Environmental Engineering Reference
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Fig. 7
Joint probability curves for estimated 96-h time-weighted average (TWA) concentrations
of chlorpyrifos in Orestimba Creek, CA modeled from Jan 1, 2000 to Dec 31, 2009 and species
sensitivity distributions for fi sh, Crustacea, and insects
The JPCs for the concentrations modeled in Orestimba Creek, CA (Fig.
7
)
showed that fi sh and insects were at
de minimis
risk. The line for crustaceans was
slightly above the reference line for low risk, indicating that some species of crusta-
ceans are at low (but not
de minimis
) risk of adverse effects in this use scenario.
The JPC for concentrations modeled in another focus-scenario, Cedar Creek, MI
(Fig.
8
) indicated
de minimis
risk for crustaceans, insects, and fi sh. The modeled
concentrations in the other focus-scenario, Dry Creek, GA were smaller than those
in Cedar Creek, MI (Table
8
in Williams et al.
2014
), hence, these risks also were
de
minimis
(JPC not shown). Overall, the probabilistic analyses of these data suggest
that risks from direct effects of CPY on fi sh are
de minimis
in all areas of use. In
most areas of use, as exemplifi ed by the modeling of concentrations in Cedar Creek,
MI and Dry Creek, GA, risks to insects and crustaceans will be
de minimis
as well.
Low risk is also predicted for crustaceans in Orestimba Creek, CA, an intensive-use
scenario that reasonably exemplifi es the worst-case.
There were insuffi cient toxicity data for CPY in sediment to conduct a probabi-
listic assessment of risk. However, comparison of the 10-d LC
50
toxicity values for
H. azteca
and
C. dilutus
(Table
3
) to the maximum modeled values of 22.2, 0.067,
and 0.074
g kg
−1
resulted in RQs of 0.06, <0.001, and <0.001 for Orestimba Creek,
Cedar Creek, and Dry Creek, respectively. The RQs for Cedar Creek and Dry Creek
are well below the Level of Concern for all species. The RQ for Orestimba Creek is
slightly greater than the Level of Concern (0.05; EPA
2004
) for endangered and
threatened (listed) invertebrates, but below the Level of Concern for other (non-
listed) species.
μ
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