DETERMINATION OF HEAVY METAL CONTENT IN THE SOIL SAMPLE FROM THE MUNICIPAL SOLID WASTE DUMP SITE IN MASERU

Heavy metals are mostly occurring naturally in the environment and their concentrations may be altered by anthropogenic activities such as wastes disposal. The study investigated and determined the presence of heavy metals in Ts’osane solid-waste dumping site in Maseru. Soil samples were randomly collected from the dumping site and screened qualitatively through chloride and hydroxide precipitation. Quantitative analyses of the acid leachate for few suspected heavy metals – cobalt, chromium, copper, iron, lead, manganese and zinc were done using Atomic Absorption Spectrometry resulting in concentration in the range of 0.2 to 95 µg g-1 of soil which are way above the soil’s holding capacity that ranged between 0.05 and 0.225 µg g-1 of soil. Other parameters studied included the effect of pH, temperature and time of exposure to water. This revealed that prolonged exposure to water mimicking continued rainy conditions could lead to different leaching rates with copper ions demonstrating the lowest leaching rate over a period of five weeks as opposed to manganese which demonstrates about 170% on the fifth week relative to the first week, while as expected lower pH and higher temperatures favoured leaching of the metal ions. Lastly the soil-metal holding capacity was determined whereby it was shown that the soil bound lead the strongest (90%) while iron was the weakest bound (20%). The obtained values are worrisome since this dumpsite is upstream of the municipal water source for the Maseru Municipality.