THE POTENTIAL OF THLASPI-CAERULESCENS FOR PHYTOREMEDIATION OF CONTAMINATED SOILS

Uptake of Cd, Zn, Pb and Mn by the hyperaccumulator Thlaspi caerulesce ns was studied by pot trials in plant growth units and in populations of wild plants growing over Pb/Zn base-metal mine wastes at Les Maline s in the south of France. The pot trials utilised metal-contaminated s oils from Auby in the Lille area. Zinc and Cd concentrations in wild p lants averaged 1.16% and 0.16% (dry weight) respectively. The unfertil ised biomass of the plants was 2.6 t/ha. A single fertilised crop with the above metal content could remove 60 kg of Zn and 8.4 kg Cd per he ctare. Experiments with pot-grown and wild plants showed that metal co ncentrations (dry weight basis) were up to 1% Zn (4% Zn in the soil) a nd just over 0.1% Cd (0.02% Cd in the soil). The metal content of the plants was correlated strongly with the plant-available fraction in th e soils as measured by extraction with ammonium acetate and was invers ely correlated with pH. Bioaccumulation coefficients (plant/soil metal concentration quotients) were in general higher for Cd than for Zn ex cept at low metal concentrations in the soil. There was a tendency for these coefficients to increase with decreasing metal concentrations i n the soil. It is proposed that phytoremediation using Thlaspi caerule scens would be entirely feasible for low levels of Cd where only a sin gle crop would be needed to halve a Cd content of 10 mu g/g in the soi l. It will never be possible to remediate elevated Zn concentrations w ithin an economic time frame (<10 yr) because of the lower bioaccumula tion coefficient for this element coupled with the much higher Zn cont ent of the soils.