中文摘要：

河流沉积物中的重金属元素对水生生物和人类具有潜在的危害性,主要是由于环境条件的变化会使沉积物中的重金属元素释放到水体中。因此,研究影响沉积物中重金属元素释放的因素是十分重要的。研究了长江下游沉积物在不同pH条件下重金属元素Cd、Pb的释放能力和释放前后Cd、Pb形态的变化。结果表明,Cd、Pb在沉积物中的释放主要是在酸性条件下发生的,并且释放率随pH的升高而迅速降低,pH〉7.0后,释放率都非常低。释放能力Cd明显大于Pb。形态分析的4个典型沉积物样品中,Cd在南京位点样品中主要存在于残渣态中,其余3个位点样品主要存在于弱酸态和可还原态中,Pb在4个典型沉积物样品中主要存在于可还原态中。pH的变化使沉积物中Cd的各形态都不同程度地发生了释放,弱酸态和可还原态释放的程度最大,而Pb的各个形态释放都不明显。

英文摘要：

Heavy metal elements in river sediments are all potentially harmful to aquatic organisms and human beings,for they can be released to the water with the change of environmental conditions.Therefore,the study of the factors that account for the release of heavy metals in sediments is very important.In this paper,the release of heavy metal elements Cd and Pb at different pH from the lower reaches of the Yangtze River sediments and the change of speciation of Cd and Pb before and after the release were investigated.The results showed that the release of Cd and Pb mainly occurred under acidic conditions,and the related rates decreased quickly with the rise of pH.When pH7.0,the release rates were all very low.At the same time,the release of Cd was significantly greater than that of Pb.Speciation analysis of Cd and Pb of four typical sediments showed that Cd in Nanjing site sample mainly existed in residue,and Cd in other three sites samples existed mostly in acid extractable and reducible states,whereas Pb was mainly in residue in these four sediment samples.With the changes of pH,all species of Cd were released in varying degrees,among which acid extractable and reducible states were released most remarkably.In contrast,Pb in various states didn＇t show evidence of obvious release.