Risks of Imazapyr Use to the Federally Listed California Red Legged Frog (Rana aurora draytonii) Pesticide Effects Determination


Risks of Imazapyr Use to the Federally Listed
California Red Legged Frog

(Rana aurora draytonii)

Pesticide Effects Determination

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

July 20, 2007

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Primary Authors

Pamela Hurley, Ph.D., Toxicologist
Lucy Shanaman, M. S., Chemist

Secondary Review
Brian Anderson, M.E.M., Biologist
James A. Hetrick, Ph.D., Senior Scientist
Anita Pease, M.S., Biologist

Branch Chief, Environmental Risk Assessment Branch 3
Karen Whitby, Ph.D.

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Table of Contents

1.	Executive Summary	13

2.	Problem Formulation	23

2.1	Purpose	24

2.2	Scope	26

2.2.1	Degradates	29

2.2.2	Total Toxic Residues	29

2.2.3	End Use Formulations	30

2.3	Previous Assessments	30

2.4	Stressor Source and Distribution	31

2.4.1	Environmental Fate Assessment	31

2.4.2	Environmental Transport Assessment	35

2.4.3	Mechanism of Action	36

2.4.4	Use Characterization	37

2.4.4.1 Imazapyr Use Characterization in California	38

2.5	Assessed Species	39

2.5.1	Distribution	39

2.5.2	Reproduction	45

2.5.3	Diet	46

2.5.4	Habitat	46

2.6	Designated Critical Habitat	47

2.6.1. Special Rule Exemption for Routine Ranching Activities	49

2.7	Action Area	50

2.8	Assessment Endpoints and Measures of Ecological Effect	58

2.8.1	Assessment Endpoints for the CRLF	58

2.8.2	Assessment Endpoints for Designated Critical Habitat	60

2.9	Conceptual Model	62

2.9.1	Risk Hypotheses	62

2.9.2	Diagram	63

2.10	Analysis Plan	67

2.10.1 Measures to Evaluate Risk Hypotheses and Conceptual Model	67

2.10.1.1	Measures of Exposure	67

2.10.1.2	Measures of Effect	68

2.10.1.3	Action Area Analysis	70

2.10.1.4	Preliminary Identification of Data Gaps and Methods	70

3.	Exposure Assessment	71

3.1	Label Application Rates and Intervals	71

3.2	Aquatic Exposure Assessment	71

3.2.1	Modeling Approach	71

3.2.2	Modeling Inputs	72

3.2.3	Results	73

3.2.4 Existing Monitoring Data	79

3.3	Terrestrial Exposure Assessment	79

3.4	Terrestrial Plant Exposure Assessment	79

4.	Effects Assessment	82

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4.1	Evaluation of Aquatic Ecotoxicity Studies (CRLF Aquatic Phase)	84

4.1.1	Toxicity to Freshwater Fish	87

4.1.1.1	Freshwater Fish (Aquatic Phase Amphibian): Acute Exposure
(Mortality) Studies	87

4.1.1.2	Freshwater Fish: Chronic Exposure (Growth/Reproduction)

Studies	88

4.1.1.3	Freshwater Fish: Sublethal Effects and Additional Open Literature
Information	89

4.1.2	Toxicity to Freshwater Invertebrates	89

4.1.2.1	Freshwater Invertebrates: Acute Exposure Studies	89

4.1.2.2	Freshwater Invertebrates: Chronic Exposure Studies	90

4.1.3	Toxicity to Aquatic Plants	90

4.1.4	Freshwater Field Studies	92

4.2	Evaluation of Terrestrial Ecotoxicity Studies (CRLF Terrestrial Phase)	92

4.2.1	Toxicity to Birds	95

4.2.1.1	Acute Exposure (Mortality) Studies	95

4.2.1.2	Chronic Exposure (Growth/Reproduction) Studies	96

4.2.1.3	Sublethal Effects and Additional Open Literature Information	96

4.2.2	Toxicity to Mammals	97

4.2.2.1	Acute Exposure (Mortality) Studies	97

4.2.2.2	Chronic Exposure (Growth/Reproduction) Studies	97

4.2.2.3	Sublethal Effects and Additional Open Literature Information	98

4.2.3	Toxicity to Terrestrial Invertebrates	98

4.2.4	Toxicity to Terrestrial Plants	99

4.3	Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern	103

4.4	Incident Database Review	103

4.4.1	Incidents Involving Aquatic Organisms	104

4.4.2	Incidents Involving Terrestrial Organisms	104

4.4.2.1	Terrestrial Animals	104

4.4.2.2	Terrestrial Plants	104

5.	Risk Characterization	105

5.1 Risk Estimation	105

5.1.1	Direct Effects	105

5.1.1.1	Direct Acute Risks	105

5.1.1.2	Direct Chronic Risks	106

5.1.2	Indirect Effects	107

5.1.2.1	Evaluation of Potential Indirect Effects via Reduction in Food
Items (Freshwater Invertebrates and Fish for the Aquatic Phase;
Terrestrial Invertebrates and Mammals for the Terrestrial Phase)	107

5.1.2.2	Evaluation of Potential Indirect Effects via Reduction in Food
Items, Habitat and/or Primary Productivity (Freshwater Aquatic
Plants)	110

5.1.2.3	Evaluation of Potential Indirect Effects via Reduction in Terrestrial
Plant Community (Riparian Habitat)	Ill

5.1.2.3.1 Terrestrial Uses of Imazapyr	Ill

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5.1.2.3.2 Aquatic Uses of Imazapyr	112

5.1.3 Adverse Modification to Designated Critical Habitat	114

5.1.3.1 Adverse Modification to Designated Critical Habitat via Direct

Effects to Aquatic Plants and/or Riparian Vegetation	115

5.1.3.1 Adverse Modification to Designated Critical Habitat via Chemical
Characteristics Necessary for Normal Behavior, Growth, and
Viability of All CRLF Life Stages 115
5.2 Risk Description	115

5.2.1	Direct Effects to the CRLF	119

5.2.2	Indirect Effects to the CRLF	121

5.2.2.1	Indirect Effects via Reduction in Food Items (Freshwater
Invertebrates and Fish for the Aquatic Phase; Terrestrial
Invertebrates and Mammals for the Terrestrial Phase)	121

5.2.2.2	Evaluation of Potential Indirect Effects via Reduction in Food
Items, Habitat and/or Primary Productivity (Freshwater Aquatic
Plants)	123

5.2.2.3	Indirect Effects via Alteration in Terrestrial Plant Community
(Riparian Habitat)	127

5.2.2.3.1 Terrestrial Uses of Imazapyr	127

5.2.2.4	Spray Drift Buffers for Non-Target Plants	129

5.2.2.5	Importance of Riparian Habitat to the CRLF	132

5.2.2.6	Effect of Imazapyr on Health and Function of Riparian Areas	135

5.2.3	Adverse Modification to Designated Critical Habitat	138

5.2.3.1	Direct Effects to Aquatic Plants	138

5.2.3.2	Adverse Modification to Designated Critical Habitat via Effects to
Riparian Vegetation	139

5.2.3.3	Adverse Modification to Designated Critical Habitat via Effects to
Chemical Characteristics Necessary for Normal Behavior, Growth,

and Viability of All CRLF Life Stages	139

6.2	Exposure Assessment Uncertainties	141

6.2.1	Modeling Assumptions	141

6.2.2	Impact of Vegetative Setbacks on Runoff	141

6.2.3	PRZM Modeling Inputs and Predicted Aquatic Concentrations	142

6.2.4	Modeling Total Toxic Residues	143

6.3	Terrestrial Assessment	143

6.3.1	Location of Wildlife Species	143

6.3.2	Routes of Exposure	143

6.3.3	Residue Levels Selection	144

6.3.4	Dietary Intake	144

6.4	Effects Assessment Uncertainties	145

6.4.1	Age Class and sensativity of Effects Threshold	145

6.4.2	Use of Freshwater Fish and Bird Toxicity Data for the CRLF	145

6.4.3	Sublethal Effects	146

6.5	Assumptions Associated with the Acute LOCs	146

6.6	Uncertainty in the Potential Effect to Riparian Vegetation vs. Increased
Sedimentation	146

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7.	Risk Conclusions: Summary of Direct and Indirect Effects to the
CRLF and Adverse Modification to Designated Critical Habitat for

the CRLF	148

8.	References	158

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Appendices

Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Appendix G
Appendix H
Appendix I
Appendix J

Appendix K
Attachment 1
Attachment 2

Environmental Fate Data

Ecological Effects Data

Imazapyr Spacial Summary Maps

Aquatic Environmental Concentrations

Incident Database Information

Risk Quotient Method and Level of Concerns

ECOTOX Papers Included in Assessment

Accepted ECOTOX Papers Not Used

Bibliography of papers excluded from ECOTOX

Submitted MRID Ecotoxicity Bibliography

Multiple Active Ingredients Data and Analysis
California Red Legged Frog Status and Life History
Baseline Status and Cumulative Effects for the California
Red Legged Frog

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List of Tables

Table 1.1	Imazapyr Effects Determination Summary for the California Red

Legged Frog (Direct and Indirect Effects)	 17

Table 1.2	Effects Determination Summary for the Critical Habitat Impact

Analysis	 20

Table 2.2	Labeled Uses of Imazapyr and the Isopropylamine Salt of

Imazapyr Within California	 27

Table 2.4.1 Some Physical, Chemical and Environmental Fate Properties of

Imazapyr, the Isopropylamine Salt of Imazapyr, and
Residues of Toxicological Concern	 31

Table 2.4.4 Summary of CDPR PUR Usage Data from 2002 to 2005 for

Imazapyr	 39

Table 2.5.1 California Red-legged Frog Recovery Units with Overlapping Core

Areas and Designated Critical Habitat	 41

Table 2.7	Summary of Environmental Fate Data Used in the Aquatic

Assessment for Total Toxic Residues of Imazapyr
(Imazapyr and CL 119,060 and CL 9,140)	 54

Table 2.8.1 Summary of Assessment Endpoints and Measures of Ecological

Effects for Direct and Indirect Effects of Imazapyr on the
California Red-legged Frog	 58

Table 2.8.2 Summary of Assessment Endpoints and Measures of Ecological

Effect for Primary Constituent Elements of Designated
Critical Habitat	 61

Table 3.1	Imazapyr Label Application Information for the Listed Red

Legged Frog	 71

Table 3.2.2a PRZM/EXAMS Scenarios Used to Estimate Concentrations of

Imazapyr Total Toxic Residues in Surface Water	 72

Table 3.2.2.b Summary of PRZM/EZAMS Environmental Fate Data Used for

Aquatic Exposure Inputs for Total Toxic Residues of
Imazapyr for the Listed Red Legged Frog Assessment	 73

Table 3.2.3.a Tier 2 Estimated Environmental Concentrations (EECs) for

Forestry Uses of Imazapyr (total toxic residues)	 73

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Table 3.2.3.b Tier 2 Estimated Environmental Concentrations (EECs) for

Rangeland/Hay Uses of Imazapyr (total toxic residues)	 74

Table 3.2.3.C Tier 2 Estimated Environmental Concentrations (EECs) for Use of

Imazapyr (total toxic residues) on Golf Course Roughs (CA
turf scenario)	 75

Table 3.2.3.d Tier 2 Estimated Environmental Concentrations (EECs) Resulting

from the Yearly Direct Application of Imazapyr (total toxic
residues) to Water (aerial or ground spray application)	 75

Table 3.2.3.e Tier 2 PRZM/EXAMS Estimated Environmental Concentrations

(EECs) for the Standard, 2 Meter Deep Pond Resulting
from the Residential Use of Imazapyr (total toxic residues
in ppb) With 12% Impervious Surface	 78

Table 3.2.3.f Tier 2 PRZM/EXAMS Estimated Environmental Concentrations

(EECs) for the Standard, 2 Meter Deep Pond Resulting
from the Use of Imazapyr on Industrial, Non-Food Non-
Residential Rights-of-Way (total toxic residues as ppb)	 78

Table 3.3	Upper-bound Kenaga values (T-REX vl.3.1)	 79

Table 3.4	Estimated Environmental Concentrations of Imazapyr for

Terrestrial Plants from California Uses	 81

Table 4.0	Summary of Toxicity Data on Imazapyr and Its Isopropylamine

Salt Used to Assess Direct and Indirect Effects and Adverse
Modification to Critical Habitat	 82

Table 4.1.a Animal and Plant Toxicity Profile of Imazapyr and Its

Isopropylamine Salt For Use in Assessing Risk to the
Aquatic Phase CRLF	 85

Table 4.1.b	Categories of Acute Toxicity for Aquatic Organisms		87

Table 4.1.1.1	Freshwater Fish Acute Toxicity for Imazapyr Acid		88

Table 4.1.1.2	Freshwater Fish Chronic Toxicity for Imazapyr Acid		89

Table 4.1.2.1	Freshwater Invertebrate Acute Toxicity for Imazapyr Acid		90

Table 4.1.2.2 Freshwater Aquatic Invertebrate Chronic Toxicity for Imazapyr

Acid	 90

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Table 4.1.3 Non-target Aquatic Plant Toxicity for Imazapyr Acid and

Isopropylamine Salt of Imazapyr	 91

Table 4.2.a Animal and Plant Toxicity Profile of Imazapyr and Its

Isopropylamine Salt For Use in Assessing Risk to the
Terrestrial Phase CRLF	 93

Table 4.2.b	Categories of Acute Toxicity for Terrestrial Organisms		95

Table 4.2.1.1.a	Avian Acute Oral Toxicity for Imazapyr Acid		95

Table 4.2.1.l.b	Avian Subacute Dietary Studies for Imazapyr Acid		96

Table 4.2.1.2	Avian Reproduction for Imazapyr Acid		96

Table 4.2.2.1	Mammalian Acute Toxicity for Imazapyr Acid		97

Table 4.2.2.2 Mammalian Developmental/Reproductive Toxicity for Imazapyr

Acid	 98

Table 4.2.3 Non-target Insects - Acute Contact (Imazapyr Acid)	 99

Table 4.2.4 Tier II Terrestrial Non-target Plant Toxicity	 101

Table 5.1.1 Summary of Direct Chronic RQs for the Terrestrial Phase CRLF

Using Avian Endpoints as a Surrogate	 107

Table 5.1.2.1.a Summary of Indirect Effect (Prey Base Mammals) Dose-Based

Chronic RQs for the Terrestrial Phase CRLF	 109

Table 5.1.2.1.b Summary of Indirect Effect (Prey Base Mammals) Dietary Chronic

RQs for the Terrestrial Phase

CRLF		109

Table 5.1.2.2 Tier 2 Peak EECs and RQs for Aquatic Vascular and Non-Vascular

Plants with Forestry, Rangeland/Hay, Turf, Aquatic, Residential
and Rights-of-Way Uses	 210

Table 5.1.2.3.a Non-Listed Terrestrial Plant Risk Quotient Summary for

Terrestrial Spray Uses	 113

Table 5.1.2.3.b Terrestrial Plant Risk Quotient Summary for Aquatic Spray

Uses	 113

Table 5.1.3 PCE Groupings for Critical Habitat Impact Analysis	 114

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Table 5.2.1 Preliminary Effects Determination Summary for the California

Red Legged Frog and Critical Habitat Impact Analysis
Based on Risk Estimation	 116

Table 5.2.2.4.a Imazapyr AGDISP Buffers for Listed and Non-Listed Terrestrial

Plant Species	 130

Table 5.2.2.4.b Imazapyr AGDISP Buffers for Forestry Uses with Listed and Non-

Listed Terrestrial Plant Species Using Various Droplet
Sizes	 131

Table 5.2.2.5 Criteria for Assessing the Health of Riparian Areas to Support

Aquatic Habitats (adapted from Fleming et al. 2001)	 133

Table 7.1	Imazapyr Effects Determination Summary for the CRLF (direct

and indirect effects)	 152

Table 7.2	Effects Determination Summary for the Critical Habitat Impact

Analysis	 155

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List of Figures

Figure 2.4.1.a Chemical Structure of Imazapyr		34

Figure 2.4.1.b Chemical Structure of Isopropylamine Salt of Imazapyr		34

Figure 2.4.1.c Chemical Structure of CL 119060		35

Figure 2.4.1.d Chemical Structure of CL 9140		35

Figure 2.5.1 Recovery Unit, Core Area, Critical Habitat, and Occurrence

Designations		44

Figure 2.5.2 CRLF Reproductive Events by Month		45

Figure 2.7.a Initial Area of Concern		53

Figure 2.7.b Action Area Map		57

Figure 2.9.2.a Effects on Aquatic Phase CRLF		64

Figure 2.9.2.b Effects on Aquatic Component of the CRLF Critical Habitat		65

Figure 2.9.2.C Effects on Terrestrial Phase CRLF		66

Figure 2.9.2.d Effects on Terrestrial Component of the CRLF Critical Habitat		67

Figure 3.2.2. Peak, 21-Day and 60-Day EECs for Direct Application of

Imazapyr to Water		76

Figure 7.1 Imazapyr Initial Area of Concern with Habitat Overlap		150

Figure 7.2 Figure 7.2 Buffered Forestry Uses and Unbuffered Urban Uses

with Habitat Overlap		151

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1. Executive Summary

Imazapyr is a systemic, non-selective herbicide used for control of most annual and
perennial broadleaf weeds and grasses, woody species, and riparian and floating and
emergent aquatic weed species in terrestrial and aquatic environmental settings.

Imazapyr is formulated both as an acid and as an isopropylamine salt. The salt
disassociates under environmental conditions to form the acid; therefore, in this
assessment, all references to the acid are applicable to either the acid or the
isopropylamine salt formulations. Aqueous imazapyr formulations may be mixed with
surfactants or oils for application as well as mixed with other herbicides and fertilizers.
Imazapyr is also available in a water dispersible granular formulation, as an emulsifiable
concentrate and in pelleted/tableted form for direct injection into plants. Typical
terrestrial application methods consist of ground and aerial spray, with granular broadcast
applications for forestry uses, while surface waters are treated directly with aqueous
formulations. Imazapyr may also be injected directly into the plant around the stem.
Imidazoline herbicides are systemic plant growth inhibitors that are normally active at
very low rates. However, imazapyr appears not to be as active as most imidazoline
herbicides at very low rates. Uptake of imazapyr is primarily through the foliage and
roots. It is then translocated to meristematic tissue where it inhibits acetohydroxyacid
synthase (AHAS, also known as acetolactate synthase or ALS), thus, disrupting protein
synthesis and interfering with cell growth and DNA synthesis. AHAS is not present in
mammals, birds, fish, or insects. As a result, imazapyr is intended to be specifically toxic
to plants.

Imazapyr is currently registered nationwide for use in terrestrial (railroads and industrial
right-of-ways, fencerows, wildlife habitats and forests) and aquatic (ponds, lakes,
reservoirs, marshes, bayous, canals, streams, rivers, and water drainage systems), non-
cropped areas and for corn fields. There are no other currently registered agricultural
products. Although the action area is likely to encompass a large area of the United
States, the scope of this assessment limits consideration of the overall action area to those
portions that are applicable to the protection of the California Red Legged Frog (CRLF)
and its designated critical habitat. As such, the action area includes the current range of
the species and designated critical habitat, which occur within the state of California.
The current labels state that imazapyr may not be used on corn crops in the state of
California. In addition, the granular labels state that the granular formulations may not be
used in the state of California. The initial area of concern for imazapyr is limited to all
the areas within the state of California where the non-agricultural uses listed above may
be applied. The initial area of concern represents the "footprint" of where imazapyr
could potentially be used based on land cover information. The initial area of concern is
then expanded as necessary based on the potential for direct and indirect effects above
levels of concern and on consideration of the fate and transport properties of the
compound. The action area is defined by the land use classes designated to represent
these non-agricultural uses in a conservative fashion and accounts for the fate and
transport characteristics of the pesticide, including transport in streams and rivers, spray
drift, and long-range transport. For imazapyr, the action area is defined as the initial area
of concern with buffers ranging from 7120 (forestry uses, ground application) to 26460

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feet (forestry uses, aerial application) to account for potential drift and long-range
transport away from the site of application and a total of 7,450 stream miles added
downstream from the initial area of concern to account for the potential downstream
movement of imazapyr residues at concentrations above levels of concern and for
transport with flowing waters.

In accordance with the methodology specified in the Agency's Overview Document
(U.S. EPA, 2004), screening level aquatic estimated environmental concentrations
(EECs), based on the PRZM/EXAMS static water body scenario, were used to derive risk
quotients (RQs) for aquatic animals and plants for all relevant imazapyr uses within the
action area. It is noted that screening level EECs based on the static water body are not
considered to be representative of all waters where the CRLF and designated critical
habitat occur. For "may affect" determinations, screening level EECs may be further
refined and characterized based on the location of the CRLF in more vulnerable waters
such as shallow ponds and streams. Terrestrial EECs for terrestrial animals were derived
from dietary concentrations of various avian and mammalian food items along with the
dissipation rate using the model TREX 1.3.1. Terrestrial EECs for plants were estimated
from the model, TerrPlant 1.2.2, which derives pesticide EECs from runoff and drift.
RQs based on screening level EECs were used to distinguish "no effect" from "may
affect" determinations for direct/indirect effects to the CRLF and the critical habitat
impact analysis.

The assessment endpoints for the CRLF included direct toxic effects on survival,
reproduction, and growth of individual CRLF's, as well as indirect effects, such as
reduction of the food source and/or modification of habitat. Risk quotients (RQs) for
direct acute effects to the CRLF were calculated using acute toxicity data from either
registrant-submitted studies or acceptable studies available in the open literature for the
surrogate species, freshwater fish for the aquatic-phase and birds for the terrestrial-phase
when toxicity data on amphibians are not available. RQs for direct chronic (reproductive,
growth) effects were also calculated using either registrant-submitted or acceptable open
literature chronic toxicity data for freshwater fish and birds. To assess potential indirect
effects to the CRLF via direct effects to potential prey (and consequently a reduction of
available food items), toxicity data for freshwater fish and invertebrates as well as birds
(surrogate for terrestrial-phase amphibians), terrestrial invertebrates and mammals were
considered. Registrant-submitted and/or acceptable open literature aquatic and terrestrial
plant toxicity studies were used to assess risk to primary producers, and in turn, potential
indirect effects to the CRLF.

Federally designated critical habitat has been established for the CRLF. Adverse
modifications to the primary constituent elements of designated critical habitat, as
defined in 50 CFR 414.12(b), were also evaluated. PCEs evaluated as part of this
assessment include the following:

•	Breeding aquatic habitat;

•	Non-breeding aquatic habitat;

•	Upland habitat; and

•	Dispersal habitat.

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RQs were derived as quantitative estimates of potential high-end risk. Acute and chronic
RQs were compared to the Agency's Levels of Concern (LOCs) to identify instances
where imazapyr use within the action area has the potential to adversely affect the CRLF
or adversely modify designated critical habitat. RQs for a particular type of effect were
below the LOCs, leads to a conclusion of "no effect". Where RQs exceeded LOCs, a
potential to cause adverse effects or habitat modification is identified, leading to a
conclusion of "may affect". If imazapyr use "may affect" the CRLF or its critical habitat,
best available data and information is considered to refine the potential for exposure and
effects, and distinguish actions that are not likely to adversely affect (NLAA) from those
that are likely to adversely affect (LAA). Effects determinations for direct/indirect
effects to the CRLF and the critical habitat impact analysis are summarized below and
presented in Tables 1.1 and 1.2.

This risk assessment indicates that no direct effects are expected on either the aquatic or
terrestrial phase CRLF. There are also no indirect effects expected for the CRLF through
direct effects to either its terrestrial or aquatic food sources. The effects determination
for direct effects on the CRLF and for indirect effects through food sources is no effect.
The CRLF may be adversely affected through direct effects on habitat and/or primary
productivity (i.e., ecosystem structure and function for both the aquatic plant community
and riparian vegetation). Critical habitat may also be adversely modified based on direct
effects to aquatic vascular plants and terrestrial plants. The risks exceed the level of
concern (LOC) for non-listed non-target terrestrial plants (monocots and dicots) for all
imazapyr uses. The risks to non-listed non-target aquatic vascular plants exceed the LOC
for aquatic, rangeland and forestry uses (aerial application) as well as rights-of-way
(assuming 50% pervious surfaces). No effects are expected for aquatic non-vascular
plants. A spatial analysis of potential imazapyr usage in California was conducted using
the national registered labels. The CRLF has no obligate relationships with either aquatic
or terrestrial plants. Therefore, the LAA/NLAA determinations are based on direct
effects to non-listed aquatic and terrestrial plants (i.e., indirect effects to habitat and/or
primary productivity). To distinguish between an LAA and an NLAA determination, for
each of the imazapyr uses, buffers based on expected spray drift were added from the site
of potential imazapyr application to the point where the LOC for non-listed terrestrial
plants would no longer be exceeded. For non-listed plants, these buffers range from 2530
(forestry uses, ground application) to 5940 feet (forestry uses, aerial application).

Buffers for the other imazapyr uses are in between the two forestry use buffers. For
aquatic plants, additional estimations were conducted to determine the number of miles
that imazapyr residues may travel downstream to the point where the LOC for non-listed
aquatic plants would no longer be exceeded. The spatial analysis shows that the potential
imazapyr use sites cover a sufficiently wide area such that 94-100% (27,300 acres) of the
CRLF range assessed, including core areas, critical habitat and known occurrences could
be affected, even when no buffers are applied. The effects determinations for aquatic
plants (indirect effects to the CRLF through direct effects on habitat and/or primary
productivity) is no effect for aquatic non-vascular plants and aquatic vascular plants for
residential, turf and forestry uses (ground application); may affect, LAA for aquatic
vascular plants for forestry (aerial application), rangeland/hay, aquatic and rights-of-way

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uses; and may affect, LAA for emergent aquatic vascular plants for all uses inside a use-
specific terrestrial buffer ranging from 2530 to 5940 feet with a NLAA for all uses
outside the use-specific terrestrial buffer. The effects determination for terrestrial plants
(monocots and dicots) is also may affect, LAA for all uses inside a use-specific terrestrial
buffer ranging from 2530 to 5940 feet with a NLAA for all uses outside the use-specific
terrestrial buffer. For the capsule injection application directly into the plant, the effects
determination is may affect, not likely to adversely affect because the exposure is
expected to be very limited and non-quantifiable. The effects determinations for the
critical habitat impact are similar to that summarized for aquatic and terrestrial plants
above. Habitat modification is not expected for aquatic non-vascular plants and aquatic
vascular plants for residential, turf and forestry uses (ground application), for aquatic
emergent vascular plants and terrestrial plants for all uses inside a use-specific terrestrial
buffer and for capsule injection directly into the plant. Habitat modification is expected
for aquatic vascular plants for forestry (aerial application), rangeland/hay, aquatic and
rights-of-way uses and for emergent aquatic vascular plants and terrestrial plants for all
uses inside a use-specific terrestrial buffer. Details of the effects determinations are listed
in Tables 1.1 and 1.2.

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Table 1.1. Imazapyr Effects Determination Summary for the CR.LF (Direct and Indirect Effects)



Effects Determination and Basis

Assessment Endpoint

Effects
Determination1

NLAA/LAA Discrimination

Basis

Aquatic Phase

1. Survival, growth,
and reproduction of
CRLF individuals via
direct effects on aquatic
phases (eggs, larvae,
tadpoles, juveniles and
adults)

Acute direct effects:
no effect

N/A

No effects in surrogate species (freshwater fish)
at highest concentration tested, which is
significantly greater than the peak aquatic
EECs

Chronic direct
effects: no effect

N/A

Chronic freshwater fish (surrogate species)
LOC is not exceeded for any uses.

2. Survival, growth,
and reproduction of
CRLF individuals via
indirect effects to prey
(freshwater
invertebrates)

Acute direct effects
to freshwater
invertebrates: no
effect

N/A

No effects in freshwater invertebrates at highest
concentration tested, which is significantly
greater than the peak aquatic EECs.

Chronic direct
effects to freshwater
invertebrates: no
effect

N/A

Chronic freshwater invertebrate LOC is not
exceeded for any uses

3. Survival, growth,
and reproduction of
CRLF individuals via
indirect effects on
habitat and/or primary
productivity (i.e.
aquatic plant
community)

Direct effects to
aquatic non-vascular
plants:
No affect

N/A

No LOCs exceeded for non-vascular plants.

Direct effects to
aquatic vascular
plants: No effect for
residential, turf and
forestry (ground)
May affect, likely to
adversely affect for
forestry (aerial),
rangeland/hay,
aquatic and rights-

N/A

Aquatic plant LOCs exceeded for vascular
plants for forestry (aerial), rangeland/hay,
aquatic and rights-of-way uses near use sites.
Aquatic plant LOCs not exceeded for vascular
plants for forestry (ground), residential or turf
uses.5

17

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Table 1.1. Imazapyr Effects Determination Summary for the CR.LF (Direct and Indirect Effects)



Effects Determination and Basis

Assessment Endpoint

Effects
Determination1

NLAA/LAA Discrimination

Basis



of-way uses.





Direct effects to
aquatic emergent
vascular plants:
May affect, likely to
adversely affect for

all uses except
capsule injection,
which is may affect,
.NLAA.

Forestry uses (ground application) NLAA > 2530 feet,
LAA < 2530 feet

Non-forestry terrestrial uses (ground application) NLAA >
2920 feet, LAA < 2920 feet

Aquatic uses (ground application) NLAA > 2940 feet, LAA
< 2940 feet

Aquatic uses (helicopter application)) NLAA > 3540 feet,
LAA < 3540 feet

Non-forestry terrestrial uses (aerial application fixed wing)
NLAA > 4640 feet, LAA < 4640 feet
Forestry uses (aerial application helicopter) NLAA > 4660
feet, LAA < 4660 feet

Forestry uses (aerial application fixed wing) NLAA > 5940
feet, LAA < 5940 feet

Aquatic plant LOCs exceeded for vascular
plants for forestry (aerial), rangeland/hay,
aquatic and rights-of-way uses near use sites.
Aquatic plant LOCs not exceeded for vascular
plants for forestry (ground), residential or turf
uses. Emergent aquatic vascular plants in
wetland areas adjacent to use sites: terrestrial
plant LOC exceeded for monocots and dicots
for all uses from flooding, runoff or spray drift2"
5 Capsule injection use expected to have very
limited nonquantifiable exposure to non-target
plants.

Terrestrial Phase

4. Survival, growth,
and reproduction of
CRLF individuals via
direct effects on
terrestrial phase adults
and juveniles

Acute direct effects:
no effect

N/A

No effects in surrogate species (birds) at
highest concentration/dose tested which are
significantly greater than the terrestrial EECs

Chronic direct
effects: no effect

N/A

Chronic bird (surrogate species) LOC is not
exceeded for any uses

5. Survival, growth,
and reproduction of
CRLF individuals via
indirect effects on prey
(i.e., terrestrial
invertebrates, small
terrestrial vertebrates)

Acute direct effects
to most sensitive
prey: no effect

N/A

No effects in mammals at highest dose tested,
which is significantly greater than the terrestrial
EEC.

Chronic direct
effects to most
sensitive prey: no
effect

N/A

Chronic terrestrial animal (mammals) LOC is
not exceeded for any uses.

6. Survival, growth,
and reproduction of
CRLF individuals via

Direct effects to
monocots: May
affect

See details in Assessment Endpoint number 3 above.

Terrestrial plant LOC exceeded for monocots in
both wetlands and uplands adjacent to use site
for all uses. Risk conclusions are supported by

18

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Table 1.1. Imazapyr Effects Determination Summary for the CR.LF (Direct and Indirect Effects)

Effects Determination and Basis

Assessment Endpoint

Effects
Determination1

NLAA/LAA Discrimination

Basis

indirect effects on
habitat (i.e. riparian
vegetatation)

Likely to adversely
affect. May affect,
NLAA for capsule
injection use

adverse ecological incident reports.2"5 Capsule
injection use expected to have very limited
nonquantifiable exposure to non-target plants.

Direct effects to
dicots: May affect
Likely to adversely
affect. May affect,
NLAA for capsule
injection use

See details in Assessment Endpoint number 3 above.

Terrestrial plant LOC exceeded for dicots in
both wetlands and uplands adjacent to use site
for all uses. Risk conclusions are supported by
adverse ecological incident reports.2"5 Capsule
injection use expected to have very limited
nonquantifiable exposure to non-target plants.

N/A = Not applicable

1 The LAA/NLAA cut will also be influenced by other factors such as height of application, timing of application, droplet size, upwind swath displacement, the
length of the boom relative to the wingspan or rotor blade diameter, wind speed, nozzle height (for ground applications), application during temperature
inversion, etc. New mitigation measures are being developed; however, products with the old labels will be allowed to be distributed for up to 18 months after
new labels are approved. Therefore, it is not possible to determine when all product labels will reflect the new mitigation measures. It could be assumed that
most users will use their existing stocks within 2 years of purchase.

2 The risk estimates for imazapyr-treated water flooding onto terrestrial sites are conservative because they do not address the uncertainty of dilution from rain
water or water from other sources that originally precipitated the overflow.

3 Some monocots exposed via spray drift alone following either ground or aerial application at 1.5 lbs ae/A and some of both monocots and dicots exposed via
spray drift alone following ground spray at 0.91 lbs ae/A (residential uses) will not exceed the LOC for terrestrial plants. However, for the terrestrial
applications, comparison of the RQs indicates that runoff, and not spray drift, is a larger contributor to potential risk for riparian vegetation.

4 In addition to affecting seedling emergence, because imazapyr is toxic to plants when it is taken up by the roots, runoff is also expected to affect emerged
plants. The RQ values for plants exposed to runoff are estimated from the seedling emergence studies because of the limitations of the vegetative vigor studies.
These studies do not measure effects to emerged plants following a runoff event. Therefore, there is an uncertainty with regard to the effect of runoff to emerged
plants.

5 It is not clear for rangeland uses, whether and to what extent the critical habitat exemption applies.

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Table 1.2. Effects Determination Summary for the Critical Habitat Impact Analysis

Assessment Endpoint

Effects
Determination1

Determination of Habitat Modification

Basis

Aquatic Phase PCEs

Aquatic breeding and non-breeding habitat

Alteration of
channel/pond
morphology and/or
water

chemistry/quality;
increase in sediment
deposition

Direct effects to
aquatic plants: no
effect for non-
vascular plants;
No effect for aquatic
vascular plants for
residential, turf and
forestry (ground).
Modification of
critical habitat for
aquatic vascular
plants for forestry
(aerial),
rangeland/hay,
aquatic and rights-
of-way uses.

N/A

No LOCs exceeded for non-vascular plants.
Aquatic plant LOC not exceeded for vascular
plants for forestry (ground), residential or turf
uses. Aquatic plant LOC exceeded for vascular
plants for forestry (aerial), rangeland/hay,
aquatic and rights-of-way uses.5



Direct effects to
aquatic emergent
vascular plants:
Modification of
critical habitat

Forestry uses (ground application): habitat modification
expected < 2530 feet and not expected > 2530 feet
Non-forestry terrestrial uses (ground application): habitat
modification expected < 2920 feet and not expected > 2920
feet

Aquatic uses (ground application): habitat modification
expected < 2940 feet and not expected > 2940 feet
Aquatic uses (helicopter application)): habitat modification
expected < 3540 feet and not expected > 3540 feet
Non-forestry terrestrial uses (aerial application fixed wing):
habitat modification expected < 4640 feet and not
expected> 4640 feet

Forestry uses (aerial application helicopter): habitat
modification expected < 4660 feet and not expected > 4660
feet

Forestry uses (aerial application fixed wing): habitat

Aquatic plant LOCs not exceeded for aquatic
vascular plants for forestry (ground), residential
or turf uses. Aquatic plant LOCs exceeded for
aquatic vascular plants for forestry (aerial),
rangeland/hay, aquatic and rights-of-way uses.
Emergent aquatic vascular plants in wetland
areas adjacent to use sites: terrestrial plant
LOC exceeded for monocots and dicots for all
uses from flooding, runoff or spray drift2"5.

Risk conclusions are supported by adverse
ecological incident reports. Capsule injection
use expected to have very limited
nonquantifiable exposure to non-target plants.







20

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Table 1.2. Effects Determination Summary for the Critical Habitat Impact Analysis

Assessment Endpoint

Effects
Determination1

Determination of Habitat Modification

Basis





modification expected < 5940 feet and not expected > 5940
feet.





Direct effects to

monocots:
Modification of
critical habitat.
Modification of
critical habitat not
expected for capsule
injection use.

See terrestrial buffer list above.

Terrestrial plant LOC exceeded for monocots in
wetlands and uplands adjacent to use site for all
uses.2"5 Risk conclusions are supported by
adverse ecological incident reports. Capsule
injection use expected to have very limited
nonquantifiable exposure to non-target plants.

Alteration of
channel/pond
morphology and/or
water

chemistry/quality;
increase in sediment
deposition

Direct effects to
dicots: modification
of critical habitat
Modification of
critical habitat not
expected for capsule
injection use.

See terrestrial buffer list above.

Terrestrial plant LOC exceeded for dicots in
wetlands and uplands adjacent to use site for all
uses.2"5 Risk conclusions are supported by
adverse ecological incident reports. Capsule
injection use expected to have very limited
nonquantifiable exposure to non-target plants.

Terrestrial Phase PCEs

Upland habitat and dispersal habitat

Elimination/disturbance
of upland habitat and/or
dispersal habitat

Direct effects to

monocots:
Modification of
critical habitat
Modification of
critical habitat not
expected for capsule
injection use.

See terrestrial buffer list above.

Terrestrial plant LOC exceeded for monocots in
wetlands and uplands adjacent to use site for all
uses.2"5 Risk conclusions are supported by
adverse ecological incident reports. Capsule
injection use expected to have very limited
nonquantifiable exposure to non-target plants.



Direct effects to
dicots: Modification
of critical habitat
Modification of
critical habitat not
expected for capsule

See terrestrial buffer list above.

Terrestrial plant LOC exceeded for dicots in
wetlands and uplands adjacent to use site for all
uses.2"5 Risk conclusions are supported by
adverse ecological incident reports. Capsule
injection use expected to have very limited
nonquantifiable exposure to non-target plants.

21

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Table 1.2. Effects Determination Summary for the Critical Habitat Impact Analysis

Assessment Endpoint

Effects
Determination1

Determination of Habitat Modification

Basis

injection use.

N/A = Not applicable

5 It is not clear for rangeland uses, whether and to what extent the critical habitat exemption applies.

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For those uses for which an LAA determination has been made, when evaluating the
significance of this risk assessment's direct/indirect and adverse habitat modification
effects determinations, it is important to note that pesticide exposures and predicted risks
to the species and its resources (i.e., food and habitat) are not expected to be uniform
across the action area. In fact, given the assumptions of drift and downstream transport
(i.e., attenuation with distance), pesticide exposure and associated risks to the species and
its resources are expected to decrease with increasing distance away from the treated field
or site of application. Evaluation of the implication of this non-uniform distribution of
risk to the species would require information and assessment techniques that are not
currently available. Examples of such information and methodology required for this
type of analysis would include the following:

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

• Quantitative information on prey base requirements for individual aquatic-
and terrestrial-phase frogs. While existing information provides a
preliminary picture of the types of food sources utilized by the frog, it
does not establish minimal requirements to sustain healthy individuals at
varying life stages. Such information could be used to establish
biologically relevant thresholds of effects on the prey base, and ultimately
establish geographical limits to those effects. This information could be
used together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.

• Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth or reproductive impairment
immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and
together with the information described above, a more complete prediction
of effects to individual frogs and potential adverse modification to critical
habitat.

2. Problem Formulation

Problem formulation provides a strategic framework for the risk assessment. By
identifying the important components of the problem, it focuses the assessment on the

-------
most relevant life history stages, habitat components, chemical properties, exposure
routes, and endpoints. The structure of this risk assessment is based on guidance
contained in U.S. EPA's Guidance for Ecological Risk Assessment (U.S. EPA 1998), the
Services' Endangered Species Consultation Handbook (USFWS/NMFS 1998) and is
consistent with procedures and methodology outlined in the Overview Document (U.S.
EPA 2004) and reviewed by the U.S. Fish and Wildlife Service and National Marine
Fisheries Service (USFWS/NMFS 2004).

2.1 Purpose

The purpose of this listed species assessment is to evaluate potential direct and indirect
effects on individuals of the federally threatened California red-legged frog (Rana aurora
draytonii) (CRLF) arising from FIFRA regulatory actions regarding use of imazapyr on
terrestrial (railroads and industrial right-of-ways, fencerows, wildlife habitats and forests)
and aquatic (ponds, lakes, reservoirs, marshes, bayous, canals, streams, rivers, and water
drainage systems) non-crop sites, and to evaluate whether these actions can be expected
to result in the destruction or adverse modification of the species' critical habitat. This
ecological risk assessment has been prepared as part of the Center for Biological
Diversity (CBD) us. EPA et al. (Case No. 02-1580-JSW(JL)) settlement entered in the
Federal District Court for the Northern District of California on October 20, 2006.

In this listed species assessment, direct and indirect effects to the CRLF and potential
adverse modification to its critical habitat are evaluated in accordance with the methods
(both screening level and species-specific refinements, when appropriate) described in
the Agency's Overview Document (U.S. EPA 2004).

In accordance with the Overview Document, provisions of the ESA, and the Services'
Endangered Species Consultation Handbook, the assessment of effects associated with
registrations of imazapyr are based on an action area. The action area is considered to be
the area directly or indirectly affected by the federal action as indicated by the
exceedance of Agency Levels of Concern (LOCs) used to evaluate direct or indirect
effects. It is acknowledged that the action area for a national-level FIFRA regulatory
decision associated with a use of imazapyr may potentially involve numerous areas
throughout the United States and its Territories. However, for the purposes of this
assessment, attention will be focused on relevant sections of the action area including
those geographic areas associated with locations of the CRLF and its designated critical
habitat within the state of California.

As part of the "effects determination," one of the following three conclusions will be
reached regarding the potential for registration of imazapyr at the use sites described in
this document to affect CRLF individuals and/or result in the destruction or adverse
modification of designated CRLF critical habitat:

-------
•	"No effect";

•	"May affect, but not likely to adversely affect"; or

•	"May affect and likely to adversely affect".

Critical habitat identifies specific areas that have the physical and biological features,
(known as primary constituent elements or PCEs) essential to the conservation of the
listed species. The PCEs for CRLFs are aquatic and upland areas where suitable
breeding and non-breeding aquatic habitat is located, interspersed with upland foraging
and dispersal habitat (Section 2.6).

If the results of initial screening level assessment methods show no direct or indirect
effects (no LOC exceedances) upon individual CRLFs or upon the PCEs of the species'
designated critical habitat, a "no effect" determination is made for the FIFRA regulatory
action regarding imazapyr as it relates to this species and its designated critical habitat.
If, however, direct or indirect effects to individual CRLF's are anticipated and/or effects
may impact the PCEs of the CRLF's designated critical habitat, a preliminary "may
affect" determination is made for the FIFRA regulatory action regarding imazapyr.

If a determination is made that use of imazapyr within the action area(s) associated with
the CRLF "may affect" this species and/or its designated critical habitat, additional
information is considered to refine the potential for exposure and for effects to the CRLF
and other taxonomic groups upon which these species depend (e.g., aquatic and terrestrial
vertebrates and invertebrates, aquatic plants, riparian vegetation, etc.). Additional
information, including spatial analysis (to determine the geographical proximity of CRLF
habitat and imazapyr use sites) and further evaluation of the potential impact of imazapyr
on the PCEs is also used to determine whether destruction or adverse modification to
designated critical habitat may occur. Based on the refined information, the Agency uses
the best available information to distinguish those actions that "may affect, but are not
likely to adversely affect" from those actions that "may affect and are likely to adversely
affect" the CRLF and/or the PCEs of its designated critical habitat. This information is
presented as part of the Risk Characterization in Section 5 of this document.

The Agency believes that the analysis of direct and indirect effects to listed species
provides the basis for an analysis of potential effects on the designated critical habitat.
Because imazapyr is expected to directly impact living organisms within the action area
(defined in Section 2.7), the critical habitat analysis for imazapyr is limited in a practical
sense to those PCEs of critical habitat that are biological or that can be reasonably linked
to biologically mediated processes (i.e., the biological resource requirements for the listed
species associated with the critical habitat or important physical aspects of the habitat that
may be reasonably influenced through biological processes). Activities that may destroy
or adversely modify critical habitat are those that alter the PCEs and appreciably diminish
the value of the habitat. Evaluation of actions related to use of imazapyr that may alter
the PCEs of the CRLF's critical habitat form the basis of the critical habitat impact
analysis. Actions that may affect the CRLF's designated critical habitat have been
identified by the Services and are discussed further in Section 2.6.

25

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2.2 Scope

Imazapyr is a systemic, non-selective herbicide used for control of most annual and
perennial broadleaf weeds and grasses, woody species, and riparian, and floating and
emergent aquatic weed species in terrestrial and aquatic environmental settings. It is
formulated as both an acid and as an isopropylamine salt; however, the salt disassociates
under environmental conditions to form the acid. Therefore, in this assessment, all
references to the acid are applicable to either the acid or the isopropylamine salt
formulations. Imazapyr is currently registered for use in terrestrial (railroads and
industrial right-of-ways, fencerows, wildlife habitats and forests) and aquatic (ponds,
lakes, reservoirs, marshes, bayous, canals, streams, rivers, and water drainage systems)
non-crop sites (Table 2.2 (Kinard and Tompkins 05/07/07 memorandum)). Additionally,
while imazapyr is also registered nationally for use on corn fields planted with
Clearfield™ Corn, that use is not allowed within the state of California, and has not been
considered in this assessment. Additionally, there are other nationally labeled, non-
agricultural uses of imazapyr, which include all of the granular uses that are not allowed
in California, and have not been included in this assessment.

26

-------
Tsihle 2.2 l.iiheled I ses of lni;iz;ipvr :tiul the Isopropvhiininc Snll of lin;iz;ipvr Willi in Ciilirorniii

(iOIICI'ill I so

Sped

lie I se

M;i\iimi in

Single
Applieiilion

K.ile
(II)
-------
Tsihle 2.2 l.iiholod I ses ol' lm;iz;ip\r :tiul llio Isopropvhiminc Snll of lm;iz:ipvr W ithin (:ilil'orni;i

CjOIH'lill I so

Specific I so

M;i\iimi in

Single
Application

Kiilc
(II) ilC/ilCIV)

Miixiimi ill
Number of
Applications/
Year

Application
Methods

Siirmgsili* Scenario
I'm' A(|ii;ilic
Modeling

Residential
(non-food)

bareground areas

storage areas

tank farms

pumping stations

pipelines under paved surfaces

0.91

Ground Spray

CA residential /
CA impervious
surfaces

Industrial

airports sewage disposal areas
military installations industrial parks
schools/universities plant sites
libraries fencerows
hospitals under asphalt
waysides pond liners
service areas other paved areas
unpaved roads

1.5

Ground Spray

CA right of way /
CA impervious
surfaces

Rights-of-Way

forest roads Roads
driveways transmission lines
highway rights-of ways parking areas
interchange ramps utility rights-of-way
railroad and utility
rights-of-way

1.5

Ground and
Aerial Spray

CA right of way /
CA impervious
surfaces

Non-Residential
(non-food)

brick walks fence rows
gravel pathways non-irrigation ditchbanks
patios barrier strips (including
along fences grazed or hayed areas)
along curbs establishment and
along cracks in sidewalks maintenance of wildlife
farmyards openings
fuel storage areas

1.5

Ground and
Aerial Spray

CA right of way /
CA impervious
surfaces

-------
The end result of the EPA pesticide registration process (the FIFRA regulatory action) is
an approved product label. The label is a legal document that stipulates how and where a
given pesticide may be used. Product labels (also known as end-use labels) describe the
formulation type (e.g., liquid or granular), acceptable methods of application, approved
use sites, and any restrictions on how applications may be conducted. Thus, the use or
potential use of imazapyr in accordance with the approved product labels for California is
"the action" being assessed. While imazapyr is formulated as both an acid and as an
isopropylamine salt, the salt disassociates under environmental conditions to form the
acid. Therefore, in this assessment, all references to the acid are applicable to either the
acid or the isopropylamine salt formulations.

Although current registrations of imazapyr allow for use nationwide, this ecological risk
assessment and effects determination address currently registered uses of imazapyr in
portions of the action area that are reasonably assumed to be biologically relevant to the
CRLF and its designated critical habitat. Further discussion of the action area for the
CRLF and its critical habitat is provided in Section 2.7.

Laboratory studies show imazapyr is essentially stable to hydrolysis, aerobic and
anaerobic soil degradation, as well as aerobic and anaerobic aquatic metabolism. Upon
direct application, or indirect release into surface water, photolysis is the only identified
mechanism for imazapyr degradation in the environment (half-life of 5.3 days).

Imazapyr is considered to be mobile in the environment through leaching and surface
run-off1

2.2.1 Degradates

Two major photolysis transformation products (referred to as degradates in this
assessment) were identified for imazapyr, pyridine hydroxy-dicarboxylic acid (maximum
of 32%) and pyridine dicarboxylic acid (maximum of 23%). No data were either
submitted or found in the open literature through an online search of ECOTOX on these 2
degradates. In the absence of a complete suite of toxicity data on these degradates, they
are assumed to be equivalent to the parent compound. Therefore, concentrations of the
imazapyr degradates are assessed with imazapyr as total toxic residues.

2.2.2 Total Toxic Residues

The first order, log linear photolysis half-life for the combined toxic residues of imazapyr
evaluated in this endangered species assessment, and the two major photolysis
transformation products is 19.9 days. Under laboratory aerobic aquatic conditions, the
aerobic aquatic metabolism half-lives for the two imazapyr degradates were in the range
of three to eight days in two different sediment/water systems. These two major
photolysis transformation products are considered to have low to slight mobility in the
environment through leaching and surface run-off2, and would be expected to bind to soil
and partition into sediment However, unlike the parent compound, these transformation

1 EFED Standardized Soil Mobility Classification Guidance, October 21,2005

2 EFED Standardized Soil Mobility Classification Guidance, October 21,2005

-------
products are not stable to biotic degradation, and, once formed, will degrade under
aerobic and anaerobic conditions. As a result, modeled aquatic concentrations are more
conservative for the total toxic residues of imazapyr than would be expected from the
total toxic residues of a pesticide with biotic degradation half-lives and soil sorption
values similar for all modeled residues.

2.2.3 End Use Formulations

The Agency does not routinely include, in its risk assessments, an evaluation of mixtures
of active ingredients, either those mixtures of multiple active ingredients in product
formulations or those in the applicator's tank. In the case of the product formulations of
active ingredients (that is, a registered product containing more than one active
ingredient), each active ingredient is subject to an individual risk assessment for
regulatory decision regarding the active ingredient on a particular use site. If effects data
are available for a formulated product containing more than one active ingredient, they
may be used qualitatively or quantitatively in accordance with the Agency's Overview
Document and the Services' Evaluation Memorandum (U.S., EPA 2004; USFWS/NMFS
2004).

Imazapyr has registered products that contain multiple active ingredients. Analysis of the
available acute oral mammalian LD50 data (and available open literature for imazapyr)
for multiple active ingredient products relative to the single active ingredient is provided
in Appendix K. The results of this analysis show that an assessment based on the toxicity
of the single active ingredient of imazapyr is appropriate.

2.3 Previous Assessments

An ecological risk assessment in support of the re-registration eligibility decision (RED)
of imazapyr (both acid and salt formulations; PC Codes: 128821 and 128829) was
finalized by EFED on September 30, 2005 (DP Barcode: D313607). The screening level
risk assessment indicated risk to both listed and non-listed non-target terrestrial plants
(monocots and dicots) and aquatic vascular plants from imazapyr use, based on the
highest application rate of various use patterns. Seedling emergence and vegetative vigor
in both monocots and dicots would be impacted by exposure to both the imazapyr acid
and the isopropylamine salt. The assessment indicated minimal risk of direct acute
effects to fish and aquatic invertebrates and minimal risks to aquatic non-vascular plants
at maximum application rates. In addition, there were no direct chronic risks to fish and
invertebrates, although there was an uncertainty for estuarine/marine fish and
invertebrates, since no toxicity data were available to observe the prolonged effects of
imazapyr to these taxa. Likewise, direct acute and chronic risks to mammals and birds
consuming food types containing imazapyr residues are not expected from the labeled
uses of the herbicide. EFED currently does not quantify risks to terrestrial non-target
insects; however, available data on honey bees indicate that the direct risk to terrestrial
non-target insects was likely to be low. The assessment indicted indirect risk to all taxa
from direct effects on plants (i.e. effects on habitat and/or primary productivity).

-------
EPA conducted an assessment of imazapyr (January 17, 2003) potential effects to 26
Environmentally Significant Units of pacific salmon and steelhead. That assessment was
conducted in accordance with a consent decree entered by the federal government with
Californians for Alternatives to Toxics (CATS). The conclusion of that assessment was
that registered forest operation uses of imazapry were Not Likely to Adversely Affect the
26 species either directly or indirectly, nor adversely modify designated crticial habitat.

EPA conducted an assessment of imazapyr (January 17, 2003) potential effects to 33
federally listed plants. That assessment was conducted in accordance with a consent
decree entered by the federal government with Californians for Alternatives to Toxics
(CATS). The conclusion of that assessment was that registered forest operation uses of
imazapyr were Not Likely to Adversely Affect the subject species. This conclusion was
based in large measure on the infrequent use of imazapyr in forestry operations; the fact
that most of the 33 plants subject to the assessment do not occur in coniferous forests
where this herbicide is typically used in forestry operations; and some reliance on the
California Department of Pesticide Regulation's endangered species program which
addresses use of this pesticide.

2.4 Stressor Source and Distribution

2.4.1 Environmental Fate Assessment

Imazapyr is an anionic, organic acid that is non-volatile, degrades through photolysis in
clear shallow waters, and is both persistent and mobile in soil. A summary of selected
physical and chemical properties for imazapyr and imazapyr isopropylamine salt are
presented in Table 2.4.1. Imazapyr is mainly present in anionic form at typical
environmental pHs, and the behavior of the acid and salt forms are expected to be similar,
therefore, the environmental fate of the imazapyr will be evaluated in terms of acid
equivalents in this assessment. The chemical structures of imazapyr and imazapyr
isopropylamine salt are shown in Figures 2.4.1 .a and 2.4.1 .b, respectively. The chemical
structures of the two major imazapyr transformation products, CL 119060 and CL 9140,
are shown in Figures 2.4.l.c and 2.4.l.d, respectively.

Tsihle 2.4.1. Some I'hvsicsil. (hemic:il ;iikI Kn\ironnienliil l-'sile Properties of lm;i/:ip\r. (lie

Isopropvhimine S:ill ol' lm;iz;ipvi\ mill Residues olTo\icolo]pyridin-5(7//)-

mcthvlcthvl)-5-o\o-1 //-imidazol-

one,7-hydroxy-

2-yl]-3-pyridinecarboxylic acid

CL 9140:

Salt:

Pyridine 2,3-dicarboxylic

2-Propanamine, 2-(4,5-dihydro-

acid

4-methyl-4-( 1 -methylethyl)-5-oxo-

l/f-imidazol-2-y 1] -3 -

pyridinecarboxylate

-------
Tsihle 2.4.1. Some Phvsiciil. (Iiemiciil :tiul Kn\ironmenl;il l ;ilc Properties of lm;i/;ip\r. (ho
Isopropvliiinine Suit of lm;i/;ipyr. :iiul Residues of To\icolo<>ic;il C oncern.

Empirical Formula

Acid:

C13H15N3O3
Salt:

C13H15N303-C3H9N

CL 119060:

C-H4N1O3
CL 9140:
C-HsNiO,

Chemical Abstract Service Number

Acid:

81334-34-1
Salt:

81510-83-0

CL 119060:

90322-54-6
CL 9140:
89-00-9

Molecular Weight

Acid:

261.28 amu
Salt:

320.39 amu

CL 119060:

137.11 amu
CL 9140:

167.12 amu

Aqueous Solubility at 25 °C

Acid:
11.1 g/L

unknown *

pKa

Acid:
3.8

unknown *

Vapor Pressure at 60 °C

Acid:

<10"7 mmHg

unknown *

Henry's Law Constant at 25 °C

Acid:

<7 x 10"17 atm x m3/mol

unknown *

Log Pow at pH 7 and 20 °C

Acid:
0.22

unknown *

/¦jiviroiiiiwiiliil I'ulc I'ropcrfic.s

Hydrolysis half life (pH 7)

Acid:
stable

unknown *

Aqueous photolysis half lives

Acid:

ti/2 = 2.5 - 5.3 days

unknown *

Aerobic metabolism half-lives

Acid:

stable (in soil)

CL 119060:

3.9 and 5.8 days **
(in water + sediment)
CL 9140:

2.9 and 4.3 days **
(in water + sediment)

Anaerobic metabolism half-lives

Acid:
stable

unknown *

Soil-water distribution coefficients
(Koc)

Acid:

30.6 (acid in sand)

99.8 (acid in silt loam sediment)

CL 119060:

134 (sand)

1020 (silt loam sediment)

CL 9140:

217 (sand)

6053 (silt loam sediment)

* Imazapyr value (acid) have been used in absence of data for degradation products: CL 119060 and CL 9140
** Imazapyr (the parent chemical) is stable to aerobic degradation, therefore degradation product half-life values were
not used in aquatic modeling

The herbicide imazapyr is a water soluble, weak acid with a pKa of about 3.8. Based on
this pKa, imazapyr is mainly in anionic form at typical environmental pHs (61% ionized

-------
at pH 4, 94% ionized at pH 5, greater than 99% ionized at pH 6 and higher). Commercial
formulations contain either imazapyr acid or the imazapyr isopropylamine salt, both of
which are generally dissolved in a water solution. Most environmental fate data available
for imazapyr are based on dissociation of the isopropylamine salt in water. The behavior
of these two moieties in the environment should be similar.

Imazapyr is susceptible to aqueous photolysis, the only identified route of rapid
degradation for imazapyr in the open environment. Photolysis half-lives in water range
between 2.5-5.3 days (MRID 00131617). Two major photolysis transformation
products identified were a pyridine hydroxy-dicarboxylic acid (CL 119060) and pyridine
dicarboxylic acid (CL 9140) which reached a maximum chemical equivalent of the parent
compound of 32% and 23%, respectively. These two major photodegradates were each
separately tested for aquatic metabolism under laboratory aerobic aquatic conditions and
their aerobic aquatic metabolism half-lives were in the range of three to eight days in two
different sediment/water systems.

Imazapyr was essentially stable to aerobic and anaerobic soil metabolism, and no major
transformation products were identified during the course of laboratory studies. The
persistence of imazapyr in soil was demonstrated by extrapolation of laboratory half-lives
in three aerobic soils to approximately 1.2 years (MRID 45119701), 1.4 years (ACC. No.
251505), and 5.9 years (MRID 41023201).

Only limited data are available for these two major aquatic photolysis transformation
products of imazapyr. Minor concentrations of identified and unidentified transformation
products were detected in the aerobic studies (MRIDs 41023201 and 45119701). In the
latter study, two transformation products reached a maximum of approximately 7% of
parent radioactivity, and, based on simple kinetics, would not be expected to significantly
exceed this maximum. These degradation products were estimated to have relatively
short half-lives of about one month.

In the absence of a full suite of environmental fate data, for modeling purposes, these
compounds are assumed to be equivalent to the parent, the acid form of imazapyr.
However, data are available which indicate that the two major transformation products do
degrade under aerobic aquatic conditions while the parent compound is stable, and that
these compounds are much less mobile than imazapyr. Currently available aquatic
modeling techniques would require conservative assumptions be made concerning
maximum amount of degradates which form under environmental conditions, and/or the
actual value of missing model input parameters when an approved method of combining
parent/degradate data is not available. As a result, modeled aquatic EEC values for total
toxic residues will be more conservative than EECs calculated for the parent only.

Laboratory bioconcentration studies with bluegill sunfish, eastern oyster, and grass
shrimp indicate that parent imazapyr, even though long-lived in the environment, is not
subject to bioconcentration (bioconcentration factor <1). Bioconcentration in caged fish
and crayfish species was also measured as part of an otherwise unacceptable aquatic field
dissipation study. The reported limit of detection for imazapyr in tissues of the caged

-------
animals (three fish and one crayfish species at each of two sites, total of seven different
species) was a relatively high at 50 parts per billion (ppb). Within the 50 ppb limit, it is
not unreasonable to conclude that parent imazapyr did not bioconcentrate during the
aquatic field study. There was no attempt to analyze for metabolites or degradates in any
of the species tested. The relatively high solubility in water and low n-octanol to water
partitioning ratio of imazapyr is also consistent with little likelihood of bioconcentration.

In summary, imazapyr is an anionic, organic acid that is non-volatile and is both
persistent and mobile in soil. Upon direct application, or indirect release into water,
photolysis is the only identified route of imazapyr degradation in the open environment.
Laboratory studies show imazapyr is essentially stable to hydrolysis, aerobic and
anaerobic soil degradation as well as aerobic and anaerobic aquatic metabolism. Field
study observations are consistent with imazapyr's intrinsic ability to persist in soils and
move via runoff in surface water and leach to groundwater. Imazapyr did not
bioconcentrate in submitted laboratory studies.

-N ^

Figure 2.4.1.a. Chemical Structure of Imazapyr

Figure 2.4.1.b. Chemical Structure of Isopropylamine Salt of Imazapyr

-------
OH

Figure 2.4.1.c. Chemical Structure of CL 119060

Figure 2.4.1.d Chemical Structure of CL 9140

2.4.2 Environmental Transport Assessment

Volatility

Based on a low vapor pressure of <10"7 mm Hg at 60 °C, volatilization is an unlikely
route of dissipation from soil. Available studies show that hydrolysis in moist soil and
photodegradation on soil are unlikely to occur.

Aquatic Transport

Present as an anion at typical environmental pH values, imazapyr tends to be weakly
sorbed to most soils, and therefore, is prone to leach and runoff. For anionic compounds,
sorption would tend to diminish with increasing environmental pH. In several studies
involving a total of 11 different soils and sediments, adsorption coefficients were low, as
demonstrated by batch/bulk equilibrium sorption coefficients that range from 0.04 to 3.4
mL/g, with a median of 0.6 mL/g. There was no apparent correlation with soil organic
matter.

In a submitted laboratory batch equilibrium study conducted with the imazapyr
transformation products included in this assessment, CL 119060 and CL 9140, these
transformation products were much less mobile than the parent, imazapyr. Reported Koc
values were 6053 and 1020 in silt loam sediment for CL 119060 and CL 9140,
respectively.

-------
Field-plot studies with the formulated product, Arsenal 2AS (MRIDs 42192101 and
42192102) did not address the mode(s) of dissipation. An additional terrestrial field
dissipation study (MRID 45119706) showed that imazapyr is prone to leach, and is
relatively long-lived. Degradation products were not tracked in these filed dissipation
studies.

Although the potential impact of discharging groundwater on CRLF populations is not
explicitly delineated, it should be noted that groundwater could provide a source of
pesticide to surface water bodies - especially low-order streams, headwaters, and
groundwater-fed pools. This is particularly likely if the chemical is persistent and
mobile. Soluble chemicals that are only subject to photolytic degradation will be very
likely to persist in groundwater, and can be transportable over long distances. Much of
this groundwater will eventually be discharged to the surface - often supporting stream
flow in the absence of rainfall. Continuously flowing low-order streams in particular are
sustained by groundwater discharge, which constitutes 100% of stream flow during
baseflow (no runoff) conditions. Thus, it is important to keep in mind that pesticides in
groundwater can have a major (detrimental) impact on surface water quality, and on
CRLF habitat.

Long Range Atmospheric Transport

The physicochemical properties of imazapyr that describe its potential to enter the air
from water or soil (e.g., Henry's Law constant and vapor pressure), pesticide use,
modeled estimated concentrations in water and air, and available air monitoring data
from the Central Valley and the Sierra Nevadas are considered in evaluating the potential
for atmospheric transport of imazapyr habitat for the CRLF.

In general, deposition of drifting or volatilized pesticides is expected to be greatest close
to the site of application. Computer models of spray drift (AgDRIFT or AGDISP) are
used to determine if the exposures to aquatic and terrestrial organisms are below the
Agency's Levels of Concern (LOCs). If the limit of exposure that is below the LOC can
be determined using AgDRIFT or AGDISP, longer-range transport is not considered in
defining the action area. For example, if a buffer zone <1,000 feet (the optimal range for
AgDRIFT and AGDISP models) results in terrestrial and aquatic exposures that are
below LOCs, no further drift analysis is required. If exposures exceeding LOCs are
expected beyond the standard modeling range of AgDRIFT or AGDISP, the Gaussian
extension feature of AGDISP may be used. In addition to the use of spray drift models to
determine potential off-site transport of pesticides, other factors such as available air
monitoring data and the physicochemical properties of the chemical are also considered.

2.4.3 Mechanism of Action

Imidazoline herbicides, such as imazapyr, are systemic plant growth inhibitors that are
normally active at very low rates. However, imazapyr appears not to be as active as most
imidazoline herbicides at very low rates. Uptake of imazapyr is primarily through the
foliage and roots. It is then translocated to meristematic tissue where it inhibits

-------
acetohydroxyacid synthase (AHAS or ALS), thus, disrupting protein synthesis and
interfering with cell growth and DNA synthesis. AHAS is not present in mammals,
birds, fish, or insects. As a result, imazapyr is specifically toxic to plants.

2.4.4 Use Characterization

The only nationally labeled agricultural use of imazapyr is for use on corn fields planted
with Clearfield™ Corn. However, that use is not allowed within the state of California.
Granular formulations of imazapyr are also labeled for national use, but not allowed
within the state of California. These uses therefore have not been considered in this
assessment.

There are no labeled indoor uses for imazapyr.

Outdoor, non-agricultural uses of imazapyr include uses:

• To control aquatic weeds in or near bodies of water which may be flowing, non-
flowing or transient: aquatic sites that include lakes, rivers, streams, ponds, seeps,
drainage ditches, canals, reservoirs, swamps, bogs, marshes, estuaries, bays, brackish
water, transitional areas between terrestrial and aquatic sites and seasonal wet areas,
including estuarine and marine sites in or around surface water in wetland, riparian
and terrestrial habitats.

• On industrial and public utility sites including: roads, transmission lines, bareground
areas, storage areas, tank farms, pumping stations, pipelines under paved surfaces,
industrial parks, plant sites, fencerows, and utility rights-of-way. Imazapyr can be
used under asphalt, pond liners and other paved areas, but only in industrial sites or
where the pavement has a suitable barrier along the perimeter that prevents
encroachment of roots from desirable plants. Imazapyr is not recommended for use
under pavement on residential properties such as driveways or parking lots, nor in
recreational areas such as under bike or jogging paths, golf cart paths, tennis courts,
or where landscape plantings could be anticipated.

• On forestry sites managed for timber production including forest roads and non-
irrigation ditch banks

• On airports, military installations, schools/universities, libraries and hospitals,
highway rights-of ways, interchange ramps, waysides, service areas, unpaved roads,
railroad and utility rights-of-way, sewage disposal areas, farmyards, fuel storage
areas, fence rows, non-irrigation ditch banks, and barrier strips (including grazed or
hayed areas on these sites, and use for establishing and maintaining of wildlife
openings).

• On pasture land and rangeland.

-------
• On non-residential established turfgrass areas maintained under high levels of cultural
management, such as: improved sections of industrial grounds, athletic fields,
cemeteries, parks, golf course roughs and institutional grounds.

• On residential driveways, parking areas, brick walks, gravel pathways, patios, along
fences, curbs and cracks in sidewalks.

Analysis of this labeled use information is the critical first step in evaluating the federal
action. The current labels for imazapyr represent the FIFRA regulatory action.

Therefore, labeled use and application rates specified on the label form the basis of this
assessment. The assessment of use information is critical to the development of the
action area and selection of appropriate modeling scenarios and inputs

2.4.4.1 Imazapyr Use Characterization in California

An analysis of county-level usage information for imazapyr was obtained from the
California's Department of Pesticide Regulation Pesticide Use Reporting (CDPR PUR)
database3 . California State law requires that pesticide application be reported to the state
and made available to the public. These data are available by county and were averaged
together over the years 2002 to 2005 to calculate average annual usage statistics by
county and usage type, including pounds of active ingredient applied and base acres
treated (when available). The summary of imazapyr usage for all use sites is provided
below in Table 2.4.4. Uncertainties regarding the CDPR PUR data are discussed in the
Uncertainties Section (Section 6.0).

Between 2002 and 2005,4 imazapyr (salt formulation) use was reported in 51 counties in
California. Reported uses were on forest trees, landscape maintenance, rights-of-way and
pest control. Data for non-professional residential and turf applications, along with
applications to rangeland/pastureland, and non-crop aquatic uses are not captured in
CDPR PUR database, and have not been estimated here. There are no labeled
agricultural uses within California. The greatest usage (average of pounds applied per
commodity across all four years) was to forestry uses in Mendocino County at 3,980 lbs
annually. By far, the greatest overall usage of imazapyr recorded in California is to
forestry uses at an average of approximately 13,000 lbs annually, followed by rights-of-
way at an average of 1325 lbs annually, landscape maintenance at 66 lbs annually, and
structural and regulatory pest control with 172 lbs applied over the total four year period.
All remaining imazapyr (salt) uses have not been captured by the CDPR PUR database.

3 The California Department of Pesticide Regulation's Pesticide Use Reporting database provides a census
of pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/purmain.htm.

4 2000 and 2001 CDPR PUR data not used in this assessment due to inclusion of outliers into the data set

-------
The only reported use for imazapyr acid is for alfalfa, which is not a currently registered
use. The uses considered in this risk assessment represent all currently registered uses
according to a review of all current labels. No other uses are relevant to this assessment.
Any reported use, such as may be seen in the CDPR PUR database, represent either
historic uses that have been canceled, mis-reported uses, or mis-use. Historical uses, mis-
reported uses, and misuse are not considered part of the federal action and, therefore, are
not considered in this assessment.

The summary of imazapyr usage for all use sites captured in the CDPR PUR database is
provided below in Table 2.4.4.

Table 2.4.4 Summary of CDPR PUR Usage Data from 2002 to 2005 for Imazapyr

Sum of average

Average

annual pounds

area treated

application rate

Use site

applied

(acres)

(lbs ai/acre)

LANDSCAPE MAINTENANCE

175

data not available

RIGHTS-OF-WAY

5302

data not available

STRUCTURAL AND

REGULATORY PEST CONTROL

172

data not available

FOREST TREES, FOREST LANDS

52,743

123,706.6

0.43

2.5 Assessed Species

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

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

2.5.1 Distribution

The CRLF is endemic to California and Baja California (Mexico) and historically
inhabited 46 counties in California including the Central Valley and both coastal and
interior mountain ranges (USFWS 1996). Its range has been reduced by about 70%, and
the species currently resides in 22 counties in California (USFWS 1996). The species has
an elevational range of near sea level to 1,500 meters (5,200 feet) (Jennings and Hayes

-------
1994); however, nearly all of the known CRLF populations have been documented below
1,050 meters (3,500 feet) (USFWS 2002).

Populations currently exist along the northern California coast, northern Transverse
Ranges (USFWS 2002), foothills of the Sierra Nevada (5-6 populations), and in southern
California south of Santa Barbara (two populations) (Fellers 2005a). Relatively larger
numbers of CRLF's are located between Marin and Santa Barbara Counties (Jennings
and Hayes 1994). A total of 243 streams or drainages are believed to be currently
occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and
Santa Barbara counties (USFWS 1996). Occupied drainages or watersheds include all
bodies of water that support CRLF's (i.e., streams, creeks, tributaries, associated natural
and artificial ponds, and adjacent drainages), and habitats through which CRLF's can
move (i.e., riparian vegetation, uplands) (USFWS 2002).

The distribution of CRLFs within California is addressed in this assessment using four
categories of location including recovery units, core areas, designated critical habitat, and
known occurrences of the CRLF reported in the California Natural Diversity Database
(CNDDB) that are not included within core areas and/or designated critical habitat (see
Figure 2.5.1). Recovery units, core areas, and other known occurrences of the CRLF
from the CNDDB are described in further detail in this section, and designated critical
habitat is addressed in Section 2.6. Recovery units are large areas defined at the
watershed level that have similar conservation needs and management strategies. The
recovery unit is primarily an administrative designation, and land area within the
recovery unit boundary is not exclusively CRLF habitat. Core areas are smaller areas
within the recovery units that comprise portions of the species' historic and current range
and have been determined by USFWS to be important in the preservation of the species.
Designated critical habitat is generally contained within the core areas, although a
number of critical habitat units are outside the boundaries of core areas, but within the
boundaries of the recovery units. Additional information on CRLF occurrences from the
CNDDB is used to cover the current range of the species not included in core areas
and/or designated critical habitat, but within the recovery units

Recovery Units

Eight recovery units have been established by USFWS for the CRLF. These areas are
considered essential to the recovery of the species, and the status of the CRLF "may be
considered within the smaller scale of the recovery units, as opposed to the statewide
range" (USFWS 2002). Recovery units reflect areas with similar conservation needs and
population statuses, and therefore, similar recovery goals. The eight units described for
the CRLF are delineated by watershed boundaries defined by US Geological Survey
hydrologic units and are limited to the elevational maximum for the species of 1,500 m
above sea level. The eight recovery units for the CRLF are listed in Table 2.5.1 and
shown in Figure 2.5.1.

-------
Core Areas

USFWS has designated 35 core areas across the eight recovery units to focus their
recovery efforts for the CRLF (see Figure 2.5.1). Table 2.5.1 summarizes the
geographical relationship among recovery units, core areas, and designated critical
habitat. The core areas, which are distributed throughout portions of the historic and
current range of the species, represent areas that allow for long-term viability of existing
populations and reestablishment of populations within historic range. These areas were
selected because they: 1) contain existing viable populations; or 2) they contribute to the
connectivity of other habitat areas (USFWS 2002). Core area protection and
enhancement are vital for maintenance and expansion of the CRLF's distribution and
population throughout its range.

For purposes of this assessment, designated critical habitat, currently occupied (post-
1985) core areas, and additional known occurrences of the CRLF from the CNDDB are
considered. Each type of locational information is evaluated within the broader context
of recovery units. For example, if no labeled uses of imazapyr occur (or if labeled uses
occur at predicted exposures less than the Agency's LOCs) within an entire recovery unit,
a "no effect" determination would be made for all designated critical habitat, currently
occupied core areas, and other known CNDDB occurrences within that recovery unit.
Historically occupied sections of the core areas are not evaluated as part of this
assessment because the USFWS Recovery Plan (USFWS 2002) indicates that CRLFs are
extirpated from these areas. A summary of currently and historically occupied core areas
is provided in Table 2.5.1 (currently occupied core areas are bolded). While core areas
are considered essential for recovery of the CRLF, core areas are not federally-designated
critical habitat, although designated critical habitat is generally contained within these
core recovery areas. It should be noted, however, that several critical habitat units are
located outside of the core areas, but within the recovery units. The focus of this
assessment is currently occupied core areas, designated critical habitat, and other known
CNDDB CRLF occurrences within the recovery units. Federally-designated critical
habitat for the CRLF is further explained in Section 2.6.

Tsihle 2.5.1. (';ilir»rniii Ued-le««e(l Krog Recovery I'nils with Overhippiii" Core
Aresis iiiul Designated ( rilicnl llnhilnl

Ucco\ cr\ I nil 1
(l- iiiiiiv 2.5.1)

("ore Arcas " (I'iiiiire 2.5.1)

Critical llahilal
I nils

Currcnlh
Occupied
(posl-l')X5)

Historically
Occupied 4

Sierra Nevada
Foothills and Central
Valley (1)

(eastern boundary is
the 1,500m elevation
line)

Cottonwood Creek (partial)
(8)

Feather River (1)

BUT-1A-B

Yuba River-S. Fork Feather
River (2)

YUB-1

NEV-16

Traverse Creek/Middle Fork
American River/Rubicon (3)

Consumnes River (4)

ELD-1

-------
Tsihle 2.5.1. (';ilir»rniii Ued-le««e(l Krog Recovery I'nils with Overlapping Core
Aresissiml Designated ( rilicnl Ihihilnl

Uec»\ er\ I nil
(ligiire 2.5.1)

("ore Areas : (l-igure 2.5.1)

( rilical llahilal
I nils

( iirrcnllt
Occupied
(|)
-------
Tsihle 2.5.1. (';ilir»rniii Uc(l-lc««c(l Krog Recovery I nits with Overhippiii" Core
Aresissiml Designated Crilic:il Ihihilnl

Ucco\ cr\ I nil 1
(ligurc 2.5.1)

( ore Arcas : (I'iguiv 2.5.1)

( rilical llahilal
I nils

( urrcnllt
Occupied
(posl-iyS5)

llisloi'icall>
Occupied 4

Slough (partial)(19)

Carmel River-Santa Lucia
(partial)(20)

Gablan Range (21)

SNB-3

Estrella River (28)

SLO-1A-B

Northern Transverse
Ranges and
Tehachapi Mountains
(7)

SLO-86

Santa Maria River-Santa
Ynez River (24)

STB-4, STB-5,
STB-7

Sisquoc River (25)

STB-1, STB-3

Ventura River-Santa Clara
River (26)

VEN-1, VEN-2,
VEN-3

LOS-16

Southern Transverse
and Peninsular
Ranges (8)

Santa Monica Bay-Ventura
Coastal Streams (27)

San Gabriel Mountain (29)

Forks of the Mojave (30)

Santa Ana Mountain (31)

Santa Rosa Plateau (32)

San Luis Rey (33)

Sweetwater (34)

Laguna Mountain (35)

Recovery units designated by the USFWS (USFWS 2000, pg 49).

2 Core areas designated by the USFWS (USFWS 2000, pg 51).

3 Critical habitat units designated by the USFWS on April 13, 2006 (USFWS 2006, 71 FR 19244-19346).

4 Currently occupied (post-1985) and historically occupied core areas as designated by the USFWS
(USFWS 2002, pg 54).

5 Critical habitat unit where identified threats specifically included pesticides or agricultural runoff
(USFWS 2002).

6 Critical habitat units that are outside of core areas, but within recovery units.

7 Currently occupied core areas that are included in this effects determination are bolded.

-------
Recovery Units

Legend

Sierra Nevada Foothills and Central Valley
North Coast Range Foothills and Western
Sacramento River Valley
North Coast and North San Francisco Bay
South and East San Francisco Bay
Central Coast

Diablo Range and Salinas Valley
Northern Transverse Ranges and Tehachapi
Mountains

Southern Transverse and Peninsular Ranges

| Recovery Unit Boundaries
Currently Occupied Core Areas
Critical Habitat
CNDDB Occurence Sections
County Boundaries q

10.

11.

12.

13.

14.

15.

16.

17.

18.

Core Areas*

Feather River

Yuba River- S. Fork Feather River

Traverse Creek/ Middle Fork/ American R.

Rubicon

Cosumnes River

South Fork Calaveras River*

Tuolumne River*

Piney Creek*

Cottonwood Creek

Putah Creek - Cache Creek*

Lake Berryessa Tributaries

Upper Sonoma Creek

Petaluma Creek - Sonoma Creek

Pt. Reyes Peninsula

Belvedere Lagoon

Jameson Canyon - Lower Napa River
East San Francisco Bay
Santa Clara Valley

19. South San Francisco Bay

20. Watsonville Slough-Elkhorn Slough

21. Carmel River - Santa Lucia

22. Gablan Range

23. Estero Bay

24. Arroyo Grange River

25. Santa Maria River - Santa Ynez River

26. Sisquoc River

27. Ventura River - Santa Clara River

28. Santa Monica Bay — Venura Coastal Streams

29. Estrella River

30. San Gabriel Mountain*

31. Forks of the Moj ave *

32. Santa Ana Mountain*

33. Santa Rosa Plateau

34. San Luis Ray*

35. Sweetwater*

36. Laguna Mountain*

1 Core areas that were historically occupied by the California red-legged frog are not included in the map

Figure 2.5.1. Recovery Unit, Core Area, Critical Habitat, and Occurrence
Designations

-------
Other Known Occurrences from the CNDBB

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

2.5.2 Reproduction

CRLFs breed primarily in ponds; however, they may also breed in quiescent streams,
marshes, and lagoons (Fellers 2005a). According to the Recovery Plan (USFWS 2002),
CRLFs breed from November through late April. Peaks in spawning activity vary
geographically; Fellers (2005b) reports peak spawning as early as January in parts of
coastal central California. Eggs are fertilized as they are being laid. Egg masses are
typically attached to emergent vegetation, such as bulrushes (Scirpus spp.) and cattails
(.Typha spp.) or roots and twigs, and float on or near the surface of the water (Hayes and
Miyamoto 1984). Egg masses contain approximately 2000 to 6000 eggs ranging in size
between 2 and 2.8 mm (Jennings and Hayes 1994). Embryos hatch 10 to 14 days after
fertilization (Fellers 2005a) depending on water temperature. Egg predation is reported
to be infrequent and most mortality is associated with the larval stage (particularly
through predation by fish); however, predation on eggs by newts has also been reported
(Rathburn 1998). Tadpoles require 11 to 28 weeks to metamorphose into juveniles
(terrestrial-phase), typically between May and September (Jennings and Hayes 1994,
USFWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until
the following year) (Fellers 2005b, USFWS 2002). Males reach sexual maturity at 2
years, and females reach sexual maturity at 3 years of age; adults have been reported to
live 8 to 10 years (USFWS 2002). Figure 2.5.2 depicts CRLF annual reproductive
timing.

Figure 2.5.2 - CRLF Reproductive Events by Month

Light Blue =

Green = lat over-winter)

Orange =

Adults and juveniles can be present all year

-------
2.5.3 Diet

Although the diet of CRLF aquatic-phase larvae (tadpoles) has not been studied
specifically, it is assumed that their diet is similar to that of other frog species, with the
aquatic phase feeding exclusively in water and consuming diatoms, algae, and detritus
(USFWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar, 1980)
via mouthparts designed for effective grazing of periphyton (Wassersug, 1984,
Kupferberg et al.\ 1994; Kupferberg, 1997; Altig and McDiarmid, 1999).

Juvenile and adult CRLFs forage in aquatic and terrestrial habitats, and their diet differs
greatly from that of larvae. The main food source for juvenile aquatic- and terrestrial-
phase CRLFs is thought to be aquatic and terrestrial invertebrates found along the
shoreline and on the water surface. Hayes and Tennant (1985) report, based on a study
examining the gut content of 35 juvenile and adult CRLFs, that the species feeds on as
many as 42 different invertebrate taxa, including Arachnida, Amphipoda, Isopoda,
Insecta, and Mollusca. The most commonly observed prey species were larval alderflies
(Sialis cf. californica), pillbugs (Armadilliadrium vulgare), and water striders (Gerris sp).
The preferred prey species, however, was the sowbug (Hayes and Tennant, 1985). This
study suggests that CRLFs forage primarily above water, although the authors note other
data reporting that adults also feed under water, are cannibalistic, and consume fish. For
larger CRLFs, over 50% of the prey mass may consists of vertebrates such as mice, frogs,
and fish, although aquatic and terrestrial invertebrates were the most numerous food
items (Hayes and Tennant 1985). For adults, feeding activity takes place primarily at
night; for juveniles feeding occurs during the day and at night (Hayes and Tennant 1985).

2.5.4 Habitat

CRLFs require aquatic habitat for breeding, but also use other habitat types including
riparian and upland areas throughout their life cycle. CRLF use of their environment
varies; they may complete their entire life cycle in a particular habitat or they may utilize
multiple habitat types. Overall, populations are most likely to exist where multiple
breeding areas are embedded within varying habitats used for dispersal (USFWS 2002).
Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al.
1997). Dense vegetation close to water, shading and water of moderate depth are habitat
features that appear especially important for CRLF (Hayes and Jennings 1988). Breeding
sites include streams, deep pools, backwaters within streams and creeks, ponds, marshes,
sag ponds (land depressions between fault zones that have filled with water), dune ponds,
and lagoons. Breeding adults have been found near deep (0.7 m) still or slow moving
water surrounded by dense vegetation (USFWS 2002); however, the largest number of
tadpoles have been found in shallower pools (0.26 - 0.5 m) (Reis, 1999). Data indicate
that CRLFs do not frequently inhabit vernal pools, as conditions in these habitats
generally are not suitable (Hayes and Jennings 1988).

CRLFs also frequently breed in artificial impoundments such as stock ponds, although

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additional research is needed to identify habitat requirements within artificial ponds
(USFWS 2002). Adult CRLFs use dense, shrubby, or emergent vegetation closely
associated with deep-water pools bordered with cattails and dense stands of overhanging
vegetation (http://www.fws.gov/endangered/features/rl frog/rlfrog.html#where).

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

Imazapyr is registered for direct application to non-irrigation water for the control of
aquatic weeds. For this assessment, concentrations were calculated resulting from thirty
annual direct applications to the entire surface of the 2.0 meter deep standard EXAMS
water body.

During dry periods, the CRLF is rarely found far from water, although it will sometimes
disperse from its breeding habitat to forage and seek other suitable habitat under downed
trees or logs, industrial debris, and agricultural features (UWFWS 2002). According to
Jennings and Hayes (1994), CRLFs also use small mammal burrows and moist leaf litter
as habitat. In addition, CRLFs may also use large cracks in the bottom of dried ponds as
refuge; these cracks may provide moisture for individuals avoiding predation and solar
exposure (Alvarez 2000).

2.6 Designated Critical Habitat

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

'Critical habitat' is defined in the ESA as the geographic area occupied by the species at
the time of the listing where the physical and biological features necessary for the
conservation of the species exist, and there is a need for special management to protect
the listed species. It may also include areas outside the occupied area at the time of
listing if such areas are 'essential to the conservation of the species.' All designated
critical habitat for the CRLF was occupied at the time of listing. Critical habitat receives
protection under Section 7 of the ESA through prohibition against destruction or adverse
modification with regard to actions carried out, funded, or authorized by a federal
Agency. Section 7 requires consultation on federal actions that are likely to result in the
destruction or adverse modification of critical habitat.

To be included in a critical habitat designation, the habitat must be 'essential to the

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conservation of the species.' Critical habitat designations identify, to the extent known
using the best scientific and commercial data available, habitat areas that provide
essential life cycle needs of the species or areas that contain certain primary constituent
elements (PCEs) (as defined in 50 CFR 414.12(b)). PCEs include, but are not limited to,
space for individual and population growth and for normal behavior; food, water, air,
light, minerals, or other nutritional or physiological requirements; cover or shelter; sites
for breeding, reproduction, rearing (or development) of offspring; and habitats that are
protected from disturbance or are representative of the historic geographical and
ecological distributions of a species. The designated critical habitat areas for the CRLF
are considered to have the following PCEs that justify critical habitat designation:

• Breeding aquatic habitat;

• Non-breeding aquatic habitat;

• Upland habitat; and

• Dispersal habitat.

Please note that a more complete description of these habitat types is provided in
Attachment I.

Occupied habitat may be included in the critical habitat only if essential features within
the habitat may require special management or protection. Therefore, USFWS does not
include areas where existing management is sufficient to conserve the species. Critical
habitat is designated outside the geographic area presently occupied by the species only
when a designation limited to its present range would be inadequate to ensure the
conservation of the species. For the CRLF, all designated critical habitat units contain all
four of the PCEs, and were occupied by the CRLF at the time of FR listing notice in
April 2006. The FR notice designating critical habitat for the CRLF includes a special
rule exempting routine ranching activities associated with livestock ranching from
incidental take prohibitions. The purpose of this exemption is to promote the
conservation of rangelands, which could be beneficial to the CRLF, and to reduce the rate
of conversion to other land uses that are incompatible with CRLF conservation. See
Section 2.6.1 below for an explanation on this special rule as it pertains to imazapyr.

USFWS has established adverse modification standards for designated critical habitat
(USFWS 2006). Activities that may destroy or adversely modify critical habitat are those
that alter the PCEs and jeopardize the continued existence of the species. Evaluation of
actions related to use of imazapyr that may alter the PCEs of the CRLF's critical habitat
form the basis of the critical habitat impact analysis. According to USFWS (2006),
activities that may affect critical habitat and therefore may result in adverse effects to the
CRLF include, but are not limited to the following:

(1) Significant alteration of water chemistry or temperature to levels beyond the
tolerances of the CRLF that result in direct or cumulative adverse effects to
individuals and their life-cycles.

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(2) Significant increase in sediment deposition within the stream channel or pond or
disturbance of upland foraging and dispersal habitat that could result in
elimination or reduction of habitat necessary for the growth and reproduction of
the CRLF by increasing the sediment deposition to levels that would adversely
affect their ability to complete their life cycles.

(3) Significant alteration of channel/pond morphology or geometry that may lead to
changes to the hydrologic functioning of the stream or pond and alter the timing,
duration, water flows, and levels that would degrade or eliminate the CRLF
and/or its habitat. Such an effect could also lead to increased sedimentation and
degradation in water quality to levels that are beyond the CRLF's tolerances.

(4) Elimination of upland foraging and/or aestivating habitat or dispersal habitat.

(5) Introduction, spread, or augmentation of non-native aquatic species in stream
segments or ponds used by the CRLF.

(6) Alteration or elimination of the CRLF's food sources or prey base (also
evaluated as indirect effects to the CRLF).

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

2.6.1. Special Rule Exemption for Routine Ranching Activities

As part of the critical habitat designation, the Service promulgated a special rule
exemption regarding routine ranching activities where there is no Federal nexus from
take prohibitions under Section 9 of the ESA. (USFWS 2006, 71 FR 19285-19290). The
Service's reasoning behind this exemption is that managed livestock activities, especially
the creation of stock ponds, provide habitat for the CRLF. Maintenance of these areas as
rangelands, rather than conversion to other uses should ranching prove to be
economically infeasible is, overall, of net benefit to the species.

Several of the specific activities exempted include situations where pesticides may be
used in accordance with labeled instructions. In this risk assessment, the Agency has
assessed the risk associated with these practices using the standard assessment
methodologies. Specific exemptions, and the reasoning behind each of the exemptions is
provided below. The rule provides recommended best management practices, but does
not require adherence to these practices by the landowner.

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1. Stock Pond Management and Maintenance

a. Chemical control of aquatic vegetation. These applications are allowed
primarily because the Service felt "it is unlikely that vegetation control
would be needed during the breeding period, as the primary time for
explosive vegetation control is during the warm summer months." The
Service recommends chemical control measures be used only "outside of
the general breeding season (November through April) and juvenile stage
(April through September) of the CRLF." Mechanical means are the
preferred method of control.

b. Pesticide applications for mosquito control. These applications are
allowed because of concerns associated with human and livestock health.
Alternative mosquito control methods, primarily introduction of nonnative
fish species, are deemed potentially more detrimental to the CRLF than
chemical or bacterial larvicides. The Service believes "it unlikely that
[mosquito] control would be necessary during much of the CRLF breeding
season," and that a combination of management methods, such as
manipulation of water levels, and/or use of a bacterial larvicide will
prevent or minimize incidental take.

2. Rodent Control. The Service notes "we believe the use of rodenticides present a
low risk to CRLF conservation." In large part, this is due to the fact that "it is
unknown the extent to which small mammal burrows are essential for the
conservation of CRLF."

a. Toxicant-treated grains. No data were available to evaluate the potential
effects of these compounds (primarily anti-coagulants) on the CRLF.

Grain is not a typical food item for the frog, but individuals may be
indirectly exposed by consuming invertebrates which have ingested
treated grain. There is a possibility of dermal contact, especially when the
grain is placed in the burrows. Placing treated grain into the burrows is
not prohibited, but should this method of rodent control be used, the
Service recommends bait-station or broadcast application methods to
reduce the probability of exposure.

b. Burrow fumigants. Use of burrow fumigants is not prohibited, but the
Service recommends "not using burrow fumigants within 0.7 mi (1.2 km)
in any direction from a water body" suitable as CRLF habitat.

The exemption for stock pond management and maintenance may be particularly relevant
to this use of imazapyr for these purposes.

2.7 Action Area

For listed species assessment purposes, the action area is considered to be the area

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affected directly or indirectly by the federal action and not merely the immediate area
involved in the action (50 CFR 402.02). It is recognized that the overall action area for
the national registration of imazapyr is likely to encompass considerable portions of the
United States based on both the one agricultural use on Clearfield™ Corn (a use not
labeled for the state of California), and on the large array of non-agricultural uses for both
liquid (use allowed in California) and granular (use not allowed in California)
formulations. However, the scope of this assessment limits consideration of the overall
action area to those portions that may be applicable to the protection of the CRLF and its
designated critical habitat within the state of California. Deriving the geographical extent
of this portion of the action area is the product of consideration of the types of effects that
imazapyr may be expected to have on the environment, the exposure levels to imazapyr
that are associated with those effects, and the best available information concerning the
use of imazapyr and its fate and transport within the state of California.

The definition of action area requires a stepwise approach that begins with an
understanding of the federal action. The federal action is defined by the currently labeled
uses for imazapyr. An analysis of labeled uses and review of available product labels
was completed. This analysis indicates that, for imazapyr, the following uses are
considered as part of the federal action evaluated in this assessment:

• Control of aquatic weeds in or near bodies of water which may be flowing, non-
flowing or transient, such as aquatic sites that include lakes, rivers, streams, ponds,
seeps, drainage ditches, canals, reservoirs, swamps, bogs, marshes, estuaries, bays,
brackish water, transitional areas between terrestrial and aquatic sites and seasonal
wet areas, including estuarine and marine sites in or around surface water in wetland,
riparian and terrestrial habitats.

• Manufacturing sites including: roads, transmission lines, bareground areas, storage
areas, tank farms, pumping stations, pipelines under paved surfaces, industrial parks,
plant sites, fencerows, and utility rights-of-way. Imazapyr can be used under asphalt,
pond liners and other paved areas, but only in industrial sites or where the pavement
has a suitable barrier along the perimeter that prevents encroachment of roots from
desirable plants. Imazapyr is not recommended for use under pavement on residential
properties such as driveways or parking lots, nor in recreational areas such as under
bike or jogging paths, golf cart paths, tennis courts, or where landscape plantings
could be anticipated.

• Forestry sites managed for timber production including forest roads and non-
irrigation ditch banks

• Airports, military installations, schools/universities, libraries and hospitals, highway
rights-of ways, interchange ramps, waysides, service areas, unpaved roads, railroad
and utility rights-of-way, sewage disposal areas, farmyards, fuel storage areas, fence
rows, non-irrigation ditchbanks, and barrier strips. This includs grazed or hayed areas
on these sites, and use for establishing and maintaining of wildlife openings.

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• Pasture land and rangeland.

. Non-residential established turfgrass areas maintained under high levels of cultural
management, such as: improved sections of industrial grounds, athletic fields,
cemeteries, parks, golf course roughs and institutional grounds.

• Residential driveways, parking areas, brick walks, gravel pathways, patios, along
fences, curbs and cracks in sidewalks.

• Golf course roughs.

The analysis indicates that the use on corn and granular formulations are not considered
in this assessment because imazapyr is not labeled for corn use within the state of
California, and is therefore not expected to result in exposure to the CRLF.

After determination of which uses will be assessed, an evaluation of the potential
"footprint" of the use pattern is determined. This "footprint" represents the initial area of
concern and is typically based on available land cover data. Local land cover data
available for the state of California were analyzed to refine the understanding of potential
imazapyr use. The overall conclusion of this analysis is that the action area contains all
the current non-agricultural uses. The initial area of concern is defined as all land cover
types that represent the labeled uses described above. No areas are excluded from the
final action area based on usage and land cover data. A map representing all the land
cover types that make up the initial area of concern is presented in Figure 2.7.a.

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Initial Area of Concern for
Imazapyr Labeled Uses in California

Legend

| CA_Counites

~ CA_State_Bou nd ary
imazapyr_all_uses

Compiled from California County boundaries (ESRI, 2002),
USDANational Agriculture Statistical Service (NASS.2002)
Gap Analysis Program Orchard/Vineyard Landcover (GAP)
National Land Cover Database (NLCD) (MRLC, 2001)

Map created by U.S. Environmental Protection Agency,
Office of Pesticides Programs, Environmental Fate and
Effects Division. April 11, 2007.

Projection: Albers Equal Area Conic USGS,

North American Datum of 1983 (NAD 1983)

Figure 2.1.m. Initial Area of Concern

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Once the initial area of concern is defined, the next step is to compare the extent of that
area with the results of the screening level risk assessment completed as part of this
assessment. The screening level risk assessment defines which taxa, if any, are predicted
to be exposed at concentrations above the Agency's Levels of Concern (LOC). For
imazapyr, these taxa include aquatic vascular plants and terrestrial plants, both monocots
and dicots. The screening level assessment also includes an evaluation of the
environmental fate properties of imazapyr to determine which routes of transport are
likely to have an impact on the CRLF.

The total toxic residues of imazapyr are expected to be mobile and persistent in areas of
the open environment not exposed to direct sunlight. The photolysis half-life for the total
toxic residues is 20 days. While the parent compound is not susceptible to hydrolytic,
aerobic or anaerobic degradation, submitted data indicate that the two major degradates
degrade quickly when exposed to aerobic aquatic conditions. The parent compound,
imazapyr, is expected to be mobile in the environment, while the two major degradates
are shown to be less mobile in submitted laboratory studies.

Tsihle 2.7. Siiiniiiiirv of Kn\ ironnienliil l ;ilc I soil in (ho Aqunlic Assessment lor Tolsil
Toxic Residues of (Iniii/iipvr it nil CI. 11(),060 ;iikI CI. (),I40)

l-iilo I'ropcrM

Value Piiivnl
OiiIj

Viiluo 1 oliil Toxic
Residues

MRU) (or source)

Molecular Weight

261 amu

2003 Science Chapter for Aquatic
Uses of Imazapyr

Henry's constant at 25°C
(acid)

< 7 x 10 17 atm -
m3/mole

< 7 x 10 17 atm -
m3/mole *

2005 Science Chapter in support of
RED

Vapor Pressure

< 10~7 mm Hg (torr)

< 10~7 mm Hg (torr) *

(< 1.3 x 10"5 Pa) at 60 °C (method
limit); 2003 Science Chapter for New
Aquatic Uses of Imazapyr

Solubility in Water

11.1 x 103 mg/L

11.1 x 103 mg/L *

25 °C, 2003 Science Chapter for New
Aquatic Uses

Photolysis in Water

4.16 days

19.9 days

MRID 00131617

Aerobic Soil Metabolism

Stable

stable

MRID 00131619

Hydrolysis

Stable

stable

MRID 00132359

Aerobic Aquatic Metabolism
(total sediment/water system)

Stable

stable

MRID 40003712

Anaerobic Aquatic Metabolism
(total sediment/water system)

Stable

stable

MRID 00131619

Mobility (KoC)

99.8

lowest non-sand (silt loam) value;
MRID 45119705

Application Efficiency

0.95 (0.99)

EFED Guidance for aerial (ground)
application

Spray Drift

0.05 (0.01)

EFED Guidance for aerial (ground)
application

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* Imazapyr value used in absence of data for degradation products: CL 119060 and CL 9140
** Highest value of degradation products used

Review of the environmental fate data, as well as physico-chemical properties of
imazapyr indicate that direct application to water, runoff to surface water and leaching to
groundwater which could, in turn, recharge surface waters are likely to be the dominant
routes of exposure. Photolysis is the only route of degradation for imazapyr in the
environment. Photolysis would predominantly occur in open water bodies exposed to
sunlight. This is not necessarily the case for all of the environments where imazapyr will
be used. Imazapyr is highly soluble in water, with an aqueous solubility value of 11.1
grams per liter. The vapor pressure (< 10"7 mm Hg) and Henry's Law Constant (<7x10"
17 atm - m3/mole) values for imazapyr are low enough to exclude atmospheric transfer as
a major route of dissipation for imazapyr in the environment.

Surface water, groundwater, rainfall and atmospheric monitoring data are not available
for imazapyr. While the potential for long range transport of imazapyr outside of the
defined action area cannot be precluded, exposure concentrations are not expected to
exceed those predicted by modeling using the residential and non-residential scenarios
(Sections 3.2 - 3.4).

For the next step in defining the action area for imazapyr, the Agency's LOC
exceedances are used to determine how far outside the initial area of concern effects may
be expected. For imazapyr, the AGDISP model with the Gaussian Far-Field Extension
provides estimates for spray drift buffers that would be needed to avoid adverse effects to
non-target terrestrial plants and aquatic vascular emergent plant species. The buffers are
based on expected spray drift from the site of potential imazapyr application to the point
where the LOC for listed terrestrial plants would no longer be exceeded. For imazapyr,
the buffers range from 7120 (forestry uses, ground application) to 26460 feet (forestry
uses, aerial application). All other imazapyr uses that are applied by either aerial or
ground spray in California have estimated spray drift buffers in between these two values.

For aquatic plants, the initial area of concern is further expanded by estimating the
downstream distance where concentrations are expected to be above the non-listed
aquatic plant LOC. Imazapyr aquatic uses provide the largest downstream distance. The
determination of the downstream distance starts with finding the use with the greatest
ratio of aquatic RQ to LOC. For aquatic uses with imazapyr, this ratio is 4.67 (4.67/1).
The downstream dilution approach (described in Section 2.10.1.3) yields a target percent
treated area (also referred to as "percent cropped area", or PCA) of 21.4% for imazapyr
aquatic uses. Using this value as an input into the downstream dilution approach adds a
total of 7,450 stream miles from the initial area of concern (footprint of use). The total
California stream miles is 332,962 miles, the total stream miles in the initial area of
concern is 222,188 miles and the total stream miles in the final action area is 229,638
miles. The stream mile maps are provided in Appendix C.

From the two methods (spray drift buffer and downstream distance), the greatest

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expansion of the initial area of concern is considered the action area. The initial area of
concern with both the buffered area and the downstream extent yields the final action
area for imazapyr use in California. The action area is presented graphically for the
whole state of California in Figure 2.1 b. These data suggest that with all the imazapyr
uses combined and the terrestrial buffer distance of 26460 feet on forestry uses only, the
action area comprises all of the land area in the state of California, including the core and
critical habitat of the CRLF.

Subsequent to defining the action area, an evaluation of usage information is conducted
to determine the area where use of imazapyr may impact the CRLF. This analysis is used
to characterize where predicted exposures are most likely to occur but does not preclude
use in other portions of the action area. The county-level data from the CDPR PUR
database suggest that the greatest overall usage of imazapyr in California is to forestry,
followed by rights-of-way, landscape maintenance and structural and regulatory pest
control. It is noted, however, that non-professional residential applications, applications
to turf and rangeland/pastureland and non-crop aquatic uses are not captured in the CDPR
PUR database. In addition, only 4 years of data are available. Therefore, these data are
very limited and are only used for general descriptions of the usage patterns in California.

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Imazapyr-AA, Overview

Legend

CA counties
CRLF Recovery Unit
CNDDB_occurence_sections
| Core areas
\777\ Forest 26460ft AA

|_[ imazapyr_For26460_ovlp
| imazapyr all uses AA

l Kilometers
0 2550 100 150 200

Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Service (NASS, 2002)
Gap Analysis Program Orchard/Vineyard Landcover(GAP)
National Land Cover Database (NLCD) (MRLC, 2001)

Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Division.
June, 2007, Projection: Albers Equal Area Conic USGS, North
American Datum of 1983 (NAD 1983)

Figure 2.7.b. Action Area Map

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2.8 Assessment Endpoints and Measures of Ecological Effect

Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."5 Selection of the assessment endpoints is based on valued
entities (e.g., CRLF, organisms important in the life cycle of the CRLF, and the PCEs of
its designated critical habitat), the ecosystems potentially at risk (e.g,. waterbodies,
riparian vegetation, and upland and dispersal habitats), the migration pathways of
imazapyr (e.g., runoff, spray drift, etc.), and the routes by which ecological receptors are
exposed to imazapyr-related contamination (e.g., direct contact, etc).

2.8.1 Assessment Endpoints for the CRLF

Assessment endpoints for the CRLF include direct toxic effects on the survival,
reproduction, and growth of the CRLF, as well as indirect effects, such as reduction of
the prey base and/or modification of its habitat. In addition, potential destruction and/or
adverse modification of critical habitat is assessed by evaluating potential effects to
PCEs, which are components of the habitat areas that provide essential life cycle needs of
the CRLF. Each assessment endpoint requires one or more "measures of ecological
effect," defined as changes in the attributes of an assessment endpoint or changes in a
surrogate entity or attribute in response to exposure to a pesticide. Specific measures of
ecological effect are generally evaluated based on acute and chronic toxicity information
from registrant-submitted guideline tests that are performed on a limited number of
organisms. Additional ecological effects data from the open literature are also
considered.

A complete discussion of all the toxicity data available for this risk assessment, including
resulting measures of ecological effect selected for each taxonomic group of concern, is
included in Section 4 of this document. A summary of the assessment endpoints and
measures of ecological effect selected to characterize potential assessed direct and
indirect CRLF risks associated with exposure to imazapyr is provided in Table 2.8.1.

Table 2.8.1 Summary of Assessment l.ndpoints and Measures of Ecological K fleets
for Direct and Indirect K fleets of Ima/apvr on the California Ued-legged Krog

Asscssiiu'iK r.iiripoini

Mcsisiiivs of Hl'lecls''

Aquatic Phase
(eggs, larvae, tadpoles, juveniles, and adults)*

1. Survival, growth, and reproduction of CRLF
individuals via direct effects on aquatic phases

la. Most sensitive fish or amphibian acute LC50:

96-hour LC50 >100 mg !L (rainbow trout)

lb. Most sensitive fish or amphibian chronic

NOAEC: 43.1 mg/L (rainbow trout)

lc. Most sensitive fish or amphibian early-life stage

data: 43.1 mg/L (rainbow trout)

2. Survival, growth, and reproduction of CRLF

2a. Most sensitive fish, aquatic invertebrate, and

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

6 All registrant-submitted and open literature toxicity data reviewed for this assessment are included in
Appendix B.

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Tsihle 2.S.I Siiiiiiiisii'y of Assessment l.ndpoinls nntl Mensures of Koolo»ie;il KITeels
lor Direel sind Indirect KITecls ol" linn/npvr on the C':ilir»rni:i Ued-leuued l ro«

Assessment l.ii(l|)(iinl

Measures of l-'.eolo*>ie:il l-'.ITecls'1

individuals via effects to food supply (i.e.,
freshwater invertebrates, non-vascular plants)

aquatic plant EC50 or LC50: >100 mg/L for both 96-
hr LC50 (rainbow trout) & 48-hr EC50 (daphnia);
EC5011.5 mg ae/L (green algae)

2b. Most sensitive aquatic invertebrate and fish
chronic NOAEC: 97.1 mg/L (daphnia), 43.1 mg/L
(rainbow trout)

3. Survival, growth, and reproduction of CRLF
individuals via ndirect effects on habitat, cover,
and/or primary productivity (i.e., aquatic plant
community)

3a. Vascular plant acute EC50: 0.018 mg ae/L
(duckweed)

3b. Non-vascular plant acute EC50: 11.5 mg ae/L
(green algae)

4. Survival, growth, and reproduction of CRLF
individuals via effects to riparian vegetation,
required to maintain acceptable water quality and
habitat in ponds and streams comprising the
species' current range.

4a. Distribution of EC25 values for monocots:
0.0046 - 0.054 lb ae/A

4b. Distribution of EC25 values for dicots7: 0.0009
- 0.034 lb ae/A

Terrestrial Phase
(Juveniles and adults)

5. Survival, growth, and reproduction of CRLF
individuals via direct effects on terrestrial phase
adults and juveniles

5a. Most sensitive birdb or terrestrial-phase
amphibian acute LC50 or LD50: >5,000 mg/kg diet or
>2,150 mg/kg bw (bobwhite quail)

5b. Most sensitive birdb or terrestrial-phase
amphibian chronic NOAEC: 1670 ppm (bobwhite
quail)

6. Survival, growth, and reproduction of CRLF
individuals via effects on prey (i.e.,terrestrial
invertebrates, small terrestrial vertebrates, including
mammals and terrestrial phase amphibians)

6a. Most sensitive terrestrial invertebrate and
vertebrate acute EC5oorLC50: LD50 >5,000 mg
ae/kgbw (rat); LD50 >100 ng/bee; LD50 >2150
mg/kg bw (bobwhite quail)

6b. Most sensitive terrestrial invertebrate and
vertebrate chronic NOAEC: 738 mg/kg bw/day or
10000 ppm diet (male rat); 1670 ppm (bobwhite
quail)

7. Survival, growth, and reproduction of CRLF
individuals via indirect effects on habitat (i.e.,
riparian vegetation)

7a. Distribution of EC25 for monocots: 0.0046 -
0.054 lb ae/A

7b. Distribution of EC25 for dicots7: 0.0009 - 0.034
lb ae/A

a Adult frogs are no longer in the "aquatic phase" of the amphibian life cycle; however, submerged adult
frogs are considered "aquatic" for the purposes of this assessment because exposure pathways in the water
are considerably different that exposure pathways on land.
b Birds are used as surrogates for terrestrial phase amphibians.

0 Although the most sensitive toxicity value is initially used to evaluate potential indirect effects, sensitivity
distribution is used (if sufficient data are available) to evaluate the potential impact to food items of the
CRLF.

7 The available information indicates that the California red-legged frog does not have any obligate
relationships.

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2.8.2 Assessment Endpoints for Designated Critical Habitat

As previously discussed, designated critical habitat is assessed to evaluate actions related
to the use of imazapyr that may alter the PCEs of the CRLFs critical habitat. PCEs for
the CRLF were previously described in Section 2.6. Actions that may destroy or
adversely modify critical habitat are those that alter the PCEs. Therefore, these actions
are identified as assessment endpoints. It should be noted that evaluation of PCEs as
assessment endpoints is limited to those of a biological nature (i.e., the biological
resource requirements for the listed species associated with the critical habitat) and those
for which imazapyr effects data are available.

Assessment endpoints and measures of ecological effect selected to characterize potential
modification to designated critical habitat associated with exposure to imazapyr are
provided in Table 2.8.2. Adverse modification to the critical habitat of the CRLF
includes the following, as specified by USFWS (2006) and previously discussed in
Section 2.6:

1. Alteration of water chemistry/quality including temperature, turbidity, and
oxygen content necessary for normal growth and viability of juvenile and
adult CRLFs.

2. Alteration of chemical characteristics necessary for normal growth and
viability of juvenile and adult CRLFs.

3. Significant increase in sediment deposition within the stream channel or pond
or disturbance of upland foraging and dispersal habitat.

4. Significant alteration of channel/pond morphology or geometry.

5. Elimination of upland foraging and/or aestivating habitat, as well as dispersal
habitat.

6. Introduction, spread, or augmentation of non-native aquatic species in stream
segments or ponds used by the CRLF.

7. Alteration or elimination of the CRLF's food sources or prey base.

Measures of such possible effects by labeled use of imazapyr on critical habitat of the
CRLF are described in Table 2.8.2. Some components of these PCEs are associated with
physical abiotic features (e.g., presence and/or depth of a water body, or distance between
two sites), which are not expected to be measurably altered by use of pesticides.
Assessment endpoints used for the analysis of designated critical habitat are based on the
adverse modification standard established by USFWS (2006).

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Tsihle 2.S.2 Siiiiiiiisii'y of Assessment l.mlpoints nml Mensures of Keologiesil Kfleel lor
Priniiirv Constituent Klenients of Designated ( ritienl llnhilnl

Asscssiiu'iK Inripoini

Measures of r.cnlniiiciil 1'.ITecls

Aquatic Phase PCEs
(. \ (iu alio Breeding Habitat and Aquatic Non-Breeding Habitat)

Alteration of channel/pond morphology or geometry
and/or increase in sediment deposition within the
stream channel or pond: aquatic habitat (including
riparian vegetation) provides for shelter, foraging,
predator avoidance, and aquatic dispersal for juvenile
and adult CRLFs.

a. Most sensitive aquatic plant EC50: 0.018 mg ae/L
(duckweed)

b. Distribution of EC25 values for terrestrial monocots:
0.0046 - 0.054 lb ae/A

c. Distribution of EC25 values for terrestrial dicots: 0.0009
- 0.034 lb ae/A

Alteration in water chemistry/quality including
temperature, turbidity, and oxygen content necessary
for normal growth and viability of juvenile and adult
CRLFs and their food source.9

a. Most sensitive EC50 values for aquatic plants: 0.018 mg
ae/L (duckweed)

b. Distribution of EC25 values for terrestrial monocots:
0.0046 - 0.054 lb ae/A

c. Distribution of EC25 values for terrestrial dicots: 0.0009
- 0.034 lb ae/A

Alteration of other chemical characteristics necessary
for normal growth and viability of CRLFs and their
food source.

a. Most sensitive EC50 or LC50 values for fish or aquatic-
phase amphibians and aquatic invertebrates: >100 mg/L for
both 96-hr LC50 (rainbow trout) & 48-hr EC50 (daphnia)

b. Most sensitive NOAEC values for fish or aquatic-phase
amphibians and aquatic invertebrates: 97.1 mg/L (daphnia),
43.1 mg/L (rainbow trout)

Reduction and/or modification of aquatic-based food
sources for pre-metamorphs (e.g., algae)

a. Most sensitive aquatic plant EC50: 0.018 mg ae/L
(duckweed)

Terrestrial Phase PCEs
(Upland Habitat and Dispersal Habitat)

Elimination and/or disturbance of upland habitat;
ability of habitat to support food source of CRLFs:
Upland areas within 200 ft of the edge of the riparian
vegetation or dripline surrounding aquatic and riparian
habitat that are comprised of grasslands, woodlands,
and/or wetland/riparian plant species that provides the
CRLF shelter, forage, and predator avoidance

a. Distribution of EC25 values for terrestrial monocots:
0.0046 - 0.054 lb ae/A

b. Distribution of EC25 values for terrestrial dicots: 0.0009
- 0.034 lb ae/A

c. Most sensitive food source acute EC50/LC50 and NOAEC
values for terrestrial vertebrates (mammals) and
invertebrates, birds or terrestrial-phase amphibians, and
freshwater fish: 96-hr LC50 >100 mg/L, NOAEC: 43.1
mg/L (rainbow trout); LD50 >5,000 mg ae/kg bw, NOAEC
10000 ppm, NOAEL 738 mg/kg bw/day (rat); LD50 >100
Hg/bee; LD50 >2150 mg/kg bw, NOAEC 1670 ppm
(bobwhite quail)

Elimination and/or disturbance of dispersal habitat:
Upland or riparian dispersal habitat within designated
units and between occupied locations within 0.7 mi of
each other that allow for movement between sites
including both natural and altered sites which do not
contain barriers to dispersal

Reduction and/or modification of food sources for
terrestrial phase juveniles and adults

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

8 All toxicity data reviewed for this assessment are included in Appendix B.

9 Physico-chemical water quality parameters such as salinity, pH, and hardness are not evaluated because
these processes are not biologically mediated and, therefore, are not relevant to the endpoints included in
this assessment.

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2.9 Conceptual Model

2.9.1 Risk Hypotheses

Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in
assessment endpoints) and may be based on theory and logic, empirical data,
mathematical models, or probability models (U.S. EPA, 1998). For this assessment, the
risk is stressor-linked, where the stressor is the release of imazapyr to the environment.
The following risk hypotheses are presumed for this listed species assessment:

• Labeled uses of imazapyr within the action area may directly affect the CRLF by
causing mortality or by adversely affecting growth or fecundity;

• Labeled uses of imazapyr within the action area may indirectly affect the CRLF
by reducing or changing the composition of food supply;

• Labeled uses of imazapyr within the action area may indirectly affect the CRLF
and/or adversely modify designated critical habitat by reducing or changing the
composition of the aquatic plant community in the ponds and streams comprising the
species' current range and designated critical habitat, thus affecting primary productivity
and/or cover;

• Labeled uses of imazapyr within the action area may indirectly affect the CRLF
and/or adversely modify designated critical habitat by reducing or changing the
composition of the terrestrial plant community (i.e., riparian habitat) required to maintain
acceptable water quality and habitat in the ponds and streams comprising the species'
current range and designated critical habitat;

• Labeled uses of imazapyr within the action area may adversely modify the
designated critical habitat of the CRLF by reducing or changing breeding and non-
breeding aquatic habitat (via modification of water quality parameters, habitat
morphology, and/or sedimentation);

• Labeled uses of imazapyr within the action area may adversely modify the
designated critical habitat of the CRLF by reducing the food supply required for normal
growth and viability of juvenile and adult CRLFs;

• Labeled uses of imazapyr within the action area may adversely modify the
designated critical habitat of the CRLF by reducing or changing upland habitat within
200 ft of the edge of the riparian vegetation necessary for shelter, foraging, and predator
avoidance.

• Labeled uses of imazapyr within the action area may adversely modify the
designated critical habitat of the CRLF by reducing or changing dispersal habitat within

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designated units and between occupied locations within 0.7 mi of each other that allow
for movement between sites including both natural and altered sites which do not contain
barriers to dispersal.

• Labeled uses of imazapyr within the action area may adversely modify the
designated critical habitat of the CRLF by altering chemical characteristics necessary for
normal growth and viability of juvenile and adult CRLFs.

2.9.2 Diagram

The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies the stressor (imazapyr), release mechanisms, biological receptor types, and
effects endpoints of potential concern. The conceptual models for aquatic and terrestrial
phases of the CRLF are shown in Figures 2.9.2.a and 2.9.2.b, and the conceptual models
for the aquatic and terrestrial PCE components of critical habitat are shown in Figures
2.9.2.C and 2.9.2.d. Exposure routes shown in dashed lines are not quantitatively
considered because the resulting exposures are expected to be so low as not to cause
adverse effects to the CRLF.

The general conceptual model of exposure for the CRLF is expected to be dominated by
direct application to water, runoff and spray drift. Imazapyr is expected to leach to
groundwater which could, in turn, recharge surface waters. In addition, long-range
transport beyond spray drift was evaluated, and based on the vapor pressure, is not
considered a significant route of exposure.

The effects of imazapyr on the aquatic phase of the CRLF and the aquatic PCEs of its
critical habitat (Figures 2.9.2 a and b) are expected to be dominated by the direct
application to water (aquatic) uses. The maximum application rates are equivalent for
terrestrial and aquatic uses of imazapyr. However, in spite of imazapyr being mobile and
persistent to biotic degradation, estimated environmental concentrations (EECs) resulting
from terrestrial uses will be attenuated by surface and subterranean transport processes to
aquatic sites. While spray drift loading will also contribute to the aquatic concentrations,
default assumptions estimate that only 5% of the terrestrial application will reach the
standard pond water body located adjacent to the treated agricultural field. The low
vapor pressure and Henry's Law constant indicate that long-range atmospheric transport
will be insignificant for imazapyr. The aquatic uses for imazapyr are intended to reduce
nuisance emergent aquatic plants. The labels state that imazapyr is not effective on
totally submerged plants. It has to be sprayed directly on emergent foliage and stems.
Therefore, although spray drift contributes to aquatic concentrations, drifting directly
onto aquatic plant emergent foliage may be a more significant route than drifting into
aquatic systems. Direct application to aquatic sites within the critical habitat may be of
significant importance.

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Figure 2.9.2.a Effects on Aquatic Phase CRLF

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Figure 2.9.2.b Effects on Aquatic Component of the CRLF Critical Habitat

The effects of imazapyr on the terrestrial phase of the CRLF and the terrestrial PCEs of
its critical habitat (Figures 2.9.2.C and d) is expected to be dominated by the direct
application to terrestrial use sites. Spray drift loading and runoff from nearby terrestrial
and aquatic use sites will also be contributing factors. Imazapyr can affect terrestrial
plants through exposure to either the foliage/stems or to the roots. Potential risk to
terrestrial plants from the aquatic uses is represented by direct application to surface
water which in turn overflows to an adjacent terrestrial site, leaving imazapyr residues in
soil and on leaves/roots/stems upon flood abatement. The low vapor pressure and
Henry's Law constant indicate that long-range atmospheric transport will be insignificant
for imazapyr.

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Stressor

Source

Exposure
Media

Long range :
atmospheric:
transport j

Receptors

Attribute
Change

Individual organisms

Reduced survival
Reduced growth
Reduced reproduction

Food chain

Reduction in prey

Habitat integrity

Reduction in primary productivity
Reduced cover
Community change

Figure 2.9.2.C Effects on Terrestrial Phase CRLF

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Stressor

Source

Exposure
Media and
Receptors

Imazapyr applied to use site

Direct

Spray drift

application

Surface Water

Runoff/

overflow
+—

.Dermal uptake/lngestior^_ Soil

Long range
atmospheric
transport

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

Root

uptake-*!

Wet/dry deposition*-

-~Ingestion

Inge^ion

Attribute
Change

Habitat
PCEs

Red-legged
Frog

Juvenile

Ingestion^

Ingestion

"jMammalsl

Individual organisms

Reduced survival
Reduced growth
Reduced reproduction

Other chemical
characteristics

Adversely modified
chemical characteristics

Population

Reduced survival
Reduced growth
Reduced reproduction

Food resources

Reduction in food
sources

Community

Reduced seedling
emergence or vegetative
vigor (Distribution)

Elimination and/or disturbance of
upland or dispersal habitat

Reduction in primary productivity
Reduced shelter
Restrict movement

Figure 2.9.2.d Effects on Terrestrial Component of the CRLF Critical Habitat
2.10 Analysis Plan

Potential risks to the California red-legged frog and to its critical habitat have been
assessed consistent with the Overview Document (EPA 2004), the Service's evaluation of
EPA's risk assessment process (USFWS/NMFS 2004), and Agency guidance for
ecological risk assessment (USEPA 1989). The quality of the Registrant submitted
environmental and ecotoxicity data has been evaluated in a rigorous and consistent
manner, according to EFED guidelines and policies. In addition, data from the outside
literature (ECOTOX) has been screened and evaluated for potential use in the risk
assessment. Levels of environmental exposure have been predicted using computer
models, based on findings from scientifically sound environmental fate studies required
under FIFRA to support registration for requested uses.

2.10.1 Measures to Evaluate Risk Hypotheses and Conceptual Model

2.10.1.1 Measures of Exposure

Estimated environmental concentrations (EECs) for aquatic and terrestrial systems are
calculated using the maximum application rates and minimum application intervals. The

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aquatic EECs for terrestrial uses are calculated using the EPA Tier IIPRZM (Pesticide
Root Zone Model) and EXAMS (Exposure Analysis Modeling System) with the most
recent linkage program (PE4-PL, version 01) and the EFED Standard Pond environment,
PRZM and EXAMS. PRZM is used to simulate pesticide transport as a result of runoff
and erosion from an agricultural field, and EXAMS estimates environmental fate and
transport of pesticides in surface water. The aquatic EECs for the aquatic uses are
calculated as application of the maximum application rate directly to the surface of the
standard pond a depth of 2.0 meters, using output from 30 years of EXAMS runs. For
residential and rights-of-way uses, an impervious surface scenario are developed, using
percent impervious surface, percent pervious surface and percent impervious area treated
for the residential scenario and percent impervious surface treated combined with percent
watershed treated for the rights-of-way scenario.

Terrestrial EECs are estimated for mammals, birds and terrestrial invertebrates using the
maximum single application rate of imazapyr in the model, T-REX version 1.3.1.

The TerrPlant (Ver.1.2.2) model is used to predict EECs from terrestrial uses for
terrestrial plants located in dry and semi-aquatic areas adjacent to the treated field or
treated water body. Terrplant is not used for the aquatic uses because the model assumes
runoff into water from a terrestrial use. With aquatic uses, the pesticide is applied
directly to water. Therefore, the concentrations in water are calculated directly from the
application. In this case, the modeled EECs for exposure to terrestrial plants adjacent to
or on the edges of the water body assume a concentration of imazapyr in a standard 2
meter pond from which 6 inches that water moves (overflows) entirely onto a hectare of
dry land and dries up on the ground with imazapyr residues. For open water bodies in a
tidal area, a further assumption may be made that a 2 meter depth of tide comes in on that
one hectare with imazapyr residues in the soil and 6 inches of that water would overflow
to flood a terrestrial site. However, since the CRLF do not inhabit higher salinity
habitats, risks to plants in tidal areas are not estimated.

In addition to the TerrPlant modeling of EECs, refinement of spray drift from treated
areas is assessed with the AgDrift (Ver. 2.0.1) and the AGDISP (Ver. 8.15) models.

These models provide estimates of drift dispersion and deposition as the result of ground
and aerial spray droplet and nozzle size, wind speed and distance from the treated field.

2.10.1.2 Measures of Effect

For imazapyr, measures of effect are based on deleterious changes in a receptor as a
result of exposure. The measures of effect for this risk assessment include changes in
survival, reproduction, or growth as determined from standard laboratory toxicity tests.
The focus on these effects for quantitative risk assessment is due to their clear
relationship to higher-order ecological systems {i.e. populations, communities,
ecosystems). Effects other than survival, reproduction, and growth are considered;
however, they are not used quantitatively to estimate risks unless the relationship
between these effects and higher-order processes has not been quantitatively established.

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Commonly used laboratory-derived toxicity values include estimates of acute mortality
(e.g., LD50, LC50) and estimates of effects due to longer term, chronic exposures (e.g.,
NOAEL, NOAEC) (Table 2.8.1). The latter can reflect changes seen in mortality,
reproduction, or growth. As previously discussed in Section 2.8, assessment endpoints
for the CRLF include not only direct toxic effects on the CRLF, but also indirect effects,
such as reduction of the prey base and/or modification of its habitat. In addition,
potential destruction and/or adverse modification of critical habitat are assessed by
evaluating effects to the PCEs, which are components of the critical habitat areas that
provide essential life cycle needs of the CRLF. Due to the lack of data on either
terrestrial or aquatic amphibians following exposure to imazapyr, direct effects to the
aquatic-phase of the CRLF are based on toxicity information for freshwater fish and the
terrestrial-phase is based on avian toxicity data since fish are generally used as a
surrogate for aquatic-phase amphibians and birds are generally used as a surrogate for
terrestrial-phase amphibians (USEPA 2004, USFWS/NMFS 2004). Given that the frog's
prey items and habitat requirements are dependent on the availability of freshwater fish
and invertebrates, small mammals, terrestrial invertebrates, and aquatic and terrestrial
plants, toxicity information for these taxa are also discussed and assessed for risk
following exposure to imazapyr.

In addition to registrant-submitted studies, a search of the open literature using EPA's
Ecotoxicology database4 is conducted. Open literature data are assessed according to
suitability for use in assessment of risk following exposure to imazapyr, either
quantitatively or qualitatively. Studies from the literature that are not applicable to this
risk assessment are listed in the Appendices along with reasons as to why they were not
used.

Information provided in the Ecological Incident Information System (EIIS) regarding
accidental exposures to commercial formulations of imazapyr is also included as
supporting lines of evidence for the risk characterization.

Estimated environmental concentrations are compared to the experimentally-determined
acute and chronic toxicity values for the surrogate aquatic and terrestrial species for the
CRLF, its food sources and habitat. The Action Area is determined, based on the risk
characterization and an evaluation of the potential "footprint" of the use pattern for
imazapyr and its salt in California. This information is then be combined with the
mapped CRLF habitats to determine where the imazapyr uses may impact the CRLF and
its critical habitat.

Inhalation and dermal pathways are not generally considered in screening level
deterministic risk assessments. The available measured data related to wildlife dermal
contact with pesticides are limited and modeling techniques to account for dermal
exposure are not yet available. Available data suggest that inhalation exposure at the

4 ECOTOX at http://www.epa.gov/ecotox

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time of application is not an appreciable route of exposure for terrestrial wildlife because
evidence suggests that less than 1% of the applied material will be within the respirable
particle size.

2.10.1.3 Action Area Analysis

The Action Area for the federal action is the geographic extent of exceedance of Listed
species Levels of Concern (LOC) for any taxon or effect (plant or animal, acute or
chronic, direct or indirect) resulting from the maximum label-allowed use of imazapyr.
For imazapyr, because the CRLF does not have an obligate relationship with any single
plant species (aquatic or terrestrial) the endpoints utilized to determine the Action Area
are for non-listed aquatic and terrestrial plants. To define the extent of the Action Area,
the following exposure assessment tools are used: PRZM-EXAMS, Terrplant, AGDISP
and ArcGIS9, a geographic information system (GIS) program. Other tools may be used
as required if these are inadequate to define the maximum extent of the Action Area.

To determine the downstream extent of the Action area for effects to aquatic plants,
imazapyr residues are also estimated for downstream from the treated areas by assuming
dilution with stream water (derived from land area) from unaffected sources propagating
downstream, until a point is reached beyond which there are no relevant LOC
exceedances. In order to determine the extent of the action area downstream from the
initial area of concern, all the aquatic risk quotients (RQs) are calculated, and the aquatic
plant or animal endpoint with the greatest ratio of the aquatic RQ to the LOC is utilized
for the analysis. Details on determination of miles downstream are provided in Appendix
C.

To determine how far in land area outside the initial area of concern effects may be
expected, the AGDISP model with the Gaussian Far-Field Extension is used to provide
spray drift buffer estimates needed to avoid adverse effects to non-target species.

This model provides estimates of drift dispersion and deposition as the result of ground
and aerial spray droplet and nozzle size, wind speed and distance from the treated field.

The action area is considered to be the greatest expansion of the initial area of concern
from either or both of the two methods (spray drift buffer and downstream distance)
summarized above.

2.10.1.4 Preliminary Identification of Data Gaps and Methods

Environmental fate data for imazapyr is mostly complete. Only two soils were tested for
aerobic soil metabolism, and one soil was tested for anaerobic soil metabolism, and both
aerobic and anaerobic aquatic metabolism. In this case, the stability of imazapyr in the
soils tested renders the requirement for three test systems of little value. Environmental
fate data gaps also arise from a supplemental field dissipation study. However, there are
sufficient environmental fate chemical data from other studies to predict the needed field
dissipation information.

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For the CRLF, with the exception of acceptable terrestrial plant studies, the toxicity data
are complete. Due to problems of overcrowding and 'fresh weight' endpoints with the
seedling emergence and vegetative vigor studies with imazapyr acid, the data set for
terrestrial plants is incomplete.

Toxicity data are available for either the acid, the salt or both. No toxicity information is
available for degradates of imazapyr.

3. Exposure Assessment

3.1 Label Application Rates and Intervals

Table 3.1

Imazapyr Label Application Information for the Listed Red Legged Frog1

Maximum

Method of
Application

Interval

Scenario

Application Rate
(Ibs/acrc)

Number of
Applications-

Formulation'1

Between
Applications

CAforestry

1.5

liquid

aerial and
ground

CAimpervious
surfaces

1.5

liquid

aerial and
ground

CArangeland-hay

1.5

liquid

aerial and
ground

CAresidential

0.91

liquid

ground

CAright-of-way

1.5

liquid

aerial and
ground

CAturf

1.5

liquid

ground

non-crop aquatic4

1.5

liquid

applied directly
to water

"Based on 2005 RED and new label submissions subsequent to the 2005 RED.

2"April 1 application date used for all modeling

3"While granular formulations are also marketed, liquid formulations, which produce the most conservative
estimates of risk, have been modeled in this assessment

4" There is also a capsule injection application to trees and brush standing in water (capsule containing 83% a.i..

This use is expected to have very limited non-quantifiable exposure to non-target plants.

3.2 Aquatic Exposure Assessment

3.2.1 Modeling Approach

The EECs (Environmental Effects Concentrations) were calculated using the EPA Tier II
PRZM (Pesticide Root Zone Model) and EXAMS (Exposure Analysis Modeling System)
with the EFED Standard Pond environment, PRZM and EXAMS. PRZM is used to
simulate pesticide transport as a result of runoff and erosion from an agricultural field,
and EXAMS estimates environmental fate and transport of pesticides in surface water.

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The most recent PRZM/EXAMS linkage program (PE4-PL, version 01) was used for all
surface water simulations. Linked crop-specific scenarios and meteorological data were
used to estimate exposure resulting from use on crops and turf. Simulations were
conducted using the standard ecological pond scenario in EXAMS.

3.2.2 Modeling Inputs

The aqueous model predictions are based on maximum labeled application rates,
estimated date of application, crop and/or use specific agronomic practices, regional
weather data, soil, crop and topography characteristics, and the chemical, physical and
environmental fate properties for imazapyr. Modeling scenarios contain crop and
location specific characteristics in a standardized modeling format. California scenarios
developed specifically for this Red legged Frog Listed Species Assessment, and a
California turf scenarios developed for EPA's Organophosphate Cumulative Assessment
have been used here to estimate surface water concentrations. Table 3.2.2a lists the
specific locations modeled for this assessment.

Tsihle 3.2.2;i. I'RZM/KXAMS Scenarios I soil to Ksliimite Concent riilions of limiziipyr Tolsil

Toxic Residues in Surlsicc Wsiler

Tier 2 Modeling Scon;iri»

l ocution Modeled

California Forestry

Trinity, Shasta, Modoc, and Humboldt Counties

California Impervious Surfaces

San Francisco Bay area of California

California Rangeland

Alameda, Contra Costa, Solano, Sonoma, and Santa Clara Counties, CA

California Residential

San Francisco Bay area of California

California Rights-of-Way

Central/Coastal California

California Turf

Central/Northern California

Selecting Input Parameters

The appropriate PRZM and EXAMS input parameters for total toxic residues (imazapyr,
CL9140 and CL 119060) were selected from the environmental fate data submitted by
the registrant and in accordance with US EPA-OPP EFED water model parameter
selection guidelines, Guidance for Selecting Input Parameters in Modeling the
Environmental Fate and Transport of Pesticides, Version II, February 28, 2002. When
data are not available for total toxic residues, values for the parent compound, imazapyr,
are used for modeling purposes. The environmental fate data used to estimate the
modeling input values appear in Table 3.2.2.b,

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Table 3.2.2.b. Summary of PRZM/EZAMS Environmental Fate Data Used for Aquatic
Exposure Inputs1 for Total Toxic Residues of Imazapyr3 for the Listed Red Legged Frog

Assessment

Fate Property

Value

MRID (or source)

Molecular Weight2

261.28

2003 Science Chapter for Aquatic Uses of
Imazapyr

Henry's constant at 25 °C2

<10"17 atm x m3/mol

2005 Science Chapter in support of RED

Vapor Pressure at 60 °C2

<10 7 mm Hg

(< 1.3 x 10~5 Pa; method limit); 2003 Science
Chapter for New Aquatic Uses of Imazapyr

Solubility in Water at 25 °C2

H.l g/L

2003 Science Chapter for New Aquatic Uses

Photolysis in Water

19.9 days

MRID 00131617
(t Vi = 5.3 days for parent only)

Aerobic Soil Metabolism Half-lives

Stable

MRID 00131619

Hydrolysis

Stable

MRID 00132359

Aerobic Aquatic Metabolism (water
column)

Anaerobic Aquatic Metabolism
(benthic)

Koc

Application Efficiency
Spray Drift Fraction

Stable
Stable

99.8

0.95 (0.99)
0.05 (0.01)

MRID 40003712

MRID 00131619

lowest non-sand (silt loam) value (parent) for
total toxic residues (Koc = 6053 and 1020 for
CL 119060 and CL 9140); MRID45119705
EFED Guidance for aerial

(ground) application
EFED Guidance for aerial
(ground) application

Inputs determined in accordance with EFED "Guidance for Chemistry and Management Practice Input Parameters

for Use in Modeling the Environmental Fate and Transport of Pesticides " dated February 28, 2002
2" Imazapyr value used in absence of data for degradation products: CL 119060 and CL 9140
3" Imazapyr value for acid moiety and the two major degradation products are used in this assessment

3.2.3 Results

The EECs resulting from the standard 2.0 meter pond depth for forestry, rangeland, hay
and golf course roughs are tabulated below.

Table 3.2.3.;t. Tier 2 Estimated Em ironmcnlal Concentrations (EEC's) lor Forestry I ses of

Ima/apyr (total toxic residues)

IViik (|)|)l)) 21 l);n (|)|)l)) 6II-I);i\ (pph)
Acrhil Application IS 5 ISO I" 2
Ground Spr;i> Application 14.1 13.8 13.1

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Tsihlc 3.2.3.h. l ior 2 Ksliimiled Kn\ironnienliil (oncenlr;ilions (KIX s) lor kiin^oliiiul/l Isiv

I sos of I in!i/!ip\ ¦' (lolitl toxic residues)

Peak (|)|)h) 21 l);i\ (ppb) (>0-l);i\ (ppb)

Acriiil Application 33.0 32.1 30.5

(•round Sprn\ Appliciilion 26.1 25.6 24.7

For golf course roughs, EECs were adjusted by 66%, as per EFED golf course adjustment
factor10. Green, tees and fairways of an established, working golf course are not
expected to ever become overgrown enough to require treatment with imazapyr.

T;ible 3.2.3.C. Tier 2 Ksliimiled Kmironmenliil (oncenlr;ilions (KK('s) lor I so of luiii/iipvr
(loliil toxic residues) on (loll'C ourse Roughs (C A lurl' sceiiiirio)

Pc;ik(ppb) 21 l);i\ (ppb) (>0-l);i\ (ppl)l

(.round Sprsij Appliciilion ''S 5 u

Direct application of imazapyr to water was calculated as application of the maximum
application rate directly to the surface of the standard pond a depth of 2.0 meters. Direct
application of imazapyr to the surface of the standard two meter ecological pond was
calculated using output from thirty years of EXAMS runs. The direct application of
imazapyr to water will result in EECs that increase in a pattern which can be described
mathematically (Nonlinear Regression: P <0.0001 ) as an exponential rise to a maximum
value (SigmaPlot 10.0):

y = a(l-e"bx)

EXAMS estimated EEC values for the 30 years of available weather data are tabulated
below, Table 3.2.2.d, Acute EECs were 84.0 ppb, chronic 21 day EECs were 82.1 ppb,
and chronic 60 day EECs were 79.6 ppb. Thirty yearly direct applications of 1.5 lbs./acre
of imazapyr to the surface of the standard two meter ecological pond were calculated
using EXAMS. Acute EECs were 971 ppb, chronic 21 day EECs were 968 ppb, and
chronic 60 day EECs were 962 ppb. Because the EEC values are steadily rising for the
thirty years that EXAMS simulates, the one in ten year value, which is normally reported
as the value that is only expected to be exceeded every ten years has little meaning and is
therefore, not reported here. Figure 3.2.2 graphically illustrates this increase.
Additionally, there are no currently accepted models to account for the label mandated V2
mile setback from drinking water intakes. As a result, this factor was not accounted for
in the estimated EECs.

10 Golf Course Adjustment Factors for Modifying Estimated Drinking Water Concentrations and Estimated
Environmental Concentrations Generated by Tier I (FIRST) and Tier II (PRZM/EXAMS) Models
http://www.epa.gov/oppefedl/models/water/golf course adjustment factors.htm

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Tsihle 3.2.2.d. l ior 2 IAAMS Ksliiiiitlcd Kmiioiimciilitl C oiuciiliitlioiis (KIX s) Resulting
from (lie "S o:ii l\ Application of liiiii/iipvr (lolnl toxic residues) to Water (Aerisil or (irouncl
Sprsiv Application)

IVilk (pph)

21 l);i\ (pph)

(>0-l)ii\ (pph)

1 application

5 yearly applications

331

328

325

10 yearly applications

557

555

550

15 yearly applications

718

715

710

20 yearly applications

833

829

824

25 yearly applications

914

910

904

30 yearly applications

971

968

962

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60-Day EECs from Direct Application of Imazapyr to Water

1200

1000 -

Years

• Yearvs60Day
x column vs y column

Figure 3.2.2. Peak, 21-Day and 60-Day EECs for Direct Application of Imazapyr to

Water

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The impervious surface scenario was developed to be used in conjunction with the
residential and rights-of-way scenarios. A post processing step is required to merge the
impervious surface output values with the output values from the residential and rights-
of-way scenarios. In order to combine these values in a way that realisticely depicts
environmental conditions, the percent of the watershed actually treated and the percent of
that treated area existing as impervious surfaces needs to be determined.

The assumption that 12% of an average, Vi acre residential lot consists of impervious
surfaces was first made in the August 22, 2006 Atrazine Endangered Species Assessment
for the Barton Springs Salamander. It was also assumed that 50% of the residential
watershed consisted of impervious, paved streets. The 12% impervious surfaces
assumption for the Vi acre residential lot is retained from the Barton Springs assessment,
but, unlike atrazine, imazapyr is applied to the cracks of pervious surfaces, and was
modeled as being applied to different percents of the 12% impervious surfaces within the
residential lot. Imazapyr is only intended to be used on pervious surfaces that are
overgrown with unwanted vegetation, and not meant to be applied directly to well
maintained residential turf. In this assessment, it was assumed that paved residential
streets that were cracked and/or crumbling to the extent that imazapyr might be used to
control vegetation growth would be repaired instead. Any overspray from use on
pervious surfaces is anticipated to be negligible compared to the intended application of
imazapyr to pervious surfaces. Such overspray is therefore not quantitatively estimated,
but is accounted for in the uncertanties associated with applications made to sidewalks,
driveways and patios located on the Vi acre residential lot.

In the absence of data to make a definitive estimate of the extent of imazapyr use on
residential sites, modeling was conducted at 50%, 25%, 10% and 1% of the impervious
surfaces (12% of total lot) on the ]A acre residential lot treated, and on 10%, 1%, and 0%
of the pervious surfaces on the ]A acre lot treated. Calculations for the ]A acre residential
lots appear in Appendices D.2 through D.4. Finally, in order to account for the 50% of
the residential watershed composed of untreated, paved streets, a simplifying assumption
was made that an equal volumes of water would runoff of the residential streets and the Vi
acre residential lot. While this assumption may underestimate the volume of water
running off of paved residential streets, the difference is eradicated in the bounding
exercise tabulated in the matrices below. As a result of that assumption, the aquatic
EECs were divided by two. The resulting matrices (Tables 3.2.3.e and 3.2.3.f., below)
were used to characterize the effects of imazapyr under the array of differing conditions.

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Tsihle 3.2.3.0. Tier 2 PUZM/KYVMS l.slimnled Kiivironincnlsil (oiuenlrnlions (KIX s) for
(lie Standard. 2 Motor Doop Pond Resulting from llio Residential I so of linsi/sipvr (total
toxic residues in pph) Willi 12% linporvioiis Surface

O'.' i. pci

*\ ions snr

face

1pci

*\ ions sin*

lilCC

pcr\ ions snr

lilCC

Peak

2 l-l);i\

Peak

2I-I)a\

(»0-l)sij

Peak

2I-I);i\

(»0-l)sij

1 "/« of impcn ions

o.lo

U. lb

U.15

0.21

0.20

u.ls

U.58

U.57

area HViilod

of impcn ions

1.6

1.5

1.7

1.6

1.5

2.1

1.9

area Ircalcd

25"ii of impcn ions

4.1

3.9

3.7

4.1

3.7

4.6

4.5

4.2

;irc;i liviilcd

50"" of impcr\ ions

8.1

7.9

7.4

8.2

7.9

7.4

8.7

8.4

8.0

iiivii Ircalcd

The rights-of-way, industrial, and non-food, non-residential imazapyr uses have been
modeled using the rights-of-way scenario. Modeling was conducted at 50%, 25%, 10%
and 1% of the impervious surfaces on the actual use site treated, with the assumption that
10%), 5%>, and 1% of the of the watershed actually consisted of these modeled imazapyr
use sites. Calculations for the use sites modeled by the right of way scenarios appear in
Appendices D.7 and D.8. The resulting matrices (below) were used to characterize the
potential effects of imazapyr under the array of differing conditions.

Table 3.2.3.1'. Tier 2 PUZM/KYVMS l.slimaled Knvironnionlal Concentrations (KKC's) lor llio
Standard. 2 Motor Doop Pond Resulting from (ho I so of Imnznpvr on lndiislri;il. Non-hood Non-
Residential Ri»hts-of-\\ a\ (lotal toxic residues as pph)

I "A> of impcn ions 10 % of impcn ions 25 % of inipcn ions 50 % of impcn ions
surfaces treated surfaces lrc;ilcd surfaces (ro;ilod surfaces trciilod

Aerial

21-

(.0-

21-

(.0-

21-

Mi-

21-

Mi-

Applicaliou

Peak

l)a\

Peak

l)a\

Peak

l)a\

Da*

Peak

Da>

Da*

1" i. of

u.3o

(i 35

U.33

(Mi1)

(Mo

Uo2

1.3

1.2

2.3

2.1

watershed

5"-i. of

1.8

1.7

1.6

3.4

3.3

3.1

6.5

6.2

5.9

11.6

11.0

10.5

watershed

10".. of

3.6

3.5

3.3

6.9

6.5

6.2

13.0

12.4

11.7

23.2

22.1

21.1

w alcrshcd

Ground Spray

21-

(.0-

21-

(.11-

21-

Mi-

21-

Mi-

Applicaliou

Peak

l)a\

l);i\

Peak

l)a\

Peak

l)a\

Da*

Peak

Daj

Da*

1 "/„ of

U.32

(i 32

u.29

(i o5

no 3

0.59

1.3

1.2

2.3

2 1

watershed

5V i. of

1.6

1.5

3.3

3.1

2.9

6.4

6.2

5.8

11.6

11.2

10.5

watershed

III",, of

3.2

2.9

6.5

6.3

5.9

12.8

12.3

11.5

23.2

22.4

20.9

watershed

Exposure from the capsule injection application to individual plants was not estimated
because it is expected to produce very limited non-quantifiable amounts into water.

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3.2.4 Existing Monitoring Data

No monitoring data for imazapyr (acid or salt), or for the major imazapyr degradation
products are available, either through the USGS NAWQA Database, from the state of
California or through any publicly available search engines on the internet.

3.3 Terrestrial Exposure Assessment

Terrestrial wildlife may be exposed to pesticides through the plant or animal material
they consume as food and/or through inhalation, dermal, and drinking water pathways.
In performing assessments for spray applications of pesticides, exposure to terrestrial
organisms is estimated using a series of tables based on a database of actual measured
pesticide residue values on plants and insects. This series of tables is called the Kenaga
nomogram, as modified by Fletcher (Hoerger, F. and E.E. Kenaga, 1972; Fletcher, J.S.,
J.E. Nellessen, and T.G. Pfleeger, 1994). These tables relate food item residues to
pesticide application rate. A computer simulation model is then used to allow
degradation of residues on foliar surfaces and insects and the concentrations are predicted
using a first-order residue decline method.

Terrestrial EECs were estimated using the maximum single application rate of imazapyr
in the model, T-REX version 1.3.1 for mammals and birds (see risk estimation Section
5.1). Acute and chronic RQs were calculated with these upper bound EECs and
appropriate toxicity data. Table 3.3 summarizes the estimated terrestrial EECs for
forestry uses at the maximum allowable rate for imazapyr. Terrestrial EECs based on
forestry uses are assumed to be protective of all the other uses in California because they
yield the highest dietary exposure concentrations.

Tiihk* 3.3 1

pper-bonnd kennun \ nines < 1

-ki:.\ \ i

^ 1)

Minimum
Inlm
-------
spray drift. Exposures can occur directly to seedlings breaking through the soil surface,
root uptake or direct deposition onto foliage to more mature plants. Riparian vegetation
is important to the water and stream quality of the CRLF habitat because it serves to filter
out sediment, nutrients, and contaminants before they enter the watersheds associated
with the CRLFs current and designated critical habitat. Riparian vegetation has been
shown to be essential in the maintenance of a stable stream (Rosgen, 1996).
Destabilization of the stream can have an effect on CRLF habitat quality by increasing
sedimentation within the watershed.

Effects on non-target terrestrial plants are most likely to occur as a result of spray drift,
overflow from direct application to water and/or runoff from aerial and ground
applications. These are important factors in characterizing the risk of imazapyr to non-
target plants, which is assumed to reach off-site soil. The TerrPlant (Ver. 1.2.2) model
predicts EECs for terrestrial plants located in dry and semi-aquatic areas adjacent to the
treated field or treated water body. The EECs are based on the application rate and
solubility of the pesticide in water and drift characteristics, which, in the case of imazapyr
in California, depend on either ground or aerial applications. The amount of imazapyr
that runs off is a proportion of the application rate and is assumed to be 5% based on
imazapyr's solubility of >100 ppm in water. Drift from ground and aerial applications
are assumed to be 1% and 5%, respectively, of the application rate. An application
efficiency of 100% is assumed for both aerial and ground applications. For a standard
scenario on an agricultural field when applications are occurring on land, the runoff
scenario for terrestrial plants inhabiting dry areas adjacent to a field is characterized as
"sheet runoff (one treated acre to an adjacent acre; a 1:1 ratio) and inhabiting semi-
aquatic or wetland areas adjacent to a field is characterized as "channelized runoff' (10
treated acre to an adjacent low-lying acre; a 10:1 ratio).

Terrplant cannot be used for the aquatic uses because the model assumes runoff into
water from a terrestrial use. With aquatic uses, the pesticide is applied directly to water.
Therefore, the concentrations in water are calculated directly from the application. When
applications are occurring on surface water such as ponds and lakes, the modeled EECs
for exposure to terrestrial plants adjacent to or on the edges of the water body assumes a
concentration (volume) of imazapyr in a 1 hectare pond with a water depth of 2 meters,
from which 6 inches that water moves (overflows) entirely onto a hectare of dry land and
dries up on the ground with imazapyr residues. The range of semi-aquatic areas
apparently allowed by this broad label for aquatic uses represents much different
exposure scenarios than open water bodies, including areas that might go dry at times,
which could lead to the potential for imazapyr to flow entirely onto a new site and soak
into the ground exposing the seedlings to the herbicide. Because the CRLF does not
inhabit higher salinity habitats, risks to plants in tidal areas are not estimated.

The inputs are based on an application rate of 1.5 lb/A to a 1 hectare area with 6 inches
(15.2 cm) of the water moving onto land. Flooding EEC values (lbs ae/A) were
calculated as described above and in the equations below, and drift EEC values from
TerrPlant were added to the runoff values.

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(84 jug/L x 1 hectare) x (15.24 cm x 10000 m2/hectare) x (10000 cm2/m2) x (1 mL/1

cm3) x (1 L/1000 mL) = 1.28 x 108 |ig/hectare

1.28 x 108 |ig/hectare x 1 kg/109 |ig = 0.128 kg/hectare

0.128 kg/hectare x 1 hectare/2.471 acres = 0.052 kg/A

0.052 kg/A x 2.2 lbs/kg = 0.114 lb ae/A

Details of the TerrPlant model EECs are presented in Table 3.4 for terrestrial and aquatic
uses. While imazapyr is formulated both as an acid and as an isopropylamine salt, all
concentrations were converted into acid equivalents for this assessment. These values are
a conservative estimate because there may be dilution of the imazapyr during the
flooding event and thus, overestimation of the EECs.

Tsihle 3.4. Kslininlcil Kn\ironmcntiil Concent nil ions of Imii/iipyr lor Tcrrcstriiil I'hinls from

C'iilirorniii I sos

Applications Occm
1 crrcslriiil I sc

rinji on l.iinri

Application
Method

Toi;il l.oiidin^ to
l)n iirc.is 1

( onccnlriilion (Ills iic/iicrc)

Toiiil l.oiidin^lo Scmi-Aipiiilic
A reus"

Drill'

Non-Crop
(1.5 lbs ae/acre)

Ground
Aerial

0.09
0.15

0.765
0.825

0.015
0.075

Non-Crop
(0.9 lbs ae/acre)

Ground

0.055

0.464

0.009

Applications Oct
Sii rl'iicc \\

Aipiiilic I sc

;iirrini£ on
.iter

Application
Method

( onccnlriilion (lbs iic/iicrc)

Miidlo\\-W;iicr Communities
iWiiler o\erllo«s)4

Non-Crop
(1.5 lbs ae/acre)

Ground
Aerial

0.114
0.114

1 EEC = Sheet Runoff + Drift (5% for aerial; 1% for ground)

2 EEC = Channelized Runoff + Drift (5% for aerial; 1% for ground)

3 EEC for ground (appl rate x 1% drift); for aerial (appl rate x 5% drift)

4 EEC = 1.5 lb/A applied to 2 meter depth of water (1 hectare area), then 6 inches of water moves onto land

Imazapyr applied according to label directions as a liquid spray for ground or aerial
applications may impact non-target plants for some distance from the application site
depending on droplet size, wind speed, and other factors.

Exposure from the capsule injection application to individual plants was not estimated
because it is expected to produce very limited non-quantifiable exposure to adjacent non-
target plants.

In addition to the TerrPlant modeling of EECs, refinement of spray drift from treated
areas was assessed with the AgDrift (Ver. 2.0.1) and the AGDISP (Ver. 8.15) models.
These models provide estimates of drift dispersion and deposition as the result of ground
and aerial spray droplet and nozzle size, wind speed and distance from the treated field.

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4. Effects Assessment

This assessment evaluates the potential for imazapyr and the isopropylamine salt of
imazapyr to directly or indirectly affect the CRLF and/or adversely modify designated
critical habitat for the CRLF. As previously discussed in Section 2.8, assessment
endpoints for the CRLF include direct toxic effects on the survival, reproduction, and
growth, as well as indirect effects, such as reduction of the prey base and/or modification
of its habitat. In addition, potential effects to critical habitat are assessed by evaluating
effects to the PCEs, which are components of the critical habitat areas that provide
essential life cycle needs of the CRLF. Direct effects to the aquatic-phase of the CRLF
are based on toxicity information for freshwater fish while the terrestrial-phase is based
on avian toxicity data since fish are generally used as a surrogate for aquatic-phase
amphibians and birds are generally used as a surrogate for terrestrial-phase amphibians
(USEPA 2004, USFWS/NMFS 2004). Given that the frog's prey items and habitat
requirements are dependent on the availability of freshwater fish and invertebrates, small
mammals, terrestrial invertebrates, and aquatic and terrestrial plants, toxicity information
for these taxa are also discussed. Toxicity data used to evaluate direct effects, indirect
effects, and effects to critical habitat are summarized in Table 4.0.

Table 4.0 Summary of Toxicity Data on Imazapyr and Its Isopropylamine Salt Used
to Assess Direct and Indirect Effects and Adverse Modification to Critical Habitat

Toxicitv Data

Assessment Endpoint

Comment

Acute and chronic studies on
freshwater fish.

- Direct effects to the aquatic
phase of CRLF

- Chemical characteristics
suitable to support normal
behavior, growth, and viability
of CRLF

No aquatic amphibian data available.
Fish data used as surrogate for
amphibians.

Acute and chronic studies on
freshwater invertebrates

Acute and chronic studies on
freshwater fish1

- Indirect effects to aquatic phase
of CRLF (reduction in prey
base)

- Chemical characteristics
suitable to support normal
behavior, growth, and viability
of CRLF

No aquatic amphibian data available.
Fish data used as surrogate for
amphibians.

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Tsihle 4.0 Siiiiiniiirv ol'Toxichv on Inisi/sipvr nnd lis 1 so propylamine Ssih I sod
lo Assess Direct mid Indirect Kfl'ecls nnd Adverse Modillcsilion to Crhicnl Ihihihil

To\ici(\ Diilii

Assossinonl l-'udpitin 1

( onimcnl

Acute studies on vascular and
non-vascular aquatic plants

- Indirect effects to aquatic phase
CRLF via reduction in food
supply, aquatic habitat, cover
and/or primary productivity

- Habitat modification to aquatic
habitat and aquatic phase PCE:
Alteration to water
chemistry/quality; channel/pond
morphology or geometry,
sediment deposition and
chemical characteristics suitable
to support normal behavior,
growth, and viability of CRLF

Acute studies on terrestrial plants

- Indirect effects to terrestrial
phase CRLF via reduction in
terrestrial habitat, cover and/or
primary productivity

- Habitat modification:
Alteration to water
chemistry/quality; channel/pond
morphology or geometry,
sediment deposition and
chemical characteristics suitable
to support normal behavior,
growth, and viability of CRLF

- Habitat modification to
terrestrial phase PCEs: upland
and dispersal habitat

Acute and chronic studies on birds

- Direct effects to the terrestrial
phase of CRLF

- Chemical characteristics
suitable to support normal
behavior, growth, and viability
of CRLF

No terrestrial amphibian data
available. Bird data used as
surrogate for amphibians.

Acute and chronic studies on
mammals

Acute studies in terrestrial
invertebrates

Acute and chronic studies on birds
(surrogate for terrestrial phase
CRLF: no amphibian data)

- Indirect effects to terrestrial
phase of CRLF (reduction in
prey base and indirect effect to
habitat (use of mammal
burrows))

- Chemical characteristics
suitable to support normal
behavior, growth, and viability
of CRLF

No terrestrial amphibian data
available. Bird data used as
surrogate for amphibians.

1 Adult frogs are no longer in the "aquatic phase" of the amphibian life cycle; however, submerged adult
frogs are considered "aquatic" for the purposes of this assessment because exposure pathways (including
diet) in the water are considerably different that exposure pathways on land.

Acute (short-term) and chronic (long-term) effects toxicity information is characterized,

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based on registrant-submitted studies and a comprehensive review of the open literature
on imazapyr and its isopropylamine salt. Other sources of information, including use of
the acute probit dose response relationship to establish the probability of an individual
effect and reviews of the Ecological Incident Information System (EIIS), were conducted
to further refine the characterization of potential ecological effects associated with
exposure to imazapyr. A summary of the available freshwater and terrestrial plant
ecotoxicity information, use of the probit dose response relationship and the incident
information for imazapyr are provided in Sections 4.1 through 4.4, respectively.

4.1 Evaluation of Aquatic Ecotoxicity Studies (CRLF Aquatic Phase)

Toxicity endpoints are established based on data generated from guideline studies
submitted by the registrant, and from open literature studies that meet the criteria for
inclusion into the ECOTOX database maintained by EPA/Office of Research and
Development (ORD) (U.S. EPA, 2004). Open literature data presented in this assessment
were obtained from the 2005 imazapyr RED as well as ECOTOX information obtained
on February 22, 2007. The February 2007 ECOTOX search included all open literature
data for imazapyr (i.e., pre- and post-RED). In order to be included in the ECOTOX
database, papers must meet the following minimum criteria:

(1) the toxic effects are related to single chemical exposure;

(2) the toxic effects are on an aquatic or terrestrial plant or animal species;

(3) there is a biological effect on live, whole organisms;

(4) a concurrent environmental chemical concentration/dose or application
rate is reported; and

(5) there is an explicit duration of exposure.

Data that pass the ECOTOX screen are evaluated along with the registrant-submitted
data, and may be incorporated qualitatively or quantitatively into this listed species
assessment. In general, effects data in the open literature that are more conservative than
the registrant-submitted data are considered. The degree to which open literature data are
quantitatively or qualitatively characterized is dependent on whether the information is
relevant to the assessment endpoints (i.e., maintenance of CRLF survival, reproduction,
and growth; alteration of PCEs in the critical habitat impact analysis) identified in the
problem formulation. For example, endpoints such as biochemical modifications are
likely to be qualitatively evaluated unless these endpoints are quantitatively linked with,
reduction in CRLF survival, reproduction, and/or growth (e.g., the magnitude of effect on
the biochemical endpoint needed to result in effects on survival, growth, or reproduction
is not known). Open literature data included as part of this assessment are listed in
Appendix G.

All open literature that was not considered as part of this assessment because it was either
rejected by the ECOTOX screen or accepted by ECOTOX but not used (e.g., the
endpoint is less sensitive and/or not appropriate for use in this assessment) are included in

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Appendices H and I. These Appendices also include a rationale for rejection of those
studies that did not pass the ECOTOX screen and those that were not evaluated as part of
this listed species assessment.

As described in Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxa is evaluated. For this assessment, evaluated taxa include
freshwater fish, invertebrates and plants, terrestrial plants and invertebrates, birds and
mammals. Table 4.1.a summarizes the most sensitive ecological toxicity endpoints for
the aquatic phase of the CRLF and its designated critical habitat, based on an evaluation
of both the submitted studies and the open literature, as previously discussed. Additional
information is provided in Appendix B. Ecotoxicity studies on both imazapyr and its
isopropylamine salt are considered in this assessment. The EC50/NOAEC values from
the toxicity tests with the isopropylamine salt of imazapyr are expressed in acid
equivalents (a.e.).

Table 4.1.a Animal and Plant Toxicity Profile of Imazapyr and Its Isopropylamine Salt For Use in

Assessing Risk to the Aquatic Phase CRLF

Assessment Endpoint

Species

Toxicity Value Used
in Risk Assessment2

Citation MR ID #
(Author & Date)

Comment

Direct effects on CRLF following
acute exposure

Rainbow trout
(Oncorhynchus
mykiss)

96-hour LC50 >100 mg /L

00131629

ABC Laboratories,

1983

Acceptable; probit
slope unavailable

Direct effects on CRLF following
chronic exposure

Rainbow trout
(Oncorhynchus
mykiss)

NOAEC/LOAEC
43.1/92.4 mg/L
(significantly reduced
percent hatch and an
observed reduction on
survival)

41315804
Ward, 1988

Supplemental:
survival of control
embryos following
thinning was below
70%.

Indirect effects on CRLF following
acute exposure (reduction in prey base)

Waterflea
(Daphnia magna)

48-hour EC50 >100 mg /L

00131632

ABC Laboratories,

1983

00131629

ABC Laboratories,

1983

Acceptable: probit
slope unavailable

Indirect effects to CRLF via
modification to Critical Habitat PCE
Alteration of other chemical
characteristics necessary for normal
growth and viability of CRLF's and
their food source.

Rainbow trout1
(Oncorhynchus
mykiss)

96-hour LC50 >100 mg /L

Acceptable; probit
slope unavailable

Indirect effects on CRLF following
chronic exposure (reduction in prey
base)

Waterflea
(Daphnia magna)

21-day NOAEC/LOAEC:
97.1/>97.1mg/L

41315805
Manning, 1988

Acceptable: No
effects on growth or
reproduction

Indirect effects to CRLF via
modification to Critical Habitat PCE
Alteration of other chemical
characteristics necessary for normal
growth and viability of CRLF's and
their food source.

Rainbow trout1
(Oncorhynchus
mykiss)

NOAEC/LOAEC
43.1/92.4 mg/L
(significantly reduced
percent hatch and an
observed reduction on
survival)

41315804
Ward, 1988

Supplemental:
survival of control
embryos following
thinning was below
70%.

-85-

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Table 4.1.a Animal and Plant Toxicity Profile of Imazapyr and Its Isopropylamine Salt For Use in

Assessing Risk to the Aquatic Phase CRLF

Assessment Endpoint

Species

Toxicity Value Used
in Risk Assessment2

Citation IMRID #
(Author & Date)

Comment

Indirect effects on CRLF (reduction in
food supply, habitat, and primary
productivity)

Indirect effects to CRLF via
modification to Critical Habitat PCE
Reduction and/or modification of
aquatic-based food sources for pre-
metamorphs

Duckweed
(Lemna gibba)

Green Algae
(Selenastrum
capricornutum)

EC50/NOAEC
0.018/0.011
(mg ae/L)

ec50/noaec

11.5/7.16
(mg ae/L)

43889102
Hughes etal., 1995

Acceptable: endpoint
based on decreased
frond production.

Slight change in cell
shape. % a.e. =23.3
for the salt.

Indirect effects to CRLF via effects to
riparian vegetation required to
maintain acceptable water quality and
habitat in ponds and streams
comprising the species' current range.

Monocots

Seedling emergence

Vegetative vigor
Dicots

Seedling emergence
Vegetative vigor

Wheat EC25: 0.0046 1b
ae/acre

Wheat EC25: 0.0121b
ae/acre

Sugar beet EC25: 0.0024
lb ae/acre

Cucumber EC25: 0.0009
lb ae/acre

40811801
Banks, 1988

Supplemental:
problems with
overcrowding and
fresh weight
endpoints

Indirect effects to CRLF via
modification to Critical Habitat PCE
(alteration to water chemistry/quality
and chemical characteristics suitable to
support normal behavior, growth, and
viability of CRLF; alteration of
channel/pond morphology, sediment
deposition and/or aquatic habitat).

Duckweed
(Lemna gibba)

Green Algae
(Selenastrum
capricornutum)

Monocots

Seedling emergence

Vegetative vigor
Dicots

Seedling emergence
Vegetative vigor

EC50/NOAEC
0.018/0.011
(mg ae/L)

ec50/noaec

11.5/7.16
(mg ae/L)

Wheat EC25: 0.0046 1b
ae/acre

Wheat EC25: 0.0121b
ae/acre

Sugar beet EC25: 0.0024
lb ae/acre

Cucumber EC25: 0.0009
lb ae/acre

43889102
Hughes etal., 1995

40811801
Banks, 1988

Acceptable: endpoint
based on decreased
frond production.

Slight change in cell
shape. % a.e. = 23.3
for the salt.

Supplemental:
problems with
overcrowding and
fresh weight
endpoints

2 The EC50/NOAEC values from the toxicity tests with the isopropylamine salt of imazapyr are expressed
in acid equivalents (a.e.). The toxicity values with the acid are not expressed in terms of acid equivalents.

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Toxicity to aquatic fish and invertebrates is categorized using the system shown in Table
4.1.b (U.S. EPA, 2004). Toxicity categories for aquatic plants have not been defined.

Table 4.1.b. Categories of Acute Toxicity for Aquatic Organisms

LC5„ (ppm)

Toxicity Category

<0.1

Very highly toxic

>0.1-1

Highly toxic

>1-10

Moderately toxic

>10 - 100

Slightly toxic

> 100

Practically nontoxic

4.1.1 Toxicity to Freshwater Fish

EPA typically uses fish as a surrogate for aquatic-phase amphibians when amphibian
toxicity data are not available (U.S. EPA, 2004). In the case of imazapyr, no acute or
chronic toxicity data are available for aquatic-phase amphibians; thus, fish were used as a
surrogate to estimate direct acute and chronic risk to the aquatic-phase CRLF.

Freshwater fish toxicity data were also used to assess potential indirect effects of
imazapyr to the CRLF. Direct effects to freshwater fish resulting from exposure to
imazapyr may indirectly affect the CRLF via reduction in available food. As discussed in
Section 2.5.3, over 50% of the prey mass of the CRLF may consist of vertebrates such as
mice, frogs, and fish (Hayes and Tennant, 1985).

4.1.1.1 Freshwater Fish (Aquatic Phase Amphibian): Acute Exposure
(Mortality) Studies

Fish toxicity studies for two freshwater species using the technical grade active ingredient
(TGAI) are required to establish the acute toxicity of imazapyr acid to fish. The preferred
test species are rainbow trout (a coldwater fish) and bluegill sunfish (a warmwater fish).
Acute studies that were submitted for three freshwater fish species (rainbow trout,
bluegill sunfish, channel catfish) showed that imazapyr is practically non-toxic with 96-hr
LC50 values of >100 mg/L (NOAEC = 100 ppm) for all three species. No mortalities and
no clinical signs of toxicity were observed in any of the studies (MRID 00131629, MRID
00131630 and MRID 00131631).

The available fish toxicity data for one of the salt formulations indicates that this
formulation may be more toxic than the acid (rainbow trout, MRID 00153778); however,
analytical verification of the test material in the test solution was not conducted at any
point during the definitive test so toxicity values and categorization derived using
nominal test concentrations may not be indicative of exposure to the test substance under
these study conditions. The 96-hour LC50 is 112 mg Arsenal/L (20.8 mg ae/L) with a
NOAEC of 10.4 mg ae/L and a LOAEC of 18.9 mg ae/L for sublethal effects (surfacing,

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loss of equilibrium, dark discoloration, fish on bottom and quiescence). This study is
discussed in the risk description (Section 5.2.1) and is summarized in more detail in
Appendix B. Results of the studies on the acid are summarized in Table 4.1.1.1.

'I'iihie 4.I.I.I Krcsliwsitcr Fish Acute Toxicity lor liiiii/npvr Acid.

Species

" i> sic

%-liour
l.( 50

(illli/l.)

To\icil>
CsiU'Siitn

MRU) No.
Aulhor/Yciir

Sluclj
Cliissiriciilion

Bluegill sunfish
(Lepomis macrochirus)

>100

Practically
non-toxic

00131630

ABC Laboratories,

1983

Acceptable

Rainbow trout
(Oncorhynchus mykiss)

>100

Practically
non-toxic

00131629

ABC Laboratories,

1983

Acceptable

Channel catfish
(Ictalurus punctatus)

>100

Practically
non-toxic

00131631

ABC Laboratories,

1983

Acceptable

4.1.1.2 Freshwater Fish: Chronic Exposure (Growth/Reproduction)

Studies

A freshwater fish early life-stage test using the TGAI is normally required for pesticide
registration if the end-use product may be transported to water from the intended use site,
and the following conditions are met: (1) the presence of imazapyr in water that is not
exposed to direct sunlight is likely to be continuous or recurrent and (2) fate properties
indicate that imazapyr is persistent in the aquatic environment not exposed to direct
sunlight. A chronic early life stage study conducted on rainbow trout showed a decrease
in larval survival at a mean measured concentration of 92.4 mg/L (MRID 41315804).
The NOAEC was 43.1 mg/L. The study was originally classified as invalid because
survival of control embryos following thinning was below 70%. However, it was
upgraded to supplemental because the Standard Evaluation Procedure (SEP) (USEPA
Hazard Evaluation Division (no date)) was met and the data were still considered useful
for the purpose of risk assessment. The results from this study will be used for risk
assessment purposes. A chronic early life stage study conducted on the fathead minnow
showed no treatment-related effects at 118 mg/L (highest concentration tested, MRID

45119711). A full life cycle study was also submitted for fathead minnow which showed
no treatment-related effects at 120 mg/L. This study was classified as supplemental
because the Fi generation was maintained for 4 weeks instead of 8 weeks (MRID

45119712). Results of the studies on the acid are summarized in Table 4.1.1.2.

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Tsihle 4.1.1.2 l-'rcshwiilcr l isli Chronic Toxicity lor Iniii/iipvr Acid

Species

0 ;k'

\()AI C/I.OAI C

(mg ae/l.)

r.ndpoinls
Al'l'ccled

MRU) Nil.
AulhorA ear

Slud>
Classification

Early Life-Stage Study under Flow-through Conditions

Rainbow Trout
(Oncorhyncus mykiss)

99.5

43.1/92.4

Larval
survival

41315804
Ward, 1988

Supplemental

Fathead Minnow
(Pimephales promelas)

99.6

118/>118

No treatment-
related effects

45119711
Drottaref a/., 1998

Acceptable

Full Life cycle Study under Flow-through Conditions

Fathead Minnow
(Pimephales promelas)

100

120/>120

No treatment-
related effects

45119712
Drottar etal., 1999

Supplemental

4.1.1.3 Freshwater Fish: Sublethal Effects and Additional Open
Literature Information

No sublethal effects were observed in the freshwater animal studies.

4.1.2 Toxicity to Freshwater Invertebrates

4.1.2.1 Freshwater Invertebrates: Acute Exposure Studies

Toxicity studies on freshwater invertebrates were evaluated to assess the potential for
imazapyr to induce indirect effects to the aquatic phase CRLF via a reduction in prey
base. A freshwater aquatic invertebrate toxicity test using the TGAI is required to
establish the toxicity of imazapyr to aquatic invertebrates. The preferred test species is
Daphnia magna. Submitted data indicate that imazapyr is practically non-toxic to
Daphnia magna with an acute 48-hour EC50 value of >100 mg/L. There were no
mortalities and no clinical signs of toxicity in this study. This value is used for
evaluating acute toxic exposure to freshwater invertebrates (MRID 00131632). The
available aquatic invertebrate toxicity data for one of the salt formulations indicates that
this formulation may be more toxic than the acid (daphnia, MRID 00153779); however,
analytical verification of the test material in the test solution was not conducted at any
point during the definitive test, so toxicity values and categorization derived using
nominal test concentrations may not be indicative of exposure to the test substance under
these study conditions. The 48-hour EC50 is 64.9 mg ae/L with a NOAEC/LOAEC of
59.3/103.8 mg ae/L. This study is discussed in the risk description (Section 5.2.2) and is
summarized in more detail in Appendix B.

An open literature study is available in which the snail, Biomphalaria tenagophila
(ECOTOX ref. number 80947) was exposed to a formulation of imazapyr containing
nonylphenol. This study is summarized and discussed in Appendix K with multiple
active ingredients.

-89-

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Tsihle 4.1.2.1 l-'ivshwsilcr ln\erlebr:ile Anile Toxicity lor Iniii/iipyr Acid

Spwics

" ii ji-

4N-hiiur

l(„,

(111^/1.)

Tii\ii'ii\

MKII) No.
AnlliiiiVN i-;ir

Slutl\

('hissilliiiiiiiii

Waterflea
(.Daphnia magna)

>100

Practically
non-toxic

00131632
ABC Laboratories, 1983

Acceptable

4.1.2.2 Freshwater Invertebrates: Chronic Exposure Studies

A freshwater aquatic invertebrate life-cycle test using the TGAI is normally required for
pesticide registration if the end-use product may be transported to water from the
intended use site, and the following conditions are met: (1) the presence of imazapyr in
water that is not exposed to direct sunlight is likely to be continuous or recurrent and (2)
fate properties indicate that imazapyr is persistent in the aquatic environment not exposed
to direct sunlight. The preferred test is a 21-day life cycle on Daphnia magna. The data
that were submitted show that imazapyr concentrations up to 97.1 mg/L did not
significantly affect survival, reproductive success, or growth of first generation daphnids.
The NOAEC of 97.1 mg/L will be used in assessing risk (MRID #41315805). Results of
the study on the acid are summarized in Table 4.1.2.2.

Tsihle 4.1.2.2 Treshwiiter Aqiintic 1 merle

mile Chronic Toxicity lor Imn/iipyr Acid

Spi-iii-s/
I'll i\\-ill i'hiii>Ii

"¦ ii ;k-

2l-tl:i\
\o.\r.c (m»/i.)

r.ndpiiinis
Al'l'iikil

MKII) No.
AiilhoiVN i-;ir

Slutl\

( l;issilli;iliiin

Waterflea
(Daphnia magna)

99.5

97.1

No effects on

growth or
reproduction

41315805
Manning, 1988

Acceptable

4.1.3 Toxicity to Aquatic Plants

Aquatic plant toxicity studies were used as one of the measures of effect to evaluate
whether imazapyr may affect primary production. In addition, aquatic plants are a
primary food source of the larval (tadpole) life stage of the CRLF. Primary productivity
is essential for indirectly supporting the growth and abundance of the CRLF. Freshwater
vascular and non-vascular plant data are used to evaluate a number of the PCEs
associated with the critical habitat impact analysis. Specifically, the data are used to
determine whether water quality parameters, including oxygen content may be adversely
modified. Laboratory studies were used to evaluate the potential of imazapyr to affect
primary productivity and to determine whether imazapyr may cause direct effects to
aquatic plants.

Several aquatic plant toxicity studies using the TGAI are required to establish the toxicity

-90-

-------
of imazapyr to non-target aquatic plants. The recommendation is for testing of five
species: freshwater green alga (Selenastrum capricornutum), duckweed (Lemna gibba),
marine diatom (Skeletonema costatum), blue-green algae (Anabaena flos-aquae), and a
freshwater diatom. The 14-day EC50 for the freshwater vascular plant (duckweed) is
0.024 mg/L (NOAEC = 0.01 mg/L), based on inhibition of population growth and
reduced frond production; and the lowest 7-day EC50 for the freshwater non-vascular
plant (blue-green algae) is 12.2 mg/L (NOAEC = 9.6 mg/L), based on reduced cell
counts. In the non-vascular plant studies, the study authors concluded that imazapyr acid
was not expected to exert detrimental effects at the maximum application rate up to 1.5
lbs ai/acre. The toxicity of the isopropylamine salt of imazapyr to duckweed was similar
to the acid, with a 14-day EC50 of 0.018 mg ae/L (NOAEC = 0.011 mg ae/L). The
isopropylamine salt of imazapyr was more toxic to the green algae than imazapyr acid
and more closely resembled the toxic response of blue-green algae (see Table 4.1.3
below; MRID 40811802; MRID 43889102; and MRID 43889102) for the five required
species. Since the isopropylamine salt is more toxic than imazapyr acid to both the
aquatic vascular and non-vascular plants (based on duckweed and green algae), the
results from the salt will be used in the risk assessment. Results of the studies are
summarized in Table 4.1.3.

Tsihle 4.1.3 \on-l:ir«>cl Aqiiiilic I'hinl Toxicity lor lm;iz;ip\r Acid iiikI Isopropyhiminc Siill of

Iniii/iipyr.

Spi-iii-s
| l ii-r ll|

0 • ¦ 1 >

•0 ;k'

l.( 5„/\().\l.(
(m»/l.)

r.iHipoinis
Al'IWkil

MRU) No.
A ill In ir, ^ i-ar

Slud\
('lassiliialiiiii

Isopropylamine Salt of Imazapyr

Duckweed
{Lemna gibba)

23.3

0.018/0.011
(mg ae/L)

Frond production

43889102
Hughes etal., 1995

Acceptable

Green Algae
{Selenastrum capricornutum)

23.3

11.5/7.16
(mg ae/L)

Slight change in
cell shape

43889102
Hughes etal., 1995

Acceptable

Imazapyr Acid

Duckweed
{Lemna gibba)

99.5

0.024/0.01

Population growth
Frond production

40811802
Hughes, 1987

Acceptable

Green Algae
{Selenastrum capricornutum)

99.5

71/50.9

Cell density

40811802
Hughes, 1987

Acceptable

Blue-green Algae
{Anabaena flos-aquae)

99.5

12.2/9.6

Cell density

40811802
Hughes, 1987

Acceptable

Diatom
{Navicula pelliculosa)

99.5

>41/41

Cell density

40811802
Hughes, 1987

Acceptable

Diatom
{Skeletonema costatum)

99.5

92/15.9

Cell density

40811802
Hughes, 1987

Acceptable

*The EC50/NOAEC values from the toxicity tests with the isopropylamine salt of imazapyr are expressed in
acid equivalents (a.e.)

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4.1.4 Freshwater Field Studies

An in situ microcosm study, published in the open literature and accessed via ECOTOX
was conducted to assess the effects of a single application of imazapyr (stirred into the
water column) at the following mean concentrations: 0.19, 2.1 or 19.8 mg/L (equivalent
to 1, 10 or 100 times the expected environmental concentration from a normal application
rate) on the macroinvertebrate community of a logged pond cypress dome. In situ
microcosms were set up in schedule-40 polyvinyl chloride water pipes (diameter 7.62
cm; height 45.7 cm; area 45.6 cm2) driven approximately 12 cm into the substrate and
leaving a mean water column depth of 32.1 cm. The microcosms were immediately
dosed with the selected treatments of imazapyr and left undisturbed for two weeks. Forty
eight microcosms were set up (3 blocks of 16, each block consisting of 4 replicates of 3
treatment levels and a control). In addition, 12 cypress dome cores, divided equally
among the 3 blocks were sampled at the end of the study. These allowed for testing for
microcosm influences on the measured parameters. Macroinvertebrates were hand
picked from each sample and prepared for identification. Organisms other than
chironomids were identified at the family level or to the lowest practical taxonomic level.
Chironomids were identified to the genus level. Effects on aquatic plants were not
examined. Changes in the macroinvertebrate composition, chironomid biomass and
chironomid head-capsule deformities were assessed. A total of 2,904 individuals
representing 44 taxa were collected. The following taxa were represented: Caecidotea,
Crangonyx, Dipteran, Chironomid, Polypedilum, Chironomus, Ablabesmyia, and
Procladius. There were three rain events following treatment. The half-life of imazapyr
was calculated to be 3.2, 3.2 and 3.4 days for the 0.19, 2.1 and 19.8 mg/L concentrations,
respectively. Imazapyr did not appear to affect any of these parameters at the
concentrations tested (ECOTOX Ref. 68204). However, these results are of limited value
because potential effects at the species level were not examined. Individual species could
have been affected and not reported because the analysis was conducted at higher
taxonomic levels. In addition, effects on aquatic plants were not examined.

4.2 Evaluation of Terrestrial Ecotoxicity Studies (CRLF Terrestrial Phase)

Table 4.2.a summarizes the most sensitive ecological toxicity endpoints for the terrestrial
phase of the CRLF and its designated critical habitat, based on an evaluation of both the
submitted studies and the open literature, as previously discussed. Additional
information is provided in Appendix B. Ecotoxicity studies on both imazapyr and its
isopropylamine salt are considered in this assessment. The EC50/NOAEC values from
the toxicity tests with the isopropylamine salt of imazapyr are expressed in acid
equivalents (a.e.).

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Table 4.2.a Animal and Plant Toxicity Profil

Assessing Risk to t

e of Imazapyr and Its Isopropylamine Salt For Use in
le Terrestrial Phase CRLF

Assessment End poi nt

Species

Toxicity Value Used
in Risk Assessment

Citation IMRID #
(Author & Date)

Comment

Direct effects on CRLF following
acute exposure

Northern bobwhite
quail

(Colinus virginianus)

LD30 >2,150 mg/kg bw
LC50 >5,000 mg/kg diet

Bio-Life Assoc.,
1983
00131633

00131635

Probit slopes
unavailable:
Acceptable

Acceptable

Direct effects on CRLF following
chronic exposure

Northern bobwhite
quail

(Colinus virginianus)

NOAEC/LOAEC
1,670^1,670 ppm

45119714
Ahmed etal., 1999

Acceptable

Indirect effects on CRLF following
acute exposure (reduction in prey base)

Rat

(Sprague Dawley)

Honey Bee
(Apis mellifera)

LD50 >5,000 mg ae/kg bw
(males/females)

>100 (ig/bee

00132030
American Cyanamid
Co., 1983

00131637
Atkins, 1983

Acceptable: probit
slope unavailable

Indirect effects on CRLF following
chronic exposure (reduction in prey
base)

Rat

(Sprague Dawley)

NOAEL = 738 mg/kg
bw/day - Males
NOAEL = 933.3 mg/kg
bw/day - Females
or 10000 ppm for both.

41039505
Robinson, 1987

Acceptable
reproduction study.

Indirect effects to CRLF via effects on
habitat (reduction in riparian
vegetation)

Monocots

Seedling emergence

Vegetative vigor
Dicots

Seedling emergence
Vegetative vigor

Wheat EC25: 0.0046 1b
ae/acre

Wheat EC25: 0.0121b
ae/acre

Sugar beet EC25: 0.0024
lb ae/acre

Cucumber EC25: 0.0009
lb ae/acre

40811801
Banks, 1988

Supplemental:
problems with
overcrowding and
fresh weight
endpoints

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Table 4.2.a Animal and Plant Toxicity Profile of Imazapyr and Its Isopropylamine Salt For Use in

Assessing Risk to t

ie Terrestrial Phase CRLF

Assessment Endpoint

Species

Toxicity Value Used

Citation IMRID #

Comment

in Risk Assessment

(Author & Date)

-Indirect effects to CRLF via adverse

Rat

modification to Critical Habitat PCE:

(Sprague Dawley)

LD50 >5,000 mg ae/kg bw

00132030

Acceptable: probit

alteration of other chemical

(males/females)

American Cyanamid

slope unavailable

characteristics necessary for normal

Co., 1983

growth and viability of juvenile and

Honey Bee

adult CRLFs and their food source.

(Apis mellifera)

>100 (ig/bee

00131637

Acceptable: probit

-Indirect effects to CRLF via adverse

Atkins, 1983

slope unavailable

modification to Critical Habitat PCE:

Rat

reduction and/or modification of food

(Sprague Dawley)

NOAEL = 738 mg/kg

41039505

Acceptable

sources for terrestrial phase juveniles

bw/day - Males

Robinson, 1987

reproduction study.

and adults

NOAEL = 933.3 mg/kg

bw/day - Females

or 10000 ppm for both.

Northern bobwhite

quail

>2,150 mg/kg bw

Bio-Life Assoc.,

Probit slopes

(Colinus virginianus)

>5,000 mg/kg diet

1983

unavailable:

00131633

Acceptable

00131635

Acceptable

Northern bobwhite

quail

NOAEC/LOAEC

45119714

Acceptable

(Colinus virginianus)

1,670^1,670 ppm

Ahmed etal., 1999

Rainbow trout

(Oncorhynchus

96-hour LC50 >100 mg /L

00131629

Acceptable: : probit

mykiss)

ABC Laboratories,

1 QS"?

slope unavailable

Rainbow trout

1 70J

(Oncorhynchus

NOAEC/LOAEC

41315804

Supplemental:

mykiss)

43.1/92.4 mg/L

Ward, 1988

survival of control

(significantly reduced

embryos following

percent hatch and an

thinning was below

observed reduction on

70%.

survival)

Indirect effects to CRLF via adverse

Monocots

Wheat EC25: 0.0046 1b

40811801

Supplemental:

modification to Critical Habitat PCE:

Seedling emergence

ae/acre

Banks, 1988

problems with

elimination and/or disturbance of

Wheat EC25: 0.0121b

overcrowding and

upland and dispersal habitat

Vegetative vigor

ae/acre

fresh weight

endpoints

Dicots

Sugar beet EC25: 0.0024

Seedling emergence

lb ae/acre

Cucumber EC25: 0.0009

Vegetative vigor

lb ae/acre

Toxicity to birds, mammals and terrestrial invertebrates is categorized using the system
shown in Table 4.2.b (U.S. EPA, 2004). Toxicity categories for terrestrial plants have not
been defined.

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Table 4.2.1) Categories of Acute Toxicity lor Tcrrcslrial Organisms

Oi'iil l.lh„ (inii/kii)

Diclan l.( (|)|)in)

To\icil> C;ik".ior\

<10

<50

Very highly toxic

10-50

50 - 500

Highly toxic

51-500

501 - 1000

Moderately toxic

501 -2000

1001-5000

Slightly toxic

>2000

>5000

Practically non-toxic

4.2.1 Toxicity to Birds

EPA typically uses birds as a surrogate for terrestrial-phase amphibians when amphibian
toxicity data are not available (U.S. EPA, 2004). Since there are no terrestrial-phase
amphibian data available for imazapyr, acute and chronic avian toxicity data were used to
assess the potential direct effects to the CRLF.

4.2.1.1 Acute Exposure (Mortality) Studies

An oral toxicity study using the technical grade of the active ingredient (TGAI) is
required to establish the acute toxicity of imazapyr to birds. The preferred guideline test
species is either mallard duck (a waterfowl) or bobwhite quail (an upland gamebird). The
submitted acute data indicate that imazapyr is practically non-toxic to waterfowl and
upland gamebirds with oral LD50 values >2,150 mg a.i./kg bw. There were no mortalities
or clinical signs of toxicity in either the bobwhite quail or the mallard ducks (MRID
00131633, MRID 00131634). Results of the studies are summarized in Table 4.2.1.1.a.

Table 4

Spi-iii-s

Z.l.l.a A\

" 11 ji-

in 11 Acute ()

I.D511 (m»

ml Toxicity for

Tii\k'ii\
C;iU-»iir\

Ima/apyr Acid.

MRU) \u.
Aiilhur, ^ i-;ir

Sillily
( l;issirii;iliiin

Northern bobwhite quail
(Colinus virginianus)

>2,150

Practically
Non-toxic

00131633
Bio-Life Assoc., 1983

Acceptable

Mallard duck
(Anas platyrhynchos)

>2,150

Practically
non-toxic

00131634
Bio-Life Assoc., 1983

Acceptable

Two dietary studies using the TGAI are required to establish the subacute toxicity of
imazapyr to birds. The preferred test species are mallard duck and bobwhite quail. The
data that were submitted show that the 8-day acute dietary LC50 for both species was
>5,000 ppm; therefore, imazapyr is categorized as practically non-toxic to avian species
on a subacute dietary basis. In the bobwhite quail study, there was one mortality at one
of the lower concentration levels but none at the higher concentration levels. There were
no clinical signs of toxicity in either study (MRID 00131635; MRID 00131636). The

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available subacute dietary study on bobwhite quail for the salt indicates that it is no more
toxic than the acid and is summarized in Appendix B. Results of the studies are
summarized in Table 4.2.1.1.b.

Tiihle -4.2.1.1 .h A\isin Snh:icnto Diclsirv Studies lor Iniii/npvr Acid.

Spwics

" ii sic

N-I);i\ l.(5„
(111" ;u-/k»-ilk-l)

lu\iiii\

C;ik-»iir\

MRU) Nil.
A ill In ir, ^ i-;ir

Slud\
('hissilkiiliiui

Northern bobwhite quail
(Colinus virginianus)

>5,000

Practically
non-toxic

00131635
Bio-Life Assoc., 1983

Acceptable

Mallard duck
(Anas platyrhynchos)

>5,000

Practically
non-toxic

00131636
Bio-Life Assoc., 1983

Acceptable

4.2.1.2 Chronic Exposure (Growth/Reproduction) Studies

Avian reproduction studies using the TGAI were required because birds may be subject
to repeated or continuous exposure to imazapyr, especially preceding or during the
breeding season. The preferred test species are mallard duck and bobwhite quail. The
submitted data indicate no evidence of adverse reproductive effects to bobwhite quail at
concentrations up to 1,670 ppm (MRID 45119714) and 2000 ppm (MRID 43831401),
and to mallard ducks at concentrations up to 1890 ppm (MRID 43831402). Results of the
studies are summarized in Table 4.2.1.2.

Tiihle 4.2.1.2. A\i:m Reproduction lor linii/iipvr Acid

Spwics

"¦'ii ;u-

\().\l ( /I.OAI

(' (111"

(licl)

I.OAI (

r.iHipiiinis

MRU) Nil.
A ill liiir. ^ i;i i'

Slud\
('l;issilK';ilinn

Northern bobwhite quail
(Colinus virginianus)

100

1,670^1,670

No treatment-
related toxicity

45119714
Ahmed etal., 1999

Acceptable

Northern bobwhite quail
(Colinus virginianus)

Technical -
% not stated

2000/>2000

No treatment-
related toxicity

438314011987

Acceptable

Mallard duck
(Anas platyrhynchos)

Technical -
% not stated

1890/>1890
(2000 nominal)

No treatment-
related toxicity

438314021987

Acceptable

4.2.1.3 Sublethal Effects and Additional Open Literature Information

No treatment-related sublethal effects were observed following either acute or chronic
exposure.

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4.2.2 Toxicity to Mammals

4.2.2.1 Acute Exposure (Mortality) Studies

Technical

Toxicity studies on mammals were evaluated to assess the potential for imazapyr to
induce indirect effects to the terrestrial phase CRLF via a reduction in prey base. Wild
mammal testing is required on a case-by-case basis, depending on the results of lower tier
laboratory mammalian studies, intended use pattern and pertinent environmental fate
characteristics. In most cases, rat or mouse toxicity values obtained from the Agency's
Health Effects Division (HED) substitute for wild mammal testing. These toxicity values
are reported below.

The results indicate that imazapyr acid is categorized as practically non-toxic to small
mammals on an acute oral basis (LD50 value >5,000 mg/kg bw, both sexes (MRID
00132030)). Results of the study are summarized in Table 4.2.2.1a. The available acute
oral studies with rats for the salt indicate that it is no more toxic than the acid and are
summarized in Appendix B.

Tsihle 4.2.2.1 Mnniiiiiiliiin Acute Toxicity lor luiii/iipvr Acid.

Spi-iii-s

" ii sic

Ti>\k'il\

Al'IWkil

I'lidpoinls

MRU) No.
Aulhiir, ^ i-;ir

Slud\
(l;issilK;iliiiii

Rat

(Sprague-Dawley)

LD50 >5,000 mg ae/kg bw
(males/females)

Mortality

00132030
American
Cyanamid Co.,
1983

Acceptable

Formulated Products Containing One or More Active Ingredients

Acute oral toxicity data (i.e., LD50 values) from mammalian studies for formulated
products that contain imazapyr and one or more additional active ingredients are
summarized in Appendix K.

4.2.2.2 Chronic Exposure (Growth/Reproduction) Studies

In a 2-generation reproduction study with rats exposed to imazapyr acid, no treatment-
related effects were observed. Consequently, the NOAEL for parental systemic,
reproductive, and offspring was 738 mg/kg bw/day for males and 933.3 mg/kg bw/day
for males. The NOAEC is 10000 ppm (MRID 41039505). The NOAEC/NOAEL from
this study will be used in assessment of risk.

In developmental toxicity studies, administration of imazapyr acid by gavage resulted in
no treatment-related effects in developmental parameters at doses up to and including
1000 and 400 mg/kg bw/day in the rat and rabbit, respectively. In the rat study, the only

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maternal toxicity observed at 300 mg/kg bw/day was salivation during gestation days 8 -
15. This effect is not likely to affect reproduction, growth or survival. Therefore, it is
not be used quantitatively in assessment of risk. The salivation is likely due to the route
of administration (gavage) with a potentially irritating substance (an acid). In the rabbit
study, no maternal toxicity was observed at 400 mg/kg bw/day, the highest dose tested.
Mortality was observed in the does at 250 mg/kg/day and above in the pilot study (MRID
00131614). Microscopic examination of the does that died showed gastric ulcers and
lesions in the gastrointestinal tract. These effects are not considered to be effects that
would occur following chronic exposure. They are considered to be acute effects and are
more likely a result of the route of administration (gavage with imazapyr acid, a probable
irritating substance (MRID 00131611; MRID 00131613)). Results of the studies are
summarized in Table 4.2.2.2.

Tsihle 4.2.2.2 Miiiniiiiiliiin Dcxclopnicnlnl/Rcproiluclixc Toxicity lor lm:iz:ip\r Acid.

Spi-iii-s

O •

l'uiil\

Ti-si
T\ pi-

Ti>\k'il\

Al'IWkil
lliulpiiinis

MRU) No.
Sllltl\ ;illlll(ir
CI;issilK;ili(in

Rat

(Sprague
Dawley)

Developmental

NOAEL/LOAEL = 300/1000 mg/kg
bw/day

NOAEL = 1000 mg/kg bw/day

Maternal tox1
Developmental

00131611
Salamon &
May hew, 1983
Acceptable

Rabbit

(New Zealand
White)

Developmental

NOAEL = 400 mg/kg bw/day
NOAEL = 400 mg/kg bw/day

No effects

00131613
Mayhew &
Salamon, 1983
Acceptable

Rat

(Sprague
Dawley)

99.5

Reproduction

NOAEL = 738 mg/kg bw/day - Males
NOAEL = 933.3 mg/kg bw/day - Females
or 10000 ppm for both.

No effects

41039505
Robinson, 1987
Acceptable

administration).

Developmental toxicity - No treatment-related effects in developmental parameters; no treatment-related
malformations.

4.2.2.3 Sublethal Effects and Additional Open Literature Information

No treatment-related sublethal effects were observed following acute exposure.

Salivation was the only sublethal effect observed following subacute exposure in a
developmental study in the rat. This effect is likely due to the route of administration
(gavage) and is not likely to occur in wild mammalian populations.

4.2.3 Toxicity to Terrestrial Invertebrates

Toxicity studies on terrestrial invertebrates were evaluated to assess the potential for
imazapyr to induce indirect effects to the terrestrial phase CRLF via a reduction in prey
base. A honey bee acute contact study using the TGAI is required for imazapyr because
its foliar application treatment use will result in honey bee exposure. The acute contact

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LD5o, using the honey bee, Apis mellifera, is an acute contact, single-dose laboratory
study designed to estimate the quantity of toxicant required to cause 50% mortality in a
test population of bees. The acute contact LD50 for imazapyr is > 100 |ig/bee and it is,
therefore, classified as practically non-toxic to bees on a contact exposure basis (MRID
00131637). Results of the study are summarized in Table 4..2.3.

Tsihlc 4.2.3 \<)ii-l:ir»cl Insects - Acute C'ontiict (lm;iz:i|)\ r Acid).

Spi-iii-s

"¦ ii Hi-

Ill" ;n-/l>i-i-)

To\ii'ii>
(;ili-»iir\

MRU) Nil.
AnlliiiiVN i-;ii-

Sluil\
C hissilli-;iiinn

Honey Bee
(Apis mellifera)

Tech

>100

Practically
non-toxic

00131637
Atkins, 1983

Acceptable

4.2.4 Toxicity to Terrestrial Plants

Terrestrial plant toxicity data are used to evaluate the potential for imazapyr to affect
riparian zone vegetation within the action area for the CRLF. These data are also used to
evaluate potential for habitat modification to terrestrial PCEs, including upland and
dispersal habitat. Riparian zone effects may result in increased sedimentation, which
may impact the aquatic phase CRLF by reducing feeding and respiratory efficiency from
clogged gills, disrupting metabolic processes, reducing growth rates and increasing
substrata instability (Ellis, 1936; Stansbery, 1971; Markings and Bills, 1979; Kat, 1982;
Vannote and Minshall, 1982; Aldridge et al., 1987; and Waters, 1995). In addition, many
of the aquatic PCEs associated with designated critical habitat for the CRLF (i.e.,
geomorphically stable banks, water temperature, quality and substrate composition) and
terrestrial PCEs (upland and dispersal habitats) rely on the presence of riparian
vegetation.

Plant toxicity data from both registrant-submitted studies and studies in the scientific
literature were reviewed for this assessment. Registrant-submitted studies are conducted
under conditions and with species defined in EPA toxicity test guidelines. Sublethal
endpoints such as plant growth, dry weight, and biomass are evaluated for both monocots
and dicots, and effects are evaluated at both seedling emergence and vegetative life
stages. Guideline studies generally evaluate toxicity to ten crop species. A drawback to
these tests in the context of this assessment, is that they are conducted on herbaceous crop
species only, and extrapolation of effects to other species, such as the woody shrubs and
trees and wild herbaceous species, contributes uncertainty to risk conclusions.

Commercial crop species have been selectively bred, and may be more or less resistant to
particular stressors than wild herbs and forbs. The direction of this uncertainty for
specific plants and stressors, including imazapyr, is largely unknown. Homogenous test
plant seed lots also lack the genetic variation that occurs in natural populations; therefore,
the range of effects seen from these tests is likely to be smaller than would be expected
from wild populations.

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Tier II terrestrial plant toxicity studies were conducted to establish the toxicity of
imazapyr and the isopropylamine salt of imazapyr to non-target terrestrial plants. The
recommendations for seedling emergence and vegetative vigor studies are for testing of
(1) six species of at least four dicotyledonous families, one species of which is soybean
{Glycine max), and the second of which is a root crop, and (2) four species of at least two
monocotyledonous families, one of which is corn {Zea mays). Due to problems of
overcrowding and 'fresh weight' endpoints with the seedling emergence and vegetative
vigor studies with imazapyr acid, only results classified as supplemental will be used to
assess risk of imazapyr acid (seedling emergence for 3 monocots and 2 dicots; vegetative
vigor for 3 monocots and 4 dicots). Tier II vegetative vigor studies were performed with
the isopropylamine salt of imazapyr for one monocot (onion) and two dicots (soybean
and sugar beet). These data will be used to assess risk to the isopropylamine salt of
imazapyr (MRID 40811801).

Results of Tier II toxicity studies with monocots and dicots indicate that seedling
emergence and vegetative vigor are impacted by exposure to imazapyr acid and to the
isopropylamine salt of imazapyr. Seedling emergence, based on weight, was adversely
impacted in monocots (wheat) at an EC25 of 0.0046 lb ae/are and in dicots (sugar beet)
with an EC25 of 0.0024 lb ae/acre. In the wheat, stunting, interveinal chlorosis, and
cessation of growth occurred at doses >0.0078 lb ae/acre. After 28 days, imazapyr acid
resulted in >60% crop injury in sugar beets at all doses >0.031 lb ae/acre. Vegetative
vigor in monocots, based on weight, was adversely impacted by both imazapyr acid and
the isopropylamine salt of imazapyr at an EC25 of 0.012 lb ae/acre in wheat and 0.012 lb
ae/acre in onion, respectively. In vegetative vigor studies with dicots, imazapyr acid was
more toxic than the isopropylamine salt of imazapyr with an acid EC25 of 0.0009 lb
ae/acre (cucumber) versus salt EC25 of 0.002 lb ae/acre (sugar beet), respectively. The
observed effects to monocots and dicots including stunting, chlorosis, and plant death
were observed for isopropylamine salt (MRID 40003711). Results of the study are
summarized in Table 4.2.4.

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Table -1

.2.4 Tier II Terreslrisil \on-l:ir»ol Phml Toxicity.'

S|>i-iii-s

Si-i-rilin

»r.nuT»i-iui-

I'lidpiiinl
AM'iiiiil

r.ndpuiiil
AM'iiiiil

MRU) Nil.

AiilhiirA i-;ir

l(:5

(II) ;k'/;kiv)

\().\l.( /|l.( i,?|

l(:5

(II) ;k'/;kiv)

\().\l.( /|l.( ll5|

Miid> ( liissiliiiiliiin

Miiimi'iiis

Isiipnipi

liimiiK' Siill hI' 1 inp\ r

Onion

0.012

[0.005]

Dry weight

43889101

Acceptable

Dicots

Feutz & Canez,
1995

Soybean

0.034

0.008

Shoot length

Sugar beet

0.002

0.001

Dry weight

1 m;i/:i|>\ r Acid

S|>i-iii-s

Si-i-rilin

» I'liK'i'miKi'

r.iHipiiiiii

AM'iiiiil

\'i»ur

r.iHipiiim
AM'iiiiil

MRU) Nil.

AiilhiirA i-;ir

l.( :5
(II) ;u-/;iiTi-)

NOAM /|l.( ll5|

l".( ;5(ll)

N().\l.( |/l.( ll5|

Siud\ Chissiriiiiiiiiii

Monocots

Corn

>0.0156

0.0078

Weight

40811801
Banks, 1988

Supplemental

Oat

0.054

0.0156

Height

0.013

0.0039

Height

Supplemental

Onion

0.034

[0.01]

Weight

Supplemental

Wheat

0.0046

[0.00099]

Weight

0.012

0.0039

Weight

Supplemental

Dicots

Sugar beet

0.0024

[0.00017]

Weight

0.00097

[0.00039]

Weight

Supplemental

Sunflower

0.0054

0.0039

Weight

Supplemental

Cucumber

0.0009

[0.000064]

Height

Supplemental

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Table -1

.2.4 Tier II Terreslrisil \<>n-l:ir»ol Phml Toxicity.'

Spwics

Sivriliii

»r.nuT»i-iui-

I'lidpiiinl
AI'I'iiUil

\'i»ur

r.ndpuiiil
AM'iiiiil

Mkll) No.
AiilhiirA i-;ir

l(:5

(II) ;k'/;kiv)

\().\l.( /|l.( i,?|

l(:5

(II) ;k'/;kiv)

\().\l.( /|l.( ll5|

S(ll(l\ ( l;issirii;ilinn

Tomato

0.008

0.0003

Weight

>0.0156

0.00097

Weight

Supplemental

The EC50/NOAEC values from the toxicity tests with the isopropylamine salt of imazapyr are expressed in acid equivalents (a.e.).

If the NOAEC value is above the EC25, equal to the EC25, or below the lowest concentration, an EC05 value is used instead.

A — = no data B No data for pea and soybeans tested with acid, and the study was invalid. c Bold values are used in risk assessment.

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

The Agency uses the probit dose response relationship as a tool for providing
additional information on the potential for acute direct effects to the CRLF and aquatic
and terrestrial animals that may indirectly affect the CRLF (U.S. EPA, 2004). As part of
the risk characterization, an interpretation of acute RQ for listed species is discussed.

This interpretation is presented in terms of the chance of an individual event (i.e.,
mortality or immobilization) should exposure at the EEC actually occur for a species with
sensitivity to imazapyr on par with the acute toxicity endpoint selected for RQ
calculation. To accomplish this interpretation, the Agency uses the slope of the dose
response relationship available from the toxicity study used to establish the acute toxicity
measures of effect for each taxonomic group that is relevant to this assessment. The
individual effects probability associated with the acute RQ is based on the mean estimate
of the slope and an assumption of a probit dose response relationship. In addition to a
single effects probability estimate based on the mean, upper and lower estimates of the
effects probability are also provided to account for variance in the slope, if available.
The upper and lower bounds of the effects probability are based on available information
on the 95% confidence interval of the slope. Studies with good probit fit characteristics
(i.e., statistically appropriate for the data set) are associated with a high degree of
confidence. Conversely, a low degree of confidence is associated with data from studies
that do not statistically support a probit dose response relationship. In addition,
confidence in the data set may be reduced by high variance in the slope (i.e., large 95%
confidence intervals), despite good probit fit characteristics. In the event that dose
response information is not available to estimate a slope, a default slope assumption of
4.5 (95%) C.I.: 2 to 9) (Urban and Cook, 1986) is used.

Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1
(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP,
Environmental Fate and Effects Division (June 22, 2004). The model allows for such
calculations by entering the mean slope estimate (and the 95%> confidence bounds of that
estimate) as the slope parameter for the spreadsheet. In addition, the acute RQ is entered
as the desired threshold.

4.4 Incident Database Review

FIFRA 6(a)(2) incident data add lines of evidence to the risk predictions from the
screening level assessment helping to indicate whether the predictions are substantiated
with actual effects in the field. Twelve incidents resulting from imazapyr and its
isopropylamine salt use have been recorded in the Ecological Incident Information
System (EIIS) as of February 22, 2007. All of the reported incidents occurred between
the dates of 04/20/1995 - 03/01/2004. Incidents reported include possible impacts to
terrestrial and aquatic plants, fish and birds. The majority of reported incidents are
damage to terrestrial plants, especially food crops as a result of exposure following

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application of formulations containing imazapyr and other pesticide active ingredients.
Due to the fact that multiple active ingredients were involved in all of the incidences
involving either aquatic or terrestrial animals, effects from exposure to imazapyr could
not be definitively determined. Therefore, these incidences are not discussed in the risk
description.

4.4.1 Incidents Involving Aquatic Organisms

One incident was reported in which a mixed herbicidal spray, containing a mixture of the
isopropylamine salt of imazapyr, diuron and metsulfuron methyl was sprayed onto a
fence row and either drifted or ran-off into a pond 60 feet away resulting in a fish and
algae kill (species unknown). The certainty index is rated possible and the legality is
undetermined. It cannot be definitively determined whether or not the fish and algae kill
was due to exposure to imazapyr.

A second incident was reported which involved a goldfish kill. There was suspected
runoff or drift into the pond following an aerial application of an imazapyr formulation to
a nearby 145 acres. The cause of the kill was undetermined.

4.4.2 Incidents Involving Terrestrial Organisms

4.4.2.1 Terrestrial Animals

The same fencerow incident as listed in the aquatic organism section drifted onto
adjacent birdnest boxes and a bird kill of nestling and mature birds located from 2-85 feet
from the application site occured. Thirty-two bluebirds, 5 Carolina chickadees and 35
unknown birds were affected. Again, this was a mixture of herbicides. The certainty
index is rated possible and the legality is undetermined. It cannot be definitively
determined whether or not the bird kill was due to exposure to imazapyr.

4.4.2.2 Terrestrial Plants

An incident was reported which involved the spraying of a mixture of glyphosate, the
isopropylamine salt of imazapyr and metsulfuron methyl to a right-of-way at a distance
of approximately 150 yards from watermelon and cantaloupe crops, and 1/4 of a mile
from tomato crops. There was damage to the crops. It cannot be definitively determined
whether or not the damage to the crops was due to imazapyr alone since glyphosate and
metsulfuron methyl, also herbicides, were used.

In a second incident, there was damage to 3 oak trees, some grape vines and 1.5 acres of
beans as a result of spray drift from an application of a formulation containing the
isopropylamine salt of imazapyr approximately 150 - 200 feet away. It is probable that
this incident was due to exposure to imazapyr.

Nine incidents of damages to plants were reported following application of imazapyr

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formulations. Several dead or dying cherry and pear trees were reported following root
uptake of residual imazapyr applied to an irrigation canal. Low yield in a 120 acre corn
crop occurred following application of two herbicidal formulations, one of which
contained imazapyr. The certainty index classified these as possibly related to imazapyr
exposure. Damage was sustained by winter wheat from carryover of imazapyr which had
been applied to peas the previous Spring. Three oaks were injured following a runoff
event from an adjacent plant site. The certainty index classified these as probably related
to the presence of imazapyr. There was a possible connection to imazapyr to the loss of
loblolly pine seedlings in one area. Other pesticides may have been involved as well:
glyphosate and hexazinone. Finally, willow and spruce were killed following application
of imazapyr to a driveway surface. No other information was provided. The certainty
index classified this event as probably related to exposure to imazapyr.

5. Risk Characterization

Risk characterization is the integration of the exposure and effects characterizations to
determine the potential ecological risk from varying imazapyr use scenarios within the
action area and likelihood of direct and indirect effects on the CRLF and their designated
critical habitat. The risk characterization provides an estimation (Section 5.1) and a
description (Section 5.2) of the likelihood of adverse effects; articulates risk assessment
assumptions, limitations, and uncertainties; and synthesizes an overall conclusion
regarding the likelihood of adverse effects to the CRLF and/or their designated critical
habitat (i.e., "no effect," "likely to adversely affect," or "may affect, but not likely to
adversely affect").

As stated in Section 2.2, for the purpose of this assessment, the toxicity of the imazapyr
degradates are assumed to be equivalent to the parent, imazapyr. Therefore, the aquatic
EECs were calculated for total toxic residues.

5.1 Risk Estimation

5.1.1 Direct Effects

Direct effects to the CRLF associated with acute and chronic exposure to imazapyr are
based on the most sensitive toxicity data available for CRLF and/or other surrogate
amphibians, fish and birds.

5.1.1.1 Direct Acute Risks

Aquatic Phase

No acute toxicity data on aquatic phase amphibians are available, either submitted or in
the open literature (ECOTOX). Therefore, freshwater fish are used as a surrogate for the
aquatic phase CRLF. All of the acute LC50s for freshwater fish are greater than the
highest concentration tested in each study. Therefore, no acute risk quotients for fish are

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calculated. Direct acute risk to aquatic phase CRLF using the rainbow trout as a
surrogate freshwater fish is discussed further in the Risk Description.

Terrestrial Phase

No acute toxicity data on terrestrial phase amphibians are available, either submitted or in
the open literature. Therefore, birds are used as a surrogate for the terrestrial phase
CRLF. All of the acute LD/LC50s for birds are greater than the highest
dose/concentration tested in each study. Therefore, no acute risk quotients for birds are
calculated. Direct acute risk to terrestrial phase CRLF using the bobwhite quail as a
surrogate bird species is discussed further in the Risk Description.

5.1.1.2 Direct Chronic Risks

Aquatic Phase

No chronic toxicity data on aquatic phase amphibians are available, either submitted or in
the open literature. Therefore, freshwater fish are used as a surrogate for the aquatic
phase CRLF. The chronic toxicity study with rainbow trout, with a NOAEC of 43.1
mg/L (43100 ppb) is used as a surrogate study for the aquatic phase CRLF. The LOAEC
is 92.4 mg/L, based on a decrease in larval survival. For estimation of the chronic RQ,
the highest modeled aquatic EEC with a 2 meter depth standard pond scenario (60-day
for chronic exposure to fish) was selected as an upper bound estimate. This EEC was
estimated for the aquatic uses. The highest modeled EEC (60-day) is 79 ppb. The
chronic RQ is estimated to be 79 ppb (EEC) ^ 43100 ppb (NOAEC) = 1.8 x 10"3, which
is orders of magnitude less than the chronic LOC of 1 for fish.

Terrestrial Phase

No chronic toxicity data on terrestrial phase amphibians are available, either submitted or
in the open literature. Therefore, birds are used as a surrogate for the terrestrial phase
CRLF. The chronic toxicity study with bobwhite quail, with a NOAEC of 1,670 ppm is
used as a surrogate study for the terrestrial phase CRLF. There were neither reproductive
nor other toxicological effects in this study, up to and including the highest concentration
tested.

Table 5.1.1 presents the avian chronic RQs as a surrogate for the terrestrial phase CRLF.
There are no exceedances of the avian chronic LOC of 1 for birds consuming upper
bound or mean predicted residues on food items based on a NOAEC of 1670 ppm from
the bobwhite quail reproduction study and a maximum application rate of 1.5 lbs. ae/acre.

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Table 5.1.1 Summary of Direct Chronic UQs for (lie Terrestrial Phase CUM'' I sing Avian

Kndpoints as a Surrogate'1"

l-'ooil type

Application of

A\ inn C'li

predicted upper hound
residues

1.5 lbs sie/sicre
ronic RQ

predicted mc:in residues

short grass

0.22

0.08

tall grass

0.10

0.03

broadleaf forage, small insects

0.12

0.04

Fruits, pods, large insects

0.01

a Chronic toxicity NOAEC =1,670 mg ae/kg-bwt.

b RQs in this table were calculated for the maximum labeled application rate for non-crop use of 1.5 lbs ae/acre.
c Avian chronic LOC = 1

5.1.2 Indirect Effects

5.1.2.1 Evaluation of Potential Indirect Effects via Reduction in Food
Items (Freshwater Invertebrates and Fish for the Aquatic Phase; Terrestrial
Invertebrates and Mammals for the Terrestrial Phase)

Acute Risks, Aquatic Phase

Acute risks to the prey base for the aquatic phase CRLF are considered for freshwater
invertebrates and fish (note: submerged adult CRLFs are considered "aquatic" for the
purposes of this assessment). All of the acute LC50/EC50S for freshwater fish and
invertebrates are greater than the highest concentration tested in each study. Therefore,
no acute risk quotients for fish and aquatic invertebrates are calculated. Acute risk to the
prey items, freshwater fish and invertebrates is discussed further in the Risk Description.

Acute Risks, Terrestrial Phase

Acute risks to the prey base for the terrestrial phase CRLF are considered for terrestrial
invertebrates and mammals. The acute LC50 for mammals (rat) is greater than the highest
dose tested in the study. Therefore, no acute risk quotients for mammals are calculated.
The acute contact LD50 for imazapyr on honey bees is also greater than the highest dose
tested in the study. Acute risk to the prey items, mammals and terrestrial invertebrates is
discussed further in the Risk Description.

Chronic Risks, Aquatic Phase

Chronic risks to the prey base for the aquatic phase CRLF are considered for freshwater
invertebrates and fish. The rainbow trout and the water flea are used as surrogate prey
species. As stated in the direct effects section (Section 5.1.1), the highest RQ for

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freshwater fish from chronic exposure to imazapyr is less than the chronic LOC for fish.
For freshwater invertebrates, the chronic toxicity study with daphnia, with a 21-day
NOAEC of 97.1 mg/L (97100 ppb) is used as a surrogate study for freshwater
invertebrate prey species. There is no LOAEC because no effects were observed, up to
and including the highest concentration tested. For estimation of the chronic RQ, the
highest modeled aquatic EEC with a 2 meter depth standard pond scenario (21-day for
chronic exposure to aquatic invertebrates) was selected as an upper bound estimate. This
EEC was estimated for the the aquatic uses. The highest modeled EEC (21-day) is 82
ppb. The chronic RQ is estimated to be 82 ppb (EEC) ^ 97100 ppb (NOAEC) = 8.4 x 10"
4, which is orders of magnitude less than the chronic LOC of 1 for aquatic invertebrates.

Chronic Risks, Terrestrial Phase

Chronic risks to the prey base for the terrestrial phase CRLF are considered for terrestrial
invertebrates and mammals. No chronic toxicity data are available for terrestrial
invertebrates. The chronic toxicity study with the rat, with a NOAEL of 738 mg/kg
bw/day and a NOAEC of 10,000 ppm from the reproduction study is used as a surrogate
for mammalian prey species. There is no LOAEL/LOAEC because no effects were
observed, up to and including the highest concentration tested.

The highest estimated chronic dose- and dietary-based RQs for mammals are detailed in
Tables 5.1.2.1.a and 5.1.2.1.b, respectively.

Assuming upper bound and mean residue levels at the maximum single application rate
(1.5 lbs ae/acre), neither the dose-based risk quotients (Table 5.1.2.1.a) nor the dietary-
based risk quotients (Table 5.1.2.1 .b) exceed the chronic LOC for all weight classes (15
g, 35 g, and lOOOg) of mammals consuming short grass, tall grass, broadleaf forage/small
insects and seeds.

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Tsihle 5.1.2.1.si Suiiiinsiry of Indirect KITcd (Prey lisisc Msimmsils) Dose-linsctl Chronic KQs

lor the Terrestrial Plisisc ( KM ''

l"ood type

Weight clsiss (»)

KQs lor 1.5

Predicted upper hound
residues

lbs iie/:icre

Predicted menn
residues

0.21

0.07

short grass

0.18

0.06

1000

0.10

0.03

0.10

0.03

tall grass

0.08

0.03

1000

0.04

0.01

0.12

0.04

broadleaf forage, small insects

0.10

0.03

1000

0.05

0.02

0.01

fruit, large insects

0.01

1000

0.01

<0.01

seeds, pods

<0.01

1000

<0.01

a Chronic reproductive toxicity NOAEL = 738 mg ae/kg/day
b Mammalian chronic LOC = 1.

Tsihle 5.1.2.1 .h. Summary of Indirect K fleet (Prcv IJasc Main in si Is) Diclary-Kascri Chronic

KQs lor the Terrestrial Phase CRM-'

I'ood type

KQs lor 1.5

Predicted upper hound
residues

Ihs sie/sicre

Predicted niesin
residues

short grass

0.04

0.01

tall grass

0.02

0.01

broadleaf forage, small insects

0.02

0.01

fruit, large insects
seeds, pods

<0.01

a Chronic reproductive toxicity NOAEC = 10000 ppm.
b Mammalian chronic LOC = 1.

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5.1.2.2 Evaluation of Potential Indirect Effects via Reduction in Food
Items, Habitat and/or Primary Productivity (Freshwater Aquatic Plants)

Risks to aquatic plants, which would indicate indirect risks to the CRLF are estimated
using the most sensitive non-vascular and vascular plant endpoints. Since there are no
obligate relationships between the CRLF and any aquatic plant species, the most sensitive
14-day ECso's were considered for RQ calculations. The most sensitive vascular plant
EC50 is 18 ppb ae (duckweed) for the isopropylamine salt of imazapyr, with effects on
population growth and frond production. The most sensitive non-vascular aquatic plant
EC50 is 11500 ppb ae (green algae) for the isopropylamine salt of imazapyr with a slight
change in cell shape as the endpoint.

RQs were estimated using the modeled peak EECs for the various uses of imazapyr in
California and the most sensitive EC50's for vascular and non-vascular plants. None of
the RQs for non-vascular plants exceed the LOC of 1 for aquatic plants. The RQs for
aquatic vascular plants do not exceed the aquatic plant LOC at the maximum rates for
residential, turf or ground applications for forestry uses. The aquatic plant LOC is
exceeded for aquatic vascular plants with forestry (aerial), rangeland (aerial and ground)
and aquatic uses. For rights-of-way uses, the aquatic vascular plant RQs exceed the
aquatic plant LOC for both ground and aerial spray, assuming 50% impervious surface
coverage and 10% treatment of the watershed. For all other assumed percentages of
watershed treated, the aquatic vascular plant LOC is not exceeded (see Table 5.1.2.2).
Additional discussion on risks to aquatic plants is provided in the Risk Description in
Section 5.2.2.2.

In summary, the preliminary effects determination is "may effect", based on indirect
effects to habitat and/or primary productivity for the aquatic phase CRLF.

Tnhit* 5.1.2.2 Tier 2 I'esik KIX's 21111I RQs lor Aqiiiitic Ysisculsir iincl \<>n-\ ;iscul;ir I'hinls with l-'oivslrv,
Ritniiolitncl/I Isiv, l ui l'. Aqiiiilic. Rcsiclcnliitl ;mcl Ri»lils-ol'-\\ jiy I scs

Indirect I.ITccl (0
('UN-

I so

iViik r.r.((|)|)i>)

\ iiscuhir pliinl RQ
l'.( IN |)|)l) :io

Noii-\ iisculiir phi 111
UQ

1.( ,,,: 11500 ppb ;ie

Reduced Food Supply,
Habitat and/or Primary
Productivity via Direct
Toxicity to Aquatic
Plants

Forestry (aerial)

18.5

1.03

Forestry (ground)

14.1

0.78

Rangeland/Hay (aerial)

33.0

1.83

Rangeland/Hay (ground)

26.1

1.45

Turf (ground)

9.8

0.54

Direct Application to
Water (aerial and ground)

4.67

Residential Uses3

8.7

0.48

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Tnhit* 5.1.2.2 Tier 2 I'csik KIX's ;tiul RQs lor Aqiiiitic Ysisculsir iincl \<>n-\ sisculsir Nsinls with l-'oreslrv.

U;iii<>cIsiihI/I Isiy. l ui l', Aqusitic. kcsidcnlisil ;mcl Ri»hls-ol'-\\ siv I so

Indirect I.ITccl lo

I so

iViik i:i:( <|)|)i>>

\ sisculsir plsinl RQ

Noii-\ sisculsir phi ill

CUM-

l'.( IS |)|)l) SIC

111500 pph sic

Rights-of-Way4
Aerial

1% of watershed treated

2.3

0.13

5% of watershed treated

11.6

0.64

10% of watershed treated

23.2

1.29

Ground

1% of watershed treated

2.3

0.13

5% of watershed treated

11.6

0.64

10% of watershed treated

23.2

1.29

1 LOC for aquatic plants = 1

2 Bold = exceeds LOC for aquatic plant

3 Ground application with 12% impervious surface, 10% pervious surface and 50% of impervious surface
treated

4 Assumed 50% impervious surfaces

5.1.2.3 Evaluation of Potential Indirect Effects via Reduction in
Terrestrial Plant Community (Riparian Habitat)

5.1.2.3.1 Terrestrial Uses of Imazapyr

Potential indirect effects to the CRLF resulting from direct effects on riparian vegetation
were assessed using RQs from terrestrial plant seedling emergence and vegetative vigor
EC25 data as a screen. Risks are estimated using the most sensitive monocot and dicot
plant endpoints (the most sensitive seedling emergence endpoints for runoff and the most
sensitive endpoint from either seedling emergence or vegetative vigor studies for spray
drift). Since there are no obligate relationships between the CRLF and any terrestrial
plant species, the most sensitive EC25S were considered for RQ calculations. The most
sensitive toxicity thresholds were 0.0046 (monocot) and 0.0024 (dicot) lb ae/acre (effects
on weight) for the seedling emergence studies and 0.012 (monocot) and 0.0009 (dicot) lb
ae/acre (stunting, chlorosis and plant death) for the vegetative vigor studies with the
isopropylamine salt of imazapyr. RQs were estimated using the Terrplant (Version 1.2.2)
model for the various uses of imazapyr in California.

Table 5.1.2.3.a presents RQs for terrestrial plants for imazapyr uses with both ground and
aerial spray applications. The terrestrial plant LOC of 1 was exceeded for all non-listed
monocots and dicots located adjacent to treated areas, in semi-aquatic areas, and as a
result of runoff and/or spray drift for the maximum application rates of 0.9 and 1.5 lbs
ae/acre. RQs were higher for aerial applications when compared to ground applications.
This would be expected given the percentages of drift assumptions of 5% and 1% for
aerial and ground sprays, respectively. Risk estimates to terrestrial plants from the
capsule injection application were not conducted because exposure to adjacent plants is
expected to be very limited and non-quantifiable.

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If the CRLF habitat is inside the treated area and the terrestrial plants in the habitat are
treated, then it is assumed that the terrestrial plants are exposed directly to either 1.5 or
0.91 pounds per acre. Using the most sensitive toxicity thresholds of 0.0046 (monocot)
and 0.0009 lbs/A (dicot), the RQs would be estimated by directly dividing the application
rates by the toxicity thresholds. The estimated RQs for application directly on CRLF
habitat plants are 326/198 for monocots (1.5/0.91 lbs/A, respectively) and 1667/1011 for
dicots (1.5/0.91 lbs/A, respectively).

5.1.2.3.2 Aquatic Uses of Imazapyr

For aquatic use patterns (direct application to surface water), RQs were estimated from
treated water overflowing to flood a terrestrial site. The aquatic EECs for exposure to
riparian plants adjacent to or on the edges of the water body were modeled, assuming a
concentration (volume) of imazapyr in a 1 hectare pond with a water depth of 2 meters,
from which 6 inches of that water moves (overflows) entirely onto a hectare of dry land
and dries up on the ground with imazapyr residues. The inputs are based on an
application rate of 1.5 lb/A to a 1 hectare area with 6 inches (15.2 cm) of the water
moving onto land. Table 5.1.2.3.b presents the RQs for this scenario.

The terrestrial plant LOC is exceeded for aquatic uses for both monocots and dicots
(Table 5.1.2.3.b).

Currently, the Agency does not perform chronic risk assessments for terrestrial plants.
Bold values in the following tables are LOC exceedances.

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Tsiblc 5.l.2.3.si Non-1.isled Tcrrcslrisil Plsinl Risk Quotient Summitry lor Tcnvslrisd Sprsiv I ses

1.. i-

Application
T\pe/Siirro»;iU'
Species

Ad.jsicenl lo
1 resiled silos
(1:1 nilio)

Semi-sKpisilie siresis
(10:1 riiiio)

Drill

Terrestrial non-crop uses high application rate (1.5 lbs ae/acre)

Ground spray application

Monocot

166

Dicot

319

Aerial spray application

Monocot

179

Dicot

344

Terrestrial residential low application rate (0.91 lbs ae/acre)

Ground spray application

Monocot

101

Dicot

193

a RQs for ground and aerial spray applications in this table were calculated for the terrestrial non-crop low and high
application rates of 1.5 and 0.91 lbs ae/A, respectively.

b Non-endangered toxicity thresholds EC25S are 0.0046, 0.0024, 0.012, and 0.0009 lb ae/acre for seedling emergence
monocot, seedling emergence dicot, vegetative vigor monocot, and vegetative vigor dicot, respectively.
c Bold indicates an exceedance of the Acute Risk LOC for plants.

Tsiblc 5.l.2.3.h Tcrrcslrhil I'lsinl Risk Quotient Summitry lor Aqnsilic Sprsiv I ses *"

Scenario

\\silcr o\erllo«s lo Hood si lerreslrisil silo'1

Aquatic non-crop high application rate (1.5 lbs ae/acre)

Ground spray application

Monocot

Dicot

Aerial spray application

Monocot

Dicot

a RQs for ground and aerial spray applications in this table were calculated for the aquatic non-crop high application
rate of 1.5 lb ae/A.

b Non-endangered toxicity thresholds (EC25) were 0.0046 and 0.0024, lb ae/acre for seedling emergence monocot and

seedling emergence dicot, respectively.

cBold indicates an exceedance of the terrestrial plant LOC.

d 1.5 lb/A applied to 2 meter depth of water (1 hectare area), then 6 inches of water moves onto land

In summary, for both the terrestrial and aquatic uses of imazapyr, the preliminary effects
determination is "may effect" based on indirect effects via reduction of terrestrial

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vegetation (i.e., riparian habitat) required to maintain acceptable water quality and
aquatic and terrestrial habitat.

5.1.3 Adverse Modification to Designated Critical Habitat

Critical habitat was designated for the CRLF by the USFWS on April 13, 2006 (USFWS
2006; 71 FR 19244-19346). Designated critical habitat receives special protection under
Section 7 of the ESA by prohibiting against the destruction or adverse modification of
critical habitat with regard to Federal actions, such as use of pesticides registered under
FIFRA. Critical habitat designations identify, to the extent known using the best
scientific and commercial data available, habitat areas that provide essential life cycle
needs of the species (i.e., areas on which the PCEs are found, as defined in 50 CFR
414.12(b)). Activities that may destroy or adversely modify critical habitat are those that
alter the PCEs and jeopardize the continued existence of the species. Evaluation of
actions related to imazapyr use that may alter the PCEs of the CRLF's critical habitat
form the basis of the critical habitat impact analysis. As previously discussed in Section
2.8 of the problem formulation, PCEs that are identified as assessment endpoints are
limited to those that are of a biological nature and those PCEs for which imazapyr effects
data are available. For the purposes of this critical habitat impact analysis, PCEs selected
as assessment endpoints for the CRLF are grouped according to the measures of
ecological effect that are used to determine whether the assessment endpoint (i.e. PCE)
may be adversely modified. As such, groupings of PCEs and the measures of ecological
effect used in this critical habitat impact analysis are identified in Table 5.1.3,

Table 5.1.3 PCE Groupings for Critical 1

abitat Impact Analysis

PCE

Measure of Ecological Effect

- Characteristics necessary for normal behavior, growth, and
viability of all CRLF life stages related to:

(1) Aquatic habitat for shelter, foraging, predator avoidance and
aquatic dispersal for juvenile and adult CRLF's

(2) Water chemistry/quality including temperature, oxygen
content and turbidity for normal growth of both CRLF and their
prey

(3) Substrates with low amount of sedimentation necessary for
viability of CRLF

(4) Alteration in channel/pond morphology

- Acute vascular and non-vascular aquatic
plant data and/or

- Terrestrial plant seedling emergence and
vegetative vigor data

Reduction/modification of aquatic-based food sources for pre-
metamorphs

Acute vascular and non-vascular aquatic
plant data

Alteration in both terrestrial (dispersal and upland) and aquatic
habitat (riparian vegetation)

Terrestrial plant seedling emergence and
vegetative vigor data

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Table 5.1.3 PCE Groupings for Critical 1

abitat Impact Analysis

PCE

Measure of Ecological Effect

Alteration of other chemical characteristics necessary for normal
behavior, growth, and viability of aquatic CRLF's and their food
source (includes juveniles and submerged adult frogs)

Most sensitive acute and chronic data on
freshwater fish and/or invertebrates

(1) Alteration of chemical characteristics necessary for normal
behavior, growth, and viability of terrestrial CRLF's and their
food source

(2) Reduction and/or modification of food sources for terrestrial
phase juveniles and adults

Most sensitive

- Acute data on honey bees and/or

- Acute and chronic data on mammals

- Acute and chronic data on birds

Risk estimates of potential adverse modification to the PCEs identified in Table 5.1.3 are
provided in Sections 5.1.3.1 through 5.1.3.4.

5.1.3.1 Adverse Modification to Designated Critical Habitat via Direct
Effects to Aquatic Plants and/or Riparian Vegetation

Adverse modification of designated critical habitat via actions that may directly impact
aquatic and terrestrial plants are associated with those characteristics necessary for
normal behavior, growth, and viability of all CRLF life stages. These characteristics are
listed in Table 5.10. In some cases, direct effects on aquatic and terrestrial plants are
assessed together because they each affect many of the same aspects of the habitat.

Indirect effects to the CRLF resulting from direct effects on aquatic and terrestrial plants
were assessed in Sections 5.1.2.2 and 5.1.2.3. These evaluations are also applicable to
the critical habitat impact analysis because the same aquatic and terrestrial EECs and
aquatic and terrestrial plant toxicity study endpoints are used for both types of analyses
(see Tables 5.1.2.2.a through 5.1.2.3b). Both aquatic vascular and terrestrial plant RQs
are exceeded for many of the imazapyr uses in California and therefore, may adversely
modify the critical habitat.

5.1.3.1 Adverse Modification to Designated Critical Habitat via
Chemical Characteristics Necessary for Normal Behavior, Growth, and Viability of
All CRLF Life Stages

Chemical characteristics necessary for normal behavior, growth, and viability of all life
stages of the CRLF are assessed by utilizing existing RQs for direct and indirect effects.
If LOCs are exceeded for either direct and/or indirect effects, the chemical environment
is presumed to be such that normal behavior, growth, and viability of the CRLF's critical
habitat may be adversely modified. No LOCs were exceeded for either direct effects on
the CRLF or for any of the prey items for the CRLF (see Sections 5.1.1 and 5.1.2).

5.2 Risk Description

The risk description synthesizes an overall conclusion regarding the likelihood of adverse
impacts and/or modification leading to an effects determination (i.e., "no effect," "may

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affect, but not likely to adversely affect," or "likely to adversely affect") for the CRLF
and its designated critical habitat.

If the RQs presented in the Risk Estimation (Section 5.1) show no direct or indirect
effects for individual CRLFs, and no adverse modification to PCEs of the CRLFs
designated critical habitat (RQs < LOC), a "no effect" determination is made, based on
screening level modeled EECs of imazapyr's use within the action area. If, however,
direct or indirect effects to the individual CRLFs are anticipated and/or effects may
adversely modify the PCEs of the CRLF's designated critical habitat (RQs > LOC, the
Agency concludes a preliminary "may affect" determination for the FIFRA regulatory
action regarding imazapyr. A summary of the results of the risk estimation (i.e., "no
effect" or "may affect" finding) presented in Sections 5.1.1 through 5.1.3 is provided in
Table 5.2.1 for direct and indirect effects to the CRLF as well as adverse modification
to PCEs of the CRLF's designated critical habitat.

Table 5.2.1. Preliminary Effects Determination Summary for the CRLF and Critical Habitat

Impact Analysis Based on Risk Estimation

Direct and Indirect Effects to CRLF"

Assessment Endpoint

Preliminarv Effects Determination

Basis for Preliminarv Determination"

1. Survival, growth, and
reproduction of assessed
CRLF individuals via direct
effects

Acute direct effects: No effect for
either aquatic or terrestrial phase.

No effects in surrogate species at highest
concentrations/doses tested which are significantly
greater than the peak aquatic and terrestrial EECs
(Sections 5.1.1 and 5.2.1.1).

Chronic direct effects: No effect for
either aquatic or terrestrial phase.

Chronic aquatic/terrestrial animal LOCs are not
exceeded for any uses (Section 5.1.1, Table 5.1.1)

2. Indirect effects to
assessed CRLF individuals
via reduction in food items

Acute indirect effects: No effect for
freshwater invertebrates and fish
(aquatic phase); terrestrial
invertebrates and mammals
(terrestrial phase)

No effects in freshwater fish and invertebrates,
honey bees and mammals at highest
concentrations/doses tested which are significantly
greater than the peak aquatic and terrestrial EECs
(Sections 5.1.1, 5.1.2, 5.2.1.1 and 5.2.1.2).

Chronic indirect effects: No effect
for freshwater invertebrates and fish
(aquatic phase); mammals (terrestrial
phase)

Chronic aquatic/terrestrial animal LOCs are not
exceeded for any uses (Sections 5.1.1, 5.1.2, Tables
5.1.2.l.a and 5.1.2.l.b)

3. Indirect effects to
assessed CRLF individuals
via reduction of food
(aquatic plants), habitat
and/or primary productivity

Indirect effects: No effect for aquatic
plant food supply for aquatic phase
CRLF.

No effect for habitat and/or primary
productivity for forestry (ground),
residential or turf uses.

May affect habitat and/or primary
productivity for forestry (aerial),
rangeland/hay, aquatic and rights-of-
way uses.

Aquatic plant LOCs exceeded for vascular plants
for forestry (aerial), rangeland/hay, aquatic and
rights-of-way use scenarios (Table 5.1.2.2).

Aquatic plant LOCs not exceeded for vascular
plants for forestry (ground), residential or turf uses.
No LOCs are exceeded for non-vascular plants
(Table 5.1.2.2).

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Table 5.2.1. Preliminary Effects Determination Summary for the C.RLF and Critical Habitat

Impact Analysis Based on Risk Estimation

Direct and Indirect Effects to CRLF"

Assessment Endpoint

Preliminary Effects Determination

Basis for Preliminary Determination"

4. Indirect effects to
assessed CRLF individuals
via reduction of terrestrial
vegetation (i.e., riparian
habitat) required to maintain
acceptable water quality and
habitat

May affect

Terrestrial plant LOC exceeded for monocots and
dicots for all uses (Table 5.1.2.3, Section 5.1.2.3).

Adverse Modification to Designated Critical Habitat via PCE Analysis

5. Aquatic habitat for
shelter, foraging, predator
avoidance and aquatic
dispersal for juveniles and
adults.

No effect for habitat and/or primary
productivity for forestry (ground),
residential or turf uses.

May affect habitat and/or primary
productivity for forestry (aerial),
rangeland/hay, aquatic and rights-of-
way uses.

Aquatic plant LOCs exceeded for vascular plants
for forestry (aerial), rangeland/hay, aquatic and
rights-of-way use scenarios (Table 5.1.2.2).

Aquatic plant LOCs not exceeded for vascular
plants for forestry (ground), residential or turf uses.
No LOCs are exceeded for non-vascular plants
(Section 5.1.2.2).

6. Water chemistry/quality
including temperature,
oxygen content and
turbidity for normal growth
of both CRLF and their
prey.

May affect habitat and/or primary
productivity

Aquatic plant LOCs exceeded for vascular plants
for forestry (aerial), rangeland/hay, aquatic and
rights-of-way use scenarios (Table 5.1.2.2.).
Terrestrial plant LOC exceeded for monocots and
dicots for all uses (Tables 5.1.2.3.a and b).

No LOCs are exceeded for non-vascular plants
(Section 5.1.2.2).

7. Substrates with low
sedimentation

May affect

8. Reduction/modification
of aquatic-based food
sources for pre-metamorphs

No affect

9. Alteration in
channel/pond morphology

May affect

Terrestrial plant LOC exceeded for monocots and
dicots for all uses (Tables 5.1.2.3.a and b).

10. Alteration in both
terrestrial (dispersal and
upland) and aquatic habitat
(riparian vegetation)

May affect

Terrestrial plant LOC exceeded for monocots and
dicots for all uses (Tables 5.1.2.3.a and b)

11. Other chemical
characteristics necessary for
normal behavior, growth,
and viability of all life
stages of CRLF

Acute direct effects: No effect for
either aquatic or terrestrial phase

No effects in freshwater fish and invertebrates,
honey bees and mammals at highest
concentration/dose tested which are significantly
greater than the peak aquatic and terrestrial EECs
(Sections 5.1.1, 5.2.1.1 and 5.2.1.2).

Chronic direct effects: No effect for
either aquatic or terrestrial phase

Chronic aquatic/terrestrial animal LOCs are not
exceeded for any uses (Sections 5.1.1 and 5.1.2,
Table Table 5.1.1)

Indirect food source- No effect for
either aquatic or terrestrial phase

Indirect food source - No effect for
either aquatic or terrestrial phase

Chronic aquatic/terrestrial animal LOCs are not
exceeded for any uses (Section 5.1.1, Table 5.1.1)

aAll screening level EECs for the preliminary effects determination are based on modeled scenarios for surface water (Table 3.6) and
terrestrial plants (Table 3.16); toxicity values are based on the most sensitive endpoint summarized in Table 43.

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Following a "may affect" determination, additional information is considered to refine
the potential for exposure at the predicted levels based on the life history characteristics
(i.e., habitat range, feeding preferences, etc.) of the CRLF.

The criteria used to make determinations that the effects of an action are "not likely to
adversely affect" the CRLF and designated critical habitat for the CRLF include the
following:

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

¦ Harm includes significant habitat modification or degradation that
results in death or injury to listed species by significantly impairing
behavioral patterns such as breeding, feeding, or sheltering.

¦ Harass is defined as actions that create the likelihood of injury to
listed species to such an extent as to significantly disrupt normal
behavior patterns which include, but are not limited to, breeding,
feeding, or sheltering.

• Likelihood of the Effect Occurring: Discountable effects are those that are
extremely unlikely to occur. For example, use of dose-response
information to estimate the likelihood of effects can inform the evaluation
of some discountable effects.

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

A description of the risk and effects determination for the established direct and indirect
assessment endpoints for the CRLF is provided in Sections 5.2.1 and 5.2.2. A description
of the risk and effects determination for the critical habitat impact analysis is provided in
Section 5.2.3.

In the conceptual model, direct application, spray drift and surface runoff/leaching to
adjacent bodies of water were predicted as the most likely sources of exposure of
imazapyr and the isopropylamine salt of imazapyr to nontarget aquatic organisms. Risks
to aquatic organisms (i.e. fish, invertebrates, and plants) were assessed based on modeled
estimated environmental concentrations (EECs) and available toxicity data. Aquatic
EECs for the ecological exposure to imazapyr were estimated using PRZM/EXAMS
employing the standard field pond scenario.

The risk hypothesis states that the labeled uses of imazapyr have the potential to cause

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direct adverse effects to both terrestrial and aquatic phase CRLF, indirect adverse effects
to its food supply and habitat, and adverse modification to designated critical habitat.
The assessment does not support the hypothesis regarding direct adverse effects to
terrestrial and aquatic CRLFs and indirect adverse effects to its animal food supply. The
hypothesis is supported for direct adverse effects to both terrestrial (monocots and dicots)
and aquatic vascular plants, and thus, through indirect effects, adverse effects to the
aquatic phase CRLF food supply, the aquatic and terrestrial phase CRLF habitat, and
adverse modification to the critical habitat.

5.2.1 Direct Effects to the CRLF

Acute Risks, Aquatic Phase

As stated previously, freshwater fish are used as a surrogate for the aquatic phase CRLF.
All of the acute LC50S for freshwater fish are greater than 100 mg/L (100,000 ppb). The
highest peak aquatic EEC for imazapyr is 84 ppb for aquatic uses. This EEC was
estimated from the aquatic uses (direct application to water) following one application.
100,000 ppb is 1190 times higher than the aquatic EEC. Even when modeled with 1
annual application for 30 years, the EEC will not reach a level where the acute LOC for
fish will be exceeded (see Figure 3.2.2 for graphical representation of the aquatic EEC).

A supplemental study has been conducted on rainbow trout with a 22.6% acid equivalent
formulation of the imazapyr salt (MRID 00153778). In this study, it appears that this
formulation may be more toxic than the acid. Nevertheless, it is noted that the toxicity
endpoints are based on nominal concentrations; therefore, there are uncertainties in the
endpoint values. The 96-hour LC50 is 112 mg Arsenal/L (20.8 mg ae/L or 20800 ppb).
This value is 248 times higher than the aquatic EEC. Again, even with this more
conservative acute toxicity endpoint, the EEC will not reach a level where the acute LOC
for fish will be exceeded.

For freshwater fish (surrogate for the CRLF), the chance of an individual mortality is
estimated using the default slope of 4.5 with default lower and upper bounds of 2 and 9
and the acute aquatic endangered species LOC of 0.05. The estimated chance of
individual mortality of freshwater fish following imazapyr application is 1 in 4.18E+08.
Using the default upper and lower values for the default mean slope estimate (2 - 9), the
upper and lower estimates of the effects probability associated with the listed species
LOC of 0.05 are 1 in2.16E+02 and 1 in 1.75E+31, respectively.

Therefore, the effects determination is "no effect" following acute exposure to the aquatic
phase CRLF.

Acute Risks, Terrestrial Phase

Acute risk quotients were not estimated for birds, the surrogate for CRLF, because there
was neither mortality nor any other signs of toxicity in either the acute oral studies or the

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acute dietary studies. For terrestrial uses with spray applications of 1.5 lb ae/acre, the
highest dose-based EEC concentration for birds is 410 mg/kg bw for short grass
consumed by a 20 g bird. The adjusted LD50 for 20 g birds is > 1549 mg/kg bw. The 8-
day dietary LC50 for bobwhite quail is > 5000 ppm. The highest dietary-based EEC
concentration for birds is 360 ppm for short grass. The acute endangered LOC for birds
is 0.1. Therefore, the acute LD50 and LC50 would have to be greater than 10 times the
highest corresponding EEC to be protective of endangered species. The acute oral LD50
is more than 4 times the highest EEC on a dose basis and the acute LC50 more than 14
times the highest EEC on a dietary basis. Birds are currently used as surrogates for
reptiles and terrestrial-phase amphibians. However, reptiles and amphibians are
poikilotherms (body temperature varies with environmental temperature) while birds are
homeotherms (temperature is regulated, constant, and largely independent of
environmental temperatures). Therefore, reptiles and amphibians tend to have much
lower metabolic rates and lower caloric requirements than birds or mammals. As a
consequence, birds are likely to consume more food than amphibians or reptiles on a
daily dietary intake basis, assuming similar caloric content of the food items. This can be
seen when comparing the estimated caloric requirements for free living iguanid lizards to
passerines (song birds) (U.S. EPA, 1993):

iguanid FMR (kcal/day)= 0.0535 (bw g)0'7"

passerine FMR (kcal/day) = 2.123 (bw g)0'749

With relatively comparable slopes to the allometric functions, one can see that, given a
comparable body weight, the free living metabolic rate of birds can be 40 times higher
than reptiles, though the requirement differences narrow with high body weights.
Consequently, use of avian food intake allometric equation is likely to result in an over-
estimation of exposure and risk for reptiles and terrestrial-phase amphibians.

For terrestrial animals, the chance of an individual mortality is estimated using the default
slope of 4.5 with default lower and upper bounds of 2 and 9 and the endangered species
acute LOC of 0.1. The corresponding estimated chance of individual mortality of
terrestrial species following imazapyr application is 1 in 2.94E+05. Using the default
upper and lower values for the default mean slope estimate (2 - 9), the upper and lower
estimates of the effects probability associated with the listed species LOC of 0.1 are 1 in
4.40E+01 and 1 in 8.86E+18, respectively.

Because of the lack of any indications of toxicity in the available acute studies in birds
and/or any other terrestrial species at the highest doses/concentrations tested, the
differences between the EECs and the LD50/LC5o's were more than 4 to 14-fold, and
because use of avian food intake allometric equation is likely to result in an over-
estimation of exposure and risk for reptiles and terrestrial-phase amphibians, no direct
effect following acute exposure is expected for the terrestrial phase CRLF. Therefore,
the effects determination is "no effect" following acute exposure to the terrestrial phase

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CRLF.

Chronic Risks, Aquatic Phase

When freshwater fish are used as a surrogate for the aquatic phase CRLF, the chronic
RQ, using the highest modeled aquatic EEC is estimated to be 1.8 x 10"3. This EEC was
estimated from the aquatic uses (direct application to water) following one application.
This value is over 555 times less than the chronic LOC of 1 for fish. Even when modeled
with 1 annual application for 30 years, the EEC will not reach a level where the chronic
LOC for fish will be exceeded (see Figure 3.2.2 for graphical representation of the
aquatic EEC). Therefore, no direct effect following chronic exposure is expected for the
aquatic phase CRLF and the effects determination is "no effect" following chronic
exposure to the aquatic phase CRLF.

Chronic Risk, Terrestrial Phase

No reproductive or other toxicological effects in the chronic study were observed with
bobwhite quail, the surrogate for the terrestrial phase CRLF. Chronic RQs based on the
predicted residues on food at the maximum application rate of 1.5 lbs. ae/acre and the
toxicity endpoint from the avian reproduction study did not exceed the chronic LOC of 1
for birds. The highest RQ was 0.22 for short grass. Therefore, no direct effect following
chronic exposure is expected for the terrestrial phase CRLF and the effects determination
is "no effect" following chronic exposure to the terrestrial phase CRLF.

5.2.2 Indirect Effects to the CRLF

5.2.2.1 Indirect Effects via Reduction in Food Items (Freshwater
Invertebrates and Fish for the Aquatic Phase; Terrestrial Invertebrates and
Mammals for the Terrestrial Phase)

As stated in Section 2.5.3, it is assumed that the diet of the CRLF aquatic-phase larvae
(tadpoles) is similar to that of other frog species, consuming diatoms, algae, and detritus
(USFWS 2002). Juvenile and adult CRLFs may feed on aquatic and terrestrial
invertebrates, amphibians, fish and small mammals. The aquatic plant food items are
addressed in the next section (5.2.1.3).

Aquatic Invertebrates

For aquatic invertebrates, all of the acute LC50s from the submitted studies for freshwater
invertebrates are greater than 100 mg/L (100,000 ppb). As stated previously, the highest
peak aquatic EEC for imazapyr is 84 ppb. Again, this EEC was estimated from the
aquatic uses (direct application to water) following one application. 100,000 ppb is 1190
times higher than the aquatic EEC. As with fish, even when modeled with 1 annual
application for 30 years, the EEC will not reach a level where the acute LOC for aquatic
invertebrates will be exceeded (see Figure 3.2.2 for graphical representation of the

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aquatic EEC).

A supplemental study has been conducted on daphnia with a 22.6% acid equivalent
formulation of the imazapyr salt (MRID 00153779). In this study, it appears that this
formulation may be more toxic than the acid. Nevertheless, it is noted that the toxicity
endpoints are based on nominal concentrations; therefore, there are uncertainties in the
endpoint values. The 48-hour EC50 is 64.9 mg ae/L or 64900 ppb. This value is 773
times higher than the aquatic EEC. Again, even with this more conservative acute
toxicity endpoint, the EEC will not reach a level where the acute LOC for aquatic
invertebrates.

For freshwater invertebrates, the chance of an individual mortality is estimated using the
default slope of 4.5 with default lower and upper bounds of 2 and 9 and the acute aquatic
endangered species LOC of 0.05. The estimated chance of individual mortality of
freshwater invertebrates following imazapyr application is 1 in 4.18E+08. Using the
default upper and lower values for the default mean slope estimate (2 - 9), the upper and
lower estimates of the effects probability associated with the listed species LOC of 0.05
are 1 in 2.16E+02 and 1 in 1.75E+31, respectively.

There is an open literature study in which an in situ microcosm study found no effects
following a single application of imazapyr up to a concentration of 19.8 mg/L on the
macroinvertebrate community of a logged pond cypress dome. Comparing this NOAEC
(19800 ppb) with the peak EEC in surface water indicates a 236-fold difference.
Although the data from this study are limited because examinations were conducted at
the family/genus level and effects on individual species were not examined, it provides
further weight of evidence that direct acute risk to freshwater invertebrates, including
benthic organisms, is not expected. The highest chronic RQ for freshwater invertebrates
is estimated to be 8.4 x 10"4. This value is 1190 times less than the chronic LOC of 1 for
aquatic invertebrates. As before, even when modeled with 1 annual application for 30
years, the EEC will not reach a level where the chronic LOC for aquatic invertebrates
will be exceeded. Therefore, direct risk to freshwater invertebrates from chronic
exposure to imazapyr is not expected.

Mammals

For mammals, the acute LD50 for rats is >5000 mg ae/kg bw. For terrestrial uses with
spray applications of 1.5 lb ae/acre, the highest dose-based EEC concentration for
mammals is 343 mg/kg bw for short grass consumed by a 15 g mammal. The adjusted
LD50 for 15 g mammals is > 10989 mg/kg bw. This is more than 32 times the highest
estimated EEC, which would be protective of endangered species when using the acute
endangered species LOC of 0.1 for mammals as a point of reference. The chance of an
individual mortality is the same as that for birds: 1 in 2.94E+05 with upper and lower
estimates of 1 in 4.40E+01 and 1 in 8.86E+18.

No reproductive or other toxicological effects were observed in the chronic study with

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the rat. The predicted residues on food at the maximum application rate of 1.5 lbs.
ae/acre coupled with the toxicity endpoint from the rat reproduction study provided no
exceedances of the chronic LOC of 1 for mammals. The highest dose-based RQ was
0.21 for short grass and the highest dietary-based RQ was 0.04 for short grass (Tables
5.1.2.1 .a and b). Therefore, indirect risk to the terrestrial phase CRLF via direct acute
and chronic risk to mammals as dietary food items is not expected.

Terrestrial Invertebrates

Acute risk to terrestrial invertebrates may be estimated using the exposure value for
seeds, pods and insects from the T-REX model 1.3.1 for the maximum application rate of
imazapyr. The exposure value for large insects for the application rate of 1.5 lbs a.i./A is
22.5 ppm or 22.5 |ig a.i./g of insect and the exposure value for small insects is 202.5 ppm
or 202.5 |ig a.i./g. The residue for one bee may be estimated using the adult honey bee
weight of 0.128 g. 22.5 |ig ae/g bee x 0.128 g bee = 2.88 |ig a.i./bee. The acute contact
LD50 for imazapyr is > 100 |ig/bee, which is 34 times greater than the estimated exposure
per honey bee. As an upper bound estimate, the residue for one bee (small insects) may
be 202.5 |ig ae/g bee x 0.128 g bee = 25.9 |ig a.i./bee. The acute contact LD50 value of
100 |ig/bee is 4 times greater than the estimate exposure per honey bee. Therefore,
indirect risk to the CRLF via direct acute risk to terrestrial invertebrates as dietary food
items is not expected.

The acute and chronic risks to fish (aquatic amphibians) and birds (terrestrial amphibians)
were discussed in the direct effects section (5.2.1.1). No acute or chronic direct risks are
expected for either fish or bird.

Based on direct risk estimates for expected food items (except aquatic plants) for both the
aquatic and terrestrial phase CRLF, no indirect effects to the CRLF through reduction in
food supply are expected. Therefore, the effects determination for indirect effects via
reduction in food items (freshwater invertebrates and fish for the aquatic phase; terrestrial
invertebrates and mammals for the terrestrial phase CRLF) is "no effect".

5.2.2.2 Evaluation of Potential Indirect Effects via Reduction in Food
Items, Habitat and/or Primary Productivity (Freshwater Aquatic Plants)

Aquatic Non-vascular Plants

None of the RQs for non-vascular aquatic plants exceed the LOC of 1 for aquatic plants
for any of the uses of imazapyr in California, even when the aquatic application is
modeled with 1 annual application for 30 years. It is assumed that like other frog species,
the aquatic phase CRLF feed exclusively in water, consuming diatoms, algae, and
detritus (USFWS 2002). These are generally non-vascular plants. Because direct risk to
non-vascular plants from imazapyr uses is not expected, indirect risk to the aquatic phase
CRLF from reduction in food supply (aquatic non-vascular plants) is not expected.
Therefore, the effects determination for indirect effects via reduction in food items

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(aquatic non-vascular plants) for the aquatic phase CRLF is "no effect".

Aquatic Vascular Plants

For aquatic vascular plants, the RQs do not exceed the aquatic plant LOC with the turf
use, the forestry use with ground application and the residential use at the maximum
application rates. However, the aquatic vascular plant RQs exceed the aquatic plant LOC
for rangeland, rights-of-way, aquatic and forestry (aerial application) uses (see Table
5.1.2.2). As indicated in the previous sections, the aquatic uses were modeled using a
single application. Since the RQ for aquatic vascular plants exceeds the aquatic plant
LOC following a single application, it is expected to exceed following either multiple
applications or single applications repeated once each year over any number of years.

Both the residential and rights-of-way uses have a variety of uses and use sites with a
wide variety of impervious/pervious surface areas and areas that can be potentially
treated. Therefore, for further characterization, residential and rights-of-way aquatic
EECs were modeled for a matrix of % impervious surface and % impervious area treated
for residential uses and % impervious surfaces treated and % watershed treated for the
rights-of-way uses. Residential uses were modeled with an assumption of a 12%
impervious surface, a range of 0% to 10% pervious surface and a range of 1% to 50% of
the impervious area treated. Rights-of-way uses were modeled with a range of 1% to
50% impervious surfaces treated with 1 - 10% of the watershed treated.

As stated above, for residential uses, none of the aquatic vascular plant RQs exceeded the
aquatic plant LOC. For rights-of-way uses, the aquatic vascular plant RQs exceed the
aquatic plant LOC, for only the assumed 50% impervious surface and 10% of the
watershed treated. None of the other aquatic vascular plant RQs exceed the aquatic plant
LOC with any of the other impervious surface scenarios.

As described in the Problem Formulation section (Section 2.5.2), egg masses of the
CRLF are typically attached to emergent vegetation, such as bulrushes (Scirpus spp.) and
cattails (Typha spp.) or roots and twigs, and float on or near the surface of the water
(Hayes and Miyamoto 1984). They frequently breed in artificial impoundments such as
stock ponds (USFWS 2002). Adult CRLFs use dense, shrubby, or emergent vegetation
closely associated with deep-water pools bordered with cattails and dense stands of
overhanging vegetation

(http://www.fws.gov/endangered/features/rl frog/rlfrog.html#where).

The labels for aquatic uses state that imazapyr is not effective on totally submerged
plants. Imazapyr is effective when applied to the emerged foliage of aquatic plants. This
statement is supported by studies conducted on smooth cordgrass (Spartina alterniflora),
a vascular plant (ECOTOX reference # 76872). Imazapyr was effective in killing these
plants when they were on dry land but not effective when the plants were totally
submerged. The labels further state that, when imazapyr is applied to the emergent part
of the plant, it can then be "translocated throughout the plant, where it accumulates in

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rapidly-growing meristematic tissue... .[It] is translocated into and kills underground or
submerged storage organs to prevent regrowth." The labels also state that "injury or loss
of non-target plants may result if [imazapyr] is applied onto or near desirable plants, or to
areas where their roots extend, or in areas where treated soil may be washed or moved
into contact with their root zone."

The design of the aquatic plant toxicity studies received by the Agency for herbicide
registrations only considers direct application to the test water. The studies do not
examine potential effects from a direct spray application or spray drift onto emergent
aquatic vegetation. Based on the label information provided above, coupled with the
study on smooth cordgrass, it would be relevant to evaluate risk to non-target aquatic
emergent vegetation using both terrestrial plant exposure estimates and the standard
estimated aquatic EECs from PRZM-EXAMS. The emergent vegetation that the CRLF
may use for deposition of egg masses (bulrushes and cattails), although technically
classified as aquatic vegetation, can act more like terrestrial plants when growing in semi-
aquatic areas (http://www.explorebiodiversitv.com/problem plants/plants-bv-habitat.htm
and http://el.erdc.usace.army.mil/aqua/apis/plants/html/typha_sp.html). Therefore, when
assessing risk to emergent aquatic vegetation using terrestrial exposure estimations, a
better surrogate for the toxicological endpoints would be to use the most sensitive
terrestrial plant toxicity endpoint.

For emergent aquatic plants, this assessment will evaluates risk from direct spray
application to CRLF habitat within the treated area, spray drift from both aquatic and
terrestrial uses, and flooding from an aquatic application into semi-aquatic areas.

Risk to Emergent Aquatic Vegetation

Risk from Direct Application Within Habitat Area

When imazapyr is used to control undesirable emergent and floating aquatic vegetation
within the habitat area, the risk from direct spray onto non-target emergent plants would
be estimated in a similar fashion as for direct spray onto terrestrial plants. It is assumed
that the emergent aquatic plants are exposed directly to either 1.5 lbs/A or 0.91 lbs/A
(residential uses). Using the most sensitive toxicity thresholds from the vegetative vigor
studies (a seedling emergence endpoint would not apply to emergent aquatic vegetation
for spray drift): 0.012 (monocot) and 0.0009 lbs/A (dicot) for terrestrial plants, the RQs
would range from 125 for monocots to 1667 for dicots. For exposure to imazapyr in
contaminated soil during the dry times after application to a semi-aquatic habitat area, the
more sensitive seedling emergence endpoint for monocots (0.0046 lbs/A) would apply
and the RQ for monocots would be increased to 326/198 for application rates of 1.5/0.91
lbs/A, respectively.

Risk from Spray Drift Adjacent to Habitat Area
Section 5.2.2.3 describes the risk to the terrestrial plant community. Risks to emergent

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plants following spray drift may be assessed using the same parameters (see Section
5.2.2.3.1). Using the most sensitive EC25 values for both dicots and monocots, the RQs
range from 2-83 with the application rates of 1.5 lbs ae/A and 0.91 lbs ae/A. Using
some of the less sensitive EC25 values, some monocots exposed via spray drift alone
following either ground or aerial spray at 1.5 lbs ae/A and some of both monocots and
dicots exposed via spray drift alone following ground spray at 0.91 lbs ae/A (residential
uses) will not exceed the LOC for terrestrial plants. Therefore, it is possible that not all
emergent aquatic plants will be affected following spray drift alone. Spray drift buffers
are estimated in Section 5.2.2.4.

For each of the imazapyr uses, buffers based on expected spray drift may be added from
the site of potential imazapyr application to the point where the LOC would no longer be
exceeded for either listed plants (for defining the action area) or non-listed plants (for
distinguishing between LAA and NLAA determinations). For listed plants, the buffers
range from 7120 (forestry uses, ground application) to 26460 feet (forestery uses, aerial
application). For non-listed plants, the buffers range from 2530 (forestry uses, ground
application) to 5940 feet (forestry uses, aerial application). Buffers for the other
imazapyr uses are in between the two forestry use buffers.

Risk from Flooding of a Treated Aquatic Area

Risks to emergent aquatic vegetation in semi-aquatic areas following flooding of an
aquatic treated area is estimated using the same calculations as were used in the risk
estimation section for terrestrial plants following flooding of an aquatic treated area to a
semi-aquatic site (Table 5.1.2.3.b). The RQs will range from 28 - 79 for ground and
aerial applications.

In summary, based on exceedance of the aquatic and terrestrial (for emergent aquatic
plants) plant LOCs, the following general conclusions can be made with respect to
potential harm to aquatic habitat:

• Imazapyr may enter aquatic areas via direct application, runoff, flooding
and/or spray drift where it may be taken up by the plant and translocated to
the root system of sensitive plants.

• Comparison of aquatic plant ECso's to estimated aquatic EECs suggests that
aquatic non-vascular plants are not affected by imazapyr applications;
therefore, reduction in aquatic plant food supply for CRLF tadpoles is not
expected to be affected.

• Comparison of aquatic plant ECso's to estimated aquatic EECs suggests that
aquatic vascular plants will not be affected by the turf uses, forestry (ground
application) and residential uses but may be affected by forestry (aerial
application), rangeland, aquatic and rights-of-way uses (where the area
contains 50% impervious surfaces), resulting in degradation of the existing

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aquatic habitat, particularly for emergent aquatic plants.

• Comparison of seedling emergence and vegetative vigor EC25 values to

estimated EECs from exposure through imazapyr treated water overflowing to
flood a terrestrial site and from spray drift estimations from Terrplant suggests
that existing aquatic emergent vegetation typically used by the CRLF for
reproduction may be affected. Since the aquatic uses of imazapyr are
formulated to affect emergent aquatic plants, it is anticipated that the emergent
vegetation upon which the CRLF attaches its egg masses may be affected by
imazapyr uses. It is noted here that the Recovery Plan (USFWS 2002) states
that CRLFs breed from November through late April. The CDPR PUR
database reports imazapyr usage in forestry, rights-of-way, some landscape
maintenance and a few pest control applications

(www.cdpr.ca.gov/docs/pur/purmain.htm). The reported application times for
these uses vary. Based on the available limited data, it appears that there is
some direct overlap with the breeding season with rights-of-way applications
and some landscape maintenance, both of which may be used all year around.
The forestry uses and pest control applications tend to be applied at opposite
times from the breeding season; however, the incidence data has shown
damage to crops from carryover of an application the previous spring. In
addition, imazapyr has been shown to be stable in aquatic environments and it
can still kill plants when present in the soil. Therefore, it is expected that
emergent vegetation may still be affected by imazapyr, even it it was applied
in the previous season.

5.2.2.3 Indirect Effects via Alteration in Terrestrial Plant Community
(Riparian Habitat)

5.2.2.3.1 Terrestrial Uses of Imazapyr

The estimated risks to terrestrial plants indicate that for all labeled non-crop terrestrial
uses in California, the terrestrial plant LOC of 1 was exceeded for all monocots and
dicots at all application rates by ground and aerial spray.

In Terrplant vl.2.2, the terrestrial plant RQs for monocots and dicots inhabiting dry and
semi-aquatic areas are derived by dividing the total EEC by the most sensitive seedling
emergence value. The EEC values from Terrplant are in Table 3.4. The seedling
emergence EC25 values for dicots range from 0.0024 - 0.008 lbs ae/A, and for monocots
range from 0.0046 - 0.0054 lbs ae/A. The RQs with the terrestrial uses of imazapyr for
monocots and dicots inhabiting dry and semi-aquatic areas (runoff and spray drift),
utilizing the most sensitive seedling emergence EC25 values range from 12 to 344. Even
with the least sensitive EC25 (0.008), the LOC for terrestrial plants would still be
exceeded with any of the crops tested. These risk estimates are based on terrestrial plant
toxicity data for a limited set of agricultural plants. Therefore, there are uncertainties
associated with potential toxicity to the wide variety of non-agricultural plants

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inhabitating the CRLF habitat. Even if imazapyr only kills the most sensitive terrestrial
plants, the habitat may still be sufficiently modified to the point such that it is no longer
viable CRLF habitat.

In addition to affecting seedling emergence, because imazapyr is toxic to plants when it is
taken up by the roots, runoff is also expected to affect emerged plants. The RQ values
for plants exposed to runoff are estimated from the seedling emergence studies because
of the limitations of the vegetative vigor studies. These studies do not measure effects to
emerged plants following a runoff event. Therefore, there is an uncertainty with regard to
the effect of runoff to emerged plants.

For RQs derived for spray drift only, TerrPlant compares estimated spray drift deposition,
without a runoff exposure component, to the more sensitive measure of effect, either
seedling emergence or vegetative vigor from both the monocot and dicot values. For
spray drift only, the RQs range from 2-83 with the application rates of 1.5 lbs ae/A and
0.91 lbs ae/A. These values were derived from the most sensitive EC25 value of 0.0009
lb ae/A (dicots). The EC25 values range from 0.0009 to >0.0156 lbs ae/A (>17.3 X
0.0009) for dicots and from 0.0046 - > 0.0156 lbs ae/A (> 3.4 X 0.0046) for monocots for
both the vegetative vigor and seedling emergence studies. Based on these ranges, some
monocots exposed via spray drift alone following either ground or aerial application at
1.5 lbs ae/A and some of both monocots and dicots exposed via spray drift alone
following ground spray at 0.91 lbs ae/A (residential uses) will not exceed the LOC for
terrestrial plants. However, for the terrestrial applications, comparison of the RQs
indicates that runoff, and not spray drift, is a larger contributor to potential risk for
riparian vegetation.

5.2.2.3.2 Aquatic Uses of Imazapyr

The risk from spray drift and flooding of terrestrial plants inhabiting semi-aquatic areas
was estimated in the risk estimation section. With the most sensitive seedling emergence
toxicity thresholds of 0.0046 (monocot) and 0.0024 lbs/A (dicot) for terrestrial plants, the
RQs range from 28-41 for monocots and 54 - 79 for dicots. Comparing the least
sensitive seedling emergence EC25 values to the estimated EECs, all of the monocots and
dicots exposed via spray drift alone following either ground or aerial spray at 1.5 lbs ae/A
(aquatic uses) will still exceed the LOC for terrestrial plants. The risk estimates for
imazapyr-treated water flooding onto terrestrial sites are conservative because they do not
address the uncertainty of dilution from rain water or water from other sources that
originally precipitated the overflow.

Summary for Terrestrial and Aquatic Uses of Imazapyr

In summary, based on exceedance of the terrestrial plant LOCs for all terrestrial plant
species following runoff, flooding and spray drift for both terrestrial and aquatic uses, the
following general conclusions can be made with respect to potential harm to riparian
habitat:

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• Imazapyr may enter riparian areas via runoff, flooding of treated aquatic areas
and/or spray drift where it may be taken up by the plant and translocated to
the root system of sensitive plants.

• Comparison of seedling emergence EC25 values to EECs estimated using
Terrplant suggests that existing vegetation may be affected or inhibition of
new growth may occur. Inhibition of new growth could result in degradation
of high quality riparian habitat over time because as older growth dies from
natural or anthropogenic causes, plant biomass may be prevented from being
replenished in the riparian area. Inhibition of new growth may also slow the
recovery of degraded riparian areas that function poorly due to sparse
vegetation because imazapyr deposition onto bare soil would be expected to
inhibit the growth of new vegetation. As stated previously, imazapyr is
persistent. The incidence reports support the fact that its presence in soil can
affect emergence of plants later in the year. The reports also support
terrestrial plants being affected by root uptake from an aquatic application
(see paragraph below).

• Because LOCs were exceeded for all species tested in the seedling emergence
and vegetative vigor studies, it is likely that many species of herbaceous
plants may be potentially affected by exposure to imazapyr via runoff and
spraydrift.

• Some monocots exposed to the maximum non-residential application rate and
some of both monocots and dicots exposed to the maximum residential
application rate may not be affected by exposure to imazapyr via spray drift
alone; however, runoff appears to be the larger contributor to potential risk for
riparian vegetation.

The incidence data supports the risk conclusions for terrestrial plants for the imazapyr
labeled uses. Damaged or dying trees (oak, cherry, pear, loblolly pine seedlings, willow
and spruce) were reported, most of which were rated as probably related to exposure to
imazapyr (a couple incidences were rated as possibly related to exposure to imazapyr).
Damage to crops (beans, corn, wheat, grape vines) was also reported. These effects were
observed following a variety of use applications, all of which are possible for imazapyr
according to its registered uses and all of which are addressed in this risk assessment: a
nearby spray application, root uptake of residual imazapyr from the soil following an
aquatic application, damage to a crop from carryover of an application the previous
spring, runoff event from a treated adjacent site and a nearby application to a driveway
surface.

5.2.2.4 Spray Drift Buffers for Non-Target Plants

The AgDrift model was used to calculate spray drift buffers that would be needed to

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avoid adverse effects to non-target terrestrial and aquatic vascular emergent plant species.
For the action area, the NOAEC of 0.000064 lb/acre (vegetative vigor study with
imazapyr acid on cucumber) was used as a reference toxicity endpoint (terrestrial plant
value used for endangered species) for estimation of the spray drift buffer distances.
Because the CRLF does not have an obligate relationship with any particular plant
species, the cucumber EC25 of 0.0009 lb/acre was used as a toxicity endpoint (terrestrial
plant value used for non-listed species) for estimation of the spray drift buffer distances
that will be used to discriminate between the LAA and the NLAA determination. All of
the buffer values for all use rates were beyond the range of the model. Therefore,
AGDISP (v. 8.15) was used to estimate spray drift buffers. Again, the buffer values were
out of range for the AGDISP model. Therefore, the Gaussian Far-Field Extension was
utilized to get an estimate of the size of the buffer needed for the effects on terrestrial
plants to be below the Level of Concern for plants. The following tables provide the
estimated buffers for the uses with the highest potential exposures for plants. For the
action area, the buffer distances required to dissipate spray drift to levels that are
protective of listed plants range from 7120 (forestry, ground application) to 26460 feet
(forestry, aerial application). These buffers are based on the listed species terrestrial
plant toxicity endpoint. For discrimination between the LAA and NLAA determinations,
the buffer distances range from 2530 to 5940 feet. Table 5.2.2.4.a provides the buffer
distances for the various uses of imazapyr and Table 5.2.2.4.b shows the differences in
buffer distances for forestry uses with varying droplet sizes.

Tsihlc 5.2.2.4.;i 1 in;i/:ip> r A(>I)ISP liulTcrs lor Listed nntl Non-Listed '

I'eiTeslrisil

Plsinl Species

I se Sile and "A, Acid

Applicalion

Release

Volume

Buffer Distance

l-'.(|iii\iilouls

lleiuhl

Product

(feel)

Applied

For LAA

I'd i- Action

((>al/lb/A)

Dclcrminalion

Area

Non-Lisled

Listed

Planls (ID

AqualK- ::.o"u

Ground

<> " 1 *

jxjj-u

9800

Aquatic 22.6%

Aerial Helicopter

0.75/1.5

3470

15110

Aquatic 23.4%

Ground

0.75/1.5

2940

9960

Aquatic 23.4%

Helicopter

0.75/1.5

3540

15420

Forestry 43.3%

Ground

0.375/1.5

2530

7120

Forestry 43.3%

Aerial Fixed
Wing

0.375/1.5

5940

26460

Forestry 43.3%

Aerial Helicopter

0.375/1.5

4660

21160

Other Terrestrial

Ground

0.75/1.5

2920

9800

22.6%

Other Terrestrial

Aerial Fixed

0.75/1.5

4640

19420

22.6%

Wing

[Bold] buffer distance used for Action Area.

Wind speed = 10 mph

Spray volume rate (volume of finished spray applied) = 5 gallons water/A
Specific gravity = 1.06

Initial average deposition (EC2s/application rate or NOAEC/application rate for Action Area: 0.0006
lb/A for non-listed plants and 0.0000426 lb/A for listed plants)

Droplet size very fine to fine

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Table 5.2.2.4b

Imazapvr A(>I)ISP liulTers lor Koreslrv I ses with Listed and

Non-Listed Terrestrial Phi ill Species I sing Various Droplet Si/es

Droplet Si/o

Application

Release

Volume

Buffer Distance

Height

Product

(I'eel)

Applied
((>al/lb/A)

For LA A
Determination

For Action
Area

Non-I.isled

Listed

Plants (ID

Very fine to fine

Ground

0.375/1.5

2530

7120

Medium

Ground

0.375/1.5

1750

2590

Medium to Coarse

Ground

0.375/1.5

1680

2200

Coarse

Ground

0.375/1.5

1670

2130

Very fine to fine

Aerial Helicopter

0.375/1.5

4660

21160

Medium

Aerial Helicopter

0.375/1.5

2210

8400

Medium to Coarse

Aerial Helicopter

0.375/1.5

2440

6870

Coarse

Aerial Helicopter

0.375/1.5

1690

5970

Very fine to fine

Aerial Fixed Wing

0.375/1.5

5940

26460

Medium

Aerial Fixed Wing

0.375/1.5

2770

10170

Medium to Coarse

Aerial Fixed Wing

0.375/1.5

2240

7590

Coarse

Aerial Fixed Wing

0.375/1.5

2050

6650

[Bold] buffer distance used for Action Area
Wind speed = 10 mph

Spray volume rate (volume of finished spray applied) = 5 gallons water/A
Specific gravity = 1.06

Initial average deposition (EC2s/application rate for Action Area: 0.0006 lb/A for non-listed plants

and 0.0000426 lb/A for listed plants)

Forestry uses: 43.3% acid equivalent formulation

The current label use information memorandum (Kinard and Tompkins 05/07/07)
provides mitigation measures to reduce environmental exposure of imazapyr. It is not
known when these measures will be implemented because the reregi strati on process will
not be completed for 2 years and the registrants will be allowed to distribute products
with old labels for up to 18 months after the new labels are approved. In addition,
existing stocks can be used until they are exhausted. It is assumed that most users will
use their existing stocks within 2 years of purchase. The mitigation measures identified
in the June 12, 2006 RED are as follows:

¦ For aerial applications, applicators are required to use a Coarse or coarser droplet
size (ASABE S572) or, if specifically using a spinning atomizer nozzle,
applicators are required to use a volume mean diameter (VMD) of 385 microns or
greater for release heights below 10 feet; Applicators are required to use a Very
Coarse or coarser droplet size or, if specifically using a spinning atomizer nozzle,
applicators are required to use a VMD of 475 microns or greater for release
heights above 10 feet; applicators must consider the effects of nozzle orientation
and flight speed when determining droplet size;

¦ For aerial applications, applicators are required to use upwind swath
displacement;

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¦ For aerial applications, the boom length must not exceed 60% of the wingspan or
90% of the rotor blade diameter, to reduce spray drift;

¦ For aerial applications, applications with wind speeds less than 3 mph and with
wind speeds greater than 10 mph are prohibited;

¦ For groundboom applications, applicators are required to use a nozzle height
below 4 feet above the ground or plant canopy and coarse or coarser droplet size
(ASABE S572) or, if specifically using a spinning atomizer nozzle, applicators
are required to use a VMD of 385 microns or greater;

¦ For groundboom applications, applications with wind speeds greater than 10 mph
are prohibited;

¦ Applications into temperature inversions are prohibited.

Based on the estimations in Table 5.2.2.4b, utilization of a coarse droplet size could
potentially reduce the buffer distance 1.5 to 4-fold. Other mitigation measures would
also be expected to reduce environmental exposure.

Because RQs for terrestrial plants are above the Agency's LOCs, imazapyr use is
considered to have the potential to directly impact plants in riparian areas, potentially
resulting in degradation of stream water quality and alteration of the CRLF's habitat.
Therefore, an analysis of the potential for habitat degradation to affect the CRLF is
necessary.

Riparian plants beneficially affect water and stream quality in a number of ways
(discussed below) in both adjacent river reaches and areas downstream of the riparian
zone. Imazapyr use in the action area, which is inclusive of the CRLF range, may
potentially affect these species by impacting riparian vegetation and subsequently causing
a degradation in water quality and alteration of available habitat. In order to characterize
the potential indirect effects caused by imazapyr-related impacts to riparian vegetation, a
general discussion of riparian habitat and its relevance to the CRLF and a description of
the types of riparian zones that may be potentially impacted by imazapyr use in the
action area for the CRLF are discussed below.

5.2.2.5 Importance of Riparian Habitat to the CRLF

Riparian vegetation provides a number of important functions in the stream/river
ecosystem for the CRLF, including the following:

• serves as an energy source;

• provides organic matter to the watershed;

• provides shading, which ensures thermal stability of the stream

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• serves as a buffer, filtering out sediment, nutrients, and contaminants before
they reach the stream; acts as a stabilizing factor for water chemistry/quality.

• provides shelter, foraging, predator avoidance, aestivating habitat and
terrestrial dispersal habitat for juveniles and adults

• provides habitat support for food source of CRLFs

• stabilizes the channel/pond morphology or geometry

The specific optimal characteristics of a riparian zone for the CRLF are expected to vary
with developmental stage, the use of the reach adjacent to the riparian zone, and the
hydrology of the watershed. Criteria developed by Fleming et al. (2001) have been used
to assess the health of riparian zones and their ability to support habitat for aquatic
communities. These criteria, which include the width of vegetated area (i.e. distance
from cropped area to water), structural diversity of vegetation, and canopy shading, are
summarized in Table 5.2.2.5.

Table 5.2.2.5. Criteria lor Assessing (lie Health of Riparian Areas lo Support Aquatic
Habitats (niliipled from Hulling el nl 2""l)

( riloriii

(„)u;ilil>

Ixcolk'iK

(ioori

l-iiir

Poor

Buffer width

>18m

12 - 18m

6- 12m

<6m

Vegetation diversity

>20 species

15-20 species

5-14 species

<5 species

Structural diversity

3 height classes
grass/shrub/tree

2 height classes

1 height class

sparse vegetation

Canopy shading

mixed sun/shade

sparse shade

90% sun

no shade

To maintain at least "good" water quality for aquatic habitats in general, riparian areas
should contain at least a 12 m (-40 feet) wide vegetated area, 15 plant species, vegetation
of at least two height classes, and provide at least sparse shade (>10% shade). In general,
higher quality riparian zones (wider vegetated areas with greater plant diversity) are
expected to have a lower probability of being significantly affected by imazapyr than
poor quality riparian areas (narrower areas with less vegetation and little diversity).
The following attributes of riparian vegetation habitat quality were evaluated for this
assessment: sedimentation; thermal stability; stabilization of channel/pond morphology;
water chemistry/quality; habitat for shelter, foraging, predator avoidance, aestivation, and
dispersal and support for food source of CRLFs. Each of these attributes and their
relative importance with respect to the CRLF is discussed briefly below.

Stabilization of channel/pond morphology

Riparian vegetation typically consists of three distinct types of plants, including a

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groundcover of grasses and forbs, an understory of shrubs and young trees, and an
overstory of mature trees. These plants serve as structural components for streams, with
the root systems helping to maintain stream stability, and the large woody debris from the
mature trees providing instream cover. Riparian vegetation has been shown to be
essential to maintenance of a stable stream (Rosgen, 1996). Destabilization of the stream
can have a severe impact on aquatic habitat quality. In fact, geomorphically stable stream
and river channels and banks are identified as PCEs for designated critical habitat of the
CRLF. Any action that would significantly alter channel morphology or geometry to a
degree that would appreciably reduce the value of the critical habitat for both the long-
term survival and recovery of the species is considered as part of the critical habitat
impact analysis. Channelization of creeks reduces or eliminates breeding sites and
increases suitability for predators such as non-native fish, bullfrogs, and raccoons, all of
that thrive in disturbed conditions.

Following a disturbance in the watershed bank, the stream may widen, releasing sediment
from the stream banks and scouring the stream bed. Changes in depth and or the
width/depth ratio via physical modification to the stability of stream and river banks may
also affect light penetration and the flow regime of the CRLF's habitat. Destabilization
of the stream can have severe effects on aquatic habitat quality by increasing
sedimentation within the watershed. The effects of sedimentation are summarized below.

Sedimentation

Sedimentation refers to the deposition of particles of inorganic and organic matter from
the water column. Increased sedimentation is caused primarily by disturbances to river
bottoms and streambeds and by soil erosion. Riparian vegetation is important in
moderating the amount of sediment loading from upland sources. The roots and stems of
riparian vegetation can intercept eroding upland soil (USDA NRCS, 2000), and riparian
plant foliage can reduce erosion from within the riparian zone by covering the soil and
reducing the impact energy of raindrops onto soil (Bennett, 1939). The CRLF recovery
plan states that high levels of sediment introduced into streams can alter primary
productivity and fill interstitial spaces in streambed materials with fine particulates,
which impede water flow, reduce dissolved oxygen levels, and restrict waste removal.

Water chemistry/quality and thermal stability

Water quality parameters, including temperature may be impacted by direct effects to
forested riparian areas. Riparian habitat includes mature woody trees which provide
stream shading, thus stabilizing the thermal environment within the stream. The CRLF
recovery plan states that early embryos of northern red-legged frogs are tolerant of
temperatures only between 9 and 21 degrees Celsius. Observations in the field indicate
that the areas with the greatest number of CRLF tadpoles had mean water temperatures
between 15.0 and 24.9 degrees Celsius and that no CRLF's were present when
temperatures exceed 22 degrees Celsius, particularly when there are no cooler sections in
the pool. In addition, increased temperatures encourages reproduction of

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bullfrog and nonnative warm water fishes.

Habitat for shelter, foraging, predator avoidance, aestivation, and dispersal

The CRLF recovery plan states that during periods of wet weather, some individuals may
make overland excursions through upland habitats. Evidence indicates that CRLF
movements, via upland habitats, of about 1.6-3 kilometers, are possible over the course
of a wet season without apparent regard to topography, vegetation type, or riparian
corridors. The manner in which CRLFs use upland habitats is not well understood.
CRLFs spend considerable time resting and feeding in riparian vegetation when it is
present. It is believed that the moisture and cover of the riparian plant community provide
good foraging habitat and may facilitate dispersal in addition to providing pools and
backwater aquatic areas for breeding. CRLFs can be encountered living within streams at
distances exceeding 3 kilometers from the breeding site, and have been found up to 30
meters from water in adjacent dense riparian vegetation, for up to 77 days (USFWS
2002).

Habitat support for food source of CRLFs

The CRLF recovery plan states that loss of streamside vegetation reduces habitat for
insects and small mammals, which are important dietary components for aquatic and
riparian associated species, including the CRLF. If the habitat changes, non-native
animals may increase, which may in turn, prey on the CRLF. In addition to non-native
animals, if the native riparian species are altered, non-native plants may invade and
threaten the integrity of aquatic systems by out-competing and replacing native plants and
thus decreasing plant diversity. These species not only change the structure and function
of a riparian corridor, but also can result in losses of surface water due to their increased
transpiration rates. Some non-native plant species may secrete toxic chemicals into the
water, which may decrease the suitability of the area for the CRLFs. The relationship
between the presence of non-native plants and habitat suitability for CRLF, however, is
currently unknown (USFWS. 2002).

5.2.2.6 Effect of Imazapyr on Health and Function of Riparian Areas

As previously summarized in Table 5.2.2.5, the parameters used to assess riparian quality
include buffer width, vegetation diversity, vegetation cover, structural diversity, and
canopy shading. Buffer width, vegetation cover, and/or canopy shading may be reduced
if imazapyr exposure impacts plants in the riparian zone or prevents new growth from
emerging. Plant species diversity and structural diversity may also be affected if only
sensitive plants are impacted (Jobin et al., 1997; Kleijn and Snoeijing, 1997), leaving
non-sensitive plants in place. Imazapyr may also affect the long term health of high
quality riparian habitats by affecting plant communities. Thus, if imazapyr exposure
impacted these riparian parameters, water quality within the action area for the CRLF
could be affected.

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According to the labels and weed control handbooks (example:
http://tncweeds.ucdavis.edu/products/handbook/17.Imazapyr.pdf), all plants, including
woody plants are expected to be affected by imazapyr applications. Effects on shading,
streambank stabilization, and structural diversity (height classes) of woody forested
vegetation are expected. The riparian health criteria described in Fleming et al. (2001;
Table 5.16) and the characteristics associated with effective vegetative buffer strips
suggest that healthy riparian zones would be less sensitive to the impacts of imazapyr
runoff than poor riparian zones. Wider buffers have more potential to reduce imazapyr
residues over a larger area, resulting in lower loading levels. According to Fleming et al.
(2001), buffer distances of >18 m (approximately 60 feet) are characterized as
"excellent" in supporting aquatic habitats. In addition, trees and woody plants in a
healthy riparian area may act to filter spray drift (Koch et al., 2003) and push spray drift
plumes over the riparian zone (Davis et al., 1994), thus reducing exposure to herbaceous
plants. Therefore, high quality riparian zones are expected to be less sensitive to
imazapyr than riparian zones that are narrow, low in species diversity, and comprised of
young herbaceous plants or unvegetated areas. Bare ground riparian areas could also be
adversely affected by prevention of new growth of grass, which can be an important
component of riparian vegetation for maintaining water quality. Since all types of
vegetation, including woody plants are expected to be sensitive to imazapyr, it is likely
that imazapyr will affect both forested and grassy riparian vegetation adjacent to use
sites.

As a note, one uncertainty associated with overstory vegetation and protection from
pesticide deposition on the ground relates to the spray-drift filtering effect of tree
canopies. These may only be temporary. Chemicals that are intercepted by tree canopies
and other overstory vegetation can be re-delivered to the surface during the first rainfall
following pesticide application (Carlisle et al., 1967). This is especially true for
chemicals that are persistent and soluble. Rainfall that contacts leaves and upper
branches that have intercepted and collected spray drift is delivered to the surface via
throughfall (rain hitting the tree canopy before reaching the ground) and stemflow (rain
flowing along the branches, stems, and trunk of a tree, to the ground). Rain from these
sources typically contains higher pesticide concentrations than rain that falls directly onto
the ground

(http://www.ars.usda.gov/research/programs/programs.htm?np_code=203&docid=1380).
The effects of stemflow and throughfall on resident flora and fauna have also been
documented. There is often a pronounced difference in soil chemistry (pH, nutrients,
etc.) between areas of soil affected by stemflow and those outside the influence of canopy
washoff (Gersper and Holowaychuk, 1971), with a concomitant impact on local
invertebrates (Carpenter, 1982). Rainfall in riparian zones is also likely to enter the
associated water body (stream, pond) rapidly in response to storms (as saturated overland
flow), carrying additional pesticide load into the surface water. Thus, the interception of
spray drift by tree canopies and the removal of the chemical from the local ecosystem
may be overestimated, depending on persistence of the chemical and the time between
application and rainfall. The chemical washed off the canopy may end up in the same
water body as runoff water from the upland application area, at approximately the same

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time. Thus, the protective effect of a healthy woody riparian zone with tree canopies and
other overstory vegetation on runoff into water bodies may be somewhat less than
anticipated.

It is difficult to estimate the magnitude of potential impacts of imazapyr use on riparian
habitat and the magnitude of potential effects on stream water quality, channel/pond
morphology, sediment loading, thermal stability and habitat as they relate to survival,
growth, and reproduction of the CRLF. The level of exposure and any resulting
magnitude of effect on riparian vegetation are expected to be highly variable and
dependent on many factors. The extent of runoff and/or drift into CRLF
aquatic/terrestrial areas is affected by the distance the imazapyr use site is offset from the
habitat, the method of application, local geography, weather conditions, and quality of the
riparian buffer itself. The sensitivity of the riparian vegetation is dependent on the
susceptibility of the plant species present to imazapyr and composition of the riparian
zone (e.g. vegetation density, species richness, height of vegetation, width of riparian
area).

Terrestrial plant RQs are above LOCs for all uses; therefore, riparian vegetation may be
affected by use of imazapyr. As previously discussed, the potential for imazapyr to affect
the CRLF via impacts on riparian vegetation depends primarily on the extent of
potentially sensitive riparian zones and their impact on water quality in the streams and
rivers where the CRLF are known to occur. Because woody plants are expected to be
sensitive to imazapyr at anticipated exposure concentrations, riparian areas where the
predominant vegetation is woody plants (e.g., trees and woody shrubs) may be impacted
by imazapyr use. Therefore, imazapyr may adversely affect populations of CRLF in
watersheds with predominantly forested riparian areas. Imazapyr is also likely to affect
herbaceous and grassy riparian zones, resulting in increased sedimentation which could
impact the CRLF in ways previously described.

Therefore, for CRLF habitats that are in close proximity to potential imazapyr use sites,
the effects determination is "may affect and likely to adversely affect" because imazapyr
may affect riparian zones with either herbaceous and grassy riparian zones or
predominantly forested riparian zones.

Given the finding of "may affect and likely to adversely affect", the Agency has
completed a summary of the environmental baseline and cumulative effects for the CRLF
included in this assessment in Attachment 2. The environmental baseline is defined as
the effects of past and ongoing human induced and natural factors leading to the status of
the species, its habitat, and ecosystem, within the action area. The baseline information
provides a snapshot of the CRLF's status at this time. A summary of all USFWS
biological opinions that are relevant to the CRLF that have been made available to EPA
included in this assessment is also provided as part of the baseline status. Cumulative
effects include the effects of future state, tribal, local, private, or other non-federal entity
activities on endangered and threatened species and their critical habitat that are
reasonably expected to occur in the action area.

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5.2.3 Adverse Modification to Designated Critical Habitat

5.2.3.1 Direct Effects to Aquatic Plants

The following PCEs are evaluated in order to determine whether adverse modification of
designated critical habitat for the CRLF may occur via actions that directly affect aquatic
vascular and non-vascular plants: (1) alteration of channel/pond morphology or
geometry, (2) maintenance of water quality parameters such as oxygen content and
temperature, (3) alteration in sediment deposition within stream channel or pond, (4)
alteration in habitat which provides shelter, foraging, predator avoidance and aquatic
dispersal territories for juveniles and adults (5) alteration of other chemical characteristics
necessary for maintenance of CRLF food source and (6) reduction and/or modification
of aquatic-based food sources for pre-metamorphs (e.g. algae).

As stated in Sections 5.1.2.2 and 5.2.2.2, direct risk to non-vascular plants from imazapyr
uses is not expected. Therefore, indirect effects on CRLF individuals via reduction in
aquatic-based food sources for pre-metamorphs are not expected. The effects
determination for the critical habitat impact analysis PCE associated with reduction
and/or modification of aquatic-based food sources for pre-metamorphs (e.g. algae) is "no
effect". This finding is based on lack of exceedances of the aquatic plant LOC for all
nonvascular plants for all imazapyr uses.

Sections 5.1.2.2 and 5.2.2.2 indicate that direct risk to aquatic vascular plants from
imazapyr uses on rangeland, rights-of-way with 50% or more impervious surfaces and
10% or more of the watershed treated, aquatic and forestry (aerial) uses is possible,
especially for vascular plants with emerged foliage such as cattails and bulrushes where
the CRLFs lay their eggs. Direct risk to emerged aquatic plants via spray drift alone from
all imazapyr uses is also possible. Most of the PCEs listed above (alteration of
channel/pond morphology or geometry, maintenance of water quality parameters,
alteration in sediment deposition within stream channel or pond, alteration in habitat
which provides shelter, foraging, predator avoidance and aquatic dispersal territories for
juveniles and adults and alteration of other chemical characteristics necessary for
maintenance of CRLF food source) are associated with a healthy aquatic vascular plant
community. Therefore, based on the screening level analysis of indirect effects to the
aquatic habitat via direct effects to aquatic plants (Sections 5.1.2.2 and 5.2.2.2), imazapyr
may adversely modify designated critical habitat of the CRLF. The effects determination
for all of these PCEs is "likely to adversely affect". This finding is based on exceedances
of the aquatic plant LOC for vascular plants for rangeland, some rights-of-way, aquatic
and some forestry uses and exceedances of the terrestrial plant LOC for all imazapyr uses
following spray drift onto emergent aquatic vegetation.

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5.2.3.2 Adverse Modification to Designated Critical Habitat via
Effects to Riparian Vegetation

Reduction in riparian vegetation could impact the following PCEs: (1)
presence/maintenance of geomorphically stable stream and river channels; (2)
maintenance of water quality parameters including temperature and turbidity; (3)
presence/maintenance of silt-free substrates necessary for viability of the CRLF; (4)
presence/maintenance of riparian habitat for shelter, foraging, predator avoidance,
aestivation and terrestrial dispersal and (5) habitat support for the food source of CRLFs.

The potential for imazapyr to affect riparian vegetation was evaluated as an indirect
effect to the CRLF and is presented in Sections 5.1.2.3 and 5.2.2.3. Conclusions from the
analysis presented in Section 5.2.2.3 are also applicable to the evaluation of riparian
vegetation as it relates to adverse modification of designated critical habitat and include
the following:

• Riparian areas comprised of predominantly grassy and herbaceous
vegetation in close proximity to imazapyr use may be affected such that
their ability to maintain water quality could be reduced.

• Riparian areas comprised predominantly of forested land in close
proximity to imazapyr use may be affected such that their ability to
maintain thermal stability of the stream may be reduced.

• Riparian areas in close proximity to imazapyr use may be affected such
that their ability to stabilize channel/pond morphology and sedimentation
may be reduced.

• Riparian areas in close proximity to imazapyr use may be affected such
that their ability to provide habitat for shelter, foraging, dispersal, predator
avoidance, aestivation and support for the CRLF food source may be
reduced.

Therefore, based on the screening level analysis of indirect effects to the riparian habitat
via direct effects to terrestrial plants (Sections 5.1.2.3 and 5.2.2.3), imazapyr may
adversely modify designated critical habitat of the CRLF. The effects determination for
all of the PCEs listed above is "likely to adversely affect". This finding is based on
exceedance of the terrestrial plant LOC of 1 for all monocots and dicots, in all modeled
locations at all application rates by either ground or aerial spray.

5.2.3.3 Adverse Modification to Designated Critical Habitat via
Effects to Chemical Characteristics Necessary for Normal Behavior, Growth, and
Viability of All CRLF Life Stages

The critical habitat impact analysis associated with chemical characteristics necessary for

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normal behavior, growth, and viability of all life stages of the CRLF is based on the
direct effects to CRLF (Sections 5.1.1 and 5.2.1) and indirect effects to CRLF via
reduction in food items (Sections 5.1.2.1, 5.1.2.2, 5.2.1, 5.2.2 and 5.2.2.2). Other indirect
effects to the CRLF (via alteration to water quality and thermal stability, silt-free
substrates and alteration in habitat) are assessed via other specified PCEs for their
designated critical habitat. If LOCs are exceeded for direct effects and for indirect effects
based on a reduction in food items, then the chemical environment is presumed to be such
that normal behavior, growth, and viability of the CRLF's critical habitat may be
adversely modified. Potential direct and indirect effects were previously evaluated.
Results of those analyses are summarized below.

Direct Effects to the Aquatic and Terrestrial Phase CRLF

Section 5.2.1 summarizes the direct effects determination for both the aquatic and
terrestrial phase CRLF. The effects determination is "no effect" following acute and
chronic exposure to both the aquatic and terrestrial phase CRLF.

Indirect Effects to the CRLF via Reduction in Food Items (Freshwater Invertebrates, Fish
and Aquatic Plants (Algae) for the Aquatic Phase; Terrestrial Invertebrates and
Mammals for the Terrestrial Phase)

The effects determination for indirect effects via reduction in food items (freshwater
invertebrates and fish for the aquatic phase and terrestrial invertebrates and mammals for
the terrestrial phase CRLF) is "no effect". This finding is based on the lack of
exceedances of the acute and/or chronic LOCs for direct effects on the food items of
either the aquatic or terrestrial phase CRLF (Sections 5.2.2.1 and 5.2.2.2).

In summary, the effects determination for chemical characteristics necessary for normal
behavior, growth, and viability of all CRLF life stages is "no effect". This finding is
based on the lack of exceedances of the acute and chronic LOCs for direct effects on
either the aquatic or terrestrial phase CRLF and for direct effects on their food items
(Sections 5.2.1 and 5.2.2).

6. Assumptions, Limitations and Uncertainties

6.1 Uncertainties Related to Exposure For All Taxa

Maximum Use Scenario

The screening-level risk assessment focuses on characterizing potential ecological risks
resulting from a maximum use scenario, which is determined from labeled statements of
maximum application rate and number of applications with the shortest time interval
between applications. The frequency at which actual uses approach this maximum use
scenario may be dependant on insecticide resistance, timing of applications, cultural
practices, and market forces.

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6.2 Exposure Assessment Uncertainties

Overall, the uncertainties inherent in the exposure assessment tend to result in both an
over-estimation and under-estimation of exposures. Factors influencing the over-
estimation of exposure in the screening level modeling include the assumption of no flow
in the modeled water body. Furthermore, the impact of setbacks on runoff estimates has
not been quantified, although well-vegetated setbacks are likely to result in significant
reduction in runoff loading of imazapyr.

This risk assessment focuses on characterizing potential ecological risks resulting from a
maximum use scenario, which is determined from labeled statements of maximum
imazapyr application rate and number of applications with the shortest time interval
between applications. The frequency at which actual uses approach this maximum use
scenario may be dependant on herbicide resistance, timing of applications, cultural
practices, and market forces.

6.2.1 Modeling Assumptions

Generally, the uncertainties addressed in this assessment cannot be quantitatively
characterized. However, given the available data and the tendency to rely on
conservative modeling assumptions, it is expected that the modeling results in an over-
prediction in exposure, particularly in the screening-level assessment.

There are also a number of assumptions that tend to result in over-estimation of exposure.
Although these assumptions cannot be quantified, they are qualitatively described. For
instance, modeling in this assessment for each imazapyr use assumes that all applications
have occurred concurrently on the same day at the exact same application rate. This is
unlikely to occur in reality, but is a reasonable conservative assumption in lieu of actual
data.

6.2.2 Impact of Vegetative Setbacks on Runoff

Unlike spray drift, tools are currently not available to evaluate the effectiveness of a
vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is
highly dependent on the condition of the vegetative strip. For example, a well-
established, healthy vegetative setback can be a very effective means of reducing runoff
and erosion from agricultural fields. Alternatively, a setback of poor vegetative quality
or a setback that is channelized can be ineffective at reducing loadings. Until such time
as a quantitative method to estimate the effect of vegetative setbacks on various
conditions on pesticide loadings becomes available, the aquatic exposure predictions are
likely to overestimate exposure where healthy vegetative setbacks exist and
underestimate exposure where poorly developed, channelized, or bare setbacks exist.

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6.2.3 PRZM Modeling Inputs and Predicted Aquatic Concentrations

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

Uncertainties associated with each of these individual components add to the overall
uncertainty of the modeled concentrations. Additionally, model inputs from the
environmental fate degradation studies are chosen to represent the upper confidence
bound on the mean, values that are not expected to be exceeded in the environment 90
percent of the time. Mobility input values are chosen to be representative of conditions in
the environment. The natural variation in soils adds to the uncertainty of modeled values.
Factors such as application date, crop emergence date, and canopy cover can also affect
estimated concentrations, adding to the uncertainty of modeled values. Factors within the
ambient environment such as soil temperatures, sunlight intensity, antecedent soil
moisture, and surface water temperatures can cause actual aquatic concentrations to differ
for the modeled values.

The standard ecological water body scenario (EXAMS pond) used to calculate potential
aquatic exposure to pesticides is intended to represent conservative estimates, and to
avoid underestimations of the actual exposure. The standard scenario consists of
application to a 10-hectare field bordering a 1-hectare, 2-meter deep (20,000 m3) pond
with no outlet. Exposure estimates generated using the EXAMS pond are intended to
represent a wide variety of vulnerable water bodies that occur at the top of watersheds
including prairie pot holes, playa lakes, wetlands, vernal pools, man-made and natural
ponds, and intermittent and lower order streams. As a group, there are factors that make
these water bodies more or less vulnerable than the EXAMS pond. Static water bodies
that have larger ratios of pesticide-treated drainage area to water body volume would be
expected to have higher peak EECs than the EXAMS pond. These water bodies will be
either smaller in size or have larger drainage areas. Smaller water bodies have limited
storage capacity and thus may overflow and carry pesticide in the discharge, whereas the
EXAMS pond has no discharge. As watershed size increases beyond 10-hectares, it
becomes increasingly unlikely that the entire watershed is planted with a single crop that
is all treated simultaneously with the pesticide. Headwater streams can also have peak

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concentrations higher than the EXAMS pond, but they likely persist for only short
periods of time and are then carried and dissipated downstream.

The Agency acknowledges that there are some unique aquatic habitats that are not
accurately captured by this modeling scenario and modeling results may, therefore,
under- or over-estimate exposure, depending on a number of variables. For example,
aquatic-phase CRLFs may inhabit water bodies of different size and depth and/or are
located adjacent to larger or smaller drainage areas than the EXAMS pond. The Agency
does not currently have sufficient information regarding the hydrology of these aquatic
habitats to develop a specific alternate scenario for the CRLF. As previously discussed in
Section 2.5.4 and Attachment 1, CRLFs prefer habitat with perennial (present year-
round) or near-perennial water and do not frequently inhabit vernal (temporary) pools
because conditions in these habitats are generally not suitable (Hayes and Jennings 1988).
Therefore, the EXAMS pond is assumed to be representative of exposure to aquatic-
phase CRLFs. In addition, the Services agree that the existing EXAMS pond represents
the best currently available approach for estimating aquatic exposure to pesticides
(USFWS/NMFS 2004).

6.2.4 Modeling Total Toxic Residues

In the absence of data concerning the toxicity of the two major imazapyr transformation
products, the assumption that these two degradates were of equal toxicity to the parent
compound was made. When the parent compound degraded under aqueous photolysis,
the sum of residues for the parent compound and for the major degradate were taken at
each sampling interval and plotted verses time, and regressed in order to obtain a total
toxic residue half-life. When the parent compound does not degrade, the modeling input
value for a stable compound was chosen, in spite of data indicating that the degradates
are not stable under aerobic conditions. This value provides more conservative EECs
than attempting to model each toxic moiety separately.

6.3 Terrestrial Assessment

6.3.1 Location of Wildlife Species

For the screening level terrestrial risk assessment, a generic bird or mammal was assumed
to occupy either the treated field or adjacent areas receiving imazapyr at the treatment
rate on the field. Actual habitat requirements of particular terrestrial species were not
considered, and it was assumed that species occupy, exclusively and permanently, the
modeled treatment area. Spray drift model predictions suggest that this assumption leads
to an overestimation of exposure to species that do not occupy the treated field
exclusively and permanently.

6.3.2 Routes of Exposure

For terrestrial animals, this screening level terrestrial assessment for spray applications of

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imazapyr only considered dietary exposure. Other routes of exposure that were not
considered in the assessment are incidental soil ingestion exposure, inhalation exposure,
dermal exposure, and drinking water exposure.

6.3.3 Residue Levels Selection

The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide
residues in wildlife dietary items. These residue assumptions are believed to reflect a
realistic upper-bound residue estimate, although the degree to which this assumption
reflects a specific percentile estimate is difficult to quantify. It is important to note that
the field measurement efforts used to develop the Fletcher estimates of exposure involve
highly varied sampling techniques. It is entirely possible that much of these data reflect
residues averaged over entire above ground plants in the case of grass and forage
sampling. Depending upon a specific wildlife species' foraging habits, whole
aboveground plant samples may either underestimate or overestimate actual exposure.

6.3.4 Dietary Intake

It was assumed that ingestion of food items in the field occurs at rates commensurate
with those in the laboratory. Although the screening assessment process adjusts dry-
weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food
intake estimates, it does not allow for gross energy differences. Direct comparison of a
laboratory dietary concentration- based effects threshold to a fresh-weight pesticide
residue estimate would result in an underestimation of field exposure by food
consumption by a factor of 1.25 - 2.5 for most food items.

Differences in assimilative efficiency between laboratory and wild diets suggest that
current screening assessment methods do not account for a potentially important aspect of
food requirements. Depending upon species and dietary matrix, bird assimilation of wild
diet energy ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85%
(U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is
formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for
underestimation of exposure may exist by assuming that consumption of food in the wild
is comparable with consumption during laboratory testing. In the screening process,
exposure may be underestimated because metabolic rates are not related to food
consumption.

Finally, the screening procedure does not account for situations where the feeding rate
may be above or below requirements to meet free living metabolic requirements.

Gorging behavior is a possibility under some specific wildlife scenarios (e.g., bird
migration) where the food intake rate may be greatly increased. Kirkwood (1983) has
suggested that an upper-bound limit to this behavior might be the typical intake rate
multiplied by a factor of 5. In contrast, there may be potential for avoidance (animals
respond to the presence of noxious chemicals in food by reducing consumption of treated
dietary elements). This response is seen in nature where herbivores avoid plant

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secondary compounds.

Risk quotients calculated using the dose-based toxicity values are generally higher than
RQs calculated using the dietary-based toxicity values. The dose-based approach
considers the uptake and absorption kinetics of a gavage toxicity study to approximate
exposure associated with uptake from a dietary matrix. Toxic response is a function of
duration and intensity of exposure. For many compounds a gavage dose represents a
very short-term high intensity exposure. Although the dose-based estimates may not
reflect reality in that animals do not receive a gavage while feeding, it is possible that a
short-duration, high-intensity exposure could occur associated with feeding on a
agricultural field since many birds may gorge themselves when food items are available.
On the other hand, the dietary-based approach assumes that animals in the field are
consuming food at a rate similar to that of confined laboratory animals despite the fact
that energy content in food items differs between the field and the laboratory as does the
energy requirements of wild and captive animals. Also, the design of dietary-based
studies precludes the estimation of food consumption on a per-bird basis since birds are
group housed and tend to spill feed further confounding any estimates of food
consumption.

6.4 Effects Assessment Uncertainties

6.4.1 Age Class and sensativity of Effects Threshold

It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids, second instar for
amphipods, stoneflies, mayflies, and third instar for midges).

Testing of juveniles may overestimate toxicity at older age classes for pesticidal active
ingredients, such as imazapyr, that act directly (without metabolic transformation)
because younger age classes may not have the enzymatic systems associated with
detoxifying xenobiotics. In so far as the available toxicity data may provide ranges of
sensitivity information with respect to age class, this assessment uses the most sensitive
life-stage information as measures of effect for surrogate aquatic animals, and is
therefore, considered as protective of the CRLF.

6.4.2 Use of Freshwater Fish and Bird Toxicity Data for the CRLF

Freshwater fish and birds were used as surrogate species for the aquatic and terrestrial
phases of the CRLF, respectively. Submitted studies indicate that imazapyr is not toxic
to either aquatic or terrestrial animals. The mode of action for imazapyr supports the
submitted data. Nevertheless, since there are no data on the effects of imazapyr on either
the CRLF or other amphibians, there is an uncertainty associated with the potential
effects on both the aquatic and terrestrial phase CRLF. However, the Agency's LOCs are

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intentionally set very low, and conservative estimates are made in the screening level risk
assessment to account for these uncertainties.

6.4.3 Sublethal Effects

For an acute risk assessment, the screening risk assessment relies on the acute mortality
endpoint as well as a suite of sublethal responses to the pesticide, as determined by the
testing of species response to chronic exposure conditions and subsequent chronic risk
assessment. Consideration of additional sublethal data in the assessment is exercised on a
case-by-case basis and only after careful consideration of the nature of the sublethal
effect measured and the extent and quality of available data to support establishing a
plausible relationship between the measure of effect (sublethal endpoint) and the
assessment endpoints.

No sublethal effects were observed in any of the studies that were more sensitive than the
endpoints used to calculate risk quotients for direct and indirect effects to the CRLF. No
treatment-related sublethal effects were observed in the freshwater animal studies. For
birds, no treatment-related sublethal effects were observed following either acute or
chronic exposure. For mammals, the only observed sublethal effect was salivation in a
gavage developmental study in the rat. The effect is likely due to the route of
administration and is not likely to occur in wild mammalian populations.

6.5 Assumptions Associated with the Acute LOCs

The risk characterization section of this listed species assessment includes an evaluation
of the potential for individual effects. The individual effects probability associated with
the acute RQ is based on the mean estimate of the slope and an assumption of a probit
dose response relationship for the effects study corresponding to the taxonomic group for
which the LOCs are exceeded.

For imazapyr, no mortality was observed in acute toxicity studies for freshwater fish
(rainbow trout, bluegill sunfish, channel catfish), freshwater invertebrates (daphnia),
birds (bobwhite quail, mallard ducks), honey bees, or mammals (Sprague-Dawley rats).
Consequently, a default slope assumption of 4.5 with default upper and lower slope
bounds of 2 and 9 were used as per original Agency assumptions of a typical slope cited
in Urban and Cook (1986). The use of a default slope assumption provides an
uncertainty in the probability of individual effects; however, as stated previously, the
mode of action for imazapyr supports a conclusion that it will have no direct effects to
either aquatic or terrestrial animals.

6.6 Uncertainty in the Potential Effect to Riparian Vegetation vs. Increased
Sedimentation

Effects to riparian vegetation were evaluated using submitted guideline seedling
emergence and vegetative vigor studies. LOCs were exceeded for seedling emergence

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and vegetative vigor endpoints with the vegetative vigor endpoint being considerably
more sensitive. Based on LOC exceedances and the lack of readily available information
to allow for characterization of riparian areas of the CRLF, it was concluded that
imazapyr use is likely to adversely affect the CRLF via potential impacts on
grassy/herbaceous and forested riparian vegetation resulting in increased sedimentation.
However, soil retention/sediment loading is dependent on a number of factors including
land management and tillage practices. Use of herbicides (including imazapyr) may be
incorporated into a soil conservation plan. Therefore, although this assessment concludes
that imazapyr is likely to adversely affect the CRLF and its designated critical habitat by
potentially impacting riparian areas, it is possible that adverse impacts on sediment
loading may be ameliorated in areas where soil retention strategies are used.

6.7 Usage Uncertainties

County-level usage data were obtained from California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database. Four years of data (2002-
2005) were included in this analysis because statistical methodology for identifying
outliers, in terms of area treated and pounds applied, was provided by CDPR for these
years only. No methodology for removing outliers was provided by CDPR for 2001 and
earlier pesticide data; therefore, this information was not included in the analysis because
it may misrepresent actual usage patterns. CDPR PUR documentation indicates that
errors in the data may include the following: a misplaced decimal; incorrect measures,
area treated, or units; and reports of diluted pesticide concentrations. In addition, it is
possible that the data may contain reports for pesticide uses that have been cancelled.
The CPDR PUR data does not include home owner applied pesticides; therefore,
residential uses are not likely to be reported. As with all pesticide use data, there may be
instances of misuse and misreporting. The Agency made use of the most current,
verifiable information; in cases where there were discrepancies, the most conservative
information was used.

6.8 Action Area

An example of an important simplifying assumption that may require future refinement is
the assumption of uniform runoff characteristics throughout a landscape. It is well
documented that runoff characteristics are highly non-uniform and anisotropic, and
become increasingly so as the area under consideration becomes larger. The assumption
made for estimating the aquatic Action Area (based on predicted in-stream dilution) was
that the entire landscape exhibited runoff properties identical to those commonly found in
agricultural lands in this region. However, considering the vastly different runoff
characteristics of: a) undeveloped (especially forested) areas, which exhibit the least
amount of surface runoff but the greatest amount of groundwater recharge; b)
suburban/residential areas, which are dominated by the relationship between
impermeable surfaces (roads, lots) and grassed/other areas (lawns) plus local drainage
management; c) urban areas, that are dominated by managed storm drainage and
impermeable surfaces; and d) agricultural areas dominated by Hortonian and focused

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runoff (especially with row crops), a refined assessment should incorporate these
differences for modeled stream flow generation. As the zone around the immediate
(application) target area expands, there will be greater variability in the landscape; in the
context of a risk assessment, the runoff potential that is assumed for the expanding area
will be a crucial variable (since dilution at the outflow point is determined by the size of
the expanding area). Thus, it important to know at least some approximate estimate of
types of land use within that region. Runoff from forested areas ranges from 45 -
2,700% less than from agricultural areas; in most studies, runoff was 2.5 to 7 times higher
in agricultural areas (e.g., Okisaka et al., 1997; Karvonen et al., 1999; McDonald et al.,
2002; Phuong and van Dam 2002). Differences in runoff potential between
urban/sub urban areas and agricultural areas are generally less than between agricultural
and forested areas. In terms of likely runoff potential (other variables - such as
topography and rainfall - being equal), the relationship is generally as follows (going
from lowest to highest runoff potential): Three-tiered forest < agroforestry < suburban <
row-crop agriculture < urban.

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

7. Risk Conclusions: Summary of Direct and Indirect Effects to the CRLF and
Adverse Modification to Designated Critical Habitat for the CRLF

In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the
information presented in this listed species risk assessment represents the best available
data to assess the potential risks of imazapyr to the CRLF and its designated critical
habitat. A summary of the risk conclusions and effects determination for the CRLF and
designated critical habitat for the CRLF, given the uncertainties discussed in Section 6, is
presented in Tables 7.1 and 7.2.

The CRLF has no obligate relationships with either aquatic or terrestrial plants.

Therefore, the LAA/NLAA discrimination is based on direct effects to non-listed aquatic
and terrestrial plants (i.e., indirect effects to habitat and/or primary productivity). To
distinguish between an LAA and an NLAA determination, for each of the imazapyr uses
that are applied either as a ground or aerial spray, buffers based on expected spray drift
are added from the site of potential imazapyr application to the point where the LOC for
non-listed terrestrial plants would no longer be exceeded. For non-listed plants, these
buffers range from 2530 to 5940 feet (see Table 7.1). For aquatic plants, a total of 7,450
downstream miles may also be used for this determination.

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After completing the analysis of the effects of imazapyr on the Federally listed threatened
California red-legged frog (Rana aurora draytonii), in accordance with methods
delineated in the Overview Document (USEPA 2004), it is concluded that the use of
imazapyr and its isopropylamine salt (PC Code #'s 128821 and 128829) is may affect,
and is likely to adversely affect the CRLF, based on indirect effects (habitat modification
to aquatic and terrestrial plants). It is also concluded that these same effects will
constitute adverse modification to critical habitat. These effects are anticipated to occur
only for those occupied core habitat areas, CNDDB occurrence sections, and designated
critical habitat for the CRLF that are located within distances ranging from 2530 to 5940
feet, depending upon the specific use from legal use sites (see Table 7.1). Rationale and
specifics for each component assessed are provided Tables 7.1 and 7.2.

Using ARGIS9, the NLCD classification data and CLRF habitat information supplied by
the U.S. FWS, habitat areas where indirect effects and designated critical habitat areas
where adverse modifications are anticipated to occur have been identified (Figure 7.1).
Even without buffers on any of the imazapyr uses, indirect effects (modification of the
terrestrial and aquatic vascular plant community) could potentially occur in
approximately 94-100% (27,300 acres) of the CRLF range assessed, including core areas,
critical habitat and known occurrences. Figure 7.1 shows the overlap of all imazapyr
uses with no buffers with the CRLF core and critical habitat as well as the known
occurrences. Firgure 7.2 shows that even with only the imazapyr forestry uses with a
5940 foot buffer, plus urban uses (no buffer) significantly overlap with the core areas,
critical habitat and known occurrences by 68 - 99%. Detailed maps are provided in
Appendix C.

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Imazapyr - Initial Area of Concern with Habitat Overlap

Legend

~~I CA counties

~ CRLF Recovety Unit
| imazapyr All Uses overlap

CNDDB occurence sections
|| Core areas
| imazapyr all uses

iKilometersi
0 2040 80 120 160

Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Setvice (NASS, 2002)
Gap Analysis Program Orchard/Vineyard Landcover (GAP)
National Land Cover Database (NLCD) (MRLC, 2001)

Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Division.
July, 2007. Projection: Albers Equal Area Conic USGS, North
American Datum of 1983 (NAD 1983)

Figure 7.1

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Imazapyr - LAA, Overview

Legend

CA counties
CRLF Recovery Unit
CNDDB_occu ren ce_secti on s
Forestry 5940 ft overlap
Critical habitat
Core areas
Forest 5940ft LAA
imazapyr Urban LAA

l Kilometers
0 2550 100 150 200

Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Seivice (NASS, 2002)
Gap Analysis Program Orchard/Vineyard Landcover (GAP)
National Land Cover Database (NLCD) (MRLC, 2001)

Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Division.
June, 2007. Projection: Alders Equal Area Conic USGS, North
American Datum of 1983 (NAD 1983)

Figure 7.2 Buffered Forestry Uses and Unbuffered Urban Uses with Habitat Overlap

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Table 7.1. Imazapyr Effects Determination Summary for the CR.LF (Direct and Indirect Effects)

Effects Determination and Basis

Assessment Endpoint

.Effects
Determination1

NLAA/LAA Discrimination

Basis

Aquatic Phase

1. Survival, growth,
and reproduction of
CRLF individuals via
direct effects on aquatic
phases (eggs, larvae,
tadpoles, juveniles and
adults)

Acute direct effects:
no effect

N/A

No effects in surrogate species (freshwater fish)
at highest concentration tested, which is
significantly greater than the peak aquatic
EECs

Chronic direct
effects: no effect

N/A

Chronic freshwater fish (surrogate species)
LOC is not exceeded for any uses.

2. Survival, growth,
and reproduction of
CRLF individuals via
indirect effects to prey
(freshwater
invertebrates)

Acute direct effects
to freshwater
invertebrates: no
effect

N/A

No effects in freshwater invertebrates at highest
concentration tested, which is significantly
greater than the peak aquatic EECs.

Chronic direct
effects to freshwater
invertebrates: no
effect

N/A

Chronic freshwater invertebrate LOC is not
exceeded for any uses

3. Survival, growth,
and reproduction of
CRLF individuals via
indirect effects on
habitat and/or primary
productivity (i.e.
aquatic plant
community)

Direct effects to
aquatic non-vascular
plants:
No affect

N/A

No LOCs exceeded for non-vascular plants.

Direct effects to
aquatic vascular
plants: No effect for
residential, turf and
forestry (ground)
May affect, likely to
adversely affect for
forestry (aerial),
rangeland/hay,
aquatic and rights-
of-way uses.

N/A

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Table 7.1. Imazapyr Effects Determination Summary for the CR.LF (Direct and Indirect Effects)

Effects Determination and Basis

Assessment Endpoint

.Effects
Determination1

NLAA/LAA Discrimination

Basis

Direct effects to
aquatic emergent
vascular plants:
May affect, likely to
adversely affect for

all uses except
capsule injection,
which is may affect,
.NLAA..

Forestry uses (ground application) NLAA > 2530 feet,
LAA < 2530 feet

Non-forestry terrestrial uses (ground application) NLAA >
2920 feet, LAA < 2920 feet

Aquatic uses (ground application) NLAA > 2940 feet, LAA
< 2940 feet

Aquatic uses (helicopter application)) NLAA > 3540 feet,
LAA < 3540 feet

Non-forestry terrestrial uses (aerial application fixed wing)
NLAA > 4640 feet, LAA < 4640 feet
Forestry uses (aerial application helicopter) NLAA > 4660
feet, LAA < 4660 feet

Forestry uses (aerial application fixed wing) NLAA > 5940
feet, LAA < 5940 feet

Aquatic plant LOCs exceeded for vascular
plants for forestry (aerial), rangeland/hay,
aquatic and rights-of-way uses near use sites.
Aquatic plant LOCs not exceeded for vascular
plants for forestry (ground), residential or turf
uses. Emergent aquatic vascular plants in
wetland areas adjacent to use sites: terrestrial
plant LOC exceeded for monocots and dicots
for all uses from flooding, runoff or spray drift2"
5 Capsule injection use expected to have very
limited nonquantifiable exposure to non-target
plants.

Terrestrial Phase

4. Survival, growth,
and reproduction of
CRLF individuals via
direct effects on
terrestrial phase adults
and juveniles

Acute direct effects:
no effect

N/A

No effects in surrogate species (birds) at
highest concentration/dose tested which are
significantly greater than the terrestrial EECs

Chronic direct
effects: no effect

N/A

Chronic bird (surrogate species) LOC is not
exceeded for any uses

5. Survival, growth,
and reproduction of
CRLF individuals via
indirect effects on prey
(i.e., terrestrial
invertebrates, small
terrestrial vertebrates)

Acute direct effects
to most sensitive
prey: no effect

N/A

No effects in mammals at highest dose tested,
which is significantly greater than the terrestrial
EEC.

Chronic direct
effects to most
sensitive prey: no
effect

N/A

Chronic terrestrial animal (mammals) LOC is
not exceeded for any uses.

6. Survival, growth,
and reproduction of
CRLF individuals via
indirect effects on

Direct effects to
monocots: May
affect
Likely to adversely

See details in Assessment Endpoint number 3 above.

Terrestrial plant LOC exceeded for monocots in
both wetlands and uplands adjacent to use site
for all uses. Risk conclusions are supported by
adverse ecological incident reports.2"5 Capsule

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Table 7.1. Imazapyr Effects Determination Summary for the CR.LF (Direct and Indirect Effects)

Effects Determination and Basis

Assessment Endpoint

Effects
Determination1

NLAA/LAA Discrimination

Basis

habitat (i.e. riparian
vegetatation)

affect. May affect,
NLAA for capsule
injection use

injection use expected to have very limited
nonquantifiable exposure to non-target plants.

Direct effects to
dicots: May affect
Likely to adversely
affect. May affect,
NLAA for capsule
injection use

See details in Assessment Endpoint number 3 above.

N/A = Not applicable

5 It is not clear for rangeland uses, whether and to what extent the critical habitat exemption applies.

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Table 7.2. Effects Determination Summary for the Critical Habitat Impact Analysis

Assessment Endpoint

Effects Determination of Habitat Modification
Determination1

Basis

Aquatic Phase PCEs

Aquatic breeding and non-breeding habitat

Alteration of
channel/pond
morphology and/or
water

chemistry/quality;
increase in sediment
deposition

Direct effects to
aquatic plants: no
effect for non-vascular

plants;
No effect for aquatic
vascular plants for
residential, turf and
forestry (ground).
Modification of critical
habitat for aquatic
vascular plants for
forestry (aerial),
rangeland/hay, aquatic
and rights-of-way uses.

N/A

No LOCs exceeded for non-vascular plants.
Aquatic plant LOC not exceeded for vascular
plants for forestry (ground), residential or turf
uses. Aquatic plant LOC exceeded for vascular
plants for forestry (aerial), rangeland/hay,
aquatic and rights-of-way uses.5

Direct effects to
aquatic emergent
vascular plants:
Modification of critical
habitat

Forestry uses (ground application): habitat modification
expected < 2530 feet and not expected > 2530 feet
Non-forestry terrestrial uses (ground application): habitat
modification expected < 2920 feet and not expected >
2920 feet

Aquatic uses (ground application): habitat modification
expected < 2940 feet and not expected > 2940 feet
Aquatic uses (helicopter application)): habitat
modification expected < 3540 feet and not expected >
3540 feet

Non-forestry terrestrial uses (aerial application fixed
wing): habitat modification expected < 4640 feet and not
expected> 4640 feet

Forestry uses (aerial application helicopter): habitat
modification expected < 4660 feet and not expected >
4660 feet

Forestry uses (aerial application fixed wing): habitat
modification expected < 5940 feet and not expected >

Aquatic plant LOCs not exceeded for aquatic
vascular plants for forestry (ground), residential
or turf uses. Aquatic plant LOCs exceeded for
aquatic vascular plants for forestry (aerial),
rangeland/hay, aquatic and rights-of-way uses.
Emergent aquatic vascular plants in wetland
areas adjacent to use sites: terrestrial plant
LOC exceeded for monocots and dicots for all
uses from flooding, runoff or spray drift2"5.

Risk conclusions are supported by adverse
ecological incident reports. Capsule injection
use expected to have very limited
nonquantifiable exposure to non-target plants.

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Table 7.2. Effects Determination Summary for the Critical Habitat Impact Analysis

Assessment Endpoint

Effects Determination of Habitat Modification
Determination1

Basis

5940 feet.

Direct effects to
monocots:
Modification of critical
habitat. Modification
of critical habitat not
expected for capsule
injection use.

See terrestrial buffer list above.

Terrestrial plant LOC exceeded for monocots in
wetlands and uplands adjacent to use site for all
uses.2"5 Risk conclusions are supported by
adverse ecological incident reports. Capsule
injection use expected to have very limited
nonquantifiable exposure to non-target plants.

Alteration of
channel/pond
morphology and/or
water

chemistry/quality;
increase in sediment
deposition

Direct effects to dicots:
modification of critical
habitat Modification
of critical habitat not
expected for capsule
injection use.

See terrestrial buffer list above.

Terrestrial plant LOC exceeded for dicots in
wetlands and uplands adjacent to use site for all
uses.2"5 Risk conclusions are supported by
adverse ecological incident reports. Capsule
injection use expected to have very limited
nonquantifiable exposure to non-target plants.

Terrestrial Phase PCEs

Upland habitat and dispersal habitat

Elimination/disturbance
of upland habitat and/or
dispersal habitat

Direct effects to
monocots:
Modification of critical
habitat Modification
of critical habitat not
expected for capsule
injection use.

See terrestrial buffer list above.

Direct effects to dicots:
Modification of critical
habitat Modification
of critical habitat not
expected for capsule
injection use.

See terrestrial buffer list above.

N/A = Not applicable

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inversion, etc. New mitigation measures are being developed; however, products with the old labels will be allowed to be distributed for up to 18 months after
new labels are approved. Therefore, it is not possible to determine when all product labels will reflect the new mitigation measures. It could be assumed that
most users will use their existing stocks within 2 years of purchase.

5 It is not clear for rangeland uses, whether and to what extent the critical habitat exemption applies.

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When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the species and its resources (i.e., food and habitat) are
not expected to be uniform across the action area. In fact, given the assumptions of drift
and downstream transport (i.e., attenuation with distance), pesticide exposure and
associated risks to the species and its resources are expected to decrease with increasing
distance away from the treated field or site of application. Evaluation of the implication
of this non-uniform distribution of risk to the species would require information and
assessment techniques that are not currently available. Examples of such information and
methodology required for this type of analysis would include the following:

Information on population responses of prey base organisms to the pesticide. Currently,
methodologies are limited to predicting exposures and likely levels of direct mortality,
growth or reproductive impairment immediately following exposure to the pesticide. The
degree to which repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may recover is not
predictable. An enhanced understanding of long-term prey responses to pesticide
exposure would allow for a more refined determination of the magnitude and duration of
resource impairment, and together with the information described above, a more
complete prediction of effects to individual frogs and potential adverse modification to
critical habitat.

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