场地实际重金属复合污染土壤生态毒性效应定量评价

Quantitative Evaluation of Ecological Toxicity Effect of Real Heavy Metal Combined Pollution in Site Soil

场地实际重金属复合污染土壤生态效应定量评价是场地生态风险评估中的难点,本研究耦合“自上而下”和“自下而上”复合污染联合效应评价的思路,构建了由“有效生物标志物响应筛选-主导污染物识别-不同暴露类型/污染物种类联合效应估算”3个步骤组成的场地实际重金属复合污染土壤生态效应定量评价方法,并以江苏省某废弃电镀污染场地为研究对象,采用蚯蚓土壤微宇宙培养实验进行了方法验证。以蚯蚓组织丙二醛(MDA)含量、金属硫蛋白(MT)含量、过氧化氢酶(CAT)活性、超氧化物歧化酶(SOD)活性和还原型谷胱甘肽(GSH)含量等生物标志物为效应终点的分析结果表明,蚯蚓对该场地的主要土壤重金属污染物包括Cd、Cu、Zn、Ni、Pb和Cr的富集能力表现为Cd>Cu>Zn>Ni>Pb>Cr;主成分分析结果表明,GSH含量、CAT活性和MDA含量为有效生物标志物,重金属Cd和Zn为主导污染物。GSH含量变化与土壤Cd总量及Zn的DTPA提取态含量之间存在多元线性关系;蚯蚓MDA含量变化能够通过土壤Cd的DTPA提取态含量进行预测;CAT活性变化能够通过Zn的土壤总量及蚯蚓生物累积量进行预测。针对场地实际污染土壤的性质及污染特征,对3类有效生物标志物响应的半效应浓度(half effect dose,EC_(50))估算的结果表明,3类有效生物标志物的敏感性从高到低的顺序为:GSH>CAT>MDA;不同元素以及不同类型暴露之间(如,与GSH含量变化对应的土壤总Cd与DTPA-Zn),以及同一元素不同暴露之间(如,与CAT活性变化对应的土壤总Zn与蚯蚓组织生物累积Zn)都有可能存在交互作用,而这些污染物暴露之间不存在暴露量变化的相关性。以上结果表明,采用多元统计分析手段,通过有效生物标志物响应、主导污染物的筛选以及联合效应估算,能够实现野外实际土壤重金属复合污染,生态效应的定量评价。

Quantitative evaluation of ecological effect of combined pollution of heavy metals in real site soil is considered as a great issue in ecological risk assessment of contaminated sites.In this work,a quantitative ecological assessment approach for combined contaminated soil in field by heavy metals was developed based on“top-down”and“bottom-up”knowledge,which was made up of three steps,namely,“screening of effective biomarkers-identification of dominant pollutants-evaluation of joint effect of different exposure types/contaminants”.Finally,taking an abandoned electronic planting site in Jiangsu Province as a case,the developed approach was verified using soil microcosm of earthworm.Results of the experiment by taking the biomarkers including malondialdehyde(MDA),metallothionein(MT),catalase(CAT),superoxide dismutase(SOD),reduced glutathione(GSH)as effect endpoints,suggested that the bioaccumulation of main heavy metal contaminants including Cd,Cu,Zn,Ni,Pb and Cr by earthworms ranged in an order:Cd>Cu>Zn>Ni>Pb>Cr.Principal component analysis(PCA)revealed that GSH,CAT and MDA were screened as effective biomarkers,and heavy metals Cd and Zn were dominant contaminants.It was found that there was a significant multivariate linear relationship between the change of GSH and concentrations of total Cd and DTPA-Zn in soil.And the change of MDA could be predicted by DTPA-Cd in soil.The change of CAT activity was predictive by the total Zn in soil and the bioaccumulated Zn in earthworm.Evaluation of half effect dose(EC_(50))based on the site-specific soil properties and heavy metal contamination characteristics revealed that the sensitivity of the 3 screened effective biomarkers ranged in an order:GSH>CAT>MDA.Interactions will occur in between different heavy metals and exposure types(e.g.,between soil total Cd and DTPA-Zn corresponding to GSH change),and(or)in between different exposure types of the same heavy metal(e.g.,between soil total Zn and bioaccumulated Zn corresponding to the change of CAT activity).While there is insignificant relationship in the change of concentrations between those contaminant exposures.It could be concluded in our work that the approach using multivariate statistics and made up of effective biomarker screening,dominant contaminant identification and joint effect evaluation was practicable in quantitative evaluation of ecological effect focusing on real soil heavy metal mixture pollution in field.