[Vertical distribution characteristics and composition of saturated hydrocarbon in soil profiles of Beijing]

Soil samples were collected from ten soil profiles with different environmental conditions in Beijing for saturated hydrocarbons (SHs) analysis. The vertical distribution of the both concentration and composition of SHs in ten soil profiles were investigated. Concentration of SHs in different profiles is significantly different, ranged from 1.5 microg x g(-1) to 54.1 microg x g(-1). The higher concentrations are found in the samples from B7, B9 and B10. A series of SHs including n-alkanes, isoprenoid alkanes, terpenoids and steranes, alkyl hexamethylene were detected in all samples. The order from higher content to lower in most profiles (except B7) is: n-alkanes, isoprenoid alkanes, terpenoids and steranes, alkyl hexamethylene, and the relative content of n-alkanes is obviously dominant in the upper horizons. Concentrations of SHs and content of soil organic carbon in each profile show similar trend with depth, declined rapidly down to 30 cm and trend consistent in the deep part( > 40 cm). CPI1, CPI2, (C25 + C27 + C29 + C31) / Sigma alkanes, terpenoids and steranes, and biomarker parameters suggest that pollutants are mainly from fossil fuel in B7, high plant-derived n-alkanes dominated in other profiles and fossil fuel contamination to different extent. The sources of n-alkanes in deep part of soil profiles are different from those in topsoil samples, which are related to the soil itself, such as soil parent material and process of soil formation, but the sources of alkyl hexamethylene, terpenoids and steranes between topsoil and deep part are constant.