The adsorption on clay minerals and sesquioxides of some polar degradation products of naphthalene and alkylated benzenes was investigated by 14C-tracer experiments. Surface charge density of the solids was measured by titration with sodium polyethene sulfonate and polydiallyl-dimethyl-ammonium chloride at pH-range 4-7. Adsorption of organic anions reduced the positive charge on oxidic surfaces and increased the density of negative charge on clay minerals, respectively. The increase of the density of charge on clay minerals indicated an effective bonding mechanism. Changes of the density of charge were due to the adsorption of anions. The method is suitable for screening the interaction between polar metabolites of hydrocarbons and mineral soil components.