Derivation of water quality criteria using the QSAR-ICE-SSD models and ecological risk assessment for typical ultra-short-chain PFASs in freshwater ecosystems

Ultra-short-chain per - and polyfluoroalkyl substances (USC-PFASs) have become global emerging contaminants requiring urgent management due to their widespread detection worldwide, high environmental mobility, and persistence in freshwater ecosystems. In this study, we integrated quantitative structure–activity relationship (QSAR), interspecies correlation estimation (ICE), and species sensitivity distribution (SSD) models, and introduced a random sampling method to derive the hazardous concentration for 5% of species (HC 5 ). Using this approach, we systematically established freshwater short-term and long-term water quality criteria ( WQC ) for four typical USC-PFASs: trifluoroacetic acid (TFA), trifluoromethanesulfonic acid (TFMS), perfluoro-2-methoxyacetic acid (PFMOAA), and bis(trifluoromethanesulfonyl)imide (TFSI). These criteria serve as effective quantitative indicators of the freshwater ecological risks posed by USC-PFASs, and the random-sampling HC₅ method improves the early warning capability for long-term exposure at low concentrations. We conducted a probabilistic ecological risk assessment of surface water using the risk quotient (RQ) method, Monte Carlo simulation, and joint probability curve (JPC) approach. The results showed that the short-term ecological risks of USC-PFASs were generally low, whereas their potential for long-term ecological impacts was increasingly significant, warranting further research. This study provides a useful framework for deriving WQC for other emerging contaminants.