Evaluation of the sorption mechanism of catechol and its chlorinated derivatives in a Palouse silt loam soil

Catechol and its chlorinated derivatives are important in soil as intermediary metabolites in the degradation of many synthetic and naturally-occurring aromatics. This study examined the sorption mechanisms of catechol, 4-chlorocatechol, 4,5-dichlorocatechol, and tetrachlorocatechol in a Palouse silt loam soil. Sorption was evaluated by the batch equilibration method using 14C-labeled chemicals and varying solvent combinations and conditions. Data were fitted to the Freundlich isotherm equation. All the catechols were strongly sorbed with isotherm slopes of one or greater indicating strong intermolecular associations upon adsorption. Sorption decreased as the catechol molecule became more chlorinated, except tetrachlorocatechol which was one of the most sorbed. Increasing the ionic strength of the solution increased sorption of dichlorocatechol and tetrachlorocatechol. Increasing quantities of acetone or 2-propanol in the equilibration solution produced little change in the sorption of catechol and chlorocatechol, but a slight decrease in the sorption of dichlorocatechol and tetrachlorocatechol. These results indicate that solubility and hydrophobicity had s significant effect on the adsorption of dichlorocatechol and tetrachlorocatechol