Behavior of Chlorpyrifos-methyl in Soil and Sediment

Abstract

This research was carried out with the aim of obtaining information regarding the possible environmental impact of Chlorpyrifos-methyl, an organophosphoric insecticide used in agriculture for its phytoiatric action against Hemiptera, Lepidoptera, Coleoptera, and Diptera. Studies relating to the degradation kinetics of the insecticide in two soils and one sediment have shown a rapid degradation process in all three. The prevalent form of degradation would appear to be the chemical type, because the degradation kinetics in a sterile soil have not demonstrated that micro-organisms play a significant part. The adsorption isotherms showed that the insecticide has a greater affinity for the sediment (Kf = 143) as opposed to the soils (Kf = 65) and that the adsorption process is practically irreversible. Moreover, hydrolysis tests in buffered solutions at pH 4, 7, and 9 revealed that the molecule is particularly unstable with a basic pH.

Keywords:

• Organophosphoric insecticide
• Persistence
• Degradation
• Sorption–desorption
• Chemical hydrolysis

Acknowledgments

This study is supported by Ministry of Education, University, and Research (MIUR), COFIN project. We thank Dr. Michèle Nègre, and Dr. Alessandro Cignetti for their valuable comments.