氧化与还原条件下水稻土重金属形态特征的对比

Comparison of heavy metal fractions distribution in paddy soil under anoxic and oxidized conditions

还原状态下的水稻土被风干处理后氧化还原等性质发生明显变化,对重金属的形态特征产生影响,进而影响对作物有效性的评价。利用BCR连续萃取法研究了张家港市南部不同pH水稻土在还原和氧化条件下Cu、Pb、Ni和Cd的形态变化状况。结果显示,氧化还原对重金属形态分配具有显著影响,而pH对Ni在还原状态下的形态分配有显著影响,对Cu、Pb和Cd形态分布影响不显著。样品经风干氧化处理后,氧化物结合态重金属均表现为不同程度的降低;Cu残渣态比例增加25%,氧化物结合态和有机结合态比例有所降低;Pb有机结合态比例增加33%,残渣态减少33%,酸可提取态和氧化物结合态变化不大;Ni受氧化还原条件影响更为强烈,表现为酸可提取态所占比例降低超过25%,氧化物结合态亦明显降低,残渣态提高超过60%;对Cd的影响主要表现为有机结合态所占比例降低约15%,残渣态提高约35%,酸可提取态和氧化物结合态变化不明显。氧化状态下的重金属形态并不是重金属在田间的真实状况,可能高估了Pb,低估Cu、Ni和Cd重金属在土壤中的危害性。

Anoxic paddy soil could be oxidized by air in dryness pretreatment procedure, which resulted in different impact on heavy metal fractions during the sequential extraction procedure, as well as resulted in impact on the assessment of their plant availability. The fractions ofCu, Pb, Ni and Cd in different pH soil in southern of Zhangjiagang City were investigated by the BCR sequential extraction schemes under anoxic and oxidized conditions. The results indicated that, the fractions of heavy metals were significantly affected by the anoxic and oxidized conditions, but were not affected by soil pH, except Ni in the anoxic condition in the paddy soil. After dryness and ground pretreatment procedure of the wet paddy soil, the heavy metals of Fe-Mn oxides fraction decreased with different degree; Cu in residual fraction increased 25% and that in Fe-Mn oxides and organic matter fraction decreased slightly; Pb in organic matter fraction increased 33% and decreased 33% for residual fraction; Ni was affected by the anoxic and oxidized conditions remarkably, acid extractable fraction decreased by 25%, Fe-Mn oxides fractions decreased slightly and more than 60% residual fraction increased. Pb in organic matter fraction decreased 15% and that in residual fraction increased about 35%, acid extractable and Fe-Mn fractions were not affected. The heavy metal fractions in the oxidized conditions were not the real situation in situ, the hazard of Pb were overrated and Cu, Ni and Cd were underrated after the paddy soil were dried.