Ecological risk assessment of heavy metals in sediments of Xiawan Port based on modified potential ecological risk index

Modified potential ecological risk index （MRI） was proposed based on the potential ecological risk index （RI） and risk assessment code （RAC） by modifying an index. The modified index was relevant to the chemical speciation of heavy metals. Xiawan Port, a typical region contaminated by industrial production, was selected as a case study area. The total concentrations and chemical speciation of heavy metals in sediments of Xiawan Port were analyzed. The experimental data indicate that Xiawan Port is seriously polluted by heavy metals, especially by Cd. The risks of heavy metals are evaluated by RI, RAC and MRI, respectively. The resluts of MRI show that the risks of heavy metals are in the decreasing order of Cd〉Pb〉Cu〉Zn. Comparison of results by different methods reveals that MRI integrates the characters of RI and RAC. MRI is recognized to be useful for risk managemnt of heavy metals in sediments.

油葵和苦荬菜根际土壤中镉和锌的活化机制及修复潜力比较

【目的】研究油葵和苦荬菜根际土壤固、液相对镉(Cd)和锌(Zn)的活化机制,比较两种植物在轻、中度复合污染农田的修复潜力。【方法】通过大田试验种油葵和苦荬菜,测定成熟期土壤的pH值、有机酸、重金属总量及其生物有效性;测定土壤溶液中的溶解性有机质(DOM)、主要离子、水溶态重金属及其形态分布;测定植物各部位中重金属的浓度及形态,通过计算重金属在植物中的富集系数(BCF)和转运系数(TF),比较两种植物对土壤重金属污染的修复潜力。【结果】油葵和苦荬菜根系分泌的低分子有机酸均使根际土壤pH值下降明显,显著低于非根际土壤(P<0.05);苦荬菜根际土中低分子有机酸及DOM的浓度显著高于油葵根际土(P<0.05)。两种植物根际土壤溶液中的Cd以离子态和DOM结合态为主,Zn以离子态为主;两种植物根际土壤中有效态的Cd差异不显著,油葵根际有效态Zn显著高于苦荬菜;两种植物根际土壤的Zn和Cd有效态与土壤溶液中Cd-DOM和Zn-DOM呈显著相关。苦荬菜根对重金属的富集能力较强,但油葵地上部分能吸收转运更多的Cd和Zn,并在叶中以毒性较低的不溶性磷酸盐结合态和草酸结合态富集。【结论】两种植物根际分泌的有机酸可以增加根际土壤中的Cd-DOM和Zn-DOM的浓度,提高土壤中的Cd和Zn的有效性,苦荬菜根际对重金属有较强的活化能力,但油葵地上部分对Cd和Zn的吸收转运能力更强。两种植物都具有较强的土壤重金属修复潜力,但从经济角度出发,油葵更适合现阶段我国农田重金属污染的修复。