# Fluoride Risk Assessment of Different Brands of Coffee Commercialized in the Canary Islands
## 1 Introduction  
Fluorise is the most electronegative and reactive element in the periodic table. Therefore, it is not found in its elemental state in nature. In water, fluorine is mainly found as fluoride ion (F\({}^{-}\)) and fluorinated organic compounds. The main natural source of fluorides in water bodies is the emission of gases rich in hydrofluoric acid (HF) from volcanic activity. Similarly, the erosion of fluorinated minerals is noteworthy [1; 2] fundamentally in fluorapatite (Ca\({}_{5}\)(PO\({}_{4}\))\({}_{5}\)F), fluorite (CaF\({}_{2}\)), and cryolite (Na\({}_{3}\)AlF\({}_{6}\)). Furthermore, fluoride levels can increase because of anthropogenic activity such as industrial activity (coal burning, electroplating, glass, steel, ceramics) as well as the use of fertilizers [3]. The presence of environmental fluoride can cause terrestrial plants close to pollution sources to accumulate inorganic fluorides [4], with the highest accumulation rate being recorded as a result of the deposition of fluorides from the air and subsequent absorptionby the stomata. Fluorapatite is the main source of fluoride in soils that have been fertilized with phosphate fertilizers containing this mineral. Although fluorine is not considered an essential element, it does have a hormetic effect, providing certain benefits to humans [5]. An adequate intake of fluorides offers protection against dental caries because, among other mechanisms, it acts by inhibiting the metabolism of cariogenic bacteria, reducing the formation of acids (acetic and butyric) that would end up decomposing dental hydroxyapatite [6; 7]. Furthermore, hydroxyapatite reacts in the presence of fluoride, yielding fluorhydroxyapatite, which is more resistant to erosion [8]. At certain doses, it has also been related to an improvement in osteoporosis [9; 10]. However, when fluoride exposure is high and sustained over time, the risk of suffering adverse effects such as dental fluorosis (mottled teeth, with weakness and malformation of teeth) increases, as well as bone fluorosis in extreme cases [11]. Various studies conducted in areas of India and China have shown that when the concentration of fluoride in water exceeds 1 mg/L, the risk of suffering from bone fluorosis increases, and the intelligence quotient (IQ) in children is reduced [12; 13]. In the Spanish Royal Decree (RD) 3/2023, which regulates parametric values in supply water in Spain, a value of 1.5 mg/L of fluoride is established for water for human consumption. When this value is exceeded, the water is not considered suitable for human consumption, and the health authority, at the proposal of the operator, is obliged to take the appropriate measures [14]. This parametric value is coincident with that established in RD 1798/2010 of December 30, which regulates the exploitation and marketing of natural mineral waters and spring waters bottled for human consumption [15] and the Directive (EU) 2020/2184 on the quality of water intended for human consumption [16]. Fluoride, coming from both natural sources and human activities, reaches humans mainly through water and food. The main known dietary sources of fluoride are drinking water, tea, and soft drinks [17; 18]. Coffee is a drink that is part of daily life for a large part of the Spanish and world population, as it is one of the most marketed products in the world. Currently, it is, along with water and tea, among the three most consumed beverages in the world [18; 19]. Therefore, a risk assessment of the presence of fluoride in this foodstuff is of great interest. Coffee is obtained from the roasted and ground grains of the fruits of the coffee plant (_Coffee_ spp. ), which is a genus of plants belonging to the Rubiaceae family [20], _C. arabica_ and _C. caenphora_ being the two most tare noteworthy varieties. These plants are shrubs or small trees with alternate, persistent, leather, and shiny leaves, native to tropical and southern Africa and tropical Asia. The white and fragrant flowers are grouped in whorls in the axis of the leaves.