The phytomining and environmental significance of hyperaccumulation of thallium by Iberis intermedia from Southern France

Unusual hyperaccumulation (>500 mu g/g dry mass) of toxic Tl has been deter mined in Iberis intermedia (Brassicaceae) from southern France. This specie s contained up to 3,070 mu g/g (0.31%) Tl in the whole-plant dry matter. Po t trials with Iberis showed that it could tolerate nearly 2,000 mu g/g avai lable Tl in the substrate compared with about 20 mu g/g for the metal-toler ant grass Arrhenatherum elatius. This unusually high accumulation of Tl has significance for animal and human health, phytoremediation of contaminated soils, and phytomining for Tl. It was determined that three crops of Iberi s would be sufficient to phytoremediate to a non-toxic level, a soil contai ning 10 mu g/g Tl, and the production of a saleable plant ash (bio-ore) wou ld probably pay for the cost of the operation. Phytoming (growing a "crop" of a metal over ores subeconomic for conventional mining) could be a viable option since it has been calculated that a net return of $1,200/ha (twice the return from a crop of wheat) would be possible with a biomass yield of 10 t/ha containing 0.08 percent Tl in dry matter. The break-even point (net yield of $500/ha) would require 170 mu g/g (0.017%) Tl in dry matter. Such a project would, however, require a large area to be able to afford econom ies of scale.