# Update on Endemic Fluorosis in a Region of Europe (Tenerife, Canary Islands)
## 1 Introduction  
Fluoride, due to its chemical properties, tends to always exist in its anionic form in the environment [1] The main sources of fluoride are natural, with volcanic emissions standing out above all, which can contribute between 60 and 6000 kilotonnes per year in the form of HF [2, 3], followed by marine aerosols, which contribute about 20 kilotonnes. However, in industrialized territories, the main sources of fluoride will be waste products resultingfrom industrial activity, and the relationship between cases of fluorosis and exposure to this type of industries have been demonstrated in different studies [4,5]. In all cases, through the bio-geological cycle, inorganic fluorides will eventually reach the biota (aquatic or terrestrial) through soil, water or air, and these fluorides will be able to bioaccumulate without biomagnification in the food chain [6,7]. Thus, it is not difficult to imagine that, in geothermal regions or regions with volcanic activity, fluoride concentrations in surface soils will be elevated [8,9]. This may have repercussions on the fluoride concentration in groundwater, especially if the soil is porous and permeable, since rainwater reaching the soil seeps into the ground, leaching the hydrofluoric acid formed into the different galleries [10,11]. This can be exacerbated by emanations of volcanic gasses from deep magmatic pockets, which are rich in hydrofluoric acid and reach these waters [12]. This is the case in the Canary Islands [13], where lichens with high fluoride content have also been found, which have been used as biomarkers of contamination by this ion [6]. Among the beneficial effects that fluoride can provide, the prevention of the carigenic process through various mechanisms stands out [7,14-16]. However, at certain doses, it can produce toxicity, highlighting changes in tooth enamel, nail changes, bone changes and effects on the nervous system, among other changes in the organism [7,17-27]. In general, fluoride exposure for humans is brought about through dietary intake [13,28]. Therefore, most studies on fluoride intake focus on the study of the fluoride composition of foods, which will depend mainly on the origin and sources of exposure. Generally, the fluoride contributed by the dietary intake of solid foods could be considered negligible, considering the quantities consumed and the concentrations that these foods usually have (in the order of mg/kg) [29]. The contribution of fluoride made by liquid foods is much more significant, particularly water and those beverages with a high content of fluoride, such as tea or infusions, which are usually considered the main source of this ion [13,29-40]. The first studies that established the relationship between fluoride concentrations in the water supply and the symptoms of fluorosis poisoning were published in India, an area of endemic fluorosis, between the end of 1944 and the beginning of 1945 in the journal _The Indian Medical Gazette_[41-43]. In these articles, fluoride was known to be present in the environment from industries and the use of fertilizers, and it was said to be unavoidable in a person's diet because of its presence in drinking water from fluorinated rocks, with the toxicological effects being related to long-term high exposure to this ion. [PERSON] (1944) [41] combines knowledge and various studies, describing how, in 1902, the high prevalence of dental fluorosis in Italian immigrants to the United States from Naples began to attract attention until, in 1932, it was determined that the etiological agent was the drinking water. [PERSON] (1944) [41] also describes how, in cases of higher exposure, the bone could be affected, observing certain examples of sclerosis in the vertebrae, ribs and coccyx with the use of radiographic techniques, as was demonstrated in 1937 with some advanced cases in patients from Madras (India) who came from areas where the drinking water contained concentrations above 6 mg/L.