Risks of Diflubenzuron 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
October 19,2009
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Primary Authors:
Stephen Wente
Fred Jenkins
Lewis Brown
Secondary Review:
Brian Anderson
Jim Lin
Ed Odenkirchen
Branch Chief, Environmental Risk Assessment Branch 1:
Nancy Andrews
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Table of Contents
1.0 Executive Summary 4
2.0 Problem Formulation 13
2.1 Purpose 13
2.2 Scope 15
2.3 Previous Assessments 17
2.4 Stressor Source and Distribution 18
2.4.1 Environmental Fate Assessment 18
2.4.2 Mechanism of Action 21
2.4.3 Use Characterization 21
2.5 Assessed Species 26
2.5.1 Distribution 26
2.5.2 Reproduction 29
2.5.3 Diet 29
2.5.4 Habitat 30
2.6 Designated Critical Habitat 31
2.7 Action Area 33
2.8 Assessment Endpoints and Measures of Ecological Effect 34
2.8.1 Assessment Endpoints for the CRLF 35
2.8.2 Assessment Endpoints for Designated Critical Habitat 37
2.9 Conceptual Model 39
2.9.1 Risk Hypotheses 39
2.9.2 Diagram 39
2.10 Analysis Plan 41
2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model 42
3.0 Exposure Assessment 46
3.1. Label Application Rates and Intervals 46
3.2. Aquatic Exposure Assessment 51
3.2.1. Modeling Approach 51
3.2.2. Model Inputs 52
3.2.3. Results 53
3.2.4. Existing Monitoring Data 57
3.3. Terrestrial Animal Exposure Assessment 57
3.5 Terrestrial Plant Exposure Assessment 60
4.0 Effects Assessment 60
4.1. Evaluation of Aquatic Ecotoxicity Studies 62
4.1.1. Toxicity to Freshwater Fish 64
4.1.2. Toxicity to Freshwater Invertebrates 65
4.1.3. Toxicity to Aquatic Plants 67
4.2. Toxicity of diflubenzuron to Terrestrial Organisms 72
4.2.1. Toxicity to Birds 72
4.2.3. Toxicity to Mammals 73
4.2.4. Toxicity to Terrestrial Invertebrates 74
4.2.5. Toxicity to Terrestrial Plants 76
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4.3. Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern 77
4.4. Incident Database Review 78
5.0 Risk Characterization 79
5.1. Risk Estimation 79
5.1.1. Exposures in the Aquatic Habitat 79
5.1.2. Exposures in the Terrestrial Habitat 83
5.1.3. Primary Constituent Elements of Designated Critical Habitat 87
5.2. Risk Description 87
5.2.1. Direct Effects 91
5.2.2. Indirect Effects (via Reductions in Prey Base) 94
5.2.3. Indirect Effects (via Habitat Effects) 97
5.2.4. Modification to Designated Critical Habitat 98
5.2.5. Spatial Extent of Potential Effects 99
6.0 Uncertainties 104
6.1 Exposure Assessment Uncertainties 104
6.1.1 Maximum Use Scenario 104
6.1.2 Crops Not Grown in California (include if you had crops that are not grown
inCA) 104
6.1.3 Aquatic Exposure Modeling of Diflubenzuron 104
6.1.4 Usage Uncertainties 106
6.1.5 Terrestrial Exposure Modeling of Diflubenzuron 106
6.1.6 Spray Drift Modeling 107
6.2 Effects Assessment Uncertainties 108
6.2.1 Age Class and Sensitivity of Effects Thresholds 108
6.2.2 Use of Surrogate Species Effects Data 108
6.2.3 Sublethal Effects 109
6.2.4 Location of Wildlife Species 109
7.0 Risk Conclusions 110
8.0 References 113
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List of Tables
Table 1-1 Effects Determination Summary for Diflubenzuron Use and the CRLF 7
Table 1-2. Effects Determination Summary for Diflubenzuron Use and CRLF Critical
Habitat Impact Analysis 8
Table 1-3 Diflubenzuron Use-specific Direct Effects Determinations1 for the CRLF 9
Table 1-4 Diflubenzuron Use-specific Indirect Effects Determinations1 Based on Effects
to Aquatic Prey 10
Table 2-1 Summary of Diflubenzuron Environmental Fate Properties 19
Table 2-2 Diflubenzuron Uses Assessed for the CRLF 22
Table 2-3 Summary of California Department of Pesticide Registration (CDPR) Pesticide
Use Reporting (PUR) Data from 1999 to 2006 for Currently Registered
Diflubenzuron Uses 25
Table 2-4. Assessment Endpoints and Measures of Ecological Effects 36
Table 2-5. Summary of Assessment Endpoints and Measures of Ecological Effect for
Primary Constituent Elements of Designated Critical Habitata 38
Table 3-1 Diflubenzuron Uses, Scenarios, and Application Information for the CRLF risk
assessment1 48
Table 3-2 Summary of PRZM/EZAMS Environmental Fate Data Used for Aquatic
Exposure Inputs for Diflubenzuron Endangered Species Assessment for the
CRLF1 53
Table 3-3 Aquatic EECs (ug/L) for Diflubenzuron Uses in California 54
Table 3-4 Input Parameters for Foliar Applications Used to Derive Terrestrial EECs for
Diflubenzuron with T-REX 58
Table 3-5. Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based
Exposures of the CRLF and its Prey to Diflubenzuron 59
Table 3-6 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via Effects to
Terrestrial Invertebrate Prey Items 60
Table 4-1 Freshwater Aquatic Toxicity Profile for Diflubenzuron 63
Table 4-2 Categories of Acute Toxicity for Fish and Aquatic Invertebrates 63
Table 4-3. Diflubenzuron Effects Reported in a Littoral Enclosure Study (MRID 443862-
01) 69
Table 4-4 Terrestrial Toxicity Profile for Diflubenzuron 72
Table 4-5 Categories of Acute Toxicity for Avian and Mammalian Studies 72
Table 4-6. Probit slopes used for taxonomic groups evaluated in this assessment 77
Table 5-1 Summary of Direct Effect RQ LOCs for the Aquatic-phase CRLF 80
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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 (diet of CRLF in tadpole life stage and habitat of
aquatic-phase CRLF) 80
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) 82
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 83
Table 5-5 Summary of RQs Used to Estimate Direct Effects to the Terrestrial-phase
CRLF 84
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 anLCSO of 234 ppm (30 jig per bee / 0.128 grams per bee) 85
Table 5-7 Summary of Chronic RQs Used to Estimate Indirect Effects to the Terrestrial-
phase CRLF via Direct Effects on Small Mammals as Dietary Food Items .. 86
Table 5-8 Risk Estimation Summary for Diflubenzuron - Direct and Indirect Effects to
CRLF 88
Table 5-9 Risk Estimation Summary for Diflubenzuron - PCEs of Designated Critical
Habitat for the CRLF 89
Table 5-10. Results from T-HERPS for the Barnyard/Mushroom Use 93
Table 5-11. Summary of AgDRIFT* Predicted Terrestrial Spray Drift Distances 102
Table 7-1. Effects Determination Summary for Diflubenzuron Use and the CRLF 110
Table 7-2. Effects Determination Summary for Diflubenzuron Use and CRLF Critical
Habitat Impact Analysis Ill
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List of Figures
Figure 2-1. Diflubenzuron use in total pounds per square mile of agricultural land in
county 24
Figure 2-2 Recovery Unit, Core Area, Critical Habitat, and Occurrence Designations for
CRLF 28
Figure 2-3 CRLF Reproductive Events by Month 29
Figure 2-4 Conceptual Model for Pesticide Effects on Terrestrial Phase of the CRLF .. 40
Figure 2-5. Conceptual Model for Pesticide Effects on Aquatic Phase of the CRLF 41
Figure 3-1. Identification of application dates based on analysis of the average pounds of
diflubenzuron applied in California to citrus via ground application methods
based on CDPR PUR data (1990-2007) 52
Figure 3-2. Variation in diflubenzuron EECs (peak, 21-day, and 60-day) as function of
application date (first application date for scenarios with multiple
applications) 56
Figure 3-3. Variation in diflubenzuron EECs (peak, 21-day, and 60-day) as function of
application date (first application date for scenarios with multiple
applications) compared to variation in the amount of diflubenzuron applied
(Ibs. ai/day) per day in California for fruit use 56
Appendices
Appendix A Summary of Registrant Submitted Ecotoxicity Data
Appendix B Multi-ai Product Analysis
Appendix C RQ Method and LOG Description
Appendix D Exposure Data
Appendix E Human Health Assessment on Diflubenzuron
Appendix F Manure Use Assessment Method
Appendix Gl Accepted ECOTOX Data Table (sorted by effect)
Appendix G2 Diflubenzuron Bibliography of Acceptable Papers
Appendix G3 Diflubenzuron Bibliography of Rejected Papers
Appendix G4 Papers Rejected by Ecotox Because they were Tested Using Mixtures
Appendix H Bibliography of all Registrant Submitted Data
Appendix I Description of Ecotox Rejection Codes
Appendix J Residential Use Assessment Method
Appendix K Right-of-Way Use Assessment Method
Attachment I. Status and Life History of the California Red-legged Frog
Attachment II. Baseline Status and Cumulative Effects for the California Red-legged
Frog
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1.0 Executive Summary
1.1. Purpose
The purpose of this assessment is to evaluate potential direct and indirect effects on the
California red-legged frog (Rana aurora draytonif) (CRLF) arising from Federal
Insecticide, Fungicide, Rodenticide, Act (FIFRA) regulatory actions regarding use of
diflubenzuron 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 (U.S. FWS) and National Marine Fisheries Service (NMFS)
Endangered Species Consultation Handbook (U.S. FWS/NMFS 1998) and procedures
outlined in the Agency's Overview Document (U.S. EPA 2004).
The CRLF was listed as a threatened species by U.S. FWS 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 (U.S. FWS 1996) in California.
1.2. Chemical Assessed
Diflubenzuron is a benzoylphenylurea insecticide that kills immature insects by
disrupting the molting process. Formulation types registered include liquid, water
dispersible granules, wettable powder, effervescent tablets (for ornamental pond
treatment), and termite bait (in bait stations).
1.3. Use Characterization
Labeled uses of diflubenzuron include citrus, cotton, forestry, mushrooms, ornamentals,
pastures, soybeans, standing water, sewage systems, termite bait stations, and wide-area
general outdoor treatment sites. All of these uses are considered as part of the federal
action evaluated in this assessment with the exception of termite bait stations (in which a
solidified form of the pesticide is placed in an enclosed bait station to minimize loss to
the environment) and soybeans, which are not grown in California.
1.4. Environmental Fate and Exposure Summary
Diflubenzuron appears to be relatively non-persistent and immobile under normal use
conditions. Diflubenzuron is relatively stable to hydrolysis and photolysis. The major
route of dissipation appears to be biotic processes (half-life of approximately 2 days for
aerobic soil metabolism). Available data indicate that it is unlikely that diflubenzuron
will contaminate ground water or appreciably volatilize and be transported through long-
range atmospheric transport processes. However, a degradate of diflubenzuron, 4-
chlorophenylurea (CPU), has a much greater potential to leach through soil. Spray drift
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and transport with eroded soil in runoff are thought to be the main mechanisms of
transport from the site of application.
Since CRLFs exist within aquatic and terrestrial habitats, exposure of the CRLF, its prey
and its habitats to diflubenzuron are assessed separately for the two habitats. Tier-II
aquatic exposure models are used to estimate high-end exposures of diflubenzuron in
aquatic habitats resulting from runoff and spray drift from different uses. Peak model-
estimated environmental concentrations resulting from different diflubenzuron uses range
from 0.01 to 113 |ig/L. Diflubenzuron is typically not measured by surface and
groundwater monitoring programs, therefore, no monitoring data are available for
comparison with the model estimated diflubenzuron concentrations.
1.4. Toxicity Summary
Diflubenzuron is very highly toxic to aquatic invertebrates. The most sensitive LCso
identified for diflubenzuron was 0.0028 |ig/L (Ecotox no. 16591). Toxicity is influenced
by species and life-stage of the test organism. The most sensitive NOAEC was 0.00025
|ig/L (Ecotox No. 9397). Diflubenzuron is less toxic to fish, with a 96-hr LCso of
129,000 |ig/L (MRID 00056150) and a reproduction NOAEC of 110 |ig/L (MRID
00099755). Diflubenzuron was not toxic to aquatic plants at up to 200 |ig/L (MRID
45252205 and 42940103).
Diflubenzuron is also practically non-toxic to birds on an acute basis. The most sensitive
study available produced an LD50 value of 3763 mg/kg-bw in the Red-Winged Blackbird
(MRID 00038614).
Using the technical grade active ingredient (TGAI), diflubenzuron is categorized as
practically non-toxic to avian species on a subacute dietary toxicity basis based on an
LC50 value of >4640 ppm for the bobwhite quail and mallard duck (MRID 00039080). A
1 % Granular formulation was also categorized as practically non-toxic to bobwhite quail
and mallard ducks based on an LC50 value of >20,000 ppm (MRID 00060381). The most
sensitive NOAEC from a reliable reproduction study was 500 mg/kg-diet (MRID
4166800102). The NOAEC of 500 mg/kg-food was based on effects on eggshell
thickness in mallard ducks and reduced egg production in bobwhite quail at 1000 mg/kg-
diet.
The available mammalian acute toxicity data demonstrate that diflubenzuron is
practically nontoxic to mammals (LD50 > 5000 mg/kg; MRID 00157103). In a 2-
generation reproduction study no effects on reproductive performance were observed at
any dose level in FO or Fl males or females. Litter and mean pup weights decreased
slightly from birth to 21 days postpartum in Fl offspring at 2500 mg/kg/day. The NOEL
for reproductive performance in parental adults is 2500 mg/kg/day. The NOEL for
developmental toxicity in progeny is 250 mg/kg/day and the LOAEL is 2500 mg/kg/day,
based on decreased body weights in Fl pups from birth to 21 days postpartum. (MRID
43578301). A NOAEL of 250 mg/kg-bw is used in this assessment.
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Currently, there are no guideline terrestrial plant toxicity data for diflubenzuron for use in
this assessment. However, given the mode of toxicity of diflubenzuron as an insect
growth regulator, the long history of use on numerous agricultural commodities without
incidence of effects to terrestrial plants that are clearly associated with diflubenzuron, and
the available efficacy data that reported minimal phytotoxic effects, the available data do
not suggest that terrestrial plants are likely to be impacted to an extent that indirect
effects will result to species that depend on them for survival or reproduction.
This assessment was based on potential risks from diflubenzuron. Several degradates
have been identified that are of equal or greater toxicity than the parent chemical. These
degradates were considered in this assessment; however, analysis of potential exposure to
and toxicity of these degradates suggests that potential risks to these degradates is
negligible relative to risks posed by parent diflubenzuron.
1.5. Effects Determination
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 effects,
such as reduction of the prey base or modification of its habitat. Direct effects to the
CRLF in the aquatic habitat are based on toxicity information for freshwater fish, which
are used as a surrogate for aquatic-phase amphibians. In the terrestrial habitat, direct
effects are based on toxicity information for birds, which are used as a surrogate for
terrestrial-phase amphibians. Given that the CRLF's prey items and designated critical
habitat requirements in the aquatic habitat are dependant on the availability of freshwater
aquatic invertebrates and aquatic plants, toxicity information for these taxonomic groups
is also discussed. In the terrestrial habitat, indirect effects due to depletion of prey are
assessed by considering effects to terrestrial insects, small terrestrial mammals, and frogs.
Indirect effects due to modification of the terrestrial habitat are characterized by available
data for terrestrial monocots and dicots. However, given the lack of guideline toxicity
studies on terrestrial plants, additional lines of evidence were used to determine if
terrestrial plants may be impacted to an extent that could result in indirect effects to the
CRLF.
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 diflubenzuron 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 diflubenzuron 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
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not likely to adversely affect" (NLAA) from those actions that are "likely to adversely
affect" (LAA) the CRLF. Similarly for critical habitat, additional information is
considered to refine the potential for exposure and effects to distinguish those actions that
do or do not result in modification of its critical habitat.
Based on the best available information, the Agency makes a Likely to Adversely Affect
determination for the CRLF from the use of diflubenzuron. Additionally, the Agency has
determined that there is a potential for modification of CRLF designated critical habitat
from the use of the chemical. A summary of the risk conclusions and effects
determinations for the CRLF and its critical habitat is presented in Table 1-1 and 1-2.
Table 1-1 Effects Determination Summary for Diflubenzuron Use and the CRLF
Assessment
Endpoint
Survival, growth,
and/or
reproduction of
CRLF individuals
Effects
Determination 1
LAA, all uses
Basis for Determination
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults):
There was an LOG exceedance for risk to fish (CRLF surrogate)
from chronic exposures to diflubenzuron posed by the rice use.
However, the risk was determined to be discountable because
effects were considered to be unlikely to occur for reasons
discussed in Section 5.2. LOCs were not exceeded for any other
use. The effects determination for direct effects to aquatic phase
CRLFs was NE for all uses except rice and NLAA for rice.
Terrestrial-phase (Juveniles and Adults):
Direct effects to CRLFs could occur from diflubenzuron' s use on
barn yards based on acute and chronic LOG exceedances for birds
and refined analysis for frogs. Direct effects to CRLFs are not
expected to occur for any other use. The effects determination is
LAA for barnyard/mushroom use and NE for all other uses.
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary
productivity
Aquatic prey of the CRLF may be impacted based on potential
impacts to aquatic invertebrate for all uses. Several lines of
evidence support the conclusion that aquatic invertebrates may be
impacted by labeled diflubenzuron uses including laboratory
studies and field studies. The effects determination is LAA for all
uses based on potential impacts to aquatic invertebrates.
Terrestrial prey items, riparian habitat
Terrestrial prey items of the CRLF are expected to be impacted
based on potential impacts to terrestrial invertebrates. The effects
determination is LAA for all uses based on potential impacts to
terrestrial invertebrates.
1 No effect (NE); May affect, but not likely to adversely affect (NLAA); May affect, likely to adversely
affect (LAA)
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Table 1-2. Effects Determination Summary for Diflubenzuron Use and CRLF Critical Habitat
Impact Analysis
Assessment
Endpoint
Modification of
aquatic-phase PCE
Modification of
terrestrial-phase
PCE
Effects
Determination 1
HM
Basis for Determination
There are LOG exceedances for risk to terrestrial
invertebrate prey of the CRLF.
There are LOG exceedances for risk to terrestrial
invertebrate prey of the CRLF.
and aquatic
and aquatic
Habitat Modification or No effect (NE)
Use-specific determinations for direct and indirect effects to the CRLF are provided in
Table 1-3, 1-4, and 1-5. Further information on the results of the effects determination is
included as part of the Risk Description in Section 5.2.
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Table 1-3 Diflubenzuron Use-specific Direct Effects Determinations1 for the CRLF
Use(s)
Barnyard/Mushroom
Spray on manure, Manure to field
Beech Nut
Brassica (head and stem) vegetables
Citrus hybrids, grapefruit, orange, pummelo (shaddock),
and tangerines
Broccoli raab, cabbage - Chinese, collards, and kale
Cotton (unspecified)
Christmas tree plantations and forest trees (softwoods -
conifers)
Apricot, nectarine, peach, pear, plum, prune, and stone
fruits
Almond, Brazil nut, cashew, chestnut, chinquapin, filbert
(hazelnut), hickory nut, macadamia nut (bushnut), pecan,
tree nuts, and walnut (English/black)
Barley, canola\rape, oats, triticale, and wheat
Forest nursery plantings (for transplant purposes),
ornamental and/or shade trees, ornamental woody shrubs
and vines, and shelterbelt plantings
Grass forage/fodder/hay, pastures, and rangeland
Pistachio
Household/domestic dwellings outdoor premises
Rice/Ornamental Pond
Agricultural rights-of-way/fencerows/hedgerows,
fencerows/hedgerows, and nonagricultural rights-of-
way/fencerows/hedgerows
Artichoke, mustard, peanuts (unspecified), and pepper
Commercial/institutional/industrial premises/equipment
(outdoor), nonagricultural outdoor buildings/structures,
paved areas (private roads/sidewalks), refuse/solid waste
sites (outdoor), and wide area/general outdoor treatment
(quarantine/eradication use)
Butternut
Agricultural fallow/idleland, golf course turf, and
nonagricultural uncultivated areas/soils
Ornamental sod farm (turf) and recreational areas
Turnip (greens)
Aquatic Habitat
Acute
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
Chronic
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NLAA
NE
NE
NE
NE
NE
NE
NE
Terrestrial Habitat
Acute
LAA
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
Chronic
LAA
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
1 NE = No effect; NLAA = May affect, not likely to adversely affect; LAA = Likely to adversely affect
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Table 1-4 Diflubenzuron Use-specific Indirect Effects Determinations1 Based on Effects to Aquatic
Prey
Use(s)
Barnyard/Mushroom
Spray on manure, Manure to field
Beech Nut
Brassica (head and stem) vegetables
Citrus hybrids, grapefruit, orange, pummelo
(shaddock), and tangerines
Broccoli raab, cabbage - Chinese, collards,
and kale
Cotton (unspecified)
Christmas tree plantations and forest trees
(softwoods - conifers)
Apricot, nectarine, peach, pear, plum, prune,
and stone fruits
Almond, Brazil nut, cashew, chestnut,
chinquapin, filbert (hazelnut), hickory nut,
macadamia nut (bushnut), pecan, tree nuts,
and walnut (English/black)
Barley, canola\rape, oats, triticale, and wheat
Forest nursery plantings (for transplant
purposes), ornamental and/or shade trees,
ornamental woody shrubs and vines, and
shelterbelt plantings
Grass forage/fodder/hay, pastures, and
rangeland
Pistachio
Household/domestic dwellings outdoor
premises
Rice/Ornamental Pond
Agricultural rights-of-
way/fencerows/hedgerows,
fencerows/hedgerows, and nonagricultural
rights-of-way/fencerows/hedgerows
Artichoke, mustard, peanuts (unspecified),
and pepper
Commercial/institutional/industrial
premises/equipment (outdoor),
nonagricultural outdoor buildings/structures,
paved areas (private roads/sidewalks),
refuse/solid waste sites (outdoor), and wide
area/general outdoor treatment
(quarantine/eradication use)
Butternut
Agricultural fallow/idleland, golf course turf,
and nonagricultural uncultivated areas/soils
Ornamental sod farm (turf) and recreational
areas
Turnip (greens)
Algae
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
Aquatic Invertebrates
Acute
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
Chronic
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
Aquatic-phase frogs
and fish
Acute
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
Chronic
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NLAA
NE
NE
NE
NE
NE
NE
NE
1 NE = No effect; NLAA = May affect, not likely to adversely affect; LAA = Likely to adversely affect
10
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Table 1-5. Diflubenzuron Use-specific Indirect Effects Determinations1 Based on Effects to
Terrestrial Prey
Use(s)
Barnyard/Mushroom
Spray on manure, Manure to field
Beech Nut
Brassica (head and stem) vegetables
Citrus hybrids, grapefruit, orange, pummelo
(shaddock), and tangerines
Broccoli raab, cabbage - Chinese, collards,
and kale
Cotton (unspecified)
Christmas tree plantations and forest trees
(softwoods - conifers)
Apricot, nectarine, peach, pear, plum, prune,
and stone fruits
Almond, Brazil nut, cashew, chestnut,
chinquapin, filbert (hazelnut), hickory nut,
macadamia nut (bushnut), pecan, tree nuts,
and walnut (English/black)
Barley, canola\rape, oats, triticale, and wheat
Forest nursery plantings (for transplant
purposes), ornamental and/or shade trees,
ornamental woody shrubs and vines, and
shelterbelt plantings
Grass forage/fodder/hay, pastures, and
rangeland
Pistachio
Household/domestic dwellings outdoor
premises
Rice/Ornamental Pond
Agricultural rights-of-
way/fencerows/hedgerows,
fencerows/hedgerows, and nonagricultural
rights-of-way/fencerows/hedgerows
Artichoke, mustard, peanuts (unspecified), and
pepper
Commercial/institutional/industrial
premises/equipment (outdoor), nonagricultural
outdoor buildings/structures, paved areas
(private roads/sidewalks), refuse/solid waste
sites (outdoor), and wide area/general outdoor
treatment (quarantine/eradication use)
Butternut
Agricultural fallow/idleland, golf course turf,
and nonagricultural uncultivated areas/soils
Ornamental sod farm (turf) and recreational
areas
Turnip (greens)
Terrestrial
Inverts.
(Acute)
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
LAA
Terrestrial-phase
frogs
Acute
LAA
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
Chronic
LAA
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
Small Mammals
Acute
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
Chronic
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
1 NE = No effect; NLAA = May affect, not likely to adversely affect; LAA = Likely to adversely affect
11
-------
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.
12
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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. Environmental Protection Agency's (EPA's) Guidance for Ecological
Risk Assessment (U.S. EPA 1998), the Services' Endangered Species Consultation
Handbook (U.S. FWS/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 (U.S. FWS/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
diflubenzuron on agricultural uses (nuts, cotton, rice, row crops, citrus, fruits, etc.),
forestry, nursery, residential, right-of-ways, and turf uses. In addition, this assessment
evaluates whether use on these sites is 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) settlement 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, and AgDRIFT, all of which are
described at length in the Overview Document. Additional refinements were made to
PRZM/EXAMS scenarios to account for heterogeneous land cover within treatment areas
in order to more accurately model residential and right-of-way uses. 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 diflubenzuron is based on an action area. The action area is the area
directly or indirectly affected by the federal action, as indicated by the exceedance 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 diflubenzuron 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
13
-------
sections of the action area including those geographic areas associated with locations of
the CRLF and its designated critical habitat within the state of California. As part of the
"effects determination," one of the following three conclusions will be reached regarding
the potential use of diflubenzuron on the CRLF 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 (no LOG exceedances) upon individual CRLFs or upon the PCEs of the species'
designated critical habitat, a "no effect" determination is made for use of diflubenzuron
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 diflubenzuron.
If a determination is made that use of diflubenzuron 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 diflubenzuron use sites) and further evaluation of the potential impact of
diflubenzuron 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 diflubenzuron is expected to directly impact living organisms within the action
area (defined in Section 2.7), critical habitat analysis for diflubenzuron 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
14
-------
appreciably diminish the value of the habitat. Evaluation of actions related to use of
diflubenzuron that may alter the PCEs of the CRLF's critical habitat form the basis of the
critical habitat impact analysis. Actions that may affect the CRLF's designated critical
habitat have been identified by the Services and are discussed further in Section 2.6.
2.2 Scope
Diflubenzuron is an insecticide that is registered for both agricultural and non-
agricultural uses in California and can be applied through ground, aerial, and airblast
methods.
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 diflubenzuron in accordance with the approved product labels for
California is "the action" relevant to this ecological risk assessment.
Although current registrations of diflubenzuron allow for use nationwide, this ecological
risk assessment and effects determination addresses currently registered uses of
diflubenzuron in portions of the action area that are reasonably assumed to be
biologically relevant to the CRLF and its designated critical habitat.
There are two reasons for considering the action area of diflubenzuron use to include the
entire state of California. First, because of the large variety of label uses for
diflubenzuron in the state of California, it would be difficult to exclude any portions of
this state from potential for diflubenzuron use. Second, a degradate of diflubenzon is a
suspected carcinogen and is genotoxic. Because there is no concentration threshold
defined that would result in no genotoxic effects to exposed organisms, it is not possible
to define a threshold below which effects can occur. Therefore, the action area is
assumed to be the entire state of California. Further discussion of the action area for the
CRLF and its critical habitat is provided in Section 2.7.
2.2.1. Chemicals Assessed
This assessment evaluates the potential for diflubenzuron to adversely affect the CRLF.
Several degradates of diflubenzuron have been identified and tested for toxicity. The
available toxicity data are summarized below and are further described in Section 4 and
Appendix A.
Degradates of diflubenzuron include 2,6-diflubenzoic acid (DFBA), 4-chlorophenylurea
(CPU), 4-chloroaniline (PCA), and 2,6-diflubenzamide (DFBAM). The available data
suggest that the degradates are several orders of magnitude less toxic than diflubenzuron
to invertebrates. For example, LCsoS in midge for PCA and DFBA are 43 mg/L and >100
mg/L, respectively, compared with an LCso of 0.07 mg/L for parent chemical in midge.
15
-------
Lower toxicity to invertebrates of degradates is consistent with the specific mode of
action of diflubenzuron as a chitin inhibitor.
Several degradates have been shown to be of similar toxicity to fish compared with
parent difbluenzuron. In particular, PCA has been shown to be more toxic than
diflubenzuron to fish with LCso values ranging from 2 mg/L to 23 mg/L. DFBA and
PCPU appear to have similar toxicity relative to parent diflubenzuron with 96-hr LCso
values of approximately 70 mg/L to >100 mg/L in fish. The most sensitive LCso in fish
was 127 mg/L for diflubenzuron.
Although PCA has been shown to be more toxic to fish, it has not formed more than 10%
of parent compound in available degradation studies. Potential risks resulting from
exposure to PCA or other degradates were not quantified. It was determined that
quantifying risks from the degradates would not affect risk conclusions because
comparing EECs for parent diflubenzuron (which would represent a highly conservative
exposure estimate for any of the degradates) with the lowest toxicity value across all
degradates still results in no LOG exceedances for fish. Therefore, degradates were not
further considered.
One diflubenzuron formulated product toxicity study provided a lower LC50 than values
from studies on the TGAI. The lowest LCso for formulated products was 57 mg/L (see
Appendix A). EFED evaluates potential risks from formulated products resulting from
drift only exposure. The highest drift fraction estimated to be deposited into water bodies
was approximately 4% from aerial spray. The highest application rate for diflubenzuron
is 8.5 Ibs a.i./Acre (barnyard/mushroom use). The resulting drift only EEC is 0.003 mg
a.i./L assuming a volume of 20,000,000 L in the receiving water. Based on an LCso of 57
mg/L, the resulting RQ would be orders of magnitude below concern levels
(approximately 10"5). Therefore, toxicity values from formulated products were not
further considered as part of this assessment.
2.2.2. Evaluation of Mixtures
The Agency does not routinely include, in its risk assessments, an evaluation of mixtures
of active ingredients, either those mixtures of multiple active ingredients in product
formulations or those in the applicator's tank. In the case of the product formulations of
active ingredients (that is, a registered product containing more than one active
ingredient), each active ingredient is subject to an individual risk assessment for
regulatory decision regarding the active ingredient on a particular use site. If effects data
are available for a formulated product containing more than one active ingredient, they
may be used qualitatively or quantitatively in accordance with the Agency's Overview
Document and the Services' Evaluation Memorandum (U.S. EPA 2004; U.S.
FWS/NMFS 2004).
Diflubenzuron has one registered product that contains multiple active ingredients
(diflubenzuron and permethrin). Analysis of the available open literature and acute oral
16
-------
mammalian LD50 data for the diflubenzuron and permethrin products relative to the
single active ingredient is provided in Appendix B. There are no product LD50 values,
with associated 95% Confidence Intervals (CIs) available for diflubenzuron.
As discussed in USEPA (2004) a quantitative component-based evaluation of mixture
toxicity requires data of appropriate quality for each component of a mixture. In this
mixture evaluation an LDso with associated 95% CI is needed for the formulated product.
The same quality of data is also required for each component of the mixture. Given that
the single formulated product for diflubenzuron does not have a 95% CI associated with
the oral LD50 value, it is not possible to undertake a quantitative or qualitative analysis
for potential interactive effects (See appendix B). However, because the active
ingredients are not expected to have similar mechanisms of action, metabolites, or
toxicokinetic behavior, it is reasonable to conclude that an assumption of dose-addition
would be inappropriate. Consequently, an assessment based on the toxicity of
diflubenzuron is the only reasonable approach that employs the available data to address
the potential acute risks of the formulated products. Studies on mixtures located in the
open literature are included in Appendix B.
2.3 Previous Assessments
A large number of risk assessments have been performed on diflubenzuron by EFED.
Two recent, comprehensive assessments are described below.
The Reregi strati on Eligibility Decision (RED) Science Chapter (6/30/95) identified risks
to aquatic invertebrates as the major environmental threat of diflubenzuron. Acute and
chronic levels of concern (LOCs) were exceeded for both freshwater and estuarine and
marine aquatic invertebrates, for the use of diflubenzuron on cotton, citrus, forest trees
and forest plantings.
In an assessment entitled "Section 3 Registration Request for Uses of Diflubenzuron on
Pears, Stone Fruits, Tree Nuts, Peppers, and Pasture Grass (Chemical # 108201, DP
Barcode D279732, D279735, D278770)" from 2/5/02, EFED identified acute concerns
for freshwater invertebrates, but not for fish, birds, or mammals for the uses assessed.
The document indicates concern for sediment dwelling aquatic organisms due to the
expectation of diflubenzuron accumulation in sediments, but did not quantify this risk
due to the lack of chronic toxicity data for these organisms. This document developed the
critical life stage hypothesis for diflubenzuron effects which is discussed in Section 4.1.2
of this document.
A major difference between this assessment and the previous assessments concerns the
inclusion of open literature toxicity values in the current assessment. This assessment is
the first to include open literature toxicity data from the Ecotox database (See Appendix
G). Inclusion of this data resulted in much lower acute and chronic freshwater
invertebrate endpoints, which result in much greater risk estimates.
17
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2.4 Stressor Source and Distribution
2.4.1 Environmental Fate Assessment
Diflubenzuron (DFB) is a member of a larger group of insecticides known as
benzoylphenylureas. Based on acceptable and supplemental registrant-submitted data,
diflubenzuron appears to be relatively non-persistent and relatively immobile under
normal use conditions. The major route of dissipation for diflubenzuron appears to be
biotic mediated processes (t/2 &2-14 days for aerobic soil metabolism). Anaerobic aquatic
metabolism was reported to be slower (tM> = 34 days). Aerobic aquatic metabolism half-
life in total water sediment system was 26 days. Other laboratory data indicate that
diflubenzuron is stable to hydrolysis (t!/2 ^30-433 days for pHs 5-9) and photolysis (t!/2 =
80 days for aquatic; tl/2 for control < light exposed for soil) and is relative immobile in
soil (Rf values = 0.01, 0.07, 0.14, and 0.34 for silty clay loam, clay loam, and two sand
loam soils, respectively). Supplemental and acceptable field data (including forestry
dissipation data) confirm the laboratory data with reported half-lives of 5.8 to 60 days,
and diflubenzuron detectable only in the 0-15 cm soil depth segments. However,
calculated half-lives for CA and OR orchard applications were higher (t!/2 = 68.2-78
days). Diflubenzuron has not been detected in well monitoring data (National Summary-
Pesticides in Ground Water Data base-A Compilation of Monitoring Studies: 1971-
1991), as well.
Under aerobic conditions diflubenzuron appears to degrade to 4-chlorophenyl urea (CPU)
which reached a maximum concentration of 37% of applied at 14 days post-treatment.
The other major degradate, CO2, was reported to reach a maximum concentration of
26.3% of applied by day 21 post-treatment. Three minor degradates, 2,6-difluorobenzoic
acid, 2,6-difluorobenzamide, and p-chloroaniline, each reaching a maximum
concentration of <10% of applied, were identified in the aerobic soil study. These
metabolites were detectable in an anaerobic metabolism study, as well. Due to the
stability of diflubenzuron to abiotic processes, limited data are available on the
persistence and mobility of diflubenzuron metabolites. However, CPU was reported in
leachate of a column leaching study (approximately 15 to 30% of applied in MRIDs
00039477 & 00040777). Even though CPU appears to be mobile under laboratory
conditions, it has not been reported below the 0 to 15 cm soil depth segment in any field
data.
Diflubenzuron does appear to accumulate at low levels and depurate rapidly in fish tissue.
The reported bioconcentration factors ranged from 34 to 200X for fillet, 78 to 360X for
whole fish, and 100 to 500X for viscera. In addition, the depuration rate indicates a rapid
decrease (99%) of accumulated residues in tissue during the 14 day depuration period.
Table 2-1 lists the environmental fate properties of diflubenzuron, along with the major
and minor degradates detected in the submitted environmental fate and transport studies.
18
-------
Table 2-1 Summary of Diflubenzuron Environmental Fate Properties
Study
Hydrolysis
Direct Aqueous
Photolysis
Soil Photolysis
Aerobic Soil
Metabolism
Anaerobic Soil
Metabolism
Anaerobic
Aquatic
Metabolism
Aerobic
Aquatic
Metabolism
Value
14C label
3H Label
Unlabeled
14C and 3H label
(units)
433days@pH5
117days@pH7
42 days @ pH 9
187days@pH5
158days@pH7
40 days @ pH 9
Stable @ pH 5
Stable @ pH 7
44 days @ pH 9
7.5days@pH
12
223.6days@pH5
247 days @ pH 7
32.5 days @ pH 9
Dark aqueous photolysis control:
Stable @ pH 7
40 days (continuous light)
80 days (assuming 12 hr. light/dark
cycle
144 days
11.3
days
2 to 14 days
2 to 14 days
34 days
26 days
5.4 days
3.7 days
Major Degradates
Minor Degradates
CPU -Not Quantified
F)T7R A TsJnt OniintifipH
CPU -Not Quantified
DFBA - Not Quantified
None Identified
CPU -8%
DFBA - 4%
DFBAM- 1%
2,6-Difluorobenzene - not
quantified
Unknown - 6%
Not Quantified
CPU -12.9% (Day 10)
DFBA -3.0% (Day 7)
UnknownSP 1-0.6%
(Day 10)
Unknown PK1 -0.1%
(Day 16)
CPU - 37 % pay 14)
~TM7~R A <" 1 HO/
DFRAA/f <10%
PCA-<10%
CPU -37% pay 2-14:
depending on
temperature)
DFBA -23% (Day 35)
CPU -31% pay 42)
DFBA -31% pay 42)
PCA - 0.4% (Day 18)
CPU - 30 % pay 16)
DFBA - 9% (Day 1)
DFBAM -1.6% (Day 2)
PCA -2% (Day 16)
DFBA -17% pay 4)
CPU - 48 % Pay 16)
MRID#
00143355
40859801
41087801
40816301
40816301
41087802
40941601
42251201
00039473
00039474
00040154
00099875
41722801
Same as
46888708
00040782
41837601
41837601
44895001
46888707
Study Status
Supplemental
Acceptable
Supplemental
(15 days only)
Acceptable
Supplemental
Acceptable
Supplemental
(39474 same
as 40 154)
Supplemental
Acceptable
Acceptable
Acceptable
Acceptable
Supplemental
19
-------
Study
Koc
Terrestrial
Field
Dissipation
Forestry Field
Dissipation
Aquatic Field
Dissipation
Accumulation
Value (units)
2878
3008
3401
6918
6801
2780
1938
The orchard and bare ground half-
lives (5. 8 to 13.2 days).
CA citrus and the OR apple
orchards half -life of approximately
68.2 to 78 days.
30 to 35 days
2 to 6 days
Bioconcentration factors of 34 to
200 x for fillet, 78 to 360 x for
whole fish, and 100, to 550 x for
viscera.
99% depuration within 14 day
Major Degradates
Minor Degradates
Not Applicable
DFBA-uptoO.Olppm
CPU - up to 0.06 ppm
None Detected
CPU
DFBAM-16%
(0.28,ug/g) in Fillet;
12% (0.37 ug/g) in Whole
Fish; and
11% (0.55 ug/g) in
Viscera.
6 unidentified minor
metabolites
MRID#
00039476
00039477
00040777
00157842
46888704
46888705
46895401
00040156
40660601
40660602
41816502
41816503
41821002
41826701
42290401
42290402
42441101
41077201
41077202
41922201
42197701
00040155
00161945
00161947
40598601
44399309
45009601
45191001
45197601
42258401
42258402
Study Status
Acceptable
Acceptable
Supplemental
Acceptable
Acceptable
2.4.2 Environmental Transport Assessment
Surface water runoff and spray drift are expected to be the major routes of exposure for
diflubenzuron.
In general, deposition of drifting pesticides is expected to be greatest close to the site of
application. Computer models of spray drift (AgDRIFT) are used to determine potential
exposures to aquatic and terrestrial organisms via spray drift. The distance of potential
impact away from the use sites (action area) is determined by the distance required to fall
below the LOG for aquatic invertebrates.
20
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2.4.2 Mechanism of Action
Diflubenzuron is an insect growth regulator and works by preventing the formation of
chitin, a molecule necessary to the formation of an insect's cuticle or outer shell. Insects
exposed to a sufficient dose of diflubenzuron cannot form their protective outer shell and
die during molting. It is most effective against insect larva, but also acts as an ovicide,
killing insect eggs (U.S. EPA 1997).
2.4.3 Use Characterization
Currently, labeled uses of diflubenzuron include citrus, cotton, forestry, mushrooms,
ornamentals, pastures, soybeans, standing water, sewage systems, termite bait stations,
and wide-area general outdoor treatment sites. All of these uses are considered as part of
the federal action evaluated in this assessment with the exception of termite bait stations
(in which a solidified form of the pesticide is placed in an enclosed bait station to
minimize loss to the environment) and soybeans, which are not grown in California
(NASS 2002). If use patterns indicate that soybeans are grown in CA in the future, the
conclusions of this assessment may need to be revisited.
Analysis of labeled use information is the critical first step in evaluating the federal
action. The current label for diflubenzuron represents the FIFRA regulatory action;
therefore, labeled use and application rates specified on the label form the basis of this
assessment. The assessment of use information is critical to the development of the action
area and selection of appropriate modeling scenarios and inputs.
Table 2-2 presents the uses and corresponding application rates and methods of
application considered in this assessment.
21
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Table 2-2 Diflubenzuron Uses Assessed for the CRLF
Use (Application Method - Ground (G), Airblast
(AB), or Air (A))
Spray on manure, Manure to field G
y~t
A
Brassica (head and stem) vegetables G
Citrus hybrids, grapefruit, orange, pummelo G
(shaddock), and tangerines A
Broccoli raab, cabbage - Chinese, collards, and
kale
f~i
A
Christmas tree plantations and forest trees G
(softwoods - conifers) A
f~i
A
Almond, Brazil nut, cashew, chestnut, chinquapin, G
filbert (hazelnut), hickory nut, macadamia nut AB
(bushnut), pecan, tree nuts, and walnut
(English/black) A
f~i
Forest nursery plantings (for transplant purposes), G
ornamental and/or shade trees, ornamental woody
shrubs and vines, and shelterbelt plantings
G
Grass forage/fodder/hay, pastures, and rangeland AB
A
Pistachio G
f~i
f\.
Rice A
Agricultural rights-of-way/fencerows/hedgerows, G
fencerows/hedgerows, and nonagricultural rights- AB
of-way/fencerows/hedgerows A
Artichoke, mustard, peanuts (unspecified), and G
pepper A
Commercial/institutional/industrial
premises/equipment (outdoor), nonagricultural
outdoor buildings/structures, paved areas (private .
roads/sidewalks), refuse/solid waste sites
(outdoor), and wide area/general outdoor
treatment (quarantine/eradication use)
y"l
A
y"l
Agricultural fallow/idleland, golf course turf, and .
f\.
Ornamental sod farm (turf) and recreational areas G
Max. Single
Appl. Rate
(Ib ai/A)
8.508
0.0408
0.0408
0.0313
0.3125
0.125
0.25
0.3125
0.3125
0.22048
0.25
0.3125
0.3125
0.3125
0.3125
0.3125
0.3125
0.25
0.125
0.25
0.25
0.25
0.25
0.25
0.75
0.25
0.25
0.625
0.25
0.25
0.25
0.3125
0.3125
0.25
0.25
0.25
0.25
0.25
0.25
0.0313
Max. Number of
Application per
Year
NS (17)
o
J
3
1
3
3
4
3
3
NS(4)
1
3
3
3
3
3
3
4
3
1
1
1
1
1
2
1
6
6
2
2
2
o
J
o
J
6
4
4
2
2
2
3
Application
Interval
NS (21)
7
7
NA
21
7
21
7
90
14
NA
7
7
7
7
7
90
21
NS (21)
NA
NA
NA
NA
NA
14
NA
10
5
5
5
5
21
14
NS (10)
15
15
14
14
5
7
22
-------
Use (Application Method - Ground (G), Airblast
(AB), or Air (A))
AB
A
Turnip (greens) G
Max. Single
Appl. Rate
(Ib ai/A)
0.0313
0.0313
0.25
Max. Number of
Application per
Year
o
J
o
J
2
Application
Interval
7
7
21
NS = Not specified on label.
Several of the agricultural crop uses for diflubenzuron may have more than one crop
cycle per year. Because many diflubenzuron labels specify application limits based on
crop cycles rather than an annual limitation, the potential exists for more diflubenzuron to
be applied than is reflected in Table2-2. However, because the persistence of
diflubenzuron is relatively short compared to the length of a crop cycle, there would be
little accumulation of the parent compound across crop cycles. Instead the greatest impact
from multiple crop cycles would likely result from the extension of the time that
diflubenzuron would be applied both earlier in the spring and later in the fall when more
runoff would occur. This extension of the time that diflubenzuron may be used is
addressed in this assessment in Section 3.2.1, which evaluates both early and late
application dates on diflubenzuron exposure.
Figure 2-1 provides a visual depiction of the spatial distribution of diflubenzuron use
across the United States in terms of pounds of diflubenzuron applied per square mile of
agricultural land in each county. The map was downloaded from a U.S. Geological
Survey (USGS), National Water Quality Assessment Program (NAWQA) website. Many
simplifying assumptions were made in order to produce this map. Non-agricultural uses
of diflubenzuron such as forestry, residential and right-of-way uses are not included in
this depiction.
23
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DIFLUBENZURON - insecticide
2002 estimated annual agricultural use
Average annual use of
active ingredient
(pounds par square mile of agricultural
land in county)
D no estimated use
D 0.001 to 0.004
D 0.005 to 0.011
D 0.012 to 0.026
D 0.027 to 0.06
>= 0.061
Crops
citrus fruit
soybeans
pears
artichokes
rice
other hay
walnuts
cotton
Total
pounds applied
29615
6090
5868
3537
3441
2942
1076
917
Percent
national use
55.37
11.39
10.97
6.61
6.43
5.50
2.01
1.71
Figure 2-1. Diflubenzuron use in total pounds per square mile of agricultural land
in county.
The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis
of both national- and county-level usage information (U.S. EPA 2009) using state-level
usage data obtained from USDA-NASS1, Doane (www.doane.com: the full dataset is not
provided due to its proprietary nature) and the California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database2 . CDPR PUR is considered
a more comprehensive source of usage data than USDA-NASS or EPA proprietary
databases, and thus the usage data reported for diflubenzuron by county in this
California-specific assessment were generated using CDPR PUR data. Eight years
(1999-2006) of usage data were included in this analysis. Data from CDPR PUR were
obtained for every 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 summarizing across all applications made within a section and then across
1 United States Depart of Agriculture (USDA), National Agricultural Statistics Service (NASS) Chemical
Use Reports provide summary pesticide usage statistics for select agricultural use sites by chemical, crop
and state. See http://www.usda.gov/nass/pubs/estindxl.htm#agchem.
2 The California Department of Pesticide Regulation's Pesticide Use Reporting database provides a census
of pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/purmain.htm.
24
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all sections within a county for each use site and for each pesticide. The county level
usage data that were calculated include: average annual pounds applied, average annual
area treated, and average and maximum application rate across all eight years. The units
of area treated are also provided where available.
A summary of diflubenzuron usage for all California use sites is provided below in Table
2-3.
Table 2-3 Summary of California Department of Pesticide Registration (CDPR) Pesticide Use
Reporting (PUR) Data from 1999 to 2006 for Currently Registered Diflubenzuron Uses
Site Name, Application Method (Aerial,
Ground, or Other), and Years of Data
AlmnnH ^ '
Almond G(3)
\micot A(1)
Apricot
G(3)
Aquatic Areas, Water Areas (All Or _
Unspec)
ArtirVinlrr (C*.]r,hr\ f All OrTTncnrr'l ^ '
(j (8)
Beets, General G (1)
Rrnrrnli ^ '
Eio^oh G(1)
Brussels Sprouts G (2)
Cherry G (1)
Christmas Tree Plantations G (6)
A ni
Pntfnn rjrnrrnl * '
G(2)
Endive (Escarole) G (1)
G(4)
Landscape Maintenance O (8)
Nectarine G (3)
A (3)
N-Outdr Container/Fid Grwn Plants G (8)
0(1)
N Oiitrlr rirvrn Put Flnrc Or rirrrnc ^ '
A ("H
NOiitHr rinvn Trnrnlnt/PrncrtT IVTtrl ^ '
G(6)
A (J\
Ornncrr ("All OrTTnrnrr^ ^ '
G(4)
Pastures (All Or Unspec) A ( 1 )
Peach G (4)
Pear G (3)
Peppers (Chili Type) (Flavoring And m
Spice Crop) (i)
Peppers (Fruiting Vegetable), r m
(Bell, Chili, Etc.) ( '
Pistachio (Pistache Nut) G (2)
Average Pounds
Applied by Use
988.30
8007.51
17.46
100.25
15.82
1737.13
1982.66
3.50
0.92
2.10
1.36
3.75
0.71
45.42
54.38
26.64
2.44
73.25
23.11
38.51
0.06
18.14
0.00
0.03
2.82
2.55
9.23
31.03
762.37
0.95
167.31
75.48
0.75
141.96
36.87
Average App.
Rate by Use
0.24
0.22
0.25
0.19
0.22
0.14
0.14
5.00
0.02
0.02
0.41
0.25
0.08
0.12
0.10
0.19
0.13
0.17
NR
0.09
0.32
0.46
0.00
0.00
0.29
0.21
0.20
0.13
0.19
0.02
0.20
0.22
0.13
0.12
0.24
Maximum App.
Rate by Use
4.05
3.74
0.25
0.24
0.25
2.23
2.97
5.00
0.02
0.02
0.70
0.25
0.13
0.14
0.13
0.19
0.13
0.78
NR
0.25
0.69
24.16
0.00
0.00
3.57
0.59
2.08
0.14
2.50
0.02
6.07
0.26
0.13
0.13
0.25
25
-------
Site Name, Application Method (Aerial,
Ground, or Other), and Years of Data
Plum (Includes Wild Plums For A (1)
Human Consumption) G (3)
Prune A(1)
PmnC G (3)
Public Health Pest Control O (8)
Rincrrlinrl f All DrTTncnrr^ ^ '
G(l)
Regulatory Pest Control O (5)
Rirr ("All DrTTncnrr^ ^ '
G(l)
Rights Of Way O (6)
Soil Application, Preplant-Outdoor
(Seedbeds,Etc.) ( '
Strawberry (All Or Unspec) G (1)
Structural Pest Control O (8)
Tangerine (Mandarin, Satsuma, ,.,
Murcott, Etc.) ( '
Uncultivated Agricultural Areas (All
Or Unspec) ()
Uncultivated Non-Ag Areas (All Or _
Unspec) U (2)
Walnut (English Walnut, Persian A (4)
Walnut) G (8)
Average Pounds
Applied by Use
5.95
94.31
5.56
66.94
527.15
3.08
2.21
42.22
789.74
4.08
9.98
213.56
23.50
284.86
30.73
1.39
8.15
37.22
1406.79
Average App.
Rate by Use
0.20
0.19
0.25
0.25
NR
0.03
0.03
NR
0.14
0.09
NR
11.28
0.25
NR
0.16
0.05
0.06
0.24
0.26
Maximum App.
Rate by Use
0.20
0.25
0.25
0.95
NR
0.03
0.03
NR
3.93
0.09
NR
12.61
0.25
NR
0.26
0.07
0.13
0.38
2.02
2.5 Assessed Species
The CRLF was federally listed as a threatened species by U.S. FWS effective June 24,
1996 (U.S. FWS 1996). It is one of two subspecies of the red-legged frog and is the
largest native frog in the western United States (U.S. FWS 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 I.
Final critical habitat for the CRLF was designated by U.S. FWS on April 13, 2006 (U.S.
FWS 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 (U.S. FWS 1996). Its range has been reduced by about 70%,
and the species currently resides in 22 counties in California (U.S. FWS 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) (U.S. FWS 2002).
26
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Populations currently exist along the northern California coast, northern Transverse
Ranges (U.S. FWS 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 (U.S. FWS 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) (U.S. FWS 2002).
The distribution of CRLFs within California is addressed in this assessment using four
categories of location including recovery units, core areas, designated critical habitat, and
known occurrences of the CRLF reported in the California Natural Diversity Database
(CNDDB) that are not included within core areas and/or designated critical habitat.
Recovery units, core areas, and other known occurrences of the CRLF from the CNDDB
are described in further detail in Attachment I, and designated critical habitat is addressed
in Section 2.6. Recovery units are large areas defined at the watershed level that have
similar conservation needs and management strategies. The recovery unit is primarily an
administrative designation, and land area within the recovery unit boundary is not
exclusively CRLF habitat. Core areas are smaller areas within the recovery units that
comprise portions of the species' historic and current range and have been determined by
U.S. FWS 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.
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.
27
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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
Legend
] Recovery Unit Boundaries
|] Currently Occupied Core Areas
^B Critical Habitat
I CNDDB Occurence Sections
_! County Boundaries
45
Core Areas
1. Feather River
Yuba River- S. Fork Feather River
Traverse Creek/ Middle Fork/ American R. Rubicon
Cosumnes River
South Fork Calaveras River*
Tuolumne River*
Piney Creek*
Cottonwood Creek
Putah Creek - Cache Creek*
9.
10. Lake Berryessa Tributaries
11. Upper Sonoma Creek
12. Petaluma Creek Sonoma Creek
13. R. Reyes Peninsula
14. Belvedere Lagoon
15. Jameson Canyon - Lower Napa River
16. East San Francisco Bay
17. Santa Clara Valley
18. South San Francisco Bay
* Core areas that were historically occupied by the California red-legged frog are not included in the map
19. Watsonville Slough-Elkhorn Slough
20. Carmel River Santa Lucia
21. Gab Ian Range
22. Estero Bay
23. Arroyo Grange River
24. Santa Maria River - Santa Ynez River
25. Sisquoc River
26. Ventura River - Santa Clara River
27. Santa Monica Bay - Venura Coastal Streams
28. Estrella River
29. San Gabriel Mountain*
30. Forks of the Mojave*
31. Santa Ana Mountain*
32. Santa Rosa Plateau
33. San Luis Ray*
Sweetwater*
Laguna Mountain*
Figure 2-2 Recovery Unit, Core Area, Critical Habitat, and Occurrence
Designations for CRLF
28
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2.5.2 Reproduction
CRLFs breed primarily in ponds; however, they may also breed in quiescent streams,
marshes, and lagoons (Fellers 2005a). According to the Recovery Plan (U.S. FWS 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,
U.S. FWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until
the following year) (Fellers 2005b; U.S. FWS 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 (U.S. FWS 2002). Figure 2-3 depicts CRLF annual reproductive
timing.
J
F
M
A
M
J
J
A
S
0
N
D
Light Blue =
Green = " ','..- . .:_ ~. . those that over-winter)
Orange = - .,...,
Adults and juveniles can be present all year
Figure 2-3 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
(U.S. FWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar 1980)
via mouthparts designed for effective grazing of periphyton (Wassersug 1984;
Kupferberg etal. 1994; Kupferberg 1997; Altig andMcDiarmid 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
29
-------
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
(Stalls cf californicd)., 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 (U.S. FWS 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 (U.S. FWS 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 (U.S.
FWS 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://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=D02D).
In general, dispersal and habitat use depends on climatic conditions, habitat suitability,
and life stage. Adults rely on riparian vegetation for resting, feeding, and dispersal. The
foraging quality of the riparian habitat depends on moisture, composition of the plant
community, and presence of pools and backwater aquatic areas for breeding. CRLFs can
be found living within streams at distances up to 3 km (2 miles) from their breeding site
and have been found up to 30 m (100 feet) from water in dense riparian vegetation for up
to 77 days (U.S. FWS 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
30
-------
trees or logs, industrial debris, and agricultural features (U.S. FWS 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 U.S. FWS (U.S. FWS 2006; FR 51 19244-19346). A
summary of the 34 critical habitat units relative to U.S. FWS-designated recovery units
and core areas (previously discussed in Section 2.5.1) is provided in Attachment I.
'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 I.
Occupied habitat may be included in the critical habitat only if essential features within
the habitat may require special management or protection. Therefore, U.S. FWS 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 the Final Rule (FR)
listing notice in April 2006 (71 FR 19243, 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 I for a full explanation on this special rule.
U.S. FWS has established adverse modification standards for designated critical habitat
(U.S. FWS 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 diflubenzuron that may alter the PCEs of the
CRLF's critical habitat form the basis of the critical habitat impact analysis. According
to U.S. FWS (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
the designated critical habitat. Because diflubenzuron is expected to directly impact
living organisms within the action area, critical habitat analysis for diflubenzuron 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.
32
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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 diflubenzuron 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 (U.S. EPA 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 diflubenzuron may be expected to have on the
environment, the exposure levels to diflubenzuron that are associated with those effects,
and the best available information concerning the use of diflubenzuron and its fate and
transport within the state of California. Specific measures of ecological effect that define
the action area include any direct and indirect toxic effect 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 diflubenzuron. 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 diflubenzuron, all uses are considered as part of the federal action evaluated in
this assessment except soybeans and termite bait station uses.
Following a determination of the assessed uses, an evaluation of the potential "footprint"
of diflubenzuron 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
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represent the labeled uses described above. Because diflubenzuron has a diverse set of
uses that encompass all land cover classes used to define the initial "footprint", the initial
area of concern is considered to be statewide.
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
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.
The action area is determined by the footprint of the action plus all offsite areas where
exposure of one or more taxonomic groups to diflubenzuron exceeds the Agency's LOCs.
The spatial extent at which the Agency's LOCs are not exceeded is based on the potential
exposure level and the most sensitive effects endpoint. The most sensitive effects
endpoint is the acute aquatic invertebrate endpoint. It is expected that invertebrates would
be the most sensitive since this chemical is an insecticide. This endpoint and all other
effects endpoints used in this assessment are discussed in Section 4.
Because diflubenzuron has a relatively short period of persistence relative to seasonal
variations in rainfall in California, the major diflubenzuron exposure route to the
organisms of concern (aquatic invertebrates) varies throughout the year. During the dry-
season (late spring, summer, and early fall) when little runoff occurs, most of the
exposure will occur via spray drift. During the wet season (late fall, winter, and early
spring) when much more runoff occurs, runoff will be a major contributor to aquatic
EECs and risks.
The initial footprint for diflubenzuron is the entire state of California given the large
various types of uses (e.g., agriculture, residential, rights of ways, forestry). In addition,
given the genotoxicity of a diflubenzuron degradates, defining a threshold below which
effects can occur is not possible. Therefore, the action area is the entire state of
California.
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."3 Selection of the assessment endpoints is based on valued
entities (e.g., CRLF, organisms important in the life cycle of the CRLF, and the PCEs of
its designated critical habitat), the ecosystems potentially at risk (e.g., waterbodies,
riparian vegetation, and upland and dispersal habitats), the migration pathways of
diflubenzuron (e.g., runoff, spray drift, etc.), and the routes by which ecological receptors
are exposed to diflubenzuron (e.g., direct contact, etc.).
3 U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
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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 (U.S. EPA 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.
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 diflubenzuron is provided in Table 2-4.
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Table 2-4. Assessment Endpoints and Measures of Ecological Effects
Assessment Endpoint
Measures of Ecological Effects4
Aquatic-Phase CRLF
(Eggs, larvae, juveniles, and adults)*
Direct Effects
1. Survival, growth, and reproduction of CRLF
la. Most sensitive fish acute LC50 (guideline study;
test species: bluegill sunfish)
Ib. Most sensitive fish chronic NOAEC (guideline;
test species: fathead minnow)
Indirect Effects and Critical Habitat Effects
1. Survival, growth, and reproduction of CRLF
individuals via indirect effects on aquatic prey food
supply (i.e., fish, freshwater invertebrates, non-
vascular plants)
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)
4. Survival, growth, and reproduction of CRLF
individuals via effects to riparian vegetation
2a. Most sensitive fish (guideline study; test
species: bluegill sunfish), aquatic invertebrate
(ECOTOX study; test species: mosquito larvae), and
aquatic plant EC50 (guideline study; test species:
Duck weed) or LC50
2b. Most sensitive aquatic invertebrate and fish
chronic NOAEC (ECOTOX study and guideline
respectively)
3a. Vascular plant acute EC50 (duckweed guideline
test)
3b. Non-vascular plant acute EC50 (guideline study;
test species: green algae)
Currently no acceptable, guideline terrestrial plant
toxicity data are available.
Terrestrial-Phase CRLF
(Juveniles and adults)
Direct Effects
5. Survival, growth, and reproduction of CRLF
individuals via direct effects on terrestrial phase
adults and juveniles
5a. Most sensitive birdb or terrestrial-phase
amphibian acute LC50 or LD50 (guideline study; test
species: Redwinged blackbird)
5b. Most sensitive birdb or terrestrial-phase
amphibian chronic NOAEC (guideline study; test
species: Bobwhite quail)
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)
7. Survival, growth, and reproduction of CRLF
individuals via indirect effects on habitat (i.e.,
riparian and upland vegetation)
6a. Most sensitive terrestrial invertebrate and
vertebrate acute EC50 (guideline study; test species:
Bobwhite quail)
Currently no acceptable, guideline terrestrial plant
toxicity data are available.
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.
4 Citations for all registrant-submitted and open literature toxicity data reviewed for this assessment are
included in Appendix A.
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2.8.2 Assessment Endpoints for Designated Critical Habitat
As previously discussed, designated critical habitat is assessed to evaluate actions related
to the use of diflubenzuron 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 diflubenzuron 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 diflubenzuron on critical habitat of
the CRLF are described in Table 2-5. 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 U.S. FWS (2006).
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Table 2-5. Summary of Assessment Endpoints and Measures of Ecological Effect for Primary
Constituent Elements of Designated Critical Habitat"
Assessment Endpoint
Measures of Ecological Effect
Aquatic-Phase CRLF 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.
Alteration in water chemistry/quality including
temperature, turbidity, and oxygen content
necessary for normal growth and viability of
juvenile and adult CRLFs and their food source.
Alteration of other chemical characteristics
necessary for normal growth and viability of
CRLFs and their food source.
Reduction and/or modification of aquatic -based
food sources for pre-metamorphs (e.g., algae)
a. Most sensitive aquatic plant EC50 (guideline study:
test species: green algae)
b. Currently no guideline terrestrial plant toxicity data
is available.
a. Most sensitive aquatic plant EC50
b. Currently, no guideline terrestrial plant toxicity
data is available.
a. Most sensitive EC50 or LC50 values for fish and
aquatic invertebrates (guideline and ECOTOX studies
respectively; respective test species: bluegill sunfish
and mosquito larvae)
b. Most sensitive NOAEC values for fish and aquatic
invertebrates (guideline and ECOTOX respectively;
respective test species: fathead minnow and water
flea)
a. Most sensitive aquatic plant EC50 (guideline study;
test species: green algae)
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
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 Currently, no guideline terrestrial plant toxicity data
are available.
b. 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.
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.
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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 diflubenzuron to the
environment. The following risk hypotheses are presumed for this endangered species
assessment:
The labeled use of diflubenzuron 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; or
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 diflubenzuron release mechanisms, biological receptor types, and effects
endpoints of potential concern. The conceptual models for all of the uses other than fly
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control at livestock operations for both terrestrial and aquatic exposures are shown in
Figure 2-4 and Figure 2-5, respectively, which include the conceptual models for the
aquatic and terrestrial PCE components of critical habitat. 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.
Stressor
Source
Exposure
Media
Diflubenzuron applied to use site
, ,Dermal uptake/lnqestiorr*
Terrestrial-phase
amphibians
Terrestrial/riparian plants
grasses/forbs, fruit, seeds
(trees, shrubs)
i Root uptake.4!
Wet/dry deposition-*1
Ingestion
Receptors
Ingestion
Birds/terrestrial-
phase amphibians/
reptiles/mammals
Attribute
Change
Individual
organisms
Reduced survival
Reduced growth
Reduced reproduction
Food chain
Reduction in prey
Modification of PCEs
related to prey availability
Habitat integrity
Reduction in primary productivity
Reduced cover
Community change
Modification of PCEs related to
habitat
Figure 2-4 Conceptual Model for Pesticide Effects on Terrestrial Phase of the
CRLF
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Stressor
Diflubenzuron applied to use site
Source | Spray drift] | Runoff |
Exposure
Media
* Groundwater:
Surface water/
Sediment
T
.T.
Long range
atmospheric
transport
.Wet/dry deposition .
Receptors
Uptake/gills
or integument
1
Uptake/gills
or integument
Aquatic Animals
Invertebrates
Vertebrates
Fish/aquatic-phase
amphibians
Piscivorous mammals
and birds
Inqe^tion
Attribute Individual
Change
organisms
Reduced survival
Reduced growth
Reduced reproduction
Uptake/cell,
roots^ leaves
Aquatic Plants
\lon-vascular
Vascular
t
Inqestion
Food chain
Reduction in algae
Reduction in prey
Modification of PCEs
related to prey availability
1
Habitat integrity
Reduction in primary
productivity
Reduced cover
ommunity change
Modification of PCEs related to
habitat
Figure 2-5. Conceptual Model for Pesticide Effects on Aquatic Phase of the CRLF.
Because the assessment methods are distinctly different for fly control at livestock
operations, a separate conceptual model diagram is included along with the detailed
description of these methods for this use in Appendix F. Other uses (right-of-ways in
Appendix J and residential uses in Appendix K) have separate appendices to describe
there unique assessment methods, but conceptually, are similar enough to use Figure 2-4
and 5 as the conceptual model diagram for these uses.
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 diflubenzuron 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 diflubenzuron is
estimated using the probit dose-response slope and either the level of concern (discussed
below) or actual calculated risk quotient value.
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2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model
2.10.1.1 Measures of Exposure
The environmental fate properties of diflubenzuron along with available monitoring data
indicate that runoff and spray drift are the principle potential transport mechanisms of
diflubenzuron to the aquatic and terrestrial habitats of the CRLF. In this assessment,
transport of diflubenzuron through runoff and spray drift is considered in deriving
quantitative estimates of diflubenzuron exposure to CRLF, its prey and its habitats.
Long-range atmospheric transport of diflubenzuron is not considered due to this
chemical's physical properties related to volatilization.
Measures of exposure are based on aquatic and terrestrial models that predict estimated
environmental concentrations (EECs) of diflubenzuron 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) and GENeric Expected Environmental Concentration (GENEEC). The
model used to predict terrestrial EECs on food items is T-REX. 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 diflubenzuron that may occur in surface water
bodies adjacent to application sites receiving diflubenzuron 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
diflubenzuron. 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
l-in-10-year 60-day mean is used for assessing chronic exposure to the CRLF and fish
and frogs serving as prey items; the l-in-10-year 21-day mean is used for assessing
chronic exposure for aquatic invertebrates, which are also potential prey items.
The EFED GENEEC (GENeric Expected Environmental Concentration) model (version
1.2) is used to estimate pesticide concentrations in a 1 hectare by 2 meter deep pond with
no outlet draining an adjacent 10 hectare field. It provides an upper-bound screening
concentration value for most types of surface water for up to 56 days after runoff.
GENEEC is a single runoff event but accounts for spray drift from single or multiple
applications. The pond receives a pesticide load from spray drift for each application plus
loading from a single-runoff event, in this case, two days after the last application. The
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runoff event transports a maximum of 10% of the pesticide remaining in the top 2.5 cm
of soil. This amount can be reduced through soil adsorption. The amount of pesticide
remaining on the field in the top 2.5 cm of soil depends on the application rate, number of
applications, interval between applications, incorporation depth, and degradation rate in
the soil.
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 1.3.1, 12/07/2006).
This model incorporates the Kenega nomograph, as modified by Fletcher et al. (1994),
which is based on a large set of actual field residue data. The upper limit values from the
nomograph represented the 95th percentile of residue values from actual field
measurements (Hoerger and Kenega 1972). For modeling purposes, direct exposures of
the CRLF to diflubenzuron 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
diflubenzuron 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.
AgDRIFT was used to assess aquatic exposures of aquatic phase CRLF and its prey to
diflubenzuron deposited in aquatic habitats by spray drift and to determine the maximum
distance from a treated area that effects may occur.
2.10.1.2 Measures of Effect
Diflubenzuron is a chitinase inhibitor, impairing the ability of insects to synthesize a
critical component of their exoskeleton (U.S. EPA, 1997). Chitin synthesis is particularly
important in the early life stages of insects, as they molt and form a new exoskeleton in
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various growth stages. Thus, aquatic guideline tests, which typically run for 48 hours for
the aquatic invertebrate (Daphnia magna), may not capture a molting stage, and are not
an appropriate "most sensitive" acute endpoint for assessments. Endpoints derived from
studies that test the toxic effects of diflubenzuron on the larval/molting stages of
freshwater invertebrates and that test the chronic exposure of freshwater invertebrates to
diflubenzuron more appropriately assess the toxicity of this type of chemical.
Diflubenzuron is fairly persistent in both aquatic and terrestrial environments. For this
reason, data that evaluated the toxic effects of diflubenzuron at life stages (larval/molting
stages) most vulnerable to this chemical were used as both acute and chronic endpoints
for aquatic invertebrate RQs. Likewise, guideline tests on honeybees frequently run for
only 48 hours and are conducted on adult bees, and, therefore, may not reflect the toxicity
of diflubenzuron.
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 U.S. EPA,
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 diflubenzuron 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.
The acute measures of effect used for animals in this screening level assessment are the
LD50, LCso and ECso- 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 LCso is the concentration of a chemical that is
estimated to kill 50% of the test organisms. EC stands for "Effective Concentration" and
the ECso is the concentration of a chemical that is estimated to produce a specific effect in
50% of the test organisms. Endpoints for chronic measures of exposure for listed and
non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL stands for "No
Ob served-Adverse-Effect-Level" and refers to the highest tested dose of a substance that
has been reported to have no harmful (adverse) effects on test organisms. The NOAEC
(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 ECso for aquatic plants).
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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
diflubenzuron, 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 diflubenzuron 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) (U.S. EPA
2004) (see Appendix C).
For this endangered species assessment, listed species LOCs are used for comparing RQ
values for acute and chronic exposures of diflubenzuron directly to the CRLF. If
estimated exposures directly to the CRLF of diflubenzuron resulting from a particular use
are sufficient to exceed the listed species LOG, 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 diflubenzuron resulting from a
particular use are sufficient to exceed the listed species LOG, then the effects
determination for that use is a "may affect." If the RQ being considered also exceeds the
non-listed species acute risk LOG, then the effects determination is a LAA. If the acute
RQ is between the listed species LOG and the non-listed acute risk species LOG, 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 LOG 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 LOG for
plants, the effects determination is "may affect". Further information on LOCs is
provided in Appendix C.
45
-------
2.10.1.4 Data Gaps
No guideline terrestrial plant toxicity data have been submitted to the Agency. However,
open literature data and other lines of evidence will be used to evaluate the potential for
diflubenzuron to indirectly affect CRLFs via impacts to terrestrial plants.
3.0 Exposure Assessment
Diflubenzuron formulations include liquid, water dispersible granules, wettable powder,
effervescent tablets (for ornamental pond treatment), and termite bait (in bait stations).
Application equipment includes ground, aerial, and airblast applicators and directed
sprayers. Risks from ground boom and aerial applications are expected to result in the
highest off-target levels of diflubenzuron due to generally higher spray drift levels.
Ground boom and aerial modes of application tend to use lower volumes of application
applied in finer sprays than applications coincident with sprayers and spreaders and thus
have a higher potential for off-target movement via spray drift.
3.1. Label Application Rates and Intervals
Diflubenzuron labels may be categorized into two types: labels for manufacturing uses
(including technical grade diflubenzuron and its formulated products) and end-use
products. While technical products which contain diflubenzuron 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 insects. The formulated product labels legally limit
diflubenzuron's potential use to only those sites that are specified on the labels.
Currently registered agricultural and non-agricultural uses of diflubenzuron within
California include: almond, Brazil nut, cashew, chestnut, chinquapin, filbert (hazelnut),
hickory nut, macadamia nut (bushnut), pecan, tree nuts, walnut (English/black), citrus
hybrids other than tangelo, grapefruit, orange, pummelo (shaddock), tangerines, broccoli
raab, cabbage - Chinese, collards, kale, soybeans (unspecified), cotton (unspecified),
Christmas tree plantations, forest trees (softwoods - conifers), apricot, nectarine, peach,
pear, plum, prune, stone fruits, commercial/institutional/industrial premises/equipment
(outdoor), nonagricultural outdoor buildings/structures, paved areas (private
roads/sidewalks), refuse/solid waste sites (outdoor), wide area/general outdoor treatment
(quarantine/eradication use), butternut, forest nursery plantings (for transplant purposes),
ornamental and/or shade trees, ornamental woody shrubs and vines, shelterbelt plantings,
turnip (greens), household/domestic dwellings outdoor premises, artichoke, mustard,
peanuts (unspecified), pepper, agricultural fallow/idleland, golf course turf,
nonagri cultural uncultivated areas/soils, barley, canola\rape, oats, triticale, wheat, grass
forage/fodder/hay, pastures, rangeland, agricultural rights-of-way/fencerows/hedgerows,
nonagri cultural rights-of-way/fencerows/hedgerows, agricultural/farm
structures/buildings and equipment, barns/barnyards/auction barns, manure, brassica
(head and stem) vegetables, ornamental sod farm (turf), recreational areas, rice, drainage
systems, forest plantings (reforestation programs)(tree farms - tree plantations - etc.),
forest trees (all or unspecified), forest trees (softwoods - conifers), intermittently flooded
areas/water, lakes/ponds/reservoirs (with human or wildlife use), lakes/ponds/reservoirs
46
-------
(without human or wildlife use), ornamental herbaceous plants, ornamental
ponds/aquaria, ornamental woody shrubs and vines, shelterbelt plantings,
streams/rivers/channeled water, swimming pool water systems, wide area/general outdoor
treatment (quarantine/eradication use), beech nut, pistachio. The uses being assessed are
summarized in Table 3-1.
47
-------
Table 3-1 Diflubenzuron Uses, Scenarios, and Application Information for the CRLF risk
assessment1
Scenario
1. Barnyard
2. Beech Nut
3. Brassica
4. Citrus
5. Cole Crop
6. Cotton
7. Forest
8. Fruit
9. General
Nuts
10. Grains
11. Nursery
12. Pasture
13. Pistachio
14.
Residential
15. Rice
16. Rights-
of-way
17. Row
Crop
18. Urban
19. Squash
Uses Represented by Scenario
Spray on manure, Manure to field
Beech Nut
Brassica (head and stem) vegetables
Citrus hybrids, grapefruit, orange,
pummelo (shaddock), and tangerines
Broccoli raab, cabbage - Chinese,
collards, and kale
Cotton (unspecified)
Christmas tree plantations and forest
trees (softwoods - conifers)
Apricot, nectarine, peach, pear, plum,
prune, and stone fruits
Almond, Brazil nut, cashew, chestnut,
chinquapin, filbert (hazelnut), hickory
nut, macadamia nut (bushnut), pecan,
tree nuts, and walnut (English/black)
Barley, canola\rape, oats, triticale, and
wheat
Forest nursery plantings (for
transplant purposes), ornamental
and/or shade trees, ornamental woody
shrubs and vines, and shelterbelt
plantings
Grass forage/fodder/hay, pastures, and
rangeland
Pistachio
Household/domestic dwellings
outdoor premises
Rice
Agricultural rights-of-
way/fencerows/hedgerows,
fencerows/hedgerows, and
nonagricultural rights-of-
way /fencerows/hedgerows
Artichoke, mustard, peanuts
(unspecified), and pepper
Commercial/institutional/industrial
premises/equipment (outdoor),
nonagricultural outdoor
buildings/structures, paved areas
(private roads/sidewalks), refuse/solid
waste sites (outdoor), and wide
area/general outdoor treatment
(quarantine/eradication use)
Butternut
Application
Rate
8.508
0.0408
0.0408
0.0313
0.3125
0.125
0.25
0.3125
0.3125
0.22048
0.25
0.3125
0.3125
0.3125
0.3125
0.3125
0.3125
0.25
0.125
0.25
0.25
0.25
0.25
0.25
0.75
0.25
0.25
0.625
0.25
0.25
0.25
0.3125
0.3125
0.25
0.25
0.25
Number of
Applications
NS (17)
o
J
3
1
o
J
3
4
o
5
o
6
NS(4)
1
o
J
o
J
o
J
3
o
J
3
4
3
1
1
1
1
1
2
1
6
6
2
2
2
o
J
o
J
6
4
4
Application
Interval
NS (21)
7
7
NA
21
7
21
7
90
14
NA
7
7
7
7
7
90
21
NS (21)
NA
NA
NA
NA
NA
14
NA
10
5
5
5
5
21
14
NS (10)
15
15
Application
Method
Ground
Ground
Air
Ground
Ground
Air
Ground
Ground
Air
Ground
Air
Ground
Airblast
Air
Ground
Airblast
Air
Ground
Air
Ground
Air
Ground
Airblast
Air
Ground
Ground
Air
Air
Ground
Airblast
Air
Ground
Air
Air
Ground
Air
48
-------
Scenario
20. Turf
(HighAppl.
Rate)
21. Turf
(Low Appl.
Rate)
22. Turnip
Uses Represented by Scenario
Agricultural fallow/idleland, golf
course turf, and nonagricultural
uncultivated areas/soils
Ornamental sod farm (turf) and
recreational areas
Turnip (greens)
Application
Rate
0.25
0.25
0.25
0.0313
0.0313
0.0313
0.25
Number of
Applications
2
2
2
o
J
o
J
o
J
2
Application
Interval
14
14
5
7
7
7
21
Application
Method
Ground
Airblast
Air
Ground
Airblast
Air
Ground
1 Uses assessed based on memorandum from SRRD dated 2/24/09.
NS = Not specified on the label.
The large number of scenarios is mainly a reflection of the diverse uses of diflubenzuron.
However, some uses were split from other similar uses because they had much higher or
lower application rates.
Some of the scenarios require additional explanation. The barnyard scenario is a direct
spray of diflubenzuron on manure. This scenario, methods of analysis, and resulting
EECs are discussed in detail in Appendix F. Similarly, the rationales for the residential
and right-of-way scenarios are described in appendices J and K.
In addition, diflubenzuron can be administered to cattle with a gun-like device that shoots
a "bolus" impregnated with diflubenzuron down the throats of the cattle. This bolus
slowly dissolves and releases diflubenzuron with the waste. One bolus treats an animal
for as long as 21 weeks. Similarly, diflubenzuron can be administered through cattle and
swine feed.
EFED does not have data indicating the diflubenzuron concentration in the manure
resulting from all three methods (direct spray on manure, bolus, or feed-through
treatments). However, the desired result from all three methods is to produce manure that
has a concentration of diflubenzuron that inhibits the growth of the same species of
nuisance flies. Therefore, EFED assumes for purposes of this assessment that the
exposure levels from all three methods of manure treatment would be similar and
considers the barnyard EECs to apply to all three manure treatment methods.
The urban scenario provides EECs for the quarantine/eradication use of diflubenzuron if
used in urban areas. It assumes 100% impervious surfaces in the watershed treated.
Another non-standard diflubenzuron use is ornamental pond care. Because this use is a
direct application to water (ornamental ponds) and results in EECs that are roughly
equivalent to the EECS produced by the tier 1 rice model for the rice uses of
diflubenzuron, the ornamental pond care use is assessed using the rice model EECs.
However, an important difference between the rice use and ornamental pond care is
ornamental ponds are required to not be connected to natural drainage-ways, while rice
paddy water is assumed to be discharged to waters off of the use site.
As an example, the ornamental pond care EEC for label registration # 400-469 is
calculated as:
49
-------
AppHed
VolumeTreated
WQQgalx3.8L/gal
where: EEC is the ornamental pond concentration after treatment in |ig/L; AmountAppUed is
the amount of diflubenzuron applied to each 1000 gallons of pond water treated
(converted to jig); and volume treated is 1000 gallons (converted to liters).
The last non-standard use is application of diflubenzuron to the material (often compost)
in which mushrooms are grown. The compost is treated with diflubenzuron to keep
nuisance flies from harming the mushroom crop. As mushrooms are grown, the ability of
the compost material to grow mushrooms decreases. Therefore, the compost material that
was treated with diflubenzuron must be periodically replaced and the old material
discarded. Often this material is land applied on farm fields.
Mushrooms can be grown outdoors or in mushroom houses. When grown outdoors, there
is potential for exposure to CRLFs while the diflubenzuron-treated compost is in use for
growing mushrooms as well as after it has been land applied. Alternatively when
mushrooms are grown indoors, exposure to the diflubenzuron-treated compost would
only occur after the compost is land applied on farm fields.
The mushroom use of diflubenzuron is very similar to the barnyard or manure use
described previously in terms of both exposure at the site of application and at the site of
disposal through land application as well as the concentration in the compost and manure.
For the barnyard or manure use (Appendix F), the resultant diflubenzuron concentration
in the manure is approximately 10 to 60 ppm (Appendix F, Figure F3). For the mushroom
use, the desired diflubenzuron concentration in the compost is approximately 30 to 50
ppm. Therefore, mushroom uses will be assessed using the EECs generated for the
barnyard use.
An important assumption in the barnyard analysis (appendix F) is that degradation
behavior and rate of diflubenzuron in manure is similar to the degradation behavior and
rate of diflubenzuron in soil. This assumption is made because EFED does not have
diflubenzuron fate data in manure. Similarly, the assumption is made that the behavior
and rate of diflubenzuron degradation in mushroom compost is similar to the degradation
behavior and rate of diflubenzuron in soil because EFED does not have diflubenzuron
fate data in mushroom compost.
50
-------
3.2. Aquatic Exposure Assessment
3.2.1. Modeling Approach
Aquatic exposures are quantitatively estimated for all of assessed uses using scenarios
that represent high exposure sites for diflubenzuron 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
have large 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 watershed 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 tend to persist for only short
periods of time and are then carried downstream.
Crop-specific management practices for all of the assessed uses of diflubenzuron were
used for modeling, including application rates, number of applications per year,
application intervals, buffer widths and resulting spray drift values modeled from
AgDRIFT, and the first application date for each crop. The date of first application was
developed based on the use information provided by BEAD and a summary of individual
applications by use from the CDPR PUR data. Because diflubenzuron persists in fields
for only a short time after application (aerobic soil metabolism half-life of 2 to 14 days)
and most runoff in the semi-arid portions of California occur mainly in the winter and
early spring, application date will greatly affect the estimated exposure to diflubenzuron.
As an example of identifying scenario application dates based on PUR data, Figure 3-1
depicts variability in diflubenzuron application by date within a calendar year for ground
citrus applications based on CDPR PUR data from 1990 through 2007. The curvy indigo
(dark blue) line indicates the average pounds of diflubenzuron applied on each day. This
average is calculated as a 15-day moving average of the average total pounds applied for
each day of the year. The solid vertical line indicates the date on which this 15-day
average is highest. The dashed vertical lines the first and last application dates which
were calculated to bracket the highest daily average. Similar analyses for other uses are
included in Appendix D, Figure D3. Because PUR data only identifies applications as
ground or air, airblast application dates are based on the highest 15-day average of
ground applications.
51
-------
S '
งD
ซ
5 -
g 4 -
4 3 -
1 -
FMAMJ JAS
Calender Date
O N D J
Figure 3-1. Identification of application dates based on analysis of the average
pounds of diflubenzuron applied in California to citrus via ground application
methods based on CDPR PUR data (1990-2007).
This method of selecting application dates works well for those uses that are well-
represented in the PUR data set. However many of the uses that can be legally applied in
California (and therefore, must be assessed in this document), do not appear in the PUR
data set. For those uses that do not occur in the PUR, the model was run for each
potential date of application and the date that resulted in the highest exposure was used in
order to ensure a conservative exposure estimate. This method is described at the end of
Section 3.2.3.
3.2.2. Model Inputs
Diflubenzuron is an insecticide used on a wide variety of food and non-food uses.
Diflubenzuron environmental fate data used for generating model parameters is listed in
Table 2-2. The input parameters for PRZM and EXAMS are in Table 3-2.
52
-------
Table 3-2 Summary of PRZM/EZAMS Environmental Fate Data Used for Aquatic
Exposure Inputs for Diflubenzuron Endangered Species Assessment for the CRLF1
Fate Property
Molecular Weight
Henry's constant
Vapor Pressure
Solubility in Water
Photolysis in Water
Aerobic Soil Metabolism Half-lives
Hydrolysis
Aerobic Aquatic Metabolism (water
column)
Anaerobic Aquatic Metabolism
(benthic)
Koc
Application rate and frequency
Application intervals
Chemical Application Method (CAM)
Application Efficiency
Spray Drift Fraction2
Value (unit)
311g/mol
1.87xlO"09atm-m3/mol
9.00 xlO"10 torr
0.2 mg/L
80 days
4.7 days
Stable @ pH 5
119days@pH7
32 days @ pH 9
23.4 days
102 days
3961
(See Table 3-1)
(See Table 3-1)
2
0.99 (Ground/Airblast) or .95 (Air)
0.0007 (Ground), .015 (Airblast),
or .039 (Air)
MRID (or source)
Product Chemistry
Product Chemistry
Product Chemistry
Product Chemistry
40816301
41087802
00039473
00039474
41722801
00143355
40859801
41087801
40816301
Combined Data
Mean= 11. 70 days
SD = 12.41 days, n=3
t90,n-l= I'638
tmput = (meanoft/2) +
(t90.n-ixSD)/n/2
34 days*3
Mean from Table 2-1 Kocs
Label or Maximum from LUIS
Report
Label or Minimum from LUIS
Report
Input Parameter Guidance1
Input Parameter Guidance1
AgDRIFT Model
1 Inputs determined in accordance with EFED "Guidance for Chemistry and Management Practice Input
Parameters for Use in Modeling the Environmental Fate and Transport of Pesticides" dated February 28,
2002.
2 Spray drift fraction assumed a buffer of 150 feet. The fraction was calculated using AgDrift and default
Tier 1 parameters.
3.2.3.
Results
The aquatic EECs for the various scenarios and application methods are listed in TableS-
3 based on the first application date indicated in column three of this table. The highest
EECs (113 |ig/L) are for rice/ornamental pond (direct application to water). Because
rice/ornamental pond EECs were calculated using the rice model which assumes no
degradation, the highest peak, 1-in-10-year 21-day average, and 1-in-10-year 60-day
average EECs are all the same. Excluding the rice/ornamental pond EECs: peak EECs
varied by a factor of 5400 between uses from 0.01 to 54 |ig/L; l-in-10-year 21-day
average EECs varied by a factor of 6900 between uses from 0.006 to 42 |ig/L; and l-in-
10-year 60-day average EECs varied by a factor of 7500 between uses from 0.004 to 27
53
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Table 3-3 Aquatic EECs (jig/L) for Diflubenzuron Uses in California
Scenario
(Ground,
Airblast, or Air)
1. Barnyard/
Mushroom
2. Beech G
Nut A
3. Brassica G
f~*
4r"Stmc
. Lxiirus .
A
5. Cole Crop G
f~*
6Pr-.ttr.Ti
f~*
7 Fnrf-ct
G
8. Fruit AB
A
G
9. General . _
M * AB
Nuts
A
f~*
1A rVninc
G
11. Nursery
A
G
12. Pasture AB
A
13. Pistachio G
14. G
Residential A
15. Rice/
Ornamental A
Pond
G
lights- ^
oi-wav
A
17. Row G
Appl.
Rate
8.508
0.0408
0.0408
0.0313
0.3125
0.125
0.25
0.3125
0.3125
0.22048
0.25
0.3125
0.3125
0.3125
0.3125
0.3125
0.3125
0.25
0.125
0.25
0.25
0.25
0.25
0.25
0.75
0.25
0.25
0.625
0.25
0.25
0.25
0.3125
1st -last
Appl. Date1
Year-round
17 appl.
NP (1/12)
NP (1/12)
NP (12/30)
4/23 - 5/14
4/23 - 5/14
9/11-12/4
5/14 - 6/4
3/14 - 12/9
6/14 - 7/5
3/10
2/20 - 3/12
2/20 - 3/12
3/24 - 4/14
1/13-4/6
1/13-4/6
1/26 - 3/29
NP (1/19)
NP (1/19)
7/4
12/5
2/28
2/28
6/6
3/30
NP (1/10)
NP (1/10)
5/14 - 6/13
NP (1/12)
NP (1/12)
NP (1/12)
8/14 - 10/16
Crops Represented
Spray on manure
Treated manure applied to field
Beech Nut
Brassica (head and stem) vegetables
Citrus hybrids, grapefruit, orange,
pummelo (shaddock), and tangerines
Broccoli raab, cabbage - Chinese,
collards, and kale
Cotton (unspecified)
Christmas tree plantations and forest
trees (softwoods - conifers)
Apricot, nectarine, peach, pear,
plum, prune, and stone fruits
Almond, Brazil nut, cashew,
chestnut, chinquapin, filbert
(hazelnut), hickory nut, macadamia
nut (bushnut), pecan, tree nuts, and
walnut (English/black)
Barley, canola\rape, oats, triticale,
and wheat
Forest nursery plantings (for
transplant purposes), ornamental
and/or shade trees, ornamental
woody shrubs and vines, and
shelterbelt plantings
Grass forage/fodder/hay, pastures,
and rangeland
Pistachio
Household/domestic dwellings
outdoor premises
Rice/Ornamental Pond
Agricultural rights-of-
way/fencerows/hedgerows,
fencerows/hedgerows, and
nonagricultural rights-of-
way /fencerows/hedgerows
Artichoke, mustard, peanuts
Peak
EEC
54.20
7.29
0.11
0.21
0.07
0.24
0.50
0.36
0.15
0.82
0.58
0.80
0.26
0.66
1.36
0.90
1.26
0.85
1.34
0.93
0.20
0.65
0.12
0.29
0.55
0.15
0.08
0.40
112.92
5.55
8.13
5.59
0.02
21-day
average
EEC
42.00
5.63
0.06
0.13
0.04
0.10
0.30
0.20
0.11
0.47
0.31
0.45
0.14
0.43
0.86
0.46
0.70
0.49
0.78
0.52
0.11
0.38
0.08
0.17
0.25
0.08
0.05
0.30
112.92
3.04
4.39
3.07
0.01
60-day
average
EEC
27.30
3.65
0.03
0.08
0.02
0.05
0.18
0.14
0.06
0.30
0.19
0.26
0.08
0.26
0.54
0.25
0.42
0.28
0.56
0.41
0.08
0.30
0.04
0.09
0.13
0.06
0.03
0.25
112.92
1.61
2.32
1.63
0.01
Crop
(unspecified), and pepper
54
-------
Scenario
(Ground,
Airblast, or Air)
A
18. Urban A
f~*
1O QmincTi
20. Turf G
(HighAppl. AB
Rate) A
21. Turf G
(Low Appl. AB
Rate) A
22. Turnip G
Appl.
Rate
0.3125
0.25
0.25
0.25
0.25
0.25
0.25
0.0313
0.0313
0.0313
0.25
1st -last
Appl. Date1
2/1-3/14
NP (1/10)
NP (1/10)
NP (1/10)
7/5 - 8/2
7/5 - 8/2
5/26 - 6/5
7/5 - 8/2
7/5 - 8/2
5/26 - 6/5
NP (1/18)
Crops Represented
Commercial/institutional/industrial
premises/equipment (outdoor),
nonagricultural outdoor
buildings/structures, paved areas
(private roads/sidewalks),
refuse/solid waste sites (outdoor),
and wide area/general outdoor
treatment (quarantine/eradication
use)
Butternut
Agricultural fallow/idleland, golf
course turf, and nonagricultural
uncultivated areas/soils
Ornamental sod farm (turf) and
recreational areas
Turnip (greens)
Peak
EEC
1.15
34.13
1.15
1.87
0.01
0.21
0.61
0.02
0.07
0.13
0.72
21-day
average
EEC
0.77
21.98
0.65
1.18
0.01
0.13
0.37
0.01
0.04
0.08
0.35
60-day
average
EEC
0.58
15.28
0.38
0.79
0.00
0.08
0.20
0.01
0.02
0.05
0.19
JNP = Not in CDPR Pesticide Use Reporting data set. Typically, the date of first application that yielded
the highest peak concentration (indicated in parentheses) was used as the first application date in the
scenario modeled (see text for date selection for residential and right-of-way uses).
The EECs for several of the uses are based on application dates that were selected
specifically because that application date would yield the highest EECs. These highest
dates were used to produce a conservative estimate EECs because there was no PUR data
available to better indicate when diflubenzuron would be applied for that use (Section
3.2.1). Figure 3-2 depicts the variation in PRZM/EXAMS EECs based on the day of the
year chosen as the first application date. As shown in Figure 3.2a, using the date that
yields the highest EECs (typically in the winter) could be extremely conservative (high
EECs) if the actual application of diflubenzuron would only occur in the summer. This is
not always the case though as is shown in Figure 3.2b. Typically, ground applications
(Figure 3.2a) will show large variations between winter and summer diflubenzuron EECs
because ground application EECs are dominated by runoff contributions which vary with
rainfall. Aerial applications (Figure 3.2b) result in a much larger spray drift contribution,
which does not vary with application date and therefore, results in less variation in EECs
between summer and winter. Appendix D, Figure D4, provides similar graphs for all of
the diflubenzuron uses for which PUR data was not available.
55
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Ground Applications
Aerial Applications
peak
21day
- -SOday
JFMAMJJASONDJ
Calendar Date
JFMAMJJASONDJ
Calendar Date
Figure 3-2. Variation in diflubenzuron EECs (peak, 21-day, and 60-day) as function of application
date (first application date for scenarios with multiple applications).
However, even for those uses for which the PUR data suggest a specific date is typically
used for diflubenzuron applications (as in Figure 3-1), it is important to consider that
diflubenzuron is applied over a range of dates. In Figure 3-3, the distribution of PUR data
application dates is compared to the diflubenzuron EECs for each first application date.
According to the PUR data, March 2nd is the most typical application date, while January
25th generates the highest EECs. It is important to consider that diflubenzuron is applied
on the date that yields the highest EECs, but because of the procedure used to select
application dates, application dates surrounding March 2nd were used in this assessment.
Appendix D, Figure D5, provides similar graphs for all of the diflubenzuron uses for
which PUR data were available.
Figure 3-3. Variation in diflubenzuron EECs (peak, 21-day, and 60-day) as function of application
date (first application date for scenarios with multiple applications) compared to variation in the
amount of diflubenzuron applied (Ibs. ai/day) per day in California for fruit use.
56
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3.2.4. Existing Monitoring Data
A critical step in the process of characterizing EECs is comparing the modeled estimates
with available surface water monitoring data. EFED was unable to locate diflubenzuron
monitoring for surface and groundwater and atmospheric data (Fellers et al 2004, LeNoir
et al 1999, and McConnell et al 1998). The sources checked included the USGS National
Water-Quality Assessment (NAWQA) Program and California Department of Pesticide
Regulation (CDPR) data sets.
3.3. Terrestrial Animal Exposure Assessment
T-REX (Version 1.4.1) is used to calculate dietary and dose-based EECs of diflubenzuron
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.
Terrestrial EECs for foliar formulations of diflubenzuron were derived for the uses
summarized in Table 3-4. Foliar dissipation half-lives were reported in Willis and
McDowell (1987) for diflubenzuron of 12, 27, and 35 days. Therefore, a 3 5-day half-life
was used in this assessment. Use specific input values, including number of applications,
application rate and application interval are provided in Table 3-4.
57
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Table 3-4 Input Parameters for Foliar Applications Used to Derive Terrestrial EECs for
Diflubenzuron with T-REX
Scenario Name"
Barnyard/Mushroom
Beech nut
Brassica
Citrus
Cole Crop
Cotton
Forest
Fruit
General Nuts
Grains
Nursery
Pasture
Pistachio
Residential
Rice/Ornamental Pond
Rights-of-way
Row Crop
Squash
Turf (High App. Rate)
Turf (Low App. Rate)
Turnip
Maximum Application Rate (Ibs/A)
Aerial
0.0408
0.125
0.3125
0.25
0.3125
0.3125
0.125
0.25
0.25
0.25
0.0625
0.25
0.3125
0.25
0.25
0.0313
Ground
0.0408
0.0313
0.3125
0.25
0.3125
0.22048
0.3125
0.3125
0.25
0.25
0.25
0.75
0.25
0.25
0.3125
0.25
0.25
0.0313
0.25
Other
8.508
Number of Applications
(Re-treatment Interval in Days)
Aerial
2.3 (7)
3(7)
3(90)
1(NA)
3(7)
3(90)
3 (NS2)
1(NA)
1(NA)
1(NA)
6(5)
1.5 (5)
3(14)
NS3 (15)
1.5 (5)
3(7)
Ground
2.3 (7)
1(NA)
3(21)
4(21)
3(7)
NSX(14)
3(7)
3(7)
4(21)
1(NA)
1(NA)
1.333(14)
6(10)
1.5 (5)
3(21)
4(15)
1.5(14)
3(7)
2(21)
Other
17 (21)
NA = Not applicable (there is no re-treatment interval if only 1 application is allowed).
NS = Not specified on any label.
"No terrestrial assessment was performed forbait, pond, and soybean exposure scenarios (see text).
'The number of applications was assumed to be 4 as a conservative assumption because 4 applications were
the most applications allowed on any non-residential label.
2A re-treatment interval of 21 days is assumed because 21 days is the smallest re-treatment interval allowed
on the ground application to grains label.
3The number of applications was assumed to be 4 as a conservative assumption because 4 applications were
the most applications allowed on any non-residential label.
T-REX is also used to calculate EECs for terrestrial insects exposed to diflubenzuron.
Dietary-based EECs calculated by T-REX for small and large insects (units of a.i./g) are
used to bound an estimate of exposure to terrestrial insects. Available acute contact
toxicity data for bees exposed to diflubenzuron (in units of jig a.i./bee), are converted to
jig a.i./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 diflubenzuron 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
58
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insects reported by T-REX as well as the resulting adjusted EECs are available in Table
3-6.
Table 3-5. Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based Exposures of the
CRLF and its Prey to Diflubenzuron.
Use
Barnyard/Mushroom
Beech nut
Brassica
Citrus
Cole Crop
Cotton
Forest
Fruit
General Nuts
Grains
Nursery
Pasture
Pistachio
Residential
Rice/Ornamental Pond
Rights-of-way
Row Crop
Squash
Turf (High App. Rate)
Turf (Low App. Rate)
Turnip
EECs for CRLF (small insect food
item)
Dietary-based
EEC (ppm)
3369
10.3
4.2
88
80
111
34
111
111
80
34
34
101
131
40
34
88
91
34
11
56
Dose-based EEC
(mg/kg-bw)
3840.66
11.742
4.788
100.32
91.2
126.54
38.76
126.54
126.54
91.2
38.76
38.76
115.14
149.34
45.6
38.76
100.32
103.74
38.76
12.54
63.84
EECs for Prey (short grass food item)
(small mammals)
Dietary-based
EEC (ppm)
5990
18.32
7.5
157
143
197
60
197
197
143
60
60
180
232
71
60
157
162
60
20
100
Dose-based EEC
(mg/kg-bw)
5690.5
17.404
7.125
149.15
135.85
187.15
57
187.15
187.15
135.85
57
57
171
220.4
67.45
57
149.15
153.9
57
19
95
59
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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
Barnyard/Mushroom
Beech nut
Brassica
Citrus
Cole Crop
Cotton, fruit, nuts
Forest
Grains
Nursery
Pasture
Pistachio
Residential
Rice/Ornamental Pond
Rights-of-way
Row Crop
Squash
Turf (High App. Rate)
Turf (Low App. Rate)
Turnip
Small Insect
3369
10.3
4.2
88
80
111
34
80
34
34
101
131
40
34
88
91
34
11
56
Large Insect
374
1.1
0.47
9.8
8.9
12
3.8
8.9
o o
3.8
3.8
11
15
4.4
3.8
9.8
10
3.8
1.2
6.2
3.5 Terrestrial Plant Exposure Assessment
Exposures to terrestrial plants were not quantified because no guideline toxicity data are
available for diflubenzuron. Therefore, RQs were not calculated for terrestrial plants.
See Section 5.2 for discussion of potential risks to terrestrial plants in the context of this
effects determination.
4.0 Effects Assessment
This assessment evaluates the potential for diflubenzuron 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 because no aquatic phase amphibian data have been submitted or were
located in the open literature. Terrestrial-phase effects assessments are based on avian
toxicity data because no open literature or registrant-submitted studies on terrestrial phase
amphibians were located. 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
60
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is characterized based on registrant-submitted studies and a comprehensive review of the
open literature on diflubenzuron.
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). A complete list of all available registrant-
submitted studies is in Appendix H. Open literature data presented in this assessment
were obtained from the ECOTOX database searched on April 28, 2009. In order to be
included in the ECOTOX database, papers must meet the following minimum criteria:
(1) the toxic effects are related to single chemical exposure;5
(2) the toxic effects are on an aquatic or terrestrial plant or animal species;
(3) there is a biological effect on live, whole organisms;
(4) a concurrent environmental chemical concentration/dose or application
rate is reported; and
(5) there is an explicit duration of exposure.
Data that pass the ECOTOX screen are evaluated along with the registrant-submitted
data, and may be incorporated qualitatively or quantitatively into this endangered species
assessment. In general, effects data in the open literature that are more conservative than
the registrant-submitted data are considered. The degree to which open literature data are
quantitatively or qualitatively characterized for the effects determination is dependent on
whether the information is relevant to the assessment endpoints (i.e., 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 diflubenzuron.
Citations of all open literature not considered as part of this assessment because they
were either rejected by the ECOTOX screen or accepted by ECOTOX but not used (e.g.,
the endpoint is less sensitive) are included in Appendix Gl to G4. Appendix G also
includes a rationale for rejection of those studies that did not pass the ECOTOX screen
5 The studies that have information on mixtures are listed in the bibliography as rejected due to the
presence of mixtures. These studies are evaluated by EFED when applicable to the assessment; however,
the data is not used quantitatively in the assessment.
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and those that were not evaluated as part of this endangered species risk assessment.
Rejection Codes are described in Appendix I.
A detailed spreadsheet of the available ECOTOX open literature data, including the full
suite of lethal and sublethal endpoints is presented in Appendix Gl. Appendix E includes
a summary of the human health effects data for diflubenzuron.
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 diflubenzuron. A summary of the available aquatic
and terrestrial ecotoxicity information, use of the probit dose response relationship, and
the incident information for diflubenzuron are provided in Sections 4.3 through 4.4
respectively. A detailed summary of the available registrant-submitted ecotoxicity
information is presented in Appendix A, and open literature information is presented in
Appendix G.
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 and open literature data considered relevant to
this ecological risk assessment for the CRLF is presented below. Additional information
is provided in Appendix A and Appendix G.
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Table 4-1 Freshwater Aquatic Toxicity Profile for Diflubenzuron
Freshwater Aquatic Toxicity Profile for Diflubenzuron (TGAr
Assessment
Endpoint
Acute Toxicity to
Fish and Aquatic-
phase Amphibians
Chronic Toxicity
Fish and Aquatic-
phase Amphibians
Acute Toxicity to
Aquatic
Invertebrates
Chronic Toxicity to
Aquatic
Invertebrates
Acute Toxicity to
non-vascular
Aquatic Plants
Acute Toxicity to
vascular Aquatic
Plants
Surrogate
Species
Bluegill sunfish
(Lepomis
macrochirus)
Fathead minnow
2nd instarAedes
albopictus
(mosquito larvae)
Water flea
(Daphnia magna)
Green algae
(Selanustmm
capricornutum)
Duckweed
Toxicity Value Used
129 mg/L
(CI: 116 to 142)
Slope: 4.7 (3.5 to 5.9)
NOAEC = 0.100 mg/L a.i.
LOAEC = >0.100 mg/L a.i.
EC50 was 0.0028 ug/L
Slope: Not available
NOAEC = 0.00025 ug/L
EC50=> 0.20 mg/L a.i.
NOAEL = 0.20 mg/L a.i.
EC50=>0. 190 mg/L a.i.
NOAEC = 0.190 mg/L
Source Citation
MRID
00056150
MRID
00099755
. Hoetal. (1987)
(Open literature
study :ECOTOX #
16591)
Kashian et al
(2002) (Open
literature study;
ECOTOX 93397)
45252205
MRID
42940103
Study Classification
Supplemental Notel
Acceptable Note2
Quantitative Note3
Quantitative Note4
Supplemental Note5
Supplemental Note6
Note 1: The available data evaluation record does not specify whether the LC50 was based on the mean measured or
nominal concentration. It is important to note that given the persistence of the compound, nominal concentrations
could potentially underestimate the toxicity.
Note 2: Although the data evaluation record (DER) deems this study as acceptable, the DER does not specify whether
the LC50 was based on the mean measured or nominal concentration. It is important to note that given the persistence
of the compound, nominal concentrations could potentially underestimate the toxicity.
Note 3: The study Authors do not specify whether the EC50 was based on the mean measured or nominal concentration.
It is important to note that given the persistence of the compound, nominal concentrations could potentially
underestimate the toxicity.
Note 4: The NOAEC is based on the nominal concentration. It is important to note that given the persistence of the
compound, nominal concentrations could potentially underestimate the toxicity.
Note 5: The study was deemed supplemental because the test procedures deviated from guidelines in the
following manner: The study was not continued after three days because of an unexpected high growth of
the algae, which caused the pH to increase to a value of 9 after 3 days. Additionally the NOAEC is based on
the nominal concentration. It is important to note that given the limited persistence of the compound, nominal
concentrations could potentially underestimate the toxicity.
Note 6: The study was deemed supplemental because 20% of the initial measured concentration. Based on the mean
measured concentration of 190 ug/1, growth ofL. gibba exposed to diflubenzuron was not reduced in comparison to the
solvent control over the 14-day study period.
Toxicity to fish and aquatic 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 Fish and Aquatic Invertebrates
LC50 (ppm)
<0.1
>0.1 - 1
>
1 -10
Toxicity Category
Very highly toxic
Highly toxic
Moderately toxic
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LC50 (ppm)
> 10 - 100
>100
Toxicity Category
Slightly toxic
Practically nontoxic
4.1.1. Toxicity to Freshwater Fish
Given that no diflubenzuron 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 diflubenzuron to the CRLF from 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 summary of acute and chronic freshwater fish data, including data from the open
literature, is provided below in Sections 4.1.1.1 through 4.1.1.3.
4.1.1.1. Freshwater Fish: Acute Exposure (Mortality) Studies
There are numerous registrant submitted freshwater fish acute toxicity studies testing the
technical grade active ingredient of diflubenzuron. These studies tested 7 different
species of freshwater fish and demonstrate that the technical grade active ingredient of
diflubenzuron is slightly to practically non-toxic to freshwater fish. The LCso from these
studies range from 129 ppm to >500 ppm. Further details about these studies are
provided in Appendix A. The most sensitive, acceptable, freshwater fish LCso of 129
ppm (MRID 00056150) will be use to assess the acute risk of the technical grade active
ingredient to the aquatic-phase CRLF and to freshwater fish prey of the CRLF.
Appendix A provides further details regarding all the fish acute toxicity studies of the
TGAI.
There are 16 registrant submitted studies testing several formulated products of
diflubenzuron. The toxicity results of these studies range from slightly to practically
nontoxic (LC50= 57 ppm to >1000 ppm), which suggests that the toxicity of formulated
products are not dramatically greater than the toxicity of the technical grade material.
Further details about these studies are also provided in Appendix A. Potential risks from
exposure to formulated products were not quantified as discussed in Section 2. No
studies were located in the open literature that reported LC50s that were lower than those
reported in the registrant-submitted studies (see Appendix G).
Degradate toxicity data are summarized in Appendix A. These data suggest that PCA is
more toxic than diflubenzuron to fish with LCso values ranging from 2 mg/L to 23 mg/L.
DFBA and PCPU appear to have similar toxicity relative to parent diflubenzuron. As
discussed in Section 2, potential risks from degradates were not quantified, and were
considered to have negligible impact on conclusions of this assessment.
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4.1.1.2. Freshwater Fish: Chronic Exposure (Early Life Stage and
Reproduction) Studies
There is one available registrant submitted freshwater fish chronic toxicity study
(Appendix A). Based on the results of this study, there were no effects to survival,
reproduction, or growth at concentrations up to 0.1 mg/L in a full life-cycle study (egg to
egg exposure). The LOAEC was > 0.1 mg a.i./L and the NOAEC was 0.1 mg a.i./L
(MRID 00099755). The NOAEC of 0.1 mg/L will be used to assess the chronic risk of
diflubenzuron to the aquatic-phase CRLF and to freshwater fish prey of the CRLF since
this endpoint is the most sensitive chronic toxic endpoint available for freshwater fish.
However, because a LOAEC was not established (no effects occurred at any test
concentration), use of 0.1 mg a.i./L as a chronic endpoint is likely conservative.
4.1.1.3. Freshwater Fish: Sublethal Effects and Additional Open
Literature Information
The available freshwater fish toxicity data do not indicate that diflubenzuron caused
sublethal effects to freshwater fish at levels below those used to calculate RQs in this
assessment.
Currently, there are no available guideline acute or chronic aquatic-phase amphibian
toxicity studies testing diflubenzuron. However, one field study was located in ECOTOX
in Pacific chorus frogs that did not observe any effects at 0.28 kg a.i./hectare (0.25 Ibs
a.i./Acre) (Ecotox No. 111232). No other test levels were evaluated, and a LOAEC was
not established. Therefore, fish are used in this assessment as a surrogate for aquatic
phase amphibians.
4.1.2. Toxicity to Freshwater Invertebrates
Freshwater aquatic invertebrate toxicity data were used to assess potential indirect effects
of diflubenzuron to the CRLF via prey reduction. 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 in Sections 4.1.2.1 through 4.1.2.3. Diflubenzuron
is a chitinase inhibitor, impairing the ability of insects to synthesize a critical component
of their exoskeleton (U.S. EPA, 1997). Chitin synthesis is particularly important in the
early life stages of insects, as they molt and form a new exoskeleton in various growth
stages. Thus, aquatic guideline tests, which typically run for 48 hours for the aquatic
invertebrate (Daphnia magna)., may not capture a molting stage, and are not an
appropriate "most sensitive" acute endpoint for assessments. Endpoints derived from
studies that test the toxic effects of diflubenzuron on the larval/molting stages of
freshwater invertebrates and that test the chronic exposure of freshwater invertebrates to
diflubenzuron more appropriately assess the toxicity of this type of chemical.
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Diflubenzuron is fairly persistent in both aquatic and terrestrial environments. For this
reason, data that evaluated the toxic effects of diflubenzuron at life stages (larval/molting
stages) most vulnerable to this chemical were used as both acute and chronic endpoints
for aquatic invertebrate RQs. Results from acute studies are also presented. Likewise,
guideline tests on honeybees frequently run for only 48 hours and are conducted on adult
bees, and, therefore, may not reflect the toxicity of diflubenzuron.
4.1.2.1. Freshwater Invertebrates: Acute Exposure (Mortality) Studies
from Registrant-Submitted Studies
There are 8 registrant submitted freshwater invertebrate aquatic toxicity studies testing
the technical grade diflubenzuron. Based on the registrant submitted freshwater
invertebrate toxicity studies diflubenzuron is very highly toxic to slightly toxic to
freshwater invertebrates (ECso ranges from 0.0026 ppm to > 100 ppm). Further details
about these studies are provided in Appendix A.
There are also several diflubenzuron formulated product studies (Appendix A). The
toxicity values of these studies range from 1300 jig/L to >1,000,000 |ig/L. These data
suggest that the toxicity of the formulated products is not greater than toxicity of the
technical grade material.
Degradate toxicity data are also summarized in Appendix A. The degradates were orders
of magnitude less toxic to invertebrates than parent diflubenzuron. For example, LCsoS in
midge for PC A and DFBA are 43 mg/L and >100 mg/L, respectively, compared with an
LC50 of 0.07 mg/L for parent chemical in midge (See Appendix A for additional details).
4.1.2.2. Freshwater Invertebrates: Chronic Exposure (Reproduction)
Studies from Registrant-Submitted Studies
Registrant-submitted chronic studies in aquatic invertebrates are summarized in
Appendix A. The most sensitive endpoint produced in these studies was a NOAEL of
0.05 |ig/L and a LOAEL of 0.075 |ig/L. In registrant submitted studies, no sublethal
effects were observed at levels lower than the NOAEC used to calculate RQs. There is
uncertainty in the most sensitive NOAEC because diflubenzuron was not detected in 4 of
the 7 test samples analyzed. Therefore, the mean measured values assumed a test
concentration of the detection limit when measured values were below the detection
limit. Appendix A contains more detail on registrant-submitted studies. Registrant-
submitted toxicity studies were not used to calculate RQs because an open literature
study was located that produced a lower toxicity value. See Section 4.1.2.3.
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4.1.2.3. Freshwater Invertebrates: Sublethal Effects and Open
Literature Data
Several open literature studies have been identified that produced more sensitive
endpoints than any of the registrant submitted studies. Ho et al. (1987) reported 30% and
44% mortality in 2nd mstarAedes albopictus (mosquito larvae) at diflubenzuron
concentrations of 0.00000025 mg/L (0.00025 |ig/L) and 0.0000025 mg/L (0.0025 |ig/L),
respectively, in a 1 day study. Pairwise comparisons between control and treated groups
were not made; however, no larval mortality occurred in controls. The EC50 was
0.0000028 mg/L (0.0028 |ig/L) in this study as determined by probit analysis. A
concentration dependent reduction in normal pupation and adult emergence was observed
in this study in 2nd, 3rd, and 4th instar animals, with younger animals being more sensitive.
A number of sublethal effects were observed in this study including physical
abnormalities and biochemical changes. However, these sublethal effects were only
observed at levels that were also associated with increased mortality. The ECso of
0.0000028 mg/L will be used to calculate the acute risk of diflubenzuron to aquatic
invertebrates because this value is based on a larval/molting stage of mosquito and
because it is the most sensitive freshwater invertebrate acute toxicity value.
In addition, Kashian et al (2002) observed significant (p<0.05) reduction in survival at
diflubenzuron concentrations of 0.01 |ig/L (NOAEC = 0.00001 mg/L) in a 6-day semi-
static study in daphnia magna (40 per test level, replicated test). Test concentrations
were not measured; however, the study was replicated. Mortality rate was approximately
30% at 0.01 |ig/L (estimated from Figure 2).
The toxicity of 0.00025 |ig/L from Ho et al. (1987) will be used to calculate the chronic
risk of diflubenzuron to aquatic invertebrates because it is the most sensitive toxicity
value available for freshwater invertebrates impacting vulnerable life stage that this
chemical is expected to impact.
4.1.3. Toxicity to Aquatic Plants
Aquatic plant toxicity studies were used as one of the measures of effect to evaluate
whether diflubenzuron 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.
Two types of studies were used to evaluate the potential of diflubenzuron to affect
aquatic plants. Laboratory and field studies were used to determine whether
diflubenzuron 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 and
4.1.3.2
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4.1.3.1. Aquatic Plants: Laboratory Data
There are four available aquatic plant toxicity studies including three nonvascular aquatic
plant studies and 1 vascular plant study. In all of these studies the ECso values were
greater than the highest diflubenzuron concentrations tested. The most sensitive
endpoints are summarized in the following table and produced an ECso and NOAEL of
>0.20 ppm and 0.20, respectively, in algae and duckweed (MRID 45252205 and
42940103). Since these are the most sensitive endpoints, these values will be used to
assess the risk of diflubenzuron to aquatic plants. Appendix A provides further details
regarding these studies.
Freshwater Aquatic Toxicity Profile for Diflubenzuron (TGAI)
Assessment
Endpoint
Acute Toxicity to
non-vascular
Aquatic Plants
Acute Toxicity to
vascular Aquatic
Plants
Surrogate
Species
Green algae
(Selanustmm
capricornutum)
Duckweed
Toxicity Value Used
EC50=>0.20mg/La.i.
NOAEL = 0.20 mg/L a.i.
EC50=>0.190mg/La.i.
NO AEC = 0.190 mg/L
Source Citation
45252205
42940103
Study Classification
Supplemental Notel
Supplemental Note2
Note 1: The study was deemed supplemental because the test procedures deviated from guidelines in the
following manner: The study was not continued after three days because of an unexpected high growth of
the algae, which caused the pH to increase to a value of 9 after 3 days. Additionally the NOAEC is based on
the nominal concentration. It is important to note that given the limited persistence of the compound, nominal
concentrations could potentially underestimate the toxicity.
Note 2: The study was deemed supplemental because 20% of the initial measured concentration. Based on the mean
measured concentration of 190 ug/1, growth of L. gibba exposed to diflubenzuron was not reduced in comparison to the
solvent control over the 14-day study period.
4.1.4.
Freshwater Field Studies
The USEPA Mid-Continent Ecology Division, Duluth, MN conducted a study of the
biological effects, persistence, and distribution of diflubenzuron in littoral enclosures
(MRID 44386201). The Duluth study investigated the distribution of diflubenzuron
(water, sediments and biota) and effects (plants, invertebrates, and fish) of diflubenzuron
applied to oligotrophic littoral enclosures (2 applications 30 days apart). The following
table (4-3) describes the observed effects in this study.
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Table 4-3. Diflubenzuron Effects Reported in a Littoral Enclosure Study (MRID 443862-01).
Endpoint
LOEC
NOEC
Comments
Aquatic plant Effects
phytoplankton
(chlorophyll a:
numbers, and
biovolume)
periphyton
(reduced biomass
and chlorophyll a)
macrophytes
(standing crop of
submerged and
floating plants,
species
composition)
decompos~t~ornat e
of plant l~tter
Not Applicable
(highest dose tested
produced no statistical
effects)
7 ug/L
Not Applicable
(highest dose tested
produced no statistical
effects)
Not Applicable
(highest dose tested
produced no statistical
effects)
30 ug/L
2.5 ug/L
30 ug/L
30 ug/L
The littoral enclosures were
determined by the study authors to be
nutrient limited with respect to
phytoplanktonic growth. Therefore, the
experiment was suitable for measuring
direct effects on phytoplankton by
diflubenzuron only. It could not
determine any indirect effects related
to adverse impacts to herbivorous
zooplankton, macroinvertebrates,
insects, or fish.
Zooplankton Effects
Cladocera (total
numbers)
Copepoda (adults,
juveniles, and total
number)
Rotifera (total number)
Ostracoda (total number)
0.7 ug/L
0.7 ug/L
Not Applicable
(highest dose tested
produced no statistical
effects)
7 ug/L
0.6 ug/L
0.3 ug/L
2.5 ug/L
Though the effects observed at 0.7
ug/L were not statistically significant,
they were very severe, with a reduction
in total cladoceran population of
>89%.
0 6 ug/L is the study authors'
extrapolated MATC value
At the lowest does tested, reductions in
the numbers of adult, juvenile, and
total copepod numbers reached 71%,
83%, and 81%, respectively.
0 3 ug/L is the study authors'
extrapolated MATC value
The control variability was very large,
thereby severely limiting the sensitivity
of the test. Reductions in ostracods at
the 7.0 and 30 ug/L doses were 59 to
98% lower than controls
69
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Endpoint
LOEC
NOEC
Comments
Macroinvertebrate Effects
Chironomidae
abundance)
Epherneroptera
(abundance)
total adjusted
macroinvertebrate
community biomass
Mean macroinvertebrate
taxa richness
7 ug/L
2.5 ug/L
2.5 ug/L
0.7 ug/L
2.5 ug/L
0.7 ug/L
0.7 ug/L
Not Applicable
(lowest dose
tested produced
adverse effects)
The high CV among treatment blocks
severely limits the sensitivity of this
endpoint.
The LOEC for this endpoint equates to
an approximate 50% reduction In
Abundance.
The high CV among treatment blocks
severely limits the sensitivity of this
endpoint.
The LOEC for this endpoint equates to
an approximate 50% reduction in
Abundance
Insect Emergence Effects
Insect emergence (all
insects)
Chironomidae
(emergence)
0.7 ug/L
0.7 ug/L
Not Applicable
(lowest dose
tested produced
adverse effects)
Not Applicable
(lowest dose
tested produced
adverse effects)
The power of the test was severely
limited by the number of replicates
within treatments. Power analysis
conducted by the study authors
concluded that mean differences
between treatments and control for
insect emergence would have to be
greater than 93% before the test would
show statistically significant results.
Emergence reductions of 17.7 to 29.9%
were observed at the lowest
concentration tested.
The power of the test was severely
limited by the number of replicates
within treatments. Power analysis
conducted by the study authors
concluded that mean differences
between treatments and control for
insect emergence would have to be
greater than 93% before the test would
show statistically significant
Emergence reductions of 17. 4 to
31.1% were observed at the lowest
concentration tested
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Endpoint
LOEC
NOEC
Comments
Fish
Bluegill sunfish
young or the year
(weight, length,
growth rate)
Indigenous fish (mean
size, population
numbers, biomass)
2.5
Not Applicable
(highest dose tested
produced no statistical
effects)
0.7 ug/L
30ug/L
The authors concluded that young of
the year bluegill growth rates were
directly correlated to the density of
several invertebrate taxa (notably
Cladocera and Copepoda) that are
preferred prey items for the species
The authors concluded that
the study clearly demonstrated the
indirect effect of the pesticide on fish
population without direct toxic effects
on the fish
There is considerable uncertainty with
respect to endpoints for indigenous
fish. No measurements of effects
variables were made immediately
following treatments. Instead,
measurements were made 70 days after
application of the first treatment of
pesticide and 37 days after the second
application.
The results indicate that reductions in the abundance of zooplankton (particularly
cladocerans and copepods) can be expected to occur at initial nominal concentrations
lower than 0.7 |ig/L. Macroinvertebrate biomass and abundance of selected insect
families are reduced at initial nominal diflubenzuron concentrations greater than 0.7
Hg/L. Aquatic insect emergence and the richness of macroinvertebrate taxa are reduced at
concentrations of diflubenzuron at or below an initial nominal concentration 0.7 |ig/L
diflubenzuron. These impacts to the aquatic community were also observed to be
correlated to reductions in the growth rate of introduced bluegill sunfish, with reductions
in length, weight, and growth rate occurring at initial nominal concentrations of 2.5 |ig/L
and above. It is important to note that MRID 44386201 fails to empirically demonstrate a
NOEC for a number of endpoints, namely effects on cladocerans, copepods, aquatic
insect emergence and richness of macroinvertebrate taxa. Therefore, the study does not
allow EFED to evaluate risks to these organisms for diflubenzuron concentrations below
0.7 |ig/L with any certainty.
Results of several field studies and mesocosm studies were presented in MRID
44460702. The results of these other studies do not materially differ from results
reported for the Duluth Study discussed above. Ali et al.(l 988) reported no observable
effects on benthos and zooplankton in a pond adjacent to citrus treated with
diflubenzuron. Concentrations were reported to range from a high of 0.197 pg/L
immediately after diflubenzuron application to the orange groves to <0.027 pg/L by 14
days after pesticide application. Booth and Ferrell (1977) reported significant (up to 97%)
reductions in aquatic invertebrates for up to 30 days in a pond with diflubenzuron at 36
Hg/L immediately after treatment to trace (4 |ig/L) after 23 days. Boyle et al. (1996)
exposed mesocosms to 5 monthly or 9 biweekly treatments of diflubenzuron at a targeted
rate of 10 pg/L. The authors observed significant reductions in zooplankton and insect
numbers, insect diversity, and growth of bass and bluegill recruit.
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4.2. Toxicity of diflubenzuron to Terrestrial Organisms
Table 4-4 summarizes the most sensitive terrestrial toxicity endpoints used to evaluate
toxicity of diflubenzuron to terrestrial phase CRLFs, 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. Additional information can be found in Appendix A.
Table 4-4 Terrestrial Toxicity Profile for Diflubenzuron
Assessment
Endpoint
Acute Toxicity to
Birds
Reproduction
Toxicity to Birds
Acute Toxicity to
Mammals
Reproduction
Toxicity to
Mammals
Acute toxicity to
Terrestrial
Invertebrates
Risk to Terrestrial
Plants
Acute/
Chronic
Acute oral
LD50
Acute
dietary
LCso
NOAEC:
LD50:
NOAEC:
LD50:
No data
submitted
Species
Red-winged blackbird
Bobwhite quail
Bobwhite quail
Rat
Rat
Honeybee
N/A
Toxicity Value
Used in Risk
Assessment
LD50= 3763 mg/kg
a.i. bwt
LC50>4640 mg/kg
a.i. bwt
NOAEC= 500
mg/kg a.i. diet
LOAEC= 1000
mg/kg a.i. diet
LD50>5,000 mg/kg
a.i. bwt
NOAEC = 250
mg/kg-bw
LD50 > 30 ug
a.i./bee a.i.
N/A
MRID
MRID
00038614
MRID
00039080
MRID
41668001
MRID
00157103
MRID
43578301
MRID
05001991
N/A
Classification
Supplemental
Acceptable
Supplemental
Acceptable
Acceptable
Acceptable
N/A
Acute toxicity to terrestrial animals is categorized using the classification system shown
in Table 4-5 (U.S. EPA 2004). Toxicity categories for terrestrial plants have not been
defined.
Table 4-5 Categories of Acute Toxicity for Avian and Mammalian Studies
Toxicity Category
Very highly toxic
Highly toxic
Moderately toxic
Slightly toxic
Practically non-toxic
Oral LDSO
< 10 mg/kg
10 - 50 mg/kg
51 -500 mg/kg
501 -2000 mg/kg
> 2000 mg/kg
Dietary LC50
< 50 ppm
50 - 500 ppm
501 - 1000 ppm
1001 -5000 ppm
> 5000 ppm
4.2.1. Toxicity to Birds
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
72
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2004). No terrestrial-phase amphibian data have been submitted or were located in the
open literature for diflubenzuron; therefore, acute and chronic avian toxicity data are used
to assess the potential direct effects of diflubenzuron to terrestrial-phase CRLFs.
4.2.1.1. Birds: Acute Exposure (Mortality) Studies
Diflubenzuron is categorized as practically non-toxic to avian species on an acute oral
toxicity basis. Studies in bobwhite quail and mallard duck did not produce toxic effects
at any dose tested (MRID 00073935). The most sensitive study available produced an
LD50 value of 3763 mg/kg-bw in the Red-Winged Blackbird (MRID 00038614). All three
studies used technical grade material (Appendix A).
Using the TGAI, diflubnezuron is categorized as practically non-toxic to avian species on
a subacute dietary toxicity basis based on an LC50 value of >4640 ppm for the bobwhite
quail and mallard duck (MRID 00039080). A 1 % Granular formulation was also
categorized as practically non-toxic to bobwhite quail and mallard ducks based on an
LC50 value of >20,000 ppm (MRID 00060381). These studies were classified as
"Acceptable". Appendix A provides further details regarding these studies.
4.2.1.2. Birds: Chronic Exposure (Growth, Reproduction) Studies
The most sensitive NOAEC from a reliable/verifiable study was 500 mg/kg-diet (MRID
4166800102). Other studies are available that produced lower NOAECs. However,
these studies either did not produce a LOAEC (no effects were observed at any test
concentration) or the NOAECs were considered unreliable. In particular, a NOAEC of
<10 mg/kg-diet has been reported in a non-guideline study in mallard ducks (MRID
99862, Reinert ett al, 1975) based on a reduction in the number of eggs embryonated at
10 mg/kg-diet. However, this effect was not observed at higher test concentrations in the
same study and has not been observed in more recent guideline studies. Therefore, a
NOAEC of <10 mg/kg-diet was not considered reliable and was not chosen for use in risk
estimation.
The NOAEC of 500 mg/kg-food was based on effects on eggshell thickness in mallard
ducks and reduced egg production in bobwhite quail at 1000 mg/kg-diet. Further details
about the avian reproduction studies are summarized in Appendix A.
4.2.2. Terrestrial-phase Amphibian Acute and Chronic Studies
No terrestrial-phase amphibian acute or chronic studies have been submitted by
registrants or were located in the open literature.
4.2.3. Toxicity to Mammals
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Mammalian toxicity data are used to assess potential indirect effects of diflubenzuron to
the terrestrial-phase CRLF. Effects to small mammals resulting from exposure to
diflubenzuron may 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).
4.2.3.1. Mammals: Acute Exposure (Mortality) Studies
The available mammalian acute toxicity data demonstrate that diflubenzuron is
practically nontoxic to mammals (LD50 > 5000 mg/kg; MRID 00157103). Appendix A
provides further details regarding this data.
4.2.3.2. Mammals: Chronic Exposure (Growth, Reproduction) Studies
In a 2-generation reproduction study technical grade diflubenzuron was administered in
the diet to rats at dose levels of 0 (control), 500, 5000 or 50000 ppm (equivalent to about
0, 25, 250 or 2500 mg/kg/day).
No effects on reproductive performance were observed at any dose level in FO or Fl
males or females. Litter and mean pup weights decreased slightly from birth to 21 days
postpartum in Fl offspring at 2500 mg/kg/day. The NOEL for reproductive performance
in parental adults is 2500 mg/kg/day. The NOEL for developmental toxicity in progeny is
250 mg/kg/day and the LEL is 2500 mg/kg/day, based on decreased body weights in Fl
pups from birth to 21 days postpartum. (MRID 43578301). A NOAEL of 250 mg/kg-bw
is used in this assessment.
4.2.4. Toxicity to Terrestrial Invertebrates
Terrestrial invertebrate toxicity data are used to assess potential indirect effects of
diflubenzuron to the terrestrial-phase CRLF. Effects to terrestrial invertebrates resulting
from exposure to diflubenzuron may indirectly affect the CRLF via reduction in available
food.
4.2.4.1. Terrestrial Invertebrates: Acute Exposure (Mortality) Studies
Guideline studies in honeybees have been submitted and accepted by the Agency. These
tests produced acute oral and contact LD50s of >30 jig/bee (MRID 05001991), resulting
in a practically non-toxic classification. However, given the short duration of these tests
(typically 48-72 hours), and the typical age of organisms used in the tests, it is unlikely
that the contact / ingestion coincided with a molting stage, and, thus, the results may not
accurately reflect the toxicity of diflubenzuron to terrestrial invertebrates.
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A number of field studies regarding effects on terrestrial invertebrates were submitted to
the Agency and reviewed in 1984 to 1985 (MRIDs 00099743, 000171816, 00071207,
00095416, 00071215, 00070179, 00071212, 00095407, and 00071210). The following
information is based on the reviews of these studies, which evaluated a number of
different organisms and exposure routes.
Three honey bee studies resulted in no effects on colonies near fields treated with
application rates of up to 0.5 oz Dimilin W-25/A or 0.06 Ibs a.i./A (MRIDs 0071816,
00099743, 00071212). Another study that exposed honey bees to 100 ppm ai in their
water source determined that the exposure "almost eliminated production of a sealed
brood" (MRID 0095407). A study on a stream receiving runoff from a treated field
indicated that amphipod and aquatic beetle larvae populations were reduced and
copepods and ostracods may also have been impacted" at an application rate of 0.08 Ib
ai/A (MRID 00071210). A study evaluating the effects of diflubenzuron (2.24 kg ai/ha)
on soil arthropods when the chemical was incorporated into the soil showed some
decrease in numbers of springtails at 2 months post-treatment and on soil mites at 6
weeks, but little effect on other soil organisms (MRID 0007121 5). Differences between
control and treatment plots were not distinguishable at 4 months post-treatment. The
Agency reviewer concluded diflubenzuron had "little adverse effect on the soil fauna." A
study on beneficial arthropods showed some species were severely affected, while other
species were not affected at all (MRID 00070179). Aerial application of granular Dimilin
to salt marsh mosquito habitat significantly reduced numbers and diversity of aquatic
invertebrates (MRID 00095416). Measured water concentrations of Dimilin
(diflubenzuron) ranged from 0.24-1.8 |ig/L. Based on a study on soil arthropods, Dimilin
appears to have "little or no effect on soil microarthropods, but may adversely affect
insect parasites" (MRID 007 1207).
Overall, studies on terrestrial invertebrates illustrate that the effect of diflubenzuron is
highly dependent on the life stage of the organism when it is exposed. Diflubenzuron is
very highly toxic to invertebrates that rely on chitin as an exoskeleton at the critical life
stage (i.e., a molting event). Available data are not sufficiently robust to estimate an
assessment endpoint (e.g, LC50 or NOAEC) for this taxon, but adverse effects on non-
target arthropods should be anticipated following use of diflubenzuron given its mode of
action as an insecticide.
4.2.4.2. Terrestrial Invertebrates: Open Literature Studies
A number of open literature studies that evaluated effects to terrestrial invertebrates were
identified in the ECOTOX database (Appendix G). These studies support the
conclusions presented in Section 4.2.4.1 and do not add additional insight into the
potential effects of diflubenzuron to terrestrial invertebrates (Ecotox Nos. 65290, 110971,
and 111061).
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4.2.5. Toxicity to Terrestrial Plants
Terrestrial plant toxicity data are used to evaluate the potential for diflubenzuron to affect
riparian zone and upland vegetation within the action area for the CRLF. Impacts to
riparian and upland (i.e.., grassland, woodland) vegetation may 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
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 scientific
literature are typically reviewed for this type of 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. Guideline studies generally evaluate toxicity to ten crop species.
A drawback to these tests is that they are conducted on herbaceous crop species only, and
extrapolation of effects to other species, such as the woody shrubs and trees and wild
herbaceous species, contributes uncertainty to risk conclusions.
Commercial crop species have been selectively bred, and may be more or less resistant to
particular stressors than wild herbs and forbs. The direction of this uncertainty for
specific plants and stressors, including diflubenzuron, 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 is likely to be smaller than would be expected from wild
populations.
Currently, there are no available guideline terrestrial plant toxicity data for use in this
assessment. However, Cooper et al. (1990) did not observe differences in characteristics
of vegetation when comparing plots treated with diflubenzuron to untreated controls.
The study evaluated 10 circular 0.04 ha plots (5 treated and 5 untreated). Vegetative
characteristics evaluated included percent litter cover, litter depth, percent herbaceous
cover, percent shrub cover, percent canopy cover in each of 5 canopy height classes,
percent deciduous canopy cover, percent coniferous canopy cover, percent total canopy
cover, and number of trees and number of snags in 6 dbh classes. Diflubenzuron was
applied at 0.06 Ibs a.i./Acre.
Similarly, Seidel and Whitmore did not observe differences in vegetative characteristics
including litter depth, number of saplings, number of 2 classes of tree snags, and presence
of herbaceous growth, shrubs. Diflubenzuron was applied to test plots at 140 g/ha by air
(0.12 Ibs a.i./Acre).
In addition, a number of efficacy studies have been submitted to the Agency that also
evaluated phytotoxic effects to target species. These studies have typically noted no or
minimal phytotoxicity (See Appendix H for citations). Last, diflubenzuron is labeled for
76
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use on numerous commodoties without reports of incidents that have been clearly
associated with difblubenzuron toxicity.
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 diflubenzuron 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.
Probit slopes used in this analysis are summarized in Table 4-6.
Table 4-6. Probit slopes used for taxonomic groups evaluated in this assessment
Taxonomic Group
Fish
Aquatic
Invertebrates
Birds
Mammals
Probit Slope
4.7
0.41
Default of 4. 5: Data
do not allow for
calculation of
reliable slope
Default of 4.5: No
mortality occurred
in acute mammal
studies
95% CI
3. 5 to 5.9
0.3 to 0.5
2 to 9
2 to 9
MRID
00056150
Hoetal., 1987
(EcotoxNo. 16591)
00038614
00157103
Species
Bluegill
Mosquito larvae
Red-winged
blackbird
Rat
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4.4. Incident Database Review
One incident (1009846-002) had been reported for diflubenzuron when the EIIS database
was queried (10/2/2009). Damage to oranges in Polk County, Florida was reported
following direct application. Legality of the application was classified as registered use,
and certainty that diflubenzuron caused the damage was rated as possible. However, the
incident was also associated with petroleum distillates, which have a number of other
terrestrial plant incidents associates with its use. Given that diflubenzuron has a long
history of use on citrus trees without other incidents and that petroleum distillates has
been associated with several similar incidents on terrestrial plants, it is more likely that
the damage to oranges was caused by use of petroleum distillates and not by
diflubenzuron.
A lack of reported incidents should not be taken as an indicator of little or no ecological
effects, especially in the case of a chemical like diflubenzuron, which acts primarily to
inhibit growth of insects. Insects and other invertebrates that are vulnerable to chitinase
inhibitors are generally not a highly visible component of the ecosystem, and even large-
scale die-offs may go unreported.
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5.0 Risk Characterization
Risk characterization is the integration of the exposure and effects characterizations.
Risk characterization is used to determine the potential for direct and/or indirect effects to
the CRLF or for modification to its designated critical habitat from the use of
diflubenzuron 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 then compared to pre-established acute and chronic levels of
concern (LOCs) for each category evaluated (Appendix C). For acute exposures to the
CRLF and its animal prey in aquatic habitats, as well as terrestrial invertebrates, the LOG
is 0.05. For acute exposures to the CRLF and mammals, the LOG is 0.1. The LOG 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 diflubenzuron usage
scenarios summarized in Table 3-3 and the appropriate aquatic toxicity endpoint from
Section 4. 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 diflubenzuron (Section 3) and the appropriate toxicity endpoint from
Section 4.
5.1.1. Exposures in the Aquatic Habitat
5.1.1.1 Direct Effects to Aquatic-Phase CRLF
Direct effects to the aquatic-phase CRLF are based on 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. Based on the RQ calculations none of the LOCs were exceeded for risk to
freshwater water fish or aquatic phase amphibians except for the aerial use of
diflubenzuron on rice crops (See Table 5-1). The LOG was exceeded for chronic risk to
freshwater fish or aquatic phase amphibians for this use. Based on these results only the
diflubenzuron aerial use on rice "may affect" aquatic-phase CRLFs. No LOCs were
exceeded for other uses. Therefore, all other registered uses are expected to have "no
effect" on the aquatic-phase CRLF. RQs presented in Table 5-1 are further discussed in
the context of an effects determination in Section 5.2.
79
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Table 5-1 Summary of Direct Effect RQ LOCs for the Aquatic-phase CRLF
Direct
Effects to
CRLFa
Chronic
Direct
Toxicity
Acute direct
toxicity
Use
Direct
Application to
rice
Manure
All other uses
All uses
Surrogate
Species
Fathead
minnow
All
species
tested
Toxicity
Value
(mg/L)
NOAEC=
0.100
129
EEC
(mg/L)b
60-day:
0.112
0.027
O.015
O.ll
RQ
1.12C
0.27
<0.15
<0.01
Probability
of Individual
Effect at
ESLOC
Probability of
Individual
Effect at RQ
Not calculated for chronic
endpoints
lin3.7E20
(lin7.8Ellto lin5E30)
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 aerial use of diflubenzuron on rice paddies (see Table 3-3).
c RQ > chronic 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)
Non-vascular Aquatic Plants
Indirect effects of diflubenzuron to the aquatic-phase CRLF (tadpoles) via reduction in
non-vascular aquatic plants in its diet or via habitat modification are based on peak EECs
and the lowest toxicity value (EC50) for aquatic non-vascular plants. Based on the RQ
calculations there were no LOC exceedances of diflubenzuron to aquatic plants.
Therefore, diflubenzuron is expected to have "no effect" to CRLFs by affecting non-
vascular aquatic plants. These RQs are further discussed in the context of an effects
determination in Section 5.2.
Table 5-2 Summary of RQs Used to Estimate Indirect Effects to the CRLF via Effects to Non-
Vascular Aquatic Plants (diet of CRLF in tadpole life stage and habitat of aquatic-phase CRLF)
Uses
All Uses
Toxicity Value
(Hg/L)
200
(MRID 45252205)
Peak EEC (jig/L)
<113
Indirect effects RQ
(food and habitat)
0.6
Aquatic Invertebrates
Indirect acute effects to the aquatic-phase CRLF via effects to prey (invertebrates) in
aquatic habitats are based on peak EECs in the standard pond and the lowest acute
toxicity value for freshwater invertebrates. Due to the mode of action of diflubenzuron,
results from chronic toxicity studies are also considered to be acute effects. Therefore,
80
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chronic RQs are calculated using peak EECs. However, chronic RQs are also presented
using 21-day EECs.
A summary of the acute and chronic RQ values for exposure to aquatic invertebrates (as
prey items of aquatic-phase CRLFs) is provided in Table 5-3. Based on RQ calculations
diflubenzuron exceeds either the acute or chronic LOG for risk to freshwater
invertebrates for all the modeled uses of diflubenzuron. The acute RQs ranged from 4 to
40,000 and the chronic LOG exceedances range from 40 to 450,000. Based on these
results, diflubenzuron "may affect" CRLFs via reduction in freshwater invertebrates prey
items. These RQs are further discussed in the context of an effects determination in
Section 5.2.
81
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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)
Scenario Group
Beech Nut
Brassica
Citrus
Cole Crop
Cotton
Forest
Fruit
General Nuts
Grains
Nursery
Pasture
Pistachio
Residential
Rice/Ornamental
Pond
Rights-of-way
Row Crop
Urban
Squash
Turf (High
Application
Rate)
Turf (Low
Application
Rate)
Turnip
Application
Type
Ground
Air
Ground
Ground
Air
Ground
Ground
Air
Ground
Air
Ground
Airblast
Air
Ground
Airblast
Air
Ground
Air
Ground
Air
Ground
Airblast
Air
Ground
Ground
Air
Air
Ground
Airblast
Air
Ground
Air
Air
Ground
Air
Ground
Airblast
Air
Ground
Airblast
Air
Ground
Water
Column
Peak EEC
(Hg/L)
0.11
0.21
0.07
0.24
0.50
0.36
0.15
0.82
0.58
0.80
0.26
0.66
1.36
0.90
1.26
0.85
1.34
0.93
0.20
0.65
0.12
0.29
0.55
0.15
0.08
0.40
112.92
5.55
8.13
5.59
0.02
1.15
34
1.15
1.87
0.01
0.21
0.61
0.02
0.07
0.13
0.72
Acute RQ
Based on a 6-
day LC50 of
0.0028 jig/L)
39.07
73.94
23.49
87.48
178.06
128.46
54.34
293.71
205.99
285.44
94.15
236.88
485.86
322.81
450.56
303.31
477.32
333.08
71.60
231.78
41.64
102.95
195.64
52.45
29.37
143.71
40327.13
1981.66
2903.57
1997.41
6.86
409.57
12187.86
409.11
666.75
3.60
76.57
216.57
7.67
23.89
46.49
256.26
Chronic RQ
Based on a 6-Day
NOAEC of
0.00025 jig/L and
a 21-Day EEC
227.21
521.28
156.96
393.05
1204.76
817.76
429.96
1874.28
1221.32
1786.60
556.48
1702.68
3424.92
1859.68
2794.92
1965.88
3117.32
2084.80
449.60
1504.92
302.73
665.00
1003.56
331.80
184.23
1207.47
451663.90
12178.53
17541.57
12268.73
59.72
3098.08
87924.00
2610.32
4736.00
24.39
506.32
1489.40
32.30
146.85
326.01
1402.12
Chronic RQ Based
on a 6-Day NOAEC
of 0.00025 jig/Land
a peak EEC
437.56*
828.16*
263.12*
979.76*
1994.32*
1438.72*
608.60*
3289.56*
2307.08*
3196.96*
1054.48*
2653.00*
5441.60*
3615.44*
5046.24*
3397.04*
5346.00*
3730.48*
801.96*
2595.88*
466.40*
1153.04*
2191.20*
587.40*
328.96*
1609.50*
451663.90*
22194.60*
32520.00*
22371.00*
76.82*
4587.20*
136504.00*
4582.00*
7467.60*
40.26*
857.60*
2425.56*
85.88*
267.52*
520.68*
2870.12*
* Exceeds the chronic LOG of 1 for risk to aquatic invertebrates
82
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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. Based on the RQ calculations none of the LOCs were exceeded for
risk to freshwater fish or aquatic phase amphibians except for the aerial use of
diflubenzuron on rice (See Table 5-1). The LOG was exceeded for chronic risk to
freshwater fish for this use. These RQs are further discussed in the context of an effects
determination in Section 5.2.
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. Based on the RQ
calculations there were no LOG exceedances for risk of diflubenzuron to aquatic plants.
Therefore, the effects determination is "no effect" for all uses. These RQs are further
discussed in the context of an effects determination in Section 5.2.
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
Uses
All Uses
Peak EEC
(HS/L)
<113
EC50
(HS/L)
190
Indirect effects RQ
(habitat)
<0.6
a RQs used to estimate indirect effects to the CRLF via toxicity to non-vascular aquatic plants are
summarized in Table 5-2
5.1.2. Exposures in the Terrestrial Habitat
5.1.2.1. Direct Effects to Terrestrial-phase CRLF
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 (Table 5-5) and acute oral and subacute dietary toxicity endpoints for
avian species.
Potential direct chronic effects of diflubenzuron 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. Subacute dietary based RQs were not calculated because the dietary toxicity
data indicated that no toxicological effects were observed at dietary concentrations that
were equivalent to the limit concentration for acute dietary toxicity.
83
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Based on the acute and chronic RQ calculations there are only LOG exceedances for risks
to the terrestrial-phase of the CRLF for use of diflubenzuron on barnyard manure. Thus,
the preliminary determination is a "may effect" only for the use on barnyard manure and
"no effect" for all other modeled uses. Table 5-5 lists only dose based acute RQs because
no dietary LCso study produced a definitive toxicity value (all LCsoS were above the limit
dose).
Table 5-5 Summary of RQs Used to Estimate Direct Effects to the Terrestrial-phase CRLF
Model Use
Barnyard (Manure)
Beech nut
Brassica
Citrus
Cole Crop
Cotton
Forest
Fruit
General Nuts
Grains
Nursery
Pasture
Pistachio
Residential
Rice
Rights-of-way
Row Crop
Squash
Turf (High App. Rate)
Turf (Low App. Rate)
Turnip
Chronic RQ
EEC
3369
10.3
4.2
88
80
111
34
111
111
80
34
34
101
131
40
34
88
91
34
11
56
RQ
6.738*
0.0206
0.0084
0.176
0.16
0.222
0.068
0.222
0.222
0.16
0.068
0.068
0.202
0.262
0.08
0.068
0.176
0.182
0.068
0.022
0.112
Acute RQ
Dose-based EEC
(based on 20-
gram bird)
3840.66
11.742
4.788
100.32
91.2
126.54
38.76
126.54
126.54
91.2
38.76
38.76
115.14
149.34
45.6
38.76
100.32
103.74
38.76
12.54
63.84
RQ
1 2**
<0.01
0.00
0.03
0.03
0.04
0.01
0.04
0.04
0.03
0.01
0.01
0.04
0.05
0.01
0.01
0.03
0.03
0.01
<0.01
0.02
* Exceeds the chronic of LOG of 1.
** Exceeds the acute LOG of 0.5.
5.1.2.2. Indirect Effects to Terrestrial-Phase CRLF via
Reduction in Prey (terrestrial invertebrates, mammals,
and frogs)
a) Terrestrial Invertebrates
In order to assess the potential risks of diflubenzuron to terrestrial invertebrates, which
are considered prey of CRLF in terrestrial habitats, the honey bee is used as a surrogate
for terrestrial invertebrates. The toxicity value for terrestrial invertebrates is calculated by
multiplying the lowest available acute contact LD50 of 30 jig a.i./bee by 1 bee/0.128g,
which is based on the weight of an adult honey bee. EECs (jig a.i./g of bee) calculated by
T-REX for small and large insects are divided by the calculated toxicity value for
84
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terrestrial invertebrates, which is 30 jig a.i./g of bee. Based on the RQ calculations, the
modeled diflubenzuron uses except beechnut and brassica exceed the LOG for risks to
terrestrial invertebrate (Table 5-6). Based on these results, the preliminary effects
determination is a "may effect" for the potential of diflubenzuron to indirectly affect the
CRLF by reducing terrestrial invertebrate prey. Section 5.2 further discusses these RQs
and additional terrestrial invertebrate toxicity information in the context of this effects
determination.
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 an LC50 of 234 ppm (30
jig per bee / 0.128 grams per bee)
Uses
Barnyard/Mushroom
Beechnut
Brassica
Citrus
Cole
Cotton
Forest
Fruit
General Nut Crop
Grain
Impervious
Nursery
Pistachio
Residential
Rice/Ornamental Pond
Rights away
Row crops
Squash
Turf (high application rate)
Turf (low application rate)
Turnip
Small Insects
EEC
3369
10.3
4.2
88
80
111
34
111
111
80
34
34
101
131
40
34
88
91
34
11
56
Small Insect RQ
14.37
0.04
0.02
0.38
0.34
0.47
0.15
0.47
0.47
0.34
0.15
0.15
0.43
0.56
0.17
0.15
0.38
0.39
0.15
0.05
0.24
Large Insects
EEC
374
1.14
0.47
9.78
8.89
12.33
3.78
12.33
12.33
8.89
3.78
3.78
11.22
14.56
4.44
3.78
9.78
10.11
3.78
1.22
6.22
Large Insect RQ
1.60
0.00
0.00
0.04
0.04
0.05
0.02
0.05
0.05
0.04
0.02
0.02
0.05
0.06
0.02
0.02
0.04
0.04
0.02
0.01
0.03
b) Mammals
Risks associated with reduction of small mammals as prey by large terrestrial-phase
CRLFs are derived for dietary-based and dose-based exposures modeled in T-REX for a
small mammal (15g) herbivore and insectivore. 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.
There were no mortalities in the mammalian acute toxicity studies at the limit dose of
5000 mg/kg-bw; therefore, acute RQs were not calculated and risk was presumed to be
below levels that could result in indirect effects to CRLFs. Based on the chronic RQ
calculations, there are no chronic LOG exceedances for risk to small mammal prey items
except for the barnyard/mushroom use (Table 5-7). Based on these results, the
preliminary effects determination is "no effect" regarding potential risks to the CRLF
85
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from reduction in mammalian prey except for the barnyard/mushroom use. The chronic
RQ is 10 for the barnyard/mushroom use. Therefore, the preliminary effects
determination for this use is "may effect." These RQs are further discussed in the context
of an effects determination in Section 5.2.
Table 5-7 Summary of Chronic RQs Used to Estimate Indirect Effects to the Terrestrial-phase CRLF
via Direct Effects on Small Mammals as Dietary Food Items
Model Use
Barnyard/Mushroom
Beech nut
Brassica
Citrus
Cole Crop
Cotton
Forest
Fruit
General Nuts
Grains
Nursery
Pasture
Pistachio
Residential
Rice/Ornamental Pond
Rights-of-way
Row Crop
Squash
Turf (High App. Rate)
Turf (Low App. Rate)
Turnip
Chronic RQ
EEC
5690.5
17.404
7.125
149.15
135.85
187.15
57
187.15
187.15
135.85
57
57
171
220.4
67.45
57
149.15
153.9
57
19
95
RQ
10.37 (exceeds LOC of 1.0)
0.03
0.01
0.27
0.25
0.34
0.10
0.34
0.34
0.25
0.10
0.10
0.31
0.40
0.12
0.10
0.27
0.28
0.10
0.03
0.17
c) Amphibians
An additional prey item of the adult terrestrial-phase CRLF is other amphibians. In order
to assess risks to these organisms, dietary-based and dose-based exposures modeled in T-
REX for a small bird (20g) consuming small invertebrates are used. See Section 5.1.2.1
and associated table (Table 5-5) for results. Based on LOC exceedances for the
barnyard/mushroom use, this labeled use of diflubenzuron may affect the CRLF. Avian
LOCs were not exceeded for any other use; therefore, the preliminary effects
determination for diflubenzuron for all other uses is "no effect." These RQs are further
discussed in the context of an effects determination in Section 5.2.
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 RQs from terrestrial plant seedling emergence and
vegetative vigor EC25 data as a screen. Currently there are no available guideline
86
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terrestrial plant toxicity data. Therefore, RQs were not calculated. Additional lines of
evidence including open literature studies and non-guideline registrant-submitted studies
regarding potential risks to terrestrial plants in the context of an effects determination for
the CRLF are described in Section 5.2.
5.1.3. Primary Constituent Elements of Designated Critical Habitat
For diflubenzuron use, the assessment endpoints for designated critical habitat PCEs
involve a reduction and/or modification of food sources necessary for normal growth and
viability of aquatic-phase CRLFs, and/or a reduction and/or modification of food sources
for terrestrial-phase juveniles and adults. Because these endpoints are also being
assessed relative to the potential for indirect effects to aquatic- and terrestrial-phase
CRLF, the effects determinations for indirect effects from the potential loss of food items
are used as the basis of the effects determination for potential modification to designated
critical habitat. As discussed in Sections 5.1.3 and 5.2.4, effects to aquatic and terrestrial
plants are not expected to occur.
However, one PCE is "alteration of other chemical characteristics necessary for normal
growth and viability of CRLFs and their food source." To assess the impact of
diflubenzuron 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. Based on LOG exceedances for aquatic invertebrates, diflubenzuron
may modify aquatic-phase PCEs of designated critical habitat related to effects of
alteration of other chemical characteristics necessary for normal growth and viability of
CRLFs and their food source.
Two terrestrial phase PCEs are not evaluated using solely terrestrial plant toxicity data.
The PCE of "reduction and/or modification of food sources for terrestrial phase juveniles
and adults" is evaluated using acute and chronic toxicity endpoints for birds, mammals,
and terrestrial invertebrates as measures of effects. RQs for these endpoints were
calculated in Section 5.1.2.2. Diflubenzuron has the potential for modifying critical
habitat via this PCE because as an insecticide, terrestrial invertebrates are likely to be
affected if diflubenzuron is used near critical habitat.
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 impacts to terrestrial invertebrates for all assessed uses,
diflubenzuron may impact critical habitat by altering chemical characteristics necessary
for normal growth and viability of juvenile and adult CRLFs for all uses assessed.
5.2. Risk Description
The risk description synthesizes an overall conclusion regarding the likelihood of adverse
impacts leading to an effects determination (i.e.., "no effect," "may affect, but not likely
87
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to adversely affect," or "likely to adversely affect") for the CRLF and its designated
critical habitat.
Based on the RQs presented in the Risk Estimation (Section 5.1) a preliminary effects
determination is "may affect" for the CRLF and modification of critical habitat.
A summary of the results of the risk estimation results are provided in Table 5-8 for
direct and indirect effects to the CRLF and in Table 5-9 for the PCEs of designated
critical habitat for the CRLF.
Table 5-8 Risk Estimation Summary for Diflubenzuron - Direct and Indirect Effects to CRLF
Assessment Endpoint
LOG Exceedances
(Y/N)
Description of Results of Risk Estimation
Aquatic Phase
(eggs, larvae, tadpoles, juveniles, and adults)
Direct Effects
Survival, growth, and
reproduction of CRLF
individuals via direct effects on
aquatic phases
Yes
Direct application to
rice only
The chronic fish RQ was 1.12 for direct
application to rice. All other chronic RQs were
lower than the LOG of 1.0. Acute RQs were
<0.01. The probability of an individual mortality
at the acute RQs of 0.01 is <1 in 1,000,000 based
on a slope of 4.7 (95% CI of 3.5 to 5.9 (MRID
56150).
Indirect Effects
Survival, growth, and
reproduction of CRLF
individuals via effects to food
supply (i.e., freshwater
invertebrates, non-vascular
plants)
Yes
All uses
Acute RQs ranged from approximately 4 to
40,000. The probability of an individual effect at
these RQs approaches 100% for reasonable lower
and upper bound slopes of 2 to 9. Chronic RQs
also exceeded LOCs and were 25 to 450,000.
Indirect Effects
Survival, growth, and
reproduction of CRLF
individuals via effects on
habitat, cover, and/or primary
productivity (i.e., aquatic plant
community)
No
No LOCs were exceeded for vascular or non-
vascular aquatic plants. RQs were less than 0.6.
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.
No
RQs were not calculated due to the lack of
guideline terrestrial plant toxicity data; further
discussion of potential risks to CRLFs resulting
from impacts to terrestrial plants is presented in
Section 5.2.
Terrestrial Phase
(Juveniles and adults)
88
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Assessment Endpoint
LOG Exceedances
(Y/N)
Description of Results of Risk Estimation
Direct Effects
Survival, growth, and
reproduction of CRLF
individuals via direct effects on
terrestrial phase adults and
juveniles
Yes
Barnyard/mushroom
use only
Acute and chronic RQs exceeded LOCs. The
acute RQ was 1.2 and the chronic RQ was 6.7. At
an RQ of 1.2, the probability of an individual
effect is 1 in 1.6 based on the default probit slope
of 4.5. The range of probabilities of an individual
effect is 1 in 1.4 to 1 in 1.8 based on lower and
upper bound probit slopes of 2 to 8.
LOCs were not exceeded for any other use.
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
All uses
Diflubenzuron is an insecticide. Therefore, there
is potential for terrestrial invertebrate abundance
to be impacted. In addition, LOCs were exceeded
for all uses based on submitted data in the honey
bee.
Indirect Effects
Survival, growth, and
reproduction of CRLF
individuals via effects on
habitat (i.e., riparian
vegetation)
No
RQs were not calculated for terrestrial plants
based on the lack of terrestrial plants toxicity data
available for diflubenzuron.
Table 5-9 Risk Estimation Summary for Diflubenzuron - PCEs of Designated Critical Habitat for
the CRLF
Assessment Endpoint
Habitat
Modification (Y/N)
Description 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.
Alteration in water chemistry /quality
including temperature, turbidity, and
oxygen content necessary for normal
growth and viability of juvenile and
adult CRLFs and their food source.
Alteration of other chemical
characteristics necessary for normal
growth and viability of CRLFs and
their food source.
Reduction and/or modification of
aquatic-based food sources for pre-
metamorphs (e.g., algae)
No
No
Yes
No
There are no LOG exceedances for risk to
aquatic plants.
~
There are acute and chronic LOG exceedances
for risk of diflubenzuron to aquatic
invertebrate prey of the CRLF for all uses.
There were no LOG exceedances for risk to
Algae for any use evaluated.
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Assessment Endpoint
Habitat
Modification (Y/N)
Description of Results of Risk Estimation
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
No
Currently, there are no guideline terrestrial
plant toxicity data available to assess this
risk. See Section 5.2 for additional
description of potential risks to CRLFs
resulting from impacts to terrestrial
vegetation.
Elimination and/or disturbance of
dispersal habitat: Upland or riparian
dispersal habitat within designated
units and between occupied locations
within 0.7 mi of each other that allow
for movement between sites including
both natural and altered sites which do
not contain barriers to dispersal
No
Currently, there are no guideline terrestrial
plant toxicity data available to assess this
risk. See Section 5.2 for additional
description of potential risks to CRLFs
resulting from impacts to terrestrial
vegetation.
Reduction and/or modification of food
sources for terrestrial phase juveniles
and adults
Yes
There are LOG exceedances for risk terrestrial
invertebrate prey for all uses, and potential
magnitude of effect could be substantial such
that CRLFs could be impacted.
Alteration of chemical characteristics
necessary for normal growth and
viability of juvenile and adult CRLFs
and their food source.
Yes
There are LOG exceedances for risk terrestrial
invertebrate prey, and potential magnitude of
effect could be substantial such that CRLFs
could be impacted.
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
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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 diflubenzuron.
No acute LOCs were exceeded for fish based on the most sensitive species tested. No
open literature studies were located that reported lower toxicity values in either fish or
amphibians than those used to calculate risk quotients. No incidents have been reported
for diflubenzuron that associate its use with effects to aquatic animals. The probability of
an individual mortality at the acute RQs of <0.01 is < 1 in 3.7E20 (<1 in 7.8E11 to
<5.1E31) based on a slope of 4.7 (95% CI of 3.5 to 5.9, MRID 56150).
Therefore, the effect determination for potential acute direct effects to the CRLF is "no
effect".
The chronic LOG was exceeded only for direct application to rice. The RQ for this use
was 1.12. RQs for other uses were <0.3. However, the RQ was based on results from a
full life-cycle study that did not achieve a LOAEC (no effects were observed in this study
at any concentration tested). In addition, the 60-day EEC used to calculate the rice
exposure values did not allow for any degradation over time. Because diflubenzuron
degradates somewhat rapidly in the standard pond, similar rates of degradation would be
expected to occur in rice paddies; therefore, the EEC is likely an over-estimation of
exposure. For these reasons (the close proximity of the RQ to the LOG, the lack of a
LOAEC in the available study, and the lack of degradation in the 60-day EEC
calculation), the effects determination for direct application to rice is "not likely to
adversely affect" because the potential for a direct effect is discountable (highly unlikely
to occur).
The effects determination for all other uses is "no effect" based on the lack of LOG
exceedances and the low probability of an individual mortality.
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5.2.1.2. Terrestrial-Phase CRLF
Barnyard/Mushroom Use
Acute and chronic RQs were exceeded for CRLFs based on the avian assessment used as
a surrogate species. The acute RQ was 1.2. Assuming a probit slope of 4.5, the
probability of an individual effect is approximately 1 in 2. The reproduction RQ was 6.7.
The reproduction RQ was based on reduced egg production at 1000 mg/kg-food
(NOAEC was 500 mg/kg-food). At an RQ of 6.7, exposure values were estimated to be
approximately 3 times higher than levels associated with reduced egg production in birds
(surrogate for CRLF). This assessment also assumed applications at the highest labeled
application rate for 17 applications per year (21 days between applications). However,
even assuming a single application results in LOG exceedances (acute RQ = 0.74; chronic
RQ = 2).
Potential effects to CRLFs depend on the proportion of its diet that may occur from
contaminated food located at or near the use site. The barnyard/mushroom use is a spot
treatment; therefore, the likelihood that a CRLF will consume contaminated food depends
on the number and size of "spots" applied to any given field, which may vary
considerably from field to field. In addition, manure use is typically associated with feed
lots, which are not attractive habitats for CRLFs due to high density of animals and
resulting lack of habitat such as clean water and vegetation.
This assessment was based on food intake equations for birds. Birds are currently used as
surrogates for reptiles and terrestrial-phase amphibians. However, reptiles and
amphibians are poikilotherms (body temperature varies with environmental temperature)
while birds are homeotherms (temperature is regulated, constant, and largely independent
of environmental temperatures). Therefore, reptiles and amphibians (collectively referred
to as herptiles) 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 or reptiles on a daily dietary intake basis, assuming similar
caloric content of the food items. This can be seen when comparing the estimated caloric
requirements for free living iguanid lizards (Iguanidae) (EQ 1) to passerines (song birds)
(EQ 2) (U.S. EPA, 1993):
iguanid FMR (kcal/day)= 0.0535 *(bw in g)ฐ 7" (EQ 1)
passerine FMR (kcal/day) = 2.123 *(bw in g)0749 (EQ 2)
With relatively comparable exponents (slopes) to the allometric functions, one can see
that, given a comparable body weight, the free living metabolic rate of birds can be 40
times higher than reptiles, though the requirement differences narrow with high body
weights. Consequently, birds are conservative surrogates for terrestrial phase CRLFs
because birds are expected to have higher potential exposures relative to terrestrial phase
amphibians.
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The potential differences in exposure of CRLFs and birds were quantified using a
modified version of T-REX, called T-HERPS (version 1.0). T-HERPs incorporates food
intake equations that are specific for terrestrial phase amphibians and includes two
additional food items of the CRLF that are not included in T-REX (CRLFs that consume
small mammals and other amphibians).
The results of this analysis for the barnyard/mushroom use are in Table 5-10. RQs
remained above the endangered species LOG for the small mammal food item (CRLFs
that consume small mammals). However, LOCs were not exceeded for other food items.
Table 5-10. Results from T-HERPS for the Barnyard/Mushroom Use.
Dose-based RQs (Dose-based
EEC/adjusted LD50)
Short Grass
Tall Grass
Broadleaf plants/sm insects
Fruits/pods/seeds/lg insects
Small herbivore mammals
Small insectivore mammals
Small terrestrial phase amphibian
Amphibian/Reptile Acute RQs for Small, Medium, and
Large Species (grams)
1.4
0.06
0.03
0.03
0.00
N/A
N/A
N/A
37
0.06
0.03
0.03
0.00
0.97
0.06
0.00
238
0.04
0.02
0.02
0.00
0.15
0.01
0.00
Although barnyards and feedlots are not likely to typically provide suitable habitat for
CRLFs, the presence of CRLFs in such habitats cannot be precluded. Therefore, based
on acute and chronic LOG exceedances and the likelihood of potential effects at the
estimated exposure levels, the effects determination for direct effects to the CRLF is
"likely to adversely affect" for the barnyard/mushroom use.
All Other Uses
No LOCs were exceeded. Acute RQs ranged from <0.01 to 0.04. At these RQs, the
probability of an individual effect is 1 in 6E9 based on the default probit slope of 4.5 (see
Section 4). Based on reasonable lower and upper bounds on the slope of 2 to 8, the
probability of an individual effect ranged from 1 in 4E2 to 1 in 7E35.
No incidents associating diflubenzuron with effects to terrestrial animals have been
reported to the Agency.
Also, as previously discussed, birds were used as a surrogate for the CRLF, which results
in a conservative estimate of exposure and risk due to the greater energetic requirements
and resulting greater food intake (and resulting potential exposures) of birds relative to
terrestrial phase CRLFs.
Based on the lack of LOG exceedances in birds, the low probability of an individual
mortality, and the lack of reported incidents, diflubenzuron is expected to have "no
effect" via direct toxic effects on terrestrial phase CRLFs.
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5.2.2. Indirect Effects (via Reductions in Prey Base)
5.2.2.1. Algae (non-vascular 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. LOCs were not exceeded
for aquatic plants. No effects were observed in any of the available toxicity studies in
aquatic plants, and all RQs were less than 1 (the highest RQ was 0.6). Therefore,
estimated diflubenzuron concentrations were lower than NOAEC values in all aquatic
plant species tested.
Therefore, the effects determination for CRLFs based on potential indirect effects from
impacts to aquatic plants is "no effect."
5.2.2.2. Aquatic Invertebrates
The potential for diflubenzuron 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.
Based on the most sensitive species tested (mosquito), RQs exceeded LOCs and ranged
from 4 to 40,000 (acute) and 25 to 450,000 (chronic). At these acute RQs, the probability
of an individual mortality approaches 100%, and potential impacts to abundance of
aquatic invertebrates could be sufficient to reduce available food of the CRLF.
As shown in Figure 5-1 below, based on open literature studies (Appendix G), the lowest
EEC across all uses of diflubenzuron is above the average acute toxicity value for a
majority of species tested (RQ >1). These values represent short-term toxicity studies,
and may, therefore, underestimate potential impacts to aquatic invertebrates as discussed
in Section 4.
The life stage of the exposed invertebrate is likely to influence potential effects. Adults
are less sensitive to diflubenzuron than larvae and juveniles. The results of littoral
enclosure studies discussed in Section 4 suggested that some taxonomic groups of aquatic
invertebrates could be impacted at diflubenzuron levels lower than 0.7 jig/L (NOEC not
achieved). These impacts to the aquatic community were also observed to be correlated
to reductions in the growth rate of introduced bluegill sunfish, with reductions in length,
weight, and growth rate occurring at initial nominal concentrations of 2.5 |ig/L and
above. Growth reductions in fish were attributed to reductions in food source (indirect
94
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effect). It is important to note that MRID 44386201 fails to empirically demonstrate a
NOEC for a number of endpoints, namely effects on cladocerans, copepods, aquatic
insect emergence and richness of macroinvertebrate taxa.
Based on the number of potential species that may be affected and the potential
magnitude of effect, diflubenzuron is likely to adversely affect the CRLF by reducing
available aquatic prey. This effects determination applied to all labeled uses included in
this assessment.
Based on AgDRIFT analysis (version 2.1.0.3, Tier 3 analysis using aerial and ground
spray), spray drift could be sufficient to result in indirect effects at applications greater
than 5000 feet from treated sites as evidenced by LOG exceedances for the most sensitive
species tested.
Mean Acute
0.1 8 -jSoHd-bme represents a pprox
_j
LU
EC50 Values from Open Literature Data (Ecotox)
Solid line represents minimum EEC
Blackfly Cyclopoid Fairy Shrimp Insect class Midge Mosquito Water flea
copepod
Species
Figure 5-1. Mean acute EC50 values from open literature data according to the Ecotox data base.
Figure note: Values for fairy shrimp and water flea are low such that they are not visible on the graph.
EC50s for two species were not included in this figure due to the scale of the graph. A single EC50 for
parasitic nematode (EC50: 4.4 ug/L) and a single EC50 for backswimmer (EC50: 1.9 ug/L).
5.2.2.3. Fish and Aquatic-phase Frogs
As described in Section 5.2.1.1, the effects determination for potential direct effects to
the CRLF is "no effect" for acute effects and chronic effects for all uses except rice and is
"not likely to adversely affect" for chronic effects for the rice use. These conclusions are
based on potential effects to the most sensitive fish species tested. The same conclusions
are reached for the potential for diflubenzuron to adversely affect the CRLF based on
reduction in fish or frogs as food. See Section 5.2.1.1 for additional detail.
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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. RQs were based on acute studies in adult bees.
Although RQs suggest that there is a potential for impacts to terrestrial invertebrates,
these RQs were based on a study that did not produce mortality at any concentration
tested (30 jig/bee). However, as discussed in Section 4, acute studies in adult bees are
not considered to represent sensitive invertebrate life stages due to the mode of action of
diflubenzuron as an insect growth regulator, which affects insects at molting. Results of
field studies have been inconsistent as discussed in Section 4; however, several field
studies have shown reduced abundance in invertebrates at currently approved application
rates. Also, given the use of diflubenzuron as an insecticide, many insect species are
presumably at risk if exposed at a sensitive life stage. Therefore, the effects
determination from labeled use of diflubenzuron is "likely to adversely affect." The
potential impact to the diet of the CRLF will depend on the timing of application and
predominance of invertebrates in sensitive life stages.
The distance from treated fields that effects may occur has not been defined because the
available data do not allow for quantitative measures of effects.
5.2.2.5. Mammals
Life history data for terrestrial-phase CRLFs indicate that large adult frogs consume
terrestrial vertebrates, including mice. No acute LOCs were exceeded for mammals. No
effects were observed in the available acute oral toxicity study at doses up to 5000
mg/kg-bw. No reproduction RQs were exceeded for any use except the
barnyard/mushroom use. Therefore, the effects determination is "no effect" for all uses
except barnyard/mushroom use based on the lack of LOG exceedances and the resulting
low magnitude of any potential effects to mammals.
Reproduction LOCs were exceeded for barnyard/mushroom use (RQ = 10). There is a
10-fold dose spacing in the available 2-generation reproduction toxicity study; therefore,
at an RQ of 10, estimated exposures are equivalent to the LOAEC in mammals. At the
LOAEC, there was a reduction in body weight in Fl pups. Frank reproductive effects
were not observed. The EECs were based on the short grass food item and assumed that
small mammal prey consume only contaminated short grass at high-end exposure levels.
However, the barnyard/mushroom use is a spot treatment (directed spray at manure).
Therefore, it is unlikely that a small mammal will obtain 100% of its diet as contaminated
short grass in environments consistent with the barnyard/mushroom use. Nonetheless,
such effects could not be precluded. Therefore, the effects determination is "likely to
adversely affect" based on potential reductions in mammalian prey. These conclusions
are highly uncertain.
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5.2.2.6. Terrestrial-phase Amphibians
Terrestrial-phase adult CRLFs also consume other amphibians. RQ values representing
direct exposures of diflubenzuron to terrestrial-phase CRLFs are used to represent
exposures of diflubenzuron to frogs in terrestrial habitats. The direct effects assessment
was "no effect" for all uses except the barnyard/mushroom use. Therefore, the effects
determination is also "no effect" via reduction in amphibian prey.
For the barnyard/mushroom use, the effects determination was "likely to adversely
affect" based on potential direct effects to the CRLF. However, the potential magnitude
of effect is expected to be relatively low when considering dietary factors of terrestrial
phase amphibians relative to the surrogate avian species.
When incorporating food intake equations specific for amphibians and reptiles using the
T-HERPS model, LOCs were not exceeded for terrestrial phase amphibians that consume
plants or insects. See Section 5.2.1.2 for additional information. Therefore, the effects
determination for potential effects to the CRLF via reductions in available amphibian
prey is "not likely to adversely affect."
5.2.3. Indirect Effects (via Habitat Effects)
5.2.3.1. Aquatic Plants (Vascular and Non-vascular)
Aquatic plants serve several important functions in aquatic ecosystems. Non-vascular
aquatic plants are primary producers and provide the autochthonous energy base for
aquatic ecosystems. 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 also provide primary productivity and oxygen to the aquatic
ecosystem. Rooted plants help reduce sediment loading and provide stability to
nearshore areas and lower streambanks. 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. No LOCs were exceeded for vascular aquatic plants. No effects were
observed in the available toxicity studies in aquatic plants at any test level. EECs were
lower than all vascular plant NOAECs. Therefore, effects to vascular plants are not
expected to occur. For this reason, the effects determination for the CRLF based on
indirect effects resulting from impacts to vascular plants is "no effect."
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
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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.
Impacts to terrestrial plants are not expected to occur at levels that may result in indirect
effects to CRLFs. Although no suitable toxicity data are available in terrestrial plants,
diflubenzuron is an insecticide that has been used to treat numerous crops and non-crop
plants for many years typically without incident. However, one incident has associated
diflubenzuron with damage to oranges. This incident may or may not have been caused
by diflubenzuron. It was assigned a certainty index of "possible".
Although the data do not allow for quantification of potential risks to terrestrial plants,
the weight of evidence suggests that effects to plants from labeled uses of diflubenzuron
are minimal.
No guideline studies have been submitted that evaluated effects to terrestrial plants.
Therefore, additional lines of evidence were used to determine if diflubenzuron may
affect terrestrial plants at a magnitude that may result in indirect effects to the CRLF.
Diflubenzuron has a long history of use on numerous types of crops including grasses,
trees, vines, and numerous fruit and vegetable crops without clear evidence of any
adverse effects to terrestrial plants. Two field studies were located in the open literature
study that evaluated impacts to vegetation from use of diflubenzuron that did not observe
impacts to vegetation (discussed in Section 4). No incidents have been reported that
definitively linked use of diflubenzuron use to damage to terrestrial plants. One incident
was associated with damage to orange trees; however, that incident is more likely
associated with use of petroleum distillates as discussed in Section 4. In addition,
numerous studies have been submitted to the Agency that evaluated efficacy of
diflubenzuron, and no evidence of plant damage was reported in these studies.
For these reasons, use of diflubenzuron is not likely to affect the CRLF by impacting
terrestrial vegetation.
The effects determination for the CRLF resulting from indirect effects from impacts to
terrestrial plants is "no effect."
5.2.4. Modification to Designated Critical Habitat
Risk conclusions for designated critical habitat of the CRLF are the same as those for
indirect effects. Critical habitat may be modified by impacting availability of prey
(terrestrial and aquatic invertebrates) as follows:
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PCE: "reduction and/or modification of food sources for terrestrial phase
juveniles and adults." This PCE may be modified by diflubenzuron by potentially
impacting invertebrate food sources. See Section 5.2.2.4.
PCE: "alteration of chemical characteristics necessary for normal growth and
viability of juvenile and adult CRLFs and their food source." This PCE may be
impacted by effects to food sources such as terrestrial invertebrates. See Section
5.2.2.4.
5.2.5. Spatial Extent of Potential Effects
Direct effects to the CRLF are limited to the barnyard/mushroom use. Locations of cattle
feed lots (locations where diflubenzuron may be used on cattle manure) are depicted in
Figure 5.2. For this use, diflubenzuron is applied as a directed spray to manure. Based
on the low magnitude of the RQ for this use and the low potential for spray drift, it is
assumed that potential risks are limited to treated sites.
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Cattle and Hog Feedlots in California (D&B)
Legend
* Cattle and Hog Feedlot
| | All feedlots 98-07
| | Occupied core areas
EISB 8/2009
Figure 5-2. Comparison of location of sites likely to use diflubenzuron for control of
flies at livestock facilities (see text) and CRLF occupied core areas.
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RQs used to estimate potential for indirect effects to aquatic phase CRLFs were as high
as approximately 500,000. The distance needed to reduce potential exposures to levels
that do not exceed LOCs is greater than distances that can be predicted with any
reliability. Potential indirect effects could occur at distances >5000 feet from the treated
sites as described in Section 5.2.5.1
Indirect effects to the CRLF may also occur via impacts to terrestrial invertebrates.
However, the data do not allow for quantification of the potential distance from treated
sites to which risks extend primarily because the toxicity data used to estimate potential
impacts to terrestrial invertebrates are based on adult honey bee studies. Sensitivity of
adult honey bees to diflubenzuron is expected to be considerably lower than sensitivity of
other insects, particularly invertebrates in early life stages. Therefore, potential impacts
to terrestrial invertebrates are assumed to extend to distances greater than 1000 feet from
treated fields.
An LAA effects 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 diflubenzuron's use pattern is identified, using
land cover data that correspond to diflubenzuron's use pattern. Areas of potential
exposure also include areas beyond the initial area of concern (e.g., use footprint) that
may be impacted by runoff and/or spray drift. The identified direct and indirect effects
and 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 >5000 feet from its
boundary. It is assumed that non-flowing waterbodies (or potential CRLF habitat) are
included within this area. Direct effects are only expected to occur for the
barnyard/mushroom use. For this use, risks are expected to be predominantly restricted
to the treated site because of the mode of application (directed spray to manure).
The determination of the buffer distance and downstream dilution for spatial extent of the
effects determination is described below.
5.2.5.1. Spray Drift
In order to determine terrestrial and aquatic habitats of concern due to diflubenzuron
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 (version 2.01). AgDRIFT was run using default parameters. Tier 3 was used
to expand the distance evaluated to 5000 feet.
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Table 5-11. Summary of AgDRIFT* Predicted Terrestrial Spray Drift Distances
Landcover
Forest
Non-cropland
agriculture
Residential
Orchard
Pasture/Rangeland
Cropland
Uses Represented
Forestry
Turf, nursery
Residential, urban, rights of
ways
Fruit, nuts, pistachio, Beech
nut
Barnyards, pastures+
Turnip, squash, row crops,
rice, grains, nuts, cotton,
cole crops, brassica,
Highest RQ
3200
2600
137,000
5400
217,000 (barnyard)
2200 (pasture)
452,000
Distance to reduce
spray drift to level that
is 5000 feet
>5000 feet
>5000 feet
>5000 feet
>5000 feet
>5000 feet
* AgDRIFT was run in Tier 3, with a maximum distance of 5000 feet and RQs for aquatic invertebrates.
AgDRIFT has not been validated at distances >1000 feet; therefore, there is uncertainty in the
estimations presented in Table 5-11.
+.Minimal drift is expected from the barnyard uses because of the mode of application (downward spray
directed at manure); therefore, the drift distance was based on the pastureland RQ of 2200.
5.2.6.2. 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 LOG was not completed
because of the large number of uses and large corresponding landcover area. The large
geographic extent of potential use sites precludes quantification of dilution potential
based on landcover data representing non-use sites.
5.2.6.3. Overlap between CRLF habitat and Spatial Extent of
Potential Effects
An LAA effects determination is made to those areas where it is expected that the
pesticide's use will directly or indirectly affect the CRLF or its designated critical habitat
and the area overlaps with the core areas, critical habitat and available occurrence data
for CRLF.
For diflubenzuron, the use pattern encompasses all land cover classes. Therefore, the
initial area of concern is the entire state of CA. As described in Section 5, diflubenzuron
could potentially impact the CRLF via indirect effects to aquatic and terrestrial
invertebrates. Effects could occur at distances >5000 feet from the site of application.
Potential overlap between the CRLF and diflubenzuron uses is graphically represented in
Figure 5.3.
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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
Southern Transverse and Peninsular Ranges
Legend
] Recovery Unit Boundaries '
[| Currently Occupied Core Areas
^B Critical Habitat
^H CNDDB Occurence Sections
County Boundaries g
45
Core Areas
1. Feather River
2. Yuba River- S. Fork Feather River
3. Traverse Creek/ Middle Fork/ American R. Rubicon
4. Cosumnes River
5. South Fork Calaveras River*
6. Tuolumne River*
7. Piney Creek*
8. Cottonwood Creek
9. Putah Creek - Cache Creek*
10. Lake Berryessa Tributaries
11. Upper Sonoma Creek
12. Petaluma Creek - Sonoma Creek
13. Pt. Reyes Peninsula
14. Belvedere Lagoon
15. Jameson Canyon Lower Napa River
16. East San Francisco Bay
17. Santa Clara Valley
18. South San Francisco Bay
* Core areas that were historically occupied by the California red-legged frog are not included in the map
19. Watsonville Slough-Elkhorn Slough
20. Carmel River - Santa Lucia
21. Gab Ian Range
22. Estero Bay
23. Arroyo Grange River
24. Santa Maria River Santa Ynez River
25. Sisquoc River
26. Ventura River Santa Clara River
27. Santa Monica Bay Venura Coastal Streams
28. Estrella River
29. San Gabriel Mountain*
30. Forks of the Mojave*
31. Santa Ana Mountain*
32. Santa Rosa Plateau
33. San Luis Ray*
34. Sweetwater*
35. Laguna Mountain*
Figure 5-3 Recovery Unit, Core Area, Critical Habitat, and Occurrence
Designations for CRLF
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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.
Several fast-maturing crops may have multiple crop cycles within a single year. For these
crops, it is often the case that labels do not specify a maximum annual application rate,
but rather a maximum crop cycle rate (maximum pounds per acre per crop cycle).
Because diflubenzuron dissipates rapidly in the environment (aerobic soil metabolism
rate is ~2 days), additional applications of diflubenzuron during following crop cycles are
not expected to greatly increase terrestrial EECs within the field where it is applied or in
the terrestrial spray drift zone. However, aquatic EECs can be affected because the
multiple crop cycles extend the growing season into those parts of the year when runoff is
more likely (fall through early spring). To address this uncertainty, aquatic EECs were
modeled across a large range of application dates (Section 3.2.3 and Appendix tables D4
and D5).
6.1.2 Crops Not Grown in California (include if you had crops that are not
grown in CA)
Soybeans are the only crop listed on diflubenzuron labels that is not grown in California
according to National Agricultural Statistical Service data. Because these crops are not
currently grown in California and are not expected to be grown in California in the future,
use of diflubenzuron was not assessed for these crops. If use patterns indicate soybeans
are grown in California in the future, the conclusions of this assessment may need to be
revisited.
6.1.3 Aquatic Exposure Modeling of Diflubenzuron
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
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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
(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 (U.S. FWS/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
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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.
Unlike spray drift, tools are currently not available to evaluate the effectiveness of a
vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is
highly dependent on the condition of the vegetative strip. For example, a well-
established, healthy vegetative setback can be a very effective means of reducing runoff
and erosion from agricultural fields. Alternatively, a setback of poor vegetative quality
or a setback that is channelized can be ineffective at reducing loadings. Until such time
as a quantitative method to estimate the effect of vegetative setbacks on various
conditions on pesticide loadings becomes available, the aquatic exposure predictions are
likely to overestimate exposure where healthy vegetative setbacks exist and
underestimate exposure where poorly developed, channelized, or bare setbacks exist.
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 1998 and
earlier pesticide data; therefore, this information was not included in the analysis because
it may misrepresent actual usage patterns. CDPR PUR documentation indicates that
errors in the data may include the following: a misplaced decimal; incorrect measures,
area treated, or units; and reports of diluted pesticide concentrations. In addition, it is
possible that the data may contain reports for pesticide uses that have been cancelled.
The CPDR PUR data does not include home owner applied pesticides; therefore,
residential uses are not likely to be reported. As with all pesticide 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 Diflubenzuron
The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide
residues in wildlife dietary items. These residue assumptions are believed to reflect a
realistic upper-bound residue estimate, although the degree to which this assumption
reflects a specific percentile estimate is difficult to quantify. It is important to note that
the field measurement efforts used to develop the Fletcher estimates of exposure involve
highly varied sampling techniques. It is entirely possible that much of these data reflect
residues averaged over entire above ground plants in the case of grass and forage
sampling.
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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. EPA 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
to an overestimation of exposure to species that do not occupy the treated field
exclusively and permanently.
6.1.6 Spray Drift Modeling
Although there may be multiple diflubenzuron applications at a single site, 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 diflubenzuron from multiple applications, each application of diflubenzuron would
have to occur under identical atmospheric conditions (e.g.., same wind speed and - for
plants - same wind direction) and (if it is an animal) the animal being exposed would
have to be present directly downwind at the same distance after each application.
Although there may be sites where the dominant wind direction is fairly consistent (at
least during the relatively quiescent conditions that are most favorable for aerial spray
applications), it is nevertheless highly unlikely that plants in any specific area would
receive the maximum amount of spray drift repeatedly. It appears that in most areas
(based upon available meteorological data) wind direction is temporally very changeable,
even within the same day. 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
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overestimate exposure even from single applications, 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 often made regarding the droplet size distributions being modeled ('ASAE Very Fine
to Fine' for orchard uses and 'ASAE Very Fine' for agricultural uses), the application
method (e.g., aerial), release heights and wind speeds. Alterations in any of these inputs
would change 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.
For diflubenzuron, the most sensitive endpoints are for immature invertebrates that are
molting. However, acute toxicity test procedures typically select organisms that are not
molting during the test. This may result in an underestimation of risk to molting
individuals of the same species.
6.2.2 Use of Surrogate Species Effects Data
Guideline toxicity tests and open literature data on diflubenzuron 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.
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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 t 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.
No open literature or registrant studies on sublethal effects associated with exposure to
diflubenzuron were identified. To the extent to which sublethal effects are not considered
in this assessment, the potential direct and indirect effects of diflubenzuron on CRLF may
be underestimated.
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
to an overestimation of exposure to species that do not occupy the treated field
exclusively and permanently.
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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 diflubenzuron 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 diflubenzuron. The Agency has determined
that there is no potential for modification of CRLF designated critical habitat from the
use of the chemical. All the uses of diflubenzuron are likely to adversely affect the
CRLF primarily because of a there is a significant risk to terrestrial and aquatic
invertebrate prey of the CRLF. There is a LAA for risk of direct effect to the aquatic
phase CRLF only for the diflubenzuron use on rice and there is a LAA for risk of direct
effect to the terrestrial phase CRLF for diflubenzuron use in barnyard/mushroom sites.
The LAA effects 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 diflubenzuron's use pattern is identified, using
land cover data that correspond to diflubenzuron's use pattern. The spatial extent of the
LAA effects determination also includes areas beyond the initial area of concern that may
be impacted by runoff and/or spray drift. The identified indirect effects 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 +
5000 feet from its boundary (refer to analysis in Section 5.1.4). It is assumed that non-
flowing waterbodies (or potential CRLF habitat) are included within this area.
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 7-2.
Table 7-1. Effects Determination Summary for Diflubenzuron Use and the CRLF
Assessment
Endpoint
Effects
Determination 1
Basis for Determination
Survival, growth,
and/or
reproduction of
CRLF individuals
LAA, all uses
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults):
Direct effects are not expected for any labeled use. All effects
determinations are either NE or NLAA.
Terrestrial-phase (Juveniles and Adults):
Direct effects are only expected for diflubenzuron's use on barn
yards based on acute and chronic LOC's for birds.
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary
productivity
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Assessment
Endpoint
Effects
Determination 1
Basis for Determination
Aquatic prey of the CRLF are expected to be impacted to an extent
that could adversely affect CRLFs.
Terrestrial prey items, riparian habitat
Terrestrial prey items of the CRLF are expected to be impacted
based on LOG exceedances for risk to terrestrial invertebrates.
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 Diflubenzuron Use and CRLF Critical Habitat
Impact Analysis
Assessment
Endpoint
Modification of
aquatic-phase PCE
Modification of
terrestrial-phase
PCE
Effects
Determination 1
Habitat
Modification
Basis for Determination
There are LOG exceedances for risk to terrestrial
invertebrate prey of the CRLF.
There are LOG exceedances for risk to terrestrial
invertebrate prey of the CRLF.
and aquatic
and aquatic
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
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
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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
Alvarez, J. 2000. Letter to the U.S. Fish and Wildlife Service providing comments on the
Draft California Red-legged Frog Recovery Plan.
Altig, R.; R.W. McDiarmid. 1999. Body Plan: Development and Morphology. In R.W.
McDiarmid and R. Altig (Eds.), Tadpoles: The Biology ofAnuran Larvae.
University of Chicago Press, Chicago, pp. 24-51.
Boyle, T. P., Fairchild, J. F., Robinson-Wilson, E. F., Haverland, P. S., and Lebo, J. A.
(1996). Ecological Restructuring in Experimental Aquatic Mesocosms due to the
Application of Diflubenzuron. Environ.Toxicol.Chem. 15: 1806-1814.
Cooper, R. J., Dodge, K. M., Martinat, P. J., Donahoe, S. B., and Whitmore, R. C. (1990).
Effect of Diflubenzuron Application on Eastern Deciduous Forest Birds.
J.WildlManag. 54: 486-493.
Fellers, G.M, L.L. McConnell, D. Pratt, S. Datta. 2004. Pesticides in Mountain Yellow-
Legged Frogs (Rana Mucosa) from the Sierra Nevada Mountains of California,
USA. Environmental Toxicology & Chemistry 23 (9):2170-2177.
Fellers, G. M. 2005a. Rana draytonii Baird and Girard 1852. California Red-legged Frog.
Pages 552-554. In: M. Lannoo (ed.) Amphibian Declines: The Conservation
Status of United States Species, Vol. 2: Species Accounts. University of
California Press, Berkeley, California, xxi+1094 pp.
(http://www.werc.usgs.gov/pt-reves/pdfs/Rana%20draytonii.PDF)
Fellers, G. M. 2005b. California red-legged frog, Rana draytonii Baird and Girard. Pages
198-201. In: L.L.C. Jones, et al (eds.) Amphibians of the Pacific Northwest.
xxi+227.
Fletcher J.S.; I.E. Nellessen; T.G. Pfleeger. 1994. Literature Review and Evaluation of
the EPA Food-chain (Kenaga) Nomogram, an Instrument for Estimating Pesticide
Residues on Plants. Environmental Toxicology and Chemistry, 13:9 (13 83-1391).
Hayes, M. P.; M. R. Jennings. 1988. Habitat correlates of distribution of the California
redlegged frog (Rana aurora draytonii) and the foothill yellow-legged frog (Rana
boylii): Implications for management. Pages 144-158 In: R. Sarzo, K. E.
Severson, and D. R. Patton (technical coordinators). Proceedings of the
Symposium on the Management of Amphibians, Reptiles, and small mammals in
NorthAmerica. U.S.D.A. Forest Service General Technical Report RM-166.
113
-------
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, M.P.; M.R. Tennant. 1985. Diet and feeding behavior of the California red-legged
frog. The Southwestern Naturalist 30(4): 601-605.
Hoerger, F.; E. E. Kenaga. 1972. Pesticide residues on plants; Correlation of
representative data as a basis for estimation of their magnitude in the
environment. In. F. Coulston and F. Korte, Eds., Environmental Quality and
Safety: Chemistry, Toxicology, and Technology. George Thieme Publishers,
Stuttgart, West Germany, pp. 9-28.
Jennings, M.R.; M.P. Hayes. 1994. Amphibian and reptile species of special concern in
California. Report prepared for the California Department of Fish and Game,
Inland Fisheries Division, Rancho Cordova, California. 255 pp.
Jennings, M.R.; S. Townsend; R.R. Duke. 1997. Santa Clara Valley Water District
California red-legged frog distribution and status - 1997. Final Report prepared
by H.T. Harvey & Associates, Alviso, California. 22 pp.
Kashian, D. R. and Dodson, S. I. (2002). Effects of Common-Use Pesticides on
Developmental and Reproductive Processes in Daphnia. Toxicol.Ind.Health 18:
225-235.
Kupferberg, S. 1997. Facilitation of periphyton production by tadpole grazing: Functional
differences between species. Freshwater Biology 37:427-439.
Kupferberg, S.J.; J.C. Marks and M.E. Power. 1994. Effects of variation in natural algal
and detrital diets on larval anuran (Hyla regilld) life-history traits. Copeia 1994:
446-457.
LeNoir, J.S., L.L. McConnell, GM. Fellers, T.M. Cahill, J.N. Seiber. 1999. Summertime
Transport of Current-use pesticides from California's Central Valley to the Sierra
Nevada Mountain Range,USA. Environmental Toxicology & Chemistry 18(12):
2715-2722.
McConnell, L.L., J.S. LeNoir, S. Datta, J.N. Seiber. 1998. Wet deposition of current-use
pesticides in the Sierra Nevada mountain range, California, USA. Environmental
Toxicology & Chemistry 17(10): 1908-1916.
National Agricultural Statistics Service (NASS). 2002. Master California NASS 2002
Use List (7 February 2007). http://www.nass.usda.gov/index.asp.
Rathburn, G.B. 1998. Rana aurora draytonii egg predation. Herpetological Review
29(3): 165.
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Reis, D.K. 1999. Habitat characteristics of California red-legged frogs (Rana aurora
draytonii): Ecological differences between eggs, tadpoles, and adults in a coastal
brackish and freshwater system. M.S. Thesis. San Jose State University. 58 pp.
Seale, D. B., and N. Beckvar. 1980. The comparative ability of anuran larvae (genera:
Hyla, Bufo, and Rana) to ingest suspended blue-green algae. Copeia 1980: 495-
503.
U.S. Environmental Protection Agency. (U.S. EPA). 1993. Wildlife Exposure Factors
Handbook. EPA/600/R-13/187a, Office of Research and Development,
Washington, DC.
U.S. EPA. 1997. Diflubenzuron. Reregistration Eligibility Decision. OPPT. EPA738-R-
97-008. August, 1997
U.S. EPA. 1998. Guidance for Ecological Risk Assessment. Risk Assessment Forum.
EPA/630/R-95/002F, April 1998.
U.S. EPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of
Pesticide Programs. Office of Prevention, Pesticides, and Toxic Substances.
Office of Pesticide Programs. Washington, D.C. January 23, 2004.
U.S. Fish and Wildlife Service (U.S. FWS). 1996. Endangered and threatened wildlife
and plants: determination of threatened status for the California red-legged frog.
Federal Register 61(101):25813-25833.
U.S. FWS and National Marine Fisheries Service (NMFS). 1998. Endangered Species
Consultation Handbook: Procedures for Conducting Consultation and Conference
Activities Under Section 7 of the Endangered Species Act. Final Draft. March
1998.
U.S. FWS. 2002. Recovery Plan for the California Red-legged Frog (Rana aurora
draytonii). Region 1, USFWS, Portland, Oregon.
(http://ecos.fws.gov/doc/recovery_plans/2002/020528.pdf)
U.S. FWS/NMFS. 2004. 50 CFR Part 402. Joint Counterpart Endangered Species Act
Section 7 Consultation Regulations; Final Rule. 69 Federal Register 47732-
47762.
U.S. FWS. 2006. Endangered and threatened wildlife and plants: determination of critical
habitat for the California red-legged frog. 71 Federal Register 19244-19346.
U.S. FWS. Website accessed: 30 December 2006.
http://www.fws.gov/endangered/features/rl frog/rlfrog.html#where
115
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Wassersug, R. 1984. Why tadpoles love fast food. Natural History 4/84.
Willis, G. H.; L.L. McDowell. 1987. Pesticide persistence on foliage. Reviews of
Environmental Contamination and Toxicology 100: 23-73.
Previous Assessments
U.S. EPA 2002a. Environmental Fate and Ecological Effects Assessment and
Characterization for a Section 3 for Aerial and Ground Spray Treatment to Pears,
Stone Fruits, Almonds, Peppers, and Pasture Grass (DP 321153, DP 321278)
Ecological Fate and Effects Division, Office of Pesticide Programs, U.S.
Environmental Protection Agency, Washington D.C. May 2002.
U.S. EPA 2006. Environmental Fate and Ecological Risk Assessment for the Registration
of Diflubenzuron (Dimilin-2L) Use on Peanuts, Okra, Small Grains-(Winter
wheat, Spring wheat, Durum, Barley, and Oats) , Pummelo, Mustard Greens,
Broccoli, Raab, Cabbage, Chinese (bok choy); Collards; Kale; Mizuna; Mustard
spinach; Rape, Greens and Turnip greens. (DP 321153, DP 321278). Ecological
Fate and Effects Division, Office of Pesticide Programs, U.S. Environmental
Protection Agency, Washington D.C., September 2006.
U.S. EPA 2008. New Use of Dimilinฎ2L (active ingredient 22% Diflubenzuron) on Fly
Breeding Areas in Livestock Operations. (DP 348755). Ecological Fate and
Effects Division, Office of Pesticide Programs, U.S. Environmental Protection
Agency, Washington D.C., September 2008.
U.S. EPA 2009. County-Level Usage for Strychnidin; Strychnine; Triclopyr, butoxyethyl
ester; Triclopyr, triethylamine salt; Diflubenzuron; Trifluralin ; Thiobencarb;
Chlorpyrifos; Vinclozolin; Iprodione in California in Support of a Red Legged Frog
Endangered Species Assessment, DP # TBD. Biological and Economic Analysis
Divis ion, Office of Pesticide Programs, U.S. Environmental Protection Agency,
Washington D.C., June 8th, 2009.
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