# Update on Endemic Fluorosis in a Region of Europe (Tenerife, Canary Islands)
## 1 Introduction
Even then, it was described how a change in the drinking water to water with a lower concentration of the ion could reverse the symptoms [41]. Fluoride concentrations in water supplies has become a public health problem in numerous countries, including Venezuela [44], Ethiopia [45], northern Iran [46], Jordan [47], India [48], Thailand [49], China [50], Ghana [51] and a multitude of countries in Africa [52], Western Estonia [53], Mexico [54], Argentina [55], Australia [56], Iran [57], Colombia [58] and the United States of America [59], among others, where fluoride concentration in the water supply can exceed 4.5 mg/L. Historically, inhabitants of the village of La Guancha on the island of Tenerife were recognized for having characteristically stained teeth, sometimes even called \"those with rotten teeth\", a condition similar to that observed in some areas of India [60,61]. However, it was not until the mid-1950s that [PERSON] and [PERSON] determined the origin of the problem in this population, and, in 1976, they published an article indicating that some springs in the region between San Juan de la Rambla and Icod de los Vinos had a fluoride concentration much higher than the rest, reaching 6.4 mg/L [62]. Subsequent reviews over the years confirmed that elevated fluoride levels persisted in this region, particularly in the Barranco de Vergara gallery. Although they were increasingly higher, it was not given greater importance, as this was considered to be an area of endemic fluorosis [63]. It was not until 1991 that an oral health study conducted by the General Directorate of Public Health determined that 26.4% of school children in the north and northwest of Tenerife exhibited some type of fluorosis. In a later study, in 1998, an increase in the incidence of fluorosis in schoolchildren was indicated not only in the north and northwest but also in the southern part of the island [63]. This coincided with tourism development on the island, necessitating the transfer of water from one area to another due to increased demand. However, the severity of chronic fluorosis cases also diminished due to interventions by authorities, such as restrictions on drinking water consumption or the installation of brackish water desalination plants (WDPs) in 1995 [63]. Over the years, the overexploitation of springs beyond their replenishment rates (attributable to decreased rainfall) has resulted in increased salt concentrations in the groundwater. This occurs due to the precipitation of stagnant water over the passage of time, being more concentrated in the lower zone. Moreover, the remaining water continues to be enriched by being in continuous contact with the rocky material, where microfractures are formed by the temperature and pressure, exposing a larger rocky surface [64, 65, 66]. For this reason, it is crucial to conduct regular monitoring of fluoride concentrations in the water supply of all municipalities of the island, particularly those in the north and northwest. Additionally, a thorough risk assessment should be performed until a satisfactory and definitive solution to the problem is found. The aims of this study are to carry out a historical review of the fluoride concentrations determined in the water supply in each of the municipalities of the island and to make a determination of the current fluoride levels as part of a risk assessment.