Assessment Of Potentially Harmful Arsenic, Cadmium, Cobalt And Lead In Soils And Plants In Nomtsoub Suburb, Tsumeb Town.

ABSTRACT

A number of environmental studies previously conducted in the Tsumeb Mining district analysed total metal concentrations in soils and vegetation; with results showing high concentrations of heavy metals such as arsenic, cadmium, copper, lead and zinc which exceed international guidelines for different land uses. However, the actual concentrations of only potentially harmful species for each element were not ascertained. This study aimed at determining the concentrations of potentially harmful As3+ , Cd2+, Co2+, and Pb2+ in soil in the Nomtsoub suburb of the Tsumeb Town as well as determining the uptake of the potentially harmful heavy metals from soil to vegetation. The research project involved sampling of soils and vegetation in residential complexes and school grounds in the Nomtsoub suburb and surroundings which has a population of approximately 2000 people. Thirty (30) surface soil samples (0-5 cm depth) were sampled. Twenty (20) vegetation samples consisting of: Mango leaves, lemon leaves, sunflower leaves, fresh and dried papaya leaves, marula fruit, marula tree bark, fig leaves and fig fruit were collected due to their availability at the time of sampling as well as their prevalent local use. Control samples were collected from Lake Otjikoto and Farm Manheim some 15 km and 25 km from Tsumeb respectively. Sequential extraction and Aqua regia were used in extraction of the following targeted species: As3+ , Cd2+, Co2+, and Pb2+ . The samples were analysed using ICP-MS and ICP-OES at the Bureau Veritas laboratory in Vancouver, Canada. Analytical results of harmful heavy metals of soils in this study revealed moderate to high concentrations in mg/kg as follows: As3+, (7 to 421), Cd 2+ (0.5 to 35.6), Co2+ (2 to 6.3) and Pb2+ (25. 9 to 3786. 9). These results exceeded levels found naturally in the geosphere. When compared to Canadian Soil Quality Guidelines for agricultural and residential land use, results of soil samples in this study exceeded As, Cd and Pb guideline values for both land uses.