The Sources, Diffusion, and Health Risks of Polycyclic Aromatic Hydrocarbons in Water and Sediment of a Typical Underground River in South China

Underground rivers serve as the primary source of drinking water in the karst area in South China and support their development. However, the aquifer structure of the karst region makes it easy for PAHs (polycyclic aromatic hydrocarbons) to enter underground rivers, which causes heavy pollution and affects water quality and safety. This study chose the Qingshuiquan underground river in Nanning City as a representative to reveal the sources, diffusion, and health risks of PAHs in water and sediment of underground rivers. The results showed that the ∑16PAHs concentration ranges in groundwater and sediment were 294.44-489.91 ng/L and 380.13-1141.97 ng/g respectively. From the upstream to the downstream, PAH concentrations increased, and the proportion of PAHs with lower rings decreased. PAHs came from three sources: the high-temperature combustion of grass, wood, and coal in the upper reaches, petroleum in the middle reaches, and coal and oil combustion in the lower reaches. As ring numbers of PAHs and organic carbon content increased, PAHs were more likely to disperse into sediment. Sediment turned from source to sink, and groundwater from sink to source. PAHs in groundwater posed only carcinogenic health risks and zero non-carcinogenic health risks, with adults suffering from higher risks than children, and dermal contacts riskier than ingestion. The levels of carcinogenic health risks differed spatially, with risks in the downstream significantly higher than those in the midstream and upstream. PAH monomers such as BaP and DaA require close attention. These results can provide scientific evidence for POPs (persistent organic pollutants) prevention and control in the karst water environment.