Fluoride concentration in Tilapia fish (Oreochromis leucostictus ) from Lake Naivasha, Kenya
Excessive ingestion of fluoride can cause dental and skeletal lesions and in severe circumstances adversely affect health and productivity performance of domestic animals. The objectives of this study were to investigate fluoride dietary sources, effects of fluoride on milk production, excretion of fluoride in cow milk and urine and fluoride toxicity in rats. Fluoride concentration was determined using fluoride ion specific electrode and the mean recovery percentages were: 92.4 ± 7.7 % (n=l 14). One hundred and four samples of feedstuff's and 149 water samples for dairy cattle were collected from six dairy co-operative societies within Kiambu and Thika districts of Kenya during the wet and dry seasons of the year 1994 in a cross-sectional study. The mean fluoride concentration in feeds from Nderi, Kikuyu, Chania, Limuru, Kiambaa and Lari co-operative societies were .19.5 ± 11.3 (n=19) 24.1 ± 28.6 (n=22), 55.2 ± 73.7 (n = 18), 67.6 ± 93.4 (n=15), 91.9 ± 226.3 (n=24) and 203.4 ± 243.2 (n=6) mgF/kg, respectively. Individual dairy co-operative society and the type of sample significantly (p <0.05) influenced fluoride concentration in feedstuff's. The overall mean fluoride concentration in water was 0.25 ± 0.45 mg/L (n=149). The fluoride concentration in water during the dry season were significantly (p< 0.05) different from fluoride concentration during the wet season. One hundred and thirty dairy milk and 106 urine samples of dairy cattle were obtained for fluoride analysis. The mean fluoride level in milk was 0.066 ± 0.14 mg F/kg while mean fluoride concentration in cows’ urine was 1.28 ± 1.0 mg F/kg. Seasons, breed of cattle, source of water and dairy cooperative society did not affect milk and urine fluoride concentration significantly (p> 0.05). Two hundred and forty six dairy cows were assessed for milk production. The mean milk production was 3.13 ± 2.78 1/cow/day. There was a significant difference (p< 0.05) in milk production due to season and dairy co-operative society. Water and feedstuff fluoride concentration did not significantly influence (p>0.05) milk production. The toxic effects of fluoride in female wistar rats (n=100) were investigated within a time-span of 96 to 843 days. Rats were randomly divided into 10 groups of 10 rats per group namely A, B, C, D, E, F, G, H, I and J. Each group was provided with commercial rat feed of known fluoride content and graded doses of fluoride in de-ionised water. Groups A, B, C, D, E and F were fed on 1,5, 10, 30, 60, 80 mg F L'1 equivalent to 0.087, 0.42, 0.823, 2.667, 5.45 and 7.804 mg/kg sodium fluoride in de-ionised water respectively. Group G, H, I and J were fed on 2 % Magadi salt solution, de-ionised water (control), 2 % commercial mineral salt solution and 2 % tea extract respectively. The following variables were monitored for each group; bodyweight, organ weights, water (fluoride) intake, feed intake, fluoride concentration in tissues and fluoride concentration in faeces. Sixty-two rats were sacrificed during the time of the experiment for tissue fluoride assays while twenty-eight rats were killed for pathology tissue processing. Ten rats died in the course of the experiment and were dissected for fluoride tissue assay and pathology. The dose of fluoride in drinking water significantly influenced (p<0.05) body weight, tissue fluoride concentration and organ weight. Rats fed on magadi salts had the lowest mean weight (186.7 ± 18.8 g) as compared to the control group of rats which had a mean weight of 280.0 ± 17.1 g whereas group C had the highest mean weight of 343.7 ± 40.7 g. Histopathological examination on liver, kidney, lungs and the heart organs of rats from groups A, B, C, H, and J revealed no pathological changes, however in groups D, E, F, G and I, degenerative changes, hepatic and myocardial haemorrhages were observed. The pathological changes became more severe as the concentration of fluoride was increased. Tumour growths were observed in three rats: uterine adenocarcinomas (group A and group C) and a fibroma (group J). One control rat from group H had a pyogranulomatous nodule as well. Fluoride concentration in the muscle, femur, incisor teeth and lower jaw were: 19.0 ± 28, 693.9 ± 536.4, 730.5 ± 576.8 and 1063.5 ± 829.6 mg /kg respectively. Fluoride concentration in lower jaw were significantly higher (p<0.05) than in muscle tissues. Faecal fluoride excretion was significantly influenced (p<0.05) by time of fluoride exposure. Nine food substances (Tilapia, Nile perch, lettuce, spinach, bovine, cabbage, kales, goat and chicken) were obtained from the local market and used to prepare fresh soups. Fluoride concentration in ninety fresh soup samples were investigated upon boiling for two hours. Soup samples were drawn from each preparation at intervals of 15 minutes. Tap water was used as a control. The type of food substance used for soup preparation and boiling significantly influenced fluoride concentration in the soup. Fluoride concentration in Tilapia, Nile perch, lettuce, spinach, bovine, cabbage, kales, goat, and chicken soup were: 5.01 ± 1.27, 2.92 ± 0.54, 0.67 ± 0.34, 0.66 ± 0.28, 0.32 ± 0.05, 0.25 ± 0.05, 0.24 ± 0.03, 0.22 ± 0.04 and 0.16 ± 0.04 ppm respectively. Soup prepared from Tilapia fish had significantly higher, (p < 0.05) fluoride concentration than other meat and vegetable soups. This cross -sectional study has shown that dairy cattle from Kiambu and Thika districts are exposed to high concentration of fluoride especially through mineral supplements. Consequently, there is need to establish standards for fluoride in mineral mixes and other animal feeds. In addition this study has shown that fluoride is essential for normal growth of rats and the optimal fluoride intake in drinking water is 10 ppm. Further, the analytical method used in this study was found suitable for determination of fluoride in water, soup, food substances and animal feeds. Overcooking may increase fluoride concentration in Tilapia soup and further investigation should be carried out on bioavailability of fluoride from fish soup. In addition further investigation should be done to establish whether fluoride is tumorigenic in rats.