Climate warming drives nonlinear shifts in mercury bioavailability and ecological risk in coastal sediments.

Mercury (Hg) contamination poses urgent ecotoxicological concerns for coastal ecosystems, yet the temperature-dependent bioavailability and ecotoxicological risks of different Hg species remain poorly understood. Here, we investigated how warming influences methylmercury (MeHg) and divalent inorganic mercury (InHg, Hg2+) in coastal sediments using diffusive gradients in thin films (DGT) to capture labile, bioavailable Hg. DGT provides a dynamic, environmentally relevant measure of Hg accessibility, integrating diffusion, adsorption, and complexation processes that regulate exposure to benthic organisms. To quantify ecological consequences, we applied the SPI (Species Sensitivity Distribution-Probabilistic Risk Assessment-Inclusion-Exclusion Principle) model, enabling evaluation of both individual and joint ecotoxicological risks. Our framework reveals nonlinear, species-specific responses of Hg bioavailability and ecotoxicological risk to rising sediment temperatures, with MeHg overwhelmingly dominating total risk, while InHg contributes modestly yet meaningfully. These findings establish a mechanistic and predictive approach for assessing temperature-sensitive Hg behavior and ecotoxicological outcomes in coastal sediments, providing critical insights for climate-adaptive risk assessment and proactive environmental management.