Geoscience Reference
In-Depth Information
Fig. 8.5 Atmospheric concentrations of trifluralin in three dugouts on the Canadian Prairies
during 1989-1990 (Waite et al.
2004
)
Because each herbicide may degrade during volatilization, it is interesting to
compare the cumulative volatilization of the parent contaminant and its metabo-
lites. This behavior was studied in a wind-tunnel experiment by Wolters et al.
(
2003
) for a mixture of parathion, terbuthylazine, and fenpropimorph, as well as
for the metabolites fenpropimorph acid and desethyl-terbuthylazine. Figure
8.6
shows the volatilization dynamics of these pesticides and their metabolites when
the products were applied initially on the surface of Gleyic Cambisol (*73 %
clay, 23 % silt, 4 % clay). The volatilization, however, is controlled not only by
the properties of the molecules but also by the properties of the subsurface
composition, moisture content, and environmental factors.
Spencer and Cliath (
1969
,
1973
) studied the effect of organic matter (OM) and
clay content on vapor density of various pesticides. In general, they found that
subsurface OM content and partition coefficients are of primary importance in
describing the rate of volatilization for compounds having a high affinity for OM.
