Transformation pathways and toxicity assessments of two triazole pesticides elimination by gamma irradiation in aqueous solution

Abstract

• The removal of two triazoles by gamma rays was evaluated under different conditions. • Reaction kinetics and absorbed doses were calculated. • Humic acid showed a negative influence on the elimination of the triazoles. • Radiolysis led to the formation of several by-products for the two triazoles. • No increase of toxicity was observed during the radiolysis of the target molecules. The presence of triazoles in the environment has received increasing attention due to their potential adverse effects on human and ecosystem health. Nevertheless, triazoles are weakly sunlight and cannot be effectively removed by solar radiation. Advanced oxidation processes (AOPs), including gamma irradiation, present an alternative technology for removing these pesticides from contaminated water. In this study, the degradation of two triazole pesticides (Myclobutanil and Penconazole) in aqueous solution was studied by gamma irradiation. Different factors such as irradiation dose, pH, radical scavenger and natural organic matter were examined for their effects on the removal of these triazoles. A kinetic study was performed and the by-products were identified by HPLC-QTOF-MS/MS. The results showed that the degradation process of the target molecules was of pseudo-first order and the elimination reached at least 90% at an absorbed dose of 575 Gy and 460 Gy for Myclobutanil and Penconazole, respectively. The percentage of elimination increased with dose and the degradation process was accelerated under neutral conditions. Humic acid showed a negative influence on the degradation efficiency, which decreased from 100% to 40.67% for Myclobutanil and to 50% for Penconazole at a dose of 1.2 kGy when the humic acid concentration was 20 mg.L −1 . Five degradation products were identified for Myclobutanil and ten for Penconazole and most of the degradation by-products were formed by hydroxylation. To check the impact of these by-products, a toxicity study was conducted on Wistar rats and no increase in toxicity was observed. The mineralization of both pesticides by gamma irradiation was studied using 1 HNMR analysis and results confirm that both molecules were completely mineralized at 1.2 kGy. According to the overall analysis, the radiolysis process seems to be an alternative to remove triazoles from contaminated waters.