长江南京段近岸沉积物中重金属富集特征与形态分析

在对长江南京段八卦洲和杨中两个冲积洲近岸沉积物及其优势野生植物中A1、Cu、zn、Cr、Pb、Nj和Cd元素含量分析的基础上,分别考查了这些重金属的富集系数(EF)和生物富集因子(BCF),并采用BCR连续提取法对Cd的赋存形态进行了研究.结果表明,本区域长江近岸沉积物和野生植物中重金属存在不同程度的富集现象,两洲沉积物中Cu、Cr、Pb、Ni、Cd均有富集趋势,各元素EF>1的样品占总样品比例分别为Cu 50%、Cr40%、Pb40%、Ni 40%、Cd20%.而在野生桐蒿和芦蒿两种优势植物中Cd富集显著,其中桐蒿的BCF平均值高达2.57.采用BCR连续提取法对沉积物中Cd进行形态分析,结果显示,沉积物中Cd主要以酸溶/交换态(B1)和可还原态(B2)为主,二者分别为31.7%和45.5%,占到总量的70%以上,B1态远高于一般土壤和沉积物中重金属的分布,表现出很强的迁移性和生物可利用性.新生成沉积物较老沉积物中的B1态有显著增加,反映出沉积物越新,Cd的迁移性越强的趋势.研究结果说明长江城市段近岸沉积物中Cd受近期人为因素影响明显,具有一定的生态风险.

Enrichment and speciation analysis of heavy metals in the sediments of Yangtze River(Nanjing section)

The contamination levels of Al, Cu, Zn, Cr, Pb, Ni and Cd were determined in some wild plants and sediments of Ba-guazhou and Yangzhong islands in Changjiang River(Yangtze River). An evaluation of the pollution status of the river sediment was carried out by enrichment factors(Efs) and biological enrichment factor(BCF) calculated using adapted background concentrations of heavy metals. The results indicated that heavy metal settling in recent sediments was serious around the both islands, especially for Cu, Cr, Pb, Ni, Cd. The sediment samples with EF_(Cu)>1.0 account for about 50% of all of them, and about 40% of the all samples with Efs>1.0 for Cr, Pb, Ni, while 21% of the samples with EF_(Cd)>1.0. It was found that Cd enriched significantly in Artemisia selengensis and Erigeron bonariensis which abundant grown on the sediments. And average BCF of Cd reached to 2.51. In order to identify Cd bioavailability, Sequential extraction procedure(acid extractable, reducible, oxidizable, and residual) proposed by BCR was applied for the determination fractions of Cd in the sediments. Generally, 31.7% and 45.5% of Cd were found in the acid ex-tractable and reducible fractions respectively, which were exceeded heavily the average level in the river sediments and soils. This trend performed more seriously in recent setting sediments. It suggested that the Cd was influenced significantly by human activities. All results demonstrated that Cd risk existed in the riverside sediments along the low reach of Changjiang River.