Environmental Engineering Reference
In-Depth Information
relative to the typical date of corn emergence across the USA. Only two application
scenarios were predicted—broadcast sprays to soil and to foliage. Volatilization was
not simulated in the foliar application scenario. Granular applications and crop-
specific label-type applications were not evaluated. The scenarios used in the sensi-
tivity analysis on use-patterns are another relative indicator of the runoff potential
of CPY because they represent a hypothetical environment—a 10-ha field draining
into a 1-ha by 2-m deep pond. The pond remains at a constant volume that receives
pesticide loads from drift and runoff, but not the corresponding influx of water that
would occur during a runoff event.
The Orestimba Creek watershed in California was predicted to have the greatest
exposure concentrations and the longest duration of exposures of the three water-
sheds. This is caused in part because of the relatively higher intensity of CPY's
use, and because of the relatively small dilution and flushing that exists in the
headwater channels. The watershed is under a water quality management plan
administered by the Westside San Joaquin River Watershed Coalition to alter
practices contributing to water quality issues associated with agricultural chemi-
cals (CURES
2013
; SJVDA
2010
). The practices needing to be altered include
education and outreach on pesticide application technologies and managing irriga-
tion and storm-water runoff that were not taken into account in the model.
Characterization of CPY in the environment could be enhanced by including
additional detail in all three watershed systems. These include heterogeneity in
cropping and soils in Georgia and Michigan; management plans being introduced
into Orestimba Creek, and weather specific drift estimates and application field
proximity to water drainage-ways.
5
Summary
Concentrations of CPY in surface waters are an integral determinant of risk to
aquatic organisms. CPY has been measured in surface waters of the U.S. in sev-
eral environmental monitoring programs and these data were evaluated to charac-
terize concentrations, in relation to major areas of use and changes to the label
since 2001, particularly the removal of domestic uses. Frequencies of detection
and 95th centile concentrations of CPY decreased more than fivefold between
1992 and 2010. Detections in 1992-2001 ranged from 10.2 to 53%, while 2002-
2010 detections ranged from 7 to 11%. The 95th centile concentrations ranged
from 0.007 to 0.056 μg L
−1
in 1992-2001 and 0.006-0.008 μg L
−1
in 2002-2010.
The greatest frequency of detections occurred in samples from undeveloped and
agricultural land-use classes. Samples from urban and mixed land-use classes had
the smallest frequency of detections and 95th centile concentrations, consistent
with the cessation of most homeowner uses in 2001. The active metabolite of
CPY, CPYO, was not detected frequently or in large concentrations. In 10,375
analyses from several sampling programs conducted between 1999 and 2012, only
25 detections (0.24% of samples) of CPYO were reported and estimated concen-
trations were less than the LOQ.
Search WWH ::
Custom Search