Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 152

more relevant to the fi eld. Results for cosms thus provided another line of evidence
for characterization of the risks of CPY under conditions that are more representa-
tive of conditions in the fi eld.
Risks to aquatic organisms from measured exposures were assessed by compar-
ing the 95th centile concentrations to the HC5s for the SSDs. These data may not
fully capture peak exposures but suggested that there were de minimis risks for all
aquatic organisms from exposures measured after use patterns were changed in
2001. The analyses also showed that risks had decreased from those prior to 2001,
which leads to the conclusion that the changes made in 2001 and 2005 to the labeled
use patterns, and possibly other changes in general pesticide stewardship, mitigated
CPY exposures and reduced risks.
Estimated exposures from models for three focus-scenarios, representing greater
vulnerability to exposures than other use scenarios (Williams et al. 2014 ), allowed
the assessment of risks based on 96-h time-weighted-mean concentrations that were
matched to the 48-96 h toxicity data. Based on the joint probabilities of distribu-
tions of data for exposure and toxicity, we concluded that risks for fi sh and aquatic
stages of insects were de minimis in all three regions. However, in the intensive-use
scenario of Orestimba Creek, in California, risk to crustaceans was greater and
deemed to be not de minimis . Further analysis of risks from repeated exposures to
CPY, in these three focus-scenarios, confi rmed the de minimis risks to crustaceans,
insects, and fi sh in the focus-scenarios in GA and MI. Repeated exposures in
Orestimba Creek, CA suggested small risks to fi sh, insects, and crustaceans. We
concluded that repeated exposures to insects and crustaceans would not be ecologi-
cally relevant because of the potential for rapid recovery in these taxa. Risks for fi sh
may be somewhat greater because there is more uncertainty regarding recovery of
the target enzyme AChE and because of their longer reproductive cycles. The lack
of fi sh-kills since 2002 in the U.S. that were associated with confi rmed exposure to
CPY is consistent with the small risks to fi sh and the smaller exposures in surface
waters since the change in the labeled uses.
Too few data on toxicity of CPYO were available to conduct a probabilistic risk
assessment but, on the basis of the available data and the large margins of exposure,
we concluded that risks of CPYO to aquatic organisms were de minimis . CPYO is
the active metabolite of CPY, and its toxicity is subsumed by the parent CPY. It is
thus not surprising that CPYO's toxicity is similar to that of CPY. CPYO is more
rapidly hydrolyzed in water and is more polar than CPY and is less likely to be taken
up into aquatic organisms. Detections of CPYO in surface waters were infrequent,
and the concentrations were all less than toxicologically signifi cant values for the
one fi sh and one invertebrate for which data were available.
This ERA was supported by several strong data-sets. There is a good database of
toxicity values for CPY, and many of these tests are of high quality. They are cer-
tainly suffi cient to characterize acute toxicity to insects, crustaceans, and fi sh. There
are also large sets of data for measured values in surface waters in a number of loca-
tions, including areas of intensive use, where greater exposures would be expected.
Several studies conducted in cosms, some of excellent quality, are available to pro-
vide points of reference for the SSDs and information on recovery of invertebrates