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.

Use of filtrate from crop residue ash for cooking in rural households in Northern Uganda.

“…Ground salt also contains high content of fluoride, an issue not seen with ash filtrate, which can lead to exceed the daily consumption limit (Mabelya et al 1997;Nielsen 1999;Nielsen & Dahi 2002;Kaseva 2006). Given its potentially numerous negative effects, these results support previous findings which suggest ground salt should not be used as a cooking additive.…”

“…In addition to high sodium, elevated levels of iron, fluoride, and manganese have been found (Ankrah & Dovlo 1978;Nielsen & Dahi 2002;Mamiro et al 2011). High fluoride exposure from use of ground salt has been linked to severe dental fluorosis (pitting of teeth) in Tanzania (Mabelya, van Palenstein Helderman, van't Hof, & Konig, 1997), while excess iron exposure can contribute to iron overload (Gordeuk et al 1992).…”

“…Ground salt is obtained most often as a precipitate from saline water sources, in a granular or rock form. There are several sources proximate to Northern Uganda capable of producing ground salt; Lake Magadi, Kenya; Lake Katwe, Uganda; Lake Natron, Tanzania; and El-Atrun, Sudan (Nielsen 1999;Nielsen & Dahi 2002). Collectively, this ground salt is referred to as 'magadi' in eastern Africa, a salt which is usually scooped from the topmost layer of earth and which can also contain a mixture of other elements and soil (Nielsen 1999).…”

“…The name varies with location however, and so in this thesis it will be called 'ground' salt. Mineralogical, chemical, and physical properties of ground salt differ slightly among studies; however, it is generally acknowledged that all contain the mineral 'trona', a hydrated sesquicarbonate of sodium, making it highly alkaline (Makanjuola & Beetlestone 1975;Nielsen & Dahi 2002;Mamiro et al 2011). …”

Leaching of lava and tephra from the Oldoinyo Lengai volcano (Tanzania): Remobilization of fluorine and other potentially toxic elements into surface waters of the Gregory Rift

“…Fluoride is generally occurring in high concentrations in waters along most of the East African Rift System (e.g. Kilham and Hecky, 1973;Nanyaro et al, 1984;Gaciri and Davies, 1993;Apambire et al, 1997;Nielsen and Dahi, 2002;Reimann et al, 2003;Davies, 2008) and many studies have shown a high prevalence of both dental and skeletal fluorosis in the region (e.g. Shorter et al, 2010;Rango et al, 2012) .…”