Discussion

Changes of the density of charge observed during the adsorption of some metabolites of hydrocarbons on mineral soil components were compared with the results derived from partitioning experiments with radiochemicals. Some hints at the interaction between 1,2-dihydroxybenzene and related compounds, respectively, with iron ions [8] or Al-OH groups [9] were found in the literature. Sigg and Stumm [10] emphasized the reactivity between metal hydroxides and those chemicals forming ring-shaped surface complexes like 2-hydroxybenzoic acid.

The adsorption of organic anions reduces the positive charge of the oxidic surfaces of manganite and goethite and increases the density of negative charge of montmorillonite, respectively. While the neutralization of positive charges on protonated surfaces by adsorbing anions seems to be plausible because of electrostatic reasons, changes in the density of charge indicate an effective bonding mechanism if — as in the case of montmorillonite — Coulomb forces were surmounted.

Changes of the density of charge were due to the adsorption of anions. The measurements of the density of charge were semiquantitative, because the interaction between metabolite and polyelectrolyte has to be taken into account. The developed method could be useful to obtain some quick information about the interaction between organic substances and soil components without using radiotracer tests, which are more sophisticated when contaminated sites have to be investigated to develop clean up strategies.

Acknowelegement This study was supported by the Deutsche Forschungsgemeinschaft.

J. Thieme J. Niemeyer P. Guttmann T. Wilhein D. Rudolph G. Schmahl

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