Measurement of in situ phytoextraction of zinc by spontaneous metallophytes growing on a former smelter site

This work was undertaken to measure the in situ phytoextraction of zinc usi ng a former zinc-smelter site where metallophyte plants have been growing f or 30 years. The site exhibited a gradient in the total metal concentration in the upper horizon (from 3230 to 8530 mg Zn kg(-1)). Soils were sampled from four different sectors (I-IV), and plant shoots were harvested, identi fied, their biomass weighed and analysed for zinc. The results showed that three plant species were dominant on the site, including Arabidopsis haller i (cress), Armeria maritima (seathrift), and Arrhenatherum elatius (froment al). A. maritima was the predominant species according to the biomass produ ction on the most polluted sector I. As the concentration of metals in soil s decreased, A. maritima disappeared and A. halleri increased. The biomass of A. elatius was the highest on the less polluted soils. Concentrations in zinc in the aerial parts of plants varied from 73 (sector IV) to 6269 mg k g(-1) DM (sector I). The concentration of Zn in A. halleri decreased with t he decrease in concentration of zinc in soil. Phytoextraction was calculate d from the biomass and its concentration of metal. It was at a maximum in s ector III with a high contribution of A. halleri and A. elatius and reached 10 kg Zn ha(-1), a promising amount for phytoextraction considering the ab sence of any agricultural practices. In sector I, phytoextraction was four times lower despite a 2.6 times higher concentration of Zn in the upper hor izon. In conclusion, phytoextraction was strongly dependent on the concentr ation of the available metal in soils which may limit the growth of plants, and favour tolerant but low biomass plant species such as A. matitima. (C) 2001 Elsevier Science B.V. All rights reserved.