Fluoride in water and fish from Kenyan rift valley lakes
Although fish is an important source of food in Kenya, limited information is available on fluoride in Kenyan fish. Fluoride is accumulated by aquatic organisms living in high fluoride environment. It was therefore found relevant to undertake a more extensive investigation of the fluoride levels in Kenyan lake water and fish, and also to study various factors related to the accumulation of fluoride in fish. Water samples were collected from Lakes Nak uru , Bogoria, Baringo, Naivasha, Elementaita and Magadi and the pH as well as fluoride concentrations measured with a pH meter and a fluoride ion specific electrode respectively. Water from all the lakes were alkaline with pH ranging from 8.4 to 10.7. The fluoride levels of water from Lakes Naivasha. Magadi, Nakuru, Elementaita, Bogoria, and Baringo were 2.4. 84, 344, 463, 738, and 5.4 mg F/1 respectively. After addition of decomplexing agents, TISi\B .(Total ionic strength adjustment buffer - Orion) II or TISAn III, the pH of water samples from lakes Naivasha, and Baringo were within the recommended pH range for fluoride analysis (5.0-5.5), while water samples from lakes Magadi, Bogoria and Elementaita had pH values above 5.5. It was therefore found relevant to study how dilution and addition of decomplexing solutions, affect the fluoride measurements in water from Lake Magadi. -xvl- Dilution of the water did not alter the pH before addition of buffer hence interfering ions could be responsible for the problem encountered in fluoride analysis in the alkaline water. Hence the commonly used methods for fluoride analysis in water, might give erroneous or unreliable results when used in the analyses of water with high pH as found in some of the lakes of the Rift valley. A total of 320 fish samples from Lakes Naivasha, Bnrtrigo and Magadi were analysed for fluoride concentration in fillet skin. gills and bones using fluoride ion selective electrode methodology after extraction from tissues. The recovery of fluoride at various spiking levels were as follows (mean ± SEM %): blanks 99.6 ± 2 %. fillet 87.4 ± 4 %. skin 101 ± 16 %, gills 105 ± 6 % and Bones 109 ± 3%. Fluoride concentration in fish tissues were as follows (mean ± SEM mg Fjkg): Lake Magadi fish; fillet 68 ± 12. skin 809 ± 140, gills 1366 ± 40 and 1661 ± 49 for bones. Lake Naivasha fish:Oreochromis ieucostictus, fillet 11 ± 1. skin 18.2 ± 2, gills 571 ± 36, and 608 ± 22 in. bones; Tilapia zilii, fillet 10 ± 0.4, skin 18 ± I, gills 435 ± 24 and 455 ± 27 for the bones; Micropterus salmoides (Black bass). fillet 7 ± 0.6, skin 83 ± 24, gills 251 ± 23 and 338 ± 24 in bones. Lake Baringo: Tilapia nilotica, fillet 7 ± I, skin 10 ± 1.6, gills 241 ± 20.8 and 268 ± 36 in bone tissues. All the values are on dry weight basis. Concentration of fluoride in tissues varied according to fish species (p < 0.05) and perhaps the feeding habit and fish growth rate. Lake Magadi Tllapta fish were surviving under a fluoride concentration of 84 mg F/1 in the water. Therefore the Lake Magadi Tilapia seems to be adapted to living in high fluoride environment possibly through an excretion mechanism. Lake Magadi fish may be unsuitable for human consumption due to the high fluoride content in the tissue which could amount to a health risk. Fish from Lakes Nalvashn and Baringo provide an important source of protein. III preparation of the fish. no part is removed except the scales and perhaps the fins. The amount of fluoride released by bones. gills and skin during the process of cooking is an area which requires further research. There is no current concensus on the level of fluoride acceptable in various foods and beverages consumed on a daily basis and therefore intensive studies are necessary with regard to fluoride levels in food and beverages as well as bioavailability of fluoride. Accordingly. the present findings indicate that there is a need to carry out fluoride bioavailability studies in food substances like soups which are prepared using fillet, skin, gills and bones which may contain high concentrations of fluoride.