Levels, sources, and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in soils of karst trough zone, Central China

Polycyclic aromatic hydrocarbons (PAHs), the priority pollutants with carcinogenic and mutagenic effects, threaten the fragile karst environment with a thin and scattered soil layer. Twenty-six surface soil samples were collected in the karstic valleys and hilltop depressions of four river basins on the south bank of the Yangtze River in the Yichang area. Their PAH concentrations were measured, aiming to investigate the distribution, possible sources, and potential health risks of PAHs in this area. The results showed that the concentrations of ΣPAHs (sum of 16 priority PAHs) in surface soils ranged from 8.26 to 397 ng·g−1 (median 24.9 ng·g−1, average 55.8 ng·g−1). The concentrations of ΣPAHs in the valleys (median 25.1 ng·g−1, average 72.9 ng·g−1) were slightly higher than that in the hilltop depressions (median 24.6 ng·g−1, average 28.2 ng·g−1), while the low molecular weight PAHs (LMW-PAHs) were dominant both hilltop depressions and valleys. Additionally, molecular diagnostic ratios and principal components analysis (PCA) suggested that PAHs in the surface soils are mainly derived from biomass and coal combustion, followed by petroleum combustion. The BaP equivalent (BaPeq) concentrations of PAHs and the incremental lifetime cancer risks (ILCRs) were used to assess their health risk. It showed that the BaPeq of 16 PAHs (BaPeq16) in the surface soils varied between 0.31 and 85.0 ng·g−1 (average 6.52 ng·g−1). The average of ILCRs in different age groups varied between 6.01 × 10−9–1.10 × 10−7 regionally. It indicated that the risks of cancer to residents in this area were within the safe limit, and PAHs showed relatively higher potential cancer risks for children than teens and adults.