County-scale distribution of polycyclic aromatic hydrocarbons in topsoil of the Yellow River Delta Region.

The Yellow River Delta (YRD) is a typical agricultural and petrochemical industrial area in China. To assess the current status of polycyclic aromatic hydrocarbons (PAHs) of soil residues, soil samples (0-15 cm) (n = 82) were collected in Bincheng District, at the geographic center of the YRD. Concentrations of 16 PAHs (∑PAHs) ranged from 181.1 to 2176.0 μg kg(-1), with an average concentration of 359.8 μg kg(-1), showing significant increase along a rural-urban gradient (p ≤ 0.05). The contribution of naphthalene and phenanthrene to ∑PAHs was 48.6-57.6 %, and the contribution of low molecular weight (two- and three-ring) PAHs was 56.3-66.4 % from urban to rural. The significant correlations between ∑PAHs and soil organic C and total N concentrations were observed (p ≤ 0.05), indicated soil organic C and total N can affect PAH distribution in the study area, especially for low molecular weight PAHs. Principal component and multiple linear regression analysis reveal that soil PAHs have different sources in different area. Various petroleum inputs (volatilization, vehicular and non-vehicle combustion) were the main sources of soil PAHs in the urban and suburban areas, and the main source was biomass burning in the rural. In general, most soil PAH contaminations in the study area were classified as weakly polluted. Even so, soil PAH contamination from petroleum, particularly near petrochemical production sites, deserves further attention, because lighter PAH compounds are more labile and can react with other pollutants to form more toxic derivates.