Assessment of the Impact of Manganese Deposit in Botswana Kgwakgwe Mine on the Environment

Abstract

The Kgwakgwe manganese deposit is 4 km southwest of Kanye village (70 km west of Gaborone, Capital City) in Botswana. The manganese deposit is surrounded by about 30 boreholes which supply the entire Kanye population with water, through pipes into each home. Weathering of manganese and other elements from rocks (due to the geology of the area) leach into underground water within the catchment. The study assessed the quality of drinking water from the boreholes and estimated their compliance with World Health Organization Recommended Guidelines. Determined physico-chemical parameters were: conductivity, alkalinity, total dissolved solids, turbidity, pH, temperature, total hardness, chloride, colour, nitrate, sulphate, sodium and potassium). Heavy (arsenic, lead, cadmium, chromium, nickel, zinc and copper) and trace (manganese, iron and magnesium) elements are determined by atomic absorption spectrophotometry; while soil and vegetation samples were analyzed using Energy Dispersive X-Ray Fluorescence (EDXRF). Multivariate Analysis was used to differentiate boreholes based on the physico-chemical parameters. Principal Component Analysis (PCA) was used to evaluate the influence of the parameters on the borehole. The study revealed that Manganese (0.038 mg/L-0.1295 mg/L) was the only element that was found to be above the recommended WHO limit for Mn in water (0.05 mg/L). Iron was below the instrumental detection limit of 0.001 mg/L. Levels of Chromium ranges from 0.02 mg/L to 0.0355 mg/L which is below the WHO limit of 0.1 mg/L, as well as for magnesium (0.097 mg/L to 1.2277 mg/L) which was below the WHO limit of 100 mg/L. The levels of Mn in two soil samples (Sample 01 and Sample 03) analyzed, which were around the manganese deposit were 9747 mg/kg and 408.7 mg/kg respectively. Although these values were above the WHO acceptable limit of 12 mg/kg, when they were comparable to values (35 mg/kg to 24907 mg/kg) obtained in a similar study conducted in the study area. Fe in the soil samples were 27524.51 mg/kg for sample 01 (about 2 km from the Kgwakgwe Mine) and 22133.65 mg/kg for sample 03 (about 500 m from the Kgwakgwe Mine); comparable to1116 mg/kg-870 766 mg/kg obtained in 2004 by Ekosse. For vegetation, Mn in spinach leaves was 69.7 mg/kg; and Hay was below detection limit. Mn in spinach was below the WHO limit of 200 mg/kg, but comparable with 26.2 mg/kg to 3611 mg/kg obtained in 2004 by Ekosse in a similar study. Fe in spinach leaves were below detection limit while Hay leaves had 122.69 mg/kg. The level obtained was within the 101.2-3758 mg/kg by Ekosse in 2004. The levels of As, Ni, Pb, Cu, Cd, Zn in water samples were all below the instrument detection limit of 0.001 mg/L. pH ranged from 7.12 to 9.47; conductivity (493 to 1129 μs/cm); Total Hardness (88-696 mg/L). TDS (28 to 552 mg/L); Chloride (9.99-99.97 mg/L); Alkalinity (10-296 mg/L). Sodium levels ranges from 17.5 to 49.3 mg/L; Potassium levels (3.9 to 45.3 mg/L). The nutrient load, sulphate (below detection limit to 9.09 mg/L); nitrates (0.171-2.527 mg/L). The chemicals parameters were like Multivariate analysis performed on the data obtained from this study for the entire borehole samples revealed Six (6) main markers responsible for differentiating the boreholes. These markers were chloride, Sodium, Hardness, dissolved solids, conductivity and magnesium which were more of the physiochemical parameters. It was also observed from the Principal Component Analysis (PCA) that the levels of these markers are dependent on proximity of the bore holes to the manganese deposit.