Bioaccumulation of potentially toxic elements by indigenous and exotic trees growing around a copper leaching plant in Mufulira, Zambia

Abstract

Potentially toxic elements (PTEs) from mining industries pollute the surrounding environment and threaten the health of communities. Worldwide, exotic and indigenous trees are being recommended for green belts to trap dust and thereby limit the dispersion of PTEs. This study compares the potential of exotic (Eucalyptus grandis and E. camaldulensis) and native (Brachystegia longifolia) tree species in Zambia to accumulate PTEs and evaluate their ability to biomonitor heavy metal pollution. Tree bark and leaf samples were collected from 10 trees per study species growing at the same site downwind from a copper-leaching plant. Thirty topsoil samples were collected one metre from each sampled tree trunk. Portable X-ray fluorescence was used to analyse the elemental composition and concentration of trace elements in plant and soil samples. Pollution indices were used to establish the status and degree of soil contamination, while the bioaccumulation factor determined the ability of the studied species to accumulate PTEs. Heavy metals, including Mn, Ni, Pb, Cd, Cu, Fe and Zn were detected across soil and biomass samples, with a significant variation between species and plant parts. The pollution indices established that the soil at the study site is highly contaminated with Cu. The concentration of the studied trace elements varied across species following the order E. grandis > B. longifolia > E. camaldulensis in both tree bark and leaves. Determined bioaccumulation factors indicated Cd, Mn and Zn accumulation abilities of all the studied species suggesting their biomonitoring and phytoremediation potential. This implies that the study species have the potential to biomonitor Cd, Mn and Zn. Furthermore, a higher concentration of Cu was detected in B. longifolia bark, suggesting that this tree species can be used to biomonitor Cu pollution attributed to emissions from industrial activities. This study presents new insights into improving the management of polluted environments through biomonitoring and bioaccumulation of PTEs which can guide the selection of appropriate species for greenbelts in industrial areas.