Geoscience Reference
In-Depth Information
Fig. 18.15 Adsorption isotherms of a paraquat and b diquat in two acidic vineyard soils (1 and
2) (modified after Pateiro-Moure et al.
2007
) reprinted with permission from Pateiro-Moure et al.
(
2007
). Copyright 2007 American Chemical Society
the mineral fraction of soil. In vineyard soils, cationic herbicides may interact with
inorganic cations such as copper, which is used as a fungicide, or from application
of animal manure. Effects of aged copper on the adsorption-desorption of paraquat
and diquat in polluted vineyard soils in Spain were studied by Pateiro-Moure et al.
(
2007
). The two studied soils were acidic (pH 5.2-5.8) and characterized by a
surface area of 66-78 m
2
/g; the total Cu
2+
contents of the two soils studied were
42 and 583 mg/kg. Both diquat and paraquat were adsorbed strongly by the soils
(Fig.
18.15
). However, the removal of Cu
2+
from soils by EDTA extraction (37
and 14 %, respectively) led to small increases in the paraquat and diquat con-
centrations (1.7 and 0.3 %, respectively). The increase in herbicide retention was
equivalent to the replacement of 6.4 and 1.6 % of the charges theoretically
released by Cu
2+
from the two studied soils.
Desorption tests showed that both diquat and paraquat are retained irreversibly
on soil even after six sequential extractions (Table
18.2
). One soil exhibited less
than 1 % desorption of the two herbicides, while the second soil exhibited a
slightly higher percentage. Paraquat was desorbed in proportions from 1 % in the
first extraction step to 0.2 % in the sixth step. Diquat desorption never exceeded
4 % and tended to decrease as the desorption sequence progressed.
The adsorption-desorption of the cationic pesticide chlordimeform on mont-
morillonite clay was shown by Hermosin and Perez Rodriguez (
1981
) to be cation
exchange coupled to coadsorption of neutral molecules and extraction of Al from
the mineral. Adsorption of chlordimeform on multilayered montmorillomite is an
irreversible process; in contrast, chlordimeform adsorbed on single layer kaolinite
is easily removed by washing with aqueous solution. XRD data suggest that a
single layer of chlordimeform cations adsorbs in the interlayer region of the
formed chlordimeform-montmorillonite complex. The d-spacing values between
