用分级方法评估土壤对重金属的缓冲能力

研究了不同Cd, Zn, Cu和Pb负荷对5种土壤(油黄泥土、棕红壤、红壤、石砂土和紫砂土)中的重金属形态的影响,分析了不同土壤对重金属的缓冲作用及其影响因素.结果表明,未污染土壤中的重金属主要以残余态为主,占土壤重金属总量的51%以上.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,对重金属的缓冲作用下降.由于Cd, Zn, Cu和Pb本身的特性不同,土壤中各组分与Cd, Zn, Cu和Pb的结合方式及程度不同.当外源重金属进入土壤后,土壤对重金属的缓冲性为:Pb》Cu》Zn》》Cd,酸性土壤和砂质土壤的缓冲能力较低.当重金属加入量较低时,重金属优先向氧化物结合态和有机质结合态转化;而当加入量较高时,向交换态和碳酸盐结合态转化的比例增加.土壤pH下降可使交换态Cd, Zn, Cu和Pb的比例递增,降低土壤对重金属的缓冲性,增加了重金属对环境影响的风险.

Assessment of Soil Buffer Capacity to Cadmium, Zinc, Copper, and Lead Using Metal Fractionation

The effects of Cd,Zn,Cu and Pb loads on fractions of the metals in five soils were studied,and buffer capacity of the soils to heavy metals was analyzed.The major fractions of heavy metals in the unpolluted soils were residual forms,which accounted for more than 51% of the total metals.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.The interactions of metals with soil components varied with metal types.The buffer capacity of soils to heavy metals decreased in the order of Pb>Cu>Zn(>>)Cd,and lower in the acid and sandy soils.When heavy metals were input in low levels,the metals were preferentially transformed into oxides-and organic matter bound fractions.However,the metals were transformed into exchangeable and carbonate bound fractions when metals were input in higher levels.The proportion of exchangeable fraction of Cd,Zn,Cu and Pb in the soils increased and buffer capacity of the soils to the metals decreased with decreasing pH.