Risks of Diuron 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
February 18, 2009

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Primary Authors:
Ron Dean, Biologist
Tiffany Mason, Environmental Engineer
Bill Shaughnessy, PhD, Environmental Scientist
Environmental Risk Branch II
Environmental Fate and Effects Division (7507C)
Secondary Review:
William P. Eckel, PhD, Senior Scientist
Environmental Risk Branch II
Environmental Fate and Effects Division (7507P)
Jean Holmes, Senior Scientist
Environmental Risk Branch II
Environmental Fate and Effects Division (7507P)
Branch Chief, Environmental Risk Branch II:
Tom Bailey, PhD, Branch Chief
Environmental Fate and Effects Division (7507P)
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Table of Contents
1.0	Executive Summary	1
2.0	Problem Formulation	11
2.1	Purpose	11
2.2	Scope	13
2.3	Previous Assessments	14
2.4	Stressor Source and Distribution	15
2.4.1	Environmental Fate Properties	15
2.4.2	Environmental Transport Mechanisms	17
2.4.3	Mechanism of Action	21
2.4.4	Use Characterization	21
2.5	Assessed Species	25
2.5.1	Distribution	25
2.5.2	Reproduction	28
2.5.3	Diet	28
2.5.4	Habitat	29
2.6	Designated Critical Habitat	30
2.7	Action Area	32
2.8	Assessment Endpoints and Measures of Ecological Effect	35
2.8.1. Assessment Endpoints for the CRLF	36
2.8.2 Assessment Endpoints for Designated Critical Habitat	37
2.9	Conceptual Model	40
2.9.1	Risk Hypotheses	40
2.9.2	Diagram	40
2.10	Analysis Plan	44
2.10.1	Measures to Evaluate the Risk Hypothesis and Conceptual Model	44
2.10.1.1	Measures of Exposure	44
2.10.1.2	Measures of Effect	46
2.10.1.3	Integration of Exposure and Effects	47
2.10.2	Data Limitations	48
3.0	Exposure Assessment	48
3.1	Label Application Rates and Intervals	49
3.2	Aquatic Exposure Assessment	49
3.2.1	Modeling Approach	49
3.2.2	Model Inputs	49
3.2.3	Results	50
3.2.4	Existing Monitoring Data	52
3.2.6 Downstream Dilution Analysis	53
3.3	Terrestrial Animal Exposure Assessment	54
3.4	Terrestrial Plant Exposure Assessment	57
3.4.1 Spray Drift Buffer Analysis	59
4.0	Effects Assessment	61
4.1 Toxicity of Diuron to Aquatic Organisms	63
4.1.1	Toxicity to Freshwater Fish	65
4.1.2	Toxicity to Freshwater Invertebrates	65
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4.1.3 Toxicity to Aquatic Plants	65
4.2	Toxicity of Diuron to Terrestrial Organisms	66
4.2.1	Toxicity to Birds	67
4.2.2	Toxicity to Mammals	68
4.2.3	Toxicity to Terrestrial Invertebrates	68
4.2.4	Toxicity to Terrestrial Plants	68
4.3	Use of Probit Slope Response Relationship to Provide Information on the Endangered
Species Levels of Concern	69
4.4	Incident Database Review	70
5.0	Risk Characterization	70
5.1	Risk Estimation	70
5.1.1	Exposures in the Aquatic Habitat	71
5.1.1.1	Direct Effects to Aquatic-Phase CRLF	71
5.1.1.2	Indirect Effects to Aquatic-Phase CRLF via Reduction in Prey (non-vascular
aquatic plants, aquatic invertebrates, fish, and frogs)	79
5.1.1.3	Indirect Effects to CRLF via Reduction in Habitat and Primary Productivity
(Freshwater Aquatic Plants)	86
Table 5.4 Summary of Acute RQs Used to Estimate Indirect Effects to the CRLF via
Effects to Vascular Aquatic Plants (habitat of aquatic-phase CRLF)a	86
5.1.2	Exposures in the Terrestrial Habitat	89
5.1.2.1	Direct Effects to Terrestrial-phase CRLF	89
5.1.2.2	Indirect Effects to Terrestrial-Phase CRLF via Reduction in Prey (terrestrial
invertebrates, mammals, and frogs)	91
5.1.2.3	Indirect Effects to CRLF via Reduction in Terrestrial Plant Community
(Riparian and Upland Habitat)	93
5.1.3	Primary Constituent Elements of Designated Critical Habitat	94
5.1.3.1	Aquatic-Phase (Aquatic Breeding Habitat and Aquatic Non-Breeding
Habitat) 	94
5.1.3.2	Terrestrial-Phase (Upland Habitat and Dispersal Habitat)	95
5.2	Risk Description	96
5.2.1	Direct Effects	100
5.2.1.1	Aquatic-Phase CRLF	100
5.2.1.2	Terrestrial-Phase CRLF	101
5.2.2	Indirect Effects (via Reductions in Prey Base)	104
5.2.2.1	Algae (non-vascular plants)	104
5.2.2.2	Aquatic Invertebrates	105
5.2.2.3	Fish and Aquatic-phase Frogs	106
5.2.2.4	Terrestrial Invertebrates	106
5.2.2.5	Mammals	107
5.2.2.6	Terrestrial-phase Amphibians	107
5.2.3	Indirect Effects (via Habitat Effects)	108
5.2.3.1	Aquatic Plants (Vascular and Non-vascular)	108
5.2.3.2	Terrestrial Plants	108
5.2.4	Modification to Designated Critical Habitat	109
5.2.4.1	Aquatic-Phase PCEs	109
5.2.4.2	Terrestrial-Phase PCEs	110
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6.0	Uncertainties	Ill
6.1. Exposure Assessment Uncertainties	Ill
6.1.1	Maximum Use Scenario	111
6.1.2	Aquatic Exposure Modeling of Diuron	112
6.1.3	Action Area Uncertainties	113
6.1.4	Usage Uncertainties	114
6.1.5	Terrestrial Exposure Modeling of Diuron	114
6.2 Effects Assessment Uncertainties	115
6.2.1	Age Class and Sensitivity of Effects Thresholds	115
6.2.2	Use of Surrogate Species Effects Data	116
6.2.3	Sublethal Effects	117
6.2.4	Location of Wildlife Species	117
7.0	Risk Conclusions	117
8.0	References	122
Appendices
Appendix A	Multi-ai Product Analysis
Appendix B	Chemical Structure of Parent and Degradates
Appendix C	Use Rates and Methods
Appendix D	CDPR PUR Usage Data
Appendix E	RQ Method and LOCs
Appendix F	Spatial Summary of Diuron
Appendix G	PRZM/EXAMS Output
Appendix H	T-REX Example Output
Appendix I	TerrPlant Example Output
Appendix J	Bibliography of ECOTOX Open Literature Not Evaluated
Appendix K	Accepted ECOTOX Data Table Spreadsheet
Appendix L	Ecological Effects Data
Appendix M	Diuron Incidents
Appendix N	T-Herps Example Output
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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List of Tables
Table 1.1 Effects Determination Summary for Effects of Diuron on the CRLF	5
Table 1.2 Effects Determination Summary for the Critical Habitat Impact Analysis	6
Table 1.3 Diuron Use-specific Direct Effects Determinations1 for the CRLF	7
Table 1.4 Diuron Use-specific Indirect Effects Determinations1 Based on Effects to Prey8
Table 2.1 Summary of Diuron Half-lives	17
Table 2.2 Active Use Sites for Diuron as Applicable to California	24
Table 3.1 Summary of PRZM/EXAMS Environmental Fate Data Used for Aquatic
Exposure Inputs for Diuron Endangered Species Assessment for the CRLF	50
Table 3.2 Table Aquatic EECs (ppb) for Diuron Uses in California	51
Table 3.3 T-REX Model Input Parameters	54
Table 3.4 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based
Exposures of the CRLF and its Prey to Diuron	55
Table 3.5 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via Effects to
Terrestrial Invertebrate Prey Items	56
Table 3.6 TerrPlant Inputs and Resulting EECs for Plants Inhabiting Dry and Semi-
aquatic Areas Exposed to diuron via Runoff and Drift	58
Table 3.7 Summary of AgDRIFT Predicted Spray Drift Buffer for Terrestrial Plants ... 60
Table 4.1 Freshwater Aquatic Toxicity Profile for Diuron	63
Table 4.2 Categories of Acute Toxicity for Aquatic Organisms	64
Table 4.3 Terrestrial Toxicity Profile for Diuron	66
Table 4.4 Categories of Acute Toxicity for Avian and Mammalian Studies	67
Table 4.5 Terrestrial Plant Toxicity Profile for Diuron	69
Table 5.1. Summary of Direct Effect RQs for the Aquatic-phase CRLF	72
Table 5.2 Summary of Acute 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)*	83
Table 5.4 Summary of Acute RQs Used to Estimate Indirect Effects to the CRLF via
Effects to Vascular Aquatic Plants (habitat of aquatic-phase CRLF)a	86
Table 5.5 Summary of Acute RQs Used to Estimate Direct Effects to the Terrestrial-
phase CRLF	90
Table 5.6 Summary of Acute and Chronic RQs* Used to Estimate Indirect Effects to the
Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary Food Items .. 92
Table 5.7 RQs* : for Non-Target Plants Inhabiting Dry and Semi-Aquatic Areas
Exposed to Diuron via Runoff and Drift	93
Table 5.8 Risk Estimation Summary for Diuron - Direct and Indirect Effects to CRLF . 97
Table 5.9 Risk Estimation Summary for Diuron - PCEs of Designated Critical Habitat
for the CRLF	98
Table 5.10. Upper-bound Kenega Nomogram T-HERPS EECs (mg/kg-diet) for Dietary-
based Exposures of the CRLF and its Prey to Diuron1	102
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Table 5.11. Revised Acute Dietary-based RQs for CRLF consuming different food items
(RQs calculated using T-HERPS)*	103
Table 7.1 Effects Determination Summary for Effects of Diuron on the CRLF	119
Table 7.2 Effects Determination Summary for the Critical Habitat Impact Analysis... 120
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List of Figures
Figure 2.1 Diuron Agricultural Use in Total Pounds per County	23
Figure 2.2 Recovery Unit, Core Area, Critical Habitat, and Occurrence Designations for
CRI.I	27
Figure 2.3 - CRLF Reproductive Events by Month	28
Figure 2.4 Initial area of concern, or "footprint" of potential use, for diuron	34
Figure 2.5 Conceptual Model for Aquatic-Phase of the CRLF	41
Figure 2.6 Conceptual Model for Terrestrial-Phase of the CRLF	42
Figure 2.7 Conceptual Model for Pesticide Effects on Aquatic Component of CRLF
Critical Habitat	43
Figure 2.8 Conceptual Model for Pesticide Effects on Terrestrial Component of CRLF
Critical Habitat	44
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1.0 Executive Summary
The purpose of this assessment is to evaluate potential direct and indirect effects on the
California red-legged frog (Rana aurora draytonii) (CRLF), from FIFRA regulatory
actions regarding use of diuron on agricultural and non-agricultural sites. In addition,
this assessment evaluates whether these actions can be expected to result in modification
of the species' designated critical habitat. This assessment was completed in accordance
with the U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service
(NMFS) Endangered Species Consultation Handbook (USFWS/NMFS, 1998) and
procedures outlined in the Agency's Overview Document (U.S. EPA, 2004).
The CRLF was listed as a threatened species by USFWS in 1996. The species is endemic
to California and Baja California (Mexico) and inhabits both coastal and interior
mountain ranges. A total of 243 streams or drainages are believed to be currently
occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and
Santa Barbara counties (USFWS, 1996) in California.
Diuron (N-(3,4-dichlorophenyl)-N,N-dimethylurea) is a systemic substituted phenylurea
herbicide. In the U.S. diuron is used on a variety of fruit and nut crops, grains, cotton,
corn, sorghum, mint, gum, asparagus, sugarcane, seed crops, coffee, hay, cut flowers, and
for fallow, idle cropland use, and impervious surfaces such as paved areas. It may be
used in irrigation and drainage systems when water is not present. Diuron is available in
wettable powder, flowable, liquid suspension, and soluble concentrate formulations for
use in California. Technical diuron is a white, crystalline, and odorless solid. Diuron is
registered for pre- and post emergent control using ground and aerial equipment. Diuron
is often applied in combination with other herbicides such as bromacil, hexazinone,
paraquat, thiadiazuron, imazapyr, monosodium, sodium chlorate, sodium metaborate, and
copper sulfate (U.S. EPA, 2004a). This assessment evaluates only those registered uses
which allow use in California.
Diuron is easily taken up by plants and rapidly translocated. Diuron primarily functions
by inhibiting the Hill reaction in photosynthesis, limiting the production of high-energy
compounds such as adenosine triphosphate (ATP) used for various metabolic processes.
Diuron is generally considered to be both mobile and persistent. It is relatively stable in
neutral water. In addition to aquatic photolysis, microbial degradation is the primary
factor in the degradation of diuron in aquatic environments.
Diuron is not expected to concentrate in aquatic organisms. Diuron is regulated as a
known ground water contaminant in California, where it has been detected in the 2 to 3
ppb range (online at http://www.cdpr.ca.gov). Because diuron has a low Henry's law
constant and a low vapor pressure, volatilization is considered insignificant.
At sufficient levels diuron residues in soil are toxic to plants. Residue levels are lower in
soils with low organic content. Residue half-lives are from one month to one year for the
parent, five months for a major degradate , and one month for a minor degradate.
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Degradate formation is summarized below. Some pineapple fields contained residues
three years after the last application.
Diuron degrades in the environment to four major (>10% of the applied parent) and four
minor (<10% of the applied parent) metabolites and impurities. The major metabolites
are: carbon dioxide (C02), N-(3,4-dichlorophenyl)-N-methylurea (DCPMU), N'-(3-
chlorophenyl)-N,N-dimethylurea (MCPDMU), and l,l-dimethyl-3-phenylurea (PDMU).
The minor metabolites include: 4-dichlorophenylurea (DCPU); 3,4-dichloroaniline (3,4-
DCA), N-(3-chlorophenyl)-N-methylurea (CPMU), and 3,3',4,4'-tetrachlorobenzene
(TCAB).
There were no acceptable toxicity studies on the major degradates identified in the
ECOTOX database. As a result, they will be assigned the same toxicity as the parent for
purposes of this assessment. Because the concentrations of parent diuron exceed levels
of concern by themselves (both in modeling and monitoring data), the non-inclusion of
degradates does not cause a different outcome for the "may affect" determination.
Therefore, this assessment only addresses ecological risks associated with exposures to
the parent compound.
Likewise, the minor degradates, 3,4-DCA and TCAB, will not be assessed further. 3,4
DCA is not a significant residue (< 1%) in any metabolism or hydrolysis study, and
TCAB is also a minor degradate (0.038 ppm) and is only found in the soil photolysis
study which is a minor degradation route for diuron.
Diuron contains two impurities from the manufacturing process, TCAB and 3,3',4,4'-
tetrachloroazoxybenzene (TCAOB), both 'dioxin-like' substances. TCAB levels between
0.15 and 28 ppm have been found in diuron samples tested. TCAOB is present at lower
levels. Since, these impurities have only been found at fairly low levels, they are not
residues of concern for diuron and will not be evaluated in this assessment.
Diuron is classified as a 'known/likely' carcinogen. EPA is required under the FFDCA,
as amended by FQPA, to develop a screening program to determine whether certain
substances (including all pesticide active and other ingredients) "may have an effect in
humans that is similar to an effect produced by a naturally occurring estrogen, or other
such endocrine effects as the Administrator may designate. " Following the
recommendations of its Endocrine Disruptor Screening and Testing Advisory Committee
(EDSTAC), EPA determined that there were scientific bases for including, as part of the
program, androgen and thyroid hormone systems, in addition to the estrogen hormone
system. EPA also adopted EDSTAC's recommendation that the Program include
evaluations of potential effects in wildlife. When the appropriate screening and/or testing
protocols being considered under the Agency's Endocrine Disrupter Screening Program
(EDSP) have been developed and vetted, diuron may be subjected to additional screening
and/or testing to better characterize effects related to endocrine disruption.
As noted in the 2003 Registration Eligibility Decision (RED), diuron has been
characterized as a "known/likely" carcinogen, based on urinary bladder carcinomas in
both sexes of the Wistar rat, kidney carcinomas in the male rat (a rare tumor), and
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mammary gland carcinomas in the female NMRI mouse. Because of this, the spatial
extent of the action area (i.e., the boundary where exposures and potential effects are less
than the Agency's LOC) for diuron cannot be determined. Therefore, it is assumed that
the action area encompasses the entire state of California, regardless of the spatial extent
(i.e., initial area of concern or footprint) of the pesticide use(s).
Since CRLFs exist within aquatic and terrestrial habitats, exposure of the CRLF, its prey
and its habitats to diuron are assessed separately for the two habitats. Tier-II aquatic
exposure models are used to estimate high-end exposures of diuron in aquatic habitats
resulting from runoff and spray drift from different uses. Peak model-estimated
environmental concentrations resulting from different diuron uses range from 3.76 to
4911 ppb for use on grasses grown for seed, and paved areas (impervious surfaces),
respectively. These estimates are supplemented with analysis of available California
surface water monitoring data from U. S. Geological Survey's National Water Quality
Assessment (NAWQA) program and the California Department of Pesticide Regulation
(CDPR). Particularly in the CDPR monitoring data, diuron is frequently detected and
exceeds levels of concern with values up to 160 ppb.
To estimate on-site diuron dietary exposures to the terrestrial-phase CRLF, and its
potential prey resulting from uses involving diuron applications, the T-REX model is
used for spray treatment. The AgDRIFT model is also used to estimate deposition of
diuron on off-site terrestrial and aquatic habitats from spray drift. The TerrPlant model is
used to estimate diuron exposures to terrestrial-phase CRLF habitat, including plants
inhabiting semi-aquatic and dry areas, from site run-off and spray drift. The T-HERPS
model is used to allow for further characterization of dietary exposures of terrestrial-
phase CRLFs relative to birds.
The effects determination assessment endpoints for the CRLF include direct toxic effects
on the survival, reproduction, and growth of the CRLF itself. Direct effects to the CRLF
in the aquatic habitat are based on toxicity information for freshwater fish, which are
generally used as a surrogate for aquatic-phase amphibians. In the terrestrial habitat,
direct effects are based on toxicity information for birds, which are used as a surrogate
for terrestrial-phase amphibians.
Given that the CRLFs 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 monocotyledonous (monocot) and dicotyledonous (dicot) plants.
Risk quotients (RQs) are derived as estimates of potential risk. Acute and chronic RQs
for animals and listed and non-listed plant RQs are compared to the Agency's levels of
concern (LOCs) to identify instances where diuron use within the action area has the
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potential to adversely affect the CRLF via direct toxicity or indirectly based on 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) or to modify its critical habitat. When RQs for each particular type of effect
are below their respective LOCs, the pesticide is determined to have "no effect" on the
CRLF or to modify its critical habitat. Where RQs exceed LOCs, a potential to cause
adverse effects is identified, leading to a conclusion of "may affect" for the CRLF and a
potential to modify its critical habitat. If a determination is made that use of diuron
within the action area "may affect" the CRLF, additional information is considered to
refine the potential for exposure and effects, and the best available information is used to
distinguish those actions that "may affect, but are not likely to adversely affect" (NLAA)
from those actions that are "likely to adversely affect" (LAA) the CRLF. Similarly for
critical habitat additional information is considered to refine the potential for exposure
and effects to distinguish those actions that do or do result in modification of its critical
habitat.
Based on the best available information, the Agency makes a May Affect, and Likely to
Adversely Affect determination for diuron exposure to the CRLF based on direct and
indirect effects to the aquatic- and terrestrial-phase CRLF. Further, registered uses of
diuron are anticipated to result in modification to critical habitat of the CRLF.
A summary of the risk conclusions and effects determinations for the CRLF and its
critical habitat is presented in Table 1.1 and Table 1.2. Use-specific determinations for
direct and indirect effects to the CRLF are provided in Table 1.3 and Table 1.4. Further
information on the results of the effects determination is included as part of the Risk
Description in Section 5.2. Given the LAA determination for the CRLF and potential
modification of designated critical habitat, a description of the baseline status and
cumulative effects for the CRLF is provided in Attachment II.
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Table 1.1 Effects Determination Summary for Effects of Diuron on the CRLF
Assessment
Endpoint
Etfeets
Determination 1
Basis for Determination
Survival,
growth, and/or
reproduction of
CRLF
individuals
LAA
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults) : The aquatic phase
amphibian acute LOCs for Listed species (0.05) are exceeded for most
uses of diuron in California. Acute RQs that exceed the Agency's LOC
range from 12.28 (paved areas) to 0.06 (papaya and walnut). Chronic
RQs that exceed the Agency's LOC for chronic exposure (1.0) range
from 131.85 (paved areas) to 1.26 (banana, plantain).
Terrestrial-phase (Juveniles and Adults): Refined acute dietary-based
RQs for CRLFs consuming large insects and small herbivore mammals
exceed the acute listed species LOC (0.1) for all uses of diuron except
Sorghum and Field Corn. The acute dietary-based RQs for CRLFs
consuming large insects exceed the acute listed species LOC for
Agricultural Rights-of-Way, Fencerows etc. No acute dietary based
LOCs were exceeded for CLRF consuming small insectivore mammals
and small terrestrial phase amphibians for any diuron use.
LAA
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary
productivity. LOCs for non-vascular plants are exceeded for all uses.
The RQs range from 2046.25 (paved areas) to 1.57 (grasses grown for
seed).
Aquatic invertebrates acute LOCs are exceeded. The acute RQs that
exceed the LOC range from 30.69 (paved areas) to 0.05 (cotton aerial
application). Chronic LOCs are exceeded for several uses. RQs that
exceed the Agency's LOC range from 21.21or paved areas to 1.02 for
bermudagrass.
RQs for vascular aquatic plants exceed the Agency's LOC (1.0) for
most uses. These range from 460.46 (paved areas) to 1.30 (hazelnut).
Terrestrial prey items, riparian habitat.
For small mammals, chronic dose based RQs exceed the Agency's
LOC (1.0) for most uses (Table 5.6). The dose based chronic RQs that
exceed the LOC range from 8.29 (Agricultural Rights-of-Way,
Fencerows, Hedgerows, Airports, etc.) to 1.31 (walnut). The dietary
based chronic RQs do not exceed the LOC for any uses. The RQs that
exceed the acute dose based LOC range from 0.41 (Agricultural Rights-
of-Way, Fencerows, Hedgerows, Airports, etc.) to 0.13 (Bermuda
grass, Blackberry, Boysenberry, Spearmint). For terrestrial phase
amphibians, the chronic LOC is exceeded for all uses of diuron and the
acute LOCs are exceeded for all uses except sorghum.
LOCs are exceeded for terrestrial riparian plants and for aquatic plants
from exposure to diuron from runoff or spray drift. Alteration of
riparian and vascular plants may result in alteration of temperature,
turbidity, and oxygen content. RQs for vascular aquatic plants exceed
the Agency's LOC (1.0) for most uses. These range from 460.46
(paved areas) to 1.30 (hazelnut).
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 the Critical Habitat Impact Analysis
Assessment
End point
Effects
Determination 1
Basis for Determination
Modification of
aquatic-phase
PCE
HM
Due to aquatic vascular and terrestrial plant communities being reduced
from all use sites, there is potential for alteration of channel/pond
morphology or geometry and/or increase in sediment deposition within
the stream channel or pond. These plant communities provide for
shelter, foraging, predator avoidance, and aquatic dispersal for juvenile
and adult CRLFs. In addition, there is potential for 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.
LOCs are exceeded for terrestrial riparian plants and for aquatic
vascular plants from exposure to diuron from runoff or spray drift.
LOCs for non-vascular plants are exceeded for all uses.
Modification of
terrestrial-phase
PCE
HM
The use of diuron at all use sites may create the following modification
of PCE: elimination and/or disturbance of upland habitat; ability of
habitat to support food source of CRLFs, elimination and/or
disturbance of dispersal habitat, reduction and/or modification of food
sources for terrestrial phase juveniles and adults, and alteration of
chemical characteristics necessary for normal growth and viability of
juvenile and adult CRLFs and their food source.
The RQs for vascular aquatic plants exceed the Agency's LOC (1.0) for
most uses of diuron in California. RQs for vascular aquatic plants
exceed the Agency's LOC (1.0) for most uses. These range from
460.46 (paved areas) to 1.30 (hazelnut). Use of diuron on most use
sites will exceed acute and chronic LOCs for many prey food items of
the CRLF. Food sources are reduced and the CRLF is therefore
indirectly affected.
The RQs for non-target terrestrial monocot and dicot plants inhabiting
semi-aquatic and upland dry areas exceed the Agency's LOC (1.0) for
all uses except for monocot plants exposed to sorghum applications
(Table 5.7). These exceedances range from 300.00 (semi-aquatic
plants exposed to non-agricultural aerial applications) to 0.19 (dicot
plants inhabiting dry areas exposed to sorghum applications). Several
diuron uses result in plant LOC exceedances from spray drift. These
exceedances range from 12.00 (dicot plants exposed to field corn
applications) to 1.13 (monocot plants exposed to cotton applications).
1 Habitat Modification (HM) or No effect (NE)
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Table 1.3 Diuron Use-specific Direct Effects Determinations1 for the CRLF
I sols)
Auiiiilie lliihiliil
lerreslriiil lliihiliil
Anile
( lironie
Aeule
(lironie-
AGRICULTURAL RIGHTS-OF-WAY / FENCEROWS/
HEDGEROWS
LAA
LAA
LAA
LAA
ALFALFA Ground
NE
NE
LAA
LAA
ALFALFA Aerial
NE
NE
LAA
LAA
APPLE
NE
NE
LAA
LAA
ARTICHOKE
LAA
NE
LAA
LAA
ASPARGUS
LAA
NE
LAA
LAA
BANANA/PLANTAIN
LAA
LAA
LAA
LAA
BLACKBERRY/BOYSENBERRY
LAA
LAA
LAA
LAA
BLUEBERRY
NE
NE
LAA
LAA
CITRUS
NE
NE
LAA
LAA
CORN, FIELD
NE
NE
NE
LAA
DEWBERRY
NE
NE
LAA
LAA
FILBERT (HAZELNUT)
NE
NE
LAA
LAA
GRAPE
NE
NE
LAA
LAA
LOGANBERRY, RASPBERRY (BLACK/RED)
NE
NE
LAA
LAA
OLIVE
NE
NE
LAA
LAA
PAPAYA
NE
NE
LAA
LAA
PEPPERMINT
NE
NE
LAA
LAA
PEACH
NE
NE
LAA
LAA
PEAR
NE
NE
LAA
LAA
PECAN
LAA
NE
LAA
LAA
SORGHUM
NE
NE
NE
LAA
SPEARMINT
LAA
LAA
LAA
LAA
WALNUT (ENGLISH/BLACK)
LAA
NE
LAA
LAA
WHEAT Pre Harvest
NE
NE
LAA
LAA
WHEAT Post Harvest
NE
NE
LAA
LAA
COTTON Ground
NE
NE
LAA
LAA
COTTON Aerial
NE
NE
LAA
LAA
AIRPORTS/ LANDING FIELDS, DRAINAGE
SYSTEMS, INDUSTRIAL AREAS (OUTDOOR),
SEWAGE DISPOSAL AREAS
LAA
LAA
LAA
LAA
BERMUDAGRASS
LAA
LAA
LAA
LAA
GRASSES GROWN FOR SEED
NE
NE
LAA
LAA
IRRIGATION SYSTEMS
LAA
LAA
LAA
LAA
ORNAMENTAL HERBACEOUS PLANTS
LAA
NE
LAA
LAA
NON-AGRICULTURAL RIGHTS OF WAY Ground
LAA
LAA
LAA
LAA
NON-AGRICULTURAL RIGHTS OF WAY Aerial
LAA
LAA
LAA
LAA
PAVED AREAS (PRIVATE
ROADS/SIDEWALKS)
LAA
LAA
LAA
LAA
UNCULTIVATED AGRICULTIRAL AREAS Ground
LAA
LAA
LAA
LAA
UNCULTIVATED AGRICULTIRAL AREAS Aerial
LAA
LAA
LAA
LAA
UNCULTIVATED NON-AGRICULTURAL AREAS
LAA
LAA
LAA
LAA
1 NE = No effect; MA/NLAA = May affect, but not likely to adversely affect; LAA = May affect and likely
to adversely affect
* No acceptable chronic data are available for amphibians or their avian surrogates by which to determine
chronic direct risks to the CRLF, therefore an LAA determination is made in the absence of these data and
because supporting information on linuron, a similar herbicide, exhibits chronic toxicity to these species.
7

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Table 1.4 Diuron Use-specific Indirect Effects Determinations1 Based on Effects to Prey
l Sl(S)
AI»;k-
A(|ii;ilk' Im
Auik-
i'i'U'l>r;ik's
(linink
TiTivsiri.il
liiM-i'k-hr.ik-s
(Auilc)
A(|ll;ilii-|
illU
Auik-
)h;isi- fni»s
llsli
(linink
1'iTivsiriiil
Auilc
-pliiisi- fni»s
('linink'"
Sni:iII \
Auik-
l.imm.ils
('linink'
AGRICULTURAL RIGIITS-OF-
WAY/FENCEROWS/
HEDGEROWS
LA A
LAA
LAA
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
ALFALFA Ground
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
ALFALFA Aerial
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
APPLE
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
ARTICHOKE
LA A
LAA
NE
NLAA
LAA
NE
LAA
LAA
NE
LAA
ASPARGUS
LA A
LAA
NE
NLAA
LAA
NE
LAA
LAA
NE
LAA
BANANA/PLANTAIN
LA A
LAA
NE
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
BLACKBERRY/
BOYSENBERRY
LA A
LAA
NE
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
BLUEBERRY
LA A
NE
NE
NLAA
NE
NE
LAA
LAA
NE
NE
CITRUS
LA A
NE
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
CORN, FIELD
LA A
NE
NE
NLAA
NE
NE
NE
LAA
NE
NE
DEWBERRY
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
FILBERT (HAZELNUT)
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
NE
GRAPE
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
LOGANBERRY,
RASPBERRY
(BLACK/RED)
LA A
NE
NE
NLAA
NE
NE
LAA
LAA
NE
NE
OLIVE
LA A
NE
NE
NLAA
NE
NE
LAA
LAA
NE
NE
PAPAYA
LA A
LAA
NE
NLAA
LAA
NE
LAA
LAA
NE
LAA
PEPPERMINT
LA A
NE
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
PEACH
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
PEAR
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
NE
PECAN
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
SORGHUM
LA A
LAA
NE
NLAA
NE
NE
NE
LAA
NE
NE
SPEARMINT
LA A
LAA
NE
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
WALNUT (ENGLISH/BLACK)
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
WHEAT Pre Harvest
LA A
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
NE
8

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I Sl(S)
AI»;k-
A(|ii;ilk' Im
.Willi-
iTU-l>r;ik-s
('liriuik
TiTivsiri.il
ln\iTli-l>i;ili-s
(.Willi-)
A(|ll;ilii-|
;ill(
.Willi-
>h;isi- fni»s
llsli
Ch in nil
Ti-nvsirkil
.Willi-
-ph.isi- fni»s
('liniiik'-'-
Sm:iII \
.Willi-
l.imm.ils
Ch milk
WHEAT Post Harvest
LAA
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
NE
COTTON Ground
LAA
NE
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
COTTON Aerial
LAA
LAA
NE
NLAA
NE
NE
LAA
LAA
NE
LAA
AIRPORTS/ LANDING
FIELDS, DRAINAGE
SYSTEMS, INDUSTRIAL
AREAS (OUTDOOR),
SEWAGE DISPOSAL
AREAS
LAA
LAA
LAA
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
BERMUDAGRASS
LAA
LAA
LAA
NLAA
NE
NE
LAA
LAA
LAA
LAA
GRASSES GROWN FOR SEED
LAA
NE
NE
NLAA
NE
NE
LAA
LAA
NE
NE
IRRIGATION SYSTEMS
LAA
LAA
NE
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
ORNAMENTAL
HERBACEOUS PLANTS
LAA
LAA
NE
NLAA
LAA
LAA
LAA
LAA
NE
LAA
NON-AGRICULTURAL
RIGHTS OF WAY Ground
LAA
LAA
LAA
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
NON-AGRICULTURAL
RIGHTS OF WAY Aerial
LAA
LAA
LAA
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
PAVED AREAS (PRIVATE
ROADS/SIDEWALKS)
LAA
LAA
LAA
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
UNCULTIVATED
AGRICULTIRAL AREAS
Ground
LAA
LAA
LAA
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
UNCULTIVATED
AGRICULTIRAL AREAS Aerial
LAA
LAA
LAA
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
UNCULTIVATED NON-
AGRICULTURAL AREAS
LAA
LAA
LAA
NLAA
LAA
LAA
LAA
LAA
LAA
LAA
1 NE = No effect; NLAA = May affect, but not likely to adversely affect; LAA = May affect and likely to adversely affect
* No acceptable chronic data are available for amphibians or their avian surrogates by which to determine chronic direct risks to the CRLF, therefore an LAA
determination is made in the absence of these data and because linuron, a similar herbicide, exhibits chronic toxicity to these species in the range of modeled
diuron surface water levels.
9

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Based on the conclusions of this assessment, a formal consultation with the U. S. Fish
and Wildlife Service under Section 7 of the Endangered Species Act should be initiated.
When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the species and its resources (i.e., food and habitat) are
not expected to be uniform across the action area. In fact, given the assumptions of drift
and downstream transport (i.e., attenuation with distance), pesticide exposure and
associated risks to the species and its resources are expected to decrease with increasing
distance away from the treated field or site of application. Evaluation of the implication
of this non-uniform distribution of risk to the species would require information and
assessment techniques that are not currently available. Examples of such information and
methodology required for this type of analysis would include the following:
•	Enhanced information on the density and distribution of CRLF life stages
within specific recovery units and/or designated critical habitat within the
action area. This information would allow for quantitative extrapolation
of the present risk assessment's predictions of individual effects to the
proportion of the population extant within geographical areas where those
effects are predicted. Furthermore, such population information would
allow for a more comprehensive evaluation of the significance of potential
resource impairment to individuals of the species.
•	Quantitative information on prey base requirements for individual aquatic-
and terrestrial-phase frogs. While existing information provides a
preliminary picture of the types of food sources utilized by the frog, it
does not establish minimal requirements to sustain healthy individuals at
varying life stages. Such information could be used to establish
biologically relevant thresholds of effects on the prey base, and ultimately
establish geographical limits to those effects. This information could be
used together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.
•	Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth or reproductive impairment
immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and
together with the information described above, a more complete prediction
of effects to individual frogs and potential modification to critical habitat.
10

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2.0	Problem Formulation
Problem formulation provides a strategic framework for the risk assessment. By
identifying the important components of the problem, it focuses the assessment on the
most relevant life history stages, habitat components, chemical properties, exposure
routes, and endpoints. The structure of this risk assessment is based on guidance
contained in U.S. EPA's Guidance for Ecological Risk Assessment (U.S. EPA 1998), the
Services' Endangered Species Consultation Handbook (USFWS/NMFS 1998) and is
consistent with procedures and methodology outlined in the Overview Document (U.S.
EPA 2004) and reviewed by the U.S. Fish and Wildlife Service and National Marine
Fisheries Service (USFWS/NMFS 2004).
2.1	Purpose
The purpose of this endangered species assessment is to evaluate potential direct and
indirect effects on individuals of the federally threatened California red-legged frog
(Rana aurora draytonii) (CRLF) arising from FIFRA regulatory actions regarding use of
diuron on terrestrial food, feed, forestry, non-food, and outdoor residential sites. In
addition, this assessment evaluates whether diuron use on these crops 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 etal. (Case No. 02-1580-JSW (JL)) settlement
entered in Federal District Court for the Northern District of California on October 20,
2006.
Diuron is a broad-spectrum residual herbicide registered for pre-emergent and post-
emergent control of both broadleaf and annual grassy weeds. When diuron is used on
pre-emergent weeds, it allows seeds to germinate normally, but causes them to lose their
green color, after which they soon die of starvation (Ferrell et al., 2004). In the U.S.
diuron is used on a variety of fruit and nut crops, grains, cotton, corn, sorghum, mint,
gum, asparagus, sugarcane, seed crops, coffee, hay, cut flowers, and for fallow and idle
cropland use. It may be used in irrigation and drainage systems when water is not
present.
It is also used to control weeds on hard surfaces, such as, roads, railway tracks, and paths
(at around 3 kg/ha), and to control weeds in crops, such as, pear and apple trees, forestry,
ornamental trees and shrubs, pineapples, sugar cane, cotton, alfalfa and wheat (at lower
rates of around 1.8 kg/ha). It can be used for both pre-emergent and knockdown weed
control. Its use in some locations is becoming limited due to the development of resistant
weed species. In some products it is combined with other active ingredients such as
glyphosate, bromacil, hexazinone, amitrole and 2,4-D. In some countries diuron is also
registered for aquatic weed control, as a cotton defoliant, and for use in home aquaria and
fish ponds. It is used as a booster biocide in antifouling paints where its activity
enhances the efficacy of copper in these products.
11

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In this assessment, direct and indirect effects to the CRLF and potential modification to
its designated critical habitat are evaluated in accordance with the methods described in
the Agency's Overview Document (U.S. EPA 2004). Screening level methods include
use of standard models such as PRZM-EXAMS, T-REX, TerrPlant, and AgDRIFT, all of
which are described at length in the Overview Document. Additional refinements
include use of the T-HERPS model. 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 diuron 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
LOCs. It is acknowledged that the action area for a national-level FIFRA regulatory
decision associated with a use of diuron may potentially involve numerous areas
throughout the United States and its Territories. However, for the purposes of this
assessment, attention will be focused on relevant sections of the action area including
those geographic areas associated with locations of the CRLF and its designated critical
habitat within the state of California. As part of the "effects determination," one of the
following three conclusions will be reached regarding the potential use of diuron 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 LOC exceedances) upon individual CRLFs or upon the PCEs of the species'
designated critical habitat, a "no effect" determination is made for use of diuron 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
CRLFs designated critical habitat, a preliminary "may affect" determination is made for
the FIFRA regulatory action regarding diuron.
If a determination is made that use of diuron 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
12

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vertebrates and invertebrates, aquatic plants, riparian vegetation, etc.). Additional
information, including spatial analysis (to determine the geographical proximity of CRLF
habitat and diuron use sites) and further evaluation of the potential impact of diuron 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 diuron is expected to directly impact living organisms within the action area
(defined in Section 2.7), critical habitat analysis for diuron is limited in a practical sense
to those PCEs of critical habitat that are biological or that can be reasonably linked to
biologically mediated processes (i.e., the biological resource requirements for the listed
species associated with the critical habitat or important physical aspects of the habitat that
may be reasonably influenced through biological processes). Activities that may modify
critical habitat are those that alter the PCEs and appreciably diminish the value of the
habitat. Evaluation of actions related to use of diuron that may alter the PCEs of the
CRLFs critical habitat form the basis of the critical habitat impact analysis. Actions that
may affect the CRLFs designated critical habitat have been identified by the Services and
are discussed further in Section 2.6.
2.2 Scope
Diuron is registered in California for a variety of agricultural and non-agricultural uses
(see Table 2.2).
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 diuron in accordance with the approved product labels for
California is "the action" relevant to this ecological risk assessment.
Although current registrations of diuron allow for use nationwide, this ecological risk
assessment and effects determination addresses currently registered uses of diuron in
portions of the action area that are reasonably assumed to be biologically relevant to the
CRLF and its designated critical habitat. Further discussion of the action area for the
CRLF and its critical habitat is provided in Section 2.7.
The major route of dissipation for diuron is microbial degradation in water. Here the
major metabolism degradate is N'-(3-chlorophenyl)-N,N-dimethylurea (MCPDMU).
Diuron also degrades through photolysis in both water and soil; here the major degradates
13

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are C02 and N'-(3,4-dichlorophenyl)-N-methylurea (DCPMU), respectively. A more
detailed discussion of the major and minor degradates formed in the decomposition of
diuron is presented in Section 2.4.
The Agency does not routinely include, in its risk assessments, an evaluation of mixtures
of active ingredients, either those mixtures of multiple active ingredients in product
formulations or those in the applicator's tank. In the case of the product formulations of
active ingredients (that is, a registered product containing more than one active
ingredient), each active ingredient is subject to an individual risk assessment for
regulatory decision regarding the active ingredient on a particular use site. If effects data
are available for a formulated product containing more than one active ingredient, they
may be used qualitatively or quantitatively in accordance with the Agency's Overview
Document and the Services' Evaluation Memorandum (U.S., EPA 2004; USFWS/NMFS
2004).
Diuron has registered products that contain multiple active ingredients. However, there
are no available data on mixtures containing diuron in the open literature. There are no
product LD50 values, with associated 95% Confidence Intervals (CIs) available for diuron
among the data submitted to the Agency. The assessment will be based on the toxicity of
a single active ingredient of diuron. Analysis of the available open literature and acute
mammalian toxicity data for multiple active ingredient products relative to the single
active ingredient is provided in Appendix A.
As discussed in USEPA (2000) a quantitative component-based evaluation of mixture
toxicity requires data of appropriate quality for each component of a mixture. In this
mixture evaluation, an LD50 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 formulated products for diuron do not have LD50 data available it is not
possible to undertake a quantitative or qualitative analysis for potential interactive effects.
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 diuron is the only reasonable approach that employs the available data
to address the potential acute risks of the formulated products.
2.3 Previous Assessments
Diuron has been registered in the United States since 1967 for use as an herbicide,
mildewcide and algaecide. A Registration Standard, titled "Guidance for the
Reregi strati on of Pesticide Products Containing Diuron as the Active Ingredient"
was released in 1983. The Registration Standard involved a thorough review of
the scientific data base underlying pesticide registrations and an identification of
essential but missing studies which may not have been required when the product
was initially registered or studies that were considered insufficient. Subsequent
Data Call-Ins (DCIs) were issued in 1990, and 1995 for diuron.
14

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In 2003, the Office of Pesticide Programs (OPP) requested the initiation of ESA section
7(a) (2) consultation regarding the potential impact of diuron on the Evolutionary
Significant Units (ESU) of the Pacific salmon and steelhead. OPP determined that the
use of diuron on certain crops (peaches, walnuts, filberts) may affect 10 ESUs at
application rates above 3.2 lb ai/A, may affect 7 ESUs at application rates above 2.2 lb
ai/A, and will have no effect on 10 ESUs at any labeled agricultural rate. The use of
diuron for non-crop sites, especially rights-of-way, may affect 25 ESUs, may affect but is
not likely to adversely affect one ESU, and will have no effect on one ESU.
To mitigate risks of concern posed by the use of diuron, EPA in its Reregi strati on
Eligibility Decision (RED) for diuron, dated September 2003, noted a number of label
amendments identified by EPA or agreed to by the registrant(s) to address the worker,
residential and ecological concerns; these included:
•	All wettable powder products will be voluntarily canceled.
•	Reduction in application rate and increased treatment intervals, and limit on the
number of applications for some crops.
•	Use of the backpack sprayer is prohibited.
•	Implement use of PPE and engineering controls for some workers.
•	Eliminate aerial applications except for rights-of-way, alfalfa, cotton, winter
barley, winter wheat, sugarcane, and grass seed crops.
•	Implement best management practices to reduce spray drift.
2.4 Stressor Source and Distribution
2.4.1 Environmental Fate Properties
The environmental fate database for diuron is essentially complete. Diuron is stable in
neutral media at normal temperatures, and is hydrolyzed by acid and alkalis. It is stable
towards oxidation and moisture under normal conditions and decomposes at 180-190° C
(Helliwell et al., 1998).
Diuron is mobile and has the potential to leach to groundwater and to contaminate surface
waters. An upgradable adsorption/desorption/leaching study (MRID 44490501) showed
that diuron has an average Koc value of 920 and Freundlich Kads values (7.9-28). Sorption
of diuron to soil is highly correlated with soil organic matter. In addition, diuron has
-8
relatively low water solubility (42 ppm) and low volatility (6.9 x 10 mm Hg at 25° C).
Although stable to hydrolysis at pH 5, 7, and 9, the minor degradate 3,4-dichloroaniline
(3,4-DCA) was identified in all hydrolysis test solutions (0.5% of applied). The
calculated half-lives for diuron in aqueous and soil photolysis studies were found to be 43
and 173 days respectively.
In soil, the photolysis degradate were all minor, N'-(3,4-dichlorophenyl)-N-methylurea
(DCPMU) at 3.6 percent, demethylated DCPMU (DCMU), 3,4-dichloroaniline (3,4-
DCA), and 3,3',4,4'-tetrachlorobenzene (TCAB) at 0.7 percent, 0.370 ppm, and 0.038
15

-------
ppm respectively. The calculated half-lives in aerobic and anaerobic soil metabolism
studies were 372 (aerobic) and 1,000 (anaerobic) days. Under aerobic conditions, the
major degradate was DCPMU (20.9-22.5 % of the amount applied at 365 days), and
minor degradates were DCPU and CO2. Under anaerobic conditions, the only major
degradate identified was DCPMU, which accounted for a maximum of 10.3% of applied
(at 45 days).
In contrast to its persistence in laboratory studies of hydrolysis, aqueous and soil
photolysis, and aerobic and anaerobic soil metabolism, diuron degraded relatively quickly
in aquatic metabolism laboratory studies, with a half-life of 33 days under aerobic
conditions and of 5 days under anaerobic conditions. The major metabolism degradate
under aerobic conditions was N'-(3-chlorophenyl)-N,N-dimethylurea (MCPDMU) which
reached 25 % of the applied dose by the end of the study and was evenly distributed
between the soil and aqueous phase. Other degradates identified were DCPMU (9.2
percent) and CPMU (8 percent), and were primarily associated with the soil phase. The
three major degradates under anaerobic conditions were MCPDMU which was mainly
associated with the aqueous phase, l,l-dimethyl-3-phenylurea (PDMU), and CPMU.
In terrestrial field dissipation studies in FL, MS, and CA with sand, silt loam, and silty
clay loam soils, diuron dissipated in bare ground plots with half-lives of 73, 139, and
133 days, respectively. The major degradate DCPMU dissipated in the same plots
with half-lives of 217, 1733, and 630 days. In aquatic field dissipation studies, half-
lives were 115-177 days and the major degradate was DCPMU. These studies were
conducted in drainage channel berms and soil, and thus should be compared
quantitatively to soil laboratory studies, not aquatic studies.
The environmental degradates of toxicological concern to humans and other non-target
species include 3,4-DCA and TCAB. However, EPA's Metabolism Assessment Review
Committee (MARC) has concluded that residues of 3,4-DCA is not a residue of concern
for diuron as 3,4-DCA (<1%) was not a significant residue in any metabolism or
hydrolysis study. Moreover, TCAB (0.038 ppm) residue was only found in the soil
photolysis study which is a minor route of degradation for diuron.
Degradation half-lives for the parent are presented in Table 2.1. This table also presents
the major and minor degradates of the parent compound. The chemical structures of
diuron and the metabolites (DCPMU, DCPU, DCA, and MCPDMU) are presented in
Appendix B.
16

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Table 2.1 Summary of Diuron Half-lives
Study
Value (units)
Major Dcgradatcs
Minor Degradates
IMRID #
Hydrolysis
Stable at pH 5, 7, 9
3,4-DCA (-2%)
41418804
Direct
Aqueous
Photolysis
T ./2 = 43 days
C02
41418805
Soil
Photolysis
T ./2 = 173 days
DCPMU (3.6%)
DCMU (< 0.7%), 3,4-
DCA (0.370ppm), TCAB
(0.038 ppm)
41719302
Aerobic Soil
Metabolism
T ./2 = 372 days
DCPMU (22.5%)
DCPU (3.4%), C02
(3.36%)
41719303
Anaerobic
Soil
Metabolism
T ./2 = 1,000 days
DCPMU (10.3 %)
41418806
Anaerobic
Aquatic
Metabolism
T >/2 = 5
MCPDMU (83%)
PDMU (13%), mCPMU
(23%)
42661901
Aerobic
Aquatic
Metabolism
T ¦/, = 33
MCPDMU (25%)
DCPMU (9.2%), CPMU
(8%)
42260501
Kd-ads / Kd-des
(mL/g)
14
Material balances were
not reported.
44490501
Terrestrial
Field
Dissipation
Sand = 73 days
Silt Loam =139 days
Silty Clay Loam =133
days
DCPMU (Sand = 217
days, Silt Loam = 1733
days, Silty Clay Loam =
630 days)
44654001
44865001
2.4.2 Environmental Transport Mechanisms
AIR
Diuron is applied by broadcast or band spray on soil surface using ground or aerial
equipment, suggesting that there is a possibility of drift. Drift is quantitatively
considered in the exposure assessment. However, diuron is non-volatile, as indicated by
its low vapor pressure of 6.90 xlO"8 mm Hg (25° C), and a low Henry's law constant of
5.10 x 10"10 atm m3 mol"1. These properties indicate that diuron is unlikely to be
dispersed in air over a large area and has a low tendency to volatilize from water or moist
soils. Volatilization is insignificant except when diuron is exposed on the soil surface for
several days or weeks under hot, dry conditions (Hess and Warren, 2002).
17

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WATER
Diuron's K0c (468-1666) indicates a relatively low tendency to sorb to soils and
sediments, while its hydrolysis and aqueous photolysis half-lives are relatively long.
Consequently diuron is both mobile and relatively persistent, and is therefore prone to
off-site movement in surface runoff, and migration to ground water. As discussed in the
field monitoring studies below, diuron in runoff water is above Agency LOCs for direct
effects on the CRLF (fish LC50 of 400 to 710 ppb).
Andrieux et al. (1997) assessed losses of diuron via runoff from vineyards under natural
Mediterranean climate conditions. During the growing season of 1994 and 1995, runoff
and diuron concentrations were monitored at two field sites, one tilled and one under no-
till management. Despite a time lag of greater than 4 months between application and the
first runoff event in 1994, diuron concentrations in overland flow exceeded 200 ug/L at
the no-till in both years of investigations. In 1995, the first strong rainfall following
application removed 60% of total diuron runoff loss at both sites, although it accounted
for 17 and 7% of the total seasonal runoff volume at the no-till and tilled site,
respectively. In 1995, seasonal diuron loss at the no-till sites was 1.71 % and at the tilled
site was 0.68%. No herbicide residues were detected in soil samples collected 1 week
prior to chemical spraying in 1994 and 1995. The authors suggested that moderate
temperatures and moisture conditions during winter facilitated complete microbial
decomposition. In four-months of soil sampling following herbicide treatment there were
no detections below a soil depth of 2 cm at the no-till plot. However, at the tilled site,
pesticides were present in samples at depths of 0-15 cm 17 days after spraying to three
months. The authors suggested that infiltration increases attributable to tillage effects
accounted for diuron distribution in the soil profile. The authors concluded that the
persistence of diuron coupled with tillage may provide the potential for leaching.
In contrast, no-till practices have been shown to contribute to ground water
contamination under certain California conditions.
Braun and Hawkins (1991) conducted a rainfall runoff monitoring study in a citrus-
growing region of Tulare County, California, where growers commonly avoid cultivation
of citrus row middles. The row middles under such a management practice are typically
compacted, with low infiltration rates and a high tendency to yield runoff during storm
events. One method of disposing of excess runoff water in the area is to utilize dry wells
that allow drainage of run off through the shallow hard-pan soil layer. This mechanism
allows direct introduction of residues to the subsurface and subsequent potential
migration to shallow ground water. Although diuron applications had occurred at least 2
months prior to sampling, relatively high concentrations of diuron in runoff water
entering dry wells were found, ranging up to 890 |ig L"1. The data provide strong
evidence that the widespread regional presence of diuron in ground water is at least
partially attributable to contaminated runoff water entering dry wells.
Spurlock et al. (1997) examined the runoff of diuron, simazine, and bromacil from citrus
orchard middles under simulated rainfall conditions. Peak diuron runoff concentrations
were comparable to those reported by Braun and Hawkins (1991), ranging from 600 to
18

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1700 jug L"1. Little difference in runoff concentrations of the three pre-emergent
herbicides was observed indicating that herbicide substitution would be an ineffective
mitigation measure. They concluded that low soil permeability arising from hardpan
layers or compaction drives the runoff process. These same factors are probably
responsible for diuron off-site movement in runoff water from rights-of-way because
rights-of-way are generally engineered to maximize water run off.
Powell et al. (1996) studied off-site movement of diuron in surface water from a highway
shoulder right-of-way application. Diuron was applied in a spray to a 2.4-meter wide
strip next to the highway pavement, at a rate of 3.59 kg diuron ha"1. Simulated rain (13
mm in 1 hr) was applied to plots on treated highway shoulders at three sites. Diuron was
detected at two of three sites. Concentrations of diuron were as high as 1770 |ig L"1 in
runoff (combined water and sediment), from sampling conducted one day after herbicide
application. From 0.2 to 5.4% of the diuron applied to highway shoulders moved off-site
in runoff during the simulations. Simulated rain was applied to treated highway shoulder
at intervals of 0, 2, and 4 wk after herbicide application. The highest percentages were
observed when rain was simulated 1 day after herbicide application. Diuron is typically
applied in winter or early spring during California's rainy season to control weeds. This
practice, coupled with relatively high use, is one reason why diuron is commonly
detected pesticides in California surface water. Diuron was detected in more than half of
955 surface water samples analyzed and reported in DPR's surface water database.
Typical reporting limits for the diuron analyses are 0.05 -0.10 jug4. While detected
concentrations range from 0.01 to 30.6 |ig L1, the majority of concentrations range from
0.1 to 1 |ig L'. These concentrations were approximately equal to the 20th and 80th
percentiles of detected concentrations. The highest concentrations and most frequent
detections occur during December-March, which coincides with both the rainy season
and the peak diuron application season.
Microbes are the primary agents in the degradation of diuron in aquatic environments.
The aerobic biodegradation pathway for diuron is well established, proceeding by
successive demethylation steps to form DCPMU, DCPU [l-(3,4-dichlorophenyl)urea]
and DCA (3,4-dichloroaniline). Reductive dechlorination has been observed in anaerobic
pond sediments and leads to the formation of the dechlorinated product, 3-(3-
chlorophenyl)-l,l dimethylurea (Field et al., 1997). Boule et al. (1997) reported that the
major photoproducts observed in the photolysis of diuron [3-(3,4-dichlorophenyl)-l,l-
dimethylurea] in aqueous solution resulted from a heterolytic substitution of chlorine by
OH. A wavelength effect was observed: at 254 nm the formation of 3-(4-chloro-3-
hydroxyphenyl)-1,1-dimethylurea accounted for more than 90% of the conversion,
whereas when the solution was irradiated in 'black light' (85% of photons emitted at 365
nm, about 7% at 344 nm), the major photoproduct was 3-(3-chloro-4-hydroxyphenyl)-
1,1-dimethylurea. However, as noted previously, photolysis is not generally a principal
route of diuron degradation in aqueous systems.
SOIL
Diuron is moderately to highly persistent and mobile in soils. The commonly reported
average field dissipation half-life is 115 days (MRID 44654001), although such half-lives
19

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are typically highly variable. Phytotoxic residues generally dissipate within a season
when applied at low selective rates. At higher application rates, residues may persist for
more than one year (Kidd and James, 1991). Microbial degradation is the primary means
of diuron dissipation from soil. Photodegradation is not considered a primary dissipation
route, but losses can be significant if diuron remains on the soil surface for several days
or weeks (Hess and Warren, 2002). Mobility in the soil is related to organic matter and
to the type of the residue. The metabolites are less mobile than the parent. Similar to
many other pesticides, diuron sorption is highly correlated with organic matter (Spurlock
andBiggar, 1994). Consequently leaching is greatest in low organic matter soils. Other
soil conditions that favor diuron leaching include high soil permeability to water, such as
in coarse soils.
Due to the diuron's persistence and mobility, the herbicide is commonly detected in
California's ground water (Troiano et al., 2001). As of June 2004, there were confirmed
detections of diuron in 418 California water wells reported in DPR's well inventory
database (WIDB). Typical diuron reporting limits in the WIDB are 0.05 |ig L"1, and
detected diuron concentrations range up to 3.96 |ig L \ Diuron's use is regulated under
DPR's ground water protection regulations (online at http://www.cdpr.ca.gov).
In a right-of-way runoff study by Powell et al. (1996) post-simulation and end of season
soil cores at the two sites with measurable runoff had detectable diuron residues only in
the top 15 cm (0.5 ft). However, cores taken prior to application had diuron down to 0.30
m, presumably from the past year's application. At a third simulated rainfall site, no
runoff left the plots. The absence of detectable residues in soil to a depth of 3.0 m (10 ft)
suggests that much of the herbicide applied to the shoulder may have leached rapidly
through the coarse gravelly soil. The soil data was insufficient to yield definite
conclusions about leaching in infiltration areas. However, the levels of diuron found in
runoff suggest that dry wells, if present, would provide an important conduit for the
transport of diuron to groundwater. The authors concluded that rights-of-ways with high
percentages of gravel and sand in the soil may be of concern, since diuron may be
transported rapidly to depths greater than 0.3 m.
Bogarets et al. (2000) studied diuron's microbial degradation and ecotoxicology to
investigate its fate after application to soils. Quantitative biodegradation assays were
executed with fungal strains, showing that diuron was degraded but not entirely
mineralized. A series of tests were carried out to choose the most efficient fungal strain
for diuron degradation. Among the fungal strains tested, only three were able to
transform diuron to any extent (up to 50%) after 7 days of incubation: B. bassiana, C.
elegans, and M. isabellina. No degradation occurred using fungal strains: F. oxysporum
and G. candidum. Although C. elegans was the most efficient since there was no diuron
remaining after seven days of incubation. Diuron degradation by the three fungal strains
led to the formation of two metabolites obtained in different ratios according to the
microorganism. For the three fungal strains, diuron degradation led to the formation of
the demethylated products. The identified metabolites were synthesized in sufficient
amounts to confirm their structures and determine their non-target toxicity using four
biotests. According to the Microtox test, the metabolites N- (3,4-dichlorophenyl)-N-
20

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methylurea and N-3, 4-dichlorophenylurea presented a three times higher toxicity than
that of diuron.
2.4.3	Mechanism of Action
Diuron is a systemic substituted phenylurea herbicide. Diuron is taken up by plants and
rapidly translocated. Diuron primarily functions by inhibiting the Hill reaction in
photosynthesis, limiting the production of high-energy compounds such as adenosine
triphosphate (ATP) used for various metabolic processes. Diuron binds to the Qb-
binding niche on D1 protein of the photosystem II complex in chloroplast thylakoid
membranes, thus blocking electron transport from QAto Qb. This process prevents CO2
fixation and the production of ATP and other high energy compounds which are needed
for plant growth. The inability to reoxidize Qa promotes the formation of triplet state
chlorophyll, which interacts with ground state oxygen to form singlet oxygen. Both
triplet chlorophyll and singlet oxygen can extract hydrogen from unsaturated lipids,
producing a lipid radical and initiating a chain reaction of lipid peroxidation. Lipids and
proteins are attacked and oxidized, resulting in loss of chlorophyll and carotenoids, and in
leaky membranes which cause cells and cell organelles to dry and disintegrate rapidly
(Hess and Warren, 2002).
2.4.4	Use Characterization
There are currently 72 product registrations for diuron including two Special Local Needs
registrations in California.
Diuron contains two significant impurities from the manufacturing process 3,3',4,4'-
tetrachloroazobenzene (TCAB) and 3,3',4,4'-tetrachloroazoxybenzene (TCAOB), both
'dioxin-like' substances that are known to cause a skin disease known as chloracne.
TCAB levels between 0.15 and 28 ppm have been found in diuron samples tested.
TCAOB is present at lower levels. Since these residues appear to be present at
insignificant levels, they are not assessed further in this assessment.
In addition to agricultural uses, diuron also has widespread use in non-agricultural
applications, especially industrial and rights of way uses, where often in combination
with other herbicides it provides total vegetation control. These applications include
along fence lines, pipelines, powerlines, railway lines, roads, footpaths; in timber yards
and storage areas; and around commercial, industrial and farm buildings, electrical
substations, and petroleum storage tanks. It has some use as an algaecide in ornamental
ponds, fountains, and aquaria, but not natural water bodies.
Diuron is one of the most commonly used pesticides in California. Reported statewide
use in 2002 was 1,303,745 pounds. Of this reported use, 48 percent was applied to rights
of way, followed by 18 percent and 14 percent on alfalfa and oranges, respectively.
Additional 2002 uses in California included grapes (4.3 percent), landscape maintenance
(3.7 percent), walnuts (2.6 percent), and cotton (1.6 percent). Diuron use has been
reported in all 58 counties in California.
21

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Diuron is often used in combination with other herbicides such as bromacil, hexazinone,
paraquat, thiadiazuron, imazapyr monosodium, sodium chlorate, sodium metaborate, and
copper sulfate (U.S. EPA, 2004a).
Diuron is available in wettable powder, granular, flowable, pelleted/tableted, liquid
suspension, and soluble concentrate formulations. However, true granular applications
are not allowed in California and are therefore not assessed further in this document.
Diuron is applied using the following equipment: groundboom sprayer, aerial equipment,
chemigation, rights-of-way sprayer, high-pressure handwand, low-pressure handwand,
tractor-drawn spreader, granular backpack spreader (since true granular applications are
not allowed in California, this application method will not be assessed), push-type
spreader, airless sprayer, paintbrush, shaker-type applicator, backpack sprayer, belly
grinder, and by hand. .
For agricultural uses, labeled single application rates range from 0.4 to 12 lbs active
ingredient (ai) per acre (A). For non-agricultural uses labeled rates are 12 lbs ai/acre.
Diuron may be applied to non-agricultural areas 1 to 2 times per year.
A national map showing the estimated poundage of diuron used for agricultural purposes
in 2002 by county is presented in Figure 2.1. The map was obtained from the U. S.
Geological Survey (USGS), National Water Quality Assessment Program (NAWQA)
website (URL: http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=02&map=ml991).
22

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DIURON - herbicide
2002 estimated annual agricultural use
Crops
Total
Percent
pounds applied
national use
citrus fruit
1233611
35.75
cotton
1001843
29.03
sugarcane
396903
11.50
alfalfa hay
290978
8.43
grapes
127492
3.69
apples
69420
2.01
asparagus
66251
1.92
field and grass seed crop
61094
1.77
pecans
42615
1.23
walnuts
34338
1.00
Average annual use of
active ingredient
(pounds per square mile of agricultural
land in county)
I	I	no estimated use
~	0.001 to 0.006
~	0.007 to 0.03
~	0.031 to 0.133
~	0.134 to 1.026
¦	>=1.027
Source: USGS, 2002
Figure 2.1 Diuron Agricultural Use in Total Pounds per County
Analysis of labeled use information is the critical first step in evaluating the federal
action. The current label for diuron 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 allowed in California that will be focused on in this
assessment along with the corresponding scenarios used for the Tier II aquatic modeling.
Please see Section 3.0 for further explanation.
23

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Table 2.2 Active Use Sites for Diuron as Applicable to Ca
ifornia
('nip
Si'i'ii;iriii
AGRICULTURAL RIGHTS-OF-WAY/FENCEROWS/HEDGEROWS
CA impervious RLF and CA
residential RLF
ALFALFA
CA alfalfa OP
APPLE, PEACH, PEAR
CA fruit STD
ARTICHOKE, ASPARGUS
CA row crop RLF
BANANA, PLANTAIN, PAPAYA
CA avocado RLF
BLACKBERRY, BOYSENBERRY, DEWBERRY, LOGANBERRY,
RASPBERRY (BLACK/RED)
OR Berries OP
BLUEBERRY
CA wine grapes RLF
CITRUS
CA citrus STD
CORN, FIELD
CA corn OP
FILBERT (HAZELNUT), PECAN, WALNUT (ENGLISH/BLACK)
CA almond STD
GRAPE
CA grapes STD
OLIVE
CAOliveRLF - V2
PEPPERMINT, SPEARMINT
OR mint STD
SORGHUM, WHEAT
CA wheat RLF
\.iii-I-'.hi(I/I-\v(I ( nips

COTTON
CA cotton STD
Nuii-Cnip I.iiihI

AIRPORTS/ LANDING FIELDS, DRAINAGE SYSTEMS, INDUSTRIAL
AREAS (OUTDOOR), SEWAGE DISPOSAL AREAS. PAVED AREAS
(PRIVATE ROADS/SIDEWALKS)
CA impervious RLF
BERMUDAGRASS
CA rangeland hay RLF
GRASSES GROWN FOR SEED
CA turf RLF
IRRIGATION SYSTEMS
CA residential RLF
ORNAMENTAL HERBACEOUS PLANTS
CA Nursery
NON-AGRICULTURAL RIGHTS OF WAY
CA impervious RLF and CA
residential RLF
UNCULTIVATED AG, UNCULTIVATED NON-AG
CA Rangeland Hay_V2 RLF
* Uses provided by BEAD - July 23, 2008, Scenarios provided by EFED
24

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The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis
of both national- and county-level usage information (Kaul and Jones, 2006) using state-
level usage data obtained from USDA-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 diuron by county in this California-
specific assessment were generated using CDPR PUR data. Four years (2002-2005) of
usage data were included in this analysis. Available 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 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 five years. The units of area treated are
also provided where available. A summary of diuron usage for all California use sites is
provided in Appendix C, and a summary of the CDPR PUR usage data can be found in
Appendix D.
2.5 Assessed Species
The CRLF was federally listed as a threatened species by USFWS effective June 24,
1996 (USFWS 1996). It is one of two subspecies of the red-legged frog and is the largest
native frog in the western United States (USFWS 2002). A brief summary of information
regarding CRLF distribution, reproduction, diet, and habitat requirements is provided in
Sections 2.5.1 through 2.5.4, respectively. Further information on the status, distribution,
and life history of and specific threats to the CRLF is provided in Attachment I.
Final critical habitat for the CRLF was designated by USFWS on April 13, 2006
(USFWS 2006; 71 FR 19244-19346). Further information on designated critical habitat
for the CRLF is provided in Section 2.6.
2.5.1 Distribution
The CRLF is endemic to California and Baja California (Mexico) and historically
inhabited 46 counties in California including the Central Valley and both coastal and
interior mountain ranges (USFWS 1996). Its range has been reduced by about 70%, and
the species currently resides in 22 counties in California (USFWS 1996). The species has
an elevational range of near sea level to 1,500 meters (5,200 feet) (Jennings and Hayes
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.eov/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.
25

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1994); however, nearly all of the known CRLF populations have been documented below
1,050 meters (3,500 feet) (USFWS 2002).
Populations currently exist along the northern California coast, northern Transverse
Ranges (USFWS 2002), foothills of the Sierra Nevada (5-6 populations), and in southern
California south of Santa Barbara (two populations) (Fellers 2005a). Relatively larger
numbers of CRLFs are located between Marin and Santa Barbara Counties (Jennings and
Hayes 1994). A total of 243 streams or drainages are believed to be currently occupied
by the species, with the greatest numbers in Monterey, San Luis Obispo, and Santa
Barbara counties (USFWS 1996). Occupied drainages or watersheds include all bodies
of water that support CRLFs (i.e., streams, creeks, tributaries, associated natural and
artificial ponds, and adjacent drainages), and habitats through which CRLFs can move
(i.e., riparian vegetation, uplands) (USFWS 2002).
The distribution of CRLFs within California is addressed in this assessment using four
categories of location including recovery units, core areas, designated critical habitat, and
known occurrences of the CRLF reported in the California Natural Diversity Database
(CNDDB) that are not included within core areas and/or designated critical habitat (see
Figure 2.2). 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 USFWS to be important in the preservation of the species. Designated
critical habitat is generally contained within the core areas, although a number of critical
habitat units are outside the boundaries of core areas, but within the boundaries of the
recovery units. Additional information on CRLF occurrences from the CNDDB is used
to cover the current range of the species not included in core areas and/or designated
critical habitat, but within the recovery units.
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.
26

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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
CD Recovery Unit Boundaries ^
|j Currently Occupied Core Areas
| Critical Habitat
| CNDDB Occurence Sections
County Boundaries	g
180 Miles
_l
Core Areas
1.
Feather River
19.
Watsonville Slough-Elkhorn Slough
2.
Yuba River- S. Fork Feather River
20.
Carmel River — Santa Lucia
3.
Traverse Creek Middle Fork/ American R. Rubicon
21.
Gahlan Range
4.
Cosumnes River
22.
Estero Bay
5.
South Fork Calaveras River*
23.
Arroyo Grange River
6.
Tuolumne River*
24.
Santa Maria River — Santa Ynez River
7.
Piney Creek*
25.
Sisquoc River
8.
Cottonwood Creek
26.
Ventura River — Santa Clara River
9.
Putah Creek - Cache Creek*
27.
Santa Monica Bay —Venura Coastal Streams
10.
Lake Berryessa Tributaries
28.
Estrella River
11.
Upper Sonoma Creek
29.
San Gabriel Mountain*
12.
Petaluma Creek — Sonoma Creek
30.
Forks of the Mojave*
13.
Pt. Reyes Peninsula
31.
Santa Ana Mountain*
14.
Belvedere Lagoon
32.
Santa Rosa Plateau
15.
Jameson Canyon - Lower Napa River
33.
San Luis Ray*
16.
East San Francisco Bay
34.
Sweetwater*
17.
Santa Clara Valley
35.
Laguna Mountain*
18.
South San Francisco Bay


* Core areas that were historically occupied by the California red-legged frog are not included in the map
figure 2.2 Recovery Unit, Core Area, Critical Habitat, and Occurrence
Designations for CRLF
27

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Other Known Occurrences from the CNDBB
The CNDDB provides location and natural history information on species found in
California. The CNDDB serves as a repository for historical and current species location
sightings. Information regarding known occurrences of CRLFs outside of the currently
occupied core areas and designated critical habitat is considered in defining the current
range of the CRLF. See: http://www.dfg.ca.gov/bdb/html/cnddb info.html for additional
information on the CNDDB.
2.5.2 Reproduction
CRLFs breed primarily in ponds; however, they may also breed in quiescent streams,
marshes, and lagoons (Fellers 2005a). According to the Recovery Plan (USFWS 2002),
CRLFs breed from November through late April. Peaks in spawning activity vary
geographically; Fellers (2005b) reports peak spawning as early as January in parts of
coastal central California. Eggs are fertilized as they are being laid. Egg masses are
typically attached to emergent vegetation, such as bulrushes (Scirpus spp.) and cattails
(Typha spp.) or roots and twigs, and float on or near the surface of the water (Hayes and
Miyamoto 1984). Egg masses contain approximately 2000 to 6000 eggs ranging in size
between 2 and 2.8 mm (Jennings and Hayes 1994). Embryos hatch 10 to 14 days after
fertilization (Fellers 2005a) depending on water temperature. Egg predation is reported
to be infrequent and most mortality is associated with the larval stage (particularly
through predation by fish); however, predation on eggs by newts has also been reported
(Rathburn 1998). Tadpoles require 11 to 28 weeks to metamorphose into juveniles
(terrestrial-phase), typically between May and September (Jennings and Hayes 1994,
USFWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until
the following year) (Fellers 2005b, USFWS 2002). Males reach sexual maturity at 2
years, and females reach sexual maturity at 3 years of age; adults have been reported to
live 8 to 10 years (USFWS 2002). Figure 2.3 depicts CRLF annual reproductive timing.




































J
F
M
A
M
J
J
A
S
o
N
D
Light Blue = Breeding/Egg Masses
Green = Tadpoles (except those that over-winter)
Orange =
Adults and juveniles can be present all year
figure 2.3 - 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
(USFWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar, 1980)
28

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via mouthparts designed for effective grazing of periphyton (Wassersug, 1984,
Kupferberg et al.\ 1994; Kupferberg, 1997; Altig and McDiarmid, 1999).
Juvenile and adult CRLFs forage in aquatic and terrestrial habitats, and their diet differs
greatly from that of larvae. The main food source for juvenile aquatic- and terrestrial-
phase CRLFs is thought to be aquatic and terrestrial invertebrates found along the
shoreline and on the water surface. Hayes and Tennant (1985) report, based on a study
examining the gut content of 35 juvenile and adult CRLFs, that the species feeds on as
many as 42 different invertebrate taxa, including Arachnida, Amphipoda, Isopoda,
Insecta, and Mollusca. The most commonly observed prey species were larval alderflies
(Sialis cf. californica), pillbugs (Armadilliadrium vulgare), and water striders (Gerris sp).
The preferred prey species, however, was the sowbug (Hayes and Tennant, 1985). This
study suggests that CRLFs forage primarily above water, although the authors note other
data reporting that adults also feed under water, are cannibalistic, and consume fish. For
larger CRLFs, over 50% of the prey mass may consists of vertebrates such as mice, frogs,
and fish, although aquatic and terrestrial invertebrates were the most numerous food
items (Hayes and Tennant 1985). For adults, feeding activity takes place primarily at
night; for juveniles feeding occurs during the day and at night (Hayes and Tennant 1985).
2.5.4 Habitat
CRLFs require aquatic habitat for breeding, but also use other habitat types including
riparian and upland areas throughout their life cycle. CRLF use of their environment
varies; they may complete their entire life cycle in a particular habitat or they may utilize
multiple habitat types. Overall, populations are most likely to exist where multiple
breeding areas are embedded within varying habitats used for dispersal (USFWS 2002).
Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al.
1997). Dense vegetation close to water, shading, and water of moderate depth are habitat
features that appear especially important for CRLF (Hayes and Jennings 1988). Breeding
sites include streams, deep pools, backwaters within streams and creeks, ponds, marshes,
sag ponds (land depressions between fault zones that have filled with water), dune ponds,
and lagoons. Breeding adults have been found near deep (0.7 m) still or slow moving
water surrounded by dense vegetation (USFWS 2002); however, the largest number of
tadpoles have been found in shallower pools (0.26 - 0.5 m) (Reis, 1999). Data indicate
that CRLFs do not frequently inhabit vernal pools, as conditions in these habitats
generally are not suitable (Hayes and Jennings 1988).
CRLFs also frequently breed in artificial impoundments such as stock ponds, although
additional research is needed to identify habitat requirements within artificial ponds
(USFWS 2002). Adult CRLFs use dense, shrubby or emergent vegetation closely
associated with deep-water pools bordered with cattails and dense stands of overhanging
vegetation (http://www.fws.gov/endangered/features/rl frog/rlfrog.html#where).
In general, dispersal and habitat use depends on climatic conditions, habitat suitability,
and life stage. Adults rely on riparian vegetation for resting, feeding, and dispersal. The
foraging quality of the riparian habitat depends on moisture, composition of the plant
29

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community, and presence of pools and backwater aquatic areas for breeding. CRLFs can
be found living within streams at distances up to 3 km (2 miles) from their breeding site
and have been found up to 30 m (100 feet) from water in dense riparian vegetation for up
to 77 days (USFWS 2002).
During dry periods, the CRLF is rarely found far from water, although it will sometimes
disperse from its breeding habitat to forage and seek other suitable habitat under downed
trees or logs, industrial debris, and agricultural features (UWFWS 2002). According to
Jennings and Hayes (1994), CRLFs also use small mammal burrows and moist leaf litter
as habitat. In addition, CRLFs may also use large cracks in the bottom of dried ponds as
refugia; these cracks may provide moisture for individuals avoiding predation and solar
exposure (Alvarez 2000).
2.6 Designated Critical Habitat
In a final rule published on April 13, 2006, 34 separate units of critical habitat were
designated for the CRLF by USFWS (USFWS 2006; FR 51 19244-19346). A summary
of the 34 critical habitat units relative to USFWS-designated recovery units and core
areas (previously discussed in Section 2.5.1) is provided in Table 2.4.
'Critical habitat' is defined in the ESA as the geographic area occupied by the species at
the time of the listing where the physical and biological features necessary for the
conservation of the species exist, and there is a need for special management to protect
the listed species. It may also include areas outside the occupied area at the time of
listing if such areas are 'essential to the conservation of the species.' All designated
critical habitat for the CRLF was occupied at the time of listing. Critical habitat receives
protection under Section 7 of the ESA through prohibition against destruction or adverse
modification with regard to actions carried out, funded, or authorized by a federal
Agency. Section 7 requires consultation on federal actions that are likely to result in the
destruction or adverse modification of critical habitat.
To be included in a critical habitat designation, the habitat must be 'essential to the
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
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• Dispersal habitat.
Further description of these habitat types is provided in Attachment 1.
Occupied habitat may be included in the critical habitat only if essential features within
the habitat may require special management or protection. Therefore, USFWS does not
include areas where existing management is sufficient to conserve the species. Critical
habitat is designated outside the geographic area presently occupied by the species only
when a designation limited to its present range would be inadequate to ensure the
conservation of the species. For the CRLF, all designated critical habitat units contain all
four of the PCEs, and were occupied by the CRLF at the time of FR listing notice in
April 2006. The FR notice designating critical habitat for the CRLF includes a special
rule exempting routine ranching activities associated with livestock ranching from
incidental take prohibitions. The purpose of this exemption is to promote the
conservation of rangelands, which could be beneficial to the CRLF, and to reduce the rate
of conversion to other land uses that are incompatible with CRLF conservation. Please
see Attachment 1 for a full explanation on this special rule.
USFWS has established adverse modification standards for designated critical habitat
(USFWS 2006). Activities that may destroy or adversely modify critical habitat are those
that alter the PCEs and jeopardize the continued existence of the species. Evaluation of
actions related to use of diuron that may alter the PCEs of the CRLF's critical habitat
form the basis of the critical habitat impact analysis. According to USFWS (2006),
activities that may affect critical habitat and therefore result in adverse effects to the
CRLF include, but are not limited to the following:
(1)	Significant alteration of water chemistry or temperature to levels beyond the
tolerances of the CRLF that result in direct or cumulative adverse effects to
individuals and their life-cycles.
(2)	Significant increase in sediment deposition within the stream channel or pond or
disturbance of upland foraging and dispersal habitat that could result in
elimination or reduction of habitat necessary for the growth and reproduction of
the CRLF by increasing the sediment deposition to levels that would adversely
affect their ability to complete their life cycles.
(3)	Significant alteration of channel/pond morphology or geometry that may lead to
changes to the hydrologic functioning of the stream or pond and alter the timing,
duration, water flows, and levels that would degrade or eliminate the CRLF
and/or its habitat. Such an effect could also lead to increased sedimentation and
degradation in water quality to levels that are beyond the CRLF's tolerances.
(4)	Elimination of upland foraging and/or aestivating habitat or dispersal habitat.
(5)	Introduction, spread, or augmentation of non-native aquatic species in stream
segments or ponds used by the CRLF.
(6)	Alteration or elimination of the CRLF's food sources or prey base (also
evaluated as indirect effects to the CRLF).
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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 diuron is expected to directly impact living
organisms within the action area, critical habitat analysis for diuron is limited in a
practical sense to those PCEs of critical habitat that are biological or that can be
reasonably linked to biologically mediated processes.
2.7 Action Area
For listed species assessment purposes, the action area is considered to be the area
affected directly or indirectly by the federal action and not merely the immediate area
involved in the action (50 CFR 402.02). It is recognized that the overall action area for
the national registration of diuron is likely to encompass considerable portions of the
United States based on the large array of agricultural uses. However, the scope of this
assessment limits consideration of the overall action area to those portions that may be
applicable to the protection of the CRLF and its designated critical habitat within the state
of California. The Agency's approach to defining the action area under the provisions of
the Overview Document (USEPA 2004) considers the results of the risk assessment
process to establish boundaries for that action area with the understanding that exposures
below the Agency's defined 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 diuron may be expected to have on the
environment, the exposure levels to diuron that are associated with those effects, and the
best available information concerning the use of diuron and its fate and transport within
the state of California. Specific measures of ecological effect for the CRLF that define
the action area include any direct and indirect toxic effect to the CRLF and any potential
modification of its critical habitat, including reduction in survival, growth, and fecundity
as well as the full suite of sublethal effects available in the effects literature. Therefore,
the action area extends to a point where environmental exposures are below any
measured lethal or sublethal effect threshold for any biological entity at the whole
organism, organ, tissue, and cellular level of organization. In situations where it is not
possible to determine the threshold for an observed effect, the action area is not spatially
limited and is assumed to be the entire state of California.
The definition of action area requires a stepwise approach that begins with an
understanding of the federal action. The federal action is defined by the currently labeled
uses for diuron. 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
32

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diuron, agricultural and non-agricultural uses listed in Table 2.2 are considered part of the
federal action evaluated in this assessment.
Following a determination of the assessed uses, an evaluation of the potential "footprint"
of diuron use patterns (i.e., the area where pesticide application occurs) is determined.
This "footprint" represents the initial area of concern, based on an analysis of available
land cover data for the state of California. The initial area of concern is defined as all
land cover types and the stream reaches within the land cover areas that represent the
labeled uses described above. A map representing all the land cover types related to
agricultural uses that make up the initial area of concern for diuron is presented in Figure
2.4. Diuron, in fact, is used in all 58 of California's counties when you consider non-
agricultural uses as well.
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Diruon use &CRLF overlap
CNDDB occurrence sections
Critical habitat
Core areas
County boundaries
Diuron Use & CRLF Habitat
Produced 12/2/2008

¦tb=mh=ihb Kil o mete rs
0 20 40 80 120 160
Compiled from California Count)' boundaries (ESRI, 2002),
USCW GapAnalysis Program Orchard/ Vineyard Landcover (GAP)
National Land Cewer Database (NLCD) (MRLC, 2001)
Map created by US Environmental Protection Agency, Office
of Pesticides Programs, Environmental Fate and Effects Division.
Projection: Albers Equal Area Conic USGS, North American
Datum of 1983 (NAD 1983).
Figure 2.4 Initial area of concern, or "footprint" of potential use, for diuron
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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.
As stated in the 2003 Registration Eligibility Decision (RED), diuron has been
characterized as a "known/likely" human carcinogen, based on urinary bladder
carcinomas in both sexes of the Wistar rat, kidney carcinomas in the male rat (a rare
tumor), and mammary gland carcinomas in the female NMRI mouse. Because of this,
the spatial extent of the action area (i.e., the boundary where exposures and potential
effects are less than the Agency's LOC) for diuron cannot be determined. Therefore, it is
assumed that the action area encompasses the entire state of California, regardless of the
spatial extent (i.e., initial area of concern or footprint) of the pesticide use(s). This
determination is supported by the fact that diuron use has been reported in all 58 counties
in California.
The AgDRIFT model (Version 2.01) is used to define how far from the initial area of
concern an effect to a given species may be expected via spray drift. The spray drift
analysis for diuron using the most sensitive endpoint (most sensitive plant toxicity study:
Vegetative Vigor - Tomato (Lycopersicon esculentum)) suggests that a maximum spray
drift distance of at least 1,000 feet is necessary. The Tier 1 ground analysis allows users
to evaluate off-site deposition and exposure out to 1,000 ft downwind from the location
of the application. Further detail on the spray drift analysis is provided in Section 3.2.5.
In addition to the buffered area from the spray drift analysis, the final action area also
considers the downstream extent of diuron that exceeds the LOC (discussed in Section
3.2.6).
An evaluation of usage information was conducted to determine the area where use of
diuron may impact the CRLF. This analysis is used to characterize where predicted
exposures are most likely to occur, but does not preclude use in other portions of the
action area. A more detailed review of the county-level use information was also
completed. These data suggest that diuron has historically been used on a wide variety of
agricultural and non-agricultural uses.
2.8 Assessment Endpoints and Measures of Ecological Effect
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."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 diuron
3 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
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(e.g., runoff, spray drift, etc.), and the routes by which ecological receptors are exposed
to diuron (e.g., direct contact, etc.).
2.8.1. Assessment Endpoints for the CRLF
Assessment endpoints for the CRLF include direct toxic effects on the survival,
reproduction, and growth of the CRLF, as well as indirect effects, such as reduction of
the prey base or modification of its habitat. In addition, potential modification of critical
habitat is assessed by evaluating potential effects to PCEs, which are components of the
habitat areas that provide essential life cycle needs of the CRLF. Each assessment
endpoint requires one or more "measures of ecological effect," defined as changes in the
attributes of an assessment endpoint or changes in a surrogate entity or attribute in
response to exposure to a pesticide. Specific measures of ecological effect are generally
evaluated based on acute and chronic toxicity information from registrant-submitted
guideline tests that are performed on a limited number of organisms. Additional
ecological effects data from the open literature are also considered. It should be noted
that assessment endpoints are limited to direct and indirect effects associated with
survival, growth, and fecundity, and do not include the full suite of sublethal effects used
to define the action area. According the Overview Document (USEPA 2004), the
Agency relies on acute and chronic effects endpoints that are either direct measures of
impairment of survival, growth, or fecundity or endpoints for which there is a
scientifically robust, peer reviewed relationship that can quantify the impact of the
measured effect endpoint on the assessment endpoints of survival, growth, and fecundity.
A complete discussion of all the toxicity data available for this risk assessment, including
resulting measures of ecological effect selected for each taxonomic group of concern, is
included in Section 4 of this document. A summary of the assessment endpoints and
measures of ecological effect selected to characterize potential assessed direct and
indirect CRLF risks associated with exposure to diuron is provided in Table 2.4.
Table 2.4 Assessment Endpoints and Measures of Ecological Effects
Assessment Ijulpoinl
Measures of l-eolouieal I-Heels'
Aquatic-Phase CRLF
(Eggs, larvae, juveniles, and adults"f
Direct Effects
1. Survival, growth, and reproduction of
CRLF
la. Amphibian acute LC50 (ECOTOX) or most sensitive
fish acute LC50 (guideline or ECOTOX) if no suitable
amphibian data are available
lb. Amphibian chronic NOAEC (ECOTOX) or most
sensitive fish chronic NOAEC (guideline or ECOTOX)
lc. Amphibian early-life stage data (ECOTOX) or most
sensitive fish early-life stage NOAEC (guideline or
ECOTOX)
Indirect Effects and Critical Habitat Effects
2. Survival, growth, and reproduction of
CRLF individuals via indirect effects on
2a. Most sensitive fish, aquatic invertebrate, and aquatic
plant EC50 or LC50 (guideline or ECOTOX)
4 All registrant-submitted and open literature toxicity data reviewed for this assessment are included in
Appendix J.
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Assessment l-ndpoinl
Measures of l-colouical I-fleets'
aquatic prey food supply (i.e., fish,
freshwater invertebrates, non-vascular plants)
2b. Most sensitive aquatic invertebrate and fish chronic
NOAEC (guideline or ECOTOX)
3. Survival, growth, and reproduction of
CRLF individuals via indirect effects on
habitat, cover, food supply, and/or primary
productivity (i.e., aquatic plant community)
3 a. Vascular plant acute EC50 (duckweed guideline test or
ECOTOX vascular plant)
3b. Non-vascular plant acute EC50 (freshwater algae or
diatom, or ECOTOX non-vascular)
4. Survival, growth, and reproduction of
CRLF individuals via effects to riparian
vegetation
4a. Distribution of EC25 values for monocots (seedling
emergence, vegetative vigor, or ECOTOX)
4b. Distribution of EC25 values for dicots (seedling
emergence, vegetative vigor, or ECOTOX)
Terrestrial-Phase CRLF
(Juveniles and adults)
Direct Effects
5. Survival, growth, and reproduction of
CRLF individuals via direct effects on
terrestrial phase adults and juveniles
5a. Most sensitive birdb or terrestrial-phase amphibian
acute LC50 or LD50 (guideline or ECOTOX)
5b. Most sensitive birdb or terrestrial-phase amphibian
chronic NOAEC (guideline or ECOTOX)
Indirect Effects and Critical Habitat Effects
6. Survival, growth, and reproduction of
CRLF individuals via effects on terrestrial
prey (i.e., terrestrial invertebrates, small
mammals, and frogs)
6a. Most sensitive terrestrial invertebrate and vertebrate
acute EC50 or LC50 (guideline or ECOTOX)0
6b. Most sensitive terrestrial invertebrate and vertebrate
chronic NOAEC (guideline or ECOTOX)
7. Survival, growth, and reproduction of
CRLF individuals via indirect effects on
habitat (i.e., riparian and upland vegetation)
7a. Distribution of EC25 for monocots (seedling
emergence, vegetative vigor, or ECOTOX
7b. Distribution of EC25 for dicots (seedling emergence,
vegetative vigor, or ECOTOX)
a Adult frogs are no longer in the "aquatic phase" of the amphibian life cycle; however, submerged adult
frogs are considered "aquatic" for the purposes of this assessment because exposure pathways in the water
are considerably different that exposure pathways on land.
b Birds are used as surrogates for terrestrial phase amphibians.
2.8.2 Assessment Endpoints for Designated Critical Habitat
As previously discussed, designated critical habitat is assessed to evaluate actions related
to the use of diuron 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 diuron effects data are available.
Adverse modification to the critical habitat of the CRLF includes, but is not limited to,
the following, as specified by USFWS (2006):
1. Alteration of water chemistry/quality including temperature, turbidity, and
oxygen content necessary for normal growth and viability of juvenile and
adult CRLFs.
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2.	Alteration of chemical characteristics necessary for normal growth and
viability of juvenile and adult CRLFs.
3.	Significant increase in sediment deposition within the stream channel or pond
or disturbance of upland foraging and dispersal habitat.
4.	Significant alteration of channel/pond morphology or geometry.
5.	Elimination of upland foraging and/or aestivating habitat, as well as dispersal
habitat.
6.	Introduction, spread, or augmentation of non-native aquatic species in stream
segments or ponds used by the CRLF.
7.	Alteration or elimination of the CRLF's food sources or prey base.
Measures of such possible effects by labeled use of diuron on critical habitat of the CRLF
are described in Table. Some components of these PCEs are associated with physical
abiotic features (e.g., presence and/or depth of a water body, or distance between two
sites), which are not expected to be measurably altered by use of pesticides. Assessment
endpoints used for the analysis of designated critical habitat are based on the adverse
modification standard established by USFWS (2006).
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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.
a.	Most sensitive aquatic plant EC50 (guideline or
ECOTOX)
b.	Distribution of EC25 values for terrestrial monocots
(seedling emergence, vegetative vigor, or ECOTOX)
c.	Distribution of EC25 values for terrestrial dicots
(seedling emergence, vegetative vigor, or ECOTOX)
Alteration in water chemistry/quality including
temperature, turbidity, and oxygen content necessary
for normal growth and viability of juvenile and adult
CRLFs and their food source.
a.	Most sensitive EC50 values for aquatic plants (guideline
or ECOTOX)
b.	Distribution of EC25 values for terrestrial monocots
(seedling emergence or vegetative vigor, or ECOTOX)
c.	Distribution of EC25 values for terrestrial dicots
(seedling emergence, vegetative vigor, or ECOTOX)
Alteration of other chemical characteristics necessary
for normal growth and viability of CRLFs and their
food source.
a.	Most sensitive EC50 or LC50 values for fish or aquatic-
phase amphibians and aquatic invertebrates (guideline or
ECOTOX)
b.	Most sensitive NOAEC values for fish or aquatic-phase
amphibians and aquatic invertebrates (guideline or
ECOTOX)
Reduction and/or modification of aquatic-based food
sources for pre-metamorphs (e.g., algae)
a. Most sensitive aquatic plant EC50 (guideline or
ECOTOX)
Terrestrial-Phase CRLF PCEs
(Upland Habitat and Dispersal Habitat)
Elimination and/or disturbance of upland habitat;
ability of habitat to support food source of CRLFs:
Upland areas within 200 ft of the edge of the riparian
vegetation or dripline surrounding aquatic and riparian
habitat that are comprised of grasslands, woodlands,
and/or wetland/riparian plant species that provides the
CRLF shelter, forage, and predator avoidance
a.	Distribution of EC25 values for monocots (seedling
emergence, vegetative vigor, or ECOTOX)
b.	Distribution of EC25 values for dicots (seedling
emergence, vegetative vigor, or ECOTOX)
c.	Most sensitive food source acute EC50/LC50 and NOAEC
values for terrestrial vertebrates (mammals) and
invertebrates, birds or terrestrial-phase amphibians, and
freshwater fish.
Elimination and/or disturbance of dispersal habitat:
Upland or riparian dispersal habitat within designated
units and between occupied locations within 0.7 mi of
each other that allow for movement between sites
including both natural and altered sites which do not
contain barriers to dispersal
Reduction and/or modification of food sources for
terrestrial phase juveniles and adults
Alteration of chemical characteristics necessary for
normal growth and viability of juvenile and adult
CRLFs and their food source.
a Physico-chemical water quality parameters such as salinity, pH, and hardness are not evaluated because these
processes are not biologically mediated and, therefore, are not relevant to the endpoints included in this assessment.
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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 diuron to the environment. The
following risk hypotheses are presumed for this endangered species assessment:
The labeled use of diuron within the action area may:
•	Directly affect the CRLF by causing mortality or by adversely affecting growth or
fecundity;
•	Indirectly affect the CRLF by reducing or changing the composition of food
supply;
•	Indirectly affect the CRLF or modify designated critical habitat by reducing or
changing the composition of the aquatic plant community in the ponds and streams
comprising the species' current range and designated critical habitat, thus affecting
primary productivity and/or cover;
•	Indirectly affect the CRLF or modify designated critical habitat by reducing or
changing the composition of the terrestrial plant community (i.e., riparian habitat)
required to maintain acceptable water quality and habitat in the ponds and streams
comprising the species' current range and designated critical habitat;
•	Modify the designated critical habitat of the CRLF by reducing or changing
breeding and non-breeding aquatic habitat (via modification of water quality parameters,
habitat morphology, and/or sedimentation);
•	Modify the designated critical habitat of the CRLF by reducing the food supply
required for normal growth and viability of juvenile and adult CRLFs;
•	Modify the designated critical habitat of the CRLF by reducing or changing
upland habitat within 200 ft of the edge of the riparian vegetation necessary for shelter,
foraging, and predator avoidance.
•	Modify the designated critical habitat of the CRLF by reducing or changing
dispersal habitat within designated units and between occupied locations within 0.7 mi of
each other that allow for movement between sites including both natural and altered sites
which do not contain barriers to dispersal.
•	Modify the designated critical habitat of the CRLF by altering chemical
characteristics necessary for normal growth and viability of juvenile and adult CRLFs.
2.9.2	Diagram
The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies the diuron release mechanisms, biological receptor types, and effects
endpoints of potential concern. The conceptual models for aquatic and terrestrial phases
of the CRLF are shown in Figure 2.5 and Figure 2.6, respectively, and the conceptual
models for the aquatic and terrestrial PCE components of critical habitat are shown in
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Figure 2.7 and Figure 2.8, respectively. Exposure routes shown in dashed lines are not
quantitatively considered because the contribution of those potential exposure routes to
potential risks to the CRLF and modification to designated critical habitat is expected to
be negligible.
Figure 2.5 Conceptual Model for Aquatic-Phase of the CRLF
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Figure 2.6 Conceptual Model for Terrestrial-Phase of the CRLF
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Figure 2.7 Conceptual Model for Pesticide Effects on Aquatic Component of CRLF
Critical Habitat
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Figure 2.8 Conceptual Model for Pesticide Effects on Terrestrial Component of
CRLF Critical Habitat
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 diuron 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 diuron is estimated
using the probit dose-response slope and either the level of concern (discussed below) or
actual calculated risk quotient value.
2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model
2.10.1.1 Measures of Exposure
The environmental fate properties of diuron along with available monitoring data indicate
that runoff and spray drift are the principle potential transport mechanisms of diuron to
the aquatic and terrestrial habitats of the CRLF. In this assessment, transport of diuron
44

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through runoff and spray drift is considered in deriving quantitative estimates of diuron
exposure to CRLF, its prey and its habitats. The reported vapor pressure of diuron is 6.9
x 10"8 torr at 25°C; therefore, volatilization is not considered a probable route of
dissipation.
Measures of exposure are based on aquatic and terrestrial models that predict estimated
environmental concentrations (EECs) of diuron 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).
T-REX is used to predict terrestrial EECs on food items. TerrPlant is used to derive
EECs relevant to terrestrial and wetland plants. 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 diuron that may occur in surface water bodies
adjacent to application sites receiving diuron 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 diuron. 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 1-in-10-year 21-day mean is used for assessing chronic exposure for aquatic
invertebrates, which are also potential prey items.
Exposure estimates for the terrestrial-phase CRLF and terrestrial invertebrates and
mammals (serving as potential prey) assumed to be in the target area or in an area
exposed to spray drift are derived using the T-REX model (version 1.3.1, 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 diuron 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
45

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for the CRLF and one of its prey items. Estimated exposures of terrestrial insects to
diuron are bound by using the dietary based EECs for small insects and large insects.
Birds are currently used as surrogates for terrestrial-phase CRLF. However, amphibians
are poikilotherms (body temperature varies with environmental temperature) while birds
are homeotherms (temperature is regulated, constant, and largely independent of
environmental temperatures). Therefore, amphibians tend to have much lower metabolic
rates and lower caloric intake requirements than birds or mammals. As a consequence,
birds are likely to consume more food than amphibians on a daily dietary intake basis,
assuming similar caloric content of the food items. Therefore, the use of avian food
intake allometric equation as a surrogate to amphibians is likely to result in an over-
estimation of exposure and risk for reptiles and terrestrial-phase amphibians. Therefore,
T-REX (version 1.3.1) has been refined to the T-HERPS model (v. 1.0), which allows for
an estimation of food intake for poikilotherms using the same basic procedure as T-REX
to estimate avian food intake.
EECs for terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant
(version 1.2.2, 12/26/2006). This model uses estimates of pesticides in runoff and in
spray drift to calculate EECs. EECs are based upon solubility, application rate and
minimum incorporation depth.
Spray drift model, AgDRIFT is used to assess exposures of terrestrial phase CRLF and its
prey to diuron deposited on terrestrial habitats by spray drift. In addition to the buffered
area from the spray drift analysis, the downstream extent of diuron that exceeds the LOC
for the effects determination is also considered.
2.10.1.2 Measures of Effect
Data identified in Section 2.8 are used as measures of effect for direct and indirect effects
to the CRLF. Data were obtained from registrant submitted studies or from literature
studies identified by ECOTOX. The ECOTOXicology database (ECOTOX) was
searched in order to provide more ecological effects data and in an attempt to bridge
existing data gaps. ECOTOX is a source for locating single chemical toxicity data for
aquatic life, terrestrial plants, and wildlife. ECOTOX was created and is maintained by
the USEPA, Office of Research and Development, and the National Health and
Environmental Effects Research Laboratory's Mid-Continent Ecology Division.
The assessment of risk for direct effects to the terrestrial-phase CRLF makes the
assumption that toxicity of diuron 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.
46

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The acute measures of effect used for animals in this screening level assessment are the
LD50, LC50 and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a material,
given all at once, that is estimated to cause the death of 50% of the test organisms. LC
stands for "Lethal Concentration" and LC50 is the concentration of a chemical that is
estimated to kill 50% of the test organisms. EC stands for "Effective Concentration" and
the EC50 is the concentration of a chemical that is estimated to produce a specific effect in
50% of the test organisms. Endpoints for chronic measures of exposure for listed and
non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL stands for "No
Ob served-Adverse-Effect-Level" and refers to the highest tested dose of a substance that
has been reported to have no harmful (adverse) effects on test organisms. The NOAEC
(i.e., "No-Observed-Adverse-Effect-Concentration") is the highest test concentration at
which none of the observed effects were statistically different from the control. The
NOEC is the No-Observed-Effects-Concentration. For non-listed plants, only acute
exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants).
It is important to note that the measures of effect for direct and indirect effects to the
CRLF and its designated critical habitat are associated with impacts to survival, growth,
and fecundity, and do not include the full suite of sublethal effects used to define the
action area. According the Overview Document (USEPA 2004), the Agency relies on
effects endpoints that are either direct measures of impairment of survival, growth, or
fecundity or endpoints for which there is a scientifically robust, peer reviewed
relationship that can quantify the impact of the measured effect endpoint on the
assessment endpoints of survival, growth, and fecundity.
2.10.1.3 Integration of Exposure and Effects
Risk characterization is the integration of exposure and ecological effects characterization
to determine the potential ecological risk from agricultural and non-agricultural uses of
diuron, 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 diuron
risks, the risk quotient (RQ) method is used to compare exposure and measured toxicity
values. EECs are divided by acute and chronic toxicity values. The resulting RQs are
then compared to the Agency's levels of concern (LOCs) (USEPA, 2004) (see Appendix
E).
For this endangered species assessment, listed species LOCs are used for comparing RQ
values for acute and chronic exposures of diuron directly to the CRLF. If estimated
exposures directly to the CRLF of diuron resulting from a particular use are sufficient to
exceed the listed species LOC, then the effects determination for that use is "may affect".
When considering indirect effects to the CRLF due to effects to animal prey (aquatic and
terrestrial invertebrates, fish, frogs, and mice), the listed species LOCs are also used. If
estimated exposures to CRLF prey of diuron resulting from a particular use are sufficient
to exceed the listed species LOC, then the effects determination for that use is a "may
affect." If the RQ being considered also exceeds the non-listed species acute risk LOC,
then the effects determination is a LAA. If the acute RQ is between the listed species
47

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LOC and the non-listed acute risk species LOC, then further lines of evidence {i.e.
probability of individual effects, species sensitivity distributions) are considered in
distinguishing between a determination of NLAA and a LAA. When considering indirect
effects to the CRLF due to effects to algae as dietary items or plants as habitat, the non-
listed species LOC for plants is used because the CRLF does not have an obligate
relationship with any particular aquatic and/or terrestrial plant. If the RQ being
considered for a particular use exceeds the non-listed species LOC for plants, the effects
determination is "may affect". Further information on LOCs is provided in Appendix E.
2.10.2 Data Limitations
No acceptable toxicity studies have submitted to the Agency, nor were any acceptable
studies found in the open literature for the chronic effects of diuron on avian or
amphibian species. Linuron, a similar chemical of the same class, has acceptable chronic
avian data. The avian reproductive studies for linuron (MRID 42541801, 42541802)
using mallard duck and bobwhite quail found reproductive effects at 300 ppm ai with an
NOAEL being established at 100 ppm.
The endpoints affected for mallard duck reproduction are egg production, adult body
weight, feed consumption, viable embryos of eggs set, number of viable embryos, and
number of live embryos. For the Bobwhite Quail the endpoints affected are hatchability
and offspring survivability. The LC50 for the Bobwhite Quail exposed to linuron was
1700ppm, where the LC50 for the Bobwhite Quail exposed to linuron was almost identical
at 1730 ppm (MRID 00022923). Therefore it is assumed that linuron and diuron have a
similar mode of action and therefore chronic effects from diuron are assumed to be
similar to those observed from linuron exposure. Chronic risks are therefore assumed to
amphibian species and their avian surrogates for uses of diuron in California.
3.0 Exposure Assessment
Diuron is a broad-spectrum residual herbicide registered for pre-emergent and post-
emergent control of both broadleaf and annual grassy weeds. In the U.S. diuron is used
on a variety of fruit and nut crops, grains, cotton, corn, sorghum, mint, gum, asparagus,
sugarcane, seed crops, coffee, hay, cut flowers, and for fallow and idle cropland use. It
may be used in irrigation and drainage systems when water is not present.
It is also used to control weeds on hard surfaces, such as, roads, railway tracks, and paths
(at around 3 kg/ha), and to control weeds in crops, such as, pear and apple trees, forestry,
ornamental trees and shrubs, pineapples, sugar cane, cotton, alfalfa and wheat (at lower
rates of around 1.8 kg/ha). Its use in some locations is becoming limited due to the
development of resistant weed species. In some products it is formulated with other
active ingredients such as glyphosate, bromacil, hexazinone, amitrole and 2,4-D. This
assessment evaluates only those registered uses which allow use in California.
48

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3.1	Label Application Rates and Intervals
Currently registered agricultural and non-agricultural uses of diuron within California
include agricultural and non-agricultural crops, as well as industrial and paved areas.
The uses and applicable PRZM/EXAMS scenarios being assessed were summarized
in Table 2.2. For a list of the application rates and intervals used, please refer to
Table 3.2 below.
3.2	Aquatic Exposure Assessment
3.2.1	Modeling Approach
As discussed in Section 2.10.1.1, the models used to predict aquatic EECs are the
Pesticide Root Zone Model coupled with the Exposure Analysis Model System
(PRZM/EXAMS). Using PRZM/EXAMS, aquatic exposures are quantitatively estimated
for all of the assessed uses with scenarios that represent high exposure sites for diuron
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 diuron were used for
modeling, including application rates, number of applications per year, application
intervals, and the first application date for each crop. The date of first application was
developed based on several sources of information including data provided by BEAD, a
summary of individual applications from the CDPR PUR data, and Crop Profiles
maintained by the USD A.
3.2.2	Model Inputs
The input parameters for PRZM and EXAMS are presented in Table 3.1.
49

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Table 3.1 Summary of PRZIVl/EXAMS Environmental Fate Data Used for Aquatic
Exposure Inputs for Diuron Endangered Species Assessment for the CRLF
Fate Property
Value (unit)
MRID (or source)
Molecular Weight
233.1 g/mol
Product Chemistry
Henry's constant
5. IE-10 atm-m"3/mol
MRID 00017763
MRID 43762901, Herbicide
Vapor Pressure
6.9E-8 torr (25°C)
Handbook 7th Edition, WSSA,
1994
Solubility in Water
420 mg/1 (42 mg/1 x 10 per input
guidance)
Product Chemistry, Input
Parameter Guidance
Photolysis in Water
43 days
MRID 41418805
Aerobic Soil Metabolism Half-lives
372 days
MRID 41719303
Hydrolysis
Stable at pH7 (>500 hrs)
MRID 41418804
Aerobic Aquatic Metabolism (water
column)
99 days (33 days x 3 per input
guidance)
MRID 42260501, Input
Parameter Guidance
Anaerobic Aquatic Metabolism
(benthic)
15 days (5 days x 3 per input
guidance)
MRID 42661901, Input
Parameter Guidance
Koc
920 (avg. of 468, 626, and 1666)
MRID 44490501
Application rate and frequency
Various (see Table 3.2)
Per Label Instructions
Application intervals
Various (see Table 3.2)
Per Label Instructions
Chemical Application Method (CAM)
1
Label; Input Guidance for Eco
Assessments

0.99 Ground
0.95 Aerial
Per Input Guidance for Eco
Application Efficiency
Assessments
Spray Drift Fraction1
0.01 Ground
0.05 Aerial
Per Input Guidance for Eco
Assessments
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
3.2.3 Results
The PRZM/EXAMS model estimated aquatic EECs for the various scenarios and
application practices are listed in Table 3.2. See Appendix G for a summary of the
outputs. Peak EECs ranged from 3.76 to 4911 ppb for use on grasses grown for seed and
paved areas (impervious surfaces), respectively.
Since some of the application data needed for modeling were not stated on the labels,
assumptions were made by EFED analysts regarding the maximum number of
applications allowed per season, and/or the interval between applications. The
assumptions were as follows:
50

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•	For the application intervals that were not stated, the most conservative (minimum)
known application interval was used (21 days for cotton). 21 days was chosen
because it was the minimum known interval that was registered.
•	If the maximum number of applications was also missing, the maximum number of
intervals a year was determine by taking the maximum allowable application of active
ingredient per year (12 lb ai/yr) and dividing it by the maximum application rate for
the use in question. The following is an example of a calculation to determine the
maximum number of applications per year for the use of diuron on blackberries:
Max No. of Appl. Yr"1 = 12 lb ai. acre _1 yr _1 ^ 2.4 lb ai. acre _1 appl._1 = 5 appl. yr"1
Table 3.2 Aquatic EECs (ppb) for Diuron Uses in California
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AGRICULTURAL RIGHTS-OF-
WAY/FENCEROWS/HEDGEROWS
12
2
21
Ground
688
672
584
457
ALFALFA
2.4
1
0
Ground
10.6
10.4
9.1
7.2
Aircraft
13.7
13.3
11.7
9.4
APPLE
3.2
2
90
Ground
11.7
11.2
9.6
7.8
ARTICHOKE
3.2
1
0
Ground
32.0
31.1
27.4
25.1
ASPARGUS
3.2
1
0
Ground
37.0
35.5
30.2
22.9
BANANA, PLANTAIN
4.8
2
42
Ground
54.2
52.0
44.3
32.8
BLACKBERRY, BOYSENBERRY
2.4
5
21
Ground
140
136
121
103
BLUEBERRY
1.6
2
112
Ground
4.65
4.48
4.05
3.21
CITRUS
3.2
2
60
Ground
6.83
6.57
5.65
4.88
CORN, FIELD
0.8
1
0
Ground
7.24
6.95
6.13
4.68
DEWBERRY
2.4
3
60
Ground
19.7
19.3
16.8
14.3
FILBERT (HAZELNUT)
2.2
2
150
Ground
18.9
18.4
15.9
12.2
GRAPE
3.2
2
90
Ground
9.71
9.32
8.10
6.37
LOGANBERRY, RASPBERRY
(BLACK/RED)
2.4
1
0
Ground
5.13
4.95
4.31
3.02
OLIVE
1.6
2
168
Ground
7.17
6.90
5.97
4.86
PAPAYA
4
1
0
Ground
25.2
24.6
21.2
15.7
PEPPERMINT
2.4
1
0
Ground
4.17
4.05
3.55
2.79
PEACH
3
1
0
Ground
11.0
10.5
9.0
7.3
PEAR
3.2
1
0
Ground
11.7
11.2
9.6
7.8
PECAN
3.2
1
0
Ground
27.0
26.3
22.8
17.3
SORGHUM
0.4
2
21
Ground
5.87
5.67
5.44
4.52
SPEARMINT
2.4
5
21
Ground
107
104
97.1
82.0
WALNUT (ENGLISH/BLACK)
3
2
150
Ground
25.8
25.1
21.8
16.6
WHEAT
1.6
1
0
Ground
18.0
17.3
14.9
12.0
12.8
12.3
11.9
10.3
Null I'lHIll I'CCll ( |M|>-








l 1 >| |t >\
1.6
3
21
Ground
8.36
8.13
7.42
5.72
Aircraft
14.2
13.9
12.9
10.2
Null ( iiip 1 mill








AIRPORTS LANDING FIELDS,
DRAINAGE SYSTEMS,
INDUSTRIAL AREAS
(OUTDOOR), SEWAGE DISPOSAL
AREAS
12
2
21
Ground
2190
2115
1825
1382
BERMUDAGRASS
2.4
5
21
Ground
226
219
204
168
GRASSES GROWN FOR SEED
1.6
1
0
Ground
3.76
3.62
3.20
2.89
51

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Vpplifiiliiin
IIIClllMll




IRRIGATION SYSTEMS
12
2
21
Ground
52.6
50.7
45.0
37.5
ORNAMENTAL HERBACEOUS
PLANTS
4
1
0
Ground
36.5
35.5
30.7
23.6
NON-AGRICULTURAL RIGHTS
OF WAY
12
2
90
Ground
630
619
560
476
Aircraft
627
616
552
468
PAVED AREAS (PRIVATE
ROADS/SIDEWALKS)
12
1
0
Ground
4911
4725
4241
3428
UNCULTIVATED AG
12
1
0
Ground
1130
1099
1023
840
Aircraft
1169
1130
1063
891
UNCULTIVATED NON-AG
12
2
21
Ground
285
276
252
203
3.2.4 Existing Monitoring Data
3.2.4.1 USGS NAWQA Surface Water Data
A critical step in the process of characterizing EECs is comparing the modeled estimates
with available surface water monitoring data. The USGS has collected 347 surface water
samples from four river basins in California (Sacramento, San Joaquin-Tulare, Santa
Ana, and Nevada) with a detection limit of 0.01 ppb. Out of these samples, 232 (69%)
were positive for diuron. The maximum concentration observed was 23.3 ppb in the
Santa Ana River Basin in San Bernardino County.
3.2.4.2	USGS NAWQA Groundwater Data
The USGS collected 428 ground water samples where 75 (17.5%) of these samples
contained diuron. The three river basins looked at were Sacramento, San Joaquin-Tulare,
and Santa Ana. The maximum concentration observed was 1.8 ppb in the San Joaquin-
Tulare water basins in Kings County.
Similar to the most recent analysis of USGS data, an "Analysis of Diuron Monitoring
Data with [an] emphasis on the USGS NAQWA Surface Water Sampling" in February
1999, observed the San Joaquin-Tulare basin as well. It was concluded that diuron
concentrations reached their peaks in the winter and spring seasons (January to June).
USGS concluded that runoff was more efficient than irrigation return flows in
transporting pesticides, in this case diuron, into surface water. Although USGS detected
diuron in more than 10% of the ground water samples, the concentrations were generally
less than 0.1 ppb.
3.2.4.3	California Department of Pesticide Regulation Data
The California Department of Pesticide Regulation (CDPR) has been collecting surface
water data on diuron since 1992. In a memo sent to the Special Review and
Reregi strati on Division (SRRD) from the Environmental Fate and Effects Division
(EFED) in 2003, titled "Surface Water Monitoring Data for Diuron", summarized surface
water monitoring data for diuron collected by CDPR over the period December 2000 to
March 2001. There were three locations (82 samples) in the Sacramento River, and two
locations (54 samples) in the San Joaquin River. One-hundred percent of the samples
52

-------
taken from the San Joaquin River had detectable diuron, with a maximum concentration
of 8.45 ppb. The average concentration at the San Joaquin River stations was 1.7 ppb.
About seventy-five percent of the samples in the Sacramento River had detectable diuron
with a maximum concentration of 1.42 ppb. The average concentration, assuming that all
non-detects were equal to the detection limit of 0.05 ppb, was 0.16 ppb.
Currently, the monitoring data available at CDPR has expanded to include data collected
from 2004, 2005, and 2006. Between 2004 and 2006, the data indicates that diuron
concentrations range from non-detect to 160 ppb (San Joaquin County, January 3, 2005,
and Tulare County, February 21, 2005). Out of 156 sampling locations, 152 locations
(97.4%) were located within 0.5 miles or less of an agricultural area. The four other
locations were 8 miles or more from the nearest agricultural area.
Sixteen percent of the 705 samples collected from 2004 to 2006 were greater than the
detection limit. The majority of the higher concentrations of diuron came from San
Joaquin County, and occurred between the end of December and the beginning of
January. The year 2005, for San Joaquin County, yielded the greatest concentrations
overall with an average concentration of 10.9 ppb for the year.
Diuron's concentrations being greatest in, and mainly only showing up in the monitoring
data during the winter months is consistent with the labeled use for pre-emergence
application. In addition, during the winter months, high concentrations may be detected
due to transport from rainfall runoff. Runoff during the winter in the San Joaquin Valley
may include large amounts of non-agricultural runoff from coastal ranges. When
comparing this monitoring data to the results from PRZM/EXAMS, the CDPR data
further supports that spray drift is a major route of off site movement.
3.2.4.4 Atmospheric Monitoring Data
The California Air Review Board has not conducted ambient air monitoring of diuron.
Therefore, no atmospheric monitoring data is available.
3.2.6 Downstream Dilution Analysis
To complete this assessment, the greatest ratio of aquatic RQ to LOC was estimated.
Using an assumption of uniform runoff across the landscape, it is assumed that streams
flowing through treated areas (i.e. the initial area of concern) are represented by the
modeled EECs; as those waters move downstream, it is assumed that the influx of non-
impacted water will dilute the concentrations of diuron present.
Using the LC50 for Selenastrum capricornutum (the most sensitive species) of 2.40 ppb
and a maximum peak EEC for applications to non-agricultural rights-of-
way/fencerows/hedgerows of 341.6 ug/L yields an RQ/LOC ratio of 142.33. Using the
downstream dilution approach (described in more detail in Appendix F) yields a target
percent crop area (PCA). This value has been input into the downstream dilution
approach resulting in a total of 285 kilometers of stream downstream from the initial area
53

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of concern (footprint of use). Similar to the spray drift buffer described above, the
LAA/NLAA determination is based on the area defined by the point where
concentrations exceed the LC50 value, in this case 2.40 ppb.
See Appendix F for the spatial summary of diuron used to determine the downstream
dilution.
3.3 Terrestrial Animal Exposure Assessment
T-REX (Version 1.3.1) is used to calculate dietary and dose-based EECs of diuron for the
CRLF and its potential prey (e.g. small mammals and terrestrial insects) inhabiting
terrestrial areas. EECs used to represent the CRLF are also used to represent exposure
values for frogs serving as potential prey of CRLF adults. T-REX simulates a 1-year
time period. For this assessment, ground spray applications of diuron are considered, as
discussed in below.
Terrestrial EECs for ground spray applications of diuron were derived for the uses
registered in California. Given that no data on interception and subsequent dissipation
from foliar surfaces is available for diuron, a default foliar dissipation half-life of 35 days
is used based on the work of Willis and McDowell (1987). Use specific input values,
including number of applications, and application rate are shown in Table 3.3. An
example output from T-REX is available in Appendix H.
Table 3.3 T-REX Model Input Parameters
Crop
Application
Kale per
Crop
Scenario
(Ihs/A)
Nil in her of
Applications
Application
interval
(davs)
Agricultural Rights-of-Way, Fencerows,
Hedgerows, Airports, landing Fields, Drainage
Systems, Outdoor Industrial Areas, Irrigation
Systems, Non-Agricultural Rights of Way,
Sewage Disposal Areas, Uncultivated Non-
Agricultural Areas
12
2
21
Alfalfa, Peppermint
2.4
1
n/a
Apple, Grape
3.2
2
90
Citrus
3.2
2
60
Artichoke, Asparagus
3.2
1
n/a
Banana, Plantain
4.8
2
42
Bermuda grass, Blackberry, Boysenberry,
Spearmint
2.4
5
21
Blueberry
1.6
2
112
Field Corn
0.8
1
n/a
Cotton
1.6
3
21
Dewberry
2.4
3
60
Filbert (Hazelnut)
2.2
2
150
Grass Seed, Wheat
1.6
1
n/a
54

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Crop
Application
Kale per
Crop
Scenario
(lbs/A)
.Number of
Applications
Application
interval
(days)
Loganberry, Raspberry
2.4
l
n/a
Olive
1.6
2
168
Pecan, Pear
3.2
1
n/a
Ornamental Herbaceous Plants, Papaya
4
1
21
Uncultivated Agricultural Areas, Paved Areas
12
1
n/a
Peach
3
1
n/a
Sorghum
0.4
1
n/a
Walnut
3
2
150
T-REX is also used to calculate EECs for terrestrial insects exposed to diuron. 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 bees. Available acute contact toxicity data for bees
exposed to diuron (in units of |ig a.i. /bee), are converted to |ig 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 diuron 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 3.4). Dietary-based EECs for small and large insects
reported by T-REX as well as the resulting adjusted EECs are available in Table 3.5.
Table 3.4 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based
Exposures of the CRLF and its Prey to Diuron		

i:i.( s for CKI.I
KIX s for Prey

(small mammals)
I sc
Dictarv-
Dose-based
Dictarv-
Dosc-bascd

bascd i:i:c
(ppin)
i:i:c
(mg/kg-bw)
bascd i:i:c
(ppm)
1 -1A
(mg/kg-
bw)
Agricultural Rights-of-
Way, Fencerows,




Hedgerows, Airports,
landing Fields, Drainage
Systems, Outdoor
Industrial Areas, Irrigation
Systems, Non-Agricultural
Rights of Way, Sewage
Disposal Areas,
Uncultivated Non-
2688.80
3062.28
4780.09
5444.05
55

-------

i:i.( s lor ( KI.I
KIX s for Prcv

(small mammals)
I sc
Dictarv-
Dosc-hascd
Dictarv-
Dosc-hascd
r i.v •

bascd i:i:(
(ppm)
i: i :c
(m«/k«-h\v)
hascd i:ix
(ppm)
1-1A
(m«/kg-
b\v)
Agricultural Areas




Alfalfa, Peppermint,
324.00
369.00
576.00
549.17
Apple, Grape
504.68
574.78
897.21
855.42
Artichoke, Asparagus
432.00
874.68
768.00
732.23
Banana, Plantain
930.06
1059.24
1653.44
1576.43
Bermuda grass,
Blackberry, Boysenberry,
833.22
948.95
1481.28
1412.29
Spearmint




Blueberry
239.50
272.77
425.79
405.95
Citrus,
563.65
641.94
1002.05
955.38
Field Corn
108.00
123.00
192.00
183.06
Cotton
452.53
515.38
804.49
767.02
Dewberry
452.83
515.73
805.03
767.54
Filbert (Hazelnut)
312.23
355.60
555.07
529.22
Grass Seed, Wheat
216.00
246.00
384.00
366.11
Loganberry, Raspberry
324.00
369.00
576.00
549.17
Olive
223.75
254.83
397.78
379.26
Ornamental Herbaceous
plants, Papaya
540.00
615.01
960.00
915.29
Uncultivated Agricultural
Areas, Paved Areas
1620.00
1845.02
2880.00
2745.86
Peach
461.25
461.25
720.00
686.46
Pear, Pecan
432.00
492.00
768.00
737.23
Sorghum
54.00
61.50
96.00
91.53
Walnut
425.76
484.9
756.92
721.66
Table 3.5 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via
Effects to Terrestrial Invertebrate Prey Items			
Use
Small Insect
Large Insect
Agricultural Rights-of-Way, Fencerows, Hedgerows,
Airports, landing Fields, Drainage Systems, Outdoor
Industrial Areas, Irrigation Systems, Non-Agricultural
Rights of Way, Sewage Disposal Areas, Uncultivated
Non-Agricultural Areas
2688.80
298.76
Alfalfa, Peppermint,
324.00
36.00
Apple, Grape
504.68
56.08
Citrus,
563.65
62.63
56

-------
Use
Small Insect
Large Insect
Artichoke, Asparagus
432.00
48.00
Banana, Plantain
930.06
103.34
Bermuda grass, Blackberry, Boysenberry, Spearmint
833.22
92.58
Blueberry
239.50
26.61
Field Corn
108.00
12.00
Cotton
452.53
50.28
Dewberry
452.83
50.31
Filbert (Hazelnut)
312.23
34.69
Grass Seed, Wheat
216.00
24.00
Loganberry, Raspberry
324.00
36.00
Olive
223.75
24.86
Pecan, Pear
432.00
48.00
Ornamental Herbaceous plants, Papaya
540.00
60.00
Uncultivated Agricultural Areas, Paved Areas
1620.00
180.00
Peach
461.25
51.25
Sorghum
54.00
6.00
Walnut
425.76
47.31
3.4 Terrestrial Plant Exposure Assessment
TerrPlant (version 1.2.2) is used to calculate EECs for non-target plants inhabiting dry
and semi-aquatic areas. Parameter values for application rate, drift assumption and
incorporation depth are based upon the use and related application method. A runoff
value of 0.02 was selected based on diuron's solubility of between 10-100 mg/L. Drift
was assumed to be 5% for aerial applications and 1% for ground applications.
TerrPlant was used to model EECs from soil and foliar applications relevant to terrestrial
plants. These EECs are presented in Table 3.6. An example output from TerrPlant
v. 1.2.2 is available in Appendix I.
57

-------
Table 3.6 TerrPlant Inputs and Resulting EECs for Plants Inhabiting Dry and
Semi-aquatic Areas Exposed to diuron via Runoff and Drift
I se
Application
rale
(lbs a.i./A)
Application
met hod
Drill
Value
(%)
Spray
drill
i: i :c
(lbs
a.i./A)
l)rv
area
i: i :c
(lbs
a.i./A)
Agricultural
Rights-of-Way,
Fencerows,
Hedgerows,
Airports, landing
Fields, Drainage
Systems, Outdoor
Industrial Areas,
Irrigation
Systems, Non-
Agricultural
Rights of Way,
Sewage Disposal
Areas,
Uncultivated
N on-Agri cultural
Areas
12
Foliar/Ground
0.12
0.36
Alfalfa,
Peppermint,
Spearmint,
Bermudagrass,
Blackberry,
Boysenberry,
Loganberry,
Raspberry,
Dewberry
2.4
Foliar/Ground
0.02
0.07
Apple, Citrus,
Pear, Grape,
Artichoke,
Asparagus, Pecan
3.2
Foliar/Ground
0.03
0.10
Asparagus
(Aerial)
3.2
Foliar/Ground
0.16
0.22
Banana, Plantain
4.8
Foliar/Ground
0.05
0.14
Blueberry,
Cotton, Grass
Seed, Olive,
Wheat
1.6
Foliar/Ground
0.02
0.05
58

-------
I si-
Application
rale
Drill
Spray
drift
l.l.(
l)rv
area
i:i.(
Seini-
aqualic
area
i:i.(
(lbs a.i./A)
Application
method
Value
(%)
(lbs
a.i./A)
(lbs
a.i./A)
(lbs
a.i./A)
Field Corn
0.8
Foliar/Ground
1
0.01
0.02
0.17
Filbert (Hazelnut)
2.2
Foliar/Ground
1
0.02
0.07
0.46
Non-agricultural
12
Aerial
5
0.60
0.84
3.00
Ornamental
Herbaceous
Plants, Papaya
4
Foliar/Ground
1
0.04
0.12
0.84
Uncultivated
Agricultural
Areas, Paved
Areas
12
Foliar/Ground
1
0.12
0.36
2.52
Peach, Walnut
3
Foliar/Ground
1
0.03
0.09
0.63
Sorghum
0.4
Foliar/Ground
1
0.00
0.01
0.08
3.4.1 Spray Drift Buffer Analysis
In order to determine terrestrial and aquatic habitats of concern due to diuron 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 and can be
found in Table 3.7.
AgDRIFT was run for terrestrial analysis only, and due to uncertainties default values
were used to determine the aquatic analysis. The default values for PRZM/EXAMS
(used for the aquatic analysis) assumed the most conservative scenario, that a buffer was
not present.
For the terrestrial assessment, the AgDRIFT model was run as a Tier I ground analysis,
as well as Tier I, and II aerial analyses focusing on determining a buffer zone for non-
listed and listed plant species. The following settings beyond the standard default
settings were implemented:
•	12 lb ai/A
•	EC25= 0.002 lb ai/A
•	ECos = 0.001 lb ai/A
•	Nonvolatile Rate (Tier II aerial only) = 25 lb/a
59

-------
•	Spray Volume Rate (Tier II aerial only) = 3 gal/a
•	Active Rate (Tier II aerial only) = 4 lb/a
The AgDRIFT model was used to evaluate potential distances beyond which exposures
would be expected to be below LOC. However, due to the limitations imposed by the
Tier 1 ground analysis, and Tiers I and II aerial analyses, which allow users to evaluate
off-site deposition and exposure out to 1,000 ft downwind from the location of the
application, the exact buffer needed for exposures to be below the LOC is uncertain.
Table 3.7 Summary of AgDRIFT Predicted Spray Drift Buffer for Terrestrial
Plants
1 iii 1 (iiuiiiMl Applitiilioii
Risk
Class
Risk Description
Application
Rate
Toxicity
Value
Used
Fraction
of
applied
Nonvolatile
Rate (lb/a)
Minimum
Spray
Volume
Rate
(gal/a)
Active
Rate
(ib
ai/a)
Distance
Non-
Listed
Plants
Potential for
effects to non-
target, non-listed
plants from
exposures
12
ec25 =
0.002 lb
ai/A
0.0002
Does not
apply
Does not
apply
Does
not
apply
> 1,000
ft
Listed
Plants
Potential for
effects to non-
target, listed
plants from
exposures
EC05 =
0.001 lb
ai/A
0.0001
1 icr 1 Vcrisil tppliiiilioii
Risk
Class
Risk Description
Application
Rate
Toxicity
Value
Used
Fraction
of
applied
Nonvolatile
Rate (lb/a)
Minimum
Spray
Volume
Rate
(gal/a)
Active
Rate
(ib
ai/a)
Distance
Non-
Listed
Plants
Potential for
effects to non-
target, non-listed
plants from
exposures
12
ec25 =
0.002 lb
ai/A
0.0002
Does not
apply
Does not
apply
Does
not
apply
> 1,000
ft
Listed
Plants
Potential for
effects to non-
target, listed
plants from
exposures
EC05 =
0.001 lb
ai/A
0.0001
Mull Vcrisil \pplit;ili<»ii
Risk
Class
Risk Description
Application
Rate
Toxicity
Value
Used
Fraction
of
applied
Nonvolatile
Rate (lb/a)
Minimum
Spray
Volume
Rate
(gal/a)
Active
Rate
(lb
ai/a)
Distance
Non-
Listed
Plants
Potential for
effects to non-
target, non-listed
plants from
exposures
12
ec25 =
0.002 lb
ai/A
0.0002
25
3
4
> 1,000
ft
Listed
Plants
Potential for
effects to non-
target, listed
plants from
exposures
EC05 =
0.001 lb
ai/A
0.0001
60

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4.0 Effects Assessment
This assessment evaluates the potential for diuron to directly or indirectly affect the
CRLF or modify its designated critical habitat. As previously discussed in Section 2.7,
assessment endpoints for the CRLF effects determination include direct toxic effects on
the survival, reproduction, and growth of CRLF, as well as indirect effects, such as
reduction of the prey base or modification of its habitat. In addition, potential
modification of critical habitat is assessed by evaluating effects to the PCEs, which are
components of the critical habitat areas that provide essential life cycle needs of the
CRLF. Direct effects to the aquatic-phase of the CRLF are based on toxicity information
for freshwater fish, while terrestrial-phase effects are based on avian toxicity data, given
that birds are generally used as a surrogate for terrestrial-phase amphibians. Because the
frog's prey items and habitat requirements are dependent on the availability of freshwater
fish and invertebrates, small mammals, terrestrial invertebrates, and aquatic and
terrestrial plants, toxicity information for these taxa are also discussed. Acute (short-
term) and chronic (long-term) toxicity information is characterized based on registrant-
submitted studies and a comprehensive review of the open literature on diuron.
As described in the Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa
include aquatic-phase amphibians, freshwater fish, freshwater invertebrates, aquatic
plants, birds (surrogate for terrestrial-phase amphibians), mammals, terrestrial
invertebrates, and terrestrial plants.
Toxicity endpoints are established based on data generated from guideline studies
submitted by the registrant, and from open literature studies that meet the criteria for
inclusion into the ECOTOX database maintained by EPA/Office of Research and
Development (ORD) (U.S. EPA, 2004). Open literature data presented in this assessment
were obtained from as well as ECOTOX information obtained on [11/30/2007], In order
to be included in the ECOTOX database, papers must meet the following minimum
criteria:
(1)	the toxic effects are related to single chemical exposure;
(2)	the toxic effects are on an aquatic or terrestrial plant or animal species;
(3)	there is a biological effect on live, whole organisms;
(4)	a concurrent environmental chemical concentration/dose or application
rate is reported; and
(5)	there is an explicit duration of exposure.
Data that pass the ECOTOX screen are evaluated along with the registrant-submitted
data, and may be incorporated qualitatively or quantitatively into this endangered species
assessment. In general, effects data in the open literature that are more conservative than
the registrant-submitted data are considered. The degree to which open literature data are
quantitatively or qualitatively characterized for the effects determination is dependent on
whether the information is relevant to the assessment endpoints (i.e., maintenance of
CRLF survival, reproduction, and growth) identified in Section 2.8. For example,
61

-------
endpoints such as behavior modifications are likely to be qualitatively evaluated, unless
quantitative relationships between modifications and reduction in species survival,
reproduction, and/or growth are 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 diuron.
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 J. This section also includes a
rationale for rejection of those studies that did not pass the ECOTOX screen and those
that were not evaluated as part of this endangered species risk assessment.
A detailed spreadsheet of the available ECOTOX open literature data, including the full
suite of lethal and sublethal endpoints is presented in Appendix J. This section also
includes a summary of the human health effects data for diuron.
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 diuron. A summary of the available aquatic and
terrestrial ecotoxicity information, use of the probit dose response relationship, and the
incident information for diuron are provided in Sections 4.1 through 4.4, respectively.
The terminal residues of concern in plants and animals are diuron (parent) and
metabolites convertible to 3, 4-DCA including desmethoxy-linuron, norlinuron,
desmethyl diuron, and hydroxy-norlinuron. The Agency determined that 3, 4-DCA was
not of regulatory concern in connection with the registered use of diuron due to the very
low levels at which the chemical is detected in plants and animals (<0.01ppm). The
Agency concluded that with the possible exception of 3,4-DCA itself, metabolites
convertible to 3,4-DCA are not likely to be more toxic than the parent compound. This
risk assessment considers the total residues of diuron as parent diuron for purposes of risk
assessment
A detailed summary of the available ecotoxicity information for all diuron degradates and
formulated products are presented in Appendix L.
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
62

-------
are available for a formulated product containing more than one active ingredient, they
may be used qualitatively or quantitatively5 6.
There are no product LD50 values, with associated 95% Confidence Intervals (CIs)
available for diuron.
As discussed in USEPA (2000) a quantitative component-based evaluation of mixture
toxicity requires data of appropriate quality for each component of a mixture. In this
mixture evaluation, an LD50 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 formulated products for diuron do not have LD50 data available it is not
possible to undertake a quantitative or qualitative analysis for potential interactive effects.
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.
4.1 Toxicity of Diuron to Aquatic Organisms
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 L.
Table 4.1 Freshwater Aquatic Toxicity Profile for Diuron
Assessment
Endpoint
Species
Toxicity Value
Used in Risk
Assessment
Citation
MRID # or
ECOTOX #
Comment
Acute Direct
Toxicity to
Aquatic-Phase
CRLF
Striped Bass
(Morone
saxatilis)
96h LC50= 400 ppb
ECOTOX
102151
Supplemental1
Chronic Direct
Toxicity to
Aquatic-Phase
CRLF
Fathead
Minnows
(Pimephales
promelas)
NOAEC = 26 ppb
ai
MRID
00141636
Acceptable
(Based on No.
of Survivors)
Indirect
Toxicity to
Aquatic-Phase
Scud
(Gammmarus
fasciatus)
48hEC50 = 160 ppb
ai
MRID
40094602
Acceptable
5	Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs, Environmental
Protection Agency (January 2004) (Overview Document).
6	Memorandum to Office of Prevention, Pesticides and Toxic Substance, US EPA conveying an evaluation
by the U.S. Fish and Wildlife Service and National Marine Fisheries Service of an approach to assessing
the ecological risks of pesticide products (January 2004).
63

-------
Table 4.1 Freshwater Aquatic Toxicity Profile for Diuron
Assessment
Endpoint
Species
Toxicity Value
Used in Risk
Assessment
Citation
MRU) # or
ECOTOX #
Comment
CRLF via
Acute Toxicity
to Freshwater
Invertebrates
(i.e. prey items)




Indirect
Toxicity to
Aquatic-Phase
CRLF via
Chronic
Toxicity to
Freshwater
Invertebrates
(i.e. prey items)
Water Flea
(Daphnia
magna)
28d NOAEC = 200
ppb ai
MRID
TN2418
Supplemental1
Indirect
Toxicity to
Aquatic-Phase
CRLF via
Acute Toxicity
to Non-vascular
Aquatic Plants
Green Algae
(Selenastrum
capricornutu
m)
EC50 = 2.40 ppb ai
MRID
42218401
Acceptable
Indirect
Toxicity to
Aquatic-Phase
CRLF via
Acute Toxicity
to Vascular
Aquatic Plants
Duckweed
{Lemna
perpusilla)
7d EC50 =15 ppb
ECOTOX
8628
Supplemental1
1 This study is considered to be supplemental due to lack of raw data and replicates.
Toxicity to aquatic fish and invertebrates is categorized using the system shown in Table
4.2 (U.S. EPA, 2004). Diuron falls in the range of "highly toxic" (0.1 to 1 ppm or 100 to
1000 ppb for fish and invertebrates. Toxicity categories for aquatic plants have not been
defined.
Table 4.2 Categories of Acute Toxicity for Aquatic Organisms
LCso (ppm)
Toxicity Category
<0.1
Very highly toxic
>0.1-1
Highly toxic
>1-10
Moderately toxic
>10-100
Slightly toxic
> 100
Practically nontoxic
64

-------
4.1.1 Toxicity to Freshwater Fish
Given that no diuron 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 diuron
to the CRLF. Effects to freshwater fish resulting from exposure to diuron could
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).
Diuron is highly toxic to both warm water and cold water freshwater fish on an acute
exposure basis. The most sensitive freshwater species tested was the warm water Striped
Bass species, which exhibited a 96-hour LC50 value of 400 ppb (ECOTOX 102151).
Another acute study accepted by the Agency showed the cold water Cutthroat Trout
having an acute 96h LC50 of 710 ppb ai (MRID 40098001). The Fathead Minnow
exhibited a chronic toxicity NOAEC of 26 ppb based on number of survivors (MRID
00141636).
4.1.2 Toxicity to Freshwater Invertebrates
Freshwater aquatic invertebrate toxicity data were used to assess potential indirect effects
of diuron to the CRLF. Effects to freshwater invertebrates resulting from exposure to
diuron could indirectly affect the CRLF via reduction in available food items. As
discussed in Section 2.5.3, the main food source for juvenile aquatic- and terrestrial-
phase CRLFs is thought to be aquatic invertebrates found along the shoreline and on the
water surface, including aquatic sowbugs, larval alderflies and water striders.
Diuron is highly acutely toxic to freshwater invertebrates based on acceptable studies on
the Scud. This species exhibited a 48-hour EC50 value of 160 ppb (MRID: 40094602).
Chronic toxicity studies showed the Water Flea as exhibiting a 28d NOAEC of 200 ppb
(MRID: TN2418).
4.1.3 Toxicity to Aquatic Plants
Aquatic plant toxicity studies were used as one of the measures of effect to evaluate
whether diuron 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 diuron to affect aquatic plants.
Laboratory and field studies were used to determine whether diuron 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 4.1.4.
The Green Alga Selenastrum capricornutum exhibited the most sensitive non-vascular
plant acute endpoint with an EC50 of 2.40 ppb. The aquatic vascular plant Lemna
65

-------
perpusilla exhibited the most sensitive vascular acute endpoint with a 7d EC50 of 15 ppb
ai (ECOTOX 8628).
4.2 Toxicity of Diuron to Terrestrial Organisms
Table 4.3 summarizes the most sensitive terrestrial toxicity endpoints for the CRLF,
based on an evaluation of both the submitted studies and the open literature. A brief
summary of submitted and open literature data considered relevant to this ecological risk
assessment for the CRLF is presented below.
Table 4.3 Terrestrial Toxicity Profile for Diuron
Endpoint
Species
Toxicity Value Used in
Risk Assessment
Citation
MR ID#
Comment
Acute Direct
Toxicity to
Terrestrial-
Phase CRLF
(LD50)
Mallard Duck
(Anas
platyrhynchos)
14d LD50 =>2000
mg/kg-bw
MRID
00160000
Acceptable
No mortality reported. Ataxia
persisted for 1 Id after study
Acute Direct
Toxicity to
Terrestrial-
Phase CRLF
(LC50)
Northern
Bobwhite Quail
(Colinus
virgianus)
9d LC50 = 1730 ppm ai
MRID
00022923
Acceptable
Chronic
Direct
Toxicity to
Terrestrial-
Phase CRLF
No Acceptable
Study Available
Indirect
Toxicity to
Terrestrial-
Phase CRLF
(via acute
toxicity to
mammalian
prey items)
Laboratory Rat
(Rattus
norvegieus)
LD50 -
<$ 5000 mg/kg-bw
$ 10000 mg/kg-bw
MRID
00146145
Acceptable
Indirect
Toxicity to
Terrestrial-
Phase CRLF
(via chronic
toxicity to
mammalian
prey items)
Laboratory Rat
(Rattus
norvegieus)
NOAEC = 250 ppm
MRID
00146145
Acceptable
Indirect
Toxicity to
Terrestrial-
Phase CRLF
(via acute
toxicity to
terrestrial
invertebrate
prey items)
Honey Bee
(Apis mellifera)
LD50 >145 (ig/bee
(1133.05 ppm)
MRID
00036935
Acceptable
(Only 2.7% mortality observed
at highest level tested)
Indirect
Dicot Seedling
EC-h = 0.075 lb ai/A
MRID
Acceptable
66

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Endpoint
Species
Toxicity Value Used in
Risk Assessment
Citation
MRID#
Comment

Emergence
Tomato

44113401


(Lycopersicon
esculentum)



Toxicity to
Terrestrial-
Dicot Vegetative
Vigor Tomato
(.Lycopersicon
esculentum)
EC25 = 0.002 lb ai/A
MRID
44113401
Acceptable
and Aquatic-




Phase CRLF
Monocot



(via toxicity
to terrestrial
plants)
Seedling
Emergence
Onion
(Allium cepa)
EC25 = 0.099 lb ai/A
MRID
44113401
Acceptable

Monocot




Vegetative Vigor
Wheat
(Triticum
aestivum)
EC25 = 0.021 lb ai/A
MRID
44113401
Acceptable
Acute toxicity to terrestrial animals is categorized using the classification system shown
in Table 4.4 (U.S. EPA, 2004). Toxicity categories for terrestrial plants have not been
defined.
Table 4.4 Categories of Acute Toxicity for Avian and Mammalian Studies
Toxicity Category
Oral LDsn
Dietary LC50
Very highly toxic
<10 mg/kg
< 50 ppm
Highly toxic
10-50 mg/kg
50 - 500 ppm
Moderately toxic
51 - 500 mg/kg
501 - 1000 ppm
Slightly toxic
501 - 2000 mg/kg
1001 - 5000 ppm
Practically non-toxic
> 2000 mg/kg
> 5000 ppm
4.2.1 Toxicity to Birds
As specified in the Overview Document, the Agency uses birds as a surrogate for
terrestrial-phase amphibians when amphibian toxicity data are not available (U.S. EPA,
2004). No terrestrial-phase amphibian data are available for diuron; therefore, acute and
chronic avian toxicity data are used to assess the potential direct effects of diuron to
terrestrial-phase CRLFs.
There are no data by which to assess chronic toxicity to avian species (surrogates for the
terrestrial phase frog) either submitted by the registrants or in the public literature.
Linuron, a similar chemical of the same class, has acceptable chronic avian data. The
avian reproductive studies for linuron (MRID 42541801, 42541802) using mallard duck
and bobwhite quail found reproductive effects at 300 ppm ai with an NOAEL being
established at 100 ppm. The endpoints affected for mallard duck reproduction are egg
production, adult body weight, feed consumption, viable embryos of eggs set, number of
viable embryos, and number of live embryos. For the bobwhite quail the endpoints
67

-------
affected are hatchability and offspring survivability. This suggests that diuron may have
chronic effects to avian species, but these risks cannot be quantified in the absence of
data.
4.2.2	Toxicity to Mammals
Mammalian toxicity data are used to assess potential indirect effects of diuron to the
terrestrial-phase CRLF. Effects to small mammals resulting from exposure to diuron
could also indirectly affect the CRLF via reduction in available food. As discussed in
Section 2.5.3, over 50% of the prey mass of the CRLF may consist of vertebrates such as
mice, frogs, and fish (Hayes and Tennant, 1985).
An acute oral LD50 of 5000 mg/kg-bw was observed in the Laboratory Rat (MRID
00146145). The Laboratory Rat NOAEC is 250 ppm (MRID 00146145).
4.2.3	Toxicity to Terrestrial Invertebrates
Terrestrial invertebrate toxicity data are used to assess potential indirect effects of diuron
to the terrestrial-phase CRLF. Effects to terrestrial invertebrates resulting from exposure
to diuron could also indirectly affect the CRLF via reduction in available food. Diuron is
classified as practically non-toxic to the Honey Bee. The acute LD50 for Honey Bee is
>145.03 |ig/bee (MRID 00036935). Only 2.7% mortality was observed in this study at
the highest level tested. The test was therefore not definitive and RQs were not
calculated. There were no additional acceptable terrestrial invertebrate data from
registrant submitted studies or from the open literature by which to calculate RQ values.
4.2.4	Toxicity to Terrestrial Plants
Terrestrial plant toxicity data are used to evaluate the potential for diuron to affect
riparian zone and upland vegetation within the action area for the CRLF. Impacts to
riparian and upland (i.e., grassland, woodland) vegetation could result in indirect effects
to both aquatic- and terrestrial-phase CRLFs, as well as modification to designated
critical habitat PCEs via increased sedimentation, alteration in water quality, and
reduction in of upland and riparian habitat that provides shelter, foraging, predator
avoidance and dispersal for juvenile and adult CRLFs.
Plant toxicity data from both registrant-submitted studies and studies in the scientific
literature were reviewed for this assessment. Registrant-submitted studies are conducted
under conditions and with species defined in EPA toxicity test guidelines. Sub-lethal
endpoints such as plant growth, dry weight, and biomass are evaluated for both monocots
and dicots, and effects are evaluated at both seedling emergence and vegetative life
stages. 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.
68

-------
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 diuron, 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.
The most sensitive endpoints reported for diuron exposure to dicot plants are a vegetative
vigor EC25 value of 0.002 lb ai/A and a seedling emergence EC25 value of 0.075 lb ai/A as
expressed by tomato plants (MRID 44113401). The most sensitive endpoints reported
for diuron exposure to monocot plants are a vegetative vigor EC25 value of 0.021 lb ai/A
as expressed by Wheat, and a seedling emergence EC25 value of 0.099 lb ai/A as
expressed by Onion (MRID 44113401). The results of the Tier II seedling emergence
and vegetative vigor toxicity tests on non-target plants are summarized below in Table
4.5.
Table 4.5 Terrestrial Plant Toxicity Profile for Diuron
Endpoint
Species
Toxicity Value Used
in Risk Assessment
Citation
MRID#
Comment

Dicot Seedling
Emergence
Tomato
(Lycopersicon
esculentum)
EC25 = 0.075 lb ai/A
MRID
44113401
Acceptable
Indirect
Toxicity to
Terrestrial-
and Aquatic-
Dicot Vegetative
Vigor Tomato
(.Lycopersicon
esculentum)
EC25 = 0.002 lb ai/A
MRID
44113401
Acceptable
Phase CRLF
(via toxicity
to terrestrial
plants)
Monocot
Seedling
Emergence
Onion
(Allium cepa)
EC25 = 0.099 lb ai/A
MRID
44113401
Acceptable

Monocot
Vegetative Vigor
Wheat
(Triticum
aestivum)
EC25 = 0.021 lb ai/A
MRID
44113401
Acceptable
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 diuron on par with the acute toxicity endpoint selected for RQ
calculation. To accomplish this interpretation, the Agency uses the slope of the dose
69

-------
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.
4.4 Incident Database Review
A review of the EIIS database for ecological incidents involving diuron was completed
on 12/18/08. Thirty highly probable, probable or possible incidents involving diuron
have been reported. These uses were either registered uses or undetermined uses. One of
these incidents resulted in a bird kill, 22 resulted in plant damage and seven resulted in
fish kills. A detailed description of incidents relating to diuron use is presented in
Appendix M. These incidents will be used in addition to other lines of evidence to draw
conclusions regarding the risks of diuron to the CRLF.
The absence of additional documented incidents does not necessarily mean that such
incidents did not occur. Mortality incidents must be seen, reported, investigated, and
submitted to the Agency in order to be recorded in the incident database. Incidents may
not be noticed because the carcasses decayed, were removed by scavengers, or were in
out-of-the-way or hard-to-see locations. Due to the voluntary nature of incident reporting,
an incident may not be reported to appropriate authorities capable of investigating it.
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 diuron 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
70

-------
concern (LOCs) for each category evaluated (Appendix E). For acute exposures to the
CRLF and its animal prey in aquatic habitats, as well as terrestrial invertebrates, the LOC
is 0.05. For acute exposures to the CRLF and mammals, the LOC is 0.1. The LOC for
chronic exposures to CRLF and its prey, as well as acute exposures to plants is 1.0.
Risk to the aquatic-phase CRLF is estimated by calculating the ratio of exposure to
toxicity using l-in-10 year EECs based on the label-recommended diuron usage scenarios
summarized in Table 3.2 and the appropriate aquatic toxicity endpoint from Table 4.1.
Risks to the terrestrial-phase CRLF and its prey (e.g. terrestrial insects, small mammals
and terrestrial-phase frogs) are estimated based on exposures resulting from applications
of diuron (Tables 3.5 through 3.6) and the appropriate toxicity endpoint from Table 4.6.
Exposures are also derived for terrestrial plants, as discussed in Section 3.3 and
summarized in Table 3.7, based on the highest application rates of diuron use within the
action area.
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 peak EECs in the standard pond
and the lowest acute toxicity value for freshwater fish. In order to assess direct chronic
risks to the CRLF, 60-day EECs and the lowest chronic toxicity value for freshwater fish
are used. The RQs for diuron uses results in acute and chronic exceedances of the
Agency's LOC for freshwater fish which are surrogates for the aquatic phase for
amphibians.
The aquatic phase amphibian acute LOCs for listed species (0.05) are exceeded for most
uses of diuron in California. Acute RQs that exceed the Agency's LOC range from 12.28
(paved areas) to 0.06 (papaya and walnut). Chronic RQs that exceed the Agency's LOC
for chronic exposure (1.0) range from 131.85 (paved areas) to 1.26 (banana, plantain). A
probit slope value for the acute fathead minnow toxicity test is not available; therefore,
the individual effect probability was estimated based on a default slope assumption of 4.5
with upper and lower 95% confidence intervals of 2 and 9 (Urban and Cook, 1986). The
estimated probability of an individual effect for treatments that exceeded the Agency's
acute RQs for listed species ranged from approximately 1 in 1 for paved areas to
approximately 1 in 1.64 E+4 for banana/plantain (upper and lower 95% confidence
intervals of 1 in 2.28 E+01 to 1 in 1.29 E+14). Based on these exceedances, diuron
May Affect the aquatic-phase of the CRLF. Results are presented in Table 5 .1.
71

-------
Table 5.1. Summary of Direct Effect RQs for the Aquatic-phase CRLF
l si-
Diivii
1'. MVils
In
C kl.l '
SuiTii»;ik-
S|K-iii-s
Tn\ii'ii>
Value
II. (
IV;ik/fiOil
RQ
Pnihiihililx
11I' liuli\ iduiil
l.lliii 1
l.(H
r.ui'i'ikiiui-
iind Risk
liiu-rpivliiliiin
AGR1CLLTLR.IL
R1GHTS-OF-
WA Y/FENCERO WS/
HEDGEROWS
Aailc
Direct
Toxicity
Si II pod
Bass
LCJV
400
l.X"
1.72
1 1111.1" (.1
in 1.47 to 1
in 1.07)b
Ycsc
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
456.81
17.57
Not
applicable
for chronic
endpoints
Yes'1
ALFALFA
Acute
Direct
Toxicity
Striped
Bass
lc50 =
400
10.63
0.03
1 in
2.75E+11 (1
in 1.00 E+16
to 1 in 8.63
E+02)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
7.20
0.28
Not
applicable
for chronic
endpoints
No
ALFALFA (Aerial)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
13.69
0.03
1 in
2.75E+11 (1
in 1.00 E+16
to 1 in 8.63
E+02)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
9.40
0.36
Not
applicable
for chronic
endpoints
No
APPLE
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
11.68
0.03
1 in
2.75E+11 (1
in 1.00 E+16
to 1 in 8.63
E+02)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
7.80
0.30
Not
applicable
for chronic
endpoints
No
ARTLCHOKE
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
32.00
0.08
1 in
2.51E+06 (1
in 1.00 E+16
to 1 in 7.08
E+l)b
Yes'
72

-------

Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
25.08
0.96
Not
applicable
for chronic
endpoints
No
ASPARGUS
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
36.99
0.09
1 in 7.90
E+05 (1 in
1.00 E+16 to
1 in 1.00
E+06)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
22.92
0.88
Not
applicable
for chronic
endpoints
No
BANANA,
PLANTAIN
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
54.21
0.14
1 in 1.64
E+4 (1 in
2.28 E+01 to
1 in 1.29
E+14)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
32.78
1.26
Not
applicable
for chronic
endpoints
Yes"
BLACKBERRY,
BOYSENBERRY
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
139.70
0.35
1 in
4.98E+01 (1
in 5.53 to 1
in 4.91
E+4)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
102.90
3.96
Not
applicable
for chronic
endpoints
Yes4
BLUEBERRY
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
4.65
0.01
<1 in
1.00E+16 (1
in 3.16 E+04
to <1 in
1.00E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
3.21
0.12
Not
applicable
for chronic
endpoints
No
CITRUS
Acute
Direct

LC50 =
400
6.83
0.02
1 in 9.48
E+13 (1 in
No
73

-------

Toxicity




2.95 E+3 to
<1 in 1.00
E+16)b

Chronic
Direct
Toxicity
Rainbow
Trout
NOAEC =
26
4.88
0.19
Not
applicable
for chronic
endpoints
No
CORN, FIELD
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
7.24
0.02
1 in 9.48
E+13 (1 in
2.95 E+3 to
<1 in 1.00
E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
4.68
0.18
Not
applicable
for chronic
endpoints
No
DEWBERRY
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
19.71
0.05
1 in 4.17
E+08 (1 in
2.16 E+02
to <1 in 1.00
E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
14.29
0.55
Not
applicable
for chronic
endpoints
No
FILBERT
(HAZELNUT)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
18.90
0.05
1 in 4.17
E+08 (1 in
2.16 E+02
to <1 in 1.00
E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
12.16
0.47
Not
applicable
for chronic
endpoints
No
GRAPE
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
9.71
0.02
1 in 9.48
E+13 (1 in
2.95 E+3 to
<1 in 1.00
E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
6.37
0.24
Not
applicable
for chronic
endpoints
No
LOGANBERRY,
RASPBERRY
Acute
Direct
Striped
Bass
LC50 =
400
5.13
0.01
<1 in
1.00E+16 (1
No
74

-------
(BLACK/RED)
Toxicity




in 3.16 E+04
to <1 in
1.00E+16)b

Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
3.02
0.12
Not
applicable
for chronic
endpoints
No
OLIVE
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
7.17
0.02
1 in 9.48
E+13 (1 in
2.95 E+3 to
<1 in 1.00
E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
4.86
0.19
Not
applicable
for chronic
endpoints
No
PAPAYA
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
25.21
0.06
1 in 5.20
E+07 (1 in
1.38 E+02 to
<1 in 1.00
E+16)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
15.72
0.60
Not
applicable
for chronic
endpoints
No
PEPPERMINT
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
4.17
0.01
<1 in
1.00E+16 (1
in 3.16 E+04
to <1 in
1.00E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
2.79
0.11
Not
applicable
for chronic
endpoints
No
PEACH
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
10.95
0.03
1 in
2.75E+11 (1
in 1.00 E+16
to 1 in 8.63
E+02)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
7.31
0.28
Not
applicable
for chronic
endpoints
No
PEAR
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
11.66
0.03
1 in
2.75E+11 (1
in 1.00 E+16
to 1 in 8.63
E+02)b
No
75

-------

Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
7.79
0.30
Not
applicable
for chronic
endpoints
No
PECAN
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
27.04
0.07
1 in 9.86
E+06 (1 in
9.57 E+l to
<1 in 1.00
E+16)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
17.33
0.67
Not
applicable
for chronic
endpoints
No
SORGHUM
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
5.87
0.01
<1 in
1.00E+16 (1
in 3.16 E+04
to <1 in
1.00E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
4.52
0.17
Not
applicable
for chronic
endpoints
No
SPEARMINT
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
106.70
0.27
1 in
1.90E+02 (1
in 7.83 to 1
in 6.46
E+06)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
81.95
3.15
Not
applicable
for chronic
endpoints
Yesd
WALNUT
(ENGLISH/BLACK)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
25.78
0.06
1 in 5.20
E+07 (1 in
1.38 E+02 to
<1 in 1.00
E+16)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
16.58
0.64
Not
applicable
for chronic
endpoints
No
WHEAT (pre-
harvest)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
18.03
0.05
1 in 4.17
E+08 (1 in
2.16 E+02
to <1 in 1.00
E+16)b
No
76

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Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
12.02
0.46
Not
applicable
for chronic
endpoints
No
WHEAT (post-
harvest)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
12.82
0.03
1 in
2.75E+11 (1
in 1.00 E+16
to 1 in 8.63
E+02)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
10.29
0.40
Not
applicable
for chronic
endpoints
No
COTTON (ground)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
8.36
0.02
1 in 9.48
E+13 (1 in
2.95 E+3 to
<1 in 1.00
E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
5.72
0.22
Not
applicable
for chronic
endpoints
No
COTTON (aerial)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
14.25
0.04
1 in 6.30
E+09 (1 in
3.86 E+02 to
<1 in 1.00
E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
10.24
0.39
Not
applicable
for chronic
endpoints
No
AIRPORTS/
LANDING FIELDS,
DRAINAGE
SYSTEMS
INDUSTRIAL
AREAS
(OUTDOOR),
SEWAGE
DISPOSAL AREAS
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
2190.00
5.48
~1 in lb
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
1382.00
53.15
Not
applicable
for chronic
endpoints
Yes"
BERMUDAGRASS
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
226.00
0.57
1 in 7.35 (1
in 3.20 to 1
in 7.14
E+01)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
167.90
6.46
Not
applicable
for chronic
endpoints
Yes'1
77

-------
GRASSES GROWN
FOR SEED
Acute
Direct
Toxicity
Striped
Bass
£ r
o
II
3.76
0.01
<1 in
1.00E+16 (1
in 3.16 E+04
to <1 in
1.00E+16)b
No
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
2.89
0.11
Not
applicable
for chronic
endpoints
No
IRRIGATION
SYSTEMS
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
52.56
0.13
1 in
2.99E+04 (1
in 2.62 E+01
to 1 in 1.29
E+15)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
37.45
1.44
Not
applicable
for chronic
endpoints
Yes'
ORNAMENTAL
HERBACEOUS
PLANTS
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
36.55
0.09
1 in 7.90
E+05 (1 in
5.48 E+01 to
<1 in 1.00
E+16)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
23.56
0.91
Not
applicable
for chronic
endpoints
No
NON-
AGRICULTURAL
RIGHTS OF WAY
(ground)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
629.91
1.57
1 in 1.23.(1
in 1.53 to 1
in 1.04)b
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
476.35
18.32
Not
applicable
for chronic
endpoints
Yes'
NON-
AGRICULTURAL
RIGHTS OF WAY
(aerial)
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
626.91
1.57
1 in 1.23.(1
in 1.53 to 1
in 1.04)b
Yes*
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
468.16
18.01
Not
applicable
for chronic
endpoints
Yesd
PAVED AREAS
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
4911.00
12.28
~1 in lb
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
3428.00
131.85
Not
applicable
for chronic
endpoints
Yes'
78

-------
UNCULTIVATED
AG
Acute
Direct
Toxicity
Striped
Bass
£ r
o
II
1130.00
2.83
~1 in lb
Yes'
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
840.40
32.32
Not
applicable
for chronic
endpoints
Yesd
UNCULTIVATED
NON-AG
Acute
Direct
Toxicity
Striped
Bass
LC50 =
400
284.80
0.71
1 in 3.97(1
in 2.61 to 1
in 1.11
E+01)b
Yes1
Chronic
Direct
Toxicity
Fathead
Minnow
NOAEC =
26
202.50
7.79
Not
applicable
for chronic
endpoints
Yes'
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 A probit slope value for the acute fathead minnow toxicity test is not available; therefore, the effect probability was calculated
based on a default slope assumption of 4.5 with upper and lower 95% confidence intervals of 2 and 9 (Urban and Cook, 1986).
c RQ > acute endangered species LOC of 0.05.
dRQ> 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 diuron to the aquatic-phase CRLF (tadpoles) via reduction in non-
vascular aquatic plants in its diet are based on peak EECs from the standard pond and the
lowest acute toxicity value for aquatic non-vascular plants. The Agency's LOC (1.0) is
exceeded for all current uses of diuron in California. The RQs range from 2046.25
(paved areas) to 1.57 (grasses grown for seed). Results are presented in Table 5.2.
Based on these exceedances, diuron May Affect the CRLF via reduction of non-
vascular plants.
79

-------
Table 5.2 Summary of Acute 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 CR
LF)*
l SI'S
Applkiilinn
nili- (II) ;ii/.\)
A|)|)lii;ili(ili
Mi-lhml
IY;ik
I.I. (
(ii»/l.)
liidiivil i-ITi-ils RQ :
(I'ikkI iiiul hiihiiiii)
2N(i.50
4.43
AGRICULTURAL RIGHTS-OF-
WAY/FENCEROW S/HEDGEROW S
ALFALFA
12
Ground
687.59
2.4
Ground
10.63
2.4
Aircraft
13.69
5.71
APPLE
3.2
Ground
11.68
4.S7
ARTICHOKE
3.2
Ground
32.00
13.33
ASPARGUS
4.8
Ground
36.99
15.41
BANANA, PLANTAIN
2.4
Ground
54.21
22.5'>
BLACKBERRY, BOYSENBERRY
1.6
Ground
139.70
5S.2I
BLUEBERRY
2.4
Ground
4.65
l.'M
CITRUS
3.2
Ground
6.83
2.S5
CORN, FIELD
0.8
Ground
7.24
3.02
DEWBERRY
2.4
Ground
19.71
S.2I
FILBERT (HAZELNUT)
2.2
Ground
18.90
7.87
80

-------
l SI'S
.\|>|>lk;ilii>ll
nili- (II) ;ii/.\)
A|)|)lii;ili(ili
\klhml
IY;ik
I.I. (
(iiS/l.)
liiriiivil i-fli-ils RQ :
(I'm id ;mkI li;il)iliil)
4.04
GRAPE
3.2
Ground
9.71
LOGANBERRY, RASPBERRY
(BLACK/RED)
2.4
Ground
5.13
2.14
OLIVE
1.6
Ground
7.17
2.')')
PAPAYA
4
Ground
25.21
10.50
PEPPERMINT
2.4
Ground
4.17
1.74
PEACH
3
Ground
10.95
4.5f.
PEAR
3.2
Ground
11.66
4.Sfi
PECAN
3.2
Ground
27.04
11.27
SORGHUM
4.8
Ground
5.87
2.45
SPEARMINT
2.4
Ground
106.70
44.4r.
WALNUT (ENGLISH/BLACK)
0.4
Ground
25.78
10.74
WHEAT
2.4
Pre-Harvest
18.03
7.51
3
Post-
Harvest
12.82
5.34
COTTON
1.6
Ground
8.36
3.4S
Aircraft
14.25
5.'M
81

-------
l SI'S
.\|>|>lk;ilii>ll
nili- (II) ;ii/.\)
A|)|)lii;ili(ili
\klhml
IY;ik
I.I. (
(iiS/l.)
liiriiivil i-ITi-ils RQ :
(I'm id ;mkI li;il)iliil)
•>12.50
AIRPORTS/ LANDING FIELDS,
DRAINAGE SYSTEMS,
INDUSTRIAL AREAS
(OUTDOOR), SEWAGE DISPOSAL
AREAS
12
Ground
2190.00
BERMUDAGRASS
2.4
Ground
226.00
'M.I 7
GRASSES GROWN FOR SEED
12
Ground
3.76
1.57
IRRIGATION SYSTEMS
1.6
Ground
52.56
2I.'>0
ORNAMENTAL HERBACEOUS
PLANTS
12
Ground
36.55
15.23
NON-AGRICULTURAL RIGHTS
OF WAY
12
Ground
629.91
2r.2.4r.
4
Aircraft
626.91
261.21
PAVED AREAS (PRIVATE
ROADS/SIDEWALKS)
12
Ground
4911.00
2IW6.25
UNCULTIVATED AG
12
Ground
1130.00
470.S3
4S7.0S
12
Ground
1169.00
UNCULTIVATED NON-AG
12
Ground
284.80
11 S.f.7
82

-------
l SI'S
Applkiilinn
nili- (II) ;ii/.\)
Application
Milliml
IY;ik
I.I. (
(ii»/l.)
Indiri-il i-lli-ils RQ-
(I'm id ;mkI h;il)iliil)




* LOC exceedances (RQ > 1.0) are bolded and shaded. RQ = use-specific peak EEC/ [Selenastrum capricornutum
EC50 = 2.40 ppb].
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. For chronic risks, 21-day EECs and the lowest
chronic toxicity value for invertebrates are used to derive RQs. The Agency's acute
Listed LOC (0.05) is exceeded for most uses of diuron in California. The acute RQs that
exceed the LOC range from 30.69 (Paved Areas) to 0.06 (grape). The chronic RQs
exceed the Agency's LOC for several used. The chronic values that exceeded range from
21.21 (Paved Areas) to 1.02 (Bermudagrass). 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 acute Listed LOC exceedances for chronic and acute
aquatic invertebrates from most use sites, diuron May Affect the CRLF indirectly
via reduction in freshwater invertebrate prey items.
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)*	
I si-s
Applkiilinn
l llll' (II)
;ii/A)
A|)|)lii;iliiin
Mi-llmd
IY;ik
l.l.t
(iiii/l-l
21 l);i>
I.I. (
|)|)l>
lndiri-il
IHTi'iis
Aiulc
RQ
Indin-ii
1". ITi-ils
Cli ii in i i'
RQ
AGRICULTURAL RIGHTS-OF-
WAY/FENCEROW S/HEDGEROW S
12
Ground
687.59
672.03
4.30
2.'>2
ALFALFA
2.4
Ground
10.63
10.37
imp
005
2.4
Aircraft
13.69
13.29
o.oy
	
83

-------







APPLE
3.2
Ground
11.68
11.22
0.07
0.05
ARTICHOKE
3.2
Ground
32.00
31.15
0.20
0.14
ASPARGUS
4.8
Ground
36.99
35.46
0.23
0.15
BANANA, PLANTAIN
2.4
Ground
54.21
51.95
0.34
0.22
BLACKBERRY, BOYSENBERRY
1.6
Ground
139.70
135.80
O.S^
0.60
BLUEBERRY
2.4
Ground
4.65
4.48
0.03
0.02
CITRUS
3.2
Ground
6.83
6.57
0.04
0.03
CORN, FIELD
0.8
Ground
7.24
6.95
0.05
0.03
DEWBERRY
2.4
Ground
19.71
19.25
0.12
0.08
FILBERT (HAZELNUT)
2.2
Ground
18.90
18.41
0.12
0.08
GRAPE
3.2
Ground
9.71
9.32
0.0(>
0.04
LOGANBERRY, RASPBERRY
(BLACK/RED)
2.4
Ground
5.13
4.95
0.03
0.02
OLIVE
1.6
Ground
7.17
6.90
0.04
0.03
PAPAYA
4
Ground
25.21
24.56
O.I(>
0.11
PEPPERMINT
2.4
Ground
4.17
4.05
1)0'
0.02
PEACH
3
Ground
10.95
10.51
0.07
0.05
PEAR
3.2
Ground
11.66
11.20
0.0"7
0.05
PECAN
3.2
Ground
27.04
26.33
o.r
0.11
SORGHUM
4.8
Ground
5.87
5.67
0.04
0.03
SPEARMINT
2.4
Ground
106.70
103.70
O.h"7
0.49
84

-------







WALNUT (ENGLISH/BLACK)
0.4
Ground
25.78
25.11
0. Hi
0.11
WHEAT
2.4
Pre-Harvest
18.03
17.34
0.1 1
1 I.I IS
0.07
3
Post-
Harvest
12.82
12.34
0.06
COTTON
1.6
Ground
8.36
8.13
0.05
0.04
Aircraft
14.25
13.88
0.1(9
IKK.
AIRPORTS/ LANDING FIELDS,
DRAINAGE SYSTEMS,
INDUSTRIAL AREAS
(OUTDOOR), SEWAGE DISPOSAL
AREAS
12
Ground
2190.00
2115.00
1
'>.13
BERMUDAGRASS
2.4
Ground
226.00
218.80
1.41
1.02
GRASSES GROWN FOR SEED
12
Ground
3.76
3.62
0.02
0.02
IRRIGATION SYSTEMS
1.6
Ground
52.56
50.67
0.33
u: ^
ORNAMENTAL HERBACEOUS
PLANTS
12
Ground
36.55
35.45
0.23
u 15
NON-AGRICULTURAL RIGHTS
OF WAY
12
Ground
629.91
619.12
3.9 4
2.S0
4
Aircraft
626.91
615.83
3.') 2
2.7(,
PAVED AREAS (PRIVATE
ROADS/SIDEWALKS)
12
Ground
4911.00
4725.00
30.6')
21.21
UNCULTIVATED AG
12
Ground
1130.00
1099.00
7.0(.
5.12
12
Ground
1169.00
1130.00
7.3I
5.31
UNCULTIVATED NON-AG
12
Ground
284.80
275.70
I.7X
1.2ft
85

-------







* LOC exceedances (acute RQ > 0.05, chronic RQ > 1.0) are bolded and shaded. RQ = use-specific peak EEC/
[Selenastrum capricornutum EC50 = 2.40 ppb].
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 chronic and acute LOC exceedances, diuron May
Affect the CRLF indirectly via reduction in freshwater fish and frogs as food items.
5.1.1.3 Indirect Effects to CRLF via Reduction in Habitat and 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. A summary of acute
RQs used to estimate indirect effects to the CRLF via effects to vascular aquatic plants is
presented in Table 5.4. The RQs for vascular aquatic plants exceed the Agency's LOC
(1.0) for most uses of diuron in California. These range from 327.40 (paved areas) to
1.26 (Filbert/Hazelnut). Because of this, and in addition to the LOC exceedances for
all uses of diuron to non-vascular aquatic plants, it is determined that diuron May
Affect the CRLF indirectly via reduction in vascular aquatic plants.
Table 5.4 Summary of Acute RQs Used to Estimate Indirect Effects to the CRLF via
I SI'S
r;ik- (II)
;ii/.\)
Applkiiliiiii
Mi-lhml
IY;ik
II. (
(ii»/l.)
Indiivi'l l-'.ITi'i'ls Auik-
RQ*
AGRICULTURAL RIGHTS-OF-
WAY/FENCEROW S/HEDGEROW S
12
Ground
687.59
45.X4
ALFALFA
2.4
Ground
10.63
0.71
2.4
Aircraft
13.69
0.91
86

-------





APPLE
3.2
Ground
11.68
0.78
ARTICHOKE
3.2
Ground
32.00
2.13
ASPARGUS
4.8
Ground
36.99
2.47
BANANA, PLANTAIN
2.4
Ground
54.21
3.61
BLACKBERRY, BOYSENBERRY
1.6
Ground
139.70
«UI
BLUEBERRY
2.4
Ground
4.65
0.31
CITRUS
3.2
Ground
6.83
0.46
CORN, FIELD
0.8
Ground
7.24
0.48
DEWBERRY
2.4
Ground
19.71
1.31
FILBERT (HAZELNUT)
2.2
Ground
18.90
1.2ft
GRAPE
3.2
Ground
9.71
0.65
LOGANBERRY, RASPBERRY
(BLACK/RED)
2.4
Ground
5.13
0.34
OLIVE
1.6
Ground
7.17
0.48
PAPAYA
4
Ground
25.21
1.68
PEPPERMINT
2.4
Ground
4.17
0.28
PEACH
3
Ground
10.95
0.73
PEAR
3.2
Ground
11.66
0.78
PECAN
3.2
Ground
27.04
1.80
87

-------





SORGHUM
4.8
Ground
5.87
0.39
SPEARMINT
2.4
Ground
106.70
"Ml
WALNUT (ENGLISH/BLACK)
0.4
Ground
25.78
l."72
WHEAT
2.4
Pre-Harvest
18.03
1.20
3
Post-
Harvest
12.82
0.85
COTTON
1.6
Ground
8.36
0.56
Aircraft
14.25
0.95
AIRPORTS/ LANDING FIELDS,
DRAINAGE SYSTEMS,
INDUSTRIAL AREAS
(OUTDOOR), SEWAGE DISPOSAL
AREAS
12
Ground
2190.00
146.00
BERMUDAGRASS
2.4
Ground
226.00
I5JP
GRASSES GROWN FOR SEED
12
Ground
3.76
0.25
IRRIGATION SYSTEMS
1.6
Ground
52.56
3.50
ORNAMENTAL HERBACEOUS
PLANTS
12
Ground
36.55
2.44
NON-AGRICULTURAL RIGHTS
OF WAY
12
Ground
629.91
41.99
4
Aircraft
626.91
41.^9
88

-------





PAVED AREAS (PRIVATE
ROADS/SIDEWALKS)
12
Ground
4911.00
32_7.4<>
UNCULTIVATED AG
12
Ground
1130.00
75.33
12
Ground
1169.00
"7"7.')3
UNCULTIVATED NON-AG
12
Ground
284.80
ix.<)y
aLOC exceedances (RQ > 1) are bolded and shaded.
RQ = use-specific peak EEC/ [Lemna major EC50 = 2.40 ppb].
5.1.2 Exposures in the Terrestrial Habitat
5.1.2.1 Direct Effects to Terrestrial-phase CRLF
As discussed in Section 3.3, potential direct effect determinations to terrestrial-phase
CRLFs are based on foliar applications of diuron. 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 3.5) and
acute oral and subacute dietary toxicity endpoints for avian species. The Bobwhite Quail
exhibited the greatest acute sensitivity to diuron and was therefore selected to serve as a
surrogate for the CRLF.
Potential direct chronic effects of diuron 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.
As mentioned, there are no acceptable data for chronic or dose based acute toxicity of
diuron to amphibians or their avian surrogates. Therefore, no RQs were calculated for
these values. Linuron, a similar chemical of the same class, has acceptable chronic avian
data. The avian reproductive studies for linuron (MRID 42541801, 42541802) using
mallard duck and bobwhite quail found reproductive effects at 300 ppm ai with an
NOAEL being established at 100 ppm. The endpoints affected for mallard duck
reproduction are egg production, adult body weight, feed consumption, viable embryos of
eggs set, number of viable embryos, and number of live embryos. For the bobwhite
quail the endpoints affected are hatchability and offspring survivability. This suggests
that diuron may have chronic effects to avian species, but these risks cannot be quantified
89

-------
in the absence of data. As a result, chronic risks are assumed to avian surrogates for all
uses of diuron in California.
The most sensitive dose based LD50 was >2000 ppm ai as exhibited by the Mallard Duck
(MRID 00160000). It is important to note that although no mortality was observed in this
study, ataxia persisted for lid after study concluded. This sublethal effect could
potentially result in the animals being more susceptible to predation as a result of being
both conspicuous to predators and by having a diminished ability to avoid capture. The
calculated acute dietary RQs for the terrestrial phase CRLF exceed the Agency's LOC
(0.1) for all uses except sorghum. The RQs in Table 5.5 below are based on the 5-day
dietary LC50 of 1730 ppm for bobwhite quail.
The acute dietary based RQs exceed the LOC for all uses except Field Corn and
Sorghum. The exceedances range from 1.55 (Agricultural Rights-of-Way, Fencerows,
Hedgerows, Airports, etc.) to 0.12 (grass for seed, wheat). These results are summarized
in Table 5.5. Based on acute dietary LOC exceedances for the listed bird surrogate
for amphibians, diuron May Affect the terrestrial-phase of the CRLF directly.
Table 5.5 Summary of Acute RQs Used to Estimate Direct Effects to the Terrestrial-
phase CRLF
Use
(Application Rate)
l)ielar\ -l>asi-d .Willi-
rq!
Agricultural Rights-of-Way, Fencerows, Hedgerows, Airports,
landing Fields, Drainage Systems, Outdoor Industrial Areas,
Irrigation Systems, Non-Agricultural Rights of Way, Sewage
Disposal Areas, Uncultivated Non-Agricultural Areas

Alfalfa, Peppermint,
0.19
Apple, Grape
0.2'>
Citrus,
0.33
Artichoke, Asparagus
0.25
Banana, Plantain
0.54
Bermuda grass, Blackberry, Boysenberry, Spearmint
0.4S
Blueberry
0.14
Field Corn
0 ()()
Cotton
0.2f.
Dewberry
0.2f.
Filbert (Hazelnut)
0.IS
Grass Seed, Wheat
0.12
Loganberry, Raspberry
0.19
Olive
0.13
Pear, Pecan
0.25
Ornamental Herbaceous plants, Papaya
0.31
Uncultivated Agricultural Areas, Paved Areas
0.94
Peach
0.23
Sorghum
0.03
90

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I si'
(Application K;ik-)
l)kl;ir\ -l>;isi-d .Willi-
RQ:
Walnul
0.25
* = LOC exceedances (acute RQ > 0.1) are bolded and shaded.
2Based on Bobwhite Quail LC50 =1730 ppm].
5.1.2.2 Indirect Effects to Terrestrial-Phase CRLF via Reduction in Prey
(terrestrial invertebrates, mammals, and frogs)
5.1.2.2.1	Terrestrial Invertebrates
In order to assess the risks of diuron to terrestrial invertebrates, which are considered
prey of CRLF in terrestrial habitats, the honeybee 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 >145.03 |ig a.i. /bee by 1 bee/0.128g, which is
based on the weight of an adult honey bee. The toxicity value for terrestrial invertebrates
is calculated to be >1133.05 ppm, but only 2.77% mortality was observed at the highest
levels tested. Therefore, this test is not definitive and acute RQs were not calculated.
However, because the terrestrial EEC's exceed the highest levels tested for several
uses, it is determined that diuron May Affect the CRLF indirectly via reduction in
terrestrial invertebrate prey items.
5.1.2.2.2	Mammals
Risks associated with ingestion of small mammals by large terrestrial-phase CRLFs are
derived for dietary-based and dose-based exposures modeled in T-REX for a small
mammal (15g) consuming short grass. Acute and chronic effects are estimated using the
most sensitive mammalian toxicity data. EECs are divided by the toxicity value to
estimate acute and chronic dose-based RQs as well as chronic dietary-based RQs.
Chronic dose based RQs exceed the Agency's LOC (1.0) for most uses (
Table 5.6). The dose based chronic RQs that exceed the LOC range from 8.29
(Agricultural Rights-of-Way, Fencerows, Hedgerows, Airports, etc.) to 1.31 (walnut).
The dietary based chronic RQs do not exceed the LOC for any uses. The RQs that
exceed the acute dose based LOC range from 0.41 (Agricultural Rights-of-Way,
Fencerows, Hedgerows, Airports, etc.) to 0.13 (Bermuda grass, Blackberry, Boysenberry,
Spearmint). Based on acute and chronic LOC exceedances on small mammal prey
items, diuron May Affect the CRLF indirectly via reduction in small mammal prey
items.
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Table 5.6 Summary of Acute and Chronic RQs* Used to Estimate Indirect Effects
to the Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary
Food Items
l si-
( linink KQ1
.Willi- KQ


l)k'l;ir\-l>;iM-(l
l)iiM'-l>;iM'(l

(lironk KQ
(liroiik KQ
.Willi' KQ
Agricultural Rights-of-Way, Fencerows,
Hedgerows, Airports, landing Fields,
Drainage Systems, Outdoor Industrial
Areas, Irrigation Systems, Non-Agricultural
Rights of Way, Sewage Disposal Areas,
Uncultivated Non-Agricultural Areas
N.2'>
0.96
0.41
Alfalfa, Peppermint
1.00
0.12
0.05
Apple, Grape
1.5ft
0.18
0.08
Artichoke, Asparagus
1.33
0.15
0.07
Banana, Plantain
2.87
0.33
0.14
Bermuda grass, Blackberry, Boysenberry,
Spearmint
2.57
0.30
0.13
Blueberry
0.74
0.09
0.04
Citrus
1.74
0.20
0.09
Field Corn
0.33
0.04
0.02
Cotton
1.40
0.16
0.07
Dewberry
1.40
0.16
0.07
Filbert (Hazelnut)
0.96
0.11
0.05
Grass Seed, Wheat
0.67
0.08
0.03
Loganberry, Raspberry
1.00
0.12
0.05
Olive
0.69
0.08
0.03
Ornamental Herbaceous Plants, Papaya
I.ft7
0.19
0.08
Uncultivated Agricultural Areas, Paved



Areas
5.00
0.58
0.25
Peach
1.25
0.14
0.06
Pear, Pecan
1.33
0.15
0.07
Sorghum
0.17
0.02
0.01
Walnut
1.31
0.15
0.07
* = LOC exceedances (acute RQ >0.1 and chronic RQ > 1) arc bolded and shaded.
1 Based on dose-based EEC and diuron rat NOAEC = 250.00 mg/kg-bw.

2 Based on dose-based EEC and diuron rat acute oral LD50 =
5000.00 mg/kg-bw.

5.1.2.2.3 Frogs
An additional prey item of the adult terrestrial-phase CRLF is other species of frogs. In
order to assess risks to these organisms, dietary-based and dose-based exposures modeled
92

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in T-REX for a small bird (20g) consuming small invertebrates are used. See Section
5.1.2.1 for results. The chronic LOC is exceeded for all uses of diuron and the acute
LOCs are exceeded for all uses except sorghum. Based on acute and chronic LOC
exceedances on the prey item of small frogs, diuron May Affect the CRLF indirectly
via reduction in small frog prey items.
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. Diuron is a systemic herbicide.
The RQs for non-target terrestrial monocot and dicot plants inhabiting semi-aquatic and
upland dry areas exceed the Agency's LOC (1.0) for all uses except for monocot plants
exposed to sorghum applications (Table 5.7). These exceedances range from 300.00
(semi-aquatic plants exposed to non-agricultural aerial applications) to 0.19 (dicot plants
inhabiting dry areas exposed to sorghum applications).
Several diuron uses result in LOC exceedances from spray drift. These exceedances
range from 12.00 (dicot plants exposed to field corn applications) to 1.13 (monocot plants
exposed to cotton applications). Based on LOC exceedances on the non-target
terrestrial plants at all use sites, diuron May Affect the terrestrial phase CRLF
indirectly via effects to riparian and upland habitat.
Table 5.7 RQs*1^ for Non-Target Plants Inhabiting Dry and Semi-Aquatic Areas
Exposed to Diuron via Runoff and Drift 				
Use
Application
rate (lbs
a.i./A)
Application
method
Drift
Value
(%)
Group
Sprav drift
RQ
Dry
area RQ
Semi-
aquatic
area RQ
Agricultural Rights-of-
Way, Fencerows,
Hedgerows, Airports,
landing Fields, Drainage
Systems, Outdoor
Industrial Areas,
Irrigation Systems,
Non-Agricultural Rights
of Way, Sewage
Disposal Areas,
Uncultivated Non-
Agricultural Areas
12.0
Foliar/Ground
1
Monocot
3.M
25.45
5.71
Dicot
4. SO
33.60
r.o.oo
Alfalfa, Peppermint,
Spearmint,
Bermudagrass,
Blackberry,
Boysenberry,
Loganberry, Raspberry,
Dewberry
2.4
Foliar/Ground
1
Monocot
0.73
5.09
1.14
Dicot
0.96
h.72
12.00
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Use
Application
rate (lbs
a.i./A)
Application
method
Drift
Value
(%)
Group
Sprav drift
RQ
Dry
area RQ
Semi-
aquatic
area RQ
Apple, Citrus, Pear,
Grape, Artichoke,
Asparagus, Pecan
3.2
Foliar/Ground
1
Monocot
0.97
h.l')
1.52
Dicot
I.2S
X.'H,
16.00
Asparagus (Aerial)
3.2
Foliar/Ground
1
Monocot
2.2f.
S.OS
7.62
Dicot
2.'W
10.67
S0.00
Banana, Plantain
4.8
Foliar/Ground
1
Monocot
1.45
10. IS
2.2')
Dicot
l.')2
13.44
24.00
Blueberry, Grass Seed,
Olive, Pear, Wheat
1.6
Foliar/Ground
1
Monocot
0.48
3.3')
0.76
Dicot
0.64
4.4S
S.00
Field Corn
0.8
Foliar/Ground
1
Monocot
0.24
1.70
0.38
Dicot
12.00
S4.00
4.00
Cotton
3
Aerial
5
Monocot
1.13
4.04
3.SI
Dicot
1.4')
5.33
40.00
Cotton
3
Ground
1
Monocot
0.48
3.3')
0.76
Dicot
24.0
K.N.O
S.00
Filbert (Hazelnut)
2.2
Foliar/Ground
1
Monocot
0.67
4.67
1.05
Dicot
0.88
6.16
11.00
Non-agricultural
12
Aerial
5
Monocot
S.4S
30.30
28.57
Dicot
11.20
40.00
300.00
Ornamental Herbaceous
Plants, Papaya
4
Foliar/Ground
1
Monocot
1.21
S.4S
l.'JO
Dicot
l.r.o
11.20
20.00
Uncultivated
Agricultural Areas,
Paved Areas
12
Foliar/Ground
1
Monocot
3.(> 4
25.45
5.71
Dicot
4. SO
33.60
60.00
Peach, Walnut
3
Foliar/Ground
1
Monocot
0.91
r,.3f.
1.43
Dicot
1.20
S.40
15.00
Sorghum
0.4
Foliar/Ground
1
Monocol
0.12
0.85
0.19
Dicot
0.16
1.12
2.00
* LOC Exceedances (RQ > 1.0) are bolded and shaded.
^ Spray drift RQs consider only spray drift alone, dry area and semi-aquatic RQs consider spray drift as well as runoff.
5.1.3 Primary Constituent Elements of Designated Critical Habitat
5.1.3.1 Aquatic-Phase (Aquatic Breeding Habitat and Aquatic Non-
Breeding Habitat)
Three of the four assessment endpoints for the aquatic-phase primary constituent
elements (PCEs) of designated critical habitat for the CRLF are related to potential
effects to aquatic and/or terrestrial plants:
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•	Alteration of channel/pond morphology or geometry and/or increase in sediment
deposition within the stream channel or pond: aquatic habitat (including riparian
vegetation) provides for shelter, foraging, predator avoidance, and aquatic
dispersal for juvenile and adult CRLFs.
•	Alteration in water chemistry/quality including temperature, turbidity, and
oxygen content necessary for normal growth and viability of juvenile and adult
CRLFs and their food source.
•	Reduction and/or modification of aquatic-based food sources for pre-metamorphs
(e.g., algae).
Based on the risk estimation for potential effects to vascular and non-vascular
aquatic and terrestrial plants provided in Sections 5.1.1.2, 5.1.1.3, and 5.1.2.3,
diuron may result in Habitat Modification of aquatic-phase PCEs of designated
habitat related to effects on aquatic and/or terrestrial plants.
•	Aquatic non-vascular plants used as food source and habitat for CRLF may be
potentially affected from all diuron uses.
•	Reduction of aquatic based food sources may occur from most use sites.
•	Due to aquatic vascular and terrestrial plant communities being reduced from
most use sites, there is potential for alteration of channel/pond morphology or
geometry and/or increase in sediment deposition within the stream channel or
pond.
•	Due to aquatic vascular and terrestrial plant communities being reduced from
most use sites, there is potential for 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.
The remaining aquatic-phase PCE is "alteration of other chemical characteristics
necessary for normal growth and viability of CRLFs and their food source." To assess
the impact of diuron on this PCE, 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 acute and chronic LOC exceedances for freshwater fish and aquatic
invertebrates, diuron may result in Habitat Modification of aquatic-phase PCEs
related to effects of alteration of other chemical characteristics necessary for normal
growth and viability of CRLFs and their food source.
5.1.3.2 Terrestrial-Phase (Upland Habitat and Dispersal Habitat)
Two of the four assessment endpoints for the terrestrial-phase PCEs of designated critical
habitat for the CRLF are related to potential effects to terrestrial plants:
•	Elimination and/or disturbance of upland habitat; ability of habitat to support food
source of CRLFs: Upland areas within 200 ft of the edge of the riparian
vegetation or dripline surrounding aquatic and riparian habitat that are comprised
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of grasslands, woodlands, and/or wetland/riparian plant species that provides the
CRLF shelter, forage, and predator avoidance
• Elimination and/or disturbance of dispersal habitat: Upland or riparian dispersal
habitat within designated units and between occupied locations within 0.7 mi of
each other that allow for movement between sites including both natural and
altered sites which do not contain barriers to dispersal
The risk estimation for terrestrial-phase PCEs of designated habitat related to potential
effects on terrestrial plants is provided in Section 5.1.2.3. These results will inform the
effects determination for modification of designated critical habitat for the CRLF.
The third terrestrial-phase PCE is "reduction and/or modification of food sources for
terrestrial phase juveniles and adults." To assess the impact of diuron on this PCE, acute
and chronic toxicity endpoints for birds, mammals, and terrestrial invertebrates are used
as measures of effects. RQs for these endpoints were calculated in Section 5.1.2.2.
Based on acute and chronic LOC exceedances for CRLF prey items of small
mammals, terrestrial invertebrates and other frogs, diuron may result in Habitat
Modification of the first three terrestrial phase PCEs.
The fourth terrestrial-phase PC is based on alteration of chemical characteristics
necessary for normal growth and viability of juvenile and adult CRLFs and their food
source. Direct acute and chronic RQs for terrestrial-phase CRLFs are presented in
Section 5.2.1.2. Due to acute and chronic LOC exceedances at all use sites to
terrestrial-phase CRLFs, diuron may result in Habitat Modification of the fourth
terrestrial phase PCE.
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
to adversely affect," or "likely to adversely affect") for the CRLF and its designated
critical habitat.
If the RQs presented in the Risk Estimation (Section 5.1) show no direct or indirect
effects for the CRLF, and no modification to PCEs of the CRLF's designated critical
habitat, a "no effect" determination is made, based on diuron's use within the action
area. However, if direct or indirect effects LOCs are exceeded, or if effects may modify
the PCEs of the CRLF's critical habitat, the Agency concludes a preliminary "may
affect" determination for the FIFRA regulatory action regarding diuron. Based on
direct and indirect LOC exceedances for CRLF, the Agency concludes a
preliminary May Affect determination for the CRLF and critical habitat. A
summary of the results of the risk estimation is 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.
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Table 5.8 Risk Estimation Summary for Diuron - Direct and Indirect Effects to
CRLF
Assessment Endpoint
LOC
Excccdanccs
(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
The aquatic phase amphibian acute LOCs for Listed species (0.05) are
exceeded for most uses of diuron in California. Acute RQs that exceed the
Agency's LOC range from 12.28 (paved areas) to 0.06 (papaya and
walnut). Chronic RQs that exceed the Agency's LOC for chronic exposure
(1.0) range from 131.85 (paved areas) to 1.26 (banana, plantain).
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects to food
supply {i.e., freshwater invertebrates,
non-vascular plants)
YES
LOCs for non-vascular plants are exceeded for all uses. The RQs range
from 2046.25 (paved areas) to 1.57 (grasses grown for seed).
Aquatic invertebrates acute a LOC are exceeded. The acute RQs that
exceed the LOC range from 30.69 (paved areas) to 0.05 (cotton aerial
application). Chronic LOCs are exceeded for several uses. RQs that
exceed the Agency's LOC range from 21.21or paved areas to 1.02 for
bermudagrass.
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects on habitat,
cover, and/or primary productivity (i.e.,
aquatic plant community)
YES
RQs for vascular aquatic plants exceed the Agency's LOC (1.0) for most
uses. These range from 460.46 (paved areas) to 1.30 (hazelnut).
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects to riparian
vegetation, required to maintain
acceptable water quality and habitat in
ponds and streams comprising the
species' current range.
YES
RQs for non-target terrestrial monocot and dicot plants inhabiting semi-
aquatic and upland dry areas exceed the Agency's LOC for all uses
except for monocot plants exposed to sorghum applications. RQs range
from 300.00 (semi-aquatic plants exposed to non-agricultural aerial
applications) to 0.19 (dicot plants inhabiting dry areas exposed to
sorghum applications).
Terrestrial Phase
(Juveniles and adults)
Direct Effects
Survival, growth, and reproduction of
CRLF individuals via direct effects on
terrestrial phase adults and juveniles
YES
The acute dietary based RQs that exceed the LOC range from 1.55
(Agricultural Rights-of-Way, Fencerows, Hedgerows, Airports, etc.) to
0.12 (grass for seed, wheat). These results are summarized in Table 5.5.
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
Chronic dose based RQs exceed the Agency's LOC (1.0) for most uses (
Table 5.6). The dose based chronic RQs that exceed the LOC range
from 8.29 (Agricultural Rights-of-Way, Fencerows, Hedgerows,
Airports, etc.) to 1.31 (walnut). The dietary based chronic RQs do not
exceed the LOC for any uses. The RQs that exceed the acute dose based
LOC range from 0.41 (Agricultural Rights-of-Way, Fencerows,
Hedgerows, Airports, etc.) to 0.13 (Bermuda grass, Blackberry,
Boysenberry, Spearmint).
Indirect Effects
Survival, growth, and reproduction of
CRLF individuals via effects on habitat
(i.e., riparian vegetation)
YES
The RQs for vascular aquatic plants exceed the Agency's LOC (1.0) for
most uses of diuron in California. These range from 373.33 (paved areas)
to 1.01 (alfalfa aerial).
The RQs for non-target terrestrial monocot and dicot plants inhabiting
semi-aquatic and upland dry areas exceed the Agency's LOC (1.0) for all
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uses except for monocot plants exposed to sorghum applications (Table
5.7). These exceedances range from 300.00 (semi-aquatic plants exposed
to non-agricultural aerial applications) to 0.19 (dicot plants inhabiting dry
areas exposed to sorghum applications). Several diuron uses result in
plant LOC exceedances from spray drift. These exceedances range from
12.00 (dicot plants exposed to field corn applications) to 1.13 (monocot
plants exposed to cotton applications).
Table 5.9 Risk Estimation Summary for Diuron - PCEs of Designated Critical
Habitat for the CRLF
Assessment Endpoint
LOC Exceedances
(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.
YES
LOCs are exceeded for terrestrial riparian plants and for
aquatic vascular plants from exposure to diuron from
runoff or spray drift.
Alteration in water chemistry/quality including
temperature, turbidity, and oxygen content
necessary for normal growth and viability of
juvenile and adult CRLFs and their food source.
YES
LOCs are exceeded for terrestrial riparian plants and for
aquatic plants from exposure to diuron from runoff or
spray drift. Alteration of riparian and vascular plants
may result in alteration of temperature, turbidity, and
oxygen content.
Alteration of other chemical characteristics
necessary for normal growth and viability of
CRLFs and their food source.
YES
LOC is exceeded for indirect effects on terrestrial and
aquatic-phase CRLF from most diuron applications.
Reduction and/or modification of aquatic-based
food sources for pre-metamorphs (e.g., algae)
YES
LOCs for non-vascular plants are exceeded for all uses.
Terrestrial Phase PCEs
(Upland Habitat and Dispersal Habitat)
Elimination and/or disturbance of upland habitat;
ability of habitat to support food source of
CRLFs: Upland areas within 200 ft of the edge
of the riparian vegetation or dripline surrounding
aquatic and riparian habitat that are comprised of
grasslands, woodlands, and/or wetland/riparian
plant species that provides the CRLF shelter,
forage, and predator avoidance
YES
The AgDRIFT model was used to evaluate potential
distances beyond which exposures would be expected to be
below LOC. However, due to the limitations imposed by
the Tier 1 ground analysis (allows users to evaluate off-site
deposition and exposure out to 1,000 ft downwind from the
location of the application), the exact buffer needed for
exposures to be below the LOC is uncertain.
The output from AgDRIFT indicated that the buffer zone
required would be greater than 1,000 feet. Since the model
is restricted to accurately discerning a buffer within 1,000
feet of the application, the exact distance needed for a
buffer to protect non-listed and listed plants is unknown.
Flowever, as seen in Table 3.7, the calculated risk quotient
(RQ) is significantly larger than the level of concern
(LOC) for non-listed and listed plant species (LOC =1).
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Assessment Endpoint
LOC Excccdanccs
(Y/N)
Description of Results of Risk Estimation


This comparison provides awareness to approximately how
much greater than 1,000 feet the buffer needs to be.
Elimination and/or disturbance of dispersal
habitat: Upland or riparian dispersal habitat
within designated units and between occupied
locations within 0.7 mi of each other that allow
for movement between sites including both
natural and altered sites which do not contain
barriers to dispersal
YES
Effects are expected to non-target terrestrial plants over
1000 ft from use site from ground application.
Reduction and/or modification of food sources
for terrestrial phase juveniles and adults
YES
LOC is exceeded for indirect effects on terrestrial and
aquatic-phase CRLF from diuron application
Alteration of chemical characteristics necessary
for normal growth and viability of juvenile and
adult CRLFs and their food source.
YES
LOC is exceeded for direct effects on terrestrial and
aquatic-phase CRLF from diuron applications.
Following a preliminary "may affect" or "habitat modification" determination, additional
information is considered to refine the potential for exposure at the predicted levels based
on the life history characteristics {i.e., habitat range, feeding preferences, etc.) of the
CRLF. Based on the best available information, the Agency uses the refined evaluation
to distinguish those actions that "may affect, but are not likely to adversely affect" from
those actions that are "likely to adversely affect" the CRLF and its designated critical
habitat.
The criteria used to make determinations that the effects of an action are "not likely to
adversely affect" the CRLF and its designated critical habitat include the following:
• Significance of Effect: Insignificant effects are those that cannot be meaningfully
measured, detected, or evaluated in the context of a level of effect where "take"
occurs for even a single individual. "Take" in this context means to harass or
harm, defined as the following:
¦	Harm includes significant habitat modification or degradation that
results in death or injury to listed species by significantly impairing
behavioral patterns such as breeding, feeding, or sheltering.
¦	Harass is defined as actions that create the likelihood of injury to listed
species to such an extent as to significantly disrupt normal behavior
patterns which include, but are not limited to, breeding, feeding, or
sheltering.
•	Likelihood of the Effect Occurring: Discountable effects are those that are
extremely unlikely to occur.
•	Adverse Nature of Effect: Effects that are wholly beneficial without any adverse
effects are not considered adverse.
A description of the risk and effects determination for each of the established assessment
endpoints for the CRLF and its designated critical habitat is provided in Sections 5.2.1
through 5.2.3.
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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 diuron.
Diuron is considered "highly toxic" to the freshwater fish, which are surrogates for the
aquatic phase CRLF. The aquatic animal acute LOCs for Listed species (0.05) are
exceeded for most uses of diuron in California. Acute RQs that exceed the Agency's
LOC range from 12.28 (paved areas) to 0.06 (papaya). The probability of an individual
effect to the aquatic-phase CRLF is based on the slope of the dose response curve for the
acute endpoint used to derive the RQ. The probability, based on the default slope of 4.5
is one in 4.18E+08. Because the upper and lower 95% confidence interval of the slope is
not known, a plausible range of slopes of 2 to 9 were used to obtain reasonable upper and
lower bounds. The resulting probability of an individual effect to the aquatic-phase
CRLF range between one in 215.83 and one in 1.75E+31.
Chronic RQs that exceed the Agency's LOC for chronic exposure (1.0) range from
131.85 (paved areas) to 1.26 (banana, plantain). The aquatic chronic animal LOC for
listed species (1.0) is exceeded for most uses of diuron in California.
The USGS collected 422 positive ground water samples containing Diuron. The three
river basins looked at were Sacramento, San Joaquin-Tulare, and Santa Ana. The
maximum concentration observed was 1.8 ppb in the San Joaquin-Tulare water basins in
Kings County.
Monitoring data from CDPR indicate that diuron concentrations range from non-
detectable to 160 ppb. The majority of the large concentrations of Diuron came from San
Joaquin County, and occurred between the end of December and the beginning of
January. The year 2005, for San Joaquin County, yielded the greatest concentrations
overall.
Moreover, the CDPR monitoring data showed that eleven samples (1.56% of the 705
samples), ranging from 31 ppb to 160 ppb, detected levels of diuron that would result in
chronic direct effects to the CRLF. Likewise, four samples (0.57%), ranging from 9.5
ppb to 15 ppb, detected diuron at levels that would result in chronic indirect effects to the
CRLF. These detects occurred during the months of December, January, and February in
years 2005 and 2006, and in March for the 2006 year. The San Joaquin County had 5
detects (3.38% of samples) resulting in chronic direct effects and 1 detect (0.68% of
samples) resulting in chronic indirect effects, Tulare County had 1 detect (2.22% of
samples) resulting in a chronic direct effect, and Stanislaus County had 5 detects (6.94%
of samples) resulting in chronic direct effects and 2 detects (2.78% of samples) resulting
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in chronic indirect effects. Consequently, almost 10% of the samples taken from
Stanislaus County, just over 4% from San Joaquin County, a little over 2% from Tulare
County contained detects at levels that would cause chronic or indirect effects to the
CRLF.
Seven reported incidents resulted in fish kills. Five of these fish kills resulted from direct
application of diuron to water bodies which is not allowed in California. However, three
incidents were from drift or runoff of diuron from applications made adjacent to water
bodies. This demonstrates that diuron may pose a threat to aquatic organisms through
labeled uses (Appendix J). It is also important to note that the absence of additional
documented incidents does not necessarily mean that such incidents did not occur.
Mortality incidents must be seen, reported, investigated, and submitted to the Agency in
order to be recorded in the incident database. Incidents may not be noticed because the
carcasses decayed, were removed by scavengers, or were in out-of-the-way or hard-to-see
locations. Due to the voluntary nature of incident reporting, an incident may not be
reported to appropriate authorities capable of investigating it. Based on these
exceedances to the aquatic-phase CRLF, reported diuron incidents resulting in fish
kills and its monitored presence in surface water, a "May Affect and Likely to
Adversely Affect (LAA)" determination is made for diuron use in California.
5.2.1.2 Terrestrial-Phase CRLF
The RQs representing acute dietary-based exposures exceed the Agency's LOC for all
uses except sorghum (Section 5.1.2.1.). These RQs were derived using the T-REX
model, which estimates exposures that are specific to food intake equations for birds.
RQs generated for birds are used as surrogates to represent RQs for the terrestrial-phase
CRLF. Based on these exceedances to the terrestrial-phase CRLF, a "May Affect"
determination was made.
The T-HERPS model was therefore employed as a refinement tool to explore amphibian-
specific food intake on potential exposures to the terrestrial phase CRLF. The T-HERPS
model incorporates the same inputs as T-REX with equations adjusted for poikilotherm
food intake. The EECs generated by T-HERPS are found in Table 5.10. An example
output from T-HERPS is available in Appendix K.
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Table 5.10. Upper-bound Kenega Nomogram T-HERPS EECs (mg/kg-diet) for
Dietary-based Exposures of the CRLF and its Prey to Diuron1.	
Scenario
Small
Insects
Large
Insects
Small
Herbivore
Mammals
Small
Insectivore
Mammals
Small
Terrestrial
Phase
Amphibians
Agricultural Rights-of-Way,
Fencerows, Hedgerows, Airports,
landing Fields, Drainage Systems,
Outdoor Industrial Areas,
Irrigation Systems, Non-
Agricultural Rights of Way,
Sewage Disposal Areas,
Uncultivated Non-Agricultural
Areas
2113.70
234.86
2476.10
154.76
73.37
Alfalfa, Peppermint,
324.00
36.00
379.55
23.72
11.25
Apple, Grape
504.68
56.08
591.21
36.95
17.52
Citrus





Artichoke, Asparagus
432.00
48.00
506.07
31.36
15.00
Banana, Plantain
930.06
103.34
1089.52
68.10
32.28
Bermuda grass, Blackberry,
Boysenberry, Spearmint
951.44
105.72
114.57
69.66
33.03
Blueberry
239.50
23.61
280.57
17.54
8.31
Field Corn
108.00
12.00
126.52
7.91
3.75
Cotton
452.53
50.28
530.11
33.13
15.71
Dewberry
452.83
50.31
530.47
33.15
15.72
Filbert (Hazelnut)
312.23
34.69
365.76
22.86
10.84
Grass Seed, Wheat
216.00
24.00
253.03
15.81
7.50
Loganberry, Raspberry
324.00
36.00
379.55
23.72
11.25
Olive
223.75
24.86
262.12
16.38
7.77
Pear, Pecan
432.00
48.00
506.07
31.63
15.00
Ornamental Herbaceous Plants,
Papaya
540.00
60.00
632.59
39.54
18.74
Uncultivated Agricultural Areas,
Paved Areas
1620.00
180.00
1897.76
118.61
56.23
Peach
405.00
45.00
474.44
29.65
14.06
Sorghum
54.00
6.00
63.26
3.95
1.87
Walnut
425.76
47.31
498.76
31.17
14.78
'weights of small herbivore and insectivore mammals are 35g
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Acute exposures
Refined acute dietary-based RQs for CRLFs consuming large insects and small herbivore
mammals exceed the acute listed species LOC (0.1) for all uses of diuron except
Sorghum and Field Corn. The acute dietary-based RQs for CRLFs consuming large
insects exceed the acute listed species LOC for Agricultural Rights-of-Way, Fencerows
etc. No acute dietary based LOCs were exceeded for CLRF consuming small insectivore
mammals and small terrestrial phase amphibians for any diuron use. Results are
presented in Table 5.11.
Table 5.11. Revised Acute Dietary-based RQs for CRLF consuming different food
items (RQs calculated using T-HERPS)*.	
Scenario
Small
111 sec Is
1 :l I'm'
111 sills
Small
lli'i'lmiiiv
Maiiiinals
Small Insectivore
Mammals
Small
Terrestrial
Phase
Amphibians
Agricultural Rights-of-
Way, Fencerows,
Hedgerows, Airports,
landing Fields, Drainage
Systems, Outdoor
Industrial Areas, Irrigation
Systems, Non-Agricultural
Rights of Way, Sewage
Disposal Areas,
Uncultivated Non-
Agricultural Areas
1.22
0.14
1.43
0.09
0.04
Alfalfa, Peppermint,
O.I')
0.02
0.22
0.01
0.01
Apple, Grape
0.2')
0.03
0.34
0.02
0.01
Citrus
0.33
0.04
0.3S
0.02
0.01
Artichoke, Asparagus
0.25
0.03
0.2')
0.02
0.01
Banana, Plantain
0.54
0.06
0.ft3
0.04
0.02
Bermuda grass,
Blackberry, Boysenberry,
Spearmint
0.55
0.06
11.64
0.04
0.02
Blueberry
0.14
0.02
0.1 ft
0.01
<0.01
Field Corn
0.06
0.01
() ()7
<0.01
<0.01
Cotton
0.2ft
0.03
0.31
0.02
<0.01
Dewberry
0.2ft
0.03
0.31
0.02
0.01
Filbert (Hazelnut)
O.IS
0.02
0.21
0.01
0.01
Grass Seed, Wheat
0.12
0.01
0.15
0.01
<0.01
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Loganberry, Raspberry
0.1')
0.02
0.22
0.01
0.01
Olive
0.13
0.01
0.15
0.01
<0.01
Ornamental Herbaceous
plants, Papaya
0.31
0.03
0.37
0.02
0.01
Uncultivated Agricultural
Areas, Paved Areas
O.'M
0.10
1.10
0.07
0.03
Peach
0.23
0.03
0.27
0.02
0.01
Pear, Pecan
0.25
0.03
0.2'>
0.02
0.01
Sorghum
0.03
<0.01
0.04
<0.01
<0.01
Walnut
0.25
0.03
0.2'>
0.02
0.01
*RQs exceeding the Listed LOC (0.10) are bolded and shaded
Based on the dietary probit dose-response slope of 7.22 the chance of individual mortality
for which RQs exceed the Listed LOC range from approximately one in 6.75E+10 at an
RQ of 0.12 (Grass Seed and Wheat uses) to approximately one in one at an RQ of 1.22
(Agricultural Rights-of-Way, etc.). Therefore, based on these refined dietary based
acute risk quotients and their exceedances of the Agency's LOC a Likely to
Adversely Affect (LAA) determination is made for diuron use in California.
5.2.2 Indirect Effects (via Reductions in Prey Base)
5.2.2.1 Algae (non-vascular plants)
Indirect effects of diuron to the aquatic-phase CRLF (tadpoles) via reduction in non-
vascular aquatic plants in its diet are based on peak EECs from the standard pond and the
lowest acute toxicity value for aquatic non-vascular plants. The Agency's LOC (1.0) is
exceeded for all current uses of diuron in California. The RQs range from 2331.67 for
Paved Areas to 1.82 for Sorghum (Section 5.1.1.2).
The fate characteristics indicate that diuron is expected to be persistent in aquatic
environments with EECs after 60 days being above the Agency's LOC for non-vascular
aquatic plants, a primary food source for aquatic-phase CRLF. The application of diuron
in California is anticipated to be in late winter and early spring. The timing of the
application would coincide with reproduction of CRLF in aquatic environments as well
as for the tadpoles to feed on non-vascular aquatic plants.
Because of non-vascular LOC exceedances from registered uses of diuron, its
monitored presence in surface water and verified non-target incidents resulting
from diuron use, based on multiple lines of evidence, the Agency concludes that
there is a potential indirect impact to the aquatic-phase of the CRLF from reduction
of food items (algae) and therefore diuron is Likely to Adversely Affect (LAA) the
CRLF.
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5.2.2.2 Aquatic Invertebrates
As discussed in Section 2.5.3, the diet of CRLF also includes aquatic invertebrates.
The potential for diuron 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.
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.
The application of diuron in California is anticipated to be in late winter and early spring.
The timing of the application would coincide with juvenile aquatic- and terrestrial-phase
CRLFs that would be feeding on aquatic and terrestrial 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. For chronic risks, 21-day EECs and the lowest
chronic toxicity value for invertebrates are used to derive RQs. The Agency's acute
Listed LOC (0.05) is exceeded for most uses of diuron in California. The acute RQs that
exceed the LOC range from 30.69 (Paved Areas) to 0.06 (grape). The chronic RQs
exceed the Agency's LOC for several used. The chronic values that exceeded range from
21.21 (paved areas) to 1.02 (bermudagrass). 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 acute Listed LOC exceedances for chronic and acute
aquatic invertebrates from most use sites, diuron May Affect the CRLF indirectly via
reduction in freshwater invertebrate prey items.
Based on the aquatic invertebrate RQs and a probit dose-response default slope of 4.5 the
estimated reduction in aquatic invertebrate populations for which RQs exceed the Listed
LOC range from <0.01% to approximately 100%. To further investigate the estimated
reduction in aquatic invertebrate populations, a plausible range of slopes of 2 to 9 were
selected to investigate the upper and lower bounds of this estimate. Using a slope of 2
led to a range of possible reduction in populations from less than 0.10% to approximately
100%). Employing a slope of 7 led to a range of possible reduction in aquatic invertebrate
populations from less than 1.0% to approximately 100%.
Because aquatic invertebrate populations are expected to be impacted from
registered uses of diuron in California, and because diuron's presence has been
observed in monitored surface water in California, the Agency concludes that there
is a potential indirect impact to the aquatic-phase of the CRLF from a reduction of
aquatic invertebrate food items and therefore diuron is Likely to Adversely Affect
(LAA) the CRLF.
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5.2.2.3	Fish and Aquatic-phase Frogs
As discussed in Section 2.5.3, the diet of CRLF also includes small fish and other
aquatic-phase frogs. Direct effects to the aquatic-phase CRLF are based on peak EECs in
the standard pond and the lowest acute toxicity value for freshwater fish. In order to
assess direct chronic risks to the CRLF, 60-day EECs and the lowest chronic toxicity
value for freshwater fish are used. The RQs for diuron uses results in acute and chronic
exceedances of the Agency's LOC for freshwater fish which are surrogates for the
aquatic phase for amphibians.
The aquatic phase amphibian acute LOCs for Listed species (0.05) are exceeded for most
uses of diuron in California. Acute RQs that exceed the Agency's LOC range from 13.99
(paved areas) to 0.053 (papaya). Based on these RQs and a probit dose-response default
slope of 4.5 the estimated aquatic vertebrate prey item population reduction for which
RQs exceed the Listed LOC range from approximately 10.0% to approximately 100%.
To further investigate the estimated aquatic vertebrate prey item population reduction, a
plausible range of slopes of 2 to 9 were selected to investigate the upper and lower
bounds of this estimate. Using a slope of 2 led to a range of estimated population
reduction of approximately 30.0% to approximately 100%. Employing a slope of 9 led to
a range of possible population reduction of approximately 3.0% to approximately 100%.
The aquatic phase amphibian acute LOCs for listed species (0.05) are exceeded for most
uses of diuron in California. Acute RQs that exceed the Agency's LOC range from 12.28
(paved areas) to 0.06 (papaya and walnut). Chronic RQs that exceed the Agency's LOC
for chronic exposure (1.0) range from 131.85 (paved areas) to 1.26 (banana, plantain).
The application of diuron in California is anticipated to be in late winter and early spring.
The timing of the application would coincide with juvenile aquatic- and terrestrial-phase
CRLFs that would be feeding on small fish, small frogs or tadpoles. Because fish and
aquatic phase amphibian populations are expected to be impacted from registered
uses of diuron in California, and because diuron's presence has been observed in
monitored surface water in California, the Agency concludes that there is a
potential indirect impact to the aquatic-phase of the CRLF from a reduction of fish
and aquatic phase amphibian food items and therefore diuron is Likely to Adversely
Affect (LAA) the CRLF.
5.2.2.4	Terrestrial Invertebrates
When the terrestrial-phase CRLF reaches juvenile and adult stages, its diet is mainly
composed of terrestrial invertebrates. Terrestrial invertebrate toxicity data are used to
assess potential indirect effects of diuron to the terrestrial-phase CRLF. Effects to
terrestrial invertebrates resulting from exposure to diuron may also indirectly affect the
CRLF via reduction in available food.
Because the estimated EEC's exceed the highest level tested for three uses for diuron, a
preliminary "May Affect" determination was made. However, the calculated EEC's for
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Agricultural Rights-of-Way etc (2688.80 ppm) was only roughly twice the highest level
tested (>1305) at which only a 2.7% mortality was observed. Therefore, it is reasonable
to assume that the effects to terrestrial invertebrate populations will be negligible for
these uses of diuron in California. Therefore, based on the weight-of-evidence, the
Agency concludes that there is a negligible potential impact to terrestrial
invertebrates that the CRLF consumes, and therefore diuron May Affect but is Not
Likely to Adversely Affect (NLAA) the CRLF.
5.2.2.5	Mammals
Life history data for terrestrial-phase CRLFs indicate that large adult frogs consume
terrestrial vertebrates, including mice. Small mammals can make up to 50% of the CRLF
food intake. Acute dose based RQs exceed the Agency's LOC (1.0) for most uses. The
dose based RQs that exceed the LOC range from 0.41 (Agricultural Areas, Rights-of-
Way, fencelines etc.) to 0.13 (Bermudagrass, Blackberry, Boysenberry, Spearmint). The
dose based chronic RQs that exceed the LOC range from 8.29 (Agricultural Areas,
Rights-of-Way, fencelines etc.) to 1.33 (Artichoke, Asparagus, Pear, Pecan).. The dietary
based chronic RQs do not exceed the LOC for any uses.
Based on the mammalian dose based acute RQs and a probit dose-response default slope
of 4.5 the estimated mammalian prey item population reduction for which RQs exceed
the Listed LOC range from <0.01% to approximately 4.00%. To further investigate the
estimated reduction in these populations, a plausible range of slopes of 2 to 9 were
selected to investigate the upper and lower bounds of this estimate. Employing a slope of
9 led to an estimated population reduction of <0.01% for all RQs. Using a slope of 2 led
to a range of possible population reduction from approximately 4.00% to approximately
22.00%. Because mammalian populations are expected to be impacted from
registered uses of diuron in California, the Agency concludes that there is a
potential indirect impact to the terrestrial phase of the CRLF from a reduction of
mammalian food items and therefore diuron is Likely to Adversely Affect (LAA) the
CRLF.
5.2.2.6	Terrestrial-phase Amphibians
Terrestrial-phase adult CRLFs also consume frogs. RQ values representing direct
exposures of diuron to terrestrial-phase CRLFs are used to represent exposures of diuron
to frogs in terrestrial habitats. The T-HERPS model was therefore employed as a
refinement tool to explore amphibian-specific food intake on potential exposures to
terrestrial phase amphibian food items for the CRLF. The T-HERPS model incorporates
the same inputs as T-REX with equations adjusted for poikilotherm food intake.
Acute exposures
Refined acute dietary-based RQs for terrestrial phase amphibians consuming small
insects and small herbivore mammals exceed the acute listed species LOC (0.1) for all
uses of diuron except Sorghum and Field Corn. The acute dietary-based RQ for
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terrestrial phase amphibians consuming large insects exceeds the acute listed species
LOC for Agricultural Rights-of-Way, Fencerows etc. Based on these refined dietary
based risk quotients, terrestrial phase amphibian populations are expected to be
impacted from registered uses of diuron in California. Therefore the Agency
concludes that there is a potential indirect impact to the terrestrial phase of the
CRLF from a reduction of terrestrial phase amphibian food items and therefore
diuron is Likely to Adversely Affect (LAA) the CRLF.
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. In addition to energy, 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.
Indirect effects of diuron to the aquatic-phase CRLF (tadpoles) via reduction in non-
vascular aquatic plants in its diet are based on peak EECs from the standard pond and the
lowest acute toxicity value for aquatic non-vascular plants. The Agency's LOC (1.0) is
exceeded for all current uses of diuron in California. The RQs range from 2331.67
(paved areas) to 1.82 (sorghum).
Indirect effects to the CRLF via direct toxicity to aquatic plants are estimated using the
most sensitive non-vascular and vascular plant toxicity endpoints. The RQs for vascular
aquatic plants exceed the Agency's LOC (1.0) for most uses of diuron in California.
These range from 373.33 (paved areas) to 1.01 (alfalfa aerial). Based on LOC
exceedances in vascular and non-vascular plants, diuron is Likely to Adversely
Affect (LAA) the CRLF indirectly via habitat degradation through reduction in
vascular and non-vascular aquatic plants.
5.2.3.2	Terrestrial Plants
Terrestrial plants serve several important habitat-related functions for the CRLF. In
addition to providing habitat and cover for invertebrate and vertebrate prey items of the
CRLF, terrestrial vegetation also provides shelter for the CRLF and cover from predators
while foraging. Terrestrial plants also provide energy to the terrestrial ecosystem through
primary production. Upland vegetation including grassland and woodlands provides
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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.
Twenty-two incidents have been reported that were either registered use or of
undetermined legality that resulted in plant damage. The RQs for non-target terrestrial
monocot and dicot plants inhabiting semi-aquatic and upland dry areas exceed the
Agency's LOC (1.0) for all uses except for monocot plants exposed to sorghum
applications. These exceedances range from 300.00 (semi-aquatic plants exposed to non-
agricultural aerial applications) to 0.19 (dicot plants inhabiting dry areas exposed to
sorghum applications). Several diuron uses result in LOC exceedances from spray drift.
These exceedances range from 12.00 (dicot plants exposed to field corn applications) to
1.13 (monocot plants exposed to cotton applications). Based on LOC exceedances in
vascular and non-vascular plants, and twenty-two reported incidents that resulted
in plant damage, diuron is Likely to Adversely Affect (LAA) the CRLF indirectly
via habitat degradation through reduction terrestrial plants.
5.2.4 Modification to Designated Critical Habitat
Risk conclusions for the designated critical habitat are the same as those for indirect
effects. Agency concludes that there is a potential indirect impact to CRLF by terrestrial
habitat degradation from diuron exposure.
5.2.4.1 Aquatic-Phase PCEs
Three of the four assessment endpoints for the aquatic-phase primary constituent
elements (PCEs) of designated critical habitat for the CRLF are related to potential
effects to aquatic and/or terrestrial plants:
•	Alteration of channel/pond morphology or geometry and/or increase in sediment
deposition within the stream channel or pond: aquatic habitat (including riparian
vegetation) provides for shelter, foraging, predator avoidance, and aquatic
dispersal for juvenile and adult CRLFs.
•	Alteration in water chemistry/quality including temperature, turbidity, and
oxygen content necessary for normal growth and viability of juvenile and adult
CRLFs and their food source.
•	Reduction and/or modification of aquatic-based food sources for pre-metamorphs
(e.g., algae).
Based on the risk estimation for potential effects to aquatic and/or terrestrial plants
provided in Sections 5.1.1.2, 5.1.1.3, and 5.1.2.3, diuron will result in habitat
modification based on effects to aquatic-phase PCEs of designated critical habitat.
•	Aquatic non-vascular plants used as food source and habitat for CRLF may be
potentially affected from all diuron uses.
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•	Reduction of aquatic based food sources may occur from most use sites.
•	Due to aquatic vascular and terrestrial plant communities being reduced from
most use sites, there is potential for alteration of channel/pond morphology or
geometry and/or increase in sediment deposition within the stream channel or
pond.
•	Due to aquatic vascular and terrestrial plant communities being reduced from
most use sites, there is potential for 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.
The remaining aquatic-phase PCE is "alteration of other chemical characteristics
necessary for normal growth and viability of CRLFs and their food source." To assess
the impact of diuron on this PCE, 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 acute and chronic LOC exceedances for freshwater fish and aquatic
invertebrates, diuron will result in habitat modification based on effects to 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.
5.2.4.2 Terrestrial-Phase PCEs
Two of the four assessment endpoints for the terrestrial-phase PCEs of designated critical
habitat for the CRLF are related to potential effects to terrestrial plants:
•	Elimination and/or disturbance of upland habitat; ability of habitat to support food
source of CRLFs: Upland areas within 200 ft of the edge of the riparian
vegetation or drip line surrounding aquatic and riparian habitat that are comprised
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.
There is a potential for habitat modification via impacts to terrestrial plants
(Section 5.2.3.2).
The risk estimation for terrestrial-phase PCEs of designated habitat related to potential
effects on terrestrial plants is provided in Section 5.1.2.3. These results will inform the
effects determination for modification of designated critical habitat for the CRLF.
The third terrestrial-phase PCE is "reduction and/or modification of food sources for
terrestrial phase juveniles and adults." To assess the impact of diuron on this PCE, acute
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and chronic toxicity endpoints for birds, mammals, and terrestrial invertebrates are used
as measures of effects. RQs for these endpoints were calculated in Section 5.1.2.2.
Based on acute and chronic LOC exceedances for CRLF prey items of small
mammals, terrestrial invertebrates and other frogs, diuron will result in habitat
modification based on effects to the terrestrial PCE relative to reduction in food
sources.
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. Direct acute and chronic RQs for terrestrial-phase CRLFs are presented in
Section 5.2.1.2. Due to acute and chronic LOC exceedances at all use sites to
terrestrial-phase CRLFs, diuron will result in habitat modification based on effects
to the terrestrial PCE related to alteration of chemical characteristics necessary for
normal growth and viability.
5.2.5.1 Downstream Dilution
The downstream extent of exposure in streams and rivers where the EEC could
potentially be above levels that would exceed the most sensitive LOC. To complete this
assessment, the greatest ratio of aquatic RQ to LOC was estimated. Using an assumption
of uniform runoff across the landscape, it is assumed that streams flowing through treated
areas (i.e. the initial area of concern) are represented by the modeled EECs; as those
waters move downstream, it is assumed that the influx of non-impacted water will dilute
the concentrations of diuron present.
Using a EC50 value of 2.40 ug/L for non-vascular aquatic plants (the most sensitive
species) and a maximum peak EEC for applications to Agricultural Rights-of-Way,
Fencerows, etc. of 688 ug/L yields an RQ/LOC ratio of 142 (142/1). Using the
downstream dilution approach (described in more detail in Appendix F) yields a distance
of 285 kilometers which represents the maximum continuous distance of downstream
dilution from the edge of the initial area of concern. Similar to the spray drift buffer
described above, the LAA/NLAA determination is based on the area defined by the point
where concentrations exceed the EC50 value.
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.
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6.1.2 Aquatic Exposure Modeling of Diuron
The standard ecological water body scenario (EXAMS pond) used to calculate potential
aquatic exposure to pesticides is intended to represent conservative estimates, and to
avoid underestimations of the actual exposure. The standard scenario consists of
application to a 10-hectare field bordering a 1-hectare, 2-meter deep (20,000 m3) pond
with no outlet. Exposure estimates generated using the EXAMS pond are intended to
represent a wide variety of vulnerable water bodies that occur at the top of watersheds
including prairie pot holes, playa lakes, wetlands, vernal pools, man-made and natural
ponds, and intermittent and lower order streams. As a group, there are factors that make
these water bodies more or less vulnerable than the EXAMS pond. Static water bodies
that have larger ratios of pesticide-treated drainage area to water body volume would be
expected to have higher peak EECs than the EXAMS pond. These water bodies will be
either smaller in size or have larger drainage areas. Smaller water bodies have limited
storage capacity and thus may overflow and carry pesticide in the discharge, whereas the
EXAMS pond has no discharge. As watershed size increases beyond 10-hectares, it
becomes increasingly unlikely that the entire watershed is planted with a single crop that
is all treated simultaneously with the pesticide. Headwater streams can also have peak
concentrations higher than the EXAMS pond, but they likely persist for only short
periods of time and are then carried and dissipated downstream.
The Agency acknowledges that there are some unique aquatic habitats that are not
accurately captured by this modeling scenario and modeling results may, therefore,
under- or over-estimate exposure, depending on a number of variables. For example,
aquatic-phase CRLFs may inhabit water bodies of different size and depth and/or are
located adjacent to larger or smaller drainage areas than the EXAMS pond. The Agency
does not currently have sufficient information regarding the hydrology of these aquatic
habitats to develop a specific alternate scenario for the CRLF. CRLFs prefer habitat with
perennial (present year-round) or near-perennial water and do not frequently inhabit
vernal (temporary) pools because conditions in these habitats are generally not suitable
(Hayes and Jennings 1988). Therefore, the EXAMS pond is assumed to be representative
of exposure to aquatic-phase CRLFs. In addition, the Services agree that the existing
EXAMS pond represents the best currently available approach for estimating aquatic
exposure to pesticides (USFWS/NMFS 2004).
In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations
that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone
Model is a process or "simulation" model that calculates what happens to a pesticide in
an agricultural field on a day-to-day basis. It considers factors such as rainfall and plant
transpiration of water, as well as how and when the pesticide is applied. It has two major
components: hydrology and chemical transport. Water movement is simulated by the use
of generalized soil parameters, including field capacity, wilting point, and saturation
water content. The chemical transport component can simulate pesticide application on
the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase concentrations in
the soil are estimated by simultaneously considering the processes of pesticide uptake by
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plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection,
dispersion, and retardation.
Uncertainties associated with each of these individual components add to the overall
uncertainty of the modeled concentrations. Additionally, model inputs from the
environmental fate degradation studies are chosen to represent the upper confidence
bound on the mean values that are not expected to be exceeded in the environment
approximately 90 percent of the time. Mobility input values are chosen to be
representative of conditions in the environment. The natural variation in soils adds to the
uncertainty of modeled values. Factors such as application date, crop emergence date,
and canopy cover can also affect estimated concentrations, adding to the uncertainty of
modeled values. Factors within the ambient environment such as soil temperatures,
sunlight intensity, antecedent soil moisture, and surface water temperatures can cause
actual aquatic concentrations to differ for the modeled values.
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.
In order to account for uncertainties associated with modeling, available monitoring data
were compared to PRZM/EXAMS estimates of peak EECs for the different uses. As
discussed above, several data values were available from NAWQA for diuron
concentrations measured in surface waters receiving runoff from agricultural areas. The
specific use patterns (e.g. application rates and timing, crops) associated with the
agricultural areas are unknown, however, they are assumed to be representative of
potential diuron use areas.
The monitoring data available are below the PZM-EXAMS predictions by an order of
magnitude. The monitoring data indicated that the time weighted mean concentration
ranged from below the 0.001 ppb to 0.86 ppb with a mean concentration of 0.21 ppb.
PRZM-EXAMS prediction (not including the scenarios for impervious surfaces)
estimated diuron to be in the surface waters at peak concentrations from 27.5 ppb to 2.6
ppb and 60 day EEC from 18.3 ppb to 1.8.
6.1.3 Action Area Uncertainties
The action area is considered to be the whole State of California since diuron is
considered to be an animal carcinogen and can not be spatially defined. Diuron use has
been reported in all 58 counties.
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6.1.4 Usage Uncertainties
County-level usage data were obtained from California's Department of Pesticide
Regulation Pesticide Use Reporting (CDPR PUR) database. Four years of data (2002 -
2005) were included in this analysis because statistical methodology for identifying
outliers, in terms of area treated and pounds applied, was provided by CDPR for these
years only. No methodology for removing outliers was provided by CDPR for 2001 and
earlier pesticide data; therefore, this information was not included in the analysis because
it may misrepresent actual usage patterns. CDPR PUR documentation indicates that
errors in the data may include the following: a misplaced decimal; incorrect measures,
area treated, or units; and reports of diluted pesticide concentrations. In addition, it is
possible that the data may contain reports for pesticide uses that have been cancelled.
The CPDR PUR data does not include home owner applied pesticides; therefore,
residential uses are not likely to be reported. As with all pesticide 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 Diuron
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.
It was assumed that ingestion of food items in the field occurs at rates commensurate
with those in the laboratory. Although the screening assessment process adjusts dry-
weight estimates of food intake to reflect the increased mass in fresh-weight wildlife food
intake estimates, it does not allow for gross energy differences. Direct comparison of a
laboratory dietary concentration- based effects threshold to a fresh-weight pesticide
residue estimate would result in an underestimation of field exposure by food
consumption by a factor of 1.25 - 2.5 for most food items.
Differences in assimilative efficiency between laboratory and wild diets suggest that
current screening assessment methods do not account for a potentially important aspect of
food requirements. Depending upon species and dietary matrix, bird assimilation of wild
diet energy ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85%
(U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is
formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for
underestimation of exposure may exist by assuming that consumption of food in the wild
is comparable with consumption during laboratory testing. In the screening process,
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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
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 diuron from multiple applications, each application of diuron would
have to occur under identical atmospheric conditions (e.g., same wind speed and same
wind direction) and (if it is an animal) the animal being exposed would have to be located
in the same location (which receives the maximum amount of spray drift) after each
application. Additionally, other factors, including variations in topography, cover, and
meteorological conditions over the transport distance are not accounted for by the
AgDRIFT model (i.e., it models spray drift from aerial and ground applications in a flat
area with little to no ground cover and a steady, constant wind speed and direction).
Therefore, in most cases, the drift estimates from AgDRIFT may overestimate exposure,
especially as the distance increases from the site of application, since the model does not
account for potential obstructions (e.g., large hills, berms, buildings, trees, etc.).
Furthermore, conservative assumptions are made regarding the droplet size distributions
being modeled (was set to the default' ASAE Very Fine to Fine'), the application method
(i.e., aerial), release heights and wind speeds (also set to the default values of 10 ft and 10
mph respectively for aerial application; the height for ground application was set to the
default 'high boom'). Alterations in any of these inputs would decrease the area of
potential effect.
6.2 Effects Assessment Uncertainties
6.2.1 Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids, second instar for
amphipods, stoneflies, mayflies, and third instar for midges).
Testing of juveniles may overestimate toxicity at older age classes for pesticide active
ingredients that act directly without metabolic transformation because younger age
classes may not have the enzymatic systems associated with detoxifying xenobiotics. In
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so far as the available toxicity data may provide ranges of sensitivity information with
respect to age class, this assessment uses the most sensitive life-stage information as
measures of effect for surrogate aquatic animals, and is therefore, considered as
protective of the CRLF.
6.2.2 Use of Surrogate Species Effects Data
CRLF
Guideline toxicity tests and open literature data on diuron 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.
Terrestrial Plants
Plant toxicity data from both registrant-submitted studies and studies in the scientific
literature were reviewed for this assessment. Registrant-submitted studies are conducted
under conditions and with species defined in EPA toxicity test guidelines. 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 diuron, 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.
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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.
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.
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 diuron to the CRLF and its designated
critical habitat.
The Agency makes a Likely to Adversely Affect determination for the CRLF from the
use of diuron. The Agency has determined that there is the potential for modification of
CRLF designated critical habitat from the use of the chemical. The direct effects and
habitat modification effects determinations are summarized in Table 7.1 and Table 7.2
respectively. Given the LAA determination for the CRLF and potential modification of
designated critical habitat, a description of the baseline status and cumulative effects for
the CRLF is provided in Attachment II.
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 iron's use pattern is identified, using land cover
data that correspond to iron'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 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. The AgDRIFT model was used to evaluate
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potential distances beyond which exposures would be expected to be below LOC.
However, due to the limitations imposed by the Tier 1 ground analysis (allows users to
evaluate off-site deposition and exposure out to 1,000 ft downwind from the location of
the application), the exact buffer needed for exposures to be below the LOC is uncertain.
The output from AgDRIFT indicated that the buffer zone required would be greater than
1,000 feet. Since the model is restricted to accurately discerning a buffer within 1,000
feet of the application, the exact distance needed for a buffer to protect non-listed and
listed plants is unknown. However, as seen in Table 3.7, the calculated risk quotient
(RQ) is significantly larger than the level of concern (LOC) for non-listed and listed plant
species (LOC = 1). This comparison provides awareness to approximately how much
greater than 1,000 feet the buffer needs to be. It is assumed that non-flowing water
bodies (or potential CRLF habitat) are included within this area.
In addition to the spray drift buffer, the results of the downstream dilution extent analysis
result in a distance of 285 kilometers which represents the maximum continuous distance
of downstream dilution from the edge of the initial area of concern. If any of these
streams reaches flow into CRLF habitat, there is potential to affect either the CRLF or
modify its habitat. These lotic aquatic habitats within the CRLF core areas and critical
habitats potentially contain concentrations of diuron sufficient to result in LAA
determination or modification of critical habitat.
Appendix F provides maps of the initial area of concern, along with CRLF habitat areas,
including currently occupied core areas, CNDDB occurrence sections, and designated
critical habitat. It is expected that any additional areas of CRLF habitat that are located
285 kilometers of stream distance (to account for downstream dilution) outside the initial
area of concern may also be impacted and are part of the full spatial extent of the
LAA/modification of critical habitat effects determination.
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Table 7.1 El
Tects Determination Summary for Effects of Diuron on the CRLF
Assessment
Endpoint
Effects
Determination 1
Basis for Determination
Survival,
growth,
and/or
reproduction
ofCRLF
individuals
LAA
Potential for Direct Effects
Aquatic-phase (Eggs, Larvae, and Adults): The aquatic phase amphibian
acute LOCs for Listed species (0.05) are exceeded for most uses of diuron in
California. Acute RQs that exceed the Agency's LOC range from 13.99
(paved areas) to 0.053 (papaya). Chronic RQs that exceed the Agency's
LOC for chronic exposure (1.0) range from 188.58 (paved areas) to 1.0003
(banana, plantain).
Terrestrial-phase (Juveniles and Adults): Refined acute dietary-based RQs
for CRLFs consuming large insects and small herbivore mammals exceed
the acute listed species LOC (0.1) for all uses of diuron except Sorghum and
Field Corn. The acute dietary-based RQs for CRLFs consuming large
insects exceed the acute listed species LOC for Agricultural Rights-of-Way,
Fencerows etc. and Ornamental Herbaceous Plants. No acute dietary based
LOCs were exceeded for CLRF consuming small insectivore mammals and
small terrestrial phase amphibians for any diuron use.
Refined chronic dietary-based RQs for CRLFs consuming insects and
mammals exceed the chronic listed species LOC for all uses of diuron across
all food item groups.
Potential for Indirect Effects
Aquatic prey items, aquatic habitat, cover and/or primary productivity.
LOCs for non-vascular plants are exceeded for all uses. The RQs range
from 2331.67 (paved areas) to 1.82 (sorghum).
Aquatic invertebrates acute a LOC are exceeded. The acute RQs that
exceed the LOC range from 34.98 (paved areas) to 0.06 (post-harvest
wheat). Chronic LOCs are exceeded for paved area applications
(RQ=1.50).
RQs for vascular aquatic plants exceed the Agency's LOC (1.0) for most
uses. These range from 373.33 (paved areas) to 1.01 (alfalfa aerial).
Terrestrial prey items, riparian habitat.
For small mammal, chronic dose based RQs exceed the Agency's LOC (1.0)
for most uses. The dose based chronic RQs that exceed the LOC range from
5.00 (paved areas) to 1.31 (walnut). The acute RQs exceed the Agency' s
LOC for several uses. The RQs that exceed the acute dose based LOC range
from 0.25 (paved areas) to 0.12 (Agricultural Rights-of-Way, Fencerows,
Hedgerows, Airports, etc.).
LOCs are exceeded for terrestrial riparian plants and for aquatic plants from
exposure to diuron from runoff or spray drift. Alteration of riparian and
vascular plants may result in alteration of temperature, turbidity, and oxygen
content. RQs for vascular aquatic plants exceed the Agency's LOC (1.0) for
most uses. These range from 373.33 (paved areas) to 1.01 (alfalfa aerial).
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 7.2 Effects Determination Summary for the Critical Habitat Impact Analysis
Assessment
Endpoint
Effects
Determination 1
Basis for Determination
Modification of
aquatic-phase PCE
HM
Due to aquatic vascular and terrestrial plant communities being reduced from all
use sites, there is potential for alteration of channel/pond morphology or
geometry and/or increase in sediment deposition within the stream channel or
pond. These plant communities provide for shelter, foraging, predator
avoidance, and aquatic dispersal for juvenile and adult CRLFs. In addition, there
is potential for 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.
LOCs are exceeded for terrestrial riparian plants and for aquatic vascular plants
from exposure to diuron from runoff or spray drift. LOCs for non-vascular
plants are exceeded for all uses.
Modification of
terrestrial-phase
PCE
HM
The use of diuron at all use sites may create the following modification of PCE:
elimination and/or disturbance of upland habitat; ability of habitat to support
food source of CRLFs, Elimination and/or disturbance of dispersal habitat,
reduction and/or modification of food sources for terrestrial phase juveniles and
adults, and alteration of chemical characteristics necessary for normal growth
and viability of juvenile and adult CRLFs and their food source.
The RQs for vascular aquatic plants exceed the Agency's LOC (1.0) for most
uses of diuron in California. These range from 373.33 (paved areas) to 1.01
(alfalfa aerial). Use of diuron on most use sites will exceed acute dietary- and
dose-based LOC and chronic LOC for prey food items of small mammals, frogs,
and invertebrates. Food source for CRLF is reduced and CRLF is indirectly
affected.
1 Habitat Modification (HM) 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
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proportion of the population extant within geographical areas where those
effects are predicted. Furthermore, such population information would
allow for a more comprehensive evaluation of the significance of potential
resource impairment to individuals of the species.
•	Quantitative information on prey base requirements for individual aquatic-
and terrestrial-phase frogs. While existing information provides a
preliminary picture of the types of food sources utilized by the frog, it
does not establish minimal requirements to sustain healthy individuals at
varying life stages. Such information could be used to establish
biologically relevant thresholds of effects on the prey base, and ultimately
establish geographical limits to those effects. This information could be
used together with the density data discussed above to characterize the
likelihood of adverse effects to individuals.
•	Information on population responses of prey base organisms to the
pesticide. Currently, methodologies are limited to predicting exposures
and likely levels of direct mortality, growth or reproductive impairment
immediately following exposure to the pesticide. The degree to which
repeated exposure events and the inherent demographic characteristics of
the prey population play into the extent to which prey resources may
recover is not predictable. An enhanced understanding of long-term prey
responses to pesticide exposure would allow for a more refined
determination of the magnitude and duration of resource impairment, and
together with the information described above, a more complete prediction
of effects to individual frogs and potential modification to critical habitat.
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8.0 References
Altig, R. and R.W. McDiarmid. 1999. Body Plan: Development and Morphology. In
R.W. McDiarmid and R. Altig (Eds.), Tadpoles: The Biology of Anuran
Larvae.University of Chicago Press, Chicago, pp. 24-51.
Alvarez, J. 2000. Letter to the U.S. Fish and Wildlife Service providing comments on
the Draft California Red-legged Frog Recovery Plan.
Andrieux, P., Lennartz, B., Louchart, X., Voltz, M., 1997. Diuron and Simazine Losses to
Runoff Water in Mediterranean Vineyards. Journal of Environmental Quality. 26:1493-
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ARSUSDA. 2004. The Agricultural Research Services Pesticide Properties Database.
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Atkins. E.L., E.A. Greywood, and R.L. MacDonald. 1975. Toxicity of pesticides and
other agricultural chemicals to honey bees. Laboratory studies. Univ. of Calif., Div.
Agric. Sci. Leaflet 2287. 38 pp. (MRID# 000369-35).
Bogarets, P., Bohatier, J., Bonnemoy, F., Cuer, A., Sancelme, M., Tixier, C.,
Twagilimana, L., Veschambre, H. 2000. Fungal Biodegradation of aPhenylurea
Herbicide, Diuron: Structure and Toxicity of Metabolites. Pest Management Science.
56:455-462.
Bonnemoy, F., Cuer, A., Sancelme, M., Tixier, C., Veschambre, H. 2001. Degradation
Products of a Phenylurea Herbicide, Diuron: Synthesis Ecotoxicity and
Biotransformation. Environmental Toxicology and Chemistry. 30:1381-1389.
Boule, P., Faure, V., Jirkovsky., J. 1997. Photolysis of Diuron. Pesticide Science. 50:42-
52.
Braun, A.L., Hawkins, L.S. 1991. Presence of bromacil, diuron, and simazine in surface
water runoff from agricultural fields and non-crop sites in Tulare County, California.
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PM91-1.
Bulcke, R., Cools, K., Dekkers, T., Eelen, H., Neus, O., Rouchaud, J. 2000. Soil
Dissipation of Diuron, Chlorotoluron, Simazine, Propyzamide, and Diflufenican
Herbicides After Repeated Application in Fruit Tree Orchards. Archives Environmental
Contamination and Toxicology. 29:60-65.
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Burns, L.A. 1997. Exposure Analysis Modeling System (EXAMSII) Users Guide for
Version 2.97.5, Environmental Research Laboratory, Office of Research and
Development, U.S. Environmental Protection Agency, Athens, GA.
Carsel, R.F. , J.C. Imhoff, P.R. Hummel, J.M. Cheplick and J.S. Donigian, Jr. 1997.
PRZM-3, A Model for Predicting Pesticide and Nitrogen Fate in Crop Root and
Unsaturated Soil Zones: Users Manual for Release 3.0; Environmental Research
Laboratory, Office of Research and Development, U.S. Environmental Protection
Agency, Athens, GA.
Crawshaw, G.J. 2000. Diseases and Pathology of Amphibians and Reptiles in:
Ecotoxicology of Amphibians and Reptiles; ed: Sparling, D.W., G. Linder, and C.A.
Bishop. SETAC Publication Series, Columbia, MO.
DPR Pesticide Chemistry Database. Environmental Monitoring Branch, Department of
Pesticide Regulation. 2003.
Ecotox. 2004. Ecotoxicology Database. U.S. EPA [Online] Available:
http://www.usepa.gov/ecotox
EXTOXNET. 1996. Diuron. [Online] Available:
http://ace.orst.edu/info/extoxnet/pips/diuron.htm
Fellers, G. M., et al. 2001. Overwintering tadpoles in the California red-legged frog
{Rana aurora draytonii). Herpetological Review, 32(3): 156-157.
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.
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