[Distribution of polycyclic aromatic hydrocarbons in soil profiles in southeast suburb of Beijing wastewater irrigation area].

3 borehole profiles samples were collected using Eijkelkamp soil sampler from the wastewater irrigation area of Beijing Southeast suburb. The soil samples were collected from surface to 5.5 m underground every 0.5 m. Physical-chemical properties of the samples such as clay content, total amount of clay minerals, cation exchange capacity (CEC), total organic compounds (TOC), etc. were analyzed. 16 polycyclic aromatic hydrocarbons (PAHs) defined by the U.S. EPA were also analyzed with gas chromatography-mass spectrometry (GC-MS). Results show that 14 PAHs were detected in the surface soil samples. The concentrations of PAHs range from 4 microg/kg to 428 microg/kg. Under the surface,both species and concentrations of PAHs in soil samples drop very fast. Only 2 rings and 3 rings PAHs were detected, which were naphthalene,phenanthrene, fluorene, acenaphthylene, acenaphthene, and fluoranthene. Clay content, total amount of clay minerals, CEC and TOC have significant correlations at 0.05 level between each other. Under the surface, clay contents also have a relationship with low-rings PAHs concentration. Where the layers have higher clay contents,the PAHs have higher concentrations. The contents of PAHs changing along the profiles also show that, low-rings PAHs are easier to migrate than high-rings PAHs. The sequence of the migration capabilities of low-ring PAHs is acenaphthene > fluorene > naphthalene > phenanthrene > acenaphthylene > fluoranthene. However, high-ring PAHs were only detected in surface soil samples. That means low-rings PAHs can reach the deep layers of the vertical profiles under long-term wastewater irrigation. Therefore, the shallow groundwater has the possibility to be contaminated.