Geoscience Reference
In-Depth Information
Fig. 8.35 Parathion adsorption from aqueous solutions by three soils, before and after oxidation,
as well as on clay and organic matter. Reprinted with permission from Saltzman et al. (
1972
).
Copyright 1972 American Chemical Society
to an understanding of the adsorption mechanism of organophosphorus compounds
on clay surfaces. For example, IR spectra indicate that, on both montmorillonite and
attapulgite, parathion was sorbed by clay coordinates through water molecules to the
metallic cations. When clay-parathion complexes are dehydrated, parathion
becomes coordinated directly, and the type of cation determines the structure of the
complex. The main interaction is through the oxygen atoms of the nitro group.
Interactions through the P=S group have also been observed, especially for com-
plexes saturated by polyvalent cations (Saltzman and Yariv
1976
; Prost et al.
1977
).
Subsurface adsorption of nonpolar or slightly polar toxic chemicals also was
found to be related to the solid-phase OM and mineralogy. Saltzman et al. (
1972
)
studied the importance of mineral and organic surfaces in parathion adsorption on
semiarid soils characterized by low OM content and different mineralogy. They
found that parathion adsorption depends on the type of association with organic
and mineral colloids. Following removal of OM by soil treatment with hydrogen
peroxide, the adsorptive affinity of mineral soils decreases, mainly due to a
decrease in the OM content and not due to other soil modifications that may occur
during OM oxidation. Figure
8.35
presents the isotherms of parathion adsorption
on three semiarid soils, before and after oxidation, as well as on clay and OM.
