施污土壤与污泥中Cu、Pb、Cd、Zn的形态分布

污泥中的重金属元素是限制其大规模农田利用的重要因素。施污土壤和污泥中重金属的形态研究可以用来评价土壤中重金属的生物有效性以及它们在土壤中的移动性。用修正BCR三步连续提取法进行分步提取研究了污水污泥和施污后的西红柿地土壤中Cu、Pb、Cd、Zn的形态分布状况。施用污泥堆肥10t hm-2后的土壤中Cu、Pb、Cd、Zn的全量与各种形态含量无明显增加,Cu、Pb、Zn含量远低于国家土壤环境质量标准。土壤中Cu的各种形态分布关系是:残渣态>可还原态=可氧化态>可交换态和弱酸溶解态,Cu在土壤中的存在是以最稳定的残渣态为主。堆肥污泥与干化污泥相比,残渣态Cu的比例明显增加。土壤中Pb的各种形态分布关系是以残渣态和可还原态为主,但可氧化态的分布比例最小。土壤中Cd的可交换态、可还原态和残渣态各占据相等的含量,但可氧化态Cd的含量几乎为零。Zn在土壤中的各种形态分布关系是:可交换态和弱酸溶解态>可氧化态>可还原态>残渣态,Zn在土壤中的存在是以最易迁移的可交换态和弱酸溶解态为主。这些金属元素在土壤中的相对稳定性顺序为:Cu>Pb>Cd>Zn。Zn在土壤中的移动性要远高于Cu。

Fractional Distribution of Copper,Lead,Cadmium and Zinc in the Soil Amended with Composted Sludge and in Sludge Itself

Heavy metals contained in sludge are important confined factor to sludge application on agricultural land on a large scale.The investigation of speciation of metals both in sludge-amended soil and in sludge may help to assess the bioavailable metal fractions and the possibility of mobilization of these metals in soil.The modified three-step sequential extraction procedure proposed by the BCR was used to predict Cu,Pb,Cd and Zn fractional distribution in the sewage sludge itself and the tomato soil amended with composted sludge.The total contents and fractional contents of Cu,Pb,Cd and Zn in soil applied with sludge at doses of 10t hm-2 didn't increase significantly,and Cu,Pb and Zn were lower in soil applied with sludge than the national soil environmental standards.The Cu contents orders in the soil fractions was: residual Cu>reducible Cu = oxidizable Cu>exchangeable and weak acid soluble Cu,and the Cu was mainly associated with the residual fraction,which represent the most stable phase.The extraction yields of residual Cu in the composted sludge greatly increased than that in dry sludge.The Pb was mainly associated with the residual fraction and reducible fraction,and only a small fraction was observed at the oxidation step for Pb.In all soil samples,the partitioning of Cd with same extractability in the first two steps of the procedure and the residual fraction,and almost zero extractability was observed at the oxidation step for Cd.The Zn contents orders in soil fractions was: exchangeable and weak acid soluble Zn>oxidizable Zn>reducible Zn>residual Zn,and the Zn was mainly associated with the exchangeable and weak acid soluble fraction,which represent the most mobile phase.The stable orders of these metals in soils was: Cu>Pb>Cd>Zn.The mobilization of Zn was higher than that of Cu in soils.