Environmental Engineering Reference
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nonionic Witconol SN70, with their extent depending on the partition coefficient
between micelles and water. Similar profiles were obtained for chlorinated alkanes
(Valsaraj and Gupta 1988) and alkenes (Kim et al. 2003; Zhang et al. 2006), where
their partition to micelles was the key factor to determine the apparent H value. By
using the group contribution method, Smith et al. (1987) proposed the simple
approach estimating the H value of small organic molecules. In the foregoing inves-
tigations, the H value is usually estimated in the equilibrated system consisting of
aqueous and air phases by gravimetrically or chromatographically measuring the
concentration of a chemical in each phase.
In assessing the volatilization profiles of a pesticide in the environment, it is
useful to know either its volatilization rate or amount from water. Maguire (1991)
measured dissipation rates of fenitrothion (5) and deltamethrin (69) in EC formula-
tions from seawater after their application either to its surface or subsurface.
Volatilization was a predominant dissipation process in the surface application and
(5), having a much smaller H value, dissipated faster. However, the subsurface
application resulted in the slower dissipation of (5) than (69), which indicated the
importance of other factors such as diffusion via micromonolayer and hydrolysis.
Assuming the classical two-film mass-transfer model for volatile chemicals, one
can estimate the volatilization rate of a chemical from natural water in the field
from the corresponding laboratory data by using the constant ratio of volatilization
rate of molecular oxygen between laboratory and field, which is independent of
surfactant concentration (Smith et al. 1980). Gavril et al. (2006) developed a
convenient method of estimating the volatilization rate of a chemical by using
reversed-flow gas chromatography. The evaporation rates of ethanol and 1,1,
1-trichloroethane were found to be reduced by the presence of Triton X-100, but
with its extent being significant only when more than two monolayers are formed
on the solution surface. Adjuvants other than surfactant such as plant oil were
found to also reduce the volatilization loss from water by increasing the pesticide
solubility (de Ruiter et al. 2003).
The volatilization loss of a pesticide from a solid surface has been investi-
gated using glass or filter paper as models. Holoman and Seymour (1983)
reported linear loss of chlorpyrifos (65) in EC formulation from a glass surface,
and the addition of alcohol ethoxylate reduced the volatilization rate. By using
the gravimetric method, Sundaram (1987, 1995) extensively analyzed the factors
in formulation to control volatilization loss of pesticide and various adjuvants.
The higher the viscosity of aqueous formulations, the lower the volatilization
rate of pesticide, but with some exceptions. The dissipation of pesticide from the
applied filter paper followed the zero-order kinetics in an early stage of
volatilization but became first order when a longer period of volatilization was
considered (Sundaram 1985; Sundaram and Leung 1986). Garratt and Wilkins
(2000) developed a convenient method to assess volatilization of pesticide from
formulation by using a glass column filled with formulation-applied glass wool.
The volatilized pesticide was collected by a C18 SepPak cartridge and analyzed
by GC.
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