Geoscience Reference
In-Depth Information
Table 5.6 Examples of
bound pesticide residues in
soils (Calderbank
1989
)
Structural type
Bound residues
(% of applied)
Parent
detected
Herbicides
Anilides and ureas
34-90
No
Bipyridyliums
10-90
Yes
Nitroanilines
7-85
No
Phenoxy
28
No
Phosphonate (glyphosphate)
12-95
Yes
Triazines
47-57
?
Insecticides
Carbamates
32-70
Yes
Organochlorines
7-25
?
Organophosphates
18-80
Yes
Pyrethoids
3-23
No
Fungicides
Chlorophenols
45-90
Yes?
Nitroaromatic (dinocap)
60-90
Yes?
or animals which persist in the matrix form of the parent substance or its
metabolites after extraction.'' Gevao et al. (
2000
) include the proviso that bound
residues do not include metabolites that are indistinguishable from naturally
occurring compounds. Expanding this definition for the subsurface environment,
we can state that bound residues may comprise all toxic chemical species of
anthropogenic origin (parent and metabolites) associated with the subsurface
solid phase that cannot be separated by current extraction technology.
Bound residues were first mentioned in the literature by Bailey and White
(
1964
), in relation to pesticide extraction from soils. Over the years, many
experiments have shown that the extraction of pesticides from soils is never
complete, even when using solvents for which the molecules are highly soluble.
Wanner et al. (
2005
) showed by analysis of
14
C-labeled molecules that the fun-
gicide dithianon in soil exhibits bound residues of &63 % of the applied amount
after 64 days. Calderbank (
1989
) showed that, for a large number of organic
agrochemicals, up to 90 % of the applied radioactive-labeled substances become
unextractable (Table
5.6
). Calderbank (
1989
) examined a series of experimental
data and noticed that different amounts of parent products become irreversibly
retained as a function of their molecular structure (Table
5.6
). Moreover, it was
observed that the extractability decreases with aging, probably because the phe-
nomena responsible for hysteresis become more efficient with increasing residence
in soil.
The environmental significance of bound residues must be considered in rela-
tion to NOM (Barraclough et al.
2005
). Contaminants entering the subsurface
contain many functional groups similar to those of NOM and thus become
involved in many of the same biological and chemical transformations. If, with
aging, the bound residues become indistinguishable from subsurface organic
