Potential Risks of Labeled S-Methoprene Uses to the
Federally Listed California Red Legged Frog
(Rana aurora draytonii)
Pesticide Effects Determination
Biopesticide & Pollution Prevention Division
Office of Pesticide Programs
Washington, D.C. 20460
February 20,2008
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Primary Authors
Miachel Rexrode Ph.D., Biologist, BPPD
Ibrahim Abdel-Saheb Chemist, EFED
Biopesticides and Pollution Prevention
Janet L. Andersen Ph.D. Director, BPPD
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Table of Contents
Executive Summary 5
Problem Formulation 12
2.1 Purpose 12
2.2 Scope 14
2.3 Previous Review 15
2.4 Stressor Source and Distribution 15
2.4.1 Environmental Chemistry and Fate Assessment 15
2.4.2 Environmental Transport Assessment 18
2.4.3 Mechanism of Action 19
2.4.4 Use Characterization 20
2.5 Assessed Species 21
2.5.1 Distribution 22
2.5.2 Reproduction 27
2.5.3 Diet 27
2.5.4 Habitat 28
2.6 Designated Critical Habitat 29
2.7 Action Area 31
2.8 Assessment Endpoints and Measures of Ecological Effects 34
2.8.1 Assessment Endpoints for the CRLF 34
2.8.2 Assessment Endpoints for Designated Critical Habitat 36
2.9 Conceptual Model 39
2.9.1 Risk Hypothesis 39
2.9.2 Diagram 39
2.10 Analysis Plan 44
2.10.1 Measures to Evaluate Risk Hypotheses and Conceptual Model 44
2.10.1.1 Measures of Exposure 44
2.10.1.2 Measures of Effects 45
Exposure Assessment 46
3.1 Measure of Aquatic Exposure 46
3.1.1 Monitoring Data 47
3.2 Measure of Terrestrial Exposure 48
3.2.1 Terrestrial Exposure Modeling 48
3.2.2 Terrestrial Plant Exposure 49
Effects Assessment 49
4.1 Evaluation of Terrestrial Ecotoxicity Studies 51
4.1.1 Terrestrial Plant Exposure 51
4.1.2 Bird and Mammal Hazard Assessment 51
4.1.2.1 Avian Toxicity 51
4.1.2.2 Mammal Studies 51
4.1.1.3 Toxicity of S-Methoprene to Insects 52
4.2 Evaluation of Aquatic Ecotoxicity Studies 53
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4.2.1 Aquatic Hazard 53
4.2.1.1 Fish Toxicity Studies 53
4.2.1.2 Toxicity to Aquatic Freshwater Invertebrates 54
4.2.1.4 Field Studies:Non-Target Organisms 54
5.0 Risk Characterization 56
5.1 Risk Estimation-Integration of Exposure and Effects Data 56
5.2 Potential for Direct Effects 56
5.2.1 Aquatic-Phase of CRLF 56
5.2.2 Terrestrial Phase of CRLF 59
5.3 Potential for Indirect Effects (Decreased Availability of Food Items) 59
5.3.1 Aquatic-Phase of CRLF 59
5.3.2 Terrestrial-Phase of CRLF 59
5.4 Potential for Adverse Effects on Designated Critical Habitat PCEs 60
6.0 Assumptions, Limitations and Uncertainties 61
6.1 Direct and Indirect Effects 61
6.1.1 Aquatic-Phase 61
6.1.2 Modeling Assumptions and Uncertainties 62
6.2 Uncertainties Related to Terrestrial Exposure 62
6.3 Effects Assessment Uncertainties 63
6.3.1 Use of Surrogate Species to Represent Sensitivity to S-Methoprene 63
6.3.2 Age Class and Sensitivity of Effects Thresholds 63
6.3.3 Sublethal Effects 63
6.3.4 Impact of Multiple Stressors on the Effects Determination 64
6.3.5 Potential Exposure to Pesticide Mixtures 64
6.3 Use Data 64
6.5 General Uncertainties 65
6.6 Uncertainties Regarding Incidents that have Suggested S-Methoprene
Affects 66
7.0 Addressing the Risk Hypothesis 68
8.0 Summary of Direct and Indirect Effects to the California Red-Legged Frog and
Modification to its Designated Critical Habitat 69
References 73
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List of Tables
Table 1.0 Registered S-Methoprene Uses That May Have Ecological Impact to
Non-Target Fish and Wildlife in California 6
Table 1.1 Effects Determination Summary for Direct and Indirect Effects of
S-Methoprene on the California Red-Legged Frog 8
Table 1.2 Effects Determination Summary for the Critical Habitat Impact Analysis 9
Table 2.0 Summary of S-Methoprene Environmental Chemistry and Fate 16
Table 2.1 Summary of CDPR PUR Usage Data From 2002-2005 for S-Methoprene 20
Table 2.2 Summary of CDPR PUR Formulation Data From 2002-2005 for
S-Methoprene 20
Table 2.3 Maximum Rate of S-Methoprene Sustainable Release Formulations that
Are Applied Directly to Water 21
Table 2.4 Maximum Rate of S-Methoprene Formulations that Are Applied to
Terrestrial Site 21
Table 2.5 Summaryof the Uses Considered as Part of the Federal Action Evaluated
in this Assessment 31
Table 2.6 Summary of S-Methoprene Uses that Are Not Considered as Part of
the Federal Action Evaluated in this Assessment 32
Table 2.7 Summary of Assessment Endpoints and Measurements of Ecological
Effects for Primary Constituent Elements of Designated Critical Habitat 38
Table 2.8 Acute and Chronic Measures of Effect 45
Table 3.0 Maximum Rates of S-Methoprene Formulations that are Applied Directly
To Water (Extrapolated Values from Label Information) 46
Table 3.1 Adjusted Environmental Concentrations of S-Methoprene Found in
Freshwater Microcosm 47
Table 3.2 Estimated Environmental Concentrations (mg/kg; ppm) on Potential
Food Items Following Label-Specified Applications (4 Applications at
0.5829 lbs ai/Acre, 7-Day Application interval) of S-Methoprene Using
T-REX 48
Table 3.3 Characterization of S-Methoprene Granular LD50/Square Foot Using
T-REX for a 20g Bird (Granular Weigh = 0.43 mg) 49
Table 3.4 Acute and Chronic RQs for Terrestrial-Phase CRLF (Based on Upper
Bound Kenaga Values from T-Rex) 49
Table 4.0 Summary of Specific Assessment Endpoints Considered in this Assessment...50
Table 4.1 Summary of Avian Toxicity for S-Methoprene 51
Table 4.2 Summary of Mammalian Toxicity Studies for S-Methoprene
and RS-Methoprene 52
Table 4.3 Toxicity of RS-Methoprene to Insects 52
Table 4.4 Summary of Fish Toxicity Studies for S-Methoprene (Parent Compound,
Metabolites, Formulations) 53
Table 4.5 Freshwater Fish: Chronic Exposure (Growth/Reproduction) Studies 54
Table 4.6 Freshwater Invertebrates Acute Toxicity Studies with S-Methoprene 54
Table 4.7 Overview of S-Methoprene Field Studies and Effects to Non-Target
Insects 55
Table 5.0 Agency Level of Concern (LOC) 56
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Table 5.1 Acute and Chronic RQs for Aquatic organisms Based on EECs from
Extrapolated S-Methoprene Release Rates for Granular, Briquets,
Sand Mix, and Liquid Formulations Applied to a Shallow (1ft) 1 Acre
Body of Water 57
Table 5.2 Acute and Chronic RQs for Aquatic Organisms based on Maximum
Adjusted EECs from Microcosm Treated With S-Methoprene Granular,
Briquets, Sand Mix, and Liquid Formulations 58
Table 5.3 Chance of Individual Acute Effects to Aquatic-Phase CRLF Using
Surrogate Freshwater Fish Toxicity Data and the Probit Slope Response
Relationship 58
Table 5.4 Chance of Individual Acute Effects to Terrestrial-Phase CRLF Using
Surrogate Mallard Duck Toxicity Data and the Probit Slope Response
Relationship 60
Table 8.0 Effects Determination Summary for Direct and Indirect Effects of
S-Methoprene on the California Red-Legged Frog 70
Table 8.1 Effects Determination Summary of S-Methoprene Exposure to
The California Red-Legged Frogs Critical Habitat 71
List of Figures
Figure 1.0 Distribution of the CRLF Range and Designated Critical Habitat 23
Figure 2.0 Recovery Unit and Core Area Designation for CRLF 26
Figure 3.0 CRLF Reproductive Events by Month 27
Figure 4.0 Conceptual Model for S-Methoprene Effects on Aquatic Phase of the
Red-Legged Frog 40
Figure 5.0 Conceptual Model for S-Methoprene Effects on Aquatic Component of the
Red-Legged Frog Critical Habitat 41
Figure 6.0 Conceptual Model for S-Methoprene Effects on Terrestrial Phase of the Red-
Legged Frog 42
Figure 7.0 Conceptual Model for S-Methoprene Effects on Terrestrial Component of
the Red-Legged Frog 43
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Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Appendix G
Attachment 1
List of Appendices
Product Formulations Containing Multiple Active Ingredients
S-Methoprene Use in California- Data and Supporting Material
From BEAD
The Risk Quotient Method and Levels of Concern
Tier I Estimation of Aqueous S-Methoprene Concentrations in Wild Rice
Paddies & Caneberries
Extrapolations for Sustainable Release Rate Formulations
Summary of Avian and Mammalian EEC and RQ values After Maximum S-
Methoprene Application
Bibliography of ECOTOX Open Literature Not Used Quantitatively or
Qualitatively
Life History of the California Red-legged Frog
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1.0 Executive Summary
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 the
insect growth regulator S-methoprene on some agricultural areas (i.e. mosquito control
during flooding and fire ant bait around citrus) and certain non-agricultural sites in
California. In addition, this assessment evaluates whether these actions can be expected
to result in the destruction or adverse modification of the species' critical habitat. The
structure of this risk assessment is based on guidance outlined in the U.S. EPA's
Guidance for Ecological Risk assessment (U.S. EPA 1998), the Services' Endangered
Species Consultation Handbook (USFWS/NMFS 1998) and is consistent with procedures
and methodology outlined in the Overview Document (U.S. EPA 20040 and reviewed by
the U.S. Fish and Wildlife Service and National Marine Fisheries Service
(USFWS/NMFS 2004).
The CRLF was listed as a threatened species by the USFWS in 1996. The species 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). A total of about 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 in California (USFWS, 1996).
Technical S-methoprene, isopropyl (E, E) - 11- methoxy-3, 7, 1 l-trimethyl-2, 4-
dodecadienoate, is a long chain hydrocarbon ester (Farm Chemical Handbook, 1997). S-
methoprene is soluble in water at 1.4 mg/L (at 25° C) and also soluble in organic
solvents. The specific gravity of technical S-methoprene is 0.9261 at 20° C. S-
methoprene has a moderate vapor pressure (2.3xl0"5 mm Hg @ 25°C) and Henry's Law
Constant (6.9xl0"6 atm m3/mole). Consequently S-methoprene has the potential to
volatilize from water or moist soil. However, volatilization is mitigated by the affinity of
S-methoprene for soils and sediments (Toxnet). S-methoprene showed rapid degradation
in both sterile and nonsterile pond water exposed to sunlight, with more than 80% of
applied S-methoprene being degraded within 13 days (US EPA, 1982). S-methoprene
has a low persistence in soil (rapidly biodegrades), with a soil half-life of 10-14 days and
a half-life in water of <1 day in sunlight and >4 weeks in darkness. The major degradate
is methoxycitronellic acid (7-methoxy-3, 7-dimethyloctanoic acid). The Koc of 2,800
suggests that S-methoprene is relatively lipophilic and upon application to water can be
expected to adsorb to suspended solids and sediments. The Koc value also suggests that
S-methoprene, if applied to soil, is slightly mobile on FAO scale and will tend to reside in
the top few centimeters with potentially little leaching or ground water exposure (Hansch,
et al., 1995). An estimated bioconcentration factor of 3,400 suggests that the potential for
bioconcentration in aquatic organisms is very high (HSDB, 2002).
S-methoprene is used throughout the United States on indoor and commercial non-
agricultural use sites, residential uses, agricultural areas, building perimeters, and
wetlands. Although this compound is widely used, especially for public health pest
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control, the scope of this assessment is limited to California and the overall action areas
that are important in the sustained protection of the CRLF. Table 1.0 shows registered
uses of S-methoprene in California that may result in exposure scenarios that might
impact non-target organisms and the CRLF. The S-methoprene formulations that are
widely used include slow release forms such as briquets, sand mix, and granulars, as well
as liquid formulations (EC and FLC). In order to insure efficacy, these formulations are
usually applied directly to aquatic areas that can include stagnant slow moving shallow
water bodies, lakes, freshwater wetlands and marshes, swamps, as well as, any place that
contains freshwater and is suitable for mosquito development (old tires, man made
depressions, fountains, etc).
Table 1.0 Registered S-Methoprene Uses That May Have Ecological Impact to Non-
Target Fish and Wildlife in California
Food Crop
Rice, caneberries, date palms, citrus, small
fruits (bogs, unspecified agricultural crops,
unspecified orchards
Aquatic Non-Food Industrial
Drainage systems, sewage systems
Aquatic Non-Food Outdoor
Intermittently flooded areas/water,
streams/rivers/channeled water, lakes,
ponds, reservoirs, swamps/marshes/wetlands
/stagnant water.
Aquatic Non-Food Residential
Ornamental ponds/aquaria, swimming pool
water systems
Terrestrial Non-Food Crop
Wide area/general outdoor treatment (public
health use), compost piles, ornamental
herbaceous flowering/foliage/vine plants,
rights-of-way, agricultural and
nonagricultural uncultivated areas,
ornamental woody, recreational areas
Forestry
Forest trees
The assessment endpoints for the CRLF include direct toxic effects on the survival,
reproduction, and growth of the CRLF itself, as well as indirect effects, such as reduction
of the prey base or modification of its habitat. Direct effects to the CRLF in the aquatic
habitat are based on toxicity information for freshwater fish, which are generally used as
a surrogate for aquatic-phase amphibians. In the terrestrial habitat, direct effects are
based on toxicity information for birds, which are used as a surrogate for terrestrial-phase
amphibians. Given that the CRLF's prey items and designated critical habitat
requirements in the aquatic habitat are dependant on the availability of freshwater aquatic
invertebrates and aquatic plants, toxicity information for these taxonomic groups is also
discussed. In the terrestrial habitat, indirect effects due to depletion of prey are assessed
by considering effects to terrestrial insects, small terrestrial mammals, and frogs. Indirect
effects due to modification of the terrestrial habitat are characterized by available data for
terrestrial monocots and dicots.
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Since, CRLFs exists within freshwater and terrestrial habitats, the potential for S-
methoprene exposure to this frog, its food sources, and its habitat, is assessed by
considering the aquatic and terrestrial life phases separately. The Agency has estimated
high-end exposures in aquatic habitats by evaluating direct applications of S-methoprene
to water (liquid or sustainable release formulations for mosquito control). In developing
peak aquatic estimated environmental concentrations the Agency has relied on
extrapolated levels (0.485 - 22.0 ug/L) from label information, as well as, adjusted
maximum measured microcosm levels (0.35 - 4.21 ug/L) from the five S-methoprene
formulations (briquete, XR briquete, granular/pellets, sand mix, and liquid). In order to
evaluate an upper bound element of risk for terrestrial estimates, a 100% application of
liquid and granular formulations to a terrestrial site are used with the T-REX model.
Risk quotients (RQs) are derived as quantitative estimates of potential high-end risk.
Acute and chronic RQs are compared to the Agency's levels of concern (LOCs) to
identify instances where S-methoprene use within the action area has the potential to
adversely affect the CRLF and its designated critical habitat via direct toxicity or
indirectly based on direct effects to its food supply (i.e., freshwater invertebrates, algae,
fish, frogs, terrestrial invertebrates, and mammals) or habitat (i.e., aquatic plants and
terrestrial upland and riparian vegetation). When RQs for a particular type of effect are
below LOCs, the pesticide is determined to have "no effect" on the subject species.
Where RQs exceed LOCs, a potential to cause adverse effects is identified, leading to a
conclusion of "may affect." If a determination is made that use of S-methoprene use
within the action area "may affect" the CRLF and its designated critical habitat,
additional information is considered to refine the potential for exposure and effects, and
the best available information is used to distinguish those actions that "may affect, but are
not likely to adversely affect" (NLAA) from those actions that are "likely to adversely
affect" (LAA) the CRLF and its critical habitat.
In addition to evaluating the parent compound and its exposure in the environment, the
Agency considered degradate exposure. Degitz e7 al. (2003) did additional studies on the
developmental toxicity of S-methoprene and its degradates (S-methoprene acid, S-
methoprene epoxide, 7-methoxycitronellal, and 7-methoxycitronellic acid) to frog
embryos (Xenopus laevis) and found that exposure to 0.5 mg/L of parent compound did
not result in developmental effects. However, several degradates did produce
developmental effects at 1.25 mg/L (S-methoprene acid), 2.5 mg/L (S-methoprene
epoxide acid), 5 mg/L S-methoprene epoxide and 2.5 mg/L (7-methoxycitronellal). La
Clair, (1998) noted that the lowest concentration of S-methoprene exposed to sunlight
shown to cause malformations was 7.5 mg/L, which is 1,700 times greater than the level
found under typical applications of S-methoprene. Degitz et al. 2003, noted that typical
field application of sustained-release formulations of S-methoprene result in S-
methoprene concentrations that do not exceed 0.01 mg/1, suggesting that S-methoprene-
mediated developmental toxicity to amphibians may be overstated. According to Ankley
(1998) it is unlikely that degradation products would accumulate to levels that would
affect amphibian development.
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Based on the best available information, the Agency has assessed the potential for direct
and indirect risk to CRLF from S-methoprene exposure. The conclusion is that there is a
"may affect", but "not likely to adversely affect" determination for the CRLF from the
use of S-methoprene. The assessment endpoints (Table 1.1) where this determination is
made include the following:
1) Survival, growth, and reproduction of CRLF individuals via effects to food
supply {i.e. freshwater fish and invertebrates, non-vascular plants);
This assessment point reflects an LOC exceedance (0.07) for acute endangered species
concerns (LOC = 0.05) calculated from one of the upper bound extrapolated sustainable
release formulations (20% granular), although, the microcosm field values for the same
formulation did not exceed this LOC concern. In order to evaluate this exceedance, the
Agency also calculated the chance of individual exposure using the Individual Effects
Chance Model (Version 1.1). These calculations suggest that the chance of individual
effect from this granular extrapolated exposure is about lin 988,000, which may be
considered as a highly unlikely event. As an additional test of possible risk, the use of
acute and chronic fish and invertebrate toxicity data produced RQs for the other
formulations (using extrapolated and microcosm exposure values) that did not exceed
LOCs for direct or indirect effects to the aquatic-phase CRLF. Therefore, the Agency
concludes a "may affect" but "not likely to adversely affect" reading for this
assessment point.
The Agency acknowledges that S-methoprene is highly efficacious to Dipteran insect
larvae and that the use of this compound can result in a decline in emerging adult
populations. However, according to information of the CRLFs diet in Section 2.5.3 these
insects are not included in their diet. The Agency assumes that the CRLF is an
opportunistic feeder and will supplement its diet with available invertebrates and small
animals. Therefore, the Agency concluded "no habitat modification" from S-
methoprene use. Although there is widespread overlap of potential S-methoprene with
watersheds of the CRLF the Agency has also determined that there is no potential for
modification of CRLF designated critical habitat (aquatic or terrestrial plants) from the
use of S-methoprene because this compound does not have herbicidal qualities or mode
of action. Further information on the results of the effects determination are included as
part of the Risk Description in Section 5.2.
Table 1.1 Effects Determination Summary for Direct and Indirect Effects of S-
methoprene on the California Red-legged Frog
Assessment Endpoint
Effects
Determination
Basis
Aquatic-Phase
(Eggs, Larvae, Tadpoles, Adults)
1. Survival, growth, and reproduction
of CRLF individuals via direct effects
on aquatic phases
No Effect
Acute RQs do not exceed LOC for direct
effects using acute and chronic fish data.
There is widespread overlap of potential S-
methoprene with watersheds of the CRLF.
2. Survival, growth, and reproduction
of CRLF individuals via effects to food
May Affect, But
not Likely to
LOC exceedance for granular formulation
(0.07) to aquatic invertebrates. However,
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Assessment Endpoint
Effects
Determination
Basis
supply (i.e. freshwater fish and
invertebrates, non-vascular plants)
Adversely Affect
exposure was an extrapolated value,
microcosm value did not exceed LOC.
There is widespread overlap of potential S-
methoprene use with watersheds of the
CRLF.
3. Survival, growth, and reproduction
of CRLF individuals via indirect
effects on habitat, cover, and/or
primary productivity (i.e., aquatic plant
community)
No Effect
S-methoprene is a larvicide and does not kill
plants. Although there is the potential for
aquatic exposure, aquatic plants are not at
risk.
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.
No Effect
S-methoprene is not toxic to plants and does
not have herbicidal qualities.
Terrestrial Phase
(Juveniles and adults)
5. Survival, growth, and reproduction
of CRLF individuals via direct effects
on terrestrial phase adults and juveniles
Not Likely to
Adversely Affect
S-methoprene does not exceed an equivalent
LOC for acute or chronic toxicity LC50
values, based on available avian and
mammal data. Most applications are granular
formulations and the liquid applications are
directed to water.
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)
Not likely to
adversely affect
RQs for possible dietary items (small
mammals, adult insects) are less than the
LOCs. Based on the non-selective feeding
behavior of adult CRLF and low magnitude
of anticipated individual effects to potential
prey items, S-methoprene is not expected to
indirectly affect the terrestrial form of the
CRLF. Although Dipterian populations may
decline momentarily in the area where S-
methoprene is used, these organisms are not
expected to be a major component of the
CRLFs diet.
7. Survival, growth, and reproduction
of CRLF individuals via indirect
effects on habitat (i.e., riparian
vegetation)
Not Likely to
Adversely Affect
S-methoprene is not toxic to plants, plants
are not at risk.
Table 1.2 Effects Determination Summary for the Critical Habitat Impact Analysis
Assessment Endpoint
Effects
Determination
Basis
Aquatic Phase PCEs
(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)
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Assessment Endpoint
Effects
Determination
Basis
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.
No Habitat
Modifications
Since S-methoprene does not control
plants at the application sites, there is no
potential for impacts to aquatic and
terrestrial plants that comprise these
habitats.
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 source2.
No Habitat
Modifications
Given that S-methoprene is not intended to
control plants on the application sites,
there is no potential for impacts to aquatic
and terrestrial plants that comprise these
habitats.
Alteration of other chemical
characteristics necessary for normal
growth and viability of CRLFs and their
food source.
No Habitat
Modifications
S-methoprene does not affect plant life and
aquatic chemical (DO) components that
are necessary for aquatic CRLF growth
and development are not affected by S-
methoprene exposure.
Reduction and/or modification of
aquatic-based food sources for pre-
metamorphoses (e.g., algae)
No Habitat
Modifications
Although S-methoprene is applied to water
bodies, it does not have the potential for
impacts to aquatic plants that comprise
these habitats (non herbicidal properties).
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 drip line surrounding
aquatic and riparian habitat that are
comprised of grasslands, woodlands,
and/or wetland/riparian plant species that
provides the CRLF shelter, forage, and
predator avoidance
No Habitat
Modifications
S-methoprene is not intended to control
terrestrial plants at the application sites.
This compound is not an herbicide and
rapidly degrades in the environment
through photolysis and biodegradation (7-
10 days).
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
No Habitat
Modifications
Given that S-methoprene is not intended to
control plants on the application sites,
there is no potential for impacts to
terrestrial plants that comprise these
habitats.
Reduction and/or modification of food
sources for terrestrial phase juveniles and
adults
No Habitat
Modifications
Although S-methoprene is toxic to
Dipterian insects this does not pose acute
risk to the CRLF. Frogs are opportunistic
feeders and should supplement their diet
with other terrestrial organisms. Dipterans
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Assessment Endpoint
Effects
Determination
Basis
Aquatic Phase PCEs
(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)
are not listed as a component of the CRLFs
diet.
Alteration of chemical characteristics
necessary for normal growth and viability
of juvenile and adult CRLFs and their
food source.
No Habitat
Modifications
Although S-methoprene is toxic to
Dipterian insects this does not pose acute
risk to the CRLF. Frogs are opportunistic
feeders and should supplement their diet
with other terrestrial organisms. Dipterans
are not listed as a component of the CRLFs
diet.
1 Physico-chemical water quality parameters such as 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.
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.
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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.
2.0 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 Document
(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 the
potential for S-methoprene exposure to amphibians from direct application to aquatic
(i.e., marshes, ponds) and terrestrial areas in order to combat human pest (such as
mosquitoes, fire ants, etc.). 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 etal. (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).
12
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In accordance with the Overview Document, provisions of the ESA, and the Services'
Endangered Species Consultation Handbook, the assessment of effects associated with
registration of S-methoprene 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 S-methoprene 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.
As part of the "effects determination," one of the following three conclusions will be
reached regarding the potential for registration of S-methoprene 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 S-methoprene 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 S-
methoprene.
If a determination is made that use of S-methoprene 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 S-methoprene use) and further evaluation of the potential impact of S-
methoprene on the PCEs is also used to determine whether destruction or adverse
modification to designated critical habitat may occur. Based on the refined information,
13
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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 S-methoprene is expected to directly impact living organisms within the action
area (defined in Section 2.7), critical habitat analysis for S-methoprene is limited in a
practical sense to those PCEs of critical habitat that are biological or that can be
reasonably linked to biologically mediated processes (i.e., the biological resource
requirements for the listed species associated with the critical habitat or important
physical aspects of the habitat that may be reasonably influenced through biological
processes). Activities that may 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 S-methoprene 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 {i.e., the FIFRA regulatory
action) is an approved product label. The label is a legal document that stipulates how
and where a given pesticide may be used. Product labels (also known as end-use labels)
describe the formulation type {e.g., liquid or granular), acceptable methods of application,
approved use sites, and any restrictions on how applications may be conducted. Thus, the
use or potential use of S-methoprene in accordance with the approved product labels for
California is "the action" relevant to this ecological risk assessment.
Although it is recognized that S-methoprene is used throughout the United States, the
scope of this assessment is limited to areas in California applicable to the protection of
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. The current California uses of S-
methoprene that will be assessed in this evaluation include direct applications to water
bodies, as well as uses around certain agricultural areas such as rice and citrus. Although
not used to combat agricultural pests, S-methoprene is used for mosquito control around
flooded rice fields and berry bogs, and fire ant control around orchards like citrus. Sites
of concern that receive S-methoprene include swamps, wetlands, turf, rights of ways,
industrial parks, landscape maintance, lakes, and intermittently flooded areas. S-
methoprene is formulated as flowable concentrates, soluble concentrates, and granular,
pelleted/tabeted, and bait/solids (briquetes). Application methods include aircraft, high
and low volume ground spray, and granular/dust application. Although this compound
degrades in the environment via photolysis and biodegradation, concern has been raised
over the expected environmental concentrations that can occur through the use of such
formulations as the briquet and granular (sustainable release). The S-methoprene
14
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briquetes (submerged in water) have been reported as having relatively long half-lives,
with a mean degradation of the briquettes at 19% by weight after 150 days and full
degradation after 1.5 years (Boxmeyer et al., 1997).
S-methoprene undergoes environmental degradation after exposure to ultraviolet (UV)
sunlight, as well as microbial breakdown. This is a concern to the Agency because of the
similarities of these degradates and retinoic acid which is a significant component in
vertebrate development, especially amphibians. The S-methoprene degradates are as
follows: S-methoprene acid, S-methoprene epoxide, 7-methoxycitronellal, 7-
methoxycitronellic acid and will be discussed in Section 4.0.
The Agency does not routinely include an evaluation of mixtures of active ingredients,
either those mixtures of multiple active ingredients in product formulations or tank
mixtures. In the case of the product formulations of different active ingredients, each
active ingredient is subject to an individual risk assessment for regulatory decisions
regarding the active ingredient on a particular use site. If effects data are available for a
formulated product containing more that one active ingredient, they must 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).
S-methoprene has registered products that contain multiple active ingredients. Analysis
of the available acute oral mammalian LD50 data for multiple active ingredient products
relative to the single active ingredient is provided in Appendix A. The results of this
analysis show that an assessment based on the toxicity of the single active ingredient of
S-methoprene is appropriate.
2.3 Previous Assessments
S-methoprene was first registered by EPA as a conventional, chemical pesticide in 1975.
The Agency issued a Registration Standard for S-methoprene in 1982, and subsequently
reclassified S-methoprene as a biochemical pesticide. The Agency completed the
Reregi strati on Eligibility Decision (RED) in 1991 (EPA, 1991) and reregi strati on of the
active ingredient and all end-uses was completed in 1997. Tolerances (40CFR 180.359)
and exemption from tolerances (40 CFR 180.1033 and 185.41500 have been established
for S-methoprene in or on a number of food commodities. S-methoprene is also
recognized by FDA as a feed additive for use in cattle feeds to control horn flies (40 CFR
186.4150).
2.4 Stressor Source and Distribution
2.4.1 Environmental Chemistry and Fate Assessment
Technical S-methoprene is a long chain hydrocarbon ester, characterized as a pale yellow
liquid with a faint fruity odor and has a boiling point of 100° C at 0.05 mm of Hg (Farm
Chemical Handbook, 1997). Samples of S-methoprene that have been stored in glass for
four years at 70° F did not show any appreciable chemical decomposition. Technical
15
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S-methoprene is soluble in water at 1.4 mg/L (at 25° C) and also soluble in organic
solvents. The specific gravity of technical S-methoprene is 0.9261 at 20° C. This
compound is intended only for reformulation into and end-use pesticide and, therefore, is
considered to be a "manufacturing-use "product (Toxnet).
S-methoprene has a moderate vapor pressure (2.3xl0"5 mm Hg @ 25°C) and Henry's
Law Constant (6.9xl0"6 atm mVmole). Consequently S-methoprene has the potential to
volatilize from water or moist soil. However, volatilization is mitigated by the affinity of
S-methoprene for soils and sediments (Toxnet). S-methoprene showed rapid degradation
in both sterile and nonsterile pond water exposed to sunlight, with more than 80% of
applied S-methoprene being degraded within 13 days (US EPA, 1982).
S-methoprene has a low persistence in soil (rapidly biodegrades), with a soil half-life of
10-14 days and a half-life in water of <1 day in sunlight and >4 weeks in darkness. S-
methoprene degrades in both sterile and nonsterile pond water with exposure to sunlight
(80% of applied S-methoprene is degraded afterl3 days). The major degradate is
methoxycitronellic acid (7-methoxy-3, 7-dimethyloctanoic acid). S-methoprene rapidly
degrades in plants, with a half-life of 1-2 days in alfalfa when applied at a rate of 1
pound per acre. In rice, the half-life is less than 1 day. In wheat, its half-life was
estimated to be 3 to 7 weeks, depending on the level of moisture in the plant. The Koc of
2,300 suggests that S-methoprene is relatively lipophilic and upon application to water
can be expected to adsorb to suspended solids and sediments. The high Koc value also
suggests that S-methoprene, if applied to soil, is slightly mobile and will tend to reside in
the top few centimeters with potentially little leaching or ground water exposure (Hansch,
et al., 1995). An estimated bioconcentration factor of 3,400 suggests that the potential for
bioconcentration in aquatic organisms is very high (HSDB, 2002). Uncharacterized S-
methoprene residues accumulate in edible tissues of bluegill sunfish and crayfish at
maximum bioconcentration factors of 457 and 75, respectively (rates of depuration are
unknown).
Table 2.0 Summary of S-Methoprene Environmental Chemistry and Fate
Properties ^
Study
Value (units)
Major Dcgradatcs
Minor Degradates
MRID #
Study
Status
Hydrolysis
Stable to hydrolysis at 20° C at pH 5-9,
for 21-30 days
No degradates
00010439
Acceptable
Direct Aqueous
Photolysis
The photolysis half-life of S-
methoprene (0.5 and 0.01 ppm) was
less than 1 day (Laboratory). After 7
days, 12% and 5% of applied
compound remained in solution. S-
methoprene is rapidly degraded in
pond water exposed to natural sunlight;
complete degradation occurs within 13
days post treatment.
The trans-2:cis-2 ratio
changed as a result of
photoisomerization from
97:3 to 46:54 . Fifty minor
photolysis were found
(all<10% of applied). These
included methoxcitronellal
(9%), methoxcitronellic
acid (7%), 92E)-4,5-epoxy-
ll-methoxy-3,7,11-
trimethyl-2-dodecenoate
(4%), and 8-methoxy-4,8-
00010443,
00010441,
00010442,
05008622,
00010542,
05008610,
00010440
Acceptable
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Study
Value (units)
Major Dc&radatcs
Minor Degradates
MRID#
Study
Status
dimethyl-2-nonanone (4%).
Soil Photolysis
Photodegradation was rapid (24% in 6
hours) on silica gel TLC plates.
Methoxcitronellal (14% of
applied).
00010542,
05008610
Acceptable
Aerobic Soil
Metabolism
S-methoprene applied at 1 lb/A is
degraded rapidly in aerobic sandy loam
and silt loam with a half-life of about
10 and 14 days, respectively. Half-life
of S-methoprene in silt loam was about
14 days.
C02 was major product
(49% of applied)
00010420,
00010541,
00010874,
05008315
Acceptable
Anaerobic
Aquatic
Metabolism
No data available
Aerobic
Aquatic
Metabolism
S-methoprene EC persists in FW and
salt water for 132 days (dark condition)
at 4.5° C (half life 28-35 days with 2-
15% of S-methoprene remaining at 132
days).
Isomerization of trans-S-
methoprene to cis-S-
methoprene did not occur.
Degradates included 7-
Methoxycitronellic acid
(29% of applied)
05009396,
00010974,
00010975,
05008622,
00010442
Acceptable
Kd-ads / Kd-des
(mL/g)
Koc- ads / Koc-des
(mL/g)
Log Kow 5.50
2,300
Degrdates not measured
42290001,
Hansch, el
al 1995
EPI Suite
Terrestrial
Field
Dissipation
No data available
Aquatic Field
Dissipation
Rice field: S-methoprene at 0.12, 0.31,
and 0.81 ppm was present in water
samples 1 hour after treatment with
0.5, 1.0, and 2.0 lbs ai/A, respectively.
S-methoprene not detected in the water
column after 72 hours
Degradates were not
measured.
00010436,
00010437,
00010438,
00011484,
00010433,
00010417,
00011091,
00011092,
00012729,
05008625,
00011485,
00010434
Acceptable
Leaching
Not mobile when applied to sand,
sandy loam, silt loam, and clay loam.
All S-methoprene that was recovered
was in the top 3 cm of soil column.
No degradates were
measured.
00010444,
00010507
Acceptable
Accumulation
Fish: Day 21 the maximum 14C levels
in edible tissue was 2.78 ppm
corresponding to a bioaccumulation
factor of 457.14C remained at 1.67
ppm (bioaccumulation factor of 253)
in the edible tissue at the end of the 42-
day experiment. Crayfish:
Degradates not measured.
00012785
Acceptable
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Study
Value (units)
Major Dc&radatcs
Minor Degradates
MRID#
Study
Status
Accumulation in edible tissues of fish
and crayfish at maximum
bioaccumulation factors of 457 and 75,
respectively. Elimination of 93-95% of
methoprene residues within 14 days
precludes bioaccumulation in fish
2.4.2. Environmental Transport Assessment
This risk assessment is intended to be used to evaluate the potential for S-methoprene
exposure to the aquatic and terrestrial-phase of the CRLF. S-methoprene is applied to
bodies of shallow water as a liquid and as a sustainable release formulation for mosquito
control. Label instructions for these formulations specify application to water in order to
achieve maximum efficacy. Unlike adulticides that are used to combat adult mosquitoes
(i.e. synthetic pyrethroids), S-methoprene is not applied as fine droplets in order to create
a mist that is intended for drift over a target site. Instead, S-methoprene is applied directly
to water in order to be efficacious to Dipterans larval forms. In addition to applications to
aquatic areas, S-methoprene is also applied to land and around certain crops as a granular
formulation. Although not used to combat agricultural pests, S-methoprene is applied in
citrus orchards as bait for fire ant control. Therefore, in deciding on the environmental
transport scenario for developing estimated environmental concentrations (aquatic and
terrestrial), the Agency has relied on transport mechanisms that can be depicted as upper
bound exposure to aquatic and terrestrial organisms. All aquatic EECs are estimates of
direct application to water. This upper bound scenario precludes concern and modeling
for runoff or drift that might occur for applications to terrestrial sites. T-REX is used to
evaluate terrestrial application of liquid and granular formulation and possible exposure
to avian species (surrogate for terrestrial-phase CRLF), as a upper bound maximum
application.
The potential exposure to aquatic organisms from S-methoprene use from granular,
briquets, pellets, and sand mix applications is approached by estimating expected release
rates that has been calculated from label information and expected efficacy. In addition to
these values, the Agency will also use adjusted field microcosm residue data that has
been generated by the registrant. Both approaches will be used to generate the risk
quotient (RQ) values for this CRLF assessment.
2.4.3 Mechanism of Action
S-methoprene is an analog of the insect juvenile hormone (JH) that is responsible for
regulating larval growth. Since this regulatory mode of action does not result in direct
toxicity to target organisms, the Agency considers S-methoprene to be a biological pesticide
where control of target pests is through disruption of primary gene regulation at the onset
of metamorphosis, thus preventing larvae from developing into adults (Hersher etal.,
1998, Degitz etal., 2003). The retention of juvenile characters in insect larval stages is
controlled by JH which is present in larvae up to their transformation from pupae to adult
stage where titer levels decline. S-methoprene mimics the JH by binding to
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corresponding receptors thus prolonging the larval stage and preventing these organisms
from reaching adult stage and reproducing.
2.4.4 Use Characterization
Analysis of labeled use information is the critical first step in evaluating the federal
action. The current label for S-methoprene 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. Table 2.1 shows usage
information that is disallowed, as well as, allowed in California. The table also shows the
registered uses that the are not expected to have an ecological impact (i.e. indoor uses,
pets, etc) and those uses that have the potential for environmental risk (i.e. rice,
freshwater aquatic areas, marshes, etc.).
The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis
of both national- and county-level usage information (BEAD: CITATIONS HERE) using
state-level usage data obtained from USDA-NASS1, Doane (www.doane.com; the full
dataset is not provided due to its proprietary nature), and the California's Department of
Pesticide Regulation Pesticide Use Reporting (CDPR PUR) database2 . 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 S-methoprene by county in
this California-specific assessment were generated using CDPR PUR data. Usage data
are averaged together over the years 2001 to 2005 to calculate average annual usage
statistics by county and crop for S-methoprene, including pounds of active ingredient
applied and base acres treated. California State law requires that every pesticide
application be reported to the state and made available to the public.
S-methoprene is registered on a variety of sites including flooded fields, rice, caneberries,
swamps, marshes, wetlands, the perimeter of buildings, livestock, indoor pet uses,
commodity storage, waste treatment, culverts, drains and any thing that may contain
water applicable for mosquito growth.
For the purpose of this assessment, EEC will be generated for uses that may have the
potential for impact to fish and wildlife. These will include all formulations that are
applied directly to water (i.e. granular, briquets, and liquid formulation) or broadcast over
post or pre-flooded areas. Since, S-methoprene exposure from indoor applications are
less likely to impact aquatic and terrestrial organisms, these uses will not be included in
this assessment. The use of S-methoprene in a briquet and/or granular form was identified
as a potential aquatic concern in earlier reviews. Since these formulations function as
1 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.
2 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.
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slow release mechanisms for delivering S-methoprene at a relatively constant
concentration over a period of time (i.e. 30- 150 days), their appears to be the potential
for impact to non-target aquatic organisms. The granule and pellet formulations are about
425 microns in size and are applied by ground or aerial equipment. The use of granules is
advantageous in areas of dense plant cover because of more efficient foliage penetration.
The briquets weigh about 5.4 - 36.2 g and are usually applied by hand to small areas (i.e.
culverts, drains, etc.). Liquid S-methoprene formulations include emulsifiable
concentrates (EC) and flowable concentrates (FLC) and are also applied directly to water.
Tables 2.1 shows the average amount of S-methoprene used annually in California during
2002 - 2005. The four listed categories reflect the highest S-methoprene usage through-
out the state with Public Health Pest Control accounting for about 97% of the the total.
Table 2.2 shows the formulations that were used. The sustainable release forms (briquets,
granular, pelleted/tableted, and impregnated material) accounted for about 69% of the
total use.
Table 2.1 Summary of CDPR PUR Usage Data from 2002 - 2005 for S-Methoprene
Use
Average Amount of S-Methoprene Used
During this Time Period (lbs)
Landscape Maintance
20.03
Public Health Pest Control
8466.70
Regulatory Pest Control
10.01
Structural Pest Control
206.77
Table 2.2 Summary of CDPR PUR Formulation Data from 2002- 2005 for S-
Methoprene
Formulation
Average Amount of S-Methoprene Used
Relative to Formulation During this
Time Period (lbs)
Briquets
3609.16
Pelleted/Tableted
2307.96
Granular
82.85
Impregnated Material
0.015
Emulsifiable Concentrate
184.39
Pressurized Liquid
11.60
Soluble Concentrate
859.41
Flowable Concentrate
1631.81
Ready-to-Use Solution
1.12
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The S-methoprene uses considered in this risk assessment represent currently registered
products as noted from 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, misreported uses, or misuse.
Historical uses, mis-reported uses, and misuse are not considered part of the federal
action and, therefore, are not considered in this assessment. Appendix B, Table B.2
shows the major formulations of S-methoprene that were used in California (2001-2005)
and the total amount applied. Table 2.3 shows maximum rates and formulations that were
used in this risk assessment for the sustainable release formulations and the liquid that
was applied to rice and caneberry bogs. The amount of S-methoprene that was expected
to be released into the aquatic environment was extrapolated from label information and
efficacy data. These rates reflect upper bound scenarios of the expected amount of S-
methoprene (see calculations Appendix I).
Table 2.3 Maximum Rate of S-Methoprene Sustainable Release Formulations that
Are Applied Directly to Water
Use
Formulation
Max. % active
ingredient
Max. Rate (lbs
ai/A/day)
Woodland pools,
swamps, rice fields,
storm drains, etc.
Briquet
Briquet XR
2.1
8.62
0.0058
0.014
Woodland pools,
swamps, berry bogs,
rice fields, irrigated
crop lands, etc.
Granular
Sand mix
4.25
3.0
0.06
0.017
Use
Formulation
Max. % active
ingredient
Max Rate (lbs ai/A)
Woodland pools,
berry bogs, rice fields,
irrigated crop lands,
etc.
Liquid
20.0
0.013
The values noted in Table 2.4 reflect maximum application of the granular formulation to
terrestrial areas where the CRLF may be found. Although frogs should not feed on
granulars this scenario was included as an upper bound scenario.
Table 2.4 Maximum Rate of S-Methoprene Formulations that Are Applied to
Terrestrial Site
Use
Formulation
Max. % active
ingredient
Max. Rate
(lbs ai/A)
Max. Rate
(lbs ai/A)
Citrus (bait)
Granular
4.25
0.3
0.0075
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
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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 Appendix C.
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 elevational range of near sea level to 1,500 meters (5,200 feet) (Jennings and
Hayes, 1994); however, nearly all of the known CRLF populations have been
documented below 1,050 meters (3,500 feet) (USFWS, 2002).
Populations currently exist along the northern California coast, northern 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 3. 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
22
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CRLF Habitat Areas
nd Wests
Sacramento
Sierra Nevada foothills
fountains
nsverse Range and Peninsular ranges
Legend
| Critical habitat
Occurrence sections
Core areas
Recovery units
County boundaries
Otto.
Southerh-Tra
V
I Kilometers
01530 60 90 120
North Coast
North San
South an
Northern Trans*'
Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Sen/ice (NASS, 2002)
Gap Analysis Program Orchard)'Vineyard Landccwer (GAP)
National Land Cwer Database (NLCD) (MRLC, 2001)
Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Erwironmental Fate arid Effects Division.
June XX, 2007. Projection: Albers Equal Area Conic USGS, North
American Datum of 1983 (NAD 19835
Figure 1. Distribution of the CRLF Range and Designated Critical Habitat.
23
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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 statuses, 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 Appendix E shown
in Figure 1.
Core Areas
USFWS has designated 35 core areas across the eight recovery units to focus their
recovery efforts for the CRLF (see Figure 1). Appendix E summarizes the geographical
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 S-methoprene occur (or if labeled
uses occur at predicted exposures less than the Agency's LOCs) within an entire recovery
unit, that particular recovery unit would not be included in the action area and 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 Appendix C (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
24
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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.
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.
25
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Recovery Units
Sierra Nevada Foothills arid Central
Valley
North Coast Range Foothills and
Western Sacramento River Valley
North Coast and North San
Francisco Bay
South and East San Francisco Bay
Central Coast
Diablo Range and Salinas Valley
Northern Transverse Ranges and
Tehachapi Mountains
Southern Transverse and Peninsular
Ranges
Core Areas
1 Pealhfif River
2 Yuba River -S. Fork Feather River
3 Traverse Creek! Mddle Folk American R! Rubicon
4 Cosumnes ftver
5 South Fork Calaveras River
6 Tuolumne River
7 Piney Creek
B Cottonwood Creek
0 Pulah Creek -Cache Creek
10 Lake Berryessa Tributaries
11 Upper Sonoma Creak
12 Petakima Greek -Sonoma Creek
13 PI. Reyes Peninsula
14 Belvedere Lagoon
16 Jameson Canyon -Lower Napa Rivei
1G East San Francisco Bay
17 Santa Clara Valley
18 Soulh San Francisco Bay
19 Watsonvllle Slough -EBthorn Slough
20 Carmoi River - Santa Lucia
21 Gabion Range
22 Ester o Bay
23 Arioyo Grande CretA
24 Santa Maiia fiver -Santa Yuez Rivet
25 Sisquoc R?ver
26 Ventura River -Santa Clara River
27 Santa Monica Bay -Ventura Coastal Streams
28 Eslrella Rrver
20 San Gabriel Mountain
30 Forks of the Mohave
31 Santa Ana Mountain
32 Santa Rosa Plateau
33 San Lute Rey
34 Sweetwater
35 Laguna Mountain
Legend
Recovery Unit Boundaries
Core Areas
(
County Boundaries
37.5 75
150 Miles
Figure 2. Recovery Unit and Core Area Designations for CRLF
26
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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 3 depicts CRLF annual reproductive timing.
Figure 3. 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)
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,
27
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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 CRLF utilizes habitat with perennial, or near perennial water (Jennings et al.,
1997). Dense vegetation close to water, shading, and water of moderate depth are habitat
features that appear especially important to CRLF (Hayes ans Jennings, 1998). 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 also show
that CRLFs do not frequently inhabit vernal pools, as conditions in these habitats
generally are not suitable (Hayes and Jennings, 1998).
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
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 (UWFWS, 2002). According to
28
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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 Appendix 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;
Upland habitat; and
Dispersal habitat.
Please note that a more complete description of these habitat types is provided in
Appendix C.
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
29
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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 Appendix D for a full explanation on this special rule. One of the exemptions is the
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.
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 the use of S-methoprene 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).
30
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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 S-methoprene is expected to directly impact
living organisms (Dipterians) within the action area, critical habitat analysis for S-
methoprene is limited in a practical sense to those PCEs of critical habitat that are
biological or that can be reasonably linked to biologically mediated processes.
2.7 Action Area
For listed species assessment purposes, the action area is considered to be the area
affected directly or indirectly by the federal action and not merely the immediate area
involved in the action (50 CFR 402.02). It is recognized that the overall action area for
the national registration of S-methoprene is likely to encompass considerable portions of
the United States based on the large array of non-agricultural uses, as appropriate.
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 S-
methoprene may be expected to have on the environment, the exposure levels to S-
methoprene that are associated with those effects, and the best available information
concerning the use of S-methoprene 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
aquatic and terrestrial uses for S-methoprene. The Agency completed an analysis and
review of labeled uses that showed that, for S-methoprene, the aquatic uses listed in
Table 2.5 are considered as part of the federal action evaluated in this assessment.
Table 2.5 Summary of the Uses Considered as Part of the Federal Action Evaluated
in this Assessment
I se Category
I ses
Agricultural
Rice, caneberries, date palms, citrus, small fruils
(bogs, unspecified agricultural crops,
unspecified orchards
Non-Agricultural
Drainage systems, sewage systems,
Salt/brackish water sites, intermittently,
Ornamental ponds/aquaria, swimming pool
water systems flooded areas/water,
streams/rivers/channeled water, lakes, ponds,
reservoirs, forest trees, compost piles,
swamps/marshes/wetlands/stagnant water, wide
area/general outdoor treatment (public health
use), ornamental herbaceous
flowering/foliage/vine plants, rights-of-way,
agricultural and nonagricultural uncultivated
areas, ornamental woody, recreational areas
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S-methoprene is also registered for use on pets (shampoos and collars), stored grains,
hospital premises, cemeteries, industrial waste disposal systems, and other indoor uses.
These uses are not evaluated for this risk assessment because the likelihood for
environmental exposure is assumed to be negligible since these are indoor uses and
warrant a determination of "no effect" (Table 2.6). Although, pet shampoo can be washed
down a drain and eventually reach a treatment plant and an adjacent body of water, the
risk to the CRLF from this application is assumed to result in "no effect". The Agency
has arrived at this conclusion because the assessment strategy used for evaluating risk
from aquatics uses represents a 100% direct application of S-methoprene to water
scenario. The maximum percent active of S-methoprene in pet shampoo is relatively low
at 0.50%. Any modeling of a Down-the-Drain scenario for this use would result in
considerable dilution of the active ingredient. The issue of down-stream dilution was not
evaluated in this assessment because the Agency has focused on a direct application to
water as an upper bound scenario for developing this risk assessment.
Table 2.6 Summary of S-Methoprene Uses that are not Considered as part of the
Federal Action Evaluated in the Assessment
I se Category
I ses
Non-AgriculturalFood
Compost, compost piles, ornamental
herbaceous flowering/foliage/vine plants
Food/feed storage area-full, cereals,
mushroom houses/mushroom casing soil,
eating establishments, commercial shipping
containers-feed/food-empty, food
processing plant premises/equipment, dairy
cattle, beef/range/feeder cattle
Indoor Non-Food
Stored tobacco, commercial transportation
facilities, tobacco processing plant
premi ses/equipment,
commercial/institutional/industrial
premises/equipment (indoors), horses,
ponies, farm premises (indoor)
Indoor Medical
Hospitals/medical institutions premises
(human/veterinary)
Indoor Residential
Kennels and/or pet sleeping quarters,
household/domestic dwellings indoor
premises, cats, dogs, pet shampoos
Terrestrial Non-Food Areas
barns, barnyards, auction barns, cemeteries,
zoos.
Terrestrial Food Crop
Stored commodities: Legume vegetables,
Corn (field and pop), Sunflower, Cotton,
Peanuts, Birdseed, Canola, Cereal grains,
Oats, Rice, Sorghum, Wheat, Millet, Cocoa
Aquatic Non-Food Outdoor
Industrial waste disposal system, Sewage
system
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The current labels for S-methoprene represent 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. In order to assess the potential
risk to aquatic organisms and the CRLF from exposure to S-methoprene at these sites, the
Agency has completed an assessment by using a upper bound scenarios of direct
application to shallow water (1ft) at the maximum liquid application rate to an aquatic
area (0.5853 lbs ai/A) and to rice (0.013 lbs ai/A). The maximum application of the
different sustainable release formulations (briquete at 0.0058 lbs ai/A/day; briquete XR at
0.014 lbs ai/A/day; granular at 0.06 lbs ai/A/day) were extrapolated and also evaluated
for this assessment. An evaluation of potential S-methoprene exposure to the terrestrial-
phase CRLF was also completed by using the maximum application rate for a liquid
formulation (0.5829 lbs ai/A) to foliage (ornamental woody plants) as well as the
application of granular S-methoprene to dry areas around citrus (0.3 lbs ai/A). The T-
REX model was used for this portion of the assessment which includes calculations of
dietary exposure for multiple classes of birds and mammals.
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
available for the state of California were analyzed to refine the understanding of potential
S-methoprene use. The overall conclusion of this analysis is that S-methoprene use is
widespread and not confined to particular regions. According to label instructions, S-
methoprene can be used anywhere mosquitoes are considered to be a potential public
health threat. The initial area of concern is defined as all land cover types that represent
the labeled uses described above. Since S-methoprene is used throughout California and
generally covers all areas where water may be present, a land cover map would show the
entire state.
Once the concern is defined, the next step is to compare the extent of that concern 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 S-methoprene to determine which
routes of transport are likely to have an impact on the CRLF. In the case of S-
methoprene, the exposure routes that are most likely to affect non-target organisms are
direct applications to water of liquid formulation and sustainable release formulations
(granular/briquette/pellet) with constant release rates. Direct application of liquid
formulations to land and granular application to land will also be considered in this
assessment for possible impact to terrestrial-phase CRLF.
LOC exceedances are used to describe how far effects may be seen from the initial area
of concern. Since the Agency is evaluating direct application to water as a upper bound
scenario, factors such as spray drift, downstream run-off, atmospheric transport, etc. are
not a part of this assessment since these exposure routes present a lower potential for
exposure. The LOCs used in the analysis were the endangered species LOC for acute
33
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effects (0.05 for aquatic animals; 0.1 for terrestrial animals) and the chronic LOC (1 for
aquatic and terrestrial animals).
2.8 Assessment Endpoints and Measures of Ecological Effect (Mortality,
Growth, and Reproduction)
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."3 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. aquatic
areas, riparian vegetation, and upland and dispersal habitats), and the routes by which
ecological receptors are exposed to S-methoprene-related contamination (e.g., direct
contact, etc).
As discussed in USEPA (2000) a quantitative component-based evaluation of mixture
toxicity requires data of appropriate quality for each component of a mixture. In this
mixture evaluation an LD50 with associated 95% confidence interval (CI) is needed for
the formulated product. The same quality of data is also required for each component
of the mixture. Given that the formulated products for methoprene do not have LD50
data available it is not possible to undertake a quantitative or qualitative analysis for
potential interactive effects. However, because the active ingredients are not expected
to have similar mechanisms of action, metabolites, or toxicokinetic behavior, it is
reasonable to conclude that an assumption of dose-addition would be inappropriate.
Consequently, an assessment based on the toxicity of methoprene is the only reasonable
approach that employs the available data to address the potential acute risks of the
formulated products.
Most S-methoprene formulations only contain a single active ingredient (e.g. S-
methoprene). Available toxicity data for aquatic organisms did not show any significant
differences between formulated product and the technical active ingredient. For aquatic
species in which comparative data are available, the confidence intervals for technical
and formulation overlap suggesting that the toxicity of technical S-methoprene and the
formulations are similar. Toxicity data on avian species is only available for the technical
active ingredient.
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
3 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
34
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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 S-methoprene is provided in Table 2.7.
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.
Table 2.7 Summary of Assessment Endpoints and Measurements of Ecological
Effects for Direct and Indirect Effects of S-Methoprene on the CRLF.
Assossmoiil I'lnripoini
Measures of r.cnlniiiciil 1"I'lVcls4
Aquatic-Phase CRLF
(Eggs, larvae, juveniles, and adults"f
Direct Effects
1. Survival, growth, and reproduction of CRLF
la. Amphibian acute LC50 (ECOTOX) or most
sensitive fish acute LC50 (guideline or ECOTOX) if
no suitable amphibian data are available
lb. Amphibian chronic NOAEC (ECOTOX) or
most sensitive fish chronic NOAEC (guideline or
ECOTOX)
lc. Amphibian early-life stage data (ECOTOX) or
most sensitive fish early-life stage NOAEC
(guideline or ECOTOX)
Indirect Effects and Critical Habitat Effects
2. Survival, growth, and reproduction of CRLF
individuals via indirect effects on aquatic prey food
supply (i.e., fish, freshwater invertebrates, non-
vascular plants)
2a. Most sensitive fish, aquatic invertebrate, and
aquatic plant EC50 or LC50 (guideline or ECOTOX)
2b. Most sensitive aquatic invertebrate and fish
chronic NOAEC (guideline or ECOTOX)
3. Survival, growth, and reproduction of CRLF
individuals via indirect effects on habitat, cover,
food supply, and/or primary productivity (i.e.,
aquatic plant community)
3a. Vascular plant acute EC50 (duckweed guideline
test or ECOTOX vascular plant)
3b. Non-vascular plant acute EC50 (freshwater algae
or diatom, or ECOTOX non-vascular)
4. Survival, growth, and reproduction of CRLF
individuals via effects to riparian vegetation
4a. Distribution of EC25 values for monocots
(seedling emergence, vegetative vigor, or
ECOTOX)
4b. Distribution of EC25 values for dicots (seedling
emergence, vegetative vigor, or ECOTOX)
4 All registrant-submitted and open literature toxicity data reviewed for this assessment are included in
Appendix A.
35
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Measures of r.cnlniiiciil 1"I'lVcls4
Terrestrial-Phase CRLF
(Juveniles and adults)
Direct Effects
5. Survival, growth, and reproduction of CRLF
individuals via direct effects on terrestrial phase
adults and juveniles
5a. Most sensitive birdb or terrestrial-phase
amphibian acute LC50 or LD50 (guideline or
ECOTOX)
5b. Most sensitive birdb or terrestrial-phase
amphibian chronic NOAEC (guideline or
ECOTOX)
Indirect Effects and Critical Habitat Effects
6. Survival, growth, and reproduction of CRLF
individuals via effects on terrestrial prey
(i.e.,terrestrial invertebrates, small mammals , and
frogs)
6a. Most sensitive terrestrial invertebrate and
vertebrate acute EC50 or LC50 (guideline or
ECOTOX)0
6b. Most sensitive terrestrial invertebrate and
vertebrate chronic NOAEC (guideline or ECOTOX)
7. Survival, growth, and reproduction of CRLF
individuals via indirect effects on habitat (i.e.,
riparian and upland 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)
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 S-methoprene 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. 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 S-methoprene effects data are available.
Assessment endpoints and measures of ecological effect selected to characterize potential
modification to designated critical habitat associated with exposure to S-methoprene are
provided in Table 2.8. 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.
36
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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 S-methoprene 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).
37
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Table 2.8 Summary of Assessment Endpoints and Measures of Ecological Effects for
Primary Constituent Elements of Designated Critical Habitat
Assessment Emlpoint | Measures of Ecological Effect
Aquatic-Phase CRLFPCEs
(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.
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 CRLF PCEs
(Upland Habitat and Dispersal Habitat)
Elimination and/or disturbance of upland habitat;
ability of habitat to support food source of CRLFs:
Upland areas within 200 ft of the edge of the riparian
vegetation or dripline surrounding aquatic and riparian
habitat that are comprised of grasslands, woodlands,
and/or wetland/riparian plant species that provides the
CRLF shelter, forage, and predator avoidance
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 EC50/LC50 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.
3 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.
38
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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 S-methoprene to the
environment. The following risk hypotheses are presumed for this endangered species
assessment:
The labeled use of S-methoprene within the action area may:
directly affect the CRLF by causing mortality or by adversely affecting growth or
fecundity;
indirectly affect the CRLF by reducing or changing the composition of food
supply;
indirectly affect the CRLF or modify designated critical habitat by reducing or
changing the composition of the aquatic plant community in the ponds and
streams comprising the species' current range and designated critical habitat, thus
affecting primary productivity and/or cover;
indirectly affect the CRLF or modify designated critical habitat by reducing or
changing the composition of the terrestrial plant community (i.e., riparian habitat)
required to maintain acceptable water quality and habitat in the ponds and streams
comprising the species' current range and designated critical habitat;
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);
modify the designated critical habitat of the CRLF by reducing the food supply
required for normal growth and viability of juvenile and adult CRLFs;
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.
modify the designated critical habitat of the CRLF by reducing or changing
ispersal 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.
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 (S-methoprene), release mechanisms, biological receptor types,
39
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and effects endpoints of potential concern. The conceptual models for aquatic and
terrestrial phases of the CRLF are shown in Figures 4 and 6, and the conceptual models
for the aquatic and terrestrial PCE components of critical habitat are shown in Figures 5
and 7. 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.
Stresso
Long range
atmospheric
transport
Groundwater
Sourc
Runoff
Exposur
Wet/dry
Uptake/gills
or
Uptake/cell;
roots,
'Riparian plant
' terrestrial
' exposure
[_ pathways
Uptake/gills
or
Ingestio
Ingestio
Receptor
Attribute
Change
[Habitat integrity
Reduction in primary
productivity
iReduced cover
Food chain
Reduction in prey
Aquatic Animals
Invertebrates
Vertebrates
Aquatic Plants
Non-vascular
Vascular
Red-legged Frog
Eggs Juveniles
Larvae Adult
Tadpoles
Surface water/
Sediment
Individual
organisms
Reduced survival
Reduced growth
S-methoprene Applied to Use Site
Figure 4.0 Conceptual Model for S-Methoprene Effects on Aquatic Phase of the
Red-Legged Frog
40
-------
Stressor
Source
Exposure
Media
Receptors
S-methoprene Applied to Aquatic Site
J
Spray drift
Water
~r~
Soil
Groundwater
i
Surface water/
Sediment
t.
Long range
atmospheric
transport
¦ Wet/dry deposition ¦*
Uptake/gills
or integument
Uptake/gills
or integument
Red-legged Frog
Eggs Juveniles
Larvae Adult
Tadpoles
Aquatic Animals
Invertebrates
Vertebrates
T
¦Ingestion
Uptake/cell,
roots,(leaves
¦Aquatic Plants
[Non-vascular
¦Vascular
L
t
Ingestion
Attribute
Change
Habitat
PCEs
'Individual organisms
iReduced survival
[Reduced growth
iReduced reproduction
¦Other chemical
[characteristics
lAdversely modified
[chemical characteristics
¦Individual organisms
iReduced survival
[Reduced growth
iReduced reproduction;
¦Food sources "!
Riparian and
Upland plants
terrestrial exposure
pathways and PCEs
see Figure 2.d
[Population ¦ iCommunity
¦Yield [ [Reduced seedling
[Reduced yield i lemergence or vegetative
[ [vigor (Distribution^
± ______:_
iHabitat quality and channel/pond
] [morphology or geometry
^Reduction in algae w Adverse water quality changes
[Reduction injprey [ [increased sedimentation
L ~ 'Reduced shelter
Figure 5.0 Conceptual Model for S-Methoprene Effects on Aquatic Component of
the Red-Legged Frog Critical Habitat
41
-------
Stressor
Source
Exposure
Media
S-Methoprene Application to Terrestrial Area
Direct
application
P
Spray drift
/
/
/ r
/ |
i
. _ i.
~
Runoff
::r
.n.r
Soil
t
Long range
atmospheric
transport
Terrestrial
insects
Ingestion
Amphibians
- Dermal uptake/Ingestion*
« Root uptake*-
Wet/dry deposition-*
Terrestrial/riparian plants
grasses/forbs, fruit, seeds
(trees, shrubs)
Ingestion
Ingestion
Receptors
Attribute
Change
Ingestion.
Ingestion
Red-legged Frog
Juvenile
Adult
xn~
Individual organisms
Reduced survival
Reduced growth
Reduced reproduction
Mammals
it-
Food chain
Reduction in prey
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Figure 6.0 Conceptual Model for S-Methoprene Effects on Terrestrial Phase of the
Red-Legged Frog
42
-------
Stressor
Long range
atmospheric
transport
_ _ _T ,
1! Runoff >
_::j; *
soil |
T - -jl
Root uptake-*- j
Wet/dry deposition-*-
Source
Spray drift
~| 1i - - Dermal uptake/Ingestion-
Exposure
Media and
Receptors
Ingestion
Ingestion
Ingestion
Ingestion
<
¦Community
[Reduced seedling emergence
"or vegetative vigor
^Distribution)
Attribute 'Individual organisms'
iReduced survival i
[Reduced growth ]
¦Reduced reproduction i
iPopulation
[Reduced survival
'Reduced growth
iReduced reproduction
Change
Elimination and/or disturbance of
upland or dispersal habitat
'Reduction in primary productivity
iReduced shelter
'Restrict movement
Habitat [Other chemical
icharacteristics
[Adversely modified
"chemical characteristics
¦Food resources
[Reduction in food
¦sources
Mammals
Terrestrial
insects
Direct
application
Red-legged Frog
Juvenile
Adult
Terrestrial plants
grasses/forbs, fruit,
seeds (trees, shrubs)
S-Methoprene Applied to Use Site
Figure 7.0 Conceptual Model for S-Methoprene Effects on Terrestrial Component
of the Red-Legged Frog Critical Habitat
43
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2.10 Analysis Plan
In order to address the risk hypothesis, the potential for direct and indirect effects to the
CRLF, its prey, and its habitat is estimated. In the following sections, the use,
environmental fate, and ecological effects of S-methoprene are characterized and
integrated to assess the risks. This is accomplished using a risk quotient (ratio of
exposure concentration to effects concentration) approach. Although risk is often defined
as the likelihood and magnitude of adverse ecological effects, the risk quotient-based
approach does not provide a quantitative estimate of likelihood and/or magnitude of an
adverse effect. However, as outlined in the Overview Document (U.S. EPA, 2004), the
likelihood of effects to individual organisms from particular uses of S-methoprene is
estimated using the probit dose-response slope and either the level of concern (discussed
below) or actual calculated risk quotient value.
The maximum label application rates for use of S-methoprene on aquatic areas use sites
in California were selected for modeling environmental concentrations for the screening-
level deterministic (risk-quotient based) portion of this assessment. The most sensitive
toxicity endpoints from surrogate test species are used to estimate treatment-related
effects on growth, and survival and reproduction. Estimated environmental
concentrations (EECs) used for this assessment are based solely on S-methoprene parent
compound.
The following sections characterize the use, environmental fate, and ecological effects of
S-methoprene and, using a risk quotient (ratio of exposure concentration to effects
concentration) approach, estimate the potential for adverse effects on non-target
terrestrial and aquatic animals. The assessment is then refined by exploring the potential
for direct and/or indirect effects to the CRLF and/or the modification of its designated
critical habitat from S-methoprene use in California to make our effects determinations.
2.10.1 Measures to Evaluate Risk Hypotheses and Conceptual Model
2.10.1.1 Measures of Exposure
The environmental fate properties and use pattern for S-methoprene suggest that runoff
and spray drift are not the principal potential transport mechanisms of S-methoprene to
the aquatic and terrestrial habitats of the CRLF. The relevant exposure pathway is direct
application of S-methoprene to water and/or to land as a liquid formulation or as a
sustainable release rate formulation.
Measures of exposure are based on aquatic and terrestrial models that predict estimated
environmental concentrations (EECs) of S-methoprene using maximum labeled
application rates and methods of application. The scenario used in this risk assessment to
predict aquatic EECs is direct application of S-methoprene formulations to 1ft of shallow
water. The sustainable release forms of S-methoprene were approached through
calculations and extrapolations of expected environmental release rate from label
44
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information and efficacy studies. In addition the Agency also used adjusted field
microcosm concentrations that were submitted by the registrant for these formulations.
Exposure estimates for the terrestrial-phase CRLF and terrestrial invertebrates and
mammals (serving as potential prey) assumed to be in the target area or in an area
exposed to S-methoprene use are derived using the T-REX model (version 1.3.1,
12/07/2006). The T-REX model incorporates the Kenega nomograph, as modified by
Fletcher et al. (1994), which is based on a large set of actual field residue data. The upper
limit values from the nomograph represented the 95th percentile of residue values from
actual field measurements (Hoerger and Kenega, 1972). For modeling purposes, direct
exposures of the CRLF to S-methoprene through contaminated food are estimated using
the EECs for the small bird (20 g) which consumes small insects. Dietary-based and
dose-based exposures of potential prey (small mammals) are assessed using the small
mammal (15 g) which consumes short grass. The small bird (20g) consuming small
insects and the small mammal (15g) consuming short grass are used because these
categories represent the largest RQs of the size and dietary categories in T-REX that are
appropriate surrogates for the CRLF and one of its prey items. Estimated exposures of
terrestrial insects to S-methoprene are bound by using the dietary based EECs for small
insects and large insects. These approaches are parameterized using relevant reviewed
registrant-submitted environmental fate data.
2.10.1.2 Measures of Effect
Measures of effect are obtained from a suite of registrant-submitted guideline studies
conducted with a limited number of surrogate species and/or from acceptable open
literature studies (EPA 2004, USFWS/NMFS 2004). The acute measures of effect
routinely used for listed and non-listed animals in screening level assessments are the
LD50, LC50 or EC50, depending on taxa (see Table 2.8). LD stands for "Lethal Dose", and
LD50 is the amount of a material, given all at once, that is estimated to cause the death of
50% of a group of test organisms. LC stands for "Lethal Concentration" and LC50 is the
concentration of a chemical that is estimated to kill 50% of a sample population. EC
stands for "Effective Concentration" and the EC50 is the concentration of a chemical that
is estimated to produce some measured effect in 50% of the test population. Endpoints
for chronic measures of exposure for listed and non-listed animals are the NOAEL or
NOAEC. NOAEL stands for "No Ob served-Adverse-Effect-Level" and refers to the
highest tested dose of a substance that has been reported to have no harmful (adverse)
effects on a test population. The NOAEC (i.e., "No-Observed-Adverse-Effect-
Concentration") is the highest test concentration at which none of the observed results
were statistically different from the control.
Table 2.8. Acute and Chronic Measures of Effect.
TAXA
ASSESSMENT
MEASURE OF EFFECT
Aquatic Animals {Freshwater fish
and inverts.
Acute
Lowest tested EC50 or LC50 (acute toxicity tests)
Chronic
Lowest NOAEC (early life-stage or full life-cycle tests)
45
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TAXA
ASSESSMENT
MEASURE OF EFFECT
Terrestrial Animals
Birds
Acute/Subacute
Lowest LD50 (single oral dose) and LC50 (subacute
dietary)
Chronic
Lowest NOAEC (21-week reproduction test)
Terrestrial Animals
Mammals
Acute
Lowest LD50 (single oral dose test)
Chronic
Lowest NOAEC (two-generation reproduction test)
3.0 Exposure Assessment
3.1 Measure of Aquatic Exposure
Although, this compound has several indoor uses, this risk assessment will be focused on
those outdoor uses that have the potential for S-methoprene exposure to fish and wildlife
and the CRLF. Since S-methoprene is efficacious to Dipteran larvae, the effective mode
of application to potential breeding areas is a direct application to water for liquid
formulations, as well as, sustainable release rate formulations (briquets, granular). Target
sites are any area or site of standing water. Non agricultural and agricultural land that is
flooded is also registered for S-methoprene use. Since the compound can be applied to
rice and caneberry flooded fields, the Agency derived EEC values by using the Tier I rice
model (Appendix G). In order to evaluate exposure from direct application to water from
application of sustainable release formulations, the Agency has used extrapolated values
from label information that reflect direct application to 1 ft of water (Appendix I).
Granular formulations were assessed by extrapolating S-methoprene release rate relative
to the size of the granular and its expected length of efficacy in the environment. The
aquatic EECs represent upper bound water column values, calculated without any
consideration for S-methoprene degradation (photolysis or biodegradation) or adsorption
to particulate/ sediment.
Table 3.0 Maximum Rate of S-Methoprene Formulations that are Applied Directly
to Water (Extrapolated Values from Label Information)
I se
l-'ormulalion
\|)|)
Max.
Peak I'.r.C
2l-da\
(>0-da\ I'l'C
Inlenals
Kale (Ills
(|)|)b)
i:i.(
(d;i\s)
;ii/ \/d;i\)
(|)|)b)
Woodland
pools,
Briquet
150
0.0058
2.0
2.0
2.0
swamps, rice
fields, storm
Briquet XR
30
0.014
5.04
5.04
5.04
drains, etc.
Woodland
pools,
Granular
7
0.06
0.06
.06
0.06
swamps,
berry bogs,
Sand mix
7
0.017
0.017
0.017
0.017
rice fields,
irrigated crop
lands, etc.
Woodland
46
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I so
l-'oi'inuliilioii
App
lnlor\;ils
ul.ijs)
M;i\.
Kiilo (Ills
;ii/.\/d;i\)
iViik r.r.c
(|)|)b)
2l-d;i\
r.r.c
)
r.r.c
(|)|>l>)
pools, heiT\
bogs, rice
fields,
irrigated crop
lands, etc.
Liquid
"
our,
4X1
In addition to extrapolated values, the Agency has also used microcosm generated field
data submitted by the registrant for various slow release formulations (Appendix I). In
order to be comparative to the formulations used in the extrapolated exercise, the
microcosm values have been adjusted. This approach provides a range of EEC values that
can be used in the development of aquatic risk quotients (RQ).
Table 3.1 Adjusted Environmental Concentrations of S-Methoprene Found in
Freshwater Microcosm
l so
roi'inuliilioii
l>o;ik l.l.( (|)|)l>)
2i-d;i\ r.r.c
r.r.c
(ppl))'
Woodland
pools,
Briquet
4.24
0.13
0.13
swamps, rice
fields, storm
Briquet XR
3.37
0.96
0.96
drains, etc.
Woodland
pools,
Granular
0.06
0.06
0.06
swamps,
berry bogs,
Sand mix
0.017
0.017
0.017
rice fields,
irrigated crop
lands, etc.
Woodland
pools, berry
bogs, rice
fields,
Liquid
2.21
0.255
0.203
irrigated crop
lands, etc.
Study was not conducted beyond 35 days. Therefore values for the 60-day EEC will be the values recorded at 35
days.
3.1.1 Monitoring Data
S-methoprene has a limited set of surface water monitoring data relevant to the CRLF
assessment. No surface water monitoring studies which specifically targeted S-
methoprene use (application period and/or sites) were available for analysis as part of this
assessment. Generally, targeted monitoring data are collected with a sampling program
designed to capture, both spatially and temporally, the maximum use of a particular
pesticide. Because none of the available regional monitoring studies were designed
specifically for S-methoprene, they are considered 'non-targeted'. Typically, sampling
frequencies employed in monitoring studies are insufficient to document peak exposure
values. This coupled with the fact that these data are not temporally or spatially
47
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correlated with pesticide application times and/or areas limit the utility of these data in
estimating exposure concentrations for risk assessment. Monitoring data can be used to
set lower bounds on the occurrence in the environment, since concentrations were at least
as high as those found in the monitoring studies. For these reasons, baseline risk
assessments rely on model-generated values for estimating acute and chronic exposure
values, and the non-targeted monitoring data are typically used for qualitative
characterizations.
3.2. Measure of Terrestrial Exposure
3.2.1 Terrestrial Exposure Modeling
The EEC values used for terrestrial animal exposure are derived from the Kenaga
nomograph, as modified by Fletcher etal. (1994), based on a large set of actual field
residue data. The upper limit values from the nomograph represent the 95th percentile of
residue values from actual field measurements (Hoerger and Kenaga, 1972). The
Fletcher et al. (1994) modifications to the Kenaga nomograph are based on measured
field residues from 249 published research papers, including information on 118 species
of plants, 121 pesticides, and 17 chemical classes. These modifications represent the 95th
percentile of the expanded data set. Risk quotients are based on the most sensitive LC50
and NOAEC for birds (Bobwhite quail and mallard duck) and LD50 for mammals (based
on lab rat studies).
S-methoprene label instructions show that the terrestrial uses for the liquid formulations
(EC and FLC) are chemigation to ornamental woody plants, lawns, low pressure spray
around building premises, and application to fire ant mounds. Since, the maximum
application to a terrestrial site (ornamental woody plants) is 0.5829 lbs ai/A, the Agency
derived EECs (Table 3.2) and assumed this to be a upper bound scenario. Using the T-
REX model (version 1.3.1, December 22, 2006) with maximum input values (4
applications at 0.5829 lb a.i./A with a 7-day application interval) the Agency was able to
estimate terrestrial exposure for avian and mammalian species.
Table 3.2 Estimated Environmental Concentrations (in mg/kg; parts per million
(ppm) on Potential Food Items Following Label-Specified Applications (4
Applications at 0.5829 lb a.i./Acre, a 7-Day Application Interval) of S-Methoprene
Using T-REX
DIETARY-BASED EECs
Estimated Environmental Concentrations
(ppm)
Upper Bound
Mean
Short Grass
262
93
Tall Grass
120
39
Broadleaf Plants/Small Insects
147
49
Fruits/Pods/Seeds/Large Insects
16
8
Table 3.3 characterizes S-methoprene granular LD50/square foot using the T-REX model.
In order to evaluate risk from exposure to granular formulations, the Agency has modeled
a scenario with maximum application to the area around citrus orchards. The label
48
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information indicates that prior to flooding or in anticipation of flooding, granular S-
methoprene can be broadcast to a terrestrial area like citrus (0.3 lbs ai/A). Although frogs
do not feed on granular particles this scenario was included as a upper bound scenario.
The values noted in Table 3.3 reflect maximum application of the granular formulation to
terrestrial areas where the CRLF may be found. A complete description of the input
parameters and output is contained in Appendix H
Table 3.3 Characterization of S-Methoprene Granular LD50/Square Foot Using T-
REX for a 20 g bird (Granular Weight = 0.43 mg)
Estimation of the number of granules needed to achieve toxicity thresholds
No. of granules needed to achieve adjusted LD50
114984.17
No. of granules needed to achieve Acute LOC exceedance (1/2
adjusted LD50)
57492.09
No. of granules needed to achieve Endangered Species LOC
exceedance (1/10 adjusted LD50)
11498.42
Minimum Foraging Area Needed to Allow for Ingestion of Sufficient Mass of a.i. to
Achieve LOC Exceedance
Foraging area (square feet) needed to achieve LOC exceedance
assuming 100% feeding efficiency
0.66
Foraging area (square feet) needed to achieve LOC exceedance
assuming 50% feeding efficiency
1.33
Foraging area (square feet) needed to achieve LOC exceedance
assuming 10% feeding efficiency
6.65
Table 3.4 shows acute and chronic RQ values for food items (e.g. small and large insects)
that terrestrial-phase CRLF may utilize. The values are based on upper bound Kenaga
values for T-REX and show no acute risk to avian species or chronic risk to mammalians.
Avian reproductive study did not show a LOEC but the NOAEC was found to be 32 ppb.
Table 3.4 Acute and Chronic RQs for Terrestrial-Phase CRLF (Based on Upper
Bound Kenaga Values from T-REX).
DIETARY CATEGORY
Acute Avian RQ:
Dose-Based
Acute Avian RQ:
Dietary-Based
Mammalian
Chronic RQ:
202
100 u
Dictarv-Bascd
Broadleaf plants/small insects
0.09
0.07
0.01
0.0
Fruits/pods/seeds/large insects
0.02
0.01
0.00
0.2
Bolded RQs exceed the Agency's endangered species LOC
3.2.2 Terrestrial Plant Exposure
S-methoprene is non-toxic to plants. Residues studies on wheat have shown that this
compound does not translocate in plants and is not picked-up from soil.
4. 0 Effects Assessment
Based on the available data, S-methoprene is characterized as acutely very high to
moderately toxic to freshwater fish. S-methoprene is highly toxic to freshwater
invertebrates on an acute basis and chronically toxic to the developing juveniles (growth
effects). Aquatic predatory insects appear to show moderate acute toxicity after S-
49
-------
methoprene exposure. Terrestrial organisms appear to be less sensitive to S-methoprene
exposure. Avian and mammal species show practically no acute toxic effects after
exposure to S-methoprene. Toxicity data for terrestrial invertebrates that are chronically
exposed to S-methoprene are not currently available. See Table 4.0 for the assessment
endpoints used in this assessment {i.e., the most sensitive acute and chronic endpoints for
each taxon assessed here).
Table 4.0 Summary of Specific Assessment Endpoints Considered in This
Assessment.
TAXA
MEASURE OF EFFECT
Survival, growth and/
or reproduction of:
Species
Toxicity
Endpoint
Freshwater Fish
Acute
Rainbow trout
('Oncorhynchus mykiss)
96 hr LC50 = 0.76 mg/L
Mortality
Chronic
Fathead minnow
(Pimephales promelas)
NOAEC = 0.048 mg/L
Growth affected
Freshwater
Acute
Invertebrates
Daphnia magna
EC.,,, = 0.33 mg/L
Mortality
Chronic
Daphnia magna
NOAEC = 0.051 mg/L
Growth Effects
Birds
Acute
Mallard duck (Anas
platyrhynchos)
LC50>10,000 ppm
Mortality
Mallard duck (Anas
platyrhynchos)
LD50>2,000 mg ai/kg
Mortality
Chronic
Mallard duck
(Anas platyrhynchos)
NOAEC at 3 and 30 ppm.
No reproductive effects
Mammals
Acute
Rat
(Rattus norvegicus)
LDso >5.000 mg/kg
Mortality
Chronic
Rat
(Rattus norvegicus)
NOEL = 2,500 ppm
No adverse effects
Aquatic Insect
Acute
Water boatman
(Corisella decolor sp.)
24 hr LC50 = 1.20 mg/L
Mortality
50
-------
4.1 Evaluation of Terrestrial Ecotoxicity Studies
4.1.1 Terrestrial Plant Exposure
S-methoprene is non-toxic to plants. Residues studies on wheat have shown that this
compound does not translocate in plants and is not picked-up from soil.
4.1.2 Bird and Mammal Hazard Assessment
4.1.2.1 Avian Toxicity Studies
An acute oral toxicity study using the technical grade of the active ingredient (TGAI) is
required to establish the toxicity of S-methoprene to birds. The preferred test species is
either mallard duck {Anasplatyrhynchos; a waterfowl) or Bobwhite quail (Colinus
virginianus', an upland game bird). Results of these studies are summarized below in
Table 4.0. S-methoprene has been shown to be practically non-toxic to avian species as
noted in the mallard duck and Bobwhite quail acute studies where toxicity ranges from
LD50 >2,000 mg/kg to LC50 = 10,000 ppm. No reproductive effects at 3 and 30 ppm for
Bobwhite quail (Table 4.1).
Table 4.1 Summary of Avian Toxicity for S-
Methoprene
Tesl Species
»» <11
I'lnripoim
To\icil>
( iilciinn
MRU) No.
Aulhor/Yciir
Sluclj
Chissiriciilion 1
Acute Toxicity
Mallard duck
Tech.
LD50>2,000 mg ai/kg
Practically non-
003202508
Acceptable
(Anas
toxic
Fink/1972
platyrhynchos)
Bobwhite quail
(Colinus
Tech
LC50 > 10,000 ppm
Practically non-
toxic
003202509
Fink/1972
Acceptable
virginianus)
Mallard duck
(Anas
Tech.
LC50>10,000 ppm
Practically non-
toxic
003202509
Fink/1972
Acceptable
platyrhynchos)
Chronic Toxicity
Bobwhite quail
(Colinus
Tech.
No reproductive effects at 3 and 30 ppm.
003202511
Fink&Reno/
Acceptable
virginianus)
1973
4.1.2.2 Mammal Studies
Summaries of the most sensitive toxicity values (acute and chronic) for mammals are
shown in Table 4.2. The acute oral LD50 for the racemic and S-methoprene in rats is
>10,000 (Hallesy et al., 1972) and 5,000 mg/kg (Shindeler and Brown, 1984),
respectively. The acute dermal LD50 for both the racemic and the S-methoprene in rabbits
is >2,000 mg/kg (Hamiliton, 1972; Brown 1984, respectively). A 2 year chronic feeding
test showed that rats expose to S-methoprene at 0, 250, 1000, or 5,000 ppm in the daily
diet did not exhibit any adverse health effects when compared to controls (Wazeter &
Goldenthal, 1975). The data show that methoprene (racemic or S-methoprene) has an
51
-------
extremely low potential for acute toxicity to mammals via oral, dermal, or chronic routes
of exposure. Data are available for evaluating reproductive effects of S-methoprene to
mammals. The three-generation rat reproduction study showes a NOEL = 2,500 ppm and
no reproductive effects. These results suggest that chronic exposure of mammals to S-
methoprene is not expected to cause developmental toxicity.
Table 4.2 Summary of Mammalian Toxicity Studies for S-Methoprene and RS-
Methoprene
Tesl
Species
o.'
*" <11
Tesl Dui'iiliun
I'lmlpoini
MRU) No.
AulhorAciir
Sluclj
Cliissiriciilion
kat
(Rattus
norvegicus)
RS-methoprene
tech
14-day
LD50 >10,000
mg/kg
00024607
Hallesy et o/./l 972
Acceptable
Rat
(Rattus
norvegicus)
S-methoprene
tech
14-day
LD50 >5,000
mg/kg
00150132
Shindler & Brown/
1984
Acceptable
Rabbit
RS-methoprene
tech
Acute dermal
LC50>2,000
mg/kg
00024617
Hamilton/ 1972
Acceptable
Rabbit
S-methoprene
Acute dermal
LCso>2,000
mg/kg
00150133
Brown/1984
Acceptable
Rat
(Rattus
norvegicus)
RS-methoprene
tech
90-days
NOEL = 500
ppm
00024612
Jorgenson &
Sasmore/1972
Acceptable
Rat
(Rattus
norvegicus)
RS-methoprene
tech
2-year
NOEL = 5,000
ppm
00010739
Wazeter &
Goldenthal/1972
Acceptable
Rat
(Rattus
norvegicus)
RS-methoprene
tech
Three
generation
reproduction
NOEL = 2,500
ppm
00010741
Kileen &
Rapp/1974
Acceptable
4.1.1.3 Toxicity of S-Methoprene to Insects
Although S-methoprene is most toxic to Dipterans, it is also toxic to non-target species
that include Hemiptera, Lepidoptera, and Coleopteran. Mosquitoes are very sensitive to
methoprene exposure at about 0.001 mg/L (Lawler, 2000). The available acute toxicity
tests that were conducted on non-target insects are presented in Table 4.3.
Table 4.3 Toxicity of RS-Methoprene to Insects
Species
--»» <11
RS-mclhoprcnc
Results
Reference
Water boatman
(Corisella decolor sp.)
10
96 hr LC50 = 1.65 mg/L
Miura, 1973
Backswimmers
(N. unifasciata)
10
24 hr LC50 = 1.20 mg/L
Miura, 1973
Honey bee
/Apis mellifera L.)
10
31 day feeding. No effect at
1000 ug/L methoprene
Barker and
Waller, 1978
Diving Beetles
(Laccophilus sp.)
10
72 hr LC50 = 2.0 mg/L
Miura, 1973
Mosquitoes larvae
(Ochlerotatus nigromaculis)
10
Toxic effect at 1.0 ug/L
Miura, 1973
52
-------
4.2 Evaluation of Aquatic Ecotoxicity Studies
4.2.2 Aquatic Hazard Assessment
4.2.1.1 Fish Toxicity Studies
The Agency has summarized available acute fish studies and concluded that S-
methoprene is highly to moderately toxic (0.37-1.52 mg/L to warm water freshwater fish
and highly to practically non-toxic (0.76-106 mg/L) to coldwater, freshwater fish. Acute
toxicity on the metabolite ZR-1946 shows an LC50 = 36.9 mg/L suggesting slight toxicity
Table 4.4).
Table 4.4 Summary of Fish Toxicity Studies for S-methoprene (Parent Compound,
Metabolites, Formulation)
Species
ai)
Results
MRU)
Cliissiricaliun
Freshwater Species
Bluegill sunfish
(Lepomis
macrochirus)
Tech.
96hrLC50 =1.52 mg/L
00010388
Acceptable
Tech
96hr LC50 > 0.37 mg/L
43351902
Supplemental
Rainbow trout
(Oncorhynchus
mykiss)
Tech.
96hr LC50= 1.6 mg/L
2033423
Supplemental
Tech
96hrLC50 = 4.39 mg/L
2033423
Supplemental
Tech
96hr LC50 > 50 mg/L
00010643
Acceptable
Tech.
96hr LC50 =106 mg/L
2033423
Supplemental
Tech
96 hr LC50 = 0.76 mg/L
(0.24 - 1.2 mg/L)
43351901
Supplemental
10
96hr LC50 = 28.4 mg/L
2033423
Supplemental
4E
96hr LC50 = 6.0 mg/L
2033423
Supplemental
Metabol
ite ZR-
1946
96hrLC50 = 36.9 mg/L
2033423
Supplemental
53
-------
Species
("<" :ii)
Results
MRU)
Chissiriciilion
(methop
rene
acid)
10
96hrLC50 =52.7 mg/L
2033423
Supplemental
10
96hr LC50=1.55 mg/L;
(1.10-2.41 mg/L)
Supplemental
68.9
24hr LC50>10.0 mg/L
Supplemental
68.9
24hr LC50=80.0 mg/L
(80 -100 mg/L)
Supplemental
A chronic toxicity study on the fathead minnow produced a NOAEC value of 48 ug/L
and a LOAEC of 84 ug/L. The effects that were noted included decreased weight and
length of juveniles. No other effects were noted (Table 4.5).
Table 4.5 Freshwater Fish: Chronic Exposure (Growth/Reproduction) Studies
Species
iii
I'.ITecl
MRU)
Cliissiriciilion
Fathead minnow
(Pimephales
promelas)
Tech
NOAEC = 48 ug/L
LOAEC = 84 ug/L
Growth effects
42811201
Supplemental
4.2.1.3 Toxicity to Aquatic Freshwater Invertebrates
Acute toxicity studies on Daphnia magna showed 48 hr EC50 =0.33 -0.36 mg/L
suggesting that S-methoprene is highly toxic to freshwater invertebrates on an acute
basis. Chronic toxicity to daphnid early life stages showed effects on growth at 0.051
mg/L (Table 4.6).
Table 4.6 Freshwater Invertebrates Acute Toxicity Studies with S-Methoprene
Species
0/ ,,!
/<» <11
i:iTec(
MRU)
( liissiriciilion
Acute Toxicity
Daphnia magna
Tech.
48 hr. EC50 = 0.36 mg/L
(0.21-0.55 mg/L)
43163301
Supplemental
Daphnia magna
Tech.
48hr. EC50 = 0.33 mg/L
(0.11 -0.52 mg/L)
003203609
Acceptable
Chronic Toxicity
Daphnia magna
Tech.
LOAEC = 0.051 mg/L
2033145
Supplemental
4.2.1.4 Field Studies: Non-target organisms
A comprehensive study on the effects of S-methoprene to nontarget aquatic organisms
was conducted in Minnesota by the Metropolitan Mosquito Control District (Hershey el
54
-------
a/.,1998). Wetlands in Wright County were sampled for three years (1988-1990) in order
to evaluate natural variability in 179 genera of insect. After this baseline sampling, eight
of the wetlands were treated six times during the spring and the summer at 3-week
intervals (1991-1993) with S-methoprene at 0.05-0.058 kg a.i./ha (0.275 - 0.32 lbs ai/A)
based on a 4% a.i. formulation as a 20-d release granule). Nine other sites were treated
with Bacillus thuringiensis israe/ensis (Bti) and nine were left untreated. During the first
year of treatment, S-methoprene exposure had minimal effects on nontarget insect
groups. However, in the second and third years researchers noted a significant reduction
in taxa richness of Tipulidae, Ceratopogonidae, and Stratiomyidae. Insect density was
reduced by 57 - 83% and biomass reduction amounted to 50-83% during this test period
(Niemi et al., 1999). Examination of the reproductive success of red-winged blackbirds
(Agelaiusphoeniceus) did not indicate that S-methoprene exposure had an adverse
impact. Ali (1991) evaluating S-methoprene (Altosid Liquid Larvicide 5%) efficacy
against midges (Chironomidae) in experimental ponds found that at 0.28 kg a.i./ha (1.5
lbs ai/A) was effective against tanytarsini and chironomini. He also noted that this
formulation had very little effect on chironomids when it was applied at 0.015 kg a.i./ha
(0.075 lbs ai/A). Pinkney et al., (2000) investigated the non-target effects of S-
methoprene (Altosid Liquid Larvicide 5%) in experimental ponds at the Patuxent
Wildlife Research Center, Maryland. Researchers sprayed (0.011 kg a.i. kg/ha, 0.06 lbs
ai/A) the ponds three times at 3-week intervals and insect-emergence was evaluated
before and after spraying. Relative to controls, the emergence data showed only isolated
cases of significant non-target insect reductions in the sprayed ponds, and the Hester-
Dendy data showed no significant difference between the S-methoprene and control
ponds. Norland and Mulla (1975) using experimental ponds, exposed caged mayfly
nymphs (Callibaetispacificus) to an emulsified concentration of S-methoprene (1.56 lbs
a.i./A; 0.30 kg a.i./ha). Emergence was tracked at 4 hours and again at 4 days after
treatment. The results show substantial decrease in the percentage emerging from
exposure groups relative to controls.
Table 4.7 Overview of S-methoprene Field Studies and Effects to Non-Target Insects
Researcher
Amount of S-mclhoprcnc
used
Results relative to iioii-
largcl insects
Pinkeny et al., (2000)
0.011 kg a.i./ha (0.06 lbs
ai/A); EC
Little to no effect to non-
target insects.
Ali (1999)
0.28 kg a.i./ha (1.5 lbs
ai/A); EC
Tanytarsini and
chironomini populations
effected.
0.015 kg a.i./ha; EC
No effects
Hershey etal., 1998
1.1 - 13.20.058 kg a.i./ha
(0.27 -0.32 lbs ai/A); 20-
day slow release granule.
1st year there were no
significant effects. 2nd and
3r years population effects
were noted for Tipulidae,
Ceratopogonidae, and
Strati omyidae.
Norland and Mulla (1975)
0.3 kg a.i./ha (1.56 lbs
Caged mayflies. Substantial
55
-------
ai/A); EC
decrease in emergence.
5.0 Risk Characterization
5.1 Risk Estimation - Integration of Exposure and Effects Data
Risk characterization is the integration of exposure and ecological effects characterization
to determine the potential ecological risk from registered uses of S-methoprene, and the
likelihood of direct and indirect effects to CRLF in aquatic and terrestrial habitats. For
the screening-level portion of this assessment, the deterministic risk quotient method is
used to provide a metric of potential risks. The RQ is a comparison of exposure
estimates to toxicity endpoints; estimated exposure concentrations are divided by acute
and chronic toxicity values. The resulting unit less RQs are compared to the Agency's
levels of concern (LOCs) (see Table 5.0). LOCs are used to indicate when the use of a
pesticide, as directed on the label, has the potential to cause adverse effects on non-target
organisms.
Table 5.0 Agency Levels of Concern (LOC)
Risk
Description
RQ
Taxa
Acute
Potential for acute risk to non-target organisms
which may warrant regulatory action in addition
to restricted use classification
acute RQ >0.5
aquatic animals,
mammals, birds
Acute Restricted
Use
Potential for acute risk to non-target organisms,
but may be mitigated through restricted use
classification
acute RQ >0.1
aquatic animals
acute RQ > 0.2
mammals and
birds
Acute Listed
Species
Listed species may be potentially affected by
use
acute RQ > 0.05
acute RQ >0.1
aquatic animals
and terrestrial
invertebrates
mammals and
birds
Chronic
Potential for chronic risk may warrant
regulatory action, listed species may potentially
be affected through chronic exposure
chronic RQ > 1
all animals
Non-Listed and
Listed Plant
Potential for effects in non-listed and listed
plants
RQ > 1
all plants
5.2 Potential for Direct Effects
5.2.1 Aquatic-Phase of CRLF
Based on surrogate freshwater toxicity data and extrapolated and actual field EECs, the
Agency has calculated RQ values to reflect a wide range of uncertainty. The extrapolated
values are theoretical expected environmental water concentration and were calculated
56
-------
from label information regarding weight of briquete or granular, the amount of active
ingredient present, and the expected efficacy of the formulation in the field. This
approach reflects upper-bound values and assumes a steady state release rate, no
degradation, and no adsorption to particulate. The aquatic areas that this approach is
expected to simulate are stagnant water bodies of about 1 foot in depth. These areas are
the most prolific breeding grounds for mosquitoes. Although S-methoprene is not used on
agricultural crops, flooded agricultural lands are registered for S-methoprene applications
(i.e. rice, caneberries). In addition to this extrapolated approach, the Agency is also using
field concentrations (Table 5.1) that were generated in a controlled freshwater microcosm
study (Judy and Howell, 1992).
Table 5.1 Acute and Chronic RQs for Aquatic Organisms Based on EECs from
Extrapolated S-Methoprene Release Rates for Granular, Briquets, Sand Mix, and
Liquid Formu
ations Applied to a Shallow (1 ft
1 Acre Body of Water
loiinulitlioii
ivak i:i:c
(ug/l.)
Acule RQ
35 day 11IX
(ug/L)
Chronic RQ
freshwater Fish
LC50 = 760 ug/L
(NOAEC = 48 ug/L)
Briquets
2.0
0.00
2.0
0.04
Briquet XR
5.04
0.01
5.04
0.10
Granular
22.0
0.03
22.0
0.46
Sand Mix
6.2
0.01
6.2
0.13
Liquid
0.5853
0.00
0.5853
0.01
Freshwater Invertebrates
EC50 = 330 ug/L
NOAEC = 51 ug/L
Briquets
2.0
0.01
2.0
0.04
Briquet XR
5.04
0.01
5.04
0.10
Granular
22.0
0.07
22.0
0.43
Sand Mix
6.2
0.02
6.2
0.12
Liquid
0.5853
0.00
0.5853
0.01
The extrapolated EEC values in Table 5.0 produced low RQs generated from the five S-
methoprene formulations that are registered for use on a wide range of aquatic areas that
may support mosquito populations (marshes, swamps, culverts, wetlands, flooded
orchards, flooded agricultural fields, old tires, etc). These formulations are slow release in
order to be efficacious over a period of time (7-150 days) when applied directly to
water. Using the acute and chronic fish data as a surrogate for the aquatic-phase of the
CRLF, the RQ values (acute RQs = 0.0 - 0.03; chronic RQs = 0.1 - 0.13) prove to be less
than the acute endangered (acute LOC >0.05; chronic LOC>1.0), suggesting a "no effect"
to these organisms. The Agency has also evaluated the EECs that were generated in the
microcosm study where actual S-methoprene levels were measured over a period of time
(35 days). The environmental concentrations that were generated in the microcosm study
were adjusted to reflect the current maximum rates and percent active of the formulations
in Table 5.2. These measured concentrations were generally lower than the extrapolated
values and reflected some initial fluctuation in S-methoprene levels (an initial high
release rate before a steady state was achieved). However, the RQs generated from the
upper bound values from this field data also suggest no direct acute or chronic risk from
S-methoprene exposure to the aquatic-phase of the CRLF.
57
-------
Table 5.2 Acute and Chronic RQs for Aquatic Organisms Based on Maximum
Adjusted EECs from Microcosm Treated With S-Methoprene Granular,Briquets,
Sand Mix, and Liquid Formulations
rormuhilion
1*0:1 k i:i:c
(llg/l.)
Acule RQs
35 day 11IX
(ug/L)
Chronic RQs
freshwater Fish
LC50= 760 ug/L
(NOAEC = 48 ug/L)
Briquets
4.24
0.00
0.14
0.00
Briquet XR
3.37
0.00
0.96
0.02
Granular
2.10
0.00
0.21
0.00
Sand Mix
0.35
0.00
0.20
0.00
Liquid
2.21
0.00
0.20
0.00
Freshwater Invertebrates
ECso = 330 ug/L
NOAEC = 51 ug/L
Briquets
4.24
0.01
0.14
0.00
Briquet XR
3.37
0.01
0.96
0.02
Granular
2.10
0.01
0.21
0.00
Sand Mix
0.35
0.00
0.20
0.00
Liquid
2.21
0.01
0.20
0.00
The probit dose-response slope can be used to calculate the chance of an individual event
corresponding to the listed species acute LOCs and/or RQs. The analysis uses the EFED
spreadsheet IEC (version 1.1 .xls). It is important to note that the IEC model output can
go as low as 1 x 10"16 in estimating the event probability for animals. This cut-off is a
limit in the Excel spreadsheet environment and is not to be interpreted as an agreed upon
lower bound threshold for concern for individual effects in any given listed species. If
information is unavailable to estimate a slope from a study, a default slope assumption of
4.5 is used as per original Agency assumptions of typical acute toxicity dose-response
slope cited in Urban and Cook (1986).
The slope for the LC50 of the most sensitive acute freshwater fish (rainbow trout; LC50 =
760 |ig a.i./L) was not available. Therefore, the default slope of 4.5 was used in
determining the chance of an individual effect. Using the acute endangered species LOC
of 0.05, the chance of an individual mortality for aquatic-phase CRLF is ~ 1 in
418,000,000 suggesting "no effect" of S-methoprene direct exposure to the aquatic-
phase CRLF (Table 5.3).
Table 5.3 Chance of Individual Acute Effects to Aquatic-Phase CRLF Using
Surrogate Freshwater Fish Toxicity Data and the Probit Slope Response
LOC OR USE
LOC
PROBIT SLOPE
CHANCE OF AN
SITE
OR RQ
INDIVIDUAL EFFECT
SCENARIO
(RQ)
Acute
0.05
Slope
4.5
~ 1 in 418,000,000
Endangered
Upper Bound
2.32
~ 1 in 418,000,000
Species LOC
Lower Bound
6.15
~ 1 in 418,000,000
58
-------
5.2.2 Terrestrial-Phase of CRLF
Based on surrogate avian toxicity data, the maximum allowable application rate (4
applications, 0.013 lbs a.i./acre/application, 7-day application interval), the body-weight
scaling factor for S-methoprene from Mineau et al. (1996) of 1.0778, and upper bound
Kenaga values from T-REX, there is no potential for direct adverse effects on terrestrial-
phase CRLF individuals from S-methoprene use in California (see Appendix H). Using
calculations based on bird ingestion rates and dietary and weight categories for the
CRLF, Table 3.4 shows RQ values for acute avian dose-base risk at 0.07 - 0.09 for 100 -
20g birds that consume small insects and RQs = 0.01 - 0.02 for the same size group
consuming large insects. The acute avian dietary-based RQs ranged from 0.0 - 0.1, while
the mammalian chronic dietary-based RQ ranged from 0.0 - 0.2. These RQ values do not
exceed the Agency's LOC for avian and mammalian endangered species concerns (acute
LOC>0.1). Additionally, the granular LD50/square foot results that were generated in T-
REX also suggest that the broadcast application of S-methoprene granulars should not
create an acute toxicity concern for the terrestrial-phase of the CRLF or to birds and
mammals in general. The number of granules needed to achieve the adjusted LD50 are
about 114,984 suggesting an unlikely event (Appendix H, Table H.2).
5.3 Potential for Indirect Effects (Decreased Availability of Food Items)
5.3.1 Aquatic-Phase of CRLF
Aquatic-phase CRLF are known to eat diatoms, algae, and detritus (larvae CRLF) and
aquatic and terrestrial invertebrates (juvenile CRLF). Since S-methoprene is not toxic to
plants, only the invertebrate food sources will be assessed for potential indirect effects to
aquatic-phase CRLF. The one aquatic invertebrate LOC exceedance (0.07) calculated by
the Agency was for the 20% granular formulation (Table 5.1). However, this exposure
value was an extrapolated upper-bound and as a comparison, the corresponding adjusted
microcosm field value did not exceed the LOC (Table 5.2). In order to evaluate this
exceedance, the Agency also calculated the chance of individual aquatic invertebrate
exposure and risk by using the Individual Effects Chance Model (Version 1.1). These
calculations suggest that the chance of effects to an invertebrate food source from this
granular extrapolated exposure is about lin 988,000, which may be considered as a
highly unlikely event. As an additional indicator of possible risk, the acute and chronic
invertebrate RQs for the other formulations (using extrapolated and microcosm exposure
values) did not exceed LOCs for direct or indirect effects to the aquatic-phase CRLF.
Therefore, the Agency concludes a "may affect" but "not likely to adversely affect" for
the assessment point regarding the survival, growth, and reproduction of CRLF
individuals via effects to aquatic food supply.
5.3.2 Terrestrial-Phase of CRLF
Adult and juvenile CRLFs forage in aquatic and terrestrial habitats. The main food
sources for juvenile terrestrial-phase CRLFs are thought to be aquatic and terrestrial
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invertebrates. In addition to aquatic and terrestrial invertebrates, adults also feed on fish,
frogs, and small mammals. S-methoprene is classified as practically non-toxic to
mammals and avian species, as well as, predatory insects. Since the acute avian dose-
based RQs range from 0.01 - 0.09, the avian dietary-based RQs = 0.0 - 0.01, and the
chronic mammalian dietary-based RQs = 0.0 - 0.2 there are no LOC exceedances for the
terrestrial-phase of the CRLF. Therefore, there should not be an indirect affect to the
CRLF from S-methoprene exposure to potential terrestrial food items. Although, S-
methoprene is efficacious to Dipterian larvae, these organisms are not major components
of the CRLFs diet. Since, these frogs appear to be opportunistic feeders, a decline in adult
mosquitoes and black flies should not influence terrestrial feeding habits.
There were no endangered species exceedances for maximum application of liquid or
granular formulations. This suggests that there is very low potential for direct adverse
effects to terrestrial-phase CRLF from S-methoprene use in California. The slope for the
LC50 of the most sensitive avian species (mallard duck LD50 >2,000 ppm) was not
available. Therefore, the default slope of 4.5 was used in determining the chance of an
individual effect. Using the acute endangered species LOC of 0.05, the chance of an
individual mortality for terrestrial-phase CRLF is ~ 1 in 294,000 (Table 5.4).
Table 5.4 Chance of Individual Acute Effects to Terrestrial-Phase CRLF Using
LOC OR USE
SITE
SCENARIO
(RQ)
LOC
PROBIT SLOPE
CHANCE OF AN INDIVIDUAL
EFFECT
Acute
Endangered
Species LOC
0.05
Slope
4.5
~ 1 in 294,000
5.4 Potential for Adverse Effects on Designated Critical Habitat PCEs
For S-methoprene use, the assessment endpoints for designated critical habitat PCEs
involve a reduction and/or modification of food sources necessary for normal growth and
viability of aquatic-phase CRLFs, and/or a reduction and/or modification of food sources
for terrestrial-phase juveniles and adults. Since these endpoints are also being assessed
relative to the potential for indirect effects to aquatic- and terrestrial-phase CRLF, the
effects determinations for indirect effects from the potential loss of food items will be the
same as the effects determinations regarding the potential for adverse effects on
designated critical habitat PCEs.
Based on the best available information, the Agency has assessed the potential for direct
and indirect risk to CRLF from S-methoprene exposure. The conclusion is that there is a
"may affect", but "not likely to adversely affect" determination for the CRLF from the
use of S-methoprene. The assessment endpoints (Table 1.1) where this determination is
made include the following:
1) Survival, growth, and reproduction of CRLF individuals via effects to food
supply (i.e. freshwater fish and invertebrates, non-vascular plants);
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This assessment point reflects an LOC exceedance (0.07) for acute endangered species
concerns (LOC = 0.05) calculated from one of the upper bound extrapolated sustainable
release formulations (20% granular), although, the microcosm field values for the same
formulation did not exceed this LOC concern. In order to evaluate this exceedance, the
Agency also calculated the chance of individual exposure using the Individual Effects
Chance Model (Version 1.1). These calculations suggest that the chance of individual
effect from this granular extrapolated exposure is about lin 988,000, which may be
considered as a highly unlikely event. As an additional test of possible risk, the use of
acute and chronic fish and invertebrate toxicity data produced RQs for the other
formulations (using extrapolated and microcosm exposure values) that did not exceed
LOCs for direct or indirect effects to the aquatic-phase CRLF. Therefore, the Agency
concludes a "may affect" but "not likely to adversely affect" reading for this
assessment point.
The Agency acknowledges that S-methoprene is highly efficacious to Dipteran insect
larvae and that the use of this compound can result in a decline in emerging adult
populations. However, according to information of the CRLFs diet in Section 2.5.3 these
insects are not included in their diet. The Agency assumes that the CRLF is an
opportunistic feeder and will supplement its diet with available invertebrates and small
animals. Therefore, the Agency concluded "no habitat modification" from S-methoprene
use. Although there is widespread overlap of potential S-methoprene with watersheds of
the CRLF the Agency has also determined that there is no potential for modification of
CRLF designated critical habitat (aquatic or terrestrial plants) from the use of S-
methoprene because this compound does not have herbicidal qualities or mode of action.
Further information on the results of the effects determination are included as part of the
Risk Description in Section 5.2.
6.0 Assumptions, Limitations and Uncertainties
6.1 Direct and Indirect Effects
6.1.1 Aquatic-Phase
Overall, the uncertainties inherent in the exposure assessment tend to result in both an
over-estimation and under-estimation of exposures. Among the most significant
overestimation of the total mass of S-methoprene to a single aquatic area is the
extrapolations of release rates for the sustainable release formulations (granulars,
briquets, sand mix). The values were calculated from label information and the expected
efficacy in the field. These were treated as upper-bound estimates because the Agency
did not take into consideration such mitigating factors as degradation and adsorption to
particulate and sediments. In addition the extrapolated values reflect a constant release
rate which may not occur in the environment. However, the Agency did temper these
uncertainties with field data from a microcosm study on similar formulations. After
adjusting these values to reflect the current maximum rates, these EECs were also used in
formulating a risk assessment.
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Additional factors that may account for under-estimation of exposure in this modeling
relative to the most vulnerable watersheds may include differences between pond
volume, field size, and flow dynamics relative to habitat characteristics of the CRLF.
6.1.2 Modeling Assumptions and Uncertainties
Overall, the uncertainties addressed in this assessment cannot be quantitatively
characterized. However, given the available data and the tendency to rely on
conservative modeling assumptions, it is expected that the modeling results in high-end
exposure estimates, particularly at the screening level.
In general, the simplifying assumptions used in this assessment appear from the
characterization in Section 3.2.6 to be reasonable. There are also a number of
assumptions that tend to result in over-estimation of exposure. Although these
assumptions cannot be quantified, they are qualitatively described. For instance,
modeling in this assessment for each S-methoprene use assumes that all applications have
occurred concurrently on the same day. This is unlikely to occur in reality, but is a
reasonable conservative assumption in lieu of actual data.
6.2. Uncertainties Related to Terrestrial Exposures
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. The field measurement
efforts used to develop the Fletcher estimates of exposure involve highly varied sampling
techniques. It is possible that much of these data reflect residues averaged over entire
above ground plants in the case of grass and forage sampling.
It was assumed that ingestion of food items in the field occurs at rates commensurate
with those in the laboratory. Although the screening assessment process adjusts dry-
weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food
intake estimates, it does not allow for gross energy differences. Direct comparison of a
laboratory dietary concentration- based effects threshold to a fresh-weight pesticide
residue estimate would result in an underestimation of field exposure by food
consumption by a factor of 1.25 - 2.5 for most food items.
Differences in assimilative efficiency between laboratory and wild diets suggest that
current screening assessment methods do not account for a potentially important aspect of
food requirements. Depending upon species and dietary matrix, bird assimilation of wild
diet energy ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85%
(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.
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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 the modeled treatment area.
6.3 Effects Assessment Uncertainties
6.3.1. Use of Surrogate Species to Represent Sensitivity to S-methoprene
Toxicity data for aquatic- or terrestrial-phase amphibians are not available for use in this
assessment. Therefore, fish and avian toxicity data, respectively, are used as a surrogate
for aquatic- and terrestrial-phase CRLFs. If the surrogate species are substantially more
or less sensitive than the CRLF, then risk would be over- or under- estimated,
respectively.
6.3.2. Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids, second instar for
amphipods, stoneflies, mayflies, and third instar for midges).
Testing of juveniles may overestimate toxicity at older age classes for pesticide active
ingredients that act directly without metabolic transformation because younger age
classes may not have the enzymatic systems associated with detoxifying xenobiotics. In
so far as the 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.
6.3.3 Sublethal Effects
For the acute risk assessment, the screening risk assessment relies on the acute mortality
endpoint. 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
is used to assess chronic risk. 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.
Some sublethal effects have been reported in toxicity studies. However, these effects
typically occurred at levels above the lowest NOAEC in fish that was used to derive risk
quotients. Also, no data are available to link the sublethal measurement endpoints to
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direct mortality or diminished reproduction, growth or survival that are used by OPP as
assessment endpoints.
6.3.4 Impact of Multiple Stressors on the Effects Determination
The influence of length of exposure and concurrent environmental stressors to the CRLF
(i.e., construction of dams and locks, fragmentation of habitat, change in flow regimes,
increased sedimentation, degradation of quantity and quality of water in the watersheds
of the action area, predators, etc.) will likely affect the species response to S-methoprene.
Additional environmental stressors may affect sensitivity to this compound, 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 an overestimation or underestimation of risk. However, as previously
discussed, the Agency's LOCs are intentionally set low, and conservative estimates are
made in the screening level risk assessment to account for these uncertainties.
6.3.5 Potential Exposure to Pesticide Mixtures
As discussed in Section 2.2, this assessment evaluates potential effects resulting from
exposure to S-methoprene and its degradates. In the environment, multiple chemical
stressors may co-occur. Quantifying the uncertainty of the presence of multiple stressors
is beyond the scope of this assessment; however, some studies have evaluated potential
interactive effects of several limited pesticide mixtures.
As discussed further in Appendix I, acute oral toxicity data (i.e., LD50 values) from
mammalian studies for formulated products that contain S-methoprene and one or more
additional active ingredients were also evaluated for potential interactive effects. The
LD50 values are potentially useful only to the extent that a wild mammal would consume
plants or animals immediately after these dietary items were directly sprayed by the
product. Given uncertainties associated with the differential rates of degradation,
transport, etc. for the active ingredients in the formulation with increasing time post
application, a qualitative discussion of potential acute mammalian risk of the multiple-ai
product relative to the single S-methoprene active ingredient is completed (USEPA
2004). While a quantitative evaluation of the data is not possible with currently accepted
scientific methods, as a screening tool, a qualitative analysis can be used to indicate if
formulated products exhibit interactive effects (e.g., synergism or antagonism).
6.4. Use Data
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
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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.
6.5 General Uncertainties
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.
When evaluating the significance of this risk assessment's direct/indirect and 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 modification to critical habitat.
6.6 Uncertainty Regarding Incidents that have Suggested S-Methoprene Affects
Insect Juvenile Hormone
Insect juvenile hormone (JH) is secreted by a pair of endocrine glands behind the brain
called the corpora allata. This compound is a regulator of insect development and
modifies the response to the molting hormone, 20-hydroxyecdysone. Most insect species
contain only juvenile hormone JHIII. To date JHO, JHI, and JHII have been identified
only in the Lepidoptera (butterflies and moths). The form JHB3 (JHIII bisepoxide)
appears to be the most important JH in the mosquitoes or flies. In larval insects, the JH-
JH receptor interaction insures that the outcome of a molt is to another larval stage, while
the absence of the JH-JH receptor binding results in a pupae or adult molt (Riddiford,
1996). Therefore, JH maintains larval and nymph characteristics in preadult insect stages
and suppresses metamorphosis from final larval to adult stage (Riddiford, 1996). Female
insect sexual maturity is also regulated by JH. Produced at high levels during larval
stages, JH is reduced to negligible amounts at the onset of the pupae stage. After or
during the transformation to mature adult the JH level increases again and influences egg
production. The development of immature insects to adult forms depends on a delicate
endocrine balance and can be affected by externally-introduced JH. Responses of insects
to this exogenous hormone may be expressed through a change in the rate of emergence,
the cessation of ecdysis, and the development of abnormal morphological features in
immature stages (Staal, 1975). S-methoprene is a pesticide that acts as an insect juvenile
hormone mimic disrupting the development of insects and preventing the larvae from
emerging as adults. Used primarily in mosquito management, S-methoprene also has the
potential to provide control against midge (Ali, 1981; Lothrop and Mulla, 1998).
Toxicity to Crustaceans
Although S-methoprene is used in mosquito management, and was developed as an
analogue to the insect juvenile hormone (JH) in order to disrupt larval development, there
have been concerns over possible impact to aquatic crustaceans. In evaluating the scope
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of possible impact to crustaceans from S-methoprene exposure we must take into
consideration the phylogenic close relationship between crustaceans and insects. This
information has been reinforced through research on the Hox gene, which shows where
the divergence in this gene can be traced in insects and crustaceans (Boore et al., 1998).
Both insects and crustaceans have similarities in their early developmental stages and
both have certain analogues compounds of similar function, insect JH and methyl
farnesoate (MF), the unepoxidated form of the insect juvenile hormone, in crustaceans
(Laufer and Biggers, 2001). Like JH in insects, the MF appears to be stimulatory to early
postembryonic larval stages and inhibitory in the larval-juvenile transitions. Because of
the conserved similarity of these two endocrine compounds in insects and crustaceans,
there is also the potential for toxic concern from S-methoprene exposure to crustaceans.
Toxicity to Amphibians
Reports of declining amphibian populations, as well as incidents of malformations in frog
(anuran) species across the United States have raised concern with various causal
explanations. Numerous reports have described occurrences of frog deformities with
links to UV radiation (Ankley et al., 1998), trematode parasites (Johnson et al., 1999),
and possible exposure to pesticides like S-methoprene. Since S-methoprene is used to
combat mosquitoes in urban and suburban wetlands, application of this compound can
coincide with anuran reproduction and subsequent early stages of tadpole development.
S-methoprene is an insect juvenile hormone (JH) analogue that can be converted to a
retinoid analogue after exposure to bacterial action and/or ultraviolet (UV) sunlight
(Harmon et al., 1995). This process occurs rapidly in an aquatic environment under
normal sunlight and temperature with a half-life of 30 hr at 1.0 ppb and 40 hr at 10 ppb
(Harmon et al., 1995). Since retinoids act as ligands during vertebrate development,
several researchers have expressed concern that S-methoprene exposure may have the
potential to cause developmental effects to amphibians, especially during metamorphosis.
Although JH is not present in vertebrate species, there is some evidence that S-
methoprene and its derivative, S-methoprene acid, are capable of binding to the retinoid
X receptor (RXR) and therefore may be able to effect vertebrate gene transcription
(Harmon et al.,\ 995). Using cell cultures CV-1 Scoff et al., (2004) found that retinoids
can affect two classes of receptors, retinoic acid receptors (RARs) and retinoid X
receptors (RXRs). The corresponding ligands that are formed were found to function as
transcription factors for regulating gene activity that is important in embryonic
development of body axes, brain and limbs. Schoff et at. (2004) noted that a degradate of
S-methoprene, methoxy-S-methoprene acid, acted as a ligand for RXRs and was capable
of activating transcription through RAR/RXR response elements. Working with frog
embryos, Minucci et al., (1996) found that during early development in Xenopus,
synthetic retinoids selective for RXR and RAR receptors caused striking malformations
along the anterior-posterior axis. In evaluating this potential problem, Degitz et al. (2003)
did additional studies on the developmental toxicity of S-methoprene and it's degradates
(S-methoprene acid, S-methoprene epoxide, 7-methoxycitronellal, and 7-
methoxycitronellic acid) to frog embryos (Xenopus laevis) and found that exposure to 0.5
mg/L of parent compound did not result in developmental effects. However, several
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degradates did produce developmental effects at 1.25 mg/L (S-methoprene acid), 2.5
mg/L (S-methoprene epoxide acid), 5 mg/L S-methoprene epoxide and 2.5 mg/L (7-
methoxycitronellal). No developmental or teratogenic effects were noted at > 30 mg/L for
7-methoxycitronellic acid. La Clair, (1998) noted that the lowest concentration of S-
methoprene exposed to sunlight shown to cause malformations was 7.5 mg/L, which is
1,700 times the level found under typical applications of S-methoprene. Degitz et al.
2003, suggested that typical field application of sustained-release formulations of S-
methoprene result in S-methoprene concentrations that do not exceed 0.01 mg/1,
suggesting that S-methoprene-mediated developmental toxicity to amphibians may be
overstated. It is unlikely that S-methoprene degradation products would accumulate in the
environment to concentrations that could affect amphibian development (Ankley, 1998).
Whether S-methoprene has played a role in the loss of the CRLF is unclear but appears to
be unlikely. The concentrations that have been reported in the environment are usually
below the toxicity threshold that has been established from laboratory studies or field
studies as noted in this assessment. There is still uncertainty in our understanding of the
long-term exposures and the additive role of predators, parasites, UV light, other
pesticides and other stressors to the wellbeing of the CRLF.
7.0 Addressing the Risk Hypotheses
In order to conclude this risk assessment, it is necessary to address the risk hypotheses
defined in Problem Formulation (Section 2.9). Based on the results of this assessment,
several hypotheses can be rejected, meaning that they are not of concern for the CRLF.
However, several of the original hypotheses cannot be rejected, meaning that the
statements represent concerns in terms of effects of S-methoprene on the CRLF.
Based on the results of this assessment, the following hypotheses can be rejected:
The labeled use of S-methoprene within the action area may:
directly affect the CRLF by causing mortality or by adversely affecting growth or
fecundity;
indirectly affect the CRLF by reducing or changing the composition of food
supply;
indirectly affect the CRLF or modify designated critical habitat by reducing or
changing the composition of the aquatic plant community in the ponds and
streams comprising the species' current range and designated critical habitat, thus
affecting primary productivity and/or cover;
indirectly affect the CRLF or modify designated critical habitat by reducing or
changing the composition of the terrestrial plant community (i.e., riparian habitat)
required to maintain acceptable water quality and habitat in the ponds and streams
comprising the species' current range and designated critical habitat;
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);
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modify the designated critical habitat of the CRLF by reducing the food supply
required for normal growth and viability of juvenile and adult CRLFs;
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.
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.
modify the designated critical habitat of the CRLF by altering chemical
characteristics necessary for normal growth and viability of juvenile and adult
CRLFs.
8.0 Summary of Direct and Indirect Effects to the California Red Legged Frog
and Modification to Designated Critical Habitat for the California Red Legged Frog
In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the
information presented in this endangered species risk assessment represents the best data
currently available to assess the potential risks of S-methoprene to the CRLF and its
designated critical habitat. A summary of the risk conclusions and effects determination
for the CRLF and its designated critical habitat, given the uncertainties discussed in
Section 6. Based on the conclusions of this assessment, a formal consultation with the U.
S. Fish and Wildlife Service under Section 7 of the Endangered Species Act should not
be initiated.
Based on the best available information, the Agency has assessed the potential for direct
and indirect risk to CRLF from S-methoprene exposure. The conclusion is that there is a
"may affect", but "not likely to adversely affect" determination for the CRLF from the
use of S-methoprene. The assessment endpoints (Table 8.0) where this determination is
made include the following:
1) Survival, growth, and reproduction of CRLF individuals via effects to food
supply {i.e. freshwater fish and invertebrates, non-vascular plants);
This assessment point reflects an LOC exceedance (0.07) for acute endangered species
concerns (LOC = 0.05) calculated from one of the upper bound extrapolated sustainable
release formulations (20% granular), although, the microcosm field values for the same
formulation did not exceed this LOC concern. In order to evaluate this exceedance, the
Agency also calculated the chance of individual exposure using the Individual Effects
Chance Model (Version 1.1). These calculations suggest that the chance of individual
effect from this granular extrapolated exposure is about lin 988,000, which may be
considered as a highly unlikely event. As an additional test of possible risk, the use of
acute and chronic fish and invertebrate toxicity data produced RQs for the other
formulations (using extrapolated and microcosm exposure values) that did not exceed
LOCs for direct or indirect effects to the aquatic-phase CRLF. Therefore, the Agency
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concludes a "may affect" but "not likely to adversely affect" reading for this
assessment point.
The Agency acknowledges that S-methoprene is highly efficacious to Dipteran insect
larvae and that the use of this compound can result in a decline in emerging adult
populations. However, according to information of the CRLFs diet in Section 2.5.3 these
insects are not included in their diet. The Agency assumes that the CRLF is an
opportunistic feeder and will supplement its diet with available invertebrates and small
animals. Therefore, the Agency concluded "no habitat modification" from S-
methoprene use. Although there is widespread overlap of potential S-methoprene with
watersheds of the CRLF the Agency has also determined that there is no potential for
modification of CRLF designated critical habitat (aquatic or terrestrial plants) from the
use of S-methoprene because this compound does not have herbicidal qualities or mode
of action. Further information on the results of the effects determination are included as
part of the Risk Description in Section 5.2.
Table 8.0 Effects Determination Summary for Direct and Indirect Effects of S-
methoprene on the California Red-legged Frog
Assessment Endpoint
Effects
Determination
Basis
Aquatic-Phase
(Eggs, Larvae, Tadpoles, Adults)
1. Survival, growth, and reproduction
of CRLF individuals via direct effects
on aquatic phases
No Effect
Acute RQs do not exceed LOC for direct
effects using acute and chronic fish data.
There is widespread overlap of potential S-
methoprene with watersheds of the CRLF.
2. Survival, growth, and reproduction
of CRLF individuals via effects to food
supply (i.e. freshwater fish and
invertebrates, non-vascular plants)
May Affect, But
not Likely to
Adversely Affect
LOC exceedance for granular formulation
(0.07) to aquatic invertebrates. However,
exposure was an extrapolated value,
microcosm value did not exceed LOC.
There is widespread overlap of potential S-
methoprene use with watersheds of the
CRLF.
3. Survival, growth, and reproduction
of CRLF individuals via indirect
effects on habitat, cover, and/or
primary productivity (i.e., aquatic plant
community)
No Effect
S-methoprene is a larvicide and does not kill
plants. Although there is the potential for
aquatic exposure, aquatic plants are not at
risk.
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.
No Effect
S-methoprene is not toxic to plants and does
not have herbicidal qualities.
Terrestrial Phase
(Juveniles and adults)
5. Survival, growth, and reproduction
of CRLF individuals via direct effects
on terrestrial phase adults and juveniles
Not Likely to
Adversely Affect
S-methoprene does not exceed an equivalent
LOC for acute or chronic toxicity LC50
values, based on available avian and
mammal data. Most applications are granular
formulations and the liquid applications are
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Assessment Endpoint
Effects
Determination
Basis
directed to water.
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)
Not likely to
adversely affect
RQs for possible dietary items (small
mammals, adult insects) are less than the
LOCs. Based on the non-selective feeding
behavior of adult CRLF and low magnitude
of anticipated individual effects to potential
prey items, S-methoprene is not expected to
indirectly affect the terrestrial form of the
CRLF. Although Dipterian populations may
decline momentarily in the area where S-
methoprene is used, these organisms are not
expected to be a major component of the
CRLFs diet.
7. Survival, growth, and reproduction
of CRLF individuals via indirect
effects on habitat (i.e., riparian
vegetation)
Not Likely to
Adversely Affect
S-methoprene is not toxic to plants, plants
are not at risk.
Table 8.1 Effects Determination Summary for S-Methoprene Exposure to the
California Red-Legged Frogs Critical Habitat
Assessment Endpoint
Effects
Determination
Basis
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.
No Habitat
Modifications
Since S-methoprene does not control
plants at the application sites, there is no
potential for impacts to aquatic and
terrestrial plants that comprise these
habitats.
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 source2.
No Habitat
Modifications
Given that S-methoprene is not intended to
control plants on the application sites,
there is no potential for impacts to aquatic
and terrestrial plants that comprise these
habitats.
Alteration of other chemical
characteristics necessary for normal
growth and viability of CRLFs and their
food source.
No Habitat
Modifications
S-methoprene does not affect plant life and
aquatic chemical (DO) components that
are necessary for aquatic CRLF growth
and development are not affected by S-
methoprene exposure.
Reduction and/or modification of
aquatic-based food sources for pre-
metamorphoses (e.g., algae)
No Habitat
Modifications
Although S-methoprene is applied to water
bodies, it does not have the potential for
impacts to aquatic plants that comprise
these habitats (non herbicidal properties).
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Assessment Endpoint
Effects
Determination
Basis
Aquatic Phase PCEs
(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)
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 drip line surrounding
aquatic and riparian habitat that are
comprised of grasslands, woodlands,
and/or wetland/riparian plant species that
provides the CRLF shelter, forage, and
predator avoidance
No Habitat
Modifications
S-methoprene is not intended to control
terrestrial plants at the application sites.
This compound is not an herbicide and
rapidly degrades in the environment
through photolysis and biodegradation (7-
10 days).
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
No Habitat
Modifications
Given that S-methoprene is not intended to
control plants on the application sites,
there is no potential for impacts to
terrestrial plants that comprise these
habitats.
Reduction and/or modification of food
sources for terrestrial phase juveniles and
adults
No Habitat
Modifications
Although S-methoprene is toxic to
Dipterian insects this does not pose acute
risk to the CRLF. Frogs are opportunistic
feeders and should supplement their diet
with other terrestrial organisms. Dipterans
are not listed as a component of the CRLFs
diet.
Alteration of chemical characteristics
necessary for normal growth and viability
of juvenile and adult CRLFs and their
food source.
No Habitat
Modifications
Although S-methoprene is toxic to
Dipterian insects this does not pose acute
risk to the CRLF. Frogs are opportunistic
feeders and should supplement their diet
with other terrestrial organisms. Dipterans
are not listed as a component of the CRLFs
diet.
1 Physico-chemical water quality parameters such as 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.
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References
Altig, R. and R.W. McDiarmid. 1999. Body Plan: Development and Morphology. In
R.W. McDiarmid and R. Altig (Eds.), Tadpoles: The Biology of Anuran
Larvae.University of Chicago Press, Chicago, pp. 24-51.
Alvarez, J. 2000. Letter to the U.S. Fish and Wildlife Service providing comments on
the Draft California Red-legged Frog Recovery Plan
Ali, A. 1991. Activity of a new formulations of S-methoprene against midges (Diptera:
Chironomidae) in experimental ponds. JAmMosq Control Assoc 7:616-620.
Borst, D., Tsukimura, B., Laufer, H., Couch, E., 1994. Regional differences in methyl
farnesoate production in the lobster mandibular organ. Biol. Bull. 186:9-16.
Boxmeyer, C.E., Leach, S., Palchick, S.M. 1997. Degradation of Altosid XR briquettes
under field conditions in Minnesota. J Amer. Mosq. Control Ass. 13: 275-277.
Crawshaw, G.J. 2000. Diseases and Pathology of Amphibians and Reptiles in:
Ecotoxicology of Amphibians and Reptiles; ed: Sparling, D.W., G. Linder, and C.A.
Bishop. SETAC Publication Series, Columbia, MO.
Degitz, SJ, Durhan, EJ, Tietge, JE, Kosian, PA, Holcombe, GH, Ankley, GT. 2003.
Developmental toxicity of S-methoprene and several degradation products in Xenopus
laevis. Aquatic Toxicology, 64(1): 97-105.
Ding, Q., Tobe, S. 1991. Production of farnesoic acid and methyl farnesoate by
mandibular organs of the cray fish, Procambarius clarkia. Insect Biochem. 21:285-291.
EPA. 1991. S-methoprene Reregi strati on Eligibility Document Facts. Washington, DC:
US Environmental Protection Agency.
Fellers, G. M., et al. 2001. Overwintering tadpoles in the California red-legged frog
{Rana aurora draytonii). Herpetological Review, 32(3): 156-157.
Fellers, G.M, L.L. McConnell, D. Pratt, S. Datta. 2004. Pesticides in Mountain Yellow-
Legged Frogs (Rana Mucosa) from the Sierra Nevada Mountains of California, USA.
Environmental Toxicology & Chemistry 23 (9):2170-2177.
Fellers, Gary M. 2005a. Rana draytonii Baird and Girard 1852. California Red-legged
Frog. Pages 552-554. hr. M. Lannoo (ed.) Amphibian Declines: The Conservation Status
of United States Species, Vol. 2: Species Accounts. University of California Press,
Berkeley, California, xxi+1094 pp. (http://www.werc.usgs.gov/pt-
reves/pdfs/Rana%20dravtonii. PDF)
73
-------
Fellers, Gary M. 2005b. California red-legged frog, Rana draytonii Baird and Girard.
Pages 198-201. hr. L.L.C. Jones, et al (eds.) Amphibians of the Pacific Northwest.
xxi+227.
Hayes, M.P. and M.M. Miyamoto. 1984. Biochemical, behavioral and body size
differences between Rana aurora aurora and R. a. draytonii. Copeia 1984(4): 1018-22.
Hayes and Tennant. 1985. Diet and feeding behavior of the California red-legged frog.
The Southwestern Naturalist 30(4): 601-605.
Harmon, M.A., Boehn, M.F., Mangelsdorf, D.J. 1995. Activation of mammalian retinoid
X receptors by the insect growth regulator S-methoprene. Proc. Natl. Acad. Sci. 92:6157-
6160.
Hershey, A.E., Shannon, L.J., Axler, R.P., Ernst, C., Mickelson, P. (1995) Effects of S-
methoprene and Bti (Bacillus thuringiensis var. israelensis) on non-target insects
Hydrobiologia. 308:219-227.
HSDB. 2002. Hazardous Substance Data Bank: S-methoprene. National Library of
Medicine, National Toxicology Program. Available at
http://www.toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen7HSDB Accessed December 17, 2002.
Jennings, M.R. and M.P. Hayes. 1985. Pre-1900 overharvest of California red-legged
frogs (Rana aurora draytonii): The inducement for bullfrog (Rana catesbeiana)
introduction. Herpetological Review 31(1): 94-103.
Jennings, Mark R. 1988. Natural history and decline of native ranids in California. Pp.
61-72. In Proceedings of the conference on California herpetology. H.F. DeLisle, P.R.
Brown, B. Kaufman, and H.M. McGurty (eds). Southwestern Herpetologists Society
Special Publication (4): 1-143.
Jennings, M.R. and M.P. Hayes. 1994. Amphibian and reptile species of special concern
in California. Report prepared for the California Department of Fish and Game, Inland
Fisheries Division, Rancho Cordova, California. 255 pp.
Jennings, M.R., S. Townsend, and R.R. Duke. 1997. Santa Clara Valley Water District
California red-legged frog distribution and status - 1997. Final Report prepared by H.T.
Harvey & Associates, Alviso, California. 22 pp.
Judy, D and Howell, B. 1992. Concentrations of methoprene found in freshwater
microcosms treated with sustained release Altosid formulations. ABC Laboratories
Columbia, Missouri. Study conducted for Zoecon corp. Dallas, Texas. MRID#428112-02
Johnson, P.T.J., Lunde, K.B., Ritchie, E.G., Launer, L.H. 1999. The effect of trematode
infection an amphibian limb development and survivorship. Science. 284:803-804.
Kupferberg, S. 1997. Facilitation of periphyton production by tadpole grazing:
Functional differences between species. Freshwater Biology 37:427-439.
74
-------
Kupferberg, S.J., J.C. Marks and M.E. Power. 1994. Effects of variation in natural
algal and detrital diets on larval anuran (Hyla regilla) life-history traits. Copeia
1994:446-457.
Laufer, H., Bigger, W.J. 2001. Unifying concepts learned from methyl farnesoate for
invertebrate reproduction and post-embryonic development. Amer. Zool. 41:442-457.
LeNoir, J.S., L.L. McConnell, G.M. Fellers, T.M. Cahill, J.N. Seiber. 1999.
Summertime Transport of Current-use pesticides from California's Central Valley to the
Sierra Nevada Mountain Range,US A. Environmental Toxicology & Chemistry 18(12):
2715-2722.
McConnell, L.L., J.S. LeNoir, S. Datta, J.N. Seiber. 1998. Wet deposition of current-use
pesticides in the Sierra Nevada mountain range, California, USA. Environmental
Toxicology & Chemistry 17(10): 1908-1916.
Metropolitian Mosquito Control District. 1996. An assessment of non-target effects of the
mosquito larvicides, Bti and S-methoprene, in metropolitan area wetlands. St. Paul, MN,
USA.
Minucci, S., Saint-Jeannet, J-P, Toyama, R., Scita, G., Deluca, L.M., Tiara, M., Levin,
A.A., Ozato, K., Dawid, I.B. 1996. Retinoid X receptor-celective ligands produce
malformations in Xenopus embryos. Proc. Natl. Acad. Sci. 93:1803-1807.
Niemi, G.J., Axler, R.P., Hanowski, J.M., Hershey, A.E., Lima, A.R., Regal, R.R.,
Shannon, L, Whiteside, M (1990) Evaluation of the effects of S-methoprene and Bti
(Bacillus thurgiensis israelensis) on non-target organisms: a summary of before-and-after
sites in western Wright County NRRI/TR-90/17.
Norland, R.L., Mulla, M.S. 1975. Impact of Altosid on selected members of an aquatic
ecosystem. Environ Entomol 4:145-152.
Olmestead, A.W., LeBlanc, G.A. 2001. Temporal and quantitative changes in sexual
reproductive cycle of the cladoceran Daphnia magna by a juvenile hormone analog. J
Exp Zool. 290: 148-155.
Pinkney, A.E., McGowan, P.C., Murphy, D.R., Lowe, T.P., Sparling, D.W., Ferrington,
L.C. 2000. Effects of the mosquito larvicides temephos and S-methoprene on insect
populations in experimental ponds. Environ Toxicol Chem 19:678-684.
75
-------
Quistad, G.B., Staiger, L.E., Schooley, D.A. 1975. Environmental degradation of the
insect growth regulator S-methoprene (isopropyl 2E, 4E)-1 l-Methoxy-3,7,11-trimethyl-
2,4-dodecadienoate), III. Photodecomposition. J. Agr. Food Chem. 23:299-303
Riddiford, L.M. 1996. Juvenile hormone: the status of its "status quo" action. Arch.
Insect Biochem. Physiol. 32:271-286.
Rathburn, G.B. 1998. Rana aurora draytonii egg predation. Herpetological Review,
29(3): 165.
Reis, D.K. 1999. Habitat characteristics of California red-legged frogs {Rana aurora
draytonii)-.Ecological differences between eggs, tadpoles, and adults in a coastal brackish
and freshwater system. M.S. Thesis. San Jose State University. 58 pp.
Scoff, P.K. and Ankley, G.T. 2004. Effects of S-methoprene, its metabolites, and
breakdown products on retinoid-activated pathways in transfected cell lines. Environ
Toxicol Chem 23:1305-1310.
Seale, D.B. andN. Beckvar. 1980. The comparative ability of anuran larvae (genera:
Hyla, Bufo and Rana) to ingest suspended blue-green algae. Copeia 1980:495-503.
D.W. Sparling, G.M. Fellers, L.L. McConnell. 2001. Pesticides and amphibian
population declines in California, USA. Environmental Toxicology & Chemistry 20(7):
1591-1595.
Staal, G.B. 1975. Insect growth regulators with juvenile hormone activity. Ann. Rev.
Entomol. 20:417-460.
Toxnet 2003. National Library of Medicine. National Institute of Health. S-methoprene.
Available: http://toxnet.nlm.nih.gOv/cgi-bin/sis/search/f7./temp/~QhG32K:l:enex.
(Accessed: September 2007).
U.S. Environmental Protection Agency (U.S. EPA). 1998. Guidance for Ecological Risk
Assessment. Risk Assessment Forum. EPA/630/R-95/002F, April 1998.
U.S. EPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of
Pesticide Programs. Office of Prevention, Pesticides, and Toxic Substances. Office of
Pesticide Programs. Washington, D.C. January 23, 2004.
U.S. Fish and Wildlife Service (USFWS). 1996. Endangered and threatened wildlife and
plants: determination of threatened status for the California red-legged frog. Federal
Register 61(101):25813-25833.
76
-------
USFWS. 2002. Recovery Plan for the California Red-legged Frog (Rana aurora
draytonii). Region 1, USFWS, Portland, Oregon.
(http://ecos.fws.gov/doc/recovery plans/2002/020528.pdf)
USFWS. 2006. Endangered and threatened wildlife and plants: determination of critical
habitat for the California red-legged frog. 71 FR 19244-19346.
USFWS. Website accessed: 30 December 2006.
http://www.fws.gov/endangered/features/rl frog/rlfrog.html#where
U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service
(NMFS). 1998. Endangered Species Consultation Handbook: Procedures for
Conducting Consultation and Conference Activities Under Section 7 of the Endangered
Species Act. Final Draft. March 1998.
USFWS/NMFS. 2004. 50 CFR Part 402. Joint Counterpart Endangered Species Act
Section 7 Consultation Regulations; Final Rule. FR 47732-47762.
Wan, M. T. K. and Wilson, D. M. (1975). Impacts of "Altosid" Juvenile Hormone on
Non-target Organisms in an Aquatic Environment of Interior British Columbia.
Rep.No.EPS 5-PR-75-9, Pollution Abatement Branch, Environ.Prot.Serv., Vancouver,
B.C. 46 p.
Wassersug, R. 1984. Why tadpoles love fast food. Natural History 4/84.
77
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