Fluoride levels in water and fish from Lake Magadi (Kenya)

Abstract

Water entering Lake Magadi from a spring contained 73 mg fluoride (F) l- ‘, while samples taken 100 and 400 m from the spring were estimated to contain 110 and 140 mg F l- I. Evaporation apparently increased the F and salt concentrations to levels at which the common method of F analyses became unreliable, even after dilution. It is recommended to re-examine the very high F levels reported in the saline lakes of Rift Valley. The F levels of Tilapia grahami living in water with about 110 mg F l- ’ averaged (mg F kg- ’ dry weight): fillet 68, skin 819, gills 1,366 and bones 1,661. The variation was highest in fillet and skin. There was no positive correlation between tissue F levels and fish size (range 3-20 g). It remains uncertain whether the fish bone was saturated at this concentration of F or if some mechanism of elimination hindered higher F accumulation in the skeletal structures.