多证据分析技术在场地重金属污染评价中的应用研究

采用多证据分析技术,综合重金属浓度相对累积频率分布规律及其在场地中的空间分布规律,推导了案例场地土壤中As、Cr6+背景浓度上限.其中,场地1土壤中As、Cr6+背景浓度上限分别为29.8 mg.kg-1、76.1 mg.kg-1,均远高于文献报道的北京地区土壤背景浓度.场地2土壤中As、Cr6+背景浓度上限分别为10.6 mg.kg-1、33 mg.kg-1,略高于文献报道浓度.以推导的背景值作为评估标准,案例场地均存在不同程度污染,与场地历史生产活动中的排污特性分析结果及元素相关性分析结果相符.其中,场地1中As、Cr6+的超标率分别为3.8%、6.0%,场地2中仅As超标,超标率为5.2%,但均远低于以文献报道的背景浓度作为评估标准确定的超标率77.7%、96.7%及41.9%.因此,具体重金属污染场地评估项目中,应避免因直接以文献报道的区域背景浓度作为标准进行评估而使结论缺乏客观性,并导致后续修复过程中投入过多不必要的修复资金.

Application of Multiple Lines of Evidence Analysis Technology in the Assessment of Sites Contaminated by Heavy Metals

A multiple lines of evidence analysis technology was applied to assess whether sites were contaminated by heavy metals (HMs). Firstly, the baseline upper limit concentration for As and Cr⁶⁺ were derived for the two investigated sites based on the analysis of the relative cumulative probability plots of the two metals and their spatial distribution in the soil. The results indicated that the baseline upper limit concentrations for As and Cr⁶⁺ at site 1 were 29.8 mg ·kg^-1 and 76.1 mg ·kg^-1, respectively, which were much higher than those reported for the local area by others. But at site 2, the baseline upper limit concentrations for As and Cr⁶⁺ were 10.6 mg ·kg^-1 and 33 mg ·kg^-1, respectively, which were only a little higher than the reported values. Taken the derived baseline concentrations as the assessment criteria, both sites were contaminated by the heavy metals to some degree, which is consistent with the site historical activities review results and element correlation analysis results. At site 1, the As concentration in 3.8% samples exceeded the derived baseline concentration, while the Cr⁶⁺concentration in 6.0% samples exceeded the baseline concentration. At site 2, only the concentration of As in 5.2% samples exceeded the derived baseline value. All the above exceeding rates were much lower than those based on the reported baseline values, which were 77.7% and 96.7% for As and Cr⁶⁺ at site 1, respectively and 41.9% for As at site 2. The difference indicates that for a specific site, the baseline concentrations for heavy metals reported in literatures should not be directly applied as the criteria to assess whether the site is contaminated or not, which may cause the results to lose the objectivity and leading to the misallocation of lots of rare resource to remediate soil that maybe not contaminated.