Mineralization of Methyl Parathion Insecticide in Soil by Hydrogen Peroxide Activated with Iron(III)-NTA or -HEIDA Complexes

Abstract

A modified Fenton reaction was carried out on 2000 mg/kg methyl parathion [O,O-dimethyl O-(4-nitrophenyl) phosphorothioate; MP] in a fine sandy loam soil containing 1.57% organic carbon. A 1:1 soil suspension was treated with H₂O₂ and an Fe(III) complex of nitrilotriacetate (Fe-NTA) or N-(2-hydroxyethyl)iminodiacetate (Fe-HEIDA). Loss of MP at 21 °C reached a practical maximum at reagent concentrations of about 0.01 mol/kg Fe(III) complex and 1 mol/kg H₂O₂ and within a 5 h reaction period. Fe-NTA was slightly more effective than Fe-HEIDA. Temperature had a marked effect on the reaction. Using the above reagent concentrations, loss of MP increased from about 20% at 10 °C to about 90% at 35 °C, with no further improvement up to 60 °C. At 35 °C, nitrate and sulfate ions were liberated stoichiometrically and dimethyl phosphate was a minor product.