Potential Risks of Thiobencarb Use to Federally
Threatened California Red-legged Frog
(Rana aurora draytonii) and Delta Smelt (Hypomesus
transpacificus)
Pesticide Effects Determinations
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
October 19,2009
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Primary Authors:
Katrina White, PhD, Biologist (Effects Scientist)
William P. Eckel, PhD, Senior Physical Scientist
William Shaughnessy, PhD, Environmental Scientist
Benjamin Carr, Biologist
Secondary Review:
Jean Holmes, DVM, MPH, Risk Assessment Process Leader
Branch Chief, Environmental Risk Assessment Branch 2:
Tom Bailey, PhD, Branch Chief
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Table of Contents
1. EXECUTIVE SUMMARY 10
1.1. PURPOSE OF ASSESSMENT 10
1.2. SCOPE OF ASSESSMENT 10
1.3. ASSESSMENT PROCEDURES 11
1.3.1. Toxicity Assessment 11
1.3.2. Exposure Assessment 11
1.3.3. Toxicity Assessment 12
1.3.4. Measures of Risk 12
1.4. THIOBENCARB USES ASSESSED 13
1.5. SUMMARY OF CONCLUSIONS 13
2. PROBLEM FORMULATION 16
2.1. PURPOSE 17
2.2. SCOPE 19
2.2.1. Evaluation of Degradates 19
2.2.2. Evaluation of Mixtures 21
2.3. PREVIOUS ASSESSMENTS 22
2.3.1. Reregistration Eligibility Decision (RED) 22
2.3.2. Ecological Risk Assessment for Proposed Use on Wild Rice 23
2.3.3. Effects Determination for Thiobencarb for Pacific Anadromous Salmonids 23
2.3.4. Registrant Submitted Data Not Considered In Previous Ecological Risk
Assessments 23
2.4. STRESSOR SOURCE AND DISTRIBUTION 23
2.4.1. Environmental Fate Properties 23
2.4.2. Environmental Transport Mechanisms 28
2.4.3. Mechanism of Action 29
2.4.4. Use Characterization 29
2.5. ASSESSED SPECIES 36
2.6. DESIGNATED CRITICAL HABITAT 38
2.7. ACTION AREA 40
2.8. ASSESSMENT ENDPOINTS AND MEASURES OF ECOLOGICAL EFFECT 44
2.8.1. Assessment Endpoints 44
2.8.2. Assessment Endpoints for Designated Critical Habitat 47
2.9. CONCEPTUAL MODEL 47
2.9.1. Risk Hypotheses 47
2.9.2. Diagram 48
2.10. ANALYSIS PLAN 49
2.10.1. Measures of Exposure 50
2.10.2. Measures of Effect 52
3. EXPOSURE ASSESSMENT 54
3.1. AQUATIC EXPOSURE ASSESSMENT 54
3.1.1. Existing Monitoring Data 58
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3.2. TERRESTRIAL ANIMAL EXPOSURE ASSESSMENT 62
3.3. TERRESTRIAL PLANT EXPOSURE ASSESSMENT 64
4. EFFECTS ASSESSMENT 65
4.1. ECOTOXICITY STUDY DATA SOURCES 66
4.2. TOXICITY CATEGORIES 67
4.3. TOXICITY OF THIOBENCARB TO AQUATIC ORGANISMS 67
4.3.1. Toxicity to Freshwater Fish and Aquatic-Phase Amphibians 69
4.3.2. Toxicity to Freshwater Invertebrates 71
4.3.3. Toxicity to Estuarine/Marine Fish 72
4.3.4. Toxicity to Estuarine/Marine Invertebrates 74
4.3.5. Toxicity to Aquatic Plants 74
4.3.6. Aquatic Field/Mesocosm Studies 75
4.4. TOXICITY OF THIOBENCARB TO TERRESTRIAL ORGANISMS 78
4.4.1. Toxicity to Birds and Terrestrial-Phase Amphibians 79
4.4.2. Toxicity to Mammals 80
4.4.3. Toxicity to Terrestrial Invertebrates 81
4.4.4. Toxicity to Terrestrial Plants 82
4.5. TOXICITY OF DEGRADATES 84
4.6. TOXICITY OF CHEMICAL MIXTURES 85
4.7. INCIDENT DATABASE REVIEW 85
4.7.1. Other Aquatic Incidents 86
5. RISK CHARACTERIZATION 86
5.1. RISK ESTIMATION 86
5.1.1. Calculation of RQs used to Assess Direct Effects to CRLF and DS 87
5.1.2. Calculation of RQs used to Assess Indirect Effects to CRLF andDS 89
5.1.3. Primary Constituent Elements of Designated Critical Habitat 94
5.2. RISK DESCRIPTION 94
5.2.1. Direct Effects 97
5.2.2. Indirect Effects, DS and Aquatic-Phase CRLF 101
5.2.3. Spatial Extent of Potential Effects 108
5.3. EFFECTS TO DESIGNATED CRITICAL HABITAT 115
5.3.1. CRLF Habitat Modification Analysis 115
5.3.2. Delta Smelt Habitat Modification Analysis 116
5.4. EFFECTS DETERMINATIONS 117
5.4.1. CRLF 117
5.4.2. Delta Smelt 118
5.4.3. Addressing the Risk Hypotheses 118
6. UNCERTAINTIES 119
6.1. EXPOSURE ASSESSMENT UNCERTAINTIES 119
6.1.1. Maximum Use Scenario 119
6.1.2. Aquatic Exposure Modeling of Thiobencarb 119
6.1.3. Uncertainties regarding dilution and chemical transformations in estuaries 120
6.1.4. Impact of Vegetative Setbacks on Runoff 121
6.1.5. Exposure Resulting from Atmospheric Transport 121
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6.1.6. Potential Ground Water Contributions to Surface Water Chemical Concentrations
122
6.1.7. Usage Uncertainties 122
6.1.8. Terrestrial Exposure Modeling of Thiobencarb 123
6.1.9. Spray Drift Modeling 124
6.2. EFFECTS ASSESSMENT UNCERTAINTIES 124
6.2.1. Data Gaps and Uncertainties 124
6.2.2. Age Class and Sensitivity of Effects Thresholds 125
6.2.3. Impact of Multiple Stressors on the Effects Determination 126
6.2.4. Use of Surrogate Species Effects Data 126
6.2.5. Sublethal Effects 126
6.2.6. Exposure to Pesticide Mixtures 126
6.2.7. Uncertainty in the Potential Effect to Riparian Vegetation vs. Water Quality
Impacts 127
6.2.8. Location of Wildlife Species 127
7. RISK CONCLUSIONS 127
8. REFERENCES 131
9. MRIDLIST 136
Appendices
Appendix A. Degradates for Consideration in the Human Health Drinking Water Risk
Assessment - EFED Report to the ROCKS Committee
Appendix B. Predicted Toxicity of the Degradates to Aquatic Organisms Using ECOSAR
Version 1
Appendix C. Multi-ai Product Analysis
Appendix D. Verification Memo for Thiobencarb for Red Legged Frog Assessment
Appendix E. Total Pounds Thiobencarb Applied to Rice in California 1994-2006
Appendix F. Risk Quotient (RQ) Method and Levels of Concern (LOCs)
Appendix G. Example Output from T-REX and T-HERPS
Appendix H. Example Output from TerrPlant Version 1.2.2
Appendix I. Summary of Ecotoxicity Data
Appendix J. Bibliography of ECOTOX Open Literature
Appendix K. Accepted ECOTOX Data Table (sorted by effect) and Bibliography
Appendix L. The HED Chapter of the Reregi strati on Eligibility Decision Document (RED) for
Thiobencarb (Case Number 2665; Chemical number 108401).
Appendix M. Predicted Atmospheric Half-Life Using EPISUITE Version 4.0
Appendix N. Spatial Analysis
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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
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List of Tables
Table 1-1. Effects Determination Summary for Potential Effects to the CRLF and DS from the
Use of Thiobencarb on Rice in California 14
Table 1-2. Effects Determination Summary for Thiobencarb Use on Rice and CRLF and DS
Critical Habitat Impact Analysis 15
Table 2-1. Degradate Occurrence Summary for Thiobencarb 20
Table 2-2. Maximum Amounts of Thiobencarb and Metabolites Found in Flood Water in Field
Dissipation Studies 26
Table 2-3. The Chemical Structure of Thiobencarb and its Metabolites 27
Table 2-4. Summary of Thiobencarb Products Registered under Section 3 and Section 24c
Special Local Needs for use In California** 30
Table 2-5. Rice Uses of Thiobencarb Assessed in California 31
Table 2-6. Summary of California Department of Pesticide Registration (CDPR) Pesticide Use
Reporting (PUR) Data from 1999 to 2006 for Currently Registered Thiobencarb Use
on Rice1 34
Table 2-7. Summary of Current Distribution, Habitat Requirements, and Life History
Information for the Assessed Listed Species1 36
Table 2-8. Designated Critical Habitat PCEs for the CRLF and DS.1 39
Table 2-9. Taxa Used in the Analyses of Direct and Indirect Effects for the Assessed Listed
Species 45
Table 2-10. Taxa and Assessment Endpoints Used to Evaluate the Potential for Use of
Thiobencarb to Result in Direct and Indirect Effects to the Assessed Listed Species. 45
Table 3-1. Chemical Specific Input Parameters for Thiobencarb 54
Table 3-2. Results of Tier 1 Rice Model 55
Table 3-3. Aquatic Exposure using 4 Ib/acre (4.48 kg/hectare) 56
Table 3-4. Summary of Air Monitoring Studies for Thiobencarb 62
Table 3-5. Summary of Monitoring Studies for Thiobencarb Measuring Residues in
Precipitation 62
Table 3-6 Summary of Dose and Dietary-based EECs Used for Estimating Dietary Risks to
Terrestrial Organisms using T-REX ver. 1.4.1. for Thiobencarb Use on Rice (Liquid
Formulation, ground or aerial application) 64
Table 3-7. Summary EECs Used for Estimating Risk to Terrestrial Invertebrates and Indirect
Effects to the CRLF using T-REX ver. 1.4.1. for Thiobencarb Use on Rice ( Liquid
Formulations) 64
Table 3-8. TerrPlant Inputs and Resulting EECs for Plants Inhabiting Dry and Semi-aquatic
Areas Exposed to Thiobencarb via Runoff and Drift 65
Table 4-1. Categories of Acute Toxicity for Terrestrial and Aquatic Animals 67
Table 4-2. Aquatic Toxicity Profile for Thiobencarb 68
Table 4-3. Summary of submitted aquatic field studies on the use of thiobencarb on rice 75
Table 4-4. Terrestrial Toxicity Profile for Thiobencarb 78
Table 4-5. Summary of submitted terrestrial plant Tier II seedling emergence toxicity results for
thiobencarb 83
Table 4-6. Summary of submitted Tier II seedling vegetative vigor toxicity testing for
thiobencarb 83
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Table 4-7. Summary of Incident Reports Involving Effects on Rice in California 85
Table 5-1. Acute and Chronic RQs for Direct Effects to the Aquatic-Phase CRLF and DS 87
Table 5-2. Acute and Chronic RQs for Aquatic Invertebrates Used to Evaluate Potential Indirect
Effects to the CRLF and the DS Resulting from Potential Impacts to Food Supply... 90
Table 5-3. Summary of EEC/Highest Dose Tested Ratio for Terrestrial Invertebrates on the Site
of Application - Used to Evaluate Potential Indirect Effects to the CRLF Resulting
from Potential Impacts to the Food Supply 91
Table 5-4. Summary of Acute and Chronic RQs for 15 g Mammals Used to Evaluate Potential
Indirect Effects to the CRLF Resulting from Potential Impacts to the Food Supply.1 92
Table 5-5. Summary of RQs for Vascular and Non-Vascular Aquatic Plants 93
Table 5-6. Non-Listed Terrestrial Plant RQs for Thiobencarb Use on Rice (one application at 4
Ibs a.i./acre).1 94
Table 5-7. Summary of Risk Estimation for Thiobencarb. The Risk Estimation Is Further
Refined in the Risk Description 95
Table 5-8. Probit Dose-Response Analysis for Direct Effect to the CRLF and DS 97
Table 5-9. Acute and Chronic RQs for Direct Effects to the Aquatic-Phase CRLF and DS based
on Aquatic Dissipation Study Results and Monitoring Data 98
Table 5-10. Upper Bound Kenaga, Acute Terrestrial Herpetofauna Dose-Based Risk Quotients
for Thiobencarb (4 Ib a.i./acre, 1 Application) 100
Table 5-11. Upper Bound Kenaga, Sub-Acute and Chronic Terrestrial Herpetofauna Dietary-
Based Risk Quotients for Thiobencarb (1 Application at 4 Ibs a.i./acre) 101
Table 5-12. Probit Dose-Response Analysis for Aquatic Invertebrates 102
Table 5-13. Acute and Chronic RQs for Aquatic Invertebrates Used to Evaluate Potential
Indirect Effects to the CRLF and the DS Resulting from Potential Impacts to Food
Supply. Exposure estimated based on aquatic dissipation studies and monitoring data.
103
Table 5-14. Summary of RQs for Vascular and Non-Vascular Aquatic Plants Using Exposure
from Aquatic Dissipation Studies and Monitoring Data 105
Table 5-15. Probit Dose-Response Analysis for Mammals and Potential Indirect Effects to
CRLF 106
Table 5-16. Distance from Thiobencarb Use Site Needed to Reduce Spray Drift to Levels that
Do Not Exceed Terrestrial Acute and Chronic LOCs for Direct and Indirect Effects
(Point Deposition Estimate) 110
Table 5-17. Distance from Thiobencarb Use Site Needed to Reduce Spray Drift to Levels that
Do Not Exceed Acute and Chronic LOCs in Aquatic Environments Ill
Table 7-1. Effects Determination Summary for Potential Effects to the CRLF and DS from the
Use of Thiobencarb on Rice in California 128
Table 7-2. Effects Determination Summary for Thiobencarb Use and CRLF and DS Critical
Habitat Impact Analysis 130
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List of Figures
Figure 2-l.Thiobencarb Use in Total Pounds per County 31
Figure 2-2. Annual Pounds Thiobencarb Applied in California per Year Between 1994 and 2006
(source California PUR database) 33
Figure 2-3. Average Annual Pounds Thiobencarb Applied in Each County for the Years 1999-
2006. Counties applying a maximum of more than 1000 pounds per year were
included in the figure. See Appendix E for additional information 34
Figure 2-4. Delta smelt critical habitat (USFWS, 2009) and Occurrence Sections identified in
Case No. 07-2794-JCS 37
Figure 2-5. Recovery Unit, Core Area, Critical Habitat, and Occurrence Designations for CRLF.
38
Figure 2-6. Initial area of concern, or "footprint" of potential use, for thiobencarb 42
Figure 2-7. Conceptual Model for Terrestrial-Phase of the Assessed Species 48
Figure 2-8. Conceptual Model for Aquatic-Phase of the Assessed Species 49
Figure 3-1. Estimated Concentrations of Thiobencarb in Water Starting with the Tier I Rice
Model Estimated Initial Concentration and Using the Field Decay Rate from an
Aquatic Dissipation Study (decay rate = 0.1252/day, half-life = 5.5 days) 55
Figure 3-2. Water Concentrations of Thiobencarb and Two Degradates in California Aquatic
Dissipation Study on Wet Seeded Rice After Application of Granular Formulation of
Thiobencarb (MRID 43404005) 57
Figure 3-3. Thiobencarb Concentrations in Water in Aquatic Field Study (Ross and Sava, 1986).
58
Figure 3-4. Monitoring Results Observed in the Colusa Basin Drain #5, Sacramento River, 1992
-2002 60
Figure 5-1. Map Showing the Overlap of CRLF Critical Habitat, Occurrence Sections, and Core
Areas with the NLCD Cultivated Crop Land Cover Class 113
Figure 5-2. Map Showing the Overlap of DS Critical Habitat and Occurrence Sections Identified
by Case No. 07-2794-JCS with the NLCD Cultivated Crop Land Cover Class 114
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1. Executive Summary
1.1. Purpose of Assessment
The purpose of this assessment is to evaluate potential direct and indirect effects on the
California red-legged frog (Rana aurora draytonif) (CRLF) and the Delta smelt (Hypomesus
transpacificus) (DS) arising from Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)
regulatory actions regarding use of thiobencarb on rice. In addition, this assessment evaluates
whether these actions can be expected to result in effects to designated critical habitat for the
CRLF and the DS. 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 (USEPA, 2004).
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.
The DS was listed as threatened on March 5, 1993 (58 FR 12854) by the USFWS (USFWS,
2007a). It is mainly found in Suisun Bay and the Sacramento-San Joaquin estuary near San
Francisco Bay. During spawning it moves into freshwaters.
1.2. Scope of Assessment
Thiobencarb is a systemic herbicide used to control grasses and broadleaf weeds (USEPA,
1997). It is currently registered as a pre-emergent or early post emergent herbicide for use on
dry or wet seeded rice. It is a thiocarbamate class pesticide and its mode of action is inhibition of
lipid synthesis (HRAC, 2005). This assessment examines risks of the use of thiobencarb on rice
in California to the CRLF and DS. Thiobencarb formulations assessed include emulsifiable
concentrates and granular formulations that may be applied via ground or aerial application
methods.
Two major degradates were observed in fate studies: 4-chlorobenzoic acid and 4-
chlorobenzaldehyde. ECOSAR version 1.0 predicted aquatic toxicity endpoints greater than
those predicted and measured for thiobencarb for these degradates, see Appendix B.
Additionally, these degradates were not considered to be of toxicological concern in the human
health risk assessment completed for the Reregi strati on Eligibility Decision (RED) and were not
recommended to be a human health concern by the Residues of Concern Knowledgebase
Subcommittee (ROCKS) (Eckel, 2008; Lewis, 1997; Scollon, 2008). The presence of these
degradates and degradates found at less than 10% applied parent equivalents is not expected to
alter risk conclusions that are based on the fate, transport, and toxicity of the parent compound
alone (see Section 2.2.1 for a complete discussion). Therefore, this assessment estimated
exposure to the parent compound alone.
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1.3. Assessment Procedures
This assessment was completed in accordance with the USFWS and NMFS Endangered Species
Consultation Handbook (USFWS/NMFS, 1998) and is consistent with procedures and
methodology outlined in the Agency's Overview Document (USEPA, 2004).
1.3.1. Toxicity Assessment
The assessment endpoints include direct toxic effects on survival, reproduction, and growth of
individuals, as well as indirect effects, such as reduction of the food source and/or modification
of habitat. Federally-designated critical habitat has been established for the CRLF and the DS.
Primary constituent elements (PCEs) were used to evaluate whether thiobencarb has the potential
to modify designated critical habitat. The Agency evaluated registrant-submitted studies and
data from the open literature to characterize thiobencarb toxicity. The most sensitive toxicity
value available from acceptable or supplemental studies for each taxon relevant for estimating
potential risks to the CRLF and DS and/or their designated critical habitat was used.
1.3.2. Exposure Assessment
1.3.2.a. Aquatic Exposures
Thiobencarb is stable to hydrolysis (MRTD 41609012) and aerobic aquatic metabolism and
anaerobic aquatic metabolism (MRTD 43252001, 42015301). It degrades slowly via photolysis
in water (half-life =190 days) and photolysis in soil (half-life = 420 day dark corrected half-life
(MRID 422257801 and 41215312). Thiobencarb dissipates in the environment by binding to soil
(K0cS range from 384 - 1435 L/kg, MRID 41215313), by aerobic soil metabolism at the
soil/H2O interface (half-lives ranged from 27-58 days, MRID 43300401, 00040925), and by
aqueous photolysis in the presence of photosensitizers (half-life was 12 days, MRID 42257801
and 41215312).
The Tier I Rice Model and a modified version of the Rice Model that accounts for dissipation
were used to estimate conservative exposures of thiobencarb in aquatic habitats resulting from
runoff and spray drift from different uses. Monitoring data were used to characterize chronic
risk to the DS as DS will not be present in rice paddies. Concentrations from aquatic dissipation
and aquatic monitoring in California rice growing areas were also used to characterize risk. The
peak model-estimated environmental concentration in the rice paddy was 2018 |ig/L using the
Tier I Rice Model and the 14-day value was 350 |ig/L. The 14-day value was estimated using a
modified Tier I Rice Model to allow for 14 days of dissipation that would occur in the required
water holding period (see Section 3.1). The maximum reported monitoring value in California
from surface water data evaluated in this assessment was 170 jig/L before the 14 day holding
period was established and 37.4 jig/L after the holding period was established (see Section 3.1.1)
(Miller, 1997; Orlando and Kuivila, 2004; Program, 2007). Modeling output showed peak
concentrations that are within a reasonable margin of error to the highest peak monitoring data
(350-2018 |ig/L compared to 170 |ig/L) and about 9-54 times higher than the peak monitoring
data from samples collected after the 14-day holding period was put in place (350-2018 jig/L
compared to 37.4 |ig/L).
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Potential transport mechanisms include pesticide spray drift and secondary drift of volatilized or
soil-bound residues leading to deposition onto nearby or more distant ecosystems. Surface water
runoff and spray drift are expected to be the major routes of exposure for thiobencarb.
1.3.2.b. Terrestrial Exposures
The T-REX model was used to estimate potential thiobencarb exposures to terrestrial species
including birds (surrogate species for terrestrial phase CRLFs), mammals (CRLF prey), and
invertebrates (CRLF prey). The AgDRIFT model was used to estimate deposition of thiobencarb
on terrestrial and aquatic habitats from spray drift and to determine the distance from thiobencarb
use sites that the CRLF and the DS may be at risk of direct or indirect effects. The TerrPlant
model was used to estimate thiobencarb exposures to terrestrial-phase CRLF habitat, including
plants inhabiting semi-aquatic and dry areas, resulting from uses involving flowable and granular
applications. The T-HERPS model was used to allow for further characterization of the dietary
exposures of terrestrial-phase CRLFs relative to birds, which were used as a surrogate species for
the CRLF.
1.3.3. Toxicity Assessment
Section 4 summarizes the ecotoxicity data available on thiobencarb. Thiobencarb and
thiobencarb formulations are moderately to highly toxic to freshwater fish and freshwater
invertebrates on an acute exposure basis. The no observed adverse effect concentration
(NOAEC) for chronic effects to the striped bass is 21 |ig/L, with a lowest observed adverse
affect concentration (LOAEC) of 23 |ig/L based on posthatch survival (Fujimura et a/., 1991).
Available chronic toxicity data for aquatic invertebrates include a NOAEC of 1.0 |ig/L, with a
LOAEC of 3.0 |ig/L based on reduction in offspring produced (MRID 00079098). Thiobencarb
is slightly to practically nontoxic to birds on an acute oral and subacute dietary exposure basis,
and slightly toxic to mammals on an acute oral exposure basis. Thiobencarb is classified as
practically nontoxic to honey bees on an acute contact exposure basis. In a reproductive study
with the mallard duck a statistically significant decreased number of eggs laid and hatchlings per
live three week embryo was observed at concentrations of 300 mg a.i./kg-diet (MRID
00025778). The associated NOAEC was 100 mg a.i./kg-diet. A two generation study on rats
with oral exposure to thiobencarb resulted in a NOAEC of less than 20 mg/kg/day with effects
on body weight and feeding efficiency observed at 100 mg/kg/day (MRID 40446201). A
reproductive NOAEL could not be determined because no reproductive effects were observed at
the highest level tested of 100 mg/kg/day. The 96-hr ECso for algae exposed to thiobencarb is 17
|ig/L (41690901). The 14-day EC50 for duckweed, a vascular plant, was 770 |ig/L (MRID
41690901).
1.3.4. Measures of Risk
Acute and chronic risk quotients (RQs) are compared to the Agency's Levels of Concern (LOCs)
to identify instances where thiobencarb use has the potential to adversely affect the CRLF or DS
or adversely modify their designated critical habitat. When RQs for a particular type of effect
are below LOCs, the pesticide is considered to have "no effect" on the species and its designated
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critical habitat. Where RQs exceed LOCs, a potential to cause adverse effects or habitat
modification is identified, leading to a conclusion of "may affect". If thiobencarb use "may
affect" the assessed species, and/or may cause effects to designated critical habitat, the best
available additional information is considered to refine the potential for exposure and effects, and
distinguish actions that are Not Likely to Adversely Affect (NLAA) from those that are Likely to
Adversely Affect (LAA).
1.4. Thiobencarb Uses Assessed
In the U.S. and California, thiobencarb is currently registered for use on rice. Only the end-use
products approved for use in California are assessed in this document. None of the products
registered in California have more than one active ingredient (a.i.) in the formulation; however,
several products recommend the use in combination with propanil for control of specific weeds.
None of the thiobencarb end-use products are labeled as Restricted Use Pesticides (RUPs).
Based on California Department of Pesticide Regulation Pesticide Use Reporting (CDPR PUR)
data, a total of 308,491 to 1,006,327 pounds of thiobencarb were applied annually to rice in
California between 1999 and 2006 (Figure 2-2). Sixty-eight percent of the average annual
pounds applied were applied in three counties: Colusa, Sutler, and Butte. Colusa and Butte have
some CRLF critical habitat. There is no DS critical habitat in these three counties. Average and
maximum application rates indicate that thiobencarb is commonly used at the maximum
application rate with the average application rate across counties ranging from 3.1 - 4 Ibs ai/acre
(Table 2-6). The maximum application rate is 4.005 Ibs a.i./acre (Table 2-5).
Thiobencarb is currently registered for pre-emergent and early post-emergent control of barnyard
grass, junglerice, sprangletop, crabgrass, fall panicum, dayflower, eclipta, False pimpernel,
emerged Watergrass, and other weeds. The formulations currently registered include the
technical grade which is used to manufacture end-use products, emulsifiable concentrates, and
granular formulations. Thiobencarb may be applied via ground and aerial applications.
Application methods include broadcast spray, granular applicator, high pressure sprayer, and
dilute high volume spray. The timing of application is at dry seeding or wet seeding, prior to rice
and weed emergence, or early post emergence of weeds.
1.5. Summary of Conclusions
Based on the best available information, the Agency makes a May Affect, and Likely to
Adversely Affect (LAA) determination for the CRLF and the DS from the labeled uses of
thiobencarb as described in Table 1-1. The effects determination is based on potential direct and
indirect effects to terrestrial-phase CRLF and potential direct and indirect effects to aquatic-
phase CRLF and the DS. The LAA determination applies to all currently registered thiobencarb
uses in California, e.g., use of thiobencarb on rice.
Additionally, the Agency has determined that there is the potential for habitat modification of
designated critical habitat of CRLF and DS from the use of the thiobencarb on rice. A summary
of the risk conclusions and effects determinations for each listed species assessed and their
designated critical habitat is presented in Table 1-1 and Table 1-2. Further information on the
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results of the effects determination is included as part of the Risk Description in Section 5.2.
Given the LAA determination for the CRLF and the DS and potential effects to designated
critical habitat for both species, 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 DS is
provided in Attachment 4.
Table 1-1. Effects Determination Summary for Potential Effects to the CRLF and DS from
the Use of Thiobencarb on Rice in California
Species
Effects
Determination
Basis for Determination
California red-
legged frog
(Rana aurora
draytonii)
May affect,
likely to
adversely affect
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults):
Acute RQs for freshwater fish (used as a surrogate for aquatic-phase amphibians)
exceed the Agency's LOCs for use of thiobencarb on rice. At the highest RQ
(4.59) and using the default slope (4.5), the probability of an effect would be
approximately 1 in 1.0. Chronic RQs for freshwater fish ranged from 0.26 -
46.10 and exceed the LOG of 1.0. The critical habitat and cultivated crop land
cover class overlap. This indicates that direct effects to aquatic-phase CRLF
have thejpotential to occur.
Terrestrial-phase (Juveniles and Adults):
The risk of direct adverse effects to terrestrial-phase CRLF from acute or sub-
acute dietary exposure is low; however, risk may not be precluded because
estimated exposure exceeds the highest doses tested where no mortality occurred
for terrestrial birds (the surrogate for terrestrial-phase CRLF) consuming small
insects and small mammals. The RQs for chronic risk to terrestrial birds exceed
the LOG of 1.0 for birds consuming broadleaf plants/small insects and small
mammals. Therefore, chronic risk to the CRLF has the potential to occur.
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary productivity
Risk quotients for FW fish, FW invertebrates, and aquatic plants exceeded LOCs.
For F W invertebrates, the probability of an effect would be approximately 1 in
1.0 (based on the highest RQ of 19.84 and slope of 4.5). Chronic FW
invertebrate RQs also exceed the LOG of 1.0. RQs for non-vascular aquatic
plants exceed the LOG of 1.0 using modeled and monitoring results. RQs for
vascular aquatic plants exceed the LOG of 1.0 based on modeling data in the rice
paddy. This indicates that indirect effects to CRLF have the potential to occur
due to loss of prey or habitat. RQs for terrestrial plants exceed the LOG of 1.0,
indicating that effects to riparian vegetation have the potential to occur.
Terrestrial prey items, riparian habitat
CRLFs could be affected as a result of potential impacts to grassy/herbaceous
vegetation and reduction of prey items such as small mammals or terrestrial
invertebrates. RQs for mammals consuming short grass, tall grass, broadleaf
plants, and small insects exceed the acute LOG of 0.1 and chronic LOG of 1.0.
The probability of individual effects for mammals is 1 in 2.73 (based on the
highest RQ of 0.40 and slope of 4.5). The risk of indirect effects to the CRLF
due to a reduction in terrestrial invertebrate prey items is low. Risk may not be
precluded for terrestrial invertebrates because the ratio of the EEC to the dose
where 15% mortality occurred exceeds the LOG of 0.05. Fifteen percent
mortality occurred at the highest dose tested. It is uncertain whether the EC50
would result in LOG exceedances for terrestrial invertebrates. RQs for terrestrial
plants exceed the corresponding LOG of 1.0.
Delta Smelt
May affect,
Potential for Direct Effects
14
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Species
Effects
Determination
Basis for Determination
(Hypomesus
transpacificus)
likely to
adversely affect
RQs for freshwater and E/M fish exceed the Agency's LOCs for use of
thiobencarb on rice. At the highest RQ (2.82) and using the default slope (4.5),
the probability of an effect would be approximately 1 in 1.02. Chronic RQs for
freshwater and estuarine/marine fish ranged from 0.26 - 13.33 and exceed the
LOG of 1.0 when based on aquatic dissipation studies. Critical habitat and the
cultivated crop NLCD land cover class overlap. This indicates that direct effects
to PS have the potential to occur with the use of thiobencarb on rice.
Potential for Indirect Effects
Use of thiobencarb on rice has the potential to adversely affect the DS by
reducing available food (aquatic plants and FW and E/M invertebrates), by
impacting the riparian habitat of grassy and herbaceous riparian areas, and/or by
impacting water quality via effects to aquatic vegetation. Acute and chronic RQs
for FW and E/M invertebrates exceed corresponding LOCs indicating that
reduction in prey items may occur. For FW invertebrates, the probability of an
effect would be approximately 1 in 1.0 (based on the highest RQ of 19.84 and
slope of 4.5). For E/M invertebrates the probability of an individual effect is
approximately 1 in 1.00 (based on the highest RQ of 3.84 and a slope of 4.5).
Chronic RQs for both E/M and FW invertebrates exceed the LOG of 1.0. Some
RQs for aquatic plants exceed the LOG of 1.0 indicating that effects on DS
habitat and reduction in food may occur. RQs for terrestrial plants exceed the
LOG of 1.0 indicating that effects to riparian vegetation have the potential to
occur.
Abbreviations: FW = freshwater, E/M = estuarine/marine, CRLF = California Red Legged Frog, DS=delta smelt,
RQ=risk quotient
Table 1-2. Effects Determination Summary for Thiobencarb Use on Rice and CRLF and
DS Critical Habitat Impact Analysis.
Assessment
Endpoint
Effects
Determination
Basis for Determination
Modification of
aquatic-phase PCEs
(DS and CRLF)
Habitat
Modification
As described in Table 1-1, the effects determination for the potential for
thiobencarb to affect aquatic-phase CRLFs and the DS is LAA. These
determinations are based on the potential for thiobencarb to indirectly affect
the DS and aquatic-phase CRLF. Additionally, the potential areas of effect
overlap with critical habitat designated for the CRLF and DS. Therefore,
potential effects to aquatic plants and terrestrial (riparian) plants identified in
this assessment could result in aquatic habitat modification.
Modification of
terrestrial-phase PCE
(CRLF)
As described in Table 1-1, the effects determination for the potential for
thiobencarb to affect terrestrial-phase CRLFs is LAA. This determination is
based on the potential for thiobencarb to directly affect terrestrial-phase
CRLFs and their food supply and habitat. Additionally, the potential areas of
effect overlap with critical habitat designated for the CRLF. Therefore, these
potential effects could result in modification of critical habitat.
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 for the CRLF
and DS. 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
15
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(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 and DS 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.
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 (USEPA, 1998), the Services' Endangered Species Consultation Handbook
(USFWS/NMFS, 1998) and is consistent with procedures and methodology outlined in the
Overview Document (USEPA, 2004) and reviewed by the USFWS and NMFS
(USFWS/NMFS/NOAA, 2004)).
16
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2.1. Purpose
The purpose of this endangered species assessment is to evaluate potential direct and indirect
effects on individuals of the federally threatened California red-legged frog (CRLF, Rana aurora
draytonii) and delta smelt (DS, Hypomesus transpacificus) arising from FIFRA regulatory
actions regarding use of thiobencarb on rice. In addition, this assessment evaluates whether use
on rice is expected to result in modification of designated critical habitat for the CRLF and/or the
DS. This ecological risk assessment has been prepared consistent with the settlement agreements
in two court cases. The first case referring to the CRLF is the Center for Biological Diversity
(CBD) vs. EPA etal. (Case No. 02-1580-JSW(JL)) settlement entered in Federal District Court
for the Northern District of California on October 20, 2006. This assessment also addresses the
DS for which thiobencarb was alleged to be of concern in a separate suit (Center for Biological
Diversity (CBD) vs. EPA etal. (CaseNo. 07-2794-JCS)).
In this assessment, direct and indirect effects to the CRLF and DS and potential modification to
designated critical habitat for the CRLF and DS are evaluated in accordance with the methods
described in the Agency's Overview Document (USEPA, 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 modification of their designated critical habitat (i.e., a taxon-level
approach). Screening level methods include use of standard models such as Tier I Rice Model,
T-REX, TerrPlant, and AgDRIFT, all of which are described at length in the Overview
Document. In addition, T-HERPS has been used to refine estimates of exposure and risk to
amphibians. Use of such information is consistent with the methodology described in the
Overview Document (USEPA, 2004), which specifies that "the assessment process may, on a
case-by-case basis, incorporate additional methods, models, and lines of evidence that EPA finds
technically appropriate for risk management objectives" (Section V, page 31 of USEPA, 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 thiobencarb is based on an action area. The action area is the area directly or
indirectly affected by the federal action, as indicated by the exceedance 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 thiobencarb 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 and DS 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 in the lawsuits regarding the potential
use of thiobencarb in accordance with current labels:
17
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"No effect";
"May affect, but not likely to adversely affect"; or
"May affect and likely to adversely affect".
The CRLF and the DS have designated critical habitats 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. The PCEs for
CRLFs are aquatic and upland areas where suitable breeding and non-breeding aquatic habitat is
located, interspersed with upland foraging and dispersal habitat. PCEs for the DS include
characteristics required to maintain habitat for spawning, larval and juvenile transport, rearing,
and adult migration.
If the results of initial screening-level assessment methods show no direct or indirect effects (no
LOG exceedances) upon individuals or upon the PCEs of the species' designated critical habitat,
a "no effect" determination is made for use of thiobencarb as it relates to each species and its
designated critical habitat. If, however, potential direct or indirect effects to individuals of each
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
thiobencarb.
If a determination is made that use of thiobencarb "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 thiobencarb use sites) and further evaluation of the
potential impact of thiobencarb on the PCEs is also used to determine whether modification of
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 result in "no effect" or potential modification to 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 thiobencarb
is expected to directly impact living organisms within the action area (defined in Section 2.7),
critical habitat analysis for thiobencarb 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 modify critical habitat are those that alter the PCEs and
appreciably diminish the value of the habitat. Evaluation of actions related to use of thiobencarb
that may alter the PCEs of the assessed species' critical habitat form the basis of the critical
habitat impact analysis. Actions that may affect the assessed species' designated critical habitat
have been identified by the Services and are discussed further in Section 2.6.
18
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2.2. Scope
Thiobencarb is a systemic herbicide used to control grasses and broadleaf weeds (USEPA,
1997). It is currently used to control weeds in rice paddies. It may be applied as a pre-emergent
or early post emergent herbicide to dry or wet seeded rice. It is a thiocarbamate class pesticide
and its mode of action is inhibition of lipid synthesis (HRAC, 2005).
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 thiobencarb
in accordance with the approved product labels for California is "the action" relevant to this
ecological risk assessment.
Although current registrations of thiobencarb allow for use nationwide, this ecological risk
assessment and effects determination addresses currently registered uses of thiobencarb in
portions of the action area that are reasonably assumed to be biologically relevant to the CRLF
and DS and their designated critical habitat. Further discussion of the action area for the CRLF
and DS and their critical habitat is provided in Section 2.7.
2.2.1. Evaluation of Degradates
This ecological risk assessment includes all potential ecological stressors resulting from the use
of thiobencarb, including thiobencarb and its potential degradates of concern. Degradates of
concern may include those that are found at significant concentrations (>10% by weight relative
to parent) in available degradation studies and/or those that are of toxicological concern. The
only major degradates (defined as those representing 10% or more of the applied radiation of the
parent test substance) identified were 4-chlorobenzoic acid (56% of applied radiation at 30 days)
and 4-chlorobenzaldehyde (29.4% at 14 days), both in a sensitized aquatic photodegradation
study. Both of these degradates are expected to be soluble and mobile in water. Both should be
subject to further degradation by metabolism (based on their simple structures), but the study
was terminated at 30 days.
Neither of these degradates was analyzed for in the aquatic field dissipation studies, thus we do
not know if their formation in laboratory studies means that they will form in the field. The only
degradates measured in the aquatic field studies were thiobencarb sulfoxide and 4-
chlorobenzylmethylsulfone) which is a possible precursor to 4-chlorobenzoic acid and 4-
chl orob enzal dehy de.
A summary of formation pathways of the two major degradates, 4-chlorobenzoic acid and 4-
chlorobenzaldehyde, is presented in Table 2-1. Appendix A provides additional information on
the percentage of applied parent equivalents in each environmental fate study.
19
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Table 2-1. Degradate Occurrence Summary for Thiobencarb
Study
MRID
Hydrolysis
41609012
Aqueous Photolysis
42257801
Aqueous Photolysis
42257801
(sensitized)
Soil Photolysis
41215312
Aerobic Soil Metabolism
43300401
Aerobic Soil metabolism
00040925
Aerobic Aquatic Metabolism
42015301
Anaerobic Aquatic
Metabolism
43252001
Aquatic field Dissipation/wet
seeded
43404005
Aquatic Field Dissipation/dry
seeded
42003404
4-chlorobenzoic acid
CAS Number:
74-11-3
3. 9% @ 30 days
max/last
56% @ 30 days
max/last
1% @ day 9 max
I.l%@day211ast
0.6% @ 120 days max
0. 13% (Si 366 days last
2.6% @ 7 days max
0.5% @ 7 days max
0.2% @ 30 days last
2.2% @ 363 days
max/last
Not analyzed
Not analyzed
4-chlorobenzaldehyde
CAS Number:
104-88-1
1. 8% @ 21 days max
1. 8% @ 30 days last
29.4% @ 14 days max
3. 7% @ 30 days last
Not analyzed
Not analyzed
No ecological toxicity data were found in the ECOTOX database for 4-chlorobenzoic acid or 4-
chlorobenzaldehyde; however, ECOSAR version 1.0 predicted aquatic toxicity endpoints greater
than those predicted and measured for thiobencarb, see Appendix B. These degradates were not
considered to be of toxicological concern in the human health risk assessment completed for the
Reregi strati on Eligibility Decision (RED) and were not recommended to be treated as a human
health concern by the ROCKS Committee (Eckel, 2008; Lewis, 1997). The toxicity of 4-
chlorobenzoic acid and 4-chlorobenzaldehyde was assumed to be less than that of thiobencarb
(see Appendix B). Concentrations of the other degradates were a very small percentage (<8.3%)
of the amount of thiobencarb applied or were only present in a few fate studies, suggesting that
they would be present at lower concentrations than those estimated for thiobencarb. The
estimated toxicity based on structure activity relationships (ECOSAR version 1.0) or the
similarity of the structure to thiobencarb indicates that the toxicity of these compounds is similar
to or less than that of thiobencarb (see Appendix B). The presence of these degradates is not
expected to alter risk conclusions that are based on the fate, transport, and toxicity of the parent
compound alone.
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2.2.2. Evaluation of Mixtures
The Agency does not routinely include 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 its risk assessments. In the case of product formulations of active ingredients (registered
products 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
ingredients, they may be used qualitatively or quantitatively in accordance with the Agency's
Overview Document and the Services' Evaluation Memorandum (USEPA, 2004;
USFWS/NMFS/NOAA, 2004). Thiobencarb does have one nationally registered end-use
product that is co-formulated with propanil; however, this product is not registered for use in
California1 (EPA Registration Number 07108500030). Therefore, none of the thiobencarb
products assessed here contains more than one active ingredient. Labels registered in California
do recommend use of thiobencarb in tank mixes with propanil and thiobencarb is often mixed or
used with propanil (see labels).
The results of available toxicity data for mixtures of thiobencarb with other pesticides are
presented in Appendix C. The limited data available do no allow a comparison of the toxicity
results of thiobencarb alone versus thiobencarb and propanil or with other chemicals. If
chemicals that show synergistic effects with thiobencarb are present in the environment in
combination with thiobencarb, the toxicity of thiobencarb may be increased, offset by other
environmental factors, or even reduced by the presence of antagonistic contaminants if they are
also present in the mixture. The variety of chemical interactions presented in the available data
set suggest that the toxic effect of thiobencarb, in combination with other pesticides used in the
environment, can be a function of many factors including but not necessarily limited to (1) the
exposed species, (2) the co-contaminants in the mixture, (3) the ratio of chemical concentrations,
(4) differences in the pattern and duration of exposure among contaminants, and (5) the
differential effects of other physical/chemical characteristics of the receiving waters (e.g.,
organic matter present in sediment and suspended water). Quantitatively predicting the
combined effects of all these variables on mixture toxicity to any given taxa with confidence is
beyond the current capabilities. However, a qualitative discussion of implications of the
available pesticide mixture effects data involving thiobencarb on the confidence of risk
assessment conclusions is addressed as part of the uncertainty analysis for this effects
determination.
1 RiceBeaux (EPA Registration Number 41085-30, label date 11/05/2008) is a Section 3 national label and contains
propanil; however, it is not for sale or registered for use in California.
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2.3. Previous Assessments
2.3.1. Reregistration Eligibility Decision (RED)
Thiobencarb was first registered in 1975 (USEPA, 1994). A Reregistration Eligibility Decision
(RED) for thiobencarb was signed in December 1997 (USEPA, 1997). In the RED, the
following mitigation measures were required that are especially relevant to the ecological risk
assessment.
Include label warnings preventing application to rice fields with catfish/crayfish farming,
and preventing application to rice fields adjacent to catfish or crayfish ponds.
Where weather conditions permit, it is required that flood waters not be released within
14 days.
Avoid application of this product within 24 hours of rainfall, or when heavy rain is
expected to occur within 24 hours.
Product Reregistration for all thiobencarb products was completed on April 10, 2006 (Ballard
and Errico, 2009). Therefore, all measures required by the RED should be reflected on current
product labels.
The following data gaps were identified in the EFED science chapter or in follow-up actions to
the RED (Mastrota, 1997, Not Specified): chronic toxicity test with shrimp did not have a
definitive NOAEC, avian acute dietary toxicity for waterfowl, avian chronic toxicity for a
waterfowl species, freshwater fish full life cycle study, seedling emergence on lettuce and
ryegrass.
The ecological risks of the various uses are summarized below for California for non-listed
species (Mastrota, 1997).
Use of liquid formulations pose some acute risk to mammals. The acute risk to birds is
minimal.
Use of liquid formulations pose a high chronic risk to birds and mammals. The chronic
risk from granular formulations could not be assessed.
Use of thiobencarb on rice in California poses a risk of causing chronic effects to aquatic
organisms in the smaller drains and waterways, but not in the larger rivers.
Its use poses minimal risk of acute effects to fish and aquatic invertebrates.
Minimal risk of both acute and chronic effects is expected for all estuarine/marine (E/M)
organisms in California.
Spray drift from aerial application of liquid thiobencarb on rice poses a high risk to
nontarget terrestrial and semi-aquatic plants. Drift of granular thiobencarb and spraying
of liquid thiobencarb applied with ground equipment pose minimal risk to these plants.
All uses of thiobencarb on rice may pose a risk of killing emerging seedlings of aquatic
plants, especially aquatic grasses. Use of thiobencarb on rice may pose a risk to aquatic
algae in smaller drains and waterways in California.
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2.3.2. Ecological Risk Assessment for Proposed Use on Wild Rice
An ecological risk assessment was completed on a proposed use of an emulsifiable concentrate
formulation for aerial or ground application to soil in wild rice paddies at a rate of 2 to 4 Ibs
a.i./acre with one application per season (Davy, 2008). In this risk assessment, the Tier I Rice
Model was used to estimate exposure. This model was not available when the RED was
completed. Many other changes in methodologies of assessing risk have occurred between 1997
and 2008. The following risk concerns were identified in the 2008 assessment:
acute and chronic risk to aquatic organisms;
risk to aquatic plants;
acute risk to mammals;
chronic risk to birds and mammals;
risk to terrestrial plants; and
risk to federally listed birds (and reptiles), mammals, freshwater and E/M fish (and
amphibians), freshwater and E/M aquatic invertebrates, and aquatic and terrestrial plants.
2.3.3. Effects Determination for Thiobencarb for Pacific Anadromous
Salmonids
A determination was made by the Field and External Affairs Division that thiobencarb use on
rice is not likely to adversely affect Federally listed threatened and endangered salmon and
steelhead, nor is it likely to adversely modify their designated critical habitat (Turner, 2002).
This determination was largely based on, "maximum residues found in natural waters providing
habitat for salmon and steelhead have been consistently below levels of concern for acute
toxicity to fish or indirectly to their invertebrate food supply". The Office of Pesticide
Programs (OPP) requested initiation of Endangered Species Act (ESA) Section 7(a)(2)
consultation with the National Marine Fisheries Service in 2002 (Williams, 2002).
2.3.4. Registrant Submitted Data Not Considered In Previous Ecological Risk
Assessments
New data are available that were not used in previous risk assessments. These studies include an
850.1075 acute freshwater fish toxicity test (MRID 46091401), freshwater fish full life cycle test
(MRID 45695101), 28-day sediment toxicity test for the midge (Chironomus riparius) (MRID
46091402), 850.3200 acute contact toxicity to the honey bee (MRID 46059804), and an acute
earthworm study (MRID 46059803).
2.4. Stressor Source and Distribution
2.4.1. Environmental Fate Properties
Thiobencarb is generally non-persistent in the water column, due to dissipation to soil, but
moderately persistent in soils and sediments. Thiobencarb dissipates in the environment by
binding to soil, by aerobic soil metabolism at the soil/H2O interface, and by aqueous photolysis
in the presence of photo-sensitizers. Thiobencarb KOCS range from 384 - 1438 L/kg indicating it
is moderately mobile to slightly mobile and it does have the potential to reach groundwater in
23
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highly vulnerable areas (based on the FAO Mobility Classification) (FAO, 2000). When used on
rice, thiobencarb is more likely to be found in the soil than in the paddy water. Greater quantities
of thiobencarb are associated with soil when applied preflood to soil rather than in standing
water. The portion of thiobencarb associated with soil was approximately 10 times more when
applied pre-flood to soil than when applied to standing water, primarily since thiobencarb has
time to bind to soil prior to flooding. As a result, sensitized aqueous photolysis is expected to be
more significant as a dissipation route when thiobencarb is applied to water than when it is
applied to dry soil, due to a greater amount of thiobencarb remaining in paddy water containing
natural photo-sensitizers.
Thiobencarb has a water solubility of 30 ppm, a vapor pressure of 1.476 x 10"6 Torr at 20°C
(Ahrens, 1994) and 2.2 x 10"5 at 23°C (MRID 00044507), and an estimated Henry's Law
Constant of 2.49 x 10"7 atm mVmol. It is stable to hydrolysis, non-sensitized aqueous photolysis,
soil photolysis, anaerobic aquatic metabolism, and aerobic aquatic metabolism. In an aqueous
photolysis study with and without the use of photo-sensitizers (acetone), the half-lives were 12
and 190 days, respectively (MRID 42257801). Since some humic substances in natural waters
have been shown to act as photo-sensitizers, the 12-day half-life may be more relevant.
Thiobencarb also degraded moderately slowly under aerobic conditions with calculated half-lives
of 27-58 days in soils that typically support rice production.
Thiobencarb slowly mineralizes in soil without forming significant quantities of non-volatile
degradates; however, major degradates are formed with photosensitized photolysis. The major
degradate in both the aqueous photolysis and soil metabolism studies was 4-chlorobenzoic acid,
reaching 56 and 5 % of applied parent equivalents respectively. Another major degradate
observed in photolysis studies was 4-chlorobenzaldehyde at a maximum of 29.4% applied parent
equivalents. CC>2 and bound residues are the primary products from soil metabolism studies,
occurring in proportions of 42-77 and 23-42 % of applied, respectively. Aqueous residues did
not exceed 4.5 % of applied radioactivity in soil metabolism studies.
Parent thiobencarb was moderately mobile to slightly mobile (based on the FAO Mobility
classification system) in the tested soils with Freundlich Kads values of 5.42-20 L/kg. The Koc
values ranged from 384-1435 L/kg. 4-Chlorobenzoic acid was mobile to moderately mobile
(based on the FAO Mobility classification system) in the tested soils with Freundlich Kads values
of 0.74-3.26 L/kg. The corresponding Koc values ranged from 84-416 L/kg. Mobility generally
decreased with increasing clay content, increasing organic matter content, and increasing cation
exchange capacity.
Results from an aquatic field dissipation study in Louisiana, where thiobencarb was applied as a
spray directly to soil and flooded seven days later, show half-lives of 5.8 days in flood water and
36 days in hydrosoil or sediment. The median ratio of soil:water thiobencarb residues was
63.5:1.
In two field studies in California rice paddies where granules were applied into standing water,
the dissipation half-lives in flood water were 8.7 days (guideline study) and 4.5 days (literature
review, Ross and Sava, 1986). The half-lives in hydrosoil or sediment were 153 and 56 days,
respectively. The median ratios of soil:water thiobencarb residues were 5.6:1 and 6.6:1.
24
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Thiobencarb moderately accumulated in bluegill sunfish with maximum bioconcentration factors
of 128x, 639x, and 41 Ix for edible (muscle) tissue, nonedible tissue, and whole fish,
respectively. Depuration is rapid, with 93-95% of the accumulated [14C]residues being
eliminated from the tissues in three days. The degradates 4-chlorobenzylmethylsulfoxide,
thiobencarb sulfoxide, desethylthiobencarb, and 2-hydroxythiobencarb were identified in edible
and nonedible tissue.
Table 2-1 lists the environmental fate properties of thiobencarb, along with the major and minor
degradates detected in the submitted environmental fate and transport studies.
Table 2.1 Summary of Physical/Chemical and Environmental Fate Properties of
Thiobencarb
Parameter
Chemical name
Molecular weight
Water Solubility
Vapor pressure
Henry's Law Constant
Log Kow
pKa
Hydrolysis half -life
Aqueous photolysis
half-life
Soil photolysis half-life
Aerobic soil metabolism
half-life
Anaerobic aquatic
metabolism half -life
Aerobic aquatic
metabolism half -life
Soil organic carbon
partition coefficient in
L/kg (Koc)
Value
S-4-chlorobenzyl
diethylthiocarbamate
257.78 g/mole
30 mg/L in water at 25°
1.476xlO"6 mm Hg at 20C°
2.2 x 10-5 mm Hg at 23°C
2.49 x 10 "7 atm-m3/mol
3.42
1.3-1.6
none
Stable
190 days
12 days in presence of 1%
acetone
168 days (irradiated)
280 days (dark control)
58 days (0-56 day data)
Stockton Clay adobe soil (CA)
37 days (Clay soil, Biggs, CA)
27 days (Silty Clay Loam,
Crowley, LA)
Stable
Stable
1084 (sandy loam)
384 (Loam)
6 18 (silly clay)
1027 (clay loam)
1435 (silt loam)
Source
Ahrens, 1994
Ahrens, 1994
Ahrens, 1994
Ahrens, 1994
MRID 00044507 as
referenced in
(Knizner, 1995)
Ahrens, 1994
MRID 0044507 as
referenced in
(Knizner, 1995)
Ahrens, 1994
MRID 41609012
MRID 42257801
MRID 412153 12
MRID 43300401
MRID 00040925
MRID 43252001
MRID 42015301
MRID 41215313
Comment
Calculated from vapor
pressure at 23°Cand water
solubility at 25°C
Stable at pH 5, 7, and 9
In non-sensitized, sterile
pH7 buffer at 25°C; stable in
dark control
Dark-corrected half -life is
420 days
25
-------
A summary of degradates found in the California and Louisiana aquatic field dissipation studies
is found in Table 2-2.
Table 2-2. Maximum Amounts of Thiobencarb and Metabolites Found in Flood Water in
Field Dissipation Studies
Study Type
Metabolite (Maximum in Flood Water)
MRID
Louisiana Aquatic Field Dissipation
(dry-seeded rice) 4 Ib/acre, aerial, spray,
flooded to 4.5 inches at 7 days post-
application
Parent Thiobencarb
Max. 12.2-14.1 ppb at 3 days post-flood (PF)
5.6-10.5ppbat7daysPF
Less than 1 ppb 28-70 days PF
Thiobencarb sulfoxide
Max. 16-13.4 ppb at 1 day PF
2.6-5.2 ppb at 3 days PF
0.8-1.5 ppb at 7 days PF
Less than 0.9 ppb at 14 to 70 days PF
4-chlorobenzylmethylsulfone
Max. 4.8-5.8 ppb at 5 days PF
1.4-1.8 ppb at 14 days PF
Less than 0.5 ppb 21-70 days PF
MRID 42003404
California Aquatic Field Dissipation
(wet-seeded rice) 4 Ib/acre, aerial,
granular, flooded to 6 inches at time of
application
Parent Thiobencarb
266 ppb at zero days
Max. 438 ppb at 3 days
1.0 ppb at 92 days
Thiobencarb sulfoxide
4.4 ppb at zero days
Max. 22 ppb at 3 days
Non-detectable at 33 days
4-chlorobenzylmethylsulfone
1.11-3.14 ppb at day zero
Max. 6.38-10.0 ppb (avg. 8.3) at day 10
5.15-6.95 ppb at day 21
Nondetect-1.52 ppb at day 33
Nondetect-1.1 ppb at day 92
MRID 43404005
Ross and Sava, 1986
(wet-seeded) 4 Ib/acre, aerial, spray,
water depth 10.4 inches
Parent Thiobencarb
Max. 576 ppb at 4 days
No Degradates measured
none
The chemical structures of the parent and some degradates are presented in Table 2-3. More
information on degradates is available in Appendix A.
26
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Table 2-3. The Chemical Structure of Thiobencarb and its Metabolites
Thiobencarb
4-chlorobenzoic acid
4-chlorobenzaldehyde
Thiobencarb sulfoxide
4-chlorobenzylmethylsulfone
27
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Volatization of Thiobencarb
A small amount of applied thiobencarb may volatilize and be transported in air. The vapor
pressure indicates that thiobencarb has an intermediate volatility from dry, non-adsorbing
surfaces and the estimated Henry's Law Constant indicates it is non-volatile from water (based
on classifications in the terrestrial field dissipation OPPTS Guidline 835.6100). Thiobencarb has
been measured in air in rice growing areas of California. The measured flux rate for air is 23
ng/cm2/hr and 58 ng/cm2/hr for water (Woodrow et al). Thiobencarb was predicted to
potentially travel up to 5 km from the site of application (Woodrow et al.). Evaporation
percentages of the amount applied are low (0.90 and 0.10% a few days after application to wet
seeded rice) (Ceesay, 2002). The atmospheric degradation half-life is 0.421 days (estimated
using EPISuite Version 4.0, Appendix M)) inidicating that long range transport is not likely to
occur. However, it has been found at trace concentrations in air and precipitation (see Section
3.1.1.fandSection3.1.1.g)
2.4.2. Environmental Transport Mechanisms
Potential transport mechanisms include rice paddy water discharge, spray drift, and secondary
drift of volatilized or soil-bound residues leading to deposition onto nearby or more distant
ecosystems. Rice paddy water discharge and spray drift are expected to be the major routes of
exposure for thiobencarb.
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; LeNoir et al., 1999;
McConnell et al., 1998; Sparling et a/., 2001). Thiobencarb was not looked for or found in these
studies; however, the vapor pressure of thiobencarb indicates that some atmospheric transport
may occur (see Section 2.4.1). 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 a/., 1999; McConnell et al, 1998).
Several sections of the range and critical habitat for the CLRF are located east of the Central
Valley. The magnitude of transport via secondary drift depends on thiobencarb's ability 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
thiobencarb 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 Nevadas are
considered in evaluating the potential for atmospheric transport of thiobencarb to locations where
it could impact the CRLF and DS.
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) 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 LOG. The
highest RQ/LOC ratio was observed for mammals (see Section 5.1).
28
-------
2.4.3. Mechanism of Action
Thiobencarb is a thiocarbamate herbicide. Thiocarbamates inhibit development of seedling
shoots and roots as they emerge from the seed (Ware and Whitacre, 2004). The mode of action
is inhibition of lipid synthesis but not via ACCase inhibition (HRAC, 2005). Thiobencarb works
best when applied after rice seedlings are at the 3-6 leaf stage and when applied prior to weed
emergence (Ampong-Nyarko and DeDatta, 1991). Post emergent applications should be applied
after the 1.5-leaf stage of rice to obtain the best weed kill without damage to rice (Ampong-
Nyarko and DeDatta, 1991).
2.4.4. Use Characterization
Analysis of labeled use information is the critical first step in evaluating the federal action. The
current labels for thiobencarb represent the FIFRA regulatory action; therefore, labeled use and
application rates specified on the labels form the basis of this assessment. The assessment of use
information is critical to the development of the action area and selection of appropriate
modeling scenarios and inputs.
Thiobencarb was first registered under FIFRA in 1975 (USEPA, 1994). There are currently 28
thiobencarb products registered in the U.S. Seven are Section 3 National registrations with one
being a technical grade for use in the manufacture of end-use products. Twenty-one Section 24
Special Local Needs products are registered, two of which may be used in California (see Table
2-4). None of the products registered in California have more than one active ingredient in the
formulation; however, several products recommend the use in combination with propanil for
control of specific weeds.
Thiobencarb is currently registered for use on rice for pre-emergent and early post-emergent
control of barnyard grass, junglerice, sprangletop, crabgrass, fall panicum, dayflower, eclipta,
False pimpernel, emerged Watergrass, and other weeds. The formulations currently registered
include the technical grade which is used to manufacture end-use products, emulsifiable
concentrates, and granular formulations. Thiobencarb may be applied via ground and aerial
applications. Application methods include broadcast spray, granular applicator, high pressure
sprayer, and dilute high volume spray. The timing of application is at dry seeding or wet
seeding, prior to rice and weed emergence, or early post-emergence of weeds.
Table 2-4 presents the uses and corresponding application rates and methods of application
considered in this assessment. There is no further pending mitigation (i.e., reduction in
application rates, cancellation of uses, label language on buffers and spray drift requirements,
etc.) that may impact the conclusions of this assessment in the near future. The following lists
some of the mitigation measures required through the reregi strati on (RED) process that could
impact the evaluation of ecological risk.
Do not apply this product to rice fields with catfish/crayfish farming.
Do not apply this product on rice fields adjacent to catfish or crayfish ponds.
When applying to rice fields, do not release permanent flood water within 14 days of
application of this product (where weather permits).
29
-------
Avoid application of this product within 24 hours of rainfall, or when heavy rain is
expected to occur within 24 hours.
The reregi strati on process was completed on April 10, 2006 and all measures required by the
RED should be reflected on current product labels (Ballard and Errico, 2009). Table 2-5
presents the uses and corresponding application rates and methods of application considered in
this assessment. Appendix D includes a summary of the labels prepared by BEAD.
Table 2-4. Summary of Thiobencarb Products Registered under Section 3 and Section 24c
Special Local Needs for use In California**
Product Name
(EPA Reg. No.)
Bolero Technical
(63588-4)
Bolero 8 EC
(59639-79)
Valent Bolero 10 G
(59639-80)
Bolero 15 G
(59639-112)
Bolero 8 EC
(63588-6)
Bolero 15 G
(63588-14)
Valent Bolero 8 EC
(CA930003)
Valent Bolero 10 G
(CA970036)
Registrant
K.-I
Chemical
U.S.A. Inc.
Valent
U.S.A.
Corporation
Valent
U.S.A.
Corporation
Valent
U.S.A.
Corporation
K.-I
Chemical
U.S.A. Inc
K.-I
Chemical
U.S.A. Inc
Valent
U.S.A.
Corporation
Valent
U.S.A.
Corporation
Percent Active
Ingredient
97.4 thiobencarb
84 thiobencarb
10 thiobencarb
15 thiobencarb
84 thiobencarb
15 thiobencarb
84 thiobencarb
10 thiobencarb
Formulation
Technical*
Emulsifiable
Concentrate
Granular
Granular
Emulsifiable
Concentrate
Granular
Emulsifiable
Concentrate
Granular
Use(s)
Used to make end-use
products
Rice
Rice
Rice
Rice
Rice
Rice
Rice
*The technical grade chemical is only labeled for use in producing end use products.
** RiceBeaux (EPA Registration Number 41085-30, label date 11/05/2008) is a Section 3 national label;
however, it is not for sale or registered for use in California.
30
-------
Table 2-5. Rice Uses of Thiobencarb Assessed in California
Formulation
Emulsifiable
Concentrate
Granular
Maximum
Single
Application
Rate
(Ibs a.i./acre)
3
4
4
4.005
Maximum
Application
Rate per Year
(Ibs a.i./acre)
4
4
NS
4.005
Maximum
Number of
Applications
per Year
NS
NS
NS
1
Minimum
Retreatment
Interval
NS
NS
NS
NS
Appl.
Methods
Aircraft
Ground
Granule
Applicator//
Broadcast
According to the United States Geological Survey's (USGS) national pesticide usage data (based
on information from 1999 to 2004), an average of 1,057,714 Ibs of thiobencarb is applied
nationally in the U.S. (Figure 2-1). All of that is applied to rice as that is the only registered use
for thiobencarb. The highest usage, geographically, is in Central California, Texas, Louisiana,
Mississippi, and Arkansas.
THIOBENCARB - herbicide
2002 estimated annual agricultural use
Average annual use of
active ingredient
(pounds par square mile of agricultural
land in county)
[j no estimated use
D 0.001 to 0.14
D 0.141 to 0.587
D 0.588 to 1.582
D 1.583 to 3.26
>= 3.262
Crops
Total
Pounds Applied
Percent
National Use
Ice
1057714
100.00
Figure 2-l.Thiobencarb Use in Total Pounds per County
31
-------
(from http://water.usgs.gov/nawqa/pnsp/usage/maps/show map.php?vear=02&map=ml903')2
The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis of both
national- and county-level usage information (Carter and Kaul, 2009) using state-level usage
data obtained from USDA-NASS3, Doane (www.doane.com: the full dataset is not provided due
to its proprietary nature) and the California's Department of Pesticide Regulation Pesticide Use
Reporting (CDPR PUR) database4. CDPR PUR is considered a more comprehensive source of
usage data than USDA-NASS or EPA proprietary databases, and thus the usage data reported for
thiobencarb by county in this California-specific assessment were generated using CDPR PUR
data. Eight years (1999-2006) of usage data were included in this analysis. Data from CDPR
PUR were obtained for every agricultural pesticide application made on every use site at the
section level (approximately one square mile) of the public land survey system.5 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. The county level
usage data that were calculated include: average annual pounds applied, average annual area
treated, and average application rate across all eight years. The units of area treated are also
provided where available.
Some uses reported in the CDPR PUR database are different than those considered in the
assessment (alfalfa, cotton, cucumber, wine grape, nursery-outdoor flower, nursery-outdoor
plants in containers, research commodity, tomato, and uncultivated agricultural areas). The uses
considered in this risk assessment represent all currently registered uses according to a review of
all current labels. No other uses are relevant to this assessment. Any other reported use, such as
may be seen in the CDPR PUR database, represent either historic uses that have been canceled,
mis-reported uses, or mis-use. Historical uses, mis-reported uses, and misuse are not considered
part of the federal action and, therefore are not considered in this assessment
According to the CDPR PUR database, a total of 308,491 to 1,006,327 pounds of thiobencarb
were applied annually to registered crops in California between 1999 and 2006 (Figure 2-2). The
average total annual number of pounds applied by county over that eight year period was
635,896 Ibs. Figure 2-3 shows the reported average annual number of pounds used in each
county between 1999 and 2006. Sixty-eight percent of the average annual pounds applied were
2 The pesticide use maps available from this site show the average annual pesticide use intensity expressed as
average weight (in pounds) of a pesticide applied to each square mile of agricultural land in a county. The area of
each map is based on state-level estimates of pesticide use rates for individual crops that were compiled by the
CropLife Foundation, Crop Protection Research Institute based on information collected during 1999 through 2004
and on 2002 Census of Agriculture county crop acreage. The maps do not represent a specific year, but rather show
typical use patterns over the five year period 1999 through 2004.
3 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/estindxl.htm#agchem.
4 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.
5 Most pesticide applications to parks, golf courses, cemeteries, rangeland, pastures, and along roadside and railroad
rights of way, and postharvest treatments of agricultural commodities are reported in the database. The primary
exceptions to the reporting requirement are home-and-garden use and most industrial and institutional uses
(http://www.cdpr.ca.gov/docs/pur/purmain.htm).
32
-------
applied in three counties: Colusa, Sutler, and Butte. Colusa, Sutler, Butte, Glenn, Yuba, Yolo,
Placer, and Sacramento used on average greater than 20,000 pounds thiobencarb a year.
Average and maximum application rates indicate that thiobencarb is commonly used at the
maximum application rate with the average application rate across counties ranging from 3.1-4
Ibs ai/acre (Table 2-6).
Total Thiobencarb Use on Rice in California, 1994 to 2006
Source: Cal PUR Database
1200000.0
1000000.0
^ 800000.0
0. 600000.0
400000.0
200000.0
0.0
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
year
Figure 2-2. Annual Pounds Thiobencarb Applied in California per Year Between 1994 and
2006 (source California PUR database).
33
-------
Average Annual Pounds Thiobencarb Applied in Each County
0 50,000 100,000 150,000 200,000 250
COLUSA
SUITER
BUTTE
GLENN
YUBA
* YOLO
c
0
0 PLACER
SACRAMENTO
FRESNO
SAN JOAQUIN
MERCED
STANISLAUS
I
^^
H
]
]
000
Figure 2-3. Average Annual Pounds Thiobencarb Applied in Each County for the Years
1999-2006. Counties applying a maximum of more than 1000 pounds per year were included in
the figure. See Appendix E for additional information.
Table 2-6. Summary of California Department of Pesticide Registration (CDPR) Pesticide
Use Reporting (PUR) Data from 1999 to 2006 for Currently Registered Thiobencarb Use
on Rice1
County
COLUSA
BUTTE
SUTTER
GLENN
YOLO
YUBA
Average Annual Pounds
Applied
179,406
139,591
130,274
74,925
49,389
18,537
Average Application Rate
(Ibs ai/acre)
3.8
3.9
3.8
4.0
3.9
3.4
34
-------
County
SACRAMENTO
FRESNO
PLACER
SAN JOAQUIN
MERCED
STANISLAUS
MADERA
BUTTE
TEHAMA
Average Annual Pounds
Applied
19,241
9,618
3,423
5,071
4,283
2,053
49
106
34
Average Application Rate
(Ibs ai/acre)
3.8
4.0
3.1
5.5
3.8
4.9*
4.0
4.0
4.0
1 Based on data supplied by BEAD (Carter and Kaul, 2009).
35
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2.5. Assessed Species
Table 2-7 provides a summary of the current distribution, habitat requirements, and life history parameters for the listed species being
assessed. Both of the species being assessed have designated critical habitat. More detailed life-history and distribution information
can be found in Attachment 1 and Attachment 3. See Figure 2-4 and Figure 2-5 for a map of the current range and designated critical
habitat, if applicable, of the assessed listed species.
Table 2-7. Summary of Current Distribution, Habitat Requirements, and Life History Information for the Assessed Listed
Species1
Assessed
Species
Size
Current Range
Habitat Type
Reproductive
Cycle
Diet
California red-
legged 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
Breeding: Nov. to Apr.
Tadpoles: Dec. to Mar.
Young juveniles: Mar. to Sept.
Aquatic-phase : algae,
freshwater aquatic
invertebrates
Terrestrial-phase: aquatic
and terrestrial
invertebrates, small
mammals, fish and frogs
Delta smelt
(Hypomesus
transpacificus)
Up to 120
mm in
length
Suisun Bay and
the Sacramento-
San Joaquin
estuary (known as
the Delta) near
San Francisco
Bay, CA
The species is adapted to living in
fresh and brackish water. They
typically occupy estuarine areas with
salinities below 2 parts per thousand
(although they have been found in
areas up to 18 parts per thousand).
They live along the freshwater edge of
the mixing zone (saltwater-freshwater
interface).
They spawn in fresh or slightly
brackish water upstream of the
mixing zone. Spawning season
usually takes place from late
March through mid-May, although
it may occur from late winter
(Dec.) to early summer (July-
August). Eggs hatch in 9 - 14
days.
They primarily eat
planktonic copepods,
cladocerans, amphipods,
and insect larvae. Larvae
feed on phytoplankton;
juveniles feed on
zooplankton.
1 For more detailed information on the distribution, habitat requirements, and life history information of the assessed listed species, see Attachment 1 and
Attachments.
2 For the purposes of this assessment, tadpoles and submerged adult frogs are considered "aquatic" because exposure pathways in the water are considerably
different than those that occur on land.
36
-------
Delta Smelt Habitat
Suffer
Legend
I Delta smelt critical habitat
Delta smelt occurrence sections
NHD water bodies
Streams and Rivers
CAcounties
(024 8 12 16
1:635,406-
Map created by US EPA on 1 0/6/2009. Projection: AlbersEqual
Area Conic USGS, North American Datum of 1983 (NAD 1983).
River data from ESRI (2004), county boundariesfrom ESRI (2002),
water bodies from NHDPIus (2006).
Delta Smelt section information obtained from Case No. 07-2794-JCS.
Critical habitat data obtained from http:/crithab.fws.govl.
i^ ^ sarta <$ruz
Figure 2-4. Delta smelt critical habitat (USFWS, 2009) and Occurrence Sections identified
in Case No. 07-2794-JCS.
37
-------
Legend
Recovery Unit Boundaries
Currently Occupied Core Areas
Critical Habitat
CNDDB Occurence Sections
County Boundanes rj
45
Figure 2-5. Recovery Unit, Core Area, Critical Habitat, and Occurrence Designations for
CRLF.
2.6. Designated Critical Habitat
Critical habitat has been designated for the CRLF and the DS. '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
38
-------
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 2-8 describes the
PCEs for the critical habitats designated for the CRLF and the DS.
Table 2-8. Designated Critical Habitat PCEs for the CRLF and PS.1
Species,
Reference
CRLF,
50 CFR
414.12(b), 2006
Delta Smelt,
59 FR 65256
65279, 1994
Primary Constituent Elements (PCEs)
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 pre-metamorphs (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
Alteration of chemical characteristics necessary for normal growth and viability of juvenile and
adult CRLFs and their food source.
Spawning Habitat shallow, fresh or slightly brackish backwater sloughs and edge waters to
ensure egg hatching and larval viability. Spawning areas also must provide suitable water
quality (i.e., low concentrations of pollutants) and substrates for egg attachment (e.g.,
submerged tree roots and branches and emergent vegetation).
Larval and Juvenile Transport Sacramento and San Joaquin Rivers and their tributary
channels must be protected from physical disturbance and flow disruption. Adequate river flow
is necessary to transport larvae from upstream spawning areas to rearing habitat in Suisun Bay.
Suitable water quality must be provided so that maturation is not impaired by pollutant
concentrations.
Rearing Habitat Maintenance of the 2 parts per thousand isohaline and suitable water quality
(low concentrations of pollutants) within the estuary is necessary to provide delta smelt larvae
and juveniles a shallow protective, food-rich environment in which to mature to adulthood.
39
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Species,
Reference
Primary Constituent Elements (PCEs)
Adult Migration Unrestricted access to suitable spawning habitat in a period that may extend
from December to July. Adequate flow and suitable water quality may need to be maintained to
attract migrating adults in the Sacramento and San Joaquin River channels and their associated
tributaries. These areas also should be protected from physical disturbance and flow disruption
during migratory periods.
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, physical-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 the DS). Activities that may destroy or
adversely modify critical habitat are those that alter the PCEs and jeopardize the continued
existence of the species. Evaluation of actions related to use of thiobencarb that may alter the
PCEs of the designated critical habitat for the CRLF and DS 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 thiobencarb is expected to directly impact living organisms within the
action area, critical habitat analysis for thiobencarb 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 thiobencarb is likely to encompass considerable portions of the United States based on the
areas where rice is grown. 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 and DS
and their designated critical habitat within the state of California.
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 thiobencarb.
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. The analysis indicates that for thiobencarb, use on rice is
considered as part of the federal action evaluated in this assessment.
40
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Following a determination of the assessed uses, an evaluation of the potential "footprint" of
thiobencarb 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 (e.g., cultivated crops representing use on rice) that
make up the initial area of concern for thiobencarb is presented in Figure 2-6.
41
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Thiobencarb Use - Initial Area of Concern
Legend
^| Cultivated
| County boundaries
0 2040
i Kilo meters
80 120 160
Compiled from California County boundaries (ESRI, 2002),
USDA Gap Analysis Program Orchard/ Vineyard La ndc over (GAP)
National Land Cover Data bass (NLCD) (MRLC, 2001)
Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Division.
Projection: Albers Equal Area Conic USGS, North American
Datumof19S3(r*D1983).
8/2009
Figure 2-6. Initial area of concern, or "footprint" of potential use, for thiobencarb.
42
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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
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
thiobencarb may be expected to have on the environment, the exposure levels to thiobencarb that
are associated with those effects, and the best available information concerning the use of
thiobencarb 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.
Due to the lack of a defined no effect concentration for the most sensitive reported effect and/or
a positive result in a mutagenicity test, the spatial extent of the action area (i.e., the boundary
where exposures and potential effects are less than the Agency's LOG) for thiobencarb cannot be
determined.6,7 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).
An evaluation of usage information was conducted to determine the area where use of
thiobencarb may impact the assessed species. This analysis is used to characterize where
predicted exposures are most likely to occur, but does not preclude use in other portions of the
action area. A more detailed review of the county-level use information was also completed.
These data suggest that thiobencarb is used on rice in California and that rice is grown in areas
where the CRLF and DS are commonly found.
6 A life-cycle Sheepshead minnow study had significant effects observed at all test concentrations (MRID
00079112).
7 Thiobencarb did not show mutagenicity in three (Ames assay, dominant lethal assay in mice, and clastogenicity
test in human lymphocytes) of four mutagenicity tests conducted (Appendix L). In a micronucleus test in mice,
statistically significant increases in the incidence of micronuclei were observed in both sexes (MRID 40352402).
43
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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."8 Selection of the assessment endpoints is based on valued entities (e.g.,
CRLF and DS, 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 transport pathways of thiobencarb (e.g.,
runoff, spray drift, etc), and the routes by which ecological receptors are exposed to thiobencarb
(e.g., direct contact, etc.).
2.8.1. Assessment Endpoints
Assessment endpoints for the CRLF and DS 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 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 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 discussion of 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. A summary of the assessment endpoints and measures of ecological effect selected to
characterize potential assessed direct and indirect risks for each of the assessed species
associated with exposure to thiobencarb is provided in Section 2.5 and Table 2-9.
As described in the Agency's Overview Document (USEPA, 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, E/M fish, invertebrates, aquatic
plants, birds (surrogate for terrestrial-phase amphibians), 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 thiobencarb.
8 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
44
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Table 2-9 identifies the taxa used to assess the potential for direct and indirect effects from the
uses of thiobencarb 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 2-10.
Table 2-9. Taxa Used in the Analyses of Direct and Indirect Effects for the Assessed Listed
s
Listed
Species
California
red-legged
frog
Delta
smelt
pecies.
Birds/
Terr.
Amphibian
Direct
Indirect
(prey)
N/A
Mammals
Indirect
(prey)
N/A
Terr.
Plants
Indirect
(habitat)
Indirect
(habitat)
Terr.
Inverts.
Indirect
(prey)
N/A
FW Fish and
Aquatic
Phase
Amphibians
Direct
Indirect
(prey)
Direct
FW
Inverts.
Indirect
(prey)
Indirect
(prey)
E/M
Fish
N/A
Direct
Estuarine
/Marine
Inverts.
N/A
Indirect
(prey)
Aquatic
Plants
Indirect
(food/
habitat)
(food/
habitat)
Abbreviations: N/A = Not applicable; Terr. = Terrestrial; Invert. = Invertebrate; FW = Freshwater;
E/M=Estuarine/marine
1 The most sensitive species across freshwater and saltwater environments was used to assess effects for the DS.
Table 2-10. Taxa and Assessment Endpoints Used to Evaluate the Potential for Use of
Thiobencarb 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
1. Freshwater Fish and
Aquatic-phase
Amphibians
Direct Effect -
-Aquatic-phase CRLF
-DS
Survival, growth, and
reproduction of individuals
via direct effects
Indirect Effect (prey)
-Aquatic and terrestrial-
phase CRLF
Survival, growth, and
reproduction of individuals
via indirect effects on
aquatic prey food supply
(i.e., fish and aquatic-phase
amphibians)
la. Amphibian acute LC50 (ECOTOX) or
most sensitive fish acute LC50 (guideline or
ECOTOX) if no suitable amphibian data are
available
Ib. Amphibian chronic NOAEC
(ECOTOX) or most sensitive fish chronic
NOAEC (guideline or ECOTOX)
Ic. Amphibian early-life stage data
(ECOTOX) or most sensitive fish early-life
stage NOAEC (guideline or ECOTOX)
2. Freshwater
Invertebrates
Indirect Effect (prey)
-Aquatic and terrestrial-
phase CRLF
-DS
Survival, growth, and
reproduction of individuals
via indirect effects on
aquatic prey food supply
(i.e., freshwater
invertebrates)
2a. Most sensitive freshwater invertebrate
EC50 (guideline or ECOTOX)
2b. Most sensitive freshwater invertebrate
chronic NOAEC (guideline or ECOTOX)
3. Estuarine/Marine Fish
Direct Effect -
- DS
Indirect Effect (prey)
-DS
Survival, growth, and
reproduction of individuals
via indirect effects on
aquatic prey food supply
(i.e., EM fish)
3a. Most sensitive E/M fish EC50 (guideline
or ECOTOX)
3b. Most sensitive E/M fish chronic
NOAEC (guideline or ECOTOX)
4. Estuarine/Marine
Invertebrates
Indirect Effect (prey)
Survival, growth, and
reproduction of individuals
4a. Most sensitive E/M invertebrate EC50
(guideline or ECOTOX)
45
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Taxa Used to Assess
Direct and/or Indirect
Effects to Assessed
Species
Assessed Listed
Species
Assessment Endpoints
Measures of Ecological Effects
via indirect effects on
aquatic prey food supply
(i.e., estuarine/marine
invertebrates)
4b. Most sensitive E/M invertebrate chronic
NOAEC (guideline orECOTOX)
5. Aquatic Plants
(freshwater/marine)
Indirect Effect
(food/habitat)
-Aquatic-phase CRLF
-DS
Survival, growth, and
reproduction of individuals
via indirect effects on
habitat, cover, food supply,
and/or primary productivity
(i.e., aquatic plant
community)
5a. Vascular plant acute EC50 (duckweed
guideline test or ECOTOX vascular plant)
5b. Non-vascular plant acute EC50
(freshwater algae or diatom, or ECOTOX
non-vascular)
6. Birds
Direct Effect
-Terrestrial-phase CRLF
Survival, growth, and
reproduction of individuals
via direct effects
Indirect Effect (prey)
-CRLF
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (birds)
6a. Most sensitive bird or terrestrial-phase
amphibian acute LC50 or LD50 (guideline or
ECOTOX)
6b. Most sensitive birdb or terrestrial-phase
amphibian chronic NOAEC (guideline or
ECOTOX)
7. Mammals
Direct Effect
-Terrestrial-phase CRLF
Survival, growth, and
reproduction of individuals
via direct effects
Indirect Effect (prey)
-Terrestrial-phase CRLF
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (mammals)
la. Most sensitive laboratory rat acute LC50
or LD50 (guideline or ECOTOX)
7b. Most sensitive laboratory rat chronic
NOAEC (guideline orECOTOX)
8. Terrestrial
Invertebrates
Indirect Effect (prey)
-Terrestrial-phase CRLF
Survival, growth, and
reproduction of individuals
via direct effects
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (terrestrial
invertebrates)
8a. Most sensitive terrestrial invertebrate
acute EC50 or LC50 (guideline or ECOTOX)C
8b. Most sensitive terrestrial invertebrate
chronic NOAEC (guideline orECOTOX)
9. Terrestrial Plants
Indirect Effect
(food/habitat) (non-
obligate relationship)
-Aquatic and terrestrial-
phase CRLF
-DS
Survival, growth, and
reproduction of individuals
via indirect effects on food
and habitat (i.e., riparian
and upland vegetation)
9a. Distribution of EC2s for monocots
(seedling emergence, vegetative vigor, or
ECOTOX
9b. Distribution of EC2s for dicots (seedling
emergence, vegetative vigor, or ECOTOX)
Indirect Effect
(food/habitat) (obligate
relationship)
-Terrestrial and aquatic
phase CRLF
-DS
46
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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 thiobencarb 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
modify 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 thiobencarb effects data are available.
Assessment endpoints used to evaluate potential for direct and indirect effects are equivalent to
the assessment endpoints used to evaluate potential effects to designated critical habitat. If a
potential for direct or indirect effects is found, then there is also a potential for effects to critical
habitat. 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.
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 (USEPA, 1998). For this assessment, the risk is stressor-linked,
where the stressor is the release of thiobencarb to the environment. The following risk
hypotheses are presumed in this assessment:
The labeled use of thiobencarb within the action area may:
directly affect the CRLF and/or DS by causing mortality or by adversely affecting growth
or fecundity;
indirectly affect the CRLF and/or DS and/or modify their designated critical habitat by
reducing or changing the composition of food supply;
indirectly affect the CRLF and/or DS 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 and/or DS 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 and/or DS 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).
47
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2.9.2. Diagram
The conceptual model is a graphic representation of the structure of the risk assessment. It
specifies the thiobencarb release mechanisms, biological receptor types, and effects endpoints of
potential concern. The conceptual models for aquatic and terrestrial phases of the CRLF and DS
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 not quantitatively considered because the
contribution of those potential exposure routes to potential risks to the CRLF and DS and
modification to designated critical habitat is expected to be negligible.
Stressor
Source
Exposure
Media
Thiobencarb Applied to
Rice
i j
Dermal uptake/lngestion
Root uptake -^ T
Wet/dry deposition
Terrestrial/riparian
plants grasses/forbs,
fruit, seeds (trees,
shrubs)
Terrestria
insects
Terrestrial-
phase
amphibians
Birds/terrestrial-
phase
amphibians/
reptiles/mammals
Receptors
Attribute
Change
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
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
Figure 2-7. Conceptual Model for Terrestrial-Phase of the Assessed Species.
48
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Stressor
Source
Exposure
Media
Receptors
Attribute
Change
Thiobencarb Applied to
Rice
1 i ... . . J
| Spray drift "| | Runoff | I Soil \
Groundwater
Surface water/
Sediment
Long range
and/or
atmospheric
transport
-Wet/dry deposition
Uptake/gills
or integument
Uptake/gills
or integument
Aquatic Animals
Invertebrates
Vertebrates
Ingestion
Fish/aquatic-
phase
amphibians
"""Piscivorous
mammals and
birds
I
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Uptake/cell,
roots, leaves
Aquatic Plants
Non-vascular
Vascular
Ingestion
Food chain
Reduction in algae
Reduction in prey
Modification of
PCEs
related to prey
availability
Riparian plant
terrestrial
exposure
pathways
Habitat integrity
Reduction in primary
productivity
Reduced cover
Community change
Modification of PCEs related to
habitat
Figure 2-8. Conceptual Model for Aquatic-Phase of the Assessed Species
2.10. Analysis Plan
In order to address the risk hypothesis, the potential for direct and indirect effects to the CRLF
and DS, prey items, and habitat is estimated based on a taxon-level approach. In the following
sections, the use, environmental fate, and ecological effects of thiobencarb 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 (USEPA, 2004), the likelihood of effects to individual organisms
from particular uses of thiobencarb is estimated using the probit dose-response slope and either
the level of concern (discussed below) or actual calculated risk quotient value.
49
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2.10.1. Measures of Exposure
The environmental fate properties of thiobencarb along with available monitoring data indicate
that water and sediment discharge from rice paddies and spray drift are the principle potential
transport mechanisms of thiobencarb to the aquatic and terrestrial habitats. Thiobencarb is also
semi-volatile (e.g., falls between nonvolatile and intermediate to high volatility) and may travel
to nearby fields in the air or to remote areas via long range transport (based on volatility
classification for vapor pressure in OPPTS Guideline 835.6100 and monitoring data). In this
assessment, transport of thiobencarb in rice paddy water, and spray drift is considered in deriving
quantitative estimates of thiobencarb exposure to CRLF and DS and their prey and habitats.
Additionally, exposure due to deposition of thiobencarb in precipitation and movement of
thiobencarb into ground water were qualitatively assessed. Some bioaccumulation may occur;
however, depuration of thiobencarb is almost complete after 30 days and the log K0w of
thiobencarb is below four (see Section 2.4.1.3g ) (Ceesay, 2002). Therefore, we do not expect
bioaccumulation of thiobencarb to be a major exposure pathway for the CRLF and DS.
Measures of exposure are based on aquatic and terrestrial models that predict estimated
environmental concentrations (EECs) of thiobencarb using maximum labeled application rates
and methods of application. The models used to predict aquatic EECs are the Tier I Rice Model
and Tier I Rice Model modified to include aquatic dissipation. Monitoring results were used to
estimate chronic exposure to the DS. The model used to predict terrestrial EECs on food items is
T-REX. The model used to derive EECs relevant to terrestrial and wetland plants is TerrPlant.
These models are parameterized using relevant reviewed registrant-submitted environmental fate
data.
2.10.1.a. Estimating Exposure in the Aquatic Environment
Concentrations of thiobencarb in surface water were estimated using the standard Tier I Rice
Model and a modified version of the Tier I Rice Model that accounts for possible dissipation in
the paddy water.
The original Tier I Rice Model relies on an equilibrium partitioning concept to provide
conservative screening estimates of EECs resulting from application of pesticides to rice paddies.
When a pesticide is applied to a rice paddy, the model assumes that it will instantaneously
partition between a water phase and a sediment phase. The Tier I Rice Model was calibrated to
generate estimates that are similar to or greater than dissolved concentrations measured within
rice paddies and in discharged paddy water. The model does not account for pesticide
degradation, volatilization, dilution, or other dissipation processes. The sediment interaction
depth was determined by calibrating the model to maximum residues measured in paddy water in
dissipation studies. Pesticide degradation, mass transfer, volatilization, dilution and other
dissipation processes may have occurred in those datasets but probably had little affect on the
calibration because the model was calibrated to the maximum measured residues. The model was
not evaluated or calibrated for concentrations measured in sediment and does not account for
residues bound to suspended sediment. Guidance for using the Tier I Rice Model may be found
50
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on the U.S. Environmental Protection Agency (EPA) Water Models web-page, see
http://www.epa.gov/oppefedl/models/water/tfrice (Bradbury, 2007).
The Tier I Rice Model was provisionally modified to account for dissipation in the paddy water
during the 14 day holding period required prior to water release from the paddy. Rates of
dissipation were based on the slowest dissipation rate observed in aquatic dissipation studies.
Assumptions of the Tier I Rice Model, other than stability to dissipation and degradation, apply
to the modified model.
2.10.1.b. Estimating Exposure in the Terrestrial Environment
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, 10/08/2009). This
model incorporates the Kenaga nomograph, as modified by Fletcher et al. (1994), which is based
on a large set of actual field residue data (Fletcher et al., 1994). The upper limit values from the
nomograph represented the 95th percentile of residue values from actual field measurements
(Hoerger and Kenaga, 1972).
For modeling purposes, direct exposures of the CRLF and DS to thiobencarb through
contaminated food are estimated using the EECs for the small bird (20 g) which consumes small
insects. Dietary-based and dose-based exposures of potential prey (small mammals) are assessed
using the small mammal (15 g) which consumes short grass. The small bird (20g) consuming
small insects and the small mammal (15g) consuming short grass are used because these
categories represent the largest RQs of the size and dietary categories in T-REX that are
appropriate surrogates for the CRLF and one of its prey items. Estimated exposures of terrestrial
insects to thiobencarb are bound by using the dietary based EECs for small insects and large
insects.
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 1.3.1) 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.
EECs for terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant (version
1.2.2, 12/26/2006). This model uses estimates of pesticides in runoff and in spray drift to
calculate EECs. EECs are based upon solubility, application rate and minimum incorporation
51
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depth. Runoff is not expected to commonly occur in rice paddies; therefore, only the exposure
estimated based on spray drift are used in the assessment.
Spray drift models, AGDISP and/or AgDRIFT are used to assess exposures of terrestrial animals
to thiobencarb deposited on terrestrial habitats by spray drift. In addition to the buffered area
from the spray drift analysis, the downstream extent of thiobencarb that exceeds the LOG for the
effects determination is also considered.
2.10.2. Measures of Effect
Data identified in Section 2.8 are used as measures of effect for direct and indirect effects to the
CRLF and DS. 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. Each publication abstracted for the ECOTOX database effort is assigned a
unique reference number. The number is an E followed by a five digit number and is used to
identify ECOTOX references in this document.
The assessment of risk for direct effects to the terrestrial-phase CRLF makes the assumption that
toxicity of thiobencarb 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 CRLF (again, this also applies to potential prey items). Data on
aquatic phase amphibians will be used qualitatively in the risk assessment.
The acute measures of effect used for animals in this screening level assessment are the LD50,
LCso and ECso. LD stands for "Lethal Dose", and LDso 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 LCso is the concentration of a chemical that is estimated to kill 50% of the
test organisms. EC stands for "Effective Concentration" and the ECso 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
NOAEC. NOAEL stands for "No Ob served-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 ECso 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
52
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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.
2.10.2.a. Integration of Exposure and Effects
Risk characterization is the integration of exposure and ecological effects characterization to
determine the potential ecological risk from agricultural and non-agricultural uses of
thiobencarb, and the likelihood of direct and indirect effects to CRLF and DS 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 thiobencarb
risks, the risk quotient (RQ) method is used to compare exposure and measured toxicity values.
EECs are divided by acute and chronic toxicity values. The resulting RQs are then compared to
the Agency's levels of concern (LOCs) (USEPA, 2004)(see Appendix F).
For this endangered species assessment, listed species LOCs are used for comparing RQ values
for acute and chronic exposures of thiobencarb directly to the CRLF and DS. If estimated
exposures directly to the assessed species of thiobencarb resulting from a particular use are
sufficient to exceed the listed species LOG, 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
thiobencarb resulting from a particular use are sufficient to exceed the listed species LOG, then
the effects determination for that use is a "may affect." If the RQ being considered also exceeds
the non-listed species acute risk LOG, then the effects determination is a LAA. If the acute RQ
is between the listed species LOG and the non-listed acute risk species LOG, 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 LOG for plants, the effects determination is "may
affect". Further information on LOCs is provided in Appendix F.
2.10.2.b. 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 (USEPA, 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
thiobencarb 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
53
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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 estimate) as the slope parameter
for the spreadsheet. In addition, the acute RQ is entered as the desired threshold.
3. Exposure Assessment
Thiobencarb is formulated as an emulsifiable concentrate and as granules. It may be applied
via ground or aerial application methods. Risks from ground boom and aerial applications
are considered in this assessment because they are expected to result in the highest off-target
levels of thiobencarb due to generally higher spray drift levels. Ground boom and aerial
modes of application tend to use lower volumes of application applied in finer sprays than
applications coincident with sprayers and spreaders and thus have a higher potential for off-
target movement via spray drift.
3.1. Aquatic Exposure Assessment
The estimated surface water environmental concentrations (EEC) presented here are based on the
Tier 1 Rice Model, which assumes flooded fields (wet seeding) and on Aquatic Field Dissipation
studies. Based on the environmental fate data for thiobencarb, input parameters used for the Tier
1 Rice Model are shown in Table 3-1.
Table 3-1. Chemical Specific Input Parameters for Thiobencarb
Parameter
Maximum application rate
Maximum number of applications
Partition coefficient Kocb
Input Value and Unit
4 Ib/acre
1
900 mL/g OC
(average of 5 values, range 384-
1435)
Source
Product Labels
Product Labels
MRID 41215313
The Tier 1 Rice Model vl.O (May 8, 2007) estimates the peak concentration of pesticide in a 0.1
meter-deep rice paddy, and does not account for any dissipation processes, with the exception of
partitioning to sediment. The relevant equation is:
Cw = m*' / (0.00105 + 0.0000013*Koc)
Where Cw is the paddy water concentration (ppb), mai' is the application rate (kg/hectare) and
Koc is the organic-carbon normalized partition coefficient. The result is given in Table 3-2.
54
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Table 3-2. Results of Tier 1 Rice Model
Application Rate
4 Ib/acre (4.48 kg/hectare)
Peak EEC, ppb
2018.
This Tier I Rice Model exposure estimate was refined by allowing the concentration in water
(2,018 ppb) to decay, using a first-order exponential decay equation, at the slower of the two
rates from the two available wet-seeded aquatic field dissipation studies (decay rate, 0.1252/day,
half-life 5.5 days). The decay rate constants were k=0.1252 (halflife 5.54 days) for MRID
43404005, and k=0.1596 (halflife 4.34 days) for Ross & Sava (1986). See Figure 3-1 for a graph
of the result. This analysis shows that at 14 days, the concentration is 350 ppb; at 19 days, 187
ppb, and at 30 days, 47 ppb. A chronic estimate of exposure in the rice paddy was estimated as
an average 14-day concentration of 968 |ig/L. A 21-day average and 60-day average were not
estimated from the Tier 1 Rice model because rice paddy water is expected to be released after
14 days. This approach neglects any thiobencarb that may be adsorbed to sediment, however the
exposures calculated in the water column are sufficient to exceed Agency Levels of Concern.
Thus, explicit consideration of adsorbed thiobencarb's direct or indirect effects would only
strengthen this conclusion.
2500 T~
2000
1500
1000
500
»
10
15
20 25
day
30
35
40
45
Figure 3-1. Estimated Concentrations of Thiobencarb in Water Starting with the Tier I
Rice Model Estimated Initial Concentration and Using the Field Decay Rate from an
Aquatic Dissipation Study (decay rate = 0.1252/day, half-life = 5.5 days).
55
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Since the Rice Model cannot provide time-averaged EECs for calculation of chronic RQ for
aquatic invertebrate and fish, respectively, a spreadsheet was used to estimate them. For risk
estimation, a 14-day average in the rice paddy was calculated using the Tier 1 Rice Model peak
concentration (2018 ppb) as a starting point. Concentrations on days 1 to 14 were calculated
using a first-order decay model with the slower field dissipation rate (5.5 days), and the results
averaged to get the 14-day average EEC for chronic RQ calculation (968 ppb). A 14th-day value
(350 ppb) was also calculated for acute exposure characterization on the day of paddy water
release
For characterization purposes, 21-day and 60-day chronic concentrations were calculated from
the field dissipation studies (MRID 43404005 and Ross & Sava). For each study, concentrations
were projected out to day 60 from the peak concentration day (not day one), using the study-
specific decay rate. The 21-day or 60-day average was then calculated from day zero to day 21
or day 60. The estimated aquatic EECs are shown in Table 3-3. The values are similar for the
two studies: about 205 ppb for the 21-day average and about 75 ppb for the 60-day average.
These values are lower than the 14-day average (968 ppb) used in risk estimation and may be
used for characterization of chronic risks.
The in-paddy exposure assessment is considered conservative, since it uses the Tier 1 Rice
Model, and produces no EECs that are below monitored concentrations. The peak concentration
(2018 ppb) is higher than the observed peak in either field dissipation study (438 to 576 ppb).
The highest observed concentration in California surface water (170 ppb in 1982 at Colusa Basin
Drain #5, which is known to the location most contaminated by rice herbicides in the state) is
lower than the concentration calculated by this method for the day of paddy water release (350
ppb on day 14). In addition, the monitoring data are considered to be robust and suitable for
exposure assessment in receiving waters.
Table 3-3. Aquatic Exposure using 4 Ib/acre (4.48 kg/hectare)
Exposure reference
Peak
EEC,
ppb
14-Day
Average
in Paddy
Water
14-day
Release
Value
21 day
average
60 day
average
Modeled Values In Paddy and When Paddy Water is Released (Risk Estimation)
Rice Model Tier I (Peak Concentration in Paddy)
Tier I Rice Model and California Wet Seeded Rice
Aquatic Dissipation Rate (MRID 43404005)
2018
2018
968
350
Concentrations Observed In Aquatic Dissipation Studies (In Rice Paddy) (Risk Characterization)
California Wet Seeded Rice Aquatic Dissipation
(MRID 43404005)
Aquatic Dissipation Study (Ross and Sava, 1986)
438
576
202
209
80
70
In the submitted study (MRID 43404005), the water concentration of parent thiobencarb fell to
107.7 ppb (n=4) on day 10 after application, and 44.2 ppb (n=4) on day 14 after a single
application of granular formulation. Including the two measured degradates (thiobencarb
56
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sulfoxide and 4-chlorobenzylmethylsulfone), the total water concentrations were 125.8 ppb on
day 10, 58.5 ppb on day 14, and 19.3 ppb on day 21. Results from the California wet seeded rice
aquatic dissipation study are graphed in Figure 3-2. The granular formulation (Bolero 10G) may
have resulted in the delayed peak concentration observed at 3 days after the application.
500
450
400
350
300
a. 250
200
150
100
50
012345678 910111213141516171819202122232425262728293031323334353637383940
day after application
Figure 3-2. Water Concentrations of Thiobencarb and Two Degradates in California
Aquatic Dissipation Study on Wet Seeded Rice After Application of Granular Formulation
of Thiobencarb (MRID 43404005).9
In Ross & Sava (1986), the water concentration of parent thiobencarb after a single application
was 367 ppb on day 8, 56 ppb on day 16, and 8 ppb on day 32. No degradates were measured.
These data are graphed in Figure 3-3.
9 The sulfoxide in the Figure legend stands for thiobencarb sulfoxide and 4cbms stands for 4-
chlorobenzylmethylsulfone.
57
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600 -
550 -
500 -
450 -
400 -
350 -
300 -
250 -
200 -
150 -
100 -
50 -
0 -
» ppb parent
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
day after application
Figure 3-3. Thiobencarb Concentrations in Water in Aquatic Field Study (Ross and Sava,
1986).
3.1.1. Existing Monitoring Data
A critical step in the process of characterizing EECs is comparing the modeled estimates with
available surface water monitoring data. Included in this assessment are thiobencarb data from
the USGS National Water Quality Assessment (NAWQA) program
(http://water.usgs.gov/nawqa) and data from the CADPR. In addition, atmospheric monitoring
data for thiobencarb from the open literature are summarized below.
3.1.1.a. Characterization of Surface Water Monitoring Data
Rice is grown in the Sacramento and San Joaquin river valleys to the north and south of San
Francisco Bay. Discharged paddy water containing thiobencarb residues flows through the Delta
on its way to the bay. In order to quantify the exposure in time and space, all surface water
monitoring results for thiobencarb from the California surface water database and from the
NAWQA program were retrieved. Data were also obtained from Orlando and Kuivila (2004).
Both the highest exposures and those furthest downstream from the rice growing areas on each
river are characterized below. These exposures were calculated to estimate CRLF and DS
exposures in habitats other than directly in rice paddies. While CRLF may use rice paddies as
habitat, DS will not be exposed to water in the rice paddy as they do not have a way to travel into
the rice paddy. They are found primarily below Isleton on the Sacramento River, below
Mossdale on the San Joaquin River, and in the Suisan Bay (USDOI, 2008). During spawning
(February through June), they may be found in:
58
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"(1) the Sacramento River as high as Sacramento, (2) the Mokelumne River system, (3)
the Cache Slough region, (4) the Delta, (5) Montezuma Slough, (6) Suisun Bay, (7)
Suisun Marsh, (8) Carquinez Strait, (9) Napa River, and (10) San Pablo Bay." (USDOI,
2008)
Since 1982, they are primarily found in the northwestern Delta in the channel of the Sacramento
River and the Suisan Bay (USDOI, 2008).
The highest concentrations observed in receiving waters occur at Colusa Basin Drain #5 on the
Sacramento River. Monitoring results for this site are shown in Figure 3-4. This waterway does
not meet state standards for water quality due to pesticide residues, principally from rice
production. The highest peak concentration observed since the 1984 establishment of a 14-day
holding requirement for paddy water treated with thiobencarb is 37.4 |ig/L in 1994. Prior to the
holding time requirement, thiobencarb was as high as 170 |ig/L in 1982 (Orlando and Kuivila,
2004). This concentration is within a factor of two of the day-14 release water concentration
(350 ppb), as calculated by the extended Tier 1 Rice Model (Table 3-3 above).
The highest time-averaged exposure observed at Colusa Basin Drain is 5.37 |ig/L, over the
period of May 9 to June 22, 2000. This was calculated as the average of 14 samples taken over
the 44-day period.
Further downstream, thiobencarb residues are lower, but still detectable. On the Sacramento
River at Freeport, the highest recent peak concentration was 0.65 |ig/L on May 22, 2002. The
chronic exposure at this station was 0.146 |ig/L over the period of May 22 to Nov 13, 2002
(based on 5 samples).
On the San Joaquin River, thiobencarb was detected as far downstream as the San Joaquin River
at Vernalis station, with a peak concentration of 0.528 |ig/L (May 22, 1993), and a chronic
concentration of 0.189 |ig/L (May 22 to May 30, 1993). At the San Joaquin River at Maze Rd
bridge station, a peak concentration of 0.697 jig/L was observed on June 12, 2001.
Each of these NAWQA stations is 20 miles or more upstream from the Suisun Bay and its
tributaries. Thus, there may be further dilution of the thiobencarb residues and lower exposure
for the DS when it is not spawning. A recent USGS paper (Kuivila and Jennings, 2007)
measured thiobencarb at Mallard Island, at the eastern end of Suisun Bay in a tidally-influenced
area, 8 km downstream of the confluence of the Sacramento and San Joaquin rivers. Samples
were collected daily or twice daily from January to June, 1996. Thiobencarb was found in 28%
of the samples with a maximum concentration of 66 ng/L (0.066 |ig/L). This is a factor often
lower than the concentrations measured at Freeport, the Maze Road bridge or Vernalis.
59
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40
35
30
25
a. 20
Q.
15
10
T
T
.
A
31-Jan-93 15-Jun-94 28-Oct-95 11-Mar-97 24-Jul-98 06-Dec-99 19-Apr-01 01-Sep-02 14-Jan-04
date
Figure 3-4. Monitoring Results Observed in the Colusa Basin Drain #5, Sacramento River,
1992 - 2002.
S.l.l.b. USGS NAWQA Surface Water Data
Data from the USGS NAWQA website for thiobencarb occurrence in surface water in California
were obtained on September 21, 2009. A total of 2,117 surface water samples were analyzed for
thiobencarb spanning a period from 1992 to 2009. Of these, a total of 1185 samples detected
thiobencarb above the long term method detection limit of 0.002 |ig/L (frequency of detection of
56%). Detections ranged from <0.002 to 4.38 |ig L"1 (Gilliom et a/., 2007). The highest
detections generally occurred in May, June, and July. The highest concentration was measured
in a sample collected in Yolo County of the Colusa Basin in May 1997.
3.1.I.C.California Department of Pesticide Regulation (CPR) Data
CDPR maintains a database of monitoring data of pesticides in CA surface waters. Data are
available from 1990-2005 for 27 counties for several pesticides and degradates. The sampled
water bodies include rivers, creeks, urban streams, agricultural drains, the San Francisco Bay
delta region and storm water runoff from urban areas. The database contains data from 51
different studies by federal, state and local agencies as well as groups from private industry and
environmental interests. Some data reported in this database are also reported by USGS in
NAWQA; therefore, there is some overlap between these two data sets. Unlike NAWQA data,
the land use (e.g., agriculture, urban) associated with the watershed of the sampled surface
60
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waters is not defined in the CDPR database; therefore, the available data do not allow for a link
of the general use pattern and the individual data.
Surface water monitoring data were obtained from the California Department of Pesticide
regulation (CDPR) and all data with analysis for thiobencarb were extracted. A total of 3,384
water samples were analyzed for thiobencarb. There were 427 detections (13% detection
frequency), ranging from 0.004 and 37.4 |ig/L. Detections of thiobencarb were reported in
Alpine, Butte, Colusa, El Dorado, Merced, Nevada, Orange, Riverside, Sacramento, San
Bernardino, San Joaquin, Stanislaus, Sutler, Yolo and Yuba counties. Samples with detections
were collected between March 1991 and January 1998. The limit of quantitation ranged from
0.0002- 1.0 |ig/L.
B.l.l.d. Halls Bayou, Arkansas (MRID 00079986)
A field study was conducted in rice fields bordering Halls Bayou, a tidally influenced, narrow
stream that empties into West Bay near Galveston, Texas. Sampling points were located 500
feet upstream and downstream of the rice paddy and in Halls Bayou. The highest concentrations
of thiobencarb were measured on a day when heavy rainfall (3.23 inches) occurred on the same
day that thiobencarb was applied, resulting in an unscheduled flush overflow. Peak thiobencarb
concentrations were 8.9 mg/L (8900 jig a.i./L) where the tail water exited the rice field and 690
|ig/L at the point where the drainage water entered Halls Bayou. The highest concentrations
measured in the Halls Bayou on days that were not associated with heavy rainfall were 83 |ig/L
at the upstream station (E) and 64 jig/L at the downstream station (F). These study results may
not be applicable to California rice growing areas.
3.1.1.e. USGS NAWQA Groundwater Data
NAWQA Database. Ground water monitoring data from the United States Geological Survey
(USGS) NAWQA program were obtained on September 21, 2009. Concentrations ranged from
0.002 to 0.025 ng/L. Thiobencarb was detected twice in Colusa County, CA, at 0.014 to 0.025
ppb (Eckel, 2008). All other detections were <0.016 - <0.002 |ig/L. The highest concentration
was detected in Colusa, County. The long term method detection level is 0.002 |ig/L (Gilliom et
al, 2007).
3.1.l.f. Atmospheric Monitoring Data
Thiobencarb has been found in atmospheric samples throughout the United States, including in
California and Mississippi. The maximum reported concentration of thiobencarb was 67.8 ng/m3
Table 3-4).
Seiber et al. 1989. Ambient air monitoring for thiobencarb was conducted in May and June
1986 at four sites in California (Seiber et al., 1989). The highest daily average concentration
detected in the vicinity of current agricultural usage was 250 ng/m3. As a control, levels of <2.0
ng/m3 (detection limit) were monitored at a background site not near the usage areas. Several
61
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days after thiobencarb usage ceased, air concentrations were below the detection limit at the use
areas. The highest measured values appeared to occur during times of usage.
Majewski et al. 1998. The greatest concentration of thiobencarb detected from whole air
sampling on a monitoring vessel was 7.1 ng/m3 traveling between New Orleans and Minneapolis
on the Mississippi River in June 1994 (Majewski etal., 1998). Thiobencarb was detected in four
consecutive locations of the ten sampling points, starting south of Memphis, TN, and ending in
St. Louis, MO.
Table 3-4. Summary of Air Monitoring Studies for Thiobencarb
Location
California
Mississippi River,
New Orleans to
Minneapolis
Maximum
Concentration
(ng/m3)
69.8
7.1
0.00 (median)
Frequency
of
Detections
NR
40%
of Det.
2.0
ng/m3
0.10
ng/m3
Date
May
and
June
1986
June
1994
Source
(Seiber et al. ,
1989)
(Majewski et
al., 1998)
Abbreviations: NR= not reported; Det.=detection or reporting limit
3.1.l.g. Precipitation Monitoring Results
One study reported on thiobencarb concentrations measured in rain (Suzuki et al., 2003). The
highest concentration measured in rainwater from 82 samples in Eastern Japan was 0.335 (ig/L
(Suzuki et al., 2003)(Table 3-5). The range of seasonal detection during this study was 75.0% in
summer and 45.8% in winter with intermediate values for winter and spring. Values measured in
Japan may not be representative of what would be found in the United States; however, these
data indicate that thiobencarb may be found in precipitation and may undergo long range
transport.
Table 3-5. Summary of Monitoring Studies for Thiobencarb Measuring Residues in
Precipitation
Location
Eastern Japan
Median
Concentration
NR
Maximum
Concentration
0.335 ug/L
Frequency
of
Detections
59.8%
Limit
of Det.
NR
Date
1999-
2000
Source
(Suzuki et al. ,
2003)
Abbreviations: NR= not reported; Det.=detection or reporting limit
3.2. Terrestrial Animal Exposure Assessment
For this assessment, spray and granular applications of thiobencarb to rice are considered.
Terrestrial EECs were derived for the uses previously summarized in Table 2-5. Exposure
estimates generated using T-REX are for the parent alone.
62
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Upper-bound Kenaga nomogram values reported by T-REX are used for derivation of dietary
EECs for the terrestrial phase CRLF and their potential prey. When data are absent EFED
assumes a 35-day foliar dissipation half life, based on the work of Willis and McDowell (1987).
The EFED RED Chapter (Mastrota, Not Specified), reported that thiobencarb residues were
measured from broadleaf weeds and sedges collected 12 m downwind of the edge of the field on
0, 7, 14, and 21 days after application (Accession Number 241484; MRID 82157). The
calculated foliage half-lives for broadleaf weeds and sedges were 5.4 and 8.6 days, respectively
(Mastrota, 1997). These values are consistent with those estimated for other pesticides (Willis
and McDowell, 1987). The upper 90th percentile confidence bound on the mean half-life value is
11.92 days and was used in this assessment.10
EFED included the aquatic application scenarios (rice) in the terrestrial exposure assessment.
Often the treated water bodies will be quite shallow, making them accessible to terrestrial
organisms. It is also likely that some thiobencarb will be deposited off the target site and onto
the land adjoining the treated water bodies.
Potential direct acute and chronic effects of thiobencarb to the terrestrial-phase CRLF are
initially derived by considering oral exposures modeled in T-REX for a small bird (20g)
consuming small invertebrates or insects. Potential impacts to mammalian prey base were
evaluated in T-REX for a small mammal (15 g) consuming short grass. Resulting dietary-based
EECs (mg/kg-food) and dose-adjusted EECs (mg/kg-bw) are summarized in Table 3-6.
Exposure calculated as mg ai/sq ft is provided for all granular applications using the weight of
one granule and the percent ai per granule as inputs into T-REX. The weight of one granule and
percent ai per granule were not available for this assessment. Therefore, an LD50/ft2 analysis
was performed to evaluate potential risks to birds and mammals (for use in risk characterization)
assuming a liquid formulation. The exposure used in this analysis is the mass of thiobencarb
applied to a square foot area (mg/ft2). Based on an application rate of 4.005 Ibs a.i./acre
(maximum single application rate), the exposure value used in the LD50/ft2 analysis is 42 mg/ft2.
m TT i -1 ^1 1 11 * r 4nn_, x Standard Deviation
Upper 90th percentile confidence bound on the mean = Mean + ^LJ
63
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Table 3-6 Summary of Dose and Dietary-based EECs Used for Estimating Dietary Risks to
Terrestrial Organisms using T-REX ver. 1.4.1. for Thiobencarb Use on Rice (Liquid
Formulation, ground or aerial application)
Use(s),
Type of
Application
Rice, ground and
aerial
Rice, ground and
aerial
App Rate (Ib
a.i./A, # Apps,
Interval (days)
4, 1, n/a
3, 1, n/a
EECs for CRLF
(small birds consuming
small insects used as a
surrogate)
Dietary-
based EEC
(mg/kg-diet)
540
405
Dose-based
EEC
(mg/kg-bw)
615
461
EECs for Prey
(small mammals consuming
short grass)
Dietary-based
EEC (mg/kg-
diet)
960
720
Dose-based
EEC
(mg/kg-bw)
915
686
Abbreviations: App= application, n/a=not applicable
T-REX is also used to calculate EECs for terrestrial insects exposed to thiobencarb. Dietary-
based EECs calculated by T-REX for small and large insects (units of a.i./g) are used to bound
an estimate of exposure to bees. Available acute contact toxicity data for bees exposed to
thiobencarb (in units of jig a.i./bee), are converted to jig a.i./g (of bee) by multiplying by 1
bee/0.128 g. The EECs are later compared to the adjusted acute contact toxicity data for bees in
order to derive RQs.
Dietary-based EECs for small and large insects reported by T-REX as well as the resulting
adjusted EECs are available in Table 3-7. An example output from T-REX v. 1.3.1 is available
in Appendix G.
Table 3-7. Summary EECs Used for Estimating Risk to Terrestrial Invertebrates and
Indirect Effects to the CRLF using T-REX ver. 1.4.1. for Thiobencarb Use on Rice ( Liquid
Formulations)
Use,
Method of Application
Rice,
aerial and ground applications
Application Rate (Ibs ai/acre), # of
app, App interval (days)
4 Ibs ai/A, 1 application
Small Insect
540
Large Insect
60
3.3. Terrestrial Plant Exposure Assessment
TerrPlant (Version 1.1.2) is used to calculate EECs for non-target plant species inhabiting dry
and semi-aquatic areas. Parameter values for application rate, drift assumption and incorporation
depth are based upon the use and related application method (Table 3-8). A runoff assessment
was not included because runoff from application to rice is not expected to occur. For aerial and
ground application methods, drift is assumed to be 5% and 1%, respectively. EECs relevant to
terrestrial plants consider pesticide concentrations in drift and in runoff. These EECs are listed
by use in Table 3-8. An example output from TerrPlant v.1.2.2 is available in Appendix H.
64
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Table 3-8. TerrPlant Inputs and Resulting EECs for Plants Inhabiting Dry and Semi-
aquatic Areas Exposed to Thiobencarb via Runoff and Drift
Use,
Formulation
Rice, liquid
Rice, liquid
Rice, liquid
Rice, liquid
Rice, granular
Application
rate
(Ibs a.i./A)
4
4
3
3
4.005
Application
method
aerial
ground
aerial
ground
n/a
Drift
Value
(%)
5
1
5
1
0
Spray drift
EEC
(Ibs a.i./A)
0.20
0.04
0.15
0.03
0
4. Effects Assessment
This assessment evaluates the potential for thiobencarb to directly or indirectly affect the CRLF
and/or DS or modify their designated critical habitat. As previously discussed in Section 2.8,
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 are based on toxicity information for freshwater fish (or amphibian data, when
amphibian data are available), while terrestrial-phase amphibian effects are based on avian
toxicity data, given that birds are generally used as a surrogate for terrestrial-phase amphibians
and reptiles. Direct effects to DS are assessed based on the most sensitive E/M or freshwater fish
species as DS spend time in estuarine and freshwater habitats.
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 thiobencarb,
consistent with the Overview Document (USEPA, 2004). Potential direct and indirect effects to
the CRLF and the DS and potential effects to critical habitat are evaluated in accordance with the
methods (both screening and species-specific refinements) described in the Agency's Overview
Document (USEPA, 2004).
Other sources of information, including use of the acute probit dose response relationships to
establish 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 thiobencarb.
A summary of the available aquatic and terrestrial organism ecotoxicity information and the
incident information for thiobencarb are provided in the following sections. A summary of the
available data directly used in this assessment is presented. A more comprehensive list of the
available toxicity data is included in Appendix I.
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4.1. Ecotoxicity Study Data Sources
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) (USEPA,
2009). Open literature data presented in this assessment were obtained from a recent assessment
(Davy, 2008), from a recent HED toxicology assessment (Lewis, 1997) as well as ECOTOX
information obtained on February 28, 2009. In order to be included in the acceptable ECOTOX
data summary, 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.
Open literature toxicity data for 'target' terrestrial plant species, which include efficacy studies,
are not currently considered in deriving the most sensitive endpoint for terrestrial plants.
Efficacy studies do not typically provide endpoint values that are useful for risk assessment (e.g.,
NOAEC, ECso, etc.), but rather are intended to identify a dose that maximizes a particular effect
(e.g., ECioo). Therefore, efficacy data and non-efficacy toxicological target data are not included
in the ECOTOX open literature summary table provided in Appendix K. The list of citations
including toxicological and/or efficacy data on target plant species not considered in this
assessment is provided in Appendix J.
Meeting the minimum criteria for inclusion in ECOTOX does not necessarily mean that the data
are suitable for use in risk estimation. 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 than the registrant-submitted data are considered. 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 behavior
modifications are likely to be qualitatively evaluated because quantitative relationships between
modifications and reduction in species survival, reproduction, and/or growth are not available.
Although the 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 thiobencarb.
Citations of all open literature not considered 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 J. Appendix J also includes a rationale for rejection of those
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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
K. Appendix L is a summary of the human health effects data for thiobencarb.
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 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 thiobencarb. A summary of the available aquatic and terrestrial
ecotoxicity information and the incident information for thiobencarb are provided in Sections 4.1
through 4.5, respectively.
4.2. Toxicity Categories
Toxicity to fish, aquatic invertebrates, birds, and mammals is categorized using the system
shown in Table 4-1 (USEPA, 2004). For non-target terrestrial insects, chemicals with LDso
values of <2, 2-11, and >11 jig/bee are classified as highly toxic, moderately toxic, and
practically nontoxic, respectively. Toxicity categories for terrestrial and aquatic plants have not
been defined.
Table 4-1. Categories of Acute Toxicity for Terrestrial and Aquatic Animals.
Toxicity Category
Very highly toxic
Highly toxic
Moderately toxic
Slightly toxic
Practically nontoxic
Aquatic Animals
[LC50/EC50 (>ig/L)]
<100
100 - 1,000
> 1,000 - 10,000
> 10,000 - 100,000
> 100,000
Birds and Mammals
[LD50 (mg/kg-bw)]
<10
10-50
51-500
501-2000
>2000
Birds
[LC50 (mg/kg-diet)]
<50
50 - 500
501 - 1000
1001 - 5000
>5000
4.3. Toxicity of Thiobencarb to Aquatic Organisms
Table 4-2 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 and DS is presented below. Additional information is provided in Appendix I. Values
used in risk quotient calculations are shown with an asterisk. All endpoints are expressed in
terms of the active ingredient (a.i.) unless otherwise specified. All available acute aquatic
toxicity endpoints ranged from 17 - 47,820 |ig/L (Appendix I). Limited data available on
amphibians suggest that they are not one of the more sensitive species (96-hr LCso ranged from
1.3 - 6.5 mg/L; see Section 4.3.1.d); however, these data are highly uncertain.
67
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Table 4-2. Aquatic Toxicity Profile for Thiobencarb
Assessment
Endpoint
Freshwater
fish
(surrogate for
aquatic-phase
amphibians)
Freshwater
invertebrates
Estuarine/
marine fish
Estuarine/
marine
invertebrates
Acute/
Chronic
Acute
Acute
Chronic
Acute
Chronic
Acute
Chronic
Acute
Chronic
Species
TGAI/TEP %
ai
Bluegill sunfish
Lepomis
macrochirus
TEP 10%
Striped Bass
Morone saxatilis
TEP 85.2%
Striped Bass
Morone saxatilis
TEP 85.2%
Daphnia magna
TGAI 94.4%
Daphnia magna
TGAI -95%
Atlantic
silverside
Menidia menidia
TGAI 90%
Atlantic
silverside
Mysid
Americamysis
bahia
TGAI 94.6%
Opossum Shrimp
Neomysis
mercedis
Toxicity Value
96-hr LC50 = 560
ug/L*
96-hr LC50 = 440
ug/L*
NOAEC/LOAEC
= 21/23 ug/L*
(9-day posthatch,
survival)
48-hr EC50= 10 1.2
tig/L*
21 -day
NOAEC/LOAEC =
1.0/3.0 ugai/L*
(offspring
produced)
96-hLC50 = 204
ug/L*
NOAEC = 6 ug
a.i./L, estimated*
96-hr LC50= 150
(110-200) ug
ai/L*
NOAEC/LOAEC
= 3. 2/6.2 ugai/L*
(survival of
offspring)
Citation or
MRID#
MRID
00050665
E154722
(Fujimura et
al, 1991)
MRID
00025788
MRID
00079098
E118682
(Borthwick
etal, 1985)
n/a
MRID
00050667
MRID
43976801/E
Supplemental,
Quantitative
(USEPA,
Comment
Acceptable, previous
discrepancies are resolved
through updated 850. 1075
guidelines (i.e. fish are <0.5g
but current methods require
fish <3g without a lower limit)
Supplemental-quantitative .
The study did not have a
solvent control; however, later
studies at the same
laboratories including solvent
controls indicated that the
solvent control was not
significantly different from the
negative control.
Quantitative. Hatching
success was not evaluated and
this may result in an
underestimated risk to
hatching success.
Acceptable
Acceptable.
Supplemental- quantitative
Estimated based on ACR for
the striped bass of 770/21 =
37 and the Atlantic
silverside 96-h LC50 of 204
ug/L.
Acceptable. Mysid were
slightly older than
suggested. Nominal
Open literature study (MRID
43976801) that is referenced
as supplemental in the RED.
Data were submitted by the
same author under MRID
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Assessment
Endpoint
Aquatic
plants
Acute/
Chronic
N/A
N/A
N/A
Species
TGAI/TEP %
ai
Green algae
Selenastrum
capricornutum
Green algae
Scenedesmus
acutus
duckweed
Lemna gibba
Toxicity Value
5-day EC50 = 17
(12 - 26) ug ai/L*
NOAEC = 13 ug
ai/L
96-hr EC50= 17
(16-19) ug ai/L*
NOAEC = 5 ug
ai/L
14-day EC50 = 770
(380 - 1600) ug
ai/L*
NOAEC = 14 ug
ai/L
Citation or
MRID#
1997)
MRID
41690901
E171142
(Sabater and
Carrasco,
1996)
MRID
41690901
Comment
40651314. NoDERwas
completed, an open literature
review has been completed.
Gravid females were
replaced if they died for the
first fourteen days.
Replacement was not
reported.
Acceptable. Endpoint based
on decreased cell density.
Supplemental-qualitative.
Endpoint based on percent
inhibition of growth.
LOAEC = 9 ug ai/L
Acceptable. Endpoint based
on decreased frond
production.
Abbreviations: a.i.=active ingredient; C.I. = confidence interval; NOAEC = No observed effect concentration;
NOAEL = No observed adverse effect level; LC50 = Lethal concentration to 50% of the test population; EC50 =
Effect concentration to 50% of the test population; IC50= inhibition concentration resulting in a 50% inhibition in the
test population response (e.g., growth); TGAI=technical grade active ingredient; TEP=typical end-use product; DO
= dissolved oxygen; ACR=acute-to-chronic ratio
1-Other endpoints affected include F0 maturation (week 24) wet weight (Males), F0 maturation (week 37) wet
weight (Females and Males), F0 eggs/female, F0 eggs/spawn' FI hatching success, FI 4-week survival, FI 4-week
length).
2-ECOTOX references are designated with an E followed by the ECOTOX reference number.
4.3.1. Toxicity to Freshwater Fish and Aquatic-Phase Amphibians
Fish toxicity data were used to evaluate potential direct effects to aquatic-phase CRLF and the
DS and indirect effects to the CRLF. A summary of acute and chronic fish and aquatic-phase
amphibian data, including data from the open literature, is provided in the following sections.
4.3.1.a. Freshwater Fish: Acute Exposure (Mortality) Studies
Thiobencarb and thiobencarb formulations are moderately to highly toxic to freshwater fish. The
only studies conducted using the technical grade active ingredient (TGAI) or typical end-use
product (TEP) with greater than 95% a.i. were considered supplemental and/or qualitative and
had incomplete reporting of the test procedures. The supplemental results of these studies
indicated that the 96-hr LCso values for carp, bluegill sunfish, channel catfish, and rainbow trout
ranged from 1180 - 2800 |ig a.i./L (MRIDs 00080859, 00080851; see Appendix I). The only
fully acceptable submitted studies on the acute toxicity of thiobencarb to fish were conducted
with Bolero 10 G. The 96-hour LCso for bluegill sunfish exposed to Bolero 10 G (10% a.i.) was
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560 jig a.i./L (MRID 00050665). This result is inconsistent with the results of other acute tests
for the bluegill sunfish where LCso values for TEPs ranged from 1660 - 2800 jig a.i./L (MRIDs
00080851, 139051). Results of tests with the TEP or TGAI with less than 91% a.i. ranged from
260 - 2480 jig a.i./L indicating that thiobencarb formulations are highly toxic to moderately
toxic to freshwater fish (MRIDs 40651315, 00080851). The most sensitive species was the
white sturgeon11 and this value may only be used qualitatively due to incomplete information
available in the test report. As little information is available on the studies conducted on the
TGAI, it is not possible to determine whether the TEP or TGAI is more toxic. The TGAI studies
are not as reliable as the TEP studies because raw data were not available and there was
incomplete reporting of the test results. Therefore, results from the TEP will be used
quantitatively in the risk assessment and it will be assumed that the toxicity to the formulation
and TGAI are similar. This assumption is supported from open literature studies (Harrington,
1990).
In addition to the acute toxicity studies discussed above, several acute toxicity studies with
freshwater fish were identified from the open literature (see Appendix I) which report more
sensitive values. The lowest of these more sensitive acute LCso values is 260 ug a.i./L (Bailey,
1984) for the white sturgeon, Acipenser transmontanus12. This study was evaluated and
considered qualitative as there was no solvent control in the study, the percent active ingredient
in the test material was not reported, and not enough information was available on the
preparation of test solutions. This value is considered qualitative. Additionally, several toxicity
studies were conducted examining toxicity to the striped bass (Fujimura et a/., 1991). The
studies examining toxicity to the striped bass had some endpoints lower than those submitted and
some of those endpoints did not include solvent controls. These 96-hour LCso values ranged
from 430 - 550 |ig/L. Control mortality was greater than 10% in the test with the lowest
endpoint of 430|ig/L; thus, this value may only be used qualitatively. Solvent controls were
completed for the studies on striped bass completed in 1989 and no differences were observed
between the negative and solvent controls. Therefore, it may be assumed that the solvents used
did not influence the results and the 96-hr LCso of 440|ig/L may be used quantitatively. The
other endpoints reported in the study are also considered quantitative and may be used to
calculate an acute-to-chronic ratio and/or risk quotient.
4.3.1.b. Freshwater Fish: Chronic Exposure (Growth/Reproduction)
Studies
One supplemental life-cycle study on fathead minnows (Pimephalespromelas) was available to
the Agency to evaluate the effects of chronic exposure to thiobencarb to freshwater fish (MRID
45695101). The study demonstrated that exposure to thiobencarb at 110 jig a.i./L has the
potential to cause reproductive toxicity. At this concentration the following endpoints were
statistically different from controls: F0 survival at 4- and 8-weeks, F0 growth at, 8 weeks (weight
and length), 24 weeks ($ and $ weight and length), and 37 ($ and $ weight and length) weeks
post-hatch; F0 reproduction (eggs/female, spawns/female and eggs/spawn); FI hatching success
11 The open literature white sturgeon study was submitted to EPA and is also available in the open literature. It is
discussed further in the open literature discussion.
12 A study report describing this study was also submitted to the Agency.
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(58%); FI survival at 4 weeks post-hatch; FI time-to-hatch; and FI growth (weight and length) at
4 weeks post-hatch. The NOAEC and LOAEC were 0.53 and 110 jig a.i./L, respectively. The
study only had two replicates. The low number of replicates and variability in the endpoints may
have resulted in an inability to statistically detect differences between treatments and controls
and thus may overestimate toxicity endpoints. Observed results suggested that if more replicates
were available a difference may have been statistically significant between the control and 53 jig
a.i./L treatment group.
Open literature data are available for the Chinook salmon and Striped bass, with the most
sensitive endpoint reported for the Striped bass (EO15472). The NOAEC and LOAEC from that
study for survival was 21 and 36 ug/L, respectively. The test was started using 1-hour prehatch
striped bass. A NOAEC was not determined in an early life stage study with striped bass at 8-
day post hatch at the test initiation. At the lowest measured test concentration of 23 ug/L,
survival was 63% as compared to 85% in controls. The NOAEC of 21 ug/L was used to evaluate
chronic risk the CRLF and DS in freshwater.
4.3.1.c. 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 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.
4.3.1.d. Aquatic-phase Amphibian: Acute and Chronic Studies
Acute, static-renewal, 96-hour early, middle, and late stage amphibian larvae toxicity tests were
completed on six species of amphibians examining toxicity of thiobencarb (TGAI, 99%
thiobencarb), an emulsifiable concentrate (EC, 50% thiobencarb), and three granular
formulations containing thiobencarb and other pesticide active ingredients (Saka, 1999). The
results indicated that the formulation toxicity and toxicity of the TGAI were similar.
Additionally, the 96-hr LC50 values for amphibians were near 1.3 - 6.5 mg a.i./L, suggesting that
amphibians may be less sensitive to thiobencarb than fish. These data are highly uncertain and
may only be used qualitatively (see Appendix I for more information on this study).
4.3.2. Toxicity to Freshwater Invertebrates
A summary of acute and chronic freshwater invertebrate data, including data published in the
open literature, is provided below in Sections 4.1.2.1 through 4.1.2.3.
4.3.2.a. Freshwater Invertebrates: Acute Exposure Studies
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The results indicate that thiobencarb is moderately to highly toxic to aquatic invertebrates on an
acute basis with LCso values ranging from 101.2 to 6500 ug a.i./L. (see Appendix I). No open
literature values resulted in more sensitive acute values for freshwater invertebrates. Available
data indicate that invertebrates have either similar to or less sensitivity to the TEP as compared to
the TGAI. The 48-hr LC50 for the water flea is 101.2 |ig a.i./L (95% Confidence Interval, C.I., is
73.8 - 138.7 |ig a.i./L) and 210.7 |ig a.i./L (95% C.I. is 175.7 - 252.7 |ig a.i./L) for the TGAI and
TEP, respectively (MRIDs 0025788, 00079118). The endpoint for the TGAI is the lowest
available value and will be used in the risk assessment.
4.3.2.b. Freshwater Invertebrates: Chronic Exposure Studies
Toxicity of thiobencarb (95.2 - 95.9% a.i.) was examined in a life-cycle toxicity study for
daphnid, Daphnia magna (MRTD 00079098). The NOAEC and LOAEC were 1.0 |ig a.i./L and
3.0 jig a.i./L, respectively. Chronic effects observed were reduced number of young produced
and adult mortality. These results indicate that concentrations of thiobencarb greater than 1 jig
a.i./L can be detrimental to the survival and reproduction of freshwater invertebrates.
Additionally, a supplemental 28-day sediment toxicity test on the Chironomus Riparius showed
that sediment toxicity (decreased percent emergence and altered sex ratio) occurred when the
time weighted average concentration of thiobencarb in overlying water was 420 |J,g/L (MRID
46091402). The NOAEC in the study was 180 |ig/L.
4.3.2.C. Freshwater Invertebrates: Open Literature Data
No open literatures studies reported lower median lethal concentrations than those obtained from
submitted studies for freshwater invertebrates.
The most important food organism for all sizes of the Delta smelt has been reported to be the
copepod Eurytemora affinis (USFWS, 1995, 2004a), which is a marine copepod. No E/M
studies were submitted examining toxicity to copepods. Supplemental toxicity data are available
from the open literature for a non-native freshwater cyclopoida and calanoida (ECOTOX
E062293). In this field study, conducted with a formulation of thiobencarb, the 7-day LOAEL
was 0.1875 mg a.i./L (effects observed were emergence success).
4.3.3. Toxicity to Estuarine/Marine Fish
A summary of acute and chronic E/M fish data, including data published in the open literature is
provided below in Sections 4.1.3.1 through 4.1.3.3.
4.3.3.a. Estuarine/Marine Fish: Acute Exposure Studies
Thiobencarb and thiobencarb formulations are moderately to highly toxic to E/M fish on an acute
basis. Sheepshead minnow were more sensitive to the TGAI than the TEP. The 96-hr LCso for
the TGAI was 660 (95% CI = 600-800) and 900 (95% CI = 700-1200) |ig a.i./L while the value
for the TEP was 96-hr LC50 was 1400 (95% CI = 1100-1800) |ig a.i./L (MRID 00079112,
00079110, 00079111). The lowest 96-hr LC50 from a submitted study for the TGAI is 660 |ig
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a.i./L (MRID 00079112). Several open literatures studies were available in the open literature
with the majority of the values being below the lowest submitted value.
All of the open literature acute values from EPA's ECOTOX database for E/M fish are presented
in Appendix I. There were 25 acute LC50 values from two open literature studies representing
four E/M fish species. Almost all of these values were below the E/M fish studies provided by
the registrant (660 ug a.i./L). The lowest of these more sensitive acute 96-hr LCso values is 204
ug a.i./L for the Atlantic silverside, Menidia menidia (Borthwick et a/., 1985). This study was
evaluated and considered supplemental quantitative. Endpoints measured for California grunion,
Atlantic silverside, and Tidewater silverside ranged from 204 - 1174 ug a.i./L (ECOTOX
Number El 1868).
4.3.3.b. Estuarine/Marine Fish: Chronic Exposure Studies
One study examining toxicity of thiobencarb to the Sheepshead minnow is available. The
NOAEC measured in an early life stage study for 28-day post hatch Sheepshead minnow was
<150 ug/L and effects on wet weight were observed at all treatment levels (MRID 00079112).
Additionally, reduced survival and hatching success were observed at 230 and 600 ug a.i./L. No
chronic E/M data were submitted to the Agency or available in the acceptable ECOTOX report.
A chronic value was estimated using the an acute-to-chronic (ACR) ratio calculated for
freshwater fish and the lowest 96-hr LCso of 204 ug a.i./L for the Atlantic Silverside (Fujimura
et a/., 1991). The estimated chronic NOAEC value for the Atlantic Silverside was calculated as
follows:
Striped Bass Highest 96 - hr LC50 Atlantic Silverside 96 - hr LC50
Striped Bass NOAEC Atlantic Silverside NOAEC
Where:
the acute striped bass value is based on the highest quantitative 96-hr LCso values of 770
ug a.i./L (Fujimura etal., 1991),
the chronic striped bass value is based on the NOAEC of 21 ug a.i./L from the same
study and,
the acute Atlantic silverside 96-hr LCso is 204 ug a.i./L as described previously
(Fujimura etal., 1991).
Therefore, 770/21 = 204/X
and,
Estimated Atlantic silverside NOAEC = (204 x 21)/770 = 6 ug a.i./L.
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This estimated NOAEC of 6 ug a.i./L for Atlantic silverside will be used to quantitatively
estimate chronic risk of thiobencarb to DS. Risk quotients could underestimate risk as the
hatching success was not measured for the NOAEC used to calculate the ACR.
4.3.4. Toxicity to Estuarine/Marine Invertebrates
A summary of acute and chronic E/M invertebrate data, including data published in the open
literature, is provided below in Sections 4.1.4.1 through 4.1.4.3.
4.3.4.a. Estuarine/Marine Invertebrates: Acute Exposure Studies
Estuarine/marine aquatic invertebrate toxicity data are used to evaluate potential indirect effects
to the DS because they depend on aquatic invertebrates for food. For the indirect effects
assessment, the most sensitive aquatic invertebrate species is initially used for risk estimation,
which is consistent with USEPA (2004). The most sensitive E/M aquatic invertebrate tested is
the mysid shrimp (Mysidopsis bahia) (96-hr LC50 = 150, 95% C.I. = 110-200 |ig a.i./L) (MRID
00050667). Other E/M invertebrates have similar to less sensitivity to thiobencarb when
compared to the mysid shrimp. All 96-hr LCso values for all shrimp and Eastern oyster species
ranged from 150 - 1100 jig a.i./L (see Appendix I). The fiddler crab was less sensitive than
other species with a 96-hr LC50 value of 4400 |ig/L (MRID 00079113).
One open literature study resulted in a lower endpoint than those observed in submitted studies
(E090259). The endpoint is not useable in the risk assessment due to incomplete reporting of
test procedures and other major limitations of the study. All other acute endpoints in the
acceptable ECOTOX report were higher than 150 |ig/L.
The most important food organism for all sizes of the Delta smelt has been reported to be the
copepod Eurytemora affinis (USFWS, 1995, 2004a), which is a marine copepod. No E/M
studies were submitted examining toxicity of thiobencarb to E/M copepods.
4.3.4.b. Estuarine/Marine Invertebrates: Chronic Exposure Studies
Three studies are available examining chronic toxicity to E/M invertebrates. Open literature
toxicity data from chronic exposure to thiobencarb are available for three the Mysid, Opossum,
and Grass shrimp. The Opossum shrimp (Neomysis mercedis) study, conducted with technical
grade thiobencarb, resulted in the lowest NOAEC of 3.2 jig a.i./L based on reduced survival of
offspring at 6.2 jig a.i./L (MRID 43976801 or 40651314). No open literatures studies with lower
endpoints were found in the acceptable ECOTOX report.
4.3.5. Toxicity to Aquatic Plants
Aquatic plant toxicity studies are used as one of the measures of effect to evaluate whether
thiobencarb may affect primary production. Aquatic plants may also serve as dietary items of
aquatic-phase CRLFs. In addition, freshwater vascular and non-vascular plant data are used to
evaluate a number of the PCEs associated with the critical habitat impact analysis.
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Thiobencarb is toxic to the freshwater green alga (Pseudokirchneriella subcapitata, formerly
Selenastrum capricornutum), with a 120-hr ECso of 17 jig a.i./L and a NOAEC of 13 jig a.i./L,
based on reduced cell density (MRID 41690901). The marine diatom was also sensitive to
thiobencarb with a 120-hr EC50 of 73 |ig a.i./L and NOAEC of 18 |ig a.i./L (MRID 41690901).
The freshwater diatom, and blue-green algae were less sensitive with 120-hr ECso values of 380
and >3100 jig a.i./L (MRID 41690901). The aquatic vascular plant tested, duckweed (Lemna
gibbet), is less sensitive to thiobencarb than the freshwater green alga [i.e., 14-day ECso= 770 jig
a.i./L; NOAEC = 140 |ig a.i./L; based on decreased frond production] (MRID 41690901).
Two open literature studies are available with endpoints lower than those measured in submitted
studies. A 4-day NOAEC was reported for green algae (Scenedesmus acutus) of 5 jig a.i./L, with
effects on percent inhibition of growth observed at 2 jig a.i./L (E15718). The LCso measured in
the study was the same as that measured in the submitted study (see Table 4-2).
4.3.6. Aquatic Field/Mesocosm Studies
The conclusion of high risk to aquatic organisms, based on results from laboratory toxicity tests,
triggered the requirement for aquatic field testing with thiobencarb (GLN 72-7). The following
aquatic field studies have been conducted on the use of thiobencarb on rice.
Table 4-3. Summary of submitted aquatic field studies on the use of thiobencarb on rice
Title
Impact of Bolero
Runoff on a
Brackish Water
Ecosystem
Thiobencarb:
Studies on Residue
Level and
Behavior in
Selected Irrigation
Creeks in
Agricultural Areas
in Saga Prefecture,
Southwestern
Japan
Location and
Date
Matagorda,
Texas
1982 - 1984
Saga
Prefecture,
Kyushu, Japan
1975
Reference
MRIDs
42130705 &
42130708
MRID 00028183
Performed By
Fujie, 1983.
Ishikawa, 1975
Sponsor
Chevron
Chemical
Company
Unknown
Classification
Acceptable1
Supplemental
1 Following the review of this study, an additional aquatic field study was requested to monitor aquatic residues in
other localities where rice is grown. This additional study, however, was waived in December 1993.
75
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4.3.6.a. Matagorda Study
A large aquatic field study was conducted in 1982-1984 near Matagorda, Texas. The site
consisted of a rice field that drained through a ditch into the tidal waters of the lower Colorado
River of eastern Texas. This estuarine area is a complex and highly important ecosystem that
supports many commercial species. No thiobencarb applications were made in 1982; this year
provided an estimate of background levels of thiobencarb. Thiobencarb concentrations were as
high as 9 jig a.i./L in 1982. In 1983 and 1984, approximately 500 acres of the field were treated
with thiobencarb at a rate of 4 Ibs a.i. per acre. Fields were flushed with water within 3 to 12
days after application. Data collected from 1982 through 1984 included (1) residues of
thiobencarb in water, sediment, fish and shrimp; (2) catch per unit effort measurements offish
and aquatic invertebrates; and (3) percentages of grass shrimp (Palaemonetespugio) that were
gravid. While samples were collected during all three years of the study, the sampling effort on
the third year was very poor.
A control station was also planned on the Colorado River upstream of the confluence with the
drainage ditch. However, during the course of the study, the Agency and the registrants agreed
that this station could not serve as a control for the field study because it contained preexisting
residues of thiobencarb. It was therefore only possible to compare residues and biological
samples collected during 1983 and 1984 to those collected during 1982, before the initial
treatment. This represents a shortcoming of this study since the results could have been
influenced by yearly fluctuations in environmental conditions that are unrelated to the
applications of thiobencarb. Another shortcoming is that other pesticides (ordram, basegran,
machette, and propanil) were applied to fields that drain into the test ditch during the period of
this study. The toxicity of these pesticides could have contributed to the observed effects.
The results of the study were:
1. Residues of thiobencarb were transported into the estuary via runoff and drift. Maximum
residues measured in water, sediment, fish, and shrimp were 25.1 |ig/L, 50 |ig/L, 2400 |ig/L,
and 970 |ig/L, respectively.
2. Although the overall population offish was apparently not affected, marked declines were
observed during the treatment years in three species, Gambusia affinis, Dormitator
maculatus, and Poecilia latipenna.
3. Several taxa of aquatic invertebrates showed substantial decline in numbers caught per unit
effort. Species richness and diversity also declined significantly during treatment years.
4. The percentage of gravid shrimp decreased significantly in 1983 compared to 1982. The
decline was about 50% at stations 1 and 2, and averaged 23% for all four stations. Sampling
was inadequate to assess the effect on the percentage of gravid shrimp in 1984.
5. A kill of the fish menhaden (Brevoortia patronus) was observed in the area where the field
runoff entered the drainage ditch. It occurred at the point of discharge from the drainage
76
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canal, one to two days after a post-application flush of the rice fields. Although other
pesticides that were applied that year (ordram, basegran, and propanil) may have been
present in the tailwater, this kill was attributed to thiobencarb contamination because the
dead fish contained high residues of thiobencarb (mean of 3.56 ppm).
6. Field BCF for thiobencarb was estimated to be 109X for fish and 44X for shrimp.
Declines in fish, aquatic invertebrates, and gravid shrimp cannot conclusively be attributed to the
use of thiobencarb. Nevertheless, the findings in the field were consistent with effects
demonstrated in laboratory studies. They suggest that the application of thiobencarb to rice
fields may result in significant environmental damage to the adjacent estuarine habitat in Texas.
Possible effects include chronic effects to sensitive fish, acute and chronic effects to ecologically
important aquatic invertebrates, chronic effects to grass shrimp and possibly to commercial
shrimp, and indirect detrimental effects to organisms at higher trophic levels that depend on
these organisms for food.
4.3.6.b. Japan Study
The EFED reviewed a study that measured residues of thiobencarb in creek water after
application to rice paddies in Japan. Thiobencarb was applied in the form of 7% granules at a
rate of 30 kg/ha, which is equivalent to 1.9 Ib a.i./A. Water samples were taken from ten stations
along creeks that flow through the rice fields and drain into the Hayatsue River. Water sampling
was conducted from March through November, with thiobencarb treatments being made from
June 28 through July 2. The creeks served as storage for irrigation water until May, when the
water is pumped onto the fields. The creeks resembled large ponds during the storage period.
Very low thiobencarb concentrations (0.2 jig a.i./L or less) were reported at all stations in March
and April before applications were made. Concentrations peaked at the sampling period of July
1, when concentrations at most stations were between 20 and 40 jig a.i./L. The greatest
concentration was measured was 40.5 jig a.i./L. Concentrations declined fairly rapidly
thereafter; the half-life of thiobencarb in creek water was estimated to be 8.8 days. This rate of
decline represents dilution as well as biological and physical degradation processes. EFED
cannot interpret the significance of these results or extrapolate conclusions to other areas because
of the lack of important information on the test conditions, such as flow rates within the creeks
and rainfall during the study.
4.3.6.C. Conclusions and Uncertainties with Field Studies
A difficulty with the field studies was that water flow measurements were not made, making it
impossible to discern effects of dissipation versus dilution. While water residues were generally
short-lived, it is not clear whether thiobencarb residues were broken down by chemical or
biological forces, or they were swept away and diluted by tidal flow. Because it is possible that
dilution was the primary mode of dissipation in all three studies, the rate at which thiobencarb
degrades by chemical or biological means in estuaries remains unknown. Thiobencarb residues
thus may persist longer in other areas where dilution is of less importance in the dissipation of
residues.
77
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The two biological field studies demonstrate that application of thiobencarb on rice can cause
significant contamination to water, sediments, and aquatic organisms in off-site aquatic habitats.
Harm to estuarine and freshwater ecosystems is possible when thiobencarb is used in
southeastern United States. Although shortcomings of these studies make it impossible to
identify thiobencarb as the sole cause of observed adverse effects, the studies fail to refute the
Agency's presumption that the use of thiobencarb on rice results in severe effects on aquatic
ecosystems.
4.4. Toxicity of Thiobencarb to Terrestrial Organisms
Table 4-4 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.
Additional information is provided in Appendix I.
Table 4-4. Terrestrial Toxicity Profile for Thiobencarb
Endpoint
Birds
(surrogate for
terrestrial-
phase
amphibians)
Mammals
Acute/
Chronic
Acute
Acute
Chronic
Acute
Chronic
Species
Bobwhite quail
(Colinus
virginianus)
TGAI 96.9%
Mallard duck
Anas
platyrhynchos
Mallard duck
Anas
platyrhynchos
TGAI 95.5%
Rat - male
TGAI 96%
Fischer 344 Rat
TGAI 95.3%
Toxicity Value
Used in Risk
Assessment
Acute oral LD50
>1938 mg/kg-
bw
5-day LC50
>5000 mg
a.i./kg-diet
1 -generation
NOAEC/
LOAEC = 1007
300 mg a.i./kg-
diet
Acute oral LD50
= 1033 mg/kg-
bw
2-generation
NOAEL/
LOAEL= 20/
100 mg/kg/day
or I/ 5 mg/kg-
bw
Citation
MRID/ ECOTOX
reference No.
MRID 42600201
MRID 44846206
MRID 00025778
MRID 42130701
MRID 40446201
Comment
Acceptable
Acceptable
No treatment related
mortality.
NOAEC = 648 mg
a.i./kg-bw (body weight
gain)
Supplemental. Raw
data were not complete
for hatching success
and 14-day survivor
weight. The effects
observed at the LOAEC
were decreased eggs
laid and hatchlings per
live 3 week embryo.
Acceptable
Acceptable. The
effects observed were
decreased bw gain,
food consumption, and
food efficiency. No
reproductive effects
were observed at any
test level and the
reproductive NOEAL >
78
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Endpoint
Terrestrial
invertebrates
Terrestrial
plants
Acute/
Chronic
Acute
Contact
N/A
N/A
N/A
N/A
Species
Honey Bee
Apis Mellifera
TGAI 97.2%
Seedling
Emergence
Monocots
Seedling
Emergence
Dicots
Vegetative Vigor
Monocots
Vegetative Vigor
Dicots
Toxicity Value
Used in Risk
Assessment
Acute contact
48-hr LD50>
100 ug/bee
EC25/NOAEC
= 0.019/0.0051
Ib a.i./A
EC25/NOAEC
= 0.082/0.071
Ib a.i./A
EC25/NOAEC
= 0.073/0.020
Ib a.i./A
EC25/NOAEC
= ND/<0.121b
a.i./A
EC25/NOAEC
= 1.2/0.801b
a.i./A*
(soybean)
Citation
MRID/ ECOTOX
reference No.
MRID 46059804
MRID 41690902
MRID 4 1690902
MRID 41690902
MRID 41690902
Comment
100 mg/kg/day.
15 percent mortality
observed at 100 ug/bee,
the highest dose tested.
Most sensitive species
was ryegrass. The most
sensitive endpoint was
mortality.
Most sensitive species
was cabbage. The most
sensitive endpoint was
shoot length.
Most sensitive species
was ryegrass. The most
sensitive endpoint was
shoot length.
Most sensitive species
was cucumber. Shoot
weight and root weight
were the most sensitive
endpoints.
For soybean, the most
sensitive endpoint was
root weight.
N/A: not applicable; ND = not determined; bw=body weight; hr=hour
4.4.1. Toxicity to Birds and Terrestrial-Phase Amphibians
As specified in the Overview Document, the Agency uses birds as a surrogate for terrestrial-
phase amphibians when toxicity data for each specific taxon are not available (USEPA, 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. No terrestrial phase amphibian data were
available in the ECOTOX summary of acceptable ecotoxicity data.
4.4.1.a. Birds: Acute Exposure (Mortality) Studies
Only two acute avian toxicity studies were available. An acute oral toxicity study on the
bobwhite quail indicates that thiobencarb is slightly toxic to practically nontoxic to bobwhite
quail (Acute oral LD50 >1938 mg a.i./kg-bw, MRID 42600201). No mortality occurred at the
highest dose tested and the only sublethal effect observed was a slight decrease in body weight
during the first three days after dosing. No mortality was observed in a subacute dietary study
with the mallard duck with the highest dose tested being 5000 mg a.i./kg-bw (MRID 44846206).
Sublethal effects observed in treatments of 1080 mg a.i./kg-diet and above include: increased
water consumption, lack of coordination, smaller appearance, decreased body weight gain (57-
79
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10% in treatments versus 76 - 77% in control), and decreased food consumption. Birds
completely recovered after 28 days.
Acute oral toxicity studies with a passerine and water fowl species were not available. The
limited data available on birds could result in an underestimation of toxicity.
No data were available in the accepted ECOTOX data examining acute toxicity of thiobencarb to
birds.
4.4.1.b. Birds: Chronic Exposure (Growth, Reproduction) Studies
An avian reproduction study with the mallard duck (MRID 00025778) resulted in a NOAEC of
100 mg a.i./kg-diet, based on decreased eggs laid and hatchlings per live three week embryo.
Sublethal effects observed in the study at 30 mg a.i./kg-diet and above included depression of
coordination, lower limb weakness, prostate posture, loss of reflexes, and wing droop. These
effects disappeared after two days. In another supplemental study with the mallard duck, the 14
day survivor weight was significantly less at 231 mg a.i./kg-diet (NOEAC = 115 mg a.i./kg-diet)
and normal hatching eggs laid and eggs set were decreased at 338 mg a.i./kg-diet (MRID
45140601). Reproductive and growth endpoints were also affected in quail. In Japanese quail,
the fertility and hatchability were reduced at 1000 mg a.i./kg-diet (MRID 00080848). In the
bobwhite quail, the percent normal embryos and weight of hatchlings was reduced at 930 mg
a.i./kg-diet (MRID 43075401).
4.4.1.c. Terrestrial-phase Amphibians: Acute and Chronic Studies
No data are currently available for the effects of thiobencarb on terrestrial-phase amphibians.
4.4.2. Toxicity to Mammals
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 4.2.1.2. A more complete analysis of
toxicity data to mammals is available in Appendix L, which is a copy of the HED chapter
prepared in support of the reregi strati on eligibility decision completed in 1997.
4.4.2.a. Mammals: Acute Exposure (Mortality) Studies
Thiobencarb is slightly toxic to mammals on an acute oral exposure basis. An acute oral study
with rats (Rattus sp.) resulted in an LD50 value of 1033 mg a.i./kg-bw (MRID 42130701).
4.4.2.b. Mammals: Chronic Exposure (Growth, Reproduction) Studies
In a combined chronic toxi city /carcinogen! city feeding study (MRID 00154506), Fischer 344
rats received 0, 20, 100 or 500 mg/kg-diet (approximately 0, 1,5, and 25 mg/kg/day by standard
conversion methods) technical thiobencarb (95.3% a.i.) in the diet for two years. Systemic
toxicity was noted at 100 mg/kg-diet and above as decreased body weight gain, food
consumption and food efficiency. There was also an increase in blood urea nitrogen. No
evidence of carcinogenicity at the dose levels tested was observed. For chronic toxicity, the
80
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NOAEL was 1 mg/kg/day (20 mg/kg-diet) and the LOAEL was 5 mg/kg/day (100 mg/kg-diet)
based on decreased body weight gains, food consumption, food efficiency, and increased blood
urea nitrogen.
In a two generation reproduction study (MRID 40446201), Charles River CD rats received either
0, 2, 20, or 100 mg/kg/day technical thiobencarb (96.7% a.i.) by daily oral gavage in 0.5% CMC
aqueous solution. Systemic toxicity was noted at 20 mg/kg/day and above based on enlargement
of centrolobular hepatocytes (both generations) and hepatocyte single cell necrosis observed in
both sexes of both generations including renal atrophic tubule consisting of regenerated
epithelium. There were increased liver weights (absolute and relative) and increased kidney
weights (absolute and relative) in the high dose group. There were also significant changes on
body weights at 100 mg/kg/day and male kidney weights were increased in the high dose group.
There were no effects on reproductive parameters. For Parental/Systemic toxicity, the NOAEL
was 2 mg/kg/day and the LOAEL was 20 mg/kg/day based on histopathological changes of the
liver and kidney. For reproductive toxicity, the NOAEL was equal to or greater than 100
mg/kg/day and the LOAEL was greater than 100 mg/kg/day. For the purpose of this risk
assessment, the endpoints used in the risk assessment are the NOAEL of 20 mg/kg/day and
corresponding LOAEL of 100 mg/kg/day based on decreased body weight. A value of > 100
mg/kg/day was also used in characterization as a decrease in body weight does not necessarily
mean a reduction in survival and reproduction may occur.
Thiobencarb was rapidly absorbed after oral administration with almost all eliminated in the
urine within 72-hours (MRID 42340302).
Other sublethal effects observed in rats include gait abnormalities, decreased sensory responses,
and decreased motor activity in an acute neurotoxicity screening at 500 mg/kg-day (NOAEL =
100 mg/kg-day, MRID 42987001, 43148202, acceptable).
4.4.3. Toxicity to Terrestrial Invertebrates
Terrestrial invertebrate toxicity data are used to evaluate potential indirect effects to the CRLF
and to adversely modify designated critical habitat. Thiobencarb is considered practically
nontoxic to honey bees (Apis melliferd) on an acute contact exposure basis (MRID 46059804).
In this study, adult bees were exposed to a TGAI via oral and contact exposure routes at nominal
concentrations of 0 and 100 jig a.i./bee. At the highest concentration tested in the oral test,
23.3% of the bees died in the treatment group as opposed to 6.7 and 3.3% in the negative and
solvent control groups, respectively. In the contact exposure group, 15% of bees died as
compared to 6.7 and 10% in the control groups. The 48-hr LDso is thus greater than 100 jig
a.i./bee for both studies. No sublethal effects were observed. This study is classified as
supplemental because the age of the bees at test initiation was not reported.
The acceptable ECOTOX data were examined for toxicity data using non-target species with
endpoints expressed in terms similar to those for the standard test with honey bees. No values
were available. Values were reported for the brown plant hopper; however, the value reported
was for an aquatic test for a snail. Two studies were available for nematodes. The LOAEL
reported for the Nemata and root-knot nematode were 0.75 kg a.i./ha with the endpoint examined
81
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being population effects (Das et a/., 1997; Das et a/., 1998). These values were not reviewed for
possible use in the calculation of a risk quotient.
4.4.4. Toxicity to Terrestrial Plants
Plant toxicity data from both registrant-submitted studies and studies in the scientific literature
were reviewed for this assessment. Registrant-submitted studies are conducted under conditions
and with species defined in EPA toxicity test guidelines. Sublethal endpoints such as plant
growth, dry weight, and biomass are evaluated for both monocots and dicots, and effects are
evaluated at both seedling emergence and vegetative life stages. Guideline studies generally
evaluate toxicity to ten crop species. These tests are conducted on herbaceous crop species only,
and extrapolation of effects to other species, such as the woody shrubs and trees and wild
herbaceous species, contributes uncertainty to risk conclusions.
Commercial crop species have been selectively bred, and may be more or less resistant to
particular stressors than wild herbs and forbs. The direction of this uncertainty for specific plants
and stressors, including thiobencarb, is largely unknown. Homogenous test plant seed lots also
lack the genetic variation that occurs in natural populations, so the range of effects seen from
tests is likely to be smaller than would be expected from wild populations.
Two terrestrial plant studies with thiobencarb have been submitted to the Agency: seedling
emergence studies (MRTD 41690902 and 44846201) and a vegetative vigor study (MRID
41690902). For the seedling emergence and vegetative vigor testing the following plant species
and groups should be tested: (1) six species of at least four dicotyledonous families, one species
of which is soybean (Glycine max), and another of which is a root crop, and (2) four species of at
least two monocotyledonous families, one species of which is corn (Zea mays).
Results of Tier II seedling emergence toxicity testing on technical thiobencarb are given in Table
4-5.
82
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Table 4-5. Summary of submitted terrestrial plant Tier II seedling emergence toxicity
results for thiobencarb
Species
Monocot~Corn
Monocot~Oat
MonocotOnion
Monocot-Ryegrass
Dicot/Root Crop-
Carrot
Dicot-Cabbage
Dicot-Cucumber
Dicot-Lettuce
Dicot-Soybean
Dicot-Tomato
Dicot - Lettuce
Monocot - Ryegrass
%
a.i.
96.6
96.5
Parameter Affected
Shoot length
Shoot length
Shoot length
Mortality
Shoot length
Shoot length
Shoot length
Mortality
Shoot length
Shoot length
None (measured
seedling emergence,
seedling survival, plant
height, dry weight, and
phytotoxicity)
EC25
(Ib a.i./A)
>1.7
0.086
2.0
0.019
>3.1
0.082
>1.7
0.27
>1.7
1.1
>0.0101b
a.i./A.
NOAEC
(Ib a.i./A)
1.7
0.055
0.94
0.00511
2.1
0.071
0.16
-
0.94
0.94
XXOlOlb
a.i./A
MRID No.
Author/Year
MRID 4 1690902
Hoberg, J.R.
1990
MRID 44846201
Chetram, R.S.
1999
Acceptable
DERI 1/16/2002
1 This NOAEL is based on 17% mortality of plants occurring at the next higher test level, 0.011 Ib a.i./A.
In the tier II seedling emergence test, mortality of test plants occurred in the tests with ryegrass
and lettuce. Mortality was the most sensitive toxic endpoint for these species (plants tended to
die shortly after emerging). The most sensitive species was ryegrass, a monocot, for which the
EC25 based on mortality (i.e.., LC2s) was 0.019 Ib a.i./A. The most sensitive dicot was cabbage.
The cabbage £25 based on shoot length was estimated to be 0.082 Ib a.i./A.
Results of Tier II seedling vegetative vigor toxicity testing on the technical thiobencarb are given
in Table 4-6.
Table 4-6. Summary of submitted Tier II seedling vegetative vigor toxicity testing for
thiobencarb
Species
Monocot- Corn
Monocot~Oat
Monocot-Onion
Monocot--
Ryegrass
Dicot/ Root Crop-
-Carrot
%
A.I.
96.6
Parameter
Affected
Shoot length,
shoot
weight, and
root weight
Shoot weight
Shoot length
Shoot length
Shoot length,
shoot
weight, and
EC25
(Ib a.i./A)
>2.2
0.17
1.2
0.073
>2.2
NOAEC
(Ib a.i./A)
2.2
0.12
0.80
0.020
2.2
MRID No.
Author/Year
MRID 4 1690902
Hoberg, J.R. 1990
Supplemental
83
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Species
Dicot-Cabbage
Dicot-Cucumber
Dicot-Lettuce
Dicot-Soybean
Dicot-Tomato
%
A.I.
Parameter
Affected
root weight
Root weight
Shoot weight
and root
weight
Root weight
Shoot weight
Root weight
EC25
(Ib a.i./A)
1.2
a
1.3
1.2
1.8
NOAEC
(Ib a.i./A)
1.4
0.12
0.80
0.80
2.2
MRID No.
Author/Year
a Greater than a 25% reduction was recorded at some or all exposure levels, but the EC2s could not be determined
because no dose-response relationship was apparent.
In the Tier II vegetative vigor tests, the cucumber and soybean were the most sensitive dicots and
ryegrass was the most sensitive monocot.
Based on the results of the submitted terrestrial plant toxicity tests, it appears seedling emergence
is the most sensitive for both dicots and monocots.
All open literature endpoints for terrestrial plants in the accepted ECOTOX data are higher than
those measured in submitted studies. Open literature toxicity data for 'target' terrestrial plant
species, which include efficacy studies, are not currently considered in deriving the most
sensitive endpoint for terrestrial plants. A list of these studies are available in the ECOTOX
bibliography in Appendix J.
4.5. Toxicity of Degradates
No ecological toxicity data were found in the ECOTOX database for 4-chlorobenzoic acid or 4-
chlorobenzaldehyde; however, ECOSAR version 1.0 predicted aquatic toxicity endpoints greater
than those predicted and measured for thiobencarb, see Appendix B. Additionally, these
degradates were not considered to be of toxicological concern in the human health risk
assessment completed for the RED (Lewis, 1997). The toxicity of 4-chlorobenzoic acid and 4-
chlorobenzaldehyde was assumed to be less than that of thiobencarb (see Appendix B).
Concentrations of the other degradates were a very small percentage (<8.3%) of the amount of
thiobencarb applied or were only present in a few fate studies, indicating that they would be
present at lower concentrations than those estimated for thiobencarb. The estimated toxicity
based on structure activity relationships (ECOSAR version 1.0) or the similarity of the structure
to thiobencarb indicates that the toxicity of these compounds is similar to or less than that of
thiobencarb (see Appendix B). The presence of these degradates is not expected to alter risk
conclusions that are based on the fate, transport, and toxicity of the parent compound alone.
84
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4.6. Toxicity of Chemical Mixtures
As previously discussed, the results of available toxicity data for mixtures of thiobencarb with
other pesticides are presented in Appendix C. The limited data available do no allow a
comparison of the toxicity results of thiobencarb alone versus thiobencarb and propanil or with
other chemicals.
4.7. Incident Database Review
A review of the EIIS database for ecological incidents involving thiobencarb was completed in
September 2009. Based on the EIIS database, there have been a total of seven reported
ecological incidents potentially involving thiobencarb. The incidents occurred at unreported
times and between 1997 and 1998. The crop damaged in six incidents was the crop that
thiobencarb was registered to be used on, rice. The damage involved an 'unknown' number of
impacted acres of rice production and was described as 'damage' and 'stunted growth'. The
legality of use was undetermined in four of the incidents and involved a registered thiobencarb
use in three incidents. No other herbicides besides thiobencarb were involved in any of the
reported incidents. The certainty that thiobencarb was responsible for the plant damage and
stunted growth ranged from 'possible' (three incidents), 'probable' (two incidents), and 'highly
probable' (one incident). In the remaining incident, the plant damaged was not specified.
Table 4-7. Summary of Incident Reports Involving Effects on Rice in California
INCIDENT
NO.
1006793-009
1006793-007
1006793-008
1007467-026
1004940-003
1007467-025
1007776-008
YEAR
NR
1997
N/R
1998
1997
1997
1997
LEGALITY
Undetermined
Registered Use
Registered Use
Registered Use
Undetermined
Undetermined
Undetermined
CERTAINTY
Possible
Probable
Probable
Possible
Highly Probable
Possible
Probable
PRODUCT
Bolero 10G
Bolero 10G
Bolero 10G
Bolero
Bolero 10G
Bolero
Bolero 10G
OTHER
CHEMICALS
INVOLVED
(PC CODE)
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Comments
Rice crop damage observed after
application of thiobencarb to rice.
Distortion of rice leaves observed
after application of thiobencarb to
rice.
Damage to rice and a reduced
yield occurred after application of
thiobencarb to rice.
Damage to rice plants and reduced
rice yield observed after
application of thiobencarb to rice.
Only reported that incident
reported with use of thiobencarb
in an agricultural area.
Rice field leaves were distorted
after application of thiobencarb.
Damage to rice field observed
after application of thiobencarb.
Abbreviations: NR=not reported; N/A= not applicable
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4.7.1. Other Aquatic Incidents
MRID 42130705 & 42130708. Aquatic field studies also suggest that application of thiobencarb
to rice paddies may result in effects to aquatic organisms. Declines in fish, aquatic invertebrates,
and gravid shrimp cannot conclusively be attributed to the use of thiobencarb. Nevertheless, the
findings in the field were consistent with effects demonstrated in laboratory studies. They
suggest that the application of thiobencarb to rice fields may result in significant environmental
damage to the adjacent estuarine habitat. Possible effects include chronic effects to sensitive
fish, acute and chronic effects to ecologically important aquatic invertebrates, chronic effects to
grass shrimp and possibly to commercial shrimp, and indirect detrimental effects to organisms at
higher trophic levels that depend on these organisms for food.
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
and DS or for modification to their designated critical habitat from the use of thiobencarb 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 assessed 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 the estimated environmental concentration (EEC)
(from aquatic modeling results, T-REX for terrestrial animals, and TerrPlant for terrestrial
plants) (Section 3) and the appropriate toxicity endpoint (Section 4). 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 F). For acute exposures to the aquatic animals,
as well as terrestrial invertebrates, the LOG is 0.05. For acute exposures to birds (and, thus,
reptiles and terrestrial-phase amphibians) and mammals, the LOG is 0.1. The LOG for chronic
exposures to animals, as well as acute exposures to plants is 1.0.
In cases where the baseline RQ exceeds one or more LOG (i.e., "may affect"), additional factors,
including the life history characteristics of the assessed species, refinement of the baseline EECs
using site-specific information, and available monitoring data are considered and used to
characterize the potential for thiobencarb to adversely affect the assessed species and/or their
designated critical habitat. Risk quotients used to evaluate potential direct and indirect effects to
the CRLF and DS and to designated critical habitat are in Sections 5.1.1 (direct effects) and 5.1.2
(indirect effects). RQs are described and interpreted in the context of an effects determination in
Section 5.2 (risk description).
86
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5.1.1. Calculation of RQs used to Assess Direct Effects to CRLF and DS
Toxicity values used to calculate RQs are discussed in Section 4, and exposure values are
discussed in Section 3. RQs used to estimate acute and chronic direct effects are in Table 5-1
(DS and aquatic-phase CRLF) and Table 5-2 (terrestrial-phase CRLF).
S.l.l.a. Direct Effects to Aquatic-phase CRLF and DS
The species considered in this risk assessment include a frog and a fish species. Direct effects to
the DS are evaluated using the lowest acute and chronic toxicity values across freshwater and
estuarine/marine fish species. Direct effects to the aquatic phase CRLF are evaluated using the
lowest freshwater acute and chronic toxicity values across fish and amphibian toxicity studies.
However, fish were consistently shown to be more sensitive than aquatic-phase amphibians and
the available amphibian studies are classified as 'supplemental' and may only be used
qualitatively; therefore, fish acute and chronic toxicity values are used to calculate RQs for
aquatic-phase amphibians. Delta smelt may inhabit both saltwater and freshwater habitat and the
most sensitive freshwater or E/M fish endpoints were used to evaluate direct risk to DS. For the
CRLF, exposure was evaluated in the rice paddy. For DS, acute exposure was evaluated for
exposure to water released from rice paddies after a required 14-day holding period because DS
are not expected to be found in rice paddies. Chronic Exposure for the DS was estimated using
time-weighted average concentrations from monitoring data.
Table 5-1. Acute and Chronic RQs for Direct Effects to the Aquatic-Phase CRLF and DS
Basis of Exposure
Estimates
Peak
EEC
(Hg/L)
Chronic
EEC
(Mg/L)
Risk Quotients
CRLF (FW
fish is
surrogate)
Acute1
CRLF and
DS (FW fish
is surrogate)
Chronic2
DS (E/M fish
is surrogate)4
Acute3
DS(E/M
fish is
surrogate)
Chronic4
Conservative Exposure Estimate in Paddy Water for CRLF Only5
Tier I Rice Model
and Aquatic
Dissipation for
CRLF
2018
9686
4.59
46.10
Conservative Exposure Estimate Where Paddy Water is Released for CRLF and DS
Tier I Rice Model
with Aquatic
Dissipation and
Monitoring Data
3507
5.378
0.80
0.26
1.72
0.90
LOG exceedances (acute RQ > 0.05; chronic RQ > 1.0) are bolded. Acute RQ = use-specific peak EEC /96-hr LC50;
Chronic RQ = 60 day EEC/NOAEC
1-The freshwater vertebrate endpoint used to calculate acute RQs for the CRLF is the 96-hr LC50 of 440 ug/L for
striped bass (ECOTOX E15472).
2-The NO AEC used to calculate chronic RQs for CRLF was 21 ug/L for the striped bass for posthatch survival
(E15472).
3-The E/M fish acute endpoint used to calculate RQs for the DS is the 96-hr LC50 of 204 ug/L for the Atlantic
Silverside(E11868).
4-The NO AEC used to calculate chronic RQs for E/M fish was 6 ug/L estimated using the ACR of 37 calculated for
the striped bass and the lowest acute toxicity endpoint for Atlantic silverside (MRID 00079112 and El 1868).
5-RQs for DS were not estimated in paddy water because DS are not expected to be present in rice paddies.
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6-Time-weighted average concentration over 14-days water is in rice paddy. Estimated based on an initial
concentration determined using the Tier I Rice Model and an aquatic dissipation rate from an aquatic dissipation
study on California wet seeded rice (MRID 43404005).
7-Exposure was estimated using the Tier I Rice Model and allowing for 14 days of dissipation using the aquatic
dissipation rate from MRID 43404005.
8-Time-weighted average concentration from monitoring data collected in rice growing areas of California (see
Section 3.1.1.a).
Risk quotients were calculated for conservative exposure estimated using the Tier I Rice Model
and modified Tier I Rice Model to account for dissipation. For the CRLF, chronic EECs were
estimated based on the 14-day average concentration in the rice paddy. The 14-day value was
used because water is not expected to be held in the rice paddy for more than 14-days and this is
a conservative estimate for a 60-day exposure estimate. Chronic exposure outside of the rice
paddy was estimated based on the time-weighted average concentration from monitoring data in
California rice growing areas. All acute risk quotients for the aquatic-phase CRLF and DS
exceed the LOC of 0.05 (CRLF RQs 0.80 - 4.59; DS RQs 0.80 - 1.72). Chronic RQs for the
CRLF exceed the LOC of 1.0 for modeled exposure. Chronic RQs for the DS did not exceed the
LOC of 1.0.
S.l.l.b. Direct Effects to Terrestrial-phase CRLF
Potential direct acute effects to the terrestrial-phase CRLF are derived by considering dose- and
dietary-based EECs modeled in T-REX for a small bird (20 g) consuming small invertebrates
and acute oral and subacute dietary toxicity endpoints for avian species (since no terrestrial-
phase amphibian toxicity data were available for thiobencarb).
The avian acute and subacute endpoints are not definitive (i.e. greater than values); therefore,
definitive RQs cannot be calculated. There was no mortality in the limited number of studies
available and the potential for direct acute or subacute effects to the CRLF are presumed low.
However, comparing the highest dose tested in toxicity studies to the EECs can provide insight
into the potential for direct effects to the CRLF. The dose-based endpoint, LD50 >1938 mg
a.i./kg-bw (bobwhite quail), is higher than the dose based EECs of 615 mg/kg-bw (MRID
42600201 and Table 3-6). The ratio of the EECs to the highest dose tested is 0.44. The subacute
dietary endpoint, LCso >5000 mg a.i./kg-bw is well above the highest dietary based EEC of 540
mg/kg-diet (MRID 44846206 and Table 3-6). The ratio of the EEC to the highest dietary
concentration tested is 0.11. If toxicity were observed slightly above the highest levels tested,
there is a potential that the LOC for listed species (0.1) could be exceeded. The EEC estimated
for granular formulations was 42 mg a.i./ft2. The adjusted avian LDso/ft2, comparable to an RQ,
is <1.49 (Appendix G). This value is greater than the acute avian LOC of 0.1.
Potential direct chronic effects of thiobencarb to the terrestrial-phase CRLF are derived by
considering dietary-based exposures modeled in T-REX for a small bird (20g) consuming small
invertebrates. Chronic effects are estimated using the lowest available toxicity data for birds.
Chronic reproductive effects to birds were observed at 300 mg a.i./kg-diet (LOAEC), with an
associated NOAEC of 100 mg a.i./kg-diet (MRID 00025778). The T-REX estimated chronic RQ
of 9.60 exceeds the chronic LOC of 1.0. These RQs are further characterized in the context of
the effects determination in Section 5.2.
88
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5.1.2. Calculation of RQs used to Assess Indirect Effects to CRLF and DS
This section presents RQs used to evaluate the potential for thiobencarb to induce indirect
effects. Pesticides have the potential to exert indirect effects upon listed species by inducing
changes in structural or functional characteristics of affected communities. Perturbation of
forage or prey availability and alteration of the extent and nature of habitat are examples of
indirect effects. A number of these indirect effects are also considered as part of the critical
habitat modification evaluation. In conducting a screen for indirect effects, direct effects LOCs
for each taxonomic group (e.g., freshwater fish, invertebrates, aquatic plants, and terrestrial
plants) are employed to make inferences concerning the potential for indirect effects upon listed
species that rely upon non-listed organisms in these taxonomic groups as resources critical to its
life cycle (USEPA, 2004). This approach used to evaluate indirect effects to listed species is
endorsed by the Services (USFWS/NMFS/NOAA, 2004). If no endangered species LOCs are
exceeded for organisms on which the assessed species depends for survival or reproduction,
indirect effects are not expected to occur.
If LOCs are exceeded for organisms on which the assessed species depends for survival or
reproduction, dose-response analysis is used to estimate the potential magnitude of effect
associated with an exposure equivalent to the EEC. The greater the probability that exposures
will produce effects on a taxa, the greater the concern for potential indirect effects for listed
species dependant upon that taxa (USEPA, 2004).
As an herbicide, indirect effects to the assessed species from potential effects on primary
productivity of aquatic plants are a principle concern. If plant RQs fall between the risk to
endangered species and non-endangered species LOCs, a no effect determination is made for
listed species that rely on multiple plant species to successfully complete their life cycle (termed
plant dependent species). If plant RQs are above risk to non-endangered species LOCs, this
could be indicative of a potential for adverse effects to those listed species that rely either on a
specific plant species (plant species obligate) or multiple plant species (plant dependant) for
some important aspect of their life cycle (USEPA, 2004). Based on the information provided in
Section 2.6, the assessed species do not have any known obligate relationship with a specific
species of aquatic plant.
Direct effects to riparian zone vegetation may also indirectly affect the assessed species by
reducing water quality and available spawning habitat via increased sedimentation. Direct
impacts to the terrestrial plant community (i.e.., riparian habitat) are evaluated using submitted
terrestrial plant toxicity data. If terrestrial plant RQs exceed the Agency's LOG for direct risk to
non-endangered plant species, based on EECs derived using EFED's Terrplant model (Version
1.2.1), a conclusion that thiobencarb may affect the CRLF and DS via potential indirect effects to
the riparian habitat (and resulting impacts to habitat due to increased sedimentation) is made.
Further analysis of the potential for thiobencarb to affect the CRLF and the DS via reduction in
riparian habitat includes a description of the importance of riparian vegetation to the assessed
species and types of riparian vegetation that may potentially be impacted by thiobencarb use
within the action area.
89
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RQs used to evaluate the potential for thiobencarb to induce indirect effects to the assessed
species are presented in Sections 5.1.2.a to 5.1.2.e. These RQs suggest that potential indirect
effects could occur by potentially impacting food availability and primary productivity as
indicated by LOG exceedances. These RQs were based on the most sensitive surrogate species
tested across aquatic invertebrate, fish, and aquatic plant species tested. Discussion of these RQs
in the context of this effects determination is presented in Section 5.2.
5.1.2.a. Aquatic Vertebrates
Indirect effects to the adult CRLF may result from reduction in aquatic vertebrate prey items.
Risk quotients for freshwater vertebrates were previously estimated in Section 5.1.1 .a. Since the
acute and chronic RQs are exceeded, there is a potential for indirect effects to listed species that
rely on freshwater fish and/or aquatic-phase amphibians (e.g., CRLF) during at least some
portion of their life-cycle.
5.1.2.b. Aquatic Invertebrates
Risk quotients were calculated exposure estimated using the Tier I Rice Model and modified Tier
I Rice Model to account for dissipation. For the CRLF, chronic EECs were estimated based on
the 14-day average concentration in the rice paddy. The 14-day value was used because water is
not expected to be held in the rice paddy for more than 14-days and this is a conservative
estimate for a 60-day exposure estimate. Chronic exposure outside of the rice paddy was
estimated based on the time-weighted average concentration from monitoring data in California
rice growing areas. Acute risk to aquatic E/M invertebrates is estimated in the same way as
those estimated for freshwater invertebrates except that risk quotients were not calculated for
exposure in rice paddies as E/M invertebrates are not expected to be present in rice paddies. The
EECs are compared to the lowest acute toxicity value for freshwater or E/M invertebrates.
Chronic risk for the E/M invertebrates is based on the time-weighted average concentration
estimated using monitoring data.
Table 5-2. Acute and Chronic RQs for Aquatic Invertebrates Used to Evaluate Potent
Indirect Effects to the CRLF and the DS Resulting from Potential Impacts to Food Su
Basis of Exposure
Estimates
Peak
EEC
(Mg/L)
Chronic
EEC
(Mg/L)
Risk Quotients
FW Invertebrates
Acute1
Chronic2
E/M Invertebrates5
Acute3
Chronic4
Conservative Exposure Estimate in Paddy Water (CRLF Only)
Tier I Rice Model
and Aquatic
Dissipation
2018
9685
19.94
968
-
-
Conservative Exposure Estimate Where Paddy Water is Released (CRLF and DS)
Tier I Rice Model
with Aquatic
Dissipation and
Monitoring Data
3506
5.377
3.46
5.37
2.33
1.68
ial
ppiy
LOC exceedances (acute RQ > 0.05; chronic RQ > 1.0) are bolded. Acute RQ = peak EEC /96-hr LC50; Chronic
RQ = 21 day EEC/NOAEC
90
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1- The freshwater invertebrate endpoint used to calculate acute RQs is the 96-hr LC50 of 101.2 ug/L for Daphnia
magna (MRID 00025788).
2-The NOEAC used to calculate chronic RQs for freshwater invertebrates is 1 ug/L for the Daphnia magna based
on reduced number of offspring produced (MRID 00079098).
3-The E/M acute endpoint used to calculate RQs is the 96-hr LC50 of 150 ug/L for the Mysid shrimp (MRID
00050667).
4-The E/M acute endpoint used to calculate RQs is the 21-day NOAEC of 3.2 ug/L for the Opossum shrimp based
on reduced survival of offspring (MRID 43976801 or 40651314).
5- 14-day average concentration in rice paddy estimated based on an initial concentration determined using the
Tier I Rice Model and an aquatic dissipation rate from an aquatic dissipation study on California wet seeded
rice (MRID 43404005).
6- Exposure was estimated using the Tier I Rice Model and allowing for 14 days of dissipation using the aquatic
dissipation rate from MRID 43404005.
7- The chronic values represents the average of concentrations measured between May 9 and June 22, 2000 in the
NAWQA monitoring data collected in rice growing areas of California.
Based on exceedances of the Agency's acute listed species LOG (RQ>0.05) and chronic risk
LOG (RQ>1) using modeled EECs and using thiobencarb concentrations measured in the
Sacramento River, there is a potential for indirect effects on the CRLF and indirect effects to the
DS, as they rely on freshwater invertebrates and/or E/M invertebrates during at least some
portion of their life-cycle. Discussion of these RQs in the context of this effects determination is
presented in Section 5.2.
5.I.2.C. Terrestrial Invertebrates
In order to assess the risks of thiobencarb to terrestrial invertebrates, which are considered prey
of CRLF in terrestrial habitats, the honey bee is used as a surrogate for terrestrial invertebrates.
The toxicity value for terrestrial invertebrates is calculated by multiplying the lowest available
acute contact LD50 greater than 100 jig a.i./bee by 1 bee/0.128g, which is based on the weight of
an adult honey bee (MRID 46059804). EECs (|ig a.i./g of bee) calculated by T-REX for small
and large insects are divided by the calculated toxicity value for terrestrial invertebrates, which is
greater than 781 jig a.i./g of bee. Terrestrial invertebrate EEC/highest dose tested are presented
in Table 5-3.
Table 5-3. Summary of EEC/Highest Dose Tested Ratio for Terrestrial Invertebrates on
the Site of Application - Used to Evaluate Potential Indirect Effects to the CRLF Resulting
from Potential Impacts to the Food Supply.
Use
Rice
Application
Rate (Ib
a.i./acre)
4
Size Class
Small insect
Large insect
EEC (ppm)
540
60
EEC/Highest Dose
Tested Ratio1
0.69
0.08
1 Available acute contact toxicity data for bees exposed to thiobencarb (in units of ug a.i./bee) are converted
to ug a.i./g (of bee) by multiplying by 1 bee/0.128 g (LD50 >100 ug a.i./bee becomes >781 ug/gbee).
2 Bolded ratios potentially exceed the interim risk to listed species LOG for terrestrial invertebrates (0.05).
In the honey bee contact study, 15% of bees died at the highest dose tested (100 jig a.i./bee) as
compared to 6.7 and 10% in the control groups (MRID 46059804). A definitive LDso value was
91
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not determined. The RQs for all thiobencarb uses are potentially above the Agency's interim
risk to listed species LOG for terrestrial invertebrates (0.05). The actual RQs would likely be
lower than the ratio of the EEC to the highest dose tested reported in Table 5-3. However, it is
not clear if the actual RQs would be above or below the Agency's LOG without definitive data,
therefore, risks cannot be precluded at this time. Discussion of these RQs in the context of this
effects determination is presented in Section 5.2.
5.1.2.d. Mammals
Potential risks to mammals are derived using T-REX and acute and chronic mammal toxicity
data. RQs are typically derived for various sizes of mammals (15 g, 35 g, and 1000 g); however,
RQs are not presented for 1000 g mammals because it is improbable that even the largest CRLF
would consume a mammal of that size. Therefore, the evaluation for potential indirect effects to
the CRLF resulting from potential reductions in mammal abundance as food is based on the 15 g
size class, which results in higher RQs than the 35 g mammal. The California mouse
(Peromyscus californicus) is a particular species known to be consumed by the CRLF. The
California mouse is omnivorous and consumes grasses, fruits, flowers, and invertebrates
(University of South Carolina, 2005). Therefore, the short grass food item was used to determine
if mammals could be impacted; however, RQs based on EECs on other food items were also
derived for characterization purposes. A range of RQs for mammals is presented in Table 5-4
(also see Appendix G).
Table 5-4. Summary of Acute and Chronic RQs for 15 g Mammals Used to Evaluate
Potential Indirect Effects to the CRLF Resulting from Potential Impacts to the Food
Supply1
Dietary Category
Dose Based
EEC (mg/kg-
bw)
Dietary Based
EEC (mg/kg-
diet)
Acute Dose-
Based RQ2
Chronic Dose
Based RQ3
Chronic
dietary-Based
RQ3
On Field Liquid Broadcast Applications (Aerial or Ground)1
Short grass
Tall grass
Broadleaf
plants/small insects
Fruits/pods/large
insects
Seeds
915.29
419.51
514.85
57.21
12.71
960.00
440.00
540.00
60..00
0.40
0.18
0.23
0.03
0.01
416.45
190.87
234.25
26.03
5.78
48.00
22.00
27.00
3.00
Granular Applications4
n/a
42 mg a.i./ft2
n/a
1.22
n/a
n/a
Abbreviations: n/a=not applicable
Bolded RQs exceed (or are near) the acute listed species LOG (0.1) or chronic listed species LOG (1) for mammals.
1- Estimated residues for potential food items using T-REX.
2- The acute oral LD50 of 1033 mg a.i./kg-bw for the rat was used to calculate acute dose based RQs (MRID
42130701).
3- The NOAEL of 1 mg/kg-bw for the Fischer rat was used to calculate chronic RQs (MRID 40446201). The
effects observed were decreased body weight gain, food consumption, and food efficiency.
RQs exceed acute LOCs for mammals consuming short grass, tall grass, and broadleaf plants or
small insects. Chronic RQs are exceeded for all diet classes. Based on an LD50/ft2 analysis,
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RQs for use of granular formulation also exceed the acute LOG of 0.1. A method to evaluate
chronic risk to granular formulations is currently not available. Therefore, the RQs estimated for
liquid formulations are assumed to represent chronic exposure to both liquid and granular
formulations.
5.1.2.e. Aquatic and Terrestrial Plants
Aquatic plants serve as food supply for both the CRLF and the DS and can impact water quality.
Additionally, effects to terrestrial plants can impact terrestrial habitat quality and water quality
parameters. Therefore, RQs for vascular and non-vascular aquatic plants are used to evaluate the
potential for thiobencarb to affect the CRLF and/or the DS by potentially impacting the food
supply and water quality, and thus habitat. RQs for terrestrial plants are used to evaluate the
potential for thiobencarb to impact aquatic habitats (i.e.., water quality) (aquatic-phase CRLF and
DS) and/or terrestrial habitats (terrestrial-phase CRLF).
i. Aquatic Plants
Risk to aquatic non-vascular plants is based on peak EECs and the lowest 120-hr ECso value for
non-vascular plants (17 |ig/L for the Green algae; MRID 41690901) or the lowest 14-day ECso
for vascular plants (770 |ig/L for Duckweed; MRID 41690901). Table 5-5 shows estimated RQs
for aquatic plants.
Table 5-5. Summary of RQs for Vascular and Non-Vascular Aquatic Plants.
Basis of Exposure
Estimates
Peak EEC
(Hg/L)
Risk Quotients
Non-vascular Plants1
Vascular Plants2
Conservative Exposure Estimate in Paddy Water (CRLF)
Tier I Rice Model and
Aquatic Dissipation
2018
118.71
2.62
Conservative Exposure Estimate Where Paddy Water is Released (CRLF and DS)
Tier I Rice Model with
Aquatic Dissipation and
Monitoring Data
3503
20.59
0.45
LOG exceedances (RQ > 1.0) are bolded. RQ = peak EEC /5-day EC50 for nonvascular plants or 14-day EC50 for
vascular plants.
1- The non-vascular plant endpoint was used to calculate RQs for the 5-day EC50 of 17 ug/L for the Green algae
(MRID 41690901).
2- The vascular plant endpoint used to calculate acute RQs is the 14-day EC50 of 770 ug/L for Duckweed (MRID
41690901).
3- Exposure was estimated using the Tier I Rice Model and allowing for 14 days of dissipation using the aquatic
dissipation rate from MRID 43404005.
LOCs for vascular plants were only exceeded based on exposure estimated in the rice paddy.
LOCs for non-vascular plants were exceeded using EECs estimated for the rice paddy but not for
exposure estimates allowing for fourteen days dissipation. Since the RQs are exceeded, there is
a potential for indirect effects to the CRLF and DS that rely on non-vascular aquatic plants
during at least some portion of their life-cycle. Indirect effects to the CRLFmay occur due to
effects to vascular plants in rice paddies.
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ii. Terrestrial Plants
Potential indirect effects resulting from effects on terrestrial vegetation were assessed using RQs
from terrestrial plant seedling emergence and vegetative vigor £25 data as a screen. Based on
the results of the submitted terrestrial plant toxicity tests, emerging seedlings are more sensitive
to thiobencarb via soil/root uptake than emerged plants via foliar routes of exposure. Therefore,
the seedling emergence data were used to estimate terrestrial plant RQs for thiobencarb use.
RQs used to estimate potential indirect effects to the CRLF and/or the DS from potential effects
to terrestrial plants within their habitat areas are summarized in Table 5-6.
Table 5-6. Non-Listed Terrestrial Plant RQs for Thiobencarb Use on Rice (one application
at 4 Ibs a.i./acre).1
Type of Application, Formulation
Aerial, Liquid
Ground, Liquid
Aerial and Ground, Granular
Drift Only
Monocot
10.53
2.11
<0.1
Dicot
2.44
0.49
<0.1
RQs greater than the LOG of 1.0 are shown in bold.
1 Based on the following: monocots - EC25 = 0.019 Ib a.i./acre (seedling emergence) and EC25 = 0.073 Ib a.i./acre
(vegetative vigor) in ryegrass; dicots - EC25 = 0.082 Ibs a.i./acre [seedling emergence, cabbage)] and EC25 =1.2 Ibs
a.i./acre [vegetative vigor, cabbage] (MRID 41690902).
Based on available data, monocots are more sensitive to thiobencarb than are dicots. RQs of
monocots exceed the LOG for non-listed plants (1.0) for liquid applications. Granular
applications are not exceeded because spray drift from application of granular formulations is
expected to be minimal and runoff is not expected to be a concern in rice paddies. For Dicots,
RQs are exceeded for aerial applications of a liquid formulation but not for ground applications.
LOCs were exceeded for both dicot and monocot terrestrial plants, which could result in indirect
effects to the CRLF or the DS. These LOCs and their impact on the effects determination are
described in Section 5.2.
5.1.3. Primary Constituent Elements of Designated Critical Habitat
For thiobencarb 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 presented in Section 5.1 are used as the basis of the effects determination for potential
modification to designated critical habitat.
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 modification
of their designated critical habitat.
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If the RQs presented in the Risk Estimation (Section 5.1) show no direct or indirect effects for
the assessed species, and no modification to PCEs of the designated critical habitat, a "no
effect" determination is made, based on thiobencarb's use within the action area. However, if
LOCs for direct or indirect effect are exceeded or effects may modify the PCEs of the critical
habitat, the Agency concludes a preliminary "may affect" determination for the FIFRA
regulatory action regarding thiobencarb. Risk quotients indicate that use of thiobencarb on rice
paddies may affect both the CRLF and DS with both direct and indirect effects. Additionally,
modification of PCEs and critical habitat may occur. A summary of the risk estimation results
are provided in Table 5-7 for direct and indirect effects to the listed species and for the PCEs of
their designated critical habitat.
Table 5-7. Summary of Risk Estimation for Thiobencarb. The Risk Estimation Is Further
Refined in the Risk Description
Listed Species
Taxonomic
Group of
Concern
Effects
Associated
with RQ
Risk
Quotients
(RQs) or
Ratios
Description
Assessed Species Potentially
Affected
Direct
Effects
Indirect
Effects
Aquatic Environment
Freshwater fish
in Paddy
(surrogate for
CRLF)
Freshwater fish
in Tailwater
(surrogate for
CRLF and DS)
Estuarine/Marine
fish
Freshwater
invertebrates in
paddy water and
where paddy
water is released
Estuarine/Marine
Invertebrates
Non-listed
Aquatic vascular
plants
Non-listed
Aquatic non-
vascular plants
Acute:
mortality
Chronic:
Posthatch
survival
Acute:
mortality
Chronic:
Posthatch
survival
Acute:
mortality
Chronic: wet
weight
Acute:
mortality
Chronic:
Offspring
produced
Acute:
mortality
Chronic:
Posthatch
survival
Frond
production
Cell Density/
Inhibition of
Growth
4.59
46.10
0.80
0.26
1.72
0.90
3.46-
19.94
5.37-968
2.33
1.68
0.45-
2.62
20.59-
118.71
All RQs exceed LOC of 0.05.
RQs exceed LOC of 1.0 for 14-day
average modified Tier I Rice model
estimate.
All RQs exceed LOC of 0.05.
RQ does not exceed the LOC of 1.0
based on monitoring data
All RQs exceed LOC of 0.05.
RQ does not exceed the LOC of 1.0
based on monitoring data
All RQs exceed the LOC of 0.05.
All RQs exceed the LOC of 1.0.
RQ exceeds the LOC of 0.05.
RQ exceeds the LOC of 1.0.
Only RQs in the rice paddy exceed
the LOC of 1.0.
All RQs exceed the LOC of 1.0
CRLF
CRLF
DS
~
DS
~
~
~
~
~
~
~
CRLF
CRLF
~
~
~
~
CRLF and DS
CRLF and DS
DS
DS
CRLF
CRLF and DS
95
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Listed Species
Taxonomic
Group of
Concern
Effects
Associated
with RQ
Risk
Quotients
(RQs) or
Ratios
Description
Assessed Species Potentially
Affected
Direct
Effects
Indirect
Effects
Terrestrial Environment
CRLF (based on
the bird as a
surrogate)
Mammals
Terrestrial
invertebrates
Non-listed Dicot
terrestrial plants
Non-listed
Monocot
terrestrial plants
Acute: No
mortality
Chronic:
Reproduction
Acute:
mortality
Chronic:
Reproductive
No mortality
Seedling
Emergence
Mortality
Seedling
Emergence
Shoot Length
0.11-
<1.49
9.6
0.01 -
0.40
(liquid)
1.22
(granular)
3.00
416.45
O.08 -
O.69
O.l-
2.44
O.l-
52.63
Uncertain, no definitive endpoints
available.
RQ exceeds LOC of 1.0 for liquid
formulations. A method to evaluate
chronic risk of granular formulations
is not available.
RQs for mammals consuming short
grass, tall grass, broadleaf plants, and
small insects exceed LOC of 0. 1 for
both liquid and granular
formulations.
All RQs exceed the chronic LOC of
1.0 for liquid formulations. A
method to evaluate chronic risk of
granular formulations is not
available.
Uncertain, no definitive endpoints
available.
RQs for aerial application of liquid
formulations exceed the LOC of 1.0
RQs for aerial and ground
application of liquid formulations
exceed the LOC of 1.0
Uncertain
CRLF
~
~
~
~
~
Uncertain
CRLF
CRLF
CRLF
Uncertain
CRLF and DS
CRLF and DS
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 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 modify 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.
96
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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 5.4.2.
5.2.1. Direct Effects
5.2.1.a. DS and Aquatic-Phase CRLFs
Acute and chronic risk quotients for both the aquatic-phase CRLF and DS exceed the LOCs for
modeled EECs in rice paddies (Table 5-1). All acute RQs estimated based on modeled
concentrations where paddy water is released also exceed the listed species LOG of 0.05. Acute
RQs for CRLF range from 0.80 - 4.59 and acute RQs for DS ranged from 0.80 - 1.72 (based on
freshwater and E/M species).
The chance of individual effect (mortality) to the aquatic-phase CRLF can be determined as
described above in Section 2.10.2.b using the acute LOG (0.05) and the RQs calculated from
water column EECs as threshold values for effects. For the CRLF, at the highest RQ (4.59) and
using the default slope (4.5), the probability of an effect would be approximately 1 in 1.0
(estimated using the Individual Effect Chance Model (IEC) Version 1.1). For the DS, at the
highest RQ (1.72) and using the default slope (4.5), the probability of an effect would be
approximately 1 in 1.17 (estimated using LEG Version 1.1). Probit dose-response analysis for
direct effects to CRLF and DS are shown in Table 5-8. Some acute data are available for
amphibians that suggest that amphibians are less sensitive than fish. The estimated 96-hr LCso
values were near 1.3-6.5 mg/L. These data are highly uncertain and cannot be used to discount
risk. No incidents were reported for fish or amphibians.
Table 5-8. Probit Dose-Response Analysis for Direct Effect to the CRLF and DS
Species Represented
CRLF (Surrogate
Freshwater fish)
DS (Surrogate FW or
E/M Fish)
Maximum
RQ
4.59
1.72
Acute Effect
Slope (95% C.I.)
Mortality
Default Slope = 4.5
(2-9)
Mortality
Default Slope = 4.5
(2-9)
Chance of Individual Effect
at Listed Species LOG
(95% C.I.)
lin4.18E+08
(1 in 216 to linl.75E+31)
lin4.18E+08
(lin216tolinl.75E+31)
Chance of
Individual Effect at
Derived Acute RQ1
(95% C.I.)
1 in 1.0
(1 in 1.10 to 1 in 1.0)
1 in 1.17
(1 in 1.47 to lin
1.02)
Risk quotients were also estimated based on data from the aquatic dissipation study resulting in
the highest exposure estimate in California and based on monitoring data to further characterize
97
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the potential for risk to the CRLF and DS from use of thiobencarb on rice. These calculations
are shown in Table 5-9. All acute RQs for the CRLF and DS still exceed the acute listed species
LOG of 0.05 when based on monitoring data. RQs ranged from 0.39 - 2.82.
Table 5-9. Acute and Chronic RQs for Direct Effects to the Aquatic-Phase CRLF and DS
based on Aquatic Dissipation Study Results and Monitoring Data
Basis of Exposure
Estimates
Peak
EEC
(Mg/L)
Chronic
EEC
Oig/L)
Risk Quotients
CRLF (FW
fish is
surrogate)
Acute1
CRLF and
DS (FW fish
is surrogate)
Chronic2
DS (E/M fish
is surrogate)4
Acute3
E/M fish
Chronic4
Realistic Exposure Estimate in Paddy Water and Where Paddy Water is Released (CRLF and DS)
Aquatic Dissipation
Study (MRID
43404005)
Aquatic Dissipation
Study (Ross and
Sava, 1986)
438
576
805
705
1.00
1.31
3.81
3.33
2.15
2.82
13.33
11.67
Exposure Estimates Based on the Measured Concentration in Rice Growing Areas of CA (CRLF and
DS)
Colusa Basin Drain
on Sacramento
River
1706
5.377
0.39
0.26
0.83
0.90
LOG exceedances (acute RQ > 0.05; chronic RQ > 1.0) are bolded. Acute RQ = use-specific peak EEC /96-hr LC50;
Chronic RQ = 60 day EEC/NOAEC
1- The freshwater vertebrate endpoint used to calculate acute RQs for the CRLF is the 96-hr LC50 of 440 ug/L for
striped bass (ECOTOXE15472).
2- The NO AEC used to calculate chronic RQs for CRLF was 21 ug/L for the striped bass for posthatch survival
(ECOTOX number E15472).
3- The E/M fish acute endpoint used to calculate RQs for the DS is the 96-hr LC50 of 204 ug/L for the Atlantic
Silverside (ECOTOX El 1868).
4- The NO AEC used to calculate chronic RQs for E/M fish was 6 ug/L estimated using the ACR of 34 calculated
for the Sheepshead minnow and the lowest acute toxicity endpoint for Atlantic silverside (MRID 00079112 and
El 1868).
5- Aquatic dissipation chronic values are average 60-day concentrations measured in rice paddies. Values are only
slightly lower when factoring in the 14 day holding period and a separate estimate was not prepared for this
characterization.
6- The peak value represents the highest measured concentration in rice growing areas of California.
7- The chronic value represents the average of concentrations measured between May 9 and June 22, 2000 in the
NAWQA monitoring.
Chronic RQs for freshwater fish were calculated based on a NOAEC of 21 jig a.i./L for the
striped bass (El 5472). At 23|ig/L posthatch survival was reduced. The chronic endpoint may
underestimate risk because hatching success was not evaluated in the study. The toxicity
endpoint for E/M fish was estimated using an ACR. Chronic RQs for the CRLF and DS exceed
the LOG of 1.0 when calculated based on concentrations measured in rice paddies and estimated
using the Tier I Rice Model. The chronic RQ for the CRLF based on the Tier I Rice Model was
46.10. Chronic RQs for the CRLF and DS, respectively, based on concentrations measured in
rice paddies were 3.33-3.81 and 11.67 - 13.33. These concentrations may be expected to occur
in the rice paddy and near where water is released from the rice paddy. Chronic RQs for the DS
and CRLF estimated based on monitoring studies indicate that chronic risk to DS and CRLF is
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less likely as the released paddy water is diluted and thiobencarb will have time to dissipate from
the water column and the RQs were below LOCs.
These results indicated that direct effects to the CRLF and DS may occur with use of thiobencarb
on rice. Risks are predicted even when using measured concentrations in rice growing areas (see
Section 3.1.1 for a description of monitoring data). The likelihood of risk is further supported by
aquatic field studies which suggest that application of thiobencarb to rice fields may result in
significant environmental damage to fish (MRID 42130705 and 42130708).
Based on the CADPR PUR data, from 1999 to 2006 an average of 308, 491 - 1,006, 327 Ibs of
thiobencarb per year were applied to rice in California. Usage of thiobencarb on rice in
California is expected to occur and thiobencarb is often used at the maximum application rate
(Table 2-6). Finally, monitoring data are shown to be highest in May and June (Orlando and
Kuivila, 2004). In May and June, the life-stage of CRLF would be young juveniles and DS may
be spawning and have moved into freshwater (Table 2-7). Finally, CRLF critical habitat and DS
critical habitat overlap with the cultivated crop NLCD land cover class.
Therefore, the weight of evidence based on the currently available data suggests that direct
effects to aquatic-phase CRLFs and DS are expected from the use of thiobencarb on rice in
California.
5.2.1.b. Terrestrial-Phase CRLF
Acute RQs for birds could not be calculated as no mortality occurred at the highest doses tested.
The ratio of the EECs to the highest dose tested is 0.44. The subacute dietary endpoint, LCso
>5000 mg a.i./kg-bw is well above the highest dietary based EEC of 540 mg/kg-diet (MRID
44846206 and Table 3-6). The ratio of the EEC to the highest dietary concentration tested is
0.11. If toxicity were observed slightly above the highest levels tested, there is a potential that
the LOG for listed species (0.1) could be exceeded. The EEC estimated for granular
formulations was 42 mg a.i./ft2. The adjusted avian LDso/ft2, comparable to an RQ, is <1.49
(Appendix G). This value could be greater than the acute avian LOG of 0.1.
Chronic reproductive effects to birds were observed at 300 mg a.i./kg-diet (LOAEC), with an
associated NOAEC of 100 mg a.i./kg-diet (MRID 00025778). Effects observed included effects
on eggs laid and hatchlings per live three week embryo. Sublethal effects observed in the study
at concentrations of 30 mg/kg-diet include loss of coordination, lower limb weakness, prostate
posture, loss of reflexes, and wing droop. The T-REX estimated chronic RQ of 9.60 exceeds the
chronic LOG of 1.0. This also indicates that directs effects to the CRLF are likely to occur with
use of liquid formulations of thiobencarb on rice. A method is not available to evaluate chronic
risk to birds from the use of granular formulations.
Birds were used as surrogate species for terrestrial-phase CRLFs. Terrestrial-phase amphibians
are poikilotherms, which means that their body temperature varies with environmental
temperature, while birds are homeotherms (temperature is regulated, constant, and largely
independent of environmental temperatures). As a consequence, the caloric requirements of
terrestrial-phase amphibians are markedly lower than birds. Therefore, on a daily dietary intake
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basis, birds consume more food than terrestrial-phase amphibians. This can be seen when
comparing the caloric requirements for free living iguanid lizards (used in this case as a
surrogate for terrestrial phase amphibians) to song birds (USEPA, 1993):
iguanid FMR (kcal/day)= 0.0535 (bw g)
0.799
0.749
passerine FMR (kcal/day) = 2.123 (bw g)'
With relatively comparable slopes to the allometric functions, one can see that, given a
comparable body weight, the free-living metabolic rate (FMR) of birds can be 40 times higher
than reptiles, though the requirement differences narrow with high body weights.
Because the existing risk assessment process is driven by the dietary route of exposure, a finding
of safety for birds, with their much higher feeding rates and, therefore, higher potential dietary
exposure, is reasoned to be protective of terrestrial-phase amphibians. For this not to be the case,
terrestrial-phase amphibians would have to be 40 times more sensitive than birds for the
differences in dietary uptake to be negated. However, existing dietary toxicity studies in
terrestrial-phase amphibians for thiobencarb are lacking. To quantify the potential differences in
food intake between birds and terrestrial-phase CRLFs, food intake equations for the iguanid
lizard were used to replace the food intake equation in T-REX for birds, and additional food
items of the CRLF were evaluated. These functions were encompassed in a model called T-
FtERPS. T-HERPS is available at: http://www.epa.gov/oppefedl/models/terrestrial/index.htm.
For the uses with the highest application rates (4 Ib a.i./acre), none of the acute dose-based RQs
for terrestrial herpetofauna exceed the Agency's listed species LOG for acute exposure (Table
5-10). Based on these calculations use of thiobencarb on rice is not expected to result in acute
direct effects to terrestrial-phase CRLF (see also Appendix G).
Table 5-10. Upper Bound Kenaga, Acute Terrestrial Herpetofauna Dose-Based Risk
Quotients for Thiobencarb (4 Ib a.i./acre, 1 Application)
Size
Class
(grams)
1.4
37
238
Highest
Dose
Tested
(mg
a.i./kg-bw)
1938.00
1938.00
1938.00
EECs (mg/kg-bw) and EEC/Highest Dose Tested Ratio
Broadleaf
Plants/
Small Insects
EEC
20.98
20.62
13.51
Ratio
<0.01
O.01
0.01
Fruits/Pods/
Seeds/
Large Insects
EEC
2.33
2.29
1.50
Ratio
0.00
0.00
0.00
Small Herbivore
Mammals
EEC
N/A1
N/A
57.69
Ratio
N/A
N/A
<0.03
Small
Insectivore
Mammal
EEC
N/A
N/A
3.61
Ratio
N/A
N/A
0.00
Small
Amphibians
EEC
N/A
0.72
0.47
Ratio
N/A
0.00
0.00
N/A = not applicable (a 1.4 or 37 g frog is not expected to be large enough to eat a 35 g mammal).
At the 4 Ib a.i./acre application rate the sub-acute EEC/highest concentration tested ratios for
terrestrial herpetofauna that eat broadleaf plants/small insects and small herbivorous mammals
have the potential to exceed the Agency's listed species LOCs based on dietary exposure to
small insects and small herbivore mammals (Table 5-11). Because a definitive LCso was not
determined for birds (i.e., the LCso >5000 mg a.i./kg-diet) all of the calculated EEC/Highest
Concentration Tested Ratios for sub-acute dietary exposure are less than values. The available
100
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data indicate that acute risk to birds is unlikely. However, the possibility that LOCs could be
exceeded exists. Additionally, only limited data are available on the acute toxicity of
thiobencarb to birds. No data are available for passerine species. Therefore, risks to terrestrial-
phase frogs from acute exposure cannot be precluded for any of the uses or dietary categories at
this time.
For chronic exposure, use of thiobencarb on rice results in RQs that exceed the Agency's chronic
listed species LOG of 1.0 for amphibians consuming broadleaf plants/small insects and small
herbivore mammals using an avian NOAEC of 100 mg a.i./kg-diet (Table 5-11). RQs range
from 0.19-9.15. Therefore, chronic risk to the CRLF may occur with the use of thiobencarb on
rice.
Table 5-11. Upper Bound Kenaga, Sub-Acute and Chronic Terrestrial Herpetofauna
Dietary-Based Risk Quotients for Thiobencarb (1 Application at 4 Ibs a.i./acre).
Highest Dose
Tested or
Endpoint
(mg a.i./kg-
diet)
EECs (mg/kg-diet) and EEC/ Highest Concentration Tested Ratio or RQ
Broadleaf
Plants/
Small Insects
EEC
Ratio
Fruits/Pods/
Seeds/
Large Insects
EEC
Ratio
Small Herbivore
Mammals
EEC
Ratio
Small
Insectivore
Mammals
EEC
Ratio
Small
Amphibians
EEC
Ratio
Sub-Acute (Dietary)
LC50 > 5000
NOAEC = 100
540.00
EEC
540.00
<0.11
RQ
5.40
60.00
EEC
60.00
0.01
RQ
0.60
915.29
Chronic (Dk
EEC
915.29
<0.18
tary)
RQ
9.15
57.21
EEC
57.21
0.01
RQ
0.57
18.74
EEC
18.74
O.O
0
RQ
0.19
- Bolded numbers (black) exceed the Agency's listed species acute LOG of 0.1 or chronic LOG of 1.0.
- Bolded numbers with a less than sign potentially exceed the Agency's acute LOG of 0.1.
These results indicate that the risk of direct adverse effects to terrestrial-phase CRLF from acute
oral or sub-acute dietary exposure is likely low. However, risk cannot be precluded because
limited data are available on the acute toxicity of thiobencarb to birds and the estimated ratios
have the potential to exceed LOG values. Chronic risk to terrestrial-phase CRLF from chronic
dietary exposure cannot be precluded and exists for the dietary classes of small insects and small
mammals.
5.2.2. Indirect Effects, DS and Aquatic-Phase CRLF
As discussed in Section 2, the diet of aquatic-phase CRLF tadpoles and DS larvae is composed
primarily of unicellular aquatic plants (i.e., algae and diatoms) and detritus. However, aquatic
invertebrates are also consumed by both CRLFs and the DS, and fish are consumed by adult
CRLFs. Therefore, potential impacts to each of these potential food items are evaluated.
101
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5.2.2.a. Potential Impacts to Fish (Indirect Effects to CRLF Only)
Fish are food items of the CRLF. As discussed in Section 5.2.1.a, all RQs exceed LOCs for
freshwater fish. Therefore, indirect effects to CRLF from a decline in potential fish prey are
expected from the use of thiobencarb on rice in California.
5.2.2.b. Potential Impacts to Aquatic Invertebrates
CRLF and DS (Freshwater Aquatic Invertebrates)
Aquatic invertebrates are a potential food item for the CRLF and DS. The acute risk to listed
and non-listed species LOCs of 0.05 and 0.5 were exceeded for freshwater invertebrates for
thiobencarb use based on toxicity values from the most sensitive freshwater invertebrates for
which data are available. The highest acute RQ is 19.94 and was estimated in rice paddies based
on an endpoint for Daphnia. At this RQ and using the default slope (4.5), the probability of an
effect would be approximately 1 in 1.0 (estimated using IEC version 1.1, see Table 5-12).
Table 5-12. Probit Dose-Response Analysis for Aquatic Invertebrates
Species Represented
Freshwater
Invertebrate (Indirect
effects to CRLF)
Freshwater
Invertebrate (Indirect
effects to DS)
E/M Invertebrate
(Indirect effects to DS
Maximum
RQ
19.94
5.69
3.84
Acute Effect
Slope (95% C.I.)
Mortality
Default Slope = 4.5
(2-9)
Mortality
Default Slope = 4.5
(2-9)
Mortality
Default Slope = 4.5
(2-9)
Chance of Individual Effect
at Listed Species LOG
(95% C.I.)
lin4.18E+08
(1 in 216 to linl.75E+31)
lin4.18E+08
(1 in 216 to linl.75E+31)
lin4.18E+08
(1 in 216 to linl.75E+31)
Chance of
Individual Effect at
Derived Acute RQ1
(95% C.I.)
1 in 1.0
(1 in 1.0 to 1 in 1.0)
1 in 1.0
(1 in 1.07 to 1 in 1.0)
1 in 1.0
(1 in 1.14 to 1 in 1.0)
In order to better characterize the potential risk to freshwater invertebrates, toxicity endpoints
were also compared to exposure estimates based on aquatic dissipation studies and monitoring
data collected in a rice growing area of California. These results are shown in Table 5-13.
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Table 5-13. Acute and Chronic RQs for Aquatic Invertebrates Used to Evaluate Potential
Indirect Effects to the CRLF and the DS Resulting from Potential Impacts to Food Supply.
Exposure estimated based on aquatic dissipation studies and monitoring data.
Basis of Exposure
Estimates
Peak
EEC
(Hg/L)
Chronic
EEC
(Mg/L)
Risk Quotients
FW Invertebrates
Acute1
Chronic2
E/M Invertebrates5
Acute3
Chronic4
Realistic Exposure Estimate in Paddy Water and Where Paddy Water is Released (CRLF and DS)
Aquatic Dissipation
Study (MRID
43404005)
Aquatic Dissipation
Study (Ross and Sava,
1986)
438
576
2025
2095
4.33
5.69
202.00
209.00
2.92
3.84
63.13
65.31
Exposure Estimates Based on Measured Concentration in Rice Growing Areas of CA
(CRLF and DS)
Colusa Basin Drain on
Sacramento River 6
1706
5.377
1.68
5.37
1.13
1.68
LOC exceedances (acute RQ > 0.05; chronic RQ > 1.0) are bolded. Acute RQ = peak EEC /96-hr LC50; Chronic
RQ = 21 day EEC/NOAEC; FW=freshwater; E/M=estuarine/marine
1- The freshwater invertebrate endpoint used to calculate acute RQs is the 96-hr LC50 of 101.2 ug/L for Daphnia
magna (MRID 00025788).
2- The NOEAC used to calculate chronic RQs for freshwater invertebrates is 1 ug/L for the Daphnia magna based
on reduced number of offspring produced (MRID 00079098).
3- The E/M acute endpoint used to calculate RQs is the 96-hr LC50 of 150 ug/L for the Mysid shrimp (MRID
00050667).
4- The E/M acute endpoint used to calculate RQs is the 21-day NO AEC of 3.2 ug/L for the Opossum shrimp
based on reduced survival of offspring (MRID 43976801 or 40651314).
5- The chronic value represents the 21-day average concentration observed in the aquatic dissipation study.
6- The peak value represents the highest measured concentration in rice growing areas of California.
7- The chronic value represents the average of concentrations measured between May 9 and June 22, 2000 in the
NAWQA monitoring.
More realistic RQs based on aquatic dissipation studies range from 4.33 - 5.69 (Table 5-2). At
these RQs and using the default slope (4.5), the probability of an effect would still be
approximately 1 in 1.0 (estimated using IEC version 1.1). The RQ (1.68) based on high
concentrations measured in the Sacramento River before the 14-day holding period was put in
place also exceed the LOC of 0.05.
Based on chronic exposure to freshwater invertebrates, the Agency's chronic risk LOC of 1 is
exceeded for the concentrations estimated in the rice paddy (RQ = 968), when tail water is
released from rice paddies after 14-days (RQ=3.46), concentrations measured in aquatic
dissipation studies (RQs = 202 - 209), and for high concentrations measured in rice growing
areas of California (RQ = 5.37). For E/M invertebrates, the LOC of 1.0 is also exceeded for all
exposure scenarios with RQs ranging from 1.68 - 65.31 (Table 5-2).
The NO AEC (1.0 |ig/L) used to calculate the chronic freshwater invertebrate RQs is based on an
endpoint of number of offspring produced and the EECs are well above the NO AEC.
The LOAEC for this study was 3.0 |ig/L. A reduction in the number of offspring has the
103
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potential to influence the abundance of aquatic invertebrates and to decrease the number of prey
items available for the CRLF and DS. Therefore, use of thiobencarb on rice is likely to
adversely affect CRLF and DS due to decreased aquatic invertebrate prey items.
DS (Estuarine/marine aquatic invertebrates)
The DS eats small zooplankton. They primarily eat planktonic copepods, cladocerans,
amphipods, and insect larvae. However, the most important food organism appears to be
Eurytemora qffinis, which is a euryhaline copepod (USFWS, 1996, 2004b). No estuarine/marine
studies were submitted examining toxicity of thiobencarb to copepods. A supplemental field
study is available from the open literature for a non-native freshwater cyclopoida and calanoida
(E62293). In this field study, conducted with a formulation thiobencarb, the 7-day LOAEL was
187.5 jig a.i./L (effects observed were emergence success). Risk quotients were calculated based
on the most sensitive aquatic invertebrate endpoint, the mysid value of 150 |ig/L (MRID
00050667). Based on toxicity data from mysid and residues measured in aquatic dissipation
studies, the RQs for thiobencarb use on rice (RQs range from 2.92 - 3.84) exceed the Agency's
acute risk LOCs (listed or non-listed species). RQs estimated using monitoring data range from
<0.00 - 1.13 and also exceed LOCs. At the highest RQ (3.84) and using a default slope of 4.5,
the probability of an effect would be approximately 1 in 1.00 (estimated using LEG version 1.1).
Therefore, impacts to potential estuarine/marine invertebrate prey are expected from acute
exposure to thiobencarb.
For chronic risk to E/M invertebrates, risk quotients were calculated based on the 21-day
NOEAC of 3.2 jig a.i./L for the Opossum shrimp which is based on survival of offspring (MRID
43976801 or 40651314). The LOAEC for this study is 6.2 |ig a.i./L. It is likely that exposure to
water released from rice paddies could result in exposures estimated using aquatic dissipation
data and measured in monitoring studies. These results indicate that effects to E/M aquatic
invertebrates may occur near rice paddies. Risk would decrease as exposure decreased with
distance from rice paddies. Based on the weight of evidence, indirect risk to DS due to
reductions in E/M aquatic invertebrate prey is likely to occur with use of thiobencarb on rice in
California.
5.2.2.C. Potential Impacts to Aquatic Plants
CRLF tadpoles consume primarily algae, and DS larvae consume phytoplankton. Algal RQs
ranged from approximately 20.59 - 118.71 based on modeling data. RQs were calculated based
on the 5-day ECso of 17 |ig/L for green algae (MRID 41690901). Vascular plant RQs were only
exceeded when based on modeled data and inside rice paddies (RQs ranged from 0.45 - 2.62).
These results indicate that there is a potential for effects on aquatic plants and indirect effects to
CRLF and DS based on effects on food and habitat. In order to better characterize potential risk
to aquatic plants, RQs were estimated based on exposure estimates from aquatic dissipation
studies and monitoring data. These results are shown in Table 5-14.
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Table 5-14. Summary of RQs for Vascular and Non-Vascular Aquatic Plants Using
Exposure from Aquatic Dissipation Studies and Monitoring Data.
Basis of Exposure
Estimates
Peak EEC
(Hg/L)
Risk Quotients
Non-vascular Plants1
Vascular Plants2
Realistic Exposure Estimate in Paddy Water and Where Paddy Water is Released
(CRLF and DS)
Aquatic Dissipation Study
(MRID 43404005)
Aquatic Dissipation Study
(Ross and Sava, 1986)
438
576
25.76
33.88
0.57
0.75
Exposure Estimates Based on the Measured Concentration in Rice Growing Areas of CA
(CRLF and DS)
Colusa Basin Drain on
Sacramento River 3
1703
10.00
0.22
LOG exceedances (RQ > 1.0) are bolded. RQ = peak EEC /5-day EC50 for nonvascular plants or 14-day EC50 for
vascular plants.
1- The non-vascular plant endpoint used to calculate RQs for the 5-day EC50 of 17 ug/L for the Green algae
(MRID 41690901).
2- The vascular plant endpoint used to calculate acute RQs is the 14-day EC50 of 770 ug/L for Duckweed (MRID
41690901).
3- Represents the highest measured concentration in rice growing areas of California.
Aquatic dissipation studies and monitoring data support the conclusions drawn from the
modeling data. Nonvascular plant RQs ranged from 10.00 - 33.88. Vascular plant RQs ranged
from 0.22 - 0.75. LOCs for vascular plants were only exceeded based on exposure estimated in
the rice paddy. LOCs for non-vascular plants were exceeded using EECs estimated for the rice
paddy, based on measured concentrations in rice paddies, and based on measured concentrations
in rice growing areas. Since the RQs are exceeded, there is a potential for indirect effects to the
CRLF and DS that rely on non-vascular aquatic plants during at least some portion of their life-
cycle.
5.2.2.d. Indirect Effects, Terrestrial-Phase CRLFs
As discussed in Section 2.5 and 2.6, the diet of terrestrial-phase CRLFs includes terrestrial
invertebrates, small mammals, and amphibians. Potential impacts to each of these potential food
items are evaluated below.
5.2.2.e. Terrestrial Invertebrates
When the terrestrial-phase CRLF reaches juvenile and adult stages, its diet is mainly composed
of terrestrial invertebrates. Thiobencarb is classified as practically nontoxic to non-target insects
on an acute contact exposure basis. An acute contact LD50 for terrestrial invertebrates could not
be determined based on available data. At the highest concentration tested in the oral test, 23.3%
of the bees died in the treatment group as opposed to 6.7 and 3.3% in the negative and solvent
control groups, respectively. In the contact exposure group, 15% of bees died as compared to 6.7
and 10% in the control groups. The 48-hr LD50 is greater than 100 jig a.i./bee for both studies.
No sublethal effects were observed. Only one concentration was used in this study; therefore, a
105
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definitive LD50 value and response slope could not be determined. Using an LD50 of > 100 jig
a.i./bee results in and EEC/highest dose tested ratio of 0.69 and 0.08 for small and large insects,
respectively; however, it is not clear if the actual RQs are above or below the interim LOG of
0.05 for acute risk to endangered terrestrial invertebrates.
In the submitted contact honey bee study, a concentration of 781 jig/g bee resulted in 15%
mortality. Based on T-REX, a flowable thiobencarb application of 4 Ib a.i./acre results in EEC
values of 60 and 540 ppm for large and small insects, respectively. Therefore, the concentration
on the site of application at the maximum allowable application rate is not expected to reach
levels high enough to cause 15% mortality in large insects. However, depending on the slope of
the dose response curve, the ECso value could be slightly above 781 jig/g bee and could result in
an RQ greater than the listed species LOG of 0.05. The likelihood of risk to terrestrial
invertebrates is low; however, risk cannot be precluded without a definitive toxicity endpoint.
5.2.2.f. Mammals
Terrestrial-phase CRLFs consume small mammals. This assessment used a 15 g mammal as a
potential mammalian prey. For thiobencarb formulations applied as a broadcast spray, RQs for
mammals consuming short grass, tall grass, and broadleaf plants/small insects exceed the
Agency's acute risk to listed species LOG (RQs range from 0.18 - 0.40). Using the highest RQ
of 0.40 and the default slope of 4.5, the probability of individual effect is approximately 1 in 2.73
(estimated using IEC version 1.1). For granular formulations, the RQ (1.22) also exceeds the
listed species LOG of 0.05 based on an LD50/ft2 analysis. Assuming a default probit slope of
4.5, the probability of an individual effect would be approximately 1 in 1.54 (estimated using
IEC version 1.1). Probit analysis for mammals are summarized in Table 5-15.
Table 5-15. Probit Dose-Response Analysis for Mammals and Potential Indirect Effects to
CRLF
Species Represented
Mammals (liquid
formulations)
Mammals (granular
formulations)
Maximum
RQ
0.40
1.22
Acute Effect
Slope (95% C.I.)
Mortality
Default Slope = 4.5
(2-9)
Mortality
Default Slope = 4.5
(2-9)
Chance of Individual Effect
at Listed Species LOG
(95% C.I.)
1 in 2.94E+05
(1 in 44 to lin8.86E+18)
1 in 2.94E+05
(1 in 44 to lin8.86E+18)
Chance of
Individual Effect at
Derived Acute RQ1
(95% C.I.)
1 in 1.0
(1 in 4.69 to 1 in
5850)
1 in 1.54
(1 in 1.76 to 1 in
1.28)
Regarding the potential for impacts from chronic exposure, all of the RQs for chronic exposure
exceed the Agency's chronic risk LOG. The RQs range from 3.00 - 416.45. These RQs are
based on a NOAEC of 1 mg/kg-diet from a 2-generation study (MRID 40446201) on the Fischer
344 rat. Decreased body weight gain, food consumption, and feeding efficiency were observed
at 100 mg/kg/day. No reproductive effects were observed in the mammalian multigeneration
studies at 100 mg/kg/day (MRID 40446201). It is uncertain whether a decrease in body weight
gain would result in effects in survival and reproduction. The prenatal developmental studies in
the rat and rabbit support the use of the body weight endpoint for the effects determination. In a
developmental study in the rat an increase in skeletal anomaly and increased number of runts
106
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were observed at 150 mg/kg/day (NOAEL = 25 mg/kg/day; MRID 00115248). A decreased
body weight gain was also observed in that study. Due to the uncertainty associated with
possible effects based on an endpoint of body weight alone, an EEC/reproductive NOAEL of
>100 mg/kg/day were calculated. Chronic dose-based ratios range from <0.53 - <83.29. Ratios
could exceed 1.0 for mammals consuming short grass, tall grass, broadleaf plants/small insects,
and fruits/pods/seeds/large insects. Chronic dietary-based ratios range from <0.60 - <9.60 and
could exceed the LOG of 1.0 for short grass, tall grass, broadleaf plants/small insects, and
fruits/pods/seeds/large insects. It is uncertain whether actual RQs would exceed the LOCs as
possible exposure exceeds the highest dose tested in the two-generation study. Based on effects
observed on body weight, in the developmental studies, and on the reproductive effects observed
in birds, chronic risk to mammals cannot be discounted. Therefore, the Agency concludes that
thiobencarb use on rice has the potential to impact mammalian prey populations and thus reduce
prey of the CRLF.
5.2.2.g. Amphibians
CRLF are known to prey on aquatic-phase amphibians. As discussed in Section 5.2.1.a, direct
effects to aquatic phase amphibians are likely. Therefore, indirect effects to CRLF from a
decline in potential aquatic phase amphibian prey are expected from the use of thiobencarb on
rice in California.
Terrestrial amphibian prey of the CRLF include small amphibians such as tree frogs that do not
prey on mammals. Therefore, the mammalian food group is not relevant in the evaluation of
potential reductions in amphibian prey abundance. As discussed in Section 5.2.1.b, direct effects
to terrestrial phase amphibians are likely. Therefore, indirect effects to CRLF from a decline in
potential terrestrial amphibian prey are expected from the use of thiobencarb on rice in
California.
5.2.2.H. Potential Effects to Habitat
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. Results of the indirect effects assessment are used as the basis for the
habitat modification analysis. As discussed in Section 5.2.2.C, aquatic plants are likely to be
impacted from the use of thiobencarb on rice. Therefore, impacts to aquatic plants found near
thiobencarb use sites are expected.
Terrestrial plants serve several important habitat-related functions for the listed assessed species.
Among other things, 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 (CRLF and DS).
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In addition to providing shelter and cover from predators while foraging, upland vegetation,
including grassland and woodlands, provides cover during dispersal (CRLF).
Based on the results of the submitted terrestrial plant toxicity studies and the reported terrestrial
plant incidents, the herbicide thiobencarb is phytotoxic to many plant species (seedling
emergence endpoints are more sensitive than vegetative vigor endpoints). Additionally,
monocots are more sensitive to thiobencarb than dicots, based on available data. Only dicots
exposed to spray drift from aerial applictions of liquid formations exceed the LOG of 1.0. Spray
drift EECs for granular formulations are assumed to be low because spray drift is expected to be
minimal. Exposure to runoff from rice paddies is not evaluated as runoff is not expected to
commonly occur in rice paddies.
A general conclusion that can be drawn from these data is that the inhibition of new growth may
occur in non-target terrestrial plants from registered uses of thiobencarb. Inhibition of new
growth could result in degradation of high quality riparian habitat over time because as older
growth dies from natural or anthropogenic causes, plant biomass may be prevented from being
replenished in the riparian area. Inhibition of new growth may also slow the recovery of
degraded riparian areas that function poorly due to sparse vegetation because thiobencarb
deposition onto bare soil would be expected to inhibit the growth of new vegetation.
Additionally, because effects were seen in most species tested in the seedling emergence and
vegetative vigor studies, it is likely that many species of herbaceous plants could be potentially
affected by exposure to thiobencarb. This is supported by the seven plant incidence where
effects on rice and an unspecified plant were reported after use of thiobencarb.
It is difficult to estimate the magnitude of potential impacts of thiobencarb use on riparian habitat
and the magnitude of potential effects on stream water quality from such impacts as they relate to
survival, growth, and reproduction of the CRLF and DS. The level of exposure and any resulting
magnitude of effect on riparian vegetation are expected to be highly variable and dependent on
many factors. The extent of runoff and/or drift into stream corridor areas is affected by the
distance the thiobencarb use site is offset from the stream, local geography, weather conditions,
and quality of the riparian buffer itself. The sensitivity of the riparian vegetation is dependent on
the susceptibility of the plant species exposed to thiobencarb and composition of the riparian
zone (e.g., vegetation density, species richness, height of vegetation, width of riparian area).
In summary, terrestrial and aquatic plant RQs are above plant LOCs; therefore, labeled use of
thiobencarb has the potential to affect both aquatic and riparian vegetation within CRLF and DS
habitats.
5.2.3. Spatial Extent of Potential Effects
Since LOCs are exceeded, analysis of the spatial extent of potential effects is needed to
determine where effects may occur in relation to the treated site. If the potential area of usage
and subsequent effects overlaps with CRLF and DS critical habitat or areas of occurrence, a
likely to adversely affect determination is made. If the area of potential effects and the CRLF
and/or DS critical habitat and areas of occurrence do not overlap, a no effect determination is
made.
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To determine this area, the footprint of thiobencarb's use pattern is identified, using
corresponding land cover data. This area is defined by the cultivated crop land cover based on
potential use on rice. Actual usage is expected to occur in a smaller area as rice is only grown in
a portion of the cultivated crop land cover class. The spatial extent of the effects determination
also includes areas beyond the initial area of concern that may be impacted by runoff and/or
spray drift (potential use areas + distance down stream or down wind from use sites where
organisms relevant to the CRLF and/or DS may be affected). The determination of the buffer
distance and downstream dilution for spatial extent of the effects determination is described
below.
5.2.3.a. Spray Drift
In order to determine terrestrial and aquatic habitats of concern due to thiobencarb 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. Applications
of thiobencarb granular formulations are not expected to result in any spray drift. For the
flowable uses, a quantitative analysis of spray drift distances was completed using AgDRIFT (v.
2.01) using default inputs for ground applications (i.e., high boom, ASAE droplet size
distribution = Very Fine to Fine, 90th data percentile) and aerial applications (i.e., ASAE Very
Fine to Fine).
Terrestrial Spray Drift Distances
Direct Effects. For direct effects to the terrestrial-phase CRLF, the highest RQs for birds that eat
small insects were used to estimate the fraction of the application rates that would no longer
exceed the listed species LOG (i.e., fraction of applied = LOC/RQ) for both acute and chronic
RQs. This number was used in AgDRIFT to calculate the distance from the field where the
amount of thiobencarb that equaled the 'fraction of applied' would be expected to occur (as
spray drift) (Table 5-16). The terrestrial spray drift distance needed to reduce exposure to levels
below LOCs for direct effects to the CRLF is 272 feet for aerial applications of liquid
formulations and 26 feet for ground applications.
Indirect Effects. For indirect effects, a spray drift analysis is conducted using endpoints used to
evaluate indirect effects. The most sensitive species were terrestrial plants for terrestrial phase
CRLF. The distance from the field for terrestrial plants is based on the most sensitive terrestrial
plant non-listed species endpoint (i.e., monocot seedling emergence EC25 = 0.0019 Ib a.i./acre).
This endpoint is used to estimate the fraction of the application rates that would no longer exceed
the 25% level of effects for terrestrial plants (i.e., fraction of applied = 0.0019 Ib a.i./acre divided
by the application rate in Ib a.i./acre) (Table 5-16). The terrestrial spray drift distance to result in
no LOG exceedances for the terrestrial-phase CRLF is greater than 1000 feet for aerial
applications and 433 feet for ground applications.
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Table 5-16. Distance from Thiobencarb Use Site Needed to Reduce Spray Drift to Levels
that Do Not Exceed Terrestrial Acute and Chronic LOCs for Direct and Indirect Effects
(Point Deposition Estimate)
Endpoint or Taxa
Evaluated
Type of
Endpoint
RQ
Range
Fraction of
Applied =
LOC/RQ*
Spray Drift Distance to Result
No Effect (feet)
Aerial
Applications
Ground
Applications
Direct Effects to CRLF
Direct Effects to
Terrestrial Phase CRLF
(surrogate bird)
Acute: No
mortality
Chronic:
Reproduction
0.00 -
0.18
0.19-9.15
<1.80
0.11
n/a
272
n/a
26
Indirect Effects to Terrestrial Phase CRLF
Mammals
Terrestrial invertebrates
Non-listed Dicot
terrestrial plants
Non-listed Monocot
terrestrial plants
Acute:
mortality
Chronic:
Body weight
15% mortality
Seedling
Emergence
Mortality
Seedling
Emergence
Shoot Length
0.01-0.40
3.00
416.45
0.08 -
0.69
O.I -
12.20
0.1-
52.63
0.25
0.0002
n/a
0.0205
0.00475
85.3
>1000
n/a
>1000
>1000
13.12
>1000
n/a
121
433
Bold values show the maximum spray drift distances needed to reduce exposure to below levels expected to result in
LOG exceedances.
*For terrestrial plants, Fraction of applied is the lowest EC25/maximum application rate in Ibs a.i./A. Endpoints used
in the calculation were the monocots - EC2s = 0.019 Ib a.i./acre (seedling emergence) and dicots - EC2s = 0.082 Ibs
a.i./acre [seedling emergence, cabbage)] (MRID 41690902).
Aquatic Spray Drift Distances
Direct Effects. For direct effects to aquatic-phase CRLF and DS, the distance from the site of
application in which spray drift could reach levels high enough to exceed the acute risk to
endangered species LOG, the 'active rate' (i.e., the highest maximum labeled rate) and the
'initial average concentration' (i.e., Toxicity Endpoint x LOG) were used as input into
AgDRJFT. For this analysis, the farm pond (i.e., a pond with a depth of 2 meters and a
downwind width of 63.61 m and flight line width of 157.21 m) was used as a proxy for CRLF
and DS habitat. The other AgDRIFT inputs were the same as described above in the terrestrial
distance analysis. The results of these calculations are shown in Table 5-17. The aquatic spray
drift distance needed to reduce exposure to levels below LOCs for direct effects for CRLF is
greater than 1000 feet for aerial applications and 207 feet for ground applications of liquid
formulations. The aquatic spray drift distance needed to reduce exposure to levels below LOCs
for direct effects to the DS is greater than 1000 feet for aerial applications and 351 feet for
ground applications.
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Table 5-17. Distance from Thiobencarb Use Site Needed to Reduce Spray Drift to Levels
that Do Not Exceed Acute and Chronic LOCs in Aquatic Environments
Endpoint or
Taxa Evaluated
Type of
Endpoint
RQ Range
Endpoint
Used to
Evaluate
Risk Qig/L)
Initial Average
Concentration =
Toxicity Endpoint
xLOC
Spray Drift Distance
to Result in No Effect
(feet)
Aerial
App
Ground
App
Direct Effects to Aquatic Phase CRLF and DS
Freshwater fish
in Paddy
Freshwater fish
in Tailwater
Estuarine/Marine
fish
Acute: mortality
Chronic:
Posthatch
survival
Acute: mortality
Chronic:
Posthatch
survival
Acute: mortality
Chronic: wet
weight
0.39-4.59
0.26-46.10
0.39-1.31
0.26-3.81
0.83-2.82
0.90-13.33
440
21
440
21
204
6
22
21
22
21
10.2
6
>1000
>1000
>1000
>1000
151
207
351
79
Indirect Effects to Aquatic Phase CRLF and DS
Freshwater
invertebrates
Estuarine/Marine
Invertebrates
Non-listed
Aquatic vascular
plants
Non-listed
Aquatic non-
vascular plants
Acute: mortality
Chronic:
Offspring
produced
Acute: mortality
Chronic:
Posthatch
survival
Frond production
Cell
Density /Inhibition
of Growth
1.68-
19.94
5.37-968
2.92-3.84
20.61-
21.33
0.22-2.62
0.04-118.71
101.2
1
150
3.2
770
17
5.06
1
7.5
3.2
770
17
>1000
>1000
>1000
>1000
0
>1000
39
358
16
89
0
207
App. = Application
Bold values show the maximum spray drift distances needed to reduce exposure to below levels expected to result in
LOG exceedances.
Indirect Effects. For indirect effects, a spray drift analysis is conducted using endpoints used to
evaluate indirect effects. The most sensitive species were freshwater invertebrates for the
aquatic phase CRLF and DS. For freshwater invertebrates, the most sensitive 21-day NOAEC of
1.0 |ig/L for the daphnia was used to estimate the maximum aquatic spray drift distance by
calculating the initial average concentration (Toxicity endpoint x LOG) for input into AgDrift.
This number is used in AgDrift to calculate the distance from the field where the amount of
thiobencarb that equals the 'initial average concentration' would be expected to occur (as spray
drift) (Table 5-17). The aquatic spray drift distance to result in no LOG exceedances for the
aquatic-phase CRLF and DS is greater than 1000 feet for aerial applications and 358 feet for
111
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ground applications (see Table 5-17).
Looking at all estimated spray drift distances indicates that effects may occur at greater than
1000 feet for both aerial and ground applications. Because the LOCs are expected to be
exceeded at greater than 1000 feet from the use site, it is not known where risk would fall below
LOCs for aerial and ground applications.
5.2.3.b. Downstream Dilution Analysis
The downstream extent of exposure in streams and rivers where the EEC could potentially be
above levels that would exceed the most sensitive LOG is calculated using the downstream
dilution model. To complete this assessment, the greatest ratio of aquatic RQ to LOG was
estimated. Using an assumption of uniform runoff across the landscape, it is assumed that
streams flowing through treated areas (i.e., the initial area of concern) are represented by the
modeled EECs; as those waters move downstream, it is assumed that the influx of non-impacted
water will dilute the concentrations of thiobencarb present. The highest RQ/LOC ratio and the
land cover class (cultivated crops) are used as inputs into the downstream dilution model.
Using a 48-hr LCso value of 101.2 |ig/L for Daphnia magna, an LOG of 0.05, and a maximum
peak EEC of 2018 |ig/L from the Tier I Rice Model yields an RQ/LOC ratio of 399 (101.2/0.05).
The downstream dilution approach is described in more detail in Appendix N. This value has
been input into the downstream dilution model and results in a distance of 285 kilometers which
represents the maximum continuous distance of downstream dilution from the edge of the initial
area of concern where LOCs may be exceeded in the aquatic environment.
5.2.3.C. Overlap of Potential Areas of Effect and CRLF and DS
Habitat
The spray drift and downstream dilution analyses help to identify areas of potential effect to the
CRLF and DS from registered uses of thiobencarb. The potential area of effects for the CRLF
and DS from thiobencarb spray drift extend from the site of application to greater than 1000 feet
from the site of application. For exposure to runoff and spray drift, the area of potential effects
extends up to 285 km downstream from the site of application. When these distances are added
to the footprint of the initial area of concern (which represents potential thiobencarb use sites)
and compared to CRLF and DS habitat, there are several areas of overlap (Figure 5-1 and Figure
5-2). The overlap between the areas of effect and CRLF and DS habitat, including designated
critical habitat, indicates that thiobencarb use in California has the potential to affect the CRLF
and DS.
112
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California Red-Legged Frog and Potential Thiobencarb Use
Legend
^^| Use overlap with CH, core, sees
CRLF occurrence sections
^B CRLF Critical habitat
^B CRLF Core areas
| | Cultivated
~~| CAcounties
iKilometers
0 2040 SO 120 160
1:4,934,243
Map created by US EPA on 10/7/2009. Projection: Albers Equal
Area Conic USGS, North American Datum of 1983 (NAD 1983).
County boundaries and streams from ESRI (2002). CRLF habitat
fromUSFWS 2002 and 2005, section data from CNDDB. Landcover
from National Land Cover Database (MRLC, 2001).
10/2009
Figure 5-1. Map Showing the Overlap of CRLF Critical Habitat, Occurrence Sections, and
Core Areas with the NLCD Cultivated Crop Land Cover Class
113
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Delta Smelt and Potential Thiobencarb Use
^ .» it
-'.
x
\
J I
^ -»
Legend
I Use overlap with CH & sections
Delta smelt critical habitat (CH)
Delta smelt occurrence sections
NHD waterbody
CAStreams and Rivers
Cultivated
CAcounties
02.55 10 15 20
1:635,406
Map created by US EPA on 10/6/2009. Projection: Albers Equal
Area Conic USGS, North American Datum of 1983 (NAD 1983).
County boundariesfrom ESRI (2002), streamsfromESRI (2004).
Water bodies from NHDPIus (2006). Delta Smelt section information
obtained from Case No. 07-2794-JCS. Critical habitat data obtained
from http:fcrithab.1ws.gov/. bandc over from National Land Cover
Database (MRLC, 2001).
Figure 5-2. Map Showing the Overlap of DS Critical Habitat and Occurrence Sections
Identified by Case No. 07-2794-JCS with the NLCD Cultivated Crop Land Cover Class.
114
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5.3. Effects to Designated Critical Habitat
The risk conclusions for the designated critical habitat are based on conclusions described for
indirect effects previously described. Potential effects to habitat are described below.
5.3.1. CRLF Habitat Modification Analysis
5.3.1.a. 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. Additionally, direct
effects to aquatic and riparian plants could result in indirect effects to aquatic invertebrates and
other aquatic vertebrates other than the CRLF. As previously discussed, thiobencarb may cause
effects to habitat by potentially impacting aquatic plants and terrestrial plants.
The remaining aquatic-phase PCE is "alteration of other chemical characteristics necessary for
normal growth and viability of CRLFs and their food source." Thiobencarb may impact algae as
food items for tadpoles. Thiobencarb may also impact riparian areas that are predominantly
grassy or herbaceous, and the potential areas of effect overlap with designated critical habitat for
the CRLF (see Figure 5-1). Therefore, there is a potential for effects to habitat by potentially
impacting the chemical characteristics of the habitat.
5.3.1.b. 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 (0.06 km) of the edge of the riparian vegetation or
drip line surrounding aquatic and riparian habitat that are comprised of grasslands,
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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 (1.1 km) of each
other that allow for movement between sites including both natural and altered sites
which do not contain barriers to dispersal.
As an herbicide, thiobencarb may affect sensitive terrestrial plants; information from the reported
terrestrial plant incident data support this. Additionally, terrestrial plant LOCs are exceeded for
use of thiobencarb on rice and the potential areas of effect overlap with designated critical
habitat for the CRLF (see Figure 5-1).
The third terrestrial-phase PCE is "reduction and/or modification of food sources for terrestrial-
phase juveniles and adults." To assess the impact of thiobencarb on this PCE, acute and chronic
toxicity endpoints for terrestrial invertebrates, mammals, and terrestrial-phase frogs are used as
measures of effects. There is a potential for habitat modification based on potential reductions in
prey base (mammals and frogs, as previously described), and, again, the areas of potential effect
overlap with CRLF critical habitat (Figure 5-1).
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. There is a
potential for habitat modification based on potential direct (Section 5.2.1) and indirect effects
(Sections 5.2.2) to terrestrial-phase CRLFs.
5.3.2. Delta Smelt Habitat Modification Analysis
Primary constituent elements (PCEs) of designated critical habitat for the DS include the
following:
Spawning Habitatshallow, fresh or slightly brackish backwater sloughs and edgewaters
to ensure egg hatching and larval viability. Spawning areas also must provide suitable
water quality (i.e., low "concentrations of pollutants) and substrates for egg attachment
(e.g., submerged tree roots and branches and emergent vegetation).
Larval and Juvenile TransportSacramento and San Joaquin Rivers and their tributary
channels must be protected from physical disturbance and flow disruption. Adequate
river flowjs necessary to transport larvae from upstream spawning areas to rearing
habitat in Suisun Bay. Suitable water quality must be provided so that maturation is not
impaired by pollutant concentrations.
Rearing HabitatMaintenance of the two parts per thousand isohaline and suitable water
quality (low concentrations of pollutants) within the estuary is necessary to provide Delta
smelt larvae and juveniles a shallow protective, food-rich environment in which to
mature to adulthood.
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Adult Migration Unrestricted access to suitable spawning habitat in a period that may
extend from December to July. Adequate flow and suitable water qualityjnay need to be
maintained to attract migrating adults in the Sacramento and San Joaquin River channels
and their associated tributaries. These areas also should be protected from physical
disturbance and flow disruption during migratory periods.
PCEs also include 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.
The potential for direct effects to the DS from thiobencarb use could not be precluded based on
incident data. Furthermore, it was concluded that thiobencarb is likely to adversely affect the DS
by potentially affecting its habitat (aquatic and terrestrial plants) and the potential areas of effect
overlap with critical habitat designated for DS (Figure 5-2). Finally, monitoring data in the
Sacramento river indicate that exposure may be high enough to result in effects on aquatic
organisms. Therefore, thiobencarb may also affect critical habitat of the DS that is located in
close proximity to thiobencarb use sites.
5.4. Effects Determinations
5.4.1. CRLF
The weight of evidence indicates that thiobencarb use has the potential to directly adversely
affect CRLF. Acute and chronic risk to aquatic-phase CRLF is high based on the RQ analyses.
Although the acute risk to terrestrial-phase CRLF from acute or sub-acute dietary exposure is
low, risks could not be precluded at this time. The potential chronic risk to terrestrial-phase
CRLF from chronic dietary exposure cannot be precluded and exists for amphibians consuming
small herbivore mammals and small insects.
Regarding the potential for indirect effects, exceedance of all acute and chronic LOCs indicates
that effects to aquatic invertebrates are likely to occur. While the available data for terrestrial
invertebrates indicate that risk to terrestrial invertebrates is low, it is possible that effects to
terrestrial invertebrate LOCs could be exceeded if the ECso was slightly higher than the highest
dose tested here 15% mortality occurred. Impacts to non-vascular aquatic and terrestrial plants,
however, are expected from use of thiobencarb. Additionally, the Agency concludes that there
exists the potential, which cannot currently be precluded, for thiobencarb use to impact
amphibian prey populations to levels high enough to impact CRLF. Spatial analyses show that
potential areas of effect from thiobencarb use overlap with CRLF habitat and their designated
critical habitat.
Monitoring data, reported incidence, and usage data support the potential for thiobencarb to
result in direct and indirect effects to the CRLF. Monitoring studies indicate that concentrations
are likely to be high enough to result in toxicity to aquatic organisms. Monitoring data are
shown to be highest in May and June, a young juvenile life stage of the CRLF (Orlando and
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Kuivila, 2004). Three incidence were reported on terrestrial plant species (rice) for registered
uses and the certainty that the use of thiobencarb caused the incidence was probable (see Section
4.7). Although aquatic field studies cannot conclusively show that exposure to thiobencarb
resulted in declines to fish, aquatic invertebrates, and gravid shrimp, they do show that these
endpoints were affected in areas where thiobencarb was applied (see Section 4.7.1). Based on
the CADPR PUR data, from 1999 to 2006 an average of 308, 491 - 1,006, 327 Ibs of thiobencarb
per year were applied to rice in California. Usage of thiobencarb on rice in California is
expected to occur and thiobencarb is often used at the maximum application rate (Table 2-6).
Therefore, the Agency makes a "may affect, and likely to adversely affect" determination for
the CRLF and a habitat modification determination for their designated critical habitat based
on the potential for direct and indirect effects and effects to the PCEs of critical habitat.
5.4.2. Delta Smelt
The weight of evidence indicates that thiobencarb use will directly adversely affect DS. Acute
and chronic RQs exceed LOCs in rice growing areas and DS may be found in those areas during
spawning. Regarding the potential for indirect effects, the impact from thiobencarb use to
estuarine/marine invertebrate populations are also expected to be large enough to impact the DS
indirectly. RQs were calculated based on a toxicity endpoint for Daphnia magna of 101.2 |ig/L
(MRID 00025788). Copepods are important in the diet of DS. A supplemental field study
suggests that freshwater copepods may have a similar sensitivity to thiobencarb as Daphnia
magna (LOAEC of 187.5 |ig/L) (E62293). Impacts to non-vascular and vascular aquatic and
terrestrial plants are expected from use of thiobencarb on rice. Spatial analyses show that
potential areas of effect from thiobencarb use overlap with DS habitat and their designated
critical habitat.
As discussed for the CRLF, monitoring data, reported incidence, and usage data support the
potential for thiobencarb to result in direct and indirect effects to the CRLF. Monitoring data are
shown to be highest in May and June, a time when DS may move into freshwater habitat to
spawn (Orlando and Kuivila, 2004).
Therefore, the Agency makes a "may affect, and likely to adversely affect" determination for
the CRLF and a habitat modification determination for their designated critical habitat based
on the potential for direct and indirect effects and effects to the PCEs of critical habitat.
5.4.3. Addressing the Risk Hypotheses
In order to conclude this risk assessment, it is necessary to address the risk hypotheses defined in
Section 2.9.1. Based on the conclusions of this assessment, none of the hypotheses can be
rejected, meaning that the stated hypotheses represent concerns in terms of direct and indirect
effects of thiobencarb on the CRLF and its designated critical habitat.
The labeled use of thiobencarb may:
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... directly affect terrestrial-phase CRLF by causing acute mortality or by adversely
affecting chronic growth or fecundity;
... indirectly affect the CRLF and the DS and/or affect their designated critical habitat by
reducing or changing the composition of the food supply;
... indirectly affect the CRLF and the DS and/or affect 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 and the DS and affect their designated critical habitat by
reducing or changing the composition of the terrestrial plant community in the species'
current range;
... indirectly affect the CRLF and the DS and affect 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).
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 Thiobencarb
The Tier 1 Rice Model estimates only the concentration in the paddy water on the day of
application, and does not account for any dissipation processes except sorption to sediment.
Thus, it is likely to overestimate concentrations at later times, and thus to overestimate chronic
exposure. The extended Tier 1 model uses the result of a single aquatic field dissipation study to
estimate a lumped dissipation/degradation parameter, which may over- or under-estimate the rate
of dissipation which would be derived from a larger number of field studies.
There are only two aquatic field dissipation studies for wet-seeded rice. Both studies were
conducted in California, and only one measured degradates. It is not known how well these
studies represent dissipation of thiobencarb in wet-seeded rice in other parts of the U.S.
Monitoring data from several states suggest that thiobencarb concentrations in open waters (not
rice paddies) are in the low ppb range. However, the proximity of many monitoring sites to
thiobencarb use sites (in time and space) is not known at this time. The best-characterized
monitoring data is from California. The most highly contaminated sampling point, Colusa Basin
Drain #5, is known to be surrounded by rice fields, and the sampling was done during the time of
year when thiobencarb was being discharged from rice fields. The highest concentration
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observed at this location (37.4 ppb in 1994), suggests that water management practices are just
adequate to meet the California public health goal of 70 ppb.
There is one field dissipation study in dry-seeded rice. It suggests that thiobencarb
concentrations in flood water are low in comparison to wet-seeded fields. It is not known
whether additional studies would yield higher or lower concentrations. Thus, the result of this
study must be taken as a lower bound for dry-seeded rice.
Further degradation and dilution is expected to occur between the many areas where the DS are
commonly found throughout much of the year.
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 over-estimate
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 that used in the Tier I Rice Model.
6.1.3. Uncertainties regarding dilution and chemical transformations in
estuaries
Tier I Rice modeled EECs are intended to represent exposure of aquatic organisms in relatively
small water bodies. Therefore it is likely that modeled EECs 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 would be found in the 'typical' rice paddy. 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 (Jordan et a/., 2008; Means, 1995; Swarzenski et a/., 2003),
changes in pH (Fernandez et aL, 2005; Parikh et a/., 2004; Wood and Baptista, 1993), Eh
changes (Velde and Church, 1999; Wood and Baptista, 1993), 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. In general, model results are 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. Monitoring data do
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indicate that concentrations in estuaries are lower than those observed in upstream monitoring
stations (see Section 3.1.1). 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 modeling results, and
may, therefore, under- or over-estimate exposure, depending on the aforementioned variables.
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.
6.1.4. Impact of Vegetative Setbacks on Runoff
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.
6.1.5. Exposure Resulting from Atmospheric Transport
Thiobencarb has been detected in precipitation samples in California. According to Suzuki et al.
(2003), thiobencarb was detected in 59.8% of rainfall samples collected in Eastern Japan at a
maximum concentration of 0.335 ug/L. These monitoring data are not expected to be
representative of California; however, they are the only data available and can be used to
determine whether further analysis of potential risk of thiobencarb in precipitation is necessary.
Based on these data, it is possible that thiobencarb can be deposited on land in precipitation.
Estimates of exposure of the CRLF, its prey and its habitat to thiobencarb included in this
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assessment are based only on transport of thiobencarb through spray drift from application sites.
Current estimates of exposures of CRLF and its prey to thiobencarb through spray drift would be
greater if consideration is given to deposition in precipitation. In the aquatic environment, the
concentration in precipitation (0.335 |ig/L) is a fraction of the aquatic EECs (968 - 2018 |ig/L)
predicted based on modeling and aquatic dissipation studies (EECs ranged from 70-438 |ig/L.
Rainwater could make a significant contribution to RQs estimated based on NAWQA and CDPR
monitoring data where the representative EEC was 0.697; however, the other exposure estimates
indicate that accounting for the contribution of rain to exposure is not necessary. Thiobencarb
concentrations in rainwater are also a fraction of the terrestrial EECs (0.60 - 540 mg/kg-diet, for
dietary exposure to birds and mammals) based on modeling. Therefore, precipitation is not
expected to be a significant source of exposure. It was assumed that exposure due to the
presence of thiobencarb in precipitation would have a minor impact on risk conclusions.
6.1.6. Potential Ground Water Contributions to Surface Water Chemical
Concentrations
Although the potential impact of discharging ground water on CRLF populations is not explicitly
delineated, it should be noted that, in some areas of the country, ground water could provide a
source of pesticide to surface water bodies - especially low-order streams, headwaters, and
ground water-fed pools. This is particularly likely if the chemical is persistent and mobile, the
pesticide is applied to highly permeable soils overlying shallow unconfmed ground water, and
rainfall is sufficient to drive the chemical through the soil to ground water. Soluble chemicals
that are primarily subject to photolytic degradation will be very likely to persist in ground water,
and can be transportable over long distances. Similarly, many chemicals degrade slowly under
anaerobic conditions (common in aquifers) and are thus more persistent in ground water. Under
the right hydrologic conditions, this ground water may 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 ground water discharge, which can constitute 100% of stream flow
during baseflow (no runoff) conditions. Thus, it is important to keep in mind that pesticides in
ground water may impact surface water quality during base flow conditions with subsequent
impact on CRLF habitats. However, many smaller streams in CA are net dischargers of water to
ground water that go dry during portions of the year and are not supplied by baseflow from
ground water.
Although concentrations in a receiving water body resulting from ground water discharge cannot
be explicitly quantified, it should be assumed that significant attenuation and retardation of the
chemical will have occurred prior to discharge. Nevertheless, where thiobencarb is applied to
highly permeable soils over shallow ground water where there is a net recharge to adjacent
streams, ground water could still be a consistent source of chronic background concentrations in
surface water, and may also add to surface runoff during storm events (as a result of enhanced
ground water discharge typically characterized by the 'tailing limb' of a storm hydrograph).
6.1.7. Usage Uncertainties
County-level usage data were obtained from California's Department of Pesticide Regulation
Pesticide Use Reporting (CDPR PUR) database. Eight years of data (1999 - 2006) were
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included in this analysis because statistical methodology for identifying outliers, in terms of area
treated and pounds applied, was provided by CDPR for these years only. 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.
6.1.8. Terrestrial Exposure Modeling of Thiobencarb
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.
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% (USEPA, 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. Based on estimated
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exposure using AgDRIFT, TerrPlant may underestimate spray drift exposure for plants less than
200 feet from the edge of the field.
6.1.9. Spray Drift Modeling
Factors, including variations in topography, cover, and meteorological conditions over the
transport distance are not accounted for by the AgDRIFT 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 may
overestimate exposure, 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 made regarding the droplet size distributions being
modeled ('ASAE Very Fine to Fine') and boom height ('High') unless spray drift restrictions are
specified on the label. Alterations in any of these inputs would decrease the area of potential
effect.
6.2. Effects Assessment Uncertainties
6.2.1. Data Gaps and Uncertainties
Avian Acute Toxicity for Passerine Species
Data are typically required on one passerine species and either one waterfowl species or one
upland game bird species for terrestrial, aquatic, forestry, and residential outdoor uses (USEPA,
2007). An acceptable acute oral toxicity study with Bobwhite quail and a subacute dietary study
for the Mallard duck are available; however, data are not available for a passerine species. The
proposed rule establishing this data requirement stated that the avian acute oral study would be
required for outdoor uses because "... of concern in the scientific community that data from tests
with mallards or quail may not always adequately characterize the risks that pesticides pose to
songbirds. Recent evaluation of the data collected over the past 10 years indicates passerines are
more sensitive to pesticides than larger birds such as mallards and quail (which are currently the
recommended test species) (Ref. 2) and in 1996, the SAP supported the need for testing on
passerines." (FR Vol. 70 No. 47; March 11, 2005; 12289). This indicates that the available avian
endpoints are not good predictors of toxicity for passerine species and data are needed to
adequately assess risk to songbirds. This could result in a misrepresentation of effects to the
CRLF as avian endpoints are used as a surrogate to estimate direct effects to the CRLF.
Avian Chronic Toxicity
Only one acceptable chronic avian toxicity study is available. Other available chronic avian
studies are missing information needed to fully evaluate and rely on the study results (Appendix
I). Usually chronic studies on both waterfowl and upland game bird species are used to
characterize chronic risk to avian species (USEPA, 2007). The limited data available to
characterize chronic risk to avian species could result in an underestimation of direct effects to
the CRLF.
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Acute Fish Toxicity
The only acceptable fish acute toxicity study available on the TGAI is for the bluegill sunfish, a
warmwater fish species. A study should also be available using the TGAI for a coldwater
species. Additionally, not enough information is available to determine whether the TGAI or
TEP is more toxic. Therefore, the most sensitive toxicity data for the TEP was used to calculate
risk quotients. Data on a coldwater species using the TGAI would 1) reduce uncertainty on
whether the formulation influenced toxicity of thiobencarb (e.g., whether the TEP or TGAI was
more toxic to fish) and 2) reduce uncertainty on possible underestimation of risk to coldwater
fish species. Available open literature data indicate that coldwater species, white sturgeon and
striped bass, are sensitive fish species (Appendix I). Available open literature data indicate that
the value used to calculate risk quotients represents a sensitive species and provides a high end
RQ value (see the species sensitivity distribution in Appendix I).
Chronic Fish Toxicity
A fish full life-cycle study was submitted for the fathead minnow. The study should have a
corresponding acute study for the same species. No acute toxicity data were submitted for the
fathead minnow. Additionally, the study only had two replicates. The low number of replicates
and variability in the endpoints may have resulted in an inability to statistically detect differences
between treatments and controls and thus may overestimate toxicity endpoints. Observed results
suggested that if more replicates were available a difference may have been statistically
significant between the control and 53 jig ai/L treatment group which would result in a higher
RQ value. Chronic risk to fish and therefore, the CRLF and DS, may be underestimated.
Seedling Emergence
A NOAEL was not established for the seedling emergence terrestrial plant study (MRID
41690902). The test was classified as supplemental for the two most sensitive species, lettuce
and ryegrass, because there was significant mortality of plants at the lowest test concentration.
Additional testing should be completed for these two sensitive species using lower test
concentrations that do not result in mortality of plants. The value added of this information is
moderate. It would increase the confidence of the risk assessment on terrestrial plants. This
data gap could result in an underestimation of indirect effects to the CRLF and DS.
6.2.2. 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
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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.
6.2.3. Impact of Multiple Stressors on the Effects Determination
The influence of length of exposure and concurrent environmental Stressors to the CRLF and the
DS (i.e.., construction of dams and locks, fragmentation of habitat, change in flow regimes,
increased sedimentation, degradation of quantity and quality of water in the watersheds of the
action area, predators, etc.) will likely affect the species' response to thiobencarb. Additional
environmental Stressors may increase sensitivity to the herbicide, although there is the possibility
of additive/synergistic reactions. Timing, peak concentration, and duration of exposure are
critical in terms of evaluating effects, and these factors are expected to vary both temporally and
spatially within the action area. Overall, the effect of this variability may result in either an
overestimation or underestimation of risk. However, as previously discussed, the Agency's
LOCs are set to be protective given the wide range of possible uncertainties.
6.2.4. Use of Surrogate Species Effects Data
Freshwater fish are used as surrogate species for aquatic-phase amphibians. Some data are
available on thiobencarb that evaluated its toxicity to amphibians. Overall, these data do not
suggest that amphibians are more sensitive than fish to thiobencarb. 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 is likely to overestimate the potential
risks to those species. 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.
6.2.5. 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 is exercised on a case-by-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.
6.2.6. Exposure to Pesticide Mixtures
In accordance with the Overview Document and the Services Evaluation Memorandum (USEPA,
2004)(USFWS/NMFS/NOAA, 2004), this assessment considers the single active ingredient of
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thiobencarb. However, the assessed species and its environments may be exposed to multiple
pesticides simultaneously. Interactions of other toxic agents with thiobencarb could result in
additive effects, more than additive effects, or less than additive effects. As previously
discussed, evaluation of pesticide mixtures is beyond the scope of this assessment because of the
myriad of factors that cannot be quantified based on the available data. Those factors include
identification of other possible co-contaminants where the CRLF and the DS reside and their
concentrations, differences in the pattern and duration of exposure among contaminants, and the
differential effects of other physical/chemical characteristics of the receiving waters (e.g. organic
matter present in sediment and suspended water). Evaluation of factors that could influence
additivity/synergism/antagonism is beyond the nature and quality of the available data to allow
for an evaluation. However, it is acknowledged that not considering mixtures could over- or
under-estimate risks depending on the type of interaction and factors discussed above.
6.2.7. Uncertainty in the Potential Effect to Riparian Vegetation vs. Water
Quality Impacts
Effects to riparian vegetation were evaluated using submitted guideline seedling emergence and
vegetative vigor studies. LOCs were exceeded for seedling emergence endpoints with the
seedling emergence endpoint being considerably more sensitive than vegetative vigor endpoints.
Based on LOG exceedances and the lack of readily available information to allow for
characterization of riparian areas of the CRLF and the DS, it was concluded that thiobencarb use
is likely to adversely affect these species by potentially impacting grassy/herbaceous riparian
vegetation resulting in increased sedimentation. However, soil retention/sediment loading is
dependent on a number of factors including land management and tillage practices. Use of
herbicides (including thiobencarb) may be incorporated into a soil conservation plan. Therefore,
although this assessment concludes that thiobencarb is likely to adversely affect the assessed
listed species and their designated critical habitat by potentially impacting sensitive herbaceous
riparian areas, it is possible that adverse impacts on sediment loading may not occur in areas
where soil retention strategies are used.
6.2.8. 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.
7. Risk 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 thiobencarb to the CRLF and DS and their designated critical
habitat.
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Based on the best available information, the Agency makes a May Affect, and Likely to
Adversely Affect (LAA) determination for the CRLF and the DS from the labeled uses of
thiobencarb as described in Table 7-1. The effects determination is based on potential direct and
indirect effects to terrestrial-phase CRLF and potential direct and indirect effects to aquatic-
phase CRLF and the DS. The LAA determination applies to all currently registered thiobencarb
uses in California, e.g., use of thiobencarb on rice.
Additionally, the Agency has determined that there is the potential for effects to designated
critical habitat of the CRLF and the DS from the use of the thiobencarb. A summary of the risk
conclusions and effects determinations for each listed species assessed and their designated
critical habitat is presented in Table 7-1 and Table 7-2. Further information on the results of the
effects determination is included as part of the Risk Description in Section 5.2. Given the LAA
determination for the CRLF and the DS and potential designated critical habitat modification for
both species, 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 DS is provided in
Attachment 4.
Table 7-1. Effects Determination Summary for Potential Effects to the CRLF and DS from
the Use of Thiobencarb on Rice in California
Species
California red-
legged frog
(Rana aurora
draytonii)
Effects
Determination
May affect,
likely to
adversely affect
Basis for Determination
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults):
Acute RQs for freshwater fish (used as a surrogate for aquatic -phase amphibians)
exceed the Agency's LOCs for use of thiobencarb on rice. At the highest RQ
(4.59) and using the default slope (4.5), the probability of an effect would be
approximately 1 in 1.0. Chronic RQs for freshwater fish ranged from 0.26 -
46.10 and exceed the LOG of 1.0. The critical habitat and cultivated crop land
cover class overlap. This indicates that direct effects to aquatic-phase CRLF
have the potential to occur.
Terrestrial-phase (Juveniles and Adults)'.
The risk of direct adverse effects to terrestrial-phase CRLF from acute or sub-
acute dietary exposure is low; however, risk may not be precluded because
estimated exposure exceeds the highest doses tested where no mortality occurred
for terrestrial birds (the surrogate for terrestrial-phase CRLF) consuming small
insects and small mammals. The RQs for chronic risk to terrestrial birds exceed
the LOG of 1.0 for birds consuming broadleaf plants/small insects and small
mammals. Therefore, chronic risk to the CRLF has the potential to occur.
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary productivity
Risk quotients for FW fish, FW invertebrates, and aquatic plants exceeded LOCs.
For F W invertebrates, the probability of an effect would be approximately 1 in
1.0 (based on the highest RQ of 19.84 and slope of 4.5). Chronic FW
invertebrate RQs also exceed the LOG of 1.0. RQs for non-vascular aquatic
plants exceed the LOG of 1.0 using modeled and monitoring results. RQs for
vascular aquatic plants exceed the LOG of 1.0 based on modeling data in the rice
paddy. This indicates that indirect effects to CRLF have the potential to occur
due to loss of prey or habitat. RQs for terrestrial plants exceed the LOG of 1.0,
indicating that effects to riparian vegetation have the potential to occur.
Terrestrial prey items, riparian habitat
CRLFs could be affected as a result of potential impacts to grassy /herbaceous
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Species
Delta Smelt
(Hypomesus
transpacificus)
Effects
Determination
May affect,
likely to
adversely affect
Basis for Determination
vegetation and reduction of prey items such as small mammals or terrestrial
invertebrates. RQs for mammals consuming short grass, tall grass, broadleaf
plants, and small insects exceed the acute LOG of 0.1 and chronic LOG of 1.0.
The probability of individual effects for mammals is 1 in 2.73 (based on the
highest RQ of 0.40 and slope of 4.5). The risk of indirect effects to the CRLF
due to a reduction in terrestrial invertebrate prey items is low. Risk may not be
precluded for terrestrial invertebrates because the ratio of the EEC to the dose
where 15% mortality occurred exceeds the LOG of 0.05. Fifteen percent
mortality occurred at the highest dose tested. It is uncertain whether the EC50
would result in LOG exceedances for terrestrial invertebrates. RQs for terrestrial
plants exceed the corresponding LOG of 1.0.
Potential for Direct Effects
RQs for freshwater and E/M fish exceed the Agency's LOCs for use of
thiobencarb on rice. At the highest RQ (2.82) and using the default slope (4.5),
the probability of an effect would be approximately 1 in 1.02. Chronic RQs for
freshwater and estuarine/marine fish ranged from 0.26 - 13.33 and exceed the
LOG of 1 .0 when based on aquatic dissipation studies. Critical habitat and the
cultivated crop NLCD land cover class overlap. This indicates that direct effects
to DS have the potential to occur with the use of thiobencarb on rice.
Potential for Indirect Effects
Use of thiobencarb on rice has the potential to adversely affect the DS by
reducing available food (aquatic plants and FW and E/M invertebrates), by
impacting the riparian habitat of grassy and herbaceous riparian areas, and/or by
impacting water quality via effects to aquatic vegetation. Acute and chronic RQs
for FW and E/M invertebrates exceed corresponding LOCs indicating that
reduction in prey items may occur. For FW invertebrates, the probability of an
effect would be approximately 1 in 1.0 (based on the highest RQ of 19.84 and
slope of 4.5). For E/M invertebrates the probability of an individual effect is
approximately 1 in 1.00 (based on the highest RQ of 3.84 and a slope of 4.5).
Chronic RQs for both E/M and FW invertebrates exceed the LOG of 1 .0. Some
RQs for aquatic plants exceed the LOG of 1.0 indicating that effects on DS
habitat and reduction in food may occur. RQs for terrestrial plants exceed the
LOG of 1.0 indicating that effects to riparian vegetation have the potential to
occur.
Abbreviations: FW = freshwater, E/M = estuarine/marine, CRLF = California Red Legged Frog, DS=delta smelt,
RQ=risk quotient
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Table 7-2. Effects Determination Summary for Thiobencarb Use and CRLF and DS
Critical Habitat Impact Analysis.
Assessment
Endpoint
Effects
Determination
Basis for Determination
Modification of
aquatic-phase PCEs
(DS and CRLF)
Habitat
Modification
As described in Table 1-1, the effects determination for the potential for
thiobencarb to affect aquatic-phase CRLFs and the DS is LAA. These
determinations are based on the potential for thiobencarb to indirectly affect
the DS and aquatic-phase CRLF. Additionally, the potential areas of effect
overlap with critical habitat designated for the CRLF and DS. Therefore,
potential effects to aquatic plants and terrestrial (riparian) plants identified in
this assessment could result in aquatic habitat modification.
Modification of
terrestrial-phase PCE
(CRLF)
As described in Table 1-1, the effects determination for the potential for
thiobencarb to affect terrestrial-phase CRLFs is LAA. This determination is
based on the potential for thiobencarb to directly affect terrestrial-phase
CRLFs and their food supply and habitat. Additionally, the potential areas of
effect overlap with critical habitat designated for the CRLF. Therefore, these
potential effects could result in modification of critical habitat.
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 for the CRLF
and DS. 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 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 and DS 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.
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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.
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71-1 Avian Single Dose Oral Toxicity
MRID Citation Reference
57222 Fletcher, D. (1972) Report to International Minerals & Chemical Corporation: Acute Oral
Toxicity Study with IMC 3950 Technical in Bobwhite Quail: IBT No. J895. (Unpublished study
received Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095494-F)
57223 Fletcher, D. (1972) Report to International Minerals & Chemical Corporation: Acute Oral
Toxicity Study with IMC 3950 in Mallard Ducks: IBT No. J896. (Unpublished study received
Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc., submitted by
Chevron Chemical Co., Richmond, Calif.; CDL: 095494-G)
80847 Fletcher, D. (1972) Report to International Minerals & Chemical Corporation: Acute Oral
Toxicity Study with IMC 3950 in Mallard Ducks: IBT No. J896. (Unpublished study received
Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc., submitted by
Chevron Chemical Co., Richmond, Calif.; CDL: 095106-C)
81903 Fletcher, D. (1972) Report to International Minerals & Chemical Corporation: Acute Oral
Toxicity Study with IMC 3950 in Mallard Ducks: IBT No. J896. (Unpublished study received
Jan 10, 1975 under 5G1582; prepared by Industrial Bio-Test Laboratories, Inc., submitted by
Chevron Chemical Co., Richmond, Calif.; CDL: 094344-G)
116152 Fletcher, D. (1972) Report to ...: Acute Oral Toxicity Study with IMC 3950 Technical in
136
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Bobwhite Quail: IBT No. J895. (Unpublished study received Aug 5, 1972 under 2G1231;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by International Minerals &
Chemical Corp., Libertyville, IL; CDL:091085-J)
124720 Fletcher, D. (1972) Report to International Minerals & Chemical Corporation: Acute Oral
Toxicity Study with IMC 3950 in Mallard Ducks: IBT No. J896. (Unpublished study received
Mar 18, 1976 under 6F1763; prepared by Industrial Bio-Test Laboratories, Inc., submitted by
Chevron Chemical Co., Richmond, CA; CDL: 095086-D)
42600201 Campbell, S.; Jaber, M. (1992) Bolero Technical: An Acute Oral Toxicity Study with the
Northern Bobwhite: Lab Project Number: 263-126. Unpublished study prepared by Wildlife
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92182001 Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00057222 and
Related MRIDs 00116152. Acute Oral Toxicity Study with IMC 3950 Technical in Bobwhite
Quail: Project No. J895. Prepared by Industrial Bio-Test Laboratories, Inc. 18 p.
71-2 Avian Dietary Toxicity
MRID Citation Reference
25774 Beavers, J.B.; Fink, R.; Grimes, I; et al. (1979) Final Report: Subacute Feeding-Reproduction
Screening Bioassay-Bobwhite Quail: Project No. 162-111. Rev. (Unpublished study including
letter dated Nov 7, 1978 from F.X. Kamienski to Bob Fink, re- ceived Dec 11, 1979 under 239-
2450; prepared by Wildlife Inter- national, Ltd., submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL:241489-C)
25775 Beavers, J.B.; Fink, R.; Grimes, I; et al. (1979) Final Report: Subacute Feeding-Reproduction
Screening Bioassay-Bobwhite Quail: Project No. 162-111. Rev. (Unpublished study including
letters dated Feb 14, 1979 from F.X. Kamienski to Bob Fink and dated Mar 23, 1979 from C. A.
Rohde to JoannB. Beavers, received Dec 11, 1979 under 239-2450; prepared by Wildlife
International, Ltd., submitted by Chevron Chemical Co., Richmond, Calif.; CDL: 241489-D)
25779 Fletcher, D. (1976) Report to Chevron Chemical Company: 8-Day Dietary LCI50A Study with
Bolero 8 EC:STAM F-34 in Mallard Duck- lings: IBT No. 8580-09342. (Unpublished study
received Dec 11, 1979 under 239-2450; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:241489-J)
34763 Fletcher, D. (1976) Report to Chevron Chemical Company: 8-Day Dietary LCI50A Study with
Bolero 8 EC:STAM F-34 in Bobwhite Quail: IBT No. 8580-09343. (Unpublished study received
Dec 11, 1979 under 239-2450; prepared by Industrial Bio-Test Laboratories, Inc., submitted by
Chevron Chemical Co., Richmond, Calif.; CDL: 241489-1)
40955 Fletcher, D. (1976) Report to Chevron Chemical Company: 8 Day Dietary LCI50A Study with
Bolero 8 ECSTAM F-34 in Mallard Duck- lings: IBT No. 8580-09342. (Unpublished study
received Nov 30, 1976 under 239-EX-77; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095622-E)
57224 Fletcher, D. (1974) Report to Chevron Chemical Company, Ortho Division: 8-Day Dietary
LCI50A Study with Bolero in Bobwhite Quail: IBT No. 651-05214. (Unpublished study received
Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc., submitted by
Chevron Chemical Co., Richmond, Calif.; CDL: 095494-H)
57225 Fletcher, D. (1974) Report to Chevron Chemical Company, Ortho Division: 8-Day Dietary
LCI50A Study with Bolero in Mallard Duck- lings: IBT No. 651-05213. (Unpublished study
received Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Corp., Richmond, Calif.; CDL:095494-I)
137
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57227
57228
79105
79106
79109
81904
85465
124721
44846206
92182002
92182003
Fletcher, D. (1975) Report to Chevron Chemical Company: Pilot Feeding Study with Untreated
Rice in Mallard Ducks: IBT No. 651- 05706. (Unpublished study received Mar 18, 1976 under
239-2449; prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical
Co., Richmond, Calif.; CDL:095494-K)
Fletcher, D. (1975) Report to Chevron Chemical Company: Toxicity and Reproduction Study
with Bolero (XE-362, Benthiocarb) Technical Treated Rice and Drinking Water in Mallard
Ducks: IBT No. 651-06236. (Unpublished study received Mar 18, 1976 under 239-2449;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL: 095494-L)
Fink, R.; Beavers, J.B.; Grimes, I; et al. (1979) Final Report: Subacute Feeding-Reproduction
Screening Bioassay-Bobwhite Quail: Project No. 162-111. Rev. (Unpublished study, including
letter dated Nov 7, 1978 from F.X. Kamienski to Bob Fink, received Dec 11, 1979 under 239-
2449; prepared by Wildlife Inter- national Ltd., submitted by Chevron Chemical Co., Richmond,
Calif.; CDL:241494-E)
Fink, R.; Beavers, J.B.; Grimes, I; et al. (1979) Final Report: Subacute Feeding-Reproduction
Screening Bioassay-Bobwhite Quail: Project No. 162-111. Rev. (Unpublished study, including
letter dated Feb 14, 1979 from F.X. Kamienski to Bob Fink, received Dec 11, 1979 under 239-
2449; prepared by Wildlife Inter- national Ltd. and Johns Hopkins Univ., Dept. of Biostatics,
sub- mittedby Chevron Chemical Co., Richmond, Calif.; CDL:241494-F)
Fletcher, D. (1976) Report to Chevron Chemical Company: 8-day Dietary LCI50A Study with
Bolero 8 EC:StamF-34 in Mallard Ducks: IBT No. 8580-09342. (Unpublished study received
Dec 11, 1979 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc., submitted by
Chevron Chemical Co., Richmond, Calif.; CDL: 241494-J)
Fletcher, D. (1974) Report to Chevron Chemical Company, Ortho Division: 8-day Dietary
LCI50A Study with Bolero in Mallard Duck- lings: IBT No. 651-05213. (Unpublished study
received Jan 10, 1975 under 5G1582; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, Calif.; CDL: 094344-1)
Fletcher, D. (1974) Report to Chevron Chemical Company, Ortho Division: 8-day Dietary
LCI50A Study with Bolero in Mallard Duck- lings: IBT No. 651-05213. (Unpublished study
received Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095106-E)
Fletcher, D. (1974) Report to ..., Ortho Division: 8-day Dietary LC50 Study with Bolero in
Mallard Ducklings: IBT No. 651-05213; Service Order No. S25507. (Unpublished study
received Mar 18, 1976 under 6F1763; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, CA; CDL: 095086-E)
Helsten, B. (1999) Acute Avian Dietary Toxicity (LC50) of Thiobencarb to Mallard Ducklings:
Lab Project Number: 133-004-02: 9900180. Unpublished study prepared by Bio-Life
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Cooper, P. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00057224 and
Related MRIDs 00081904. Eight-Day Dietary LC50 Study with BOLERO in Bobwhite Quail:
Project No. IBT No. 651-05214. Prepared by Industrial Biotest Laboratories, Inc. 18 p.
Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00057225 and
Related MRIDs 00081904, 00085465, 00124721. Eight-Day Dietary LC50 Study with
BOLERO in Mallard Ducklings: Project No. IBTNo. 651-05213. Prepared by Industrial Bio-
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71-4 Avian Reproduction
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25776
25778
57226
57228
79107
79108
80848
81905
43075401
45140601
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Beavers, J.B.; Fink, R.; Joiner, G.; et al. (1979) Final Report: One-Generation Reproduction
Study--Bobwhite Quail: Project No. 162-116. (Unpublished study including letters dated Apr 10,
Apr 25, May 25, Jul 9, Aug 28, 1979 from J. Grimes, J.B. Beavers, J.B. Leary, J. Grimes, J.
Grimes, respectively, to Francis X. Kamienski and addendum, received Dec 11, 1979 under 239-
2450; prepared by Wildlife International, Ltd., submitted by Chevron Chemical Co., Richmond,
Calif.; CDL:241489-E)
Beavers, J.B.; Fink, R.; Joiner, G.; et al. (1979) Final Report: One-Generation Reproduction
Study-Mallard Duck: Project No. 162-117. (Unpublished study including letters dated Apr 10,
Apr 25, May 25, Jul 9, Jul 24, Aug 28, 1979 from J. Grimes, J.B. Beavers, J.B. Leary, J. Grimes,
J. Grimes, J. Grimes, respectively, to Francis X. Kamienski and addendum, received Dec 11,
1979 under 239-2450; prepared by Wildlife International, Ltd., submitted by Chevron Chemical
Co., Richmond, Calif.; CDL: 241489-G)
Chevron Chemical Company (1974) Report on the Tests Carried Out in Order To Determine the
Action of Saturn 50% E.G. on Egg-Laying in Japanese Quails. (Unpublished study received Mar
18, 1976 under 239-2449; CDL:095494-J)
Fletcher, D. (1975) Report to Chevron Chemical Company: Toxicity and Reproduction Study
with Bolero (XE-362, Benthiocarb) Technical Treated Rice and Drinking Water in Mallard
Ducks: IBT No. 651-06236. (Unpublished study received Mar 18, 1976 under 239-2449;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL: 095494-L)
Fink, R.; Beavers, J.B.; Joiner, G.; et al. (1979) Final Report: One-generation Reproduction
Study-Bobwhite Quail: Project No. 162-116. (Unpublished study, including letters dated Apr
10, 1979 from J. Grimes to Francis X. Kamienski, Apr 25, 1979 from J.B. Beavers to Francis X.
Kamienski and Jul 9, Aug 28, 1979 from J. Grimes to Francis X. Kamienski, received Dec 11,
1979 under 239-2449; prepared by Wildlife International, Ltd., submitted by Chevron Chemical
Co., Richmond, Calif.; CDL: 241494-G)
Fink, R.; Beavers, J.B.; Joiner, G.; et al. (1979) Final Report: One-generation Reproduction
Study-Mallard Duck: Project No. 162-117. (Unpublished study, including letters dated Apr 10,
1979 from J. Grimes to Francis X. Kamienski, Apr 25, 1979 from J.B. Beavers to Francis X.
Kamienski and Jul 9, 1979, Jul 24, 1979, Aug 28, 1979 from J. Grimes to Francis X. Kamienski,
received Dec 11, 1979 under 239-2449; prepared by Wildlife International Ltd., submitted by
Chevron Chemical Co., Richmond, Calif.; CDL:241494-H)
Chevron Chemical Company (1974) Report on the Tests Carried Out in Order To Determine the
Action of Saturn 50% E.G. on Egg-laying in Japanese Quails. (Unpublished study received Mar
18, 1976 under 239-2449; CDL:095106-F)
Chevron Chemical Company (1974) Report on the Tests Carried Out in Order To Determine the
Action of Saturn 50% E.G. on Egg-laying in Japanese Quails. (Unpublished study received Jan
10, 1975 under 5G1582; CDL:094344-J)
Bavers, J.; Chafey, K.; Mitchell, L.; et al. (1993) A Reproduction Study With The Northern
Bobwhite: Lab Project Number: 263-128. Unpublished study prepared by Wildlife International
Ltd. 188 p.
Helsten, B. (2000) Thiobencarb: An Avian Reproductive Toxicity Study in Mallards: Lab
Project Number: 133-005-08: 200000241: VP-12123. Unpublished study prepared by Bio-Life
Associates, Ltd. 567 p. {OPPTS 850.2300}
Holzer, M. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00025774 and
Related MRIDs 00025775, 00025776. One-Generation Reproduction Study-Bobwhite Quail
BOLERO Technical (SX-1053): Project No. 162-116. Prepared by Wildlife International, Ltd.
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35 p.
92182005 Holzer, M. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00025778. One-
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72-1 Acute Toxicity to Freshwater Fish
MRID Citation Reference
80851
80852
80859
116143
139051
139052
155428
161691
161692
40651313
41215302
Johnson, W.W. (1973) Letter sent to H.T. Huang dated Apr 9, 1973 Toxicity data of IMC-3950
and Bolero SEC to freshwater fish and crayfish|. (U.S. Fish and Wildlife Service, Fish-Pesticide
Re- search Laboratory; unpublished study; CDL:095106-L)
Hamlin, J. (1971) Report to International Minerals & Chemical Corporation: Four-day Static
Fish Toxicity Studies with IMC-3950 SEC in Channel Catfish and Bluegills: IBT No. A830.
(Unpublished study received Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test
Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095106-M)
Watari, N.; Shinohara, R.; Kojima, K. (1974) Fish Toxicity Studies on Technical Product, Their
By-Products and Some Potential Metabolites of Benthiocarb in the Carp and Bluegill:
Toxicological Study Part II. (Unpublished paper presented at the annual meeting of the Japanese
Society of Toxicology; Feb 5, 1974, Tokyo, Japan; unpublished study received Mar 18, 1976
under 239-2449; prepared by Kumiai Chemical Industry Co., Ltd., Japan, submitted by Chevron
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Hamlin, J. (1971) Report to ...: Four-day Static Fish Toxicity Studies with IMC 3950 SEC in
Channel Catfish and Bluegills: IBT No. A830. (Unpublished study received Aug 3, 1972 under
2G1231; prepared by Industrial Bio-Test Laboratories, Inc., submitted by International Minerals
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Sanders, H.; Hunn, J. (1982) Toxicity, bioconcentration, and depuration of the herbicide Bolero
SEC in freshwater invertebrates and fish. Bulletin of the Japanese Society of Scientific Fisheries
48(8): 1139-1143. (Also In unpublished submission received Feb 28, 1984 under 239-2450;
submitted by Chevron Chemical Co., Richmond, CA; CDL:252526-F)
Schaefer, C.; Miura, T.; Stewart, R.; et al. (1981) Studies on the Potential Environmental Impact
of the Herbicide Thiobencarb (Bolero). (Unpublished study received Feb 28, 1984 under 239-
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Chevron Chemical Co. (1986) Bolero SEC: Wildlife & Aquatic Organ- isms Data. Unpublished
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Bailey, H. (1984) 96-Hour Flow-through Assay with Chevron Thiobencarb (SX-1381) in
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Faggella, G.; Finlayson, B. (1988) Hazard Assessment of Rice Herbicides Molinate and
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42754203 Finlayson, B.; Faggella, G. (1984) Acute & Chronic Effects of Molinate & Thiobencarb on
Freshwater & Anadromous California Fishes: Molinate, Thiobencarb. Unpublished study
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92182006 Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00050665. Acute
Toxicity of BOLERO 10G (SX-1252) to Bluegill Sunfish (Lepomis macrochirus): Project No.
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92182007 Manza, S. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00050664. Acute
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72-2 Acute Toxicity to Freshwater Invertebrates
MRID Citation Reference
79118 Wheeler, R.E. (1978) 48 Hour Acute Static Toxicity of Bolero SEC (SX981) to 1st Stage
Nymph Water Fleas (Daphnia magna). (Unpublished study received Dec 11, 1979 under 239-
2449; submitted by Chevron Chemical Co., Richmond, Calif.; CDL: 241494-V)
80851 Johnson, W.W. (1973) Letter sent to H.T. Huang dated Apr 9, 1973 ?Toxicity data of IMC-3950
and Bolero SEC to freshwater fish and crayfish|. (U.S. Fish and Wildlife Service, Fish-Pesticide
Re- search Laboratory; unpublished study; CDL:095106-L)
80858 Ward, S. (1975) Acute Toxicity of Bolero 8-emulsive to Four Species of Decapod Crustaceans.
(Unpublished study received Mar 18, 1976 under 239-2449; prepared by Bionomics-EG & G,
Inc., sub- mittedby Chevron Chemical Co., Richmond, Calif.; CDL:095106-S)
85633 Wheeler, R.E. (1978) 48 Hour Acute Static Toxicity of Bolero (SX796) to 1st Stage Nymph
Water Fleas (Daphnia magna). (Unpublished study received Dec 11, 1979 under 239-2449;
submit- ted by Chevron Chemical Co., Richmond, Calif.; CDL:241494-U)
138077 Wheeler, R. (1978) 48 Hour Acute Static Toxicity of Bolero (SX796) to 1st Stage Nymph Water
Fleas (Daphnia magna Straus). (Unpublished study received Dec 1, 1978 under 239-EX-77;
submitted by Chevron Chemical Co., Richmond, CA; CDL:097658-J)
139051 Sanders, H.; Hunn, J. (1982) Toxicity, bioconcentration, and depuration of the herbicide Bolero
SEC in freshwater invertebrates and fish. Bulletin of the Japanese Society of Scientific Fisheries
48(8): 1139-1143. (Also In unpublished submission received Feb 28, 1984 under 239-2450;
submitted by Chevron Chemical Co., Richmond, CA; CDL:252526-F)
40031001 Rich, E. (1986) Toxicity Bioassay - Effect of Bolero 8 EC onHatching Apple Snails: Lab. Proj.
ID 8616165. Unpublished study pre- pared by Rio Palenque Research Corp. 31 p.
41215303 Hirata, H. (1984) Effects of benthiocarb herbicide on cultivation of rotifer. Min. Rev. Data File
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41215304 Young, R.; Morgan, E. (1989) Acute Toxicity of Bolero SEC to the Freshwater Mussel,
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41215307 Chen, S.; Hsu, E.; Chen, Y. (1982) Fate of the herbicide benthiocarb (thiobencarb) in a rice
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41215308 Hirata, H. (1984) Effects of benthiocarb on growth of planktonic organisms, Chlorella
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44628602 Ogle, R. (1998) The Acute Toxicity of Thiobencarb to the Freshwater Insect, Chironomus
tentans: Lab Project Number: 1719: 9800104. Unpublished study prepared by Pacific Eco-Risk
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92182008 Holzer, M. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00025788 and
Related MRIDs 00085633, 00138077. 48-Hour Acute Static Toxicity of BOLERO (SX-796) to
First-Stage Nymph Water Fleas (Daphnia magna Strauss): Project No. S-1262. Prepared by
CHEVRON CHEMICAL CO. 14 p.
92182009 Holzer, M. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079118. 48-Hour
Acute Toxicity of BOLERO 8 EC (SX-981) to First-Stage Nymph Water Fleas (Daphnia magna
Straus): Project No. S-1263. Prepared by Chevron Chemical Company. 15 p.
92182010 Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00050666. Acute
Toxicity of BOLERO 10G (SX-1252) to Daphnia magna: Project No. 26079. Prepared by
Analytical Bio-Chemistry Laboratories, Inc. 16 p.
92182011 Manza, S. (1990) Chevron Chemical Company Phase 3 Summary of MRID 40031001. Toxicity
Bioassay - Effect of BOLERO SEC on Hatchling Apple Snails (Pomacea aludosa Say): Project
No. 8616165. Prepared by Rio Palenque Research Corporation. 12 p.
72-3 Acute Toxicity to Estuarine/Marine Organisms
MRID Citation Reference
79110 Heitmuller, T. (1979) Acute Toxicity of Bolero Technical to Sheepshead Minnows
(-Cyprinodon variegatus-): Report No. BP-79-9-133. (Unpublished study received Dec 11,
1979 under 239-2449; pre- pared by EG & G, Bionomics, submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL:241494-L)
79111 Heitmuller, T. (1979) Acute Toxicity of Bolero 8 EC to Juvenile Sheepshead Minnows
(-Cyprinodon variegatus-): Report No. BP- 79-9-134. (Unpublished study received Dec 11,
1979 under 239- 2449; prepared by EG & G, Bionomics, submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL:241494-M)
79113 Heitmuller, T. (1979) Acute Toxicity of Bolero 8 EC to Fiddler Crabs (Uca pugilator): Report
No. BP-79-9-135. (Unpublished study received Dec 11, 1979 under 239-2449; prepared by EG
& G, Bionomics, submitted by Chevron Chemical Co., Richmond, Calif.; CDL:241494-P)
79114 Hollister, T. (1979) Acute Toxicity of Bolero Technical to Embryos-larvae of Eastern Oysters
(-Crassostreavirginica-): Report No. BP-79-9-131. (Unpublished study received Dec 11, 1979
under 239-2449; prepared by EG & G, Bionomics, submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL:241494-Q)
79115 Hollister, T. (1979) Acute Toxicity of Chevron's Bolero 8 EC to Embryos-larvae of Eastern
Oysters (-Crassostreavirginica-): Report No. BP-79-9-132. (Unpublished study received Dec
11, 1979 under 239-2449; prepared by EG & G, Bionomics, submitted by Chevron Chemical
Co., Richmond, Calif.; CDL:241494-R)
79116 Lauck, J.E. (1979) Field Bioassay-palaeomonid Grass Shrimp. (Un- published study received
Dec 11, 1979 under 239-2449; submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:241494-S)
142
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80853
80854
80856
80857
81906
141967
40651314
40651315
43976801
92182012
92182013
92182014
92182015
92182016
Rausina, G. (1974) Report to Chevron Chemical Company, Ortho Division: Four-day Static
Aquatic Toxicity Study with XE-362 Technical (Benthiocarb) in Eastern Oysters: IBT No. 621-
05226. (Un- published study received Mar 18, 1976 under 239-2449; prepared by Industrial Bio-
Test Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095106-N)
Rausina, G. (1974) Report to Chevron Chemical Company, Ortho Division: Four-day Static
Aquatic Toxicity Study with Benthiocarb Technical in Shore Crabs: IBT No. 621-05226.
(Unpublished study received Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test
Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095106-O)
Rausina, G. (1975) Report to Chevron Chemical Company, Ortho Division: Four-day Static
Aquatic Toxicity Study with Bolero SEC in Ghost Shrimp: IBT No. 621-06754. (Unpublished
study received Mar 18, 1976 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095106-Q)
Rausina, G. (1975) Report to Chevron Chemical Company, Ortho Division: Four-day Static
Aquatic Toxicity Study with Bolero 8 Emulsifiable Concentrate in Grass Shrimp: IBT No. 621-
06754. (Un- published study received Mar 18, 1976 under 239-2449; prepared by Industrial Bio-
Test Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095106-R)
Rausina, G. (1974) Report to Chevron Chemical Company, Ortho Division: Four-day Static
Aquatic Toxicity Study with XE-362 Technical (Benthiocarb) in Eastern Oysters: IBT No. 621-
05226. (Un- published study received Jan 10, 1975 under 5G1582; prepared by Industrial Bio-
Test Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.; CDL:094344-
M)
Borthwick, P.; Walsh, G. (1981) Initial Toxicological Assessment of Ambush, Bolero, Bux,
Dushan, Fentrifanil, Larvin, and Pydrin: Static Acute Toxicity Tests with Selected Estuarine
Algae, In- vertebrates, and Fish: EPA-600/4-81-076. Unpublished study pre- pared by
Environmental Protection Agency, Environmental Research Laboratory. 9 p.
Bailey, H. (1988) Acute Toxicity of Rice Herbicides to Neomysis mercedis: Laboratory Project
ID: R and RA 88-14. Unpublished study prepared by SRI International. 28 p.
Bailey, H. (1988) Acute Toxicity of Rice-field Herbicides to White Sturgeon (Acipenser
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Bailey, H. (1993) Acute and chronic toxicity of the rice herbicide thiobencarb and molinate to
Opossum Shrimp (Neomysis mercedis). Marine Environmental Research 36:197-215.
Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079110 and
Related MRIDs 00052169. Acute Toxicity of BOLERO Technical to Sheepshead Minnows
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Cooper, P. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079114. Acute
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Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00050667. Acute
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Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079117. Acute
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Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079111 and
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92182017 Manza, S. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079115. Acute
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92182018 Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079113. Acute
Toxicity of BOLERO 8 EC to Fiddler Crabs (Uca pugilator): Project No. LO1-500. Prepared by
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92182055 Manza, S. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079112. Effects
of BOLERO Technical on Survival, Growth, and Development of Sheepshead Minnows
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72-4 Fish Early Life Stage/Aquatic Invertebrate Life Cycle Study
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25781 Heitmuller, T. (1979) Acute Toxicity of Bolero 8 EC to Juvenile Sheepshead Minnows
(Cyprinodonvariegatus): Report No. BP- 79-9-134. (Unpublished study received Dec 11, 1979
under 239- 2450; prepared by EG&G, Bionomics, submitted by Chevron Chemical Co.,
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25782 Ward, G.S. (1979) Effects of Bolero(R) Technical on Survival, Growth, and Development of
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25783 Rausina, G. (1976) Report to Chevron Chemical Company: Four-Day Static Aquatic Toxicity
Studies with a 1:1 Mixture of Bolero SEC and STAMF-34 Active Ingredients inBluegills and
Channel Cat- fish: IBT No. 8560-09314. (Unpublished study received Dec 11, 1979 under 239-
2450; prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co.,
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33754 Lauck, J. (1979) Field Bioassay-Palaeomonid Grass Shrimp. (Unpublished study received Jan
15, 1980 under 239-EX-77; submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:241723-C)
50664 Thompson, C.M.; Griffen, J.; Boudreau, P.; et al. (1980) Acute Toxicity of Bolero 10G (SX-
1252) to Rainbow Trout (Salmo gairdner): S-1819: ABC Report # 26078. (Unpublished study
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50665 Thompson, C.M.; Griffen, J.; Boudreau, P.; et al. (1980) Acute Toxicity of Bolero 10G (SX-
1252) to Bluegill Sunfish (Lepomis macrochirus): S-1820: ABC Report # 26077. (Unpublished
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52169 Heitmuller, T. (1979) Acute Toxicity of Bolero Technical to Sheepshead Minnows (Cyprinodon
variegatus): Report No. BP-79-9-133. (Unpublished study received Dec 11, 1979 under 239-
2450; prepared by EG&G, Bionomics, submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:241489-L)
79098 Vilkas, A.G.; Browne, A.M. (1979) Daphnia magna Chronic Study: Testing Bolero Technical
(SX-1127) 95.2-95.9% Purity: UCES Project No. 11507-41. (Unpublished study received Dec
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84752 Bentley, R.E.; Macek, K.J. (1976) Some Effects of Exposure to Herbicides on Behavior,
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138076 Parrish, R. (1978) Letter sent to L. Stelzer dated Jul 31, 1978 (Effects of Bolero SEC on grass
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Bionomics, submitted by Chevron Chemical Co., Richmond, CA; CDL: 097658-H)
141967 Borthwick, P.; Walsh, G. (1981) Initial lexicological Assessment of Ambush, Bolero, Bux,
Dushan, Fentrifanil, Larvin, and Pydrin: Static Acute Toxicity Tests with Selected Estuarine
Algae, In- vertebrates, and Fish: EPA-600/4-81-076. Unpublished study pre- pared by
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40651313 Faggella, G.; Finlayson, B. (1988) Hazard Assessment of Rice Herbicides Molinate and
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98 p.
41215305 Hirata, H. (1981) Sub-acute toxicity of benthiocarb herbicide on Heamato-diagnosis and growth
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41636101 McNamara, P. (1990) Bolero Technical: The Chronic Toxicity to Daphnia magna under Flow-
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42356901 Grady, K. (1992) Raw Data for "Time to Hatch and Larval Survival" Supplement to: "Effects of
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42754202 Finlayson, B.; Faggella, G. (1984) Effects of Rice Herbicides on Larval Striped Bass: Molinate,
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42754204 Harrington, J. (1990) Hazard Assessment of the Rice Herbicides Molinate & Thiobencarb to
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43031701 Grandy, K. (1993) Raw Data for "Mysid Shrimp Chronic Toxicity Test" Supplement to: "Acute
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00079117: Lab Project Number: L01/500/600. Unpublished study prepared by Springborn Labs.
296 p.
43976801 Bailey, H. (1993) Acute and chronic toxicity of the rice herbicide thiobencarb and molinate to
Opossum Shrimp (Neomysis mercedis). Marine Environmental Research 36:197-215.
92182019 Manza, S. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079112 and
Related MRIDs 00025781. Effects of BOLERO Technical on Survival, Growth, and
Development of Sheepshead Minnows (Cyprinodon variegatus): Report No. BP-79-9-140.
Prepared by EG&G Bionomics, Marine Research Lab. 21 p.
92182020 Wang, C. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00079117. Acute
and Chronic Toxicity of BOLERO Technical to Mysid Shrimp (Mysidopsis bahia): Project No.
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72-5 Life cycle fish
MRID Citation Reference
45695101 Dionne, E. (2002) Thiobencarb TechnicalThe Chronic Toxicity to the Fathead
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72-6 Aquatic org. accumulation
MRID Citation Reference
41215306 Watanabe, S. (1985) Accumulation and excretion of herbicides in various tissues of mussel. ?
26(5):496-499.
42460401 Thacker, I; Strauss, K.; Smith, G. (1992) Thiobencarb: A Metabolic Fate Study with the
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72-7 Simulated or Actual Field Testing
MRID Citation Reference
25786 Lauck, J.E. (1979) Field Bioassay-Palaeomonid Grass Shrimp. (Un- published study received
Dec 11, 1979 under 239-2450; submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:241489-S)
33753 Chevron Chemical Company (1979) Details of Application of Ortho Bolero 8 EC Herbicide
under the EPA Experimental Use Permit No. 239-EUP-77 to Rice in the Chocolate Bayou Area
of Texas. 1st inter, rept. (Unpublished study received Jan 15, 1980 under 239-EX-77;
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79986 Harper, D.E., Jr.; Landry, A.M., Jr.; Ray, S.M.; et al. (1979) Studies in Halls Bayou To Test the
Effects of a Pre-emergent Herbicide, Bolero, on Aquatic Organisms. (Unpublished study
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80860 Barrows, M.E. (1974) Kinetics of 14C-XE-362 in a Model Aquatic Eco- system. (Unpublished
study received Mar 18, 1976 under 239- 2449; prepared by Bionomics, EG & G, submitted by
Chevron Chemical Co., Richmond, Calif.; CDL:095106-U)
41215309 Ahlstedt, S.; Jenkinson, J. (1987) Distribution and Abundance of Potamilus capax and other
Freshwater Mussels in the St. Francis River System, Arkansas and Missouri: Project ID TV-
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42130706 Finlayson, B.; Lew, T. (1983) Rice Herbicide Concentration in Sacramento River and
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42130707 Finlayson, B.; Nelson, I; Lew, T.; et al. (1982) Colusa Basin Drain and Reclamation Slough
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42130708 Fujie, G. (1983) Addendum to a Baseline Assessment to a Brackish Water Ecosystem, April 1,
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92182021 Manza, S. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00133563 and
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81-1 Acute oral toxicity in rats
MRID Citation Reference
40567 Kretchmar, B. (1972) Report to IMC Corporation: Acute Oral Toxicity Study with 3950
Technical in Albino Mice: IBT No. A1053. (Un- published study received Mar 18, 1976 under
239-EX-78; prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical
Co., Richmond, Calif.; CDL:095493-B)
40568 Ueda, K.; Nomura, K. (1969) Report on Acute Toxicity of Saturn (B- 3015) Rat, Oral: Report
No. 617. (Unpublished study received Mar 18, 1976 under 239-EX-78; prepared by Tokyo
Dental Univ., Hygiene Laboratory, submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:095493-C)
40569 Kojima, K.; Takagaki, T. (1970) Report on Acute Toxicity of Saturn (B-3015) Rats, Oral, Male:
Report No. 45-T-21. (Unpublished study received Mar 18, 1976 under 239-EX-78; prepared by
Kumiai Chemical Industry Co., Ltd., submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:095493-D)
40570 Kojima, K.; Takagaki, T. (1970) Report on Acute Toxicity of Saturn (B-3015) Rats, Oral,
Female: Report No. 45-T-20. (Unpublished study received Mar 18, 1976 under 239-EX-78;
prepared by Kumiai Chemical Industry, Co., Ltd., submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL:095493-E)
40571 Chevron Chemical Company (1952?) Acute Toxicity Studies on S-(4- Chlorobenzyl)-N,N-
diethylthiolcarbamate. (Unpublished study received Mar 18, 1976 under 239-EX-78;
CDL:095493-F)
40572 Rittenhouse, J.R.; Narcisse, J.K. (1974) S-716: The Acute Oral Toxicity of Bolero 8E (CC
5333): SOCAL 652/XVIIL102. (Unpublished study received Mar 18, 1976 under 239-EX-78;
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095493-G)
40573 Ueda, K.; Kondo, T. (1969) Report on Acute Toxicity of Saturn (B-3015) Mice, Oral: Report
No. 607. (Unpublished study received Mar 18, 1976 under 239-EX-78; prepared by Tokyo
Dental Univ., Hygiene Laboratory, submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:095493-H)
147
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40574
40576
81896
84127
84128
88591
116138
116148
116149
116154
134969
134971
139398
164578
42130701
Narcisse, J.K. (1976) S-955: The Acute Oral Toxicity of Ortho Bolero 10G (PN-5298): SOCAL
883/XXIII:79. (Unpublished study received Mar 18, 1976 under 239-EX-78; submitted by
Chevron Chemical Co., Richmond, Calif.; CDL:095493-I)
Kojima, K.; Inoue, H.; Seki, S. (1972) Oral Median Lethal Dose (LD-50) in Determination of
Some Metabolites of Benthiocarb in the Rat. (Unpublished study received Mar 18, 1976 under
239-EX- 78; prepared by Kumiai Chemical Industry Co., Ltd., submitted by Chevron Chemical
Co., Richmond, Calif.; CDL:095493-K)
Chevron Chemical Company (1952?) Acute Toxicity Studies on S-(4- Chlorobenzyl)-N,N-
diethylthiocarbamate. (Unpublished study received Jan 10, 1975 under 5G1582; CDL:094343-
G)
Rittenhouse, J.R. (1977) The Acute Oral Toxicity of RE 25501: SOCAL 959/XXIIL138 (S-
1036). (Unpublished study received Dec 11, 1979 under 6F1763; submitted by Chevron
Chemical Co., Richmond, Calif.; CDL:099125-B)
Rittenhouse, J.R. (1977) The Acute Oral Toxicity of RE 22370-2: SOCAL 1012/21:16 (S-1062).
(Unpublished study received Dec 11, 1979 under 6F1763; submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL:099125-D)
Rittenhouse, J.R.; Narcisse, J.K. (1974) The Acute Oral Toxicity of Bolero 8E (CC 5333):
SOCAL 652/XVIII:102 (S-716). (Unpublished study received Jan 10, 1975 under 5G1582;
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:094343-H)
International Minerals & Chemical Corp. (1952?) Acute Toxicity Studies on S-(4-
Chlorobenzyl)-N,N-diethylthiolcarbamate. (Unpublished study received Aug 3, 1972 under
2G1231;CDL:091083-A)
International Minerals & Chemical Corp. (19??) ?Study: Benthiocarb Metabolic Residues-Rat).
(Unpublished study received Aug 5, 1972 under 2G1231; CDL:091085-F)
Kretchmar, B. (1972) Report to IMC Corp.: Acute Oral Toxicity Study with 3950 Technical in
Albino Mice: IBT No. A1053. (Unpublished study received Aug 5, 1972 under 2G1231;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by International Minerals &
Chemical Corp., Libertyville, IL; CDL:091085-G)
Kretchmar, B. (1971) Report to ...: Acute Oral Toxicity Studies with Eleven Samples in Albino
Rats: IBT No. A482. (Unpublished study received Aug 5, 1972 under 2F1232; prepared by
Industrial Bio-Test Laboratories, Inc., submitted by Quaker Oats Co., Chicago, IL;
CDL:091086-B)
Rittenhouse, J.; Narcisse, J. (1974) The Acute Oral Toxicity of Bolero 8E (CC 5333): SOCAL
652/XVIII: 102 (S-716). (Unpublished study received Mar 18, 1976 under 239-EX-77;
submitted by Chevron Chemical Co., Richmond, CA; CDL:095492-G)
Seki, S.; Inoue, H.; Kojima, K. (1974) Acute Toxicity Studies on Technical Product, Their By-
products and Some Potential Metabolites of Benthiocarb in the Rats: ?Toxicological Study Part
IV|. (Unpublished study received Mar 18, 1976 under 239-EX-77; pre- pared by Kumiai
Chemical Industry Co., Ltd, Japan, submitted by Chevron Chemical Co., Richmond, CA;
CDL:095492-J)
Rittenhouse, J.R. (1977) The Acute Oral Toxicity of RE 25502: SOCAL 958/XXIIL137 (S-
1035). (Unpublished study received Dec 11, 1978 under 6F1763; submitted by Chevron
Chemical Co., Richmond, Calif.; CDL:099125-C)
International Minerals & Chemical Corp. (19??) Part II-C: [Acute Oral LD50 in Rats].
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Nishimura, N. (1985) Acute Toxicity Study of Benthiocarb by Oral and Dermal Administration
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44797401 Hoffman, G. (1999) Bolero 10 G: Acute Oral Toxicity Study in Rats: Lab Project Number: 99-
1970: VP-20061: 9900120. Unpublished study prepared by Huntingdon Life Sciences. 27 p.
{OPPTS 870.1100}
44797402 Hoffman, G. (1999) Bolero 8 EC: Acute Oral Toxicity Study in Rats: Lab Project Number:
9900122: 99-1972: VP-20095. Unpublished study prepared by Huntingdon Life Sciences. 57 p.
{OPPTS 870.1100}
45114001 Hoffman, G. (2000) Bolero 15 G: Acute Oral Toxicity Study in Rats: Lab Project Number: 99-
0543: 200000203. Unpublished study prepared by Huntingdon Life Sciences. 30 p. {OPPTS
870.1100}
92182022 Silveira, R. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00040572 and
Related MRIDs 00088591, 00134969. The Acute Oral Toxicity of BOLERO 8E (CC-5333):
Project No. SOCAL 652. Prepared by Chevron Environmental Health Center, lip.
92182023 Silveira, R. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00040574. The
Acute Oral Toxicity of BOLERO 10G: Project No. SOCAL 883. Prepared by Chevron
Environmental Health Center. 9 p.
92182056 Kodama, J. (1990) Chevron Chemical Company Phase 3 Summary of MRID 92182082. Acute
Toxicity Study of Benthiocarb by Oral and Dermal Administration in the Rat: BOZO/B-671. 30
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81-2 Acute dermal toxicity in rabbits or rats
MRID Citation Reference
40577 Ueda, K.; Nomura, K. (1969) Report on Acute Toxicity of Saturn (B-3015) Rat, Cutaneous:
Report No. 629. (Unpublished study received Mar 18, 1976 under 239-EX-78; prepared by
Tokyo Dental Univ., Hygiene Laboratory, submitted by Chevron Chemical Co., Richmond,
Calif.; CDL:095493-L)
40578 Rittenhouse, J.R.; Narcisse, J.K. (1974) S-719: The Acute Dermal Toxicity of Bolero Technical:
SOCAL 655/XV:87. (Unpublished study received Mar 18, 1976 under 239-EX-78; submitted by
Chevron Chemical Co., Richmond, Calif.; CDL:095493-M)
40579 Rausina, G. (1971) Report to International Minerals & Chemical Corporation: Acute Toxicity
Studies with IMC-3950 EC: IBT No. A656. (Unpublished study received Mar 18, 1976 under
239- EX-78; prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical
Co., Richmond, Calif.; CDL: 095493-N)
40580 Bullock, C.H.; Narcisse, J.K. (1976) S-956: The Acute Dermal Toxicity of Ortho Bolero 10G
(PN-5298): SOCAL 881/XV:136. (Unpublished study received Mar 18, 1976 under 239-EX-78;
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095493-O)
81897 Ueda, K.; Nomura, K. (1969) Report on Acute Toxicity of Saturn (B-3015): Rat, Cutaneous:
Report No. 629. (Unpublished study received Jan 10, 1975 under 5G1582; prepared by Tokyo
Dental Univ., Hygiene Laboratory, Japan, submitted by Chevron Chemical Co., Richmond,
Calif.; CDL:094343-J)
81898 Rittenhouse, J.R.; Narcisse, J.K. (1974) The Acute Dermal Toxicity of Bolero Technical:
SOCAL 655/XV:87 (S-719). (Unpublished study received Jan 10, 1975 under 5G1582;
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:094343-K)
149
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134973 Ueda, K.; Nomura, K. (1969) Report on Acute Toxicity of Saturn (B-3015): Rat, Cutaneous:
Report No. 629. (Unpublished study received Mar 18, 1976 under 239-EX-77; prepared by
Tokyo Dental Univ., Japan, submitted by Chevron Chemical Co., Richmond, CA; CDL:095492-
L)
134974 Bullock, C.; Narcisse, J. (1976) The Acute Dermal Toxicity of Ortho Bolero 10G (PN-5298):
SOCAL 881/XV: 136 (S-956). (Unpublished study received Mar 18, 1976 under 239-EX-77;
submitted by Chevron Chemical Co., Richmond, CA; CDL:095492-O)
140389 Rausina, G. (1971) Report to ...: Acute Toxicity Studies with IMC- 3950 EC: IBT No. A656.
(Unpublished study received Aug 3, 1972 under 2G1231; prepared by Industrial Bio-Test
Laboratories, Inc., submitted by International Minerals & Chemical Corp., Libertyville, IL;
CDL:091083-B)
161695 Korenaga, G. (1982) The Acute Dermal Toxicity of Bolero SEC in Adult Male and Female
Rabbits: SOCAL 1942. Unpublished study prepared by Chevron Environmental Health Center.
8 p.
42130701 Nishimura, N. (1985) Acute Toxicity Study of Benthiocarb by Oral and Dermal Administration
in the Rat: Lab Project ID: BOZO/B- 671. Unpublished study prepared by Bozo Research
Center, Inc. 80 p.
44797403 Hoffman, G. (1999) Bolero 10 G: Acute Dermal Toxicity Study in Rats: Lab Project Number:
991971: 9900121: VP-20079. Unpublished study prepared by Huntingdon Life Sciences. 27 p.
{OPPTS 870.1200}
45104601 Hoffman, G. (2000) Bolero 8 EC: Acute Dermal Toxicity Study in Rats: Lab Project Number:
VP-22111: 200000209. Unpublished study prepared by Huntingdon Life Sciences. 32 p.
{OPPTS 870.1200}
45104602 Hoffman, G. (2000) Thiobencarb Technical: Acute Dermal Toxicity Study in Rats: Lab Project
Number: VP-22103: 200000210. Unpublished study prepared by Huntingdon Life Sciences. 31
p. {OPPTS 870.1200}
45114002 Hoffman, G. (2000) Bolero 15 G: Acute Dermal Toxicity Study in Rats: Lab Project Number:
99-0544: 200000204. Unpublished study prepared by Huntingdon Life Sciences. 29 p. {OPPTS
870.1200}
92182024 Silveira, R. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00040578 and
Related MRIDs 00081898. The Acute Dermal Toxicity of BOLERO Technical: Project No.
SOCAL 655. Prepared by CHEVRON CHEMICAL CO. 9 p.
92182025 Silveira, R. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00040580 and
Related MRIDs 00134974. Acute Dermal Toxicity of Ortho BOLERO 10G: Project No. SOCAL
881. Prepared by Chevron Environmental Health Center, Inc. 9 p.
92182026 Silveira, R. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00161695. The
Acute Dermal Toxicity of BOLERO 8 EC in Adult Male and Female Rabbits: Project No.
SOCAL 1942. Prepared by Chevron Environmental Health Center, Inc. 14 p.
92182056 Kodama, J. (1990) Chevron Chemical Company Phase 3 Summary of MRID 92182082. Acute
Toxicity Study of Benthiocarb by Oral and Dermal Administration in the Rat: BOZO/B-671. 30
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81-3 Acute inhalation toxicity in rats
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150
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40585 Narcisse, J.K. (1976) S-959: The Acute Inhalation Toxicity of Bolero Technical Vapor: SOCAL
885/XXL148. (Unpublished study received Mar 18, 1976 under 239-EX-78; submitted by
Chevron Chemical Co., Richmond, Calif.; CDL:095493-T)
40586 Grapenthien, J.R. (1971) Report to International Minerals & Chemical Corporation: Acute
Aerosol Inhalation Toxicity Study with IMC 3950 SEC in Albino Rats: IBT No. N831.
(Unpublished study received Mar 18, 1976 under 239-EX-78; prepared by Industrial Bio-Test
Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095493-U)
116139 Grapenthien, J. (1971) Report to ...: Acute Aerosol Inhalation Toxicity Study with IMC 3950
SEC in Albino Rats: IBT No. N831. (Unpublished study received Aug 3, 1972 under 2G1231;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by Interna Minerals & Chemical
Corp., Libertyville, IL; CDL:091083-C)
134976 Narcisse, J. (1976) The Acute Inhalation Toxicity of Bolero Technical Vapor: SOCAL 885/XXI:
148 (S-959). (Unpublished study received Mar 18, 1976 under 239-EX-77; submitted by
Chevron Chemical Co., Richmond, CA; CDL:095492-T)
161698 Rittenhouse, J. (1982) The Acute Inhalation Toxicity of Bolero SEC (PN 5281) in Rats: SOCAL
1960. Unpublished study prepared by Chevron Environmental Health Center. 15 p.
44797404 Hoffman, G. (1999) Thiobencarb Technical: An Acute (4-Hour) Inhalation Toxicity Study in the
Rats via Nose-Only Exposure: Lab Project Number: 99-5384: 9900123: VP-20044. Unpublished
study prepared by Huntingdon Life Sciences. 39 p. [OPPTS 870.1300}
44797405 Hoffman, G. (1999) Bolero 10 G: An Acute (4-Hour) Inhalation Toxicity Study in the Rats via
Nose-Only Exposure: Lab Project Number: 99-5385: 9900124: VP-20087. Unpublished study
prepared by Huntingdon Life Sciences. 37 p. {OPPTS 870.1300}
45114003 Hoffman, G. (2000) Bolero 15 G: Acute (4-Hour) Inhalation Toxicity Study in the Rat via Nose-
Only Exposure: Lab Project Number: 99-5407: 200000208. Unpublished study prepared by
Huntingdon Life Sciences. 52 p. {OPPTS 870.1300}
92182027 Kodama, J. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00040585 and
Related MRIDs 00134976. The Acute Inhalation Toxicity of BOLERO Technical Vapor: Project
No. SOCAL 885. Prepared by Chevron Environmental Health Center, Inc. 9 p.
92182028 Kodama, J. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00161698. The
Acute Inhalation Toxicity of BOLERO SEC (PN 5281) in Rats: Project No. SOCAL 1960.
Prepared by Chevron Environmental Health Center, Inc. 13 p.
Neurotoxicity study in hens
MRID Citation Reference
84135 Ben-Dyke, R.; Bagley, K.; Cavanagh, J.B. (1978) Bolero: Examination for Potential To Cause
Delayed Neurotoxicity in Hens: LSR Report No. 78/KCI26/407. (Unpublished study received
Dec 11, 1979 under 6F1763; prepared by Life Science Research, England, sub- mitted by
Chevron Chemical Co., Richmond, Calif.; CDL:099125-K)
92182060 Kodama, J. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00135284 and
Related MRIDs 00084135. BOLERO: Examination for Potential to Cause Delayed
Neurotoxicity in Hens: Project No. 78/KCI26/407. Prepared by Life Science Research. 12 p.
92182076 Kodama, J. (1990) Chevron Chemical Company Phase 3 Reformat of MRID 0013 5284 and
Related MRIDs 00084135. BOLERO: Examination for Potential to Cause Delayed
Neurotoxicity in Hens: Project No. 78/KCI 26/407. Prepared by Life Science Research. 30 p.
151
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81-8 Acute neurotoxicity screen study in rats
MRID Citation Reference
42987001 Lamb, I. (1993) An Acute Neurotoxicity Study of BOLERO Technical in Rats: Lab Project
Number: WIL-194010: VP-10007. Unpublished study prepared by WIL Research Labs, Inc.
1052 p.
43148202 Lamb, I. (1994) A Range-Finding Study of BOLERO Technical in Rats: Lab Project Number:
WIL/194009. Unpublished study prepared by WIL Research Lab., Inc. 206 p.
82-1 Subchronic Oral Toxicity: 90-Day Study
MRID Citation Reference
40588 Smith, P.S.; Yost, D.H. (1972) Report to International Minerals & Chemical Corporation: 90-
Day Subacute Oral Toxicity Study with IMC 3950 Technical in Albino Rats: IBT No. B353.
(Unpublished study received Mar 18, 1976 under 239-EX-78; prepared by Indus- trial Bio-Test
Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif; CDL:095493-W)
40589 Hartke, K.; Gordon, D.E. (1972) Report to International Minerals & Chemical Corporation: 90-
Day Subacute Oral Toxicity Study with IMC 3950 Technical in Beagle Dogs: IBT No. C610.
(Unpublished study received Mar 18, 1976 under 239-EX-78; prepared by Indus- trial Bio-Test
Laboratories, Inc., submitted by Chevron Chemical Co., Richmond Calif.; CDL:095493-Y)
41176 McCollum, K. (1973) Report to International Minerals & Chemical Corporation: 21-Day Paired-
Feeding Study with IMC 3950 in Albino Rats: IBT No. 621-03628. (Unpublished study received
Mar 18, 1976 under 239-EX-78; prepared by Industrial Bio-Test Laboratories, Inc., submitted by
Chevron Chemical Co., Richmond, Calif.; CDL:095491-F)
41178 Kieckebusch, W.; Griem, W.; Lang, K. (1975) The Toxicity of p-Chlo- robenzoic acid. A
translation of: Die Vertraglichkeit der p-Chlorbenzoesaure. Arzneitmittel Forschung 10(12):999-
1001. (Unpublished study including German text, received Mar 18, 1976 under 23 9-EX-78;
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095491-H)
69694 McCollum, K. (1973) Report to International Minerals & Chemical Corporation: 21-day Paired-
feeding Study with IMC 3950 in Al- bino Rats: IBT No. 621-03628. (Unpublished study
received Mar 18, 1976 under 6F1763; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095085-F)
84130 Cummins, H.A.; Ashby, R. (1979) BoleroA(R)I: Toxicity in Dietary Administration to Rats for
Up to Eight Weeks (Range-finding Study): LSR Report No. 79/KC127/074. (Unpublished study
received Dec 11, 1979 under 6F1763; prepared by Life Science Research, England, submitted by
Chevron Chemical Co., Richmond, Calif.; CDL:099125-F)
86870 Cummins, H.A.; Ashby, R. (1980) BoleroA(R)I: Combined Oncogenicity and Chronic Feeding
Study in the Rat: Summary Report after Premature Termination after 25 Weeks of Treatment:
LSR Report No. 80/KCI028/207. (Unpublished study received Nov 30, 1981 under OF2322;
prepared by Life Science Research, England, sub- mitted by Chevron Chemical Co., Richmond,
Calif.; CDL:070486-A)
86871 Cummins, H.A.; Ashby, R.; Finn, J.P.; et al. (1980) BoleroA(R)I: Palatability Study by Paired
Feeding in the Rat: LSR Report No. 80/KCI043/034. Final rept. (Unpublished study received
Nov 30, 1981 under OF2322; prepared by Life Science Research, England, submitted by
Chevron Chemical Co., Richmond, Calif.; CDL:070487-A)
152
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116141 Industrial Bio-Test Laboratories, Inc. (1971) Study Review: IMC 3950|: IBT No. B-353.
(Unpublished study received Aug 3, 1972 under 2G1231; submitted by International Minerals &
Chemical Corp., Libertyville, IL; CDL:091083-E)
116142 Industrial Bio-Test Laboratories, Inc. (1971) Study Review: IMC 3950|: IBT No. C-610.
(Unpublished study received Aug 3, 1972 under 2G1231; submitted by International Minerals &
Chemical Corp., Libertyville, IL; CDL:091083-F)
116150 Smith, P. (1972) Report to ...: 90-day Subacute Oral Toxicity Study with IMC 3950 Technical in
Albino Rats: IBT No. B353. (Unpublished study received Aug 5, 1972 under 2G1231; prepared
by Industrial Bio-Test Laboratories, Inc., submitted by International Minerals & Chemical
Corp., Libertyville, IL; CDL:091085-H)
116151 Hartke, K. (1972) Report to ...: 90-day Subacute Oral Toxicity Study with IMC 3950 Technical
in Beagle Dogs: IBT No. C610. (Unpublished study received Aug 5, 1972 under 2G1231;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by Inter- national Minerals and
Chemical Corp., Libertyville, IL; CDL: 091085-1)
144742 Johnson, D. (1985) One Year Subchronic Oral Toxicity Study with Thiobencarb Technical in
Dogs: 415-042. Unpublished study pre- pared by International Research and Development Corp.
408 p.
164576 Richter, W. (1972) 90-Day Subacute Oral Toxicity Study with IMC 3950 Technical in Albino
Rats: Addendum Report to International Minerals & Chemical Corp.: P.O. No. ILV-001305:
IBT No. B353. Unpublished study prepared by Industrial Bio-Test Laboratories, Inc. 4 p.
82-2 21-day dermal-rabbit/rat
MRID Citation Reference
40590 Lukes, T.H.; Paa, H.; Robl, M.G. (1974) Report to Chevron Chemical Company: 21-Day
Subacute Dermal Toxicity Study with Bolero 8 Emulsive (Benthiocarb 8 Emulsive, XE-362 8
Emulsive) in Albino Rabbits: IBT No. 601-05223. (Unpublished study received Mar 18, 1976
under 239-EX-78; prepared by Industrial Bio-Test Indus- tries, Inc., submitted by Chevron
Chemical Co., Richmond, Calif.; CDL:095493-Z)
134977 Lukes, T.; Paa, H. (1974) Report to ...: 21-Day Subacute Dermal Toxicity Study with Bolero &
Emulsive (Benthiocarb & Emulsive, XE-362 & Emulsive) in Albino Rabbits: IBT No. 601-
05223. (Un- published study received Mar 18, 1976 under 239-EX-77; prepared by Industrial
Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, CA; CDL:095492-
Y)
42003401 Machado, M. (1991) Three-Week Repeated-Dose Dermal Toxicity Study in Adult Male and
Female Rats with Bolero SEC (SX-1843): Lab Project Number: CEHC/3142. Unpublished study
prepared by Chevron Environmental Health Center, Inc. 382 p.
42893001 Machado, M. (1993) Three-Week Repeated-Dose Dermal Toxicity Study in Adult Male and
Female Rats with BOLERO SEC (SX-1843) MRID 42003401: Revised Report Number One:
Lab Project Number: 5510. Unpublished study prepared by Chevron Research & Technology
Co. 391 p.
82-4 90-day inhal.-rat
MRID Citation Reference
153
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40591 Churukian, P.V.; Arceo, R. (1974) Report to Chevron Chemical Company, Ortho Division: 14-
Day Subacute Aerosol Inhalation Toxicity Study with Bolero 8 EC (Benthiocarb SEC, XE-362 £
EC) in Albino Rats: IBT No. 663-05224. (Unpublished study received Mar 18, 1976 under 239-
EX-78; prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL:095493-AA)
82-5 Subchronic Neurotoxicity: 90-Day Study
MRID Citation Reference
84134 Fletcher, D.; Arceo, RJ. (1977) Report to Kumiai Chemical Indus- tries Company, Inc.:
Neurotoxicity Study with Bolero Technical in Chickens: IBT No. 8580-10025. (Unpublished
study received Dec 11, 1979 under 6F1763; prepared by Industrial Bio-Test Laboratories, Inc..
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:099125-J)
135283 Fletcher, D.; Arceo, R. (1977) Report to Kumiai Chemical Industries Company, Inc.:
Neurotoxicity Study with Bolero Technical in Chickens: IBT No. 8580-10025. (Unpublished
study received Dec 1, 1978 under 239-EX-77; prepared by Industrial Bio-Test Laboratories,
Inc., submitted by Chevron Chemical Co., Richmond, CA; CDL:097658-C)
82-7 Subchronic Neurotoxicity
MRID Citation Reference
43001001 Lamb, I. (1993) A Subchronic (13-Week) Neurotoxicity Study of Bolero Technical in Rats: Lab
Project Number: WIL/194011: 194011: VP/10008. Unpublished study prepared by WIL
Research Labs., Inc. 1634 p.
83-1 Chronic Toxicity
MRID Citation Reference
41175 Morrow, L.; Arceo, RJ. (1974) Report to Chevron Chemical Company, Ortho Division: Two-
Year Chronic Oral Toxicity Study with Benthiocarb Technical (XE-362 Technical, Bolero
Technical) in Albi- no Rats: IBT No. 621-02095. (Unpublished study received Mar 18, 1976
under 239-EX-78; prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron
Chemical Co., Richmond, Calif.; CDL:095491-E)
41177 Mastalski, K.; Robl, M.G. (1974) Report to Chevron Chemical Company, Ortho Division: Two-
Year Chronic Oral Toxicity Study with XE-362 Technical (Bolero, Benthiocarb) in Beagle
Dogs: IBT No. 651-02096. (Unpublished study received Mar 18, 1976 under 239-EX-78;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL: 095491-G)
69693 Morrow, L. (1974) Report to Chevron Chemical Company, Ortho Division: Two-year Chronic
Oral Toxicity Study with Benthiocarb Technical (XE-362 Technical, Bolero Technical) in
Albino Rats: IBT No. 621-02095. (Unpublished study received Mar 18, 1976 under 6F1763;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL:095085-E)
72675 Morrow, L.; Sullivan, D.J. (1976) Report to Chevron Chemical Company, Ortho Division: Two-
year Chronic Oral Toxicity Study with Bolero (XE-362, Benthiocarb) in Albino Rats: IBT No.
621-04652. (Unpublished study received Dec 11, 1979 under 239-2449; prepared by Industrial
154
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Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.; CDL:
241496-A)
72676 Mastalski, K.; Richter, W.R. (1976) Report to Chevron Chemical Company, Ortho Division:
Two-year Chronic Oral Toxicity Study with XE-362 Technical (Bolero, Benthiocarb in Beagle
Dogs): IBTNo. 651-05143. (Unpublished study received Dec 11, 1979 under 239-2449;
prepared by Industrial Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co.,
Richmond, Calif.; CDL: 241496-B)
81902 Mastalski, K.; Robl, M.G. (1974) Report To Chevron Chemical Company, Ortho Division: Two-
year Chronic Oral Toxicity Study with XE-362 Technical (Bolero, Benthiocarb) in Beagle Dogs:
IBT No. 651-02096. (Unpublished study received Jan 10, 1975 under 5G1582; prepared by
Industrial Bio-Test Laboratories, Inc., sub- mitted by Chevron Chemical Co., Richmond, Calif.;
CDL:095344-E)
82633 Mastalski, K. (1974) Report to Chevron Chemical Company, Ortho Division: Two-year Chronic
Oral Toxicity Study with XE-362 Technical (Bolero, Benthiocarb) in Beagle Dogs: IBT No.
651-02096. (Unpublished study received Mar 18, 1976 under 6F1763; prepared by Industrial
Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:095085-G)
83625 Morrow, L. (1976) Report to Chevron Chemical Company, Ortho Division: Two-year Chronic
Oral Toxicity with Bolero (XE-362, Benthiocarb) in Albino Rats: IBT No. 621-04652.
(Unpublished study received Dec 12, 1979 under 6F1763; prepared by Industrial Bio- Test
Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif; CDL:099126-A)
83626 Mastalski, K. (1976) Report to Chevron Chemical Company, Ortho Division: Two-year Chronic
Oral Toxicity Study with XE-362 Technical (Bolero, Benthiocarb) in Beagle Dogs: IBT No.
651- 05143. (Unpublished study received Dec 12, 1979 under 6F1763; prepared by Industrial
Bio-Test Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:099126-B)
86004 Macrae, S.M.; Amyes, S.J.; Holmes, P.; et al. (1981) Technical Bolero(R): Potential
Oncogenicity in Dietary Administration to Mice: LSR Report No. 81/KCI040/527. Final rept.
(Unpublished study received Nov 30, 1981 under OF2322; prepared by Life Science Research,
England, submitted by Chevron Chemical Co., Richmond, Calif.; CDL:070480-A; 070479;
070483;070484;070485; 070491; 070488; 070489)
86821 Cummins, H.A.; Bhatt, A.; Afzaal, M.; et al. (1981) Technical BoleroA(R)I: Combined
Oncogenicity and Toxicity Study in Dietary Ad- ministration to the Rat: 81/KCI045/478.
Interim rept. 3: 0-52 weeks. (Unpublished study received Nov 30, 1981 under OF2322; prepared
by Life Science Research, England, submitted by Chevron Chemical Co., Richmond, Calif.;
CDL:070493-A; 070482; 070481)
108670 Morrow, L.; Sullivan, D. (1976) Report to ..., Ortho Division: Two-year Chronic Oral Toxicity
Study with Bolero (XE-362, Benthiocarb) in Albino Rats: IBT No. 621-04652. (Unpublished
study received Dec 11, 1979 under 239-2449; prepared by Industrial Bio-Test Laboratories, Inc.,
submitted by Chevron Chemical Co., Richmond, CA; CDL:241486-A)
108671 Mastalski, K.; Richter, W. (1976) Report to ..., Ortho Division: Two-year Chronic Oral Toxicity
Study with XE-362 Technical (Bolero, Benthiocarb) in Beagle Dogs: IBT No. 651-05143.
(Unpublished study received Dec 11, 1979 under 239-2449; prepared by Industrial Bio-Test
Laboratories, Inc., submitted by Chevron Chemical Co., Richmond, CA; CDL:241486-B)
148570 Life Science Research Ltd. (1984) Technical Bolero: Combined Oncogenicity and Toxicity
Study in Dietary Administration to the Rat: Final Report: 83/KC1045/248. Unpublished study.
1094 p.
150139 Cummings, H. (1984) Combined Oncogenicity and Toxicity Study in Dietary Administration to
155
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the Rat: Technical Bolero: Final Report: Report No. 83/KCI045/248. Unpublished study
prepared by Life Science Research Ltd. 264 p.
150894 Life Science Research Ltd. (1984) Technical Bolero: Combined Oncogenicity and Toxicity
Study in Dietary Administration to the Rat Final Report: [Appendices Vol. 2 and 3].
Unpublished study. 765 p.
154506 Cummins, H. (1984) Technical Bolero: Combined Oncogenicity and Toxicity Study in Dietary
Administration to the Rat: Amended Final Report: 84/KCI045/579. Unpublished study prepared
by Life Science Research Ltd. 2135 p.
92182035 Kodama, J. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00154506 and
Related MRIDs 00084130, 00086821, 00086870, 00086871, 00148570, 00150139, 00150894.
BOLERO Technical: Combined Oncogenicity and Toxicity Study in Dietary Administration to
the Rat: Amended Final Report: LSR Report No. 84/KCI045/579. Prepared by Life Science
Research. 46 p.
92182036 Kodama, J. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00144742. One-
Year Subchronic Oral Toxicity Study with Thiobencarb Technical in Dogs: IRDC Study No.
415-042 (415-041: Pilot Study). Prepared by International Research and Devi. Corp. 19 p.
1 Phytotoxicity
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31750 Locascio, S.; Layton, I; Sheets, W.A.; et al. (1976) ?Weed Control in Strawberries with
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122-1 Seed Germination/Seedling Emergence and Vegetable Vigor
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122-2 Aquatic plant growth
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41690902 Hoberg, J. (1990) Thiobencarb Technical: Determination of Effects on Seed Germination,
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123-2 Aquatic plant growth
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41690901 Giddings, J. (1990) Thiobencarb Technical-Toxicity to Five Species of Aquatic Plants: Lab
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161-1 Hydrolysis
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39099 Cheng, H.M. (1976) Photodegradation Studies with ?Ring-U-14C| Benthiocarb. (Unpublished
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44493 Ishikawa, K.; Nakamura, Y.; Niki, Y.; et al. (1973) Benthiocarb Volatilization from and
Photodecomposition in Aqueous Solution. Rev. (Unpublished study received Mar 18, 1976
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44494 Cheng, H.M. (1976) Photodegradation Studies with Ring-U-14C| Benthiocarb. (Unpublished
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44498 Pack, D.E. (1974) The Stability of Benthiocarb in Water: File No. 741.10. (Unpublished study
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87205 Ishikawa, K.; Nakamura, Y.; Niki, Y.; et al. (1977) Photodegradation of benthiocarb herbicide.
Journal of Pesticide Science 2 (1): 17-25. (Also In unpublished submission received Dec 11,
1979 under 239-2450; submitted by Chevron Chemical Co., Richmond, Calif.; CDL:099129-K)
87206 Ishikawa, K.; Nakamura, Y.; Kuwatsuka, S. (1977) Volatilization of benthiocarb herbicide from
the aqueous solution and soil. Journal of Pesticide Science 2(2):127-134. (Also In unpublished
submission received Dec 11, 1979 under 239-2450; submitted by Chevron Chemical Co.,
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123979 Chevron Chemical Co. (1974) Bolero Herbicide: The Results of Tests on the Amount of Residue
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124724 Pack, D. (1974) The Stability of Benthiocarb in Water: File No. 741.10. (Unpublished study
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124730 Ishikawa, K.; Nakamura, Y.; Niki, Y.; et al. (1973) Benthiocarb Volatilization from and
Photodecomposition in Aqueous Solution. Rev. (Unpublished study received Mar 18, 1976
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125180 Chevron Chemical Co. (1974) Bolero Herbicide: Name, Chemical Identity and Composition of
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152311 Crosby, D. (1983) The fate of herbicides in California rice culture. P. 339-346 in Pestic. Chem.:
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41609012 Chen, Y. (1990) Hydrolysis of ?Phenyl-U-?carbon 14||-Thiobencarb in Water: Lab Project
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123979 Chevron Chemical Co. (1974) Bolero Herbicide: The Results of Tests on the Amount of Residue
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42257801 Chen, Y. (1988) Photodegradation of Phenyl-U-14C|-Thiobencarb in Water: Lab Project
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Ishikawa, K.; Nakamura, Y.; Niki, Y.; et al. (1973) Benthiocarb Volatilization from and
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Ishikawa, K.; Nakamura, Y.; Niki, Y.; et al. (1977) Photodegradation of benthiocarb herbicide.
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Ishikawa, K.; Nakamura, Y.; Kuwatsuka, S. (1977) Volatilization of benthiocarb herbicide from
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Ishikawa, K.; Nakamura, Y.; Niki, Y.; et al. (1973) Benthiocarb Volatilization from and
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39102 Pack, D.E. (1974) A Comparison of the Rates of Soil Degradation of Benthiocarb under flooded
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39103 Pack, D.E. (1974) The Effect of Sterilization on the Rate of Soil Degradation of Benthiocarb.
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39104 Nakamura, Y.; Kuwatsuka, S. (1974) Degradation of Benthiocarb in Soil. (Unpublished study
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87204 Nakamura, Y.; Ishikawa, K.; Kuwatsuku, S. (1977) Degradation of benthiocarb in soils as
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96954 Pack, D.E. (1974) The Soil Metabolism of Ring-ULA14IC|-benthiocarb: File No. 773.21.
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123979 Chevron Chemical Co. (1974) Bolero Herbicide: The Results of Tests on the Amount of Residue
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135374 Pack, D. (1975) The Soil Metabolism of ?Ring-U-14C|Benthiocarb: File No. 773.21.
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43300401 Patterson, T. (1994) Aerobic Metabolism of (Phenyl-(carbon 14))-Thiobencarb in Soil: Lab
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92182049 Pack, D. (1990) Chevron Chemical Company Phase 3 Summary of MRID 00040925. The Soil
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162-4 Aerobic aquatic metab.
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39100 Ishikawa, K.; Nakamura, Y.; Niki, Y.; et al. (1973) Benthiocarb Volatilization from and
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39106 Warnock, R.E. (1975) Adsorption, Desorption and Freundlich Constants of Benthiocarb in Soil.
(Unpublished study received Mar 18, 1976 under 239-2450; submitted by Chevron Chemical
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40928 Warnock, R.E. (1974) Mobility of Benthiocarb and pCl-Benzoic acid in Soil As Determined by
Soil TLC Techniques. (Unpublished study received Mar 18, 1976 under 239-2449; submitted by
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40929 Warnock, R.E. (1974) Benthiocarb Leaching Study~EPA Protocol. (Unpublished study received
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40930 Warnock, R.E. (1975) Adsorption, Desorption and Freundlich Constants of Benthiocarb in Soil.
(Unpublished study received Mar 18, 1976 under 239-2449; submitted by Chevron Chemical
Co., Richmond, Calif.; CDL:095091-K)
40931 Warnock, R.E. (1975) Volatilization of Benthiocarb~Laboratory Studies. (Unpublished study
received Mar 18, 1976 under 239- 2449; submitted by Chevron Chemical Co., Richmond, Calif.;
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41813 Warnock, R.E. (1974) Benthiocarb Leaching Study~EPA Protocol. (Unpublished study received
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44500 Warnock, R.E. (1975) Adsorption, Desorption and Freundlich Constants of Benthiocarb in Soil:
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44501 Warnock, R.E. (1975) Volatilization of Benthiocarb-Laboratory Studies: File No. 721.2
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44511 Pack, D.E. (1975) The Soil Metabolism of ?Ring-U-14C| Benthiocarb: File No. 773.21.
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44512 Warnock, R.E. (1974) Benthiocarb Leaching Study~EPA Protocol: File No. 721.14 (Bolero).
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162
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86782 Sachs, E.S. (1976) Comparative Soil Sorption, Movement and Volatility of Three
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87206 Ishikawa, K.; Nakamura, Y.; Kuwatsuka, S. (1977) Volatilization of benthiocarb herbicide from
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96972 Pack, D.E. (1977) Soil Mobility of Captan, Folpet and Captafol As Determined by Soil Thin-
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123979 Chevron Chemical Co. (1974) Bolero Herbicide: The Results of Tests on the Amount of Residue
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124725 Warnock, R. (1975) Adsorption, Desorption and Freundlich Constants of Benthiocarb in Soil:
File No. 741.11. (Unpublished study received Mar 18, 1976 under 239-2450; submitted by
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124728 Warnock, R. (1975) 14C-Benthiocarb Residues in Soil and Uptake by Carrots~EPA Protocol:
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135375 Warnock, R. (1974) Benthiocarb Leaching Study: File No. 721.14 (Bolero). (Unpublished study
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135376 Warnock, R. (1975) Volatilization of Benthiocarb-Laboratory Studies: File No. 721.2 (Bolero).
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40924
Ishikawa, K.; Nakamura, Y.; Niki, Y.; et al. (1973) Benthiocarb Volatilization from and
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163
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123979
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164-1 Terrestrial field dissipation
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32808 Chevron Chemical Company (19??) Recovery of Bolero 10G and Bolero SEC from Rice Field:
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40927 Tucker, B.V. (1974) Simulated Field Study of Rice Treated with 14C-Ring-Labeled
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72530 Serat, W.F. (1975) Work Unit D-Experimental Use Permit Health Effects: ?Bolero in Rice|.
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44650601 Okumura, D. (1998) (Thiobencarb and Other Chemicals: California Surface Water Monitoring
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850.1075 Fish acute toxicity test, freshwater and marine
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Project Number: 200300280, KCI/236/032204, 17797. Unpublished study prepared by
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850.3020 Honey bee acute contact toxicity
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Selected Citations Found under Non Guideline
25175 or Kamienski, F.X. (1978) Evaluation of Hazard to Shrimp from Use of Bolero (Thiobencarb) SEC for
138075 Rice Weed Control. (Unpublished study received Dec 11, 1979 under 239-2450; submitted by
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25780 Lauck, J.E. (1979) Observations on Avian Wildlife in Bolero Treated Rice Fields, Brazoria County,
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Co., Richmond, Calif.; CDL:241489-K)
33755 Lauck, J.E.; LeCompte, R.; Johnson, L.; et al. (1979) Observations on Avian Wildlife in Bolero
Treated Rice Fields, Brazoria County, Texas. (Unpublished study received Jan 15, 1980 under 239-
EX-77; prepared in cooperation with Chocolate Bayou Co., submit- ted by Chevron Chemical Co.,
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39117 Warnock, R.E.; Cheng, H.M. (1974) Benthiocarb Metabolism in the Duck. (Unpublished study
167
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44510 Pack, D.E. (1976) Residues of Total Radioactivity in Daphnia magna Living in Water Treated with
14C-Benthiocarb: File No. 741.10. (Unpublished study received Mar 18, 1976 under 239-2449;
submitted by Chevron Chemical Co., Richmond, Calif.; CDL:095095-R)
46059803 Rodgers, M. (2003) Thiobencarb Technical Acute Toxicity (LC 50) to the Earthworm. Project
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46059805 Carter, J. (2003) Thiobencarb Effects on Soil Non-Target Micro-Organisms: Nitrogen
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46091402 Albuquerque, R. (2003) Thiobencarb Technical Toxicity to the Sediment Dwelling Phase of the
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168
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