Availability of cadmium and zinc accumulated in the leaves of Thlaspi caerulescens incorporated into soil

When grown on contaminated soil, hyperaccumulator plants contain high conce ntrations of metals which may return to the soil after senescence. This wor k was undertaken to assess the availability of Cd and Zn associated to the leaves of the hyperaccumulator Thlaspi caerulescens after incorporation int o an uncontaminated soil. A Zn- and Cd- accumulator population of T. caerul escens was grown on a Cd- and Zn- contaminated soil previously labelled wit h Cd-109. Leaves (TCL) were harvested, dried, ground and incorporated into the soil at a rate of 2.07 mg Cd kg(-1) and 51.9 mg Zn kg(-1). Then a pot e xperiment was conducted for 3 months with rye grass (Lolium perenne) and T. caerulescens. Rye grass was harvested monthly and T. caerulescens at the e nd of the experiment. Plant biomass was measured, along with the concentrat ion of Cd, Zn and Cd-109. Results showed that water-extractable metals in T CL were 69% for Zn and 33% for Cd. Addition of TCL to soil, depleted growth of rye grass, and improved that of T. caerulescens. At harvest, concentrat ions of both metals were increased in plants by TCL. Concentrations of Cd i n rye grass increased with the cut number, while that of Zn decreased sligh tly. Rye grass extracted 1.6% of the total Cd and 0.9% of the total Zn, and T. caerulescens extracted up to 22.4% of the Cd and 7% of the Zn. About 94 % of the Cd in rye grass and 86% in T. caerulescens was derived from TCL. I n conclusion, metals associated with leaves of the hyperaccumulator T. caer ulescens were very mobile after incorporation into the soil.