# Risks of Methidathion Use to Federally Threatened California Red-legged Frog ( Rana aurora draytonii )

Pesticide Effects Determination

Environmental Fate and Effects Division Office of Pesticide Programs Washington, D.C. 20460

February 18, 2009

### Primary Authors: Colleen Flaherty, Biologist Keara Moore, Chemist Pamela Hurley, Toxicologist

Secondary Review: Brian Anderson, Biologist James Hetrick, Senior Scientist

Branch Chief, Environmental Risk Assessment Branch 3: Dana Spatz

2Table of Contents

1. Executive S ummary ...............................................................................................8 2. Problem Formulation ..........................................................................................16 2.1 Purpose ..........................................................................................................................16 2.2 Scope ..............................................................................................................................1 8 2.3 Previous Assessmen ts ...................................................................................................18 2.3.1 Methidathion Interim Registra tion Elig ibility Decision, 2002 ................................18 2.3.2. Organophosphate Cumulative Assessment, and Methidathion Reregistration Eligibility Decision, 2006 .........................................................20 2.4 Stressor So urce and Distribution ...............................................................................20 2.4.1 Environmental Fate an d Transport ...................................................................20 2.4.2 Mechanism of Action ...........................................................................................25 2.4.3 Use Characteriz ation ...........................................................................................25 2.5 Assessed Species ................................................................................................................29 2.5.1 Distribution ...........................................................................................................29 2.5.2 Reproduction ........................................................................................................32 2.5.3 Diet ........................................................................................................................32 2.5.4 Habitat ..................................................................................................................33 2.6 Designated Critica l Habitat ........................................................................................34 2.7 Action Area ...................................................................................................................36 2.8 Assessment Endpoints and Measures of Ecological Effect ......................................39 2.8.1. Assessment Endpoints for the CRLF .................................................................39 2.8.2 Assessment Endpoints for Desi gnated Critical Habitat ...................................40 2.9 Conceptual Model ........................................................................................................43 2.9.1 Risk Hypo theses ...................................................................................................43 2.9.2 Diagram ................................................................................................................43 2.10 Analysis Plan ................................................................................................................45 2.10.1 Measures to Evaluate the Risk Hy pothesis and Conceptual Model ................46 2.10.2 Data Gaps .............................................................................................................49 3.1 Label Application Rates and Intervals ......................................................................50 3.2 Aquatic Exposure Assessment ....................................................................................51 3.2.1 Modeling Approach .............................................................................................51 3.2.2 Model Inputs .........................................................................................................51 3.2.3 Results ...................................................................................................................54 3.2.4 Existing Monitoring D ata ....................................................................................55 3.3 Terrestrial Animal Exposure Assessment .................................................................59 3.3.1 Modeling Approach .............................................................................................59 3.4 Terrestrial Plant Exposure Assess ment .....................................................................62 4. Effects Assessment ...............................................................................................62 4.1 Toxicity o f Methidathion to Aquatic Organisms ......................................................63 4.1.1 Toxicity to Freshw ater Fish ................................................................................64 4.1.2 Toxicity to Freshw ater Invertebrates .................................................................67 4.1.3 Toxicity to Aquatic Plants ...................................................................................68 4.2 Toxicity o f Methidathion to Terrestrial Organisms .................................................68 4.2.1 Toxicity to Birds ...................................................................................................69

34.2.2 Toxicity to Mammals ...........................................................................................71 4.2.3 Toxicity to Terrestrial Invertebrates .................................................................72 4.2.4 Toxicity to Terrestrial Plants ..............................................................................72 4.3 Use of Probit Slope Response Relation ship to P rovide Information on the Endangered Species Levels of Concern .................................................................................73 4.4 Incident Database Review ...........................................................................................73 4.4.1 Terrestrial Incidents ............................................................................................74 4.4.2 Aquatic Incidents .................................................................................................75 5. Risk Characteriz ation ..........................................................................................75 5.1 Ri sk Estimation ............................................................................................................75 5.1.1 Exposures in the Aquatic Habitat ......................................................................76 5.1.2 Exposures in the Terrestria l Habitat .................................................................80 5.1.3 Primary Co nstituent Elements of Designated Critical Habitat .......................87 5.1.4 Spatial Extent of Poten tial Effects ......................................................................89 5.2 Risk Description ...........................................................................................................93 5.2.1 Direct Effects ........................................................................................................97 5.2.2 Indirect Effects (v ia Reductions in Prey Base) ................................................105 5.2.3 Indirect Effects (v ia Habitat Effects) ...............................................................109 5.2.4 Modification to Designated Critical Habitat ...................................................110 6. Uncertainties .......................................................................................................112 6.1 Exposure Assessment Uncertainties .........................................................................112 6.1.1 Maximum Use Scenario .....................................................................................112 6.1.2 Aquatic Exposure Modeling of Methidathion .................................................112 6.1.3 Potential Groundw ater Contribut ions to Surface Water Chemical Concentrations ................................................................................................114 6.1.4 Action Area Uncertain ties .................................................................................114 6.1.5 Usage Uncertainties ...........................................................................................115 6.1.6 Terrestrial Exposure Modeling o f Methidathion ............................................116 6.1.7 Spray Drift Modeling .........................................................................................117 6.2 Effects Ass essment Uncertainties .............................................................................117 6.2.1 Age Class and Sensitivity of Effects Thresholds .............................................117 6.2.2 Use of Surrogate Species Effects Data .............................................................118 6.2.3 Sublethal Effects .................................................................................................118 6.2.4 Location of Wildlife Sp ecies ..............................................................................119 7. Risk Conclusions ................................................................................................119 8. References ...........................................................................................................123

4Appendices

Attachment 1 CRLF Life History Attachment 2 Final CRLF Baseline Status and Cumulative Effects Appendix A Bibliography of submitted fate studies Appendix B Chemical Names and Structures Appendix C California PUR Data Appendix D CRLF Spatial Summary Appendix E Risk Quotient Me thod and Levels of Concern Appendix F PRZM/EXAMS Model Outputs Appendix G T-REX Example Output Appendix H Bibliography of ECOTOX Papers Appendix I Accepted ECOTOX Da ta Table (sorted by effect) Appendix J Ecological Effects Appendix K Data Table for Mammalian Studies from Health Effects Division Appendix L Incident Data Appendix M T-HERPS Example Output Appendix N Bibliography of Submitted Ecotoxicity Studies

List of Tables

Table 1.1 Effects Determination Summary for Methidathion Use and the CRLF .......................12 Table 1.2 Effects Determination Summary for Methidathion Use and CRLF Critical Habitat Im pact Analysis .........................................................................................13 Table 1.3 Methidathion Use-specifi c Direct Effects Determ inations 1 for the CRLF ...................13 Table 1.4 Methidathion Use-specific Indirect Effects Determ inations 1 Based on Effects to Prey ........................................................................................................................14 Table 2.1. Summary of Methidathion Environmental Fate Properties .........................................22 Table 2.2 Methidathion Uses Assessed for the CRLF .................................................................28 Table 2.3 Assessment Endpoints and Measures of Ecological Effects ........................................40 Table 2.4 Summary of Assessment Endpoints and Measures of Ecological Effect for Prim ary Constituent Elements of Designated Critical Habitat a .............................42 Table 3.1. PRZM/EXAMS Environmental Fate Inputs for Aquatic Exposure to Methid athion ..........................................................................................................51 Table 3.2. PRZM/EXAMS Crop-Specific Inputs for Aquatic Exposure to Methidathion ...........53 Table 3.3 Aquatic EECs ( μ g/L) for Methidathion Uses in California ...........................................54 Table 3.4 Input Parameters for Foliar Applica tions Used to Derive Terrestrial EECs for Methid athion with T-REX .....................................................................................60 Table 3.5 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based Exposures of the CRLF and its Prey to Methidathion ...........................................61 Table 3.6 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via Effects to Terres trial Invertebrate Prey Items ........................................................................61

5Table 4.1 Freshwater Aquatic To xicity Profile for Methidathion ................................................64 Table 4.2 Categories of Acute T oxicity for Aquatic Organism s ..................................................64 Table 4.3 Terrestrial Toxicity Profile for Methidathion ...............................................................68 Table 4.4 Categories of Acute Toxic ity for Avian and Mamm alian Studies .................................69 Table 5.1 Summary of Acut e Direct Effect RQs for the Aquatic-phase CRLF a ..........................77 Table 5.2 Summary of Chronic Direct E ffect RQs for the Aquatic-phase CRLF a ........................78 Table 5.3 Summary of Acute RQs Used to Es tim ate Indirect Effects to the CRLF via Direct Effects on Aquatic Invert ebrates as Dietary Food Items ............................79 Table 5.4 Summary of Chronic RQs Used to Es tim ate Indirect Effects to the CRLF via Direct Effects on Aquatic Invert ebrates as Dietary Food Items ............................80 Table 5.5. Summary of Direct Effect Acute Dose-Based RQs for the Terrestrial-phase CRLF for Spray Applications of Methidathion .....................................................81 Table 5.6. Summary of Direct Effect Acute Dietary-Based R Qs for the Terrestrial-phase CRLF for Spray Applications of Methidathion .....................................................82 Table 5.7. Summary of Direct Effect Chr onic R Qs for the Terrestrial-phase CRLF for Spray Applications of Methidathion ......................................................................83 Table 5.8 Summary of RQs For Indirect Effect s to the Terrestrial-phase CRLF via Direct Effects on Terres trial Invertebrates as Dietary Food Items ...................................84 Table 5.9. Summary of Acute RQs For Indirect Effects to the Terre strial-phase CRLF via Direct Effects on Sm all Mammals as Dietary Food Items ....................................85 Table 5.10. Summary of Chronic RQs For Indirect Effects to the Terrestrial-phase CRL F via Direct Effects on Small Ma mmals as Dietary Food Items ...............................86 Table 5.11. Input parameters for simulation of m ethidathion in spray drift using AgDisp (v. 8.15) with Gaussian far field extension. ...........................................................90 Table 5.12 Summary of maximum predicted dist ances for potential spray drift effects. ..............91 Table 5.13 Risk Estimation Summary for Methid athion - Direct and I ndirect Effects to CRLF ......................................................................................................................94 Table 5.14 Risk Estimation Summary for Meth idathion – P CEs of Designated Critical Habitat for the CRLF .............................................................................................95 Table 5.15. Upper Bound Kenaga, Acute Terres trial Herpetofauna Dose-Based Risk Quotients ..............................................................................................................100 Table 5.16. Upper Bound Kenaga, Acute Terres trial Herpetofauna Dose-Based Risk Quotients ..............................................................................................................107 Table 7.1 Effects Determination Summary for Methidathion Use and the CRLF .....................121 Table 7.2 Effects Determination Summary for Methidathion Use and CRLF Critical Habitat Im pact Analysis .......................................................................................122

6List of Figures

Figure 2.1. Map of Estimated Annual Agri cultural Use of Methidathion in 2002 ................26 Figure 2.2 Recovery Unit, Core Area, Critical Habitat, and Occurrence Designation s for CRLF ........................................................................................31 Figure 2.3 – CRLF Reproductive Events by Month .................................................................32 Figure 2.4 Initial area of concern, or “footprint” of poten tial use, for methidathion ..........38 Figure 2.5 Conceptual Model for Methidath ion Effects o n Terrestrial Phase of the CRLF .....................................................................................................................44 Figure 2.6 Conceptual Model for Methidath ion Effects on Aquatic Phase of the CRLF .....................................................................................................................45 Figure 5.1. Overlap Map: CRLF Habitat an d Methidathion Initia l Area of Concern ........93

71. Executive Summary

The purpose of this assessment is to evaluate potential direct and i ndirect effects on the California red-legged frog (Rana aur ora draytonii ) (CRLF) arising from FIFRA regulatory actions regarding use of methidat hion on agricultural and non-agricultural sites. In addition, this assessment evaluate s whether these actions can be expected to result in modification of the species’ designa ted critical habitat. This assessment was completed in accordance with the U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS) Endangered Species Consultation Handbook (USFWS/NMFS, 1998 and procedures outlined in the Agency’s Overview Document (U.S. EPA, 2004).

The CRLF was listed as a threatened species by USFWS in 1996. The species is endem ic to California and Baja California (Mexico) and inhabits both co astal and interior mountain ranges. A total of 243 streams or drainages are believed to be currently occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and Santa Barbara counties (USFWS , 1996) in California.

Methidathion is a non-systemic organophosphate insecticide/acaricide registered for use to control a wide range of su cking, leaf-eating, and scale inse cts. Currently labeled uses of m ethidathion considered as part of the federal action evaluated in this assessment include: Alfalfa, almond, apple, apricot, artichoke, calemondin, cherry, citron, citrus, clover, cotton, grapefruit, kiwi, kumquat, le mon, lime, mango, nectarine, olive, peach, pear, plum, prune, pummelo, safflower, sunf lower, tangelo, tangerine, timothy, walnut, and nursery stock. Methidathion is formulat ed as an emulsifiable concentrate or a wettable powder. Applications can be applie d by ground, airblast, or aerial spray with annual application rates that range from 1 lb active ingredient/A to 10 lb a.i./A. Label requirements include restrictions on spray he ights and buffer widths in order to reduce risk from spray drift.

Based on laboratory studies, methidathion has generally low persistence in soil, with aerobic and anaerobic soil metabolism half-liv es of less than two weeks. Dissipation rates appear to slow over time, however, so th ere is a possibility that in some conditions low levels may persist. Terre strial field dissipation studies found half-lives of less than 30 days. In water, methidathion has limited hydrolysis except in al kaline conditions, but it is subject to aquatic photolysis with a half-life of 10 days. There are no aquatic metabolism data available. Soil adsorption studies indicate that methidathion is moderately mobile, but it has not been detected below 18 inch es in any terrestrial field dissipation studies. There is some potential for long range atmospheric transport. Although the physical properties suggest that volatilization would be limited, monitoring studies have found methidathion residues at more than 20 km from any use site.

Soil metabolism of methidathion leads prim arily to carbon dioxide and bound residues, but one unidentified degradate was form ed at up to 13% and appeared to be persistent. Other major degradates include S-12956 1 , formed through hydrolysis and through aquatic

1 5-methyl-1-3,4-thiadazol-2 (3H)-one

8and soil photolysis, and des-methyl GS-13007 2 and PAMMTO 3 , formed through hydrolysis in some conditions. Methidathion oxon 4 is formed only as a minor degradate, but it is included as a stressor of concern in this assessment because, based on data for other organophosphate pesiticide s, oxon degradates have the potential to be much more toxic than the parent. Labor atory studies demonstrate that at least 4.9% of applied methidathion can be transformed to methidathion oxon through soil photolysis, but no data are available regarding photo-oxidation in air, which could also be an important route of transformation.

Since CRLFs exist within aquatic and terrestria l habitats, exposure of the CRLF, its prey and its habitats to m ethidathion are assesse d separately for the two habitats. Tier-II aquatic exposure models are used to estim ate high-end exposures of methidathion inaquatic habitats resulting from runoff and spray drift from different uses. Peak modelestimated aquatic environmental concentrations resulting from different methidathion uses range from 7.3 to 114.7 μg/L. These estimates are supplemented with analysis of available California surface wa ter monitoring data from U. S. Geological Survey’s National Water Quality Assessment (NAWQA) program and the California Department of Pesticide Regulation. The maximum con centration of methidathion reported by NAWQA for California surface waters from 15 sites is 0.31 μg/L. The California Department of Pesticide Regulation surf ace water database included more than 4,000 samples from 135 locations in agricultura l areas and reported a maximum measured concentration of 15.1 μg/L, which is in the range of peak mode led values for the different uses of methidathion. Ground water per se is not evaluated herei n, but it is nonetheless significant because discharging groundwater is likely to support low-order streams, wetlands, and intermittent ponds – environments that are favorable to CRLFs. Long-term chronic concentrations derived from th e PRZM-EXAMS model could reflect background concentrations that might be found in discharged groundwater/stream baseflow. NAWQA monitoring data did no t detect methidathion in ground water sampling at more than 200 sites, most of whic h were collected in counties with high methidathion use in areas with land cover classified as agricultural or mixed use.

To estimate methidathion exposures to the te rrestrial-phase CRLF, and its potential prey resulting from uses involving m ethidathion ap plications, the T-REX model is used for foliar uses. AgDRIFT is used to estimate deposition of methidat hion on terrestrial and aquatic habitats from spray drift. The TerrPla nt model is used to estimate methidathion exposures to terrestrial-phas e CRLF habitat, including plants inhabiting semi-aquatic and dry areas, resulting from uses involving fo liar methidathion applications. The T-HERPS model is used to allow for further character ization of dietary expos ures of terrestrialphase CRLFs relative to birds.

There are also atmospheric monitoring data which dem onstrate long range transport of both methidathion and methidathion oxon. Both species have been detected in air, fog, and/or rain at local, intermediate, and long-range locations. In the monitoring study with

2 des-methyl S-[(5-methoxy-2-oxo-1, 3, 4-thiadiazol-3 (2-1)-yl-methyl O,O-dimethylphosphorothioate]
3 phosphorthioic acid, 4-(mercaptomethy1)-2-meth-oxy-A2-,13 ,4-thiadiazolin-5-one
4 S-[(5-methione-2-oxo-1,3,4-thiodiazol-3(2H)-yl methyl o,o dimethyl phosphorothioate; (GS-13007)

9data at the furthest range, methidathion was de tected in air at 22 km from the nearest use site and methidathion oxon was detected at a site another 10 km away. Methidathion oxon was also detected on pine needles at the 22 km site.

The effects determination assessment endpoints for the CRLF include direct toxic effects on the survival, reproduction, and growth of th e CRLF itself, as well as indirect effects, such as reduction of the prey base or m odifi cation of its habitat. Direct effects to the CRLF in the aquatic habitat are based on toxic ity information for freshwater fish, which are generally used as a surrogate for aquatic-pha se amphibians. In the terrestrial habitat, direct effects are based on toxicity informati on for birds, which are used as a surrogate for terrestrial-phase amphibians. Given th at the CRLF’s prey items and designated critical habitat requirements in the aquatic habitat are dependant on the availability of freshwater aquatic invertebrates and aquati c plants, toxicity information for these taxonomic groups is also discussed. In the te rrestrial habitat, indi rect effects due to depletion of prey are assessed by considering eff ects to terrestrial insects, small terrestrial mammals, and frogs. Indirect effects due to modification of the te rrestrial habitat are characterized by available data for terrestrial monocots and dicots.

This assessment primarily considers effect s of exposures to m ethidathion only but quantitative characterization is provided fo r methidathion oxon, the one known degradate of concern. Although no toxicity data are av ailable for methidathion oxon, it is presumed to be of concern because toxicity data for oxon transformation products of similar pesticides in the organophospate class suggest they will be of equal or greater toxicity than the parent. There are other degradates suggested by the degrad ation pathway but not tested for in laboratory studies that may al so be of concern. No data are available regarding the formation and decl ine or the toxicity of meth idathion oxon or of any of the other potential OP or oxon degradates. Given that acute and chronic risk quotients are exceeded for the parent compound alone, any co ntribution in toxicity from any of the major degradates or from methidathion oxon or other OP degradates would increase the risk estimates.

Risk quotients (RQs) are derived as quantita tive estim ates of potential high-end risk. Acute and chronic RQs are compared to the Agency’s levels of concern (LOCs) to identify instances where methidathion use within the action area has the potential to adversely affect the CRLF and its designated critical habitat via direct toxicity or indirectly based on direct eff ects to its food supply (i.e., freshwater invertebrates, algae, fish, frogs, terrestrial inverteb rates, and mammals) or hab itat (i.e., aquatic plants and terrestrial upland and riparian vegetation). Wh en RQs for each particular type of effect are below LOCs, the pesticide is determined to have “no effect” on the CRLF. Where RQs exceed LOCs, a potential to cause adve rse effects is identified, leading to a conclusion of “may affect.” If a determin ation is made that use of methidathion use within the action area “may affect” the CRLF and its designated critical habitat, additional information is consid ered to refine the potential for exposure and effects, and the best available information is used to distinguish those acti ons that “may affect, but are not likely to adversely affect” (NLAA) from those actions that are “likely to adversely affect” (LAA) the CRLF and its critical habitat.

10Based on the best available information, the Ag ency m akes a Likely to Adversely Affect determination for the CRLF from the use of methidathion. Additionally, the Agency has determined that there is the potential for m odification of CRLF designa ted critical habitat from the use of the chemical. For direct effects, the acute listed species LOCs for freshwater fish and for birds (surrogate to the aquatic-and terre strial-phase CRLF, respectively) are exceeded for all uses. Th e chronic LOC for both freshwater fish and birds is also exceeded for all uses. For indi rect effects, with th e exception of mangos on an acute dietary basis for non-listed species , the acute dose-based, acute dietary-based and chronic dietary-based RQs for birds (terrestrial-phase amphibians) exceed both the acute non-listed species LOC and/or the chroni c LOC for all of the assessed uses. Foraquatic and terrestrial invertebrates and mammals, the acute RQs exceed the acute nonlisted LOC for aquatic and/or terrestrial animals for all uses. The chronic LOC for aquatic and/or terrestrial animals is also ex ceeded for aquatic invertebrates, mammals and fish/aquatic-phase amphibi ans (all uses). No studies are available for aquatic vascular and non-vascular and terrestrial plants; however, the weight of the evidence indicates an effect determination of may a ffect, not likely to adve rsely affect (NLAA).

A summary of the risk conclusions and e f fects determinations for the CRLF and its critical habitat is presented in Tables 1.1 and 1.2 . Use-specific determinations for direct and indirect effects to the CRLF are provided in Tables 1.3 and 1.4 . Further information on the results of the effects dete rmination is included as part of the Risk Description in Section 5.2. Given the LAA determination for the CRLF and potential modification of designated critical habitat, a description of the baseline status and cumulative effects for the CRLF is provided in Attachment 2

.

11Table 1.1 Effects Determination Summary for Methidathion Use and the CRLF
Assessment

Endpoint Effects Determination 1 Basis for Determination

Potential for Direct Effects Aquatic-phase (Eggs, Larvae, and Adults) : Highly toxic to freshwater fis h. Acute listed species LOC exceeded for all uses for three tested surrogate sp ecies. Chronic effects based on survival and growth. Chronic LOC exceeded for all uses. Proba bility of an individual effect on an acute basis is high, both at the acute LOC and at the RQ levels. Incident data also indicate freshwater fi sh vulnerability, and monito ring has detected surface water concentrations above the acute endp oint. Significant overlap expected to exist between use sites and CRLF habitat, particularly when the spraydrift and downstream dilution buffers are added to the methidathion use area. Spraydrift distances range from 23 to over 1000 feet and the downstream dilution buffer is 285 km. Terrestrial-phase (Juveniles and Adults) : Moderately toxic to very highly toxic to avian species. Acute dose-based, acute dietary-ba sed and chronic dietary-base d RQs for the terrestrial-phase CRLF, using avian data as a surrogate, exceed acute listed species LOC and chronic LOC for all of the assessed uses. Chroni c effects based on reduction in number of normal hatchlings/live 3-week embryos. Limited data indicate that on a dose basis, the acute LOC is exceeded for all uses, even with the least sensitive species at the lowest application rate (ma ngos). On a dietary basis, the same is true for all uses except mangos. Probability of an individual effect on an acute basis is high at the RQ levels. Incident data indicate that birds are vulnerable. Significant overlap exists between use sites and CRLF habitat, particularly when the spraydrift buffers are ap plied to the methidathion use area. Spraydrift distances range from 194 to over 1000 feet. Potential for Indirect Effects Aquatic prey items, aquatic habitat, cover and/or primary productivity Very highly toxic to fresh water invertebrates. Acute and chronic RQs exceed

acu te LOC for non-listed species and chr onic LOC, respectively for all assessed uses. The percentage effect to the aquatic invertebrate prey base for all uses is very high. For fish (aquatic-phase amphibians), acute non-listed species LOC exceeded for all uses. Chronic LOC exceeded for all uses. Percentage effect to the freshwater fish/aquatic-phase amphibian prey base is very high. No studies are available for aquatic vascular and non-vascular plants. Survival, growth, and/or reproduction of CRLF individuals LAA 1

Terrestrial prey items, riparian habitat RQs for both small and large insects exce ed acute LOC for non-listed species for all methidathion uses, even with only a single use. Insufficient studies to conduct a sensitivity analysis; however, lowest RQ, using highest terrestrial invertebrate endpoint still exceeds the acut e list species LOC. Percentage effect to the terrestrial invertebrate prey base for all uses is very high. For terrestrialphase amphibians using avian data as a surrogate, with the exception of mangos on an acute dietary basis, the acute do se-based, acute dietary-based and chronic dietary-based RQs exceed the acute non- listed species LOC and the chronic LOC for all of the assessed methidathion uses, respectively. Percentage effect to the avian/terrestrial-phase amphi bian prey base is very high. For mammals, the acute and chronic RQs exceed the non-lis ted species acute LOC and the chronic LOC, respectively for all uses. At the lowest RQ, the percentage effect to the mammalian prey base is very high. No studi es are available for terrestrial plants.

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

1213 Table 1.2 Effects Determination Summary for Methidathion Use and CRLF Critical Habitat Impact Analysis
Assessment

Endpoint Effects Determination 1 Basis for Determination

Modification of aquatic-phase PCE No studies available for aquatic vascular and non-vascular plants and terrestrial plants.

For the aquatic-phase CRLF, acute non-listed species LOC for freshwater fi sh (aquatic-phase amphibians) exceeded for all uses. Chronic LOC for freshwater fish exceeded for all uses. Probability of an individual effect and percentage effect to the freshwater fish/aquatic-phase amphibian prey base on an acute basis at the RQ are high. Incident data support freshwater fish vulnerability. For freshwater inverteb rates, acute and chronic RQs exceed acute LOC (non-listed species) and chronic LOC, respectively for all assessed uses. Again, the percentage ef fect to the aquatic invertebrate prey base is very high. Significant overlap expected between use sites and CRLF habitat, particularly when the spraydri ft and downstream dilution buffers are added to the use area. Spraydrift distances range from 23 (mangos) to over 1000 feet and the downstream dilution buffer is 285 km. Modification of terrestrial-phase PCE Habitat Mo dification 1

No studies are available for terrestrial plants.

For the terrestrial-phase CRLF, using av ian data as a surrogate, with the exception of mangos on a dietary basis for non-listed species, the acute dosebased, acute dietary-based and chronic dietary-based RQs for the terrestrialphase CRLF, exceed both the acute listed and non-listed species LOC and chronic LOC for all of the assessed uses. Probability of an individual effect on an acute basis at the lowest RQ level and percentage effect to the avian/terrestrial-phase amphi bian prey base are very high. Incident data indicate that birds are vulnerable. RQs for both small and large insects exceed acute LOC for non-listed species fo r all methidathion uses, even with only a single use. Percentage effect to terrestrial invertebrate prey base for all uses are very high. For mammals , the acute and chronic RQs exceed the non-listed species acute LOC and the chro nic LOC, respectively for all uses. The percentage effect to the mammalian prey base is very high for all uses. Significant overlap exists between use sites and CRLF habitat, particularly when the spraydrift buffers are app lied to the methidathion use area. Spraydrift distances range from 194 (mangos) to over 1000 feet.

1 Habitat Modification or No effect (NE)

Table 1.3 Methidathion Use-specif ic Direct Effect s Determinations 1 for the CRLF

Aquatic Habitat Terrestrial Habitat Use(s) Acute Chronic Acute Chronic All uses LAA LAA LAA LAA

1 NE = No effect; NLAA = May affect, but not likely to adversely affect; LAA = Li kely to adversely affect14Table 1.4 Methidathion Use-specificIndirect Effects Determinations1Based on Effects to PreyAquaticInvertebratesAquatic-phasefrogs and fishTerrestrial-phasefrogsSmall MammalsUse(s)AlgaeAcuteChronicTerrestrialInvertebrates(Acute)AcuteChronicAcuteChronicAcuteChronicAll usesNLAALAALAALAALAALAALAALAALAALAA1NE = No effect; NLAA = May affect, not likely toadversely affect; LAA = Likely to adversely affectBased on the conclusions of this assessment, a formal consultation with the U. S. Fish and Wildlife Service under Secti on 7 of the Endangered Species Act should be initiated.

When evaluating the significance of this ri sk assessment’s direct /indirect and adverse habitat m odification 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 ar ea. In fact, given the assumptions of drift and downstream transport (i.e., attenuation with distance), pes ticide exposure and associated risks to the species and its resour ces 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 re quire information and assessment techniques that are not currently avai lable. Examples of such information and methodology required for this type of an alysis would include the following:

• Enhanced infor mation on the density and distribution of CRLF life stages within specific recovery units and/or designated critical habitat within the action area. This information would allow for quantitative extrapolation of the present risk assessment’s pred ictions of individual effects to the proportion of the population extant with in geographical areas where those effects are predicted. Furthermore, such population information would allow for a more comprehensive eval uation of the significance of potential resource impairment to individuals of the species.

• Quantita tive information on prey base requirements for individual aquaticand terrestrial-phase frogs. Wh ile existing information provides a preliminary picture of the types of food sources util ized by the frog, it does not establish minimal requirements to sustain healthy individuals at varying life stages. Such informa tion could be used to establish biologically relevant thresholds of ef fects 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.

• Inform ation on population responses of prey base organisms to the pesticide. Currently, methodologies are limited to predicting exposures and likely levels of direct mortalit y, 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 ex tent to which prey resources may recover is not predictable. An e nhanced 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 descri bed above, a more complete prediction of effects to individual frogs and potential modificati on to critical habitat.

152. Problem Formulation

Problem formulation provides a strategic framework for the risk assessment. By identifying the im portant components of the problem, it focuses the assessment on the most relevant life history st ages, habitat components, chemical properties, exposure routes, and endpoints. The structure of th is risk assessment is based on guidance contained in U.S. EPA’s Guidance for Ecological Risk Assessment (U.S. EPA 1998), the Services’ Endangered Species C onsultation Handbook (USFWS/NMFS 1998) and is consistent with procedures and methodology outlined in the Overview Document (U.S. EPA 2004) and reviewed by the U.S. Fish and Wildlife Service and National Marine Fisheries Service (USFWS/NMFS 2004).

2.1 Purpose

The purpose of this endangered species assessme nt is to evaluate potential direct and indirect effects on individuals of the fede rally thr eatened California red-legged frog (Rana aurora draytonii ) (CRLF) arising from FIFRA regul atory actions regarding use of methidathion on various agri cultural and non-agri cultural uses. In addition, this assessment evaluates whether use on these crop s is expected to result in modification of the species’ designated critical habitat. This ecological risk assessment has been prepared consistent with a settlement agreement in the case Center for Biological Diversity (CBD) vs. EPA et al . (Case No. 02-1580-JSW(JL)) ente red in Federal District Court for the Northern District of California on October 20, 2006.

In this assessment, direct a nd ind irect effects to the CRLF and potential modification to its designated critical habitat are evaluated in accordance w ith the methods described in the Agency’s Overview Document (U.S. EP A 2004). Screening level methods include use of standard models such as PRZM-EXAM S, T-REX, and AgDRIFT, all of which are described at length in the Over view Document. Use of such information is consistent with the methodology described in the Over view Document (U.S . EPA 2004), which specifies that “the assessment process may, on a case-by-case basis, incorporate additional methods, models, and lines of eviden ce that EPA finds technically appropriate for risk management objectives” (Sec tion V, page 31 of U.S. EPA 2004).

In accordance with the Overview Document, provisions of the ESA, and the Serv ices’ Endangered Species Consultation Handbook, the assessment of effects associated with registrations of methidathion is based on an action area. The action area is the area directly or indirectly affect ed by the federal action, as indi cated by the exceedence of the Agency’s Levels of Concern (LOCs). It is acknowledged that the action area for a national-level FIFRA regulatory decision associated with a use of methidathion 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 ge ographic areas associated with locations of the CRLF and its designated critical habitat with in the state of California. As part of the “effects determination,” one of the following three conclusions will be reached regarding the potential use of methidathion in accordance with current labels:

16• “No effect”;

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

• “May affect and likely to adversely affect”.

Designated critical habitat identifies specific areas that have the phys ical and biological features, (kn own as primary constituent elem ents or PCEs) essential to the conservation of the listed species. The PCEs for CRLFs ar e aquatic and upland areas where suitable breeding and non-breeding aquatic habitat is located, interspe rsed with upland foraging and dispersal habitat.

If the results of initial scr eening-level assessm ent methods show no direct or indirect effects (no LOC exceedances) upon individual CRLFs or upon the PCEs of the species’ designated critical habitat, a “ no effect” determination is made for use of methidathion as it relates to this species and its designated crit ical habitat. If, howev er, potential direct or indirect effects to individual CRLFs are anticip ated or effects may impact the PCEs of the CRLF’s designated critical habita t, a preliminary “may affect ” determination is made for the FIFRA regulatory acti on regarding methidathion.

If a determination is made that use of meth idathion within th e action area(s) associated with the CRLF “may affect” this species or its designated critical habitat, additional information is considered to refine the poten tial for exposure and fo r effects to the CRLF and other taxonomic groups upon wh ich these species depend (e.g

., aquatic and terrestrial vertebrates and invertebrates, aquatic plan ts, riparian vegetation, etc.). Additional information, including spatial analysis (to de termine the geographical proximity of CRLF habitat and methidathion use sites) and fu rther evaluation of the potential impact of methidathion on the PCEs is also used to determine whether modification of designated critical habitat may occur. Based on the re fined information, the Agency uses the best available information to disti nguish 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 CRLF or 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 di rect and indirect effects to lis ted species provides the basis for an analys is of potential effects on the designated critical habitat. Because methidathion is expected to directly impact living organisms within the action area (defined in Section 2.7), critical habitat analysis fo r methidathion 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 bi ological 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 ma y modify critical habitat are th ose that alter the PCEs and appreciably diminish the value of the habitat. Evaluation of actions related to use of methidathion that may alter the PCEs of the CR LF’s critical habitat form the basis of the critical habitat impact analysis. Actions that may affect the CRLF’s designated critical habitat have been identified by the Services and are discus sed further in Section 2.6.

172.2 Scope

Methidathion is used as an insecticide on a variety of terre strial food and feed crops and terrestrial non-food crops. Based on usage data provided by the Bi ological and Econom ic Analysis Division (BEAD), on average, roughly 110,000 pounds of methidathion are applied annually to agricultural crops. Me thidathion usage is hi ghest on almonds and oranges, with annual average applications of 20,000 lbs. a.i. applie d. The crop with the highest average percent crop tr eated with methidathion is artichokes at 60% (10,000 lbs. a.i. applied).

The end result of the EPA pesticide registration process ( i.e. , the FIFRA regulatory action) is an approved product label. The la bel is a legal docum ent 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), accepta ble methods of application, approved use sites, and any rest rictions on how applications may be conducted. Thus, the use or potential use of methidathion in accord ance with the approved product labels for California is “the action” relevant to this ecol ogical risk assessment.

Although current registrations of methidathion allow for use nationwide, this ecological risk as sessment and effects determination addresses currently registered uses of methidathion in portions of th e action area that are reasonably assumed to be biologically relevant to the CRLF and its de signated critical habitat. Fu rther discussion of the action area for the CRLF and its critical ha bitat is provided in Section 2.7.

Methidathion degrades into one known degradate of concern, m ethidathion oxon. Although no toxicity data are available for me thidathion oxon, it is presumed to be of concern because toxicity data for oxon transformation products of si milar pesticides in the organophospate class suggest they will be of equal or greater toxicity than the parent. Methidathion oxon is the only degradate cons idered in this analysis. There are no toxicity data for the four major degradat es, but these compounds no longer contain the OP moiety and so are assumed to be of lower toxicity than the parent.

Methidathion has no registered products that contain multiple active ingredients.

2.3 Previous Assessments

2.3.1 Methidathion Interim Registra tion Elig ibility Decision, 2002

The Agency completed a screening-level eco logical risk assessm ent (USEPA, 1999) in support of the Interim Rere gistration Eligibility Deci sion (IRED) for methidathion (USEPA 2002). Completion of the or ganophosphate (OP) cumulative assessment (USEPA 2006b) resulted in fi nalization of the IRED as a Reregistration Eligibility Decision (RED) (USEPA 2006a), which is summarized below.

The Agency’s ecological risk assessment was based principally on methidathion’s use on cotton, citrus, stone fruits, nut crops, a nd artichokes. The assessm ent was based on data collected in the laboratory and in the field to characterize the fate and

18ecotoxicological effects of methidathion. Data sources used in this assessment included: 1) registrant subm issions in support of reregist ration, 2) publicly available literature on ecological effects, and 3) incide nt reports of adverse effects on aquatic and terrestrial organisms associated with the use of methidathion.

The RED concluded that methidathion poses a ri s k to ecosystems in use areas. The levels of concern were exceeded for both acute and ch ronic effects to mammals, birds, fish, and aquatic invertebrates. In addition, risk to terrestrial invertebra tes was presumed. The presumption of risk to non-target aquatic and terrestrial animals was supported by field studies and adverse ecological in cidents. The potential risk to terrestrial plants was not assessed due to a lack of toxi city data. Toxicity data available for degradates of methidathion, including methidathion oxon, were not available for consideration in this
assessment.

To address the presumed risk to birds, th e Agency required the additional dilution of

m ethidathion products (a minimum of 500 gallo ns of water per acre) in an attempt to reduce the amount of methidathion on food ite ms. In addition, precautionary statements regarding the risk to birds were required to be added to the label in order to protect avian species.

To address the presumed risk to fish a nd aquatic invertebrates, the following risk

m itigation strategies were required:

For all applications applied at rates greater than 3.0s a.i./A:

o Do not apply within 50 feet of lakes, reservo irs, rivers, permanent streams, natural ponds, marshes or estuaries

- For all applications applied at rates of 3.0s a.i./A or less:

o Do not apply within 25 feet of lakes, reservo irs, rivers, permanent streams, natural ponds, marshes or estuaries

- For ground applications:

o Shut off sprayer when turning at end rows

o Do not apply when gusts or sustained winds exceed 12 m ph

- For air b last application:

o Adjust deflectors and aim ing devices so that spray is only directed into the
canopy

o Block off upward pointed nozzles w hen there is no overhanging canopy

o Use only enough air volum e to pene trate the canopy and provide good
coverage

o Do not allow spray to go beyond the edge of the cultivated area. Spray the outside row only from outside the planting

- For aerial ap plication:

o Do not apply within 150 feet of water

o Do not apply when gusts or sustained winds exceed 8 mph

In addition, to mitigate the risk to aquatic anim als, a label amendment was required to include a surface water advisory statement.

19The Agency was also concerned about the risk to beneficial insects from the use of methidathion. To reduce the likelihood for significant mortality to bees, precautionary labeling was required.

2.3.2. Organophosphate Cumulative Assessment, and Methidathion Reregistration Eligibility Decision, 2006

Because the Agency determined that meth idathio n shares a common mechanism of toxicity with the structura lly-related organophosphate insecticides, a cumulative human health risk assessment for the organophosphate (OP) pesticides was necessary before the Agency could make a final determination of reregistration eligibility of methidathion. This cumulative assessment was finalized in 2006 (USEPA 2006b). The results of the Agency’s ecological assessments for methid athion are discussed in the July 31, 2006, final Reregistration Eligibility Decision (RED) (USEPA 2006a).

The OP cumulative relied on a combined assessm ent metho dology of modeling and monitoring data for human heal th exposure via drinking water. Unlike other assessments, the cumulative approach focused on regions of high OP use. No ecological risks were evaluated in the OP cumulative process, but its analysis of methidathion fate properties and its modeling approach remain relevant to this assessment. Additionally, the Agency requested toxicity data on methidat hion oxon to further refine estimates.

2.3.3 Assessment of Potential Effects to 26 Evolutionarily Significant Units of Pacific Salmon and Steelhead

In April 2004, an assessment of methidathion us es in the Pacific northwest and California was conducted to determine potential effects to 26 evolutionarily si gnificant units (ES Us) of Pacific salmon and steelhead. Based on toxi city and fate data, the usage information, habitat information and other factors, that assessment determined that uses of methidathion would have no effect on 7 ESUs, was not likely to adversely affect 9 ESUs and may affect the remaining 10 ESUs.

2.4 Stressor Source and Distribution

2.4.1 Environmental Fate and Transport

2.4.1.1. Physical and Chemical Properties

Chemical name: 3-Dimethoxyphosphinothioylthiomethyl-5-methoxy-1,3,4- thiadiazol-2(3H)-one

.

Chemical structure:

20Molecular formula: C 6 H 11 N 2 O 4 PS 3
. Molecular weight: 302.3 g/mol Physical state: Colorless crystals. Melting point: 39-40 ° C. Solubility (20 ° C): 250 mg/L water; Vapor pressure (20 ° C): 2.48 x 10 -6 mm Hg Henry's Law Constant: 3.97 x 10 -9 atm m 3 /mol Octanol/Water Partition 295 at pH 6.1 Coefficient:

2.4.1.2. Environmental Fate Properties

Methidathion is classified as moderate ly m obile, and through most routes of transformation for which data are available, initial degradation is rapid and occurs with half-lives of less than two weeks, although in some cases, transformation slows and lower levels can persist for a longer time. Table 2.1 summarizes the environmental fate properties of methidathion, along with the ma jor and minor degradates detected in the submitted environmental fate and transport studies. See Appendix A for a bibliography of these submitted studies.

21Table 2.1. Summary of Methidathion Environmental Fate Properties

Study Value (units) Major Degradates a Minor Degradates MRID # Study Status

Hydrolysis half life pH 5: 37, 27d pH 7: 48, 25d pH 9: 13, 8d GS-12956 Des-methyl GS-13007 42037701
44554501 Acceptable Acceptable

Direct Aqueous Photolysis 10.0 d b GS-12956 42081709 Supplemental

Soil Photolysis 40 d c GS-12956 Methidathion oxon (4 .9%) GS-28307 42081710 Supplemental

Air Photolysis No data -- 42215101 Unacceptable

Aerobic Soil Metabolism 11.3 d (sandy loam) 8.5 d (sandy loam) d Unidentified e Methidathion oxon (0.2%) GS-12956, GS-28369 GS-28370, GS-20865 44545101
42262501 Acceptable Supplemental

Anaerobic Soil Metabolism DT90 < 30 d (System) GS-28369, GS-12956, Two unidentified 42262501 Supplemental

Anaerobic Aquatic Metabolism No data -- No study

su bmitted
Aerobic Aquatic Metabolism No data -- No study

su bmitted
Mobility K d : 2.5 to 14.8 mL/g Avg = 6.5 mL/g K oc : 194 to 589 mL/g oc Avg = 364 mL/g oc n/a 00158529 Acceptable

Laboratory Volatility No da ta -- 42098801 Unacceptable

Terrestrial Field Dissipation CA: 5-30 d (4 plots) NE: <15 d (1 plot) GS-12956 methidathion oxon 40094103 41924401 41924402 Supplemental Supplemental Supplemental

a Major degradates are those formed at >10% of the applied. Although a minor degradate, methid athion oxon is of toxicological concern and so the maximum percentage det ected is reported here. Other oxon degradates that may be of toxicological concern ma y not have been detected because available studies did not include radiolabeling on the phosphate ester side chain of the parent compound. b The RED reported half-life of 11.6 days was not corrected for sunlight or for results from the dark control.

c Problems with the study suggest that the measured half-life of 40 days is not representative of actual behavior. An assessment by the CDPR reports a soil photolysis half-life of 1.5 days. d Previous assessments reported this value as 3 days. That is in fact the DT50 and so this wa s updated to represent the linear first order half-life.

e The degradate was unidentified but was tentatively characterized as a cyclic structure resulting from the reaction of carbazic acid and cysteine.

Both aerobic and anaerobic soil metabolism s how initially rapid degradation. In two aerobic soil m etabolism studies, DT50s were 3 to 7 days and linear first order half-lives were less than 2 weeks, although one study sh owed some slowing over time, indicating that methidathion may persist at lower leve ls for several months . One anaerobic study

22was conducted but sampling was insufficient to determine a half-life. At the time of flooding, methidathion represented 41% of the initially applied radioactivity and by the first sampling point at 30 days post-flooding, it had been reduced to 6%. However, by 30 days later metabolism had not progressed, with 5% of the initially applied radioactivity remaining as methidathion. On the soil su rface, photodegradation of methidathion may occur, but there is some uncertainty regardi ng the rate. In the submitted laboratory study, photolysis was slow with a half-life of 40.6 days, but problems in the study suggest this may underestimate the actual rate. An a ssessment by the California Department of Pesticide Regulation (CDPR) reports a much more rapid soil photolysis half-life of 1.5 days (Washburne, 2003).

Methidathion may reach water bodies through spray drift or runoff, in the dissolved phase or adsorbed to eroding soil. In water, m e thidathion is only moderately susceptible to abiotic hydrolysis in acidic and neutral condit ions with half-lives in two studies ranging from 25 to 48 days. Dissipation rates increase in alkaline conditions with half-lives of 8 to 13 days at pH 9. In clear, shallow wate r, transformation may be more rapid due to photodegradation. A laboratory aquatic photo lysis study measured a half life of 10.0 d, corrected for the dark control and natural sunlight. There are no data available for metabolism rates in aquatic environments.

In supplemental terrestrial field dissipati on studies on four plots in California,

m ethidathion had reported DT50s in the top 6 in ches of 5 to 30 days, and in one plot in Nebraska, the DT50 was <15 days. Methidathi on was not detected at depths below 18 inches in the field studies. There were se veral detections of methidathion in samples collected from the 12-18 inch cores, but thes e detections occurred in samples collected before any irrigation or rainfall event occurr ed and so appear to have been due to contamination during sample collection.

Dissipation of dislodgeable resi dues on foliar surfaces was found to occur with half-lives of ≤ 3 days based on the results of six studi es, and two studies f ound half-lives for dissipation of total residues in foliage to be 3.5 and 5 days. Additionally, methidathion is not expected to bioaccumulate.

2.4.1.3. Transformation Products

Soil metabolism of methidathion leads primar ily to carbon dioxide and bound residues. Other m ajor degradates include GS-12956, formed through hydrolysis and through aquatic and soil photolysis (maxima from 18% to 66% of the applie d radioactivity); desmethyl GS-13007 and PAMMTO, formed through hydrolysis at up to 21% and 18%, respectively; and an unidentified compound formed through aerobic soil metabolism and tentatively characterized as a cyclic structur e resulting from the reaction of carbazic acid and cysteine. This compound appears to be pers istent, as it reaches its maximum level of 13% of the applied radioactiv ity on day 11 but remained at 10% by the end of the study (day 263). Multiple minor degradates were formed, not all of them identified. See Appendix B for chemical names and structures of a ll identified degradates. None of the

23major degradates contain the OP moiety and so they are likely to be less toxic than the parent.

The only detected degradate of toxicologica l concern is m inor degradate methidathion oxon. Many of the OP pesticides can under go oxidative desulfonation (cleavage of P=S bond to form P=O bond) to form oxons, e ither through photo-oxidation or chemical oxidation in the presence of oxidizing agents, and oxons have the potential to be considerably more toxic than the parent compounds. In submitted laboratory studies, methidathion oxon has been documented to form via chlorination, soil photolysis (up to 4.9% of the applied), and aerobic soil metabo lism (0.2%), and the oxon was also detected in studies of terrestrial field dissipation and of dislodgeable fo liar residues. The results of the soil photolysis study may underestimate oxon formation, because the maximum level was measured in the final sampling period a nd so oxon levels may continue to increase, and also because the study review concluded that due to a study defi ciency, the rate of transformation observed may have been too low, supported by the more rapid transformation cited by CDPR (Washburn, 2003) . In the dislodgeable residue study, methidathion was detected in citrus at up to 15 ng/cm 2 on leaves, with detectable residues through 7 days after application (MRID 00131096) . No data are available regarding photo-oxidation in air of volatili zed methidathion to its oxon forms, which could be an important route of transformation, as demonstr ated by air monitoring data that find both methidathion and methidathion oxon at more that 20 km away from any use location. There are no data to characteri ze the fate of methidathion oxon.

It should be noted that due to an issue in the laboratory study design, there could be additional degradates of toxicological conc ern that were not observed. In laboratory transform ation studies, only the thiadiazo le ring of the compound had radioactive labeling and so degradates containing the phos phate ester portion of the parent compound may not have been observed. In particular , major degradate GS-12956 is formed through cleavage of the C-N bond. Therefore, GS-12956 does not contain the OP moiety but the cleavage would result in a corresponding phos phate ester (phophorod ithioic acid, o-o-strimethyl ester) which retains the OP moiety a nd so can be assumed to be toxic. Given that GS-12956 is formed in amounts up to 66% of the applied radi oactivity, it is likely that the corresponding phosphate ester is formed as well. Additionally, this phosphate ester degradate could also undergo oxidative desulfonation to lead to additional oxon transformation products that would not have b een detected in laboratory studies and may be of toxicological concern as well.

2.3.1.4. Environmental Transport Properties

The K oc model appears to be appropriate to de scribe methidathion adsorption. Based on measured K oc values of 113 to 342 mL/g oc , methidathion is classified as moderately mobile according to the FAO classification scheme.

A number of studies have documented at m ospheric transport and re-deposition of pesticides from the Central Valley to the Sierra Nevada Mountains (Fellers et al., 2004, Sparling et al., 2001, LeNoir et al., 1999, a nd McConnell et al., 1998). Prevailing winds

24blow across the Central Valley eastward to the Sierra Nevada M ountains, transporting airborne industrial and agricultural pollutants into the Sierra Nevada ecosystems (Fellers et al., 2004, LeNoir et al., 1999, and McConnell et al., 1998). Several se ctions of critical habitat for the CLRF are located east of the Central Valley. The magnitude of transport via secondary drift depends on methidathion’s ability to be mobilized into air and its eventual removal through wet and dry depos ition of gases/particles and photochemical reactions in the atmosphere. The va por pressure of me thidathion (2.48 x 10 -6 mm Hg) and its Henry’s Law constant (3.97 x 10 -9 atm m 3 /mol) would suggest that it has a low potential to volatize fr om dry or moist soils or from water, but monitoring studies have detected methidathion and its oxon in air at di stances intermediate and up to 20 km away from any use sites (Royce et al, 1993; Ast on and Seiber, 1997; Majewski, 2006). Given the potential toxicity of these residues, this route of transport could be significant for assessing the extent of ecological effects.

2.4.2 Mechanism of Action

Methidathion is an insecticide belonging to the organophosphate class of pesticides. The pesticide acts through inhibition of acetylcholines terase and is used to kill a broad range of insects and mites. Organophosphate toxicity is based on the inhibition of the enzyme acetylcholinesterase which cleaves the neurotransmitter acetylcholine. Inhibition of acetylcholinesterase by organophosphate insectic ides, such as methidathion, interferes with proper neurotransmission in cholinergi c synapses and neuromuscular junctions (USEPA 2000).

Target pests include the peach twig bore r, scale insects, artichoke plum e moth, leafminers, spider mites, boll weevils, bo llworms, lygus bug, whitefly, aphid, pear psylla, mealybugs, thrips, sunflower stern weevil, sunflower moth, sunflower seed weevil, sunflower midge, Banks grass mite, flea be etle, hornworm, tobacco budworm, codling moth and hickory shuckworm.

2.4.3 Use Characterization

2.4.3.1 Use Statistics

Methidathion is used as an insecticide on a variety of terre strial food and feed crops and terrestrial non-food cr ops. As shown in Figure 2.1 , U.S. Geological Survey (USGS) National Water Quality Assessment Program (NAWQA) data indicate that in 2002, methidathion was used on agricultural crops predominantly in Calif ornia, Washington, southern Texas, Pennsylvania, and New Jersey. At that time, the use of methidathion on citrus fruit represented about 30% of the national use. Based on national usage data compiled by the Biological and Economic Analysis Division (BEAD) primarily from 2001 to 2006, on average, roughly 110,000 pounds of methidathion are applied annually to agricultural crops, 95% of it in California. These data show that usage is highest on almonds and oranges, with annual average ap plications to each of 20,000 lbs. a.i. The crop with the highest average percent crop treated with methidathion is artichokes (60%).

25Figure 2.1. Map of Estimated Annual Agri cultural Use of Methidathion in 2002

. Source: http://water.usgs.go v/nawqa/pns p/usage/maps/sh ow_map.php?year=02&map=m6037

Use data specific to California are available from the California Department of Pesticide Regulation ’s (CDPR) Pesticide Use Reporti ng (PUR) database, which includes every pesticide application made by professional applicators. The Biological and Economic Analysis Division (BEAD) summarized thes e data, from 1999 to 2006, to the county level by site, pesticide, and unit treated. Ba sed on this analysis, an average of 82,031 lbs of methidathion was applied in California to an average of 52,823 acres per year. Use was at a maximum of 177,105 lbs in 1999 and then dropped by nearly half the following year, to 98,129 lbs, and remained relativel y stable between 2003 and 2006 with average applications ranging from around 50,000 lb /year to 60,000 lb/year. From 1999-2006, methidathion was used in a total of 34 counties involving 41 different uses. Four counties accounted for 70% of the total lbs applied on aver age per county [Kern (25%), Tulare (20%), Monterey (14%), Fresno (11%)] (see Figure 2.2 ). Fruit orchards, including apple, apricot, cherry, nectarine, peach, pear, plum, and prune, accounted for approximately 30% of the total lbs applied per year in CA on average. Other major crops include almonds (23%), oranges (17%), and ar tichokes (14%). This analysis may not be entirely representative of cu rrent use patterns because labeled uses may have changed since these data were collected, and because it may also include misreporting. Complete data from the BEAD analysis of the CDPR PUR database are presented in Appendix C

.

26Figure 2.2 Average Pounds of Methidath ion Applied Per County from 1996 - 2005

272.4.3.2 Application Rates and Methods

Analysis of labeled use information is the cr itica l first step in evaluating the federal action. The current label for methidathion represents the FIFRA regulatory action; therefore, labeled use and app lication rates specified on the label form the basis of this assessment. The assessment of use information is critical to the deve lopment of the action area and selection of appropriate modeling scenarios and inputs. Table 2.2 presents the uses and corresponding application rates cons idered in this assessment, based on a verification memorandum from SRRD (Dirk Helder, September 2, 2008).

Methidathion is formulated as a wettable powder in water-soluble bags (25% active ingred ient) or as an emulsifiable concentrate (22% - 24% active ingredient). Application rates range from 0.25 to 5.0 lbs ac tive ingredient/acre. Appli cation is via foliar treatment and application equipment includes fixed wi ng aircraft, ground boo m, air blast, lowpressure handwand or backpack sprayer, al though based on applica tion instructions for citrus, olives, and nursery stock, these us es are assumed to be applied through ground methods only. Labels have additional requiremen ts in order to reduce spray drift. These include the buffers and other mitigation ac tions listed in Section 2.3.1 as well as a requirement for a spray with medium to coar se droplet size applied at a maximum boom height of 4 ft about the ground or canopy for ground spray and of 10 ft for aerial spray.

Table 2.2 Methidathion Uses Assessed for the CRLF

Use Max. Single Appl. Rate (lb ai/A) Max. Number of Applications Number of Crop Cycles Per Year Minimum Application Interval (Days)

NON-FOOD/NON-FEED USES alfalfa 1 NS 2-9 a NS nursery stock b (includes ornamental herbaceous plants and ornamental woody shrubs and vines) 10 c 1/cc d 1 e NA

FOOD/FEED USES alfalfa 1 1/cc 2-9 a NA almond 3 1/cc 1 e EC: 14 WP: NS apple 3 1/cc 1 a NA apricot 3 1/cc 1 e NA artichoke 1 8/cc 1 e 14 calamondin b 4 1/cc 1 e NA cherry 3 1/cc 1 e NA citron (citrus) b 4 1/cc 1 e NA citrus b 5 2/cc 1 e 45 citrus hybrids other than tangelo 4 1/cc 1 e NA

clover 1 2/cc NS cotton (unspecified) 1 4/cc 1 a 5

28Table 2.2 Methidathion Uses Assessed for the CRLF

Use Max. Single Appl. Rate (lb ai/A) Max. Number of Applications Number of Minimum Application Interval (Days) Crop Cycles Per Year grapefruit 5 2/cc 1 a 45 kiwi fruit 2 1/1 yr NA NA kumquat b 4 1/cc 1 e NA lemon b 5 2/cc 1 a 45 lime b 4 1/cc 1 e NA
mango b 0.25 5/cc 1 e 21 nectarine 3 1/cc 1 a NA olive b 3 1/cc 1 e NA
orange 5 2/cc 1 a 45 peach 3 1/cc 1 a NA
pear 3 1/cc 1 a NA plum 3 1/cc 1 e NA
prune 3 1/cc 1 e NA pummelo (shaddock) 4 1/cc 1 e NA safflower (unspecified) 0.5 3/1 yr NA 7 sunflower 0.5 3/cc 1 e 7 tangelo b 4 1/cc 1 a NA tangerines b 4 1/cc 1 a NA timothy 1 NS 1 e NA walnut (english/black) EC: 2 WP: 2 EC: 2/cc WP: 3/cc 1 e EC: 2 WP: 2 NA = Not Applicable NS = Not Specified on the label

a U.S. EPA. 2007. Memo from Monisha Kaul (BEAD) to Melissa Panger (EFED). Subject: Maximum Number of Crop Cycles Per Year in California for Methomyl Use Sites. Dated February 28. b Ground spray only

c The nursery stock application rate is re ported on labels as 0.5 lb a.i./100 gal spra y with no instructions for application on areal basis. Therefore, this rate is based on the general labels statement th at methidathion should not be applied at greater than 10 lb a.i ./A. d cc = crop cycle

e Number of crop cycles per year as assumed by EFED.

2.5 Assessed Species

The CRLF was federally listed as a threaten ed species by U SFWS effective June 24, 1996 (USFWS 1996). It is one of two subspecies of the red-legged frog and is the largest native frog in the western United States (U SFWS 2002). A brief summary of information regarding CRLF distribution, repr oduction, diet, and habitat re quirements is provided in Sections 2.5.1 through 2.5.4, respectively. Furt her information on the status, distribution, and life history of and specific threats to the CRLF is provided in Attachment 1.

Final critical habitat for the CRLF wa s designated by USFWS on April 13, 2006 (USFWS 2006; 71 FR 19244-19346). Further information on designated critical habitat for the CRLF is provided in Section 2.6.

2.5.1 Distribution

29The CRLF is endemic to California and Baja California (Mexico) and historically inhabited 46 counties in Ca lifornia including the Central Valley and both coastal and interior mountain ranges (USF WS 1996). Its range has b een reduced by about 70%, and the species currently resides in 22 counties in California (USFWS 1996). The species has an elevational range of near sea level to 1,500 meters ( 5,200 feet) (Jennings and Hayes 1994); however, nearly all of the known CRLF populations have been documented below 1,050 meters (3,500 feet) (USFWS 2002).

Populations currently exist along the northern California coast, northern T ransverse Ranges (USFWS 2002), foothills of the Sierra Ne vada (5-6 populations), and in southern California south of Santa Barbara (two populat ions) (Fellers 2005a). Relatively larger numbers of CRLFs are located between Mari n and Santa Barbara Counties (Jennings and Hayes 1994). A total of 243 streams or draina ges are believed to be currently occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and Santa Barbara counties (USFWS 1996). Occupied drai nages or watersheds include all bodies of water that support CRLFs (i.e., streams, cr eeks, tributaries, associated natural and artificial ponds, and adjacent drainages), and habitats through which CRLFs can move (i.e., riparian vegetation, uplands) (USFWS 2002).

The distribution of CRLFs with in California is addressed in this assessm ent using four categories of location including r ecovery units, core areas, desi gnated critical habitat, and known occurrences of the CRLF reported in the California Natural Diversity Database (CNDDB) that are not included within core ar eas and/or designated critical habitat (see Figure 2.2 ). Recovery units, core areas, and other known occurrences of the CRLF from the CNDDB are described in further detail in this section, and designa ted critical habitat is addressed in Section 2.6. Recovery units are large areas defined at the watershed level that have similar conservation needs and mana gement strategies. The recovery unit is primarily an administrative designation, and land area within the recovery unit boundary is not exclusively CRLF habitat. Core areas are smaller areas within the recovery units that comprise portions of the species’ hi storic and current range and have been determined by USFWS to be important in th e preservation of the species. Designated critical habitat is generally contained within the core ar eas, although a number of critical habitat units are outside the boundaries of core areas, but within the bound aries of the recovery units. Additional information on CRLF occurrences from the CNDDB is used to cover the current range of the species not included in core areas and/or designated critical habitat, but within the recovery units.

Other Known Occurrences from the CNDBB

The CNDDB provides location and natural history inform ation on species found in California. The CNDDB serves as a repositor y for historical and current species location sightings. Information regarding known occurrences of CRLFs outside of the currently occupied core areas and designated critical ha bitat is considered in defining the current range of the CRLF. See: http://www.dfg.ca.gov/bdb/html/cnddb_info.html for additional information on the CNDDB.

30Recovery Units 1. Sierra Nevada Foothills and Central Valley 2. North Coast Range Foothills and Western Sacramento River Valley 3. North Coast and North San Francisco Bay 4. South and East San Francisco Bay 5. Central Coast 6. Diablo Range and Salinas Valley 7. Northern Transverse Ranges and Tehachapi Mountains 8. Southern Transverse and Peninsular Ranges

Core Areas

1. Feather River 2. Yuba River- S. Fork Feather River 3. Traverse Creek/ Middle Fork/ American R. Rubicon 4. Cosumnes River 5. South Fork Calaveras River* 6. Tuolumne River* 7. Piney Creek* 8. Cottonwood Creek 9. Putah Creek – Cache Creek* 10. Lake Berryessa Tributaries 11. Upper Sonoma Creek 12. Petaluma Creek – Sonoma Creek 13. Pt. Reyes Peninsula 14. Belvedere Lagoon 15. Jameson Canyon – Lower Napa River 16. East San Francisco Bay 17. Santa Clara Valley 18. South San Francisco Bay 19. Watsonville Slough-Elkhorn Slough 20. Carmel River – Santa Lucia 21. Gablan Range 22. Estero Bay 23. Arroyo Grange River 24. Santa Maria River – Santa Ynez River 25. Sisquoc River 26. Ventura River – Santa Clara River 27. Santa Monica Bay – Venura Coastal Streams 28. Estrella River 29. San Gabriel Mountain* 30. Forks of the Mojave* 31. Santa Ana Mountain* 32. Santa Rosa Plateau 33. San Luis Ray* 34. Sweetwater* 35. Laguna Mountain*

* Core areas that were historically occupied by the California red-legged frog are not included in the map Recovery Units 1. Sierra Nevada Foothills and Central Valley 2. North Coast Range Foothills and Western Sacramento River Valley 3. North Coast and North San Francisco Bay 4. South and East San Francisco Bay 5. Central Coast 6. Diablo Range and Salinas Valley 7. Northern Transverse Ranges and Tehachapi Mountains 8. Southern Transverse and Peninsular Ranges

Core Areas

1. Feather River 2. Yuba River- S. Fork Feather River 3. Traverse Creek/ Middle Fork/ American R. Rubicon 4. Cosumnes River 5. South Fork Calaveras River* 6. Tuolumne River* 7. Piney Creek* 8. Cottonwood Creek 9. Putah Creek – Cache Creek* 10. Lake Berryessa Tributaries 11. Upper Sonoma Creek 12. Petaluma Creek – Sonoma Creek 13. Pt. Reyes Peninsula 14. Belvedere Lagoon 15. Jameson Canyon – Lower Napa River 16. East San Francisco Bay 17. Santa Clara Valley 18. South San Francisco Bay 19. Watsonville Slough-Elkhorn Slough 20. Carmel River – Santa Lucia 21. Gablan Range 22. Estero Bay 23. Arroyo Grange River 24. Santa Maria River – Santa Ynez River 25. Sisquoc River 26. Ventura River – Santa Clara River 27. Santa Monica Bay – Venura Coastal Streams 28. Estrella River 29. San Gabriel Mountain* 30. Forks of the Mojave* 31. Santa Ana Mountain* 32. Santa Rosa Plateau 33. San Luis Ray* 34. Sweetwater* 35. Laguna Mountain*

* Core areas that were historically occupied by the California red-legged frog are not included in the map Figure 2.2 Recovery Unit, Core Area, Critical Habitat, and Occurrence Designation s for CRLF

312.5.2 Reproduction

CRLFs breed primarily in ponds; however, they m ay also breed in quiescent streams, marshes, and lagoons (Fellers 2005a). Accord ing to the Recovery Plan (USFWS 2002), CRLFs breed from November through late April. Peaks in spawning activity vary geographically; Fellers (2005b) re ports peak spawning as early as January in parts of coastal central California. Eggs are fertili zed as they are being laid. Egg masses are typically attached to emergent vegetation, such as bulrushes ( Scirpus spp.) and cattails ( Typha spp.) or roots and twigs, and float on or near the surface of the water (Hayes and Miyamoto 1984). Egg masses contain approx imately 2000 to 6000 eggs ranging in size between 2 and 2.8 mm (Jennings and Hayes 1994). Embryos hatch 10 to 14 days after fertilization (Fellers 2005a) depending on water temperature. Egg predation is reported to be infrequent and most mortality is associated with the larval stage (particularly through predation by fish); however, predation on eggs by newts has also been reported (Rathburn 1998). Tadpoles re quire 11 to 28 weeks to me tamorphose into juveniles (terrestrial-phase), typica lly between May and Septem ber (Jennings and Hayes 1994, USFWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until the following year) (Fellers 2005b, USFWS 200 2). Males reach sexual maturity at 2 years, and females reach sexual maturity at 3 years of age; adults have been reported to live 8 to 10 years (USFWS 2002). Figure 2.3 depicts CRLF annual reproductive timing.

Figure 2.3 – CRLF Reproductive Events by Month

J F M A M J J A S O N D

Light Blue = Breeding/Egg Masses Green = T adpoles (except those that over-winter) Orange = Yo ung Juveniles Adults and juveniles can be present all year

2.5.3 Diet

Although the diet of CRLF aquatic-phase la rvae (tadpoles) has not been studied specif ically, it is assumed that their diet is si milar to that of other frog species, with the aquatic phase feeding exclusiv ely in water and consuming diatoms, algae, and detritus (USFWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar, 1980) via mouthparts designed for effectiv e grazing of periphyton (Wassersug, 1984, Kupferberg et al. ; 1994; Kupferberg, 1997; A ltig and McDiarmid, 1999).

Juvenile and adult CRLFs forage in aquatic a nd terrestrial habitats, and their diet differs greatly from that of larvae. The m ain food source for juvenile aquatic- and terrestrialphase CRLFs is thought to be aquatic a nd terrestrial invert ebrates found along the shoreline and on the water surface. Hayes a nd Tennant (1985) report, based on a study examining the gut content of 35 juvenile a nd adult CRLFs, that the species feeds on as many as 42 different invertebrate taxa , including Arachnida, Amphipoda, Isopoda,

32Insecta, and Mollusca. The most commonly obs erved prey species were larval alderflies ( Sialis cf. californica ), pillbugs ( Armadilliadrium vulgare ), and water striders ( Gerris sp). The preferred prey species, however, was the sowbug (Hayes and Tennant, 1985). This study suggests that CRLFs forage primarily above water, although the authors note other data reporting that adults also feed under water, are cannibalistic, and consume fish. For larger CRLFs, over 50% of the prey mass may c onsists of vertebrates such as mice, frogs, and fish, although aquatic and terrestrial inve rtebrates were the most numerous food items (Hayes and Tennant 1985). For adults, feeding activity takes place primarily at night; for juveniles feeding o ccurs during the day and at ni ght (Hayes and Tennant 1985).

2.5.4 Habitat

CRLFs require aquatic habitat for breeding, but also use other habitat types including riparian and upland areas throughout their lif e cycle. CRLF use of their environm ent varies; they may complete their entire life cycl e in a particular habitat or they may utilize multiple habitat types. Overall, populations are most likely to exist where multiple breeding areas are embedded within varying ha bitats used for dispersal (USFWS 2002). Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al. 1997). Dense vegetation close to water, shadin g, and water of modera te depth are habitat features that appear especially impor tant for CRLF (Hayes and Jennings 1988). Breeding sites include streams, deep pools, b ackwaters within stream s and creeks, ponds, marshes, sag ponds (land depressions between fault zones that have filled with water), dune ponds, and lagoons. Breeding adults have be en found near deep (0.7 m) still or slow moving water surrounded by dense vegetati on (USFWS 2002); however, the largest number of tadpoles have been found in sha llower pools (0.26 – 0.5 m) (Reis, 1999). Data indicate that CRLFs do not fre quently inhabit vernal pools, as conditions in these habitats generally are not suitable (Hayes and Jennings 1988).

CRLFs also frequently breed in artificial im poundments such as stock ponds, although additional research is needed to identify habitat requirements within artificial ponds (USFWS 2002). Adult CRLFs use dense, sh rubby, or emergent vegetation closely associated with deep-water pools bordered w ith cattails and dense stands of overhanging vegetation ( http://www.fws.gov/endangered/f eatures/rl_frog/rlfrog.html#where ).

In general, dispersal and habitat use depends on clim atic conditions, habitat suitability, and life stage. Adults rely on riparian vegetation for resti ng, feeding, and dispersal. The foraging quality of the riparian habitat depends on moisture, composition of the plant community, and presence of pools and backwa ter aquatic areas for breeding. CRLFs can be found living within streams at distances up to 3 km (2 miles) from their breeding site and have been found up to 30 m (100 feet) from water in dense riparian vegetation for up to 77 days (USFWS 2002).

During dry periods, the CRLF is rarely found far from water, although it will sometimes disperse from its breeding hab itat to forage and seek othe r suitable habitat under downed trees or logs, industrial debr is, and agricultural features (UWFWS 2002). According to Jennings and Hayes (1994), CRLFs also use sm all mammal burrows and moist leaf litter

33as habitat. In addition, CRLFs may also use larg e cracks in the bottom of dried ponds as refugia; these cracks may provide moisture for individuals avoidi ng predation and solar exposure (Alvarez 2000).

2.6 Designated Critical Habitat

In a final rule published on April 13, 2006, 34 se parate units of critical habitat were designated for the CRLF by USFWS (USF W S 2006; FR 51 19244-19346). A summary of the 34 critical habitat units relative to USFWS-designated recovery units and core areas (previously discussed in Section 2.5.1) is provided in Attachment 1

.

‘Critical habitat’ is defined in the ESA as th e geo graphic area occupi ed by the species at the time of the listing where the physical and biological features necessary for the conservation of the species exis t, and there is a need for special management to protect the listed species. It may also include ar eas outside the occupied area at the time of listing if such areas are ‘essential to the c onservation of the species.’ All designated critical habitat for the CRLF was occupied at the time of listing. Cr itical habitat receives protection under Section 7 of the ESA th rough prohibition against destruction or modification with regard to actions carried out, funded, or authorized by a federal Agency. Section 7 requires consultation on fede ral actions that are likely to result in the destruction or modificati on of critical habitat.

To be included in a critical habitat desi gnation, the habitat m ust be ‘essential to the conservation of the species.’ Critical hab itat designations identify, to the extent known using the best scientific a nd commercial data available, habitat areas that provide essential life cycle needs of the species or areas that contai n 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 a nd for normal behavior; food, water, air, light, minerals, or other nutritional or physiolo gical requirements; cove r or shelter; sites for breeding, reproduction, rearing (or developmen t) of offspring; a nd habitats that are protected from disturbance or are represen tative of the histor ic geographical and ecological distributions of a species. The de signated critical habitat areas for the CRLF are considered to have the following PCEs that justify critical habitat designation:

• Breeding aquatic habitat;

• Non-breeding aquatic habitat;

• Upland habitat; and

• Dispersa l habitat.

Further description of these ha bitat types is provided in Attac hment 1

. Occupied habitat may be include d in the cr itical habitat only if essential features within the habitat may require special management or protection. Theref ore, USFWS does not include areas where existing management is su fficient to conserve the species. Critical habitat is designated outside the geographic area presently occupied by the species only when a designation limited to its present ra nge would be inadequa te to ensure the

34conservation of the species. For the CRLF, all designated critical habi tat units contain all four of the PCEs, and were occupied by th e CRLF at the time of FR listing notice in April 2006. The FR notice designating critic al habitat for the CRLF includes a special rule exempting routine ranchi ng activities associated with livestock ranching from incidental take prohibitions. The purpose of this exemption is to promote the conservation of rangelands, which could be bene ficial to the CRLF, and to reduce the rate of conversion to other land uses that are incompatible with CRLF conservation. Please see Attachment 1 for a full explanation on this special rule.

USFWS has established modification standard s for designated critical habitat (USFW S 2006). Activities that may destroy or modify critical habitat are those that alter the PCEs and jeopardize the continued existence of the species. Eval uation of actions related to use of methidathion that may a lter the PCEs of the CRLF’s critical habitat form the basis of the critical habitat impact analysis. According to USFWS (2006) , activities that may affect critical habitat and therefore result in adverse effects to the CRLF include, but are not limited to the following:

(1) Significant alteration of water chem istr y or temperature to levels beyond the tolerances of the CRLF that result in di rect or cumulative adverse effects to individuals and their life-cycles. (2) Altera tion of chemical characteristics n ecessary for normal growth and viability of juvenile and adult CRLFs. (3) Significant increase in sedim ent deposition within the stream channel or pond or disturbance of upland fora ging and dispersal habitat that could result in elimination or reduction of habitat necessary for the growth and reproduction of the CRLF by increasing the sediment deposit ion to levels that would adversely affect their ability to co mplete their life cycles. (4) Significant alteration of ch annel/pond m orphology or geometry that may lead to changes to the hydrologic functioning of the stream or pond and alter the timing, duration, water flows, and levels that would degrade or eliminate the CRLF and/or its habitat. Such an effect coul d also lead to increased sedimentation and degradation in water quality to levels that are beyond the CRLF’s tolerances. (5) Elim ination of upland foraging and/or aes tivating habitat or dispersal habitat. (6) Introduction, spread, or augm entation of non-native aquatic species in stream segments or ponds used by the CRLF. (7) Alteration or elim ination of the CRLF ’s food sources or prey base (also evaluated as indirect effects to the CRLF).

As previously noted in Section 2.1, the Agency believes that the analysis of direct and indirect effects to lis ted species provides the basis for an analysis of potential effects on the designated critical habitat. Because methid athion is expected to directly impact living organisms within the action area, critical hab itat analysis for methidathion is limited in a practical sense to those PCEs of critical habitat that are biological or that can be reasonably linked to biological ly mediated processes.

352.7 Action Area

For listed species assessment purposes, the actio n area is considered to be the area affected directly or indirec tly 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 meth idathion is likely to encomp ass considerable portions of the United States based on the large array of ag ricultural uses. However, the scope of this assessment limits considerati on of the overall action area to those portions that may be applicable to the protection of the CRLF and its designated critical ha bitat within the state of California. The Agency’s approach to defining the action area unde r the provisions of the Overview Document (USEPA 2004) cons iders the resu lts 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. For the purposes of this assessment, attenti on will be focused on the footprint of the action (i.e., the area where pesticide applica tion occurs), plus all areas where offsite transport (i.e., spray drift, downstream dilu tion, etc.) may result in potential exposure within the state of California th at exceeds the Agency’s LOCs.

Deriving the geographical extent of this portion of the action area is based on consideration of the types of effects that m ethidathion may be expected to have on the environment, the exposure levels to methidathi on that are associated with those effects, and the best available information concerni ng the use of methidathion and its fate and transport within the state of California. Sp ecific measures of ecol ogical effect for the CRLF that define the action area include any di rect and indirect toxic effect to the CRLF 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 eff ect threshold for any biological entity at the whole organism, organ, tissue, and cellular level of organization. In s ituations 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.

The definition of action area requires a stepwis e approach that begins with an understanding of the federal act ion. The federal action is de fined by the currently labeled uses for methidathion. An analysis of labele d 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 th is assessment. In addition, a distinction has been made between food use crops and those that are non-food/nonagricultural uses. For those uses relevant to the CRLF, the analysis indicates that, for methidathion, the following agricultural uses ar e considered as part of the federal action evaluated in this assessment:

• Alfalfa, almond, apple, apricot, artic hoke, calem ondin, cherry, citron, citrus, clover, cotton, grapefruit, kiwi, kumquat, lemon, lime, mango, nectarine, olive, oranges, peach, pear, plum, prune, pu mmelo, safflower, sunflower, tangelo, tangerine, timothy, and walnut.

36In addition, the following non-food and non-agricultural uses are considered:

• Nursery stock, ornam ental and herbaceous plants, woody shrubs and vines

Following a determination of the assessed uses , an evaluation of the potential “footprint” of m ethidathion 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 repr esenting all the land cover types that make up the initial area of conc ern for methidathion is presented in Figure 2.4

. The following land cover types were used for m ethidathion: cultivated crops, developed (low, medium and high intensity and open sp ace), forest, open water, orchards and vineyards, pasture/hay, wetlands , turf and rights-of-way. More information regarding which specific uses are represented for each land cover types can be found in Appendix D.

37Figure 2.4 Initial area of concern, or “footprint” of poten tial use, for methidathion

Once the initial area of concern is defined, the ne xt step is to define the potential boundaries of the action area by determining the ex tent of offsite tran sport via spray drift

38and runoff where exposure of one or more ta xonomic groups to the pe sticide exceeds the listed species LOCs.

As previously discussed, the action area is defined by the most sensitive measure of direct and indirect ecological toxic effects including re duction in survival, growth, reproduction, and the entire suite of sublethal effects from va lid, peer-reviewed studies.

Due to the lack of a defined no effect concentration for a m ammalian toxicity study (Yavuz et al., 2005; see Section 4.2.2 for study details), the spatial extent of the action area (i.e., the boundary where exposures and pot ential effects are less than the Agency’s LOC) for methidathion cannot be determined. Therefore, it is assumed that the action area encompasses the entire state of California, regardless of the spatial extent (i.e., initial area of concern or footprint) of the pesticide use(s).

2.8 Assessment Endpoints and Measures of Ecological Effect

Assessment endpoints are defined as “explicit expressions of the ac tual environm ental value that is to be protected.” 5 Selection of the assessment endpoints is based on valued entities ( e.g., CRLF, organisms important in the life cycle of the CRLF, and the PCEs of its designated critical habitat), the ecosystems potentially at risk ( e.g., waterbodies, riparian vegetation, and upla nd and dispersal habitats), the migration pathways of methidathion ( e.g., runoff, spray drift, etc.), and the routes by which ecological receptors are exposed to methidathion (e.g., direct contact, etc.).

2.8.1. Assessment Endpoints for the CRLF

Assessment endpoints for the CRLF include direct toxic effects on the survival, reproduction, and growth of the CRLF, as well as indirect effects, such as reduction of the prey base or m odification of its habitat. In addition, potential m odification of critical habitat is assessed by evaluating potential eff ects to PCEs, which are components of the habitat areas that provide essential life cycle needs of the CRLF. Each assessment endpoint requires one or more “measures of ecological effect,” defined as changes in the attributes of an assessment endpoint or cha nges 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 dir ect and indirect effects associated with survival, growth, and fecundity, and do not incl ude the full suite of sublethal effects used to define the action area. According th e Overview Document (USEPA 2004), the Agency relies on acute and chronic effects endpoi nts that are either direct measures of impairment of survival, growth, or fec undity or endpoints for which there is a scientifically robust, peer reviewed relationship that ca n quantify the impact of the measured effect endpoint on the assessment endpoi nts of survival, growth, and fecundity.

5 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.

39A complete discussion of all the toxicity data available for this risk assessment, including resulting measures of ecologica l effect selected for each ta xonomic 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 po tential assessed direct and indirect CRLF risks associated with e xposure to methidathion is provided in Table 2.3

.

Table 2.3 Assessment Endpoints and Measures of Ecological Effects Assessment Endpoint Measures of Ecological Effects 6 Aquatic-Phase CRLF (Eggs, larvae, juveniles, and adults) a Direct Effects
1. Survival, growth, and reproduction of CRLF 1a. Freshwater fish 96-hour acute LC 50 1b. Freshwater fish chronic NOAEC Indirect Effects and Critical Habitat Effects
2. Survival, growth, and reproduction of CRLF individuals via indirect effects on aquatic prey food supply ( i.e., fish, freshwater invertebrates, nonvascular plants) 1a. Freshwater fish 96-hour acute LC 50 ; freshwater invertebrate 48-hr EC 50 ; aquatic non-vascular plant acute EC 50 2b. Freshwater fish chronic NOAEC ; freshwater invertebrate chronic NOAEC 3. Survival, growth, and reproduction of CRLF individuals via indirect effects on habitat, cover, food supply, and/or primary productivity ( i.e., aquatic plant community) 3a. Vascular plant acute EC 50 3b. Non-vascular plant acute EC 50
4. Survival, growth, and reproduction of CRLF individuals via effects to riparian vegetation 4a. Distribution of EC 25 ’s for monocots 4b. Distribution of EC 25 ’s for dicots Terrestrial-Phase CRLF

(Juveniles and adults) Direct Effects 5. Survival, growth, and reproduction of CRLF individuals via direct effects on terrestrial phase adults and juveniles 5a. Avian acute LD 50 5b. Avian chronic NOAEC
Indirect Effects and Critical Habitat Effects 6. Survival, growth, and reproduction of CRLF individuals via effects on terrestrial prey ( i.e., terrestrial invertebrates, small mammals , and frogs) 6a. Terrestrial invertebrate acute LD 50 ; mammalian acute LD 50 6b. Mammalian chronic NOAEC 7. Survival, growth, and reproduction of CRLF individuals via indirect effects on habitat ( i.e., riparian and upland vegetation) 7a. Distribution of EC 25 ’s for monocots 7b. Distribution of EC 25 ’s for dicots

a Adult frogs are no longer in the “aquatic phase” of the amphibi an life cycle; however, submerged adult frogs are considered “aquatic” for the purposes of this assessment because exposure pa thways in the water are considerably different that exposure pathways on land.
b According to Mayer, D. & C. Johansen. 1990. Pollinator Protection: A Bee & Pesticide Handbook . Wicwas Press. Cheshire, Conn. p. 161
2.8.2 Assessment Endpoints for De signated Critical Habitat

As previously discussed, designa ted c ritical habitat is assessed to evaluate actions related to the use of methidathion that may alter the PCEs of the CRLF’s cri tical habitat. PCEs for the CRLF were previously described in S ection 2.6. Actions that may modify critical habitat are those that alter the PCEs and jeopa rdize the continued existence of the CRLF.

6 All registrant-submitted and open literature toxicity da ta reviewed for this assessment are included in Appendix A.

40Therefore, these actions are id entified as assessment endpoints. It should be noted that evaluation of PCEs as assessment endpoints is lim ited to those of a biological nature (i.e., the biological resource requirements for the list ed species associated with the critical habitat) and those for which methidat hion effects data are available.

Modification to the critical habitat of th e CRLF i ncludes, but is not limited to, the following, as specified by USFWS (2006):

1. Altera tion of water chemistry/quality including temperature, turbidity, and oxygen content necessary for normal grow th and viability of juvenile and adult CRLFs. 2. Alteration o f chemical characterist ics necessary for normal growth and viability of juvenile and adult CRLFs. 3. Significant increase in sedim ent depositi on within the stream channel or pond or disturbance of upland fora ging and dispersal habitat. 4. Significant alteration of channe l/pond m orphology or geometry. 5. Elim ination of upland foraging and/or aes tivating habitat, as well as dispersal habitat. 6. Introduction, spread, or augm entation of non-native aquatic species in stream segments or ponds used by the CRLF. 7. Alteration or elim ination of the CRLF’s food sources or prey base.

Measures of such possible effects by labeled use of m ethidathion on cr itical habitat of the CRLF are described in Table 2.4 . 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 exp ected to be measurably alte red by use of pesticides. Assessment endpoints used for the analysis of designated critical ha bitat are based on the modification standard es tablished by USFWS (2006).

41Table 2.4 Summary of Assessment Endpoints and Measures of Ecological Effect for Primary Constituent Elements of Designated Critical Habitat a

Assessment Endpoint Measures of Ecological Effect
Aquatic-Phase CRLF PCEs (Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat) 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. a. Most sensitive aquatic plant EC 50 b. Distribution of EC 25 values for terrestrial monocots c. Distribution of EC 25 values for terrestrial dicots

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. a. Most sensitive EC 50 values for aquatic plants b. Distribution of EC 25 values for terrestrial monocots c. Distribution of EC 25 values for terrestrial dicots

Alteration of other chemical characteristics necessary for normal growth and viability of CRLFs and their food source. a. Freshwater fish 96-hour acute LC 50 ; freshwater invertebrate 48-hr EC 50 ; aquatic plant acute EC 50 b. Freshwater fish chronic NOAEC ; freshwater invertebrate chronic NOAEC Reduction and/or modification of aquatic-based food sources for pre-metamorphs ( e.g., algae) a. Most sensitive aquatic plant EC 50

Terrestrial-Phase CRLF PCEs (Upland Habitat and Dispersal Habitat) 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 a. Distribution of EC 25 values for monocots b. Distribution of EC 25 values for dicots c. Mammalian acute LD 50 ; mammalian chronic NOAEC d. Freshwater fish 96-hour acute LC 50 ; freshwater fish chronic NOAEC e. Avian acute LD 50 ; avian acute LC 50 ; avian chronic NOAEC f. Honey Bee acute LD 50

Alteration of chemical ch aracteristics necessary for normal growth and viability of juvenile and adult CRLFs and their food source.

a Physico-chemical water quality parameters such as salinity, pH , and hardness are not evaluated because these processes are not biologically mediated and, therefore, are not releva nt to the endpoints included in this assessment.
b According to Mayer, D. & C. Johansen. 1990. Pollinator Protection: A Bee & Pesticide Handbook . Wicwas Press. Cheshire, Conn. p. 161

422.9 Conceptual Model

2.9.1 Risk Hypotheses

Risk hypotheses are specific assumptions about potential adverse effects ( i.e., changes in

assessm ent endpoints) and may be based on theory and logic, empirical data, mathematical models, or probability models (U .S. EPA, 1998). For this assessment, the risk is stressor-linked, where the stresso r is the release of methidathion to the environment. The following risk hypotheses are presumed for this endangered species
assessment:

The labeled use of methidathion within the action area may:

• directly affect the CRLF by causing mortal ity or by adversely a ffecting growth or fecundity;

• indirectly affect the CRLF by reducing or changing the composition of food supply;

• indirectly affect the CRLF or modify designated critical habitat by reducing or changing the composition of the aquatic pl ant community in the ponds and streams comprising the species’ current range and desi gnated critical habita t, thus affecting primary productivity and/or cover;

• indirectly affect the CRLF or modify designated critical habitat by reducing or changing the composition of the terrestrial plant community (i.e., riparian habitat) required to maintain acceptable water qual ity and habitat in the ponds and streams comprising the species’ current range and designated critical habitat;

• modify the designated critical habita t of the CRLF by reducing or changing breeding and non-breeding aquatic habitat (via modification of water quality parameters, habitat morphology, and/or sedimentation);

• modify the designated critical habita t of the CRLF by reducing the food supply required for normal growth and viabili ty of juvenile and adult CRLFs;

• modify the designated critical habita t of the CRLF by reducing or changing upland habitat within 200 ft of the edge of the riparian vegetation necessary for shelter, foraging, and predator avoidance.

• modify the designated critical habita t of the CRLF by reducing or changing dispersal habitat within designa ted units and between occupied locations within 0.7 mi of each other that allow for movement between si tes including both natural and altered sites which do not contain barriers to dispersal.

• modify the designated critical habi tat of the CRLF by altering chemical characteristics necessary for normal growth a nd viability of juven ile and adult CRLFs.

2.9.2 Diagram

The conceptual model is a graphic representation of the structure of the risk assessment. It specifies the m ethidathion and methid athion oxon release mechanisms, biological receptor types, and effects endpoints of poten tial concern. The conceptual models for terrestrial and aquatic exposures are shown in Figure s 2.5 and 2.6 , respectively, which

43include the conceptual models for the aquatic and terrestrial PCE components of critical habitat. Exposure routes shown in dashed lines are not quantitatively considered because the contribution of those poten tial exposure routes to potential risks to the CRLF and modification to designated critical habitat is expected to be negligible.

Stressor

Source

Receptors

Attribute Change Methidathion applied to use site and its degradate, methidathion oxon, formed after application

Direct application Spra y drift

Birds/terrestrialphase amphibians/ reptiles/mammals

Terrestrial

insects

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 Terrestrial/riparian plants grasses/forbs, fruit, seeds (trees, shrubs) Runoff

Mammals/ birds Exposure Media Soil

Ingestion In g estion

Ingestion In g estion Dermal u p take/In g estion Long range atmospheric

transport

Root uptake

Wet/dr y de p osition

Terrestrial-phase amphibians Ingestion

Figure 2.5 Conceptual Model for Methidath ion Effects o n Terrestrial Phase of the CRLF

44Stre ssor

Source

Receptors

Attribute Change Methidathion applied to use site and its degradate, methidathion oxon, formed after application

Spra y drift

Fish/aquatic-phase amphibians **Piscivorous mammals and birds

Individual organisms Reduced survival Reduced growth Reduced reproduction Food chain Reduction in algae Reduction in prey Modification of PCEs related to prey availability Habitat integrity Reduction in primary productivity Reduced cover Community change Modification of PCEs related to habitat Surface water/ Sediment Runoff

Aquatic Animals Invertebrates Vertebrates Exposure Media

Uptake/gills or integument

In g estion In g estion Long range atmospheric

transport

Wet/dry deposition Soil Groundwate r

Uptake/gills or integument

A quatic Plants Non-vascular Vascula r Uptake/cell,

r oots, l ea v es Riparian plants terrestrial exposure pathways see

Figure 2.5

Figure 2.6 Conceptual Model for Methidath ion Effects on Aquatic Phase of the CRLF

2.10 Analysis Plan

In order to address the risk hypot hesis, the potential for direct and indirect effects to the CRLF, its prey, and its h abitat is estimat ed. In the following sections, the use, environmental fate, and ecological effect s of methidathion are characterized and integrated to assess the risks. This is accomplished using a risk quotient (ratio of exposure concentration to effect s concentration) approach. Although risk is often defined as the likelihood and magnitude of adverse ecological effect s, the risk quotient-based approach does not provide a quantitative estim ate of likelihood and/or magnitude of an adverse effect. However, as outlined in the Overview Document (U.S. EPA, 2004), the likelihood of effects to indivi dual organisms from particular uses of methidathion is estimated using the probit dose-response slope and either the level of concern (discussed below) or actual calculated risk quotient value.

452.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model

2.10.1.1 Measures of Exposure

The environmental fate properties of methid athion along with available m onitoring data indicate that runoff and spra y drift are the principle poten tial transport mechanisms of methidathion to the aquatic and terrestrial habitats of the CRLF, and monitoring data indicate that long range atmos pheric transport is a concern as well. In this assessment, transport of methidathion through runoff a nd spray drift is considered in deriving quantitative estimates of methidathion exposur e to CRLF, its prey and its habitats. Long range atmospheric transport is considered qualitatively.

Measures of exposure are based on aquatic and terrestrial m odels that predict estimated environmental concentrations (EECs) of methidathion using maximum labeled application rates and methods of application. The models used to predict aquatic EECs are the Pesticide Root Zone Model coupled with the Exposure Analysis Model System (PRZM/EXAMS). The model used to predict terrestrial EECs on food items is T-REX. The model used to derive EECs relevant to te rrestrial and wetland plants is TerrPlant. These models are parameterized using relevant reviewed registrant-submitted environmental fate data.

PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are screening sim ulation models coupled with the input shell pe5.pl (Aug 2007) to generate daily exposures and 1-in-10 year EECs of methidathi on that may occur in surface water bodies adjacent to application sites receiving methidathion through runoff and spray drift. PRZM simulates pesticide application, move ment and transformation on an agricultural field and the resultant pesticide loadings to a receiving water body via runoff, erosion and spray drift. EXAMS simulates the fate of th e pesticide and resulting concentrations in the water body. The standard scenario used for ecological pesticide assessments assumes application to a 10-hectare agri cultural field that drains in to an adjacent 1-hectare water body, 2-meters deep (20,000 m 3 volume) with no outlet. PRZM/EXAMS was used to estimate screening-level exposure of aquatic organisms to methidathion. The measure of exposure for aquatic species is the 1-in-10 year return peak or rolling mean concentration. The 1-in-10 year peak is used for estimati ng acute exposures of direct effects to the CRLF, as well as indirect effects to the CRLF through effects to potential prey items, including: algae, aquatic inve rtebrates, fish and frogs. The 1-in-10-year 60-day mean is used for assessing chronic exposure to the CRLF and fish and frogs serving as prey items; the 1-in-10-year 21-day mean is us ed for assessing chronic exposure for aquatic invertebrates, which are al so potential prey items.

Exposure estimates for the terrestrial-phase CRLF and terrestria l invertebrates and

m ammals (serving as potential prey) assumed to be in the target area or in an area exposed to spray drift are derived usi ng the T-REX model (version 1.3.1, 12/07/2006). This model incorporates the Kenega nomograph, as modified by Fletcher et al. (1994), which is based on a large set of actual field residue data. The upper limit values from the nomograph represented the 95t h percentile of residue values from actual field

46measurements (Hoerger and Ke nega, 1972). For modeling pur poses, direct exposures of the CRLF to methidathion through contaminat ed 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 categ ories represent the largest RQs of the size and dietary categorie s in T-REX that are appropriate surrogates for the CRLF and one of its prey items. Es timated exposures of terrestrial insects to methidathion are bound by using the dietary based EECs for small insects and large insects.

Birds are currently used as surrogates for te rrestrial-phase C RLF. However, amphibians are poikilotherms (body temperat ure varies with environmenta l temperature) while birds are homeotherms (temperature is regulate d, constant, and largely independent of environmental temperatures). Therefore, am phibians 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 on a daily dietary intake basis, assuming similar caloric content of the f ood items. Therefore, the use of avian food intake allometric equation as a surrogate to amphibians is likely to result in an overestimation of exposure and risk for reptiles a nd terrestrial-phase amphibians. Therefore, T-REX (version 1.3.1) has been refined to th e 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 a nd wetland areas are derived using TerrPlant (version 1.2.2, 12/26/2006). This m odel uses es timates of pesticides in runoff and in spray drift to calculate EECs. EECs are based upon solubility, application rate and minimum incorporation depth.

The spray drift model AgDrift (v. 2.01) was used to assess exposures of terrestrial phase CRLF and its prey to m ethidathion deposited on terrestrial habitats by spray drift from ground and aerial applications. In addition to the buffered area from the spray drift analysis, the downstream extent of methidat hion that exceeds the LOC for the effects determination is also considered.

2.10.1.2 Measures of Effect

Data identified in Section 2.8 are used as measur es of effect for direct and indirect effects to the CRLF. Data were obtained f rom regi strant 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 wa s created and is maintained by the USEPA, Office of Research and Devel opment, and the National Health and Environmental Effects Research Laboratory's Mid- Continent Ecology Division.

47The assessment of risk for direct effect s to the terrestrial-phase CRLF makes the assumption that toxicity of methidathion to bird s is similar to or less than the toxicity to the terrestrial-phase CRLF. The same assu mption is made for fish and aquatic-phase CRLF. Algae, aquatic invertebrates, fish, and amphibians represent potential prey of theCRLF in the aquatic habitat. Terrestrial invertebrates, small mammals, and terrestrialphase amphibians represent potential prey of th e CRLF in the terrestrial habitat. Aquatic, semi-aquatic, and terrestrial plants represent habitat of CRLF.

The acute measures of effect used for animal s in this scr eening level assessment are the LD 50 , LC 50 and EC 50 . LD stands for "Lethal Dose", and LD 50 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 LC 50 is the concentration of a chemical that is estimated to kill 50% of the test organisms. EC stands for “Effective Concentration” and the EC 50 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 an d NOEC. NOAEL stands for “No Observed-Adverse-Effect-Level” and refers to the highest tested dose of a substance that has been reported to have no harmful (adve rse) 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 statis tically different from the control. The NOEC is the No-Observed-Effects-Concentra tion. For non-listed plants, only acute exposures are assessed ( i.e. , EC 25 for terrestrial plants and EC 50 for aquatic plants).

It is important to note that the measures of effect for direct an d indirect effects to the CRLF and its designated critical habitat are as sociated 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 Docu ment (USEPA 2004), the Agency relies on effects endpoints that are either direct measures of impairme nt 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.

2.10.1.3 Integration of Exposure and Effects

Risk characterization is the integration of exposure and ecological e ffects characterization to determ ine the potential ecolo gical risk from agricultural and non-agricultural uses of methidathion, and the likelihood of direct a nd indirect effects to CRLF in aquatic and terrestrial habitats. The expos ure and toxicity effects data are integrated in order to evaluate the risks of adverse ecological effects on non-target species. For the assessment of methidathion risks, the ri sk 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 Ag ency’s levels of c oncern (LOCs) (USEPA, 2004) (see Appendix E ).

For this endangered species assessment, listed sp ecies LOCs are used for comparing RQ values for acute and chronic exposures of methidathion directly to the CRLF. If

48estimated exposures directly to the CRLF of methidathion resulting from a particular use are sufficient to exceed the listed species LOC, then the effects determination for that use is “may affect”. When considering indirect effects to the CRLF due to effects to animal prey (aquatic and terrestrial invertebrates, fish, frogs, and mice), the listed species LOCs are also used. If estimated exposures to CRLF prey of methidathion resulting from a particular use are sufficient to exceed th e listed species LOC, then the effects determination for that use is a “may affect.” If the RQ being considered also exceeds the non-listed species acute risk LOC, then the eff ects determination is a LAA. If the acute RQ is between the listed species LOC and th e non-listed acute risk species LOC, then further lines of evidence ( i.e . probability of individual effects, species sensitivity distributions) are considered in distinguishing between a determination of NLAA and a LAA. When considering indir ect effects to the CRLF due to effects to algae as dietary items or plants as habitat, the non-listed sp ecies LOC for plants is used because the CRLF does not have an obligate relationship with any pa rticular aquatic and/or terrestrial plant. If the RQ being considered for a particul ar use exceeds the non-listed species LOC for plants, the effects determination is “may affect”. Further information on LOCs is provided in Appendix E

. 2.10.2 Data Gaps

For environmental fate, there are no data gaps w hich will affect conclusions regarding potential environmental exposure to the parent compound, methidathion. Guideline aerobic and anaerobic aquatic metabolism studies have not been submitted, and the anaerobic soil metabolism study is not sufficien t to determine a degr adation half-life. These data would be useful to refine char acterization of the environmental fate of methidathion, but they would not change quantitative exposure estimates. Submitted laboratory volatility and photodegradation in air were determined to be unacceptable. These studies would be necessary to quantit atively assess the potential for atmospheric transport of methidathion and methidathion oxon.

Several fate studies do not pr ovid e adequate identification of potential degradates of methidathion. None of the available laborat ory transformation studies include labeling of the phosphate ester portion of the methidathion compound and so potentially toxic degradates would not have been observed. This may lead to increased risk but cannot be characterized based on existing data and so is addressed as an uncertainty.

For environmental effects, there are no aquati c o r terrestrial plant data. Limited data from ECOTOX are discussed in the risk description section along with the risk conclusions for aquatic and terrestrial plants from assessments with other organophosphate pesticides.

There are no toxicity data for m ethidathion oxon. Toxi city information for other organophosphate insecticides ( e.g. , diazinon, chlorpyrifos) indi cate that oxon degradates may be considerably more toxic than th e parent OP. Methidathion oxon has been detected in monitoring data and has been obser ved to form in field and laboratory studies.

49Without toxicity data, risk from this degr adate of toxicological concern is calculated based on assumptions about formation and toxicity.

Although not specifically a data gap, it is noted that the chroni c NOAEC of 6.3 μg/L for the f athead minnow is similar to the acute 96-hour LC 50 of several other freshwater fish species: rainbow trout (6.6 to 14 μg/L), bluegi ll sunfish (2.2 to 9 μg /L), and goldfish (6.8 μg/L). A chronic NOAEC for any of these othe r species would likely be lower than the available fathead minnow NOAEC. Therefore, the estimation of risk to freshwater fish and aquatic-phase amphibians is based on the most conservative acute to chronic ratio from other organophosphates that have both an acute and chronic study for rainbow trout.

3. Exposure Assessment

Methidathion is formulated as a wettable powder in water-soluble bags (25% active ingred ient) and emulsifiable concentrate (2 2% - 24% active ingredient). Application equipment includes fixed wing aircraft, ground boom, air blast, low-pressure handwand or backpack sprayer. Applicat ion is via foliar treatment, and annual application rates range from 1.0 to 10.0 lbs a.i./A. Risks from ground boom and aerial applications are expected to result in the hi ghest off-target levels of methidathion due to generally higher spray drift levels. Ground boom and aerial modes of application tend to use lower volumes of application ap plied 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 Label Application Rates and Intervals

Methidathion labels may be categorized into two types: labels for m anufacturing uses (including technical grade methidathion and its formulated products) and end-use products. While technical products, which contain methidathion of high purity, are not used directly in the environment, th ey are used to make formulated products, which can be applied in specific areas to control insects. The formulated product labels legally limit methidathion’s potential use to only those sites that are specified on the labels.

Currently registered agricu ltural and non-agricultural uses of m ethidathion within California are alfalfa, almond, apple, apri cot, artichoke, cherr y, citrus (calemondin, citron, grapefruit, kumquat, lemon, lime, orange, pummelo, tangelo, and tangerine), clover, cotton, kiwi, mango, nectarine, nurse ry stock (including ornamental herbaceous plans ant ornamental woody shrubs and vi nes), olive, peach, pear, plum, pruneo, safflower, sunflower, timothy, and walnut. Application rates and information for these uses were reported in Table 2.2

.

503.2 Aquatic Exposure Assessment

3.2.1 Modeling Approach

Surface water aquatic exposures for all assesse d uses are qu antitatively estimated using the Pesticide Root Zone Model coupled w ith the Exposure Analysis Model System (PRZM/EXAMS). These screening level mode ls are operated based on scenarios that represent high exposure sites for methidathion use and represent a 10 hectare field that drains into a 1-hectare pond that is 2 meters deep a nd has no outlet. PRZM/EXAMS modeling does not account for transport to groundwater followed by discharge to surface water as a possible route of aquatic exposure. In this assessment, long-term chronic concentrations derived from the PRZM -EXAMS model are assumed to reflect background concentrations that might be found in discharged groundwater/stream baseflow, but this factor remains an uncertain ty, and will be discussed as such in Section 6.1.3.

3.2.2 Model Inputs

3.2.2.1 Physical Properties and Environmental Fate Inputs

Methidathion environmental fate data were discussed previously and are listed in Table 2.1. Chemical-specific model input paramete rs for PRZM and EXAMS are based on these data and are listed in Table 3.1

.
Table 3.1. PRZM/EXAMS Environmental Fate Inputs for Aquatic Exposure to Methidathion Fate Property Value Comment 1 Source
Molecular Weight 302.3 Henry’s constant 3.97 x 10 -9 atm m 3 /mol USEPA, 1999

Vapor Pressure 2.5 x 10 -6 mm Hg USEPA, 1999

Solubility in Water 2500 mg/L Measured value x 10 USEPA, 1999

Photolysis in Water 10 days MRID 42081709

Aerobic Soil Metabolism Half-lives 17.5 days Upper 90% confidence b ound on the mean of two values MRID 44545101, MRID 42262501

Hydrolysis at pH 7 48 days Maximum of two values MRID 42037701

Aerobic Aquatic Metabolism (water column) 35 days Twice the aerobic soil metab olsim half-life.

Anaerobic Aquatic Metabolism (benthic) Stable No data available

51Table 3.1. PRZM/EXAMS Environmental Fate Inputs for Aquatic Exposure to Methidathion Fate Property Value Comment 1 Source

K oc 364 mL/g OC MRID 00158529 Mean of four values

1 – Inputs determined in accordance with EFED “ Guidance for Chemistry and Management Practice Input Parameters for Use in Modeling the Environmenta l Fate and Transport of Pesticides” dated February 28, 2002
3.2.2.2 Use-specific Man agement Practices Inputs

Crop-specific management practices for all of the assessed uses of m ethidathion were accounted for in aquatic exposure modeling. Ap plication rates and in tervals, application dates, and crop scenarios used as modeling inputs are listed in Table 3.2 and the justification for these inputs are described below.

Use-specific parameters are input into modeli ng scenarios which have been developed to represent locally specific soil a nd clim atic conditions in vulnerable use sites. Scenarios also include crop specific agronomic data a nd management practices such as planting and harvest date. The scenarios used in modeli ng were selected from the group of standard and CRLF-specific scenarios representing cr ops grown in California. For most methidathion uses, scenarios are available which were developed specifically for that use. In cases where a scenario does not exist for a specific use, it is necessary to assign a surrogate scenario. For sunflower, the Calif ornia Corn scenario was selected because it represents a non-irrigated row crop. For safflower, the California Wheat scenario was used because it is an annual, broadleaf oilseed crop that can be grown in the small-grain production areas of California. For kiwi, the California Grape scenario was used because the kiwi is a woody vine grown primarily in the same counties as grapes. Some scenarios represent multiple uses, as listed in Table 3.2 . For these uses, the application rate modeled is the highest from all uses within the group. Unless ot herwise specified, the application method is aerial spray.

Application dates are not specified on pr oduct labels. For m odeling, an estimated application window was develope d based on label instructions, crop profiles maintained by the USDA ( http://www.ipmcenters.org/cropprofiles/GetCropProfiles.cfm ; accessed 12/08), historical use data from the Calif ornia PUR dataset, and planting dates and precipitation data specific to each scenar io. From within this window, multiple application dates were modeled using a multi-run tool in pe5 and the date leading to the most conservative EEC was used. For example, the distribution of applications seen in the CDPR PUR data indicates that methidathi on is typically applied to olives between mid-October and mid-December, while the scenar io precipitation data show that within this time period, late November has the highest precipitation and so the greatest likelihood of runoff. Using the pe5 multi-run to ol for this window, an application date of December 1 was shown to lead to the most conservative aquatic exposure estimates.

52Table 3.2. PRZM/EXAMS Crop-Specific Inputs for Aquatic Exposure to Methidathion Scenario Uses Represented by Scenario Date of first application Application Rate (lbs a.i./A) Number of Applications Per Crop Cycle Application Interval (Days)

CA Alfalfa Alfalfa, Clover Timothy 8/15 1 2 5 a

CA Almond Almond, Walnut 1/7 2 3 2

CA Citrus b Calemondin, Citron, Citrus, Grapefruit, Kumquat, Lemon, Lime, Orange, Pummelo, Tangelo, Tangerine 8/15 5 2 45

CA Citrus c Mango 8/15 0.25 1 NA

CA Corn Sunflower 1/7 0.5 3 7

CA Cotton Cotton 7/10 1 4 5
CA Grapes Kiwi 2/15 2 1 NA

CA Tree Fruit Apple, Apricot, Cherry, Nectarine, Peach, Pea r, Plum, Prune 12/18 3 1 NA

CA Olive b Olive 12/1 3 1 NA

CA Row Crop Artichoke 7/25 1 8 14

CA Wheat Safflower 5/25 0.5 3 7
CA Nursery d Nursery 1/22 10 c 1 NA

a The application interval is not specified on the label. A 5 day interval was assumed to be conservative because the target pests are similar to those for cotton.
b Application through ground spray only.

c Mango was modeled separately from the ot her citrus uses because it is the lowest applicat ion rate of all labeled uses and so EECs were needed to provide char acterization of the full range of exposures.
d The nursery stock application rate is re ported on labels as 0.5 lb a.i./100 gal sp ray with no instructi ons for application on areal basis. Therefore, this rate is based on the general labels statement th at methidathion should not be applied at greater than 10 lb a.i./A.
For all uses, application was modeled as fo liar applied (CAM = 2) with no removal of foliar pesticide after harvest (IPSCND = 3). A pplication efficiency inputs were set to the default values corresponding to each application method: 99% efficiency for ground applications (citrus, olives, and nursery stock) and 95% for a ll other aerial spray applications. Spray drift inputs were estim ated using the AgDRIFT model in order to account for the effect of the labels’ mitiga tion requirements, which include buffer zones of 25 to 150 ft between cropped areas and wa ter bodies (see Section 2.3.1) and a medium to coarse droplet size. Usi ng these inputs, AgDRIFT estimated spray drift of 0.6% of the applied active ingredient for ground app lications and of 2% for aerial uses.

533.2.3 Results

PRZM/EXAMS EECs representing 1-in-10 year peak, 21-day, and 60-day concentrations of

total toxic residues of methidathion in the aquatic environment are located in Table 3.5 . All model outputs are included in Appendix F . Estimated aquatic exposures from terrestrial food and feed uses are highest for the CA Almond scenario, representing methidathion use on almonds and walnuts, with a peak EEC of 49.3 ug/L. Peak EECs for other agricultural crops range d from 4.6 ug/L for alfalfa to 20.7 ug/L for sunflowers.

The non-food use in ornamental nurseries resu lted in a peak EEC of 115.6 ug/L. This result is based on an applic ation rate of 10 lb a.i./A, the m aximum application rate reported in the general instructions, because labeled application ra tes specific to the nursery use are reported in terms of product per foot of plant, rather than per unit area, as modeling requires. Aquatic EECs for the non-food uses on alfalfa, clover, and timothy have a peak EEC of 4.6 ug/L, but these re sults may underestimate exposure because the modeled use only includes a single crop cycle, while these crops can be grown at up to nine crop cycles per year.

Table 3.3 Aquatic EECs ( μ g/L) for Methidathion Uses in California

Scenario Crops Represented Peak EEC 21-day average EEC 60-day average EEC

CA Alfalfa Alfalfa, Clover Timothy 4.6 3.4 2.5

CA Almond Almond, Wal nut 49.3 40.2 26.8

CA Citrus Calemondin, Citron, Citru s, Grapefruit, Kumquat, Lemon, Lime, Orange, Pummelo, Tangelo, Tangerine 18.3 13.6 9.0

CA Citrus Mango 0.45 0.34 0.22

CA Corn Sunflower 20.7 16.2 10.9

CA Cotton Cotton 13.0 9.3 6.4

CA Grapes Kiwi 6.6 5.0 3.2

CA Tree Fruit Apple, Apricot, Cherry, Nectarine , Peach, Pear, Plum, Prune 15.6 9.2 5.0

CA Olive Olive 15.2 11.7 7.6

CA Row Crop Artichoke 16.0 12.1 8.7

CA Wheat Safflower 13.6 10.4 6.6

CA Nursery Nursery 115.6 84.8 54.3

543.2.4 Existing Monitoring Data

3.2.4.1 USGS NAWQA Surface Water Data

The USGS NAWQA surface wate r dataset in C alifornia in cludes 322 samples collected between 2001 and 2007 at 15 sites, all but on e in the San Joaquin and Sacramento study areas. Six of the sites are located on Mustang Creek in Me rced County in an area with landcover classified as “other, ” and the re maining sites represent a mix of landcover classes. Methidathion was detected 13 times at 7 sites, but more than half of the detections (8 detections, 0.01 to 0.04 ppb) we re measured in one 24 hour period at two sites on Mustang Creek. At these and ot her Mustang Creek sites, sampling was conducted in winter months with multiple sampling per day, with the detections occurring in February, 2004. The other nine sites were generally sampled between 30 and 60 times, biweekly or bimonthly for one to several years. Methid athion was detected at four of these sites at levels of 0.1 to 0.31 ppb. Limits of quantitation (LOQ) were 0.006 ug/L to 0.009 ug/L. The sampling did no t include analysis for any of the degradates of methidathion.

3.2.4.2 USGS NAWQA Groundwater Data

The NAWQA groundwater California data set included 271 samples from 223 wells analyzed for methidathion between 2001 and 2006, with no detections. Detection limits were 0.0058 to 0.0087 ug/L. Most of the samples (77%) were in the San Joaquin study area, primarily in Fresno, Merced, and St anislaus Counties. The remaining sites were in the Sacramento study area with a few in the Santa Ana study area as well. 30 sites in Sacramento county were classified as urban landcover, while the remaining samples were about half classified as ag ricultural landcove r and half classified as mixed or other. No samples were analyzed for methidathion degradates.

3.2.4.3 California Department of Pesticide Regulation (CDPR) Surface Wa ter Data

CDPR’s monitoring dataset for methidathion includes 4,044 samples from 135 sites, most targeted to agricultural use areas, alt hough specific land cover information is not available. The sampling was conducted for 19 different studies, primarily in the Sacramento and San Joaquin River draina ges, although there was no sampling in the southern San Joaquin Valley (Fresno, Kern, and Tulare Counties), which is the area with the greatest methidathion use (see Figure 2.2). More than half of the samples (58%) were collected at five sites. They are primarily from two studies which were targeted to OP use areas and that had daily to weekly samp ling over several years. These studies have implications more specific to methidathion and so the results will be discussed separately in more detail below.

55The remainder of the sampling includ ed 1,694 samples from 130 sites, with approximately one-third of the samples (28% ) from the Sacramento Valley and another 44% in the northern San Joaquin Valley. LOQs were between 0.0028 ug/L to 0.10 ug/L. In the Sacramento Valley, methidathion was detected in 46 out of 472 samples, with a maximum detection of 15.1 ug/L in Sutter County, and an average across all detections of 1.2 ug/L. In the San Joaquin Valley, there we re 30 detections out of 738 samples, with the the maximum detection of 2.4 ug/L found in San Joaquin County and the average of 0.3 ug/L. Additionally, there were 5 detections at two sites in Orange County at concentrations of 0.05 ug/L to 0.17 ug/L. Acut e toxicity endpoints for fish and aquatic invertebrates are 2.2 ug/L and 3.0 ug/L, respec tively, so monitoring data demonstrate the potential for surface water concentrations in excess of these endpoints. Although Monterey is one of the highest use counties, methidathion was not detected in any of the 144 samples taken there, which were mos tly from sites on waterways dominated by summer agricultural runoff. Overall, although only 35% of the total samples were collected in January or Februa ry, 90% of the detections (72 samples) were measured in those months. This reflects the fact that the typical use period of methidathion on fruit and nut orchards is in the winter dormant season.

Two studies monitored for methidathion oxon in surface water as well as for the parent. There were no detections of the oxon in either study, even though in some cases

m ethidathion had been detected in samples coll ected at the same time. In most cases, the limit of quantitation was 0.05 ug/L. One study included 450 samples, collected weekly to monthly at 7 sites, with no detections (Gan apathy, 1997). At one Me rced County site in this study, methidathion had been detected in each of 4 samples collected weekly in January and February. The second methid athion monitoring study included 290 samples at 26 sites, primarily in Stanislaus and Me rced County (Ross et al , 2000). Methidathion had been detected at 7 sites in this study area, at concentrations up to 12.4 ug/L. There were no detections of methidathi on oxon sampled at the same times.

Studies targeted to organophosphate pesticid e use included extensive m onitoring at several sites on Orestimba Creek, a tributar y of the San Joaquin River located in Stanislaus County in an area expected to be vulnerable to runoff due to local soil and hydrology conditions. Agriculture in the area includes almond and walnut orchards as well as alfalfa. The sampling sites were se lected primarily due to expected use of diazinon and chlorpyrifos, but methidathion is us ed in this area as well. In one study (Poletika & Robb, 1998), daily samples were taken at three sites on Orestimba Creek between June, 1996 to April, 1997. Methidathi on was detected in 58 of 967 samples at levels from 0.001 ug/L to 0.331 ug/L, with an average across detected samples of 0.035, and based on an LOQ of 0.002 ug/L. There were 9 detections at the upstream site, with a maximum of 0.023 ug/L and mostly occurring in the first week of November, 1996. The midstream location had 22 detections, up to 0.078 ug/L, and the downstream site near the confluence with the San Joaquin River had 27 detections of up to 0.331 ug/L. Both sites had multiple detections in late July and early August. The highest peak occurred at the downstream site on March 20 and had decreased to undetectable levels by April 12. The study report indicates that, according to data from the county agricultural commisioner, five applications of methidathion were made in fields in the drainage during the sampling

56period. However, the timing of the detec tions did not correspond with any of the reported pesticide applications, so there were either unreporte d applications or alternative sources of runoff. Additional monitoring at the downstream site on Orestimba Creek was conducted by CDPR, with 136 samples collected , primarily during winter months in 1997 to 2002. There were four detections of 0.06 ug/L to 2.14 ug/L (CDPR, metadata reference 10).

Another study conducted by the USGS incl uded long term monitoring at two sites draining to the San Francisco Bay (Maccoy, et al, 1995). Unlike the previously discussed study, which was in a small water body local to use areas, the sites sampled here are near outlets of large agricultural watersheds, one site on the Sacramento River and downstream of most other riverine inputs in the Sacramento Valley, and one on the San Joaquin River and downstream of most other ri vierine inputs in the San Joaquin Valley. The San Joaquin Valley is the area of highe st methidathion use and the Sacramento Valley has substantial use as well, so th ese locations represent high potential for methidathion exposure. On the San Joaqui n River near Vernalis, sampling went from January, 1991 to April, 1994, and methid athion was detected 49 times out of 515 samples. All detections occurred in January or February at concentrations of 0.028 ug/L to 0.802 ug/L. On the Sacramento River, sampling began in May, 1991 and methidathion was detected in 23 of the 562 samples taken, all in February. In 1993, methidathion was detected in 16 of 23 samples collected in February at levels from 0.03 ug/L to 0.21 ug/L, and in 1994, 7 of the 17 samples collected in February had methidathion, concentrations of 0.04 ug/L to 0.7 ug/L.

3.2.4.4 Atmospheric Monitoring Data

There are several studies available which m onitor for methidathion and methidathion oxon in air, fog, and/or rain onsite and at intermediate and long range distances from treated fields. A literature review by Maje wski (1996) found three studies which tested air and fog and two studies which tested f og only for a total of 11 sites tested in California, both in the San Joaquin Valley and on the coast near Monterey. At eight of the sites, monitoring was also conducted for methidathion oxon. Methidathion was detected in both matrices at all 11 locati ons in all samples tested, while methidathion oxon was detected at 7 locations (all but one of those monitored) and in most of the samples tested. Detected concentrations of methidathion in air ranged from 0.01 ng/m 3 to 23.8 ng/m 3 and in fog from 4 x 10 -5 ug/L (0.04 ng/L) to 15.5 ug/L. This maximum concentration in fog exceeds the effects leve ls for fish and aquatic invertebrates. Concentrations for methidathion oxon were not reported. Majewski attributes the high detection frequency to the fact that most sa mpling was done in or near orchards, and the fact that most samples were collected in January, during the typical use period. It is likely, then, that at least some of these detecti ons were the result of sp ray drift rather than atmospheric transport. The study near M onterey, however, was conducted in September and states that at least one of the three sites was in a non-agri cultural area, so there is the possibility that longer range transport occurr ed. The frequency of detection of the oxon indicates that oxidation was occu rring, either in the air dir ectly or in soil or on plant surfaces followed by volatilization.

57Another air monitoring study was conducted fo r the California DPR in support of their Toxic Air Contaminant Program (Ross, 1991). In Tulare County, an area with high methidathion use on oranges, air sampling wa s conducted at five sites, four within a quarter mile of orange groves. The fifth s ite was intended to be used as background and was located in a downtown location with no or ange groves in the immediate area. At each site, 17 samples per site were taken from June 27, 1991 to July 25, 1991, the time of peak use locally. Samplers were placed on th e roof of a building or in an open area and collection occurred over a 23 to 25 hour period. All sites, including the intended background site, had samples with measured c oncentrations above th e level of detection (LOD) for both methidathion (16 samples; LOD = 10 ng/m3) and methidathion oxon (27 samples; LOD = 30 ng/m3). Methidathion was detected above the LOQ in 7 samples (32 to 78 ng/m3) at two sites and methidathion oxon was detected in 7 samples (11 to 120 ng/m3) at 4 sites, with the lowest detecti on found at the background site. Methidathion oxon was detected more frequently and at higher concentrations than the parent compound, including detections at a site with no use in the immedi ate area, indicating that transformation occurs and that there is a potential for off-site at mospheric transport.

Vogel et al. (2008) monitored for methidathion in rain at a local and interm ediate scale at a site in the Merced River basin where a va riety of crops, including grapes, almonds, and corn, were grown. Between February a nd April of 2003 and December 2003 and April 2004, methidathion was measured for in 23 single event rain samples at lower, middle, and upper positions in the watershed. Detect ions above the limit of quantitation of 0.006 ug/L were found in 11 samples, with th e highest detection of 0.69 ug/L found on December 16, 2003. Seven samples had detections between 0.01 ug/L and 0.1 ug/L and the other three were <0.01 ug/L. The detec tions were presumed to be the result of atmospheric transport because while the highe st detection occurred before spraying began in local orchards, during that time methidat hion was used on crops at the intermediate and broad scales. No sampling for methidathion oxon was conducted.

Another study by Aston and Seiber (1997) show ed the m ost clear evidence of long range transport of both methidathion and its oxon degr adate with detections in air at up to 30 km from any agricultural site and on pine needles 22 km aw ay from use areas. In May through October of 1994, Aston and Seiber (1997) monitored for methidathion and methidathion oxon at three sites near Sequoia National Park. Biweekly samples of air and of pine needles were taken at three sites; the first was located in Tulare County next to a citrus grove treated with methidathion and within an area of high citrus production, the second was at a site within Sequoia Nationa l Park that was 22 km east of the nearest agricultural spraying, an d the third site at an eleva tion on 1920 m was another 10 km away to the northeast. Each air sample re presented air collected over a 24 h period, and pine needles were collected from potted pines pl aced at each site. The flow of air from the agricultural areas of the Central Valley to the two long range sites was reported to be unobstructed.

Methidathion was detected in air in ever y sam ple at the citrus grove location and concentrations and detection frequency decr eased with distance. Methidathion oxon was also detected in all samples at the citrus gr ove and it was more pers istent with distance

58than the parent. One week following sp raying in the onsite grove, methidathion was detected in air at the high est concentration of 17.0 ng/m 3 . Concentrations at the four sampling events prior to sp raying ranged from 1.1 ng/m 3 to 15.0 ng/m 3 and in the four following sampling events air con centrations ranged from 0.4 ng/m 3 to 2.7 ng/m 3 . Over the sampling period, methidathion oxon was de tected onsite at levels from 0.28 ng/m 3 to 10.0 ng/m 3 , with the highest concentration at the initial sampling period, followed by steady decline interrupted by a peak after spraying. At the intermediate site, methidathion was detected only in th e initial sampling, June 7, at 0.23 ng/m 3 . The oxon degradate was detected on the fi rst date as well, at 0.66 ng/ng/m 3 , and declined over the next month when it was detected a third time, at 0.21 ng/m 3 . At all but one of the 5 final sampling events, methidathion oxon was detected but it was either below the limit of quantitation (0.17 ng/m 3 ) or it was not quantifiable due to inconsistencies in duplicate samples. At the far site, methidathion was reported as being unquantifiable in all samples and methidathion oxon was detected at 0.21 ng/m 3 on June 20 and was undetected or unquantifiable in all other samples.

In pine needles, both methidathion and methid athion oxon were detected in all sam ples at the citrus grove site but only the oxon degradat e was detected at the first site in Sequoia National Park and neither was detected at th e further site. Next to the citrus grove, methidathion concentrations ranged fr om approximately 50 ng/g to 65 ng/g and methidathion oxon from approximately 15 ng/ g to 150 ng/g (values estimated based on charts presented in the study report). Th e highest methidathion concentration was measured a week after spraying. Local spray dr ift is unlikely to be the cause because the pots had been removed before spraying and were not returned for 48 hours, although spray drift from other fields may be a possibility if they were treated at the same time. At this site, methidathion oxon was highest on Sept ember 18. At the intermediate site, there were no detections of methidathion, but methidathion oxon was detected at the three sampling events between July 11 and August 8 at levels from approximately 8 ng/g to 50 ng/g. There were no detections of either co mpound on pine needles at the furthest site.

3.3 Terrestrial Animal Exposure Assessment

3.3.1 Modeling Approach

T-REX (Version 1.3.1) is used to calculate dietary and dose-based EECs of m ethidathion for the CRLF and its potential prey ( e.g . small mammals and terrestrial insects) inhabiting terrestrial areas. EECs used to re present the CRLF are also used to represent exposure values for frogs serving as potentia l prey of CRLF adults. T-REX simulates a 1- year time period. For this assessment, spray applications of methidathion are considered, as discussed in below.

Terrestrial EECs for foliar formulations of m ethidathion were derived for the uses summarized in Table 3.4 . In an effort to be consis tent with the aquatic exposure assessment, the same uses and rates were modeled for terrestrial exposure estimation (see Table 3.2 ). For terrestrial exposure estimation pur poses, a half-life of 6.6 days was used as an input parameter based the 90% upper bound of the total foliar dissipation half-life

59values, 3.5 and 5.0 days, on alfalfa (Willis and McDowell, 1987). Use specific input values, including number of applications, appl ication rate and app lication interval are provided in Table 3.4 . An example output from T-REX is available in Appendix G

.
Table 3.4 Input Parameters for Foliar Appl ications Used to D erive Terrestrial EECs for Methidathion with T-REX
Uses Application Rate (lbs a.i./A) Number of Applications Per Crop Cycle Application Interval (Days) Artichoke 1 8 14 Citrus 5 2 45 Clover 1 2 7 (assum ed) Cotton 1 4 5 Kiwi 2 1 NA Nursery 10 1 NA Safflower, Sunflower 0.5 3 7 Tree Fruit, Olives, Almonds 3 1 NA

Walnut 2 3 2

T-REX is also used to calculate EECs for terrestrial insects expos ed to m ethidathion. Dietary-based EECs calculated by T-REX for sma ll and large insects (units of a.i./g) are used to bound an estimate of exposure to terre strial invertebrates. Available acute contact toxicity data for bees exposed to methidathion (in units of μg a.i./bee), are converted to μg 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 fo r bees in order to derive RQs.

For modeling purposes, exposures of the CRLF to methidathion through contaminated food are estim ated using the EECs for the small bird (20 g) which consumes small insects. Dietary-based and dose-based exposures of potential mammalian prey are assessed using the small mammal (15 g) which consumes short grass. Upper-bound Kenega nomogram values reported by T-REX fo r these two organism types are used for derivation of EECs for the CRLF and its potential prey ( Table 3.5 ). Dietary-based EECs for small and large insects reported by T-RE X as well as the resulting adjusted EECs are available in Table 3.6 . An example output from T-REX v. 1.3.1 is available in Appendix G

.

60Table 3.5 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based Exposures of the CRLF and its Prey to Methidathion

EECs for CRLF EECs for Prey (small mammals) Use Dietary-based EEC (ppm) Dose-based EEC (mg/kg-bw) Dietary-based EEC (ppm) Dose-based EEC (mg/kg-bw)
Artichoke 175 200 312 297 Citrus 681 776 1211 1154 Clover 200 227 355 339 Cotton 290 330 516 492 Kiwi 270 308 480 458 Nursery 68 77 120 114 Safflower, Sunflower 115 131 205 196 Tree Fruit, Olive, Almonds 405 461 720 686 Walnut 666 759 1184 1129

Table 3.6 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via Effects to Terrestria l Invertebrate Prey Items

Use Small Insect Large Insect

Artichoke 175 19 Citrus 681 76 Clover 200 22 Cotton 290 32 Kiwi 270 30 Nursery 68 8 Safflower, Sunflower 115 13 Tree Fruit, Olive, Almonds 405 45 Walnut 666 74

3.3.2 Field Studies

In a field study on California citrus (B rewer et al., 1998; MRID 44806601), m ethidathion was applied to foliage by air blast spray e quipment for one application at 10.0 lb ai/A. Immediately after applicati on the residues on hulled millet seed ranged from 248 to 305 (mean 276) ppm, and residues on crickets ranged from 22 to 59 (mean 40) ppm. T-REX model estimates – 150 ppm for seeds, 1350 ppm for small insects, and 150 ppm for large insects – are similar to actual field residue s, and in the case of residues on seeds, the model may underestimate exposure. It is noted, however, that although it may underestimate potential risks to seed eaters, this dietary food item is not used in the assessment, and the foliage data did not suggest an underestim ation of exposures.

613.4 Terrestrial Plant Ex posure Assessment

Since there are no terrestrial plant toxici ty data available, exposures were not quantitatively estim ated. See Section 5.2 fo r a qualitative discussion regarding the potential effects of methidathion on CRL F via effects to terrestrial plants.

4. Effects Assessment

This assessment evaluates the potential for methidathion to directly or indirectly affect the CRLF or m odify its designated critical habi tat. As previously discussed in Section 2.7, assessment endpoints for the CRLF effects de termination include direct toxic effects on the survival, reproduction, and growth of CR LF, 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 lif e cycle needs of the CRLF. Direct effects to the aquatic-phase of the CRLF are based on toxicity information for freshwater fish, while terrestrial-phase e ffects are based on avian toxicity data, given that birds are generally used as a surrogate for terrestrial-phase am phibians. Because the frog’s prey items and habitat requirements are dependent on the availability of freshwater fish and invertebrates, small mammals, te rrestrial invertebrates, and aquatic and terrestrial plants, toxicity information for these taxa are also di scussed. Acute (shortterm) and chronic (long-term) toxicity inform ation is characterized based on registrantsubmitted studies and a comprehensive review of the open literature on methidathion.

As described in the Agency’s Overview Document (U.S. EPA, 2004), the most sensitive endpoint for each taxon is used for risk estim ation. For this assessment, evaluated taxa include aquatic-phase amphibians, freshwater fish, freshwater i nvertebrates, aquatic plants, birds (surrogate for terrestria l-phase amphibians), mammals, terrestrial invertebrates, and te rrestrial plants.

Toxicity endpoints are esta blished based on data gene rated 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) (U.S. EPA, 2004). Open l iterature data presented in this assessment were obtained from ECOTOX information obt ained on 24 August 2008. In order to be included in the ECOTOX database, papers must meet the following minimum criteria:

(1) the toxic effects are related to single chem ical exposure; (2) the tox ic effects are on an aquatic or terrestrial plant or animal species; (3) there is a b iological effect on live, whole organisms; (4) a concurrent environm ental chemical concentration/dose or application rate is reported; and (5) there is an explicit duration of exposure.

Data that pass the ECOTOX screen are ev aluated along with the regis trant-submitted data, and may be incorporated qualitatively or quantitatively into this endangered species

62assessment. In general, effects data in the open literature that are mo re 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 releva nt to the assessment endpoints ( i.e. , maintenance of CRLF survival, reproduction, and growth) identified in Section 2.8. For example, endpoints such as behavior modifications are likely to be qualitativ ely evaluated, because quantitative relationships between modificat ions and reduction in species survival, reproduction, and/or growth ar e not available. Although the effects determination relies on endpoints that are relevant to the asse ssment endpoints of survival, growth, or reproduction, it is important to note that the full suite of subletha l endpoints potentially available in the effects literature (regardle ss of their significance to the assessment endpoints) are considered to define the action area for methidathion.

Citations of all open literature not considered as part of this assessm ent 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 H. Appendix H also includes a rationale for rejection of t hose studies that did not pass the ECOTOX screen and those that were not evaluated as part of th is endangered species risk assessment.

A detailed spreadsheet of the available ECOT OX open literature data, including the full suite of lethal and subletha l endpoints is presented in Appendix I. Appendix I also includes a summ ary of the human hea lth effects data for methidathion.

In addition to registrant-submitted and open lite rature toxicity inform ation, other sources of information, including use of the acute pr obit dose response rela tionship to establish the probability of an individual effect and re views of the Ecological Incident Information System (EIIS), are conducted to further refi ne the characterization of potential ecological effects associated with exposure to methidat hion. A summary of the available aquatic and terrestrial ecotoxicity information, use of the probit dose res ponse relationship, and the incident information for methidathi on are provided in Sections 4.1 through 4.4, respectively.

There are no toxicity data available f or methidathion oxon, a degradate of the parent methidathion; however, based on toxicity information for other organophosphate insecticides ( e.g. , diazinon, chlorpyrifos), methidat hion oxon may be considerably more toxic than methidathion. The pot ential for additional risk to the CRLF from exposure to methidathion oxon as a transformation product of applied methidathion will be characterized in the risk description ( Section 5.2 ).

A detailed summary of the available ecot oxicity inf ormation for all methidathion degradates and formulated products is presented in Appendix A

. 4.1 Toxicity of Methidathion to Aquatic Organisms

Table 4.1 summarizes th e most sensitive aquatic toxicity endpoints for the CRLF, based on an evaluation of both the submitted studies and the open literature, as previously

63discussed. A brief summary of submitted and open literature data considered relevant to this ecological risk assessment for the CRLF is presented below. Additional information is provided in Appendix J.

Table 4.1 Freshwater Aquatic Toxicity Profile for Methidathion Assessment Endpoint Species Toxicity Value Used in Risk Assessment MRID Study Classification Acute Direct Toxicity to Aquatic-Phase CRLF Bluegill Sunfish Lepomis macrochirus LC 50 = 2.2 μg/L 00011841 Supplemental
Chronic Direct Toxicity to Aquatic-Phase CRLF Fathead minnow Pimephales promelas NOAEC = 6.3 μg/L LOAEC = 12.0 μg/L post-hatch survival; growth 00015735 Acceptable

Indirect Toxicity to Aquatic-Phase CRLF via Acute Toxicity to Freshwater Invertebrates (i.e. prey items) Water Flea Daphnia magna LC 50 = 3.0 μg/L 42081704 Acceptable

Indirect Toxicity to Aquatic-Phase CRLF via Chronic Toxicity to Freshwater Invertebrates (i.e. prey items) Water Flea Daphnia magna NOAEC = 0.66 μg/L LOAEC = 1 .13 μg/L survival; number of young per female per reproductive day 42081707 Acceptable

Indirect Toxicity to Aquatic-Phase CRLF via Toxicity to Non-vascular Aquatic Plants No data available

Indirect Toxicity to Aquatic-Phase CRLF via Toxicity to Vascular Aquatic Plants No data available

Toxicity to aquatic fish a nd invertebrates is categorized using the system shown in Table 4.2 (U.S. EPA, 2004). Toxicity categories fo r aquatic plants have not been defined.

Table 4.2 Categories of Acute Toxicity for Aquatic Organisms
LC 50 (ppm) Toxicity Category < 0.1 Very highly toxic 0.1 – 1 Highly toxic 1 – 10 Moderately toxic 10 – 100 Slightly toxic

> 100 Practically nontoxic

4.1.1 Toxicity to Freshwater Fish

Given that no methidathion toxicity data are available for aqu a tic-phase amphibians, freshwater fish data were used as a surrogate to estimate direct acute and chronic risks to the CRLF. Freshwater fish toxicity data were also used to assess poten tial indirect effects of methidathion to the CRLF. Effects to fr eshwater fish resulting from exposure to methidathion could indirectly affect th e CRLF via reduction in available food. As

64discussed in Section 2.5.3, over 50% of th e prey mass of the CRLF may consist of vertebrates such as mice, frogs, and fish (Hayes and Tennant, 1985).

A summary of acute and chr onic freshwater fish data, including data from the open literature, is provided belo w in Sections 4.1.1.1 through 4.1.1.3.

4.1.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies

Available data indicate that methidathion is very highly toxic on an acute basis to thr ee surrogate freshwater fish species ( Appendix J ). The acute 96-hour LC 50 s for bluegill sunfish, rainbow trout, and goldfish range fr om 2.2 to 14 μg/L. The most sensitive endpoint, the bluegi ll sunfish 96-hour LC 50 of 2.2 (0.9 – 5.1) μg a.i./L (MRID 00011841), will be used to calculate RQs for direct e ffects to the aquatic-phase CRLF. The probit dose-response slope is 2.9 (1.9 – 4.0) for this study.

Two acute toxicity studies w ith the m ethidathion formula tion 2E (25.2% a.i.) are also available for consideration in this risk asse ssment. These studies suggest that the tested formulation and technical grade methidathion ar e similarly toxic to bluegill sunfish and rainbow trout on an acute basis.

4.1.1.2 Freshwater Fish: Chronic Exposure (Grow th/Reproduction) Studies

Chronic fish toxicity data for m ethidathion are limited to one early life stage study with fathead minnow as the test organism (MRID 00015730 or 45822701) ( Appendix J ). The 35-day flow-through study investigated the chronic effects following mean-measured concentration levels up to 12 μg ai/L. For survival, total length, and wet weight, the NOAEC, LOAEC, and EC 50 were 6.3, 12, and >12 μg ai/L respectively. It is important to note that the chronic NOAEC of 6.3 μg/L for the fathead minnow is similar to the acute 96-hour LC 50 of several other test species: rainbow trout (6.6 to 14 μg/L), bluegill sunfish (2.2 to 9 μg/L), and goldfish (6.8 μg /L). A chronic NOAEC for any of these other species would likely be lower than the avai lable fathead minnow NOAEC. Therefore, instead of using the chronic NOAEC for fath ead minnows, this assessment estimates a chronic NOAEC for rainbow trout using an acu te to chronic ratio (ACR) calculation. Methidathion is an organophosphate insectic ide. The EFED toxicity database, which contains the results from submitted studies that have been previously reviewed for scientific soundness, was accessed to derive an acute to chr onic ratio of all organophosphate insecticides that have an acute LC 50 and an early life stage fish study for rainbow trout (the species which would most likely have chronic data). Nineteen organophosphates were found that have both an acute and chronic study for rainbow trout. The ACRs ranged from 5.4 for Terbufos to 140 for Dichlorvos. Using this range of ACRs, the estimated chronic NOAECs for rainbow trout tested with methidathion would range from 0.07 to 1.9 ppb. In order to provide the most conservative estimate for the chronic freshwater fish NOAEC for methidathion, the ACR of 140 is utilized. Using that value and an LC 50 of 10 ppb for rainbow trout tested with methidathion (MRID 00011841), the estimated chronic NOAEC for rainbow trout is 0.07 ppb.

65The following section presents a modificat ion (for m ethidathion) of the methodology used in deriving a freshwater fish ACR for the acephate CRLF assessment (http://www.epa.gov/espp/litstatus/effects/re dleg-frog/acephate/analysis_acephate.pdf). Of the 19 organophosphates found to have both acute and chronic ra inbow trout data, 12 were evaluated for the ACR extrapolation Table 4.3.

The estimated fish (aquatic phase amphi bians) chronic NOAEC for methidathion is derived as follows. The (met hidathion) rainbow trout LC 50 used for the ACR calculation is 10 ppb ai. The largest acute-to-chroni c ratio from the organophosphates is 140 for Dichlorvos. This ratio is used to ca lculate the final NOAEC for methidathion.

ACR ratio for Dichlorvos: 0.75 ppm (acute LC 50 )/0.0052 ppm (chronic NOAEC) = 140

Estimated NOAEC for methidathion = LC 50 = 10 ppb = 140 NOAEC est. NOAEC

Estimated Trout NOAEC for methidathion = 10/140 = 0.07 ppb ai

The table below (4.3) shows the inputs for the organophosphates that were considered for the m ethidathion ACR.

Acute to Chronic Table for Organophosphates

Table 4.3. Methidathion Acute to Chro nic Ratio for Rainbow Trout NOAEC

Chemical 96-hr LC
50 (ppm ai) a MRIDs NOAEC (ppm ai) a MRIDs ACR a Methidathion NOAEC (ppb ai) a Azinphos methyl 0.0088 03125193 0.00029 00145592 30 0.33 Coumaphos 0.89 40098001 0.012 43066301 76 0.13 Dichlorvos 0.75 43284702 0.0052 43788001 140 0.07 Dimethoate 7.5 TN 1069 b 0.43 43106303 17 0.59 Disulfoton 1.9 40098001 0.22 41935801 8.4 1.2 Fenamiphos 0.07 40799701 0.0038 41064301 18 0.56 Fenitrothion 2.0 40098001 0.046 40891201 43 0.23 Fenthion 0.83 40214201 0.0075 40564102 110 0.09 Fonofos 0.05 00090820 0.0047 40375001 11 0.91 Isofenphos 1.8 00096659 0.15 00126777 12 0.83 Phosmet 0.11 40098001 0.0032 40938701 33 0.30 Terbufos 0.0076 40098001 0.0014 41475801 5.4 1.9

a Rounded to two significant figures
b TN 1069 is test number for EPA’s Animal Biology Lab, McCann, 1977

4.1.1.3 Freshwater Fish: Sublethal Effects and Additional Open Literatur e Information

In the bluegill sunfish acute toxicity st udy (MRID 00011841) used to calculate RQs, it was reported that test organism s in the highest exposure group (1000 μg/L) exhibited slight spastic motions and swam on their sides.

66In the chronic fish early life stag e study for m ethidathion (MRID 00015730 or 45822701), clinical signs of toxicity during the de finitive toxicity test were not provided in the raw data. Total length and wet weight were the most sensitive endpoints. There were statistically significan t reductions detected for bot h endpoints at the highest measured treatment level (12 μg ai/L) rela tive to the pooled control. The NOAEC and LOAEC for both endpoints were 6.3 and 12 μg ai/L, respectively.

There is one additional fish toxicity st udy available in the open literature f or methidathion. The test organism, the common eel ( Anguilla anguilla ), appears to be about 3 orders of magnitude less sensitive than the bluegill sunfish, the surrogate organism used here to assess direct effects to the aquatic-phase CRLF. See Appendix I for more details.

4.1.2 Toxicity to Freshwater Invertebrates

Freshwater aquatic invertebrate toxicity data were used to as sess potential indirect effects of m ethidathion to the CRLF. Effects to fres hwater invertebrates re sulting from exposure to methidathion could indirectly affect the CRLF via reduction in available food items. As discussed in Section 2.5.3, the main food s ource for juvenile aquatic- and terrestrialphase CRLFs is thought to be aquatic inve rtebrates found along the shoreline and on the water surface, including aquatic sowbugs, larval alderf lies and water striders.

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.

4.1.2.1 Freshwater Invertebrates: Acute Exposure Studies

Available data indicate that methidathion is very highly toxic on an acute basis to a surrogate freshwater inv ertebrate species, Daphnia magna ( Appendix J ). A daphnid acute toxicity study is available for meth idathion technical grade active ingredient (TGAI) and for the methidathion formulation 2E (25.2% a.i.). The 48-hour LC 50 for methidathion (TGAI) is 7.2 μg a.i./L, and the LC 50 for methidathion formulation 2E (25.2% a.i.) is 11.9 μg product/L or 3.0 μg a.i./L. The most sensitive endpoint, 48-hour LC 50 of 3.0 μg a.i./L (MRID 42081704), will be used to calculate RQs for indirect effects to the aquatic-phase CRLF. The probit dose-re sponse slope is the default of 4.5 (2–9) for this study because there are le ss than two concentrations at which the percent dead is between 0 and 100.

4.1.2.2 Freshwater Invertebrates: Chronic Exposure Studies

Chronic toxicity data are availabl e for a comm on freshwater zooplankton, Daphnia
magna ( Appendix J ). In a 21-day lifecycle study (MRID 42081707), survivorship was reduced by 97% at 1.1 μg a.i./L; the NOAE C (mortality) was 0.66 μg a.i./L. This endpoint will be used to calculate RQs in this assessment. There were no significant effects of methidathion on reproduc tion or growth in the study.

674.1.2.3 Freshwater Invertebrates: Open Literature Data

There are no freshwater invertebrate toxicity stud ies identified in the open literature for methidathion ( Appendix H ).

4.1.3 Toxicity to Aquatic Plants

There are no aquatic plant toxicity data for methidathion with which to assess the potential for indirect effects to the C RLF vi a effects on habitat, cover, and/or primary productivity or effects to the primary constituent elements (P CEs) relevant to the aquaticphase CRLF.

4.2 Toxicity of Methidathion to Terrestria l Organisms

Table 4.4 summarizes th e most sensitive terrestr ial toxicity endpoints for the CRLF, based on an evaluation of both the submitted studies and the open literature. A brief summary of submitted and open literature data co nsidered relevant to this ecological risk assessment for the CRLF is presented below.

Table 4.4 Terrestrial Toxicity Profile for Methidathion Endpoint Species Toxicity Value Used in Risk Assessment MRID Study Classification Acute Direct Toxicity to Terrestrial-Phase CRLF (LD 50 ) Mallard duck Anas platyrhynchos LD 50 = 6.7 mg/kg 00159201 Supplemental

Acute Direct Toxicity
to Terrestrial-Phase CRLF (LC 50 ) Bobwhite quail Colinus virginianus LC 50 = 224 ppm 42081701 Acceptable

Chronic Direct Toxicity
to Terrestrial-Phase CRLF Mallard Duck Anas platyrhynchos NOAEC = 10 ppm LOAEC = 30 ppm Number of normal h atchlings/live 3-week embryos 44381602 Acceptable

Indirect Toxicity to Terrest rial-Phase CRLF (via acute toxicity to mammalian prey items) Rat Rattus norvegicus LD 50 = 12 mg/kg 00012714 Acceptable

Indirect Toxicity to Terrest rial-Phase CRLF (via chronic toxicity to mammalian prey items) Rat Rattus norvegicus NOAEL = 5 ppm LOAEL = 25 ppm Decreased mating index, decrease d pup weight, tremors, decreased food consumption during lactation, transient decrease in body weight 40079812 40079813 Acceptable

68Table 4.4 Terrestrial Toxicity Profile for Methidathion Endpoint Species Toxicity Value Used in MRID Risk Assessment Study Classification (males and females)

Indirect Toxicity to Terrest rial-Phase CRLF (via acute toxicity to terrestrial invertebrate prey items) Honey Bee Apis mellifera LD 50 = 0.236 μg a.i./bee 0036935 Acceptable

Seedling Emergence Monocots

Seedling Emergence Dicots

Vegetative Vigor Monocots Indirect Toxicity to Terrestrial- and Aquatic-Phase CRLF (via toxicity to terrestrial plants)

Vegetative Vigor No data available

Dicots

Acute toxicity to terrestrial animals is categ orized using the classi fication system shown in Table 4.5 (U.S. EPA, 2004). Toxicity categories for terrestrial plants have not been defined.

Table 4.5 Categories of Acute Toxicity for Avian and Mammalian Studies

Toxicity Category Oral LD 50 Dietary LC 50 Very highly toxic < 10 mg/kg < 50 ppm Highly toxic 10 - 50 mg/kg 50 - 500 ppm Moderately toxic 51 - 500 mg/kg 501 - 1000 ppm

Slightly toxic 501 - 2000 mg/kg 1001 - 5000 ppm Practically non-toxic > 2000 mg/kg > 5000 ppm

4.2.1 Toxicity to Birds

As specified in the Overview Document, the Agency uses birds as a surrogate for terrestrial-p hase amphibians when amphibian to xicity data are not available (U.S. EPA, 2004). No terrestrial-phase amphibian data are available for methidathion; therefore, acute and chronic avian toxicity data are used to asse ss the potential dire ct effects of methidathion to terrestrial-phase CRLFs.

4.2.1.1 Birds: Acute Exposure (Mortality) Studies

Based on acute oral toxicity studies for severa l b ird species, methidat hion is categorized as moderately to very highly toxic to birds ( Appendix J ). The mallard duck was the most sensitive of the species tested, with an 8-day LD 50 of 6.7 (5.4 – 8.4) mg/kg methidathion (MRID 00159201). This endpoint will be used fo r risk estimation in this assessment. These data do not fit the probit dose-respons e model; thus, a default slope of 4.5 (2-9)

69will be used to calculate the probability of individual effects to the terrestrial-phase CRLF.

Avian subacute dietary studies are av ailable for methidathion (TGAI) and a formulation (40% a.i.) ( Appendix J ). Based on the available information, methidathion and the tested formulation appear to be similarly toxic to birds on a subacute dietary basis. The bobwhite quail (Colinus virginianus) was the most sensitive of the species tested, with an 8-day LC 50 of 224 (177 – 281) ppm a.i. (MRID 42081701). This endpoint will be used for risk estimation in this assessment. The probit dose-response slope was 8.7 (3.5 – 13.8).

4.2.1.2 Birds: Chronic Exposure (Growth, Reproduction) Studies

Several avian chronic toxicity studies are available for m ethidathion. The mallard duck study (MRID 44381602) reported the most sensitive chronic toxicity endpoint, which will be used for risk estimation. In this study, the one-generation reproductive toxicity of methidathion TGAI to 6-month-old mallard ducks was assessed over 140 days. Methidathion TGAI was administered to the birds in the diet at 0, 1, 10, and 30 ppm diet. The number of normal hatchlings/live 3-week embryos was significantly reduced (a ratio of 0.5 versus 0.61 or 18% less than the contro l ratio) at the highest treatment, 30 ppm (LOAEC); the NOAEC for this effect is 10 ppm . A significant increase in the number of eggs cracked was observed when compared to the control group at the 10 ppm dietary level. In addition, a decrease in the number of eggs not cracked/eggs laid was observed at the same dietary level (i.e., NOAEC = 1 ppm); however, this is not a relevant assessment endpoint for the CRLF because endpoints having to do with egg cracking are not relevant to frogs, whose eggs do not have shells. There were no apparent behavioral abnormalities or other treatment-related signs of toxicity on the parental generation.

4.2.1.3 Birds: Sublethal Effects and Additional Open Literature Informatio n

In the mallard duck acute oral toxicity st udy that was used to calculate R Qs (MRID 00159201), toxic symptoms included depression, re duced reaction to ex ternal stimuli, wing droop, convulsions, and salivation. In th e bobwhite quail subacute dietary study used for risk estimation, toxic symptoms including depression, reduced reaction to external stimuli, wing droop, loss of coor dination, lower limb weakness, ruffled appearance, prostrate posture, and loss of righting reflex were observed at and above 178 ppm a.i., and body weight gain and food consum ption were reduced at levels above 316 ppm a.i.

In the mallard duck chronic toxicity st udy (MRID 44381602) used for risk estim ation, methidathion technical was administered to the birds in the diet at 0 (control), 1, 10, and 30 ppm diet. None of the ducks showed sympto ms of toxicity or be havioral abnormalities during the experiment. The number of eggs cr acked was significantly increased in the 10 ppm (150%) and 30 ppm (86%) exposure conc entrations. The number of eggs not

70cracked/eggs laid was also significantly reduced in the 10 ppm and 30 ppm treatment groups. The number of normal hatchlings/liv e 3-week embryos was significantly reduced (5%) at the highest treatmen t, 30 ppm. Body weight of 14-day-old survivors was reduced (6%) at 10 ppm , but not at the higher treatment levels. Brain cholinesterase activity was significantly reduced in drakes at the 10 ppm treatment level during weeks 2, 10, and 20, and at the 30 ppm level duri ng weeks 10 and 20. During week 20, hens showed a trend toward reduced brain cholin esterase activity at the 10 ppm and 30 ppm treatment levels.

Additional avian acute toxicity studies for m ethidathion were identified in the open literature ( Appendices H and I ). However, none of the open lit erature studies resulted in a more sensitive acute toxicity threshold than the 8-day mallard duck LD 50 of 6.7 mg/kg (MRID 00159201).

4.2.2 Toxicity to Mammals

Mammalian toxicity data are used to assess po ten tial indirect effects of methidathion to the terrestrial-phase CRLF. Effects to small mammals resulting from exposure to methidathion could also indirectly affect the CRLF via reduction in available food. As discussed in Section 2.5.3, over 50% of th e prey mass of the CRLF may consist of vertebrates such as mice, frogs, and fish (Hayes and Tennant, 1985).

The study used to expand the in itial area of concern to define the action area exam ined the effects of subchronic methidathion admini stration on vascular wall damage (Yavuz et al., 2005; ECOTOX ref. 80451). Methidathion was administered by gavage for 5 days a week for 4 weeks at a dose level of 5 mg/ kg/day. The levels of malondialdehyde (MDA), a biomarker for oxidative stress, were determined in the vascular tissue. Histopathological examination was performed in the thoracic aortic tissue. The level of MDA was significantly higher, a nd cholinesterase activity was significantly lower in the methidathion group (p < 0.01). Subchronic meth idathion administration led to irregular, prominent breaks and fragmentation of the elastic fibers in the aortic wall. Aortic lesions such as these are similar to the precursor lesion of a human aortic aneurysm. Since only one treatment level was tested, the LOAE C is 5 mg/kg/day, and a NOAEC was not defined. Therefore, a threshold for this eff ect could not be defined, and thus, this study was used to define the action area as the enti re state of California for this assessment.

4.2.2.1 Mammals: Acute Exposure (Mortality) Studies

Available acute toxicity information suggests that m ethidathion is very highly toxic (Category I) to small mammals on an acute oral basis ( Appendices J and K ). The most sensitive endpoint, the acute rat (weanling) LD 50 of 12 mg/kg, will be used to estimate risk to the CRLF via indirect effects to mammals. The probit dose-response slope is assumed to be 4.5 (2–9) for this study becau se individual animal data are not readily available for this study.

4.2.2.2 Mammals: Chronic Exposure (Growth, Reproduction) Studies

71Chronic mammalian reproduction toxicity st udies are available for m ethidathion ( Table 9 ). In a 2-generation reproduction study in rats (MRID 40079812, -13), rats were treated with 0 (control), 5, 25, or 50 ppm methidat hion in the diet. The parental systemic NOAEC was 5 ppm and the LOAEC was 25 ppm, based on tremors and decreased food consumption during lactation, a nd decreased ovarian weight. In addition, there was also a slight decrease in body weight early in the F1 growth phase at 50 ppm. The reproductive NOAEC was 5 ppm and the LOAEC was 25 ppm based on a decreased mating index and a generalized indication of pup unthriftyne ss while nursing (e.g., decreased pup weight and an increased incidence of hypothermia with an appearance of starvation). In addition, there was an increase in s tillbirths and decreased pup su rvival at birth and during lactation at the 50 ppm treatment level. An NOAEL of 5 ppm will be used for risk estimation in this assessment.

4.2.3 Toxicity to Terrestrial Invertebrates

Terrestrial invertebrate toxici ty data are used to assess pot ential ind irect effects of methidathion to the terrestrial-phase CRLF. Effects to terrestrial invertebrates resulting from exposure to methidathion could also in directly affect the CRLF via reduction in available food.

4.2.3.1 Terrestrial Invertebrates: Acut e Exposure (Mortality) Studies

Methidathion is classified as very highl y toxic to bees, with an acute contact LD 50 of 0.236 μg/bee or 1.84 ppm (MRID 00036935). This endpoint will be used to quantitatively assess the risk to the CRLF via indirect effects to terrestrial invertebrates. The probit dose-response slope from this study was 9.06.

In addition, a residual toxici ty study indicates that the RT 25 (i.e., the residual time to kill 25% of the tested population) is greater than 3 days when methidathion (Supracide 2E, 25.2% a.i.) is applied at a rate of 5 lbs a. i./A (MRID 42081708). That is, in addition to very high acute contact toxici ty, field weathered spray resi dues of methidathion can result in significant honey bee mortality for more than several days.

4.2.3.2 Terrestrial Invertebrates: Open Literature Studies

There are several terrestrial invertebrate toxici ty s tudies available in the open literature ( Appendices H and I ). However, none of these studies identified a more sensitive endpoint than the submitted honey bee toxicity study that determined an acute contact LD50 of 0.236 μg/bee or 1.84 ppm (MRID 00036935).

4.2.4 Toxicity to Terrestrial Plants

Terrestrial plant toxicity data are used to evaluate the potential for methidathion to affect riparian zone and upland vegetation within th e action area for the CRLF. Impacts to riparian and upland (i.e., gra ssland, woodland) vegetation coul d result in indirect effects

72to both aquatic- and terrestri al-phase CRLFs, as well as modification to designated critical habitat PCEs via increased sedi mentation, alteration in water quality, and reduction in of upland and riparian habitat that provides shelter, foraging, predator avoidance and dispersal for j uvenile and adult CRLFs.

There are no registrant-submitted terrestrial plan t toxicity data for methidathion with which to assess the potential for indirect effects to the aquatic- and terrestrial-phase CRLF via effects to riparian vegetation or e ffects to the primary constituent elements (PCEs) relevant to the aquatic- and terrest rial-phase CRLF. However, there is limited evidence in the open literature that methid athion has the potentia l to elicit phototoxic effects: Godfrey and Holtzer (1992; Ecotox ref. 64451) re ported that methidathion significantly affected corn photosynthesis when applied at 0.5 lbs a.i. /A, a rate that is lower than many of the currently registered rates. In addi tion, potential phytotoxic effects have been highlighted on methidathion la bels; e.g., EPA SLN N o. TX-050003 warns that methidathion application may result in phytotox ic effects, such as spotting, reddening, or chlorosis of the leaves, in certain sorghum va rieties. In the absence of vegetative vigor and seedling emergence toxicity data, the pot ential risk to the CRLF via indirect effects to terrestrial plants is described in a qualitative manner (Section 5.2).

4.3 Use of Probit Slope Response Relati onship to Provide Information on the Endangered Species Levels of Concern

The Agency uses the probit dose response rela tionship as a tool for providing additional inf ormation on the potential for acute direct effects to individual listed species and aquatic animals that may indirectly affect the listed species of concern (U.S. EPA, 2004). As part of the risk characterization, an inte rpretation of acute RQ for listed species is discussed. This interpretation is presented in terms of the chance of an individual event (i.e., mortality or immobilization) should expos ure at the EEC actually occur for a species with sensitivity to methidathi on on par with the acute toxici ty endpoint selected for RQ calculation. To accomplish this interpretati on, 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 relationshi p. In addition to a single effects probability es timate based on the mean, upper and lower estimates of the effects probability are also pr ovided to account for variance in the slope, if available.

Individual effect probabilitie s are calculated based on an Ex cel spreadsheet tool IECV1.1 (Individual Effect Chance Model V ersion 1.1) developed by the U.S. EPA, OPP, Environmental Fate and Effects Division (J une 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 spread sheet. In addition, the acute RQ is entered as the desired threshold.

4.4 Incident Database Review

73A review of the EIIS database for ecol ogical incidents involving methidathion was completed on 08 September 2008. A total of two aquatic and six terrest rial incidents are reported, all of which occurred in California. The reported aq uatic incidents occurred in 1976 and 2002; all of the reported terrestrial incidents occurred in 1994 and 1995. A brief description of each of the reported incide nts is provided below. A complete list of the incidents involving meth idathion is included as Appendix L

.

4.4.1 Terrestrial Incidents

On January 18, 1994, one red-tailed hawk wa s found dead in Colusa County, California following application of m ethidathion to an unknown treatment site. No residue analysis was completed. The certainty index for this incident (I00335 1-003) is probable.

Following application of methidathion to an unknown treatm ent site, a red-tailed hawk was found dead on January 27, 1994, in Stan islaus County, California. Blood and footwash sample were collected and sent to the PIU (Department of Fish and Game Pesticides Investigation Unit (California)) for examination. Blood plasma cholinesterase and acetlycholinesterase levels were within th e normal range. The results of the footwash showed detections of methidathion at 2.7 ppb. In addition, organophosphates including chlorpyrifos and diazinon were also detect ed in the footwash sample at respective concentrations of 0.2 ppb and 4.1 ppb. It is lik ely that the hawk was exposed by perching on substrates which had recently been coated w ith the detected pesticides. The certainty index for this incident (I005042-012) is probable.

On February 3, 1994, a red-tailed hawk was foun d entangled in a fence near an alm ond orchard in Merced County. The hawk was handed over to the Stanislaus Wildlife Care Center. Upon admission to the care center, bl ood and footwash samples were collected. The hawk was released following recovery from the injuries. Samples were sent to the PIU for examination. Plasma cholinesterase and acetylcholinesterase levels were found significantly below the normal range. Footwash analysis results show that methidathion was detected at a concentration of 2.7 ppb. Ch lorpyrifos and diazinon were also detected in the footwash sample at respective c oncentrations of 0.7 ppb and 0.4 ppb. It appears that the hawk was affected due to exposur e via perching on substrates, such as tree branches, which had recently been treated with these organophosphate pesticides. The certainty index for this incident (I05042-010) is highly probable.

A red-tailed hawk was recovered from an orchard on December 23, 1994 and taken to the Stanislaus Wildlife Care Center. The bird died one day later. A blood sample and the carcass were sent to the PIU for examination. The plasma cholinesterase level was low and the brain cholinesterase level was severely depressed. Feathers and footskin samples were analyzed. Methidathion was detected at a concentration of 0.7 pp m in the footskin. In addition, chloropyrifos and di azinon were detected in both the feathers and footskin at concentrations ranging from 0.02 to 0.08 ppb. It is likely that all three organophosphates contributed to the death of th is bird. The certainty index for this incident (I005042-015) is possible.

74Following spraying of plum trees in Madera County, California with methidathion on Feb. 4, 1995 and spraying of a nearby location on the 5 th and 6th, pollination hives were placed in the orchard on those same da tes. Heavy fog was present the 4 th and 5 th , which limited foraging activity of the bees. Dead bees (number not specified) were found beginning Feb. 8 and continuing until Feb. 13. Residue analysis of the dead bees was completed, showing the presence of 2.6 ppm methidathion and 0.02 ppm diazinon. The Madera County authorities did not indicate a ny fault or liability, and attributed the bee kill to poor weather and too early an introduction of the hives. The certainty index for this incident (I001920-001) is possible.

The most recent terrestrial incident invol ving m ethidathion was reported on March 15, 1995. Following application of methidathion to an agricultural ar ea, an unknown number of bees were killed in an unknown county in California. The incident was reported as accidental under the misuse category. No further information was provided in the incident report. No residue analysis was completed, and the certainty index for this incident (I005895-512) is probable.

4.4.2 Aquatic Incidents

On May 25, 1976, approximately 3,000 fish of unknown species were killed following an aerial application of m ethidathion to an agricultural area in Sacramento County, California. Methidathion had been aerially sprayed on a nearby seed clover field, and irrigation water from the field had entered La guna Creek in the area directly upstream of the fish kill. The incident was attributed to accidental misuse of methidathion. Samples of the water collected from the field drain si x days after the material was applied to the field showed methidathion concentrations of 60 ppb. It is presumed that the concentration of methidathion would have been much higher if the samples had been collected immediately following ae rial application of the fiel d. No fish tissue analysis was completed. The certainty index for this incident (B0000-218-10) is highly probable.

5. Risk Characterization

Risk characterization is the integration of the exposure and ef fects characterizations. Risk characterization is used to determine the potential for direct and/or indirect effects to the CRLF or for modification to its designated critical habita t from the use of methidathion in CA. The risk characterizat ion provides an estima tion (Section 5.1) and a description (Section 5.2) of the likelihood of adverse effect s; articulates risk assessment assumptions, limitations, and uncertainties; and synthesizes an overall conclusion regarding the likelihood of adverse effects to the CRLF or its designated critical habitat (i.e., “no effect,” “likely to a dversely affect,” or “may affect , but not likely to adversely affect”).

5.1 Risk Estimation

Risk is estimated by calculating the ratio of e xposure to toxicity. Th is ratio is the risk quotient (R Q), which is then compared to pr e-established acute a nd chronic levels of

75concern (LOCs) for each category evaluated ( Appendix E ). For acute exposures to the CRLF and its animal prey in aquatic habitats, as well as terrestrial invertebrates, the LOC is 0.05. For acute exposures to the CRLF and mammals, the LOC is 0.1. The LOC for chronic exposures to CRLF and its prey, as well as acute exposures to plants is 1.0.

Risk to the aquatic-phase CRLF is estimated by calculating the ratio of exposure to toxicity using 1-in-10 year EECs based on the label-recommended methidathion usage scenarios summarized in Table 3.2 and the appropriate aquatic toxicity endpoint from Table 4.1 . Risks to the terrestrial-phase CRLF and its prey ( e.g . terrestrial insects, small mammals and terrestrial-phase frogs) are es timated based on exposures resulting from applications of methidathion ( Tables 3.5 through 3.6 ) and the appropriate toxicity endpoint from Table 4.3 . Due to lack of toxicity da ta, exposures are not derived for terrestrial plants.

The minor degradate methidathion oxon is of toxicolog ical concern, but because there are no toxicity data, this degradate cannot be in cluded directly in cal culations of RQs. Potential risk from methidathion oxon is characterized in the risk description ( Section 5.2 ).

5.1.1 Exposures in the Aquatic Habitat

5.1.1.1 Direct Effects to Aquatic-Phase CRLF

Direct effects acute RQs for the a quatic-phase CRLF are presented in Table 5.1 . Based on 1-in-10 year peak aquatic EECs from th e PRZM/EXAMS model and the lowest acute 96-hour LC 50 for freshwater fish (surrogate for the aquatic-phase CRLF), acute RQs for the aquatic-phase CRLF exceed the listed sp ecies LOC (0.05) for all of the assessed methidathion uses. Acute RQs for methidathion range from 2.1 for the alfalfa scenario to 52.5 for the nursery scenario. As a note, for the spatial analyses sect ions, the lowest and highest EECs were estimated following a single application. The lowest acute RQ for a single application is calculat ed to be 0.20 for the lowest use scenario, on mangoes. Therefore, even after a single applicati on, the acute listed sp ecies LOC would be exceeded for all of the methidathion use scenarios.

76Table 5.1 Summary of Acute Direct E ffect RQs for the Aquatic-phase CRLF a

Scenario Crops Represented Peak 1-in-10 Year EEC

( μ g/L) b Acute RQ c Probability of Individual Effect at LOC d Probability of Individual Effect at RQ d

Alfalfa Alfalfa, Clover, Tim othy 4.6 2.1 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1.2

Almond Almond, Walnut 49.3 22.4 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

Citrus Calemondin, Citron, Citru s, Grapefruit, Kumquat, Lemon, Lime, Mango, Pummelo, Tangelo, Tangerine 18.3 8.3 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

Corn Sunflower 20.7 9.4 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

Cotton Cotton 13.0 5.9 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

Grapes Kiwi 6.6 3.0 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1.1

Tree Fruit Apple, Apricot, Cherry, Nectarine, Peach, Pea r, Plum, Prune 15.6 7.1 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

Olive Olive 15.2 6.9 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

Row Crop Artichoke 16.0 7.3 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

Wheat Safflower 13.6 6.2 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

Nursery Nursery 115.6 52.5 ~1 in 12,400 (~1 in 10,300,000 to ~1 in 149) ~1 in 1

a Based on bluegill sunfish ( Lepomis macrochirus ) acute 96-hour LC 50 = 2.2 μg/L
b See Table 3.3

. c Acute RQs that exceed the acute endangered species LOC of 0.05 are in bold

. d The effect probability was calculated based on a probit dose-re sponse slope of 2.9 (1.9 – 4.0) for the bluegill sunfish acute toxicity study.
Direct chronic risk estimates for the aqua tic-phase CRLF are based on the 60-day average EECs from the PRZM/EXAMS model and the lowest chronic NOAEC for freshwater fish (surrogate for the aquatic-phase CRL F). Using the estimated chronic NOAEC of 0.07 ppb based on an ACR of 140 and the acute LC 50 value of 10 ppb, the chronic RQs exceed the LOC (1.0) for all of the assessed methidathion uses ( Table 5.2 ). Based on

77acute and chronic LOC exceedances, methidathion may affect the aquatic-phase of the CRLF.

Table 5.2 Summary of Chronic Direct Ef fect RQs for the Aquatic-phase CRLF a
Scenario Crops Represented 60-day EEC ( μ g/L) b Chronic RQ c

Alfalfa Alfalfa, Cl ov er, Timothy 2.5 35.7 Almond Almond, Walnut 26.8 383 Citrus Calemondin, Citron, Citrus, Grapefruit, Kum quat, Lemon, Lime, Mango, Pummelo, Tangelo, Tangerine 9.0 129

Corn Sunflower 10.9 156 Cotton Cotton 6.4 91.4 Grapes Kiwi 3.2 45.7 Tree Fruit Apple, Apricot, Che rry, Necta rine, Peach, Pear, Plum, Prune 5.0 71.4

Olive Olive 7.6 109 Row Crop Artichoke 8.7 124 Wheat Safflower 6.6 94.3 Nursery Nursery 54.3 776

a Based on estimated chronic NOAEC of 0.07 μg/L from ACR ratio (see Section 4.1.1.2).
b See Table 3.3

. c Chronic RQs that exceed the chronic LOC of 1.0 are in bold

.

5.1.1.2 Indirect Effects to Aquatic-Ph ase CRLF via Reduction in Prey (non-vascular aquatic plants, aquati c invertebrates, fish, and frogs)

Non-vascular Aquatic Plants

Indirect effects of methidat hion to the aquatic-phase CRL F (tadpoles) via reduction in non-vascular aquatic plants in its d iet cannot be quantitatively estimat ed because there are no aquatic plant toxicity da ta available for methidathi on. For a qualitative risk description, see Section 5.2.2.1.

Aquatic Invertebrates

Indirect acute effects to the aquatic-phase CRLF via effects to prey (invertebrates) in aquatic habitats are based on peak 1-in-10 year E ECs from the PRZM/EXAMS model and the lowest 48-hour LC 50 for freshwater invertebrates. These acute RQs for aquatic invertebrates range from 1.5 to 38.5, and thus exceed the acute risk LOC for non-listed species (0.5) ( Table 5.3 ).

78Table 5.3 Summary of Acute RQs Used to Es timate Indirect Effe cts to the CRLF via Direct Effects on Aquatic Invertebrates as Dietary Food Items

Scenario Crops Represented Peak 1-in-10 Year EEC ( μ g/L) b Indirect Effects Acute RQ c % Expected Effect on Prey Population at RQ d

Alfalfa Alfalfa, Clover, Tim othy 4.6 1.5 79

Almond Almond, Walnut 49.3 16.4 100

Citrus Calemondin, Citron, Citru s, Grapefruit, Kumquat, Lemon, Lime, Mango, Pummelo, Tangelo, Tangerine 18.3 6.1 100

Corn Sunflower 20.7 6.9 100 Cotton Cotton 13.0 4.3 100 Grapes Kiwi 6.6 2.2 94

Tree Fruit Apple, Apricot, Cherry, Nectarine , Peach, Pear, Plum, Prune 15.6 5.2 100

Olive Olive 15.2 5.1 100 Row Crop Artichoke 16.0 5.3 100 Wheat Safflower 13.6 4.5 100 Nursery Nursery 115.6 38.5 100

a Based on water flea ( Daphnia magna ) acute 48-hour LC 50 = 3.0 μg/L
b See Table 3.3

. c Acute RQs that exceed the acute LOC for nonlisted species of 0.5 are in bold

. d The acute daphnid toxicity study data do not fit the probit model; therefore, the effect probability was calculated based on a default slope assumption of 4.5 with upper and lower 95% confidence intervals of 2 and 9 (Urban and Cook, 1986).

Risk estimates for indirect effects to the CRL F via chronic effects to aquatic inverteb rates are based on 21-day average EECs and th e lowest chronic NOAEC for freshwater invertebrates. Chronic RQs for freshwater invertebrates range from 3.4 to 128.4, and thus exceed the LOC (1.0) for all of the assessed methidathion uses ( Table 5.4 ). Based on acute and chronic LOC exceedences for all of the assessed uses, methidathion may indirectly affect the CRLF via reduction in freshwater invertebrates prey items.

79Table 5.4 Summary of Chronic RQs Used to Es timate Indirect Effects to the CRLF via Direct Effects on Aquatic Invertebrates as Dietary Food Items

Scenario Crops Represented 21-day EEC (μg/L) b Indirect Effects Chronic RQ c Alfalfa Alfalfa, Cl ov er, Timothy 3.4 5.2 Almond Almond, Walnut 40.2 60.9 Citrus Calemondin, Citron, Citrus, Grapefruit, Kum quat, Lemon, Lime, Mango, Pummelo, Tangelo, Tangerine 13.6 20.6

Corn Sunflower 16.2 24.5 Cotton Cotton 9.3 14.1 Grapes Kiwi 5.0 7.6 Tree Fruit Apple, Apricot, Che rry, Necta rine, Peach, Pear, Plum, Prune 9.2 13.9

Olive Olive 11.7 17.7 Row Crop Artichoke 12.1 18.3 Wheat Safflower 10.4 15.8 Nursery Nursery 84.8 128.4

a Based on water flea ( Daphnia magna ) chronic NOAEC = 0.66 μg/L
b See Table 3.3

. c Chronic RQs that exceed the chronic LOC of 1.0 are in bold

.

Fish and Frogs

Fish and frogs also represent potential prey item s of adult aquatic-phase CRLFs. RQs associated with acute and chronic direct toxicity to the CRLF ( Tables 5.1 - 5.2 ) are used to assess potential indirect effects to the CRLF based on a reduction in freshwater fish and frogs as food items. Since the acute a nd chronic RQs exceed the LOC, methidathion may indirectly affect the CRLF via reduction in freshwater fish and frogs as food items.

5.1.1.3 Indirect Effects to CRLF via Reduction in Habitat and/or Primary Productivity (Freshw ater Aquatic Plants)

Indirect effects to the CRLF vi a direct toxicity to aquatic plants cannot be quantitatively estim ated because there are no aquatic plant toxicity data available for methidathion. For a qualitative risk description, see Section 5.2.3.1.

5.1.2 Exposures in the Terrestrial Habitat

5.1.2.1 Direct Effects to Terrestrial-phase CRLF

As previously discussed in Section 3.3, potenti al direct effects to terrestrial-phase CRLFs are based on foliar applications of m ethidat hion. Potential direct acute effects to the terrestrial-phase CRLF are derived by c onsidering dose- and dietary-based EECs modeled in T-REX for a small bird ( 20 g) consuming small invertebrates ( Table 3.5 ) and acute oral and subacute dietary toxicity e ndpoints for avian species . Potential direct chronic effects of methidathi on to the terrestrial-phase CRL F are derived by considering

80dietary-based exposures mode led in T-REX for a small bird (20g) consuming small invertebrates. Chronic effects are estimated using the lowest available toxicity data for birds. EECs are divided by toxi city values to estimate chronic dietary-based RQs. Acute dose-based, acute dietary-based, and chronic RQ s exceed the LOCs for all of the assessed methidathion uses ( Table 5.5-5.7 ). As a result, methidathion may affect the terrestrialphase of the CRLF.

Table 5.5. Summary of Direct Effect Ac ute Dose-Based RQs for the Terrestrialphase CRLF for Spray Applications of Methidathion
Broadleaf Plants/

Small Insects Use App. Rate (lb ai/A) Number of Apps. App. Interval (days) Probability of Individual Effect at LOC bAcute DoseBased RQ a Probability of Individual Effect at RQ b

Artichoke 1 lb a.i./acre 8 apps 14 days 57.39 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Citrus 5 lb a.i./acre 2 apps 45 days 222.94 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Clover 1 lb a.i./acre 2 apps. 7 days 65.39 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Cotton 1 lb a.i./acre 4 apps 5 days 94.95 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Kiwi 2 lb a.i./acre 1 app NA 88.39 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Mango 0.25 lb a.i./acre 5 apps. 21 days 12.42 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Nursery 10 lb a.i./A 1 app NA 441.97 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Safflower, Sunflower 0.5 lb a.i./acre 3 apps 7 days 37.77 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Tree Fruit, Olives 3 lb a.i./acre 1 app NA 132.59 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

Walnut 2 lb a.i./acre 3 apps. 2 days 218.11 ~1 in 294,000 (~1 in 8.86E+18

to ~1 in 44) ~1 in 1

a Based on mallard duck acute oral LD 50 = 6.7 mg/kg
b The acute data do not fit the probit model; therefore, th e effect probability was calculated based on a default slope assumption of 4.5 with upper and lower 95% conf idence intervals of 2 and 9 (Urban and Cook, 1986).

c Acute RQs that exceed the acute endangered species LOC of 0.1 are in bold.

81Table 5.6. Summary of Direct Effect Acute Dietary-Based RQs for the Terrestrial-phase CRLF for Spray Applications of Methidathion
Broadleaf Plants/

Small Insects Use App. Rate (lb ai/A) Number of Apps. Acute Dietary-Based RQ a Probability of Individual Effect at LOC b App. Interval (days) Probability of Individual Effect at RQ b

Artichoke 1 lb a.i./acre 8 apps 14 days 0.78 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 5 (~1 in 14 to ~1 in 2)

Citrus 5 lb a.i./acre 2 apps 45 days 3.04 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 1

Clover 1 lb a.i./acre 2 apps. 7 days 0.89 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 3 (~1 in 4 to ~1 in 2)

Cotton 1 lb a.i./acre 4 apps 5 days 1.29 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 1

Kiwi 2 lb a.i./acre 1 app NA 1.21 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 1

Mango 0.25 lb a.i./acre 5 apps. 21 days 0.17 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 9.28E+10 (~1 in 8.3E+25
to ~1 in 2.83E+2)

Nursery 10 lb a.i./A 1 app NA 6.03 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 1

Safflower, Sunflower 0.5 lb a.i./acre 3 apps 7 days 0.52 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 148 (~1 in 22,500

to ~1 in 6)

Tree Fruit, Olives 3 lb a.i./acre 1 app NA 1.81 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 1

Walnut 2 lb a.i./acre 3 apps. 2 days 2.97 ~1 in 6.03E+17 (~1 in 7.85E+42
to ~1 in 4,300) ~1 in 1

a Based on bobwhite quail acute dietary LC 50 = 224 ppm
b The effect probability was calculated using a probit dose-response slope of 8.7 (3.5 – 13.8) from the bobwhite quail study.

c Acute RQs that exceed the acute endangered species LOC of 0.1 are in bold.

82Table 5.7. Summary of Direct Effect Chronic RQs for the Terrestrial-phase CRLF for Spray Applications of Methidathion
Broadleaf Plants/

Small Insects Use App. Rate (lb ai/A) Number of Apps. App. Interval (days) Chronic RQ a

Artichoke 1 lb a.i./acre 8 apps 14 days 17.53 b

Citrus 5 lb a.i./acre 2 apps 45 days 68.10

Clover 1 lb a.i./acre 2 apps. 7 days 19.97

Cotton 1 lb a.i./acre 4 apps 5 days 29.00

Kiwi 2 lb a.i./acre 1 app NA 27.00

Nursery 10 lb a.i./A 1 app NA 135.00

Mango 0.25 lb a.i./acre 5 apps. 21 days 3.79

Safflower, Sunflower 0.5 lb a.i./acre 3 apps 7 days 11.54

Tree Fruit, Olives 3 lb a.i./acre 1 app NA 40.50

Walnut 2 lb a.i./acre 3 apps. 66.62 2 days

a Based on mallard duc k chronic NOAEC = 10 ppm
b Chronic RQs that exceed the chronic LOC of 1.0 are in bold.

5.1.2.2 Indirect Effects to Terrestrial-Phase CRLF via Reduction in Prey (terres trial invertebrates, mammals, and frogs)

5.1.2.2.1 Terrestrial Invertebrates

In order to assess the risks of methidathion to terrestrial invertebrates, which are considered prey of CRLF in terrestrial habita ts, 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 LD 50 of 0.236 μg/bee by 1 bee/0.128g, which is based on the weight of an adu lt honey bee. EECs (ppm) calculated by T-REX for small and large insects are divided by the calculated toxicity value for terrestrial invertebrates, which is 1.84 ppm ( Table 5.8 ). Based on acute LOC exceedances for all of

83the assessed uses, methidathion may affect the CRLF via reduction in terrestrial invertebrate prey items.

Table 5.8 Summary of RQs For Indirect Ef fects to the Terrestrial-phase CRLF via Direct Effects on Terrestrial Invertebrates as Dietary Food Items

Use App. Rate (lb ai/A) Number of Apps. App. Interval (days) Small Insect

RQ Large Insect

RQ Small Insect % Expected Effect on Prey Population at RQ b Large Insect % Expected Effect on Prey Population at RQ b

Artichoke 1 lb a.i./acre 8 apps 14 days 95 10 100 100

Citrus 5 lb a.i./acre 2 apps 45 days 370 41 100 100

Clover 1 lb a.i./acre 2 apps. 7 days 109 12 100 100

Cotton 1 lb a.i./acre 4 apps 5 days 158 17 100 100

Kiwi 2 lb a.i./acre 1 app NA 147 16 100 100

Mangos 0.25 lb a.i./acre 5 apps 21 days 21 2 100 100

Nursery 10 lb a.i./A 1 app NA 734 82 100 100

Safflower, Sunflower 0.5 lb a.i./acre 3 apps 7 days 63 7 100 100

Tree Fruit, Olives 3 lb a.i./acre 1 app NA 220 24 100 100

Walnut 2 lb a.i./acre 3 apps. 2 days 362 40 100 100

a Based on honey bee LD 50 of 0.236 μg/bee or 1.84 ppm

b The % population was calculated using a probit dose-re sponse slope of 9.06 from the honey bee study.

c Acute RQs that exceed the acute non-listed species LOC of 0.5 are in bold.

5.1.2.2.2 Mammals

Risks associated with ingestion of contaminated small mammals by large terrestrial-phase CRLFs are derived for dietary-based and dos e-based exposures m odeled in T-REX for a small mammal (15g) consuming short grass. Acute and chronic effects are estimated using the most sensitive mamma lian toxicity data. EECs are divided by the toxicity value to estimate acute dose-based RQs as well as chronic dietary- and dose-based RQs. As shown in Tables 5.9-5.10 , the acute and chronic RQs ex ceed the LOC for all of the

84assessed methidathion uses. As a result, methidathion may affect the CRLF via reduction in small mammal prey items.

Table 5.9. Summary of Acute RQs For Indi rect Effects to th e Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary Food Items

Use App. Rate (lb ai/A) Number of Apps. App. Interval (days) Acute Dose-Based RQ a % Expected Effect on Prey Population at RQ b

Artichoke 1 lb a.i./acre 8 apps 14 days 11.27 100

Citrus 5 lb a.i./acre 2 apps 45 days 43.76 100

Clover 1 lb a.i./acre 2 apps. 7 days 12.84 100

Cotton 1 lb a.i./acre 4 apps 5 days 18.64 100

Kiwi 2 lb a.i./acre 1 app NA 17.35 100

Mango 0.25 lb a.i./A 5 apps 21 days 2.44 96

Nursery 10 lb a.i./A 1 app NA 86.76 100

Safflower, Sunflower 0.5 lb a.i./acre 3 apps 7 days 7.41 100

Tree Fruit, Olives 3 lb a.i./acre 1 app NA 26.03 100

Walnut 2 lb a.i./acre 3 apps. 2 days 42.82 100

a Based on rat acute oral LD 50 = 12 mg/kg-bw.
b The effect probability was calculated based on a default slope a ssumption of 4.5 with upper and lower 95% confidence intervals of 2 and 9 (Urban and Cook, 1986).

c Acute RQs that exceed the acute non-listed species LOC of 0.5 are in bold.

85Table 5.10. Summary of Chronic RQs For I ndirect Effects to the Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary Food Items

Use App. Rate (lb ai/A) Number of Apps. App. Interval (days) Chronic Dose-Based RQ a Chronic Dietary-Based RQ b

Artichoke 1 lb a.i./acre 8 apps 14 days 540.74 62.33

Citrus 5 lb a.i./acre 2 apps 45 days 2100.70 242.13

Clover 1 lb a.i./acre 2 apps. 7 days 616.11 71.01

Cotton 1 lb a.i./acre 4 apps 5 days 894.65 103.12

Kiwi 2 lb a.i./acre 1 app NA 832.90 96.00

Mango 0.25 lb a.i./A 5 apps 21 days 117.00 13.49

Nursery 10 lb a.i./A 1 app NA 4164.5 480.00

Safflower, Sunflower 0.5 lb a.i./acre 3 apps 7 days 355.92 41.02

Tree Fruit, Olives 3 lb a.i./acre 1 app NA 1249.35 144.00

Walnut 2 lb a.i./acre 3 apps. 2 days 2055.21 236.88

a Based on rat NOAEL = 0.25 mg/kg-bw.

b Based on rat NOAEC = 5 mg/kg-diet.

c Chronic RQs that exceed the chronic LOC of 1 are in bold.

5.1.2.2.3 Frogs

An additional prey item of the adult terrestrial -ph ase CRLF is other species of frogs. In order to assess risks to these organisms, di etary-based and dose-based exposures modeled in T-REX for a small bird (20g) consuming small invertebrates are used. See Section 5.1.2.1 and associated tables ( Tables 5.3 – 5.5 ) for results. Acute and chronic RQs exceed the LOCs for all of the assessed methidathion uses. As a result, methidathion may affect the CRLF via reduction in frogs as prey items.

865.1.2.3 Indirect Effects to CRLF via Re duction in Terrestrial Plant Community (Riparian and Upland Habitat)

Indirect effects to the CRLF via reducti on in terrestrial plan t community cannot be quantitatively estim ated because there are no vegetative vigor or seedling emergence plant toxicity data available for methidat hion. For a qualitative ri sk description, see Section 5.2.3.2.

5.1.3 Primary Constituent Elements of Designated C ritical Habitat

For methidathion use, the assessment endpoint s for designated cri tical habitat PCEs involve a reduction and/or modi fication of food sources neces sary for normal growth and viability of aquatic-phase CRLFs, and/or a reduction and/or modification of food sources for terrestrial-phase juveniles and adults. Because these endpoints are also being assessed relative to the potential for indirect effects to aquatic- and terrestrial-phase CRLF, the effects determinations for indirect effects from the potential loss of food items are used as the basis of the effects determin ation for potential modi fication to designated critical habitat.

5.1.3.1 Aquatic-Phase (Aquatic Breed ing Habitat an d Aquatic NonBreeding Habitat)

Three of the four assessment endpoints for the aquatic-phase prim ary constituent elements (PCEs) of designated critical ha bitat for the CRLF are related to potential effects to aquatic and/or terrestrial plants:

• Alteration of channel/pond m orphology or ge ometry and/or increase in sediment deposition within the stream channel or pond: aquatic ha bitat (including riparian vegetation) provides for shelter, fora ging, predator avoidance, and aquatic dispersal for juvenile and adult CRLFs.

• Altera tion 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 m odification of aquatic-b ased food sources for pre-metamorphs ( e.g., algae).

Risk estimations for potential effects to a quatic and/or terrestrial plants were not conducted because no toxicity data are available for either aquatic or terrestrial plants. Therefore, it cannot be estimated whether or not methidathion is likel y to affect aquaticphase PCEs of designated habitat related to effects on aquatic and/or terrestrial plants. Risks to aquatic and terrestr ial plants will be discussed qualitatively in sections 5.2.2.1, 5.2.3.2 and 5.2.3.2.

The remaining aquatic-phase PCE is “altera tion o f other chemical characteristics necessary for normal growth and viability of CRLFs and their food source.” To assess the impact of methidathion on this PCE, acute and chronic freshwater fish and

87invertebrate toxicity endpoints, as well e ndpoints for aquatic non-vascular plants, are used as measures of effects. RQs for thes e endpoints were calculated in Sections 5.1.1.1 and 5.1.1.2. Based on exceedances of the liste d and non-listed species LOCs following both acute and chronic exposure for freshwater fish and invertebrates, methidathion is likely to affect aquatic-phase PC Es of designated habitat relate d to effects of alteration of other chemical characteristics necessary fo r normal growth and viability of CRLFs and their food source. As stated previously, ther e are no aquatic plant t oxicity data available for methidathion. Therefore, effects to this aquatic-phase PCE based on effects to aquatic non-vascular plants will be discussed qualita tively in Section 5.2.2.1.

5.1.3.2 Terrestrial-Phase (Upland Habi ta t and Dispersal Habitat)

Two of the four assessment endpoints for the te rrestrial-phase PCEs of designated critical habitat for the CRLF are related to poten tial effects to terrestrial plants:

• Elimination and/or disturbance of upland ha bitat; ability of hab itat to support food source of CRLFs: Upland areas within 200 ft of the edge of the riparian vegetation or dripline surroundi ng aquatic and riparian ha bitat that are comprised of grasslands, woodlands, and/or wetland/r iparian plant species that provides the CRLF shelter, forage, and predator avoidance

• Elim ination and/or disturbance of dispersa l habitat: Upland or riparian dispersal habitat within designated un its and between occupied locations within 0.7 mi of each other that allow for movement be tween sites including both natural and altered sites which do not cont ain barriers to dispersal

The risk estimation for terrestrial-phase PCEs of designated habitat related to potential effects on terres trial plants cannot be qua ntitatively addressed because there are no vegetative vigor or seedling emergence plant toxicity data available for methidathion. The risk will be discussed qualitatively in Section 5.2.3.2.

The third terrestrial-phase PCE is “reducti on and/or m odification of food sources for terrestrial phase juveniles and adults.” To assess the impact of methidation on this PCE, acute and chronic toxicity e ndpoints for birds, mammals, and terrestrial invertebrates are used as measures of effects. RQs for thes e endpoints were calculated in Sections 5.1.2.1 and 5.1.2.2. Acute and chronic LOCs for listed and non-listed species were exceeded for all uses for birds and mammals and acute LOCs for listed and non-listed terrestrial invertebrates were also exceeded for all uses. Therefore, methidiathion is likely to affect the third terrestrial-phase PCE.

The fourth terrestrial-phase PC is based on alteration of chemi cal characte ristics necessary for normal growth and viability of juvenile and adult CRLFs and their food source. Direct acute and chronic RQs for terrestrial-phase CRLFs are presented in Section 5.1.2.1. Acute and/or chronic LOCs for listed and non- listed species were exceeded for freshwater fish and inverteb rates, birds, mammals and terrestrial invertebrates. No data are available for eith er aquatic or terrestrial plants. However, based on the results with aquatic and terrestria l animals, methidathion is likely to affect the fourth terrestrial - phase PCE.

885.1.4 Spatial Extent of Potential Effects

Since this screening level risk assessm ent defines taxa that are predicted to be exposed through runoff and drift to methidathion at conc entrations above the Agency’s Levels of Concern (LOC), analysis of the potential spat ial extent of effects requires expansion of the area from the treated site to include a ll areas potentially impacted by this federal action. Two methods are used to define thes e areas: (1) the spra y drift assessment for determining the extent of terr estrial and aquatic habitats potentially affected through drift alone; and (2) the down stream dilution asse ssment for determining the extent of the affected lotic aquatic habitats (flowing water). This analysis is described briefly below and in more detail in Appendix D

. An LAA effects determination applies to t hos e areas where it is expected that the pesticide’s use will directly or indirectly affect the CRLF or its designated critical habitat. To determine this area, the footprint of me thidathion’s use pattern is identified, using corresponding land cover data. The spatial ex tent of the effects determ ination also includes areas beyond the initial area of concern that may be impacted by runoff and/or spray drift. The identified direct and indir ect effects and modification to critical habitat are anticipated to occur only for those curr ently occupied core habitat areas, CNDDB occurrence sections and designated critical habitat for the CRLF that overlap with the initial area of concern plus greater than 1000 feet from its boundary. It is assumed that non-flowing waterbodies (or potential CRLF hab itat) are included within this area.

In addition to the spray drift buffer, the resu lts o f the downstream dilution extent analysis result in a distance of 285 kilometers which represents the maximum continuous distance of downstream dilution from the edge of th e initial area of concern. If any of these streams reaches flow into CRLF habitat, there is potential to affect either the CRLF or modify its habitat. These lotic aquatic habi tats within the CRLF core areas and critical habitats potentially contain concentrations of methidathion sufficient to result in LAA determination or modificati on of critical habitat.

The determination of the buffer distance and downstream dilution for spatial extent of the effects determ ination is described below.

5.1.4.1 Spray Drift

In order to determine terrestrial and aquati c habitats of concern due to m ethidathion exposures through spray drift, it is nece ssary to estimate the distance that spray applications can drift from the treated area and still be present at concentrations that exceed levels of concern. A quantitative analysis of spray drift distances was completed using AgDrift (v. 2.01).

Spatial analysis of spray drift effects is lim ited to consideration of a single application because, due to variable wind conditions, m ultiple applications are not likely to impact the same location each time. Spray drift distances depend on both application rate and

89method, and so, in order to understand the ra nge of possible impacts, modeling was done for the uses with the highest single applic ation rates for each me thod, which include tree fruit and nuts treated by aeria l spray, nursery stock trea ted by ground spray, and citrus treated by spray that is presumed to be ai rblast. Use on mangos was modeled as well to represent the lowe r boundary of potential effects.

Methidathion labels have specific application requirements in order to reduce potential spray drift, including restrictions on wind spee d, release height and dr oplet size. AgDrift inputs are based on these requirements, as presented in Table 5.11 . For inputs not specified on the labels, default values are use d. When Tier I models were used, it is because no higher tier mode ls are available.

Table 5.11. Input parameters for simulation of methidathion in spray drift using AgDrift (v. 2.01) Parameter Description Tree Fruit / Nuts Nursery Stock Citrus Mangos

Single Application Rate 3 lb a.i./A 10 lb a.i./A 5 lb a.i./A 0.5 lb a.i./A Application method Aerial Ground Airblast Airblast Droplet Size Distribution (DSD) Medium to Co arse Fine to Medium 1 NA NA

Release height NA High Boom 2 NA NA

Orchard type NA NA Dense Orchard Dense Orchard

1 Labels require a medium to coarse DSD, but AgDrift does not include this as an option for Tier I Ground mode.
2 Labels require a release hei ght for ground spray applications of less than 4 feet above the crop ca nopy. AgDrift does not use specific release heights, so m odeling for this use is based high boom spra y, the option with the highest release height, 4 ft (1.27 m).

The terrestrial analysis is base d on the honey bee acute contact LD 50 of 0.236 μg/bee, or 1.84 ppm, which is the most sensitive terrestr ial endpoint and is used as a surrogate for terrestrial invertebrate s. Based on this endpoint, the initi al average deposi tion level that would lead to exceedance of the terrestrial invertebrate LOC (0.05) is 0.00068 lb a.i./A, where the deposition is calculated as the RQ divided by the LOC and multiplied by the application rate. The most sensitive endpoint upon which the aquatic analysis is based is the bluegill sunfish 96-hour acute LC 50 of 2.2 μg a.i./L. With this toxicity endpoint, the endangered species LOC of 0.05 will be exceeded at any concentration greater than 0.11 μg a.i./L.

Table 5.12 includes uses with the m aximum single application rates fo r each application method and presents a summary of the buffer distances at which spray drift deposition from these uses drop below levels of con cern (e.g., RQs will be below LOCs). These distances represent the maximum extent wh ere effects are possible using the most sensitive data and the listed species LOC of 0.05 for either terrestrial invertebrates or freshwater fish. For each application method, lower application rate s will yield a smaller buffer distance than reported here.

90Table 5.12 Summary of maximum predicted distances for potential spray drift effects. Application

Method Application Rate (lb a.i/A) Uses Represented Terrestrial LD 50 Distance (ft) Aquatic LC 50 Distance (ft)

Aerial 3 Almond & Tree Fruit > 1000 >1000

Ground 10 Nursery > 1000 > 1000 Airblast 5 Citrus > 1000 > 1000 Airblast 0.25 Mango 197 23

The use of methidathion on almonds and tree fruit is predicted to have effects for terrestrial invertebrates at di stances greater than 1,000 ft (0.3 km ), the limit of AgDrift modeling. Given the uncertainty in AgDrift and the assumptions used in the modeling, the potential for effects from drift cannot be quantified beyond 1000 ft and so this value is used to represent the potential for effects to terrestrial invertebra tes and to define the spatial extent of the effects determination (i.e ., this buffer distance is added to the initial area of concern). Given the to xicity of methidathion and the calculated RQs, the extent of spray drift effects may be at least an order of magnitude higher than this.

5.1.4.2 Downstream Dilution Analysis

The maximum downstream extent of methidathi on exposure in stream s and rivers where the EEC can potentially be above levels th at would exceed the most sensitive LOC may be estimated by utilizing the gr eatest ratio of aquatic RQ to LOC. This is based on the assumption that there is uniform runoff across the landscape in treated areas with streams flowing through them (i.e. the initial area of concern), repr esented by the modeled EECs, and that as those waters move downstream, th e influx of non-impacted water will dilute the concentrations of methidathion present.

Using an LC 50 value of 2.2 ug/L for freshwater fish (the most sensitive species) and a maximum peak EEC of 114.7 μg/L for applicatio ns to nursery stock yields an RQ/LOC ratio of 1042 (52.2/0.05). Using the downstrea m dilution approach (described in more detail in Appendix D ) yields a target percent crop ar ea (PCA) of 27.8%. This value has been input into the downstream dilution ap proach 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 concer n. Similar to the spray drift buffer described above, the LAA/NLAA determination is base d on the area defined by the point where concentrations exceed the LC 50 value.

5.1.4.3 Overlap between CRLF habitat and Spatial Extent of Potentia l Effects

An LAA effects determination is made for those areas where it is expected that the pesticide ’s use will directly or indirectly affect the CRLF or its designated critical habitat and the area overlaps with the core areas, crit ical habitat and available occurrence data for CRLF.

91Figure 5.1 shows that there is some overlap betw een the initial area of concern mapped according to methidathion’s use pattern a nd the CRLF habitat, including currently occupied core areas, CNDDB occurrence sections , and designated critical habitat. This map does not include areas beyond the initial ar ea of concern that may be impacted by runoff and/or spray drift. It is expected th at any additional areas of CRLF habitat that are located >1000 ft (to account for offsite migra tion via spray drift) a nd 285 kilometers of stream reach (to account for downstream diluti on) outside the initial area of concern may also be impacted and are part of the full spa tial extent of the LAA/modification of critical habitat effects determination.

92Figure 5.1. Overlap Map: CRLF Habitat and Methidathion Initial Area of Concern

5.2 Risk Description

93The risk description synthesizes an overall conclusion regarding th e likelihood of adverse impacts leading to an effects determination ( i.e ., “no effect,” “may affect, but not likely to adversely affect,” or “likely to advers ely affect”) for the CRLF and its designated critical habitat.

If the RQs presented in the Risk Estimati on (Section 5.1) show no direct or indirect effects for the CRLF, and no modification to PCEs of the CRLF’s designated critical habitat, a “no effect” determination is ma de, based on methidathi on’s use within the action area. However, if direct or indire ct effect LOCs are exceeded or effects may modify the PCEs of the CRLF’s critical hab itat, the Agency concludes a preliminary “may affect” determination for the FIFRA regulatory action regard ing methidathion. A summary of the results of the risk estimation results are provided in Table 5.13 for direct and indirect effects to the CRLF and in Table 5.14 for the PCEs of designated critical habitat for the CRLF.

These results represent risk from exposure to applied m ethidathion and do not include the additional risk posed by any degradates of toxicological concer n. Given that acute and chronic risk quotients are exceeded for the parent compound alone, any contribution in toxicity from any of the major degradat es or from methidathion oxon or other OP degradates would increase the risk estimates . Potential risk from methidathion oxon is characterized in Section 5.2.1.3

.

Table 5.13 Risk Estimation Summary for Meth idathion - Direct and Indirect Effects to CRLF

Assessment Endpoint LOC Exceedances (Y/N) Description of Results of Risk Estimation

Aquatic Phase (eggs, larvae, tadpoles, juveniles, and adults) Direct Effects Survival, growth, and reproduction of

CRLF individuals via direct effects on aquatic phases Y There are LOC exceedances for listed species f ollowing both acute and chronic exposure using freshwater fish as the surrogate for aquatic-phase amphibians.

Indirect Effects Survival, growth, and reproduction of

CRLF individuals via effects to food supply ( i.e., fish, freshwater invertebrates, non-vascular plants) Y The acute LOC for non-listed species (all uses) and the chronic LOC (all uses except alfalfa, clover, timothy and kiwi) are exceeded for freshwater fish. There are LOC exceedances for non-listed species following both acute and chronic exposure to freshwater invertebrates. No aquatic plant data are available. A qualitative discussion of risk will be provided.

Indirect Effects Survival, growth, and reproduction of

CRLF individuals via effects on habitat, cover, and/or primary productivity ( i.e., aquatic plant community) Unknown No aquatic plant data are available. A qualitative d iscussion of risk to aquatic plants will be provided.

94Table 5.13 Risk Estimation Summary for Meth idathion - Direct and Indirect Effects to CRLF
LOC Exceedances (Y/N) Assessment Endpoint Description of Results of Risk Estimation

Indirect Effects Survival, growth, and reproduction of

CRLF individuals via effects to riparian vegetation, required to maintain acceptable water quality and habitat in ponds and streams comprising the species’ current
range. No terrestrial plant data are available. A qualitative d iscussion of risk will be provided. Unknown

Terrestrial Phase (Juveniles and adults) Direct Effects Survival, growth, and reproduction of

CRLF individuals via direct effects on terrestrial phase adults and juveniles Y There are LOC exceedances for listed species f ollowing both acute and chronic exposure using birds as the surrogate for terrestrial-phase amphibians.

Indirect Effects Survival, growth, and reproduction of

CRLF individuals via effects on prey ( i.e., terrestrial invertebrates, small terrestrial mammals and terrestrial phase amphibians) Y There are LOC exceedances for non-listed species fo llowing both acute and/or chronic exposure to terrestrial invertebrates, mammals and birds (surrogate to terrestrial-phase amphibians).

Indirect Effects Survival, growth, and reproduction of

CRLF individuals via effects on habitat ( i.e., riparian vegetation) No terrestrial plant data are available. A qualitative d iscussion of risk will be provided. Unknown

Table 5.14 Risk Estimation Summary for Methidat hion – PCEs of Design ated Critical Habitat for the CRLF

Assessment Endpoint Habitat Modification (Y/N) Description of Results of Risk Estimation

Aquatic Phase PCEs (Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat) 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. Unknown No aquatic and terrestrial pl ant data are available. A qualitative discussion of risk will be provided.

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. Unknown No aquatic and terrestrial pl ant data are available. A qualitative discussion of risk will be provided.

95Table 5.14 Risk Estimation Summary for Methidat hion – PCEs of Design ated Critical Habitat for the CRLF

Habitat Modification (Y/N) Assessment Endpoint Description of Results of Risk Estimation

Alteration of other chemical characteristics necessary for normal growth and viability of CRLFs and their food source. Y LOC exceedances for both listed and non-listed species following both acute and chronic exposure for freshwater fish and invertebrates. No aquatic plant toxicity data are available.

Reduction and/or modification of aquaticbased food sources for pre-metamorphs (e.g., algae) No aquatic plant data are available. A qualitative d iscussion of risk will be provided. Unknown

Terrestrial Phase PCEs (Upland Habitat and Dispersal Habitat) 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 Unknown No terrestrial plant data are available. A qualitative d iscussion of risk will be provided.

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 Unknown No terrestrial plant data are available. A qualitative d iscussion of risk will be provided.

Reduction and/or modification of food sources for terrestrial phase juveniles and adults Y Acute and chronic LOCs for listed and non-listed species were exceeded for all uses for birds and mammals and acute LOCs for listed and non-listed terrestrial invertebrates were also exceeded for all

uses.

Alteration of chemical characteristics necessary for normal growth and viability of juvenile and adult CRLFs and their food

source. Acute and/or chronic LOCs for listed and non-listed species were exceeded for freshwater fish and invertebrates, birds, mammals and terrestrial invertebrates. No data are available for either aquatic or terrestrial plants. Y

Following a “may affect” determination, additio nal inform ation is considered to refine the potential for exposure at th e predicted levels based on th e life history characteristics ( i.e. , habitat range, feedi ng preferences, etc.) of the CRLF. Based on the best available information, the Agency uses the refined ev aluation to distinguish those actions that “may affect, but are not likely to adversely a ffect” from those actions that are “likely to adversely affect” the CRLF and its designated critical habitat.

The criteria used to make determinations that the effects of an acti on are “not likely to adversely affect” the CRLF and its designated cr itical habitat include the following:

96• Significance of Effect : Insignificant effects are those that cannot be meaningfully measured, detected, or evaluated in the c ontext of a level of effect where “take” occurs for even a single individual. “T ake” in this context means to harass or harm, defined as the following:

 Harm includes significant habitat m odification or degradation that results in death or injury to listed species by significantly impairing behavioral patterns such as br eeding, feeding, or sheltering.

 Harass is defined as actions that crea te the likelihood of injury to listed species to such an extent as to significantly disrupt normal behavior patterns which include, but are no t limited to, breeding, feeding, or sheltering.

• Likelihood of the Effect Occurring : Discountable effect s are those that are extremely unlikely to occur.

• Adverse Nature of Effect : Effects that are wholly be neficial without any adverse effects are not considered adverse.

A description of the risk and effects determ ination for each of the established assessment endpoints for the CRLF and its designated critical habitat is provided in Sections 5.2.1 through 5.2.3

.

5.2.1 Direct Effects

5.2.1.1 Aquatic-Phase CRLF

The aquatic-phase considers life stages of th e frog that are obligatory aquatic organism s, including eggs and larvae. It also considers submerged te rrestrial-phase juveniles and adults, which spend a portion of their time in water bodies that may receive runoff and spray drift containing methidathion.

As stated in the risk esti m ation section, acute RQs for the aquatic-phase CRLF exceed the listed species LOC (0.05) for all of the asse ssed methidathion uses. The acute RQs range from 2.1 for the alfalfa scenario to 52.5 for the nursery scenar io. In addition, the lowest acute RQ following a single application is estimated to be 0.20 for the lowest mango scenario, which still exceeds th e acute LOC for listed species.

Limited acute toxicity data ar e available to assess sensitivity across freshwater fish species. The lowest an d highest acute 96-hour LC 50 s values from the submitted studies on bluegill sunfish, rainbow trout and goldfish are 2.2 (bluegill sunfish) and 14 μg/L (rainbow trout). Estimated acute RQs from th ese studies indicate that they would exceed the listed species acute LOC for all of the a ssessed methidathion uses for any one of these three surrogate freshwater fish species. It is noted that one study on the common eel ( Anguilla anguilla ) was available in the open lite rature with a 96-hr acute LC 50 that is close to three orders of magnitude higher (1510 μg/L) than the most sensitive submitted freshwater fish species. If acute RQs were estimated based on that study, they would range from 0.003 for the alfalfa scenario to 0.08 for the nursery scenario, the only

97scenario that exceeds the acute LOC for listed sp ecies. Therefore, there will be some fish species that may not be at ri sk following acute exposure to some of the methidathion use scenarios, and the relative sensitivity of aquatic amphi bians to fish is unknown.

Based on a probit dose-response slope of 2.9 (1.9 – 4.0) from the bluegill sunfish acute toxicity study with an acute LC 50 of 2.2 μg/L, the proba bility of an individual effect at the LOC is estimated to be 1 in 12,400 and the probabil ity of an individual effect at the RQ is close to 1 in 1 for all scenarios. Subletha l effects were reported in the bluegill sunfish acute toxicity study at concentra tion levels higher than the end points utilized in this risk assessment (MRID 00011841). In this study, it was reported that test organisms in the highest exposure group (1000 μg/L) exhibited slight spastic motions and swam on their sides.

As stated previously, the chronic NOAEC of 6.3 μg/L for the fathead m innow is similar to the acute 96-hour LC 50 of several other test species , ranging from 2.2 to 14 μg/L. A chronic NOAEC for any of these other species would likely be lower than the available fathead minnow NOAEC. Therefore, this assessment estimated a chronic NOAEC for rainbow trout using an acute to chronic ra tio (ACR) calculation from data from other organophosphates. The most conservative acu te to chronic ratio from the other organophosphate data is 140. Using th at ACR value with an acute LC 50 value of 10 ppb for rainbow trout, the chronic NOAEC used in this assessment is estimated to be 0.07 ppb. With this value, the chronic RQs exceedthe LOC (1.0) for all of the assessed methidathion uses ( Table 5.2 ). If the chronic NOAEC of 6.3 ppb from the fathead minnow study is used, then the chronic RQs would exceed the LOC (1.0) for all of the assessed methidathion uses except for the alfa lfa scenario (RQ = 0.40: alfalfa, clover and timothy); the grape scenario (RQ = 0.51: kiwi) and the tree fruit scenario (RQ = 0.79: apple, apricot, cherry, nectarine, peach, pear, plum and prune). Therefore, even with the endpoint from the chronic study in fathead mi nnows, the chronic LOC is still exceeded with many methidathion uses.

Sublethal effects in the chronic study include effects on total length a nd wet weight at the highest m easured treatment level (12 μg ai/L) relative to the pooled control.

Surface water monitoring data support the conclusion of risk determined based on calculated R Qs. Monitoring in the Sacram ento Valley found 46 detections out of 472 samples with a maximum of 15.1 ug/L and an av erage across the detections of 1.2 ug/L. In the San Joaquin Valley, the maximum of 30 detections out of 738 samples was 2.4 ug/L and the average was 0.3 ug/L. Atmospheric monitoring detected methidathion concentrations in fog of 15.5 ug/L. Compared to 96-hr acute LC 50 values of 2.2 ug/L to 14 ug/L, these data demonstrate the potential for aquatic exposures that could lead to direct effects, particularly because monitori ng is generally not expected to capture peak values.

In 1976, approximately 3,000 fish of unknown sp ecies in a nearby creek were killed following an aerial application of m ethidathi on to an agricultural area in Sacramento County, California. The incident was attribut ed to accidental misuse of methidathion.

98Samples of the water collected from the field drain six days after the material was applied to the field showed methidat hion concentrations of 60 ppb. The certainty index for this incident is highly probable.

In summary, methidathion is very highly t oxic to freshwater fish, the surro gate for the aquatic-phase CRLF. The acute LOC (listed species) and the chronic LOC are exceeded for all of the methidathion uses. There is one study in the open lit erature that indicates that there will be some fish species that may not be at risk follow ing acute exposure from some of the methidathion use scenarios. This is an uncertainty. The probability of an individual effect on an acute basis approaches 100% at the RQ levels. Incident data indicate that freshwater fish are vulnerable, particularly if there are misuses. Spatial analyses indicate that a significant over lap will exist between the use sites for methidathion and the CRLF habitat, partic ularly when the spraydrift and downstream dilution buffers are applied to the “footprint” of the methidathion use area. Therefore, based on the weight-of-evidence, there is a po tential for direct impact to the aquaticphase CRLF based on the endpoints generated from the freshwater fish data and the effects determination is Likely to adversely affect (LAA).

As stated previously, the only detected degradate of toxico log ical concern is the minor degradate methidathion oxon, which may be more toxic than the parent. However, no data are available on the environmental fate , toxicity, and occurrence of methidathion oxon in the environment and so it is not consid ered directly in cal culated RQs. Given that acute and chronic risk quotients are exceeded for the parent compound alone, any contribution in toxicity from any of the ma jor degradates or from methidathion oxon or other OP degradates would increase the risk es timates. Further characterization of risk from methidathion oxon is provided in Section 5.2.1.3

.

5.2.1.2 Terrestrial-Phase CRLF

As stated in the risk estimation section, acute dose-based and acute dietary-based RQ s for the terrestrial-phase CRLF exceed the listed sp ecies LOC (0.1) for all of the assessed methidathion uses. The acute RQs range from 0.17 for mangos on a dietary basis to 442.0 for nursery uses on a dose basis. Limited acute toxicity data are available to assess sensitivity across avian species on a dose-basis. The acute oral LD 50 ’s range from 6.7 mg/kg for mallard ducks (Anas platyrhynchos) (MRID 000159201) to 225 mg/kg for Chukar (Alectoris chukar ) (MRID 00060823). Other species fa ll within that range. Even with the highest LD 50 for the Chukar, the dose-based acute RQ for avian species is still over 150 times higher than the acute LOC of 0.1 for listed terrestrial animals with the nursery uses. With the lowe st application rate of 0.25 lb a.i./A for mangos and the highest acute LD 50 value for the Chukar, the acute dose-based RQ for small birds eating small insects (0.29) is still greater than the acute LOC of 0.1 for endangered birds. On a dietary basis, there are only two studies w ith the technical material, one with bobwhite quail and one with mallard ducks. The acute dietary LC 50 s are 224 and 543 ppm for bobwhite quail and mallard ducks, respectively. Again, with the lowe st application rate of 0.25 lb a.i./A for mangos and using the bobwhite quail LC 50 value of 224 ppm, the acute RQ on a dietary basis for small birds eating small insects is 0.17, which exceeds the

99LOC for listed species. Using the mallard duck LC 50 value of 543 ppm, the acute RQ on a dietary basis for small birds eating small insects is 0.07, which is just under the LOC for endangered species. However, with the next highest application ra te of 0.5 lbs a.i./A for safflower, even when applied only on ce per year, the RQ using the highest LC 50 of 543 ppm for mallard ducks, the RQ would be 0.12, which is greater than the acute LOC for endangered birds. Therefore, even within the range of dose- a nd dietary-based acute toxicity values for avian speci es, there is potential acute ri sk to endangered birds for all uses with the possible exception of mangos w ith some of the less sensitive birds.

Chronic RQs also exceed the chronic LOC for all of the assessed methidathion uses ( Table 5.7 ). The chronic endpoint used in this assessm ent (10 ppm) is based on a study with mallard ducks (MRID 44381602). In bobwh ite quail, no effects were observed in two studies at the highest concentrations tested (3 0 and 35 ppm; MRIDs 44381601 and 44381602, respectively). Using the highest bobw hite quail NOAEC value of 35 ppm, the chronic RQ with the lowest application rate (mangos) is 1.08, which is still greater than the chronic LOC of 1. Theref ore, within the available range of dietary-based chronic toxicity values for avian speci es (two), there is potential risk follo wing chronic exposure for all of the assessed methidathion uses.

In an effort to refine the acute dose-based risk estim ates, the T-REX model was modified to account for the lower metabolic rate a nd lower caloric requirement of amphibians (compared to birds). Acute dose-based RQ s were recalculated using the T-HERPS (Version 1.0) model for small (1 g), medi um (37 g), and large (238 g) frogs ( Table 5.15, Appendix M ). Using this refinement, the ac ute dose-based RQs still exceed the LOC (0.1) for nearly all of the modeled scenar ios for methidathion. The T-HERPS model can only be used to refine dose-based risk estimat es at this time; thus, further refinement of the acute or chronic dietary- based RQs is not possible.

Table 5.15. Upper Bound Kenaga , Acute Terrestrial Herpetofauna Dose-Based Risk Quotients
EECs and RQs Broadleaf

Plants/ Small Insects Fruits/Pods/ Seeds/ Large Insects Small Herbivore Mammals Small Insecti vore

Mammal Small Amphibi ans Size Class (grams) Adjusted LD50

EEC RQ 1 EEC RQ 1 EEC RQ 1 EEC RQ 1 EEC RQ 1

ARTICHOKE

1.4 6.70 6.81 1.02 0.76 0.11 N/A N/A N/A N/A N/A N/A 37 6.70 6.69 1.00 0.74 0.11 194.24 28.99 12.14 1.81 0.23 0.03 238 6.70 4.39 0.65 0.49 0.07 30.20 4.51 1.89 0.28 0.15 0.02 CITRUS 1.4 6.70 26.46 3.95 2.94 0.44 N/A N/A N/A N/A N/A N/A 37 6.70 26.00 3.88 2.89 0.43 754.62 112.63 47.16 7.04 0.90 0.13 238 6.70 17.04 2.54 1.89 0.28 117.31 17.51 7.33 1.09 0.59 0.09

CLOVER 1.4 6.70 7.76 1.16 0.86 0.13 N/A N/A N/A N/A N/A N/A 37 6.70 7.63 1.14 0.85 0.13 221.32 33.03 13.83 2.06 0.26 0.04

100Table 5.15. Upper Bound Kenaga , Acute Terrestrial Herpetofauna Dose-Based Risk Quotients
EECs and RQs Broadleaf

Plants/ Small Insects Fruits/Pods/ Seeds/ Large Insects Small Herbivore Mammals Small Amphibians Small Insecti vore

Mammal Size Class (grams)
EEC RQ 1 EEC RQ 1 EEC RQ 1 EEC RQ 1 Adjusted LD50

EEC RQ 1
238 6.70 5.00 0.75 0.56 0.08 34.41 5.14 2.15 0.32 0.17 0.03

COTTON 1.4 6.70 11.27 1.68 1.25 0.19 N/A N/A N/A N/A N/A N/A 37 6.70 11.07 1.65 1.23 0.18 321.38 47.97 20.09 3.00 0.38 0.06 238 6.70 7.26 1.08 0.81 0.12 49.96 7.46 3.12 0.47 0.25 0.04

KIWI 1.4 6.70 10.49 1.57 1.17 0.17 N/A N/A N/A N/A N/A N/A 37 6.70 10.31 1.54 1.15 0.17 299.20 44.66 18.70 2.79 0.36 0.05 238 6.70 6.76 1.01 0.75 0.11 46.51 6.94 2.91 0.43 0.23 0.04 MANGO 1.4 6.70 1.47 0.22 0.16 0.02 N/A N/A N/A N/A N/A N/A 37 6.70 1.45 0.22 0.16 0.02 42.03 6.27 2.63 0.39 0.05 0.01 238 6.70 0.95 0.14 0.11 0.02 6.53 0.98 0.41 0.06 0.03 0.00 NURSERY 1.4 6.70 2.62 0.39 0.29 0.04 N/A N/A N/A N/A N/A N/A 37 6.70 2.58 0.38 0.29 0.04 74.80 11.16 4.67 0.70 0.09 0.01 238 6.70 1.69 0.25 0.19 0.03 11.63 1.74 0.73 0.11 0.06 0.01 SAFFLOWER, SUNFLOWER 1.4 6.70 4.48 0.67 0.50 0.07 N/A N/A N/A N/A N/A N/A 37 6.70 4.41 0.66 0.49 0.07 127.85 19.08 7.99 1.19 0.15 0.02 238 6.70 2.89 0.43 0.32 0.05 19.88 2.97 1.24 0.19 0.10 0.01 TREE FRUIT, OLIVES 1.4 6.70 15.73 2.35 1.75 0.26 N/A N/A N/A N/A N/A N/A 37 6.70 15.46 2.31 1.72 0.26 448.79 66.98 28.05 4.19 0.54 0.08 238 6.70 10.14 1.51 1.13 0.17 69.77 10.41 4.36 0.65 0.35 0.05 WALNUT 1.4 6.70 25.88 3.86 2.88 0.43 N/A N/A N/A N/A N/A N/A 37 6.70 25.44 3.80 2.83 0.42 738.28 110.19 46.14 6.89 0.88 0.13 238 6.70 16.67 2.49 1.85 0.28 114.77 17.13 7.17 1.07 0.58 0.09

a Acute RQs that exceed the acute endangered species LOC of 0.1 are in bold.

On a dose basis, based on a default probit dose-response slope of 4.5 (2 – 9) from the

m allard duck acute oral toxic ity study with an acute LD 50 of 6.7 mg/kg bw, the probability of an individual effect at the RQ is approximately 1 in 1 for all scenarios. On a dietary basis, the probit dose-response sl ope was 8.7 (3.5-13.8) from the bobwhite quail dietary study with an LC 50 of 224 ppm. The probability of an individual effect at the RQ ranged from 1 in 1 for 5 use scenarios to 1 in 9.28E+10 for use on mangos (see Tables 5.5 and 5.6)

.

101Sublethal effects were reported in the mallard acute oral toxicity study (MRID 00159201). Toxic symptoms included depression, reduced reaction to external stimuli, wing droop, convulsions, and salivation. In duc ks, pheasants and/or partridges (MRID 00060823), toxic symptoms included goose-stepping, ataxia, dyspnea, lacrimation, salivation, ataxia, wing-spread seiz ures, and terminal opisthotonos. Symptoms appeared as soon as 20 mi nutes after dosage; recovery of survivors took 1-2 days. The NOAELs and LOA ELs for these sublethal effects were not reported.

There are no other acute or ch ronic toxicity data with bi rds that have lower endpoints than the stud ies used in this assessment.

Four incidents were reported in which red-tailed hawks were found either dead or injured after potential exposure to m eth idathion. One incident was cla ssified as possible, two as probable and the fourth as hi ghly probable. The incidents were all reported in 1994 in several counties in California (Colusa, Stanislaus and Merced). In one case, blood plasma cholinesterase and acetlycholinestera se levels were within the normal range; however, the results of the footwash showed detections of methidathion at 2.7 ppb (other organophosphates, including chlorpyrifos a nd diazinon were also detected in the footwash sample at respectiv e concentrations of 0.2 ppb a nd 4.1 ppb). In a second case, the hawk recovered. Plasma cholinesterase and acetylcholinesterase levels were found significantly below the normal range. Footwash analysis results show that methidathion was detected at a concentration of 2.7 ppb. Again, chlorpyrifos and diazinon were also detected in the footwash sample at resp ective concentrations of 0.7 ppb and 0.4 ppb. In the third case where the hawk died, the plasma cholinesterase level was low and the brain cholinesterase level was severely depr essed. Methidathion was detected at a concentration of 0.7 ppm in the footskin. Chloropyrifos and diazi non were detected in both the feathers and footskin at concen trations ranging from 0.02 to 0.08 ppb. It is likely that all three organophosphates cont ributed to the death of this bird.

In summary, the acute dose-based, acute diet a ry-based and/or chr onic dietary-based RQs for the terrestrial-phase CRLF, using avian data as a surrogate, exceed the acute listed species LOC (0.1) and/or the chronic non-listed species LOC (1) for all of the assessed methidathion uses. In addition, the probability of an individual effect on an acute basis is high at the RQ levels. Incident data indicate that birds are vulnerable. Spatial analyses indicate that a significant ove rlap will exist between the use sites for methidathion and the CRLF habitat, particularly when the sprayd rift buffers are applie d to the “f ootprint” of the methidathion use area. Therefore, ba sed on the weight-of-evidence, there is a potential for direct impact to the terres trial-phase CRLF using the endpoints generated from the avian data and the effects determination is LAA.

As stated previously, the only detected degradate of toxico log ical concern is the minor degradate methidathion oxon, which may be more toxic than the parent. However, no data are available on the environmental fate , toxicity, and occurrence of methidathion oxon in the environment and so it is not consid ered directly in cal culated RQs. Given that acute and chronic risk quotients are exceeded for the parent compound alone, any

102contribution in toxicity from any of the ma jor degradates or from methidathion oxon or other OP degradates would increase the risk es timates. Further characterization of risk from methidathion oxon is provided in Section 5.2.1.3

. 5.2.1.3 Direct Effects from Methidathion Oxon to Aquatic-Phase and Terrestrial-Phase CRLF

As described in Section 2.1.4 , m ethidathion oxon formation in soil was demonstrated in soil photolysis, aerobic soil metabolism, and terrestrial field dissipation studies, and formation on foliage was demonstrated in dislodgeable residue studies. Long range transport has also been shown to occur, w ith methidathion oxon detected in air and on pine needles at more than 20 km from the nearest use site. Although formed at less than 10%, methidation oxon is a degradate of c oncern based on comparison with other OP pesticides ( e.g. , diazinon, chlorpyrifos), for which oxon degradates have been shown in many cases to be of equal or greater toxicity than the parent. This analysis does not include consideration of ot her oxon degradates which, based on the degradation pathway for methidathion, may have been formed but were not detected in fate studies due to the lack of appropriate labeling.

No environmental fate or ecological effects data are available for m ethidathion oxon. Therefore, it is difficult to quantify the incr eased risk which may result from potential exposure to this degradate; however, base d on conservative assumptions, some broad conclusions can be reached. In laboratory st udies, transformation to the oxon occurred at maximum amounts under soil photolysis conditi ons, where 5% of the applied parent was present as methidathion oxon at study term ination. For quantitative modeling purposes, then, the assumption can be made that meth idathion oxon is initially present on soil and on foliage at 5% of the initi ally applied parent compound.

For both aquatic modeling using PRZM/EXAMS and terrestrial m odeling using T-REX, EECs are linear with the application rate. Ther efore, based on an application rate of 5% of the applied methidathion for the meth idathion oxon, and assuming that its fate properties are similar to the parent, aquatic and terrestrial EECs for the oxon alone would be approximately 5% of those estimated for the parent 7 . If the oxon were of equal toxicity to the parent, then the acute aquatic and terrestrial RQs fo r the oxon alone would be 5% of those calculated for the parent. For acute aquatic risk, the acute RQs would range from 0.01 for the use on mangos to 1.12 for almonds and 2.62 for the nursery use, as shown in Table 5.16 . For terrestrial risk, acute dose-based RQs would range from 0.62 for mangos to 11.1 for citrus and 22.1 for the nursery use, as shown in Table 5.17

. Therefore, at equal toxicity to the pare nt, risk from the oxon degradate alone would exceed the endangered species LOCs for acute risk to both the aquatic phase CRLF (LOC = 0.05) and the terrestrial phase CRLF (LOC = 0.1) for all except th e lowest application
rates.

7 Modeled aquatic EECs for the oxon would not be exactly 5% because spray drift would not be a factor and so model inputs would change to 100% application efficiency and 0% drift, rather than 95% and 2%, respectively. This, along with a correction for molecular weight, would be likely to change the percentage slightly but not enough to affect conclusions.

103However, oxons can be considerably more toxic than the parent and risk from

m ethidathion oxon alone could be even greate r than that from the parent. In the cumulative assessment for OP insecticides 8 , if there were no toxici ty data available for a given OP-oxon, high-end adjustment factors of 10X to 100X were applied to account for the presumed increased toxicity of the oxon rela tive to the parent chemical. To explore the potential risk if methidathion oxon were more toxic than the parent, RQs based on these factors are reported as well in Tables 5.16 and 5.17 , for direct effects to the aquatic and terrestrial phase CRLF, respectively.

Table 5.16 Summary of Direct Effect Ac ute RQs for the Aquatic-phase CRLF, based on exposure to methidathion oxon degradate Oxon Only (no parent) b Use Parent Only a Equal Toxicity 10X Toxicity 100X Toxicity Mango 0.20 0.01 0.1 1.0
Alfalfa 2.1 0.10 1.0 10
Almond 22.4 1.12 11.2 112 Nursery 52.5 2.62 26.2 262

a Previously calculated in Table 5.1 using blueg ill sunfish (Lepomis macrochirus) acute 96-hour LC 50 = 2.2 μg/L
b Assumes EECs to be 5% of those for the parent, base d on the maximum percent formation observed in laboratory studies.

Table 5.17 Summary of Direct Effect Acute Dose-based RQs for the Terrestrial-phase CRLF, based on expo sure to methidathion oxon degradate Oxon Only (no parent) b Use Parent Only a Equal Toxicity 10X Toxicity 100X Toxicity Mango 12.4 0.62 6.2 60
Clover 65.4 3.3 33 330
Citrus 222.9 11.1 111 1110 Nursery 442.0 22.1 221 2210

a Previously calculated in Table 5. 5 based on mallard duck acute oral LD 50 = 6.7 mg/kg.
b Assumes EECs to be 5% of those for the parent, base d on the maximum percent formation observed in laboratory studies.

There is a great deal of uncertainty in th ese es timates because of the assumptions on which they are based, including those for forma tion (e.g., fate propertie s) and toxicity of the methidathion oxon. For the aquatic-phase CRLF, exposure estimates are based on the assumptions that all of the applied methidathion is available on the soil surface for photolysis and that all of the transformation product is available for runoff at one time. For the terrestrial-phase CRLF, exposure estim ates assume that labo ratory soil photolysis rates are also reflective of the photolysis rates that may occur on foliage. Additionally, the fate properties of methidathion ox on are unknown, and assuming the same fate behavior of the parent may lead to overestimation because OP oxons tend to be more

8 More detail on the OP cumulative assessment and the characterization of additional risk due to oxon occurrence may be found at http://www.epa.gov/pesticides/cumula tive/2006-op/op_cra_appendices_part2.pdf

104transient than the parent. Methidathion oxon has not been detected in surface water monitoring done in two studies, even in samp les in which the parent methidathion was detected. Despite the uncertainty, the potential for acute direct effects to aquatic-phase and terrestrial-phase CRLF from exposure to methidathion oxon alone cannot be precluded, even if the toxicity is no greater than that of th e parent. Exposure from the parent methidathion already l eads to conclusions of risk; thus, consideration of the oxon degradate as well increases the likelihood of direct effects.

5.2.2 Indirect Effects (v ia Reductions in Prey Base)

5.2.2.1 Algae (non-vascular plants)

As discussed in Section 2.5.3, the diet of CRLF tadpoles is composed primarily of unicellular aquatic plants (i.e., algae and diatom s) and detritus. Due to a lack of aquatic plant toxicity data indirect effects to the CRL F via direct toxicity to aquatic plants cannot be quantitatively estimated for methidathion. There are no incident data for aquatic plants and no relevant data in the open li terature. An examination of the completed CRLF assessments for nine other organophosphates indicates that nearly all of the effects determinations for aquatic non-vascular plants were either “no effect ” or “not likely to adversely affect”. In addition, the m ode of action for methidathion as an organophosphate insecticide is by disrupting ne rvous system function of exposed animals via acetylcholinesterase inhibition. Unless ther e is a separate herbicidal mode of action as with bensulide, a pre-emergent organophos phate herbicide which inhibits cell division in root tips and inhibits seedling growth by conjugation of acetyl co-enzyme A, this mode of action on animals is not expected to affect plants. Methidathion also has a history of being applied to a m yriad of ag ricultural crops (as pe r the label), with no known incidents of adverse phytotoxic effects to aquatic plants. Therefore, based on the weight-of-evidence, the potential indirect impact to the CRLF is expected to be minimal. The effects determination is may affect, not likely to adversely affect (NLAA).

5.2.2.2 Aquatic Invertebrates

The potential for methidathion to elicit i ndirect effects to the CRLF via effects on freshwater invertebrate food item s is depende nt on several factor s including: (1) the potential magnitude of effect on freshwater invertebrate individuals and populations; and (2) the number of prey species potentially affected relative to the expected number of species needed to maintain the dietary needs of the CRLF. Together, these data provide a basis to evaluate whether the number of indivi duals within a prey species is likely to be reduced such that it may indirectly affect the CRLF.

The acute RQs for aquatic invertebrates rang e from 1.5 to 38.5, thus exceeding the acute risk LOC for non-listed species for all of the assessed uses (LOC = 0.5; see Table 5.3 ). Chronic RQs for freshwater inverteb rate s range from 8.9 to145.0, thus exceeding the LOC (1.0) for all of the assessed methidathion uses (see Table 5.4 ). Only one other acute toxicity study with the same species ( daphnia magna , MRID 00011350) provides any other data relevant to this assessment, either from submitted studies or from the open

105literature. With the endpoint from that study, the lowest acute RQ would be 1.0, which still exceeds the acute LOC for non-listed species. At the lowest application rate with the default slope of 4.5 and the lowest RQ of 1.5, the probability of an individual effect is approximately 1 in 1.3 and the percentage effect to the aquatic invertebrate prey base is 79% (e.g., the percentage of the aquatic invert ebrate population that is expected to be affected following exposure to methidathion). Based on the weight-of-evidence, there is a potential indirect impact to the CRLF via effects on freshwat er invertebrate food items. The effects determination is LAA.

5.2.2.3 Fish and Aquatic-phase Frogs

Methidathion is very highly toxic to freshw ater fish, the surro gate for the aquatic-phase CRLF. The acute LOC for non-listed species (all uses) and the ch ronic LOC (all uses) are exceeded; however, one study in the open lite rature indicates that there will be some fish species that may not be at risk following acute exposure from some of the methidathion use scenarios. At the lowest application rate, th e probability of an individual effect on an acute basis at the RQ is approximate ly 1 in 1 and the percentage effect to the fish and aquatic-phase frog prey base is 93.4%. In addi tion, the incident data indicate that freshwater fish are vulnerable . Therefore, based on the weight-of-evidence, there is a potential indirect impact to the aquatic-pha se CRLF based on the endpoints generated from the freshwater fish data. The effects determination is LAA.

5.2.2.4 Terrestrial Invertebrates

When the terrestrial-phase CRLF reaches juveni le and adult s tages, its diet is mainly composed of terrestrial invertebrates. Th e RQs for both small and large insects exceed the acute LOC for non-listed species for all me thidathion uses, even with only a single use. The acute RQs for small insects range from 21 (mangos) to 734 (nursery) and the acute RQs for large insects range from 2.3 (ma ngos) to 82 (nursery). Following a single use, the lowest RQ is 2.0 for large insects (mangos). There are insufficient studies to conduct a sensitivity analysis; however, the highe st terrestrial invertebrate endpoint is from the open literature with an acute toxi city value of 0.416 μg/bee (ECOTOX reference 70351). The lowest RQ, using the endpoint from this study is 1.1 (mangos), which still exceeds the acute list species LO C of 0.05. The probability of an individual effect at the LOC of 0.5 is 1 in 4.41E+31 and the probability of an individual effect at the RQ for all uses is 1 in 1. In addition, the percentage effect to the terrestrial invertebrate prey base is 99.9 - 100%.

Two incidents were reported following applic ation of m ethidathion in California. The first involved spraying of plum trees near some pollination hives. Dead bees (number not specified) were found along with residues of methidathion and diazinon. This incident was rated as possible. The second incident reported that an u nknown number of bees were killed in an unknown county. The incident was attributed to accidental misuse. No residue analysis was completed; however, the ce rtainty index for this incident is probable.

106Based on the weight-of-evidence, there is a potential indirect impact to the CRLF based on this endpoint. The eff ects determination is LAA.

5.2.2.5 Mammals

Life history data for terres trial-phase CRLFs indicate that large adult frogs consum e terrestrial vertebrates, including mice. Th e acute and chronic RQs exceed the listed species acute LOC and the chronic LOC for all uses. The acute RQs range from 2.4 (mangos) to 86.8 (nursery). The chronic di etary RQs range from 117 (mangos) to 4164.5 (nursery, dose-based) and from 13.5 (mangos) to 480.0 (nurse ry, dietary-based). There is one study from the open literature conducted with the mouse ( mus musculus ) that appears to have a lower endpoint (E85173) ; however, the study is not avai lable for review at this time. The acute LD 50 for this study is 10.5 mg a.i./kg. Using the endpoint from this study and assuming that a mouse weighs 20 g, the lowest RQ (mangos) would be 5.70, which exceeds the non-listed sp ecies LOC by 10 times. No other relevant studies are available in the open literature. At the lowest application ra te (0.25 lb a.i./A for mangos), with the default slope of 4.5 and the lowest RQ of 2.4, the probability of an individual effect is approximately 1 in 1 and the percen tage effect to the mammalian prey base is 95.6%. Based on the weight-of-evidence, th e labeled uses for methidathion may indirectly impact the CRLF through effects to the mammalian prey base. The effects determination is LAA.

5.2.2.6 Terrestrial-phase Amphibians

Terrestrial-phase adult CRLFs also consume frogs. RQ values representing direct exposures of methidathion to terrestrial-phase CRLFs are used to represent exposures of methidathion to frogs in terrestrial habita ts. With the exception of mangos on an acute dietary basis, the acute dose-based, acute di etary-based and/or chronic dietary-based RQs for terrestrial-phase amphibians, using avia n data as a surrogate, exceed the acute nonlisted species LOC and the chronic LOC for all of the assessed methidathion uses.Refining the RQ values with T-HERPS, the acute dose-based RQs still exceed the nonlisted LOC (0.5) for at least one food categ ory for all of the modeled scenarios for methidathion.

Table 5.18. Upper Bound Kenaga , Acute Terrestrial Herpetofauna Dose-Based Risk Quotients
EECs and RQs Broadleaf

Plants/ Small Insects Fruits/Pods/ Seeds/ Large Insects Small Herbivore Mammals Small Insecti vore

Mammal Small Amphibi ans Size Class (grams) Adjusted LD50

EEC RQ 1 EEC RQ 1 EEC RQ 1 EEC RQ 1 EEC RQ 1

ARTICHOKE

1.4 6.70 6.81 1.02 0.76 0.11 N/A N/A N/A N/A N/A N/A 37 6.70 6.69 1.00 0.74 0.11 194.24 28.99 12.14 1.81 0.23 0.03 238 6.70 4.39 0.65 0.49 0.07 30.20 4.51 1.89 0.28 0.15 0.02 CITRUS

107Table 5.18. Upper Bound Kenaga , Acute Terrestrial Herpetofauna Dose-Based Risk Quotients
EECs and RQs Broadleaf

Plants/ Small Insects Fruits/Pods/ Seeds/ Large Insects Small Herbivore Mammals Small Amphibians Small Insecti vore

Mammal Size Class (grams)
EEC RQ 1 EEC RQ 1 EEC RQ 1 EEC RQ 1 Adjusted LD50

EEC RQ 1
1.4 6.70 26.46 3.95 2.94 0.44 N/A N/A N/A N/A N/A N/A 37 6.70 26.00 3.88 2.89 0.43 754.62 112.63 47.16 7.04 0.90 0.13 238 6.70 17.04 2.54 1.89 0.28 117.31 17.51 7.33 1.09 0.59 0.09

CLOVER 1.4 6.70 7.76 1.16 0.86 0.13 N/A N/A N/A N/A N/A N/A 37 6.70 7.63 1.14 0.85 0.13 221.32 33.03 13.83 2.06 0.26 0.04 238 6.70 5.00 0.75 0.56 0.08 34.41 5.14 2.15 0.32 0.17 0.03

COTTON 1.4 6.70 11.27 1.68 1.25 0.19 N/A N/A N/A N/A N/A N/A 37 6.70 11.07 1.65 1.23 0.18 321.38 47.97 20.09 3.00 0.38 0.06 238 6.70 7.26 1.08 0.81 0.12 49.96 7.46 3.12 0.47 0.25 0.04

KIWI 1.4 6.70 10.49 1.57 1.17 0.17 N/A N/A N/A N/A N/A N/A 37 6.70 10.31 1.54 1.15 0.17 299.20 44.66 18.70 2.79 0.36 0.05 238 6.70 6.76 1.01 0.75 0.11 46.51 6.94 2.91 0.43 0.23 0.04 MANGO 1.4 6.70 1.47 0.22 0.16 0.02 N/A N/A N/A N/A N/A N/A 37 6.70 1.45 0.22 0.16 0.02 42.03 6.27 2.63 0.39 0.05 0.01 238 6.70 0.95 0.14 0.11 0.02 6.53 0.98 0.41 0.06 0.03 0.00 NURSERY 1.4 6.70 2.62 0.39 0.29 0.04 N/A N/A N/A N/A N/A N/A 37 6.70 2.58 0.38 0.29 0.04 74.80 11.16 4.67 0.70 0.09 0.01 238 6.70 1.69 0.25 0.19 0.03 11.63 1.74 0.73 0.11 0.06 0.01 SAFFLOWER, SUNFLOWER 1.4 6.70 4.48 0.67 0.50 0.07 N/A N/A N/A N/A N/A N/A 37 6.70 4.41 0.66 0.49 0.07 127.85 19.08 7.99 1.19 0.15 0.02 238 6.70 2.89 0.43 0.32 0.05 19.88 2.97 1.24 0.19 0.10 0.01 TREE FRUIT, OLIVES 1.4 6.70 15.73 2.35 1.75 0.26 N/A N/A N/A N/A N/A N/A 37 6.70 15.46 2.31 1.72 0.26 448.79 66.98 28.05 4.19 0.54 0.08 238 6.70 10.14 1.51 1.13 0.17 69.77 10.41 4.36 0.65 0.35 0.05 WALNUT 1.4 6.70 25.88 3.86 2.88 0.43 N/A N/A N/A N/A N/A N/A 37 6.70 25.44 3.80 2.83 0.42 738.28 110.19 46.14 6.89 0.88 0.13 238 6.70 16.67 2.49 1.85 0.28 114.77 17.13 7.17 1.07 0.58 0.09

a Acute RQs that exceed the acute non- listed species LOC of 0.5 are in bold.

In addition, on an acute dose-basis, the probability of an indivi dual effect is 1 in 1 at the lowest RQ level and the percen tage e ffect to the avian/terr estrial-phase amphibian prey base is 100%. Incident data indicate that birds are vulnerable. Therefore, based on the

108weight-of-evidence, there is a potential indirect impact to the terrestrial-phase CRLF based on these endpoints. The effects determination is LAA.

5.2.3 Indirect Effects (v ia Habitat Effects)

5.2.3.1 Aquatic Plants (Vascular and Non-vascular)

Aquatic plants serve several important functi ons in aquatic ecosystem s. Non-vascular aquatic plants are primary producers and pr ovide the autochthonous energy base for aquatic ecosystems. Vascular plants provide structure as at tachment sites and refugia for many aquatic invertebrates, fish, and juvenile organisms, such as fish and frogs. In addition, vascular plants al so provide primary productivity and oxygen to the aquatic ecosystem. Rooted plants help reduce se diment loading and provide stability to nearshore areas and lower streambanks. In a ddition, vascular aquatic plants are important as attachment sites for egg masses of CRLFs.

Potential indirect effects to the CRLF ba sed on im pacts to habitat and/or primary production would normally be asse ssed using RQs from freshw ater aquatic vascular and non-vascular plant data; howev er, there are no aquatic plan t data for methidathion and quantitative risk estimations cannot be conducted. There are no incident data for aquatic plants and no relevant data in the open li terature. An examination of the completed CRLF assessments for nine other organophosphates indicates that nearly all of the effects determinations for aquatic vascular and non-vasc ular plants were eith er no effect or not likely to adversely affect. Not all of th e other CRLF organophosphate chemicals have aquatic vascular plant data. In those cas es, determinations were based on the nonvascular plant data and any av ailable terrestrial plant data. As stated previously, the mechanism of action for methidathion as an organophosphate insectic ide is by disrupting nervous system function of exposed animals vi a acetylcholinesterase inhibition, which is not a mode of action that is expected to aff ect plants. Methidathion also has a history of being applied to a myriad of agricultural cr ops (as per the label), with no known incidents of adverse phytotoxic effects to aquatic pl ants. Therefore, based on the weight-ofevidence, the potential indirect impact to the CRLF is minimal. The effects determination is may affect, NLAA.

5.2.3.2 Terrestrial Plants

Terrestrial plants serve several important ha b itat-related functions for the CRLF. In addition to providing habitat and cover for inve rtebrate and vertebrate prey items of the CRLF, terrestrial vegetation also provides sh elter for the CRLF and cover from predators while foraging. Terrestrial plan ts also provide energy to th e terrestrial ecosystem through primary production. Upland vegetation incl uding grassland and woodlands provides cover during dispersal. Riparian vegetation he lps 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 r each the watershed, and serving as an energy

source.

109Again, as with aquatic plants, there are no re gistrant-submitted terrestrial plant toxicity data for methidathion for assessment of the potential for indirect effects to the aquaticand terrestrial-phase CRLF via effects to ripa rian vegetation or e ffects to the primary constituent elements (PCEs) relevant to the aquatic- and terrestrial-phase CRLF. However, there is limited evidence in the open literature that methidathion has the potential to elicit phototoxic effects (Ecotox ref. 64451). This paper reported that methidathion significantly affected corn photos ynthesis when applied at 0.5 lbs a.i./A, a rate that is lower than many of the current ly registered rates. In addition, potential phytotoxic effects have been highlighted on methidathion labels (i.e., spotting, reddening, or chlorosis of the leav es) in certain sorghum varieties. An examination of the completed CRLF assessments for nine other organophosphate s indicates that the majority of the effects determinations for terrestrial plants were either “no effect” or “not likely to adversely affect”. Two were determined to be “LAA”; however, one had herbicidal activity from a known mechanism and the ot her used surrogate data from another pesticide. For some of these organophosphate s, as with the study mentioned above, there is the potential for some damage to plants. Nevertheless, the conc lusions in those cases were generally that while effects to terrest rial plants may affect the CRLF via habitat modification, they are not likely to advers ely affect the CRLF based on the type and extent of damage as observed. The m ode of action for methidathion as an organophosphate insecticide is not one known to affect plants. Therefore, based on the weight-of-evidence, methidathion is not likely to impact plants to an extent that is expected to adversely affect the CRLF at th e labeled application rates. Although some phytotoxicity could occur, these effects are considered to be insignificant in the context of a “take”. The effects determination is may affect, NLAA.

5.2.4 Modification to Designated Critical Habitat

The risk conclusions for the designated critic al habitat are based on conclusions described for indirect effects previous ly described. Potential habitat m odification is described below.

5.2.4.1 Aquatic-Phase PCEs

Three of the four assessment endpoints for the aquatic-phase prim ary constituent elements (PCEs) of designated critical ha bitat for the CRLF are related to potential effects to aquatic and/or terrestrial plants:

• Alteration of channel/pond m orphology or ge ometry and/or increase in sediment deposition within the stream channel or pond: aquatic ha bitat (including riparian vegetation) provides for shelter, fora ging, predator avoidance, and aquatic dispersal for juvenile and adult CRLFs.

• Altera tion 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 m odification of aquatic-b ased food sources for pre-metamorphs ( e.g., algae).

110Conclusions for potential indire ct effects to the CRLF via di rect effects to aquatic and terrestrial plants are used to determine whet her modification to critical habitat may occur. The potential for habitat medication via im pacts to aquatic plants (Sections 5.2.2.1 and 5.2.3.1) and terrestrial plants ( 5.2.3.2) is not considered to be significant. No habitat modification is expected.

The remaining aquatic-phase PCE is “altera tion o f other chemical characteristics necessary for normal growth and viability of CRLFs and their food source.” Other than impacts to algae as food items for tadpoles (discussed above), this PCE is assessed by considering direct and indirect effects to the aquatic-phase CRLF via acute and chronic freshwater fish and invertebrate toxicity e ndpoints as measures of effects. Based on the potential direct impact to the aquatic -phase CRLF (Section 5.2.1.1) and impacts to freshwater invertebrates a nd fish as food items (Sections 5.2.2.2 and 5.2.2.3), there is a potential for habitat modification.

5.2.4.2 Terrestrial-Phase PCEs

Two of the four assessment endpoints for the te rrestrial-phase PCEs of de signated critical habitat for the CRLF are related to poten tial effects to terrestrial plants:

• Elimination and/or disturbance of upland ha bitat; ability of hab itat to support food source of CRLFs: Upland areas within 200 ft of the edge of the riparian vegetation or drip line surr ounding aquatic and riparian ha bitat that are comprised of grasslands, woodlands, and/or wetland/r iparian plant species that provides the CRLF shelter, forage, and predator avoidance.

• Elim ination and/or disturbance of dispersa l habitat: Upland or riparian dispersal habitat within designated un its and between occupied locations within 0.7 mi of each other that allow for movement be tween sites including both natural and altered sites which do not cont ain barriers to dispersal.

No habitat modification is expected thr ough im pacts to terrest rial plants (5.2.3.2).

The third terrestrial-phase PCE is “reducti on and/or m odification of food sources for terrestrial phase juveniles and adults.” To assess the impact of methidathion on this PCE, acute and chronic toxicity endpoints for terrestrial i nvertebrates, 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 (Sectio n 5.2.2.4 for terrestrial invertebrates, Section 5.2.2.5 for mammals, and 5.2.2.6 for frogs).

The fourth terrestrial-phase PCE is based on alteration of che mical characteristics necessary for normal growth and viability of juvenile and adult CRLFs and their food source. There is a potential for habitat m odification based on poten tial direct (Section 5.2.1.2) and indirect effects (Sections 5.2.2.4, 5.2.2.5, and 5.2.2.6) to terrestrial-phase CRLFs.

1116. Uncertainties

6.1 Exposure Assessment Uncertainties

6.1.1 Maximum Use Scenario

The screening-level risk assessment focuses on characterizing poten tial ecological risks resulting from a m aximum use scenario, which is determined from labeled statements of maximum application rate and number of appli cations with the shortest time interval between applications. The frequency at whic h actual uses approach this maximum use scenario may be dependant on pest resistance, timing of applications, cultural practices, and market forces. In particular, the applic ation rate assumed for use on nursery stock is conservative. The label does not provide explicit application rates for this use and so it is assessed based on an assumption of applicati on at the general maxi mum application rate required by the labels.

6.1.2 Aquatic Exposure Modeling of Methidathion

The standard ecological water body scenario (EXAMS pond) used to calculate potential aquatic exposure to pesticides is in tended to represent conservative estimates, and to avoid underestimations of the actual exposure. The standard scenario consists of application to a 10-hectare field border ing a 1-hectare, 2-meter deep (20,000 m 3 ) pond with no outlet. Exposure estimates genera ted using the EXAMS pond are intended to represent a wide variety of vulnerable water bodies that occur at the top of watersheds including prairie pot holes, playa lakes, wetlands, vernal pools, man-made and natural ponds, and intermittent and lower order streams. As a group, there are factors that make these water bodies more or less vulnerable than the EXAMS pond. Static water bodies that have larger ratios of pesticide-treate d drainage area to water body volume would be expected to have higher peak EECs than the EXAMS pond. These water bodies will be either smaller in size or have larger drainage areas. Sm aller water bodies have limited storage capacity and thus may overflow and carry pesticide in the discharge, whereas the EXAMS pond has no discharge. As waters hed size increases beyond 10-hectares, it becomes increasingly unlikely that the entire watershed is planted w ith a single crop that is all treated simultaneously with the pesticid e. Headwater streams can also have peak concentrations higher than the EXAMS pond, but they likely persist for only short periods of time and are then car ried and dissipated downstream.

The Agency acknowledges that there are so m e unique aquatic habitats that are not accurately captured by this modeling scenar io and modeling results may, therefore, under- or over-estimate exposure, depending on a number of variables. For example, aquatic-phase CRLFs may inhabit water bodies of different size a nd depth and/or are located adjacent to larger orsmaller drainage areas than the EXAMS pond. The Agency does not currently have sufficient informa tion regarding the hydrology of these aquatic habitats to develop a specific alternate scenar io for the CRLF. CRLFs prefer habitat with perennial (present year-round) or near-perennial water and do not frequently inhabit

112vernal (temporary) pools because conditions in these habitats are generally not suitable (Hayes and Jennings 1988). Therefore, the EXAMS pond is assumed to be representative of exposure to aquatic-phase CRLFs. In addi tion, the Services agree that the existing EXAMS pond represents the best currently available approach for estimating aquatic exposure to pesticid es (USFWS/NMFS 2004).

In general, the linked PRZM/EXAMS model produces estim ated aquatic concentrations that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone Model is a process or “simulation” model that calculates what happens to a pesticide in an agricultural field on a day-to-day basis. It considers factors such as rainfall and plant transpiration of water, as well as how and when the pesticide is applied. It has two major components: hydrology and chemical transport. Water movement is simulated by the use of generalized soil parameters, including fi eld capacity, wilting point, and saturation water content. The chemical transport com ponent can simulate pesticide application on the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase concentrations in the soil are estimated by simultaneously cons idering the processes of pesticide uptake by plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection, dispersion, and retardation.

Uncertainties associated with each of thes e individual com ponents add to the overall uncertainty of the modeled concentrations . Additionally, model inputs from the environmental fate degradation studies ar e chosen to represen t the upper confidence bound on the mean values that are not expected to be exceeded in the environment approximately 90 percent of the time. M obility input values are chosen to be representative of conditions in the environment. The natural va riation in soils adds to the uncertainty of modeled values. Factors such as application date, crop emergence date, and canopy cover can also affect estimated c oncentrations, adding to the uncertainty of modeled values. Factors within the ambien t environment such as soil temperatures, sunlight intensity, antecedent soil moistu re, and surface water temperatures can cause actual aquatic concentrations to differ for the modeled values.

Unlike spray drift, tools are currently not availa ble to ev aluate the effectiveness of buffers on runoff and loadings. The effect of buf fers on runoff is highly dependent on the condition of the vegetative strip. For exam ple, a well-establishe d, healthy vegetative setback can be a very effective means of re ducing runoff and erosion from agricultural fields. Alternatively, a setback of poor vegeta tive quality or a setbac k 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 pred ictions are likely to overestimate exposure where healthy vegetative setbacks exist and underestimate exposure where poorly developed, channelized, or bare setbacks exist.

In order to account for uncertainties associ ated w ith modeling, available monitoring data were compared to PRZM/EXAMS estimates of peak EECs. The surface water dataset for methidathion has several thousand samples collected from 135 sites primarily in agricultural areas, and includes several monitoring studi es targeted to water bodies

113receiving runoff from high OP use areas and with a high frequency of sampling, factors which reduce the uncertainty inherent in monitoring data. This monitoring detected methidathion in surface waters at concentr ations of up to 15.1 ug/L. Peak modeling EECs range from 7.3 ug/L for alfalfa to 52.4 ug/L for the almond use. (The maximum modeled EEC is 114.7 ug/L for the use on nurse ry stock, but this result is based on conservative assumptions about application rate s.) The highest mon itoring detection of 15.1 ug/L is within this range, below the peak EECs for some uses but higher than EECs for others. Although the use in the locati on with the highest de tection is unknown, the majority of the sampling was conducted in areas with high acreag e of fruit and nut orchards, which had modeled EECs of 17.8 ug/L for fruit trees, 20.0 ug/L for olives, and 52.4 ug/L, suggesting that the detection is not in excess of relevant modeled EECs. Additionally, the next highest monitored detec tion from this relatively large dataset is 2.4 ug/L, suggesting that the modeled EECs are reasonably c onservative representations of 1- in-10 year concentrations.

6.1.3 Potential Groundwater Contributions to Surface Water Chemical Concentrations

Although the potential impact of discharging ground water on CRLF populations is not explicitly delineated, it shoul d be noted that ground wate r could provide a source of pesticide to surface water bodies – especially low-order streams, headwaters, and ground water-fed pools. Terrestrial field diss ipation studies did not find leaching of methidathion below 12 inches, but given th e fact that methidathion is soluble and classified as moderatley mobile, and that its abiotic and biotic degr adation in anaerobic aquatic environments may be slow, the possi bility of methidathion reaching ground water cannot be precluded. Much of available ground water will eventually be discharged to the surface – often supporting stream flow in the absence of rainfall. Continuously flowing low-order streams in particular are sustained by ground water discharge, which can constitute 100% of stream flow during ba seflow (no runoff) conditions. Thus, it is important to keep in mind that pesticides in groundwater may have a major (detrimental) impact on surface water qualit y, and on CRLF habitats.

Concentrations in a receivi ng water body resulting from gr oundwater discharge cannot be explicitly quantified, but it can be assumed th at significant attenuati on and retardation of the chemical will have occurred prior to disc harge. Nevertheless, groundwater could still be a significant consis tent source of chronic background co ncentrations in surface water, and may also add to surface runoff during storm events (as a result of enhanced groundwater discharge typical ly characterized by the ‘tailing limb’ of a storm hydrograph). In this assessment, long-term chronic concentrations derived from the PRZM-EXAMS model are assumed to reflect background concentrations that might be found in discharged groundwater/s tream baseflow, but this fact or remains an uncertainty.

6.1.4 Action Area Uncertainties

An example of an important simplifying assumption that may require future refinement is the assum ption of uniform runoff characteri stics throughout a lands cape. It is well

114documented that runoff characteristics ar e highly non-uniform and anisotropic, and become increasingly so as the area under consideration becomes larger. The assumption made for estimating the aquatic action area (b ased on predicted in-stream dilution) was that the entire landscape exhi bited runoff properties identical to those commonly found in agricultural lands in this re gion. However, considering the vastly different runoff characteristics of: a) undeveloped (especially forested) areas, which exhibit the least amount of surface runoff but the greatest amount of groundwater recharge; b) suburban/residential areas, which are do minated by the relationship between impermeable surfaces (roads, lots) and grasse d/other areas (lawns) plus local drainage management; c) urban areas, that are do minated by managed storm drainage and impermeable surfaces; and d) agricultural areas dominated by Hortonian and focused runoff (especially with row crops), a re fined assessment should incorporate these differences for modeled stream flow ge neration. As the z one around the immediate (application) target area expands, there will be greater variability in the landscape; in the context of a risk assessment, the runoff potential that is assumed for the expanding area will be a crucial variable (since dilution at th e outflow point is determined by the size of the expanding area). Thus, it important to know at least some approximate estimate of types of land use within that region. R unoff from forested areas ranges from 45 – 2,700% less than from agricultural areas; in mo st studies, runoff was 2.5 to 7 times higher in agricultural areas (e.g., Okisaka et al ., 1997; Karvonen et al., 1999; McDonald et al., 2002; Phuong and van Dam 2002). Differe nces in runoff potential between urban/suburban areas and agricultural areas ar e generally less than between agricultural and forested areas. In terms of likely r unoff potential (other variables – such as topography and rainfall – being equal), the relationship is ge nerally as follows (going from lowest to highest runoff potential):

Three-tiered forest < agroforestry < suburban < row-crop agriculture < urban.

There are, however, other uncertainties that should serve to counter act the effects of the aforementioned issue. For example, the di lution model considers that 100% of the agricultural area has the chemical applied, which is almost certainly a gross overestimation. Thus, there will be assumed chemic al contributions from agricultural areas that will actually be contributing only runoff water (dilutant); so some contributions to total contaminant load will really serve to lessen rather than increase aquatic concentrations. In light of these (and ot her) confounding factors, Agency believes that this model gives us the best available estimates under current circumstances.

6.1.5 Usage Uncertainties

County-level usage data were obtained from California’s Departm ent of Pesticide Regulation Pesticide Use Reporti ng (CDPR PUR) database. Ei ght years of data (1999 – 2006) were included in this analysis. CDPR PUR documentation indicates that errors in the data may include the following: a mi splaced decimal; incorrect measures, area treated, or units; and reports of diluted pesticide concentratio ns. In addition, it is possible that the data may contain reports for pesticid e uses that have been cancelled. The CPDR PUR data does not include home owner applied pe sticides; therefore, residential uses are

115not 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 disc repancies, the most conservative information was used.

6.1.6 Terrestrial Exposure Modeling of Methidathion

The Agency relies on the work of Fletcher et al. (1994) for setting the assum ed pesticide residues in wildlife dietary it ems. These residue assumptions are believed to reflect a realistic upper-bound residue estimate, alt hough 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 devel op 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 pl ants 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 laborato ry. Although the screening a ssessm ent process adjusts dryweight 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 concentrati on- 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 betw een laboratory and wild diets suggest that current screening assessm ent me thods 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 mamm al’s assimilation ranges from 41 – 85% (U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is formulated to maximize assimilative efficien cy (e.g., a value of 85%), a potential for underestimation of exposure may exist by assu ming that consumption of food in the wild is comparable with consumption during labora tory testing. In th e screening process, exposure may be underestimated because me tabolic rates are not related to food consumption.

For the terrestrial exposure analysis of this risk assessm ent, 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 sugges t that this assumption leads to an overestimation of exposure to species that do not occupy the treated field exclusively and permanently.

1166.1.7 Spray Drift Modeling

Although there may be multiple methidathion app lications at a single site, it is unlikely that the same organism would be exposed to the maximum amount of spray drift from every application made. In order for an or ganism to receive the maximum concentration of methidathion from multiple applications, each application of methidathion would have to occur under identical atmospheric conditions ( e.g. , same wind speed and – for plants – same wind direction) and (if it is an animal) the animal being exposed would have to be present directly downwind at the same distance after each application. Although there may be sites where the dominant wind directi on is fairly consistent (at least during the relatively quiescent conditions that are most fa vorable for aerial spra y applications), it is nevertheless highly unlikely that plants in any specific area would receive the maximum amount of spray drift re peatedly. It appears that in most areas (based upon available meteorological data) wind direction is temporal ly very changeable, even within the same day. Additionally, other factors, includi ng variations in topography, cover, and meteorological conditions over the trans port distance are not accounted for by the AgDRIFT/AGDISP model ( i.e ., it models spray drift from aerial and ground applications in a flat area with little to no ground cover and a steady, constant wind speed and direction). Therefore, in most cases, th e drift estimates from AgDRIFT/AGDISP may overestimate exposure even from single applica tions, especially as the distance increases from the site of application, since the m odel does not account for potential obstructions ( e.g ., large hills, berms, buildings, trees, etc .). Furthermore, conservative assumptions are often made regarding the application method ( e .g., aerial), release heights and wind speeds. Alterations in any of these inputs would change the area of potential effect.

6.2 Effects Assessment Uncertainties

6 .2.1 Age Class and Sensitivity of Effects Thresholds It is generally recognized that test orga nism 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. Aqua tic 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 overe stim ate toxicity at older age classes for pesticide active ingredients that act direc tly without metabolic transf ormation because younger age classes may not have the enzymatic systems a ssociated with detoxifying xenobiotics. In so far as the available toxicity data may provide ranges of sensitivity information with respect to age class, this assessment uses th e most sensitive life-stage information as measures of effect for surrogate aquatic an imals, and is therefore, considered as protective of the CRLF.

1176.2.2 Use of Surrogate Species Effects Data

Guideline toxicity tests and open literature d ata on methidathion are not available for frogs or any other aquatic-phase amphibian; therefore, freshwater fish are used as surrogate species for aquatic-pha se amphibians. Efforts are ma de to select the organisms most likely to be affected by the type of compound and usage pattern; however, there is an inherent uncertainty in ex trapolating across phyla. In addition, the Agency’s LOCs are intentionally set very low, and conservati ve estimates are made in the screening level risk assessment to account for these uncertainties.

6.2.3 Sublethal Effects

When assessing acute risk, the screening risk assessment relies on the acute mortality endpoint as well as a suite of sublethal respon ses to the pesticide, as determ ined by the testing of species response to chronic expos ure conditions and subsequent chronic risk assessment. Consideration of additional sublet hal 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 fu ll suite of sublethal effects from valid open literature studies is considered for the purposes of defining the action area.

When assessing acute risk, the screening risk assessment relies on the acute mortality endpoint as well as a suite of sublethal respon ses to the pesticide, as determ ined by the testing of species response to chronic expos ure conditions and subsequent chronic risk assessment. Consideration of additional sublet hal 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 fu ll suite of sublethal effects from valid open literature studies is considered for the purposes of defining the action area.

In fish, slight spastic motions and sw imming on their sides were observed f ollowing acute exposure at 1000 μg/L (MRID 00011841). Fo llowing chronic exposure, total length and wet weight are affected (MRI D 00015730 or 45822701) with a NOAEC/LOAEC of 6.3/12 μg ai/L respectively. No sublethal effects were reported in the freshwater invertebrate studies.

In birds, depression, reduced reaction to ex ternal stim uli, wing droop, convulsions, and salivation were observed following acute e xposure via gavage. In subacute dietary studies, toxic symptoms includ ing depression, reduced reaction to external stimuli, wing droop, loss of coordination, lower limb weakne ss, ruffled appearance, prostrate posture, and loss of righting reflex were observed at 178 ppm a.i. and above. Reductions on body weight gain and food consumption were redu ced at levels above 316 ppm a.i.. Following chronic exposure (MRID 44381602), none of the duc ks showed symptoms of toxicity or behavioral abnormalities during the experime nt. An increase in the number of eggs

118cracked and a decrease in the number of eggs not cracked/eggs laid were observed at 10 ppm. Brain cholinesterase was in consistently affected at 30 ppm.

The study used to define the action area exam ined the effects of subchronic m ethidathion administration on vascular wall damage in ra ts (ECOTOX ref. 80451). At the lowest dose tested (5 mg/kg/day), the levels of mal ondialdehyde (MDA), a biomarker for oxidative stress was significantly higher and cholineste rase activity was significantly lower. There were irregular, prominent breaks and fragmentatio n of the elastic fibers in the aortic wall.

In a 2-generation reproduction study in rats (MRID 40079812, -13), the parental systemic NOAE C was 5 ppm and the LOAEC was 25 ppm, based on tremors and decreased food consumption during lactation, a nd decreased ovarian weight. In addition, there was also a slight decrease in body weight early in the F1 growth phase at 50 ppm. The reproductive NOAEC was 5 ppm and the LOAEC was 25 ppm based on a decreased mating index and a generalized indication of pup unthriftyne ss while nursing. In addition, there was an increase in stillbirths and decreased pup surv ival at birth and duri ng lactation at the 50 ppm treatment level.

To the extent to which sublethal effects ar e not considered in this as sessment, the potential direct and indirect effects of methidathion on CRLF may be underestimated.

6.2.4 Location of Wildlife Species

For the terrestrial exposure analysis of this risk assessm ent, 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 sugges t 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 inform ation presented in this endangered specie s risk assessment represents the best data currently available to assess the potential risks of methidathion to the CRLF and its designated critical habitat.

Based on the best available information, the Ag ency m akes a Likely to Adversely Affect determination for the CRLF from the use of methidathion. Additionally, the Agency has determined that there is the potential for m odification of CRLF designa ted critical habitat from the use of the chemical.

There is potential for direct risk to the aquatic- and terrestrial-phase CRLF following either acute or chronic exposure to m ethidathion with its curre nt use patterns in California. The acute listed species LOC for freshwater fish (surrogate to the aquatic119phase CRLF) is exceeded for all uses; however , there are limited data which indicate that there will be some fish species that may not be at risk following acute exposure from some of the methidathion use scenarios. Th e chronic LOC for freshwater fish is also exceeded for all uses. For the terrestrial-pha se CRLF, using avian data as a surrogate, with the exception of mangos on a dietary basis for non-listed sp ecies, the acute dosebased, acute dietary-based and chronic dietar y-based RQs for the te rrestrial-phase CRLF, exceed both the acute listed and non-listed sp ecies LOC and chronic LOC for all of the assessed uses.

There is a potential for indirect effects to both the aquatic- and te rrestrial-phase CRLF. For aquatic inverteb rates (food source), the acute and chronic RQs exceed the acute nonlisted LOC for aquatic animals and chronic LO C for aquatic animals respectively, for all assessed uses. For fish and aquatic-phas e amphibians (food source) , the acute non-listed species LOC is exceeded for all uses. The chronic LOC is also exceeded for all uses. No studies are available for aquatic vascular and non-vascular plants (food source and habitat); however, the weight of the evidence indicates an effect determination of may affect, not likely to adversely affect (NL AA). For terrestrial invertebrates (food source), the RQs for both small and large insects exc eed acute LOC for non-li sted species for all methidathion uses, even with only a single use. For terrestria l-phase amphibians (food source), see the direct eff ects paragraph. For mammals (food source), the acute and chronic RQs exceed the non-listed species acute LOC and the chronic LOC, respectively for all uses. No studies are available for terrestrial plants (habitat). There is some evidence for potential for terrestrial plant damage; however, the weight of the evidence indicates that the effect to terrestrial plants is may affect, not likel y to adversely affect (NLAA). Habitat modification is expected for both the aq uatic- and terrestrial-phase CRLF based on indirect effects from the reduc tion in prey base. A significant overlap is expected to exist between the use sites and CRL F habitat, particularly when the spraydrift and downstream dilution buffers are added to the methidathion use area. Spraydrift distances range from 23 to greater than 1000 feet and the downstream dilution buffer is 285 km. Figure 5.1 references the overlap of frog habitat with NLCD land cover data for use patterns that result in LAA determinations. Given the LAA determination for the CRLF and potential modification of designated critical habitat, a description of the baseline status and cumulative effects for the CRLF is provided in Attachment 2

. A summary of the risk conclusions and e f fects determinations for the CRLF and its critical habitat, given the uncertainties discussed in Section 6, is presented in Tables 7.1 and 7.2

.

120Table 7.1 Effects Determination Summary for Methidathion Use and the CRLF
Assessment

Endpoint Effects Determination 1 Basis for Determination

Potential for Direct Effects Aquatic-phase (Eggs, Larvae, and Adults) :

Highly toxic to freshwater fis h. Acute listed species LOC exceeded for all uses for three tested surrogate sp ecies. Chronic effects based on survival and growth. Chronic LOC exceeded for all uses. Proba bility of an individual effect on an acute basis is high, both at the acute LOC and at the RQ levels. Incident data also indicate freshwater fi sh vulnerability, and monito ring has detected surface water concentrations above the acute endp oint. Significant overlap expected to exist between use sites and CRLF habitat, particularly when the spraydrift and downstream dilution buffers are added to the methidathion use area. Spraydrift distances range from 23 to over 1000 feet and the downstream dilution buffer is 285 km. Terrestrial-phase (Juveniles and Adults) :

Moderately toxic to very highly toxic to avian species. Acute dose-based, acute dietary-ba sed and chronic dietary-base d RQs for the terrestrial-phase CRLF, using avian data as a surrogate, exceed acute listed species LOC and chronic LOC for all of the assessed uses. Chroni c effects based on reduction in number of normal hatchlings/live 3-week embryos. Limited data indicate that on a dose basis, the acute LOC is exceeded for all uses, even with the least sensitive species at the lowest application rate (ma ngos). On a dietary basis, the same is true for all uses except mangos. Probability of an individual effect on an acute basis is high at the RQ levels. Incident data indicate that birds are vulnerable. Significant overlap exists between use sites and CRLF habitat, particularly when the spraydrift buffers are ap plied to the methidathion use area. Spraydrift distances range from 194 to over 1000 feet. Potential for Indirect Effects Aquatic prey items, aquatic habitat, cover and/or primary productivity

Very highly toxic to fresh water invertebrates. Acute and chronic RQs exceed

acu te LOC for non-listed species and chr onic LOC, respectively for all assessed uses. The percentage effect to the aquatic invertebrate prey base for all uses is very high. For fish (aquatic-phase amphibians), acute non-listed species LOC exceeded for all uses. Chronic LOC exceeded for all uses. Percentage effect to the freshwater fish/aquatic-phase amphibian prey base is very high. No studies are available for aquatic vascular and non-vascular plants. Survival, growth, and/or reproduction of CRLF individuals LAA 1

Terrestrial prey items, riparian habitat

RQs for both small and large insects exce ed acute LOC for non-listed species for all methidathion uses, even with only a single use. Insufficient studies to conduct a sensitivity analysis; however, lowest RQ, using highest terrestrial invertebrate endpoint still exceeds the acut e list species LOC. Percentage effect to the terrestrial invertebrate prey base for all uses is very high. For terrestrialphase amphibians using avian data as a surrogate, with the exception of mangos on an acute dietary basis, the acute do se-based, acute dietary-based and chronic dietary-based RQs exceed the acute non- listed species LOC and the chronic LOC for all of the assessed methidathion uses, respectively. Percentage effect to the avian/terrestrial-phase amphi bian prey base is very high. For mammals, the acute and chronic RQs exceed the non-lis ted species acute LOC and the chronic LOC, respectively for all uses. At the lowest RQ, the percentage effect to the mammalian prey base is very high. No st udies are available for terrestrial plants.

1211 No effect (NE); May affect, but not likely to adversely affect (NLAA) ; May affect, likely to adversely affect (LAA)

Table 7.2 Effects Determination Summary for Methidathion Use and CRLF Critical Habitat Impact Analysis
Assessment

Endpoint Effects Determination 1 Basis for Determination

Modification of aquatic-phase PCE No studies available for aquatic vascular and non-vascular plants and terrestrial plants.

For the aquatic-phase CRLF, acute non-listed species LOC for freshwater fi sh (aquatic-phase amphibians) exceeded for all uses. Chronic LOC for freshwater fish exceeded for all uses. Probability of an individual effect and percentage effect to the freshwater fish/aquatic-phase amphibian prey base on an acute basis at the RQ are high. Incident data support freshwater fish vulnerability. For freshwater inverteb rates, acute and chronic RQs exceed acute LOC (non-listed species) and chronic LOC, respectively for all assessed uses. Again, the percentage ef fect to the aquatic invertebrate prey base is very high. Significant overlap expected between use sites and CRLF habitat, particularly when the spraydri ft and downstream dilution buffers are added to the use area. Spraydrift distances range from 23 (mangos) to over 1000 feet and the downstream dilution buffer is 285 km. Modification of terrestrial-phase PCE Habitat M odification 1

No studies are available for terrestrial plants.

For the terrestrial-phase CRLF, using av ian data as a surrogate, with the exception of mangos on a dietary basis for non-listed species, the acute dosebased, acute dietary-based and chronic dietary-based RQs for the terrestrialphase CRLF, exceed both the acute listed and non-listed species LOC and chronic LOC for all of the assessed uses. Probability of an individual effect on an acute basis at the lowest RQ level and percentage effect to the avian/terrestrial-phase amphi bian prey base are very high. Incident data indicate that birds are vulnerable. RQs for both small and large insects exceed acute LOC for non-listed species fo r all methidathion uses, even with only a single use. Percentage effect to terrestrial invertebrate prey base for all uses are very high. For mammals , the acute and chronic RQs exceed the non-listed species acute LOC and the chro nic LOC, respectively for all uses. The percentage effect to the mammalian prey base is very high for all uses. Significant overlap exists between use sites and CRLF habitat, particularly when the spraydrift buffers are app lied to the methidathion use area. Spraydrift distances range from 194 (mangos) to over 1000 feet.

1 Habitat Modification or No effect (NE)

Based on the conclusions of this assessment, a form al consultation with the U. S. Fish and Wildlife Service under Sect ion 7 of the Endangered Spec ies Act should be initiated to seek concurrence with the LAA determinations and to determine whether there are reasonable and prudent alternatives and/or m easures to reduce and/or eliminate potential incidental take.

When evaluating the significance of this ri sk assessment’s direct /indirect and adverse habitat m odification 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

122not expected to be uniform across the action ar ea. In fact, given the assumptions of drift and downstream transport (i.e., attenuation with distance), pes ticide exposure and associated risks to the species and its resour ces 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 re quire information and assessment techniques that are not currently avai lable. Examples of such information and methodology required for this type of an alysis would include the following:

• Enhanced infor mation on the density and distribution of CRLF life stages within specific recovery units and/or designated critical habitat within the action area. This information would allow for quantitative extrapolation of the present risk assessment’s pred ictions of individual effects to the proportion of the population extant with in geographical areas where those effects are predicted. Furthermore, such population information would allow for a more comprehensive eval uation of the significance of potential resource impairment to individuals of the species.

• Quantita tive information on prey base requirements for individual aquaticand terrestrial-phase frogs. Wh ile existing information provides a preliminary picture of the types of food sources util ized by the frog, it does not establish minimal requirements to sustain healthy individuals at varying life stages. Such informa tion could be used to establish biologically relevant thresholds of ef fects 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.

• Inform ation on population responses of prey base organisms to the pesticide. Currently, methodologies are limited to predicting exposures and likely levels of direct mortalit y, 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 ex tent to which prey resources may recover is not predictable. An e nhanced 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 descri bed above, a more complete prediction of effects to individual frogs and pot ential modification to critical habitat.

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