Spatial and vertical variations of perfluoroalkyl substances in sediments of the Haihe River, China.

The levels of six perfluoroalkyl substances (PFASs) in surface sediment and their vertical variations in dated sediment cores from the Haihe River were investigated; studied substances included perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctane sulfonate (PFOS), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnA), and perfluorododecanoic acid (PFDoA). Results showed that the total PFAS concentration in surface sediment ranged between 0.52 and 16.33 ng/g dry weight (dw) with an average of 3.47 ng/g dw, with PFOS and PFOA as the dominant PFASs. In general, the PFAS concentrations in the mainstream increased from the upper to the lower reaches, except that a drop occurred downstream of the Erdao dam. Although the PFASs in the sediment cores did not show a clear decreasing or increasing trend with depth, the three cores had a similar vertical variation. The PFAS levels were relatively low in the surface sediment, and reached the first high point at 8-20 cm as a result of the wide use of PFASs from 1990 to 2000. After that the PFAS levels decreased, and then increased to a second high point at about 40-48 cm, which might be caused by the leaching of PFASs in sediment. Because PFASs have hydrophilic groups and relatively high solubility, the PFASs will transfer from the upper to lower layers of sediment when water infiltration occurs, leading to the fluctuation of PFAS levels in sediment cores. This study suggests that both the temporal variation of sources and transfer processes of PFASs in sediments are important factors influencing the vertical variation of PFASs in sediment cores.