Assessment of heavy metal concentration in soil and leaves of tree species around a scrap metal recycling factory in Ile-Ife, Osun State, Nigeria

Abstract

The gaseous emissions from scrap metal recycling factory could cause pollution to the environment if the concentrations are substantial and not properly controlled. This study determined the concentration of some heavy metals (Iron, Copper, Lead and Cadmium) in the leaves of selected tree species and soils around the scrap metal recycling factory in Ile-Ife, Osun state, Nigeria. The heavy metals were analysed, using the Buck Atomic Absorption Spectrophotometer. Samples for analysis were taken from the leaves and soil underneath Newbouldia laevis, Trema orientalis, Tectona grandis, Alstonia boonei, Bridelia micrantha and Senna siamea, trees. The results showed that the mean concentration of Pb and Fe (mg/kg) in the soil underneath these tree species were greater in the dry season than the wet season except in the soil underneath Alstonia boonei that showed no relative change in Pb concentration. The Pb content in the leaves of all the tree species was higher in the wet season relative to dry season, with Tectona grandis having the highest Pb concentration (90.2 mg/kg) in the wet season. However, the concentration of Fe in both wet and dry season was greater than the concentration of other heavy metals analysed in all the tree species. The soil under Tectona grandis was observed to accumulate more Cu (19.3 mg/kg) in the dry season than the other tree species. The study revealed increase in accumulation of heavy metals in the soil during the dry season and the leaves of the studied tree species during the wet season. Tree species whose heavy metal content exceeded permissible levels should be encouraged around metal polluted sites due to their high tolerance for heavy metal concentration.

Keywords: Concentration, heavy metals, wet and dry season, recycling factory, tree species