Photochemical degradation of methylparathion in the presence of humic acid

Abstract

Photochemical degradation of methylparathion (O,O,-dimethyl O-4 nitrophenylphosphorothioate) in the presence of humic acid between pH 2 and 7 was monitored by differential pulse polarography. Humic acid was not electro-active under the experimental conditions used in this study. Only the pesticide and its main degradation product at pH 2 exhibited polarographic signals. Photolysis of methylparathion in acid media was sensitized by humic acid since the pesticide did not degrade in the absence of this compound. Methylparathion degradation in the presence of humic acid was observed at each of the studied pHs. The reaction was first-order with rate constant values ranging from 2 × 10⁻³ to 6.3 × 10⁻³ min⁻¹.

Keywords:

• Methylparathion
• organophosphorus pesticide degradation
• humic acid
• sensitized photolysis
• differential pulse polarography

Acknowledgments

This research was funded by the Consejo Nacional de Ciencia y Tecnología (project 36809-E).