An evaluation of Berkheya coddii Roessler and Alyssum bertoloni Desv. for phytoremediation and phytomining of nickel

This review is based on field and pot trials carried out on the Ni-hyperaccumulator plants Alyssum bertolonii (from Italy) and Berkheya coddii (from South Africa), and assesses their potential use for phytoremediation (removal of pollutants from soils) and phytomining, growing a 'crop' of nickel. Fertilization of wild plants of A. bertolonii in Italy increased the biomass by a factor of three, to give a yield of 9 t ha(-1) without consequent reduction of the nickel concentration of 7000 mg kg(-1) dry mass. This species can thus be used for phytoremediation of soils lightly polluted with nickel. Analogous experiments with B. coddii gave a fertilized dry biomass of 22 t ha(-1) with 5000 mg kg-1 nickel in dry biomass. This species would need only half the number of crops required for A. bertolonii to remediate weakly polluted soils. A single crop of B. coddii could remove about 110 kg ha(-1) of nickel (worth US$579 in November 2001) compared with 63 kg ha(-1) by A. bertolonii, worth $331. Assuming that only half of the value of the nickel was returned to the grower, the phytomining operation could be potentially economic for B. coddii but not for A. bertolonii. Sale of the energy derived from combustion of the biomass could improve the economics, but only in the case of a large-scale operation. It is proposed that the economics of phytomining could be improved by selective breeding of plants with greater blomasss and higher metal concentrations as well as by transferring the hyperaccumulating gene to plants of large natural biomass.