Semivolatile organic compounds (SVOCs), typified by polycyclic aromatic hydrocarbons (PAHs), are notorious pollutants that significantly affect aquatic ecosystems and public health. Sediments serve as major sinks for anthropogenic PAHs. However, their role in modulating the risks that PAHs pose to aquatic ecosystems under climate change scenarios remains underexplored. We combined a global meta-analysis of PAH concentrations in air, water, and sediment from 1993 to 2021 with a robust multimedia fugacity model to assess PAH transport and distribution. The toxicity equivalent concentration approach was used to calculate the risk ratio and dioxin toxicity equivalent of PAHs. The majority of reported measurements clustered in three major watersheds: the Yangtze (n = 488) and Huanghe (n = 196) in China and the St. Lawrence (n = 337) in the United States. Sediment sinks contribute substantially to the persistence and redistribution of PAHs. By 2050, high-molecular-weight PAHs will dominate the sediment–water exchange pathway, whereas low-molecular-weight PAHs will be largely depleted in sediments, primarily driven by projected shifts in the composition of emissions, 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 aquatic PAH concentrations and the associated risks in China, quantified by the risk quotient and dioxin toxicity equivalence. Although this trend holds for most regions, the St. Lawrence watershed is projected to experience lower ecological risk owing to higher PAH degradation rates. This research underscores the critical role of sediment sinks in shaping the risks posed by PAHs in climate change scenarios and emphasizes the need for integrated management strategies, including sediment remediation and climate change adaptation.

With the rapid urbanization in the last decades, especially after the year 2000, several metropolitans were formed. e.g., Beijing, Shanghai, Guangzhou, Shenzhen, Tianjin, and Chongqing that locate at four world-class megalopolises across China. The generation and management of municipal solid waste (MSW) are important components for city development, both of which are spatiotemporally heterogeneous among these metropolitans, as a result of diverse socioeconomic statuses. This study attempts to sufficiently reveal the spatiotemporal heterogeneity by determining the MSW per capita, MSW composition, and proportion of each management strategy (landfilling, incineration, and compositing). Singapore is taken for comparison, for it is a Chinese community and well-known for its outstanding performance in environmental sanitation. Results show that MSW per capita is highly dependent on GDP per capita, and exerts an increasing tendency with time, but can be relieved with MSW reduction policy. For each metropolitan, the development of landfilling and incineration fits the Kuznets curve well, and government policy is a more determinant factor than GDP. MSW composition is also time- and location-dependent, and source sorting generally favors the subsequent resource utilization including the mainstream incineration. In addition to MSW generation and management, the action, goal, and experience in Singapore are expatiated, which are believed to be of referential significance for these metropolitans.