Environmental Engineering Reference
In-Depth Information
63% of the original mass of volatilized substance is degraded or deposited. Based
on a conservative concentration of •OH radicals of 0.7 × 10
6
molecules cm
−3
in the
atmosphere which would result in a half-life of 3 h, the CTD for CPY was estimated
to be 62 km. At lesser concentrations of •OH radical, such as occur at night and at
lesser temperatures or in less urbanized regions, the CTD would be proportionally
longer. The calculated fugacities of CPY in air and other media decrease propor-
tionally with increasing distance from sources. This information provided an
approximate prediction of downwind concentrations that are generally consistent
with concentrations measured in nearby and semi-remote sites. This analysis was an
improvement over previous estimates of LRT of CPY and CPYO, but a need for
improved estimates of the chemical-physical properties of CPYO was identifi ed.
The properties of CPY were assessed against criteria for classifi cation as a per-
sistent organic pollutant (POP) under the Stockholm convention or as persistent,
bioaccumulative and toxic (PBT) under the European Community regulation EC
1107/2009 (Mackay et al.
2014
). CPY and CPYO do not trigger criteria for classifi -
cation as a POP or LRT under the Stockholm convention or a PB chemical under EC
1107/2009. Although CPY is toxic at concentrations less than the trigger for clas-
sifi cation as “T” under EC1107/2009, this simple trigger needs to be placed in the
context of low risks to non-target organisms close to the areas of use. Overall, nei-
ther CPY nor CPYO trigger the criteria for PBT under EC 1107/2009.
CPYO is not predicted to persist in the environment, and indeed is not found in
surface waters. Because CPYO is the metabolically activated toxic form of CPY, the
toxicity of CPYO is implicitly measured when testing CPY. For these reasons, we
concluded that additional fate studies for CPYO in the environment by either mod-
eling or monitoring or additional studies of toxicity are not warranted. There is
suffi cient monitoring and toxicity testing to determine that the uncertainties in con-
clusions about the oxon are not large.
4
Chlorpyrifos in Surface Water
The fourth paper in the series characterizes the measured and modeled concentra-
tions of CPY in surface waters of the U.S. (Williams et al.
2014
). The frequencies
of detection and 95th centile concentrations of CPY in surface waters in the U.S.
have decreased more than fi ve-fold between 1992 and 2010. Detections of CPY in
1992-2001 ranged from 10 to 53% of samples. In the period 2002-2010, detections
were 7 to 11%. The 95th centile concentrations ranged from 0.007 to 0.056
μ
g L
−1
in 1992-2001 and 0.006 to 0.008
g L
−1
in 2002-2010. The greatest frequency of
detections and 95th centile concentrations occurred in undeveloped and agricultural
land-use classes.
The two classes of land-use with the most urban land (urban and mixed) had the
smallest frequency of detections and 95th centile concentrations. This result is con-
sistent with cessation of sale of CPY-based products for residential uses in December
2001. Overall, the U.S. Geological Survey (USGS) database with the greatest
μ
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