Environmental Engineering Reference
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MO is particularly noticeable when considering soil applications of CPY (Fig.
5
).
Overall, runoff losses are much smaller in the more arid western states and in areas
with lighter textured soil.
Sensitivity analysis of the effect of use practices on runoff of CPY
. The national
vulnerability assessment compared the relative runoff potentials of CPY across the
U.S., based on soil properties and weather conditions. However, labels for CPY
permit different use practices that cannot be assessed in a comprehensive manner at
a national scale. Therefore, a sensitivity analysis was performed on use practices of
CPY to determine conditions that can result in the highest potential runoff of CPY
to aquatic systems. The sensitivity analysis was used to narrow the application prac-
tices and geographical areas of the country that we considered in selecting particu-
lar watersheds for more detailed analyses.
The analysis was conducted using model scenarios and procedures developed by
USEPA's Office of Pesticide Programs for ecological risk assessments (USEPA
2000
). The scenarios represent a hypothetical environment—a 10-ha field draining
into a 1-ha by 2-m deep pond. The pond remains at a constant volume that receives
pesticide loads from drift and runoff, but not the corresponding influx of water that
would occur during a runoff event. Scenario selection began with review of a pre-
liminary drinking water assessment of CPY conducted by USEPA (USEPA
2011
).
The scenarios associated with the highest exposures were selected for the sensitivity
analysis: CA-grape, PA-turf, GA-pecans, MI-cherries, and FL-citrus. Several addi-
tional scenarios developed by USEPA were included in the analysis to account for
other geographical areas and crops that were associated with either high use of CPY
(Figs.
1
and
2
) and/or high runoff potential (Figs.
5
and
6
). The additional scenarios
include CA-citrus, IL-corn, IN-corn, NC-corn, NE-corn, NC-apples, and NY-grape.
The counties associated with these scenarios are depicted (Fig.
7
).
Environmental fate properties of CPY (Table
5
) and patterns of application
(Table
6
) developed for this study were used in the simulations. Certain application
patterns for CPY were not represented correctly by USEPA (
2011
) in their assess-
ment (see Racke et al.
2011
) and therefore, the application patterns were reviewed
and modified as necessary to better represent labeled uses. Specific items reviewed
included: application methods, dates, rates, and timing. To simulate the greatest
concentrations of CPY in aquatic systems, maximum label rates and minimum
reapplication intervals were evaluated in the modeling. In some cases, several dif-
ferent application practices were represented for a specific crop location (Table
6
).
Two sets of simulations were conducted for each scenario—one using the shorter
aerobic soil metabolism half-life value of 28 d and the other using a longer aerobic
soil metabolism half-life value of 96 d. The source and rationale for these chemical
properties were discussed in Sect. 1.2.
Estimated environmental concentrations from the short and long aerobic soil
half-live scenarios are presented in Fig.
8
. Concentrations are markedly greater for
certain scenarios (e.g., GA-pecan1, FL-citrus2, MI-cherries1, and IL-corn3). For
other scenarios (e.g., CA-citrus3 and FL-citrus2) differences were negligible. Two
scenarios (GA-pecans1 and MI-cherries1) resulted in the highest estimates of expo-
sure concentrations and became a significant factor in selecting watersheds for the
exposure assessment.
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