天津地区表层土中饱和烃的组成与分布特征

Composition and distribution characteristics of saturated hydrocarbons in soil samples collected from Tianjin area

为揭示天津地区不同环境功能区表层土壤中饱和烃污染特征及其来源,分析了该地区几个具代表性的环境功能区表层土(0～25cm)中饱和烃化合物的组成和分布特征,重点讨论了正构烷烃和甾、萜烷烃类化合物的组成、分布及环境意义,比较了不同层次(亚层)(0～5cm,5～10cm,10～15cm,15～20cm,20～25cm)中这些化合物及相关的地球化学参数的变化规律。结果表明,不同采样点以及同一采样点的不同亚层之间正构烷烃的组成特征存在不同程度的差别,而甾、萜烷烃类化合物组成与分布特征均较为接近。正构烷烃以及甾、萜类地球化学参数综合分析揭示,不同采样点之间正构烷烃的来源多样,中低分子量的正构烷烃主要来源于石油等化石燃料,高分子量正构烷烃主要来源于高等植物蜡的分解产物,但甾、萜烷烃类化合物的来源是一致的,且主要来源于石油烃污染。不同采样点表层土中饱和烃的来源及污染程度均存在一定的差别,市区、油田附近、经济开发区以及近郊区受石油源影响较重,北部山区污染较轻,且主要来源于高等植物的降解。除个别采样点外,同一采样点不同亚层之间饱和烃的组成特征基本一致,表明污染源是一致的,主要来源由表层污染物往下迁移所致。

The composition and distribution characteristics of saturated hydrocarbons in surface soil samples （0-25 cm） collected from different function districts of Tianjin were analyzed to reveal the sources and contamination levels of these compounds. In addition, the environmental significance, composition and distribution of normal alkanes, steranes and terpanes were also discussed. Furthermore, the geochemical indices and vertical variation of saturated hydrocarbons from different horizons （sub-horizon） （0-5 cm, 5-10 era, 10-15 cm, 15-20 cm, and 20-25 cm） were compared. The results show that the composition of saturated hydrocarbons from different localities or different horizons of the same locality were various to some extent, but the composition and distribution of steranes and terpanes were similar. It also reveals that the sources of normal alkanes were various and the primary source for the low and moderate molecular weight n-alkane was fossil fuel, which is dominated by crude oil. The source for the high molecular weight n-alkanes was the degraded products of higher plants. However, the sources for steranes and terpanes were much the same and mainly derived from petroleum hydrocarbons. The sources and contamination levels were different at surface soil samples collected from different environmental function districts. Crude oil may be the primary sources in the urban area, the vicinity of oil fields, economic development zone and inner suburbs, while the north mountain area has a lighter pollution and the degraded products of higher plant were the primary source. Except for some particular localities, different sub-horizons of the same sample locality have the similar composition characteristics of saturated hydrocarbons, which means the pollutants were derived from the same sourceand have moved downwards through the surface soils.