Aerobic biodegradation of [14C]3-chloro-P-toluidine hydrochloride in a loam soil

Abstract

Degradation of the pesticide 3-chloro-p-toluidine hydrochloride (CPTH) occurred in a loam soil when applied at concentrations of 3.5 and 35 μg/g. The compound degraded according to pseudo-first-order kinetics, with a calculated rate constant of 2.74 X 10 -2 h -1 , at a soil temperature of 22°C ; this rate constant yielded a half-life of 25 h. The loss of radiolabeled CPTH from soil was suggested to be controlled by both irreversible binding to the soil colloids and microbial transformation. Mineralization of the radiolabeled CPTH was interpreted as involving two zero-order kinetic rates ; an initial rate of carbon dioxide release was estimated to be 0.33% d-' (half-life of 152 d), followed by a slower rate of 0.07% d-', which resulted in a half-life of 718 d. Approximately 13% of the radiolabeled CPTH that was applied to soil at 3.5 μg/g was mineralized to [ 14 C] carbon dioxide during the 99-d incubation period. A primary metabolite was identified as N-acetyl-3-chloro-p-toluidine (ACPTH) ; this metabolite reached a maximum concentration at the 1-d sampling period, and degraded with a pseudo-first-order rate constant of 2.67 x 10 -2 h -1 ; the half-life for ACPTH was calculated to be 26 h. When CPTH was applied to soil at 35 μg/g, the compound was also mineralized in soil by a similar metabolic pathway to that observed at the lower concentration. However, the rate of mineralization was slower, which suggests that elevated soil concentrations of CPTH may affect the viability of certain microorganisms.