Climate change increases aqueous ecological risks of semi-volatile organic compounds: a meta-analysis and mechanistic modeling in three major watersheds

Semi-volatile organic compounds (SVOCs), represented particularly by polycyclic aromatic hydrocarbons (PAHs), are notorious pollutants that significantly affect aquatic ecosystems and public health. Sediments serve as major sinks for anthropogenic PAHs, yet their role in modulating aquatic ecological risks of PAHs under climate change scenarios remains underexplored. We combined a global meta-analysis of PAHs concentrations in air, water, and sediment from 1993 to 2021 with a robust multimedia fugacity model to assess the transport and distribution of PAHs. The toxicity equivalent concentration approach is used to calculate the Risk Quotient and Dioxin Toxicity Equivalence of PAHs. We found that the majority of the reported measurements clustered in three major watersheds: Yangtze (n = 488) and Huanghe (n = 196) in China, and St. Lawrence (n = 337) in the United States. We reveal that sediment sinks contribute substantially to the persistence and redistribution of PAHs. By 2050, high molecular weight PAHs will dominate the sediment–water exchange pathway, while low molecular weight PAHs will be largely depleted in sediments, primarily driven by projected shifts in emission composition, enhanced volatilization and degradation of low molecular weight compounds, and the absence of continuous external inputs. Climate-induced changes in sediment fluxes are predicted to elevate the aquatic PAHs concentrations and associated risks, quantified by Risk Quotient and Dioxin Toxicity Equivalence, in China. While this trend holds for most regions, the St. Lawrence watershed is projected to see lower ecological risk due to higher PAHs degradation rates. This research underscores the critical role of sediment sinks in shaping PAHs risks under climate change and emphasizes the need for integrated management strategies, including sediment remediation and climate change adaptation.