Environmental Engineering Reference
In-Depth Information
number of samples (more than 10,000) and broadest geographical representation
showed that CPY was detected in 9% of samples between 2002 and 2010 and that
95% of samples contained less than 0.007
g L
−1
.
Regional databases maintained by the California Department of Pesticide Regulation
(CDPR) and Washington State Department of Ecology (WDOE), which were more
focused on areas of pesticide use than the USGS database, had more frequent detec-
tions (13-17%) and greater concentrations (95th centiles 0.010-0.3
μ
g L
−1
, and the maximum was 0.33
μ
g L
−1
). No
detections were reported in the 42 samples of saltwater and few data (total = 123)
were available for analyses of CPY in sediments. Only three sediments had concen-
trations above the limit of detection (LOD = 2
μ
μ
g kg
−1
dwt) and the largest concen-
tration detected was 59
g kg
−1
. Overall, the results indicate decreasing trends in
concentrations of CPY that are explained largely by corresponding decreases in
annual use and removal of residential uses from the labels.
Detections of CPYO were infrequent and all were less than the level of quantita-
tion (LOQ = 0.011-0.054
μ
g L
−1
). Only 25 detections were reported in a total of
10,375 samples analyzed between 1999 and 2012. The low frequency of detection
and the small concentrations found are consistent with the reactivity of CPYO and
its shorter hydrolysis half-life (Mackay et al.
2014
). These fi ndings suggest that
concerns for the presence of CPYO in drinking-water (USEPA
2011a
), where
CPYO may be formed during chlorination, are not transferable to surface waters.
Collectively, the monitoring data on CPY provide relevant insight for quantify-
ing the range of concentrations in surface waters. However, relatively few monitor-
ing programs have sampled at a frequency suffi cient to quantify the temporal pattern
of exposure. Therefore, numerical models were used to characterize concentrations
of CPY in water and sediment for three representative high exposure environments
in the U.S. (Williams et al.
2014
). The environments were selected by parallel
examination of patterns and intensity of use across the U.S. Simulations were con-
ducted to understand relative vulnerabilities of CPY to runoff with respect to soil,
and weather variability across the U.S. From the analyses, three geographical
regions, one each in central California, southwestern Georgia, and the Leelanau
peninsula of Michigan, were identifi ed as having greater potential exposure to CPY
and were used as focal scenarios for detailed modeling.
A small watershed, defi ned as a 3rd order stream, was selected from each region
based on high density of cropland eligible for receiving applications of CPY accord-
ing registered uses. The modeling used two versions of PRZM, one (V-3.12.2) for
modeling applications to fi eld-crops and the other (WinPRZM), which was modi-
fi ed for use of CPY in fi elds irrigated by fl ood and furrow. Additional models used
were EXAMS, AgDRIFT
®
, and SWAT. Models were confi gured for each watershed
and simulated for up to 30 yr of consecutive use of CPY using historical weather
records for those geographical areas of the country. Daily mean concentrations of
CPY in water and sediment from runoff, erosion, and drift sources were predicted
at the outlet of the watersheds. Conservative assumptions were used in the confi gu-
ration of the Georgia and Michigan watersheds. For example, all eligible crop acre-
age in each watershed was assumed to be treated, and the soil properties and number
and frequency of applications of CPY were those of the use pattern that produced
μ
Search WWH ::
Custom Search