Accumulation of heavy metals in plants grown on mineralised soils of the Austrian Alps

Abstract

A field survey of higher terrestrial plants growing on 18 metalliferous sites of the Austrian Alps was conducted to identify species accumulating exceptional large concentrations of Cd, Cu, Ni, Pb and Zn in shoots. Minuartia verna ( Caryophyllaceae) was confirmed and Biscutella laevigata ( Brassicaceae) newly identified as hyperaccumulators of Pb (>1000 mg kg −1 Pb in shoots). Metal concentrations in shoots exceeded those in roots. Cadmium concentrations detected in shoots of Thlaspi rotundifolium ssp. cepaeifolium (up to 108 mg kg −1), Cardaminopsis halleri (up to 80 mg kg −1), Biscutella laevigata (up to 78 mg kg −1) and Minuartia verna (up to 59 mg kg −1) may represent hyperaccumulation. In addition, populations of Thlaspi goesingense (up to 12400 mg kg −1 Ni) and Thlaspi rotundifolium ssp. cepaeifoliium (up to 1934 mg kg −1 Pb) were confirmed to be hyperaccumulators. The strategy of neighboring Thlaspi rotundifolium ssp. cepaeifolium populations to tolerate high Pb and Zn was found to switch from hyperaccumulation at moderate and large, to exclusion at very large metal concentrations in soil. Metal partitioning in soils determined by sequential extraction gives evidence for large proportions of potentially mobile fractions. Metals stored in shoots typically do not exceed the soil metal pool in fractions 1 (exchangeable) and 2 (readily mobile). There is evidence that hyperaccumulation may be associated with depressed translocation of K from roots to shoots. Under natural conditions metals accumulated in shoots are annually recycled to the soil, hyperaccumulators do not necessarily rely on metal phases less soluble than fractions 1 and 2. These should be considered in future development of phytoremediators, because after extraction of these phases by harvesting shoots, further metal removal may be limited by dissolution kinetics of oxides and silicates.