acute dose-based RQs calculated using the dose-based EECs and adjusted, acute dose-based 

toxicity values of 14.5 and 18.5 mg/kg-bw for the 20g and 100g bird, respectively. Unadjusted LD50 

= 28 mg/kg-bw based on mallard duck (MRID 136998). (4) Acute diet-based RQs calculated using diet-based EECs and a diet-based LC50 of 805 ppm for 

bobwhite quail (MRID 22923) 

(5) Chronic diet-based RQs calculated using diet-based EECs and an avian dietary NOAEC of 30 

ppm for mallard duck (MRID: 40335001) 

 

Spatial Overlap 

For the CTS, a relatively small amount of overlap was identified based on GIS mapping of the 

occurrence of CTS or its critical habitat and cultivated crop/orchard use areas (Figure E.7 of 

Appendix E), suggesting a potential for spatial overlap in endosulfan use and subsequent 

exposure. Therefore, assuming that the sensitivity of tested freshwater fish species reasonably 

approximates the distribution of sensitivities of aquatic-phase CTS, there appears to be a 

reasonable potential for direct effects to the aquatic phase CTS as result of labeled endosulfan 

use in California, particularly for those areas where crop/orchard sites, endosulfan use, and 

CTS occurrence overlap. 

5.2.2.2 Indirect Effects (via Reductions in Prey Base) 

Potential forage items of aquatic phase CTS includes algae, snails, zooplankton, small 

crustaceans, aquatic larvae, aquatic invertebrates, and smaller tadpoles of Pacific tree frogs, 

CRLF, and toads. Forage items for the terrestrial phase include terrestrial invertebrates, 

insects, frogs, and worms 

 

Freshwater Fish and Aquatic-phase Amphibians

RQ values representing exposures of freshwater fish and aquatic-phase amphibians to 

endosulfan that may serve as prey for the aquatic-phase CRLF are also used to represent 

exposures to freshwater fish and aquatic-phase amphibians that may serve as prey for the 

CTS. As described in Section 5.2.1.2, the Agency determined a reasonable potential for 

direct effects on freshwater fish and aquatic-phase amphibians based on RQ exceedences of 

listed LOCs for freshwater fish and aquatic phase amphibians using modeled and monitoring 

data-based EECs, the high probability of an individual mortality occurrence for all crop use 

scenarios, the high percentage of freshwater fish that would be affected at model-based EECs 

and the reported number of probable and highly probable aquatic incidents involving 

endosulfan and fish. 

For the CTS, a relatively small amount of overlap was identified based on GIS mapping of the 

occurrence of CTS or its critical habitat and cultivated crop/orchard use areas (Figure E.7 of 

Appendix E), suggesting a potential for spatial overlap in endosulfan use and subsequent 

191 
exposure. Therefore, assuming that the sensitivity of tested freshwater fish species reasonably 

approximates the distribution of sensitivities of freshwater fish and aquatic-phase amphibians 

used as prey by the CTS, there appears to be a reasonable potential for indirect effects to the 

aquatic phase CTS as result of labeled endosulfan use in California, particularly for those 

areas where crop/orchard sites, endosulfan use, and CTS occurrence overlap. 

Freshwater Invertebrates

RQ values representing exposures of endosulfan to freshwater invertebrates that may serve as 

prey for the aquatic-phase CRLF are also used to represent exposures of endosulfan to 

freshwater invertebrates that may serve as prey for the CTS. As described in Section 5.2.1.2, 

the Agency determined that based on the exceedances of non-listed species acute and chronic 

risk LOCs for freshwater invertebrates for all of the modeled scenarios assessed and the high 

probability of an individual mortality occurrence using both the highest and lowest acute RQ 

for freshwater invertebrates, there appears to be a potential for direct effects to freshwater 

invertebrates as result of labeled endosulfan use in California. 

For the CTS, a relatively small amount of overlap was identified based on GIS mapping of the 

occurrence of CTS or its critical habitat and cultivated crop/orchard use areas (Figure E.7 of 

Appendix E), suggesting a potential for spatial overlap in endosulfan use and subsequent 

exposure. Therefore, assuming that the sensitivity of tested freshwater invertebrate species 

reasonably approximates the distribution of sensitivities of freshwater invertebrates and used 

as prey by the CTS, there appears to be a reasonable potential for indirect effects to the 

aquatic phase CTS as result of labeled endosulfan use in California, particularly for those 

areas where crop/orchard sites, endosulfan use, and CTS occurrence overlap. 

Terrestrial Invertebrates

RQ values representing exposures of endosulfan to terrestrial invertebrates that may serve as 

prey for the terrestrial-phase CRLF are also used to represent exposures of endosulfan to 

terrestrial invertebrates that may serve as prey for the CTS. As described in Section 5.2.1.2, 

the Agency determined that based on the fact that endosulfan is a highly efficacious broad 

spectrum insecticide, exceedances of the Agency’s interim LOC for listed terrestrial 

invertebrates for all of the modeled scenarios assessed, the high percentage of tested terrestrial 

invertebrate species that would be affected at the modeled EECs and the high probability of 

an individual mortality occurrence based on the RQs for terrestrial invertebrates, there 

appears to be a reasonable potential for direct effects to terrestrial invertebrates as a result of 

labeled endosulfan use in California. 

For the CTS, a relatively small amount of overlap was identified based on GIS mapping of the 

occurrence of CTS or its critical habitat and cultivated crop/orchard use areas (Figure E.7 of 

Appendix E), suggesting a potential for spatial overlap in endosulfan use and subsequent 

exposure. Therefore, assuming that the sensitivity of tested terrestrial invertebrate species 

reasonably approximates the distribution of sensitivities of terrestrial invertebrates and used as 

prey by the CTS, there appears to be a reasonable potential for indirect effects to the terrestrial 

192 
phase CTS as result of labeled endosulfan use in California, particularly for those areas where 

crop/orchard sites, endosulfan use, and CTS occurrence overlap. 

Aquatic and Terrestrial Plants

As noted in Section 5.2.1.3, no data are available to reliably, quantitatively evaluate the 

effects and the potential risks of endosulfan to vascular aquatic plants. No incidents have been 

reported to the Agency that involve any aquatic plants, despite that it is regularly directly 

applied on or near a very wide variety of agricultural plants. Only one reported incident 

involved plants and this was classified as ‘possible,’ but the plant species was not identified 

(Section 4.4 and Appendix L). No data on the effects of endosulfan on terrestrial plants 

were considered acceptable for quantitative use in this risk assessment. Based on efficacy 

studies, available information indicates that agricultural crops are not adversely affected by 

endosulfan use rates that are associated with pest control. This, in conjunction with the 

insecticidal mode of action of endosulfan, suggests that terrestrial plants may not be sensitive 

to endosulfan compared to aquatic and terrestrial animals. However, use of efficacy studies 

can be confounded by lack of experimental controls, multiple stressors (pesticide and insect 

pest), and plant species that may not be representative of those upon which the CTS may 

depend. Therefore, although effects to aquatic and terrestrial plants cannot be quantified due 

to the lack of data, the available lines of evidence provide no compelling reason to believe 

that there is a potential for indirect effects to the CTS from loss of plant food items as result of 

labeled endosulfan use in California. 

5.2.2.3 Modification to Designated Critical Habitat 

The primary constituent elements (PCEs) of the CTS critical habitat include: 

• (PCE1) Standing bodies of fresh water, including natural and man-made (e.g., 

stock) ponds, vernal pools, and dune ponds, and other ephemeral or permanent 

water bodies that typically become inundated during winter rains and hold water 

for a sufficient length of time (i.e., 12 weeks) necessary for the species to complete 

the aquatic (egg and larval) portion of its life cycle. 

• (PCE2) Barrier-free uplands adjacent to breeding ponds that contain small 

mammal burrows. Small mammals are essential in creating the underground 

habitat that juvenile and adult California tiger salamanders depend upon for food, 

shelter, and protection from the elements and predation. 

• (PCE3) Upland areas between breeding locations (PCE 1) and areas with small 

mammal burrows (PCE 2) that allow for dispersal among such sites. 

Aquatic (Vascular and Non-vascular) and Terrestrial Plants

Aquatic plants serve several important functions in aquatic ecosystems such as primary 

production (non-vascular, vascular) and refugia structure (vascular plants). Rooted plants help 

reduce sediment loading and provide stability to nearshore areas and lower streambanks. In 

addition, vascular aquatic plants are important as attachment sites for egg masses of aquatic 

species. Terrestrial plants serve several important functions such as providing habitat and 

193 
cover for invertebrate and vertebrate prey items of the CTS. Terrestrial plants also provide 

energy to the terrestrial ecosystem through primary production. Upland vegetation including 

grassland and woodlands provides cover during dispersal. Riparian vegetation helps to 

maintain the integrity of aquatic systems by providing bank and thermal stability, serving as a 

buffer to filter out sediment, nutrients, and contaminants before they reach the watershed, and 

serving as an energy source. 

As stated in Section 5.2.1.3 covering the evaluation of potential indirect effects to the CRLF 

via habitat effects, although effects to vascular aquatic and terrestrial plants cannot be 

quantified due to the lack of data, available lines of evidence provide no compelling reason to 

believe that endosulfan will affect any type of plants to the extent that it would affect the 

habitat integrity of the CTS. Labeled endosulfan use in California appears not to indirectly 

affect the CTS via impacts to habitat and/or primary production. Please refer to Section 

5.2.1.3 for additional discussion and characterization of potential risks to plants that may be 

foraged upon by the CTS. 

5.2.3 San Francisco Garter Snake 

5.2.3.1 Direct Effects 

Endosulfan is currently registered for numerous diverse agricultural uses that span a large 

variety of geographical regions throughout the entire state of California. Therefore, there is 

the potential for endosulfan use across the state to spatially and temporally coincide with the 

SFGS breeding season. 

Temporal and Spatial Overlap 

SFGSs mate in the spring (March and April) and fall (September through November), with 

mating being heavily concentrated in the first few warm days of March. Female SFGS can 

store the male’s sperm over the winter and can retain viable sperm for periods ranging from 3 

to 53 months. Ovulation in the common garter snake typically occurs in late spring with 

pregnancy occurring in early summer. The young are typically born about three to four 

months after successful mating. SFGS are ovoviviparous, and females give birth from June 

through September with young typically born in July or August; however, young can be born 

as late as early September. Typically, neonate snakes, 18 to 20 cm in length, are born in the 

upland areas near the aquatic feeding habitats and disperse immediately after they are born. 

194 
Figure 5.1 and Figure 5.8 show the extent that endosulfan use and SFGS sensitive life stages 

(young juveniles) could potentially overlap. Endosulfan application from May - October 

coincides with young juvenile birth. 

 Young Juveniles (Neonates) 

 

Breeding/Egg 

Masses Breeding/Egg Masses 

J F M A M J J A S O N D 

Figure 5.8 SFGS Reproductive Events by Month; Adults can be present all year 

All known populations of the San Francisco garter snake occur in San Mateo County near 

freshwater marshes, ponds, and slow-moving streams along the coast. Since pesticide use 

information is only available at the county level, the degree that the SFGS and endosulfan 

actually coincide cannot be precisely determined. The spatial overlap of endosulfan use and 

SFGS distribution is summarized at the county level in Table 5.7 and Figure 5.7. Only 0.25 

lb ai were reported used from 2005-2006 that coincided with San Mateo County, less than 

0.001% of the total endosulfan use. Thus, the prospect of spatial overlap between current

endosulfan use and SFGS occurrence appears negligible. The long-range transport of 

endosulfan would extend exposure beyond current crop/orchard/vineyard areas in other 

counties, however, the prevailing winds would likely lead to dispersal eastward, away from 

SFGS occurrence regions in San Mateo County. If cultivated crop/orchard/vineyard uses are 

considered areas of potential endosulfan use in the future, then a substantial amount of spatial 

overlap can be observed relative to the total area of SFGS occurrence sections (Figure E.2 of 

Appendix E). 

Direct Exposure 

Direct acute and chronic exposures of the SFGS were evaluated using the same approaches 

employed for estimating direct exposures to the terrestrial-phase CRLF (Section 5.2.1.1). In 

addition, toxicity estimates for both listed species, the terrestrial-phase CRLF and the SFGS, 

are based on the same surrogate avian toxicity data. Therefore, RQ values representing the 

potential for direct exposures and effects of endosulfan to the terrestrial-phase CRLF, are also 

used to represent the potential for direct exposures and effects of endosulfan to the SFGS. 

Based on the risk characterization presented in Section 5.2.1.1 for terrestrial-phase CRLF, 

there is potential for labeled endosulfan use to cause direct adverse effects to the SFGS via 

chronic toxicity based on the weight-of-evidence involving acute and chronic risk LOC 

exceedances with T-REX and the refined T-HERPS model. However, the average amount of 

current endosulfan use at the county level and SFGS distribution do not coincide, and direct 

effects to the SFGS appear to be unlikely based on current endosulfan use patterns (Figure 

5.7). Although the potential for endosulfan to be transported long distances from the 

application site could extend exposure well beyond current use areas, such long-range 

transport would need to overcome the direction of the prevailing winds (west to east) in order 

to reach SFGS occurrence sections in San Mateo County, which appears unlikely. Refer to 

Section 3.2.4.4 for more information on long-range transport of endosulfan. If cultivated 

crop/orchard/vineyard uses are considered areas of potential endosulfan use in the future, then 

195 
a substantial amount of spatial overlap can be observed relative to the total area of SFGS 

occurrence sections (Figure E.2 of Appendix E). Therefore, based on the potential future use 

of endosulfan in cultivated crop/orchard/vineyard areas of San Mateo County, there appears to 

be a reasonable potential for direct effects on SFGS from labeled uses of endosulfan. 

5.2.3.2 Indirect Effects (via Reductions in Prey Base) 

Newborn and juvenile SFGS prey almost exclusively on Pacific tree frogs in temporary pools 

during the spring and early summer to the point that the SFGS may be so dependent on their 

anuran prey that they are not able to switch to other available prey sources if necessary to 

survive. SFGS under 500 mm snout-to-vent length (SVL) require Pacific tree frogs in various 

stages of metamorphosis, whereas individuals over 500 mm SVL can consume Pacific tree 

frog, CRLF, and bullfrog tadpoles and adults. 

The main diet of adult SFGS consists of CRLF. Adult SFGSs may also feed on smaller 

juvenile non-native bullfrogs (Rana catesbeiana). Immature California newts (Taricha 

torosa), California toads (Bufo boreas halophilus), recently metamorphosed western toads 

(Bufo boreas), threespine stickleback (Gasterosteus aculeatus), and non-native mosquito fish 

(Gambusia affinis) are also known to be consumed by SFGS. Small mammals, reptiles, 

amphibians, possibly invertebrates, and some fish species may also be consumed by the 

SFGS. 

Freshwater Fish and Aquatic-phase Amphibians

RQ values representing exposures of endosulfan to freshwater fish and aquatic-phase 

amphibians that may serve as prey for the aquatic-phase CRLF are also used to represent 

exposures of endosulfan to freshwater fish and aquatic-phase amphibians that may serve as 

prey for the SFGS. As described in Section 5.2.1.2, the Agency determined a reasonable 

potential for direct effects to freshwater fish and aquatic-phase amphibians based on RQ 

exceedences of listed LOCs for freshwater fish and aquatic phase amphibians using modeled 

and monitoring data-based EECs, the high probability of an individual mortality occurrence 

for all crop use scenarios, the high percentage of freshwater fish that would be affected at 

model-based EECs, and the reported number of probable and highly probable aquatic 

incidents involving endosulfan and fish 

As discussed in Section 5.2.3.1 for direct effects on the SFGS, there does appear to be a 

potential for spatial overlap between SFGS distribution and cultivated/orchard/vineyard 

agricultural areas where endosulfan could be used in the future, although overlap in current 

use patterns appears negligible. Therefore, based on the potential future use of endosulfan in 

cultivated crop/orchard/vineyard areas of San Mateo County, there appears to be a reasonable 

potential for indirect effects on the SFGS from loss of freshwater fish and amphibian prey 

items. 

Freshwater Invertebrates

RQ values representing exposures of endosulfan to freshwater invertebrates that may serve as 

prey for the aquatic-phase CRLF are also used to represent exposures of endosulfan to 

freshwater invertebrates that may serve as prey for the SFGS. As described in Section 

196 
5.2.1.2, the Agency determined that based on the exceedances of non-listed species acute and 

chronic risk LOCs for freshwater invertebrates for all of the modeled scenarios assessed and 

the high probability of an individual mortality occurrence using both the highest and lowest 

acute RQ for freshwater invertebrates, there appears to be adequate lines of evidence to 

conclude there is a potential for direct effects to freshwater invertebrates as result of labeled 

endosulfan use in California. 

As discussed in Section 5.2.3.1 for direct effects on the SFGS, there does appear to be a 

potential for spatial overlap between SFGS distribution and cultivated/orchard/vineyard 

agricultural areas where endosulfan could be used in the future, although overlap in current 

use patterns appears negligible. Therefore, based on the potential future use of endosulfan in 

cultivated crop/orchard/vineyard areas of San Mateo County, there appears to be a reasonable 

potential for indirect effects on the SFGS from loss of freshwater invertebrate prey items. 

Terrestrial Invertebrates

RQ values representing exposures of endosulfan to terrestrial invertebrates that may serve as 

prey for the terrestrial-phase CRLF are also used to represent exposures of endosulfan to 

terrestrial invertebrates that may serve as prey for the SFGS. As described in Section 5.2.1.2, 

the Agency determined that based on the fact that endosulfan is a highly efficacious broad 

spectrum insecticide, exceedances of the Agency’s interim LOC for listed terrestrial 

invertebrates for all of the modeled scenarios assessed, the high percentage of tested terrestrial 

invertebrate species that would be affected at the modeled EECs, the high probability of an 

individual mortality occurrence based on the RQs for terrestrial invertebrates, there appears to 

be a reasonable potential for direct effects on terrestrial invertebrates from the labeled 

endosulfan use in California. 

As discussed in Section 5.2.3.1 for direct effects on the SFGS, there does appear to be a 

potential for spatial overlap between SFGS distribution and cultivated/orchard/vineyard 

agricultural areas where endosulfan could be used in the future, although overlap in current 

use patterns appears negligible. Therefore, based on the potential future use of endosulfan in 

cultivated crop/orchard/vineyard areas of San Mateo County, there appears to be a reasonable 

potential for indirect effects on the SFGS from loss of terrestrial invertebrate prey items. 

 

Small Terrestrial Vertebrates

RQ values representing exposures of endosulfan to small terrestrial vertebrates that may serve 

as prey for the terrestrial-phase CRLF are also used to represent exposures of endosulfan to 

terrestrial small terrestrial vertebrates that may serve as prey for the SFGS. Similarly, the 

Agency determined a reasonable potential exists for direct effects on birds (surrogate for 

terrestrial phase amphibians) based on exposure to food items receiving direct deposition 

from endosulfan application (i.e., T-REX, T-HERPS modeling); consumption of 

contaminated aquatic prey (i.e., KABAM bioaccumulation modeling), and consumption of 

contaminated terrestrial prey (i.e., earthworm fugacity modeling; Section 5.2.1.1). 

As discussed in Section 5.2.3.1 for direct effects on the SFGS, there does appear to be a 

potential for spatial overlap between SFGS distribution and cultivated/orchard/vineyard 

197 
agricultural areas where endosulfan could be used in the future, although overlap in current 

use patterns appears negligible. Therefore, based on the potential future use of endosulfan in 

cultivated crop/orchard/vineyard areas of San Mateo County, there appears to be a reasonable 

potential for indirect effects on the SFGS from loss of small terrestrial vertebrate prey items. 

5.2.3.3 Indirect Effects (via Habitat Effects) 

SFGS inhabit areas near densely vegetated ponds and in open hillsides where it can sun, feed, 

and find cover in rodent burrows. It forages extensively in aquatic habitats. Fresh-water 

habitats including natural and manmade (e.g. stock) ponds, slow moving streams, vernal pools 

and other ephemeral or permanent water bodies which typically support inundation during 

winter rains and hold water for a minimum of 12 weeks in a year of average rainfall and 

upland habitats within 200 ft of the mean high water mark of such aquatic habitat. 

Aquatic (Vascular and Non-vascular) and Terrestrial Plants

Aquatic plants serve several important functions in aquatic ecosystems such as primary 

production (non-vascular, vascular) and refugia structure (vascular plants). Rooted plants help 

reduce sediment loading and provide stability to nearshore areas and lower streambanks. In 

addition, vascular aquatic plants are important as attachment sites for egg masses of aquatic 

species. 

Terrestrial plants serve several important habitat-related functions for the SFGS. In addition 

to providing habitat and cover for invertebrate and vertebrate prey items of the SFGS, 

terrestrial vegetation also provides shelter for the SFGS and cover from predators while 

foraging. Terrestrial plants also provide energy to the terrestrial ecosystem through primary 

production. Upland vegetation including grassland and woodlands provides cover during 

dispersal. Riparian vegetation helps to maintain the integrity of aquatic systems by providing 

bank and thermal stability, serving as a buffer to filter out sediment, nutrients, and 

contaminants before they reach the watershed, and serving as an energy source. 

As noted in Section 5.2.1.3, no data are available to reliably, quantitatively evaluate the 

effects and the potential risks of endosulfan to vascular aquatic plants. No incidents have been 

reported to the Agency that involve any aquatic plants, despite that it is regularly directly 

applied on or near a very wide variety of agricultural plants. Only one reported incident 

involved plants and this was classified as ‘possible,’ but the plant species was not identified 

(Section 4.4 and Appendix L). No data on the effects of endosulfan on terrestrial plants 

were considered acceptable for quantitative use in this risk assessment. Based on efficacy 

studies, available information indicates that agricultural crops are not adversely affected by 

endosulfan use rates that are associated with pest control. This, in conjunction with the 

insecticidal mode of action of endosulfan, suggests that terrestrial plants may not be sensitive 

to endosulfan compared to aquatic and terrestrial animals. However, use of efficacy studies 

can be confounded by lack of experimental controls, multiple stressors (pesticide and insect 

pest), and plant species that may not be representative of those upon which the SFGS may 

depend. Although effects to aquatic and terrestrial plants cannot be quantified due to the lack 

of data, the available lines of evidence provide no compelling reason to believe that there is a 

198 
potential for indirect effects to the SFGS from loss of plant food items as result of labeled 

endosulfan use in California. 

5.2.4 Salt Marsh Harvest Mouse

5.2.4.1 Direct Effects 

Endosulfan is currently registered for numerous diverse agricultural uses that span a large 

variety of geographical regions throughout the entire state of California (Figure 2.6 and 

Figure 2.5). Therefore, there is the potential for endosulfan use across the state to spatially 

and temporally coincide with the SMHM breeding season. 

The SMHM is a small, mostly nocturnal rodent that lives in tidal and diked salt marshes, only 

around the San Francisco Bay and its tributaries. SMHM depend on dense, perennial cover 

and prefer habitat in the middle and upper parts of the marsh dominated by pickleweed and 

peripheral halophytes as well as similar vegetation in diked wetlands adjacent to the Bay. Salt 

marsh harvest mice are cover-dependent species and only live under thick vegetation. Salt 

marsh harvest mice use pickleweed (Salicornia virginica) as their primary/preferred habitat as 

long as they have non-submerged, salt-tolerant vegetation for escape during the highest tides. 

Their diet consists of seeds, grasses, forbs and insects. 

Temporal and Spatial Overlap 

The SMHM breeds from spring through the fall and there is strong potential for periods of 

breeding activity to overlap temporally with peak usage of endosulfan from May through 

September (Figure 5.1). While male SMHM are described as reproductively active from 

April through September, with some active throughout the year, female SMHM have a long 

breeding season that extends from as early as March to November. In general, the northern 

subspecies of SMHM breeds from May to November and the southern subspecies breeds from 

March to November. Despite the long breeding season, the SMHM is characterized as having 

a low reproductive potential, with each female typically having only one or two litters per 

year with an average litter size of about three or four. 

Since pesticide use information is only available at the county level, the degree that the 

SMHM actually coincides in the same or similar locations cannot be precisely determined. 

The spatial overlap of endosulfan use and SMHM distribution is summarized at the county 

level in Table 5.7 and Figure 5.7). Approximately 1.25% of endosulfan use (1,120 lbs) is 

applied in counties in which the SMHM occurs. These counties represent approximately 66% 

of the SMHM range by county. Thus, the potential for direct effects to the SMHM appears to 

be low based on current endosulfan use patterns. The potential for endosulfan to be 

transported long distances from the application site could extend exposure well beyond 

current use areas, which appears to be most relevant for SMHM occurrence sections in Solano 

County (where current cultivated crop areas are west of the occurrence sections). Refer to 

Section 3.2.4.4 for more information on long-range transport of endosulfan. If cultivated 

crop/orchard/vineyard uses are considered areas of potential endosulfan use in the future, then 

199 
a very small amount of spatial overlap can be observed relative to the total area of SMHM 

occurrence sections (Figure E.3 of Appendix E). 

Direct Exposure: Deposition on Forage Items

Direct exposure of the SMHM and the resulting risks in terrestrial environments were 

evaluated based on dose- and dietary-based EECs estimated using two approaches: (1) T-REX 

for foliar spray applications and (2) fugacity modeling for predicting endosulfan 

contamination of terrestrial prey. For dose-based exposure calculations, a body weight of 15 

g was used for small mammals which correspond to the body weight of the SHMH mouse (8-

14 g). All estimated EECs (i.e., EECs for short grass, tall grass, broadleaf plants/small insects, 

fruits/pods/seeds/large insects) were considered relevant for evaluation of direct effects 

because the SMHM has been known to feed on leaves, seeds, plant stems, insects, and 

grasses. 

Based on surrogate toxicity data (LD50=10 mg/kg-bw and NOAEL = 15 mg/kg-diet), the 

maximum allowable application rate (1 application, 2.5 lbs a.i./acre/application), the foliar 

dissipation half-life of 4 days for endosulfan from Willis and McDowell (1987), and upper 

bound Kenaga values from T-REX, there is a potential for direct adverse effects on SMHM 

individuals from foliar spray applications of endosulfan in CA (see Table 5.4). Although 

EECs for small mammals feeding on short grass yield the highest risk estimates, it appears 

that the potential impact of endosulfan use to the SMHM potentially extend beyond those 

feeding on short grass. 

For spray applications of endosulfan, the dose-based acute RQs for 15 g mammal range from 

5.21 to 26.03, from 2.39 to 11.93, from 2.93 to 14.64, and from 0.33 to 1.63 for the short 

grass, tall grass, broadleaf plants/small insects, and fruits/pods/seeds/large insects dietary 

categories, respectively (Table 5.4).For acute dose-based RQs, all modeled scenarios (N=20) 

resulted in an exceedance of the Agency’s acute listed species LOC (RQ>0.1) for mammals 

that feed on short grass, tall grass, broadleaf plants/small insects, and fruits/pods/seeds/large 

insects. 

The dose-based chronic RQs ranged from 69.41 to 347.04, from 31.81 to 159.06, from 39.04 

to 195.21, and from 4.34 to 21.69, for the short grass, tall grass, broadleaf plants/small insects, 

and fruits/pods/seeds/large insect dietary categories, respectively (Table 5.4). For chronic 

dose-based RQs, all modeled scenarios (N=20) resulted in an exceedance of the Agency’s 

acute listed species LOC (RQ≥1) for mammals that feed on short grass, tall grass, broadleaf 

plants/small insects, and fruits/pods/seeds/large insects. 

The dietary-based chronic RQs range from 8 to 40.00, from 3.67 to 18.33, from 4.50 to 22.50, 

and from 0.50 to 2.50, for the short grass, tall grass, broadleaf plants/small insects, and 

fruits/pods/seeds/large insects dietary categories, respectively (Table 5.4). For chronic 

dietary-based RQs, all modeled scenarios (N=20) resulted in an exceedance of the Agency’s 

acute listed species LOC (RQ≥1) for mammals that feed on short grass, tall grass, and 

broadleaf plants/small insects. Thirteen out of 20 modeled scenarios resulted in an exceedance 

of the Agency’s chronic risk LOC (RQ≥1) for mammals that feed on fruits/pods/seeds/large 

200 
insects. RQs exceed the Agency’s acute listed species LOC (RQ>0.1) and chronic risk LOC 

(RQ>1) for mammals for foliar spray applications of endosulfan. 

Direct Exposure: Contaminated Soil 

In addition to the consumption of food items subject to direct deposition of endosulfan 

applied to agricultural areas discussed above, the potential exists for direct effects to the 

SMHM via soil contaminated with endosulfan. In order to explore the potential exposures of 

SMHM to total residues of endosulfan that have accumulated in earthworms inhabiting 

endosulfan-treatment sites, a simple fugacity approach was employed to estimate endosulfan 

concentrations in earthworms and subsequent exposures to the SMHM consuming 

earthworms. Pesticide application rates, the foliar dissipation rate, toxicity data, body weights 

and consumption weights were identical to that used for the mammalian T-REX modeling 

described in Section 5.1. A log Kow for endosulfan of 4.76 was used based on the weighted 

mean Kow for alpha and beta isomers of 70:30, respectively (MRID 414215-01). A soil 

distribution coefficient (Kd) of 69 cm3/g was used based on the weighted mean Kd for alpha 

and beta isomers of 70:30, respectively (MRID 414129-06). This Kd represents the lower 

range of four Kd values available for different soils in this study, wherein an upper range of 

Kd were 320 and 428 cm3/g for alpha and beta endosulfan was reported. Using the lower 

value for Kd represents a conservative assumption since for a given Kow, concentrations in 

earthworms increase with decreasing Kd. For this analysis, the two crop exposure scenarios 

that produce the highest and lowest dietary EECs (Citrus/Fruits and Eggplant, respectively) 

were evaluated in order to provide information on the overall range of potential risks to 

SMHM consuming contaminated earthworms. Risks were evaluated for the 15g mammalian 

size classes (Table 5.23; the 1000g size class was included for evaluating risk to the SJKF 

which is discussed in Section 5.2.5). Details on this approach are provided in Appendix N. 

Results presented in Table 5.23 indicate dose-based RQs exceed the Agency’s listed acute a 

LOC for 15g mammal even when using the exposure scenario with the lowest soil EECs 

(eggplant). Furthermore, chronic dose- and dietary-based RQs exceed the chronic LOC for 

the eggplant exposure scenario. 

Table 5.23 Estimated concentrations of total endosulfan in earthworms and mammalian risk quotients 

for two crop exposure scenarios 

Eggplant Citrus 

Results 15g(6) 1000g (6) 15g (6) 1000g (6)

Dose-based EEC (1)

(mg/kg-bw) 61.2 9.8 212.7 34.1 

Acute Dose-based RQ (2,3) 2.8 1.3 9.7 4.4 

Chronic Dose-based RQ (2,4) 37.1 17.0 129.0 59.08 

Diet-based EEC (1)

(ppm w.w. in earthworm) 64 64 

Chronic Dietary-based RQ (2,5) 4.3 4.3 

 (1) Based on fugacity modeling for earthworm using total endosulfan concentrations in soil and soil 

pore water of 22.4 and 0.183 g/m3, respectively for Citrus and 5.3 and 0.066 g/m3, respectively, for 

Eggplant exposure scenarios; See Appendix N for details. 

(2) RQ values in bold exceed the acute listed species LOC of 0.1 or the chronic LOC of 1.0 

(3) Acute dose-based RQs calculated using the dose-based EECs and adjusted, acute dose-based 

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Table 5.23 Estimated concentrations of total endosulfan in earthworms and mammalian risk quotients 

for two crop exposure scenarios 

Eggplant Citrus 

toxicity values of 21.98 and 7.69 mg/kg-bw for the 15g and 1000g mammal, respectively. 

Unadjusted LD50 = 10 mg/kg-bw based on rat (MRID 00038307). (4) Chronic dose-based RQs calculated using dose-based EECs and an adjusted, dose-based 

chronic NOAEC of 1.65 mg/kg-d for 15g mammals and 0.58 for 1000g mammals; Unadjusted dosebased NOAEC for rat calculated as 0.75 mg/kg-bw for the rat(MRID 00148264) 

(5) Chronic diet-based RQs calculated using diet-based EECs and a mammalian dietary NOAEC of 

15 ppm for rat (MRID: 00148264) 

(6) 15 g mammal used for estimating risks to SMHM; 1000g used for SJKF 

In conclusion, based on: 

1. exceedances of the Agency’s listed species acute risk LOC (RQ>0.1) and chronic risk 

LOC (RQ>1) for small mammals feeding on a variety of terrestrial food items for the 

various endosulfan application scenarios considered, 

2. the high probability of an individual mortality occurrence based on the highest acute 

RQ for mammals (~1 in 1; Table 5.12), 

3. LOC exceedences via consumption of earthworms via soil contamination (Table 

5.23), evidence of similar sensitivity of rats and mice to endosulfan (Section 4 and 

Appendix K), 

4. a significant degree of temporal overlap with endosulfan applications w/ SHMH life 

stages, and 

5. some spatial overlap between SMHM occurrence sections and cultivated/ 

orchard/vineyard crop use areas; 

it appears there is a potential for direct effects to the SMHM as result of labeled endosulfan 

use in California, although this potential is likely to be limited to small areas spatially. 

5.2.4.2 Indirect Effects (via Reductions in Prey Base) 

Potential forage items of the SMHM include leaves, seeds, plant stems, and insects, although 

seasonal variation has been observed in SMHM stomach contents with fresh green grasses 

more prevalent in the winter, and pickleweed and saltgrass dominating during the rest of the 

year. 

Terrestrial Invertebrates

RQ values representing exposures of endosulfan to terrestrial invertebrates that may serve as 

prey for the terrestrial-phase CRLF are also used to represent exposures of endosulfan to 

terrestrial invertebrates that may serve as prey for the SMHM. As described in Section 

5.2.1.2, the Agency determined that based on the fact that endosulfan is a highly efficacious 

broad spectrum insecticide, exceedances of the Agency’s interim LOC for listed terrestrial 

invertebrates for all of the modeled scenarios assessed, the high percentage of tested terrestrial 

invertebrate species that would be affected at the modeled EECs, and the high probability of 

an individual mortality occurrence based on the RQs for terrestrial invertebrates, there appears 

202 
to be a reasonable potential for direct effects on terrestrial invertebrates from the labeled 

endosulfan use in California. 

However, as discussed previously in Section 5.2.4.1 for directs effects on SMHM, the 

potential overlap of current and future endosulfan use patterns with the occurrence of the 

SMHM (and by extension, its terrestrial invertebrate prey) appears to be very small. 

Nevertheless, in these areas of spatial overlap, there does appear to be sufficient lines of 

evidence for a direct effect on the SMHM through reductions in terrestrial invertebrate prey, 

assuming the sensitivity of tested terrestrial invertebrates is similar to the terrestrial 

invertebrate prey being consumed by the SMHM. 

Aquatic (Vascular and Non-vascular) and Terrestrial Plants

As noted in Section 5.2.1.3, no data are available to reliably, quantitatively evaluate the 

effects and the potential risks of endosulfan to vascular aquatic plants or terrestrial plants. 

Only one reported incident involved plants (I014404-001, June 1, 1990 in Washington State), 

but no damage was reported and the incident classified only as ‘possible’ (i.e., exposure 

concentrations were not documented). Although effects to vascular aquatic and terrestrial 

plants cannot be quantified due to the lack of data, the available lines of evidence provide no 

compelling reason to believe that there is a potential for indirect effects to the SMHM from 

loss of plant food items as result of labeled endosulfan use in California. 

5.2.4.3 Indirect Effects (via Habitat Effects) 

Aquatic (Vascular and Non-vascular) and Terrestrial Plants

Aquatic plants serve several important functions in aquatic ecosystems. Non-vascular aquatic 

plants are primary producers and provide the autochthonous energy base for aquatic 

ecosystems. Vascular plants provide structure as attachment sites and refugia for many 

aquatic invertebrates, fish, and juvenile organisms, such as fish and frogs. In addition, 

vascular plants also provide primary productivity and oxygen to the aquatic ecosystem. 

Rooted plants help reduce sediment loading and provide stability to nearshore areas and lower 

streambanks. In addition, vascular aquatic plants are important as attachment sites for egg 

masses of aquatic species. 

Terrestrial plants serve several important habitat-related functions for the SMHM. In addition 

to providing habitat and cover for invertebrate prey items of the SMHM, terrestrial vegetation 

also provides nesting material, shelter, and cover from predators while foraging. Terrestrial 

plants also provide energy to the terrestrial ecosystem through primary production. Upland 

vegetation including grassland and woodlands provides cover during dispersal. Riparian 

vegetation helps to maintain the integrity of aquatic systems by providing bank and thermal 

stability, serving as a buffer to filter out sediment, nutrients, and contaminants before they 

reach the watershed, and serving as an energy source. 

As stated in Section 5.2.1.4 covering the evaluation of potential indirect effects to the CRLF 

via habitat effects, although effects to vascular aquatic and terrestrial plants cannot be 

quantified due to the lack of data, since the RQs do not exceed the Agency’s LOC (1) for 

203 
aquatic non-vascular plants based on the most sensitive data available to the Agency, and 

because available lines of evidence provide no compelling reason to believe that endosulfan 

will affect any type of plants to the extent that it would affect the habitat integrity of the 

SMHM, labeled endosulfan use in California appears not likely to indirectly affect the SMHM 

via impacts to habitat and/or primary production. Please refer to Section 5.2.1.4 for additional 

discussion and characterization of potential risks to plants that may be foraged upon by the 

SMHM. 

Small Terrestrial Vertebrates

SMHM do not burrow, but some winter nests may be constructed in burrows and small 

crevices. SMHM nests are described as minimal, and the SMHM may build over old birds’ 

nests or use nests built by Suisun shrews, after the young shrews have dispersed. Therefore, 

the potential for indirect effects to the SMHM via affects to small mammals and birds that 

may help to provide suitable habitat was evaluated. 

 

RQ values representing exposures of endosulfan to small mammals that may serve as prey for 

the terrestrial-phase CRLF, are also used to represent exposures of endosulfan to small 

mammals that may help to provide suitable habitat (nests) for the SMHM. As described in

Section 5.2.4.1 for direct effects on the SMHM, the Agency determined that a potential for 

direct effects to the SMHM exits as result of labeled endosulfan use in California, although 

this potential is likely to be limited to small areas spatially. The Agency further determined 

that a potential for direct effects of endosulfan use exists on birds, as described for the 

terrestrial phase CRLF (Section 5.2.1.1). Therefore, the same potential exists for habitat 

modification due to loss of mammalian and avian-created nesting sites. 

5.2.5 San Joaquin Kit Fox 

5.2.5.1 Direct Effects 

Endosulfan is currently registered for numerous diverse agricultural uses that span a large 

variety of geographical regions throughout the entire state of California. Therefore, there is 

the potential for endosulfan use across the state to spatially and temporally coincide with the 

SJKF breeding season. 

SJKF occupies a variety of habitats, including grasslands, scrublands (e.g., chenopod scrub 

and sub-shrub scrub), vernal pool areas, oak woodland, alkali meadows and playas, and an 

agricultural matrix of row crops, irrigated pastures, orchards, vineyards, and grazed annual 

grasslands. Kit foxes dig their own dens, modify and use those already constructed by other 

animals (ground squirrels, badgers, and coyotes), or use human-made structures (culverts, 

abandoned pipelines, or banks in sumps or roadbeds). They move to new dens within their 

home range often (likely to avoid predation by coyotes). The SJKF forages in California 

prairie and Sonoran grasslands in the vicinity of freshwater marshes and alkali sinks, where 

there is a dense ground cover of tall grasses and San Joaquin saltbush. Seasonal flooding in 

such habitats is normal. It feeds on small animals including blacktailed hares, desert 

cottontails, mice, kangaroo rats, squirrels, birds, lizards, insects and grass. The San Joaquin 

204 
kit fox satisfies its moisture requirements from prey and does not depend on freshwater 

sources. 

Temporal and Spatial Overlap

The breeding season of the SJKF is from late December – March, with a gestation period of 

48 to 52 days. Litters are born February - late March. Pups emerge from their dens at about 1-

month of age and may begin to disperse after 4 – 5 months usually in Aug. or Sept. Pup 

dispersal coincides with the peak endosulfan application in August through September 

(Figure 5.1). 

The SJKF inhabits grasslands in the San Joaquin Valley and eastern Bay Area counties of 

California. Since pesticide use information is only available at the county level, the degree 

that the SJKF and endosulfan actually coincide cannot be precisely determined. The spatial 

overlap of endosulfan use and SJKF distribution is summarized at the county level in Table 

5.7. Approximately 80% of endosulfan use (71,104 lbs) is applied in counties in which the 

SJKF occurs. These counties represent approximately 73% of the SJKF range by county. 

Examination of the overlap of SJKF occurrence sections and distribution records (Figure E.4 

of Appendix E) with cultivated crop, orchard and vineyard areas suggests a moderate amount 

of spatial overlap with potential endosulfan use areas. 

Direct Exposure

Direct exposure of the SJKF and the resulting risks in terrestrial environments were evaluated 

based on dose- and dietary-based EECs estimated using two approaches (i.e., T-REX for 

foliar spray applications and using fugacity-based modeling for insectivorous wildlife). All 

estimated EECs (i.e., EECs for short grass, tall grass, broadleaf plants/small insects, 

fruits/pods/seeds/large insects) were considered relevant for evaluation of direct effects 

because the SJKF has been known to feed on insects and grasses. A mammalian body weight 

of 1000g was modeled based on the adult size of the kit fox. 

Based on surrogate toxicity data (LD50=10 mg/kg-bw and NOAEL = 15 mg/kg-diet), the 

maximum allowable application rate (1 application, 2.5 lbs a.i./acre/application), the foliar 

dissipation half-life of 4 days for endosulfan from Willis and McDowell (1987), and upper 

bound Kenaga values from T-REX, there is a potential for direct adverse effects on SJKF 

individuals from foliar spray applications of endosulfan in CA (Table 5.4). 

For spray applications of endosulfan, the dose-based acute RQs range from 2.38 to 11.92, 

from 1.09 to 5.46, from 1.34 to 6.70, and from 0.15 to 0.74 for the short grass, tall grass, 

broadleaf plants/small insects, and fruits/pods/seeds/large insect dietary categories, 

respectively (Table 5.4). For acute dose-based RQs, all modeled scenarios (N=20) resulted in 

an exceedance of the Agency’s acute listed species LOC (RQ>0.1) for mammals that feed on 

short grass, tall grass, broadleaf plants/small insects, and fruits/pods/seeds/large insects. 

The dose-based chronic RQs ranged from 31.78 to 158.90, from 14.57 to 72.83, from 17.88 to 

89.38, and from 1.99 to 9.93, for the short grass, tall grass, broadleaf plants/small insects, and 

205 
fruits/pods/seeds/large insect dietary categories, respectively (Table 5.4). For chronic dosebased RQs, all modeled scenarios (N=20) resulted in an exceedance of the Agency’s acute 

listed species LOC (RQ≥1) for mammals that feed on short grass, tall grass, broadleaf 

plants/small insects, and fruits/pods/seeds/large insects. 

The dietary-based chronic RQs range from 8 to 40.00, from 3.67 to 18.33, from 4.50 to 22.50, 

and from 0.50 to 2.50, for the short grass, tall grass, broadleaf plants/small insects, and 

fruits/pods/seeds/large insects dietary categories, respectively (Table 5.4). For chronic 

dietary-based RQs, all modeled scenarios (N=20) resulted in an exceedance of the Agency’s 

acute listed species LOC (RQ≥1) for mammals that feed on short grass, tall grass, and 

broadleaf plants/small insects. Thirteen out of 20 modeled scenarios resulted in an exceedance 

of the Agency’s chronic risk LOC (RQ≥1) for mammals that feed on fruits/pods/seeds/large 

insects. Therefore, RQs for exceed the Agency’s acute listed species LOC (RQ>0.1) and 

chronic risk LOC (RQ>1) for mammals (see Table 5.4) for foliar spray applications of 

endosulfan. 

As described in Section 5.2.4.1, the potential exists for direct effects to insectivorous wildlife 

(including SJKF) via soil contaminated with endosulfan. In order to explore the potential 

exposures of SJKF to total residues of endosulfan that have accumulated in earthworms 

inhabiting endosulfan-treatment sites, a simple fugacity approach was employed to estimate 

endosulfan concentrations in earthworms and subsequent exposures to the SJKF consuming 

earthworms. Additional description of this approach is provided in Appendix N. Results 

presented in Table 5.23 indicate dose-based RQs exceed the Agency’s listed acute a LOC for 

a 1000g mammal even when using the exposure scenario with the lowest soil EECs 

(eggplant). Furthermore, chronic dose- and dietary-based RQs for a 1000g mammal exceed 

the chronic LOC for the eggplant exposure scenario. 

In conclusion, the Agency determines that based on: 

1. Exceedances of the Agency’s listed species acute risk LOC (RQ>0.1) and chronic risk 

LOC (RQ>1) for large mammals feeding on a variety of terrestrial food items for the 

various endosulfan application scenarios considered, 

2. The high probability of an individual mortality occurrence based on the highest acute RQ 

for mammals (~1 in 1; Table 5.12), 

3. LOC exceedences via consumption of earthworms via soil contamination (Table 5.23), 

and 

4. A moderate degree of spatial and temporal overlap of SJKF occurrence and potential 

endosulfan use areas, 

It appears there is a potential for direct effects to the SJKF as result of labeled endosulfan use 

in California. 

 

5.2.5.2 Indirect Effects (via Reductions in Prey Base) 

Potential forage items of the SJKF include small mammals, grasses, and insects. 

206 
Terrestrial Invertebrates

RQ values representing exposures of endosulfan to terrestrial invertebrates that may serve as 

prey for the terrestrial-phase CRLF, CTS, SFGS SMHM are also used to represent exposures 

of endosulfan to terrestrial invertebrates that may serve as prey for the SFKF. As described in

Section 5.2.1.2, the Agency determined that based on the fact that endosulfan is a highly 

efficacious broad spectrum insecticide, exceedances of the Agency’s interim LOC for listed 

terrestrial invertebrates for all of the modeled scenarios assessed, the high percentage of tested 

terrestrial invertebrate species that would be affected at the modeled EECs, and the high 

probability of an individual mortality occurrence based on the RQs for terrestrial 

invertebrates, there appears to be a reasonable potential for direct effects on terrestrial 

invertebrates from the labeled endosulfan use in California. Furthermore, there appears to be 

a moderate amount of spatial overlap between SJKF occurrence and both current and potential 

future endosulfan use areas, as described in Section 5.2.5.2. Therefore, the Agency 

determines that there are sufficient lines of evidence for indirect effect on the SJKF through 

reductions in terrestrial invertebrate prey, assuming the sensitivity of tested terrestrial 

invertebrates is similar to the terrestrial invertebrate prey being consumed by the SLKF. 

Small Mammals

RQ values representing exposures of endosulfan to small mammals that may serve as prey for 

the terrestrial-phase CRLF, are also used to represent exposures of endosulfan to small 

mammals that may help to provide prey for the SJKF. As described in Section 5.2.1.2 for the 

terrestrial-phase CRLF, the Agency determined that based on the exceedances of the 

Agency’s listed species acute risk LOC and chronic risk LOC for small mammals feeding on 

a variety of terrestrial food items for the various endosulfan seed, spray, and granular 

application scenarios considered, the high probability of an individual mortality occurrence 

based on the highest acute RQ for mammals (~1 in 1), and the relative insensitivity of risk 

conclusions to selection of less conservative acute and chronic endpoints, there are adequate 

lines of evidence for potential direct effects on mammals as a result of labeled endosulfan use 

in California. Furthermore, there appears to be a moderate amount of spatial overlap between 

SJKF occurrence and both current and potential future endosulfan use areas, as described in 

Section 5.2.5.2. Therefore, the Agency determines that there are sufficient lines of evidence 

for indirect effect on the SJKF through reductions in small mammalian prey, assuming the 

sensitivity of tested mammals is similar to the mammalian prey being consumed by the SLKF. 

Aquatic (Vascular and Non-vascular) and Terrestrial Plants

As noted in Section 5.2.1.3, no data are available to reliably, quantitatively evaluate the 

effects and the potential risks of endosulfan to vascular aquatic plants or terrestrial plants. No 

incidents have been reported to the Agency that involve any plants (all terrestrial plants), and 

none have reliably linked endosulfan to the observed effects with a certainty index of 

“probable” or higher, despite that it is regularly directly applied on or near a very wide variety 

of agricultural and home garden plants. Therefore, although effects to vascular aquatic and 

terrestrial plants cannot be quantified due to the lack of data, the available lines of evidence 

207 
provide no compelling reason to believe that there is a potential for indirect effects to the 

SJKF from loss of plant food items as result of labeled endosulfan use in California. 

5.2.5.3 Indirect Effects (via Habitat Effects) 

Aquatic (Vascular and Non-vascular) and Terrestrial Plants

Aquatic plants serve several important functions in aquatic ecosystems. Non-vascular aquatic 

plants are primary producers and provide the autochthonous energy base for aquatic 

ecosystems. Vascular plants provide structure as attachment sites and refugia for many 

aquatic invertebrates, fish, and juvenile organisms, such as fish and frogs. In addition, 

vascular plants also provide primary productivity and oxygen to the aquatic ecosystem. 

Rooted plants help reduce sediment loading and provide stability to nearshore areas and lower 

streambanks. In addition, vascular aquatic plants are important as attachment sites for egg 

masses of aquatic species. 

Terrestrial plants serve several important habitat-related functions for the SJKF. In addition 

to providing habitat and cover for invertebrate prey terrestrial plants also provide energy to 

the terrestrial ecosystem through primary production. Upland vegetation including grassland 

and woodlands provides cover during dispersal. Riparian vegetation helps to maintain the 

integrity of aquatic systems by providing bank and thermal stability, serving as a buffer to 

filter out sediment, nutrients, and contaminants before they reach the watershed, and serving 

as an energy source. 

As stated in Section 5.2.1.3 covering the evaluation of potential indirect effects to the CRLF 

via habitat effects, although effects to vascular aquatic and terrestrial plants cannot be 

quantified due to the lack of data, since the RQs do not exceed the Agency’s LOC (1) for 

aquatic non-vascular plants based on the most sensitive data available to the Agency, and 

because available lines of evidence provide no compelling reason to believe that endosulfan 

will affect any type of plants to the extent that it would affect the habitat integrity of the 

SJKF, labeled endosulfan use in California appears not to indirectly affect the SJKF via 

impacts to habitat and/or primary production. 

5.2.6 Bay Checkerspot Butterfly 

5.2.6.1 Direct Effects 

The BCB’s life cycle is closely tied with the biology of its host plants. The host plants 

germinate anytime from early October to late December and senesce from early April to mid 

May, and most of the active parts of the BCB life cycle also occur during this time (see 

Figure 5.9). The BCB reproduces once and dies within a single year. Adults emerge from 

pupae, feed on nectar, mate and lay eggs during a flight season that lasts 4 to 6 weeks from 

late February to early May. While females normally (although not always) only mate once, 

males emerge up to 10 days prior to the emergence of females and may mate several times 

before dying. Adults of both sexes live on average for 10 days (with a maximum adult life 

span of over 3 weeks reported). Females lay up to 5 egg masses (250 eggs/mass) typically in 

208 
March and April. Eggs are deposited primarily near the base of dwarf plantain plants, and less 

commonly on purple owl’s-clover and exserted paintbrush. 

Larvae hatch from eggs in roughly 10 days and grow to the 4th instar in about two weeks. 

Once reaching the 4th instar, the larvae then spend a period of dormancy (diapause) under 

rocks or in soil cracks that lasts through the summer. The larvae resume activity with the start 

of the rainy season and the germination of dwarf plantain plants. The post-diapause larvae are 

more mobile than the pre-diapause larvae and may travel tens of meters in search of food 

and/or warm microclimates to bask or pupate in. Larvae pupate, with the pupae suspended 

few meters above the ground on vegetation, once they reach a weight of 300 - 500 milligrams. 

Adults emerge within 15 to 30 days depending on thermal conditions, although there is some 

evidence that a few larvae in very dry years may enter into a second diapause and complete 

their development the second spring after hatching. 

Figure 5.9 General Annual Life-History Parameters for the BCB 

As previously discussed in Section 5.2.1.1, endosulfan is currently registered for a wide 

variety of agricultural in crops, orchards, and nursery (only one non-agricultural use: ear tags 

for cattle), which span a large variety of use sites and geographical regions throughout the 

entire state of California and allow for the potential for almost year-round use (see Figure 

5.1). Therefore, there is the potential for endosulfan use in any given area across the state to 

spatially and temporally coincide with all of the critical life-stages of the BCB, and disrupt its 

life-cycle at various points. However, during the months of peak usage August and September 

(Figure 5.1), larvae are in their dormancy stage (see Figure 5.9). 

For the purposes of evaluating direct exposure and effects to the BCB, larvae for the BCB 

were considered ‘small insects’ in this assessment, while the adults of this species were 

considered ‘large insects’. Therefore, the potential for direct exposure and effects specifically 

to the BCB resulting from endosulfan spray applications was evaluated by considering the 

lowest available acute contact toxicity endpoint for terrestrial invertebrates along with the TREX estimated EECs for small (broadleaf plants/small insects dietary category) and large 

(fruits/pods/seeds/large insects dietary category) insects. Based on the beet webworm 

(Pyrausta sticticalis) toxicity data (LD50 = 0.15 ug a.i./g) the RQs for small insects ranged 

from 547 to 2250, and those for large insects from 50 to 250). 

RQ values representing exposures of endosulfan to terrestrial invertebrates that may serve as 

prey for the terrestrial-phase CRLF, are also used to represent direct exposures of endosulfan 

to the BCB. As described in Section 5.2.1.2, the Agency determined that based on the fact 

that endosulfan is a highly efficacious broad spectrum insecticide, the exceedances of the 

Agency’s interim LOC for listed terrestrial invertebrates for all of the modeled scenarios 

assessed (for both large (adult BCB) and small (BCB larvae) insects), and the high probability 

of an individual mortality occurrence based on the highest acute RQ for terrestrial 

209 
invertebrates (~1 in 1), it appears that there are adequate lines of evidence to conclude that 

there is a potential for direct effects to the BCB as result of labeled endosulfan use in 

California. 

However, it should be noted that the spatial distribution of current average endosulfan use and 

BCB distribution do not coincide (see Table 5.7; Figure 5.7). If cultivated crop, orchard and 

vineyard use areas are considered as regions of potential endosulfan use in the future, then a 

substantial degree of overlap between BCB occurrence, its critical habitat and where 

endosulfan use could occur (Figure E.5 of Appendix E). Furthermore, there is potential for 

endosulfan to be transported long distances from the application sites (Section 3.2.4.4). 

5.2.6.2 Indirect Effects (via Reduction in Prey Base & Habitat Effects) 

The primary diet for the BCB larvae are dwarf plantain plants (although they may also feed 

on purple owl’s-clover or exserted paintbrush if the dwarf plantains senesce before the larvae 

pupate). Adults feed on the nectar of a variety of plants found in association with serpentine 

grasslands [e.g., California goldfields, tidy-tips, desert parsley, scytheleaf (Allium 

falcifolium), sea muilla (muilla maritime), false babystars (Linanthus androsaceus), and 

intermediate fiddleneck (Amsinckia intermedia)]. 

In addition to serving as the primary dietary item of the BCB, terrestrial plants serve several 

important habitat-related functions that are described below in Section 5.2.6.3 in detail with 

regards to critical habitat. Therefore, the potential for indirect effects to the BCB via loss of 

terrestrial plant food items and impacts to habitat and/or primary production was considered. 

Terrestrial Plants

For the purposes of this assessment, the potential for indirect effects to the BCB via loss of 

terrestrial plant food items and impacts to habitat and/or primary production was assessed by 

considering effects to terrestrial plants. As noted in Section 5.2.1.3, there were no data to 

reliably quantitatively evaluate the effects and the potential risks of endosulfan to terrestrial 

plants. However, aquatic non-vascular plants are not particularly sensitive to endosulfan, 

endosulfan has a neural toxic mode of action, and no studies demonstrating significant 

adverse effects of endosulfan to any vascular aquatic or terrestrial plant have been identified 

in the open literature. The only terrestrial plant information comes from studies of single 

application to food crops to determine the efficacy of endosulfan for the control of insect 

pests. By design, the exposure concentrations for the control of insect pests are intended not to 

harm the crop plants. However, these studies are only available for herbaceous plants and 

none for woody plants. In addition, since 1970 no ecological incidents have been reported to 

the Agency that involved any documented harm to either aquatic or terrestrial plants, despite 

that it is regularly directly applied on or near a very wide variety of agricultural and home 

garden plants. Therefore, although effects to terrestrial plants cannot be quantified due to the 

lack of data, the available lines of evidence provide no compelling reason to believe that there 

is a potential for indirect effects to the BCB via loss of terrestrial plant food items and impacts 

to habitat and/or primary production as result of labeled endosulfan use in California. 

5.2.6.3 Modification to Designated Critical Habitat 

The primary constituent elements (PCEs) of the BCB include: 

210 
• The presence of annual or perennial grasslands with little to no overstory that provide 

north/south and east/west slopes with a tilt of more than 7 degrees for larval host plant 

survival during periods of atypical weather (e.g., drought). 

• The presence of the primary larval host plant, dwarf plantain (Plantago erecta) (a 

dicot) and at least one of the secondary host plants, purple owl's-clover or exserted 

paintbrush, are required for reproduction, feeding, and larval development. 

• The presence of adult nectar sources for feeding. 

• Aquatic features such as wetlands, springs, seeps, streams, lakes, and ponds and their 

associated banks, that provide moisture during periods of spring drought; these 

features can be ephemeral, seasonal, or permanent. 

• Soils derived from serpentinite ultramafic rock (Montara, Climara, Henneke, Hentine, 

and Obispo soil series) or similar soils (Inks, Candlestick, Los Gatos, Fagan, and 

Barnabe soil series) that provide areas with fewer aggressive, nonnative plant species 

for larval host plant and adult nectar plant survival and reproduction. 

• The presence of stable holes and cracks in the soil, and surface rock outcrops that 

provide shelter for the larval stage of the bay checkerspot butterfly during summer 

diapause. 

For the purposes of this assessment, the potential for indirect effects to the BCB as result of 

effects to the PCEs of its designated critical habitat is assessed by considering effects to 

terrestrial plants. Similar to what was noted in Section 5.2.6.2 above, in which the potential 

for indirect effects to the BCB via loss of terrestrial plant food items and impacts to habitat 

and/or primary production was assessed, although effects to terrestrial plants cannot be 

quantified due to the lack of data, the Agency concludes that the weight-of-evidence suggests 

that effects to terrestrial plants as a result of labeled endosulfan use in California are not 

expected to the extent that there will be modification of BCB designated critical habitat. 

5.2.7 Valley Elderberry Longhorn Beetle 

 

5.2.7.1 Direct Effects 

The VELB “feeds on at least one species of elderberry (Sambucus) and perhaps as many as 

three elderberry taxa” including S. glauca, S. caerulea, and S. mexicana (USFWS, 1984). 

VELB adults consume elderberry foliage and possibly also the flowers whereas the “larvae 

are borers and feed on the soft pith in stems and roots of the elderberry” (USFWS, 1984 and 

2007 b; and LSA, 2004). The adults eat from when they emerge in the spring until about June 

when they begin to mate (California’s Endangered Insects). 

The life cycle of the VELB is divided into four stages: egg, larva, pupa, and adult, and has 

been assumed to encompass two years, but recent information from rearing experiments 

suggests that a one year cycle is possible, if not probable (Barr, 1991). Female VELB lay their 

eggs singly or in small groups on live elderberry leaves, in crevices in the bark, at the 

stem/trunk junctions, or at the stem/petiole junctions of the elderberry (Barr, 1991; 

California’s Endangered Insects; and Talley, no date). The first instar larvae are exposed on 

the surface of the shrub anywhere from a few minutes to a day before they bore to the center 

of elderberry stems where they create a characteristic feeding gallery in the pith at the center 

of the stem (Talley et al., 2006 and Barr, 1991). The larvae develop for 1 or 2 years feeding 

211 
on pith (Talley et al., 2006), eventually creating a pupal chamber. In the pupal chamber, the 

larvae metamorphose into their pupae between December and April (Talley et al., 2006). 

Pupation is thought to take about one month and the adult may remain in the chamber for up 

to several weeks (Talley et al., 2006). The VELB adults typically emerge at about the same 

time the elderberry flowers, between mid-March and mid-June” (USFWS, 1984 and Talley et 

al., 2006). The adults live for a few days to a few weeks between mid-March and early-June 

(Talley, no date and 2006; and USFWS, 1984). However, most records are for late-April to 

mid-May (Talley et al., 2006 and USFWS, 1984). During this period, the adults feed on 

elderberry leaves and possibly flowers, and reproduce within the canopy (Talley, no date and 

2006). The females also lay their eggs during this period (USFWS, 2006). The lifespan of the 

adult VELB is unknown; however, it is suspected that they die after reproducing (LSA, 2004). 

As with the BCB, there is the potential for endosulfan use in any given area across the state to 

temporally coincide with all of the critical life-stages of the BCB, and disrupt its life-cycle at 

various points. For the purposes of evaluating direct exposure and effects to the VELB, larvae 

were considered ‘small insects’ in this assessment, while the adults of this species were 

considered ‘large insects’. Therefore, the potential for direct exposure and effects specifically 

to the VELB resulting from endosulfan spray applications was evaluated by considering the 

lowest available acute contact toxicity endpoint for terrestrial invertebrates along with the TREX estimated EECs for small (broadleaf plants/small insects dietary category) and large 

(fruits/pods/seeds/large insects dietary category) insects. The RQ analysis for VELB is the 

same as evaluated previously for BCB (Section 5.2.5). Therefore, as with BCB, it appears that 

there are adequate lines of evidence to conclude that there is a potential for direct effects to 

the VELB as result of labeled endosulfan use in California. However, the VELB or its critical 

habitat occurs in counties with less than 0.01% of the average endosulfan use in California 

from 2005-2006 (Table 5.7 and Figure 5.7). When the cultivated crop, orchard, and vineyard 

agricultural uses are considered as potential area of future endosulfan use, then a moderate 

amount of spatial overlap with VELB occurrence can be observed (Figure E.6 of Appendix 

E). Furthermore, there is potential for endosulfan to be transported long distances from the 

application sites (Section 3.2.4.4). 

5.2.7.2 Indirect Effects (via Reduction in Prey Base & Habitat Effects) 

The VELB feeds on at least one species of elderberry (Sambucus) and perhaps as many as 

three elderberry taxa including S. glauca, S. caerulea, and S. mexicana (USFWS, 1984). In 

addition to serving as the primary dietary item of the VELB, terrestrial plants serve several 

important habitat-related functions that are described below in Section 5.2.5.2 in detail with 

regards to critical habitat. Therefore, the potential for indirect effects to the VELB via loss of 

terrestrial plant food items and impacts to habitat and/or primary production was considered. 

Terrestrial Plants

For the purposes of this assessment, the potential for indirect effects to the VELB via loss of 

terrestrial plant food items and impacts to habitat and/or primary production was assessed by 

considering effects to terrestrial plants. As noted in Section 5.2.1.3, there were no data to 

reliably quantitatively evaluate the effects and the potential risks of endosulfan to terrestrial 

plants. However, aquatic non-vascular plants are not particularly sensitive to endosulfan, 

endosulfan has a neural toxic mode of action, and no studies demonstrating significant 

adverse effects of endosulfan to any vascular aquatic or terrestrial plant have been identified 

212 
in the open literature. The only terrestrial plant information comes from studies of single 

application to food crops to determine the efficacy of endosulfan for the control of insect 

pests. By design, the exposure concentrations for the control of insect pests are intended not to 

harm the crop plants. However, these studies are only available for herbaceous plants and 

none for woody plants. In addition, since 1970 no ecological incidents have been reported to 

the Agency that involved any documented harm to either aquatic or terrestrial plants, despite 

that it is regularly directly applied on or near a very wide variety of agricultural and home 

garden plants. Therefore, although effects to terrestrial plants cannot be quantified due to the 

lack of data, the available lines of evidence provide no compelling reason to believe that there 

is a potential for indirect effects to the VELB via loss of terrestrial plant food items and 

impacts to habitat and/or primary production as result of labeled endosulfan use in California. 

5.2.7.3 Modification to Designated Critical Habitat 

The primary constituent elements (PCEs) of the VELB include the presence of riparian 

elderberry trees during its entire life cycle. For the purposes of this assessment, the potential 

for indirect effects to the VELB as result of effects to the PCEs of its designated critical 

habitat is assessed by considering effects to terrestrial plants. Similar to what was noted in 

Section 5.2.6.2 above, in which the potential for indirect effects to the VELB via loss of 

terrestrial plant food items and impacts to habitat and/or primary production was assessed, 

although effects to terrestrial plants cannot be quantified due to the lack of data, the Agency 

concludes that the weight-of-evidence suggests that effects to terrestrial plants as a result of 

labeled endosulfan use in California are not expected to the extent that there will be 

modification of VELB designated critical habitat. 

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6 Uncertainties 

6.1 Exposure Assessment Uncertainties

6.1.1 Maximum Use Scenario 

The screening-level risk assessment focuses on characterizing potential ecological risks 

resulting from a maximum use scenario, which is determined from labeled statements of 

maximum application rate and number of applications with the shortest time interval between 

applications. The frequency at which actual uses approach this maximum use scenario may 

be dependant on pest resistance, timing of applications, cultural practices, and market forces. 

6.1.2 Aquatic Exposure Modeling of Endosulfan 

The standard ecological water body scenario (EXAMS pond) used to calculate potential 

aquatic exposure to pesticides is intended to represent conservative estimates, and to avoid 

underestimations of the actual exposure. The standard scenario consists of application to a 

10-hectare field bordering a 1-hectare, 2-meter deep (20,000 m3

) pond with no outlet. 

Exposure estimates generated using the EXAMS pond are intended to represent a wide variety 

of vulnerable water bodies that occur at the top of watersheds including prairie pot holes, 

playa lakes, wetlands, vernal pools, man-made and natural ponds, and intermittent and lower 

order streams. As a group, there are factors that make these water bodies more or less 

vulnerable than the EXAMS pond. Static water bodies that have larger ratios of pesticidetreated drainage area to water body volume would be expected to have higher peak EECs than 

the EXAMS pond. These water bodies will be either smaller in size or have larger drainage 

areas. Smaller water bodies have limited storage capacity and thus may overflow and carry 

pesticide in the discharge, whereas the EXAMS pond has no discharge. As watershed size 

increases beyond 10-hectares, it becomes increasingly unlikely that the entire watershed is 

planted with a single crop that is all treated simultaneously with the pesticide. Headwater 

streams can also have peak concentrations higher than the EXAMS pond, but they likely 

persist for only short periods of time and are then carried and dissipated downstream. 

The Agency acknowledges that there are some unique aquatic habitats that are not accurately 

captured by this modeling scenario and modeling results may, therefore, under- or overestimate exposure, depending on a number of variables. For example, some organisms may 

inhabit water bodies of different size and depth and/or are located adjacent to larger or smaller 

drainage areas than the EXAMS pond. In addition, the Services agree that the existing 

EXAMS pond represents the best currently available approach for estimating aquatic 

exposure to pesticides (USFWS/NMFS 2004).

PRZM-EXAMS modeled EECs are intended to represent exposure of aquatic organisms in 

relatively small ponds and low-order streams. Therefore it is likely that EECs generated from 

the PRZM-EXAMS model will over-estimate potential concentrations in larger receiving 

water bodies such as estuaries, embayments, and coastal marine areas because chemicals in 

runoff water (or spray drift, etc.) should be diluted by a much larger volume of water than 

214 
would be found in the ‘typical’ EXAMS pond. However, as chemical constituents in water 

draining from freshwater streams encounter brackish or other near-marine-associated 

conditions, there is potential for important chemical transformations to occur. Many chemical 

compounds can undergo changes in mobility, toxicity, or persistence when changes in pH, Eh 

(redox potential), salinity, dissolved oxygen (DO) content, or temperature are encountered. 

For example, desorption and re-mobilization of some chemicals from sediments can occur 

with changes in salinity (e.g., Means 1995; Swarzenski et al. 2003; Jordan et al. 2008), 

changes in pH (e.g., Wood and Baptista 1993; Parikh et al. 2004; Fernandez et al. 2005), Eh 

changes (Wood and Baptista 1993; Velde and Church 1999), and other factors. Thus, 

although chemicals in discharging rivers may be diluted by large volumes of water within 

receiving estuaries and embayments, the hydrochemistry of the marine-influenced water may 

negate some of the attenuating impact of the greater water volume; for example, the effect of 

dilution may be confounded by changes in chemical mobility (and/or bioavailability) in 

brackish water. In addition, freshwater contributions from discharging streams and rivers do 

not instantaneously mix with more saline water bodies. In these settings, water will 

commonly remain highly stratified, with fresh water lying atop denser, heavier saline water – 

meaning that exposure to concentrations found in discharging stream water may propagate 

some distance beyond the outflow point of the stream (especially near the water surface). 

Therefore, it is not assumed that discharging water will be rapidly diluted by the entire water 

volume within an estuary, embayment, or other coastal aquatic environment. PRZM-EXAMS 

model results should be considered consistent with concentrations that might be found near 

the head of an estuary unless there is specific information – such as monitoring data – to 

indicate otherwise. Conditions nearer to the mouth of a bay or estuary, however, may be 

closer to a marine-type system, and thus more subject to the notable buffering, mixing, and 

diluting capacities of an open marine environment. Conversely, tidal effects (pressure waves) 

can propagate much further upstream than the actual estuarine water, so discharging river 

water may become temporarily partially impounded near the mouth (discharge point) of a 

channel, and resistant to mixing until tidal forces are reversed. 

The Agency does not currently have sufficient information regarding the hydrology and 

hydrochemistry of estuarine aquatic habitats to develop alternate scenarios for assessed listed 

species that inhabit these types of ecosystems. The Agency acknowledges that there are 

unique brackish and estuarine habitats that may not be accurately captured by PRZMEXAMS modeling results, and may, therefore, under- or over-estimate exposure, depending 

on the aforementioned variables. 

In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations that 

are expected to be exceeded once within a ten-year period. The Pesticide Root Zone Model is 

a process or “simulation” model that calculates what happens to a pesticide in an agricultural 

field on a day-to-day basis. It considers factors such as rainfall and plant transpiration of 

water, as well as how and when the pesticide is applied. It has two major components: 

hydrology and chemical transport. Water movement is simulated by the use of generalized 

soil parameters, including field capacity, wilting point, and saturation water content. The 

chemical transport component can simulate pesticide application on the soil or on the plant 

foliage. Dissolved, adsorbed, and vapor-phase concentrations in the soil are estimated by 

215 
simultaneously considering the processes of pesticide uptake by plants, surface runoff, 

erosion, decay, volatilization, foliar wash-off, advection, dispersion, and retardation. 

Uncertainties associated with each of these individual components add to the overall 

uncertainty of the modeled concentrations. Additionally, model inputs from the 

environmental fate degradation studies are chosen to represent the upper confidence bound on 

the mean values that are not expected to be exceeded in the environment approximately 90 

percent of the time. Mobility input values are chosen to be representative of conditions in the 

environment. The natural variation in soils adds to the uncertainty of modeled values. 

Factors such as application date, crop emergence date, and canopy cover can also affect 

estimated concentrations, adding to the uncertainty of modeled values. Factors within the 

ambient environment such as soil temperatures, sunlight intensity, antecedent soil moisture, 

and surface water temperatures can cause actual aquatic concentrations to differ for the 

modeled values. 

Unlike spray drift, tools are currently not available to evaluate the effectiveness of a 

vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is highly 

dependent on the condition of the vegetative strip. For example, a well-established, healthy 

vegetative setback can be a very effective means of reducing runoff and erosion from 

agricultural fields. Alternatively, a setback of poor vegetative quality or a setback that is 

channelized can be ineffective at reducing loadings. Until such time as a quantitative method 

to estimate the effect of vegetative setbacks on various conditions on pesticide loadings 

becomes available, the aquatic exposure predictions are likely to overestimate exposure where 

healthy vegetative setbacks exist and underestimate exposure where poorly developed, 

channelized, or bare setbacks exist. 

6.1.2.1 Potential Groundwater Contributions to Surface Water Chemical 

Concentrations 

Although the potential impact of discharging groundwater on CRLF populations is not 

explicitly delineated, it should be noted that groundwater could provide a source of pesticide 

to surface water bodies – especially low-order streams, headwaters, and groundwater-fed 

pools. This is particularly likely if the chemical is persistent and mobile. Soluble chemicals 

that are primarily subject to photolytic degradation will be very likely to persist in 

groundwater, and can be transportable over long distances. Similarly, many chemicals 

degrade slowly under anaerobic conditions (common in aquifers) and are thus more persistent 

in groundwater. Much of this groundwater will eventually be discharged to the surface – 

often supporting stream flow in the absence of rainfall. Continuously flowing low-order 

streams in particular are sustained by groundwater discharge, which can constitute 100% of 

stream flow during baseflow (no runoff) conditions. Thus, it is important to keep in mind that 

pesticides in groundwater may have a major (detrimental) impact on surface water quality, 

and on CRLF habitats. 

SciGrow may be used to determine likely ‘high-end’ groundwater vulnerability, with the 

assumption (based upon persistence in sub- and anoxic conditions, and mobility) that much of 

the compound entering the groundwater will be transported some distance and eventually 

216 
discharged into surface water. Although concentrations in a receiving water body resulting 

from groundwater discharge cannot be explicitly quantified, it should be assumed that 

significant attenuation and retardation of the chemical will have occurred prior to discharge. 

Nevertheless, groundwater could still be a significant consistent source of chronic background 

concentrations in surface water, and may also add to surface runoff during storm events (as a 

result of enhanced groundwater discharge typically characterized by the ‘tailing limb’ of a 

storm hydrograph). 

6.1.3 Multiple Growing Seasons per Year 

Most endosulfan product labels specify application rates on a per crop cycle basis (not on a 

per year basis). Information from BEAD indicates that several crops can be grown more than 

one time/year in California, as indicated in Section 3. Since standard PRZM scenarios only 

consist of one crop per year, applications to only one crop per year were modeled. The crops 

that may be grown multiple times in a calendar year that can be treated by endosulfan include 

Broccoli & Lettuce (two crops); Cabbage, Chinese cabbage, Cauliflower, Collards, Mustard 

Green & Sweet Corn (three crops ); and Kale (four crops). If endosulfan is applied for 

multiple cropping cycles within a year, EECs presented in this assessment may underpredict 

exposures. For all other labeled uses, it was assumed that a maximum seasonal application 

specified on the label was equivalent to a maximum annual application. 

6.1.4 Usage Uncertainties 

County-level usage data were obtained from California’s Department of Pesticide Regulation 

Pesticide Use Reporting (CDPR PUR) database. Thirteen years of data (1994– 2006) were 

included in this analysis although error identification was not available for the older data from 

1994 t0 1998. Statistical methodology for identifying outliers, in terms of area treated and 

pounds applied, was provided by CDPR for later years only (1999 to 2006). All data was 

included in order to analyze historical usage of endosulfan and no data was used as input 

parameter for modeling. CDPR PUR documentation indicates that errors in the data may 

include the following: a misplaced decimal; incorrect measures, area treated, or units; and 

reports of diluted pesticide concentrations. In addition, it is possible that the data may contain 

reports for pesticide uses that have been cancelled. The CPDR PUR data does not include 

home owner applied pesticides; therefore, residential uses are not likely to be reported. As 

with all pesticide usage data, there may be instances of misuse and misreporting. The Agency 

made use of the most current, verifiable information; in cases where there were discrepancies, 

the most conservative information was used.

6.1.5 Terrestrial Exposure Modeling of Endosulfan 

The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide 

residues in wildlife dietary items. These residue assumptions are believed to reflect a realistic 

upper-bound residue estimate, although the degree to which this assumption reflects a specific 

percentile estimate is difficult to quantify. It is important to note that the field measurement 

efforts used to develop the Fletcher estimates of exposure involve highly varied sampling 

techniques. It is entirely possible that much of these data reflect residues averaged over entire 

above ground plants in the case of grass and forage sampling. 

217 
It was assumed that ingestion of food items in the field occurs at rates commensurate with 

those in the laboratory. Although the screening assessment process adjusts dry-weight 

estimates of food intake to reflect the increased mass in fresh-weight wildlife food intake 

estimates, it does not allow for gross energy differences. Direct comparison of a laboratory 

dietary concentration- based effects threshold to a fresh-weight pesticide residue estimate 

would result in an underestimation of field exposure by food consumption by a factor of 1.25 

– 2.5 for most food items. 

Differences in assimilative efficiency between laboratory and wild diets suggest that current 

screening assessment methods do not account for a potentially important aspect of food 

requirements. Depending upon species and dietary matrix, bird assimilation of wild diet 

energy ranges from 23 – 80%, and mammal’s assimilation ranges from 41 – 85% (U.S. 

Environmental Protection Agency, 1993). If it is assumed that laboratory chow is formulated 

to maximize assimilative efficiency (e.g., a value of 85%), a potential for underestimation of 

exposure may exist by assuming that consumption of food in the wild is comparable with 

consumption during laboratory testing. In the screening process, exposure may be 

underestimated because metabolic rates are not related to food consumption. 

For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal was 

assumed to occupy either the treated field or adjacent areas receiving a treatment rate on the 

field. Actual habitat requirements of any particular terrestrial species were not considered, 

and it was assumed that species occupy, exclusively and permanently, the modeled treatment 

area. Spray drift model predictions suggest that this assumption leads to an overestimation of 

exposure to species that do not occupy the treated field exclusively and permanently. 

Exposure assessment for the SJKF did not include small mammal, avian, and reptilian dietary 

items. Diet items of SJKF include small animals (e.g. blacktailed hares, desert cottontails, 

mice, kangaroo rats, squirrels), birds, lizards, insects and grass. Although grass and insects are 

included in the dietary assessment of the fox, the current assessment is not inclusive of direct 

effects to the fox through all of its diet items. Exclusion of vertebrate dietary items is a 

limitation of the T-Rex model, but is not expected to affect the risk characterization outcome 

for the SJKF. For acute dose-based RQs, all modeled scenarios (N=20) resulted in an 

exceedance of the Agency’s acute listed species LOC (RQ>0.1) for mammals and it was 

determined that there is a potential for direct adverse effects on SJKF individuals from foliar 

spray applications of endosulfan in CA. Inclusion of mammalian and avian dietary items 

would increase the potential risk to SJKF. The current assessment, while conservative, 

represents the potential risk of SJKF exposure to endosulfan as highly probable for foliar 

spray applications. 

The potential for endosulfan biomagnification in terrestrial food webs (i.e., increasing 

concentration with increasing trophic level) was not evaluated due to limitations in current 

risk assessment tools. However, a number of recent studies have been conducted for 

evaluating and predicting the bioaccumulation of organic chemicals in food webs that involve 

terrestrial (air-respiring) organisms (e.g., Armitage and Gobas, 2007; Kelly et al., 2007; Czub 

and McLachlan, 2004; Kelly and Gobas, 2003; Sharp and Mackay, 2000; McLachlan, 1996). 

218 
A key component from these studies has been the relationship between observed or predicted 

bioaccumulation of poorly metabolized chemicals in terrestrial animals and the octanol-air 

partition coefficient (KOA). For terrestrial organisms, the relationship between the KOA and 

bioaccumulation is somewhat analogous to the use of the octanol-water partition coefficient 

(KOW) for predicting the bioaccumulation of nonionic organic chemicals by aquatic (waterrespiring) organisms. Based on model simulations and supporting observations of chemical 

accumulation in Arctic terrestrial, purely aquatic and marine mammalian food webs, Kelly et 

al. (2007) indicate that slowly-metabolized organic chemicals with relatively low to moderate 

KOW values (i.e., log KOW between 2-5) and high KOA values (i.e., log KOA > 6) have the 

potential to biomagnify in terrestrial and marine mammal food webs but not purely aquatic 

food webs. In their model, the conceptual basis for biomagnification of this group of 

compounds by terrestrial organisms relates largely to the greater ability of terrestrial 

organisms to assimilate food from their diet and their slower ability to eliminate these 

chemicals through respiratory processes relative to aquatic organisms. 

Based on a log KOW of 3.7 and log KOA of 7.9 for β-endosulfan, Kelly et al. (2007) calculate

that biomagnification factors (BMFs) range from 2.5 to 28 for various herbivorous and 

carnivorous terrestrial organisms, but are all less than 1 for aquatic organisms. Importantly, 

these calculated BMF values assume that the chemical is not metabolized in tissues of biota. 

Model predictions were evaluated against measured concentrations in tissues of organisms 

occupying terrestrial, piscivorous, and marine arctic food webs (e.g., lichen, caribou, wolf 

food chain; macroalgae, zooplankton, bivalve, fish, whale/seal, polar bear food web) for a 

variety of chlorinated biphenyls, chlorinated benzenes, hexachlorocyclohexanes, cyclodienes 

(including endosulfan), and DDT-related compounds. Agreement between the mean modelpredicted and observed concentrations in biota (lipid normalized) was generally good (i.e., 

many fell within a factor of three and all fell within a factor of 10 of observed data). Limited 

data were available for endosulfan to directly verify model predictions and thus, the potential 

for biomagnifications in terrestrial food webs is largely based on indirect evidence (e.g., 

model predictions). 

Regarding the bioaccumulation assessment in aquatic ecosystems (e.g., using the KABAM 

model as described in Section 5), a significant sources of uncertainty pertains to the 

variability associated with measured values of Kow for endosulfan isomers (alpha, beta). The 

reported log Kow values for the ά isomer range from 3.55 to 4.74 (McConnell et al., 1998 and 

MRID 41421501, respectively) and those for the β isomer range from 3.62 to 4.79 from the 

same sources. For parameterizing the KABAM model, the higher value of Kow was selected 

6.1.6 Spray Drift Modeling 

Although there may be multiple endosulfan applications at a single site, it is unlikely that the 

same organism would be exposed to the maximum amount of spray drift from every 

application made. In order for an organism to receive the maximum concentration of 

endosulfan from multiple applications, each application of endosulfan would have to occur 

under identical atmospheric conditions (e.g., same wind speed and – for plants – same wind 

direction) and (if it is an animal) the animal being exposed would have to be present directly 

downwind at the same distance after each application. Although there may be sites where the 

219 
dominant wind direction is fairly consistent (at least during the relatively quiescent conditions 

that are most favorable for aerial spray applications), it is nevertheless highly unlikely that 

plants in any specific area would receive the maximum amount of spray drift repeatedly. It 

appears that in most areas (based upon available meteorological data) wind direction is 

temporally very changeable, even within the same day. Additionally, other factors, including 

variations in topography, cover, and meteorological conditions over the transport distance are 

not accounted for by the AgDRIFT/AGDISP model (i.e., it models spray drift from aerial and 

ground applications in a flat area with little to no ground cover and a steady, constant wind 

speed and direction). Therefore, in most cases, the drift estimates from AgDRIFT/AGDISP 

may overestimate exposure even from single applications, especially as the distance increases 

from the site of application, since the model does not account for potential obstructions (e.g., 

large hills, berms, buildings, trees, etc.). Furthermore, conservative assumptions are often 

made regarding the droplet size distributions being modeled (‘ASAE Very Fine to Fine’ for 

orchard uses and ‘ASAE Very Fine’ for agricultural uses), the application method (e.g., 

aerial), release heights and wind speeds. Alterations in any of these inputs would change the 

area of potential effect. 

6.2 Effects Assessment Uncertainties 

6.2.1 Age Class and Sensitivity of Effects Thresholds 

 

It is generally recognized that test organism age may have a significant impact on the 

observed sensitivity to a toxicant. The acute toxicity data for fish are collected on juvenile 

fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on 

recommended immature age classes (e.g., first instar for daphnids, second instar for 

amphipods, stoneflies, mayflies, and third instar for midges). 

Testing of juveniles may overestimate toxicity at older age classes for pesticide active 

ingredients that act directly without metabolic transformation because younger age classes 

may not have the enzymatic systems associated with detoxifying xenobiotics. In so far as the 

available toxicity data may provide ranges of sensitivity information with respect to age class, 

this assessment uses the most sensitive life-stage information as measures of effect for 

surrogate aquatic animals, and is therefore, considered as protective. 

6.2.2 Use of Surrogate Species Effects Data 

Guideline toxicity tests and open literature data on endosulfan considered suitable for 

quantitative use are not available for frogs or any other aquatic-phase amphibian; therefore, 

freshwater fish are used as surrogate species for aquatic-phase amphibians. Although no data 

are available for endosulfan , the available open literature information on endosulfan toxicity 

to aquatic-phase amphibians shows that acute and chronic ecotoxicity endpoints for aquaticphase amphibians range from approximately 2 to > 4000 times less sensitive than the most 

sensitive freshwater fish (LC50 0.01 ug a.i./L) used in this assessment. Therefore, endpoints 

based on freshwater fish ecotoxicity data are assumed to be protective of potential direct 

effects to aquatic-phase amphibians including the CRLF, and extrapolation of the risk 

conclusions from the most sensitive tested species to the aquatic-phase CRLF and CTS and 

220 
may overestimate the potential risks to those species. For reptiles (SFGS) and terrestrial 

phase amphibians (CRLF, CTS), no data on their sensitivity to endosulfan was identified. 

Therefore, the uncertainty in using avian effects data as a surrogate for reptiles and terrestrialphase amphibians could not be characterized. Efforts are made to select the organisms most 

likely to be affected by the type of compound and usage pattern; however, there is an inherent 

uncertainty in extrapolating across phyla. In addition, the Agency’s LOCs are intentionally 

set very low, and conservative estimates are made in the screening level risk assessment to 

account for these uncertainties. 

6.2.3 Sublethal Effects 

When assessing acute risk, the screening risk assessment relies on the acute mortality 

endpoint as well as a suite of sublethal responses to the pesticide, as determined by the testing 

of species response to chronic exposure conditions and subsequent chronic risk assessment. 

Consideration of additional sublethal data in the effects determination t is exercised on a caseby-case basis and only after careful consideration of the nature of the sublethal effect 

measured and the extent and quality of available data to support establishing a plausible 

relationship between the measure of effect (sublethal endpoint) and the assessment endpoints. 

However, the full suite of sublethal effects from valid open literature studies is considered for 

the purposes of defining the action area. 

6.2.4 Location of Wildlife Species 

For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal was 

assumed to occupy either the treated field or adjacent areas receiving a treatment rate on the 

field. Actual habitat requirements of any particular terrestrial species were not considered, 

and it was assumed that species occupy, exclusively and permanently, the modeled treatment 

area. Spray drift model predictions suggest that this assumption leads to an overestimation of 

exposure to species that do not occupy the treated field exclusively and permanently. 

6.2.5 Endocrine Disruption 

EPA is required under the FFDCA, as amended by FQPA, to develop a screening program to 

determine whether certain substances (including all pesticide active and other ingredients) 

“may have an effect in humans that is similar to an effect produced by a naturally occurring 

estrogen, or other such endocrine effects as the Administrator may designate.” Following the 

recommendations of its Endocrine Disruptor Screening and Testing Advisory Committee 

(EDSTAC), EPA determined that there were scientific bases for including, as part of the 

program, androgen and thyroid hormone systems, in addition to the estrogen hormone system. 

EPA also adopted EDSTAC’s recommendation that the Program include evaluations of 

potential effects in wildlife. When the appropriate screening and/or testing protocols being 

considered under the Agency’s Endocrine Disrupter Screening Program (EDSP) have been 

developed and vetted, endosulfan may be subjected to additional screening and/or testing to 

better characterize effects related to endocrine disruption. 

221 
7 Summary and Conclusions 

In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the 

information presented in this endangered species risk assessment represents the best data 

currently available to assess the potential risks of endosulfan to the CRLF, CTS, SFGS, 

SMHM, SJKF, BCB, and VELB and the designated critical habitat for CRLF, CTS, BCB and 

VELB. 

Based on the best available information, the Agency makes a Likely to Adversely Affect 

determination for the CRLF, CTS, SFGS, SMHM, SJKF, BCB, and VELB from the use of 

endosulfan. Additionally, the Agency has determined that there is the potential for effects to 

the designated critical habitat for the CRLF, CTS, BCB and VELB from the use of the 

chemical. Given the LAA determination for the CRLF, CTS, SFGS, SMHM, SJKF, BCB, 

and VELB and potential effects to designated critical habitat for CRLF, CTS, BCB and 

VELB, a description of the baseline status and cumulative effects for the CRLF is provided 

in Attachment 2 and the baseline status and cumulative effects for the CRLF, CTS, SFGS, 

BCB, VELB, SMHM, and SJKF in Attachment 4. 

A summary of the risk conclusions and effects determinations for the CRLF, CTS, SFGS, 

SMHM, SJKF, BCB, and VELB and their critical habitat, given the uncertainties discussed in 

Section 6, is presented inError! Reference source not found. and Table 7.2. 

Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects 

Determination 1

Basis for Determination 

POTENTIAL FOR DIRECT EFFECTS

California redlegged frog 

(Rana aurora 

draytonii) 

(CRLF) 

LAA1 Aquatic-phase CRLF (Eggs, Larvae, and Adults): 

Freshwater Fish RQ

- Acute RQs for freshwater fish (used as a surrogate for aquatic-phase CRLFs) exceed 

the listed species acute risk LOC for all 20 modeled crop scenarios. 

- Chronic RQs for freshwater fish (used as a surrogate for aquatic-phase CRLFs) 

exceed the chronic risk LOC for all 20 modeled crop scenarios. 

Likelihood of Individual Mortality

-The chance of individual effects (i.e., mortality) for freshwater fish (surrogate for 

aquatic-phase CRLFs) is as high as ~1 in 1. 

Ecological Incident Reports 

- 67 of the 83 endosulfan-associated ecological incidents reported to the Agency 

involve fish and 53 of these are classified as ‘probable’ or ‘highly probable;’ 18 of the 

20 incident reports associated with ‘registered uses’ involved mortality to fish. 

Species Sensitivity Differences

- Model-based EECs exceed the LOC for approximately 80 to 97% of the tested 

freshwater fish species 

Surface Water Monitoring Data

- The highest reported values of total endosulfan in California equal or exceed the 

acute LOC for freshwater fish. 

222 
Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

Bioaccumulation in Aquatic Prey

- Based on consumption of aquatic prey that is predicted to bioaccumulate 

endosulfan, acute dose-based RQs exceed the acute listed LOC in all 20 crop 

exposure scenarios modeled for small, medium and large CRLF. 

Temporal and Spatial Overlap

- Based on current endosulfan use data and potential endosulfan use on agricultural 

crops/orchards/vineyard areas, there appears to be a potential for both temporal and 

spatial overlap between aquatic-phase CRLF distribution and endosulfan agricultural 

use (Appendix E). 

Terrestrial-phase CRLF (Juveniles and Adults): 

Direct Deposition on Forage Items: Avian RQ

- Acute-dose based RQs for 20g birds (surrogate for terrestrial-phase amphibians) 

consuming large and small insects contaminated with endosulfan from direct 

deposition exceed LOC for all 20 crop scenarios modeled. 

- Chronic RQs for the small and large insect categories exceed the Agency LOC of 1 

for 20 and 3 crop exposure scenarios, respectively. 

Direct Deposition on Forage Items: Refined Herpetofauna Modeling

- Using refined modeling, acute listed LOC was exceeded in 39% or more of the 

acute dose-based; and acute dietary-based species/diet combinations modeled. The 

chronic LOC was exceeded in 46% of the chronic dietary-based species/diet 

combinations modeled. 

Likelihood of Individual Mortality

The chance of individual effects (i.e., mortality) for birds (surrogate for terrestrial -

phase CRLFs) and herpetofauna based on direct deposition onto food items is as high 

as ~1 in 1. 

Temporal and Spatial Overlap

- Based on current endosulfan use data and potential endosulfan use on agricultural 

crops/orchards/vineyard areas, there appears to be a potential for both temporal and 

spatial overlap between terrestrial -phase CRLF distribution and endosulfan 

agricultural use (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS

CRLF Aquatic Prey Items, Aquatic Habitat, Cover and/or Primary Productivity 

Freshwater fish and aquatic-phase amphibians: 

- Acute and chronic RQs exceed the listed species acute and chronic LOCs; high 

likelihood of individual mortality, EECs exceed the LOC for 80% or more of the 

tested fish species and a large number of aquatic incidents involving fish, as 

described above for CRLF (see “Potential Direct Effects; Aquatic Phase CRLF 

[eggs, larvae, adults])” 

.Freshwater Invertebrates: 

-Acute and chronic RQs for freshwater invertebrates exceed the listed species acute 

and chronic risk LOC for all 20 crop exposure scenarios modeled. 

-The chance of individual effects (i.e., mortality) for freshwater invertebrates is as 

high as ~1 in 1. 

- Model-based EECs exceed the LOC for approximately 45% to 60% of the tested 

freshwater invertebrate species 

- The highest reported values of total endosulfan in California equal or exceed the 

listed acute LOC and chronic LOC for freshwater invertebrates. 

223 
Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

CRLF Terrestrial Prey Items, Riparian Habitat 

Terrestrial-phase Amphibians: 

- Exceedence of acute and chronic LOCs for terrestrial-phase amphibians as 

described above for CRLF (see “Potential Direct Effects; Terrestrial Phase CRLF 

[juveniles and adults])” 

Terrestrial Invertebrates: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled. 

- EECs exceed for large and small insects exceed the LD50 values for 80% and 99% 

of the tested terrestrial invertebrate species, respectively. 

-The chance of individual effects (i.e., mortality) for terrestrial invertebrates resulting 

from direct deposition in application sites is as high as ~1 in 1. 

- When indirect effects are considered via exposure of terrestrial insects to spray drift, 

spatial overlap between potential endosulfan use on agricultural crops, orchards, and 

vineyard areas can extend up to 2 miles from the source (Appendix E). 

Small Mammals: Direct Deposition on Forage Items 

- Acute and chronic dose-based RQs for small mammals foraging on food items 

receiving direct deposition of applied endosulfan exceed the acute listed LOC for 

mammals in all 20 crop scenarios modeled 

- Chronic diet-based RQs for small mammals foraging on food items receiving direct 

deposition of applied endosulfan exceed the chronic LOC for mammals in 13 of the 

20 crop scenarios modeled 

- The chance of individual effects (i.e., mortality) for small mammals is as high as ~1 

in 1. 

Small Mammals: Bioaccumulation in Terrestrial Prey 

 - RQs exceed of acute listed and chronic LOCs in all 20 exposure scenarios modeled 

based on small mammals eating earthworms that are predicted to bioaccumulate 

endosulfan from soil. 

California POTENTIAL FOR DIRECT EFFECTS 

tiger 

salamander 

(Ambystoma 

californiense

LAA1

Direct Deposition on Forage Items: Avian RQ (Terrestrial-Phase CTS)

- Acute-dose based RQs for 20g birds (surrogate for terrestrial-phase amphibians) 

consuming large and small insects contaminated with endosulfan from direct 

deposition exceed LOC for all 20 crop scenarios modeled. 

- Chronic RQs for the small and large insect categories exceed the Agency LOC of 1 

for 20 and 3 crop exposure scenarios, respectively. 

Direct Deposition on Forage Items: Refined Herpetofauna Modeling

- Using refined modeling, acute listed LOC was exceeded in 39% or more of the 

acute dose-based; acute dietary-based species/diet combinations modeled. The 

chronic LOC was exceeded in 46% of the chronic dietary-based species/diet 

combinations modeled. 

Likelihood of Individual Mortality

The chance of individual effects (i.e., mortality) for birds (surrogate for reptiles and 

terrestrial phase amphibians) and herpetofauna based on direct deposition onto food 

items is as high as ~1 in 1. 

Bioaccumulation in Aquatic Prey

224 
Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

- Based on consumption of aquatic prey that is predicted to bioaccumulate 

endosulfan, acute dose-based RQs exceed the acute listed LOC in all 20 crop 

exposure scenarios modeled for small CRLF (used as surrogate for CTS exposure 

potential). 

Bioaccumulation in Terrestrial Prey

- Based on consumption of terrestrial prey (earthworm) that is predicted to 

bioaccumulate endosulfan, acute dose-based RQs and chronic diet-based RQs for 

small birds (surrogate for terrestrial-phase amphibians) exceed the acute listed and 

chronic LOCs in all 20 crop exposure scenarios modeled. 

Freshwater Fish (Aquatic-phase CTS): 

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, EECs exceed the LOC for 80% or more of the 

tested fish species and a large number of aquatic incidents involve fish, as described 

above for CRLF (see “Potential Direct Effects; Aquatic Phase CRLF [eggs, larvae, 

adults])” 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of CTS was 

identified. 

- A large amount of spatial overlap between CTS occurrence and current (and 

potential future use) of endosulfan was identified (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS 

Freshwater Fish: 

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, EECs exceed the LOC for 80% or more of the 

tested fish species and a large number of aquatic incidents involve fish, as described 

above for CRLF (see “Potential Direct Effects; Aquatic Phase CRLF [eggs, larvae, 

adults])” 

Freshwater Invertebrates:

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, and exceedence of LOCs for 45-60% of 

freshwater invertebrate species tested, as described above for CRLF (see “Potential 

Indirect Effects; CRLF Aquatic Prey Items, Aquatic Habitat, Cover and/or Primary 

Productivity)” 

Terrestrial Invertebrates: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled, there is a high likelihood of individual 

mortality, and EECs exceed LD50 values for vast majority of tested species, as 

described above for CRLF (see “Potential for Indirect Effects: CRLF Terrestrial Prey 

Items, Riparian Habitat)

San Francisco POTENTIAL FOR DIRECT EFFECTS

garter snake 

(Thamnophis 

sirtalis 

tetrataenia) 

LAA1

Direct Deposition on Forage Items: Avian RQ

- Acute-dose based RQs for 20g birds (surrogate for terrestrial-phase amphibians) 

consuming large and small insects contaminated with endosulfan from direct 

deposition exceed LOC for all 20 crop scenarios modeled. 

- Chronic RQs for the small and large insect categories exceed the Agency LOC of 1 

for 20 and 3 crop exposure scenarios, respectively. 

225 
Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

Direct Deposition on Forage Items: Refined Herpetofauna Modeling

- Using refined modeling, acute listed LOC was exceeded in 39% or more of the 

acute dose-based; and acute dietary-based species/diet combinations modeled. The 

chronic LOC was exceeded in 46% of the chronic dietary-based species/diet 

combinations modeled. 

Likelihood of Individual Mortality

The chance of individual effects (i.e., mortality) for birds (surrogate for reptiles and 

terrestrial phase amphibians) and herpetofauna based on direct deposition onto food 

items is as high as ~1 in 1. 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of SFGS was 

identified. 

- No spatial overlap identified at the County level based on current endosulfan use 

reported for California. If cultivated crop/orchard/vineyard uses are considered areas 

of potential endosulfan use in the future, then a substantial amount of spatial overlap 

can be observed relative to the total area of SFGS occurrence sections (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS

Prey Items, Habitat, Cover And/Or Primary Productivity 

Freshwater Fish: 

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, EECs exceed the LOC for 80% or more of the 

tested fish species and a large number of aquatic incidents involve fish, as described 

above for CRLF (see “Potential Direct Effects; Aquatic Phase CRLF [eggs, larvae, 

adults])” 

Freshwater Invertebrates:

- Acute and chronic RQs exceed the listed species acute and chronic LOCs, there is a 

high likelihood of individual mortality, and exceedence of LOCs for 45-60% of 

freshwater invertebrate species tested, as described above for CRLF (see “Potential 

Indirect Effects; CRLF Aquatic Prey Items, Aquatic Habitat, Cover and/or Primary 

Productivity)” 

Terrestrial Invertebrates: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled, there is a high likelihood of individual 

mortality, and EECs exceed LD50 values for vast majority of tested species, as 

described above for CRLF (see “Potential for Indirect Effects: CRLF Terrestrial Prey 

Items, Riparian Habitat)

Small Terrestrial Vertebrates

- Acute and chronic LOC exceedence for birds (surrogate for reptiles and terrestrialphase amphibians) and herpetofauna for direct deposition on food items, a high 

likelihood of individual mortality, and RQ exceedence of acute listed LOC and 

chronic LOC based on consumption of terrestrial and aquatic prey by birds and 

mammals as described above for the CRLF (see “Potential Direct Effects; 

Terrestrial Phase CRLF [juveniles and adults] and “Potential for Indirect Effects: 

CRLF Terrestrial Prey Items, Riparian Habitat)” 

Salt marsh POTENTIAL FOR DIRECT EFFECTS

harvest mouse 

LAA1

Direct Deposition on Forage Items: Mammalian RQ 

226 
Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

- Acute and chronic dose-based RQs for small mammals foraging on food items 

receiving direct deposition of applied endosulfan exceed the acute listed LOC for 

mammals in all 20 crop scenarios modeled 

- Chronic diet-based RQs for small mammals foraging on food items receiving direct 

deposition of applied endosulfan exceed the chronic LOC for mammals in 13 of the 

20 crop scenarios modeled 

Likelihood of Individual Mortality

- The chance of individual effects (i.e., mortality) for small mammals resulting from 

direct deposition onto forage items is as high as ~1 in 1. 

Bioaccumulation in Terrestrial Prey 

 - RQs exceed of acute listed and chronic LOCs in all 20 exposure scenarios modeled 

based on small mammals eating earthworms that are predicted to bioaccumulate 

endosulfan from soil. 

Temporal and Spatial 

- Temporal overlap between endosulfan application and all life stages of the SMHM 

was identified. 

- A small amount of spatial overlap identified at the County level based on current 

endosulfan use reported for California and based on areas of potential endosulfan use 

in the future (i.e., cultivated crop, orchard and vineyard use areas). 

- The potential for endosulfan to be transported long distances in the atmosphere may 

increase SMHM exposure, particularly in areas of potential endosulfan use west of 

SMHM occurrence sections in Solano County (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS

(Reithrodonto

mys 

raviventris) 

(SMHM) 

Prey items, habitat, cover and/or primary productivity 

Terrestrial invertebrates: 

-- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled, there is a high likelihood of individual 

mortality, and EECs exceed LD50 values for vast majority of tested species, as 

described above for CRLF (see “Potential for Indirect Effects: CRLF Terrestrial Prey 

Items, Riparian Habitat)

Small Birds and Mammals (rearing sites): 

- Acute and chronic RQ for birds and mammals (whose rearing sites are potentially 

used by SMHM) exceed listed acute and chronic LOCs as a result of direct deposition 

onto forage items and bioaccumulation in terrestrial prey as described above for the 

CRLF (Potential for Direct Effects: Terrestrial-phase CRLF [Juveniles and Adults])

and for the SMHM (see “Potential for Direct Effects”) 

San Joaquin POTENTIAL FOR DIRECT EFFECTS 

kit fox 

(Vulpes 

macrotis 

mutica) 

LAA1

Direct Deposition on Forage Items: Mammalian RQ 

- Acute and chronic dose-based RQs exceed the Agency acute listed and chronic LOC 

in all modeled scenarios (N=20) for large mammals. Chronic dietary-based RQs 

exceed the chronic LOC in all 20 modeled scenarios for large mammals that feed on 

short grass, tall grass, and broadleaf plants/small insects (chronic dietary-based RQs 

for 13/20 scenarios exceed the LOC for large mammals consuming 

fruits/pods/seeds/large insects). 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of SJKF was 

227 
Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

identified. 

- A moderate amount of spatial overlap between SJKF occurrence and current (and 

potential future use) of endosulfan was identified (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS 

Terrestrial Invertebrates: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled, there is a high likelihood of individual 

mortality, and EECs exceed LD50 values for vast majority of tested species, as 

described above for CRLF (see “Potential for Indirect Effects: CRLF Terrestrial Prey 

Items, Riparian Habitat)

Small Birds and Mammals: 

- Acute and chronic RQ for birds and mammals serving as prey to the SJKF exceed 

listed acute and chronic LOCs as a result of direct deposition onto forage items and 

bioaccumulation in terrestrial prey as described above for the CRLF (Potential for 

Direct Effects: Terrestrial-phase CRLF [Juveniles and Adults]) and for the SMHM 

(see “Potential for Direct Effects”) 

POTENTIAL FOR DIRECT EFFECTS

Terrestrial Invertebrate RQs: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled. 

- EECs exceed for large and small insects exceed the LD50 values for 80% and 99% 

of the tested terrestrial invertebrate species, respectively. 

Likelihood of Individual Mortality

-The chance of individual effects (i.e., mortality) for terrestrial invertebrates resulting 

from direct deposition in application sites is as high as ~1 in 1. 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of BCB was 

identified. 

- No spatial overlap identified at the County level based on current endosulfan use 

reported for California. If cultivated crop/orchard/vineyard uses are considered areas 

of potential endosulfan use in the future, then a substantial amount of spatial overlap 

can be observed relative to the total area of BCB occurrence sections. 

- When exposure of terrestrial insects via spray drift is considered, spatial overlap 

between potential endosulfan use on agricultural crops, orchards, and vineyard areas 

can extend up to 2 miles from the source. 

- The potential for endosulfan to be transported long distances in the atmosphere may 

increase BCB exposure, particularly in areas of potential endosulfan use west of BCB 

occurrence sections in Santa Clara County (Appendix E). 

POTENTIAL FOR INDIRECT EFFECTS

Bay 

checkerspot 

butterfly 

(Euphydryas 

editha 

bayensis) 

(BCB) 

LAA1

-Although effects to terrestrial plants cannot be quantified due to the lack of data, 

aquatic non-vascular plants are not particularly sensitive to endosulfan 

- Endosulfan has a neural toxic mode of action. 

- No studies demonstrating significant adverse effects of endosulfan to any vascular 

aquatic or terrestrial plant have been identified in the open literature. The one toxicity 

study found to be acceptable for quantitative use suggests that aquatic nonvascular 

228 
Table 7.1 Effects Determination Summary for Effects of Endosulfan on the CRLF, CTS, SFGS, SMHM, SJKF, 

BCB, AND VELB 

Species Effects Basis for Determination 

Determination 1

plants are insensitive relative to aquatic animals. 

- No ecological incidents have been reported to the Agency that involve any plants 

and this was classified with a certainty index of “probable” or higher linking 

endosulfan as a cause, despite that it is regularly directly applied on or near a very 

wide variety of agricultural plants.

POTENTIAL FOR DIRECT EFFECTS

Terrestrial Invertebrate RQs: 

- Acute RQs exceed the Agency’s interim LOC for listed terrestrial invertebrates in 

all 20 crop exposure scenarios modeled. 

- EECs exceed for large and small insects exceed the LD50 values for 80% and 99% 

of the tested terrestrial invertebrate species, respectively. 

Likelihood of Individual Mortality

-The chance of individual effects (i.e., mortality) for terrestrial invertebrates resulting 

from direct deposition in application sites is as high as ~1 in 1. 

Temporal and Spatial Overlap

- Temporal overlap between endosulfan application and all life stages of VELB was 

identified. 

- A small amount of spatial overlap identified at the County level based on current 

endosulfan use reported for California. If cultivated crop/orchard/vineyard uses are 

considered areas of potential endosulfan use in the future, then a moderate amount of 

spatial overlap can be observed relative to the total area of VELB occurrence sections 

(Appendix E). 

- When exposure of terrestrial insects via spray drift is considered, spatial overlap 

between potential endosulfan use on agricultural crops, orchards, and vineyard areas 

can extend up to 2 miles from the source 

- The potential for endosulfan to be transported long distances in the atmosphere may 

increase VELB exposure, particularly in areas of potential endosulfan use west of 

VELB occurrence sections. 

POTENTIAL FOR INDIRECT EFFECTS

Valley 

elderberry 

longhorn 

beetle 

(Desmocerus 

californicus 

dimorphus) 

LAA1

-Although effects to terrestrial plants cannot be quantified due to the lack of data, 

aquatic non-vascular plants are not particularly sensitive to endosulfan 

- Endosulfan has a neural toxic mode of action. 

- No studies demonstrating significant adverse effects of endosulfan to any vascular 

aquatic or terrestrial plant have been identified in the open literature. The one toxicity 

study found to be acceptable for quantitative use suggests that aquatic nonvascular 

plants are insensitive relative to aquatic animals. 

- No ecological incidents have been reported to the Agency that involve any plants 

and this was classified with a certainty index of “probable” or higher linking 

endosulfan as a cause, despite that it is regularly directly applied on or near a very 

wide variety of agricultural plants.

Table 7.2 Effects Determination Summary for the Critical Habitat Impact Analysis 

Designated 

Critical Habitat 

for: 

Effects 

Determination 1

Basis for Determination 

229 
CRLF May Affect 

-There is a potential for direct effects to the aquatic-phase CRLF and 

indirect effects via reduction of aquatic-phase prey items (aquatic 

invertebrates, fish, and aquatic-phase amphibians) as described in Table 7.1 

above. 

- There is a potential for direct effects to the terrestrial-phase CRLF and 

indirect effects via reduction of terrestrial-phase prey items (mammals, 

amphibians, and terrestrial invertebrates) as described in Table 7.1 above. 

CTS May Affect 

There is a potential for direct effects to the CTF and indirect effects via 

reduction of aquatic-phase prey items (aquatic invertebrates and fish) as 

described in Table 7.1 above. 

- There is a potential for direct effects to the CTF and indirect effects via 

reduction of terrestrial-phase prey items (terrestrial invertebrates) as 

described in Table 7.1 above. 

BCB NE1

-Although effects to terrestrial plants cannot be quantified due to the lack of 

data, aquatic non-vascular plants are not particularly sensitive to endosulfan 

- Endosulfan has a neural toxic mode of action. 

-No studies demonstrating significant adverse effects of endosulfan to any 

vascular aquatic or terrestrial plant have been identified in the open 

literature. The one toxicity study found to be acceptable for quantitative use 

suggests that aquatic nonvascular plants are insensitive relative to aquatic 

animals. 

- No ecological incidents have been reported to the Agency that involve any 

plants and this was classified with a certainty index of “probable” or higher 

linking endosulfan as a cause, despite that it is regularly directly applied on 

or near a very wide variety of agricultural plants. 

VELB NE1

-Although effects to terrestrial plants cannot be quantified due to the lack of 

data, aquatic non-vascular plants are not particularly sensitive to endosulfan 

- Endosulfan has a neural toxic mode of action. 

-No studies demonstrating significant adverse effects of endosulfan to any 

vascular aquatic or terrestrial plant have been identified in the open 

literature. The one toxicity study found to be acceptable for quantitative use 

suggests that aquatic nonvascular plants are insensitive relative to aquatic 

animals. 

- No ecological incidents have been reported to the Agency that involve any 

plants and this was classified with a certainty index of “probable” or higher 

linking endosulfan as a cause, despite that it is regularly directly applied on 

or near a very wide variety of agricultural plants. 1

 No effect (NE) 

Based on the conclusions of this assessment, a formal consultation with the U. S. Fish and 

Wildlife Service under Section 7 of the Endangered Species Act should be initiated. 

When evaluating the significance of this risk assessment’s direct/indirect and adverse habitat 

modification effects determinations, it is important to note that pesticide exposures and 

predicted risks to the listed species and its resources (i.e., food and habitat) are not expected to 

be uniform across the action area. In fact, given the assumptions of drift and downstream 

transport (i.e., attenuation with distance), pesticide exposure and associated risks to the 

species and its resources are expected to decrease with increasing distance away from the 

treated field or site of application. Evaluation of the implication of this non-uniform 

distribution of risk to the species would require information and assessment techniques that 

are not currently available. 

When evaluating the significance of this risk assessment’s direct/indirect and adverse habitat 

modification effects determinations, it is important to note that pesticide exposures and 

230 
predicted risks to the species and its resources (i.e., food and habitat) are not expected to be 

uniform across the action area. In fact, given the assumptions of drift and downstream 

transport (i.e., attenuation with distance), pesticide exposure and associated risks to the 

species and its resources are expected to decrease with increasing distance away from the 

treated field or site of application. Evaluation of the implication of this non-uniform 

distribution of risk to the species would require information and assessment techniques that 

are not currently available. Examples of such information and methodology required for this 

type of analysis would include the following: 

• Enhanced information on the density and distribution of CRLF, CTS, SFGS, 

BCB, VELB, SMHM, and SJKF life stages within the action area and/or 

applicable designated critical habitat. This information would allow for 

quantitative extrapolation of the present risk assessment’s predictions of 

individual effects to the proportion of the population extant within 

geographical areas where those effects are predicted. Furthermore, such 

population information would allow for a more comprehensive evaluation of 

the significance of potential resource impairment to individuals of the assessed 

species. 

• Quantitative information on prey base requirements for the assessed species. 

While existing information provides a preliminary picture of the types of food 

sources utilized by the assessed species, it does not establish minimal 

requirements to sustain healthy individuals at varying life stages. Such 

information could be used to establish biologically relevant thresholds of 

effects on the prey base, and ultimately establish geographical limits to those 

effects. This information could be used together with the density data 

discussed above to characterize the likelihood of adverse effects to individuals. 

• Information on population responses of prey base organisms to the pesticide. 

Currently, methodologies are limited to predicting exposures and likely levels 

of direct mortality, growth or reproductive impairment immediately following 

exposure to the pesticide. The degree to which repeated exposure events and 

the inherent demographic characteristics of the prey population play into the 

extent to which prey resources may recover is not predictable. An enhanced 

understanding of long-term prey responses to pesticide exposure would allow 

for a more refined determination of the magnitude and duration of resource 

impairment, and together with the information described above, a more 

complete prediction of effects to individual species and potential modification 

to critical habitat. 

231 
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