Hazard assessment and environmental fate of propiconazole degradation by microalgae: Differential tolerance, antioxidant and detoxification pathway

Abstract

Propiconazole (PCZ), a triazole broad spectrum fungicide has been frequently detected in agricultural water webs. This emerging contaminant imposes a serious toxic impact on soil and aquatic microbiota. Thus, we aimed to investigate the potential of the microalgae as PCZ phycoremediator. To this end, its toxicity, degradation and detoxification mechanisms by Scenedesmus obliquus and Nostoc muscorum were studied. Over a week, both species were exposed to mild (5 mg/L) and high (10 mg/L) PCZ concentrations. Results showed a dose-dependent accumulation of PCZ typically higher in S. obliquus than in N. muscorum. Moreover, S. obliquus degraded PCZ into a less toxic environmental product; 1-[2-(2,4-dichlorophenyl)− 4-(hydroxypropyl)− 1,3-dioxolan-2ylmethyl]− 1,2,4-triazole and 1-(2,4-dichlorophenyl)− 2-(1,2,4-triazol-1-yl) ethanone. The metabolic pathway assumed cellular dehydroxylation and side chain breakdown in S. obliquus. The high PCZ dose significantly decreased cell growth, chlorophyll a content and inhibited photosynthesis activity and machinery (PEPC and RuBisCo) in both species but, to lesser extend in S. obliquus. Additionally, the exposure to high concentration of PCZ caused a serious oxidative damage especially in N. muscorum. This damage is evident by increased lipid peroxidation, H2O2 level, protein oxidation and NADPH oxidase activity. The two species experienced differential antioxidant and detoxification mechanisms using glutathione-S-transferases, phytochelatins and metalothionine to alleviate PCZ-oxidative stress. This study represented S. obliquus as an efficient PCZ phycoremediator and provided new data on the PCZ toxicity, environmental fate and risk of PCZ to aquatic environment.