Cadmium and zinc accumulation by the hyperaccumulator thlaspi caerulescens from soils enriched with insoluble metal compounds

Thlaspi caerulescens J. & C. Presl is a hyperaccumulator of both Zn and Cd. A pot experiment was carried out to investigate whether T. caerulescens (the Ganges ecotype) could utilize Cd and Zn from insoluble sources. An uncontaminated soil was enriched with either insoluble Cd compounds (CdS or CdC0₃), or soluble Cd (CdS0₄) at a rate of 56 mg Cd kg^-1 soil. In a separate experiment, soil was enriched with either ZnS0₄, Zn₃(P0₄)₂, or ZnS at a rate of 100 mg Zn kg^-1. Neither soluble nor insoluble forms of Cd or Zn affected the growth of T. caerulescens. The Cd concentration of the shoots of the plants grown on the unenriched soil was 40 mg kg^-1 dry wt., whereas the concentration in the case of the enriched soil reached 2,050 to 2,900 mg kg^-1 dry wt. However, there were no significant differences in the shoot Cd concentration between the treatments with soluble or insoluble Cd compounds, even though the Cd concentration in the soil solution was in the order of CdS04 ≫CdC03 < CdS. T. caerulescens grown on the ZnS-enriched soil accumulated up to 6,900 mg kg^-1 Zn in the shoots, although Zn accumulation was 1.5-fold higher with the addition of the more soluble compounds Zn₃(P0₄)₂ or ZnS0₄. These results indicate that the Ganges ecotype of T. caerulescens is able to utilize both insoluble Cd and Zn compounds.