Risks of Strychnine Use to:
Federally Threatened California Red-legged Frog
(Rana aurora draytonii)
California Tiger Salamander
(Ambystoma calif or niense)
CENTRAL CALIFORNIA DISTINCT POPULATION SEGMENT Federally
Threatened AND SONOMA AND SANTA BARBARA COUNTY DISTINCT
POPULATION SEGMENTS Federally Endangered
Federally Endangered San Joaquin Kit Fox
(Vulpes macrotis muticd)
Pesticide Effects Determinations
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
October 19,2009
-------
Primary Authors: James J. Goodyear, Ph.D., Biologist
Stephanie Syslo, Environmental Scientist
Secondary Review: James Hetrick, Ph.D., Senior Chemist
Pamela Hurley, Ph.D., Senior Toxicologist
Branch Chief,
Environmental Risk Assessment Branch 3: Dana Spatz
-------
Table of Contents
1. Executive Summary 6
2. Problem Formulation 11
2.1 Purpose 11
2.2 Scope 16
2.3 Previous Assessments 17
2.4 Stressor Source and Distribution 17
2.4.1 Environmental Fate Properties 18
2.4.2 Environmental Transport Mechanisms 19
2.4.3 Mechanism of Action 19
2.4.4 Use Characterization 20
2.5 Assessed Species 24
2.6 Designated Critical Habitat 29
2.7 Action Area 31
2.8 Assessment Endpoints and Measures of Ecological Effect 33
2.8.1 Assessment Endpoints 33
2.8.2 Assessment Endpoints for Designated Critical Habitat 35
2.9 Conceptual Model 36
2.9.1 Risk Hypotheses 36
2.9.2 Diagram 37
2.10 Analysis Plan 38
2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model 38
2.10.2 Data Gaps 40
3. Exposure Assessment 40
3.1 Label Application Rates and Intervals 41
3.2 Aquatic Exposure Assessment 41
3.2.1 Modeling Approach 41
3.2.2 Existing Monitoring Data 42
3.3 Terrestrial Animal Exposure Assessment 43
3.4 Terrestrial Plant Exposure Assessment 44
4. Effects Assessment 45
4.1 Toxicity of Strychnine to Aquatic Organisms 46
4.2 Toxicity of Strychnine to Terrestrial Organisms 47
4.2.1 Toxicity to Birds and Terrestrial-Phase Amphibians 48
4.2.2 Toxicity to Mammals 49
4.2.3 Toxicity to Terrestrial Invertebrates 49
4.2.4 Toxicity to Terrestrial Plants 49
4.3 Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern 50
4.4 Incident Database Review 50
5. Risk Characterization 50
5.1 Risk Estimation 51
5.1.1 Exposures in the Aquatic Habitat 51
5.1.2 Exposures in the Terrestrial Habitat 51
5.1.3 Primary Constituent Elements of Designated Critical Habitat 52
-------
5.2
Risk Description 52
5.2.1 The CRLF and CTS 54
5.2.1.3 Modification of Designated Critical Habitat 57
5.2.2.3 Modification of Designated Critical Habitat 59
5.2.3 Spatial Extent of Potential Effects 59
6. Uncertainties 60
6.1 Exposure Assessment Uncertainties 60
6.1.1 Maximum Use Scenario 60
6.1.2 Aquatic Exposure Modeling of Strychnine 60
6.2 Effects Assessment Uncertainties 60
6.2.1 Age Class and Sensitivity of Effects Thresholds 60
6.2.2 Location of Wildlife Species 61
7. Risk Conclusions 61
8. References 65
Appendices
Appendix A Estimation of Upper-Bound Aquatic Exposure
Appendix B Accepted ECOTOX Data Table for Strychnine
Appendix C Bibliography of ECOTOX Open Literature
Appendix D HED Effects
Appendix E Strychnine Incidents
Attachment I.
Attachment II.
Attachment III.
Attachment IV.
Status and Life History of the California Red-legged Frog
Baseline Status and Cumulative Effects for the California Red-
legged Frog
Status and Life Histories for the California Tiger Salamander and
San Joaquin Kit Fox
Baseline Status and Cumulative Effects for the California Tiger
Salamander and San Joaquin Kit Fox
List of Tables
Table 2.1. Summary of Strychnine Environmental Fate Properties 18
Table 2.2 Strychnine Products allowed for use in California 20
Table 2.3 Summary of California Department of Pesticide Registration (CDPR) Pesticide
Use Reporting (PUR) Data from 1999 to 2006 for Currently Registered
Strychnine Uses 23
Table 2.4. Summary of Current Distribution, Habitat Requirements, and Life History
Information for the Assessed Listed Species 25
-------
Table 2.5. Designated Critical Habitat PCEs for the CRLF and the CIS 30
Table 2.6 Special Local Needs (SLN) Registration for use in California 31
Table 2.7. Uses of Strychnine Considered as Part of the Federal Action Evaluated in this
Assessment 32
Table 2.8. Taxa Used in the Analyses of Direct and Indirect Effects for the Assessed
Listed Species 34
Table 2.9. Taxa and Assessment Endpoints Used to Evaluate the Potential for the Use of
Strychnine to Result in Direct and Indirect Effects to the Assessed Listed
Species 35
Table 2.10. Summary of Assessment Endpoints and Measures of Ecological Effect for
Primary Constituent Elements of Designated Critical Habitat for the CRLF
andtheCTS 36
Table 3.1 Strychnine Use Rates Assessed for California 41
Table 4.1 Aquatic Toxicity Profile for Strychnine 46
Table 4.2 Terrestrial Toxicity Profile for Strychnine 47
Table 4.3 Categories of Acute Toxicity for Avian and Mammalian Studies 48
Table 4.4 Acute Toxicity of Strychnine in Selected Mammalian Species 49
Table 5.1. Risk Estimation Summary for Strychnine 52
Table 5.2. Risk Estimation Summary for Strychnine - Effects to Designated Critical
Habitat (PCEs) 53
List of Figures
Figure 2.1. A gopher probe 13
Figure 2.2. Basic parts of the burrow builder 14
Figure 2.3. Recovery Unit, Core Area, Critical Habitat, and Occurrence Designations for
CRLF 26
Figure 2.4. Range and Critical Habitat for CTS 27
Figure 2.5. Current Distribution of the SJKF 28
Figure 2.6. Conceptual Model for Terrestrial Phase of the CRLF, CTS, and SJKF 38
-------
1. Executive Summary
The purpose of this assessment is to evaluate potential direct and indirect effects on the
California red-legged frog (Rana aurora draytonii) (CRLF), the California tiger
salamander (Ambystoma californiense) (CTS), and the San Joaquin kit fox (Vulpes
macrotis mutica) (SJKF) arising from FIFRA regulatory actions regarding use of
strychnine on agricultural and non-agricultural sites. In addition, this assessment
evaluates whether these actions can be expected to result in modification of designated
critical habitat for the CRLF, the CTS, and the SJKF. This assessment was completed in
accordance with the U.S. Fish and Wildlife Service (USFWS) and National Marine
Fisheries Service (NMFS) Endangered Species Consultation Handbook (USFWS/NMFS,
1998 and procedures outlined in the Agency's Overview Document (U.S. EPA, 2004).
The CRLF was listed as a threatened species by USFWS in 1996. The species is endemic
to California and Baja California (Mexico) and inhabits both coastal and interior
mountain ranges. A total of 243 streams or drainages are believed to be currently
occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and
Santa Barbara counties (USFWS 1996) in California. Critical habitat has been
designated for the CRLF.
The CTS was listed as a threatened species in 2004. The CTS occurs in the Santa Rosa
area of Sonoma County, southern San Mateo County south to San Luis Obispo County,
and the vicinity of northwestern Santa Barbara County. In the Central Valley and
surrounding Sierra Nevada foothills and Coast Range, the species occurs from northern
Yolo County (Dunnigan area) southward to northwestern Kern County and northern
Tulare and Kings Counties. In the Federal Register notice (50-CFR 17) the USFWS
(2004) listed the CTS as threatened rangewide. This listing was vacated by the U.S.
District Court. The Sonoma and Santa Barbara Distinct Population Segments (DPSs) are
currently listed as endangered while the Central California DPS is listed as threatened.
Critical habitat has been designated for the CTS (USFWS, 2005).
The SJKF was listed as endangered by the USFWS on March 11, 1967. Its current range
includes Alameda, Contra Costa, Fresno, Kern, Kings, Madera, Merced, Monterey, San
Benito, San Joaquin, San Luis Obispo, Santa Barbara, Santa Clara, Stanislaus, Tulare and
Ventura counties in California. The SJKF inhabits a variety of habitats, including
grasslands, scrublands, vernal pool areas, oak woodland, alkali meadows and playas, and
an agricultural matrix of row crops, irrigated pastures, orchards, vineyards, and grazed
annual grasslands. Critical habitat has not been designated for the SJKF.
Strychnine is a highly toxic, colorless crystalline alkaloid. Strychnine causes muscular
convulsions and death through asphyxia and exhaustion. Its only labeled uses are
restricted to the below-ground control of pocket gophers (Thomomys spp. and Geomys
spp. in the US). The uses considered as part of the federal action are hand baiting and
mechanical baiting of active burrows in California; these uses were evaluated in this
assessment.
-------
The acceptable environmental fate data are limited. Neither hydrolysis nor soil
photolysis is a significant transformation pathway; no data are available for aqueous
photodegradation. No acceptable metabolism data have been submitted to the Agency;
qualitative information from the submitted studies suggest that aerobic degradation in soil
can sometimes not occur, may be very slow, or can occur rapidly following a significant
lag period under as yet undefined conditions. Due to the low vapor pressure and Henry's
Law constant, strychnine is not expected to volatilize. Batch adsorption/desorption data
demonstrate strychnine's strong binding to a number of soils. With the present use pattern
of applying strychnine into specific below-ground burrows, leaching, spray drift, runoff,
atmospheric transport, and volatilization are not potential transport mechanisms, and so
are not quantitatively or qualitatively considered in the assessment. No monitoring data
are available from either the U. S. Geological Survey's National Water Quality
Assessment (NAWQA) program or the California Department of Pesticide Regulation.
The effects determination for each listed species assessed is based on a weight-of-
evidence method that relies heavily on an evaluation of risks to each taxon relevant to
assess both direct and indirect effects to the listed species and the potential for
modification of their designated critical habitat (i.e., a taxon-level approach). Exposure
of the listed species, their prey and their habitats to strychnine are assessed separately.
Since strychnine is exclusively applied to below-ground burrows, runoff and spray drift
are not expected to result in exposure to aquatic habitats, so no aquatic modeling was
performed. Also, spray drift is not expected to result in exposure to aquatic or terrestrial
habitats, so neither the AgDRIFT nor the AGDISP modeling were performed. The
TerrPlant, T-REX, and T-HERPS models were not used to estimate strychnine exposures
to terrestrial-phase animals and plants, because strychnine is neither applied as a foliar
application nor as a traditional granular application. No degradates have been identified
in any of the environmental fate data, so degradates were not considered in this
assessment.
Usually risk quotients (RQs) are derived as quantitative estimates of potential high-end
risk. Strychnine is not used in a manner that lends itself to the calculation of an RQ.
Therefore, risk is addressed qualitatively.
If a determination is made that the use of strychnine "may affect" the listed species being
assessed and/or its designated critical habitat, additional information is considered to
refine the potential for exposure and effects. Best available information is used to
distinguish those actions that "may affect, but are not likely to adversely affect" (NLAA)
from those actions that are "likely to adversely affect" (LAA) for each listed species
assessed. For designated critical habitat, distinctions are made for actions that are
expected to have "no effect" on a designated critical habitat from those actions that have
a potential to result in "habitat modification."
Based on the best available information, the Agency makes a "May Affect, Likely to
Adversely Affect" determination for the CRLF, the CTS, and the SJKF from the use of
strychnine. Additionally, the Agency has determined that there is potential for
-------
modification of designated critical habitat for the CRLF and the CIS from use of the
chemical.
Strychnine-treated bait is placed in underground burrows The CRLF and CIS are
known to use burrows for shelter and so they may encounter the bait. Amphibians have
permeable, non-scaly skin that is important for respiration; therefore, it can be presumed
that the poison can be absorbed through amphibian skin. There is little expectation that
strychnine can be inhaled because it is not expected to volatilize.
Pocket gophers plug the entrances to their burrows, which helps to protect them from
carnivores. The SJKF is able to dig far enough to reach the gopher, but with more
difficulty than would other predators. The gophers generally eat roots from within the
burrow but may leave and forage near the entrance. During those time, the SJKF can dig
into the burrow or prey on the gopher while it is outside the burrow. Since a SJKF would
eat a gopher that had died in the burrow or was foraging on the surface, they could be
exposed to strychnine. Schitoskey (1975) found that a kangaroo rat (Dipodomys sp.)
killed with 12.8 mg of strychnine contained 10 times the LDso for a desert kit fox (Vulpes
macrotis arsipus) and killed the desert kit fox within 30 minutes.
A summary of the risk conclusions and effects determinations for each listed species
assessed here and their designated critical habitat is presented in Tables 1.1 and 1.2.
Further information on the results of the effects determination is included as part of the
Risk Description in Section 5.2.
Table 1.1 Effects Determination Summary for Effects of Strychnine on the CRLF, the CTS, and
the SJKF.
Due to the nature of the application method, a meaningful estimation of exposure cannot be
determined; thus RQs cannot be estimated.
Species
Effects
Determination
Basis for Determination
California
red-legged
frog
(Rana aurora
draytonii)
and
California
tiger
salamander
(Ambystoma
californiense)
LAA
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults using fish as a surrogate):
Due to the current use pattern, no aquatic exposure is expected. Even if strychnine
were used on ditchbanks or earthen dams it would be expected to reach aquatic
environments at maximum estimated concentrations in the parts per trillion range,
which is roughly 0.02 of the LOG for the most sensitive aquatic sp_ecies tested_.
Terrestrial-phase (Juveniles and Adults using birds as a surrogate):
Strychnine is highly toxic to birds on a subacute dietary basis (no acute oral data
available). Dermal exposure to the bait is possible when the CRLF/CTS uses gopher
burrows. Although dermal absorption in mammals may be very low; amphibians
have thin, permeable skin. Therefore, it is assumed that it may be absorbed dermally
and would also be highly toxic to terrestrial-phase amphibians.
There is a potential for secondary poisoning through consumption of soil-
dwelling/burrowing invertebrates that have either consumed the strychnine bait or
are transporting/tracking it.
-------
Table 1.1 Effects Determination Summary for Effects of Strychnine on the CRLF, the CTS, and
the SJKF.
Due to the nature of the application method, a meaningful estimation of exposure cannot be
determined; thus RQs cannot be estimated.
Species
San
Joaquin kit
fox (Vulpes
macrotis
mutica)
Effects
Determination
LAA
Basis for Determination
Although exposures via dermal absorption and via consumption of invertebrates
cannot be estimated, the potential exists for dermal exposure and consumption of
invertebrates that have been in contact with the bait. Therefore, due to the high
toxicity of strychnine, risk cannot be discounted.
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary productivity
Due to the current use pattern, no aquatic exposure is expected. Even if strychnine
were used on ditchbanks or earthen dams it would be expected to reach aquatic
environments at maximum estimated concentrations are in the parts per trillion range,
which is roughly 0.02 of the LOG for the most sensitive aquatic species tested.
Terrestrial prey items
There is a possible reduction in the amphibian prey base if there are a significant
number of amphibians that utilize the gopher burrows and come in dermal contact
with the bait.
Potential Modification of Habitat
It has been reported that some amphibians will use gopher burrows for resting and
avoiding hot weather. The removal of pocket gophers will cause some burrows to
become abandoned and unavailable to the amphibians for resting and shelter.
California tiger salamanders spend much of their lives in underground retreats, often
in burrowing mammal (ground squirrel, pocket gopher, and other burrowing
mammal) burrows.
Potential for Direct Effects
The LD50 of strychnine is 0.75 mg/kg for the desert kit fox (Vulpes macrotis arsipus).
SJKFs might receive a harmful or fatal dose of strychnine by eating a poisoned pocket
gopher it dug out of its burrow or found above ground. One dose of bait contains from
43.2 mg to 65.7 mg of strychnine. Consumption of a kangaroo rat (Dipodomys sp.)
killed with 12.8 mg of strychnine killed a desert kit fox within 30 minutes. A gopher
with 12.8 mg of strychnine in its cheek pouches would carry enough poison to kill the
fox. There is also a potential to secondary poisoning through consumption of soil-
dwelling/burrowing invertebrates that have either consumed the strychnine bait or have
been transporting/tracking it. Although exposures via consumption of pocket gophers
and/or invertebrates cannot be estimated, due to the high toxicity and the potential for
consumption of pocket gophers and/or invertebrates that have been in contact with the
bait, risk cannot be discounted.
Potential for Indirect Effects
To the extent SJKF depend on gophers as a prey animal, the SJKF could be affected
by their reduction in numbers.
-------
Table 1.2 Effects Determination Summary for the Critical Habitat Impact Analysis
Designated
Critical Habitat
for:
Effects
Determination
Basis for Determination
Due to the nature of the application method, a meaningful estimation of exposure cannot be
determined; thus ROs cannot be estimated.
California
red-legged frog
(Rana aurora
draytonii) and
California
tiger salamander
(Ambystoma
californiense)
Habitat
Modification
There is potential risk from dermal exposure in the gopher burrows and from
consumption of terrestrial invertebrates that have been in contact with the bait.
Due to the potential risk from dermal exposure, there is a possible reduction in the
amphibian prey base. Finally, there is a potential loss of habitat following removal
of pocket gophers (e.g., some burrows will become abandoned and unavailable to
the amphibians for resting and shelter).
Based on the conclusions of this assessment, a formal consultation with the U. S. Fish
and Wildlife Service under Section 7 of the Endangered Species Act should be initiated.
When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the listed species and its resources (i.e., food and habitat)
are not expected to be uniform across the action area.
Evaluation of the implication of this non-uniform distribution of risk to the species would
require information and assessment techniques that are not currently available. Examples
of such information and methodology required for this type of analysis would include the
following:
• Enhanced information on the density and distribution of CRLF, CTS and
SJKF life stages within the action area and/or applicable designated
critical habitat. This information would allow for quantitative
extrapolation of the present risk assessment's predictions of individual
effects to the proportion of the population extant within geographical areas
where those effects are predicted. Furthermore, such population
information would allow for a more comprehensive evaluation of the
significance of potential resource impairment to individuals of the
assessed species.
• Quantitative information on prey base requirements for the assessed
species. While existing information provides a preliminary picture of the
types of food sources utilized by the assessed species, it does not establish
minimal requirements to sustain healthy individuals at varying life stages.
Such information could be used to establish biologically relevant
thresholds of effects on the prey base, and ultimately establish
geographical limits to those effects. This information could be used
10
-------
together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.
Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth or reproductive impairment
immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and
together with the information described above, a more complete prediction
of effects to individual species and potential modification to critical
habitat.
2. Problem Formulation
Problem formulation provides a strategic framework for the risk assessment. By
identifying the important components of the problem, it focuses the assessment on the
most relevant life history stages, habitat components, chemical properties, exposure
routes, and endpoints. The structure of this risk assessment is based on guidance
contained in U.S. EPA's Guidance for Ecological Risk Assessment (U.S. EPA 1998), the
Services' Endangered Species Consultation Handbook (USFWS/NMFS 1998) and is
consistent with procedures and methodology outlined in the Overview Document (U.S.
EPA 2004) and reviewed by the U.S. Fish and Wildlife Service and National Marine
Fisheries Service (USFWS/NMFS 2004).
2.1 Purpose
The purpose of this endangered species assessment is to evaluate potential direct and
indirect effects on individuals of the federally threatened California red-legged frog
(Rana aurora draytonif) (CRLF), the federally endangered SJKF (Vulpes macrotis
muticd), and the federally threatened/endangered CTS (Ambystoma californiense)arising
from FIFRA regulatory actions regarding use of strychnine to control burrow-dwelling
rodents (specifically of the genus Thomomys) that are native to California. In addition,
this assessment evaluates whether use on these sites is expected to result in modification
of designated critical habitat for the CRLF and the Central California Distinct Population
Segment (DPS) of the CTS.
Because the pesticide/pest relationship for strychnine is so different from conventional
agricultural pesticides, the risk assessment is modified from EFED's standard risk
assessment approach. A detailed description of the pest and the pesticide as used in
California follows.
11
-------
Use Profile
Strychnine is a Restricted Use rodenticide for the control of pocket gophers (the genus of
concern in California is Thomomys - five species, with the valley pocket gopher (T.
bottae) being most widespread). Strychnine is formulated as a bait composed of
strychnine-treated grains (0.5% a.i. by weight on oats, milo, mixed grains or 1.8% by
weight for a single CA SLN) and is lethal with a single feeding. Currently registered
uses of Strychnine in California include both agricultural land and non-agricultural uses,
which include public health treatments and structural treatments.
Habits of pocket gophers
Mounds of fresh soil are the best sign of gopher presence. Mounds are formed as the
gopher digs its tunnel and pushes the loose dirt to the surface. Typical mounds are
crescent- or horseshoe-shaped when viewed from above. The hole, which is off to one
side of the mound, is usually plugged. Short, sloping lateral tunnels connect the main
burrow system to the surface and are created during construction of the main tunnel for
pushing dirt to the surface. The burrows are about 2-1/2 to 3-1/2 inches in diameter;
feeding burrows (called main runways on labels) are usually 6 to 12 inches below
ground, whereas the nest and food storage chamber may be as deep as 6 feet. Gophers
seal the openings to the burrow system with earthen plugs.
Pocket gophers are herbivorous, feeding on a wide variety of vegetation, but generally
preferring herbaceous plants, shrubs, and trees. Gophers use their sense of smell to locate
food. Most commonly they feed on roots and fleshy portions of plants they encounter
while digging. However, sometimes they feed above ground, venturing only a body
length or so from their tunnel opening. Burrow openings used in this manner are called
"feed holes." These are identified by the absence of a dirt mound and a circular band of
clipped vegetation around the hole.
Application methods
Manual
Because lateral tunnels may not be revisited by the gopher, baiting in them is not as
successful as in the main burrow. Access to the main runways can be made by
excavating the earthen plug from the lateral tunnels until the main runway is reached and
then applying the bait with a long spoon. A metal probe (Figure 2.1) can also be used to
find the main burrows by probing about 8 to 12 inches from the plug side of the mound; it
is usually located 6 to 12 inches deep1. When the probe penetrates the gopher's burrow,
there will be a sudden, noticeable drop of about 2 inches.
1 Illustration and descriptive text derived from Salmon, T. P., and R. E. Lickliter. 1984. Wildlife Pest
Control around Gardens and Homes. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 21385.
12
-------
Figure 2.1. A gopher probe.
After locating the main gopher burrow, the opening is enlarged by rotating the probe or
inserting a larger rod or stick. Following label directions, the bait is carefully placed in
the opening using a spoon or other suitable implement that is used only for that purpose.
(A funnel is useful for preventing spillage; any spilled bait is removed from the soil
surface by burying it or gathering it up.) After placing the bait in the main burrow
(approximately 1 teaspoon per hole), the lateral tunnel or probe hole is closed with sod,
rocks, or some other material to exclude light and prevent dirt from falling on the bait.
Several bait placements within a burrow system are made. Application rates for manual
application range from 0.125 to 1 pounds bait per acre
Field-scale Equipment
Large-scale application to fields that have extensive pocket gopher populations at
high densities can be made by tractor-operated mechanical burrow builder
equipment2. Burrow builders (Figure 2.2) create tunnels through the soil by a
"torpedo tube" and drop a measured amount of toxic grain bait into the newly-formed
tunnels.
Figure and descriptive text derived from Using Burrow Builders for Pocket Gopher Control. D.R.
Virchow, S.E. Hygnstrom, andB.E. Anderson. NebGuide G03-1510. Published by University of
Nebraska-Lincoln Extension. Institute of Agriculture and Natural Resources. ©2003
13
-------
See J box
But latter
Shank with
tofpf do tubf
Figure 2.2. Basic parts of the burrow builder: 1) rolling
coulter, 2) shank with torpedo tube, 3) bait box, 4)
bait meter, 5) press wheel(s).
The machines are drawn by a tractor across the field where the tunnels intercept or
come near the burrows of pocket gophers. The rolling coulter blade cuts surface trash
and shallow roots ahead of the shank, and the bait is metered into the tunnel created
by the torpedo tube. The press wheel closes the narrow slit at the top of the tunnel
formed by the upper portion of the shank, taking care not to collapse the tunnel or to
allow light to enter the tunnel. (Pocket gophers avoid light entering their burrows by
blocking entrances with soil.) Pocket gophers subsequently, through their natural
digging activities, intercept and enter the tunnels, and eat the toxic bait. Application
rates for burrow builders range from 1 to 3 pounds bait per acre.
Ecological Risk Assessment
This ecological risk assessment has been prepared consistent with the settlement agreement
in Center for Biological Diversity (CBD) vs. EPA et al. (Case No. 02-1580-JSW(JL)) entered
in Federal District Court for the Northern District of California on October 20, 2006. This
assessment also addresses the CTS and the SJKF for which strichnine was alleged to be of
concern in a separate suit (Center for Biological Diversity (CBD) vs. EPA et al. (Case No.
07-2794JCS)).
In this assessment, direct and indirect effects to the CRLF, the SJKF, and the CTS and
potential modification to designated critical habitat for the CRLF and the Central
California DPS of the CTS are evaluated. The effects determinations for each listed
species assessed is based on a weight-of-evidence method that relies heavily on an
evaluation of risks to each taxon relevant to assess both direct and indirect effects to the
listed species and the potential for modification of their designated critical habitat (i.e., a
taxon-level approach).
Screening level methods include use of standard exposure models, if appropriate, such as
PRZM-EXAMS, T-REX, TerrPlant, AgDRIFT, and AGDISP, all of which are described
14
-------
at length in the Overview Document. Use of such information is consistent with the
methodology described in the Overview Document (U.S. EPA 2004), which specifies that
"the assessment process may, on a case-by-case basis, incorporate additional methods,
models, and lines of evidence that EPA finds technically appropriate for risk management
objectives" (Section V, page 31 of U.S. EPA 2004). ). However, since strychnine is
applied to a burrow that is six to 12 inches below the surface of the ground, these
exposure models were not used.
In accordance with the Overview Document, provisions of the ESA, and the Services'
Endangered Species Consultation Handbook, the assessment of effects associated with
registrations of strychnine is based on an action area. The action area is the area directly
or indirectly affected by the federal action. It is acknowledged that the action area for a
national-level FIFRA regulatory decision associated with a use of strychnine 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, the SJKF, and the CTS and their designated critical habitat within the state of
California. As part of the "effects determination," one of the following three conclusions
will be reached separately for each of the assessed species in the lawsuits regarding the
potential use of strychnine in accordance with current labels:
• "No effect";
• "May affect, but not likely to adversely affect"; or
• "May affect and likely to adversely affect".
The CRLF and the Central California DPS of the CTS have designated critical habitats
associated with them. Designated critical habitat identifies specific areas that have the
physical and biological features, (known as primary constituent elements or PCEs)
essential to the conservation of the listed species. Short descriptions of the PCEs for the
CRLF and the CTS are presented in Table 2.5.
If the results of initial screening-level assessment methods show no direct or indirect
effects (no LOG exceedances) upon individuals or upon the PCEs of the species'
designated critical habitat, a "no effect" determination is made for use of strychnine as it
relates to each species and its designated critical habitat. If, however, potential direct or
indirect effects to individuals of each species are anticipated or effects may impact the
PCEs of the designated critical habitat, a preliminary "may affect" determination is made
for the FIFRA regulatory action regarding strychnine.
If a determination is made that use of strychnine "may affect" a listed species or its
designated critical habitat, additional information is considered to refine the potential for
exposure and for effects to each species and other taxonomic groups upon which these
species depend (e.g, prey items). Additional information, including spatial analysis (to
determine the geographical proximity of the assessed species' habitat and strychnine use
sites) and further evaluation of the potential impact of strychnine on the PCEs is also
used to determine whether modification of designated critical habitat may occur. Based
on the refined information, the Agency uses the best available information to distinguish
15
-------
those actions that "may affect, but are not likely to adversely affect" from those actions
that "may affect and are likely to adversely affect" the assessed listed species and/or
result in "no effect" or potential modification to the PCEs of its designated critical
habitat. This information is presented as part of the Risk Characterization in Section 5 of
this document.
The Agency believes that the analysis of direct and indirect effects to listed species
provides the basis for an analysis of potential effects on the designated critical habitat.
Because strychnine is expected to directly impact living organisms within the action area
(defined in Section 2.7), critical habitat analysis for strychnine is limited in a practical
sense to those PCEs of critical habitat that are biological or that can be reasonably linked
to biologically mediated processes (i.e.., the biological resource requirements for the listed
species associated with the critical habitat or important physical aspects of the habitat that
may be reasonably influenced through biological processes). Activities that may modify
critical habitat are those that alter the PCEs and appreciably diminish the value of the
habitat. Evaluation of actions related to use of strychnine that may alter the PCEs of the
assessed species' critical habitat form the basis of the critical habitat impact analysis.
Actions that may affect the assessed species' designated critical habitat have been
identified by the Services and are discussed further in Section 2.6.
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 strychnine in accordance with the approved product labels for
California is "the action" relevant to this ecological risk assessment.
Although current registrations of strychnine allow for use nationwide, this ecological risk
assessment and effects determination addresses currently registered uses of strychnine in
portions of the action area that are reasonably assumed to be biologically relevant to the
CRLF, the CTS, and the SJKF and their designated critical habitat. Further discussion of
the action area for the CRLF, the CTS, and the SJKF and their critical habitat is provided
in Section 2.7.
No degradates were identified for strychnine in the environmental fate studies submitted.
Toxicity from degradates would not be of concern in any case, since strychnine is an
acute poison.
The Agency does not routinely include in its risk assessments, an evaluation of mixtures
of active ingredients, either those mixtures of multiple active ingredients in product
formulations or those in the applicator's tank. In the case of the product formulations
with multiple active ingredients each active ingredient is subject to an individual risk
assessment for regulatory decision regarding the active ingredient on a particular use site.
16
-------
If effects data are available for a formulated product containing more than one active
ingredient, they may be used qualitatively or quantitatively in accordance with the
Agency's Overview Document and the Services' Evaluation Memorandum (U.S., EPA
2004; USFWS/NMFS 2004).
Strychnine does not have any registered products that contain multiple active ingredients.
2.3 Previous Assessments
"The above ground uses of strychnine were 'temporarily canceled' by EPA
([OPP-3900I7E; PH-FRL 2451-2] Federal Register VOL 48, No. 203 /
Wednesday, October 19, 1983). Above ground uses of strychnine are canceled by
a court order (April 11, 1988, U.S. District Court for the District of Minnesota in
the case of Defenders of Wildlife v. Administrator, EPA . Civil No. 4-86-687) that
enjoins EPA from continuing the registrations of Strychnine for above ground use.
We believe that the danger from the below ground uses of Strychnine is minimal when
used as directed. When the precautions recommended are taken, it does not constitute a
threat to nontarget and endangered species."
In the disciplinary review of the 1996 Reregi strati on Eligibility Decision (RED) (USEPA,
1996a) EFED found that "The studies have demonstrated that the use of
Strychnine above ground poses a threat to nontarget animals and may cause
jeopardy to members of endangered, or threatened species...We believe that the danger
from the below ground uses of Strychnine is minimal when used as directed. When the
precautions as recommended are taken, it does not constitute a threat to nontarget or
endangered species."
In a reevaluation of the use of strychnine in Canada, the Pest Management Regulatory
Agency (2005) proposed that "the use of strychnine to control Northern pocket gophers,
skunks, pigeons, wolves, coyotes and black bears does not represent an unacceptable risk
to human health or the environment provided that the proposed mitigation measures are
adopted." These uses include above ground poisoning.
2.4 Stressor Source and Distribution
Physical and Chemical Properties
Chemical name: (4br,7as,8ar,13S,13ar,13bs)-5,6,7a,8,8a,ll,13a,13b-octahydro-13H-
13,14-ethano-7,9-methanooxepino(3,4-a)pyrrolo(2,3-d)carbazol-15-
one
CAS No.: 57-24-9
17
-------
Chemical structure:
Molecular formula:
Molecular weight:
Physical state:
Melting point:
Solubility (20°C):
Dissociation constant
(pKa):
Vapor pressure (20°C):
Henry's Law Constant:
Octanol/Water Partition
Coefficient:
334.40 g/mol
White crystalline powder.
273°C.
11.5 mg/L water
-\-9
8.26
2.9 x KTmrnHg
6. Ox 10"14atmm3/mol
0.9 at pH 5
4.0 at pH 7
114.0atpH9
2.4.1 Environmental Fate Properties
The acceptable environmental fate data are limited. Neither hydrolysis nor soil
photolysis is a significant transformation pathway; no data are available for aqueous
photodegradation. No acceptable metabolism data have been submitted to the Agency;
qualitative information from the submitted studies suggest that aerobic degradation in soil
can sometimes not occur, may be very slow, or can occur rapidly following a significant
lag period under as yet undefined conditions. Batch adsorption/desorption data
demonstrate strychnine's strong binding to a number of soils. With the present use pattern
of applying strychnine into specific below-ground burrows, strychnine is not likely to
reach ground or surface water.
Table 2.1 lists the environmental fate properties of strychnine.
Table 2.1. Summary of Strychnine Environmental Fate Properties
Study
Hydrolysis
Direct Aqueous
Value (units)
Stable
No data
Major Degradates
Minor Degradates
None
-
MRID#
41122301
Study Status
Acceptable
No study submitted
18
-------
Table 2.1. Summary of Strychnine Environmental Fate Properties
Study
Photolysis
Soil Photolysis
Aerobic Soil
Metabolism
Anaerobic Soil
Metabolism
Anaerobic Aquatic
Metabolism
Aerobic Aquatic
Metabolism
Kd.ads / Kd.des (mL/g)
Terrestrial Field
Dissipation
Aquatic Field
Dissipation
Value (units)
Stable
No acceptable data
No data
No data
No data
39-168
No data
No data
Major Degradates
Minor Degradates
None detected
—
—
—
—
—
—
MRID#
42973401
42366501
Study Status
Acceptable
Submitted studies
invalid1
No study submitted
No study submitted
No study submitted
Acceptable
No study submitted
No study submitted
Aerobic soil metabolism studies did not determine material balances and did not identify degradates
(MRIDs 42234201 and 43407601).
The strychnine molecule (parent) does not hydrolyze at pH 5, 7, or 9 (MRID 41122301).
Strychnine is apparently stable to soil photolysis, since only a minimal amount of
strychnine is transformed within the experimental period (30 days of irradiation with
xenon light); no products of the transformation could be detected (MRID 42973401).
The data indicate that strychnine is immobile; the parent is adsorbed to organic matter
and clay. Using batch equilibrium techniques, strychnine had Freundlich Kadsin loamy
sand, sandy loam, loam, and sandy clay loam soils of 39.79, 94.65, 118.87, and 168.97
mL/g, respectively; adsorption increased with increasing cation exchange capacity
(CEC). Desorption (Kdes) values were 55.0, 89.4, 114.6, and 146.1 mL/g for the loamy
sand, the sandy loam, the loam, and the sandy clay loam soils, respectively (MRID
42366501).
2.4.2 Environmental Transport Mechanisms
Because strychnine is used only as a burrow-buried grain bait, surface water runoff and
spray drift are not expected to be routes of exposure. Strychnine is not expected to
volatilize, due to its low vapor pressure and Henry's Law Constant. In addition, soil-
bound residues of strychnine are not expected to migrate to nearby or more distant
ecosystems under subsurface application scenarios.
2.4.3 Mechanism of Action
Strychnine is a powerful convulsant. Glycine, an important inhibitory transmitter to
motorneurons and interneurons in the spinal cord, is affected by strychnine. Strychnine
acts as a selective competitive antagonist to block the inhibitory effects of glycine at all
19
-------
glycine receptors. The convulsant action of strychnine results from interference with
postsynaptic inhibition normally mediated by glycine, causing excessive excitation that
manifests itself as convulsions.
2.4.4 Use Characterization
Analysis of labeled use information is the critical first step in evaluating the federal
action. The current label for strychnine 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 2.2 presents the current registered products, use sites, and application methods
considered in this assessment. Strychnine use in California is currently limited to only
below-ground application to control pocket gophers (Thomomys spp.).
Table 2.2 Strychnine Products allowed for use in California .
EPA Reg.
No.
322-1
641-1
641-2
814-4
909-2
4271-10
4271-17
5042-32
5042-34
10031-2
Product Name
Fort Dodge Gopher
Bait
Gopher-GO
Gopher-GO AG Bait
Ro-Dex for Pocket
Gophers
Cooke Quick Action
Gopher Mix
Pocket Gopher Bait
containing strychnine
1-10 formulation on
oats
Pocket Gopher Bait
containing strychnine
1-10 formulation on
milo
RCO Omega Gopher
Grain Bait
RCO Avalon Mixed
Grain Gopher Bait
Petersen's Pocket
Gopher Killer II for
%ai
by wt
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Use site
Rangeland, pastures,
cropland and non-ag
areas
Yard and garden areas
around homes
Rangeland, pastures,
cropland and non-ag
areas
Outdoor residential
areas including lawns
Outdoor residential
areas including lawns
Orchards, alfalfa fields,
hay fields, pastures,
rangelands, and
noncrop areas.
Orchards, alfalfa fields,
hay fields, pastures,
rangelands, and
noncrop areas.
Terrestrial food crops,
and terrestrial nonfood
and forestry areas
Rangelands, pastures,
croplands, forests, and
non-agricultural areas
Cropland, rangelands,
and noncrop areas.
Application method
Burrow builder
Probe-assisted manual
applications, or manually operated
bait-dispensing probes
Probe-assisted manual
applications, or manually operated
bait-dispensing probes
Burrow builder
Probe-assisted manual
applications, or manually operated
bait-dispensing probes
Long handled spoon only
Long handled spoon only
Burrow builder
Long handled spoon
Burrow builder
Long handled spoon
Long handled spoon
Probe-assisted manual applications
Tractor-operated mechanical
burrow builder
Probe-assisted hand-held bait
dispensers, or standard manual
hand baiting techniques
Mechanical burrow builder
20
-------
Table 2.2 Strychnine Products allowed for use in California1.
EPA Reg.
No.
10031-3
10031-6
35380-1
35380-3
36029-1
36029-7
36029-16
53883-23
53883-24
56228-11
56228-12
56228-19
56228-20
CA
79014500
Product Name
pocket gopher
control only
Petersen's Pocket
Gopher Killer III for
pocket gopher
control only
Petersen's Pocket
Gopher Bait
Elston Gopher Getter
Bait
G. G. Jr. Gopher Getter
Bait
Wilco Gopher Getter
Type-1 Bait
Wilco Gopher Getter
AGBait
Wilco Pocket Gopher
Milo Bait for Hand
Baiting
Martin's Gopher Bait
50
Martin's Gopher Bait
50
0.5% Strychnine Milo
Pocket Gopher Bait for
use in burrow builders
0.5% Strychnine Pocket
Gopher Oat Bait for use
in burrow builders
0.5% Strychnine Milo
for Hand-
Baiting Pocket Gophers
0.5% Strychnine on
Oats for Hand-Baiting
Pocket Gophers
Wilco Gopher Getter
Restricted Use Bait
1.80% Bait
%ai
by wt
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1.8
Use site
Cropland, rangelands,
and noncrop areas.
Cropland, rangelands,
and noncrop areas.
Rangelands, pastures,
croplands, and non-
agricultural areas
Rangeland, pastures,
cropland and non-ag
areas
Yard and garden areas
around homes
Rangeland, pastures,
cropland and non-ag
areas
Rangeland, pastures,
cropland and non-ag
areas
Rangelands, pastures,
croplands and non-crop
areas
Rangelands, pastures,
croplands and non-crop
areas
Rangelands, pastures,
croplands, forests, and
non-agricultural areas
Rangelands, pastures,
croplands, forests, and
non-agricultural areas
Rangelands, pastures,
croplands, forests, and
non-agricultural areas
Rangelands, pastures,
croplands, forests, and
non-agricultural areas
Rangeland, pastures,
cropland, and
nonagricultural areas
Application method
Probe-assisted manual applications
Mechanical burrow builder
Probe assisted manual applications
Mechanical burrow builder
Probe-assisted manual applications
Long handled spoon
Mechanical burrow builders
Probe-assisted manual applications
Mechanical hand probe
Applied manually
Tractor-operated mechanical
burrow builders, probe-assisted
manual applications, or manually
operated bait-dispensing probes
Probe-assisted manual
applications, or by use of manually
operated bait-dispensing probes
Long handled spoon
Burrow builder
Long handled spoon
Burrow builder only
Burrow builder only
Probe assisted manual applications
Long handled spoon
Probe assisted manual applications
Long handled spoon
Tractor-operated mechanical
burrow builders, probe-assisted
manual applications, or manually
operated bait-dispensing probes
1. Based on data supplied by BEAD (County-level Usage for Strychnidin; Strychnine; Triclopyr,
butoxyethyl ester; Triclopyr, triethylamine salt; Diflubenzuron; Trifluralin; Thiobencarb; Chlorpyrifos;
Vinclozalin; Iprodione in California in Support of a Red Legged Frog Endangered Species Assessment.
J. Carter, BEAD/OPP. June 8, 2009).
21
-------
No national map is available showing the estimated poundage of strychnine uses across
the United States.
The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis
of both national- and county-level usage information using state-level usage data
obtained from USDA-NASS3, Doane (www.doane.com: the full dataset is not provided
due to its proprietary nature) and the California's Department of Pesticide Regulation
Pesticide Use Reporting (CDPR PUR) database4. CDPR PUR is considered a more
comprehensive source of usage data than USDA-NASS or EPA proprietary databases,
and thus the usage data reported for strychnine by county in this California-specific
assessment were generated using CDPR PUR data. Eight years (1999-2006) of usage
data were included in this analysis. Data from CDPR PUR were obtained for every
agricultural pesticide application made on every use site at the section level
(approximately one square mile) of the public land survey system.5 BEAD summarized
these data to the county level by site, pesticide, and unit treated. Calculating county-level
usage involved summarizing across all applications made within a section and then across
all sections within a county for each use site and for each pesticide. The county level
usage data that were calculated include: average annual pounds applied, average annual
area treated, and average and maximum application rate across all eight years. The units
of area treated are also provided where available.
The following analysis of the CDPR PUR data is a summarization of reported values, for
the purpose of providing a characterization of the extent and nature of strychnine use in
California. Based on the label information presented in Table 2.2, the only use sites for
which strychnine-containing products are allowed for use in California are: outdoor
residential areas (including lawns/yard and garden areas around homes) and rangelands,
pastures, croplands, forests, and non-agricultural areas. Since the site names for which
data are reported do not correspond exactly to the use sites allowed on the labels, reported
data were grouped into Non-agricultural and Agricultural use sites based on the site
names reported in the CALPUR data. The non-agricultural and agricultural use data were
further grouped into broad categories to better show the sectors with the greatest usage.
Over the 8 years of data, a total of 12199.46 Ibs of strychnine as active ingredient were
applied to 745797.34 acres in 57 California counties. The most pounds of strychnine
(3711.33, or 30.4%) were applied to the grouping Public Health sites (which also
includes vertebrate control, structural pest control, fumigation other, and commodity
fumigation). The predominant reported usage within that grouping was for vertebrate
3 United States Department 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.htnrfagchem.
4 The California Department of Pesticide Regulation's Pesticide Use Reporting database provides a census
of pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/purmain.htm.
5 Most pesticide applications to parks, golf courses, cemeteries, rangeland, pastures, and along roadside and
railroad rights of way, and postharvest treatments of agricultural commodities. The primary exceptions to
the reporting requirement are home-and-garden use and most industrial and institutional uses
(http://www.cdpr.ca.gov/docs/pur/purmain.htm).
22
-------
control; however, it is not possible to determine an average application rate in pounds per
acre based on the data as reported.
There were no obvious trends in usage over the eight-year reporting timeframe.
A summary of Strychnine usage for all CDPR PUR use sites is provided below in Table
2.3.
Table 2.3 Summary of California Department of Pesticide Registration (CDPR) Pesticide
Use Reporting (PUR) Data from 1999 to 2006 for Currently Registered Strychnine Uses1
Site Name
Total
Pounds
Applied
Average
Annual
Pounds
Applied 2
Average
Application
Rate
(Ibs a.i./A)2
Maximum
Application
Rate
(Ibs a.i./A)
NON-AGRICULTURAL USES
Public health
(also includes vertebrate control, structural pest
control, fumigation other, commodity
fumigation)
Household/domestic dwellings/outdoor premises
(Includes poultry, recreation area, landscape
maintenance, animal premises)
Nonagricultural uncultivated areas/soils
(Also includes water area, rights of way,
ditchbank)
Nursery plants
(includes outdoor transplants, plants in
containers, flowers; greenhouse; transplants,
plants in containers, flowers; turf /sod)
Forest trees
(Includes forest timberland, Christmas trees)
3711.33
2631.93
942.39
9.53
79.63
24.93
34.99
31.68
0.11
1.75
N/A3
N/A3
N/A3
0.006
0.002
0.066
1.5
0.18
0.208
0.029
AGRICULTURAL USES
Grapes, wine
Agricultural uncultivated areas
Citrus
(also includes oranges, tangerine, tangelo, lime,
lemon, kumquat, grapefruit)
Vegetable crops
(includes yam, watermelon, tomato, sweet
potato, strawberry, squash, small fruits,
pumpkin, potato, pepper, peas, lettuce, jojoba
bean, herbs, cucumber, corn, celery, cantaloupe,
broccoli, bean (all), asparagus)
Alfalfa
Nut orchards
(includes walnut, pistachio, pecan, chestnut,
almond)
Orchards
(includes orchard floor, nectarine, mango, olives,
stone fruit, raspberry, prune, pomegranate, plum,
persimmon, pear, peach, kiwi, fig, date, cherry,
cherimoya, boysenberry, blueberry, avocado,
apricot, apple, grapes)
Pastureland
Rangeland
Forage/fodder/hay
(also includes oat forage/fodder, wheat
forage/fodder, peas forage/fodder, corn
forage/fodder)
1871.35
125.16
302.52
12.19
430.07
1132.86
901.77
8.59
1.54
6.72
44.82
11.53
10.77
0.05
2.70
11.19
4.10
0.07
0.02
0.10
0.091
0.044
0.030
0.015
0.015
0.014
0.009
0.009
0.008
0.008
0.288
0.738
0.158
0.18
0.318
0.288
0.450
0.120
0.060
0.029
23
-------
Table 2.3 Summary of California Department of Pesticide Registration (CDPR) Pesticide
Use Reporting (PUR) Data from 1999 to 2006 for Currently Registered Strychnine Uses1
Site Name
Agricultural crops/soils
(includes oats, wheat, research commodity,
county ag comm., cotton, clover, barley,
sugarbeet, soil fumigant preplan!)
Total
Pounds
Applied
22.00
Average
Annual
Pounds
Applied 2
0.83
Average
Application
Rate
(Ibs a.i./A)2
0.006
Maximum
Application
Rate
(Ibs a.i./A)
0.045
1. Based on data supplied by BEAD (County-level Usage for Strychnidin; Strychnine; Triclopyr, butoxyethyl ester; Triclopyr,
triethylamine salt; Diflubenzuron; Trifluralin; Thiobencarb; Chlorpyrifos; Vinclozalin; Iprodione in California in Support of a Red
Legged Frog Endangered Species Assessment. J. Carter, BEAD/OPP. June 8, 2009).
2. The average annual pounds applied was calculated as the weighted average of the average application rate for one county or average
annual pounds applied for one county. The values reflect the average annual pounds applied to those sites across all counties and the
average application rate for those sites across all counties.
3. Because of the nature of the application method or the sites treated insufficient info was provided from PUR data to calculate this
value.
2.5 Assessed Species
Table 2.4 provides a summary of the current distribution, habitat requirements, and life
history parameters for the listed species being assessed. More detailed life-history and
distribution information can be found in Attachments I, II, III, and IV. See Figure 2.3
for a map of the current range and critical habitat of the CRLF. See Figure 2.4 for a map
of the range and critical habitat of the CIS. See Figure 2.5 for a map of the current
range of the SJKF.
24
-------
Table 2.4. Summary of Current Distribution, Habitat Requirements, and Life History Information for the Assessed Listed Species
Assessed
Species
California red-
legged frog
(Rana aurora
draytonii)
San Joaquin kit
fox
(Vulpes macrotis
mutica)
California tiger
salamander
(Ambystoma
californiense)
Size
Adult
(85-1 38 cm in
length),
Females -
9-238 g,
Males -
13-163 g;
Juveniles
(40-84 cm in
length)
Adult
~2kg
50 g
Current Range
Northern CA coast,
northern Transverse
Ranges, foothills of Sierra
Nevada, and in southern
CA south of Santa Barbara
Alameda, Contra Costa,
Fresno, Kem, Kings,
Madera, Merced,
Monterey, San Benito,
San Joaquin, San Luis
Obispo, Santa Barbara,
Santa Clara, Stanislaus,
Tulare and Ventura
counties
There are two distinct
population segments; one
in Santa Barbara County
and the other in Sonoma
County.
Habitat Type
Freshwater perennial or near-perennial
aquatic habitat with dense vegetation;
artificial impoundments; riparian and
upland areas
A variety of habitats, including grasslands,
scrublands (e.g., chenopod scrub and sub-
shrub scrub), vernal pool areas, oak
woodland, alkali meadows and playas, and
an agricultural matrix of row crops,
irrigated pastures, orchards, vineyards, and
grazed annual grasslands. Kit foxes dig
their own dens, modify and use those
already constructed by other animals
(ground squirrels, badgers, and coyotes), or
use human-made structures .(culverts,
abandoned pipelines, or banks in sumps or
roadbeds). They move to new dens within
their home range often (likely to avoid
predation by coyotes)
Freshwater pools or ponds (natural or man-
made, vernal pools, ranch stock ponds,
other fishless ponds); Grassland or oak
savannah communities, in low foothill
regions; Small mammal burrows
Designated
Critical
Habitat?
Yes
No
Yes
Reproductive
Cycle
Breeding: Nov. to Apr.
Tadpoles: Dec. to Mar.
Young juveniles: Mar. to
Sept.
Mating and conception:
late December - March.
Gestation period: 48 to 52
days.
Litters bom: February -
late March
Pups emerge from their
dens at about 1 -month of
age and may begin to
disperse after 4-5
months usually in Aug. or
Sept.
Emerge from burrows and
breed: fall and winter rains
Eggs: laid in pond Dec. -
Feb., hatch: after 10 to 14
days
Larval stage: 3-6 months,
until the ponds dry out,
metamorphose late spring
or early summer, migrate
to small mammal burrows
Diet
Aquatic-phase2: algae.
freshwater aquatic
invertebrates
Terrestrial-phase :
aquatic and terrestrial
invertebrates, small
mammals, fish and
frogs
Small animals
including blacktailed
hares, desert cottontails,
mice, kangaroo rats,
squirrels, birds, lizards,
insects and grass. It
satisfies its moisture
requirements from prey
and does not depend on
freshwater sources.
Aquatic Phase: algae.
snails, zooplankton,
small crustaceans, and
aquatic larvae and
invertebrates, smaller
tadpoles of Pacific tree
frogs, CRLF, toads;
Terrestrial Phase:
terrestrial invertebrates,
insects, frogs, and
worms
1 For more detailed information on the distribution, habitat requirements, and life history information of the assessed listed species, see Attachments I, II, and III.
2 For the purposes of this assessment, tadpoles and submerged adult frogs are considered "aquatic" because exposure pathways in the water are considerably different than those that
occur on land.
25
-------
Recovery Units
1. Sierra Nevada Foothills and Central Valley
2. North Coast Range Foothills and Western
Sacramento River Valley
3. North Coast and North San Francisco Bay
4. South and East San Francisco Bay
5. Central Coast
6. Diablo Range and Salinas Valley
7. Northern Transverse Ranges and Tehachapi
Mountains
8. Southern Transverse and Peninsular Ranges
Legend
J Recovery Unit Boundaries
| Currently Occupied Core Areas
|^| Critical Habitat
MH CNDDB Occurence Sections
] County Boundaries g-
Core Areas
1. Feather River
2. Yuba River- S. Fork Feather River
3. Traverse Creek/ Middle Fork/ American R. Rubicon
4. Cosumnes River
5. South Fork Calaveras River*
6. Tuolumne River*
7. Piney Creek*
8. Cottonwood Creek
9. Putah Creek - Cache Creek*
10. Lake Berryessa Tributaries
11. Upper Sonoma Creek
12. Petaluma Creek — Sonoma Creek
13. R. Reyes Peninsula
14. Belvedere Lagoon
15. Jameson Canyon - Lower Napa River
16. East San Francisco Bay
17. Santa Clara Valley
18. South San Francisco Bay
* Core areas that were historically occupied by the California red
19. Watsonville Slough-Elkhorn Slough
20. Carmel River — Santa Lucia
21. Gablan Range
22. EsteroBay
23. Arroyo Grange River
24. Santa Maria River — Santa Ynez River
25. Sisquoc River
26. Ventura River — Santa Clara River
27. Santa Monica Bay - Venura Coastal Streams
28. Estrella River
29. San Gabriel Mountain*
30. Forks of the Mojave*
31. Santa Ana Mountain*
32. Santa Rosa Plateau
33. San Luis Ray*
34. Sweetwater*
35. Laguna Mountain*
-legged frog are not included in the map
Figure 2.3. Recovery Unit, Core Area, Critical Habitat, and Occurrence Designations for CRLF
26
-------
California Tiger Salamander Habitat
Legend
| CATiger Salamander CH
^J CA Tiger Salamander (sections)
CAcounties
• Kilometers
0 510 20 30 40
1:1.752,468
Map created by US EPA on 1 [(7/2009. Projection: Alters Equal
Area Conic USGS, North American Datum of 1983 (NAD 1933).
County boundariesfrom ESRI (2002). Occurrence section data
obtained from Case No. 07-2794-JCS. Critical habitat from
http 'M c rit ha b .fws. govf.
10/2009
Figure 2.4. Range and Critical Habitat for CTS
27
-------
San Joaquin Kit Fox Habitat
AA A* Merced
SJ Kit Fox distribution (RP)
^| SJ Kit Fox occurrence sections
^| CAcounties
Map created by US EPA on 1 [17/2009. Projection: Albers Equal ba™a Barbara
Area Conic USGS, North American Datum of 1983 (NAD 1983).
County boundaries from ESRI (2002). Occurrence section data
from Case No. 07-2794-JCS, distribution data from
USFWS Recovery Plan 1 998.
Figure 2.5. Current Distribution of the SJKF
28
-------
2.6 Designated Critical Habitat
Critical habitat has been designated for the CRLF and the CTS. 'Critical habitat' is
defined in the ESA as the geographic area occupied by the species at the time of the
listing where the physical and biological features necessary for the conservation of the
species exist, and there is a need for special management to protect the listed species. It
may also include areas outside the occupied area at the time of listing if such areas are
'essential to the conservation of the species.' Critical habitat receives protection under
Section 7 of the ESA through prohibition against destruction or adverse modification
with regard to actions carried out, funded, or authorized by a federal Agency. Section 7
requires consultation on federal actions that are likely to result in the destruction or
adverse modification of critical habitat.
To be included in a critical habitat designation, the habitat must be 'essential to the
conservation of the species.' Critical habitat designations identify, to the extent known
using the best scientific and commercial data available, habitat areas that provide
essential life cycle needs of the species or areas that contain certain primary constituent
elements (PCEs) (as defined in 50 CFR 414.12(b)). PCEs include, but are not limited to,
space for individual and population growth and for normal behavior; food, water, air,
light, minerals, or other nutritional or physiological requirements; cover or shelter; sites
for breeding, reproduction, rearing (or development) of offspring; and habitats that are
protected from disturbance or are representative of the historic geographical and
ecological distributions of a species. Table 2.5 describes the PCEs for the critical
habitats designated for the CRLF and the CTS.
29
-------
Table 2.5. Designated Critical Habitat PCEs for the CRLF and the CIS1.
Species
CRLF
CTS
PCEs
Alteration of channel/pond morphology or geometry and/or increase
in sediment deposition within the stream channel or pond.
Alteration in water chemistry /quality including temperature,
turbidity, and oxygen content necessary for normal growth and
viability of juvenile and adult CRLFs and their food source.
Alteration of other chemical characteristics necessary for normal
growth and viability of CRLFs and their food source.
Reduction and/or modification of aquatic-based food sources for pre-
metamorphs (e.g., algae)
Elimination and/or disturbance of upland habitat; ability of habitat to
support food source of CRLFs: Upland areas within 200 ft of the
edge of the riparian vegetation or dripline surrounding aquatic and
riparian habitat that are comprised of grasslands, woodlands, and/or
wetland/riparian plant species that provides the CRLF shelter,
forage, and predator avoidance
Elimination and/or disturbance of dispersal habitat: Upland or
riparian dispersal habitat within designated units and between
occupied locations within 0.7 mi of each other that allow for
movement between sites including both natural and altered sites
which do not contain barriers to dispersal
Standing bodies of fresh water, including natural and man-made
(e.g., stock) ponds, vernal pools, and dune ponds, and other
ephemeral or permanent water bodies that typically become
inundated during winter rains and hold water for a sufficient length
of time (i.e., 12 weeks) necessary for the species to complete the
aquatic (egg and larval) portion of its life cycle2
Barrier-free uplands adjacent to breeding ponds that contain small
mammal burrows. Small mammals are essential in creating the
underground habitat that juvenile and adult CTS depend upon for
food, shelter, and protection from the elements and predation
Upland areas between breeding locations (PCE 1) and areas with
small mammal burrows (PCE 2) that allow for dispersal among such
sites
Reference
50CFR414.12(b),
2006
FR Vol. 69 No. 226
CTS, 68584, 2004
1 These PCEs are in addition to more general requirements for habitat areas that provide essential life cycle needs of
the species such as, space for individual and population growth and for normal behavior; food, water, air, light,
minerals, or other nutritional or physiological requirements; cover or shelter; sites for breeding, reproduction, rearing
(or development) of offspring; and habitats that are protected from disturbance or are representative of the historic
geographical and ecological distributions of a species.
2 PCEs that are abiotic, including, physico-chemical water quality parameters such as salinity, pH, and hardness are not
evaluated because these processes are not biologically mediated and, therefore, are not relevant to the endpoints
included in this assessment.
More detail on the designated critical habitat applicable to this assessment can be found
in Attachment I (for the CRLF) and Attachment III (for the CTS). 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 strychnine
that may alter the PCEs of the designated critical habitat for the CRLF and the CTS form
the basis of the critical habitat impact analysis.
30
-------
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 strychnine is expected to directly impact living
organisms within the action area, critical habitat analysis for strychnine 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 strychnine is likely to encompass considerable portions of the
United States based on the large array of agricultural and/or non-agricultural uses.
However, the scope of this assessment limits consideration of the overall action area to
those portions that may be applicable to the protection of the CRLF, the SJKF, and the
CIS and their designated critical habitat within the state of California. Although the
watershed for the San Francisco Bay extends northward into the very southwestern
portion of Lake County, Oregon, and westward into the western edge of Washoe County,
Nevada, the non-California portions of the watershed are small. In addition, because of
the nature of the application methods for strychnine (burial in rodent burrows) and its low
mobility in soil, strychnine is expected to contribute a negligible amount from use in
these areas, and so they are not considered as part of the action area applicable to this
assessment.
The definition of action area requires a stepwise approach that begins with an
understanding of the federal action. The federal action is defined by the currently labeled
uses for strychnine. An analysis of labeled uses and review of available product labels
was completed (Table 2.2). There is only one special local needs (SLN) use registered in
California (CA) (Table 2.6):
Table 2.6 Special Local Needs (SLN) Registration for use in California.
EPA Reg. No.
CA79014500
Product Name
Wilco Gopher Getter
Restricted Use Bait
1.80% Bait
%ai
by wt
1.8
Use site
Rangeland, pastures,
cropland, and
nonagricultural areas
Application method
Tractor-operated mechanical
burrow builders, probe-assisted
manual applications, or manually
operated bait-dispensing probes
For strychnine, the site names in Table 2.7 are considered as part of the federal action
evaluated in this assessment:
31
-------
Table 2.7. Uses of Strychnine Considered as Part of the Federal Action Evaluated in this
Assessment
Site Name
Maximum rate per
application
(Ib bait / acre)
Maximum Number
of Applications (per
year)
Minimum
Application Interval
(days)
Agricultural Uses1
Agricultural crops/soils
(unspecified)
Agricultural uncultivated areas
Alfalfa
Grass forage/fodder/hay
Orchards (unspecified)
Pastures
Rangeland
1 Ib bait treats 1 to 8
acres (hand treatment)
1 to 3 Ib bait treats 1
acre (burrow builder)
Not specified
Not specified
Non-Agricultural Uses2
Forest trees (all or unspecified)
Nonagricultural uncultivated
areas/soils
Residential lawns
Household/domestic dwellings
outdoor premises
1 Ib bait treats 1 to 8
acres (hand treatment)
1 to 3 Ib bait treats 1
acre (burrow builder)
1 Ib bait treats 1 to 8
acres (hand treatment)
Not specified
Not specified
1 Table A2. Food/Feed Use Patterns Summary for Strychnine (Case 3133). Current as of 11/13/2008.
LUIS Report generated 3/26/2009.
2 Table A3. Non-Food/Non-Feed Use Patterns Summary for Strychnine (Case 3133). Current as of
11/13/2008. LUIS Report generated 3/26/2009.
Following a determination of the assessed uses, an evaluation of the potential "footprint"
of strychnine use patterns (i.e., the area where pesticide application occurs) is determined.
This "footprint" represents the initial area of concern, based on an analysis of available
land cover data for the state of California. The initial area of concern is defined as all
land cover types and the stream reaches within the land cover areas that represent the
labeled uses described above. Based on the many and varied uses sites, and the
widespread use of strychnine based on the CalPUR data, the initial area of concern is the
entire state of California. The potential boundaries of the action area are usually
determined by estimating the extent of offsite transport via spray drift and runoff;
however, since strychnine is a bait used as burrow treatment, spray drift and runoff of
strychnine residues will not occur.
The Agency's approach to defining the action area under the provisions of the Overview
Document (USEPA 2004) considers the results of the risk assessment process to establish
boundaries for that action area with the understanding that exposures below the Agency's
defined Levels of Concern (LOCs) constitute a no-effect threshold. Deriving the
geographical extent of this portion of the action area is based on consideration of the
types of effects that strychnine may be expected to have on the environment, the
exposure levels to strychnine that are associated with those effects, and the best available
information concerning the use of strychnine and its fate and transport within the state of
California. Specific measures of ecological effect for the assessed species that define the
action area include any direct and indirect toxic effect to the assessed species and any
32
-------
potential modification of its critical habitat, including reduction in survival, growth, and
fecundity as well as the full suite of sublethal effects available in the effects literature.
Therefore, the action area extends to a point where environmental exposures are below
any measured lethal or sublethal effect threshold for any biological entity at the whole
organism, organ, tissue, and cellular level of organization. In situations where it is not
possible to determine the threshold for an observed effect, the action area is not spatially
limited and is assumed to be the entire state of California.
An evaluation of usage information was conducted to determine the area where use of
strychnine may impact the assessed species. This analysis is used to characterize where
predicted exposures are most likely to occur, but does not preclude use in other portions
of the action area. A more detailed review of the county-level use information was also
completed. These data suggest that strychnine has historically been used on a wide
variety of agricultural and non-agricultural uses.
2.8 Assessment Endpoints and Measures of Ecological Effect
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."6 Selection of the assessment endpoints is based on valued
entities (e.g., CRLF, the SJKF, and the CTS, organisms important in the life cycle of the
assessed species, and the PCEs of its designated critical habitat), the ecosystems
potentially at risk (e.g., waterbodies, riparian vegetation, and upland and dispersal
habitats), the migration pathways of strychnine (e.g., runoff, spray drift, etc.), and the
routes by which ecological receptors are exposed to strychnine (e.g., direct contact, etc.).
2.8.1 Assessment Endpoints
Assessment endpoints for the CRLF, the SJKF, and the CTS include direct toxic effects
on the survival, reproduction, and growth of individuals, as well as indirect effects, such
as reduction of the prey base or modification of its habitat. In addition, potential
modification of critical habitat is assessed by evaluating potential effects to PCEs, which
are components of the habitat areas that provide essential life cycle needs of the assessed
species. Each assessment endpoint requires one or more "measures of ecological effect,"
defined as changes in the attributes of an assessment endpoint or changes in a surrogate
entity or attribute in response to exposure to a pesticide. Specific measures of ecological
effect are generally evaluated based on acute and chronic toxicity information from
registrant-submitted guideline tests that are performed on a limited number of organisms.
Additional ecological effects data from the open literature are also considered. It should
be noted that assessment endpoints are limited to direct and indirect effects associated
with survival, growth, and fecundity, and do not include the full suite of sublethal effects
used to define the action area. According the Overview Document (USEPA 2004), the
Agency relies on acute and chronic effects endpoints that are either direct measures of
impairment of survival, growth, or fecundity or endpoints for which there is a
scientifically robust, peer reviewed relationship that can quantify the impact of the
measured effect endpoint on the assessment endpoints of survival, growth, and fecundity.
' U.S. EPA (1992). Framework of Ecological Risk Assessment. EPA/630/R-92/001.
33
-------
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 risks for each of the assessed species associated with exposure to strychnine is
provided in Section 2.5 and Table 2.6.
As described in the Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa
do not include aquatic-phase amphibians, freshwater fish, freshwater invertebrates, or
aquatic plants, because strychnine is not applied near water and is not expected to wash
into water. It also did not include terrestrial plants, because strychnine is not applied to or
near plants. The assessment did include birds (surrogate for terrestrial-phase
amphibians), mammals, and terrestrial invertebrates. Acute (short-term) toxicity
information is characterized based on registrant-submitted studies and a comprehensive
review of the open literature on strychnine. No chronic (long-term) studies were found.
Table 2.8 identifies the taxa used to assess the potential for direct and indirect effects
from the uses of strychnine for each listed species assessed here. The specific assessment
endpoints used to assess the potential for direct and indirect effects to each listed species
are provided in Table 2.9.
Table 2.8. Taxa Used in the Analyses of Direct and Indirect Effects for the Assessed
Listed Species.
Listed Species
California Red
Legged Frog
San Joaquin
kit fox
California tiger
salamander
Birds
Direct
Indirect (prey)
Indirect (prey)
Direct
Mammals
Indirect (prey)
Direct
Indirect (prey)
N/A
Terrestrial Invertebrates
Indirect (prey)
Indirect (prey)
Indirect (prey)
N/A = Not applicable
34
-------
Table 2.9. Taxa and Assessment Endpoints Used to Evaluate the Potential for the Use of Strychnine to
Result in Direct and Indirect Effects to the Assessed Listed Species.
Taxa Used to Assess
Direct and/or Indirect
Effects to Assessed
Species
Assessed Listed
Species
Assessment Endpoints
Measures of Ecological Effects
Direct Effect
-Terrestrial-phase CRLF
and CTS
Survival, growth, and
reproduction of individuals
via direct effects
1. Birds
Indirect Effect (prey)
-SJKF
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (birds)
la. Most sensitive bird3 or terrestrial-
phase amphibian acute LC50 or LD50
(guideline or ECOTOX)
Ib. Most sensitive bird3 or terrestrial-
phase amphibian chronic NOAEC
(guideline or ECOTOX)
Direct Effect
-SJKF
Survival, growth, and
reproduction of individuals
via direct effects
2. Mammals
Indirect Effect
(prey/habitat from
burrows)
-Terrestrial-phase CRLF
and CTS
-SJKF
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (mammals)
2a. Most sensitive mammal acute LC50 or
LD50 (guideline or ECOTOX)
2b. Most sensitive laboratory rat chronic
NOAEC (guideline or ECOTOX)
3. Terrestrial
Invertebrates
Indirect Effect (prey)
-Terrestrial-phase CRLF
-SJKF
Survival, growth, and
reproduction of individuals
via indirect effects on
terrestrial prey (terrestrial
invertebrates)
3a. Most sensitive terrestrial invertebrate
acute EC50 or LC50 (guideline or
ECOTOX)
3b. Most sensitive terrestrial invertebrate
chronic NOAEC (guideline or ECOTOX)
1 Birds are used as surrogates for terrestrial phase amphibians.
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 strychnine that may alter the PCEs of the assessed species' designated
critical habitat. PCEs for the assessed species were previously described in Section 2.6.
Actions that may modify critical habitat are those that alter the PCEs and jeopardize the
continued existence of the assessed species. Therefore, these actions are identified as
assessment endpoints. It should be noted that evaluation of PCEs as assessment
endpoints is limited to those of a biological nature (i.e., the biological resource
requirements for the listed species associated with the critical habitat) and those for
which strychnine effects data are available.
Some components of these PCEs are associated with physical abiotic features (e.g.,
presence and/or depth of a water body, or distance between two sites), which are not
expected to be measurably altered by use of pesticides. Measures of ecological effect
used to assess the potential for adverse modification to the critical habitat of the CRLF
and the CTS are described in Table 2.10.
35
-------
Table 2. 10. Summary of Assessment Endpoints and Measures of Ecological Effect for
Primary Constituent Elements of Designated Critical Habitat for the CRLF and the CTS.
Taxon Used to
Assess
Modification of
PCE
1. Birds
2. Mammals
3. Terrestrial
Invertebrates
Assessed Listed
Species Associated
with the PCE
Direct Effect
-Terrestrial-phase
CRLF and CTS
Indirect Effect
(prey/habitat from
burrows)
-Terrestrial-phase
CRLF and CTS
Indirect Effect
(prey)
-Terrestrial-phase
CRLF and CTS
Assessment
Endpoints
Survival, growth, and
reproduction of
individuals via direct
effects
Modification of critical
habitat via change in
terrestrial prey
(mammals)
Modification of critical
habitat via change in
terrestrial prey
(terrestrial
invertebrates)
Measures of Ecological Effects
la. Most sensitive bird3 or
terrestrial-phase amphibian acute
LC50 or LD50 (guideline or
ECOTOX)
Ib. Most sensitive bird3 or
terrestrial-phase amphibian
chronic NOAEC (guideline or
ECOTOX)
2a. Most sensitive mammals acute
LC50 or LD50 (guideline or
ECOTOX)
2b. Most sensitive laboratory rat
chronic NOAEC (guideline or
ECOTOX)
3a. Most sensitive terrestrial
invertebrate acute EC50 or LC50
(guideline or ECOTOX)
3b. Most sensitive terrestrial
invertebrate chronic NOAEC
(guideline or ECOTOX)
3 Birds are used as surrogates for terrestrial phase amphibians.
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 strychnine to the environment.
Because strychnine is used in California only as a bait that is placed in the underground
burrows of pocket gophers, surface water runoff and spray drift are not expected to be
routes of exposure. Strychnine is not expected to volatilize, due to its low vapor pressure
and low Henry's law Constant. In addition, soil-bound residues of strychnine are not
expected to migrate to nearby or more distant ecosystems via long-range atmospheric
transport.
Effects on designated critical habitat in the CRLF and/or the CTS species' current ranges
such as effects on primary productivity and/or cover provided by aquatic plants, and the
composition of the aquatic and terrestrial plant communities, are not expected due to the
insignificant potential for exposure of aquatic and terrestrial plants to strychnine.
36
-------
Effects on designated critical habitat in the CRLF and/or the CIS species' current ranges
such as a reduction or change in aquatic habitat (via modification of water quality
parameters, habitat morphology, and/or sedimentation) are not expected due to the
insignificant potential for strychnine to reach aquatic systems.
The following risk hypotheses are presumed for each assessed species in this assessment.
The labeled use of strychnine within the action area may:
• directly affect the CRLF, the SJKF, or the CTS by causing mortality or by
adversely affecting growth or fecundity;
• indirectly affect the CRLF, the SJKF or the CTS or modify the designated critical
habitat of the CRLF or CTS, by reducing or changing the composition of their food
supply;
2.9.2 Diagram
The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies strychnine release mechanisms, biological receptor types, and effects
endpoints of potential concern. The conceptual model for the terrestrial phases of the
CRLF, the SJKF, and the CTS is shown in Figure 2.6. Although the conceptual models
for direct/indirect effects and modification of designated critical habitat PCEs are shown
on the same diagram, the potential for direct/indirect effects and modification of PCEs
will be evaluated separately in this assessment. Exposure routes shown in dashed lines
are not quantitatively considered because the contribution of those potential exposure
routes to potential risks to the CRLF, the SJKF, and the CTS and modification to
designated critical habitat is expected to be negligible.
Because there is an insignificant potential for aquatic exposure, a conceptual model for
aquatic phases of the CRLF and the CTS is not presented.
37
-------
Stressor
Source
Exposure
Media
Receptors
Attribute
Change
Strychnine applied to underground burrows of pocket gophers
Primary consumers
(Mammals, invertebrates)
Birds/terrestrial-
phase amphibians/
reptiles/mammals/
invertebrates
V
ndividual organisms
Reduced survival
Reduced growth
Reduced reproduction
Food chain
Reduction in
prey
Modification of
PCEs related to
prey availability
Habitat integrity
Reduced cover
ommunity change
Modification of PCEs
related to habitat
Figure 2.6. Conceptual Model for Terrestrial Phase of the CRLF, CTS, and SJKF.
2.10 Analysis Plan
In order to address the risk hypothesis, the potential for direct and indirect effects to the
CRLF, the SJKF, and the CTS, prey items, and habitat is estimated based on a taxon-
level approach. In the following sections, the use, environmental fate, and ecological
effects of strychnine are characterized and integrated to assess the risks. Although this is
usually accomplished using a risk quotient (ratio of exposure concentration to effects
concentration) approach, the nature of the use profile requires a qualitative assessment of
risk. This does not allow for an estimate of likelihood and/or magnitude of an adverse
effect.
2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model
2.10.1.1 Measures of Exposure
38
-------
The application methods for strychnine-containing products (burial in rodent burrows)
indicate that runoff and spray drift will not be potential transport mechanisms of
strychnine to the aquatic and terrestrial habitats of the CRLF, the SJKF, and the CTS. In
addition, the low vapor pressure of strychnine in combination with no interaction with the
above ground air indicate that atmospheric transport is unlikely. Therefore, measures of
exposure based on aquatic models that predict estimated environmental concentrations
(EECs) of strychnine are not applicable to strychnine, and so aquatic modeling was not
performed. Exposure of terrestrial and wetland plants to strychnine is not expected, so
TerrPlant modeling was not performed.
Direct dietary exposures of the CRLF, CTS and SJKF to strychnine bait were not
calculated. Although they may be able to come into contact with the bait while either
digging into the burrow or going into the burrow entrance while the gopher is on the
surface, it is believed that the bait, which is formulated as a grain to attract rodents,
would not attract amphibians or the fox. Direct dermal exposure to the CRLF and CTS
was not calculated because there are no data available to predict skin absorption in
amphibians. Direct dermal exposure for the SJKF was also not calculated because there
are no dermal absorption data for mammals and because existing acute dermal data on
mammals indicate that dermal absorption in mammals may be very low.
2.10.1.2 Measures of Effect
Data identified in Section 2.8 are used as measures of effect for direct and indirect effects
to the CRLF, the CTS, and the SJKF. Data were obtained from registrant submitted
studies. In addition, the ECOTOXicology database (ECOTOX) was searched in order to
provide more ecological effects data and in an attempt to bridge existing data gaps.
ECOTOX is a source for locating single chemical toxicity data for aquatic life, terrestrial
plants, and wildlife. ECOTOX was created and is maintained by the USEPA, Office of
Research and Development, and the National Health and Environmental Effects Research
Laboratory's Mid-Continent Ecology Division.
The assessment of risk for direct effects to the terrestrial-phase CRLF and terrestrial-
phase CTS makes the assumption that toxicity of strychnine to birds is similar to or less
than the toxicity to terrestrial-phase amphibians and reptiles (this also applies to potential
prey items).
The acute measures of effect used for animals in this screening level assessment are the
LDso, LCso and ECso. LD stands for "Lethal Dose", and LDso is the amount of a material,
given all at once, that is estimated to cause the death of 50% of the test organisms. LC
stands for "Lethal Concentration" and LCso is the concentration of a chemical that is
estimated to kill 50% of the test organisms. EC stands for "Effective Concentration" and
the ECso is the concentration of a chemical that is estimated to produce a specific effect in
50% of the test organisms. Endpoints for chronic measures of exposure for listed and
non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL stands for "No
Ob served-Adverse-Effect-Level" and refers to the highest tested dose of a substance that
has been reported to have no harmful (adverse) effects on test organisms. The NOAEC
39
-------
(i.e., "No-Observed-Adverse-Effect-Concentration") is the highest test concentration at
which none of the observed effects were statistically different from the control. The
NOEC is the No-Observed-Effects-Concentration. For non-listed plants, only acute
exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants).
It is important to note that the measures of effect for direct and indirect effects to the
assessed species and their designated critical habitat are associated with impacts to
survival, growth, and fecundity, and do not include the full suite of sublethal effects used
to define the action area. According the Overview Document (USEPA 2004), the
Agency relies on effects endpoints that are either direct measures of impairment of
survival, growth, or fecundity or endpoints for which there is a scientifically robust, peer
reviewed relationship that can quantify the impact of the measured effect endpoint on the
assessment endpoints of survival, growth, and fecundity.
2.10.1.3 Integration of Exposure and Effects
Risk characterization is the integration of exposure and ecological effects characterization
to determine the potential ecological risk from agricultural and non-agricultural uses of
strychnine, and the likelihood of direct and indirect effects to the CRLF, the CTS, and the
SJKF in terrestrial habitats. The exposure and toxicity effects data are integrated in order
to evaluate the risks of adverse ecological effects on non-target species. Exposure is not
expected in aquatic habitats.
Usually risk quotients (RQs) are derived as quantitative estimates of potential high-end
risk. In the case of strychnine, the data are insufficient to calculate RQs. Strychnine is
not used in such a manner that allows for a meaningful estimation of exposure. It is
placed in burrows as a bait and buried so that only the target animal or animals that can
enter the burrow, can reach it. There is no spray drift or runoff. The risk characterization
will be based on a qualitative assessment of the effects of strychnine when used as a
burrow treatment.
2.10.2 Data Gaps
In order to quantitatively evaluate the effect of strychnine-poisoned gophers on SJKFs,
studies on secondary poisoning of predatory mammals that are fed rodents that have been
killed with strychnine would need to be evaluated. No such studies were located nor are
any scheduled to be conducted as data requirements under FIFRAto support registration.
3. Exposure Assessment
Strychnine is formulated as a bait composed of strychnine-treated grains (0.5 or 1.8 %
a.i. by weight on oats, milo, mixed grains) for the control of pocket gophers
(Thomomys spp. in California). The poisoned bait can be applied by hand to
individual main runways of gopher burrows, or by tractor-operated mechanical
burrow builder equipment.
40
-------
3.1 Label Application Rates and Intervals
Strychnine labels may be categorized into two types: labels for manufacturing uses
(including technical grade Strychnine and its formulated products) and end-use products.
While technical products which contain strychnine of high purity are not used directly in
the environment, they are used to make formulated products, which can be applied in
specific areas to control burrowing rodents. The formulated product labels legally limit
strychnine's potential use to only those sites that are specified on the labels.
All strychnine product labels specify that the product is for underground use only.
All agricultural labels for strychnine are identified as Restricted Use Pesticides,
meaning that only certified applicators or persons under their supervision may apply
them. Certified applicators have special training in using the pesticide, the
presumption being that they will know and obey all of the handling instruction for the
use of pesticides. In addition, there are extensive instructions on the labels regarding
safety regulations.
Currently registered agricultural and non-agricultural uses of strychnine within
California include orchards, alfalfa fields, hay fields, pastures, rangelands, cropland
and noncrop areas and forestry areas. Non-agricultural uses include yard and garden
areas around homes, and outdoor residential areas including lawns. The use rates
being assessed are summarized in Table 3.1.
Table 3.1 Strychnine Use Rates Assessed for California1
Application Method
Long handled spoon; Probe-assisted manual
applications; manually operated bait-dispensing probes
(all uses)
Burrow builder (where conditions allow)
Max. Appl. Rate
(Ib a.i./acre)
0.00225 to 0.018
0.018 to 0.054
Max. Number of
Applications per
Year
As needed
As needed
1 Based on SLN CA 79014500
3.2 Aquatic Exposure Assessment
3.2.1 Modeling Approach
Because the nature of the application methods (direct subterranean application of
strychnine-treated baits to main runway of rodent burrows followed by covering of
treatment holes, or construction of artificial subterranean tunnels that intersect gopher-
formed burrows using a burrow builder), the potential for aquatic exposure to strychnine
by spray drift does not exist under currently labeled use conditions. Also, pocket gopher
burrow depths of 6 to 12 inches lie below the extraction zone for surface water runoff as
would be modeled in PRZM/EXAMS (4-cm depth).
41
-------
Ditchbanks and earthen dams have been mentioned as likely sites for gopher control,
since gopher tunnels may weaken these structures, causing water loss by seepage and
piping through a bank or the complete loss or washout of a canal bank (Case and Jasch
(in Hygnstrom, et al., 1994). In addition, ditchbank use of strychnine was reported four
times in Ventura county in two years during the 1999-2006 reporting interval: a total of
0.0805 Ib ai were applied to a total of 22 acres in 2004; a total of 0.0875 Ib ai were
applied to 25 acres in 2006 (CDPR PUR data). Since the ditchbank use may result in
strychnine residues reaching adjacent water bodies in the event that bait is washed out of
treated gopher burrows by water movement through a ditchbank, GENEEC was used to
estimate possible aquatic exposure from this use of strychnine-containing products.
Assumptions used were: three pounds per acre of strychnine bait (the maximum rate
allowed for a product containing 1.8% strychnine w:w) was applied twice at the surface
at a 7-day interval. Application at the surface is obviously a misuse of the product, but
this exercise provides an upper limit of strychnine exposure. Based on those
assumptions, a peak strychnine EEC in water in the ditches or behind the dams is 925 ppt
(trillion). (Modeling results are presented in Appendix A.) The lowest aquatic endpoint
is 0.76 ppm (fish LCso), so the resulting RQ would be 0.00122, or roughly 41 times lower
than the LOG for aquatic endangered species (0.05).
Aquatic exposure, even under these extreme model parameters, is such that it would
result in a no effect determination. Therefore, no further aquatic analysis is performed
for this assessment.
3.2.2 Existing Monitoring Data
As an additional line of evidence surface water, ground water and atmospheric
monitoring data were sought. However, no monitoring data for strychnine were found.
The sources queried for such data are discussed below.
3.2.2.1 USGS NAWQA Surface Water Data
The USGS NAWQA program (http://water.usgs.gov/nawqa) was queried for strychnine
surface water data. Strychnine is not one of the analytes for the program, so no data were
found.
3.2.2.2 USGS NAWQA Groundwater Data
The USGS NAWQA program (http://water.usgs.gov/nawqa) was queried for strychnine
ground water data. Strychnine is not one of the analytes for the program, so no data were
found.
3.2.2.3 California Department of Pesticide Regulation (CPR)
Data
The California Department of Pesticide Regulation (CDPR) Surface Water Database
(URL:http://www.cdpr.ca.gov/docs/emon/surfwtr/surfcont.htm) was queried for
42
-------
strychnine monitoring data. The monitoring data available through this web site were
updated as of June 2008; no strychnine data were reported.
No ground water monitoring data were reported for California by the CDPR for strychnine
(http://www.cdpr.ca.gov/docs/emon/grndwtr/list mon.htm) nor is it listed to be added to
the Ground Water Protection List (3CCR section 6800[b];
http://www.cdpr.ca.gov/docs/legbills/calcode/040101.htmtfa6800).
3.2.2.4 Atmospheric Monitoring Data
No toxic air contaminant monitoring data were reported for California by the CDPR for
strychnine (http://www.cdpr.ca.gov/docs/emon/pubs/tac/tacstdys.htm). In addition, no
toxic air contaminant monitoring data have been reported for strychnine in general
(Pesticides in the Atmosphere, M.S. Majewski and P.D. Capel. 1995. Volume One of the
series Pesticides in the Hydrologic System. RJ Gilliom, Series Editor).
3.2.2.5 Other Sources of Monitoring Data
No ground water contaminant monitoring data have been reported for strychnine (Pesticides
in Ground Water, I.E. Barbash and E.A. Resek. 1996. Volume Two of the series Pesticides
in the Hydrologic System. R. J Gilliom, Series Editor). No surface water contaminant
monitoring data have been reported for strychnine (Pesticides in Surface Waters, S. J. Larson,
P.D. Capel, and M.S. Majewski. 1997. Volume Three of the series Pesticides in the
Hydrologic System. R. J Gilliom, Series Editor)
3.2.3 Spray Drift Buffer and Downstream Dilution Analysis for Action
Area
Because the nature of the application method (direct subterranean application of
strychnine-treated baits to main runway of rodent burrows, followed by covering of
treatment hole), the potential for exposure from spray drift does not exist under currently
labeled use conditions for strychnine rodent baits, and as a result, spray drift modeling
was not performed for this assessment. In addition, the potential for stream exposure
does not exist under currently labeled use conditions for strychnine rodent baits, so the
downstream dilution analysis was not performed for this assessment.
3.3 Terrestrial Animal Exposure Assessment
Direct exposure
Usually risk quotients (RQs) are derived as quantitative estimates of potential high-end
risk. Strychnine is not used in such a manner that allows for a meaningful estimation of
exposure and therefore, RQs are not calculated. It is placed in burrows as a bait and
buried. There is no spray drift or runoff.
In order to be exposed to strychnine, the SJKF, CRLF, and the CTS can dig down to the
burrow or go into a burrow's entrance while the gopher is on the surface. This would
43
-------
give them access to the poison bait. Since the bait is composed of grain to attract rodents,
it is believed that it would not attract amphibians or a fox. Therefore, direct dietary
exposure to strychnine bait is a possibility, but it is believed to be minor and cannot be
evaluated. As stated previously, direct dermal exposure to the CRLF and CIS resting in
the burrows was not calculated because there are no data available to predict skin
absorption in amphibians. In addition, direct dermal exposure for the SJKF was not
calculated because there are no dermal absorption data for mammals and because existing
acute dermal data on mammals indicate that dermal absorption in mammals is probably
very low.
An assessment of terrestrial dietary exposure was not conducted because food items
(plant foliage and seeds, flying and above ground insects) would not be exposed to
strychnine baits.
Secondary and nontarget poisoning
As a qualitative assessment of terrestrial exposure from scavenging of poisoned
carcasses, a rough estimate of the maximum amount of strychnine contained in a typical
recommended dose of bait (one teaspoon) was calculated using the following
assumptions:
1 gram (g) of bait contains 0.018 g strychnine (label info for CA 79014500; 1.8% w:w).
The bulk density of oat grains7 (typical carrier for bait) is 0.48 g/cubic centimeter (cc).
The bulk density of sorghum seed (also called milo; typical carrier for bait) is 0.73 g/cc.
One teaspoon is approximately 5 cc.
One teaspoon of oat grains is 0.48 g/ccx 5 cc = 2.4 g; one teaspoon of milo is 3.65 g.
One teaspoon of oat bait contains 2.4 g x 0.018 g strychnine/g bait; one teaspoon of milo
bait contains 3.65 g x 0.018 g strychnine/g bait.
Therefore, one dose of bait contains from 43.2 mg to 65.7 mg of strychnine. Since a
single dose is considered lethal (Salmon and Gorenzel, 2002), this amount of strychnine
could persist in the tissues, the gut, or the external cheek pouches of a pocket gopher
carcass and could be scavenged by the SJKF.
3.4 Terrestrial Plant Exposure Assessment
Since there is no above-ground exposure to strychnine, effects to plants are not expected.
There is no evidence that roots of plants encountering bait in burrows take up the
strychnine and transport it to the above-ground portions of the plant.
7 Source of information on bulk density of grain: http://www.a-a-c-a.org/information/bulkdensity.pdf
44
-------
4. Effects Assessment
This assessment evaluates the potential of strychnine to affect, directly or indirectly, the
CRLF, SJKF and the CIS or to modify their designated critical habitat. As previously
discussed in Section 2.7, assessment endpoints for the effects determination for each
assessed species include direct toxic effects on the survival, reproduction, and growth, as
well as indirect effects, such as reduction of the prey base or modification of its habitat.
In addition, potential modification of critical habitat is assessed by evaluating effects to
the PCEs, which are components of the critical habitat areas that provide essential life
cycle needs of each assessed species. Direct effects to the aquatic-phase CRLF and CTS
are not assessed because aquatic exposure is not expected. Direct effects to the
terrestrial-phase CRLF and CTS are based on avian toxicity data, given that birds are
generally used as a surrogate for terrestrial-phase amphibians.
As described in the Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa
include birds (used as a surrogate for terrestrial-phase amphibians), mammals and
terrestrial invertebrates. Acute (short-term) and chronic (long-term) toxicity information
is characterized based on registrant-submitted studies and a comprehensive review of the
open literature on strychnine.
Toxicity endpoints are established based on data generated from guideline studies
submitted by the registrant, and from open literature studies that meet the criteria for
inclusion into the ECOTOX database maintained by EPA/Office of Research and
Development (ORD) (U.S. EPA, 2004). Data presented in this assessment were obtained
from Registration Eligibility Documents, Data Evaluation Reports (registrant submitted
data), Risk Evaluations, USFWS documents and ECOTOX information obtained on
02/28/2009. In order to be included in the ECOTOX database, papers must meet the
following minimum criteria:
(1) the toxic effects are related to single chemical exposure;
(2) the toxic effects are on an aquatic or terrestrial plant or animal species;
(3) there is a biological effect on live, whole organisms;
(4) a concurrent environmental chemical concentration/dose or application
rate is reported; and
(5) there is an explicit duration of exposure.
Data that pass the ECOTOX screen are evaluated along with the registrant-submitted
data, and may be incorporated qualitatively or quantitatively into this endangered species
assessment. In general, effects data in the open literature that are more conservative than
the registrant-submitted data are considered. The degree to which open literature data are
quantitatively or qualitatively characterized for the effects determination is dependent on
whether the information is relevant to the assessment endpoints (i.e., survival,
reproduction, and growth) identified in Section 2.8. For example, endpoints such as
behavior modifications are likely to be qualitatively evaluated, because quantitative
45
-------
relationships between modifications and reduction in species survival, reproduction,
and/or growth are not available. Although the effects determination relies on endpoints
that are relevant to the assessment endpoints of survival, growth, or reproduction, it is
important to note that the full suite of sublethal endpoints potentially available in the
effects literature (regardless of their significance to the assessment endpoints) are
considered to define the action area for strychnine. The ECOTOX database was queried,
and with the exception of an acute toxicity study with mammals, none of the open
literature data provided more sensitive endpoints than those generated from the submitted
guideline studies.
Citations of all open literature that were not considered as part of this assessment because
they were either rejected by the ECOTOX screen or were accepted by ECOTOX but not
used (e.g., the endpoint was less sensitive) are included in Appendix C. Appendix C
also includes a rationale for rejection of those studies either that did not pass the
ECOTOX screen or were not utilized in this assessment for other reasons.
A detailed spreadsheet of the available ECOTOX open literature data, including the full
suite of lethal and sublethal endpoints is presented in Appendix B. Appendix D
provides a summary of the human health effects data for strychnine.
In addition to registrant-submitted and open literature toxicity information, other sources
of information, including use of the acute probit dose response relationship to establish
the probability of an individual effect and reviews of the Ecological Incident Information
System (EIIS), are conducted to further refine the characterization of potential ecological
effects associated with exposure to strychnine. A summary of the available terrestrial
ecotoxicity information, use of the probit dose response relationship, and the incident
information for strychnine are provided in Sections 4.1 through 4.4, respectively.
Strychnine does not have any known toxic degradates and strychnine is not co-formulated
with other toxicants.
4.1 Toxicity of Strychnine to Aquatic Organisms
Based on the use patterns in California, aquatic exposure to strychnine is not expected.
Therefore, assessment of risk to aquatic organisms will not be conducted. However, the
aquatic toxicity profile is provided below in Table 4.1.
Table 4.1 Aquatic Toxicity Profile for Strychnine
Assessment
Endpoint
Acute/
Chronic
Surrogate
Species
Toxicity Value
LC50 (95% C.I.)
ppm
Author, Date
MRID
Acceptability
Freshwater fish and aquatic-phase amphibians
Survival
Acute
Acute
Rainbow trout
(Oncorhynchus
mykiss)
Bluegill sunfish
(Lepomis
2.3 (1.7-3.2)
0.76 (0.61-0.96)
Bowman, 1989
41126501
Bowman, 1989
41126502
Acceptable
Acceptable
46
-------
Reproduction
and growth
Chronic
macrochirus)
Waived
Freshwater invertebrate
Survival
Acute
Waterflea
(Daphnia magna)
10(8-12)
Forbis, 1989
41126503
Acceptable
4.2 Toxicity of Strychnine to Terrestrial Organisms
Table 4.2 summarizes the most sensitive terrestrial toxicity endpoints, based on an
evaluation of both the submitted studies and the open literature. A brief summary of
submitted data considered relevant to this ecological risk assessment for the CRLF, the
CIS, and the SJKF is presented below. Based on the use patterns in California, exposure
to terrestrial plants is not expected. Therefore, assessment of risk to terrestrial plants will
not be conducted and the toxicity to terrestrial plants is not summarized in this document.
Table 4.2 Terrestrial Toxicity Profile for Strychnine
Assessment
Endpoint
Acute/
Chronic
Surrogate
Species
Toxicity Value
Effects
Author,
Date MRID
/ ECOTOX
Acceptability
Avian
Survival
Survival
Repro-
duction
Acute
oral
Subacute
dietary
Chronic
Waived
Bobwhite quail
(Colinus
virginianus)
Mallard duck
(Anus
platyrhynchos)
Bob white quail
(Colinus
virginianus)
Mallard duck
(Anus
platyrhynchos)
LC50: 3536 ppm
NOAEC: 1250
ppm
LC50: 2 12 ppm
NOAEC: 78
ppm
NOAEC:
11 14/1200 ppm
(highest
measured/
nominal levels
NOAEC not
reported/
LOAEC: 33
ppm
Internal bleeding, pale
liver, gaseous intestines,
loss of reflexes,
immobility, death
Lethargy, loss of reflexes,
muscle spasms, death
None
No. of eggs chick wt,
testes wt, adult wt
Pederson,
1989
41322602
Pederson,
1998
41322601
Pederson,
1993
42716801
Pederson,
1993
42716802
Acceptable
Acceptable
Acceptable
Acceptable
Mammalian
Survival
Acute
oral
Desert kit fox
Vulpes macrotis
arsipus
LD50: 0.75
mg/kg bw
Mortality
Schitoskey,
1975
E35428
Supplemental
47
-------
Dietary
Subacute
dietary
Red fox
(Vulpes fulva)
LC50: 70 (52-
96) ppm
Mortality
4029650
Record/ 1987
Supplemental
Acute toxicity to terrestrial animals is categorized using the classification system shown
in Table 4.3 (U.S. EPA, 2004). Toxicity categories for terrestrial plants have not been
defined.
Table 4.3 Categories of Acute Toxicity for Avian and Mammalian Studies
Toxicity Category
Very highly toxic
Highly toxic
Moderately toxic
Slightly toxic
Practically non-toxic
Oral LD50
< 10 mg/kg
10 - 50 mg/kg
51 -500 mg/kg
50 1-2000 mg/kg
> 2000 mg/kg
Dietary LC50
< 50 ppm
50 - 500 ppm
501- 1000 ppm
1001 - 5000 ppm
> 5000 ppm
4.2.1 Toxicity to Birds and Terrestrial-Phase Amphibians
As specified in the Overview Document, the Agency uses birds as a surrogate for
terrestrial-phase amphibians when toxicity data for each specific taxon are not available
(U.S. EPA, 2004).
In addition to the avian toxicity studies summarized in Table 4.1, a subacute dietary study
was conducted on the black-billed magpie (Picapica) and the American kestrel (Falco
sparverius) (MRID 40815201). Strychnine was highly toxic in both species with LCso's
of 99 and 234 ppm, respectively.
A field evaluation of strychnine (0.5, 1.15, and 1.8 % baits) to control the Valley pocket
gopher (Thomomys bottae) was performed (MRID 42488601). Strychnine residues were
found in the muscle tissue of the gophers; the mean was approximately 0.5 ppm and
ranged as high as 5.4 ppm. It was also found in the gastrointestinal tract with a mean of
approximately 5 ppm and as high as 35.8 ppm. There also was evidence of secondary
poisonings, in that three dead vertebrates were found. Strychnine residues in a horned
lark (Eremophila alpestris) were 0.3491 and 1.6133 ppm for the muscle tissue and
gastrointestinal tract, respectively; for a brewer's blackbird (Euphagus cyanocephalus),
residues were 0.5606 and 23.3283 ppm for the muscle tissue and gastrointestinal tract,
respectively. A striped skunk (Mephitis mephitis) was also found, but it was not analyzed
for strychnine.
A summary of the acute and chronic bird data used in this assessment was provided in
Table 4.1.
48
-------
4.2.2 Toxicity to Mammals
A summary of acute and chronic mammalian data, including data published in the open
literature, is provided below in Sections 4.2.2.1 through 4.2.1.2.
4.2.2.1 Mammals: Acute Oral and Dietary Exposure Studies
Table 4.4 Acute Toxicity of Strychnine in Selected Mammalian Species
Species
Laboratory rat
(Rattus
norvegicus)
Striped skunk
(Mephitis
mephitis)
Desert kit fox
(Vulpes macro tis
arsipus)
European ferret
(Mustela putorius)
Red fox
(Vulpes fulva)
Study Type
Acute oral
Acute mg per egg
bait
Acute oral
Dietary 5 -day
Dietary 5 -day
Endpoint
LD50 = 2.2 mg/kg
LD100 = 3
mg/egg/skunk
LD50 = 0.75 mg/kg
LC50 = 198 ppm
LC50 = 70 ppm
(52-96)
MRID, ECOTOX
Reference or
Citation Date
40908901
4029650
Record 1987
E35428
Schitoskey, 1975
40296502
Record 1987
40296503
Record 1987
Study
Classification
Supplemental
Supplemental
Supplemental
Supplemental
Supplemental
These results show that strychnine is very highly toxic to small mammals on both an
acute oral and dietary basis. Clinical signs of toxicity, including death, occurred within
one hour. This is considered to be typical of strychnine. There was one open literature
study that indicated a more sensitive acute oral endpoint for mammals than those
observed in the submitted studies. This study (ECOTOX ref. no. E35428) reported an
LDso for another species of kit fox {Vulpes macrotis arsipus). The study is classified as
supplemental because it had no control group and only used eight animals. The LDso was
0.75 mg/kg.
4.2.2.2 Mammals: Chronic Exposure (Growth, Reproduction) Studies
No chronic data for mammals are available.
4.2.3 Toxicity to Terrestrial Invertebrates
No toxicity data are available for terrestrial invertebrates.
4.2.4 Toxicity to Terrestrial Plants
The use patterns state that the strychnine formulation is to be buried in rodent burrows.
Since foliar deposition is not expected either from spray drift or direct deposition, no risk
49
-------
to terrestrial plants is expected. Therefore, no plant toxicity data are presented in this
document.
4.2.5 Terrestrial Field Studies
A field efficacy study conducted with strychnine baits (0.5, 1.15, and 1.8 % w:w) to
control the Valley pocket gopher (Thomomys bottae) was assessed (MRID# 42488601;
USEPA, 1994). Strychnine residues were found in the muscle tissue of the gophers; the
mean was approximately 0.5 ppm and ranged as high as 5.4 ppm. It was also found in
the gastrointestinal tract with a mean of approximately 5 ppm and as high as 35.8 ppm.
Three dead vertebrates were found: a horned lark (Eremophila alpestris), a brewer's
blackbird (Euphagus cyanocephalus) and a striped skunk (Mephitis mephitis).
Strychnine residues in the horned lark were 0.3491 and 1.6133 ppm for the muscle tissue
and gastrointestinal tract, respectively and, for the brewer's blackbird they were 0.5606
and 23.3283 ppm for the muscle tissue and gastrointestinal tract, respectively. The skunk
was not analyzed for strychnine residues. This study confirmed the possibility of
secondary exposure (i.e., dead gophers were preyed upon by red-tailed hawks) and that
direct exposure occurs to birds).
4.3 Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern
The chance of an individual event (i.e., mortality or immobilization) occurring is certain,
because a single exposure to strychnine (one dose) is lethal. Therefore a probit dose
response analysis was not conducted.
4.4 Incident Database Review
A review of the EIIS database for ecological incidents involving strychnine was
completed in August 2009. A complete list of the incidents involving strychnine
including associated uncertainties is included as Appendix E. Between 1981 and 1993
(before above-ground application was banned), 30 incidents were reported.
There have been 16 incidents since strychnine above-ground uses were banned (1994 to
the present). One was classified as an accidental misuse and three were classified as
intentional misuses. No incidents were attributed to the currently labeled uses for
strychnine. In eleven poisonings, the certainty that strychnine was the responsible
chemical was classified as "Highly Probable"; in five poisonings the certainty was
"Probable". Nine of the incidents occurred in California.
5. Risk Characterization
Risk characterization is the integration of the exposure and effects characterizations.
Risk characterization is used to determine the potential for direct and/or indirect effects to
the CRLF, the CTS, and the SJKF or for modification to their designated critical habitat
50
-------
from the use of strychnine in California. The risk characterization provides an estimation
(Section 5.1) and a description (Section 5.2) of the likelihood of adverse effects;
articulates risk assessment assumptions, limitations, and uncertainties; and synthesizes an
overall conclusion regarding the likelihood of adverse effects to the assessed species or
their designated critical habitat (i.e., "no effect," "likely to adversely affect," or "may
affect, but not likely to adversely affect").
5.1 Risk Estimation
A quantitative estimation of risk is usually estimated by calculating the ratio of exposure
to toxicity. This ratio is the risk quotient (RQ), which is then compared to pre-
established acute and chronic levels of concern (LOCs) for each category evaluated. RQs
are derived as quantitative estimates of potential high-end risk. In the case of strychnine
use in California, RQs cannot be estimated. Strychnine is not used in a manner that
allows for a meaningful estimation of exposure. It is placed in burrows as a bait and
buried and there is no spray drift or runoff.
Acute and chronic risks to aquatic organisms and acute risks to terrestrial plants from
strychnine are not expected. Acute and chronic risks to terrestrial animals are estimated
qualitatively based on observations in submitted studies and the open literature.
5.1.1 Exposures in the Aquatic Habitat
Because the nature of the application method (direct subterranean application to main
runway of rodent burrows, followed by covering of the treatment hole), surface waters
are not expected to be exposed to runoff of strychnine residues. Therefore, the potential
for aquatic exposure does not exist under currently labeled use conditions for strychnine
rodent baits, and as a result, quantitative risk estimation for aquatic organisms was not
conducted for this assessment. Due to lack of exposure, strychnine has no potential to
directly affect the aquatic-phase CRLF and CTS. Additionally, there is no potential for
indirect effects to those listed species that rely on freshwater fish, and/or aquatic-phase
amphibians, freshwater invertebrates and aquatic plants during at least some portion of
their life-cycle (i.e., CRLF and CTS).
5.1.2 Exposures in the Terrestrial Habitat
As stated in the aquatic exposure section, due to the nature of the application method,
there is no direct foliar application. In addition, with the exception of the target species,
no direct exposure to the bait itself is expected. There is no evidence of transport of
strychnine through terrestrial plant roots to the leaves; thus, no exposure to terrestrial
plants is expected. Therefore, the current models for estimating terrestrial exposure, T-
REX (v. 1.4.1) and TERRPLANT (v. 1.2.2) cannot be used for a quantitative estimation
of risk. Nevertheless, there is potential for direct dermal exposure (CRLF and CTS)
while utilizing gopher burrows and secondary exposure through consumption of poisoned
gophers (SJKF) and invertebrates (CRLF, CTS and SJKF) which have consumed the bait.
Further discussion is found in the risk description (Section 5.2). Due to the possibility of
51
-------
secondary exposure and dermal absorption, strychnine has the potential to directly affect
the terrestrial-phase CRLF and CTF and the SJFK. Strychnine has the potential to
indirectly affect the terrestrial-phase CRLF and CTS through the reduction in gopher
burrows (habitat) and the SJFK through the reduction in the small mammal prey base
(gophers).
5.1.3 Primary Constituent Elements of Designated Critical Habitat
For strychnine use, the assessment endpoints for designated critical habitat PCEs involve
the same endpoints as those being assessed relative to the potential for direct and indirect
effects to the listed species assessed here. Therefore, the effects determinations for direct
and indirect effects are used as the basis of the effects determination for potential
modification to designated critical habitat.
5.2 Risk Description
The risk description synthesizes overall conclusions regarding the likelihood of adverse
impacts leading to an effects determination (i.e., "no effect," "may affect, but not likely
to adversely affect," or "likely to adversely affect") for the assessed species and the
potential for modification of their designated critical habitat.
A summary of the risk estimation results are provided in Table 5.1 for direct and
indirect effects to the listed species assessed here and in Table 5.2 for the PCEs of their
designated critical habitat.
Table 5.1. Risk Estimation Summary for Strychnine1
Taxa
Freshwater Fish
and Aquatic -phase
Amphibians
Freshwater
Invertebrates
Vascular and Non-
Vascular Aquatic
Plants
Birds, Reptiles, and
Terrestrial-Phase
Description of Results of Risk Estimation
No aquatic exposure is expected.
No aquatic exposure is expected.
No aquatic exposure is expected.
No aquatic exposure is expected.
No aquatic exposure is expected.
No aquatic exposure is expected.
Possible absorption of strychnine through the skin
upon contact within the burrows.
Assessed Species Potentially
Affected
Direct Effects: None
Indirect Effects: None
Direct Effects: None
Indirect Effects: None
Direct Effects: None
Indirect Effects: None
Direct Effects: Terrestrial-phase
CRLF and CTS
52
-------
Table 5.1. Risk Estimation Summary for Strychnine1
Taxa
Amphibians
Mammals
Terrestrial
Invertebrates
Terrestrial Plants -
Monocots and
Dicots
Description of Results of Risk Estimation
Possible reduction in amphibian prey base due to
absorption through skin upon contact with the bait
within the burrows
Secondary poisoning through consumption of
poisoned gophers
Possible reduction in prey base and gopher
burrows (habitat)
Secondary poisoning through consumption of
invertebrates that have consumed bait
None
No exposure to terrestrial plants expected
Assessed Species Potentially
Affected
Indirect Effects: Terrestrial-
phase CRLF and CTS
Direct Effects : SJKF
Indirect Effects: Terrestrial-phase
CRLF and CTS and SJKF
Direct Effects: Terrestrial-phase
CRLF and CTS and SJKF
Indirect Effects: None
Direct and Indirect Effects: None
1 Direct and indirect effects RQs could not be calculated.
Table 5.2. Risk Estimation Summary for Strychnine - Effects to Designated Critical
Habitat (PCEs)
Taxa
Freshwater Fish,
Aquatic -phase
Amphibians,
Invertebrates and
Aquatic Vascular
and Non- Vascular
Plants
Birds, Reptiles, and
Terrestrial-Phase
Amphibians
Mammals
Terrestrial
Invertebrates
Description of Results of
Risk Estimation
No aquatic exposure is expected.
Possible reduction in amphibian
prey based due to absorption
through skin upon contact with the
bait within the burrows
Possible reduction in prey base
and gopher burrows (habitat)
None
Species Associated with a Designated
Critical Habitat that May Be Modified by
None
Terrestrial-phase CRLF and CTS
Terrestrial-phase CRLF and CTS and SJFK
None
53
-------
Table 5.2. Risk Estimation Summary for Strychnine - Effects to Designated Critical
Habitat (PCEs)
Taxa
Terrestrial Plants -
Monocots and
Dicots
Description of Results of
Risk Estimation
No exposure to terrestrial plants
expected
Species Associated with a Designated
Critical Habitat that May Be Modified by
None
Following a "may affect" determination, additional information is considered to refine
the potential for exposure at the predicted levels based on the life history characteristics
(i.e., habitat range, feeding preferences, etc.) of the assessed species. Based on the best
available information, the Agency uses the refined evaluation to distinguish those actions
that "may affect, but are not likely to adversely affect" from those actions that are "likely
to adversely affect" the assessed species and its designated critical habitat.
The criteria used to make determinations that the effects of an action are "not likely to
adversely affect" the assessed species or modify its designated critical habitat include the
following:
• Significance of Effect: Insignificant effects are those that cannot be meaningfully
measured, detected, or evaluated in the context of a level of effect where "take"
occurs for even a single individual. "Take" in this context means to harass or
harm, defined as the following:
• Harm includes significant habitat modification or degradation that
results in death or injury to listed species by significantly impairing
behavioral patterns such as breeding, feeding, or sheltering.
• Harass is defined as actions that create the likelihood of injury to listed
species to such an extent as to significantly disrupt normal behavior
patterns which include, but are not limited to, breeding, feeding, or
sheltering.
• Likelihood of the Effect Occurring: Discountable effects are those that are
extremely unlikely to occur.
• Adverse Nature of Effect: Effects that are wholly beneficial without any adverse
effects are not considered adverse.
A description of the risk and effects determination for each of the established assessment
endpoints for the assessed species and their designated critical habitat is provided in
Sections 5.2.1 through 5.2.2. The effects determination section for each listed species
assessed will follow a similar pattern. Each will start with a discussion of the potential
for direct effects, followed by a discussion of the potential for indirect effects. For those
listed species that have designated critical habitat, the section will end with a discussion
on the potential for modification to the critical habitat from the use of strychnine.
5.2.1 The CRLF and CTS
5.2.1.1 Direct Effects
54
-------
No aquatic exposure is expected. Therefore, there is no potential for direct effects to the
aquatic-phase CRLF or CTS. For the terrestrial-phase CRLF and CTS, direct dietary
exposure through consumption of the bait (if accessed from inside the burrow) is
assumed to be negligible due to observed dietary habits in the field (see Table 2.4).
Dermal exposure to the bait is possible while the CRLF and particularly the CTS are
resting in the gopher burrows. The Reregi strati on Eligibility Decision (RED) for
strychnine (USEPA, 1996) indicates that based on the acute oral and acute dermal
toxicity of strychnine in mammals, dermal absorption in mammals may be very low.
However, amphibians have thin, permeable skin. There are currently no data nor models
available to the Agency to predict the dermal absorption and/or dermal toxicity of
strychnine with amphibians. Therefore, there is an uncertainty associated with the
potential risk to amphibians following dermal exposure to strychnine. The subacute
dietary LCso to mallard ducks is 212 ppm. This classifies strychnine as highly toxic via
the dietary route to birds, the surrogate for terrestrial-phase amphibians. There are no
available avian acute oral toxicity data. Due to the fact that strychnine is highly toxic via
the diet in birds, it is assumed that if dermally absorbed, it would also be highly toxic to
terrestrial-phase amphibians.
There is a potential for secondary poisoning through consumption of soil-
dwelling/burrowing invertebrates that have either consumed the strychnine bait or have
been transporting/tracking it. The terrestrial-phase CRLF and CTS both consume
terrestrial invertebrates. Again, there are neither data nor models to predict exposure to
the bait from consumption of terrestrial invertebrates and associated strychnine either in
or on the invertebrate. In the Final Rule for the status of the CTS, USFWS (2004) stated:
"there may be potential for secondary exposure from this application
method if estivating salamanders consume burrow-dwelling invertebrates
that have ingested the treated grains. While no definitive risk assessment
can be made for these possible exposures, we believe this application
method would result in an increased risk for take of the CTS and should
therefore be avoided whenever possible."
They were writing about anti-coagulants and the CTS, but the same reasoning would be
applicable to strychnine and CRLF.
Based on the weight-of-evidence, there is a potential for direct effects to the terrestrial-
phase of the CRLF and CTS, supported by the possibility of dermal absorption following
contact within the gopher burrows and secondary poisoning through consumption of soil-
dwelling/burrowing invertebrates that have been in contact with the bait. Although
exposure cannot be estimated, due to the high toxicity, the potential for dermal exposure
and consumption of invertebrates that have been in contact with the bait, risk cannot be
discounted.
5.2.1.2 Indirect Effects.
55
-------
Potential Loss of Prey
Terrestrial-phase CRLFs and CIS' feed on invertebrates, small fish, frogs, and small
mammals (Jennings, et al 1997; Hayes and Tennant (1985)). There may be a possible
reduction in the amphibian prey base if there are a significant number of amphibians that
utilize the gopher burrows and come in dermal contact with the bait.
Potential Modification of Habitat
Elimination of Burrow Systems
It has been reported that some amphibians will use the gophers' burrows for resting and
avoiding hot weather. The removal of pocket gophers will cause some burrows to
become abandoned and unavailable to the amphibians for resting and shelter.
"California tiger salamanders spend much of their lives in underground
retreats, often in burrowing mammal (ground squirrel, pocket gopher, and
other burrowing mammal) burrows. Therefore, widespread burrowing
mammal control may pose threats to the salamander". (U.S. Fish and
Wildlife Service. 2004).
"This underground phase has often been referred to as estivation (the
summertime equivalent of hibernation), but true estivation has never been
observed, and fiber optic cameras in burrows have allowed researchers to
witness salamanders actively foraging. . . . [T]he burrow complexes of
various ground dwelling mammals are vitally important in the life cycle of
the CTS. These burrows serve as shelters and estivation sites for the
terrestrial adult and juvenile salamanders. In addition, the presence of
these burrows near suitable water bodies may be critical for any water
body to become a successful, long-term breeding site for the CTS."
(USFWS, 2004).
Active ground-burrowing rodent populations probably are required to sustain CTS
because inactive burrow systems become progressively unsuitable over time. Loredo et
al. (1996) found that California ground squirrel burrow systems collapsed within 18
months following abandonment by, or loss of, the mammals. This probably applies to
pocket gopher burrows as well.
The USFWS (2004) wrote
"The baiting of pocket gopher burrows with strychnine would not cause
modifications of the burrow system directly, but, in-so-far as the poisoning
campaign is successful, it would leave the burrows vacant. Although there
is no data on the subject, it is believed that a vacant burrow would collapse
56
-------
because of the natural action of the weather and gravity. This would result
in a significant loss of suitable sheltering and aestivation habitats."
5.2.1.3 Modification of Designated Critical Habitat
Based on the weight-of-evidence, there is a potential for the modification of CRLF and
CTS designated critical habitat based on the potential for both direct and indirect effects
discussed in the above sections 5.2.1.1 and 5.2.1.2. Due to the fact that the Action Area
is the entire State of California, the areas of effect overlap with the assessed species'
designated critical habitat. Modification to critical habitat is expected.
5.2.2 SJKF
5.2.2.1 Direct Effects
Based on the observed dietary habits in the field (see Table 2.4) and that there is no
exposure to terrestrial plants, direct dietary exposure to strychnine is not expected.
The SJKF may be dermally exposed to strychnine in burrows. Again, the RED for
strychnine (USEPA, 1996) indicates that based on the acute oral and acute dermal
toxicity of strychnine in mammals, dermal absorption in mammals may be very low.
Therefore, it seems unlikely it would be absorbed through the skin.
SJKFs might receive a harmful or fatal dose of strychnine by eating a poisoned pocket
gopher dug out of its burrow or found above ground. Gophers can forage from below
ground by pulling the roots of plants into their burrows, but they do leave their burrows
to forage (Jones and Baxter, 2004). SJKFs have been reported to eat a wide variety of
rodents and lagomorphs. Jones and Baxter (2004) report that many mammals, birds and
reptiles prey on the gophers including the SJKF, but specific data are not given. A SJKF
would eat a gopher that had died or was foraging on the surface. A rough estimate of the
maximum amount of strychnine contained in a typical recommended dose of bait (one
teaspoon) was calculated (see Section 3.3). One dose of bait contains from 43.2 mg to
65.7 mg of strychnine. Since a single dose is considered lethal (Salmon and Gorenzel,
2002), this amount of strychnine could persist in the tissues, the gut, or the external cheek
pouches of a pocket gopher carcass and could be scavenged by the SJKF. The following
studies support the assumption that when a single dose of bait is consumed by a pocket
gopher, it could be lethal to the SJKF.
Schitoskey (1975) found that a kangaroo rat (Dipodomys sp.) killed with 12.8 mg of
strychnine contained 10 times the LDso for a fox and killed the desert kit fox within 30
minutes. A gopher with 12.8 mg of strychnine in its cheek pouches would carry enough
poison to kill the fox.
A field evaluation of strychnine (0.5, 1.15, and 1.8 % baits) to control the Valley pocket
gopher (Thomomys bottae) has been reviewed (MRTD# 42488601). Strychnine residues
were found in the muscle tissue; the mean was approximately 0.5 ppm and ranged as high
57
-------
as 5.4 ppm. It was also found in the gastro-intestinal tract with a mean of approximately
5 ppm and as high as 35.8 ppm. Secondary poisoning with strychnine rodenticide baits
may depend on whether or not the stomach or intestines of the poisoned rodent are
consumed by the kit fox.
Hegdal, Gatz, and Fite (1981) wrote that, "Hegdal and Gatz (1976) evaluated the
secondary effects of underground strychnine baiting for pocket gophers. They found no
indication of secondary poisoning among radio-equipped badgers, striped skunks, red
foxes (Vulpes vulpes\ or coyotes. Pocket gophers are the predominant prey item found
in badger's scats (Sargeant and Warner, 1972; Lampe, 1976). Lampe (1976), Hegdal and
Gatz, and Sargeant and Warner (1972) found that badgers spend considerable effort
digging in pocket gopher burrows, apparently in search of food. Although pocket gopher
remains are rare in skunk stomachs or fecal passages (R. Mead, per. Comm. in Hegdal
and Gatz) and Sargeant and Warner (1972) indentified one skunk in California that died
after consuming a pocket gopher that had been killed by a strychnine bait applied with a
burrow-builder."
Evans, et al (1970) reported that cage- and field-strychnine poisoned jackrabbits were
lethal to coyotes, but only when the stomach contents were eaten.
Wood (1965) reported possible secondary poisoning in two grey foxes and two coyotes
found dead on a study area treated with strychnine bait for rodent control. "O.E. Stephl
and E.G. Gates (unpublished data 1928) reported that no coyotes or badgers were found
dead during a prairie dog control operation in Montana although they were observed
feeding on the carcasses of dead prairie dogs. O.E. Stephl (unpublished data, 1925)
reported 'a few' dead skunks in a strychnine baited area."
There is also a potential for secondary poisoning through consumption of soil-
dwelling/burrowing invertebrates that have either consumed the strychnine bait or have
been transporting/tracking it. Again, there are neither data nor models to predict
exposure to the bait from consumption of terrestrial invertebrates and associated
strychnine either in or on the invertebrate.
Based on the weight-of-evidence, there is a potential for direct effects to the SJKF
through secondary poisoning by consumption of poisoned gophers and through
consumption of soil-dwelling/burrowing invertebrates that have been in contact with the
bait.
5.2.2.2 Indirect Effects.
Potential Loss of Prey
In the northern portion of their range, SJKF most commonly prey on California ground
squirrels, cottontails (Sylvilagus auduboni\ black-tail jackrabbits (Lepus califormcus\
pocket mice (Perognathus spp.), and kangaroo rats (Dipodomys spp.). Secondary prey
taken opportunistically may include ground-nesting birds, reptiles, and insects.
58
-------
McGrew (1979) quoted sources saying that the primary item in the kit fox diet is usually
the most abundant nocturnal rodent or lagomorph in the vicinity of the den. Kangaroo
rats (Dipodomys spp.) accounted for its distribution in California. Kangaroo rat remains
occurred in over 80% of 52 V. m. mutica scats from Kern County, California, while rabbit
remains (Lepus, Sylvilagus) occurred in 52%. In another study black-tailed jackrabbits
(Lepus califomicus) made up over 94% of the food eaten by a family (two adults and five
pups) of V. m. nevadensis.
Cypher, et al (2007) said kangaroo rats and ground squirrels are among the SJKF's prey.
The USFWS (1998) said, "Diet varies geographically, seasonally and annually, based on
abundance of prey. In the southern part of the range, one-third of the kit fox's diet
consists of kangaroo rats (Dipodomys spp.), pocket mice (Perognathus spp.), white-
footed mice (Peromyscus spp.) and other nocturnal rodents. In the northern portion of the
range (San Joaquin, Alameda and Contra Costa counties), kit foxes most often prey on
California ground squirrels (Spermophilus beecheyi). Kit foxes also prey on black-tailed
hares (Lepus californicus), San Joaquin antelope squirrels (Ammospermophilus nelsoni\
desert cottontails (Sylvilagus audubonii), ground-nesting birds and insects."
Therefore, there is a potential for reduction in the pocket gopher population, the target
species, which is one of many potential prey item for the SJKF.
Potential Modification of Habitat
There is no potential modification of habitat for the SJFK.
5.2.2.3 Modification of Designated Critical Habitat
The SJKF does not have a designated critical habitat.
5.2.3 Spatial Extent of Potential Effects
5.2.3.1 Spray Drift
Because the nature of the application method (direct subterranean application of
strychnine-treated baits to main runway of rodent burrows, followed by covering of
treatment hole), terrestrial and aquatic habitats of concern are not expected to be exposed
to strychnine residues from spray drift. As a result, spray drift modeling was not
conducted for this assessment.
5.2.3.2 Downstream Dilution Analysis
Because the nature of the application method (direct subterranean application to main
runway of rodent burrows, followed by covering of treatment holes), surface waters are
not expected to be exposed to runoff of strychnine residues. Therefore, the potential for
stream exposure does not exist under currently labeled use conditions for strychnine
59
-------
rodent baits, and as a result, the downstream dilution analysis was not conducted for this
assessment.
5.2.3.3 Overlap between CRLF, CTS, and SJKF habitat and Spatial
Extent of Potential Effects
An LAA effects determination is made for those areas where it is expected that the
pesticide's use will directly or indirectly affect the CRLF, CTS or SJKF or the CRLF or
CTS designated critical habitat, and the area overlaps with the core areas, critical habitat
and available occurrence data for CRLF, CTS or SJKF.
6. Uncertainties
6.1 Exposure Assessment Uncertainties
6.1.1 Maximum Use Scenario
The screening-level risk assessment focuses on characterizing potential ecological risks
resulting from a maximum use scenario, which is determined from labeled statements of
maximum application rate and number of applications with the shortest time interval
between applications. The frequency at which actual uses approach this maximum use
scenario may be dependant on pest resistance, timing of applications, cultural practices,
and market forces.
6.1.2 Aquatic Exposure Modeling of Strychnine
Because the nature of the application method (direct subterranean application to main
runway of rodent burrows, followed by covering of treatment holes), strychnine-treated
baits are not expected to be exposed to rainfall that would result in runoff of strychnine
residues to surface water bodies. In addition, the strychnine on the treated baits in the
burrow will not be exposed to sufficient percolating water to leach from the bait into
groundwater, in particular since the material is strongly sorbed to soil.
Therefore, the potential for aquatic exposure is insignificant under currently labeled use
conditions for strychnine rodent baits, and as a result, aquatic exposure modeling was not
performed for this assessment.
6.2 Effects Assessment Uncertainties
6.2.1 Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids, second instar for
amphipods, stoneflies, mayflies, and third instar for midges).
60
-------
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.
Strychnine is not expected to have effects that differ by age class.
6.2.2 Location of Wildlife Species
For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal
was assumed to occupy either the treated area or adjacent areas where poisoned pocket
gophers may be found. Actual habitat requirements of any particular terrestrial species
were not considered, and it was assumed that species occupy, exclusively and
permanently, the treatment area. In this case, strychnine is placed in a hole in the ground.
It does not have drift or runoff. Therefore, the above assumptions have been modified to
fit this particular assessment.
7. Risk Conclusions
In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the
information presented in this endangered species risk assessment represents the best data
currently available to assess the potential risks of Strychnine to the CRLF, CTS, and
SJKF and their designated critical habitats.
Based on the best available information, the Agency makes a Likely to Adversely Affect
determination for the CRLF, CTS and SJKF from the use of strychnine.
Additionally, the Agency has determined that there is the potential for modification of the
designated critical habitat for the CRLF and the CTS from the use of the chemical.
Given the LAA determination for the CRLF and CTS, and potential modification of
designated critical habitat for the CRLF and CTS, a description of the baseline status and
cumulative effects for the CRLF is provided in Attachment II and the baseline status and
cumulative effects for the CTS and SJKF is provided in Attachment IV.
A summary of the risk conclusions and effects determinations for the CRLF, the CTS,
and the SJKF, and the critical habitat of the CRLF and the CTS, given the uncertainties
discussed in Section 6, is presented in Tables 7.1 and 7.2.
Table 7.1 Effects Determination Summary for Effects of Strychnine on the CRLF, the CTS, and
the SJKF.
Due to the nature of the application method, a meaningful estimation of exposure cannot be
determined; thus RQs cannot be estimated.
61
-------
Species
Effects
Determination
Basis for Determination
California
red-legged
frog
(Rana aurora
draytonii)
and
California
tiger
salamander
(Ambystoma
californiense)
LAA
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults using fish as a surrogate):
Due to the current use pattern, no aquatic exposure is expected. Even if strychnine
were used on ditchbanks or earthen dams, it would be expected to reach aquatic
environments at maximum estimated concentrations in the parts per trillion range,
which is roughly 0.02 of the LOG for the most sensitive aquatic species tested.
Terrestrial-phase (Juveniles and Adults using birds as a surrogate):
Strychnine is highly toxic to birds on a subacute dietary basis (no acute oral data
available). Dermal exposure to the bait is possible when the CRLF/CTS uses gopher
burrows. Although dermal absorption in mammals may be very low; amphibians
have thin, permeable skin. Therefore, it is assumed that it may be dermally absorbed
and would also be highly toxic to terrestrial-phase amphibians.
There is a potential to secondary poisoning through consumption of soil-
dwelling/burrowing invertebrates that have either consumed the strychnine bait or are
transporting/tracking it.
Although exposures via dermal absorption and via consumption of invertebrates
cannot be estimated, the potential exists for dermal exposure and consumption of
invertebrates that have been in contact with the bait. Therefore, due to the high
toxicity of strychnine, risk cannot be discounted.
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary productivity
Due to the current use pattern, no aquatic exposure is expected. If strychnine were to
reach an aquatic environment after being used on ditchbanks or earthen dams,
maximum estimated concentrations are in the parts per trillion range, which is
roughly 0.02 of the LOG for the most sensitive aquatic species tested.
Terrestrial prey items
There is a possible reduction in the amphibian prey base if there are a significant
number of amphibians that utilize the gopher burrows and come in dermal contact
with the bait.
Potential Modification of Habitat
It has been reported that some amphibians will use the gopher burrows for resting and
avoiding hot weather. The removal of pocket gophers will cause some burrows to
become abandoned and unavailable to the amphibians for resting and shelter.
California tiger salamanders spend much of their lives in underground retreats, often
in burrowing mammal (ground squirrel, pocket gopher, and other burrowing
mammal) burrows.
San
Joaquin kit
fox (Vulpes
macrotis
mutica)
LAA
Potential for Direct Effects
The LD50 of strychnine is 0.75 mg/kg for the desert kit fox (Vulpes macrotis arsipus).
SJKFs might receive a harmful or fatal dose of strychnine by eating a poisoned pocket
gopher it dug out of its burrow or found above ground. One dose of bait contains from
43.2 mg to 65.7 mg of strychnine. Consumption of a kangaroo rat (Dipodomys sp.)
killed with 12.8 mg of strychnine killed a desert kit fox within 30 minutes. A gopher
with 12.8 mg of strychnine in its cheek pouches would carry enough poison to kill the
fox. There is also a potential to secondary poisoning through consumption of soil-
62
-------
Table 7.1 Effects Determination Summary for Effects of Strychnine on the CRLF, the CTS, and
the SJKF.
Due to the nature of the application method, a meaningful estimation of exposure cannot be
determined; thus RQs cannot be estimated.
Species
Effects
Determination
Basis for Determination
dwelling/burrowing invertebrates that have either consumed the strychnine bait or have
been transporting/tracking it. Although exposures via consumption of pocket gophers
and/or invertebrates cannot be estimated, due to the high toxicity and the potential for
consumption of pocket gophers and/or invertebrates that have been in contact with the
bait, risk cannot be discounted.
Potential for Indirect Effects
To the extent SJKF depends on gophers as a prey animal, the SJKF could be affected
by their reduction in numbers.
63
-------
Table 7.2 Effects Determination Summary for the Critical Habitat Impact Analysis
Designated
Critical Habitat
for:
Effects
Determination
Basis for Determination
Due to the nature of the application method, a meaningful estimation of exposure cannot be
determined; thus ROs cannot be estimated.
California
red-legged frog
(Rana aurora
draytonii) and
California
tiger salamander
(Ambystoma
californiense)
Habitat
Modification
There is potential risk from dermal exposure in the gopher burrows and from
consumption of terrestrial invertebrates that have been in contact with the bait.
Due to the potential risk from dermal exposure, there is a possible reduction in the
amphibian prey base. Finally, there is a potential loss of habitat following removal
of pocket gophers (e.g., some burrows will become abandoned and unavailable to
the amphibians for resting and shelter.
When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the listed species and its resources (i.e., food and habitat)
are not expected to be uniform across the action area. 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, the SJKF,
and the CTS life stages within the action area and/or applicable designated
critical habitat. This information would allow for quantitative
extrapolation of the present risk assessment's predictions of individual
effects to the proportion of the population extant within geographical areas
where those effects are predicted. Furthermore, such population
information would allow for a more comprehensive evaluation of the
significance of potential resource impairment to individuals of the
assessed species.
• Quantitative information on prey base requirements for the assessed
species. While existing information provides a preliminary picture of the
types of food sources utilized by the assessed species, it does not establish
minimal requirements to sustain healthy individuals at varying life stages.
Such information could be used to establish biologically relevant
thresholds of effects on the prey base, and ultimately establish
geographical limits to those effects. This information could be used
together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.
64
-------
• Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth or reproductive impairment
immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and
together with the information described above, a more complete prediction
of effects to individual species and potential modification to critical
habitat.
8. 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.
Atkins. E.L., E.A. Greywood, and R.L. MacDonald. 1975. Toxicity of pesticides and
other agricultural chemicals to honey bees. Laboratory studies. Univ. of Calif,
Div.Agric. Sci. Leaflet 2287. 38pp. (MRID# 000369-35).
Burns, L.A. 1997. Exposure Analysis Modeling System (EXAMSII) Users Guide for
Version 2.97.5, Environmental Research Laboratory, Office of Research and
Development, U.S. Environmental Protection Agency, Athens, GA.
Carsel, R.F., J.C. Imhoff, P.R. Hummel, J.M. Cheplick and J.S. Donigian, Jr. 1997.
PRZM-3, A Model for Predicting Pesticide and Nitrogen Fate in Crop Root and
Unsaturated Soil Zones: Users Manual for Release 3.0; Environmental Research
Laboratory, Office of Research and Development, U.S. Environmental Protection
Agency, Athens, GA.
Case, R.M and B.A. Jasch. 1994. Pocket Gophers. Pages B17-B29. in Hygnstrom, S.E.,
R.M. Timm, and G.E. Larson, editors. 1994. Prevention and Control of Wildlife
Damage. Cooperative Extension Service, University of Nebraska, Lincoln, NE,
USA.
Cook, D.C., P.C. Trenham, and P.T. Northern. 2006. Demography and breeding
phenology of the CTS (Ambystoma californieme) in an urban landscape.
Northwestern Naturalist 87:215-224
65
-------
Evans, J.M., P.L. Hegdal, and R.E. Griffiths, Jr. 1970. Methods of controlling
jackrabbits. Proc. Vert. Pest Conf. 4:109-116.
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%20draytonii.PDF)
Fellers, Gary M. 2005b. California red-legged frog, Rana draytonii Baird and Girard. pp
198-201. In: L.L.C. Jones, et al (eds.) Amphibians of the Pacific Northwest.
xxi+227.
Fernandez, S., C. Santin, J. Marquinez, and M.A. Alvarez. 2005. Changes in soils due to
pulverization in coastal plain estuaries. Geophysical Research Abstracts 7, 3pp.
Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation
of the EPA food-chain (Kenaga) nomogram, and instrument for estimating
pesticide residues on plants. Environmental Toxicology and Chemistry 13
(9):1383-1391.
Hayes, M.P. and M.R. Jennings. 1988. Habitat correlates of distribution of the
California red-legged frog (Rana aurora draytonii} and the foothill yellow-legged
frog (Rana boylii): Implications for management, pp. 144-158. in Proceedings
of the Symposium on the Management of Amphibians, Reptiles, and Small
Mammals in North America. R. Sarzo, K.E. Severson, and D.R. Patton (technical
coordinators). USDA Forest Service General Technical Report RM-166.
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.
Hegdal, P.L., and T.A. Gatz. 1976. Hazards to wildlife associated with underground
strychnine baiting for pocket gophers. Proc. Vert. Pest Conf. 7:258-266.
Hegdal, P.L., T.A. Gatz, and E.C Fite. 1980. Secondary effects on mammalian predators.
Proceedings of the Worldwide Furbearer Conference, pp. 1781-1901.
66
-------
Hoerger, F., and E.E. Kenaga. 1972. Pesticide residues on plants: Correlation of
representative data as a basis for estimation of their magnitude in the
environment. In F. Coulston and F. Korte, eds., Environmental Quality and
Safety: Chemistry, Toxicology, and Technology, Georg ThiemePubl., Stuttgart,
West Germany, pp. 9-28.
Hygnstrom, S.E., R.M. Timm, and G.E. Larson, editors. 1994. Prevention and control of
Wildlife Damage. Cooperative Extension Service, University of Nebraska,
Lincoln, NE, USA.
Jennings, M.R. and M.P. Hayes. 1985. Pre-1900 overharvest of California red-legged
frogs (Rana aurora draytonii): The inducement for bullfrog (Rana catesbeiand)
introduction. Herpetological Review 31(1): 94-103.
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.
Jones, C.A. and C.N. Baxter. 2004. Thomomys bottae. Mammalian Species, No 742.
American society of Mammalogists. 14 pp.
Jordan, T.E., J.C. Cornwell, R.B. Walter, and J.T. Anderson. 2008. Changes in
phosphorus biogeochemistry along an estuarine salinity gradient. Limnology and
Oceanography 53(1): 172-184.
Karvonen, T., Koivusalo, H., Jauhiainen, M., Palko, J. and Weppling, K. 1999. A
hydrological model for predicting runoff from different land use areas, Journal of
Hydrology, 217(3-4): 253-265.
Kuhn, J.O. 1991. Acute Oral Toxicity Study in Rats. CIBA-GEIGY Corporation,
Agricultural Division, Greensboro, NC. Study Number 7803-91.
Kupferberg, S. 1997. Facilitation of periphyton production by tadpole grazing:
Functional differences between species. Freshwater Biology 37:427-439.
Kupferberg, S.J., J.C. Marks and M.E. Power. 1994. Effects of variation in natural
algal and detrital diets on larval anuran (Hyla regilld) life-history traits. Copeia
1994:446-457.
Lampe, R.P. 1976. Aspects of the predatory strategy of the North American badger
(Taxidea taxus). Ph.D. Dissertation. University of Minnesota, Minneapolis,
Minnesota, 106pp.
67
-------
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, USA. Environmental Toxicology &
Chemistry 18(12): 2715-2722.
Loredo, I, D., D. Van Vuren, and M. L. Morrison. 1996. Habitat use and migration
behavior of the California tiger salamander. Journal Herpetology 30:282-285.
Majewski, M.S. and P.D. Capel. 1995. Pesticides in the atmosphere: distribution, trends,
and governing factors. Ann Arbor Press, Inc. Chelsea, MI.
Marsh, R.E., R.H. Schmidt, and W.E. Howard. 1987. Secondary hazards to coyotes of
ground squirrels poisoned with 1080 or strychnine. Wildlife society Bulletin
15(3):380-385.
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.
McDonald M.A.I; Healey J.R.; Stevens P. A. 2002. The effects of secondary forest
clearance and subsequent land-use on erosion losses and soil properties in the
Blue Mountains of Jamaica. Agriculture, Ecosystems & Environment, Volume
92, Number 1: 1-19.
McGrew, John C. 1979. Vulpes macrotis. Mammalian Species, No. 123. American
Society of Mammalogists. 6 pp.
Means, J.C. 1995. Influence of salinity upon sediment-water partitioning of aromatic
hydrocarbons. Marine Chemistry 51(1): 3-16.
Nowak, R.M. 1999. Walker's Mammals of the World, vol. 2. Johns Hopkins University
Press, Baltimore. 1936pp.
Okisaka S.; Murakami A.; Mizukawa A.; Ito J.; Vakulenko S.A.; Molotkov LA.; Corbett
C.W.; Wahl M.; Porter D.E.; Edwards D.; Moise C. 1997. Nonpoint source runoff
modeling: A comparison of a forested watershed and an urban watershed on the
South Carolina coast. Journal of Experimental Marine Biology and Ecology,
Volume 213, Number 1: 133-149.
Parikh S.J., J. Chorover, and W.D Burgos. 2004. Interaction of phenanthrene and its
primary metabolite (l-hydroxy-2-naphthoic acid) with estuarine sediments and
humic fractions. Journal of Contaminant Hydrology 72(1-4): 1-22.
Phuong V.T. and van Dam J. Linkages between forests and water: A review of research
evidence in Vietnam, in, Forests, Water and Livelihoods European Tropical
Forest Research Network. ETFRN NEWS (3pp).
68
-------
PMRA. 2005. Re-evaluation of Strychnine: Proposed Acceptable for continuing
Registration. PACR2005-08. Pest Management Regulation Agency, Health
Canada, 2720 riverside Drive, A.L. 6605C, Ottawa, Ontario, F1A OK9.
Rathburn, G.B. 1998. Rana aurora draytonii egg predation. Herpetological Review,
29(3): 165.
Reis, D.K. 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.
Salmon, T.P. and W.P. Gorenzel. 2002. Pocket Gophers. UC Davis Agriculture and
Natural Resources, IPM Education and Publications, No. 7433. UC Statewide
IPM Project, University of California, Davis, CA 95616-8620.
Sargeant, A.B. and D. W. Warner. 1972. Movements and denning habits of a badger. J.
Mammal. 53:207-210.
Schitoskey, F., Jr. 1975. Primary and secondary hazards of three rodenticides to kit fox.
J. Wildlife Management 39:416-418.
Schwartze, E.W. 1922. The relative toxicity of strychnine to the rat. U.S. Department of
Agriculture Bulletin 1023. 19pp.
Seale, D.B. andN. Beckvar. 1980. The comparative ability of anuran larvae (genera:
Hyla, Bufo and Rand) to ingest suspended blue-green algae. Copeia 1980:495-
503.
Sparling, D.W., G.M. Fellers, L.L. McConnell. 2001. Pesticides and amphibian
population declines in California, USA. Environmental Toxicology & Chemistry
20(7): 1591-1595.
Swarzenski, P.W., D. Porcelli, P.S. Andersson, and J.M Smoak. 2003. The behavior of
U- and Th-series nuclides in the estuarine environment. Reviews in Mineralogy
and Geochemistry 52(1): 577-606.
Teske, Milton E., and Thomas B. Curbishley. 2003.AgDisp ver. 8.07 Users Manual.
USDA Forest Service, Morgantown, WV.
Timm, R.M. 1983. Description of active ingredients, in R.M. Timm, ed. 1983.
Prevention and control of wildlife damage. Great Plains agriculture Council and
Nebraska Cooperative Extension Service. University of Nebraska, Lincoln. 660
pp.
69
-------
U.S. Environmental Protection Agency (USEPA). 1994. Review of field efficacy study
conducted in California on strychnine baits used to control Valley pocket gopher
(MRID 42488601) and assessment of hazard associated with underground use.
EFED Report dated May 20, 1994.
USEPA. 1996a. Strychnine RED Chapter. Ecological Effects Branch report dated
March 29, 1996.
USEPA. 1996b. Reregi strati on Eligibility Decision (RED) Strychnine. EPA 738-R-96-
33, July, 1996.
USEPA. 1998. Guidance for Ecological Risk Assessment. Risk Assessment Forum.
EPA/630/R-95/002F, April 1998.
USEPA. 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.
USFWS. 1998. Recovery Plan for Upland Species of the San Joaquin Valley, California.
U.S. Fish and Wildlife Service, Portland, Oregon. 319 pages. Available online at:
http://ecos.fws.gov/docs/recovery_plans/l998/98093Oa.pdf (Accessed on March
31,2008).
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. 2004. 50 CFR Part 17, Endangered and Threatened Wildlife and Plants;
Determination of Threatened Status for the California Tiger Salamander; and
Special Rule Exemption for Existing Routine Ranching Activities; Final Rule.
USFWS. 2005. Endangered and threatened wildlife and plants: designation of critical
habitat for the California tiger salamander, Central population. Federal Register
70 (162):49380-49458. Available online at:
http://a257.g.akamaitech.net/7/257/2422/01jan20051800/edocket.access.gpo.gov/
2005/pdf/05-16234.pdf (Accessed on March 16, 2009).
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
70
-------
U.S. Fish and Wildlife Service and National Marine Fisheries Service (USFWS/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. Memorandum to Office of Prevention, Pesticides, and Toxic
Substances, U.S. EPA conveying an evaluation by the U.S. Fish and Wildlife
Service and National Marine Fisheries Service of an approach to assessing the
ecological risks of pesticide products.
USFWS/NMFS. 2004. 50 CFR Part 402. Joint Counterpart Endangered Species Act
Section 7 Consultation Regulations; Final Rule. FR 47732-47762.
Velde B. and T. Church. 1999. Rapid clay transformations in Delaware salt marshes.
Applied Geochemistry 14(5): 559-568.
Verts, BJ. and L.N. Carraway. 1999. Thomomys talpoides. Mammalian Species, No.
618. American Society of Mammalogists. llpp.
Verts, BJ. and L.N. Carraway. 2000. Thomomys mazama. Mammalian Species, No.
641. American Society of Mammal ogists. 7pp.
Willis, G.H. and L.L. McDowell. 1987. Pesticide Persistence on foliage in Reviews of
Environmental Contamination and Toxicology. 100:23-73.
Wassersug, R. 1984. Why tadpoles love fast food. Natural History 4/84.
Wood, I.E. 1965. Response of rodent populations to controls. Journal of Wildlife
Management, 29(3):425-438.
Wood, T.M. and A.M. Baptista. 1993. A model for diagnostic analysis of estuarine
geochemistry. Water Resources Research 29(1): 51-71.
71
------- |