铅在不同污染级土壤中的环境风险

Environmental risks of lead in soils with different pollution levels

根据EuropeanCommunitiesBureauofReference提出的BCR法加以改进,对不同铅污染程度土壤中Pb的有效态和4种化学形态含量进行分析,比较红壤和水稻土两种土壤类型之间有效态及分级中存在的差异;利用污染因子风险评价法(Cf)和风险评价代码法(RAC)评估土壤污染的环境风险。结果表明,红壤和水稻土中铅的有效态含量均随着污染程度加深而显著提高,但在污染为重度时其占总量的比例较之低度污染分别下降了18.7%和23.0%。对土壤进行BCR分级后,不同形态含量随污染程度的加深而有所增加,在比例上呈现可还原态>残渣态>可氧化态>酸可提取态,在重度级污染时,残渣态所占比例大幅提高,生物有效性降低。Cf值和RAC环境风险评估中,低、中、重度铅污染土壤均为轻度和中度风险,特别是重度污染红壤与水稻土Cf、RAC环境风险均为轻度。另外,pH值影响重金属形态的分布,pH值降低,生物有效性提高。

In this study,we investigated the differences in bioavailable state and classification between two different soil types(red soil and paddy soil)by analyzing the bioavailable state content in soils with different Pb pollution levels and the four chemical forms of Pb in soil obtained with a three-step extraction method(BCR)proposed by European Communities Bureau of Reference;environmental risks of soil pollution were assessed by the contamination factors evaluation method(Cf)and the risk assessment code method(RAC).The results indicated that the bioavailable state content of Pb in both red soil and paddy soil rose significantly with the increase of contamination degree,but compared severe pollution with low pollution,its proportion in total content decreased by 18.7%and 23.0%,respectively.The four different forms contents increased with the increase of contamination degree,revealing the trend of proportion as reducible>residual>oxidizable>acid-extractable after classifying the soil with BCR.The proportion of the residual state was greatly increased and the biological availability decreased in severe pollution condition.After environmental risk assessment with C f and RAC method,the risks were mild or moderate regardless of the Pb pollution degree being low,medium or heavy,especially for heavily polluted red soil and paddy soil,the environmental risks were relatively mild.In addition,the pH values affected the chemical forms distribution of heavy metal,and the biological availability increased while the pH value decreased.