耕地土壤铜、镉、锌形态及生物有效性研究

土壤重金属总量常被用来评估土壤质量安全,但是大量事实说明单纯用土壤重金属总量并不能完全说明土壤重金属的生物有效性及其环境风险。相对于国内外常用的Tessier的五态方法,欧共体标准物质局提出的三步提取法(BCR法),中国地质调查局地质连续提取法的七态标准少见报道。本研究选取河南平原耕地样品,采用中国地质调查局地质连续提取法(DD2005-03)进行耕地中重金属元素(Cu、Cd、Zn)的形态分布,结果表明:Cu、Zn主要以残渣态存在,其残渣态分别占全量的55.80%和67.35%。Cd以离子交换态为主,占全量的27.30%。Cu、Cd、Zn各态含量占全量比例的顺序是,Cu:残渣态弱有机结合交换态铁锰氧化态碳酸盐结合态强有机结合态水溶态离子交换态。Cd:离子交换态弱有机结合交换态强有机结合态残渣态碳酸盐结合态铁锰氧化态水溶态。Zn:残渣态铁锰氧化态弱有机盐结合态离子交换态强有机结合态碳酸盐态水溶态。从生物可利用性系数k来看,Cd主要以活动性较大的状态存在,很容易被作物吸收。

Fractionations and bioavailability of Cu, Cd and Zn in cultivated land

The complexity of metal contaminated sites has and continues to be simplified to a measure of the total metal content. While total metal content is a critical measure in assessing risk of a contaminated site, total metal content alone does not provide predictive insights on the bioavailability, mobility, and fate of the metal contaminant. The paper was based on heavy metal speciation of soil-plant system in cultivated land, Henan plain, the order of Cd in each fraction was Exchangeable (27.3%) ) Weakly bound to organic matter (22.7%) ) Strongly bound to organic matter (16.4%) ) Residual (15.1%) ) Carbonate (12.1%) ) Fe/Mn oxide bound (4.5%) ) Water soluble (2.0%), Zn was Residual (66.3%) ) Fe/Mn oxide bound (10.9%) ) Weakly bound to organic matter (9.4%) ) Exchangeable (6.0%) ) Strongly bound to organic matter (3.9%) ) Carbonate (2.9%) ) Water soluble (0.6%). The accuracy of the sequential extraction was judged by the relative error (RE). RE for Cd ranged from 0 to 45% with mean 16.3%.RE for Zn ranged from 0.1%-11.4% with mean 3.4%. On average, bioavailability index (BI) for Cd and Zn is 39.1% and 9.0% respectively. The mobil-ity of the elements in the order Cd ) Zn corresponds with the plant-availability of individual elements.