Distribution, composition, levels, source, and risk assessment of PAHs in surface water and sediment from the mainstream Three Gorges Reservoir

Polycyclic aromatic hydrocarbons (PAHs) pose risks to the environment and human beings. Distribution, composition, levels, source, and risk assessment of PAHs in water and sediment samples collected from 19 sites in the Three Gorges Reservoir (TGR) were analyzed systematically during the wet season and the dry season from 2015 to 2016. The results indicated that Sigma PAHs in surface water were 3.9-139.3 ng/L (mean 42.4 ng/L), whereas Sigma PAHs in sediment were 185.5-2055.6 ng/g (mean 726.1 ng/g); PAH monomers with 2-3 rings were dominant in water, whereas PAH monomers with 3-5 rings were dominant in sediment. Distribution of Sigma PAHs had no significant regularity in water and sediment. Compared with rivers at home and abroad, Surface water levels of Sigma PAHs were low, whereas the sediment levels of Sigma PAHs were moderate, but surface water PAH monomers including anthracene, benzo[a]pyrene, indeno[1,2,3-c,d]pyrene, and dibenzo[a,h]anthracene at some sampling points exceeded the USEPA water quality standard or the Canadian environmental quality guidelines. These indicated potentially detrimental effects on human health and ecological integrity due to PAHs bioaccumulation. Diagnostic ratios showed that the main sources of PAHs in water and sediment were pyrogenic sources, such as biomass, coal, and petroleum combustion. The research result could provide valuable data and technical support for the protection of the TGR.