Environmental Engineering Reference
In-Depth Information
equilibrium” condition prevails in which the ratio
MM
2
1
increases monotonically
with time.
Using the above relationships, half-lives, and yields, the following are the
approximate quantities for an initial value of
M
0
of 100 mol. After 0.46 h, when
10% of the initial CPY has degraded, 3 mol of CPYO are formed and the ratio
CPYO/CPY is 0.033 (3/90). After 3 h, 50% of the initial CPY would have degraded,
14 mol of CPYO would be formed and the ratio CPYO/CPY would increase to 0.28.
After 7 h, 80% of the CPY would have reacted and both
M
2
and
M
1
are 20 and their
ratio would reach 1.0. After 10 h,
M
1
is 10 and
M
2
would reach its maximum value
of 21, their ratio becoming 2.1. At longer times, the ratio would continue to increase,
because, although
M
1
and
M
2
would both be decreasing,
M
1
would be decreasing
faster. For example, at 12 h, the ratio would be 3.2. This behavior results in the pos-
sibility that the CPYO/CPY ratio can provide insights into the approximate “age” of
the air parcel, although this ratio may be influenced by conversion during sampling
and prior to analysis. This ratio was observed to be approximately 1.0 in the summer
of 1994 at Lindcove near Fresno CA, which suggests a transit time of ~5 h (Aston
and Seiber
1997
). A test using SF
6
as a tracer gave comparable transit times. At a
more distant location, Ash Mountain in Sequoia National Park, the ratio increased
to 7-30, corresponding to a longer transit time. At the even more distant location of
Kaweah Canyon (elevation 1,920 m) the CPYO/CPY ratio was 2.7 in June to early
July 1994 but later the CPY was less than the LOQ for much of the summer and
only CPYO was measurable. Generally, similar results were obtained by LeNoir
et al. (
1999
). The similar concentrations of CPY and CPYO observed in air at
Lindcove were also observed in pine needles from the same location. In surface
waters in the same region, concentrations of CPY exceeded those of CPYO, possi-
bly because of faster hydrolysis of CPYO or differences in deposition rates and
hydrology (LeNoir et al.
1999
).
From knowledge of the kinetics or transformation, local meteorology, transit
times, and atmospheric deposition characteristics, these results indicate that it is fea-
sible to predict formation and fate of CPYO, and thus, to estimate concentrations in
air and other media at distant locations. An implication is that, whereas CPY is the
substance of greatest exposure and concern in areas of application, its transformation
product CPYO might be of most concern in more distant locations subject to LRT.
The absolute quantities of CPY transported to and retained in terrestrial media are
small and the concentrations and exposures to aquatic organisms are relatively small,
and much smaller than concentrations sufficient to cause toxicity (Aston and Seiber
1997
; LeNoir et al.
1999
). However, to quantify the risk of impacts on distant ter-
restrial and aquatic ecosystems, improved information is needed on the properties of
CPYO and the parameters required by the simulation models. Seasonally stratified
monitoring is also desirable. Concentrations of pesticides in surface water at altitudes
greater than 2,040 m in the Sierra Nevada were below detection limits. This result
suggests that, because of meteorological constraints, there is less effective transport
to higher elevations (LeNoir et al.
1999
). Concentrations also become lower because
of faster wind speeds at high altitudes. The postulated “cold-condensation” effect, in
which low temperatures associated with high elevations cause high deposition rates
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