# Update on Endemic Fluorosis in a Region of Europe (Tenerife, Canary Islands)
## 2 Material and Methods  
### Samples  
A total of 62 samples were taken on the island of Tenerife, in the archipelago of the Canary Islands, located off the northeast coast of Africa between coordinates 27\({}^{\circ}\)37\({}^{\prime}\) and 29\({}^{\circ}\)25\({}^{\prime}\) north latitude and 13\({}^{\circ}\)20\({}^{\prime}\) and 18\({}^{\circ}\)10\({}^{\prime}\) west longitude. This island represents the emerged part of a large pyramidal volcanic edifice, with its triangular base being located about 3000 m below sea level. It boasts the largest surface area (2058 km\({}^{2}\)) and the highest peak (Pico del Teide, 3718 m) of the Canary Islands archipelago [67]. The central sector of the island is occupied by the Canadas Edifice. Its hydrographic network is configured by ravines that only carry water during rainy seasons, but they are characterized by significant depth and steep slopes. In general, they follow a radial direction from the edge of Las Canadas towards the sea [67]. Tenerife is also the most populous island in the archipelago, with a population of 955,063 inhabitants in 2024, accounting for approximately 42% of the Canary Islands' population [68]. The distribution of the population by municipality is as follows: Adeje (5.29%), Arafo (0.60%), Arico (0.95%), Arona (9.07%), Buenavista del Norte (0.49%), Candelaria (3.01%), Fasnia (0.32%), Garachico (0.52%), Granadilla de Abona(5.98%), La Guancha (0.59%), Guia de Isora (2.37%), Guimar (2.27%), Icod de los Vinos (2.54%), San Cristobal de La Laguna (16.78%), La Matanza de Acentejo (0.96%), La Orotava (4.46%), Puerto de la Cruz (3.29%), Los Realejos (3.93%), El Rosario (1.88%), San Juan de la Rambla (0.51%), San Miguel de Abona (2.42%), Santa Cruz de Tenerife (22.13%), Santa Ursula (1.61%), Santiago del Teide (1.30%), El Sauzal (0.97%), Los Silos (0.49%), Tacoronte (2.59%), El Tangue (0.29%), Tegueste (1.19%), La Victoria de Acentejo (0.98%) and Vialflor de Chasna (0.20%).  
Two samples were taken from each municipality. Sampling prioritized those districts that are most representative or that have had the most problems with official consumption restrictions due to fluoride in compliance with Directive 2020/2184 and RD 3/2023, which establish a parametric value of 1.5 mg/L [69,70]. This approach aims to determine the approximate average fluoride concentration in each municipality's water supply. All samples were collected in the month of August 2023 directly from the tap of users of the public water supply, with each sample being 100 mL. The 3 sampled regions into which the island has been divided for subsequent analysis are shown below (Figure 1); a topographic and the water supply system infrastructure map of the island is also included (Figures 2 and 3):  
* Metropolitan region: Santa Cruz de Tenerife, La Laguna, El Rosario and Tegueste.
* Northern region: Tacoronte, el Sauzal, la Matanza de Acentejo, la Victoria de Acentejo, Santa Ursula, la Orotava, Puerto de la Cruz, los Realejos, San Juan de la Rambla, la Guancha, Icod de los Vinos, Garachico, el Tangue, los Silos and Buenavista.
* Southern region: Candelaria, Arafo, Guimar, Fasnia, Arico, Granadilla de Abona, San Miguel de Abona, Vialflor, Arona, Adeje, Guia de Isora and Santiago del Teide.