Risks of Norflurazon Use to Federally Threatened
California Red-legged Frog
(Rana aurora draytonii)
Pesticide Effects Determination
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
02.18.2008
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Primary Authors:
Brian D. Kiernan, Biologist, ERB IV
Amy A. McKinnon, Environmental Scientist, ERB IV
Secondary Reviewers:
Thomas Steeger, Ph. D, ERB IV
Marietta Echeverria, RAPL, ERB IV
Branch Chief:
Elizabeth Behl, Chief ERB IV
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Table of Contents
Table of Contents iii
1.0 Executive Summary 1
2.0 Problem Formulation 6
2.1 Purpose 6
2.2 Scope 8
2.3 Previous Assessments 8
2.4 Stressor Source and Distribution 9
2.4.1 Environmental Fate Assessment 9
2.4.2 Environmental Transport Assessment 12
2.4.3 Mechanism of Action 12
2.4.4 Use Characterization 12
2.5 Assessed Species 17
2.5.1 Distribution 17
2.5.2 Reproduction 20
2.5.3 Diet 20
2.5.4 Habitat 21
2.6 Designated Critical Habitat 22
2.7 Action Area 24
2.8 Assessment Endpoints and Measures of Ecological Effect 27
2.8.1 Assessment Endpoints for the CRLF 27
2.8.2 Assessment Endpoints for Designated Critical Habitat 29
2.9 Conceptual Model 31
2.9.1 Risk Hypotheses 31
2.9.2 Diagram 31
2.10 Analysis Plan 33
2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model 33
2.10.1.1 Measures of Exposure 33
2.10.1.2 Measures of Effect 35
2.10.1.3 Integration of Exposure and Effects 36
2.10.2 Data Gaps 37
3.0 Exposure Assessment 37
3.1 Aquatic Exposure Assessment 37
3.1.1 Modeling Approach 37
3.1.2 Model Inputs 38
3.1.3 Results 40
3.1.4 Existing Monitoring Data 41
3.1.4.1 USGS NAWQA Surface Water Data 42
3.1.4.2 USGS NAWQA Groundwater Data 42
3.1.4.3 California Department of Pesticide Regulation (CPR) Data 42
3.1.4.4 Prospective Groundwater Study 43
3.1.4.5 Atmospheric Monitoring Data 43
3.2 Terrestrial Exposure Assessment 43
3.2.1 Terrestrial Animal Exposure Assessment 43
3.2.2 Terrestrial Plant Exposure Assessment 45
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4.0 Effects Assessment 45
4.1 Evaluation of Aquatic Ecotoxicity Studies 47
4.1.1 Toxicity to Freshwater Fish 48
4.1.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies 49
4.1.1.2 Freshwater Fish: Chronic Exposure (Early Life Stage and Reproduction)
Studies 49
4.1.2 Toxicity to Freshwater Invertebrates 49
4.1.2.1 Freshwater Invertebrates: Acute Exposure (Mortality) Studies 49
4.1.2.2 Freshwater Invertebrates: Chronic Exposure (Reproduction) Studies 50
4.1.3 Toxicity to Aquatic Plants 50
4.1.3.1 Aquatic Plants: Laboratory Data 50
4.2 Toxicity of Norflurazon to Terrestrial Organisms 50
4.2.1 Toxicity to Birds 52
4.2.1.1 Birds: Acute Exposure (Mortality) Studies 52
4.2.1.2 Birds: Chronic Exposure (Growth, Reproduction) Studies 52
4.2.2 Toxicity to Mammals 53
4.2.2.1 Mammals: Acute Exposure (Mortality) Studies 53
4.2.2.2 Mammals: Chronic Exposure (Growth, Reproduction) Studies 53
4.2.3 Toxicity to Terrestrial Invertebrates 53
4.2.4 Toxicity to Terrestrial Plants 53
4.3 Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern 55
4.4 Incident Database Review 56
4.4.1 Plant Incidents 56
4.4.2 Aquatic Incidents 56
5.0 Risk Characterization 57
5.1 Risk Estimation 57
5.1.1 Exposures in the Aquatic Habitat 57
5.1.1.1 Direct Effects to Aquatic-Phase CRLF 57
5.1.1.2 Indirect Effects to Aquatic-Phase CRLF via Reduction in Prey (non-
vascular aquatic plants, aquatic invertebrates, fish, and frogs) 58
5.1.1.3 Indirect Effects to CRLF via Reduction in Habitat and/or Primary
Productivity (Freshwater Aquatic Plants) 60
5.1.2 Exposures in the Terrestrial Habitat 61
5.1.2.1 Direct Effects to Terrestrial-phase CRLF 61
5.1.2.2 Indirect Effects to Terrestrial-Phase CRLF via Reduction in Prey
(terrestrial invertebrates, mammals, and frogs) 62
a) Terrestrial Invertebrates 62
5.1.2.3 Indirect Effects to CRLF via Reduction in Terrestrial Plant Community
(Riparian and Upland Habitat) 64
5.1.3 Primary Constituent Elements of Designated Critical Habitat 64
5.1.3.1 Aquatic-Phase (Aquatic Breeding Habitat and Aquatic Non-Breeding
Habitat) 64
5.1.3.2 Terrestrial-Phase (Upland Habitat and Dispersal Habitat) 65
5.1.4 Spatial Extent of Potential Effects 66
5.1.4.1 Spray Drift 67
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5.1.4.2 Downstream Dilution Analysis 67
5.2 Risk Description 68
5.2.1 Direct Effects 71
5.2.1.1 Aquatic-Phase CRLF 71
5.2.1.2 Terrestrial-Phase CRLF 72
5.2.2 Indirect Effects (via Reductions in Prey Base) 72
5.2.2.1 Algae (non-vascular aquatic plants) 72
5.2.2.2 Aquatic Invertebrates 72
5.2.2.3 Fish and Aquatic-phase Frogs 72
5.2.2.4 Terrestrial Invertebrates 73
5.2.2.5 Mammals 73
5.2.2.6 Terrestrial-phase Amphibians 73
5.2.3 Indirect Effects (via Habitat Effects) 73
5.2.3.1 Aquatic Plants (Vascular and Nonvascular) 73
5.2.3.2 Terrestrial Plants 74
5.2.4 Modification to Designated Critical Habitat 76
5.2.4.1 Aquatic-Phase PCEs 76
5.2.4.2 Terrestrial-Phase PCEs 76
6.0 Uncertainties 78
6.1 Exposure Assessment Uncertainties 78
6.1.1 Maximum Use Scenario 78
6.1.2 Aquatic Exposure Modeling of Norflurazon 78
6.1.3 Potential Groundwater Contributions to Surface Water Chemical
Concentrations 80
6.1.4 Usage Uncertainties 80
6.1.5 Terrestrial Exposure Modeling of Norflurazon 81
6.1.6 Spray Drift Modeling 82
6.2 Effects Assessment Uncertainties 82
6.2.1 Age Class and Sensitivity of Effects Thresholds 82
6.2.2 Use of Surrogate Species Effects Data 82
6.2.3 Sublethal Effects 83
6.2.4 Location of Wildlife Species 83
7.0 Risk Conclusions 84
8.0 References 87
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List of Tables
Table 1.1 Effects Determination Summary for Norflurazon Use and the CRLF 4
Table 1.2 Effects Determination Summary for Norflurazon Use and CRLF Critical
Habitat Impact Analysis 4
Table 2.1. General Chemical Properties 10
Table 2.2. Summary of Norflurazon Environmental Fate Properties 11
Table 2.3. Norflurazon Uses Assessed for the CRLF 14
Table 2.4. Summary of CDPR PUR Data from 1999 to 2006 for Currently Registered
Norflurazon Uses 16
Table 2.5 Assessment Endpoints and Measures of Ecological Effects 28
Table 2.6 Summary of Assessment Endpoints and Measures of Ecological Effect for
Primary Constituent Elements of Designated Critical Habitata 30
Table 3.1. Norflurazon Uses, Scenarios, and Application Information for the CRLF risk
assessment1 39
Table 3.2. Chemical-Specific PRZM/EXAMS Input Parameters Used in Aquatic
Exposure Modeling for Norflurazon 40
Table 3.3. Aquatic EECs ((J-g/L) for Norflurazon Uses in California 41
Table 3.4 Input Parameters for Foliar Applications Used to Derive Terrestrial EECs for
Norflurazon with T-REX 44
Table 3.5 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based
Exposures of the CRLF and its Prey to Norflurazon 44
Table 3.6 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via Effects to
Terrestrial Invertebrate Prey Items 45
Table 3.7 TerrPlant Inputs and Resulting EECs for Plants Inhabiting Dry and Semi-
aquatic Areas Exposed to Norflurazon via Runoff and Drift 45
Table 4.1 Freshwater Aquatic Toxicity Profile for Norflurazon 48
Table 4.2 Categories of Acute Toxicity for Aquatic Animals 48
Table 4.3 Terrestrial Toxicity Profile for Norflurazon 50
Table 4.4 Categories of Acute Oral and Subacute Dietary Toxicity for Avian and
Mammalian Studies 52
Table 4.5 Non-target Terrestrial Plant Seedling Emergence Toxicity (Tier II) Data 54
Table 5.1 Summary of Direct Effect RQs for the Aquatic-phase CRLF) 58
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Table 5.2 Summary of RQs Used to Estimate Indirect Effects to the CRLF via Effects to
Non-Vascular Aquatic Plants (EC50=9.7 |ig/L)(diet of CRLF in tadpole life
stage and habitat of aquatic-phase CRLF) 59
Table 5.3 Summary of Acute and Chronic RQs Used to Estimate Indirect Effects to the
CRLF via Direct Effects on Aquatic Invertebrates as Dietary Food Items (prey
of CRLF juveniles and adults in aquatic habitats) Based on Acute LC50 and
Chronic NOAEC Toxicity Endpoints for Daphnia magna of >15000 g/L and
1,000 |ig/L, respectively 60
Table 5.4 Summary of RQs Used to Estimate Indirect Effects to the CRLF via Effects to
Vascular Aquatic Plants (habitat of aquatic-phase CRLF)a Based on L. gibba
EC50 of 58.2 Lig/I. 61
Table 5.5 Summary of Chronic RQs* Used to Estimate Direct Effects to the Terrestrial-
phase CRLF 62
Table 5.6 Summary of RQs Used to Estimate Indirect Effects to the Terrestrial-phase
CRLF via Direct Effects on Terrestrial Invertebrates as Dietary Food Items
Based on a Terrestrial Invertebrate Toxicity Value of 1,836 |ig a.i./g of bee. 63
Table 5.7 Summary of Acute and Chronic RQs* Used to Estimate Indirect Effects to the
Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary
Food Items Based on an Acute Oral LD50 of 9300 mg/kg-bw and Chronic
NOAEC of 150 mg/kg-diet 63
Table 5.8 RQs for Monocots Inhabiting Dry and Semi-Aquatic Areas Exposed to
Norflurazon via Runoff and Drift 64
Table 5.9 RQs for Dicots Inhabiting Dry and Semi-Aquatic Areas Exposed to
Norflurazon via Runoff and Drift 64
Table 5.10 Risk Estimation Summary for Norflurazon - Direct and Indirect Effects to
CRLF 69
Table 5.11 Risk Estimation Summary for Norflurazon - PCEs of Designated Critical
Habitat for the CRLF 70
Table 7.1 Effects Determination Summary for Norflurazon Use and the CRLF 85
Table 7.2 Effects Determination Summary for Norflurazon Use and CRLF Critical
Habitat Impact Analysis 86
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List of Figures
Figure 2.4.4-1 Norflurazon Use in Total Pounds per County 15
Figure 2.5.1-1 Recovery Unit, Core Area, Critical Habitat, and Occurrence Designations
for CRLF 19
Figure 2.5.2-1 CRLF Reproductive Events by Month 20
Figure 2.5.4-1. Initial area of concern, or "footprint" of potential use, for norflurazon.. 26
Figure 2.9.2-1 Conceptual Model for Norflurazon Effects on Aquatic Phase of the CRLF
32
Figure 2.9.2-2 Conceptual Model for Norflurazon Effects on Terrestrial Phase of the
CRLF 33
Appendix A Norflurazon CDPR Data
Appendix B CRLF Spatial Summary
Appendix C Sample TREX Output
Appendix D Sample TerrPlant Output
Appendix D Papers Excluded from ECOTOX
Appendix E Norflurazon ECOTOX
Appendix G HED Norflurazon
Attachment 1 Life History of the California red-legged frog
Attachment 2 Baseline Status and Cumulative Effects for the California red-legged frog
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1.0 Executive Summary
The purpose of this assessment is to evaluate potential direct and indirect effects on the
California red-legged frog (Rana aurora draytonii) (CRLF) arising from FIFRA
regulatory actions regarding use of norflurazon on agricultural and non-agricultural sites.
In addition, this assessment evaluates whether these actions can be expected to result in
modification of the species' designated critical habitat. This assessment was completed
in accordance with the U.S. Fish and Wildlife Service (USFWS) and National Marine
Fisheries Service (NMFS) Endangered Species Consultation Handbook (USFWS/NMFS,
1998 and procedures outlined in the Agency's Overview Document (U.S. EPA, 2004).
The CRLF was listed as a threatened species by USFWS in 1996. The species is endemic
to California and Baja California (Mexico) and inhabits both coastal and interior
mountain ranges. A total of 243 streams or drainages are believed to be currently
occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and
Santa Barbara counties (USFWS, 1996) in California.
Norflurazon was registered in the United States in 1974 as a broad spectrum pre-
emergent herbicide used to control germinating annual grasses and broadleaf weeds in
certain crop and noncrop areas. Norflurazon is currently labeled for use on alfalfa,
avocado, cranberries, cotton, orchard crops (e.g. almonds, walnuts, apples, cherries),
blueberries, caneberries, citrus, grapes, hops, soybeans and non-agricultural uses (e.g.
industrial areas (outdoors), rights-of-way (ROWs), refuse/solid waste sites) and nursery
stock. All of the current uses are considered as part of the federal action evaluated in this
assessment, with the exception of soybeans and cranberries because these crops are not
grown in California and cotton because norflurazon is not registered for this use in the
state of California.
Norflurazon is formulated as a liquid concentrate. Application method for most uses of
norflurazon is limited to ground spray. Aerial application is permitted for alfalfa, at a
much lower application rate. Risks from ground boom and aerial applications are
expected to result in the highest off-target levels of norflurazon due to generally higher
spray drift levels.
Norflurazon is persistent and weakly sorbs to soil. According to the Food and Agriculture
Organization (FAO) classification scheme the compound would be classified as
moderately mobile and may readily move into ground water (depending on the
permeability of the soil) and surface water. The primary route of dissipation appears to
be photodegradation in water and on soil. Norflurazon is stable to hydrolysis and
biodegrades slowly in soil and water under aerobic and anaerobic conditions.
Norflurazon has relatively low volatility and is soluble in water. Therefore, potential
transport mechanisms considered in this assessment are limited to spray drift,
groundwater discharge and runoff, as volatilization and atmospheric transport are not
expected to occur. Because of its persistence, substantial fractions of applied norflurazon
could be available for runoff for several months post-application. The moderate
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soil/water partitioning of norflurazon indicates that norflurazon runoff may occur through
runoff of dissolved and sediment-bound residues (erosion).
This assessment quantitatively considers exposure from parent norflurazon as well as the
desmethyl degradation product. Desmethyl norflurazon is a major degradate that is
slowly formed from biodegradation under aerobic and anaerobic conditions in soil and
aquatic systems. Desmethyl norflurazon was still increasing at the end of the aerobic soil
metabolism and anaerobic aquatic metabolism study and may be more stable than the
parent compound. Desmethyl norflurazon was detected in 50% of surface water samples
nationwide in the NAWQA monitoring program further suggesting that it is more
persistent than the parent compound. Laboratory data on the mobility of desmethyl
norflurazon are limited to peat soils, in which it was found to be moderately mobile.
Since CRLFs exist within aquatic and terrestrial habitats, exposure of the CRLF, its prey
and its habitats to norflurazon are assessed separately for the two habitats. The Tier-II
aquatic exposure models Pesticide Root Zone Model (PRZM) and Exposure Analysis
Modeling System (EXAMS) are used to estimate high-end exposures of norflurazon in
aquatic habitats resulting from runoff and spray drift from different uses. Peak aquatic
model-estimated environmental concentrations (EEC) of total toxic residues (norflurazon
and desmethyl norfluazon) range from 5.0 to 79 |ig/L for various uses. These estimates
are supplemented with analysis of available California surface water monitoring data
from U. S. Geological Survey's National Water Quality Assessment (NAWQA) program
and the California Department of Pesticide Regulation. Surface water monitoring studies
which specifically targeted norflurazon use (application period and/or sites) were not
available for analysis as part of this assessment. The maximum concentration of
norflurazon reported by NAWQA for California surface waters with agricultural
watersheds is 0.62 |ig/L. This value is approximately 127 times less than the maximum
model-estimated environmental concentration. The maximum concentration of
norflurazon reported by the California Department of Pesticide Regulation surface water
database (0.98 |ig/L) is roughly 81 times lower than the highest 1-inlO year peak model-
estimated environmental concentration. It is important to note these are detections of
parent norflurazon only. Although not an analyte in the California monitoring program,
NAWQA reports that the desmethyl degradate was detected in 50% of surface water
samples nationwide at concentrations up to 6.1 |ig/L. A Prospective Groundwater
(PGW) study in the Central Ridge of Florida had detections of norflurazon and the
desmethyl degradate at peak concentrations of 29.9 and 23.8 |ig/L, respectively.
The T-REX model is used to estimate forage item residues of norflurazon for exposures
to the terrestrial-phase CRLF and its potential prey. The AgDRIFT model is used to
estimate deposition of norflurazon on terrestrial and aquatic habitats from spray drift.
The TerrPlant model is used to estimate norflurazon exposures to terrestrial-phase CRLF
habitat, including plants inhabiting semi-aquatic and dry areas, resulting from uses
involving foliar applications. The T-HERPS model is used to characterize dietary
exposures of terrestrial-phase CRLFs relative to birds.
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The effects determination assessment endpoints for the CRLF include direct toxic effects
on the survival, reproduction, and growth of the CRLF itself, as well as indirect toxic
effects, such as reduction of the CRLF prey base or modification of CRLF habitat. In the
absence of aquatic phase-phase amphibian toxicity data, direct effects to the CRLF in the
aquatic habitat are based on toxicity information for freshwater fish, which are generally
used as a surrogate for aquatic-phase amphibians. In the absence of terrestrial-phase
amphibian toxicity data, direct effects are based on toxicity information for birds, which
are used as a surrogate for terrestrial-phase amphibians. Given that the CRLF's prey
items and designated critical habitat requirements in the aquatic habitat are dependant on
the availability of freshwater aquatic invertebrates and aquatic plants, toxicity
information for these taxonomic groups is also discussed. In the terrestrial habitat,
indirect effects due to depletion of prey are assessed by considering effects to terrestrial
insects, small terrestrial mammals, and frogs. Indirect effects due to modification of the
terrestrial habitat are characterized by available data for terrestrial monocots and dicots.
Norflurazon is practically nontoxic on an acute exposure basis to aquatic and terrestrial
animal species. No chronic effects to aquatic fauna were observed in the available
toxicity studies, although chronic effects are present for birds (and by extension
terrestrial-phase CRLFs) and mammals. As expected with an herbicide, there are
deleterious effects to plants, both aquatic and terrestrial. Given the structural similarities
between the desmethyl degradate and parent norflurazon, equal toxicity is assumed in the
absence of data indicating otherwise.
Risk quotients (RQs) are derived as quantitative estimates of potential high-end risk.
Acute and chronic RQs are compared to the Agency's levels of concern (LOCs) to
identify instances where norflurazon use within the action area has the potential to
adversely affect the CRLF and its designated critical habitat via direct toxicity or
indirectly based on direct effects to its food supply {i.e., freshwater invertebrates, algae,
fish, frogs, terrestrial invertebrates, and mammals) or habitat {i.e., aquatic plants and
terrestrial upland and riparian vegetation). When RQs for each particular type of effect
are below LOCs, the pesticide is determined to have "no effect" on the CRLF. Where
RQs exceed LOCs, a potential to cause adverse effects is identified, leading to a
conclusion of "may affect." If a determination is made that use of norflurazon use within
the action area "may affect" the CRLF and its designated critical habitat, additional
information is considered to refine the potential for exposure and effects, and the best
available information is used to distinguish those actions that "may affect, but are not
likely to adversely affect" (NLAA) from those actions that are "likely to adversely affect"
(LAA) the CRLF and modify its critical habitat.
Analysis indicates there is an overlap between norflurazon use areas and CRLF habitat.
Based on the best available information, the Agency makes a may affect and likely to
adversely affect determination for the CRLF from the use of norflurazon. Additionally,
the Agency has determined that there is potential for modification of CRLF designated
critical habitat from the use of the chemical. This determination is based on direct
chronic effects to the terrestrial-phase CRLF and, indirectly, to its terrestrial-phase
amphibian and mammalian prey base. Potential effects to aquatic nonvascular plants and
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terrestrial plants may result in disruption of the CRLF food source and critical habitat. A
summary of the risk conclusions and effects determinations for the CRLF and its critical
habitat is presented in Table 1.1 and Table 1.2. Further information on the results of the
effects determination is included as part of the Risk Description in Section 5.2.
Table 1.1 Effects Determination Summary for Norflurazon Use and the CRLF
Assessment
Endpoint
Effeets
Determination 1
Basis for Determination
Survival, growth,
and/or reproduction
of CRLF
individuals
LAA
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults) :
No effects to freshwater fish (as a surrogate to the aquatic-phase frog) that result
in acute and/or chronic risk LOC exceedances
Terrestrial-phase (Juveniles and Adults) :
Chronic effects to birds (as a surrogate to the terrestrial-phase frog) result in
exceedance of the chronic risk LOC
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary productivity
No effects to freshwater invertebrates, fish or frogs or are expected. Effects to
non-vascular aquatic plants result in exceedance of the LOC, and for locations
proximal to ROWs, effects to vascular aquatic plants may occur.
Terrestrial prey items, riparian habitat
Chronic effects to small terrestrial vertebrates including mammals and terrestrial-
phase amphibians (using birds as a surrogate), and effects to terrestrial plants,
result in LOC exceedances
1 No effect (NE); May affect, but not likely to adversely affect (NLAA); May affect, likely to adversely
affect (LAA)
Table 1.2 Effects Determination Summary for Norflurazon Use and CRLF Critical
Habitat Impact Analysis
Assessment
Endpoint
Effects
Determination 1
Basis for Determination
Modification of
aquatic-phase PCE
HM1
Effects to riparian vegetation (terrestrial plants) and aquatic nonvascular
plants result in LOC exceedances. Exposure to aquatic vascular plants
proximal to use on ROWs may be sufficient to elicit deleterious effects.
These effects may indirectly affect the CRLF via reduction in food supply,
changes in available cover, physical parameters of the waterbody (e.g.
increase temperature or turbidity)
Modification of
terrestrial-phase
PCE
Effects to riparian vegetation (terrestrial plants) result in LOC exceedances,
based on the seedling emergence study. Effects may result in changes in
community composition or relative abundance of riparian plant species,
possibly altering terrestrial - phase CRLF habitat
1 Habitat Modification or No Effect (NE)
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Based on the conclusions of this assessment, a formal consultation with the U. S. Fish
and Wildlife Service under Section 7 of the Endangered Species Act should be initiated.
When evaluating the significance of this risk assessment's direct, indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the 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 modification to critical habitat.
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2.0 Problem Formulation
Problem formulation provides a strategic framework for the risk assessment. By
identifying the important components of the problem, it focuses the assessment on the
most relevant life history stages, habitat components, chemical properties, exposure
routes, and endpoints. The structure of this risk assessment is based on guidance
contained in U.S. EPA's Guidance for Ecological Risk Assessment (U.S. EPA 1998), the
Services' Endangered Species Consultation Handbook (USFWS/NMFS 1998) and is
consistent with procedures and methodology outlined in the Overview Document (U.S.
EPA 2004) and reviewed by the U.S. Fish and Wildlife Service and National Marine
Fisheries Service (USFWS/NMFS 2004).
2.1 Purpose
The purpose of this endangered species assessment is to evaluate potential direct and
indirect effects on individuals of the federally threatened California red-legged frog
(Rana aurora draytonii) (CRLF) arising from FIFRA regulatory actions regarding use of
norflurazon on alfalfa, avocado, orchard crops (e.g. almonds, walnuts, apples, cherries),
blueberries, caneberries, citrus, grapes, hops and non-agricultural uses (e.g. industrial
areas (outdoors), rights-of-way, refuse/solid waste sites, nursery stock). In addition, this
assessment evaluates whether these uses are expected to result in modification of the
species' designated critical habitat. This ecological risk assessment has been prepared
consistent with a settlement agreement in the case Center for Biological Diversity (CBD)
vs. EPA et al. (Case No. 02-1580-JSW(JL)) entered in Federal District Court for the
Northern District of California on October 20, 2006.
In this assessment, direct and indirect effects to the CRLF and potential modification to
its designated critical habitat are evaluated in accordance with the methods described in
the Agency's Overview Document (U.S. EPA 2004). Screening level methods include
use of standard models such as PRZM-EXAMS, T-REX, TerrPlant, and AgDRIFT, all of
which are described at length in the Overview Document. Additional refinements
include the use of the T-HERPS model to better characterize the potential for direct acute
effects to the terrestrial-phase CRLF. Use of such information is consistent with the
methodology described in the Overview Document (U.S. EPA 2004), which specifies that
"the assessment process may, on a case-by-case basis, incorporate additional methods,
models, and lines of evidence that EPA finds technically appropriate for risk management
objectives" (Section V, page 31 of U.S. EPA 2004).
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 norflurazon is based on an action area. The action area is the area directly
or indirectly affected by the federal action, as indicated by the exceedances of the
Agency's Levels of Concern (LOCs). It is acknowledged that the action area for a
national-level FIFRA regulatory decision associated with a use of norflurazon 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
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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 specific uses of norflurazon in accordance with current labels:
"No effect";
"May affect, but not likely to adversely affect"; or
"May affect and likely to adversely affect".
Designated critical habitat identifies specific areas that have the physical and biological
features, (known as primary constituent elements or PCEs) essential to the conservation
of the listed species. 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.
If the results of initial screening-level assessment methods show no direct or indirect
effects (i.e. no LOC exceedances) upon individual CRLFs or upon the PCEs of the
species' designated critical habitat, a "no effect" determination can be made for use of
norflurazon as it relates to this species and its designated critical habitat. If, however,
potential direct or indirect effects to individual CRLFs are anticipated 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 norflurazon.
If a determination is made that use of norflurazon within the action area(s) associated
with the CRLF "may affect" this species 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 norflurazon use sites) and further evaluation of the potential impact of
norflurazon on the PCEs is also used to determine whether modification of designated
critical habitat may occur. Based on the refined information, the Agency uses the best
available information to distinguish 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 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 norflurazon is expected to directly impact living organisms within the action
area (defined in Section 2.7), critical habitat analysis for norflurazon is limited in a
practical sense to those PCEs of critical habitat that are biological or that can be
reasonably linked to biologically-mediated processes (i.e., the biological resource
requirements for the listed species associated with the critical habitat or important
physical aspects of the habitat that may be reasonably influenced through biological
processes). Activities that may modify critical habitat are those that alter the PCEs and
appreciably diminish the value of the habitat. Evaluation of actions related to use of
norflurazon that may alter the PCEs of the CRLF's critical habitat form the basis of the
7
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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.
2.2 Scope
Norflurazon is a pre-emergent herbicide with broad spectrum activity on grasses, broad
leaf weeds and sedges. It is registered for use on 25 crops, 27 field grown ornamental
trees and shrubs, and non-cropland uses. Primary use sites in California include alfalfa,
avocado, orchard crops (e.g. almonds, walnuts, apples, cherries), blueberries, caneberries,
citrus, grapes, hops, and, to a lesser extent, non-agricultural uses (e.g. industrial areas
(outdoors), rights-of-way, refuse/solid waste sites, nursery stock).
The end result of the EPA pesticide registration process (i.e., the FIFRA regulatory
action) is an approved product label. The label is a legal document that stipulates how
and where a given pesticide may be used. Product labels (also known as end-use labels)
describe the formulation type (e.g., liquid or granular), acceptable methods of application,
approved use sites, and any restrictions on how applications may be conducted. Thus, the
use or potential use of norflurazon in accordance with the approved product labels for
California is "the action" relevant to this ecological risk assessment.
Although current registrations of norflurazon allow for use nationwide, this ecological
risk assessment and effects determination addresses currently registered uses of
norflurazon 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.
This assessment quantitatively considers exposure from parent norflurazon as well as the
desmethyl degradation product. Desmethyl norflurazon is a major degradate that is
slowly formed from biodegradation under aerobic and anaerobic conditions in soil and
aquatic systems. Desmethyl norflurazon was still increasing at the end of the aerobic soil
metabolism and anaerobic aquatic metabolism study and may be more stable than the
parent compound. Desmethyl norflurazon was detected in 50% of surface water samples
nationwide from NAWQA further suggesting that it is more persistent than the parent
compound. Laboratory data on the mobility of desmethyl norflurazon are limited to peat
soils, in which it was found to be moderately mobile. Although there are no data on the
toxicity of desmethyl norflurazon, given the similarity in chemical structure to the parent
this assessment assumes equal toxicity and uses a total toxic residues approach.
2.3 Previous Assessments
Norflurazon was registered in the United States in 1974 as a broad spectrum pre-
emergent herbicide used to control germinating annual grasses and broadleaf weeds in
certain crop and noncrop areas. The Registration Standard was issued in December 1984.
A Reregi strati on Eligibility Decision (RED) was issued in 1995 and concluded that data
suggest that norflurazon leaches to ground water as a result of normal agricultural use
8
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triggering the requirement of a Prospective Groundwater (PGW) Study. For this reason,
norflurazon product labels carry a ground water advisory.
2.4 Stressor Source and Distribution
2.4.1 Environmental Fate Assessment
Norflurazon (4-chloro-5-(methylamino)-2-(a,a,a-trifluoro-m-tolyl)-3-(2H)-pyridazinon)
is persistent and weakly sorbs to soil. According to the Food and Agriculture
Organization (FAO) classification scheme, norflurazon would be classified as moderately
mobile and may readily move into ground water (depending on the permeability of the
soil) and surface water. The primary route of dissipation appears to be photodegradation
on soil and in water when the compound is present on the surface of the soil or in clear
and shallow surface water under favorable light conditions. Norflurazon degrades slowly
in aerobic soil conditions. In addition, norflurazon is resistant to biotic degradation
under aerobic and anaerobic aquatic conditions and is stable to hydrolysis. Norflurazon
has relatively low volatility (1.5 xlO"5 torr) and is soluble in water (28 ppm, at 20°C).
The Log Kow of norflurazon is 2.3 indicating the compound has a low potential to
bioaccumulate; a fish bioconcentration study also indicates that norflurazon has a low
potential to bioconcentrate. Bioconcentration factors ranged from 6 to 8X, 16 to 28X,
and 30 to 59X for fillet, whole fish and viscera, respectively. Tissue residues decreased
(depurated) rapidly when fish were moved to clean water; greater than 90%, 96%, and
97%) of the radio-labeled norflurazon was eliminated from fillet, whole fish, and viscera,
respectively after 14 days. General chemical properties of norflurazon are summarized in
Table 2.1.
9
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Table 2.1. General Chemical Properties
Parameter
Value
Reference
PC code
105801
CAS No.
27314-13-2
Structure
Chemical name
4-chloro-5-(methylamino)-2-(a,a,a-trifluoro-m-
tolyl)-3 -(2H)-pyridazinon
Chemical formula
C12H9C1F3N30
Molecular weight
303.7 g/mol
Water solubility (20 °C)
28 mg/L
Product chemistry
Vapor pressure
1.5 xlO"5 torr
Product chemistry
Henry's law constant
2.1 x 10"7 atm-m3/mol
Calculated
Log Kqw
2.3
U.S. EPA 1998
Photodegradation of norflurazon is rapid in clear, shallow surface water (ti/2 = 2-3 d, pH
7) and on soil (ti/2 = 12-15 d) resulting in the formation of a dimer (two molecules
covalently bonded) and the degradates desmethyl norflurazon, and deschloronorflurazon.
However, direct photolytic degradation of the parent or its degradates in turbid and/or
deeper waters will be limited by the attenuation of sunlight. Norflurazon degrades slowly
under aerobic soil conditions (ti/2 = 130 d in loam) forming desmethyl norflurazon and
carbon dioxide. In addition, norflurazon is resistant to biotic degradation under aerobic
and anaerobic aquatic conditions with half lives ranging from six to eight months and is
stable to hydrolysis at pH 5, 7 and 9.
Norflurazon is moderately to slightly mobile (based on the Food and Agricultural
Organization classification scheme), with Freundlich adsorption coefficients (Kf) that
range from 0.14 (in sand) to 72.5 ml/g (in peat) (Kfoc = 205 to 1,532 ml/goc) for 13 soils.
The Kfoc numbers were calculated using the soil-organic matter basis rather than the soil-
organic carbon basis, therefore, a conversion factor of 1.724 was applied to the organic
matter partition coefficient (Kom) to arrive at the Kfoc. Adsorption of norflurazon to these
13 soils is correlated to organic carbon content and cation exchange capacity (CEC).
In the aqueous photolysis study, the only major transformation product was the
norflurazon dimer that was detected at 16% of the parent at 3 days. In addition, two
minor degradates, desmethyl norflurazon and deschloroflurazon accounted for 7% and
8% of parent at 3 days, respectively. Desmethyl norflurazon and carbon dioxide are
major degradates that are slowly formed under aerobic soil conditions, accounting for
approximately 31-36% and 23-31%, respectively of parent at 365 days. Desmethyl
10
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norflurazon was still increasing at the end of the aerobic soil metabolism and anaerobic
aquatic metabolism studies and may be more stable than the parent compound.
Desmethyl norflurazon and carbon dioxide are also formed via anaerobic aquatic
metabolism accounting for 19 % and 8% of parent at 365 days. Desmethyl norflurazon is
formed under aerobic aquatic conditions at 11% of parent by 90 days. The mobility of
the major degradate, desmethyl norflurazon, is not currently well defined except in peat
soils. Freundlich Kads were 22 and 41 mL/g and Freundlich Koc were 329 and 60 mL/goc,
for a Wisconsin peat and a Washington peat, respectively. Based on these data, it can be
concluded that desmethyl norflurazon is moderately mobile in high organic content peat
soils. No laboratory data are available for the mobility of desmethyl norflurazon in any
additional soils, however, it has been detected in 50% of NAWQA surface water
monitoring samples nationwide. Additionally, a Prospective Groundwater (PGW) study
conducted in 1994 on the Central Ridge of Florida had detections of norflurazon and the
desmethyl degradate at peak concentrations of 29.9 and 23.8 |ig/L, respectively. Table
2.2 lists the environmental fate properties of norflurazon, along with the major and minor
degradates detected in the submitted environmental fate and transport studies.
Table 2.2. Summary of Norflurazon Environmental Fate Properties
Study
Value (units)
Major Degradates
Minor Degradates
MRID #
Study Status
Hydrolysis
Stable at pH 5, 7 and 9
-
00146165
Acceptable
Direct
Aqueous
Photolysis
pH 7: DT50 = 2-3 d (parent)
pH 7: ti/2 = 3 d (parent and
desmethyl)
Norflurazon dimer
(Desmethyl norflurazon
and
Deschloronorflurazon)
00148311
Acceptable
Soil
Photolysis
DT50 = 12-15 d
(Desmethyl
Norflurazon)
00148311
Acceptable
Aerobic Soil
Metabolism
ti/2 = 130 d (loam; parent)
ti/2 = 375 d (parent and desmethyl)
Desmethyl
Norflurazon, Carbon
Dioxide
40079601
Acceptable
Anaerobic
Soil
Metabolism
No data
--
--
--
Anaerobic
Aquatic
Metabolism
DT50 = 8 months (loam)
ti/2 = 678 d (parent and desmethyl)
Desmethyl
Norflurazon, Carbon
Dioxide
40079601
Acceptable
Aerobic
Aquatic
Metabolism
DT50 = 6-8 months (loam)
ti/2 = 275 d (parent and desmethyl)
Desmethyl Norflurazon
40079601
Acceptable
Freundlich
Kads (mL/g),
Koc- ads
(mL/g0c)
1) 0.716 (1/n = 0.939), 206 (sand)
2.37 (1/n = 0.802), 681 (sandy
loam)
2.51 (l/n= 0.863), 618 (silt loam)
1)41986904
2)00148312
3)42710901
4)43681001
1) Acceptable
2) Acceptable
3) Acceptable
4) Supplemental
11
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Study
Value (units)
Major Dcgradatcs
Minor Degradates
mrii) #
Study Status
2.77 (l/n= 0.825), 531 (sediment)
7.11(l/n = 0.786), 1532 (clay
loam)
2) 1.9 (l/n= 0.75), 1092 (loam)
2.3 (l/n= 0.80), 441 (loam)
1.9 (l/n= 0.75), 1092 (sediment)
2.2 (l/n= 0.79), 1264 (sandy
loam)
26 (1/n = 0.74), 393 (clay)
0.14 (l/n= 0.84), 241 (sand)
3) 72.5, 1082 (peat)
62.6, 915 (peat)
4) 22.1 (1/n = 0.914), 330 (peat)
41.4 (1/n =0.912), 605 (peat)
(desmethyl norflurazon only)
2.4.2 Environmental Transport Assessment
Potential transport mechanisms include pesticide surface water runoff, groundwater
recharging surface water, spray drift, and secondary drift of volatilized or soil-bound
residues leading to deposition onto nearby or more distant ecosystems. Surface water
runoff and spray drift are expected to be the major routes of exposure for norflurazon;
although under certain soil conditions, i.e., high organic content, the compound could
move via runoff of sediment-bound residues (erosion).
In general, deposition of drifting pesticides is expected to be greatest close to the site of
application. The computer model of spray drift (AgDRIFT) is used to determine
potential exposures to aquatic and terrestrial organisms via spray drift at distance from
the use site.
2.4.3 Mechanism of Action
Norflurazon is a pre-emergent herbicide with broad spectrum activity on grasses, broad
leaf weeds and sedges. Norflurazon is a carotenoid synthesis inhibitor that disrupts the
plant's ability to produce carotenoid pigments. Carotenoids absorb blue light energy for
photosynthesis and protects chlorophyll from damage. Norflurazon is generally active
only through root uptake.
2.4.4 Use Characterization
Nationally, uses include alfalfa, avocado, cranberries, cotton, orchard crops (e.g.
almonds, walnuts, apples, cherries), blueberries, caneberries, citrus, grapes, hops,
soybeans and non-agricultural uses (e.g. industrial areas (outdoors), rights-of-way,
refuse/solid waste sites, nursery stock). All of the current uses are considered as part of
12
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the federal action evaluated in this assessment, with the exception of soybeans and
cranberries because these crops are not grown in California and cotton because
norflurazon is not registered for this use in the state of California.
Norflurazon is formulated as a liquid concentrate. Application method for most uses of
norflurazon is limited to ground spray. Aerial application is permitted for alfalfa, at a
much lower application rate. Risks from ground boom and aerial applications are
expected to result in the highest off-target levels of norflurazon due to generally higher
spray drift levels.
Analysis of labeled use information is the critical first step in evaluating the federal
action. The current labels for norflurazon 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. Table 2.3 presents the
uses and corresponding application rates and methods of application considered in this
assessment. In cases where application parameters are not explicitly prescribed on the
labels, reasonable conservative assumptions were employed. For instance, the label for
the alfalfa application does not specify a re-application interval. For this assessment, a
seven day re-application interval was assumed to be a reasonable period of time between
when a farmer would re-apply a pre-emergent herbicide treatment to a field. In addition,
for uses such as tree nuts {i.e. almonds, pecans, etc.), grapes, hops, and tree fruits {i.e.
apples, apricots, etc.) one application was assumed because the label specifies that no
more than 3.93 lb ai/A should be applied per year. There are no multiple a.i. products
formulated with norflurazon.
13
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Table 2.3. Norflurazon Uses Assessed for the CRLF
Use(s)
Maximum Single
Application Rate
(lbs a.i./A)
Number of
Applications Per
Year
Annual Application
Rate (lbs a.i./A)
Application
Interval (days)
Application
Method
Alfalfa
0.983
2
1.966
7 (assumed)
Aerial, Ground
boom sprayer
Almonds, walnuts,
filberts, pecans
3.93
NS1 (1 assumed)
3.93
NA1
Ground boom
sprayer
Avocado
3.93
NS1 (1 assumed)
3.93
NA1
Ground boom
sprayer
Blueberries
3.93
NS1 (1 assumed)
3.93
NA1
Ground boom
sprayer
Caneberries
(Raspberries and
Blackberries)
3.93
NS1 (1 assumed)
3.93
NA1
Ground boom
sprayer
Citrus
Ground boom
3.93
NS1 (1 assumed)
3.93
NA1
sprayer,
drip/sprinkler
irrigation
Apples, Apricots,
nectarines, peaches,
pears, cherries,
plums, prunes
3.93
NS1 (1 assumed)
3.93
NA1
Ground boom
sprayer
Grapes
3.93
NS1 (1 assumed)
3.93
NA1
Ground boom
sprayer
Hops
3.93
NS1 (1 assumed)
3.93
NA1
Ground boom
sprayer
Nursery Stock
2.358
1
2.358
NA1
Ground boom
sprayer
Industrial Areas,
Refuse/Solid Waste
Sites (outdoors),
Non Agricultural
ROW/fencerows/he
dgerows, Non
Agricultural
uncultivated
areas/soils
3.93
1
3.93
NA1
Ground boom
sprayer
1 NS = not specified, but implied from annual maximum application rate, NA = not applicable
Figure 2.4.4-1 presents the national agricultural usage pattern of norflurazon in 20021.
Usage was concentrated in California, the Pacific Northwest, the lower Midwest, and in
portions of the eastern and southeastern United States. Cotton and citrus fruit dominated
the agricultural use patterns at that time accounting for an estimated 36% and 29% of
The map was downloaded from a U.S. Geological Survey (USGS), National Water Quality Assessment Program (NAWQA)
website, (http://water.usgs.gov/nawqa/pnsp/usage/maps/compound_listing.php?year=02)
14
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norflurazon usage, respectively (USGS 2007); however, as noted previously, norflurazon
is not registered for use on cotton in California.
NORFLURAZON - herbicide
2002 estimated annual agricultural use
Crops
Total
Percent
pounds applied
national use
cotton
426977
36.74
citrus fruit
341204
29.35
alfalfa hay
69578
5.99
apples
68950
5.93
grapes
62973
5.42
ether hay
44200
3.80
almonds
40431
3.48
peaches
23925
2.06
blueberries
20780
1.79
asparagus
9827
0.85
Average annual use of
active ingredient
(pounds per square mile of agricultural
land in county)
D no estimated use
~ 0.001 to 0.005
~ 0.006 to 0.023
~ 0.024 to 0.126
~ 0.127 to 0.636
¦ >=0.637
Figure 2.4.4-1 Norflurazon Use in Total Pounds per County
The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis
of both national- and county-level usage information (Kaul and Jones, 2006) using state-
level usage data obtained from USDA-NASS2, Doane (www.doane.com; the full dataset
is not provided due to its proprietary nature) and the California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database3. The CDPR PUR database
is considered a more comprehensive source of usage data than USDA-NASS or EPA
proprietary databases, and thus the usage data reported for norflurazon by county in this
California-specific assessment were obtained using CDPR PUR data. Usage data for the
years 1999-2006 of were included in this analysis. Data from CDPR PUR were obtained
for every pesticide application made on every use site at the section level (approximately
one square mile) of the public land survey system. BEAD summarized these data to the
county level by site, pesticide, and unit treated. Calculating county-level usage involved
2 United States Depart of Agriculture (USDA), National Agricultural Statistics Service (NASS) Chemical
Use Reports provide summary pesticide usage statistics for select agricultural use sites by chemical, crop
and state. See http://www.usda.gov/nass/pubs/estindxl.htm#agchem.
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/punnain.htm.
15
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summarizing across all applications made within a section and then across all sections
within a county for each use site and for each pesticide. The county-level usage data that
were calculated include: average annual pounds applied, average annual area treated, and
average and maximum application rate across eight years (1999-2006). The units of area
treated are also provided where available.
A summary of norflurazon usage for all California use sites based on CDPR PUR data is
provided below in Table 2.4. The highest average annual usages in California include
almond (2,409 lbs) and alfalfa (1,823 lbs). These use sites are followed by grape (1,479
lbs) and orange (1,355 lbs). Rights-of-way and industrial uses combined totaled only an
annual average of 320 lbs. Further details are in Appendix A.
Table 2.4. Summary of CDPR PUR Data from 1999 to 2006 for Currently
Registered Norflurazon Uses
Site Name
Avjj Annual
App. (lbs a.i.)
Av$j A|)p Rate
(lbs a.i./A)
95"' %-ile App
Rate (lbs a.i./A)
99"' %-ile App
Rate (lbs a.i./A)
Max App Rate
(lbs a.i./A)
Alfalfa
1823
1.44
2.96
3.68
31.44
Almond
2409.45
1.19
2.41
3.07
9.01
Apple
117.87
1.50
2.20
2.32
8.0
Apricot
101.03
1.07
2.70
3.21
7.86
Asparagus
195.56
2.18
2.67
3.44
8.84
Avocado
242.28
2.60
5.99
6.03
29.48
Blackberry
0.55
0.63
0.63
0.63
0.63
Blueberry
19.87
1.16
1.50
1.50
2.75
Buildings/ Non-Ag Outdoor
0.49
0.79
0.79
0.79
0.79
Cherry
95.03
1.23
2.03
3.39
11.79
Citrus
98.39
1.89
3.14
3.73
4.72
Grape
1478.97
0.95
1.80
2.51
13.36
Grapes, wine
432.15
1.48
2.30
3.38
18.08
Grapefruit
53.31
1.65
2.49
2.83
6.29
Lemon
161.19
1.41
2.62
2.98
3.93
Nectarine
272.95
1.13
2.08
2.53
8.52
Orange
1355.48
1.34
2.71
3.02
23.58
Non-Agriculture: rights of
way/fencerow/hedgerows
314.10
1.561
1.561
1.561
1.561
Non-Agriculture Areas
6.59
2.30
2.58
2.58
6.29
Peach
349.38
1.35
2.65
3.24
15.72
Pear
49.84
1.62
2.41
2.44
3.93
Pecan
12.94
1.63
1.87
1.87
3.93
Plum
465.53
1.19
2.23
2.49
12.58
Prune
317.71
1.69
2.71
3.95
14.15
Tangelo
39.28
1.47
2.66
3.83
9.83
Tangerine
618.64
1.72
2.35
2.91
30.71
Uncultivated agriculture
24.35
1.74
2.16
2.16
3.93
16
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Site Name
Avjj Annual
App. (lbs a.i.)
Avg App Rate
(lbs a.i./A)
95"' %-ilc App
Rate (lbs a.i./A)
99"' %-ilc App
Rate (lbs a.i./A)
Max App Rate
(lbs a.i./A)
Walnut (English, black)
303.82
1.51
2.70
3.74
15.72
Average
11359.75
1.48
2.39
2.85
10.98
1 = Indicates an incomplete data set because most records lacked usage data.
There are some inconsistencies between the current product labels and the CDPR PUR
data. Some uses reported in the CDPR PUR data are not currently allowed by label in
California for these uses. This assessment is conducted on the current labeled uses for
California. Additionally, the maximum application rates reported often exceed the
maximum allowed by the current label. The current legal uses upon which this
assessment is based, are listed in table 2.3.
2.5 Assessed Species
The CRLF was federally listed as a threatened species by USFWS effective June 24,
1996 (USFWS 1996). It is one of two subspecies of the red-legged frog and is the largest
native frog in the western United States (USFWS 2002). A brief summary of information
regarding CRLF distribution, reproduction, diet, and habitat requirements is provided in
Sections 2.5.1 through 2.5.4, respectively. Further information on the status, distribution,
and life history of and specific threats to the CRLF is provided in Attachment 1.
Final critical habitat for the CRLF was designated by USFWS on April 13, 2006
(USFWS 2006; 71 FR 19244-19346). Further information on designated critical habitat
for the CRLF is provided in Section 2.6.
2.5.1 Distribution
The CRLF is endemic to California and Baja California (Mexico) and historically
inhabited 46 counties in California including the Central Valley and both coastal and
interior mountain ranges (USFWS 1996). Its range has been reduced by about 70%, and
the species currently resides in 22 counties in California (USFWS 1996). The species has
an elevational range of near sea level to 1,500 meters (5,200 feet) (Jennings and Hayes
1994); however, nearly all of the known CRLF populations have been documented below
1,050 meters (3,500 feet) (USFWS 2002).
Populations currently exist along the northern California coast, northern Transverse
Ranges (USFWS 2002), foothills of the Sierra Nevada (5-6 populations), and in southern
California south of Santa Barbara (two populations) (Fellers 2005a). Relatively larger
numbers of CRLFs are located between Marin and Santa Barbara Counties (Jennings and
Hayes 1994). A total of 243 streams or drainages are believed to be currently occupied
by the species, with the greatest numbers in Monterey, San Luis Obispo, and Santa
Barbara counties (USFWS 1996). Occupied drainages or watersheds include all bodies
of water that support CRLFs (i.e., streams, creeks, tributaries, associated natural and
artificial ponds, and adjacent drainages), and habitats through which CRLFs can move
(i.e., riparian vegetation, uplands) (USFWS 2002).
17
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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 2.5.1-1), Recovery units, core areas, and other known occurrences of the CRLF
from the CNDDB are described in further detail in this section and Attachment 1; 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.
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Recovery Units
1. Sierra Nevada Foothills and Central Valley
2. North Coast Range Foothills and Western
Sacramento River Valley
3. North Coast and North San Francisco Bay
4. South and East San Francisco Bay
5. Central Coast
6. Diablo Range and Salinas Valley
7. Northern Transverse Ranges and Tehachapi
Mountains
8. Southern Transverse and Peninsular Ranges
Core Areas
1.
Feather River
19.
Watsonville Slough-Elkhorn Slough
2.
Yuba River- S. Fork Feather River
20.
Carmel River Santa Lucia
3.
Traverse Creek Middle Fork/ American R. Rubicon
21.
Gahlan Range
4.
Cosumnes River
22.
Estero Bay
5.
South Fork Calaveras River*
23.
Arroyo Grange River
6.
Tuolumne River*
24.
Santa Maria River Santa Ynez River
7.
Piney Creek*
25.
Sisquoc River
8.
Cottonwood Creek
26.
Ventura River Santa Clara River
9.
Putah Creek - Cache Creek*
27.
Santa Monica Bay Venura Coastal Streams
10.
Lake Berryessa Tributaries
28.
Estrella River
11.
Upper Sonoma Creek
29.
San Gabriel Mountain*
12.
Petaluma Creek Sonoma Creek
30.
Forks of the Mojave*
13.
Pt. Reyes Peninsula
31.
Santa Ana Mountain*
14.
Belvedere Lagoon
32.
Santa Rosa Plateau
15.
Jameson Canyon - Lower Napa River
33.
San Luis Ray*
16.
East San Francisco Bay
34.
Sweetwater*
17.
Santa Clara Valley
35.
Laguna Mountain*
18.
South San Francisco Bay
* Core areas that were historically occupied by the California red-legged frog are not included in the map
CNDDB Occurence Sections
County Boundaries q
180 Miles
_l
Legend
~ Recovery Unit Boundaries ^
|] Currently Occupied Core Areas
I Critical Habitat
Figure 2.5.1-1 Recovery Unit, Core Area, Critical Habitat, and Occurrence
Designations for CRLF
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Other Known Occurrences from the CNDBB
The CNDDB provides location and natural history information on species found in
California. The CNDDB serves as a repository for historical and current species location
sightings. Information regarding known occurrences of CRLFs outside of the currently
occupied core areas and designated critical habitat is considered in defining the current
range of the CRLF. See: http://www.dfg.ca.gov/bdb/html/cnddb info.html for additional
information on the CNDDB.
2.5.2 Reproduction
CRLFs breed primarily in ponds; however, they may also breed in quiescent streams,
marshes, and lagoons (Fellers 2005a). According to the Recovery Plan (USFWS 2002),
CRLFs breed from November through late April. Peaks in spawning activity vary
geographically; Fellers (2005b) reports peak spawning as early as January in parts of
coastal central California. Eggs are fertilized as they are being laid. Egg masses are
typically attached to emergent vegetation, such as bulrushes (Scirpus spp.) and cattails
(Typha spp.) or roots and twigs, and float on or near the surface of the water (Hayes and
Miyamoto 1984). Egg masses contain approximately 2000 to 6000 eggs ranging in size
between 2 and 2.8 mm (Jennings and Hayes 1994). Embryos hatch 10 to 14 days after
fertilization (Fellers 2005a) depending on water temperature. Egg predation is reported
to be infrequent and most mortality is associated with the larval stage (particularly
through predation by fish); however, predation on eggs by newts has also been reported
(Rathburn 1998). Tadpoles require 11 to 28 weeks to metamorphose into juveniles
(terrestrial-phase), typically between May and September (Jennings and Hayes 1994,
USFWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until
the following year) (Fellers 2005b, USFWS 2002). Males reach sexual maturity at 2
years, and females reach sexual maturity at 3 years of age; adults have been reported to
live 8 to 10 years (USFWS 2002). Figure 2.5.2-1 depicts CRLF annual reproductive
timing.
J
F
M
A
M
J
J
A
S
o
N
D
Light Blue = Breeding/Egg Masses
Green = Tadpoles (except those that over-winter)
Orange =
Adults and juveniles can be present all year
Figure 2.5.2-1 CRLF Reproductive Events by Month
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)
20
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via mouthparts designed for effective grazing of periphyton (Wassersug, 1984,
Kupferberg et al.\ 1994; Kupferberg, 1997; Altig and McDiarmid, 1999).
Juvenile and adult CRLFs forage in aquatic and terrestrial habitats, and their diet differs
greatly from that of larvae. The main food source for juvenile aquatic- and terrestrial-
phase CRLFs is thought to be aquatic and terrestrial invertebrates found along the
shoreline and on the water surface. Hayes and Tennant (1985) report, based on a study
examining the gut content of 35 juvenile and adult CRLFs, that the species feeds on as
many as 42 different invertebrate taxa, including Arachnida, Amphipoda, Isopoda,
Insecta, and Mollusca. The most commonly observed prey species were larval alderflies
(Sialis cf. californica), pillbugs (Armadilliadrium vulgare), and water striders (Gerris sp).
The preferred prey species, however, was the sowbug (Hayes and Tennant, 1985). This
study suggests that CRLFs forage primarily above water, although the authors note other
data reporting that adults also feed under water, are cannibalistic, and consume fish. For
larger CRLFs, over 50% of the prey mass may consists of vertebrates such as mice, frogs,
and fish, although aquatic and terrestrial invertebrates were the most numerous food
items (Hayes and Tennant 1985). For adults, feeding activity takes place primarily at
night; for juveniles feeding occurs during the day and at night (Hayes and Tennant 1985).
2.5.4 Habitat
CRLFs require aquatic habitat for breeding, but also use other habitat types including
riparian and upland areas throughout their life cycle. CRLF use of their environment
varies; they may complete their entire life cycle in a particular habitat or they may utilize
multiple habitat types. Overall, populations are most likely to exist where multiple
breeding areas are embedded within varying habitats used for dispersal (USFWS 2002).
Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al.
1997). Dense vegetation 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
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
21
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be found living within streams at distances up to 3 km (2 miles) from their breeding site
and have been found up to 30 m (100 feet) from water in dense riparian vegetation for up
to 77 days (USFWS 2002).
During dry periods, the CRLF is rarely found far from water, although it will sometimes
disperse from its breeding habitat to forage and seek other suitable habitat under downed
trees or logs, industrial debris, and agricultural features (UWFWS 2002). According to
Jennings and Hayes (1994), CRLFs also use small mammal burrows and moist leaf litter
as habitat. In addition, CRLFs may also use large cracks in the bottom of dried ponds as
refugia; these cracks may provide moisture for individuals avoiding predation and solar
exposure (Alvarez 2000).
2.6 Designated Critical Habitat
In a final rule published on April 13, 2006, 34 separate units of critical habitat were
designated for the CRLF by USFWS (USFWS 2006; FR 51 19244-19346).
'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 (Section 7) through prohibition against destruction
or adverse modification with regard to actions carried out, funded, or authorized by a
federal Agency. Section 7 requires consultation on federal actions that are likely to result
in the destruction or adverse modification of critical habitat.
To be included in a critical habitat designation, the habitat must be 'essential to the
conservation of the species.' Critical habitat designations identify, to the extent known
using the best scientific and commercial data available, habitat areas that provide
essential life cycle needs of the species or areas that contain certain primary constituent
elements (PCEs) (as defined in 50 CFR 414.12(b)). PCEs include, but are not limited to,
space for individual and population growth and for normal behavior; food, water, air,
light, minerals, or other nutritional or physiological requirements; cover or shelter; sites
for breeding, reproduction, rearing (or development) of offspring; and habitats that are
protected from disturbance or are representative of the historic geographical and
ecological distributions of a species. The designated critical habitat areas for the CRLF
are considered to have the following PCEs that justify critical habitat designation:
Breeding aquatic habitat;
Non-breeding aquatic habitat;
Upland habitat; and
Dispersal habitat.
Further description of these habitat types is provided in Attachment 1.
22
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Occupied habitat may be included in the critical habitat only if essential features within
the habitat may require special management or protection. Therefore, USFWS does not
include areas where existing management is sufficient to conserve the species. Critical
habitat is designated outside the geographic area presently occupied by the species only
when a designation limited to its present range would be inadequate to ensure the
conservation of the species. For the CRLF, all designated critical habitat units contain all
four of the PCEs, and were occupied by the CRLF at the time of FR listing notice in
April 2006. The FR notice designating critical habitat for the CRLF includes a special
rule exempting routine ranching activities associated with livestock ranching from
incidental take prohibitions. The purpose of this exemption is to promote the
conservation of rangelands, which could be beneficial to the CRLF, and to reduce the rate
of conversion to other land uses that are incompatible with CRLF conservation. Please
see Attachment 1 for a full explanation on this special rule.
USFWS has established adverse modification standards for designated critical habitat
(USFWS 2006). Activities that may destroy or adversely modify critical habitat are those
that alter the PCEs and jeopardize the continued existence of the species. Evaluation of
actions related to use of norflurazon that may alter the PCEs of the CRLF's critical
habitat form the basis of the critical habitat impact analysis. According to USFWS
(2006), activities that may affect critical habitat and therefore result in adverse effects to
the CRLF include, but are not limited to the following:
(1) Significant alteration of water chemistry or temperature to levels beyond the
tolerances of the CRLF that result in direct or cumulative adverse effects to
individuals and their life-cycles.
(2) 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 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.
(4) 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.
(5) Elimination of upland foraging and/or aestivating habitat or 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 (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
23
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the designated critical habitat. Because norflurazon is expected to directly impact living
organisms within the action area, critical habitat analysis for norflurazon is limited in a
practical sense to those PCEs of critical habitat that are biological or that can be
reasonably linked to biologically mediated processes.
2.7 Action Area
For listed species assessment purposes, the action area is considered to be the area
affected directly or indirectly by the federal action and not merely the immediate area
involved in the action (50 CFR 402.02). It is recognized that the overall action area for
the national registration of norflurazon is likely to encompass considerable portions of the
United States based on the large array of agricultural uses. However, the scope of this
assessment limits consideration of the overall action area to those portions that may be
applicable to the protection of the CRLF and its designated critical habitat within the state
of California. The Agency's approach to defining the action area under the provisions of
the Overview Document (USEPA 2004) considers the results of the risk assessment
process to establish boundaries for that action area with the understanding that exposures
below the Agency's defined Levels of Concern (LOCs) constitute a no-effect threshold.
For the purposes of this assessment, attention will be focused on the footprint of the
action (i.e., the area where pesticide application occurs), plus all areas where offsite
transport (i.e., spray drift, downstream dilution, etc.) may result in potential exposure
within the state of California that exceeds the Agency's LOCs.
Deriving the geographical extent of this portion of the action area is based on
consideration of the types of effects that norflurazon may be expected to have on the
environment, the exposure levels to norflurazon that are associated with those effects, and
the best available information concerning the use of norflurazon and its fate and transport
within the state of California. Specific measures of ecological effect for the CRLF that
define the action area include any direct and indirect toxic effect to the CRLF and any
potential modification of its critical habitat, including reduction in survival, growth, and
fecundity as well as the full suite of sublethal effects available in the effects literature.
Therefore, the action area extends to a point where environmental exposures are below
any measured lethal or sublethal effect threshold for any biological entity at the whole
organism, organ, tissue, and cellular level of organization. In situations where it is not
possible to determine the threshold for an observed effect, the action area is not spatially
limited and is assumed to be the entire state of California.
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 norflurazon. An analysis of labeled uses and review of available product labels
was completed. Several of the currently labeled uses are special local needs (SLN) uses
or are restricted to specific states and are excluded from this assessment. In addition, a
distinction has been made between food use crops and those that are non-food/non-
agricultural uses. For those uses relevant to the CRLF, the analysis indicates that, for
norflurazon, the following agricultural uses are considered as part of the federal action
evaluated in this assessment:
24
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alfalfa, avocado, orchard crops (e.g. almonds, filbert, walnuts, apples, apricot,
cherries, nectarines), blueberries, caneberries, citrus, grapes and hops.
In addition, the following non-food or non-agricultural uses are allowed:
industrial areas (outdoors), non agricultural rights-of-way, fencerows, hedgerows,
non agricultural uncultivated areas/soils, refuse/solid waste sites and nursery stock
Following a determination of the assessed uses, an evaluation of the potential "footprint"
of norflurazon use patterns (i.e., the area where pesticide application occurs) is
determined. This "footprint" represents the initial area of concern, based on an analysis
of available land cover data for the state of California. The initial area of concern is
defined as all land cover types and the stream reaches within the land cover areas that
represent the labeled uses described above. A map representing all the land cover types
that make up the initial area of concern for norflurazon is presented in Figure 2.5.4-1.
25
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Norflurazon Initial Area of Concern
Developed-open space
Developed-low density
Developed-medium density
Developed-high density
Pasturehay use
Orchard vineyard use
Cultivated crop use
County boundaries
i Kilometers
0 20 40 80 120 160
Compiled from California County boundaries (ESRI, 2002),
USQA Gap Analysis Program Orchard* Vineyard Landcover (GAP)
National Land Ccwer Database (NLCD) (MRLC, 2001)
Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Erwironmental Fate and Effects Division.
Projection: Albers Equal Area Conic USGS, North American
Datum of 1083 (NAD 1 083).
Produced 11/13/2008
Figure 2.5.4-1. Initial area of concern, or "footprint" of potential use, for
norflurazon.
Once the initial area of concern is defined, the next step is to define the potential
boundaries of the action area by determining the extent of offsite transport via spray drift
26
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and runoff where exposure of one or more taxonomic groups to the pesticide exceeds the
listed species LOCs.
As previously discussed, the action area is defined by the most sensitive measure of
direct and indirect ecological toxic effects including reduction in survival, growth,
reproduction, and the entire suite of sublethal effects from valid, peer-reviewed studies.
Due to the lack of a defined no observed adverse effect concentration for the most
sensitive reported chronic toxicity endpoint (maternal body weight) in mammals from a
rat developmental toxicity study (MRID 00063621), the spatial extent of the action area
(i.e., the boundary where exposures and potential effects are less than the Agency's LOC)
for norflurazon cannot be determined. Therefore, it is assumed that the action area
encompasses the entire state of California, regardless of the spatial extent {i.e., initial area
of concern or footprint) of the pesticide use(s).
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."4 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
norflurazon (e.g., runoff, spray drift, etc.), and the routes by which ecological receptors
are exposed to norflurazon (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 or modification of its habitat. In addition, potential modification of critical
habitat is assessed by evaluating potential effects to PCEs, which are components of the
habitat areas that provide essential life cycle needs of the 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. It should be noted
that assessment endpoints are limited to direct and indirect effects associated with
survival, growth, and fecundity, and do not include the full suite of sublethal effects used
to define the action area. According the Overview Document (USEPA 2004), the
Agency relies on acute and chronic effects endpoints that are either direct measures of
impairment of survival, growth, or fecundity or endpoints for which there is a
scientifically robust, peer reviewed relationship that can quantify the impact of the
measured effect endpoint on the assessment endpoints of survival, growth, and fecundity.
4FromU.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
27
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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 4.0 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 norflurazon is provided in Table 2.5.
Table 2.5 Assessment Endpoints and Measures of Ecological Effects
Assessment Endpoint
Measures of Ecological Effects5
Aquatic-Phase CRLF
(Eggs, larvae, juveniles, and adults"f
Direct Effects
1. Survival, growth, and reproduction of CRLF
la. Most sensitive fish acute LC50 (guideline or
ECOTOX) if no suitable amphibian data are
available
Most sensitive fish chronic NOAEC (guideline or
ECOTOX)
Indirect Effects and Critical Habitat Effects
2. Survival, growth, and reproduction of CRLF
individuals via indirect effects on aquatic prey food
supply (i.e., fish, freshwater invertebrates, non-
vascular plants)
2a. Most sensitive fish, aquatic invertebrate, and
aquatic plant EC50 or LC50 (guideline or ECOTOX)
2b. Most sensitive aquatic invertebrate and fish
chronic NOAEC (guideline or ECOTOX)
3. Survival, growth, and reproduction of CRLF
individuals via indirect effects on habitat, cover,
food supply, and/or primary productivity (i.e.,
aquatic plant community)
3a. Vascular plant acute EC50 (duckweed guideline
test or ECOTOX vascular plant)
3b. Non-vascular plant acute EC50 (freshwater algae
or diatom, or ECOTOX non-vascular)
4. Survival, growth, and reproduction of CRLF
individuals via effects to riparian vegetation
4a. Distribution of EC25 values for monocots
(seedling emergence, vegetative vigor, or
ECOTOX)
4b. Distribution of EC25 values for dicots (seedling
emergence, vegetative vigor, or ECOTOX)
Terrestrial-Phase CRLF
(Juveniles and adults)
Direct Effects
5. Survival, growth, and reproduction of CRLF
individuals via direct effects on terrestrial phase
adults and juveniles
5a. Most sensitive birdb acute LC50 or LD50
(guideline or ECOTOX)
5b. Most sensitive birdb chronic NOAEC (guideline
or ECOTOX)
Indirect Effects and Critical Habitat Effects
6. Survival, growth, and reproduction of CRLF
individuals via effects on terrestrial prey
(i.e.,terrestrial invertebrates, small mammals , and
frogs)
6a. Most sensitive terrestrial invertebrate and
vertebrate acute EC50 or LC50 (guideline or
ECOTOX)0
6b. Most sensitive terrestrial invertebrate and
vertebrate chronic NOAEC (guideline or ECOTOX)
7. Survival, growth, and reproduction of CRLF
individuals via indirect effects on habitat (i.e.,
riparian and upland vegetation)
7a. Distribution of EC25 for monocots (seedling
emergence, vegetative vigor, or ECOTOX
7b. Distribution of EC25 for dicots (seedling
emergence, vegetative vigor, or ECOTOX)
5 All registrant-submitted and open literature toxicity data reviewed for this assessment are included in
Appendix A.
28
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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.
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 norflurazon that may alter the PCEs of the CRLF's critical habitat. PCEs for
the CRLF were previously described in Section 2.6. Actions that may modify critical
habitat are those that alter the PCEs and jeopardize the continued existence of the CRLF.
Therefore, these actions are identified as assessment endpoints. It should be noted that
evaluation of PCEs as assessment endpoints is limited to those of a biological nature (i.e.,
the biological resource requirements for the listed species associated with the critical
habitat) and those for which norflurazon effects data are available. Adverse modification
to the critical habitat of the CRLF includes, but is not limited to, those listed in Section
2.6.
Measures of such possible effects by labeled use of norflurazon on critical habitat of the
CRLF are described in Table 2.6. 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).
29
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Table 2.6 Summary of Assessment Endpoints and Measures of Ecological Effect for
Primary Constituent Elements of Designated Critical Habitat3
Assessment Endpoint
Measures of Ecological Effect
Aquatic-Phase CRLFPCEs
(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)
Alteration of channel/pond morphology or geometry
and/or increase in sediment deposition within the
stream channel or pond: aquatic habitat (including
riparian vegetation) provides for shelter, foraging,
predator avoidance, and aquatic dispersal for juvenile
and adult CRLFs.
a. Most sensitive aquatic plant EC50 (guideline or
ECOTOX)
b. Distribution of EC25 values for terrestrial monocots
(seedling emergence, vegetative vigor, or ECOTOX)
c. Distribution of EC25 values for terrestrial dicots
(seedling emergence, vegetative vigor, or ECOTOX)
Alteration in water chemistry/quality including
temperature, turbidity, and oxygen content necessary
for normal growth and viability of juvenile and adult
CRLFs and their food source.
a. Most sensitive EC50 values for aquatic plants (guideline
or ECOTOX)
b. Distribution of EC25 values for terrestrial monocots
(seedling emergence or vegetative vigor, or ECOTOX)
c. Distribution of EC25 values for terrestrial dicots
(seedling emergence, vegetative vigor, or ECOTOX)
Alteration of other chemical characteristics necessary
for normal growth and viability of CRLFs and their
food source.
a. Most sensitive EC50 or LC50 values for fish or aquatic-
phase amphibians and aquatic invertebrates (guideline or
ECOTOX)
b. Most sensitive NOAEC values for fish or aquatic-phase
amphibians and aquatic invertebrates (guideline or
ECOTOX)
Reduction and/or modification of aquatic-based food
sources for pre-metamorphs (e.g., algae)
a. Most sensitive aquatic plant EC50 (guideline or
ECOTOX)
Terrestrial-Phase CRLF PCEs
(Upland Habitat and Dispersal Habitat)
Elimination and/or disturbance of upland habitat;
ability of habitat to support food source of CRLFs:
Upland areas within 200 ft of the edge of the riparian
vegetation or dripline surrounding aquatic and riparian
habitat that are comprised of grasslands, woodlands,
and/or wetland/riparian plant species that provides the
CRLF shelter, forage, and predator avoidance
a. Distribution of EC25 values for monocots (seedling
emergence, vegetative vigor, or ECOTOX)
b. Distribution of EC25 values for dicots (seedling
emergence, vegetative vigor, or ECOTOX)
c. Most sensitive food source acute EC50/LC50 and NOAEC
values for terrestrial vertebrates (mammals) and
invertebrates, birds or terrestrial-phase amphibians, and
freshwater fish.
Elimination and/or disturbance of dispersal habitat:
Upland or riparian dispersal habitat within designated
units and between occupied locations within 0.7 mi of
each other that allow for movement between sites
including both natural and altered sites which do not
contain barriers to dispersal
Reduction and/or modification of food sources for
terrestrial phase juveniles and adults
Alteration of chemical characteristics necessary for
normal growth and viability of juvenile and adult
CRLFs and their food source.
a 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.
30
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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 norflurazon to the environment.
The following risk hypotheses are presumed for this endangered species assessment:
The labeled use of norflurazon within the action area may:
directly affect the CRLF by causing mortality or by adversely affecting growth or
fecundity;
indirectly affect the CRLF by reducing or changing the composition of food
supply;
indirectly affect the CRLF or modify designated critical habitat by reducing or
changing the composition of the aquatic plant community in the ponds and
streams comprising the species' current range and designated critical habitat, thus
affecting primary productivity and/or cover;
indirectly affect the CRLF or modify designated critical habitat by reducing or
changing the composition of the terrestrial plant community (i.e., riparian habitat)
required to maintain acceptable water quality and habitat in the ponds and streams
comprising the species' current range and designated critical habitat;
modify the designated critical habitat of the CRLF by reducing or changing
breeding and non-breeding aquatic habitat (via modification of water quality
parameters, habitat morphology, and/or sedimentation);
modify the designated critical habitat of the CRLF by reducing the food supply
required for normal growth and viability of juvenile and adult CRLFs;
modify the designated critical habitat of the CRLF by reducing or changing
upland habitat within 200 ft of the edge of the riparian vegetation necessary for
shelter, foraging, and predator avoidance.
modify the designated critical habitat of the CRLF by reducing or changing
dispersal habitat within designated units and between occupied locations within
0.7 mi of each other that allow for movement between sites including both natural
and altered sites which do not contain barriers to dispersal.
modify the designated critical habitat of the CRLF by altering chemical
characteristics necessary for normal growth and viability of juvenile and adult
CRLFs.
2.9.2 Diagram
The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies the norflurazon release mechanisms, biological receptor types, and effects
endpoints of potential concern. The conceptual models for terrestrial and aquatic
exposures are shown in Figure 2.9.2-1 and Figure 2.9.2-2, respectively, which include
the conceptual models for the aquatic and terrestrial PCE components of critical habitat.
31
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Exposure routes shown in dashed lines are not quantitatively considered because the
contribution of those potential exposure routes to potential risks to the CRLF and
modification to designated critical habitat is expected to be negligible.
Figure 2.9.2-1 Conceptual Model for Norflurazon Effects on Terrestrial Phase of
the CRLF
32
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Figure 2.9.2-2 Conceptual Model for Norflurazon Effects on Aquatic Phase of the
CRLF
2.10 Analysis Plan
In order to address the risk hypothesis, the potential for direct and indirect effects to the
CRLF, its prey, and its habitat is estimated. In the following sections, the use,
environmental fate, and ecological effects of norflurazon are characterized and integrated
to assess the risks. This is accomplished using a risk quotient (ratio of exposure
concentration to effects concentration) approach. Although risk is often defined as the
likelihood and magnitude of adverse ecological effects, the risk quotient-based approach
does not provide a quantitative estimate of likelihood and/or magnitude of an adverse
effect. However, as outlined in the Overview Document (U.S. EPA, 2004), the
likelihood of effects to individual organisms from particular uses of norflurazon is
estimated using the probit dose-response slope and either the level of concern (discussed
below) or actual calculated risk quotient value.
2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model
2.10.1.1 Measures of Exposure
The environmental fate properties of norflurazon along with available monitoring data
indicate that runoff and spray drift are the principle potential transport mechanisms of
norflurazon to the aquatic and terrestrial habitats of the CRLF. In this assessment,
33
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transport of norflurazon through runoff and spray drift is considered in deriving
quantitative estimates of norflurazon exposure to CRLF, its prey and its habitats.
Measures of exposure are based on aquatic and terrestrial models that predict estimated
environmental concentrations (EECs) of norflurazon using maximum labeled application
rates and methods of application. The models used to predict aquatic EECs are the
Pesticide Root Zone Model coupled with the Exposure Analysis Model System
(PRZM/EXAMS). The model used to predict terrestrial EECs on food items is T-REX.
The model used to derive EECs relevant to terrestrial and wetland plants is TerrPlant.
These models are parameterized using relevant reviewed registrant-submitted
environmental fate data.
PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are screening
simulation models coupled with the input shell pe5.pl (Aug 2007) to generate daily
exposures and l-in-10 year EECs of norflurazon that may occur in surface water bodies
adjacent to application sites receiving norflurazon through runoff and spray drift. PRZM
simulates pesticide application, movement and transformation on an agricultural field and
the resultant pesticide loadings to a receiving water body via runoff, erosion and spray
drift. EXAMS simulates the fate of the pesticide and resulting concentrations in the
water body. The standard scenario used for ecological pesticide assessments assumes
application to a 10-hectare agricultural field that drains into an adjacent 1-hectare water
body, 2-meters deep (20,000 m3 volume) with no outlet. PRZM/EXAMS was used to
estimate screening-level exposure of aquatic organisms to norflurazon. The measure of
exposure for aquatic species is the l-in-10 year return peak or rolling mean concentration.
The l-in-10 year peak is used for estimating acute exposures of direct effects to the
CRLF, as well as indirect effects to the CRLF through effects to potential prey items,
including: algae, aquatic invertebrates, fish and frogs. The 1-in-10-year 60-day mean is
used for assessing chronic exposure to the CRLF and fish and frogs serving as prey
items; the 1-in-10-year 21-day mean is used for assessing chronic exposure for aquatic
invertebrates, which are also potential prey items.
Exposure estimates for the terrestrial-phase CRLF and terrestrial invertebrates and
mammals (serving as potential prey) assumed to be in the target area or in an area
exposed to spray drift are derived using the T-REX model (version 1.4.1, 10/2008). This
model incorporates the Kenega nomograph, as modified by Fletcher etal. (1994), which
is based on a large set of actual field residue data. The upper limit values from the
nomograph represented the 95th percentile of residue values from actual field
measurements (Hoerger and Kenega, 1972). For modeling purposes, direct exposures of
the CRLF to norflurazon through contaminated food are estimated using the EECs for the
small bird (20 g) which consumes small insects. Dietary-based and dose-based exposures
of potential prey (small mammals) are assessed using the small mammal (15 g) which
consumes short grass. The small bird (20g) consuming small insects and the small
mammal (15g) consuming short grass are used because these categories represent the
largest RQs of the size and dietary categories in T-REX that are appropriate surrogates
for the CRLF and one of its prey items. Estimated exposures of terrestrial insects to
34
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norflurazon are bound by using the dietary based EECs for small insects and large
insects.
Birds are currently used as surrogates for terrestrial-phase CRLF. However, amphibians
are poikilotherms (body temperature varies with environmental temperature) while birds
are homeotherms (temperature is regulated, constant, and largely independent of
environmental temperatures). Therefore, amphibians tend to have much lower metabolic
rates and lower caloric intake requirements than birds or mammals. As a consequence,
birds are likely to consume more food than amphibians on a daily dietary intake basis,
assuming similar caloric content of the food items. Therefore, the use of avian food
intake allometric equation as a surrogate to amphibians is likely to result in an over-
estimation of exposure and risk for reptiles and terrestrial-phase amphibians. Therefore,
T-REX (version 1.3.1) has been refined to the T-HERPS model (v. 1.0), which allows for
an estimation of food intake for poikilotherms using the same basic procedure as T-REX
to estimate avian food intake.
EECs for terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant
(version 1.2.2, 12/26/2006). This model uses estimates of pesticides in runoff and in
spray drift to calculate EECs. EECs are based upon solubility, application rate and
minimum incorporation depth.
The spray drift model AgDRIFT (v2.01) is used to assess exposures of terrestrial-phase
CRLF and its habitat to norflurazon deposited on terrestrial habitats by spray drift. In
addition to the buffered area from the spray drift analysis, the downstream extent of
norflurazon that exceeds the LOC for the effects determination is also considered.
Additional information is provided in Appendix B.
2.10.1.2 Measures of Effect
Data identified in Section 2.8 are used as measures of effect for direct and indirect effects
to the CRLF. Data were obtained from registrant submitted studies or from literature
studies identified by ECOTOX. The ECOTOXicology database (ECOTOX) was searched
in order to provide more ecological effects data and in an attempt to bridge existing data
gaps. ECOTOX is a source for locating single chemical toxicity data for aquatic life,
terrestrial plants, and wildlife. ECOTOX was created and is maintained by the USEPA,
Office of Research and Development, and the National Health and Environmental Effects
Research Laboratory's Mid-Continent Ecology Division.
The assessment of risk for direct effects to the terrestrial-phase CRLF makes the
assumption that toxicity of norflurazon to birds is similar to or less than the toxicity to the
terrestrial-phase CRLF. The same assumption is made for fish and aquatic-phase CRLF.
Algae, aquatic invertebrates, fish, and amphibians represent potential prey of the CRLF
in the aquatic habitat. Terrestrial invertebrates, small mammals and terrestrial-phase
amphibians represent potential prey of the CRLF in the terrestrial habitat. Aquatic, semi-
aquatic, and terrestrial plants represent habitat of CRLF.
35
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The acute measures of effect used for animals in this screening level assessment are the
LD50, LC50 and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a material,
given all at once, that is estimated to cause the death of 50% of the test organisms. LC
stands for "Lethal Concentration" and LC50 is the concentration of a chemical that is
estimated to kill 50% of the test organisms. EC stands for "Effective Concentration" and
the EC50 is the concentration of a chemical that is estimated to produce a specific effect in
50% of the test organisms. Endpoints for chronic measures of exposure for listed and
non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL stands for "No
Ob served-Adverse-Effect-Level" and refers to the highest tested dose of a substance that
has been reported to have no harmful (adverse) effects on test organisms. The NOAEC
(i.e., "No-Observed-Adverse-Effect-Concentration") is the highest test concentration at
which none of the observed effects were statistically different from the control. The
NOEC is the No-Observed-Effects-Concentration. For non-listed plants, only acute
exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants).
It is important to note that the measures of effect for direct and indirect effects to the
CRLF and its designated critical habitat are associated with impacts to survival, growth,
and fecundity, and do not include the full suite of sublethal effects used to define the
action area. According the Overview Document (USEPA 2004), the Agency relies on
effects endpoints that are either direct measures of impairment of survival, growth, or
fecundity or endpoints for which there is a scientifically robust, peer reviewed
relationship that can quantify the impact of the measured effect endpoint on the
assessment endpoints of survival, growth, and fecundity.
2.10.1.3 Integration of Exposure and Effects
Risk characterization is the integration of exposure and ecological effects characterization
to determine the potential ecological risk from agricultural and non-agricultural uses of
norflurazon, and the likelihood of direct and indirect effects to CRLF in aquatic and
terrestrial habitats. The exposure and toxicity effects data are integrated in order to
evaluate the risks of adverse ecological effects on non-target species. For the assessment
of norflurazon risks, the risk quotient (RQ) method is used to compare exposure and
measured toxicity values. EECs are divided by acute and chronic toxicity values. The
resulting RQs are then compared to the Agency's levels of concern (LOCs) (USEPA,
2004).
For this endangered species assessment, listed species LOCs are used for comparing RQ
values for acute and chronic exposures of norflurazon directly to the CRLF. If estimated
exposures directly to the CRLF of norflurazon resulting from a particular use are
sufficient to exceed the listed species LOC, then the effects determination for that use is
"may affect". When considering indirect effects to the CRLF due to effects to animal
prey (aquatic and terrestrial invertebrates, fish, frogs, and mice), the listed species LOCs
are also used. If estimated exposures to CRLF prey of norflurazon resulting from a
particular use are sufficient to exceed the listed species LOC, then the effects
determination for that use is a "may affect." If the RQ being considered also exceeds the
non-listed species acute risk LOC, then the effects determination is a LAA. If the acute
36
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RQ is between the listed species LOC and the non-listed acute risk species LOC, then
further lines of evidence {i.e. probability of individual effects, species sensitivity
distributions) are considered in distinguishing between a determination of NLAA and a
LAA. When considering indirect effects to the CRLF due to effects to algae as dietary
items or plants as habitat, the non-listed species LOC for plants is used because the CRLF
does not have an obligate relationship with any particular aquatic and/or terrestrial plant.
If the RQ being considered for a particular use exceeds the non-listed species LOC for
plants, the effects determination is "may affect".
2.10.2 Data Gaps
All ecological effects data relevant to this assessment have been submitted, reviewed and
used in this assessment. There are no acceptable anaerobic soil metabolism studies or
terrestrial field dissipation studies available for norflurazon.
3.0 Exposure Assessment
Norflurazon is formulated as a liquid concentrate. Application method for most uses of
norflurazon is limited to ground spray. Aerial application is permitted for alfalfa, at a
much lower application rate. Risks from ground boom and aerial applications are
expected to result in the highest off-target levels of norflurazon due to generally higher
spray drift levels. The maximum total annual application rate for current norflurazon
uses in California is 3.93 lbs ai/A.
Norflurazon labels may be categorized into two types: labels for manufacturing uses
(including technical grade norflurazon) and end-use products. While technical products,
which contain norflurazon of high purity, are not used directly in the environment, they
are used to make formulated products, which can be applied in specific areas to control
grasses, broad leaf weeds and sedges. The formulated product labels legally limit
potential norflurazon use to only those sites that are specified on the labels.
Currently registered agricultural and non-agricultural uses of norflurazon within
California and being assessed are summarized in Table 2.3.
3.1 Aquatic Exposure Assessment
3.1.1 Modeling Approach
Aquatic exposures are quantitatively estimated for all of the assessed uses using scenarios
that represent high exposure sites for norflurazon use. Each of these sites represents a 10-
hectare field that drains into a 1-hectare pond that is 2 meters deep and has no outlet.
Exposure estimates generated using the standard 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 first-order streams. As a group, there are factors that make these water
bodies more or less vulnerable than the standard surrogate pond. Static water bodies that
have larger ratios of drainage area to water body volume would be expected to have
higher peak EECs than the standard pond. These water bodies will be either shallower or
37
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have larger drainage areas (or both). Shallow water bodies tend to have limited
additional storage capacity, and thus, tend to overflow and carry pesticide in the
discharge whereas the standard pond has no discharge. As field size increases beyond 10
hectares, at some point, it becomes unlikely that the entire watershed is planted to a
single crop, which is all treated with the pesticide. Headwater streams can also have peak
concentrations higher than the standard pond, but they typically persist for only short
periods of time and are then carried downstream.
EPA modeled Total Toxic Residues which includes the parent compound (norflurazon)
and the degradate desmethyl norflurazon. The aqueous photolysis, aerobic soil
metabolism and the aerobic and anaerobic aquatic metabolism half-lives determined for
the parent compound in the guideline studies were recalculated using concentration data
for the parent compound plus desmethyl norflurazon when the latter compound was
present in the study samples. Additionally, there are soil adsorption data for the parent
compound and limited adsorption data for the degradate desmethyl norflurazon which
indicates that desmethyl norflurazon approaches the mobility of the parent compound.
Regardless, because the parent data were used in lieu of definitive adsorption coefficient
data for the degradate, this introduces an uncertainty in relation to the EECs.
3.1.2 Model Inputs
The model input parameters used in PRZM/EXAMS to simulate norflurazon application-
specific and chemical-specific parameters are listed in Table 3.1 and Table 3.2. Crop-
specific management practices for all of the assessed uses of norflurazon were used for
modeling, including application rates, number of applications per year, application
intervals, and the first application date for each crop. The date of first application was
based on several sources of information including data provided by BEAD and Crop
Profiles maintained by the USD A. When a range of application dates was possible, the
first application was chosen to correspond to the wetter portion of the year, winter/early
spring. Standard and CRLF-specific PRZM crop scenarios, which consist of location-
specific soils, weather, and cropping practices, were used in the simulations to represent
labeled uses of norflurazon. These scenarios were developed to represent high-end
exposure sites in terms of vulnerability to runoff and erosion and subsequent off-site
transport of pesticide.
Registered uses were grouped into categories according to similarity of crop growth and
morphology, product use and cropping area; representative PRZM scenarios for each
category were used for modeling. Particular attention was given to grouping crops
according to the areas in which they are grown because rainfall is understood to be a
driving variable in the PRZM model. Modeling inputs were selected according to
EFED's Input Parameter Guidance (USEPA 2002). Pesticide applications were
simulated as ground spray applications as prescribed by product labels and default spray
drift estimates were assumed. The dates chosen for "foliar application" were based on
when weed pressure was expected to be present since the herbicide is applied to the
ground and not to the crop directly. The disposition of the pesticide remaining on foliage
after harvest was determined to be not applicable because the herbicide is not applied to
the crop directly and therefore post-harvest practices would not impact modeling.
38
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For the rights-of way (ROW) scenario, the conceptual modeling integrates simultaneous
modeling of the individual scenario (ROW) and an impervious surface. This approach
assumes that no watershed is completely covered by either the undeveloped land of the
rights-of-way or an impervious surface. Post-processing of the output was performed
two ways: first a conservative assumption was made for a 10.0% overspray of impervious
surfaces within the rights-of-way with a resulting peak EEC of 79 (|ig/L), A second run
was performed for the rights-of-way scenario which had a less conservative approach of a
1.0% overspray of impervious surfaces and resulted in a slightly lower peak EEC of 65
Table 3.1. Norflurazon Uses, Scenarios, and Application Information for the CRLF
risk assessment1
Category
Uses
PRZM
Scenario
App.
rate (lbs
ai/A)
# Apps/
year
Min.
interval
Date of
1st App
App. Date Comment
Alfalfa
Alfalfa
CA
alfalfa Wirrig
OP
0.983
2
72
January
1st
W inter/Dormant
application based on
label directions
Almonds
Almonds, filberts,,
walnut, pecans
CAalmond_W
irrigSTD
3.93
1
(assumed)3
NA
August
15th
Pre-Harvest application
based on label directions
Avocado
Avocado
CAavocadoR
LF_v2
3.93
1
(assumed)3
NA
March
15th
Foliar Application based
on label directions;
spring application
assumed
Citrus
Citrus
CAcitrus
_WirrigSTD
3.93
1
(assumed)3
NA
March
15th
Foliar Application based
on label directions;
spring application
assumed
Fruit tree
Apples, apricots,
nectarines, peaches,
pears, cherries, plums,
prunes
CAfruit
_WirrigSTD
3.93
1
(assumed)3
NA
March
15th
Foliar Application based
on label directions;
spring application
assumed
Grapes
Grapes, Blueberries,
Caneberries, Hops
CAWineGrap
esRLF_v2
3.93
1
(assumed)3
NA
March
15th
Foliar Application based
on label directions;
spring application
assumed
Nursery
Nursery Stock
CAnurseryST
D
2.36
1
(assumed)3
NA
March
15th
Foliar Application based
on label directions;
spring application
assumed
Rights of
Way
Industrial Areas,
Refuse/Solid Waste
Sites (outdoors),
Non Agricultural
ROW/fencerows/hedge
rows, Non Agricultural
uncultivated areas/soils
CArightofway
RLF_V2.
3.93
1
(assumed)3
NA
March
15th
Foliar Application based
on label directions;
spring application
assumed
1 Uses assessed based on memorandum from SRRD dated 9/3/08.
2Minimum interval not specified on label.
3 Maximum number of application per year not specified on label and one cropping season was assumed based on
maximum amount of active ingredient allowed per calendar year.
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Table 3.2. Chemical-Specific PRZM/EXAMS Input Parameters Used in Aquatic
Exposure Modeling for Norflurazon and Desmethylnorflurazon.
Input Parameter
Value
Source
Comment
Molecular mass (g/mol)
303.7
Product chemistry
Vapor pressure (Torr)
1.5 xlO"5 torr
Product chemistry
Henry's law constant (atm-m3/mol)
2.1 x 10-7
Calculated
HLC = (VP/760) / (SOL/MWT)
Water solubility (mg/L)
280
Product chemistry
multiplied by 101
Adsorption partition coefficient (Kd,
ml/g)
14.2
MRID 41986904,
00148312,42710901
Average Kd1
Aerobic soil metabolism ty2 (d)
1,125
MRID 40079601
Value calculated from data for parent plus
desmethyl norflurazon and represents 3x
aerobic soil ti/21
Aerobic aquatic metabolism ty2 (d)
825
MRID 40079601
Value calculated from data for parent plus
desmethyl norflurazon and represents 3x
aerobic aquatic ti/21
Anaerobic aquatic metabolism ty2
(d)
2,034
MRID 40079601
Value calculated from data for parent plus
desmethyl norflurazon and represents 3x
anaerobic aquatic ty21
Hydrolysis ty2 (d)
0
MRID 00146165
Stable at pH 7.
Photolysis ty2 (d)
3
MRID 00148311
Value calculated from data for parent plus
desmethyl norflurazon.
1 EFED input parameter guidance is located at: httD://www.eDa.aov/oDDefedl/models/water/inDut auidance2 28 02.htm.
3.1.3 Results
Aquatic EECs using PRZM/EXAMS for the various use categories are listed in Table
3.3. Tier II peak aquatic EECs range from 5 to 79|ig/L for citrus and rights-of-way,
respectively. The variability in EECs is driven by yearly application rate, application
timing relative to rainfall events, and variability in the vulnerability of the PRZM
scenario (rainfall and soils) selected.
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Table 3.3. Aquatic Total Toxic Residue EECs (jig/L) for Norflurazon Uses in
California
Scenario
Application
Rate
Date of First
Application
Crops Represented
Peak
EEC
21-day
average
EEC
60-dav
average
EEC
California
fruit trees
3.93
March 15
Apples, apricots, cherries,
nectarines, peaches, pears,
plums and prunes
7.4
7.0
6.5
Alfalfa
0.983x2
January 1
Alfalfa
27.3
26.5
25.6
Avocado
3.93
March 15
Avocado
36.4
35.1
33.4
Almond
3.93
August 15
Almonds, filberts
(hazelnuts) and walnuts
(black and English)
34.7
34.0
32.7
Citrus
3.93
March 15
Citrus
5.0
4.8
4.6
Grapes
3.93
March 15
Grapes, blueberries,
caneberries, hops
14.4
14.1
13.5
Nursery
2.36
March 15
Nursery Stock
41.8
40.8
39.3
Rights-of-
Way
3.93
March 15
Industrial areas, refuse/solid
waste sites (outdoors),
non agricultural
ROW/fencerows/hedgerows,
non agricultural uncultivated
areas/soils
79
78
78
3.1.4 Existing Monitoring Data
Norflurazon has a limited set of surface and ground water monitoring data relevant to the
CRLF assessment. Surface water monitoring studies which specifically targeted
norflurazon use (application period and/or sites) were not available for analysis as part of
this assessment. Generally, targeted monitoring data are collected with a sampling
program designed to capture, both spatially and temporally, the maximum use of a
particular pesticide and as such, peak residue levels. Typically, sampling frequencies
employed in monitoring studies are insufficient to document peak exposure values. The
lack of targeted sampling data, coupled with the fact that these data are not temporally or
spatially correlated with pesticide application times and/or areas, limit the utility of these
data in estimating peak exposure concentrations for risk assessment purposes. Therefore
model-generated values are used for estimating both acute and chronic exposure values,
and the non-targeted monitoring data are typically used for qualitative characterizations
of environmental concentrations. Included in this assessment are norflurazon data from
the USGS NAWQA program (http://water.usgs.gov/nawqa) and data from the California
Department of Pesticide Regulation (CDPR). In addition, a targeted Prospective
41
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Groundwater (PGW) study has been conducted for parent norflurazon and
desmethylnorflurazon and the results are discussed below.
3.1.4.1 USGS NAWQA Surface Water Data
Surface water monitoring data from the United States Geological Survey (USGS)
NAWQA program were obtained on November 24, 2008. A total of 8,026 water samples
across various sites throughout the U.S. were analyzed for norflurazon. This included
346 samples taken in CA at 31 sites located in 11 counties (Alpine, El Dorado, Merced,
Nevada, Orange, Sacramento, San Bernadino, San Joaquin, Stanislaus, Sutter and Yolo)
between March 1993 and September 2005. There were 334 (4%) detections of
norflurazon nationwide ranging in concentration from 0.007 to 1.4 |ig/L and 74 (21%)
detections in the state of California ranging in concentrations from 0.0031 to 0.62 |ig/L.
Levels of detection (LOD) varied over time ranging from 0.0008 to 0.53 |ig/L. Of the
detections in California, sites were classified as agricultural land use (25 sites), mixed
land use (46 sites), and urban (three sites).
A total of 635 water samples across various sites throughout the U.S. were analyzed for
desmethyl norflurazon. Of these samples, 317 (50%) samples had positive detections
with estimated concentrations ranging from 0.05 to 6.1 |ig/L. None of the samples
collected from sites in California were analyzed for desmethyl norflurazon.
3.1.4.2 USGS NAWQA Groundwater Data
Ground water monitoring data from the United States Geological Survey (USGS)
NAWQA program were obtained on December 1, 2008. A total of 6,102 water samples
across various sites throughout the US were analyzed for norflurazon. This included 429
samples taken in CA at sites located in 20 counties (Butte, Colusa, Fresno, Glenn, Kern,
Kings, Los Angelos, Madera, Merced, Orange, Placer, Riverside, Sacramento, San
Bernadino, San Joaquin, Stanislaus, Sutter, Tulare, Yolo and Yuba) between August 1993
and September 2006. There were 14 detections of norflurazon which ranged from 0.0037
to 0.24 |ig/L. Sites were classified as agricultural land use (210 sites), mixed use (111
sites), urban (70 sites) and other (38 sites).
A total of 45 water samples across various sites throughout the US were analyzed for
desmethyl norflurazon. Of these samples, 10 (22%) samples had positive detections with
estimated concentrations ranging from 0.05 to 1.91 |ig/L. None of the samples collected
from sites in California were analyzed for desmethyl norflurazon.
3.1.4.3 California Department of Pesticide Regulation (CPR) Data
Surface water monitoring data were obtained from the California Department of Pesticide
regulation (CDPR) on November 24, 2008, and all data with analysis for norflurazon
were extracted. A total of 199 water samples were analyzed for norflurazon. There were
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28 (14%) detections of norflurazon ranging from 0.05 and 0.98 |ig/L. Detections of
norflurazon were reported from eight sites on the Highline Spillway to the San
Joaquin.River in Merced County on March 7, 2002; from one site on the Colusa Basin
Drain above Knights Landing in Yolo County on April 15, 1998; from 14 sites in
Wadsworth Canal at South Butte Road in Sutter County between January 8, 2001 and
March 14, 2001; from four sites on Sutter Bypass at Karnak Pumping Station between
January 15, 2001 and March 7, 2001; and at one site on the Sacramento River at Alamar
Marina Dock, 9 mi below the confluence of the Feather River on January 12, 2001.
3.1.4.4 Prospective Groundwater Study
A Prospective Groundwater (PGW) study was conducted on a citrus grove located on the
Central Ridge in Florida (US EPA, 2002). Two applications of norflurazon were made
March and July 1994, at a reported total rate of 5 to 10 lbs a.i./A. The study was
conducted for approximately two years. Both norflurazon and desmethylnorflurazon
were measured in multiple wells at the site throughout the duration of the study, with
peak concentrations of 29.9 and 23.8 |ig/L, respectively in two separate sampling events.
Several samples contained residues of both parent and degradate in relatively high
concentrations (greater than 20 ppb) and were observed to persist more than 700 days
after application.
The maximum concentrations from the PGW study are within the range of peak, 21-day
and 60-day concentrations estimated from surface water (4.6 - 79 |ig/L) for various uses
of norflurazon. Exposure resulting from discharging groundwater to surface water is
therefore reasonably represented by the concentrations estimated for surface water.
Particularly since attenuation and retardation of the chemical would occur prior to
discharge.
3.1.4.5 Atmospheric Monitoring Data
Atmospheric monitoring data is not available for norflurazon.
3.2 Terrestrial Exposure Assessment
3.2.1 Terrestrial Animal Exposure Assessment
T-REX (Version 1.4.1) is used to calculate dietary and dose-based EECs of norflurazon
for the CRLF and its potential prey (e.g. small mammals and terrestrial insects)
inhabiting terrestrial areas. EECs used to represent the CRLF are also used to represent
exposure values for frogs serving as potential prey of CRLF adults. T-REX simulates a 1-
year time period. For this assessment, spray applications of norflurazon are considered,
as discussed in below.
43
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Terrestrial EECs for foliar formulations of norflurazon were derived for the uses
summarized in Table 3.4. Given that no data on interception and subsequent dissipation
from foliar surfaces is available for norflurazon, a default foliar dissipation half-life of 35
days is used based on the work of Willis and McDowell (1987). Since norflurazon is a
pre-emergent herbicide, the default foliar dissipation half-life of 35 day is likely
conservative since the presence of foliar surfaces is likely limited. However, the majority
of uses have a single application per year, so the use of this half-life is relevant only to
the alfalfa use where there are two applications per year. Use-specific input values,
including number of applications, application rate and application interval are provided in
Table 3.4. The nursery stock use is included under the higher 3.93 lb ai/A rate. An
example output from T-REX is available in Appendix E.
Table 3.4 Input Parameters for Foliar Applications Used to Derive Terrestrial EECs
for Norflurazon with T-REX
Use (Application method)
Application rate
(lbs ai/A)
Number of
Applications
All uses (except alfalfa)
3.93
1
Alfalfa
0.9833
2
aTwo applications, seven day interval
T-REX is also used to calculate EECs for terrestrial insects exposed to norflurazon.
Dietary-based EECs calculated by T-REX for small and large insects (units of ai/g) are
used to bound an estimate of exposure to bees. Available acute contact toxicity data for
bees exposed to norflurazon (in units of |ig ai/bee), are converted to |ig ai/g (of bee) by
multiplying by 1 bee/0.128 g. The EECs are later compared to the adjusted acute contact
toxicity data for bees in order to derive RQs.
For modeling purposes, exposures of the CRLF to norflurazon through contaminated
food are estimated using the EECs for the small bird (20 g) which consumes small
insects. Dietary-based and dose-based exposures of potential prey are assessed using the
small mammal (15 g) which consumes short grass. Upper-bound Kenega nomogram
values reported by T-REX for these two organism types are used for derivation of EECs
for the CRLF and its potential prey (Table 3.5). Dietary-based EECs for small and large
insects reported by T-REX as well as the resulting adjusted EECs are available in Table
3.6. An example output from T-REX vl.4.1 is available in Appendix C.
Table 3.5 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based
Exposures of the CRLF and its Prey to Norflurazon
r.r.Cs lor cm.i
I'.l'.Cs lor Pre.\
(small mammals)
I se
Dielan-based
Dose-based I I.(
Dielan-based
Dose-based I'.r.C
I I.( (ppni)
(mg/kg-lm)
1.1.C (ppni)
(in }»/kj»-bw)
All uses (except alfalfa)
531
604
943
899
Alfalfa*
248
283
441
421
*assuming 7-day reapplication interval
44
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Table 3.6 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via
Effects to Terrestrial Invertebrate Prey Items
Use
Small Insect
(ppm)
Large Insect (ppm)
All uses (except alfalfa)
604
67
Alfalfa*
283
31
*assuming 7-day reapplication interval
3.2.2 Terrestrial Plant Exposure Assessment
TerrPlant (Version 1.2.2) is used to calculate EECs for non-target plant species inhabiting
dry and semi-aquatic areas. Parameter values for application rate, drift assumption and
incorporation depth are based upon the use and related application method (Table 3.7).
A runoff value of 0.02 is utilized based on the solubility of norflurazon. For aerial and
ground application methods, drift is assumed to be 5% and 1%, respectively. EECs
relevant to terrestrial plants consider pesticide concentrations in drift and in runoff.
These EECs are listed by use in Table 3.7. An example output from TerrPlant v. 1.2.2 is
available in Appendix D.
Table 3.7 TerrPlant Inputs and Resulting EECs for Plants Inhabiting Dry and
Semi-aquatic Areas Exposed to Norflurazon via Runoff and Drift
Use
Application
rate
(lbs a.i./A)
Application
method
Drift
Value
<%)
Spray drift
EEC
(lbs ai/A)
Drv area
EEC
(lbs ai/A)
Semi-aquatic
area EEC
(lbs ai/A)
All uses (except
alfalfa)
3.93
Foliar - ground
1
0.039
0.118
0.825
Alfalfa
0.983
Foliar-air
5
0.049
0.069
0.246
4.0 Effects Assessment
This assessment evaluates the potential for norflurazon to directly or indirectly affect the
CRLF or modify its designated critical habitat. As previously discussed in Section 2.7,
assessment endpoints for the CRLF effects determination include direct toxic effects on
the survival, reproduction, and growth of CRLF, as well as indirect effects, such as
reduction of the prey base or modification of its habitat. In addition, potential
modification of critical habitat is assessed by evaluating effects to the PCEs, which are
components of the critical habitat areas that provide essential life cycle needs of the
CRLF. Direct effects to the aquatic-phase of the CRLF are based on toxicity information
for freshwater fish, while terrestrial-phase effects are based on avian toxicity data, given
that birds are generally used as a surrogate for terrestrial-phase amphibians. Because 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. Acute (short-
term) and chronic (long-term) toxicity information is characterized based on registrant-
submitted studies and a comprehensive review of the open literature on norflurazon.
45
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As described in the Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa
include aquatic-phase amphibians, freshwater fish, freshwater invertebrates, aquatic
plants, birds (surrogate for terrestrial-phase amphibians), mammals, terrestrial
invertebrates, and terrestrial plants.
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 submitted studies, as well as ECOTOX information obtained in
August 2008. 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.
ECOTOX data that pass the screen are evaluated along with the registrant-submitted data,
and may be incorporated qualitatively or quantitatively into this endangered species
assessment. In general, effects data in the open literature that are more conservative than
the registrant-submitted data are considered. The degree to which open literature data are
quantitatively or qualitatively characterized for the effects determination is dependent on
whether the information is relevant to the assessment endpoints (i.e., maintenance of
CRLF survival, reproduction, and growth) identified in Section 2.8. For example,
endpoints such as behavior modifications are likely to be qualitatively evaluated, because
quantitative relationships between modifications and reduction in species survival,
reproduction, and/or growth are not available. Although the effects determination relies
on endpoints that are relevant to the assessment endpoints of survival, growth, or
reproduction, it is important to note that the full suite of sublethal endpoints potentially
available in the effects literature (regardless of their significance to the assessment
endpoints) are considered to define the action area for norflurazon.
Citations of all open literature not considered as part of this assessment because they
were rejected by the ECOTOX screen is included in Appendix E. Appendix E also
includes a rationale for rejection of those studies that did not pass the ECOTOX screen
and those that were not evaluated as part of this endangered species risk assessment. A
detailed spreadsheet of the available ECOTOX open literature data, including the full
suite of lethal and sublethal endpoints is presented in Appendix F. There were no more
sensitive endpoints available in the ECOTOX database other than the registrant-
submitted studies used for this assessment. Appendix G includes the Health Effects
Division summary of mammalian effects data for norflurazon.
46
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In addition to registrant-submitted and open literature toxicity information, other sources
of information, including use of the acute probit dose response relationship to establish
the probability of an individual effect and reviews of the Ecological Incident Information
System (EIIS), are conducted to further refine the characterization of potential ecological
effects associated with exposure to norflurazon. A summary of the available aquatic and
terrestrial ecotoxicity information, use of the probit dose response relationship, and the
incident information for norflurazon are provided in Sections 4.1 through 4.4,
respectively.
No degradate toxicity data have been identified by HED, and there are no
ecotoxicological studies on the toxicity of norflurazon degradates. Therefore,
desethylnorflurazon is assumed to have equivalent toxicity to the parent. Available
formulated product studies report similar toxicity to the TGAI.
4.1 Evaluation of Aquatic Ecotoxicity Studies
Table 4.1 summarizes the most sensitive aquatic toxicity endpoints for the CRLF, based
on an evaluation of both the submitted studies and the open literature, as previously
discussed. A brief summary of submitted data considered relevant to this ecological risk
assessment for the CRLF is presented below.
47
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Table 4.1 Freshwater Aquatic Toxicity Profile for Norflurazon.
Assessment Endpoint
Species
Toxicity Value Used in
Risk Assessment
Citation
MRID #
(Author &
Date)
Comment
Acute Direct Toxicity to
Aquatic-Phase CRLF
Rainbow
trout
LC50=8.1 mg ai/L
00246434
Acceptable
Chronic Direct Toxicity
to Aquatic-Phase CRLF
Rainbow
trout
NOAEC=0.77 mg ai/L
00248829
Acceptable
Indirect Toxicity to
Aquatic-Phase CRLF via
Acute Toxicity to
Freshwater Invertebrates
(i.e. prey items)
Daphnia
magna
LC50>15 mg ai/L
0035709
Acceptable
(no mortality)
Indirect Toxicity to
Aquatic-Phase CRLF via
Chronic Toxicity to
Freshwater Invertebrates
(i.e. prey items)
Daphnia
magna
NOAEC=1.0 mg ai/L
0118049
Acceptable
Indirect Toxicity to
Aquatic-Phase CRLF via
Toxicity to Non-vascular
Aquatic Plants
Green
algae
EC50=9.7 |ig ai/L
420804-06
Acceptable
Indirect Toxicity to
Aquatic-Phase CRLF via
Toxicity to Vascular
Aquatic Plants
Duckweed
EC50=58.2 |ig ai/L
420804-07
Acceptable
Toxicity to aquatic fish and invertebrates is categorized using the system shown in Table
4.2 (U.S. EPA, 2004). Toxicity categories for aquatic plants have not been defined.
Table 4.2 Categories of Acute Toxicity for Aquatic Animals
LC50 (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
Given that no norflurazon toxicity data are available for aquatic-phase amphibians,
freshwater fish data were used as a surrogate to estimate direct acute and chronic risks to
the CRLF. Freshwater fish toxicity data were also used to assess potential indirect effects
of norflurazon to the CRLF. Effects to freshwater fish resulting from exposure to
norflurazon 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).
48
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Agency guideline aquatic animal studies are supposed to test up to 100 mg/L, which the
available studies did not; however, the solubility limit of the compound is 28 mg/L.
Presumably, solubility was an issue in the aquatic studies.
A summary of acute and chronic freshwater fish data, including data from the open
literature, is provided below.
4.1.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies
Two submitted guideline studies provide insight into the potential acute effects of
norflurazon on freshwater fish, and by extension, on the aquatic-phase CRLF as well.
One study, with bluegill sunfish, Lepomis macrochirus, resulted in an LC50 of 16.3 mg
ai/L with no adverse effects observed at 10 mg ai/L. A second study, with rainbow trout,
resulted in an LC50 of 8.1 mg ai/L with no adverse effects observed at 4 mg ai/L. For a
protective assessment, the LC50 of 8.1 mg ai/L will be used for RQ calculation.
Norflurazon is categorized as moderately toxic to freshwater fish on an acute exposure
basis.
4.1.1.2 Freshwater Fish: Chronic Exposure (Early Life Stage
and Reproduction) Studies
Two guideline early life stage (ELS) studies are available for evaluation of potential
chronic effects of norflurazon on the aquatic-phase CRLF. Both studies are with the
rainbow trout and result in similar NOAECs, based on reduced growth. One study
resulted in a NOAEC of 1.1 mg ai/L, with a LOAEC of 2.1 mg ai/L. The other study
resulted in a NOAEC of 0.77 mg ai/L and the LOAEC is 1.5 mg ai/L. The most sensitive
endpoint used in the chronic assessment for CRLF is the NOAEC of 0.77 mg ai/L.
4.1.2 Toxicity to Freshwater Invertebrates
Freshwater aquatic invertebrate toxicity data were used to assess potential indirect effects
of norflurazon to the CRLF. Effects to freshwater invertebrates resulting from exposure
to norflurazon may indirectly affect the CRLF via reduction in available food items. As
discussed in Section 2.5.3, the main food source for juvenile aquatic- and terrestrial-
phase CRLFs is thought to be aquatic invertebrates found along the shoreline and on the
water surface, including aquatic sowbugs, larval alderflies and water striders.
A summary of acute and chronic freshwater invertebrate data, including data published in
the open literature, is provided below.
4.1.2.1 Freshwater Invertebrates: Acute Exposure (Mortality)
Studies
The guideline study with Daphnia magna resulted in a nondefinitive LC50 of >15 mg
ai/L, with no observed adverse effects to the animals in the study at the highest
concentration tested. Norflurazon is categorized as slightly toxic to freshwater
invertebrates on an acute exposure basis.
49
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4.1.2.2 Freshwater Invertebrates: Chronic Exposure
(Reproduction) Studies
The guideline study evaluating potential chronic effects to aquatic invertebrates, with
Daphnia magna, resulted in a NOAEC of 1.0 mg ai/L. The LOAEC in the study is 2.6
mg ai/L, based on reduced number of offspring produced compared to the control.
4.1.3 Toxicity to Aquatic Plants
Aquatic plant toxicity studies were used as one of the measures of effect to evaluate
whether norflurazon may affect primary production and the availability of aquatic plants
as food for CRLF tadpoles. Primary productivity is essential for indirectly supporting the
growth and abundance of the CRLF. Additionally, aquatic vascular plants provide cover
and habitat for the CRLF.
Laboratory studies were used to determine whether norflurazon may cause direct effects
to aquatic plants. A summary of the laboratory data and freshwater field studies for
aquatic plants is provided in Sections 4.1.3.1.
4.1.3.1 Aquatic Plants: Laboratory Data
A 5-day study with Lemna gibba resulted in an EC50 of 58.2 |ig ai/L, the endpoint used
for estimating effects to aquatic vascular plants, a component of CRLF habitat. A 5-day
study with the green algae, Pseudokirchneriella subcapitata (formerly Selenastrum
capricornutum), resulted in an EC50 of 9.7 |ig ai/L, the endpoint used for assessing
potential effects to aquatic nonvascular plants, a component of the aquatic-phase CRLF
diet.
4.2 Toxicity of Norflurazon to Terrestrial Organisms
Table 4.3 summarizes the most sensitive terrestrial toxicity endpoints for the CRLF,
based on an evaluation of both the submitted studies and the open literature. A brief
summary of submitted and open literature data considered relevant to this ecological risk
assessment for the CRLF is presented below.
Table 4.3 Terrestrial Toxicity Profile for Norflurazon
Endpoint
Species
Toxicity Value Used
in Risk Assessment
MR ID#
Comment
Acute Direct
Toxicity to
Terrestrial-Phase
CRLF
Mallard duck
LD5o >2,510 mg
ai/kg-bw
00048362
No mortalities or clinical observation of
effect
Acute Direct
Toxicity to
Terrestrial-Phase
CRLF
Bobwhite
quail
LC5o >10,000 mg
ai/kg-diet
0037051
No mortalities or clinical observation of
effect
Chronic Direct
Bobwhite
quail
NOAEC=40 mg
ai/kg-diet
426153-01
No adult mortality; based on reduced # of
14-d old survivors
50
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Endpoint
Species
Toxicity Value Used
in Risk Assessment
MR ID#
Comment
Toxicity to
Terrestrial-Phase
CRLF
Indirect Toxicity to
Terrestrial-Phase
CRLF (via acute
toxicity to
mammalian prey
items)
Laboratory rat
LD5o=9,300 mg
ai/kg-bw
00111612
Indirect Toxicity to
Terrestrial-Phase
CRLF (via chronic
toxicity to
mammalian prey
items)
Laboratory rat
NOAEC=150 mg
ai/kg-diet
00082019
Decreased pup weights
Indirect Toxicity to
Terrestrial-Phase
CRLF (via acute
toxicity to
terrestrial
invertebrate prey
items)
Honey bee
LD50>235 |ig/bcc
00146168
No mortalities
Indirect Toxicity to
Terrestrial- and
Aquatic-Phase
CRLF (via toxicity
to terrestrial plants)
Seedlins
Emersence
Monocots
EC25=0.034 lbs ai/A
433125-01
Onion fresh weight
Seedlins
Emersence
Dicots
EC25=0.002 lbs ai/A
433125-01
Mustard fresh weight
Vesetative
Visor
Monocots
EC25=0.13 lbs ai/A
420804-05
Onion fresh weight
Vesetative
Visor
Dicots
EC25=0.08 lbs ai/A
420804-05
Cucumber fresh weight
Acute toxicity to terrestrial animals is categorized using the classification system shown
in Table 4.4 (U.S. EPA, 2004). Toxicity categories for terrestrial plants have not been
defined.
51
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Table 4.4 Categories of Acute Oral and Subacute Dietary Toxicity for Avian and
Mammalian Studies
Toxicity Category
Oral LD5o
Dietary LC50
Very highly toxic
<10 mg/kg
< 50 ppm
Highly toxic
10-50 mg/kg
50 - 500 ppm
Moderately toxic
51 -500 mg/kg
501 - 1000 ppm
Slightly toxic
501 - 2000 mg/kg
1001 - 5000 ppm
Practically non-toxic
> 2000 mg/kg
> 5000 ppm
4.2.1 Toxicity to Birds
As specified in the Overview Document, the Agency uses birds as a surrogate for
terrestrial-phase amphibians when amphibian toxicity data are not available (U.S. EPA,
2004). No terrestrial-phase amphibian data are available for norflurazon; therefore, acute
and chronic avian toxicity data are used to assess the potential direct effects of
norflurazon to terrestrial-phase CRLFs.
4.2.1.1 Birds: Acute Exposure (Mortality) Studies
An avian acute oral toxicity study with mallard duck is available for norflurazon. The
study was conducted with five doses, with five males and five females at each level. No
mortalities were observed at the highest concentration tested (2150 mg ai/kg body weight
(bw)). The LD50 for avian acute effects is >2150 mg ai/kg-bw. Norflurazon is
categorized as practically nontoxic to avian species on an acute oral exposure basis.
Two avian subacute dietary studies are available for norflurazon, one with bobwhite quail
and the other with mallard duck. No mortalities were reported in either study at the
highest concentration tested (10,000 mg ai/kg diet). Some loss of feathers was reported
for bobwhite quail at the highest dose. The LC50 for subacute dietary exposure to avian
species is >10,000 mg ai/kg-diet. Norflurazon is categorized as practically nontoxic on a
subacute dietary exposure basis.
4.2.1.2 Birds: Chronic Exposure (Growth, Reproduction)
Studies
Effects to avian species from chronic exposure are assessed with one-generation
reproduction studies. Two studies, one with bobwhite quail and one with mallard duck
are used to evaluate the chronic toxicity of norflurazon to avian species. No effects on
adult in either study were reported. The mallard study determined an NOAEC of 40 mg
ai/kg-diet, based on decreased hatchling weights relative to the control (15%). The quail
study determined an NOAEC of 40 mg ai/kg-diet, based on decreased hatchling survival
at the second highest dose (200 mg ai/kg-diet) relative to the control; however, this effect
may not be treatment related. The LOAEC for both studies is 200 mg ai/kg-diet.
52
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4.2.2
Toxicity to Mammals
Mammalian toxicity data are used to assess potential indirect effects of norflurazon to the
terrestrial-phase CRLF. Effects to small mammals resulting from exposure to
norflurazon could also 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).
A NOAEL was not determined in the rat developmental toxicity study (MRID
00063621). The LOAEL for the study is 100 mg ai/kg-bw/day, the lowest dose tested,
base on maternal weight loss. There were no developmental effects observed in the
offspring. For more information, see the HED Human Health Risk Assessment in
Appendix G.
4.2.2.1 Mammals: Acute Exposure (Mortality) Studies
Effects to mammals are assessed with the acute oral toxicity study with the laboratory rat.
The LD50 from this study (MRID 00111612) is 9,300 mg ai/kg-bw; therefore norflurazon
is categorized as practically nontoxic to mammalian species on an acute exposure basis.
4.2.2.2 Mammals: Chronic Exposure (Growth, Reproduction)
Studies
The two-generation study with the laboratory rat is used to assess potential for effects to
mammals from chronic exposure. The study for norflurazon determined a NOAEC for
both parental and offspring of 150 mg ai/kg-diet. The parental LOAEC is 750 mg ai/kg-
bw, based on increased liver and kidney weights in both generations. The offspring
LOAEC is also 750 mg ai/kg-bw, based on decreased pup weights.
4.2.3 Toxicity to Terrestrial Invertebrates
Terrestrial invertebrate toxicity data are used to assess potential indirect effects of
norflurazon to the terrestrial-phase CRLF. Effects to terrestrial invertebrates resulting
from exposure to norflurazon could also indirectly affect the CRLF via reduction in
available food. The honeybee acute oral and contact studies indicate norflurazon is
practically nontoxic to adult honeybees on an acute exposure basis, with an LD50 in both
studies >235 |ig ai/bee. The acute contact toxicity of formulated norflurazon (80% ai)
reports an LC50S >90 |ig ai/bee, the highest concentration test. No effects were observed
in any study.
4.2.4 Toxicity to Terrestrial Plants
53
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Terrestrial plant toxicity data are used to evaluate the potential for norflurazon to affect
riparian zone and upland vegetation within the action area for the CRLF. Impacts to
riparian and upland (i.e., grassland, woodland) vegetation could result in indirect effects
to both aquatic- and terrestrial-phase CRLFs, as well as modification to designated
critical habitat PCEs via increased sedimentation, alteration in water quality, and
reduction in of upland and riparian habitat that provides shelter, foraging, predator
avoidance and dispersal for juvenile and adult CRLFs.
Plant toxicity data from both registrant-submitted studies and studies in the open
literature were reviewed for this assessment. Registrant-submitted studies are conducted
under conditions and with species defined in EPA toxicity test guidelines. Sub-lethal
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.
The results of the Tier II seedling emergence and vegetative vigor toxicity tests on non-
target plant biomass are summarized below in Table 4.5 and 4.6. Sensitivity varied
widely across species, indicating tat some species of plants are more sensitive to
norflurazon. Grasses exhibited low sensitivity to norflurazon in both studies. As
expected with a pre-emergent herbicide, the most sensitive endpoint is in the seedling
emergence study (mustard; 0.002 lbs ai/A), and effects were seen in more species in that
study. However, effects were seen in the vegetative vigor study in sensitive species (e.g.
cucumber).
Table 4.5 Non-target Terrestrial Plant Seedling Emergence Toxicity (Tier II) Data
Crop
Type of Study
Species
ec25
(lb ai/A)
NOAEC
(lb ai/A)
Most sensitive parameter
Monocots
Onion
0.034*
0.016
Fresh weight
Corn
2.0
0.40
Fresh weight
Oat
0.45
0.08
Fresh weight
Sorghum
0.40
0.08
Fresh weight
Dicots
Buckwheat
2.0
0.40
Fresh weight
Cucumber
0.40
0.08
Fresh weight
Mustard
0.002*
0.00064
Fresh weight
Radish
0.08
0.0032
Fresh weight
Soybean
>2.00
>2.00
Fresh weight
tomato
0.03
0.016
Fresh weight
*Bold indicates inputs to TerrPlant.
54
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Table 4.6 Non-target Terrestrial Plant Vegetative Vigor Toxicity (Tier II) Data
Crop
Type of Study
Species
ec25
(lb ai/A)
NOAEC
(lb ai/A)
Most sensitive parameter
Monocots
Onion
0.40
0.08
Fresh weight
Corn
0.55
0.08
Fresh weight
Oat
1.8
0.40
Fresh weight
Sorghum
2.0
0.08
Fresh weight
Dicots
Buckwheat
>2.0
0.40
Fresh weight
Cucumber
0.08
0.0032
Fresh weight
Mustard
0.39
0.08
Fresh weight
Radish
>2.0
0.40
Fresh weight
Soybean
2.00
0.40
Fresh weight
Tomato
0.27
0.08
Fresh weight
*Bold indicates endpoint inputs to TerrPlant.
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 individual listed species and
aquatic animals that may indirectly affect the listed species of concern (U.S. EPA, 2004).
As part of the risk characterization, an interpretation of acute RQ for listed species is
discussed. This interpretation is presented in terms of the chance of an individual event
(i.e., mortality or immobilization) should exposure at the EEC actually occur for a species
with sensitivity to norflurazon 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.
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.
For norflurazon, there are no acute effect LOC exceedances; therefore IEC results
presented in Table 5.1 are only are for the effects chance at the LOC and the LC50,
assuming the default slope.
55
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4.4 Incident Database Review
A review of the EIIS database for ecological incidents involving norflurazon was
completed on November 25, 2008. The results of this review for terrestrial, plant, and
aquatic incidents are discussed below.
4.4.1 Plant Incidents
Seven terrestrial incidents are reported for norflurazon, all for adverse effects to plant
species, with the certainty determination for most as "possible". Of these, three were the
result of misuse and one was the result of a registered use (on plums in Tulare County,
CA).
4.4.2 Aquatic Incidents
Three aquatic incidents are reported. Two are for uses in Louisiana on cotton which were
classified as unlikely to be due to norflurazon. In these two incidents, mortality of
'thousands' of fish occurred in a nearby lake. Both of these incidents (1004021-005 and
1004021-004) are for the same date and the same county in LA, and therefore may be two
reports for the same incident. The other aquatic incident occurred in Delaware and was
of undetermined legality (of use) and undetermined target application. It is classified as
'possible' and involves the mortality of an unknown number of an unspecified species of
fish in 1992 (1000180-001).
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5.0 Risk Characterization
Risk characterization is the integration of the exposure and effects characterizations and
is used to determine the potential for direct and/or indirect effects to the CRLF or for
modification to its designated critical habitat from the use of norflurazon in CA. 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 or its designated critical habitat (i.e., "no effect," "likely to adversely
affect," or "may affect, but not likely to adversely affect").
5.1 Risk Estimation
Risk is estimated by calculating the ratio of exposure to toxicity. This ratio is the risk
quotient (RQ), which is compared to pre-established acute and chronic levels of concern
(LOCs) for each taxon evaluated. For acute exposures to the CRLF and its animal prey
in aquatic habitats, as well as terrestrial invertebrates, the LOC is 0.05. For acute
exposures to the CRLF and mammals, the LOC is 0.1. The LOC for chronic exposures to
CRLF and its prey, as well as acute exposures to plants is 1.0.
Risk to the aquatic-phase CRLF is estimated by calculating the ratio of exposure to
toxicity using l-in-10 year EECs based on the label-recommended norflurazon usage
scenarios summarized in Table 2.3 and the appropriate aquatic toxicity endpoint from
Table 4.1. Risks to the terrestrial-phase CRLF and its prey (e.g. terrestrial insects, small
mammals and terrestrial-phase frogs) are estimated based on exposures resulting from
applications of norflurazon (Section 3) and the appropriate toxicity endpoint from Table
4.3. Exposures are also derived for terrestrial plants, as discussed in Section 3.2 and
summarized in Table 3.7, based on the highest application rates of norflurazon use within
the action area.
5.1.1 Exposures in the Aquatic Habitat
5.1.1.1 Direct Effects to Aquatic-Phase CRLF
Direct acute effects to the aquatic-phase CRLF are based on peak EECs in the standard
pond and the lowest acute toxicity value for freshwater fish. In order to assess direct
chronic risks to the CRLF, 60-day EECs and the lowest chronic toxicity value for
freshwater fish are used. Aquatic EECs were generated using the Tier IIPRZM/EXAMS
model, as described in Section 3.1.1, RQs calculated with the highest acute (peak) and
chronic (60-day) EECs (from the rights-of-way use) do not exceed either the acute or
chronic LOC (Table 5.1); norflurazon will have no effect directly on the aquatic-phase
CRLF.
57
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Table 5.1 Summary of Direct Effect RQs for the Aquatic-phase CRLF
Direct Effects
to CRLF'1
Surrogate
Species
Toxicity
Value
(Hg/L)
EEC
(Hg/L)b
RQ
Probability of
Individual
Effect at
ES LOC
Probability of
Individual
Effect at RQ
Acute Direct
Toxicity
Rainbow
trout
LC50 = 8100
Peak: 79
0.009d
1 in 4.18E+11
1 in 5.9 E+19
Chronic Direct
Toxicity
NOAEC =
770
60-day: 78
0.10e
Not calculated for chronic
endpoints
a RQs associated with acute and chronic direct toxicity to the CRLF are also used to assess potential indirect
effects to the CRLF based on a reduction in freshwater fish and frogs as food items.
b The highest EEC based on foliar use of norflurazon on orchard crops at 3.93 lb ai/A.
0 A probit slope value for acute toxicity is not available; therefore, the effect probability was based the default
slope assumption.
d RQ < acute risk to endangered species LOC of 0.05.
e RQ < chronic risk LOC of 1.0.
5.1.1.2 Indirect Effects to Aquatic-Phase CRLF via Reduction in
Prey (non-vascular aquatic plants, aquatic invertebrates,
fish, and frogs)
a) Non-vascular Aquatic Plants
Indirect effects of norflurazon to the aquatic-phase CRLF (tadpoles) via reduction in non-
vascular aquatic plants as a food source are based on l-in-10 year peak EECs and the
lowest toxicity value (EC50) for aquatic non-vascular plants. All uses except fruit trees
and citrus exceed the LOC for nonvascular aquatic plants (Table 5.2). The maximum
EEC, for rights of way, results in an 8-fold exceedance of the LOC (RQ=7.9). Avocado
and almonds result in the highest EECs among the agricultural uses, with an
approximately 3.5-fold exceedance of the LOC. Based on these results, norflurazon is
likely to indirectly affect the CRLF via reduction in nonvascular plants for all uses except
fruit trees and citrus.
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Table 5.2 Summary of RQs Used to Estimate Indirect Effects to the CRLF via
Effects to Non-Vascular Aquatic Plants (ECso=9.7 jig/L) (diet of CRLF in tadpole
life stage and habitat of aquatic-phase CRLF).
Scenario
Application
Rate
Date of First
Application
Crops Represented
Peak
EEC
RQ
California
fruit trees
(non-
citrus)
3.93
March 15
Apples, apricots, cherries,
nectarines, peaches, pears,
plums and prunes
7.4
0.76
Alfalfa
0.983x2
January 1
Alfalfa
27.3
2.8*
Avocado
3.93
March 15
Avocado
36.4
3.8*
Almond
3.93
August 15
Almonds, filberts
(hazelnuts) and walnuts
(black and English)
34.7
3.6*
Citrus
3.93
March 15
Citrus
5.0
0.52
Grapes
3.93
March 15
Grapes, blueberries,
caneberries, hops
14.4
1.5*
Nursery
2.358
March 15
Nursery Stock
41.8
4.3*
Rights of
Way
3.93
March 15
Industrial areas, refuse/solid
waste sites (outdoors),
non agricultural
ROW/fencerows/hedgerows,
non agricultural uncultivated
areas/soils
79
8.1*
*Exceeds risk to non-vascular plant LOC (RQ>1.0)
b) Aquatic Invertebrates
Indirect acute effects to the aquatic-phase CRLF via effects to invertebrate prey in
aquatic habitats are based on peak EECs and the lowest acute toxicity value for
freshwater invertebrates. For chronic risks, 21-day EECs and the lowest chronic toxicity
value for invertebrates are used to derive RQs. The highest acute and chronic aquatic
invertebrate RQ values do not exceed the LOC (Table 5.3). Because the acute aquatic
invertebrate endpoint (EC50) is greater than 15 mg ai/L, the highest dose tested, the acute
RQ is a less than value. Based on these RQs, norflurazon is not likely to indirectly affect
the CRLF via reduction in freshwater invertebrate prey items (no effect).
59
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Table 5.3 Summary of Acute and Chronic RQs Used to Estimate Indirect Effects to
the CRLF via Direct Effects on Aquatic Invertebrates as Dietary Food Items (prey
of CRLF juveniles and adults in aquatic habitats) Based on Acute LC50 and Chronic
NOAEC Toxicity Endpoints for Daphttia magna of >15,000 jig/L and 1,000 jig/L,
respectively.
Uses
Application rate
(lb ai/A)
Peak EEC
(Hg/L)
21-day
EEC
(Mg/L)
Indirect
Effects
Acute RQ*
Indirect
Effects
Chronic RQ*
Highest aquatic
exposure (ROWs)
3.93
79
78
<0.005
0.08
c) Fish and Frogs
Fish and frogs also represent potential prey items of adult aquatic-phase CRLFs. RQs
associated with acute and chronic direct toxicity to the CRLF (Table 5.1) are used to
assess potential indirect effects to the CRLF based on a reduction in freshwater fish and
frogs as food items. Because the RQs for direct acute effects to the CRLF, which are
based on the more conservative listed species LOC, do not result in exceedances,
norflurazon is not likely to acutely indirect affect the CRLF via reduction in freshwater
fish and frogs as food items (no effect).
5.1.1.3 Indirect Effects to CRLF via Reduction in Habitat and/or
Primary Productivity (Freshwater Aquatic Plants)
Indirect effects to the CRLF via direct toxicity to aquatic plants are estimated using the
most sensitive non-vascular and vascular plant toxicity endpoints. Because there are no
obligate relationships between the CRLF and any aquatic plant species, the most sensitive
EC50 values, rather than NOAEC values, were used to derive RQs. The EECs for the
rights-of-way use resulted in an exceedance for aquatic vascular plants based on the
sensitivity of Lemna gibba (RQ=1.4). No other use resulted in an exceedance for aquatic
vascular plants. Based on this result, norflurazon may indirectly affect the CRLF via
effects to vascular plants in proximity to rights of way and industrial areas.
Potential effects to nonvascular aquatic plants were presented in Section 5.1.1,2a. RQs
exceed the LOC for all use patterns except citrus and fruit trees.
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Table 5.4 Summary of RQs Used to Estimate Indirect Effects to the CRLF via
Effects to Vascular Aquatic Plants (habitat of aquatic-phase CRLF) Based on L.
gibba EC50 of 58.2 jig/L.
Scenario
Application
Rate
Date of First
Application
Crops Represented
Peak EEC
RQ
California
fruit trees
3.93
March 15
Apples, apricots, cherries,
nectarines, peaches, pears,
plums and prunes
7.4
0.13
Alfalfa
0.983x2
January 1
Alfalfa
27.3
0.47
Avocado
3.93
March 15
Avocado
36.4
0.62
Almond
3.93
August 15
Almonds, filberts
(hazelnuts) and walnuts
(black and English)
34.7
0.60
Citrus
3.93
March 15
Citrus
5.0
0.09
Grapes
3.93
March 15
Grapes, blueberries,
caneberries, hops
14.4
0.25
Nursery
2.358
March 15
Nursery Stock
41.8
0.72
Rights-of-
Way
3.93
March 15
Industrial areas, refuse/solid
waste sites (outdoors),
non agricultural
ROW/fencerows/hedgerows,
non agricultural uncultivated
areas/soils
79
1.4*
*Exceeds vascular aquatic plant LOC.(RQ>1.0)
5.1.2 Exposures in the Terrestrial Habitat
5.1.2.1 Direct Effects to Terrestrial-phase CRLF
As previously discussed in Section 3.2, potential direct effects to terrestrial-phase CRLFs
are based on foliar applications of norflurazon.
Potential direct acute effects to the terrestrial-phase CRLF are derived by considering
dose- and dietary-based EECs modeled in T-REX for a small bird (20 g) consuming
small invertebrates and acute oral and subacute dietary toxicity endpoints for avian
species.
Potential direct chronic effects of norflurazon to the terrestrial-phase CRLF are derived
by considering dietary-based exposures modeled in T-REX for a small bird (20g)
consuming small invertebrates. Chronic effects are estimated using the lowest available
toxicity data for birds. EECs are divided by toxicity values to estimate chronic dietary-
based RQs.
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The avian acute and subacute endpoints are not definitive {i.e. greater than values),
therefore definitive RQs cannot be calculated. There was no mortality in any of the
studies, and the potential for direct acute or subacute effects to the CRLF are presumed
low. However, using these endpoints to calculate RQs can provide insight into the
potential for direct effects to the CRLF. Using the subacute dietary endpoint, LC50
>10,000 mg ai/kg-diet, results in a dietary RQ value of <0.05, which is below the acute
risk LOC of 0.1 for listed avian species. The dose-based endpoint, LD50 >2510 mg ai/kg-
bw, results in an RQ <0.46, below the acute risk LOC but potentially greater than the
acute risk to listed species LOC.
Although the avian acute RQ is not definitive, and the potential for direct acute risk to
birds is low, the T-HERPS model was used to refine the dietary-based risk estimate based
on the lower food demand of amphibians. The use of this model, using the LD50> 2,510
mg ai/kg-bw as if it were an endpoint, results in RQs <0.01. Based on these results,
norflurazon is not likely to directly affect the terrestrial-phase of the CRLF.
Direct effects to the CRLF from chronic exposure are estimated using the results from the
avian reproduction studies (NOAEC = 40 mg ai/kg-diet). The resulting dietary-based RQ
= 13, based on the upper-bound EECs. The T-REX model indicates EECs may remain at
or above 40 ppm for up to 76 days following application. Based on these results, direct
effects through chronic exposure may affect the terrestrial-phase CRLF.
Table 5.5 Summary of Chronic RQs* Used to Estimate Direct Effects to the
Terrestrial-phase CRLF.
Use
(Application Rate)
Dictary-bascd Chronic RQ1
Non agriculture and Agricultural uses (except
alfalfa)
13*
Alfalfa
6*
* = chronic risk LOC exceeded (chronic RQ > 1)
1 Based on avian NOAEC = 40 mg ai/kg-diet.
5.1.2.2 Indirect Effects to Terrestrial-Phase CRLF via
Reduction in Prey (terrestrial invertebrates, mammals,
and frogs)
a) Terrestrial Invertebrates
Chemicals with an acute toxicity value of >11 |ig ai/bee are classified as practically
nontoxic to bees. Norflurazon was tested up to 235 |ig ai/ bee in both acute contact and
acute ingestion studies (LD50 >235 |ig ai/bee). Given that no mortality or sublethal
effects were observed in either study, the potential of norflurazon to affect terrestrial
62
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invertebrates is considered low, and given the nondefinitive endpoint, RQs are not
calculated. Norflurazon is not likely to indirectly affect CRLF through effects on the
terrestrial invertebrate prey items.
b) Mammals
Risks associated with ingestion of small mammals by large terrestrial-phase CRLFs are
derived for dietary-based and dose-based exposures modeled in T-REX for a small
mammal (15g) consuming short grass. Acute and chronic effects are estimated using the
most sensitive mammalian toxicity data. EECs are divided by the toxicity value to
estimate acute and chronic dose-based RQs as well as chronic dietary-based RQs (Table
5.6). The acute dose-based RQ, calculated with the LD50 = 9,300 mg ai/kg-bw, is 0.04,
well below the acute risk LOC for mammals; therefore acute effects to mammals are not
likely to affect the CRLF mammalian prey items.
RQs for mammalian effects from chronic exposure to norflurazon are possible, due to
exceedance of the LOC by both the dose-based and the dietary-based RQs (Table 5.7).
Because of the roughly 26- to 55-fold exceedances of the LOC, norflurazon may
indirectly affect the CRLF via reduction in small mammal prey items via chronic effects
on offspring growth.
Table 5.6 Summary of Acute and Chronic RQs* Used to Estimate Indirect Effects
to the Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary
Food Items Based on an Acute Oral LD50 of 9300 mg/kg-bw and Chronic NOAEC of
150 mg/kg-diet.
Use
(Application Rsite)
Chronic RQ
Acute RQ
Dosc-bascd Chronic RQ1
Dictary-bascd
Chronic RQ2
Dosc-bascd Acute RQ3
All uses (except alfalfa)
(3.93 lbai/A)
55*
6.3*
0.04
Alfalfa (0.983 x 2)
26*
2.9*
0.02
* = chronic risk LOC exceeded (chronic RQ >1)
c) Frogs
An additional prey item of the adult terrestrial-phase CRLF is other species of frogs. In
order to assess risks to these organisms, dietary-based and dose-based exposures modeled
in T-REX and T-HERPS for a small bird (20g) consuming small invertebrates are used.
As noted previously (Section 5.1.2.1), norflurazon is practically nontoxic to birds on both
an acute oral and subacute dietary exposure basis and based on birds serving as
surrogates for terrestrial-phase amphibians, indirect risk to terrestrial CRLF from acute
effects to frogs serving as prey is assumed to be low. However, chronic effects (RQ
range: 6-13) to the CRLF terrestrial-phase amphibian prey items are possible (Table 5.5).
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5.1.2.3 Indirect Effects to CRLF via Reduction in Terrestrial
Plant Community (Riparian and Upland Habitat)
Potential indirect effects to the CRLF resulting from direct effects on riparian and upland
vegetation are assessed using the EC25S from terrestrial plant seedling emergence and
vegetative vigor studies to calculate RQs (Table 5.7 and Table 5.8). Based on LOC
exceedances for all use patterns at the maximum single application rate, norflurazon may
indirectly affect the CRLF via reduction in terrestrial plants as habitat. Example output
from TerrPlant v. 1.2.2 is provided in Appendix F.
Table 5.7 RQs for Monocots Inhabiting Dry and Semi-Aquatic Areas Exposed to
Norflurazon via Runoff and Drift.
Use
Application
rate
(lbs a.i./A)
Application
method
Drift
Value
(%)
Sprav drift
RQ
Drv area
RQ
Semi-aquatic
area RQ
All uses (except
alfalfa)
3.93
Ground
1
1.2*
3.5*
24*
Alfalfa
0.983
Aerial
5
1.4*
2.0*
7.2*
Alfalfa
0.983
Ground
1
0.3
0.9
6.1*
* = Terrestrial plant risk LOC exceeded (RQ > 1); exceedances are bolded and shaded.
Table 5.8 RQs for Dicots Inhabiting Dry and Semi-Aquatic Areas Exposed to
Norflurazon via Runoff and Drift
Use
Application
rate
(lbs a.i./A)
Application
method
Drift
Value
(%)
Sprav drift
RQ
Drv area
RQ
Semi-aquatic
area RQ
All uses (except
alfalfa)
3.93
Ground
1
20*
58*
413*
Alfalfa
0.983
Aerial
5
25*
34*
123*
Alfalfa
0.983
Ground
1
4.9*
15*
103*
* = Terrestrial plant risk LOC exceeded (RQ > 1); exceedances are bolded and shaded.
5.1.3 Primary Constituent Elements of Designated Critical Habitat
5.1.3.1 Aquatic-Phase (Aquatic Breeding Habitat and Aquatic
Non-Breeding Habitat)
Three of the four assessment endpoints for the aquatic-phase primary constituent
elements (PCEs) of designated critical habitat for the CRLF are related to potential
effects to aquatic and/or terrestrial plants:
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.
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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.
Reduction and/or modification of aquatic-based food sources for pre-metamorphs
(e.g., algae).
Based on the risk estimation for potential effects to aquatic and terrestrial plants provided
in Sections 5.1.1.2, 5.1.1.3, and 5.1.2.3, norflurazon is likely to affect aquatic-phase PCEs
of designated habitat related to effects on aquatic and/or terrestrial plants. Although the
RQ for aquatic vascular plants (Table 5.4) only indicates potential for indirect effects to
the CRLF for the rights-of-way use, effects to water quality may occur through effects on
aquatic nonvascular plants (Table 5.2) for all uses except fruit trees and citrus, as
indicated by the roughly 8-fold exceedance of the LOC for rights-of-way and
exceedances for other use patterns. Alterations can be expected in the species
composition of and/or relative abundance in terrestrial plant communities, especially in
riparian areas. The RQs for terrestrial plants for the highest application rate range from
1.2 for sensitive monocots based on drift exposure alone to 413 for sensitive dicots for
areas receiving higher runoff (semi-aquatic areas).
The remaining aquatic-phase PCE is "alteration of other chemical characteristics
necessary for normal growth and viability of CRLFs and their food source." To assess
the impact of norflurazon on this PCE (i.e., alteration of food sources), acute and chronic
freshwater fish and invertebrate toxicity endpoints, as well endpoints for aquatic non-
vascular plants, are used as measures of effects. RQs for these endpoints were calculated
in Sections 5.1.1.1 and 5.1.1.2. Although indirect effects to the CRLF due to norflurazon
are not likely based on the acute and chronic RQs for fish and aquatic invertebrates,
reductions in the availability of algae as a food source for the aquatic-phase CRLF can be
expected, based on the roughly 8-fold exceedance of the LOC for nonvascular aquatic
plants. Therefore, norflurazon may affect aquatic-phase PCEs of designated habitat
related to effects of alteration of other chemical characteristics necessary for normal
growth and viability of CRLFs and their food source.
5.1.3.2 Terrestrial-Phase (Upland Habitat and Dispersal
Habitat)
Two of the four assessment endpoints for the terrestrial-phase PCEs of designated critical
habitat for the CRLF are related to potential effects to terrestrial plants:
Elimination and/or disturbance of upland habitat; ability of habitat to support food
source of CRLFs: Upland areas within 200 ft of the edge of the riparian
vegetation or dripline surrounding aquatic and riparian habitat that are comprised
of grasslands, woodlands, and/or wetland/riparian plant species that provides the
CRLF shelter, forage, and predator avoidance
Elimination and/or disturbance of dispersal habitat: Upland or riparian dispersal
habitat within designated units and between occupied locations within 0.7 mi of
65
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each other that allow for movement between sites including both natural and
altered sites which do not contain barriers to dispersal
The risk estimation for terrestrial-phase PCEs of designated habitat related to potential
effects on terrestrial plants is provided in Section 5.1.2.3. These results will inform the
effects determination for modification of designated critical habitat for the CRLF.
The third terrestrial-phase PCE is "reduction and/or modification of food sources for
terrestrial phase juveniles and adults." To assess the impact of norflurazon on this PCE,
acute and chronic toxicity endpoints for birds, mammals, and terrestrial invertebrates are
used as measures of effects. RQs for these endpoints were calculated in Section 5.1.2.2.
Based on the chronic LOC exceedance for birds (terrestrial-phase frogs) and mammals
that serve as prey for CRLFs, norflurazon may affect the third terrestrial-phase PCE.
The fourth terrestrial-phase PCE is based on chemical alteration of characteristics
necessary for normal growth and viability of juvenile and adult CRLFs and their food
source. Because of the potential effects to terrestrial plants as habitat for the CRLF and
its food sources and because the chronic risk LOC for direct effects to the CRLF is
exceeded, norflurazon may affect the fourth terrestrial-phase PCE.
5.1.4 Spatial Extent of Potential Effects
An LAA determination applies to those areas where it is expected that the pesticide's use
will directly or indirectly affect the CRLF or its designated critical habitat. To determine
this area, the footprint of norflurazon's use pattern is identified, using land cover data that
correspond to norflurazon's use pattern. The spatial extent of the effects determination
also includes areas beyond the initial area of concern that may be impacted by runoff
and/or spray drift. The identified effects and/or modification to critical habitat are
anticipated to occur only for those currently occupied core habitat areas, CNDDB
occurrence sections, and designated critical habitat for the CRLF that overlap with the
initial area of concern plus 1867' spray drift distance from its boundary, based on Tier 3
modeling. It is assumed that non-flowing waterbodies (or potential CRLF habitat) are
included within this area.
In addition to the spray drift buffer, the results of the downstream dilution extent analysis
result in a distance of 58 kilometers which represents the maximum continuous distance
of downstream dilution from the edge of the initial area of concern. If any of these
streams reaches flow into CRLF habitat, there is potential to affect either the CRLF or
modify its habitat. These lotic aquatic habitats within the CRLF core areas and critical
habitats potentially contain concentrations of norflurazon sufficient to result in LAA
determination and modification of critical habitat.
The determination of the buffer distance and downstream dilution for spatial extent of the
effects determination is described below.
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5.1.4.1 Spray Drift
In order to determine terrestrial and aquatic habitats of concern due to norflurazon
exposures through spray drift, it is necessary to estimate the distance that spray
applications can drift from the treated area and still be present at concentrations that
exceed levels of concern. An analysis of spray drift distances was completed using
AgDrift.
For norflurazon use relative to the terrestrial-phase CRLF, the results of the screening-
level risk assessment indicate that spray drift using the most sensitive endpoints for
terrestrial plants extends as far as 1,867'. Based on this assessment, effects from spray
drift are not expected beyond this distance.
In order to characterize the spatial extent of the effects determination that is relevant to
the CRLF {i.e. NLAA versus LAA), the analysis was conducted using the most sensitive
non-endangered plant EC25 of 0.002 lbs ai/A, for dicot seedling emergence. The NOAEC
is used when there is an obligate relationship between the species being assessed and
endangered plants (or other taxa). However, there is no obligate relationship between the
CRLF and any endangered plant; therefore the LAA/NLAA determination is based on the
area defined by the non-listed species LOC {i.e., EEC/EC25).
The estimated buffer distance identifies those locations where terrestrial landscapes can
be impacted by spray drift deposition alone (no runoff considered) at concentrations
above the LOC for terrestrial plants. The LOC was compared to the highest RQ for aerial
applications to alfalfa at 0.983 lbs ai/A. The maximum effect distance for the alfalfa
aerial use of norflurazon on dicot seedling emergence is 1,867 ft. For ground
applications at the 3.93 lbs ai/A, the maximum distance LOC is exceeded is 990 ft.
Given that the greatest buffer distance is 1,867 ft for terrestrial plants, this value was used
to define the spatial extent of the effects determination (i.e., this buffer distance is added
to the initial area of concern).
5.1.4.2 Downstream Dilution Analysis
The downstream extent of exposure in streams and rivers where the EEC could
potentially be above levels that would exceed the most sensitive LOC was evaluated. To
complete this assessment, the greatest ratio of aquatic RQ to LOC was estimated. Using
an assumption of uniform runoff across the landscape, it is assumed that streams flowing
through treated areas (i.e. the initial area of concern) are represented by the modeled
EECs; as those waters move downstream, it is assumed that the confluence of non-
impacted water will dilute the concentrations of norflurazon present.
Using a EC50 value of 9.7 |ig/L for non-vascular aquatic plants (the most sensitive
species) and a peak EEC for the avocado use 36 |ig/L yields an RQ/LOC ratio of 3.6
(3.6/1). Although the rights-of-way use has a higher EEC, this use pattern is likely to be
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quite marginal based on the PUR data, which indicates rights-of way account for <2% of
total pounds applied. Using the downstream dilution approach (described in more detail
in Appendix B) results in a distance of 58 kilometers, which represents the maximum
continuous distance of downstream dilution from the edge of the initial area of concern.
5.2 Risk Description
The risk description synthesizes an overall conclusions regarding the likelihood of
adverse impacts leading to an effects determination (i.e., "no effect," "may affect, but not
likely to adversely affect," or "likely to adversely affect") for the CRLF and its
designated critical habitat.
If the RQs presented in the Risk Estimation (Section 5.1) show no direct or indirect
effects for the CRLF, and no modification to PCEs of the CRLF's designated critical
habitat, a "no effect" determination is made, based on norflurazon's use within the
action area. However, if direct or indirect effect LOCs are exceeded and effects may
modify the PCEs of the CRLF's critical habitat, the Agency concludes a preliminary
"may affect" determination for the FIFRA regulatory action regarding norflurazon.
A preliminary effects determination of "may affect" is made for the CRLF and critical
habitat from the uses of norflurazon. A summary of the results of risk estimation are
provided in Table 5.9 for direct and indirect effects to the CRLF and in Table 5.10 for
the PCEs of designated critical habitat for the CRLF.
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Table 5.9 Risk Estimation Summary for Norflurazon - Direct and Indirect Effects to
CRLF
Assessment Endpoint
LOC
Exceedances
(Y/N)
Description of Results of Risk Estimation
Aquatic-Phase CRLF
(eggs, larvae, tadpoles, juveniles, and adults)
Direct Effects
Survival, growth, and reproduction
of CRLF individuals via direct
effects on aquatic phases
No
There are no LOC exceedances for fish, the surrogate for the
aquatic-phase CRLF
Indirect Effects
Survival, growth, and reproduction
of CRLF individuals via effects to
food supply (i.e., freshwater
invertebrates, non-vascular plants)
Yes
Although there are no LOC exceedances for aquatic
invertebrates, there are exceedances for aquatic non-vascular
plants.
Indirect Effects
Survival, growth, and reproduction
of CRLF individuals via effects on
habitat, cover, and/or primary
productivity (i.e., aquatic plant
community)
Yes
There are exceedances of the LOC for both vascular and non-
vascular plants.
Indirect Effects
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.
Yes
Effects are possible to aquatic vascular plants. RQs for
terrestrial plants vary, but effects on the seedling emergence of
sensitive plant species are expected.
Terrestrial-Phase CRLF
(Ju veniles and adults)
Direct Effects
Survival, growth, and reproduction
of CRLF individuals via direct
effects on terrestrial phase adults and
juveniles
Yes
Although no direct acute effects to the CRLF are expected,
there is a possibility for effects from chronic exposure
Indirect Effects
Survival, growth, and reproduction
of CRLF individuals via effects on
prey (i.e., terrestrial invertebrates,
small terrestrial mammals and
terrestrial phase amphibians)
Yes
Although acute effect to these prey items are not expected,
effects from chronic exposure to mammalian and amphibian
prey items may occur
Indirect Effects
Survival, growth, and reproduction
of CRLF individuals via effects on
habitat (i.e., riparian vegetation)
Yes
RQs for terrestrial plants vary, but effects on the seedling
emergence of sensitive plant species are expected
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Table 5.10 Risk Estimation Summary for Norflurazon - PCEs of Designated
Critical Habitat for the CRLF
Assessment Endpoint
LOC Exceedances
(Y/N)
Deseription of Results of Risk Estimation
Aquatic Phase PCEs
(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)
Alteration of channel/pond morphology or
geometry and/or increase in sediment
deposition within the stream channel or
pond: aquatic habitat (including riparian
vegetation) provides for shelter, foraging,
predator avoidance, and aquatic dispersal
for juvenile and adult CRLFs.
Yes
Effects to aquatic vascular plants are expected for
ROW uses. RQs for terrestrial plants vary, but
effects on the seedling emergence of sensitive plant
species are expected
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.
Yes
Aquatic plants may be affected by norflurazon use.
RQs for terrestrial plants vary, but effects on
sensitive plant species are expected
Alteration of other chemical characteristics
necessary for normal growth and viability of
CRLFs and their food source.
Yes
Due to potential effects on aquatic plants and
terrestrial riparian plant species, alteration in
chemical characteristics of aquatic habitat (e.g.
dissolved oxygen) may occur.
Reduction and/or modification of aquatic-
based food sources for pre-metamorphs
(e.g., algae)
Yes
Effects to aquatic plant species are expected
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
Yes
RQs for terrestrial plants vary, but effects on
sensitive plant species are expected
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
Yes
RQs for terrestrial plants vary, but effects on
sensitive plant species are expected; these effects
may alter plant communities necessary for dispersal
habitat
Reduction and/or modification of food
sources for terrestrial-phase juveniles and
adults
Yes
Chronic effects are expected on amphibians and
mammal that serve as prey for CRLFs
Alteration of chemical characteristics
necessary for normal growth and viability of
juvenile and adult CRLFs and their food
source.
Yes
Changes in aquatic vegetation and riparian
communities may alter the chemical characteristic of
CRLF habitat
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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. Based on the best available
information, the Agency uses the refined evaluation to distinguish those actions that
"may affect, but are not likely to adversely affect" from those actions that are "likely to
adversely affect" the CRLF and its designated critical habitat.
The criteria used to make determinations that the effects of an action are "not likely to
adversely affect" the CRLF and its designated critical habitat include the following:
Significance of Effect: Insignificant effects are those that cannot be meaningfully
measured, detected, or evaluated in the context of a level of effect where "take"
occurs for even a single individual. "Take" in this context means to harass or
harm, defined as the following:
¦ Harm includes significant habitat modification or degradation that
results in death or injury to listed species by significantly impairing
behavioral patterns such as breeding, feeding, or sheltering.
¦ Harass is defined as actions that create the likelihood of injury to listed
species to such an extent as to significantly disrupt normal behavior
patterns which include, but are not limited to, breeding, feeding, or
sheltering.
Likelihood of the Effect Occurring: Discountable effects are those that are
extremely unlikely to occur.
Adverse Nature of Effect: Effects that are wholly beneficial without any adverse
effects are not considered adverse.
A description of the risk and effects determination for each of the established assessment
endpoints for the CRLF and its designated critical habitat is provided in Sections 5.2.1
through 5.2.3.
5.2.1 Direct Effects
5.2.1.1 Aquatic-Phase CRLF
The aquatic-phase considers life stages of the frog that are obligatory aquatic organisms,
including eggs and larvae. It also considers submerged terrestrial-phase juveniles and
adults, which spend a portion of their time in water bodies that may receive runoff and
spray drift containing norflurazon.
No acute or chronic RQs presented in Section 5.1.1.1 and Table 5.1 exceed the LOCs for
direct effects to the aquatic-phase CRLF. No direct effects to the aquatic-phase CRLF
are expected from the labeled uses of norflurazon. Although there are reported fish kill
incidents for norflurazon, they are considered unlikely to be due to norflurazon (NE).
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5.2.1.2 Terrestrial-Phase CRLF
Acute and chronic RQs presented in Section 5.1.2.1 provide the basis for risk estimation
to the terrestrial-phase CRLF. Direct acute effects to the CRLF are not expected, based
on the lack of LOC exceedances. No mortalities were observed in any of the acute oral
or sub-acute dietary toxicity studies of birds that serve as surrogates for terrestrial-phase
amphibians, although some loss of breast feathers was noted in the bobwhite quail sub-
acute dietary toxicity study. However, direct chronic effects to the CRLF are possible,
based on the exceedances of the chronic risk LOC. The NOAEC is based on decreased
survival of 14-d chicks, and this effect could represent potential effects to the CRLF
(LAA).
5.2.2 Indirect Effects (via Reductions in Prey Base)
5.2.2.1 Algae (non-vascular aquatic plants)
As discussed in Section 2.5.3, the diet of CRLF tadpoles is composed primarily of
unicellular aquatic plants {i.e., algae and diatoms) and detritus. Because the aquatic
nonvascular plant RQs exceed the LOC for all uses except citrus and non-citrus fruit
trees, norflurazon is considered likely to indirectly affect the aquatic-phase CRLF via
effects on aquatic nonvascular plants (LAA).
5.2.2.2 Aquatic Invertebrates
The potential for norflurazon to elicit indirect effects to the CRLF via effects on
freshwater invertebrate food items is dependent on several factors including: (1) the
potential magnitude of effect on freshwater invertebrate individuals and populations; and
(2) the number of prey species potentially affected relative to the expected number of
species needed to maintain the dietary needs of the CRLF. Together, these data provide a
basis to evaluate whether the number of individuals within a prey species is likely to be
reduced such that it may indirectly affect the CRLF.
Neither the acute nor chronic aquatic invertebrate RQs presented in Section 5.1.1.2
(Table 5.3) exceed the LOCs, based on results from the modeling. Therefore,
norflurazon is not considered likely to indirectly affect the CRLF via effects on aquatic
invertebrates (NE).
5.2.2.3 Fish and Aquatic-phase Frogs
Based on the results from Section 5.2.1.1, which report acute and chronic LOCs for fish
and aquatic invertebrates are not exceeded, indirect effects to the CRLF are not expected
via effects to fish and aquatic-phase frogs as food items (NE).
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5.2.2.4 Terrestrial Invertebrates
When the terrestrial-phase CRLF reaches juvenile and adult stages, its diet is mainly
composed of terrestrial invertebrates. In the absence of other relevant data, potential
effects to terrestrial invertebrates are assessed using registrant-submitted acute toxicity
studies for honey bees. For norflurazon, no mortality or sublethal effects were reported
for the acute contact and acute oral honey bee studies at the highest dose tested (235 |ig
ai/bee). The Agency considers an LD50 >11 |ig ai/bee to be practically nontoxic to bees.
Therefore, indirect affects to the CRLF via decreased availability of terrestrial
invertebrate prey items from the use of norflurazon are not expected (NE).
5.2.2.5 Mammals
Life history data for terrestrial-phase CRLFs indicate that large adult frogs consume
terrestrial vertebrates, including mice. Acute RQs for mammals do not exceed the LOC,
and therefore indirect effects to the terrestrial-phase CRLF from acute effects to
mammalian prey are not expected. However, both the dietary-based and the dose-based
chronic RQs (Table 5.6) exceed the LOC for all uses (3- 55-fold). Therefore indirect
effects to the CRLF via reduction in small mammal prey items that are exposed to
norflurazon are likely (LAA).
5.2.2.6 Terrestrial-phase Amphibians
Terrestrial-phase adult CRLFs also consume frogs. RQ values representing direct
exposures of norflurazon to terrestrial-phase CRLFs are used to represent exposures of
norflurazon to frogs in terrestrial habitats. Indirect effects to frogs as food items are
based on results from the direct effects analysis for terrestrial-phase CRLF.
Results from Section 5.2.1.2 indicate that no acute effects on amphibian food items are
expected. However, the frog prey base may be adversely affected from chronic exposure
to norflurazon, based on the 6- to 13-fold exceedance of the chronic risk LOC (Table
5.5) (LAA).
5.2.3 Indirect Effects (via Habitat Effects)
5.2.3.1 Aquatic Plants (Vascular and Nonvascular)
Aquatic plants serve several important functions in aquatic ecosystems. Nonvascular
aquatic plants are primary producers and provide the autochthonous energy base for
aquatic ecosystems and affect water quality. Vascular plants provide structure as
attachment sites and refugia for many aquatic invertebrates, fish, and juvenile organisms,
such as fish and frogs. In addition, vascular plants provide primary productivity and
oxygen to the aquatic ecosystem. Rooted plants help reduce sediment loading and
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provide stability to near shore areas and lower stream banks. In addition, vascular
aquatic plants are important as attachment sites for egg masses of CRLFs.
Potential indirect effects to the CRLF based on impacts to habitat and/or primary
production were assessed using RQs from freshwater aquatic vascular and non-vascular
plant data. The RQ for nonvascular plants exceeds the LOC for all uses except citrus and
fruit trees (previously described in Section 5.2.2.1 and summarized in Table 5.2).
Therefore, there is a potential for indirect impact to CRLF habitat through adverse effects
to nonvascular plants (HM).
The aquatic vascular plant RQ (RQ=1.4) exceeds the LOC for the rights-of -
way/industrial sites use. No other use pattern results in an exceedance for aquatic
vascular plants. The nonagricultural uses of norflurazon have a reported total annual
average usage of 320 lbs. out of a total annual average usage of 11,360 lbs, for the State
of California (CDPR-PUR; Table 2.4). These data indicate that nonagricultural uses
average <2% of the total norflurazon use in California.
As a pre-emergent herbicide, norflurazon is likely to be applied in limited, highly
managed rights of way and industrial areas, as opposed to more rural rights-of-way likely
to be adjacent to CRLF habitat, where the use of post-emergent (established plant)
herbicides are likely to be more effective.
The RQ of 1.4 for rights-of-way is based on the EEC of 75 ppb. If the model's input
parameters, such as amount of impervious surface or application rate, are higher than
those actually used, the EEC would be less than estimated by the model. If the EEC was
60 ppb or less, the RQ would not exceed the LOC.
Although widespread affects on the habitat of the CRLF via effects of norflurazon on
aquatic vascular plants unlikely, norflurazon use is likely to effect to aquatic vascular
plants in specific local situations (HM).
5.2.3.2 Terrestrial Plants
Terrestrial plants serve several important habitat-related functions for the CRLF. In
addition to providing habitat and cover for invertebrate and vertebrate prey items of the
CRLF, terrestrial vegetation also provides shelter for the CRLF and cover from predators
while foraging. Terrestrial plants also provide energy to the terrestrial ecosystem through
primary production. Upland vegetation including grassland and woodlands provides
cover during dispersal. Riparian vegetation helps to maintain the integrity of aquatic
systems by providing bank and thermal stability, serving as a buffer to filter out sediment,
nutrients, and contaminants before they reach the watershed, and serving as an energy
source.
As expected for a pre-emergent herbicide, the most sensitive toxicity endpoints were for
biomass reductions in the seedling emergence study. While the vegetative vigor study
demonstrated effects from exposure to norflurazon, the effects (on biomass) occurred at
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higher exposures than in the seedling emergence study. Based on TerrPlant, endpoints
from the vegetative vigor studies do not result in exceedances of the LOC, except for
dicots from drift alone for the alfalfa use (RQ =3.1). This exceedance is due to the higher
drift assumption for aerial use. The RQ results from the radish endpoint; none of the
other nine species tested in the vegetative vigor study results in an exceedance for any
use pattern. Given that norflurazon is a pre-emergent herbicide, it is expected that broad
across-species sensitivity to established plants would be low. However, as exhibited by
radish, sensitive dicots exposed to a sufficient amount norflurazon drift may be adversely
affected.
Because loading is based on runoff plus spray drift, there is uncertainty regarding the
exposure estimate. It is not known whether plants will be exposed to both the spray drift
and runoff components at the same time. Exceedances for seedling emergence occur for
both monocots and dicots, although only for the onion, mustard and tomato endpoints.
However, given the RQs range from 3.5 to more than 413, effects to the emergence of
sensitive plant are likely, especially those in vulnerable areas, such as wetlands.
Sensitivity to norflurazon varied widely across test species in the seedling emergence
study, and highly sensitive species (as evidenced with mustard) may be affected at very
low exposures. The highest RQs are for areas receiving the greatest amount of runoff
(e.g. wetland areas) adjacent to application sites. As with dryer areas, these RQs are
estimated using loading to adjacent areas, which is runoff (based on solubility) plus drift
(e.g. 1% for ground applications). Therefore the exposure values will decrease with
distance from the application site and will be limited by the distance the runoff maintains
the modeled EECs and the distance norflurazon spray will drift.
Application method, aerial or ground, is an important factor in how far from the
application site norflurazon may drift in sufficient amounts to affect sensitive plant
species. As a pre-emergent herbicide, norflurazon is likely to be applied to bare ground
or over the top of insensitive crop species. The distance spray drift can travel is affected
by wind speed and direction and the height of application above the ground, droplet size
and the potential for interception by established nontarget plants (such as windrows and
established plants). Ground spray application at the lowest practical boom height greatly
reduces the distance drift will travel. Because the alfalfa use pattern allows aerial spray,
drift mitigation is likely limited to specifying a larger droplet size for application.
To refine the potential effect of spray drift on terrestrial plants, the AgDRIFT model is
used. Using the results from AgDRIFT, highly sensitive plants such as mustard may
have their emergence affected as far as 1,867' from the application area for aerial
application (alfalfa use). For ground applications at the 3.93 lbs ai/A rate, emergence
effects may occur to sensitive plants such as mustard 990 ft from the application site.
Possible emergence effects to plants less sensitive than mustard or from effects to
vegetative vigor of any species are likely not to occur great than 150 ft from the
application area.
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Based on this assessment, the labeled use of norflurazon has the potential to indirectly
affect the CRLF through disruption in plant communities and habitat modification (HM).
5.2.4 Modification to Designated Critical Habitat
5.2.4.1 Aquatic-Phase PCEs
Three of the four assessment endpoints for the aquatic-phase primary constituent
elements (PCEs) of designated critical habitat for the CRLF are related to potential
effects to aquatic and/or terrestrial plants:
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.
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.
Reduction and/or modification of aquatic-based food sources for pre-metamorphs
(e.g., algae).
Conclusions for potential indirect effects to the CRLF via direct effects to aquatic and
terrestrial plants are used to determine whether modification to critical habitat may occur.
While widespread habitat modification due to effects on aquatic vascular plants is not
expected, local effects may occur. There is a potential for habitat modification via
impacts to aquatic nonvascular plants (Sections 5.2.2.1) and terrestrial plants (5.2.3.2)
The remaining aquatic-phase PCE is "alteration of other chemical characteristics
necessary for normal growth and viability of CRLFs and their food source." Other than
impacts to algae as food items for tadpoles (discussed above), this PCE is assessed by
considering direct and indirect effects to the aquatic-phase CRLF via acute and chronic
freshwater fish and invertebrate toxicity endpoints as measures of effects. Based on the
absence of LOC exceedances, there is not a potential for habitat modification via impacts
to aquatic-phase CRLFs (Sections 5.2.1.1) and effects to freshwater invertebrates and fish
as food items (Sections 5.2.2.2 and 5.2.2.3).
5.2.4.2 Terrestrial-Phase PCEs
Two of the four assessment endpoints for the terrestrial-phase PCEs of designated critical
habitat for the CRLF are related to potential effects to terrestrial plants:
Elimination and/or disturbance of upland habitat; ability of habitat to support food
source of CRLFs: Upland areas within 200 ft of the edge of the riparian
vegetation or drip line surrounding aquatic and riparian habitat that are comprised
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of grasslands, woodlands, and/or wetland/riparian plant species that provides the
CRLF shelter, forage, and predator avoidance.
Elimination and/or disturbance of dispersal habitat: Upland or riparian dispersal
habitat within designated units and between occupied locations within 0.7 mi of
each other that allow for movement between sites including both natural and
altered sites which do not contain barriers to dispersal.
As previously described, there is a potential for habitat modification via impacts to
terrestrial plants (5.2.3.2).
The third terrestrial-phase PCE is "reduction and/or modification of food sources for
terrestrial phase juveniles and adults." To assess the impact of norflurazon on this PCE,
acute and chronic toxicity endpoints for terrestrial invertebrates, mammals, and
terrestrial-phase frogs are used as measures of effects. As previously described, there is a
potential for habitat modification via indirect effects to terrestrial-phase CRLFs via
reduction in prey base (Section 5.2.2.4 for terrestrial invertebrates, Section 5.2.2.5 for
mammals, and 5.2.2.6 for frogs).
The fourth terrestrial-phase PCE is based on alteration of chemical characteristics
necessary for normal growth and viability of juvenile and adult CRLFs and their food
source. Based on potential effects of norflurazon on terrestrial plant communities, there
is potential for habitat modification to terrestrial-phase CRLFs.
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6.0 Uncertainties
6.1 Exposure Assessment Uncertainties
6.1.1 Maximum Use Scenario
The screening-level risk assessment focuses on characterizing potential ecological risks
resulting from a maximum use scenario, which is determined from labeled statements of
maximum application rate and number of applications with the shortest time interval
between applications. The frequency at which actual uses approach this maximum use
scenario may be dependant on pest resistance, timing of applications, cultural practices,
and market forces.
6.1.2 Aquatic Exposure Modeling of Norflurazon
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
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. 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
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(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).
In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations
that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone
Model is a process or "simulation" model that calculates what happens to a pesticide in
an agricultural field on a day-to-day basis. It considers factors such as rainfall and plant
transpiration of water, as well as how and when the pesticide is applied. It has two major
components: hydrology and chemical transport. Water movement is simulated by the use
of generalized soil parameters, including field capacity, wilting point, and saturation
water content. The chemical transport component can simulate pesticide application on
the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase concentrations in
the soil are estimated by simultaneously considering the processes of pesticide uptake by
plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection,
dispersion, and retardation.
Uncertainties associated with each of these individual components add to the overall
uncertainty of the modeled concentrations. Additionally, model inputs from the
environmental fate degradation studies are chosen to represent the upper confidence
bound on the mean values that are not expected to be exceeded in the environment
approximately 90 percent of the time. Mobility input values are chosen to be
representative of conditions in the environment. The natural variation in soils adds to the
uncertainty of modeled values. Factors such as application date, crop emergence date,
and canopy cover can also affect estimated concentrations, adding to the uncertainty of
modeled values. Factors within the ambient environment such as soil temperatures,
sunlight intensity, antecedent soil moisture, and surface water temperatures can cause
actual aquatic concentrations to differ for the modeled values.
Additionally, there are soil adsorption data for the parent compound and limited
adsorption data for the degradate desmethyl norflurazon which indicates that desmethyl
norflurazon approaches the mobility of the parent compound. Regardless, because the
parent data were used in lieu of definitive adsorption coefficient data for the degradate,
this increases the uncertainty surrounding the EECs.
In order to account for uncertainties associated with modeling, available monitoring data
were compared to PRZM/EXAMS estimates of peak EECs for the different uses. As
discussed above, several data values were available from NAWQA for norflurazon
concentrations measured in surface waters receiving runoff from agricultural areas. The
specific use patterns (e.g. application rates and timing, crops) associated with the
agricultural areas are unknown, however, they are assumed to be representative of
potential norflurazon use areas. Although the available monitoring data are not target to
norflurazon application times and/or sites, the maximum concentration of norflurazon
reported by NAWQA for California surface waters with agricultural watersheds is 0.62
|ig/L. This value is approximately 127 times less than the maximum model-estimated
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environmental concentration. The maximum concentration of norflurazon reported by
the California Department of Pesticide Regulation surface water database (0.98 |ig/L) is
roughly 81 times lower than the highest peak model-estimated environmental
concentration. Therefore, EECs provide a conservative measure of exposure.
6.1.3 Potential Groundwater Contributions to Surface Water Chemical
Concentrations
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 primarily subject to photolytic degradation will be
very likely to persist in groundwater, and can be transportable over long distances.
Similarly, many chemicals degrade slowly under anaerobic conditions (common in
aquifers) and are thus more persistent in groundwater. 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 can constitute 100% of stream flow during baseflow (no
runoff) conditions. Thus, it is important to keep in mind that pesticides in groundwater
may have an impact on surface water quality, and on CRLF habitats. However, many
smaller streams in CA are net dischargers of water to groundwater and go dry during
portions of the year; they are not supplied by baseflow from groundwater.
Groundwater monitoring data from NAWQA and the PGW study suggest that both
norflurazon and desmethyl norflurazon may leach and persist in groundwater. Given
these detections in ground water, it can be assumed (based upon persistence in sub- and
anoxic conditions, and mobility) that much of the compounds entering the groundwater
will be transported some distance and eventually discharged into surface water.
Although concentrations in a receiving water body resulting from groundwater discharge
cannot be explicitly quantified, it should be assumed that attenuation and retardation of
the chemical will have occurred subsequent to recharge and prior to discharge.
Nevertheless, groundwater could still be a significant consistent source of chronic
background concentrations in surface water, and may also add to surface runoff during
storm events (as a result of enhanced groundwater discharge typically characterized by
the 'tailing limb' of a storm hydrograph).
6.1.4 Usage Uncertainties
County-level usage data were obtained from California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database. Eight years of data (1999 -
2006) 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
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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: misplaced decimals,, incorrect measures (
area treated or units), reports of diluted pesticide concentrations, and off-label uses. 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 usage 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.
6.1.5 Terrestrial Exposure Modeling of Norflurazon
The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide
residues in wildlife dietary items. These residue assumptions are believed to reflect a
realistic upper-bound residue estimate, although the degree to which this assumption
reflects a specific percentile estimate is difficult to quantify. The field measurement
efforts used to develop the Fletcher estimates of exposure involve highly varied sampling
techniques. It is entirely possible that much of these data reflect residues averaged over
entire above ground plants in the case of grass and forage sampling.
It was assumed that ingestion of food items in the field occurs at rates commensurate
with those in the laboratory. Although the screening assessment process adjusts dry-
weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food
intake estimates, it does not allow for gross energy differences. Direct comparison of a
laboratory dietary concentration- based effects threshold to a fresh-weight pesticide
residue estimate would result in an underestimation of field exposure by food
consumption by a factor of 1.25 - 2.5 for most food items.
Differences in assimilative efficiency between laboratory and wild diets suggest that
current screening assessment methods do not account for a potentially important aspect of
food requirements. Depending upon species and dietary matrix, bird assimilation of wild
diet energy ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85%
(U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is
formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for
underestimation of exposure may exist by assuming that consumption of food in the wild
is comparable with consumption during laboratory testing. In the screening process,
exposure may be underestimated because metabolic rates are not related to food
consumption.
For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal
was assumed to occupy either the treated field or adjacent areas receiving a treatment rate
on the field. Actual habitat requirements of any particular terrestrial species were not
considered, and it was assumed that species occupy, exclusively and permanently, the
modeled treatment area. Spray drift model predictions suggest that this assumption leads
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to an overestimation of exposure to species that do not occupy the treated field
exclusively and permanently.
6.1.6 Spray Drift Modeling
It is unlikely that the same organism would be exposed to the maximum amount of spray
drift from every application made. In order for an organism to receive the maximum
concentration of norflurazon from multiple applications, each application of norflurazon
would have to occur under identical atmospheric conditions (e.g., same wind speed and
same wind direction) and (if it is an animal) the animal being exposed would have to be
located in the same location (which receives the maximum amount of spray drift) after
each application. Additionally, other factors, including variations in topography, cover,
and meteorological conditions over the transport distance are not accounted for by the
AgDRIFT model (i.e., it models spray drift from aerial and ground applications in a flat
area with little to no ground cover and a steady, constant wind speed and direction).
Therefore, in most cases, the drift estimates from AgDRIFT may overestimate exposure,
especially as the distance increases from the site of application, since the model does not
account for potential obstructions (e.g., large hills, berms, buildings, trees, etc.).
Furthermore, conservative assumptions are made regarding the droplet size distributions
being modeled ' ASAE Very Fine' for agricultural uses), the application method (i.e.,
aerial), release heights and wind speeds. Alterations in any of these inputs would
decrease the area of potential effect.
6.2 Effects Assessment Uncertainties
6.2.1 Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids, second instar for
amphipods, stoneflies, mayflies, and third instar for midges).
Testing of juveniles may overestimate toxicity at older age classes for pesticide active
ingredients that act directly without metabolic transformation because younger age
classes may not have the enzymatic systems associated with detoxifying xenobiotics. In
so far as the available toxicity data may provide ranges of sensitivity information with
respect to age class, this assessment uses the most sensitive life-stage information as
measures of effect for surrogate aquatic animals, and is therefore, considered as
protective of the CRLF.
6.2.2 Use of Surrogate Species Effects Data
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Guideline toxicity tests and open literature data on norflurazon are not available for frogs
or any other aquatic-phase amphibian; therefore, freshwater fish are used as surrogate
species for aquatic-phase amphibians. Therefore, endpoints based on freshwater fish
ecotoxicity data are assumed to be protective of potential direct effects to aquatic-phase
amphibians including the CRLF, and extrapolation of the risk conclusions from the most
sensitive tested species to the aquatic-phase CRLF is likely to overestimate the potential
risks to those species. Efforts are made to select the organisms most likely to be affected
by the type of compound and usage pattern; however, there is an inherent uncertainty in
extrapolating across phyla. In addition, the Agency's LOCs are intentionally set very
low, and conservative estimates are made in the screening level risk assessment to
account for these uncertainties.
Guideline studies generally evaluate toxicity to ten crop species. These tests are typically
conducted on herbaceous crop species only, and extrapolation of effects to wild
herbaceous species or woody plants contributes uncertainty to risk conclusions. The
primary goal of these studies is to determine effects on biomass and shoot length; effects
on seed production or other reproductive mechanisms are not evaluated.
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 norflurazon, is largely unknown. Homogenous
test plant seed lots also lack the genetic variation that occurs in natural populations, so the
range of effects seen from tests may be smaller than might be expected from wild
populations.
6.2.3 Sublethal Effects
When assessing acute risk, 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 effects determination 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. However, the full suite of sublethal effects from valid
open literature studies is considered for the purposes of defining the action area.
6.2.4 Location of Wildlife Species
For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal
was assumed to occupy either the treated field or adjacent areas receiving a treatment rate
on the field. Actual habitat requirements of any particular terrestrial species were not
considered, and it was assumed that species occupy, exclusively and permanently, the
modeled treatment area. Spray drift model predictions suggest that this assumption leads
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to an overestimation of exposure to species that do not occupy the treated field
exclusively and permanently.
7.0 Risk Conclusions
In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the
information presented in this endangered species risk assessment represents the best data
currently available to assess the potential risks of norflurazon to the CRLF and its
designated critical habitat.
Based on the best available information, the Agency makes a Likely to Adversely Affect
determination for the CRLF from the use of norflurazon. Additionally, the Agency has
determined that there is the potential for modification of CRLF designated critical habitat
from the use of norflurazon. The potential effects, both direct and indirect, presented in
this document are for all norflurazon use patterns. Although the application rate for
alfalfa is considerably lower than for other use patterns, it can be applied twice, at an
undefined interval, and it too exceeds the LOC in all of the same categories, such as
direct chronic effects to the CRLF, as the other uses at higher rates of application.
A summary of the risk conclusions and effects determinations for the CRLF and its
critical habitat, given the uncertainties discussed in Section 6, is presented in Table 7.1
and Table 7.2.
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Table 7.1 Effects Determination Summary for Norflurazon Use and the CRLF
Assessment
Endpoint
Effects
Determination 1
Basis for Determination
Survival, growth,
Potential for Direct Effects
and/or reproduction
of CRLF
individuals
LAA
Aquatic-phase (Eggs, Larvae, and Adults) :
No effects to freshwater fish (as a surrogate to the aquatic-phase frog) that result
in acute and/or chronic risk LOC exceedances
Terrestrial-phase (Juveniles and Adults) :
Chronic effects to birds (as a surrogate to the terrestrial-phase frog) result in
exceedance of the chronic risk LOC
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary productivity
No effects to freshwater invertebrates, fish or frogs or are expected. Effects to
non-vascular aquatic plants result in exceedance of the LOC, and for locations
proximal to ROWs, effects to vascular aquatic plants may occur.
Terrestrial prey items, riparian habitat
Chronic effects to small terrestrial vertebrates including mammals and terrestrial-
phase amphibians (using birds as a surrogate), and effects to terrestrial plants,
result in LOC exceedances
1 No effect (NE); May affect, but not likely to adversely affect (NLAA); May affect, likely to adversely
affect (LAA)
Table 7.2 Effects Determination Summary for Norflurazon Use and CRLF Critical
Habitat Impact Analysis
Assessment
Endpoint
Effects
Determination 1
Basis for Determination
Modification of
aquatic-phase PCE
HM1
Effects to riparian vegetation (terrestrial plants) and aquatic nonvascular
plants result in LOC exceedances. Exposure to aquatic vascular plants
proximal to use on ROWs may be sufficient to elicit deleterious effects.
These effects may indirectly affect the CRLF via reduction in food supply,
changes in available cover, physical parameters of the waterbody (e.g.
increase temperature or turbidity)
Modification of
terrestrial-phase
PCE
Effects to riparian vegetation (terrestrial plants) result in LOC exceedances,
based on the seedling emergence study. Effects may result in changes in
community composition or relative abundance of riparian plant species,
possibly altering terrestrial - phase CRLF habitat
1 Habitat Modification or No effect (NE)
Based on the conclusions of this assessment, a formal consultation with the U. S. Fish
and Wildlife Service under Section 7 of the Endangered Species Act should be initiated.
When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the species and its resources (i.e., food and habitat) are
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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 modification to critical habitat.
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8.0 References
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the Draft California Red-legged Frog Recovery Plan.
Crawshaw, G.J. 2000. Diseases and Pathology of Amphibians and Reptiles in:
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C.A. Bishop. SETAC Publication Series, Columbia, MO.
Fellers, G. M., et al. 2001. Overwintering tadpoles in the California red-legged frog
{Rana aurora draytonii). Herpetological Review, 32(3): 156-157.
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Legged Frogs (Rana Mucosa) from the Sierra Nevada Mountains of California,
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Frog. Pages 552-554. hr. M. Lannoo (ed.) Amphibian Declines: The Conservation
Status of United States Species, Vol. 2: Species Accounts. University of
California Press, Berkeley, California, xxi+1094 pp.
(http://www.werc.usgs.gov/pt-reves/pdfs/Rana%20dravtonii.PDF)
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Pages 198-201. hr. L.L.C. Jones, et al (eds.) Amphibians of the Pacific Northwest.
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Hayes, M.P. and M.M. Miyamoto. 1984. Biochemical, behavioral and body size
differences between Rana aurora aurora and R. a. draytonii. Copeia 1984(4):
1018-22.
Hayes and Tennant. 1985. Diet and feeding behavior of the California red-legged frog.
The Southwestern Naturalist 30(4): 601-605.
Jennings, M.R. and M.P. Hayes. 1985. Pre-1900 overharvest of California red-legged
frogs (Rana aurora draytonii): The inducement for bullfrog (Rana catesbeiana)
introduction. Herpetological Review 31(1): 94-103.
Jennings, M.R. and M.P. Hayes. 1994. Amphibian and reptile species of special concern
in California. Report prepared for the California Department of Fish and Game,
Inland Fisheries Division, Rancho Cordova, California. 255 pp.
LeNoir, J.S., L.L. McConnell, G.M. Fellers, T.M. Cahill, J.N. Seiber. 1999.
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Chemistry 18(12): 2715-2722.
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McConnell, L.L., J.S. LeNoir, S. Datta, J.N. Seiber. 1998. Wet deposition of current-use
pesticides in the Sierra Nevada mountain range, California, USA. Environmental
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freshwater system. M.S. Thesis. San Jose State University. 58 pp.
D.W. Sparling, G.M. Fellers, L.L. McConnell. 2001. Pesticides and amphibian
population declines in California, USA. Environmental Toxicology & Chemistry
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Assessment. Risk Assessment Forum. EPA/630/R-95/002F, April 1998.
U.S. EPA. 2002. Refined Estimated Environmental Concentrations (EECs) for
Norflurazon and its Degradate Desmethylnorflurazon in Surface Water and
Groundwater. DP 282196. Washington, D.C. May 1, 2002.
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Pesticide Programs. Office of Prevention, Pesticides, and Toxic Substances.
Office of Pesticide Programs. Washington, D.C. January 23, 2004.
U.S. EPA. 2006. Risks of Atrazine Use to Federally Listed Endangered Barton Springs
Salamanders (Eurycea sosorum). Pesticide Effects Determination. Office of
Pesticide Programs, Environmental Fate and Effects Division. August 22, 2006.
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plants: determination of threatened status for the California red-legged frog.
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(http://ecos.fws.gov/doc/recovery plans/2002/020528.pdf)
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habitat for the California red-legged frog. 71 FR 19244-19346.
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http://www.fws.gov/endangered/features/rl frog/rlfrog.html#where
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(NMFS). 1998. Endangered Species Consultation Handbook: Procedures for
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Conducting Consultation and Conference Activities Under Section 7 of the
Endangered Species Act. Final Draft. March 1998.
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Section 7 Consultation Regulations; Final Rule. FR 47732-47762.
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