AEROBIC BIODEGRADATION OF [C-14] 3-CHLORO-P-TOLUIDINE HYDROCHLORIDE IN A LOAM SOIL

Degradation of the pesticide 3-chloro-p-toluidine hydrochloride (CPTH) occurred in a loam soil when applied at concentrations of 3.5 and 35 mu g/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 te mperature of 22 degrees C; this rate constant yielded a half-life of 2 5 h. The loss of radiolabeled CPTH from soil was suggested to be contr olled by both irreversible binding to the soil colloids and microbial transformation. Mineralization of the radiolabeled CPTH was interprete d as involving two zero-order kinetic rates; an initial rate of carbon dioxide release was estimated to be 0.33% d(-1) (half-life of 152 d), followed by a slower rate of 0.07% d(-1), which resulted in a half-li fe of 718 d. Approximately 13% of the radiolabeled CPTH that was appli ed to soil at 3.5 mu g/g was mineralized to [C-14] carbon dioxide duri ng the 99-d incubation period. A primary metabolite was identified as N-acetyl-3-chloro-p-toluidine (ACPTH); this metabolite reached a maxim um concentration at the 1-d sampling period, and degraded with a pseud o-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 m u g/g, the compound was also mineralized in soil by a similar metaboli c pathway to that observed at the lower concentration. However, the ra te of mineralization was slower, which suggests that elevated soil con centrations of CPTH may affect the viability of certain microorganisms .