北京东南郊污灌区PAHs垂向分布规律

Distribution of Polycyclic Aromatic Hydrocarbons in Soil Profiles in Southeast Suburb of Beijing Wastewater Irrigation Area

采用Eijkelkamp土壤采样器对北京东南郊污灌区进行了3个钻孔剖面采样,分析了土壤样品的理化参数,并且采用气相色谱-质谱联用仪对土壤样品的多环芳烃（PAHs）进行了定量分析,研究了土壤理化参数和16种PAHs从表层到5.5 m深的范围内垂向变化规律.结果表明,污灌区表层土壤中有14种PAHs检出,检出浓度在4－428μg/kg之间,表层以下PAHs的检出种类显著减少,主要以2环和3环的萘、菲、芴、苊烯、二氢苊、荧蒽6种为主.粘粒含量、粘土矿物总量、阳离子交换容量以及总有机碳4个理化参数相互之间在垂向变化上具有一致性,均在0.05水平上显著相关.表层以下粘粒含量与低环PAHs在垂向含量变化也有较好的一致性,粘粒含量高的层位,PAHs含量也较高.从剖面PAHs含量变化可以判断,低环PAHs较易迁移,它们的迁移性强弱顺序为：二氢苊〉芴〉萘〉菲〉苊烯〉荧蒽,其它高环PAHs难以迁移,仅在表层土壤中检出,说明在长期污灌条件下,迁移性较好的低环PAHs能够迁移到较深的土层中,有可能导致浅层地下水的污染.

3 borehole profiles samples were collected using Eijkelkamp soil sampler from the wastewater irrigation area of Beijing Southeast suburb. The soil samples were collected from surface to 5.5 m underground every 0.5 m. Physical-chemical properties of the samples such as clay content, total amount of clay minerals, cation exchange capacity （CEC）, total organic compounds （TOC）, etc. were analyzed. 16 polycyclic aromatic hydrocarbons （PAHs） defined by the U. S. EPA were also analyzed with gas chromatography-mass spectrometry （GC-MS）. Results show that 14 PAHs were detected in the surface soil samples. The concentrations of PAHs range from 4 μg/kg to 428 μg/kg. Under the surface, both species and concentrations of PAHs in soil samples drop very fast. Only 2 rings and 3 rings PAHs were detected, which were naphthalene, phenanthrene, fluorene, acenaphthylene, acenaphthene, and fluoranthene. Clay content, total amount of clay minerals, CEC and TOC have significant correlations at 0.05 level between each other. Under the surface, clay contents also have a relationship with low-rings PAHs concentration. Where the layers have higher clay contents, the PAHs have higher concentrations. The contents of PAHs changing along the profiles also show that,low-rings PAHs are easier to migrate than high-rings PAHs. The sequence of the migration capabilities of low-ring PAHs is acenaphthene 〉 fluorene 〉 naphthalene 〉 phenanthrene 〉 acenaphthylene 〉 fluoranthene. However,high-ring PAHs were only detected in surface soil samples. That means low-rings PAHs can reach the deep layers of the vertical profiles under long-term wastewater irrigation. Therefore, the shallow groundwater has the possibility to be contaminated.