Metal extraction by Arabidopsis halleri grown on an unpolluted soil amended with various metal-bearing solids: a pot experiment

Most studies dealing with phytoremediation have considered metal extraction efficiency in relation to metal concentration of bulk soil samples or meta l concentration of the soil solution. However, little is known about the ef fect of various metal-bearing solids on plant growth and metal extraction o f hyperaccumulators. In this study, we investigated the ability of Arabidop sis halleri to grow and extract metals from different substrates consisting in an unpolluted soil amended with various metal-bearing solids collected in soils around a Zn smelter complex. The metal-bearing solids used as amen dments were: fresh and decomposing organic residues in the soil, a soil cla y fraction and two waste slags. Pure mono-metallic salt (ZnSO4) was also us ed. Two series of substrates were produced, one moderately polluted, and th e other highly polluted. An additional substrate was formed by the unamende d soil, and used as an unpolluted control. Zn, Cd, Cu, and Pb were measured in the substrates, and in the roots and shoots of A. halleri. The dry matt er yield of A. halleri was shown not to depend on the nature of the metal-b earing solid used, except when Cu-toxicity was suspected. On highly-pollute d substrates, Zn extraction by A. halleri depended on the nature of metal-b earing solids used, showing the following trend: pure mono-metallic salt>wa ste slags and soil clay fraction>fresh and decomposing organic matter. We e xplained these differences by the high solubility of Zn in the mono-metalli c salt, whereas in the mineral metal-bearing solids and in both fresh and d ecomposing organic matter, Zn release required mineral weathering or organi c matter mineralization, respectively. This work clearly showed that phytor emediation studies have to consider the nature of metal-bearing solids in c ontaminated soils to better predict the efficiency of plant extraction. (C) 2001 Elsevier Science Ltd. All rights reserved.