Environmental Engineering Reference
In-Depth Information
of dissipation by vertical and lateral atmospheric dispersion. Concentrations in the
range of 100 ng CPY m −3 ± a factor of 10 are regarded as typical of areas immedi-
ately downwind (~1 km) of application sites, but large variability is expected from
differences in rates of application, nature of the crops treated, site area and meteo-
rological conditions, especially temperature and wind-speed.
In support of these concentration ranges, Raina et al. ( 2010 ) have reported CPY
concentrations at the Canadian agricultural field site at Bratt's Lake SK in 2003 and
2005. Over a 4-d sampling period, concentrations were 1-100 ng CPY m −3 with
some values as high as 250 ng CPY m −3 . These are similar to measured concentra-
tions in the range 4-180 ng CPY m −3 adjacent to a citrus orchard at the Lindcove
Field Station in California (Aston and Seiber 1997 ). Concentrations of a variety of
pesticides, including CPY, have been measured at locations across Canada (Yao
et al. 2008 ). In the intensive fruit and vegetable growing area of Vineland, Ontario, the
greatest concentrations of CPY were 21.9 ng CPY m −3 in 2004 and 20.6 ng CPY m −3
in 2005. These concentrations suggest that sampling was at a site within a few km
of treated areas and possibly during or shortly after application. It has been confirmed
that the samples were taken immediately adjacent to the application and were timed
to coincide with the application (Personal communication, Dr. T. Harner).
Volatilization from water . It is possible that some CPY enters nearby ponds or
streams as a result of spray drift and run-off and subsequently evaporates from these
water bodies or flows downstream. To assess the significance of this process a sim-
ple kinetic analysis was conducted using the two-resistance or two-film model. If
typical water and air mass transfer coefficients (MTCs) for water to air exchange are
assumed of 0.05 and 5 m h −1 and K AW is 4.5 × 10 −4 , respectively, then the water and
air phase resistances are
1
005
1
54510
and
1
, respectively, i.e., 20 and
h m
.
××
4
.
444 h m −1 and the overall water phase MTC would be 0.0021 m h −1 as follows ( 1 ):
1
20 444
1
(1)
) =
0 0021
. h
(
+
The primary resistance to transport thus lies in the air phase. For a water depth of
1 m, the rate constant for evaporation would be 0.0021 h −1 and the half-life would
be 322 h, which is 13 d. This is similar to the half-lives estimated for transformation
of CPY in water, which suggests that both volatilization and transformation are
significant pathways of dissipation of CPY in such bodies of water. Partitioning to
suspended solids and deposition to bottom sediments are also likely to remove some
CPY from solution (Gebremariam et al. 2012 ) and reduce the volatilization rate.
CPY reaching water bodies will thus be subject to other loss processes and rela-
tively slow and delayed evaporation over a period of weeks. It is concluded that
secondary volatilization from water bodies is unlikely to be significant compared
with the primary volatilization immediately following application.
 
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