Assessment of atmospheric profile of some heavy metals in barks of Parkia biglobosa (African locust bean) trees

Abstract

Natural resource exploitation involving the mining of iron-ore from earth's deposits result in the release of aerodynamic size particulate metals, dusts and other atmospheric pollutants. The atmospherics baseline levels some iron-ore associated heavy metals were assessed around Itakpe iron-ore deposit, North Central Nigeria, using tree barks of African locust bean (Parkiabiglobosa) as indicator. Tree barks of P. biglobosa were randomly scaled off dried and digested using standard procedures. The digests were quantified for Cd, Mn, Cr, Ni, Cu, Zn and Pb in flame of Unicam 969 atomic absorption spectrophotomer. The concentration of Zn, 20.387-52.07 mg/kg was the highest in respect of other metals determined, followed by Mn, 8.74-24.18 mg/kg and then Pb, 2.95-8.66 mg/kg. Cu levels ranged 0.68-3.14 mg/kg, Ni, 0.34-3.12 mg/kg and Cr, 0.34-0.91 mg/kg. Cd concentration was the least; 0.16-0.48 mg/kg in barks of P. biglobosa trees. The overall mean concentrations (mg/kg) were: Zn, 34.21 ± 4.09; Mn, 13.59 ± 2.04; Pb, 25 ± 0.75; Cu, 1.34 ± 0.34; Ni, 1.18 ± 1.05; Cr, 0.55 ± 0.09; and Cd, 0.33 ± 0.06, with availability sequence is in the order Zn > Mn > Pb > Cu > Ni > Cr > Cd. The detected heavy metals levels in the barks of P. biglobosa trees were variable, and may be a function of vegetation proximity/orientation to source points, plant distribution/population density, level of exposure and atmospheric stability, which is dependent on prevailing climatic factors. The evaluated P. biglobosa barks did not contain the heavy metals at concentrations capable of impacting negatively on the plant. Thus, the tree barks concentration of the evaluated metals were within natural concentration levels, and are therefore regarded as not polluted. This implies that atmospheric levels of the aerodynamic particulates heavy metals were low and not hazardous. The detected levels could serve as baseline concentration for monitoring against potential atmospheric deposit build up of heavy metals when mining becomes fully operational