广西岩溶洞穴土壤中多环芳烃污染特征与解析

首次研究相对封闭稳定环境条件下的岩溶洞穴土壤中PAHs的污染特征及其影响因素.以广西桂林大岩洞穴为例，结果表明，在洞穴内部PAHs总量为7.22～117.29 ng·g^-1，远低于洞外土壤中的含量（51.35～235.73 ng·g^-1），与其他地区相比，表明桂林近郊土壤PAHs污染较轻.大岩土壤中PAHs总量呈现出洞外和洞口附近明显高于洞内而洞内变化不大；洞外和洞口附近土壤中重环组芳烃含量高于轻环组（平均值69.25 ng·g^-1＞38.81 ng·g^-1），但在洞内土壤中则相反（平均值3.93 ng·g^-1＜7.41 ng·g^-1），说明洞内PAHs不仅来自于大气迁移过程，而且也来自于洞顶雨水淋滤作用.土壤中PAHs浓度分布表明在洞口附近存在陷阱效应、在洞穴最里端有裂隙存在.陷阱效应使洞口附近重环芳烃浓度显著高于洞外（88.19 ng·g^-1＞31.28 ng·g^-1），而且PAH分子量与”易陷落性”呈线性相关（R²=0.49）；通过实测值推测从洞口输入的PAHs浓度约为裂隙输入的17倍.温度和分子量差异是影响PAHs在土壤中浓度分布模式的重要因素.

Distribution Character of Polycyclic Aromatic Hydrocarbons in Soils from the Karst Cavity,Guilin City, South China

We investigated the distribution characteristic of polycyclic aromatic hydrocarbons (PAHs) of soils from Dayan cave, a karst cavity in Guilin City, South China. The total PAHs concentrations from the inner cave ranged from 7.22 to 117.29 ng·g-1 were much lower than those of outside cave (range of 51.35-235.73 ng·g-1). PAHs in studied area polluted slightly compared with other area. PAHs contents outside the cave and near cave gate were much higher than those within the cave with a little concentration change. In outside cave soils, the heavy molecular weight PAH(HMW) concentrations were higher than those of the light molecular weight PAH(LMW)(mean value 69.25 ng·g-1＞38.81 ng·g-1)while it was reverse inside cave(mean value 3.93 ng·g-1＜7.41 ng·g-1),which indicated the inner PAHs might came from atmosphere introduction and rainwater filtering from the top of the cave too. PAHs concentration distribution in the soils presented "trap effect" near the cave gate and a concentration superposition from the slope in the north cave wicket. HMW concentration near the cave gate was even larger by three times than that outside cave gate and a positive relation was found between PAH molecular weight and its falling tendence(R2=0.49). Deducing from the analysed data, PAHs concentration contributed by the cave gate was about 17 times of that of the slope. Temperature and molecular weight diversity were important factors influencing PAH concentration distribution.