外源铅铜镉在长三角和珠三角农业土壤中的转化

选择了我国经济发达地区的长江三角洲和珠江三角洲10个代表性农业土壤，采用室内培养和化学分级方法研究了加入外源铅、铜、镉在土壤中的动态变化及转化趋势，探讨了碳酸钙、粉煤灰、猪粪和钢渣等土壤改良剂对土壤重金属形态的影响。结果表明，随着土壤重金属负荷的提高，土壤中交换态重金属的比例增大，残余态比例下降，有效性提高，对环境威胁增大。当重金属加入最较低时，重金属优先向氧化物结合态、有机质结合态转化；而当加入最较高时，向交换态和碳酸盐结合态转化的比例明皿增加。pH和土壤组分对重金属在土壤中的转化有显著的影响，土壤pH下降可使交换态Cd、Cu、Pb的比例递增。加入碳酸钙、粉煤灰、猪粪和钢渣等改良剂可显著地降低土壤中交换态重金属比例，增加其它形态的重金属比例。

Transform of lead,copper,and cadmium added in agricultural soils in the Changjiang and Zhujiang Deltas

Chemical forms of heavy metals in soils can affect mobility and bio-availability of the heavy metals in the soils. Understanding evolution of chemical fractions of the heavy metals in the soil pollution process is helpful to predict effects of heavy metal accumulation on soil environments. In this study, the transform processes of Pb, Cu and Cd in ten agricultural soils, collected from the Changjiang and Zhujiang deltas were characterized, and effects of Cd, Cu and Pb loads on their chemical forms in the soils were studied. The results showed that the major fraction of heavy metals in the unpolluted soils was residual forms, proportions of extractable fractions were Cd>Cu>Pb and varied with the soils. With increasing loads of heavy metals in the soils, the proportions of metals as exchangeable form increased, those as residual form decreased, and thus increased availability of the metals and their impacts on the environments. When heavy metals were added in low levels, the metals were preferentially transformed into oxides- and organic matter bound fractions. However, the higher proportions of metals were transformed into exchangeable and carbonate bound fractions when metals were added in higher levels. The proportions of exchangeable Pb, Cu, and Cd fractions in the soils increased with decreasing pH. Application of amendments such as limestone, fly ash, organic manure and furnace slag could decrease the proportion of exchangeable metal fractions.