Protective freshwater thresholds for neonicotinoids: Multi-endpoint species sensitivity distributions and tiered...

Neonicotinoids are widely used, persistent neurotoxic insecticides that pose risks to non-target freshwater organisms, yet ecologically relevant and globally harmonized water quality criteria (WQC) remain limited. Here, we integrate multi-endpoint species sensitivity distributions (SSDs) with a four-tiered probabilistic ecological risk assessment to derive short- and long-term freshwater WQC for six major neonicotinoids: acetamiprid (ACE), clothianidin (CLO), dinotefuran (DNT), imidacloprid (IMI), thiacloprid (THA), and thiamethoxam (THM). We compiled measured environmental concentrations from 276 global studies and 503 acute and 773 chronic toxicity endpoints from the USEPA ECOTOX database (1993-2025), covering invertebrates, fish, and amphibians. Threshold toxicity was quantified using HC₅ values derived from multi-endpoint SSDs, while WQC were derived within a four-tier probabilistic risk framework. IMI and THA were the most toxic compounds, with acute HC₅ values of 355 and 917 ng/L and chronic HC₅ values of 46 and 21 ng/L, respectively. Derived short-term WQC ranged from 178 ng/L (IMI) to 3960 ng/L (DNT), and long-term WQC ranged from 10.5 ng/L (THA) to 318 ng/L (DNT). Probabilistic risk characterization using measured surface-water concentrations indicated low overall acute risk (joint exceedance probabilities of 1.17%-2.90%), but potential chronic risks (1.68%-2.80%) that may disproportionately affect the most sensitive 5% of species in some regions. Insects and spiders were generally the most sensitive taxa, while fish were most sensitive to IMI. These results provide broadly useful probabilistic WQC for protecting freshwater ecosystems from neonicotinoid pollution across temperate and subtropical regions.