Binding mechanisms of pesticides to soil humic substances.

This review-paper summarizes and discusses the nature of the binding forces involved and the types of mechanisms operating, often simultaneously, in the adsorption processes of several pesticides onto soil humic substances, humic acids and fulvic acids. These include ionic, hydrogen and covalent bonding, charge-transfer or electron donor-acceptor mechanisms, Van der Waals forces, ligand exchange, and hydrophobic bonding or partitioning. Experimental evidence obtained and interpretation provided for the various adsorption processes proposed are briefly presented and commented. The review ends with some concluding remarks and recommendations for future work needed to be done.