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of aquatic insects, from 0.05 to >300
μ
g L −1 ; and for 25 species of fi sh, from 0.53 to
>806
g L −1 . The concentrations affecting 5% of species (HC5) derived from the
SSDs were 0.034, 0.091, and 0.820
μ
g L −1 for crustaceans, insects, and fi sh, respec-
tively. Limited toxicity data for amphibians suggested that they were less sensitive
to CPY than fi sh. The NOAEC eco in 16 micro- and meso-cosm studies conducted in
a variety of climatic zones was consistently close to 0.1
μ
g L −1 . These results indi-
cated that measured concentrations of CPY in surface waters (see Williams et al.
2014 ) are rarely greater than the thresholds for acute toxicity to even the most sensi-
tive aquatic species. Comparison of limited toxicity data for benthic organisms to
measured concentrations of CPY in sediments suggested de minimis risks. These
conclusions are consistent with the small number (4) of kills of fi sh and/or inverte-
brates reported for use of CPY in U.S. agriculture between 2002 and 2012. The four
incidents over that period of time were the result of misuse.
Analysis of risks from measured exposures showed that the decline in CYP con-
centrations in surface waters after labeled use-patterns changed in 2001 resulted in
decreased risks for crustaceans, aquatic stages of insects, and fi sh. A probabilistic
analysis of 96-h time-weighted mean concentrations, predicted by use of model
simulation for three focus-scenarios selected for regions of more intense use of CPY
and vulnerability to runoff, showed that risks from individual and repeated expo-
sures to CPY in the Georgia and Michigan watersheds were de minimis . Risks from
individual exposures in the intense-use scenario from California were de minimis
for fi sh and insects. Risk was small for crustaceans, which are the most sensitive
class of organisms.
Risks from repeated exposures in the California intense-use scenario were judged
not to be ecologically relevant for insects and crustaceans, but there were some risks
to fi sh. Limited data show that CPYO is of similar toxicity to the parent compound.
Concentrations of CPYO in surface waters are smaller than those of CPY and less
frequently detected (Williams et al. 2014 ). Risks for CPYO in aquatic organisms
were found to be de minimis .
Limited data on recovery of AChE activity after inhibition with CPY suggested
that conservative intervals between sublethal exposures of 2 weeks for arthropods
and 4-8 weeks for fi sh would be suffi cient to mitigate against cumulative toxicity.
In the focus scenarios in Michigan and Georgia, the likelihood of cumulative toxic-
ity was very small, although some cumulative toxicity might occur in the high-use
focus scenario in California. Lack of good information on recovery of AChE in
relevant species of fi sh and arthropods was identifi ed as a source of uncertainty.
μ
6
Risks of Chlorpyrifos to Birds
The sixth paper in this series (Moore et al. 2014 ) evaluated the risks of CPY to birds
and built upon past assessments of CPY, including the most recent EPA re-registra-
tion assessment (USEPA 1999 ), and a refi ned probabilistic assessment of risk to
birds by Solomon et al. ( 2001 ). Since these assessments were completed, there have
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