Vertical distribution characteristics and sources of polycyclic aromatic hydrocarbons in soils in industrial zone in Nanchong City

Soil is one of the important assembling and transiting places of polycyclic aromatic hydrocarbons(PAHs)in the environ- ment.This paper is aimed to present a report on the vertical distribution characteristics and sources of 16 mainly controlled PAHs in soil collected from Nanchong City.Refinery plant and gas station were chosen as the typical sampling sites.The soil samples were collected every 10 cm of distance from the surface to 100 cm underground.Gas chromatography was adopted to detect and analyze the concentrations of PAHs in soils from the sampling sites.Cluster analytical methodology was used to identify the possible sources of PAHs in soil.The study has showed that 12 kinds of the PAHs were detected in the refinery plant soil whereas 14 kinds of the compounds were found in the gas station soil.The total concentrations of PAHs were found to have peak values at layer 10_30 cm beneath the surface.Both numbers of PAHs species and concentrations of PAHs in soil samples drop with depth.For the spot of 50 cm from the surface in particular,the concentrations of PAHs rapidly reduce.The analytical results of our investigation have exhibited the vertical distribution characteristics of PAHs in the soil of Nanchong s industrial zone corresponding on Tianjin with heavy industry and some cities abroad.There were only PAHs with 2-ring and 3-ring existed with a high proportion in each profile.The principal PAHs compounds were fluorine,phenanthrene and fluoranthene.It means that low-ring PAHs can reach the deeper layers according to the vertical profiles.On the other hand,high-ring PAHs were only detected in surface soil samples.The content of PAHs changed along the profiles indicating that low-rings PAHs are easier to migrate compared to high-rings PAHs.The cluster analytical results have identified the main sources of PAHs in the soils as the incomplete combustion of coal plus the contribution of leakage, volatilization as well as the combustion of petroleum and related products.