Heavy Metal Contamination in Riverine Soils Upstream and Downstream of a Hydroelectric Dam on the Lancang River, China

Topsoil samples (0-20 cm) were collected from the upstream and downstream riverine zones of a Manwan hydroelectric dam on the Lancang River in October, 2005. Total concentrations of seven heavy metals, that is, arsenic (As), chromium (Cr), cadium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in soils were determined using the inductively coupled plasma atomic absorption spectrometry in order to assess their contamination levels of the upstream and downstream riverine zones of a hydroelectric dam. Results showed that the average concentrations of these heavy metals in the upstream riverine soils were significantly lower than those in the downstream ones. Average heavy metal concentrations were generally lower in the upstream riverine soils and higher in the downstream compared with the respective background value. Contamination indices showed no contamination for As, Cr, Cu, Ni, Pb, and Zn, and low contamination levels for Cd in all of the upstream soil samples. However, they showed low contamination levels for As, Cr, Cu, and Ni, and no contamination for Pb and Zn, while moderate contamination for Cd in the downstream riverine soils. Integrated contamination index was moderate for the downstream area, but showed no contamination for the upstream area. Using factor analysis a strong association among these heavy metals indicating the same contamination source was found. This work could provide a new quantitative index for environmental impact assessments of hydroelectric development and contributed to building an integrated assessment index system.