Defluorination
Fluoride (F-) is an ion, that is, a chemical entity that has an electrical charge, derived from fluorine.
It is found in nature in the mineral called fluorite.
It is present in almost all waters, in fact, although it is also contained in many foods, water remains the main source of fluoride for humans.
Fluoride in biology
Fluoride belongs to the class of trace elements, that is, those elements that the human body needs in small quantities.
The main physiological role of fluoride is the prevention of caries and the strengthening of the skeleton (especially in the first 8 years of life).
In areas of the world where water does not contain fluoride, it is added to aqueducts (e.g. in the USA) precisely because of its properties.
However, this phenomenon is very controversial, because, considering that fluoride isalso present in many foods, supplements, toothpastes, etc., it is very difficult to determine what is the optimal amount to add to the water without the risk of excessive intake by consumers.
In Italy, no fluoridation of the water is necessary, because it is already naturally rich in fluoride.
Excess fluoride
An excessive intake of fluoride, paradoxically, is harmful precisely to the structures that fluoride develops and protects: teeth and bones.
In fact, the main symptoms of an overabundance of fluoride in the diet are dental fluorosis, a disease that causes yellowish stains on teeth, and bone fluorosis that, by contrast, alters calcium metabolism, causing calcification of the bones.
For these reasons, European Directive 98/83/EC sets the maximum limit for fluoride in water intended for human consumption at 1.5 mg/l.
Removal of fluorides
Fluoride in our body performs fundamental biological functions, but if taken in excessive doses, it can have negative effects on health.
The system used for the removal of fluorides is adsorption. In this specific case, the solid adsorbent is granular aluminium oxide hydroxide (activated alumina).
The fluoride is retained by the filter material that the water to be treated passes through, at a speed that guarantees an ideal activated alumina-water contact time for adsorption.
Limits of activated alumina
Adsorption onto activated alumina has been used for years as a fluoride elimination technique, however, experience has shown that this choice comes with its own issues.
The first is durability: indeed, this material tends to become saturated in a relatively short time and must be replaced frequently.
Another difficulty related to durability is that the latter cannot be estimated with sufficient accuracy.
The other drawback is the possibility that the material, once saturated, starts releasing the fluoride it has retained into the water, thus doing the opposite of its intended function.
For these reasons, in the presence of fluoride, the recommended removal technology is reverse osmosis which is a completely safe and reliable technique.
