Risks of Methamidophos Use to Federally Listed
California Red Legged Frog
(Rana aurora draytonii)
Pesticide Effects Determination
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
July 18, 2007
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Primary Authors
Michael Davy, Agronomist
William P. Eckel, Ph.D., Agronomist
Carolyn Hammer, Environmental Scientist
Secondary Review
Donna Randall, Senior Biologist
Nelson Thurman, Senior Science Advisor
Branch Chief, Environmental Risk Assessment Branch 2
Dana Spatz
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Table of Contents
1. Executive Summary 7
2. Problem Formulation 11
2.1 Purpose 11
2.2 Scope 13
2.2.1. Degradates 14
2.2.2 Product Formulations Containing Multiple Active Ingredients 14
2.3 Previous Assessments 14
2.3.1 Methamidophos Assessments 14
2.3.2 California Red-legged Frog Assessments 15
2.4 Stressor Source and Distribution 15
2.4.1 Environmental Fate Assessment 16
2.4.2 Environmental Transport Assessment 17
2.4.3 Mechanism of Action 18
2.4.4 Use Characterization 18
2.5 Assessed Species 25
2.5.1 Distribution 25
2.5.2 Reproduction 31
2.5.3 Diet 31
2.5.4 Habitat 32
2.6 Designated Critical Habitat 33
2.6.1. Special Rule Exemption for Routine Ranching Activities 35
2.7 Action Area 36
2.8 Assessment Endpoints and Measures of Ecological Effect 42
2.8.1. Assessment Endpoints for the CRLF 42
2.8.2. Assessment Endpoints for Designated Critical Habitat 44
2.9 Conceptual Model 46
2.9.1 Risk Hypotheses 46
2.9.2 Diagram 47
2.10 Analysis Plan 49
2.10.1 Exposure Analysis 49
2.10.2 Effects Analysis 50
2.10.3 Action Area Analysis 51
3. Exposure Assessment 53
3.1 Label Application Rates and Intervals 53
3.2 Aquatic Exposure Assessment 54
3.2.1. Conceptual Model of Exposure 54
3.2.2 Existing Monitoring Data 54
3.2.3 Modeling Approach 54
3.2.4. Aquatic EEC Results 57
3.3. Terrestrial Exposure Assessment 57
3.3.1 Conceptual Model of Exposure 57
3.3.2. Modeling Approach 57
3.3.3. Model Inputs 58
3.3.4 Results 58
4. Effects Assessment 60
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4.1 Evaluation of Ecotoxicity Studies: Aquatic and Terrestrial 60
4.2. Evaluation of Aquatic Effects 63
4.2.1 Toxicity to Freshwater Fish 64
4.2.2. Toxicity to Freshwater Invertebrates 65
4.3. Toxicity to Birds 67
4.3.1. Birds: Acute Exposure (Mortality) Studies 67
4.3.2. Acute Oral LD50 67
4.3.3. Avian sub acute dietary endpoint analysis 67
4.3.4 Birds: Chronic Exposure (Reproduction) Studies 68
4.3.5 Birds: Sublethal Effects and Additional Open Literature
Information 68
4.4 Toxicity to Mammals 68
4.4.1. Mammals: Acute Exposure (Mortality) Studies 68
4.4.2. Mammals: Chronic Exposure (Reproduction) Studies 68
4.4.3. Mammals: Sublethal Effects and Additional Open Literature
Information 69
4.5 Toxicity to Insects 69
4.6 Toxicity to Plants 69
4.6.1 Toxicity to Aquatic Plants 69
4.6.2. Terrestrial Plants 69
4.7 Aquatic and Terrestrial Field Studies 70
4.7.1. Terrestrial Field Studies 70
4.7.2 Aquatic Field Studies 71
4.8 Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern 71
4.9 Incident Database Review 72
5. Risk Characterization 73
5.1 Risk Estimation 73
5.1.1 Direct Effects 73
5.1.2 Indirect Effects 75
5.1.3 Individual Effect Chance Calculation 78
5.2 Risk Description 79
5.2.1. Direct Effects to the CRLF 80
5.2.2. Indirect Effects to the CRLF 83
5.3 Action Area 83
5.3.1. Aquatic Phase 84
5.3.2. Terrestrial Phase 84
5.4 Listed Species Effect Determination for the California Red-Legged Frog 87
5.4.1. "May Affect" Determination 87
5.4.2 "Adverse Effect" Determination 87
5.5 Risk Hypotheses Revsisted 90
6. Uncertainties 92
6.1. Exposure Assessment Uncertainties 92
6.2 PRZM Modeling Inputs and Predicted Aquatic Concentrations 92
6.3 Effects Assessment Uncertainties 93
6.3.1 Age Class and Sensitivity of Effects Thresholds 93
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6.3.2 Extrapolation of Long-term Environmental Effects from
Short-Term Laboratory Tests 93
6.4 Assumptions Associated with the Acute LOCs 94
6.5 Use of avian data as surrogate for amphibian data 94
6.6 Maximum Use Scenario 94
6.7 Usage Uncertainties 94
6.8 Action Area 95
6.9 Aquatic Exposure Estimates 95
6.10 Residue Levels Selection 96
6.11 Dietary Intake 97
6.12 Sublethal Effects 97
6.13 Location of Wildlife Species 97
7. References 98
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Appendices
Appendix
A
Appendix
A1
Appendix
B
Appendix
C
Appendix
D
Appendix
E
Appendix
F
Appendix
G
Appendix
H
Ecological Effects Data
Detail of Some Toxicity Studies Not Used in RQ Calculations
Aquatic Exposure Modeling Runs
Terrestrial Modeling Runs (TREX)
Terrestrial modeling Runs (THERPS)
Incident Database Information
RQ Method and LOCs
ECOTOX Database
GIS Mapping Appendix
Attachments
1. Life History of the California Red-Legged Frog
2. Baseline Status and Cumulative Effects for the California Red-Legged Frog
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1. Executive Summary
Background
Methamidophos is an organophosphate insecticide currently registered for use on four
agricultural crops in California: tomato, potato, cotton and alfalfa grown for seed. It is
applied by aircraft, groundspray, or irrigation at a rate of up to 1 lb a.i./acre up to four
times per year. Methamidophos is very soluble and very mobile and may move through
the environment and be transported away from the site of application by run-off or spray
drift. Methamidophos is not persistent in terrestrial or aerobic aquatic environments but
may be more persistent in anaerobic aquatic environments where it will be associated
with the aqueous phase. Studies show that bioaccumulation of methamidophos in fish is
insignificant.
Methamidophos exhibits a range of toxicity from practically non-toxic to plants, to very
highly toxic to avian species. Methamidophos is considered:
o very highly to highly toxic to avian species on an acute oral basis (LC50= 42 ppm)
o slightly toxic to very highly toxic to avian species on a subacute dietary basis
o highly toxic to mammals on an acute oral basis (LD50=7.9 mg/kg-bw)
o highly toxic to bees on an acute contact basis (LD50 =1.37 |ig/bee)
o slightly toxic to freshwater fish on an acute basis (LC50 =25,000 (J,g/L)
o very highly toxic to aquatic invertebrates on an acute basis (EC5o= 26 (J,g/L)
o practically non-toxic to plants (EC50>50 ppm)
The California red-legged frog inhabits a mosaic of aquatic and upland habitat that it
requires to complete its life history. This assessment considers direct and indirect effects
on the frog and its critical habitat. To ensure clarity and ease of understanding this
assessment, the lifecycle of the frog was separated into an aquatic phase and a terrestrial
phase, as the exposure and effects modeling for these two ecosystems are different. The
aquatic phase includes eggs, larvae, tadpoles, juveniles, and adults. Although juveniles
and adults spend a significant amount of time in terrestrial habitats, they also use the
aquatic portion of their habitat, especially during breeding. The terrestrial phase
evaluation includes juveniles and adults. Components of the ecosystem addressed in the
assessment include aquatic plants, aquatic invertebrates, fish, terrestrial plants, terrestrial
invertebrates, and terrestrial vertebrates (e.g. small mammals,) in addition to the various
life stages of the frog itself.
Aquatic Phase
Direct, acute effects to the aquatic phase CRLF are not expected as there are no LOC
exceedences for freshwater fish, the surrogate test species for the aquatic phase CRLF.
An acute-to-chronic ratio analysis with other organophosphate insecticides indicated no
LOC exceedence for reproductive effects. Indirect effects to the aquatic phase of the
frog, due to effects on critical habitat are not expected, since there were no LOC
exceedences to aquatic plants, nor effects to water quality. Indirect effects to CRLF,
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based on food availability are not expected, because the effect on invertebrate food
sources is discountable. Thus it was determined that methamidophos use is not likely to
adversely affect the aquatic phase CRLF, or its critical habitat.
Terrestrial Phase
Methamidophos use is likely to adversely affect the terrestrial phase of the CRLF
directly, as determined by acute and chronic LOC exceedences for birds, the surrogate
test species for terrestrial phase CRLF. Avian reproductive effects indicate direct chronic
fecundity effects to CRLF. Toxic effects on the CRLF prey base are likely to adversely
affect the terrestrial phase CRLF as several taxa from the CRLF diet exceed the LOC.
Birds, mammals, insects, small amphibians and fish are all part of the terrestrial CRLF
diet. Because multiple components of the diet are expected to be affected, including
mammals, birds and insects, an LAA determination was made for indirect effects. An
LAA determination for terrestrial critical habitat was concluded based on adverse
modification of terrestrial food resources.
Based on LOC exceedences, the overlap of use sites with frog habitat and core areas, and
other factors, the following table summarizes the effects determination for the CRLF
from methamidophos use.
Methamidophos Effects Determination Summary
Assessment
Endpoint
Effects
determination
Basis for Determination
Aquatic Phase
(Eggs, larvae, tadpoles, juveniles, and adults)
Direct Effects
1. Survival, growth,
and reproduction of
CRLF
No Effect
All Acute and Chronic RQ are below the listed LOC for
surrogate species (rainbow trout)
Indirect Effects and Critical Habitat Effects
2. Reduction or
modification of
aquatic prey base
May Affect,
Not Likely to
Adversely Affect
Acute LOC is exceeded for aquatic invertebrates,
however effect is considered discountable based on
low likelihood of individual effect.
3. Reduction or
modification of
aquatic plant
community
No Effect
No LOC Exceedences for any plant species
4. Degradation of
riparian vegetation
No Effect
No LOC Exceedences for any plant species
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Assessment
Endpoint
Effects
determination
Basis for Determination
Terrestrial Phase
(Juveniles and Adults)
Direct Effects
5. Survival, growth,
and reproduction of
CRLF
May Affect,
Likely to
Adversely Affect
Acute and Chronic LOC exceedences for birds, the
surrogate species for direct effects to frogs. Initial
Area of Concern overlaps habitat. Use is widespread
(23-26 counties). Use is documented in all months
except November, December, January. Probability of
effect approaches 100% at calculated RQs.
Indirect Effects and Critical Habitat Effects
6. Reduction or
modification of
terrestrial prey base
May Affect,
Likely to
Adversely Affect
Acute and Chronic LOC exceedences for multiple
components of CRLF prey base (mammals, birds, and
terrestrial invertebrates). LAA to terrestrial phase
CRLF and its critical habitat based on acute RQs
exceeding 0.5 for mammals, insects, birds.
7. Degradation of
riparian vegetation
No Effect
No plant LOC exceedences.
When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the species and its resources (i.e., food and habitat) are
not expected to be uniform across the action area. In fact, given the assumptions of drift
and downstream transport (i.e., attenuation with distance), pesticide exposure and
associated risks to the species and its resources are expected to decrease with increasing
distance away from the treated field or site of application. Evaluation of the implication
of this non-uniform distribution of risk to the species would require information and
assessment techniques that are not currently available. Examples of such information and
methodology required for this type of analysis would include the following:
Enhanced information on the density and distribution of CRLF 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 predictions of individual effects to the
proportion of the population extant within geographical areas where those
effects are predicted. Furthermore, such population information would
allow for a more comprehensive evaluation of the significance of potential
resource impairment to individuals of the species.
Quantitative information on prey base requirements for individual aquatic-
and terrestrial-phase frogs. While existing information provides a
preliminary picture of the types of food sources utilized by the frog, it
does not establish minimal requirements to sustain healthy individuals at
varying life stages. Such information could be used to establish
biologically relevant thresholds of effects on the prey base, and ultimately
establish geographical limits to those effects. This information could be
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used together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.
Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth or reproductive impairment
immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and
together with the information described above, a more complete prediction
of effects to individual frogs and potential adverse modification to critical
habitat.
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2. Problem Formulation
Problem formulation provides a strategic framework for the risk assessment. By
identifying the important components of the problem, it focuses the assessment on the
most relevant life history stages, habitat components, chemical properties, exposure
routes, and endpoints. This assessment was completed in accordance with the August 5,
2004 Joint Counterpart Endangered Species Act (ESA) Section 7 Consultation
Regulations specified in 50 CFRPart 402 (USFWS/NMFS 2004; FR 69 47732-47762).
The structure of this risk assessment is based on guidance contained in U.S. EPA's
Guidance for Ecological Risk Assessment (U.S. EPA 1998), the Services' Endangered
Species Consultation Handbook (USFWS/NMFS 1998) and procedures outlined in the
Overview of the Ecological Risk Assessment Process in the office of Pesticide Programs
(U.S. EPA 2004).
2.1 Purpose
The purpose of this endangered species assessment is to evaluate potential direct and
indirect effects on individuals of the federally threatened California red-legged frog
(Rana aurora draytonii) (CRLF) arising from FIFRA regulatory actions regarding use of
methamidophos on potatoes, tomatoes, and alfalfa for seed. In addition, this assessment
evaluates whether these actions can be expected to result in the destruction or adverse
modification of the species' critical habitat. Key biological information for the CRLF is
included in Section 2.5, and designated critical habitat information for the species is
provided in Section 2.6 of this assessment. This ecological risk assessment has been
prepared as part of the Center for Biological Diversity (CBD) us. EPA et al. (Case No.
02-1580-JSW(JL)) settlement entered in the Federal District Court for the Northern
District of California on October 20, 2006. It is one in a series of endangered species
effects determinations for pesticide active ingredients involved in this litigation.
In this endangered species assessment, direct and indirect effects to the CRLF and
potential adverse modification to its critical habitat are evaluated in accordance with the
methods (both screening level and species-specific refinements, when appropriate)
described in the Agency's Overview Document (U.S. EPA 2004).
In accordance with the Overview Document, provisions of the ESA, and the Services'
Endangered Species Consultation Handbook, the assessment of effects associated with
registrations of methamidophos are based on an action area. The action area is
considered to be the area directly or indirectly affected by the federal action, as indicated
by the exceedance of Agency Levels of Concern (LOCs) used to evaluate direct or
indirect effects. It is acknowledged that the action area for a national-level FIFRA
regulatory decision associated with a use of methamidophos may potentially involve
numerous areas throughout the United States and its Territories. However, for the
purposes of this assessment, attention will be focused on relevant sections of the action
area including those geographic areas associated with locations of the CRLF and its
designated critical habitat within the state of California.
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As part of the "effects determination," one of the following three conclusions will be
reached regarding the potential for registration of methamidophos at the use sites
described in this document to affect CRLF individuals and/or result in the destruction or
adverse modification of designated CRLF critical habitat:
"No effect";
"May affect, but not likely to adversely affect"; or
"May affect and likely to adversely affect".
Critical habitat identifies specific areas that have the physical and biological features,
(known as primary constituent elements or PCEs) essential to the conservation of listed
species. The PCEs for CRLFs are aquatic and upland areas where suitable breeding and
non-breeding aquatic habitat is located, interspersed with upland foraging and dispersal
habitat (Section 2.6).
If the results of initial screening-level assessment 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 the FIFRA regulatory
action regarding methamidophos as it relates to this species and its designated critical
habitat. If, however, direct or indirect effects to individual CRLFs are anticipated and/or
effects may impact the PCEs of the CRLF's designated critical habitat, a preliminary
"may affect" determination is made for the FIFRA regulatory action regarding
methamidophos.
If a determination is made that use of methamidophos within the action area(s) associated
with the CRLF "may affect" this species and/or its designated critical habitat, additional
information is considered to refine the potential for exposure and for effects to the CRLF
and other taxonomic groups upon which these species depend (e.g.., aquatic and
terrestrial vertebrates and invertebrates, aquatic plants, riparian vegetation, etc.).
Additional information, including spatial analysis (to determine the overlay of CRLF
habitat with methamidophos use) and further evaluation of the potential impact of
methamidophos on the PCEs is also used to determine whether destruction or adverse
modification to designated critical habitat may occur. Based on the refined information,
the Agency uses the best available information to distinguish those actions that "may
affect, but are not likely to adversely affect" from those actions that "may affect and are
likely to adversely affect" the CRLF and/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 direct and indirect effects to listed species
provides the basis for an analysis of potential effects on the designated critical habitat.
Because methamidophos is expected to directly impact living organisms within the action
area (defined in Section 2.7), critical habitat analysis for methamidophos is limited in a
practical sense to those PCEs of critical habitat that are biological or that can be
reasonably linked to biologically mediated processes (i.e., the biological resource
requirements for the listed species associated with the critical habitat or important
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physical aspects of the habitat that may be reasonably influenced through biological
processes). Activities that may destroy or adversely modify critical habitat are those that
alter the PCEs and jeopardize the continued existence of the species. Evaluation of
actions related to use of methamidophos that may alter the PCEs of the CRLF's critical
habitat form the basis of the critical habitat impact analysis. Actions that may affect the
CRLF's designated critical habitat and jeopardize the continued existence of the species
have been identified by the Services and are discussed further in Section 2.6.
2.2 Scope
The end result of the EPA pesticide registration process (the FIFRA regulatory action) is
an approved product label. The label is a legal document that stipulates how and where a
given pesticide may be used. Product labels (also known as end-use labels) describe the
formulation type (e.g., liquid or granular), acceptable methods of application, approved
use sites, and any restrictions on how applications may be conducted. Thus, the use or
potential use of methamidophos in accordance with the approved product labels for
California is "the action" being assessed.
Methamidophos was first registered in the United States in 1972 under the trade name
Monitor. It was used principally on potatoes, cotton, and cole crops to control a broad
spectrum of insects by inhibiting cholinesterase through contact. A Registration Standard,
which describes the terms and conditions for the continued registration of
methamidophos, was issued for methamidophos in 1982. In 1997, the technical registrant,
Bayer Corporation, voluntarily cancelled all uses of methamidophos except for use on
cotton, potatoes, and tomatoes (in California, a special local need 24(c) label only). In
1998, a special local need registration was issued for use on alfalfa grown for seed in
California. By December 1999, the registrant had also voluntarily phased-in closed
mixing and loading systems for all remaining uses to address potential worker exposures.
Use of methamidophos on cotton was canceled based on the Interim Reregi strati on
Eligibility Decision (IRED) published in 2002 (April 7), scheduled to be phased out
within 5 years (67 FR 63423-4, Oct. 11, 2002).
"Therefore, EPA expects that registrant will implement the risk mitigation measures as soon as possible. The
IRED document describes, in detail, what is necessary measures, such as submission of label amendments for
end-use products and submission of any required data. Mitigation measures for methamidophos include a
phase out of methamidophos use on cotton by 2007. Should a registrant fail to implement any of the risk
mitigation identified in the IRED document, the Agency may take regulatory action to address risk concerns
from the use of methamidophos."
However, because the labels have not yet been amended to reflect the mitigation
measures outlined in the IRED, cotton use will again be considered in this assessment as
the published label is considered the most current description of legal, registered uses.
This ecological risk assessment is for currently registered uses of methamidophos in
portions of the action area that are reasonably assumed to be biologically relevant to the
CRLF and its designated critical habitat. Further discussion of the action area for the
CRLF and its critical habitat is provided in Section 2.7.
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2.2.1. Degradates
The identified major degradates of methamidophos are S-methyl phosphoramidothioate
(CAS Reg. No. 17808-29-6), 0,S-dimethyl phosphorothioate (DMPT, CAS Reg. No.
42576-53-4), methyl mercaptan, dimethyl disulfide, and methyl disulfide. These
degradates are not considered in this assessment due to (1) their rapid dissipation in the
environment as shown in laboratory studies (hours to days), (2) the tendency of methyl
mercaptan, dimethyl disulfide and methyl sulfide to partition to air, and (3) lack of
toxicity data on S-methyl phosphoramidothioate and DMPT on which to base an
assessment. It is anticipated that LOCs will be exceeded based on parent methamidophos
alone.
2.2.2 Product Formulations Containing Multiple Active Ingredients
The Agency does not routinely include, in its risk assessments, an evaluation of mixtures
of active ingredients, either those mixtures of multiple active ingredients in product
formulations or those in the applicator's tank. In the case of the product formulations of
active ingredients (that is, a registered product containing more than one active
ingredient), each active ingredient is subject to an individual risk assessment for
regulatory decision regarding the active ingredient on a particular use site. If effects data
are available for a formulated product containing more than one active ingredient, they
may be used qualitatively or quantitatively in accordance with the Agency's Overview
Document and the Services' Evaluation Memorandum (U.S., EPA 2004; USFWS/NMFS
2004).
Methamidophos does not have any registered products that contain multiple active
ingredients.
2.3 Previous Assessments
2.3.1 Methamidophos Assessments
Assessments of potential ecological risks were conducted to support the Re-registration
Eligibility Decision (RED) and IRED for methamidophos in 19981 and 20022,
respectively. Acute and chronic risks to birds and mammals, bees and other non-target
beneficial insects, and some risk to freshwater and estuarine invertebrates were identified.
To mitigate ecological risks to terrestrial birds and mammals, and to freshwater and
estuarine invertebrates, EPA took the following actions in 2002:
o Phased out and canceled the cotton use over 5 years,
o For cotton during the phase-out period, reduced the maximum number of
applications to 2 per season,
o For tomatoes, reduced the maximum number of applications to 4 per season.
1 http://www.epa.gov/pesticides/op/methamidophos/efedlabc.pdf
2 http://www.epa.gov/oppsrrdl/op/methamidophos.htm
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The RED and IRED summarized methamidophos hazard to organisms as:
o very highly to highly toxic to avian species on an acute oral basis
o slightly toxic to very highly toxic to avian species on a subacute dietary basis
o highly toxic to mammals on an acute oral basis
o highly toxic to bees on an acute contact basis
o slightly toxic to freshwater fish on an acute basis
o very highly toxic to aquatic invertebrates on an acute basis
On March 31, 2004 EPA released an assessment of the potential effects of
methamidophos to 26 listed Environmentally Significant Units (ESUs) of Pacific salmon
and steelhead. That assessment concluded that methamidophos would have no effect on
the species under consideration. While methamidophos was noted to have significant
toxicity to aquatic invertebrates, as does this assessment, the minimal usage, the size of
the watersheds under consideration and the volume of the water bodies serving as habitat
to these species taken together, resulted in the determination of no effect to the listed
salmon and steelhead.
2.3.2 California Red-legged Frog Assessments
The Agency is currently developing a number of risk assessments for the CLRF, each
addressing different pesticide active ingredients. A total of 66 chemicals will be
assessed. Methamidophos is among the first group of ten chemicals to be completed.
For information regarding the other chemicals in this group3 please see the relevant
document.
2.4 Stressor Source and Distribution
Methamidophos is a colorless crystal with a melting point of 44.9°C. The technical
product (40%) is a colorless to pale yellow liquid with a mercaptan-like odor.
Methamidophos is miscible in water, and soluble in isopropanol (>200 g/L at 20°C),
dichloromethane (>200 g/L at 20°C), hexane (0.1-1 g/L), and toluene (2-5 g/L).
Case number: 0043
CAS registry number: 10265-92-6
OPP chemical code: 101201
Empirical formula: C2H8NO2PS
Molecular weight: 114.12 g/mol
Vapor Pressure: 3.5 x 10-smm Hg at 25 oC
Trade and other names: Monitor, Tamaron
Technical registrants: Bayer CropScience
3 Other chemicals assessed in the first group include methamidaphos, methomyl, azinphos-methyl,
acephate, imazpyr, aldicarb, metam sodium, diazinon and chloropicrin
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2.4.1 Environmental Fate Assessment
Information from laboratory studies indicates that methamidophos is not persistent in
aerobic environments but may be more persistent in anaerobic aquatic environments
where it will be associated with the aqueous phase. Terrestrial field dissipation studies
for methamidophos and acephate (methamidophos is the major degradate of acephate)
indicated that methamidophos was not persistent.
Aerobic soil metabolism is the main degradation process for methamidophos.
Methamidophos degraded with a calculated half-life of 14 hours in a sandy loam soil at
greater than the currently registered application rate (nominal application rate of 6.5 ppm,
compared to the expected 0.5 ppm from the maximum label rate of 1 lb ai/A), producing
the intermediate degradate S-methyl phosphoramidothioate, which is itself rapidly
metabolized by soil microorganisms to carbon dioxide and microbial biomass (half-life of
< 5 days). Supplemental information also identifies DMPT as a major degradate which is
also rapidly degraded in soil (half-life of < 4 days). Methamidophos photodegrades
rapidly on soil irradiated with a mercury vapor lamp (dark control-corrected half-life 63
hours); however, in sterile aqueous solutions, methamidophos photodegrades slowly
(dark control-corrected half-life > 200 days) and is stable against hydrolysis at acid pHs.
Hydrolysis degradates at neutral and alkaline pHs include O-desmethyl, DMPT, and the
volatile degradate dimethyldisulfide.
Supplemental information showed that methamidophos degraded in anaerobic sandy
loam sediment: pond water systems in the laboratory with a DT50 (degradation time in
which 50% degrades)of 41 days. Observed major degradates in the same study were
DMPT and O-desmethyl methamidophos, but their persistence could not be determined
due to incomplete material balances after 3 months of anaerobic incubation. Carbon 14
[14C] labeled residues were distributed between the water and sediment fractions with the
majority of residues observed in the water phase in a ratio of approximately 10 to 1. This
study was repeated with a silty clay sediment with similar results (incomplete mass
accounting due to loss of methane), DT50 7-14 days, and DT90 5 8-93 days; the calculated
half-life was 19.4 days. There are no acceptable data for the aerobic aquatic metabolism
of methamidophos.
Soil dissipation of methamidophos (0,S-dimethyl phosphoramidothioate) was conducted
under U.S. field conditions in four replicate bare plots of loamy sand soil from
Washington. Dissipation of methamidophos was rapid in this study. The average
measured zero time concentration was 322 parts per billion (ppb). Under field conditions
in the loamy sand soil, methamidophos had a log-linear half-life of 0.49 days in soil. The
observed DT50 of methamidophos was 0.33-1 days. No major transformation products
were identified. In the 0-15 centimeter (cm) soil layer, two minor transformation
products were identified: S-methyl phosphoramidothioate (O-desmethyl methamidophos)
was a maximum average of 27.1 ppb and 0,S-dimethyl phosphorothioate was a
maximum average of 14.3 ppb each at day zero. In the 0-15 cm soil layer, no
transformation products were detected after 1 day. In the 15-30 cm soil layer, dimethyl
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phosphorothiate was detected once at 3.7 ppb at 3 days (single replicate). No
transformation products were detected in the 30-46 cm soil layer.
Laboratory studies showed that bioaccumulation of methamidophos in largemouth bass
was insignificant; the maximum bioconcentration factor of 0.09 times the water
concentration in whole fish occurred on day 28 and decreased to <0.014 ppm in the fish
(quantification limit) after one day depuration.
2.4.2 Environmental Transport Assessment
Potential transport mechanisms include pesticide surface water runoff, spray drift, and
secondary drift of volatilized or soil-bound residues leading to deposition onto nearby or
more distant ecosystems. The magnitude of pesticide transport via secondary drift
depends on the pesticide's ability to be mobilized into air and its eventual removal
through wet and dry deposition of gases/particles and photochemical reactions in the
atmosphere. A number of studies have documented atmospheric transport and
redeposition of pesticides from the Central Valley to the Sierra Nevada mountains
(Fellers et al., 2004, Sparling et al., 2001, LeNoir et al., 1999, and McConnell et al.,
1998). Prevailing winds blow across the Central Valley eastward to the Sierra Nevada
mountains, transporting airborne industrial and agricultural pollutants into Sierra Nevada
ecosystems (Fellers et al., 2004, LeNoir et al., 1999, and McConnell et al., 1998).
Methamidophos was not included in these monitoring studies. Therefore,
physicochemical properties of the pesticide that describe its potential to enter the air from
water or soil (e.g., Henry's Law constant and vapor pressure), pesticide use, and modeled
estimated concentrations in water and air are considered in evaluating the potential for
atmospheric transport of methamidophos to habitat for the CRLF.
In general, deposition of drifting or volatilized pesticides is expected to be greatest close
to the site of application. Computer models of spray drift (AgDRIFT or AGDISP) are
used to determine if the exposures to aquatic and terrestrial organisms are below the
Agency's Levels of Concern (LOCs). If the limit of exposure that is below the LOC can
be determined using AgDRIFT or AGDISP, longer-range transport is not considered in
defining the action area. For example, if a perimeter less than 1,000 feet (the range for
AgDRIFT and AGDISP Tier 1 models) results in terrestrial and aquatic exposures that
are below LOCs, no further drift analysis is required. If exposures exceeding LOCs are
expected beyond the standard modeling range of AgDRIFT or AGDISP, the Gaussian
far-field extension feature of AGDISP may be used. In addition to the use of spray drift
models to determine potential off-site transport of pesticides, other factors such as
available air monitoring data and the physicochemical properties of the chemical are also
considered.
Methamidophos is very soluble (>200 grams per liter (g/L); 2.0 x 105 parts per million
(ppm)) and very mobile octanol water coefficient (Koc = 1.5) in the laboratory. Only one
Koc value is available, because methamidophos was adsorbed in only one of the five soils
(a clay loam) used in the batch equilibrium studies. The methamidophos degradate
DMPT is also very mobile (Koc = 1.6); no data are available for O-desmethyl
17
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methamidophos, but it is expected to have similar mobility as its parent compound.
Because methamidophos and its degradates are not persistent under aerobic conditions,
little methamidophos residue could be expected to leach to groundwater. If any
methamidophos residues did reach ground water, they might be expected to persist based
on an observed anaerobic aquatic DT50 of 41 days for methamidophos and undetermined
persistence for DMPT and O-desmethyl methamidophos. Volatilization from soil or
water is not expected to be a major route of dissipation for methamidophos because of its
rapid metabolism in soil and its calculated Henry's constant (1.6 x 10"11 atm-m3/mole).
2.4.3 Mechanism of Action
Some of the information for the mode of action below comes from Davies et. al., 1981.
Organophosphate insecticides (such as Methamidophos) act upon target pests through a
neurotoxic action, which affects the central nervous system. Specifically, the mechanism
of action is known to be acetylcholinesterase inhibition. The transmission of nerve
impulses across synapses and the junctions between nerve and an organ (gland, muscle,
nerve) is accomplished by the release of a chemical agent, acetylcholine. Acetylcholine
must be rapidly destroyed or inactivated at or near the site of its release to continue
transmission of new impulses. The destruction of acetylcholine at such sites is
accomplished by an enzyme, acetylcholinesterase. Acetylcholinesterase is located at the
neurosynaptic junctions and breaks the acetylcholine into acetyl and choline fragments.
Acetylcholinesterase functions to increase the precision of nerve firing, enabling some
nerve cells to fire as rapidly as 1,000 times per second without overlap of the of the
neural impulses. Acetylcholinesterase inhibitors prevent the acetylcholinesterase from
removing the acetylcholine and thereby causing disruption to the central nervous system.
At a high enough concentration of the inhibitors, the muscles may not contract the
diaphragm and breathing ceases and death results.
Depending on the organophosphate involved, the dose received, and the duration of
exposure; the period for regeneration of the acetylcholinesterase to occur varies among
organisms.
2.4.4 Use Characterization
2.4.4.1 Use Profile
Methamidophos is a restricted-use insecticide, which means that it can be used only by or
under the direct supervision of applicators who have been trained and certified by the
state in which the pesticide is applied. Use sites are limited to four crops in California:
cotton, potatoes, and under FIFRA section 24c, tomatoes and alfalfa grown for seed.
Labeled Uses
For the current labeled uses, methamidophos is applied as a post-emergence foliar
application during the growing season. Table 2-1 lists the current labels that define the
18
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Federal Action, the labeled uses and their maximum application rates, maximum number
of applications per season, and methods of application.
Table 2-1. Labeled Methamidophos Uses (all application timing is foliar)
Uses
Label
%
ai
Max
Application
Rate (lb
ai/Acre)
Max # of
Applications
per season
Application
Interval
Method of Application
Alfalfa
CA980013
40
0.985
1
up to 3 days
prior to
placing bees
in or around
the field
Aircraft; Ground
Potatoes
264-729
40
1
4
Apply in a 7-
to 10-day
preventative
program or as
necessary
Aircraft, ground,
sprinkler irrigation
(chemigation for
potatoes only)
Tomatoes
(fresh
market)
CA780163
40
1
4
7 to 10 days
Aircraft- Low volume
spray
Tomatoes
CA780163
40
1
4
7 to 10 days
High volume ground
sprayer- High volume
spray
Cotton
CA-
790188
40
1
2
as needed,"
"do not apply
after 65% of
the bolls are
open
Chemigation by
overhead irrigation
systems
2.4.4.2. Use and Usage in California
Analysis of labeled use information is the critical first step in evaluating the federal
action. The current label for methamidophos represents the FIFRA regulatory action;
therefore, labeled use and application rates specified on the label form the basis of this
assessment. The assessment of use information is critical to the development of the action
area and selection of appropriate modeling scenarios and inputs.
The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis
of both national- and county-level usage information using state-level usage data
obtained from USDA-NASS4, Doane (www.doane.com); the full dataset is not provided
due to its proprietary nature), and the California's Department of Pesticide Regulation
4 United States Depart of Agriculture (USDA), National Agricultural Statistics Service (NASS) Chemical
Use Reports provide summary pesticide usage statistics for select agricultural use sites by chemical, crop
and state. See http://www.usda.gov/nass/pubs/estindxl,htm#agchem.
19
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Pesticide Use Reporting (CDPR PUR) database5 . CDPR PUR is considered a more
comprehensive source of usage data than USDA-NASS or EPA proprietary databases,
and thus the usage data reported for methamidophos by county in this California-specific
assessment were generated using CDPR PUR data. Usage data are averaged together
over the years 2002 to 2005 to calculate average annual usage statistics by county and
crop for methamidophos, including pounds of active ingredient applied and base acres
treated.
Methamidophos use is not distributed evenly in the state of California. Table 2-2.
displays the average amount of the active ingredient applied annually in each county,
with reported methamidophos use between 2002 and 2005. Only 24 of the 58 counties in
California reported use of methamidophos between 2002 and 2005.
Table 2-2. Average annual pounds of methamidophos applied, the total number of
records from 2002-2005 and the average annual acres treated.
Sum of
Sum of Average
Number
Sum of Average
Annual Pounds
Records
Annual Acres
Sum of Number
County
Applied
Pounds
Treated
Records Area
Alameda
0.03
1
.
0
Colusa
82.04
3
83.0
3
Fresno
12,783.91
758
15,852.7
758
Imperial
1,095.66
106
1,781.8
106
Kern
1,874.91
131
1,404.5
105
Kings
3,644.61
101
4,587.3
101
Los Angeles
310.20
21
391.9
21
Madera
26.51
2
33.5
2
Merced
841.86
98
1,347.2
98
Modoc
2,593.75
202
3,007.4
202
Monterey
158.13
81
250.6
81
Orange
54.90
9
75.0
9
Riverside
149.22
6
166.9
6
Sacramento
250.65
40
258.3
40
San Diego
876.72
68
1,128.3
68
San Joaquin
1,073.43
144
1,294.8
144
San Luis Obispo
18.59
3
18.8
3
San Mateo
13.88
6
14.0
6
Santa Barbara
429.38
85
546.7
85
Santa Clara
0.12
2
-
0
Siskiyou
1,123.24
110
1,358.5
110
Solano
703.44
50
743.2
50
Stanislaus
201.37
12
243.8
12
Sutter
1,388.22
76
1,535.0
76
Ventura
103.87
30
130.1
30
Yolo
4,395.68
304
4,540.7
300
5 The California Department of Pesticide Regulation's Pesticide Use Reporting database provides a census
of pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/purmain.htm.
20
-------
County
Sum of Average
Annual Pounds
Applied
Sum of
Number
Records
Pounds
Sum of Average
Annual Acres
Treated
Sum of Number
Records Area
54.25*
4
Grand Total
34,194.30
2449
40,793.5
2420
* square feet (not acres)
The average annual acreage treated with methamidophos is these counties is summarized
by crop use and county in California in Table 2-3. The number of acres treated with
methamidophos annually in California is approximately 40,277 acres; the highest acreage
treated annually occurs in Fresno County (approximately 15,852.7 acres), followed by
Kings County (approximately 4,587.3 acres), Yolo (approximately 4,527.3 acres) and
Modoc County (approximately 3,007.4 acres). Of the 24 counties with reported use, the
highest use occurred in Fresno County where it was applied on alfalfa for seed, cotton,
and tomato, followed by Kings County, where the reported uses were cotton and alfalfa
for seed. Except for Imperial, the primary use for the remaining counties was on potato
and tomato crops.
Table 2-3 Average annual acres treated by county in California, 2002-2005 (Cotton
County
Alfalfa
Cotton
Potato
Tomatoes
Grand
Total
Colusa
83.0
83.0
Fresno
6,624.2
8,347.0
881.5
15,852.7
Imperial
996.0
275.8
108.9
-
1,380.6
Kern
143.8
635.1
625.7
1,404.5
Kings
4,048.0
539.3
-
4,587.3
Los Angeles
391.9
-
391.9
Madera
33.5
-
33.5
Merced
7.5
1,339.7
1,347.2
Modoc
3.5
3,003.9
-
3,007.4
Monterey
161.0
161.0
Orange
75.0
75.0
Riverside
18.6
148.3
-
166.9
Sacramento
256.8
256.8
San Diego
132.5
995.8
1,128.3
San Joaquin
297.0
997.8
1,294.8
San Luis Obispo
18.8
-
18.8
Santa Barbara
546.7
-
546.7
Siskiyou
1,354.8
-
1,354.8
Solano
743.2
743.2
Stanislaus
243.8
243.8
Sutter
1,535.0
1,535.0
Ventura
6.0
76.5
82.5
Yolo
30.3
4,4970
4,527.3
54.25*
54.3
21
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County
Alfalfa
Cotton
Potato
Tomatoes
Grand
Total
Grand Total
11,702.0
9,365.3
6,643.6
12,511.6
40,276.8
* square feet (not acres)
Source: CDPR PUR 2007
Alfalfa
On alfalfa, one pre-bloom application per crop season at a maximum single application
rate of 0.985 lb a.i./acre is allowed by the label (Table 2-1). Methamidophos applications
on alfalfa occur from April through November in California, but most applications occur
June through September (Figure 2-2).
Annually in California from 2001-2005 on average 10,908 pounds of active ingredient
were applied to approximately 11,702.0 acres of alfalfa (Table 2-3); pounds applied
annually ranged from 6,631 to 18,570 (Figure 2-3). The average application rate was
0.77 lbs ai/acre (Table 2-3). From 2002 through 2005, methamidophos was reportedly
applied to alfalfa grown for seed in the following counties: Fresno, Imperial, Kings,
Modoc, Sutter, and Yolo (Table 2-3).
Potatoes
On potatoes, methamidophos may be applied at a maximum single application rate of 1 lb
a.i./acre: at a maximum of four applications per year the seasonal maximum rate is 4 lbs
~.i./acre (Table 2-1). Methamidophos applications on potatoes occur year round in
California but most applications occur January through October (Figure 2-2).
On average in California from 2002-2005, 6,555 pounds of a.i. was applied annually to
~,643.6 acres of potatoes (Table 2-3); pounds applied annually ranged from
approximately 3,270 to 7,100. The average single application rate was 0.79 lb a.i./acre
(Table 2-3). From 2002 through 2005, methamidophos was reportedly applied to
potatoes in the following counties: Imperial, Kern, Los Angeles, Modoc, Riverside, San
Diego, San Joaquin, San Luis Obispo, Santa Barbara, Siskiyou, Tulare, and Ventura
(Table 2-2).
Tomatoes
Considering tomatoes grown both for the fresh market and for processing, the average
annual pounds of methamidophos applied in California from 2002-2005 was 11,600 lbs
and ranged from approximately 6,740 to 15,830 pounds annually (Figure 2-3).
Methamidophos applications on tomatoes occur in California from March through
October with most applications occurring May through July, and October (Figure 2-2).
Tomatoes (fresh market)
On tomatoes grown for the fresh market, the maximum single application rate is 1 lb
a.i./acre at a maximum of 4 applications per crop cycle (season) the maximum
application is 4 lbs a.i./acre per season (Table 2-1). There is a seven to ten day spray
interval between applications. For the years 2002-2005, annual average of 4,211 lbs a.i.
were applied to 5,790 acres (Table 2-3). The average single application rate was 0.76 lb
22
-------
a.i./acre (Table 2-3). From 2002 through 2005, methamidophos was reportedly applied to
tomatoes in the following counties: Fresno, Imperial, Kern, Madera, Merced, Monterey,
Orange, Sacramento, San Diego, San Joaquin, Stanislaus, Ventura, and Yolo
Tomatoes (processing)
On tomatoes grown for processing the application rate and interval is the same as those
grown for the fresh market (Table 2-1). For the years 2002-2005, an annual average of
5,125 lb a.i. were applied to an average 6,046 (Table 2-3). The average application rate
was 0.85 lb a.i./acre (Table 2-3). From 2002 through 2005, methamidophos was
reportedly applied to tomatoes grown for processing in the following counties: Colusa,
Fresno, Kern, Merced, Sacramento, San Joaquin, Solano, Stanislaus, Sutter, and Yolo.
The value for methamidophos use on tomatoes for processing in Yolo county is not
included in this assessment due to a data transcription error in the data set which results
in an estimate of over 400 lbs a.i./acre as an application rate.
Cotton
In 2000, 17,646 lb a.i. was applied to 2.2% of California's cotton acreage (23,153 acres).
In 1998, 114,377 lb a.i. were applied to 116,850 acres (11.35%), and in 1999, 17,900 lb
a.i. were applied to 24,861 acres (2.5%). Thus, there was a decline in usage from 1998 to
2000.
-th
Table 2-4 below presents the maximum application rate and the range of the 95
percentile of the application rate. Most applications were at or below the rates on the
label.
Table 2-4. Methamidophos Typical Usage (lb. ai./A) in California between 2002-2005
Maximum
Minimum of 95
Maximum of 95
Site Name
Application
Rate
Percentile
Application Rate
Percentile Application
Rate
Alfalfa
11.87
0.77
0.80
Broccoli
0.50
0.50
0.50
Brussels Sprout
0.99
0.99
0.99
Cabbage
0.80
0.80
0.80
Cantaloupe
0.40
0.40
0.40
Cotton
1.03
0.59
0.99
Greenhouse Flower
0.51
0.51
0.51
Greenhouse Transplants
0.12
0.12
0.12
Potato
1.54
0.79
0.99
Research Commodity
1.06
0.99
1.06
Sugarbeet
0.77
0.76
0.76
Tomato
7.05
0.79
1.09
Tomato, Processing
10.41
0.79
1.10
Unknown
0.99
0.99
0.99
Source: CDPR PUR 2007
23
-------
The uses considered in this risk assessment represent all currently registered uses
according to a review of all current labels. No other uses are relevant to this assessment.
Any reported use, such as may be seen in the CDPR PUR database, represent either
historic uses that have been canceled, mis-reported uses, or mis-use. Historical uses, mis-
reported uses, and misuse are not considered part of the federal action and, therefore, are
not considered in this assessment.
It is important to consider the timing of pesticide application relative to the life-cycle of
the CRLF. The figure below shows the average amount (pounds) of methamidophos
applied to each registered use, by month from 2003 to 2005 as reported in the California
PUR database.
Ĥa
Ğ
Q.
Q.
<
o
-C
Q.
O
"D
E
rc
5,000
4,000
£ 3,000
"D
C
3
O
Q.
rc
3
C
C
<
CD
U)
2
a)
>
<
2,000
1,000
II ALFALFA m COTTON
~ POTATO H TOMATO
1
^
\5-v'
Application Month
Figure 2A. Timing of Methamidophos Application: Average number of pounds of active
ingredient applied in California for each registered crop, per month, between January
2003 through December 2005. source: cdpr pur 2007
In addition to considering the amount applied each month, the figure below show that the
amount applied to each use varies annually and may not follow a predictable trend,
although the total quantity applied each year has been decreasing over the last decade.
24
-------
e.
e.
<
16.000
14.000
12.000
10.000
8.000
6.000
4.000
2.000
2002
2003 2004
Year
2005
I ALFALFA Ĥ COTTON Ĥ POTATO
I TOMATO
Figure 2B. Pounds of Methamidophos Applied Each Year by Crop .source: cdpr pur 2007
2.5 Assessed Species
The CRLF was federally listed as a threatened species by USFWS 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 (USFWS 2002). A brief summary of information
regarding CRLF distribution, reproduction, diet, and habitat requirements is provided in
Sections 2.5.1 through 2.5.4, respectively. Further 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 was 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
The CRLF is endemic to California and Baja California (Mexico) and historically
inhabited 46 counties in California including the Central Valley and both coastal and
interior mountain ranges (USFWS 1996). Its range has been reduced by about 70%, and
the species currently resides in 22 counties in California (USFWS 1996). The species has
an elevation 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).
25
-------
Populations currently exist along the northern California coast, northern Transverse
Ranges (USFWS 2002), foothills of the Sierra Nevada (5-6 populations), and in southern
California south of Santa Barbara (two populations) (Fellers 2005a). Relatively larger
numbers of CRLFs are located between Marin and Santa Barbara Counties (Jennings and
Hayes 1994). 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). Occupied drainages or watersheds include all bodies
of water that support CRLFs (i.e., streams, creeks, 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 within California is addressed in this assessment using four
categories of location including recovery units, core areas, designated critical habitat, and
known occurrences of the CRLF reported in the California Natural Diversity Database
(CNDDB) that are not included within core areas and/or designated critical habitat (see
Figure 2.D). Recovery units, core areas, and other known occurrences of the CRLF from
the CNDDB are described in further detail in this section, and designated critical habitat
is addressed in Section 2.6. Recovery units are large areas defined at the watershed level
that have similar conservation needs and management 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' historic and current range and have been
determined by USFWS to be important in the preservation of the species. Designated
critical habitat is generally contained within the core areas, although a number of critical
habitat units are outside the boundaries of core areas, but within the boundaries 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.
Recovery Units
Eight recovery units have been established by USFWS for the CRLF. These areas are
considered essential to the recovery of the species, and the status of the CRLF "may be
considered within the smaller scale of the recovery units, as opposed to the statewide
range" (USFWS 2002). Recovery units reflect areas with similar conservation needs and
population status, and therefore, similar recovery goals. The eight units described for the
CRLF are delineated by watershed boundaries defined by US Geological Survey
hydrologic units and are limited to the elevational maximum for the species of 1,500 m
above sea level. The eight recovery units for the CRLF are listed in Table 2.5 and shown
in Figure 2.D.
Core Areas
USFWS has designated 35 core areas across the eight recovery units to focus their
recovery efforts for the CRLF (see Figure 2.D). Table 2.5 summarizes the geographical
26
-------
relationship among recovery units, core areas, and designated critical habitat. The core
areas, which are distributed throughout portions of the historic and current range of the
species, represent areas that allow for long-term viability of existing populations and
reestablishment of populations within historic range. These areas were selected because
they: 1) contain existing viable populations; or 2) they contribute to the connectivity of
other habitat areas (USFWS 2002). Core area protection and enhancement are vital for
maintenance and expansion of the CRLF's distribution and population throughout its
range.
For purposes of this assessment, designated critical habitat, currently occupied (post-
1985) core areas, and additional known occurrences of the CRLF from the CNDDB are
considered. Each type of locational information is evaluated within the broader context
of recovery units. For example, if no labeled uses of acephate occur (or if labeled uses
occur at predicted exposures less than the Agency's LOCs) within an entire recovery unit,
a "no effect" determination would be made for all designated critical habitat, currently
occupied core areas, and other known CNDDB occurrences within that recovery unit.
Historically occupied sections of the core areas are not evaluated as part of this
assessment because the USFWS Recovery Plan (USFWS 2002) indicates that CRLFs are
extirpated from these areas. A summary of currently and historically occupied core areas
is provided in Table 2.5 (currently occupied core areas are bolded). While core areas are
considered essential for recovery of the CRLF, core areas are not federally-designated
critical habitat, although designated critical habitat is generally contained within these
core recovery areas. It should be noted, however, that several critical habitat units are
located outside of the core areas, but within the recovery units. The focus of this
assessment is currently occupied core areas, designated critical habitat, and other known
CNDDB CRLF occurrences within the recovery units. Federally-designated critical
habitat for the CRLF is further explained in Section 2.6.
Table 2.5. California Red-legged Frog Recovery Units with Overlapping Core
Areas and Designated Critical Habitat
Recovery Unit1
(Figure 2.D)
Core Areas1,1 (Figure 2.D)
Critical Habitat
Units3
Currently
Occupied
(post-1985)
4
Historically
Occupied 4
Sierra Nevada
Foothills and Central
Valley (1)
(eastern boundary is
the 1,500m elevation
line)
Feather River (1)
BUT-1A-B
Yuba River-S. Fork Feather
River (2)
YUB-1
--
NEV-1
Traverse Creek/Middle Fork
American River/Rubicon (3)
--
Consumnes River (4)
ELD-1
S. Fork Calaveras River (5)
--
Tuolumne River (6)
--
Piney Creek (7)
--
East San Francisco Bay
(partial)(16)
--
North Coast Range
Cottonwood Creek (8)
--
27
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Table 2.5. California Red-legged Frog Recovery Units with Overlapping Core
Areas and Designated Critical Habitat
Recovery Unit1
(Figure 2.D)
Core Areas1,1 (Figure 2.D)
Critical Habitat
Units3
Currently
Occupied
(post-1985)
4
Historically
Occupied 4
Foothills and Western
Sacramento River
Valley (2)
Putah Creek-Cache Creek (9)
--
North Coast and
North San Francisco
Bay (3)
Putah Creek-Cache Creek
(partial) (9)
--
Lake Berryessa Tributaries
(10)
NAP-1
Upper Sonoma Creek (11)
Petaluma Creek-Sonoma
Creek (12)
--
Pt. Reyes Peninsula (13)
MRN-1, MRN-2
Belvedere Lagoon (14)
Jameson Canyon-Lower
Napa River (15)
SOL-1
South and East San
Francisco Bay (4)
--
CCS-1A
East San Francisco Bay
(partial) (16)
ALA-1A, ALA-
IB, STC-1B
--
STC-1A
South San Francisco Bay
(partial) (18)
SNM-1A
Central Coast (5)
South San Francisco Bay
(partial) (18)
SNM-1A, SNM-
2C, SCZ-1
Watsonville Slough- Elkhorn
Slough (partial) (19)
SCZ-2 5, MNT-1
5
Carmel River-Santa Lucia
(20)
MNT-2
Estero Bay (22)
Arroyo Grande Creek (23)
SLO-8
Santa Maria River-Santa
Ynez River (24)
--
Diablo Range and
Salinas Valley (6)
East San Francisco Bay
(partial) (16)
MER-1A-B
--
SNB-1, SBB-2
Santa Clara Valley (17)
~
Watsonville Slough- Elkhorn
Slough (partial)(19)
~
Carmel River-Santa Lucia
(partial)(20)
~
Gablan Range (21)
SNB-3
Estrella River (28)
SLO-1
Northern Transverse
Ranges and
Tehachapi Mountains
(7)
--
SLO-8
Santa Maria River-Santa
Ynez River (24)
STB-4, STB-5,
STB-7
Sisquoc River (25)
STB-1, STB-3
Ventura River-Santa Clara
River (26)
VEN-1, VEN-2,
VEN-3
--
LOS-1
28
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Table 2.5. California Red-legged Frog Recovery Units with Overlapping Core
Areas and Designated Critical Habitat
Recovery Unit1
(Figure 2.D)
Core Areas1,1 (Figure 2.D)
Critical Habitat
Units3
Currently
Occupied
(post-1985)
4
Historically
Occupied 4
Southern Transverse
and Peninsular
Ranges (8)
Santa Monica Bay-Ventura
Coastal Streams (27)
--
San Gabriel Mountain (29)
--
Forks of the Mojave (30)
--
Santa Ana Mountain (31)
--
Santa Rosa Plateau (32)
San Luis Rey (33)
--
Sweetwater (34)
--
Laguna Mountain (35)
--
1 Recovery units designated by the USFWS (USFWS 2000, pg 49)
2 Core areas designated by the USFWS (USFWS 2000, pg 51)
3 Critical habitat units designated by the USFWS on April 13, 2006 (USFWS 2006, 71 FR 19244-19346)
4 Currently occupied (post-1985) and historically occupied core areas as designated by the USFWS
(USFWS 2002, pg 54)
5 Critical habitat unit where identified threats specifically included pesticides or agricultural runoff (USFWS
6 Critical habitat units that are outside of core areas, but within recovery units
7 Currently occupied core areas that are included in this effects determination are bolded.
29
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CRLF Habitat Areas
North Coast Foothills &
Western Sacramento River
/V
N. San Franciscq
Bay/North Coast
Foothills
South & East San
Francisco Bay
Central Coast *
i Mountains
01530 60 90 120
County boundaries
Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Service (NASS, 2002)
Gap Analysis Program Orchard/Vineyard Landcwer (GAP)
National Land Cover Database (NLCD) (MRLC, 2001)
Map created bv US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Dvision.
June 15, 2007. Projection: Albers Equal Area Conic USGS, North
American Datum of 1933 (NAD 1983)
Figure 2C. CRLF Habitat areas
30
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Other Known Occurrences from the CNDBB
The CNDDB provides location and natural history information on species found in
California. The CNDDB serves as a repository for historical and current species location
sightings. Information regarding known occurrences of CRLFs outside of the currently
occupied core areas and designated critical habitat 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.
2.5.2 Reproduction
CRLFs breed primarily in ponds; however, they may also breed in quiescent streams,
marshes, and lagoons (Fellers 2005a). According to the Recovery Plan (USFWS 2002),
CRLFs breed from November through late April. Peaks in spawning activity vary
geographically; Fellers (2005b) reports peak spawning as early as January in parts of
coastal central California. Eggs are fertilized 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 approximately 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 require 11 to 28 weeks to metamorphose into juveniles
(terrestrial-phase), typically between May and September (Jennings and Hayes 1994,
USFWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until
the following year) (Fellers 2005b, USFWS 2002). 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 2D depicts CRLF annual reproductive timing.
Figure 2D - CRLF Reproductive Events by Month
J
F
M
A
M
J
J
A
S
o
N
D
Light Blue = Breeding/Egg Masses
Green = Tadpoles (except those that over-winter)
Orange =
Adults and juveniles can be present all year
2.5.3 Diet
Although the diet of CRLF aquatic-phase larvae (tadpoles) has not been studied
specifically, it is assumed that their diet is similar to that of other frog species, with the
aquatic phase feeding exclusively in water and consuming diatoms, algae, and detritus
(USFWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar, 1980)
31
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via mouthparts designed for effective grazing of periphyton (Wassersug, 1984,
Kupferberg et al.\ 1994; Kupferberg, 1997; Altig and McDiarmid, 1999).
Juvenile and adult CRLFs forage in aquatic and terrestrial habitats, and their diet differs
greatly from that of larvae. The main food source for juvenile aquatic- and terrestrial-
phase CRLFs is thought to be aquatic and terrestrial invertebrates found along the
shoreline and on the water surface. Hayes and Tennant (1985) report, based on a study
examining the gut content of 35 juvenile and adult CRLFs, that the species feeds on as
many as 42 different invertebrate taxa, including Arachnida, Amphipoda, Isopoda,
Insecta, and Mollusca. The most commonly observed 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 consists of vertebrates such as mice, frogs,
and fish, although aquatic and terrestrial invertebrates were the most numerous food
items (Hayes and Tennant 1985). For adults, feeding activity takes place primarily at
night; for juveniles feeding occurs during the day and at night (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 life cycle. CRLF use of their environment
varies; they may complete their entire life cycle 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 habitats used for dispersal (USFWS 2002).
Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al.
1997). Dense vegetation, shading water of moderate depth is a habitat feature that
appears especially important for CRLF (Hayes and Jennings 1988). Breeding sites
include streams, deep pools, backwaters within streams and creeks, ponds, marshes, sag
ponds (land depressions between fault zones that have filled with water), dune ponds, and
lagoons. Breeding adults have been found near deep (0.7 m) still or slow moving water
surrounded by dense vegetation (USFWS 2002); however, the largest number of tadpoles
have been found in shallower pools (0.26 - 0.5 m) (Reis, 1999). Data indicate that
CRLFs do not frequently inhabit vernal pools, as conditions in these habitats generally
are not suitable (Hayes and Jennings 1988).
CRLFs also frequently breed in artificial impoundments such as stock ponds, although
additional research is needed to identify habitat requirements within artificial ponds
(USFWS 2002). Adult CRLFs use dense, shrubby, or emergent vegetation closely
associated with deep-water pools bordered with cattails and dense stands of overhanging
vegetation (http://www.fws.gov/endangered/features/rl frog/rlfrog.html#where).
In general, dispersal and habitat use depends on climatic conditions, habitat suitability,
and life stage. Adults rely on riparian vegetation for resting, feeding, and dispersal. The
32
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foraging quality of the riparian habitat depends on moisture, composition of the plant
community, and presence of pools and backwater 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 habitat to forage and seek other suitable habitat under downed
trees or logs, industrial debris, and agricultural features (USFWS 2002). According to
Jennings and Hayes (1994), CRLFs also use small mammal burrows and moist leaf litter
as habitat. In addition, CRLFs may also use large cracks in the bottom of dried ponds as
refugia; these cracks may provide moisture for individuals avoiding predation and solar
exposure (Alvarez 2000).
2.6 Designated Critical Habitat
In a final rule published on April 13, 2006, 34 separate units of critical habitat were
designated for the CRLF by USFWS (USFWS 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 Table 2.D.
'Critical habitat' is defined in the ESA as the geographic area occupied by the species at
the time of the listing where the physical and biological features necessary for the
conservation of the species exist, and there is a need for special management to protect
the listed species. It may also include areas outside the occupied area at the time of
listing if such areas are 'essential to the conservation of the species.' All designated
critical habitat for the CRLF was occupied at the time of listing. Critical habitat receives
protection under Section 7 of the ESA through prohibition against destruction or adverse
modification with regard to actions carried out, funded, or authorized by a federal
Agency. Section 7 requires consultation on federal actions that are likely to result in the
destruction or adverse modification of critical habitat.
To be included in a critical habitat designation, the habitat must be 'essential to the
conservation of the species.' Critical habitat designations identify, to the extent known
using the best scientific and commercial data available, habitat areas that provide
essential life cycle needs of the species or areas that contain certain primary constituent
elements (PCEs) (as defined in 50 CFR 414.12(b)). PCEs include, but are not limited to,
space for individual and population growth and for normal behavior; food, water, air,
light, minerals, or other nutritional or physiological requirements; cover or shelter; sites
for breeding, reproduction, rearing (or development) of offspring; and habitats that are
protected from disturbance or are representative of the historic geographical and
ecological distributions of a species. The designated 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;
33
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Upland habitat; and
Dispersal habitat.
Please note that a more complete description of these habitat types is provided in
Attachment I.
Occupied habitat may be included in the critical habitat only if essential features within
the habitat may require special management or protection. Therefore, USFWS does not
include areas where existing management is sufficient 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 range would be inadequate to ensure the
conservation of the species. For the CRLF, all designated critical habitat units contain all
four of the PCEs, and were occupied by the CRLF at the time of FR listing notice in
April 2006. The FR notice designating critical habitat for the CRLF includes a special
rule exempting routine ranching activities associated with livestock ranching from
incidental take prohibitions. The purpose of this exemption is to promote the
conservation of rangelands, which could be beneficial to the CRLF, and to reduce the rate
of conversion to other land uses that are incompatible with CRLF conservation. Please
see Attachment I. for a full explanation on this special rule.
USFWS has established adverse modification standards for designated critical habitat
(USFWS 2006). Activities that may destroy or adversely modify critical habitat are those
that alter the PCEs and jeopardize the continued existence of the species. Evaluation of
actions related to use of acephate that may alter 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 chemistry or temperature to levels beyond the
tolerances of the CRLF that result in direct or cumulative adverse effects to
individuals and their life-cycles.
(2) Significant increase in sediment deposition within the stream channel or pond or
disturbance of upland foraging 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 deposition to levels that would adversely
affect their ability to complete their life cycles.
(3) Significant alteration of channel/pond morphology 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 could also lead to increased sedimentation and
degradation in water quality to levels that are beyond the CRLF's tolerances.
(4) Elimination of upland foraging and/or aestivating habitat or dispersal habitat.
(5) Introduction, spread, or augmentation of non-native aquatic species in stream
segments or ponds used by the CRLF.
(6) Alteration or elimination of the CRLF's food sources or prey base (also
evaluated as indirect effects to the CRLF).
34
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As previously noted in Section 2.1, the Agency believes that the analysis of direct and
indirect effects to listed species provides the basis for an analysis of potential effects on
the designated critical habitat. Because acephate is expected to directly impact living
organisms within the action area, critical habitat analysis for acephate is limited in a
practical sense to those PCEs of critical habitat that are biological or that can be
reasonably linked to biologically mediated processes.
2.6.1. Special Rule Exemption for Routine Ranching Activities
As part of the critical habitat designation, the Service promulgated a special rule
exemption regarding routine ranching activities where there is no Federal nexus from
take prohibitions under Section 9 of the ESA. (USFWS 2006, 71 FR 19285-19290). The
Service's reasoning behind this exemption is that managed livestock activities, especially
the creation of stock ponds, provide habitat for the CRLF. Maintenance of these areas as
rangelands, rather than conversion to other uses should ranching prove to be
economically infeasible is, overall, of net benefit to the species.
Several of the specific activities exempted include situations where pesticides may be
used in accordance with labeled instructions. In this risk assessment, the Agency has
assessed the risk associated with these practices using the standard assessment
methodologies. Specific exemptions, and the reasoning behind each of the exemptions is
provided below. The rule provides recommended best management practices, but does
not require adherence to these practices by the landowner.
1. Stock Pond Management and Maintenance
a. Chemical control of aquatic vegetation. These applications are allowed
primarily because the Service felt "it is unlikely that vegetation control
would be needed during the breeding period, as the primary time for
explosive vegetation control is during the warm summer months." The
Service recommends chemical control measures be used only "outside of
the general breeding season (November through April) and juvenile stage
(April through September) of the CRLF." Mechanical means are the
preferred method of control.
b. Pesticide applications for mosquito control. These applications are
allowed because of concerns associated with human and livestock health.
Alternative mosquito control methods, primarily introduction of nonnative
fish species, are deemed potentially more detrimental to the CRLF than
chemical or bacterial larvicides. The Service believes "it unlikely that
[mosquito] control would be necessary during much of the CRLF breeding
season," and that a combination of management methods, such as
manipulation of water levels, and/or use of a bacterial larvicide will
prevent or minimize incidental take.
2. Rodent Control. The Service notes "we believe the use of rodenticides present a
low risk to CRLF conservation." In large part, this is due to the fact that "it is
35
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unknown the extent to which small mammal burrows are essential for the
conservation of CRLF."
a. Toxicant-treated grains. No data were available to evaluate the potential
effects of these compounds (primarily anti-coagulants) on the CRLF.
Grain is not a typical food item for the frog, but individuals may be
indirectly exposed by consuming invertebrates which have ingested
treated grain. There is a possibility of dermal contact, especially when the
grain is placed in the burrows. Placing treated grain into the burrows is
not prohibited, but should this method of rodent control be used, the
Service recommends bait-station or broadcast application methods to
reduce the probability of exposure.
b. Burrow fumigants. Use of burrow fumigants is not prohibited, but the
Service recommends "not using burrow fumigants within 0.7 mi (1.2 km)
in any direction from a water body" suitable as CRLF habitat.
2.7 Action Area
For listed species assessment purposes, the action area is considered to be the area
affected directly or indirectly by the federal action and not merely the immediate area
involved in the action (50 CFR 402.02). It is recognized that the overall action area for
the national registration of methamidophos is likely to encompass considerable portions
of the United States based on the large array of agricultural uses. However, the scope of
this assessment limits consideration of the overall action area to those portions that may
be applicable to the protection of the CRLF and its designated critical habitat within the
state of California. Deriving the geographical extent of this portion of the action area is
the product of consideration of the types of effects that methamidophos may be expected
to have on the environment, the exposure levels to methamidophos that are associated
with those effects, and the best available information concerning the use of
methamidophos and its fate and transport within the state of California.
The definition of action area requires a stepwise approach that begins with an
understanding of the federal action. The federal action is defined by the currently labeled
uses for methamidophos. An analysis of labeled uses and review of available product
labels was completed. This analysis indicates that, for methamidophos, the following
uses are considered as part of the federal action evaluated in this assessment:
Tomato
Potato
Alfalfa, for seed production
Cotton
After determination of which uses will be assessed, an evaluation of the potential
"footprint" of the use pattern should be determined. This "footprint" represents the initial
area of concern and is typically based on available land cover data. Local land cover data
36
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available for the state of California were analyzed to refine the understanding of potential
methamidophos use. The overall conclusion of this analysis is that there is an overlap
between the use areas and known occurrences and critical habitat of the CRLF and
therefore no areas are excluded from the final action area based on usage and land cover
data. The initial area of concern is defined as all land cover types that represent the
labeled uses described above. A map representing all the land cover types that make up
the initial area of concern is presented in Figure 2E.
37
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Methamidophos Agriculture - Initial Area of Concern
a
Del Norte
Modoc -
Htimboldt
Trjrity A
# /c^TaSSSfk * H
^sr^fg^v-
*7 Ca /
, PtamSs -
V/VJL J/;
J^efa T ,
Mendocino qi
~ '* f tike e
Nevada
Pla
-------
Once the initial area of concern is defined, the next step is to compare the extent of that
area with the results of the screening level risk assessment. The screening level risk
assessment will define which taxa, if any, are predicted to be exposed at concentrations
above the Agency's Levels of Concern (LOC). The screening level assessment includes
an evaluation of the environmental fate properties of methamidophos to determine which
routes of transport are likely to have an impact on the CRLF.
The exceedances are then used to describe how far outside the initial area of concern
effects may be seen. For example, AgDRIFT modeling can be used to define how far
from the initial area of concern an effect to non-target terrestrial plants may be expected.
Other processes considered in expanding the initial area of concern can include
downstream distance where concentrations are expected to be above the LOC, long-range
transport, and secondary exposure through biological vectors. The process of expanding
the initial area of concern is repeated for all taxa where exceedances of the LOC occur,
and the greatest expansion of the initial area of concern is considered the action area.
Review of the environmental fate data of as well as physico-chemical properties of
methamidophos indicates that run-off and spray drift are likely to be the dominant
mechanisms by which methamidophos is transported off-site. Methamidophos was
detected in 10% of 168 samples taken in a 2002 air monitoring study in Fresno County,
with a maximum value of 2.8 parts-per-trillion (ppt) by volume6. Methamidophos was
not one of the pesticides included in eight long-range transport studies in the Sierra
Nevada mountains. However, based on its low persistence, it is not anticipated that
meaningful quantities of volatilized or resuspended methamidophos will be transported
by the air route. Additionally, ground water transport is considered unlikely due to the
non-persistence of methamidophos and its degradates, even when their mobility is
considered.
These data suggest that the Action Area will be defined by spray drift perimeters from the
aquatic and terrestrial exposure analysis, and by downstream dilution analysis of the
ecological pond concentrations.
LOC exceedances are used to describe how far effects may be seen from the initial area
of concern. Factors considered include: spray drift, downstream run-off, atmospheric
transport, etc. This information is incorporated into GIS and a map of the action area is
created (Figure 2F).
6 http://www.cdpr.ca.gov/docs/empm/pubs/tac/tacstdys.htm
39
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Methamidophos Agriculture - Action Area (AA)
Del Norte
Mendocino
: an F
iimne
Bernardino
U
<9;
Legend
Ftecovery units
Aquatic AA- Agriculture
Agriculture Use
County boundaries
Terrestrial AA- Agriculture
l Kilometers
0 2040 80 120 160
Compiled from California County boundaries (ESRI, 2002), Map created by US Environmental Protection Agency, Office
USDft National Agriculture Statistical Sen/ice (NASS, 20035 of Pesticides Programs, Environmental Fate and Effects Division.
Gap Analysis Program Orchard/ Vineyard Landcwer (GAP) June XX, 2007. Projection: A lb ers Equal Area Conic USGS, North
National Land Cower Database (NLCD) (MRLC, 2001) American Datum of 1983 (NAD 1983)
Figure 2F Action Area for Methamidophos
40
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Action Area Calculation
The Action Area due to effects on Listed species is also defined by the geographic extent
of LOC exceedence. Quantitative estimates of exposure of avian (including reptiles and
terrestrial amphibians) and mammal species is done with the TREX model, which
automates exposure analysis according to the Hoerger-Kenaga nomogram, as modified
by Fletcher (1994).
For methamidophos, the Action Area was calculated on the basis of the smallest avian
(20-gram body weight) or mammal (15-gram), consuming the most highly contaminated
food category (short grass). This results in the highest RQs, and thus the most
conservative estimate of the Action Area.
The lowest ratio between the LOC for Listed terrestrial avian and mammalian species
(0.1 for acute effects and 1.0 for chronic effects) and the RQ, times the maximum single
application rate, is used to determine the exposure (in lb/acre) that is below LOC, as
shown in Table 5-4.
Minimum exposure = (RQ/Listed species LOC)*(l lb/acre).
In the case of methamidophos, the target exposure is 0.00066 lb/acre, due to acute effects
on avian species (including reptiles and terrestrial amphibians, acute RQ = 493).
The distance from the use site (sprayed field) needed to achieve the target exposure of
0.00066 lb/acre was calculated with the Gaussian Far-Field extension of the AgDISP
model. The input parameters for AgDISP are given below; all other parameters were the
default values.
Table 2-6. Input Parameters for AgDISP Gaussian Far-Field Extension Analysis
Input Parameter
Value
Release Height
15 feet
Wind Speed
15 mph
Spray Quality
ASAE very fine to fine
Non-Volatile fraction
0.083
Active fraction
0.033
Surface Canopy
None
Specific Gravity, Carrier
1.19
Deposition type
Terrestrial point
Initial Average Deposition
0.00066 lb/acre
The result of this analysis is that a perimeter of 7,241 feet from the edge of the sprayed
field is needed to bring the acute mammal RQ to below the LOC of 0.1. Thus, the Action
Area extends to a distance of 7,241 feet from the edge of fields sprayed with
methamidophos.
41
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2.8 Assessment Endpoints and Measures of Ecological Effect
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."7 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,. water bodies,
riparian vegetation, and upland and dispersal habitats), the migration pathways of
methamidophos (e.g., runoff, spray drift, etc.), and the routes by which ecological
receptors are exposed to methamidophos-related contamination (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 and/or modification of its habitat. In addition, potential destruction and/or
adverse modification of critical habitat is assessed by evaluating potential effects to
PCEs, which are components of the habitat areas that provide essential life cycle needs of
the CRLF. Each assessment endpoint requires one or more "measures of ecological
effect," defined as changes in the attributes of an assessment endpoint or changes in a
surrogate entity or attribute in response to exposure to a pesticide. Specific measures of
ecological effect are generally evaluated based on acute and chronic toxicity information
from registrant-submitted guideline tests that are performed on a limited number of
organisms. Additional ecological effects data from the open literature are also
considered.
A complete discussion of all the toxicity data available for this risk assessment, including
resulting measures of ecological effect selected for each taxonomic group of concern, is
included in Section 4 of this document. A summary of the assessment endpoints and
measures of ecological effect selected to characterize potential assessed direct and
indirect CRLF risks associated with exposure to methamidophos is provided in Table 2.6.
Table 2.6 Summary of Assessment Endpoints and Measures of Ecological Effects for Direct
and Indirect Effects of methamidophos on the California Red-legged Frog
Assessment Endpoint
Measures of Ecological Effects8
Toxicity Endpoint (see effects
table for endpoint selection,
Section 4)
Aquatic Phase
(eggs, larvae, tadpoles, juveniles, and adults)11
1. Survival, growth, and
reproduction of CRLF
individuals via direct
effects on aquatic phases
la. Most sensitive fish acute LC50
lb. Most sensitive fish chronic
NOAEC
lc. Most sensitive fish early-life stage
NOAEC
la. Rainbow trout acute 96-hr LC50
lb. none available
lc. Rainbow trout (Acute-Chronic-
Ratio)
7 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
8 All registrant-submitted and open literature toxicity data reviewed for this assessment are included in
Appendix A and G.
42
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2. Survival, growth, and
reproduction of CRLF
individuals via effects to
food supply (i.e.,
freshwater invertebrates,
non-vascular plants)
2a. Most sensitive fish (1), aquatic
invertebrate (2), and aquatic plant (3-)
EC50 or LC50 (guideline)
2b. Most sensitive aquatic invertebrate
(1 -) and fish (2) chronic NOAEC
(guideline or ECOTOX)
2al. Rainbow trout acute 96-hr LC50
2a2. -Daphnia magna acute 48-hr
2a3. Skeletonema costatum algae
(5-day)
2b 1. Daphnia magna NOAEC
2b2. none available - use rainbow
trout (Acute-Chronic-Ratio)
3. Survival, growth, and
reproduction of CRLF
individuals via indirect
effects on habitat, cover,
and/or primary
productivity (i.e., aquatic
plant community)
3a. Vascular plant EC50 (duckweed
guideline test or ECOTOX vascular
plant)
3b. Non-vascular plant EC50 ()
3 a. none available
3b. Skeletonema costatum algae 5-
day
4. 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.
4a. Distribution ofEC25 values for
monocots (seedling emergence,
vegetative vigor, or ECOTOX)
4b. Distribution ofEC25 values for
dicots (seedling emergence, vegetative
vigor, or ECOTOX)9
4a and b. Tier I seedling emergence
and vegetative vigor
Terrestrial Phase (Juveniles and adults)
5. Survival, growth, and
reproduction of CRLF
individuals via direct
effects on terrestrial
phase adults and
juveniles
5a. Most sensitive birdb () or terrestrial-
phase amphibian acute LC50 or LD50
(guideline)
5b. Most sensitive birdb () or
terrestrial-phase amphibian chronic
NOAEC (guideline or ECOTOX)
5a. Dark eyed junco acute oral LD50
5b. Mallard duck Reproductive
study NOEL
6. Survival, growth, and
reproduction of CRLF
individuals via effects on
prey (i.e., terrestrial
invertebrates, small
terrestrial vertebrates,
including mammals and
terrestrial phase
amphibians)
6a. Most sensitive terrestrial
invertebrate (1-) and vertebrate (2-)
acute EC50 or LC50 (guideline or
ECOTOX)0
6b. Most sensitive terrestrial
invertebrate(l) and vertebrate(2-)
chronic NOAEC (guideline or
ECOTOX)
6al. Honey bee acute contact LD50
6a2. Rat Acute oral LD50
6b 1. None available
6b2. Rat 3- generation reproductive
study NOAEL
7. Survival, growth, and
reproduction of CRLF
individuals via indirect
effects on habitat (i.e.,
riparian vegetation)
7a. Distribution of EC25 for monocots
(seedling emergence, vegetative vigor,
or ECOTOX
7b. Distribution of EC25 for dicots
(seedling emergence, vegetative vigor,
or ECOTOX)5
7a. and b. Tier I seedling
emergence and vegetative vigor
a Adult frogs are no longer in the "aquatic phase" of the amphibian life cycle; however, submerged adult
frogs are considered "aquatic" for the purposes of this assessment because exposure pathways in the water
are considerably different that exposure pathways on land.
b Birds are used as surrogates for terrestrial phase amphibians.
0 Although the most sensitive toxicity value is initially used to evaluate potential indirect effects, sensitivity
9 The available information indicates that the California red-legged frog does not have any obligate
relationships.
43
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distribution is used (if sufficient data are available) to evaluate the potential impact to food items of the
CRLF.
2.8.2. Assessment Endpoints for Designated Critical Habitat
As previously discussed, designated critical habitat is assessed to evaluate actions related
to the use of methamidophos that may alter the PCEs of the CRLF's critical habitat.
PCEs for the CRLF were previously described in Section 2.6. Actions that may destroy
or adversely modify critical habitat are those that alter the PCEs and jeopardize the
continued existence of the CRLF. Therefore, these actions are identified as assessment
endpoints. It should be noted that evaluation of PCEs as assessment endpoints is limited
to those of a biological nature (i.e., the biological resource requirements for the listed
species associated with the critical habitat) and those for which methamidophos effects
data are available.
Assessment endpoints and measures of ecological effect selected to characterize potential
modification to designated critical habitat associated with exposure to methamidophos
are provided in Table 2.e. Adverse modification to the critical habitat of the CRLF
includes the following, as specified by USFWS (2006) and previously discussed in
Section 2.6:
1. Alteration of water chemistry/quality including temperature, turbidity, and
oxygen content necessary for normal growth and viability of juvenile and
adult CRLFs.
2. Alteration of chemical characteristics necessary for normal growth and
viability of juvenile and adult CRLFs.
3. Significant increase in sediment deposition within the stream channel or pond
or disturbance of upland foraging and dispersal habitat.
4. Significant alteration of channel/pond morphology or geometry.
5. Elimination of upland foraging and/or aestivating habitat, as well as dispersal
habitat.
6. Introduction, spread, or augmentation of non-native aquatic species in stream
segments or ponds used by the CRLF.
7. Alteration or elimination of the CRLF's food sources or prey base.
Measures of such possible effects by labeled use of methamidophos on critical habitat of
the CRLF are described in Table 2.7. Some components of these PCEs are associated
with physical abiotic features (e.g., presence and/or depth of a water body, or distance
between two sites), which are not expected to be measurably altered by use of pesticides.
Assessment endpoints used for the analysis of designated critical habitat are based on the
adverse modification standard established by USFWS (2006).
44
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Table 2.7. Summary of Assessment Endpoints and Measures of Ecological Effect for
Primary Constituent Elements of Designated Critical Habitat
Assessment Endpoint Measures of Ecological Effect10
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.
a. Most sensitive aquatic plant EC50 (guideline or
ECOTOX)
b. Distribution of EC25 values for terrestrial monocots
(seedling emergence, vegetative vigor, or ECOTOX)
c. Distribution of EC25 values for terrestrial dicots
(seedling emergence, vegetative vigor, or ECOTOX)
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.11
a. Most sensitive EC50 values for aquatic plants (guideline
or ECOTOX)
b. Distribution of EC25 values for terrestrial monocots
(seedling emergence or vegetative vigor, or ECOTOX)
c. Distribution of EC25 values for terrestrial dicots
(seedling emergence, vegetative vigor, or ECOTOX)
Alteration of other chemical characteristics necessary
for normal growth and viability of CRLFs and their
food source.
a. Most sensitive EC50 or LC50 values for fish or aquatic-
phase amphibians and aquatic invertebrates (guideline or
ECOTOX)
b. Most sensitive NOAEC values for fish or aquatic-phase
amphibians and aquatic invertebrates (guideline or
ECOTOX)
Reduction and/or modification of aquatic-based food
sources for pre-metamorphs (e.g., algae)
a. Most sensitive aquatic plant EC50 (guideline or
ECOTOX)
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
a. Distribution of EC25 values for monocots (seedling
emergence, vegetative vigor, or ECOTOX)
b. Distribution of EC25 values for dicots (seedling
emergence, vegetative vigor, or ECOTOX)
c. Most sensitive food source acute EC5o/LC5o and NOAEC
values for terrestrial vertebrates (mammals) and
invertebrates, birds or terrestrial-phase amphibians, and
freshwater fish.
Elimination and/or disturbance of dispersal habitat:
Upland or riparian dispersal habitat within designated
units and between occupied locations within 0.7 mi of
each other that allow for movement between sites
including both natural and altered sites which do not
contain barriers to dispersal
Reduction and/or modification of food sources for
terrestrial phase juveniles and adults
Alteration of chemical characteristics necessary for
normal growth and viability of juvenile and adult
CRLFs and their food source.
10 All toxicity data reviewed for this assessment are included in Appendix A and G.
11 Physico-chemical water quality parameters such as salinity, pH, and hardness are not evaluated because
these processes are not biologically mediated and, therefore, are not relevant to the endpoints included in
this assessment.
45
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2.9 Conceptual Model
2.9.1 Risk Hypotheses
Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in
assessment endpoints) and may be based on theory and logic, empirical data,
mathematical models, or probability models (U.S. EPA, 1998). For this assessment, the
risk is stressor-linked, where the stressor is the release of methamidophos to the
environment. The following risk hypotheses are presumed for this endangered species
assessment:
Labeled uses of methamidophos within the action area may directly affect the
CRLF by causing mortality or by adversely affecting growth or fecundity;
Labeled uses of methamidophos within the action area may indirectly affect the
CRLF by reducing or changing the composition of food supply;
Labeled uses of methamidophos within the action area may indirectly affect the
CRLF and/or adversely modify designated critical habitat by reducing or changing the
composition of the aquatic plant community in the ponds and streams comprising the
species' current range and designated critical habitat, thus affecting primary productivity
and/or cover;
Labeled uses of methamidophos within the action area may indirectly affect the
CRLF and/or adversely modify designated critical habitat by reducing or changing the
composition of the terrestrial plant community (i.e., riparian habitat) required to maintain
acceptable water quality and habitat in the ponds and streams comprising the species'
current range and designated critical habitat;
Based on the results of the submitted terrestrial plant toxicity tests, it appears that
seedlings and emerged plants may not be sensitive to methamidophos, therefore
methamidophos will have NO EFFECT on the CRLF based on these endpoints. For
more information on plant toxicity studies, see Appendix A.
Labeled uses of methamidophos within the action area may adversely modify the
designated critical habitat of the CRLF by reducing or changing breeding and non-
breeding aquatic habitat (via modification of water quality parameters, habitat
morphology, and/or sedimentation);
Labeled uses of methamidophos within the action area may adversely modify the
designated critical habitat of the CRLF by reducing the food supply required for normal
growth and viability of juvenile and adult CRLFs;
Labeled uses of methamidophos within the action area may adversely modify the
designated critical habitat 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.
Labeled uses of methamidophos within the action area may adversely modify the
designated critical habitat of the CRLF by reducing or changing dispersal habitat within
designated units and between occupied locations within 0.7 mi of each other that allow
46
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for movement between sites including both natural and altered sites which do not contain
barriers to dispersal.
Labeled uses of methamidophos within the action area may adversely modify the
designated critical habitat of the CRLF by altering chemical characteristics necessary for
normal growth and viability of juvenile and adult CRLFs.
2.9.2 Diagram
The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies the stressor (methamidophos), release mechanisms, biological receptor types,
and effects endpoints of potential concern. The conceptual models for aquatic and
terrestrial phases of the CRLF are shown in Figures 2.F and 2.G, and the conceptual
models for the aquatic and terrestrial PCE components of critical habitat are shown in
Figures 2.H and 2.1. Exposure routes shown in dashed lines are not quantitatively
considered because the resulting exposures are expected to be so low as not to cause
adverse effects to the CRLF.
Long-range atmospheric transport is not expected due to the non-persistent nature of
methamidophos. Likewise, groundwater transport is considered unlikely due to the non-
persistence of methamidophos, even when its mobility is considered. The operative
routes of exposure will be spray drift at the time of application, and run-off due to
precipitation within a few days of application.
Stressor
Long range
atmospheric
\ Spray drift [Ĥ
| Runoff"|
Source
Dermal uptake/lngestion*
Exposure
Media and
Receptors
Root uptake
Terrestrial
insects
Wet/dry deposition*-
Ingestion
Ingestion
Ingestion
Ingestion
n.
Attribute
Change
Habitat
PCEs
Soil
Direct
application
Red-legged Frog
Juvenile
Adult
Food resources
Reduction in food
Population
Reduced survival
Reduced growth
Reduced reproduction
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Other chemical
characteristics
Adversely modified
chemical characteristics
Community
Reduced seedling emergence
or vegetative vigor
(Distribution)
Riparian & Upland
Terrestrial plants
grasses/forbs, fruit,
seeds (trees, shrubs)
(Figure 2G) Methamidophos applied to use site
Elimination and/or disturbance of
upland or dispersal habitat
Reduction in primary productivity
Reduced shelter
Restrict movement
Figure 2G . Conceptual Diagram for Terrestrial Phase Effects on CRLF
47
-------
Stressor
Long range
atmospheric
transport
Groundwater j
Source
Exposure
Media
Wet/dry deposition -*
Uptake/gills
or integument
Uptake/cell,
roots, leaves
Uptake/gills
or integument
Receptors
Ingestion
Ingestion
fl
Community
Reduced seedling
emergence or vegetative
vigor (Distribution)
Population
Yield
Reduced yield
Attribute
Change
Habitat
PCEs
Aquatic Animals
Invertebrates
Vertebrates
Aquatic Plants
Non-vascular
Vascular
Surface water/
Sediment
Food sources
Reduction in algae
Reduction in prey
Red-legged Frog
Eggs Juveniles
Larvae Adult
Tadpoles
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Riparian and
Upland plants
terrestrial exposure
pathways and PCEs
see Figure 2G
Other chemical
characteristics
Adversely modified
chemical characteristics
(Figure 2H) Methamidophos applied to use site
Habitat quality and channel/pond
morphology or geometry
Adverse water quality changes
Increased sedimentation
Reduced shelter
Figure 2H . Conceptual Diagram for Effects on Aquatic Phase CRLF
Stressor
Long range
atmospheric
transport
Ĥ] Spray drift [Ĥ
| Runoff"|
Source
Dermal uptake/lngestion*
Exposure
Media and
Receptors
Root uptake
Terrestrial
insects
Wet/dry deposition*
Ingestion
Ingestion
Ingestion
Ingestion
Attribute
Change
Habitat
PCEs
Soil
Direct
application
Red-legged Frog
Juvenile
Adult
Food resources
Reduction in food
Population
Reduced survival
Reduced growth
Reduced reproduction
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Other chemical
characteristics
Adversely modified
chemical characteristics
Community
Reduced seedling emergence
or vegetative vigor
(Distribution)
Riparian & Upland
Terrestrial plants
grasses/forbs, fruit,
seeds (trees, shrubs)
(Figure 21) Methamidophos applied to use site
Elimination and/or disturbance of
upland or dispersal habitat
Reduction in primary productivity
Reduced shelter
Restrict movement
Figure 2 I . Conceptual Diagram for Effects Terrestrial Critical Habitat
48
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Stressor
Long range j
atmospheric I
transport j
Ĥ~i Groundwater
Source
Exposure
Media
Wet/dry deposition
Uptake/gills
or integument
Uptake/cell,
roots, leaves
Uptake/gills
or integument
Receptors
Ingestion
Ingestion r ^
r T.
Population
Yield
Reduced yield
Community
Reduced seedling
emergence or vegetative
vigor (Distribution)
Attribute
Change
Habitat
PCEs
Aquatic Animals
Invertebrates
Vertebrates
Aquatic Plants
Non-vascular
Vascular
Surface water/
Sediment
Food sources
Reduction in algae
Reduction in prey
Red-legged Frog
Eggs Juveniles
Larvae Adult
Tadpoles
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Riparian and
Upland plants
terrestrial exposure
pathways and PCEs
see Figure 2G
Other chemical
characteristics
Adversely modified
chemical characteristics
(Figure 2J) Methamidophos applied to use site
Habitat quality and channel/pond
morphology or geometry
Adverse water quality changes
Increased sedimentation
Reduced shelter
Figure 2 J . Conceptual Diagram for Effects on Aquatic Critical Habitat
2.10 Analysis Plan
Analysis of risks to the California Red-Legged Frog (both direct and indirect) and to its
critical habitat will be assessed consistent with the Overview Document (USEPA, 2004)
and Agency guidance for ecological risk assessment (USEPA 1998).
2.10.1 Exposure Analysis
Exposure in Aquatic Phase
Risks (direct effects) to the aquatic phase CRLF will be assessed by comparing modeled
surface water exposure concentrations of methamidophos to acute and chronic (early life
stage hatching success and growth) effect concentrations for aquatic phase amphibians
(or surrogate freshwater fish) from laboratory studies (Tables 2.6 and 2.7). Risks to
aquatic dietary food resources (aquatic invertebrates, algae) of the aquatic phase CRLF or
risks to aquatic habitat that support the CRLF will also be assessed by comparing
modeled surface water exposure concentrations of methamidophos to laboratory
established effect levels appropriate for the taxa (Tables 2.6 and 2.7).
Surface water methamidophos concentrations will be quantified using a model, PRZM-
EXAMS., For the screening assessment, the standard EXAMS water body of 2 meters
maximum depth, and 20,000 cubic meters volume, will be used. Loading of
49
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methamidophos into the surface water via run-off and spray drift is considered.
Agricultural scenarios appropriate for labeled methamidophos uses (California potatoes,
cotton, tomatoes, and alfalfa) will be used to account for local soils, weather and growing
practices which impact the magnitude and frequency of methamidophos loading to the
surface water. Maximum labeled application rates, with maximum number of
applications and shortest intervals will be used to help define (1) the Action Area within
California for the Federal Action and (2) for evaluating effects to the CRLF.
Measurement endpoint values which will be used to evaluate risks (direct effects) to the
CRLF and to its aquatic prey and habitat (i.e., aquatic animals and plants) (Table 2.6 and
Table 2.7) will be derived from registrant submitted laboratory toxicity studies, and
studies from the scientific literature (ECOTOX database). If there are data gaps (e.g., no
fish early life stage NOAEC), the best available method for extrapolating a value for the
missing data will be used. Such extrapolation methods range from development of
simple empirical models like acute-to-chronic ratios using methamidophos data for other
taxa, or for the same taxa but based on other organophosphates to more complex
empirical models such as ACE (acute effects) and ICE (chronic survival), or quatitative
structure activity models (QSARs). The need to use such models (i.e., identification of
data gaps), and which model to use will be determined as part of the Effects Analysis.
Surface water exposure concentrations and measurement endpoints will be compared
quantitatively for RQ values. The RQs will be interpreted according to established
Agency guidance (Levels of Concern).
Exposure in Terrestrial Phase
Risks to the terrestrial phase CRLF will be assessed by comparing modeled exposure to
effect concentrations from laboratory studies. Risks to other Listed and non-Listed
species will be assessed in the same way.
Exposure in the terrestrial phase will be quantified using the TREX model, which
automates the calculation of dietary exposure according to the Hoerger-Kenaga
nomogram, as modified by Fletcher (ref). The nomogram tabulates the 90th and 50th
percentile exposure expected on various classes of food items, and scales the exposure (in
dietary terms) to the size and daily food intake of several size classes of birds and
mammals. Birds are also used as surrogates to represent reptiles and terrestrial-phase
amphibians. A foliar decay half-life of 6.5 days, the maximum found in Willis and
McDowell (1987) will be substituted for the default 35-day value.
Exposure of terrestrial plants will be quantified using the TerrPlant model, which
automates exposure comprising run-off and spray drift.
2.10.2 Effects Analysis
As previously discussed in Section 2.8.1 and 2.8.2, assessment endpoints for the frog
include direct toxic effects on survival, reproduction, and growth of the species itself, as
50
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well as indirect effects, such as reduction of the prey base and/or modification of its
habitat. Direct effects to the red-legged frog are based on toxicity information for
freshwater fish and birds, which are generally used as a surrogate for aquatic and
terrestrial phase amphibians, respectively. Effects on the CRLF and other potentially
affected animals and plants will be assessed using toxicity endpoints derived from
laboratory toxicity studies, and from the scientific literature (ECOTOX database).
Assessment endpoints to be considered are mortality, and adverse effects on growth and
reproduction. Sub-lethal effects will be considered if any are described in the laboratory
studies or literature; effects that are not related to mortality, growth or reproduction may
be considered only qualitatively.
Methamidophos' toxicity dataset is incomplete; chronic fish studies are lacking. Other
organophosphates will be screened for available chronic fish data that can be used to
derive ACRs (acute to chronic ratio) for methamidophos.
Indirect effects to the red legged frog are assessed by looking at available toxicity
information of the frog's prey items and habitat requirements (freshwater invertebrates,
freshwater vertebrates, aquatic plants, terrestrial invertebrates, terrestrial vertebrates, and
terrestrial plants).
Exposure concentrations and effects thresholds will be compared quantitatively, and Risk
Quotients (RQ) calculated if quantitative endpoints have been established. The RQs will
be interpreted according to established Agency guidance (Levels of Concern).
2.10.3 Action Area Analysis
The Action Area for the federal action is the geographic extent of exceedence of Listed
species Levels of Concern (LOC) for any taxon or effect (plant or animal, acute or
chronic, direct or indirect) resulting from the maximum label-allowed use of
methamidophos. To define the extent of the Action Area, the following exposure
assessment tools will be used: PRZM-EXAMS, TREX, AgDrift, AgDISP (with far-field
Gaussian extension), and Arc View, a geographic information system (GIS) program.
Other tools may be used as required if these are inadequate to define the maximum extent
of the Action Area.
To determine the downstream extent of the Action area for any aquatic effects,
methamidophos residues are also estimated for downstream from the treated areas by
assuming dilution with stream water (derived from land area) from unaffected sources
propagating downstream, until a point is reached beyond which there are no relevant
LOC exceedances. Once the distribution of predicted stream water concentrations is
obtained, it is further processed using a model that calculates expected dilution in the
stream according to contributing land area. As the land area surrounding the field on
which methamidophos is applied is enlarged, it encompasses a progressively greater
drainage area; in effect, a progressively larger 'sub-watershed' is created, with a
concomitant increase in dilution at the drainage point. This drainage point moves down-
gradient along the stream channel as the sub-watershed is expanded. At a certain point
51
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the predicted stream concentrations will fall below the LOC. The area below this point is
then assumed not to be at risk, with the upstream areas (up to the initial application area)
assumed to present the potential for (direct and indirect) impact on the RLF. Additional
methamidophos inputs within the same watershed will cause the area bounded by (that is,
within) the LOC to increase, extending the length of stream that is likely to be impacted.
In order to determine the extent of the action area downstream from the initial area of
concern, the Agency will need to complete the screening level risk assessment. Once all
aquatic risk quotients (RQs) are calculated, the Agency determines which RQ to level of
concern (LOC) ratio is greatest for all aquatic organisms (plant and animal). For
example, if both fish and aquatic plants have the same RQ of 1, the fish RQ to LOC ratio
(1/0.05) would be greater than for plants (1/1). Therefore, the Agency would identify all
stream reaches downstream from the initial area of concern where the PCA for the land
uses identified for methamidophos are greater than 1/20, or 5%. All streams identified as
draining upstream catchments greater than 5% of the landclass of concern, will be
considered part of the action area.
52
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3. Exposure Assessment
3.1 Label Application Rates and Intervals
The registered uses of methamidophos in California include cotton, tomatoes, potatoes,
and alfalfa grown for seed. The relevant labels are EPA Reg. No. 264-729 (Monitor 4
Liquid Insecticide) for the use on potatoes, 24(c) label CA-790188 for cotton, 24(c) label
CA-780163 for tomatoes, and 24(c) label CA-980013 for alfalfa grown for seed. The
application rates, intervals, and frequency are summarized in Table 3-1.
Table 3-1. La
jel Use rates for Methamidophos in California
Use
Label
Application
Rate, lb/acre
Number of
applications
allowed
Application
Interval
Application
Type
Potatoes
264-729
0.75 to 1.0
4 at
"Apply in a
Aerial,
(1.5 to 2
maximum
7- to 10-day
Ground,
pints
product)
rate (implied
by
maximum
seasonal rate
of 8 pints)
preventative
program or
as
necessary"
Chemigation
Tomatoes
CA-780163
0.75 - 1.0
4
7 to 10 days
Aerial,
Ground
Alfalfa for
CA-980013
1.0
"Do no
"up to 3
Aerial,
seed
make more
than one
pre-bloom
application
per crop
season"
days prior to
placing bees
in or around
the field"
Ground
Cotton
CA-790188
1.0
2 per season
"as needed,"
"do not
apply after
65% of the
bolls are
open"
Chemigation
53
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3.2 Aquatic Exposure Assessment
As discussed in section 2.5, the CRLF occupies a variety of shallow, static and flowing
aquatic habitats in the aquatic phase of its life cycle (egg to tadpole). The current range
of the CRLF is represented by the core areas and critical habitat in Figure 2.C.
3.2.1. Conceptual Model of Exposure
Aquatic exposure of the CRLF within the action area is estimated with the PRZM-
EXAMS model consistent with the Overview Document (EPA, 2004). Estimated
Environmental Concentrations (EECs) are produced using the standard farm pond of
20,000 cubic meters volume. Watersheds where methamidophos is used are assumed to
have 100% cropped area. The downstream extent of streams with exposures above the
Level of Concern (LOC) is estimated (using GIS methods) by diluting the pond
concentration with flow from streams outside the use area.
Standard assumptions of 1% spray drift for ground application and 5% drift for aerial
application are used. If the pond concentration from PRZM-EXAMS exceeds LOC, a
spray drift perimeter is calculated (using AgDrift model) that will reduce the pond
concentration to below the LOC.
3.2.2 Existing Monitoring Data
There is very little useful water monitoring data for methamidophos, due to its non-
persistent nature. The California Surface Water database and NAWQA have no data on
methamidophos. The assessment will be based on modeled concentrations as described
in section 3.2.1.
3.2.3 Modeling Approach
Risk quotients (RQs) were initially based on EECs derived using the Pesticide Root Zone
Model/Exposure Analysis Modeling System (PRZM/EXAMS) standard ecological pond
scenario. Where LOCs for direct/indirect effects and/or habitat modification are
exceeded based on the modeled EEC using the static water body (i.e., "may affect"),
refined modeling may be used to differentiate "may affect, but not likely to adversely
affect" from "may affect and likely to adversely affect" determinations for the CRLF and
its designated critical habitat.
The general conceptual model of exposure for this assessment is that the highest
exposures are expected to occur in the headwater streams adjacent to agricultural fields.
Many of the streams and rivers within the action area defined for this assessment are in
close proximity to agricultural use sites.
Twenty-six (26) California-specific PRZM scenarios are available for this assessment.
Each scenario is intended to represent a high-end exposure setting for a particular crop.
Each scenario location is selected based on various factors including crop acreage, runoff
54
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and erosion potential, climate, and agronomic practices. Once a location is selected, a
scenario is developed using locally specific soil, climatic, and agronomic data. Each
PRZM scenario is assigned a specific climatic weather station providing 30 years of daily
weather values.
Specific PRZM scenarios were chosen for this assessment for each crop (potato, tomato,
alfalfa, cotton) that represent agricultural areas in California. All scenarios are non-
irrigated meaning that only natural precipitation drives the potential for run-off to the
farm pond. The potato scenario was developed specifically for the CRLF assessments,
and so may not be conservative for a national assessment, however it is representative of
Kern County. Finally, the alfalfa scenario was developed for the organophosphate
cumulative assessment, and so may not be conservative for a national assessment,
however it is representative of the Central Valley. All scenarios were used within the
standard framework of PRZM/EXAMS modeling using the standard graphical user
interface (GUI) shell, PE4v01.pl.
3.2.3.1 Model Inputs
The estimated water concentrations from surface water sources were calculated using
Tier II PRZM (Pesticide Root Zone Model) and EXAMS (Exposure Analysis Modeling
System). PRZM is used to simulate pesticide transport as a result of runoff and erosion
from a standardized watershed, and EXAMS estimates environmental fate and transport
of pesticides in surface waters. The linkage program shell (PE4v01.pl) that incorporates
the site-specific scenarios was used to run these models.
The PRZM/EXAMS model was used to calculate concentrations using the standard
ecological water body scenario in EXAMS. Weather and agricultural practices were
simulated over 30 years so that the 1 in 10 year exceedance probability at the site was
estimated for the standard ecological water body.
Models to estimate the effect of setbacks on load reduction for runoff are not currently
available. It is well documented that vegetated setbacks can result in a substantial
reduction in pesticide load to surface water (USDA, NRCS, 2000). Therefore, the
aquatic EECs presented in this assessment are likely to over-estimate exposure in areas
with well-vegetated setbacks. While the extent of load reduction cannot be accurately
predicted through each relevant stream reach in the action area, data from USD A (USD A,
2000) suggest reductions could range from 11 to 100%.
The date of first application for all uses was set at March 1, to coincide with the frog's
reproductive season, and a period of higher rainfall, so that exposure due to run-off was
not underestimated.
The appropriate PRZM input parameters were selected from the environmental fate data
submitted by the registrant and in accordance with US EPA-OPP EFED water model
parameter selection guidelines, Guidance for Selecting Input Parameters in Modeling the
Environmental Fate and Transport of Pesticides, Version 2.3, February 28, 2002.
55
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Table 3-2 Summary of PRZM/EZAMS Environmental Fate Data Used for Aquatic
Exposure Inputs for Methamidophos CRLF Assessment
Fate Property
Value
MRID (or sourec)
Molecular Weight
141.2
Calculated from structure
Henry's constant
1.62 xlO E-ll atm-m3/mole
MRID
Vapor Pressure
1.73 x 10 E-5 torr
MRID
Solubility in Water
200,000 mg/1
MRID 43661003
Photolysis in Water
200 days
MRID 00150610
Aerobic Soil Metabolism Half-lives
1.75 days
MRID 41372201
Hydrolysis
27 days
MRID 00150609
Aerobic Aquatic Metabolism (water
column)
Anaerobic Aquatic Metabolism
(benthic)
3.5 days
19.4 days
Per Input Parameter Guidance,
2x soil input value
MRID 46934002
Koc
0.88 ml/g
MRID 40504811
Application Efficiency
Spray Drift Fraction13
95 % for aerial
99 % for ground
5 % for aerial
1 % for ground
Default value0
Default value
Application method (CAM)
2
Foliar spray
Incorporation depth
0 cm
Foliar spray
Master Record Identification (MRID) is record tracking system used within OPP to manage data submissions to the
Agency. Each data submission if given a unique MRID number for tracking purposes.
Inputs determined in accordance with EFED "Guidance for Chemistry and Management Practice Input Parameters for
Use in Modeling the Environmental Fate and Transport of Pesticides" dated February 28, 2002.
56
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3.2.4. Aquatic EEC Results
The table below (3.3) presents the results of the PRZM-EXAMS modeling.
Table 3-3. Modeled Aquatic Exposures for Methamidophos with No Irrigation and
March 1 as First Application Date
Crop
Aerial/Ground
Drift, %
Peak, ppb
21-day avg,
60-day avg,
Application
ppb
ppb
Tomato
A
5
11.6
5.8
2.7
4 apps @ 7
0
8.8
3.1
1.2
days
G
1
9.7
3.8
1.6
0
9.1
3.3
1.3
Potato
A
5
5.2
3.5
1.9
4 apps @ 7
0
1.7
0.60
0.22
days
G
1
2.5
1.1
0.55
0
1.8
0.63
0.23
Seed Alfalfa
A
5
6.4
2.5
0.99
1 application
0
4.2
1.5
0.61
G
1
4.8
1.8
0.71
0
4.3
1.6
0.63
Cotton
A
5
5.6
2.9
1.3
2 apps at 7
0
3.0
1.1
0.44
days
G
1
3.6
1.5
0.62
0
3.1
1.2
0.46
3.3. Terrestrial Exposure Assessment
As discussed in section 2.5, adult CRLF occupy a variety of terrestrial dispersal habitats.
The current range of the CRLF is represented by the core areas and critical habitat in
Figure 2.C.
3.3.1 Conceptual Model of Exposure
Terrestrial exposure of the CRLF on agricultural fields within the Action Area is
estimated with the TREX model, which automates exposure analysis according to the
Hoerger-Kenaga nomogram. Off-field exposure of animals is estimated with the AgDrift
and AgDISP model.
3.3.2. Modeling Approach
On-field exposure of the CRLF and its prey was estimated with TREX, using both
maximum label rates of 1 lb/acre, 4 applications spaced at 7 days (or 1 application for
alfalfa). The decay rate used on foliage and other food items was 6.5 days (Willis &
McDowell, 1987, p. 45). Direct risk to the CRLF was bounded using 20-gram and 100-
gram avian weight classes, since the weight of the frog falls in between these weights
57
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(Fellers & Guscio, 2004). The CRLF was assumed to consume the broadleaf plant/small
insect food category, since the bulk of its diet is invertebrates, and the small insect food
category provides a higher dose.
Indirect risk to the CRLF through effects on its prey base was estimated in two ways.
First, indirect effects via larger prey (small amphibian and mammal) were estimated
conservatively using the 20-gram weight class for the amphibian and the 15-gram weight
class for the mammal. The short-grass food category was used since it provides the
highest dose. The dose (in lb/acre) needed to bring all RQs below their respective LOC
(0.1 for acute, birds and mammals, and 1.0 for chronic) was calculated by dividing the
LOC by the RQ, and multiplying the result by the single application rate (1 lb/acre):
Dose below LOC (lb/acre) = (LOC/RQ)*(application rate, lb/acre).
The AgDrift or AgDISP model was then used to calculate the perimeter distance needed
to reduce the dose to below the LOC. If the result was beyond the range of these models,
then the Gaussian extension to AgDISP was used.
Indirect effects via smaller prey (terrestrial invertebrates) were estimated using the LD50
data for the honey bee, and an assumed body weight of 0.128 grams. The dose was
calculated as the large insect EEC in ppm (avian, dose-based, 20-gram animal), divided
by the body weight of the bee. The LD50 (ppm) was calculated as the LD50
(micrograms per bee) divided by the body weight. The RQ was then the dose divided by
the LD50 (ppm). The LOC for terrestrial invertebrates (insects) is 0.05.
3.3.3. Model Inputs
TREX model inputs included application rate (1 lb/acre) number of applications (1 to 4),
application interval (7 days), and foliar decay rate (6.5 days).
3.3.4 Results
See Appendix C for T-REX details of EEC calculations. Summaries are given here
Direct Effects
Table 3-4 and 3-5 presents the results of the TREX analysis for direct effects.
Table 3-4. Potato and tomato EEC (ppm) at 1 lb ai/A appied 4 times with 7 day interval
(maximum exposure)
Food items
20 gram bird
100 gram bird
Broadleaf plants/sm Insects
Fruits/pods/seeds/lg insects
277.56
30.84
158.28
17.59
Table 3-5. Alfalfa for Seed EEC (ppm) at 1 lb ai/A appied once (minimum exposure)
58
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Food items
20 gram bird
100 gram bird
Broadleaf plants/sm Insects
Fruits/pods/seeds/lg insects
153.75
17.08
87.68
9.74
Indirect Effects
Table 3-6 and 3-7 presents the results of the TREX analysis for indirect effects.
Table 3-6. Potato and tomato EEC (ppm) at 1 lb ai/A appied 4 times with 7 day interval
(maximum exposure)
Food Items
20 gram bird
15 gram mammal
Short Grass
493.45
157.94
Tall Grass
226.16
72.39
Broadleaf plants/sm Insects
277.56
88.84
Fruits/pods/seeds/lg insects
30.84
9.87
Table 3-7. Alfalfa for Seed EEC (ppm) at 1 lb ai/A appied once (minimum exposure)
Food Items
20 gram bird
15 gram mammal
Short Grass
273.34
228.82
Tall Grass
125.28
104.88
Broadleaf plants/sm Insects
153.75
128.71
Fruits/pods/seeds/lg insects
17.08
14.30
59
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4. Effects Assessment
This assessment evaluates the potential for methamidophos to adversely affect the
California Red-Legged Frog (CRLF). As described in Agency's Overview Document
(U.S. USEPA, 2004) and evaluation by the U.S. Fish and Wildlife Service
(USFWS/NMFS, 2004), the most sensitive endpoint for each taxa is evaluated. As
previously discussed in Section 2.7, assessment endpoints for the CRLF include direct
toxic effects on the survival, reproduction, and growth of the frog itself, as well as
indirect effects, such as reduction of the prey base and/or modification of its habitat.
According to the Recovery Plan for the California Red-Legged Frog, CRLF are sensitive
to salinity. When the eggs are exposed to salinity levels greater than 4.5 parts per
thousand, there is 100% mortality. Therefore, this assessment will not evaluate estuarine
species.
For this assessment, evaluated taxa include freshwater fish (surrogate for aquatic phase of
CRLF), freshwater aquatic invertebrates, birds (surrogates for terrestrial phase of CRLF),
small mammals, terrestrial invertebrates, algae, and terrestrial plants. Given that the
frog's prey items and habitat requirements are dependent on the availability of small
mammals and frogs, insects, algae, aquatic invertebrates; toxicity information for aquatic
and terrestrial plants (habitat) and food items are also discussed. Acute (short-term) and
chronic (long-term) toxicity information is characterized based on registrant-submitted
studies and a comprehensive review of the open literature on methamidophos. In
addition to registrant-submitted and open literature toxicity information, indirect effects
to CRLF, via impacts to aquatic terrestrial plant community structure and function are
also evaluated based on community-level threshold concentrations. Other sources of
information, including use of the acute probit dose response relationship to establish the
probability of an individual effect and reviews of the Ecological Incident Information
System (EIIS), are conducted to further refine the characterization of potential ecological
effects associated with exposure to methamidophos. Currently, no guideline tests exist
for frogs, and no frog data were available for methamidophos; thus, surrogate species,
freshwater fish and birds, are used as described in the Overview Document (U.S. EPA,
2004). In addition, section 4.3 discusses available frog toxicity data for other
organophosphates. A summary of the available ecotoxicity information, the community-
level endpoints, use of the probit dose response relationship, and the incident information
for methamidophos are provided in Sections 4.1 through 4.4, respectively.
4.1 Evaluation of Ecotoxicity Studies: Aquatic and Terrestrial
Toxicity endpoints are established based on data generated from guideline studies
submitted by the registrant, and from open literature studies that meet the criteria for
inclusion into the ECOTOX database maintained by EPA/Office of Research and
Development (ORD) (U.S. EPA, 2004). Open literature data presented in this assessment
were obtained from an ECOTOX search that included all open literature data for
methamidophos. In order to be included in the ECOTOX database, papers must meet the
following minimum criteria:
60
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(1) the toxic effects are related to single chemical exposure;
(2) the toxic effects are on an aquatic or terrestrial plant or animal species;
(3) there is a biological effect on live, whole organisms;
(4) a concurrent environmental chemical concentration/dose or application
rate is reported; and
(5) there is an explicit duration of exposure.
Data that pass the ECOTOX screen are evaluated along with the registrant-submitted
data, and may be incorporated qualitatively or quantitatively into this endangered species
assessment. In general, effects data in the open literature that are more conservative than
the registrant-submitted data are considered. In addition, data for taxa that are directly
relevant to the California Red-Legged Frog (i.e., aquatic-phase and terrestrial-phase
amphibians) were also considered. The degree to which open literature data are
quantitatively or qualitatively characterized is dependent on whether the information is
relevant to the assessment endpoints (i.e., maintenance of California Red-Legged Frog
survival, reproduction, and growth) identified in Section 2.7. For example, endpoints
such as behavior modifications are likely to be qualitatively evaluated unless quantitative
relationships between modifications and reduction in species survival, reproduction,
and/or growth are available.
Table 4.1 summarizes the most sensitive ecological toxicity endpoints for the CRLF,
based on an evaluation of both the submitted studies and the open literature, as previously
discussed. A brief summary of submitted and open literature data considered relevant to
this ecological risk assessment for the CRLF is presented below. Additional information
is provided in Appendix A, A1 and G.
61
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Table 4.1 Methamidophos measurement endpoints and values selected for use in
RQ calculations in this effects det
ermination.
Assessment
Endpoint50,000
|ig/L ai
NOEC = 50,000
|ig/L ai
Supplemental
(Most sensitive)
MRID
40228401
(Mayer,
1986)1
Freshwater green
algae,
cyanobacteria or
diatom 96-h
NOAEC (orECos)
for biomass
Abundance (i.e.,
survival,
reproduction, and
growth) of
individuals and
populations of
birds in close
proximity to sites,
(b)
Avian (single
dose) acute oral
LD50
Common
grackle
4.1 mg ai/kg-bw
Supplemental
(Most sensitive)
MRID
00144428
(Lamb, 1972)
Avian subacute
5-day dietary LC50
Bobwhite
quail
dietary sub-acute
LC50 = 42 ppm ai
Supplemental
(Most sensitive)
MRID
00093904
(Beavers &
Fink, 1979)
Avian reproduction
NO A F.I.
Mallard duck
Reproductive study
NOEL = 3 ppm ai3
Acceptable
(Most sensitive)
MRID
00014114
(Beavers &
Fink, 1978)
62
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Assessment
Endpoint4.0 lb ai/A
Acceptable
MRID
46655802
Christ and
Lam, 2005
6b. Seedling
emergence
NOAEC
4.0 lb ai/A
6c. Vegetative
vigor EC25
>4.0 lb ai/A
Acceptable
MRID
46655802
Christ and
Lam, 2005
6d. Vegetative
vigor NOAEC
4.0 lb ai/A
1 Most sensitive measure of effect in study that NOAEC is based on
2 Most sensitive measure of effect in study that NOAEC is based on.
3 Most sensitive measure of effect in study that NOAEC is based on.
4 Since there are no aquatic plant studies for methamidophos, acephate RED was used to provide information on
aquatic plant endpoint.
5 Decrease in number of births, pup viability and body weight. There does not appear to be a palatability problem in
the studies (personal communication Nancy McCarroll, HED, 2/10/98).
Table 4.2 Levels of Concern for Terrestrial and Aquatic Organisms
Taxa
Listed
Species
Acute LOC
Chronic LOC
Avian' (terrestrial phase amphibians)
0.1
1
Mammalian"
0.1
1
Terrestrial plants''
1
Aquatic Animals1 (aquatic phase
amphibians)
0.05
1
Used in RQ calculations:
1 LD50 and estimated NOAEL
2LD50andNOAECL
3 NOAEC
4
LC/EC50 and estimated and reproductive NOAEC
4.2. Evaluation of Aquatic Effects
No guideline tests exist for frogs. The available open literature has no information on
methamidophos toxicity to aquatic-phase amphibians. Fish toxicity from open literature
shows that acute and chronic ecotoxicity endpoints are generally less sensitive than the
63
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registrant submitted fish studies. A summary of acute and chronic freshwater fish data,
including sublethal effects, is provided below.
4.2.1 Toxicity to Freshwater Fish
4.2.1.1. Freshwater Fish: Acute Exposure (Mortality) Studies
Freshwater fish acute toxicity studies were used to assess potential direct effects to the
CRLF. Methamidophos toxicity has been evaluated in some freshwater fish species,
including rainbow trout, bluegill sunfish, and carp, and the results of these studies
demonstrate a narrow range of sensitivity. The range of acute freshwater fish LC50
values for methamidophos is from 25,000 to 68,000 (J,g/L; therefore, methamidophos is
categorized as slightly (>10,000 to 100,000 (J,g/L) toxic to freshwater fish on an acute
basis. The freshwater fish acute LC50 value of 25,000 (ig/L is based on a static 96-hour
toxicity test using rainbow trout (Oncorhynchus mykiss) (MRID 00041312, Nelson,
1979). No sublethal effects were reported as part of this study. A complete list of all the
acute freshwater fish toxicity data for methamidophos is provided in Appendix A.
4.2.1.2. Freshwater Fish: Chronic Exposure (Growth/Reproduction) Studies
Since there are no chronic data for freshwater fish, an acute to chronic ratio (ACR) was
determined. Methamidophos is an organophosphate insecticide. The EFED database
was accessed to derive an acute to chronic ratio of all organophosphate insecticides that
have an acute LC50 and an early life stage fish study for rainbow trout. Rainbow trout
was chosen since the most sensitive fish acute endpoint for methamidophos is rainbow
trout. Nineteen organophosphates were found that have both an acute and chronic study
for rainbow trout. The ACR ranged from 0.28 for oxydemeton-methyl to 511.0 for
sulprofos. In order to provide the most conservative estimate for the chronic freshwater
fish NOEC for methamidophos, the ACR of 511 will be used to estimate the NOEC for
rainbow trout. The estimated chronic NOEC for rainbow trout as derived from and ACR
of 511 and a LC50 of 25 is 0.0489 ppm or 48.9 jig/L.
The following section presents the methodology used in deriving an avian ACR for
organophosphates, the group to which methamidophos belongs, that was used to
extrapolate a chronic fish NOAEC for methamidophos. The resulting early life stage for
freshwater fish NOAEL was used as a surrogate for the aquatic-phase amphibian (U.S.
EPA 2006). Of the organophosphates, 12 were evaluated for this extrapolation Table 4.4.
The EFED toxicity database was accessed to derive an acute to chronic ratio of all
organophosphate insecticides that have an acute LC50, an early life stage fish study for
rainbow trout, and have been reviewed previously for scientific soundness. Rainbow
trout is usually the most sensitive fish species among pesticides and is the most sensitive
fish acute endpoint for methamidophos. A species and chemical specific ACR would
ideally be determined which will then be used in the final organophosphate ACR
derivation.
64
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The estimated fish (aquatic phase amphibians) chronic NOAEC for methamidophos is
derived as follows. The (methamidophos) rainbow trout LC50 used in this assessment is
25 ppm ai. The largest acute-to-chronic ratio from the organophosphates is 144 for
Dichlorvos. This ratio is used to calculate the final NOEC for methamidophos.
Estimated Trout NOEC for methamidophos = 25,000/144 = 1.736 jig ai/L
The table below shows the inputs for the organophosphates that were considered for the
methamidophos ACR.
Acute to Chronic Table for Organophosphates
Table 4.4. Methamidophos Acute to Chronic Ratio for Rainbow Trout NOEC
96-hr
LCS0
NOAEC
Chemical
(US ai/L)
MRIDs
(US ai/L )
MRIDs
ACR
Azinphos
8.8
03125193
0.29
00145592
methyl
30.344
Coumaphos
890
40098001
11.7
43066301
76.068
Dichlorvos
750
43284702
5.2
43788001
144.23
Dimethoate
7,000
TN 1069*
430
43106303
17.441
Disulfoton
1,850
40098001
220
41935801
8.4090
Fenamiphos
68
40799701
3.8
41064301
17.894
Fenitrothion
2,000
40098001
46
40891201
43.478
Fenthion
830
40214201
7.5
40564102
110.66
Fonofos
50
00090820
4.7
40375001
10.638
Isofenphos
1,800
00096659
153
00126777
11.764
Phosmet
105
40098001
3.2
40938701
32.812
terbufos
7.6
40098001
1.4
41475801
5.4285
* TN 1069 is test number for EPA's Animal Biology Lab, McCann, 1977
4.2.1.3. Freshwater Fish: Sublethal Effects and Additional Open Literature
Information
The open literature ECOTOX did not identify any data that report sublethal effect levels
to freshwater fish that are less sensitive than the selected measures of effect summarized
in Table 4.1 for methamidophos. Appendix G provides the reasons for the rejection of
studies identified using the ECOTOX database.
4.2.2. Toxicity to Freshwater Invertebrates
Freshwater aquatic invertebrate toxicity data were used to assess potential indirect effects
of methamidophos to the CRLF. Adverse effects to freshwater invertebrates resulting
from exposure to methamidophos may indirectly affect the CRLF via reduction in
available food. As discussed in the CRLF Life History, Attachment 1, the CRLF aquatic-
65
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phase larvae (tadpoles) is presumed to be an algae grazer consuming diatoms, algae, and
detritus. Hayes and Tennant (1985) report, based on a study examining the gut content of
35 juvenile and adult CRLFs, that the species feeds on as many as 42 different
invertebrate taxa. Most frequently encountered were: carabid (11) and tenebrionid (9)
beetles; water striders (9); lycosid spiders (7); larval neuropterans (e.g., alderflies) (7).
Therefore, aquatic invertebrates are also assumed to be a food source for CRLF aquatic-
phase.
A summary of acute and chronic freshwater invertebrate data, including published data in
ECTOX is provided below in Sections 4..2..2.1 through 4.2.2.3.
4.2.2.1 Freshwater Invertebrates: Acute Exposure Studies
The most sensitive acceptable study (MRID 00041311, Nelson, 1979) found the Daphnia
magna LC50 to be 26 jig ai/L (200-34). Two other Daphnia magna were tested with the
LC50 found to be 27 to 50 jug ai/L (MRID 00041311, 00014110) which is similar to the
most sensitive endpoint. Appendix A provides a summary and description of other
freshwater invertebrate studies not used in the RQ calculations. Methamidophos is
classified as very highly toxic to freshwater invertebrates on an acute basis.
4.2.2.2. Freshwater Invertebrates: Chronic Exposure Studies
A submitted freshwater invertebrate life-cycle study (MRID 46554501, Kern, 2005)
using Daphnia magna was reviewed. Despite there being some questions regarding the
concentration levels of study, the reviewer believes that the results are acceptable enough
to use for risk assessment.
The NOEC is found to be 4.49 jig ai/L (0.0045 ppm) for 21-day dry weight, 21-day
immobility, and 21-day reproduction endpoint. The LOEC is 53 jag ai/L (0.053 ppm) for
all of the above endpoints.
4.2.2.3. Freshwater Invertebrates: Open Literature Data
In addition to submitted studies, data were located in the open literature12 that report
effect levels to freshwater invertebrates that are less than the selected measures of effect
summarized in Table 4.1. This sensitive endpoint was not used since the mortality in the
controls ranged from 60% to 80% which indicate the study to be not very sound. No
sublethal effects to freshwater aquatic invertebrates were found in open literature for
methamidophos.
12 Juarez, L.M., J. Sanchez, 1989. Toxicity of the Organophosphorous Insecticide Methamidophos (0,S-
Dimethyl Phosphoramidothioate) to Larvae of the Freshwater Prawn, Macrobachium rosenbergii (DeMan)
and the Blue Shrimp, Penaeus stylirostris Stimpson. Bull. Environ. Contam. Toxicol. (1989) 43:302-309.
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4.3. Toxicity to Birds
There are no registrant submitted nor open literature data on methamidophos toxicity to
terrestrial-phase amphibians. Avian toxicity from open literature shows that acute and
chronic ecotoxicity endpoints are generally less sensitive than the registrant submitted
avian studies. A summary of acute and chronic avian data, including sublethal effects, is
provided below.
4.3.1. Birds: Acute Exposure (Mortality) Studies
Avian acute toxicity studies were used to assess potential direct effects to the CRLF.
Methamidophos toxicity has been evaluated in some avian species, including mallard
duck, bobwhite quail, dark-eyed junco, common grackle, starling, redwing blackbird, and
Japanese quail and the results of these studies demonstrate a narrow range of sensitivity.
The range of acute oral LD50 values for methamidophos is from 1.78 mg/kg-bw to 29.5
mg/kg-bw. The range of subacute dietary LC50 is from 42 ppm to 1650 ppm; therefore,
methamidophos is categorized as very highly to highly toxic to avian species on an acute
oral basis (<10 mg/kg-bw to 10-50 mg/kg-bw) to birds and as slightly toxic to very
highly toxic to avian species on a subacute dietary basis.
4.3.2. Acute Oral LD50
Based on professional judgment, the lower 95% confidence limit on the acute oral LD50
of 4.1 mg/kg-bw (MRID 00144428) for the common grackle was selected to evaluate
acute oral risks to birds and terrestrial-phase amphibians. The common grackle study
was selected because it had the most scientifically sound lowest acute oral value. Though
classified as supplemental, the study covered a larger portion of the dose-response curve
(i.e., 6 doses) and control results indicated handling and environmental conditions were
sound. To address concerns that the results were potentially not as precise as a guideline
study because fewer birds were tested the 95% lower confidence limit on the LD50 (4.1
mg/kg-bw) was selected for use rather than the mean LD50 study result (6.7 mg/kg-bw).
(note: however, it is unknown if fewer common grackles would need to be tested to
achieve the same precision as with mallards and bobwhite quail in guideline studies). For
a more detailed discussion of studies considered but not selected for use in RQ
calculations, see Appendix Al.
4.3.3. Avian sub acute dietary endpoint analysis
The most sensitive avian LC50 is an acceptable bobwhite quail study (MRID 00093904,
Beavers, 1979) with an LC50 of 42 ppm (34 - 52). The study shows a dose response
slope of 3.4. Noted in the study, was the observation that the birds were too sick to eat
when exposed to methamidophos. Another bobwhite study (MRID 00014064) reported
that repellency was observed at 826 ppm. Other bobwhite studies show LC50 values of
57.9 and 59 ppm which is near the most sensitive LC50 value, thus supporting the
selection of the chosen LC50 used in RQ calculations. The mallards tend to be less
sensitive with LC50 values ranging from 848 to 1650 ppm. The Japanese quail LC50 has a
67
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LC50 value of 92 ppm which is comparable in magnitude to the bobwhite studies.
Methamidophos is considered to be very highly toxic to quail and slightly toxic to
mallard ducks on a sub acute dietary basis.
A complete list of all the acute bird toxicity data for methamidophos is provided in
Appendix A.
4.3.4 Birds: Chronic Exposure (Reproduction) Studies
Similar to the acute data, chronic avian toxicity studies would be used to assess potential
direct effects to the CRLF because direct chronic toxicity guideline data for frogs do not
exist. The most sensitive avian reproductive study is a bobwhite quail (MRID 00014114,
Beavers, 1978) with a NOEL of 3 ppm and a LOEL of 5 ppm. The NOEL was based on
eggshell thickness, embryo viability, embryo development, hatchability, and survivability
of hatchlings. There does not appear to be a palatability problem in this study (personal
communication Nancy McCarroll, HED, 2/10/98).
4.3.5 Birds: Sublethal Effects and Additional Open Literature Information
In addition to submitted studies, data on sublethal effects data were located in the open
literature on birds but effects are observed at similar exposure rates or less sensitive than
those selected as measures of effect summarized in Table 4.1. Stromborg (ECOTOX ref.
40022) shows northern bobwhites to have eggs laid affected by methamidophos at 7.8
ppm and NOEL of 5 ppm. This would confirm reproductive endpoint of 3 ppm selected.
4.4 Toxicity to Mammals
Toxicity data on small mammals is used in this assessment to assess their availability as a
food items for the CRLF.
4.4.1. Mammals: Acute Exposure (Mortality) Studies
The mouse studies (MRID 00014047, 1968; MRID00014048, 1968) have similar LD50
values as the most sensitive rat studies (00014044, 1968) with LD50 of 16.2 mg/kg-bw
and 18 mg/kg-bw for the mouse and 15.6 mg/kg-bw (male) and 13.0 mg/kg-bw (female),
respectively. Since the CRLF diet includes small mammals like a small mouse and the
adjusted LD50 (7.92 mg/kg-bw) value is more sensitive than the rat LD50(13.0 mg/kg-bw)
the LD50 value chosen is from the mouse study (MRID 00014048, 1968) with LD50 of
16.2 mg/kg-bw.
4.4.2. Mammals: Chronic Exposure (Reproduction) Studies
A two-generation rat reproductive study (MRID 00148455, 41234301; 1984) found the
NOAEL to be 0.5 mg/kg/day (10 ppm) and the LOAEL to be 1.65 mg/kg/day (33 ppm).
The NOEL was based on decrease in number of births, pup viability and pup body
weight.
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4.4.3. Mammals: Sublethal Effects and Additional Open Literature Information
In addition to submitted studies, no data more sensitive than the selected measures of
effect summarized in Table 4.1 were located in the open literature.
4.5 Toxicity to Insects
Toxicity data on insects is used in this assessment to assess their availability as a food
items for the CRLF.
A honey bee acute contact study (MRID 00036935, Atkins, 1975) found an LD50 of 1.37
jig/bee. The dose response slope is 10.32. Methamidophos is categorized as highly toxic
to bees on an acute contact basis.
4.6 Toxicity to Plants
4.6.1 Toxicity to Aquatic Plants
Aquatic plant toxicity studies were used as one of the measures of effect to evaluate
whether methamidophos may affect primary production. Primary productivity is
essential for indirectly supporting the growth and abundance of the CRLF aquatic phase.
In addition to providing cover, other aquatic plants harbor a variety of aquatic
invertebrates that CRLF may eat.
Aquatic Plants: Laboratory Data
There are no aquatic plant studies submitted for methamidophos. There are no aquatic
plant studies found in ECOTOX literature database. Acephate, another organophosphate
and of which methamidophos is the primary degradate, was found to have an aquatic
plant study, Skeletonema costatum, which is a marine diatom. The EC50 is greater than
50 ppm (Mayer, 1986; MRID 40228401). This 96-hr static study was found to have an
EC50 value greater than 50,000 ppb; it appears that methamidophos is practically
nontoxic to aquatic plants. This study is considered to be supplemental due to lack of
available raw data.
4.6.2. Terrestrial Plants
Phytotoxicity tests of methamidophos exposure to numerous plant species (seedling
emergence and vegetative vigor) were submitted by the registrant. The EC25 is greater
than 4.5 lb ai/A and the NOEC is 4.5 lb ai/A. A typical application rate for
methamidophos is 1.0 lb/A and it is relatively short-lived in the environment. Based on
the results of the submitted terrestrial plant toxicity tests, it appears that seedlings and
emerged plants are not sensitive to methamidophos and effects to both aquatic and
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terrestrial plants will not be considered in this assessment. For more information on plant
toxicity studies, see Appendix A and Al.
4.7 Aquatic and Terrestrial Field Studies
4.7.1. Terrestrial Field Studies
Perritt (MRID 41548803) considered the aerial application of Monitor 4 on cotton at 1 lb
ai/A with 8 day intervals applied 7 times in Alabama. Thirty percent of the placed
carcasses were found. EFED concluded that thirty-four casualties were found during the
study at eight test fields. Ten of the casualties were found during pre-application periods,
and six were found post application under circumstances that did not indicate that
exposure to Monitor 4 Spray was a potential cause of mortality. Only one casualty was
found under circumstances suggesting that it was likely treatment related. Cause of death
could not be determined for another seventeen casualties, but exposure to Monitor 4
Spray could not be precluded as a potential cause of mortality and therefore the study is
classified as supplemental.
Die-offs of sage grouse (Centrocercus urophasiannus) were noted in 1981 near potato
fields sprayed with methamidophos (Blus et al, 1989). Five intoxicated sage grouse were
collected and inhibition of brain ChE activity ranged from normal to 61%. Although
methamidophos half-life is <4 days, low levels of methamidophos may persist for several
weeks in plants. Thus, intoxicated grouse may be exposed to additional residues when
ChE reversal is initiated and the grouse resumes feeding on the contaminated foliage.
According to the authors, these findings suggest that OP insecticides may adversely
affect sage grouse populations whose summer range include cropland. The authors also
noted that this study may provide some evidence for the claim that pesticides are partly
responsible for the declining populations of upland game birds in the U.S. and Europe.
Adult radio-equipped hens were released near potato fields and compared with radio-
equipped hens in Tule Lake National wildlife Refuge during the summers of 1990 - 1992
(Grove et al, 1998). Hens were monitored after methamidophos application to potato
fields and later captured. Measurements of Brain AChE were taken. Direct toxicity of
the radio- equipped adult hens did not occur. Two juveniles (not radio-equipped) were
found dead as a result of methamidophos exposure. Brain AChE activity inhibition in the
captured hens ranged from 19% to 62%. Six of the pheasants had inhibition of brain
AChE that is greater than 55%. Twenty-five of the 41 adult pheasants captured within 20
days of spray application had detectable methamidophos residues on food items taken
from their upper GI tract. Seven of the adults had food items that ranged from 0.18 to
2.10 ppm (wet basis). Hens captured near potato fields that were sprayed appear to have
lost weight when compared to controls. It appears that the application of methamidophos
have impacted the availability of food items for the birds and juveniles. None of the
radio-equipped hens died as a direct result of methamidophos exposure or predation. In
addition, authors concluded that most of the nesting failures of radio-equipped hens
occurred prior to insecticide applications.
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In a study comparing methamidophos and permethrin, Temple and Palmer (1995)
conclude that methamidophos applications (1 lb ai/A) have equal or less adverse impact
on avian reproduction than the permethrin insecticide (which is practically not toxic to
vertebrates) which was used as the control. This study was limited to the European
Starling reproduction and did not address the other species in the area. This study also is
designed not to look at acute toxicity but focused on reproductive endpoints. There was
some avian mortalities in the study but it is not apparent if these mortalities are chemical
related. Fourteen percent of the post application blood samples > 50% ChE inhibition.
These findings suggest that animals that have greater exposure to contaminated food, or
are more sensitive to OP pesticides than are starlings, could die from ChE inhibition.
4.7.2 Aquatic Field Studies
In a field study evaluating the effects of acephate and methamidophos, (Hussain, et al.
1985), backswimmer (aquatic insect) and rainbow trout displayed ChE inhibition for 4
hours before recovery began. This suggests that aquatic insects and fish that are exposed
to acephate/methamidophos may not recover by spontaneous reactivation of AchE.
Therefore aquatic insects or fish may be stressed for some time because of physiological
effects caused by inhibition of AchE.
4.8 Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern
The Agency uses the probit dose response relationship as a tool for providing additional
information on the potential for acute direct effects to individual listed species and
aquatic animals that may indirectly affect the listed species of concern (U.S. EPA, 2004).
As part of the risk characterization, an interpretation of acute 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 exposure at the EEC actually occur for a species
with sensitivity to methamidophos on par with the acute toxicity endpoint selected for
RQ calculation. To accomplish this interpretation, the Agency uses the slope of the dose
response relationship available from the toxicity study used to establish the acute toxicity
measures of effect for each taxonomic group that is relevant to this assessment (i.e.,
freshwater fish used as a surrogate for aquatic-phase amphibians and freshwater
invertebrates). The individual effects probability associated with the acute RQ is based
on the mean estimate of the slope and an assumption of a probit dose response
relationship. In addition to a single effects probability estimate based on the mean, upper
and lower estimates of the effects probability are also provided to account for variance in
the slope, if available. The upper and lower bounds of the effects probability are based
on available information on the 95% confidence interval of the slope. A statement
regarding the confidence in the estimated event probabilities is also included. Studies
with good probit fit characteristics (i.e., statistically appropriate for the data set) are
associated with a high degree of confidence. Conversely, a low degree of confidence is
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associated with data from studies that do not statistically support a probit dose response
relationship. In addition, confidence in the data set may be reduced by high variance in
the slope (i.e., large 95% confidence intervals), despite good probit fit characteristics.
Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1
(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP,
Environmental Fate and Effects Division (June 22, 2004). The model allows for such
calculations by entering the mean slope estimate (and the 95% confidence bounds of that
estimate) as the slope parameter for the spreadsheet. In addition, the acute RQ is entered
as the desired threshold.
4.9 Incident Database Review
A number of incidents have been reported in which methamidophos has been associated
with some type of environmental effect. Incidents are maintained and catalogued by
EFED in the Ecological Incident Information System (EIIS). As of the writing of this
assessment, 17 incidents are in EIIS for methamidophos spanning the years 1985 to 2000.
Most (11/17, 65%) of the incidents involved bee kills. Of the remaining 6 incidents, 4
involved bird mortalities and 2 involved plants. One plant incident involved another
herbicide that may have caused the plant damage and another incident involved having
methamidophos residues on a crop that does not have any established tolerances for
methamidophos. These incidents are summarized in Appendix E.
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5. Risk Characterization
Risk characterization is the integration of the exposure and effects characterizations to
determine the potential ecological risk from varying methamidophos use scenarios within
the action area and likelihood of direct and indirect effects on the California Red Legged
frog. The risk characterization provides estimation and description of the likelihood of
adverse effects; articulates risk assessment assumptions, limitations, and uncertainties;
and synthesizes an overall conclusion regarding the effects determination (i.e., "no
effect," "likely to adversely affect," or "may affect, but not likely to adversely affect") for
the California Red Legged frog.
5.1 Risk Estimation
Risk is estimated by calculating the ratio of the expected environmental concentration
and the appropriate toxicity endpoint. This value is the risk quotient (RQ), which is then
compared to pre-established levels of concern (LOC) for each category evaluated. The
RQ methodology, LOCs , and specific details of the calculations are contained in
Appendix F. The highest EECs and most sensitive endpoints are used to determine the
screening level RQ. Using these two values theoretically results in a conservative
estimate of risk. Risk quotients are presented in 5.1.1. (direct effect) and in 5.1.2.
(indirect effect).
Table 5.1. Levels of Concern for Terrestrial and Aquatic Organisms
Taxa
Listed
species
Acute LOC
Chronic LOC
Avian' (terrestrial phase amphibians)
0.1
1
Mammalian-
0.1
1
Terrestrial plants''
1
Aquatic Animals1 (aquatic phase
amphibians)
0.05
1
Insects
0.05
1
Used in RQ calculations:
1 LD50 and estimated NOEL
2LD50andNOEC
3 EC25
4 LC/EC50 and estimated and reproductive NOEC
5.1.1 Direct Effects
5.1.1.1 Aquatic Phase.
Direct effects to the CRLF in the aquatic phase were estimated using exposure
estimates from PRZM-EXAMS and surrogate fish toxicity. For acute effects, the fish
LC50 endpoint was used. For chronic effects, there were no data (fish early life stage
study) for methamidophos. Therefore a chronic endpoint (NOAEC) for the fish was
estimated from the Acute-to-Chronic ratios for other organophosphate insecticides. See
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section 4.1 for details. There are no LOC exceedences for direct acute or chronic risk to
CRLF aquatic-phase from the use of methamidophos, based on RQ's calculated using
freshwater fish (LC50 = 25,000 ppb) as a surrogate for the aquatic phase of the frog.
Tables 5-2 and 5-3 below give the exposures, endpoints and risk quotients for acute and
chronic effects, respectively.
Table 5-2. Acute Risk Quotients for Fish in
Crop
Application
Peak EEC, ppb
Risk Quotient
Potato
Aerial
5.2
0.00021
Ground
2.5
0.0001
Tomato
Aerial
11.6
0.0046
Ground
9.7
0.00039
Alfalfa
Aerial
6.4
0.00026
Ground
4.8
0.00019
Cotton
Aerial
5.6
0.00022
Ground
3.6
0.00014
reshwater Environments
Table 5-3. Chronic Risk Quotients for Fish (NOEC = 48.9 ppb) in Freshwater
Environments
Crop
Application
21-day average
EEC, ppb
Risk
Quotient
Potato
Aerial
3.5
0.07
Ground
1.1
0.02
Tomato
Aerial
5.8
0.12
Ground
3.8
0.08
Alfalfa
Aerial
2.5
0.05
Ground
1.8
0.04
Cotton
Aerial
2.9
0.06
Ground
1.5
0.03
Notes: (a) Estimated from acute-to-chronic ratio for other OP insecticides,
(b) Exceeds Chronic LOC (1)
5.1.1.2 Terrestrial Phase.
Direct effects to the terrestrial phase CRLF were estimated using TREX, assuming that
the frog was represented by a bird weighing 20 or 100 grams, and consumed a diet of
small insects. Invertebrates make up the bulk of the CRLF diet. Indirect risk to the
CRLF via effects on prey items, such as the tree frog and mouse are considered below
(section 5.1.2).
Tables 5-4 and 5-5 below summarizes the direct risks to the CRLF. The TREX results
are given in Appendix C.
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Table 5-4. Summary of Direct, Acute and Chronic Risks to Terrestrial Phase CRLF, as
represented by effects to avian species. Potato and tomato EEC (ppm) at 1 lb ai/A
Effect
Endpoint
Size Class
(grams)
Food Item
EEC (ppm)
RQ (a)
Acute
LD50 (3.67)
(mg/kg-bw)
20
Small insect
277
75.7
Large insect
31
8.4
LD50 (4.67)
(mg/kg-bw)
100
Small insect
158
33.9
Large insect
18
3.8
Subacute
Dietary
LC50 (42)
(ppm)
Small insect
244
5.8
Large insect
27
0.64
Reproductive
NOAEC (3)
(ppm)
""
Small insect
244
81.2
Large insect
27
9.0
Notes: (a) Bold RQ values exceed LOC for listed species,
(b) LOC for acute is 0.1 and for chronic is 1.0
Table 5-5. Summary of Direct, Acute and Chronic Risks to Terrestrial Phase CRLF, as
represented by effects to avian species. Alfalfa EEC (ppm) at 1 lb ai/A appied once
(minmum exposure)
Effect
Endpoint
Size Class
(grams)
Food Item
EEC (ppm)
RQ (a)
Acute
LD50 (3.67)
20
Small insect
153.7
41.9
(mg/kg-bw)
Large insect
17.1
4.7
LD50 (4.67)
100
Small insect
87.7
18.8
(mg/kg-bw)
Large insect
9.7
2.1
Subacute
LC50 (42)
Small insect
135
3.2
Dietary
(ppm)
Large insect
15
0.36
Reproductive
NOAEC (3)
Small insect
135
45.0
(ppm)
Large insect
15
5.0
Notes: (a) Bole
RQ values exceed LOC for listed species.
(b) LOC for acute is 0.1 and for chronic is 1.0
The RQ's in the table above are based on protective assumptions, modeled with highest
and lowest labeled uses and consumption of the most contaminated part of the frog's diet
(i.e. small insect and large insect). Even with a minimal number of applications (1), the
calculated RQ's still exceed the LOC for Listed species.
Both acute and chronic direct effects are expected from terrestrial phase exposure.
5.1.2 Indirect Effects.
5.1.2.1. Aquatic Phase
In the aquatic phase, CRLF larvae are thought to be algal grazers, like other amphibians
(Recovery Plan, p. 16). Aquatic plant data indicate no significant difference from
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controls. Therefore no RQs are calculated. Because there are no adverse effects
expected on aquatic plants, there is No Effect on the CRLF based on these endpoints.
Sub-adult and adult CRLF consume invertebrates. Since acute RQs for freshwater
invertebrates range up to 0.45 (Table 5-6), there is a "May Affect" finding. However,
since the RQ is below the Acute Risk LOC (0.5), other factors must be considered in
determining if this constitutes a "Likely to Adversely Affect" or "Not Likely to
Adversely Affect" finding, as explained below in section 5.4.2. Based on the likelihood
of individual effects on aquatic invertebrates (Table 5-9b below), indirect risk to the
CRLF via effects on aquatic invertebrates is considered "NLAA."
Adverse or toxic effects to other aquatic animals were estimated using acute and chronic
endpoints for the appropriate test species. Tables 5-6 and 5-7 below give the exposures,
endpoints and risk quotients for acute and chronic effects, respectively. The chronic RQ
for invertebrtates exceeds the LOC for the tomato use with aerial application, only. Thus,
adverse reproductive effects are expected for this use.
Table 5-6. Acute Risk Quotients for Invertebrates (LC50 = 26 ppb)in Freshwater
Environments
Crop
Application
Peak EEC, ppb
RQ
Potato
Aerial
5.2
0.20
Ground
2.5
0.10
Tomato
Aerial
11.6
0.45
Ground
9.7
0.37
Alfalfa
Aerial
6.4
0.25
Ground
4.8
0.18
Cotton
Aerial
5.6
0.22
Ground
3.6
0.14
Notes: (a) bold RQs exceed Listed Species LOC (0.05)
(b) Maximum RQ/LOC ratio for Action Area Downstream Dilution Analysis is
0.45/0.05 = 8.9.
Table 5-7. Chronic Risk Quotients for Invertebrates (NOEC = 4.5 ppb) in Freshwater
Environments
Crop
Application
21-day average
EEC, ppb
RQ
Potato
Aerial
3.5
0.78
Ground
1.1
0.24
Tomato
Aerial
5.8
1.29 (a)
Ground
3.8
0.84
Alfalfa
Aerial
2.5
0.40
Ground
1.8
0.40
Cotton
Aerial
2.9
0.64
Ground
1.5
0.33
Notes: (a) Exceeds Chronic LOC (1)
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5.1.2.2. Terrestrial Phase
As described in the Exposure Assessment, indirect effects to CRLF through its diet are
assessed via adverse toxic effects on its prey items, namely small birds, mammals,
amphibians (represented by the bird), and terrestrial invertebrates. The frog and mouse
are represented in TREX by a 20-gram bird and 15-gram mammal, respectively. The
short grass food item category was chosen because it gives the highest, and therefore
most conservative exposure. Table 5-8 below summarizes the acute and chronic risks to
the CRLF via effects on these prey items. The complete TREX output is given in
Appendix C.
Table 5-8. Summary of Acute and Chronic Risks to Terrestrial Phase Prey Animals that
Consume Short Grass Food Category (Maximum Use, Tomato and Potato'
Prey
Risk
EEC
RQ (a)
Listed
LOC/RQ for
Category
(ppm)
Species
LOC
Action Area
20-g bird or
Acute,
493
134.5
0.1
0.0007 (b)
frog
Dose-based
Chronic,
433
144.4
1
0.007
Dietary
15-g mammal
Acute, dose-
based
413
23.8
0.1
0.004
Chronic,
433
43.3
1
0.02
Dietary
Chronic,
413
375.9
1
0.003
dose-based
Notes: (a) Bold RQs indicate values above Listed species LOC.
(b) Lowest LOC/RQ ratio will be used to calculate terrestrial Action Area.
Indirect effects to the CRLF through the invertebrate portion of its diet may be estimated
by comparing the contact LD50 for the honey bee (1.37 micrograms/bee) to the EEC
calculated for large insects by TREX (27 micrograms/gram)*(0.128 grams body weight
for the bee) = 3.46 micrograms. The RQ is then EEC/LD50 = 3.46/1.37 = 2.52. The
small insect EEC (244 ppm) is used to bound this estimate, giving an LD50 of
(244)*(0.128) = 31.2 micrograms. The RQ is then 31.2/1.37 = 22.8. Both of these RQ
values are well above the LOC (0.05), so toxic effects on terrestrial invertebrates are
presumed. The label for methamidophos (EPA Reg. No. 264-729) does indicate that the
product is "highly toxic to bees," and that it should not be applied if bees are visiting an
adjacent field. Indirect effects to the CRLF via adverse effects on its terrestrial prey base
are expected as multiple components of the CRLF diet, including invertebrates,
mammals, and birds, may be affected..
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5.1.2.3 Effects on Critical Habitat
Effects on Critical Habitat that will be considered are limited to those that are
biologically mediated. PCE #2 (alteration of chemical quality) is affected by
contamination with methamidophos. PCE #5 (alteration of upland habitat) may be
affected by loss of prey items, and by loss of mammals burrows for shelter due to adverse
effects on small mammals. PCE #7 (Alteration or elimination of the CRLF's food
sources or prey base) is affected in the terrestrial environment via effects on prey animals
and insects.
5.1.3 Individual Effect Chance Calculation
The chance of an individual mortality for a CRLF, based on the T-REX surrogate of a 20-
gram or 100-gram bird, was calculated using the IECvl.l Excel spreadsheet. Diet
consisted of small or large insects. The slopes used were 7.4 for the acute toxicity data,
based on a bobwhite quail study, and 3.4 for the subacute dietary study, based on
Japanese quail. The results are given below in tables 5-9a and 5-9b. At the calculated
risk quotients, the chance of individual mortality approaches 100%.
Table 5-9a Individual Effect Proba
)ility Calculation:
or CRLF
Surrogate Organism
Small
Chance of
Large Insect
Chance of
Insect RQ
Effect, 1-in...
RQ
Effect, 1-in...
20-gram bird
75.7
1
9.49
1
100-gram bird
33.9
1
4.25
1
Sub acute dietary
5.8
1
0.64
1
Level of Concern
0.1
1.47E+13
0.1
1.47E+13
(slope 7.4)
Level of Concern
0.1
2970
0.1
2970
(slope 3.4)
Table 5-9b Individual Effect Probability Calculation for Prey Items
Organism
Slope
Threshold (LOC or RQ)
Chance of Effect, 1-in-...
Daphnia magna at
LOC
4.5 (default)
0.05 (LOC)
4.18E+8
Daphnia magna,
tomato aerial RQ
4.5 (default)
0.45 (RQ)
16.9
Daphnia magna,
tomato ground RQ
4.5 (default)
0.37 (RQ)
38.5
Honey bee at LOC
10.32
0.05 (LOC)
4.74E+40
Honey bee, Large
insect EEC
10.32
2.52 (RQ)
1
Honey bee, Small
insect RQ
10.32
22.8 (RQ)
1
15-gram mammal
4.5 (default)
0.1 (LOC)
2.94E+5
15-gram mammal
4.5 (default)
23 .8 (RQ)
1
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5.2 Risk Description
The risk description synthesizes an overall conclusion regarding the likelihood of adverse
impacts leading to an effects determination (i.e., "no effect," "may affect, but not likely
to adversely affect," or "likely to adversely affect") for the California Red Legged frog.
If the RQs presented in the Risk Estimation (Section 5.1.2) show no indirect effects, and
LOCs for the CRLF are not exceeded for direct effects (Section 5.1.1), a "no effect"
determination is made based on methamidophos's use within the action area. If,
however, indirect effects are anticipated and/or exposure exceeds the LOCs for direct
effects, the Agency concludes a preliminary "may affect" determination for the CRLF.
Following a "may affect" determination, additional information is considered to refine
the potential for exposure at the predicted levels based on the life history characteristics
(i.e., habitat range, feeding preferences, etc) of the CRLF and potential community-level
effects to aquatic plants and terrestrial plants growing in semi-aquatic areas. Based on
the best available information, the Agency uses the refined evaluation to distinguish those
actions that "may affect, but are not likely to adversely affect" from those actions that are
"likely to adversely affect" the CRLF.
The criteria used to make determinations that the effects of an action are "not likely to
adversely affect" the CRLF include the following:
Significance of Effect: Insignificant effects are those that cannot be
meaningfully measured, detected, or evaluated in the context of a level of effect
where "take" occurs for even a single individual. "Take" in this context means to
harass or harm, defined as the following:
Harm includes significant habitat modification or degradation that
results in death or injury to listed species by significantly impairing
behavioral patterns such as breeding, feeding, or sheltering.
Harass is defined as actions that create the likelihood of injury to listed
species to such an extent as to significantly disrupt normal behavior
patterns which include, but are not limited to, breeding, feeding, or
sheltering.
Likelihood of the Effect Occurring: Discountable effects are those that are
extremely unlikely to occur. For example, use of dose-response information to
estimate the likelihood of effects can inform the evaluation of some discountable
effects.
Adverse Nature of Effect: Effects that are wholly beneficial without any
adverse effects are not considered adverse.
A description of the risk and effects determination for each of the established assessment
endpoints for the CRLF is provided in Sections 5.2.1 through 5.2.3.
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5.2.1. Direct Effects to the CRLF
5.2.1.1. Aquatic Phase
Risk Quotients for freshwater fish (surrogates for the CRLF) are below LOC for both
acute and chronic effects (Tables 5-1 and 5-2).
5.2.1.2. Terrestrial Phase
Risk Quotients for terrestrial-phase CRLF, as represented by 20-gram and 100-gram
birds, greatly exceed LOC for both acute and chronic (reproductive) effects (Table 5-4
and 5-5). Acute RQs range from 0.6 to 75.7 for CRLF for maximum exposure from
tomato and potato (1 lb ai/A applied 4 times with 7 day interval) and from 0.36 to 41.9
for a minimum exposure of 1 lb ai/A applied once onto alfalfa fields. Chronic RQs range
from 9.0 to 81 for CRLF for maximum exposure from tomato and potato (1 lb ai/A
applied 4 times with 7 day interval) and from 5 to 45 for a minimum exposure of 1 lb
ai/A applied once onto alfalfa fields. Both mortality and adverse reproductive effects to
the CRLF are anticipated based on labeled uses of methamidophos and risk quotients.
Refinement of RQ for CRLF terrestrial phase
Birds are currently used as surrogates for reptiles and terrestrial-phase amphibians.
However, reptiles and amphibians are poikilotherms (body temperature varies with
environmental temperature) while birds are homeotherms (temperature is regulated,
constant, and largely independent of environmental temperatures). Therefore, reptiles
and amphibians (collectively referred to as herptiles in this guidance) 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 or reptiles on a
daily dietary intake basis, assuming similar caloric content of the food items. This can be
seen when comparing the estimated caloric requirements for free living iguanid lizards
(Iguanidae) (EQ 1) to passerines (song birds) (EQ 2) (U.S. EPA, 1993):
iguanid FMR (kcal/day)= 0.0535 *(bw in g)0'799 (EQ 1)
passerine FMR (kcal/day) = 2.123 *(bw in g)0'749 (EQ 2)
With relatively comparable exponents (slopes) to the allometric functions, one can see
that, given a comparable body weight, the free living metabolic rate of birds can be 40
times higher than reptiles, though the requirement differences narrow with high body
weights. Consequently, use of avian food intake allometric equation as a surrogate to
herptiles is likely to result in an over-estimation of exposure for reptiles and terrestrial-
phase amphibians.
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There is a current need to evaluate dietary exposure to terrestrial-phase amphibian species
(e.g., California Red-Legged Frog, CRLF) and an anticipated need to evaluate dietary
exposure for amphibians and reptiles in the future for the purpose of conducting
endangered species effects determinations. Therefore, T-REX (version 1.3.1.) has been
altered to allow for an estimation of food intake for herptiles (T-HERPS) using the same
basic procedure that T-REX uses to estimate avian food intake.
A comparison is made between the T-REX model which uses the bird as a surrogate for
the CRLF and the T-HERPS model which calculates the allometric functions for
amphibians.
T-REX model shows that the ranges of direct affects to birds as surrogate for CRLF is
from 3.6 to 72.4 for dose-based acute, from 0.6 to 5.6(LOC for listed terrestrial animals)
for dietary acute, and from 8.6 to 77.7 for chronic dietary.
T-HERPS model show the ranges of RQ for amphibians that was corrected for body
weight, metabolic rates and caloric intake requirements from avian data. The ranges of
RQ for T-HERPS is from 0.05 to 79.72 (LOC for listed terrestrial animals) for the dose-
based acute, 0.19 to 6.5 for dietary acute, and from 2.7 to 91.0 for chronic dietary.
The refinement of models show a slight decrease in RQs in T-HERPS but the LOC
for CRLF is still exceeded (see Tables 5-10 and 5-11).
Results of the T-HERPS model are below:
Table 5-10 Summary of T-HERPS Risk Quotient Calculations Based on Upper
Bound Kenaga EECs for Potato and Tomato (Maximum Exposure)
Table 5-10a. Upper Bound Kenaga, Acute Terrestrial Herpetofauna Dose-Based Risk Quotients
Size
Class
(grams)
Adjusted
LD50
EECs and RQs
Broadleaf
Plants/
Small Insects
Fruits/Pods/
Seeds/
Large Insects
Small
Herbivore
Mammals
Small
Insectivore
Mammal
Small
Amphibians
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
1.4
1.98
9.47
4.78
1.05
0.53
N/A
N/A
N/A
N/A
N/A
N/A
37
3.24
9.31
2.87
1.03
0.32
270.07
83.37
16.88
5.21
0.32
0.10
238
4.28
6.10
1.42
0.68
0.16
41.98
9.80
2.62
0.61
0.21
0.05
Table 5-10b. Upper Bound Kenaga, Subacute Terrestrial Herpetofauna Dietary Based Risk
Quotients
LC50
(ppm)
EECs and RQs
Broadleaf Plants/
Small Insects
Fruits/Pods/
Seeds/
Large Insects
Small
Herbivore
Mammals
Small
Insectivore
Mammals
Small
Amphibians
81
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EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
42
243.71
5.80
27.08
0.64
285.50
6.80
17.84
0.42
8.46
0.20
Size class not used for dietary risk quotients
Table 5-10c. Upper Bound Kenaga, Chronic Terrestrial Herpetofauna Dietary Based Risk Quotients
NOAEC
(ppm)
EECs and RQs
Broadleaf Plants/
Small Insects
Fruits/Pods/
Seeds/
Large Insects
Small
Herbivore
Mammals
Small
Insectivore
Mammals
Small
Amphibians
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
3
243.71
81.24
27.08
9.03
285.50
95.17
17.84
5.95
8.46
2.82
Size class not used for dietary risk quotients
Bold RQs exceed Listed species LOC
Table 5-11 Summary of T-HERPS Risk Quotient Calculations Based on Upper
Bound Kenaga EECs for Alfalfa (Minimum Exposure)
Table 5-1 la. Upper Bound Kenaga, Acute Terrestrial Herpetofauna Dose-Based Risk Quotients
Size
Class
(grams)
Adjusted
LD50
EECs and RQs
Broadleaf
Plants/
Small Insects
Fruits/Pods/
Seeds/
Large Insects
Small
Herbivore
Mammals
Small
Insectivore
Mammal
Small
Amphibians
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
1.4
1.98
5.24
2.65
0.58
0.29
N/A
N/A
N/A
N/A
N/A
N/A
37
3.24
5.15
1.59
0.57
0.18
149.60
46.18
9.35
2.89
0.18
0.06
238
4.28
3.38
0.79
0.38
0.09
23.26
5.43
1.45
0.34
0.12
0.03
Table 5-llb. Upper Bound Kenaga, Subacute Terrestrial Herpetofauna Dietary Based Risk
Quotients
LC50
(ppm)
EECs and RQs
Broadleaf Plants/
Small Insects
Fruits/Pods/
Seeds/
Large Insects
Small
Herbivore
Mammals
Small
Insectivore
Mammals
Small
Amphibians
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
EEC
RQ
42
135.00
3.21
15.00
0.36
158.15
3.77
9.88
0.24
4.69
0.11
Size class not used for dietary risk quotients
Table 5-llc. Upper Bound Kenaga, Chronic Terrestrial Herpetofauna Dietary Based Risk Quotients
NOAEC
(ppm)
EECs and RQs
Broadleaf Plants/
Small Insects
Fruits/Pods/
Seeds/
Large Insects
Small
Herbivore
Mammals
Small
Insectivore
Mammals
Small
Amphibians
EEC RQ
EEC RQ
EEC RQ
EEC RQ
EEC RQ
82
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Size class not used for dietary risk quotients
Bold RQs exceed Listed species LOC
5.2.2. Indirect Effects to the CRLF
5.2.2.1. Aquatic Phase
Sub-adult and adult CRLF consume invertebrates. Since acute RQs for freshwater
invertebrates range up to 0.45 (Table 5-6), there is a "May Affect" finding. However,
since the RQ is below the Acute Risk LOC (0.5), other factors must be considered in
determining if this constitutes a "Likely to Adversely Affect" or "Not Likely to
Adversely Affect" finding, as explained below in section 5.4.2. Based on the likelihood
of individual effects on aquatic invertebrates (Table 5-9b below), indirect risk to the
CRLF via effects on aquatic invertebrates is considered "NLAA "
5.2.2.2. Terrestrial Phase
Risk quotients for two common prey animals (frog and small mammal and bird) greatly
exceed both acute and chronic LOC (Table 5-8). These prey animals are anticipated to
suffer adverse effects (mortality and reproductive effects) from labeled methamidophos
uses . The acute RQ for a terrestrial invertebrate (honey bee), representing the bulk of the
terrestrial phase CRLF diet, ranges from 2.5 to 22.8. Thus, adverse indirect effects to the
CRLF, mediated via reduction in prey base, are anticipated.
The terrestrial-phase CRLF uses small mammal burrows for shelter. If populations of
small mammals are reduced, as is anticipated from the RQs for individual effects on
them, then there may be fewer burrows for the CRLF to exploit. Thus, there may be an
indirect effect on the CRLF through loss of terrestrial phase habitat.
5.3 Action Area
The Action Area for endangered species from the labeled use of a pesticide is defined by
exceedence of the Level of Concern for any Listed species. Risk Quotients from the
screening risk assessment are compared to the Listed Species LOCs for all taxa to
determine the geographic extent of the Action Area.
If necessary, standard modeling assumptions are changed to determine the limits of LOC
exceedence. For example, the spray drift assumption for aerial application can be
lowered from the standard 5% until LOC is no longer exceeded, and that spray drift
amount entered into AgDrift or AgDISP to determine the distance from the sprayed field
to the standard pond that will lower RQ to below LOC. That distance around the sprayed
field then determines the Action Area (assuming no secondary poisoning effects from
movement of contaminated animals).
83
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5.3.1. Aquatic Phase
The Action Area for effects on aquatic species consists of two parts. One is a spray drift
perimeter around the use site, and the other is a downstream dilution factor. Both parts
are intended to find the geographic extent of Listed species LOC exceedence.
5.3.1.1 Spray Perimeter.
The Action Area for effects on aquatic species was based on acute effects to Listed
aquatic invertebrates, since these were the only LOCs exceeded (Tables 5-6 and 5-7). To
be below the LOC for Listed aquatic invertebrates (0.05), the peak concentration in the
EXAMS pond would need to (0.05)*(26 ppb) =1.3 ppb, where 26 ppb is the EC50 for
Daphnia magna.
Spray drift assumptions for aerial application were varied from the standard 5%, to
determine if spray drift perimeters could delimit the Action Area. Table 3-3 shows the
results of PRZM-EXAMS modeling runs with assumptions of 5%, 1% (default
assumptions for aerial and ground application, respectively), or 0% drift.
In all cases, the LOC for acute effects on invertebrates is exceeded, both under default
spray drift assumptions (1% or 5%), and when spray drift is set to 0%. Thus, no spray
drift buffer can be set that will reduce EECs, and therefore RQs, to below LOC. A spray
drift buffer to set the Action Area for aquatic effects therefore cannot be established.
5.3.1.2 Downstream Dilution
The downstream dilution analysis calculates how far downstream the EEC remains above
the Listed species LOC, given flow contributions from both contaminated and
uncontaminated streams in the watersheds of potential methamidophos use. The initial
area of concern was defined by Figure 2.E., which shows all agricultural land in all
counties in California where tomatoes, potatoes, cotton, or alfalfa for seed are grown.
Flow contributions from streams in the corresponding watersheds are included in a GIS
(Geographic Information System) analysis, until the pesticide concentrations (initially the
EXAMS pond peak EEC) from contaminated and uncontaminated streams, weighted for
flow, fall below the Listed species LOC.
The downstream dilution factor that must be achieved is defined by the maximum ratio
between an RQ and its corresponding LOC. In the case of methamidophos, this is the
acute RQ for aquatic invertebrates from aerial application to potatoes (0.45), divided by
the LOC (0.05) for a factor of 8.9. See Table 5-6.
5.3.2. Terrestrial Phase
The Action Area due to effects on Listed species is also defined by the geographic extent
of LOC exceedence. Quantitative estimates of exposure of avian (including reptiles and
84
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terrestrial amphibians) and mammal species is done with the TREX model, which
automates exposure analysis according to the Hoerger-Kenaga nomogram, as modified
by Fletcher (1994).
For methamidophos, the Action Area was calculated on the basis of the smallest avian
(20-gram body weight) or mammal (15-gram), consuming the most highly contaminated
food category (short grass). This results in the highest RQs, and thus the most
conservative estimate of the Action Area.
The lowest ratio between the LOC for Listed terrestrial avian and mammalian species
(0.1 for acute effects and 1.0 for chronic effects) and the RQ, times the maximum single
application rate, is used to determine the exposure (in lb/acre) that is below LOC, as
shown in Table 5-8.
Exposure below LOC = (LOC/RQ )*(1 lb/acre).
In the case of methamidophos, the target exposure is 0.0007 lb/acre, due to acute effects
on avian species (acute RQ = 134.5).
The distance from the use site (sprayed field) needed to achieve the target exposure of
0.0007 lb/acre was calculated with the Gaussian Far-Field extension of the AgDISP
model. The input parameters for AgDISP are given below (Table 5-12); all other
parameters were the default values.
Table 5-12. Input Parameters for AgDISP Gaussian Far-Field Extension Analysis
Input Parameter
Value
Release Height
15 feet
Wind Speed
15 mph
Spray Quality
ASAE very fine to fine
Non-Volatile fraction
0.083
Active fraction
0.033
Surface Canopy
None
Specific Gravity, Carrier
1.19
Deposition type
Terrestrial point
Initial Average Deposition
0.0007 lb/acre
The result of this analysis is that a perimeter of 7,241 feet from the edge of the sprayed
field is needed to bring the acute avian RQ to below the LOC of 0.1. Thus, the Action
Area extends to a distance of 7,241 feet from the edge of fields sprayed with
methamidophos.
Figure 5A shows the full extent of the Action Area, based on the terrestrial effects
distance of 7,241 feet and the downstream dilution factor of 8.9.
85
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Methamidophos Agriculture - Action Area (AA)
Del Norte
Mendocino
: an F
iimne
Bernardino
U
<9;
Legend
Ftecovery units
Aquatic AA- Agriculture
Agriculture Use
County boundaries
Terrestrial AA- Agriculture
l Kilometers
0 2040 80 120 160
Compiled from California County boundaries (ESRI, 2002), Map created by US Environmental Protection Agency, Office
USDft National Agriculture Statistical Sen/ice (NASS, 20035 of Pesticides Programs, Environmental Fate and Effects Division.
Gap Analysis Program Orchard/ Vineyard Landcwer (GAP) June XX, 2007. Projection: A lb ers Equal Area Conic USGS, North
National Land Cower Database (NLCD) (MRLC, 2001) American Datum of 1983 (NAD 1983)
Figure 5A Action Area for Methamidophos
86
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5.4 Listed Species Effect Determination for the California Red-Legged Frog
5.4.1. "May Affect" Determination
When the action area overlaps (spatially) the designated Core Areas and Critical Habitats
a "may affect" determination is made. If there is no overlap, and thus no expected
exposure, a "no effect" determination is made. Upon a "may affect" determination the
probability of effect is considered and a "Likely to Adversely Affect" or "Not Likely to
Adversely Affect" determination is made.
Based on the action area for methamidophos use in California, the use of methamidophos
"May Effect" the CRLF. Table 5.13 displays the proportion of the core area within each
recovery unit that overlaps with the potential use areas.
Table 5.13 Terrestrial spatial summary results for Methamidophos agriculture uses with a 7241 ft
buffer.
Measure
RU1
RU2
RU3
RU4
RU5
RU6
RU7
RU8
Total
Initial Area of
66,524 sq km
Concern (no buffer)
Action Area - Initial
105,492 sq km
area of concern +
buffer
Established species
3054
2742
1323
3271)
3o5<)
53<)0
4^ 1 7
3320
2S.N7
range area (sq km)
Overlapping area (sq
5 00
344
219
1175
1734
1047
2104
773
8,550
km)
Percent area affected
15%
13%
17%
36%
48%
31%
43%
23%
30%
# Occurrence Sections
3
2
21
171
228
75
76
25
601
5.4.2 "Adverse Effect" Determination
Risk Quotients for direct, acute and chronic effects to the terrestrial-phase CRLF (Tables
5-4, 5-5, 5-10 and 5-11) are well above their respective LOCs. Risk quotients for animals
that may serve as prey for the CRLF are also well above LOCs (Table 5-8). The risk
quotient for a terrestrial invertebrate (honey bee), representing the bulk of the CRLF diet,
is 2.9, well above the LOC of 0.05. Thus, both direct and indirect adverse effects to
the terrestrial-phase CRLF and its critical habitat are anticipated.
Risk quotients for direct, acute and chronic effects to the aquatic-phase CRLF, as
represented by freshwater and estuarine fish, are below the LOC (Tables 5-2 and 5-3).
Acute and chronic effects on the aquatic phase CRLF and its critical habitat are not
anticipated.
87
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Aquatic invertebrate acute RQs (tables 5-6 and 5-7) are below the acute LOC (0.5) for all
uses, and the likelihood of individual effects is low (Table 5-9b). Thus adverse indirect
effects on the CRLF due to loss of prey items are discountable, and therefore NLAA.
Methamidophos is not toxic to aquatic plants, so no indirect effects to the CRLF via
reduction in primary production as a food source are anticipated.
Based on this analysis, it is concluded that the labeled uses of methamidophos in
California "may affect, and are likely to adversely effect" the California Red-Legged
Frog, where the Action area overlaps its habitat, due to terrestrial effects.
Table 5.12 Methamidophos Effects Determination Summary
Assessment
Endpoint
Effects
determination
Basis for Determination
Aquatic Phase
(Eggs, larvae, tadpoles, juveniles, and adults)
Direct Effects
1. Survival, growth,
and reproduction of
CRLF
No Effect
All Acute and Chronic RQ are below the listed LOC for
surrogate species (rainbow trout)
Indirect Effects
2. Reduction or
modification of
aquatic prey base
May Affect,
Not Likely to
Adversely Affect
Acute LOC is exceeded for aquatic invertebrates,
however effect is considered discountable based on
low likelihood of individual effect.
3. Reduction or
modification of
aquatic plant
community
No Effect
No LOC Exceedences for any plant species
4. Degradation of
riparian vegetation
No Effect
No LOC Exceedences for any plant species
Terrestrial Phase
(Juveniles and Adults)
Direct Effects
5. Survival, growth,
and reproduction of
CRLF
May Affect,
Likely to
Adversely Affect
Acute and Chronic LOC exceedences for birds, the
surrogate species for direct effects to frogs. Initial
Area of Concern overlaps habitat. Use is widespread
(23-26 counties). Use is documented in all months
except November, December, January. Probability of
effect approaches 100% at calculated RQs.
Indirect Effects and Critical Habitat Effects
6. Reduction or
modification of
terrestrial prey base
May Affect,
Likely to
Adversely Affect
Acute and Chronic LOC exceedences for multiple
components of CRLF prey base (mammals, birds, and
terrestrial invertebrates). LAA to terrestrial phase
CRLF and its critical habitat based on acute RQs
exceeding 0.5 for mammals, insects, birds.
7. Degradation of
riparian vegetation
No Effect
No plant LOC exceedences.
88
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When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the species and its resources (i.e., food and habitat) are
not expected to be uniform across the action area. In fact, given the assumptions of drift
and downstream transport (i.e., attenuation with distance), pesticide exposure and
associated risks to the species and its resources are expected to decrease with increasing
distance away from the treated field or site of application. Evaluation of the implication
of this non-uniform distribution of risk to the species would require information and
assessment techniques that are not currently available. Examples of such information and
methodology required for this type of analysis would include the following:
Enhanced information on the density and distribution of CRLF 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 predictions of individual effects to the
proportion of the population extant within geographical areas where those
effects are predicted. Furthermore, such population information would
allow for a more comprehensive evaluation of the significance of potential
resource impairment to individuals of the species.
Quantitative information on prey base requirements for individual aquatic-
and terrestrial-phase frogs. While existing information provides a
preliminary picture of the types of food sources utilized by the frog, it
does not establish minimal requirements to sustain healthy individuals at
varying life stages. Such information could be used to establish
biologically relevant thresholds of effects on the prey base, and ultimately
establish geographical limits to those effects. This information could be
used together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.
Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth or reproductive impairment
immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and
together with the information described above, a more complete prediction
of effects to individual frogs and potential adverse modification to critical
habitat.
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5.5 Risk Hypotheses Revsisted
Table 5.13 below revisits the risk hypotheses presented in section 2.9.1. The risk
hypotheses were accepted or rejected in accordance with the "No Effect," "May Affect,"
and "Likely to Adversely Affect," or "Not Likely to Adversely Affect" findings in this
assessment.
Table 5.13 Risk Hypotheses Revisited
Risk Hypothesis
Conclusions
Labeled uses of methamidophos within the
action area may directly affect the CRLF
by causing mortality or by adversely
affecting growth or fecundity
Rejected for Aquatic exposure. "No
Effect" finding.
Accepted for Terrestrial exposure. "LAA"
finding.
Labeled uses of methamidophos within the
action area may indirectly affect the CRLF
by reducing or changing the composition of
food supply
Accepted for Terrestrial exposure. "LAA"
finding.
Rejected for Aquatic exposure. "NLAA"
finding.
Labeled uses of methamidophos within the
action area may indirectly affect the CRLF
and/or adversely modify designated critical
habitat by reducing or changing the
composition of the aquatic plant
community in the ponds and streams
comprising the species' current range and
designated critical habitat, thus affecting
primary productivity and/or cover
Rejected. "No Effect" finding for aquatic
plants.
Labeled uses of methamidophos within the
action area may indirectly affect the CRLF
and/or adversely modify designated critical
habitat by reducing or changing the
composition of the terrestrial plant
community (i.e., riparian habitat) required
to maintain acceptable water quality and
habitat in the ponds and streams
comprising the species' current range and
designated critical habitat
Rejected. "No Effect" finding for
terrestrial plants.
Labeled uses of methamidophos within the
action area may adversely modify the
designated critical habitat of the CRLF by
reducing or changing breeding and non-
Rejected. "No Effect" for aquatic plants
and "NLAA" for indirect effects via
invertebrates.
90
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breeding aquatic habitat (via modification
of water quality parameters, habitat
morphology, and/or sedimentation)
Labeled uses of methamidophos within the
action area may adversely modify the
designated critical habitat of the CRLF by
reducing the food supply required for
normal growth and viability of juvenile and
adult CRLFs
Accepted for Terrestrial exposure. "LAA"
finding via effects on vertebrate and
invertebrate food items.
Rejected for Aquatic exposure. "NLAA"
finding for aquatic invertebrates, "No
Effect" for aquatic plants.
Labeled uses of methamidophos within the
action area may adversely modify the
designated critical habitat 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
Accepted. Effects on small mammals may
reduce number of burrows used for shelter.
Labeled uses of methamidophos within the
action area may adversely modify the
designated critical habitat of the CRLF by
reducing or changing 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
Accepted. Effects on small mammals may
reduce number of burrows used for shelter.
Labeled uses of methamidophos within the
action area may adversely modify the
designated critical habitat of the CRLF by
altering chemical characteristics necessary
for normal growth and viability of juvenile
and adult CRLFs
Accepted. Presence of methamidophos in
terrestrial habitat is believed to have direct
and indirect effects on CRLF.
91
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6. Uncertainties
6.1. Exposure Assessment Uncertainties
All exposure estimates were done with maximum application rates, minimum intervals,
and maximum number of applications, to define the Action Area for the Federal action.
Actual exposures will depend on actual use rates, which may be lower.
Aquatic exposure modeling inputs were based on the available guideline data. Some
inputs (e.g., soil metabolism half-life = 1.75 days) were based on a single value, which by
EFED policy is multiplied by 3 to account for uncertainty. The aquatic metabolism rates
(both aerobic and anaerobic) were set by policy at 2 times the soil input value. The
partition coefficient (Koc) used was the highest and only quantified value obtained
(0.88). The use of values for the other soils (essentially, Kd = 0) would have resulted in
somewhat higher exposure estimates.
Spray drift estimates were set at 1% for ground application and 5% for aerial application,
per EFED policy. Actual spray drift from aerial application may be higher.
The decay half-life of methamidophos on foliage and other food items for the TREX
analysis was set at 6.5 days, rather than the default value of 35 days. This value was
obtained from Willis & McDowell (1987) from a field experiment on citrus in Florida;
this is the same reference used to obtain the default value of 35 days. The value of 6.5
days was the highest of the half-lives for methamidophos, so it is the most protective of
the measured values.
6.2 PRZM Modeling Inputs and Predicted Aquatic Concentrations
The standard ecological water body scenario (EXAMS pond) used to calculate potential
aquatic exposure to pesticides is intended to represent conservative estimates, and to
avoid underestimations of the actual exposure. The standard scenario consists of
application to a 10-hectare field bordering a 1-hectare, averages 2-meter deep (20,000
m3) pond with no outlet. Exposure estimates generated using the EXAMS pond are
intended to represent a wide variety of vulnerable water bodies that occur at the top of
watersheds including prairie pot holes, playa lakes, wetlands, vernal pools, man-made
and natural ponds, and intermittent and lower order streams. As a group, there are factors
that make these water bodies more or less vulnerable than the EXAMS pond. Static
water bodies that have larger ratios of pesticide-treated drainage area to water body
volume would be expected to have higher peak EECs than the EXAMS pond. These
water bodies will be either smaller in size or have larger drainage areas. Smaller water
bodies have limited storage capacity and thus may overflow and carry pesticide in the
discharge, whereas the EXAMS pond has no discharge. As watershed size increases
beyond 10-hectares, it becomes increasingly unlikely that the entire watershed is planted
with a single crop that is all treated simultaneously with the pesticide. Headwater
streams can also have peak concentrations higher than the EXAMS pond, but they likely
persist for only short periods of time and are then carried and dissipated downstream.
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The Agency acknowledges that there are some unique aquatic habitats that are not
accurately captured by this modeling scenario and modeling results may, therefore,
under- or over-estimate exposure, depending on a number of variables. For example,
aquatic-phase CRLFs may inhabit water bodies of different size and depth and/or are
located adjacent to larger or smaller drainage areas than the EXAMS pond. The Agency
does not currently have sufficient information regarding the hydrology of these aquatic
habitats to develop a specific alternate scenario for the CRLF. As previously discussed in
Section 2.X and Attachment 1, CRLFs prefer habitat with perennial (present year-round)
or near-perennial water and do not frequently inhabit vernal (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 addition, the Services agree that the existing EXAMS pond represents
the best currently available approach for estimating aquatic exposure to pesticides
(USFWS/NMFS 2004).
6.3 Effects Assessment Uncertainties
6.3.1 Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids, second instar for
amphipods, stoneflies, mayflies, and third instar for midges).
Testing of juveniles may overestimate toxicity at older age classes for pesticide active
ingredients, such as methamidophos, that act directly without metabolic transformation
because younger age classes may not have the enzymatic systems associated with
detoxifying xenobiotics. In so far as the available toxicity data may provide ranges of
sensitivity information with respect to age class, this assessment uses the most sensitive
life-stage information as measures of effect for surrogate aquatic animals, and is
therefore, considered as protective of the California Red Legged Frog.
6.3.2 Extrapolation of Long-term Environmental Effects from Short-Term
Laboratory Tests
The influence of length of exposure and concurrent environmental stressors to the
California Red Legged Frog (i.e., urban expansion, habitat modification, decreased
quantity and quality of water in CRLF habitat, predators, etc.) will likely affect the
species' response to methamidophos. Additional environmental stressors may decrease
the CRLF's sensitivity to the insecticide, although there is the possibility of
additive/synergistic reactions. Timing, peak concentration, and duration of exposure are
critical in terms of evaluating effects, and these factors will vary both temporally and
spatially within the action area. Overall, the effect of this variability may result in either
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an overestimation or underestimation of risk. However, as previously discussed, the
Agency's LOCs are intentionally set very low, and conservative estimates are made in the
screening level risk assessment to account for these uncertainties.
6.4 Assumptions Associated with the Acute LOCs
The risk characterization section of this endangered species assessment includes an
evaluation of the potential for individual effects. The individual effects probability
associated with the acute RQ is based on the mean estimate of the slope and an
assumption of a probit dose response relationship for the effects study corresponding to
the taxonomic group for which the LOCs are exceeded.
6.5 Use of avian data as surrogate for amphibian data.
Toxicity data for terrestrial phase amphibians was not available for use in this
assessment. Therefore, avian toxicity data were used as a surrogate for risk estimation.
There is uncertainty regarding the relative sensitivity of herptiles and birds to
methamidophos. If birds are substantially more or less sensitive than the California red
legged frog, then risk would be over or under estimated, respectively.
6.6 Maximum Use Scenario
The screening-level risk assessment focuses on characterizing potential ecological risks
resulting from a maximum use scenario, which is determined from labeled statements of
maximum application rate and number of applications with the shortest time interval
between applications. The frequency at which actual uses approach this maximum use
scenario may be dependant on insecticide resistance, timing of applications, cultural
practices, and market forces.
6.7 Usage Uncertainties
County-level usage data were obtained from California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database. Four years of data (2002 -
2005) were included in this analysis because statistical methodology for identifying
outliers, in terms of area treated and pounds applied, was provided by CDPR for these
years only. No methodology for removing outliers was provided by CDPR for 2001 and
earlier pesticide data; therefore, this information was not included in the analysis because
it may misrepresent actual usage patterns. CDPR PUR documentation indicates that
errors in the data may include the following: a misplaced decimal; incorrect measures,
area treated, or units; and reports of diluted pesticide concentrations. In addition, it is
possible that the data may contain reports for pesticide uses that have been cancelled.
The CPDR PUR data does not include home owner applied pesticides; therefore,
residential uses are not likely to be reported. As with all pesticide use data, there may be
instances of misuse and misreporting. The Agency made use of the most current,
verifiable information; in cases where there were discrepancies, the most conservative
information was used.
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6.8 Action Area
An example of an important simplifying assumption that may require future refinement is
the assumption of uniform runoff characteristics throughout a landscape. It is well
documented that runoff characteristics are 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 (based on predicted in-stream dilution) was
that the entire landscape exhibited runoff properties identical to those commonly found in
agricultural lands in this region. 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 dominated by the relationship between
impermeable surfaces (roads, lots) and grassed/other areas (lawns) plus local drainage
management; c) urban areas, that are dominated by managed storm drainage and
impermeable surfaces; and d) agricultural areas dominated by Hortonian and focused
runoff (especially with row crops), a refined assessment should incorporate these
differences for modeled stream flow generation. As the zone 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 the 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. Runoff from forested areas ranges from 45 -
2,700% less than from agricultural areas; in most 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). Differences in runoff potential between
urban/sub urban areas and agricultural areas are generally less than between agricultural
and forested areas. In terms of likely runoff potential (other variables - such as
topography and rainfall - being equal), the relationship is generally 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 counteract the effects of the
aforementioned issue. For example, the dilution model considers that 100% of the
agricultural area has the chemical applied, which is almost certainly a gross over-
estimation. Thus, there will be assumed chemical 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 other) confounding factors, Agency believes that
this model gives us the best available estimates under current circumstances.
6.9 Aquatic Exposure Estimates
In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations
that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone
Model is a process or "simulation" model that calculates what happens to a pesticide in a
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farmer's field on a day-to-day basis. It considers factors such as rainfall and plant
transpiration of water, as well as how and when the pesticide is applied. It has two major
components: hydrology and chemical transport. Water movement is simulated by the use
of generalized soil parameters, including field capacity, wilting point, and saturation
water content. The chemical transport component can simulate pesticide application on
the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase concentrations in
the soil are estimated by simultaneously considering the processes of pesticide uptake by
plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection,
dispersion, and retardation.
Uncertainties associated with each of these individual components add to the overall
uncertainty of the modeled concentrations. Additionally, model inputs from the
environmental fate degradation studies are chosen to represent the upper confidence
bound on the mean values that are not expected to be exceeded in the environment
approximately 90 percent of the time. Mobility input values are chosen to be
representative of conditions in the environment. The natural variation in soils adds to the
uncertainty of modeled values. Factors such as application date, crop emergence date,
and canopy cover can also affect estimated concentrations, adding to the uncertainty of
modeled values. Factors within the ambient environment such as soil temperatures,
sunlight intensity, antecedent soil moisture, and surface water temperatures can cause
actual aquatic concentrations to differ for the modeled values.
Unlike spray drift, tools are currently not available to evaluate the effectiveness of a
vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is
highly dependent on the condition of the vegetative strip. For example, a well-
established, healthy vegetative setback can be a very effective means of reducing runoff
and erosion from agricultural fields. Alternatively, a setback of poor vegetative quality
or a setback that is channelized can be ineffective at reducing loadings. Until such time
as a quantitative method to estimate the effect of vegetative setbacks on various
conditions on pesticide loadings becomes available, the aquatic exposure predictions are
likely to overestimate exposure where healthy vegetative setbacks exist and
underestimate exposure where poorly developed, channelized, or bare setbacks exist.
6.10 Residue Levels Selection
The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide
residues in wildlife dietary items. These residue assumptions are believed to reflect a
realistic upper-bound residue estimate, although the degree to which this assumption
reflects a specific percentile estimate is difficult to quantify. It is important to note that
the field measurement efforts used to develop the Fletcher estimates of exposure involve
highly varied sampling techniques. It is entirely possible that much of these data reflect
residues averaged over entire above ground plants in the case of grass and forage
sampling.
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6.11 Dietary Intake
It was assumed that ingestion of food items in the field occurs at rates commensurate
with those in the laboratory. Although the screening assessment process adjusts dry-
weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food
intake estimates, it does not allow for gross energy differences. Direct comparison of a
laboratory dietary concentration- based effects threshold to a fresh-weight pesticide
residue estimate would result in an underestimation of field exposure by food
consumption by a factor of 1.25 - 2.5 for most food items.
Differences in assimilative efficiency between laboratory and wild diets suggest that
current screening assessment methods do not account for a potentially important aspect of
food requirements. Depending upon species and dietary matrix, bird assimilation of wild
diet energy ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85%
(U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is
formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for
underestimation of exposure may exist by assuming that consumption of food in the wild
is comparable with consumption during laboratory testing. In the screening process,
exposure may be underestimated because metabolic rates are not related to food
consumption.
6.12 Sublethal Effects
For an acute risk assessment, the screening risk assessment relies on the acute mortality
endpoint as well as a suite of sublethal responses to the pesticide, as determined by the
testing of species response to chronic exposure conditions and subsequent chronic risk
assessment. Consideration of additional sublethal data in the assessment 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.
6.13 Location of Wildlife Species
For this baseline terrestrial risk assessment, a generic bird or mammal was assumed to
occupy either the treated field or adjacent areas receiving a treatment rate on the field.
Actual habitat requirements of any particular terrestrial species were not considered, and
it was assumed that species occupy, exclusively and permanently, the modeled treatment
area. Spray drift model predictions suggest that this assumption leads to an
overestimation of exposure to species that do not occupy the treated field exclusively and
permanently.
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