Occurrence, partition behavior and environmental risk of PAHs in water and sediment of a typical Karst wetland, southwest China

Huixian wetland is one of the largest karst wetlands in China, existing both karst and wetland characteristics, thereby playing a pivotal role in ecological buffering within the Guilin region. Due to the toxicity and ubiquity of PAHs in aquatic systems, understanding the distribution, flux, sources, and risk assessment is crucial for the sustainable development of the reserve. To explore the PAHs pollution of this area, water and surface sediment samples in wet season and dry season were collected from Huixian wetland. The results revealed that PAHs in the study area exhibited a low level of pollution in the wet season, and the concentration of PAHs in the dry period was significantly higher compared to the wet season in both water and sediment. Both diagnostic ratios and Positive Matrix Factorization (PMF) model indicated that biomass burning and traffic emissions are potentially the primary sources of PAHs. Fugacity analysis revealed that sediment serves as a sink for PAHs, particularly for the high molecular weight PAHs (HMW-PAHs). Furthermore, the sediments also act as secondary sources of PAHs, capable of releasing them back into the water. Species sensitivity distribution analysis indicated that Phe and Fla should be closely monitored, as the concentrations of most sites exceeded the value of the Hazardous Concentration for 5% of species (HC ₅ ). Overall, the ecological risks within the study area generally were low-moderate, with certain individual sites, such as SD1-1 and SD2-1, have high levels of contamination, thus closer attention and monitoring should be paid.