Interaction of pesticides with the soluble fraction of natural and artificial humic substances

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Abstract
The adsorption of two cationic pesticides on the soluble part of natural and artificial humic substances, and their mechanisms of interaction, have been studied using the equilibrium dialysis method. Paraquat and chlordimeform in diverse concentrations have been used. A natural fulvic acid extracted from a spodosol soil, a commercial humic acid and polymaleic acid vere used as comparison. Chlordimeform adsorption data from this work are higher than those obtained in a previous paper without dissolving the humic substances. Paraquat isotherms always present values lower than chlordimeform ones. Natural fulvic acid adsorbs more than the commercial humic substance for both pesticides. The results show that acidified soluble fraction of the commercial HA is more similar to natural FA than polymaleic acid. However the latter is generally used as a model for fulvic acid. The interaction mechanisms between these humic substances and cationic pesticides were principally cation‐exchange processes, but H‐bonding and charge transfer mechanisms are also possible, as shown by IR study.

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