| Summary: | Fluoride in the environment distributes to water and vegetation from both natural and industrial sources. Vertebrates exposed to high levels of fluoride, accumulate fluoride in calcified tissues of the body, and are in danger of developing either acute or chronic symptoms of fluoride toxicity. The objective of this study was to provide background levels of fluoride concentration in the Icelandic horse and estimate whether a difference in fluoride accumulation is found in horses between regions and age. Mandibular fluoride concentrations were measured in 223 horses from four regions in Iceland (South, West, North and East) and divided by five age groups (foals, 1-4 y.o., 5-12 y.o., 13-20 y.o. and 21+ y.o.). The average mandibular fluoride concentration of the 223 horses was 244 ± 11.8 ppm, and 286 ± 12.6 ppm in horses over one year old, values beneath known tolerance levels. The highest mandibular fluoride concentrations for each age group were observed in horses from the West. A significant positive correlation was found between fluoride concentration and age of the horse, where the highest correlation coefficient was found in horses from the South. Furthermore, a significant difference was found between the regions, where horses from the West had significantly higher mandibular fluoride concentrations than horses from the South, but a significant difference was not found between horses from the West, North and East. Additionally, a correlation of fluoride concentration in horses from the West exclusively and increasing distance from the aluminium smelter in the region (Hvalfjörður) showed a significant negative regression, indicating that the greatest source of fluoride in the environment originates from the aluminium industry. The results are the first of their kind and can be used as a guideline of fluoride concentration in the Icelandic horse. Moreover, the results indicate that the Icelandic horses accumulate less fluoride on average than Icelandic sheep, which makes them less appropriate as an indicator ...
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