A Study on the Environmental Degradation of Pesticides Azinphos Methyl and Parathion Methyl

Abstract

The effect of environmental parameters (temperature and relative humidity) on the degradation rate of azinphos methyl and parathion methyl was studied. Proprietary emulsifiable concentrates were diluted and added to each of 90 glass Petri dishes for each pesticide and were left overnight to dry. Petri dishes were placed in 18 air-tight containers (9 for each pesticide) in which were created environments with relative humidity (RH) of 60, 82, and 96%. The containers were stored at 0, 20, and 40°C. From the experimental results best fit curves, kinetic equations, rate constants, and half-lives were calculated. Half-lives of azinphos methyl for the RH studied were, from 124 to 267 days at 0°C, from 89 to 231 days at 20°C, and from 25 to 71 days at 40°C. Corresponding half-lives for parathion methyl were from 48 to 57 days at 0°C, from 9.2 to 10.5 days at 20°C and from 1.3 to 1.5 days at 40°C. The results were correlated with relevant results from the decomposition of the same or similar pesticides on apples both, on the trees and during refrigerated storage. These correlations are suggesting that biological factors strongly affected the decomposition rate of azinphos methyl. On the contrary the decomposition of parathion methyl was mainly affected by environmental rather than biological factors.

Keywords:

• Azinphos methyl
• Parathion methyl
• Relative humidity
• Temperature
• Insecticide degradation