土壤理化性质对污染场地环境风险不确定性的影响

以某化工污染场地中挥发性有机物苯的环境风险评价为例,研究了土壤有机质含量、土壤含水率、土壤容重等理化性质对风险评价结果的影响.在土壤污染物苯浓度不变的前提下,土壤有机质含量、土壤含水率和土壤容重在场地条件下随机取值的变异范围分别为0.31%～2.31%、0.12～0.25和1.25～1.75 g/cm3.10 000次蒙特卡罗模拟结果表明,在95%置信水平下,苯的总致癌风险(概率值)在1.45×10-5～2.74×10-5之间.在该场地条件下,土壤有机质含量是影响苯风险不确定性的最主要因素,其对风险评价结果不确定性的贡献率高达90.2%;土壤含水率和土壤容重的贡献率分别为5.6%和4.2%.因此,在土壤污染健康风险评价过程中,应对理化参数进行敏感性分析,对评价结果影响较大的关键参数取值需慎重. 

Effects of Soil Physical-Chemical Properties on Risk Uncertainty in a Contaminated Site

The effects of spatial heterogeneity of soil organic matter(SOM),soil moisture(Pws) and soil bulk density(ρb) on benzene risk in a benzene-contaminated chemical plant were evaluated using Monte Carlo simulation.Under the conditions of identical benzene concentration,the values of SOM,Pws and ρb acquired from site investigation varied in the range of 0.31%-2.31%,0.12-0.25 and 1.25-1.75 g/cm3,respectively.The results of 10,000 times Monte Carlo simulation showed that at the 95% confidence level,the minimum and maximum carcinogenic risk of benzene was 1.45×10-5 and 2.74×10-5,respectively.SOM was the most sensitive soil parameter evaluated;it could explain 90.2% of the variance in the carcinogenic risk of benzene.The remaining variance was explained by Pws and ρb,with contributions of 5.6% and 4.2%,respectively.Therefore,the sensitivity analysis of the model parameters,especially soil physical-chemical parameters,is very important in contaminated site risk assessment.The value of the sensitive soil parameters must be determined very carefully to ensure a reasonable risk assessment result.