Bioavailability of metals in some selected plants grown on an abandoned coal mine overburden using energy dispersive X-ray fluorescence technique

Abstract

This study focuses on the bioavailability of some metals in Mangifera indica, Parkia biglobosa, Proposis africanus, Anacardium occidentale and Manihot esculenta plants grown on an abandoned coal mine overburden. The analytical technique used in this study is energy dispersive x-ray fluorescence spectrometry. The results indicate that the plants have the tendency to bioaccumulate the metals studied in this order: Proposis africanus > Anacardium occidentale > Manihot esculenta > Parkia biglobosa > Mangifera indica. The various concentrations of the observed metals in the plants grown in overburden soil were considerably lower than those observed from the control soil. This however was attributed to the increase in the sorption of metals with increasing pH. The concentration of metals in the overburden plants ranged from 0.60 – 18.00 mg/kg (Ti); 1.03 – 1.78 mg/kg (Cr); 5.81 – 67.27 mg/kg (Mn); 6.03 – 51.17 mg/kg (Fe); 0.30 – 2.91 mg/kg (Ni); 2.32 – 15.66 mg/kg (Cu); 0.54 – 6.15 mg/kg (Re); 3.50 – 8.90 mg/kg (Au); 0.16 – 3.69 mg/kg (Zn); 0.69 – 3.55 mg/kg (Sr); 14.04 – 111.57 mg/kg (Ru); 0.67 – 2.84 mg/kg (Y) and 1.79 – 15.22 mg/kg (Ba). For the control plants 50 Km from mine site overburden, the observed concentration ranged from 2.34 – 14.40 mg/Kg (Ti); 1.16 – 2.56 mg/kg (Cr); 4.19 – 54.95 mg/kg (Mn); 15.05 – 101.50 mg/kg (Fe); 0.79 – 4.56 mg/kg (Ni); 5.99 – 24.45 mg/kg (Cu); 2.77 – 10.77 mg/kg (Re); 4.70 – 12.00 mg/kg (Au); 0.08 – 49.08 mg/kg (Zn); 1.10 – 5.08 mg/kg (Sr); 41.37 – 210.24 mg/kg (Ru); 1.18 – 4.10 mg/kg (Y) and 0.29 – 7.52 mg/kg (Ba). The values obtained are far above World Health Organization tolerable daily intake and are attributed to the nature of the soil in the mineral rich coal basin.

Keywords: Biosorption, bioremediation, absorption, heavy metals, overburden