The Influence of Surfactants and Metals on the Mineralization of 14C-Labeled Methyl Parathion in a Mediterranean Soil under Aerobic Conditions

The mineralization of C-14-labeled methyl parathion, in a soil from a semiarid Mediterranean area, was followed by a simple method. This method consisted in trapping evolved CO2 in a NaOH trap, using common laboratory glassware and low quantities of reagents. Volatiles were trapped in polyurethane foams, which are cheap and easy to handle. The influence of soil water content (10-20%) and the addition of surfactants [Aerosol 22 and hexadecyl trimethyl ammonium bromide (HD)] and metals (Cu and Zn) were assessed. Different models were applied to evaluate parathion mineralization kinetics. Mineralization kinetics was initially faster for 20% soil water content, although the final mineralization extent was similar in the range of tested soil water content. Surfactants behaved differently: HD decreased mineralization rate while Aerosol 22 did not affect parathion mineralization. A bimetal Cu and Zn solution led to a significant decrease in methyl parathion mineralization, which persisted when applied together with HD. Results suggest a possible reduction of pesticide availability in soil or a direct effect of the exogenous chemicals on soil microbial community.