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

Abstract

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 1,378 freshwater samples as high risk (risk quotient, RQ>10) and 7.1% as medium risk (1<RQ<10), with majority of sites at risk located in American. In contrast, applying the mesocosm-based threshold revealed a substantial increase in risk, with 5% of sites classified as high risk and 32% as medium risk. In addition, the dominant medium-risk sites shifted from America to Asia and Europe. These findings underscore that the laboratory-based threshold significantly underestimates aquatic ecological risk of imidacloprid on a large scale, especially in Asia. Alternatively, the mesocosm-based threshold provides a more ecologically relevant assessment of risks in real-world aquatic environments. The present study highlights the critical need for incorporating ecologically relevant toxicity data into global risk assessments to better inform regulatory decisions and environmental protection strategies.