土壤铜、铬(Ⅵ)复合污染重金属形态转化及其对生物有效性的影响

Transformation of Copper and Chromium in Co-contaminated Soil and Its Influence on Bioavailability for Pakchoi(Brassica chinensis)

通过盆栽试验和室内化学分析相结合的方法,研究了外源铜、铬(Ⅵ)单一和复合污染中土壤金属形态转化及其对生物有效性的影响.结果表明,外源铜、铬(Ⅵ)单一污染土壤中,铬主要以残渣态和有机结合态形式存在,而铜则主要以铁锰氧化物结合态和残渣态形式存在.铜、铬(Ⅵ)复合污染时,低浓度铜(≤400 mg.kg-1)促进铬向交换态转化,低浓度铬(≤5mg.kg-1)促进了铜向残渣态转化,而高浓度铜(≥800 mg.kg-1)和铬(≥20 mg.kg-1)却抑制了这种转化.不同浓度的铜、铬复合污染对其在土壤中的形态分布影响不同.此外,生物有效性试验结果显示,铜能够促进土壤有机结合态铬转化成残渣态而抑制小白菜对铬的吸收;同样铬因为促进土壤交换态铜向残渣态转化而抑制小白菜对铜的吸收.因此,在对铜铬(Ⅵ)复合污染土壤进行评价及植物修复时,应考虑二者的综合效应.

Heavy metal fractions in soil play an important role in the bioavailability for plants.A pot experiment was carried out to study the transformation and bioavailability for pakchoi of exogenetic copper and hexavalent chromium in co-contaminated soil.The results showed that one month after tested heavy metals were added into soil,the chromium was present mainly in residual and organic bonded form while copper was mainly bound to hydrated oxides of iron and manganese as well as residual form.Lower concentrations copper（≤400 mg·kg-1） in soil could promote chromium transform from other forms to exchangeable form while higher concentrations copper（≥800 mg·kg-1） in soil would inhibit this transformation.Similarly,chromium in low concentrations（≤5 mg·kg-1） could facility copper transform to residual form while chromium in high concentrations（≥20 mg·kg-1） would reduce such transformation process.Both added chromium to soil polluted by high concentrations copper and added copper to high chromium content soil could promote the polluted soil reach quasi-equilibrium state.Additionally,adding copper in soil could inhibit chromium uptake of pakchoi by promoting soil OM-Cr transformed into RES-Cr.While adding chromium in soil could reduce copper uptake of pakchoi by stimulating the EXE-Cu transformed into the RES-Cu.Therefore,it is necessary to take into consideration the synthetic effects of copper and chromium when carrying on assessment and phytoremediation to co-contaminated soil.