Strobilurin fungicides in four wastewater treatment plants and the receiving river in Guangzhou, China: Occurrence, fate, and ecological risk

Strobilurin fungicides (SFs), a class of novel pesticides extensively applied in agricultural production, have raised growing concerns because of their escalating usage and persistent environmental presence. This study investigated the occurrence, fate, mass balance, and ecological risks of SFs in four wastewater treatment plants (WWTPs) in a megacity in southern China, Guangzhou. Nineteen SFs were detected in the aqueous phase, suspended particulate matter, sludge and surface water. The concentrations of individual SFs in the influent were determined to be 0.04–13.9 ng/L. In the effluent, their concentrations decreased to 0.017.68 ng/L. The mean removal efficiency for individual SFs varied between -19% and 93% across the WWTPs, indicating that a considerable proportion of these contaminants may not be fully eliminated through the current processing technology. Analysis of paired parent compound and metabolites in different processing units in the WWTPs indicate the generation of unknown transformation products in the treatment system, suggesting neglected environmental burden from SFs. Mass balance analysis revealed that the daily mass loads of the individual SFs ranged from 1.04 mg/d to 20,384.2 mg/d, with per-capita emissions spanning 0.01–8.43 mg/d/1,000 persons. Risk assessment showed that the pyraclostrobin, famoxadone, and azoxystrobin in the effluent could pose moderate ecological risks for the aquatic environment. These findings demonstrate that WWTP effluents serve as critical pathways for SFs into aquatic environments, and conventional treatment cannot fully mitigate their ecological risks.