Speciation, distribution and migration pathways of polycyclic aromatic hydrocarbons in a typical underground river system in Southwest China

Water, colloid, and suspended particulate matter (SPM) samples were collected during one given year at two sites from the Laolongdong (LLD) underground river in Southwest China and analyzed for 16 priority polycyclic aromatic hydrocarbons (PAHs), dissolved organic carbon (DOC), and particulate organic carbon (POC). The concentrations of the SPM-associated, colloid-associated, freely dissolved, and dissolved organic matter (DOM)associated PAHs varied from 202 to 1731 ng/L, 142 to 956 ng/L, 228 to 1280 ng/L, and 7.3 to 173 ng/L, respectively. The mean percentages of 4- and 5-6 ring PAHs showed increasing trends along the order of the dissolved phase, colloidal phase and particulate phase. The behavior and fate of PAHs influence by DOC and POC were examined. Overall, organic carbon was the primary factor controlling the environmental behaviors and fates of the 16 PAH species in the LLD underground river. POC in underground river has more lipophilicity to PAHs in this study. The correlation analysis suggested that the migration pathways of PAHs from the surface soil to the underground river through the sinkholes and soil seepage water both had important contribution during the rainy season. However, PAHs mainly transferred through soil seepage water in the form of dissolved PAHs during the dry season.