北京典型土壤剖面中饱和烃的组成及垂向分布特征

分析了北京地区不同环境功能区具有代表性的10个土壤剖面样品中饱和烃污染物的含量和组成特征.结果表明,不同剖面饱和烃的浓度差别明显,其变化范围为1.5～54.1 μg·g-1,其中城区(B7)、污灌农田(B9)和工业区(B10)浓度较高.所有的剖面均检出了正构烷烃、类异戊间二烯烷烃、烷基环己烷和甾、萜类等饱和烃污染物,大部分剖面中各类化合物的相对含量为正构烷烃＞类异戊间二烯烷烃＞甾萜类＞烷基环己烷,而且在表层土中正构烷烃的含量明显占优势.不同剖面中饱和烃浓度随深度增加而降低,在表层30 cm内饱和烃含量随深度增加而明显降低,40 cm以下含量基本保持恒定,且与有机碳含量的变化趋势基本一致,地球化学参数(如CPI1、CPI2、甾萜类生物标志物参数等)分析表明,城区表土(B7)主要受化石燃料污染,而其它剖面表土正构烷烃主要来源于高等植物,但也受不同程度的化石燃料及其燃烧产物的污染;剖面深部土样中正构烷烃来源与表层土不同,其来源与土壤本身或成土母岩中所含的有机质的地球化学演化有关,而甾萜类化合物和烷基环己烷与表层土中的来源可能基本相同.

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.