ABIOTIC HYDROLYSIS OF AZINPHOS –METHYL AT VARYING pHs

Abstract

The assessment and impact of the environmental fate of azinphos methyl (3(dimethoxyphosphinothioylsulfanylmethyl)-1,2,3-benzotriazin-4-one), a currently-used pesticide was studied. It was subjected to acid and base driven hydrolysis to determine which process plays a more crucial role on its fate once released into the environment. Hydrolysis of azinphos methyl was studied in solutions buffered to pH 4, 7, 9 and 11 with varying temperatures of 15 oC ± 0.5 oC, 27± 0.5 oC and 37 ± 0.5 oC. The rate of degradation of azinphos- methyl was determined as a function of phosphate formation within the reaction solution. Results obtained indicated that both processes followed a pseudo-first order rate kinetics under the different temperatures. The rate constants for the hydrolysis experiments at 27± 0.5 oC were calculated to be kpH 4 as 1.49 × 10-2 hr-1; kpH 7, 1.15×10-2 hr-1; kpH 9, 1.54×10-2 hr-1 and kpH 11, 1.64 × 10-2 hr-1 with corresponding half – lives of 46.51 h, 60.26 h, 45 h and 42.26 h respectively. While, the rate constants and half-lives for the hydrolysis experiments at 15± 0.5 oC was pH 4 (1.9 x 10-2 hr-1; 36.45 h), pH 7 (1.38 x 10-2 hr-1; 50.22 h), pH 9 (1.24 x 10-2 hr-1; 48.17 h), pH 11 (7.6 x 10-3 hr-1; 91.18 h) and for conditions at 37± 0.5 oC had pH 4 (1.9 x 10-2 hr-1; 36.28 h), pH 7 (1.25 X 10-2 hr-1; 55.44 h), pH 9 (1.45 X 10-2 hr-1; 47.783 h) and pH 11 (6.6 X 10-3 hr-1; 105 h). This showed that temperature has an influence on the degradation of azinphos-methyl. The implication for this study is relevant in understanding the fate of azinphos-methyl once released into the environment with possible application in water/wastewater treatment. Keywords: azinphos methyl, hydrolysis, buffered, degradation.