Abstract:
Indiscriminate and uncontrolled mining activities give rise to significant negative environmental impacts such as pollution of water bodies and farm lands, thus leading to decrease in soil fertility and soil quality as well as land degradation and changes in landscape. Therefore, this research was conducted to evaluate the impact of solid minerals mining at the Enyigba Lead-Zinc mining district in Abakaliki L.G.A of Ebonyi State and to document the present state of soil physico-chemical properties and heavy metal status of both soil and surrounding water bodies. The study examined the extent to which heavy metals from mining activities have contaminated the soil as well as the surface waters within the vicinity of mine sites. In the study, two factors were considered: factor A - Soil depths (surface soil: 0-15 cm and subsurface soil: 15-30 cm) and factor B - Distances from mine pits (100 m, 200 m, 300 m, 400 m and 500 m away from mine pit). Four mining sites (Mbaraeke Enyigba, Mkpoda Ugwvu, Nwamgbam Uchakuru and Azu Enyigba) within Enyigba mining vicinity were selected for the study to represent four replications. These were compared alongside a control (located 1.5 km away from Enyigba mining vicinity). Core and auger soil samples were collected and analysed in the laboratory following standard methods. The pH of the mine sites ranged from 5.9 to 6.3. The bulk density value at the subsurface soil of mine area (1.67 g/cm3) was significantly (p < 0.05) higher than the surface soil (1.53 g/cm3) and control (1.59 g/cm3). The values of total porosity in all distances and depths were significant, recording a reverse trend compared to bulk density values. The textural classes at different distances and depths were predominantly sandy clay loam including those of the control. However, higher values of clay were obtained at lower depths (15 – 30 cm) at both mine area and control. Available phosphorus (5.22 mg/kg – 2.98mg/kg), soil organic carbon (1.65 % - 1.15 %) and magnesium (2.67 cmol/kg – 2.21 cmol/kg ) decreased with depths in the mine area. The CEC (15.5 cmol/kg) and percent total nitrogen (0.16 %) of the mine area were lower than the control (20.00 cmol/kg and 0.16 % for CEC and percent total nitrogen respectively). Heavy metal concentrations (Arsenic (As) 0.166 mg/kg, Cadmium (Cd) 20.373 mg/kg, Copper (Cu) 2.042 mg/kg, Lead (Pb) 0.498 mg/kg and Zinc (Zn) 4.769 mg/kg) at the mine area were higher compared to the control (As 0.025 mg/kg, Cd 11.097 mg/kg, Cu 0.702 mg/kg, Pb 0.05 mg/kg and Zn 2.3 mg/kg). The heavy metal levels in Enyigba mine site decreased in the order Cd>Zn>Cu>Pb>As in the surface soil and Cd>Zn>Cu>Pb>As in the subsurface soil. The highest concentrations of heavy metals at mine sites were recorded at 100 m top (0-15 cm) soil with significant reduction in concentration levels as a result of increase in distance. The heavy metal concentrations (As 0.166 mg/kg, Cu 2.042 mg/kg, Pb 0.498 mg/kg and Zn 4.769 mg/kg) at mine area were within the acceptable limits in soil with the exception of cadmium (Cd 11.097 mg/kg). The heavy metal concentrations of the water bodies were all above the WHO standards (As 0.01 mg/l, Cd 0.3 mg/l, Cu 2 mg/l, Pb 0.01 mg/l and Zn 3 mg/l) though insignificant concentrations (below WHO regulatory standard for drinking water) of lead (Pb) was recorded in abandoned mine pit, Akpara Izzi stream and Ebonyi river. The ranking of the distribution of heavy metals in the surface waters is Zn>As>Cd>Cu>Pb. Though the concentrations of these metals in soils with the exception of cadmium were found to be low compared to WHO regulatory limits, contamination of soil with heavy metals even in traces is considered a serious environmental concern as these elements can persist in soil for a long time with chances of increasing their concentrations with time.
