Risks to Aquatic Organisms from Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 154

(annual maxima) of chlorpyrifos in small streams in agricultural watersheds in
Michigan and Georgia were estimated to be g L −1 ; in a reasonable worst-

case California watershed, the 90th centile 96-h annual maximum concentrations
ranged from 1.32 to 1.54

≤ 0.02 μ

g L −1 . Measured concentrations of chlorpyrifos are less
than estimates from simulation models. The 95th centile for more than 10,000
records compiled by the US Geological Survey was 0.008

μ

g L −1 . Acute toxicity
endpoints for 23 species of crustaceans ranged from 0.035 to 457

μ

μ g L −1 ; for 18 spe-

cies of aquatic insects, from 0.05 to 27 μ g L −1 ; and for 25 species of fi sh, from 0.53

to >806 g L −1 . The No Observed Adverse Effect Concentration (NOAEC eco ) in

more than a dozen microcosm and mesocosm studies conducted in a variety of cli-
matic zones, was consistently 0.1

μ

g L −1 . These results indicated that concentrations
of CPY in surface waters are rarely great enough to cause acute toxicity to even the
most sensitive aquatic species. This conclusion is consistent with the lack of fi sh-
kills reported for CPY's normal use in agriculture in the U.S.
Analysis of measured exposures showed that concentrations in surface waters
declined after labeled use-patterns changed in 2001, and resulted in decreased risks
for crustaceans, aquatic stages of insects, and fi sh. 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 exposures to CPY in the
Georgia and Michigan watersheds were de minimis . Risks from individual expo-
sures in the intense-use scenario from California were de minimis for fi sh and
insects and low for crustaceans. Risks from repeated exposures in the California
intense-use scenario were judged not to be ecologically relevant for insects and fi sh,
but there were some risks to crustaceans. Limited data show that chlorpyrifos oxon
(CPYO), the active metabolite of CPY is of similar toxicity to the parent compound.
Concentrations of CPYO in surface waters are smaller than those of CPY and less
frequently detected. Risks for CPYO in aquatic organisms were judged to be de
minimis .
Several uncertainties common to all AChE inhibitors were identifi ed. Insuffi cient
data were available to allow interpretation of the relevance of effects of CPY (and
other pesticides that also target AChE) on behavior to assessment endpoints such as
survival, growth, development, and reproduction. Data on the recovery of AChE
from inhibition by CPY in fi sh are limited. Such data are relevant to the character-
ization of risks from repeated exposures, and represent an uncertainty in the assess-
ment of risks for CPY and other pesticides that share the same target and
toxicodynamics. More intensive monitoring of areas of greater use and more com-
prehensive models of cumulative effects that include rates of accumulation, metabo-
lism and recovery of AChE in the more sensitive species would be useful in reducing
this uncertainty.

μ

Acknowledgements We wish to thank Julie Anderson for assistance with review and collation of
the toxicity data. We thank the anonymous reviewers of this paper for their suggestions and con-
structive criticism. Prof. Giesy was supported by the Canada Research Chair program, a Visiting
Distinguished Professorship in the Department of Biology and Chemistry and State Key Laboratory