Metal contamination in a riparian wetland: Distribution, fractionation and plant uptake.

Heavy metal pollution in aquatic system is of concern due its ecologic risk. In this study, we investigated the distribution, fractionation and plant uptake of heavy metals (As, Cd, Cr, Co, Cu, Ni, Pb and Zn) in a riparian wetland impacted by mining activities in Yunnan, southwest China. The results showed that excluding Cr, metal contents in sediment were higher than the background values, especially for As, which was 100-fold higher. While Cd showed high levels in the acid-soluble fraction with high availability, As, Cr, Cu, Ni and Pb mainly existed in the residual fraction with low availability. Two native aquatic plants including Phragmites australis (common reed) and Typha orientalis (bullrush) showed different uptake ability. T. orientalis accumulated more As, while P. australis accumulated more other metals. Based on geoaccumulation index (Igeo), As, Cd and Zn were more contaminated (Igeo> 3), followed by Cu, Pb and Co (Igeo<3), with Cr and Ni being slightly polluted (Igeo<1). According to risk assessment code, Cd showed high availability, followed by Zn and Co, with As exhibiting the lowest. The data suggested that both total and bioavailable metals should be considered for risk assessment of metal pollution in a wetland.