Regional Neonicotinoid Pollution in Wastewater Treatment Plants and Point Source Emissions

Neonicotinoids, currently the most widely used insecticides, pose ecological risks to aquatic systems through runoff into waterways. While nonpoint source emissions have been studied, the spatial patterns of their point source emissions within watersheds remain poorly understood. Here, we quantified neonicotinoid residues in the influents, effluents, and various treatment stages of wastewater treatment plants (WWTPs) in the Yangtze River Delta, China. Results showed that influent concentrations were significantly higher than those typically found in surface waters, with municipal WWTPs exhibiting lower removal rates (53.1 ± 20.8%) compared to industrial ones (83.3 ± 4.36%). WWTP influent neonicotinoid concentrations were positively associated with precipitation and population. The study identified the hydrolysis acidification process in industrial WWTPs and the aerobic sludge stage as key to higher neonicotinoid degradation, with Nitrospirota and Chloroflexi as the dominant microbial degraders. Using these quantitative relationships and empirical degradation rates, we constructed a point source emission model. This model estimates the annual emission of neonicotinoids via WWTPs at 5.27 tons/year (95% CI: 5.24–5.30 tons/year) in the studied region, with municipal WWTPs accounting for approximately 90%, especially during June and July. This study accurately assesses secondary point source emissions, offering critical data for basin-wide neonicotinoid pollution control.