S7^
PRO^
Risks of Hexazinone 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 20,2008
-------
Primary Authors:
Ronald Parker, PhD
Senior Environmental Engineer
Environmental Fate and Effects Division
Valerie Woodard, PhD
Biologist
Environmental Fate and Effects Division
Secondary Review:
Jean Holmes, D.V.M., M.P.H.
Mohammed Ruhman, Ph.D, Agronomist
Branch Chief, Environmental Risk Assessment Branch #:
Mah Shamim
-------
Table of Contents
1. Executive Summary 6
2. Problem Formulation 21
2.1 Purpose 21
2.2 Scope 23
2.3 Previous Assessments 25
2.4 Stressor Source and Distribution 25
2.4.1 Environmental Fate Properties 25
2.4.2 Environmental Transport Mechanisms 27
2.4.3 Mechanism of Action 27
2.4.4 Use Characterization 27
2.5 Assessed Species 30
2.5.1 Distribution 30
2.5.2 Reproduction 36
2.5.3 Diet 37
2.5.4 Habitat 37
2.6 Designated Critical Habitat 38
2.7 Action Area 40
2.8 Assessment Endpoints and Measures of Ecological Effect 46
2.8.1 Assessment Endpoints for the CRLF 46
2.8.2 Assessment Endpoints for Designated Critical Habitat 48
2.9 Conceptual Model 51
2.9.1 Risk Hypotheses 51
2.9.2 Diagram 52
2.10 Analysis Plan 56
2.10.1 Measures of Exposure 57
2.10.2 Measures of Effect 59
3 Exposure Assessment 61
3.1 Label Application Rates and Intervals 61
3.2 Aquatic Exposure Assessment 63
3.2.1 Modeling Approach 63
3.2.2 Model Inputs 64
3.2.3 PRZM/EXAMS Aquatic Exposure Modeling Results 65
3.2.4 Existing Monitoring Data 65
3.2.5 Spray Drift Buffer Analysis 66
3.2.6 Downstream Dilution Analysis 69
3.3 Terrestrial Exposure 70
3.3.1 Bird and Mammal Exposure (T-REX Model) 70
Granular Applications 72
3.3.2 Terrestrial Invertebrate Exposure 74
3.4 Terrestrial Plant Exposure Assessment 75
3.4.1 TerrPlant 75
4. Effects Assessment 76
4.1 Toxicity of Hexazinone to Aquatic Organisms 78
4.1.1 Toxicity to Freshwater Fish 80
4.1.2 Toxicity to Freshwater Invertebrates 80
3
-------
4.1.3 Toxicity to Aquatic Plants 81
4.2 Toxicity of Hexazinone to Terrestrial Organisms 81
4.2.1 Toxicity to Birds 83
4.2.2 Toxicity to Mammals 83
4.2.3 Toxicity to Terrestrial Invertebrates 84
4.2.4 Toxicity to Terrestrial Plants 84
4.3 Incident Database Review 85
4.3.1 Terrestrial Animal Incidents 85
4.3.2 Plant Incidents 85
4.3.3 Aquatic Animal Incidents 86
5. Risk Characterization 86
5.1 Risk Estimation 86
5.1.1 5.1.1 Use of Probit Slope Response Relationship to Provide Information on
the Endangered Species Levels of Concern 87
5.1.2 Exposures in the Aquatic Habitat 87
5.1.3 Exposures in the Terrestrial Habitat 91
5.1.4 Primary Constituent Elements of Designated Critical Habitat 96
5.2 Risk Description 98
5.2.1 Direct Effects 107
5.2.2 Indirect Effects (via Reductions in Prey Base) 110
5.2.3 Indirect Effects (via Habitat Effects) 115
5.2.4 Modification to Designated Critical Habitat 119
6 Uncertainties 121
6.1 Exposure Assessment Uncertainties 121
6.1.1 Maximum Use Scenario 121
6.1.2 Aquatic Exposure Modeling of Hexazinone 121
6.1.3 Action Area Uncertainties 123
6.1.4 Usage Uncertainties 124
6.1.5 Terrestrial Exposure Modeling of Hexazinone 124
6.1.6 Spray Drift Modeling 127
6.2 Effects Assessment Uncertainties 127
6.2.1 Age Class and Sensitivity of Effects Thresholds 127
6.2.2 Use of Surrogate Species Effects Data 127
6.2.3 Sub lethal Effects 128
6.2.4 6.2.4 Location of Wildlife Species 128
7 Risk Conclusions 128
8. References 143
4
-------
Appendices
Appendix A
Multi-ai Product Analysis
Appendix B
RQ Method and LOCs
Appendix C
T-REX Output
Appendix D
T-HERPS Output
Appendix E
TERRPLANT Output
Appendix F
GIS Analysis
Appendix G
Bibliography of ECOTOX Open Literature
Attachment I
Status and Life History of the California Red-Legged Frog
Attachment II
Baseline Status and Cumulative Effects for the California Red-Legged
5
-------
1. Executive Summary
The purpose of this assessment is to evaluate potential direct and indirect effects on the
California red-legged frog (Rana aurora draytonii) (CRLF) arising from FIFRA regulatory
actions regarding use of hexazinone 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.
Hexazinone is a triazinone herbicide used to control a broad spectrum of weeds including many
annual, biennial and perennial weeds, as well as some woody plants in alfalfa, rangeland and
pasture, woodland, pineapples, sugarcane and blueberries. It is also used for forest trees and
other non-crop areas. Hexazinone is registered for pre-emergent, post-emergence, layby, directed
spray and basal soil applications. It is used as a non-selective herbicide in noncropland areas and
as a selective herbicide in reforestation practices. Current labels also include drainage areas,
industrial sites, sewage disposal areas and airports. Of these uses, only a single application to one
industrial site is recorded in the California PUR data reviewed for this assessment.
Although the maximum number of applications from the label for pasture, alfalfa and Christmas
tree uses is one, other uses do not specify a maximum rate or maximum number of applications
per year. For this assessment, one application per year for those other uses is based on additional
information from the label. Blueberry uses are modeled at a maximum of one application per
year due to no application within 450 days of harvest. Pineapple is modeled as one application
per year due to the growing season, which is nearly a year in length. Noncrop uses and all
granular uses, non-agricultural rights-of-way (ROW), forest site preparation and rangeland, are
modeled as one application per year due to the requirement for rain to activate hexazinone and
because maximum effects are achieved after 12-24 months.
The environmental fate properties of hexazinone, along with available monitoring data
identifying its presence in surface water, air, and in precipitation in California, indicate that
runoff, spray drift, volatilization, atmospheric transport and subsequent deposition represent
potential transport mechanisms of hexazinone to the aquatic and terrestrial habitats of the CRLF.
In this assessment transport of hexazinone from initial application sites through runoff and spray
drift are considered in deriving quantitative estimates of hexazinone exposure to CRLF, its prey
and its habitats. Although volatilization of hexazinone from treated areas resulting in
atmospheric transport and eventual deposition represent relevant transport pathways leading to
exposure of the CRLF and its habitats, it is expected that detected hexazinone concentrations in
atmospheric monitoring data are reflective of near field spray drift and not long range transport,
given hexazinone's low volatility and a lack of detections at higher elevations. In addition,
adequate tools are not available at this time to quantify exposures through these pathways.
6
-------
Therefore, volatilization, and potential atmospheric transport are discussed only qualitatively in
this assessment.
Based on the available information, hexazinone appears to be persistent and mobile in soil and
aquatic environments. The mobility of hexazinone was demonstrated in batch equilibrium data.
The field and forestry dissipation data also confirm that hexazinone is persistent and mobile.
Furthermore, the batch equilibrium data also suggests that degradates are very mobile. Based on
the environmental fate properties of hexazinone, it can be concluded they may be of concern for
surface water and groundwater contamination. This assessment is based on the parent because
hexazinone is so persistent in the field, therefore consideration of toxicity of degradates will not
change the result of this assessment.
Since CRLFs exist within aquatic and terrestrial habitats, exposure of the CRLF, its prey and its
habitats to hexazinone are assessed separately for the two habitats. Tier-II aquatic exposure
models are used to estimate high-end exposures of hexazinone in aquatic habitats resulting from
runoff and spray drift from different uses. Peak model-estimated environmental concentrations
resulting from different hexazinone uses range from 10.6 tol56.6 |ig/L. These estimates are
supplemented with analysis of available California surface water monitoring data from the
California Department of Pesticide Regulation (CDPR). Hexazinone is not on the list of
pesticides for which the NAQWA program samples, therefore the NAQWA database will not be
used.. There are three measured hexazinone concentrations above the limit of quantitation in the
CDPR data. All three CDPR measured concentrations were recorded at the River Road sampling
station on Orestimba Creek, tributary to the San Joaquin River in Stanislaus County. The sample
with the highest of these three concentration values (0.5 (j.g/1) was collected on February 14,
2001. This maximum concentration of hexazinone reported by the California Department of
Pesticide Regulation surface water database from 2000-2005 (x |ig/L) is roughly 300 times lower
than the highest peak model-estimated environmental concentration.
To estimate hexazinone exposures to the terrestrial-phase CRLF and its potential prey resulting
from uses involving hexazinone applications, the T-REX model is used. For spray application
uses AgDRIFT and AGDISP models are also used to estimate deposition of hexazinone on
terrestrial and aquatic habitats from spray drift. The TerrPlant model is used to estimate
hexazinone exposures to terrestrial-phase CRLF habitat, including plants inhabiting semi-aquatic
and dry areas, resulting from uses involving foliar hexazinone applications. The T-HERPS model
is used to allow for further characterization of dietary exposures of terrestrial-phase CRLFs
relative to birds as a surrogate to the CRLF.
The assessment endpoints for the CRLF include direct toxic effects on the survival, reproduction,
and growth of the CRLF itself, as well as indirect effects, such as reduction of the prey base or
modification of its habitat. Direct effects to the CRLF in the aquatic habitat are based on toxicity
information for freshwater fish, which are 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 CRLF's prey items
and designated critical habitat requirements in the aquatic habitat are dependant on the
availability of freshwater aquatic invertebrates and aquatic plants, toxicity information for these
taxonomic groups is also discussed. In the terrestrial habitat, indirect effects due to depletion of
prey are assessed by considering effects to terrestrial insects, small terrestrial mammals, and
7
-------
frogs. Indirect effects due to modification of the terrestrial habitat are characterized by available
data for terrestrial monocots and dicots.
Risk quotients (RQs) are derived as quantitative estimates of potential high-end risk. Acute and
chronic RQs are compared to the Agency's levels of concern (LOCs) to identify instances where
Hexazinone use within the action area has the potential to adversely affect the CRLF and its
designated critical habitat via direct toxicity or indirectly based on direct effects to its food
supply (i.e., freshwater invertebrates, algae, fish, frogs, terrestrial invertebrates, and mammals)
or habitat (i.e., aquatic plants and terrestrial upland and riparian vegetation). When RQs for a
particular type of effect are below LOCs, the pesticide is determined to have "no effect" on the
subject species. Where RQs exceed LOCs, a potential to cause adverse effects is identified,
leading to a conclusion of "may affect." If a determination is made that use of hexazinone use
within the action area "may affect" the CRLF and its designated critical habitat, additional
information is considered to refine the potential for exposure and effects, and the best available
information is used to distinguish those actions that "may affect, but are not likely to adversely
affect" (NLAA) from those actions that are "likely to adversely affect" (LAA) the CRLF and its
critical habitat.
There is an overall "LAA" determination for hexazione exposure to the CRLF based on direct
and indirect effects to the aquatic and terrestrial-phase CRLF. There is expected to be an effect
of hexazinone exposure to the aquatic-phase CRLF. There is a "No Effect" determination for
direct effects for the aquatic-phase CRLF using the fish as a surrogate due to no LOC
exceedence.
There is an "LAA" determination for indirect prey reduction to the aquatic-phase CRLF.
Indirect effects to the aquatic-phase CRLF via direct effects to food supply are determined using
freshwater invertebrates, non-vascular plants, fish and frogs. There was no LOC exceedence for
aquatic invertebrates resulting in a "no effect' determination for indirect effects to aquatic-phase
CRLF via direct effects to food supply for all uses of hexazinone. There was an "LAA"
determination for indirect dietary effects to the aquatic-phase CRLF consuming aquatic
invertebrates. There was no LOC exceedence for fish resulting in a "no effect' determination for
indirect effects to aquatic-phase CRLF via direct effects to food supply for all uses of
hexazinone. There was no LOC exceedence for aquatic frogs using the fish as a surrogate,
resulting in a "no effect' determination for indirect effects to aquatic-phase CRLF via direct
effects to food supply for all uses of hexazinone.
There is an indirect "habitat modification" determination for the aquatic-phase CRLF due to
LOC exceedences for non-vascular and vascular plants and the mode-of-action for hexazinone.
A "likely to adversely affect" determination is made for some uses of hexazinone for indirect
effects on habitat (i.e., aquatic and terrestrial plants) for the aquatic-phase CRLF.
There is expected to be an effect of hexazinone exposure to the terrestrial-phase CRLF. There is
an "LAA" determination for direct effects for the terrestrial-phase CRLF using the birds as a
surrogate due to endangered species LOC exceedence for (8 lb/A).
There is an "LAA" determination for indirect prey reduction to the terrestrial-phase CRLF due to
the weight of evidence from results from T-REX and probit analysis, no relevant incident reports
8
-------
and no available open literature. Indirect effects to the terretrial-phase CRLF via direct effects to
food supply are determined for terrestrial invertebrates, mammals, and.terrestrial amphibians
using the bird as a surrogate. There was an "LAA" determination for terrestrial invertebrates due
to the uncertainty due to no mortality at the highest concentration tested for all uses. There is an
"LAA" determination for the CRLF consuming mammals for noncrop uses (8 lb/A) due to the
RQ exceeding the non-listed LOC. There is a "LAA" determination for the CRLF consuming
terrestrial amphibians using the bird as a surrogate for (8 lb/A) and (3 lb/A).There was an "LAA"
determination for indirect dietary effects to the terrestrial-phase CRLF consuming aquatic
invertebrates. There was an LOC exceedence for amphibians using birds resulting in a "no
effect' determination for indirect effects to aquatic-phase CRLF via direct effects to food supply
for all uses of hexazinone. There was no LOC exceedence for aquatic frogs using the fish as a
surrogate, resulting in a "no effect' determination for indirect effects to aquatic-phase CRLF via
direct effects to food supply for all uses of hexazinone.
There is an indirect "habitat modification" determination for all uses for the terrestrial-phase
CRLF due to LOC exceedences for monocots and dicots and the mode-of-action for hexazinone.
Table 1.1 and 1.2 summarize hexazinone determinations.
'I'iihlc I.I KITccls DcU'i'iiiiiiiilion Suininnrv lor Direct iind Indirect KITccts of llcxiizinonc on (lie
( KM-
Assessment I'.nripoinl
l.lfecls
Delcrminalion1
Basis lor Determination
Aquatic-Phase CRLF
(Eggs, Larvae, and Adults)
Direct Effect s of Hexazinone on the Aquatic-Phase CRLF
Survival, growth, and reproduction of
CRLF individuals via direct effects on
aquatic phases
Using fish as a
surrogate:
No Effect
Using freshwater fish as a surrogate, no acute and
chronic LOCs are exceeded for applications of Non-crop
(agricultural Rights-of-Way) (12 lb/A-granular), there is
no expectation for adverse effects for lower rates:
noncrop uses (8 lb/A), forest site preparation (5 lb/A),
conifer release (3 lb/A), pineapple (3.6 lb/A), blueberry
(3 lb/A), Christmas Tree (2 lb/A), alfalfa (1.5 lb/A) and
pasture (1.1 lb/A).
Indirect Effect s of Hexazinone on the A(
uatic -Phase CRLF
Survival, gth, and reproduction of CRLF
individuals via effects to food supply (i.e.,
freshwater invertebrates, non-vascular
plants, fish, and frogs)
Freshwater
invertebrates:
9
-------
No effect
Using freshwater invertebrates, no acute and chronic
LOCs are exceeded for applications of Non-agricultural
Rights-of-way (12 lb/A-granular). Due to no exceedence
for the 12 lb/A rate, it is assumed that there would also
be no exceedence for the lower rates: Noncrop uses (8
lb/A), forest site preparation (5 lb/A), conifer release (3
lb/A), pineapple (3.6 lb/A), blueberry (3 lb/A), Christmas
tree (2 lb/A), alfalfa (1.5 lb/A) and pasture (1.1 lb/A).
Indirect Effects of
Prev Reduction for
Non-vascular aauatic
olants for all uses:
May Affect
The May Affect for hexazinone uses related to
applications for non-crop (non-agricultural ROW) (12
lb/A)non-crop uses (8 lb/A), conifer release (3 lb/A),
pineapple (3.6 lb/A), rangeland (3 lbs/A), Christmas trees
(2.0 lb ai/A), alfalfa (1.5 lb ai/A) and pasture (1. lib
ai/A), exceed LOCs; therefore, indirect effects to
tadpoles that feed on algae are possible. RQs range from
22.37 to 1.52.
LAA
The LAA determination is due to mode of action
Non-vascular aquatic
plants: No Effect
Blueberry uses (RQ = 0.81) resulted in no LOC
exceedence.
Indirect Effects of
Prey Reduction for
Fish as surrogate for
Frogs for all uses:
No effect
Using freshwater fish as a surrogate, no acute and
chronic LOCs are exceeded for applications of non-crop
(12 lb/A-granular), Noncrop uses (8 lb/A), forest site
preparation (5 lb/A), conifer release (3 lb/A), pineapple
(3.6 lb/A), blueberry (3 lb/A), Christmas tree (2 lb/A),
alfalfa (1.5 lb/A) and pasture (1.1 lb/A).
10
-------
Survival, growth, and reproduction of
CRLF individuals via indirect effects on
habitat, cover, and/or primary
productivity (i.e., aquatic plant
community)
Non-vascular
aauatic olants: Mav
Affect
LAA
Hexazinone uses related to applications on Non-crop
(12 lb/A-granular), Noncrop uses (8 lb/A), forest site
preparation (5 lb/A), pineapple (3.6 lb/A), conifer
release (3 lb/A), rangeland (3 lb/A), Christmas Tree (2
lb/A), alfalfa (1.5 lb/A) and pasture (1.1 lb/A) exceed
LOCs. Indirect effects to tadpoles that feed on algae are
possible due to the MO A, which interferes with
photosynthesis and RNA.
No Effect
There is no LOC exceedence for blueberry (3 lb/A)
(RQ=0.81).
Indirect Effects on
habita for Vascular
aauatic olants for all
uses: Mav Affect
The "May Affect" is based on the LOC exceedence for
vascular aquatic plants for liquid applications of
hexazinone to non-crop (12 lb/A), non-crop uses (8
lbs/A), Forest Site Preparation (5 lb/A), Conifer Release
(3 lb/A).RQs range from 4.19 to 1.25.
LAA
The "LAA" determination is based on the Mode of
Action.
No Effect
No LOC exceedence resulted for blueberry (3 lb/A),
rangeland (3 lb/A) Christmas tree (2 lb/A), alfalfa (1.5
lb/A) or pasture (1.1 lb/A).
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.
Fforested and
srassv/herbaceous
riparian vesetation:
May Affect
Riparian vegetation may be affected because terrestrial
plant RQs exceed LOCs. RQs for semi-aquatic areas
range from 87.66 to 937.50 Hexazinone effects on
shading, bank stabilization, and structural diversity of
riparian areas in the action area are expected. Aquatic-
phase CRLFs may be indirectly affected by adverse
effects to sensitive herbaceous vegetation (based on all
hexazinone uses), which provides habitat and cover for
the CRLF and attachment sites for its egg masses.
11
-------
LAA < 3366 ft
(ground)
The LAA determination is based on MOA for ground
applications of hexazinone within a drift buffer of 3366 ft
based on the AGDISP results.
NLAA > 3366 ft
(ground)
LAA <3589 ft
(aerial);
There is an "NLAA' determination fro animals outside
the drift buffer of 3589 ft resulting from the AGDISP
model.
The LAA determination is based on MOA for aerial
applications of hexazinone within a drift buffer of 3589 ft
based on the AGDISP results.
NLAA > 3589 ft
(aerial)
There is an "NLAA" determination for animals outside
the drift buffer of 3589 ft resulting from the AGDISP
model.
Terrestrial-Phase CRLF
(Juveniles and adults)
Direct Effect s of Hexazinone on the Terr
cstrial-Phasc CRLF
Survival, growth, and reproduction of
CRLF individuals via direct effects on
terrestrial phase adults and juveniles
Nongranular acute for
medium size froe
usins the bird as a
surrogate: Mav affect
An adverse effect is expected based on weight of
evidence for acute avian toxicity. The T-Rex analysis
resulted in an endangered species exceedence for all
crops.
LAA for the medium
size frog
Further refinement using the T-HERPS analysis resulted
in an endangered species exceedence for the CRLF
consuming small herbivore mammals with RQs ranging
from 0.53 for (8 lb/A) resulting from T-Rex analysis.
NLAA for the
medium size frog
Further refinement using a T-HERPS analysis resulted in
RQS falling between the endangered species (0.1) and
acute risk (0.5) LOCs exceedence for the CRLF
consuming small herbivore mammals for pineapple,
blueberry, conifer release and Christmas tree uses for a
37 g animal. The RQs from the T-HERPS analysis were
analyzed using probit analysis and resulted in
discountable effects for prey reduction.
No Effect for medium
sized frog
A "No effect"determination for pasture (1.1 lb/A) is due
to no LOC exceedence using the bird as a surrogate for
the CRLF for the 37 g animal resulting from the T-REX
analysis.
12
-------
Nongranular Acute
Small Frog
May Affect:
The May Affect resulted from LOC exceedence using the
bird as a surrogate from the T-Rex analysis for all crops.
NLAA
An "NLAA" determination is due to no LOC exceedence
for any use for the small CRLF (1.4 g) from the T-Herps
analysis for consumption of small insect, large insect
small, small herbivore mammal, insectivore mammals or
small amphibian prey..
Nongranular Acute
Large Frog: May
Affect:
The May Affect resulted from LOC exceedence using the
bird as a surrogate in the T-Rex analysis for all crops.
NLAA
An "NLAA" determination is due to no LOC exceedence
for any use for the juvenile CRLF (238 g) from the T-
Herps analysis for consumption of small insect, large
insect small, small herbivore mammal, insectivore
mammals or small amphibian prey.
Acute granular direct
effects on the CRLF:
No Effect
The no effect determination is due to no LOC
exceedence using the bird as a surrogate from the LDft2
results for noncrop (non-agricultural ROW), forest site
preparation (5 lb/A) and rangeland (3 lb/A).
Nongranular chronic
direct effects usins
the bird as a
surrogate:
May Affect:
The May affect is based on LOC exceedence using the
bird as a surrogate from te T-REX analysis. T-Herps was
used to refine the May Affect from T-REX to either an
"LAA" or "NLAA" determination. Chronic reproductive
effects are possible, based on non-granular uses of
hexazinone.
Direct chronic effects
Using the bird as a
surrogate:
LAA for small
herbivore mammal
T-Herps was used to refine the May Affect from T-Rex.
The LAA determination resulted from LOC exceedence
based on T-Herps for noncrop (8 lb/A) to Christmas tree
(2 lb/A). RQs range from 4.22 to 1.05.
prey
Direct chronic effects
using the bird as a
surrogate:
NLAA for small
herbivore mammal
The NLAA determination for alfalfa (1.5 lb/A) and
pasture (1.1 lb/A) resulted from no LOC exceedence.
RQs range from 0.79-0.58.
prey
13
-------
Direct chronic effects
using the bird as a
surrogate:
LAA for CRLF
consuming small
insect prey
Direct chronic effects
using the bird as a
surrogate: NLA A for
CRLF consuming
small insect prey
T-Herps was used to refine the May Affect from T-REX
to an "LAA" determination.
All uses except Christmas tree, alfalfa and pasture
resulted in LOC exceedences for broadleaf. RQs range
from 3.6 (8 lb/A) to 1.35 (3 lb/A).
Christmas tree (2 lb/), alfalfa (1.5 lb/A) and pasture (1.1
lb/A) did not result in LOC exceedences for small small
insect prey resulting from T-Herps modeling. RQs for
small herbivore mammals range from 0.90 (1.5 lb/A) to
0.50 (1.1 lb/A).
Direct chronic effects
using the bird as a
surrogate:
NLAA consuming
large insect prey
Direct chronic
effects uaing the bird
as a surrogate:
NLAA consuming
small insectivore
mammals
Direct chronic
effects using the bird
as a surrogate:
NLAA consuming
small insectivore
mammals
Non-crop ( 8 lb/A), pineapple (3.6 lb/A), blueberry ( 3
lb/A) Christmas tree (2 lb/A), alfalfa (1.1 lb/A) and
pasture (1.1 lb/A) did not result in LOC exceedences for
large insect prey resulting from T-Herps modeling. RQs
for broadleaf range from 0.90 (2 lb/A) to 0.5 (1.1 lb/A)
based on T-Herps analysis.
An NLAA determination resulted from no LOC
exceedence for small insectivore mammal,. RQs for
small insectivore mammals range from 0.26 (8 lb/A) to
0.04 (1.1 lb/A).
RQs for small amphibians range from for 0.12 (8 lb/A) to
0.02 (1.1 lb/A) based on T-Herps analysis.
Chronic direct effects
using the bird as a
surrogate (Granular):
May Affect LAA
Granular formulations for noncrop(12 lb/A), forest site
preparation (5 lb/A) and rangeland ( 3 lb/A) resulted in
LOC exceedences resulting from the T-REX analysis.
RQs range from 1.35 for rangeland to 5.4 for noncrop.
Indirect Effect s of Hcxa/lnone on the Terrestrial -Phase CRLF
14
-------
Survival, growth, and reproduction of
CRLF individuals via effects on prey (i.e.,
terrestrial invertebrates, small terrestrial
vertebrates, including mammals and
terrestrial phase amphibians)
Noneranualr Acute
Indirect orcv
reduction for
Terrestrial
Invertebrates:
May Affect
LAA
An LAA determination for small insect prey is based on
the uncertainty regarding the effects of hexazinone on
terrestrial invertebrates due to related toxicity values
reporting no mortality at the highest concentration tested
for all uses.
Nongranular Acute
Indirect orcv
reduction for
terrestrial
invertebrates (Laree
Insect Prey):
May Affect
LAA
An LAA determination for large insect prey is based on
the uncertainty regarding the effects of hexazinone on
terrestrial invertebrates due to related toxicity values
reporting no mortality at the highest concentration tested
for noncrop (8 lb/A), pineapple (3.6 lb/A) and
blueberry/conifer release (3 lb/A).
Nongranular Acute
No Effect
A "No effect" determination for large insect prey for
Christmas tree (2 lb/A), alfalfa (1.5 lb/A) and pasture
(1.1 lb/A) uses was based on no LOC exceedence from
the T-REX analysis.
Indirect mammal
orcv reduction:
Non-granular Acute
May Affect
The May Affect is based on T-Rex results for 15 g
mammal with a diet of shortgrass for non-crop (8 lb/A)
through pasture (1.1 lb/A) uses.
LAA
The LAA determination is due to noncrop (8 lb/A) and
blueberry (3 lb/A) LOC exceedence from the T-REX
analysis.
15
-------
Indirect mammal prey
reduction
Nongranular Acute:
May Affect
The May Effect is based on RQs falling between the
endangered species and acute risk LOC.
NLAA
Due to RQs falling between the endangered species and
acute risk LOC further refinement used the the probit
analysis. The potential reduction in abundance of
terrestrial mammals as food for Christmas tree, alfalfa
and pasture uses would be < 1%; therefore a "not likely
to adversely affect" determination can be made.
Granular Acute
Indirect mammal prey
reduction:
A No effect determination is based on the LDft2 results
from the T-REX analysis for non-crop(12 lb/A), forest
site preparation (5 lb/A) and rangeland (3 lb/A).
No Effect (granular
uses)
Indirect orcv
reduction for
mammal Nongranular
Chronic:
May Affect:
Chronic reproductive effects are possible, based on non-
granular uses of hexazinone. The May affect is due to
LOC exceedences for all nongranular uses.
16
-------
LAA
All uses resulted in LOC exceedences for short grass.
RQs range from 9.60 (8 lb/A) to 1.32 (1.1 lb/A) based on
T-Rex.
Indirect prey
reduction for
amphibian using the
bird as a surrogate
Nongranular Acute
May Affect
LAA
The May affect is due to LOC exceedence using the bird
as a surrogate for all crops resulting from the T-Rex
analysis.
An "LAA" determination using the bird as a surrogate is
based on LOC exceedence for noncrop (8 lb/A) uses. RQ
for noncrop = 0.76 resulted from the T-REX analysis.
Indirect prey
reduction for
amphibian using the
bird as a surrogate
NLAA
Conifer release, blueberry, Christmas tree, alfalfa and
pasture uses resulted in RQs falling between the listed
and non-listed LOCs from the T-REX analysis. Based on
this assessment, the probit analysis was used as a further
refinement for the determination. The potential reduction
in abundance of amphibians as food for these uses would
be < 1% at most; therefore a "not likely to adversely
affect" determination can be made.
Indirect orcv
reduction for
amphibian usine the
bird as a surrogate
Nongranular Chronic
May Affect:
Chronic reproductive effects are possible, based on non-
granular uses of hexazinone resulting from the T-REX
analysis using the bird as a surrogate.
17
-------
LAA
All nongranular uses except Christmas tree, alfalfa and
pasture resulted in LOC exceedences for broadleaf. RQs
for broadleaf range from 1.35 (3 lb/A) to 3.60 (8 lb/A).
Amphibian usins the
bird as a surrogate
Nongranular Chronic
No Effect
Christmas tree, alfalfa and pasture did not result in LOC
exceedences broadleaf. RQs for broadleaf range from
0.5 (3 lb/A) to 0.90 (1.5 lb/A) resulting from the T-Rex
analysis.
Survival, growth, and reproduction of
CRLF individuals via indirect effects on
habitat (i.e., riparian vegetation)
Woodv and
srassv/herbaceous
riparian vesetation:
May Affect
Riparian woody and herbaceous vegetation may be
affected because terrestrial plant RQs are above LOCs.
LAA < 184 ft
(ground)
Due to MO A, which interferes with photosynthesis and
RNA, terrestrial-phase CRLFs may be indirectly affected
by adverse effects to sensitive woody and herbaceous
vegetation which provide habitat and cover for the CRLF
and its prey.
NLAA> 184 ft
(ground)
There was an "NLAA" determination for animals
outside the aerial drift buffer of 184 ft resulting from the
AGDISP model..
18
-------
LAA < 850 ft (aerial);
Due to MO A, which interferes with photosynthesis and
RNA, terrestrial-phase CRLFs may be indirectly affected
by adverse effects to sensitive woody and herbaceous
vegetation which provide habitat and cover for the CRLF
and its prey.
NLAA > 850 ft
(aerial)
There was an "NLAA" determination for animals
outside the aerial drift buffer of 850 ft resulting from the
AGDISP model.
'I'iihlc 1.2 KITccls Dclcrminnlion Siiiniiiiirv for the ( rilicnl llnhilnl linpncl Annlvsis
Anni'nniik'iK I'lnripoini r.l'kiis
l)i-UTiiiin;iiinn
liiisis for IkMcrmiiiiiliuii
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.
Habitat
modification
Due to the MOA which interferes with
photosynthesis and RNA sensitive herbaceous
riparian vegetation may be affected based on all
modeled uses of hexazinone; therefore, critical
habitat may be modified by an increase in sediment
deposition and reduction in herbaceous riparian
vegetation that provides for shelter, foraging,
predator avoidance, and aquatic dispersal for
juvenile and adult aquatic-phase 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.1
Habitat
modification
Sensitive non-vascular aquatic plants may be
affected; therefore, critical habitat may be modified
via turbidity and reduction in oxygen content
necessary for normal growth and viability of
juvenile and adult aquatic-phase CRLFs.
Alteration of other chemical characteristics necessary
for normal growth and viability of CRLFs and their
food source.
No effect to
growth and
viability
Habitat
modification
based on
alteration of
food source
Direct effects to the aquatic-phase CRLF, via
mortality, growth, and/or fecundity, are not
expected. However, critical habitat of the CRLF
may be modified via hexazinone-related impacts to
non-vascular aquatic plants as food items for
tadpoles. LOCs are exceeded for non-vascular uses
for non-crop (non-agricultural ROW) (12 lb/A),
noncrop (8 lb/A), conifer release (3 lb/A), rangeland
(3 lb/A), Christmas Trees (2 lb/A), alfalfa (1.5 lb/A)
and pasture (1.1 lb/A).
No Habitat
Modification
There was no LOC exceedence for blueberry uses
for nonvascular plants.
Reduction and/or modification of aquatic-based food
sources for pre-metamorphs (e.g., algae)
Habitat
modification
Based on the results of the effects determinations
for aquatic plants, critical habitat of the CRLF may
1 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.
19
-------
be modified via hexazinone-related impacts to non-
vascular aquatic plants as food items for tadpoles.
LOCs are exceeded for modeled uses for (12 lb/A),
noncrop uses (8 lb/A), conifer release (3 lb/A),
rangeland (3 lb/A), Christmas trees (2 lb/A), alfalfa
(1.5 lb/A) and pasture (1.1 lb/A).
No Habitat
Modification
Blueberry use resulted in no LOC exceedence.
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
Habitat
modification
Based on MO A, modification to critical habitat may
occur via hexazinone-related impacts to sensitive
woody and herbaceous vegetation, which provide
habitat and cover for the terrestrial-phase CRLF and
its prey, based on all assessed uses of hexazinone.
Terrestial incident reports support a "habitat
modification" determination.
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
Habitat
modification
Based on the MOA for hexazione modification to
dispersal habitat may occur via hexazinone-related
impacts to sensitive woody and herbaceous
vegetation, which provide habitat and cover for the
terrestrial-phase CRLF and its prey, based on all
assessed uses of hexazinone. Terrestrial incident
reports support the "habitat modification'
determination.
Reduction and/or modification of food sources for
terrestrial phase juveniles and adults
Habitat
modification
Based on the characterization of indirect effects to
terrestrial-phase CRLFs via reduction in the prey
base, critical habitat may be modified via a
reduction in mammals and terrestrial-phase
amphibians as food items.
Alteration of chemical characteristics necessary for
normal growth and viability of juvenile and adult
CRLFs and their food source.
Habitat
modification
Direct acute effects, via mortality, are expected for
the terrestrial-phase CRLF. Chronic reproductive
effects are also possible. Therefore, hexazinone
may modify critical habitat by altering chemical
characteristics necessary for normal growth and
viability of terrestrial-phase CRLFs and their
mammalian and amphibian food sources.
When evaluating the significance of this risk assessment's direct/indirect and 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
20
-------
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.
2. Problem Formulation
Problem formulation provides a strategic framework for the risk assessment. By identifying the
important components of the problem, it focuses the assessment on the most relevant life history
stages, habitat components, chemical properties, exposure routes, and endpoints. The structure
of this risk assessment is based on guidance contained in U.S. EPA's Guidance for Ecological
Risk Assessment (U.S. EPA 1998), the Services' Endangered Species Consultation Handbook
(USFWS/NMFS 1998) and is consistent with procedures and methodology outlined in the
Overview Document (U.S. EPA 2004) and reviewed by the U.S. Fish and Wildlife Service and
National Marine Fisheries Service (USFWS/NMFS 2004).
2.1 Purpose
21
-------
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 hexazinone on both
agricultural and non-agricultural sites. These includes: agricultural rights-of-way, fencerows and
hedgerows; agricultural uncultivated areas; airports and landing fields; alfalfa; blueberries;
Christmas tree plantations; conifer release applications; drainage systems; forest plantings in
reforestation programs; tree farms and plantations; forest trees; outdoor industrial areas; non-
crop/nonagricultural rights-of-way; nonagricultural uncultivated areas and soils; pastures;
pineapples; rangeland; sewage disposal areas and sugarcane.
In addition, this assessment evaluates whether use on these crop sites is expected to result in
modification of the species' designated critical habitat. This ecological risk assessment has been
prepared consistent with a settlement agreement in the case Center for Biological Diversity
(CBD) vs. EPA etal. (Case No. 02-1580-JSW (JL)) settlement entered in Federal District Court
for the Northern District of California on October 20, 2006.
In this assessment, direct and indirect effects to the CRLF and potential modification to its
designated critical habitat are evaluated in accordance with the methods described in the
Agency's Overview Document (U.S. EPA 2004). Screening level methods include use of
standard models such as PRZM-EXAMS, T-REX, TerrPlant, AgDRIFT, and AGDISP, all of
which are described at length in the Overview Document. 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 hexazinone is based on an action area. The action area is the area directly or
indirectly affected by the federal action, as indicated by the exceedence of the Agency's Levels
of Concern (LOCs). It is acknowledged that the action area for a national-level FIFRA
regulatory decision associated with a use of hexazinone 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 hexazinone 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
22
-------
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 hexazinone as it relates to this species and
its designated critical habitat. If, however, potential direct or indirect effects to individual CRLFs
are anticipated or effects may impact the PCEs of the CRLF's designated critical habitat, a
preliminary "may affect" determination is made for the FIFRA regulatory action regarding
hexazinone.
If a determination is made that use of hexazinone within the action area(s) associated with the
CRLF "may affect" this species or its designated critical habitat, additional information is
considered to refine the potential for exposure and for effects to the CRLF and other taxonomic
groups upon which these species depend (e.g., aquatic and terrestrial vertebrates and
invertebrates, aquatic plants, riparian vegetation, etc.). Additional information, including spatial
analysis (to determine the geographical proximity of CRLF habitat and hexazinone use sites) and
further evaluation of the potential impact of hexazinone 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 hexazinone is
expected to directly impact living organisms within the action area (defined in Section 2.7),
critical habitat analysis for hexazinone 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 hexazinone
that may alter the PCEs of the CRLF's critical habitat form the basis of the critical habitat impact
analysis. Actions that may affect the CRLF's designated critical habitat have been identified by
the Services and are discussed further in Section 2.6.
2.2 Scope
Hexazinone is an herbicide registered nationally for control of weeds on alfalfa, forestry (conifer
release, forest tree planting), rights-of-ways, pastures, rangeland, Christmas trees, crops
(sugarcane, pineapple and blueberries) and uncultivated areas, (non-crop/non-agricultural ROW,
agricultural ROW, outdoor industrial, fencerows, airports, sewage, drainage).
The end result of the EPA pesticide registration process (the FIFRA regulatory action) is an
approved product label. The label is a legal document that stipulates how and where a given
pesticide may be used. Product labels (also known as end-use labels) describe the formulation
23
-------
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 hexazinone
in accordance with the approved product labels for California is "the action" being assessed.
Although current registrations of hexazinone allow for use nationwide, this ecological risk
assessment and effects determination addresses currently registered uses of hexazinone 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 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).
Hexazinone has seven registered products that contain multiple active ingredients. Analysis of
the available acute oral mammalian LD50 data for multiple active ingredient products relative to
the single active ingredient is provided in Appendix A. The results of this analysis show that an
assessment based on the toxicity of the single active ingredient of hexazinone is appropriate.
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
LD50s, with associated 95% confidence intervals, are needed for the formulated product. The
same quality of data is also required for each component of the mixture. Given that many of the
formulated products do not have LD50 values of the required quality, and since LD50 values are
not available for all the components of these formulations, a quantitative analysis of potential
interactive effects is not possible.
Hexazione has seven registered products that contain multiple active ingredients. Analysis of
the available open literature data and acute oral mammalian LD50 data for multiple active
ingredient products relative to the single active ingredient is provided in Appendix A. The
result of this analysis show that an assessment based on the toxicity of the single active
ingredient of hexazinone is appropriate.
In the case of hexazinone, only two products (EPA Reg. Nos. 352-603 and 352-618) have
definitive product oral LD50 values. Although there are no confidence intervals associated with
these products, the LD50 values for the products (1421 and 2073 mg/kg, respectively) are greater
than the LD50 value for hexazinone (1200 mg/kg) and therefore do not indicate that the
formulated products exhibit interactive effects. No further analysis is possible when LD50
values with associated confidence intervals are not available.
24
-------
One open literature article (Ludy 2004) reported the use of hexazinone and diuron in mixtures
for toxicity tests with Chironomus tentans. The resulting EC50MOOO |ig/L for the aquatic midge
for both chemicals for individual toxicity tests. However, this study was not used in this
assessment because the hexazinone and diuron were mixed with organo-phosphates, not other
herbicides.
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
hexazinone is the only reasonable approach that employs the available data to address the
potential acute risks of the formulated products
2.3 Previous Assessments
A Reregistration Eligibility Decision (RED) that included an ecological risk assessment for
aquatic fish, invertebrates, and plants, was issued in September 1994. The data were sufficient to
allow the Agency to assess the registered uses of hexazinone and to determine that hexazinone
could be used without resulting in unreasonable adverse effects to humans and the environment.
Due to the risk to non-target plants, reduction of the maximum application rate from 13.5 lb a. i.
per acre to 8 lb a.i. per acre was required. The 13.5 lb a.i. per acre rate is no longer in use, but
there are still rates of 10.0 and 12.0 lbs a.i. per acre included on the label for selected non-
agricultural uses. These rates are included in this assessment.
That assessment also determined that exposure of non-target organisms to hexazinone could
result from direct application, spray drift from treated areas, and runoff from treated areas. Such
exposure would be chronic as well as acute. Hexazinone exceeded the levels of concern (LOC)
for terrestrial and aquatic plants, at all application rates, using aerial and ground equipment.
Contamination of aquatic sites adjacent to treated areas could be of great ecological significance
and may be exacerbated by the persistence and mobility of hexazinone. Effects to aquatic plants
expected from the use of hexazinone may alter aquatic ecosystems, the severity of which is
dependent on the frequency of application and the nature of the receiving body of water.
Hexazinone also exceeded the LOC for small mammals at several of the higher application rates.
Hexazinone exceeded the endangered species LOCs for grass- and insect-eating mammals at use
rates of 3.6 pounds active ingredient per acre (lb ai/acre) or greater. It also exceeded the LOCs
for both aquatic and terrestrial plants at all use rates.
2.4 Stressor Source and Distribution
2.4.1 Environmental Fate Properties
Hexazinone is a systemic herbicide used to control weeds and woody plants. Its potency is a
function of soil texture, soil organic matter and post-application weather as it is activated by
moisture. It is toxic to some evergreen trees and most broadleaf trees. The labels suggest field
testing by the user for possible toxicity to evergreens for which the toxicity is uncertain. Based
on the available information, hexazinone appears to be persistent and mobile in soil and aquatic
environments and is considered as the stressor in this assessment (Table 2.1). The mobility of
25
-------
hexazinone was demonstrated in batch equilibrium as well as field and forestry dissipation data.
It is stable to hydrolysis and photolysis and degrades only slowly by aerobic metabolism.
Aerobic aquatic and aerobic soil half-life values are 60 and 216 days, respectively, and field
dissipation half-lives were 123 to 154 days in bare ground silt loam soil. Laboratory adsorption
data show low water/soil partitioning for hexazinone (Koc = 37). These data indicate that
hexazinone is highly mobile, thus having strong potential to leach to ground water systems,
especially in soil systems such as loam and sand soils that are poor in organic matter.
Hexazinone is very soluble in water at 20°C with a solubility of 33,000 mg/L. Based on its low
vapor pressure (2.0 x 10"7 mm Hg at 20°C) and Henry's Law Constant (2.0 x 10"12 atm-m3/mol at
25°C), volatilization loss of hexazinone from soil and water systems is expected to be
insignificant. Degradates and transformation products are formed slowly and are also mobile and
persistent. Based on laboratory bioaccumulation in rainbow trout, hexazinone is not expected to
bioaccumulate in fish, which is in concurrence with the low Kow value of 15 (log Kow = 1.12).
Hexazinone has been shown to accumulate in rotational crops.
T;ihlc2.l Siimmsirv ol'llexnzioncClK'inicjil siiul Knvironinenliil I nto Properties
Study Tvpe/1 lexsi/iiioue
Value
Source (M KID)
Water solubility
ppm (25 C)
33,000
Product Chemistry
Vapor pressure
mm Hg
2x10-7
Product Chemistry
Kow
15
Product Chemistry
Henry's Law Const
atm-m3/mol
2x10-12
Product Chemistry
Hydrolysis
pH 5
Stable
41587301 (acceptable)
pH 7
Stable
41587301 (acceptable)
pH 9
Stable
41587301 (acceptable)
Aqueous Photolysis (pH 7)
Stable
41300801 (acceptable)
Soil Photolysis
82 days
41300802 (acceptable)
Aerobic Soil
216 days
41807401; 42635001
(acceptable)
Anaerobic Aquatic
230 days
41807402 (acceptable)
Aerobic Aquatic
60 days
41811801 (acceptable)
Adsorption Ka
0.45
0.18
41528101 (acceptable)
43621501 (supplemental)
Adsorption Koc
37
50
41528101 (acceptable)
43621501 (supplemental)
26
-------
2.4.2 Environmental Transport Mechanisms
Potential transport mechanisms include pesticide surface water runoff and spray drift.
The magnitude of pesticide transport via secondary drift depends on the pesticide's
ability to be mobilized into air and its eventual removal through wet and dry deposition
of gases/particles and photochemical reactions in the atmosphere. A number of studies
have documented atmospheric transport and redeposition of pesticides from the Central
Valley to the Sierra Nevada Mountains (Fellers et al., 2004, Sparling et al., 2001, LeNoir
et al., 1999, and McConnell et al., 1998). Prevailing winds blow across the Central Valley
eastward to the Sierra Nevada Mountains, transporting airborne industrial and
agricultural pollutants into Sierra Nevada ecosystems (Fellers et al., 2004, LeNoir et al.,
1999, and McConnell et al., 1998). Therefore, physicochemical properties of the pesticide
that describe its potential to enter the air from water or soil (e.g., Henry's Law constant
and vapor pressure), pesticide use, modeled estimated concentrations in water and air,
and available air monitoring data from the Central Valley and the Sierra Nevadas are
considered in evaluating the potential for atmospheric transport of hexazinone to habitat
for the CRLF.
In general, deposition of drifting or volatilized pesticides is expected to be greatest close
to the site of application. Computer models of spray drift (AgDRIFT or AGDISP) are
used to determine if the exposures to aquatic and terrestrial organisms are below the
Agency's Levels of Concern (LOCs). If the limit of exposure that is below the LOC can
be determined using AgDRIFT or AGDISP, longer-range transport is not considered in
defining the action area. For example, if a buffer zone <1,000 feet (the optimal range for
AgDRIFT and AGDISP models) results in terrestrial and aquatic exposures that are
below LOCs, no further drift analysis is required. If exposures exceeding LOCs are
expected beyond the standard modeling range of AgDRIFT or AGDISP, the Gaussian
extension feature of AGDISP may be used. In addition to the use of spray drift models to
determine potential off-site transport of pesticides, other factors such as available air
monitoring data and the physicochemical properties of the chemical are also considered.
Vegetative vigor and seedling emergence toxicity studies show that hexazinone is toxic to
monocot and dicot terrestrial plants, thus the distance of potential impact away from the
use sites (action area) is determined by the distance required to fall below the LOC for
these non-target plants.
2.4.3 Mechanism of Action
Hexazinone is a systemic insecticide activated by irrigation water or rainfall in the period
after application. It inhibits photosynthesis and, at higher levels of exposure, inhibits the
synthesis of RNA, proteins, and lipids in plants.
2.4.4 Use Characterization
Both liquid and granular formulations of hexazinone may be applied by aircraftas well as
ground sprayer.While the specific equipment for ground application varies between the
liquid and granular formulations, both types of formulations are applied such that the
-------
herbicide sprayer for liquid or suspended granules or other equipment for granules is
carried by backpack or some other appropriate container. Usually, hexazinone is applied
directly to the soil rather than sprayed on the vegetation; however, sometimes, directed
foliar applications are used. In soil applications, the hexazinone is applied in spots using a
defined pattern.
Analysis of labeled use information is the critical first step in evaluating the federal
action. The current label for hexazinone 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.
Nationally, hexazinone is an herbicide used to control a broad spectrum of weeds
including undesirable woody plants in alfalfa, rangeland and pasture, woodland,
pineapples, sugarcane and blueberries. It is also used on ornamental plants, forest trees
and other non-crop areas. Hexazinone is registered for pre-emergent, post-emergence,
layby, directed spray and basal soil applications. It is used as a non-selective herbicide in
noncropland areas and as a selective herbicide in reforestation practices. Hexazinone
products are formulated as granulars, pellets/tablets, emulsifiable concentrates, ready-to-
use liquids, soluble concentrates/solids and a technical grade active ingredient. Products
are applied using aerial or ground equipment or by hand, or using a hand-held, boom,
knapsack or power sprayer. Use practice limitations prohibit application of hexazinone
through any type of irrigation system. There are no indoor uses.
National (Section 3) uses for hexazinone are presented in Table 2.2 with label maximum
application rates. Although the maximum number of applications from the label for
pasture, alfalfa and Christmas tree uses is one, other uses do not specify a maximum rate
or maximum number of applications per year. For this assessment, one application per
year for those other uses is based on additional information from the label. Blueberry
uses are modeled at a maximum of one application per year due to no application within
450 days of harvest. Pineapple is modeled as one application per year due to the growing
season, which is nearly a year in length. Noncrop uses and all granular uses, non-crop,
forest site preparation and rangeland, are modeled as one application per year due to the
requirement for rain to activate hexazinone and because maximum effects are achieved
after 12-24 months.
Tsihle 2.2 llexii/inone I scs1 iincl Applic:ilion Inloi iiiitlion
Crop
M:i\ Appl kiilo
(Ihs si.i./A)
NON-Crop (granular)
12
SEWAGE DISPOSAL AREAS (Non-granular)
8.
AGRICULTURAL RIGHTS-OF-
WAY/FENCEROWS/HEDGEROWS (Non-granular)
8.
AGRICULTURAL UNCULTIVATED AREAS (Non-
granular)
8.
AIRPORTS/LANDING FIELDS (granular)
8.
CONIFER RELEASE (non-granular)
3
28
-------
Sugarcane (non-granular)
3.6
Pineapple (non-granular)
3.6
BLUEBERRY (non-granular)
3
RANGELAND (granular)
3
CHRISTMAS TREE PLANTATIONS (non-granular)
2.
ALFALFA (non-granular)
1.5
PASTURES (non-granular)
1.1
2 Uses assessed based on memorandum from SRRD dated 07/31/2007
The Agency's Biological and Economic Analysis Division (BEAD) provides an analysis
of both national- and county-level usage information (Hexazinone LUIS Report, 2007)
using state-level usage data obtained from USDA-NASS2, Doane (www.doane.com; the
full dataset is not provided due to its proprietary nature), and the California Department
of Pesticide Regulation Pesticide Use Reporting (CDPR PUR) database3. 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 hexazinone by county in this
California-specific assessment were generated using CDPR PUR data. Usage data are
averaged together over the years 2002 to 2005 to calculate average annual usage statistics
by county and crop for hexazinone, including pounds of active ingredient applied and
base acres treated. California State law requires that every commercial pesticide
application be reported to the state and made available to the public. The summary of
hexazinone usage for all use sites, including both agricultural and non-agricultural, is
provided below in Table 2.3.
The two main hexazinone uses in the usage summary are the alfalfa and forest/timberland
categories. Other uses include one to a few applications over the four-year period. There
are several applications recorded in the rights-of-way category but only one single
application is recorded on a per-acre basis and the data is categorized as questionable.
There is no recorded usage on any of the three food crops on the label (blueberry, sugar
cane, pineapple) in the 2002-2005 time periods.
Table 2.3 Summary of CALPUR Usage Data for Hexazinone (2002-2C
105)
Active
Ingredient
Site Name
Range of
Average
Application
Rates
Range of
95th
Percentile
Application
Rates
Range of
99th
Percentile
Application
Rates
Range of
Maximum
Application
Rates
HEXAZINONE
ALFALFA
0.31-0.81
0.50-2.25
0.50-2.25
0.50-2.25
HEXAZINON E
FOREST,
TIMBERLAND
0.56-3.14
0.71-16.39
0.71-16.74
0.71-29.77
HEXAZINONE
CHRISTMAS
TREES
1.00-1.43
1.00-4.13
1.00-4.13
1.00-4.13
HEXAZINONE
RIGHTS OF WAY
0.30
0.30
0.30
0.30
21 United States Department of Agriculture (USDA), National Agricultural Statistics Service (NASS)
Chemical Use Reports provide summary pesticide usage statistics for select agricultural use sites by
chemical, crop and state. See http://www.usda.gOv/nass/pubs/estindxl.htm#agchem.
23 The California Department of Pesticide Regulation's Pesticide Use Reporting database provides a census
of pesticide applications in the state. See http://www.cdpr.ca.gov/docs/pur/punnain.htm.
29
-------
HEXAZINONE
FORAGE HAY/
SILAGE
0.75
0.75
0.75
0.75
HEXAZINONE
UNCULTIVATED
NONAG
1.19
1.53
1.53
1.53
HEXAZINONE
PASTURELAND
2.5
2.5
2.5
2.5
HEXAZINONE
RANGELAND
0.8
0.8
0.8
0.8
Some of the reported maximum rates are higher than labeled maximum rates for alfalfa,
forest, Christmas trees and pasture. This may be due mis-reporting, misuse, uses no
longer permitted by the label or to applications made on a less than per-acre basis.
2.5 Assessed Species
The CRLF was federally listed as a threatened species by USFWS effective June 24,
1996 (USFWS 1996). It is one of two subspecies of the red-legged frog and is the largest
native frog in the western United States (USFWS 2002). A brief summary of information
regarding CRLF distribution, reproduction, diet, and habitat requirements is provided in
Sections 2.5.1 through 2.5.4, respectively. Further information on the status, distribution,
and life history of and specific threats to the CRLF is provided in Attachment 1.
Final critical habitat for the CRLF was designated by USFWS on April 13, 2006
(USFWS 2006; 71 FR 19244-19346). Further information on designated critical habitat
for the CRLF is provided in Section 2.6.
2.5.1 Distribution
The CRLF is endemic to California and Baja California (Mexico) and historically
inhabited 46 counties in California including the Central Valley and both coastal and
interior mountain ranges (USFWS 1996). Its range has been reduced by about 70%, and
the species currently resides in 22 counties in California (USFWS 1996). The species has
an elevational range of near sea level to 1,500 meters (5,200 feet) (Jennings and Hayes
1994); however, nearly all of the known CRLF populations have been documented below
1,050 meters (3,500 feet) (USFWS 2002).
Populations currently exist along the northern California coast, northern Transverse
Ranges (USFWS 2002), foothills of the Sierra Nevada (5-6 populations), and in southern
California south of Santa Barbara (two populations) (Fellers 2005a). Relatively larger
numbers of CRLFs are located between Marin and Santa Barbara Counties (Jennings and
Hayes 1994). A total of 243 streams or drainages are believed to be currently occupied by
the species, with the greatest numbers in Monterey, San Luis Obispo, and Santa Barbara
counties (USFWS 1996). Occupied drainages or watersheds include all bodies of water
that support CRLFs (i.e., streams, creeks, tributaries, associated natural and artificial
ponds, and adjacent drainages), and habitats through which CRLFs can move (i.e.,
riparian vegetation, uplands) (USFWS 2002).
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
30
-------
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 2.1). Recovery units, core areas, and other known occurrences of the CRLF from
the CNDDB are described in further detail in this section, and designated critical habitat
is addressed in Section 2.6. Recovery units are large areas defined at the watershed level
that have similar conservation needs and management strategies. The recovery unit is
primarily an administrative designation, and land area within the recovery unit boundary
is not exclusively CRLF habitat. Core areas are smaller areas within the recovery units
that comprise portions of the species' historic and current range and have been
determined by USFWS to be important in the preservation of the species. Designated
critical habitat is generally contained within the core areas, although a number of critical
habitat units are outside the boundaries of core areas, but within the boundaries of the
recovery units. Additional information on CRLF occurrences from the CNDDB is used to
cover the current range of the species not included in core areas and/or designated critical
habitat, but within the recovery units.
Recovery Units
Eight recovery units have been established by USFWS for the CRLF. These areas are
considered essential to the recovery of the species, and the status of the CRLF "may be
considered within the smaller scale of the recovery units, as opposed to the statewide
range" (USFWS 2002). Recovery units reflect areas with similar conservation needs and
population statuses, and therefore, similar recovery goals. The eight units described for
the CRLF are delineated by watershed boundaries defined by US Geological Survey
hydrologic units and are limited to the elevational maximum for the species of 1,500 m
above sea level. The eight recovery units for the CRLF are listed in Table 2.4 and shown
in Figure 2.1.
Core Areas
USFWS has designated 35 core areas across the eight recovery units to focus their
recovery efforts for the CRLF (Figure 2.1). Table 2.5 summarizes the geographical
relationship among recovery units, core areas, and designated critical habitat. The core
areas, which are distributed throughout portions of the historic and current range of the
species, represent areas that allow for long-term viability of existing populations and
reestablishment of populations within historic range. These areas were selected because
they: 1) contain existing viable populations; or 2) they contribute to the connectivity of
other habitat areas (USFWS 2002). Core area protection and enhancement are vital for
maintenance and expansion of the CRLF's distribution and population throughout its
range.
For purposes of this assessment, designated critical habitat, currently occupied (post-
1985) core areas, and additional known occurrences of the CRLF from the CNDDB are
considered. Each type of locational information is evaluated within the broader context
of recovery units. For example, if no labeled uses of hexazinone occur (or if labeled uses
31
-------
occur at predicted exposures less than the Agency's LOCs) within an entire recovery unit,
a "no effect" determination would be made for all designated critical habitat, currently
occupied core areas, and other known CNDDB occurrences within that recovery unit.
Historically occupied sections of the core areas are not evaluated as part of this
assessment because the USFWS Recovery Plan (USFWS 2002) indicates that CRLFs are
extirpated from these areas. A summary of currently and historically occupied core areas
is provided in Table 2.4 (currently occupied core areas are bolded). While core areas are
considered essential for recovery of the CRLF, core areas are not federally-designated
critical habitat, although designated critical habitat is generally contained within these
core recovery areas. It should be noted, however, that several critical habitat units are
located outside of the core areas, but within the recovery units. The focus of this
assessment is currently occupied core areas, designated critical habitat, and other known
CNDDB CRLF occurrences within the recovery units. Federally-designated critical
habitat for the CRLF is further explained in Section 2.6.
Table 2.4. California Red-legged Frog Recovery Units with Overlapping Core
Areas and Designated Critical Habitat
Recovery Unit1
(Figure 2.a)
Core Areas2'7 (Figure 2.1)
Critical Habitat
Units3
Currently
Occupied
(post-1985)
4
Historically
Occupied 4
Sierra Nevada
Foothills and Central
Valley (1)
(eastern boundary is
the 1,500m elevation
line)
Cottonwood Creek (partial)
(8)
--
Feather River (1)
BUT-1A-B
Yuba River-S. Fork Feather
River (2)
YUB-1
--
NEV-16
Traverse Creek/Middle Fork
American River/Rubicon (3)
--
Consumnes River (4)
ELD-1
S. Fork Calaveras River (5)
--
Tuolumne River (6)
--
Piney Creek (7)
--
East San Francisco Bay
(partial)(16)
--
North Coast Range
Foothills and
Western Sacramento
River Valley (2)
Cottonwood Creek (8)
--
Putah Creek-Cache Creek (9)
--
Jameson Canyon - Lower
Napa Valley (partial) (15)
--
Belvedere Lagoon (partial)
(14)
-
Pt. Reyes Peninsula (partial)
(13)
--
North Coast and
North San Francisco
Bay (3)
Putah Creek-Cache Creek
(partial) (9)
Lake Berryessa Tributaries
(10)
NAP-1
Upper Sonoma Creek (11)
--
Petaluma Creek-Sonoma
Creek (12)
--
32
-------
Pt. Reyes Peninsula (13)
MRN-1, MRN-2
Belvedere Lagoon (14)
-
Jameson Canyon-Lower
Napa River (15)
SOL-1
--
CCS-1A6
East San Francisco Bay
ALA-1A, ALA-
South and East San
(partial) (16)
IB, STC-1B
Francisco Bay (4)
--
STC-1A6
South San Francisco Bay
(partial) (18)
SNM-1A
South San Francisco Bay
SNM-1A, SNM-
(partial) (18)
2C, SCZ-1
Watsonville Slough- Elkhorn
Slough (partial) (19)
SCZ-2 5
Central Coast (5)
Carmel River-Santa Lucia
(20)
MNT-2
Estero Bay (22)
—
--
SLO-86
Arroyo Grande Creek (23)
-
Santa Maria River-Santa
Ynez River (24)
East San Francisco Bay
MER-1A-B,
(partial) (16)
STC-1B
--
SNB-16, SNB-26
Diablo Range and
Salinas Valley (6)
Santa Clara Valley (17)
--
Watsonville Slough- Elkhorn
Slough (partial)(19)
MNT-1
Carmel River-Santa Lucia
(partial)(20)
Gablan Range (21)
SNB-3
Estrella River (28)
SLO-1A-B
--
SLO-86
Northern Transverse
Ranges and
Tehachapi Mountains
(7)
Santa Maria River-Santa
STB-4, STB-5,
Ynez River (24)
STB-7
Sisquoc River (25)
STB-1, STB-3
Ventura River-Santa Clara
VEN-1, VEN-2,
River (26)
VEN-3
--
LOS-16
Santa Monica Bay-Ventura
Coastal Streams (27)
San Gabriel Mountain (29)
~
Southern Transverse
Forks of the Mojave (30)
~
and Peninsular
Santa Ana Mountain (31)
~
Ranges (8)
Santa Rosa Plateau (32)
~
San Luis Rey (33)
--
Sweetwater (34)
~
Laguna Mountain (35)
~
1 Recovery units designated by the USFWS (USFWS 2000, pg 49).
Core areas designated by the USFWS (USFWS 2000, pg 51).
Critical habitat units designated by the USFWS on April 13, 2006 (USFWS 2006, 71 FR 19244-
19346).
Currently occupied (post-1985) and historically occupied core areas as designated by the USFWS
(USFWS 2002, pg 54).
33
-------
Critical habitat unit where identified threats specifically included pesticides or agricultural runoff
(USFWS 2002).
Critical habitat units that are outside of core areas, but within recovery units.
7 Currently occupied core areas that are included in this effects determination are bolded.
34
-------
Recovery Units
Sierra Nevada Foothills and Central Valley
North Coast Range Foothills and Western
Sacramento River Valley
North Coast and North San Francisco Bay
South and East San Francisco Bay
Central Coast
Diablo Range and Salinas Valley
Northern Transverse Ranges and Tehachapi
Mountains
Southern Transverse and Peninsular Ranges
at*,
Legend
Recovery Unit Boundaries
Currently Occupied Core Areas
Critical Habitat
CNDDB Occurence Sections
County Boundaries
Core Areas
I Feather River
2Yuba River- S. Fork Feather River
3Traverse Creek/ Middle Fork/ American R. Rubicon
4Cosumnes River
5 South Fork Calaveras River*
6Tuolumne River*
Piney Creek*
8Cottonwood Creek
9Putah Creek - Cache Creek*
lOLake Berryessa Tributaries
II Upper Sonoma Creek
12Petaluma Creek - Sonoma Creek
13Pt. Reyes Peninsula
14Belvedere Lagoon
15 Jameson Canyon - Lower Napa River
16East San Francisco Bay
17Santa Clara Valley
18South San Francisco Bay
19Watsonville Slough-Elkhorn Slough
20Carmel River - Santa Lucia
2Gablan Range
2Estero Bay
2Arroyo Grange River
2Santa Maria River - Santa Ynez River
2Sisquoc River
26Ventura River - Santa Clara River
27Santa Monica Bay - Venura Coastal Streams
28Estrella River
29San Gabriel Mountain*
30Forks of the Mojave*
31 Santa Ana Mountain*
32Santa Rosa Plateau
33 San Luis Ray*
34Sweetwater*
35Laguna Mountain*
35
-------
Core areas that were historically occupied by the California red-legged frog are not included in the map
Figure 2.1. Recovery Unit, Core Area, Critical Habitat, and Occurrence Designations for
CRLF
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 2.2 depicts CRLF annual reproductive timing.
Figure 2.2 - CRLF J
teproductive Events by Mont
h
J
F
M
A
M
J
J
A
S
o
N
D
Light Blue =
Green = ¦ cm [it'll .1 \ v .vw |f i murtv in ¦Hat over-winter)
Orange = Young Juveniles
Adults and juveniles can be present all year
36
-------
2.5.3 Diet
Although the diet of CRLF aquatic-phase larvae (tadpoles) has not been studied
specifically, it is assumed that their diet is similar to that of other frog species, with the
aquatic phase feeding exclusively in water and consuming diatoms, algae, and detritus
(USFWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar, 1980)
via mouthparts designed for effective grazing of periphyton (Wassersug, 1984,
Kupferberg et al.\ 1994; Kupferberg, 1997; Altig and McDiarmid, 1999).
Juvenile and adult CRLFs forage in aquatic and terrestrial habitats, and their diet differs
greatly from that of larvae. The main food source for juvenile aquatic- and terrestrial-
phase CRLFs is thought to be aquatic and terrestrial invertebrates found along the
shoreline and on the water surface. Hayes and Tennant (1985) report, based on a study
examining the gut content of 35 juvenile and adult CRLFs, that the species feeds on as
many as 42 different invertebrate taxa, including Arachnida, Amphipoda, Isopoda,
Insecta, and Mollusca. The most commonly observed prey species were larval alderflies
(Sialis cf. calif ornica), 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).
37
-------
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#wherey
In general, dispersal and habitat use depends on climatic conditions, habitat suitability,
and life stage. Adults rely on riparian vegetation for resting, feeding, and dispersal. The
foraging quality of the riparian habitat depends on moisture, composition of the plant
community, and presence of pools and backwater aquatic areas for breeding. CRLFs can
be found living within streams at distances up to 3 km (2 miles) from their breeding site
and have been found up to 30 m (100 feet) from water in dense riparian vegetation for up
to 77 days (USFWS 2002).
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 2.5.
'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 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,
38
-------
light, minerals, or other nutritional or physiological requirements; cover or shelter; sites
for breeding, reproduction, rearing (or development) of offspring; and habitats that are
protected from disturbance or are representative of the historic geographical and
ecological distributions of a species. The designated critical habitat areas for the CRLF
are considered to have the following PCEs that justify critical habitat designation:
Breeding aquatic habitat;
Non-breeding aquatic habitat;
Upland habitat; and
Dispersal habitat.
Please note that a more complete description of these habitat types is provided in
Attachment 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 modification standards for designated critical habitat (USFWS
2006). Activities that may destroy or modify critical habitat are those that alter the PCEs
and jeopardize the continued existence of the species. Evaluation of actions related to use
of hexazinone 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.
39
-------
(3) Significant alteration of channel/pond morphology or geometry that may lead to
changes to the hydrologic functioning of the stream or pond and alter the timing,
duration, water flows, and levels that would degrade or eliminate the CRLF
and/or its habitat. Such an effect could also lead to increased sedimentation and
degradation in water quality to levels that are beyond the CRLF's tolerances.
(4) Elimination of upland foraging and/or aestivating habitat or dispersal habitat.
(5) Introduction, spread, or augmentation of non-native aquatic species in stream
segments or ponds used by the CRLF.
(6) Alteration or elimination of the CRLF's food sources or prey base (also
evaluated as indirect effects to the CRLF).
As previously noted in Section 2.1, the Agency believes that the analysis of direct and
indirect effects to listed species provides the basis for an analysis of potential effects on
the designated critical habitat. Because hexazinone is expected to directly impact living
organisms within the action area, critical habitat analysis for hexazinone 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 hexazinone is likely to encompass considerable portions of the
United States based on the large array of agricultural and non-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. Deriving the geographical extent of this
portion of the action area is the product of consideration of the types of effects that
hexazinone may be expected to have on the environment, the exposure levels to
hexazinone that are associated with those effects, and the best available information
concerning the use of hexazinone and its fate and transport within the state of California.
The definition of action area requires a stepwise approach that begins with an
understanding of the federal action. The federal action is defined by the currently labeled
uses for hexazinone. An analysis of labeled uses and review of available product labels
was completed. This analysis indicates that, for hexazinone, the following uses are
considered as part of the federal action evaluated in this assessment:
Airports
Industrial (outdoor)
40
-------
Sewage disposal
Drainage
Alfalfa
Blueberries
Pineapple
Christmas Tree Plantations
Forestry
Rangeland
Agricultural Rights-of-Way
Non-Agricultural Rights-of-Way
Pastures
Rangeland
Agricultural Uncultivated Areas
Non- Agricultural Uncultivated Areas
After a determination of which uses will be assessed, an evaluation of the potential
"footprint" of the use pattern should be determined. This "footprint" represents the initial
area of concern and is typically based on available land cover data. Local land cover data
available for the state of California were analyzed to refine the understanding of potential
hexazinone use. The initial area of concern is defined as all land cover types that
represent the labeled uses described above. A map representing all the land cover types
that make up the initial area of concern is presented in Fig 2.3.Sugar cane use patterns
were excluded from our assessment because itis not grown in California. No areas are
excluded from the final action area based on usage and land cover data.
Fig. 2.3 Hexazinone Initial Area of Concern
41
-------
Hexazinone Initial Area of Concern
Compiled from California County boundaries (ESRI, 2002),
USCA National Agriculture Statistical Sen/ice (NASS, 2002)
Gap Analysis Program Orchard/ Vineyard Undcover (GAP)
National Land Cover 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 (WD 1983).
Produced: 1/23/2008
42
-------
Once the initial area of concern is defined, the next step is to compare the extent of that
area with the results of the screening level risk assessment. The screening level risk
assessment will define which taxa, if any, are predicted to be exposed at concentrations
above the Agency's Levels of Concern (LOC). The screening level assessment includes
an evaluation of the environmental fate properties of hexazinone to determine which
routes of transport are likely to have an impact on the CRLF.
For hexazinone, the principal routes of transport away from the application site are
expected to be runoff and spray drift due to its mobility and moderate persistence.
Furthermore, the vapor pressure of hexazinone suggests that volatilization leading to
long-range transport is unlikely.
LOC exceedances are used to describe how far effects may be seen from the initial area
of concern. Factors considered include: spray drift, downstream run-off, atmospheric
transport, etc. This information is incorporated into GIS and a map of the action area is
created.
The AgDRIFT model (Version 2.01) is used to define how far from the initial area of
concern an effect to a given terrestrial species may be expected. The spray drift analysis
for hexazinone using the most sensitive terrestrial toxicity endpoint, terrestrial plants,
suggests that the distance for potential effects from the treated area of concern is beyond
the range of the AgDRIFT model {i.e., 1000 feet). Subsequently, the AgDISP model
(Version 8.15) with the Gaussian extension (used for longer range transport because the
limits of the regular AgDISP model were exceeded) was used to define this distance. The
AgDISP model was run in ground mode using default settings (except for wind speed at
10 mph and release height at 4 feet). Using the Gaussian extension, a maximum spray
drift distance of 4,501 feet for the listed species LOC was derived. The maximum spray
drift distance of 3,366 feet for relevant portion of the action area is based on the non-
listed species LOC for ground applications. A maximum spray drift distance of 4,200 feet
for the listed species LOC was derived for the aerial application. The maximum spray
drift distance of 3,589 feet for relevant portion of the action area is based on the non-
listed species LOC for aerial applications. 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 hexazinone that exceeds the LOC (discussed in
Section 3.2.6). It should be noted that the action area for hexazinone is based on the
endangered species LOCs for aquatic and terrestrial plants. However, the portion of the
action area that is relevant to the CRLF is based on the non-listed species LOCs for
aquatic and terrestrial plants because the CRLF does not have an obligate relationship
with plants.
The action area including the overlap between the CRLF and cultivated crop, pasture and
forest uses (Fig. 2.4) and non-crop non-agriacultural ROW (Fig. 2.5) uses is depicted in
two separate maps to increase the clarity of the maps.
43
-------
Hexazinone Cultivated crop. Pasture. Forest Action Area & CRLF overlap
Legend
]] Cult, Pas, For& CRLF overlap
Cult, Pas, For (4200-ft buffer)
| Critical habitat
Core areas
CNDDB occurence sections
Recovery units
County boundaries
Compiled from California County boundaries (ESRI, 2002),
US DA National Agriculture Statistical Service (NASS, 2002)
Gap Analysis Program Orchard/ Vineyard Landcower (GAP)
National Land Cover 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).
Produced: 1/23/2008
44
-------
Hexazinone Rights-of-Way (ROW) Action Area & CRLF Overlap
f
Legend
I ROW A A & CRLF overlap
ROWAA (4501 buffer)
| Critical habitat
Core areas
_] CNDDB occurence sections
Recovery units
County boundaries
\
i Kilometers
0 20 40 80 120 160
s
Compiled from California County boundaries (ESRI, 2002),
USDA National Agriculture Statistical Service ijslASS, 2002)
Gap Analysis Program Orchard/ Vineyard Landcwer (GAP)
National Land Cover 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).
Produced: 1/23/2008
Subsequent to defining the action area, an evaluation of usage information was conducted
to determine the area where use of hexazinone may impact the CRLF. This analysis is
used to characterize where predicted exposures are most likely to occur but does not
45
-------
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 hexazinone has
historically been used on a wide variety of agricultural and non-agricultural use sites.
Further information regarding buffer analysis and down stream dilution analysis used to
define the action area may be found in sections 3.2.5 and 3.2.6, respectively.
2.8 Assessment Endpoints and Measures of Ecological Effect
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."4 Selection of the assessment endpoints is based on valued
entities (e.g., CRLF, organisms important in the life cycle of the CRLF, and the PCEs of
its designated critical habitat), the ecosystems potentially at risk (e.g,. waterbodies,
riparian vegetation, and upland and dispersal habitats), the migration pathways of
hexazinone (e.g., runoff, spray drift, etc.), and the routes by which ecological receptors
are exposed to hexazinone-related contamination (e.g., direct contact, etc).
2.8.1 Assessment Endpoints for the CRLF
Assessment endpoints for the CRLF include direct toxic effects on the survival,
reproduction, and growth of the CRLF, as well as indirect effects, such as reduction of
the prey base and/or modification of its habitat. In addition, potential destruction and/or
modification of critical habitat is assessed by evaluating potential effects to PCEs, which
are components of the habitat areas that provide essential life cycle needs of the CRLF.
Each assessment endpoint requires one or more "measures of ecological effect," defined
as changes in the attributes of an assessment endpoint or changes in a surrogate entity or
attribute in response to exposure to a pesticide. Specific measures of ecological effect are
generally evaluated based on acute and chronic toxicity information from registrant-
submitted guideline tests that are performed on a limited number of organisms.
Additional ecological effects data from the open literature are also considered.
A complete discussion of all the toxicity data available for this risk assessment, including
resulting measures of ecological effect selected for each taxonomic group of concern, is
included in Section 4 of this document. A summary of the assessment endpoints and
measures of ecological effect selected to characterize potential assessed direct and
indirect CRLF risks associated with exposure to hexazinone is provided in Table 2.5.
Tsihie 2.5 Siimniiin of Assessment l-'udpitints ;inri Measures of l-lcolo^icid l-'.ITeels lor Direct
iind Indirect l-'.ITeels of hc\;i/inonc on (lie ( iilil'orniii Rcd-lciiiicd l"ro»
Measures of l-'.colo^icid l-'.ITeels
(l)iilii Sources Rc\ic\\cd)
Specific Selected Toxicity \ .due
(hiisis)
Aquatic Phase
(t-'KKs. larvae, latlpo/cs, juveniles, and at/nils)''
1. Survival, growth, and
reproduction of CRLF
la. Most sensitive fish acute LC50
la. Fathead minnow 274 mg/L
4 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
46
-------
Tsihie 2.5 Siimniiin of Assessment l-'udpitints ;inri Measures of l-'.eolo^ie;d l-'.ITeels lor Direel
iind Indii'eel l-'.ITeels of he\;i/inone on (lie ( ;ilil'nrni;i Keri-leggeri l"ro»
Measures of l-'.eolo^ieiil l-'.ITeels
(l)iilii Sources Reviewed)
Speeifie Seleeled To\iei(\ \ .due
(hiisis)
individuals via direct
effects on aquatic phases
lb. Most sensitive fish chronic
NOAEC
lb. Fathead minnow early-life stage
NOAEL = 17mg/Lai
lc. Most sensitive fish early-life
stage NOAEC
lc. same as lb.
2. Survival, growth, and
reproduction of CRLF
individuals via effects to
food supply (i.e.,
freshwater invertebrates,
non-vascular plants)
2a. Most sensitive (1) fish, (2)
aquatic invertebrate, and (3)
aquatic plant EC50 or LC50
2al. Fathead minnow 274 mg/L
ai
2a2. Daphnia magna 48-hr EC50 =110
mg/L ai
2a3. Green algae 96-hr EC50 = 0.007
mg/L ai
2b. Most sensitive (1) aquatic
invertebrate and (2) fish chronic
NOAEC
2b 1. Daphnia magna reproduction
NOAEC = 20 mg/Lai
2b2. Fathead minnow NOAEL = 17
mg/L ai
3. Survival, growth, and
reproduction of CRLF
individuals via indirect
effects on habitat, cover,
and/or primary
productivity (i.e., aquatic
plant community)
3 a. Vascular plant acute EC50
3a. Lemna gibba 14-dEC50 = 0.0374
mg/1 ai
3b. Non-vascular plant acute
EC50 (freshwater algae
3b. Green Algae 96-hr EC50 = 0.007
mg/1 ai
4. Survival, growth, and
reproduction of CRLF
individuals via effects to
riparian vegetation,
required to maintain
acceptable water quality
and habitat in ponds and
streams comprising the
species' current range.
4a. Distribution of (1) seedling
emergence and (2) vegetative
vigor monocot EC25 values
4a 1. Sorghum seedling emergence 21-
dEC25= 0.019 lbs ai/A
4a2. Wheat vegetative vigor 21-d EC25
= 0.02 lbs ai/A
4b. Distribution of (1) seedling
emergence and (2) vegetative
vigor EC25 values for dicots
4b 1. Tomato seedling emergence 21-d
EC25= 0.0064 lbs ai/A
4b2. Rape vegetative vigor 21-d EC25=
0.011 lbs ai/A
Terrestrial Phase (Juveniles and adults)
5. Survival, growth, and
reproduction of CRLF
individuals via direct
effects on terrestrial
phase adults and juveniles
5a. Most sensitive bird2 acute
LC50 or LD50
5a. Mallard duck LD50 = 2258 mg
ai/kg-bw
5b. Most sensitive bird2 chronic
NOAEC
5b. Bobwhite quail reproduction
NOAEC = 100 ppm
6. Survival, growth, and
reproduction of CRLF
individuals via effects on
prey (i.e.,terrestrial
invertebrates, small
terrestrial vertebrates,
including mammals and
terrestrial phase
amphibians)
6a. Most sensitive terrestrial (1)
invertebrate and (2) vertebrate
acute EC5o or LC50
6al. Honey bee acute contact LD50
>100 ng ai/bee
6a2. Rat LD50 = 5 3 0 mg ai/kg-bw
6b. Most sensitive terrestrial (1)
invertebrate and (2) vertebrate
chronic NOAEC
6b 1. No chronic NOAEC data for
terrestrial invertebrates
6b2. Rat 2-generation reproduction
study NOAEL = 200 mg/kg-bw
47
-------
Tsihie 2.5 Siimniiin of Assessment l-'udpitints ;inri Measures of l-lcolo^icid l-'.ITeels lor Direct
iind Indirect l-'.ITeels of hc\;i/inonc on (lie ( iilil'orniii Rcd-lciiiicd l"ro»
Measures of l-'.colo^icid l-'.ITeels
(l)iilii Sources Rc\ic\\cd)
Specific Selected Toxicity \ .due
(hiisis)
7. Survival, growth, and
reproduction of CRLF
individuals via indirect
effects on habitat (i.e.,
riparian vegetation)
7a. Distribution of (1) seedling
emergence and (2) vegetative
vigor EC25 values for monocots
7al. Sorghum seedling emergence 21-
dEC25 = 0.019 lbs ai/A
7a2. Wheat vegetative vigor 21-d EC25
= 0.02 lbs ai/A
7b. Distribution of (1) seedling
emergence and (2) vegetative
vigor EC25 values for dicots
7b 1. Tomato seedling emergence 21-d
EC25 = 0.0064 lbs ai/A
7b2. Rape vegetative vigor 21-d EC25
= 0.011 lbs ai/
1 Adult frogs are no longer in the "aquatic phase" of the amphibian life cycle; however, submerged
adult frogs are considered "aquatic" for the purposes of this assessment because exposure pathways in
the water are considerably different than exposure pathways on land.
2 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 hexazinone that may alter the PCEs of the CRLFs critical habitat. PCEs for
the CRLF were previously described in Section 2.6. Actions that may destroy or modify
critical habitat are those that alter the PCEs. Therefore, these actions are identified as
assessment endpoints. It should be noted that evaluation of PCEs as assessment endpoints
is limited to those of a biological nature (i.e., the biological resource requirements for the
listed species associated with the critical habitat) and those for which hexazinone effects
data are available.
Assessment endpoints and measures of ecological effect selected to characterize potential
modification to designated critical habitat associated with exposure to hexazinone are
provided in Table 2.6. Modification to the critical habitat of the CRLF includes the
following, as specified by USFWS (2006) and previously discussed in Section 2.6:
1. Alteration of water chemistry/quality including temperature, turbidity, and
oxygen content necessary for normal growth and viability of juvenile and
adult CRLFs.
2. Alteration of chemical characteristics necessary for normal growth and
viability of juvenile and adult CRLFs.
3. Significant increase in sediment deposition within the stream channel or pond
or disturbance of upland foraging and dispersal habitat.
4. Significant alteration of channel/pond morphology or geometry.
48
-------
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 hexazinone on critical habitat of the
CRLF are described in Table 2.6. Some components of these PCEs are associated with
physical abiotic features (e.g., presence and/or depth of a water body, or distance between
two sites), which are not expected to be measurably altered by use of pesticides.
Assessment endpoints used for the analysis of designated critical habitat are based on the
modification standard established by USFWS (2006).
Tabic 2.6. Summary of Assessment Endpoints and Measures of Ecological Effect for Primary
Constituent Elements of Designated Critical Habitat
Assessment Endpoint
Measures of Ecological
Effect5
(Data Sources Reviewed)
Specific Selected Toxicity Value
(basis)
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.
a. Most sensitive aquatic plant
EC50
a. Green Algae 96-hr EC50 = 0.007
ppm ai
b. Distribution of terrestrial
monocot (1) seedling
emergence and (2) vegetative
vigor EC25
bl. Sorghum seedling emergence 21-d
EC25 = 0.019 lbs ai/A
b2. Wheat vegetative vigor 21-d EC25
= 0.02 lbs ai/A
c. Distribution of terrestrial
dicot (1) seedling emergence
and (2) vegetative vigor EC25
values
cl. Tomato seedling emergence 21-d
EC25 = 0.0064 lbs ai/A
c2. Rape vegetative vigor 21-d EC25 =
0.011 lbs ai/A
Alteration in water
chemistry/quality including
temperature, turbidity, and oxygen
a. Most sensitive EC50 values
for aquatic
a. Green Algae 96-hr EC50 = 0.007
mg/L ai
5 All toxicity data reviewed for this assessment are included in Appendices D through F.
49
-------
Tsihie 2.(i. Siimniiin of Assessment l-lndpoinls ;iihI Measures of l-'.eolo^ieiil l-'.ITccl lor Primnn
( (insliliienl r.lemenls «il" Dcsi^iiiilcd ( rilic.d lliihiliil
Measures of llcolo^icul
I.ITecf
(l)iilii Sources Rc\ic\\cd)
Specific Selected Toxicity Value
(hiisis)
content necessary for normal
growth and viability of juvenile
and adult CRLFs and their food
source.6
b. Distribution of terrestrial
monocot (1) seedling
emergence and (2) vegetative
vigor EC25 values
bl. Sorghum seedling emergence 21-d
EC25 = 0.019 lbs ai/A
b2. Wheat vegetative vigor 21-d EC25
= 0.02 lbs ai/A
c. Distribution of terrestrial
dicot (1) seedling emergence
and (2) vegetative vigor EC25
values
cl. Tomato seedling emergence 21-d
EC25 = 0.0064 lbs ai/A
c2. Rape vegetative vigor 21-d EC25 =
0.011 lbs ai/A
Alteration of other chemical
characteristics necessary for
normal growth and viability of
CRLFs and their food source.
a. Most sensitive EC50 or LC50
values for (1) fish or aquatic-
phase amphibians and (2)
aquatic invertebrates
al. Fathead minnow 274 mg/L ai
a2. Daphnia magna 48-hr EC50 =110
mg/L ai
b. Most sensitive reproductive
NOAEC values for (1) fish or
aquatic-phase amphibians and
(2) aquatic invertebrates
bl. Fathead minnow early-life stage
NOAEL = 17 mg/L ai
b2. Daphnia magna reproduction
NOAEC = 20 mg/L ai
Reduction and/or modification of
aquatic-based food sources for
pre-metamorphs (e.g., algae)
a. Most sensitive aquatic plant
EC50
a. Green Algae 96-hr EC50 = 0.007
mg/L ai
Terrestrial Phase PI Us
(I pi ami 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 terrestrial
monocot (1) seedling
emergence and (2) vegetative
vigor EC25 values
b. Distribution of terrestrial
dicots (1) seedling emergence
and (2) vegetative vigor EC25
values
al. Sorghum seedling emergence 21-d
EC25 = 0.019 lbs ai/A
a2. Wheat vegetative vigor 21-d EC25
= 0.02 lbs ai/A
bl. Tomato seedling emergence 21-d
EC25 = 0.0063 lbs ai/A
b2. Rape vegetative vigor 21-d EC25 =
0.011 lbs ai/A
6 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.
50
-------
Tsihie 2.(». Siimniiin of Assessment l-lndpoinls ;inri Measures of l-'.eolo^ieiil l-'.ITccl for Priniiin
( onsliliicnl r.lemenls of Dcsi^iiiilcd ( rilic.d lliihiliil
Measures of l-leolo^ieiil
l.ffecf
(l)iilii Sources Rc\ic\\cd)
Specific Selected Toxicity Value
(hiisis)
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.
c. Most sensitive food source
acute EC50 or LC50 and
NOAEC values for terrestrial
vertebrates (mammals) and
invertebrates, birds, and
freshwater fish.
Cla. rat LD50 = 5 3 0 mg ai/kg-bw
(most sensitive terrestrial mammalian)
clb. rat 2-generation reproduction
study NOAEC = 200 mg/kg-bw
(most sensitive terrestrial mammalian)
c2a. Honey bee acute contact LD50 >
100 |ig ai/bee
(most sensitive terrestrial invertebrate)
c2b. No chronic NOAEC data for
terrestrial invertebrates
c3a. Mallard duck LD50 = 2258 mg
ai/kg-bw
(most sensitive bird test as surrogate
for terrestrial-phase amphibian)
C3b. Bobwhite quail reproduction
NOAEC = 100 ppm
(most sensitive bird test as surrogate
for terrestrial-phase amphibian)
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 hexazinone to the environment.
The following risk hypotheses are presumed for this endangered species assessment:
Labeled uses of hexazinone within the action area may directly affect the CRLF
by causing mortality or by adversely affecting growth or fecundity;
Labeled uses of hexazinone within the action area may indirectly affect the CRLF
by reducing or changing the composition of food supply;
Labeled uses of hexazinone within the action area may indirectly affect the CRLF
and/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;
51
-------
Labeled uses of hexazinone within the action area may indirectly affect the CRLF
and/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;
Labeled uses of hexazinone within the action area may modify the designated
critical habitat of the CRLF by reducing or changing breeding and non-breeding aquatic
habitat (via modification of water quality parameters, habitat morphology, and/or
sedimentation);
Labeled uses of hexazinone within the action area may modify the designated
critical habitat of the CRLF by reducing the food supply required for normal growth and
viability of juvenile and adult CRLFs;
Labeled uses of hexazinone within the action area may modify the designated
critical habitat of the CRLF by reducing or changing upland habitat within 200 ft of the
edge of the riparian vegetation necessary for shelter, foraging, and predator avoidance.
Labeled uses of hexazinone within the action area may 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.
Labeled uses of hexazinone within the action area may modify the designated
critical habitat of the CRLF by altering chemical characteristics necessary for normal
growth and viability of juvenile and adult CRLFs.
2.9.2 Diagram
The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies the stressor hexazinone release mechanisms, biological receptor types, and
effects endpoints of potential concern. The conceptual models for aquatic and terrestrial
phases of the CRLF are shown in Figures 2.6 and 2.7, respectively, and the conceptual
models for the aquatic and terrestrial PCE components of critical habitat are shown in
Figures 2.8 and 2.9, respectively.
Exposure routes shown in dashed lines (long-range atmospheric transport) 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.
Exposure Pathways and Routes in Aquatic Phase Conceptual Model
52
-------
Eggs, larvae, tadpoles, juveniles, and adult frogs may potentially absorb hexazinone
across their membranes or gills and integuments.
Aquatic animals that serve as prey to the juvenile and adult CRLF may be exposed via
gills and their integument to hexazinone and its major degradates in surface water.
Aquatic vascular and non-vascular plants may sorb to their membranes or transfer across
their membranes dissolved hexazinone and its major degradates in surface water.
Terrestrial plants in semi-aquatic areas (i.e. wetlands, riparian zones) may uptake
dissolved hexazinone and its major degradates from soil pore water, surface water, or
groundwater.
The exposure pathways discussed here in the aquatic phase conceptual model are
modified to address attributes assessed in aquatic component of critical habitat and PCEs
in conceptual model 2.8
Figure 2.6 Conceptual Model for Pesticide Effects on Aquatic Phase of the Red-
Legged Frog
Exposure Pathways and Routes in Terrestrial Phase Conceptual Model
53
-------
Juvenile and adult frogs may experience dermal exposure to soil residues of hexazinone
and its major degradates when seeking refuge in ground crevices from solar radiation or
traversing across soils with hexazinone-related residues.
Juvenile and adult frogs may also incidentally ingest soil residues of hexazinone and its
major degradates along with prey items.
CRLF prey items, small mammals (mice) and terrestrial insects, may uptake across their
dermal/cuticle, residues of hexazinone and its major degradates.
The exposure pathways discussed here in the terrestrial phase conceptual model are
modified to address attributes assessed in terrestrial component of critical habitat and
PCEs in conceptual model 2.9.
Figure 2.7 Conceptual Model for Pesticide Effects on Terrestrial Phase of Red-
Legged Frog
54
-------
Figure 2.8 Conceptual Model for Pesticide Effects on Aquatic Components of Red-
Legged Frog Critical Habitat
55
-------
Figure 2.9 Conceptual Model for Pesticide Effects on Terrestrial Components of
Red-Legged Frog Critical Habitat
2.10 Analysis Plan
The analysis plan is the final step in Problem Formulation. In order to address the risk
hypothesis, the potential for adverse direct and indirect effects to the CRLF, its prey, and
its habitat is estimated. The integration of exposure and ecological effects
characterization determines the potential ecological risk from agricultural and non-
agricultural uses of hexazinone, and the likelihood of direct and indirect effects to CRLF
in aquatic and terrestrial habitats.
In the following sections, the use, environmental fate, and ecological effects of
hexazinone are characterized and integrated to assess the risks. This is accomplished
using a risk quotient (ratio of exposure concentration to effects concentration) approach.
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 B).
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 hexazinone is estimated using the probit dose-response slope and either
the level of concern (discussed below) or actual calculated risk quotient value.
56
-------
2.10.1 Measures of Exposure
The environmental fate properties of hexazinone along with available monitoring data
indicate that runoff and spray drift are the principle potential transport mechanisms of
hexazinone to the aquatic and terrestrial habitats of the CRLF. In this assessment,
transport of hexazinone through runoff and spray drift is considered in deriving
quantitative estimates of hexazinone exposure to CRLF, its prey and its habitats. Long-
range transport of hexazinone is highly unlikely, given the chemical characteristics,
formulation, and application methods. A vapor pressure of 2 x 10"7 mm Hg and Henry's
Law Constant of 2 xlO"12 atm m3/mole mean that hexazinone is not likely to volatilize and
be transported offsite in the atmosphere. Some hexazinone residues may be transported
as a component of field runoff, but dilution by receiving water bodies should limit the
extent of long-range transport via surface water. Thus, the Agency believes that risk of
long-range transport of hexazinone is minimal.
Measures of exposure are based on aquatic and terrestrial models that predict estimated
environmental concentrations (EECs) of hexazinone using maximum labeled application
rates and methods. The highest screening-level EEC based on granular use of hexazinone
(non-crop/non-agricultural ROW at 12 lbs ai/A) or nongraular use (noncrop uses at 8 lb ai
/A) was initially used to derive risk quotients. In cases where LOCs were not exceeded
based on this use pattern, additional RQs were not derived because it was assumed that
RQs for lower EECs would also not exceed LOCs. However, if LOCs were exceeded
based on the highest EECs, use-specific RQs were also derived. The models used to
predict aquatic EECs are the Pesticide Root Zone Model coupled with the Exposure
Analysis Model System (PRZM/EXAMS). If there are any "May effect" determinations
in the aquatic exposure assessment, an analysis of spray drift buffers needed to get below
concentrations that exceed the endangered species level of concern will be conducted and
a dilution model will be used and described in the risk characterization section of this risk
assessment.
PRZM (v3.12beta, May 24, 2001) and EXAMS (v2.98.04, Aug. 18, 2002) are screening
simulation models coupled with the input shell pe4v01.pl (Aug.8, 2003) to generate daily
exposures and l-in-10 year EECs of hexazinone that may occur in surface water bodies
adjacent to application sites receiving hexazinone 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 that is 2 meters deep (20,000 m3 volume) with no outlet. PRZM/EXAMS is used to
estimate screening-level exposure of aquatic organisms to hexazinone. The measure of
exposure for aquatic species is the l-in-10 year return peak or rolling mean concentration.
The l-in-10 year peak is used for estimating acute exposures of direct effects to the
CRLF, as well as indirect effects to the CRLF through effects to potential prey items,
including: algae, aquatic invertebrates, fish, and frogs. The 1-in-10-year 60-day mean is
used for assessing chronic exposure to the CRLF and fish and frogs serving as prey items.
57
-------
The 1-in-10-year 21-day mean is used for assessing chronic exposure to aquatic
invertebrates, which are also potential prey items.
Hexazinone residues are also estimated for waters downstream from the treated areas by
assuming dilution with stream water (derived from land area) from unaffected sources,
propagating downstream, until a point is reached beyond which there are no relevant
LOC exceedences. Once the distribution of predicted stream water concentrations is
obtained, it is further processed using a model that calculates expected dilution in the
stream according to contributing land area. As the land area surrounding the field on
which hexazinone is applied is enlarged, it encompasses a progressively greater drainage
area; in effect, a progressively larger 'sub-watershed' is created, with a concomitant
increase in dilution at the drainage point. This drainage point moves down-gradient
along the stream channel as the sub-watershed is expanded. At a certain point the
predicted stream concentrations will become sufficiently diluted; the region beyond this
then falls outside the Action Area.
Terrestrial wildlife exposure estimates are typically calculated for birds and mammals,
which are surrogates for terrestrial-phase amphibians and reptiles. These estimates focus
on potential dietary exposures to the pesticide active ingredient and are estimated
assuming the organisms are exposed to a singe pesticide residue on food items in a given
exposure scenario. 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). The Fletcher et al. (1994)
modifications to the Kenega nomograph are based on measured field residues from 249
published research papers, including information on 118 species of plants, 121 pesticides,
and 17 chemical classes. These modifications represent the 95th percentile of the
expanded data set. For modeling purposes, direct exposures of the CRLF to hexazinone
through contaminated food are estimated using the EECs for the small bird (20 g) which
consumes small insects. Dietary-based and dose-based exposures of potential prey (small
mammals) are assessed using the small mammal (15 g) which consumes short grass. The
small bird (20g) consuming small insects and the small mammal (15g) consuming short
grass are used because these categories represent the largest RQs of the size and dietary
categories in T-REX that are appropriate surrogates for the CRLF and one of its prey
items. Estimated exposures of terrestrial insects to hexazinone are bound by using the
dietary based EECs for small insects and large insects. In addition, terrestrial exposures
from granular applications (mg ai/square foot) for the CRLF are also estimated using T-
REX (Appendix C).
If there are any "may effect" determinations in the terrestrial exposure assessment,
terrestrial exposure and risk for the terrestrial-phase of the CRLF will be refined using T-
HERPS (version 1.0, 2007), which is a modified version of T-REX (version 1.3.1) that
allows for estimation of food intake for herptiles. Birds are typically used as surrogates
58
-------
for reptiles and terrestrial-phase amphibians. However, reptiles and terrestrial-phase
amphibians (i.e., herptiles) tend to have much lower metabolic rates and lower caloric
intake requirements than birds or mammals. As a consequence, birds are likely to
consume more food than amphibians or reptiles on a daily dietary intake basis, assuming
similar caloric content of the food item. T-REX (version 1.3.1.) has been altered to allow
for an estimation of food intake for herptiles (T-HERPS) using the same basic procedure
that T-REX uses to estimate avian food intake (see Appendix D for details).
EECs for terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant
(version 1.2.2, 12/26/2006)(Appendix E). 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.
Two spray drift models, AgDISP and AgDRIFT are used to assess exposures of terrestrial
phase CRLF and its prey to hexazinone deposited on terrestrial habitats by spray drift.
AgDISP (version 8.13; dated 12/14/2004) (Teske and Curbishley, 2003) is used to
simulate aerial and ground applications using the Gaussian farfield extension
2.10.2 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 Agency's
Office of Research and Development, and the National Health and Environmental Effects
Research Laboratory's Mid-Continent Ecology Division.
As previously discussed in Section 2.8.1 and 2.8.2, assessment endpoints for the CRLF
include direct toxic effects on survival, reproduction, and growth of the species itself, as
well as indirect effects, such as reduction of the prey base and/or modification of its
habitat. The assessment of risk for direct effects to the terrestrial-phase CRLF makes the
assumption that toxicity of hexazinone to birds is similar 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.
Acute (short-term) and chronic (long-term) toxicity information for hexazinone is
characterized based on registrant-submitted studies and an updated review of the open
literature. Based on an updated review of the open literature for October 2007, no
endpoints for aquatic organisms were more sensitive than registrant submitted data.
Although no open literature avian endpoints were more sensitive than registrant
submitted data, there was an acute oral rat LD50 that was more sensitive than registrant
59
-------
submitted data. No endpoints for either aquatic or terrestrial plants were more sensitive
than registrant submitted data. Therefore the more sensitive mammal acute oral LD50 =
530 mg/g (Kennedy 1984) was included and used in this assessment to modify the Action
Area and evaluate direct and indirect effects to the CRLF and its critical habitat.
The acute measures of effect used for animals in this screening level assessment are the
LD50, LC50 and ECso- LD stands for "Lethal Dose", and LD50 is the amount of a material,
given all at once, that is estimated to cause the death of 50% of the test organisms. LC
stands for "Lethal Concentration" and 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 NOAEC. 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).
2.10.3 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 hexazinone, 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 hexazinone 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 B).
For this endangered species assessment, listed species LOCs are used for comparing RQ
values for acute and chronic exposures of hexazinone directly to the CRLF. If estimated
exposures directly to the CRLF of hexazinone 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 hexazinone 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 acute RQ being considered also
exceeds the non-listed species acute risk LOC, then the effects determination is a LAA.
If the RQ is between the listed species LOC and the non-listed 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
60
-------
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 LAA.
3 Exposure Assessment
Hexazinone products are formulated as granulars, pellets/tablets, emulsifiable
concentrates, ready-to-use liquids, soluble concentrates/solids and a technical grade
active ingredient. Products are applied using aerial or ground equipment or by hand, or
using a hand-held, boom, knapsack or power sprayer. Use practice limitations prohibit
application of hexazinone through any type of irrigation system. The majority of labels
do not specify the allowed maximum application rate per year nor do they specify the
maximum number of applications per year, therefore a conservative estimate will be used
for this assessment.
Although the maximum number of applications from the label for pasture, alfalfa and
Christmas tree uses is one, other uses do not specify a maximum rate or maximum
number of applications per year. For this assessment, one application per year for those
other uses is based on additional information from the label. Blueberry uses are modeled
at a maximum of one application per year due to no application within 450 days of
harvest. Pineapple is modeled as one application per year due to the growing season,
which is nearly a year in length. Noncrop uses and all granular uses, non-crop/non-
agricultural ROW, forest site preparation and rangeland, are modeled as one application
per year due to the requirement for rain to activate hexazinone and because maximum
effects are achieved after 12-24 months.
Risks from ground boom and aerial applications are considered in this assessment
because they are expected to result in the highest off-target levels of hexazinone due to
generally higher spray drift levels. Ground boom and aerial modes of application tend to
use lower volumes of application applied in finer sprays than applications coincident with
sprayers and spreaders and thus have a higher potential for off-target movement via spray
drift.
3.1 Label Application Rates and Intervals
Nationally, hexazinone is an herbicide used to control a broad spectrum of weeds
including undesirable woody plants in alfalfa, rangeland and pasture, woodland,
pineapples, sugarcane and blueberries. It is also used on ornamental plants, forest trees
and other non-crop areas. Hexazinone is registered for pre-emergent, post-emergence,
layby, directed spray and basal soil applications. It is used as a non-selective herbicide in
noncropland areas and as a selective herbicide in reforestation practices.
The purpose of the exposure assessment is to determine if the currently permitted label
uses do not harm the CRLF, therefore conservative assumptions are developed for each
61
-------
use. Analysis of labeled use information is the critical first step in evaluating the action.
The current label for hexazinone 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.
A review of uses from the Label Use Information System (LUIS) produced by Office of
Pesticide Programs (OPP) Biological and Economic Analysis Division (BEAD) revealed
that many labels do not specify maximum number of applications per year/ crop cycle or
maximum rates per year. This requires assumptions be made in the design for these
conservative scenarios.
Although the maximum number of applications from the label for pasture, alfalfa and
Christmas tree uses is one, other uses do not specify a maximum rate or maximum
number of applications per year. For this assessment, one application per year for those
other uses is based on additional information from the label: blueberry uses are modeled
at a maximum of one application per year due to no application within 450 days of
harvest; pineapple is modeled as one application per year due to the growing season,
which is nearly a year in length; all noncrop and granular uses are modeled with one
application per year. This assumption based on the availability for moisture to activate
the pesticide and maximum effects not being achieved until 12-24 months after
activation. Based on the assumption of a single application per year, the highest
maximum rate identified for this assessment is identified for noncrop(12 lb/A).
Currently registered agricultural and non-agricultural uses of hexazinone within
California are listed in Table 3.1 based on the conservative assumptions.
Table 3.1 llexa/inone Labeled I ses ol'and Application 1 nI'orin:ition lor (lie ( Kl
1 Kisk
Assessment
Crop
M;i\ Appl.
Max # ol"
Modeled
Seasonal
kale (Ihs
Appl./Crop
Max#
Max
a.i./A)
Cycle
Appl
Dose/Year
(Ihs a.i./A)
NON-CROP
12
NS
1
NS
NONAGRICULTURAL UNCULTIVATED
8
NS
1
NS
AREAS/SOILS
AGRICULTURAL RIGHTS-OF-
8.
NS
1
NS
WAY/FENCEROWS/HEDGEROWS
AGRICULTURAL UNCULTIVATED
8.
NS
1
NS
AREAS
AIRPORTS/LANDING FIELDS
8.
NS
1
NS
SEWAGE DISPOSAL AREAS
8.
NS
1
NS
FOREST Site Preparation (g)
5
NS
1
NS
SUGARCANE
3.6
NS
1
NS
PINEAPPLE
3.6
NS
1
NS
CONIFER RELEASE
3
NS
1
NS
RANGELAND (g)
3
NS
1
NS
BLUEBERRY
3
NS
1
NS
62
-------
CHRISTMAS TREE PLANTATIONS
2.
1
1
NS
ALFALFA
1.5
NS
1
1.5
PASTURES
1.1
1
1
NS
NS = Not stated on the label.
1 Uses assessed based on memorandum from SRRD dated 07/31/2007
3.2 Aquatic Exposure Assessment
3.2.1 Modeling Approach
Aquatic exposures are quantitatively estimated for all of assessed uses using scenarios
that represent high exposure sites for hexazinone 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 hexazinone were used
for modeling, including application rates, number of applications per year, application
intervals, buffer widths and resulting spray drift values modeled using standard EFED
default values. These are 5% of the application rate for aerial application and 1% of the
application rate for ground application. 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. More detail on the crop profiles and the previous assessments may be found at:
http://pestdata.ncsu.edu/cropprofiles/cropprofiles.cfm
The highest screening-level EEC (based on granular use of hexazinone on noncrop at 12
lbs ai/A or nongranular use for noncrop uses at 8 lb ai /A) was initially used to derive risk
quotients. In cases where LOCs were not exceeded based on this use pattern, additional
RQs were not derived because it was assumed that RQs for lower EECs would also not
63
-------
exceed LOCs. However, if LOCs were exceeded based on the highest EECs, use-specific
RQs were also derived
3.2.2 Model Inputs
Table 3.2 summarizes the PRZM/EXAMS environmental fate data used for aquatic
exposure Inputs for the hexazinone Endangered Species Assessment for the CRLF
Table 3.2 llexazinone Model In puts lor PUZM/IA VMS lor (lie CUII Risk
assessment
Parameter
Value
Comments
Source
Molecular Weight (grams/mole)
252.3
Solubility (mg/L)
Vapor Pressure (torr)
Henry's Constant (atm m3/mol)
Kd (L/kg)
33,000
2.0E"7
2.0E"12
0.45
10X reported value
product
chemistry
MRID41528101
Koc (L/kg)
37.0
MRID41528101
Aerobic Soil Metabolism Half-
life (days)
648
(216x3)
Based on 3X single
aerobic soil
metabolism linear
first order half-life
MRID41807401
MRID42635001
Aerobic Aquatic Metabolism
Half-life (days)
180
(60x3)
Based on 3X single
aerobic aquatic
metabolism linear
first order half-life
MRID41811801
Anaerobic Aquatic Metabolism
Half-life (days)
Photodegradation in Water Half-
life (days)
690
(230x3)
Stable
Based on 3X single
anaerobic aquatic
metabolism linear
first order half-life
MRID41807402
MRID41300801
Photodegradation in Soil Half-life
(days)
Stable
MRID413 00802
Hydrolysis Half-life
(days)
pH 5
Stable
MRID41587301
pH 7
Stable
MRID41587301
pH 9
Stable
MRID41587301
Spray Drift Fraction
5%
1%
Aerial
Ground
Default value
1 - Spray drift not included in final EEC due to edge-of-field estimation approach
2 - 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
64
-------
3.2.3 PRZM/EXAMS Aquatic Exposure Modeling Results
The aquatic EECs for the various scenarios and application practices are listed in Table
3.3. Peak EEC's for all uses permitted by the label range from 5.7 ug/1 for blueberry to
156.6 ug/1 for non-crop/non-agricultural ROW. Twenty-one and sixty-day EEC's range
from 5.6 ug/1 for blueberry to 153.7 ug/1 for the noncropuse.
Tabic 3.3 Aquatic EECs in the Standard EXAMS Water Body (1 in 10 year EEC (ug/L))
Crop/Usage
Applic"'b'c
Rate (#/ac)
Application
Method"
Peak
21 day
Average
60 day
Average
Notes
NonAgRofW ay/Fence
12
Ground Spray
156.6
153.7
148.8
Noncrop:
AgRofW ay/Fence
(Granular)
8.
Granule
Applicator/
Broadcast
98.558
95.946
92.276
Noncrop:
AgUnCultivated
(Granular)
8.
Aircraft/Granule
Applicator/Soil
Broadcast
84.49
83.338
81.291
Forest Site
preparation
(Granular)
5.
Hand gun/ Soil
Treatment
16.20
15.92
15.47
Conifer Release
3
Ground Spray
52.139
51.144
49.744
Rangeland (Granular)
3
Aircraft/Granule
Applicator/Soil
Broadcast
35.507
35.02
34.156
BlueBerry
3
Sprayer/Spot Soil
Treatment
5.6815
5.6033
5.4706
No Recorded
Usage
Christmas Trees
2.
Air/Ground Spray
46.594
46.014
45.385
Alfalfa
1.5
Aircraft/ Sprinkler
Irrig/Chemigation/
Boomsprayer
24.788
24.437
23.583
Pasture
1.1
Boom sprayer/
Ground sprayer/
Broadcast
10.629
10.48
10.2124
aAll crops/usages are one single application.
b All crops/usages are simulated at the highest rate allowed on any of the labels.
c Application rates for PRZM-EXAMS input are the labels multiplied by a conversion to kilograms/hectare (1.121 * lb/A)
3.2.4 Existing Monitoring Data
A critical step in the process of characterizing EECs is comparing the modeled estimates
with available surface water monitoring data. Hexazinone has a limited set of monitoring
data relevant to the CRLF assessment. There are only three measured Hexazinone
concentrations above the limit of quantification in the California Department of Pesticide
Regulation (CDPR) data, (http ://www. cdpr. ca. gov/docs/sw/surfdata.htm) All three
CDPR measured concentrations were recorded at the River Road sampling station on
Orestimba Creek, tributary to the San Joaquin River in Stanislaus County. The
concentrations of 0.06 j_ig/l, 0.5 j_ig/l and 0.154 |Jg/l were collected on January 31, 2001;
February 14, 2001; and July 2, 2002, respectively. All three are non-targeted samples
(i.e., study was not specifically designed to capture hexazinone concentrations in high use
areas).
65
-------
Hexazinone is not on the list of pesticides for which the NAQWA program samples in
either of the two California sampling units. There is also no data for hexazinone or its
degradates in the California Pesticide Air Monitoring Results: 1986-2000 (Kollman,
2002).
3.2.5 Spray Drift Buffer Analysis
When considering the terrestrial habitats of the CRLF, spray drift onto non-target areas
from use sites could potentially result in exposures of the CRLF, its prey and its habitat to
hexazinone. Therefore, it is necessary to estimate the distance from the application site
where spray drift exposures do not result in LOC exceedences for organisms within the
terrestrial habitat.
Since spray drift is the most likely means through which non-target terrestrial organisms
will be potentially exposed to hexazinone, the AGDISP model (version 8.15) is used to
estimate the terrestrial distance from the site of application to where RQs are predicted to
fall below the endangered species LOC. The highest single maximum application rate
allowed on the label was modeled to determine the maximum potential off-site estimated
environmental concentrations (EECs) based on upper bound Kenaga values. The noncrop
usage has the highest application rate (12 pounds per acre), but permits ground
application only. The hexazinone usage with the highest aerial application rate is a
conifer release forestry application (40 pounds per acre). These two applications produce
the longest buffer widths. Typically aerial application is modeled for the assessment since
aerial application produce much higher spray drift due the higher release heights. Tables
3.4 and 3.5 have selected input parameters used in AGDISP modeling.
Table 3.4. \(.I)ISP Input Parameters l or Hexazinone Pineapple Application by
Aerodyne W asp Helicopter
Application. Method
Aoriiil
( Aoi ckImk' Wsisp Helicopter)
Canopy Height (Forest)
30 ft
Release Height
15 ft
Swath Displacement
Vi swath
Application Rate
4.0 pounds a.i. per acre
Spray Volume
5 gal-acre"1
Non-volatile Fraction
0.3
Active Fraction
0.075
Specific Gravity (Carrier)
1.0
Specific Gravity (Hexazinone)
0.542
Fraction of Applied1
0.00087
Initial Average Deposition2
0.00348
1 = LOC/RQ
2 = (Fraction of applied) x (Application rate for forestry conifer release in lbs a.i/acre)
66
-------
Tsihlc 3.5. A(>I)ISP Input P;iminders l-'or llcxii/inonc Non-Crop Application hy
(iroiiml liooin Sprsivcr
Application. Method
Aerial
(Acroriwic Wiisp Helicopter)
Canopy Heiglil ( Furesl)
nunc
Release Height
4ft
Swath Displacement
Vi swath
Application Rate
12.0 pounds a.i. per acre
Spray Volume
10 gal-acre"1
Non-volatile Fraction
0.15
Active Fraction
0.0375
Specific Gravity (Carrier)
1.0
Specific Gravity (Hexazinone)
0.542
Fraction of Applied1
0.00064
Initial Average Deposition2
0.0064
1 = LOC/RQ
2 = (Fraction of applied) x (Application rate for non-agricultural rights-of-way in lbs a.i/acre)
A single application was modeled for both applications because it is unlikely that the
same terrestrial invertebrate would be exposed to the maximum amount of spray drift
from multiple applications. There is also no data showing more than one application per
year. For a terrestrial organism to receive the maximum concentration of hexazinone
from multiple applications, it would require that each application is made under identical
atmospheric conditions (e.g., same wind speed and same wind direction) and the
terrestrial organism being exposed is located in the same location (which receives the
maximum amount of spray drift) after each application. Certain factors, including
variations in topography, cover, and meteorological conditions over the transport distance
are not accounted for by the AGDISP 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 AGDISP
will 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.).
Conservative assumptions are made regarding the droplet size distributions being
modeled ('ASAE Very Fine to Fine' for rights-of way uses, the application method (i.e.,
aerial), release heights and wind speeds. Alterations in any of these inputs would
decrease the area of potential effect. As noted in Section 3.2.4, no hexazinone was
detected in the air monitoring studies conducted in California. Therefore, it is unlikely
that any terrestrial invertebrate outside the buffer from the site of hexazinone application
would actually receive a level of exposure high enough to cause an adverse effect.
The analysis of spray drift distances was completed using the Gaussian extension to
AGDISP
For the terrestrial phase, an analysis was conducted using the most sensitive terrestrial
67
-------
endpoint, the terrestrial plant NOAEC of 0.00348 lbs ai/acre. This distance identifies
those locations where terrestrial landscapes can be impacted by spray drift deposition
alone (no runoff considered) at concentrations above the listed species LOC for terrestrial
plants. The LOC was compared to the highest RQ for aerial applications to noncrop at
12.0 lbs ai/acre. In this analysis, the most sensitive endpoint was the NOAEC of 0.00348
lbs ai/A (0.00390 kg ai/hectare), which yielded a terrestrial spray drift distance of 4,501
feet. Each lower application rate yields a lower buffer distance. These distances represent
the maximum extent where effects are possible using the most sensitive data and the
endangered species LOC for plants (1.0).
In order to characterize the portion of the action area that is relevant to the CRLF and
specific to the area where the effects determination (i.e. NLAA versus LAA) will be
made, a similar analysis was conducted using the most sensitive non-endangered plant
EC25 of 0.0064 lbs ai/acre. Typically the NOAEC is used when there is an obligate
relationship between the species being assessed and endangered plants (or other taxa).
However, there is no obligate relationship between the CRLF and any endangered plant;
therefore the LAA/NLAA determination is based on the area defined by the non-listed
species LOC (i.e., EEC/ECso)- Using the same approach described above, the maximum
distance for the aerial use of hexazinone on noncrop at 12 lbs ai/acre is 3,3669 feet with
reductions in distance for lower application rates. A summary of the modeled distances
for these application rates is presented in Table 3.6.
The LOC was compared to the highest RQ for aerial applications to pineapple at 4.0 lbs
ai/acre. In this analysis, the most sensitive endpoint was the NOAEC of 0.00348 lbs ai/A
(0.00390 kg ai/hectare), which yielded a terrestrial spray drift distance of 4,200 feet. Each
lower application rate yields a lower buffer distance. These distances represent the
maximum extent where effects are possible using the most sensitive data and the
endangered species LOC for plants (1.0).
In order to characterize the portion of the action area that is relevant to the CRLF and
specific to the area where the effects determination (i.e. NLAA versus LAA) will be
made, a similar analysis was conducted using the most sensitive non-endangered plant
EC25 of 0.0064 lbs ai/acre. Using the same approach described above, the maximum
distance for the aerial use of hexazinone on pineapple at 4 lbs ai/acre is 3,589 feet with
reductions in distance for lower application rates. A summary of the modeled distances
for these application rates is presented in Table 3.6.
T:ihlc3.6 Siiniiiiiirv ol'AgDISP Predicted
Terreslrinl Spnn
Drill Distances
Application R;i(e:
Ihs/iic (HUMhod)
I sos Repivsenk'il
\o\r.<
Disliiiicc (ID1
r.(:;
Disliinco (fir
12.0 (ground boom)
Non-crop
4501
3366
4.0 (helicopter)
Pineapple
4200
3589
1 The NOAEC value is used to define the buffer associated with the Ml extent of the action area.
2 The EC25 value is used to define the buffer associated with the relevant portion of the action area.
Given that the greatest buffer distance is 4501 feet for terrestrial plants, this value was
used to define the action area (i.e., this buffer distance is added to the initial area of
68
-------
concern depicted in Figure 2.3. The action area (based on the buffer distance of 4501
feet) and the portion of the action area that is relevant to the CRLF (based on impacts to
terrestrial plants at the non-listed LOC and a corresponding buffer distance of 3589 feet)
is shown in Figure 2.4 and Figure 2.5.
3.2.6 Downstream Dilution Analysis
The final step in defining the action area is to determine 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
hexazinone present.
The use of the "RQ to LOC ratio" provides information on the concentration that must be
reached in downstream water to be below the LOC. Therefore, the analysis defines the
point where the percentage of treated area with the watershed would yield sufficient non-
impacted water to dilute the EECs to concentrations below the LOC. Further details on
this approach are provided in Appendix B.
Using a NOAEC for non-vascular aquatic plants (the most sensitive species) of 7 ug/L
and a maximum peak EEC for applications to non-crop (non-agricultural ROW) equal to
156.6 ug/L yields an RQ/LOC ratio of 39.15 (39.15).] Using the downstream dilution
approach (described in more detail in Appendix F) yields a target percent crop area
(PCA) of 4.2%. This value has been input into the downstream dilution approach for
cultivated crop and pasture, forest and non-agricultural uses. Cultivated crop and pasture
use added 4,853 kilometers, and resulted in a total of 68,257 kilometers of stream
downstream from the initial area of concern. Forest use resulted in the largest addition,
22,416 kilometers, for a total of 160,771 kilometers of stream downstream from the
initial area of concern. Non-agricultural uses resulted in the smallest addition, 1,868
kilometers, for a total of 105,929 kilometers of stream downstream from the initial area
of concern. By way of comparison, there are 332,962 kilometers of streams within the
initial area of concern all of which are assumed to be at the modeled EEC.
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 non-vascular aquatic
plant EC50 value, in this case 22.37 ug/L. Applying the same approach to downstream
extent yields a RQ/LOC ratio of 22.37 (22.37) which equates to a downstream dilution
factor of 27.8%. Cultivated crop and pasture use added 3,534 kilometers, and resulted in
a total of 66,938 kilometers of stream downstream from the initial area of concern. Forest
use resulted in the largest addition, 18,772 kilometers, for a total of 157,127 kilometers of
stream downstream from the initial area of concern. Non-agricultural uses resulted in the
69
-------
smallest addition, 1,081 kilometers, for a total of 105,142 kilometers of stream
downstream from the initial area of concern.
3.3 Terrestrial Exposure
3.3.1 Bird and Mammal Exposure (T-REX Model)
EFED estimates exposure of birds (Table 3.8) and mammals (Table 3.9) to pesticides
using the Terrestrial Exposure Model (T-REX). T-REX uses the Kenaga nomagram, as
modified by Fletcher et al. (1994) to determine pesticide residues on several categories of
food items, and then calculates the potential dose an organism might receive from
ingesting contaminated items using allometric equations. Dose estimates are based on an
upper bound dose and the assumptions that the organism exclusively eats one type of
food item and forages only in the treated and/or overspray areas. Hexazinone translocates
in plant tissue and the residence time of the parent compound or any degradates is
unknown, residues in the plant are not expected to exceed residues on the plant.
Assessments for applications were completed for the non-crop/nonagricultural ROW
granular uses (12 lb/A) noncrop uses (airports/sewage) (8 lb/A), forest site preparation
(g) (5 lb/A), pineapple (3.6 lb/A), conifer release ( 3 lb/A), blueberry (3 lb/A), rangeland
(g) (3 lb/A), Christmas tree (2 lb/A), alfalfa (1.5 lb/A) and pasture (1.1 lb/A) which
comprise almost all recorded uses in California.
Tabic 3.7 Input Parameters for TREX and T-HERPS
Parameter
Value
Source
Percentage active ingredient for
maximum rate
100%
Labels, application rate already
adjusted
Number of applications
1
Labels
Application interval
None, single application
Labels
Dissipation half-life
35 days
Default
Table 3.8 TREX Avian Dose Estimates
Feeding Category
Dietarv-bascd
Aeute Dose-based EECs (mg/kg-bw)
EECs (mg/kg-food
Small
Medium
item)
(20 g)
(100 g)
Noncrop (airports)(8 lb/A)
Short grass
1920.00
2186.69
1246.94
Tall grass
880.00
1002.23
571.52
Broadleaf plants/small insects
1080.00
1230.01
701.40
Fruits/pods/seeds/large insects
120.00
136.67
77.93
Pineapple (3.6 lb/A)
Short grass
864.00
984.01
561.12
Tall grass
396.00
451.00
257.18
Broadleaf plants/small insects
486.00
553.51
315.63
Fruits/pods/seeds/large insects
54.00
61.50
35.07
Blueberry and conifer release (3 lb/A)
70
-------
Short grass
720.001
820.01
467.60
Tall grass
330.00
375.84
214.32
Broadleaf plants/small insects
405.00
461.25
263.03
Fruits/pods/seeds/large insects
45.00
51.25
29.23
Christmas Tree (2 lb/A)
Short grass
480.00
546.67
311.74
Tall grass
220.00
250.56
142.88
Broadleaf plants/small insects
270.00
307.50
175.35
Fruits/pods/seeds/large insects
30.00
34.17
19.48
Alfalfa 1.5 lb ai/A
Short grass
360.00
410.00
233.80
Tall grass
165.00
187.92
107.16
Broadleaf plants/small insects
202.50
230.63
131.51
Fruits/pods/seeds/large insects
22.50
25.63
14.61
Pasture (1.1 lb/A)
Short grass
264.00
300.67
171.45
Tall grass
121.00
137.81
78.58
Broadleaf plants/small insects
148.50
169.13
96.44
Fruits/pods/seeds/large insects
16.50
18.79
10.72
TiihlcJ.'J TUI-'.X Miiimiiiil Dose I'.sliniiilcs
1-eeiliiiii ( iileiion
Chronic l)ic(;ir\-
Doso-I);isod I'.r.Cs (ill
hiisod r.r.Cs
(inii/kii-l'ood item
Sniiill
(15 »)
Medium
(35 »)
Noncrop (airports)(8 lb/A)
Short grass
1920.00
1830.57
1265.17
Tall grass
880.00
839.01
579.87
Broadleaf plants/small insects
1080.00
1029.70
711.66
Fruits/pods/seeds/large insects
120.00
114.41
79.07
Granivore
25.42
17.57
Pineapple (3.6 lb/A)
Short grass
864.00
823.76
569.33
Tall grass
396.00
377.56
260.94
Broadleaf plants/small insects
486.00
463.36
320.25
Fruits/pods/seeds/large insects
54.00
51.48
35.58
Granivore
11.44
7.91
Blueberry and conifer release (3 lb/A)
Short grass
720.00
686.46
474.44
Tall grass
330.00
314.63
217.45
Broadleaf plants/small insects
405.00
386.14
266.87
Fruits/pods/seeds/large insects
45.00
42.90
29.65
Granivore
9.53
6.59
Christmas Tree (2 lb/A)
Short grass
480.00
457.64
316.29
Tall grass
220.00
209.75
144.97
Broadleaf plants/small insects
270.00
257.42
177.91
Fruits/pods/seeds/large insects
30.00
28.60
19.77
Granivore
6.36
4.39
Alfalfa 1.5 lb ai/A
Short grass
360.00
343.23
237.22
Tall grass
165.00
157.31
108.73
Broadleaf plants/small insects
202.50
193.07
133.44
71
-------
Fruits/pods/seeds/large insects
22.50
21.45
14.83
Granivore
4.77
3.29
Pasture (1.1 lb/A)
Short grass
264.00
251.70
173.96
Tall grass
121.00
115.36
79.73
Broadleaf plants/small insects
148.50
141.58
97.85
Fruits/pods/seeds/large insects
16.50
15.73
10.87
Granivore
3.50
2.42
Granular Applications
Terrestrial exposures from granular applications (mg ai/square foot) for the CRLF are
also estimated using the T-REX Version 1.3.1. Broadcast treatment of hexazinone-
treated granules assumes that 100% of the granules are unincorporated on the ground.
Risk to terrestrial animals from ingesting granules is based on LD50/ft2 values. Although
the habitat of the CRLF and its prey items are not limited to a square foot, there is
presumably a direct correlation between the concentration of a pesticide in the
environment (mg/ft2) and the chance that an animal will be exposed to a concentration
that could adversely affect its survival. Further description of the mg/ft2 index is
provided in U.S. EPA (1992 and 2004).
In order to derive an estimate of the granular exposure per square foot, the granular
application rates for hexazinone were converted from lb ai/A to mg/ft2 in Table 3.10
using the following equation: mg/ft2 EEC = (application rate in lb ai/A x 453,590 mg/lb)
/ 4,560 ft2/A). The LD50/ft2 values are calculated using the avian toxicity value (adjusted
LD50 of the assessed animal and its weight classes) as a surrogate for the terrestrial-phase
CRLF and the EEC (mg ai/ft2).
Table 3.10 Terrestrial KIX s lor (iranular I ses of llexazione
I SO
Application Ksili*
(II)
-------
insectivore mammals, and small terrestrial phase amphibians (note the "N. A." at the
small frog location within the last three columns of Table 3.11).
Because it is the small herbivore mammal food item that is estimated to have the highest
concentration and only the medium and large CRLF ingest this food item, it is the
medium CRLF (with their higher metabolic rate than the large CRLF) that receive the
highest doses. Dose based estimates for individual exposure scenarios vary from 0.64 to
41.96 mg/kg-bw for small frogs, 0.20to 1196.78 mg/kg-bw for medium frogs, and 0.130
to 186.05 mg/kg-bw for large frogs.
Iiihlc3.ll
. Assessment of Direct LITccts oil California Kcd-lc
gged Lrog (CKI.L) I sing Dosc-ISascd llstimalcd
l-'n\ironmcntal Concentrations (LLCs) of llcxa/inonc liascd on (lie T-llcrps Model lor Sniiill (1.4 g).
Medium I3"7 g).
iiml Large
<23Xg)CKI.I.
Maximum
Dosc-hascd LLCs (ing/l
;g-h\\) lor Small. Medium, and Large ( Kl.l-'
Application
(Small / Medium / l.ar*.
.c)
Kales'
l-'ruit/ Pods/
Small
Small
Small
(II) a.i./A)
liroadlcaf Plants/
Seeds/
llcrl>i\orc
lnsccli\orc
Terrestrial Phase
I sc
Small Insects
Large Insects
Mammals
Mammals
Amphibian
Agricultural Uses
Noncrop:
airport,
8
41.96/41.24/27.03
4.66/4.58/3.00
N.A./ 1196.78/186.05
N.A. / 74.80/ 11.63
N.A. / 1.43/0.94
AgROW
Pineapple
3.6
18.88/ 18.56/ 12.16
2.10/2.06/1.35
N.A. /538.55 / 83.72
N.A. / 33.66/5.23
N.A. /0.64 / 0.42
Blueberry
and
conifer
3
15.73 / 15.46/ 10.14
1.75/1.72/ 1.13
N.A. / 448.79/69.77
N.A. / 28.05/4.36
N.A. / 0.54/0.35
release
Christmas
10.49/10.31/6.76
1.17/1.15/0.75
N.A. / 299.20/46.51
N.A. / 18.70/2.91
N.A. / 0.36/0.23
Tree
2
Alfalfa
1.5
7.87/7.73 /5.07
0.87/0.86/0.56
N.A. / 224.40/34.89
N.A. / 14.02/2.18
N.A. / 0.27/0.18
Pasture
1.1
5.77/5.67/3.72
0.64/0.63/0.41
N.A. / 164.56/25.58
N.A. / 10.28/1.60
N.A./0.20/0.13
73
-------
Table 3.12
Assessment of Direct I'.ITecls
oil C alifornia Red-legged l-'rog (CKI.I-) I sing Chronic Dose-ISased l-lslimalcd
l.n\ir
onmcnlal Conccnlralions (l-'.l-'.Cs) of llcxa/inonc liascd on (lie T-llcrps Model
Maximum
Chronic Diclan-bascd l-'.l-'.Cs (nig/kg)
Application
Kales'
IJroadleaf
l- ruil/ Pods/
Small
Small
Small
(II) a.i./A)
Planls/
Seeds/
llerhi\ore
lnsccli\orc
Terrestrial Phase
l sc
Small Insects
Large In see Is
Mammals
Mammals
Amphibian
Agricultural Uses
Noncrop:
airport,
8
1080.00
120.00
1265.17
79.07
37.49
AgROW
Pineapple
3.6
486.00
54.00
569.33
35.58
16.87
Blueberry
and
conifer
3
405.00
45.00
474.44
29.65
14.06
release
Christmas
Tree
2
270.00
30.00
316.29
19.77
9.37
Alfalfa
1.5
202.50
22.50
237.22
14.83
7.03
Pasture
1.1
148.50
16.50
173.96
10.87
5.15
Chronic dietary EECS are estimated using the T-Herps model to assess direct effects for the
CRLF. Table 3.12 depicts the highest EECs for small herbivore mammals ranging from 173.96
to 1265.17 mg/kg. EECs for small insects ranged from 148.50 to 1080.0 mg/kg with EECs for
large insect ranging from 16.50 to 120.00 mg/kg and EECs for small insectivore mammals
ranging from 10.87 to 79.07. The lowest exposure for small amphibian resulted in EECs ranging
from 5.15 to 37.49 mg/kg.
3.3.2 Terrestrial Invertebrate Exposure
Exposure of terrestrial invertebrates was estimated using the dietary-based EECs
produced by T-REX for the two insect categories, small and large (Table 3.13). The
value produced by T-REX, mg a.i./kg insect, is equivalent to ng a.i./g insect. The
hexazinone residue for a bee (|ig a.i./bee) using an adult honey bee weight of 0.128 g and
multiplying it by the assumed weight of a honey bee (0.128 g) to establish a dose per bee.
This method assumes that contact is the relevant route of exposure, rather than ingestion.
This method of estimation is believed to be adequate for hexazinone.
Table 3.13 Terrestrial Invertebrate Estimated Dietary-Based Environmental Concentrations
(EECs)
Application Rate
(lb ai/A)
Noncrop 8 lb/A
Insect Size Category
EECs
(mg ai/kg insect)
Small insects
Large insects
1080.00
120.00
Large insects
Conifer Release 3 lb/A
Small insects
405.00
Large insects
Small insects
45.00
405.00
Blueberry 3 lb/A
74
-------
Large insects
45.00
Christmas Tree 2 lb/A
Small insects
270.00
Large insects
30.00
Alfalfa 1.5 lb ai/A
Small insects
202.50
Large insects
22.50
Pasture 1.1 lb/A
Small insects
148.50
Large insects
16.50
3.4 Terrestrial Plant Exposure Assessment
Currently, EFED uses the TerrPlant Model (Version 1.2.2) to evaluate exposure of
terrestrial plants to pesticides applied on agricultural fields. TerrPlant estimates a runoff
component based on application rate and solubility of the compound, and a spray drift
component based on application method. Because non-target plants are of concern for
herbicide uses, EFED also used two spray drift models, AgDrift and AgDisp, to more
fully evaluate spray drift effects. Screening level estimates from TerrPlant are presented
here in the exposure section and in the risk estimation section. AgDrift is used in the risk
characterization section to more fully evaluate potential off-site effects. AgDisp has an
additional module which mathematically estimates drift beyond the range of AgDrift,
which is based on empirical data, and has only been parameterized to approximately 950
ft from the application site. In general, spray drift is more dependent on the atmospheric
physics of droplet transport than on the physico-chemical properties of the pesticide and
carrier liquid.
3.4.1 TerrPlant
TerrPlant has two basic exposure scenarios. The first is an adjacent upland area, which is
exposed to the pesticide via drift and dissolved concentrations in sheet runoff. The second
is an adjacent semi-aquatic (wetland) area, which is exposed to the pesticide via drift and
to dissolved concentrations in channelized runoff. Drift is calculated as a percentage of
the application rate (1% for ground, and 5% for aerial, airblast, or spray chemigation) and
is not adjusted for distance from the application site. The amount of dissolved pesticide in
the runoff component is estimated based on solubility of the active ingredient. TerrPlant
estimates are shown in Table 3.14. Total loading in upland areas (runoff plus drift)
ranged from 0.007 lb ai/A (pasture, ground boom) to 0.84 lb ai/A (noncrop, aerial). Total
loading in wetland areas (runoff plus drift) ranged from 0.5 lb ai/A (pasture, ground
boom) to 6 lb ai/A (non-crop/non-agricultural ROW, granular). Pesticide loading to the
different areas is affected by application rate and depth of incorporation. Concentrations
of hexazinone in the runoff are more important in the wetland than for the upland. Thus,
the specific crops used for the bounding estimates may not be the same. Based on the
TerrPlant model, spray drift to either a wetland or an upland area ranged from 0 lb ai/A
(non-crop/nonagricultural ROW, site preparartion and rangeland, granular) to 0.4 lb/A
75
-------
(noncrop, aerial). In this model, spray drift is strictly a function of application rate and
method (ground vs. aerial). Loading estimates are presented in Table 3.14.
Tiil>lc3.l4 1 crivslriiil Phinl l.xnosurc ( IcrrPhiiH)
Crop iind Application K;i(o (II) sii/A)
l oliil l.o;i(lin;i (RuiioIT+l)ril'n l.l.(
(II)
-------
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 (October 2007) as well as ECOTOX information obtained on
October 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 is dependent on whether the information is
relevant to the assessment endpoints {i.e., maintenance of CRLF survival, reproduction,
and growth) identified in Section 2.8. For example, endpoints such as behavior
modifications are likely to be qualitatively evaluated, because quantitative relationships
between modifications and reduction in species survival, reproduction, and/or growth are
not generally available.
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 and/or not appropriate for use in this assessment) are
included in AppendixG. Appendix G 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.
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 hexazinone. A summary of the available aquatic and
77
-------
terrestrial ecotoxicity information, and the incident information for hexazinone are
provided in Sections 4.1 through 4.4, respectively.
4.1 Toxicity of Hexazinone to Aquatic Organisms
Toxicity to fish and aquatic invertebrates is categorized using the system shown in Table
4.1 (U.S.EPA, 2004). Toxicity categories for plants have not been defined.
Table 4.1 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
Table 4.2 summarizes the most sensitive aquatic toxicity endpoints for the CRLF, based
on an evaluation of both the submitted studies and the open literature, as previously
discussed. A brief summary of submitted data considered relevant to this ecological risk
assessment for the CRLF is presented below.
Tabic 4.2 Freshwater Aquatic Toxicitv Profile for Hcxa/Jnonc
Assessment
Endpoint
Species
Toxicity Value Used in
Risk Assessment
MRID
Comment
Acute Direct
Toxicity to
Aquatic-Phase
CRLF
Fathead
Minnow
Rainbow Trout
Bluegill sunfish
Bluegill sunfish
96-hr LCS0 = 274 mg/L
96-hr LC50 >320 mg/L
96-hr LC50 >370 mg/L
96-hr LC50 = 505 mg/L
00104980
00104980
00104980
00076959
TGAI is
Practically
nontoxic
Rainbow Trout
Bluegill Sunfish
96-hr LC50 >1000 mg/L
96-hr LC50 > 585.6 mg/L
41235002
41235001
25% TEP is
Practically
nontoxic
Chronic Direct
Toxicity to
Aquatic-Phase
CRLF
Fathead minnow
Estimated chronic
NOAEL = 17 ppm
41406001
Endpoints were
juvenile survival
(day 39), length
and weight.
Indirect Toxicity
to Aquatic-Phase
CRLF via Acute
Toxicity to
Freshwater
Invertebrates (i.e.
prey items)
Daphnia magna
48-hr ECS0 = 151.6 mg/L
00116269
TGAI is practically
nontoxic to
freshwater
invertebrates.
Daphnia magna
48-hr EC50 = 339.9 mg/L
41235003
25% TEP is
practically
nontoxic to
freshwater
invertebrates.
78
-------
Tabic 4.2 Freshwater Aquatic Toxicitv Profile for Hcxa/Jnonc
Assessment
Endpoint
Species
Toxicity Value Used in
Risk Assessment
MRID
Comment
Indirect Toxicity
to Aquatic-Phase
CRLF via
Chronic Toxicity
to Freshwater
Invertebrates (i.e.
prey items)
Daphnia magna
NOAEC = 20 mg/L
00078041
Reproduction is
the endpoint.
Classified as
supplemental due
to dilution water
and dilution
preparation not
reported.
Daphnia magna
NOAEC = 29 mg/L
LOAEC = 81 mg/L
41406002
Classified
supplemental due
to no information
on dry weight of
first generation
reported. Endpoint
was daphnid
survival.
Indirect Toxicity
to Aquatic-Phase
CRLF via Acute
Toxicity to
Vascular Aquatic
Plants
Lemna gibba
EC50 = 0.0374 mg/L ai
43225101
Endpoint is frond
count. Study is
classified as
acceptable.
Indirect Toxicity
to Aquatic-Phase
CRLF via Acute
Toxicity to Non-
vascular Aquatic
Plants
Selenastrum
capricornutum
120-hr ECS0 =7 ng/L
NOAEC = 4.0 jig/L
41287001
Study is classified
as acceptable.
Results based on
nominal
concentrations.
Anabaena flos-
aquae
EC50=210 (ig/L
43302701
Study is classified
as acceptable.
Navicula
pelliculosa
EC50=12 ng/L
43302701
Study is classified
as acceptable for a
freshwater diatom.
79
-------
Tabic 4.2 Freshwater Aquatic Toxicitv Profile for Hcxa/Jnonc
Assessment
Species
Toxicitv Value Used in
MRID
Comment
Endpoint
Risk Assessment
Values in bold were used in the assessment.
4.1.1 Toxicity to Freshwater Fish
A comprehensive search of the open literature provided no toxicity information on lethal
or sub lethal effects of hexazinone to amphibians. Given that no hexazinone 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 hexazinone to the CRLF. Direct effects to
freshwater fish resulting from exposure to hexazinone couldindirectly affect the CRLF
via reduction in available food. As discussed in Section 2.5.3, over 50% of the prey mass
of the CRLF may consist of vertebrates such as mice, frogs and fish (Hayes and Tennant,
1985).
A summary of acute and chronic freshwater fish data is provided below in Sections
4.1.1.1 through 4.1.1.2.
4.1.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies
With respect to technical grade hexazinone, the reported acute 96-hour LC50 values were
>320 mg/1 for rainbow trout (MRID 00104980), and 274 mg/1 for Fathead minnow
(MRID 00104980). Two studies were available for bluegill sunfish, 96-hour LC50 >370
mg/L and 96-hour LC50 = 505 mg/L (MRID 00104980 and 00076959). The results of
these tests indicate that hexazinone is practically nontoxic to fish. The fathead minnow
LC50 = 274 mg/1 will be used to assess direct and indirect (dietary) effects for the CRLF.
4.1.1.2 Freshwater Fish: Chronic Exposure (Growth/Reproduction)
Studies
Chronic freshwater fish toxicity studies were used to assess potential direct effects via
growth and reproduction to the aquatic-phase of the CRLF. A fish life cycle test with
fathead minnow was submitted for hexazinone (MRID 41406001). A chronic
NOAEC=17 mg/L was reported for juvenile survival (day 39), length and weight. This
value will be used in this assessment.
4.1.2 Toxicity to Freshwater Invertebrates
Freshwater aquatic invertebrate toxicity data were used to assess potential indirect effects
of hexazinone to the CRLF. Direct effects to freshwater invertebrates resulting from
exposure to hexazinone 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 sow bugs, larval alderflies and water striders.
80
-------
A summary of acute and chronic freshwater invertebrate data is provided below in
Section 4.1.2.1 through 4.1.2.2.
4.1.2.1 Freshwater Invertebrates: Acute Exposure Studies
Acute toxicity data for hexazinone are available for the preferred test species, Daphnia
magna. A 48-hour EC5o=151.6 mg/1 (MRID 00116269) indicates that hexazinone is
practically nontoxic to aquatic invertebrates. This value will be used in this assessment.
4.1.2.2 Freshwater Invertebrates: Chronic Exposure Studies
Chronic toxicity data are available for daphnia magna. Two supplemental studies for
daphnia resulted in NOEACs of 20 mg/L for reproduction (MRID 00078041) and 29 mg
a.i./L for daphnid survival (MRID 41406002). The reproductive NOEAC will be used in
this assessment as the most sensitive endpoint.
4.1.3 Toxicity to Aquatic Plants
Aquatic plant toxicity studies were used as one of the measures of effect to evaluate
whether hexazinone 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.
An acceptable study is available for vascular aquatic plants using Lemna gibba with
frond count as an endpoint. The ECso=0.0374 mg/L (MRID 43225101) was used in this
assessment.
Three studies for nonvascular aquatic plants were available. The acceptable nonvascular
aquatic plant study with Anabaena flos-aquae resulted in an ECso=210 |ig/L (MRID
43302701). The acceptable study with the freshwater diatom Naviculapelliculosa
resulted in an ECso=12 |ig/L (MRID 43302701). An acceptable study is available for
nonvascular aquatic plants using Selenastrum capricornutum. The ECso=7.0 |ig/L with a
NOAEC=4.0 |ig/L (MRID 41287001) were based on nominal concentrations. The most
sensitive value for Selenastrum capricornutum will be used to determine an LAA/NLAA
effect, while the NOAEC will be used in the action area map.
4.2 Toxicity of Hexazinone to Terrestrial Organisms
Acute toxicity to terrestrial animals is categorized using the classification system shown
in Table 4.3 (U.S. EPA, 2004). Toxicity categories for terrestrial plants have not been
defined.
Table 4.3 Categories of Acute Toxicity lor Avian and Mammalian Studies
Toxicity Csiicgon
Ol'ill l.lhn
Dicliin l.(
Very highly toxic
<10 mg/kg
< 50 ppm
Highly toxic
10 - 50 mg/kg
50 - 500 ppm
81
-------
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
Table 4.4 summarizes the most sensitive terrestrial toxicity endpoints for the CRLF,
based on evaluation of both 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.
Tabic 4.4 Terrestrial Toxicitv Profile for Hcxa/Jnonc
Assessment
Endpoint
Species
Toxicity Value Used in
Risk Assessment
MRU), Author and Date
Comment
Acute Direct
Toxicity to
T errestrial-Phase
CRLF (LD50)
Mallard duck
acute oral
LD50 = 2,258 mg ai/kg-bw
00073988
Hexazinone is
practically
nontoxic to birds.
Acute Direct
Toxicity to
T errestrial-Phase
CRLF (LC50)
Mallard duck
Bobwhite quail
Bobwhite quail
LC50 >5,000 mg/kg
00104981
00072663
00107878
All studies were
classified as
acceptable.
Hexazinone is
practically
nontoxic to birds
Chronic Direct
Toxicity to
T errestrial-Phase
CRLF
Bobwhite quail
NOAEC = 300 mg/kg
41764901
NOAEC was
based on effects
to the 14 day
survivors.
Mallard Duck
NOAEC > 1000 mg/kg
41764902
No observable
treatment effects.
Indirect Toxicity
to Terrestrial-
Phase CRLF (via
acute toxicity to
mammalian prey
items)
Rat acute oral/ rat
LD50= 5 3 0mg/Kg bw
LD50 = 1200 mg ai/kg bw
(Kennedy 1984)
41235004
Indirect Toxicity
to Terrestrial-
Phase CRLF (via
chronic toxicity
to mammalian
prey items)
Rat reproduction
Chronic NOAEL = 200
mg/kg bw (2-generation
reproduction study)
LOAEC=2000 mg/kg
42066501
98% a.i in the diet.
Endpoints are
systemic and
reproductive
toxicity.
Indirect Toxicity
to Terrestrial-
Phase CRLF (via
acute toxicity to
terrestrial
invertebrate prey
items)
Honey bee
Acute contact LD50 >100
ug/bee
41216502
Indirect Toxicity
to Terrestrial- and
Aquatic-Phase
CRLF (via
toxicity to
terrestrial plants)
Tomato (dicot)
Seedling emergence 21-d
EC25 = 0.0064 lbs ai/A.
NOAEC = 0.00348 lb/A
43162501
Based on weight.
Sorghum
(monocot)
Seedling emergence 21-d
EC25 = 0.019 lbs ai/A.
NOAEC = 0.0139
43162501
Based on weight.
82
-------
Tabic 4.4 Terrestrial Toxicitv Profile for Hcxa/Jnonc
Assessment
Endpoint
Species
Toxicity Value Used in
Risk Assessment
MRID, Author and Date
Comment
Rape (dicot)
Vegetative Vigor 21-d EC25
= 0.011 lbs ai/A. NOAEC =
0.0071 lb/A
43162501
Based on weight.
Wheat (monocot)
Vegetative Vigor 21-d EC25
= 0.020 lbs ai/A. NOAEC=
0.010 lb/A
43162501
Based on total
weight
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 is not available (U.S.EPA, 2004).
No terrestrial-phase amphibian data are available for hexazinone, therefore acute and
chronic avian toxicity data are used to assess the potential direct effects of hexazinone to
terrestrial-phase CRLFs.
4.2.1.1 Birds: Acute Exposure (Mortality) Studies
Acute oral toxicity data are available for quail (LD50= 2,258 mg/kg MRID 00073988)
using 98% a.i. The results indicate that hexazinone is practically nontoxic to birds. This
result will be used in this assessment.
Dietary acute toxicity studies resulted in an LC50 > 5,000 mg/kg for mallard duck
(MRID 0010498), and bobwhite quail (MRID 00107878 and MRID 00072663)
indicating that hexazinone is practically nontoxic to birds. These studies are not used
quantitatively in this assessment because no mortality was observed at the highest test
concentration.
4.2.1.2 Birds: Chronic Exposure (Growth, Reproduction) Studies
Chronic reproductive toxicity data is available for the bobwhite quail (NOAEC = 300
mg/kg MRID 417649-01). The endpoint was a statistically significant increase in food
consumption for survivors from day 14 through test termination. This endpoint will be
used in this assessment.
Chronic reproductive toxicity data is available for the mallard duck (NOAEC >1,000
mg/kg, MRID 41764902). However, this is not the most sensitive endpoint reported,
therefore this value will not be used in the assessment.
4.2.2 Toxicity to Mammals
4.2.2.1 Mammals: Acute Exposure (Mortality) Studies
A registrant submitted rat acute oral (LD50=1,200 mg/kg, MRID 41235004) was reported.
The results indicate that hexazinone is practically nontoxic to mammals.
83
-------
There is an open literature endpoint that is more sensitive than the registrant submitted
data. An acute oral toxicity study is available for rat LD50 = 5 3 0 mg/kg (Kennedy 1984).
The results indicate that hexazinone is practically nontoxic to mammals. This result will
be used in this assessment.
4.2.2.2 Mammals: Chronic (Growth, Reproduction) Studies
An acceptable two-generation rat study (MRID 42066501) resulted in a systemic and
reproductive NOAC=200 mg/kg. This value will be used in this assessment to calculate
RQs for dietary effects for the CRLF.
4.2.3 Toxicity to Terrestrial Invertebrates
Terrestrial invertebrate toxicity data are used to assess potential indirect effects of
hexazinone to the terrestrial-phase CRLF. Effects to terrestrial invertebrates resulting
from exposure to hexazinone could also indirectly affect the CRLF via reduction in
available food.
An acceptable honey bee study (LD50 > 100 |ig/bee, MRID 41216502) indicates that
hexazinone is practically nontoxic to terrestrial invertebrates. This value will be used
qualitatively in the risk description.
4.2.4 Toxicity to Terrestrial Plants
Terrestrial plant toxicity data are used to evaluate the potential for hexazinone 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.
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 hexazinone, is largely unknown. Homogenous
84
-------
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 results of the Tier II seedling emergence and vegetative vigor toxicity tests on non-
target plants are summarized in Table 4.4.
Toxicity data are available for seedling emergence and vegetative vigor for terrestrial
plant exposure to hexazinone. The results from the seedling emergence test study
resulted in an EC25 of 0.0064 lbs/A for tomato. The monocot EC25 result for sorghum was
0.019, lbs/A.
The vegetative vigor EC25 for dicots was 0.011 for rape. The EC25 for emergence for
monocots was 0.020 for wheat. These values will be used in this assessment.
4.3 Incident Database Review
A review of the EIIS database for ecological incidents involving hexazinone was
completed on November 8, 2007. The results of this review for terrestrial, plant, and
aquatic incidents are discussed below in Sections 4.5.1 through 4.5.3, respectively.
4.3.1 Terrestrial Animal Incidents
No terrestrial animal incidents were reported for hexazinone.
4.3.2 Plant Incidents
Nine hexazinone incidents have been reported for terrestrial plants. One incident,
1000548-001 reporting non-target plant exposure, was classified as highly probable.
Velpar ULW, a product with hexazinone, was applied using an aerial application method
on a forest site in Florida. No application rate or total magnitude was reported.
Five reports were classified as possible.
1016312-001: Westar and Velpar, products containing hexazinone, were applied on a
forest site in Oregon (2005). Aerial and ground methods were used to apply 2 lbs/A with
a total magnitude of 300 acres. The caller reported the appearance of reddening on
Ponderosa Pine needle growth. Damage could be due to the application of multiple
products.
1016680-001: Velpar, a product containing hexazinone, was applied on a right-of-way
site in Oregon (2005). Thirteen acres of vineyards were damaged through spray in a
ground application. No application rate was reported. Damage could be due to the
application of multiple products.
85
-------
1000611-001: Velpar L, a product containing hexazinone, was applied in Georgia (1993).
No report of use site, total magnitude, or application rate was provided. The report cited
foliar damage (mottling and yellow-spotting) to the trees. Grasses were not affected.
1014407-036: A product containing hexazinone was applied on an alfalfa site in
Washington (1994). No report of total magnitude, or application rate was provided. The
damage to yield was to be assessed after the crop was harvested.
1015265-001: Outstar, a product containing hexazinone, was applied at a forest product
site in Texas (2004) The loss of sixty-five percent of 129 ares of loblolly pine seedlings
was reported, but. no application rate or method was provided. Damage could be due to
the application of multiple products.
Two incidents reported were classified as misuse, 1005822-001 reporting damage to flora
and 1007984-008 reporting damage to a tree. A report of trees dying, 10012233-001, was
classified as unlikely. None of these incidents were used in this risk assessment.
4.3.3 Aquatic Animal Incidents
No aquatic animal incidents were reported for hexazinone.
5. 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 hexazinone
in CA. The risk characterization provides an estimation (Section 5.1) and a description
(Section 5.2) of the likelihood of adverse effects; articulates risk assessment assumptions,
limitations, and uncertainties; and synthesizes an overall conclusion regarding the
likelihood of adverse effects to the CRLF or its designated critical habitat (i.e., "no
effect," "likely to adversely affect," or "may affect, but not likely to adversely affect").
5.1 Risk Estimation
Risk is estimated by calculating the ratio of exposure to toxicity. This ratio is the risk
quotient (RQ), which is then compared to pre-established acute and chronic levels of
concern (LOCs) for each category evaluated (Appendix B). 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 hexazinone usage
scenarios summarized in Table 3.3 and the appropriate aquatic toxicity endpoint from
Table 4.1. Risks to the terrestrial-phase CRLF and its prey (e.g. terrestrial insects, small
86
-------
mammals and terrestrial-phase frogs) are estimated based on exposures resulting from
applications of hexazinone (Tables 3.5 through 3.6) and the appropriate toxicity
endpoint from Table 4.3. 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
hexazinone use within the action area.
5.1.1 5.1.1 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
indirect effects to aquatic or terrestrial animals that may 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 hexazinone on par with the acute toxicity
endpoint selected for RQ calculation. To accomplish this interpretation, the Agency uses
the slope of the dose response relationship available from the toxicity study used to
establish the acute toxicity measures of effect for each taxonomic group that is relevant to
this assessment. The individual effects probability associated with the acute RQ is based
on the mean estimate of the slope and an assumption of a probit dose response
relationship. In addition to a single effects probability estimate based on the mean, upper
and lower estimates of the effects probability are also provided to account for variance in
the slope, if available.
Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1
(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP,
Environmental Fate and Effects Division (June 22, 2004). The model allows for such
calculations by entering the mean slope estimate (and the 95% confidence bounds of that
estimate) as the slope parameter for the spreadsheet. In addition, the acute RQ is entered
as the desired threshold. Probit analyses will be provided for direct and indirect effects
(section 5.1). Calculations from probit analyses are reviewed under direct and indirect
effects sections.
5.1.2 Exposures in the Aquatic Habitat
The highest screening-level aquatic EEC (based on non-granular use of hexazinone on
non-agricultural Right-Of-Way at 12 lbs ai/A was initially used to derive risk quotients.
In cases where LOCs were not exceeded based on this use pattern, additional RQs were
not derived because it was assumed that RQs for lower EECs would also not exceed
LOCs. However, if LOCs were exceeded based on the highest EECs, use-specific RQs
were also derived.
5.1.2.1 Direct Effects to Aquatic-Phase CRLF
87
-------
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. As shown in Table 5.1, acute and chronic RQs for the highest EEC for
applications of hexazinone are well below their respective LOCs; therefore, direct effects
associated with acute and chronic exposure to hexazinone are not expected to occur for
the aquatic-phase CRLF. These RQs are further characterized in Section 5.2.1.1. The
highest screening-level EEC (non-crop/non-agricultural ROW at 12 lbs ai/A) was initially
used to derive risk quotients. LOCs were not exceeded based on this use pattern,
therefore additional RQs were not derived because it was assumed that RQs for lower
EECs would also not exceed LOCs. A preliminary no effect determination for acute and
chronic exposure for the aquatic-phase CRLF is based no LOC exceedence for any
scenario.
Table 5.1 Summary of Direct K
Ted UQs for (he Aquatic-phase ( Kl.l'
Direct 1. IToc Is
in cm.P'
Siimiiiiile
Species
Toxicity
Yiiluc
(HS/L)
r.r.C ipii/l.)
HQ
IOC
l-Aceeclence
iiml Risk
Inlcrp reunion
Acute Direct
Toxicity
Fathead
minnow
LC50 =
274,000
Peak: 156.6
0.0006
Nob
Chronic Direct
Toxicity
NOAEC =
17,000
60 day 136.6
0.009
2
O
0
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 RQ < acute endangered species LOC of 0.05.
0 RQ < chronic LOC of 1.0.
5.1.2.2 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 hexazinone 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. As shown in Table 5.2, RQs
exceed the acute risk LOC (RQ >1.0) for aquatic plants for applications of hexazinone to
non-crop (12 lb ai/A), noncrop (agricultural ROW, and forest site preparation (5.0 lbs/A),
conifer release (3 lb ai/A), Christmas trees (2 lbs/A), alfalfa (1.5 lbs/A) and pasture (1.1
lbs/A) with RQ values ranging from 1.52 to 22.37. There is no exceedence for
blueberries (3 lbs/A). The preliminary effects determination is "may affect" based on
indirect effects to aquatic-phase CRLFs due to a reduction in non-vascular aquatic plants
as food items.
88
-------
'I'iihlc 5.2 Siiiiiinsirv of Acute UQs I sod lo Ksliniiile Indirect Kflccts to the CUM'' vi;i
K fleets to \on-Vsisculsir Aqusitic Plnnts (diet ol'CUI.I'" in tsidpolc lile stsige sind
hsihitiil of ;Kiu;itic-i)h;isc CUM' )
I SOS
Application rate (II)
1) are bolded and shaded. RQ = use-specific peak EEC / [lemna EC50=37.4
M-g/L].
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. As shown in Table 5.3 all
acute and chronic RQs are well below their respective LOCs; therefore, indirect effects
associated with acute and chronic exposure to hexazinone are not expected to occur for
the aquatic-phase CRLF. RQs were calculated only for the use that resulted in the
highest EEC (foliar use on non-crop /non-agricultural ROW at 12 lb ai/A) because none
of the acute or chronic LOCs were exceeded. A "no effect" determination for acute and
chronic aquatic invertebrates is based on the highest EECs application rates.
'I'iihie 5.3 Siiiiiinsirv of Acute nnd Chronic UQs I sctl to Kstininte Indirect K fleets lo the
CUM'" vin Direct Kfl'ccts on Aqusitic Invertehrsites ns Dielnrv l-'ood Items (prev of
CUM-" juveniles iind sidults in ii(|iiiitic h;ihitnts)
I ses
Appliciition i ;i(c
(II) pe
Pcidt t:i:(
(fi»/i.)
2l-dsi>
i:i.(
(HSi/l.)
Indirect
1. fleets
Acute UQ
Indirect
1. fleets
( lironic UQ
Non-crop (Non-
agriculture ROW)
12 (granular)
156.6
153.7
0.001
0.005
89
-------
* = LOC exceedences (acute RQ > 0.05; chronic RQ > 1.0) are bolded and shaded. Acute RQ = use-specific
peak EEC / [daphnia 1.52 ppm]. Chronic RQ = use-specific 21-day EEC / [chronic daphnia 20 ppm],
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. Given that acute and chronic RQs for direct toxicity to the CRLF are
less than LOCs, indirect effects based on a reduction of fish and frogs as prey items are
not expected. Therefore, a preliminary "no effect" determination is based on no RQ
exceedence for any LOCs.
5.1.1.3 Indirect Effects to CRLF via Reduction in Habitat and/or Primary Productivity
(Freshwater Aquatic Plants)
Indirect effects to the CRLF via direct toxicity to aquatic plants are estimated using the
most sensitive non-vascular and vascular plant toxicity endpoints. Because there are no
obligate relationships between the CRLF and any aquatic plant species, the most sensitive
EC50 values, rather than NOAEC values, were used to derive RQs. Table 5.4 includes
RQs for vascular plants (RQs for non-vascular plants are presented in Section 5.1.2.1 and
Tables 5.2). RQs for Christmas tree, conifer release, airports, agricultural ROW,
agricultural uncultivated, and non-crop/non-agricultural ROW exceed the LOC for
indirect effects to the CRLF via effects to vascular plants. RQs range from 1.25-4.19 for
effects to vascular plants for granular and liquid applications. RQs for forest site
preparation, blueberry, rangeland, alfalfa and pasture do not exceed the LOC (RQs 0.15-
0.95). In addition to the LOC exceedence for vascular plants LOCs are exceeded for
non-vascular aquatic plants for all applications of hexazinone as previously discussed in
Section 5.1.2.2 and summarized in Table 5.2. A "may affect" determination for indirect
effects to CRLF via reduction in habitat and/or primary production is based on the LOC
exceedence for both non-vascular and vascular aquatic plants.
'I'iihlc 5.4 Summary of Acute UQs I sed lo Kslimale Indirect K ITcd s lo the CUM'' vi;i
KITecls lo Vascular Aquatic Plants (diet of ( KIT in tadpole lile stage and habitat of
aquatic-phase CUM')
I SOS
Application r:ilo (II)
-------
Blueberry
3
5.68
0.15
Rangeland
3
35.51
0.95
Christmas Trees
2
46.59
1.25
Alfalfa
1.5
24.79
0.66
Pasture
1.1
10.63
0.28
a RQs used to estimate indirect effects to the CRLF via toxicity to non-vascular aquatic plants are
summarized in Table 5.2.
* = LOC exceedences (RQ > 1) are bolded and shaded. RQ = use-specific peak EEC / [lemna EC50=37.4
M-g/L].
5.1.3 Exposures in the Terrestrial Habitat
5.1.3.1 Direct Effects to Terrestrial-phase CRLF
As previously discussed in Section 3.3, potential direct effects to terrestrial-phase CRLFs
are based on granular and liquid applications of hexazinone.
Acute Effects
Potential direct acute effects to the terrestrial-phase CRLF are derived by considering
dose- and dietary-based EECs modeled in T-REX for a small bird (20 g) consuming
small invertebrates (Table 5.5) and acute oral and sub acute dietary toxicity endpoints for
avian species. Dietary RQs could not be estimated because no mortality was observed
at the highest tested level of hexazinone (LC50 >5,000 mg/kg-diet, MRIDs 00107878,
001040498 and 00072663).
Potential direct acute effects of non-granular hexazinone applications to terrestrial-phase
CRLF are evaluated by calculating RQs from the most sensitive avian acute oral
LD50=2,258 mg/kg. All non-granular uses exceed endangered species LOCs, with RQs
ranging from alfalfa (0.14 to) 0.76 (Table 5.5) except pasture (0.10). The preliminary
effects determination for direct acute effects to the terrestrial-phase CRLF is "may
effect".
T;il>lc5.5 TcrrcMrhil Direct r.lTccls 10 lIuCRII from llc\;i/inonc r.xposurc
Siiito»;i(c
Species
Toxicity Y;iliic
(nig/kg)
I ses
MX (ppni)
HQ
Bobwhite Quail
LD5o = 2258
Noncrop (8 lb/A)
1537.51
0.76
Pineapple (3.6 lb/A)
553.51
034
Blueberry/Conifer
release (3 lb/A)
461.25
0.28
Christmas Trees
307.50
0.19
91
-------
(2.0 lb/A)
Alfalfa (1.5 lb/A)
230.63
0.14
Pasture
(1.1 lb/A)
169.13
0.10
Chronic Nongranular liquid spray avvlications
As shown in Table 5.6, chronic RQs, which range from 1.35 to 3.6, exceed LOCs for all
non-granular uses of hexazinone. No exceedences resulted for pasture, alfalfa, or
Christmas trees uses, with RQs ranging from 0.50 to 0.90. Therefore, the preliminary
effects determination is "may effect" for direct chronic effects to the terrestrial-phase
CRLF.
Tsihlc 5.6 Siiiiiinsirv of ( hronio UQs- I sod lo Ksliniiilc Direct KITocls lo (lie
I crrcslriiil-phiisc ( KM' (non-«r;mul;ir sipplicnlion)
I SOS
Application r;Ko (II)
iii/A) iiml (\po
Dioliin-hiisod Chronic RQ1
Noncrop: Ag ROW, airport
8
3.0
Pineapple
3.6
1.62
Blueberry/conifer release
(3 lbs/A)
3
1.35
Christmas Tree
2
0.90
Alfalfa
1.5
0.68
Pasture
1.1
0.50
* = LOC exceedences (chronic RQ > 1) are bolded and shaded.
1 Based on bobwhite quail chronic reproduction NOAEC = 300 mg/kg-diet (MRID 417649-01).
Granular applications
The RO for direct effects of granular applications of hexazinone was calculated using the
bird as a surrogate for the terrestrial-phase CRLF. The EEC for the granular application
of 12 lb/A is shown in Table 5.7. Using the avian LD^n/2258 mg/kg) and the EEC
(93.72s) from the LDft2 model, the RO is 0.04. which does not exceed the endangered
species LOC.
EEC/toxicitv value = RO
93.72/2258 = 0.04
92
-------
The highest screening-level EEC (non-crop/non-agricultural ROW at 12 lbs ai/A) was
initially used to derive risk quotients. LOCs were not exceeded based on this use pattern,
therefore additional RQs were not derived because it was assumed that RQs for lower
EECs would also not exceed LOCs.
Table 5.7 Comparison of Granular EECs to Adjusted LD50 Value Used to Estimate
Direct Effects to the Terrestrial-phase CRLF (granular application)
Use
Application Rate
(lb ai/A)
EEC
(mg/ft2)
Adjusted LDS0 Value (mg/kg-bw)1
20 g (juvenile)
lOOg (adult)
Non-crop/NonAg
ROW
12
93.72
1626.73
2070.91
1 Adjusted Avian LD50 = LD50 (AW/TW)(
.15-1)
Based on no LOC exceedence, there is a No Effect determination for acute effects from
granular uses of hexazinone.
Chronic Effects from Granular Applications
Potential direct chronic effects of granular hexazinone applications 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 shown in Table 5.8, chronic RQs, which range from 1.35 to 5.48, exceed LOCs for
modeled granular uses of hexazinone. Therefore, the preliminary effects determination is
"may effect" for direct chronic effects to the terrestrial-phase CRLF.
Table 5.8 Summary of Chronic UQs- I sed to Estimate Direct Effects to the
Terrestrial-phase CUI.E (granular application)
Uses
Application rale (lb
ai/A)
Dielan-based Chronic RO1
Non-crop:Non-agricullural ROW
areas
12
5.4
Forest Site Preparation
5
2.25
Rangcland
3
1.35
93
-------
* = LOC exceedences (chronic RQ > 1) are bolded and shaded.
1 Based on bobwhite quail chronic reproduction NOAEC = 300 mg/kg-diet (MRID 417649-01).
5.1.3.2 Indirect Effects to Terrestrial-Phase CRLF via Reduction in
Prey (mammals, and frogs)
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. The
potential for acute and chronic indirect effects for the terrestrial-phase CRLF via
reduction in small mammals is shown in Table 5.9. All non-granular uses result in RQs
that exceed the acute and chronic LOCs. Chronic dose-based RQs range from 11.45 to
83.32, while dietary based chronic RQs range from 1.32 to 9.60. Acute RQs range from
0.22 to 1.57. Therefore, the preliminary effects determination for indirect effects to
terrestrial-phase CRLFs via reduction in small mammals (exposed to non-granular
applications of hexazinone) as dietary food items is "may affect" for both acute and
chronic exposure for noncrop uses, conifer release, Christmas trees, pineapple and
blueberry. There were chronic LOC exceedences for alfalfa and pasture, but not acute
exceedences.
Table 5.9 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 (non-granular application)
Use
(Application Rate)
Chronic RC
)
Acute RQ
Dosc-bascd Chronic RQ1
Dictarv-bascd
Chronic RQ2
Dosc-bascd Acute RQ3
Noncrop: Agricultural ROW.
Agricultural uncultivated,
airport (8 lbs/A)
83.32
9.60
1.57
Blueberry. Rangcland. conifer
release
(3 lbs/A)
31.23
3.60
0.59
Christmas Trees
(2 lbs/A)
20.82
2.40
0.39
Alfalfa (1.5 lb/A)
15.62
1.80
0.29
Pasture (1.125 lbs/A)
11.45
1.32
0.22
* = LOC exceedences (acute RQ > 0.1 and chronic RQ > 1) are bolded and shaded.
1 Based on dose-based EEC and Hexazinone rat NOAEL =10 mg/kg-bw.
2 Based on dietary-based EEC and Hexazinone rat NOAEC = 200 mg/kg-diet.
3 Based on dose-based EEC and Hexazinone rat acute oral LD50 = 5 30 mg/kg-bw.
94
-------
Frogs
An additional prey item of the adult terrestrial-phase CRLF is other species of frogs. In
order to assess risks to these organisms, dietary-based and dose-based exposures modeled
in T-REX for a small bird (20g) consuming small invertebrates are used. The RQs from
the T-REX model are discussed presented in section 5.1.2.1, Therefore the preliminary
effects determination for indirect effects to terrestrial-phase CRLFs via reduction in small
amphibians (exposed to non-granular applications of hexazinone as dietary food items) is
"may affect".
5.1.3.3 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. Based on the results of the submitted terrestrial
plant toxicity tests, it appears that dicot plants are more sensitive in the e seedling
emergence test than the vegetative vigor test. However, all tested plants, with the
exception of cucumber (invalid), exhibited adverse effects in both the seedling emergence
and vegetative vigor test, following exposure to hexazinone. The results of these tests
indicate that a variety of terrestrial plants that may inhabit riparian and upland zones may
be sensitive to hexazinone exposure.
For monocot and dicot plants inhabiting dry and semi-aquatic areas, the LOC (RQ > 1.0)
is exceeded for exposures resulting from applications of all non-granular and granular
uses of hexazinone (Tables 5.10 and 5.11). Dry area RQs range from 3.47 to 31.58 and
semi-aquatic area RQs from 29.53-315.79 for monocots. Dry area RQs range from 10.31
to 93.75 and semi-aquatic areas RQs from 87.66 to 937.5 for dicots. In addition, spray
drift RQs exceed LOCs for all non-granular uses of hexazinone for dicot plants. Spray
drift RQs exceed LOCs for all monocot plants except for pasture. For both monocots and
dicots, spray draft does not exceed for non-crop/non-agricultural ROW, forest site
preparation and rangeland granular applications. The preliminary effects determination
for indirect effects to terrestrial- and aquatic-phase CRLFs via reduction in the terrestrial
plant community is "may affect".
Table 5.10 UQs- for Monocots Inhabiting l)rv and Semi-Aquatic Areas Kxposcd to Hexazinone via
UiinolTand Drift
I SO
Application
I'illO
I Ills ii.i./A)
Application
method
Drill
Yiiluc
rvi.i
Spr;i\ drill
RQ
l)r\ iiivii
K()
Scmi-iupiiilic
iiivii uy
Non-crop/Non-
agricultural ROW
12
Granular Spray
<0.1
31.58
315.79
Agricultural
8
Spray
0.05
21.05
42.11
231.58
95
-------
uncultivated, Airports,
Sewage
Forest Site Preparation
5.0
Granular
0
<0.1
13.16
131.58
Ag ROW, Sugarcane
3.625
Liquid
0.05
9.54
19.08
104.93
Blueberries/Conifer
release
3
Spray
0.05
7.89
15.79
86.84
Rangeland
3
Granular
0
<0.1
7.89
78.95
Christmas Trees
2
Spray
0.01
1.05
6.32
53.68
Alfalfa
1.5
Spray
0.05
3.95
7.89
43.42
Pasture
1.1
Spray
0.01
.0.58
3.47
29.53
* = LOC exceedences (RQ > 1) are bolded and shaded.
Table 5.11 RQs* for Dicots Inhabiting Dry and Semi-Aquatic Areas Kxposed to llexazinonc via
Uunoffand Drift
Use
Application
rate
(lbs a.i./A)
Application
nuMhod
Drill
Value
r;.i
Spra\ (li il'l
HQ
l)r\ area
HQ
Scnii-a(|iialic
area UQ
Non-crop/Non-
agricullural ROW
12
Granular
0
<0.1
93.75
937.50
Agricultural
uncultivated. Airports.
Sewage
8
Spray
0.05
62.50
125.00
687.50
Forest Site Preparation
5.0
Granular
0
<0.1
39.06
390.63
Ag ROW. Sugarcane
3.625
Spray
0.05
28.32
56.64
311.52
Blucbcrrics/conifcr
release
3
Spray
0.05
23.44
46.88
257.81
Rangeland
3
Granular
0
<0.1
23.44
234.38
Christmas Trees
2
Spray
0.01
3.13
18.75
159.38
Alfalfa
1.5
Spray
0.05
11.72
23.44
128.91
Pasture
1.1
Spray
0.01
1.72
10.31
87.66
* = LOC exceedences (RQ > 1) are bolded and shaded.
5.1.4 Primary Constituent Elements of Designated Critical Habitat
5.1.4.1 Aquatic-Phase (Aquatic Breeding Habitat and Aquatic Non-
Breeding Habitat)
Three of the four assessment endpoints for the aquatic-phase primary constituent
elements (PCEs) of designated critical habitat for the CRLF are related to potential
effects to aquatic and/or terrestrial plants:
• Alteration of channel/pond morphology or geometry and/or increase in sediment
deposition within the stream channel or pond: aquatic habitat (including riparian
96
-------
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).
The preliminary effects determination for aquatic-phase PCEs of designated habitat
related to potential effects on aquatic and/or terrestrial plants is "may affect", based on
the risk estimation provided in Sections 5.1.1.2, 5.1.1.3, and 5.1.2.3.
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 hexazinone 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 these results, the preliminary effects determination for alteration of
characteristics necessary for normal growth and viability of the CRLF is "no effect" (see
Section 5.1.1.1). However, aquatic vascular and non-vascular aquatic plant food items of
the CRLF may be affected; therefore the preliminary effects determination for potential
impacts to these food items is "may affect" (see Section 5.1.1.2).
5.1.4.2 Terrestrial-Phase (Upland Habitat and Dispersal Habitat)
Two of the four assessment endpoints for the terrestrial-phase PCEs of designated critical
habitat for the CRLF are related to potential effects to terrestrial plants:
• Elimination and/or disturbance of upland habitat; ability of habitat to support food
source of CRLFs: Upland areas within 200 ft of the edge of the riparian
vegetation or dripline surrounding aquatic and riparian habitat that are comprised
of grasslands, woodlands, and/or wetland/riparian plant species that provides the
CRLF shelter, forage, and predator avoidance
• Elimination and/or disturbance of dispersal habitat: Upland or riparian dispersal
habitat within designated units and between occupied locations within 0.7 mi of
each other that allow for movement between sites including both natural and
altered sites which do not contain barriers to dispersal
The preliminary effects determination for terrestrial-phase PCEs of designated habitat
related to potential effects on terrestrial plants is "habitat modification", based on the risk
estimation provided in Section 5.1.2.3.
97
-------
The third terrestrial-phase PCE is "reduction and/or modification of food sources for
terrestrial phase juveniles and adults." To assess the impact of hexazinone on this PCE,
acute and chronic toxicity endpoints for birds, mammals, and terrestrial invertebrates are
used as measures of effects. RQs for these endpoints, which were calculated in Section
5.1.2.2, exceed the LOCs for all hexazinone non-granular uses. Uses of hexazinone are
not expected to cause direct acute effects to frog prey items of the terrestrial-phase
CRLF; however, chronic effects to small insectivorous mammals that ingest granules
may occur. The preliminary effects determination for habitat modification via impacts
of non-granular uses of hexazinone to terrestrial-phase CRLF food items is "habitat
modification".
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 effects, via mortality, are expected for the terrestrial-phase CRLF
(see Section 5.2.1.2). Chronic reproductive effects are possible for all non-granular uses
of hexazinone. Therefore the preliminary effects determinations for habitat modification
are "habitat modification" via direct acute effects to terrestrial-phase CRLFs and "habitat
modification" based on chronic exposures to non-granular applications of hexazinone.
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 hexazinone's use within the
action area. However, if direct or indirect effects LOCs are exceeded or there are
modifications to PCEs of the CRLF's critical habitat, the Agency concludes a
preliminary "may affect" determination for the FIFRA regulatory action regarding
hexazinone.
Following a "may affect" determination, additional information is considered to refine
the potential for exposure at the predicted levels based on the life history characteristics
(i.e., habitat range, feeding preferences, etc.) of the CRLF. Based on the best available
information, the Agency uses the refined evaluation to distinguish those actions that
"may affect, but are not likely to adversely affect" from those actions that are "likely to
adversely affect" the CRLF and its designated critical habitat.
The criteria used to make determinations that the effects of an action are "not likely to
adversely affect" the CRLF and its designated critical habitat include the following:
98
-------
• 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.
Tiihk'5.12 K fleets Dclcrminnlion Siimimirv lor Direct iind In direct K fleets of llexii/inone on the
( KM-
Assessment l.nripoinl
l.lfecls
Delcrminalion1
IJasis for Delcrminalion
Aquatic-Phase CRLF
(Eggs, Larvae, and Adults)
Direct Effect s of Hcxazinonc on the Aquatic-Phase CRLF
Survival, growth, and reproduction of
CRLF individuals via direct effects on
aquatic phases
Using fish as a
surrogate:
No Effect
Using freshwater fish as a surrogate, no acute and
chronic LOCs are exceeded for applications of Non-
agricultural Rights-of-way (12 lb/A-granular), there is no
expectation for adverse effects for lower rates: noncrop
uses (8 lb/A), forest site preparation (5 lb/A), conifer
release (3 lb/A), pineapple (3.6 lb/A), blueberry (3 lb/A),
Christmas Tree (2 lb/A), alfalfa (1.5 lb/A) and pasture
(1.1 lb/A).
Indirect Effect s of Hcxa/lnone on the Aquatic -Phase CRLF
99
-------
Survival, growth, and reproduction of
CRLF individuals via effects to food
supply (i.e., freshwater invertebrates,
non-vascular plants, fish, and frogs)
Freshwater
invertebrates:
No effect
Using freshwater invertebrates, no acute and chronic
LOCs are exceeded for applications of Non-agricultural
Rights-of-way (12 lb/A-granular). Due to no exceedence
for the 12 lb/A rate, it is assumed that there would also
be no exceedence for the lower rates: Noncrop uses (8
lb/A), forest site preparation (5 lb/A), conifer release (3
lb/A), pineapple (3.6 lb/A), blueberry (3 lb/A), Christmas
tree (2 lb/A), alfalfa (1.5 lb/A) and pasture (1.1 lb/A).
Indirect Effects of
Prev Reduction for
Non-vascular aauatic
olants for all uses:
May Affect
The May Affect for hexazinone uses related to
applications for non-agricultural ROW (12 lb/A)non-crop
uses (8 lb/A), conifer release (3 lb/A), pineapple (3.6
lb/A), rangeland (3 lbs/A), Christmas trees (2.0 lb ai/A),
alfalfa (1.5 lb ai/A) and pasture (1. lib ai/A), exceed
LOCs; therefore, indirect effects to tadpoles that feed on
algae are possible. RQs range from 22.37 to 1.52.
Non-vascular aquatic
plants: No Effect
Blueberry uses (RQ = 0.81) resulted in no LOC
exceedence.
Indirect Effects of
Prey Reduction for
Fish as surrogate for
Frogs for all uses:
No effect
Using freshwater fish as a surrogate, no acute and
chronic LOCs are exceeded for applications of non-
crop/non-agricultural Rights-of-way (12 lb/A-granular),
Noncrop uses (8 lb/A), forest site preparation (5 lb/A),
conifer release (3 lb/A), pineapple (3.6 lb/A), blueberry
(3 lb/A), Christmas tree (2 lb/A), alfalfa (1.5 lb/A) and
pasture (1.1 lb/A).
100
-------
Survival, growth, and reproduction of
CRLF individuals via indirect effects on
habitat, cover, and/or primary
productivity (i.e., aquatic plant
community)
Non-vascular
aauatic olants: Mav
Affect
No Effect
Hexazinone uses related to applications on Non-
crop/non-agricultural Rights-of-Way (12 lb/A-
granular), Noncrop uses (8 lb/A), forest site preparation
(5 lb/A), pineapple (3.6 lb/A), conifer release (3 lb/A),
rangeland (3 lb/A), Christmas Tree (2 lb/A), alfalfa (1.5
lb/A) and pasture (1.1 lb/A) exceed LOCs.
There is no LOC exceedence for blueberry (3 lb/A)
(RQ=0.81).
Indirect Effects on
habita for Vascular
aauatic olants for all
uses: Mav Affect
No Effect
The "May Affect" is based on the LOC exceedence for
vascular aquatic plants for liquid applications of
hexazinone to non-crop/non-agricultural ROW (12
lb/A), non-crop uses (8 lbs/A), Forest Site Preparation
(5 lb/A), Conifer Release (3 lb/A).RQs range from 4.19
to 1.25.
No LOC exceedence resulted for blueberry (3 lb/A),
rangeland (3 lb/A) Christmas tree (2 lb/A), alfalfa (1.5
lb/A) or pasture (1.1 lb/A).
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.
Forested and
srassv/herbaceous
riparian vesetation:
May Affect
Riparian vegetation may be affected because terrestrial
plant RQs exceed LOCs. RQs for semi-aquatic areas
range from 87.66 to 937.50 Hexazinone effects on
shading, bank stabilization, and structural diversity of
riparian areas in the action area are expected. Aquatic-
phase CRLFs may be indirectly affected by adverse
effects to sensitive herbaceous vegetation (based on all
hexazinone uses), which provides habitat and cover for
the CRLF and attachment sites for its egg masses.
Terrestrial-Phase CRLF
(Juveniles and adults)
Direct Effect s of Hexazinone on the Terrestrial-Phase CRLF
101
-------
Survival, growth, and reproduction of
CRLF individuals via direct effects on
terrestrial phase adults and juveniles
Nongranular acute for
medium size froe
usins the bird as a
surrogate: Mav affect
An adverse effect is expected based on weight of
evidence for acute avian toxicity. The T-Rex analysis
resulted in an endangered species exceedence.
No Effect for medium
sized frog
A "No effect"determination for pasture (1.1 lb/A) is due
to no LOC exceedence using the bird as a surrogate for
the CRLF for the 37 g animal resulting from the T-REX
analysis.
Nongranular Acute
Small Frog
May Affect:
The May Affect resulted from LOC exceedence using the
bird as a surrogate in the T-Herps analysis.
Nongranular Acute
Large Frog: May
Affect:
The May Affect resulted from LOC exceedence using the
bird as a surrogate in the T-HERPS analysis.
Acute Granular for
direct effects on the
CRLF:
No Effect
The no effect determination is due to no LOC
exceedence using the bird as a surrogate from the LDft2
results for noncrop non-agricultural ROW, forest site
preparation (5 lb/A) and rangeland (3 lb/A).
102
-------
Nongranular Chronic
Direct Effects Usine
the Bird as a
Surrogate:
May Affect:
The May affect is based on non-listed LOC exceedence
using the bird as a surrogate from the T-REX analysis.
Granular: May Affect
Granular formulations for non-crop/non-agricultural
ROW, forest site preparation and rangeland resulted in
LOC exceedences resulting from the T-REX analysis.
RQs range from 1.35 to 5.4.
Indirect Effect s of Hcxa/lnone on the Terrestrial -Phase CRLF
Nongranular Acute
Terrestrial
Invertebrates (Laree
Insect Prey):
May Affect
Nongranular Acute
No Effect
An May Affect determination for large insect prey is
based on the uncertainty regarding the effects of
hexazinone on terrestrial invertebrates due to related
toxicity values reporting no mortality at the highest
concentration tested for noncrop (8 lb/A), pineapple (3.6
lb/A) and blueberry/conifer release (3 lb/A).
A "No effect" determination for large insect prey for
Christmas tree (2 lb/A), alfalfa (1.5 lb/A) and pasture
(1.1 lb/A) uses was based on no LOC exceedence from
the T-REX analysis.
103
-------
Indirect orcv
reduction:
Mammals:
Non-granular Acute
May Affect
The May Affect is based on T-Rex LOC exceedence
results for 15 g mammal with a diet of shortgrass for
non-crop (8 lb/A) through pasture (1.1 lb/A) uses.
Granular Acute
Mammal Prey
Reduction:
No Effect (granular
uses)
A No effect determination is based on the LDft2 results
from the T-REX analysis for non-crop/non-agricultural
ROW (12 lb/A), forest site preparation (5 lb/A) and
rangeland (3 lb/A).
Indirect orcv
reduction-Mammal
Nongranular Chronic:
May Affect:
Chronic reproductive effects are possible, based on non-
granular uses of hexazinone. The May affect is due to
LOC exceedences from the T-Rex analysis for all
nongranular uses.
Amphibian using the
bird as a surrogate
Nongranular Acute
May Affect
The May affect is due to LOC exceedence using the bird
as a surrogate from the T-Rex analysis.
104
-------
Amphibian usins the
bird as a surrogate
Nongranular Chronic
May Affect:
Chronic reproductive effects are possible, based on non-
granular uses of hexazinone resulting from the T-REX
analysis using the bird as a surrogate.
Amphibian usins the
bird as a surrogate
Nongranular Chronic
No Effect
Christmas tree, alfalfa and pasture did not result in LOC
exceedences broadleaf. RQs for broadleaf range from
0.5 (3 lb/A) to 0.90 (1.5 lb/A) resulting from the T-Rex
analysis.
Survival, growth, and reproduction of
CRLF individuals via indirect effects on
habitat (i.e., riparian vegetation)
Woodv and
srassv/herbaceous
riparian vesetation:
May Affect
Riparian woody and herbaceous vegetation may be
affected because terrestrial plant RQs are above LOCs.
Til hit* 5.13 KIToels Dclcrminnlion Siiiniiiiirv lor Ihc ( rilicnl Ihihilnl linpncl Annlvsis
AsscssiiU'iK I.M(l|)oinl KITi-iis
Di'li'iiniiiiiliiin
ISiisis lor IkMiTiniiiiilion
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
Habitat
modification
Due to the MOA which interferes with
photosynthesis and RNA sensitive herbaceous
riparian vegetation may be affected based on all
modeled uses of hexazinone; therefore, critical
habitat may be modified by an increase in sediment
105
-------
and adult CRLFs.
deposition and reduction in herbaceous riparian
vegetation that provides for shelter, foraging,
predator avoidance, and aquatic dispersal for
juvenile and adult aquatic-phase 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.7
Habitat
modification
Sensitive non-vascular aquatic plants may be
affected; therefore, critical habitat may be modified
via turbidity and reduction in oxygen content
necessary for normal growth and viability of
juvenile and adult aquatic-phase CRLFs.
Alteration of other chemical characteristics necessary
for normal growth and viability of CRLFs and their
food source.
No effect to
growth and
viability
Habitat
modification
based on
alteration of
food source
Direct effects to the aquatic-phase CRLF, via
mortality, growth, and/or fecundity, are not
expected. However, critical habitat of the CRLF
may be modified via hexazinone-related impacts to
non-vascular aquatic plants as food items for
tadpoles. LOCs are exceeded for non-vascular uses
for non-crop/non-agricultural ROW (12 lb/A),
noncrop (8 lb/A), conifer release (3 lb/A), rangeland
(3 lb/A), Christmas Trees (2 lb/A), alfalfa (1.5 lb/A)
and pasture (1.1 lb/A).
No Habitat
Modification
There was no LOC exceedence for blueberry uses
for nonvascular plants.
Reduction and/or modification of aquatic-based food
sources for pre-metamorphs (e.g., algae)
Habitat
modification
Based on the results of the effects determinations
for aquatic plants, critical habitat of the CRLF may
be modified via hexazinone-related impacts to non-
vascular aquatic plants as food items for tadpoles.
LOCs are exceeded for uses for non-crop/non-
agricultural ROW (12 lb/A), noncrop uses (8 lb/A),
conifer release (3 lb/A), rangeland (3 lb/A),
Christmas trees (2 lb/A), alfalfa (1.5 lb/A) and
pasture (1.1 lb/A).
No Habitat
Modification
Blueberry use resulted in no LOC exceedence.
Terrestrial-Phase PCEs
(Upland Habitat and Dispersal Habitat)
7
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.
106
-------
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
Habitat
modification
Based on MO A, modification to critical habitat may
occur via hexazinone-related impacts to sensitive
woody and herbaceous vegetation, which provide
habitat and cover for the terrestrial-phase CRLF and
its prey, based on all assessed uses of hexazinone.
Terrestial incident reports support a "habitat
modification" determination.
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
Habitat
modification
Based on the MOA for hexazione modification to
dispersal habitat may occur via hexazinone-related
impacts to sensitive woody and herbaceous
vegetation, which provide habitat and cover for the
terrestrial-phase CRLF and its prey, based on all
assessed uses of hexazinone. Terrestrial incident
reports support the "habitat modification'
determination.
Reduction and/or modification of food sources for
terrestrial phase juveniles and adults
Habitat
modification
Based on the characterization of indirect effects to
terrestrial-phase CRLFs via reduction in the prey
base, critical habitat may be modified via a
reduction in mammals and terrestrial-phase
amphibians as food items.
Alteration of chemical characteristics necessary for
normal growth and viability of juvenile and adult
CRLFs and their food source.
Habitat
modification
Direct acute effects, via mortality, are expected for
the terrestrial-phase CRLF. Chronic reproductive
effects are also possible. Therefore, hexazinone
may adversely critical habitat by altering chemical
characteristics necessary for normal growth and
viability of terrestrial-phase CRLFs and their
mammalian and amphibian food sources.
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 hexazinone.
As shown in Table 5.1, acute and chronic RQs based on the highest modeled EECs for
hexazinone use on non-crop/non-agricultural ROW (12 lb ai/A) and the most sensitive
freshwater fish data (used as a surrogate for aquatic-phase amphibians) are well below
the Agency's acute and chronic risk LOCs.
All uses resulted in no RQs exceeding either the acute or chronic LOCs for fish.
107
-------
No open literature was available that provided more sensitive endpoints than registrant
submitted studies. No relevant incident reports are available for hexazinone. In summary,
the Agency concludes a "no effect" determination for direct effects to the aquatic-phase
CRLF, via mortality, growth, or fecundity, based on all available lines of evidence.
5.2.1.2 Terrestrial-Phase CRLF
Direct Acute Effects Determination
Direct acute terrestrial effects were further refined following the "May Affect"
determination using the T-Herps model to adjust for size and dietary effects.Based on
acute avian toxicity data as a surrogate for the terrestrial-phase amphibians, direct acute
mortality is expected for the terrestrial-phase CRLF via exposure to hexazinone
applications due to LOC exceedences resulting from the T-Herps refinement analysis
(Table 5.16).
For the medium-sized frog (37 g) there is an "LAA" determination for acute indirect
effects using the 20 g bird as a surrogate based on T-Herps small herbivore mammal
results for noncrop uses (8 lb/A).
Pineapple (3.6 lb/A), blueberry (3 lb/A), Christmas tree (2 lb/A) uses for small herbivore
mammals resulted in RQs falling between the listed and non-listed LOCs. Therefore, the
probit analysis will be used to further analyze those uses.
There was a "LAA" determination based on the probit results for pineapple, blueberry,
conifer release and Christmas tree uses. The probability of an individual effect to the bird
as as a surrogate for the CRLF for pineapple, blueberry and conifer release with a slope
of 4.2132 were ~1 in 222.
There was a "NLAA" determination due to discountable effects based on the probability
of an individual effect to the bird as as a surrogate for the CRLF for Christmas tree from
the probit analysis. Usinga slope of 4.2132, there was ~1 in 10,600.
There is an NLAA determination for alfalfa and pasture uses for the 37g frog consuming
small herbivore mammals due to no LOC exceedence resulting from the T-Herps
analysis.
There is an NLAA determination for the small frog (1.4 g) for all scenarios due to no
LOC exceedence resulting from the T-Herps analysis.
There is an NLAA determination for the large frog (238 g) for all scenarios due to no
LOC exceedence resulting from the T-Herps analysis.
There is a no effect determination for acute direct effects for the terrestrial-phase
CRLF based on results for non-crop/non-agricultural ROW, forest site preparation
108
-------
and rangeland granular applications for which LOCs were not exceeded resulting
from the T-Rex LDft analysis, as well as no reported terrestrial animal incidents.
Tiihlc 5.1(>. Assessment
l.s(ini;Kcd l'n\iroiimoii
(1.4 £). Medium (J"7 £).
ol' Direct 1'. fleets on Ciililoi'iiiii Ucd-lciiiicd I'roii i(UI.I') I sinii l)osc-l};iscd
liil (onccntriitions (1'.I'.( s) or llc\;i/iii(>nc l};iscd oil (lie T-llcrps Model lor Suiidl
iind l.;uiic(23S»)( Kl.l .
KQs (iii«/k«-l»\\) lor Sniiill. Medium. ;iud l.sirgi* ( Kl.l
(Siiiiill / Medium / l.sirgi*)
1 so
M ;i\imil in
Application
Kiilcs
(l.hs. ;ii/.\)
ISroiidk-iil"
I'liiiils/Siiiiill
1nsocls
l-'ruil/ Pods/
Seeds/
l.iiriie Insects
Sniiill llcrl)i\orc
Miimuiiils
Sniiill
1 used i\ore
Miimuiiils
Sniiill
lerres(ri;il
Phiise
Aniphihiiiii
Noncrop:
airport,
AgROW
8
0.02/0.02/0.01
0.0/0.0/0.0
N.A./0.53* / 0.08
N.A. / 0.03/
0.01
N.A./O.O/O.O
Pineapple
3.6
0.01/0.01/0.01
0.0/0.0/0.0/
N.A./0.24*/0.04
N.A.//0.01/0.0
N.A./0.0/0.0/
Blueberry/
conifer
release
3
0.01/0.01/0.0
.0 /o.o /o.o
N.A. / 0.20* /0.03
N.A./.01/O.O
N.A./O.O/O.O
Christmas
Tree
2
0.0/0.0/0.0
0.0 /o.o /o.o
N.A. / 0.13*/ 0.02
N.A. / 0.01/O.O
N.A. / .0.0/0.0
Alfalfa
1.5
0.0/0.0/0.0
.0.0/0.0/0.0
N.A. / 0.1/0.02
N.A. / 0.1/O.O
N.A./.0.0/03.0
Pasture
1.1
0.0/0.0/0.0
.0.0/0.0/0.0
N.A. / 0.07/0.01
N.A. /O.O /O.O
N.A. /O.O /O.O
* RQ > acute endangered species LOC of 0.1.
Direct Chronic Terrestrial Effects Determination
Direct chronic terrestrial effects were further refined following the "May Affect"
determination using the T-Herps model to adjust for size and dietary effects. Table 5.17
summaraizes the effects of chronic hexazinone exposure using the bird as a surrogate for
the CRLF.There is an LAA determination for the CRLF using the bird as a surrogate for
broadleaf plants/small insects for noncrop, conifer release and blueberry uses due to LOC
exceedence resulting from the T-Herps analysis.
There is an LAA determination for the CRLF using the bird as a surrogate consuming
small herbivore mammals for noncrop, conifer release, blueberry and Christmas tree uses
due to LOC exceedence resulting from the T-Herps analysis.
There is an NLAA determination for the CRLF using the bird as a surrogate consuming
broadleaf/small insects for Christmas tree, alfalfa and pasture uses due to no LOC
exceedence resulting from the T-Herps analysis.
109
-------
There is an NLAA determination for the CRLF using the bird as a surrogate consuming
small herbivore mammals for alfalfa and pasture uses due to no LOC exceedence
resulting from the T-Herps analysis.
There is an NLAA determination for the CRLF using the bird as a surrogate consuming
fruits/seeds/large insects, small insectivore mammals and small amphibians as prey due
to no LOC exceedence resulting from the T-Herps analysis.
Tiihle5.1"7.
Did
Assessment ol Direct 0 Hoc Is 011 1 crrcstriiil pliiisc ( iililorniii Rcd-lciijicd 1- ro« (( Rl.l- ) I sing
;ir\ hiiscd Chronic Risk Quotients (RQs) l-'roni (lie T-llcrps Model lor llc\ii/inonc.
Chronic l)ic(;ir\-h;iscd RQs lor 1 crrcstriiil Pliiisc ( Rl.l Dirccl I.ITccls
Sceiiiirio
(.roup:
Cmp/Sili*
Sniiill In see (
Pre\
Liirjic Insect Prc\
Sniiill llcrhi\orc
Miininiiil
Prc\
Sniiill
lnsccli\orc
Miininiiil
Prc\
Sniiill
1 crrcstriiil
Pliiisc
Aniphihiiin
Prc\
NonCrop
(8 lb/A)
3.60*
0.40
4.22*
0.26
0.12
Blueberry
/conifer release
(3 lb/A)
1.35*
.0.15
1.58*
0.10
0.05
Christmas
Trees ( 2 lb/A)
.0.90
0.10
1.05*
0.07
0.03
Alfalfa
( 1.5 lb/A)
0.68
.0.08
0.79
0.05
0.02
Pasture
( 1.1 lb/A)
0.50
0.06
0.58
0.04
0.02
RQ > chronic LOC of 1
5.2.2 Indirect Effects (via Reductions in Prey Base)
5.2.2.1 Algae (non-vascular plants)
As discussed in Section 2.5.3, the diet of CRLF tadpoles is composed primarily of
unicellular aquatic plants {i.e., algae and diatoms) and detritus. Based on RQs for algae
(Table 5.2), liquid applications of hexazinone to pasture (1.1 lb/A), alfalfa (1.5 lb/A),
Christmas trees (2 lb a/A), blueberry (3 lb ai/A), conifer release (3 lb ai/A), and granular
applications of hexazinone to non-crop/non-agricultural ROW (12 lb/A), forest site
preparation (51b/A) and rangeland (3 lb ai/A) may affect this food source. RQs for non-
vascular plants were based on the most sensitive EC50 value of 7 [j,g/L for freshwater
algae {Selenastrum).
Typically, algal populations are relatively dynamic, although the presence of hexazinone
in the water may result in an overall reduction in biomass, and/or a shift in community
composition as more sensitive species are eliminated. Although recovery of algal
110
-------
populations has been shown to occur, if the timing of hexazinone applications co-occur
with the presence of tadpole life stages of the CRLF (from December to March), a
reduction in algae as a food source for the tadpole may occur.
There is an LAA determination for indirect dietary effects based on nonagricultural
ROW, noncrop, conifer release, Christmas tree, alfalfa and pasture for nonagricultural
ROW, noncrop, conifer release and Christmas tree uses and mode of action for non-
vascular plants based on LOC exceedence and mode-of-action for hexazinone.
There is a no effect determination for indirect effects for the aquatic-phase CRLF
based on blueberry using non-vascular plants resulting from no LOC exceedence,
as well as no open literature or reported incidents.
5.2.2.2 Aquatic Invertebrates
The potential for hexazinone 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.
As previously discussed in Section 5.1.1.2, acute RQs for the highest application rate
(industrial outdoor uses at 10 lbs/A)Table 5.3) calculated using modeled peak aquatic
EECs and the 48-hour EC50 for the water flea, Daphnia magna, do not exceed the acute
LOC for hexazinone exposure.
Chronic RQs for invertebrates were less than the Agency's LOC, based on the highest
21-day modeled EECs for all hexazinone uses Therefore, chronic risks to freshwater
invertebrates and potential indirect effects to aquatic-phase CRLFs that consume them as
prey are not expected.
All uses resulted in no RQs exceeding either the acute or chronic LOCs for aquatic
invertebrates. No open literature was available that provided more sensitive endpoints
than registrant submitted studies. No incident reports for aquatic invertebrates are
available for hexazinone. In summary, the Agency concludes a "no effect" determination
for indirect dietary effects to the aquatic-phase CRLF, via mortality, growth, or fecundity
of aquatic invertebrates, based on all available lines of evidence.
5.2.2.3 Fish and Aquatic-phase Frogs
111
-------
No endangered species acute or chronic LOCs were exceeded for any uses for freshwater
fish used as a surrogate for aquatic-phase amphibians. Therefore, indirect effects to the
CRLF via a reduction in freshwater fish and other aquatic-phase frog species as prey
items is not expected, and the effects determination for this assessment endpoint is "no
effect". No incident reports are available for fish or aquatic-phase frogs. No open
literature provides a more sensitive endpoint than registrant data for fish or frogs.
5.2.2.4 Terrestrial Invertebrates
When the terrestrial-phase CRLF reaches juvenile and adult stages, its diet is mainly
composed of terrestrial invertebrates.
In order to assess the risks of hexazinone to terrestrial invertebrates the honey bee is used
as a surrogate for terrestrial invertebrates. The toxicity value for terrestrial invertebrates
is calculated by multiplying the lowest available acute contact LD50 of >100 |ig a.i. /bee
by 1 bee/0.128g, which is based on the weight of an adult honey bee. EECs (|ig a.i. /g of
bee) calculated by T-REX for small and large insects are divided by the calculated
toxicity value for terrestrial invertebrates, which is >781 |ig a.i. /g of bee. Given that the
toxicity endpoint is non-definitive {i.e., the LD50 value is greater than the highest test
concentration), the reported RQ values represent an upper bound. The resulting non-
definitive RQ values for large insect and small insect exposures bound the potential range
of exposures for terrestrial insects to hexazinone. RQs may exceed the LOC for small
insects, with RQs ranging from <1.57 to <0.22. With the exception of the 1.1, 1.5 and 2
hexazinone use rates (for pasture, alfalfa and Christmas trees) on large insects, RQ values
may exceed the LOC (RQ > 0.05). Christmas tree (<0.04), alfalfa (<0.03) and pasture
(<0.02) resulted in no RQ exceedence (Table 5.18).
In addition to calculating RQs, other sources were reviewed for weight of evidence.
No probit analysis was conducted for terrestrial invertebrate effects due to no observed
dose-response. No open literature for terrestrial invertebrates was available to provide
additional information. No relevant incident reports were available for terrestrial
invertebrates.
112
-------
Table 5.IS Summary of KQs I sod lo l.slimale Indirect K fleets lo (lie Terrestrial-
phase CUI.I'" via Direct K fleets on Terrestrial In vert eh rntcs as Dietary l-ootl
Items
I SO
Sniiill Insect UO
l.iiriie Insect UQ -
Agricultural uiiculln ;ileJ. airport (8
lbs/A)
<1.57
<0.17
Pineapple
(3.6 lbs/A)
<0.71
<0.08
Blucberrv. Conifer release. Rangeland
(3 lbs/A)
<0.59
<0.06
Christmas Trees
(2 lbs/A)
<0.39
<0.04
Alfalfa (1.5 lbs/A)
<0.26
<0.03
Pasture (1.12 lbs/A)
<0.22
<0.02
* = LOC exceedences (RQ> 0.05) are bolded and shaded. Because a definitive endpoint was not
established for terrestrial invertebrates (i.e., the value is greater than the highest test concentration), the
RQ represents an upper bound value.
There is uncertainty based on no mortality at the highest tested concentration for the
toxicity study, which is reflected in the results for this analysis. The RQs need to exceed
an LOC = 0.05 to establish an adverse effect. RQs for Christmas tree, alfalfa and pasture
are below the LOC.
There is an "LAA" determination for indirect small insect dietary effects for terrestrial
invertebrates based on the uncertainty due to no mortality at the highest tested
concentration for the honeybee toxicity study for all scenarios. There was no acceptable
open literature or reported incidents for terrestrial invertebrates.
5.2.2.5 Mammals
Life history data for terrestrial-phase CRLFs indicate that large adult frogs consume
terrestrial vertebrates, including mice. A reported acute oral rat LD50=5 3 0 mg/kg was
used to assess indirect effects of hexazinone on the CRLF (Kennedy 1984). This value
was lower than the registrant submitted value of 1,200 mg/kg. The acute RQs resulting
from the 15 g mammal eating short grass were further refined using the probit analysis
Table 5.19).
An analysis of potential adverse mammal population affects was assessed for hexazinone
uses at the LOC threshold (.1) and at the RQ between the endangered species LOC and
the acute risk LOC using the acute oral rat LD50 of 530 mg/kg and a default probit slope
113
-------
of 4.5. The likelihood of individual effect for hexazinone is 1 in 294,000 (with respective
upper and lower bounds of 1 in 44 and 1 in 8.86E+18).
Noncrop (RQ=1.57), pineapple (RQ=0.71) and blueberry/conifer release (RQ=0.59) uses
resulted in RQs exceeding the non-listed LOC (0.5) and therefore a "LAA" determination
was concluded.
Although RQs for Christmas tree, alfalfa and pasture did not exceed the nonlisted LOC,
RQs fell between the endangered species and nontarget LOCs. Therefore, these uses
were also refined using the probit analysis.
For Christmas tree uses, the corresponding estimated chance of an individual acute
mortality/immobilization to a terrestrial mammal at an RQ level of 0.39 is 1 in 30.4 (with
respective upper and lower bounds of 1 in 859 and 1 in 4.84).
For alfalfa uses, the corresponding estimated chance of an individual acute
mortality/immobilization to a terrestrial mammal at an RQ level of 0.29 is 1 in 129 (with
respective upper and lower bounds of 1 in 7.09 and 1 in 1.04).
For pasture uses, the corresponding estimated chance of an individual acute
mortality/immobilization to a terrestrial mammal at an RQ level of 0.22 is 1 in 648 (with
respective upper and lower bounds of 1 in 1,530,000 and 1 in 1.53).
Based on this assessment, the potential reduction in abundance of terrestrial mammals as
food for these uses would be < 1% at most (range 0.001%-0.03%); therefore a "not likely
to adversely affect" determination can be made.
l;il)k'5.l'J lloMi/inonc I sos I linl l.xcml I Ik- I.ikI;iii^oiv(I Species !.()( (l?;isod oil M;imm;il lo\icl> l);iln)
Use
I.OC
or RQ
Likelihood of Individual
!¦ fleet (' 1 in ...')
Probability
of A fleet
Acute Endangered Species LOC hexazinone uses
0.1
~1 in 2.94E +05
3.4E-06
Christmas Tree
0.39
~1 in 30.4
0.0329%
Alfalfa
0.29
~1 in 129
0.008%
Pasture
0.22
~1 in 648
0.001%
Hexazinone acute oral rat LD50=530 mg/kg (MRID# 4074902); Probit slope 4.5 (default)
2 Chance of individual effect and probability of affect were only calculated if the LOC was between 0.1-0.5
5.2.2.6 Terrestrial-phase Amphibians
Terrestrial-phase adult CRLFs also consume frogs. RQ values representing direct
exposures of hexazinone to terrestrial-phase CRLFs are used to represent exposures of
hexazinone to frogs in terrestrial habitats.
114
-------
An analysis of the likelihood of individual mortality as an indirect dietary effect indicates
that at the listed species LOC, i.e., RQ=0.1, the likelihood of individual mortality for
hexazinone is 1 in 79,000 (Table 5.20)
Table 5.20 llc\ii/inonc I sos I h.H l'.\cced (ho llndiiniicml Species I.OC I sinji (lie Bird As ;i Siiito»;Mc lor
Amphihiiins
l si-
I.OC
hi RO
Liki-lihimd hI' lndi\ idu;il
I.ITiU (1 in ...)
Prnl>;il>ilil\
ill Al'l'i-il
Acute Endangered Species LOC hexazinone uses
0.1
~1 in 79,000
1.26E-05%
Pineapple
0.34
~1 in 41.3
0.00242%
Blueberry
0.28
~1 in 101
0.00992%
Christmas Tree
0.19
~1 in 842
0.00119%
Alfalfa
0.14
~1 in 6230
0.000161%
Pasture
0.10
~1 in 79,400
0.0000126%
Hexazinone acute oral quail LD50=2258 mg/kg (MRID# 0073988); Probit slope 4.2132
2 Chance of individual effect and probability of affect were only calculated if the LOC was between 0.1-0.5
There is an "LAA" determination for indirect effects of hexazinone for the CRLF
consuming amphibians based on the RQ (0.76) for noncrop uses exceeding the non-listed
LOC (0.5).
Based on this assessment, the potential reduction in abundance of amphibians as food for
these uses would be < 1% at most (range 0.0000161%-0.00242%); therefore a "not likely
to adversely affect" determination can be made for pineapple, blueberry, Christmas tree
and alfalfa.
There is a "no effect" determination for pasture (RQ=0.1) based on no LOC exceedence.
5.2.3 Indirect Effects (via Habitat Effects)
5.2.3.1 Aquatic Plants (Vascular and Non-vascular)
Aquatic plants serve several important functions in aquatic ecosystems. Non-vascular
aquatic plants are primary producers and provide the autochthonous energy base for
aquatic ecosystems. Vascular plants provide structure, rather than energy, to the system,
as attachment sites for many aquatic invertebrates, and refugia for juvenile organisms,
such as fish and frogs. Emergent plants help reduce sediment loading and provide
stability to nearshore areas and lower stream banks. In addition, vascular aquatic plants
are important as attachment sites for egg masses of CRLFs.
115
-------
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.
Based on RQs for non-vascular plants (previously described in Section 5.2.2.1 and
summarized in Table 5.2), LOCs are exceeded for all modeled uses of hexazinone. RQs
for vascular plants exceed the LOC for all uses except rangeland, blueberry, alfalfa and
pasture. Therefore, indirect effects to the CRLF via direct effects to vascular plants as
habitat are expected.
In summary, the overall effects determination for indirect effects of hexazinone to CRLFs
via impacts to habitat and/or primary production through direct effects to non-vascular
plants and vascular plants is "likely to adversely affect" or "LAA" for hexazinone
exposure.
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. Upland vegetation including grassland and woodlands provides cover
during dispersal. Riparian vegetation helps to maintain the integrity of aquatic systems by
providing bank and thermal stability, serving as a buffer to filter out sediment, nutrients,
and contaminants before they reach the watershed, and serving as an energy source.
Loss, destruction, and alteration of habitat were identified as a threat to the CRLF in the
USFWS Recovery Plan (USFWS, 2002). Herbicides can adversely impact habitat in a
number of ways. In the most extreme case, herbicides in spray drift and runoff from the
site of application have the potential to kill (or reduce growth and/or biomass in) all or a
substantial amount of the vegetation, thus removing or impacting structures which define
the habitat, and reducing the functions (e.g., cover, food supply for prey base) provided
by the vegetation.
Hexazinone is a systemic herbicide that is absorbed by the plant through both the leaves
and the roots. It acts by inhibiting photosynthesis within the targeted plant. Based on the
available toxicity data for terrestrial plants, it appears that emerged dicot seedlings are
similar in sensitivity to hexazinone in the vegetative vigor test. This is demonstrated by
the difference in dicot response to the two guideline studies. The dicot EC25 values for
the seedling emergence and vegetative vigor tests are 0.0064 lb ai/A and 0.011 lb ai/A,
respectively. Monocots show similar levels of sensitivity in the seedling emergence and
vegetative vigor toxicity tests.
Riparian vegetation typically consists of three tiers of vegetation, which include a
groundcover of grasses and forbs, an understory of shrubs and young trees, and an
overstory of mature trees. Frogs spend a considerable amount of time resting and feeding
in riparian vegetation; the moisture and cover of the riparian plant community provides
116
-------
good foraging habitat, and may facilitate dispersal in addition to providing pools and
backwater aquatic areas for breeding (USFWS, 2002). According to Hayes and Jennings
(1988), the CRLF tends to occupy waterbodies with dense riparian vegetation including
willows (Salix sp.). Upland habitat includes grassland and woodlands, as well as
scrub/shrub habitat. While no guideline data are available on the toxicity of woody
plants, the available toxicity information indicates that hexazinone is likely to cause
adverse effects to non-target woody plants. In addition, hexazinone is labeled for use
around fields for woody species, as well as uses associated with forestry, reforestation,
conifer release and Christmas trees. Therefore, hexazinone is generally toxic to woody
plants. Woody trees and shrubs in both upland and riparian habitats are expected to
intercept some of the hexazinone that might otherwise be deposited on the more sensitive
herbaceous species. Additionally, in natural systems, older plants, fallen leaves, and
other debris often provide a litter layer, which may serve to protect newly emerging
herbaceous plants.
As shown in Tables 5.10 and 5.11, RQs exceed LOCs for monocots and dicots inhabiting
dry and semi-aquatic areas exposed to hexazinone via runoff and drift. In general, it
appears that dicots are more sensitive than monocots to hexazinone in semi-aquatic areas.
Dicots in semi-aquatic and dry areas are approximately 3 times more sensitive than
monocots in similar areas; as well as sensitivity to hexazinone in spray drift. In
summary, based on exceedence of the terrestrial plant LOCs for all hexazinone use
patterns following runoff and spray drift to semi-aquatic and dry areas, the following
general conclusions can be made with respect to potential harm to riparian habitat:
• Hexazinone may enter riparian areas via runoff and/or spray drift where it
may be taken up by the plant by the leaves and roots of sensitive plants.
• Comparison of seedling emergence EC25 values to EECs estimated using
Terrplant suggests that existing vegetation may be affected or inhibition of
new growth may occur. Inhibition of new growth could result in degradation
of high quality riparian habitat over time because as older growth dies from
natural or anthropogenic causes, plant biomass may be prevented from being
replenished in the riparian area. Inhibition of new growth may also slow the
recovery of degraded riparian areas that function poorly due to sparse
vegetation because hexazinone deposition onto bare soil would be expected to
inhibit the growth of new vegetation. As stated previously, hexazinone is
persistent and mobile; therefore, it is likely to be transported from soil
surfaces during runoff events.
Based on a review of the hexazinone incidents for terrestrial plants, only three have been
reported. In the first incident, a section of lawn grass was damaged following application
of hexazinone to a swimming pool. In the remaining two incidents, both of which
occurred on May 9, 2000, 130 acres of corn was damaged following aerial application of
hexazinone and atrazine to corn, although both incidents were reported as "unlikely".
Although the reported number of hexazinone incidents for terrestrial plants is low, and
117
-------
due to uses either not relevant for this assessment {i.e. application to swimming pools) or
cancelled (aerial application to corn), an absence of reports does not necessarily provide
evidence of an absence of incidents. The only plant incidents that are reported are those
that are alleged to occur on more than 45 percent of the acreage exposed to the pesticide.
Therefore, an incident could impact 40% of an exposed crop and not be included in the
EIIS database (unless it is reported by a non-registrant, such as a state agency, where data
are not systemically collected.
In summary, terrestrial plant RQs are above LOCs; therefore, upland and riparian
vegetation may be affected. Woody plants are generally sensitive to environmentally-
relevant hexazinone concentrations; therefore, effects on shading, bank stabilization,
structural diversity (height classes) of vegetation, and woodlands are expected. Given
that both upland and riparian areas are comprised of a mixture of both sensitive woody
(trees and shrubs) and sensitive grassy herbaceous vegetation, CRLFs may be indirectly
affected by adverse effects to both woody and herbaceous vegetation which provides
habitat and cover for the CRLF and its prey. Therefore, the effects determination for this
assessment endpoint is "likely to adversely affect" or "LAA" for all assessed hexazinone
use patterns.
As previously described in Section 3.2.5, downwind spray drift buffers were developed to
determine the distance required to dissipate spray drift to below the LOC, based on both
NOAEC and EC25 levels for terrestrial plants. Dissipation to the no effect level was
modeled in order to provide potential buffer distances that are protective of endangered
terrestrial plant species; this distance beyond the site of application is considered as the
action area for hexazinone. However, because no obligate relationship exists between the
CRLF and terrestrial plants, the portion of the action area that is relevant to the CRLF is
defined by the dissipation distance to the EC25 level {i.e., the potential buffer distance
required to protect non-endangered terrestrial plant species). The spray drift distances
presented in Table 3.4 were derived based on the most sensitive EC25 value for dicots in
the seedling emergence test (0.0063 lb ai/A). Based on the maximum hexazinone aerial
application rate of 12 lb ai/A a spray drift buffer of 3,366 feet from the site of application
is required to dissipate to levels below the LOC (for the portion of the action area that is
relevant to the CRLF). The vegetative vigor toxicity test is intended to assess the
potential effects on plants following deposition of hexazinone on the leaves and above-
ground portions of plants, which are more likely to receive exposure via spray drift.
Therefore, spray drift distances are derived for the vegetative vigor endpoint, as well as
the seedling emergence endpoint, for both monocots and dicots, in Table 5.15. As
discussed in Section 3.2.5, the drift buffers for the more sensitive seedling emergence
endpoint for dicots were derived using the AgDISP model with the Gaussian extension
because the 1,000 foot limit of the AgDrift model was exceeded. However, spray drift
dissipation distances reported for the vegetative vigor endpoints and for the monocot
seedling emergence endpoint were based on the Agdrift model because the limits of the
model were not exceeded using the spray drift parameters provided in Section 3.2.5. As
shown in Table 5.15, adverse effects to terrestrial plants might reasonably be expected to
occur up to 3589 feet from the use site for aerial applications and 3366 feet from the use
site for ground applications of hexazinone. In some cases, topography (such as an
118
-------
intervening ridge) or weather conditions (such as prevailing winds towards or away from
the frog habitat) could affect the estimates presented in Table 5.15. However, analysis of
these site-specific details is beyond the scope of this assessment.
5.2.4 Modification to Designated Critical Habitat
5.2.4.1 Aquatic-Phase PCEs
Three of the four assessment endpoints for the aquatic-phase primary constituent
elements (PCEs) of designated critical habitat for the CRLF are related to potential
effects to aquatic and/or terrestrial plants:
• Alteration of channel/pond morphology or geometry and/or increase in sediment
deposition within the stream channel or pond: aquatic habitat (including riparian
vegetation) provides for shelter, foraging, predator avoidance, and aquatic
dispersal for juvenile and adult CRLFs.
• Alteration in water chemistry/quality including temperature, turbidity, and oxygen
content necessary for normal growth and viability of juvenile and adult CRLFs
and their food source.
• Reduction and/or modification of aquatic-based food sources for pre-metamorphs
(e.g., algae).
The effects determinations for indirect effects to the CRLF via direct effects to aquatic
and terrestrial plants are used to determine whether modification to critical habitat may
occur.
Based on the results of the effects determinations for aquatic plants (see Sections 5.2.2.1
and 5.2.3.1), critical habitat of the CRLF may be modified via hexazinone-related
impacts to non-vascular aquatic plants as food items for tadpoles and habitat for aquatic-
phase CRLFs. Critical habitat may be modified by an increase in sediment deposition
and associated turbidity (via impacts to herbaceous riparian vegetation), potential
reduction in oxygen (via impacts to the aquatic plant community and primary
productivity), and reduction in herbaceous riparian vegetation that provides for shelter,
foraging, predator avoidance, and aquatic dispersal for juvenile and adult aquatic-phase
CRLFs. Hexazinone uses may result in modification to critical habitat via direct effects
to non-vascular plants for all modeled applications. Based on the results of the effects
determination for terrestrial plants (see Section 5.2.3.2), hexazinone-related effects on
shading (i.e., temperature), bank stabilization, and structural diversity (height classes) of
vegetation are expected because woody plants are generally sensitive to environmentally-
relevant concentrations of hexazinone. However, modification to critical habitat may
occur via hexazinone-related impacts to sensitive herbaceous vegetation, which provide
habitat and cover for the CRLF and its prey, based on all assessed uses of hexazinone.
119
-------
The remaining aquatic-phase PCE is "alteration of other chemical characteristics
necessary for normal growth and viability of CRLFs and their food source." Other than
impacts to algae as food items for tadpoles (discussed above), this PCE was assessed by
considering direct and indirect effects to the aquatic-phase CRLF via acute and chronic
freshwater fish and invertebrate toxicity endpoints as measures of effects. As discussed
in Section 5.2.1.1, direct effects to the aquatic-phase CRLF, via mortality, growth, and/or
fecundity are not expected. In addition, hexazinone-related effects to freshwater
invertebrates and freshwater fish as food items are also not likely to occur (see Sections
5.2.2.2 and 5.2.2.3). Therefore, hexazinone is not likely to modify critical habitat by
altering chemical characteristics necessary for normal growth and viability of aquatic-
phase CRLFs and their non-plant food sources.
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.
As discussed above, modification to critical habitat may occur via hexazinone-related
impacts to sensitive herbaceous vegetation, which provides habitat, cover, and a means of
dispersal for the terrestrial-phase CRLF and its prey, based on all monocot and dicot
assessments for hexazinone uses. Modification to critical habitat is expected to occur in
woodland areas because woody plants are sensitive to environmentally relevant
concentrations of hexazinone. Terrestrial plant incident reports support the habitat
modification detetmination.
The third terrestrial-phase PCE is "reduction and/or modification of food sources for
terrestrial phase juveniles and adults." To assess the impact of hexazinone on this PCE,
acute and chronic toxicity endpoints for terrestrial invertebrates, mammals, and
terrestrial-phase frogs are used as measures of effects. Based on the characterization of
indirect effects to terrestrial-phase CRLFs via reduction in the prey base (see Section
5.2.2.4 for terrestrial invertebrates, Section 5.2.2.5 for mammals, and 5.2.2.6 for frogs),
critical habitat may be modified via a reduction in mammals and terrestrial-phase
amphibians as food items. No open literature studies are available for terrestrial
invertebrates, mammals or frogs resulting in more sensitive endpoints than registrant
120
-------
submitted studies. No incident reports are available for terrestrial invertebrates,
mammals or frogs.
The fourth terrestrial-phase PCE is based on alteration of chemical characteristics
necessary for normal growth and viability of juvenile and adult CRLFs and their food
source. As discussed in Section 5.2.1.2, direct acute effects, via mortality, are expected
for the terrestrial-phase CRLF. Chronic reproductive effects are possible for all uses of
hexazinone except alfalfa and pasture. Therefore, hexazinone may adversely affect
critical habitat by altering chemical characteristics necessary for normal growth and
viability of terrestrial-phase CRLFs and their mammalian and amphibian food sources.
6 Uncertainties
6.1 Exposure Assessment Uncertainties
6.1.1 Maximum Use Scenario
The screening-level risk assessment focuses on characterizing potential ecological risks
resulting from a maximum use scenario, which is determined from labeled statements of
maximum application rate and number of applications with the shortest time interval
between applications. The frequency at which actual uses approach this maximum use
scenario may be dependant on pest resistance, timing of applications, cultural practices,
and market forces.
6.1.2 Aquatic Exposure Modeling of Hexazinone
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.
121
-------
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
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
122
-------
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 Hexazinone
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 Hexazinone use areas.
6.1.3 Action Area Uncertainties
An example of an important simplifying assumption that may require future refinement is
the assumption of uniform runoff characteristics throughout a landscape. It is well
documented that runoff characteristics are highly non-uniform and anisotropic, and
become increasingly so as the area under consideration becomes larger. The assumption
made for estimating the aquatic action area (based on predicted in-stream dilution) was
that the entire landscape exhibited runoff properties identical to those commonly found in
agricultural lands in this region. However, considering the vastly different runoff
characteristics of: a) undeveloped (especially forested) areas, which exhibit the least
amount of surface runoff but the greatest amount of groundwater recharge; b)
suburban/residential areas, which are dominated by the relationship between
impermeable surfaces (roads, lots) and grassed/other areas (lawns) plus local drainage
management; c) urban areas, that are dominated by managed storm drainage and
impermeable surfaces; and d) agricultural areas dominated by Hortonian and focused
runoff (especially with row crops), a refined assessment should incorporate these
differences for modeled stream flow generation. As the zone around the immediate
(application) target area expands, there will be greater variability in the landscape; in the
context of a risk assessment, the runoff potential that is assumed for the expanding area
will be a crucial variable (since dilution at the outflow point is determined by the size of
the expanding area). Thus, it important to know at least some approximate estimate of
types of land use within that region. Runoff from forested areas ranges from 45 -
2,700% less than from agricultural areas; in most studies, runoff was 2.5 to 7 times higher
in agricultural areas (e.g., Okisaka et al., 1997; Karvonen et al., 1999; McDonald et al.,
2002; Phuong and van Dam 2002). Differences in runoff potential between
urban/suburban areas and agricultural areas are generally less than between agricultural
and forested areas. In terms of likely runoff potential (other variables - such as
topography and rainfall - being equal), the relationship is generally as follows (going
from lowest to highest runoff potential):
Three-tiered forest < agroforestry < suburban < row-crop agriculture < urban.
There are, however, other uncertainties that should serve to counteract the effects of the
aforementioned issue. For example, the dilution model considers that 100% of the
123
-------
agricultural area has the chemical applied, which is almost certainly a gross over-
estimation. Thus, there will be assumed chemical contributions from agricultural areas
that will actually be contributing only runoff water (dilutant); so some contributions to
total contaminant load will really serve to lessen rather than increase aquatic
concentrations. In light of these (and other) confounding factors, Agency believes that
this model gives us the best available estimates under current circumstances.
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 Hexazinone
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 reflects
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
124
-------
food requirements. Depending upon species and dietary matrix, bird assimilation of wild
diet energy ranges from 23 - 80%, and mammal's assimilation ranges from 41 - 85%
(U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is
formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for
underestimation of exposure may exist by assuming that consumption of food in the wild
is comparable with consumption during laboratory testing. In the screening process,
exposure may be underestimated because metabolic rates are not related to food
consumption.
For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal
was assumed to occupy either the treated field or adjacent areas receiving a treatment rate
on the field. Actual habitat requirements of any particular terrestrial species were not
considered, and it was assumed that species occupy, exclusively and permanently, the
modeled treatment area. Spray drift model predictions suggest that this assumption leads
to an overestimation of exposure to species that do not occupy the treated field
exclusively and permanently.
T-HERPS Modeling
Uncertainties in the Mammal and Herptile Prey Item EEC
T-HERPS calculates EECs for terrestrial-phase herptiles that consume mammals and
other terrestrial phase herptiles. The amount of chemical estimated to be in the prey
animal, in most cases, is thought to be a conservative estimate of potential dietary
exposure because T-HERPS assumes that a small prey animal is consuming its daily
intake of contaminated food before being consumed by the assessed species. Depuration
of the pesticide from the prey item due to excretion or metabolism was not included in
the estimation. Therefore, the EECs for chemicals that are short-lived in an animal are
expected to represent an over-estimate of exposure. However, for chemicals that are
bioaccumulative and are not readily degraded or excreted in an animal, the resulting
exposure estimates could be low-end estimates because body burdens within the prey
species would be expected to increase over time for bioaccumulative chemicals, resulting
in potential body burdens that exceed the estimated daily dose calculated by T-HERPS.
In addition, potential residues on the surface of potential prey items (e.g. in the fur) were
not estimated by T-HERPS. Additional residues would be expected to be on prey item
surface as well as within the prey item. Residues could be on prey items by several
pathways including direct deposition of spray drift or by contact of the prey animal with
contaminated soil or foliage.
In addition, the mammal prey item assessment assumes consumption of a 35-gram
mammal by the assessed species. A body weight of 35 grams was chosen because it
represents a higher end body weight of deer mice (U.S. EPA, 1993). Use of larger sized
prey mammals would result in higher dose-based RQs, but lower dietary-based RQs. It is
uncertain if dose-based or dietary-based RQs are more appropriate for this exposure
pathway. Therefore, in cases where neither dietary-based nor dose-based RQs exceed
125
-------
LOCs, effects of using a smaller mammal prey item (i.e., 15 grams) on the dietary based
RQs should be considered by the assessor.
Uncertainties Associated with the Food Intake Allometric Equation
The daily food intake is estimated in T-HERPS using an iguanid lizard allometric
equation as presented in U.S. EPA (1993). This equation is used in T-HERPS to estimate
potential exposures to all herptiles, including the CRLF. Allometric equations specific
for terrestrial-phase amphibians were not identified. To test the assumption that use of
the iguanid lizard allometric equation results in a reasonable approximation of terrestrial
phase amphibian food intake, measured food intake values reported for juvenile bullfrogs
(Rana catesbeiana) of various weights reported by Modzelewski and Culley (1974, as
cited in U.S. EPA, 1993) were compared to estimates derived using the iguanid food
intake allometric equation incorporated into T-HERPS for the same body weight range.
The analysis suggests that food intake values for juvenile bullfrogs in the Modzelewski
and Culley (1974) study are reasonably approximated using the allometric equation for
iguanid lizards. The data in juvenile bullfrogs reported daily food intake values that
range from approximately 3% to 7% of their body weight. Estimates of daily food intake
using T-HERPS for the same range of body weights (13 grams to 100 grams) ranged
from approximately 3% to 5% body weight daily. This analysis suggests that use of the
iguanid lizard allometric equation results in a reasonable approximation of food intake
reported for terrestrial phase frogs.
An additional uncertainty of T-HERPS is associated with temperature influence on the
food intake allometric equation. Given that terrestrial phase frogs are poikilothermic,
temperature may impact feeding rate. Temperature has not specifically been incorporated
into the food ingestion allometric equation, and is not directly considered in T-HERPS.
Uncertainties associated with the Feeding Behavior of the Assessed Species
The allometric equation used to estimate daily food intake assumes a typical or constant
food intake rate daily. In reality, the amount of food consumed (and, therefore, potential
exposures to pesticides) may vary significantly from day to day, depending on a number
of factors including availability of particular food items and energy needs.
T-HERPS estimates potential exposures for a number of food items. EECs for a
particular food item are calculated with the assumption that one food item is consumed
daily. Terrestrial-phase herptiles may receive 100% of their daily diet from one food
item for a particular day, especially if larger prey, such as a small mammal, is available.
However, many terrestrial-phase herptiles (including the California red-legged frog) may
consume a variety of food items in a given day. T-HERPS estimates potential exposures
resulting from consumption of a range of food items for the purpose of giving a high-end
and low-end bounding estimate. All exposure values may be used in characterizing
potential exposures.
126
-------
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 hexazinone from multiple applications, each application of hexazinone
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/AGDISP 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/AGDISP may
overestimate exposure, especially as the distance increases from the site of application,
since the model does not account for potential obstructions (e.g., large hills, berms,
buildings, trees, etc.). Furthermore, conservative assumptions are made regarding the
droplet size distributions being modeled ( 'ASAE Very Fine' for agricultural uses), the
application method (i.e., aerial), release heights and wind speeds. Alterations in any of
these inputs would decrease the area of potential effect.
6.2 Effects Assessment Uncertainties
6.2.1 Age Class and Sensitivity of Effects Thresholds
It is generally recognized that test organism age may have a significant impact on the
observed sensitivity to a toxicant. The acute toxicity data for fish are collected on
juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on
recommended immature age classes (e.g., first instar for daphnids, second instar for
amphipods, stoneflies, mayflies, and third instar for midges).
Testing of juveniles may overestimate toxicity at older age classes for pesticide active
ingredients that act directly without metabolic transformation because younger age
classes may not have the enzymatic systems associated with detoxifying xenobiotics. In
so far as the available toxicity data may provide ranges of sensitivity information with
respect to age class, this assessment uses the most sensitive life-stage information as
measures of effect for surrogate aquatic animals, and is therefore, considered as
protective of the CRLF.
6.2.2 Use of Surrogate Species Effects Data
Guideline toxicity tests and open literature data on hexazinone 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
127
-------
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.
6.2.3 Sub lethal Effects
When assessing acute risk, the screening risk assessment relies on the acute mortality
endpoint as well as a suite of sub lethal responses to the pesticide, as determined by the
testing of species response to chronic exposure conditions and subsequent chronic risk
assessment. Consideration of additional sub lethal data in the assessment is exercised on a
case-by-case basis and only after careful consideration of the nature of the sub lethal
effect measured and the extent and quality of available data to support establishing a
plausible relationship between the measure of effect (sub lethal endpoint) and the
assessment endpoints.
To the extent to which sub lethal effects are not considered in this assessment, the
potential direct and indirect effects of hexazinone on CRLF may be underestimated.
6.2.4 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 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 hexazinone to the CRLF and its
designated critical habitat.
Based on the best available information, the Agency makes a Likely to Adversely Affect
determination for the CRLF from the use of hexazinone. Additionally, the Agency has
determined that there is the potential for modification of CRLF designated critical habitat
from the use of the chemical.
In order to confirm that uses of hexazinone have the potential to affect the CRLF and its
critical habitat through direct applications to spray drift to non-target areas, it is necessary
to determine whether the final action area for hexazinone uses overlap with CRLF
habitats. Using ArcGIS 9.2, the National Land-Cover Dataset (NLCD, 2001), and the
128
-------
CRLF habitat information provided by the USFWS, the Agency has identified the areas
where indirect effects to the CRLF and modification to designated critical habitat are
anticipated to occur. These areas are depicted with a 4,200 foot buffer for cultivated
crops, forest and pasture (Fig. 2.4) and non-crop/non-agricultural ROW (2.5).
Modification to CRLF designated critical habitat could potentially occur in 89%
(approximately 20,846 out of 23,440 acres) of the currently designated habitat area.
Based on the results of this effects determination, the CRLF may be indirectly affected
within 930 core areas within the eight recovery units.
A summary of the risk conclusions and effects determinations for the CRLF and its
critical habitat, given the uncertainties discussed in Section 6, is presented in Tables 5.12
and 5.13.
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 hexazinone to the CRLF and its
designated critical habitat.
Based on the best available information, the Agency makes a Likely to Adversely Affect
determination for the CRLF from the use of hexazinone. Additionally, the Agency has
determined that there is the potential for modification of CRLF designated critical habitat
from the use of the chemical. No direct effect for the aquatic-phase CRLF is expected
using fish as a surrogate due to no LOC exceedence.
No indirect dietary effect is expected for the aquatic-phase CRLF consuming aquatic
invertebrates for hexazinone based on no LOC exceedence. A "May Affect"
determination for indirect dietar effects for the CRLF consuming non-vascular aquatic
plants effect is due to the LOC exceedence for all uses except blueberry. An "LAA"
determination for non-vascular aquatic plants resulted for all uses of hexazinone except
blueberry due to mode-of-action for hexazinone. A "May Affect" determination is due to
LOC exceedence for non-agricultural uncultivated areas (10 lb/A), conifer release (4
lb/A) and Christmas tree (2 lb/A) uses for vascular plants and the "LAA" determination is
due to the mode-of-action for hexazinone.
A determination of "May Affect" for alteration of critical habitat for monocots and dicots
was based on LOC exceedence for all hexazinone uses. The "LAA" determination is due
to the mode-of-action for hexazinone, which interferes with photosynthesis and RNA
production.
A determination of habitat modification for critical habitat was based on LOC
exceedence resulting from the TerrPlant analysis for all hexazinone uses. The "LAA"
determination is due to the mode-of-action for hexazinone, which interferes with
photosynthesis and RNA production.
129
-------
A summary of the risk conclusions and effects determinations for the CRLF and its
critical habitat, given the uncertainties discussed in Section 6, is presented in Tables 7.1
and 7.2.
Table 7.1 Klleels Delerminnlion Sum inn rv lor Direct iind Imlireel Klleels of llexii/inone on 1 lie
(KIT
Effects
Determination'
IJasis for Determination
Aquatic-Phase CRLF
(Eggs, Larvae, and Adults)
Direct Effect s of Hcxazinonc on the Aquatic-Phase CRLF
Survival, growth, and reproduction of
CRLF individuals via direct effects on
aquatic phases
Using fish as a
surrogate:
No Effect
Using freshwater fish as a surrogate, no acute and
chronic LOCs are exceeded for applications of Non-
agricultural Rights-of-way (12 lb/A-granular), there is no
expectation for adverse effects for lower rates: noncrop
uses (8 lb/A), forest site preparation (5 lb/A), conifer
release (3 lb/A), pineapple (3.6 lb/A), blueberry (3 lb/A),
Christmas Tree (2 lb/A), alfalfa (1.5 lb/A) and pasture
(1.1 lb/A).
Indirect Effect s of Hcxa/lnone on the Aquatic -Phase CRLF
Survival, growth, and reproduction of
CRLF individuals via effects to food
supply (i.e., freshwater invertebrates,
non-vascular plants, fish, and frogs)
Freshwater
invertebrates:
No effect
Using freshwater invertebrates, no acute and chronic
LOCs are exceeded for applications of Non-agricultural
Rights-of-way (12 lb/A-granular). Due to no exceedence
for the 12 lb/A rate, it is assumed that there would also
be no exceedence for the lower rates: Noncrop uses (8
lb/A), forest site preparation (5 lb/A), conifer release (3
lb/A), pineapple (3.6 lb/A), blueberry (3 lb/A), Christmas
tree (2 lb/A), alfalfa (1.5 lb/A) and pasture (1.1 lb/A).
Indirect Effects of
Prev Reduction for
Non-vascular aauatic
olants for all uses:
May Affect
The May Affect for hexazinone uses related to
applications for non-agricultural ROW (12 lb/A)non-crop
uses (8 lb/A), conifer release (3 lb/A), pineapple (3.6
lb/A), rangeland (3 lbs/A), Christmas trees (2.0 lb ai/A),
alfalfa (1.5 lb ai/A) and pasture (1. lib ai/A), exceed
LOCs; therefore, indirect effects to tadpoles that feed on
algae are possible. RQs range from 22.37 to 1.52.
130
-------
LAA
The LAA determination is due to mode of action
Non-vascular aquatic
plants: No Effect
Blueberry uses (RQ = 0.81) resulted in no LOC
exceedence.
Indirect Effects of
Prey Reduction for
Fish as surrogate for
Frogs for all uses:
No effect
Using freshwater fish as a surrogate, no acute and
chronic LOCs are exceeded for applications of non-crop
(12 lb/A-granular), Noncrop uses (8 lb/A), forest site
preparation (5 lb/A), conifer release (3 lb/A), pineapple
(3.6 lb/A), blueberry (3 lb/A), Christmas tree (2 lb/A),
alfalfa (1.5 lb/A) and pasture (1.1 lb/A).
Survival, growth, and reproduction of
CRLF individuals via indirect effects on
habitat, cover, and/or primary
productivity (i.e., aquatic plant
community)
Non-vascular
aauatic olants: Mav
Affect
LAA
Hexazinone uses related to applications on Non-crop
(12 lb/A-granular), Noncrop uses (8 lb/A), forest site
preparation (5 lb/A), pineapple (3.6 lb/A), conifer
release (3 lb/A), rangeland (3 lb/A), Christmas Tree (2
lb/A), alfalfa (1.5 lb/A) and pasture (1.1 lb/A) exceed
LOCs. Indirect effects to tadpoles that feed on algae are
possible due to the MO A, which interferes with
photosynthesis and RNA.
No Effect
There is no LOC exceedence for blueberry (3 lb/A)
(RQ=0.81).
131
-------
Indirect Effects on
habita for Vascular
aquatic plants for all
uses: May Affect
LAA
No Effect
The "May Affect" is based on the LOC exceedence for
vascular aquatic plants for liquid applications of
hexazinone to non-crop (12 lb/A), non-crop uses (8
lbs/A), Forest Site Preparation (5 lb/A), Conifer Release
(3 lb/A).RQs range from 4.19 to 1.25.
The "LAA" determination is based on the Mode of
Action.
No LOC exceedence resulted for blueberry (3 lb/A),
rangeland (3 lb/A) Christmas tree (2 lb/A), alfalfa (1.5
lb/A) or pasture (1.1 lb/A).
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.
Fforested and
grassv/herbaceous
riparian vegetation:
May Affect
LAA < 3366 ft
(ground)
NLAA > 3366 ft
(ground)
LAA <3589 ft
(aerial);
NLAA > 3589 ft
(aerial)
Riparian vegetation may be affected because terrestrial
plant RQs exceed LOCs. RQs for semi-aquatic areas
range from 87.66 to 937.50 Hexazinone effects on
shading, bank stabilization, and structural diversity of
riparian areas in the action area are expected. Aquatic-
phase CRLFs may be indirectly affected by adverse
effects to sensitive herbaceous vegetation (based on all
hexazinone uses), which provides habitat and cover for
the CRLF and attachment sites for its egg masses.
The LAA determination is based on MOA for ground
applications of hexazinone within a drift buffer of 3366 ft
based on the AGDISP results.
There is an "NLAA' determination fro animals outside
the drift buffer of 3589 ft resulting from the AGDISP
model.
The LAA determination is based on MOA for aerial
applications of hexazinone within a drift buffer of 3589 ft
based on the AGDISP results.
There is an "NLAA" determination for animals outside
the drift buffer of 3589 ft resulting from the AGDISP
model.
Terrestrial-Phase CRLF
(Juveniles and adults)
Direct Effect s of Hexazinone on the Terrestrial-Phase CRLF
132
-------
Survival, growth, and reproduction of
CRLF individuals via direct effects on
terrestrial phase adults and juveniles
Nongranular acute for
medium size froe
usins the bird as a
surrogate: Mav affect
An adverse effect is expected based on weight of
evidence for acute avian toxicity. The T-Rex analysis
resulted in an endangered species exceedence for all
crops.
LAA for the medium
size frog
Further refinement using the T-HERPS analysis resulted
in an endangered species exceedence for the CRLF
consuming small herbivore mammals with RQs ranging
from 0.53 for (8 lb/A) resulting from T-Rex analysis.
NLAA for the
medium size frog
Further refinement using a T-HERPS analysis resulted in
RQS falling between the endangered species (0.1) and
acute risk (0.5) LOCs exceedence for the CRLF
consuming small herbivore mammals for pineapple,
blueberry, conifer release and Christmas tree uses for a
37 g animal. The RQs from the T-HERPS analysis were
analyzed using probit analysis and resulted in
discountable effects for prey reduction.
No Effect for medium
sized frog
A "No effect"determination for pasture (1.1 lb/A) is due
to no LOC exceedence using the bird as a surrogate for
the CRLF for the 37 g animal resulting from the T-REX
analysis.
Nongranular Acute
Small Frog
May Affect:
The May Affect resulted from LOC exceedence using the
bird as a surrogate from the T-Rex analysis for all crops.
NLAA
An "NLAA" determination is due to no LOC exceedence
for any use for the small CRLF (1.4 g) from the T-Herps
analysis for consumption of small insect, large insect
small, small herbivore mammal, insectivore mammals or
small amphibian prey..
Nongranular Acute
Large Frog: May
Affect:
The May Affect resulted from LOC exceedence using the
bird as a surrogate in the T-Rex analysis for all crops.
NLAA
An "NLAA" determination is due to no LOC exceedence
for any use for the juvenile CRLF (238 g) from the T-
Herps analysis for consumption of small insect, large
insect small, small herbivore mammal, insectivore
mammals or small amphibian prey.
133
-------
Acute granular direct
effects on the CRLF:
No Effect
The no effect determination is due to no LOC
exceedence using the bird as a surrogate from the LDft2
results for noncrop non-agricultural ROW, forest site
preparation (5 lb/A) and rangeland (3 lb/A).
Nongranular chronic
direct effects using
the bird as a
surrogate:
May Affect:
Direct chronic effects
Using the bird as a
surrogate:
LAA for small
herbivore mammal
prey
Direct chronic effects
using the bird as a
surrogate:
NLAA for small
herbivore mammal
prey
Direct chronic effects
using the bird as a
surrogate:
LAA for CRLF
consuming small
insect prey
Direct chronic effects
using the bird as a
surrogate: NLAA for
CRLF consuming
small insect prey
The May affect is based on LOC exceedence using the
bird as a surrogate from te T-REX analysis. T-Herps was
used to refine the May Affect from T-REX to either an
"LAA" or "NLAA" determination. Chronic reproductive
effects are possible, based on non-granular uses of
hexazinone.
T-Herps was used to refine the May Affect from T-Rex.
The LAA determination resulted from LOC exceedence
based on T-Herps for noncrop (8 lb/A) to Christmas tree
(2 lb/A). RQs range from 4.22 to 1.05.
The NLAA determination for alfalfa (1.5 lb/A) and
pasture (1.1 lb/A) resulted from no LOC exceedence.
RQs range from 0.79-0.58.
T-Herps was used to refine the May Affect from T-REX
to an "LAA" determination.
All uses except Christmas tree, alfalfa and pasture
resulted in LOC exceedences for broadleaf. RQs range
from 3.6 (8 lb/A) to 1.35 (3 lb/A).
Christmas tree (2 lb/), alfalfa (1.5 lb/A) and pasture (1.1
lb/A) did not result in LOC exceedences for small small
insect prey resulting from T-Herps modeling. RQs for
small herbivore mammals range from 0.90 (1.5 lb/A) to
0.50 (1.1 lb/A).
Direct chronic effects
using the bird as a
surrogate:
NLAA consuming
large insect prey
Non-crop ( 8 lb/A), pineapple (3.6 lb/A), blueberry ( 3
lb/A) Christmas tree (2 lb/A), alfalfa (1.1 lb/A) and
pasture (1.1 lb/A) did not result in LOC exceedences for
large insect prey resulting from T-Herps modeling. RQs
for broadleaf range from 0.90 (2 lb/A) to 0.5 (1.1 lb/A)
based on T-Herps analysis.
134
-------
Direct chronic
effects uaing the bird
as a surrogate:
NLAA consuming
small insectivore
mammals
Direct chronic
effects uaing the bird
as a surrogate:
NLAA consuming
small insectivore
mammals
An NLAA determination resulted from no LOC
exceedence for small insectivore mammal,. RQs for
small insectivore mammals range from 0.26 (8 lb/A) to
0.04 (1.1 lb/A).
RQs for small amphibians range from for 0.12 (8 lb/A) to
0.02 (1.1 lb/A) based on T-Herps analysis.
Chronic direct effects
using the bird as a
surrogate (Granular):
May Affect LAA
Granular formulations for noncrop(12 lb/A), forest site
preparation (5 lb/A) and rangeland ( 3 lb/A) resulted in
LOC exceedences resulting from the T-REX analysis.
RQs range from 1.35 for rangeland to 5.4 for noncrop.
Indirect Effect s of Hcxa/lnone on the Terrestrial -Phase CRLF
Survival, growth, and reproduction of
CRLF individuals via effects on prey (i.e.,
terrestrial invertebrates, small terrestrial
vertebrates, including mammals and
terrestrial phase amphibians)
Noneranualr Acute
Indirect orcv
reduction for
Terrestrial
Invertebrates:
May Affect
LAA
An LAA determination for small insect prey is based on
the uncertainty regarding the effects of hexazinone on
terrestrial invertebrates due to related toxicity values
reporting no mortality at the highest concentration tested
for all uses.
135
-------
Nongranular Acute
Indirect orcv
reduction for
terrestrial
nvertebrates (Larue
Insect Prey):
May Affect
LAA
An LAA determination for large insect prey is based on
the uncertainty regarding the effects of hexazinone on
terrestrial invertebrates due to related toxicity values
reporting no mortality at the highest concentration tested
for noncrop (8 lb/A), pineapple (3.6 lb/A) and
blueberry/conifer release (3 lb/A).
Nongranular Acute
No Effect
A "No effect" determination for large insect prey for
Christmas tree (2 lb/A), alfalfa (1.5 lb/A) and pasture
(1.1 lb/A) uses was based on no LOC exceedence from
the T-REX analysis.
Indirect mammal
orcv reduction:
Non-granular Acute
May Affect
The May Affect is based on T-Rex results for 15 g
mammal with a diet of shortgrass for non-crop (8 lb/A)
through pasture (1.1 lb/A) uses.
LAA
The LAA determination is due to noncrop (8 lb/A) and
blueberry (3 lb/A) LOC exceedence from the T-REX
analysis.
Indirect mammal prey
reduction
Nongranular Acute:
May Affect
The May Effect is based on RQs falling between the
endangered species and acute risk LOC.
NLAA
Due to RQs falling between the endangered species and
acute risk LOC further refinement used the the probit
analysis. The potential reduction in abundance of
terrestrial mammals as food for Christmas tree, alfalfa
and pasture uses would be < 1%; therefore a "not likely
to adversely affect" determination can be made.
136
-------
Granular Acute
Indirect mammal prey
reduction:
No Effect (granular
uses)
A No effect determination is based on the LDft2 results
from the T-REX analysis for non-crop(12 lb/A), forest
site preparation (5 lb/A) and rangeland (3 lb/A).
Indirect orcv
reduction for
mammal Nongranular
Chronic reproductive effects are possible, based on non-
Chronic:
granular uses of hexazinone. The May affect is due to
LOC exceedences for all nongranular uses.
May Affect:
LAA
All uses resulted in LOC exceedences for short grass.
RQs range from 9.60 (8 lb/A) to 1.32 (1.1 lb/A) based on
T-Rex.
Indirect prey
reduction for
amphibian using the
bird as a surrogate
Nongranular Acute
May Affect
The May affect is due to LOC exceedence using the bird
as a surrogate for all crops resulting from the T-Rex
analysis.
137
-------
LAA
An "LAA" determination using the bird as a surrogate is
based on LOC exceedence for noncrop (8 lb/A) uses. RQ
for noncrop = 0.76 resulted from the T-REX analysis.
Indirect prey
reduction for
amphibian using the
bird as a surrogate
NLAA
Conifer release, blueberry, Christmas tree, alfalfa and
pasture uses resulted in RQs falling between the listed
and non-listed LOCs from the T-REX analysis. Based on
this assessment, the probit analysis was used as a further
refinement for the determination. The potential reduction
in abundance of amphibians as food for these uses would
be < 1% at most; therefore a "not likely to adversely
affect" determination can be made.
Indirect orcv
reduction for
amphibian usins the
bird as a surrogate
Nongranular Chronic
May Affect:
LAA
Chronic reproductive effects are possible, based on non-
granular uses of hexazinone resulting from the T-REX
analysis using the bird as a surrogate.
All nongranular uses except Christmas tree, alfalfa and
pasture resulted in LOC exceedences for broadleaf. RQs
for broadleaf range from 1.35 (3 lb/A) to 3.60 (8 lb/A).
138
-------
Amphibian usins the
bird as a surrogate
Nongranular Chronic
No Effect
Christmas tree, alfalfa and pasture did not result in LOC
exceedences broadleaf. RQs for broadleaf range from
0.5 (3 lb/A) to 0.90 (1.5 lb/A) resulting from the T-Rex
analysis.
Woodv and
srassv/herbaceous
riparian vesetation:
Riparian woody and herbaceous vegetation may be
affected because terrestrial plant RQs are above LOCs.
May Affect
Survival, growth, and reproduction of
CRLF individuals via indirect effects on
habitat (i.e., riparian vegetation)
LAA < 184 ft
(ground)
Due to MO A, which interferes with photosynthesis and
RNA, terrestrial-phase CRLFs may be indirectly affected
by adverse effects to sensitive woody and herbaceous
vegetation which provide habitat and cover for the CRLF
and its prey.
NLAA > 184 ft
(ground)
There was an "NLAA" determination for animals
outside the aerial drift buffer of 184 ft resulting from the
AGDISP model..
LAA < 850 ft (aerial);
Due to MO A, which interferes with photosynthesis and
RNA, terrestrial-phase CRLFs may be indirectly affected
by adverse effects to sensitive woody and herbaceous
vegetation which provide habitat and cover for the CRLF
and its prey.
NLAA > 850 ft
(aerial)
There was an "NLAA" determination for animals
outside the aerial drift buffer of 850 ft resulting from the
AGDISP model.
'I'iihlc 7.2 KITcels Dclcrminnlion Siiiniiiiirv for the ( rilicnl llnhilnl linpncl Annlvsis
Assossiiu'iK I'lnripoini r.l'kiis
l)i-UTiiiin;iiinn
liiisis for IkMcrmiiiiiliuii
Aquatic-Phase PCEs
(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)
Alteration of channel/pond morphology or geometry Habitat
and/or increase in sediment deposition within the modification
Due to the MOA which interferes with
photosynthesis and RNA sensitive herbaceous
139
-------
stream channel or pond: aquatic habitat (including
riparian vegetation) provides for shelter, foraging,
predator avoidance, and aquatic dispersal for juvenile
and adult CRLFs.
riparian vegetation may be affected based on all
modeled uses of hexazinone; therefore, critical
habitat may be modified by an increase in sediment
deposition and reduction in herbaceous riparian
vegetation that provides for shelter, foraging,
predator avoidance, and aquatic dispersal for
juvenile and adult aquatic-phase 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.8
Habitat
modification
Sensitive non-vascular aquatic plants may be
affected; therefore, critical habitat may be modified
via turbidity and reduction in oxygen content
necessary for normal growth and viability of
juvenile and adult aquatic-phase CRLFs.
Alteration of other chemical characteristics necessary
for normal growth and viability of CRLFs and their
food source.
No effect to
growth and
viability
Habitat
modification
based on
alteration of
food source
Direct effects to the aquatic-phase CRLF, via
mortality, growth, and/or fecundity, are not
expected. However, critical habitat of the CRLF
may be modified via hexazinone-related impacts to
non-vascular aquatic plants as food items for
tadpoles. LOCs are exceeded for non-vascular uses
for non-agricultural ROW (12 lb/A), noncrop (8
lb/A), conifer release (3 lb/A), rangeland (3 lb/A),
Christmas Trees (2 lb/A), alfalfa (1.5 lb/A) and
pasture (1.1 lb/A).
No Habitat
Modification
There was no LOC exceedence for blueberry uses
for nonvascular plants.
Reduction and/or modification of aquatic-based food
sources for pre-metamorphs (e.g., algae)
Habitat
modification
Based on the results of the effects determinations
for aquatic plants, critical habitat of the CRLF may
be modified via hexazinone-related impacts to non-
vascular aquatic plants as food items for tadpoles.
LOCs are exceeded for modeled uses for (12 lb/A),
noncrop uses (8 lb/A), conifer release (3 lb/A),
rangeland (3 lb/A), Christmas trees (2 lb/A), alfalfa
(1.5 lb/A) and pasture (1.1 lb/A).
No Habitat
Modification
Blueberry use resulted in no LOC exceedence.
Terrestrial-Phase PCEs
(Upland Habitat and Dispersal Habitat)
8 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.
140
-------
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
Habitat
modification
Based on MO A, modification to critical habitat may
occur via hexazinone-related impacts to sensitive
woody and herbaceous vegetation, which provide
habitat and cover for the terrestrial-phase CRLF and
its prey, based on all assessed uses of hexazinone.
Terrestial incident reports support a "habitat
modification" determination.
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
Habitat
modification
Based on the MOA for hexazione modification to
dispersal habitat may occur via hexazinone-related
impacts to sensitive woody and herbaceous
vegetation, which provide habitat and cover for the
terrestrial-phase CRLF and its prey, based on all
assessed uses of hexazinone. Terrestrial incident
reports support the "habitat modification'
determination.
Reduction and/or modification of food sources for
terrestrial phase juveniles and adults
Habitat
modification
Based on the characterization of indirect effects to
terrestrial-phase CRLFs via reduction in the prey
base, critical habitat may be modified via a
reduction in mammals and terrestrial-phase
amphibians as food items.
Alteration of chemical characteristics necessary for
normal growth and viability of juvenile and adult
CRLFs and their food source.
Habitat
modification
Direct acute effects, via mortality, are expected for
the terrestrial-phase CRLF. Chronic reproductive
effects are also possible. Therefore, hexazinone
may modify critical habitat by altering chemical
characteristics necessary for normal growth and
viability of terrestrial-phase CRLFs and their
mammalian and amphibian food sources.
Table 5.14 Hexazione Use-Specific Direct Effect Determinations
Use
Aquatic phase frogs
Terrestrial-phase frogs
Aquatic Animals
Aquatic Plants
Terrestrial Animals
Terrestrial
Plants
Acute
Chronic
Non
Vasular
Vascular
Acute
Chronic
Noncrop
NE
NE
LAA
LAA
LAA
LAA
LAA
Conifer Release
NE
NE
LAA
NE
NLAA
LAA
LAA
Blueberry
NE
NE
NE
NE
NLAA
LAA
LAA
Christmas Tree
NE
NE
LAA
NE
NLAA
NE
LAA
Alfalfa
NE
NE
NE
NE
NLAA
NE
LAA
Pasture
NE
NE
NE
NE
NE
NE
LAA
141
-------
Table 5.15 Hexazinone Use-Specific Indirect Effeci
ts Determinations1 Based on Effects to Prey
Use
Algae
Aquatic Invertebrates
Terrestrial
Invertebrates
(Acute)
Aquatic phase
frogs and fish
Terrestria
froi
l-phase
•S
Small Mammals
Acute
Chronic
Acute
Chronic
Acute
Chronic
Acute
Chronic
Noncrop
LAA
NE
NE
LAA
NE
NE
LAA
NE
LAA
LAA
Pineapple
LAA
NE
NE
LAA
NE
NE
NLAA
LAA
LAA
LAA
Conifer Release
LAA
NE
NE
LAA
NE
NE
NLAA
LAA
LAA
LAA
Blueberry
NE
NE
NE
LAA
NE
NE
NLAA
LAA
LAA
LAA
Christmas Tree
LAA
NE
NE
LAA
NE
NE
NLAA
NE
NLAA
LAA
Alfalfa
LAA
NE
NE
LAA
NE
NE
NLAA
NE
NLAA
LAA
Pasture
LAA
NE
NE
LAA
NE
NE
NE
NE
NLAA
LAA
' LAA = likely to adversely affect; NLAA = not likely to adversely affect; NE = no effect
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
to seek concurrence with the LAA determinations and to determine whether there are
reasonable and prudent alternatives and/or measures to reduce and/or eliminate potential
incidental take.
When evaluating the significance of this risk assessment's direct/indirect and 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
142
-------
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.
8. 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.
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.
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. Environmental Toxicology & Chemistry 23 (9):2170-2177.
Fellers, Gary M. 2005a. Rana draytonii Baird and Girard 1852. California Red-legged
Frog. Pages 552-554. hr. M. Lannoo (ed.) Amphibian Declines: The Conservation
Status of United States Species, Vol. 2: Species Accounts. University of
California Press, Berkeley, California, xxi+1094 pp. (
http://www.werc.usus.uov/pt-reves/pdfs/Rana%20dravtonii.PDF)
Fellers, Gary M. 2005b. California red-legged frog, Rana draytonii Baird and Girard.
Pages 198-201. hr. L.L.C. Jones, et al (eds.) Amphibians of the Pacific Northwest.
xxi+227.
143
-------
Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation
of the EPA food-chain (Kenaga) nomogram, and instrument for estimating
pesticide residues on plants. Environmental Toxicology and Chemistry 13
(9): 1383-1391.
Hayes, M.P. and M.M. Miyamoto. 1984. Biochemical, behavioral and body size
differences between Rana aurora aurora and R. a. draytonii. Copeia 1984(4):
1018-22.
Hayes and Tennant. 1985. Diet and feeding behavior of the California red-legged frog.
The Southwestern Naturalist 30(4): 601-605.
Hoerger, F., and E.E. Kenaga. 1972. Pesticide residues on plants: Correlation of
representative data as a basis for estimation of their magnitude in the
environment. In F. Coulston and F. Korte, eds., Environmental Quality and
Safety: Chemistry, Toxicology, and Technology, Georg Thieme Publ, Stuttgart,
West Germany, pp. 9-28.
Jennings, M.R. and M.P. Hayes. 1985. Pre-1900 overharvest of California red-legged
frogs (Rana aurora draytonii): The inducement for bullfrog (Rana catesbeiana)
introduction. Herpetological Review 31(1): 94-103.
Jennings, M.R. and M.P. Hayes. 1994. Amphibian and reptile species of special concern
in California. Report prepared for the California Department of Fish and Game,
Inland Fisheries Division, Rancho Cordova, California. 255 pp.
Karvonen, T., Koivusalo, H., Jauhiainen, M., Palko, J. and Weppling, K. 1999. A
hydrological model for predicting runoff from different land use areas, Journal of
Hydrology, 217(3-4): 253-265.
Kupferberg, S. 1997. Facilitation of periphyton production by tadpole grazing:
Functional differences between species. Freshwater Biology 37:427-439.
Kupferberg, S.J., J.C. Marks and M.E. Power. 1994. Effects of variation in natural
algal and detrital diets on larval anuran (Hyla regilla) life-history traits. Copeia
1994:446-457.
LeNoir, J.S., L.L. McConnell, G.M. Fellers, T.M. Cahill, J.N. Seiber. 1999.
Summertime Transport of Current-use pesticides from California's Central Valley
to the Sierra Nevada Mountain Range, USA. Environmental Toxicology &
Chemistry 18(12): 2715-2722.
144
-------
McConnell, L.L., J.S. LeNoir, S. Datta, J.N. Seiber. 1998. Wet deposition of current-use
pesticides in the Sierra Nevada mountain range, California, USA. Environmental
Toxicology & Chemistry 17(10): 1908-1916.
McDonald M.A.I; Healey J.R.; Stevens P. A. 2002. The effects of secondary forest
clearance and subsequent land-use on erosion losses and soil properties in the
Blue Mountains of Jamaica. Agriculture, Ecosystems & Environment, Volume
92, Number 1: 1-19.
Modzelewski, E. H., Jr.; Culley, D. D., Jr. (1974) Growth responses of the bullfrog, Rana
catesbeiana fed various live foods. Herpetologica 30: 396-405.
Okisaka S.; Murakami A.; Mizukawa A.; Ito J.; Vakulenko S.A.; Molotkov I.A.; Corbett
C.W.; Wahl M.; Porter D.E.; Edwards D.; Moise C. 1997. Nonpoint source runoff
modeling: A comparison of a forested watershed and an urban watershed on the
South Carolina coast. Journal of Experimental Marine Biology and Ecology,
Volume 213, Number 1: 133-149.
Phuong V.T. and van Dam J. Linkages between forests and water: A review of research
evidence in Vietnam. In. Forests, Water and Livelihoods European Tropical
Forest Research Network. ETFRN NEWS (3pp).
Rathburn, G.B. 1998. Rana aurora draytonii egg predation. Herpetological Review,
29(3): 165.
Reis, D.K. Habitat characteristics of California red-legged frogs (Rana aurora draytonii):
Ecological differences between eggs, tadpoles, and adults in a coastal brackish
and freshwater system. M.S. Thesis. San Jose State University. 58 pp.
Seale, D.B. and N. Beckvar. 1980. The comparative ability of anuran larvae (genera:
Hyla, Bufo and Rana) to ingest suspended blue-green algae. Copeia 1980:495-
503.
Sparling, D.W.G.M. Fellers, L.L. McConnell. 2001. Pesticides and amphibian
population declines in California, USA. Environmental Toxicology & Chemistry
20(7): 1591-1595.
Teske, Milton E., and Thomas B. Curbishley. 2003. AgDisp ver 8.07 Users Manual.
USDA Forest Service, Morgantown, WV.
U.S. EPA (1993). Wildlife Exposure Factors Handbook. EPA/600/R-93/187. Office of
Research and Development. December, 1993.
U.S. Environmental Protection Agency (U.S. EPA). 1998. Guidance for Ecological Risk
Assessment. Risk Assessment Forum. EPA/630/R-95/002F, April 1998.
145
-------
U.S. EPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of
Pesticide Programs. Office of Prevention, Pesticides, and Toxic Substances.
Office of Pesticide Programs. Washington, D.C. January 23, 2004.
U.S. EPA (2006). User's Guide. T-REX Version 1.3.1. Environmental Fate and Effects
Division. Office of Pesticide Programs. U.S. Environmental Protection Agency.
Washington, D.C. December 07, 2006.
U.S. Fish and Wildlife Service (USFWS). 1996. Endangered and threatened wildlife and
plants: determination of threatened status for the California red-legged frog.
Federal Register 61(101):25813-25833.
USFWS. 2002. Recovery Plan for the California Red-legged Frog (Rana aurora
draytonii). Region 1, USFWS, Portland, Oregon. (
http://ecos.fws.gov/doc/recoverv_plans/2002/02Q528.pdf)
USFWS. 2006. Endangered and threatened wildlife and plants: determination of critical
habitat for the California red-legged frog. 71 FR 19244-19346.
USFWS. Website accessed: 30 December 2006.
http: //www, fws. gov/ endangered/features/rl_fro eJ rlfro g. html# where
U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service
(NMFS). 1998. Endangered Species Consultation Handbook: Procedures for
Conducting Consultation and Conference Activities Under Section 7 of the
Endangered Species Act. Final Draft. March 1998.
USFWS/NMFS. 2004. 50 CFR Part 402. Joint Counterpart Endangered Species Act
Section 7 Consultation Regulations; Final Rule. FR 47732-47762.
Wassersug, R. 1984. Why tadpoles love fast food. Natural History 4/84.
146
------- |