Heavy metal accumulation characteristics of Nepalese alder (Alnus nepalensis) growing in a lead-zinc spoil heap, Yunnan, Southwestern China

Abstract

A fast-growing alder species native to the eastern Himalayas, Nepalese alder (Alnus nepalensis), has recently received considerable attention in the restoration of contaminated lands due to its significant economic benefits and ecological functions. The bioaccumulation characteristics and phytoremediation potential of naturally regenerated Nepalese alder were evaluated in a lead-zinc spoil heap located in Lancang county, Yunnan province, south-western China. Results showed that bioaccumulation factors (BFs) of A. nepalensis for Zn and Pb were always >1 in slightly contaminated soils (extractable Zn, Pb of 4.2- 17.9 and 3.4-13.1 mg kg-1, respectively) and >1 for Cd in contaminated soils (extractable Cd 0.3- 6.8 mg kg-1). By contrast, translocation factors (TFs) for Zn were <1 in all sampling plots, but >1 for Pb in soil slightly contaminated by 13.1 mg kg-1 extractable Pb and >1 for Cd in contaminated soils (extractable Cd 2.6-6.8 mg kg-1). Significant positive correlations were found between heavy metals (HMs) in roots and extractable HMs in soils (p<0.01) and between HMs in shoots and extractable HMs in soils (p<0.05) except for Cd. Based on the accumulation capacity revealed in this study, we suggest that A.nepalensis is a promising tree species for phytostabilization of zinc and lead in soils slightly contaminated with Zn and Pb and for phytoextraction of cadmium in Cd-polluted soil.