Fluoride exposure of East African consumers using alkaline salt deposits known as magadi (trona) as a food preparation aid

Abstract

The fluoride content of Tanzanian and Kenyan magadi has been estimated to be in the range 0.1-17.9 mg F-g-1, which is comparable with that reported elsewhere, but indicating a considerable variation in levels. The median fluoride content of crystalline magadi harvested from the alkaline lakes was 2.1 mg g-1, which was higher than the median of 1.4 mg g-1 for scooped magadi harvested from the surface soil. The highest median fluoride contents of 3.2 and 2.9 mg g-1 were found in magadi originating from Lake Magadi, Kenya, and Lake Natron, Tanzania, respectively. It was found that the fluoride content varied significantly even for magadi originating from the individual lake, e.g. the fluoride content in magadi from Lake Magadi was between 0.1 and 8.7 mg g-1. In a lump of magadi originating from Lake Magadi, it was found that the fluoride content in 20 smaller part samples was subject to considerable variation indicating that the fluoride-bearing minerals were unevenly distributed in the lump. Results show that the fluoride is mainly present in grains <1.0 mm that made up 25% of the magadi sample. When daily eating the popular meal makande as in Tanzania, the exposure to fluoride through magadi in 70% of cases was estimated to be <4 mg per adult day-1, as recommended by the WHO. Thus, the health hazard from magadi-fluoride is estimated to be significant in cases where the magadi is heavily contaminated.