Hyperaccumulative characteristics of weed species to heavy metals

Phytoremediation, which mainly employs hyperaccumulators to remove heavy metals from contaminated soils, is receiving more attention world-wide. The identification of hyperaccumulators is still a key step for phytoremediation. This research is devoted to identify some plants with hyperaccumulative characteristics from weed species. In a pot culture experiment, the hyperaccumulative characteristics of 13 weed species in 11 families to Cd, Pb, Cu and Zn were examined. The result showed that Taraxacum mongolicum and Rorippa globosa indicated some Cd hyperaccumulative properties. In a sample-analysis experiment conducted in a Pb-Zn mining area, T. mongolicum and R. globosa also displayed the same hyperaccumulative characteristics. However, in a concentration gradient experiment, Cd content in shoot of T. mongolicum was not higher than 100 mg/kg (DW, dry weight), the minimum Cd concentration for a Cd-hyperaccumulator in any treatment. The concentration of Cd in the stems and leaves of R. globosa were greater than 100 mg/kg, under the conditions of the soils spiked with 25 and 50 mg/kg Cd. The Cd accumulation factors and translocation factors in the shoots of R. globosa were higher than 1 too, and the plant biomasses did not decrease significantly (p<0.05) compared with the control. Thus, we conclude that only R. globosa showed the whole Cd-hyperaccumulator properties, which is a Cd-hyperaccumulator.