Fate, occurrence, and regional-scale emissions of neonicotinoid pesticides and their metabolites in wastewater treatment plants in suburban Shanghai, China

Neonicotinoid pesticides (NEOs) are emerging contaminants with potential ecological and human health risks. However, their sources, transformation dynamics, and emission pathways in urban wastewater systems remain poorly quantified. This study systematically investigates the spatial distribution, sources, and transformation of 8 parent NEOs (pNEOs) and 6 metabolites (mNEOs) in the influents of 21 wastewater treatment plants (WWTPs) in suburban Shanghai, China. The average concentrations of ΣpNEOs and ΣmNEOs were 568.17 ng/L and 478.20 ng/L, respectively, with significant spatial variations. pNEOs were dominated by nitenpyram (NIT) and dinotefuran (DIN), while mNEOs, such as desnitro-imidacloprid (DN-IMI) and dinotefuran-urea (DIN-U), showed higher abundances. Correlation and cluster analyses reveal pNEOs primarily originate from agricultural activities, whereas mNEOs likely stem from both agricultural and industrial sources, including pesticide production residues. A novel model incorporating Monte Carlo simulations estimates point-source emissions from the 21 WWTPs at 264.57 kg/a for pNEOs and 269.34 kg/a for mNEOs, with total Shanghai-wide emissions reaching 2947.03 kg/a and 1056.56 kg/a, respectively. This study highlights the critical role of WWTPs in discharging NEOs into receiving water bodies, underscoring the need for integrated management strategies targeting agricultural and industrial inputs to WWTPs as well as for the advancement of WWTP processes designed to eliminate emerging contaminants.