Winter behavior of polycyclic aromatic hydrocarbons in frozen lakes: fugacity insights into partitioning, transport, and key driving mechanisms

Polycyclic aromatic hydrocarbons (PAHs) pose ecological risks when the ice in lakes melts, which may trigger sharp increases in pollution in the spring. Nevertheless, there is insufficient information about the behavior of PAHs in lakes in cold regions during winter. This study investigated the partitioning and transport of PAHs during a freezing period in a representative lake. The dynamic distribution of PAHs was assessed across five environmental media: ice, suspended particulate matter (SPM) in the ice column, bulk water, SPM in the water column, and sediment. Based on field data collected in 2021, a multimedia fugacity model and Spearman correlation analysis were used to characterize the fate of PAHs and identify key influencing mechanisms. The results show that over 87.00% of low-ring PAHs are trapped in the ice column in aerosol form, while more than 88.00% of total PAHs are bound to SPM in the water column. The fugacity fraction revealed opposing vertical migrations in that low-ring PAHs tended to move upward from sediment to water, while high-ring PAHs exhibited the opposite trend. The Spearman correlation analysis indicated that the key driving mechanisms included the total suspended matter, chlorophyll-a, and temperature, which play critical roles in shaping the distribution of PAHs across different media. The distribution of PAHs during the freezing period was strongly influenced by the physicochemical properties, the natural conditions of the study area, and anthropogenic activities such as oil extraction and irrigation return flow. These findings highlight the need for revised monitoring protocols to address SPM-mediated PAH transport in winter.