The influence of pH on the release behavior of heavy metal elements Cd and Pb in the sediments of the lower reaches of the Yangtze River

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 pH＞7.0, 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.