An assessment of the level of soil contamination with heavily metals around Letseng and Kao diamond mining in Lesotho

Abstract

The study was aimed at determining the extent of soil contamination with heavy metals due to wastes from Kao and Letseng Diamond Mining and to determine the potential risks to the soil and crops in nearby farmlands. A number of physical and chemical soil parameters were tested namely; texture, pH, Organic matter, and CEC to find out their impact on bioavailability of heavy metals in the soils and crops around Kao, Letseng and Mokhotlong Agricultural Research. Furthermore, study was made to assess the effects of heavy metals on soil microbial activity, and to determine whether heavy metals in plants and soils are mild, sufficient or toxic. Heavy metals were tested whether available or not available (not detected) in three sites. The samples were collected from three sites, two of which are from contaminated (Kao and Lets’eng mining) sites and one from uncontaminated (Mokhotlong Agricultural Research Station) site in Lesotho. Basic cations and metals were extracted by DTPA method (Lindsay and Norvell, 1978) and later determined using an AAS 500 model. The results indicated that there are higher concentrations of heavy metals around Letseng Diamond Mining in the order of Cr > Pb > Cd > Ni > Fe > Mn > Cu > Co > Zn. Around Kao Diamond site, three metals were in the toxic range in the order of Cd > Pb > Cr. Kao Diamond mining site is located within Kao Village, where the effluent from the mining drains into farmlands, which obviously poses health threat. Chlorosis and stunting of plants have been observed especially in the rangelands around Letseng Diamond Mining. This is to high concentrations of heavy metals, which could hinder plant growth and affect the food chain thus posing serious risk to health of animals, humans and microorganisms. Again the results showed the plants with high concentrations of heavy metals have stunt growth andsoils with high concentrations of heavy metals showed lower microbial population which has negative impact on soil fertility. Results of this study indicate that the heavy metal risk around the mining sites is alarming and hence appropriate measures need to be taken to rectify the situation by applying biochar. Whilst Mokhotlong Agricultural Research shows only essential heavy metals and their concentrations are not alarming with high population of microorganisms.