Neonicotinoid insecticides in global agricultural surface waters - Exposure, risks and regulatory challenges

Neonicotinoids are the most widely used insecticides worldwide. However, the widespread usage of neonicotinoids has sparked concerns over their effects on non-target ecosystems including surface waters. We present here a comprehensive meta-analysis of 173 peer-reviewed studies (1998-2022) reporting measured insecticide concentrations (MICs; n = 3983) for neonicotinoids in global surface waters resulting from agricultural nonpoint source pollution. We used compound-specific regulatory threshold levels for water (RTL_SW) and sediment (RTL_SED) defined for pesticide authorization in Canada, the EU and the US, and multispecies endpoints (MSE_SW) to assess acute and chronic risks of global neonicotinoid water-phase (MIC_SW; n = 3790) and sediment (MIC_SED; n = 193) concentrations. Results show a complete lack of exposure information for surface waters in >90 % of agricultural areas globally. However, available data indicates for MIC_SW overall acute risks to be low (6.7 % RTL_{SW_acute} exceedances), but chronic risks to be of concern (20.7 % RTL_{SW_chronic} exceedances); exceedance frequencies were particularly high for chronic MSE_SW (63.3 %). We found RTL_SW exceedances to be highest for imidacloprid and in less regulated countries. Linear model analysis revealed risks for global agricultural surface waters to decrease significantly over time, potentially biased by the lack of sensitive analytical methods in early years of neonicotinoid monitoring. The Canadian, EU and US RTL_SW differ considerably (up to factors of 223 for RTL_{SW_acute} and 13,889 for RTL_{SW_chronic}) for individual neonicotinoids, indicating large uncertainties and regulatory challenges in defining robust and protective RTLs. We conclude that protective threshold levels, in concert with increasing monitoring efforts targeting agricultural surface waters worldwide, are essential to further assess the ecological consequences from anticipated increases of agricultural neonicotinoid uses.