Vertical distribution of polycyclic aromatic hydrocarbons in soils in Tianjin Area

Soil samples were collected in the mountainous areas, agricultural land and oil fields in Tianjin. Vertical distributions of polycyclic aromatic hydrocarbons (PAHs) in soils were investigated in this paper. The sources of PAHs were also analyzed. The total concentrations of 16 prior PAHs was found to have peak at or just below the soil surface and declined with depth. High PAHs concentrations were found in 0～{40?cm} in agricultural soil, while PAHs were only enriched in 0～3?cm in oil field soils. It is estimated that this is caused by the long-term cultivation in the agricultural areas. Low ring PAHs transformed easier than high ring PAHs in the soil. Soil properties (e.g. Total organic carbon, clay content) played major roles in the vertical distribution of PAHs. PAHs in mountainous areas and agricultural soils were mainly derived from precipitation of pollutants caused by the combustion of fossil fuels, while PAHs in oil field soil were originated from both petroleum and combustion contamination sources.