ABSTRACT

The effects of Zn and Pb contamination due to mining activities on the microbial diversity and physicochemical properties of soil in the Pb and Zn mining area of Ishiagu Ebonyi State, Nigeria were investigated. Soil samples were collected from six sampling points; the mining pits, the waste dumps, the centre of the distance between the mining pits and the waste dumps, lOOm and 200m away from the mining pits and a distance far away from the sites (1.0km) as the control. The experiment was replicated in three mining sites. The extent of Pb and Zn contamination was determined using Atomic Absorption Spectrophotometry and the results revealed that the area was highly contaminated by Pb and Zn with the extent of contamination decreasing as the distance from the mining site increases. The highest concentrations of Pb and Zn were found at the mining pit (source of contamination) Pb-263,008mgfkg and Zn-2 10,676mg/kg, while the least concentrations were at the control site (Pb-233mg1kg and Zn- 283mg/kg). The results of the physicochemical analyses showed that the pH and the concentration of all the other chemical properties investigated were lowest at the mining pits followed by the waste dumps but increased as the distance from mining sites increases, corresponding with a decrease in the concentration of the heavy metals. All the microbial parameters analysed were adversely affected by increasing concentrations of Pb and Zn with the least microbial loads found at the mining pits where the concentrations of the metals were highest. The counts of Total Heterotrophic bacteria, coliform bacteria, spore-forming bacteria, oligotrophic bacteria and fungi were 2.987x103cfiu/g, 9. 88x10'cfu/g, 3.713x lO2cfu/g, 3.22x102cfiu/g and 5.03x102cfu/g at the pits and 1.9lxlo7cfiu/g, 4.089x104cfu/g, 8.20x105cfu/g, 9.l96xlo3cfu/g and 3.5OxlO5cfu/g at the control respectively. A total of seven species of bacteria; Bacillus, Psevdomonas, Staphylococcus aureus, Micrococcus, E. coli Azotobacter and Proteus, as well as six species of Fungal; Fusarium, Peniciiium, Aspergillus, Candida, Rhizopus and Mucor were isolated in the study. Species of Bacillus, Pseudomonas, Fusarium and Aspergillus were the predominant organisms at the most contaminated areas. The species of Bacillus, Pseudomonas, Fusarium and Aspergillus were found to tolerate high levels of Pb and Zn concentrations. This study therefore shows that contamination by Pb and Zn due to mining activities adversely affected both the microbial diversity and the physicochemical properties of the Ishiagu mining area.