Determination of the fate of propanil in a simulated rice field environment through electrochemical detection of 3,4-DCA

Abstract

Electrochemical investigation of 3,4dichlorophenylamine (3,4-dicholoroaniline or 3,4-DCA), the principal degraded product of propanil, in aqueous medium reveals that the most intense peak appears at +0.75 V vs. saturated calomel reference electrode (SCE). The diffusioncontrolled behaviour of this peak enables direct detection of 3,4-DCA in the environment, which can be extended for investigation of the fate of propanil. Rice cultivation grown in three beds of equal dimensions prepared in a polytunnel, an effective simulated environment to which the recommended dose of propanil was applied, was used for this study. Determination of the concentrations of 3,4-DCA throughout the rice cultivation cycle indicated that the concentration of 3,4-DCA initially increases up to 4 days followed by a decrease up to 10 days, and finally reaches a plateau. The concentration-time relationships of 3,4-DCA suggest that the initial degradation of propanil and subsequent degradation of 3,4-DCA follow the mechanism of consecutive reactions, where the product of the first step becomes the reactant of the second step. Further, comparison of kinetic data with integrated rate law expressions and the mathematical model of consecutive first order reactions indicated that the degradation of both processes is of first order with relatively low rate constants, being the degradation of 3,4-DCA as the rate limiting step.