Humic acid is an important pool of heavy metals in sediments. Generally, the presence of refractory humic matter in aquatic systems would decrease the bioavailability of Cd and hence control the bioaccumulation of Cd in benthic animals. In the present work, we applied a suspending system to determine the relative importance of particulate and dissolved fractions of humic acid as Cd sources for the bivalve Meretrix meretrix and to investigate the difference of bioaccumulation characteristics of Cd adsorbed on different fractions of humic acid. The results showed that.the bioaccumulation characteristics of Cd from particulate and dissolved fractions of humic acid were apparently different due to biological responses of the clam to the particulates. At Cd concentration of 140 mg/kg, the accumulation of Cd from Cd associated with humic acid mixtures was mainly attributed to the dissolved fractions of humic acid. Compared to particulate fractions, Cd associated with the dissolved fractions of humic acid may be more bioavailable.
This work investigated the distribution and speciation of Cd, Cu, Pb, Fe and Mn in the shallow sediments of Jinzhou Bay, Northeast China, which has been heavily contaminated by nonferrous smelting activities. The concentrations of Cd, Cu and Pb in sediments were found to be 100, 13 and 7 times, respectively, being higher than the national guideline （GB 18668-2002）. Sequential extraction test showed that 39%-61% of Cd were exchangeable fractions, indicating that Cd in the sediments posed a high risk to local environments. While Cu and Pb were at moderate risk levels. According to the relationships between percentage of metal speciation and total metal concentration, it was concluded that the distributions of Cd, Cu and Pb in some geochemical fractions were dynamic in the process of pollutants migration and the stability of metals in sediments of Jinzhou Bay decreased in the order of Pb 〉 Cu 〉 Cd.
Shaofeng Wang, Yongfeng Jia, Shuying Wang, Xin Wang, He Wang, Zhixi Zhao, Bingzhu LiuKey Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China.
