sfcPotential Risks of Labeled Atrazine Uses
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Pesticide Effects Determination
August 31,2007
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Potential Risks of Labeled Atrazine Uses to the
Topeka Shiner (Notropis topeka)
Pesticide Effects Determination
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
August 31,2007
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Table of Contents
1. Executive Summary 4
1.1. Purpose of Assessment 4
1.2. Assessment Procedures 4
1.3. Atrazine Uses and Locations Assessed 4
1.4. Endpoints Assessed 5
1.5. Summary of Conclusions 5
2. Problem Formulation 9
2.1 Purpose 9
2.2. Stressor Identification, Source, and Distribution in the Environment 10
2.3. Assessed Species 15
2.4. Designated Critical Habitat 18
2.5 Action Area 20
2.6. Assessment Endpoints and Measures of Ecological Effect 23
2.7. Conceptual Model 26
2.8. Analysis Plan 28
2.9. Previous Assessments and Status of Forthcoming Data 32
3. Exposure Assessment 33
3.1 Label Application Rates and Intervals 33
3.2 Aquatic Exposure Assessment 35
4. Effects Assessment 51
4.1 Ecotoxicity Study Data Sources 54
4.2. Toxicity to Freshwater Fish 56
4.3 Toxicity to Freshwater Invertebrates 59
4.4 Toxicity to Aquatic Plants 61
4.5. Toxicity to Terrestrial Plants 63
4.6. Toxicity to Terrestrial Invertebrates 66
4.7 Community-Level Endpoints: Threshold Concentrations 67
4.8 Use of Probit Slope Response Relationship to Provide Information on the Endangered
Species Levels of Concern 70
4.9 Incident Database Review 71
5. Risk Characterization 72
5.1 Risk Estimation 73
5.2 Risk Description 78
5.3 Adverse Modification to Designated Critical Habitat 91
5.4. Environmental Baseline and Cumulative Effects 93
6. Uncertainties 94
6.1. Exposure Assessment Uncertainties 94
6.2 Effects Assessment Uncertainties 96
6.3 Assumptions Associated with the Acute LOCs 99
7. Summary of Direct and Indirect Effects to the Topeka shiner and
Adverse Modification to Designated Critical Habitat 99
8. References 103
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List of Appendices
Appendix A Ecological Effects Data
Appendix B Description of Available Monitoring Data
Appendix C Incident Database Information
Appendix D RQ Method and LOCs
Appendix E Bibliography of ECOTOX Open Literature Not Evaluated and
Papers Not Accepted by ECOTOX
Appendix F Maps of Designated Critical Habitat Locations
Appendix G Multiple Active Ingredient Product Analysis
Appendix H Description of Healthy Riparian Habitat Characteristics
Appendix I Environmental Baseline and Cumulative Effects Analysis
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1. Executive Summary
1.1. Purpose of Assessment
The purpose of this assessment is to make an "effects determination" by evaluating the
potential direct and indirect effects of the herbicide atrazine on the survival, growth, and
reproduction of the Topeka shiner (Notropis topeka), a small minnow that inhabits the
upper Great plains of the United States. In addition, this assessment evaluates the
potential for atrazine use to result in the destruction or adverse modification of critical
habitat designated by the U.S. Fish and Wildlife Service (USFWS, 2004: 70 FRNo. 57,
15239- 15245).
1.2. Assessment Procedures
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 is consistent with procedures and
methodology outlined in the Agency's Overview Document (U.S. EPA, 2004).
Acute and chronic risk quotients (RQs) were compared to the Agency's Levels of
Concern (LOCs) to identify instances where atrazine use within the action area has the
potential to adversely affect the Topeka shiner or adversely modify designated critical
habitat. When RQs for a particular type of effect are below LOCs, the pesticide is
considered to have "no effect" on the species and its designated critical habitat. Where
RQs exceed LOCs, a potential to cause adverse effects or habitat modification was
identified, leading to a conclusion of "may affect". If atrazine use "may affect" the
Topeka shiner, and/or may cause adverse modification to designated critical habitat, the
best available additional information was considered to refine the potential for exposure
and effects, and distinguish actions that are NLAA (not likely to adversely affect) from
those that are LAA (likely to adversely affect).
Atrazine degradates were not assessed because degradates have been shown to be orders
of magnitude less toxic than atrazine to aquatic organisms and are presumed to be less
toxic than atrazine to terrestrial plants (Section 4). Therefore, potential risks from
exposure to atrazine's degradates were not quantified in this assessment.
1.3. Atrazine Uses and Locations Assessed
All potential uses of atrazine within the action area were evaluated as part of this
assessment. Atrazine is used throughout the United States on a number of agricultural
commodities (primarily corn and sorghum) and on non-agricultural sites (including
residential uses, forestry, and turf). It is typically applied as a spray by air or ground, but
residential use products include a granular formulation. Although the action area is likely
to encompass a large area of the United States, given its extensive use, the scope of this
assessment limits consideration of the overall action area to those portions that are
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applicable to the protection of the Topeka shiner. As such, the action area was defined by
the current range of the species and designated critical habitat.
1.4. Endpoints Assessed
The assessment endpoints include direct toxic effects on survival, reproduction, and
growth of individuals, as well as indirect effects, such as reduction of the food source
and/or modification of habitat.
Federally designated critical habitat has been established for the Topeka shiner. Primary
constituent elements (PCEs), as described in U.S. FWS (2004) were used to evaluate
whether atrazine has the potential to adversely modify designated critical habitat. PCEs
evaluated as part of this assessment include the following:
Water quality related to potential effects of atrazine (for example, potential effects
on water quality resulting from reduction in aquatic or terrestrial plants);
Presence of instream aquatic cover; and
An adequate food base that allows for unimpaired growth, reproduction, and
survival of all life stages.
1.5. Summary of Conclusions
Effects determinations for direct/indirect effects to the Topeka shiner and the critical
habitat impact analysis, by assessment endpoint, are presented in Tables 1.1 and 1.2. In
summary, a likely to adversely affect (LAA) determination was made for direct chronic
effects to the Topeka shiner and for indirect effects resulting from potential effects to
aquatic and terrestrial plants. This assessment considers an LAA determination to mean
that effects to a single individual Topeka shiner could occur that are not "insignificant" or
"discountable" as defined in Section 5.2.
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Table 1.1 Effects Determination Summary for the Topeka shiner by Assessment
Endpoint
Assessment Endpoint
Effects Determination
Basis for Conclusion
1. Survival, growth, and
reproduction of
individuals via direct
acute or chronic effects
Acute effects
No Effect - all uses
RQs across all uses did not exceed any acute LOC based on
the most sensitive available freshwater fish LC50.
See Section 5.2.1.1
Chronic effects11
LAA
Corn (all regions);
Fallow (west region)
No effect
All other uses
RQs based on the maximum labeled application rates were up
to 1.3 to 1.6 for corn and fallow uses, respectively, based on
60-day EECs estimated using PRZM/EXAMS. The LOAEC
in the most sensitive life-cycle study was 120 ug/L based on a
7% reduction in length and 16% reduction in weight in brook
trout. 60-Day EECs were lower than the fish life-cycle
LOAEC; therefore, at the 60-day EECs, the magnitude of
potential effect to the Topeka shiner would be expected to be
lower than effects observed at the LOAEC if the Topeka
shiner is equally sensitive to atrazine as brook trout. Life-
cycle studies were also conducted in bluegill sunfish
(NOAEC = 95 ug/L, MRID 00024377) and fathead minnows
(NOAEC <150 ug/L, MRID 42547103; NOAEC = 210 ug/L,
MRID 00024377). Only EECs for the fallow use exceed the
NOAEC in bluegill sunfish, and no EECs exceed the NOAEC
for fathead minnows. Chronic RQs based on EECs that
incorporate typical use rates for corn or fallow uses (0.6 - 0.9
lbs a.i./acre) would not exceed the LOC of 1.0.
See Section 5.2.1.2.
2. Indirect effects to
individuals via potential
effects to aquatic plants
(food and primary
productivity)
LAA
Corn, sorghum, fallow,
and forestry uses (all
regions)
NLAA
All other uses
Community level effects thresholds are exceeded based on
PRZM/EXAMS 14- to 90-day EECs.
See Section 5.2.2.3.
NLAA conclusion was based on significance of effect as
defined in Section 5.2.
3. Indirect effects to
individuals via direct
effects to aquatic and
terrestrial invertebrates as
food items
NLAA for all uses
NLAA conclusion was based on significance of effect as
defined in Section 5.2. The potential magnitude of effect to
aquatic and terrestrial invertebrate food items is expected to
be low such that measurable effects to the Topeka shiner are
not expected.
See Section 5.2.2.1.
4. Indirect effects to
individuals via direct
effects to other fish
needed for spawning
habitat (e.g., sunfish) and
diet.
NLAA for all uses
NLAA conclusion was based on significance of effect as
defined in Section 5.2. No acute LOCs were exceeded for
fish. The chronic LOC was exceeded for the most sensitive
species tested (brook trout); however, the potential magnitude
of effect to fish is expected to be low such that measurable
indirect effects to the Topeka shiner are not expected.
See Section 5.2.2.4.
4. Indirect effects to
individuals via reduction
of terrestrial vegetation
(i.e., riparian habitat)
required to maintain
acceptable water quality
and habitat
Direct effects to
sensitive riparian
vegetation: LAA
Riparian areas within the Great Plains are expected to be
predominantly grasslands. Data presented in Section 4 of this
assessment indicates that grassy and herbaceous vegetation
may be sensitive to atrazine at estimated exposure levels.
Therefore, riparian areas that are predominantly
grassy/herbaceous vegetation and that receive runoff or
spraydrift from atrazine use sites may be affected. Until data
on specific land management practices and sensitivity of
riparian vegetation adjacent to Topeka shiner habitat is
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Assessment Endpoint
Effects Determination
Basis for Conclusion
available, potential effects to riparian vegetation as indicated
by terrestrial plant LOC exceedance, is presumed to
potentially adversely affect the Topeka shiner and its
designated critical habitat.
See Section 5.2.2.5.
a Topeka shiner habitats include side pools of low-order streams with low/negligible flow rates. PRZM/EXAMS was
considered appropriate to represent both short-term and long-term potential exposures in these types of habitats.
However, there is uncertainty in this assumption as discussed in Section 3 of this assessment.
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Table 1.2 Effects Determination Summary
'or the Critical Habitat Impact Analysis
PCEa
Conclusions
Basis for Conclusions
(see Section 5.3. for additional information)
Streams and side-channel pools with water
quality necessary for unimpaired behavior,
growth, and viability of all life stages. The
water quality components can vary
seasonally and include-temperature (1 to
30[deg]Centigrade), total suspended solids
(0 to 2000 ppm), conductivity (100 to 800
mhos), dissolved oxygen (4 ppm or
greater), pH (7.0 to 9.0), and other
chemical characteristics
LAA
As described in Table 1.1, RQs were exceeded for
aquatic and terrestrial plants (Sections 5.2.2.3 and
5.2.2.5), which suggest that effects to aquatic and
sensitive riparian plants could occur and potentially
result in alteration of suspended solid levels, oxygen
levels, and other chemical characteristics.
Living areas for juvenile Topeka shiners
with water velocities less than 0.5
meters/second (approx. 20 inches/second)
with depths less than 0.25 meters (approx.
10 inches) and moderate amounts of
instream aquatic cover, such as woody
debris, overhanging terrestrial vegetation,
and aquatic plants
LAA
As described in Table 1.1, RQs were exceeded for
aquatic and terrestrial plants (Sections 5.2.2.3 and
5.2.2.5), which suggests that "amounts of instream
aquatic cover, such as woody debris, overhanging
terrestrial vegetation, and aquatic plants" could be
affected. Woody plant species are not expected to be
adversely affected by atrazine at EECs presented in
this assessment; however, other overhanging
vegetation and aquatic plants could potentially be
impacted in areas that are in close proximity to
atrazine use.
Sand, gravel, cobble, and silt substrates
with amounts of fine sediment and
substrate embeddedness that allows for
nest building and maintenance of nests and
eggs by native Lepomis sunfishes (green
sunfish, orangespotted sunfish, longear
sunfish) and Topeka shiner as necessary
for reproduction, unimpaired behavior,
growth, and viability of all life stages
LAA
Atrazine may affect riparian vegetation of the
Topeka shiner's habitats that are in close proximity
to atrazine use sites. However, sedimentation /
siltation in a stream may depend on numerous
factors, and determining whether atrazine use is
expected to result in an overall increase in
sediment/silt levels in a habitat is difficult.
Nonetheless, sensitive riparian areas exposed to
atrazine could be adversely impacted (MRID
42041403), which could indirectly affect the Topeka
shiner. Until further analysis is performed on
specific land management practices in areas
surrounding Topeka shiner habitats, terrestrial plant
LOC exceedance is presumed to indicate potential
adverse indirect effects the Topeka shiner and its
designated critical habitat.
An adequate terrestrial, semiaquatic, and
aquatic invertebrate food base that allows
for unimpaired growth, reproduction, and
survival of all life stages
NLAA
As indicated in Table 1.1, atrazine is not likely to
adversely affect the Topeka shiner via reduction in
aquatic and terrestrial invertebrates as food supply.
a Other PCEs (described in Section 2.4) were not evaluated because there was no perceived direct link
between those PCEs and processes that could be affected by atrazine use.
When evaluating the significance of this risk assessment's direct/indirect and adverse
habitat modification effects determinations, it is important to note that pesticide
exposures and predicted risks to the species and its resources (i.e., food and habitat) are
not expected to be uniform across the action area. In fact, given the assumptions of drift
and downstream transport (i.e., attenuation with distance), pesticide exposure and
associated risks to the species and its resources are expected to decrease with increasing
distance away from the treated field or site of application. Evaluation of the implication
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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 the Topeka shiner
within its current range 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.
Enhanced information on land use and land management practices within
watersheds inhabited by the Topeka shiner. Terrestrial plant LOC
exceedances were used to indicate whether atrazine is likely to adversely
modify riparian areas adjacent to the Topeka shiner's habitat and
subsequently affect water quality characteristics. However, the potential
for atrazine to affect water quality characteristics (e.g., sediment levels,
temperature, etc.) depends on a number of factors (discussed in Section
5.2) including riparian area characteristics, soil conservation practices, and
land use adjacent to the riparian area of Topeka shiner habitat.
2. Problem Formulation
2.1 Purpose
The purpose of this endangered species risk assessment is to evaluate the potential direct
and indirect effects resulting from the Federal Insecticide, Fungicide, and Rodenticide
Act (FIFRA) registered uses of the herbicide atrazine (6-chloro-N-ethyl-N-isopropyl-l, 3,
5-triazine-2, 4-diamine) on the survival, growth, and/or reproduction of Topeka shiner
individuals. In addition, this assessment evaluates whether FIFRA regulatory actions
regarding atrazine use can be expected to result in the destruction or adverse modification
of critical habitat. Critical habitat has been designated by the USFWS for the Topeka
shiner (USFWS, 2004: 70 FRNo. 57, 15239 - 15245) and is further described in Section
2.4. This ecological risk assessment is a component of the settlement for the Natural
Resources Defense Council, Civ. No: 03-CV-02444 RDB (filedMarch 28, 2006).
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2.2. Stressor Identification, Source, and Distribution in the Environment
2.2.1. Identification
Atrazine is an herbicide that inhibits photosynthesis by associating with a protein
complex of the Photosystem II in chloroplast photosynthetic membranes, which stops
electron flow in Photosystem II (Schulz et al., 1990). The result is an inhibition in the
transfer of electrons that in turn inhibits the formation and release of oxygen. Chemical
identity and physical characteristics of atrazine are summarized in Table 2.1 below.
Table 2.1. Summary of Chemical Identification and Selected Physicochemical
Properties of Atrazine
Chemical Property
Value
Chemical Name
Atrazine
CAS RN
1912-24-9
PC Code
080803
Chemical Structure
H H
Molecular Weight
215.7 g/mole
Vapor Pressure
3 x 10"7 mm Hg at 20 deg C
Solubility in Water
33 mg/1
2.2.2. Stressor Source and Distribution
2.2.2.1. Use Characterization
Atrazine is widely used to control broadleaf and many other weeds, primarily in corn,
sorghum, and sugarcane (U.S. EPA, 2003a). As a selective herbicide, atrazine is applied
pre-emergence and post-emergence.
Atrazine is used on a variety of terrestrial food crops, non-food crops, forests,
residential/industrial uses, golf course turf, recreational areas and rights-of-way. Atrazine
yields season-long weed control in corn, sorghum and certain other crops. The major
atrazine uses include: corn (83 percent of total ai produced per year - primarily applied
pre-emergence), sorghum (11 percent of total ai produced), sugarcane (4 percent of total
ai produced) and others (2 percent ai produced). Atrazine formulations include dry
flowable, flowable liquid, liquid, water dispersible granule, wettable powder and coated
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fertilizer granule. The maximum registered use rate for atrazine is 4 lbs ai/acre; and 4 lbs
ai/acre is the maximum, single application rate for the following uses: sugarcane, forest
trees (softwoods, conifers), forest plantings, guava, macadamia nuts, ornamental sod (turf
farms), and ornamental and/or shade trees.
Assessment of the use information is critical to the development of appropriate modeling
scenarios and evaluation of the appropriate model inputs (Kaul and Jones, 2006).
Information on the agricultural uses of atrazine in the states comprising the regionalized
exposure assessment approach (see Section 3.2.2 for more details) for the Topeka shiner
(Missouri, Iowa, Kansas, Nebraska, South Dakota, Minnesota, and North Dakota), as
defined in Section 2.6 of this assessment, was gathered (Kaul and Jones, 2006). Use
information within the action area is utilized to determine which uses should be modeled,
while the application methods, intervals, and timing are critical model inputs. No state or
county level usage information is available on non-agricultural uses (residential, rights-
of-way, forestry, or turf) of atrazine.
Agricultural cropland (presented as cultivated cropland and hay/pasture) and atrazine use
relative to the Topeka shiner's action area are depicted in Figures 2.1 and 2.2,
respectively. Non-agricultural uses associated with urban/suburban areas (residential,
turf, and rights-of-way) are also likely to be co-located with the listed species habitat
ranges. The landuse mapping presented in Figure 2.1 provides a breakout of aggregated
turf uses (residential, recreational, and golf course). No consistent coverage is available
for rights- of-way uses. Given the potential use pattern shown in Figure 2.1, atrazine
could be used in close proximity to the species range.
.A
Topkea Shiner Action Area Relative
to Potential Atrazine Use Sites from 2001 NLCD Landcover Data
Legend
Landcover class
Cultivated Crops
¦¦ Developed, Low Intensity
Developed, Medium Intensity
Developed, Open Space
I I Hay/Pasture
(^3Topeka_Shiner_HUC8_watersheds outline
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Figure 2.1 Agricultural Cropland Relative to Topeka shiner Action Area
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|_| To peka_Shin er_HU C8_wate rshe ds o utline.
Topkea Shiner Action Area
Relative to Atrazine Use (lbs/county)
Legend
Atrazine Use (lbs/county)
I 10 - 27729
B 27730 - 82603
H 82604 - 165432
165433 - 441435
w
1441436- 1090674
Figure 2.2 Atrazine Use Relative to Action Area
All agricultural use information for atrazine within the action area was considered in
order to determine which uses occur within the action area for the Topeka shiner
(discussed further in Section 2.5). As noted above, information is not available for non-
agricultural uses; therefore, they are presumed to occur within the action area and are
included in this assessment. Agricultural uses of atrazine within the action area include
corn, sweet corn, sorghum, and fallow land. Specifically, county level data for the areas
within and immediately surrounding the action area were used (Kaul and Jones, 2006).
County level estimates of atrazine use were derived using state level estimates from
USDA-NASS and data obtained from Doane (www.doane.com; the full dataset is not
provided due to its proprietary nature). State level data from 1998 to 2004 were averaged
together and extrapolated down to the county level based on apportioned county level
crop acreage data from the 2002 USDA Agriculture of Census (AgCensus).
Of the six principal states making up the regionalized approach for conducting the
exposure assessment (several states far removed from the species location were not
evaluated for use information because it is assumed that use in states in close proximity
will have the greatest impact on the species), atrazine was used between 1998 and 2004
on average approximately 27,600,000 total pounds across all use sites (Table 2.2). The
state with the highest use was Iowa with approximately 8,200,000 lbs used and the least
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use was reported in North Dakota. Atrazine was used on corn, sorghum, sweet corn, and
fallow land. The crop with the greatest use was corn with approximately 23,000,000 lbs.
All other crops averaged considerably less use than corn. Of the remaining crops, only
sorghum was used at amounts at or above 1,000,000 lbs.
In general, this information suggests that the central portion of the action area is located
on the fringe of the highest atrazine use area, but within the areas where atrazine use is
moderate (Nebraska and Iowa). In general, atrazine use decreases in intensity further
south and north of this area, with the lowest use in the northern Great Plains (North
Dakota) and southern Missouri. The atrazine use pattern within the action area is
graphically presented in Figure 2.2. It should be noted, however, that information on
non-agricultural use of atrazine is not available and, therefore, was not included in Figure
2.2.
Typical use information for atrazine is summarized in Table 2.2. For all uses, the typical
application rate and number of applications are fairly consistent across all states and all
uses. For all uses, the average application rate is 0.7 lbs per acre, while the average
number of applications is 1.1. For corn, the average application rate is 0.9 lbs per acre,
and the number of applications is 1.2.
Table 2.2 Summary of Typical Atrazine Use Information Collected between 1998
and 2004 for all States in the Topeka s
liner Action Area
Crop
Total Pounds
by Crop
Average Number of
Applications by
Crop
Average Application
Rate (lbs/acre) by
Crop
corn
23,100,000
1.2
0.9
F allow/hay/pasture
273,000
1.0
0.9
sorghum
4,480,000
1.1
1.2
sweet corn
2000
1.4
0.6
Wheata
85,000
1.1
0.6
a atrazine is used on wheat fields to control fallow conditions and is not applied directly to wheat
2.2.2.2. Environmental Fate and Transport Assessment
Environmental fate and transport characteristics were described in detail in previous
assessments (U.S. EPA 2003a; U.S. EPA 2006a,c,d,e). A summary of information
pertinent to this assessment is provided below; previous assessments may be referenced
for additional information.
In general, atrazine is expected to be mobile and persistent in the environment. The main
route of dissipation is microbial degradation under aerobic conditions. Because of its
persistence and mobility, atrazine is expected to reach surface and ground water. This is
confirmed by the widespread detections of atrazine in surface water and ground water.
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Atrazine is persistent in soil, with a half-life (time until 50% of the parent atrazine
remains) exceeding 1 year under some conditions (Armstrong et al., 1967). Atrazine can
also enter or contact nearby non-target plants, soil, and surface water via spray drift
during application. Atrazine is applied directly to target plants during foliar application,
but pre-plant and pre-emergent applications are generally more prevalent. A summary of
atrazine's degradation half-lives are reported in Table 2.3 below.
Table 2.3. Summary of Environment
tal Dissipation and Degradation Half-Lives
Dissipation / Degradation Route
Half-Life
Photolysis
Stable
Hydrolysis
Stable
Aerobic Soil Metabolism
3-4 Months
Henry's Law constant
2.6 x 10"9 atm-nrVmol
Terrestrial field dissipation
13 - 261 days
Anaerobic aquatic metabolism
Total system: 608 days
Water: 578 days
Sediment: 330 days
a The Log Kow (2.7) and Freundlich Kads (<1 to <3) may somewhat offset the low Henry's Law constant
value, thereby possibly resulting in some volatilization from foliage, and its relatively low adsorption
characteristics indicate that atrazine may undergo substantial washoff from foliage.
A number of degradates of atrazine were detected in laboratory and field environmental
fate studies. Deethyl-atrazine (DEA) and deisopropyl-atrazine (DIA) were detected in all
studies, and hydroxy-atrazine (HA) and diaminochloro-atrazine (DACT) were detected in
all but one of the listed studies. Deethylhydoxy-atrazine (DEHA) and
deisopropylhydroxy-atrazine (DIHA) were also detected in one of the aerobic studies.
Typically, these degradates have been detected predominantly in groundwater at
concentrations less than, or equal to, those of atrazine. In surface water, the degradates
are typically found at concentrations below that of atrazine.
All of the chloro-triazine and hydroxy-triazine degradates detected in the laboratory
metabolism studies were present at less than the 10% of applied that the Agency uses to
classify degradates as "major degradates" (U.S. EPA, 2004). However, several
degradates were detected at percentages greater than 10% in soil and aqueous photolysis
studies (see Section 3). Insufficient data are available to allow for an estimate of half-
lives for these degradates. The dealkylated degradates are more mobile than parent
atrazine, while HA is less mobile than atrazine and the dealkylated degradates. As
discussed in Section 2.8, degradates are not specifically evaluated as part of this
assessment.
2.3. Assessed Species
General information, including a summary of habitat requirements, designated critical
habitat, food habits, and reproduction data relevant to this endangered species risk
assessment is provided below. Additional information can be found in the following
references: KS DWP, 2004; Dahle, 2001; U.S. FWS, 1998, and SD DGFPWD, 2003 and
at the following url: http://mountain-prairie.fws.gov/species/fish/shiner/.
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The Topeka shiner is a small minnow (<3 inches long) found in small low-order prairie
streams with cool temperatures and good water quality, typically with clean gravel, rock,
or sand bottoms (U.S. FWS, 1998; KS DWP, 2004; Dahle, 2001). The Topeka shiner is
pelagic (prefers open waters) and prefers mid-water and surface areas of streams. It is
seldom found in choppy waters. It may be found in streams that are small enough to stop
flowing during dry summer months and are, therefore, fed by seepage of groundwater
(U.S. FWS, 1998).
Topeka shiners spawn from late May to mid August. Spawning occurs over gravel nests
of sunfish (U.S. FWS, 1998). It is unknown if the Topeka shiner utilizes other silt-free
substrates for spawning or if it relies solely on sunfish nests for spawning.
Dietary behavior of the Topeka shiner is described as a generalist omnivore. Its diet
consists primarily of aquatic insects (particularly midges) in addition to plant material
and zooplankton (SDDGFP, 2003). Dahle (2001) studied the stomach content of a
population of Topeka shiners in Minnesota and reported that 75% of their diet consisted
of microcrustaceans and insects, and the remaining 25% consisted of vascular plant
matter, algae, sand/ detritus, and various fish and other invertebrates.
Topeka shiners are currently found in a small fraction of its historical range including
fragmented populations primarily in scattered tributaries of the Missouri and Mississippi
rivers and the Flint Hills region of Kansas (http://www.fws.gov/mountain-
prairie/species/fish/shiner/facts.htm). The species is known to occur in the following
watersheds (http://www.epa.gov/fedrgstr/EPA-SPECIES/1998/December/Dav-
15/e33100.htm) (see Figure 2.3):
Kansas: Kansas River Basin (Smoky Hill, Big Blue, and Lower Kansas
watersheds); Arkansas River Basin (Neosho watershed)
Missouri: Missouri River Basin (Missouri, Grand, Lamine, Chariton, and Des
Moines watersheds)
Nebraska: Elkhorn and Loup watersheds
Iowa: Des Moines, Raccoon, Boone, Big Sioux, and Rock watersheds
South Dakota: Big Sioux, Vermillion, and James watersheds
Minnesota: Big Sioux and Rock watersheds
16
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frown
Coding
-kiinlinL
South Dakota
Bead
iv lu rm /
RockN
obleu
yonUscEola
icolii
10 a
Hutchi
B
Nebraska
M ush ill
Potlawatom
eart/S"K1w"ee
Die km
V 'allac e
nanusee
Kansas
h la noil Chase
n wood
iutlei
Minnesota
CalhounVjfrig^t
lie
C4iol|Bo4ne|own
egg
H.VrisWp^1"
Pettis
Figure 2.3. Current Known Locations (County Level) of the Topeka Shiner.
County level data was obtained from U.S. FWS (2007)
17
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2.4. Designated Critical Habitat
Effective August 26, 2004, the USFWS designated critical habitat for the Topeka shiner
(USFWS, 2005: FR Vol. 69 No. 143 pp. 44735 - 44770; revised in FR Vol. 70 No. 57
pp. 15239 - 15245). Critical habitat has been designated in Iowa, Minnesota, and
Nebraska. A total of 83 stream segments and 836 stream miles are included in the critical
habitat. Most of the critical habitat is in Minnesota (57 stream segments and 605 stream
miles) followed by Iowa (25 stream segments; 225 stream miles), then Nebraska (1
stream segment; 6 stream miles). Maps of designated critical habitat locations are in
Appendix F.
'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. Critical habitat may also include specific areas outside the geographic
area occupied by the species at the time it is listed in accordance with provisions of
Section 3(5)(A) of the ESA, upon determination that such areas are essential for
conservation of the species. Critical habitat receives protection under Section 7 of the
ESA through prohibition against destruction or adverse modification of critical habitat
with regard to actions carried out, funded, or authorized by a Federal Agency. Section 7
requires consultation on Federal actions that are likely to result in the destruction or
adverse modification of critical habitat.
To be included in a critical habitat designation, the habitat must first 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 (i.e., areas on which the PCEs are found, as
defined in 50 CFR 414.12(b)).
The designated critical habitat areas are considered to have the PCEs that justify critical
habitat designation. Activities that may destroy or adversely modify critical habitat are
those that alter the PCEs and jeopardize the continued existence of the species.
Evaluation of actions related to use of atrazine that may alter the PCEs of the Topeka
shiner's critical habitat form the basis of the critical habitat impact analysis. The primary
constituent elements for the Topeka shiner consist of the following:
1. Streams most often with permanent flow, but that can become intermittent during
dry periods;
2. Side-channel pools and oxbows either seasonally connected to a stream or
maintained by groundwater inputs, at a surface elevation equal to or lower than
the bankfull discharge stream elevation. The bankfull discharge is the flow at
which water begins leaving the channel and flowing into the floodplain; this level
is generally attained every 1 to 2 years. Bankfull discharge, while a function of
the size of the stream, is a fairly constant feature related to the formation,
maintenance, and dimensions of the stream channel;
18
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3. Streams and side-channel pools with water quality necessary for unimpaired
behavior, growth, and viability of all life stages. The water quality components
can vary seasonally and includetemperature (1 to 3 0[deg] Centigrade), total
suspended solids (0 to 2000 ppm), conductivity (100 to 800 mhos), dissolved
oxygen (4 ppm or greater), pH (7.0 to 9.0), and other chemical characteristics;
4. Living and spawning areas for adult Topeka shiner with pools or runs with water
velocities less than 0.5 meters/second (approx. 20 inches/second) and depths
ranging from 0.1 to 2.0 meters (approximately 4 to 80 inches);
5. Living areas for juvenile Topeka shiners with water velocities less than 0.5
meters/second (approx. 20 inches/second) with depths less than 0.25 meters
(approx. 10 inches) and moderate amounts of instream aquatic cover, such as
woody debris, overhanging terrestrial vegetation, and aquatic plants;
6. Sand, gravel, cobble, and silt substrates with amounts of fine sediment and
substrate embeddedness that allows for nest building and maintenance of nests
and eggs by native Lepomis sunfishes (green sunfish, orangespotted sunfish,
longear sunfish) and Topeka shiner as necessary for reproduction, unimpaired
behavior, growth, and viability of all life stages;
7. An adequate terrestrial, semiaquatic, and aquatic invertebrate food base that
allows for unimpaired growth, reproduction, and survival of all life stages;
8. A hydrologic regime capable of forming, maintaining, or restoring the flow
periodicity, channel morphology, fish community composition, off-channel
habitats, and habitat components described in the other primary constituent
elements; and
9. Few or no nonnative predatory or nonnative competitive species present.
The analysis for listed species' direct and indirect effects provides a basis for the
evaluation of potential effects to the designated critical habitat. Atrazine effects are
limited to those that are linked to biologically-mediated processes. Therefore, the critical
habitat analysis for atrazine is limited in a practical sense to those PCEs of the critical
habitat that are biological or that can be reasonably linked to biologically mediated
processes. Therefore, only PCEs Nos. 3, 5, 6, and 7 above are assessed with respect to
potential effects from labeled use of atrazine.
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2.5 Action Area
For listed species assessment purposes, the action area is considered to be the area
affected 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 atrazine uses is likely to encompass considerable portions of the United States based
on the large array of both agricultural and non-agricultural uses. Based on the available
atrazine monitoring data (discussed further in Section 3.2.5) and the toxicity data for the
most sensitive non-vascular aquatic plant, the Agency's LOCs are likely to be exceeded
for at least one taxonomic group in many watersheds that are in proximity to or
downstream of atrazine use sites. Therefore, the overall action area for atrazine is likely
to include many watersheds of the United States that co-occur and/or are in proximity to
agricultural and non-agricultural atrazine use sites. However, in order to focus this
assessment, the scope limits consideration of the overall action area to those geographic
portions that may be applicable to the protection of the Topeka shiner included in this
assessment. Based on the available information on potential atrazine use sites, none of
the streams and rivers that are within the range of the Topeka shiner could be excluded
from the action area. Therefore, the portion of the atrazine action area that is assessed as
part of this ESA includes the area within the boundary of the watersheds that drain to
known current locations of the Topeka shiner.
The Topeka shiner is known to currently exist in a wide geographic range from the
western corn belt in Iowa and Missouri to the central and northern great plains in Kansas,
Nebraska, and South Dakota. In general, the species is found in headwater streams (e.g.
1st and 2nd order streams by the Strahler classification system) throughout the region.
Historically, the Topeka shiner is presumed to have ranged over a much broader area;
however, this assessment focuses on the current range of the species. In many instances,
the location information obtained from U.S FWS (1998) and NatureServe
(www, nature serve. org, accessed on May 3, 2007) for the Topeka shiner is non-specific
and has therefore been identified as county-level occurrence. The Nature Serve
information has been augmented with county-level occurrence information provided by
USFWS (V. Tabor, USFWS, personal communication, 2007). Both sets of county-level
information were compiled, and these data have been used to identify watersheds for
inclusion as occupied stream miles. The "action area" is the overall geographic scope
where effects may occur. However, because this assessment is limited to evaluation of
the potential effects of atrazine use to the Topeka shiner, the action area is defined as the
geographic scope where effects may occur, either directly or indirectly, to the Topeka
shiner or its designated critical habitat. Therefore, the initial definition of the action area
for this species is defined by the watersheds that drain to the known current range and
designated critical habitats of the Topeka shiner.
20
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As shown in Figure 2.4, the action area for the Topeka shiner represents a patchwork of
watersheds stretching from southeastern North Dakota south through Iowa and into
Missouri and Kansas, with isolated portions in western Kansas and Nebraska. Deriving
the geographical extent of this portion of the action area is the product of consideration of
the types of effects atrazine may be expected to have on the environment, the exposure
levels to atrazine that are associated with those effects, and the best available information
concerning the use of atrazine and its fate and transport within the area identified in
Figure 2.4.
Specifically, a map was created using ESRI's ArcMap GIS. Each of the counties where
the Topeka shiner is reportedly located was added to the map using the geographical
location information from the Nature Serve website
(http://www.natureserve.org/explorer/). Additional locations not included in the Nature
Serve data were provided by the USFWS (V. Tabor, USFWS, personal communication,
2007). These locations were assigned to a watershed (HUC8, or USGS hydrologic unit
code) and added to the map. The next step in defining the action area was to assume that
all waters, within or draining to the identified watersheds, are part of the action area.
Areas draining to the specified watersheds were defined by identifying all watersheds
located upstream of the known species' locations using the USGS' hydrologic unit code
(HUC) watersheds. In this case, USGS cataloging unit watersheds, or HUC8 watersheds,
were used to define the extent of the action area.
More detail on the USGS' HUC classification scheme may be found at the following
website:
http://water.usgs.gov/GIS/huc.html
The results of the screening level assessment suggest that effects on aquatic plants are
possible anywhere within the defined area. In general, available monitoring data for the
action area show that peak concentrations are consistent with modeling and are above the
Agency's screening levels of concern for indirect effects (see Section 3.2).
Longer term exposures from monitoring data are difficult to assess relative to the
Agency's LOCs. Preliminary analysis of the Ecological Monitoring Program data
(Appendix B), which is targeted for watersheds most vulnerable to atrazine runoff,
suggests that longer-term exposures (e.g. 30-day average concentrations) in selected
watersheds exceed the Agency's LOCs. However, these samples are collected from 2nd
and 3rd order streams, which may or may not be representative of some flow regimes (e.g.
headwater streams with limited flow and side pools of low-order streams) in which the
Topeka shiner resides. For monitoring data that is not specifically targeted to highly
vulnerable areas (described further in Appendix B), the limited sampling frequency
precludes a direct comparison of longer-term exposures (e.g. 30-day average
concentrations) with modeling.
In addition, an evaluation of use information was conducted to determine whether any or
all of the area described above should be included in the action area. As part of this
21
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effort, current labels were reviewed and local use information was evaluated to determine
which atrazine uses could potentially be present within the defined area. This data
suggest that extensive agricultural uses are present within the defined area and that the
existence of non-agricultural uses cannot be precluded. Finally, local land cover data
were considered to refine the characterization of potential atrazine use in the areas
defined above. The overall conclusion of this analysis was that while certain agricultural
uses (e.g., guava, macadamia nuts, sugarcane) could likely be excluded and some non-
agricultural uses of atrazine were unlikely, none of the full extent depicted in Figure 2.4
could be excluded from the final action area based on usage and land cover data.
The environmental fate properties of atrazine were also evaluated to determine which
routes of transport are likely to have an impact on the listed species included in this
assessment. Review of the environmental fate data, as well as physico-chemical
properties of atrazine, suggest that transport via runoff and spray drift are likely to be the
dominant routes of exposure. In addition, long-range atmospheric transport of pesticides
could potentially contribute to atrazine concentrations in the aquatic habitat used by the
Topeka shiner. Given the physico-chemical profile for atrazine and data showing that
atrazine has been detected in both air and rainfall samples, the potential for long range
transport from outside the area defined above cannot be precluded. However, the
contribution of atrazine via long-range atmospheric transport is not expected to approach
the concentrations predicted by modeling (see Section 3.2).
Atrazine transport away from the site of application by both spray drift and volatilization
has been documented. Spray drift is addressed as a localized route of transport from the
application site in the exposure assessment. However, quantitative models are currently
unavailable to address the longer-range transport of pesticides from application sites.
The environmental fate profile of atrazine, coupled with the available monitoring data,
suggest that long-range transport of volatilized atrazine is a possible route of exposure to
non-target organisms; therefore, the full extent of the action area could be influenced by
this route of exposure. However, given the amount of direct use of atrazine within the
immediate area surrounding the species, the magnitude of documented exposures in
rainfall at or below available surface water and groundwater monitoring data (as well as
modeled estimates for surface water), and the lack of modeling tools to predict the impact
of long range transport of atrazine, the extent of the action area is defined by the transport
processes of runoff and spray drift for the purposes of this assessment.
Based on this analysis, the action area for atrazine as it relates to the Topeka shiner is
defined by the entire watersheds depicted in Figure 2.4.
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Action Area for Topeka Shiner
Figure 2.4 Topeka Shiner Action Area Defined by Hvdrologic Unit Code (HUC8)
Watersheds
2.6. Assessment Endpoints and Measures of Ecological Effect
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."1 Selection of the assessment endpoints is based on valued
entities (i.e., Topeka shiner and PCEs of designated critical habitat), the ecosystems
potentially at risk (i.e., streams and rivers of Topeka shiner), the migration pathways of
atrazine (i.e., runoff and spray drift), and the routes by which ecological receptors are
exposed to atrazine-related contamination (i.e., direct contact).
Assessment endpoints include direct toxic effects on the survival, reproduction, and
growth of individuals, as well as indirect effects, such as reduction of the prey base
and/or modification of its habitat. In addition, potential destruction and/or adverse
modification of critical habitat is evaluated via potential effects to PCEs, which are
components of the habitat areas that provide essential life cycle needs (Section 2.3).
Each assessment endpoint requires one or more "measures of ecological effect," which
1 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
Legend
West_States
i i Upper_Great_Plains_States
I ITnnftka Rhinp.r HI J OR watersheds outline
Topeka_Shiner_HUC8_watersheds
23
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are 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 evaluated based on a variety of data sources including registrant-
submitted studies and information from the open literature. Acute and chronic toxicity
information from registrant-submitted guideline tests are required to be conducted on a
limited number of organisms. Additional ecological effects data from the open literature,
including effects data on aquatic freshwater microcosm and mesocosm data, were also
considered.
Measures of effect from microcosm and mesocosm data provide an expanded view of
potential indirect effects of atrazine on aquatic organisms, their populations and
communities in the laboratory, in simulated field situations, and in actual field situations.
With respect to the microcosm and mesocosm data, threshold concentrations were
determined from realistic and complex time variable atrazine exposure profiles
(chemographs) for modeled aquatic community structure changes. Methods were
developed to estimate ecological community responses for monitoring data sets of
interest based on their relationship to micro- and mesocosm study results, and thus to
determine whether a certain exposure profile within a particular use site and/or action
area may have exceeded community-level threshold concentrations. Ecological modeling
with the Comprehensive Aquatic Systems Model (CASM) (Bartell et al., 2000; Bartell et
al., 1999; and DeAngelis et al., 1989) was used to integrate direct and indirect effects of
atrazine to indicate changes to aquatic community structure and function.
A complete discussion of all the toxicity data available for this risk assessment, including
use of CASM and associated aquatic community-level threshold concentrations, and the
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 Topeka shiner risks
associated with exposure to atrazine are provided in Table 2.4.
Table 2.4 Summary of Assessment Endpoints and Measures of Ecological Effect for
Topeka shiner
Assessment Endpoint
Measures of Ecological Effect
1. Survival, growth, and reproduction of the
Topeka shiner via direct effects resulting from
atrazine exposure or via indirect effects to other fish
needed for spawning habitat (e.g., sunfish).
la. Freshwater fish acute LC50
lb. Freshwater fish life-cycle NOAEC
2. Survival, growth, and reproduction of the
Topeka shiner individuals via indirect effects on
food source (i.e., aquatic invertebrates, aquatic
plants, fish)
2a. Freshwater fish, invertebrate, and aquatic plant
EC50 or LC50
2b. Freshwater fish and invertebrate NOAEC
2c. Microcosm/mesocosm threshold concentrations
showing aquatic primary productivity community-
level effects.
3. Survival, growth, and reproduction of the
Topeka shiner via indirect effects on habitat and/or
primary productivity (i.e., aquatic plant community)
3a. Vascular plant (duckweed) acute EC50
3b. Non-vascular plant (freshwater algae) acute
EC50
3c. Microcosm/mesocosm threshold concentrations
showing aquatic primary productivity community-
level effects
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4. Survival, growth, and reproduction of the
Topeka shiner via indirect effects on terrestrial
vegetation (riparian habitat) required to maintain
acceptable water quality and habitat
4a. Monocot and dicot seedling emergence EC25
4b. Monocot and dicot vegetative vigor EC25
Assessment endpoints and measures of ecological effect selected to characterize potential
designated critical habitat modification associated with exposure to atrazine are provided
in Table 2.5. As previously discussed, the basis of the designated critical habitat analysis
is protection of the PCEs identified for the designated critical habitat. PCEs that are
identified as assessment endpoints are limited to those that are of a biological nature (i.e.,
the biological resource requirements for the listed species associated with the critical
habitat) and those PCEs for which atrazine effects data are available. Therefore, abiotic
PCEs, such as flow regime, pH, and hardness are not evaluated because there is no
perceived link between the biotic assessment endpoints and the abiotic PCEs (i.e.,
atrazine in surface water is unlikely to impact flow, pH, and hardness levels). In
addition, the PCE related to the presence of competitive or predacious nonnative species
is also not evaluated because there is no ecotoxicity data to differentiate native versus
non-native species sensitivity to atrazine.
Table 2.5 Summary of Assessment Endpoints and Measures of Ecological Effect for
Primary Constituent Elements of Designated Critical Habitat3
Assessment Endpoint
Measures of Ecological Effect
Streams and side-channel pools with water quality
necessary for unimpaired behavior, growth, and
viability of all life stages. The water quality
components can vary seasonally and include-
temperature (1 to 30 [deg] Centigrade), total
suspended solids (0 to 2000 ppm), dissolved oxygen
(4 ppm or greater), and other chemical
characteristics
la. Monocot and dicot seedling emergence EC25
lb. Monocot and dicot vegetative vigor EC25
lc. Vascular and non-vascular plant (freshwater
algae) acute EC50
Id. Microcosm/mesocosm threshold concentrations
showing aquatic primary productivity community-
level effects
Living areas for juvenile Topeka shiners with water
velocities less than 0.5 meters/second (approx. 20
inches/second) with depths less than 0.25 meters
(approx. 10 inches) and moderate amounts of
instream aquatic cover, such as woody debris,
overhanging terrestrial vegetation, and aquatic
plants;
Sand, gravel, cobble, and silt substrates with
amounts of fine sediment and substrate
embeddedness that allows for nest building and
maintenance of nests and eggs by native Lepomis
sunfishes (green sunfish, orangespotted sunfish,
longear sunfish) and Topeka shiner as necessary for
reproduction, unimpaired behavior, growth, and
viability of all life stages
3a. Monocot and dicot seedling emergence EC25
3b. Monocot and dicot vegetative vigor EC25
An adequate terrestrial, semiaquatic, and aquatic
invertebrate food base that allows for unimpaired
growth, reproduction, and survival of all life stages.
4a. Terrestrial and aquatic invertebrate EC50s
4b. Terrestrial and freshwater invertebrate NOAEC
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a Water quality parameters including pH and hardness are also included in this PCE; however these components of
water quality are not evaluated because there is no perceived link between the risk assessment biotic endpoints and
water pH and hardness.
2.7. Conceptual Model
2.7.1 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 atrazine to the environment.
Based on the results of the 2003 atrazine IRED (U.S. EPA, 2003a), the following risk
hypotheses are presumed for this endangered species risk assessment:
Atrazine in surface water and/or runoff/drift from treated areas within the action
area may directly affect the Topeka shiner by causing mortality or adversely affecting
growth or fecundity;
Atrazine in surface water and/or runoff/drift from treated areas within the action
area may indirectly affect the Topeka shiner by reducing or changing the composition of
food supply and/or perturbing fish required for reproduction habitat of the Topeka shiner;
Atrazine in surface water and/or runoff/drift from treated areas within the action
area may indirectly affect the Topeka shiner by reducing or changing the composition of
the aquatic plant community in the waters of the species' current range, thus affecting
primary productivity and/or cover;
Atrazine in surface water and/or runoff/drift from treated areas within the action
area may indirectly affect the Topeka shiner 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 rivers and streams comprising the species' current range;
Atrazine in surface water and/or runoff/drift from treated areas within the action
area may adversely modify one or more of the PCEs of the designated critical habitat of
the Topeka shiner.
2.7.2 Diagram
The conceptual model is a graphic representation of the structure of the risk assessment.
It specifies the stressor (atrazine), release mechanisms, abiotic receiving media,
biological receptor types, and effects endpoints of potential concern. The conceptual
models for the atrazine endangered species risk assessment for the Topeka shiner and
designated critical habitat are shown in Figure 2.5. Exposure routes shown in dashed
lines are not quantitatively considered because the resulting exposures are expected to be
sufficiently low such that they are not expected to measurably contribute to potential
adverse effects to the Topeka shiner and/or designated critical habitat.
26
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Stressor
Vapor phase and
long range
transport
Source
Groundwater
Receptors
Attribute
Change
Runoff
Spray drift
Riparian Zone
Terrestrial plants
Food chain
Decrease in abundance
Shift in prey base
Atrazine applied to agricultural
fields, residential lawns, golf
courses, rights-of-way, and forestry
Habitat of Topeka shiner
Topeka shiner
Aquatic plants
Aquatic animals
Terrestrial invertebrates
Reduced survival
growth, or reproduction
of the Topeka shiner or
organisms on which it
depends.
Adverse Modification of
PCEs
Habitat integrity
Stream and bank destabilization
Decreased water quality
Sedimentation
Adverse modification of PCEs
Figure 2.5 Conceptual Model for Topeka Shiner
The conceptual model provides an overview of the expected exposure routes for the
Topeka shiner and its designated critical habitat within the atrazine action area previously
described in Section 2.5. In addition to the Topeka shiner, other aquatic receptors that
may be potentially exposed to atrazine include freshwater invertebrates and aquatic
plants. Designated critical habitat may also be adversely modified based on alteration of
the PCEs, which are those habitat components that support feeding, sheltering, and
reproduction of the Topeka shiner. For freshwater vertebrate and invertebrate species,
including the Topeka shiner, the major routes of exposure are considered to be via the
respiratory surface (gills) or the integument. Direct uptake and adsorption are the major
routes of exposure for aquatic plants. Direct effects to freshwater invertebrates and
aquatic plants resulting from exposure to atrazine may indirectly affect the Topeka shiner
and/or adversely modify its designated critical habitat via reduction and/or alteration in
food and habitat (i.e., substrate, water quality including oxygen content) availability
necessary for normal behavior, growth, and viability of all life stages. The available data
indicate that atrazine is not likely to bioconcentrate in aquatic food items at levels of
concern; fish bioconcentration factors (BCFs) range from 2 to 8.5 (U.S. EPA, 2003c).
In addition to aquatic receptors, terrestrial invertebrates and plants may also be exposed
to spray drift and runoff from atrazine use in the vicinity of streams that comprise the
current range and designated critical habitat for the Topeka shiner. Detrimental changes
in the riparian vegetation adjacent to the Topeka shiner's current habitat and designated
27
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critical habitat may cause adverse effects to water quality (i.e., temperature and turbidity),
stream bank stability, substrate composition, sediment loading, and spawning habitat.
The source and mechanism of release of atrazine into surface water are applications via
foliar spray and coated fertilizer granules for agricultural (i.e., corn, sorghum, and
fallow/idle land) and non-agricultural uses (i.e., golf courses, residential lawns, rights-of-
way, and forestry). Surface water runoff from the areas of atrazine application is
assumed to follow topography, resulting in direct runoff to the rivers and streams within
the action area. Spray drift and runoff of atrazine may also affect the foliage and
seedlings of terrestrial plants that comprise the riparian habitat that may be adjacent to the
habitat including designated critical habitat. Additional release mechanisms include
spray drift and atmospheric transport via volatilization, which may potentially transport
site-related contaminants to the surrounding air. Atmospheric transport is not considered
as a significant route of exposure for this assessment because the magnitude of
documented exposures in rainfall are at or below available surface water and monitoring
data, as well as modeled estimates of exposure.
2.8. Analysis Plan
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).
2.8.1. Scope of Assessment
Atrazine is currently registered as an herbicide in the U.S. to control annual broadleaf and
grass weeds in corn, sorghum, sugarcane, and other crops. In addition to food crops,
atrazine is also used on a variety of non-food crops, forests, residential/industrial uses,
golf course turf, recreational areas, and rights-of-way.
In accordance with the Overview Document, provisions of the Endangered Species Act
(ESA), and the Services' Endangered Species Consultation Handbook, the assessment of
effects of the FIFRA regulatory action is based on a defined action area and the extent of
association of this action area with locations of the Topeka shiner and its designated
critical habitat. It is acknowledged that the action area for a national-level FIFRA
regulatory decision involving a potentially widely used pesticide may potentially involve
numerous areas throughout the United States and its Territories. However, for the
purposes of his assessment, attention will be focused on those parts of the action area
with the potential to be associated with locations of the Topeka shiner and its designated
critical habitat.
The end result of the EPA pesticide registration process is an approved product label.
The label is a legal document that stipulates how and where a given pesticide may be
used. Product labels (also known as end-use labels) describe the formulation type,
acceptable methods of application, approved use sites, and any restrictions on how
28
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applications may be conducted. Thus, the use or potential use of atrazine in accordance
with the approved product labels is "the action" being assessed.
This ecological risk assessment is for currently registered uses of atrazine in portions of
the action area reasonably assumed to be biologically relevant to the Topeka shiner and
its designated critical habitat. Further discussion of the action area(s) and designated
critical habitat is provided in Section 2.4 and 2.5.
Degradates of atrazine include hydroxyatrazine (HA), deethylatrazine (DEA),
deisopropylatrazine (DIA), and diaminochloroatrazine (DACT). Comparison of available
toxicity information for the degradates of atrazine indicates lesser aquatic toxicity than
the parent for fish, aquatic invertebrates, and aquatic plants. Specifically, the available
degradate toxicity data for HA indicate that it is not toxic to freshwater fish and
invertebrates at the limit of its solubility in water. In addition, no adverse effects were
observed in fish or daphnids at DACT concentrations up to 100 mg/L. Acute toxicity
values for DIA are 8.5- and 36-fold less sensitive than acute toxicity values for atrazine in
fish and daphnids, respectively. In addition, available aquatic plant degradate toxicity
data for HA, DEA, DIA, and DACT report non-definitive EC50 values (i.e., 50% effect
was not observed at the highest test concentrations) at concentrations that are at least 700
times higher than the lowest reported aquatic plant EC50 value for parent atrazine.
Although degradate toxicity data are not available for terrestrial plants, lesser or
equivalent toxicity is assumed, given the available ecotoxicological information for other
taxonomic groups including aquatic plants and the likelihood that the degradates of
atrazine may lose efficacy as an herbicide. Therefore, given the lesser toxicity of the
degradates as compared to the parent, and the relatively small proportion of the
degradates expected to be in the environment and available for exposure relative to
atrazine, the focus of this assessment is parent atrazine. Additional details on available
toxicity data for the degradates are provided in Section 4 and Appendix A.
The Agency does not routinely include 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 its risk assessments. In the case of product formulations of active
ingredients (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).
Atrazine has registered products that contain multiple active ingredients. Analysis of the
available open literature and acute oral mammalian LD50 data for multiple active
ingredient products relative to the single active ingredient is provided in Appendix G.
The results of this analysis show that an assessment based on the toxicity of the single
active ingredient of atrazine is appropriate.
The results of available toxicity data for environmental mixtures of atrazine with other
pesticides are presented in Section A. 6 of Appendix A. According to the available data,
29
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other pesticides may combine with atrazine to produce synergistic or additive toxic
effects. Based on the results of the available data, study authors claim that synergistic
effects with atrazine may occur for a number of organophosphate insecticides including
diazinon, chlorpyrifos, and methyl parathion, as well as herbicides including alachlor. If
chemicals that show synergistic effects with atrazine are present in the environment in
combination with atrazine, the toxicity of atrazine may be increased, offset by other
environmental factors, or even reduced by the presence of antagonistic contaminants if
they are also present in the mixture. The variety of chemical interactions presented in the
available data set suggests that the toxic effect of atrazine, in combination with other
pesticides used in the environment, can be a function of many factors including but not
necessarily limited to: (1) the exposed species, (2) the co-contaminants in the mixture, (3)
the ratio of atrazine and co-contaminant concentrations, (4) differences in the pattern and
duration of exposure among contaminants, and (5) the differential effects of other
physical/chemical characteristics of the receiving waters (e.g., organic matter present in
sediment and suspended water). Quantitatively predicting the combined effects of all
these variables on mixture toxicity to any given taxa with confidence is beyond the
capabilities of the available data. However, a qualitative discussion of implications of the
available pesticide mixture effects data involving atrazine on the confidence of risk
assessment conclusions for the Topeka shiner is addressed as part of the uncertainty
analysis for this effects determination.
In this assessment, potential direct and indirect effects to the Topeka shiner and potential
adverse modification to critical habitat are evaluated in accordance with the methods
(both screening and species-specific refinements) described in the Agency's Overview
Document (U.S. EPA, 2004).
2.8.2. Analysis of Toxicity
Analysis of potential sensitivity of the Topeka shiner to atrazine is evaluated using the
most sensitive available acute and chronic endpoints reported from either registrant
submitted studies or the open literature. For acute effects, the most sensitive reliable
acute LC50 from the available submitted and open literature studies are used. For
chronic effects, the most sensitive NOAEC from submitted life-cycle studies and the
open literature are used. The open literature contains numerous studies. Only studies
that produced reliable toxicity values that are based on toxicological endpoints that are
directly correlated with survival or reproduction of the Topeka shiner are used for RQ
calculations.
Potential sensitivity of species on which the Topeka shiner may depend for survival and
reproduction (invertebrates, aquatic and terrestrial plants, and other fish) is also evaluated
using the most sensitive acute and chronic toxicity value from the most sensitive species
tested. If LOCs are exceeded based on the most sensitive toxicity value, then other
factors, including the potential magnitude of effect and the biology and behavior of the
Topeka shiner, are considered in the effects determination.
30
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Potential risk to aquatic plant communities utilizes more refined data than is generally
available for ecological risk assessment. Specifically, a robust set of microcosm and
mesocosm data and aquatic ecosystem models are available for atrazine that allowed for a
refinement of the indirect effects associated with potential aquatic community-level
effects (via aquatic plant community structural change and subsequent habitat
modification). Use of such information is consistent with the guidance provided 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).
2.8.3. Analysis of Exposure
Atrazine has been subject to a number of monitoring studies. Preliminary data are
available from an ongoing monitoring study that was designed to detect high end atrazine
concentrations in vulnerable watersheds. These data, together with other monitoring
studies and PRZM/EXAMS modeling are used to evaluate potential exposures of atrazine
to the Topeka shiner.
2.8.4. Analysis of Risk
As part of the effects determination, the Agency will reach one of the following three
conclusions regarding the potential for FIFRA regulatory actions regarding atrazine to
directly or indirectly affect Topeka shiner individuals and/or result in the destruction or
adverse modification of designated critical habitat:
"No effect";
"May affect, but not likely to adversely affect" ("NLAA"); or
"May affect and likely to adversely affect" ("LAA").
If the results of the initial baseline assessment show no LOC exceedances to the Topeka
shiner or any species on which the Topeka shiner may depend for survival or
reproduction, a "no effect" determination is made for the FIFRA regulatory action. If,
however, LOC exceedances suggest that potential direct or indirect effects to individuals
are anticipated and/or effects may impact the PCEs of the designated critical habitat, the
Agency concludes a preliminary "may affect" determination for the FIFRA regulatory
action regarding atrazine.
If a determination is made that use of atrazine within the action area "may affect"
individual Topeka shiners and/or designated critical habitat, additional information is
considered to refine the potential for exposure at the predicted levels and for effects to the
Topeka shiner and other taxonomic groups upon which the species depends (i.e.,
freshwater fish and invertebrates, aquatic plants, riparian vegetation). Additional
information including further evaluation of the potential impact of atrazine on the PCEs
is also used to determine whether destruction or adverse modification to designated
critical habitat may occur. Based on the refined information, the Agency uses the best
31
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available information 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 Topeka shiner and/or PCEs of designated critical habitat. This information
is presented as part of the Risk Characterization in Section 5.
2.9. Previous Assessments and Status of Forthcoming Data
Atrazine has been the subject of a number of ecological risk assessments conducted by
U.S. EPA. Several assessments have recently been conducted on the potential for
atrazine to affect a number of listed species as part of the Natural Resources Defense
Counsel settlement agreement and one listed species included in a second settlement
agreement with the Center for Biological Diversity and Save Our Springs Alliance.
These effects determinations, which are available on the web at www.epa.gov/espp.
review atrazine's potential direct and indirect effects to the following listed species:
1) Barton Springs salamander (Eurycea sosorum) (U.S. EPA, 2006c);
2) Shortnose sturgeon (Acipenser brevirostrum), dwarf wedgemussel
(Alasmidonta heterodon), loggerhead turtle (Caretta caretta), Kemp's ridley
turtle (Lepidochelys kempii), leatherback turtle (Dermochelys coriacea), and
green turtle (Chelonia mydas) in the Chesapeake Bay (U.S. EPA, 2006d);
3) Alabama sturgeon (Scaphirhynchus suttkusi) (U.S. EPA, 2006e).
4) Pink mucket pearly mussel, Rough pigtoe mussel, Shiny pigtoe pearly mussel,
Fine-rayed pigtoe mussel, Heavy pigtoe mussel, Ovate clubshell mussel,
Southern clubshell mussel, and Stirrupshell mussel (U.S. EPA, 2007).
In addition, the Agency completed a refined ecological risk assessment for potential
aquatic impacts of atrazine use in January 2003 (U.S. EPA, 2003a). This assessment was
based on laboratory ecotoxicological data as well as microcosm and mesocosm field
studies found in publicly available literature, a substantial amount of monitoring data for
freshwater streams, lakes, reservoirs, and estuarine areas, and incident reports of adverse
effects on aquatic and terrestrial organisms associated with the use of atrazine.
The results of the Agency's ecological assessments for atrazine are fully discussed in the
January 31, 2003, Interim Reregi strati on Eligibility Decision (IRED)2. The assessment
identified the need for the following information related to potential ecological risks was
established: 1) a monitoring program to identify and evaluate potentially vulnerable
waterbodies in corn, sorghum, and sugarcane use areas; and 2) further information on
potential amphibian gonadal developmental responses to atrazine. On October 31, 2003,
EPA issued an addendum that updated the IRED issued on January 31, 2003 (U.S. EPA,
2003b). This addendum described new scientific developments pertaining to monitoring
of watersheds and potential effects of atrazine on endocrine-mediated pathways of
amphibian gonadal development. As of the writing of this assessment, preliminary data
from the ecological monitoring study have been submitted and are used to characterize
potential exposures. However, analyses of the data are ongoing.
2 The 2003 Interim Reregistration Eligibility Decision for atrazine is available at the following Web site:
http://www.epa.gov/oppsrrdl/REDs/0001 .pdf.
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Finally, On August 1, 2003, EPA released an assessment of the potential effects of
atrazine to 26 listed Environmentally Significant Units (ESUs) of Pacific salmon and
steelhead. That assessment concluded that registered uses of atrazine would have "no
effect", directly or indirectly to the 26 ESUs nor to designated critical habitat. While
potential effects to riparian vegetation were noted, the extent of atrazine use in the large
geographic areas comprising the relevant watersheds, lead to a conclusion that use would
have no effect on the species from any potential effects to riparian areas.
As discussed in the October 2003 IRED, the Agency also conducted an evaluation of the
submitted studies regarding the potential effects of atrazine on amphibian gonadal
development and presented its assessment in the form of a white paper for external peer
review to a FIFRA Scientific Advisory Panel (SAP) in June 20033. In the white paper
dated May 29, 2003, the Agency summarized seventeen studies consisting of both open
literature and registrant-submitted laboratory and field studies involving both native and
non-native species of frogs (U.S. EPA, 2003d). The Agency concluded that none of the
studies fully accounted for environmental and animal husbandry factors capable of
influencing endpoints that the studies were attempting to measure. The Agency also
concluded that the current lines-of-evidence did not show that atrazine produced
consistent effects across a range of exposure concentrations and amphibian species tested.
Based on this assessment, the Agency concluded and the SAP concurred that there was
sufficient evidence to formulate a hypothesis that atrazine exposure may impact gonadal
development in amphibians, but there were insufficient data to confirm or refute the
hypothesis (http://www.epa.gov/oscpmont/sap/2003/June/iunemeetingreport.pdf).
Because of the inconsistency and lack of reproducibility across studies and an absence of
a dose-response relationship in the currently available data, the Agency determined that
the data did not alter the conclusions reached in the January 2003 IRED regarding
uncertainties related to atrazine's potential effects on amphibians. The SAP supported
EPA in seeking additional data to reduce uncertainties regarding potential risk to
amphibians. Subsequent data collection has followed the multi-tiered process outlined in
the Agency's white paper to the SAP (U.S. EPA, 2003d). In addition to addressing
uncertainty regarding the potential use of atrazine to cause these effects, these studies are
expected to characterize the nature of any potential dose-response relationship. A data
call-in for the first tier of amphibian studies was issued in 2005. The results of these
studies, as well as other recent open literature data which focus on the potential effects of
atrazine on amphibian gonadal development, are being reviewed. This information will
be presented and discussed as part of a second SAP to be held in October 2007.
3. Exposure Assessment
3.1 Label Application Rates and Intervals
3 The Agency's May 2003 White Paper on Potential Developmental Effects of Atrazine on Amphibians is
available at http://www.epa.gov/oscpmont/sap/2003/iune/finaliune2002telconfreport.pdf.
33
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Atrazine labels may be categorized into two types: labels for manufacturing uses
(including technical grade atrazine) and end-use products. Technical products, which
contain atrazine of high purity, are not labeled for environmental release, but for making
formulated products, which can be applied in specific areas to control weeds. The
formulated product labels legally limit atrazine's potential use to only those sites that are
specified on the labels and under the conditions of use (rate, timing, etc.) specified on the
label.
In the January and October 2003 IREDs (U.S. EPA, 2003a and b), EPA stipulated
numerous changes to the use of atrazine including label restrictions and other mitigation
measures designed to reduce risk to human health and the environment. Specifically
pertinent to this assessment, are provisions of a Memorandum of Agreement (MOA)
between the Agency and atrazine registrants. In the MO A, the Agency stipulated that
certain label changes must be implemented on all manufacturing-use product labels for
atrazine and on all end-use product labels for atrazine prior to the 2005 growing season.
These label changes included cancellation of certain uses, reduction in application rates,
and requirements for harmonization across labels including setbacks from waterways.
Specifically, the label changes prohibit atrazine use within 50 feet of sinkholes, 66 feet of
intermittent and perennial streams, and 200 feet of lakes and reservoirs.
While these setbacks were required to reduce atrazine deposition to water bodies as a
result of spray drift, it is expected that they will also result in a reduction in loading due
to runoff across the setback zone; however, current models do not address this reduction
quantitatively. Therefore, these restrictions are not quantitatively evaluated in this
assessment. A qualitative discussion of the potential impact of these setbacks on
estimated environmental concentrations of atrazine for the Topeka shiners is discussed
further in Section 3.2.3. Table 3.1 provides a summary of label application rates for
atrazine uses evaluated in this assessment.
Currently registered non-agricultural uses of atrazine within the action area include
residential areas such as playgrounds and home lawns, turf (golf courses and recreational
fields), rights-of-way, and forestry. Agricultural uses within the action area include corn,
sorghum, and fallow/idle land4. Other agricultural uses (macadamia nut, guava, and
sugarcane) are not present in the action area.
Atrazine is formulated as liquid, wettable powder, dry flowable and granular
formulations. Application methods for the agricultural uses includes ground application
(the most common application method), aerial application, band treatment, and
incorporated treatment, and applications using various sprayers (low-volume, hand held,
directed, and spreaders for granular applications). Risks from ground boom and aerial
applications are considered in this assessment because they are expected to result in the
4 Fallow or idle land is defined by the Agency as arable land not under rotation that is set at rest for a period
of time ranging from one to five years before it is cultivated again, or land usually under permanent crops,
meadows or pastures, which is not being used for that purpose for a period of at least one year. Arable land,
which is normally used for the cultivation of temporary crops, but which is temporarily used for grazing, is
also included.
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highest off-target levels of atrazine due to generally higher spray drift levels. Ground
boom and aerial modes of application tend to use lower volumes applied in finer sprays
than applications coincident with sprayers and spreaders, and thus have a higher potential
for off-target movement via spray drift.
Table 3.1 Atrazine Label Application Information for the Topeka Shiner
Assessment3
Scenario
Maximum
Application
Rate
(lbs/acre)
Maximum
Number of
Applications
Formulation
Method of
Application
Interval
Between
Applications
Forestry
4.0
1
Liquid
Aerial and
Ground
NA
Residential
2.0
2
Granular
Ground
30 days
Residential
1.0
2
Liquid
Ground
30 days
Rights-of-
Way
1.0
1
Liquid
Ground
NA
Fallow/ Idle
land
2.25
1
Liquid
Ground and
Aerial
NA
Corn
2.5b
2
Liquid
Ground and
Aerial
NA
Sorghum
2.0
1
Liquid
Ground and
Aerial
NA
Turf
2.0
2
Granular
Ground
30 days
Turf
1.0
2
Liquid
Ground
30 days
a Based on 2003 IRED and Label Change Summary Table memorandum dated June 12, 2006 (U.S. EPA, 2006b).
3.2 Aquatic Exposure Assessment
3.2.1 Introduction
As discussed in Section 2.3, the Topeka shiner resides principally in headwater streams in
the mid-continent of the United States. It is found primarily in low-order streams in
Minnesota, Missouri, Iowa, Kansas, Nebraska, and South Dakota. The action area
includes the entire watershed of streams and rivers in the areas defined above and are
presented graphically in Figure 2.4.
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The assessment of exposure within the action area is dependent upon a combination of
modeling and monitoring data. In accordance with the Overview Document (U.S. EPA,
2004), baseline exposures were based on modeling which assumes a static water body.
Available monitoring data for atrazine were also evaluated and incorporated into the
exposure assessment.
For this assessment, baseline modeling using a static water body indicates long-term (e.g.
60-day average) exposure concentrations that are similar to the estimated peak value and
considerably higher than concentrations seen in most monitoring data. However, the
Topeka shiner's habitat includes headwater streams and side pools with low to negligible
annual flow. The standard ecological water body is considered to represent headwater
streams adjacent to treated fields; therefore, the static water body EECs are considered
representative of high-end estimates of potential exposure for the Topeka shiner. In
addition, because the Topeka shiner resides in shallow waters with volumes lower than
assumed by PRZM/EXAMS, the estimated acute exposures could be underestimated by
PRZM/EXAMS. However, the lower volume of water could be offset by other factors.
Previous atrazine endangered species assessments (U.S. EPA 2006c,d,e) have included a
refinement to exposure modeling with the static water body by incorporating flowing
water into the assessment. However, because the Topeka shiner resides in headwater
streams with low flow and in side pools of streams (Figure 3.1), no refinement to account
for flowing water has been conducted for this assessment.
Figure 3.1. Example habitat of the Topeka shiner in Minnesota (Image obtained
from Minnesota Department of Natural Resources, 2006).
Atrazine has been the subject of a number of monitoring studies. Targeted monitoring
data (monitoring study specifically correlated with atrazine use in vulnerable watersheds)
has recently been completed for atrazine in streams throughout the Midwest atrazine use
area. These data are considered to provide context to potential atrazine levels in some
Topeka shiner habitats because samples were collected from low (2nd and 3!(i) order
36
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streams. However, the Topeka shiner also resides in 1st order streams and in side pools of
low-order streams. These types of habitats are not typically included in monitoring
studies. Therefore, the representativeness of the monitoring data to Topeka shiner
habitats is uncertain.
In addition to targeted monitoring studies, a number of non-targeted (i.e., monitoring data
in which the study design was not specifically targeted to detect atrazine in high use
areas) monitoring studies are also available, which suggest a similar pattern of exposure
as the targeted data. However, many of these sites are located in the most vulnerable
areas represented by the targeted data; therefore, similar exposure patterns would be
expected to occur.
As summarized below, baseline EECs based on the PRZM/EXAMS static water body are
used in the risk estimation to derive initial RQs and distinguish between "no effect" and
may affect" determinations. Although the monitoring data provide context to these
modeled EECs, it is uncertain if the monitoring data or the modeling exercises provide
exposure estimates that are more relevant to the Topeka shiner's habitat. Therefore, both
are used to characterize potential exposures to the Topeka shiner. The monitoring data
has been described in detail in previous endangered species assessments (U.S. EPA,
2006a,c,d,e); therefore, a summary of the monitoring data is presented in this assessment,
and additional detail is provided in Appendix B.
3.2.2 Modeling Approach
The general conceptual model of exposure for this assessment is that the highest
exposures are expected to occur in the headwater streams adjacent to agricultural fields
and non-agricultural use sites (residential, right-of-way, turf, and forestry). The Topeka
shiner is known to inhabit headwater streams, and the EECs derived for this assessment
are relevant to habitats that are in close proximity to atrazine use sites. The action area
was divided into representative regions and modeling scenarios were selected to represent
each area. These areas (described in more detail in Section 3.2.3) represent the western
tier (Missouri and Kansas) and the upper great plains tier (Iowa, Nebraska, South Dakota,
and Minnesota) (Figure 3.2).
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Regionalization of Atrazine Action Area for
the Topeka Shiner Exposure Assessment
Legend
West_States
i i Upper_Great_Plains_States
t^3Topeka_Shiner_HUC8_watersheds outline
Topeka_Shiner_HUC8_watersheds
o 50 100
200
300
400
Figure 3.2 Regionalization of Topeka shiner Action Area
Available usage data (Kaul, et al., 2005) suggest that the heaviest usage of atrazine
relative to the action area is likely to be in a band stretching from western Illinois across
Iowa to central Nebraska with decreasing intensity south and north of this area. As noted
above, the action area was segmented into regions to allow for modeling that covers the
expected range of runoff vulnerability. All existing PRZM scenarios were evaluated, and
a subset was selected for use in this assessment. The scenarios were selected to provide a
spatial context to predicted exposures.
Currently a suite of 63 PRZM standard scenarios and 7 Barton Springs scenarios
(recently developed for use in the Barton Springs salamander endangered species risk
assessment (U.S. EPA, 2006c), are available for use in ecological risk assessments
representing predominantly agricultural uses. Each scenario is intended to represent a
high-end exposure setting for a particular crop. Each scenario location is selected based
on various factors including crop acreage, runoff and erosion potential, climate, and
agronomic practices. Once a location is selected, a scenario is developed using locally
specific soil, climatic, and agronomic data. Each PRZM scenario is assigned a specific
climatic weather station providing 30 years of daily weather values.
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Specific scenarios were selected for use in this assessment using two criteria. First, an
evaluation of all available PRZM scenarios was conducted, and those scenarios that
represent atrazine uses (e.g. Ohio corn) were selected for modeling. Weather information
was assigned to these scenarios at development. Second, an additional suite of scenarios
was identified to represent both agricultural and non-agricultural uses for which scenarios
within the action area is not available (e.g. residential). These scenarios were used in the
assessment as surrogates for atrazine uses without current scenarios (e.g. Oregon
Christmas tree as surrogate for forestry) and to provide geographic coverage where no
current scenario exists (e.g. Ohio corn scenario modeled using Springfield, Missouri
weather data).
Each scenario selected as a surrogate for this assessment is considered to be a
conservative representation of exposure in the action area because the surrogate scenarios
(Oregon Christmas tree and Kansas sorghum) were developed using a hydrologic group
C soil with relatively high curve numbers and moderate slopes. These are the most
important parameters within a PRZM scenario for generating runoff coupled with
rainfall, which is higher within the action area than the areas where the scenarios were
originally developed. In addition, the curve numbers and slopes are expected to be higher
than those present in the action area, which generally have lower slopes and less runoff
prone soils.
Further description (metadata) and copies of the existing PRZM scenarios may be found
at the following websites.
http://www.epa.gOv/oppefedl/models/water/index.htm#przmexamsshell
http://www.epa.gov/oppefedl/models/water/przmenvironmentdisclaim.htm
For this assessment, available PRZM weather stations were associated with watersheds
highly vulnerable to atrazine runoff. As shown in Figure 3.3, weather stations associated
with Sioux City, Iowa and Springfield, Missouri was selected to represent highly
vulnerable locations for modeling surrogate scenarios (both agricultural and non-
agricultural). As such, surrogate scenarios used to model this region were run using
weather data from these locations to represent exposures within the entire region.
For this assessment, the following corn scenarios were modeled to represent all the
various regions of the action area: North Dakota (this is a standard scenario using weather
data from Fargo) representative of corn use in the upper great plains states and the Ohio
scenario using the Springfield, Missouri weather data is representative of the western
states. The Kansas sorghum scenario (the only existing sorghum scenario) was modeled
with local weather stations including Topeka, Kansas (western states) and Sioux City,
Iowa (upper great plain states).
Currently, the only non-agricultural scenarios available for use in aquatic exposure
assessment are those developed specifically for the Barton Springs Salamander
39
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Endangered Species Risk Assessment (U.S. EPA, 2006c). For the Barton Springs
assessment, a suite of non-agricultural scenarios was developed including a residential,
impervious (to be used in tandem with the residential scenario), and rights-of-way
scenarios. These scenarios were used in this assessment in a manner similar to the
agricultural scenarios described above. Each scenario was modeled using a
representative weather station for each region. For example, the residential scenario was
modeled using the Sioux City, Iowa weather data to represent the upper great plains
states and the Springfield, Missouri weather data to represent the western states. There is
some uncertainty associated with using a scenario developed for a given geographic area
with climatic data from another area. However, runoff is driven primarily by hydrologic
soil type (defining the curve number) and the rainfall. Thus, a scenario that represents a
similar hydrologic soil type as would be found in the area being assessed and
representative weather data for that region should yield high end exposures. Figure 3.3
shows the locations of these weather stations relative to the action area. A summary of
all the modeled scenarios along with associated weather information is included in Table
Both the agricultural and non-agricultural scenarios were used within the standard
framework of PRZM/EXAMS modeling using the standard graphical user interface
(GUI) shell, PE4v01.pl.
3.2.
Location of Weather Stations used in the
Exposure Assessment
NDcori
Springfield
Legend
^3 We st_St at e s
Up per_G reat_Plain s_State s
|^3Topeka_Shiner_HUC8_watersheds outline
Topeka_Shiner_HUC8_watersheds
O Topeka_Shiner_Met_Stations
O Topeka_Shiner_PRZM_Scenarios
0 50 100 200 300 400
I Miles
40
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Figure 3.3 Location of Various Weather Stations Used to Model Non-Agricultural
Uses (Residential, Right-of-Way, Turf, and Forestry)
41
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Table 3.2 Summary of PRZM Scenarios
Region
Use
Scenario
First Application
Weather Station
(WBAN #)
Corn
IL corn
April 15
Springfield, MO
(13995)
Sorghum
KS sorghum
May 1
Topeka, KS
(13996)
Fallow
BSS meadow
November 1
Springfield, MO
(13995)
West
Residential
BSS residential
April 15
Springfield, MO
(13995)
Right-of-way
BSS row
June 1
Springfield, MO
(13995)
Forestry
OR Christmas tree
June 1
Springfield, MO
(13995)
Turf
BSS turf
April 15
Springfield, MO
(13995)
Corn
ND corn
April 1
Fargo, ND
(14914)
Sorghum
KS sorghum
May 1
Sioux City, SD
(14943)
Fallow
BSS meadow
November 1
Sioux City, SD
(14943)
Upper Great Plains
Residential
BSS residential
May 1
Sioux City, SD
(14943)
Right-of-way
BSS row
June 1
Sioux City, SD
(14943)
Forestry
OR Christmas tree
June 1
Sioux City, SD
(14943)
Turf
BSS turf
May 1
Sioux City, SD
(14943)
a BSS scenarios developed for Barton Springs Salamander (BSS) Endangered Species Risk Assessment (U.S. EPA, 2006c).
Peak concentrations, as well as 90th percentile rolling time-weighted averages of 14 days,
21 days, 30 days, 60 days, and 90 days were derived for comparison with the appropriate
ecotoxicity endpoints (including the community-level threshold concentrations) for
atrazine (see Section 4). The 30-year time series output file was used to recalculate the
peak, 14-day, 21-day, 30-day, 60-day, and 90-day rolling averages at the 90th percentile.
All model outputs were post-processed manually using Microsoft Excel to provide the
equivalent of the standard one in ten year return frequency exposures, as predicted by
PRZM/EXAMS. A sample of how this post-processing was conducted may be found in
the previous atrazine assessments for the Chesapeake Bay and Alabama Sturgeon (U.S.
EPA 2006c,d,e).
Additional information on the modeling approach for the non-agricultural residential,
rights-of-way, and forestry use scenarios may be found in the previous atrazine
endangered species risk assessments (U.S. EPA, 2006c,d).
42
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3.2.3 Model Inputs
The estimated water concentrations from surface water sources were calculated using
Tier IIPRZM (Pesticide Root Zone Model) and EXAMS (Exposure Analysis Modeling
System). PRZM is used to simulate pesticide transport as a result of runoff and erosion
from a standardized watershed, and EXAMS estimates environmental fate and transport
of pesticides in surface waters. The linkage program shell (PE4v01.pl) that incorporates
the site-specific scenarios was used to run these models.
Scenarios used in this assessment consist of agricultural scenarios for corn and sorghum
developed previously for other geographic areas. Scenarios developed for the Barton
Springs Salamander assessment (U.S. EPA, 2006c) not specific to watersheds included in
the action area, are used in this assessment for one agricultural use (fallow/idle land) and
several non-agricultural uses (residential, turf, forestry, and rights-or-way). All scenarios
were modeled using local weather data as described above. Linked use site-specific
scenarios and meteorological data were used to estimate exposure as a result of specific
use for each modeling scenario. The PRZM/EXAMS model was used to calculate
concentrations using the standard ecological water body scenario in EXAMS. Weather
and agricultural practices were simulated over 30 years so that the 1 in 10 year
exceedance probability at the site was estimated for the standard ecological water body.
One outcome of the 2003 IRED process was a modification to all existing atrazine labels
that requires setback distances around intermittent/perennial streams and lakes/reservoirs.
The label changes specify setback distances of 66 feet and 200 feet for atrazine
applications surrounding intermittent/perennial streams and lakes/reservoirs, respectively.
The Agency incorporated these distances into this assessment and has modified the
standard spray drift assumptions accordingly using U.S. EPA's AgDrift model
(http://www.agdrift.com/AgDRIFt2/Download.htm) to estimate the impact of a setback
distance of 66 feet on the fraction of drift reaching a surface water body. The revised
spray drift percentages, which are incorporated into the PRZM/EXAMS modeling, are
0.6% for ground applications and 6.5% for aerial applications.
Models to estimate the effect of setbacks on load reduction for runoff are not currently
available. It is well documented that vegetated setbacks can result in a substantial
reduction in pesticide load to surface water (USDA, NRCS, 2000). Specifically for
atrazine, data reported in the USD A study indicate that well vegetated setbacks have been
documented to reduce atrazine loading to surface water by as little as 11% and as much
as 100%) of total runoff compared to the loading without a setback. It is expected that the
presence of a well-vegetated setback between the site of atrazine application and
receiving water bodies would result in reduction in loading. Therefore, the aquatic EECs
presented in this assessment are likely to over-estimate exposure in areas with well-
vegetated setbacks.
The date of first application was developed based on several sources of information
including data provided by the Biological and Economic Analysis Division (BEAD) and
43
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Crop Profiles maintained by the USD A. More detail on the crop profiles may be found
at:
http://pestdata.ncsu.edu/cropprofiles/cropprofiles.cfm
The appropriate PRZM input parameters were selected from the environmental fate data
submitted by the registrant and in accordance with US EPA-OPP EFED water model
parameter selection guidelines, Guidance for Selecting Input Parameters in Modeling the
Environmental Fate and Transport of Pesticides, Version 2.3, February 28, 2002. These
parameters are consistent with those used in both the 2003 IRED (U.S. EPA, 2003a) and
the cumulative triazine risk assessment (U.S. EPA, 2006a) and are summarized in Table
3.3. More detail on these assessments may be found at:
http://www.epa.gov/oppsrrdl/REDs/atrazine ired.pdf
http://www.epa.gov/pesticides/cumulative/common mech groups.htm#chlpro
Table 3.3 Summary of PRZM/EXAMS Environmental Fate Data Used for Aquatic
Exposure Inputs for Atrazine Topeka shiner Assessment
Fate Property
Value
MRTD" (or source)
Molecular Weight
215.7 g/mole
MRID 41379803
Henry's constant
2.58 xlO-9
MRID 41379803
Vapor Pressure
3 x 10 7
MRID 41379803
Solubility in Water
33 mg/1
MRID 41379803
Photolysis in Water
335 days
MRID 42089904
Aerobic Soil Metabolism Half-lives
152 days
MRID 40431301
MRID 40629303
MRID 42089906
Hydrolysis
stable
MRID 40431319
Aerobic Aquatic Metabolism (water
column)
304 days
2x aerobic soil metabolism
rate constant
Anaerobic Aquatic Metabolism
(benthic)
608 days
MRID 40431323
Koc
88.78 ml/g
MRID 40431324
MRID 41257901
MRID 41257902
MRID 41257904
MRID 41257905
MRID 41257906
Application Efficiency
95 % for aerial
99 % for ground
Default value0
Spray Drift Fraction13
6.5 % for aerial
0.6 % for ground
AgDrift adjusted values based
on label restrictions
44
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Fate Property
Value
MRIDa (or source)
Master Record Identification (MRID) is record tracking system used within OPP to manage data submissions to the
Agency. Each data submission if given a unique MRID number for tracking purposes.
b Spray drift not included in final EEC due to edge-of-field estimation approach.
c Inputs determined in accordance with EFED "Guidance for Chemistry and Management Practice Input Parameters for
Use in Modeling the Environmental Fate and Transport of Pesticides" dated February 28, 2002.
3.2.4 Modeling Results
As noted above, a total of seven scenarios were evaluated in this assessment. Of these,
four were developed as part of the Barton Springs salamander endangered species risk
assessment (U.S. EPA, 2006c). Two of the Barton Springs scenarios (residential and
rights-of-way) were used in tandem with an impervious scenario, while two (fallow/idle
land and turf) are standard PRZM/EXAMS scenarios. The remaining three scenarios
(corn, sorghum, and Christmas trees as surrogate for forestry) were taken from existing
scenarios developed for other regions of the United States and modeled using local
weather data. No new scenarios were developed specifically for this assessment. The
results of the modeling are summarized in Table 3.4.
In general, these EECs show a pattern of exposure for all durations that is influenced by
the persistence of the compound and the lack of flow through the static water body.
Predicted atrazine concentrations, though high across durations of exposure for a single
year, do not increase across the 30-year time series; therefore accumulation is not a
concern.
45
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Table 3.4 Summary of PRZM/EXAMS Output Baseline EECs for all Modeled Scenarios
(Using the Standard Water Body)
Region
Use Site
(see Table 3.2
for Scenarios
Used)
Application
Rate (lbs/acre)
No. of
Applications
90th Percentile of 30 Years of Output
Peak
EEC
(Hg/L)
14-day
EEC
(Hg/L)
21-day
EEC
(Hg/L)
30-day
EEC
(Hg/L)
60-day
EEC
(Hg/L)
90-day
EEC
(Hg/L)
West
Corn3
2.0
2
(not to exceed
2.5 lbs/year)
92.8
91.7
91.4
90.7
88.0
85.4
Upper Great
Plains
Corn3
2.0
2
(not to exceed
2.5 lbs/year)
84.8
84.0
83.6
83.5
82.3
80.8
West
Sorghum
2.0
1
60.1
59.4
58.9
58.4
57.3
56.3
Upper Great
Plains
Sorghum
2.0
1
57.2
56.6
56.3
55.8
54.4
52.8
West
Fallow
2.25
1
103.4
103.1
103.1
103.1
103.0
103.0
Upper Great
Plains
Fallow
2.25
1
49.2
49.1
49.1
49.1
49.1
48.8
West
Residential13
Granular
2.0
2
(not to exceed
4.0 lbs/year)
11.9
11.8
11.7
11.6
11.3
11.0
Upper Great
Plains
Residential13
Granular
2.0
2
(not to exceed
4.0 lbs/year)
10.9
10.9
10.9
10.8
10.8
10.8
West
Residential13
Liquid
1.0
2
(not to exceed
2.0 lbs/year)
9.9
9.7
9.7
9.6
9.3
9.1
Upper Great
Plains
Residential13
Liquid
1.0
2
(not to exceed
2.0 lbs/year)
8.2
8.1
8.1
8.0
7.8
7.6
West
Rights-of-way
1.0
1
3.8
3.8
3.8
3.8
3.6
3.5
Upper Great
Plains
Rights-of-wayv
1.0
1
3.3
3.2
3.2
3.2
3.1
3.0
46
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Region
Use Site
(see Table 3.2
for Scenarios
Used)
Application
Rate (lbs/acre)
No. of
Applications
90th Percentile of 30 Years of Output
Peak
EEC
(Hg/L)
14-day
EEC
(Hg/L)
21-day
EEC
(Hg/L)
30-day
EEC
(Hg/L)
60-day
EEC
(Hg/L)
90-day
EEC
(Hg/L)
West
Forestry
4.0
1
27.4
26.9
26.8
26.5
25.6
24.8
Upper Great
Plains
Forestry
4.0
1
64.5
61.0
60.7
60.2
58.3
56.5
West
Turf Granular
2.0
2
(not to exceed
4.0 lbs/year)
7.2
7.1
7.0
7.0
6.7
6.5
Upper Great
Plains
Turf Granular
2.0
2
(not to exceed
4.0 lbs/year)
10.1
10.1
10.1
10.1
10.0
9.9
West
Turf Liquid
1.0
2
(not to exceed
2.0 lbs/year)
7.6
7.5
7.5
7.5
7.4
7.2
Upper Great
Plains
Turf Liquid
1.0
2
(not to exceed
2.0 lbs/year)
8.2
8.1
8.1
8.0
8.0
7.9
a Actual labeled maximum rates are 2.0 lb/acre for a single application with no more than 2.5 lbs/acre per year. The rate and number of applications reported in this table are an
approximation of the label maximum given the current limitation in the Agency's PRZM/EXAMS graphical user interface (GUI) PE4v01.pl. Currently, PE4v01.pl allows
multiple applications but the rate cannot be varied from one application to the next. The impact of this assumption was assessed using an interim version of the GUI and yielded
an approximately 6% increase in concentration. The corn EECs has been adjusted upwards by 6% for each duration of exposure to reflect this issue.
b Assumes 1% overspray of atrazine to the impervious surfaces.
c Assumes only 10% of any watershed is in right-of-way.
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3.2.5 Existing Monitoring Data
The second step in the process of characterizing EECs used for risk estimation was to
compare the modeling results with available surface water monitoring data. A fairly
robust set of surface water monitoring data exists for atrazine from a variety of targeted
and non-targeted studies. Targeted studies are those studies whose design is specifically
tailored to the use pattern for a specific compound. Sample location, number of samples,
frequency of sampling, and when the samples are collected are designed specifically to
capture exposures for the target compound. Non-targeted monitoring is typically more
general in nature and is not designed for a specific compound. The study design for non-
targeted studies are typically broad with the intent of capturing as many compounds as
possible but not necessarily focused on the main exposure period for a single compound.
Data from a number of monitoring programs are available, including data from the USGS
NAWQA program (http://water.usgs. gov.nawqa). Watershed Regression for Pesticides
(WARP), Heidelberg College, Community Water System (CWS) data from drinking
water sources, published USGS studies, other published data, and recently submitted data
collected by the registrant of atrazine (Ecological Stream Monitoring Program). In
general, relevance of the available monitoring data is uncertain given that the Topeka
shiner resides in headwater streams with low flow and in side pools of low order streams,
while the bulk of the monitoring data (including the targeted ecological stream
monitoring) represents samples collected from 3rd order streams and higher, typically
from mid-stream sampling stations. Therefore, only a summary of the available
monitoring studies is presented in this assessment. Additional data can be obtained from
Appendix B.
The available monitoring data typically report consistent information. The recent
Ecological Monitoring Program Data are summarized below. Other monitoring studies,
including USGS NAWQA, USGS Watershed Regression of Pesticides (WARP) Data,
Heidelberg College Data, and other open literature sources report atrazine levels and
patterns that are similar to those reported in the targeted ecological monitoring program.
However, the targeted data are considered to be more robust due to its targeted nature.
Details on both the targeted and the non-targeted studies may be found in Appendix B.
Overall, the targeted monitoring data suggest a similar pattern of atrazine exposure in
surface water as in the other data sets evaluated as part of this assessment. In the targeted
study, atrazine was detected in a total of 2,979 out of 3,601 samples for an overall
frequency of detection of 79%. The frequency of detection ranged across all watersheds
and years from a maximum of 100% to a minimum of 11%. The maximum concentration
detected from all watersheds was 208.8 |ig/L from the Indiana 11 site in 2005. The mean
annual concentrations ranged from a maximum of 9.5 |ig/L from the Missouri 01 site in
2004 to a low of 0.1 |ig/L for the Nebraska 06 site in 2006, while the median values
ranged from 4.2 |ig/L for the Missouri 02 site in 2004 to 0.1 |ig/L for the Ohio 03 site in
2004. It should be noted that a number of watersheds, particularly in Nebraska,
experienced dry periods where scheduled sampling did not take place; therefore, the
48
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statistics for those watersheds may not represent actual conditions expected in normal or
wetter years.
Patterns observed in the other monitoring studies were consistent with those reported in
the targeted ecological monitoring data. Details on all available monitoring studies are in
Appendix B.
3.2.6 Comparison of Modeling and Monitoring Data
Modeling with the static water body provides screening-level EECs for use in risk
estimation (Section 5.1). In this case, the listed species' habitat includes headwater
streams with low flow and in side pools of low-order streams. Therefore, the modeled
static water body EECs used for risk estimation are considered to be a reasonable
approximation of high end exposure which the Topeka shiner may be exposed. Both
monitoring data targeted to atrazine use and non-targeted data provide context to these
modeled exposures.
The peak EECs are relatively consistent across modeling and targeted and non-targeted
monitoring studies (highest maximum peaks detected across the studies are typically 100
to 200 ug/L). However, monitoring studies suggest that longer duration EECs are
considerably lower than the highest detected peak concentrations. The Topeka shiner
habitat includes small pools connected to low order streams with low flow rates (see
Section 2.3. and 3.1). The monitoring studies may not represent these types of habitats.
Therefore, the modeled longer-duration EECs will be used for RQ calculations. In
addition, because the Topeka shiner resides in shallow waters with volumes lower than
assumed by PRZM/EXAMS, the estimated acute exposures could be underestimated by
PRZM/EXAMS. However, the lower volume of water could be offset by other factors.
3.2.7. Impact of Typical Usage Information on Exposure Estimates
A final piece of the exposure characterization includes an evaluation of usage
information. Label application information was provided by EPA's Biological and
Economic Analysis Division and summarized in Table 2.2. This information suggests
that atrazine use on agricultural crops (non-agricultural usage data is not available as part
of this analysis) ranges from 0.6 lbs/acre for sweet corn and wheat to 1.2 lbs/acre for
sorghum in the states considered within the action area of this assessment. This suggests
that if typical application rates were used in modeling as opposed to maximum label
rates, atrazine exposures would be reduced below those modeled by roughly 40%
depending on the use pattern. Typically usage information is not incorporated into these
assessments, but does provide context to the exposures predicted. Caution is used when
evaluating "typical" application rate information because this represents the average of
all reported applications and thus roughly 50% of the time higher application rates are
being applied. Also, typical application rates would not alter EECs from monitoring
studies.
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3.3 Terrestrial Plant Exposure Assessment
Terrestrial plants in riparian areas may be exposed to atrazine residues carried from
application sites via surface water runoff or spray drift. Exposures can occur directly to
seedlings breaking through the soil surface and through root uptake or direct deposition
onto foliage to more mature plants. Riparian vegetation is important to the water and
stream quality of the Topeka shiner because it serves as a buffer and filters out sediment,
nutrients, and contaminants before they enter the watersheds associated with Topeka
shiner habitat. Riparian vegetation has been shown to be essential in the maintenance of
a stable stream (Rosgen, 1996). Destabilization of the stream can have an adverse effect
on habitat quality by increasing sedimentation within the watershed.
Concentrations of atrazine on the riparian vegetation were estimated using OPP's
TerrPlant model (U.S. EPA, 2007; Version 1.2.2), considering use conditions likely to
occur in the watersheds associated with the action area. The TerrPlant model evaluates
exposure to plants via runoff and spray drift and is EFED's standard tool for estimating
exposure to non-target plants. The runoff loading of TerrPlant is estimated based on the
solubility of the chemical and assumptions about the drainage and receiving areas. As
previously discussed in Section 3.1 (model inputs), the standard spray drift assumptions
were modified using AgDrift to estimate the impact of a setback distance of 66 feet on
the fraction of drift reaching a surface water body. These revised spray drift percentages
were also incorporated into the TerrPlant model, assuming that non-target terrestrial
plants adjacent to atrazine use sites would receive the same percentage of spray drift as
an adjacent surface water body. The revised spray drift percentages are 0.6% for ground
applications and 6.5% for aerial applications.
Although TerrPlant calculates exposure values for terrestrial plants inhabiting two
environments (i.e., dry adjacent areas and semi-aquatic areas), only the exposure values
from the dry adjacent areas are used in this assessment. The 'dry, adjacent area' is
considered to be representative of a slightly sloped area that receives relatively high
runoff and spray drift levels from upgradient treated fields. In this assessment, the 'dry,
adjacent area' scenario is used to estimate baseline exposure values for terrestrial plants
in riparian areas. The 'semi-aquatic area' is considered to be representative of depressed
areas that are ephemerally flooded, such as marshes, and, therefore, is not used to
estimate exposure values for terrestrial riparian vegetation.
The following input values were used to estimate terrestrial plant exposure to atrazine
from all uses: solubility = 33 ppm; minimum incorporation depth = 1 (TerrPlant default
for incorporation depths < 1 inch; from product labels); application methods: ground
boom, aerial, and granular (from product labels). The following agricultural and non-
agricultural scenarios were modeled: ground/aerial application to fallow/idle land at 2.25
lbs ai/A, corn/sorghum at 2.0 lb ai/A, and forestry at 4.0 lbs ai/A, and granular
application to residential lawns at 2 lbs ai/A.
Terrestrial plant EECs are summarized in Table 3.5.
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Table 3.5. Baseline Exposure Estimates for Terrestrial Plants to Atrazine
Use/ App. Rate
(lbs/acre)
Application
Method
Total Loading to Dry
Adjacent Areas (lbs/acre)
Drift EEC (lbs/acre)
Fallow/idle land / 2.25
Aerial
0.19
0.15
Ground
0.06
0.01
Corn and Sorghum / 2.0
Aerial
0.17
0.13
Ground
0.05
0.01
Forestry / 4.0
Aerial
0.34
0.26
Ground
0.10
0.02
Residential / 2.0
Granular
0.04
NA
4. Effects Assessment
This assessment evaluates the potential for atrazine to directly or indirectly affect the
Topeka shiner and/or adversely modify designated critical habitat. As previously
discussed in Section 2, assessment endpoints for the Topeka shiner include direct toxic
effects on the survival, reproduction, and growth, as well as indirect effects, such as
reduction of the prey base and/or modification of its habitat. In addition, potential
destruction and/or adverse modification of critical habitat are assessed by evaluating
potential effects to the PCEs, which are components of the critical habitat areas that
provide essential needs to the Topeka shiner, such as water quality and food base (see
Section 2.4). Toxicity data used to evaluate direct effects, indirect effects, and adverse
modification to critical habitat are summarized in Table 4.1.
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Table 4.1 Summary of Toxicity Data Used to Assess Direct and Indirect Effects and
Adverse Modificat
tion to Critical Habitat
Toxicity Data Used to
Evaluate Assessment
Endpoint
Assessment Endpoint
Comment
Acute and chronic studies
in freshwater fish
Direct effects to the Topeka shiner
Indirect effects: Reduction in spawning habitat;
reduction in food abundance
Most sensitive toxicity values used
for direct effects assessment.
Acute and chronic studies
in freshwater aquatic
invertebrates and
terrestrial invertebrates
Indirect effects: reduction in food supply
Adverse Modification: PCE No. 7, adequate
supply of invertebrate food base.
Toxicity value from the most
sensitive species tested is initially
used for RQ calculation; however,
data across all species tested
(particularly known food items) is
also used in the effects
determination.
Acute studies in vascular
and non-vascular aquatic
plants
Indirect effects via reduction in food supply,
habitat, and primary productivity
Adverse Modification:
PCE No. 3, water quality such as dissolved
oxygen levels and pH; PCE No. 5, presence of
moderate in-stream cover such as aquatic plants.
Most sensitive vascular and non-
vascular aquatic plant studies
initially used for baseline RQ
calculations; refinements include
use of threshold concentrations to
predict community-level effects.
Terrestrial plant toxicity
data
Indirect effects via potential effects to habitat,
reproduction, and water quality
Adverse Modification:
PCE No. 3, water quality such as temperature and
suspended solids.
PCE No. 5, presence of moderate cover such as
woody debris and overhanging terrestrial
vegetation;
PCE No. 6, Sand, gravel, cobble, and silt
substrates with amounts of fine sediment and
substrate embeddedness that allows for nest
building and maintenance of nests and eggs by
native sunfishes and Topeka shiner;
Distribution of seedling emergence
and vegetative vigor terrestrial
plant data used in combination
with toxicity data for woody
vegetation, and riparian habitat
characteristics.
Acute (short-term) and chronic (long-term) toxicity information is characterized based on
registrant-submitted studies and a comprehensive review of the open literature on
atrazine, consistent with the Overview Document (U.S. EPA, 2004). In addition to
registrant-submitted and open literature toxicity information, indirect effects to the
Topeka shiner, via impacts to aquatic plant community structure and function are also
evaluated based on community-level threshold concentrations. 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 atrazine.
A summary of the available freshwater and terrestrial organism ecotoxicity information,
the community-level endpoints, use of the probit dose response relationship, and the
incident information for atrazine are provided in Sections 4.1 through 4.9 . A summary
52
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of the available data directly used in this assessment is presented. A more comprehensive
discussion of the available toxicity data are included in Appendix A of this assessment.
Atrazine degradates have been shown to be less toxic to aquatic organisms than atrazine.
As shown in Table 4.2, comparison of available toxicity information for HA, DIA, and
DACT indicates lesser aquatic toxicity than the parent for freshwater fish, invertebrates,
and aquatic plants.
Table 4.2 Comparison of Acute Freshwater Toxicity Values for Atrazine and
Degradates
Substance
Fish LC50
Daphnid EC50 (jig/L)
Aquatic Plant EC50
Tested
(Ug/L)
(Ug/L)
Atrazine
5,300
3,500
1
HA
>3,000 (no effects at
saturation)
>4,100 (no effects at
saturation)
>10,000
DACT
>100,000
>100,000
No data
DIA
17,000
126,000
(NOAEC: 10,000)
2,500
DEA
No data
No data
1,000
Although degradate toxicity data are not available for terrestrial plants, lesser toxicity is
assumed, given the available ecotoxicological information for other taxonomic groups
including aquatic plants and the likelihood that the atrazine degradates are expected to
lose efficacy as an herbicide.
Therefore, given the lesser toxicity of the degradates, as compared to the parent,
concentrations of the atrazine degradates are not assessed, and the focus of this
assessment is limited to parent atrazine. The available information also indicates that
aquatic organisms are more sensitive to the technical grade (TGAI) than the formulated
products of atrazine; therefore, the focus of this assessment is on the TGAI. A detailed
summary of the available ecotoxicity information for all atrazine degradates and
formulated products is presented in Appendix A.
As previously discussed in the problem formulation, the available toxicity data show that
other pesticides may combine with atrazine to produce synergistic, additive, and/or
antagonistic toxic interactions. The results of available toxicity data for mixtures of
atrazine with other pesticides are presented in Section A.6 of Appendix A. Potential
synergistic effects with atrazine have been demonstrated for a number of
organophosphate insecticides including diazinon, chlorpyrifos, and methyl parathion, as
well as herbicides including alachlor. If chemicals that show synergistic effects with
atrazine are present in the environment in combination with atrazine, the toxicity of the
atrazine mixture may be increased relative to the toxicity of each individual chemical,
offset by other environmental factors, or even reduced by the presence of antagonistic
contaminants if they are also present in the mixture. The variety of chemical interactions
presented in the available data set suggest that the toxic effect of atrazine, in combination
with other pesticides used in the environment, can be a function of many factors
including but not necessarily limited to (1) the exposed species, (2) the co-contaminants
53
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in the mixture, (3) the ratio of atrazine and co-contaminant concentrations, (4) differences
in the pattern and duration of exposure among contaminants, and (5) the differential
effects of other physical/chemical characteristics of the receiving waters (e.g. organic
matter present in sediment and suspended water). Quantitatively predicting the combined
effects of all these variables on mixture toxicity to any given taxa with confidence is
beyond the capabilities of the available data. However, a qualitative discussion of
implications of the available pesticide mixture effects data involving atrazine on the
confidence of risk assessment conclusions is addressed as part of the uncertainty analysis
for this effects determination.
4.1 Ecotoxicity Study Data Sources
Toxicity endpoints are established based on data generated from guideline studies
submitted by the registrant, and from open literature studies that meet the criteria for
inclusion into the ECOTOX database maintained by EPA/Office of Research and
Development (ORD) (U.S. EPA, 2004). Open literature data presented in this assessment
were obtained from the 2003 atrazine IRED as well as ECOTOX information obtained on
May 31, 2007. The May 2007 ECOTOX search included all open literature data for
atrazine (i.e., pre- and post-IRED). In order to be included in the ECOTOX database,
papers must meet the following minimum criteria:
the toxic effects are related to single chemical exposure;
the toxic effects are on an aquatic or terrestrial plant or animal species;
there is a biological effect on live, whole organisms;
a concurrent environmental chemical concentration/dose or application rate is
reported; and
there is an explicit duration of exposure.
Meeting the minimum criteria for inclusion in ECOTOX does not necessarily mean that
the data are suitable for use in risk estimation. 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 risk assessment. In general, only effects
data in the open literature that are more conservative than the registrant-submitted data
are considered. Based on the results of the 2003 IRED for atrazine, potential adverse
effects on sensitive aquatic plants and non-target aquatic organisms including their
populations and communities, are not likely to occur if concentrations in water do not
exceed approximately 10 to 20 [j,g/L on a recurrent basis or over a prolonged period of
time (U.S. EPA, 2003a). Given the large amount of microcosm/mesocosm and field
study data for atrazine, only effects data that are less than the 10 |ig/L aquatic-community
effect level identified in the 2003 atrazine IRED were 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
survival, reproduction, and growth; alteration of PCEs in the critical habitat impact
analysis) identified in the problem formulation. For example, endpoints such as
biochemical modifications are not likely to be used to calculate risk quotients unless it is
possible to quantitatively link these endpoints with reduction in survival, reproduction, or
54
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growth (e.g., the magnitude of effect on the biochemical endpoint needed to result in
effects on survival, growth, or reproduction is known).
Citations of all open literature not considered as part of this assessment because it was
either rejected by the ECOTOX screen or accepted by ECOTOX but not used (e.g., the
endpoint is less sensitive and/or not appropriate for use in this assessment) are included in
Appendix E. Appendix E also includes a rationale for rejection of those studies that did
not pass the ECOTOX screen and those that were not evaluated as part of this ESA.
As described in the Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxa is used for RQ calculation. For this assessment, evaluated taxa
include freshwater fish, freshwater aquatic invertebrates, freshwater aquatic plants,
terrestrial plants, and terrestrial invertebrates. Table 4.3 summarizes the most sensitive
ecological toxicity endpoints for the Topeka shiner and its designated critical habitat,
based on an evaluation of both the submitted studies and the open literature, as previously
discussed. Toxicity information used in this assessment are further described in Sections
4.2 to 4.9. Additional information on the available submitted and open literature toxicity
studies is provided in Appendix A. Appendix A also includes ecotoxicity data for
taxonomic groups that are not relevant to this assessment (i.e., birds, estuarine/marine
organisms) because the Agency is completing endangered species risk assessments for
other species concurrently with this assessment.
Table 4.3 Freshwater Aquatic and Terrestrial Plant Toxicity Profile for Atrazine
Assessment Endpoint
Species
Toxicity Value Used
in Risk Assessment
Citation MRID #
(Author & Date)
Comment
Direct Toxicity to Topeka Shiner;
indirect effect via reduction in food
supply; indirect effect via reduction in
spawning habitat (fish, such as sunfish
provide spawning habitat for the
Topeka shiner)3
Rainbow
Trout
96-hour LC50 = 5,300
(ig/L
Probit slope = 2.72
00024716
(Beliles and Scott,
1965)
Acceptable study
Brook Trout
NOAEC = 65 |ig/L
LOAEC = 120 (ig/L
00024377
(Macek et al.,
1976)
Acceptable life-
cycle study: 7.2%
reduction in length;
16% reduction in
weight occurred at
the LOAEC
Indirect effects: reduction in food
supply
Adverse Modification: PCE No. 7,
adequate supply of invertebrate food
base.
Midge
LC50: 720 (ig/L
00024377
Macek et al. 1976
Supplemental
Scud
NOAEC = 60 |ig/L
LOAEC = 120 (ig/L
00024377
(Macek et al.,
1976)
Acceptable: 25 %
reduction in
development of Fi
to seventh instar at
the LOAEC
Indirect effects via reduction in habitat
and primary productivity; reduction in
food supply
Adverse Modification of critical
habitat: PCE No. 3, water quality such
as dissolved oxygen levels and pH;
PCE No. 5, presence of moderate cover
such as aquatic plants.
Freshwater
algae
7-day EC50 = 1 |ig/L
00023544
(Torres &
O'Flaherty, 1976)
Supplemental study
Duckweed
14-day EC50 = 37
(ig/L
43074804
(Hoberg, 1993)
Supplemental study
55
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Assessment Endpoint
Species
Toxicity Value Used
in Risk Assessment
Citation MRID #
(Author & Date)
Comment
Indirect Effects to Topeka Shiner
resulting from potential effects to
riparian habitat
Adverse modification of critical
habitat: PCE Nos. 3 and 5 as described
for aquatic plants; PCE No. 6,
Substrates with amounts of fine
sediment and substrate embeddedness
that allows for nest building and
maintenance of nests and eggs by
native sunfishes and Topeka shiner.
Oat
(monocot)
Tier II Seedling
Emergence EC25 =
0.004 lb ai/A
42041403
(Chetram, 1989)
Acceptable:
EC25 based on
reduction in dry
weight
Carrot
(dicot)
Tier II Seedling
Emergence EC25 =
0.003 lb ai/A
42041403
(Chetram, 1989)
Acceptable:
EC25 based on
reduction in dry
weight
a Sunfish data are also used to characterize potential indirect effects to the Topeka shiner because sunfish
are known to provide spawning habitat. Sunfish data are described in Section 5 and in Appendix A.
Toxicity to fish and aquatic invertebrates is categorized using the system shown in Table
4.4 (U.S. EPA, 2004). Toxicity categories for aquatic plants have not been defined.
Table 4.4 Categories of Acute Toxicity for Aquatic Organisms
LC/EC (mg/L)
Toxicity Category
<0.1
Very highly toxic
>0.1-1
Highly toxic
>1-10
Moderately toxic
>10 - 100
Slightly toxic
> 100
Practically nontoxic
4.2. Toxicity to Freshwater Fish
4.2.1. Acute Exposure (Mortality) Studies
Freshwater fish acute toxicity studies were used to assess potential direct effects to the
Topeka shiner. Atrazine toxicity has been evaluated in numerous freshwater fish species,
including rainbow trout, brook trout, bluegill sunfish, fathead minnow, tilapia, zebrafish,
goldfish, and carp. The results of these studies demonstrate a wide range of sensitivity.
The range of acute freshwater fish LC50 values for atrazine spans one order of magnitude,
from 5,300 to 60,000 (J,g/L; therefore, atrazine is categorized as moderately (>1,000 to
10,000 |ig/L) to slightly (>10,000 to 100,000 ug/L) toxic to freshwater fish on an acute
basis. The freshwater fish acute LC50 value of 5,300 [j,g/L is based on a static 96-hour
toxicity test using rainbow trout (Oncorhynchus mykiss) (MRID 00024716).
Sunfish data are also used to evaluate potential indirect effects to the Topeka shiner
because sunfish are known to provide spawning habitat to the Topeka shiner. Sunfish
LC50s range from >8,000 ug/L (00024377) to 57,000 ug/L (MRID 00147125). Details
of these studies along with a complete list of all available freshwater fish toxicity data
considered for this assessment is provided in Appendix A.
56
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4.2.2. Chronic Exposure (Growth/Reproduction) Studies
Chronic freshwater fish toxicity studies were used to assess potential direct effects to the
Topeka shiner via potential effects to growth and reproduction. Freshwater fish life-cycle
studies for atrazine are available and summarized in Table A-12 of Appendix A.
Following 44 weeks of exposure to atrazine in a flow-through system, statistically
significant reductions in brook trout mean length (7.2%) and body weight (16%) were
observed at a concentration of 120 |ig/L, as compared to the control (MRID 00024377).
The corresponding NOAEC for this study is 65 (J,g/L. Although the acute toxicity data
for atrazine show that rainbow trout are the most sensitive freshwater fish, available
chronic rainbow trout toxicity data indicate that it is less sensitive to atrazine, on a
chronic exposure basis than the brook trout with respective LOAEC and NOAEC values
of 1,100 |ig/L and 410 |ig/L. Further information on chronic freshwater fish toxicity data
for atrazine is provided in Section A.2.2 of Appendix A.
Sunfish data are also used to evaluate potential indirect effects to the Topeka shiner
because sunfish are known to provide spawning habitat to the Topeka shiner. A life-
cycle NOAEC of 95 ug/L was reported in sunfish. Details of these studies along with a
complete list of all available freshwater fish toxicity data considered for this assessment
is provided in Appendix A.
4.2.3. Sublethal Effects and Additional Open Literature Information
In addition to registrant submitted studies, data were located in the open literature that
report sublethal effect levels to freshwater fish that are less than the selected measures of
effect summarized in Table 4.2. Although these studies report potentially sensitive
endpoints, effects on survival, growth, or reproduction were not observed in the available
life-cycle studies at concentrations that induced the reported sublethal effects described
below and in Appendix A.
Reported sublethal effects in rainbow trout show increased plasma vitellogenin levels in
both female and male fish and decreased plasma testosterone levels in male fish at
atrazine concentrations of approximately 50 [j,g/L (Wieser and Gross, 2002 [MRID
456223-04]). Vitellogenin (Vtg) is an egg yolk precursor protein expressed normally in
female fish and dormant in male fish. The presence of Vtg in male fish is used as a
molecular marker of exposure to estrogenic chemicals. It should be noted, however, that
there is a high degree of variability with the Vtg effects in these studies, which confounds
the ability to resolve the effects of atrazine on plasma steroids and vitellogenesis.
Effects of atrazine on freshwater fish behavior, including a preference for the dark part of
the aquarium following one week of exposure (Steinberg et al., 1995 [MRID 452049-10])
and a reduction in grouping behavior following 24-hours of exposure (Saglio and Trijase,
1998 [MRID 452029-14]), have been observed at atrazine concentrations of 5 (J,g/L. In
addition, alterations in rainbow trout kidney histology have also been observed at atrazine
concentrations of 5 |ig/L and higher (Fischer-Scherl et al., 1991 [MRID 452029-07]).
57
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In salmon, atrazine effects on gill physiology and endocrine-mediated olfactory functions
have been studied. Data from Waring and Moore (2004; ECOTOX #72625) suggest that
salmon smolt gill physiology, represented by changes in Na-K-ATPase activity and
increased sodium and potassium levels, was altered at 1 [j,g/L atrazine and higher.
However, the Topeka shiner occurs in freshwater habitats; therefore, seawater survival is
not a relevant endpoint for this assessment. Moore and Lower (2001; ECOTOX #67727)
reported that endocrine-mediated functions of male salmon parr were affected at 0.5 [j,g/L
atrazine. The reproductive priming effect of the female pheromone prostaglandin F2a on
the levels of expressible milt in males was reduced after exposure to atrazine at 0.5 (J,g/L.
Although the hypothesis was not tested, the study authors suggest that exposure of smolts
to atrazine during the freshwater stage may potentially affect olfactory imprinting to the
natal river and subsequent homing of adults. However, no quantitative relationship is
established between reduced olfactory response of male epithelial tissue to the female
priming hormone in the laboratory and reduction in salmon reproduction (i.e., the ability
of male salmon to detect, respond to, and mate with ovulating females). A negative
control was not included as part of the study design; therefore, potential solvent effect
cannot be evaluated. Furthermore, the study did not determine whether the decreased
response of olfactory epithelium to specific chemical stimuli would likely impair similar
responses in intact fish.
Tierney et al. (2007) studied the effect of 30 minute exposure to atrazine on behavioral
and neurophysiological responses of juvenile rainbow trout to an amino acid odorant (L-
histidine at 10"7 M). L-histidine was chosen because it has been shown to elicit an
avoidance response in salmonids; however, control fish exposed to L-histidine at 10"7 M
showed a slight preference (1.2 response ratio). Although the study authors conclude that
L-histidine preference behavior was altered by atrazine at exposures > 1 ug/L, no
significant decreases in preference behavior were observed at 1 ug/L. Furthermore, no
dose response relationship was observed in the behavioral response following pesticide
exposure. At 1 and 100 ug/L, non-significant decreases in L-histidine preference were
observed; however a statistically significant avoidance of L-histidine was observed at 10
ug/L, but not 100 ug/L. Hyperactivity (measured as the number of times fish crossed the
centerline of the tank) was observed in trout exposed to 1 and 10 ug/L atrazine. In the
study measuring neurophysiological responses following atrazine exposure, electro-
olfactogram (EOG) response was significantly reduced (EOG measures changes in nasal
epithelial voltage due to response of olfactory sensory neurons). Although this study
produced a more sensitive effects endpoint for freshwater fish, the data were not used
quantitatively in the risk assessment because of the following reasons: 1) A negative
control was not used; therefore, potential solvent effects cannot be evaluated; 2) The
study did not determine whether the decreased response of olfactory epithelium to
specific chemical stimuli would likely impair similar responses in intact fish; and 3) A
quantitative relationship between the magnitude of reduced olfactory response to an
amino acid odorant in the laboratory and reduction in trout imprinting and homing, alarm
response, and reproduction (i.e., the ability of trout to detect, respond to, and mate with
ovulating females) in the wild is not established.
58
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Although these studies raise questions about the effects of atrazine on plasma steroid
levels, behavior modifications, gill physiology, and endocrine-mediated functions in
freshwater and anadromous fish, it is not possible to quantitatively link these sublethal
effects to the selected assessment endpoints for the Topeka shiner (i.e., survival, growth,
and reproduction of individuals). Also, effects on survival, growth, or reproduction were
not observed in the available life-cycle studies at concentrations that induced these
reported sublethal effects. Therefore, potential sublethal effects on fish are not used as
part of the quantitative risk characterization. Further detail on sublethal effects to fish is
provided in Sections A.2.4a and A.2.4b of Appendix A.
4.3 Toxicity to Freshwater Invertebrates
The Topeka shiner is an opportunistic omnivore, which means they typically eat what is
available to them. However, a predominant component of its diet has been documented
to be aquatic invertebrates (Dahle, 2001). Toxicity data for the most sensitive freshwater
invertebrate tested are used to assess: (1) potential indirect effects of atrazine to the
Topeka shiner via reduction in available food; and (2) potential effects to designated
critical habitat (PCE No. 7, adequate supply of invertebrate food base).
4.3.1. Acute Exposure Studies
Atrazine is classified as highly toxic to slightly toxic to aquatic invertebrates. A wide
range of EC50/LC50 values have been reported for freshwater invertebrates with values
ranging from 720 to >33,000 (J,g/L. The lowest freshwater LC50 value of 720 |ig/L is
based on an acute 48-hour static toxicity test for the midge, Chironomus tentans (MRID
000243-77). Further evaluation of the available acute toxicity data for the midge shows
high variability with the LC50 values, ranging from 720 to >33,000 (J,g/L. With the
exception of the midge, reported acute toxicity values for the other five freshwater
invertebrates tested (including the water flea, scud, stonefly, leech, and snail) are 3,500
[j,g/L and higher. Further evaluation of the available acute toxicity data for the water flea
also shows high variability similar to other freshwater invertebrates with LC50 values
ranging from 3,500 to >30,000 |ig/L, All of the available acute toxicity data for
freshwater invertebrates are provided in Section A.2.5 and Table A-18 of Appendix A.
The LC50/EC50 distribution for freshwater invertebrates is graphically represented in
Figure 4.1. The columns represent the lowest reported value for each species, and the
positive y error bar represents the maximum reported value. Values in parentheses
represent the number of studies included in the analyses.
59
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Summary of Reported Acute LC50/EC50 Values in Freshwater Invertebrates
for Atrazine
35000 n
30000 r
25000
o
U j 20000
10000
5000 1-'
0 n I I I I I
Midge (5) Waterflea (5) Scud (3) Stonefly(1) Leech (1) Snail (1)
Species
Figure 4.1 Summary of Reported Acute LC50/EC50 Values in Freshwater
Invertebrates for Atrazine
4.3.2 Chronic Exposure Studies
The most sensitive chronic endpoint for freshwater invertebrates is based on a 30-day
flow-through study on the scud (Gammarus fasciatus), with respective NOAEC and
LOAEC values of 60 and 140 |ig/L, based on a 25% reduction in the development of Fi
to the seventh instar (MRID 00024377) (see Section 4.1.1.2). Although the acute toxicity
data for atrazine show that the midge (Chironomus tentcms) is the most sensitive
freshwater invertebrate, available chronic midge toxicity data indicate that it is less
sensitive to atrazine, on a chronic exposure basis, than the scud, with respective LOAEC
and NOAEC values of 230 |ig/L and 110 |ig/L. Additional information on the chronic
toxicity of atrazine to freshwater invertebrates is provided in Section A.2.6 and Table A-
20 of Appendix A.
60
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4.4 Toxicity to Aquatic Plants
Aquatic plant toxicity studies were used as one of the measures of effect to evaluate
whether atrazine may affect primary production. Aquatic plants may also serve as a
dietary item of the Topeka shiner. In addition, freshwater vascular and non-vascular
plant data are used to evaluate a number of the PCEs associated with the critical habitat
impact analysis. The following PCEs are evaluated using aquatic plant toxicity data:
Streams and side-channel pools with water quality necessary for unimpaired
behavior, growth, and viability of all life stages. The water quality components
can vary seasonally and includetemperature (1 to 3 0[deg] Centigrade), total
suspended solids (0 to 2000 ppm), conductivity (100 to 800 mhos), dissolved
oxygen (4 ppm or greater), pH (7.0 to 9.0), and other chemical characteristics;
Living areas for juvenile Topeka shiners with water velocities less than 0.5
meters/second (approx. 20 inches/second) with depths less than 0.25 meters
(approx. 10 inches) and moderate amounts of instream aquatic cover, such as
woody debris, overhanging terrestrial vegetation, and aquatic plants;
Two types of studies were used to evaluate the potential of atrazine to affect primary
productivity. Laboratory studies were used to determine whether atrazine may cause
direct effects to aquatic plants. In addition, the community-level effect threshold
concentrations, described in Section 4.7, were used to further characterize potential
community-level effects resulting from potential effects to aquatic plants. A summary of
the laboratory data and field data for aquatic plants is provided in Sections 4.4.1 and
4.4.2.
4.4.1. Laboratory Data
Numerous aquatic plant toxicity studies have been submitted to the Agency. A summary
of the data for freshwater vascular and non-vascular plants is provided below. Section
A.4.2 and Tables A-40 and A-41 of Appendix A include a more comprehensive
description of these data.
The Tier II results for freshwater aquatic plants produced EC50 values for four different
species of freshwater algae at concentrations as low as 1 |ig/L, based on data from a 7-
day acute study (MRID 00023544). Vascular plants are less sensitive to atrazine than
freshwater non-vascular plants with an EC50 value of 37 |ig/L, based on reduction in
duckweed growth (MRID 43074804).
Comparison of atrazine toxicity levels for three different endpoints in algae suggests that
the endpoints in decreasing order of sensitivity are cell count, growth rate and oxygen
production (Stratton, 1984). Walsh (1983) exposed Skeletonema costatum to atrazine and
concluded that atrazine is only slightly algicidal at relatively high concentrations (i.e.,
500 and 1,000 (J,g/L). Caux et al. (1996) compared the cell count IC50 and fluorescence
LC50 and concluded that atrazine is algicidal at concentrations affecting cell counts.
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Abou-Waly et al. (1991) measured growth rates on days 3, 5, and 7 for two algal species.
The pattern of atrazine effects on growth rates differs sharply between the two species.
Atrazine had a strong early effect on Anabaena flos-aquae followed by rapid recovery in
clean water (i.e., EC50 values for days 3, 5, and 7 are 58, 469, and 766 (J,g/L,
respectively). The EC50 values for Selenastrum capricornutum continued to decline from
day 3 through 7 (i.e., 283, 218, and 214 (J,g/L, respectively). Based on these results, it
appears that the timing of peak effects for atrazine may differ depending on the test
species.
It should be noted that recovery from the effects of atrazine and the development of
resistance to the effects of atrazine in some vascular and non-vascular aquatic plants have
been reported and may add uncertainty to these findings. However, reports of recovery
are often based on differing interpretations of recovery. Thus, before recovery can be
considered as an uncertainty, an agreed upon interpretation is needed. For the purposes
of this assessment, recovery is defined as a return to pre-exposure levels for the affected
population, not for a replacement population of more tolerant species. Further research
would be necessary in order to quantify the impact that recovery and resistance would
have on aquatic plants.
4.4.2. Freshwater Field Studies
Microcosm and mesocosm studies with atrazine provide measurements of primary
productivity that incorporate the aggregate responses of multiple species in aquatic plant
communities. Because plant species vary widely in their sensitivity to atrazine, the
overall response of the plant community may be different from the responses of the
individual species measured in laboratory toxicity tests. Mesocosm and microcosm
studies allow observation of population and community recovery from atrazine effects
and of indirect effects on higher trophic levels. In addition, mesocosm and microcosm
studies, especially those conducted in outdoor systems, incorporate partitioning,
degradation, and dissipation, factors that are not usually accounted for in laboratory
toxicity studies, but that may influence the magnitude of ecological effects.
Atrazine has been the subject of many mesocosm and microcosm studies in ponds,
streams, lakes, and wetlands. The durations of these studies have ranged from a few
weeks to several years at exposure concentrations ranging from 0.1 |ig/L to 10,000 |ig/L.
Most of the studies have focused on atrazine effects on phytoplankton, periphyton, and
macrophytes; however, some have also included measurements on animals.
As described in the 2003 IRED for atrazine (U.S. EPA, 2003a), potential adverse effects
on sensitive aquatic plants and non-target aquatic organisms including their populations
and communities are likely to be greatest when atrazine concentrations in water equal or
exceed approximately 10 to 20 |ig/L on a recurrent basis or over a prolonged period of
time. A summary of all the freshwater aquatic microcosm, mesocosm, and field studies
that were reviewed as part of the 2003 IRED is included in Section A.2.8a and Tables A-
22 through A-24 of Appendix A. Given the large amount of microcosm and mesocosm
and field study data for atrazine, only effects data less than or more conservative than the
62
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10 |ig/L aquatic community effect level identified in the 2003 IRED were considered
from the open literature search that was completed in October 2006. Based on the
selection criteria for review of new open literature, all of the available studies show
effects levels to freshwater fish, invertebrates, and aquatic plants at concentrations greater
than 10 |ig/L.
It should be noted that the 10 to 20 |ig/L community effect level has been further refined,
since completion of the 2003 IRED. The community-level effects thresholds for various
durations of exposure from 14 to 90 days are described in further detail in Section 4.2. In
summary, the potential for atrazine to induce community-level effects depends on both
atrazine concentration and duration. As the exposure duration increases, atrazine
concentrations that may produce community level effects decrease. For example, 14-day
atrazine concentrations of 38 |ig/L or lower are not considered likely to result in aquatic
community level effects, whereas 90-day atrazine concentrations of 12 |ig/L or lower are
not expected to produce community level effects.
Community-level effects to aquatic plants that are likely to result in indirect effects to the
rest of the aquatic community are evaluated based on threshold concentrations. These
threshold concentrations, which are discussed in greater detail in Section 4.2, incorporate
the available micro- and mesocosm data included in the 2003 IRED (U.S. EPA, 2003a) as
well as additional information gathered following completion of the 2003 atrazine IRED
(U.S. EPA, 2003e).
4.5. Toxicity to Terrestrial Plants
Terrestrial plant toxicity data are used to evaluate the potential for atrazine to affect
riparian zone vegetation within the action area. Riparian zone effects may impact water
quality characteristics, which could impact the Topeka shiner. In addition, several PCEs
associated with designated critical habitat are associated with the presence of riparian
vegetation.
Streams and side-channel pools with water quality necessary for unimpaired
behavior, growth, and viability of all life stages. The water quality components
can vary seasonally and includetemperature (1 to 3 0[deg] Centigrade), total
suspended solids (0 to 2000 ppm), conductivity (100 to 800 mhos), dissolved
oxygen (4 ppm or greater), pH (7.0 to 9.0), and other chemical characteristics;
Living areas for juvenile Topeka shiners with water velocities less than 0.5
meters/second (approx. 20 inches/second) with depths less than 0.25 meters
(approx. 10 inches) and moderate amounts of instream aquatic cover, such as
woody debris, overhanging terrestrial vegetation, and aquatic plants;
Sand, gravel, cobble, and silt substrates with amounts of fine sediment and
substrate embeddedness that allows for nest building and maintenance of nests
and eggs by native Lepomis sunfishes (green sunfish, orangespotted sunfish,
63
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longear sunfish) and Topeka shiner as necessary for reproduction, unimpaired
behavior, growth, and viability of all life stages;
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. Atrazine is labeled for use on
conifers and softwoods; therefore, effects to evergreens would not be anticipated at
exposure concentrations less than the application rate. In addition, preliminary data
submitted to the Agency (discussed below) suggests that sensitive woody plant species
exist; however, damage to most woody species at labeled application rates of atrazine is
not expected.
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 atrazine, is largely unknown. Homogenous test
plant seed lots also lack the genetic variation that occurs in natural populations; therefore,
the range of effects seen from these tests is likely to be smaller than would be expected
from wild populations.
Based on the results of the submitted terrestrial plant toxicity tests, it appears that
seedlings are more sensitive to atrazine via soil/root uptake exposure than emerged plants
via foliar routes of exposure. However, all tested plants, with the exception of corn in the
seedling emergence and vegetative vigor tests and ryegrass in the vegetative vigor test,
exhibited adverse effects following exposure to atrazine. Tables 4.5 and 4.6 summarize
the respective seedling emergence and vegetative vigor terrestrial plant toxicity data used
to derive risk quotients in this assessment.
In Tier II seedling emergence toxicity tests, the most sensitive monocot and dicot species
are oats and carrots, respectively. EC25 values for carrots and oats, which are based on a
reduction in dry weight, are 0.003 and 0.004 lb ai/A, respectively; NOAEC values for
both species are 0.0025 lb ai/A. Dry weight was the most sensitive parameter evaluated;
emergence was not significantly affected at any level tested.
For Tier II vegetative vigor studies, the most sensitive dicot and monocot species are the
cucumber and onion, respectively. In general, dicots appear to be more sensitive than
monocots via foliar routes of exposure with all tested dicot species showing a significant
reduction in dry weight at EC25 values ranging from 0.008 to 0.72 lb ai/A. In contrast,
two of the four tested monocots showed no effect to atrazine (corn and ryegrass), while
EC25 values for onion and oats were 0.61 and 2.4 lb ai/A, respectively.
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Table 4.5 Non-target Terrestrial Plant Seedling Emergence Toxicity (Tier II) Data
(Chetram, 1989; MRU) 42041403)
Surrogate Species
% ai
EC25 / NOAEC (lbs ai/A)
Endpoint Affected
Study Classification
Monocot - Corn
{Zea mays)
97.7
>4.0/>4.0
No effect
Acceptable
Monocot - Oat
(Avena sativa)
97.7
0.004/0.0025
red. in dry weight
Acceptable
Monocot - Onion
(Allium cepa)
97.7
0.009/0.005
red. in dry weight
Acceptable
Monocot - Ryegrass
(Lolium perenne)
97.7
0.004/0.005
red. in dry weight
Acceptable
Dicot - Root Crop - Carrot
(Daucus carota)
97.7
0.003 I 0.0025
red. in dry weight
Acceptable
Dicot - Soybean
(4.0/>4.0
No effect
Acceptable
Monocot - Oat
97.7
2.4 / 2.0
red. in dry weight
Acceptable
Monocot - Onion
97.7
0.61 / 0.5
red. in dry weight
Acceptable
Monocot - Ryegrass
97.7
>4.0/>4.0
No effect
Acceptable
Dicot - Carrot
97.7
1.7 / 2.0
red. in plant height
Acceptable
Dicot - Soybean
97.7
0.026/0.02
red. in dry weight
Acceptable
Dicot - Lettuce
97.7
0.33 / 0.25
red. in dry weight
Acceptable
Dicot - Cabbage
97.7
0.014/0.005
red. in dry weight
Acceptable
Dicot - Tomato
97.7
0.72 / 0.5
red. in plant height
Acceptable
Dicot - Cucumber
97.7
0.008/ 0.005
red. in dry weight
Acceptable
65
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In addition, a report on the toxicity of atrazine to woody plants (Wall et al., 2006; MRID
46870401) was reviewed by the Agency. A total of 35 species were tested at application
rates ranging from 1.5 to 4.0 lbs ai/A. Twenty-eight species exhibited either no or
negligible phytotoxicity. Seven of 35 species exhibited >10% phytotoxicity. However,
further examination of the data indicate that atrazine application was clearly associated
with severe phytotoxicity in only one species (Shrubby Althea). These data suggest that,
although sensitive woody plants exist, atrazine exposure to most woody plant species at
application rates of 1.5 to 4.0 lbs ai/A is not expected to cause adverse effects. A
summary of the available woody plant data is provided in Table A-39b of Appendix A.
4.6. Toxicity to Terrestrial Invertebrates
Terrestrial invertebrate toxicity data are used to evaluate potential indirect effects to the
Topeka shiner and to adversely modify designated critical habitat (PCE 7 - an adequate
terrestrial, semiaquatic, and aquatic invertebrate food base that allows for unimpaired
growth, reproduction, and survival of all life stages). A summary of the available
terrestrial insect data is summarized in Table 4.7 below. Additional details on the data
are included in Appendix A.
Atrazine is practically non-toxic to honey bees (LD50: 97 ug/bee). It also did not cause
adverse effects in fruit flies exposed to 15 ug/fly. LC50 values in earthworms ranged
from 273 to 926 ppm soil (Mosleh et al., 2003; Haque and Ebing, 1983). Atrazine did
not produce statistically significant (p<0.05) adverse effects in studies on several beetle
species at any level tested, which ranged from application rates of approximately 1 lb
a.i./Acre to 8 lbs a.i./Acre (Kegel, 1989; Brust, 1990; Samsoe-Petersen, 1995).
The most sensitive terrestrial invertebrate species tested was the springtail (Onychiurus
apuanicus and O. armatus). Exposure to O. apuanicus at 2.5 ppm resulted in 18%
mortality, and exposure to O. armatus at 20 ppm resulted in 51% mortality (Mola et al.,
1987); lower levels were not tested. These soil concentrations are associated with an
application rate of approximately 1 lb a.i./Acre and 7 lbs a.i./Acre, respectively, assuming
a soil density of 1.3 grams/cm3 and a soil depth of 3 cm. Additional details on these
studies may be found in Appendix A.
Available terrestrial insect toxicity data are summarized in Table 4.7.
66
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Table
.7. Summary of Available Terrestrial Invertebrate Toxicity Studies
Species
Toxicity Summary
Comment
Citation
Beetles
NOAECs ranged from 0.8
lbs a.i./Acre to 8 lbs
a.i./Acre
Soil sprayed with atrazine at
levels that ranged from 0.8 to 8
lbs a.i./Acre did not result in
statistically significant (p<0.05)
reductions in survival.
LOAEC: Not achieved
Kegel, 1989
Ecotox No. 64007
Brust, 1990
Ecotox No. 70406
Samsoe-Petersen, 1995
Ecotox No. 63490
Earthworms
28-day LC50:
381 mg/kg soil
14-Day LC50:
273- 926 mg/kg soil
Spiked soil studies; endpoints
included mortality and body mass
Mosleh et al., 2003
Ecotox No. 77549
Haque and Ebing, 1983
Ecotox No. 40493
Micro
arthropods
NOAEC: 0.9-1.8
lbs/Acre
LOAEC: 5.4 lbs a.i./Acre
The LOAEC was based on
reduced abundance from a field
study (Fretello et al., 1985); it
could not be determined if
reduced abundance was caused
by migration (repellency), by
toxic effects, or both.
Cortet et al., 2002
Ecotox No. 75784
Fratello et. al., 1985
Ecotox No.
59428
Springtails
30-Day LD50: 17ppmto
20 ppm (approximately 7
lbs a.i./Acre)a
LOAEC: 2.5 - 20 ppm soil
(approx. 1-7 lbs/Acre)3
Exposure occurred via treated
soil; mortality rate at 2.5 and 20
was 18% and 51%, respectively,
compared with 0% in controls.
Mola et al., 1987.
Ecotox No. 71417
Fruit flies
Drosphilia
NOAEC: 15 ug/fly
No increased mortality occurred
in groups exposed to atrazine
alone relative to controls.
Lichtenstein et al., 1973
Ecotox No. 2939
Honey bees
LD50: >97 ug/bee
5% mortality occurred at the
highest dose tested (97 ug/bee)
MRID 00036935
Earthworm
LOAEC: 8 lb/acre
NOAEC: Not achieved
Field study examining the
impacts of several herbicides on
soil invertebrate populations.
The endpoint measured was
abundance of several species.
Study authors suggested that
reduced abundance was likely
caused by repellency and not
direct toxicity.
Fox, 1964
Ecotox No. 36668
Wire worm
Springtail
a Application rate was estimated from soil concentration by assuming a soil density of 1.3 grams/cm3 and a
soil depth of 3 cm.
4.7 Community-Level Endpoints: Threshold Concentrations
Direct and indirect effects to the Topeka shiner are evaluated in accordance with the
screening level methodology described in the Agency's Overview Document (U.S. EPA,
2004). If aquatic plant RQs exceed the Agency's non-listed species LOC (because the
Topeka shiner does not have an obligate relationship with any one particular plant
67
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species, but rather rely on multiple plant species), based on available EC50 data for
vascular and non-vascular plants, risks to individual aquatic plants are assumed.
It should be noted, however, that the indirect effects and components of the critical
habitat impact analyses in this assessment are unique, in that the best available
information for atrazine-related effects on aquatic communities is significantly more
extensive than for other pesticides. Hence, atrazine effects determinations can utilize
more refined data than is generally available to the Agency. Specifically, a robust set of
microcosm and mesocosm data and aquatic ecosystem models are available for atrazine
that allowed EPA to refine the indirect effects and critical habitat impact analysis
associated with potential aquatic community-level effects (via aquatic plant community
structural change and subsequent habitat modification) to the Topeka shiner. Use of such
information is consistent with the guidance provided 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 EPA, 2004). This
information, which represents the best scientific data available, is described in further
detail below and in previous effects determinations for atrazine (U.S. EPA 2006c,d,e).
This information is also considered a refinement of the 10-20 |ig/L range reported in the
2003 IRED (U.S. EPA, 2003a).
The Agency has selected an atrazine level of concern (LOC) in the 2003 IRED (U.S.
EPA, 2003a and b) that is consistent with the approach described in the Office of Water's
(OW) draft atrazine aquatic life criteria (U.S. EPA, 2003c). Through these previous
analyses (U.S. EPA, 2003a, b, and c), which reflect the current best available
information, predicted or monitored aqueous atrazine concentrations can be interpreted to
determine if a water body is likely to be significantly affected via indirect effects to the
aquatic community. Potential impacts of atrazine to plant community structure and
function that are likely to result in indirect effects to the rest of the aquatic community,
including the Topeka shiner, are evaluated as described below.
As described further in U.S. EPA (2006c,d,e), responses in microcosms and mesocosms
exposed to atrazine were evaluated to differentiate no or slight, recoverable effects from
significant, generally non-recoverable effects (U.S. EPA, 2003e). Because effects varied
with exposure duration and magnitude, there was a need for methods to predict relative
differences in effects for different types of exposures. The Comprehensive Aquatic
Systems Model (CASM) (Bartell et al., 2000; Bartell et al., 1999; DeAngelis et al., 1989)
was selected as an appropriate tool to predict these relative effects, and was configured to
provide a simulation for the entire growing season of a 2nd and 3rd order Midwestern
stream as a function of atrazine exposure. CASM simulations conducted for the
concentration/duration exposure profiles of the micro- and mesocosm data showed that
CASM seasonal output, represented as an aquatic plant community similarity index,
correlated with the micro- and mesocosm effect scores, and that a 5% change in this
index reasonably discriminated micro- and mesocosm responses with slight versus
significant effects. The CASM-based index was assumed to be applicable to more
diverse exposure conditions beyond those present in the micro- and mesocosm studies.
68
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To avoid having to repeatedly run CASM, simulations were conducted for a variety of
actual and synthetic atrazine chemographs to determine 14-, 30-, 60-, and 90-day average
concentrations that discriminated among exposures that were unlikely to exceed the
CASM-based index (i.e., 5% change in the index). It should be noted that the average
14-, 30-, 60-, and 90-day concentrations were originally intended to be used as screening
values to trigger a CASM run (which is used as a tool to identify the 5% index change
LOC), rather than actual thresholds to be used as an LOC (U.S. EPA, 2003e). The
following threshold concentrations for atrazine were identified (U.S. EPA, 2003e):
14-day average = 38 [^g/L
30-day average = 27 [^g/L
60-day average =18 [^g/L
90-day average =12 [^g/L
Effects of atrazine on aquatic plant communities that have the potential to subsequently
pose indirect effects to the Topeka shiner and its designated critical habitat are best
addressed using the robust set of micro- and mesocosm studies available for atrazine and
the associated risk estimation techniques (U.S. EPA, 2003a, b, c, and e). The 14-, 30-,
60-, and 90-day threshold concentrations developed by EPA (2003e) are used to evaluate
potential indirect effects to aquatic communities for the purposes of this ESA. Use of
these threshold concentrations is considered appropriate because: (1) the CASM-based
index meets the goals of the defined assessment endpoints for this assessment; (2) the
threshold concentrations provide a reasonable surrogate for the CASM index; and (3) the
additional conservatism built into the threshold concentration, relative to the CASM-
based index, is appropriate for an endangered species risk assessment (i.e., the threshold
concentrations were set to be conservative, producing a low level (1%) of false negatives
relative to false positives). Therefore, these threshold concentrations are used to identify
potential indirect effects (via aquatic plant community structural change) to the Topeka
shiner and its designated critical habitat. If modeled atrazine EECs exceed the 14-, 30-,
60- and 90-day threshold concentrations following refinements of potential atrazine
concentrations with available monitoring data, CASM could be employed to further
characterize the potential for indirect effects. A step-wise data evaluation scheme
incorporating the use of the threshold concentrations is provided in Figure 4.2.
69
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Action Area
Exposure
Profile
Data /
Derive EECs for
various averaging
periods from
modeling data
Peak EEC
> Aquatic
Plant
\Ec50y
Yes
No
'No effect" W
30-day
rolling
averages
60-day
rolling
averages
90-day
rolling
averages
14-day
rolling
averages
60-day
AVG.
>18 ug/L?
30-day
AVG.
> 27 ug/L?
14-day
AVG.
> 38 ug/L!h
90-day
AVG.
> 12 ug/Lj,
No
Yes
"May affect, bul
not likely to
adversely affect'
Refine EECs based on site-specific information and/or monitoring data.
Do refined EECs exceed the threshold concentrations above?
,es
"May affect, but
not likely to
adversely affect"
"Likely to
adversely affect'
No
Figure 4.2 Use of Threshold Concentrations in Endangered Species Assessment
4.8 Use of Probit Slope Dose-Response Relationship to Provide Information on the
Endangered Species Levels of Concern
The Agency uses the probit dose-response relationship as a tool for providing additional
information on the potential for acute direct effects to individual listed species and
aquatic animals that may indirectly affect the listed species of concern (U.S. EPA, 2004).
As part of the risk characterization, an interpretation of acute RQ for listed species is
discussed. This interpretation is presented in terms of the chance of an individual event
(i.e., mortality or immobilization) should exposure at the EEC actually occur for a species
with sensitivity to atrazine 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.
70
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The upper and lower bounds of the effects probability are based on available information
on the 95% confidence interval of the slope. Studies with good probit fit characteristics
(i.e., statistically appropriate for the data set) are associated with a high degree of
confidence. Conversely, a low degree of confidence is associated with data from studies
that do not statistically support a probit dose response relationship. In addition,
confidence in the data set may be reduced by high variance in the slope (i.e., large 95%
confidence intervals), despite good probit fit characteristics. In the event that dose
response information is not available to estimate a slope, a default slope assumption of
4.5 (lower and upper bounds of 2 to 9) (Urban and Cook, 1986) is used.
Individual effect probabilities are calculated using 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.
The following probit slopes were used (probability of individual mortality calculations
are presented in Section 5.2):
Fish: Probit slope = 2.7 (95% C.I. of 1.6 - 3.9), rainbow trout - MRID 00024716
Aquatic Invertebrate: Probit slope = 4.4, scud - MRID 45202917
Slope information on the most sensitive aquatic invertebrate (midge) is not available. Therefore,
the probability of an individual effect was calculated using the probit slope of 4.4, which is the
only technical grade atrazine value reported across invertebrate studies; 95% confidence intervals
could not be calculated based on the available data (MRID 45202917; Table A-18).
4.9 Incident Database Review
A number of incidents have been reported in which atrazine has been associated with
some type of environmental effect. Incidents are maintained and catalogued by EFED in
the Ecological Incident Information System (EIIS). Each incident is assigned a level of
certainty from 0 (unrelated) to 4 (highly probable) that atrazine was a causal factor in the
incident. As of the writing of this assessment, 358 incidents are in EIIS for atrazine
spanning the years 1970 to 2005. Most (309/358, 86%) of the incidents involved damage
to terrestrial plants, and most of the terrestrial plant incidences involved damage to crops
treated directly with atrazine. Of the remaining 49 incidents, 47 involved aquatic animals
and 2 involved birds. Because the species included in this effects determination are
aquatic species, incidents involving aquatic animals assigned a certainty index of 2
(possible) or higher (N=33) were re-evaluated. Results are summarized below, and
additional details are provided in Appendix C. The 33 aquatic incidents were divided
into three categories:
1. Aquatic incidents in which atrazine concentrations were confirmed to be
sufficient to either cause or contribute to the incident, including directly via toxic
71
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effects to aquatic organisms or indirectly via effects to aquatic plants, resulting in
depleted oxygen levels;
2. Aquatic incidents in which insufficient information is available to conclude
whether atrazine may have been a contributing factor - these may include
incidents where there was a correlation between atrazine use and a fish kill, but
the presence of atrazine in the affected water body was not confirmed; and
3. Aquatic incidents in which causes other than atrazine exposure are more plausible
(e.g., presence of substance other than atrazine confirmed at toxic levels).
The presence of atrazine at levels thought to be sufficient to cause either direct or indirect
effects was confirmed in 3 (9%) of the 33 aquatic incidents evaluated. Atrazine use was
also correlated with 11 (33%) additional aquatic incidents where its presence in the
affected water was not confirmed, but the timing of atrazine application was correlated
with the incident. Therefore, a definitive causal relationship between atrazine use and the
incident could not be established. The remaining 19 incidents (58%) were likely caused
by some factor other than atrazine. Other causes primarily included the presence of other
pesticides at levels known to be toxic to affected animals. Although atrazine use was
likely associated with some of the reported incidents for aquatic animals, they are of
limited utility to this assessment for the following reasons:
No incidents in which atrazine is likely to have been a contributing factor have
been reported after 1998. A number of label changes, including cancellation of
certain uses, reduction in application rates, and harmonization across labels to
require setbacks for applications near waterbodies, have occurred since that time.
For example, several incidents occurred in ponds that are adjacent to treated
fields. The current labels require a 66-foot buffer between application sites and
water bodies.
The habitat of the assessed species is not consistent with environments in which
incidents have been reported. For example, no incidents in streams or rivers were
reported.
Although the reported incidents suggest that high levels of atrazine may result in impacts
to aquatic life in small ponds that are in close proximity to treated fields, the incidents are
of limited utility to the current assessment. However, the lack of recently reported
incidents in flowing waters does not indicate that effects have not occurred. Further
information on the atrazine incidents and a summary of uncertainties associated with all
reported incidents are provided in Appendix C.
5. Risk Characterization
Risk characterization is the integration of the exposure and effects characterizations to
determine the potential ecological risk from varying atrazine use scenarios within the
action area and likelihood of direct and indirect effects on the Topeka shiner and its
72
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designated critical habitat. The risk characterization provides an estimation (Section 5.1)
and a description (Section 5.2) of the likelihood of adverse effects; articulates risk
assessment assumptions, limitations, and uncertainties; and synthesizes an overall
conclusion regarding the likelihood of adverse effects to the Topeka shiner and/or its
designated critical habitat (i.e., "no effect," "likely to adversely affect," or "may affect,
but not likely to adversely affect"). In accordance with the Agency's Overview
Document (U.S. EPA, 2004), RQs derived in the risk estimation are based on baseline
EECs using the PRZM-EXAMS static water body modeling. In the risk description,
atrazine exposures are refined by considering additional lines of evidence available
regarding habitat information and exposure and effects information used in this
assessment.
5.1 Risk Estimation
Risk was estimated by calculating the ratio of the PRZM/EXAMS estimated
environmental concentration (EEC) (Table 3.4) and the appropriate toxicity endpoint
(Table 4.3). 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 D). Screening-level RQs are based on the most sensitive effects endpoints
and the PRZM/EXAMS EECs listed in Table 3.4.
The highest PRZM/EXAMS EEC (fallow land) was initially used to derive risk quotients.
In cases where LOCs were not exceeded based on the highest EEC, 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 EEC, use/region-specific
RQs were also derived.
In cases where the baseline RQ exceeds one or more LOCs (i.e., "may affect"), additional
factors, including the Topeka shiner life history characteristics, refinement of the baseline
EECs using site-specific information, available monitoring data, and consideration of
community-level threshold concentrations, are considered and used to characterize the
potential for atrazine to adversely affect the Topeka shiner and its designated critical
habitat. Risk quotients used to evaluate potential direct and indirect effects to the Topeka
shiner and to designated critical habitat are in Sections 5.1.1. and 5.1.2. RQs are
described and interpreted in the context of an effects determination in Section 5.2 (risk
description).
5.1.1 Direct Effects
Direct effects to the Topeka shiner associated with acute and chronic exposure to atrazine
are based on the most sensitive toxicity data available for freshwater fish. RQs used to
estimate acute and chronic direct effects to the Topeka shiner are in Tables 5.1 and 5.2,
respectively.
73
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Table 5.1 Summary of Acute RQs Used to Estimate Direct Effects to the Topeka
Shiner
Effect
Surrogate
Species
Toxicity
Value
(ng/L)
EEC (fig/L)
RQ
Probability of
Individual
Effect
LOC (0.05)
Exceedance
Direct acute
effects to the
Topeka shiner
Rainbow
trout
lc50 =
5,300a
Peak = 103b
0.02
1 in 5.2E+05
(1 in 249 to 1 in
5.2E+10)0
Nod
a Based on a 96-hour LC50 value of 5,300 (ig/L for the rainbow trout (MRID #000247-16).
b Based on peak fallow land baseline EEC (Table 3.4).
c Based on a probit slope value of 2.72 for the rainbow trout with 95% confidence intervals of 1.56 and 3.89 (MRID
00024716).
d RQ < acute endangered species LOC of 0.05.
Table 5.2 Summary of Chronic RQs Used to Estimate Direct Effects to the Topeka
Shiner
Effect to
Topeka shiner
Use (appl. Method; rate;
# appl.; interval between
appl.)
Range of 60-
day EECs
(Hg/L)
Freshwater Fish
Chronic RQ
(NOAEC= 65
ug/L r
LOC (1.0) Exceeded
Chronic Direct
Toxicity
Fallow/Idle land (aerial
liquid; 2.25 lb ai/A; 1
appl.)
West: 103
Great Plains: 49
1.6
0.75
Yes (West region)
Corn (aerial liquid; 2.5 lb
ai/A; 2 appl.)
West: 88
Great Plains: 82
1.4
1.3
Yes (both regions)
Forestry
West: 26
Great Plains: 58
0.40
0.89
No
Sorghum (aerial liquid; 2
lb ai/A; 1 appl.)
West: 57
Great Plains: 54
0.88
0.83
No
All other uses
<12
<0.18
No
a Based on a 44-week NOAEC value of 65 (ig/L for the brook trout (MRID 00024377).
Based on the highest baseline EEC modeled for atrazine use patterns within the action
area, acute direct effects RQs do not exceed the endangered species LOC of 0.05.
Therefore, atrazine is not expected to result in acute direct effects to the Topeka shiner
within the action area. However, chronic RQs for fallow land and corn exceeded the
chronic LOC of 1. These RQs are further characterized in the context of the effects
determination in Section 5.2.
5.1.2 Indirect Effects
This section presents RQs used to evaluate the potential for atrazine to induce indirect
effects. Pesticides have the potential to exert indirect effects upon listed species by
inducing changes in structural or functional characteristics of affected communities.
Perturbation of forage or prey availability and alteration of the extent and nature of
habitat are examples of indirect effects. A number of these indirect effects are also
considered as part of the critical habitat adverse modification evaluation. In conducting a
screen for indirect effects, direct effects LOCs for each taxonomic group (i.e., freshwater
fish, invertebrates, aquatic plants, and terrestrial plants) are employed to make inferences
concerning the potential for indirect effects upon listed species that rely upon non-listed
74
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organisms in these taxonomic groups as resources critical to its life cycle (U.S. EPA,
2004). This approach used to evaluate indirect effects to listed species is endorsed by the
Services (USFWS/NMFS, 2004b). If no direct effect listed species LOCs are exceeded
for organisms on which the Topeka shiner depends for survival or reproduction, indirect
effects to the Topeka shiner are not expected to occur.
If LOCs are exceeded for organisms on which the Topeka shiner depends for survival or
reproduction, dose-response analysis is used to estimate the potential magnitude of effect
associated with an exposure equivalent to the EEC. The greater the probability that
exposures will produce effects on a taxa, the greater the concern for potential indirect
effects for listed species dependant upon that taxa (U.S. EPA, 2004).
As an herbicide, indirect effects to the Topeka shiner from potential effects on primary
productivity of aquatic plants are a principle concern. If plant RQs fall between the
endangered species and non-endangered species LOCs, a no effect determination for
listed species that rely on multiple plant species to successfully complete their life cycle
(termed plant dependent species) is determined. If plant RQs are above non-endangered
species LOCs, this could be indicative of a potential for adverse effects to those listed
species that rely either on a specific plant species (plant species obligate) or multiple
plant species (plant dependant) for some important aspect of their life cycle (U.S. EPA,
2004). Based on the information provided in Section 2.3, the Topeka shiner does not
have any known obligate relationship with a specific species of aquatic plant.
Direct effects to riparian zone vegetation may also indirectly affect the Topeka shiner by
reducing water quality and available spawning habitat via increased sedimentation.
Direct impacts to the terrestrial plant community (i.e., riparian habitat) are evaluated
using submitted terrestrial plant toxicity data. If terrestrial plant RQs exceed the
Agency's LOC for direct effects to non-endangered plant species, based on EECs derived
using EFED's Terrplant model (Version 1.2.1) and submitted guideline terrestrial plant
toxicity data, a conclusion that atrazine may affect the Topeka shiner via potential
indirect effects to the riparian habitat (and resulting impacts to habitat due to increased
sedimentation) is made. Further analysis of the potential for atrazine to affect the Topeka
shiner via reduction in riparian habitat includes a description of the importance of
riparian vegetation to the assessed species and types of riparian vegetation that may
potentially be impacted by atrazine use within the action area.
RQs used to evaluate the potential for atrazine to induce indirect effects to the Topeka
shiner are in Table 5.3 below. These RQs suggest that potential indirect effects to the
Topeka shiner from reduction in food availability, primary productivity, and spawning
habitat could occur as indicated by LOC exceedances. Highest RQs occurred for the
corn, sorghum, fallow, and forestry uses, although LOCs were exceeded for aquatic
plants for all uses assessed. These RQs were based on the most sensitive surrogate
species tested across aquatic invertebrate, fish, and aquatic plant species tested.
Discussion of these RQs in the context of this effects determination is presented in
Section 5.2.
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Table 5.3. RQs used to evaluate the potential for atrazine to induce indirect effects to the Topeka
shiner.
Indirect
Taxa
Toxicity
Corn, sorghum, fallow,
Residential, rights of
LOC Exceedances
Effect
Value
and forestry
ways, and turf uses
(ug/L)
EEC
RQ
EEC
RQ
Reduction in
Aquatic
LC50:
Peak (ug/L):
0.04 - 0.14
Peak (ug/L):
<0.02
Acute and chronic RQs
Food Supply
Invertebrate
720
27 -103
3.3 - 12
exceed the endangered
NOAEC:
21-Day (ug/L):
0.45 - 1.7
21-Day
species acute (0.05) and
chronic LOC (1.0) for corn,
60
27 - 103
(ug/L):
3.2- 12
<0.2
and fallow uses. The acute
RQ was also exceeded for
the sorghum and forestry
use. LOCs were not
exceeded for residential,
rights of ways, or turf uses.
Terrestrial
LC50:
2 - 4 lbs
0.29- 0.57
1 - 2 lbs
0.14-
Interim LOC for terrestrial
Invertebrate
approx. 7 lbs
a.i./Acreb
a.i./Acre
a.i./Acre
0.29
invertebrates of 0.05 was
exceeded for all uses.
Reduction in
Vascular
EC50: 37
Peak (ug/L):
0.73 - 2.8
Peak (ug/L):
<=0.32
RQs exceed the LOC (1.0)
food supply;
Primary
productivity
Aquatic
Plants
27 -103
3.3 - 12
for corn, sorghum,
forestry, and fallow uses.
LOCs were not exceeded
for residential, rights of
ways, or turf uses.
Non-
EC50: 1
Peak (ug/L):
27 - 103
Peak (ug/L):
3.3 - 12
LOCs were exceeded for all
Vascular
27 -103
3.3 - 12
uses.
Aquatic
Plants
Reduction in
Rainbow
LC50: 5300
Peak (ug/L):
0.03
Peak (ug/L):
<0.01
No LOCs were exceeded.
food supply;
trout LC50
103
3.3 - 12
reduction in
Brook trout
NOAEC: 65
60-Day (ug/L):
0.42 - 1.6
<12
<=0.18
Chronic LOC was exceeded
suitable
NOAEC
27 - 103
for the corn and fallow,
spawning
habitat
uses.
a The direct effects RQs presented in Tables 5.1 and 5.2 were also used to characterize potential chronic risks to freshwater fish.
However, sunfish are a predominant species that provides spawning habitat to the Topeka shiner,
b LC50 is an empirical value that was not statistically derived; 51% mortality occurred at 20 ppm soil (Mola et al., 1987;
Ecotox No. 71417). Assuming a soil depth of 3 cm and a soil density of 1.3 g/cm3, an application rate of 7 lbs a.i./Acre would be
associated with a soil concentration of 20 ppm. This calculation assumes no foliar interception (e.g., direct spraying of bare ground)
and is, therefore, conservative.
Potential indirect effects to the Topeka shiner resulting from direct effects on riparian
vegetation were 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 emerging seedlings are more sensitive to atrazine via
soil/root uptake than emerged plants via foliar routes of exposure. However, all tested
plants, with the exception of corn in the seedling emergence and vegetative vigor tests,
and ryegrass in the vegetative vigor test, exhibited adverse effects following exposure to
atrazine. The results of these tests indicate that a variety of terrestrial plants that may
inhabit riparian zones may be sensitive to atrazine exposure. RQs used to estimate
potential indirect effects to the Topeka shiner from seedling emergence and vegetative
76
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vigor effects on terrestrial plants within riparian areas are summarized in Tables 5.4 and
5.5, respectively.
As shown in Table 5.4, terrestrial plant RQs are above the Agency's LOC for all species
except corn. For species with LOC exceedances, RQ values based on aerial application
of atrazine to forestry at 4.0 lb ai/A range from 1.8 to 113; the maximum RQ value based
on an equivalent ground application is 35, approximately a three-fold reduction as
compared to aerial applications. Granular application of atrazine to residential lawns at
2.0 lb ai/A may also impact terrestrial plants exposed to atrazine via runoff with RQs
ranging from <1 (corn and soybeans) to 13 (carrots). Monocots and dicots show similar
sensitivity to atrazine; therefore, RQs are similar across both taxa.
Table 5.4 Non-target Terrestrial Plant Seedling Emergence RQs
Surrogate Species
ec25
(lbs ai/A)a
EEC
Dry adjacent areasb
RQ
Dry adjacent areasb
Monocot - Corn
>4.0
Aerial: 0.17-0.34
Ground: 0.05 - 0.10
Granular: 0.04
-------
three dicot species (soybeans, cabbage, and cucumber), based on aerial application of
atrazine at 2 to 4 lb ai/A, with RQs ranging from 5 to 33. For ground applications, LOCs
are exceeded for two dicot species, cabbage and cucumber, with RQs ranging from 1.5 to
3. Vegetative vigor RQs do not exceed LOCs for any of the tested monocot species.
Table 5.5 Non-targetr
"errestrial Plant Vegetative Vigor Toxicity RQs
Surrogate Species
ec25
(lbs ai/A)a
Drift EEC
(lbs ai/A)b
Drift RQb
Monocot - Corn
>4.0
Aerial: 0.13-0.26
Ground: 0.01-0.02
4.0
Aerial: 0.13-0.26
Ground: 0.01-0.02
LOC), the Agency concludes a
preliminary "may affect" determination for the FIFRA regulatory action regarding
78
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atrazine. Following a "may affect" determination, additional information is considered to
refine the potential for exposure at the predicted levels based on monitoring data, the life
history characteristics (i.e., habitat range, feeding preferences, etc.) of the Topeka shiner,
and potential community-level effects to aquatic plants.
Based on the best available information, refined evaluations were 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 Topeka shiner and
designated critical habitat. The criteria used to make determinations that the effects of an
action are "not likely to adversely affect" the Topeka shiner and designated critical
habitat include the following:
Significance of Effect: Insignificant effects are those that cannot be
meaningfully measured, detected, or evaluated in the context of a level of
effect where "take" occurs for even a single individual. "Take" in this
context means to harass or harm, defined as the following:
¦ Harm includes significant habitat modification or
degradation that results in death or injury to listed species
by significantly impairing behavioral patterns such as
breeding, feeding, or sheltering.
¦ Harass is defined as actions that create the likelihood of
injury to listed species to such an extent as to significantly
disrupt normal behavior patterns which include, but are not
limited to, breeding, feeding, or sheltering.
Likelihood of the Effect Occurring: Discountable effects are those that are
extremely unlikely to occur. For example, use of dose-response
information to estimate the likelihood of effects can inform the evaluation
of some discountable effects.
Adverse Nature of Effect: Effects that are wholly beneficial without any
adverse effects are not considered adverse.
A description of the risk and effects determination for each of the established direct and
indirect assessment endpoints for the Topeka shiner is in Section 5.2.1 and 5.2.2.,
respectively. A description of the risk and effects determination for the critical habitat
impact analysis in less vulnerable watersheds is provided in Section 5.3.
5.2.1 Potential for Atrazine to Directly Affect the Topeka Shiner
5.2.1.1. Acute Exposures
All acute RQs for the most sensitive freshwater fish species tested were <=0.02. The
endangered species LOC is 0.05. Therefore, no RQs exceed the endangered species
LOC. At the RQ of 0.02, the probability of an individual mortality would be
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approximately 1 in 500,000 (95% C.I. of 1 in 249 to 1 in 5E10) based on a probit slope
value of 2.72 for the rainbow trout with 95% confidence intervals of 1.56 and 3.89
(MRID 00024716).
There are a number of uncertainties in the acute risk assessment. The most sensitive
freshwater fish species tested was used to calculate RQs. The Topeka shiner has not been
tested in acute studies; therefore, the sensitivity of the Topeka shiner to atrazine is
uncertain. However, a number of freshwater fish species have been tested in acute
studies including rainbow trout, brook trout, Nile river fish, bluegill sunfish, tilapia,
fathead minnow, carp, brown trout, zebra fish, and gold fish. LC50s range from 5300
ug/L to 60,000 ug/L. The Topeka shiner would need to be approximately 2-fold more
sensitive than the most sensitive freshwater species tested to result in an LOC
exceedance.
There is also uncertainty in the potential exposure levels to the Topeka shiner. The shiner
lives in low order streams with little to negligible flow. The EECs used to calculate RQs
were based on PRZM/EXAMS modeling, which suggested that peak exposures could be
up to 100 ug/L. As previously discussed, recent targeted and non-targeted monitoring
from highly vulnerable and less vulnerable watersheds reported peak EECs that are
higher than the highest peak PRZM/EXAMS EEC used to calculate RQs. Based on the
highest peak EEC reported in the recent targeted monitoring studies in vulnerable
watersheds, the acute RQ would be 0.04 (highest EEC across monitoring studies of 209
|ig/L / LC50 of 5,300 |ig/L = RQ of 0.04), which is also below the acute endangered
species LOC. Therefore, based on the lack of LOC exceedance from the most sensitive
species tested, a conclusion of "no effect" to the Topeka shiner was made.
5.2.1.2. Chronic Exposures
Chronic RQs (presented in Table 5.2) exceed the LOC of 1.0 for corn (both regions) and
fallow/idle land (west region only), with RQ values as high as 1.6 (see Table 5.2). Fish
chronic RQs were based on PRZM/EXAMS 60-day EECs and the freshwater fish chronic
NOAEC for brook trout of 65 |ig/L.
The highest 60-day average atrazine concentration from the available targeted vulnerable
watershed monitoring study was 26 ug/L. Nonetheless, Topeka shiner habitats include
first order streams and small inlets or side pools within streams (Figure 5.1). However,
monitoring studies typically sample mid-instream locations within a water body.
Atrazine concentrations within side pools of low-order streams will depend on a number
of factors that influence residence time, and longer term concentrations within these
inlets may exceed those reported in both the targeted and non-targeted monitoring
studies. Therefore, the PRZM/EXAMS 60-day EEC was considered an appropriate
measure of exposure for the Topeka shiner.
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Figure 5.1. Examples of Topeka Shiner Habitat in Minnesota. Images obtained from
Minnesota Department of Natural Resources (2005, 2006)
81
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There is also one known Topeka shiner population in an enclosed farm pond (Dehle,
2001). Therefore, the PRZM/EXAMS estimate for long-term exposures are considered
appropriate for exposure estimation for this location.
The magnitude of potential effects at the highest 60-day EEC for corn and fallow uses of
88 ug/L and 103 ug/L, respectively, is uncertain. In the submitted life-cycle studies,
LOAEC values ranged from 120 ug/L to 870 ug/L, which are all above the
PRZM/EXAMS 60-day EECs. The LOAEC in the most sensitive study was based on
growth effects; a 7.2% reduction in mean length and a 16% reduction in body weight
relative to controls occurred at the LOAEC of 120 ug/L. If the Topeka shiner sensitivity
to atrazine is similar to brook trout (the most sensitive species tested), then the magnitude
of potential effects would be expected to be somewhat less than effects reported at the
LOAEC of 120 ug/L in brook trout. Effects at the LOAEC from other studies included:
reduced growth (fathead minnows at 150 ug/L); equilibrium loss (bluegill sunfish at 500
ug/L); and mortality (fathead minnows at 870 ug/L). These studies are described in
Appendix A.
Chronic EECs were based on the maximum labeled application rates. Typical application
rates for corn and fallow uses were 0.6 to 0.9 lbs a.i./Acre, which is >50% lower than the
maximum labeled application rates. Therefore, EECs based on typical application rates
would be reduced by more than 50%, which would not result in LOC exceedance.
Also, as discussed in Section 4.2.3, several open literature studies raise questions about
sublethal effects of atrazine on plasma steroid levels, behavior modifications, gill
physiology, and endocrine-mediated functions in freshwater and anadromous fish. These
data were not used to determine if atrazine is likely to adversely affect the Topeka shiner
or not for a number of reasons including (1) study design limitations, (2) lack of a
quantifiable link between the sublethal effects and the assessment endpoints assessed
(i.e., survival, growth, and reproduction), and (3) effects to reproduction, growth, and
survival were not observed in the four submitted fish life-cycle studies at levels that
produced the reported sublethal effects (Appendix A). These studies are discussed in
greater detail in Sections A.2.4a and A.2.4b of Appendix A.
5.2.1.3. Summary of Conclusions
The effects determination for potential direct effects to the Topeka shiner is summarized
in Table 5.7 below.
Table 5.7. Effects Determination Summary for Potential Direct Effects to the
Topeka Shiner from Labeled
Jses of Atrazine
Endpoint
Use
Region
Effects
Determination
Basis for Conclusion
Acute direct
effects
All
West, Great
Plains
No effect
No acute LOCs are exceeded for the most sensitive
species tested.
Chronic
direct effects
Corn
West, Great
Plains
Likely to
adversely affect
RQs for corn and fallow were 1.3 to 1.6 based on the
PRZM/EXAMS standard static pond. Based on the
habitat of the Topeka shiner, the PRZM/EXAMS EECs
Fallow
West
Likely to
82
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adversely affect
were considered to be appropriate measures of exposure
for this species. The LOAEC in the most sensitive life-
cycle study was 7% reduction in length and 16%
reduction in weight at 120 ug/L. The magnitude of
potential effect to the Topeka shiner would be expected
to be somewhat lower than effects observed at the most
sensitive LOAEC.
All
other
uses
West, Great
Plains
No effect
The chronic LOC was not exceeded for these uses.
5.2.2 Potential for Atrazine to Indirectly Affect the Topeka Shiner
Indirect effects assessed include reduced food supply (invertebrates, plants, or other fish),
by changes in water quality via alterations in the aquatic or terrestrial (riparian) plant
community, and effects to reproductive habitat (sunfish nests provide spawning habitat
for Topeka shiners). Dietary behavior of the Topeka shiner is described as a generalist
omnivore. Its diet consists primarily of aquatic insects (particularly midges) and other
aquatic invertebrates, but it also consumes plant material, terrestrial invertebrates, and
other fish (Dahle, 2001). Therefore, the potential for atrazine to affect the Topeka shiner
via reduction in available food is evaluated using RQs for aquatic invertebrates, aquatic
plants, fish, and terrestrial invertebrates.
RQs presented in Section 5.1 indicate that LOCs were exceeded for some organisms that
the Topeka shiner could rely on for food, reproduction, or habitat suitability/stability.
These RQs are further described in sections 5.2.2.1 to 5.2.2.3 below.
5.2.2.1. Potential for Atrazine to Indirectly Affect the Topeka Shiner via Reduction
in Aquatic Invertebrates as Food Items
Acute baseline RQs were based on the lowest LC50 value across all aquatic invertebrate
taxa of 720 |ig/L for the midge (Chironomus spp.). Consideration of all acute toxicity
data for the midge shows a wide range of sensitivity within and between species of the
same genus (2 orders of magnitude) with values ranging from 720 to >33,000 |ig/L. The
highest acute RQ for the midge was 0.14. A probit slope was not available from any of
the midge studies. However, based on the most conservative (lowest) probit slope
reported for freshwater invertebrates of 4.4 (scud, MRID 45202917), the probability of an
individual effect at an RQ of 0.14 would be approximately 1 in 12,000.
Therefore, assuming that the Topeka shiner consumes only animals that are as sensitive
as the most sensitive species tested in the most sensitive study conducted in that species,
potential reduction in abundance of aquatic invertebrates as food would be approximately
0.01% (1/12,000).
Given the low magnitude of potential impact on abundance of the most sensitive aquatic
invertebrate species based on the most sensitive bioassay, potential impacts to the Topeka
shiner resulting from reduced availability of aquatic invertebrates as food is considered to
be sufficiently low such that any potential effect to the Topeka shiner would be
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insignificant. Therefore, a take is not anticipated to occur from any labeled use of
atrazine as a result of reduced aquatic invertebrate food base. This conclusion is further
supported by the observation that LOCs were not exceeded for any aquatic invertebrate
species other than the most sensitive species, the generalist feeding behavior of the
assessed species, and the wide range of LC50s in the most sensitive species (720 ug/L to
>33,000 ug/L).
Chronic LOCs were also exceeded for the most sensitive aquatic invertebrate (scud,
NOAEC = 60 ug/L) for corn (both regions) and fallow (west region) uses. The highest
21-day EEC of 103 ug/L exceeded the NOAEC of 60 ug/L reported for the scud. The
LOAEC in this study (MRID 00024377) was 120 ug/L based on 25% reduction in
development of F1 to seventh instar. NOAECs were not exceeded for any other aquatic
invertebrate tested including midge, daphnids, green hydra, snail, or leech. The baseline
EEC of 103 ug/L did not exceed any level that elicited a response (LOAEC) in the
available studies, and no LOCs were exceeded for the predominant food items (insects
such as midges) of the Topeka shiner. Given the magnitude of potential impact on
abundance of the most sensitive aquatic invertebrate species based on the most sensitive
bioassay, potential impacts to the Topeka shiner resulting from reduced availability of
aquatic invertebrates as food is considered to be sufficiently low such that any potential
effect to the Topeka shiner would be insignificant or unmeasurable. Therefore, atrazine
is "not likely to adversely affect" (NLAA) the Topeka shiner via reductions in aquatic
invertebrate food base.
5.2.2.2. Potential for Atrazine to Adversely Affect the Topeka Shiner by
Affecting Terrestrial Invertebrates
Studies that showed statistically significant (p<0.05) effects to terrestrial invertebrates
were typically at levels that were above highest labeled application rate of 4 lbs a./Acre
for forestry and 2.5 lbs a.i./Acre for corn and sorghum. The most sensitive terrestrial
insect tested was the springtail (iOnychiuridae). Mortality rate in Onychiurus armatus
was approximately 50% at 20 ppm soil, which is associated with an application rate of 7
lbs a.i./Acre assuming a soil depth of 3 cm and a soil density of 1.3 g/cm3. Another
species of springtail, O. armatus, was associated with 18% mortality at soil levels
associated with approximately 1 lb a.i./Acre (Mola et al., 1987), which is within the range
of labeled atrazine application rates. An application rate of 5.4 lbs a.i./Acre was
associated with reduced abundance of microarthropods (Fratello et. al., 1985); however,
reduced abundance could have been caused by indirect effects (migration/repellency).
Application rates of 0.9 and 1.8 lbs a.i./Acre did not affect abundance of microarthropods
(Cortet et al., 2002; Fratello et. al., 1985).
Atrazine did not affect survival in a number of beetle species at application rates that
ranged from 0.8 to 8 lbs a.i./Acre (Kegel, 1989; Brust, 1990; Samsoe-Petersen, 1995).
No studies in beetles established definitive LOAEC or EC50 values. Because the studies
in beetles produced free-standing NOAECs, their utility is somewhat limited; however,
they do suggest that abundance would not likely be affected to an extent that would result
84
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in indirect effects to the Topeka shiner at atrazine applications up to 8 lbs a.i./Acre for
ground beetles (Poecilus) and 2 lbs a.i./Acre for carabid beetles.
In addition, earthworm LC50s were 270 and 380 ppm soil (Mosleh et al., 2003; Haque
and Ebing, 1983). The highest soil concentrations expected from the maximum labeled
application rate (4 lbs a.i./Acre) on the treated field would be approximately 11 ppm in
the top 3 cm of soil (RQ would be approximately 0.04).
Also, the acute contact LD50 in honey bees was >97 ug/bee (5% mortality occurred at the
highest dose level) (MRID 00036935). A dose of 97 ug/bee corresponds to an atrazine
concentration on the bee of approximately 757 ppm, assuming an adult honey bee weighs
128 mg (Mayer and Johansen, 1990). The corresponding exposure value to honey bees at
an application rate of 4 lbs a.i./Acre is approximately 60 ppm. Although the resulting RQ
(0.079) would be above the interim LOC for terrestrial invertebrates of 0.05, the resulting
probability of an individual mortality would be approximately 1 in 3,000,000 assuming a
probit slope of 4.5. The default probit slope was used because insufficient mortality
occurred at the highest dose tested in the honey bee study (MRID 00036935).
Overall, the available data suggest that some species of terrestrial invertebrates could be
directly or indirectly affected by atrazine at labeled application rates. However, the
magnitude of such effects is not likely to result in indirect effects to the Topeka shiner.
For this reason, atrazine is not likely to adversely affect the Topeka shiner by affecting
terrestrial invertebrate food source.
5.2.2.3. Potential for Atrazine to Adversely Affect the Topeka Shiner by
Affecting the Aquatic Plant Community
Aquatic plants may serve as food and shelter for the Topeka shiner in addition to
contributing to water quality parameters essential to its habitat. RQs presented in Section
5.1 exceeded the LOC for all uses (non-vascular plants) in both the west and Great Plains
regions. The vascular plant LOC was also exceeded for all agricultural uses assessed.
The potential for atrazine to affect the Topeka shiner via effects to aquatic plants is
initially based on the most sensitive EC50 in vascular plants (duckweed, EC50 = 37
ug/L) and non-vascular aquatic plants (algae, EC50 = 1 ug/L). As noted above LOCs
were exceeded for all use scenarios for algae and for corn, sorghum, and forestry uses for
vascular plants. Therefore, a preliminary "may effect" determination is made.
RQs used for the preliminary "may effect" determination were based on the most
sensitive single species EC50s. In order to determine whether potential effects to
individual plant species would likely result in community-level effects to the Topeka
shiner's habitat, the time-weighted baseline EECs (for 14-, 30-, 60-, and 90-day averages
from Table 3.4) were compared to their respective time-weighted threshold
concentrations (described in Section 4). As discussed in Section 4.2, concentrations of
atrazine from the exposure profile at a particular use site and/or action area that exceed
any of the following time-weighted threshold concentrations indicate that changes in the
85
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aquatic plant community structure (including food items for the Topeka shiner) could be
affected:
14-day average = 38 |ig/L
30-day average = 27 |ig/L
60-day average =18 |ig/L
90-day average =12 |ig/L
A comparison of the range of the baseline 14-, 30-, 60-, and 90-day EECs for the Topeka
shiner with the atrazine threshold concentrations representing potential aquatic
community-level effects is provided in Table 5.8.
Table 5.8. Summary of Modeled Scenario Time-Weighted Baseline EECs with
Threshold Concentrations
'or Potential Community-Level Effects
Use Scenario
14-day
30-day
60-day
90-day
EECs
(Hg/L)
a
Threshold
Cone.
(Hg/L)
EECs
(Hg/L)
a
Threshold
Cone.
(Hg/L)
EECs
(Hg/L)
a
Threshold
Cone.
(Hg/L)
EECs
(Hg/L)
a
Threshold
Cone.
(Hg/L)
Corn
84-92
38
84-91
27
82-88
18
81-85
12
Sorghum
57-59
56-58
54-57
53-56
Fallow / idle
land
49-
103
49-
103
49-
103
49-
103
Forestry
27-61
27-60
26-58
25-57
Residential,
turf, and
rights of ways
3 - 12
3 - 11
3 - 11
3 - 11
a Baseline EECs from Table 3.4.
Based on the results of this comparison, estimated baseline 14- to 90-day EECs for corn,
sorghum, fallow/idle land, and forestry modeled uses exceed their respective threshold
concentrations for community level effects.
The recently submitted targeted monitoring data suggests that longer duration atrazine
concentrations are typically considerably lower than the peak atrazine levels. For
example, the median 14-day atrazine concentration across all sites was approximately
50% of the maximum (Appendix B). Nonetheless, sampling stations used for the
monitoring study may not represent small side pools such as those commonly inhabited
by the Topeka shiner (see Figure 5.1). For this reason, the EECs are not further refined
from PRZM/EXAMS estimates and the effects determination is not changed by
86
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considering habitat characteristics of the assessed species relative to the PRZM/EXAMs
standard ecological pond.
In conclusion, consideration of the community-level effects thresholds does not
dramatically impact the conclusions of this assessment. EECs for corn, sorghum, fallow
land, and forestry exceed at least one of the community level effects thresholds listed in
Table 5.8. EECs for residential, turf, rights of ways uses do not exceed any of the
community level effects thresholds.
For this reason, the effects determination for potential indirect effects to the Topeka
shiner via effects to aquatic plants is "likely to adversely affect, or LAA" for agricultural
and forestry uses. However, because PRZM/EXAMS EECs for turf, rights-of-ways, and
residential uses were lower than the community level effects threshold concentrations,
atrazine is not likely to adversely affect the Topeka shiner by impacting the plant
community from these uses.
5.2.2.4. Indirect Effects via Reduction in Fish Necessary for Food and
Reproduction
Spawning of the Topeka shiner occurs over gravel nests of sunfish. As described in
Section 5.2.1, atrazine use is considered to have "no effect" to the Topeka shiner via
acute direct toxicity. This conclusion was based on the most sensitive acute LC50 in fish
available. Therefore, a conclusions of "no effect" is also made with respect to the
potential for indirect effects associated with acute effects to other fish species.
However, the conclusion for the direct effects assessment for potential chronic effects to
the Topeka shiner presented in Section 5.2.1 was "likely to adversely affect." Therefore,
additional analysis is needed to evaluate whether the Topeka shiner may be adversely
affected by potential chronic effects to other fish species.
The highest chronic fish RQ was 1.6 (EEC = 103 ug/L, NOAEC = 65 ug/L) based on
EECs for the fallow use. The most sensitive NOAEC was based on a life-cycle study in
brook trout that produced a NOAEC of 65 ug/L and a LOAEC of 120 ug/L. The LOAEC
was based on growth effects (7% reduction in length and a 16% reduction in weight).
The highest EEC (fallow) was 103 ug/L, which is somewhat lower than the LOAEC of
120 ug/L (MRID 00024377). The Topeka shiner is known to depend on sunfish nests for
spawning. Sunfish were somewhat less sensitive than brook trout to atrazine. Although
the NOAEC in bluegill sunfish was 95 ug/L, which is similar to the brook trout NOAEC
of 65 ug/L, the LOAEC in sunfish was 500 ug/L based on loss of equilibrium. This
analysis suggests that fish could be exposed to atrazine at levels that approach the
LOAEC in the most sensitive species; however, the magnitude of potential effects to fish
species is expected to be sufficiently low such that indirect effects to the Topeka shiner
are unlikely to occur. Therefore, atrazine is not likely to adversely affect the Topeka
shiner via impacts on other fish species. This conclusion is based on significance of
effect as defined in Section 5.2.
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5.2.2.5. Indirect Effects via Alteration in Terrestrial Plant Community
(Riparian Habitat)
As shown in Tables 5.4 and 5.5, seedling emergence or vegetative vigor RQs exceed
LOCs for a number of the tested plant species. Based on exceedance of the seedling
emergence LOCs for all species tested except corn, the following general conclusions can
be made with respect to potential harm to riparian habitat via runoff exposures:
Atrazine may enter riparian areas via runoff where it may be taken up through
the root system of sensitive plants.
Comparison of seedling emergence EC25 values to EECs estimated using
TERRPLANT suggests that 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 atrazine deposition
onto bare soil would be expected to inhibit the growth of new vegetation.
Because LOCs were exceeded for most species tested (9/10) in the seedling
emergence studies, it is likely that many species of herbaceous plants may be
potentially affected by exposure to atrazine in runoff.
Because RQs for terrestrial plants are above the Agency's LOCs, atrazine use is
considered to have the potential to directly impact plants in riparian areas, potentially
resulting in degradation of stream water quality via sedimentation and alteration of
habitat. Therefore, an analysis of the potential for habitat degradation to affect the
Topeka shiner is necessary.
Riparian plants beneficially affect water and stream quality in a number of ways in both
adjacent river reaches and areas downstream of the riparian zone. Riparian vegetation
provides a number of important functions in the stream/river ecosystem, including the
following:
serves as an energy source;
provides organic matter to the watershed;
provides streambank stability;
provides shading, which ensures thermal stability of the stream; and
serves as a buffer, filtering out sediment, nutrients, and contaminants before
they reach the stream.
A general discussion of riparian habitat and its relevance to the Topeka shiner is provided
below. Additional details are presented in Appendix H.
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It is difficult to estimate the magnitude of potential impacts of atrazine use on riparian
habitat and the magnitude of potential effects on stream water quality from such impacts
as they relate to survival, growth, and reproduction of the Topeka shiner. The level of
exposure and any resulting magnitude of effect on riparian vegetation are expected to be
highly variable and dependent on many factors. The extent of runoff and/or drift into
stream corridor areas is affected by the distance the atrazine use site is offset from the
stream, local geography, weather conditions, and quality of the riparian buffer itself. The
sensitivity of the riparian vegetation is dependent on the susceptibility of the plant species
present to atrazine and composition of the riparian zone (e.g. vegetation density, species
richness, height of vegetation, width of riparian area).
Quantification of risk to the Topeka shiner from potential effects to riparian areas is
precluded by the following factors:
The relationship between distance of soil input into the watershed and sediment
deposition in areas critical to survival, reproduction, and growth of the Topeka shiner
is not known;
Riparian areas within the action area are highly variable in their composition and
location with respect to atrazine use; therefore, their sensitivity to potential damage is
also variable; and
The action area for the Topeka shiner is a large geographic area, encompassing
multiple states.
In addition, even if plant community structure was quantifiably correlated with riparian
function, it may not be possible to discern the effects of atrazine on species composition
separate from other agricultural actions or determine if atrazine is a significant factor in
altering community structure. Plant community composition in agricultural field margins
is likely to be modified by many agricultural management practices. Vehicular impact
and mowing of field margins and off-target movement of fertilizer and herbicides are all
likely to cause changes in plant community structure of riparian areas adjacent to
agricultural fields (Jobin et al., 1997; Kleijn and Snoeijing, 1997; Schippers and Joenje,
2002). Although herbicides are commonly identified as a contributing factor to changes
in plant communities adjacent to agricultural fields, some studies identify fertilizer use as
the most important factor affecting plant community structure near agricultural fields
(e.g. Schippers and Joenje, 2002) and community structure is expected to be affected by a
number of other factors (de Blois et al., 2002). Thus, the effect of atrazine alone on
riparian community structure is complicated by other multiple stressors likely to occur
within the action area.
In summary, terrestrial plant RQs are above terrestrial plant LOCs for all uses; therefore,
labeled use of atrazine has the potential to affect riparian vegetation within the Topeka
shiner's habitats. However, water quality and sedimentation / siltation in a stream may
depend on numerous factors, and determining whether atrazine use is expected to result
in an overall increase in sediment/silt levels in a habitat is difficult. Until further analysis
is performed on specific land management practices and sensitivity of riparian vegetation
in areas surrounding Topeka shiner habitats, potential effects to riparian vegetation as
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indicated by terrestrial plant RQ exceedance, is presumed to potentially adversely affect
the Topeka shiner and its designated critical habitat
Because woody plants are typically not sensitive to atrazine at expected exposure
concentrations, riparian areas which have predominantly forested vegetation containing
woody shrubs and trees are not likely to be adversely impacted by atrazine use to an
extent that would be expected to result in measurable effects on the Topeka shiner.
Therefore, atrazine is not likely to adversely affect populations of Topeka shiners in
watersheds with predominantly forested riparian areas. However, given that the Topeka
shiner's habitat is located in the Great Plains, the presence of forested riparian areas is not
expected to be predominant landcover.
Therefore, habitats of the Topeka shiner that are in close proximity to potential atrazine
use sites and where the riparian vegetation is comprised of sensitive grasses and non-
woody plants, the effects determination is "likely to adversely affect." A graphic
representation of the effects determination for this assessment endpoint, based on
evaluation of the sedimentation, streambank stability, and thermal stability attributes for
riparian vegetation is provided in Figure 5.2.
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Sedimentation
Thermal
Stability
Streambank
Stability
Wider and shallower
channels resulting from
eroding streambanks may
adversely modify habitat.
Water temperature
increases in the absence
of shading by forested
vegetation.
Increased sedimentation may
reduce spawning habitat.
Terrestrial plant RQs exceed LOCs; therefore, riparian vegetation may be affected.
Not likely to
adversely affect
(NLAA). Forested
riparian areas (woody
shrubs and trees) are
not expected to be
affected by atrazine.
Riparian health is associated with many water quality parameters. The assessment links
riparian vegetation to the following potential effects:
Effects to vegetation are expected to be limited to areas with grassy and herbaceous
plants; woody shrubs and trees within forested riparian areas are not expected to be
affected. More species are expected to be sensitive to atrazine at the seedling stage.
Not likely to adversely affect (NLAA)
for forested riparian areas: Woody
shrubs and trees are not expected to be
affected by atrazine.
Likely to adversely affect (LAA) for
riparian areas with herbaceous/grassy
vegetation: Atrazine-related impacts to
herbaceous (grassy and non-woody
plants) riparian areas may cause
alteration of streambank stability.
Not likely to adversely affect (NLAA)
for forested riparian areas: Woody
shrubs and trees are not expected to be
adversely affected by atrazine to such an
extent that measurable indirect effects to
the Topeka shiner may occur.
Likely to adversely affect (LAA) for
riparian areas with herbaceous/grassy
vegetation: Atrazine-related impacts to
herbaceous (grasses and non-woody
plants) riparian areas may cause
alteration of water quality (i.e., turbidity)
and increased siltation that could impact
spawning habitat.
Figure 5.2 Summary of the Potential of Atrazine to Affect the Topeka shiner via
Riparian Habitat Effects
5.3 Adverse Modification to Designated Critical Habitat
As previously discussed, designated critical habitat for the Topeka shiner is located in
Iowa, Minnesota, and Nebraska. The potential for atrazine to adversely affect critical
habitat is evaluated using adverse modification of principle constituent elements (PCEs)
as defined in Section 2.6. The designated critical habitat areas are considered to have the
PCEs that justify critical habitat designation. Activities that may destroy or adversely
modify critical habitat are those that alter the PCEs and jeopardize the continued
existence of the species. Evaluation of actions related to use of atrazine that may alter the
PCEs of the Topeka shiner's critical habitat form the basis of the critical habitat impact
analysis. The primary constituent elements for the Topeka shiner that may be affected by
biological processes, and, thus, may be affected by use of atrazine include the following:
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Streams and side-channel pools with water quality necessary for unimpaired
behavior, growth, and viability of all life stages. The water quality components can
vary seasonally and includetemperature (1 to 30[deg]Centigrade), total suspended
solids (0 to 2000 ppm), conductivity (100 to 800 mhos), dissolved oxygen (4 ppm or
greater), pH (7.0 to 9.0), and other chemical characteristics;
Living areas for juvenile Topeka shiners with water velocities less than 0.5
meters/second (approx. 20 inches/second) with depths less than 0.25 meters (approx.
10 inches) and moderate amounts of instream aquatic cover, such as woody debris,
overhanging terrestrial vegetation, and aquatic plants;
Sand, gravel, cobble, and silt substrates with amounts of fine sediment and substrate
embeddedness that allows for nest building and maintenance of nests and eggs by
native Lepomis sunfishes (green sunfish, orangespotted sunfish, longear sunfish) and
Topeka shiner as necessary for reproduction, unimpaired behavior, growth, and
viability of all life stages; and
An adequate terrestrial, semiaquatic, and aquatic invertebrate food base that allows
for unimpaired growth, reproduction, and survival of all life stages.
The potential for atrazine to adversely modify the aforementioned PCEs is summarized in
Table 5.9. The assessment is evaluated using RQs derived for direct and indirect effects
as described in Sections 5.1 and 5.2.
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Table 5.9. Summary of conclusions regarding the potential for atrazine to adversely
modify critical habitat PCEs
PCE
Conclusions
Basis for Conclusions
(see Section 5.3. for additional information)
Streams and side-channel pools with water
quality necessary for unimpaired behavior,
growth, and viability of all life stages. The
water quality components can vary
seasonally and include-temperature (1 to
30[deg]Centigrade), total suspended solids
(0 to 2000 ppm), conductivity (100 to 800
mhos), dissolved oxygen (4 ppm or
greater), pH (7.0 to 9.0), and other
chemical characteristics
LAA
As described in Sections 5.2.2.3 and 5.2.2.5, atrazine
was concluded to likely to adversely affect the
Topeka shiner by potentially aquatic and sensitive
riparian plants. These potential effects could result
in alteration of suspended solid levels, oxygen levels,
and other chemical characteristics.
Living areas for juvenile Topeka shiners
with water velocities less than 0.5
meters/second (approx. 20 inches/second)
with depths less than 0.25 meters (approx.
10 inches) and moderate amounts of
instream aquatic cover, such as woody
debris, overhanging terrestrial vegetation,
and aquatic plants
LAA
As described in Table 1.1, RQs were exceeded for
aquatic and terrestrial plants (Sections 5.2.2.2 and
5.2.2.4), which suggests that "amounts of instream
aquatic cover, such as woody debris, overhanging
terrestrial vegetation, and aquatic plants" could be
affected. Woody plant species are not expected to be
adversely affected by atrazine at EECs presented in
this assessment; however, other overhanging
vegetation and aquatic plants could potentially be
impacted in areas that are in close proximity to
atrazine use.
Sand, gravel, cobble, and silt substrates
with amounts of fine sediment and
substrate embeddedness that allows for
nest building and maintenance of nests and
eggs by native Lepomis sunfishes (green
sunfish, orangespotted sunfish, longear
sunfish) and Topeka shiner as necessary
for reproduction, unimpaired behavior,
growth, and viability of all life stages
LAA
Atrazine may affect riparian vegetation of the
Topeka shiner's habitats that are in close proximity
to atrazine use sites. However, sedimentation /
siltation in a stream may depend on numerous
factors, and determining whether atrazine use is
expected to result in an overall increase in
sediment/silt levels in a habitat is difficult.
Nonetheless, if riparian habitat is exposed to
atrazine, the plant biomass of the riparian habitat
could be adversely impacted primarily by reduction
in biomass of exposed seeds (MRID 42041403).
Until further analysis is performed on specific land
management practices in areas surrounding Topeka
shiner habitats, potential effects to riparian
vegetation as indicated by terrestrial plant RQ
exceedance, is presumed to potentially adversely
affect the Topeka shiner and its designated critical
habitat
An adequate terrestrial, semiaquatic, and
aquatic invertebrate food base that allows
for unimpaired growth, reproduction, and
survival of all life stages.
NLAA
Atrazine was found to not likely adversely affect the
Topeka shiner via reduction in aquatic and terrestrial
invertebrates as food supply.
5.4. Environmental Baseline and Cumulative Effects
Given the "LAA" finding, the Agency has completed a summary of the environmental
baseline and cumulative effects included in this assessment in Appendix I. The
environmental baseline is defined as the effects of past and ongoing human induced and
natural factors leading to the status of the species, its habitat, and ecosystem, within the
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action area. The baseline information provides a snapshot of the Topeka shiner's status
at this time. A summary of all USFWS biological opinions that are relevant to the
Topeka shiner that have been made available to EPA included in this assessment is also
provided as part of the baseline status. Cumulative effects include the effects of future
state, tribal, local, private, or other non-federal entity activities on endangered and
threatened species and their critical habitat that are reasonably expected to occur in the
action area.
6. Uncertainties
6.1. Exposure Assessment Uncertainties
6.1.1 Modeling Assumptions
Overall, the uncertainties addressed in this assessment cannot be quantitatively
characterized. Given the available data and use of conservative modeling assumptions, it
is expected that the baseline modeled EECs over-predict exposure for longer-term
durations, but are within a factor of two as compared with peak monitored
concentrations.
In general, the simplifying assumptions used in this assessment appear from the
characterization in Section 3 to be reasonable given the analysis completed and the
available monitoring data. There are also a number of assumptions that tend to result in
over-estimation of exposure. Although these assumptions cannot be quantified, they are
qualitatively described. For instance, modeling in this assessment for each atrazine use
assumes that all applications have occurred concurrently on the same day at the exact
same application rate. This is unlikely to occur in reality, but is a reasonable
conservative assumption in lieu of actual data.
6.1.2 Impact of Vegetative Setbacks on Runoff
Unlike spray drift, models 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 (USDA, NRCS, 2000). Alternatively, a setback of
poor vegetative quality or a setback that is channelized can be ineffective at reducing
loadings. Until such time as a quantitative method to estimate the effect of vegetative
setbacks on various conditions on pesticide loadings becomes available, the aquatic
exposure predictions are likely to overestimate exposure where healthy vegetative
setbacks exist and underestimate exposure where poorly developed, channelized, or bare
setbacks exist.
6.1.3. Best Management Practices for Atrazine
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A number of best management practices (BMPs) are recommended by State Agencies for
the purpose of reducing atrazine exposure to surface waters. These include (but are not
limited to) the following:
Soil incorporation
Crop rotation
Use of banded applications
Use of split applications
Use early pre-plant applications
Reduced application rates
Reduce soil-applied atrazine application rates, use postemergence atrazine
applications or post-emergent alternative.
Establish vegetative and riparian buffer strips.
Use conservation practices and structures.
If any or all of the aforementioned BMPs are in place over the predominant cropland
within the watershed, then atrazine concentrations in the associated Topeka shiner
habitats would be expected to be lower than EECs presented in this assessment.
However, such possible reductions cannot be quantified over the entire action area.
6.1.3 PRZM Modeling Inputs and Predicted Aquatic Concentrations
In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations
that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone
Model (PRZM) is a process or "simulation" model that calculates what happens to a
pesticide in a farmer's field on a day-to-day basis. It considers factors such as rainfall and
plant transpiration of water, as well as how and when the pesticide is applied. It has two
major components: hydrology and chemical transport. Water movement is simulated by
the use of generalized soil parameters, including field capacity, wilting point, and
saturation water content. The chemical transport component can simulate pesticide
application on the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase
concentrations in the soil are estimated by simultaneously considering the processes of
pesticide uptake by plants, surface runoff, erosion, decay, volatilization, foliar wash-off,
advection, dispersion, and retardation.
Uncertainties associated with each of these individual components add to the overall
uncertainty of the modeled concentrations. Additionally, model inputs from the
environmental fate degradation studies are chosen to represent the upper confidence
bound on the mean, values that are not expected to be exceeded in the environment 90
percent of the time. Mobility input values are chosen to be representative of conditions in
the environment. The natural variation in soils adds to the uncertainty of modeled values.
Factors such as application date, crop emergence date, and canopy cover can also affect
estimated concentrations, adding to the uncertainty of modeled values. Factors within the
ambient environment such as soil temperatures, sunlight intensity, antecedent soil
moisture, and surface water temperatures can cause actual aquatic concentrations to differ
for the modeled values.
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Additionally, the rate at which atrazine is applied and the percent of crops that are
actually treated with atrazine may be lower than the Agency's default assumption of the
maximum allowable application rate being used and the entire crop being treated. The
geometry of a watershed and limited meteorological data sets also add to the uncertainty
of estimated aquatic concentrations.
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 pesticidal active
ingredients, such as atrazine, 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 protective.
6.2.2 Impact of Multiple Stressors on the Effects Determination
The influence of length of exposure and concurrent environmental stressors to the Topeka
shiner (i.e., construction of dams and locks, fragmentation of habitat, change in flow
regimes, increased sedimentation, degradation of quantity and quality of water in the
watersheds of the action area, predators, etc.) will likely affect the species' response to
atrazine. Additional environmental stressors may increase sensitivity to the herbicide,
although there is the possibility of additive/synergistic reactions. Timing, peak
concentration, and duration of exposure are critical in terms of evaluating effects, and
these factors are expected to vary both temporally and spatially within the action area.
Overall, the effect of this variability may result in either an overestimation or
underestimation of risk. However, as previously discussed, the Agency's LOCs are set to
be protective given the wide range of possible uncertainties.
6.2.4 Use of Threshold Concentrations for Community-Level Endpoints
For the purposes of this ESA, threshold concentrations are used to predict potential
indirect effects to the Topeka shiner and adverse modification to designated critical
habitat (via aquatic plant community structural change). The conceptual aquatic
ecosystem model used to develop the threshold concentrations is intended to simulate the
ecological production dynamics in a 2nd or 3rd order Midwestern stream; however, the
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model has been correlated to the micro- and mesocosm studies, which were derived from
a wide range of experimental studies (i.e. Jar studies to large enclosures in lentic and
lotic systems), that represent the best available information for atrazine-related
community-level endpoints.
The threshold concentrations are intended to be predictive of potential atrazine-related
community-level effects in aquatic ecosystems, such as those that occur in known
locations for the Topeka shiner and its designated critical habitat, where the species
composition may differ from those included in the micro- and mesocosm studies.
Although it is not possible to determine how well the responses observed in the micro-
and mesocosm studies reflect the action area watersheds for the Topeka shiner, estimated
chronic atrazine exposure concentrations in less vulnerable watersheds of the action area
(from modeled EECs assuming flow) are predicted to be between 5 to 12 times lower
than the community-level threshold concentrations, depending on the modeled atrazine
use and averaging period. However, an evaluation of targeted monitoring data from
vulnerable watersheds suggests that chronic exposure concentrations of atrazine exceed
these threshold concentrations in a number of areas. Given that threshold concentrations
were derived based on the best available information from available community-level
data for atrazine, these values are intended to be protective of the aquatic community,
including the Topeka shiner and its designated critical habitat. Additional uncertainties
associated with use of the thresholds to estimate community-level effects are discussed in
Section B.8 of Appendix B from U.S. EPA (2006c,d,e).
6.2.5. Sublethal Effects
The assessment endpoints used in ecological risk assessment include potential effects on
survival, growth, and reproduction of the Topeka shiner and organisms on which this
species depend for survival and reproduction such as fish and invertebrates. A number of
studies were located that evaluated potential sublethal effects to fish from exposure to
atrazine. Although many of these studies reported toxicity values that were less sensitive
than the submitted studies, they were not considered for use in risk estimation. In
particular, fish studies were located in the open literature that reported effects on
endpoints other than survival, growth, or reproduction at concentrations that were
considerably lower than the most sensitive endpoint from submitted studies.
Upon evaluation of the available studies, however, the most sensitive NOAEC from the
submitted full life-cycle studies was considered to be the most appropriate chronic
endpoint for use in risk assessment. In the full life cycle study, fish are exposed to
atrazine from one stage of the life cycle to at least the same stage of the next generation
(e.g. egg to egg). Therefore, exposure occurs during the most sensitive life stages and
during the entire reproduction cycle. Four life cycle studies have been submitted in
support of atrazine registration. Species tested include brook trout, bluegill sunfish, and
fathead minnows. The most sensitive NOAEC from these studies was 65 |ig/L.
Reported sublethal effects including changes in hormone levels, behavioral effects,
kidney pathology, gill physiology, and potential olfaction effects have been observed at
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concentrations lower than 65 |ig/L (see Appendix A and Section 4.1.2.). In accordance
with the Overview Document (U.S. EPA, 2004) and the Services Evaluation
Memorandum (USFWS/NMFS, 2003), these studies were not considered appropriate for
risk estimation in place of the life cycle studies because quantitative relationships
between these effects and the ability of fish to survive, grow, and reproduce has not been
established. The magnitude of the reported sublethal effect associated with reduced
survival or reproduction has not been established; therefore it is not possible to
quantitatively link sublethal effects to the selected assessment endpoints for this ESA. In
addition, in the fish life cycle studies, no effects were observed to survival, reproduction,
and/or growth at levels associated with the sublethal effects. Also, there were limitations
to the studies that reported sublethal effects that preclude their quantitative use in risk
assessment (see Appendix A and Section 4.2.1). Nonetheless, if future studies establish a
quantitative link between the reported sublethal effects and fish survival, growth, or
reproduction, the conclusions may need to be revisited.
6.2.6. Exposure to Pesticide Mixtures
In accordance with the Overview Document and the Services Evaluation Memorandum
(U.S. EPA, 2004; USFWS/NMFS, 2004), this assessment considers the single active
ingredient of atrazine, as well as available information on registered products containing
multiple active ingredients in addition to atrazine. However, the assessed species and its
environments may be exposed to multiple pesticides simultaneously. Interactions of
other toxic agents with atrazine could result in additive effects, synergistic effects, or
antagonistic effects. The available data suggest that pesticide mixtures involving atrazine
may produce either synergistic or additive effects. Mixtures that have been studied
include atrazine with insecticides such as organophosphates and carbamates or with
herbicides including alachlor and metolachlor. A number of study authors claim additive
or synergistic effects in several taxa including fish, amphibians, invertebrates, and plants.
As previously discussed, evaluation of pesticide mixtures is beyond the scope of this
assessment because of the myriad of factors that cannot be quantified based on the
available data. Those factors include identification of other possible co-contaminants
where the Topeka shiner resides and their concentrations, differences in the pattern and
duration of exposure among contaminants, and the differential effects of other
physical/chemical characteristics of the receiving waters (e.g. organic matter present in
sediment and suspended water). Evaluation of factors that could influence
additivity/synergism/antagonism is beyond the nature and quality of the available data to
allow for an evaluation. However, it is acknowledged that not considering mixtures
could over- or under-estimate risks depending on the type of interaction and factors
discussed above.
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6.3 Assumptions Associated with the Acute LOCs
The risk characterization section of this endangered species assessment includes an
evaluation of the potential for individual effects. The individual effects probability
associated with the acute RQ is based on the mean estimate of the slope and an
assumption of a probit dose response relationship for the effects study corresponding to
the taxonomic group for which the LOCs are exceeded.
Sufficient dose-response information was not available to estimate the probability of an
individual effect on the midge (one of the dietary food items of the Topeka shiner).
Acute ecotoxicity data from the midge were used to derive RQs for freshwater
invertebrates. Based on a lack of dose-response information for the midge, the
probability of an individual effect was calculated using the only probit dose response
curve slope value reported in available freshwater invertebrate ecotoxicity data for
technical grade atrazine. Therefore, a probit slope value of 4.4 for the amphipod was
used to estimate the probability of an individual effect on the freshwater invertebrates. It
is unclear whether the probability of an individual effect for freshwater invertebrates
other than amphipods would be higher or lower, given a lack of dose-response
information for other freshwater invertebrate species. However, the assumed probit dose
response slope for freshwater invertebrates of 4.4 would have to decrease to
approximately 1 to 2 to cause an effect probability ranging between 1 in 10 and 1 in 100,
respectively, for freshwater invertebrates.
6.4. Uncertainty in the Potential Effect to Riparian Vegetation vs. Water Quality
Impacts
Effects to riparian vegetation were evaluated using submitted guideline seedling
emergence and vegetative vigor studies and non-guideline woody plant effects data.
LOCs were exceeded for seedling emergence and vegetative vigor endpoints with the
seedling emergence endpoint being considerably more sensitive. Based on LOC
exceedances and the lack of readily available information to allow for characterization of
riparian areas of the Topeka shiner, it was concluded that atrazine use is likely to
adversely affect the Topeka shiner via potential impacts on grassy/herbaceous riparian
vegetation resulting in increased sedimentation. However, soil retention/sediment
loading is dependent on a number of factors including land management and tillage
practices. Use of herbicides (including atrazine) may be incorporated into a soil
conservation plan. Therefore, although this assessment concludes that atrazine is likely
to adversely affect the assessed listed species and its designated critical habitat by
potentially impacting sensitive herbaceous riparian areas, it is possible that adverse
impacts on sediment loading may not occur in areas where soil retention strategies are
used.
7. Summary of Direct and Indirect Effects to the Topeka shiner and Adverse
Modification to Designated Critical Habitat
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In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the
information presented in this ESA represents the best data currently available to assess
the potential risks of atrazine to the Topeka shiner and its designated critical habitat. A
summary of the risk conclusions and effects determination for the Topeka shiner and
designated critical habitat, given the uncertainties discussed in Section 6, by assessment
endpoint, is presented in Tables 7.1 and 7.2.
Overall, this assessment suggests that atrazine has the potential to adversely affect the
Topeka shiner or adversely modify its critical habitat by direct chronic effects and from
potential impacts to aquatic plants and riparian habitat.
Table 7.1. Effects Determination Summary for the Topeka shiner (by Assessment
Endpoint)
Assessment Endpoint
Effects Determination
Basis for Conclusion
1. Survival, growth, and
reproduction of individuals
via direct acute or chronic
effects
Acute effects
No Effect - all uses
RQs across all uses did not exceed any LOC based on the
most sensitive available freshwater fish LC50.
See Section 5.2.1.1
Chronic effectsa
LAA
Corn (all regions);
fallow (west region)
No effect
All other uses
RQs were up to 1.3 to 1.6 for corn and fallow uses,
respectively, based on 60-day EECs estimated using
PRZM/EXAMS. The LOAEC in the most sensitive life-
cycle study was 120 ug/L based on a 7% reduction in
length and 16% reduction in weight in brook trout. 60-
Day EECs were lower than the fish life-cycle LOAEC;
therefore, at the 60-day EECs, the magnitude of potential
effect to the Topeka shiner would be expected to be lower
than effects observed at the LOAEC if the Topeka shiner
is equally sensitive to atrazine as brook trout.
See Section 5.2.1.2.
2. Indirect effects to
individuals via potential
effects to aquatic plants
(food, and primary
productivity)
LAA
Corn, sorghum, fallow,
and forestry uses
NLAA
All other uses
Community level effects thresholds are exceeded based
on PRZM/EXAMS 14- to 90-day EECs.
See Section 5.2.2.2.
NLAA conclusion was based on significance of effect as
defined in Section 5.
3. Indirect effects to
individuals via direct effects
to aquatic and terrestrial
invertebrates as food items
NLAA for all uses
NLAA conclusion was based on significance of effect as
defined in Section 5. The potential magnitude of effect to
aquatic and terrestrial invertebrate food items is expected
to be low such that measurable effects to the Topeka
shiner are not expected.
See Section 5.2.2.1.
4. Indirect effects to
individuals via direct effects
to other fish needed for
spawning habitat (e.g.,
sunfish) and diet.
NLAA for all uses
NLAA conclusion was based on significance of effect as
defined in Section 5. No acute LOCs were exceeded for
fish. The chronic LOC was exceeded for the most
sensitive species tested (brook trout); however, the
potential magnitude of effect to fish is expected to be low
such that measurable effects to the Topeka shiner are not
expected.
See Section 5.2.2.3.
4. Indirect effects to
individuals via reduction of
terrestrial vegetation (i.e.,
riparian habitat) required to
Direct effects to
sensitive riparian
vegetation: LAA
Riparian areas within the Great Plains are expected to be
predominantly grasslands. Data presented in Section 4 of
this assessment indicates that grassy and herbaceous
vegetation may be sensitive to atrazine. Therefore,
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Assessment Endpoint
Effects Determination
Basis for Conclusion
maintain acceptable water
quality and habitat
riparian areas that are predominantly grassy/herbaceous
vegetation and that receive runoff or spray drift from
atrazine use sites may be affected. Until further analysis
on specific land management practices and sensitivity of
riparian vegetation adjacent to Topeka shiner habitat is
performed, potential effects to riparian vegetation as
indicated by terrestrial plant LOC exceedance, is
presumed to potentially adversely affect the Topeka
shiner and its designated critical habitat.
See Section 5.2.2.4.
a Topeka shiner habitats include side pools of low-order streams with low/negligible flow rates. PRZM/EXAMS was
considered appropriate to represent both short-term and long-term potential exposures in these types of habitats.
However, there is uncertainty in this assumption as discussed in Section 3 of this assessment.
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Table 7.2 Effects Determination Summary
'or the Critical Habitat Impact Analysis
PCEa
Conclusions
Basis for Conclusions
(see Section 5.3. for additional information)
Streams and side-channel pools with water
quality necessary for unimpaired behavior,
growth, and viability of all life stages. The
water quality components can vary
seasonally and include-temperature (1 to
30[deg]Centigrade), total suspended solids
(0 to 2000 ppm), conductivity (100 to 800
mhos), dissolved oxygen (4 ppm or
greater), pH (7.0 to 9.0), and other
chemical characteristics
LAA
As described in Table 1.1, RQs were exceeded for
aquatic and terrestrial plants (Sections 5.2.2.2 and
5.2.2.4), which suggest that effects to aquatic and
sensitive riparian plants could occur and potentially
result in alteration of suspended solid levels, oxygen
levels, and other chemical characteristics.
Living areas for juvenile Topeka shiners
with water velocities less than 0.5
meters/second (approx. 20 inches/second)
with depths less than 0.25 meters (approx.
10 inches) and moderate amounts of
instream aquatic cover, such as woody
debris, overhanging terrestrial vegetation,
and aquatic plants
LAA
As described in Table 1.1, RQs were exceeded for
aquatic and terrestrial plants (Sections 5.2.2.2 and
5.2.2.4), which suggests that "amounts of instream
aquatic cover, such as woody debris, overhanging
terrestrial vegetation, and aquatic plants" could be
affected. Woody plant species are not expected to be
adversely affected by atrazine at EECs presented in
this assessment; however, other overhanging
vegetation and aquatic plants could potentially be
impacted in areas that are in close proximity to
atrazine use.
Sand, gravel, cobble, and silt substrates
with amounts of fine sediment and
substrate embeddedness that allows for
nest building and maintenance of nests and
eggs by native Lepomis sunfishes (green
sunfish, orangespotted sunfish, longear
sunfish) and Topeka shiner as necessary
for reproduction, unimpaired behavior,
growth, and viability of all life stages
LAA
Atrazine may affect riparian vegetation of the
Topeka shiner's habitats that are in close proximity
to atrazine use sites. However, sedimentation /
siltation in a stream may depend on numerous
factors, and determining whether atrazine use is
expected to result in an overall increase in
sediment/silt levels in a habitat is difficult.
Nonetheless, sensitive riparian areas exposed to
atrazine could be adversely impacted (MRID
42041403), which could indirectly affect the Topeka
shiner. Until further analysis is performed on
specific land management practices in areas
surrounding Topeka shiner habitats, terrestrial plant
LOC exceedance is presumed to indicate potential
adverse indirect effects the Topeka shiner and its
designated critical habitat.
An adequate terrestrial, semiaquatic, and
aquatic invertebrate food base that allows
for unimpaired growth, reproduction, and
survival of all life stages
NLAA
As indicated in Table 1.1, atrazine is not likely to
adversely affect the Topeka shiner via reduction in
aquatic and terrestrial invertebrates as food supply.
a Other PCEs (described in Section 2.4) were not evaluated because there was no perceived direct link
between those PCEs and processes that could be affected by atrazine use.
102
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