Fluoride in groundwater : investigating the cause, scale, effect and treatment of fluoride in drinking water in Northern Tanzania

Abstract

High fluoride in drinking water sources is a problem throughout the East African Rift Valley and can lead to dental fluorosis and skeletal fluorosis in exposed local populations. One such area is the Hai District of Northern Tanzania. The study began by mapping the concentrations of fluoride in drinking water across the Hai district. Measured at 152 locations, fluoride concentrations varied from <0.1 mg/L to 33.2 mg/L, with a mean value of 1.6 mg/L. 12.5% of samples had fluoride above the World Health Organization recommended water quality standard (1.5 mg/L). Along with mapping the levels of fluoride, rock samples were also taken in an attempt to identify the source of the fluoride. Rock samples taken from areas with high levels of fluoride in the drinking water contained fluorite that shows textural evidence of dissolution. Other geological evidence from studies in a neighbouring district suggest that a geological system only present in part of the Hai district is responsible for the high levels of fluoride in the drinking water. Two villages where fluoride was identified as a problem from the mapping were investigated. The prevalence of dental fluorosis and deformities due to skeletal fluorosis were assessed in children attending school in the two villages. Over 25% of children in each village had skeletal deformities, though one village had much higher levels of fluoride in the drinking water, a mean of 23.5 mg/l compared to 5.4 mg/l) in the other village. Over 99% of children in both villages had dental fluorosis. Deformities relating to skeletal fluorosis are common, but the reasons for individual susceptibility remain unclear and may include low calcium diets, ingestion of magadi (local salt) with high fluoride, or genetic factors. iv The study concluded by considering possible treatment options and installed a bone char treatment plant in the village of Tindigani. Throughout the study, the communities were educated about the issue of fluoride in the drinking water. The village of Tindigani responded by mobilizing to provide piped water for themselves, removing the need for the bone char treatment plant.