风干对淹水稻田土重金属形态及其作物有效性的影响

Effect of Air Drying on Speciation and Plant Availability of Heavy Metals in Flooded Rice Paddies

为探索淹水稻田土风干处理后重金属形态及作物有效性的变化规律,在长江三角洲典型地区采集淹水土壤样品,原样与风干样均采用BCR连续提取方法结合原子吸收分光光度法测定Cd、Cr、Cu、Ni、Pb等重金属不同形态含量。结果表明:淹水状态下各形态占全量质量分数为酸可溶态11.5%、可氧化态21.5%、可还原态33.7%、残留态29.2%。风干后重金属酸可溶态、可还原态明显减少,可氧化态有增有减,残留态增加;对风干处理敏感程度从大到小依次为Ni、Pb、Cd、Cu,Cr保持稳定。田间淹水状态Cd、Ni、Cu作物有效性较高,Pb次之,Cr较低;样品风干处理后Ni、Cd、Cu表观活性降低,Pb反而明显增加,Cr保持稳定。主要结论是土壤风干样品不能如实反映田间淹水状态重金属形态分布,低估了土壤重金属作物有效性。

In order to explore the changes in speciation and plant availability of heavy metals in flooded rice paddies after air drying, flooded soil samples were collected in the typical area in Yangtze River Delta, and the flooded and air dried soil samples were treated with BCR sequential extraction method. Amended with atomic absorption spectrophotometer, the fractions of Cd, Cr, Cu, Ni and Pb were measured. The result showed that acid soluble was 11.5%, oxidisable was 21.5%, residual was 29.2%, reducible was 33.7% for flooded soil. After air drying, acid soluble and reducible fraction decreased while the residual fraction increased. The sensitive order was Ni 〉 Pb 〉 Cd 〉 Cu, and Cr remained steady. In flooded condition, the plant availability of Cd, Ni and Cu were higher than Pb, and Cr was the lowest. After being air-dried, the plant availability of Ni, Cd and Cu decreased while Pb increased. It was concluded that the air dried samples could not exactly show the real speciation of heavy metals, and the plant availability of heavy metals was underestimated.