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where the rate of detection for 2,025 analyses of surface water between 2001 and 2012
was 0.44%, and the greatest estimated concentration was 0.0356
g CPYO L −1 .
Databases of pesticide concentrations in surface waters of California (288 analyses,
CDPR 2012 ) and Washington State (964 analyses, WDOE 2012 ) contained no detec-
tions for CPYO. In a study of pesticides in surfaces waters at various elevations above
the Central Valley of California (LeNoir et al. 1999 ), CPYO was detected at concentra-
tions ranging from 0.024 to 0.037
μ
μ
g CPYO L −1 as compared to CPY which ranged
from 0.089 to 0.124
g CPY L −1 at the same locations. Thus, the frequency of detec-
tion was small and the concentrations, when measurable, also were small.
Risks from measured concentrations of CPYO were all small. The RQ for the
greatest measured concentration of CPYO in surface waters (0.054
μ
μ
g L −1 ) and the
LC 50 of 1.1
g L −1 for the most sensitive freshwater (FW) organism tested ( L. mac-
rochirus ) was 0.049, which is below the level of concern (LOC) for highly valued
species (USEPA 2004 ).
The small estimated risks from CPYO are supported by several lines of evidence.
CPYO is formed from CPY in the atmosphere and is detected in air near sites of
application and at more distant locations (see discussion in Mackay et al. 2014 ).
Because CPYO is more polar than CPY (log KOW of 2.89 vs. 5, Tables 5 and 6 in
Mackay et al. 2014 ) it would be expected to partition into precipitation and accumu-
late to a greater extent than CPY in surface waters. However, this does not occur; for
example, LeNoir et al. ( 1999 ) showed that CPYO was detected in water at smaller
concentrations than CPY, the opposite of those in air sampled at the same locations.
The most likely reason for this is the greater rate of hydrolysis of CPYO compared
to CPY with half-lives of 13 d vs. 30-50 d, respectively (Tables 7 and
μ
6 in Mackay
et al. 2014 ). Since CPYO is more polar than CPY (Mackay et al. 2014 ), it would not
be expected to be taken up into and accumulate in organisms as much as CPY.
Finally, because CPYO is the active toxic form of CPY and is transformed in vivo ,
the toxicity of CPYO would be implicitly included in toxicity testing in the labora-
tory and cosms where animals are exposed to CPY. For all these reasons, environ-
mental risks from CPYO were smaller than those for CPY. Therefore, a separate and
detailed risk assessment was not required.
4.2
Risks from Modeled Exposures to CPY
Probabilistic analysis of risks . The higher-tier modeling of CPY concentrations in
surface waters for three scenarios of intensive use and vulnerability to runoff and
contamination of surface waters (Sect. 6.2 in Williams et al. 2014 ) provided fre-
quency distributions of annual maximum 96-h time-weighted mean concentrations.
These values could then be compared to distributions of 48- to 96-h toxicity values
from the SSDs (Sect. 3.2 ) using probabilistic approaches. To characterize the risks
graphically, these values were used to construct joint probability curves (JPCs,
ECOFRAM 1999 ; Giesy et al. 1999 ). Reference lines proposed for interpretation of
JPCs (Moore et al. 2010 ) were added to the graphs.
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