Risks of Prometon Use to Federally Listed
Endangered Barton Springs Salamander
(Eurycea sosorum)
Pesticide Effects Determination
Environmental Fate and Effects Division
Office of Pesticide Programs
Washington, D.C. 20460
September 18, 2007
(Final)
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Primary Authors
Paige Doelling Brown, Ph.D., Fisheries Biologist
James A. Hetrick, Ph.D., Senior Science Advisor
Secondary Review
Edward Odenkirchen, Ph.D., Senior Science Advisor
Acting Branch Chief, Environmental Risk Assessment Branch 1
Thomas Bailey, Ph.D.
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Table of Contents
1.0 Executive Summary 6
2.0 Problem Formulation 9
2.1 Purpose 9
2.2 Scope 10
2.3 Previous Assessments 11
2.3.1 Prometon 11
2.3.2 Barton Springs Salamander 11
2.4 Stressor Source and Distribution 12
2.4.1 Environmental Fate and Transport Assessment 13
2.4.2 Mechanism of Action 14
2.4.3 Use Characterization 14
2.5 Assessed Species 17
2.6 Action Area 19
2.7 Assessment Endpoints and Measures of Ecological Effect 21
2.8 Conceptual Model 22
2.8.1 Risk Hypotheses 22
2.8.2 Diagram 23
2.9 Analysis Plan 23
3.0 Exposure Assessment 24
3.1 Monitoring Data 24
3.2 Exposure Estimate Based on Modeling 29
3.2.1 Background 29
3.2.3 Modeling Approach 30
3.2.4 Equations to Estimate Prometon Concentrations 31
3.2.3 Label Application Rates and Intervals 34
3.2.7 Exposure Modeling Input and Output 34
4.0 Effects Assessment 36
4.1 Summary of Aquatic Ecotoxicity Studies 37
4.1.1 Toxicity to Freshwater Fish 37
4.1.2 Toxicity to Aquatic Phase Amphibians 37
4.1.3 Toxicity to Freshwater Invertebrates 38
4.1.4 Toxicity to Aquatic Plants 39
4.2 Use of Probit Slope Response Relationship 40
4.3 Incident Database Review 41
5.0 Risk Characterization 42
5.1 Risk Estimation 42
5.2 Risk Description 44
5.2.1 Direct Effects 44
5.2.2 Indirect Effects (Reduction in Prey B ase) 44
5.2.3 Indirect Effects (Habitat Degradation) 44
5.3 Risk Conclusions 45
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6.0 Uncertainties 47
6.1 Exposure Assessment Uncertainties 47
6.1.1 Modeling Assumptions 47
6.2.2 Impact of Vegetative Setbacks on Runoff 48
6.2.3 PRZM Modeling inputs and Predicted Aquatic Concentrations 48
6.2 Effects Assessment Uncertainties 49
6.2.1 Age Class and Sensitivity of Effects Thresholds 49
6.2.2 Use of Surrogate Species Data 49
6.2.3 Extrapolation of Effects 50
6.2.4 Acute LOC Assumptions 50
References 51
ECOTOX References 53
Appendix A - Barton Springs Salamander Life History
Appendix B - PRZM Scenario Development
Appendix C - Ecological Effects
Appendix D -ECOTOX Bibliography
Appendix E - RQ Methods and LOCs
Appendix F -RQ Calculations
Appendix G - Multi-AI Products
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Table of Figures
Figure 1 Chemical structure of prometon 12
Figure 2 Right-of-Way Locations in Barton Springs Action Area 16
Figure 3 Location Map of Barton Springs 18
Figure 4 Aerial Photo of Barton Springs 18
Figure 5 Prometon Action Area 20
Figure 6 Conceptual Model for Barton Springs Salamander 23
Figure 7 Ground and Surface Water Sampling Sites For Monitoring Data 25
Table of Tables
Table 1 Effects Determination for Prometon 8
Table 2 Fate Profile for Prometon 13
Table 3 Products containing prometon 14
Table 4 Land Use in the Barton Springs Watershed Representing Potential Prometon Use
Sites 16
Table 5 Summary of Assessment Endpoints and Measures of Ecological Effect 21
Table 6 Summary of USGS Monitoring Data for Barton Springs Complex 26
Table 7 Summary of USGS Monitoring Data for Surface Water in the BSSEA 27
Table 8 Summary of USGS Monitoring Data for Ground Water in the BSSEA 28
Table 9 Label Application Rates 34
Table 10 Input Parameters for PRZM Modeling 34
Table 11 Estimated Concentrations in the Standard Pond for Prometon Based on a Texas
Rights-of-Way Scenario 35
Table 12 Spring EECs Based on 0.23/500ft2 Ground Spray Application 35
Table 13 Aquatic Toxicity Profile for Prometon 36
Table 14 Probability of Individual Effects 40
Table 15 Risk Quotients for Prometon 42
Table 16 Correlation Between Percentage of ROW Treated and Amount of Prometon
Applied 43
Table 17 Effects Determination for Prometon 46
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1.0 Executive Summary
This ecological risk assessment evaluates the potential for the use of the herbicide
prometon to affect the Barton Springs salamander (Eurycea sosorum). The Barton
Springs salamander was Federally listed as an endangered species on May 30, 1997. No
critical habitat was designated. The salamander has an extremely limited geographic
range, inhabiting only four freshwater springs known as the Barton Springs complex in
Austin, Texas. The salamanders are aquatic throughout their entire lifespan, and in
addition to the springs, their habitat includes fractures in the karst system which supplies
ground water to the springs (USFWS 2005). The distance they travel into the fractures,
and the specific habitat use of this area is unknown. This assessment is one of a series of
ecological risk assessments developed consistent with the settlement for the court case
Center for Biological Diversity and Save Our Springs Alliance v. Leavitt, No.
1:04CV00126-CKK (filed January 26, 2004).
Prometon (PC 080804, CAS Registry #) is a nonselective "bare-ground" herbicide
labeled for pre- and post-emergence applications to manage annual and perennial grasses
and broadleaf weeds. It is a photosynthesis inhibitor and acts by disrupting CO2 fixation
and production of intermediary energy components - ATP and NADPH2. Prometon is
registered for weed control around buildings, storage areas, fences, pumps, machinery,
fuel tanks, recreational areas, roadways, guard rails, airports, military installations,
highway medians, pipelines, railroads, lumberyards, rights-of-way, and industrial sites.
Prometon is currently undergoing re-registration. The sole registrant, Makhteshim-Agan
of North America, Inc. (MANA) is supporting a maximum single application rate of 0.23
lb ai/500 ft2, applied once a year. Label analysis indicates this is the current maximum
rate. Unlike many agricultural chemicals, prometon is generally only applied to small
areas. This assessment considers the use pattern, and presents the risk associated with
application of specific amounts of active ingredient in the action area.
Prometon is persistent and mobile in the environment. It is stable to abiotic hydrolysis,
photodegradation, aerobic soil metabolism, and anaerobic soil metabolism. It is
frequently detected in both ground and surface water. On an acute basis, it is slightly
toxic to freshwater and saltwater fish and invertebrates. Aquatic plants are sensitive to
prometon, with EC50S ranging from 0.098 mg/L (green algae) to 0.624 mg/L (duckweed).
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The salamander is neotenic (aquatic throughout its life history), thus the assessment
focuses on the components of the aquatic system, including aquatic plants, invertebrates,
and the salamander itself. Although terrestrial plants serve important functions in
riparian systems, analysis of the Barton Springs action area indicated no terrestrial plants
near the springs were likely to be exposed to prometon. No prometon is used in Zilker
Park, where the springs are located, and as prometon can only be applied via ground
spray or granular formulation, effects on terrestrial plants are not anticipated to occur
further than 1,000 ft1 away from the use site.
The Environmental Fate and Effects Division (EFED) evaluated direct effects (survival,
reproduction, and growth) of prometon on the Barton Springs salamander, and indirect
effects (reduction of prey base, habitat modification) on the ecosystem which supports
the salamander. Effects determinations were made in accordance with procedures
described in the Agency's Overview Document (U.S. EPA 2004), using the best available
data. Effects determinations for prometon are made based on threshold yearly use rates
in the BSSEA.
After completing the analysis of the effects of prometon on the Federally listed
endangered Barton Springs salamander (Eurycea sosorum) in accordance with methods
delineated in the Overview document (USEPA 2004), EFED concludes that the use of
prometon (PC 080804) in the Barton Springs Segment of the Edwards Aquifer (BSSEA)
is anticipated to have the following effects:
Total yearly use
<1,650 lbs ai No effect
>1,650 lbs ai but <22,000 lb ai May affect, not likely to adversely affect (Indirect)
>22,000 lbs ai May affect, likely to adversely affect (Direct)
Assessment endpoints and the basis of determination for each endpoint evaluated are
shown in Table 1.
1 Details for terrestrial plant analysis in the Ecological Risk Assessment for the Re-registration of
Prometon, prepared concurrently with this document but not yet publically available. EFED anticipates
this document will be publically available in the Nov-Dec 2007 timeframe. Further references to the Re-
registration risk assessment in this document are designated as Prometon RED ERA 2007.
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Table 1 Effects Determination for Prometon
Assessment Endpoint Effects determination
Basis for Determination
Direct Effects
Survival, growth, and
reproduction of Barton
Springs salamander
<22,000 lbs yearly
No effect
> 22,000 lbs yearly
May affect
LAA
No chronic risk LOCs are exceeded at any
yearly application assessed.
At applications of<22,000 lbs yearly, acute risk
LOCs for the salamander are not exceeded.
At applications of > 22,000 lbs yearly, acute
risk LOCs for the salamander are exceeded.
Due to the uncertainties associated with actual
usage, EFED has not attempted to discern an
NLAA point for direct effects on the
salamander.
Indirect Effects
Reduction of prey
(i.e., freshwater
invertebrates)
<55,000 lbs yearly
No effect
> 55,000 lbs yearly
May affect
LAA
No chronic risk LOCs are exceeded at any
yearly application assessed.
At applications of<55,000 lbs yearly, acute risk
LOCs for freshwater invertebrates are not
exceeded.
At applications of >55,000 lbs yearly, acute risk
LOCs for aquatic invertebrates are exceeded.
Due to the uncertainties associated with actual
usage, EFED has not attempted to discern an
NLAA point for indirect effects on the
salamander.
Degradation of habitat
and/or primary
productivity
(i.e., aquatic plants)
<1,650 lbs yearly
No effect
>1,650 but <22,000
lbs yearly
May affect
NLAA
(insignificant)
> 22,000 lbs yearly
May affect
LAA
No LOC exceedences at <1,650 lbs yearly.
At 1,650 lbs yearly, acute risk LOCs exceeded
for non-vascular aquatic plants, but not
vascular aquatic plants. Recovery of plant
community is expected. Reduction and/or
modifications in plant community not
anticipated to be severe enough to affect
growth, survival, or reproduction of
salamander.
At applications of >22,000 lbs yearly, acute risk
LOCs for both vascular and non-vascular
aquatic plants are exceeded. Reduction and/or
modifications in plant community may be
severe enough to affect growth, survival, or
reproduction of salamander.
1 Determinations are based on total lbs of active ingredient used yearly in the BSSEA, assuming
all applications are made simultaneously
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2.0 Problem Formulation
2.1 Purpose
This ecological risk assessment has been conducted consistent with the settlement of the
court case Center for Biological Diversity and Save Our Springs Alliance v. Leavitt, No.
L04CV00126-CKK (filed January 26, 2004). The purpose of this ecological risk
assessment is to determine if the registration of the herbicide prometon (PC 108801)
could affect the Barton Springs salamander (Eurycea sosorum), implementing the
Environmental Protection Agency's (the Agency) responsibility as directed in Section
7(a)(2) of the Endangered Species Act (ESA). The Barton Springs salamander was
Federally listed as an endangered species on May 30, 1997 (62 FR 23377-23392) by the
U.S. Fish and Wildlife Service (USFWS or the Service). No critical habitat has been
designated for this species.
In this assessment, direct and indirect effects to the survival, growth, and reproduction of
the Barton Springs salamander are evaluated in accordance with methodologies described
in the Agency's Overview Document (U.S. EPA 2004).
As part of the "effects determination", the Agency reaches one of the following three
conclusions regarding the potential for prometon to affect the Barton Springs salamander:
"No effect";
"May affect, but not likely to adversely affect"; or
"May affect, likely to adversely affect".
If the results of the screening-level assessment show that pre-established levels of
concern (LOCs) are not exceeded for direct effects on the Barton Springs salamander
(U.S. EPA 2004), and no indirect effects are expected (e.g., degradation of habitat or
reduction of prey availability), a "no effect" determination is made. Exposure estimates
are made based on both the potential and reported use of prometon within the action
area. If, however, indirect effects are anticipated and/or estimated exposure exceeds the
LOCs for direct effects, the Agency concludes a preliminary "may affect" determination
for the Barton Springs salamander.
If a determination is made that use of prometon within the action area "may affect" the
Barton Springs salamander, additional information is considered to refine the potential
for exposure and evaluate the anticipated effects. The Agency uses the best available
information to determine if the registered uses are "not likely to adversely affect
(NLAA)" or "likely to adversely affect (LAA)" the Barton Springs salamander.
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2.2 Scope
The end result of the Agency's pesticide registration process is an approved product
label. The label is a legal document that stipulates how and on what use sites 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
prometon in accordance with the approved product labels is the "action" being assessed.
The majority of guideline toxicity data available pertains to the active ingredient ("ai"),
and the effects of the active ingredient form the basis of the evaluation. When
formulation-based toxicity data are available, they are considered in the assessment.
Prometon (PC 080804, CAS Registry #) is a nonselective "bare-ground" herbicide
labeled for pre- and post-emergence applications to manage annual and perennial grasses
and broadleaf weeds. Its primary purpose is complete control of all vegetation. It is a
photosynthesis inhibitor and acts by disrupting CO2 fixation and production of
intermediary energy components - ATP and NADPH2. Prometon is registered for weed
control around buildings, storage areas, fences, pumps, machinery, fuel tanks,
recreational areas, roadways, guard rails, airports, military installations, highway
medians, pipelines, railroads, lumberyards, rights-of-way, and industrial sites (such as
cross connects, pedestals, transformers, vaults, buried cable closures, telephone booths,
fire plugs).
According to OPPIN, there are currently a total of 64 registered products as of January
2007, of which three are technical or manufacturing concentrate formulations. Prometon
is currently in the re-registration process, and an ecological risk assessment for uses
nationally is being developed concurrently with this effects determination. The sole
registrant, Makhteshim-Agan of North America, Inc. (MANA) is supporting a maximum
single application rate of 0.23 lb ai/500 ft2 applied once a year. According to registrant
provided data, typical use rates range from 0.175 to 0.23 lb ai/500 ft2 (Prometon Use
Closure Memorandum Case No. 2545, January 22, 2007). Unlike many agricultural
chemicals, prometon is generally only applied to small areas.
The current registration for prometon allows for use nationwide, thus the action area for
the entire registration would include areas throughout the United States and its territories.
However, because this ecological risk assessment is species specific for the Barton
Springs salamander (BSS), the BSS-prometon action area is defined as the locations
where prometon, if used in accordance with label instructions, might reasonably be
expected to be transported to a location where the salamander and/or key components of
its supporting ecosystem might be exposed to it (i.e.,completed exposure pathways).
Further discussion of the action area for the Barton Springs salamander is provided in
Section 2.6.
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2.3 Previous Assessments
2.3.1 Prometon
An ecological risk assessment for prometon has been conducted concurrently with the
development of this effects determination (Prometon RED ERA 2007). This assessment
concluded:
Use of prometon at the maximum supported rate poses an acute and chronic risk to
terrestrial animals residing in or foraging at the treated site. Acute risks for both birds
and mammals are expected to drop below levels of concern approximately 10 ft away
from the treated site. Residue levels posing chronic risks extend further from the
treatment site, potentially as far away as 70 ft for birds and 1,000 ft for mammals. Non-
target terrestrial plants, both monocots and dicots, could be affected by spray drift or
runoff from the treated site. Drift effects potentially extend up to 1,000 ft from the
treated site for ground or truck-mounted sprayers. Granular treatments may cause non-
target plant effects in locations receiving runoff.
At the maximum supported rate, no risk for aquatic animals is anticipated. Endangered
species acute risk LOCs for aquatic animals were exceeded at EECs produced by some,
but not all of the scenarios modeled. Based on modeling, effects on aquatic non-vascular
plants, both freshwater and saltwater, are anticipated. Reduction of algal populations
(primary productivity) could affect higher trophic levels but the specific impact is
difficult to predict or quantify, and may differ from site to site. Effects to aquatic
vascular plants are also anticipated based on model outputs.
2.3.2 Barton Springs Salamander
The Agency has also completed (U.S. EPA 2006b) ecological risk assessments evaluating
the potential effects of atrazine, metolachlor, and diazanon on the Barton Springs
Salamander. These assessments were conducted consistent with the settlement for the
court case Center for Biological Diversity and Save Our Springs Alliance v. Leavitt, No.
1:04CV00126-CKK (filed January 26, 2004).
Conclusions regarding atrazine use (U.S. EPA 2006) in the action area were that it:
• Would have no (direct) effect on the Barton Springs salamander (survival,
growth or reproduction),
• Was not likely to adversely affect salamander prey, and
• Was not likely to adversely affect aquatic plants.
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Conclusions regarding metolachlor (U.S. EPA 2006a) use in the action area were that it:
• Would have no (direct) effect on the Barton Springs salamander (survival,
growth or reproduction)
• Was not likely to adversely affect salamander prey, and
• Was not likely to adversely affect aquatic plants.
Conclusions regarding diazinon use (U.S. EPA 2007b) in the action area were that it:
• Would have no (direct) effect on the Barton Springs salamander (survival,
growth or reproduction)
• Was not likely to adversely affect salamander prey, and
• Was not likely to adversely affect aquatic plants.
2.4 Stressor Source and Distribution
H CHS
H3C—Ck —CH—CHa
/N\
H CH—CH3
ch3
Figure 1 Chemical structure of prometon
Empirical formula: C10H19N5O
Molecular weight: 225 g/mol
CAS Registry Nos.: 1610-18-0
Chemical Class: Triazine herbicides
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2.4.1 Environmental Fate and Transport Assessment
Probable routes of prometon dissipation are through runoff into surface water and
leaching into ground water. Prometon is stable to abiotic hydrolysis, photodegradation in
water, aerobic soil metabolism, and anaerobic soil metabolism (Table 2). Half-lives of
prometon range from 462 to 932 days in aerobic soil. In anaerobic soil the half-life is
557 days. Degradation products of prometon include 2 amino-4-(isopropylamino)-6-
methyoxy-s-triazine (GS-14626), 2,4-diamino-6-methoxy-s-triazine (GS-12853), and 2-
hydroxy-4,6 bis (isopropylamino)-s-triazine (GS-11526). Due to persistence of parent
compound, formation of degradates is expected to be slow and in low quantities.
Prometon is expected to be mobile in soil and aquatic environments. The average Koc of
prometon is 117 L/kg-OC. Based on its physical properties, prometon is anticipated to
remain in surface water for extended periods and has a high potential to leach into
groundwater.
Table 2 Fate Profile for Prometon
Physico-chemical
Characteristic
Value
Source
Vapor Pressure
(mbar)
3.1 x 10~6
EFED files
Water Solubility
(mg/L(S)20C)
620
EFED files
Log KOW(@20C)
4.3
EFED files
Hydrolysis
Stable in pH 5, 7, and 9
MRID 41114801
Photodgradation in
Water
Stable
MRID 40225801
Photodegradation on
Soil
Stable
MRID 41114802
Aerobic Soil
Metabolism
t-i/2 >365 days
t-i/2 = 462 days
Stable for 368 days,
t-i/2 =932 days
MRID 4145501
MRID 42313501
Anerobic Soil
Metabolism
Stable during 90 days, after 30 days aerobic
t-i/2 = 462 days
Stable during 60 days, after 32 days aerobic
t-i/2 = 557 days
MRID 40145501
MRID 42313501
Adsorption/desorption
Kf=2.61 (1/n=0.893) Koc 149.6 CA sandy loam
Kf=2.90 (1/n=0.895) Koc 172.0 Dubuque silt loam
Kf=2.40 (1/n=0.868) Koc 82.6 Kewaunee clay loam
Kf=1.20 (1/n=0.911) Koc 98.3 MS silt loam
Kf=0.398 (1/n=0.738) Koc 85.6 Plainfield sand
MRID 40225803
Terrestrial Field
Dissipation
ti/2 =200 to 400 days Fresno, CA
MRID 162534
MRID 162535
MRID 162536
Aerobic and
Anaerobic Soil
Metabolites
2-amino-4-(isopropylamino)-6-methoxy-s-triazine
(GS-14626)
2,4-diamino-60methoxy-s-triazine (GS 12853)
2-hydroxy-4,6 bis(isolproylamino-s-triazine)
MRID 4145501
MRID 42313501
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2.4.2 Mechanism of A ction
Prometon is a photosynthesis inhibitor and acts by disrupting CO2 fixation and
production of intermediary energy components - ATP and NADPH2. Prometon and other
s-triazines affect photosystem II, competing with plastoquinone and disrupting the
electron transport processes (Drost et. al, 2003).
2.4.3 Use Characterization
An analysis of available usage and land cover information (SRC 2006), including
extensive discussions with local experts in the fields of agriculture and soil science, was
completed to determine which prometon use sites are likely to be present in the area
contributing surface or ground water to Barton Springs.
Prometon is a non-selective herbicide for use on rights-of way and perimeters around
buildings, railroads, pipelines, airports, fuel tanks, etc. There is approximately 600,000
lbs of prometon annual use in the United States, according to the registrant. Prometon
use can be categorized among farmsteads (60% of use), industrial sites (30% of use), and
rights-of-way (10% of use). Table 3 lists examples of the products containing prometon.
Table 3 Products containing prometon
Product
Percent Al
Registration Number
Additional Als
Pramitol MG 25E
26.3%
66222-24
No
Pramitol 4 MUP
45.3%
60222-43
No
Pramitol 25E
25%
66222-22
No
Pramitol 5PS
5%
66222-23
Boric acid, sodium
chlorate, simazine
Pramitol 2.5
2.5%
66222-26
No
Pramitol 3.75
3.75%
66222-27
No
Pramitol 45C
45.3%
66222-38
No
Pramitol 1.8
1.8%
66222-44
No
Pramitol 2.2 L
2.2%
66222-45
No
Pramitol 1.8 RTU
1.8%
66222-52
No
Pramitol 2L/Diuron
21.62%
66222-55
Diuron
Prometon 5PS
5%
53883-97
Boric acid, sodium
chlorate, simazine
Prometon 25E
25%
53883-98
No
Prometon 4SC
45.3%
53883-99
No
In Texas, prometon is classified as state-limited use herbicide2. When distributed in
containers of "a capacity larger than 1 quart for liquid material or 2 lbs for dry or solid
material" it is classified as a regulated herbicide. Container measurements are based on
end-use products, and the actual volume of active ingredient in these containers may
vary. As either a state-limited use or a regulated herbicide, it must be applied by a
certified applicator. Applicators are required to keep records, but currently there is no
requirement for reporting use to the state or county.
2 http://www.agr.state.tx.us/agr/program render/0.1987.1848 5539 0 0.00.html?channelld=5539.
accessed 9/12/07 PDB
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The Agency's Office of Pesticide Programs Biological and Economic Analysis Division
(OPP/BEAD) provided an analysis of both national and local use information for the
pesticides involved in this litigation (Kaul et al., 2005, Zinn and Jones, 2006, Kaul, et al.,
2006), but were unable to locate usage data for prometon. Unlike agricultural crops,
where usage reporting is generally available, unless there is a state-mandated reporting
requirement data for other types of uses is generally not available. Some sales data,
provided by the registrant, indicates that prometon is sold in Texas, but not in large
quantities. County-specific data were not available, thus EFED was unable to estimate
how much prometon may be applied in the BSSEA on a yearly basis.
Prometon is often applied in discrete areas, or as bands. It is formulated as an
emulsifiable concentrate, a ready-to-use, a water-based flowable concentrate, and as
pelleted granules. Liquid applications may be made by handheld sprayer. Granular
prometon may be applied using a whirly-bird spreader, or other similar hand-held
spreader. Granular applications are typically not incorporated, but are often "wetted-in".
Wetting-in consists of applying sufficient water to ensure the granules dissolve and the
prometon is released. In some cases, granules are left until sufficient rainfall occurs to
dissolve them. Aerial applications are not permitted.
Based on information provided by the registrants, typical use rates range from 0.175 to
0.23 lb ai/500ft2 (Prometon Use Closure Memo, 1/22/07). There is currently no seasonal
or annual maximum application rate, but the registrant is supporting a single maximum
application rate of 0.23 lb ai/500ft2 for re-registration. This is equivalent to a rate of
20.04 lb ai/A if the entire acre were to be treated. As a first approximation, EFED used
the rate per acre and the assumption the entire acre was treated to estimate water
concentrations.
Because of the type of use sites for prometon, and the fact no usage data were available,
EFED opted to model rights-of-way as the primary use site for the chemical. A right-of-
way specific scenario was developed for the Barton Springs area. Post-processing of the
PRZM-generated water concentrations was done in an Excel spreadsheet.
Analysis of land-use/land-cover data (SRC 2006) identified three major types of land use
that was classified as rights-of-way, accounting for 4.3% of the watershed (Table 3). Of
the areas designated as rights-of-way, approximately 43% is in the recharge zone, and
57%) is in the contributing zone. Specific land uses associated with the remainder of the
watershed are presented in Appendix B, Table 3. For this assessment, rights-of-way
include streets and roads, utilities, and railroad facilities. Because prometon may be
applied around buildings and industrial sites, several of these categories are also included
in the table, but were not modeled specifically. Exposure to prometon based on use
around buildings is anticipated to be lower than the high end assumption {i.e., all rights-
of-way treated simultaneously) used in modeling. Buildings account for 1.4% of total
land use in the watershed
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Table 4 Land Use in the Barton Springs Watershed Representing Potential Prometon Use
Sites
Land use
Area (sq.meters)
Area (acres)
Percent of Watershed
Rights-of-way
44,427,570
10,978
4.3
Streets and roads
43,237,121
10,684
4.2
Utilities
1,009,376
249
0.1
Railroad facilities
181,073
45
0.0 j
Buildings
14,741,828
3,643
1.4
Commercial
9,523,023
2,353
0.9
Warehousing
4,597,267
1,136
0.4
Miscellaneous
621,538
154
0.1
Industrial
Entire Watershed
1,029,906,541
254,495
100
Rights-of-V\foy within the Barton Springs Action Area
Zilker Park
Figure 2 Right-of-Way Locations in Barton Springs Action Area
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2.5 Assessed Species
The Barton Springs salamander is aquatic throughout its entire life cycle. Members of
the Plethodontidae Family (lungless salamanders), they retain their gills, become sexually
mature, and eventually reproduce in freshwater aquatic ecosystems. The best available
information indicates the Barton Springs salamander is restricted to the four springs
outlets that make up the Barton Springs complex (Figure 3 and Figure 4), located in
Zilker Park near downtown Austin, Texas. As such, this species has one of the smallest
ranges of any vertebrate species in North America (Chippindale 1993). The Barton
Springs segment of the Edwards Aquifer and its contributing zone supply all of the water
in the springs that make up the Barton Springs complex. Flows of clean spring water are
essential to maintaining well-oxygenated water necessary for salamander respiration and
survival.
The subterranean component of the Barton Spring salamander's habitat may provide a
location for reproduction (USFWS, 2005); however, little is known about the
reproductive biology of the Barton Springs salamander in the wild. It appears that
salamanders can reproduce year-round, based on observations of gravid females, eggs,
and larvae throughout the year in Barton Springs (USFWS 2005). Survey results indicate
Barton Springs salamanders prefer areas near the spring outflows, with clean, loose
substrate for cover, but they may also be associated with aquatic plants, especially moss.
In addition to providing cover, moss and other aquatic plants harbor a variety and
abundance of the salamander's prey, freshwater invertebrates. Based on available
information, both adults and juveniles eat freshwater invertebrates (USFWS 2005).
Further information on the status and life history of the Barton Springs salamander is
provided in Appendix A.
17
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Figure 3 Location Map of Barton Springs
Figure 4 Aerial Photo of Barton Springs
18
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2.6 Action Area
It is recognized by the Agency that the overall action area for the national registration of
prometon includes any locations where registered uses might result in ecological effects.
However, the scope of this assessment limits consideration of the overall action area to
locations of those use sites applicable to the protection of the Barton Springs salamander.
Thus, the BSS-prometon action area is defined largely by the hydrogeologic framework
of Barton Springs. Deriving the geographical extent of this portion of the action area is
the product of consideration of the types of effects prometon may be expected to have on
the environment, the concentrations of prometon that are associated with those effects,
and the best available information concerning the use of prometon and its fate and
transport within the Barton Springs area.
Unlike exposure pathways for most aquatic organisms, where stressors are transported
via surface water to the receptor within a defined watershed, the habitat of the Barton
Springs salamander is almost completely ground water driven. Runoff from treated
fields, transported through the fractured limestone (karst) of the Edwards Aquifer is the
principal route of exposure for the salamander (U.S. EPA 2006). Thus, the action area
for this assessment is defined by those areas within the hydrogeologic "watershed,"
including the Barton Springs Segment of the Edwards Aquifer and the Contributing Zone
(BSSEA), that supply water to the four springs (Main Barton Springs, Eliza Springs, Old
Mill Springs, and Upper Barton Springs) occupied by the salamanders (USFWS 2005).
During high flow conditions, surface water flow from Barton Creek may enter the pool if
it overtops the dam at the upper end of the pool. Any pesticide used in the land areas
contributing to the ground water in the Barton Springs segment of the aquifer or to the
surface water in Barton Creek could potentially be transported to the springs.
Flow to the Barton Springs is controlled by the geology and hydrogeology of the BSSEA.
Numerous geological and ground water studies (Slade et al., 1986, Hauwert el al., 2004)
have been conducted to define the extent of the area contributing to the Barton Springs
and characterize the flow within the system. The BSSEA is a 354 square mile area,
comprised of four hydrogeologic zones. These are, from west to east, the Contributing
Zone, the Recharge Zone, the Transition Zone, and the Artesian Zone. Of these zones,
the Contributing and Recharge Zones have the greatest and most direct influence on
Barton Springs. There is evidence that the Transition Zone has some limited input into
the Barton Springs, while the Artesian Zone contributes no subsurface flow to the springs
(Slade et al., 1985, Hauwert et al., 2004). The BSSEA is characterized as a karst system
permitting relatively rapid transit of ground water, with velocities along the dominant
flow path of 1-5 miles/day, depending on ground water flow conditions (USFWS 2005)
particularly within the fracture portions. Based on dye tracer studies, pesticides applied
within the recharge and contributing zones could potentially be present in the water of the
springs on a time scale of days to weeks (Hauwert et al., 2004)
19
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Spray drift and/or long-range atmospheric transport of pesticides could potentially
contribute to concentrations in the aquatic habitat used by the salamander. Given the
physico-chemical profile for prometon and the fact that prometon has been detected in
both air and rainfall samples, the potential for long range transport from outside the area
defined by the BSSEA cannot be precluded, but is not expected to approach
concentrations in runoff predicted by modeling. Prometon introduced to the ground
water system via atmospheric deposition or other environmental processes not
specifically accounted for in the assessment is addressed by evaluation of the monitoring
data, and assessment of a background concentration.
Thus, the action area for prometon as it relates to the Barton Springs salamander (the
"BSS-prometon action area") is defined by the Contributing Zone, Recharge Zone, and
Transition Zone within the BSSEA (Figure 5).
Legend
# Barton Springs
Interstate 35
Creeks
Action Area Zones
~ Contributing Zone
~ Recharge Zone
~ Transition Zone
Figure 5 BSS-Prometon Action Area
20
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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., Barton Springs salamanders), the ecosystems potentially at risk (i.e, Barton
Springs), the migration pathways of prometon {i.e.,ground water and surface water
tranport), and the routes by which ecological receptors are exposed to prometon-related
contamination {i.e., direct contact in aqueous medium).
Assessment endpoints for the Barton Springs salamander include direct toxic effects on
the survival, reproduction, and growth of the salamander itself, 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," defined as changes in the
attributes of an assessment endpoint itself or changes in a surrogate entity or attribute in
response to exposure to a pesticide. Measures of ecological effect are evaluated based on
acute and chronic toxicity information from registrant-submitted guideline tests, and data
from open literature which meets specific acceptance criteria4.
Guideline tests are performed on a limited number of organisms, which serve as
surrogates for other types of organisms expected to have similar responses. Open
literature data may expand the number of organisms for which toxicity data are available,
but these tests may or may not have been conducted in accordance with standardized
protocols and are often not directly comparable to the guideline tests. EFED guidance
(U.S. EPA 2004) specifies that, in absence of data from more closely related species, fish
data are used for aquatic-phase amphibians. Species-sensitivity distributions are not well
understood, thus to provide a conservative estimate of risk EFED uses the most sensitive
organism in the representative phylogenic class. Barton Springs salamanders are
neotenic (retain gills throughout their lives) and are considered aquatic-phase
amphibians. No species-specific toxicity data were available at the time of this risk
assessment. Thus, fish data are used as surrogates for the Barton Springs salamander.
Table 5 Summary of Assessment Endpoints and Measures of Ecological Effect
Assessment Endpoint
Measures of Ecological Effect3
1. Survival, growth, and reproduction of Barton
Springs salamander individuals via direct
effects
1 a. Rainbow trout acute LC502
1 b. Fathead minnow chronic NOAEC1
2. Survival, growth, and reproduction of Barton
Springs salamander individuals via indirect
effects on prey (i.e., freshwater invertebrates)
2a. Water flea acute EC501
2b. Water flea chronic NOAEC1
3. Survival, growth, and reproduction of Barton
Springs salamander individuals via indirect
effects on habitat and/or primary productivity
(i.e., aquatic plant community)
3a. Non-vascular plant (freshwater algae)
EC501
3b. Vascular plant (duckweed) EC502
1 Guideline study
2 ECOTOX study
3 From U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001.
4 For exact guidelines, see the "Overview Document, "(U.S EPA 2004)
5 All toxicity data reviewed for this assessment are included in Appendix C.
21
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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 intentional release of prometon to the
environment by application on approved use sites. Based on the results of previous
ecological risk assessments regarding prometon, the following risk hypotheses are
evaluated in this endangered species assessment:
Prometon in ground water, surface water, and/or runoff from treated areas
may directly affect Barton Springs salamanders by causing mortality or
adversely affecting growth or fecundity;
Prometon in ground water, surface water, and/or runoff from treated areas
may indirectly affect Barton Springs salamanders by reducing or changing the
composition of prey populations; and
Prometon in ground water, surface water, and/or runoff from treated areas
may indirectly affect Barton Springs salamanders by reducing or changing the
composition of the plant community in the springs, thus affecting primary
productivity and/or cover.
22
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2.8.2 Diagram
The conceptual model diagram is a graphic representation of the structure of the risk
assessment. It specifies the stressor, release mechanisms, abiotic receiving media,
biological receptor types, and effects endpoints of potential concern. The conceptual
model for the potential effects of prometon on the Barton Springs salamander is shown in
Figure 6. Exposure routes shown in dashed lines are not quantitatively considered
because these exposures are expected to be sufficiently low as not to cause direct or
indirect effects to the Barton Springs salamander.
Stressor
Source
Prometon applied to right-of-way
^
! Spray Drift
Runoff
Ground water/
Surface Water
Atmospheric
transport
Receptor
Attribute
Change
Springs
Aquatic plants
Aquatic invertebrates
Aquatic vertebrates
Individual
salamander
Reduced survival
Reduced growth
Reduced reproduction
<—
Food chain
Decrease in abundance
Shift in prey base
«-
Habitat
integrity
Reduced cover
1
Figure 6 Conceptual Model for Barton Springs Salamander
2.9 Analysis Plan
This ecological risk assessment employs the standard methods as described in the
Overview Document (U.S. EPA 2004), with the exception of the exposure assessment,
which has been tailored specifically to the Barton Springs ecosystem.
23
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3.0 Exposure Assessment
The exposure assessment includes evaluations based on monitoring data and modeled
concentrations. Recent (2000-2004) USGS monitoring data for the surface streams,
ground water wells, and the four springs making up the Barton Springs system (Mahler
2005) were available, and are summarized below. Exposure modeling is an application
of the standard approach outlined in the Overview Document (U.S. EPA, 2004), modified
to reflect the hydrogeologic conditions in the area surrounding Barton Springs. Both sets
of exposure estimates are considered in the risk estimation.
3.1 Monitoring Data
Nationwide, prometon is frequently detected in surface water (between 10-60% detects in
various monitoring programs) at a relatively low concentration (99th percentile of
maximum concentration generally between 0.1-0.5 |~ig/L). The maximum reported peaks
in the monitoring data examined were 40 |j,g/L in ground water and 25.1 |j,g/L in surface
water6. Although it is not manufactured in large quantities (approximately 600,000 lb
ai/year, according to the registrant), its frequent occurrence in surface water may be due
to the fact that it is highly soluble, and essentially stable in water. Additionally, although
it is typically only applied to small areas, equivalent per acre use rates are in the range of
20 lb ai, thus the overall mass of pesticide in the runoff may be equivalent to a larger area
treated at a lower rate.
In the USGS provided monitoring data for surface streams, ground water wells, and the
four springs making up the Barton Springs system prometon was one of the most
frequently detected compounds (Mahler 2005a). Figure 7 shows sampling sites, with
springs designated in yellow, surface wate sites in black, and ground water wells in red.
In 2000-04, USGS conducted monitoring in the springs complex and in surface and
ground water sources across the BSSEA for an extensive list of pesticides. This study
included detection limits an order of magnitude lower than studies conducted earlier
(0.01-0.02 ng/L, rather than 0.1-0.2 |_ig/L), In addition, the recent data from the USGS
targeted single runoff events within the spring systems, with attempts to correlate
composition of the sample with the storm hydrograph.
6 Details for monitoring analysis in the Prometon RED ERA 2007.
24
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Barton Springs
Legend
Interstate 35
— Creeks
Action Area Zones
Contributing Zone
~ Recharge Zone
~ Transition Zone
Figure 7 Ground and Surface Water Sampling Sites For Monitoring Data
In Figure 7, springs are designated in yellow, ground water wells in red, and surface
water sites in black. While of high quality and targeted specifically to the Barton Springs
system, the monitoring data may not capture the highest prometon concentrations,
primarily due to the inherent difficulty of measuring contaminants in runoff events.
However, the monitoring data provide a good cross-check to the modeled concentrations
and can be used to establish a background concentration in the ground water
25
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Four springs were included in the USGS analysis: Main Spring, Eliza Spring, Upper
Spring, and the Old Mill Spring. These four springs represent the main source of inflow
into the Barton Springs pool system, with the Main Spring providing roughly 80% of
overall flow.
Monitoring data (Table 6) showed prometon was regularly detected in one of the springs
(Upper Spring) inhabited by the salamander. It was also detected once (3% detection
rate) in Main Spring. It was not detected in either Old Mill Spring or Eliza Spring in any
of the sampling. Based on the 2001-2004 data, prometon concentrations are at the
detection limit of 0.01 ng/L. Out of 27 samples taken at Main Spring, prometon occurred
in one. In Upper Springs, 9 out of 12 samples (75%) contained detectable concentrations
of prometon, quantified as 0.01 |j,g/L in all cases.
Table 6 Summary of USGS Monitoring Data for Barton Springs Complex
Spring
Range of
Sample
Dates
# of
Samples
# of
Detects
Frequency
of Detection
(%)
Maximum
Cone.1
(ng'L)
Minimum
Cone.2
(ng'L)
Average
Cone.
(ng/L)
Main
1982-1987
1987-1993
2001-2004
3
10
27
0
0
1
0
0
3
<0.1
<0.2
0.01
<0.1
<0.1
<0.01
N/A
N/A
N/A
Upper
2001-2004
12
9
75
0.01
<0.01
0.01
Old Mill
2001-2003
7
0
0
<0.01
<0.01
N/A
Eliza
2000-2003
11
0
0
<0.02
<0.01
N/A
1 If there were no quantifiable measurements, this is given as the highest LOD/LOQ in the series
2 If there were no quantifiable measurements, this is given as the highest LOD/LOQ in the series
3 Average includes quantified detections, values below detection limit not included.
NA Not applicable, not enough values to average
26
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USGS also had monitoring data for several creeks (Barton Creek, Bear Creek, Onion
Creek, Slaughter Creek, and Williamson Creek) in the BSSEA and for ground water
wells
Monitoring data for surface water included 5 creeks and a total of 16 sites. Recent data
(2000-2004) were available for 3 of the sites (Barton Creek, Onion Creek, and
Williamson Creek). Overall, prometon was detected in 22 out of the 90 samples (25%)
Of the creeks sampled, only one, Williamson Creek, consistently had detectable
concentrations of prometon, ranging from 0.01 |j,g/L (2000-2004) to 5.6 |j,g/L (1982-
1985). In the overall dataset, prometon detections appear more frequently in the samples
taken in the 1980s than in samples from 1990 and later. Prometon was detected in
Williamson Creek in the 2000-2004 sampling round, but at concentrations two orders of
magnitude lower than the earlier samples. During the 2000-2004 sampling round no
other creeks had detectable concentrations of prometon (LOD 0.02 |~ig/L).
Table 7 Summary of USGS Monitoring Data for Surface Water in the BSSEA
Water
Source
Range of
Sample
Dates
# of
Samples
# of
Detects
Frequency
of
Detection
(%)
Max
Cone.1
(mq/l)
Min
Cone.2
(mq/l)
Avg ^
Cone.3
(mq/l)
1981-1982
3
0
0
<0.1
<0.1
N/A
1993-1995
6
0
0
<0.2
<0.2
N/A
Barton
Creek
(6 sites)
2002-2004
7
0
0
<0.01
<0.01
N/A
1993-1995
5
0
0
<0.2
<0.2
N/A
1983-1985
7
0
0
<0.1
<0.1
N/A
1981-1985
12
1
8
0.1
<0.1
N/A
2000-2004
10
0
0
<0.02
<0.2
N/A
1982
1
0
0
<0.1
<0.1
N/A
Bear
Creek
(2 sites)
1982-1983
3
2
67
0.2
0.1
0.15
1982-1983
2
1
50
0.1
<0.1
N/A
Onion
Creek
(3 sites)
1982-1985
2003-2004
5
2
0
0
0
0
<0.1
<0.01
<0.1
<0.01
N/A
1981-1983
4
0
0
<0.1
<0.1
N/A
1982-1985
5
4
80
0.4
0.1
N/A
Slaughter
Creek
(2 sites)
1984
1
0
0
<0.1
<0.1
N/A
1984
1
0
0
<0.1
<0.1
N/A
1982-1985
10
6
60
5.3
0.1
1.6
Williamson
2004
1
0
0
<0.01
<0.01
N/A
Creek
(3 sites)
2000-2004
7
4
57
0.04
0.01
0.02
1982-1985
5
4
80
0.3
0.2
0.23
1 If there were no quantifiable measurements, this is given as the highest LOD/LOQ in the series
2 If there were no quantifiable measurements, this is given as the highest LOD/LOQ in the series
3 Estimated
27
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In 2001-2004 eleven ground water wells in the BSSEA were analyzed for pesticides,
including prometon. The limit of detection for the analysis was 0.01 ng/L. Samples
were taken once yearly, thus temporal variability of pesticide concentrations are not
accounted for in this dataset. However, given the persistent nature of prometon in water
EFED anticipates that it would be detectable up to a year following application, although
it may appear distant from the source, and will be at lower concentrations due to dilution.
In this dataset, prometon appeared to have a clear source affinity. It was detected in 3 of
the 11 wells in every year of sampling, but never detected in any of the other wells.
Generally, concentrations were close to the detection limit (0.01 |_ig/L), The maximum
detected in ground water was 0.06 |_ig/L.
Table 8 Summary of USGS Monitoring Data for Ground Water in the BSSEA
Water
Source
Range of
Sample
Dates
# of
Samples
# of
Detects
Frequency
of
Detection
(%)
Max
Cone.1
(mq/l)
Min
Cone.2
(mq/l)
Avg ^
Cone.3
(mq/l)
Buda
2001-2004
4
0
0
<0.01
<0.01
N/A
Buda
West
2001-2004
4
0
0
<0.01
<0.01
N/A
Ford Oaks
2001-2004
4
4
100
0.06
0.05
0.053
Ford Oaks
North
2001-2004
4
0
0
<0.01
<0.01
N/A
Mancheca
2001-2004
4
0
0
<0.01
<0.01
N/A
Pleasant
Hill
2001-2004
4
0
0
<0.01
<0.01
N/A
South
Lamar
2001-2004
4
0
0
<0.01
<0.01
N/A
Sunset
Valley
North
2001-2004
4
0
0
<0.01
<0.01
N/A
Sunset
Valley
South
2001-2004
4
4
100
0.02
0.01
0.013
Sunset
Valley
East
2001-2004
3
0
0
<0.01
<0.01
N/A
Sunset
Valley
West
2001-2004
3
3
100
0.01
0.01
0.01
1 If there were no quantifiable measurements, this is given as the highest LOD/LOQ in the series
2 If there were no quantifiable measurements, this is given as the highest LOD/LOQ in the series
3 Estimated
28
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3.2 Exposure Estimate Based on Modeling
The exposure assessment is an application of the standard approach outlined in the
Overview Document (U.S. EPA 2004), modified to reflect the hydrogeologic conditions
in the area surrounding Barton Springs. New regionally-specific PRZM scenarios,
representing both agricultural and non-agricultural use sites were developed for the
Barton Springs assessments (Appendix B), following the standard methodology for
scenario development (U.S. EPA 2005). Using standard methods, runoff estimates
predicted by the PRZM model are linked to the Exposure Analysis Modeling System
(EXAMS), simulating the runoff entering a natural water body. For most ecological risk
assessments, EFED uses a standard water body of fixed volume and geometry in
EXAMS. EXAMS incorporates the processes of degradation and sorption expected to
occur in ponds, canals, and first and second order streams. The standard water body is
static (no outflow). Concentrations in larger water bodies are expected to be lower, thus
the standard water body generally provides a conservative estimate of concentrations to
which aquatic organisms may be exposed.
Because of the potentially rapid transit of the applied pesticide to Barton Springs via a
ground water pathway, EFED opted to modify the standard methods, and calculate an
estimated spring concentration rather than using the standard pond. A short explanation
of the modeling is provided below, and more extensive descriptions can be found in
U.S. EPA 2006 and U.S. EPA 2007b.
3.2.1 Background
The Barton Springs salamander resides in a geographically limited area defined by a set
of spring-fed pools in the outskirts of the city of Austin. All of the springs are fed via
subsurface flow originating in fractured limestone (karst) of the Edwards Aquifer, which
extends to the south-southwest away from the pool system. This area is known as the
Barton Springs Segment of the Edwards Aquifer (BSSEA). The BSSEA includes four
distinct hydrogeologic zones. From west to east, these are the Contributing Zone, the
Recharge Zone, the Transition Zone, and the Artesian Zone.
Based on existing studies, surface water from the Contributing Zone and the Recharge
Zone are most likely to contribute directly to the Barton Springs system (Slade et al.,
1985, Hauwert et al., 2004). Ground water supplying the springs is derived from a
combination of perennial ground water flow and recharge that originates from both
infiltration of rainfall and downwelling from surface streams. Therefore, the exposure
assessment focuses on the subsurface pathway delivering ground water to the springs.
An extensive summary of how ground water in the BSSEA system travels is provided in
the ecological risk assessment for atrazine (EPA 2006b). This information is derived
from a number of studies conducted by the U.S. FWS, the U.S.GS, and the City of
29
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Austin, and is considered best available data (Slade et al., 1986, Hauwert et al., 2004,
USFWS 2005).
This assessment assumes that the estimated environmental concentration (EEC) is
derived from both ground water and surface runoff; thus, spray drift is not a factor in the
exposure assessment.
3.2.3 Modeling Approach
The Barton Springs are supplied predominantly with water discharging from fractures
and conduits formed in the Barton Springs Segment of the Edwards Aquifer (BSSEA) as
a result of dissolution of the fractured limestone aquifer over time. Approximately 85%
of the water that recharges this aquifer infiltrates through the beds of six creeks that cross
the recharge zone (Slade et al. 1986, Barrett and Charbeneau 1996), with the remaining
approximately 15% of the recharge derived from precipitation and recharge in interbed
areas in the recharge zone. In the BSSEA, natural ground water discharge occurs
primarily at Barton Springs complex (Lindgren et al., 2004). Recharge features in creek
bottoms overlying the recharge zone allow only a limited flow of water during a storm
event; therefore, water that is in excess of the flow capacities of recharge features leaves
the recharge zone as creek flow. The Contributing Zone encompasses the watersheds of
the upstream portions of the six major creeks that cross the Recharge Zone, and therefore
provides the source for most of the water that will enter the BSSEA as recharge. These
streams gain water, as they flow across the land surface in the Contributing Zone, from
the lower-permeability Glen Rose limestone of the Trinity aquifer (Lindgren et al., 2004).
Kuniansky (1989) estimated baseflow discharge from the Trinity aquifer to streams and
creeks in this area ranging from 25% to 90% of total flow. In the portion of the Trinity
aquifer nearest the contributing zone this was loosely estimated at 30%. The remainder
of water in creeks in the Contributing Zone is derived from precipitation and runoff.
The exposure modeling attempts to capture the most important aspects of the hydrology
unique to the Barton Springs area. Thus, the contributing zone and the recharge zone are
distinguished and treated separately. Runoff from the recharge zone is assumed to enter
the karst environment directly, whereas runoff from the contributing zone is assumed to
mix with stream water prior to entering the karst environment of the recharge zone. The
long-term average flow volume in the streams in the contributing zone was assumed to be
due 30%) to aquifer discharge (base flow) and 70 % to runoff, consistent with Kuniansky
(1989).
Masses and volumes of runoff were determined for this assessment from the right-of-way
scenario developed for this assessment. As with the Agency's standard exposure
modeling, 30 years of meteorological data for the Austin area were used to estimate 1-in-
10-year exposure in the Barton Springs.
30
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3.2.4 Equations to Estimate Prometon Concentrations
Contributing Zone.
Using the 70:30 contribution ratio established by Kuniansky (1989) the long-term
average stream flow was used to calculate an approximate average daily stream flow in
the contributing zone. The long-term (30 years simulated) runoff volume was calculated
for the right-of-way scenario using PRZM and the respective areas determined by the
landuse analysis.
n / \
^CZ '[Y^CZripht-nf-wav 1^'cXnon t (^*"0
where Vcz= 30 year simulated cumulative runoff volume [volume]
Vczdght-of-way,t = right-of-way runoff volume on day t in the contributing zone
[volume]
Vcznon-use,t = non-use runoff volume on day t in the contributing zone [volume]
n = number of days in simulation
The estimated daily aquifer-driven base flow in the streams within the contributing zone
was calculated from the 70:30 ratio as given by Kuniansky (1989):
Vbase
n I 0.70
(3.2)
where Vbase = the long-term average daily aquifer-driven stream volume
Daily runoff volume was calculated by adding the daily runoff flows as follows:
'X./ ^CZright-of-wayJ ^CZnon-useJ
where Vcz,t = the total runoff volume on day t in the contributing zone
Vczi,t= the volume for scenario i on any day t in the contributing zone
Daily stream volume was calculated by adding the base stream flow to the daily runoff
volume as follows:
^stream,t ~ ^CZ,t + ^base (3*4)
where Vstream,t = the total stream volume on day t in the contributing zone
31
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The concentration in runoff in the contributing zone was calculated directly from the
PRZM output and the area of the scenarios as follows:
C,
(M,
CZright—of—way ,t
)
(3.5)
where Ccz,t = the concentration in runoff across the contributing zone on any day t
MCzi,t = the mass of prometon in runoff in the contributing zone for scenario i on
any day t
Daily stream concentrations were calculated from the PRZM output, the area of the
scenario, the stream base flow, and the average base flow concentration as follows:
where Cstream,t = the concentration in contributing zone streams on any day t
Cbase = the average concentration monitored in base flow
The stream volume (Vstream,t) calculated in Eqn. 3.4, along with its associated
concentration (Cstream,t), calculated in Eqn. 3.6 are assumed to enter the recharge zone
where they mix with recharge zone runoff.
Recharge Zone.
Runoff originating in the recharge zone was determined in a similar manner as for the
contributing zone:
^RZJ ^'RZright-of-way^RZnon-useJ
where Vrz = runoff volume on day t in the recharge zone
VRZright-of-way, t = right-of-way runoff volume on day t in the recharge zone
VRZnon-use = non-use runoff volume on day t in the recharge zone
stream,t
(3.6)
32
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The concentration of prometon in recharge zone runoff was determined from the PRZM
mass output, the area represented by the scenario, and the volume of runoff in the
recharge zone as follows:
RZright-of-wayJ,)
v
v RZ,t
where Crz,i = the concentration in runoff across the recharge zone on any day t
MRZdght-of-way = the mass of prometon in runoff in the recharge zone for right-of-
way on any day t
Barton Springs Daily Concentrations.
The stream flow from the contributing area and the runoff from the recharge area are
assumed to mix in the groundwater, flow through the karst, and then upwell into Barton
Springs. Due to the assumption of instantaneous mixing of pesticide in the stream, the
volume of groundwater not passing through the springs is unimportant. Therefore, the
total discharge into the springs is calculated by:
^Springs,t ~ ^stream,t ^RZ,t (3*9)
where VsPrings,t= the total flow through the Barton Springs on day t
Based on these calculations, runoff from the recharge zone provides 11% of discharge
through the Barton Springs, on average. This corresponds with estimates by Slade et al.
(1986) and Barrett and Charbeneau (1996) that 15% of recharge to the Barton Springs
originates in the recharge zone and 85% originates in the contributing zone.
The concentration of prometon in Barton Springs is calculated:
n CrzjVrZj Cstream,stream,t t
^Springs,t —^ y (3.10)
" Springs, t
where Csprings,t = the daily concentration in Barton Springs
Daily EECs in the Barton Springs were post-processed (see Appendix E for details) in
order to provide durations of exposure. Peak, 21-day, and 60-day, average concentrations
were calculated across 30 years of daily EEC values. In order to match the standard
PRZM/EXAMS output, the maximum values for each of the 30 years of daily averages
were ranked and the 90th percentiles from the rankings were selected as the final 1-in-10-
year EECs for use in risk estimation.
33
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3.2.3 Label Application Rates and Intervals
Table 9 shows application rates, methods, and specific dates used in the exposure
assessment.
Table 9 Label Ap
plication Rates
Application Rate
(lbs ai /500ft )
Application Rate
(lb ai/A)
Application
Date
Application Method
Reference
0.23
20.04
Jan 32
Ground Spray
Prometon
Use Closure
Memorandum
1/22/07
0.23
20.04
Jan 32
Granular
1- Application rate calculated by lbs ai/500ft2*43,560 ft2/A
2- Based on emergence date in scenario
3.2.7 Exposure Modeling Input and Output
Table 10 shows input parameters for PRZM modeling, based on acceptable
environmental fate data from guideline studies.
Table 10 Input Parameters for PRZM Modeling
Parameter
Value
Source
Application Rate (kg a.i./ha)1-
ground spray
22.43
Use Closure
Memorandum
1/22/07
Molecular Weight (grams/mole)
225.3
Calculated
Solubility (mg/L)
620
Product Chemistry
Vapor Pressure (torr)
2.32E-6
Product Chemistry
Henry's Constant (atm mJ/mol)
1.21E-9
Calculated
Koc (L/kg-OC)
117.6
MRID 40225803
MRID 40145501
MRID 42313501
90th percentile half-life
Aerobic Soil Metabolism Half-life (days)
1422.49
Mean=697
SD=332.34
tgo n-1=3.078
n=2
Estimated from 2X
Aerobic Aquatic Metabolism Half-life (days)
2844.98
aerobic soil half-life
Anaerobic Aquatic Metabolism Half-life
(days)
557
MRID 40145501
Photodegradation in Water (days)
Stable
MRID 40225801
Hydrolysis Half-life (days)
Stable
MRID 41114801
Spray Drift Fraction
1%
Default value for
Ground
34
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Table 11 shows the estimated concentrations of prometon in the standard EXAMS pond
based on various application times and methods. This is for comparison purposes only,
and these concentrations are not used to calculate RQs.
Table 11 Estimated Concentrations in the Standard Pond for Prometon Based on a Texas
Rights-of-Way Scenario
Application
Application Rate
Peak
21 days
60 days
Technique
ug/L
Ground Spray
20.04
1670
1669
1659
Granular
20.04
1628
1618
1608
Because there was no way to directly determine how much of the watershed might be
treated with prometon, EFED used a process of what-if scenarios to determine what
percentage of the rights-of-way portion of the watershed could be treated without
exceeding the LOC for the most sensitive aquatic organism (freshwater algae, EC50 = 98
l_ig/L), Initially, the treated area was apportioned equally between the recharge zone and
the contributing zone. Once an overall clearance level was determined, zone-specific
clearance levels were determined. Table 12 shows the EECs for the 0.23/500ft2
application rate (maximum supported by registrant). Values shown are for the ground
spray, which is anticipated to be slightly higher than granular applications.
Table 12 Spring EECs Based on 0.23/500ft2 Ground Spray Application
Percentage of
right-of-way
treated
Percent in
contributing
zone
Percent in
recharge
zone
Peak
(ug/L)
21-day
(ug/L)
60 day
(ug/L)
What-if values
100
50
50
2,720
233
84
50
50
50
1,342
89
35
25
50
50
1,246
82
32
10
50
50
593
32
27
1
50
50
65
4.1
1.6
Clearance values
1.25
50
50
80
5.1
1.9
1
0
100
65
4.1
1.6
0.75
100
0
49
3.1
1.2
35
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4.0 Effects Assessment
Acute toxicity data for prometon used to evaluate the assessment endpoints is presented
in Table 13. EFED uses the most sensitive species in each evaluation category to assess
risk. The complete set of toxicity data available to EFED at the time of the assessment is
contained in Appendix B. The data set consists of toxicity data from acceptable guideline
tests submitted to the Agency by the registrant and open literature toxicity data that meets
established acceptability criteria (ECOTOX data).
Prometon is slightly toxic to both freshwater fish (surrogate for the salamander) and
freshwater invertebrates. EC50 for non-vascular aquatic plants is 0.098 mg/L. EC50 for
aquatic vascular plants is 0.624 mg/L. Some sublethal effects (potential endocrine
disrupting) were noted in a open literature study located by ECOTOX. These effects
occurred at prometon concentrations higher than concentrations in the assessment
endpoints.
Table 13 Aquatic Toxicity Profile for Prometon
Assessment
Endpoint
Surrogate
Species
Toxicity Value Used
Source
Citation
Comments
Direct Effects
Acute Toxicity to
Salamander
Rainbow
trout
LC50 = 12 mg/L
ECOTOX
5461
No comments
LC50 =19.6 mg/L
95% CI = 17.1-22.4 mg/L
Slope = 8.6
MRID
418109082
Sub-lethal effects:
(11.4 mg/L) lethargy,
hyperventilation
Chronic Toxicity
to Salamander
Fathead
minnow
NOAEC = 9.5 mg/L
LOAEC = 19.7 mg/L
MRID
41810902
Reduced survival and
hatching success at
19.7 mg/L
Indirect Effects (Prey Reduction)
Acute Toxicity to
Prey
Water flea
LC50 = 25.7 mg/L
95% CI =20.6-32.0
Slope = 3.2
MRID
41609109
No comments
Chronic Toxicity
to Prey
Water flea
NOAEC = 3.5 mg/L
LOAEC = 6.8 mg/L
MRID
41810903
Decreased
reproduction
Indirect Effects (Habitat Modification)
Acute Toxicity to
Plants
(non-vascular)
Green
alga
LC50 = 0.098 mg/L
MRID
41725305
No comments
Acute Toxicity to
Plants (vascular)
Duckweed
LC50 = 0.624 mg/L
ECOTOX
81431
Experimental pH (5.5)
lower than most natural
waters.
' Most sensitive endpoint, used to develop RQs
2 Similar range to most sensitive endpoint, and fits probit curve. Used to develop probability of
individual effects estimate.
36
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4.1 Summary of Aquatic Ecotoxicity Studies
Information used to develop the toxicity profile for prometon included registrant-
submitted guideline studies and open literature studies that met the criteria for inclusion
into ECOTOX.
4.1.1 Toxicity to Freshwater Fish
4.1.1.1 Acute Exposure (Mortality) Studies
Three registrant-submitted acute studies for freshwater fish were available. The most
recent study was one conducted on rainbow trout in 1991. This study determined the
LC50 to be 19.6 mg ai/L (95% CI 17.1-22.4 mg ai/L). Sublethal effects were noted
beginning at concentrations of 11.4 mg ai/L. These effects included discoloration,
lethargy, loss of equilibrium, and hyperventilation. Based on the test, the NOAEC was
6.4 mg/L. Toxicity of prometon to rainbow trout and to bluegill sunfish was also
evaluated in earlier tests (Accession # 231814, 1965). For the bluegill, the 96-hour LC50
was greater than the highest concentration tested (32 mg/L). No mortality occurred at
any of the test concentrations, although at the highest concentration test fish exhibited
darkened pigmentation on the skin. A definitive LC50 of 20 mg/L was determined for
rainbow trout. The trout exhibited darkened pigmentation of the skin at concentrations of
10 and 18 mg/L.
ECOTOX located a study of prometon toxicity to freshwater fish. The study examined
five species of fish: rainbow trout, crucian carp, brown bullhead catfish, bluegill, and
guppy (ECOTOX # 546). The 96-hour LC50S for these species ranged from 12 mg ai/L to
70 mg ai/L. Rainbow trout and guppy were the most sensitive, with an LC50 of 12 mg
ai/L, and crucian carp were the least sensitive. This study established an LC50 of 40 mg
ai/L for the bluegill. Fish exhibited dose-dependent paling in this study.
4.1.1.2 Chronic Exposure (Growth/Reproduction) Studies
The registrant submitted an early-life stage (ELS) test for the fathead minnow (MRID
41810902). Endpoints affected included survival and hatching success. The NOAEC
and LOAEC were 9.49 mg/L and 19.7 mg/L, respectively. Five test concentrations were
used, with mean-measured concentrations of 4.85, 9.49, 19.7, 37.0 and 82.5 mg/L. In the
37.0 mg/L treatment group, hatching success was significantly reduced (2.5-20%) as
compared to controls (68.6-72.6%). None of the fish in the 37.0 or 82.5 mg/L treatment
groups survived more than 4 days post hatch.
4.1.2 Toxicity to Aquatic Phase Amphibians
No studies regarding the toxicity of prometon to aquatic phase amphibians were located.
37
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4.1.3 Toxicity to Freshwater Invertebrates
4.1.3.1 Acute Exposure (Mortality) Studies
Two registrant-submitted studies were available for freshwater invertebrates, both using
Daphnia magna. A study conducted in 1977 (Accession #231814) determined a 48-hr
EC50 of 59.8 mg/L (95% CI 52.0-68.6 mg/L). No sublethal effects were described. A
later study (MRID 41609109, 1991) determined a 48-hr EC50 of 25.7 mg ai/L (95% CI
20.6-32.0 mg ai/L). This data fit a probit curve, and the slope was determined to be 3.2.
Immobilization and/or mortality, which were differentiated in this study, occurred at all
concentrations >11.1 mg/L. No sublethal effects were noted below the ECso-
ECOTOX located two open literature studies reporting effects of prometon on freshwater
invertebrates. In one study (ECOTOX#2820) exposure conditions were similar to
guideline studies, with the exception of the test duration, which the authors set at 26
hours (for operational convenience). Based on this study, the EC50 for Daphnia magna
was 35 mg/L. The focus of this study was on optimizing rearing conditions for the
animals, and developing a methodology for dose-response curves rather than determining
endpoints for specific chemicals. No mention of analytical confirmation of pesticide
concentrations is made, so values reported were assumed to be nominal. Neither a
confidence interval nor a slope was reported.
The second study used OECD Guideline #202 as the protocol for evaluating the effects of
a number of triazine herbicides (ECOTOX #13154). This study determined a 48-hr LC50
of 38 mg/L. No confidence interval or slope was included in study, and as raw data was
not provided, it could not be recalculated.
4.1.3.2 Chronic Exposure (Growth/Reproduction) Studies
The registrant submitted a Daphnia magna life-cycle toxicity test (MRID 41810903,
1991). Growth, survival, and reproduction endpoints were all affected. Reproduction
was the most sensitive endpoint, with a NOAEC of 3.5 mg ai/L and a LOAEC of 6.8 mg
ai/L. At the test concentration of 6.8 mg ai/L, reproduction was significantly reduced
compared to the controls. At a test concentration of 28.5 mg ai/L, reproduction ceased.
Growth (length) was also reduced at the 6.8 mg ai/L test concentration. The percentage
of daphnids surviving did not follow a dose-response curve. Mortality ranged from 0-
45%), with the 45%> kill occurring at the highest dose. The study was classified core.
Sub-lethal effects other than measure endpoints were not reported.
4.1.3.3 Sublethal Effects
ECOTOX located a study evaluating potential endocrine disrupting effects of prometon
and several other methoxytriazine herbicides (ECOTOX#86407). Paired fish were
exposed to concentrations of prometon ranging from 19.6 to 999 |j,g/L (mean-measured)
For prometon, the study also included a 21-day fathead minnow reproduction test.
Exposure to prometon did not reduce cumulative fecundity, although there a slight
decrease was noted in the first 7 days of the test. By the end of the test, fish appeared to
have recovered and/or adapted. Authors measured a number of endocrine system-
38
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mediated endpoints, including plasma vitellogenin and estradiol concentrations, brain and
ovary aromatase activity, male tubercle development, and development of the male fat
pad (an androgen-responsive tissue). Exposure to >19.6 |j,g/L lowered the weight of the
fat pad relative to body wet weight. Female plasma testosterone concentrations were
increased at 19.6 ng/L, but not at higher concentrations. The authors concluded
"prometon may cause subtle endocrine and/or reproductive effects in fathead minnows,
but no clear mechanism of action was observed." Based on data presented, EFED
concluded that modification of some endocrine-mediated activity occurred in this
laboratory situation, but the majority of endpoints measured appeared unaffected.
Likelihood of such effects occurring, and/or the ramifications of those modifications on
the survival, growth, and reproduction of wild populations of fish are uncertain.
4.1.4 Toxicity to Aquatic Plants
A registrant-submitted guideline study on the effects of prometon on green algae
(Scenedesmus capricornutum) was available (MRID 41725305). The study determined a
120 hr (5 day) EC50 of 0.098 mg/L (95% CI 0.088-0.108 mg/L) and aNOAEL of 0.032
mg/L. The study author calculated a 168 hr (7 day) EC50 of 0.210 mg/L (95% CI 0.133-
0.334 mg/L), indicating there may be some recovery with longer exposures. EC50S were
determined based on reduction in cell growth.
ECOTOX located a study evaluating toxicity of several triazine pesticides to duckweed
(Lemna minor). The study (ECOTOX#81431) determined an EC50 of 0.624 mg/L and an
EC50 of 0.246 mg/L. The study also evaluated the effects of exposure to multiple
triazines, and evaluated recovery response of the plants following removal to clean water.
Authors concluded that the triazines tested (ametryn, atrazine, prometon, and prometryn)
had an additive toxicity. They also noted the growth rate of the exposed plants displayed
an almost complete recovery within 3 days after removal to clean water.
39
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4.2 Use of Probit Slope Response Relationship
Generally, available toxicity data provides and LC50 or an EC50, (the concentration at
which 50% of the test populatin exhibits the designated endpoint, usually mortality).
Because the Endangered Species Act (ESA) requires determination of potential effects at
an individual level, this information must be extrapolated from existing data. The Agency
uses the probit dose response relationship as a tool for deriving the probability of effects
on a single individual (U.S. EPA, 2004). The individual effects probability associated
with the acute RQ is based on the mean estimate of the probit dose response slope and an
assumption of that probit model is appropriate for the data set. In some cases, probit is
not the appropriate model for the data, and EFED has low confidence in extrapolations
from these types of data sets. 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. 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). Probability of individual
effects for the various assessment endpoints is provided below in Table 14.
Table 14 Probability of Individual Effects
Assessment
Endpoint
Surrogate
Species
LC and Slope
Fits Probit
Chance of
Individual
Effect
Direct Effects
Acute Toxicity to
Salamander
Rainbow
trout
19.6 mg/L and 5.0 (lower bound)
19.6 mg/L and 8.6
19.6 mg/L and 12.2 (upper bound)
Yes
1 in 2.6 x10 lu
1 in 4.3 x1028
1 in 2.0 x1056
Chronic Toxicity
to Salamander
Fathead
minnow
Evaluated based on no effects level,
chance of individual effects evaluation not applicable
Indirect Effects (Prey Reduction)
Acute Toxicity to
Prey
Water flea
25.7 mg/L and 2.2 (lower bound)
25.7 mg/L and 3.2
25.7 mg/L and 4.1 (upper bound)
Yes
1 in 4.8
1 in 6.4 x104
1 in 2.1 x107
Chronic Toxicity
to Prey
Water flea
Evaluated based on no effects level,
chance of effects evaluation not required
Indirect Effects (Habitat Modification)
Acute Toxicity to
Plants (vascular)
Green
algae
Evaluated based on no effects level,
chance of individual effects evaluation not applicable
Acute Toxicity to
Plants
(non-vascular)
Duckweed
40
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4.3 Incident Database Review
EFED's incident database contained only two incidents related to prometon. Based on
information reported, one of these incidents (Incident ID 1014409-078) appears to have
been a case of misuse, where a paving contractor used prometon on a roadway and the
resulting runoff killed trees and lawn plants near the road. The report notes that the
application was not in accordance with the label. The second incident (Incident ID
1005895-355) was a fish kill. The magnitude of the kill is listed as unknown, and the kill
is attributed to an accidental spill of a prometon product into a contained pond.
EFED's incident database contains information regarding adverse effects associated with
particular pesticide applications that are reported to the manufacturer/distributor of the
chemical. While the registrant is required by law to report adverse effects to the Agency,
reporting of incidents by the public and/or state and local agencies is largely voluntary.
Thus, there may be incidents that are not reported to the Agency. Generally, a large
number of reported incidents may indicate a high degree of hazard for non-target species
exposed to the pesticide. However, the converse is not necessarily true, and a small
number of reported incidents should not be interpreted as implying any degree of "safety"
for non-target species.
41
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5.0 Risk Characterization
5.1 Risk Estimation
Risk quotients (RQs) were calculated for all of the what-if scenarios and for the
background concentration. Background concentration was estimated at 0.01 |_ig/L, based
on the concentrations detected by USGS in Upper Springs and in the groundwater wells.
Table 15 shows the RQs for background concentrations, for EECs when 100% of the
right-of-way landuse (4.3% of the entire watershed) is treated and for EECs when 1%
right-of-way landuse (4.3% of the entire watershed) is treated (0.043% of the entire
watershed). No chronic risk LOCs are exceeded at any concentration. Acute risk LOCs
are exceeded for all assessment endpoints if 100% of the right-of-way landuse area is
treated at the rate of 0.23 mg ai/500 ft2. No acute risk LOCs for any assessment
endpoints are exceeded if only 1% of the right-of-way landuse area is treated, assuming
the area is equally divided between recharge zone and contributing zone. If the treated
area is exclusively in the contributing zone (which supplies more water to the springs
complex), only 0.15% of the right-of-way landuse area can be treated without exceeding
any acute risk LOCs. These estimations assume all areas are treated on the same day.
Table 15 Risk Quotients for Prometon
Assessment
Endpoint
Surrogate
Species
Concentration Estimate
RQ
LOC
Exceedence
Direct Effects
Acute Toxicity to
Salamander
Rainbow
trout
Background
Spring EEC (100% ROW treated)
Spring EEC (1% ROW treated)
<0.05
0.23
<0.05
No
Yes
No
Chronic Toxicity to
Salamander
Fathead
minnow
Background
Spring EEC (100% ROW treated)
Spring EEC (1% ROW treated)
<0.05
<1.0
<1.0
No
No
No
Indirect Effects (Prey Reduction)
Acute Toxicity to
Prey
Water flea
Background
Spring EEC (100% ROW treated)
Spring EEC (1% ROW treated)
<0.05
0.11
<0.05
No
Yes
No
Chronic Toxicity
to Prey
Water flea
Background
Spring EEC (100% ROW treated)
Spring EEC (1% ROW treated)
<0.05
<1.0
<1.0
No
No
No
Indirect Effects (Habitat Modification)
Acute Toxicity to
Plants (vascular)
Green
algae
Background
Spring EEC (100% ROW treated)
Spring EEC (1% ROW treated)
<0.05
28
<1.0
No
Yes
No
Acute Toxicity to
Plants
(non-vascular)
Duckweed
Background
Spring EEC (100% ROW treated)
Spring EEC (1% ROW treated)
<0.05
4.4
<1.0
No
Yes
No
1 LOCs used in this assessment:
Aquatic animals acute risk endangered species 0.05
Aquatic animals chronic risk 1.0
Aquatic plants acute risk 1.0.
42
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Because no usage data was located, EFED opted to use the EECs to back calculate the
amount of land area treated and amount of active ingredient that would need to be
applied, and then make a reasoned decision regarding potential impacts of prometon use.
Table 16 shows the number of acres treated and the amount of active ingredient applied
that correspond with each what-if scenario and clearance values. The 1% treated area
(50% recharge, 50% contributing) is the clearance level for direct effects on the
salamander and effects on the freshwater non-vascular plant (algae), which would
constitute a potential indirect effect on the salamander. Clearance levels for prey items,
(represented by Daphnia magna), and for the freshwater vascular plants are at the 10%
treated right-of-way area.
Table 16 shows the correlation between the percentage of land treated and the actual
amount of acres that would be treated and the amount of prometon applied. As no usage
data is available, and the use sites may actually be located anywhere within the action
area, evaluating the amount of prometon necessary to cause exceedences and comparing
it against the number of acres reasonably expected to be treated is essentially the only
way for EFED to make a determination regarding potential impacts on the salamander.
Table 16 Correlation Between Percentage of ROW Treated and Amount of Prometon
Applied
Percentage of
Right-of-way
Land use
Treated
Percent in
Recharge Zone
Percent in
Contributing
Zone
Acres Treated
Prometon
Applied
(lb ai)
What-if Scenarios
100
50
50
10,978
220,006
50
50
50
5,489
110,003
25
50
50
2,745
55,001
10
50
50
1,098
22,001
1
50
50
110
2,200
Clearance
1
100
0
110
2,200
0.75
0
100
82
1,650
43
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5.2 Risk Description
The estimation of water concentration is based on the assumption that all locations in the
watershed are treated simultaneously. For prometon, which is persistent in aquatic
systems, and may typically be applied once a year, EFED has opted to consider the
amount of active ingredient associated with each water concentration as a maximum per
year. EFED believes that this is a reasonable method for evaluating risk associated with
this chemical in the absence of usage data. The assumption of simultaneous applications,
along with some conservative estimators in the modeling process, is anticipated to
provide the benefit of doubt to the species. Effects determinations, described below, are
made in terms of amount of active ingredient applied.
5.2.1 Direct Effects
Based on LOC exceedences, using the fish as a toxicity surrogate, acute effects from
prometon application may occur if approximately 22,000 lbs of prometon are applied to
the contributing zone and recharge zone, with the treatments divided equally between the
two zones. Thus, application of this amount of prometon constitutes a may affect, and
application of less than 22,000 lbs of prometon is no effect. Based on available toxicity
data, chronic effects are not anticipated even if the entire right-of way acreage is treated
with prometon.
5.2.2 Indirect Effects (Reduction in Prey Base)
LOC exceedences for aquatic invertebrates occur when 25% of the rights-of-way are
treated, equivalent to application of approximately 55,000 lbs prometon in the
contributing zone and recharge zone. This constitutes a may affect. At total yearly
applications lower than this amount, it would be a no effect. Based on available toxicity
data, chronic effects are not anticipated even if the entire right-of way acreage is treated
with prometon.
5.2.3 Indirect Effects (Habitat Degradation)
As part of the indirect effects analysis, reduction of both non-vascular plants and vascular
plants in the Barton Springs system is considered. Non-vascular plants (plankton,
periphyton, and some bryophytes) are primarily a food source for the salamander's prey
items. Vascular plants serve as structure in the Barton Springs system, providing
attachment points for periphyton, and refugia for both the salamander and its prey.
Of the assessment endpoints selected for ecosystem supporting the Barton Springs
salamander, the green algae is most sensitive to the effects of prometon. To clear the
acute risk LOC for the algae, only 1% of the right-of-way landuse area can be treated
with prometon, equivalent to application of 2,200 lbs in the watershed in a year. If the
application is all in the contributing zone, only 1,650 lbs can be applied. Yearly
applications of >1,650 lbs of prometon in the BSSEA constitute a may effect based on
exceedences for aquatic non-vascular plants. Applications of less than 1,650 are
considered no effect based on current determination criteria.
44
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The freshwater vascular plants, represented by duckweed, are slightly less sensitive than
the non-vascular plants represented by the green algae. Acute risk LOCs for the vascular
plants are not exceeded when 10% of the watershed is treated with prometon, equivalent
to 22,000 lbs. Yearly applications of >22,000 lbs of prometon in the BSSEA constitute a
may effect based on exceedences for aquatic non-vascular plants. Applications of less
than 22,000 are considered no effect based on current determination criteria.
Based on data (ECOTOX 81431) that indicate aquatic plants recover when prometon is
removed from the systems, and the extent of impact that may be necessary to reduce plant
growth sufficiently to affect the growth, survival, or reproduction of the salamander,
exceedence of only the LOC for non-vascular plants for a short duration is not anticipated
to have a measurable effect on the growth, survival, or fecundity of the salamander. This
results in a determination of not likely to adversely affect (insignificant). Although fate
modeling indicates the concentration of prometon in the static pond decreases very little
in the 60-day period evaluated, decreases will occur in a flowing system like Barton
Springs unless there is continuous loading of the pesticide. However, exceedence of both
the vascular and non-vascular plant LOCs indicates that a substantial portion of the
aquatic plant community could be at risk. Thus, yearly applications of >1,650 lbs but <
22,000 lbs prometon ai in the BSSEA is determined to be may affect, but not likely to
adversely affect the Barton Springs salamander due to indirect effects on primary
productivity. Yearly applications of > 22,000 lbs prometon ai care deteremined to be
may affect, likely to adversely affect.
5.3 Risk Conclusions
After completing the analysis of the effects of prometon on the Federally listed
endangered Barton Springs salamander (Eurycea sosorum) in accordance with methods
delineated in the Overview document (USEPA 2004), EFED concludes that the use of
prometon (PC 080804) in the BSSEA is anticipated to have the following effects:
Total yearly use
<1,650 lbs ai No effect
>1,650 lbs ai but <22,000 lb ai May affect, not likely to adversely affect (Indirect)
>22,000 lbs ai May affect, likely to adversely affect (Direct)
Rationale for each component assessed is provided in Table 17.
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Table 17 Effects Determination for Prometon
Assessment Endpoint Effects determination
Basis for Determination
Direct Effects
Survival, growth, and
reproduction of Barton
Springs salamander
<22,000 lbs yearly
No effect
> 22,000 lbs yearly
May affect
LAA
No chronic risk LOCs are exceeded at any
yearly application assessed.
At applications of<22,000 lbs yearly, acute risk
LOCs for the salamander are not exceeded.
At applications of > 22,000 lbs yearly, acute
risk LOCs for the salamander are exceeded.
Due to the uncertainties associated with actual
usage, EFED has not attempted to discern an
NLAA point for direct effects on the
salamander.
Indirect Effects
Reduction of prey
(i.e., freshwater
invertebrates)
<55,000 lbs yearly
No effect
> 55,000 lbs yearly
May affect
LAA
No chronic risk LOCs are exceeded at any
yearly application assessed.
At applications of<55,000 lbs yearly, acute risk
LOCs for aquatic invertebrates are not
exceeded.
At applications of >55,000 lbs yearly, acute risk
LOCs for aquatic invertebrates are exceeded.
Due to the uncertainties associated with actual
usage, EFED has not attempted to discern an
NLAA point for indirect effects on the
salamander.
Degradation of habitat
and/or primary
productivity
(i.e., aquatic plants)
<1,650 lbs yearly
No effect
>1,650 but <22,000
lbs yearly
May affect
NLAA
(insignificant)
> 22,000 lbs yearly
May affect
LAA
No LOC exceedences at <1,650 lbs yearly.
At 1,650 lbs yearly, acute risk LOCs exceeded
for non-vascular aquatic plants, but not
vascular aquatic plants. Recovery of plant
community is expected. Reduction and/or
modifications in plant community not
anticipated to be severe enough to affect
growth, survival, or reproduction of
salamander.
At applications of >22,000 lbs yearly, acute risk
LOCs for both vascular and non-vascular
aquatic plants are exceeded. Reduction and/or
modifications in plant community may be
severe enough to affect growth, survival, or
reproduction of salamander.
1 Determinations are based on total lbs of active ingredient used yearly in the BSSEA, assuming
all applications are made simultaneously
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6.0 Uncertainties
Risk assessment, by its very nature, is not exact, and requires the risk assessor to make
assumptions regarding a number of parameters, to use data which may or may not
accurately reflects the species of concern, and to use models which are a simplified
representation of complex ecological processes. In this risk assessment, EFED has
attempted to locate the best available data regarding such important parameters as the life
history of the Barton Springs salamander, typical environmental conditions in the
proximity of Barton Springs, toxicity of prometon, and uses of prometon in the action
area. Frequently, such information are better expressed as ranges rather then points, and
when this is the case, EFED has opted to make use of the end of range which would
result in a conservative estimate of risk, in order to provide the benefit of doubt to the
species. These uncertainties, and the directions in which they may bias the risk estimate,
are described below.
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, estimated peak exposures are generally 3-4 orders of
magnitude above the highest detections in any of the four springs or surface waters in the
Barton Springs area. 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 assumptions of no degradation, dilution, or mixing in
the subsurface transport from the use site to the Barton Springs complex. The modeling
exercise conservatively assumes that the spring and the application site are adjacent. In
reality, they are not, and there are likely to be environmental processes not accounted for
that will reduce the predicted exposures.
6.1.1 Modeling Assumptions
The uncertainties incorporated in the exposure assessment cannot be quantitatively
characterized. However, given the available data and EFED's policy to rely on
conservative modeling assumptions, it is expected that the modeling results in an over-
prediction in exposure. Qualitatively, conservative assumptions which may affect
exposure include the following:
• The assessment assumes all applications have occurred concurrently on
the same day at the exact same application rate.
• The assessment assumes all applications are at maximum label rate.
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6.2.2 Impact of Vegetative Setbacks on Runoff
EFED does not currently have an effective tool to evaluate the impact of vegetative
setbacks on runoff and pesticide loadings. The effectiveness of such setbacks is highly
dependent on the condition of the vegetative strip. A well-established, healthy vegetative
setback can be a very effective means of reducing runoff and erosion from agricultural
fields and may substantially reduce loading to aquatic ecosystems. However, a setback
that is narrow, of poor vegetative quality, or channelized is likely to be ineffective at
reducing loadings. The presence and quality of setbacks are site-specific, and may vary
widely, even within a small geographic area. EFED does not currently incorporate any
"buffer reduction" in its exposure estimates. Until such time as quantitative methods to
estimate the effect of vegetative setbacks of various conditions on pesticide loadings
become available, EFED's aquatic exposure predictions are likely to overestimate
exposure where healthy vegetative setbacks exist and may underestimate exposure where
poorly developed, channelized or no setbacks exist.
6.2.3 PRZMModeling inputs and Predicted A quatic Concentrations
EFED currently typically uses the linked PRZM/EXAMS model which produces
estimated aquatic concentrations based on site conditions and historical meteorological
files (generally 30-year), although for this assessment, EXAMS has been decoupled, and
other methods are used to estimate water concentrations. The "peak" pesticide
concentration used in the assessment is probability-based, and is expected to be exceeded
once within a ten-year period. PRZM is a process-based "simulation" model, which
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. The two major components affecting estimated pesticide
loading are hydrology and chemical transport. Water movement in and off the field is
simulated by the use of generalized soil parameters, including field capacity, wilting
point, and saturation water content. Soils in each scenario are selected to represent high
availability conditions for the pesticide. The chemical transport component simulates the
method of pesticide application on the soil or on the plant foliage and the environmental
processes acting on the pesticide. Dissolved, adsorbed, and vapor-phase concentrations
in the soil are estimated by simultaneously considering the processes of pesticide uptake
by plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection,
dispersion, and retardation.
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Uncertainty associated with each of these individual components adds to the overall
uncertainty of the modeled concentrations. Equations in the model have not been shown
to exert any directional bias. Model inputs from the required environmental degradation
studies are chosen to represent the upper confidence bound of the mean, and are not
expected to be exceeded in the environment 90% of the time. Mobility input values are
selected to be representative of conditions in the open environment. Natural variation in
soils adds to the uncertainty of modeled values. Factors such as application date, crop
emergence date, and canopy cover can affect estimated concentrations. Ambient
environmental factors, such as soil temperatures, sunlight intensity, antecedent soil
moisture, and surface water temperatures may cause actual aquatic concentrations to
differ from the modeled values..
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. For guideline tests, young (and theoretically more
sensitive) organisms are used. Testing of juveniles may overestimate toxicity at older age
classes for active ingredients of pesticides which act directly (without metabolic
transformation) on the organism, because younger age classes often have not developed
enzymatic systems associated with the detoxification of xenobiotics. When the available
toxicity data provides a range of sensitivity information with respect to age class, the risk
assessors use the most sensitive life-stage information as measures of effect.
6.2.2 Use of Surrogate Species Data
Currently, there are no FIFRA guideline toxicity tests for amphibians. Therefore, in
accordance with EFED policy, data for the most sensitive freshwater fish are used as a
surrogate for aquatic-phase amphibians such as the Barton Springs salamander. Species
sensitivity distribution data for amphibians indicates the range of sensitivity is similar to
that of freshwater fish (Birge et al., 2000). Therefore, the endpoint based on freshwater
fish ecotoxicity data is assumed to be protective and extrapolation of the risk conclusions
from the most sensitive tested species to the Barton Springs salamander is more likely to
overestimate the potential risks than to underestimate the potential risk. At the time of
the assessment, it was not known where Barton Springs salamanders may fall in a species
sensitivity distribution.
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6.2.3 Extrapolation of Effects
Length of exposure and concurrent environmental stressors (e.g, urban expansion, habitat
modification, decreased quantity and quality of water in Barton Springs, predators) will
likely affect the response of the Barton Springs salamander to prometon. Because of the
complexity of an organism's response to multiple stressors, the overall "direction" of the
response is unknown. Additional environmental stressors may decrease or increase the
sensitivity to the herbicide. 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
6.2.4 Acute LOC Assumptions
The risk characterization section of this assessment includes an evaluation of the potential
for individual effects. The individual effects probability associated with the acute RQ is
based on the assumption that the dose-response curve fits a probit model. It uses the
mean estimate of the slope and the LC50 to estimate the probability of individual effects.
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