Sources of heavy metals in soils of Changsha, Zhuzhou and Xiangtan, Hunan, China

In order to trace the sources of heavy metals such as Cd, As and Pb in topsoils in the dries of Changsha, Zhuzhou and Xiangtan, Hunan, the authors analyzed the heavy metal mass balances among carriers such as topsoils, bedrocks, wet and dry atmospheric depositions, water and suspended materials of the Xiangjiang River as well as the characteristics of the change of heavy metal concentrarions in topsoils themselves with time. Except arsenic, the concentrations of heavy metals in bedrocks of the study area are lower than their crustal abundances. The Cd concentration in residual deposits is less than that in bedrocks, while the concentrations of the heavy metals such as As, Pb, Cu and Hg in residual deposits decrease three times relative to those in bedrocks. The concentrations of heavy metals in wet and dry atmospheric depositions are a few times to dozens of times those in topsoils. The Xiangjiang River supplies As and Cd to overbank soils. The concentrations of heavy metals in topsoils have increased at a higher rate in the past five decades. The heavy metal mass balances among different carriers supports the idea that atmospheric depositions are the main sources of heavy metals in topsoils in the aforesaid three cities, while the flow water and suspended particles are main providers for heavy metals in overbank soils along the Xianjiang River and bedrocks only provide limited heavy metals in topsoils.