Risks of Atrazine Use to Federally Listed
Endangered Alabama Sturgeon
(Scaphirhynchus suttkusi)
Pesticide Effects Determination
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
August 31,2006
(March 14,2007 - amended during informal consultation with
U.S. Fish and Wildlife Service and National Marine Fisheries
Service)

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Table of Contents
1.	Executive Summary	7
2.	Problem Formulation	10
2.1	Purpose	10
2.2	Scope	11
2.3	Previous Assessments	12
2.4	Stressor Source and Distribution	15
2.4.1	Environmental Fate and Transport Assessment	15
2.4.2	Mechanism of Action	16
2.4.3	Use Characterization	16
2.5	Assessed Species	22
2.6	Action Area	24
2.7	Assessment Endpoints and Measures of Ecological Effect	28
2.8	Conceptual Model	29
2.8.1	Risk Hypotheses	29
2.8.2	Diagram	29
3.	Exposure Assessment	31
3.1	Label Application Rates and Intervals	31
3.2	Aquatic Exposure Assessment	33
3.2.1	Conceptual Model of Exposure	34
3.2.2	Existing Monitoring Data	34
3.2.3	Modeling Approach	37
3.2.3.1	Model Inputs	45
3.2.3.2	Results	47
3.2.4	Additional Modeling Exercises Used to Characterize Potential Exposures	53
3.2.4.1	Residential Uses (Impact of Overspray and Impervious Surfaces)	53
3.2.4.2	Impact of Flowing Water on Modeled EECs	56
3.2.4.3	Comparison of Modeled EECs with Available Monitoring Data	60
3.2.5	Modeling with Typical Usage Information	70
3.2.6	Summary of Modeling vs. Monitoring Data	72
3.3	Terrestrial Plant Exposure Assessment	72
4.	Effects Assessment	73
4.1 Evaluation of Aquatic Ecotoxicity Studies	75
4.1.1	Toxicity to Freshwater Fish	78
4.1.1.1	Freshwater Fish: Acute Exposure (Mortality) Studies	78
4.1.1.2	Freshwater Fish: Chronic Exposure (Growth/Reproduction) Studies	78
4.1.1.3	Freshwater Fish: Sublethal Effects and Additional Open Literature
Information	78
4.1.2	Toxicity to Freshwater Invertebrates	80
4.1.2.1	Freshwater Invertebrates: Acute Exposure Studies	80
4.1.2.2	Freshwater Invertebrates: Chronic Exposure Studies	81
4.1.2.3	Freshwater Invertebrates: Open Literature Data	81
4.1.3	Toxicity to Aquatic Plants	81
4.1.3.1 Aquatic Plants: Laboratory Data	81
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4.1.4	Freshwater Field Studies	82
4.1.5	Toxicity to Terrestrial Plants	83
4.2	Community-Level Endpoints: Threshold Concentrations	86
4.3	Use of Probit Slope Response Relationship to Provide Information on the Endangered
Species Levels of Concern	88
4.4	Incident Database Review	89
5.	Risk Characterization	90
5.1	Risk Estimation	91
5.1.1	Direct Effects	92
5.1.2	Indirect Effects	92
5.1.2.1	Evaluation of Potential Indirect Effects via Reduction in Food Items
(Freshwater Invertebrates)	93
5.1.2.2	Evaluation of Potential Indirect Effects via Reduction in Habitat and/or
Primary Productivity (Freshwater Aquatic Plants)	94
5.1.2.3	Evaluation of Potential Indirect Effects via Reduction in Terrestrial
Plant Community (Riparian Habitat)	96
5.2	Risk Description	98
5.2.1	Direct Effects to the Alabama Sturgeon	99
5.2.2	Indirect Effects via Reduction in Food Items (Freshwater Invertebrates)	100
5.2.3	Indirect Effects via Reduction in Habitat and/or Primary Productivity
(Freshwater Aquatic Plants)	102
5.2.3.1 Additional Characterization of EECs in Flowing Streams and Rivers	104
5.2.4	Indirect Effects via Alteration in Terrestrial Plant Community (Riparian
Habitat)	106
5.2.4.1	Importance of Riparian Habitat to the Alabama Sturgeon	107
5.2.4.2	Sensitivity of Forested Riparian Zones to Atrazine	109
5.2.4.3	Sediment Loading in the Lower Alabama River Watershed and the
Potential for Atrazine to Affect the Alabama Sturgeon via Effects on
Riparian Vegetation	113
6.	Uncertainties	118
6.1 Exposure Assessment Uncertainties	118
6.1.1	Modeling Assumptions	119
6.1.2	Impact of Vegetative Setbacks on Runoff	119
6.1.3	PRZM Modeling Inputs and Predicted Aquatic Concentrations	119
6.2	Effects Assessment Uncertainties	120
6.2.1	Age Class and Sensitivity of Effects Thresholds	120
6.2.2	Use of Acute Freshwater Invertebrate Toxicity Data for the Midge	120
6.2.3	Extrapolation of Long-term Environmental Effects from Short-Term
Laboratory Tests	121
6.2.4	Use of Threshold Concentrations for Community-Level Endpoints	121
6.2.5.	Sublethal Effects	122
6.2.6.	Exposure to Pesticide Mixtures	122
6.3	Assumptions Associated with the Acute LOCs	123
7.	Summary of Direct and Indirect Effects to the Alabama Sturgeon	124
8.	References	126
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Appendices
Appendix A Ecological Effects Data
Appendix B Supporting Information for the Aquatic Community-Level
Threshold Concentrations
Appendix C Status and Life History of the Alabama Sturgeon
Appendix D Stepwise Approach to Modeling Using the Residential Scenario as
an Example
Appendix E Incident Database Information
Appendix F RQ Method and LOCs
Appendix G Bibliography of ECOTOX Open Literature Not Evaluated and
Papers Not Accepted by ECOTOX
List of Tables
Table 1.1. Effects Determination Summary for the Alabama Sturgeon	9
Table 2.1. Summary of Assessment Endpoints and Measures of Ecological Effect	29
Table 3.1. Label Application Information for the Alabama Sturgeon Endangered Species
Assessment	33
Table 3.2. Summary of PRZM/EZAMS Environmental Fate Data Used for Aquatic
Exposure Inputs for Atrazine Endangered Species Assessment for the
Alabama Sturgeon	46
Table 3.3. Summary of PRZM/EXAMS Output EECs for all Modeled Scenarios (Using
the Standard Water Body)	47
Table 3.4. Revised PRZM/EXAMS EECs for all Modeled Scenarios Using the Action
Area-Specific PCA	52
Table 3.5. Comparison of Residential EECs (granular w/ 30% impervious surface)
Assuming Variable Percentages of Overspray (0, 1, and 10%) onto
Impervious Surfaces	55
Table 3.6. Comparison of Residential EECs (granular w/1% overspray) Assuming
Variable Percentages of Impervious Surface (5, 30, and 50%)	56
Table 3.7. Comparison of Residential (granular) EECs Assuming Various Percentages of
Treated Vi Acre Lot (10, 50, and 75%)	56
Table 3.8. Comparison of Alternative PRZM Modeling (assuming flow) with EECs
Generated Using the Static Water Body	59
Table 3.9. Annualized Time Weighted Mean (TWM) Concentration ((J,g/L) for the Top
Ten NAWQA Surface Water Sites (Ranked by Maximum Concentration
Detected)	62
Table 3.10. Maximum Concentration ((J,g/L) for the Top Ten NAWQA Surface Water
Sites (Ranked by Maximum Concentration Detected)	63
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Table 3.11. Annual Time Weighted Mean and Annual Maximum Concentration (|ig/L)
for the Top Six NAWQA Surface Water Sites in Alabama (Ranked by
Maximum Concentration Detected)	66
Table 3.12. Annual Time Weighted Mean and Annual Maximum Concentration (|ig/L)
for the Top Six NAWQA Surface Water Sites in Alabama (Ranked by
Maximum Concentration Detected)	67
Table 3.13. Annual Time Weighted Mean and Maximum Concentrations (|ig/L) for
Atrazine in Two Ohio Watersheds from the Heidelberg College Data	68
Table 3.14. Magnitude and Duration Estimates (|ig/L) from the 1997 Data from Sandusky
Watershed Using Stepwise Interpolation Between Samples	69
Table 3.15. Comparison of Maximum Labeled Use Information with Typical Rates and
Number of Applications	71
Table 3.16. Comparison of Non-PCA-Adjusted Corn EECs Using Maximum and Typical
Application Rates	71
Table 3.17. Screening-Level Exposure Estimates for Terrestrial Plants to Atrazine	73
Table 4.1 Comparison of Acute Freshwater Toxicity Values for Atrazine and Degradates	74
Table 4.2. Freshwater Aquatic and Terrestrial Plant Toxicity Profile for Atrazine	77
Table 4.3. Categories of Acute Toxicity for Aquatic Organisms	77
Table 4.4. Non-target Terrestrial Plant Seedling Emergence Toxicity (Tier II) to Atrazine	84
Table 4.5. Non-target Terrestrial Plant Vegetative Vigor Toxicity (Tier II) to Atrazine	85
Table 5.1. Summary of Direct Effect RQs for the Alabama Sturgeon	92
Table 5.2. Summary of Acute and Chronic RQs Used to Estimate Indirect Effect to the
Alabama Sturgeon via Direct Effects on Dietary Items	94
Table 5.3. Summary of RQs Used to Estimate Indirect Effects to the Alabama Sturgeon
via Direct Effects on Aquatic Plants	95
Table 5.4. Non-target Terrestrial Plant Seedling Emergence RQs	96
Table 5.5. Non-target Terrestrial Plant Vegetative Vigor Toxicity RQs	97
Table 5.6. Summary of RQs Used to Assess Potential Risk to Freshwater Invertebrate
Food Items of the Alabama Sturgeon Based on Forestry Use of Atrazine	101
Table 5.7. Summary of Modeled Scenario Time-Weighted EECs with Threshold
Concentrations for Potential Community-Level Effects	103
Table 5.8. Summary of Alternative Modeling (assuming flow) and Available Monitoring
Data	105
Table 5.9. Criteria for Assessing the Health of Riparian Areas to Support Aquatic
Habitats	108
Table 7.1. Effects Determination Summary for the Alabama Sturgeon	124
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List of Figures
Figure 2.1. National Extent of Atrazine Use (lbs)	17
Figure 2.2. Agricultural Cropland Relative to Alabama River	19
Figure 2.3. Atrazine Use in Alabama Relative to Action Area	20
Figure 2.4. Alabama Sturgeon Habitat Range (U.S. Fish and Wildlife Service Daphne,
Alabama Field Office, July 2006)	23
Figure 2.5. Alabama Sturgeon Action Area Defined by Alabama River Watershed	27
Figure 2.6. Conceptual Model for Alabama Sturgeon	30
Figure 3.1. Summary of All Available USGS NAWQA Data for Atrazine in the
Alabama River	35
Figure 3.2. Location of USGS NAWQA Site on Alabama River near Claiborne,
Alabama	36
Figure 3.3. Percentage of Impervious Surfaces in Southern and Central Alabama Near
the Alabama Sturgeon Action Area	41
Figure 3.4. Density of Road, Railways, and Pipelines as Surrogate for Rights-of-Way
Density in Alabama River Watershed (Action Area)	43
Figure 3.5 Percent Cropped Area (PCA) Analysis in the Alabama River Sturgeon
Action Area	50
Figure 4.1. Summary of Reported Acute LC5o/EC5o Values in Freshwater
Invertebrates for Atrazine	81
Figure 4.2. Use of Threshold Concentrations in Endangered Species Assessment	88
Figure 5.1. Land Use Within the Range of the Alabama Sturgeon	110
Figure 5.2. Forested Land Cover in the Lower Alabama River Watershed	111
Figure 5.3. Estimated Sources of Sediment Loading into the Lower Alabama River	115
Figure 5.4. Summary of the Potential of Atrazine to Affect the Alabama Sturgeon via
Riparian Habitat Effects	118
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1. Executive Summary
The purpose of this assessment is to make an "effects determination" for the Alabama
sturgeon (Scaphirhynchus suttkusi) by evaluating the potential direct and indirect effects
of the herbicide atrazine on the survival, growth, and reproduction of this Federally
endangered species. 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), the August 5, 2004
Joint Counterpart Endangered Species Act Section 7 Consultation Regulations specified
in 50 CFR Part 402 (USFWS/NMFS, 2004a; FR 69 47732-47762), and procedures
outlined in the Agency's Overview Document (U.S. EPA, 2004).
The current range of the Alabama Sturgeon is restricted to a 134-mile reach of the
Alabama River channel below the Millers Ferry Lock and Dam, downstream to the
mouth of the Tombigbee River. The best available data indicate that the Alabama
sturgeon has disappeared from 85 percent of its historic range. Its decline has been
associated with construction of dams, flow regulation, navigation channel development,
other forms of channel modification, and pollution (USFWS, 2000a). Although the range
of the Alabama sturgeon is limited to the area south of the Millers Ferry Lock and Dam,
the action area includes the entire Alabama River Basin watershed because drainage from
atrazine use sites above the dam flows to areas south of the dam. The action area
includes the entire Alabama River Basin watershed because modeled exposure
concentrations based on atrazine use exceed the Agency's screening-level LOCs for
aquatic plants.
Environmental fate and transport models were used to estimate high-end exposure values
as a result of agricultural and non-agricultural atrazine use in accordance with label
directions. Modeling was initially performed using the Agency's standard ecological
water body, which does not account for flow. The non-flowing nature of the standard
water body provides a reasonable estimation of peak exposures for many smaller
headwater streams found in agricultural areas; however, it appears to overestimate
exposures for longer time periods. Exposure concentrations based on the standard
ecological body are likely to overestimate exposure for the Alabama sturgeon because
this species requires strong currents in deep water habitats of the main channel of the
Lower Alabama River and its major tributaries. Therefore, additional modeling was used
together with available monitoring data to refine atrazine exposures in flowing waters. In
addition, the estimated agricultural exposure concentrations were refined to consider
available land cover data for agricultural crops within the action area. Estimated
residential and turf exposure concentrations were also refined, based on impervious
surface and land cover data specific to the action area in the Alabama River Basin
watershed. The highest overall modeled exposures were predicted to occur from
combined agricultural and non-agricultural uses of atrazine, and the highest individual
agricultural and non-agricultural modeled exposures were predicted to result from
atrazine use on corn and forestry, respectively. Although the available information
indicates that atrazine is rarely used on forestry in Alabama (personal communications
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with K. McNabb, Auburn University School of Forestry, and J. Michael, U.S. Forest
Service, Southern Research Station, August 2006), this use pattern was considered as part
of the risk description to account for potential changes in current herbicide use practices
on forestry, which may include atrazine in the future. The results of the refined analysis
indicate that peak atrazine concentrations are expected to be approximately 10 |ig/L,
while longer-term (weeks) exposures are expected to be in the low |ig/L range. Available
monitoring data from one sampling location in the defined action area of the Alabama
River watershed show that detected concentrations of atrazine are < 1 (J,g/L.
The assessment endpoints for the Alabama sturgeon include direct toxic effects on the
survival, reproduction, and growth of the sturgeon itself, as well as indirect effects, such
as reduction of the prey base and/or modification of its habitat. Direct effects to the
Alabama sturgeon are based on toxicity information for freshwater fish. Given that the
sturgeon's prey items and habitat requirements are dependant on the availability of
freshwater aquatic invertebrates, aquatic plants, and terrestrial plants (i.e., riparian
habitat), toxicity information for these taxonomic groups is also discussed. In addition to
the registrant-submitted and open literature toxicity information, indirect effects to the
Alabama sturgeon, via impacts to aquatic plant community structure and function, are
also evaluated based on time-weighted threshold concentrations that correspond to
potential aquatic plant community-level effects.
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 freshwater and estuarine/marine fish, aquatic invertebrates, and aquatic
plants. 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. Because degradates are not of greater
toxicological concern than atrazine, concentrations of the atrazine degradates are not
assessed further, and the focus of this assessment is parent atrazine.
Risk quotients (RQs) are derived as quantitative estimates of potential high-end risk.
Acute and chronic RQs are compared to the Agency's levels of concern (LOCs) to
identify instances where atrazine use within the action area has the potential to adversely
affect the Alabama sturgeon via direct toxicity or indirectly based on direct effects to
their food supply (i.e., freshwater invertebrates) or habitat (i.e., aquatic plants and
terrestrial riparian vegetation). When RQs for a particular type of effect are below LOCs,
the potential for adverse effects to the Alabama sturgeon is expected to be negligible,
leading to a conclusion of "no effect". Where RQs exceed LOCs, a potential to cause
adverse effects is identified, leading to a conclusion of "may affect". If a determination
is made that use of atrazine within the action area "may affect" the Alabama sturgeon,
additional information is considered to refine the potential for exposure and effects, and
the best available information is used to distinguish those actions that "may affect, but are
not likely to adversely affect" from those actions that are "likely to adversely affect" the
Alabama sturgeon.
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The best available data suggest that atrazine will either have no effect or is not likely to
adversely affect the Alabama sturgeon by direct toxic effects or by indirect effects
resulting from effects to aquatic plants, aquatic animals, and riparian vegetation. A
summary of the risk conclusions and effects determination for the Alabama sturgeon is
presented in Table 1.1. Further information on the results of the effects determination is
included as part of the Risk Description in Section 5.2.
Table 1.1. Effects Determination Summary for the Alabama Sturgeon
Assessment Endpoint
Effeets determination
Basis for Determination
Survival, growth, and
reproduction of Alabama
sturgeon individuals via
direct effects
No effect
No acute and chronic LOCs are exceeded.
Indirect effects to the
Alabama sturgeon via
reduction of prey (i.e.,
freshwater invertebrates)
May affect, but not
likely to adversely
affect
Acute LOCs are exceeded for the forestry use, based on the most
sensitive ecotoxicity value for the midge; however RQs for other
dietary items (stoneflies and snails) are less than LOCs. Based on the
non-selective nature of feeding behavior of the Alabama sturgeon and
low magnitude of anticipated individual effects to all evaluated prey
species, atrazine is not likely to indirectly affect the Alabama
sturgeon via a reduction in freshwater invertebrate food items. This
finding is based on insignificance of effects (i.e., effects to freshwater
invertebrates are not likely to be extensive over the suite of possible
food items to result in "take" of a single Alabama sturgeon).
Indirect effects to the
Alabama sturgeon via
reduction of habitat
and/or primary
productivity (i.e., aquatic
plants)
May affect, but not
likely to adversely
affect
Individual aquatic plant species within the Alabama River may be
affected. However, refined 14-, 30-, 60-, and 90-day EECs, which
consider the impact of flow, are well below the threshold
concentrations representing community-level effects. In addition, the
available monitoring data for the Alabama River show that all
detected concentrations are < 1 (ig/L. This finding is based on
insignificance of effects (i.e., community-level effects to aquatic
plants are not likely to result in "take" of a single Alabama sturgeon).
Indirect effects to the
Alabama sturgeon via
reduction of terrestrial
vegetation (i.e., riparian
habitat) required to
maintain acceptable
water quality and
spawning habitat
May affect, but not
likely to adversely
affect
Riparian vegetation may be affected because terrestrial plant RQs are
above LOCs. However, the majority of riparian area adjacent to the
current range of the Alabama sturgeon in the Lower Alabama River
watershed is forested vegetation, which is not associated with forestry
plantation operations. Woody plants are generally not sensitive to
environmentally-relevant concentrations of atrazine; therefore, effects
on shading, streambank stabilization, and structural diversity of
riparian areas in the action area are not expected. Although grassy
and herbaceous riparian habitat is expected to be sensitive to atrazine
effects, the presence of herbaceous riparian areas in the Lower
Alabama River watershed is minimal. Therefore, atrazine-related
impacts to riparian habitat are expected to have minimal impact on
overall sediment loads in the Lower Alabama River watershed, based
on surrounding land use and other sources of sedimentation including
forestry management practices and annual dredging of navigational
channels. This finding is based on insignificance of effects (i.e.,
atrazine effects to riparian vegetation in the Lower Alabama River
cannot be meaningfully measured, detected, or evaluated in the
context of a level of effect where "take" of a single Alabama sturgeon
would occur).
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2. Problem Formulation
Problem formulation provides a strategic framework for the risk assessment. By
identifying the important components of the problem, it focuses the assessment on the
most relevant life history stages, habitat components, chemical properties, exposure
routes, and endpoints. This assessment was completed in accordance with the August 5,
2004 Joint Counterpart Endangered Species Act (ESA) Section 7 Consultation
Regulations specified in 50 CFRPart 402 (USFWS/NMFS, 2004a; FR 69 47732-47762).
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 procedures outlined in the
Overview Document (U.S. EPA, 2004).
2.1 Purpose
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). The
purpose of this ecological risk assessment is to make an "effects determination," as
directed in Section 7(a)(2) of the ESA, for the Alabama sturgeon {Scaphirhynchus
suttkusi) by evaluating the potential direct and indirect effects resulting from use 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 this Federally endangered species. The Alabama
sturgeon was federally listed as an endangered species on May 5, 2000 by the U.S. Fish
and Wildlife Service (USFWS or the Service; 65 FR 26437-26461; USFWS, 2000a).
USFWS is the branch of the Department of Interior responsible for listing endangered
fish, such as the Alabama sturgeon. No critical habitat has been designated for this
species.
In this endangered species assessment, direct and indirect effects to the Alabama sturgeon
are evaluated in accordance with the screening-level methodology described in the
Agency's Overview Document (U.S. EPA, 2004). It should be noted, however, that the
indirect effects analysis in this assessment utilizes 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 the Agency to refine the
indirect effects associated with potential aquatic community-level effects (via aquatic
plant community structural change and subsequent habitat modification) to the Alabama
sturgeon. Use of such information is consistent with the guidance provided in the
Overview Document, which specifies that "the assessment process may, on a case-by-
case basis, incorporate additional methods, models, and lines of evidence that the Agency
finds technically appropriate for risk management objectives" (Section V, page 31 of
U.S. EPA, 2004).
As part of the "effects determination", the Agency will reach one of the following three
conclusions regarding the potential for atrazine to adversely affect the Alabama sturgeon:
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•	"No effect";
•	"May affect, but not likely to adversely affect"; or
•	"Likely to adversely affect".
If the results of the screening-level assessment show no indirect effects and levels of
concern (LOCs) for the Alabama sturgeon are not exceeded for direct effects, a "no
effect" determination is made based on atrazine's use within the action area. If,
however, indirect effects are anticipated and/or exposure exceeds the LOCs for direct
effects, the Agency concludes a preliminary "may affect" determination for the Alabama
sturgeon.
If a determination is made that use of atrazine within the action area "may affect" the
Alabama sturgeon, additional information is considered to refine the potential for
exposure at the predicted levels and for effects to the Alabama sturgeon and other
taxonomic groups upon which this species depends (i.e., freshwater invertebrates, aquatic
plants, riparian vegetation). Based on the refined information, the Agency uses the best
available information to distinguish those actions that "may affect, but are not likely to
adversely affect" from those actions that are "likely to adversely affect" the Alabama
sturgeon. This information is presented as part of the Risk Characterization in Section 5.
2.2 Scope
Atrazine is currently registered as a 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. It is one of the most widely used
herbicides in North America (U.S. EPA, 2003a).
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
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 the action
area associated with the Alabama sturgeon. Further discussion of the action area for the
Alabama sturgeon is provided in Section 2.6.
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 freshwater fish, aquatic invertebrates, and aquatic plants. Specifically, the
available degradate toxicity data for HA indicates 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
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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. A detailed summary of the
available ecotoxicity information for all of the atrazine degradates is presented in
Appendix A.
The results of available toxicity data for mixtures of atrazine with other pesticides are
presented in Section A.6 of Appendix A. According to the available data, other
pesticides may combine with atrazine to produce synergistic, additive, and/or antagonistic
toxic effects. Synergistic effects with atrazine have been demonstrated for a number of
organophosphate insecticides including diazanon, 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 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 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
Alabama sturgeon is addressed as part of the uncertainty analysis for this effects
determination.
2.3 Previous Assessments
The Agency completed a refined ecological risk assessment for 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. In the refined
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assessment, risk is described in terms of the likelihood that concentrations in water bodies
(i.e., lakes/reservoirs, streams, and estuarine areas) equaled or exceeded concentrations
shown to cause adverse effects to aquatic communities and populations of aquatic
organisms. The results of the refined aquatic ecological assessment indicated that
exposure to atrazine is likely to result in adverse community-level and population-level
effects to aquatic communities at concentrations greater than or equal to 10-20 |ig/L on a
recurrent basis or over a prolonged period of time.
During this time, the Agency extensively reviewed a probabilistic ecological risk
assessment submitted by the registrant (Giddings et al., 2000). The Agency's review of
Syngenta's probabilistic risk assessment is included in Appendix XVII of the 2003
atrazine IRED. EPA's refined risk assessment incorporates some of the data submitted
by the registrant in its probabilistic risk assessment.
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)1. Because the
Agency had determined that atrazine shares a common mechanism of toxicity with the
structurally-related chlorinated triazines, simazine and propazine, a cumulative human
health risk assessment for the triazines was necessary before the Agency could make a
final determination of reregi strati on eligibility. However, the Agency issued the interim
decision in order to identify risk reduction measures that were necessary to support the
continued use of atrazine. The January 2003 IRED requires extensive drinking water
monitoring in Community Water Systems (CWSs) where atrazine levels have exceeded
or are predicted to have the potential to exceed drinking water levels of concern. In
addition, the need for the following information related to potential ecological risks was
established: 1) an ecological monitoring program of potentially vulnerable waterbodies in
corn, sorghum, and sugarcane use areas; and 2) further information on potential
amphibian gonadal developmental responses to atrazine.
EPA issued an addendum on October 31, 2003 that updated the IRED issued on January
31, 2003 (U.S. EPA, 2003b). This addendum describes new scientific developments
pertaining to ecological monitoring and mitigation of watersheds and potential effects of
atrazine on endocrine-mediated pathways of amphibian gonadal development.
The January 2003 IRED required atrazine registrants to develop a watershed monitoring
protocol. The resulting protocol identifies 40 indicator watersheds in corn and sorghum
growing areas in which monitoring has been required for a two-year period within each
watershed. The first 20 watersheds were monitored in 2004 and 2005. The second set of
20 watersheds was monitored in 2005, and the second year of sampling for these
watersheds is currently in progress. The goal of the monitoring is to ascertain the extent
to which any of the watersheds have streams with atrazine concentrations that could
cause significant changes in aquatic plant community structure, the most sensitive
endpoint in the aquatic ecosystem. Streams in watersheds exceeding the Agency's levels
of concern will be subject to mitigation consistent with watershed management principles
1 The 2003 Interim Reregistration Eligibility Decision for atrazine is available at the following Web site:
http://www.epa.gov/oppsrrdl/REDs/0001 .pdf.
13

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described by the Agency's Office of Water program requirements
(http://www.epa.gov/owow/tmdl/). These monitoring sites are representative of 1,172
watersheds determined to be among the most vulnerable to atrazine surface water loading
from use on corn and sorghum. Therefore, the results from the 40 watersheds will be
used to determine if further monitoring or remedial efforts are needed in the larger
population of watersheds. EPA has selected an atrazine level of concern (LOC) that is
based on significant aquatic community effects consistent with those described in the
Office of Pesticide Programs (OPP) 2003 ecological risk assessment (U.S. EPA, 2003a
and b) and the Office of Water's (OW) draft atrazine aquatic life criteria (U.S. EPA,
2003c). Further discussion of the aquatic community-level LOC is provided in Section
4.2 and Appendix B of this assessment. Aqueous atrazine concentrations obtained from
monitoring studies can be interpreted with the LOC to determine if a water body is likely
to be significantly affected.
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 20032. 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 and studies are on-going;
however, as of this writing, results are not available.
2 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.
14

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2.4 Stressor Source and Distribution
2.4.1 Environmental Fate and Transport Assessment
The following fate and transport description for atrazine was summarized based on
information contained in the 2003 IRED (U.S. EPA, 2003a). 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. 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
contaminate 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 far more prevalent.
The resistance of atrazine to abiotic hydrolysis (stable at pH 5, 7, and 9) and to direct
aqueous photolysis (stable under sunlight at pH 7), and its only moderate susceptibility to
degradation in soil (aerobic laboratory half-lives of 3-4 months) indicates that atrazine is
unlikely to undergo rapid degradation on foliage. Likewise, a relatively low Henry's
Law constant (2.6 X 10"9 atm-m3/mol) indicates that atrazine is not likely to undergo
rapid volatilization from foliage. However, its relatively low octanol/water partition
coefficient (Log Kow = 2 .7), and its relatively low soil/water partitioning (Freundlich Kads
values < 3 and often < 1) may somewhat offset the low Henry's Law constant value,
thereby possibly resulting in some volatilization from foliage. In addition, its relatively
low adsorption characteristics indicate that atrazine may undergo substantial washoff
from foliage. It should also be noted that foliar dissipation rates for numerous pesticides
have generally been somewhat greater than otherwise indicated by their physical
chemical and other fate properties.
In terrestrial field dissipation studies performed in Georgia, California, and Minnesota,
atrazine dissipated with half lives of 13, 58, and 261 days, respectively. The
inconsistency in these reported half-lives could be attributed to the temperature variation
between the studies in which atrazine was seen to be more persistent in colder climate.
Long-term field dissipation studies also indicated that atrazine could persist over a year in
such climatic conditions. A forestry field dissipation study in Oregon (aerial application
of 4 lb ai/A) estimated an 87-day half-life for atrazine on exposed soil, a 13-day half-life
in foliage, and a 66-day half-life on leaf litter.
Atrazine is applied directly to soil during pre-planting and/or pre-emergence applications.
Atrazine is transported indirectly to soil due to incomplete interception during foliar
application, and due to washoff subsequent to foliar application. The available laboratory
and field data are reported above. For aquatic environments, reported half-lives were
much longer. In an anaerobic aquatic study, atrazine overall (total system), water, and
sediment half-lives were given as 608, 578, and 330 days, respectively.
15

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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.
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 of these
degradates were detected at percentages greater than 10% in soil and aqueous photolysis
studies. Insufficient data are available to estimate half-lives for these degradates from the
available data. The dealkylated degradates are more mobile than parent atrazine, while
HA is less mobile than atrazine and the dealkylated degradates.
2.4.2	Mechanism of Action
Atrazine inhibits photosynthesis by stopping electron flow in Photosystem II. Triazine
herbicides associate with a protein complex of the Photosystem II in chloroplast
photosynthetic membranes (Schulz et al., 1990). The result is an inhibition in the transfer
of electrons that in turn inhibits the formation and release of oxygen.
2.4.3	Use Characterization
Atrazine has the second largest poundage of any herbicide in the U.S. and 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. Figure 2.1 presents the national distribution of use of atrazine (Kaul et al.,
2005).
16

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National Distribution of Atrazine Use (lbs)
1J000
Miles
Legend
Lbs Atrazine
I 10 - 27729
f 127730 - 82603
H 82604- 165432
H 165433 -441435
¦¦ 441436 - 1090674
Figure 2,1, National Extent of Atrazine Use (lbs)
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
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.
Critical to the development of appropriate modeling scenarios and to the evaluation of the
appropriate model inputs is an assessment of usage information (Kaul et al., 2005; Kaul
and Jarboe, 2006; Zinn and Jones, 2006). Information on the agricultural uses of atrazine
in the state of Alabama immediately surrounding the Alabama River and within the
Alabama River Watershed as defined in this assessment was gathered (Kaul et al., 2005).
In addition, reported atrazine crop use information, application rates (for use in
characterization), and methods of application, application timing, and intervals between
17

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applications were considered (Kaul and Jarboe, 2006; Zinn and Jones, 2006). Usage
information within the Alabama River watershed is utilized to determine which uses
should be modeled, while the application methods, intervals, and timing are critical
model inputs. While the modeling described in Section 3.2 relies initially on maximum
label application rates and numbers of applications, information on typical ranges of
application rates and number of applications is also presented to characterize the
modeling results. No information is available on non-agricultural uses (residential,
rights-of-way, forestry, or turf) of atrazine.
General information on the main agricultural uses of atrazine in Alabama was gathered.
Agricultural cropland and atrazine use relative to the Alabama River Basin watershed are
depicted in Figures 2.2 and 2.3, respectively.
18

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Agricultural Cropland Relative to
Alabama River Drainage
:S F|
CK.
Legend

Cropland
£Jab ama_F? rirer_D rain age_0 utline
J Yiypi y
Miles
100
Figure 2.2. Agricultural Cropland Relative to Alabama River
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Atrazine Use in Alabama Relative
to Alabama River Drainage
Legend
¦ Dams
AJab ama_R rwer	D rain age_0 utline
counties_albers
TTL_AIAMT
5001 -100CO
10001 - 500000
Figure 2.3. Atrazine Use in Alabama Relative to Action Area
20

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Locally, usage information was obtained for agricultural uses of atrazine in the state of
Alabama. Only use sites known to be present within the action area are included in this
assessment. Agricultural uses that are included in this assessment include corn, sorghum
and fallow/idle land in the Conservation Reserve Program (CRP); non-agricultural uses
include turf, residential, rights-of-way, and forestry. These uses are discussed in more
detail in Section 3.2.
Specifically, county level data for the areas immediately surrounding the Alabama River
in southern and central Alabama were used (Kaul et al., 2005). These counties
encompass the majority of the action area (defined below) for atrazine relative to the
Alabama sturgeon. 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).
In general, this information suggests that approximately 300,000 lbs of atrazine was used
statewide on corn and sorghum. It should be noted, however, that information on non-
agricultural use of atrazine is not available.
Application rates, the number of applications, and application intervals were also
estimated at the state level for Alabama (Kaul, et al, 2005, Zinn and Jones, 2006). The
information was developed from a combination of USDA and Doane data, and is
discussed in further detail as part of the exposure assessment in Section 3.1. Application
rates of atrazine are provided at the national level for crops grown in the immediate
vicinity of the Alabama River including corn, pasture (as a surrogate for fallow/idle
land), and sorghum. Based on data developed for the triazine cumulative risk assessment
(U.S. EPA, 2006a; Kaul, et al., 2005), the typical atrazine application rates for corn,
sorghum and fallow/idle land in Alabama are 1.1 lbs/acre. Although the 90th percentile
of reported application rates is typically used as an upper bound on actual use, data on the
90th percentile is currently unavailable.
In order to refine the exposure assessment, the minimum and typical application intervals
are needed when more than one application is made per year on a site. Therefore,
registered herbicide/site combinations within Alabama were determined, and sites with
the average number of applications greater than one were selected. If the average number
of applications equals one, it is assumed that only one application is made, and, therefore,
the typical interval is not needed. Only sites with greater than one pesticide application
are discussed below. Because typical application interval usage data is not available,
crop experts were contacted, label information was reviewed, and other sources, such as
previous assessments, were consulted to estimate or otherwise characterize the
application intervals.
For corn, most growers apply atrazine only once per season. However, approximately 12
percent of growers apply atrazine more than once, following a pre-emergence application
with a post-emergence application (Assessment of Potential Mitigation Measures for
21

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Atrazine, 2003). According to atrazine label information for corn, the minimum
application interval is either 14 days or not specified on the label.
For sorghum, atrazine may be applied at various timings. "Atrazine is effective at many
application timings including: winter weed control, and pre-plant for control of weeds
prior to planting through post-plant as long as weeds are no more than one and one-half
inches and sorghum is six to 12 inches tall" (Assessment of Potential Mitigation
Measures for Atrazine, 2003). According to atrazine label information for sorghum, the
minimum application interval is either 21 days or not specified on the label.
For fallow/idle land use, according the Aatrex® 4L label and some other atrazine labels,
only one application of atrazine may be made in fallow period (CDMS search). In
addition, the IRED states that only one application per year may be made for chemical
fallow applications (U.S. EPA, 2003a).
Typical application rates and number of intervals should be evaluated with caution
because these values represent an average, which implies that a significant percentage of
the time atrazine is actually being applied at rates higher than those reported as typical.
2.5 Assessed Species
A brief introduction to the Alabama sturgeon, including a summary of habitat, diet, and
reproduction data relevant to this endangered species risk assessment is provided below.
Further information on the status and life history of the Alabama sturgeon is provided in
Appendix C.
The Alabama sturgeon (Scaphirynchus suttkusi) is a freshwater fish (Figure C. 1 of
Appendix C) found in the main stems of the Lower Alabama River from Millers Ferry
Lock and Dam, downstream to the mouth of the Tombigbee River (Figure 2.4). The best
available data indicate that the Alabama sturgeon has disappeared from 85 percent of its
historic range. Its decline has been associated with construction of dams, flow regulation,
navigation channel development, other forms of channel modification, and pollution
(USFWS, 2000a). Dams in the Alabama River have reduced the amount of riverine
habitat, impeded migration of Alabama sturgeon for feeding and spawning needs, and
changed the river's flow patterns. The Alabama sturgeon's historic range once included
about 1,000 miles of the Mobile River system in Alabama. However, recent collection
efforts indicate that very low numbers of Alabama sturgeon continue to survive in
portions of the 134-mile reach of the Alabama River channel below the Millers Ferry
Lock and Dam, downstream to the mouth of the Tombigbee River. The decline of
collection records and anecdotal accounts of captures over the past century coincide with
construction of dams and the cumulative loss and fragmentation of riverine habitat in the
Mobile River Basin over time. These habitat changes, coupled with what is known about
life history requirements and life span of other species of river sturgeon, suggest that the
Alabama sturgeon is close to extinction (personal communication with Jeff Powell of the
USFWS, 2006).
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Very little is known about the life history, habitat, or other ecological requirements of the
Alabama sturgeon. Observations by Burke and Ramsey (1985) indicate that the species
)refers relatively stable gravel and sand substrates in flowing river channels. Verified
TN
Lock t
Smith Dam
Aberdeen I & D
A^TLoyan Martin Danr
Harris Dam
Heflin L &
Mitchell Dam
Martin Dam
Yates Dam
Thurlow Dam
MS
R. L Henry L & D
Dams
Mobile
Mobile River Basin
Figure 2.4. Alabama Sturgeon Habitat Range (U.S. Fish and Wildlife Service
Daphne, Alabama Field Office, July 2006)
23

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captures of Alabama sturgeon have primarily occurred in large channels of big rivers
(Williams and Clemmer, 1991). Examination of Alabama sturgeon stomach contents
show that they are opportunistic bottom feeders, preying primarily on aquatic insect
larvae (Mayden and Kuhajda, 1996). Alabama sturgeon are likely to migrate upstream
during late winter and spring to spawn. Downstream migrations may occur to search for
feeding areas and/or deeper, cooler waters during the summer. Although specific
locations have not been identified, eggs are likely deposited on hard bottom substrates,
such as bedrock, armored gravel, or channel training works (water diversion structures
used to direct currents to main channels) in deep water habitats, and possibly tributaries
to major rivers (USFWS, 2000a). The eggs are adhesive and require current for proper
development. Sturgeon larvae are planktonic, drifting with river currents. Post-larval
stages eventually settle on the river bottom. Information from other riverine sturgeon
species suggests that the Alabama sturgeon may require some minimum distance of
flowing river conditions for development of larval to juvenile stage, and for sustainable
recruitment of the species (Powell, personal communication, 2006). Sexual maturity is
believed to occur at 5 to 7 years of age. Spawning frequency of both sexes is influenced
by food supply and fish condition, and may occur every 1 to 3 years. Although the life
span of the Alabama sturgeon is unknown, they may live up to 15 or more years of age
(USFWS, 2000a)
2.6 Action Area
For listed species assessment purposes, the action area is considered to be the area
affected directly or indirectly by the federal action and not merely the immediate area
involved in the action (50 CFR 402.02). It is recognized that the overall action area for
the national registration of 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 modeling results (discussed further in Section 3.2.3) and the toxicity data
for the most sensitive non-vascular aquatic plant, the Agency's LOCs are likely to be
exceeded 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 Alabama sturgeon as they occur within the watershed
of the Alabama River. 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
the Alabama River.
Modeled concentrations of atrazine for labeled uses expected to occur within the
Alabama River watershed exceed Agency established ecological risk levels of concern
for aquatic plants, suggesting that adverse effects on components of the environment is
possible. The results of the screening level assessment suggest that effects on
components of the environment are possible anywhere within the Alabama River.
Although the available monitoring data for the Alabama River watershed show that
24

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detected concentrations are less than the Agency's screening levels of concern, the
dataset is limited to one sampling location, and is, therefore, not considered to be
representative of the entire watershed. Therefore, the action area for the Alabama
sturgeon is defined as the entire Alabama River watershed and its tributaries. Further
information on the definition of the action area for the Alabama sturgeon follows.
The Alabama Sturgeon is known to exist in the Alabama River from the mouth of the
confluence with the Tombigbee River near Mobile, Alabama north to Millers Ferry Lock
and Dam in Southwestern Alabama in Wilcox County (Figure 2.4). The Alabama River
is located principally in southern and central Alabama and drains a watershed roughly
6,000 square miles reaching as far north as northwestern Georgia. Historically, this
species ranged much farther north into central Alabama and as far west as Mississippi.
Currently, only a few specimens have been found since the mid 1990s in the free flowing
portion of the Alabama River in Clarke, Monroe, and Wilcox counties with a single
exception north of Claiborne Lock and Dam (USFWS, 2000a). Therefore, the initial
definition of the action area for this species is defined by the watershed draining to the
stretches of the Alabama River south of Millers Lock and Dam. Although the Millers
Lock and Dam may limit the range of the sturgeon northward into central Alabama, the
dam does not prevent the flow of water. Therefore, the potential action area includes the
entire Alabama River watershed.
In addition, an evaluation of usage information was conducted to determine whether any
or all of the area defined by the Alabama River watershed should be included in the
action area. As part of this 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 limited agricultural uses are present within the
defined area and that non-agricultural uses cannot be precluded from being assessed.
Finally, local land cover data and interviews with local agricultural and land use
specialists were considered to refine the characterization of potential atrazine use in the
areas defined by the Alabama River watershed. The overall conclusion of this analysis
was that while certain agricultural uses could likely be excluded and some non-
agricultural uses of atrazine were unlikely, no areas 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 impact on the Alabama sturgeon. 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 sturgeon. Given the physico-
chemical profile for atrazine and the fact that atrazine has been detected in both air and
rainfall samples, the potential for long range transport from outside the area defined by
the Alabama River watershed cannot be precluded, but is not expected to approach
concentrations predicted by modeling (see Section 3.2).
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Atrazine has been documented to be transported away from the site of application by both
spray drift and volatilization. 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 Alabama sturgeon is
defined by the entire watershed draining to the Alabama River both above and below the
Millers Lock and Dam extending as far as northwestern Georgia. Figure 2.5 presents the
action area graphically.
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AJab ama_R iver	D rain age_D utline
Alabama River Drainage
Dams
Figure 2.5. Alabama Sturgeon Action Area Defined by Alabama River
Watershed
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2.7 Assessment Endpoints and Measures of Ecological Effect
Assessment endpoints are defined as "explicit expressions of the actual environmental
value that is to be protected."3 Selection of the assessment endpoints is based on valued
entities (i.e., Alabama sturgeon), the ecosystems potentially at risk (i.e., Alabama River),
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 for the Alabama sturgeon include direct toxic effects on the
survival, reproduction, and growth of the sturgeon, as well as indirect effects, such as
reduction of the prey base and/or modification of its habitat. Each assessment endpoint
requires one or more "measures of ecological effect," which 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 acute and chronic toxicity information from registrant-submitted guideline tests
that are performed on a limited number of organisms. Specific measures of ecological
effect are evaluated based on acute and chronic toxicity information from registrant-
submitted guideline tests that are performed on a limited number of organisms.
Additional ecological effects data from the open literature, 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 mescocosm 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 the CASM model 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 Alabama sturgeon risks associated with exposure to atrazine is provided in
Table 2.1.
3 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
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Table 2.1. Summary of Assessment End
joints and Measures of Ecological Effect
Assessment Endpoint
Measures of Ecological Effect
1. Survival, growth, and reproduction of Alabama
sturgeon individuals via direct effects
la. Rainbow trout acute LC50
lb. Brook trout chronic NOAEC
2. Survival, growth, and reproduction of Alabama
sturgeon individuals via indirect effects on prey
(i.e., freshwater invertebrates)
2a. Midge acute EC50
2b. Scud chronic NOAEC
2c. Acute EC/LC50 data for freshwater invertebrates
that are potential food items for the Alabama
sturgeon
3. Survival, growth, and reproduction of Alabama
sturgeon individuals 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
ECS0
3c. Microcosm/mesocosm threshold concentrations
showing aquatic primary productivity community-
level effects
4. Survival, growth, and reproduction of Alabama
sturgeon individuals via indirect effects on
terrestrial vegetation (riparian habitat) required to
maintain acceptable water quality and spawning
habitat
4a. Monocot and dicot seedling emergence EC25
4b. Monocot and dicot vegetative vigor EC25
2.8 Conceptual Model
2.8.1 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 assessment:
•	Atrazine in surface water and/or runoff/drift from treated areas may directly affect
the Alabama sturgeon by causing mortality or adversely affecting growth or fecundity;
•	Atrazine in surface water and/or runoff/drift from treated areas may indirectly
affect the Alabama sturgeon by reducing or changing the composition of prey
populations;
•	Atrazine in surface water and/or runoff/drift from treated areas may indirectly
affect the Alabama sturgeon by reducing or changing the composition of the aquatic plant
community in the Alabama River, thus affecting primary productivity and/or cover; and
•	Atrazine in surface water and/or runoff/drift from treated areas may indirectly
affect the Alabama sturgeon by reducing or changing the composition of the terrestrial
plant community (i.e., riparian habitat) required to maintain acceptable water quality and
spawning habitat in the Alabama River.
2.8.2 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,
29

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biological receptor types, and effects endpoints of potential concern. The conceptual
model for the atrazine endangered species assessment for the Alabama sturgeon is shown
in Figure 2.6. Exposure routes shown in dashed lines are not quantitatively considered
because the resulting exposures are expected to be so low as not to cause adverse effects
to the Alabama sturgeon.
Stressor
Source
Receptors
] Vapor phase and
• long range
"l transport
Groundwater
Runoff
Spray drift
Riparian Zone
Terrestrial plants
Alabama River
Aquatic plants
Aquatic invertebrates
Aquatic vertebrates
Atrazine applied to agricultural
fields, residential lawns, golf
courses, rights-of-way, and forestry
Attribute
Change
Food chain
Decrease in abundance
Shift in prey base
Habitat integrity
Decreased water quality
Reduced cover
Stream destabilization
Individual sturgeon
Reduced survival
Reduced growth
Reduced reproduction
Figure 2.6. Conceptual Model for Alabama Sturgeon
The conceptual model provides an overview of the expected exposure routes for Alabama
sturgeon within the atrazine action area previously described in Section 2.6. In addition
to freshwater aquatic vertebrates including Alabama sturgeon, other aquatic receptors that
may be potentially exposed to atrazine include freshwater invertebrates and aquatic
plants. For freshwater vertebrate and invertebrate species, 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 Alabama sturgeon via reduction in food and habitat availability. The
available data indicate that atrazine is not likely to bioconcentrate in aquatic food items,
with fish bioconcentration factors (BCFs) ranging from 2 to 8.5 (U.S. EPA, 2003c).
Therefore, bioconcentration of atrazine in sturgeon via the diet was not considered as a
significant route of exposure.
In addition to aquatic receptors, terrestrial plants may also be exposed to spray drift and
runoff from atrazine use in the vicinity of the Alabama River. A significant change in the
30

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riparian vegetation adjacent to spawning areas of the sturgeon in the Alabama River may
adversely affect sturgeon egg development and reduce the amount of suitable spawning
habitat via increased sedimentation.
Individual fish with the greatest potential to experience direct adverse effects from
atrazine use are those that occur in surface water with the highest concentrations of
atrazine. Individual fish with the greatest potential to experience indirect effects are
those fish that rely on the sections of the Alabama River that are most vulnerable to
atrazine contamination (i.e., those near or adjacent to application areas) for food, shelter,
and/or spawning habitat.
The source and mechanism of release of atrazine into surface water are ground and aerial
application via foliar spray and coated fertilizer granules to agricultural (i.e., corn,
sorghum, and fallow/idle land) and non-agricultural crops (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 Alabama
River. Spray drift and runoff of atrazine may also affect the foliage and seedlings of
terrestrial plants that comprise the riparian habitat surrounding the Alabama River.
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. In addition, modeling tools are not available to predict the potential impact
of long range atmospheric transport of atrazine.
3. Exposure Assessment
3.1 Label Application Rates and Intervals
Atrazine labels may be categorized into two types: labels for manufacturing uses
(including technical grade atrazine and its formulated products) and end-use products.
While technical products, which contain atrazine of high purity, are not used directly
in the environment, they are used to make formulated products, which can be applied
in specific areas to control weeds. The formulated product labels legally limit
atrazine's potential use to only those sites that are specified on the labels.
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, the Agency entered into a Memorandum of Agreement
(MO A) with the 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 including
cancellation of certain uses, reduction in application rates, and requirements for
harmonization across labels including setbacks from waterways. Specifically, the label
31

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changes restrict atrazine use within 50 feet of sinkholes, 66 feet of intermittent and
perennial streams, and 200 feet of lakes and reservoirs. It is expected that a setback
distance will 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 Alabama sturgeon is discussed further in Section 3.2.3.1. 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 for the
Alabama sturgeon 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 equipment for the agricultural uses includes ground
application (the most common application method), aerial application, band
treatment, incorporated treatment, 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 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.
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.
32

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Table 3.1. Label Application Information for the Alabama Sturgeon Endangered
Species Assessment1
Scenario
Maximum
Application
Rate
(lbs/acre)
Maximum
Number of
Applications
Date of Fi rst
Application
Formulation
Method of
Application
Interval
Between
Applications
Forestry
4.0
1
June 1
Liquid
Aerial and
Ground
NA
Residential
2.0
2
April 1
Granular
Ground
30 days
Residential
1.0
2
April 1
Liquid
Ground
30 days
Rights-of-
Way
1.0
1
June 1
Liquid
Ground
NA
Fallow/ Idle
land
2.25
1
November 1
Liquid
Ground and
Aerial
NA
Corn
2.0
1
April 1
Liquid
Ground and
Aerial
NA
Sorghum
2.0
1
April 1
Liquid
Ground and
Aerial
NA
Turf
2.0
2
April 1
Granular
Ground
30 days
Turf
1.0
2
April 1
Liquid
Ground
30 days
- Based on 2003 IRED and Label Change Summary Table memorandum dated June 12, 2006 (U.S. EPA,
2006b).
3.2 Aquatic Exposure Assessment
As discussed in Section 2.5 and Appendix C, the Alabama Sturgeon resides principally in
the main stem of the Alabama River below the Millers Ferry Lock and Dam. Even
though it appears that the dam limits the range of the species northward into central
Alabama, the dam does not prevent the flow of water. The potential action area is
defined as the entire watershed that drains to the Alabama River both above and below
the Millers Ferry Lock and Dam because use sites that drain to the Alabama River and its
tributaries above the dam can reach the areas south of the dam.
In general, Alabama sturgeon are found primarily within the confines of the Alabama
River and the mouths of the major tributaries. For the purposes of this assessment, the
principal location of direct stressor exposure is presumed to be within the Alabama River
33

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and the mouths of its tributaries. The rationale for this assumption is discussed further in
Appendix C, which details the life history information for the Alabama sturgeon.
For the purposes of this assessment, it is assumed that the highest exposures within the
entire Alabama River watershed occur within the areas immediately proximate to the
Alabama River including central and southern Alabama and northwestern Georgia.
Figure 2.5 shows this location in more detail.
3.2.1	Conceptual Model of Exposure
The general conceptual model of exposure in this assessment is that the highest exposures
will occur in the headwater streams adjacent to agricultural fields and other non-
agricultural use sites (residential, right-of-way, turf, and forestry). For the most part,
these stream segments are far removed from the Alabama River itself. Figure 2.2 depicts
the general relationship between agricultural cropland and the Alabama River where the
species resides. The Agency's exposure model, Pesticide Root Zone Model/Exposure
Analysis Modeling System (PRZM/EXAMS), is generally intended to estimate exposures
in headwater streams and not the main stem of major rivers such as the Alabama River.
Available Alabama River monitoring data from the United States Geological Survey
(USGS) National Water Quality Assessment (NAWQA) Program
(http://water.usgs. gov/nawqa/) are also used to refine the typical modeling approach (as
specified in the Overview Document; U.S. EPA, 2004) and characterize exposure
estimates to the Alabama sturgeon within the Alabama River proper. However, it is
expected that the available monitoring data are insufficient to predict all possible
exposure in these areas, given the likelihood that significant amounts of atrazine are used
in both southern and central areas of Alabama that drain to the Alabama River.
3.2.2	Existing Monitoring Data
Site-specific Alabama River monitoring data were obtained from the USGS NAWQA
Program (http://water.usgs.gov/nawqa/). A summary of the data are presented in Figure
3.1. Only one sample location with atrazine detections was located within the current
range of the Alabama sturgeon below the Millers Ferry Lock and Dam. This data
indicate that atrazine concentrations appear to be consistently below 1 [j,g/L in the main
stem of the Alabama River. It should be noted, however, that two of the higher detected
concentrations of 0.12 [j,g/L coincide with the spawning period of the Alabama sturgeon
(April - May). The general location of this sampling station is presented in Figure 3.2.
Although other sampling locations are not available, it is anticipated that higher atrazine
concentrations may occur both upstream of this location and within the tributaries of the
Alabama River. This pattern suggests that an emphasis on predicting exposures in the
tributaries is the most conservative approach for assessing both direct and indirect effects
to the Alabama sturgeon.
34

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Atrazine in Alabama River at Claiborne, AL
Atrazine in Alabama River at
Figure 3.1. Summary of All Available USGS NAWQA Data for Atrazine in the
Alabama River
NAWQA groundwater data were evaluated to determine the importance of groundwater
on potential loadings to the Alabama River. Groundwater data from Alabama were
downloaded from the USGS NAWQA data warehouse (http://water.usgs.gov/nawqa/) on
May 11, 2006. A total of 205 well samples were analyzed for atrazine in groundwater
between 1993 and 2003. Of these samples, a total of 85 had positive detections of
atrazine, with 13 of those estimated at below the limit of quantitation (LOQ). The
frequency of detection for all detections was 42%. The maximum concentration detected
was 1.8 [j,g/L in an agricultural setting in Madison County located along the Tennessee
state line in north Alabama. Of all detections, only 2 samples had detections greater than
1 |ig/L. Overall, the data suggest that atrazine recharge to the waters of the Alabama
River watershed is possible; however, surface runoff is expected to be the dominant route
of exposure, given the detection frequency, travel times, and magnitude of exposures in
the available groundwater data.
35

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NAWQA Surface Water Sites
on the Alabama River
Maj
Choctaw
'Icox
SATILPA CREEK NEAR COFFEEVILLE AL
V
Cho
Clarke
Monroe
ALABAMA RIVER AT CLAIBORN
Conecuh
Washington
Escambia
-O
Legend
O NAWQA SW Sites
Mobile NAWQA Stud/ Unit
AtrazineUse (lbs)
Escambia
Santa
isa
EK NEAR KUSHlAAL
1- 1000
~ 1001 - 5000
5001 - 10000
I 10001 - 500000
Miles
figure 3.2. Location of USGS NAWQA Site on Alabama River near Claiborne,
Alabama
36

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3.2.3 Modeling Approach
The analysis of available monitoring data and usage information indicates that the
exposure assessment cannot rely exclusively on monitoring data. Although generally of
high quality, the USGS NAWQA data available for the Alabama River are limited in that
they represent a single location on the river, and the frequency of sampling is not
considered sufficient to provide a reasonable upper bound on exposure. The available
monitoring data are considered to provide a good estimation of lower bound exposures.
In addition, the monitoring data provide context to model predictions, particularly when
considering the impact of flow on the modeled predictions.
The modeling approach for this assessment incorporates the standard assessment
approach of PRZM/EXAMS scenarios for corn and sorghum with the other scenarios
(residential, impervious, rights-of-way, turf, and fallow/idle land) recently developed for
use in the Barton Springs salamander endangered species assessment (U.S. EPA, 2006c).
In addition, the Oregon Christmas tree scenario (developed for the organophosphate [OP]
cumulative assessment; U.S. EPA, 2006d) was used as a surrogate for forestry use.
Available usage data (Kaul, et al., 2005; Kaul and Jarboe, 2006; Zinn and Jones, 2006)
suggest that the heaviest usage of atrazine is likely to be on corn in south-central
Alabama, where agricultural uses are highest. Therefore, all selected modeling scenarios
were run using the weather data from the Mobile, Alabama meteorological station that is
closest to the high use area and likely to give a higher runoff amount than other nearby
weather stations such as Montgomery, Alabama. 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 (Mississippi corn, 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 of the
existing PRZM scenarios may be found at the following website.
http://www.epa.gov/oppefedl/models/water/przmenvironmentdisclaim.htm
The non-agricultural scenarios were used within the standard framework of
PRZM/EXAMS modeling using the standard graphical user interface (GUI) shell,
PE4v01.pl, which may be found at;
http://www.epa.gOv/oppefedl/models/water/index.htm#przmexamsshell
Peak concentrations, as well as 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. Several
of these are non-standard durations of exposure; therefore, the 30 year time series output
37

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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. This information is provided in Appendix D.
As specified in the Overview Document (USEPA, 2004), it is assumed that a standard
water body, of fixed geometry, receives the edge of field runoff. Further discussion of
the Agency's standard modeling approach including more detail on PRZM/EXAMS may
be found at the following website:
http://www.epa.gov/oppefedl/models/water/index.htm
Additional information on the modeling approach for the non-agricultural residential,
rights-of-way, and forestry use scenarios is provided below.
Residential Scenario
The residential scenario was used in tandem with the impervious scenario. It is likely
that some overspray does reach the impervious surfaces in the residential setting. In
order to account for potential overspray, impervious surfaces were modeled using three
separate assumptions. For the purposes of this assessment, it was assumed that 1% of the
application rate could reach the impervious surfaces surrounding each residential lot.
This amount of overspray is not based on empirical data (i.e. studies on the actual
occurrence of overspray are not available); however, the overspray assumption is
expected to be reasonable given that the principal drift assumption for ground spray in
ecological risk assessments is 1%. In order to test this assumption and address the
potential uncertainty associated with the lack of data for overspray, two alternate
scenarios were modeled to characterize the effect the 1% assumption. The impervious
surface was also modeled assuming 0% and 10% overspray to provide a lower and upper
bound of the 1% assumption. The results of these alternate modeling exercises are
discussed more fully in Section 3.2.4.1.
In this exercise, it is assumed that 1% overspray is applied to impervious surfaces and
50% of the ]A acre lot is treated with atrazine. The assumption of 1% overspray may
underestimate exposure, given that more overspray of impervious surfaces is possible.
However, this impervious scenario represents general impervious surfaces within a
watershed that are not part of the Vi acre lot, and includes roads, parking lots, and
buildings where overspray from residential lots is expected to be minimal. The Vi acre lot
by comparison was developed with a curve number reflective of the fact that the lot is
covered with both pervious surfaces (grass and landscaped gardens) and impervious
surfaces (driveways, sidewalks, and buildings). In this case, the assumption that 50% of
the lot is treated likely overestimates the amount of landscaped area treated, but
underestimates unintentional overspray of driveways and sidewalks within the lot itself.
Overall, these are simplifying assumptions, given the limitations of the modeling
approach and lack of empirical data, and are likely to provide a reasonable high-end
estimate of exposure. Comparison of modeled exposures with available monitoring data
is critical to this evaluation.
38

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In order to justify the assumption of Vi acre lot as a typical exposure scenario, publicly
available data from the United States Census (Census) were reviewed. Specifically, data
from 2003 from the American Housing Survey (AHS) were reviewed and are available at
the following website:
http://www.census.gov/hhes/www/housing/ahs
The data for all suburban homes available nationally were evaluated. It is assumed that
most pesticide applications, particularly herbicide applications, occur in suburban
settings. To test the assumption of the Vi acre lot as the best representation, the AHS data
for suburban homes that list total number of houses by lot size and by square footage of
house (see Table 1C-3 at the AHS website above) were considered. With a total of
45,552,000 total units reported nationally for all suburban areas, 12,368,000 units (the
largest class at 27%) were on lots between 1/8 acre and Vi acre, while 9,339,000 units (the
second largest class at 21%) were on lots between ]A acre and '/2 acre. Overall, the
median lot size was 0.37 acre. This analysis suggests that the Vi acre lot is a reasonable
approximation of suburban pesticide use.
It was also assumed in this assessment that 50% of a typical Vi acre lot would be treated
with atrazine. This assumption was based partially on data from the AHS website and
partially from professional judgment about typical features and the percentage of a
typical lot those features might require. For example, the AHS survey data report that of
a total of 43,328,000 single detached homes in suburban areas, 10,124,000 (the largest
group at 23%) were between 1,500 and 2,000 square feet, while 7,255,000 (the third
largest group at 17%) were between 2,000 and 2,500 square feet, and 9,513,000 (the
second largest group at 22%) were between 1,000 and 1,500 square feet. From this data,
it was assumed that a typical home is 2,000 square feet with a 1,000 square foot footprint.
The lower sized houses less than 1,500 square feet are more likely to represent single
floor structures; thus, the 1,000 square foot estimate for a house footprint is reasonable.
In addition to the footprint of the typical house, it was also assumed that a typical house
would have a driveway of approximately 25 by 30 feet or 750 square feet and roughly
250 square feet of sidewalk. A typical suburban home was also assumed to have roughly
300 square feet of deck space and 900 square feet of garage. Finally, a substantial
portion of the typical home is assumed to be planted in landscaping with an estimate of
2,000 square feet. All of the previous estimates are based on professional judgment and
are not derived from the AHS data. All of these areas are assumed to not be treated with
a turf herbicide, resulting in a total area not treated with atrazine of 5,200 square feet.
Taking a total Vi acre lot size of 10,890 square feet and subtracting the untreated square
footage yields a total remaining area of 5,690, or roughly 50% of the total lot that could
be potentially treated.
Assumptions of lot size and percentage of the area that is treated are based on national
data and may vary at the local level. Data from the U.S. Census for Alabama
(http://www/census.gov/population/censusdata/places/01al.txf) suggest that housing
39

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density is typically less than those assumed at a national level (approximately 2,560 lots
per square mile); therefore, it is likely that typical lot sizes are greater than the assumed Vi
acre. If the lot sizes are larger, the percentage of a typical lot that is treated may be also
be greater than the assumed value of 50%. However, the impact of larger lot sizes and
greater percentage of treated area is likely tempered by the fact that central and southern
Alabama is largely rural (see Section 3.2.3.2), with fewer housing developments where
large-scale homeowner pesticide use is likely to occur. Overall, it is expected that given
the generally rural nature of the action area, the impact of residential exposure is over-
estimated in this assessment.
Currently two categories of formulations are registered for atrazine use on residential
sites. These are granular and liquid formulations (wettable powder and dry flowables).
Both formulations are modeled separately because application rates are different (2
lbs/acre for granular and 1 lb/acre for liquid) and the standard assumption for modeling
granular formulations is different from liquid formulations. Granular formulations are
typically modeled as soil applied (CAM is set to 8 with a minimized incorporation depth
of 1 cm) with 0% spray drift, as compared with a foliar application (CAM is set to 2 with
a 4-cm depth of incorporation), which assumes the standard spray drift assumption of 1%
for ground applications.
For the residential scenarios, it was assumed that some percentage of the watershed is
represented by the Vi acre lot and by impervious surfaces. In order to account for
potential variability in impervious surfaces, an analysis of the relative contribution of the
impervious and residential scenarios for different portions of the region surrounding the
Alabama River Watershed was completed. Figure 3.3 depicts impervious coverage in the
area surrounding the Alabama River relative to available atrazine use data. For this
screening level exposure assessment, it is assumed that 30% of the area surrounding the
watershed is impervious.
40

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Percentage of Impervious Surfaces
I O ¦ IT /*\ V IA V I* j~\ K* 4" Mrt I f\ I f~\ U\ 1^4 A

1
FERRY
RHOUSE

Legend
Mobile NAWQA Study Unit
% Impervious
Value
| I 0- 10
| 11 - 20
| 21 - 30
| 31 - 40
~	41 - 50
| 51 - 60
~	61 - 70
~	71 - 30
| 81 - 90
31 -1 oo
0 12.5 25
Mgure 3.3. Percentage of Impervious Surfaces in Southern and Central Alabama
Near the Alabama Sturgeon Action Area
41

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It was also assumed that 50% of the ]A acre lot is treated with atrazine. The ]A acre lot
was developed with a curve number reflective of the fact that the lot is covered with both
pervious surfaces (grass and landscaped gardens) and impervious surfaces (driveways,
sidewalks, and buildings). In this case, the assumption that 50% of the lot is treated
likely overestimates the amount of landscaped area treated, but underestimates
unintentional overspray of driveways and sidewalks, although empirical data to support
this assumption are not available.
Rights-of-Wav Scenario
For the rights-of-way scenario, it was assumed that rights-of-way consist of 50%
impervious and 50% pervious cover. In addition, it was assumed that no single
watershed is completely covered by rights-of-way use. This assumption seems
reasonable given that rights-of-way (roads, rail and utility lines) are typically long, linear
features that traverse a watershed. For the screening level exposure assessment, it was
assumed that no more than 10% of the watershed is covered in rights-of-way. However,
analysis of spatial data suggests that the 10% assumption is likely an over-estimation of
the percentage of the action area covered in rights-of-ways.
In the Barton Springs Assessment (U.S. EPA, 2006c), an evaluation of the local land
cover data indicated that a reasonably conservative assumption of the percentage of the
area in rights-of-way was 10%. The analysis included land cover types including roads,
fence lines, power lines, and railroads. More information on this analysis can be found in
Appendix C of the Barton Springs Salamander Assessment for atrazine (U.S. EPA,
2006c). A similar analysis was conducted for this assessment.
In this analysis, national data for roads and railways (http://nationalatlas.gov) and internal
EPA data for pipelines were obtained (spatial data for utility easements were not
available). The road, rail, and pipeline land cover data were added to a GIS map of the
action area (Figure 3.4) and a comparison of the density of the total network of potential
use sites was made. Each land cover feature in the GIS map is presented as a line with no
width associated. A buffer was applied using the Arc Toolbox within Arc Map in order
to account for the potential width of the each linear feature. This assignment of area to
each feature was done in order to compare the total area of each feature type (e.g.
railways) with the total area of the action area.
For each feature, an assumption was made about the typical width of the feature (e.g.
width of the road surface plus shoulders) plus the rights-of-way area adjacent to the
feature that could potentially be treated. In each case, a conservative assumption for the
width of the feature zone plus the potentially treated area surrounding each was assumed.
These assumed feature width estimates, which were based on professional judgment,
were skewed to the largest feature in the class. For example, the largest width was
assumed for national highways, and this width was also applied to all primary and
secondary highways within the action area. This approach is assumed to be conservative
42

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Right-of-Way Density
in Alabama River Action Area
Legend
AJab arna_R rver_D rain age_Q utline
[ Ra ilw ay with 200 ft b uffe r
' | Roads with 200 ft buffer
| Pipelines with 100 ft buffer
Tombigb
£Jabam
Mobil* River
Miles
0 12.5 25 50 75 100
igure 3.4. Density of Road, Railways, and Pipelines as Surrogate for Rights-of-
Way Density in Alabama River Watershed (Action Area)
43

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because it is unlikely that all features will be of similar width, and not all areas will be
treated with atrazine (e.g., many areas are likely to be maintained using mechanical
methods, such as mowing, or not treated at all). The following assumptions were made
for the width of each feature:
•	Roads - 200 feet
•	Rail - 200 feet
•	Pipeline - 100 feet
•	Utility Line - 200 feet
Given these assumptions, the percentage of rights-of-way land cover types plus
associated buffers for roads, railways, and pipelines within the action area for the
Alabama sturgeon is 0.6% of the total area for rail, 1.5% for roads, and 0.6% for
pipelines. Locally, it appears that higher percentages occur near more urbanized areas;
however, it was assumed that less rights-of-way pesticide application occurs in urbanized
areas. The aggregate percentage of land cover in roads and railways of 2.1 % appears to
be a reasonable estimate. Additional roads may be present in the action area that are not
captured by the available spatial data, and the analysis does not include utilities and
pipelines for which no spatial data are available. Therefore, although the assumption of
10%) used in this assessment for treated rights-of-way uses may over-estimate exposure, it
is expected to be conservative and protective, given the associated uncertainties.
Forestry Scenario
Use of atrazine on commercial forestry operations cannot be precluded as a potential non-
agricultural use; however, the available information suggests that atrazine is rarely used
on commercial forestry operations in Alabama (McNabb, personal communication, 2006;
Michael, personal communication, 2006). However, because this registered use pattern is
widely prevalent in Alabama, it has been addressed using the Oregon Christmas tree
scenario. This scenario was developed specifically for the OP cumulative assessment
recently completed by the Agency (U.S. EPA, 2006d) and represents a vulnerable site
based on OP use information intended to represent a commercial nursery operation.
Information on the OP cumulative and scenarios used in modeling may be found at:
http://www.epa.gov/pesticides/cumulative/2006-op/index.htm
The Oregon Christmas tree scenario is expected to approximate commercial forestry
operations where herbicides are typically applied during the seedling emergence and
juvenile growth stages to prevent competition with newly planted trees. The scenario
was not modified to represent local conditions but was modeled using local weather data
from Mobile, Alabama. Several factors suggest that modeling of forestry uses of atrazine
is likely to result in an over-estimation of exposure. As previously mentioned, atrazine
use in forestry operations in the state of Alabama is considered to be rare. The available
information indicates that the herbicides of choice in Alabama forestry are Roundup®,
Oust®, Velpar®, Garlon®, and Arsenal® (Michael, personal communication, 2006).
Secondly, modeled estimates represent a one in ten year return frequency using 30 years
44

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of modeled output; however, if atrazine were used at all, it would likely be applied for
only one or two years during early growth stages. Finally, the available information
suggests that most commercial forestry operations are removed from the immediate
vicinity of the Alabama River (Michael, personal communication, 2006). Taken
together, these facts suggest that the modeled exposures for atrazine forestry use are
likely to over-estimate exposure; therefore, these EECs are not used to derive risk
quotients. However, they are discussed as part of the risk description in order to account
for potential changes in current herbicide use practices in Alabama forestry to include
atrazine in the future.
3.2.3.1 Model Inputs
In accordance with the Agency's Overview Document (U.S. EPA, 2004), 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.
As noted above, new and existing scenarios were used in this assessment. Existing
scenarios consist of agricultural scenarios for corn and sorghum developed previously for
other geographic areas. New scenarios were developed for one agricultural use
(fallow/idle land) and several non-agricultural uses including residential, turf, forestry,
and rights-of-way. These new scenarios were developed for the Barton Springs
Salamander assessment (U.S. EPA, 2006c) and are not specific to Alabama River
Watershed. All existing and new scenarios were modeled using local weather data
(Mobile, Alabama). Linked use site-specific scenarios and meteorological data were
used to estimate exposure as a result of specific use for each modeling scenario.
PRZM/EXAMS 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 AgDrift 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
45

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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 without a setback. It is expected that the presence of a well
vegetated setback between the site of atrazine application and receiving water bodies
could 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.
While the extent of load reduction can not be accurately predicted through each relevant
stream reach in the action area, data from USD A (USD A, 2000) suggest reductions could
range from 11 to 100%.
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
3.2. 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#chloro
Table 3.2. Summary of PRZM/EZAMS Environmental Fate Data Used for Aquatic
Exposure Inputs for Atrazine Endangered Species Assessment for the Alabama
	 Sturgeon		
Fate Property
Value
IM RID (or sou rce)
Molecular Weight
215.7
MRID 41379803
Henry's constant
2.58x10 -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
46

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Fate Property
Value
IM RID (or sou rce)
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 value2
Spray Drift Fraction1
6.5 % for aerial
0.6 % for ground
default value2
-	Spray drift not included in final EEC due to edge-of-field estimation approach
2
-	Inputs determined in accordance with EFED "Guidance for Chemistry and Management Practice Input Parameters
for Use in Modeling the Environmental Fate and Transport of Pesticides " dated February 28, 2002
3.2.3.2 Results
As noted above, a total of eight scenarios were evaluated in this assessment. Of these,
three were developed as part of the Barton Springs salamander endangered species
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 a third
(fallow/idle land) is a standard PRZM/EXAMS scenario. The remaining four scenarios
(corn, sorghum, Christmas trees as surrogate for forestry, and turf) were taken from
existing scenarios developed for other regions of the United States and modeled using
weather data from the Mobile, Alabama. No new scenarios were developed for this
assessment. In order to address the potential use of atrazine on the labelled use sites
within the action area, all of the scenarios were modeled. In addition, the results are
characterized to place emphasis on those concentrations actually expected to be present.
The results of the modeling are summarized in Table 3.3. An example of the modeling
approach and the model input files are provided in Appendix D.
Table 3.3. Summary of PRZM/EXAMS Output EECs for all Modeled Scenarios

Application
Number of
First

90th Percentile of 30 Years of Output

Use Site
Rate
(lbs/acre)
Applications
(interval)
Application
Date






Peak
EEC
14-dav
EEC
21-day
EEC
30-dav
EEC
60-dav
EEC
90-dav
EEC




(Hg/L)
(Hg/L)
(Hg/L)
Oig/L)
(Hg/L)
(Hg/L)
Residential-
Granular1
2.0
2
(30 days)
April 1
19.9
19.6
19.4
19.2
18.6
17.9
Residential-
Liquid1
1.0
2
(30 days)
April 1
14.6
14.4
14.2
14.1
13.7
13.4
Right-of-Way
i
1
1
June 1
2.4
2.4
2.4
2.4
2.3
2.2
47

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Application Number of First
90
-------
assessed lives is adjacent to the treated field. It is also assumed that this treated field
represents a small watershed that is 100% treated and drains directly to the water body.
Based on the land cover data, it appears that habitat for the Alabama sturgeon is removed
from the location where agricultural crops are grown. Therefore, the generic conceptual
model discussed above does not apply for agricultural crops modeled in this assessment
(corn, sorghum, and fallow/idle land).
Based on the analysis of land cover data, the conceptual model for human health drinking
water assessments is considered to be more appropriate for estimating exposures related
to agricultural uses of atrazine in the Alabama River where the Alabama sturgeon may
reside. In the human health drinking water assessment, it is assumed that some portion,
but not all, of the watershed is treated when assessing an agricultural crop use. The
Agency has developed a suite of national and regional percent cropped area (PCA)
adjustment factors for use in drinking water assessments. Crop-specific PCAs have been
developed for corn, sorghum, cotton, and soybeans, and a national default PCA has been
identified for all cropland. This national assessment is typically conducted to assess the
potential for drinking water exposures in all watersheds in the area of interest that is
typically national. The rational for this adjustment and details on how the PCAs were
developed can be found at the following website.
http://www.epa.gov/oppfeadl/trac/science/reservoir.pdf
In the case of the Alabama sturgeon, exposure concentrations are derived for a single
watershed; therefore, use of a watershed-specific PCA is appropriate. As part of this
effort, the total area for the entire action area and the cropland portion of the action area
was tabulated. This analysis, which is presented graphically in Figure 3.5, shows that the
bulk of agricultural land is restricted to areas well upstream of the sturgeon's habitat
range. The total percentage of cropland within the Alabama River action area is 9.8%.
This value has been used to adjust all PRZM/EXAMS predicted EECs for agricultural
uses included in this assessment. The PCA-adjusted exposure concentrations for corn,
sorghum, and fallow/idle land, which are summarized in Table 3.4, are used for risk
estimation. None of the non-agricultural uses were PCA adjusted using this crop-specific
PCA. However, the non-agricultural uses (right-of-way, residential, and turf) were
adjusted using action area-specific factors for each use.
Action Area-Specific Adjustment Factors for Non-Agricultural Uses
As previously discussed above, an action area-specific adjustment factor of 10% was
assumed for rights-of-way. An additional analysis was conducted to determine the
relevance of turf and residential uses within the action area. Evaluation of the impervious
surface data and other land cover data suggests that much of the area within the Alabama
River watershed is predominantly rural. As such, it is unlikely that 100% of any sub-
watershed within the action area is surrounded by residential/turf use sites. In fact, the
available information suggests that population density is restricted to only a few isolated
urbanized areas. Available data from the U.S. Census (http://factfinder.census.gov) for
49

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all Alabama counties in the action area suggest that the average density of housing is 38.3
units per square mile (640 acres). An estimate of the total acreage of residential lots in
Legend
.jf	Cropland
.AJab ama_R iver_D rain age_
j'.1;,	Cr opl and in Action Are a
'^i^'Total Ati,izine (lbs)
5001 - 10000
10001 • 500000
Figure 3.5. Percent Cropped Area (PCA) Analysis in the Alabama River
Sturgeon Action Area
50

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the action area was generated using a conservative assumption of 2.5 acres for the
maximum lot size (a much higher lot size estimate than used in modeling). Multiplying
the average number of lots (38.3) by the assumed lot size (2.5 acres) yields a total of 95.8
acres of residential lots within the action area. This acreage is then divided by the total
number of acres per square mile (640 acres) to estimate the percentage of residential area
within the action area. The estimated value is 15%. This action area adjustment factor is
applied to the residential and turf EECs presented in Table 3.3 to yield adjusted EECs for
use in risk estimation. These values are presented along with the PCA-adjusted EECs for
the agricultural scenarios in Table 3.4.
Typically, ecological risk exposure assessments assume that 100% of the watershed
immediately surrounding the receiving water body is treated. Modeling all potential uses
separately and assigning the highest exposure scenario to the risk estimation provides a
level of conservativeness to the assessment. If multiple uses were present in the 10
hectare watershed (an unlikely occurrence), the aggregation of these exposures would
yield a lower estimate than assuming 100% of the watershed is the maximum use site.
However, in this assessment, a set of action area-specific PC As were estimated and
applied to the modeled individual uses. Use of action area-specific PCAs is appropriate
because land cover data analysis suggests that the major use sites (agricultural,
residential, rights-of-way, and turf) are not proximate to the species location in the
Alabama River. Because these uses are likely removed from the species location, no
single use site will dominate exposure, and an aggregation of exposure is necessary to
reflect the co-occurrence of agricultural and non-agricultural uses of atrazine within the
action area. In order to account for this, each modeled use pattern modeled is assigned a
general PCA. For example, three agricultural crops (corn, sorghum, and fallow land)
were modeled separately and each assigned a PCA associated with general agricultural
land. No detailed land cover information is available to assign crop specific PCA. The
concept of aggregating PCA-adjusted EECs is similar to that employed in human health
cumulative risk assessments, where the PCA adjustment alters the mass of pesticide
reaching a receiving water body that is generally removed from the treated fields. In
contrast, the standard conceptual model for ecological risk assessment is that the water
body is proximate to the entire treated field. Because, the receiving water body (in this
case the portion of the Alabama River) is removed from most treated areas, receives
water from a larger drainage area than the standard assumption (10 hectares), and has
significant flow, it is similar to the Index Reservoir used in drinking water exposure
conceptual models. Exposures were aggregated by selecting the agricultural use pattern
that yields the highest exposure (in this case corn), assuming it covers the entire
agricultural land cover class, and aggregating it with other non-agricultural use sites from
the other general land use types including residential, rights-of-way, and turf. The
individual use scenarios that were selected to represent each land class for the aggregate
EECs are bolded in Table 3.4.
Similar to the methodology used in human health cumulative risk assessments, the
addition of these exposures is likely to be conservative because it assumes that all
51

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applications occur at the same time and at the maximum application rate across the entire
suite of land cover classes. In reality, aggregated exposure concentrations are expected to
be lower than the modeled predicted values because applications are unlikely to occur
simultaneously across the landscape at the maximum rate, and not all of the specific use
types are likely to be treated (i.e. percent crop treated, or PCT, for corn represents the
portion of land in corn that is actually treated). However, no information is available to
estimate these factors; therefore, conservative assumptions are used to derive the
aggregate EECs. Using the techniques developed for assessing multiple pesticide uses
within a watershed, the time series concentrations from each of the four land use classes
were added, rather than simply adding the maximum concentrations for each duration of
exposure. This analysis accounts for the differences in application timing (still assuming
that all applications within a land use class occur at the same time) between land classes.
Further detail on the approach used in the cumulative risk assessments for assessing
multiple exposures within a watershed may be found at the following website:
http://www.epa.g0v/pesticides/cumulative/rra-0p/l E.pdf
The resulting aggregate EECs represent the impact of co-mingling simultaneous
agricultural and non-agricultural exposures and account for the diluting effect of non-
treated areas as well as the interplay of high and low exposure scenarios. The results of
this analysis are presented in Table 3.4
Table 3.4. Revised PRZM/EXAMS EECs for all Modeled Scenarios Using the
		Action Area-Specific PCA1	
Application Number of First
90th Percentile of 30 Years of Output
use one
l\dlt
(Ibs/acrc)
(interval)
A|J |JMV*IMUM
Date
Peak
EEC
(Hg/L)
14-day
EEC
(Hg/L)
21-day
EEC
(Hg/L)
30-dav
EEC
(Hg/L)
60-dav
EEC
(Hg/L)
90-day
EEC
(Hg/L)
Residential-
Granular
2.0
2
(30 days)
April 1
3.0
2.9
2.9
2.9
2.8
2.7
Residential-
Liquid
1.0
2
(30 days)
April 1
2.2
2.2
2.1
2.1
2.1
2.0
Right-of-Way
2
1
1
June 1
2.4
2.4
2.4
2.4
2.3
2.2
Corn
2
1
April 1
10.1
10.0
9.9
9.9
9.7
9.4
Sorghum
2
1
May 1
6.2
6.2
6.1
6.0
5.8
5.6
Fallow/idle
land
2.25
1
November 15
5.8
5.7
5.7
5.6
5.5
5.4
52

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Applieation
Number of
First

90th Percentile of 30 Years of Output

Use Site
Rate
(Ibs/aere)
Applieations
(interval)
Applieation
Date






Peak
EEC
14-day
EEC
21-dav
EEC
30-day
EEC
60-day
EEC
90-day
EEC




0*g/L)
(jig/L)
(Hg/L)
(Hg/L)
(jig/L)
(Hg/L)
Turf-
Granular
2.0
2
(30 days)
April 1
2.7
2.7
2.7
2.7
2.6
2.6
Turf - Liquid
1.0
2
(30 days)
April 1
2.2
2.2
2.2
2.1
2.1
2.0
Aggregate









EECs from all









atrazine land



16.3
16.2
16.1
16.1
15.8
15.7
classes in









action area3









1	- Action area-specific PCA-adjusted EECs are used for risk estimation.
2	- Rights-of-Way EECs from Table 3.3, which incorporate an action area-specific adjustment factor of 10%.
3	- Action Area Weighted EEC estimated by summing the time-series concentrations from each of the general land
classes (agricultural land, residential, right-of-way, and turf) assuming 100% of the general class is treated with the
highest scenario modeled. Differences in application timing between land classes are considered. For example, general
cropland is estimated at 9.8%) of the entire action area and therefore, because a distinction cannot be made within the
cropland class for specific agricultural crops modeled (corn, sorghum, and fallow land) the highest use scenario
modeled (corn) is assumed to represent the entire class, providing a conservative estimate. Similar assumptions are
made for the residential and turf uses. This provides an estimation of the impact of co-mingling of atrazine exposures
from different application sites at various locations within the action area.
3.2.4 Additional Modeling Exercises Used to Characterize Potential Exposures
A number of uncertainties are associated with the modeling described above. Additional
characterization of these results has been completed, including a detailed analysis of
monitoring data, alternative modeling assumptions, and characterization of the
importance of flowing water on modeled EECs. These analyses are described in the
sections that follow.
3.2.4.1 Residential Uses (Impact of Over spray and Impervious Surfaces)
To evaluate the assumption of 1% overspray, alternative variable percentages of
overspray that could occur on the impervious surface were modeled. For the residential
and rights-of-way scenarios, 1% overspray onto impervious surface was assumed. An
alternative modeling exercise was conducted to evaluate the significance of overspray.
To account for potential overspray, the impervious scenario (assuming 30% of watershed
is impervious and 50% of the Vi acre lot is treated as above) was modeled by assuming
that variable percentages of the application rate could be applied to non-target impervious
surfaces. It was assumed that no more than 10% of the intended application rate would
be applied to the impervious surface. Given that the impervious scenario is intended to
represent non-target surfaces such as roads, parking lots and buildings, the assumption of
10%) overspray is likely to result in an over-estimation of exposure. To model overspray,
the binding coefficient was set to zero and the aerobic soil metabolism half life was set to
stable in lieu of actual data. Thus, it is assumed that non-binding would occur on these
53

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surfaces and that limited degradation would occur. The total application rate was then
multiplied by the percentage overspray. For the residential scenario, this yielded an
application rate on the impervious surface of 0.2 lbs/acre. In addition, the same analysis
using an assumption of 0% over spray was modeled.
Comparison of the resulting residential use pattern EECs indicates that with 10%
overspray the overall EECs are increased by roughly a factor of two, while assuming 0%
overspray only slightly decreases the EECs as compared to 1% overspray. This is not
unexpected given the increased runoff, lack of binding, and lack of degradation being
assumed. Without actual data for these processes, it is not possible to determine whether
these exposures reflect reality; although, it is expected that these assumptions are likely to
be conservative (some binding and degradation could occur). The analysis suggests that
overspray onto impervious surfaces may be a significant issue when the percentage of
overspray is high. The comparison of residential EECs based on varying percentages of
overspray is presented in Table 3.5.
54

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Table 3.5. Comparison of Residential EECs (granular w/ 30% impervious surface)
Assuming Variable Percentages of Overspray (0,1, and 10%) onto Impervious
Surfaces

Application
Number of
First

90th Percentile of 30 Years of Output

Use Site
Rate
(lbs/acre)
Applications
(interval)
Applieation
Date






Peak
EEC
14-dav
EEC
21-day
EEC
30-dav
EEC
60-dav
EEC
90-day
EEC




0ig/L)
(Hg/L)
(Jig/L)
(Jig/L)
fag/L)
fag/L)
Residential









with 1%
Overspray
2.0
L
(30 days)
April 1
19.9
19.6
19.4
19.2
18.6
17.9
Residential









with 0%
Overspray
2.0
L
(30 days)
April 1
17.8
17.5
17.3
17.1
16.5
15.8
Residential









with 10%
Overspray
2.0
L
(30 days)
April 1
42.4
42.1
41.9
41.6
40.8
39.8
Other assumptions within this assessment, which can have a significant impact on the
overall predicted EECs, include the percentage of impervious surfaces and the percentage
of Vi acre lot that is treated. In both instances, the relationship between the assumption
and the predicted EEC is linear. In other words, the assumed impervious surface
percentage of 30% within the action area of the Alabama River watershed decreases
dramatically with increasing distance away from urban areas, such as Mobile or
Montgomery, and from the sturgeon's habitat. The available data show that the
percentage of impervious surface decreases to less than 10% with increasing distance to
the north of Mobile, Alabama, although there are likely to be isolated pockets of
urbanized areas with higher percentages of impervious surfaces within the action area
(Figure 3.3). The impact of this assumption was evaluated by readjusting the output to
reflect the impact of a 5% impervious cover assumption on predicted exposures. In
general, peak and longer-term average concentrations generally double as the percentage
of impervious surface decreases. The increase in EECs is likely due to the increase in
treated area contributing more pesticide mass and a decrease in the impervious surface,
which results in a reduction in the amount of non-contaminated runoff. The impact of a
higher percentage of impervious surfaces was also modeled by assuming 50% impervious
surface that is representative of a core urban setting. The comparison of residential EECs
assuming variable percentages of impervious surface is presented in Table 3.6.
55

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Table 3.6. Comparison of Residential EECs (granular w/1% overspray) Assuming
Variable Percentages of Impervious Surface (5, 30, and 50%)




90th Percentile of 30 Years of Output

Pcreent
Impervious
Application
Number of






Use Site
Rate
(lbs/acre)
Applications
(interval)
Peak
EEC
(Hg/L)
14-
day
21-
day
30-
day
60-
day
90-
day




EEC
EEC
EEC
EEC
EEC




(Hg/L)
(US/L)
(Ug/L)
(US/L)

-------
liters and is modeled without flow. The standard water body was developed in order to
provide an approximation of high end exposures expected in ponds, lakes, and
perennial/intermittent streams adjacent to treated agricultural fields. Typically, this has
been interpreted as a stream with little, or low flow. For pesticides with low to moderate
persistence, the standard water body provides a reasonably high end estimate of exposure
in headwater streams and other low flow water bodies for both acute and longer-term
exposures. For more persistent compounds, the non-flowing nature of the standard water
body provides a reasonable high end estimate of peak exposure for many streams found
in agricultural areas; however, it appears to over-estimate exposure for longer time
periods in all but the most static water bodies.
The hydrologic landscape of the Alabama River watershed can be generalized by
categorizing the stream network into broad classifications. A simplified approach of
categorization for this assessment places the streams in the watershed into several broad
classifications including headwater streams, upper tributary (relative to the Alabama
River) streams, main stem of the tributaries, and the Alabama River itself. The purpose
of this classification scheme is to describe the modeled EECs in the context of where
these exposures are most representative and where they may be over- or under-estimated.
Modeled concentrations derived with the non-flowing standard water body (presented in
Table 3.3), are expected to be representative of exposures in headwater streams in areas
of low topography. It is also expected that the chronic EECs over-estimate exposure in
water bodies with flowing water, including the Alabama River between the Millers Ferry
Dam and Lock and the junction with the Tombigbee River, as well as the main tributaries
off the Alabama River.
In order to characterize the potential impact of flowing water on the longer-term
exposures (14-day, 21-day, 30-day, 60-day, 90-day, and annual average), additional
modeling and analysis of available monitoring data was conducted. Alternate approaches
to modeling with the standard water body were conducted to provide a general sense of
the relative reduction in long term exposure that might be occurring in water bodies
where flow is higher than small headwater streams in low topographic regions of central
and southern Alabama.
The corn scenario was re-modeled with non-standard assumptions of flow (described
below) because it yielded the highest non-PCA-adjusted EECs, based on the input
parameters presented in Table 3.2. As previously discussed, the standard EXAMS static
ecological water body is typically used as the receiving body for runoff from a 10 hectare
field. The standard ecological water body is intended to represent a pond or an
ecologically sensitive stream adjacent to an agricultural field. Typically, this is
conceptualized as a headwater stream; however, it may also be representative of higher
order streams with very low flow rates (e.g. small tidal inlets, oxbow lakes occasionally
fed by stream flow only, etc.).
In order to test the effect of flow on predicted EECs, the standard ecological water body
described above was used; however, the model was revised to route runoff water from the
10 hectare field through the 1 hectare water body as flow. The net effect of this analysis
57

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was to decrease both the peak and longer-term average concentrations by roughly 50%
and the annual average by nearly two times. The results of the alternative modeling are
presented in Table 3.8.
Further analysis was conducted by pairing the PRZM output from the corn scenario with
the Agency's variable volume water model (VVWM), which was developed for the
Probabilistic Risk Assessment (PRA) process. The VVWM was developed based on the
recommendation of the Scientific Advisory Panel (SAP) to account for the influence of
input and output (flow) on model predictions. In this case, the VVWM was used to
evaluate the impact of varying volume on the overall EECs. In general, the VVWM
yielded EECs less than the standard EXAMS water body EECs, but still above the annual
averages from the available monitoring data (see discussion below). Two alternate model
runs were conducted with the VVWM. The first was done using standard assumptions
and environmental fate parameters generally consistent with the non-flowing standard
water body run discussed above. The first model run assumed a 2-meter depth water
body that can drop to 0.02 meter and rise to 3 meters before flow occurs. The second
model run assumed a larger volume water body that maximizes flow into the water body.
This was accomplished by increasing the overall maximum depth of the water body to 10
meters. The net effect of this change is to reduce the original estimates for both peak and
long-term exposures with the VVWM by roughly a factor of two to four, depending on
water depth. The results are summarized in Table 3.8. Documentation and rationale for
the assumptions used in the VVWM may be found at:
http://www.epa.gOv/scipoly/sap/2004/index.htm#march
In order to further characterize the impact of larger water bodies with flow, the corn
scenario was also modeled using the Index Reservoir as the receiving water body. The
Index Reservoir represents a 5.3 hectare water body draining a 172 hectare watershed. In
the case of the Index Reservoir, the standard approach is to allow EXAMS to estimate
total runoff accumulated from the 172 hectare watershed and route that volume of water
as flow through the reservoir while assuming no change in reservoir volume. The
predicted peak EECs and flow rates from these alternate approaches assuming flow are
similar to those from the static water body with flow and the VVWM and are
summarized in Table 3.8. More information on the Index Reservoir may be found at:
http://www.epa.gov/oppfeadl/trac/science/reservoir.pdf
The USGS collected flow rates from 196 streams, creeks, and rivers from across
Alabama representing the range of physiographic provinces that are typical of stream
types found in the Alabama River watershed. Average 7Q10 (7 day average with a return
frequency of 10 years that is indicative of base-flow values) flow rates were derived for
all gauging stations and for the Alabama River alone (six sites). As shown in Table 3.8,
the 7Q10 values indicate that flow varies dramatically both within Alabama and when
compared to the Alabama River alone. Although neither flow estimate is an exact
representation of flow conditions, they are intended to provide a reasonable range of flow
rates. These flow values ranged by nearly one order of magnitude across the state.
58

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Comparison with the modeled flow rates suggests that the PRZM modeling yields
significantly lower flow rates than those recorded in Alabama watersheds. Flow data
may be found at the following website:
http://waterdata.usgs.gov/nwis/rt
In order to test the influence of these flow data on modeled EECs, a final analysis was
conducted with the Index Reservoir by modifying the GUI (PE4v01.pl) that runs
PRZM/EXAMS. The STFLO parameter responsible for reporting flow through the
receiving water body was modified by using the USGS data for Alabama instead of the
runoff volume described above. Two alternate Index Reservoir scenarios were then
modeled using the 7Q10 flow rates for the entire Alabama River watershed and Alabama
River alone. This exercise was intended to provide a range of possible flow rates and
modeled EECs within the Alabama River and its tributaries (streams, creeks, and rivers)
where the Alabama sturgeon is expected to occur. The results of this analysis are
presented in Table 3.8 and indicate that using both 7Q10 values yields EECs appreciably
below those predicted using the static water body.
Table 3.8. Comparison of Alternative PRZM Modeling (assuming flow) with EECs
Generated Using the Static Water Body
Scenario
Flow
(ftVsec)
Peak
EEC
(Hg/L)
96-hour
EEC
(jig/L)
21-(lav
EEC
(Hg/L)
60-dav
EEC
(Hg/L)
90-dav
EEC
(jig/L)
Ycarlv
EEC
(jig/L)
AL corn with static water
body1
0
104.8
104.8
102.8
99.1
95.8
73.1
AL corn with flow thru
standard water body
0.033
79.8
78.8
75.7
67.4
61.7
30.1
AL corn with WWM2
0.035
54.1
47.2
46.7
44.8
44.8
33.8
AL corn with WWM3
0.032
30.5
29.5
29.4
29.2
29.2
28.1
AL corn with Index
Reservoir4
0.574
78.3
76.4
72.0
58.8
50.6
40.3
AL corn (IR) with 7Q10
flow from entire AL River
Watershed
274.75
58.5
9.6
2.0
0.70
0.47
0.12
AL corn (IR) with 7Q10
flow from AL River only
5981.3s
58.5
9.5
1.9
0.68
0.46
0.11
1	- EECs generated using PE4v01 .pi in this table are slightly different from those presented in Table 3.3 due to
different duration of exposure and slight differences in the manual estimation technique used in Table 3.3.
2	- VVWM parameters: initial depth = 2 m; minimum depth = 0.02 m;,maximum depth = 3 m
3	- VVWM parameters: initial depth = 2 m; minimum depth = 0.02 m;,maximum depth = 10 m
4	- Corn IR scenario EEC reported using percent cropped area (PCA) of 46% for corn
5	- USGS flow data reported as 7Q10 values.
59

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3.2.4.3 Comparison of Modeled EECs with Available Monitoring Data
The second step in the process of characterizing modeled EECs was to compare the
modeling results with available surface water monitoring data. Unlike many pesticides,
atrazine has a fairly robust data set of surface water monitoring from a variety of sources.
Included in this assessment are atrazine data from the USGS NAWQA program
(http://water.usgs.gov.nawqa; national, local, and Watershed Regression for Pesticides),
and Heidelberg College. These monitoring data were characterized in terms of general
statistics including number of samples, frequency of detection, maximum concentration,
and mean from all detections. In addition, several sample sites from each data set were
selected for further analysis including calculation of annual maximum and annual time
weighted mean concentrations by site by year. The sample sites chosen for this
additional analysis were based on those locations from the national and local data with
the highest detected concentrations of atrazine. Finally, an interpolation of a single
year's worth of data from one sample site in the Heidelberg College data was completed
in order to estimate 14-day, 30-day, 60-day, and 90-day averages.
USGS NAWQA Data
An analysis of the entire USGS NAWQA data set was completed for atrazine. A data
download was conducted from the USGS data warehouse (http://water.usgs.gov/nawqa).
Overall, a total of 20,812 samples were analyzed for atrazine. Of these, 16,742 samples
had positive detections (including estimated values) yielding a frequency of detection of
roughly 80%. The maximum detection from all samples was 201 [j,g/L from the Bogue
Chitto Creek in Alabama near Memphis (outside of the Alabama Sturgeon action area) in
1999. Overall, the average concentration detected was 0.26 [j,g/L when considering only
detections and 0.21 [j,g/L when considering all detections and non-detections (using the
detection limit as the value for estimation).
The top ten sites with the highest atrazine concentrations from the national NAWQA data
were selected for refined analysis of the detections. All values from the national data set
were ranked and the top ten sites were selected based on maximum concentration. Each
location was analyzed separately by year, and the annual maximum and annual time
weighted mean concentrations were calculated. The minimum criterion for calculating
time weighted means for each sampling station was at least 4 samples in a single year.
The equation used for calculating the time weighted annual mean is as follows:
[(( T^-To) + (CWT™ )/2))*C Wl + (((Tw-Ti.! )/2)*Q) + [((T^-T^) + ((T^-T^)^)*^.
01/365
where: Ci = Concentration of pesticide at sampling time (Ti)
Ti = Julian time of sample with concentration Ci
T0 = Julian time at start of year = 0
Tend = Julian time at end of year = 365
The modeling and national NAWQA monitoring data are not directly comparable
because the monitoring data are generally from high atrazine use areas in the Midwest
60

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and South vulnerable to runoff, while the modeling was conducted exclusively for the
action area of the Alabama River watershed. In the Alabama River watershed, the
atrazine use intensity and runoff vulnerability (as identified by Williams et al., 2004) are
less than areas in the Midwest and South. The Ecological Exposure in Flowing Water
Bodies (Williams, et al., 2004) utilized the WARP model to identify highly vulnerable
watersheds for sampling and determined that the top 20% watersheds (based on relative
vulnerability) were predominantly located in the Midwest and South, while the
watersheds in the immediate vicinity of the Alabama River watershed are in the lower
40th percentile .
Given that the watersheds surrounding the Alabama River are significantly less
vulnerable to atrazine runoff than those in the Midwest, a comparison with monitoring
data from more vulnerable areas was conducted to provide context on the modeled
exposures. Modeled concentrations that exceed monitoring data suggest that the
modeling is not conservative for the most vulnerable watersheds (represented by the
national monitoring sites), but could still be conservative for less vulnerable sites. Model
results that are less than the monitoring data from the highly runoff vulnerable atrazine
use areas suggest that modeling is not conservative. In the case of atrazine, the modeling
tends to under predict the highest single day concentrations and over predict the annual
average concentration from the national NAWQA data. This is not unexpected given that
the majority of the high atrazine detections are from the 1990s when labeled application
rates were higher and because runoff vulnerability is much lower in the area surrounding
the Alabama River. The analysis suggests that modeling in the action area for atrazine
provides a reasonable estimate of short term exposure but over-estimates longer term
exposure.
Generally, the maximum (peak) values from this analysis are similar to, or above, the
model predictions from PRZM/EXAMS, while the annual time weighted mean (TWM)
concentrations are roughly an order of magnitude below the static water body model
predictions for annual average and are roughly two to four times below the flow
influenced model predictions described above. Comparison of these data and model
predictions for the intermediate durations exposures (14-day, 30-day, etc.) was not
conducted because the NAWQA data generally do not have the frequency needed to
conduct a meaningful interpolation between data points. Table 3.9 presents a summary
of the annual time weighted mean concentrations, and Table 3.10 presents a summary of
the annual maximum concentrations.
61

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Table 3.9. Annualized Time Weighted Mean (TWM) Concentration (jig/L) for the Top Ten NAWQA Surface Water Sites
(Ranked by Maximum Concentration Detected)

Station Name (ID)
Year
Bogue
Chitto
Creek, near
Memphis,
TN
(02444490)
Tributary
to S Fork
Dry Creek,
near
Schuvlcr,
NE
(06799750)
Sugar Creek, New
Palestine, IN
(394340085524601)
Kessinger
Ditch, near
Monroe
City, IN
(03360895)
LaMoine
River @
Colmar, IL
(05584500)
Sugar
Creek @
Milford, IL
(05525500)
Tensas
River @
Ten dill, LA
(07369500)
Maple
Creek near
Nickcrson,
NE
(06800000)
Auglaize
River near
Ft
Jennings,
OH
(04186500)
1991









1992


0.98




1.32

1993


0.77
3.80



1.43

1994


0.87
2.56





1995


2.28
0.74





1996


1.30



4.32

2.18
1997


5.36

3.45

5.55
1.03
2.82
1998


0.82

1.79

2.94
1.21
1.88
1999
9.62

0.28



2.50
0.68

2000
6.49

0.56


1.26

0.15

2001
1.20

0.83


0.78

0.22
1.28
2002
2.88

0.51


2.22

1.26
0.80
2003
2.14
4.46
0.70


7.83

2.23
1.42
2004
1.77
68.781
0.67


1.24

3.31
1.93
- TWM concentration likely biased because the first sample on May 8 is the peak sample from this year.
62

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Table 3.10. Maximum Concentration (jig/L) for the Top Ten NAWQA Surface Water Sites (Ranked by Maximum
Concentration Detected)

Station Name (ID)
Year
Bogue Chitto
Creek, near
Memphis, TN
(02444490)
Tributary
to S Fork
Dry Creek,
near
Sehuyler,
NE
(06799750)
Sugar Creek, New
Palestine, IN
(394340085524601)
Kcssinger
Ditch, near
Monroe
City, IN
(03360895)
LaMoine
River (at,
Colmar, IL
(05584500)
Sugar
Creek {a\
Milford, IL
(05525500)
Tensas
River (ai
Tendal, LA
(07369500)
Maple
Creek near
Niekerson,
NE
(06800000)
Auglaize
River near
Ft
Jennings,
OH
(04186500)
1991









1992


14




25

1993


8.5
120



11.2

1994


11
24





1995


27
2.6





1996


14.2





18
1997


129

108

92.3
10.3
85.2
1998


7.88

27.7

19.3
30
9.96
1999
201

2.39



13.9
10.7

2000
136

3.84


2§°

0.87

2001
4.5

14.4


6.96

1.21
10.4
2002
24.8

4.01


21.3

16.4
2.58
2003
18.8
21.3
10.5


108

34.8
13.4
2004
14.6
191
28.3


10.9

91.9
18.7
63

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USGS Watershed Regression of Pesticides (WARP) Data
The NAWQA data were then compared against the percentiles used to develop the USGS
WARP model. Comparison against WARP percentiles was conducted because the
WARP model has been reported to be a valuable tool for site selection and assessing
overall vulnerability. More information on the WARP model may be found at:
http://pubs.usgs.gov/wri/wri034047/wrir034Q47.pdf
The WARP data were developed using a subset of the national data described above (all
WARP data are included in the national data analysis described above). Data collected
between 1992 and 1999 from a total of 113 sample sites were used to create the model.
Sample sites were selected based on the robustness of the data available at a given site.
The model yields predicted daily exposures at various percentiles of occurrence. The
Agency compared the national NAWQA data and the model predictions against the mean
and 95th percentile values from the data used. The maximum 95th percentile value from
the WARP data was 20.2 |ig/L as compared to a maximum of 201 [j,g/L from all data.
The maximum mean value used in the WARP model development data was 3.82 (J,g/L,
which is consistent with the annual TWM values discussed above.
Alabama River Watershed NAWQA Data
The PRZM/EXAMS EECs were compared to surface water data from sites specific to the
Alabama River watershed (Figure 3.2). The data from both the entire state of Alabama
and from the single sample location on the Alabama River where atrazine was analyzed
were evaluated. The data were included in the national assessment described above;
however, because the national evaluation focused on all sample sites, some bias was
given to higher use areas (even though the highest sample site from NAWQA is from
Alabama Bogue Chitto Creek near Memphis and not in the Alabama River watershed).
Therefore, the same technique applied to the national data (maximum and TWM) was
used for these two data sets to provide a more regionally specific snapshot of the
available NAWQA data. Generally, the statewide data were consistent with the national
data for maximum exposures with a peak concentration of 201 (J,g/L, which is the national
maximum, while the average concentration from all statewide data was greater with an
average for all detections of 1.69 |ig/L (compared to national average of 0.21 |ig/L) and
an average for all data (detects and non-detects) of 1.63 [j.g/L (compared to national
average of 0.21 (J,g/L). The higher average and peak concentrations are likely biased due
to the high concentration of atrazine detected in the Bogue Chitto Creek sample and the
limited number of data points in Alabama. Eliminating the Bogue Chitto Creek data
from the analysis yields a maximum concentration of 23.6 [j.g/L and an average for all
samples of 0.27 (J,g/L, indicating that the higher average concentration is significantly
influenced by the single site.
The refined analysis for the Alabama River Watershed NAWQA data was completed
using the same approach used for the national data. The data were separated by site and
year and the annual maximum and TWM concentrations were calculated for the entire
64

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Alabama data set. The results suggest that, with the exception of the Bogue Chitto Creek
site, the maximum and TWM concentrations are well below the national analysis. The
results of this analysis are presented in Table 3.11.
For data specific to the Alabama River, the results indicate a much lower overall picture
of atrazine concentrations relative to both the statewide and national trends. The
maximum concentration of atrazine detected in the Alabama River was 0.142 |ig/L and
the overall average (there were no non-detections) was 0.046 [ig/L. The results of the
refined analysis indicate that, while statewide results are higher (or similar if the Bogue
Chitto Creek site is removed from the data set) than the national average, the site-specific
results for the Alabama River are significantly below the national and statewide averages.
An analysis of the annual maximum and annual time weighted mean (TWM)
concentrations for the data from the Alabama River was also completed. A summary of
the monitoring results for the Alabama River is presented in Table 3.12.
65

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Table 3.11. Annual Time Weighted Mean and Annual Maximum Concentration (^ig/L) for the Top Six NAWQA
Surface Water Sites in Alabama (Ranked by Maximum Concentration Detected)
Year
Station ID
THREE MILE
BRANCH (a)
NORTH BLVD
AT
MONTGOMERY,
AL
(02419977)
BOGUE CHITTO
CREEK NEAR
MEMPHIS,
ALABAMA
(02444490)
TOMBIGBEE R
BL
COFFEEVILLE
L&D NEAR
COFFEEVILLE
(02469762)
FLINT RIVER
AT
BROWNS BORO,
AL
(03575100)
CAHABA
VALLEY CREEK
AT CROSS CR
RD AT PELHAM,
AL.
(0242354750)
HESTER CREEK a
BUDDY
WILLIAMSON
ROAD NR
PLEVNA, AL
(0357479650)
TWM
Max
TWM
Max
TWM
Max
TWM
Max
TWM
Max
TWM
Max
1999
0.21
1.40
9.62
201.00
0.84
2.86
1.44
3.22
0.04
0.15
0.48
23.60
2000
0.45
1.20
6.49
136.00
0.22
0.49
0.24
6.58
0.05
0.68
0.08
0.36
2001
0.40
4.83
1.20
4.50
0.13
0.57
0.17
1.70
0.04
0.19
0.24
1.99
2002


2.88
24.80
0.15
0.42
0.09
0.62
0.04
0.08
0.09
0.71
2003


2.14
18.80
0.11
0.49
0.21
2.04
0.06
0.19
0.24
2.45
2004


1.77
14.60
0.38
2.56
0.16
1.49
0.06
0.19
0.04
0.22
66

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Table 3.12. Annual Time Weighted Mean and Annual Maximum Concentration
(jig/L) for the Top Six NAWQA Surface Water Sites in Alabama (Ranked by
	Maximum Concentration Detected)	
Station ID - 02429500
Year
TWM
Max
2000
0.039
0.142
2001
0.036
0.059
2002
0.046
0.083
2003
0.048
0.120
2004
0.042
0.122
Heidelberg College Data
Data from Heidelberg College, which consists of two intensively sampled watersheds
(Maumee and Sandusky) in Ohio, were also analyzed. Like the national NAWQA data,
the data are outside of the action area but are included in this analysis to provide context
to the modeled exposures. More information on the water quality monitoring program at
Heidelberg College may be found at the following website:
http://wql-data.heidelberg.edu/
The Heidelberg data were collected more frequently than other data included in this
assessment. The study design was specifically established to capture peak and longer
term trends in pesticide exposures. Data were collected between 1983 and 1999 and
consist of an average of roughly 100 samples per year with several days of multiple
sampling.
For the Sandusky watershed, a total of 1,597 samples were collected with 1,444
detections of atrazine (90.4% frequency of detection). The maximum concentration
detected in the Sandusky watershed was 52.2 [ig/L, and the overall average concentration
was 4.5 (J,g/L. For the Maumee watershed, a total of 1,437 samples were collected with
1,305 detections of atrazine (90.8% frequency of detection). The maximum
concentration detected in the Maumee watershed was 38.7 [j,g/L with an overall average
concentration of 3.7 |ig/L,
This analysis was further refined by deriving the annual TWM and maximum
concentrations by sampled watershed by year. The results of this analysis are presented
in Table 3.13. The results show a consistent pattern with that seen in other data collected
from high atrazine use areas with general TWM concentrations between 1 and 3 (J,g/L.
67

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Table 3.13. Annual Time Weighted Mean and Maximum Concentrations (jig/L) for
	Atrazine in Two Ohio Watersheds from the Heidelberg College Data	
Year
Sandusky Watershed
Maumce Watershed
TWM
Max
TWM
Max




1983
1.34
7.97
0.98
5.42
1984
1.08
8.73
1.27
11.71
1985
1.83
19.46
1.00
6.21
1986
3.32
24.61
1.64
10.01
1987
1.76
16.45
1.80
9.92
1988
0.41
1.53
0.43
2.15
1989
1.30
15.71
1.07
8.49
1990
1.96
19.31
1.69
14.78
1991
1.49
20.59
2.044
21.45
1992
0.39
40.53
0.51
7.35
1993
1.27
26.34
1.21
22.66
1994
0.86
10.10
0.82
4.02
1995
1.39
15.46
1.30
14.06
1996
1.56
23.40
1.19
16.19
19971
2.16
53.21
2.09
38.74
1998
1.49
40.03
1.41
27.62
1999
1.57
17.11
1.88
19.37
68

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1 Sample year 1997 from Sandusky selected for data infilling by interpolation in order to calculate CASM duration
exposure values.
Unlike other data sets included in this assessment, an effort at interpolation between data
points was completed in order to estimate 14-day, 30-day, 60-day, and 90-day average
concentrations. A final analysis of the data was completed by selecting one years worth
of data from the Heidelberg data. The 1997 sampling year was selected because it was
one of the more recent data sets and because the maximum and TWM concentrations
were higher than most other year's data. To process this data, it was necessary to "fill in
the gaps". A total of 126 samples were collected during 1997 with 50 days with multiple
samples yielding a time series of roughly 75 days. A step-wise approach was used to
estimate daily concentrations between sampling dates that consisted of simply extending
an analytical result from the date of analysis to the next date. For example, on January 6,
1997, atrazine was detected at a concentration of 0.475 (J,g/L. On the next sample date of
January 20, 1997, no atrazine was detected (0 (J,g/L). In the step-wise interpolation, all
dates between January 6 and January 20 were assigned the concentration of 0.475 |ig/L,
Also, because January 6 was the first sample date of the year, all previous days were also
assigned a value of 0.475 [ig/L. This process was repeated throughout the year to fill in
the time series and yield 365 days worth of data. In addition, where multiple samples
were analyzed on any given day, the highest of the values on that day was assigned.
There is significant uncertainty with this type of interpolation because there is no
information to suggest whether the interpolated value represents actual exposure. For
example, where a significant gap in time exists between two samples, it is unlikely that a
continuous concentration exists. It is more likely that there are upward and downward
fluctuations in exposure, with a greater likelihood that higher exposures are missed
between sample times with larger gaps in data points. The greatest fluctuations are likely
to occur either before, or well after, an application of atrazine. It is expected that
variation in concentration is less pronounced immediately after application due to the
persistence of atrazine.
Table 3.14 presents the results of this analysis. The analysis suggests that, for the
Sandusky watershed, in 1997, the estimated longer-term exposures are less than the
modeled estimates for the Alabama River by a factor of two to three.
Table 3.14. Magnitude and Duration Estimates (jig/L) from the 1997 Data from

14 day
21 day
30 day
60 day
90 day
Maximum
28.26
21.11
18.30
12.38
8.89
90th Percentile
7.55
7.08
7.82
10.23
8.22
Summary of Open Literature Sources of Monitoring Data for Atrazine
Atrazine is likely to be persistent in ground water and in surface waters with relatively
long hydrologic residence times (such as in some reservoirs) where advective transport
69

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(flow) is limited. The reasons for atrazine's persistence are its resistance to abiotic
hydrolysis and direct aqueous photolysis, its only moderate susceptibility to
biodegradation, and its limited volatilization potential as indicated by a relatively low
Henry's Law constant. Atrazine has been observed to remain at elevated concentrations
longer in some reservoirs than in flowing surface water or in other reservoirs with
presumably much shorter hydrologic residence times in which advective transport (flow)
greatly limits its persistence.
A number of open literature studies have been cited in the 2003 IRED (U.S. EPA,
2003a), which document the occurrence of atrazine and its degradates in both surface
water and groundwater. These data support the general conclusion that higher exposures
tend to occur in the most vulnerable areas in the Midwest and South and that the most
vulnerable water bodies tend to be headwater streams and water bodies with little or no
flow.
The analysis in the IRED also documents the occurrence of atrazine in the atmosphere.
The data indicate that atrazine can enter the atmosphere via volatilization and spray drift.
The data also suggest that atrazine is frequently found in rain samples and tends to be
seasonal, related to application timing. Finally, the data suggest that although frequently
detected, atrazine concentrations detected in rain samples are less than those seen in the
monitoring data and modeling conducted as part of this assessment and support the
contention that runoff and spray drift are the principal routes of exposure. More details
on these data can be found in the 2003 IRED (U.S. EPA, 2003a).
3.2.5 Modeling with Typical Usage Information
As previously discussed, agricultural use information within the state of Alabama was
taken from the data prepared for the cumulative triazine risk assessment (Kaul, et al.,
2005). This information does not include analysis of non-agricultural uses such as
residential, turf, rights-of-way, and forestry. However, this information does provide a
sense of actual atrazine use on sites similar to those assessed including corn, sorghum,
and fallow/idle land. This data suggest that the typical application rates (equivalent to the
average of the available data) and number of applications are less than the maximum
rates on the labels used above. Table 3.15 summarizes the typical rates and number of
applications relative to those used in this assessment. Clearly, if these lower application
rates were used, the overall exposure predicted for these uses would be decreased by at
least a factor of two for all three uses.
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Table 3.15. Comparison of Maximum Labeled Use Information with Typical Rates
		 and Number of Applications		

Maximum
Maximum
Number of
Applications


Scenario
Application
Rate
(lbs/acre)
Typical Application Rate
(lbs/acre)
Typical Number of
Applications
Corn
2.0
1
1.1
1.51
Sorghum
2.0
1
1.0
1.71
Fallow/ Idle
2.25
1
1.0
0.9
land
1 - Typical number of applications greater than 1 reflect the impact of multiple applications at less than the
single maximum rate of 2 lbs/acre. An example would be when atrazine is applied as a mixture with
another herbicide but at less than the labeled maximum.
Alternative modeling of the corn scenario using the typical application rate information
was completed (corn yielded the highest non-PCA-adjusted EECs using maximum
application rates specified on the atrazine label). The rates and number of applications
are similar with a typical application rate of 1 lb/acre and 1.1 applications per growing
season (Kaul, et al., 2005). Data reported with 1.1 applications represent an average of
multiple applications applied at lower than maximum rates and are interpreted in this
analysis as a single application. In order to simplify this part of the assessment, the
refined application rate was modeled at 1 lb/acre with one application. Data on 90th
percentile use rates were not available for this assessment. Comparison of typical
applications rates (essentially equivalent to the average of all available reported data)
with monitoring data and modeling with labeled maximum rates is used for
characterization only because a typical, or average, rate implies that a substantial number
of applications may occur above this value. Given the site-specific nature of an
endangered species assessment, it is impossible to rule out the possibility that some
percentage of actual applications are occurring in proximity to the Alabama sturgeon.
However, the results of this analysis show that use of atrazine at the typical application
rates results in a reduction of EECs across the board by a factor of two. The results of
this analysis are summarized in Table 3.16.
Table 3.16. Comparison of Non-PC A-Adjusted Corn EECs Using Maximum and
		Typical Application Rates	
Use Site
Application
Number of
Applications
(interval)
First
Application
Date
90th Percentile of 30 Years of Output
Rate (lbs/acre)
Peak
EEC
(Hg/L)
14-dav
EEC
(Hg/L)
21-day
EEC
(Hg/L)
30-dav
EEC
(Jig/L)
60-dav
EEC
(Jig/L)
90-day
EEC
0ig/L)
Corn
2
1
April 1
103.2
102
101.3
101.1
98.9
95.9
Corn
1
1
April 1
51.8
51.0
50.7
50.5
49.5
48.0
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3.2.6 Summary of Modeling vs. Monitoring Data
Overall, comparison of the monitoring data with the modeling indicates that, in general,
the peak concentrations are reasonably well predicted by modeling with PRZM/EXAMS
for all scenarios and iterations of the modeling; however, the longer-term average
concentrations are over-estimated. For this analysis, only the peak and annual average
(approximated by averaging across the sample range from the monitoring data) from the
monitoring data were comparable to the model output, with the exception of the analysis
from the Heidelberg data. The Heidelberg analysis, although highly uncertain due to the
nature of the interpolation necessary, suggests that in a highly vulnerable watershed, the
longer-term exposures will be less than model predictions for streams and rivers with
even moderate flow rates.
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 Alabama
sturgeon water and stream quality because it serves as a buffer and filters out sediment,
nutrients, and contaminants before they enter the Alabama River watershed. Riparian
vegetation has been shown to be essential in the maintenance of a stable stream (Rosgen,
1996). Destabilization of the stream can have a severe effect on sturgeon 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, 2005; Version 1.2.1), considering use conditions likely to
occur in the Alabama River watershed. 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. The spray drift
component of TerrPlant assumes that 1% and 5% of the application rate deposits in the
receiving area for ground boom and aerial applications, respectively.
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 screening-level 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.
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The following input values were used to estimate terrestrial plant exposure to atrazine
from all uses: solubility = 33 ppm; minimum incorporation depth = 0 (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 and corn/sorghum at 2.0 lb ai/A, and
granular application to residential lawns at 2 lbs ai/A. Although atrazine is also labeled
for forestry use on conifers at an application rate of 4 lb ai/A, EECs for this use were not
modeled because the best available information indicates that atrazine is rarely used in
forestry in Alabama (see Section 3.2.3). However, potential impacts to riparian
vegetation resulting from atrazine use on forestry (should herbicide use patterns on
Alabama forestry change in the future) are discussed as part of the risk description in
Section 5.2.4.
Terrestrial plant EECs for non-granular and granular formulations are summarized in
Table 3.17. EECs resulting from spray drift are derived for non-granular applications
only.
Table 3.17. Screening-Level Exposure Estimates for Terrestrial Plants to Atrazine
Use/ A pp. Rate
(Ibs/aerc)
Application
Method
Total Loading to
Drv Adjacent Areas
(lbs/acre)
Drift EEC (lbs/acre)
Fallow/idle land /
2.25
Aerial
0.16
0.14
Ground
0.07
0.02
Corn and Sorghum /
2.0
Aerial
0.14
0.10
Ground
0.06
0.02
Residential / 2.0
Granular
0.04
NA
For non-granular applications of atrazine, the highest off-target loadings of atrazine
predicted by TerrPlant are approximately 7% of the application rate for dry adjacent
areas. As expected, resulting exposure estimates for terrestrial plants are higher for aerial
than ground boom applications. Granular applications associated with residential use of
atrazine result in estimated exposures, as a percentage of the associated application rate,
of 2% for adjacent areas.
4. Effects Assessment
This assessment evaluates the potential for atrazine to adversely affect the Alabama
sturgeon. As previously discussed in Section 2.7, assessment endpoints for the Alabama
sturgeon include direct toxic effects on the survival, reproduction, and growth of the
sturgeon itself, as well as indirect effects, such as reduction of the prey base and/or
modification of its habitat. Direct effects to the Alabama sturgeon, a freshwater species,
are based on toxicity information for freshwater fish. Given that the Alabama sturgeon's
prey items and habitat requirements are dependent on the availability of freshwater
aquatic invertebrates and aquatic plants, toxicity information for various freshwater
aquatic invertebrates and plants is also discussed. In addition, terrestrial plant data are
used to evaluate indirect effects on the sturgeon via direct effects to terrestrial vegetation
(i.e., riparian habitat) required to maintain acceptable water quality and spawning habitat.
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Acute (short-term) and chronic (long-term) effects toxicity information is characterized
based on registrant-submitted studies and a comprehensive review of the open literature
on atrazine. In addition to registrant-submitted and open literature toxicity information,
indirect effects to the Alabama sturgeon, 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 plant 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 4.4, respectively.
With respect to atrazine degradates, including hydroxyatrazine (HA), deethylatrazine
(DEA), deisopropylatrazine (DIA), and diaminochloroatrazine (DACT), it is assumed
that each of the degradates are less toxic than the parent compound. As shown in Table
4.1, 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 4.1 Comparison of Acute Freshwater Toxicity Values for Atrazine and
Degradates
Substance
Fish LC5„
Daphnid ECs# (|x^/L)
Aquatic Plant EC
Tested
Oig/L)

fag/L)
Atrazine
5,300
3,500
1
HA
>3,000 (no effects at
>4,100 (no effects at
>10,000

saturation)
saturation)

DACT
>100,000
>100,000
No data
DIA
17,000
126,000
2,500


(NOAEC: 10,000)

DEA
No data
No data
1,000
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 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
74

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atrazine with other pesticides are presented in Section A.6 of Appendix A. Synergistic
effects with atrazine have been demonstrated for a number of organophosphate
insecticides including diazanon, 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 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 Alabama sturgeon is addressed as part of the uncertainty
analysis for this effects determination.
4.1 Evaluation of Aquatic Ecotoxicity Studies
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
February 16, 2006. The February 2006 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:
(1)	the toxic effects are related to single chemical exposure;
(2)	the toxic effects are on an aquatic or terrestrial plant or animal species;
(3)	there is a biological effect on live, whole organisms;
(4)	a concurrent environmental chemical concentration/dose or application
rate is reported; and
(5)	there is an explicit duration of exposure.
Data that pass the ECOTOX screen are evaluated along with the registrant-submitted
data, and may be incorporated qualitatively or quantitatively into this endangered species
assessment. In general, effects data in the open literature that are more conservative than
the registrant-submitted data are considered. 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 likely to be greatest when
atrazine concentrations in water equal or exceed approximately 10 to 20 [j,g/L on a
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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 or more conservative than the 10 [j,g/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 Alabama
sturgeon survival, reproduction, and growth) identified in the problem formulation. For
example, endpoints such as behavior modifications are likely to be qualitatively
evaluated, because it is not possible to quantitatively link these endpoints with reduction
in species survival, reproduction, and/or growth (e.g., the magnitude of effect on the
behavioral endpoint needed to result in effects on survival, growth, or reproduction is not
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 G. Appendix G also includes a rationale for rejection of those studies that did
not pass the ECOTOX screen and those that were not evaluated as part of this ESA.
As described in Agency's Overview Document (U.S. EPA, 2004), the most sensitive
endpoint for each taxa is evaluated. For this assessment, evaluated taxa include
freshwater fish, freshwater aquatic invertebrates, freshwater aquatic plants, and terrestrial
plants. Table 4.2 summarizes the most sensitive ecological toxicity endpoints for the
Alabama sturgeon, based on an evaluation of both the submitted studies and the open
literature, as previously discussed. A brief summary of submitted and open literature
data considered relevant to this ecological risk assessment for the Alabama sturgeon is
presented below. Additional information is provided in Appendix A. It should be noted
that Appendix A also includes ecotoxicity data for taxonomic groups that are not relevant
to this assessment (i.e., birds, estuarine/marine fish and invertebrates) because the
Agency is completing endangered species assessments for other species concurrently
with this assessment.
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Table 4.2. Freshwa
ter Aquatic and Terrestrial Planl
Toxicity Profile for Atrazine
Assessment Endpoint
Species
Toxicity Value Used in
Risk Assessment
Citation
IMRID#
(Author &
Date)
Comment
Acute Direct Toxicity to
Sturgeon
Rainbow
trout1
96-hour LC50 = 5,300
(ig/L
Probit slope = 2.72
000247-16
(Beliles and
Scott, 1965)
Acceptable
Chronic Direct Toxicity
to Sturgeon
Brook
trout1
NOAEC = 65 |ig/L
LOAEC = 120 (ig/L
000243-77
(Macek et al.,
1976)
Acceptable: 7.2%
reduction in
length; 16%
reduction in
weight
Indirect Toxicity to
Sturgeon via Acute
Toxicity to Freshwater
Invertebrates (i.e. prey
items)
Midge
48-hour LC50 = 720 |ig/L
Probit slope unavailable
000243-77
(Macek et al.,
1976)
Supplemental:
raw data
unavailable
Indirect Toxicity to
Sturgeon via Chronic
Toxicity to Freshwater
Invertebrates (i.e. prey
items)
Scud
NOAEC = 60 |ig/L
LOAEC = 120 (ig/L
000243-77
(Macek et al.,
1976)
Acceptable: 25 %
reduction in
development of Fi
to seventh instar
Indirect Toxicity to
Sturgeon via Acute
Toxicity to Non-vascular
Aquatic Plants
4 species
of
freshwater
algae
1-week EC50 = 1 |ig/L
000235-44
(Torres &
O'Flaherty,
1976)
Supplemental: 41
to 98% reduction
in chlorophyll
production; raw
data unavailable
Indirect Toxicity to
Sturgeon via Acute
Toxicity to Vascular
Aquatic Plants
Duckweed
14-day EC50 = 37 |ig/L
430748-04
(Hoberg, 1993)
Supplemental:
50% reduction in
biomass; NOAEC
not determined
Indirect Toxicity to
Sturgeon via Acute
Toxicity to Terrestrial
Monocot Plants
Oat
Tier II Seedling
Emergence EC25 = 0.004
lbai/A
420414-03
(Chetram,
1989)
Acceptable:
25% reduction in
dry weight
Indirect Toxicity to
Sturgeon via Acute
Toxicity to Terrestrial
Dicot Plants
Carrot
Tier II Seedling
Emergence EC2s = 0.003
lbai/A
420414-03
(Chetram,
1989)
Acceptable:
25% reduction in
dry weight
1 Used as a surrogate for the Alabama sturgeon.
Toxicity to aquatic fish and invertebrates is categorized using the system shown in Table
4.3 (U.S. EPA, 2004). Toxicity categories for aquatic plants have not been defined.
Table 4
.3. Categories of Acute Toxicity for Aquatic Organisms
LCso (ppm)
Toxicity Category
<0.1
Very highly toxic
>0.1-1
Highly toxic
>1-10
Moderately toxic
>10 - 100
Slightly toxic
> 100
Practically nontoxic
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4.1.1 Toxicity to Freshwater Fish
Freshwater fish toxicity data were used to assess potential direct effects of atrazine to the
Alabama sturgeon. A summary of acute and chronic freshwater fish data, including data
from the open literature, is provided below in Sections 4.1.1.1 through 4.1.1.3.
4.1.1.1	Freshwater Fish: Acute Exposure (Mortality) Studies
Freshwater fish acute toxicity studies were used to assess potential direct effects to the
Alabama sturgeon because the observed range of this species occurs within freshwater of
the Alabama River. Atrazine toxicity has been evaluated in numerous freshwater fish
species, including rainbow trout, brook trout, bluegill sunfish, fathead minnow, tilapia,
zebrafish, goldfish, and carp, and 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 (J,g/L) to slightly (>10,000 to 100,000 (J,g/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 # 000247-16).
No sublethal effects were reported as part of this study. A complete list of all the acute
freshwater fish toxicity data for atrazine is provided in Table A-8 of Appendix A.
4.1.1.2	Freshwater Fish: Chronic Exposure (Growth/Reproduction) Studies
Chronic freshwater fish acute toxicity studies were used to assess potential direct effects
via growth and reproduction to the Alabama sturgeon. Freshwater fish full 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 # 000243-
77). 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.
4.1.1.3 Freshwater Fish: Sublethal Effects and Additional Open Literature
Information
In addition to 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 four available full
life-cycyle studies at concentrations that induced the reported sublethal effects described
below and in Appendix A.
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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]).
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 Alabama sturgeon occurs in freshwater habitats of the Alabama River;
therefore, seawater survival is not a relevant endpoint for potential host fish. 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 [ig/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.
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 Alabama sturgeon (i.e., survival,
growth, and reproduction of individuals). Also, effects on survival, growth, or
reproduction were not observed in the four available full life-cycle studies at
concentrations that induced these reported sublethal effects. Therefore, potential
sublethal effects on fish are evaluated qualitatively in Section 5.2 and not used as part of
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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.
4.1.2 Toxicity to Freshwater Invertebrates
Freshwater aquatic invertebrate toxicity data were used to assess potential indirect effects
of atrazine to the Alabama sturgeon. Direct effects to freshwater invertebrates resulting
from exposure to atrazine may indirectly affect the Alabama sturgeon via reduction in
available food. As previously discussed in Section 2.5, the Alabama sturgeon is a benthic
omnivore, feeding primarily on freshwater invertebrates including aquatic insect larvae.
A summary of acute and chronic freshwater invertebrate data, including data published in
the open literature, is provided below in Sections 4.1.2.1 through 4.1.2.3.
4.1.2.1 Freshwater Invertebrates: Acute Exposure Studies
Atrazine is classified as highly toxic to slightly toxic to aquatic invertebrates. There is a
wide range of EC50/LC50 values for freshwater invertebrates with values ranging from
720 to >33,000 (J,g/L. The freshwater LC50 value of 720 [^g/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 (including the
water flea, scud, stonefly, leech, and snail) are 3,500 [^g/L and higher. 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.
Summary of Reported Acute LC50/EC50 Values in Freshwater Invertebrates
for Atrazine
35000 n
30000 	j	
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
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Figure 4.1. Summary of Reported Acute LC50/EC50 Values in Freshwater
Invertebrates for Atrazine
4.1.2.2	Freshwater Invertebrates: 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), which showed a 25% reduction in
the development of Fi to the seventh instar at atrazine concentrations of 140 |ig/L; the
corresponding NOAEC is 60 |ig/L (MRID # 000243-77). Although the acute toxicity
data for atrazine show that the midge (Chironomus tentans) 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.
4.1.2.3	Freshwater Invertebrates: Open Literature Data
One additional acute study for an underrepresented taxon of freshwater mussels was
located in the open literature. The results of the study by Johnson et al. (1993) suggest
that 48-hour exposures at atrazine concentrations up to 60 mg/L do not affect the survival
of juvenile and mature freshwater mussels, Anodonta imbecilis., therefore, A. imbecilis is
less acutely sensitive to atrazine than other freshwater invertebrates.
4.1.3 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. In the Alabama River, primary
productivity is essential for indirectly supporting the growth and abundance of the
Alabama sturgeon.
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 threshold concentrations, described in
Section 4.2, were used to further characterize potential community level effects to
Alabama sturgeon resulting from potential effects to aquatic plants. A summary of the
laboratory data for aquatic plants is provided in Section 4.1.3.1. A description of the
threshold concentrations used to evaluate community-level effects is included in Section
4.2.
4.1.3.1 Aquatic Plants: 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.
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The Tier II results for freshwater aquatic plants indicate that atrazine causes a 41 to 98%
reduction in chlorophyll production of freshwater algae; the corresponding EC50 value for
four different species of freshwater algae is 1 |ig/L, based on data from a 7-day acute
study (MRID # 000235-44). 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 # 430748-04).
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.
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 theses 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 is
needed to quantify the impact that recovery and resistance would have on aquatic plants.
4.1.4	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.
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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
10 |ig/L aquatic community effect level identified in the 2003 IRED were considered as
part of the open literature search that was completed in February 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.
Community-level effects to aquatic plants that are likely to result in indirect effects to the
rest of the aquatic community, including the Alabama sturgeon, are evaluated based on
threshold concentrations. These screening threshold concentrations, which are discussed
in greater detail in Section 4.2 and Appendix B, 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).
4.1.5 Toxi city to Terre stri al PI ants
Terrestrial plant toxicity data are used to evaluate the potential for atrazine to affect
riparian zone vegetation within the action area for the Alabama sturgeon. Riparian zone
effects may result in increased sedimentation, which may impact the spawning habitat of
the Alabama sturgeon. As previously discussed in Section 2.5, Alabama sturgeon require
strong currents in deep waters over relatively stable substrates for feeding and spawning.
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. However, atrazine is labeled for use
on conifers and softwoods; therefore, effects to evergreens would not be anticipated. In
83

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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 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, so the
range of effects seen from 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
emerged 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 4.4
and 4.5 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.
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.
Table 4.4. Non-target Terrestrial Plant Seedling Emergence Toxicity (Tier II) to
Atrazine
Surrogate Species
% ai
K( '25 / NOAKC (lbs ai/A)
Probit Slope
Knd point Affected
MRU) No.
Author/Year
Study
( iiissitlciition
Monocot - Corn
{Zea mays)
97.7
>4.0/>4.0
No effect
420414-03
Chetram 1989
Acceptable
Monocot - Oat
(Avena sativa)
97.7
0.004/0.0025
red. in dry weight
420414-03
Chetram 1989
Acceptable
Monocot - Onion
(Allium cepa)
97.7
0.009/0.005
red. in dry weight
420414-03
Chetram 1989
Acceptable
Monocot - Ryegrass
(.Lolium perenne)
97.7
0.004/0.005
red. in dry weight
420414-03
Chetram 1989
Acceptable
Dicot - Root Crop - Carrot
(Daucus carota)
97.7
0.003 / 0.0025
red. in dry weight
420414-03
Chetram 1989
Acceptable
Dicot - Soybean
(Glycine max)
97.7
0.19 / 0.025
red. in dry weight
420414-03
Chetram 1989
Acceptable
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Surrogate Species
% al
K( >? / NOAl'X' (lbs ai/A)
l'robit Slope
l ull point Affected
MRII) No.
Author/Year
Study
Classification
Dicot - Lettuce
(Lactuca sativa)
97.7
0.005/0.005
red. in dry weight
420414-03
Chetram 1989
Acceptable
Dicot - Cabbage
(Brassica oleracea alba)
97.7
0.014/0.01
red. in dry weight
420414-03
Chetram 1989
Acceptable
Dicot - Tomato
(Lycopersicon esculentum)
97.7
0.034/0.01
red. in dry weight
420414-03
Chetram 1989
Acceptable
Dicot - Cucumber
(Cucumis sativus)
97.7
0.013/ 0.005
red. in dry weight
420414-03
Chetram 1989
Acceptable
Table 4.5. Non-target Terrestrial Plant Vegetative Vigor Toxicity (Tier II) to
Atrazine
Surrogate Species
% ai
EC2S / NOAEC
(lbs ai/A)
l ull point Affected
MRII) No.
Author/Year
Studv ( lassification
Monocot - Corn
97.7
>4.0/>4.0
No effect
420414-03
Chetram 1989
Acceptable
Monocot - Oat
97.7
2.4 / 2.0
red. in dry weight
420414-03
Chetram 1989
Acceptable
Monocot - Onion
97.7
0.61 / 0.5
red. in dry weight
420414-03
Chetram 1989
Acceptable
Monocot - Ryegrass
97.7
>4.0/>4.0
No effect
420414-03
Chetram 1989
Acceptable
Dicot - Carrot
97.7
1.7 / 2.0
red. in plant height
420414-03
Chetram 1989
Acceptable
Dicot - Soybean
97.7
0.026/0.02
red. in dry weight
420414-03
Chetram 1989
Acceptable
Dicot - Lettuce
97.7
0.33 / 0.25
red. in dry weight
420414-03
Chetram 1989
Acceptable
Dicot - Cabbage
97.7
0.014/0.005
red. in dry weight
420414-03
Chetram 1989
Acceptable
Dicot - Tomato
97.7
0.72 / 0.5
red. in plant height
420414-03
Chetram 1989
Acceptable
Dicot - Cucumber
97.7
0.008/ 0.005
red. in dry weight
420414-03
Chetram 1989
Acceptable
In addition, a report on the toxicity of atrazine to woody plants (Wall et al., 2006; MRID
46870400-01) 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.
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4.2 Community-Level Endpoints: Threshold Concentrations
In this endangered species assessment, direct and indirect effects to the Alabama sturgeon
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 sturgeon does not have an obligate
relationship with any one particular plant species, but rather relies 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 analysis in this assessment is 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
associated with potential aquatic community-level effects (via aquatic plant community
structural change and subsequent habitat modification) to the Alabama sturgeon. 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 Appendix B.
As previously mentioned in Section 2.3, 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 Alabama sturgeon, are evaluated as
described below.
As described further in Appendix B, 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
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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.
To avoid having to routinely run the CASM model, 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 Alabama sturgeon 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 endangered species assessment. 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 Alabama
sturgeon. If modeled atrazine EECs exceed the 14-, 30-, 60- and 90-day threshold
concentrations following refinements of potential atrazine concentrations with available
monitoring data, the CASM model could be employed to further characterize the
potential for indirect effects. A step-wise data evaluation scheme incorporating the use of
the screening threshold concentrations is provided in Figure 4.2. Further information on
threshold concentrations is provided in Appendix B.
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Action Area
Exposure
Profile
Data /
Derive EECs for
various averaging
periods from
modeling data
Peak EEC
> Aquatic
Plant
\pC5q?/
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?,
90-day
AVG.
> 12 ug/L9,
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
4.3 Use of Probit Slope Response Relationship to Provide Information on the
Endangered Species Levels of Concern
The Agency uses the probit dose response relationship as a tool for providing
additional information on the potential for acute direct effects to individual listed species
and aquatic animals that may indirectly affect the listed species of concern (U.S. EPA,
2004). As part of the risk characterization, an interpretation of acute RQ for listed
species is discussed. This interpretation is presented in terms of the chance of an
individual event (i.e., mortality or immobilization) should exposure at the EEC actually
occur for a species with sensitivity to 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 (i.e., freshwater fish used as a surrogate for aquatic-phase amphibians and
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freshwater invertebrates). 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. The upper and lower bounds of the effects probability are based
on available information on the 95% confidence interval of the slope. A statement
regarding the confidence in the estimated event probabilities is also included. 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.
Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1
(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP,
Environmental Fate and Effects Division (June 22, 2004). The model allows for such
calculations by entering the mean slope estimate (and the 95% confidence bounds of that
estimate) as the slope parameter for the spreadsheet. In addition, the acute RQ is entered
as the desired threshold.
4.4 Incident Database Review
A 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 E. 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
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).
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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 E.
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 Alabama sturgeon. The risk
characterization provides an estimation and a description 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
Alabama sturgeon and/or its habitat (i.e., "no effect," "likely to adversely affect," or
"may affect, but not likely to adversely affect").
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5.1 Risk Estimation
Risk was estimated by calculating the ratio of the estimated environmental concentration
(Table 3.4) and the appropriate toxicity endpoint (Table 4.2). 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 F). Screening-level RQs are
based on the most sensitive endpoints and the following surface water concentration
scenarios for atrazine:
•	residential granular use @ 2 lb ai/A; 2 applications with 30 days between
applications (assumes 1% over-application of atrazine granules to impervious
surfaces)
•	residential liquid use @ 1 lb ai/A; 2 applications with 30 days between
applications (assumes 1% over-spray of atrazine to impervious surfaces)
•	turf granular use @ 2 lb ai/A; 2 applications with 30 days between applications
•	turf liquid use @ 1 lb ai/A; 2 applications with 30 days between applications
•	rights-of-way liquid use @ 1 lb ai/A; 1 application (assumes 1% over-spray of
atrazine to impervious surfaces)
•	fallow/idle land use @ 2.25 lb ai/A; 1 application
•	corn use @ 2 lbs ai/A; 1 application
•	sorghum use @ 2 lbs ai/A; 1 application
•	aggregate EEC based on combined agricultural, residential, turf, and rights-of-
way atrazine uses
As previously discussed in Section 3.2.3, RQs were not derived for the forestry use
because available information indicates that atrazine is rarely used on forestry in
Alabama (personal communications with K. McNabb, Auburn University School of
Forestry, and J. Michael, U.S. Forest Service, Southern Research Station, August 2006).
Although the forestry EECs are not used to derive risk quotients, this use pattern is
considered as part of the risk description in Section 5.2 to account for potential changes
in current herbicide use practices on forestry, which may include atrazine in the future.
In cases where the screening-level RQ exceeds one or more LOCs, additional factors,
including Alabama sturgeon life history characteristics, refinement of the EECs using
available monitoring data, and consideration of community-level threshold
concentrations, are considered and used to characterize the potential for atrazine to result
in a "likely to adversely affect" determination for the Alabama sturgeon. Risk
estimations of direct and indirect effects of atrazine to the Alabama sturgeon are provided
in Sections 5.1.1 and 5.1.2, respectively.
As previously discussed in the effects assessment, the toxicity of the atrazine degradates
has been shown to be less than the parent compound based on the available toxicity data
for freshwater fish, invertebrates, and aquatic plants; therefore, the focus of the risk
characterization is parent atrazine (i.e., RQ values were not derived for the degradates).
91

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5.1.1 Direct Effects
Direct effects associated with acute and chronic exposure to atrazine are not expected to
occur for the Alabama sturgeon. RQs used to estimate direct effects to the Alabama
sturgeon are provided in Table 5.1 below. RQs were calculated only for the use that
resulted in the highest EEC (aggregate agricultural and non-agricultural uses) because
none of the acute or chronic LOCs were exceeded. These RQs are further characterized
in Section 5.2.1.
Table 5.1. Summary of Direct Effect RQs for the Alabama Sturgeon
I.ITctI lo
Aliihiiniii
sUiriicon
SuiTo»;i(e
Species
Toxicity
Value (pii/l.)
r.r.c (fiii/i.i
RQ
Pmhiihilil.t of
lndi\ idiuil
ll'lccl
I.OC
r.\ccc(l;iucc
iiiid Risk
Inlorpivliilion
Acute Direct
Toxicity
Rainbow
trout
LCso = 5,300
Peak: 16.3
0.003
1 in 3.0E+11
(1 in 24,100 to 1
in 2.0E+22)3
Nob
Chronic Direct
Toxicity
Brook trout
NOAEC = 65
60-day:
15.8
0.24
Not calculated
for chronic
endpoints
2
o
o
a Based on a probit slope of 2.72 for the rainbow trout with 95% confidence intervals of 1.56 and 3.89
(MRID # 000247-16).
bRQ < acute endangered species LOC of 0.05.
0 RQ < chronic LOC of 1.0.
5.1.2 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.
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 organisms in these taxonomic groups as resources critical to their 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 non-endangered organisms that are critical to the Alabama
sturgeon's life cycle, the concern for indirect effects to the Alabama sturgeon is expected
to be minimal.
If LOCs are exceeded for freshwater invertebrates that are prey items of the Alabama
sturgeon, there is a potential for atrazine to indirectly affect the sturgeon by reducing
available food supply. In such cases, the dose response relationship from the toxicity
study used for calculating the RQ of the surrogate prey item is analyzed to estimate the
probability of acute effects associated with an exposure equivalent to the EEC. The
greater the probability that exposures will produce effects on a taxa, the greater the
92

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concern for potential indirect effects for listed species dependant upon that taxa (U.S.
EPA, 2004).
As an herbicide, indirect effects to the Alabama sturgeon 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 Appendix C, the Alabama sturgeon does
not rely on a specific plant species (i.e., the sturgeon does not have an obligate
relationship with a specific species of aquatic plant).
Direct effects to riparian zone vegetation may also indirectly affect the Alabama sturgeon
by reducing the amount of 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 Alabama sturgeon via potential
indirect effects to the riparian habitat (and resulting impacts to spawning habitat due to
increased sedimentation) is made. Further analysis of the potential for atrazine to affect
the Alabama sturgeon via reduction in riparian habitat includes consideration of the land
use and types of riparian buffers surrounding the Alabama River action area (i.e., forested
versus grassy), toxicity of atrazine to woody plant species, and the relative contribution
of other factors which are likely to cause sedimentation in areas that the sturgeon could
potentially use as spawning habitat.
In summary, the potential for indirect effects to the Alabama sturgeon was evaluated
using methods outlined in U.S. EPA (2004) and described below in Sections 5.1.2.1
through 5.1.2.3.
5.1.2.1 Evaluation of Potential Indirect Effects via Reduction in Food Items
(Freshwater Invertebrates)
Alabama sturgeon feed on a wide range of freshwater insect larvae, as well as
oligochaetes, mollusks, and small fish. The most prevalent larval insect families found in
stomach contents from a limited number of adult Alabama sturgeon specimens were
midges, mayflies, stoneflies, damselflies, dragonflies, and netspinners (Haynes et al.,
2005).	Although data on the relative percentage of each type of aquatic invertebrate in
the sturgeon's diet are unavailable, the available information indicates that they are
opportunistic bottom feeders, preying primarily on aquatic insect larvae (Mayden and
Kuhajda, 1996). Potential indirect effects from direct effects on animal food items (i.e.,
freshwater invertebrates) were evaluated by considering the diet of the Alabama sturgeon
93

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and the effects data for the most sensitive food item (i.e., the midge). The RQs used to
characterize potential indirect effects to the Alabama sturgeon from direct acute and
chronic effects on freshwater invertebrate food sources are provided in Table 5.2.
Table 5.2. Summary of Acute and Chronic RQs Used to Estimate Indirect Effect to
	 the Alabama Sturgeon via Direct Effects on Dietary Items 	
liulirecl
ll'lecl lo
Aliihiiniii
Sturgeon
SuiTo»;i(e
Species
Toxicity
Value (fiii/l.)
r.r.c (pii/i.i
RQ
Pmhiihilil.t of
lndi\ iduiil
IITeel
I.OC
r.\eeed;inee
iind Risk
Inlerpreliilion
Reduced Food
Supply via
Acute Direct
Toxicity to
Invertebrates
Midge
EC50 = 720
Peak: 16.3
0.023
1 in 3.5E+123
Nob
Reduced Food
Supply via
Chronic Direct
Toxicity to
Invertebrates
Scud
NOAEC = 60
21-day:
16.1
0.27
Not calculated
for chronic
endpoints
No0
a Slope information on the toxicity study that was used to derive the RQ for freshwater invertebrates is not
available. Therefore, the probability of an individual effect was calculated using a probit slope of 4.4,
which is the only technical grade atrazine value reported in the available freshwater invertebrate acute
studies; 95% confidence intervals could not be calculated based on the available data (Table A-18). Use of
a probit slope of 4.4 would result in a more conservative estimation of the probability of an individual
effect than the default slope recommended in U.S. EPA (2004a) of 4.5.
bRQ < acute endangered species LOC of 0.05.
0 RQ < chronic LOC of 1.0.
Indirect effects to the Alabama sturgeon based on direct acute and chronic effects to
dietary items are not expected to occur. As shown in Table 5.2, acute and chronic LOCs
are not exceeded for freshwater invertebrates, based on the use that results in the highest
EECs (aggregate agricultural and non-agricultural uses) and the most sensitive food item
of the Alabama sturgeon. These risk quotients are further characterized in Section 5.2.2.
5.1.2.2 Evaluation of Potential Indirect Effects via Reduction in Habitat and/or
Primary Productivity (Freshwater Aquatic Plants)
Potential indirect effects from effects on habitat and/or primary production were assessed
using RQs from freshwater aquatic vascular and non-vascular plant data as a screen. If
aquatic plant RQs exceed the Agency's non-endangered species LOC (because the
Alabama sturgeon relies on multiple plant species), potential community-level effects are
evaluated using the threshold concentrations, as described in Section 4.2. RQs used to
estimate potential indirect effects to the Alabama sturgeon from effects on aquatic plant
primary productivity are summarized in Table 5.3.
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Table 5.3. Summary of RQs Used to Estimate Indirect Effects to the Alabama
Sturgeon via I
>irect Effects on Aquatic Plants
Indirect I.ITccl
lo Aliihiiniii
Sturgeon
I so (;ippl. Method:
nilc: # iippl.: inter\;il
between iippl.)
Pe;ik r.r.Cs
(fiii/i.i
\on-\ iisculiir
pliinl RQ
(i:(,„= 1
HU/I-'I
\ iisculiir
pliinl RQ
ii:c,„ = 3^
I.OC r.\eeed;inee
iiiul Risk
Interpretation
Reduced
Habitat and/or
Primary
Productivity via
Direct Toxicity
to Aquatic
Plants
Aggregate agricultural
and non-agricultural
uses
16.3
16.3
0.44
Yes0
Corn (aerial liquid; 2 lb
ai/A; 1 appl.)
10.1
10.1
0.27
Yes0
Sorghum (aerial liquid;
2 lb ai/A; 1 appl.)
6.2
6.2
0.17
Yes0
Fallow/Idle land (aerial
liquid; 2.25 lb ai/A; 1
appl.)
5.8
5.8
0.16
Yes0
Residential (granular; 2
lb ai/A; 2 appl.; 30 d
interval)
3.0
3.0
0.08
Yes0
Turf (granular; 2 lb
ai/A; 2 appl.; 30 d
interval)
2.7
2.7
0.07
Yes0
Residential and Turf
(ground liquid; 1 lb
ai/A; 2 appl.; 30 d
interval)
2.2
2.2
0.06
Yes0
Rights-of-Way (liquid;
1 lb ai/A; 1 appl.)
2.4
2.4
0.06
Yes0
11 Based on 1-week EC50 value of 1 |ig/L for four species of freshwater algae (MRID # 000235-44).
b Based on 14-day EC50 value of 37 |ig/L for duckweed (MRID # 430748-08).
0 RQ > non-endangered aquatic plant species LOC of 1.0 for non-vascular plants; RQ < non-endangered
plant species LOC of 1.0 for vascular plants. Direct effects to non-vascular aquatic plants are possible.
Further evaluation of the EECs relative to the threshold concentrations (for community-level effects) is
necessary.
Based on the results shown in Table 5.3, LOCs for direct effects to aquatic non-vascular
plants are exceeded for all modeled atrazine use scenarios; however, RQs for aquatic
vascular plants are less than LOCs for all use scenarios. Therefore, atrazine may
indirectly affect the Alabama sturgeon via direct effects on non-vascular aquatic plants
for all modeled use scenarios. However, this screening-level analysis was based on the
most sensitive EC50 value from all of the available freshwater non-vascular plant toxicity
information. No known obligate relationship exists between the Alabama sturgeon and
any single freshwater non-vascular plant species; therefore, endangered species RQs
using the NOAEC/EC05 values for aquatic plants were not derived. Further analyses of
the 14-, 30-, 60-, and 90-day time-weighted EECs relative to their respective threshold
concentrations was completed to determine whether effects to individual non-vascular
plant species would likely result in community-level effects to the Alabama sturgeon.
This analysis is presented as part of the risk description in Section 5.2.3.
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5.1.2.3 Evaluation of Potential Indirect Effects via Reduction in Terrestrial Plant
Community (Riparian Habitat)
Potential indirect effects to the Alabama sturgeon 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 Alabama sturgeon from seedling emergence and
vegetative vigor effects on terrestrial plants within riparian areas are summarized in
Tables 5.4 and 5.5, respectively.
Table 5.4. Non-target Terrestrial Plant Seedling Emergence RQs
Surrogate Species
EC2S
(lbs ai/A)1
EEC
Dry adjacent areas
RQ
Dry adjacent areas
Monocot - Corn
>4.0
Aerial: 0.16
Ground: 0.07
Granular: 0.04

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As shown in Table 5.4, terrestrial plant RQs are above the Agency's LOC for all species
except corn and soybeans. For species with LOC exceedances, RQ values based on aerial
application of atrazine to fallow/idle land at 2.25 lb ai/A range from 4.7 to 53; RQ values
based on an equivalent ground application rate range from 2.1 to 23, a two-fold reduction
as compared to aerial applications. Granular application of atrazine to residential lawns
at 2.0 lb ai/A is also likely to impact terrestrial plants 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 5.5. Non-target Terrestrial Plant Vegetative Vigor Toxicity RQs
Surrogate Species
ec25
(lbs ai/A)1
Drift EEC
(lbs ai/A)
Drift RQ
Monocot - Corn
>4.0
Aerial: 0.11
Ground: 0.02
4.0
Aerial: 0.11
Ground: 0.02

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5.2 Risk Description
The risk description synthesizes an overall conclusion regarding the likelihood of adverse
impacts leading to an effects determination (i.e., "no effect," "may affect, but not likely
to adversely affect," or "likely to adversely affect") for the Alabama sturgeon.
If the RQs presented in the Risk Estimation (Section 5.1) show no indirect effects and
LOCs for the Alabama sturgeon are not exceeded for direct effects, a "no effect"
determination is made, based on atrazine's use within the action area. If, however,
indirect effects are anticipated and/or exposure exceeds the LOCs for direct effects, the
Agency concludes a preliminary "may affect" determination for the Alabama sturgeon.
Following a "may affect" determination, additional information is considered to refine
the potential for exposure at the predicted levels based on additional modeling and
monitoring data, the life history characteristics (i.e., habitat range, feeding preferences,
etc.) of the Alabama sturgeon, and potential community-level effects to aquatic plants.
Based on the best available information, the Agency uses the refined evaluation to
distinguish those actions that "may affect, but are not likely to adversely affect" from
those actions that are "likely to adversely affect" the Alabama sturgeon.
The criteria used to make determinations that the effects of an action are "not likely to
adversely affect" the Alabama sturgeon 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.
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A description of the risk and effects determination for each of the established assessment
endpoints for the Alabama sturgeon is provided in Sections 5.2.1 through 5.2.4.
5.2.1 Direct Effects to the Alabama Sturgeon
Respective acute and chronic RQs of 0.003 and 0.24 (based on aggregate EECs from the
combined agricultural and non-agricultural use scenario) are well below the Agency's
acute and chronic risk LOCs for all modeled uses of atrazine within the action area.
Additional modeling of the residential scenario was completed to account for potential
variability in overspray (1 vs. 10%), percentage of impervious surface (30 vs. 5%), and
percentage of lot treated (50 vs. 75%) (Section 3.2.4.1). The results of the additional
modeling show that overall EECs are increased by no more than a factor of two, when
accounting for overspray, impervious surface, and treated area variability. Assuming
peak and 60-day EECs of 6.0 and 5.6 [j,g/L (derived by multiplying the residential
granular EECs in Table 3.4 by two), respective acute and chronic RQs of 0.001 and 0.09
are also well below the Agency's LOCs.
As previously discussed in Section 3.2.3, RQs for labeled uses of atrazine related to
forestry were not derived as part of the risk estimation because its use within the action
area is considered unlikely, given the available information. However, the forestry use is
considered as part of the risk description in order to characterize an upper bound of
potential exposure, should herbicide forestry use patterns within the action change in the
future. Based on modeled EECs from Table 3.3 for forestry use of atrazine at an
application rate of 4.0 lb ai/A (peak EEC = 46.1 (J,g/L; 60-day EEC = 42.2 (J,g/L),
respective acute and chronic RQs of 0.009 and 0.65 are also less than the Agency's
LOCs.
The Agency, consistent with the Overview Document (U.S. EPA, 2004) and the
alternative consultation agreement with the Services (USFWS/NMFS, 2004a and b),
interprets RQs below the endangered species LOC to be consistent with a finding of no
effect for direct effects on the listed species for the taxa being assessed. To provide
additional information, the probability of an individual mortality to the Alabama sturgeon
was calculated for the acute RQ of 0.003, based on the dose response curve slope from
the acute toxicity study for the rainbow trout of 2.72 (MRID # 000247-16). The
corresponding estimated chance of an individual acute mortality to the Alabama sturgeon
at an RQ level of 0.003 (based on the acute toxic endpoint for surrogate freshwater fish)
is 1 in 300 billion. It is recognized that extrapolation of very low probability events is
associated with considerable uncertainty in the resulting estimates. In order to explore
the possible bounds to such estimates, the upper and lower default values for the rainbow
trout dose response curve slope estimate (95% C.I.: 1.56 to 3.89) were used to calculate
upper and lower estimates of the effects probability associated with the acute RQ. The
respective lower and upper effects probability estimates are 1 in 24,100 (0.004%) and 1
in 2.0E+22 (~5E-21%).
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As discussed in Section 4.1.1.3, 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 fish and anadromous fish.
Consideration of the sublethal data indicates that effects associated with alteration of gill
physiology and endocrine-mediated olfactory functions may occur in anadromous fish
including salmon at atrazine concentrations as low as 0.5 |ig/L (Waring and Moore, 2004;
Moore and Lower, 2001). However, there are a number of limitations in the design of
these studies, which are addressed in detail in Sections A.2.4 of Appendix A, that
preclude quantitative use of the data in this risk assessment. For example, Moore and
Lower (2001) exposed epithelial tissue (after removal of skin and cartilage) and not intact
fish to atrazine, and potential solvent effects could not be reconciled (i.e., no negative
control was tested). Furthermore, no quantitative relationship is established between
reduced olfactory response (measured as electrophysiological 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 recognize and mate with ovulating
females). Other sublethal effects observed in fish studies have included behavioral
modifications, alterations of plasma steroid levels, and changes in kidney histology at
atrazine concentrations ranging from 5 to 35 |ig/L (see Section 4.1.2.3). However, a
number of uncertainties were also identified with each of the studies, which are discussed
in Section A.2.4 of Appendix A.
In summary, it is not possible to quantitatively link the sublethal effects to the selected
assessment endpoints for the Alabama sturgeion (i.e., survival, growth, and reproduction
of individuals). Also, 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). In addition, there are a number of limitations in the design of these
studies, which are addressed in detail in Sections A.2.4a and A.2.4b of Appendix A, that
preclude quantitative use of the data in risk assessment.
In summary, the Agency concludes a "no effect" determination for direct effects to the
Alabama sturgeon, via mortality, growth, or fecundity, based on all available lines of
evidence.
5.2.2 Indirect Effects via Reduction in Food Items (Freshwater Invertebrates)
Respective acute and chronic RQs for freshwater invertebrates of 0.023 and 0.27 (based
on the modeled aggregate EECs from the combined agricultural and non-agricultural use
scenario) are well below the Agency's acute and chronic risk LOCs for all modeled uses
of atrazine within the action area. In addition, acute and chronic RQs based on
residential EECs considering upper bound assumptions of overspray (10%), impervious
surface (5%), and treated area (75%) (peak EEC = 6.0 [j,g/L and acute RQ = 0.008; 21-
day EEC = 5.9 [j,g/L and chronic RQ = 0.98) are also below the Agency's LOCs.
Based on an upper bound assumption of forestry use EECs (peak EEC = 46.1 (J,g/L; 21-
day EEC = 44.7 |ig/L), respective acute and chronic RQs are 0.06 and 0.75. While the
chronic RQ, based on the forestry use, is less than the Agency's LOC, the acute RQ
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exceeds the endangered species LOC of 0.05. Although the available information
indicates that atrazine is not used on forestry within the action area of the Alabama
sturgeon, current usage patterns may change in the future. Therefore, if future use of
atrazine within the action area is modified to include forestry, this use may have the
potential to indirectly affect the Alabama sturgeon via reduction in the availability of
sensitive aquatic invertebrate food items.
However, this analysis was based on the lowest LC50 value 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. Although the midge is a
component of the Alabama sturgeon's diet, this species reportedly consumes a wide
range of freshwater invertebrates that also include oligochaetes, mollusks (Williams and
Clemmer, 1991; USFWS, 2000a), as well as aquatic insect larvae including mayflies,
stoneflies, damselflies and dragonflies, and common netspinners (Haynes et al., 2005).
Although reported acute atrazine toxicity data are not available for many of these food
items, the available information for other freshwater invertebrates that are included in the
Alabama sturgeon's diet (stoneflies and snails) are 6,700 |ig/L and higher.
The potential for atrazine to elicit indirect effects to the Alabama sturgeon via effects on
food items is dependent on several factors including: (1) the potential magnitude of effect
on freshwater invertebrate individuals and populations; and (2) the number of prey
species potentially affected relative to the expected number of species needed to maintain
the dietary needs of the Alabama sturgeon. Together, these data provide a basis to
evaluate whether the number of individuals within a prey species is likely to be reduced
such that it may indirectly affect the Alabama sturgeon. Table 5.6 presents acute RQs
and the probability of individual effects for dietary items of the Alabama sturgeon
including stoneflies and snails. The species sensitivity distribution of all acute toxicity
data for freshwater aquatic invertebrates tested is represented in Figure 4.1. This analysis
considers only acute risk to aquatic invertebrate food items because chronic RQs for
invertebrates were less than the Agency's LOC, based on EECs assuming forestry use of
atrazine at 4.0 lb ai/A.
Table 5.6. Summary of RQs Used to Assess Potential Risk to Freshwater
Invertebrate Food Items of the Alabama Sturgeon Based on Forestry Use of
Atrazine
Alabama Sturgeon
Food Item Species
Acute
Toxicity
Value Range
Qig/L) (No. of
Studies)
RQ Range
(based on
an EEC of
46.1 jig/L)
Probability of
Individual
Effect*
Risk Interpretation
Midge
720 - >33,000
(5)
<0.01-0.06
Up to 1 in
1.34E+07
Atrazine may affect sensitive food
items, such as the midge; however
the low probability of an individual
effect to the midge is not likely to
indirectly affect the Alabama
sturgeon via reduction in midge
prey items.
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Stonefly
6,700 (1)


RQs are well below acute LOCs,


<0.01
Up to 1 in
which are interpreted to represent no
direct effect; therefore, atrazine is
Snail
>16,000 (1)
1.4E+21
not likely to indirectly affect the
Alabama sturgeon via reduction in
stonefly or snail prey items.
*The probability of an individual effect was calculated using a probit slope of 4.4, which is the only
technical grade atrazine value reported in the available freshwater invertebrates studies; 95% confidence
intervals could not be calculated based on the available data (Table A-18).
As shown in Table 5.6, the listed species LOC, based on forestry use of atrazine, is
exceeded for the midge (RQ = 0.06), based on the LC50 value of 720 (J,g/L. However,
acute RQs based on the other acute toxicity data for the midge are <0.05, less than the
acute risk to endangered species LOC. Sufficient dose-response information was not
available to allow for an estimation of the probability of an individual effect on the
midge. Therefore, the probability of an individual effect was calculated using a probit
dose response curve slope of 4.4; this is the only slope for technical grade atrazine
reported in available ecotoxicity data for freshwater invertebrates (MRID # 452029-17).
Based on a probit slope of 4.4, the probability of an individual mortality to the midge at
an RQ of 0.06 is approximately 1 in 13.4 million (7.46E-06%).
Acute LOCs are not exceeded for other dietary items of the Alabama sturgeon including
the stonefly and snail, based on the forestry use of atrazine. As previously discussed, the
upper bound forestry use EEC, upon which the acute LOC exceedance is based, is likely
to overestimate exposure; therefore, use of this EEC to derive RQs is also likely to result
in overestimation of risk to potential food items of the Alabama sturgeon.
Based on the non-selective nature of feeding behavior in the Alabama sturgeon, the low
magnitude of anticipated individual effects to all evaluated prey species, and the
likelihood that EECs assuming forestry use of atrazine overestimate exposure, atrazine is
not likely to indirectly affect the Alabama sturgeon via a reduction in freshwater
invertebrate food items. This finding is based on insignificance of effects (i.e., effects to
freshwater invertebrates are not likely to result in "take" of a single Alabama sturgeon).
Therefore, the effects determination for the assessment endpoint of indirect effects on the
Alabama sturgeon via direct effects on prey (i.e., freshwater invertebrates) is "may affect,
but not likely to adversely affect."
5.2.3 Indirect Effects via Reduction in Habitat and/or Primary Productivity (Freshwater
Aquatic Plants)
Direct adverse effects to non-vascular aquatic plants are possible, based on all modeled
atrazine uses within the action area. Based on these direct effects, atrazine may indirectly
affect the Alabama sturgeon via direct effects on aquatic plants. Therefore, the time-
weighted EECs (for 14-day, 30-day, 60-day, and 90-day averages) were compared to
their respective time-weighted threshold concentrations to determine whether potential
effects to individual plant species would likely result in community level effects. 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
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threshold concentrations indicate that changes in the aquatic plant community structure
could be affected:
•	14-day average = 38 [^g/L
•	30-day average = 27 [^g/L
•	60-day average =18 [^g/L
•	90-day average =12 [^g/L
A comparison of the 14-, 30-, 60-, and 90-day EECs for the Alabama sturgeon with the
atrazine threshold concentrations representing potential aquatic community-level effects
is provided in Table 5.7.
Table 5.7. Summary of Modeled Scenario Time-Weighted EECs with Threshold
		Concentrations for Potential Community-Level Effects	
Use Scenario
14-dav
30-dav
60-dav
90-dav
EEC
(Jig/L)
Threshold
Cone.
(Hg/L)
EEC
(Jtg/L)
Threshold
Cone.
(Hg/L)
EEC
(Jig/L)
Threshold
Cone.
(Hg/L)
EEC
(jig/L)
Threshold
Cone.
(Jig/L)
Aggregate
agricultural
and non-
agricultural
uses
16.2
38
16.1
27
15.8
18
15.7
12
Corn
10.0
9.9
9.7
9.4
Sorghum
6.2
6.0
5.8
5.6
Fallow / idle
land
5.7
5.6
5.5
5.4
Res.
(granular)
(1%0S/
10% OS)
2.9/
5.8
2.9/
5.8
2.8/
5.6
2.7/
5.4
Res. and Turf
(liquid)
2.2
2.1
2.1
2.0
Turf
(granular)
2.7
2.7
2.6
2.6
Rights-of-
Way
2.4
2.4
2.3
2.2
Forestry
45.2
44.1
42.2
40.8
OS = overspray
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Based on the results of this comparison, predicted 14-, 30-, 60-, and 90-day EECs for all
modeled individual uses (including residential scenarios that consider overspray) are less
than their respective threshold concentrations, with the exception of the forestry use and
90-day EECs for the combined agricultural and non-agricultural uses. Although
predicted EECs for the forestry and aggregate scenarios exceed thresholds of concern for
community level effects, these EECs were estimated using PRZM/EXAMS and the non-
flowing standard water body scenario, which is intended to be representative of
exposures in headwater streams. As previously discussed in Section 3.2.4.2, these
chronic EECs are expected to over-estimate exposure in water bodies with flowing water,
including the current range of the Alabama sturgeon in the Alabama River between the
Millers Ferry Dam and Lock and the junction with the Tombigbee River, as well as the
main tributaries of the Alabama River. Alabama sturgeon require strong currents in deep
waters over relatively stable substrates for feeding and spawning (Appendix C);
therefore, chronic EECs based on a non-flowing water body are expected to over-
estimate actual exposure concentrations of atrazine for the sturgeon in its expected range.
Additional information on the impact of flowing water on the modeled EECs, including
available monitoring data, was used to refine exposure concentrations of atrazine for the
Alabama sturgeon, relative to those presented for the standard water body scenario. This
analysis was presented in detail in Sections 3.2.4.2 and 3.2.4.3 and is summarized below
in Section 5.2.3.1 for the Alabama sturgeon.
5.2.3.1 Additional Characterization of EECs in Flowing Streams and Rivers
Given that the range of the Alabama sturgeon is reported to occur in the flowing waters
of the Alabama River and its main tributaries between the Millers Ferry Dam and Lock
and the junction with the Tombigbee River, EECs derived from the standard ecological
water body are not likely to be representative of actual chronic exposure concentrations.
Chronic exposure concentrations estimated using the standard ecological water body
pond are not representative of the Alabama River and its main tributaries because the
River and its main tributaries are flowing water bodies, subject to extensive mixing and
dilution. In contrast, the standard ecological water body is a static water body.
As described in Section 3.2.4.2, the Agency performed a number of additional modeling
exercises to allow for characterization of potential effects of flow rate on the EECs. This
analysis, together with monitoring data (presented in Section 3.2.4.3), was used to further
characterize and refine potential exposures associated with future forestry use of atrazine
to the Alabama sturgeon.
First, the Agency's variable volume water model (VVWM) was used to account for the
influence of input and output (flow) on model predictions. The Agency conducted two
alternate model runs with the VVWM. The first was conducted using standard
assumptions and environmental fate parameters that are generally consistent with the
non-flowing standard water body. The second assumption was designed to represent a
larger volume water body that maximizes flow into the water body.
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Second, the impact of various flow rates was characterized using the Index Reservoir (IR)
as the receiving water body. Standard and non-standard flow assumptions considered
representative of the Alabama River watershed where the sturgeon is located were used
to derive alternative EECs based on the IR approach.
The net effect of the additional VVWM modeling was to reduce the longer-term average
exposure concentrations by approximately 4 times, based on a water depth of 10 meters.
Refined long-term average EECs, based on the IR modeling and 7Q10 flow rates for the
Alabama River watershed, are reduced by approximately 50 to 200 times, as compared to
EECs derived using the static water body model (see Table 4.9).
In addition to the modeling exercises, The Agency used existing monitoring data to
further characterize atrazine concentrations in the Alabama River. For data specific to
the Alabama River, the results indicate a much lower overall atrazine concentration
picture relative to both the statewide and national trends. The maximum concentration of
atrazine detected in the Alabama River was 0.142 |ig/L and the overall average was 0.046
[j,g/L. A detailed description of these data is provided in Section 3.2.4.3.
A summary of the refined EECs, which consider both flowing water bodies and the
available monitoring data, relative to the community-level effect threshold concentrations
is provided in Table 5.8.
Table 5.8. Summary of Alternative Modeling (assuming flow) and Available
		Monitoring Data	
Analvsis
Results
Modeling using WWM
Refined 14-, 30-, 60-, and 90-day EECs for the forestry use
scenario (EECs are reduced by a factor of approximately four) are
less than their respective community-level threshold
concentrations.
Modeling using Index Reservoir
and various flow rates
EECs decrease as flow rate increases. Flow rates representative of
the Alabama River result in EECs that are well below the
community-level threshold concentrations.
Monitoring data, Alabama River
The maximum atrazine concentration detected in the Alabama
River was 0.142 |ig/L and the overall average was 0.046 |ig/L.
well below the community-level threshold concentrations.
Monitoring, other representative
water bodies
High peak atrazine concentrations have been observed; however,
longer-term (14- to 90-day) exposure durations (when the data
allow for calculation) are in the low |ig/L range, well below the
community-level threshold concentrations.
Collectively, the refined modeling considering flow and the available monitoring data for
the Alabama River suggest that atrazine concentrations in the River and its main
tributaries are expected to be in the low [j,g/L range, well below the 14-, 30-, 60-, and 90-
day threshold concentrations for community-level effects.
Although atrazine use may directly affect individual aquatic non-vascular plants in the
Alabama River, its use within the action area is not likely to adversely affect the Alabama
sturgeon via indirect community-level effects to aquatic vegetation. This finding is based
on insignificance of effects (i.e., community-level effects to aquatic plants are not likely
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to result in "take" of a single Alabama sturgeon). Therefore, the effects determination for
the assessment endpoint of indirect effects on the Alabama sturgeon via direct effects on
habitat and/or primary productivity of aquatic plants is "may affect, but not likely to
adversely affect."
5.2.4 Indirect Effects via Alteration in Terrestrial Plant Community (Riparian Habitat)
As shown in Tables 5.4 and 5.5, seedling emergence and 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 and soybeans, 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 existing vegetation may be affected, or inhibition
of new growth may occur. Inhibition of new growth could result in
degradation of high quality riparian habitat over time because as older growth
dies from natural or anthropogenic causes, plant biomass may be prevented
from being replenished in the riparian area. Inhibition of new growth may
also slow the recovery of degraded riparian areas that function poorly due to
sparse vegetation because atrazine deposition onto bare soil would be
expected to inhibit the growth of new vegetation.
•	Because LOCs were exceeded for most species tested (8/10) in the seedling
emergence studies, it is likely that many species of herbaceous plants may be
potentially affected by exposure to atrazine in runoff.
A number of dicots in riparian habitats may also be impacted via foliar exposure from
atrazine in spray drift as evidenced by vegetative vigor LOC exceedances in three dicots.
Therefore, riparian habitats comprised of herbaceous plants sensitive to atrazine may be
adversely affected by spray drift. However, comparison of the seedling emergence and
vegetative vigor RQs indicates that runoff, and not spray drift, is a larger contributor to
potential risk for riparian vegetation. Vegetative vigor risk quotients were not exceeded
for monocots; therefore, drift would not be anticipated to affect riparian zones comprised
primarily of monocot species such as grasses.
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 loss of available
spawning habitat. Therefore, an analysis of the potential for habitat degradation to affect
the sturgeon is necessary. In addition, if forestry uses of atrazine are considered (at an
application rate of 4.0 lb ai/A), the RQ values shown in Tables 5.4 and 5.5 would be
expected to increase by a factor of approximately two.
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Riparian plants beneficially affect water and stream quality in a number of ways
(discussed below) in both adjacent river reaches and areas downstream of the riparian
zone. Atrazine use in the area of the Alabama sturgeon's range, below the Millers Ferry
Lock and Dam, downstream to the mouth of the Tombigbee River (Figure 2.4), may
potentially affect the sturgeon by impacting riparian vegetation and subsequently causing
sedimentation that results in degraded water quality and reduction of available spawning
habitat. Although the watershed above the Millers Ferry Lock and Dam is included in the
action area for this assessment, the focus of impacts to riparian vegetation is limited to
the areas adjacent to the Lower Alabama River, downstream of the dam. Given the
presence of the Millers Ferry Lock and Dam, sedimentation resulting from impacts to
riparian areas is likely to be limited to the area downstream of the dam in the area of the
Alabama sturgeon's range.
As shown in Figure 2.2, the majority of agricultural cropland in the Alabama River Basin
watershed is restricted to areas well upstream from the range of the Alabama sturgeon.
The land adjacent to the Lower Alabama River surrounding the habitat range of the
Alabama sturgeon contains only a small percentage of area devoted to cropland, and
available information indicates that cropped riparian zones do not exist in the Lower
Alabama River watershed (Michael, personal communication, 2006). Within the entire
action area for the Alabama sturgeon (including upstream and downstream of the Millers
Ferry Lock and Dam), the total percentage of cropland is approximately 9.8%.
Therefore, atrazine is not likely to impact cropped riparian zones because they are
unlikely to occur on land adjacent to the Lower Alabama River watershed. According
the Alabama River Basin Management Plan (Kleinschmidt, 2005), land use in the
Alabama River Basin watershed is dominated by forests (67%), with pastureland at 17%
and cropland at 9%. Approximately 98 to 99% of land use in the Lower Alabama River
Basin is rural in nature.
A general discussion of riparian habitat and its relevance to the Alabama sturgeon is
discussed in Section 5.2.4.1. Forested riparian zones that may be potentially impacted by
atrazine use in the Alabama River are discussed in Section 5.2.4.2, and sediment loading
in the Lower Alabama River watershed and the potential risks to the Alabama sturgeon
caused by atrazine-related impacts to riparian vegetation are discussed in Section 5.2.4.3.
5.2.4.1 Importance of Riparian Habitat to the Alabama Sturgeon
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 shading, which ensures thermal stability of the stream; and
•	serves as a buffer, filtering out sediment, nutrients, and contaminants before
they reach the stream.
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The specific characteristics of a riparian zone that are optimal for the Alabama sturgeon
are expected to vary with developmental stage, the use of the reach adjacent to the
riparian zone, and the hydrology of the watershed. Criteria developed by Fleming et al.
(2001) have been used to assess the health of riparian zones and their ability to support
fish habitat. These criteria, which include the width of vegetated area (i.e. distance from
cropped area to water), structural diversity of vegetation, and canopy shading, are
summarized in Table 5.9.
Table 5.9. Criteria for Assessing the Health of Riparian Areas to Support Aquatic
	 Habitats (adapted from Fleming et al. 2001)	
Criteria
Quality
Excellent
Good
Fair
Poor
Buffer width
>18m
12 - 18m
6 - 12m
<6m
Vegetation diversity
>20 species
15-20 species
5-14 species
<5 species
Structural diversity
3 height classes
grass/shrub/tree
2 height classes
1 height class
sparse vegetation
Canopy shading
mixed sun/shade
sparse shade
90% sun
no shade
To maintain at least "good" water quality for fish in general, riparian areas should contain
at least a 12 m (-40 feet) wide vegetated area, 15 plant species, vegetation of at least two
height classes, and provide at least sparse shade (>10% shade). In general, higher quality
riparian zones (wider vegetated areas with greater plant diversity) are expected to have a
lower probability of being significantly affected by atrazine than poor quality riparian
areas (narrower areas with less vegetation and little diversity).
The following three attributes of riparian vegetation habitat quality were evaluated for
this assessment: water temperature, stream bank stability, and sediment loading. Each of
these attributes is discussed briefly below.
Streambank Stabilization: Riparian vegetation typically consists of three distinct types of
plants, which include a groundcover of grasses and forbs, an understory of shrubs and
young trees, and an overstory of mature trees. These plants serve as structural
components for streams, with the root systems helping to maintain stream stability, and
the large woody debris from the mature trees providing instream cover. Riparian
vegetation has been shown to be essential to maintenance of a stable stream (Rosgen,
1996). Destabilization of the stream can have a severe impact on aquatic habitat quality.
Following a disturbance, the stream may widen, releasing sediment from the stream
banks and scouring the stream bed. Destabilization of the stream can have severe effects
aquatic habitat quality by increasing sedimentation within the watershed. The effects of
sedimentation are summarized below.
Sedimentation: Sedimentation refers to the deposition of particles of inorganic and
organic matter from the water column. Increased sedimentation is caused primarily by
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disturbances to river bottoms and streambeds and by soil erosion. Riparian vegetation is
important in moderating the amount of sediment loading from upland sources. The roots
and stems of riparian vegetation can intercept eroding upland soil (USDANRCS, 2000),
and riparian plant foliage can reduce erosion from within the riparian zone by covering
the soil and reducing the impact energy of raindrops onto soil (Bennett, 1939).
According to the USFWS Recovery Plan of the Mobile River Basin Aquatic Ecosystem
(USFWS, 2000b), sedimentation is considered the greatest factor threatening the aquatic
ecosystems across the basin. Sediment loading alters streambeds, transports pollutants
and nutrients, smothers and kills benthic plants and animals, and eliminates suitable
breeding and foraging habitat for mobile species (e.g., fish, turtles, snails) (USFWS,
2000b). Increased sedimentation may affect spawning by settling on spawning gravel
and reducing flow of water and dissolved oxygen to the eggs and fry (Everest et al.,
1987). In addition, fine particles settling on the streambed can also disrupt the food chain
by reducing habitat quality for aquatic invertebrates, and adversely affect groundwater-
surface water interchange (Nelson et al., 1991). Increased turbidity from sediment
loading may also reduce light transmission, potentially affecting aquatic plants (Cloern,
1987; Weissing and Huisman, 1994) that are important for shelter and food.
Thermal stability. Riparian habitat provides stream shading resulting in thermal
stability. While thermal stability is generally considered to be an important variable for
most river sturgeons (Scaphirhynchus spp.) (USFWS, 2000a), the sensitivity of the
Alabama sturgeon to fluctuations in temperature is unknown.
5.2.4.2 Sensitivity of Forested Riparian Zones to Atrazine
Available land use information from the Alabama Soil and Water Conservation
Committee (SWCC), as shown in Figure 5.1, indicates that the majority of land
surrounding the Lower Alabama River watershed is forestland. The area defined as
"forestland" is expected to include land that is commercially harvested (i.e., plantations),
as well as undisturbed forested areas that are not harvested. As shown in Figure 5.2,
forested land cover data for the Lower Alabama River watershed shows that the land
adjacent to the current range for the Alabama sturgeon is dominated by forested wetlands
and deciduous and evergreen forest, with very little herbaceous riparian area (USGS,
2004).
As previously summarized in Table 5.9, the parameters used to assess riparian quality
include buffer width, vegetation diversity, vegetation cover, structural diversity, and
canopy shading. Buffer width, vegetation cover, and/or canopy shading may be reduced
if atrazine exposure impacts plants in the riparian zone or prevents new growth from
emerging. Plant species diversity and structural diversity may also be affected if only
sensitive plants are impacted (Jobin et al., 1997; Kleijn and Snoeijing, 1997), leaving
non-sensitive plants in place. Atrazine may also affect the long term health of high
quality riparian habitats by affecting seed germination. Thus, if atrazine exposure
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impacted these riparian parameters, water quality within the Lower Alabama River
watershed could be affected.
SWCC Alabama River Selected Watersheds
Land Use Break Down
	Alabama Sturgeon Range
O Miller's Ferry Lock and Dam
Selected Watersheds Land Use

¦ CROPLANDS
PASTURELAND
| FORESTLAND
| URBAN LAND
| PONDS AND LAKES
| MINED LANDS
OTHER LANDS
Alabama River
Figure 5.1. Land Use Within the Range of the Alabama Sturgeon
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Forested Land in the Vicinity of the
Alabama River below Millers Ferry Dam


•n O"


Dams
Alab ama_R Krer_D rain age JO utline
Deciduous forest
Evergreen forest
Mfc
-------
Because woody plants are generally not sensitive to environmentally-relevant atrazine
concentrations (MRID 46870400-01), effects on shading, streambank stabilization, and
structural diversity (height classes) of woody forested vegetation are not expected.
Effects are expected to be limited to herbaceous (non-woody) plants, which are not
generally associated with shading or considered to represent vegetation of higher height
classes. Therefore, plant diversity, vegetation cover, and buffer width are expected to be
the most sensitive riparian quality criteria for herbaceous plants.
The riparian health criteria described in Fleming et al. (2001; Table 5.9) and the
characteristics associated with effective vegetative buffer strips suggest that healthy
riparian zones would be less sensitive to the impacts of atrazine runoff than poor riparian
zones. Although riparian zones rich in species diversity and woody species may contain
sensitive species, it is unlikely that they would consist of a high proportion of very
sensitive plants. Wider buffers have more potential to reduce atrazine residues over a
larger area, resulting in lower levels. In addition, trees and woody plants in a healthy
riparian area act to filter spray drift (Koch et al., 2003) and push spray drift plumes over
the riparian zone (Davis et al., 1994), thus reducing exposure to herbaceous plants, which
tend to be more sensitive. Therefore, high quality riparian zones are expected to be less
sensitive to atrazine than riparian zones that are narrow, low in species diversity, and
comprised of young herbaceous plants or unvegetated areas. The available data suggest
that riparian zones comprised largely of herbaceous plants and grasses would likely be
most sensitive to atrazine effects. However, as shown in Figure 5.2, there is little, if any,
riparian area that is composed predominantly of herbaceous vegetation located adjacent
to the Lower Alabama River watershed. Bare ground riparian areas could also be
adversely affected by prevention of new growth of grass, which can be an important
component of riparian vegetation for maintaining water quality.
Although atrazine is rarely used in commercial forestry in Alabama (Michael, personal
communication, 2006; McNabb, personal communication, 2006), its use within the
Lower Alabama River watershed and potential impacts to riparian vegetation are
qualitatively evaluated. Herbicides are used in forest management primarily to enhance
reforestation on areas that have been recently harvested. As part of site preparation,
herbicide treatments are applied to bare ground after harvest and before trees are planted
(or naturally regenerated) to control woody vegetation and fast-growing herbaceous
plants that can kill or suppress the growth of planted tree seedlings (Wagner et al., 2004).
If atrazine is applied to bare pine plantation areas (as part of site preparation) that are in
close proximity to the Lower Alabama River watershed, water quality could be impacted.
The best available information indicates that riparian areas adjacent to the watershed are
forested; however, the forested vegetation within these areas is not harvested as part of
forestry operations (i.e., plantations) (Michael, personal communication, 2006). The
forest land cover map (Figure 5.2), which shows that the area directly adjacent to the
watershed is predominantly forested wetland, provides additional evidence that areas
directly adjacent to the watershed are not harvested. In addition, Best Management
Practices (BMPs), specified by the Alabama Forestry Commission, recommend
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streamside management zones (SMZs) for forestry in Alabama. A SMZ is a strip of land
(approximately 35 to 100 feet wide) immediately adjacent to a water of the state where
soils, organic matter, and vegetation are managed to protect the physical, chemical, and
biological integrity of the surface water adjacent to and downstream from forestry
operations (Alabama Forestry Commission, 1993). SMZs are used to: 1) reduce channel
and floodplain erosion, 2) control deposition of pollutants directly into waters of the state,
3) maintain biological integrity of aquatic ecosystems, and 4) retain the capability of the
forest floor to filter out pollutants from upland runoff (Alabama Forestry Commission,
1993). In its BMP guidance document, the Alabama Forestry Commission (1993)
specifies that herbicides should not be used within SMZs. Although SMZs are not
legally required within the state of Alabama, use of this BMP within forestry plantation
management is generally followed in areas surrounding the Alabama River Basin
watershed (Michael, personal communication, 2006). In addition, labeling requirements
for atrazine specify no use within 66 feet of intermittent and perennial streams.
Given the forested nature of the riparian zone adjacent to the Lower Alabama River
watershed, the low sensitivity of woody plants to atrazine, the existence of recommended
BMPs (i.e., SMZs) adjacent to the watershed, and existing atrazine labels requiring
setbacks for applications near water bodies, it is unlikely that atrazine will adversely
affect forested vegetation in the area of the Lower Alabama River watershed.
5.2.4.3 Sediment Loading in the Lower Alabama River Watershed and the
Potential for Atrazine to Affect the Alabama Sturgeon via Effects on Riparian Vegetation
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 Alabama sturgeon. 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 Alabama sturgeon is precluded by the following factors:
•	Locations of Alabama sturgeon spawning habitat within the Lower Alabama
River watershed are not known;
•	The relationship between distance of soil input into the river and sediment
deposition in spawning areas critical to survival and reproduction of the Alabama
sturgeon is not known; and
•	Riparian areas are highly variable in their composition and location with respect
to atrazine use; therefore, their sensitivity to potential damage is also variable.
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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). Specifically, the construction of dams and
locks in the Alabama River watershed is a critical factor that impacts water quality for the
Alabama sturgeon. Thus, the effect of atrazine on riparian community structure would be
expected to be one influence complicated by a myriad of other factors. Although the data
do not allow for a quantitative estimation of risk from potential riparian habitat alteration,
a qualitative discussion is presented below.
The magnitude of potential impacts of atrazine use on riparian habitat within the Lower
Alabama River watershed and resulting indirect effects to Alabama sturgeon water
quality via sedimentation and destruction of available spawning habitat are evaluated by
considering the dominant forestry land use within the area, available data on sediment
loading contributions from all potential sources of erosion within the Lower Alabama
River watershed, and a study of the potential impact of annual dredging activities on the
Alabama sturgeon.
Data on sediment loading estimates (in units of tons per year) are available from the
Alabama SWCC database that is published on the web
(www.swcc.state.al.us/watershedmenu.htm; July 31, 2006). Alabama Department of
Environmental Management data for 2002 indicate that woodlands are the dominant
source of sediment (27%) to the Lower Alabama River Basin, followed by cropland
(18%), dirt roads and road banks (15%), and sand and gravel pits (13%). Estimated
sources of sediment loading into the Lower Alabama River watershed, based on data
compiled by the Alabama SWCC, are depicted in Figure 5.3. SWCC data on each of the
subwatersheds of the Lower Alabama River show that the management practices
associated with woodlands/forestry account for the majority of sedimentation (>75%)
into the Lower Alabama River. Intensive forest management practices, particularly road
building, harvesting and mechanical site preparation, result in the greatest increases in
erosion from forest sites. The most used type of mechanical site preparation is shear and
pile (Prince, 2003). In this method, a tractor is used to cut down residual tree stands,
using a shear blade, followed by a second tractor that uses a root rake to move the residue
into piles or windrows. The available studies on the impact of mechanical versus
chemical (i.e., herbicide) site-preparation for forestry show that use of mechanical site
preparation methods result in 20 to 400% more sediment than observed on paired sites
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'	
	\
0
Miller's Ferry Lock and Dan'
	
Sturgeon Range


~
CROPLANDS
1 1
SAND AND GRAVEL

MINED LAND

DEVELOPING LAND
~
CRITICAL AREA LAND
~
GULLIES

STREAMBANKS

DIRTROADS

WOODLANDS
-
J
SWCC Estimated Sources of Sediment Loading
by Watershed
&
.m
Alabama River
Figure 5.3. Estimated Sources of Sediment Loading into the Lower Alabama
River
which are prepared with herbicides (Michael et al., 2000). Therefore, the best available
information shows that the primary source of sedimentation into the Lower Alabama
River is from woodland and forestry management practices, consistent with the majority
of land use for the surrounding area.
Although forestry management practices are likely to contribute the largest percentage of
sediment loads from land-based activities, the impacts of dredging on potential
sedimentation loading to the Lower Alabama River within the habitat range of Alabama
sturgeon are also evaluated.
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In 1994, the Services and the U.S. Army Corp of Engineers reviewed the anticipated
impacts of a variety of activities in the Lower Alabama River to the Alabama sturgeon in
a document that has become widely known as the White Paper (Biggins, 1994).
Specifically, the impact of annual dredging required to maintain navigation channels in
the Lower Alabama River was evaluated. Maintenance dredging continues to be
necessary to remove the accumulated material (i.e., unconsolidated substrates) that settles
in slower current depositional areas in the Lower Alabama River. Based on the findings
of 1994 White Paper, maintenance dredging and disposal activities in the Lower Alabama
River had no effect on the Alabama sturgeon. The available information indicates that
Alabama sturgeon require strong currents over relatively stable substrates for feeding and
spawning (USFWS, 2000a). As such, they are not likely to be present in shallow, slower
current areas with unconsolidated substrates, where dredging occurs annually to maintain
navigation. Therefore, removal and disposal of unconsolidated materials is not perceived
as a threat to the sturgeon or to its feeding or spawning habitat. Furthermore, the
following activities, which do not include labeled pesticide use, are listed in the 1994
White Paper as having the potential to result in a "take" of the Alabama sturgeon:
1.	Illegal collection of the Alabama sturgeon;
2.	Unlawful destruction or alteration of the Alabama sturgeon's habitat (e.g.,
un-permitted instream dredging, channelization, discharge of fill material);
and
3.	Illegal discharge or dumping of toxic chemicals or other pollutants into
waters supporting the Alabama sturgeon.
Despite the findings of the 1994 White Paper, the USFWS maintains that dredging
activities have the potential to permanently alter or degrade habitat quality for the
Alabama sturgeon (USFWS, 2000b). More importantly, the construction of dams and
locks is recognized as the major contributing factor to the extinction and impediment of
listed aquatic species, including the Alabama sturgeon, in the Alabama River Basin
(USFWS, 2000b). Impoundments fragment habitat, change flow regimes, increase
sedimentation, and limit the movement of species within the ecosystem. Other activities
that permanently alter or degrade habitat quality include channelization of streams, in-
stream mining, and point source wastewater discharges. Lastly, any increases in
intensive land-based activities that promote erosion (e.g., deforestation, road and building
construction, mining) exacerbate sedimentation in streams and rivers and may potentially
lead to habitat degradation for the Alabama sturgeon (Kleinschmidt, 2005).
As previously discussed, the potential for atrazine to affect the Alabama sturgeon via
impacts on riparian vegetation depends primarily on the extent of sensitive (herbaceous
and grassy) riparian zones and its impact on water quality in the Lower Alabama River
watershed. The extent to which herbaceous or grassy riparian areas are present in the
area surrounding the Alabama sturgeon's range is expected to be minimal (see Figure
5.2). Forested riparian areas are more prevalent, given the dominant forested land use
surrounding the watershed. Because woody plants are generally not sensitive to atrazine,
impacts to forested riparian vegetation adjacent to atrazine use areas (and resulting
sedimentation) are unlikely to occur In addition, the majority of sediment loading into
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the Lower Alabama River watershed is associated with forestry practices, and the smaller
percentage of sediment loading that is attributed to cropland is likely to be associated
with related management practices (such as soil disturbance), rather than atrazine-related
impacts to riparian vegetation. Therefore, potential impacts on herbaceous riparian
habitat from atrazine use are expected to result in negligible effects on overall sediment
loading into the Lower Alabama River adjacent to potential habitat for the Alabama
sturgeon, as compared to other sources of sedimentation including forestry management
practices and annual dredging of navigational channels.
In summary, terrestrial plant RQs are above LOCs; therefore, riparian vegetation may be
affected. However, woody plants are generally not sensitive to environmentally-relevant
atrazine concentrations; therefore, effects on shading, streambank stabilization, and
structural diversity (height classes) of vegetation are not expected. In addition, the best
available data on surrounding land use (i.e., forested) and the relative contribution of
sediment loading from a variety of sources suggest that atrazine is not likely to adversely
affect the Alabama sturgeon from potential reduction in riparian habitat and resulting
sedimentation to available spawning habitat. This finding is based on insignificance of
effects (i.e., effects to riparian vegetation in the Lower Alabama River watershed cannot
be meaningfully measured, detected, or evaluated in the context of a level of effect where
"take" of a single Alabama sturgeon would occur). Therefore, the effects determination
for the assessment endpoint of indirect effects on the Alabama sturgeon via direct effects
on terrestrial vegetation (riparian habitat) required to maintain acceptable water quality
and spawning habitat is "may affect, but not 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 5.4.
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Sedimentation
Thermal
Stability
Streambank
Stability
Wider and shallower
channels resulting from
eroding streambanks may
adversely modify habitat.
Not likely to
adversely affect.
Woody vegetation is
not expected to be
affected by atrazine.
Water temperature
increases in the absence
of shading by forested
vegetation.
Increased sedimentation may
reduce available spawning
habitat.
Terrestrial plant RQs exceed LOCs; therefore, riparian vegetation may be affected
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 herbaceous plants; woody species in
forested 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.
Atrazine-related impacts to grassy
riparian buffers are expected to be
insignificant with respect to other
sources of sediment loading in the
Lower Alabama River watershed.
Not likely to adversely affect.
Atrazine is not expected to harm the
roots of large, mature woody plants,
which provide stablity to
streambanks, and denuded
streambanks, which would be most
sensitive to the plant growth
inhibition effects of atrazine.
Figure 5.4. Summary of the Potential of Atrazine to Affect the Alabama Sturgeon
via Riparian Habitat Effects
6. Uncertainties
6.1 Exposure Assessment Uncertainties
Overall, the uncertainties inherent in the exposure assessment tend to result in over-
estimation of exposures. This is apparent when comparing modeling results with
monitoring data. In particular, peak exposures are generally several orders of magnitude
above the highest detection found in any of the samples collected from the Alabama
River. In general, the monitoring data should be considered a lower bound on exposure,
while modeling represents an upper bound. Factors influencing the over-estimation of
exposure include the assumption of no flow in the modeled water body. Analysis
indicates that increasing flow will result in significant reduction in exposure, particularly
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for longer-term durations of exposure (14-day, 30-day, etc.). In addition, many of the
atrazine use sites are likely to be far removed from the Alabama River; thus, significant
dilution is likely to occur between modeled EECs that are representative of headwater
streams immediately adjacent to agricultural fields and exposure concentrations expected
to occur in the Alabama River below Millers Ferry Dam. Furthermore, the impact of
setbacks on runoff estimates has not been quantified, although well-vegetated setbacks
are likely to result in significant reduction in runoff loading of atrazine.
6.1.1	Modeling Assumptions
Overall, the uncertainties addressed in this assessment cannot be quantitatively
characterized. However, given the available data and the tendency to rely on
conservative modeling assumptions, it is expected that the modeling results in an over-
prediction in exposure. In general, the simplifying assumptions used in this assessment
appear from the characterization in Section 3.2.4 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 can be qualitatively described. For instance, modeling in this assessment
for each use site 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, tools are currently not available to evaluate the effectiveness of a
vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is
highly dependent on the condition of the vegetative strip. For example, a well-
established, healthy vegetative setback can be a very effective means of reducing runoff
and erosion from agricultural fields. Alternatively, a setback of poor vegetative quality
or a setback that is channelized can be ineffective at reducing loadings. Until such time
as a quantitative method to estimate the effect of vegetative setbacks on various
conditions on pesticide loadings becomes available, the aquatic exposure predictions are
likely to overestimate exposure where healthy vegetative setbacks exist and
underestimate exposure where poorly developed, channelized, or bare setbacks exist.
6.1.3	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
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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.
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 as protective of the Alabama sturgeon.
6.2.2	Use of Acute Freshwater Invertebrate Toxicity Data for the Midge
The initial acute risk estimate for freshwater invertebrates was based on the lowest
toxicity value from Chironomus studies, which showed a wide range of sensitivity within
and between species of the same genus (2 orders of magnitude). Therefore, acute RQs
based on the most sensitive toxicity endpoint for freshwater invertebrates may represent
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an overestimation of potential direct risks to freshwater invertebrates and indirect effects
to the Alabama sturgeon via a reduction in available food.
6.2.3	Extrapolation of Long-term Environmental Effects from Short-Term Laboratory
Tests
The influence of length of exposure and concurrent environmental stressors to the
Alabama sturgeon (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 Alabama River watershed, predators, etc.) will likely affect the species response to
atrazine. Additional environmental stressors may decrease the Alabama sturgeon's
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 will 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
intentionally set very low, and conservative estimates are made in the screening level risk
assessment to account for these uncertainties.
6.2.4	Use of Threshold Concentrations for Community-Level Endpoints
For the purposes of this endangered species assessment, threshold concentrations are used
to predict potential indirect effects (via aquatic plant community structural change) to the
Alabama sturgeon. 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 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 predictive of potential atrazine-related community-level
effects in aquatic ecosystems, such as the Alabama River, 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 Alabama River Basin aquatic community, estimated chronic atrazine
exposure concentrations in the action area (from modeled EECs assuming flow) are
predicted to be between 2 to 5 times lower than the community-level threshold
concentrations, depending on the modeled atrazine use and averaging period. An
evaluation of monitoring data suggests that concentrations of atrazine could be even
further removed from these threshold concentrations. 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 Alabama sturgeon. Additional uncertainties associated
with use of the screening thresholds to estimate community-level effects are discussed in
Section B.8 of Appendix B.
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6.2.5. Sublethal Effects
The assessment endpoints used in ecological risk assessment include potential effects on
survival, growth, and reproduction of the Alabama sturgeon. 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
concentrations lower than 65 |ig/L (see Appendix A and Section 4.1.2.). 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 with
respect to potential effects to the Alabama sturgeon may need to be revisited.
6.2.6. Exposure to Pesticide Mixtures
This assessment considered only the single active ingredient of atrazine. However, the
Alabama sturgeon may be exposed to multiple pesticides simultaneously. Interactions of
other toxic agents with atrazine could result in additive effects (l/LC50mix =
l/LC50pesticide A l/LC50pesticide_B- • ¦ )- Synergistic effects (l/LC50mix l/LC50pesticide_A
1/[.CSOpeMicuie i;.. .x Y; where Y >1) or antagonistic effects (l/LC50mix = l/LC50pesticide_A
+ l/LC50pesticide b- x Y; where Y <1). Conceptually, the combined effect of the mixture
is equal to the sum of the effects of each stressor (1 + 1=2) for additive toxicity.
Synergistic effects occur when the combined effect of the mixture is greater than the sum
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of each stressor (1 + 1 >2), and antagonistic effects occur when the combined effect of
the mixture is less than the sum of each stressor (1 + 1 <2).
The available data suggest that pesticide mixtures involving atrazine may produce either
synergistic, additive, or antagonistic effects. Mixtures that have been studied include
atrazine with insecticides such as organophosphates and carbamates or with herbicides
including alachlor and metolachlor. Additive or synergistic effects have been reported 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 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 is beyond the scope of this
assessment and is beyond the capabilities 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.
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 Alabama sturgeon).
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.
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7. Summary of Direct and Indirect Effects to the Alabama Sturgeon
In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the
information presented in this endangered species risk assessment represents the best data
currently available to assess the potential risks of atrazine to the Alabama sturgeon. The
best available data suggest that atrazine will either have no effect or is not likely to
adversely affect the Alabama sturgeon by direct toxic effects or by indirect effects
resulting from effects to aquatic plants, aquatic animals, and riparian vegetation. A
summary of the risk conclusions and effects determination for the Alabama sturgeon,
given the uncertainties discussed in Section 6, is presented in Table 7.1.
Table 7.1. El
fects Determination Summary for the Alabama Sturgeon
Assessment Endpoint
Effects determination
Basis for Determination
Survival, growth, and
reproduction of Alabama
sturgeon individuals via
direct effects
No effect
No acute and chronic LOCs are exceeded.
Indirect effects to the
Alabama sturgeon via
reduction of prey (i.e.,
freshwater invertebrates)
May affect, but not likely
to adversely affect
Acute LOCs are exceeded for the forestry use, based on the
most sensitive ecotoxicity value for the midge; however RQs
for other dietary items (stoneflies and snails) are less than
LOCs. Based on the non-selective nature of feeding behavior
of the Alabama sturgeon and low magnitude of anticipated
individual effects to all evaluated prey species, atrazine is not
likely to indirectly affect the Alabama sturgeon via a reduction
in freshwater invertebrate food items. This finding is based on
insignificance of effects (i.e., effects to freshwater
invertebrates are not likely to be extensive over the suite of
possible food items to result in "take" of a single Alabama
sturgeon).
Indirect effects to the
Alabama sturgeon via
reduction of habitat and/or
primary productivity (i.e.,
aquatic plants)
May affect, but not likely
to adversely affect
Individual aquatic plant species within the Alabama River may
be affected. However, refined 14-, 30-, 60-, and 90-day EECs,
which consider the impact of flow, are well below the
threshold concentrations representing community-level effects.
In addition, the available monitoring data for the Alabama
River show that all detected concentrations are < 1 (ig/L. This
finding is based on insignificance of effects (i.e., community-
level effects to aquatic plants are not likely to result in "take"
of a single Alabama sturgeon).
Indirect effects to the
Alabama sturgeon via
reduction of terrestrial
vegetation (i.e., riparian
habitat) required to
maintain acceptable water
quality and spawning
habitat
May affect, but not likely
to adversely affect
Riparian vegetation may be affected because terrestrial plant
RQs are above LOCs. However, the majority of riparian area
adjacent to the current range of the Alabama sturgeon in the
Lower Alabama River watershed is forested vegetation, which
is not associated with forestry plantation operations. Woody
plants are generally not sensitive to environmentally-relevant
concentrations of atrazine; therefore, effects on shading,
streambank stabilization, and structural diversity of riparian
areas in the action area are not expected. Although grassy and
herbaceous riparian habitat is expected to be sensitive to
atrazine effects, the presence of herbaceous riparian areas in
the Lower Alabama River watershed is minimal. Therefore,
atrazine-related impacts to riparian habitat are expected to have
minimal impact on overall sediment loads in the Lower
Alabama River watershed, based on surrounding land use and
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other sources of sedimentation including forestry management
practices and annual dredging of navigational channels. This
finding is based on insignificance of effects (i.e., atrazine
effects to riparian vegetation in the Lower Alabama River
cannot be meaningfully measured, detected, or evaluated in the
context of a level of effect where "take" of a single Alabama
sturgeon would occur).	
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Hoberg, J. R. 1993. Atrazine technical: Toxicity to duckweed, (Lemnagibba). SLI Rep.
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