Advancing aquatic ecological risk assessment of imidacloprid in global surface water with mesocosm-based thresholds

Aquatic ecological risk posed by neonicotinoids has become a growing concern due to their widespread use and documented environmental impacts. However, current risk assessments predominantly rely on laboratory-based toxicity data, which often lack ecological relevance and may introduce substantial biases. In this study, we addressed a critical knowledge gap in neonicotinoid risk assessment by establishing the first global-scale comparison between traditional laboratory-based and ecologically realistic mesocosm-derived toxicity thresholds. Analysis of literature-reported concentrations revealed significant regional variations in imidacloprid pollution at a global scale, with the highest median concentrations detected in Oceania, followed by Asia, Africa, America, and Europe, although extreme concentrations were observed in America. The mesocosm-based hazard concentration for 5 % of species (HC5) was determined to be 0.013 μg/L, which was significantly lower than the laboratory-based HC5 of 0.086 μg/L. Risk assessment using the laboratory-based threshold identified 1.2 % of the 1378 freshwater samples as high risk (risk quotient, RQ>10) and 7.1 % as medium risk (1