Minor element geochemistry of groundwater from an area with prevailing saline groundwater in Chikhwawa,lower Shire valley (Malawi) |
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| Institution: | 1. U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Cincinnati, OH, USA;2. Tetra Tech, 10711 Red Run Blvd., Suite 105, Owings Mills, MD 21117, USA;3. U.S. Environmental Protection Agency, Office of Water, Office of Science and Technology, Health and Ecological Criteria Division, Washington, DC 20460, USA;1. School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China;2. Department of Geosciences, Bremen University, Klagenfurter Straße, 28359 Bremen, Germany |
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| Abstract: | Groundwater resources with high salinity content are found in some parts of the lower Shire River valley (Malawi). This paper discusses the geochemistry of minor elements with regards to the prevailing salinity. Hierarchical clustering and principal component analyses were used to identify factors which relate to both minor elements and samples and were interpreted as reflecting the influence of prevailing saline/brackish groundwater. Concentrations of lead (Pb), boron (B), strontium (Sr) and chromium (Cr) were associated with groundwater with high content of total dissolved solids (TDS). Speciation calculations indicated that dissolved Sr, barium (Ba) and lithium (Li) were mainly in the form of free aqueous ions whereas hydrolysed species were significant for aluminium (Al) and Cr, and carbonate complexes for Pb. Chloride complexes were prevalent for silver (Ag). Solubility of cerussite (PbCO3) and barite (BaSO4) was shown to act as a control on the levels of Pb and Ba, respectively. Thus, Ba concentrations were very low in saline groundwater owing to their high sulphate content. A relatively variable B concentration in the groundwater samples was explained using a binary mixing model of saline and fresh groundwater. The mixing of fresh groundwater with saline groundwater was concomitant with high Na+/Ca2+ ratios and enrichment of B, probably by desorption from clays. The WHO drinking water guidelines for Ba, B, Cr and Pb were exceeded in 6.5%, 9.7%, 16.1% and 64.5% of all the samples, respectively. However, all samples were below the Malawian specification of B in borehole and shallow well water quality (MS 733:2005) of 5.0 mg/L. |
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