Making Waves: Advancing risk profiling of emerging water contaminants at low concentrations

Emerging contaminants in natural waters, typically present at low concentrations, pose largely unrecognized hazards and exhibit a concealed risk profile. Recently, low-dose contaminant-induced hormesis has been identified as a significant contributor to bacterial resistance and harmful algal blooms, often described as a "phantom menace". However, the widely observed hormesis are greatly marginalized in current ecological risk assessment (ERA) guidelines, resulting in missed opportunities for proactive risk management and timely intervention during early contamination stage. To address this gap, the present work reveals the mismatch between laboratory designs and realistic scenarios, highlights the overlooked subthreshold hormesis, and reframes the dose-response relationship at low exposure levels. Building on these findings, we propose and further empirically validate a conceptual framework for integrating hormesis into conventional ERA. This framework enables the derivation of low-concentration risk thresholds grounded in the concept of hormesis. Consequently, a paradigm shift from the traditional single-threshold approach for risk identification and decision-making to a multi-threshold strategy is achieved. This advancement facilitates more precise risk profiling of emerging contaminants across low to high concentrations and calls on the scientific and regulatory communities to critically reassess existing risk assessment guidelines and water quality standards.