Phytoextraction of Cd and Zn with Thlaspi caerulescens in field trials

Phytoextraction is the remediation of heavy metal contaminated soils using plants that take up metals. Hyperaccumulating plants such as Thlaspi caerulescens are often studied for their possible use for decontamination of Cd and Zn rich soils, but few field trials have been reported, although they are necessary to validate the results of hydroponic and pot studies. This article reports field data for T. caerulescens grown on a calcareous and an acidic soil, both contaminated 20 years ago by either atmospheric depositions or septic-tank wastes. Accelerated cropping using transplants grown three times in eight months was compared to Thlaspi sown twice during the same period. Both were followed by one crop of sown Thlaspi. High Cd and Zn concentrations in the plant shoots compensated for the low biomass production. Annual metal exports with transplanted Thlaspi were 130 g Cd ha(-1) and 3.7 kg Zn ha(-1) on the calcareous soil and 540 g Cd ha(-1) and 20 kg Zn ha(-1) on the acidic soil. We concluded that within the framework of the Swiss legislation, remediation of Cd-contaminated soils could be achieved within less than 10 years with one crop of Thlaspi per year, but differences in soil properties could affect the rate of phytoextraction significantly. Total Zn content in both soils was too high to be remediated by T. caerulescens in a realistic time span. Thlaspi did not decrease the NaNO(3)-extractable fraction of Cd or Zn in either of the soils.