Drinking water quality and identification of fluoritic areas in Machinga, Malawi

Abstract

There is prevalence of dental fluorosis in certain parts of Machinga District that can be attributed to elevated drinking water fluoride content in the areas. Therefore, it is important to know the actual quality of water within the district and identify specific fluoride endemic areas that may require immediate adoption of remedial measures to manage the water resource and thus protect consumers. In this study, drinking water samples were collected from boreholes and pipes at 23 sampling sites, mostly villages within the district, for fluoride and other water physicochemical parameters during dry and rainy seasons of 2004 and 2005 respectively. Fluoride endemic sites were identified from the fluoride data. A survey of school children was also done in order to examine symptoms of dental fluorosis. Levels of fluoride ranged from 0.35 to 10.30 mg/L with 70 % of the sites sampled indicating levels above the World Health Organization (WHO) guideline of 1.50 mg/L. Fluoride endemic areas were identified as those villages around Mtubwi F.P School and Liwonde L.E.A School. This finding was supported by the prevalence of a high proportion of dental fluorosis in standard 3 and 4 pupils in these two schools. Values of pH ranged from 6.70 to 9.37; electroconductivity from 1950 to 31000 mS/cm; turbidity from 0.00 to 2.41, Formazin Turbidity Units (FTU); phosphates from 0.0 to 1.88mg/L; nitrates from trace to 58 mg/L; hardness from 1.08 to 276 mg CaCO₃/L; sulphates from 6.09 to 109.98 mg/L; chlorides from 0.003 to 0.576 mg/L; carbonates from 2.01 to 85.30 mg/L and bicarbonates from 51.02 to 677.52 mg/L. Correlation of fluoride with other drinking water parameters was assessed using simple graphical methods. Positive correlation was observed between concentrations of fluoride with pH, total dissolved solids and carbonates, while phosphates correlated negatively with the fluorides. No correlation was observed between concentrations of fluoride with nitrates, electroconductivity, total hardness, carbonates and chlorides.

Keywords: Machinga; fluoride; fluorosis; physicochemical parameters