SEPA
United States
Environmental Protection
Agency
Office of
Pesticides and Toxic Substances
Washington DC 20460
September 1980
Pesticides
Strychnine
Position Document No. 2/3
.
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Strychnine Position Document 2/3
Office of Pesticide Programs
Office of Pesticides and Toxic Substances
U.S. Environmental Protection Agency
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Acknowledgements
Project Team
Kyle Barbehenn, Biologist, HED
Dennis Carluzzo, Attorney, OGC
Douglas Chambers, Biologist, BFSD
David Eberly, Project Manager, SPRD
Thomas Edwards, Pharmacologist, HED
Linda Garczynski, Writer/Editor, SPRD
Andrew Gordon, Attorney, OGC
Roger Holtorf, Economist, BFSD
William Jacobs, Biologist, RD
Daniel Peacock, Biologist, RD
EPA Pesticide Chemical Review Committee (PCRC)
Charles Gregg, OWWM
Richard Hill, OPTS
Allen Jennings, 0PM
Donna Kuroda, ORD
Lois Jacobs, OE
Ray Smith, OANR
Marcia Williams, Chairperson, SPRD, OPP
Michael Winer, XC
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Table of Contents
I. Introduction 1
A. Background 1
1. The RPAR Process 1
2. Strychnine RPAR 2
B. Strychnine 3
1. Physical and Chemical Properties 3
2. Production 3
3. RPAR Uses 3
4. Estimated Usage 7
II. Rebuttal Analysis 9
A. Background 9
B. Risk Criterion - Acute Toxicity to Birds and Mammals 9
1. LD™ Range 9
2. Exposure to Bait 10
3. Other studies on Birds 10
C. Risk Criterion - Significant Reduction in Population
Nontarget Species and Endangered Species 1 1
1. Hegdal and Gatz Study 11
2. Howell and Wishart Study 13
3. Rebuttals Regarding Other Field Observations 14
4. Rebuttals on Secondary Poisoning and Endangered 14
Species
5. Miscellaneous Rebuttals 15
III. Risk Analysis 17
A. Strychnine 17
1. Methods of Application for Target Species 17
a. Ground Squirrels 17
b. Prairie Dog 17
c. Other Mammals 18
1) Jackrabbit 18
2) Kangaroo and Cotton Rats - 18
3) Porcupines 18
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Table of Contents (Continued)
Page
d. Pigeons and House Sparrows
e. Cropland Birds
2. General
19
a. Toxicology '^
b. Acute Toxicity ^
c. Subacute and Chronic Toxicity I)?
d. Bioaccumulation and Tissue Residues ^
e. Secondary Toxicity ^n
f* Summary
3. Direct Risks to Nontarget Species ^.
4. Indirect Risks to Nontarget Species ^
5. Risks to Members of Endangered Species 2'
a. Black-Footed Ferret 31
b. San Joaquin Kit Fox 32
c. California Condor 32
d. Peregrine Falcon 33
e. Other Species 3*+
6. Human/Domestic Risks 34
B. Alternatives - Mammals 36
1. Sodium Fluoroacetate (Compound 1080) 36
a. Method of Application 37
1) Ground Squirrel 37
2) Prairie Dog 37
b. General 37
1) Toxicology 37
2) Acute Toxicity 38
a) Laboratory Data 38
b) Field Studies 38
3) Subacute and Chronic Toxicity j*2
4) Bioaccumulation and Tissue Residues 42
5) Secondary Toxicity JJ3
6) Human Risks
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Table of Contents (Continued)
Page
2. Zinc Phosphide 45
a. Method of Application 45
1) Ground Squirrel 45
2) Prairie Dog 45
b. General 45
1) Toxicology 45
2) Residue 46
3) Acute Toxicity 46
a) Laboratory Data 46
b) Field Studies 47
4) Secondary Toxicity 47
5) Human Risks 48
3. Anticoagulants 48
a. Method of Application 48
b. Toxicity 48
1) CPN 48
2) DPN 49
3) Other Anticoagulants 49
c. Human Risks 50
1) CPN 50
2) DPN 50
3) Other Anticoagulants 50
4. Fumigants 50
a. Carbon Disulfide 50
b. Gas Cartridges 51
c. Methyl Bromide 51
d. Other Fumigants 51
5. Repellents 51
6. Relative Risks and Comparative Data 51
7. Summary 55
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Table of Contents (Continued)
Page
C. Alternatives - Bird Control 56
D. Summary of Relative Risks by Use Pattern 56
1. General 56
2. Rangeland and Pasture Rodents 57
a. Prairie Dogs 57
b. Ground Squirrels 57
c. Miscellaneous Rodents and Lagomorphs 57
3. Cropland Rodents 58
a. Prairie Dogs 58
b. Ground Squirrels 58
c. Miscellaneous Rodents and Lagomorphs 58
4. Nonagricultural Sites for Rodents and Lagomorphs 58
5. Cropland Birds 58
6. Nonagricultural Sites for Birds 58
IV. Benefit Analysis 59
A. Introduction 59
B. General Production and Use Patterns 60
C. Analysis of Benefits of Strychnine Use on 60
Rangeland/Pasture
1. Ground Squirrels 60
2. Prairie Dogs 63
3. Other Rodents and Lagomorphs 65
D. Analysis of Benefits of Strychnine Use on Cropland 65
1. Prairie Dogs 65
2. Ground Squirrels 67
3. Other Rodents 67
E. Analysis of Benefits of Strychnine Use on Cropland for 67
Bird Control
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Table of Contents (Continued)
F. Analysis of Benefits of Strychnine Use on Non- 69
agricultural Sites
1. Birds 69
2. Rodents and Lagomorphs 71
V. Risk/Benefit Analysis and Regulatory Options 73
A. General 73
B. Risk/Benefit Analysis 73
1. Rangeland Rodents 73
2. Cropland Rodents 75
3. Nonagricultural Site Rodents and Lagomorphs 76
4. Cropland Birds 76
5. Nonagricultural Site Birds 76
C. Regulatory Options 77
1. Rangeland Rodents - ground squirrels 77
2. Rangeland Rodents - prairie dogs 84
3. Rangeland Rodents - other rodents and lagomorphs 85
4. Cropland Rodents - ground squirrels 88
5. Cropland Rodents - prairie dogs 88
6. Cropland Rodents - other rodents and lagomorphs 89
7. Rodents and Lagomorphs on Nonagricultural Sites 89
8. Birds on Cropland 90
9. Birds on Nonagricultural Sites 91
D. Proposed Actions 93
1. Rangeland Rodents - ground squirrels 93
2. Rangeland Rodents - prairie dogs 95
3. Rangeland Rodents - other rodents and lagomorphs 95
4. Cropland Rodents - ground squirrels 97
5- Cropland Rodents - prairie dogs 97
6. Cropland Rodents - other rodents and lagomorphs 97
7. Rodents and Lagomorphs on Nonagricultural Sites 97
8. Birds on Cropland 98
9. Birds on Nonagricultural Sites 99
E. Summary 100
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List of Tables
Table Title
1-1 Strychnine, Federal-State Registrations 4
1-2 Percentage of Use by Site/Pest Combination 8
III-1 Acute Oral Toxicity of Strychnine Alkaloid 20
III-2 Acute Oral Toxicity of Compound 1080 39
III-3 Relative Risks of Alternative Toxicants 52
IV-1 Estimated Annual Above-Ground Usage of 61
Strychnine Bait to Rodent and Bird Control,
1977-78
IV-2 Chemical Alternatives to Strychnine for Rodents 62
and Lagomorph Control
IV-3 Estimated U.S. Acreage of Range and Pasture 64
Infested with Prairie Dogs
IV-4 Estimated Acreages of Cropland Treated with 66
Strychnine for Prairie Dogs and Ground Squirrels,
1978
IV-5 Chemical Alternatives to Strychnine for Bird 70
Control
IV-6 Major Pests on Nonagricultural Sites Controlled 72
with Strychnine
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Appendices
Appendix Title
A Strychnine, Position Document 1 and RPAR
Notice, Dec., 1, 1976.
B List of Rebutters.
C Rebuttal Analysis.
D USDI Fish and Wildlife Service Endangered
Species Report.
E Preliminary Benefit Analysis.
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I. Introduction
A. Background
1. The RPAR Process
Through the Federal Insecticide, Fungicide and Rodenticide Act as
Amended (FIFRA), the United States Environmental Protection Agency (EPA) has
the authority for regulating the use of pesticides. This authority includes
the registration, reregistration, and classification of pesticides. The
process for administering this authority provides for the identification of
pesticides that appear to cause unreasonable adverse effects on human health
and the environment.
Under this process, each pesticide and its metabolites or degradation
products is evaluated for its potential to meet or exceed any of certain risk
criteria. The three general risk criteria (acute toxicity, chronic toxicity,
and lack of emergency treatment) are described in 40 CFR 162.11. If the
Agency's evaluation of a pesticide, from available information, indicates that
the potential for unreasonable adverse effects exists, a notice of rebuttable
presumption against registration and continued registration (RPAR) is published
in the Federal Register. The notice explains the reasons for the presumption(s)
and provides an opportunity for registrants, applicants, and other interested
parties to rebut or support the presumption.
EPA examines the rebuttals and the supporting evidence to determine if the
original presumption(s) are still valid. If the rebuttal analysis results in a
conclusion that one or more of the criteria is met or exceeded, a complete risk
assessment is performed. This assessment documents the risks associated with
the use(s) of the pesticide, methods for reducing or eliminating these risks,
and the risks associated with the substitution of alternatives. A benefit
analysis of the use(s) of the pesticide is also performed. The principal
concern in the benefit analysis is an assessment of the economic impacts on
pesticide users and on the consumers of the user's products. The benefit
analysis identifies the major and minor uses of the pesticide and the
registered alternative products. A determination is made of the change in
costs for treatment with available substitute products. The regulatory impact
on use productivity, in terms of yield per acre or total output, is assessed.
Also, the impact on major agricultural commodities and retail food prices,
should the uses of the pesticide be cancelled, is assessed.
A comparison of the risks and benefits of each use is made and available
regulatory options are developed. The impact on the risks and benefits is
evaluated for each regulatory option. The final Agency decision is based upon
achieving the goal of a pesticide performing its intended function without
causing unreasonable adverse effects on the environment. Tnus, the Agency
attempts to determine the regulatory position at which benefits exceed risks
and at which further risk reduction is not appropriate given the corresponding
benefit reduction which could occur.
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2. Strychnine RPAR
The RPAR notice for strychnine was published in the Federal Register of
December 1, 1976 (41 FR 52810). The presumption was against all outdoor above-
ground uses of strychnine. Three other actions by the Federal government
involving strychnine should be noted. In March of 1972, Executive Order 11643
was issued. This order prohibited the use of all toxicants, including
strychnine, for control of predators on Federal lands or in Federal programs.
In the same year, EPA cancelled the registrations of thallium sulfate,
cyanide, strychnine, and compound 1080 for predator control. Additionally, in
February 1978, EPA restricted use of several pesticides, including strychnine
formulations with concentrations greater than 0.5 percent, for use only by
certified applicators (43 FR 5791). The criteria influencing the restriction
for strychnine were acute oral toxicity, hazards to nontarget species, and use
and accident history.
The criteria that were determined to have been met or exceeded for the
outdoor above-ground uses of strychnine are: 1) acute toxicity to mammals and
birds and 2) significant reduction in populations of nontarget organisms and
fatalities to members of endangered species. The reasons for the determination
were explained in detail in the RPAR notice and accompanying Position Document 1
(Appendix A). The following paragraphs summarize the information available at
the time the PD1 was issued.
The acute toxicity criterion was based on a determination that nontarget
mammals and birds are likely to consume lethal quantities of strychnine bait.
A lethal quantity could be consumed directly by eating the bait, or indirectly
by eating a strychnine-poisoned organism. Strychnine LD^Q values were not,
and are not, available for many of the suspected nontarget species. Risk
to such nontarget species was based on available LD,- values of target and
^
,-Q
nontarget species of the same genus as those for which LD^ values were
unavailable.
The reasoning that the significant reduction in nontarget organism
populations criterion was met is based on three items . First , t u acute oral
toxicity data suggest a risk to nontarget species through direct ingestion of
strychnine-treated bait can reasonably be expected. The second factor was the
deaths of eight Canada geese in 1968. Their deaths were attributed to the
ingestion of strychnine-treated gopher bait (Howell and Wishert, 1969). The
third item was a draft report on a study assessing the field hazards of 0.5
percent strychnine ground squirrel bait (Hegdal, 1976). The preliminary
conclusion was that several thousand birds could have been killed as a result
of the treatment with strychnine of 9,000 acres for ground squirrel control.
The criterion for endangered species was based on a laboratory study that
demonstrated a hazard to the endangered San Joaquin kit fox from secondary
poisoning. In this study, a kangaroo rat was killed with a quantity of
strychnine that could be consumed by the rat by ingesting strychnine treated
grain bait. A desert kit fox, a subspecies of kit fox related to the San
Joaquin kit fox, was fatally poisoned by eating the kangaroo rat.
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B. Strychnine
1. Physical and Chemical Properties
Strychnine is a highly toxic product extracted from the seeds of an Asiatic
tree (Strychnos nux-vomica). The crude extract may be purified to form
strychnine alkaloid, strychnine sulfate, or other strychnine salts. Strychnine
alkaloid is a colorless or white solid which is practically insoluble in water,
alcohol, and ether, but is slightly soluble in chloroform and benzene.
Strychnine sulfate is soluble in water and alcohol and insoluble in ether.
Strychnine compounds are stable in the environment but are either metabolized
or excreted by animals.
2. Production
The entire U.S. strychnine supply is imported, mainly as strychnine or its
salts. A small quantity of the seed is imported for processing in the United
States. In 1978, India supplied 91 percent and Israel nine percent of the
approximately 14,500 pounds of the processed strychnine imported by -the United
States. The bait is then formulated in the United States for domestic use. In
previous years, France, United Kingdom, West Germany, Canada, and Laos have
also exported strychnine to the United States (Pesticide Review, USDA, 1978).
3. RPAR Uses
Currently 116 strychnine products are federally registered for control of
major rodent pests (including ground squirrel, prairie dogs, house mice, and
field mice of the genus Microtus ); minor rodent pests (including
chipmunks,woodchucks, kangaroo rats, cotton rats, porcupines, and field mice of
the genus Peromyscus ); lagomorphs (jackrabbits); and birds (pigeons and
house sparrows).
In addition, 277 products have state registrations. Certain states have
issued their own state registrations for strychnine uses covered by Federal
registrations. Also, specific states have issued their own registrations for
uses not covered by Federal registrations. For example, California has
registered strychnine for use against marmots, rabbits, blackbirds, cowbirds,
horned larks, house finches, white-crowned sparrows, and golden-crowned
sparrows. Wyoming has registered strychnine for mountain beavers, opposums,
marmots, and magpies. Nevada has registered strychnine for magpies, and Oregon
has registered strychnine for rabbits. See Table 1-1 for a summary of the
registered uses of strychnine.
For the purposes of analysis, the uses of strychnine have been grouped into
five site/pest categories. In many cases, these sites are not specified on
labels, and the analysis reflects historical use.
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Table 1-1.
Strychnine, Federal-State Registrations
Pest
A. Biros
o Pigeons
o House sparrows
o Blackbirds
o Cowbirds
o Horned larks
o Starlings
o House finches
o White and goloen
crowned sparrow
o Magpies
o Meadowlark
o Crows
o Bluejays
Regis-
tration
Fed.
Fed.
State (Ca.)
State (Ca.)
State (Ca.)
State (Ca.)
State (Ca.)
State (Ca.)
State (Nv. & Wy.)
State (Ca.)
State (Ca.)
State (Ca.)
Major use sites
Agricultural Nonaqricultural
Cash Range, Forests, Buildings,
crops, pasture, reforestation areas, warehouses Non-Crop £/
livestock fallow tree plantations and homes I/
Ca. X
Ca. X
X
X
X
X
X
X
X
X
X
X
I/ Induces aojacent areas.
2/ Includes golf courses, parks, cemeteries, athletic fields, ditch banks, canals and levees.
Source: Feoeral Registration: Site/pest listing from EPA registration files, I960
State Registration: State Agencies: California Department of Food and Agriculture
Nevaoa Department of Agriculture
Oregon Department of Agriculture
Wyoming Department of Agriculture
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Table 1-1.
Strychnine, Federal-State Registrations
Agricultural
Pest
B. Mammals
o House mice
o Ground squirrels
o Prairie dogs
o Jackrabbits
o Deer mice
o Meadow mice
o Kangaroo rats
o Cotton rats
o Chipmunks
o Porcupines
o Marmots/
Wooochucks
o Rabbits
o Mountain beavers
o Opossums
Regis-
tration
Fed.
Fed.
Fed.
Fed.
Fed.
Feo.
Fed.
Feo.
Fed.
Fed.
Fed.
State (Ca. & Or.)
State (Wy.)
State (Wy.)
Cash
crops,
livestock
X
X
X
X
X
X
X
X
X
X
Range ,
pasture,
fallow
X
X
X
X
X
X
X
X
X
Major use sites
Nonagricultural
Forests, Buildings,
reforestation areas, warehouses Non-Crop 2/
tree plantations and homes I/
X
X X
X
X
X
X
X
X
X
X
X
Or.
X
X
I/ Includes adjacent areas.
£/ Includes golf courses, parks, cemeteries, athletic fields, ditch banks, canals and levees.
Source: Federal Registration: Site/pest listing from EPA registration files, I960
State Registration: State Agencies: California Department of Food and Agriculture
Nevada Department of Agriculture
Oregon Department of Agriculture
Wyoming Department of Agriculture
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a. Rangeland/pasture rodents:
sites - rangeland and pastures
pests - ground squirrels, prairie dogs, jackrabbits, deer mice, meadow
mice, kangaroo rats, cotton rats, chipmunks, and
raarmots/woodchucks.
b. Cropland rodents and lagomorphs:
sites - field crops such as grains and forages
and horticultural crops such as nuts, fruits, and
vegetables
pests - ground squirrels, prairie dogs, meadow mice, deer mice,
chipmunks, rabbits, cotton rats, kangaroo rats, jackrabbits,
and marmots/woodchucks
c. Nonagricultural rodents and lagomorphs:
sites - grain elevators, other crop storage areas
and facilities, commercial buildings and
warehouses, open dumps, farmsteads, urban
dwellings, ditch banks, levees, dikes,
canals, earthen dams, golf courses,
parks, cemeteries, athletic fields,
recreational areas, airport turf runways,
military bases, tree nurseries, tree
plantations and reforestation areas.
pests - rabbits, jackrabbits, chipmunks, marmots/
woodchucks, ground squirrels, prairie
dogs, kangaroo rats, cotton rats, deer mice,
meadow mice, house mice, porcupines,
mountain beavers, and opossums
d. Cropland Birds:
sites - grape, cherry, lettuce, sugarbeet, rice, tomatoe,
plum, melon, strawberry, vegetable crop, soft fruit,
and small grain areas.
pests - house finches (linnets), horned larks, meadow larks,
starlings, cowbirds, crows, magpies, blackbirds,
pigeons (rock doves), house sparrows
(English sparrows), and crowned sparrows.
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e. Nonagricultural birds:
sites - structures and roosting sites
pests - pigeons and house (or English) sparrows
4. Estimated Usage
Approximately one-half million pounds of strychnine bait were used annually
for above-ground control of rodents, lagomorphs, and birds during 1977-1978.
The majority of the bait usage was in 17 western states for controlling ground
squirrels and prairie dogs. Ninety percent of the bait was used for rodent
control, the remaining 10 percent for birds. Rangeland/pasture use and
cropland use were approximately equal and accounted for 91 percent of the
strychnine bait. The other nine percent was used on nonagricultural sites.
The percentage of use for each site/pest combination is shown in Table 1-2.
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PEST
Table 1-2
Percentage of Use by Site/Pest Combination
SITE
Rangeland/Pasture Cropland Nonagriculture Total
Prairie Dogs 17.6?
Ground Squirrels 27.6%
Other Rodents 1 and 0.4?
Lagomorphs—
All Rodents and
Lagomorphs
Birds
Total 45.6$
2.8%
38.4?
0.9?
3.6?
45.7?
20.4?
66.0?
1.3?
2.4? 2.4?
6.3? 9.9?
8.7? 100.0?
J/ Other than prairie dogs and ground squirrels.
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II. Rebuttal Analysis
A. Background
Registrants and other interested parties were offered an opportunity to
review the data upon which the RPAR against strychnine was based and to submit
information to rebut the presumptions. Respondents could rebut the presumption
by showing that the Agency's initial determination of risk was in error or by
showing that common use patterns and actual exposure indicate that use of the
pesticide is not likely to result in any significant adverse effects (40 CFR
Registrants and other interested persons were also offered the opportunity
to submit evidence as to whether the economic, social, and environmental
benefits of continuing to use this pesticide outweigh the risks of its use
(I62.11(a)(5)(iii)). These comments are considered in the development of
Section IV of this document.
The Agency received 100 rebuttal submissions in response to the RPAR on
strychnine. No scientific data were submitted to support the majority of the
comments received. Moreover, the little scientific data submitted were either
insufficient or contained inadequate test methods to support the position
taken. Significant rebuttal comments and the Agency's responses are presented
in this Section. The complete rebuttal analysis is contained in Appendix C.
B. Risk Criterion - Acute Toxicity to Birds and Mammals
1. LD Range
A number of respondents said that the Agency erred in PD 1 by stating that
there is a narrow range of LD,-n values for strychnine among birds and mammals
tested (30000/7: # 1B, 1C, 1D? 74, 82, 89, 94).
Admittedly, the LD,-Q values in Table III-l (page 20) show a range from
0.7 mg/kg (coyote) to ?12 mg/kg (California Quail). The specific values or the
range of toxicity values are not the only factors to consider in evaluating the
hazard to nontarget species. The similarities between target and nontarget
species in terms of exposure to the bait and feeding behavior must also be
considered .
Of the 40 species for which toxicity data were available, however, all but
four (nutria, California quail, sage grouse, turkey) had LD^Q'S approximately
equal to or less than that of major target species (ground squirrels and
pigeons). Thus, baits formulated to control ground squirrels and pigeons are
potentially hazardous to most other species. From this consideration alone, the
presumption is not rebutted for this risk criterion.
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2. Exposure to bait
Many respondents maintained that relative toxicity alone was inadequate to
presume that risks to wildlife exist. Proper selection of baits (form, size,
color) and method of application coupled with the behavior and ecology of
target and nontarget species greatly influence the results (30000/7: # 1B, 1C,
1D, 39, 74, 81, 82, 91, 96). The use of dyes to deter birds from feeding on
baits used in rodent control was emphasized in these rebuttals.
The Agency agrees in principle that there are several factors that deter-
mine the degree of risk to any particular local population from a particular
treatment. Whether or not, for instance, the routine use of dyes in surface
baiting for rodents can be relied on to substantially reduce risks to birds is
a germane question, since it provides a potential method for reducing risk, and
one that is easily enforceable.
The Agency has reviewed all documents submitted to support the contention
that dyes are effective in protecting birds (Kalmbach, 1943, Kalmbach and
Welch, 1946, Howard, 1950, Davidson, 1962, Clark, 1975). The accumulated
observations suggest that the use of certain dyes may prevent some birds from
taking lethal doses of treated grain. There is nothing in these studies,
however, that could enable predictions of the general degree of risk reduction
in the field or to understand those factors that influence the success of risk
reduction in any particular operation. Furthermore, the general enthusiasm for
the usefulness of dyes as a feeding deterrent is not without some
qualifications. Schaefer (1978) stated that dyes provide only a short term
deterrent and that their effect is soon lost unless it is reinforced by
ingestion of doses of bait that cause illness. Hegdal et al. (1979) noted that
the bright yellow dye applied to a compound 1080 bait faded noticeably after
three to four days of exposure to the sun and that exposed surfaces of the dyed
oats were virtually indistinguishable from undyed oats after two weeks. In
conclusion, the use of dyes may contribute some degree of protection to various
bird species, but this has not been quantified under normal conditions of use.
Other relevant comments regarding exposure and its reduction will be
considered by the Agency in assessing risks and in developing regulatory
options for each use. In general, however, current levels of use do not
preclude exposure to all nontarget organisms and, thus, rebuttals on the acute
toxicity criterion based on exposure arguments are not valid.
3. Other Studies on Birds
Howell and Wishart's (1969) report of Canada geese killed by strychnine was
used by the Agency in its presumption to illustrate that the use of strychnine
can result in wildlife mortality. This report was criticized by several
respondents (30000/7: # 1B, 1C, 1D, 7, 39, 82, 91) on the following grounds:
that the death of eight geese is insignificant compared to the number killed by
hunters; that there was no conclusive evidence that strychnine was the cause of
death or that the deaths resulted from the stated use of strychnine; that there
was no evidence that the bait had been properly dyed; that the surface baiting
for gopher control did not follow directions for use.
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All of the above arguments fail to rebut the Agency's point. The deaths of
the geese illustrate the potential for causing wildlife mortality and the
magnitude of this particular incident is not relevant. The laboratory analysis
which indicated the presence of strychnine in the gizzards and livers of the
geese strongly supports the conclusions that strychnine was the cause of
death.
The dying of bait for surface application is not a requirement on federally
registered labels and the application of bait around the burrows of ground
squirrels and prairie dogs is a usual practice. Thus, it is reasonable to
conclude that proper application of strychnine baits for certain registered
uses presents a risk to geese and other susceptible species that may be feeding
in the treated area.
Several respondents referred to studies that lead to the conclusion that
strychnine-treated baits present little or no hazard in gallinaceous birds
(30000/7: # 1B, 1C, 1D, 7, 39, 74, 81, 82, 91, 96). The inference was that
risks were negligible for birds in general.
The referenced studies (Ward, et. al. 1942, Scheffer, 1922, Oman, 1923,
Garlough and Keyes, 1925, and Knowles, 1937) all suffer from deficiencies in
procedures that are not acceptable by current standards (Appendix B). Major
weaknesses include inadequate sample sizes and exposure protocols. However,
collectively, the studies suggest that strychnine baits are not highly toxic to
several species of gallinaceous birds and such a result is consistent with
available information on LD^g's. These limited data suggest that
gallinaceous bird are the least susceptible of all bird species tested and,
therefore, one cannot infer a lack of acute toxic risk to birds in general.
In summary, the Agency's presumption that the use of strychnine treated
baits would result in the exposure of nontarget wildlife to toxic levels of
strychnine has not been rebutted either on the grounds of basic.toxicity of
common formulations to most species or on the absence of exposure.
C. Risk Criterion - Significant Reduction in Populations of
Nontarget Species
In presuming that the above-ground use of strychnine caused significant
reductions in local population, the Agency cited studies by Hegdal and Gatz
(1976) and by Howell and Wishart (1967). One or both of these studies were
criticized by a number of respondents (30000/7: # 1B, 1C, 1D, 7, 39, 74, 82,
91, 96).
1. Hegdal and Gatz Study
Under an Environmental Protection Agency (EPA) Interagency Agreement, The
Fish and Wildlife Service (Denver Wildlife Research Center) evaluated the
hazards associated with surface strychnine baiting for Richardson's ground
squirrel. In south-central Wyoming (during late April and early May 1976)
- 11 -
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approximately 3650 ha (hectare)— (9000 acres) were treated with 0.5
percent strychnine-treated bait. Approximately one tablespoon of bait was
placed (from horseback) at or near ground squirrel burrows. Application rate
varied between one and two kg/ha (one to two Ib/acre). Treated areas were
scattered between .Saratoga and Encampment, Wyoming. Effectiveness on ground
squirrels varied, with some plots showing almost no effect while others
indicated up to 85 percent control. An average of 3.5 dead ground 'squirrels/ha
searched (1.4/acre) were found. Data also indicate many territorial horned
larks were killed by the bait. An average of 2.5 dead horned larks/ha searched
(1.0/acre) were found. In addition, after treatment, horned larks were scarce
in treated areas and most marked horned larks were killed by the bait.
Blackbirds, especially red-winged and Brewer's, were killed early in the
season, while migrating through the area. Territorial red-winged and yellow-
headed blackbirds appeared to be reduced in number- Populations of vesper
sparrows and western meadowlarks were not seriously affected. Mourning doves
did not arrive until early May when baiting was well underway. Nevertheless,
an average of 1.1 dead doves/ha searched (0.4/acre) were found. In addition,
telemetry data coupled with residue data indicate that many radio-equipped
doves using treated areas were killed by the bait. Two female ducks (one
mallard and one pintail) nested in treated fields and telemetry data indicated
they were not affected by the treatment but one treatment-killed mallard was
found. No detrimental effects on raptors and mammalian predators were detected
and most active raptor nests fledged relatively high numbers of young.
Respondents argued that the bait had not been dyed, that it had been
applied from horseback and therefore could not have been placed under cover as
required on the label and that the application rate was higher than that on the
label (but less than that reported by Hegdal and Gatz). Questions were also
raised regarding the adequacy of the area sampled, the limited number of dead
birds analyzed for strychnine, the lack of replication, and the ability of the
Agency to draw conclusions from this study concerning risks to be expected from
other uses of strychnine and other geographical areas.
While many of these comments point to difficulties inherent in the conduct
of comprehensive research on wildlife risks associated with pesticide usage,
they do not, either individually or collectively, constitute a rebuttal against
the general presumption of risk. In the absence of valid risk measurements
from other use situations, the Agency must exercise appropriate judgment in
weighing available evidence and in making extrapolations.
It is important to note that the study by Hedgal and Gatz was conducted
under the auspices of the Wyoming Department of Agriculture and that the
poisoning operation was under the supervision of the Carbon County Weed and
Pest Control District using a registered label. The only unusi il aspect of the
control operation was that the effects were monitored by the U.S. Fish and
Wildlife Service under an agreement with the EPA. The Agency has no basis,
either from comments by respondents or otherwise, for believing that the
]_/ One hectare = 10,000 square meters or 2.4? acres
- 12 -
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practices used, whether or not they were in precise accordance with the
label directions, were not representative of widespread and commonly recognized
practice.
The state of California does require that rodent baits be dyed but this is
not a federal requirement and the formulation used in Wyoming was produced by
the USDI (EPA Reg. No. 6704-58). The label is internally inconsistent in that,
while it does state that all placements must be made in or under cover where a
hazard to wildlife is present, directions for treating ground squirrels (and
kangaroo rats) direct the user to "scatter one teaspoon of bait over a square
foot of clean ground within two or three feet of the burrow entrance."
Conceivably, horned larks and blackbirds are not considered as "wildlife" by
many users and the spring arrival of doves after the bait had been placed might
not be anticipated. Direction for treating prairie dogs, on the same label,
call for the scattering of "tablespoon quantities of bait at the edge of
mounds, where forage and soil meet." Thus, while it may be true that over-
baiting was done in the Wyoming operation (some prairie dogs were present), and
this apparent mis-use may have led to greater bird mortality than otherwise
would have occured, the use of such quantities is recommended for prairie dog
control and one could anticipate a hazard from this use.
While the 19.5 ha searched for dead animals may appear small (0.5 percent)
in relation to the 3,650 ha treated, the effort assigned to this task had to be
consistent with available resources and priorities allocated to components of
the total project. The number of birds analyzed for strychnine was intention-
ally limited so that most carcasses would be available to assess risks to any
scavengers. The failure of chemical analysis to detect strychnine in the
gastrointestinal tract of some of the dead birds is an anticipated result since
just-lethal doses would be totally absorbed before death. The Agency's judg-
ment regarding the significance of the observed mortality will be described
below, but it is notable that an independent consultant (Ketron, Inc., 1979),
employed by the USDA to assess the results of this study, indicated that
"Mortality resulting from strychnine as used for control of ground squirrels
would occur just before the breeding season-that is, at the worst possible
point in the population cycle. Pesticide-induced mortality of 10 to 20 percent
at this time, especially if sustained from year to year, would probably have
significant effects on local populations of mourning doves ..." Hegal and Gatz
observed a strychnine-induced mortality of 49 percent (23 out of 47) among the
doves tracked by radio-telemetry.
2. Howell and Wishart Study
The Agency agrees with rebuttal comments that the data regarding mortality
to geese (Howell and Wishart, 1969) are insufficient to conclude that the
incident represents a significant reduction of a local population. The
observed mortality (two geese at the baited site and six falling from the air)
may or may not represent the total mortality and it is impossible to know the
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relationship between a migrating flock and a local breeding population. The
incident does indicate a potential for significant impacts from the use of
strychnine.
In general, the argument that mortality in local populations is quickly
compensated for by natural processes (30000/7: # 74) is not acceptable. It
cannot be assumed, a priori, that all local nontarget populations are substan-
tially less susceptible to poisoning than is the target population. If the aim
is to significantly reduce the target population, it follows that some local
nontarget populations will be similarly affected.
3. Rebuttals regarding other field observations
Several respondents claimed that the Agency failed to adequately demonstrate
hazards to nontarget species and that few or no nontarget animals have been
found dead in searches following strychnine treatments (30000/7: # 1B, 1C, 1D,
8, 8A, 44, 81, 91). Such allegations of no observable effect are difficult to
evaluate. Presumably there may be conditions where the use of strychnine has
not led to substantial nontarget mortality but, even where searches have been
made, it is possible that the actual mortality has been underestimated for
various reasons. Many of the birds (Hegdal and Gatz 1976) and mammals (Hegdal
et al. 1979) found by Hegdal and his associates would have gone undetected had
it not been for the use of radio telemetry. To balance the general denial of
observed mortality, the Agency should note the report from Nevada (30000/7: #8)
indicating that 16 dogs, 18 cats, 44 cottontails, 142 jackrabbits, 12 field
mice, one badger, three hawks, 33 crows, and 24 magpies were found dead fol-
lowing a baiting operation of strychnine treated cabbage. Although no chemical
analyses for strychnine were conducted, it would be unreasonable to assume that
the observed mortality was somehow independent of the baiting operation. How-
ever, the significance of the mortality to local populations cannot be assessed
from the available information.
4. Rebuttals on secondary poisoning and endangered species
The Agency relied primarily on a laboratory study by Schitosky (1973) to
demonstrate that endangered species such as the kit fox, the black-footed
ferret, and the California condor were at risk from indirect exposure to
strychnine through the consumption of poisoned rodents. Several respondents
maintained either that the laboratory demonstration could not be used to
predict risks of secondary poisoning in the field or that various field
observations failed to support the predication in any substantial way (30000/7:
# 1B, 1C, 1D, 8, 39, 74, 81, 82, 91, 94, 96, 100 ).
While there are limits on the ability to quantify risks in the field from
laboratory studies, the potential for risk can only be rebutted by demonstrat-
ing either that the study was invalid or that the Agency's interpretation of
the study was faulty. Respondents did not demonstrate any basic flaw either in
the laboratory study or in the Agency's interpretation. Some respondents
(30000/7: # 8, 81, 86) have reported deaths of cats, dogs, gray foxes, coyotes
and other species in close association with strychnine baiting operations for
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rodents. While none of this mortality was confirmed by residue analysis, it is
reasonable to conclude from the basic toxicity data and the anecdotal reports
that some secondary poisoning of carnivores has occurred from the use of
strychnine to control rodents. Additionally, the Agency has new information on
raptor mortality associated with the use of strychnine to control pigeons.
These data will be presented below in the risk assessment. The risk criterion
has not been rebutted by claims that secondary poisoning cannot occur in the
field.
Respondents (30000/7: # 1B, 1C, 1D, 74, 82, 94) also argued either that
endangered species generally were not being jeopardized by pesticides but by
habitat loss; that the population of the San Joaquin kit fox was increasing;
that designation of some populations as endangered species is based on a
taxonomic technicality; or that no endangered species were present in many
areas of use. Such arguments do not serve to rebut the criterion.
While habitat loss may be the major reason for the endangerment of some
species, it does not logically follow that additional losses due to pesticides
will not exacerbate the situation. The precise status of most species is
difficult to establish. Claims that the number of kit foxes is increasing
rests on estimates so crude that little confidence can be placed on the
suggested trend. Until such time that the species may be removed from
the endangered list, any losses due to pesticides are of significant concern
to the Agency.
The authority for designating endangered species and their critical habitat
rests with the Department of Interior, and the EPA makes appropriate responses
to their determinations on the status of various populations when it can be
expected that the use of a pesticide will cause mortality to individuals. Most
current strychnine labels do not restrict the use of strychnine in ways that
would preclude exposure to endangered species, and allegations concerning the
absence of endangered species in certain locations where strychnine is likely
to be used do not serve to rebut the general criterion. The Agency agrees that
endangered species do not reside in many areas where the use of strychnine is
desired. The feasibility of permitting use under such circumstances is
considered in formulating regulatory options in Section V.
5. Miscellaneous Rebuttals
Many respondents indicated that special formulations or modes of
application for certain pests reduced or eliminated exposure to nontarget
species. Comments regarding bird control (30000/7: # 1B, 1C, 49, 56, 82),
porcupine control (30000/7: # 50, 51, 74, 85), commensal rodent control
(30000/7: #44, 74, 96), rabbit control on crops and rangeland and certain
other minor uses (30000/7: # 63, 71, 83, 89, 90, 91, 95) failed to rebut all
presumptions but the appropriate details of these submissions will be discussed
in the risk/benefit analysis and regulatory options (Section V). Comments
regarding rabbit control in reforestation areas (30000/7: # 85) and mountain
beaver control (30000/7: # 50) deal with unregistered uses. Comments on skunk
- 15 -
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control (30000/7: # 49, 94) and on the pocket gopher/mole control (30000/7: #2,
8, 48, 57, 56, 58, 62, 65, 74, 79, 91, 98) deal with uses that are not the
subject of the strychnine RPAR. Coranents on these latter uses, therefore,
will not be discussed.
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III. Risk Analysis
The risk analysis is a detailed study of the risks associated with the
registered uses of the RPAR chemical. The specific risks examined are those
for which the RPAR notice was issued. In the case of strychnine, the focus of
the analysis is the risk to nontarget birds and mammals, including members of
endangered species, from exposure to treated bait.
The approach taken is to first present the common methods of baiting for
various target birds and mammals. This information will form the background
for the subsequent analysis of the risks to nontarget species. Next, acute and
chronic toxicity data, from laboratory and field studies, are presented. Tne
data are for both target and nontarget organisms, and form the basis for the
assessment of the risks associated with the baiting practices.
The same approach is used in analyzing the risks of the various
alternatives. The alternatives examined are those that are currently
registered for the same uses as strychnine.
Following the analysis of the risks of using strychnine and the
alternatives, the relative risks are assessed and-summarized for each use
pattern.
A. Strychnine
1. Methods of Application for Target Species
a. Ground Squirrels
Strychnine is mixed into baits, usually grains such as oats or barley,
but also chopped cabbage or dandelion greens. Tne final use strength of the
baits ranges from 0.2 percent to 0.52 percent strychnine alkaloid. Either one
teaspoon or one tablespoon of bait is scattered near the burrow entrance or on
runways used by the ground squirrels. This is most often done in the spring
during the breeding season but some labels call for repeated treatments if
squirrels remain after initial treatment. Many of these labels recommend that
bare ground is the best bait placement site. A few others call for placing the
bait in the burrow or under brush cover if other wildlife is present. On the
average, there are approximately 80 bait placements per pound of bait and a
pound should treat 10-15 acres. For heavy infestation, one pound may treat
only two-three acres. Oat baits may retain full strength for three days or
more on the ground in the absence of rain. Approximately an 85 percent residue
loss through degradation occurred in baits 10-18 days after application (Hegdal
and Gatz, 1977a).
b. Prairie Dog
The concentration of the active ingredient of strychnine grain baits
for control of prairie dogs vary from 0.3 percent to 0.5 percent. Two
teaspoons to one tablespoon of bait is scattered near prairie dog mounds on the
- 17 -
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side away from the dirt pile. About 0.5 to 3.0 pounds of bait are used per
acre in this manner. Some labels caution against use if black-footed ferrets
are in the area or direct the user to place the bait under cover of brush or
weeds if wildlife hazards exist.
c. Other Mammals
1) Jackrabbits
Baits consist of grains (mostly rolled barley, but oats are also
used), root vegetables and fruit, or greens. The concentration of strychnine
in the bait ranges from 0.28 percent to 1.5 percent for grain baits. For
green baits, formulations range from one ounce of five percent strychnine on
three pounds of bait (0.1 percent) to one ounce of 99.5 percent strychnine on
20 pounds of bait (0.3 percent).
A variety of methods are used for applying the bait; a heaping
tablespoon of bait in mounds 10 feet apart, a half cup at locations where pre-
baiting is accepted, one or two heaping tablespoons at intervals of 35 to 50
feet, or one teaspoonful where pre-baiting is accepted. Applications are made
along the rabbit trails, around the perimeter of the field, along tree rows or
where trails meet.
2) Kangaroo and Cotton Rats
Strychnine grain bait is formulated at concentrations of from
0.25 percent to 1.0 percent. Application rates are made by hand in amounts
of one or two teaspoonfuls eight to ten feet apart.
3) Porcupines
Strychnine treated salt blocks (5.8 percent concentration)
are nailed to trees, placed in porcupine dens, or placed under shelters. Also,
strychnine pellets are placed in bait boxes.
d. Pigeons and House Sparrows
For pigeon control, whole corn bait with a concentration of 0.6 percent
strychnine is scattered on the ground following prebaiting with untreated grain.
For house sparrows, grain bait with a concentration of 0.25 percent to 0.8 per-
cent strychnine is either scattered on the ground or placed in troughs.
e. Croplands Birds
For orchards and vineyards, troughs containing bait are placed in
trees or on standards. The bait may be milo, rice, oats, corn or vegetables
and the concentration of strychnine ranges from 0.25 percent to 0.90 percent.
For the protection of sprouting vegetable seeds, baits may be applied on the
ground between the furrows.
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2. General
a. Toxicology
The toxic effect of strychnine is reported to be primarily against the
nervous system. The threshold for stimulation of motor effects by external
stimuli is lowered, resulting in such signs and symptoms as apparent hyperacusis
(painful sensitiveness to sounds), recurrent convulsions or tetanic seizures.
Slight touches or light stimuli produce exaggerated responses and often
seizures (Tucker and Crabtree, 1970).
The fact that symptoms appear in many species as soon as 10 minutes
after ingestion and that recovery of survivors is generally complete within a
few hours implies rapid and thorough absorption of strychnine. Also implied is
rapid metabolism in the animal body and/or elimination of the compound and
metabolites (Tucker and Crabtree, 1970).
A compound which is rapidly absorbed in undiluted form and either
produces death quickly, or rapid recovery, often displays a "feed-dilution
effect." That is, a high concentration of the material, quickly ingested and
absorbed, will produce toxic effects. However, if the compound is in such low
concentration in feed that absorption is slowed, some of the ingested dosage
may be detoxified before all is absorbed. This would effectively reduce the
toxic effect (Howard and Marsh, 1973). Strychnine appears to be subject to
this effect and hence there are reports of somewhat lower toxicity from baits
than would be expected from single oral tests (Ward, et al., 1942). If
administered slowly, repeated oral treatments may appear to produce increased
tolerance of strychnine. This apparent tolerance may be the result of
increasingly rapid elimination and/or metabolism.
Gross pathological examination of numerous wildlife species treated
with strychnine at lethal levels revealed occasional hyperemia (excess of
blood) and hemorrhaging of the gastrointestinal tract, minor endocardial
hemorrhages, and massive hemorrhages in the myocardium. Very often no gross
pathological change attributable to the action of strychnine occurred.
b. Acute Toxicity
Table III-1 provides a summary of acute oral toxicity values for
strychnine relating to various species of mammals, amphibians, and birds.
The acute oral ID™ values for the species given in Table III-1
range from 0.75 mg/kg for trie coyote and desert kit fox to 112 rag/kg for the
California quail. Most LD,-Q values fall into the range of 1.0 to 25 mg/kg
for both mammals and birds.
c. Subacute and Chronic Toxicity
While there are few reports of effects of long-term, low-level
exposure to strychnine, it seems likely that rapid metabolism and/or
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TABLE III-l - ACUTE ORAL TOXICITY OF STRYCHNINE ALKALOID
SPECIES
/kgl/
mg/kg.
REFERENCE!/
I. MAMMALS
WILD RODENTS & RELATIVES
Calif, ground squirrel
Black-tailed prairie dog
Northern pocket-gopher
Banner-tailed kangaroo rat
Meadow .vole
Calif, meadow vole
Norway rat (wild)
White rat (male)
White rat (female)
Black rat
Polynesian rat
Black-tailed jack rabbit
Nutria
19.9 -28.0
1.5
8.3
3.7
6.8
22.2
12.0
14.0
5.8
10.1
6.8
4.4
27.0 - 42.0
DWRC Files,
DWRC Annua
DWRC Files
DWRC Files
DWRC Files
DWRC Files
DWRC Files
DWRC Files
DWRC Files
DWRC Files
DWRC Files
DWRC Files
DWRC Files
DWRC Annua.
Reports/DWRC
Unpublished Data
!/ Data marked (S) if the sulfate was known to be used.
!/ DWRC indicates Denver Wildlife Research Center.
-------
TABLE III - 1 (Continued)
SPECIES
i/
mg/kgA/
REFERENCE!/
B. CARNIVOROUS MAMMALS
Cat
Dog
Desert kit fox
Coyote
C. OTHER MAMMALS
Man
Hog
Horse
Cow
Sheep
Mule deer
II. AMPHIBIANS
Bull frog
III. BIRDS
A. WATERFOWL
Mallard
Canada goose
0.75
1-1.2
0.75
0.7
1.0
10.0
2.0
15.0
7.5
17.0 - 24.0
2.21
2.9
4.0
DWRC Files
DWRC Files
DWRC Files
DWRC Files
Howard and Marsh
DWRC Files
DWRC Files
DWRC Files
DWRC Files
Tucker and Crabtree
Tucker and Crabtree
Tucker and Crabtree
Tucker and Crabtree
I Data marked (S) if the sulfate was known to be used.
2/ DWRC indicates Denver Wildlife Research Center.
-------
TABLE III - 1 (continued)
SPECIES
B. UPLAND GAME BIRDS AND RELATIVES
Mourning dove
Pigeon
Ring-necked pheasant
Ring-necked pheasant
Chukar
California quail
Sage grouse
Turkey
Coturnix
C. PASSERINES
Robin
House finch
English sparrow
English sparrow
Starling
Red-winged blackbird
L°50 i/
rng/kgl/
REFERENCE!/
5.12(S)
21.3
24.7
8.48 (S)
16.0
112
35-50
50
22.6
10.0
5.6
4.18
4.0 - 8.0 (S)
5.0(S)
6.0
DWRC Files
Tucker and Crabtree
Tucker and Crabtree
Tucker and Crabtree
Tucker and Crabtree
Tucker, et al
Ward, et al
DWRC Files
Tucker and Crabtree
DWRC Files
DWRC Files
Tucker and Crabtree
Tucker and Crabtree
Schafer
DWRC Annual Reports
~ Data marked (S) if the sulfate was known to be used.
!/ DWRC indicates Denver Wildlife Research Center
-------
TABLE III - 1 (continued)
LD50
SPECIES mq/kgl/ REFERENCE?./
D. RAPTORS
Golden eagle 5.0 Tucker and Crabtree
Golden eagle >5.0 (S) Tucker and Crabtree
Data marked (S) if the sulfate was known to be used.
DWRC indicates Denver Wildlife Research Center
-------
elimination of this material would preclude cumulative toxic action to any
marked degree. In addition, the bitter taste of strychnine and rapid onset of
symptoms have been demonstrated to produce "bait-shyness" or poor reacceptance
of strychnine-containing diets by many species. This phenomenon is known for
sage grouse (Farm Chemicals Handbook, 1973), pheasants (Schaffer, 1973), and
other species. It is conceivable that "bait-shy" animals might consume such
baits after prolonged starvation. Two pheasants starved for two days died
within an hour after consuming 20 and 34 grams, respectively, of a bait
containing one ounce, strychnine per 10 Ibs. grain. Unstarved pheasants,
however, accepted this bait poorly and showed no signs of intoxication (Rudd 4
Genelly, 1956). Twenty grams of this bait would contain 125 mg. strychnine.
Assuming a body weight of 1.2 kg, the total dosage for the starved pheasants
amounted to 104 mg/kg, substantially more than the acute oral LA-0 of 24.7
rag/kg. Pheasants typically eat 50-100 grams of grain feed per day (Tucker,
Personal Communication 1978). Thus, if bait shyness did not occur, ingestion
of lethal amounts of strychnine could occur.
d. Bioaccumulation and Tissue Residues
There is little evidence in the literature to indicate that elevated
residues of strychnine can accumulate in animal tissue. Data from a study of
530 albino mice showed no accumulation of strychnine and no tolerance
development to increasing dosages of the chemical. Detoxification seemed to be
complete within the first 24 hours after administration (Kalning, 1968).
e. Secondary Toxicity
Low persistence of strychnine residues in tissues of animals greatly
reduces the chance for secondary toxicity. However, unabsorbed residues in the
gastrointestinal tract or cheek pouches of an animal ingesting a large dosage
and quickly dying could be sufficient to poison a raptor or carnivore ingesting
it. The calculation that fifty squirrels killed by strychnine would have to be
eaten by a hawk for a fatal dose (Garlough and Ward, 1932) ignores this major
source of risk. There is also a report, described briefly in Section I, of
secondary poisoning of a kit fox as a result of ingesting strychnine-poisoned
kangaroo rats under laboratory conditions (Schitosky, 1975).
f. Summary
Indications are that any likely potential field effects will not be
the result of the compound's properties in regard to accumulation, chronic
toxicity, reproductive effects, or secondary hazard from the consumption of
flesh. Any potential for ecological vulnerability of terrestrial wildlife
would appear to be the result of the high degree of acute toxicity by the oral
(including dietary) route from either the bait or bait residue in the
gastrointestinal tract or cheek pouches of poisoned animals.
3- Direct Risks to Nontarget Species
Since the purpose of placing strychnine treated bait in the field is to
kill offending mammals and birds, it is obvious that a risk is present to
- 24 -
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individuals of many nontarget vertebrate species that may feed on the bait.
The major issue is whether such feeding generally results in significant
population reductions in the nontarget species. The best available
information regarding this issue can be found in the observations of Hegdal
and Gatz (1977a).
By using various methods to monitor the effects of applying 0.5 percent
strychnine on steam-rolled oats to control ground squirrels in Wyoming, Hegdal
and Gatz (1977a) determined that a majority of the territorial horned larks in
the treated areas was killed, as were several blackbirds. Large numbers of
mourning doves were also killed. The impact on certain other species of birds
(vesper sparrows and meadowlarks) appeared to be substantially less (only three
dead birds found).
The observed mortality varied substantially from area to area, presumably
in relation to habitat details. For instance, of 19-5 ha searched, 42 percent
(54/129) of all birds found dead were in a two ha plot in a wheatfield. Three
"rangeland" plots totalling four ha produced only eight dead birds while a two
ha lot in "crested wheat rangeland" yielded 24 bird carcasses. A two ha plot
in alfalfa produced but a single bird carcass.
The observed impact on birds ranged from 0.5 to 27 deaths per ha. However,
no conclusion can be drawn from the study as to whether the site (i.e.
cropland, pasture and range, noncropland) had any effect on the risks to the
birds. Therefore, extrapolation of the results of this study to predict the
effects in other situations cannot be accomplished with a high degree of
accuracy.
A reasonable conclusion is that reductions in local populations are likely
but that the magnitude of this impact may vary with the species present and the
area treated. Any long-term impact on vulnerable species could vary with
factors such as the frequency of application, the scale of the operation and
the distribution and abundance of the species. The Agency has no reason to
believe that there are substantial geographical areas where strychnine might be
used in surface baiting operations without exposure to one or more susceptible,
nontarget species.
4. Indirect Risks to Nontarget Species
A potential for an indirect or secondary risk to vertebrates that feed on
rodents killed by strychnine has been demonstrated (Schitosky, 1975).
Translating this potential into realistic probabilities, however, should be
done with caution. Sublethal doses of strychnine may be rapidly metabolized
and eliminated from the body and, presumably, death occurs when this defense
mechanism is overwhelmed by the dose. A general assumption, therefore, is that
most of the strychnine absorbed by a victim has little potential for secondary
poisoning; the major risk comes from the strychnine that may remain in the gut
and in the cheek pouches.
- 25 -
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If a 0.5 kg ground squirrel were to eat two g of a 0.5 percent strychnine
bait, the ten mg of strychnine ingested may be just the lethal amount, since
its LD,-n is 20 rag/kg. Little or no strychnine would remain in the gut.
Hegdal and Gatz (1977a) analyzed three Richardson's ground squirrels that
apparently had been killed by strychnine. One contained 0.03 mg (2.8 ppm)
strychnine in the stomach but no strychnine was detected at the limit of 0.5
ppm in the other two squirrels. These three squirrels would have posed little
risk to any predator/scavenger- Three squirrels, however, are hardly an
adequate sample and the Agency does not know the probability of a squirrel's
consuming substantially more than a lethal dose of this rapidly acting poison.
There is some evidence that ground squirrels poisoned by the strychnine remove
the contents of the cheek pouches before dying (Stephl and Gates, 1928), but,
again, the Agency has no reasonable measure of the level of pouched poison to
be expected or the likelihood that such material will be ingested by predators
and scavengers. The meager evidence suggests that secondary risk from ground
squirrel control may be generally low.
On the other hand, should a prairie dog ingest the same two g of 0.5
percent strychnine, the situation may be quite different. Since the LDcQ for
prairie dogs is only 1.5 mg/kg as much as eight mg may remain in the gut.
Such quantities of strychnine would be highly lethal for any swift fox or black-
footed ferret that fed on the gut of the prairie dog. Again, data are not
available as to how much bait a prairie dog is likely to consume before it
dies, but it seems reasonable to conclude that the risk from eating a
strychnine-poisoned prairie dog may be much greater than that from eating such
a ground squirrel.
In the case of birds poisoned by strychnine, substantially more information
is available. Hegdal and Gatz (1977a) analyzed the gastrointestinal tracts of
40 mourning doves apparently killed by strychnine baits. Of these birds, the
maximum amount of strychnine found was 1.6 mg and the next highest amount was
0.86 mg. The median level was 0.1 mg strychnine. It should be noted that most
of these spring immigrants were not exposed to fresh bait since they did not
arrive until the baiting was well underway and that the strychnine level in the
bait decreased progressively with time. The levels of strychnine in the doves
also decreased according to the length of time elapsed after baiting before
they consumed lethal doses. A reasonable assumption is that if most of the
doves were killed on the day the bait was placed, the levels of strychnine in
the gastrointestinal tract would have averaged somewhat higher. Nevertheless,
of the amounts of strychnine found, most were not at levels that would be
generally hazardous to scavenging vertebrates. Six of the 39 birds contained
more than 0.5 mg strychnine and such amounts would be of toxicological signifi-
cance only to small carnivores whose LD^'s are in the 0.7 to 1.0 mg/kg
range, such as the swift fox.
While the Agency cannot conclude that the available evidence is entirely
adequate for an accurate risk assessment, the weight of the evidence suggests
that the use of strychnine to control ground squirrels is not generally likely
to create a high risk to nontarget species from secondary poisoning. Risks
from prairie dog control, however, may be substantially higher.
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5. Risks to Members of Endangered Species
Section 7 of the Endangered Species Act of 1973 (ESA) (16 USC 1531 et seq.)
requires all Federal agencies, in consultation with and with assistance of the
Secretary of the Interior, to take such action as is "necessary to insure that
actions authorized, funded, or carried out by them do not jeopardize the
continued existence of ... endangered species and threatened species or result
in the destruction or modification of habitat of such species which is deter-
mined by the Secretary .... to be critical." Accordingly, the Departments of
the Interior and Commerce have established joint regulations implementing
Section 7 of ESA, which include provisions for interagency cooperation and
consultation concerning endangered and threatened species and their habitats
(50 CFR 402, 43 FR 870-875).
On March 13, 1978, EPA requested formal consultation with the U.S.
Department of Interior, Fish and Wildlife Service, under Section 7 of the
Endangered Species Act of 1973» on the above-ground uses of strychnine as they
affect endangered and threatened species.
As a result of that consultation, 43 endangered species were identified
as likely to be exposed to strychnine as presently registered by EPA
(Appendix D). These are listed as follows:
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Endangered Species Likely to be Exposed to Strychnine
Reptiles
American Alligator (Alligator mississippiensis)
American Crocodile (Crocodylus actus)
Eastern Indigo Snake (Drymarchon nnrais couperi)
Birds
Aleutian Canada Goose (Branta canadensis leucopareia)
Hawaiian Goose (Nene) (Branta sandvicensis)
Marianas Mallard (Anas outstaleti)
Hawaiian Duck (Koloa) (Anas wyvilliana)
California Condor (Gymnogyps californianus)
Hawaiian Hawk (Buteo solitarius)
Bald Eagle (Haliaeetus leucocephalus)
American Peregrine Falcon (Falco peregrinus anatum)
Arctic Peregrine Falcon (Falco peregrinus tundrinus)
Attwater's Greater Prairie Chicken (Tympanuchus cupido attwateri)
Masked Bobwhite (Colinus virginianus ridgewayi)
Mississippi Sandhill Crane (G_rus canadensis pulla)
Whooping Crane (Grus americana)
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Hawaiian Gallinule (Gallinula chloropus sandvicensis)
Hawaiian Coot (Fulica americana alai)
Hawaiian Stilt (Himantopus himantopus knudseni)
LaPerouse's Megapode (Megapodius laperouse)
Puerto Rican Plain Pigeon (Columba inornata wetmorei)
Palau Ground Dove (Gallicolumba canifrons)
San Clemente Loggerhead Shrike (Lanius ludoricianus mearnsi)
Ponape1 Mountain Starling (Aplonis pelzelni)
Yellow-shouldered Blackbird (Agelaius xanthomus)
Laysan and Nihoa Finches (Psittirostra cantans cantans; P.c. ultima)
Cape Sable Sparrow (Ammospiza maritima mirabilis)
Dusky Seaside Sparrow (Ammospiza maritima nigrescens)
San Clemente Sage Sparrow (Amphispiza belli clementae)
Mammals
Grizzly Bear (Ursus arctos horribilis)
Black-footed Ferret (Mustela nigripes)
San Joaquin Kit Fox (Vulpes macrotis mutica)
Red Wolf (Canis rufus)
Gray Wolf (Canis lupus)
Eastern Cougar (Felis concolor cougar)
Florida Panther (Felis concolor coryi)
Utah Prairie Dog (Cynomys parvidens)
Delmarva Peninsula Fox Squirrel (Sciurus niger cinereus)
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Morro Bay Kangaroo Rat (Dipodomys heermanni morroensis)
Salt Marsh Harvest Mouse (Reithrodontomys raviventris)
Key Deer (Odocoileus virginianus clavium)
Columbian White-tailed Deer (Odocoileus virginianus leucurus)
Sonoran Pronghorn (Antilocapra americana sonoriensis)
30
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Strychnine's ability to kill members pf endangered species is anticipated
because strychnine is highly toxic to mammals and birds and strychnine-treated
baits may be applied in areas inhabited by endangered species.
As with other nontarget species, those endangered species with feeding
habits similar to target animals would be expected to eat the treated baits
placed above ground for the target organisms. Additionally, indirect exposure
may occur if predators or scavengers feed on the carcasses of strychnine
victims, such as doves, ground squirrels, prairie dogs, and pigeons.
Of the 43 endangered species in the preceeding list, 18 were identified by
the USD! as likely to be jeopardized if strychnine is used where these species
are found. They are the Utah prairie dog, Morro Bay kangaroo rat, salt marsh
harvest mouse, red wolf, masked bobwhite, dusky seaside sparrow, Cape Sable
sparrow, Mississippi sandhill crane, Puerto Rican plain pigeon, Attwater's
greater prairie chicken, yellow-shouldered blackbird, California condor, black-
footed ferret, San Joaquin kit fox, gray wolf, and grizzly bear, Laysan finch
and Nihoa finch. The Agency does not believe a possibility exists for
strychnine use on the islands of Laysan and Nihoa, since they are not
inhabited by man. Therefore, the Laysan and Nihoa finches will not be
considered as needing special precautions. The specific use(s) of strychnine
of concern for each of the other 16 species is discussed in Section V. The
Agency believes that certain other species, the Peregrine Falcon and the
Aleutian Canada Goose, require special concern. The following analyses provide
the bases for the Agency's assessment of risks to the various species from the
use of strychnine.
The Agency's interim procedure for estimating a "no effect" level in
assessing risks to endangered bird and mammals (EPA, 1980) utilizes either a
value of 1/5 the subacute dietary LC^ or 1/5 the acute LD-Q expected to
occur in or on the average daily intake of treated feed to which members of the
species may be exposed. This information is not available for strychnine. The
only basis for assessing risk consists of various LD^Q values, anticipated
exposure levels, and the knowledge that strychnine appears not to be cummula-
tive in its effects.
Accurate use of the available data is hampered by the facts that the LDcn
data provide no information on the range of individual variability and that
interspecific sensitivity to strychnine is relatively high. The limited data
base indicates that two species in the same genus (Microtus) have LD^'s
that differ by a factor of three and, within the same family, the chokar is
seven times as sensitive as the California quail (Table III-1).
As an interim procedure for strychnine, the Agency will consider, for each
endangered species, the suitability of the toxicity data in regard to related
species, the probabilities of various exposures and the status of the
endangered species in making determinations as to whether the margins of safety
are sufficient.
a. The Black-Footed Ferret
This rare mammal is thought to be highly dependent on the existence of
prairie dog colonies. Its present plight is doubtlessly due to the fact that
prairie dogs have been eliminated over the majority of the acreage previously
occupied. While further reduction of prairie dog acreage by whatever means
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cannot but serve to worsen the situation of the ferret, mere maintenance of the
present prairie dog population by controlling with strychnine has a high
potential for killing ferrets by secondary poisoning.
The USDI (Appendix D) has concluded that the use of strychnine to
control prairie dogs could jeopardize the continued existence of the black-
footed ferret. The Agency concurs in this opinion. While the critical
habitat of the ferret has not been defined by the USDI, the Agency believes
that any area now occupied by prairie dogs must be considered with great
concern due to the relationship between the ferret and the prairie dog.
The USDI did not address the problem of controlling ground squirrels.
White-tailed prairie dogs generally occur at lower densities than do black-
tails and their populations are frequently intermixed with those of certain
species of ground squirrels (Richardson's, Uinta and, to a lesser extent,
Townsend's). For ground squirrel control grain bait is usually applied in the
spring before green vegetation becomes available For prairie dogs, baiting is
usually done in the late summer after the vegetation has become dry. Due to
the different baiting seasons, prairie dogs are not especially vulnerable to
control efforts aimed at ground squirrels, although some mortality can be
expected (Hegdal and Gatz, 1977a).
Available data suggest that the use of strychnine to control ground
squirrels is substantially less hazardous to the ferret than is the use to
control prairie dogs. However,it must be recognized that a potential risk
exists to the ferret if ground squirrel control is conducted when prairie dogs
are present.
b. The San Joaquin Kit Fox
The USDI (Appendix D) has concluded that the use of strychnine within
the area of this sub-species of the kit fox would jeopardize its continued
existence. The Agency concurs in this opinion. The major target species
within this area would be the California ground squirrel and, by extrapolation
from limited data, the probability of risk to the kit fox would appear to be
moderate were strychnine to be used for squirrel control. The use of
strychnine to control birds in cropland poses negligible risk to the species
since kit foxes are unlikely to range in those cultivated fields, orchards and
vineyards where strychnine is used.
c. The California Condor
Only 25-35 individuals of this species remain (Wilbur, 1980) and the
USDI concludes that "the loss of even one condor must be considered signifi-
cant" (Appendix D). Current uses of strychnine in the condor's range are
mainly for underground pocket gopher control and for horned larks and finches
in cultivated land and orchards. The Agency concurs with the USDI that these
uses are unlikely to expose condors to strychnine. A concern, however, remains
for the potential use of strychnine to control ground squirrels.
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While strychnine is registered to control ground squirrels, little, if
any, is used for this purpose in the condor's range because compound 1080 is
judged to be much more efficacious. Should this use of compound 1080 be
cancelled under the RPAR process, use of strychnine could increase.
Of the species for which strychnine toxicity data are available, the
one most closely related to the condor is the golden eagle, for which the
LD^gis 5 mg/kg. For a nine kg condor, 45 mg strychnine may be highly lethal
and an exposure of as much as two mg would not provide an acceptable margin of
safety for this highly endangered species. This level of exposure can be
obtained indirectly from consuming 0.4 g of a 0.5 percent bait. Such exposure
from the use of strychnine for rodent control appears likely since the condor's
diet consists entirely of dead animals including poisoned ground squirrels
(Koford, 1953)- While the amounts of strychnine to be expected in the car-
casses of the poisoned animals are largely unknown, the potential for an excess
of 0.4 g bait in a dead squirrel is easily visualized and the Agency must
conclude that an ample margin of safety for the condor has not been
demonstrated for this use of strychnine.
d. The Peregrine Falcon
The USDI concluded that peregrines could be adversely affected by a
strychnine pigeon cont: ol program if proper precautions (unspecified) are not
followed. Since there was no evidence of improper precautions the USDI opinion
was that the continued use of strychnine is not likely to jeopardize the con-
tinued existance of the Arctic or American peregrine. Since that assessment,
the Agency has received the following new information and conducted additional
analyses that lead it to conclude that, when strychnine is used according to
current practices for control of pigeons and ground squirrels, some risk to
peregrine falcons is likely. /
1. Several raptors, including owls and hawks, have been poisoned by
strychnine in association with a control operation for pigeons in Duluth,
Minnesota (Redig, 1978). This event clearly indicates that a potential exists
for secondary poisoning of some species of raptors associated with this use of
strychnine. Procedures such as pre-baiting flocks of pigeons and exposing them
to high concentrations of bait are likely to maximize residue levels. Redig's
(1978) observation that the dead raptors did not contain bait casts doubt on
the generalization (derived from studies with rats) that the flesh of animals
killed with strychnine is not hazardous.
2. A prairie falcon was killed during a pigeon control operation
in Colorado in January 1980 (Locke, 1980). Similarities in the feeding
patterns of prairie and peregrine falcons demonstrate the potential risk to the
peregrine.
3. In Baltimore, Maryland, July, 1979, a young peregrine was
observed to exhibit convulsions. Several days later, its body was found (Cade,
1980). Autopsy revealed feathers and seeds in the bird's stomach. Although a
chemical analysis for strychnine had not been conducted at that time (Locke,
1980, personal communication), the presence of seeds in the falcon's stomach
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demonstrates that peregrines could be exposed to strychnine bait in pigeon
control operations.
4. Strychnine levels found in the gastrointestinal tracts of
poisoned doves (Hegdal and Gatz, 1977a) were at a maximum of 1.6 rag and a
median of 0.1 rag.Poisoned birds represent the most likely form of exposure for
peregrines and 1.6 mg of strychnine would provide a dose of 3 mg/kg for a 0.5
kg bird and 1.5 mg/kg for a 1.0 kg bird. Compared to the LD^Q of 5 mg/kg for
a golden eagle, such a dose is of critical concern. The median exposure of 0.1
mg strychnine would be of marginal concern.
Whether a quantity of strychnine in the gut of a bird poses a risk
to a peregrine depends on several circumstances. Peregrine falcons are
unlikely to feed on carrion; a falcon must be on the scene when a poisoned bird
is in distress. A flock of convulsing pigeons is much more likely to attract a
falcon than is a single dove in convulsions. Having secured a poisoned bird,
the risk to the falcon depends largely on how much strychnine is in the
gastrointestinal tract and how much of that present is consumed. For pigeons
and larger birds, the gizzard may be eaten intact but the contents of the crop
are less likely to be eaten by a peregrine (Cade, 1980). For doves and smaller
birds, the entire carcass may be eaten.
Risks to the peregrine falcon from the use of strychnine to control
birds and rodents vary. If a falcon is in the vicinity of a pigeon control
operation, the risks are high — virtually every poisoned individual of the
target species may be potentially lethal to a peregrine. The risks from birds
poisoned incidental to the control of rangeland rodents are somewhat lower.
About 15 percent of the doves analyzed by Hegdal and Gatz (1977) contained
toxicologically significant levels of strychnine (>0.5 mg). In order for the
use of strychnine to not jeopardize the continued existence of peregrine
falcons, proper precautions beyond those currently being employed are necessary
for ground squirrel and pigeon control. For sparrow control, however, little
or no risk is probable because these small target species are unlikely to be
fed on by peregrines.
e. Other Species
The Agency concurs with the USDI for the remaining species listed as
likely to be jeopardized by the above-ground use of strychnine with the
exception of the Laysan and Nihoa finches. In addition to the peregrine
falcon, however, the Agency believes that the Aleutian Canada goose merits
special concern due to a potential exposure to strychnine bait. These geese
arrive in the Sacramento Valley in October, then move mainly to the upper San
Joaquin Valley by winter. They generally return north to the vicinity of
Crescent City in March and depart for the Aleutians in April (Woolington
et al., 1979). Although ground squirrel control operations are not likely to
take place at the time these geese are present on their wintering grounds, such
operations could expose large flocks of geese to toxic baits.
6. Human/Domestic Risks
The lack of emergency treatment criteria was also examined in the PD1 in
deciding if strychnine qualified as an RPAR chemical. After reviewing the
available information, the conclusion reached was that an emergency treatment
(activated charcoal, barbituates, and muscle relaxants) did exist and a
presumption against registration because of that criteria was not warranted.
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A recommendation was made by the Agency working group, however, for
consideration of three points during the reregistration process. These are:
o Products with concentrations above 0.5 percent should be restricted to
certified applicators.
o Dilute baits should only be available to untrained applicators when
adequate packaging (child resistant containers), labeling, and use
cautions are used.
o Intentional poisoning of domestic animals
Since the RPAR notice, additional data on morbidity and mortality have been
analyzed. Data on poisonings, hospitalizations, and fatalities were obtained
from four sources: 1) rodenticide poisonings and inquiries for the years 1974-
1976 from the National Clearinghouse for Poison Control Centers, Food and Drug
Administration, 2) hospital!zation figures from "National Hospitalization Study
of Acute Pesticide Poisoning, Admitted to General Care Hospitals", 1976,
3) mortality data based on episodes reported to the Pesticide Episode Reporting
System (PERS) for the years 1967-1976, and 4) pesticide poisoning reports by
Wayland Hayes, MD, PhD, Vanderbilt University School of Medicine (1956, 1961,
1969, 1973-74). The data for the three categories (poisonings, hospitaliza-
tions, fatalities) were thus from different sources and for different years.
For the years 1974-1976, 5,610 cases of inquiries and poisonings were
reported for rodenticides. Of these, 26 were confirmed as being strychnine
related. Since many cases do not specify the rodenticide, 26 is the lower
bound on the number of strychnine poisonings. Fifteen of the 26 involved
children under five years of age.
Hospitalization figures for 1971-1973, based on a 12 percent sample of
general-care hospitals in the United States, were classified as being occu-
pational, non-occupational,or intentional. Estimated numbers were obtained by
multiplying each observation by eight to approximate hospitalization figures
for all general-care hospitals. The estimated hospitalizations for uninten-
tional, non-occupational strychnine poisonings ranged from 16 to 48 and totaled
88 for the three years. Twenty-seven percent of the cases involved children
under five years of age (3 of 11).
Sixty four reports were located in the PERS files that involved strychnine
(out of over 10,000 entries). Twenty eight reports involved humans, 28
involved domestic animals, five involved wildlife, and three were for environ-
mental contamination.
Thirty people were affected in the 28 reports involving humans. Ten of the
people died from strychnine poisoning.
Nineteen of the 28 reports were for incidents occurring in the home and all
involved children age 15 or younger. Five of the 19 episodes resulted from the
ingestion of strychnine baits placed in the home for rodent control. Two of the
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five resulted in fatalities. The other eight fatalities were one agricultural
worker, two 15-year-olds who ingested LSD cut with strychnine (not a
pesticide), three suicides, and two preachers who ingested strychnine as part
of the religious service.
The Hayes studies reported a total of 21 deaths due to strychnine for the
years 1956, 1961, 1969, 1973 and 1974. Four were children five years old or
younger. Three of the 21 were also reported in the PERS data, leaving a total
of 28 deaths reported in the two sources. Tnese are not the total deaths due
to strychnine, but rather those deaths that were documented for specific years.
Domestic use also includes areas where pets may be in contact with a
pesticide (40 CFR 162.3 (m)). As stated earlier, the PERS data contained
reports of 28 domestic animal poisoning incidents. Twenty-six incidents were
home related and all involved dogs (one also involved cats). Twenty-three of
the incidents were fatalities (86 dogs and 5 cats). Tne majority of the
poisonings resulted from undetermined sources (14 reports) or intentional
poisonings (10 reports). Two resulted from ingesting rodent control baits
(two dogs).
In summary, the availability of strychnine for domestic use has resulted in
human and pet poisonings and fatalities. For the years 1974-1976, 26 cases of
strychnine poisonings and inquiries were reported. Fifteen involved children
five years old or younger. For the years 1971-1973, an estimated 88 hospitali-
zations occurred for unintentional, non-occupational strychnine poisonings.
Twenty-seven percent involved children five years old or younger. For the
years 1956 through 1976, 28 deaths were reported. Six of the 28 were children
five years old or younger.
Although emergency treatment is available and possible, as concluded in
PD 1, it must begin within 30 minutes of ingestion. The case histories
examined for PD 1 did not include any fatalities. The data reviewed since then
indicates a risk to humans, particularly to children. Most of the hospitaliza-
tions and fatalities, however, involved strychnine use that was unrelated to
rodent control, (e.g. suicide) or a misuse of the rodenticide. Also, as
stated in Section I, strychnine products with concentrations greater than
0.5 percent are now restricted for use only by certified operators. The Agency
is of the opinion, therefore, that the human risk from the registered uses of
strychnine that are the subject of this RPAR are not sufficient to warrant the
consideration of regulatory actions.
B. Alternatives - Mammals
1. Sodium Fluoroacetate (Compound 1080)
A rebuttable presumption against registration was issued by the Agency for
compound 1080 in December, 1976. Its use as a strychnine alternative will
depend on the result of the RPAR review currently underway. The following
discussion in no way implies its continued availability.
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a. Method of Application
1) Ground Squirrel
Sodium fluoroacetate (compound 1080) is registered in California,
Nevada, and Colorado used for ground squirrel control as a spot bait on bare
ground near burrows. It is also ground applied by mechanical broadcaster or
aerially applied in approximately 30-foot-wide swaths. The baits are usually
made with oat groats, barley, chopped cabbage, or chopped dandelion greens.
The concentration of compound 1080 in the various baits ranges from 0.05
percent to 0.12 percent. When hand applied it is most often accomplished by
scattering a teaspoon to a tablespoonful over two to three square feet of bare
ground near each active burrow. When applied by air or broadcast, about five-
six or five-ten pounds per swath acre are used. Treatments are usually in the
late spring.
2) Prairie Dog
A single state registration for prairie dog control (Colorado)
was found for an 0.11 percent grain bait with yellow dye. According to the
product use directions, the bait is to be scattered over three square feet
near burrows, but the amount per bait placement was not stated.
b. General
1) Toxicology
Compound 1080 is essentially colorless, odorless, and nearly
tasteless (Atzert, 1971). The onset of signs and symptoms of poisoning
generally occur after a delay period which would allow ingestion of a complete
meal containing the toxicant before effects commenced. Regurgitation is not
commonly induced by compound 1080. For these reasons bait acceptance is
usually excellent.
Because the LD^Q'S by intravenous and oral routes are usually
similiar, it can be inferred chat compound 1080 is well absorbed from the
gastrointestinal tract. Gal, et al. (1961) determined by radioisotope tracer
technique upon rats that intraperitoneally administered compound 1080 was
rather evenly distributed in the animal four hours post administration. Little
had been expired as CCL or excreted in the urine. It is generally
thought that compound 1050 is not changed in the body to any great extent and
is largely eliminated in the urine intact.
Signs and symptoms of compound 1080 poisoning vary. However,
they may be classified into three categories: CNS (central nervous system),
cardiac, and depression syndromes. The CNS syndrome is characterized by
hyperactivity, phonation, tonic spasms and convulsions which lead to respir-
atory paralysis. The cardiac syndrome is associated with blanching of the
retina, muscular weakness, clonic convulsions, and ventricular fibrillation.
The depression syndrome is associated with decreased activity, respiratory
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depression, and bradycardia. Additionally, muscarinic effects are produced in
certain species of terrestrial wildlife such as ferrets. The onset of symptoms
of poisoning almost always exceeds 1/4 hour and death most often occurs between
one hour and one day after ingestion of a lethal dosage. Long latent periods
preceding symptoms are common.
The development of pathologies is frequent, even after single
dosages. Definite histologic abnormalities in the myocardium have been
reported (Chenoweth, 1950). Heraorrhagic changes in the liver, heart, aorta,
and brain are sometimes evident. Gastrointestinal purpura and petechial
pulmonary hemmorrhages particularly occur in poisoned mammals.
Biochemically, compound 1080 is thought to exert its toxic effect
by inhibition or blocking of citrate and succinate metabolism within the Kreb's
cycle (Atzert, 1971).
2) Acute Toxicity
a) Laboratory Data
Table III-2 gives a summary of acute oral toxicity figures
of compound 1080 for numerous species of mammals, amphibians, and birds. The
median lethal single oral dosages (mg 1080 per kg. animal wgt.) range from a
very low figure of 0.056 mg/kg for nutria to 60 mg/kg for the opossum. Even
though a 1000-fold range in susceptibility exists between species, all species
listed are very sensitive to the toxic action of compound 1080. Relatively few
pesticidal chemicals in use are more orally toxic than compound 1080.
Generally, mammals are most sensitive, notably nutria,
prairie dog, kit fox, other members of the dog and cat families, and the big
brown bat. Over a third of the species listed in the table exhibit LDcg's
below one mg/kg. This compound, like strychnine, is not readily absorbed
through intact skin. Inhalation contact for wildlife is not likely (Pattison,
1959).
b) Field Studies
Under an Environmental Protection Agency (EPA) Interagency
Agreement, the U.S. Fish and Wildlife Service, Denver Wildlife Research Center
(DWRC) evaluated the hazards to wildlife associated with aerial 1080 baiting
for California ground squirrels. The study was conducted in Tulare County, in
south-central California, in the eastern foothills of the San Joaquin Valley.
The study monitored a large-scale operational baiting program conducted by the
Tulare County Agricultural Commissioner.
During early June 1977, (in the vicinity of the study area)
about 25,000 ha (60,000 acres) were spot-treated with 0.075 percent 1080-
treated oat groats at about 6.7 kg/ha (6 Ib per swath acre). The actual
surface area baited was about 3.4 percent of the range.
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TABLE III-2 - ACUTE ORAL TOXICITY OF COMPOUND 1080i/
SPECIES
I. MAMMALS
LD50
mg/kgf/
REFERENCES!/
A. RODENTS
Wood rat
Calif. Ground squirrel
Tuza pocket gopher
Northern pocket gopher
Fresno kangaroo rati/
Polynesian rat
Black rat
Norway rat
White rat (male)
White rat (female)
Cotton rat
Rice rat
House mouse
White mice
Meadow mouse
Meadow vole
Deer moused/
Plains prairie dog
Plains prairie dog-i/
Black-tailed prairie dog
Nutria
DOMESTIC MAMMALS
1.5 Chenoweth
0.35 DWRC Files
0.25 (60%) Howard and Marsh
0.33 DWRC Files
1.0 (100%) DWRC Files
6.60 DWRC Files
0.10 Chenoweth
0.22-3.0 Chenoweth
2.1 DWRC Files
2.2 DWRC Files
0.1 Chenoweth
3.4 DWRC Files
8.0 Chenoweth
12.0 Chenoweth
0.5 Chenoweth
0.92 Atzert
4.0-5 Howard and Marsh; Chenoweth
0.3 (100%) Howard and Marsh
0.9 (100%) Howard and Marsh
0.33 DWRC Files
0.056 Atzert
Hereford cows
Hereford calves and steer
Mules (M & F)
(M & F)
Horse
F)
Swine (M
Sheep
Dog, mixed breeds-*^
OTHER MAMMALS
Man (children only)
Rhesus Monkey
Mule deer (Male)
Domestic ferrets (Male)
Big brown bat
0.393 Robinson
0.221 Robinson
0.22-0.44 Tucker and Crabtree
0.35-0.55 Tucker and Crabtree
1.0 Chenoweth
0.25-0.50 Atzert
0.06 DWRC Files
2.0 est. Howard and Marsh
4.0 Chenoweth
0.30-1.00 Tucker and Crabtree
1.41 Tucker and Crabtree
0.15 DWRC Files
I/ Oral Toxicity by gavage unless otherwise indicated.
2/ If % mortality other than 50%, this appears in parentheses after the mg/kg figure.
3/ DWRC indicates Denver Wildlife Research Center.
4/ Voluntary Feeding
5_/ Intravenous
-------
TABLE III-2 - ACUTE ORAL TOXICITY OF COMPOUND 1080 (Continued)!/
SPECIES
Commercial mink
Desert kit fox
Black-tailed jack rabbit
Opossum
Black Bear
Bobcati/
II. AMPHIBIANS
Bull frog (Male)
III. BIRDS
A. RAPTORS
Golden eagle
American rough-legged hawk!./
Marsh hawk!/
Great horned owl!/
Turkey vulture
Black vulture
54.4
1.25-5.0
10.0
10.0
10.0
20.0 (71%)
15.0
REFERENCE!/
DWRC Files
DWRC Files
DWRC Files
Atzert
Atzert
Atzert
Tucker and Crabtree
Tucker and Crabtree
Howard and Marsh
Howard and Marsh
Howard and Marsh
Howard and Marsh
Howard and Marsh
A/ Oral Toxicity by gavage unless otherwise indicated.
"L' If % mortality other than 50%, this appears in parentheses after the mg/kg figure.
I/ DWRC indicates Denver Wildlife Research Center
!/ Voluntary Feeding
^/ Intravenous
£/ Intraperitoneal
-------
TABLE III-2 - ACUTE ORAL TOXICITY OF COMPOUND 1080 (Continued)!/
SPECIES
mg/kg
REFERENCE!/
B. GAME BIRDS
Gambel's quail (young)—/
Pigeon
Mourning dove
Ring-necked pheasant (Male)
California quail (Female)
Chukar partridge (M & F)
Coturnix (Male)
Merriam's turkey (Female)
C. PASSERINES
Brewer's blackbird!/
English sparrow
Magpie
D. WILD WATERFOWL
Mallard (Male)
Mallard (Female)
Pintail (Male)
Pintail (Female)
Widgeon (Male)
White-fronted goose
E. DOMESTIC BIRDS
10.
4.24
8.55-14.6
6.46
4.63
3.51
17.7
4.0
2.0-3.0
(33%)
3.00
0.6-1.3
9.11
15.0
10.0
8.0
3.0
5.90
Chenoweth
Tucker and
Tucker and
Tucker and
Tucker, et
Tucker and
Tucker and
Tucker and
Crabtree
Crabtree
Crabtree
al.
Crabtree
Crabtree
Crabtree
Howard and Marsh
Tucker and Crabtree
Atzert
Tucker
Howard
Howard
Howard
Howard
Tucker
and Crabtree
and Marsh
and Marsh
and Marsh
and Marsh
and Crabtree
White leghorn chicken
Rhode Island red chicken
Pigeon - Florida
Pigeon - Colorado!/
7.5
5.0
10.0 (42%)
2.0-3.0
Chenoweth
Chenoweth
Howard and Marsh
Howard and Marsh
.i/ Oral Toxicity by gavage unless otherwise indicated.
2/ If % mortality other than 50%, this appears in parentheses after the mg/kg figure.
.?_/ DWRC indicates Denver Wildlife Research Center
A/ Voluntary Feeding
-------
California ground squirrel populations were reduced about 85
percent following baiting. Primary hazards to seed-eating birds appeared
minimal as indicated from intensive carcass searching and the results from 31
radio-equipped mourning doves and ten radio-equipped California quail. One of
two white-breasted nuthatches found dead after treatment contained compound
1080 residue. One of two samples of dead ants also contained compound 1080
residue. Twelve cottontail rabbits were found dead after treatment and four
contained 1080 residue, indicating some primary hazard to this species.
Secondary hazards to raptors and mammalian predators were
evaluated by attaching radio transmitters to 24 raptors (red-tailed hawks,
turkey vultures, a golden eagle, great horned owls, barn owls, a screech owl,
common ravens, a common crow), and 42 mammalian predators (bobcats, coyotes,
gray fox, badgers, striped skunks, raccoons, and opossum) and monitoring their
movements before, during, and after treatment. Five of the six radio-equipped
coyotes and three of the ten radio-equipped bobcats (one bobcat was emaciated,
possibly the result of a trap injury) were found dead after treatment. Three
dead striped skunks (not radio-equipped) were also found dead after treatment
and one contained compound 1080 residue. No other treatment-related
mortalities were indicated among the remaining radio-equipped birds or
mammals. Also, monitoring of 58 active raptor nests indicated no treatment-
related mortalities.
3) Subacute and Chronic Toxicity
While it was determined that the single oral LDj-Q of compound
1080 for mallards was 9.11 mg/kg, repeated oral dosages of just 0.5 mg/kg/day
for 30 days produced mortality in the same mallard stock. Relative to a number
of other pesticides, this indicates a moderate to high degree of cumulati/
toxic action for this species (Tucker and Crabtree, 1970).
Repeated sublethal doses of compound 1080 have increased the
tolerance of some species to subsequent challenging doses. This increase in
tolerance is most often slight, however. In other species, such as in the
mallard, cumulative intoxication occurs. Accumulation and tolerance for
compound 1080 are time-related phenomena such that short-interval treatments
(less than 30-hr- spacing) are more likely to accumulate. Longer interval
treatments (three or more days apart) are more likely not to have cumulative
effects. Reports concerning effects of long-term feeding upon low levels of
compound 1080 were not found.
4) Bioaccumulation and Tissue Residues
As previously stated, the distribution of compound 1080 in animal
tissues after ingestion is widespread and somewhat evenly concentrated in most
soft tissues of the body. Residue chemists often use the whole carcass, or
stomach and intestinal tract, as the sample for analyses in suspected compound
1080 poisoning cases. Massive concentrations can be found in the gastroin-
testinal tract, but residues are not frequently found in higher than LDcQ
amounts in absorbed form.
- 42 -
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Thus, tissue residues in compound 1080-killed animals may not
exceed the LA-n amount and in many cases may be somewhat lower than the
LD(-Q while gastrointestinal contents may sometimes be much higher.
Rats fed 5.8 mg/kg were killed after five hours and tissues
analyzed. Heart, brain, kidney, skin plus hair, and whole carcass contained
five ppm (Rudd and Genelly, 1956). In summary, compound 1080 does not tend to
accumulate to any great degree. Death of the animal normally prevents great
residue buildup in any tissue or organ system except the gastrointestinal tract,
5) Secondary Toxicity
Several laboratory studies lead to the conclusion that secondary
poisoning of animals (poisoning of animals which eat a species directly
exposed) can readily occur with compound 1080. Chemical stability of compound
1080 would favor the possibility of secondary poisoning.
Tucker (1965-72) offered domestic ferrets the intact bodies of
albino rats which had been stomach-tubed with compound 1080 two hours
previously. As the ferrets ate their respective rats over several days, the
stated amounts (expressed as mg of compound 1080 per kg of ferret) were not
ingested at once nor completely and represented much higher than the actual
dosage to the ferrets. Even so, ferrets eating rats containing dosages of 2.0
mg/kg or less exhibited strong symptoms while 8.0 mg/kg and above on this basis
was fatal to ferrets.
A similar experiment by Tucker with Peromyscus sp. and ferrets
produced death in ferrets if the mice eaten had been stomach-tubed to contain
one mg 1080/kg or more for the ferret. The acute oral LD5Q of 1080 stomach-
tubed in aqueous solution directly to ferrets was found to be 1.41 mg/kg. If
fed in ground beef, the LD^Q was between one and two mg/kg. It was
concluded that a ferret which receives two mg/kg whether by direct ingestion or
by feeding upon a prey species is very likely to succumb and that levels as low
as 0.5 mg/kg can produce severe symptoms lasting up to a week. From this, it
was considered likely that a 650-gram ferret ingesting 1.3 mg (2 mg/kg) of 1080
could die. This would mean that if a little as 1.0 gram of a 2 oz/100 Ib.
(0.125 percent) bait were ingested directly by a ferret it would likely be
lethal. If compound 1080-poisoned prairie dogs were fed upon by black-footed
ferrets a similar hazard could exist. The domestic ferrets in these studies
ate all parts of the mice completely and variable parts of the rats, including
the gastrointestinal tract. Some left only portions of the pelt.
In an experiment by Rudd and Genelly (1956), a dog was killed by
eating the heart tissue of a horse five hours after the horse had eaten
4.41 mg/kg of compound 1080.
- 43 -
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6) Human Risks
The RPAR notice against compound 1080 was based on three
criteria, one of them being the lack of emergency treatment for human poison-
ing. Since the RPAR review has not been completed on this chemical, the
treatment question cannot be addressed here. The data on potential risks,
however, will be presented.
The USDI reported 22 human poisonings with compound 1080 for the
period 1946-1949. This period was the first 4 years of compound 1080 use as a
rodenticide, and before use was restricted and controlled. Of these 22 cases,
four were reported as suicides and 16 were accidents involving children. Two
were accidental adult poisonings. Eleven of the 16 children died. One of the
two adults died.
More recently, reports of three cases of human poisonings have
been published. Two (1970 and 1975) were accidents involving children. Both
survived. One child was reported to have suffered neurological damage. A
third accident involved an adult, said to be a suicide. EPA's Registration
files contain a report of the accidential fatal poisoning of a man, who
ingested 436 rag (estimated) of compound 1080 from a bottle left by a licensed
pest control operator.
Another case (1968) was reported in the rebuttal from the
California Department of Food and Agriculture (30000/7:#82) and involved a
child, who recovered following hospitalization.
Eighteen accidental cases and four cases alleged to have been
suicides were reported for the four years ending with 1949. For the period
1950-1976, nine poisonings were reported. For these 26 years, the average was
approximately one poisoning every 21/2 years.
The completeness of accident reports can always be questioned but
it appears that there have been few human poisonings by these compounds since
restrictions and controls were placed on compound 1080. The greatest hazard is
still in and around the home.
The EPA's PERS reports, for the period 1972- May 1976, include 94
to 104 (the number in one group was estimated as 40 to 50) poisoning deaths of
domestic pets associated with compound 1080. These include 69-70 confirmed
compound 1080 pet poisonings. Forty-four to fifty-five were considered the
results of deliberate vandalism using compound 1080. Four were identified as
occurring in locations near industrial sites where compound 1080 was used.
Five were near a home where mice had been poisoned with compound 1080 by a pest
control operator. This last group of poisonings occurred in 1975.
- 44 -
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2. Zinc Phosphide
a. Method of Application
1) Ground Squirrel
Oat groat, rolled oat, cabbage or dandelion baits are used for
zinc phosphide. The concentration of the active ingredient in the bait varies
from 0.5 percent to 2.0 percent. Baiting is accomplished by scattering a
tablespoon of bait over two to three square feet at the side of a burrow on
bare ground or around rock or log piles used by ground squirrels. Such bait
may be broadcast by ground equipment or by airplane at about six pounds per
swath acre. Zinc phosphide is registered in California and Nevada for this use.
2) Prairie Dog
A 2.0 percent steam-rolled oat bait is placed in a heaping
teaspoon (4 gm) amount on open ground near a burrow. Formerly, heaping .
tablespoon amounts (14 gm) per bait placement were recommended. Usually the
rate works out to about 0.35 pounds of bait per acre. Ihe label recommend
baiting in late summer or fall. Zinc phosphide is federally registered for
this use.
b. General
1) Toxicology
Zinc phosphide is a heavy, finely ground gray-black powder that
is practically insoluble in water and alcohol. When exposed to moisture, it
decomposes slowly and releases phosphine gas. Phosphine, which is highly
flammable, may be generated rapidly if the material comes in contact with
dilute acids. Zinc phosphide concentrate is a stable material when kept dry
and hermetically sealed.
When zinc phosphide comes into contact with dilute acids in the
stomach, phosphine (PRO is released and it is this substance which probably
causes death. Animals that ingest lethal amounts of bait usually succumb
overnight with terminal symptoms of convulsions, paralysis, and coma. Death
usually results from asphyxia. If death does not occur for several days,
intoxication occurs similar to that observed with yellow phosphorous in which
the liver is heavily damaged. The surface of the liver is spotted and dis-
colored. Prolonged exposure to phosphine can produce chronic phosphorous
poisoning. To this extent, zinc phosphide may possess some characteristics of
accumulative toxic materials.
Early symptoms of zinc phosphide poisoning are: nausea, vomiting
(yielding black stomach contents and smell of phosphine), abdominal pain, chest
tightness, excitement, and a feeling of coldness. In fatal cases, there is
liver, kidney and heart damage. The time between ingestion and death is fre-
quently about 30 hours. Victims who are alive three days after exposure are
- 45 -
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said to recover completely. Mild poisoning from breathing minute amounts of
phosphine gas can be mistaken for food poisoning because of the diarrhea and
stomach pains produced.
Zinc phosphide baits have a strong, pungent, phosphorous-like
odor (garlic-like), this characteristic seems to attract rodents, particularly
rats, but apparently makes the bait unattractive to some other animals.
2) Residue
In soil, zinc phosphide breaks down rapidly to phosphine which is
either released into the atmosphere or converted to phosphates which remain as
a residue and zinc complexes.
There is only a small amount of deterioration of zinc phosphide
on baits due to the evolution of phosphine gas; therefore, dry baits must be
considered to be toxic indefinitely and must be used accordingly. Lecithin-
mineral oil, added to zinc phosphide to adhere it to grain bait, offers pro-
tection aginst moisture, and therefore, may increase its stability. Under
field conditions, zinc phosphide baits may remain toxic for several months
until eroded by weathering or decomposition of the carrier or the grain is
removed by insects. Physical erosion does not seem to occur rapidly. In one
instance zinc phosphide-treated bait, exposed in the field for two to three
months and ten to twelve inches of rain, continued to maintain some toxicity.
Residues of zinc phosphide in treated baits collected from the
ground were at 1/3 of pre-treated amounts by one day post-treatment but did not
further decline for 21 days. About ten percent of the original residue was
found 200 days post-treatment (Hegdal and Gatz, 1977).
3) Acute Toxicity
a) Laboratory Data
A 2.5 percent zinc phosphide wheat bait single oral ID™
for ring-necked pheasants was determined to be 1067 mg/kg. This value is
equivalent to 26.7 mg/kg actual zinc phosphide. For the gray partridge
(Perdix perdix), the LD™ was 16.0 mg/kg for zinc phosphide. On this basis
18 to 25 poisoned wheat kernels would be lethal to some pheasants and six to
nine kernels would be lethal to some partridges. Neither zinc phosphide nor
the red color on the bait prevented the birds from consuming the grains. More
than 80 percent of the bait strength remained after 3-27 days exposure to
weather including multiple rains (Janda and Bosseova, 1970). There is evidence
that black dye on bait exerts some repellency to bobwhite quail (Hines and
Dimmick, 1970).
The oral LD™ of zinc phosphide to a wide array of avian
species lies in the 10 to 30 mg/kg range. Among the more sensitive are geese
(7.5 - 8.8 mg/kg), pheasants (8.8 - 26.7 mg/kg) and California quail (13.5
mg/kg) (Tucker and Crabtree, 1970). A 5-day dietary LC,-n for mallard
ducklings was reported to be 1285 ppm (Hill, et al. 19757. Ungulate and
- 46 -
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carnivorous mammal LDcn values are 40-50 mg/kg. Most rodents are in the 15-
40 mg/kg range with exceptions (nutria, 5.6; northern pocket gopher, 6.8;
kangaroo rats, 8.0 mg/kg). The jackrabbit LD5Q is 8.2 mg/kg (Hood, 1972).
b) Field Studies
A field study (Collins, 1966) used 8-14 pounds of two
percent zinc phosphide with oat groats (not cracked corn) aerially applied to
96 miles of ditches and canals for rat control, researchers found seven dead
and 71 live pheasants along the route. Other dead nontarget animals included
two mallards, two bitterns, and one rabbit. Whether zinc phosphide was the
cause of the deaths was not determined by residue analysis.
The degree of persistence of the toxicity of two percent
cracked corn zinc phosphide baits is shown by data of Hayne (1951). When such
baits are allowed to weather outdoors, the laboratory mouse LDc-Q from dosing
with these baits increased from 2.8 mg/kg as zinc phosphide on day zero to 4.4
mg/kg in 4-6 days, to 14.6 mg/kg in 27 days (USDI, May, 1974).
In a nontarget wildlife safety study done under field
conditions (Hegdal and Gatz, 1977), some mortality among rabbits and pheasants
resulted from orchard mouse control on several square miles of orchards with
zinc phosphide. Chemical residue analyses established zinc phosphide poisoning
as the cause of the mortality. One blue jay was also killed by zinc
phosphide. Otherwise, raptors, predatory mammals, passerines, gallinaceous
birds, waterfowl, and avian scavengers suffered no observed mortality.
Radiotelemetry tracking of nontarget wildlife provided a useful tool in
monitoring the effects.
4) Secondary Toxicity
Golden eagles, great horned owls, and coyotes receiving multiple
feedings of zinc phosphide-poisoned jackrabbits showed no signs of secondary
intoxication (Evans, 1970).
Bell and Dimmick (1975) briefly describe several secondary hazard
tests with zinc phosphide involving the feeding of prairie voles to red foxes.
Two individuals were fed voles which were dead or dying from zinc phosphide
treatment at 5.3 times the LD5Q for the voles (a total of 86.94 mg/kg). The
red foxes consumed 11.5 voles each in 3 days or 10.64 mg/kg zinc phosphide (if
the toxicant had been unaltered) and survived though exhibiting briefly altered
behavior. The study concluded that "little hazard...may" exist from secondary
poisoning.
Zinc phosphide failed to be lethal in a study in which secondary
toxicity of compound 1080 and strychnine was shown for kit foxes ingesting
poisoned kangaroo rats. These foxes survived repeated feedings of kangaroo
rats each killed by 480 rag of zinc phosphide. This is equivalent to 3 times
the LDgQ for a kit fox and 29 times the amount one kangaroo rat might consume
in fieia-applied baits (Schitoskey, 1975). The direct dose LDc0 of zinc
phosphide for the kit fox was 93 mg/kg.
- 47 -
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Collectively, the literature on secondary poisoning for zinc
phosphide shows the low probability of secondary hazard to predatory wildlife
which consume target rodents (USDI, April, 1976). Some risk to predators may
be associated with the consumption of bait stored in the cheek pouches of
certain rodents.
5) Human Risks
No reports of dermal toxicity determinations were found.
Although the pesticide is toxic when inhaled, no LD5Q figures are available.
The Agency has no data on skin or eye irritation, but workers are required to
wear gloves when prepairing or handling baits to prevent skin contact.
3. Anticoagulants
a. Methods of Application
CPN (Chlorophacinone) ground squirrel grain baits (usually oat
groats or chopped cabbage or dandelion greens) range from 0.005 percent to
0.01 percent CPN. Typically, about one to five pounds of bait are placed in
a bait box or hopper bait station intended to exclude wildlife larger than the
squirrel. Bait is replenished every few days to give 1-to-4 week repeated
exposure to the squirrels. Some labels call for broadcasting a handful of bait
every other day, three times over a 40-50 square foot area near each burrow or
runway.
The methods and rates of DPN (Diphacinone) application are nearly
identical to those for CPN given above. Residue persistence data for CPN and
DPN were not found.
The other anticoagulants, Pival, Fumarin, Warfarin, PMP, and
Talon, are applied in a nearly identical manner as CPN, but the concentration
of the active ingredient is approximately five times greater than for CPN.
b. Toxicity
1) CPN
Chlorophacinone (CPN) causes death from internal bleeding by
hindering blood clotting and increasing capillary permeability.
A great degree of species selectivity occurs with CPN.
Rodents such as pine voles and deer mice have single oral LDc-n values of 3.58
mg/kg and 0.49 mg/kg, respectively. On.the other hand, the LD,-0 values for
red-winged blackbirds, mallards, and ring-necked pheasants are 430, greater
than 100, and greater than 100 mg/kg, respectively (Giban, 1969).
In 1969, Giban conduted an experiment to measure the toxic
effects of CPN 0.0075 percent baits on the gray partridge during a 15-day
exposure. A daily oral dose of 2.25 mg CPN per bird was calculated to be the
- 48 -
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equivalent of free-feeding on 0.0075 percent baits. All 10 partridges survived
15 consecutive daily doses of 2.25 mg. None of 10 survived this level for 30
daily doses. Seven of 10 survived 15 daily doses of 4.5 rag/bird (Giban, 1969).
2) DPN
Diphacinone (DPN), as with CPN, causes death from internal
bleeding by hindering blood clotting and increasing capillary permiability.
With the amounts of DPN used in baits, rodents must ingest several bait
applications in order to receive a lethal dose. DPN is also used in human
medicine as an anticoagulant.
The acute oral LD^o in rats of the technical material is
2.31 mg/kg. An acute dermal LD5Q was not found in the literature. It was
reported that three or four rabBits were killed in a dermal toxicity test in
which a 200 mg/kg dose was used.
The Velsicol Chemical Corporation-(1976) reported the average
5-day dietary LC™ of DPN (technical) to be 4485 ppm for 14-day-old bobwhite
quail. Concentrations of 1000 and 2150 ppm produced 10 and 20 percent
mortality. A similar study with 14-day-old mallards found an LC,-Q of greater
than 10,000 ppm, although 20 percent mortality and reduced food cons.ir.ption
occurred at this level. (Velsicol Chemical Corporation, 1976).
Truslow Farms, Inc. (1976) reported on an eight week secondary
toxicity study with sparrow hawks (Falco sparverius) in which 0.005 percent DPN
baits were fed to Swiss mice for three to five days. Six wild hawks (which had
been trapped) received two treated mice each day. After 10 days of exposure
the hawks were fed untreated mice and held for six weeks observation. There
was no effect upon the hawks except lack of weight gain. The mice were
terminally poisoned at the time of ingestion by the hawks as shown by studies
on identically treated mice not fed to the hawks.
Mendenhall and Pank (unpublished) demonstrated a potential
hazard to avian predators of secondary poisoning from DPN in an experiment
using three species of owls. Two DPN poisoned mice were fed twice daily to the
owls for five days. The mice had consumed a lethal dose of 0.01 percent DPN
bait over a 10-day period. Three of the four owls in the test died 7-14 days
after the experiment began.
3) Other Anticoagulants
The effects of the other anticoagulants, Warfarin, Pival,
Fumarin, PMP, and Talon are similar to CPN and DPN in that they all cause death
through hemorraging. Repeated doses are generally required to cause death.
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c. Human Risks
1) CPN
Human volunteers were given a 20 mg/kg dose and their
prothrombin ratings were monitored for eight days thereafter. The rating fell
to 35 percent of normal, but it almost completely recovered by the end of the
study. It was concluded that ingestion of 400 g of a bait containing 0.005
percent chlorophacinone would depress prothrombin activity to dangerously low
levels.
Pesticide Incident Monitoring System (PIMS) files for the
year 1966 to June 1979 contain nine reports on CPN poisoning. Five of the
reports involved children, one report involved an adult, and the other three
involved animals. None of the human incidents were fatal.
2) DPN
The Agency has no data on the human risks associated with the
use of DPN as a rodenticide.
3) Other Anti-Coagulants
The Agency has no data on the human risks associated with the
use of Warfarin, Pival, Fumarin, PMP, or Talon as a rodenticide.
4. Fumigants
a. Carbon Bisulfide
Carbon disulfide is a highly volatile liquid which boils at
84.1°C (183.4 F). Its LD5Q (subcutaneous in rabbits) is 300 mg/kg.
Carbon disulfide vapor is absorbed largely through the lungs,
although toxic quantities can also be absorbed through the skin. Its effects
are mostly on the nervous system; single exposures are characterized by
narcosis and its sequelae. Human symptoms of repeated exposure are
nervousness, irritability, indigestion, bizarre dreams leading to insomnia,
excessive fatigue, loss of appetite, headaches, euphoria, restlessness, mocous
membrane irritation, nausea, vomiting, unconsciousness, and terminal
convulsions.
PIMS files for the period 1966 to August 1979 contain 21
reports of carbon disulfide exposure through inhalation . Eleven incidents
involved carbon disulfide alone. The other ten cited carbon disulfide in
combination with other ingredients. Five fatalities resulted, all adults, and
all from exposure of fumigants where carbon disulfide was one of two or more
active ingredients.
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b. Gas Cartridges
Gas cartridges emit gases, mostly carbon monoxide, and smoke when
ignited. The cartridges are cardboard cylinders filled with sulfur, charcoal,
red phosphorus, mineral oil, sodium nitrate, and sawdust.
The affects on animals is assumed to be the same as those on
humans, i.e., unconsciousness followed by a drop in blood pressure, loss of
muscular control, and finally a stoppage in breathing.
c. Methyl Bromide
Methyl bromide is a colorless liquid that boils at 4.5°C (40.1°F).
It is 3-5 times heavier than air, has a burning taste, and an odor resembling
that of chloroform. Methyl bromide is usually packaged, under moderate
pressure, in metal cylinders.
The effects of methyl bromide are on both the respiratory and
central nervous systems. The central nervous system effects occur with or
follow the respiratory system effects by several hours. Respiratory effects
include coughing, chestpains, painful breathing, and broncho-pneumonia.
Central nervous, system effects include nausea, vomiting, blurred vision,
convulsions, muscle weakness, and respiratory paralysis.
Methyl bromide can cause burns if allowed to saturate clothing, or
if splashed in the eye.
d. Other Fumigants
Calcium cyanide is applied as a dust for house mouse control. For
woodchuck control, it is applied either as a solid or a dust. Death is caused
by respiratory arrest, following nausea, unconsciousness, convulsions, and
paralysis. Reactions to the gas occur within seconds after inhalation, and
death results within minutes.
Carbon tetrachloride (under RPAR review), paradichlorobenzene, and
ethylene dichloride, all contained in one product, are applied as a liquid.
Death results from either respiratory arrest or circulatory collapse.
5. Repellants
The repellants Hinder and Thiram are sprayed on plants and trees prior to
the onset of damage. No risks to nontargets are anticipated since these are
not toxicants.
6. Relative Risks and Comparative Data
Data for making precise comparisions of relative toxicity are not abundant;
however, some reasonable generalizations can be derived from Table III-3- The
values for the LD^'s are from a variety of sources and have been freely
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TABLE II1-3
Relative Risks of Alternative Toxicants
LD50
Strychnine
(0.5% bait)
LD50 Relative
(mg/kg) Risk!/
Compound 1080
(0.075% bait)
LD50 Relative
(mq/kg) Risk!/
Zinc Phosphide
(2.0% bait)
LD5Q Relative
(mq/kg Risk!/
Quail
Pheasant
Duck
Goose
Dove
Blackbird
Sparrow
Eagle
Ground Squirrel
Prairie Dog
Jackrabbit
Cat
Dog
Kit Fox
135.0
25.0
5.0
4.0
9.0
5.0
5.0
5.0
20.0
1.5
4.4
0.75
1.1
0.75
1.0
1.9
6.7
8.4
8.2
3.3
4.0
1.7-6.6
1.0
3.0
8.4
13.0
9.1
31.0
4.0, 20.0
7.0
5.0
5.0
11.0
2.5
3.0
1.2, 5.0
0.35
0.3
5.6
0.2
0.06
0.22
5.1, 1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
8.6
2.3
1.0
7.4
25.0
16.0
13.0
18.0
36.0
8.0
34.0
24.0
-
-
33.0
18.0
8.2
40.0
40.0
93.0
42.0
10.0
3.7
17.0
8.6
2.7
-
-
2.4
1.0
18.0
1.0
1.0
1.0
I/ The least toxic bait for each animal is arbitrarily assigned a value of 1.0.
-------
rounded and averaged. Each of the table values has been derived from one or
more species or tests as appropriate.
Some variation between species in reported LD^Q'S is apparent. The
source of this variation is uncertain and most reported differences have not
been considered important for the present purposes of seeking generalizations.
Substantial variation in toxic response is reported among quail for compound
1080; the LD50 for the California quail is about four mg/kg while that for
the Gambel's quail is 20 mg/kg . With limited data, therefore, the accuracy
of the values is uncertain and the generalizations to be made cannot apply to
any similar species that may be either extremely sensitive or extremely
resistant to a particular toxicant.
To obtain the relative risk from the consumption of bait for each
species, the LD^0 values for each toxicant were divided by the concentrations
of the toxicant in the bait formulation employed by the USDI. This procedure
gives the relative amount of bait that is equitoxic to the species. Assigning
an arbitrary value of 1.0 to the least toxic formulation and dividing the
relative amount of bait for the formulation by that for an alternative gives
the relative toxicity of the alternative- . Thus, for pheasant, compound
1080 has the lowest ID™ but its dilution (0.075 percent) in the bait makes
it the least hazardous, other things being equal. Strychnine is less toxic to
pheasants than compound 1080 but its higher concentration in bait makes the
bait about twice as toxic to pheasants. Considering the quality of the data
and other variables, however, the observed difference between the estimates of
the two formulations cannot lead to a conclusion that substantial differences
in risk can be anticipated from use in the field.
For zinc phosphide, different estimates of the ID™ for pheasant (9-27
mg/kg) range from near that for compound 1080 to several times as great;
however, the concentration of "zinc" in the bait gives a relative risk factor
of from 7 to 21 and averaging 10. From this analysis, it is reasonable to
conclude that the risk to pheasants from the use of zinc phosphide is
substantially greater than that for both strychnine and compound 1080.
Allowing for the variable quality of these data, and species variability,
Table III-3 indicates some generalizations that are relevant for a comparative
risk assessment.
1. For a wide variety of birds, compound 1080 bait is the least
hazardous. For gallinaceous birds, zinc is the most hazardous but for
waterfowl, doves and blackbirds, zinc and strychnine are about equal.
\J Example: Dividing each ID™ for the pheasant by the concentration of
the bait for each pesticide yields the following: strychnine = 25/0.5 =
50; compound 1080 = 7/0.75 = 93; zinc phosphide = 18/2 = 9. Tne relative
risk for each toxicant is therefore: strychnine = 93/50 = 1.9; compound
1080 = 93/93 = 1.0; zinc phosphide = 93/9 = 10.
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2. Responses among rodents and rabbits appear to be more variable and
hence less predictable. Zinc phosphide is the most toxic bait for the
jackrabbit and the least for the prairie dog (black-tailed). Compound 1080 is
the most toxic bait for the ground squirrel (California) and least for the
jackrabbit.
3. For carnivores, the risk from zinc phosphide appears to be relatively
low although good toxicity data are difficult to obtain because zinc phosphide
may induce vomiting in treated animals. The risk of secondary hazard is
further reduced by detoxification of zinc phosphide in the stomach of poisoned
animals. In general, the risk to carnivores from strychnine and compound 1080
bait do not differ substantially. The most common exposure of carnivores to
grain baits is, however, indirect. The greatest hazard'from feeding on
strychnine-killed animals is associated with the ingestion of unabsorbed poison
in the digestive tract. This factor would generally make secondary hazards to
carnivores lower for strychnine than those for compound 1080.
4. For raptors (including vultures) comparative data are limited to those
on strychnine and compound 1080 for the golden eagle. Because of the problem
of indirect exposure to strychnine bait in the digestive system, it is not
clear that a substantial difference in secondary risk exists between strychnine
and 1080. While no raptor toxicity data for zinc phosphide are available, the
detoxification of zinc in the stomach of victims would lead to a prediction of
relatively low risk to raptors. Some degree of confidence in this prediction
is supported by the observations that (1) compared to strychnine and 1080, the
variability of toxic response is low (reported LDcn range over two orders of
magnitude in strychnine and 1080 and less than an order of magnitude for zinc
phosphide) and thus more predictable, and (2) raptors are capable of
regurgitating their stomach contents (although not reported for raptors, zinc
phosphide may induce regurgitation in carnivores).
Comparative data for anticoagulants are not extensive. Studies using
ducks, quail, and blackbirds have suggested very low potential for risk.
BDwever, some secondary mortality to raptors has'occurred and recent laboratory
studies confirm that owls are sensitive to diphacinone poisoning (Mendenhall
and Pank, unpublished). Additionally, fatalities to dogs have been associated
with the use of diphacinone to control orchard mice and it is apparent that
these compounds, which have long been emphasized because of their relative
safety to humans, may pose significant risks for raptors and carnivores.
Fumigants will kill most vertebrates inhabiting the treated burrow. The
occupants may include black-footed ferrets, burrowing owls, snakes and other
species in addition to the target species. No secondary hazards are
anticipated from the use of fumigants.
The above observations on apparent relative risk are generally supported by
field observation (Hegdal and Gatz 1977, 1977a, 1979). It can be concluded
that all rodenticides pose risks of varying degree for nontarget birds and
mammals and that the substitution of one toxicant for another may merely shift
the risk from one set of nontarget species to another. For instance,
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substituting zinc phosphide for strychnine may substantially reduce risk to
carnivores but would increase risks to gallinaceous birds and not substantially
alter the risks for waterfowl, doves, and passerines. The actual magnitude of
any effects or changes in effect can not be predicted but the direction of the
change in risks from substitute rodenticides can reasonably be anticipated.
Variation in concentrations of the toxicants, acceptability of the bait and
other factors influencing exposure must be considered in the assessments. Of
substantial concern in this regard is the persistence of toxic bait in the
field. Fresh baits (leaves, fruits) and pelletized baits may be expected to
lose their attractiveness to birds and mammals rather rapidly when exposed to
the environment. Highly persistent poisons would thus not be needed with fresh
baits since acceptance would be low. The observation that strychnine-treated
oats were still killing doves after more than two months in the field (Hegdal
and Gatz 1977), however, is disturbing, since little benefit is likely to be
derived from such persistence.
7. Summary
Considering use rates, treatment strategies, toxicity data, and field
studies, the following discussion characterizes the relative risks inherent in
the use of compound 1080 and strychnine and their alternatives for ground
squirrel control on pasture or rangeland.
The risk of strychnine as used in above-ground squirrel control appears to
center upon population reduction of small birds, such as songbirds and doves,
by direct poisoning of birds eating the bait. Other birds and mammals may also
be killed but available field evidence does not demonstrate that this effect is
generally substantial.
The risk of compound 1080 appears to center upon carnivorous species such
as coyotes or bobcats by way of secondary poisoning. Other unrelated families
of wildlife, though susceptible according to toxicological studies, did not
appear to suffer significant mortality from current compound 1080 ground
squirrel control techniques in California.
Zinc phosphide provides some demonstrable hazard to pheasants and rabbits,
but little hazard to other unrelated wildlife species has been established.
The anticoagulants do not appear to have produced any significant
nontarget wildlife kills, but do appear to be very selective for rodent-type
mammals, and possess ample safety margins for most birds. Some owls and
perhaps other untested species are susceptible to secondary poisoning by DPN.
Effects of CPN and DPN upon small nontarget wild carnivorous mammals would
need investigation prior to conclusions of safety for such mammals.
Fumigants pose no secondary risk to wildlife but will kill most nontarget
occupants of treated burrows.
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C. Alternatives - Bird Control
The objective in using strychnine baits is to obtain a rapid reduction in a
local pest population. Since, when used properly, no other federally regis-
tered pesticide can normally achieve this objective for birds, there are no
chemical alternatives to strychnine. In managing a pest situation, however,
there are alternatives when rapid population reduction is not required.
Federally registered pesticides that may provide alternative solutions to
specific problems include 14-aminopyridine (avitrol), polyisobutylene, polybu-
tene, mesurol, starlicide, endrin and fenthion, and for pigeons, azacosterol
(ornitrol), diphacinone, and pival.
The compound 4-aminopyridine is formulated in baits to function primarily
as a repellent. Members of a flock that ingest lethal or near-lethal levels
produce distress calls and other behaviors that frighten the remainder of the
flock, causing it to disperse from the site to be protected. Direct risks to
non-target species are generally low since this is not used as a toxicant and
risks from secondary poisoning seem highly unlikely (Clark, 1975, Schafer and
Marking, 1975).
Polyisobutylene, polybutene, and mesurol are repellents with no
recognizable risk to nontarget species. They are used, respectively, on
roosting places on structures and on certain small fruits.
Starlicide is a slow acting toxicant, highly toxic to starlings, less toxic
to most other birds, and relatively nontoxic to rats.
Eiidrin and fenthion are both used in artificial perches placed in roosting
areas around structures. Birds landing on the perches many absorb lethal doses
through the feet. While, in proper use, nontarget species are unlikely to land
on these perches, some potential for secondary risks may be associated with
the use of endrin. The Agency has prohibited such use in the vicinity of
peregrine falcon aeries.
Azacosterol baits are used to inhibit reproduction in pigeons. No risks
to nontarget species are recognized.
In summary, chemicals used in control strategies that do not require a
rapid reduction in the pest population pose less of a risk to nontarget species
than does strychnine.
D. Summary of Relative Risk by Use Pattern
1. General
The following section presents the Agency's conclusions regarding the
risk to nontarget wildlife from the above-ground uses of strychnine and its
alternatives. These conclusions reflect a judgment of the available
information presented above and reasonable extrapolations. In many cases, it
was not possible to conclude that substantial risks would result from the use
- 56 -
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of strychnine to control specific pests on specific sites providing that proper
precautions were taken. These extrapolations take into consideration the fact
that site conditions vary substantially, that operator judgment is required,
and that label directions and formulations vary. It has long been a policy in
the registration of pesticides to require that risks to wildlife be reduced by
any appropriate means that would not substantially reduce the benefits of use.
Such reasonable precautions are required, independent of the RPAR process.
Where appropriate, the precautions will be considered ur ier regulatory
options. In other cases, data are not available for the Agency to determine
whether or not substantial risks are likely.
2. Rangeland and Pasture Rodents
a. Prairie Dogs
The use of strychnine may jeopardize the continued existence of the
black-footed ferret and cause population reductions in other nontarget species
that feed on the bait. Use of the most likely alternative, zinc phosphide,
would substantially reduce the possibility of secondary hazards to ferrets and
other predators/scavengers that may feed on dead or dying prairie dogs. Direct
risks to gallinaceous birds, such as prairie chickens and sharp-tailed grouse,
may increase substantially if zinc phosphide is used but specific information
on these species is unavailable.
b. Ground Squirrels-
The use of strychnine may cause population reductions in various
species of birds that feed on the bait. The extent to which dyeing the bait
can reduce this risk is uncertain. Use in the vicinity of various endangered
species (black-footed ferret, San Joaquin kit fox, California condor, peregrine
falcon and others) may result in mortality to individuals. If, in fact, dyeing
the bait reduces risks to nontarget avian species, such as doves, indirect
risks to endangered species that may feed on those nontarget species would be
reduced. Use of the most likely alternative, carbon disulfide, would eliminate
all secondary risks to nontarget organisms associated with the use of poisoned
baits. Risks to any nontarget occupants of burrows (ferrets, burrowing owls,
snakes) would increase substantially over that associated with the use of
strychnine in any particular area. Use of compound 1080 (California, Nevada,
and Colorado) would probably increase the risk to carnivores (coyote, bobcat)
and decrease the risk to birds in general.
c. Miscellaneous Rodents and Lagomorphs
At this time, available evidence does not permit the Agency to
conclude that substantial risks to nontarget organisms would generally result
from the use of strychnine to meet sporadic needs to control local infestations
of various rangeland rodents if proper precautions are taken. Some nontarget
mortality would be expected and due concern for any endangered species must be
given.
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3. Cropland Rodents
a. Prairie Dogs
Risk from strychnine and its alternatives would be generally
similar to that for rangeland.
b. Ground Squirrels
Risks from the use of strychnine and its alternatives would be
generally similar to those for rangeland. Fresh baits in some situations are
likely to be used instead of grain baits, transferring risk to a different
subset of nontarget species and perhaps having a lower potential for overall
risks.
c. Miscellaneous Rodents and Lagomorphs
At this time, available evidence does not permit the Agency to
conclude that substantial risks to nontarget organisms would generally result
from the use of strychnine to meet sporadic needs to control local infestations
of various cropland rodents if proper precautions are taken. Some nontarget
mortality would be expected and due concern for any endangered species must be
given.
4. Nonagricultural Sites for Rodents and Lagomorphs
At this time, available evidence does not permit the Agency to conclude
that substantial risk to nontarget organisms would generally result from the
use of strychnine to control rodents and lagomorphs on nonagricultural sites
if proper precautions are taken. Some nontarget mortality can be expected and
due concern must be given for any endangered species.
5. Cropland Birds
At the present time, available evidence does not permit the Agency to
conclude that the use of strychnine to control birds in California cropland
(sprouting seeds, rice, sunflowers, cherries, grapes, feedlots) is likely to
have substantial effects on nontarget wildlife. Some direct and indirect
nontarget mortality is to be expected and due precautions must be taken to
protect endangered species. The same assessment applies to the use of
strychnine to control magpies in Nevada and Wyoming.
6. Nonagricultural Sites for Birds
At the present time, available evidence does not permit the Agency to
conclude that the use of strychnine to control pigeons and house sparrows on
nonagricultural sites is likely to have substantial effects on nontarget
wildlife. Some direct and indirect nontarget mortality is to be expected and
due precautions must be taken to protect endangered species.
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IV. Benefit Analysis
A. Introduction
The Agency has evaluated the potential economic impacts of cancelling
strychnine for outdoor above-ground use. The conclusions are based on
information, from a number of sources, principally the Preliminary Benefit
Analysis.- In addition, rebuttal comments from registrants, users, and
other parties; federal and state vertebrate pest control specialists; and
available published data, were considered in the Agency's conclusions.
The Agency's analysis focuses on two general types of pests - birds
and rodents (including rodent-like animals) and three broad areas
rangeland/pasture, cropland, and nonagricultural sites. Within these
general categories, the Agency identified the major and minor uses of
strychnine; estimated the quantities used; listed the registered alterna-
tives, including an evaluation of their efficacy and availability; and
evaluated the impact upon users and the agricultural sector. The Agency
estimated the economic impact which could result if registrations of strychnine
for above-ground uses are cancelled and users shift to alternative control
materials or strategies. In addition, the Agency evaluated the simultaneous
cancellation of sodium monofluoroacetate (compound 1080) on those sites where
compound 1080 is used or could be used as a substitute for strychnine.
The Agency faced severe data limitations in this analysis and has had to
use considerable judgment in evaluating the potential economic consequences of
cancelling the outdoor, above-ground uses of strychnine. The analysis often
provides qualitative estimates or discussions of impacts due to the lack of
sufficient usage or comparative efficacy data to support precise quantitative
estimates. Although estimates in this document are reported as point
estimates, they represent rough predictions of strychnine bait distribution and
economic impact. The Agency used reasonable assumptions in its estimates to
reflect the general economic consequences of cancelling strychnine usage.
In general, the economic impacts of cancelling the outdoor, above-ground
uses of strychnine would not significantly affect U.S. production or prices of
major commodities or services. Impacts on agricultural productivity and
production costs would generally be limited to users in western states.
Regional or local impacts to users are indicated where no registered
alternatives exist or where registered alternatives are more costly,
impractical, or ineffective.
\J Prepared under contract by Development Planning and Research
Associates, Manhattan, Kansas. EPA Contract No. 68-01-4339. 1979.
See Appendix E.
Unless otherwise noted, the sources for this chapter will be
Appendix E.
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B. General Production and Use Patterns
Approximately 90.1 percent (449,200 pounds) of the estimated 498,700
pounds of strychnine baits - used annually (average for 1977-78) are for
control of rodent or lagoraorphs (e.g., rabbits) in western states (Table IV-1).
Range/pasture and cropland usage for rodent or lagornorph control comprise
about 45.6 percent (227,400 pounds) and 42.1 percent, (209,900 pounds)
respectively, of annual strychnine bait usage, An estimated 9.9 percent, or
49,500 pounds of strychnine baits are used annually for bird control —
3.6 percent (18,000 pounds of bait) in cropland and 6.3 percent (31,500 pounds
of bait) in nonagricultural sites. The remaining 2.4 percent (11,900 pounds
of bait) of annual strychnine bait usage is in nonagricultural sites, primarily
for control of commensal rodents.
C. Analysis of Benefits of Strychnine Use on Rangeland/Pasture
Strychnine is federally registered for use in the control of such
rangeland rodents as ground squirrels (many species), prairie dogs,
cotton rats, kangaroo rats and jackrabbits. Federally registered alternatives
for ground squirrels include gas cartridges, carbon disulfide, Thiram, and
carbon tetrachloride (under RPAR review). Anticoagulants, methyl bromide, zinc
phosphide, and compound 1080 are registered in some states for ground squirrel
control. Zinc phosphide is federally registered for the control of prairie
dogs, cotton rats, field and meadow mice, and kangaroo rats. For the control
of jackrabbits, the repellants Thiram and Hinder are federally registered and
the anticoagulants are state registered in California. Table 1V-2 lists the
chemical alternatives to strychnine with their registrations by site and pest.
1. Ground Squirrels
In North America, there are 22 recognized species of ground squirrels.
Some species contain as many as 14 subspecies or races which are distinguished
not only by morphological characteristics or distribution characters, but by
behavioral differences and varying ecological strategies as well. These latter
characteristics frequently affect the efficacy of various control methods.
Currently, six ground squirrel species are of sufficient economic
importance to justify regular control efforts: Richardson's ground
squirrel, California ground squirrel, Columbian ground squirrel, Belding's
ground squirrel, Townsend's ground squirrel, and Uinta ground squirrel.
Other species which occasionally require control include the antelope
ground squirrel, thirteen-lined ground squirrel, round-tailed ground
squirrel, golden-mantled ground squirrel, and rock squirrel. Columbian, Uinta,
and Townsend's ground squirrels have increased in numbers during recent years,
and demands for control efforts are increasing.
2/ Outdoor above-ground usage only.
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Table IV-1
Estimated Annual Above-Ground Usage of Strychnine
Bait for Rodent and Bird Control, 1977-78
Pest
Rodents
Birds
Total
Range/
Pasture Cropland Other Total
(Ibs) (%) (Ibs) (%) (Ibs) (%) (Ibs) (%)
227,400 45.6 209,900 42.1 11,900 2.4 449,200 90.1
18,000 3.6 31,500 6.3 49,500 9.9
227,400 45.6 227,900 45.7 43,400 8.7 498,700 100.0
SOURCE: Development Planning and Research Associates, 1979.
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Table IV-2
Chemical Alternatives to Strychnine for Rodent and Lagomorph Control
Pest
Acute Toxics
loeol/
Zinc
phosphide
Enorin
Ground
Squirrels
Nv., Ca., Co.
Ca., Nv., Or.
Marmots/
Wood- Porcu- Prairie Jack
chucks pines dogs Rabbits
Co.
F
Rabbits
Nv.
Ca.
Cotton
rats
Ca., Nv.
F
Nv.
Deer Meadow Mountain House
Mice Mice Opossum Beavers mice
Ca. Ca. F
F F F
F
Repellents
Hinde r
Thiram
Fumigants
Gas cartridges
Carbon disuifide
Methyl bromide
Calcium cyanide
Carbon tetra-
chloriae!/ £/
Anti-coagulants
Pival
Fumarin
Diphacinone
Chlorophacinone
Warfarin
PMP
Talon
Haki
F
F
Ca., Nv.
2/
2/
Ca.
4_/
Ca., Id.
Ca.
Ca.
Ca.
Ca.
Ca.
Fl.
3/ 3/
Or.,Ca. Jl.,0r.
F
F
F
F
F
F
FRP
I/ RPAH Chemical
~2/ For ground squirrel and orchard mice control, most states have one or more anticoagulants
registered under Section 24(c) of FIFRA (special local need).
3/ State registrations for Ca., Co., Id., Mi., Nc., Ny., Oh., Or., Pa., Ut., Va., Wa.
j*/ State registration for Az., Ca., Co., Id., Mt., Nm., Nv., Or., Ut., Wa., Wy
5/ Formulated with paradichlorobenzene and ethylene dichloride
F: Federally Registered
FRP: Federal Registration Pending
-------
In range and pasture lands, ground squirrel foraging reduces the amount of
plant material available to grazing livestock. In addition to forage consumed,
ground squirrels eliminate vegetation by clearing and tramping areas near
burrows and runways. Ground squirrels will invade cropland and reduce yields
in alfalfa, small grains and a variety of fruit and nut crops. Losses are
particularly significant in fields bordered by infested rangeland or infested
woodland. Crop losses of 10 to 30 percent are common while some small fields
(i.e. 10 to 50 acres) can be almost completely destroyed. In addition, damage
to harvest and other farm machinery, caused when the equipment runs into or
over burrows, can be quite substantial.
If strychnine were cancelled for ground squirrel control in rangeland, the
only registered alternative available in all states is fumigation with either
carbon disulfide, gas cartridges, or carbon tetrachloride. While these
materials can be used effectively, their usage has historically been confined
to relatively limited areas due to labor requirements and high costs, ranging
from about $12 to $17 per acre compared to about $2.35 per acre for
strychnine. Currently an estimated 233,110 acres or about 0.02 percent of the
grazing acreage in the 48 contiguous states are treated annually with
strychnine for ground squirrel control at a cost of about $543,000. If
strychnine were cancelled and compound 1080 were to be available (currently
registered in three states) user control costs would increase by about $900,000
annually. If compound 1080 is not available, annual control costs would total
about $2.1 million, an increase of nearly $1.5 million. Most likely these
increased costs would be absorbed by users or publicly supported rodent control
programs rather than passed along to consumers. The annual increased rodent
control cost on individual ranch operations, while extremely variable, is
estimated to average about $320, which represents annual production cost
increases of about 4 percent on smaller ranches and about 0.5 percent on larger
ones. Expenditures for rangeland rodent control are extremely minor when com-
pared with other production costs such as veterinary expenses and feed costs.
Also, only a minute amount of the grazing land is treated with strychnine.
Consequently, the impact of cancelling strychnine use on rangeland for control
of ground squirrels would be generally limited to affected individuals but
should have no appreciable effects on livestock markets or consumer meat
prices.
2. Prairie Dogs
Prairie dog numbers and density decreased greatly between 1930 and
1973. However, in recent years the area occupied by prairie dogs has
increased from an estimated 1.3 million acres in 1973 to 2.1 million acres
in 1979 (Table IV-3). Black-tailed prairie dogs, occurring in
approximately 59 percent of this acreage, are the major pest species.
Approximately 88,000 pounds of strychnine baits are used to treat an
estimated 96,000 acres of range and pasture for prairie dog control.
Zinc phosphide, the most likely alternative if strychnine use were
cancelled, is slightly less expensive (approximately $0.25/acre less) than
strychnine and is about equally effective. The use of zinc phosphide
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Table IV-3
Estimated U.S. Acreage of Range and Pasture
Infested with Prairie Dogs
State
N. Dakota
S. Dakota
Nebraska
Kansas
Oklahoma
Texas
New Mexico
Arizona
Colorado
Montana
Wyoming
Utah
Total
All
1973
8,000
60,000
15,000
36,000
15,000
77,500
248,000
2,000
417,000
132,000
178,500
68,000
1,257,000
1961
1,715,000
1968
Prairie Dogs
1979
11,000
300,000
55,500
60,000
20,000
90,000
300,000
5,000
500,000
309,500
300,000
190,000
2,141,000
1965
1,668,000
1971
Black-tailed
Prairie Dog
1979
11,000
300,000
55,500
60,000
20,000
90,000
200,000
100,000
232,000
200,000
•"*-•—
1,268,500
1,621,000 1,574,000
Source: Development Planning and Research Associates, 1979
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could reduce total control costs by about $24,000 annually. Therefore, a
shift from strychnine to zinc phosphide would create slight savings to the
user and would have no consumer or commodity market impacts.
3. Other Rodents and Lagomorphs
Considering the number of the rodents and lagomorphs, only a small group
adversely affect rangeland under modern management. In local situations some
species of kangaroo rats, cotton rats, meadow mice, and jackrabbits can become
problems requiring control efforts. Strychnine is federally registered for
control of kangaroo rats, cotton rats, meadow mice and jackrabbits
(Table IV-2). An estimated 4,500 pounds of strychnine baits are used annually
for control of these pests (less than one percent of total strychnine usage).
Alternatives are quite limited. Only zinc phosphide and Thiram are federally
registered for control of cotton rats and meadow mice. The repellants are
federally registered and anticoagulants are available in California for
jackrabbit control.
If strychnine were to be cancelled, losses on rangeland would increase
during periods of high population outbreaks, since no toxicants are registered
to replace strychnine in many states. However, since the estimated usage of
strychnine for control of these pests is relatively small, impacts would most
likely be limited to local user-level effects and would not be expected to
appreciably affect livestock markets or consumer meat prices.
D. Analysis of Benefits of Strychnine Use on Cropland
An estimated 210,000 pounds of strychnine baits are used on about 254,000
acres of cropland annually to control depredation by ground squirrels, prairie
dogs and other rodents. About 91 percent of the bait (191,100 pounds) is used
for ground squirrel control on about 240,000 acres; seven percent of the bait
(14,310 pounds) is used for prairie dog control on 14,310 acres; and two
percent of the bait (4,500 pounds) is used for miscellaneous rodent control.
In descending order, Nevada, Montana, California, and Idaho were the largest
users of strychnine bait for rodent control in cropland.
The six species of ground squirrels identified as economically important in
rangeland damage and the black-tailed prairie dog are also the rodents most
often involved in damaging cropland.
1. Prairie Dogs
An estimated 14,300 pounds of strychnine baits are used annually to
control prairie dogs on about 14,300 acres of cropland (Table IV-4).
If strychnine were to be cancelled for prairie dog control in
cropland, the most likely federally-registered alternative would be gas
cartridges. Zinc phosphide is not registered for use on cropland.Gas
cartridges are more expensive than strychnine and would result in increased
costs to users of about $14 to $19 per acre or about $206,300 to $270,900
annually, if used on all acres currently treated with strychnine.
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Table DM
Estimated Acreages of Cropland Treated with Strychnine
for Prairie Dogs and Ground Squirrels, 1978
Region and State
Northern Plains:
North Dakota
South Dakota
Nebraska
Kansas
Southern Plains:
Oklahoma
Texas
Mountain :
Montana
Idaho
Wyoming
Colorado
New Mexico
Arizona
Utah
Nevada
Pacific:
Washington
Oregon
California
TOTAL
Prairie
dogs \J
1,800
0
1,460
340
0
3,125
0
3,125
9,385
0
0
2,640
0
6,445
0
300
0
0
0
0
0
14,310
Ground
squirrels 2/
23,214
742
5,500
11,692
5,280
978
0
978
142,040
72,007
33,957
6,383
6,200
1,807
0
3,353
18,333 y
73,692
4,875
25,155
43,662 _4/
239,923
J_/ Pounds of bait from Table IV-2 : 1 pound of bait per acre application
rate (Henderson, 1979).
2/ Pounds of bait from Table IV-2 : 0.6 pounds of bait per acre application
rate (Clark, 1975) unless noted otherwise.
3/ 55,000 pounds of cabbage bait used mostly at 1-3 pounds per acre (Rowe,
1979). It was assumed that 3 pounds per acre were applied.
4/ Includes 43,262 acres that were treated with grain bait at an assumed rate
of 0.6 Ibs/acre and 400 acres that were treated with cabbage bait applied
by hand at the rate of 10 Ibs/acre (Sauer, 1976; O'Brien, 1978).
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No macroeconomic impacts would be anticipated if strychnine were
cancelled for prairie dog control. The impact, while important in
individual cases at the user level, would, in the aggregate, be too small
to result in macroeconomic impacts.
2. Ground Squirrels
About 240,000 acres of cropland are treated annually with an estimated
191,000 pounds of strychnine bait to control ground squirrels. Tne
mountain states (Montana, Idaho, Wyoming, Colorado, New Mexico, Arizona,
Utah and Nevada) use 6? percent of the strychnine bait to control
ground squirrels on cropland, and the Pacific states (Washington, Oregon
and California) use 25 percent. Together these two areas'account for nearly
92 percent of the strychnine baits used to control ground squirrels on
croplands.
The most likely alternatives to strychnine, depending on available
registrations and ground squirrel species, include diphacinone, compound 1080,
zinc phosphide and carbon disulfide. If strychnine were cancelled and
compound 1080 were available, producer control costs could increase by a
minimum of $5.80 per acre or $1.4 million annually. Without compound 1080,
producer control costs could increase about $1.6 million annua" ly or $6.60
per acre.
No macroeconomic impacts would be anticipated as a result of cancellation
of strychnine for above-ground rodent control on cropland. The impact, while
important in individual cases would be, in the aggregate, too small to result
in macroeconomic impacts.
3. Other Rodents and Lagomorphs
Complete data on strychnine bait usage to protect cropland from
rodent and rabbit damage are not available. In local situations, field and
meadow mice and jackrabbits can become problems, particularly during
periods of high population outbreaks. Since no registered alternatives
are available in many states for control of particular pests,
cropland losses will increase when and where such pest outbreaks occur.
Since only a small amount of strychnine bait is used annually for control
of these pests, impacts would most likely be limited to the user level
effects and should not appreciably affect major crop markets or consumer
prices.
E. Analysis of Benefits for Strychnine Use on Cropland for Bird Control
All Federal registration of strychnine' for bird control are for use on
nonagricultural sites. However, a variety of strychnine products are state-
registered in California, Nevada, and Wyoming for control of bird depredation
in croplands. The Agency's analysis is limited to California since Nevada and
Wyoming registrations are for magpie control only and sufficient data were not
available for analysis of this pest situation.
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Approximately 18,250 pounds of strychnine bait are used to kill birds on
an estimated 36,500 acres of California croplands. No consistent and reliable
data are available to estimate the use of strychnine-treated baits by
individual crop. However, principal crops damaged include grapes, cherries,
sugar beets, lettuce, nuts, vegetables, rice and other small grains, tomatoes,
plums and melons. In general, strychnine bait is distributed across crop
groups as follows: 45 percent on vegetables and melons, or 16,400 acres; 35
percent on fruits and nuts,or 12,800 acres; and 20 percent on field crops, or
7,300 acres.
If strychnine were cancelled for this use, the most likely alternatives
include repellants (on selected sites), mechanical and electronic
devices, trapping, shooting, and habitat manipulation. However, these
alternatives do not provide the toxic control presently available only
through the use of strychnine. No alternative toxicants are federally
registered for bird control in cropland, although starlicide is federally
registered for use on feedlots.
Since no alternative chemical toxicants are available for control of bird
depredation in cropland, and since strychnine is used only where bird damage
occurs, producers who currently use strychnine to control depredation would
likely suffer increased losses if strychnine were cancelled. Quantitative data
to estimate the extent and value of bird depredation are generally lacking,
spotty or incomplete. Quantitative analysis is further complicated by the wide
diversity of bird species which damage a wide variety of crops. Many crops can
suffer losses ranging from about 5 to 20 percent of yield on treated acreage.
Individual acreages of specific crops can be completely destroyed. However,
comprehensive infestation and damage estimates for the cropland acres currently
treated with strychnine are not available.
If strychnine were cancelled for control of birds on cropland, the
incremental loss would occur only on those acres where strychnine is now
used. Thus, the incremental loss would be confined to the total area now
treated, about 36,500 acres. In California, this could result in crop losses
estimated at $1.5 million annually.
The estimated 36,500 acres currently treated represent about 0.4$ of the
total acreage of fruits, nuts, vegetables, melon and field crop produced in
California. Clearly, the use of strychnine is of minor importance to the total
California cropland picture which totals $5.5 to $6.0 billion on about 9.1
million acres annually. Thus, while individual producers may be seriously
affected, the U.S. supply and price of fruits, nuts, vegetables and field crops
would be largely unaffected by cancelling strychnine for bird control in
cropland.
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F. Analysis of Benefits of Strychnine Use on Nonagricultural Sites
1. Birds
Strychnine is federally registered for outdoor use in the control of
pigeons and house sparrows on structures, vacant lots, and roosting
places. Pigeon control uses account for more than 98 percent of the
estimated 31,500 pounds of strychnine baits used annually for pigeon and
sparrow control.
Alternatives include U-aminopyridine (Avitrol), polyisobutylene, polybutene,
azacosterol, endrin, and fenthion (Table IV-5). Mechanical means such as traps,
frightening devices and structural changes designed to eliminate roosting and
nesting places are also useful.
In assessing the costs involved in a bird control program it is important
to consider the time required for a comparable level of control in addition to
the costs of materials and costs of application. Thus the particular situation
and the reason for desiring to reduce or eliminate the pest birds and the time
required for a specific control method are factors, especially when potential
health problems are indicated.
The costs involved in structural changes in buildings to eliminate or
screen roosting or nesting places are site-specific and usually more expensive
than chemical control, although they may represent a more satisfactory long
term solution to pigeon or house sparrow problems at that site.
Mechanical methods may ultimately offer essentially the same level of
reduction of bird populations as strychnine. They are, however, much more
labor intensive and thus more expensive and require a longer period of time.
For the satisfactory management of any pest species, the integration of
structural repair and improved sanitation, as well as repellants and toxicants,
is required.
The major impact resulting from the cancellation of strychnine for outdoor
control of pigeons and sparrows would be the elimination of a very quick-acting
tool when public health is an issue. The pigeon and the house sparrow have
been implicated in the spread of many human diseases such as, ornithosis,
salmonellosis, cryptococcosis, Newcastle disease, histoplasmosis and
encephalitis. Birds have been implicated in the spread of livestock diseases
such as transmissible gastroenteritis (TGE). Pigeons and house sparrows that
form large concentrations and roost near human habitations can increase the
chances for the spread of histoplasmosis, a fungus that can grow in accumu-
lation of bird droppings. The direct impacts from cancellation of strychnine
for pigeon and sparrow control on nonagricultural sites are unknown. In the
aggregate, no significant consumer impacts would be expected since some
alternatives are available. However, there could be potentially serious
Impacts in local areas due to the inability to quickly control pigeons and
sparrows.
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Table IV-5
Chemical Alternatives to Strychnine for Bird Control
Pest
Pigeons
House sparrows
Crowned sparrows
blackbirds
Starlings
Starlings, black-
biras, sparrows
House t inches
(linnet)
Horned larks
Cowbiras
Magpies
Meadowlark
Crows
Blue jays
Site
Structure roost
Structure roost
Sprouting crops
Structure roosts
Sprouting crops
Feedlots-t/
Structure roosts
Feeolots
Cherries
Grapes
Sprouting crops
Structure roost
Crops
Sprouting crops
Koos ts
Cherries
4-amino- Star- Polyiso- Aza-
pyridine licide butylene & costerol Fenthion Mesurol Endrin Diphacinone Pival
polybutene
F Ca. F F F F Ca. Ca.
F F F F
Ca.
F
Ca.
F F
F F F F
F
F
Ca.
Ca.
F
F
F
F: Federal Registration
I/ Strychine registered for this use only in California.
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2. Rodents and Lagomorphs
Strychnine is registered for use in the control of ground squirrels,
prairie dogs, cotton rats, kangaroo rats, deer mice, meadow mice, chipmunks,
house mice, porcupines, jackrabbits, marmots/woodchucks, mountain beavers,
opossums, and rabbits on nonagricultural sites. For purposes of this
analysis, nonagricultural sites have been defined as areas which are not
involved in the direct production of crops or livestock. They include
structures, premises, embankments, nonagricultural turf areas and private
forest areas (Table IV-6).
Very little data are available to estimate the overall use of strychnine
on these sites. Most of the strychnine use on nonagricultural sites appears
to be for below-ground control of pocket gophers and moles in turf. These uses
are not part of this RPAR. Lesser quantities are used indoors (Non-RPAR) to
control house mice. Most of the outdoor, above-ground strychnine use is
restricted to ground squirrel treatments on embankments and turf areas and
control of porcupines.
Federally registered alternatives for rats and mice include compound 1080,
zinc phosphide, diphacinone, chlorophacinone, warfarin, carbon disulfide
and methyl bromide. Zinc phosphide is federally registered for control of
cotton rats and kangaroo rats. For ground squirrel control, federally
registered alternatives include gas cartridges and carbon disulfide. Compound
1080, zinc phosphide, diphacinone, methyl bromide, Warfarin, Fumarin, Pival,
and chlorophacinone are registered in some states for ground squirrel control.
If strychnine were to be cancelled for use on nonagricultural sites, some
increased incidences of ditch bank, levee, and canal washouts are likely,
particularly if compound 1080 were also to be cancelled. Each incidence of
major failure of a canal, levee, or ditch bank can cost in excess of $10,000 to
repair. The estimated total increased incidence of this damage is not known
however. No other significant user impacts are anticipated if above-ground,
outdoor uses of strychnine for control of rodents on nonagricultural sites are
cancelled.
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Table IV-6
Major Pests on Nonagricultural Sites Controlled
With Strychnine
Nonagricultural Sites
Major Target Pests
(outdoor, above ground)
Structures, Premises and Related Sites —
Grain elevators
Other crop storage areas and facilities
Coomercial buildings and warehouses
Farmsteads
Urban dwellings
Embankments
Ditch banks
Levees
Dikes
Canals
Earthen dams (small)
Nonagricultural Turf Areas
Golf courses
Parks
Cemetaries
Athletic fields
Recreational areas
Airport turf runways
Military bases
Forest Areas (privately owned)
Tree nursery
Tree plantations
Reforestation areas
House mice
House mice
House mice
House mice
House mice
Ground squirrels
Ground squirrels
Ground squirrels
Ground squirrels
Ground squirrels
Ground
Ground
Ground
Ground
Ground
Ground
Ground
squirrels
squirrels
squirrels
squirrels
squirrels
squirrels
squirrels
Ground squirrels, rabbits
Ground squirrels, porcupines,
rabbits
Ground squirrels, porcupines
I/
The strychnine RPAR applies only to outdoor, above-ground uses. Thus,
strychnine is assumed to be registered for use inside structures and
related sites.
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V. Risk/Benefit Analysis and Regulatory Options
A. General
The previous two sections have examined the risks and benefits of using
strychnine for the control of mammals and birds on rangeland and pasture sites,
croplands, and nonagricultural sites. The purpose of this chapter is to
compare the risks and benefits for each use, and to evaluate possible
regulatory options. Since the risk and benefit data do not always allow for
specific site/pest analysis (e.g. jackrabbits on cropland, linnets on
cherries), the evaluation will, for the most part, be presented in general
terms.
Certain points are important in the risk/benefit evaluation. These form the
key issues in developing the actions which might be taken:
1. Actions to be taken,are determined by the existence of risks, not the
absence of benefits.
2. The use of a substitute must not increase the risks relative to the
benefits.
3. Risk mitigating and risk reducing measures must be economically
feasible and viable.
B. Risk/Benefit Analysis
1. Rangeland Rodents
The use of strychnine for the control of ground squirrels, prairie dogs and
other rodents and lagomorphs on rangeland and pastures presents a risk to non-
target birds and mammals, both from primary and secondary poisoning. The
Hegdal and Gatz study demonstrated the risk of primary poisoning by documenting
the kill of the majority of the territorial horned larks as well as a number of
other birds in a ground squirrel treatment area. Also, the LDcn data
presented in Section III demonstrated the potential for nontarget seedeating
wildlife to ingest a lethal dose of treated grain.
The secondary risks associated with controlling ground squirrels appear to
be slight. The relatively high ID™ of the ground squirrel suggests that
little strychnine would generally remain in the gut for ingestion by a
predator. The relatively low LDfrn of the prairie dog, however, suggests that
for this mammal the possibility or secondary risks to nontarget species does
exist. The black-footed ferret, an endangered species that lives with and
feeds on the prairie dog, would be especially susceptible.
The risks of controlling other rodents and lagomorphs are -similar to those
for ground squirrels and prairie dogs. The difference is one of degree, since
less than one percent of the strychnine bait used annually is for controlling
mammals other than ground squirrels and prairie dogs.
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No comprehensive estimates are available to document rangeland and pasture
damage caused by rodents and lagomorphs. Damage estimates, although largely
unsubstantiated, generally provide an indication that a pest problem does exist
and that control is believed to be required.
For ground squirrel control, the increased costs from using alternatives
could range from $900,000 to $1.5 million annually, depending on the
availability of compound 1080 (currently used in two states). For prairie dog
control, the use of the zinc phosphide, the most likely alternative, could
result in a slight cost reduction. Due to data limitations, estimates for
other rodents and lagomorphs are not available.
Strychnine is not used extensively for rodent and lagomorph control on
rangeland. Although this use accounts for approximately 45 percent of the
strychnine bait used, approximately 0.02 percent of the grazing acreage in the
48 contiguous States is treated annually for ground squirrels and less than
0.01 percent is treated for prairie dogs.
The alternatives for ground squirrel control are few. Only fumigants are
federally registered and they are generally used only for spot controls. Zinc
phosphide is available for prairie dogs. As shown in the risk analysis, the
available alternatives for rangeland rodent and lagomorph control all present
a direct risk to nontarget wildlife, but, with the exception of compound 1080
(registered in three states) and possibly DPN, do not present a risk of
secondary poisoning as does strychnine.
Although the geographical extent of the risks and benefits are limited,
they may be locally significant. The risks are of particular importance when
the nontarget wildlife includes one or more endangered species. The following
is a listing of the endangered species potentially at risk for each rangeland
use:
o pest - ground squirrel
o endangered species - Utah prairie dog, California condor, black-footed
ferret, San Joaquin kit fox, gray wolf, grizzly
bear, Aleutian Canada goose, peregrine falcon
o pest - prairie dog
o endangered species - black-footed ferret, gray wolf, grizzly bear
o pest - kangaroo rat
o endangered species - Utah prairie dog, masked bobwhite, San Joaquin
kit fox
o pest - cotton rat
o endangered species - red wolf, dusky seaside sparrow, Cape Sable
sparrow, Mississippi sandhill crane, Attwater's
greater prairie chicken, black-footed ferret
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o pest - jackrabbit
o endangered species - Utah prairie dog, San Joaquin kit fox, Morro Bay
kangaroo rat, red wolf, masked bobwhite,
Attwater's greater prairie chicken, black-footed
ferret
With the exception of the Aleutian Canada goose and the peregrine falcon,
both the USDI and the Agency believe the above ground use of strychnine, as
presently registered, is likely to jeopordize the continued existence of the
endangered species listed above. The Agency believes this same risk applies to
the goose and the falcon.
No above ground rangeland uses of strychnine are known to occur in the
.ranges of the salt marsh harvest mouse, the masked bobwhite, the California
condor, the Mbrro Bay kangaroo rat, the red wolf, the gray wolf, the grizzly
bear, the dusky seaside sparrow, or the Cape Sable sparrow. In the case of an
endangered species, however, the Agency believes the potential for exposure is
sufficient basis for concern. The benefits of use in their ranges are
apparently negligible since strychnine is not currently being used.
Although strychnine may be used in the range of the Utah prairie dog for
rodent and lagomorph control, less than one percent of the strychnine bait is
used in Utah.
The winter range of the Aleutian Canada goose overlaps that of the
California ground squirrel. Most ground squirrel control in California is
accomplished with compound 1080, however, and the winter residence time of the
goose in California does not generally coincide with the time of ground
squirrel baiting.
The use of strychnine in the range of the black-footed ferret is relatively
extensive, since it may be found wherever prairie dogs exist. Strychnine may
also be used in the range of the San Joaquin kit fox for ground squirrel and/or
jackrabbit control.
2. Cropland Rodents
The risks of using strychnine for the control of rodents and lagomorphs on
cropland are the same as those for use on rangeland. The amount of bait used
is essentially equal (227,400 Ibs. for rangeland vs. 209,900 Ibs. for
cropland).
As with rangeland use, the benefits are stated in terms of the cost
differential of using an alternative should strychnine be cancelled. For
ground squirrel control, the cost would increase by an estimated $1.4 to $1.6
million annually. For prairie dog control, the cost could increase by an
estimated $290,000 if fumigants were to be used. Due to data limitations,
estimates for the control of other rodents and lagomorphs are not available.
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The endangered species potentially at risk from the above ground use of
strychnine for the control of rodents and lagomorphs on croplands are the same
as those at risk from rangeland use.
3. Nonagricultural Site Rodents and Lagomorphs
No specific risk data were available for this use. A reasonable
assumption, however, is that a risk to nontarget organisms does exist. In
particular, all of the endangered species mentioned under the preceeding
rangeland and cropland manmal categories could potentially be exposed to
strychnine bait. Additionally, the salt marsh harvest mouse, yellow-shouldered
blackbird, and Puerto Rico plain pigeon could be exposed, although no
strychnine uses are known to occur in their ranges. This potential for
exposure is a result of the wide range of site/pest uses in this category.
No benefit data are available, other than for the use of ground squirrel
control on canals, levees, and ditch banks. Each canal, levee, or ditch bank
failure can result in repairs costing at least $10,000, but the total cost of
all repairs is not known. Also unknown is the increase in the number of
repairs that could be anticipated should strychnine registration be cancelled.
4. Cropland Birds
Use of strychnine to control birds on croplands accounts for approximately
3.6 percent of strychnine use. Only three State registrations exist for this
use, and two are for magpie control only. California accounts for virtually
the entire usage of strychnine for the control of bird depredation on
cropland.
No specific information is available on the risks associated with these
uses. A reasonable assumption, however, is that some primary and secondary
risks to nontarget species do exist. The Agency does not believe any
endangered species are at risk from the use of strychnine to control cropland
birds.
Benefit data are limited to California, and are not available for all
individual crops. Only an estimated 0.4 percent of the total cropland in
California is treated with strychnine for control of birds. Crop losses, if
strychnine were to be cancelled and no alternative were used, could increase by
an estimated $1.5 million annually. As stated in Section IV, the total
California cropland production is valued at an estimated $5.5 to $6.0 billion
annually.
5. Nonagricultural Site Birds
Approximately 6.2 percent of the strychnine bait is used to control pigeons
and house sparrows on nonagricultural sites. Virtually all of this bait is
used for pigeon control.
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No specific risk information is available for this use with the important
exception of a risk to raptors. A reasonable assumption, as with all uses of a
toxicant such as strychnine, is that a risk to nontarget species does exist.
The data on raptor kills are evidence of a risk to the peregrine falcon. Also,
although no uses of strychnine are known to occur in Puerto Rico, the yellow-
shouldered blackbird and the Puerto Rican plain pigeon could be at risk from
this use.
Benefit information is similarly lacking for this use. Other chemicals are
available, but they do not provide the fast-acting control believed to be
necessary for public health protection.
C. Regulatory Options
1. Rangeland Rodents - ground squirrels
Option - No Action
With this option, the potential for risks to nontargets, including
certain endangered species, would continue unabated. The benefits would be
similarly unaltered.
Option - Cancellation
Adoption of this option would eliminate the risks of the use of
strychnine for ground squirrel control on rangeland and pastures. The lack of
economically feasible alternatives could produce a locally significant increase
in control costs. Also, the risks of control would not be completely
eliminated, since compound 1080 and fumigants, the most likely alternatives,
have risks associated with their use. The risk of secondary poisoning would be
eliminated if fumigants are used, but the risk of direct effects to nontarget
species would still exist. Also, an increase in the use of fumigants could
result in an increase in human risks.
Option - Modification of the Terms and Conditions of Registration
The general conclusion of the risk assessment for most uses of strychnine
was that available evidence did not now permit the Agency to conclude that
substantial risks to nontarget wildlife would generally occur if proper
precautions are taken and if due concern is given to protect endangered
species. Some nontarget mortality is to be expected from all uses. Certain
use modifications, however, could reduce the risks to an acceptable level.
These risk reduction measures must not reduce usage to the point of eliminating
the benefits, since this would result in an implicit cancellation.
In addition to the use of dyed bait, discussed in Section II, other general
procedures may be appropriate for reducing risks from the use of strychnine in
vertebrate pest management. General reductions of risks are possible through
changes in the characteristics of the bait formulations and the procedures for
use. For the protection of endangered species, the major methods of risk
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reduction are changes in where and when a bait can be used. The following
discussion elaborates on these methods.
Bait Formulations
A wide variety of strychnine bait formulations are in use and it seems
apparent that the balance between efficacy and safety can be improved. The
characteristics of the bait formulations that can be manipulated include the
concentration of the toxicant, the attractiveness of the bait to nontarget
species, and the persistence of the bait. The following discussion illustrates
the problems and potential solutions.
A common formulation for pigeon control contains 0.6 percent strychnine on
whole corn1. Since the ID™ for the pigeon is about 15 mg/kg, ingestion of
about two g bait per bird should give adequate efficacy (Faulkner, 1964
estimates that six kernels are adequate). With proper prebaiting, a hungry
pigeon may quickly ingest one ounce or more bait (30 g). A substantial
reduction in the concentration of strychnine in the bait could probably be made
with no loss of efficacy. The observations of Hegdal and Gatz (1977) indicate
that the level of strychnine in poisoned doves decreased with the concentration
of strychnine remaining on the bait. It see;ns probable, therefore, that risks
can be reduced by altering bait formulations but the lowest level of strychnine
that will maintain adequate efficacy must be determined.
As discussed in Section II, several rebuttals of the Agency's presumption
of risk indicated that dyeing the bait inhibited its consumption by birds.
From the available evidence, the Agency could not conclude that the efficacy of
this procedure had been established. In principle, however, making the bait
less attractive to nontarget species has much merit. Further development of
this concept is desirable.
If a resident target individual is not killed by strychnine the first time
it consumes the bait, it is less likely to be killed by subsequent feeding
because of bait aversion. In general, persistence of acutely toxic baits
beyond the first few days of exposure does not contribute significantly to the
success of the control effort but, as indicated by the observations of Hegdal
and Gatz (1977a), nontarget immigrants or transients may continue to suffer
mortality. ^ bait that could remain relatively stable for a few days and then
rapidly lose its toxic properties could serve to reduce risks that occur after
the control operation is effectively complete.
Application Procedures
During a control effort, factors which may alter the risk to nontarget
organisms include the application rate, the frequency of application and the
method of distributing bait (broadcast vs. spot treatment with or without
prebaiting). These variables are largely under the control of the operator and
involve decisions that affect efficacy, efficiency and other cost/benefit
considerations. These are important components of the management strategy.
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Assuming that population reduction is necessary, if just the right amount
of suitable bait could be placed so that at the economic threshold, every
individual in the target population was likely to be killed with little or no
bait remaining, the risks would be minimized and the benefits, in terms of long-
term damage reduction, would be maximized. There are practical limitations
to achieving such a goal but improvement over the present situation with regard
to various uses of strychnine is desirable.
The Agency has no present legal or factual basis to prescribe general
curatives for risk situations that result from less than optimal management
decisions to use strychnine in accordance with the label. The development and
use of management systems that minimize risks, however, would tend to forestall
any future findings of unreasonable adverse effects from the use of strychnine
and other vertebrate toxicants.
Temporal Restrictions
Some populations of endangered species are migratory; hence, individuals
are at risk from the use of strychnine only during the time of year when use
coincides with their presence. For example, Arctic peregrine falcons may be
present in any of the 48 contiguous states during the period of migration -
generally from mid-March through April and from mid-September through October.
If uses of strychnine that would lead to the presence of poisoned birds were
prohibited during those periods, risks to this peregrine falcon would be
substantially reduced in areas that do not support a breeding population.
Geographic Restrictions
Many endangered species have highly restricted distributions. Prohibiting
the use of strychnine within the areas likely to be occupied - with an added
buffer zone if necessary - could effectively eliminate the potential for
exposure. The scale of the restriction, whether micro- or macrogeographic,
would vary with circumstances concerning the predictability of the species'
presence and needs to prevent disclosure of the locations of individuals.
Thus, the Agency believes four general risk reduction measures have the
potential for reducing risks without affecting the benefits. These are: 1) a
reduction of the concentration of the active ingredient in the bait, 2)
standardization of bait and post-baiting procedures to protect nontarget
species, 3) use of dyed baits to repel nontarget seedeaters, and 4) a
prohibition of use of the pesticide where or when a significant potential
exists for exposure to endangered species.
A fifth measure, integrated pest management (IPM), was investigated as a
possible risk reduction method. The goal of IPM is to reduce, if not
eliminate, the dependency on chemicals and still achieve the degree of pest
control believed to be necessary. This could be through habitat manipulation,
introduction of another species (e.g. a predator), and/or an optimal use of the
chemical. The optimal use of a chemical requires exposing the target species
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to the amount necessary to be fatal, at the time when it is most likely to
ingest the bait. This would minimize the bait exposure to nontarget species.
The application of possible IPM methods as substitutes or risk reduction
measures was discussed with authorities within the Agency, the environmental
community, and private enterprises. All believed that this was a desirable
area for research and an ideal application of IPM.
Unfortunately, no data were found to form a basis for an IPM option. IPM
programs are currently feasible only where there is sufficient knowledge of
those parameters involved and when it is possible to exercise control over the
parameters. A knowledge of all relevant factors within the ecosystem is
mandatory to assure not only the intended results but to preclude any adverse,
unintended results. Such information has not been developed for the situations
in which strychnine is used. Most IPM work to date has been confined to insect
control on specific crops.
The control of mammals and birds on larger areas using IPM techniques is a
matter for further research. Range management techniques are being investi-
gated by the Agency and, when available, will be evaluated. Implementation of
an IPM program presents further problems. For example, even if a program is of
demonstrated feasibility its use cannot be mandated, only stimulated through
the elimination or restriction of conventional alternatives.
Therefore, the Agency does not believe that IPM is a fea-sible option for
reducing the risks associated with the use of strychnine at this time. It
will, therefore, not be considered for this use, ground squirrels on rangeland,
or the others under investigation in this document. The other four measures
will be developed under this use and the discussions will be applicable, when
noted, for the other site/pest uses.
o Reduction of active ingredient concentrations -
The registered labels of strychnine specify a range of concentrations
and use instructions for the various site/pest combinations. On the theory
that such formulations are designed to be cost-effective, all of the labels
except the one with the lowest concentration/dosage combination would appear to
contain more strychnine than necessary.
Risks to nontargets from strychnine bait could then be reduced
without reducing .benefits by standardizing all labels to conform to the one
with the least amount of poison per application. For the control of ground
squirrels on rangeland, the bait would have an active ingredient concentration
of 0.20 percent and a dosage of one level tablespoon to cover one-two square
feet, as per accession number 11150-08490, for Riverside County, California.
o Standardization of baiting and post-baiting procedures -
As with the previous risk reduction method, the Agency is assuming a
lower exposure with no impact on benefits. The procedures were taken from
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currently registered labels, and the rationale is the same as for the reduction
in active ingredient concentrations, i.e. standardization of best current
practice.
For the control of ground squirrels on rangeland, the procedures to be
followed are:
do not expose bait where pets, poultry, or livestock are
present
do not place bait in piles
pick up and burn or bury dead animals
o Use of dyed bait -
The rebuttal analysis discussed the use of dyes in bait as a deterrent
to feeding by birds during rodent and lagomorph control operations. From an
examination of available data, the conclusion was that some risk reduction from
dyed baits would be possible for some species of birds. The data were not
sufficient to detail the type or color of the dye, nor to predict the bird
species that would be protected. No evidence was presented that argued against
the use of dyes either due to a reduction in efficacy or to being an attractant
to nontarget species. An unpublished report by Palmateer (1980) suggests that
some dyes may reduce acceptance by target species. The increased cost involved
with producing dyed baits versus undyed is approximately one cent a pound, an
increase of less than 0.5 percent.
The durability of the dye in the environment, the effectiveness of dye
as a repellent, the time required for a bird to overcome a reluctance to ingest
the dyed bait, and the overall risk reduction effects are all unknown. A
requirement that bait used for rodent and lagomorph control be dyed in
accordance with recommendations of the Fish and Wildlife Service could reduce
the primary and secondary risks to nontarget organisms. The impact on
benefits is anticipated to be negligible.
o Prohibition of use in the range of endangered species -
1. Utah prairie dog
A critical habitat has not been determined for this species. An
estimated 5,700 members live in a six-county area in South Central Utah.
This is apparently the permanent residence of the Utah prairie dog. Thus, use
of strychnine in this area for rodent control at any time could endanger its
existence. Theoretically, baiting might be done safely during the period of
hibernation, but the Agency has no information that would permit it to
conclude that all of the bait would deteriorate during the winter period.
Since the range of this species is apparently contained within
the six counties of Garfield, Iron, Kane, Piute, Sevier, and Wayne, and since
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no temporal restrictions are applicable, the only enforceable alternative for
the protection of the Utah prairie dog is prohibition of strychnine use within
this region. Such a prohibition of use would eliminate the risk to the Utah
prairie dog associated with the registered use of strychnine. Since very
little use is made of strychnine for rodent control in this region, no impact
on benefits would be anticipated.
2. California Condor
A critical habitat has been determined for this species. The
estimated population of approximately 30 members inhabits an area in the
Central California. Although most ground squirrel control efforts in
California utilize compound 1080, almost 100,000 Ibs. of strychnine bait are
also used. Additionally, over 18,000 Ibs. of strychnine bait is used in
California for bird control.
The risk to the condor from the use of strychnine is apparently
slight. The only major uses of strychnine in the condor's range are for pocket
gopher, horned lark, and finch control. The use of strychnine for pocket
gopher control is not considered in the RPAR action, and, as discussed in
Section III, the risk to the condor from the use of strychnine for the control
of birds on cropland is generally low.
The benefits of strychnine would increase if compound 1080 were
cancelled for ground squirrel control. Tne risks to the condor for strychnine
could also increase substantially. For the condor, the loss of one member
would be excessive, given its population status. Prohibition of use in the
range of the condor would eliminate the risks to the condor from the use
strychnine and have no impact on benefits.
3. Black-footed Ferret
The risk to the black-footed ferret from prairie dog control was
discussed on page 31. The question to be addressed in this part is the action
to be taken in the areas where prairie dogs and ground squirrels occupy the
same area. As previously mentioned, this question was not addressed by USDI
in their report to EPA (Appendix D). The primary problem is with the white-
tailed prairie dog, whose populations are sometimes intermixed with those of
ground squirrels.
For the states affected, (Wyoming, and to a lesser extent Utah
and Colorado) ground squirrel control accounted for 23,115 pounds of strychnine
bait in 1977-78. Wyoming, with a majority of the white-tailed prairie dogs,
used 11,800 pounds. The total .amount of strychnine bait for ground squirrel
control for all states in this period was 337,230 pounds.
If the use of strychnine for ground squirrel control were to be
prohibited in the range of the prairie dog, fumig; its or anticoagulants would
have to be used for control. Use of fumigants would eliminate the
secondary risk to the ferret, but the potential for such effects from the use
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of anticoagulants is uncertain. Either would increase ground squirrel control
costs.
A lesser action would be prohibition of strychnine use for ground
squirrel control within any county where the black-footed ferret has been
sighted since 1973, the year of enactment of the Endangered Species Act. The
use of strychnine in any area where a ferret has been sighted implies a risk of
a prairie dog ingesting the poison and a subsequent risk to the ferret from
eating a poisoned prairie dog. This is based on the knowledge that the ferret
is closely associated with the prairie dog.
A third alternative would be to prohibit use of strychnine for
ground squirrel control within some distance of a prairie dog town. If a town
is not definable, the locus would be an active prairie dog burrow.
4. San Joaquin Kit Fox
A critical habitat has not been determined for this species. The
current population is located in certain areas in the San Joaquin Valley,
portions of which are included in the range of the California ground squirrel.
The current risk to the kit fox from strychnine is not high,
since compound 1080 is the primary control method for ground squirrel control
in California. Should compound 1080 be cancelled, however, the use of
strychnine could increase.
Prohibition of the use of strychnine within the range of the San
Joaquin kit fox would eliminate the risk from this pesticide to the kit fox.
The current benefit impacts of prohibition are not known but are expected to be
negligible.
5. Gray Wolf
A critical habitat has been determined only for that portion of
the gray wolf population in Minnesota. The present use of strychnine does
not pose a serious threat to the gray wolf, as it is rarely if ever used in its
range. USDI did not define a range for this species, but recommended
prohibition of strychnine use in known gray wolf areas. This option would
apparently have no impact on benefits.
6. Grizzly Bear
Areas in four states, Montana, Wyoming, Idaho, and Washington,
have been identified as important grizzly bear habitat. Several National
Forests, Indian Reservations, National Parks and Wilderness areas are included
in this habitat.
The use of strychnine in the range of the grizzly appears to be
very small, if used at all. A prohibition of use of strychnine within known
grizzly bear areas would virtually eliminate the risks from the use of
strychnine and have no impact on benefits.
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7. Aleutian Canada Goose
A critical habitat has not been determined for this species. Its
migration route in the fall includes the northwestern California coast and
interior California valleys. In early spring, they migrate back to the
Aleutian Islands.
While total prohibition of strychnine use in the migratory range
does not seem warranted, one of two options would be advisable. These would be
to prohibit baiting in its California range or prohibit baiting in its
California range only during the months of October through April.
8. Peregrine Falcon
At this time, the only method of reducing the risk to the
peregrine falcon from ground squirrel control would appear to be from the
dyeing of bait. The optimal time for controlling ground squirrels generally
coincides with the period of spring migration, making a temporal or geo-
graphical use restriction unfeasible. The risk to peregrines from this use
appears to be relatively low, however.
2. Rangeland Rodents - prairie dogs
Option - No Action
With this option, the potential for risks to nontargets, including
certain endangered species, would continue unabated. The benefits would be
similarly unaffected.
Option - Cancellation
The effect of this option would be an elimination of risks from the
use of strychnine for prairie dog control on rangeland and pasture.
Zinc phosphide, the alternative most likely to be used if strychnine
is cancelled for this use, is of approximately equal efficacy and cost. The
risks to gallinaceous birds (and possibly geese and rabbits) are apparently
greater from zinc phosphide than strychnine. Otherwise, zinc phosphide poses
little demonstrated hazard to other wildlife species when properly used.
Risks of secondary poisoning are also generally essentially eliminated. Of
particular importance, the toxic risk to the black-footed ferret is virtually
eliminated, since secondary poisoning would no longer be likely. Destruction
of the ferret's habitat - prairie dog towns - would still be of concern.
Option - Modification of the Terms and Conditions of Registration
o Reduction of active ingredient concentration (see discussion under
"Rangeland Rodents-ground squirrels" on page 80) -
-------
For the control of prairie dogs on rangeland, the bait would have an
active ingredient concentration of 0.35 percent and a dosage of two teaspoons
per square foot (as per EPA registration number 6704-57).
o Standardization of baiting and post-baiting procedures -
The discussion under "Rangeland Rodents-ground squirrels" for this
method is applicable here also.
o Use of dyed bait -
The discussion under "Rangeland Rodents-ground squirrels" for this
method is applicable here also.
o Prohibition of use in the range of endangered species -
The discussions under "Rangeland Rodents-ground squirrel" for the gray
wolf and the grizzly bear are applicable here. A prohibition of use for
prairie dog control within the range of black-footed ferret, however, would
amount to a cancellation, since the precise range of the black-footed ferret is
not known, but can be assumed to be wherever the prairie dog exists.
3. Rangeland Rodents - other rodents and lagomorphs (kangaroo rats,
cotton rats, deer mice, meadow mice, jackrabbits, chipmunks, woodchucks)
Option - No Action
With this option, the potential for risks to nontargets, includiung
certain endangered species, would continue unabated. Tne benefits would be
similarly unaffected.
Option - Cancellation
This option would eliminate the risk from the use of strychnine for
the control of rodents and lagomorphs on rangeland. Very little strychnine
bait is used for this purpose (less than one percent of the total usage), and
only the cotton rat, kangaroo rat, and jackrabbit cause enough damage to
require regular control. Cancellation would therefore have impacts only on a
local level. Alternatives are limited, but zinc phosphide is federally
registered for control of cotton rats, deer mice and meadow mice. Gas
cartridges are federally registered for woodchucks, and Thiram is federally
registered for chipmucks. Cancellation would result in an increase in losses
in local situations, particularly from pests for which no federally registered
toxic alternatives exist (i.e. jackrabbbits, chipmunks and kangaroo rats).
Option - Modification of the Terms and Conditions of Registration
o Reduction of active ingredient concentration (see discussion under
"Rangeland Rodents-ground squirrels" on page 80) -
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For the jackrabbit, the concentration would depend on whether a grain
or green bait were used. If a grain bait is used the concentration would be
0.28 percent and the dosage would be one tablespoon (as per accession number
11224-08504 for Tulare County, California). If a green bait is used, the
concentration of strychnine would be 0.1$ (one ounce on three Ibs.) and the
dosage would be four to five alfalfa shoots (as per accession number 11198-
05260 for Sonoma County, California).
Chipmunk bait would have a concentration of 0.50 percent and a dosage
of one pound per 10-15 acres (as per EPA registration number 6704-58).
Meadow mouse and deer mouse bait would have a concentration of 0.20
percent with a dosage of 10-15 Ibs/acre (as per accession number 11165-08602
for San Benito County, California).
Woodchuck bait would have a concentration of 0.50 percent and a
dosage of one teaspoon (as per EPA registration number 728-74).
Kangaroo rat and cotton rat bait would have a strychnine concentration
of 0.16 percent. The dosage would be three-four tablespoons if applied by hand
or 1/2-3/4 pound per swath-acre if mechanically applied (both the concentration
and dosage are as per accession number 11231-05307 for Ventura County,
California).
o Standardization of baiting and post-baiting procedures -
The discussion under "Rangeland Rodents-ground squirrels" for this
method is applicable here also.
o Use of dyed bait -
The discussion under "Rangeland Rodents-ground squirrels" for this
method is applicable here also.
o Prohibition of use in the range of endangered species -
The discussions under "Rangeland Rodents-ground squirrels" for the
Utah prairie dog and San Joaquin kit fox are applicable here also.
1. Masked Bobwhite
No critical habitat has been determined for this species. An
attempt is being made to reintroduce masked bobwhites in Arizona. The
locations are in two valleys, the Altar Valley in Pima County and the Santa
Cruz Valley in Santa Cruiz and Pima Counties. These counties are included in
the ranges of the jackrabbit and kangaroo rat. Although there is no evidence
of strychnine use in these ranges, the possibility does exist. Also, since
efforts are underway to establish a population, any use would be posing an
unacceptable risk. No alternative toxicants are available for the jackrabbit
and kangaroo rat.
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2. Red Wolf
No critical habitat has been determined for this species. The
range appears to be limited to three counties in Texas (Chambers, Orange, and
Jefferson) and two parishes in Louisiana (Cameron and Calcasieu). These
counties are included in the range of the cotton rat and possibly the
jackrabbit. While no known Federal or State control programs occur in the
range of the red wolf, some commercial uses may exist. Since the extent would
be limited, no impact on benefit would be anticipated and the risk would be
eliminated by prohibition of use in it's range. Use of zinc phosphide for
controlling cotton rats would reduce risks to the red wolf without affecting
benefits.
3. Dusky Seaside Sparrow
The critical habitat has been determined for this species. The
sparrow inhabits salt marshes in Florida on Merritt Island and on the
mainland near Titusville. The only target organism in this area is the cotton
rat. Since most of the birds inhabit federally controlled lands, the chance
of their encountering strychnine is slight.
Since the areas inhabited are apparently the permanent residence
for this bird, no temporal use restrictions are possible. Also, the apparently
low probability of use indicates prohibition within the range would not result
in any benefit impacts. The relative toxicity of zinc phosphide is not
predictable for this species, but its registered use in cotton rat infested
areas could increase the risk to this sparrow. Chlorophacinone is registered
in Florida for the control of cotton rats and would appear to pose very little
risk to this sparrow.
4. Cape Sable Sparrow
A critical habitat has been determined for this species. The
sparrow is found only in a few herb and brackish marshes in .Southwest Florida.
No strychnine use is known to occur in its habitat at this time although it is
included in the range of the cotton rat. The lack of use indicates a lack of
impact on benefits if prohibition is imposed. This habitat appears to be a
permanent residence, making anything less than total prohibition in its range
ineffective for risk reduction. The relative toxicity of zinc phosphide is not
predictable for this species, but its registered use in cotton rat infested
areas could increase the risk to this sparrow. Chlorophacinone is registered
in Florida for the control of cotton rats and would appear to pose very little
risk to this sparrow.
5. Mississippi Sandhill Crane
The range of this non-migratory crane is limited to a small area
in Southern Jackson County, Mississippi. This area is within the range of the
cotton rat. A critical habitat was determined for this species. The
present population estimate for this crane is 30 to 50 members.
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Any use in the range of this species would be unacceptable due to
the small population. Benefit impacts of prohibition would be negligible, but
the elimination of risk is critical. The use of zinc phosphide, the only
available toxicant, as an alternative may or may not reduce the risks.
6. Attwater's Greater Prairie Chicken
A critical habitat has not been determined for this species. The
current population is under 2,000, and is limited to the prairies on the
Texas Gulf Coast. This area is included in the ranges of the jackrabbit and
the cotton rat. Texas uses less than three percent of the total strychnine
used by all the states, virtually all going for the control of ground squirrels
and prairie dogs. Thus, the cancellation of strychnine use in the range of the
Attwater's greater prairie chicken would have no impact on benefits. Since the
present range is the permanent residence of the chicken, no restrictions other
than prohibition of use in that range would eliminate the risks from
strychnine. Since zinc phosphide formulations are sustantially more toxic to
gallinaceous birds than is strychnine, cancellation of strychnine for cotton
rat control would increase risks to this prairie chicken.
7- Morro Bay Kangaroo Rat
Approximately 3,000 members of this species exist only in a few
square miles on the south side of Morro Bay, San Luis Obispo County,
California. Roughly one square mile of private property has been designated as
the critical habitat.
With the possible exception of the black-tailed jackrabbit,
none of the target rodents inhabit the range of this endangered species. Since
no evidence exists that strychnine is being used in the range of the Morro Bay
kangaroo rat, however, no impact or benefits should result from prohibition.
Also, no restrictions other than prohibition of use in its range would
eliminate the potential risk to the species from strychnine. Anticoagulants
are registered in California for the control of jackrabbits, and they may
or may not reduce the risks to this kangaroo rat.
4. Cropland Rodents - ground squirrels
The available options, and their impacts, are the same as for ground
squirrels on rangeland.
5. Cropland Rodents^- prairie dogs
The available options, and their impacts, are the same as for prairie
dogs on rangeland, with the important distinction that if strychnine were
cancelled, the only federally registered alternative is gas cartridges. This
increases the costs of control, but reduces the risk to nontarget species,
especially the black-footed ferret.
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6. Cropland Rodents - other rodents and lagomorphs
The available options, and their impacts, are the same as for other
rodents and lagomorphs on rangeland, with the exception that no federally
registered alternatives are available for the control of cotton rats and
kangaroo rats. Gas cartridgesare federally registered for use on woodchucks;
repellants are federally registered for jackrabbits, and anticoagulants are
available for meadow mice and deer mice.
7- Rodents and Lagomorphs on Nonagricultural Sites
Option - No Action
With this option, the potential for risks to nontarget species, including
certain endangered species, would continue unabated. The benefits would be
similarly unaffected.
Option - Cancellation
Cancellation of strychnine uses to control rodents and lagomorphs
on nonagricultural sites would eliminate the risks from strychnine to non-
target organisms. Some benefits are realized from this use, particularly for
canals and levees, but alternatives are available for the primary pest, the
ground squirrel. Alternatives most likely to be used, fumigants, are not
without risks. The risks are less than those for strychnine, however, and
secondary risks would be eliminated. Federally registered alternatives are not
available for the porcupine, jackrabbit, kangaroo rat, chipmunk, opossum and
mountain beaver.
Option - Modification of the Terms and Conditions of Registration
o Reduction of active ingredient concentration -
The discussion under the rangeland uses for this method are
applicable here also.
o Standardization of baiting and post-baiting procedures -
The discussion under "Rangeland Rodents-ground squirrels" for this
method is applicable here also.
o Use of dyed bait -
The discussion under "Rangeland Rodents-ground squirrels" for this
method is applicable here also.
o Prohibition in the range of endangered species -
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The discussion for all species under rangeland uses are applicable
here also. In addition, the salt marsh harvest mouse should be considered.
No critical habitat has been determined for this species. The range is
apparently confined to certain salt marshes and adjoining habitats around San
Francisco Bay. No known strychnine uses occur within this range. The
prohibition of use within the range should eliminate any potential risks and
have no impact on benefits.
8. Birds on Cropland
Option - No Action
With this option, the potential for risks to nontarget organisms would
continue unabated. No endangered species are known to be at substantial risk
from these uses of strychnine. Benefits would be similarly unaffected.
Option - Cancellation
This cancellation would apply to the current state registrations in
California, Nevada, and Wyoming, since strychnine is not federally registered
for these uses. Since no alternative toxicants are available, cancellation
could result in an increase in crop damage. The available alternatives are
primary repellants or frightening agents and may or may not be as effective as
strychnine, but comparisons with a toxicant are not possible.
The risks to nontarget species from strychnine would be eliminated,
and, since no alternative toxicants are available, the use of substitutes would
present less risks than strychnine.
Option - Modification of the Terms and Conditions of Registration
o Reduction of active ingredient concentration -
As with the uses of strychnine to control mammals, the registered
lables for strychine bait used for the control of birds specify a range of
concentrations. The concentrations differ not only for different birds, but
also for each bird. For the available ID™ data for passerines, a reasonable
assumption is that one concentration, namely the lowest one currently
registered, should be appropriate for all bird control operations on cropland.
The concentration would thus be 0.20 percent (as per accession number 11019-
09355 for blackbirds in Fresno County, California)-
o Standardization of baiting and post-baiting procedures -
(See the discussion under "Rangeland Rodents-ground squirrels"on
page 80.)
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For the control of birds in orchards and vineyards, the proce-
dures to be followed are:
bait must be placed in troughs no less than three inches
deep (v-shaped with ends blocked to avoid spillage).
troughs must be made removable so that they can be cleaned
out after each change of bait.
troughs must be at least four feet from ground level
placement of troughs must be made near the edge of the
affected field near the areas where the birds perch and
rest, not directly under these perching places. Placement
of troughs inside the fields must be avoided.
Expose poisoned bait sparingly - one inch deep in each trough
pick up all remaining bait at end of day; burn any bait
spillage.
pick up and bury or burn of all dead birds at the end of
each day
For the control of horned larks on crops the procedures to be followed
are:
expose bait sparsely in a depression between bedded crops
pick up remaining bait at the end of day, burn any bait
spillage
pick up and bury or burn all dead birds at the end of the
day
9. Birds - on Nonagricultural Sites
Option - No Action
With this option, the potential for risks to nontarget organisms, and
particularly to the peregrine falcon, would continue unabated. The benefits
would be similarly unaffected.
Option - Cancellation
The impact on benefits from this option would apparently be limited to
the elimination of a fast-acting control of pigeons in the case of a possible
local public health issue. Alternatives are available, but they do not provide
this benefit.
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The risks from the use of strychnine would be eliminated, and the
alternatives, with the possible exception of starlicide (registered in
California only), do not present toxic risks equal to strychnine. In
particular, the risks to the peregrine falcon from the use of strychnine for
pigeon control would be eliminated.
Option - Modification of the Terms and Conditions of Registration
o Reduction of active ingredient concentration -
(See the discussion under "Birds on Cropland" on page 90.)
For the control of pigeons on nonagricultural sites, the bait would
have a strychnine concentration of 0.6 percent as per al,l current federally
registered labels.
For the control of house sparrows on nonagricultural sites, the bait
would have a strychnine concentration at 0.25 percent (as per accession number
11198-05259 for Sanoma County, California).
o Standardization of baiting and post-baiting procedures -
(See the discussions under "Rangeland Rodents-ground squirrels".)
pick up and burn or bury any uneaten bait
where uneaten bait is not easily retrievable, place
bait in trays or v-shaped troughs
pick up and bury or burn all dead birds daily
o Prohibition of use in the range of endangered species -
1. Puerto Rican Plain Pigeon
A critical habitat has not been determined for this species. Its
range is confined to a relatively small area in east central Puerto Rico in and
around the municipalities of Cidra, Camerio, Aguas Buenas, Caguas, and Cayey.
No information is available on the use of strychnine in Puerto
Rico, but it is assumed to be negligible. No methods are available to
eliminate the risk to the pigeon, should strychnine be used, since the range
described is its permanent residence. Prohibition of use would apparently have
no impact on benefits. The only potential use would be for the control of
pigeons, and federally registered alternatives are available.
2. Yellow-shouldered Blackbird
A critical habitat has been determined for this species. The
bird is concentrated in three areas in Puerto Rico, coastal Southwestern Puerto
Rico, coastal Northeastern Puerto Rico, and Mona Island. As with the Puerto
Rican plane pigeon, the extent of strychnine use in the area of the blackbird
is not known, but is assumed to be insignificant. Thus, no impact on benefits
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is anticipated from any action taken. The only option for eliminating risks
would be prohibition of use. The only potential use would be for the control
of pigeons, and federally registered alternatives are available.
3. Peregrine Falcon
The potential for risk to the peregrine falcon from
secondary poisoning is of particular concern during strychnine baiting for
pigeon control. The Arctic peregrine's migration route could bring it through
any of the lower 48 States. The American peregrine breeds west of the
Mississippi River, but its migratory patterns are not well documented.
The potential for peregrine falcons to be exposed to strychnine
during pigeon control operations varies geographically. In the eastern part of
the country, the urban location of falcons that have been established as a
result of the restoration program are generally well known. The risks can thus
be greatly reduced by prohibition of use of strychnine for pigeon control
within a five mile radius of aeries.
In the Rocky Mountain Region, most potential exposure to
peregrines from pigeon control is to falcons that winter in or near urban
areas. A prohibition of use for pigeon control during the winter months would
therefore greatly reduce the risk to the falcon.
In California, a critical habitat has been established for the
peregrine falcon. Adults are apparently permanent residents in California,
Oregon, and Washington. A prohibition of use for pigeon control within a
five mile radius of the critical habitat would greatly reduce the risk to the
peregrine falcons.
Prohibition of use for pigeon control nationwide from mid-March
through April and, from mid-September through October would protect most Arctic
migrants.
D. Proposed Action
1. Rangeland Rodents - ground squirrel
The Agency proposes adoption of the modification of the terms and
conditions option. The lack of alternatives, the potential impact on benefits,
and the potential for risk reduction, particularly to endangered species, are
the major factors in this proposed action. With certain risk reduction
measures, the Agency concludes that the benefits will outweigh the risks.
For this use, then, the Agency proposes the following modifications:
a. Standardize bait concentrations of 0.20 percent active ingredient,
and a dosage of one level tablespoon/burrow
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b. Standardize baiting and post-baiting procedures to read:
do not expose bait where pets, poultry, or livestock are
present
do not place bait in piles
pick up and burn or bury all dead animals
c. Use bait dyed in accordance with recommendations of the Fish and
Wildlife Service
d. Prohibit use for the protection of endangered species as follows:
species
Utah prairie dog
California condor
prohibited area
Garfield, Iron, Kane, Piute, Sevier, and
Wayne Counties, Utah
Fresno, Kern, Kings, Los Angeles, Merced,
Monterey, San Benito, San Luis Obispo, Santa
Barbara, Santa Clara, Santa Cruz, Stanislaus,
Tulare, and Ventura counties, California
within one mile of a prairie dog town or an
active prairie dog burrow
Alameda, Contra Costa, Fresno, Kern, Kings,
Merced, Monterey, San Benito, San Joaquin,
San Luis Obispo, Santa Barbara, Santa Clara,
Stanislaus, and Tulare counties, California
known gray wolf areas
known grizzly bear areas
Butte, Colusa, Contra Costa, Del Norte, Glen,
Humboldt, Mendocino, Merced, San Joaquin,
Solano, Stanislaus, Sutter, Yolo, and Yuba
counties, California during the months from
October through March.
Additionally, for the general protection of all endangered
species, the following will be included on all labels:
"This product must not be used in areas where adverse impact on
federally designated endangered or threatened species is likely.
Prior to making applications of this product, the user must determine
that such species are not located in or immediately adjacent to the
area to be treated. Consult your Regional U.S. Fish and Wildlife
Black-footed
ferret
San Joaquin
kit fox
Gray wolf
Grizzly bear
Aleutian Canada
goose
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Service Office (Ehdangered Species Specialist) or the local Fish and
Game Office for specific information on endangered species."
2. Rangeland Rodents - prairie dogs
The Agency proposes adoption of the cancellation of use option. The
inability to reduce the risk to the black-footed ferret and the availability of
zinc phosphide are the major factors in this proposed action. The Agency
concludes that the risks of using strychnine to control prairie dogs outweigh
the benefits, and that no risk reduction measures are available to change the
situation.
3- Rangeland Rodents - other rodents and lagomorphs
For deer mice, meadow mice, chipmunks and woodchucks, the Agency
proposes the cancellation of use option. The use of strychnine for these uses
presents a risk to non-target species. The benefits of the use of strychnine
for these pests is very low, chemical alternatives are available for all four
manmals.
For the cotton rat, kangaroo rat, and jackrabbit, the Agency proposes the
modification of terms and conditions option. The lack of specific risk
information, and the potential for reducing risks without impacting benefits
are the major factors in this proposed action.
The Agendy concludes that, with certain risk reduction measures, the
benefits of vising strychnine for this use will outweigh the risks.
For these uses, then, the Agency proposes the following modifications:
a. Standardize bait concentrations at:
for the jackrabbit, 0.28 percent with a dosage of one tablespoon for
grain bait or 0.1 percent with a dosage of four-five alfalfa shoots
for green bait; for the kangaroo rat and the cotton rat, 0.16 percent
with a dosage of three-four tablespoons for hand application or
1/2-3/4 pound per swath-acre for mechanical application.
b. Standardization of baiting and post-baiting procedures as per
the proposal for "Rangeland Rodents - ground squirrels."
c. Use bait dye in accordance with recommendations of the Fish and
Wildlife Service.
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d. Prohibit use, for the protection of endangered species, as
follows:
species
Utah prairie dog
San Joaquin
kit fox
Masked bobwhite
Red wolf
use
kangaroo rat
jackrabbit
jackrabbit
kangaroo rat
jackrabbit
kangaroo rat
jackrabbit
cotton rat
prohibited area
See "Rangeland Rodents-
ground squirrel"
See "Rangeland Rodents-
ground squirrels"
Pima and Santa Cruz
counties, Arizona
Chambers, Orange, and
Jefferson counties,
Texas; Cameron and
Calcasieu Parishes,
Louisiana
IXisky seaside
sparrow
cotton rat
Cape Sable sparrow cotton rat
Mississippi
sandhill crane
cotton rat
Attwater's greater jackrabbit
prairie chicken
Morro Bay
kangaroo rat
jackrabbit
Brevard county, Florida
Collier, Eade, and Monroe
counties, Florida
Jackson county,
Mississippi
Aransas, Austin,
Brazoria, Calhoun,
Chambers, Colorado,
DeWitt, Fort Bend,
Galveston, Goliad,
Harris, Jackson,
Jefferson, Lavaca,
Matogorda, Refugio,
Victoria, Waller, and
Wharton counties, Texas
San Luis Obispo county,
California
Additionally, for the protection of all endangered species, the
same wording for labels proposed for the control of ground squirrels on
rangeland will be applicable here also.
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Cropland Rodents - ground squirrels
The proposed action for this use is the same as for ground squirrels
on rangeland, i.e., modification of the terms and conditions of registration.
5. Cropland Rodents - prairie dogs
The proposed action for this use is the same as for prairie dogs on
rangeland, i.e. cancellation.
6. Cropland Rodents - other rodents and lagomorphs
The proposed action for this use is the same as for other rodents and
lagomorphs on rangeland, i.e. cancellation for use to control deer mice, meadow
mice, woodchucks and chipmunks, and modification of the terms and conditions of
registration for use to control cotton rats, kangaroo rats, and jackrabbits.
7. Rodents and Lagomorphs on Nonagricultural Sites
Tne only uses under this category for which the Agency concludes that
the benefits will outweigh the risks, with modifications of the terms and
conditions of registration, are ground squirrels on ditch banks, levees,
canals, and earthen dams, and porcupines in tree nursuries, tree plantations,
and reforestation areas (forests). For all other site/pest uses under this
category, the Agency proposes cancellation.
For rodents and lagomorphs on nonagricultural sites, the Agency proposes the
following actions:
rabbits and jackrabbits,
chipmunks, marmots/
woodchucks, prairie dogs,
kangaroo rats, cotton rats,
meadow mice, marmots,
mountain beavers,
opossums
ground squirrels
sites
grain elevators, crop
storage areas and
facilities, commercial
open dumps, farmsteads,
urban dwellings, ditch
banks, levees, dikes,
canals, earthen dams,
golf courses, parks,
cemetaries, airport turf
runways, military bases,
forests, reforestation
areas, tree plantations
and similar nonagri-
cultural sites
ditch banks, levees,
canals, earthen dams
action
cancel
modification of
the terms and
conditions of
registration
porcupines
forests, reforesta-
tion areas, tree
plantations
modification of the
terms and conditions
of registration
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For the control of ground squirrels, the use modifications will be identical
to those proposed for the control of ground squirrels on rangeland. For the
control of porcupines, the following modifications are proposed:
standardization of bait concentration at 5.8 percent in salt
blocks
nail salt block at least ten feet above the ground
do not use in known gray wolf or grizzly bear areas
Additionally, for the protection of all endangered species, the same
wording for labels proposed for control of ground squirrels on rangeland will
be applicable here also.
8. Birds on Cropland
The Agency proposes the adoption of the modification of terms and
conditions options. The lack of specific risks to nontarget organisms, the
apparent low risks to endangered species, the absence of comparative data on
alternatives, and the potential for local impact on benefits were the major
factors in this proposed action.
With certain risk reduction measures, the Agency concludes that the
benefits will outweigh the risks.
For these uses, then, the Agency proposes the following modifications:
a. standardize bait concentrations at 0.20 percent active ingredient
b. standardize baiting and post-baiting procedures to read:
For the control of birds in orchards and vineyards:
bait must be placed in troughs no less than three inches deep
(v-shaped with ends blocked to avoid spillage)
troughs must be made removable so that they can be cleaned
out after each change of bait
troughs must be at least four feet from ground level
placement of troughs must be made near the edge of the
affected field near the areas where the birds perch and
rest, not directly under these perching places. Placement
of troughs inside the fields must be avoided
expose poisoned bait sparingly - one inch deep in each trough
pick up all remaining bait at end of day; burn any bait
spillage
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pick up and burn or bury all dead birds at the end of each
day
For the control of horned larks on crops:
expose bait sparsely in a depression between bedded crops
pick up remaining bait at the end of day, burn any bait
spillage
pick up and burn or bury all dead birds at the end of the day
Additionally, for the protection of all endangered species, the same
wording for labels proposed for control of ground squirrels on rangeland will
be applicable here also.
9. Birds on Nonagricultural Sites
The Agency proposes the adoption of the modification of the terms and
conditions option. The lack of specific risk information (with the exception
of the risk to the peregrine falcon), the potential for eliminating the risk to
the falcon, and the benefits of potential disease control, were the major
factors in this proposed action. With certain risk reduction measures, the
Agency concludes that the benefits outweigh the risks.
For these uses, then, the Agency proposes the following modificatic >3:
a. standardize pigeon bait concentrations at 0.6 percent active
ingredient
b. standardize house sparrow bait concentrations at 0.25 percent active
ingredient
c. standardize baiting and post-baiting procedures to read:
pick up and burn all uneaten bait at the end of each day
where uneaten bait is not easily retrievable, place bait in
trays or v-shaped troughs
pick up and burn or bury all dead birds daily
d. prohibit use for the protection of endangered species as follows:
species prohibited area
Yellow-shouldered Puerto Rico
blackbird
Puerto Rican Puerto Rico
Plain Pigeon
- 99 -
-------
species prohibited area (Continued)
Peregrine falcon In the Eastern U.S: prohibit use within five
(pigeon control miles of aeries
only)
In the Rocky Mountain Region: prohibit use from
November through March
In California, Oregon, and Washington prohibit
use within five miles of critical habitats.
48 contiguous states: prohibit use during the
months from mid-September through October and
mid-March through April.
Additionally, for the protection of all endangered species, the same
wording for labels proposed for control of ground squirrels on rangeland will
be applicable here also.
E. Summary
For each use of strychnine to control a pest on an outdoor, above-ground
site, the Agency has proposed either cancellation of use, or a modification of
the terms and conditions of registration. This section summarizes those
proposed actions.
For rangeland and pasture uses, the proposed action for each pest is:
ground squirrels - modification of the terms and conditions of registra-
tion
prairie dogs - cancellation
deer mice - cancellation
meadow mice - cancellation
chipmunks - cancellation
marmots/woodchucks - cancellation
cotton rats - modification of the terms and conditions of
registration
kangaroo rats - modification of the terms and conditions of
registration
jackrabbits - modification of the terms and conditions of
registration
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-------
For cropland uses, the proposed activity for each pest is:
ground squirrels - modification of the terms and conditions of
registration
prairie dogs
deer mice
meadow mice
chipmunks
- cancellation
- cancellation
- cancellation
- cancellation
marmots/woodchucks - cancellation
cotton rats
kangaroo rats
jackrabbits
birds
- modification of the terms and conditions of
registration
- modification of the terms and conditions of
registration
- modification of the terms and conditions of
registration
- modifications of the terms and conditions of
registration
For nonagricultural site uses, the proposed action for each pest is:
jackrabbits - cancellation
chipmunks - cancellation
marraots/woodchucks - cancellation
prairie dogs
kangaroo rats
cotton rats
deer mice
meadow mice
- cancellation
- cancellation
- cancellation
- cancellation
- cancellation
mountain beavers - cancellation
opossums
rabbits
- cancellation
- cancellation
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-------
ground squirrels
porcupines
pigeons
house sparrows
- modification of the terms and conditions of
registration
- modification of the terms and conditions of
registration
- modification of the terms and conditions of
registration
- modification of the terms and conditions of
registration
- 102 -
-------
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Clayton, S.E., Agricultural Commissioner, Jan. 14, 1977. Monterey Co. Dept. of
Agric., Salinas, Calif. (30000/7 #56).
Deck. E., Coordinator, Dec. 20, 1976, Office of Environmental Quality
Activities, U.S. Dept. of Agric., Wash., D.C. (30000/7 #7).
Gal I ion, S., Environmental Protection Specialist, Dec. 20, 27, 1976. EPA Region
IX, San Francisco, California (30000/7 #8,8A).
Gauditz, I., Program Manager, Mar. 3, 1977..Forest Pesticides, Forestry
Research Center, Centralia, Wash. (30000/7 # 85).
Grisham, J.R., Commissioner, Jan 24, 1977. Siskiyou Co. Dept. of Agric.,
Yreka, California (30000/7 #58).
Harkness, B.J., President, Dec. 31, 1976. Montana Farm Bureau Federation,
Bozeman, Montana (30000/7 #57).
Hooven, E.F., Associate Professor, Jan 3, 1977. Oregon State Univ., Dept. of
Forest Science, Corvallis, Oregon (30000/7 #50).
Hoverson, R., Feb 15, 1977. Boise, Idaho (30000/7 # 95).
Humphreys, L.M., Dec. 8, 1976. Korinek Remedy Company (30000/7 #2).
Judge, T.L., Mar. 8, 1977. Office of the Governor, Helena, Montana (30000/7
#94).
Kaczor, S., Mar. 16, 1977. J.D. Ehrlich Chem. Co., Inc. (30000/7 #96).
Lou, E.E., Feb. 14, 1977. Soda Springs, Idaho (30000/7 # 63).
Lewandowski, E., Fob. 15, 1977. Boise, Idaho (30000/7 #93).
Miller, E., Feb. 15, 1977- Boise, Idaho (30000/7 #83).
Morrison, H. and W. Morrison, Feb. 25, 1977. Caldwell, Idaho (30000/7 #79).
Morrison, J., Fob. 23, 1977. Caldwell, Idaho (30000/7 #98).
Pank, L. Staff Biologist, Mar. 7, 1977. U.S. Dept. of the Interior, Fish and
Wildlife Service, Wash., D.C. (30000/7 #81).
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Roberts, B.H., Jan. 20, 1977. Weiser, Idaho (30000/7 #62).
Rogers, R., Technical Director, Mar. 3, 1977. B&G Company, Dallas, Texas
(30000/7 # IB, 1C, ID)-
Rydolius, J.A., Reforestation Supervisor, Jan. 3, 1977. Simpon Timber Co.,
Arcata, Calif. (30000/7 #51).
Sebesta, O.L., Dec. 31, 1976. Sebesta Bait Mixing Plant, Mitchell, South
Dakota (30000/7 # 39).
Spear, P.J., Acting Executive Director, Mar. 4, 1977. National Pest Control
Association, Inc., Vienna, Virginia (30000/7 #74).
Stee, R.L., Director of Regulations and Inspection Division, Dec. 27, 1976.
South Dakota Dept. of Agric., Pierre, South Dakota (30000/7 #48).
Stewart, C.W., Feb. 15, 1977. Boise, Idaho (30000/7 #71).
Stewart, D.W., Feb 15, 1977. Boise, ldaho(30000/7 #90).
Stewart, R., Feb. 15, 1977. Individual letter (30000/7 #89).
Stout, R., Feb. 15, 1977. Weiser, Idaho (30000/7 #65).
Trevcott, G., Associate Director, May 16, 1977. U.S. Dept. of the Interior,
Wash., D.C. (30000/7 #100).
Wright, K.W., Mar. 7, 1977. Modoc Co. Dept. of Agric., Alturas, California
(30000/7 #86).
U. S. GOVERNMENT PRINTING OFFICE ; 1980 — 341-085/3941
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