Speciation and ecological risk of heavy metals and metalloid in the sediments of Zhalong Wetland in China

A total of 271 sediments samples from the Zhalong Wetland were analyzed for concentration and distribution of Hg, Cd, As, Cu, Pb, Zn, Cr, and Zn; their speciation according to the modified European Community Bureau of Reference sequential extraction procedures and their ecological risk based on Lars Hakanson’s potential ecological risk assessment and risk assessment code were made. The results can be summarized as the followings: (1) Concentrations of all metals measured were above soil background values of Songnen Plain, and their spatial distributions were distinctly different. The concentrations of metals (except Pb) were high in the east, followed by the north, and were relatively low in the core zone and south. The concentration of Pb was high in the north, south, and west, compared with low concentration in the core zone and east. (2) The dominant proportion of Pb, Zn, and Cr was in the residual fraction, suggesting that they were environmental stable. The concentrations of Cu and As in the reducible fraction, the concentration of Cd in the acidsoluble fraction, and the concentration of Hg in the oxidizable fraction were relatively high, indicating they had greater environmental effects. (3) The evaluation of the ecological risk showed that Cd, Hg, and As had relatively high ecological risk index, especially the ecological risk of Cd should be paid attention to. In general, the ecological risk of the heavy metals and metalloid by zone was experimental zone > buffering zone > ecological tourism zone > core zone.

Keywords
Heavy metals; Speciation; Ecological risk; Spatial distribution; Zhalong Wetland