Heavy metal distribution of natural and reclaimed tidal riparian wetlands in south estuary, China.

We evaluated the distribution and accumulation of Cd, Cr, Cu, Ni, Pb and Zn in two plant species (Scirpus tripueter Linn. and Cyperus malaccensis Lam.), in water and soils sampled from the reclaimed tidal riparian wetlands (RTRWs) and the natural riparian wetlands (NRWs) in the Pearl River Estuary (PRE). The results showed that the concentrations of studied heavy metals in soils exceeded the eco-toxic threshold recommended by US EPA. The concentrations of Cd, Cr and Zn in plants may lead to toxic effects. The heavy metal concentrations were high in water and low in soils of RTRWs compared with that in the NRWs. The accumulation of heavy metals in the roots of plants was higher in NRWs than those in RTRWs while the opposite result was found for heavy metal accumulation in shoots. Based on the bioaccumulation and translocation factors, the plants in NRWs had a higher capacity to accumulate heavy metals while higher abilities to transport heavy metals from roots to shoots were observed in RTRWs. Heavy metal contaminations in RTRWs were dominated by anthropogenic sources from both side uplands and river water, whereas in NRWs, the metal accumulations were simultaneously affected by anthropogenic and natural factors