土壤包气带含水率对氯代烃垂向迁移影响的模拟研究

Effects of Moisture Content on Vertical Migration of Chlorinated Hydrocarbons in Soil Unsaturated Zone

氯代烃类挥发性有机物在土壤包气带中的垂向迁移是该类污染物呼吸暴露风险的重要途径.为探究氯代烃在土壤包气带中的垂向迁移规律,通过室内土柱模拟试验,研究土壤包气带含水率对不同氯代烃[TCE(三氯乙烯)、PCE(四氯乙烯)]气相扩散速率的影响,并通过线性拟合筛选出更准确的气相有效扩散系数预测模型.结果表明,土壤含水率与氯代烃气相有效扩散系数呈显著负相关[R=-0.89,P<0.01,n=7(TCE);R=-0.86,P<0.01,n=7(PCE)].随着土壤含水率由0.5%增至40.0%,TCE气相有效扩散系数(DT)由0.035 9 cm^2/s降至0.002 5 cm^2/s,平衡时间由13 h增至91 h,平衡时气体浓度由4.22 g/m^3降至0.31 g/m^3;PCE气相有效扩散系数(DP)由0.033 9 cm^2/s降至0.001 1 cm^2/s,平衡时间由15 h增至103 h,平衡时气体浓度由3.01 g/m^3降至0.12 g/m^3.与Penman模型、Marshall模型模拟值相比,Millington-Quirk模型模拟值与氯代烃气相有效扩散系数实测值的拟合程度更好(R>0.95,P<0.01,n=7).研究显示,土壤包气带含水率的增加对氯代烃气相扩散有明显的抑制作用.

The vertical migration of chlorinated hydrocarbons in soil is an important source of risk of inhalation exposure to volatile organic compounds. Serial soil column experiments were developed to investigate the vertical migration of chlorinated hydrocarbons. The effects of moisture content in the soil unsaturated zone on the diffusion rate of chlorinated hydrocarbons（ e. g.,trichloroethylene,TCE and tetrachloroethylen,PCE） were studied,and a prediction model of effective vapor diffusion coefficient was optimized by linear fitting. The results showed that moisture content in soil was significantly negatively correlated with the effective vapor diffusion coefficient of chlorinated hydrocarbons（ R =-0. 89,P〈0. 01,n = 7（ TCE）; R =-0. 86,P〈0. 01,n = 7（ PCE））. When the moisture content increased from0. 5% to 40. 0%,the effective vapor diffusion coefficient of TCE（ DT） decreased from 0. 0359 cm^2/s to 0. 0025 cm^2/s,equilibrium time increased from 13 h to 91 h and the equilibrium vapor concentration decreased from 4. 22 g/m^3to 0. 31 g/m^3. When the effective vapor diffusion coefficient of PCE（ DP） decreased from 0. 0339 cm^2/s to 0. 0011 cm^2/s,equilibrium time increased from 15 h to 103 h and the equilibrium vapor concentration decreased from 3. 01 g/m^3to 0. 12 g/m^3. The effective vapor diffusion coefficient values of chlorinated hydrocarbons were well fitted with the values from the Millington-Quirk model（ R 0. 95,P〈0. 01,n = 7） compared with the Penman and Marshall Models. The increase of moisture content of the soil unsaturated zone could obviously inhibit the vapor diffusion of chlorinated hydrocarbons.