Roles of Koelreuteria bipinnata as a suitable accumulator tree species in remediating Mn, Zn, Pb, and Cd pollution on Mn mining wastelands in southern China

Abstract

The necessity and urgency of remediating soil polluted with heavy metals have been recognized both politically and socially at the global level. Phytoremediation is a sustainable technology to remove or stabilize heavy metals in soil at former mine sites. The aim of this study was to clarify the ability of the tree species Koelreuteria bipinnata to phytoremediate heavy metal (Mn, Zn, Pb, and Cd)-contaminated soils. Concentrations of the four heavy metals were measured in soils from an un-remediated plot and from three K. bipinnata stands of different ages at the former Xiangtan manganese (Mn) mine, also forest stand growth and heavy metal concentrations were measured within different tissue of trees at three stands planted in heavy metal-contaminated soil for different years. The results showed that stand biomass of trees increased from 2.32 t ha−1 for 3-year-old trees, through 34.11 t ha−1 at 5 years, to 102.06 t ha−1 at 9 years. Total and individual heavy metal concentrations accumulated in the trees also increased with stand age; 9-year-old trees had accumulated 2.18 times the total heavy metals as the 3-year-old trees. Furthermore, soil heavy metal concentrations significantly (p < 0.05) decreased as stand age increased; total heavy metal concentrations in the contaminated soils remediated by 9-year-old trees were 85.29 % lower than its un-remediated plot. The results indicate that K. bipinnata is a suitable accumulator species to remediate Mn, Zn, Pb, and Cd pollution on mining wasteland.