Polycyclic aromatic hydrocarbons contamination in subsoil from outskirts of Beijing, People's Republic of China

Forty-five pooled subsoil samples, collected from the outskirts of Beijing at the depths of 1.5-1.8 m, were analyzed for 17 polycyclic aromatic hydrocarbons (PAHs) using gas chromatography and mass spectrometry (GC-MS) to determine their total contents and distribution patterns. The sum of 17 PAHs concentrations varied from not detected to 0.982 μg g−1 in subsoil. The higher total contents of PAHs were observed in the southeast areas where there are some industries. PAHs in most of the subsoil were lower than those in the topsoil (0.016-3.884 μg g−1). PAHs concentrations displayed no relationship with the organic materials. In subsoil, the dominated PAHs were perylene>benzo(a)pyrene>benzo(g,h,i)perylene>indeno(1,2,3-cd)pyrene. It was notable that the content of 8 carcinogenic PAHs represented 47% of the total priority PAHs and the concentration of benzo(a)pyrene in the subsoil was comparable to that in the topsoil, which was much higher. The distribution of target compounds especially perylene and the fluoranthene/pyrene ratio shows that the sources in the subsoil are characterized by combustion such as traffic and incorporation of the diagenetic PAHs.