[Vertical distribution and possible sources of polycyclic aromatic hydrocarbon in sewage area soil]

Nine profile soil samples were collected from Xiaodian sewage irrigation area, Taiyuan city, China. The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were analyzed by gas chromatography equipped with a mass spectrometry detector (GC/ MS). The rank order of the average concentrations of PAHs in the 0-10 cm upper soil layer was background area < swamp area < groundwater irrigation area < sewage irrigation area. The concentrations of PAHs in most profile soils decreased with the increase of depth, and the PAHs were mainly accumulated in the surface soil layer (0-40 cm). 4-6 rings of PAHs were mainly accumulated in the 0-50 cm soil layer, and the accumulation capacity in groundwater-irrigation area was better than that in sewage irrigation area. The correlation between different rings of PAHs and TOC was positive (r(max) = 0.791, P = 0), and the same situation was found for PAHs and sand (r(max) = 0. 882, P = 0). The correlation between PAHs and pH was negative (r(min) = -0.1, P = 0.702). The main source of PAHs in the surface soil layer (0-40 cm) of study area was coal combustion. There were two pollution ways of PAHs in soil, one was settled into soil directly, the other was first settled into water and absorbed on the surface of solid particles, and then got enrichment in soil as irrigation water flew.